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ENGINEERING THE 

NEXT GENERATION #r== 

0F STEM ^ 




Page 26 



Addressing critical-area analysis 
and memory redundancy 

Page 21 

Audio-converter-subsystem design 
challenges in the 21st century 

Page 33 



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Engineering the next 
generation of STEM 

^\ Industry participants, reacting to the 
J \ \ so-called engineering crisis, are doing 
what they can to foster science, 
technology, engineering, and math talent and 
encourage more students to pursue engineering 
careers. 

by Suzanne Deffree, 
Managing Editor, Online 



EDN 

contents 

3.1.12 



Addressing critical- 
area analysis and 
memory redundancy 

Q A How susceptible is 
^ I your design to random 
defects, and which areas of the 
layout could benefit from modi- 
fications that would provide the 
greatest positive effect on over- 
all yield? 

by Simon Favre, 
Mentor Graphics 



Audio-converter- 
subsystem design 
challenges in the 
21st century 

Q QSome key strategies 
OOenable you to achieve 
optimum audio-converter 
performance. 

by Ian Dennis, 
Prism Sound Group 




COVER IMAGE: SHUTTERSTOCK/GIULIA FINI-GULOTTA 



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MARCH 1, 2012 | EDN 5 




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contents 3i 12 



p 




Value-priced scopes extend 
bandwidth to 1 GHz 

Outdoor unit brings integration 
to the microwave backhaul 

SOC enables measurement 
for high-power monitoring in 
industrial applications 



High-current storage chokes 
come in ERU 20 case size 



Dilbert 



3-D computer simulations 
reveal diffusional behavior 

Digital-audio processor inte- 
grates power management 

Robust three-axis sensor 
targets automotives 

Energy-measurement IC eases 
utility meters' transition to 
smart grid 



DEPARTMENTS & COLUMNS 




EDN online: Join the conversation; Content; Engineering Community 



EDN.comment: Do, make, design, build, and fix the future of STEM 



Signal Integrity: Series resonance in power systems 



Connecting Wireless: Smart wireless for your world 



Product Roundup: Test and Measurement 



Tales from the Cube: Printer parking brake 



EDN® (ISSN# 0012-7515) is published semimonthly by UBM Electronics, 600 Community Drive, Manhasset, NY 1 1030-3825. Periodicals 
postage paid at Manhasset, NY, and at additional mailing offices. SUBSCRIPTIONS— Free to qualified subscribers as defined on the subscrip- 
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is taken to ensure accuracy of content; however, the publishers cannot accept responsibility for the correctness of the information supplied or 
advertised or for any opinion expressed herein. POSTMASTER— Send address changes to EDN, PO Box 3609, Northbrook, IL 60065-3257. 
CANADA POST: Publications Mail Agreement 40612608. Return undeliverable Canadian addresses to APC, PO Box 503, RPO West BVR CRE, 
Rich Hill. ON L4B 4R6. Copyright 201 2 by UBM. All rights reserved. Reproduction in whole or part without written permission is prohibited. 
Volume 57, Number 5 (Printed in USA). 



[www.edn.com] 



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JOIN THE CONVERSATION 

Comments, thoughts, and opinions shared by EDN's community 




In response to "Adafruit, Sparkfun point to 
the democratization of hardware," a blog 
post by EDN's Margery Conner, http://bit.ly/ 
xsOTeF, Chris G comments: 

"The best thing about Sparkfun and Adafruit for a 
casual experimenter is that they offer components 
and subassemblies with most of the difficult work 
already done. Sure, the nitty-gritty details need 
to be understood before putting out a robust product, but, as my own 
efforts have shown, just trying to get a microprocessor to communicate 
to another device over l 2 C can be daunting enough while also working out 
the communication handshaking, even after reading the device maker's 
spec sheets. Having these things worked out in an experimenters' kit is the 
reason that these companies are the ones to watch. " 



In response to "Cow tipping," a 
Tales from the Cube column by 
Arnold N Simonsen, http://bit.ly/ 
zaho6V, "bandit" comments: 



"A moooving story, ranging by 
degrees from fence post to fence 
post. Our intrepid engineer bore- 
sighted right to the horns of the 
problem. The solution? Beefing up 
the trailer site, making hamburger of 
the problem, avoiding the cow patties 
in his path. Another government job 
properly steered away from danger. " 



EDN invites all of its readers to constructively and creatively comment 
on our content You'll find the opportunity to do so at the bottom of each 
article and blog post To review current comment threads on EDN.com, 
visit http://bitly/EDN_Talkback. 




CONTENT 



Can't-miss content on EDN.com 



5 ENGINEERS: WHY DID YOU 
BECOME AN ENGINEER? 

We asked, and you're answering. 
More than 1 85 comments have been 
posted so far, ranging from "I wanted 
to make the world a better place" 
to "The devil made me do it." Share 
what it was that inspired you to 
pursue engineering as a career path 
in this blog post's comment section. 

http://bit.ly/yD1hsg 




SAMSUNG LED-LIGHT- 
BULBTEARDOWN INCLUDES 
OBJECTIVE DIMMING 
NUMBERS 

Samsung sent EDN's Margery 
Conner an LED-replacement bulb to 
put through its paces and then tear 
down. How does the bulb do with 
the onerous TRIAC-dimming test? 
Pretty darned good, and Margery 
has posted a graph to prove it. 

http://bit.ly/xElkmE 



• ENGINEERING COMMUNITY fQ\ 

Opportunities to get involved and show your smarts 

designwest 

center of the engineering universe 

FREE BEER! 

Now that we have your attention, be sure to register for Design West, a new event this year that collocates 
seven summits for four days of training and education, hands-on knowledge exchanges, teardowns, 
giveaways, and more throughout the day ... and, yes, free beer, snacks, and prizes during its expo 
networking event on Tuesday, March 27, 5:30 pm to 7 pm. Find out more at www.ubmdesign.com. 



[www.edn.com] 



MARCH 1, 2012 | EDN 9 




EDN. COMMENT 




BY SUZANNE DEFFREE, MANAGING EDITOR, ONLINE 



Do, make, design, build, and fix 
the future of STEM 

^^^^^^^ y now, you've seen this issue's cover. You may have even 

■ flipped through to the cover story. And you may be wonder- 
^^j^^^F ing what such a story — sans schematics, technical jargon, 
and just plain design basics — is doing in EDN. We are about 

m engineering, after all, so where 's the engineering in the cover 
^H^^^^ story? In this issue's cover story, instead of presenting a design 
topic for you to build from, we're presenting a challenge for all of us to 
overcome. That challenge is how to engineer a new generation of STEM 
(science/technology/engineering/math) talent. 

We all know the problem. Too few 

new engineers, as well as other STEM 

professionals, are graduating from US 

colleges. The underlying issue is that 

kids these days aren't taking an interest 

in science and math, without which 

they can't develop critical-thinking 

skills and that sense of curiosity that 

contributes to entrepreneurial attitudes 

and life-long discovery. 

Many people reading this editorial 

will say that we shouldn't be encourag- 
ing kids to study STEM because of a 

claimed lack of engineering jobs in the 

United States. This situation isn't just 

about jobs, though. It's about creating 

a climate of more creative and more 

intelligently thinking, and, ultimately, 

more proactive people. We can be sure 

of this: If engineers — who are creative, 

intelligent, productive people — ran 

things in this country, we'd all be in 

a better position when it came to the 

employment market, as well as many 

other hot-button concerns. 

Engineering the next generation is 

about creating leaders who can help 

us build a better tomorrow. Although 
8 these leaders would preferably be 
I new engineers, we also need more 
jji professionals in other fields, inside 
I or outside STEM, who think like 



engineers to help brighten the picture. 

It's easy to point fingers; politicians 
do it all the time. But, as engineers, you 
do, you make, you design, you build, and 
you fix. Those abilities — not the degree 
you received — make you an engineer. 
Those same principles make the topic 
of next-generation STEM talent an 
engineering issue. We know there is a 
problem. Let's do something to fix it; 
let's engineer it. 

As issues about STEM evolve, you'll 
see more content like this cover story 
on how to engineer this crisis into a 
healthier state. This content will appear 
in print, on EDN.com, through our 
social-media efforts, in our webcasts, 
and through the events we attend. For 
example, EDN is presenting a Design 
West panel on this topic on March 28 
at the San Jose McEnery Convention 
Center. Look for it in the show-floor 
theater at 1:30 pm. After the panel, 
we'll also host a networking session in 
which we'll invite experienced engi- 
neers and executives to connect with 
incoming and new STEM talent. 

Further, the IEEE has asked me 
and my colleague at UBM Electronics, 
Naomi Price, online brand manager for 
Innovation Generation, to speak at its 
Integrated STEM Conference on March 





If engineers— who 
are creative, intel- 
ligent, productive 
people— were run- 
ning things, we'd all 
be in a better posi- 
tion in the employ- 
ment market. 

9, at the College of New Jersey (Ewing, 
NJ). Naomi and I will also attend the 
USA Science and Engineering Festival 
in Washington, DC, during the last 
weekend in April to celebrate the bril- 
liance this next generation brings to 
the game. 

We hope to see you at these events 
in March and April. You can find more 
information about them in the online 
version of this editorial. In the mean- 
time, we invite you to share your own 
thoughts on what we can all be doing to 
help encourage the next generation of 
STEM at http://bit.ly/zC6wYA. 

We'll bring back the design focus 
in EDN's March 15 cover story. But 
don't walk away thinking that this need 
for more STEM talent isn't an engi- 
neering topic. It is vital to the future of 
engineering itself and something that 
we can together engineer — do, make, 
design, build, and fix — toward a better 
future.EDN 

Contact me at suzanne.deffree@ubm.com. 



10 EDN | MARCH 1, 2012 



[www.edn.com] 




SENIOR VICE PRESIDENT, 
UBM ELECTRONICS 

David Blaza 
1-415-947-6929; 
david.blaza@ubm.com 

DIRECTOR OF CONTENT, 
EDN AND DESIGNLINES 

Patrick Mannion 
1-631-543-0445; 
patrick.mannion@ubm.com 

EXECUTIVE EDITOR, 
EDN AND DESIGNLINES 

Rich Pell 
Consumer 
1-516-474-9568; 
rich.pell@ubm.com 

MANAGING EDITOR 

Amy Norcross 
Contributed technical articles 
1-781-869-7971; 
amy.norcross@ubm.com 

MANAGING EDITOR, ONLINE 

Suzanne Deffree 
Electronic Business, Distribution 
1-631-266-3433; 
suzanne.deffree@ubm.com 

SENIOR TECHNICAL EDITOR 

Steve Taranovich 
Analog, Systems Design 
1-631-413-1834; 
steve.taranovich@ubm.com 

TECHNICAL EDITOR 

Margery Conner 
Design Ideas, Power Sources, 
Components, Green Engineering 
1-805-461-8242; 
margery.conner@ubm.com 

DESIGN IDEAS 
CONTRIBUTING EDITOR 

Glen Chenier 
edndesignideas@ubm.com 

SENIOR ASSOCIATE EDITOR 

Frances T Granville, 1 -781 -869-7969; 
frances.granville@ubm.com 

ASSOCIATE EDITOR 

Jessica MacNeil, 1-781-869-7983; 
jessica.macneil@ubm.com 

COLUMNISTS 

Howard Johnson, PhD, Signal Consulting 
Bonnie Baker, Texas Instruments 
Pallab Chatterjee, SiliconMap 
Kevin C Craig, PhD, Marquette University 

CONTRIBUTING TECHNICAL EDITORS 

Dan Strassberg, strassbergedn@att.net 
Brian Bailey, brian_bailey@acm.org 
Robert Cravotta, 
robert.cravotta@embeddedinsights.com 



•• •• 
•• •• 
•• •• 



VICE PRESIDENT/DESIGN DIRECTOR 

Gene Fedele 

CREATIVE DIRECTOR 

David Nicastro 

ART DIRECTOR 

Giulia Fini-Gulotta 

PRODUCTION 

Adeline Cannone, Production Manager 

Laura Alvino, Production Artist 
Yoshihide Hohokabe, Production Artist 
Diane Malone, Production Artist 

EDN EUROPE 

Graham Prophet 
Editor, Reed Publishing 
gprophet@reedbusiness.fr 

EDN ASIA 

Huang Hua 
Operations General Manager 
huang.hua@ednasia.com 
Grace Wu 
Associate Publisher 
grace.wu@ednasia.com 
Vivek Nanda, Executive Editor 
vnanda@globalsources.com 

EDN CHINA 

Huang Hua 
Operations General Manager 
huang.hua@ednchina.com 
Grace Wu 
Associate Publisher 
grace.wu@ednasia.com 
Jeff Lu, Executive Editor 
jeff.lu@ednchina.com 

EDN JAPAN 

Masaya Ishida, Publisher 
mishida@mx.itmedia.co.jp 

Makoto Nishisaka, Editor 
mnishisa@mx.itmedia.co.jp 

UBM ELECTRONICS 
MANAGEMENT TEAM 

Paul Miller, Chief Executive Officer, 
UBM Electronics, UBM Canon (Publishing), 
UBM Channel, and UBM Design Central 

Kathy Astromoff, 
Chief Executive Officer, UBM Electronics 
Brent Pearson, 
Chief Information Officer 
David Blaza, 
Senior Vice President 
Karen Field, 
Senior Vice President, Content 
Jean-Marie Enjuto, 
Vice President, Finance 
Barbara Couchois, 
Vice President, Partner Services 
and Operations 
Felicia Hamerman, 
Vice President, Marketing 
Amandeep Sandhu, 
Director of Audience Engagement 
and Analytics 



I IDK/1 For a complete list of editorial contacts, 

U D I V I see http://ubmelectronics.com/editorial-contacts 



Electronics 



[www.edn.com] 



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EDITED BY FRAN GRANVILLE 




INNOVATIONS & INNOVATORS 



Value-priced scopes extend 
bandwidth to 1 GHz 



Agilent is adding four models to its 
InfiniiVision 3000 X series of value- 
priced digital oscilloscopes, dou- 
bling to 1 GHz the maximum bandwidth, 
increasing the maximum acquisition rate 
from 4G to 5G samples/sec/active chan- 
nel, and adding such optional features as a 
±3-digit digital voltmeter/five-digit frequency 
counter that uses the same signal leads as 
the scope. This option simplifies simultane- 
ous numeric measurements and waveform 
display. The company has also expanded 
its Waveform Builder software line, which 
supports the built-in function/waveform- 
generator option. Memory depth is, option- 
ally, 4M points/channel, and the maximum 
waveform-update rate remains 1 million 
waveforms/sec, a spec that only one com- 
petitor can equal without the use of special 
operating modes. 

The wider bandwidth and increased acqui- 
sition rate position the new units, which 
include two- and four-channel analog scopes 
and mixed-signal oscilloscopes, to invade 
portions of the turf of higher-priced 
scopes. US list prices 
for 1 -GHz-bandwidth 
units start at $9950 
for a unit with two 
analog channels. 
According to Agi- 
lent, the 3000 X 
series' designed- 
in upgrade capa- 
bilities more effec- 
tively extend the 
instruments' life- 
time and preserve 
users' investment 



than do competitive devices. Prices for 
upgrades from lower analog bandwidths to 
1 GHz begin at $2340. 

The company has also announced the 
$1000, 1-GHz N2795A active probe. The 
probe has one-quarter the input capacitance 
of passive probes that provide similar band- 
width. Although Agilent specs this device's 
bandwidth at 1 GHz, a company spokesman 
says that, when you use the 1-GHz probe 
with the 1 -GHz scope, the combined -3-dB 
bandwidth remains higher than 1 GHz. The 
probe also sports a pair of LED "headlights" 
that make it easier to find probe points on 
dense PCBs. You can use one or two of 
these probes with a 1 -GHz-bandwidth 3000 
X scope. For applications that require both 
probing and 1 -GHz bandwidth on more than 
two channels, the company recommends its 
1 1 57 A probes, which draw less power from 
the scope's internal power supply. 

— by Dan Strassberg 

Agilent Technologies, 
www.agilent.com. 



E8TALKBACK 

"I became an 
engineer because 
I like clarity and 
specifics. I've 
learned from expe- 
rience that, when- 
ever a company 
avoids giving spec- 
ifications, espe- 
cially those involv- 
ing price, be wary 
of fraud. Too many 
companies substi- 
tute [disreputable] 
marketing strate- 
gies for engineer- 
ing transparency/' 

— EDN reader Neil Baker, in EDA/'s 
Talkback section, at http://bit.ly/ 
wLqanx. Add your comments. 




The four-channel MSO-X 
3054A provides 1-GHz 
maximum bandwidth, 
2M-sample/channel 
acquisition memory (4M 
samples optional), and 
16 digital timing-analysis 
channels. A digital 
multimeter/frequency counter 
with on-screen readout, a 
built-in function/waveform 
generator, and a 1 -GHz active 
probe are extra-cost options. 



12 EDN | MARCH 1, 2012 



[www.edn.com] 



Name 

Peter Sim on sen 

JobTitle 

Design Engineer, 
Embedded Software 

Area of Expertise 

Renewable Energy 

LabVIEW Helped Me 

Perform real-world 
simulations with total 
control of the application 

Latest Project 

Develop a test architecture 
for verification of wind 
turbine control systems 




LabVIEW makes me better because I can 

IMULAT 





real-world systems 



Find out how LabVIEW can make you better at ni.com/labview/better 



800 453 6202 



©2010 National Instruments. All rights reserved. LabVIEW, National Instruments, N I, and ni.com are trademarks of National Instruments. 
Other product and company names listed are trademarks or trade names of their respective companies. 2811 



^NATIONAL 
^INSTRUMENTS 



HIGH-CURRENT 
STORAGE 
CHOKES COME IN 
ERU 20 CASE SIZE 

TDK-EPC has extended 
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power inductors with the 
new ERU 20 series. The 
devices have inductance 
values of 1 to 35 uH and 
a current rating of 93 to 
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values range from 0.62 
to 7 mO. The ERU case 
sizes suit use in high- 
current, low-voltage dc/ 
dc converters, point- 
of-load converters, and 
multiphase modules. The 
design employs ferrite 
cores and flat-wire wind- 
ing technology. Low core 
losses and efficient de- 
sign with self-supporting 
winding permit ultra- 
compact dimensions and 
good storage density. 

The inductors have a 
21x21.5-mm 2 footprint 
and an insertion height 
of 9.8 to 14.2 mm, de- 
pending on type. The 
ROHS-compatible de- 
vices are also available 
in customer-specific 
versions. Applications in- 
clude power supplies in 
telecommunications and 
IT systems and inverters 
for photovoltaic systems, 
—by Fran Granville 

TDK-EPC, 
www.epcos.com. 



The ERU 20 series has in- 
ductance values of 1 to 35 
uH and a current rating of 
93 to 50A. 



)Ulse 



Outdoor unit brings integration 
to the microwave backhaul 



B r 
; 




I roadcom's new BCM85810 microwave 
.outdoor-unit IC combines the functions 
'of as many as 10 off- ^^^^ m 
the-shelf application-specific 
standard products, including IF 
and RF synthesizers, low-noise 
amplifiers, automatic-gain con- 
trollers, bandpass-filter banks, 
lowpass-filter banks, IR mix- 
ers, variable-gain and variable- 
voltage attenuators with auto- 
matic-gain control of more than 
70 dB, and power-amplifier 
drivers and power detectors. 

The BCM85810 addresses 
the need for higher bandwidth 
and faster time to market in 
microwave split-mount and full- and all-outdoor 
units. With support for high modulation and with 
only two variants to cover all standard point-to- 



BROADCOM 



•i .* Agss 



BCM858W 



The BCM85810 fulfills the need for 
higher bandwidth in outdoor units. 



point microwave-frequency bands and channel 
bandwidths, the BCM85810 simplifies system 
manufacturing, deploy- 
ment, and inventory man- 
agement, according to the 
company. 

The device offers an 
automatic-gain -control 
dynamic range of more 
than 70 dB, internal power 
controls, and on-chip- 
selectable baseband fil- 
ters. It maintains receiver 
output power over the full 
input-power range and 
complies with European 
Telecommunications Stan- 
dards Institute and Federal Communications 
Commission standards. — by Fran Granville 
Broadcom, www.broadcom.com. 



SOC enables measurement 
for high-power monitoring 
in industrial applications 



I axim's new Teridian- 
based, three-phase 
I78M6631 power- 
measurement system on chip 
embeds power monitoring 
into high-load applications. 
The self-contained and cus- 
tomizable system suits use in 
industrial panels and motors, 
solar-panel inverters, storage 
power supplies, and data cen- 
ters. The device's embedded 



metrology engine includes a 
range of embedded energy 
diagnostics, including power 
factor, harmonic distortion, volt- 
age sag, and voltage dip. The 
78M6631 also provides better 
than 0.5% system accuracy 
across a 2000-to-1 dynamic 
range, enabling the use of the 
lowest-value shunt for the cur- 
rent sensor, thus reducing heat 
and parasitic-power loss. 



Preloaded firmware supports 
both Delta and Wye three- 
phase applications, reducing 
both development costs and 
time to market. The 78M6631 
SOC is available in a lead-free 
QFN package and sells for 
$5.78 (1000). 

— by Fran Granville 

Maxim Integrated 
Products, 
www.maxim-ic.com. 



DILBERT By Scott Adams 



THERE WERE ELEVEN 
WAYS TO INTERPRET 
THE VAGUE ASSIGN- 
MENT YOU GAVE IAE 
BY VOICEMAIL 




GIVEN THE RISKS 
OF CHOOSING WRONG. 
AND KY ENGINEERING 
OATH TO DO NO HARhV 
IT WAS MY ETHICAL 
DUTY TO DO NOTHING, 




YOU 






COULD 






HAVE 






ASKED 


SOUNDS 


FOR 


RISKY. 


CLARIFI- 






CATION. 




) r 






I 7 















14 EDN | MARCH 1, 2012 



[www.edn.com] 




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Dulse 



3-D computer simulations reveal 
diffusional behavior 



A team of researchers at 
the Georgia Institute of 
Technology is exploring 
how nanoparticles move and 
diffuse on a surface or in a fluid 
under nonideal to extreme con- 
ditions. Rigoberto Hernandez, 
a professor at the university's 
school of chemistry and bio- 
chemistry, investigates these 
relationships by studying 3-D 
particle-dynamics simulations 
on high-performance com- 
puters. His findings focus on 
the movements of a spherical 
probe among static needles 
(Reference 1). 



Hernandez and his for- 
mer doctoral student, Ashley 
Tucker, assembled the rod- 
like scatterers in one of two 
states during his simulations: 
disordered, or isotropic, and 
ordered, or nematic. When dis- 
ordered, the nanorods point in 
various directions and typically 
diffuse normally in all directions. 
When every rod points in the 
same direction, the particle, on 
average, diffuses more in the 
same direction as the rods than 
against the grain of the rods. In 
this nematic state, the probe's 
movement mimics the elon- 




Georgia Tech Professor Rigoberto Hernandez and his former 
doctoral student, Ashley Tucker, assembled the rodlike scatter- 
ers in one of two states during simulations: disordered, or isotro- 
pic, and ordered, or nematic. 



gated shape of the scatterers. 

Surprisingly, however, the par- 
ticles sometimes diffuse faster 
in the nematic environment than 
in the disordered environment. 
That is, the channels left open 
between the ordered nanorods 
don't just steer nanoparticles 
along a direction; they also 
enable them to speed right 
through. As the density of the 
scatterers increases, the chan- 
nels become more crowded. 
The particle diffusing through 
these assemblies slows dra- 
matically in the simulation. Nev- 
ertheless, the nematic scatter- 
ers continue to accommodate 
faster diffusion than do disor- 
dered scatterers, according to 
the researchers. 

"These simulations bring 
us a step closer to creating 
a nanorod device that allows 
scientists to control the flow of 
nanoparticles," says Hernan- 
dez. "Blue-sky applications of 
such devices include the cre- 
ation of new light patterns, infor- 
mation flow, and other micro- 
scopic triggers." For example, 
if scientists need a probe to dif- 
fuse in a specific direction at 
a particular speed, they could 
trigger the nanorods to move 



into a specified direction. When 
they need to change the par- 
ticle's direction, they could trig- 
ger scatterers to rearrange into 
a different direction. The trig- 
ger could even be the absence 
of sufficient nanoparticles 
in a given part of the device. 
The ensuing reordering of the 
nanorods would then drive a 
repopulation of nanoparticles 
that would then be available to 
perform a desired action, such 
as to stimulate light flow. 

The National Science Foun- 
dation-funded work targets a 
better understanding of the 
motion of particles within com- 
plex arrays at the nanoscale. 
The work has significant long- 
term implications on device 
fabrication and performance at 
such scales. 

— by Fran Granville 

Georgia Institute of 
Technology, 
www.gatech.edu. 

REFERENCE 

H Tucker, Ashley K, and 
Rigoberto Hernandez, "Dif- 
fusion of a Spherical Probe 
through Static Nematogens: 
Effect of Increasing Geo- 
metric Anisotropy and Long- 
Range Structure," The Jour- 
nal of Physical Chemistry B, 
Dec 8, 2011, pg 1328, 
http://bit.ly/zFH6Yd. 



Digital-audio processor integrates power management 



Conexant's new dual-core, 32-bit 
CX20805 digital-audio processor 
integrates high-speed USB 2.0, an 
800-MIPS DSP, and support for as many 
as eight endpoints. The chip comes with 
a C compiler, software tools, and a suite 
of DSP algorithms. It uses the vendor's 
CAPE (Conexant audio-processing-engine) 
architecture. Each dual-core DSP includes 
dual media-access controllers operating 
at 200 MHz. The CX20805 also includes 
520 kbytes of embedded SRAM and 352 
kbytes of embedded ROM; a full-duplex, 
l 2 S-multiplexed stereo with a four-channel 



PCM interface; an l 2 C master and slave; 
and an SPI master and slave. 

Other features include support for a 
quad digital microphone with pulse-density 
modulation, SPDIF receiving and transmit- 
ting, tricolor PWM-LED drivers, and 24 
programmable l/Os. A custom audio bus 
connects to multichannel audio 
devices, and the product 
has an AES 128 decryp- 
tion engine, an on-chip logic 



The CX20805 processor sup- 
ports eight endpoints. 



•4* 



analyzer and JTAG, a UART, and dedicated 
peripheral and memory-to-memory DMA 
channels. Integrated dc/dc conversion, 
power gating, power retention, dynamic 
voltage scaling, and frequency scaling 
reduce power consumption. 

Housed in a 9x9-in., 1 1 6-pin, dual- 
row QFN package, the device sells 
for $5.50 (10,000). Evaluation kits 
are available to qualified custom- 
i ers and partners. 

— by Fran Granville 
Conexant Systems Inc, 
www.conexant.com. 



16 EDN | MARCH 1, 2012 



[www.edn.com] 



Robust three-axis sensor targets automotives 



STMicroelectronics' new 
A3G4250D angular- 
rate gyroscope aims 
to add position accuracy and 
stability to a range of automo- 
tive applications, including in- 
dash navigation, telematics, 
and vehicle-tolling systems. 
The AEC-Q1000-qualified 
gyroscopes provide accurate 
measurements of angular- 
motion detection, significantly 
enhancing dead-reckoning and 
map-matching capabilities in 
car-navigation and telematics 
applications. 

By monitoring motion, dis- 
tance traveled, and altitude, 
dead-reckoning systems com- 
pensate for the loss of satellite 
signals indoors and in urban 
canyons between tall build- 
ings. Precise gyroscope read- 



ings also improve 
map-matching, the 
process of aligning a 
sequence of observed 
user positions with the 
road network on a digi- 
tal map, such as those 
for traffic-flow analysis 
and driving directions. 

The device employs 
one sensing struc- 
ture for motion meas- 
urement along the 
orthogonal yaw, roll, 
and pitch axes, eliminating 
interference between the axes, 
increasing measurement pre- 
cision, and providing output 
stability over time and tempera- 
ture. The A3G4250D measures 
angular rates to ±2507sec. An 
on-chip IC interface converts 
the angular motion into a 1 6-bit 




digital bit stream that transmits 
to a dedicated microcontroller 
chip through a standard SPI or 
l 2 C protocol. The device pro- 
vides interrupt and data-ready 
output lines and four user- 
selectable output-data rates. 

The 3V-single-supply sen- 
sor integrates power-down 



The three-axis 
A3G4250D auto- 
motive gyroscope 
provides motion 
measurement along 
all three orthogonal 
axes. 

and sleep modes and 
an embedded first-in/ 
first-out memory block 
for power manage- 
ment. The A3G4250D 
embeds an 8-bit tem- 
perature sensor and 
operates at an extended 
temperature range of -40 to 
+85°C. The device is robust 
against EMI and withstands 
shocks as large as 10,000g. It 
sells for $6 (1000). 

— by Fran Granville 
STMicroelectronics, 
www.st.com. 



Energy-measurement IC eases 
utility meters' transition to smart grid 



Look out, you spinning-disk utility 
meters out there. Your days of rul- 
ing the power line are coming to a 
close— at least you'll get that im- 
pression as smart meters that em- 
ploy electronic sensing to provide 
advanced connectivity continue 
to replace the venerable glass-en- 
cased meters that have served the 
utility industry for more than 100 
years. The latest entry in the 
metering-IC arena is the 
CS548x/9x family from Cirrus 
Logic. The family supports single- 
and multiple-phase ac-line meas- 
urement of voltage and current 
through per-channel ADCs and 
then calculates the power usage 
using an internal digital core. 

Other ICs for this application 
use SOC front ends and separate 
communications processors, but 
the topology of the Cirrus devices 
puts the converters and calculat- 
ing core at the front end, lowering 
cost through the elimination of 



unneeded hardware blocks, ac- 
cording to the vendor, and using 
optocouplers, thus requiring fewer 
signal lines to isolate. Applications 
for these IC-based energy meters 
go beyond residential lines and 
their metering. Vendors are looking 
to incorporate them into applianc- 
es, smart power strips, power sup- 
plies, and power-hungry servers in 
enterprise applications. 

The devices offer measurement 
accuracy for both active and reac- 
tive power (power factor) of 0.1% 
over a 4000-to-1 dynamic range, 
surpassing industry requirements, 
whereas current rms measurement 
accuracy is 0.1% over a 1000-to-1 
range with readings using simul- 
taneous-sampling converters and 
24-bit, fourth-order delta-sigma 
modulators. On-chip measure- 
ments include active, reactive, and 
apparent power; rms voltage and 
current; power factor; and line 
frequency. 



For transducer I/O— critical to 
this application— the ICs support 
shunt resistor, current transformer, 
and Rogowski-coil pickups, with 
configurable digital outputs for 
energy pulses, zero crossing, or 
energy direction. The chip's self- 
calibration time is less than 2 sec, 
which Cirrus claims is one-tenth 
the time of other available de- 
vices. Calibration time is important 
because these meters and their 
sensors require calibration at the 
factory's production line. At the 
other side of the I/O situation, the 
family offers SPI and UART inter- 
faces, depending on IC model. The 
devices operate from a single 3.3V 
supply, and power consumption is 
less than 1 3 mW. 

The CS548x/9x family includes 
two-, three-, and four-channel 
front ends, which are available in 
16-lead SOIC, 24-lead QFN, and 
28-lead QFN packages. Prices be- 
gin at 75 cents (100,000) for the 
smallest member of the family. 

—by Bill Schweber 

Cirrus Logic, www.cirrus.com. 



[www.edn.com] 



MARCH 1, 2012 | EDN 17 




SIGNAL INTEGRITY 




BY HOWARD JOHNSON, PhD 



Series resonance in power 
systems 




any digital systems suffer excessive power-supply noise at 
frequencies relating to the system clock. Could a series- 
resonant circuit, such as the one in Figure 1 , connected 
between the power and the ground planes attenuate that 
noise? The answer can be yes, but only if your circuit satis- 
fies the following improbable conditions. 



First, the frequency of the system 
clock must remain fixed. In systems 
without a crystal-controlled clock, the 
clock frequency may wander ±30% or 
more. Low-power systems often slow 
the clock to conserve power when idle. 
High-performance systems sometimes 
come in speed variants, for which cus- 
tomers pay extra to gain performance. 
As a diagnostic test, a designer may 
slow the system clock to reveal certain 
timing-related failures. No power-sup- 
ply-noise-mitigation strategy employ- 
ing careful tuning of exact noise fre- 



;0 



1 



2ttVLC 



r 



Figure 1 The impedance of this network 
attains its smallest value at the resonant 
frequency. 



quencies can possibly work under these 
conditions. 

The allure of a series-resonant circuit 
is that it permits the use of a smaller 
value of capacitor than otherwise might 
be necessary i/you match that capacitor 
with appropriate values of inductance 
and resistance, creating the series-reso- 
nant effect. Unfortunately, the smaller 
the capacitor, the more precise the cir- 
cuit must become. 

For example, a capacitor of one-fifth 
the ordinary value requires capacitor 
and inductor components with ±10% 
tolerance. A capacitor of one-tenth 
the normal value requires ±5% toler- 
ance, and so on. It is difficult to imple- 
ment high-frequency inductors with 
such tight tolerances. If you think of 
the layout inductance as fixed and plan 
a smaller value of capacitance to place 
the series-resonant point at a favorable 
location, you will face the same difficul- 
ty: You cannot easily control the exact 
values of capacitance and inductance. 

The clock must play continuously, 
repeating forever without stops or gaps. If 
the clock stops, your resonant circuit will 
spin on, plunging out of control, creating 
disturbances just as bad as the problem 
you were trying to mitigate. When the 
clock restarts, the resonant circuit takes 
many cycles to catch up — providing zero 
benefit during that period. A resonant 



circuit is useful only with continuous 
stimulation. It is powerless to prevent 
noise from random data events. 

You must place the series-resonant 
circuit within a small fraction of one 
wavelength of any device that it is 
protecting. Within that limited radius, 
the spreading inductance of the power 
and ground planes modifies the effec- 
tive series inductance of the resonant 
circuit. Consequently, the exact posi- 
tioning of a resonant circuit matters 
tremendously, so you cannot alter the 
layout without implementing a com- 
plete redesign. Even worse, a resonant 
element that provides substantial atten- 
uation for clock noise emanating from 
one location may provide no benefit 
or may even exacerbate the noise from 
another source. 

In a sinusoid-based 
system, such as an 
AM or an FM radio, 
resonating power- 
supply components 
can provide aston- 
ishing benefits. 

Last, remember that a resonant cir- 
cuit attenuates noise at only one fre- 
quency. It provides little or no benefit at 
other harmonics of the clock rate. In a 
sinusoid-based system, such as an FM or 
an AM radio, resonating power-supply 
components can provide truly astonish- 
ing benefits. 

In a digital system that starts and 
stops at various clock speeds and in 
which the layout constantly changes 
from one version to the next, the use of 
resonating power-supply-filter elements 
does not pass the KISS (keep it simple, 
stupid) test. A digital-power system is 
better served by lots of large, simple, 
nonresonant bypass capacitors.EDN 

Howard Johnson, PhD, of Signal Consult- 
ing, frequently conducts technical work- 
shops for digital engineers at Oxford Uni- 
versity and other sites worldwide. Visit his 
Web site at www.sigcon.com, or e-mail him 
at howie03@sigcon.com. 



18 EDN | MARCH 1, 2012 



[www.edn.com] 




http://ims2012.mtt.org/ 

Look What's Happening at IMS2012! 




Closing Ceremony Speaker: Thomas H. Lee 

Professor, Stanford University 

The Fourth Age of Wireless and the Internet of Everything 



Thursday, 2 1 June 20 12 
1700-1830 



"Making predictions is hard, particularly about the future/The patterns of history are rarely 
discernible until they're obvious and perhaps irrelevant. Wireless may be an exception, 
at least in broad outline, for the evolution of wireless has been following a clear pattern ^ * 
that tempts us to extrapolate. Marconi's station-to-station spark telegraphy gave way to a 
second age dominated by station-to-people broadcasting, and then to today's ubiquitous 

people-to-people cellular communications. Each new age was marked by vast increases in I m 

value as it enlarged the circle of interlocutors. Now, these three ages have covered all combinations of "stations" and 
"people," so any Fourth Age will have to invite "things" into the mix to provide another stepwise jump in the number 
of interlocutors. This talk will describe how the inclusion of multiple billions of objects, coupled with a seemingly 
insatiable demand for ever-higher data rates, will stress an infrastructure built for the Third Age. Overcoming the 
challenges of the coming Fourth Age of Wireless to create the Internet of Everything represents a huge opportunity 
for RF engineers. History is not done. 



The IMS201 2 Housing Bureau and Registration are now open! 

Don't miss your chance to see the latest RF/Microwave technology advancements while accessing over 500 companies 
technologies and services. 

Visit http://ims2012.mtt.org for complete details and to download your Program Book. Review technical sessions, 
workshop descriptions and exhibiting companies so you can make the most of your time at Microwave Week! 



Plenary Session Speaker: Steve Mollenkopf Monday, 18 June 201 2 

President and Chief Operating Officer, Qualcomm 1730-1900 

3G/4G Chipsets and the Mobile Data Explosion 

The rapid growth of wireless data and complexity of 3G and 4G chipsets drives new design 
and deployment challenges for radio and device manufacturers along with carriers. This 
talk will provide a perspective on the problem from the point of view of a large, worldwide 
manufacturer of semiconductors and technology for cellular and connected consumer 
electronics devices. The increase in device and network complexity will result in significant 
business opportunities for the industry. 



Ifl http://ims201 2.mtt.org O IEEE 

MTT-S® 1 




CONNECTING WIRELESS 




BY PALLAB CHATTERJEE 



Smart wireless for your world 

Wireless for data transmission has been around for a 
long time and has slowly been creeping into com- 
puting devices in networks. Although RF interfaces 
were previously on IT and industrial- control systems, 
which had full-time management, the prevalence of 
high-performance embedded computing has created 
a need for distributed networks without full-time administration. This need 
exists independently of the platform you use — whether a microcontroller, 
a DSP, or a processor. 



The digital-function and control 
side of the network has advanced to 
the point that it can address the self- 
handshaking and protocol negotiation 
necessary for these devices to both con- 
nect and identify themselves with mini- 
mal user intervention. A key portion of 
this task is the ability for the software 
and controller to manage the nonse- 
quential turn-on and turn-off cycles of 
devices in the network as people move 
the devices to multiple locations 
and run multiple tasks without 
administration. 

This control function is now 
influencing the RF side to move 
from individual power amplifiers, 
SAW (surface-acoustic- wave) fil- 
ters, multiplexers, and low-noise 
amplifiers to full modules ranging 
from single-frequency transceiv- 
ers to multiple -frequency cellular 
blocks. The resulting challenges 
in the RF area are spectrum 
crowding and the existence of 
multiple standards. 

The RF spectra neatly divide 
into discrete data bands that 
all serve different system goals. 
These discrete functions, how- 
ever, are all blending into the 
Internet of Things, which is 
growing daily (Figure 1). Most 
embedded computing devices are 
now transferring data to other 



applications and across spectra. This 
trend shifts the interoperability issue to 
the RF from the digital as reconstructed 
data becomes reconstructed data in the 
digital domain. 

The common domains for the device 
networks are Z-Wave in the 900-MHz 
spectrum; Zigbee in the 2.4-GHz spec- 
trum, which the IEEE 802.15.4 stan- 
dard covers; Bluetooth, also in the 2.4- 
GHz band; WiMax, which the IEEE 



INTERNET OF THINGS 
CONNECTED DEVICES AND NETWORKS 




Figure 1 The RF spectra neatly divide into discrete data 
bands that all serve different system goals. These dis- 
crete functions, however, are all blending into the Internet 
of Things, which is growing daily. 



802.16 standard covers and which sup- 
ports PHY- layer devices from the 2- to 
1 1-GHz and the 10- to 66-GHz spectra; 
and the mainstream wireless-data net- 
works of Wi-Fi, under the IEEE 802.11 
standards, which use multiple simul- 
taneous data streams on the 2.4- and 
5 -GHz bands. 

Manufacturers are integrating these 
device domains into peer-to-peer net- 
works, mesh networks, LANs, and 
WANs. These networks supplement 
the multiple bands and protocols for 
cellular communication. Cell networks 
currently employ the 850-, 900-, 1800-, 
and 1900-MHz bands. All of these net- 
works have made the digital shift to 
requiring little user intervention for 
communication, including automated 
handshaking, network connection, and 
device identification. The challenge for 
the end device is to determine which 
network to use. RF must appear in the 
end devices as a selection of one of mul- 
tiple blocks. 

A typical tablet PC with cellular 
connection may have more than seven 
RF-amplifier-transceiver blocks — four 
quad bands for the 3G cellular system, 
at least two blocks for 2.4 and 5G Wi-Fi 
bands, and one block for Zigbee or 
Z-Wave home- and industrial- 
automation network control and 
interface. The Wi-Fi blocks may 
support as many as four antennas, 
which the 801.1 lac spec allows, 
and the RF must run in parallel. 

The size, power, and module 
integration of the required bias, 
amps, filters, multiplexers, and 
multiple signal paths are driving 
the analog and RF community to 
move to its equivalent of an RF 
SOC. Manufacturers are releas- 
ing these devices with full sig- 
nal conditioning, and they will 
soon include data-conversion 
and postsignal-recovery capa- 
bilities that are driving both the 
growth and the consolidation of 
the industry. EDN 



Pallab Chatterjee has been an in- 
dependent design consultant since 
1985. 



20 EDN | MARCH 1, 2012 



[www.edn.com] 



ADDRESSING 




CRITICAL-AREA 
ANALYSIS Qj 

MEMORY CX 
REDUNDANCY 

HOW SUSCEPTIBLE IS YOUR DESIGN TO 
RANDOM DEFECTS, AND WHICH AREAS OF THE 
LAYOUT COULD BENEFIT FROM MODIFICATIONS 
THAT WOULD PROVIDE THE GREATEST POSITIVE 
EFFECT ON OVERALL YIELD? 

BY SIMON FAVRE • MENTOR GRAPHICS 

Design teams — whether using fabless, fablite, or IDM 
( integrated-device-manufacturer ) processes — 
should handle the goal of reducing a design's 
sensitivity to manufacturing issues. The further 
downstream a design goes, the less likely it is that 
you can address a manufacturing problem without 
| costly redesign. By promptly addressing DFM (design-for-manu- 
§ facturing) problems when the design is still in progress, you can 

lij 

I avoid manufacturing-ramp-up issues. 



[www.edn.com] 



MARC 



One aspect of DFM is determining 
how sensitive a physical design, or lay- 
out, is to random particle defects. The 
probability of a random particle defect 
is a function of the spacing of layout 
features, so tighter spacing increases 
random defects- Because memories are 
relatively dense structures, they are 
inherently more sensitive to random 
defects, so embedded memories in an 
SOC design can affect the overall yield 
of the device- 
Understanding how to employ criti- 
cal-area analysis becomes more impor- 
tant at each successive node- Memories 
keep getting bigger, and smaller dimen- 
sions introduce new defect types. The 
trade-offs that have worked well on 
previous nodes may give suboptimal 
results at the 28-nm node. For example, 
although manufacturers have avoided 
the use of row redundancy because they 
considered it too costly in access time, 
the technique becomes necessary at 
the 28-nm node so that vendors can 
achieve acceptable yields. All of these 
factors make careful analysis more valu- 
able as a design tool. 

CRITICAL-AREA ANALYSIS 

Critical area is the area of a layout in 
which a particle of a given size will 
cause a functional failure. Critical area 
depends only on the layout and the 
range of particle sizes you are simulat- 
ing. Critical-area analysis calculates val- 



AT A GLANCE 

□ The probability of a random par- 
ticle defect is a function of the 
spacing of layout features. Because 
memories are relatively dense struc- 
tures, they are inherently more sen- 
sitive to random defects, so they 
can affect the overall yield of the 
device. 



□ For a critical-area-analysis tool 
to accurately analyze memory 
redundancy, it must know the repair 
resources available in each memory 
block, a breakdown of the failure 
modes by layer and defect type, 
and which repair resource these 
modes are associated with. 



□ If you do not apply redundancy, 
then you may need to use alterna- 
tive methods to improve die yield. 
These methods may include making 
the design smaller or reducing 
defect rates. If you apply redundan- 
cy in designs in which it has no 
benefit, then you waste die area 
and test time, increasing manufac- 
turing cost. 



/ 



ues for the expected average number of 
faults and yield based on the dimensions 
and spacing of layout features and the 
particle size and density distribution 
that the fab measures. In addition to 
classic short- and open-circuit calcula- 
tions, current practice in critical-area 
analysis includes via and contact fail- 



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OCreafling Memaiy Plot tar Totals . 



Figure 1 A critical-area analysis using Calibre shows the effects of memory redundan- 
cy on the average number of faults for different configurations. 



ures. Analysis often shows that via and 
contact failures are the dominant failure 
mechanisms- You can incorporate other 
failure mechanisms into the analysis, 
depending on the defect data the fab 
provides. 

Critical area increases with increas- 
ing defect, or particle, size- At the limit, 
the entire area of the chip is critical 
for a large-enough defect size. In prac- 
tice, however, most fabs limit the range 
of defect sizes that they can simulate, 
based on the range of defect sizes that 
they can detect and measure with test 
chips or metrology equipment. 

DEFECT DENSITIES 

Semiconductor fabs have various meth- 
ods for collecting defect-density data. 
For use with critical-area analysis, the 
fab must convert the defect-density data 
into a form compatible with the analy- 
sis tool. The most common format is 
the following simple power equation: 
D(X)=K/X Q , where K is a constant you 
derive from the density data, X is the 
defect size, and Q is the fall power. The 
fabs curve-fit the open and short cir- 
cuits' defect data for each layer to an 
equation of this form to support criti- 
cal-area analysis. In principle, a defect 
density must be available for every layer 
and defect type to which you will apply 
critical-area analysis. In practice, how- 
ever, layers that have the same process 
steps, layer thickness, and design rules 
typically use the same defect-density 
values. 

Manufacturers may also provide 
defect-density data in a table form 
that lists each defect's size and den- 
sity value. A simplifying assumption is 
that, beyond the range of defect sizes 
for which the fab has data, the defect 
density is zero. 

CALCULATING ANF, YIELD 

To determine the average number of 
faults for a design, manufacturers use a 
tool that supports critical-area analy- 
sis, such as Mentor Graphics' Calibre, 
to extract the critical area for each 
layer over the range of defect sizes. 
To achieve this goal, manufacturers 
measure the layout and determine all 
of the areas in which a particle of a 
given size could result in a failure. 
The tool then uses numerical inte- 
gration, along with the defect's size 
and density data, to calculate the 



22 EDN | MARCH 1, 2012 



[www.edn.com] 



expected average number of faults, 
according to the following equation: 

ANF= fc XcA ( x ) xE) ( x ) DX ' 

where ANF is the average number of 
faults; D X „ X1 and D X , AV are the minimum 

' MIN MAX 

and the maximum defect sizes, respec- 
tively, according to the defect data 
available for that layer; and CA(X) and 
D(X) are the critical area and the 
defect-density data, respectively. 

Once the manufacturer has calculated 
the average number of faults, it is usually 
desirable to apply one or more yield mod- 
els to make a prediction of the defect- lim- 
ited yield of a design. The defect-limited 
yield cannot account for parametric-yield 
issues, so be careful when attempting to 
correlate this figure to actual die yields. 
One of the simplest and most com- 
mon yield models is the Poisson model: 
Y=E~ ANF , where Y is the yield, E is a con- 
stant, and ANF is the average number 
of faults. It is generally simpler to calcu- 
late the average number of faults and the 
yield for cut layers, such as contacts and 



vias, than for other layers. Most foundries 
define a probabilistic failure rate for all 
single vias in the design and assume that 
via arrays do not fail. This simplifying 
assumption ignores the fact that a large 
enough particle can cause multiple fail- 
ures, but it greatly simplifies the calcula- 
tion of the average number of faults and 
reduces the amount of data the fab must 
provide. The designer needs only a sum of 
all the single cuts on a layer and can cal- 
culate the average number of faults as the 
product of the count and the failure rate. 

MEMORY REDUNDANCY 

Embedded memories can account for 
significantly large yield loss in SOCs 
due to random defects. Although SOCs 
can use other types of memories, assume 
that the design uses embedded SRAM. 
Typically, SRAM-IP (intellectual-prop- 
erty) providers make redundancy an 
option that designers can choose. The 
most common form of redundancy is 
the use of redundant rows and columns. 
Redundant columns are typically easier 
to apply because they address only the 



multiplexing of bit lines and I/O ports — 
not the address decoding. 

To analyze failures with critical-area 
analysis, it is important to define which 
layers and defect types are associated 
with which memory-failure modes. By 
examining the layout of a typical six- 
or eight-transistor SRAM bit cell, you 
can make some simple associations. For 
example, by looking at the connections 
of the word lines and the bit lines to the 
bit cell, you can associate diffusion and 
contact to diffusion on column lines with 
column failures. Because contacts to dif- 
fusion and contacts to poly both connect 
to Metal 1 , row and column layers must 
share the Metal 1 layer. Most of the lay- 
ers in the memory design find use in mul- 
tiple places, so not all defects on these 
layers will cause failures that are associ- 
ated with repair resources. Irreparable, 
or fatal, defects, such as short circuits 
between power and ground, also occur. 

REPAIR RESOURCES 

Embedded-SRAM designs typically 
use either built-in self-repair or fuse 



[www.edn.com] 



MARCH 1, 2012 | EDN 23 



structures that allow multiplexing out 
the failed structures and replacing 
them with the redundant structures. 
Regardless of the method of applying 
the repair, the use of redundant struc- 
tures in the design adds area, which 
directly increases the cost of manufac- 
turing the design. Additional test time 
also increases cost, and designers may 
have a poor basis for calculating that 



cost. The goal of analyzing memory 
redundancy with critical-area analysis 
is to maximize defect-limited yield and 
minimize the effect on die area and 
test time. 

A critical-area-analysis tool can 
accurately analyze memory redundancy 
only if it knows the repair resources 
available in each memory block, the 
breakdown of the failure modes by 



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Figure 3 A memory plot shows the average number of faults for various memory- 
redundancy configurations. The combination of one redundant row and one redundant 
column causes a large decrease in the average number of faults. 



layer and defect type, and which repair 
resource these failure modes are asso- 
ciated with. Calibre can specify these 
variables as a series of critical-area- 
analysis rules. Each memory block also 
requires a count of total and redundant 
rows and columns. To identify the areas 
of the memory that can be repaired, 
you can either specify the bit-cell name 
that each memory block uses or use a 
marker layer in the layout database to 
allow the tool to identify the core areas 
of the memory. 

Listing 1 provides the sramConfig 
memory-redundancy specification. The 
first two lines list the critical-area-analy- 
sis rules — that is, the type of defects 
that can occur — that have redun- 
dant resources for a family of memory 
blocks. The first two lines also contain 
the column rules and the row rules. 
These rules depend on the type and the 
structure of the memory block but are 
independent of the number of rows and 
columns and the redundancy resources. 
The last two lines describe an SRAM 
block design and specify, in order, the 
block name, the rule-configuration 
name, the total columns, the redundant 
columns, the total rows, the redundant 
rows, the dummy columns, the dummy 
rows, and the name of the bit cell. In 
this example, both block specifications 
refer to the same rule configuration, 
sramConfig. Given these parameters, 
Calibre calculates the unrepaired yield 
using the defect-density data that the 
fab provides. 

YIELD WITH REDUNDANCY 

Once the critical-area-analysis tool 
has performed the initial analysis, pro- 
viding the average number of faults 
without redundancy, you can calcu- 
late the yield with redundancy. Calibre 
uses a calculation method employing 
the principle of the Bernoulli Trials, 
according to the following equation: 

Yr=Ek:o R C(N F ,(N F -K))xp(N F -K) xQ K 

where N p is the number of functional, 
nonredundant memory units; N R is the 
number of redundant memory units; P is 
the probability of success, or yield, you 
derive from the average number of 
faults; Q is the probability of a failure 
(1-P); and C(N p> (N -K)) is the bino- 
mial coefficient, which is a standard 
mathematical function. If the critical- 



24 EDN | MARCH 1, 2012 



[www.edn.com] 



area-analysis tool can postprocess the 
calculations with different memory- 
redundancy specifications, it can present 
numeric and graphical output that 
makes it easy to visually determine the 
optimal amount of redundancy. The goal 
is to ensure the required number of good 
units out of a total number of units. 

To see how effective memory redun- 
dancy can be, consider a hypothetical 
example. The memory of interest is a 
4-Mbit, 32-kbitxl28-bit SRAM. The 
goal is to realize at least 128 good units 
from a total of 130 units. In this case, 
there are two units needing repair and 
no defective units. Analysis determines 
that the unit yield considering one defect 
type is 0.999. The unrepaired yield of 
the entire core is then 0.999 raised to 
the 128th power, or 0.8798. If you per- 
form the analysis for all defect types, the 
expected yield is approximately 0.35. 

If you add redundancy to repair any 
unit defects, the repaired overall yield is 
0.999. Memory designers use the repair- 
ratio metric to express the efficacy of 
memory redundancy. It stipulates that 
the repaired yield minus the unrepaired 
yield divided by one minus the unre- 
paired yield equals the repair ratio. A 
value in the high 90s is good. In this 
case, the repair ratio is (0.99-0.35)/ 
(1-0.35), or 0.985. 



Using Calibre to determine an opti- 
mum redundancy configuration, you 
must first set up a configuration file 
for the tool (Listing 2). The bit-cell 
name, ram6t, tells the tool the name 
of the hierarchical-layout element that 
describes a memory unit that can be 
repaired and that you should consider 
in this analysis. This name enables the 
tool to calculate the critical area of 
the entire memory core, including all 
instantiations of ram6t. 

With this configuration informa- 
tion, Calibre calculates the average 
number of faults for memory with 
no redundancy, as well as for various 
redundancy configurations. Figure 1 
shows the results as a table with values 
of the average number of faults for dif- 
ferent redundancy configurations. The 
table rows show the results for the entire 
design, for just the memory, and for spe- 
cific types of defects. In the highlighted 
row, the average number of faults for 
the 1024x3 2-bit memory core improves 
substantially; the failure rate in Column 
6 is half that in Column 5. To achieve 
this improvement, Column 6 includes 
one redundant row, but adding a second 
redundant row shows almost no further 
improvement (Column 7). 

Figure 2 lists the effects of redun- 
dancy schemes in terms of repair ratio 



LISTING 1 MEMORY-REDUNDANCY-SPECIFICATION EXAMPLE 



sramConfig = 

{ {DIFF.OPEN} {DIFF. SHORT} {single. ODCO} {Ml {0.4}} 

{single .VIAl} {M2} } 
{ { PO.OPEN} {single . POCO} {Ml {0.4} } 

{single .VIAl} {M2} { single . VIA2 } {M3} } 

R128x32 sramConfig 34 2 128 ram6t 
R2048x32 sramConfig 34 2 2048 ram6t 



LISTING 2 CONFIGURATION ENTRIES FOR 4-MBIT SRAM 



sramConfig = 

{ {DIFF.OPEN} {DIFF. SHORT} { single . ODCO } {Ml. SHORT} 
{Ml. OPEN} {single .VIAl} {M2. SHORT 0.6} 
{M2 .OPEN 0.6} } 

{ {PO. SHORT} { PO.OPEN} {single. POCO} {Ml. SHORT} 
{Ml. OPEN} {single .VIAl} {M2. SHORT 0.4} 
{ M2 . OPEN 0.4} { single. VIA2 } {M3. SHORT} 
{ M3 . OPEN} } 

spram_2048x32_core sramConfig 34 2 2050 2 ram6t 
spram_12 8x3 2_core sramConfig 34 2 130 2 ram6t 



by design total, by total of all analysis 
layers, by memory, by block, and by 
layers or groups. Figure 3 shows a tool- 
created plot depicting the average num- 
ber of faults for each redundancy con- 
figuration and for each type of defect. 
The combination of one redundant row 
and one redundant column causes a 
large decrease in the average number 
of faults, and adding resources has little 
further effect. From these results, you 
can deduce that the expected average 
number of faults is based on the layout 
of the memory under consideration and 
the defect density of the fab and the 
process. The designer can now deter- 
mine the effect of various redundancy 
configurations on the expected yield of 
an embedded memory. 

Memory redundancy is intended to 
reduce manufacturing cost by improving 
die yield. If no redundancy is applied, 
alternative methods to improve die 
yield may include making the design 
smaller or reducing defect rates. If you 
apply redundancy to parts of the design 
in which it has no benefit, then you 
waste die area and test time, increasing 
manufacturing cost. Between these two 
extremes, you apply redundancy or not, 
depending on broad guidelines. Designs 
with high defect rates may require more 
redundancy; those with low defect rates 
may require no redundancy. The analysis 
of memory redundancy using critical- 
area analysis and accurate foundry-defect 
statistics is necessary for quantifying the 
yield improvement and determining the 
optimal configuration. EDN 

ACKNOWLEDGMENT 

A version of this article originally appeared 
on EDN s sister site, EDA Designline, 
http:llbit.ly/yg3Fq. 

AUTHOR'S BIOGRAPHY 

Simon Favre is a technical- 
marketing engineer in the 
Mentor Graphics Calibre di- 
vision, where he supports 
and directs improvements to 
the Calibre Yield Analyzer 
product. Before joining Mentor Graphics, 
Favre worked for Ponte Solutions , which 
Mentor acquired in 2008. He previously 
worked at other EDA companies, as well as 
at several semiconductor companies. Favre 
has bachelors and masters degrees in elec- 
trical engineering and computer science from 
the University of California — Berkeley. 




[www.edn.com] 



MARCH 1, 2012 | EDN 25 



ENGINEERING THE 




INDUSTRY PARTICIPANTS, REACTING TO THE SO-CALLED 
ENGINEERING CRISIS, ARE DOING WHAT THEY CAN 
TO FOSTER SCIENCE, TECHNOLOGY ENGINEERING, 
AND MATH TALENT AND ENCOURAGE MORE STUDENTS 
TO PURSUE ENGINEERING CAREERS. 

The engineering industry is concerned about the lack of interest in 
STEM (science/technology/engineering/math) studies and careers 
from the youth of the United States. Some in the electronics 
industry refer to this concern as the "engineering crisis." The fear 
is that, as baby boomers exit the work force, there will be too few 
engineers to replace them. The problem has reached all levels of 
public acknowledgment — from President Obama's commenting on the need for 
STEM graduates in his January 24 State of the Union address to Sesame Street, 
which is incorporating more science and technology into its programming and 
which made "engineer" a word of the day in a September 201 1 episode. 

Despite these concerns, more undergraduate students graduated in 2011 than in 2010 with 
engineering degrees in all of the eight top engineering disciplines — aerospace, biomedical, 
chemical, civil, computer, electrical and electronic, mechanical, and nuclear (Reference 1). 
Yet, at a year-over-year increase of only 5071 new US bachelor's degrees in engineering for a 
total of 84,599 new degrees in 2011, the numbers are low, especially when you compare them 
with estimates from the President's Council of Advisors in Science and Technology describing 
a need for 1 million more STEM graduates over the next decade (Reference 2). Moreover, new 
degrees for electrical and electronic engineering declined from 2005 's high of 14,742 through 
2010's 11,968, only to inch up last year with an additional 37 degrees for 12,005 new degrees 
total in 201 1. 



MARCH 1, 2012 | EDN 27 



Steve Lyle, director of education, 
work-force development, and diver- 
sity at Texas Instruments, admits that 
the number of engineering graduates 
is a concern. "The competition today 
for STEM talent is very, very tight in 
the United States," he says, noting 
that, although the unemployment rate 
remains generally high in the United 
States, the rate is below 4% for elec- 
trical engineers- "From an education 
standpoint, we [and our competitors] 
recognize that other countries — namely, 
India and China — are outpacing us in 
the number of engineers that are com- 
ing out of their universities." 

TI, like many other electronics 
companies, isn't ignoring the prob- 
lem. Instead, it's working toward a fix. 
The company has invested more than 
$150 million in STEM programs in the 
last five years and, like many others 
in the space, focuses its STEM efforts 
on student-achievement and teacher- 
effectiveness programs. 

Like TI, Microchip Technology has 
engaged in STEM efforts through simi- 
lar programs. "In the US political cir- 
cuit, we often talk about the end prod- 
uct, which is jobs, but that [product] is 
the output of the rest of it," says Steve 
Sanghi, Microchip's president and chief 
executive officer. "We have to work 
on it well ahead of time and get kids 
excited about science, math, engineer- 
ing, and technology. Corporations need 
to help nurture the resources and the 
community in which they operate. That 
[goal is] what we are trying to [achieve]: 
Prepare our future engineers; prepare 
our future employees; and educate the 
youth in math, science, engineering, 
and technologies." 

Both Microchip and TI are pro- 
ponents of FIRST (For Inspiration 
and Recognition of Science and 
Technology), an international program 
for children that combines hands-on, 
interactive robotics with a sportslike 
atmosphere and that provides more 
than $14 million in college scholar- 
ships. FIRST started in 1989 with 
approximately 20 teams. It has grown to 
more than 26,800 teams and currently 
reaches nearly 300,000 students. That 
growth is clear evidence that STEM can 
attract new young talent. 

Microchip is the organizing spon- 
sor of the FIRST Robotics Competition 
Arizona Regional, and Sanghi, who is 



AT A GLANCE 

El Competition for STEM (science/ 
technology/engineering/math) talent 
remains high. 

□ The industry is using several 
tactics, including robotics competi- 
tions, to spark students' interest 

in STEM. 



El Mutual respect between mentors 

and mentees can lead to a reward- 
ing experience for both parties. 

□ "Do engineering"— allowing next- 
generation talent the experiences of 
actual engineering, as opposed to 
theory-focused education — is a 
strong way to encourage interest 

in STEM. / 



also a member of the FIRST board of 
directors, notes that the competition 
had to turn away teams because of venue 
size. Next year, organizers may add a sec- 
ond competition or utilize a larger venue 
to accommodate more teams. 

Carol Popovich, senior community 
relations representative for FIRST and 
Vex Robotics and a 16-year Microchip 
veteran whose full-time job is to work 
within the community on STEM, 
expects further expansion in the future. 
She notes a dramatic 30% growth in 
9- to 14-year-old participants in the 
local FIRST Lego League in 2011 and 
anticipates that these young partici- 
pants will continue to explore robotics 
as they enter high school. Popovich 
is one of approximately 40 Microchip 
employees involved in the competition. 
She describes the programs as having "a 
high fun quotient" that keeps not just 
the kids but also the sponsors and men- 
tors returning each year. 

MENTORING AND HIRING 

Daniel Kinzer, a technical- support engi- 
neer who has worked at Raytheon for 
28 years, started volunteering six years 
ago with his local high school's robotics 
club. The club's 40 students are spread 
over three FIRST Tech Challenge 
teams, which Raytheon sponsors. On 
a strictly volunteer basis, he spends four 
to five hours a week at Palm Harbor 
University High School (Palm Harbor, 
FL) during the building cycle and double 
that time, plus weekends, during compe- 
titions. "If I could retire, I'd do this full 
time," Kinzer says. "I'm not sure who's 



having more fun — me or the kids!" 

Kinzer requires his teams to apply 
a full discipline to their projects. "The 
robotics portion isn't just robotics. It's 
mechanics, it's physics, it's programming, 
[and] it's engineering documentation," 
he says. "It's the difference between a 
bunch of kids molding things together 
until it works and [kids] really think- 
ing out the process and identifying how 
things are going to work. Those are the 
types of abilities that [make you not only 
a] successful engineer but also successful 
in life." As a mentor, Kinzer recognizes 
that he is there to guide the students, not 
direct them. "I really don't like giving 
students ideas," he explains. "I only want 
[them] to expand on theirs. That [factor 
is] a key element of [being] a mentor." 

Ed Smith, president of Avnet 
Electronics Marketing Americas, has 
previously mentored younger employees 
and interns at the company and has also 
tried to develop next-generation talent 
as a former president of the National 
Electronics Distributors Association 
Education Foundation. Smith advises 
mentors to listen more than they talk 
when working with their students. He 
also reminds mentors to be cautious of 
time commitments when entering a 
mentoring relationship. Recognition 
that the student's time is as valuable as 
the mentor's time is significant. "Don't 
do it unless you have the right amount 
of time," says Smith. "If you don't have 
the right amount of time, it really frus- 
trates [the mentees]. They don't feel 
important." 

Respecting the importance of the 
mentees, not only about their available 
time but also about the value of their 
ideas, goes a long way and is key to a 
rewarding experience for both parties. 
"A lot of these students tend to take us 
under their wing, as well," says Stewart 
Christie, product-marketing engineer in 
the intelligent-systems group at Intel. 
Christie works with interns at Intel; is 
engaged in student robotics and STEM 
activities at local schools; and often 
acts as a judge and a mentor in student 
competitions, including this spring's 
Cornell Cup, a college-level embedded- 
design competition. Intel and Tektronix 
sponsor this competition, which gives 
teams the opportunity to win as much 
as $10,000 (references 3 and 4). "It's 
great to have the fresh perspective and 
a much younger outlook than some of 



28 EDN | MARCH 1, 2012 



[www.edn.com] 



us here have [at the office]- It's a mutual 
respect," Christie says- 

"We who have been in the work 
force for a long [time] don't appreciate 
that what took us awhile to learn these 
young kids seem to have in their genes," 
says Pranav Mehta, senior principal 
engineer and chief technology officer 
for the intelligent-systems group at 
Intel- "It is amazing how advanced they 
are. If you just point them in the right 
direction, the kind of results that they 
can produce is mind-boggling. Many 
of my years-old assumptions shatter in 
seconds. Knowledge of society and the 
collective conscience has advanced to 
a point where these kids just see things 
that some of us cannot." 

That excellence has encouraged 
Intel, as well as Avnet and TI, to hire 
many of its mentored interns. The 
companies often bring in young tal- 
ent through internships or cooperative 
arrangements and then place them into 
rotational programs, allowing them to 
test-drive several design and business 
units. "As you increase the number 
of students coming in from college 
campuses, it's more important to have 
very robust development programs," 
says TPs Lyle, who notes that even TPs 
current chief executive officer, Rich 
Templeton, started at TI on a rotational 
basis. "We want to expose them to as 
many aspects of TI as possible so that 
they feel like they are getting a good 
start at the company." 

The companies rarely work a con- 
tinued mentoring responsibility into 
job descriptions, but, as Lyle says, "Part 
of being a leader is leading people. Part 
of leading a group is either directly 
providing that mentorship or ensuring 
that individuals in the organization, 
especially your high-potential talent, 
have the proper mentorship. It's not 
necessarily written down in everyone's 
job description, but it is understood 



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CONVERSATION 




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readers what they could do 
each day to help inspire more 
interest in STEM. Share your 
answer and review other 
responses from your peers at 
http://bit.ly/zC6wYA. 



that [mentoring] is an important part 
of leadership." 

GETTING ON THE STEM PATH 

Chris Gammell, a 28-year-old analog 
engineer, didn't wander into STEM 
until a high-school physics class sparked 
an interest. "My high-school physics 
teacher was really engaging," he says. 
"That set it off. I was always a science 
geek, but I had never done electronics 
before that. That's a big problem. 

"My first digging into circuits was a 
co-op, and I just kind of hacked along," 
Gammell explains. "I'm a big proponent 
of co-ops. That's where I really learned 
how to solder. Someone finally sat me 
down and said, 'You're doing this wrong; 
let's show you how to do this.' There 
are a lot of engineers like that. As long 
as you actually want to listen and learn 
and you aren't egotistical about it, men- 
tors are around and are gold." 

Mentoring college students, interns, 
and entry-level employees helps cement 
STEM interest and give rise to young 
careers — a necessary effort because 
45% of students who receive engineer- 
ing degrees are not practicing engineers 
10 years later, according to the ASEE 
(American Society of Engineering 
Education). But tapping interest at 
a younger age is important, as well. 
"[Kindergarten to Grade 12] is where it 
all starts," says Susan Donohue, general 
co-chairwoman of the IEEE Integrated 
STEM Education Conference, program 
chairwoman elect of the ASEE K-12 
program, and lecturer at the University 
of Virginia School of Engineering and 
Applied Science. "If you [shortchange] 
them at the K-12 level, it's going to be 
so hard for them to catch up, and we 
can't afford to lose anybody." 

Donohue has for several years been 
presenting engineering-teaching-kit 
workshops through the ASEE and 
Frontiers in Education. These kits 
include such tools as lesson plans, objec- 
tives, worksheets, bills of materials, and 
project materials, when possible. The 
self-contained kits enable teachers to 
open them and immediately bring more 
STEM into the classroom. 

National Instruments has also taken 
steps to bring more STEM directly into 
the K-12 classroom. "We've had data 
come in that suggests that, if we don't 
have [children] interested before sev- 
enth and eighth grade, the likelihood 



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The "Spectacular Seven" team from Oak Canyon Junior High in Lindon, UT, was the 
winner of the iGen fall 201 1 LED Challenge. 



[that they will go] into an engineering 
career is less," says Amanda Webster, 
community-relations manager at NI. 
For that reason, NI partners with Lego 
Group for educational robots and 
includes work with the FLL (FIRST 
Lego League) among its STEM and 
mentoring activities- FLL is an alliance 
between FIRST and the Lego Group 
that uses robotics to ramp up excite- 
ment about STEM at an earlier age than 
the FIRST Robotics Competition or 
FIRST Tech Challenge. 

"I don't think that Dr T, our founder, 
thought that, years down the road, this 
high-tech company would be partnering 
with this toy company. But, with Lego 
being a top brand . . . , it has been a huge 
opportunity for us to get into the K-12 
space," says Webster. "[Lego] lends cred- 
ibility when you are standing in front 
of a 7 -year-old trying to get him or her 
interested in math and science con- 
cepts that, unfortunately, even young 
children are showing a disinterest in." 

When looking at root causes of the 
lack of interest, NI finds that a lot of 
teachers are either not interested in 
this area or feel that this area is not 
their strong suit. "We don't have a lot 
of EEs graduating and then going back 
to teach elementary school," Webster 
explains. "Our society has built up this 
dynamic [of not encouraging STEM to 
younger children. So] more than 150 
[NI] employees go in, week after week, 
to the same classroom with the same 
teacher and students. As they go in 
every week, [they become] role models." 

In the past, NI teamed with local 



universities to train its employees before 
they entered classrooms and began men- 
toring. Currently, the company hosts its 
own technical training for mentors and 
relies on teachers to help set expecta- 
tions for the mentor's role in the class- 
room. "The training helps, but there is 
certainly a little trial by fire," Webster 
says. "By session two or three, the kids 
know them, and they become superhe- 
roes in the classroom. So it's just getting 
past that barrier and fear of going in." 

That fear can be a major barrier 
when a STEM professional considers 
entering a classroom or working one 
on one with next-generation talent as a 
mentor. "After all, we are talking about 
science and engineering, and these sys- 
tems can be very complex," says Dave 
Wilson, academic-relations director at 
NI. "But we have to take small steps and 
be willing to have something not work. 
While these things can be daunting, the 
technology is really reaching a point 
where it helps out a lot. Just try it." 

"DO ENGINEERING" 

One of the best ways to encourage 
interest in STEM is to let children 
actually engineer or, as Naomi Price, 
online brand manager for Innovation 
Generation, says, "let them get their 
hands dirty." Innovation Generation, or 
iGen, is a Web site that aims to develop 
excitement about STEM for the K-12 
segment. UBM Electronics, the parent 
company of EDN, owns iGen, which 
hosts LED challenges that see student 
teams design and build based on a pro- 
vided kit. For the fall 2011 iGen LED 



Challenge, the sponsored kit had a value 
of approximately $150 and included 
LEDs and a microcontroller. Students 
blog about their progress as their projects 
move along. In January, iGen named 
the "Spectacular Seven" team from Oak 
Canyon Junior High (Lindon, UT) as 
the winner of the fall challenge. The 
seven girls on the team, along with 
their teacher and their mentor, built a 
small Christmas tree made from PVC 
(poly vinyl-chloride) piping and loaded 
with flashing LEDs on the branches and 
a star on the top that flashes a count- 
down sign. "We're seeing a lot of energy 
from these kids," Price says, comment- 
ing on all of the teams who entered the 
challenge. "They are actually building 
something, and that [step] is important." 

As part of its STEM efforts, Math- 
Works emphasizes hands-on, project- 
based learning. "I see more and more 
professors looking to integrate projects 
into their classrooms to get students 
excited and get a better understanding 
of what they are actually going to be 
doing when they graduate," says Tom 
Gaudette, principal education evan- 
gelist at the company. Math Works has 
had close links to academia since its 
inception; its first customer was the 
Massachusetts Institute of Technology. 
Part of the company's support for 
project-based learning comes from its 
work on an integrated curriculum that 
includes its tools, as well as its work 
to provide support materials for those 
tools, such as free video tutorials. 

The company works with universities 
to incorporate these tools, starting in 
basic classes and throughout the educa- 
tion process, so that students spend less 
class time on tool review and more on 
theory and lab work. "Having those base 
learning classes where students come in 
and are able to touch and feel and try to 
program a robot or try to control some- 
thing gives the student a better idea of 
what it is to be an engineer versus fresh- 
man classes [such as] calculus, where 
they may not get the insight into what 
it is to be an engineer," Gaudette says. 

MathWorks also supports hands- 
on engineering through EcoCar 2, a 
three-year competition during which 
engineering students design and build 
environmentally friendly vehicles. 
MathWorks equips all 16 participat- 
ing university teams with its tools for 
model-based design, including Matlab 



30 EDN | MARCH 1, 2012 



[www.edn.com] 



and Simulink. "EcoCar is teaching that 
process where you . . . do the design work 
and go through all the way to the last 
year of the competition, where you 
actually have a car driving around with 
the algorithms that the students created 
running on systems," Gaudette says- 
"That [achievement is] pretty impres- 
sive for undergraduate students. [When 
they graduate], they can say, 'I built a 
car, and I was part of a team that worked 
and did it all'" 

NI's Wilson reiterates this need for 
actually engineering to attract new engi- 
neers: "Theory is important. Simulation 
has its place, but, at some point, we 
honestly believe that a big answer to the 
question of how to attract, inspire, and 
ultimately mint new scientists and engi- 
neers is to give them the experiences 
and do engineering — not only theorize 
about it, not only conceptualize it, and 
not only simulate it. Those are parts of 
a process that have to culminate in the 
'do-engineering' experience. If we can 
give relevant, exciting, real, experien- 
tial elements to students, the response 
can be very good." 

Supporting that view, NI offers 
reasonably priced versions of its uni- 
versity- and student-targeted tools — 
ELVIS (Educational Laboratory Virtual 
Instrumentation Suite) and myDAQ 
(data-acquisition). ELVIS, a Lab View- 
based design and prototype platform 
for universities, has midpoint prices 



of approximately $2000; myDAQ, a 
student-owned measurement-and-con- 
trol tool that is slightly bigger than an 
iPhone, has student pricing as low as 
$175. "[The myDAQ tool] gives exten- 
sibility of the lab time to the students 
so they can experience the instrumenta- 
tion as well as create their own instru- 
mentation anyplace in or outside the 
lab," Wilson says. "We're seeing little 
back rooms and small areas with a table 
suddenly becoming labs because stu- 
dents can walk in with their laptop, 
myDAQ, and a little accessory board; 
plug in; and do their labs right there." 

With lab time often scarce, such 
nooks of engineering practice are 
becoming more commonplace on col- 
lege campuses, as well as elsewhere. 
As the "maker movement" continues 
rising with, as Gammell describes, "a 
resurgence of electronics and kits," so 
do hacker spaces. "I never realized that 
the students who come to these [hacker- 
space] meetings aren't allowed to sol- 
der in the dorms," says Intel's Christie. 
"They have to have a place to go where 
it is safe for them to use power tools and 
those sorts of equipment. Often, those 
tools are not available at the university." 

SIGNAL RECEIVED 

The need for more next-generation 
skilled STEM professionals is on the 
radar of companies and individuals, and, 
as such, they just may beat the engi- 



CD 




MARK YOUR 
CALENDAR 

for these upcoming STEM events: 

• IEEE Integrated STEM 
Education Conference, March 
9, 2012, at The College of New 
Jersey in Ewing, NJ 
http://bit.ly/wZH08o 

• "Engineering the next gen- 
eration of STEM" panel ses- 
sion and networking event at 
Design West, San Jose, March 
28, 2012 

www.ubmdesign.com 

• Second USA Science and 
Engineering Festival, April 28 
to 29, 2012, Washington, DC 
http://bit.ly/xZtX1N 



neering crisis- Still, much more effort is 
necessary. "We all need to participate 
in this [effort]," says NI's Wilson. "We 
need not to be so focused on the fact 
that there is a problem. We've figured 
that out. Now, let's challenge ourselves 
to bring our best ideas to the table. And 
let's set the bar — for pricing, accessibil- 
ity, functionality, and ease of use for 
educators. If we do that, everyone will 
respond. But a fully defined problem 
is a half-solved problem. We need to 
start with the challenges. Once the con- 
straints are clear, people will be really 
creative on how to solve them."EDN 

REFERENCES 

\M "Bachelor's degrees in engineering, 
by discipline, 2002-201 1 ," Engineering 
Workforce Commission. 
3 Deffree, Suzanne, "President Obama: 
We need 1 million STEM graduates," 
EDN, Feb 7, 2012, http://bit.ly/x8isBb. 
9 Deffree, Suzanne, "The next genera- 
tion: amazing student innovation and 
the Cornell Cup," EDN Tech Clips, 
http://bit.ly/zuu1Jy. 

a "Cornell Cup USA," Cornell Universi- 
ty, http://bit.ly/wtc7GJ. 



Members of The Ohio State University team pose with their EcoCar vehicle. 



You can reach 
Managing 
Editor, Online, 

at 1-631-266-3433 
and suzanne. 
deffree@ubm.com, 



[www.edn.com] 



MARCH 1, 2012 | EDN 31 





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Audio-converter-subsystem 
design challenges in the 
21st century 

SOME KEY STRATEGIES ENABLE YOU TO ACHIEVE OPTIMUM AUDIO-CONVERTER PERFORMANCE. 




1 he habitat of audio converters is ever-changing. 
Designers built early converters into stand- 
alone digital-audio equipment- Later, they 
built them as stand-alone conversion devices 
with dedicated digital-audio connectivity- 
Nowadays, converters are increasingly avail- 
able as peripherals for PCs or computer networks- Meanwhile, 
performance targets have been rising. In some ways, these 
changes have affected audio-converter design; in other ways, 
it's business as usual. 

It seems that the plan of campaign for most engineers set- 
ting out to design an audio-converter subsystem — that is, a 
stand-alone converter or that part of the equipment that deals 
with audio conversion — is as follows: First, choose a data- 
converter device — an ADC, a DAC, 
or a codec chip — which will meet 
the project's requirements for per- 
formance, channel count, cost, and 
features. Then, implement a design 
around the device using the manufac- 
turer's application note plus whatever 
additional features and interfaces the 
design requires. Most converter sub- 
systems, however, either always or 
sometimes perform somewhat below 
the potential of their chosen data 
converter — usually because of several 
issues: clocking, unruly switch-mode 
power supplies, low-quality analog- 
signal paths, lack of attention to the 
voltage reference, and digital parts 
that go awry. 

When digital audio was new, the 
data converter itself was almost the 
only consideration because it was 
impossible to build one with as much 
dynamic range and linearity as the 
professional or high-end consumer 
user required in analog equipment. 
Designers asked only, "What chip is in 
it?" Nowadays, workmanlike data con- 
verters can exceed a dynamic range of 



130 dB and total harmonic distortion plus noise of 1 10 dB rms, 
unweighted, in the audio band. The weak link in a conversion 
system is most often elsewhere. No case exists for applying 
design effort or budget to the data converter itself, except in 
the most exacting of applications, and where it has already been 
applied in great measure to the rest of the converter subsystem. 
To get the best from your chosen data converter, you must apply 
painstaking design and relentless assessment. 

TYPICAL ADC AND DAC SUBSYSTEMS 

Figures 1 and 2 show typical ADC and DAC subsystems. You 
must take special care of the analog bits; several parts of the 
subsystem will try to make that task difficult. A dashed line 
indicates where you might consider isolating the analog and 



ANALOG 




-o; 



Figure 1 In a typical ADC, you must take special care of the analog bits (blue shading); 
several parts of the subsystem will try to make that task difficult. 





DIGITAL 
PARTS 






DIGITAL- 
INTERFACE 
RECEIVER 


DSP 
FUNCTIONS 




INTERPOLATOR 
AND SIGMA- 

DELTA 
MODULATOR 



OUTPUT 
CONDITIONING 



Figure 2 In a typical DAC system, the dashed line indicates where you might consider 
isolating the analog parts (blue shading) and the digital parts, but many ways are avail- 
able for doing so, or you can opt not to isolate the parts. 



[www.edn.com] 



MARCH 1, 2012 | EDN 33 



REFERENCE I [] I O 

o or 



PHASE 
COMPARATOR 



LOOP FILTER 



vco 



REFERENCE 



/2 N 



CONVERTER 
* CLOCK 



HIGH CORNER 
FREQUENCY 



LL U± 



LOW CORNER 
FREQUENCY 



JITTER REJECTION 



OUTPUT-PHASE-NOISE (INTRINSIC-JITTER) SPECTRUM 



Figure 3 You might use a conventional analog PLL to lock a converter to a reference clock. 



the digital parts, but many ways are available for doing so, or 
you can opt not to isolate the parts. 

CLOCK RECOVERY 

The conversion clock of a data converter is critical to its 
linearity because any variation in the regularity of the clock 
results in sampling jitter, which causes phase modulation of 
the converted signal (Reference 1 ). You can most easily assess 
this parameter by passing a high-amplitude, high-frequency 
signal through the converter and looking for phase -modula- 
tion sidebands or skirts in the spectrum of the output- 
Converter clocks are usually derived from phase-locked 
loops rather than local oscillators; it is unusual for a device 
to be able to always be the system-clock master. It must be 
able to lock to an external reference or to its digital- audio or 
computer interface. To lock to all references, the lock range 
may need to be as wide as ±1000 ppm and must usually accom- 
modate different sample rates (Reference 2). 

The need to lock converter clocks to various wide-ranging 
references and to maintain low jitter tends to be among the 
most difficult challenges in converter design because it embod- 
ies some tough trade-offs. Although other applications, such 
as telecommunications, had somewhat solved this problem 
before digital audio emerged, audio engineers had to start 
from scratch, and it's taken a couple of decades to reinvent a 
good approach. The situation has become more challenging 
now that you must lock to software-generated syncs and time 
stamps arriving over computer interfaces because they can 
embody large amounts of jitter with uncontrolled spectrum 
and may not come around as often as you'd like (Reference 3 ). 

Figure 3 shows a conventional analog PLL that you might 
use to lock a converter to a reference clock. A phase com- 
parator continually compares the external reference with the 
regenerated version, and decides whether you should speed 
up or slow down the voltage-controlled oscillator to make 
them match in frequency and phase. You need to respond 
in a leisurely fashion; otherwise, you'll track any incoming 
jitter. Smooth out the up/down requests with a lowpass loop 
filter before passing them to the control input of the VCO. 

The tough trade-offs, however, are mostly about choosing 
the right loop-filter characteristics and the right VCO. The 
design must reject incoming jitter down to low frequencies so 
that it does not become prey to audible sampling jitter. That 
requirement also potentially allows you to accommodate a 
low comparison frequency, such as a reference comprising 
infrequent software time stamps or a video sync that lines up 
with an audio sample only every few seconds. 



Unfortunately, a low loop-filter corner frequency makes 
the PLL slow to lock up. Worse, though, it prevents suppres- 
sion of the phase noise of the VCO around the loop. To avoid 
unacceptable intrinsic jitter, you must keep the loop filter's 
corner frequency high, or choose a VCO with low phase noise 
in the first place. 

A good low-noise oscillator is a quartz VCXO. Because 
of their high-Q factor, however, you can't pull them far from 
their natural frequency, so they may have a pull range of only 
±100 ppm, which may be insufficient for your requirements. 
On the other hand, a humble RC multivibrator VCO can 
have all the pull range you need but is essentially untuned, so 
it has large phase noise and is prey to all manner of interfer- 
ence. A few other VCO options exist between these extremes. 
To solve the pull-range problem with quartz, you could com- 
mission some VCXOs made of a special material with a lower 
Q, such as LGS (langasite) or lithium tantalate, which are 
expensive. 

You could use a tuned-circuit LC VCO, which has a lower- 
Q factor than that of crystals, but at least it has a Q factor, so it 
can be designed with lower phase noise than a multivibrator. 
These circuits' wide range can cover both 44-1- and 48-kHz 
rates and can easily accommodate ±1000-ppm reference 
inaccuracy. Overall, this circuit is not a bad choice; if you're 



PLL 



REFERENCEC 
(a) 

REFERENCED 
(b) 



HIGH F c 



RC 
VCO 



PLL 




PLL 



PLL, 



REFERENCEC 
(c) 



LOW F c 

LI 



LGS 
VCO 



HIGH F r 



LC 
VCO 



Figure 4 Three analog PLL examples are shown. A basic PLL 
chip operates in a digital-audio-interface receiver (a). A purpose- 
designed PLL provides converter-clock recovery, with a higher-Q 
VCO and a low loop-filter corner frequency (b). Two cascaded 
PLLs— the first, with an LGS VCXO for wide lock range and a 
low-corner-frequency filter, which rejects jitter, and the second, 
with a tuned-circuit VCO and a high loop-filter corner frequency 
to cover all sample-rate multiples— provide good intrinsic jitter (c). 



34 EDN | MARCH 1, 2012 



[www.edn.com] 



picky, though, the intrinsic jitter won't be top-class if the 
corner frequency of the loop is dropped to where you'd like it. 

In considering these trade-offs, it is helpful to look at some 
real-world examples of applying analog PLL technology to 
converter subsystems (Figure 4). The circuit in Figure 4a uses 
a basic PLL chip or, for an AES3 (Audio Engineering Society 
3) or SPDIF (Sony/Philips-digital- interface) DAC, uses the 
PLL in the digital-audio- interface receiver. The VCO, how- 
ever, has a low-Q factor and high phase noise, usually in the 
form of an RC multivibrator, which is vulnerable to all sorts 
of interference, especially power-rail and ground noise, and 
the corner frequency of the loop filter is high. These prob- 
lems result in high intrinsic jitter and poor jitter rejection at 
audible frequencies. 

The circuit in Figure 4b uses a purpose-designed PLL for 
converter-clock recovery, with a higher-Q VCO and a low 
loop-filter corner frequency. This setup results in good intrin- 
sic jitter and jitter rejection, but the pull range may be insuf- 
ficient, and you must carry the cost of two or more VCXOs. 

The circuit in Figure 4c uses two cascaded PLLs — the first, 
with an LGS VCXO for wide lock range and a low corner- 
frequency filter, which rejects jitter, and the second, with a 
tuned-circuit VCO and a high loop-filter corner frequency 
to cover all sample-rate multiples. This circuit has no jitter 
so it requires no jitter rejection. If you make the LGS VCXO 
frequency 44.1 and 48 kHz, you can provide a sample-rate 
reference for the second PLL with a simple programmable 
divider. This approach has good intrinsic jitter and jitter 
rejection, works for all sample-rate multiples of 44-1 and 
48 kHz, and has a wide lock range. Even with one VCXO, 
though, it's still expensive, and it still may have questionable 
performance at low comparison rates. 

An even better approach is to adapt the dual-loop archi- 
tecture as a hybrid PLL by implementing the first PLL in the 



digital domain, thus eliminating the trade-off of phase noise 
versus low corner frequency because the loop filter and the 
VCO are both entirely digital. The VCO— now an "NCO"— 
is jittery because it is a varying integer division of a fixed 
master clock, but inclusion of a sigma-delta modulator in the 
loop means that you can confine its jitter to high frequencies. 

It is therefore straightforward to cascade the NCO's out- 
put into an analog PLL with a high corner frequency, which 
can then use an inexpensive VCO without intrinsic jitter. 
Furthermore, you can change the corner frequency in soft- 
ware to achieve fast lock and then extreme jitter rejection. 
The hybrid PLL is inexpensive because it requires no reso- 
nator-based VCO. Similar approaches are now available for 
audio use from a number of vendors, including Cirrus Logic 
(Reference 4 and Figure 5). Some manufacturers even built 
them into data converters. 

Another way to approach this problem is to use mod- 
ern, low-cost SRC (sample-rate-converter) chips, which 
are achieving performance that can exceed that of the data 
converter itself. You might elect to operate the conversion 
element at a fixed rate provided by a local crystal, thus elimi- 
nating sampling jitter, and to convert the converter's input 
or output data rate. This approach can lead to other issues 
and places the responsibility on the SRC to achieve jitter 
rejection that matches the same standard as in the PLL model 
while also protecting the quality of your audio components. 

POWER SUPPLIES 

High-quality line-powered audio equipment has traditionally 
employed linear PSUs, but these devices have disadvan- 
tages of size, weight, heat, and cost and may need a manual 
line-voltage selector. Properly designed PSUs do have the 
advantage of not providing a source of high-frequency inter- 
ference into the analog circuits. An SMPS eliminates these 



DELTA-SI G MA FRACTIONAL-N FREQUENCY SYNTHESIZER 



LCO 



PHASE 
COMPARATOR 



INTERNAL 
LOOP FILTER 



VCO 



FRACTIONAL-N 
DIVIDER 



' PLL OUTPUT 



DELTA-SIGMA 
MODULATOR 



N 

DIGITAL PLL AND FRACTIONAL-N LOGIC A 



DIGITAL FILTER 



FREQUENCY 
REFERENCE O- 
CLOCK 



FREQUENCY 
COMPARATOR FOR 
FRACTIONAL-N GENERATION 



Figure 5 Cirrus Logic's C2000 hybrid PLL is inexpensive because it requires no resonator-based VCO. 



[www.edn.com] 



MARCH 1, 2012 | EDN 35 



disadvantages, but it must be carefully designed if it is not 
to become a major source of hostile switching noise- High- 
end-audio designers have traditionally shied away from using 
SMPSs. 

You must design an SMPS in any type of equipment to 
meet the appropriate electromagnetic-compatibility stan- 
dards for conducted and radiated emissions- Nowadays, this 
task is not difficult, with SMPS controller vendors providing 
application circuits that comply with these standards — usu- 
ally, just meeting compliance requirements to save the costs of 
filter components- Unfortunately, the same sorts of misbehav- 
iors that might cause an SMPS to be noncompliant can wreak 
havoc with audio performance, even at much lower levels. 
Thus, SMPS design for audio applications can be elaborate. 

DRAWBACKS OF LOW-COST SMPSs 

Converter systems often need a large number of power rails 
and may benefit from isolation between the digital and the 
analog parts, so a flyback architecture is a popular choice 
because it conveniently offers these benefits, which may also 
be useful in dc-powered situations. A variety of other simple 
SMPS architectures can be used instead; the problem for the 
uninitiated is generally how to choose among them. 

In a flyback converter, dc — either directly input or rec- 
tified from the ac-line voltage — is switched through the 
primary of the flyback transformer by a transistor under the 
control of a device that regulates the duty cycle of a train of 
switching pulses to regulate the various secondary outputs. 
Rectified and filtered secondaries provide the power rails. 

Figure 6 shows a flyback converter and its switching 
waveform. Stray capacitance, C D , across the switch and the 
leakage inductance of inductor L LK causes the high-frequency 
oscillation at the point at which the switch turns off. This 
oscillation is a largely unavoidable source of hostile RE You 
can control its amplitude with snubbers to protect the switch, 
but this approach can make the interference even worse. 
The low-frequency oscillation before the switch turns on 



is a consequence of the stray capacitance and the primary 
inductance, L p . The switch interrupts the oscillation at a 
random voltage, causing potential interference from the large 
switching voltage and current. 

The main problem, then, with the basic flyback topol- 
ogy — and with most other basic topologies — is that the 
transistor switches hard and randomly, causing high levels 
of radiated and conducted interference to invade the analog 
audio parts. You are now on a slippery slope, and can't do 
much to reduce the source of the problem. You can keep 
the switching loops as small as possible to reduce radiation, 
you can optimize the ground topology and make critical 
tracks wider to reduce ground noise, and you can tame the 
edge times with snubbers, but only at the cost of reduced 
efficiency and increased heat. So you end up having to take 
disproportionate steps in the vulnerable parts to make sure 
that the audio remains clean. These steps can include the use 
of screening cans, split grounds, or galvanic isolation. 

Another problem is the random frequency of the SMPS 
controller, which can produce interference at the beat fre- 
quency between itself and, for example, the audio sample 
rate, thus making it impossible to confine it to some incon- 
spicuous part of the spectrum. A possible approach is to 
lock the switching frequency to some multiple of the sample 
rate to remove the beat frequency, but this approach can be 
problematic. The regulatory variation of the duty cycle can 
cause its own beat, and some types of SMPS controllers vary 
the switching frequency to effect regulation. You could even 
introduce a situation in which a software bug or a wayward 
sample rate could collapse the power rails. It's easy to see why 
designers are reluctant to use SMPSs in high-performance 
audio equipment, but they often have no choice in dc-pow- 
ered situations, and SMPSs are small and inexpensive. 

RESONANT AND QUASIRESONANT SMPSs 

Ideally, to combine the benefits of a linear supply and an 
SMPS, you would like to find a way of passing a high-frequen- 



L LK ANDC D 



6- 



S _l_ w 1 

-p V OUT 





(§) - Cd Vi 

o 



t=0 



L p AND C D 



(a) 




Figure 6 In a flyback converter (a) and its switching waveform (b), stray capacitance, C D , across the switch and the leakage induc- 
tance of inductor L LK causes the high-frequency oscillation at the point at which the switch turns off. 



36 EDN | MARCH 1, 2012 



[www.edn.com] 



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cy sine wave through the transformer. An approximation to 
such an approach is a resonant SMPS. To losslessly achieve 
this architecture, it is usual to generate the sine wave by plac- 
ing a resonant LC-tank circuit in the primary; a neat trick is 
to use the primary inductance as the inductor. The stimulus 
for the waveform is still a hard-switching transistor under 
clever control, but the resonant circuit tunes the primary 
waveform to an approximation of a simple sine wave, with 
the switching happening at OV or OA moments, all of which 
leads to less hostile switching noise. 

On the other hand, resonant designs tend to be somewhat 
more costly and larger than flyback designs. A major draw- 
back with many resonant architectures is that you must tailor 
the LC-tank circuit to the switching frequency and dc input 
voltage to maintain resonant and zero-switching operation, 
which makes offline universal input design problematic unless 
you incorporate power-factor correction. 

A good compromise is a quasiresonant converter. The 
idea here is that, because the problems in a simple flyback 
converter happen only at the moments of switching, it is 
necessary to find a way of creating a resonant waveform only 
at the switching points. You can achieve this goal by simply 
introducing primary resonance into an ordinary flyback topol- 
ogy and making the controller clever about deciding when to 
switch. Figure 7 shows a zero-voltage-switching, or valley- 
switching, quasiresonant converter, which is a low-cost way 
to cut SMPS emissions at their source (Reference 5). 

In this case, you create the tank circuit by simply adding a 
large capacitor across the switch. The tank circuit slows the 
switch-off rise time, and the controller arranges the switch- 
on instant to coincide with a valley in the low-frequency 
oscillation; this approach inherently makes the cycle period 
variable with an attendant spread-spectrum effect, which 



TIME 

Figure 7 A zero-voltage-switching, or valley-switching, quasiresonant converter 
is a low-cost way to cut SMPS emissions at their source. 



can improve interference and which increases EMC margins 
(Figure 8 and Reference 6). 

SMPS SELECTION 

It is often difficult for the uninitiated to make the correct 
choice of SMPS architecture for audio because most SMPS- 
controller vendors organize their selection tables by power 
capability. They assume that audio designers, like other 
designers, will want to choose the cheapest approach for their 
power requirement. The recommended SMPS for low-power 
applications such as this one — say, less than 20W — is usually 
a basic, hard- switching type because the power is low enough 
for its emissions to remain below statutory EMC limits with 
minimal filtering and for the losses resulting from its indis- 
criminate switching to be insufficient to set it on fire. 

Higher-power applications in which you must control 
switching noises and losses require the use of resonant and 
quasiresonant topologies. For audio, however, it's often a good 
idea to make a low-power implementation of a high-power 
topology in the interest of achieving minimum emissions; 
you can usually make up for the extra cost by not having to 
armor-plate the audio parts. 

OTHER CONSIDERATIONS 

Cross-regulation — varying load conditions on individual 
rails — can cause the voltages of other rails to vary and is often 
a problem with multirail-SMPS designs because the regulatory 
mechanism of the controller can generally operate on only one 
rail. In performance-critical applications, it may be necessary 
to provide linear postregulation on analog-power rails from the 
SMPS. If so, take care to provide adequate cooling for the lin- 
ear regulators. Linear regulators can usually regulate over only 
a limited frequency range, and the switching products from 
the SMPS can easily exceed this range, causing 
them to pass straight through the regulator. It is 
therefore a good idea to use ferrite beads ahead 
of linear postregulators. 

Line-powered linear and SMPS equipment 
usually draws current from the mains only during 
voltage peaks, which can cause distortion to the 
power line, with possible detriment to the per- 
formance of other sensitive audio equipment. It 
may be beneficial to incorporate PFC into your 
SMPS design to cause the least possible distor- 
tion to the power waveform. You can be sure, 
however, that all the other equipment around 
the SMPS will probably be causing distortion 
anyway. Some PFC schemes allow tight control 
of the rectified voltage ahead of the SMPS, 
which can allow you to further reduce switch- 
ing noise in resonant and quasiresonant designs 
by ensuring no switching for any input voltage. 

As well as applicable safety, EMC, and dis- 
posal legislation, line-powered equipment is sub- 
ject to or will become subject to various territo- 
rial legislation for standby-power consumption, 
when applicable, and operating efficiency — for 
example, under the European Union's Ecodesign 
Directive and the voluntary US EnergyStar 
program. Although territorial legislations vary, 




VALLEY 



38 EDN | MARCH 1, 2012 



[www.edn.com] 



maximum standby-power consumption 
of 0.5W and minimum operating effi- 
ciency of approximately 80% are typical 
for a 20W device. 

ANALOG-SIGNAL PATH 

Analog performance is the limit- 
ing factor in many converter designs. 
Somewhere along the line, perhaps you 
forgot some of this wisdom. All of the 
buffer amplifiers, gain stages, and other 
components between the outside world 
and the ADC and between the DAC 
and the outside world are obvious areas 
in which good design practice will pay 
dividends. It is no mean feat to main- 
tain the performance of a flagship data 
converter through the analog circuits, 
particularly if you must incorporate sig- 
nificantly high performance. 

In general, use a ground plane for 
analog circuits and take advantage of 
the small surface-mount-technology 
packages that are now available. Lay 
things down instead of standing them 
up. These measures are free and will 
reduce susceptibility to interference and 
crosstalk. 

Of particular importance are the buf- 
fer circuits, which drive by the input of 
the ADC or are driven by the output of 
the DAC. In general, the safest policy 
is to stick with the exact circuit topol- 
ogy and components that the converter 
manufacturer recommends. The vendor 
will have spent a long time coaxing the 
best out of the device by tweaking its 
buffer. However, this scenario is not 
always true. With experience and care, 
it is sometimes possible to exceed the 
application-note performance. On the 
other hand, if cost is important, you 
can often scrimp a bit on op -amp types. 

Sigma-delta ADC inputs often have 
a nonlinear-input characteristic and 
produce aliasing components if subject 
to high frequency, so an ideal ADC buf- 
fer must achieve a lot of high-frequency 
roll-off — but without compromising in- 
band flatness — and a low output imped- 
ance. It's better to avoid the passive pole 
between the output of the buffer and the 
input of the converter and to instead 
use, for example, an analog-input buffer 
(Reference 7). 

Many high-quality DACs have cur- 
rent outputs, requiring an outboard 
current-to-voltage-converter circuit. 
Sigma-delta DACs often produce sig- 
nificant out-of-band noise, and the IVC 



[www.edn.com] 



must filter, cancel, or both filter and 
cancel this noise in the first instance. 
Therefore, to maintain in-band linear- 
ity, the IVC must behave linearly at fre- 
quencies well above the audio band. If 
you are tempted to stray from the manu- 
facturer's recommended IVC design, 
bear in mind the bandwidth require- 
ment and note that the data converter's 
output loading will probably have to be 
similar to that of the application circuit 
for optimum performance. 

As for the rest of the analog-signal 
path, it is important to choose the right 
components and circuit topologies. The 
most straightforward way is to use op 
amps. This approach is currently a good 
policy except in a few situations, such 
as microphone/phonograph preamps 
and high-current outputs. It will pay to 
familiarize yourself with the noise models 
for op-amp circuits, such as those that 
Reference 8 describes, and to implement 
a spreadsheet to calculate noise levels for 
your circuit. A simpler but less versatile 
approach is to use op-amp manufacturers' 
noise-reckoning tools (Reference 9). 
The best approach is to use a full-blown 
Spice simulator (Reference 10). 

You will find that your choice of op 
amps in each stage is generally restricted 
to relatively few that have the requi- 
site voltage-noise, current-noise, or 
both voltage- and current-noise per- 
formance. The world is full of op amps, 
most of which are not good for audio. 
On the other hand, beware the best- 
audio-op-amp syndrome. 

No op amp will behave best in every 
audio stage. In each case, you must select 
the right one for the job. Usually, you 
can make this selection from looking at 
available data or by trading off require- 
ments against cost, power, and other 
factors. But don't be afraid to use trial 
and error in the end, although doing so 
requires some determination and good 
eyesight in this age of SMT. With some 
dexterity, you can persuade dual- inline 
sockets onto the SOIC sites in your pro- 
totype. In general, it's a good idea to use 
dual-op-amp sites because doing so is a 
good trade-off of cost and choice and 
allows tight layout in balanced circuits. 

Designers generally prefer inverting- 
op-amp topologies over noninverting 
models because the inverting devices' 
input terminals operate at virtual earth. 
The dynamic input-common-mode 
voltage of noninverting configurations 




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Stall 160 kHz 
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Figure 8 The tank circuit slows the switch-off rise time (a), and the controller arranges the switch-on instant to coincide with a valley 
in the low-frequency oscillation (b). 



may add distortion, particularly at high frequencies with some 
op amps. Consider adopting a fully balanced topology end to 
end — perhaps using a "symmetrizer" in the ADC's case to 
achieve balance through the channel even with unbalanced 
inputs. Avoid mode-conversion types, however. Using a fully 
balanced topology not only reduces interference and crosstalk 
but also can achieve higher performance because distortion 
mechanisms often tend to cancel. Most high-end data con- 
verters operate in a balanced mode anyway. 

It is important to select a gain structure that maximizes 
the dynamic range, or SNR, and thus minimizes the need for 
excessively low-noise design, with its attendant cost. Even so, 
resistor values must be low enough for their thermal noise to 
be out of the picture but not low enough to bring problems 
of overdissipation or circuit loading. 

The linearity of resistors and capacitors is also important. 
Resistors must be metal-film or thin-film types, not the usual 
chip resistors, which change resistance according to voltage 
and the seasons. Capacitors must be low-k ceramic types, such 
as COG and NPO types, or low-loss plastic, such as polysty- 
rene. Failure to observe these rules leads to nonlinearity and 
distortion in most circuit topologies. Keep electrolytics out 
of the signal path; there are other ways to ensure extended 
low-frequency response. 

PCB layout of the channel circuits is critical for minimiz- 
ing both interference and interchannel crosstalk. Make sure 
that the op amp's output and the ground nodes of the stages 
are outermost and that the op amp's input nodes are inner- 
most in your channel-strip layout. 

Pay attention to the bandwidth of your stages. It's not 
always better to go for a dc- to- light approach. Limiting the 
bandwidth at the top end reduces susceptibility to interfer- 
ence, and the presence of excessive high frequency, even if 
inaudible, does no good to the in-band signal. Limiting the 
bandwidth at the bottom end removes wandering dc, which 
can cause problems with mixing and switching, as well as 
the risk of unexpected overload. On the other hand, keep 
a healthy disrespect for the -3-dB, 20- to 20-kHz approach. 
Extend the top and the bottom end beyond the bare essentials 



when possible and strive to keep the area between flat; you 
will notice the difference. 

REFERENCE VOLTAGE 

Nearly all data converters have at least one accessible refer- 
ence-voltage pin, reference-current pin, or both. The refer- 
ence multiplies the input to the converter to produce the 
output, so how you handle the reference is just as important 
as the analog-signal path. Any noise or interference on the 
reference modulates the converter's output. You must filter 
internally generated voltage references by placing suitable 
capacitors close to the pins. This approach usually requires 
an assortment of low- value, high-frequency, large electrolytic 
or tantalum capacitors. 

In some cases, you may want to drive a voltage reference 
externally from a well-regulated and filtered source. Some 
converter devices require both high and low reference volt- 
ages to define their operating range, and some require sepa- 
rate references per channel. Although users can sometimes 
to some degree modify the reference voltages, manufactur- 
ers often optimize converter performance at a particular 
voltage, and it's best to stick with that voltage. When your 
design has distortion or noise problems, remember to look 
at the reference. If modulation issues, such as sidebands 
or noise skirts around the signal frequency, get worse with 
increasing signal frequency, it's jitter. If those issues don't 
get worse, then the problem is most likely the reference 
voltage (Reference 11). 

DIGITAL PARTS 

Any low-quality digital processing in the signal path can undo 
all of your good work in the analog domain. Make sure that 
your design has enough precision everywhere and that algo- 
rithms are beyond reproach. Culprits often include dithering, 
noise-shaping, and dynamics processing. Remember, too, those 
parts of the digital-signal path that designers often overlook. 
For computer interfaces, the driver or parts of the operating 
system that you thought you had bypassed sometimes let you 
down. You must be able to test your entire signal path, so make 



40 EDN | MARCH 1, 2012 



[www.edn.com] 



sure that your dual-domain audio-test equipment can work in 
the computer domain, directly interfacing with your driver 
layers. 

In the old days, it was almost possible to keep all of the 
digital parts of a converter system ticking at some multiple 
of the sample rate- Consider the simple case of an AES3- 
interfaced converter with no DSP and no microcontroller. 
Nowadays, though, you must have a boxload of computers, 
including DSPs, RISC processors, and FPGAs, all running 
asynchronously, and probably a computer interface buzzing 
away across the entire spectrum. Although lower operating 
power, lower core voltages, and smaller dice and packages 
contribute to reducing the hostile intent of digital electron- 
ics, a designer can do little to fix it beyond observing good 
EMC design at ports and good power decoupling and filtering. 

You must make some fundamental decisions at the outset 
of your design. These decisions include the choice between 
line power and dc power, as well as choices regarding 
whether you can put your design into its own metal box, 
whether it must cohabit with digital parts, or whether 
it must reside in a host computer. You also must decide 
whether you need and whether you can afford screening 
cans. Another decision comes up when you consider con- 
struction: Can you use a multilayer PCB with groundplanes, 
a small SMT device, or another configuration? What about 
isolation? Can you galvanically isolate the analog and digi- 
tal domains using optical or magnetic isolators? This isola- 
tion can be beneficial in computer or computer-interface 
cases, in which the digital ground can be toxic. You also 
need to weigh EMC compliance and efficiency. Project 
requirements and component budget probably dictate the 
answers to these questions. 

The objective assessment of converter systems, both 
during design and in general, is a complex subject and the 
subject of many international standards, such as IEC 61606-3 
and AES17-1998 (references 12, 13, and 14). It is useful, 
however, in many situations to make a simpler assessment. 
For many engineers, this assessment involves instead using 
listening tests to determine audibility. The debate about 
whether measuring or listening is better will rage forever. 
However, developing high-performance audio requires both 
methods. Some engineers believe that it is better to use 
measurement to debug the design and to worry about listen- 
ing tests after that. 

For debugging, first equip yourself with an audio ana- 
lyzer, which can stimulate and measure in the analog, 
digital, and computer domains. Analyzers should be able 
to display a continuous high-resolution FFT, and they 
should be user-programmable so that you can automat- 
ically hop among key measurements. You must be able 
to define all of the key measurement parameters when 
you set up the debugger. Make a lead to connect a pair 
of small probes to the analog analyzer's input so that you 
can measure between all the stages. SMPS and computer- 
based devices also need a means of seeing the wideband 
spectrum, which EMC precompliance also requires. Table 
1, available with the Web version of this article at http:// 
bit.ly/w29NCL, provides a guide to the most important 
audio-performance parameters that apply to conversion 
systems. EDN 



REFERENCES 

9 Dunn, Julian, and Ian Dennis, "The diagnosis and solution 
of jitter-related problems in digital audio systems," Preprint 
3868, Audio Engineering Society, February 1994, http://bit. 
ly/w6uBUo. 

a "AES1 1 -2009: AES recommended practice for digital 
audio engineering - Synchronization of digital audio equip- 
ment in studio operations (Revision of AES1 1-2003)," Audio 
Engineering Society, 2009, http://bit.ly/w1S33y. 
9 Dunn, Julian, "Sample clock jitter and real-time audio over 
the IEEE1394 high performance serial bus," Preprint 4920, 
Audio Engineering Society, 1999, http://bit.ly/wKIQpU. 
El CS2000-CP, "Fractional-N Clock Synthesizer & Clock 
Multiplier," Cirrus Logic, http://bit.ly/yJlmqU. 
a Kleuskens, J, and R Kennis, "75W SMPS with TEA1507 
QuasiResonant Flyback controller," Philips Semiconductors, 
June 30, 2000, http://bit.ly/AurkSB. 
9 "L6565 quasi-resonant SMPS controller," STMicroelec- 
tronics, http://bit.ly/xoMAVu. 

9 "AK5394A Super High Performance 192kHz 24-bit AX 
ADC," Asahi Kasei, 2005, http://bit.ly/wNJAzw. 
[3 Karki, James, "Calculating noise figure in op amps," Texas 
Instruments, http://bit.ly/A27aF3. 
3 "Noise Calculator, Generator and Examples," Texas 
Instruments, http://bit.ly/x2xDGU. 
BS'TI TINA-TI SPICE-based Analog Simulation Program," 
Texas Instruments, http://bit.ly/wniJs3. 
KB Dennis, Ian; Julian Dunn; and Doug Carson, "The Numeri- 
cally-Identical CD Mystery: A Study in Perception versus 
Measurement," 1997, http://bit.ly/zU0BZs. 
ffi"IEC 61606-3: Audio and audiovisual equipment - 
Digital audio parts - Basic measurement methods of audio 
characteristics - Part 3: Professional use," International 
Electrotechnical Commission, October 2008, http://bit.ly/ 
AckWHL. 

ffi"AES17-1998 (r2009): AES standard method for digital 
audio engineering - Measurement of digital audio equipment 
(Revision of AES17-1991)," Audio Engineering Society, 
1998, http://bit.ly/xgOPWH. 

ffi"AES-12id-2006 (r201 1): AES Information Document for 
digital audio measurements - Jitter performance specifica- 
tions," Audio Engineering Society, Oct 5, 201 1 , http://bit.ly/ 
zKCKfq. 



AUTHOR'S BIOGRAPHY 

lan Dennis is technical director of the Prism Sound 
Y Group, a manufacturer of audio converters, test- 
H[ and-measurement equipment, audio workstations , 
{ pAV and media servers . He has been designing audio 
fl equipment since the early 1 980s. At Prism Sound, 
Vl he focuses on R&D and production activities but 
also works on a few design projects now and then. Current inter- 
ests include audio conversion, audio-test equipment and methods, 
media-streaming devices, and audio networking. Dennis is vice 
chairman of the Audio Engineering Society SC-02-01 Standards 
Committee for audio test and measurement and also works on 
standards development within the BSi and International Electro- 
technical Commission, most recently contributing to IEC 61606- 
3 test methods for professional digital-audio equipment and ITU 
BS.l 770 loudness metering. 



[www.edn.com] 



MARCH 1, 2012 | EDN 41 



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TECHNOLOGY 




READERS SOLVE DESIGN PROBLEMS 



CMOS gate makes long-duration 
timers using RC components 

Raju Baddi, Tata Institute of Fundamental Research, Pune, India 



The CD4011 CMOS NAND 
gate has a typical input current of 
10 pA at room temperature. You can 
charge a capacitor connected to the 
gate input with currents on the order of 
hundreds of picoamperes and neglect 
the influence of the gate- input current 
on the charging time of the capacitor. 
You normally need large-value resistors 
to limit currents to this low level. These 
resistors are not commonly available. 
You can instead use a transistor as a 
current attenuator, despite its more 
usual amplifying nature. 

The circuit in Figure 1 uses one 
CD4011 package containing four 
NAND gates, which you can use to 
build four independent long-duration 
timers. Note, however, that temperature 
variations and component parameters 
affect the timing, a situation 
that may be acceptable if you are 
not concerned about accurate 
timing and need only a simple 
circuit without large-value elec- 
trolytic capacitors and resistors. 

The series-connected diode 
voltage drops of D x and D 2 bias 
current source Q r The resulting 
voltage across R t is a Q l base- 
to-emitter- voltage junction drop 
less and sets the Q collector cur- 
rent, which is also the Q 2 emitter 
current. The resulting Q 2 base 
current is its emitter current 
divided by its current gain and 
charges timing capacitor C r 

Before the start of the timed 
period, the gate output is high, 
biasing on Q 3 and Q , allowing 



sufficiently below its switching thresh- 
old to maintain its high output state. 
Momentarily closing and then releasing 
S 1 starts the timed period by discharging 
C r This action drives the gate output 
low and ensures that Q 3 is biased off, 
which allows Q l and Q 2 to slowly charge 
Cj through the constant-current action. 
The power-supply current draw of the 
gate increases somewhat as its input 
voltage pulls away from the 5V rail. 

When the C l charge reaches the gate- 
switching threshold of approximately 
2.5V, the gate output begins to rise, turn- 
ing on Q . This action increases the cur- 
rent through Q 1 and Q 2 , resulting in satu- 
ration of Q 2 and a faster charging of C . 
This positive feedback provides the neces- 
sary hysteresis to complete the charging 
of Cj and return the gate output high. 



5V 

Q 



R 2 
10k TO 
47k 



R 3 

1M 



:100 ijF 



100 nF 



D 1 

1N4148. 

D 2 
1N4148- 



( Q TH Wr 



R 1 

iom: 



BC549 



BC549 




CD401 1 



TIMER 



NOTE: SEE TEXT REGARDING VALUE OF C v 



C 1 to charge through the base- 
emitter junction of Q 2 . This 
action holds the gate input 



Figure 1 A constant-current source and current divider 
reduce the timing capacitor current to a low level to in- 
crease the charging time. 



DIs Inside 

44 Microcontroller drives piezo- 
electric buzzer at high voltage 

44 Circuit simultaneously 
delivers square and square root 
of two input voltages 

47 Conversion circuit handles 
binary or BCD 

►To see and comment on all 
of EDA/'s Design Ideas, visit 
www.edn.com/designideas. 

Linearity with changes in R t is 
impossible due to variations in the 
transistor's current gain. The built and 
tested circuit does exhibit linearity with 
the value of timing capacitor C v which 
you can choose experimentally for the 
required time. Once you determine a 
time for a short interval, such as that for 
a 10- or a 100-nF capacitor, you can use 
this knowledge to scale to longer tim- 
ing. In the tested circuit, with 
Rj set to 1 MQ, a C 1 value of 10 
nF results in a time of 10 sec; a 
C l value of 100 nF increases the 
time to 100 sec. 

Editor's notes: Constructing 
a low-current circuit is chal- 
lenging. Some types of PCB- 
soldering flux can become con- 
ductive, wreaking havoc with 
what should be a tiny current. 
Consider "open-air" connec- 
tion of the Q 1 -emitter collector 
and the Q 2 -emitter base leads to 
remove them from the board. 

Transistor-leakage currents 
and current gains vary widely 
from device to device and with 
temperature. This variation can 
drastically affect the expected 
low-level current and capaci- 
tor charge time. Although the 
CD4011's typical input current 



- START 



r 



[www.edn.com] 



MARCH 1, 2012 | EDN 43 



designideas 



is 10 pA at room temperature, it could 
be as high as 100 nA and increase to 
1 pA at high temperature- Likewise, 
the transistor collector-to-base leakage 
could be a maximum of 15 nA at room 
temperature and 125 pA at high tem- 
perature, and it approximately doubles 
for every 10°C rise in temperature- It 



might be necessary to hand-select tran- 
sistors and CD401 1 inputs or devices to 
overcome this problem. Also, remember 
to tie any other unused CD4011-gate 
inputs to ground or 5V to avoid float- 
ing-input problems- 

Do not set R 1 so low that Q 1 or Q 2 
saturates during the timed period; they 



must remain in their linear region as set 
by the value of the Q 2 collector resistor. 

Timing capacitor C l should have 
a high-quality, low-leakage dielectric, 
such as polyester; check the leakage 
specifications of the size and type you 
intend to use for suitability with the 
low-level current. EDN 



Microcontroller drives piezoelectric buzzer at high voltage 

Mehmet Efe Ozbek, PhD, Atilim University, Ankara, Turkey 



Piezoelectric buzzers find wide use 
in embedded systems for audible- 
signal generation. You can drive a piezo- 
electric element directly from a micro- 
controller's I/O pins, but the 
maximum voltage rating and 
loudness of a piezoelectric 
buzzer are typically several 
times larger than the voltage 
an I/O pin supplies. Using four 
enhancement-mode MOSFETs 
that connect in an H-bridge 
configuration, the microcon- 
troller can drive the buzzer at a 
high alternating voltage. The 
gate terminals of the N -channel 
transistors in the lower arms of 
the bridge can connect directly 
to the microcontroller's I/O 
pins. The voltage level on the 
I/O pins is insufficient for 



switching the P-channel transistors, 
however. 

The circuit in Figure 1 solves the 
problem using a cross-coupled configu- 



i/O pin 1 




PIEZOELECTRIC 
BUZZER 




Figure 
drive a 



1 This cross-coupled configuration enables you to 
piezoelectric buzzer from a microcontroller's I/O pins 



ration. The operation is as follows: The 
microcontroller turns Q 2 on and Q 4 off 
by applying high- and low-logic-level 
voltages to I/O Pin 1 and I/O Pin 2, 
respectively. The voltage on 
Node A goes low, turning on 
Q 3 . Node B is now 15 V, which 
is sufficient to keep Q 1 off. The 
voltage on the piezoelectric 
buzzer is 15 V. The microcon- 
troller then toggles I/O Pin 1 
and I/O Pin 2, resulting in a 
piezoelectric voltage of -15V 
for an effective 30V p-p. These 
cycles are repeated to gener- 
ate an alternating voltage with 
the desired frequency. By using 
MOSFETs with proper voltage 
ratings, you can use higher sup- 
ply voltages that the piezoelec- 
tric element can tolerate. EDN 



I/O PIN 2 



Circuit simultaneously delivers square 
and square root of two input voltages 

Marian Stofka, Slovak University of Technology, Bratislava, Slovakia 



This Design Idea requires inputs 
from the circuit in a previous 
Design Idea (Reference 1). IC 1 and IC 3 
are ADG5213 quad switches with indi- 
vidual logic-level control inputs (Figure 
1 and Reference 2). With a high input, 
switches S 2 and S 3 are open, and switch- 
es Sj and S 4 are closed. The switches 
toggle to opposite states with their con- 
trol inputs low. The circuit is in the idle 
pretriggered condition. During the ini- 
tial idle condition before a clock rising- 



edge trigger, Q is high and, through IC g , 
holds switches S 2 and S 3 of IC 1 in the 
open position. 

Q is low, and, through IC ? 's Reset 
high closes IC^s S x and S 4 , discharg- 
ing C T2 and C T4 and zeroing the input 
voltage to_unity-gain amplifiers IC 2D 
and IC 2C . Q low also sets Track 2 low 
through IC 6 and holds IC 3 's S 1 and S 4 in 
the open position. The circuit retains 
any sampled voltages from a previous 
operation in sample-and-hold capaci- 



tors C S1 and C S2 ; these voltages appear 
at V QUTX and V QUTY through unity-gain 
amplifiers IC 2A and IC 2B . 

Signals V QUTL and V QUTQ from the 
linear and quadratic pulse generator are 
at 0V during idle, holding comparator 
outputs IC 4 and IC 5 low. A rising trig- 
ger edge at the clock signal begins the 
ramp generation of V QUTL and V QUTQ . 
The Q and IC g outputs fall low, closing 
IC^s S 2 and S 3 and ensuring that Track 
2 remains low. Q rises and forces Reset 
low through IC ? , opening S x and S 4 of 
IC 1 and allowing C T2 to follow the ris- 
ing V OUT0 and C T4 to follow the rising 
V 

OUTL 

When linear ramp V QUTL rises to 




44 EDN | MARCH 1, 2012 



[www.edn.com] 



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All other company names may be trade names or trademarks of their respective owners. 



designideas 



analog input V x , IC 4 's output rises and, 
through IC 8 , Track 1L opens S 2 of IC 1 
and allows C T2 to hold the present level 
of V QUTQ . In a similar manner, when qua- 
dratic ramp V QUTQ rises to analog input 
V Y , IC 5 's output rises and, through IC g , 
Track 1Q opens IC^s S 3 and allows C T4 
to hold V QUTL 's present level The pulse 
generator terminates when the ramps 
reach 5 V. The ramps then fall back to 
OV, Q returns high, and Q returns low. 

The rise of Q immediately triggers IC 6 
to generate a high pulse of approximately 
20 psec on Track 2 based on R m and C D1 . 
This action closes IC 3 's S x and S 4 , allow- 



ing the sampled voltages on C T2 and C T4 
to transfer to C S1 and C S2 through unity- 
gain amplifiers IC 2D and IC 2C . Unity-gain 
amplifiers IC 2A and IC 2B present the C S1 
and C S2 voltages at V QUTX and V QUTY . 
When Track 2 returns low, IC 3 's S x and 
S 4 open, and the sampled voltages on C, 



and C S2 are retained. 

The fall of Q triggers IC ? to produce 
a 50-psec delayed rise on Reset, which 
R D2 and C D2 time to occur after Track 2 
has returned low and the sampled volt- 
ages are safely captured on C S1 and C gr 
Reset's high state closes IC^s S x and S 4 , 
discharging C T2 and C T4 in preparation 



for the next trigger. V QUTX is the squared 
voltage of input V x , and V OUTY is the 
square root of the voltage of input V y . 
You can view the equations at www.edn. 
com/120301dia.EDN 

REFERENCES 

MStofka, Marian, "Positive edges trig- 
ger parabolic timebase generator," 
EDN, July 28, 201 1 , pg 51 , http://bit.ly/ 
yYvu3F. 

a "ADG5212/ADG5213 High Voltage 
Latch-up Proof, Quad SPST Switch- 
es," Analog Devices, 201 1 , http://bit.ly/ 
W6XT03. 



5V 

Q 



LINEAR AND 
QUADRATIC 
CLOCK CH PARABOLIC 
PULSE 
GENERATOR 



330 



Q |Q 



'.m 15V ... ! 
' IN? INo ' 
K>- 2 , : -'-On 



330 > >330 



0^ ^ 

| q ADG5213 q ; 

1 r^O 



Di 




. in 1 ; ; in 4 

rP- J V 

GND -15V | 

O o--- j 




-O : 

JN 2 1 5V |N 3 I 
f^)-- 2 -..__, : 3 .^_i 



p 2 Y 9 D s ' x 



C T 4 

1 nF 



1k 



RESET 



GROUND UNUSED 
INPUTS 



SN74AHC1G08 



! Sh ADG5213 s, ; 

o J — i i — i o 



c s 

1 nF -r 





R T2 
1k 



^v 0UTX 

OUTPUTS 

^v OUTY 



15VO- 
-15VO- 



5VO- 



SN74AHC1G02 



1 

I 



100 nF 



Figure 1 With this circuit, you can find the square at Channel X and the square root at Channel Y for any positive dc or slowly varying 
voltages of to 5V. 



46 EDN | MARCH 1, 2012 



[www.edn.com] 



designideas 
CLASSICS 

Originally published in the April 5, 1979, issue of EDN 

Conversion circuit handles 
binary or BCD 

R Srinivasan, R Ramesh, and DK Murthi, 
National Aeronautical Lab, Bangalore, India 



Systems requiring arithmetic oper- 
ations on data usually perform 
those operations in binary form. As a 
result, they must convert the data to BCD 
form for display purposes- Address- 
selection information from digit switches, 
on the other hand, must be converted to 
binary form for use in memory-addressing 
operations. 



For applications not requiring fast con- 
version, a single circuit that can perform 
both conversions proves adequate. One 
such circuit (Figure 1 ) utilizes up/down 
counters to obtain the desired results. To 
perform binary- to-BCD conversion, preset 
the binary value in the binary counter and 
clear the BCD counter. The binary count- 
er counts down while the BCD counter 





WANT TO 
SEE MORE 
OF THE 
CLASSICS? 






Revisit 50 of the 




best Design Ideas 


from the Golden 




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http://bit.ly/DesignldeasClassics 



counts up, and when the binary coun- 
ter reaches zero, the BCD counter holds. 
For BCD-to-binary operation, the BCD 
counter counts down from the BCD value 
while the binary counter counts up.EDN 



BINARY INPUT DATA 
Bo Bi B 2 B 3 B 4 B s B 5 Bj 



S B B t Bi* Bh MC=Q BCD TO BINARY 

MC=1 BINARY TO BCD 




BCD OUTPUT 



UNITS 



TENS HUNDREDS 
SCO INPUT DATA 



THOUSANDS 



Figure 1 Separate binary and BCD up/down counters permit both binary-to-BCD and BCD-to-binary conversion in one circuit. 



[www.edn.com] 



MARCH 1, 2012 | EDN 47 



productroundup 



TEST AND MEASUREMENT 








J0_ .V_ ^ 

M 


a kilt 

I □ [ , [ v. 
^ (f 1* 



Agilent E5515E wireless-communication 
test set accelerates design 

The E55 15E 8960 series 10 wireless-communication test set supports GSM, 
GPRS, EGPRS, E-EDGE, WCDMA, CDMA2000, lxEVDO, EHRPD, 
TDSCDMA, TDHSDPA, TDHSUPA, IS-95, TIA/EIA-136, and AMPS wireless- 
device testing. The device has a 292- to 2700-MHz frequency range, including all 
commercial 3GPP and 3GPP2 frequency bands. Other features include a -1 10 to 
-13-dBm output-level range with modulation, a VSWR of less than L2-to-l at 
400 to 2000 MHz, and less than ±l-dB channel-power measurement accuracy. The 
Agilent E5515E mainframe is priced at $59,200, including all hardware options; 
software options are available at additional cost. 
Agilent Technologies, www.agilent.com 



Planar Caban R54 vec- 
tor reflectometer meas- 
ures parameters 

The Caban R54 vector reflec- 
tometer measures S n parameters 
over an 85 -MHz to 4- 2 -GHz frequency 
range. The device measures magnitude 
and phase of reflection coefficient, 
cable loss, and distance to fault. Per- 
point measurement time is 200 usee, 
and frequency-setting resolution is as 
high as 10 Hz. The USB-powered 
device measures 117x39x19 mm, 
weighs 0.25 kg, and sells for $2995. 
Planar LLC, www.planar.chel.ru 




Aaron ia spectrum 
analyzer offers real-time 
data streaming 

Aaronia's Spectran V5 series of 
spectrum analyzers, scheduled to 
start shipping in 2012, offers extremely 
low-noise signal processing — up to 170 
dBm/Hz — as well as a 200-MHz real-time 
bandwidth. Each spectrum analyzer pro- 
vides real-time streaming and a real-time 
remote control for GSM, WLAN, and 
USB and has a TFT display with 
800x480-pixel resolution. The analyzer 
utilizes an integrated 3-D motion sensor 
and a 3-D magnetic-field sensor. It uses 
480-kbps USB 2.0 and has a USB slave 
interface to connect devices such as 
GSM, WLAN, printer, and memory. A 
micro-SD slot supports SDHC cards with 



more than 10 Mbytes/sec, and an inte- 
grated lithium-polymer battery with 8000 
or 16,000 mAhr provides as much as 
three or six hours of runtime, respective- 
ly. The analyzer features modular con- 
struction for fast extension and custom- 
ization of the front end and also includes 
a directional-tracking and EMC antenna, 
an aluminum carrying case, a battery 
charger, a power supply, and an interna- 
tional adapter set. The included MCS 
real-time spectrum-analyzer software runs 
with any operating system, including Mac 
OS, Linux, and Windows, and provides 
real-time remote control with any of the 
vendor's Spectran spectrum analyzers. 
Pricing starts at €2998 (approximately 
$3950) for the 10-MHz to 2.5-GHz 
Spectran HF-8025 V5. 
Aaronia AG, www.aaronia.com 

Pico 4262 scope 
includes arbitrary- 
waveform generator 

The two-channel, 16-bit Pico- 
Scope 4262 has a built-in low- 
distortion signal generator. With a 5 -MHz 
bandwidth, it can analyze audio, ultra- 
sonic, and vibration signals; characterize 
noise in switched-mode power 
supplies; measure distor- 
tion; and perform pre- 
cision-measurement 
tasks. The scope t 
includes a function <S! 
generator and an 
arbitrary-waveform genera- 
tor that has a sweep function to enable 
frequency-response analysis. It also offers 
mask-limit testing, math and reference 
channels, advanced triggering, serial 
decoding, automatic measurements, and 
a color-persistance display. In spectrum- 
analyzer mode, the scope provides a menu 
of 1 1 automatic frequency-domain meas- 
urements, such as IMD, THD, SFDR, and 
SNR. The PicoScope 4262 connects to 
any Windows XP, Vista, or Windows 7 





48 EDN | MARCH 1, 2012 



[www.edn.com] 



computer with a USB 2.0 port. The unit 
sells for £750 (approximately $1200). 
Pico Technology, www.picotech.com 

Tektronix TPI4000 
analyzer lets users test 
multiple serial protocols 

The TPI4000 protocol-analyzer 
series allows users to perform 
multiple test functions and to look at a 
variety of protocols, such as Ethernet, 
Fibre Channel, and common public- 
radio interface. A user-edit- 
able database allows users to 
define custom protocols using 
the optional protocol-editor 
tool. The series includes the 
portable TPI4202, which 
has a built-in monitor 
and keyboard and sup- 
ports as many as eight ports, and the 
4U-rack-mount TPI4208, which sup- 
ports as many as 32 ports. Pricing for a 
complete system starts at $40,000. 
Tektronix, www.tektronix.com 





2 




Rigol's DS4000 oscil- 
loscopes have 1 00- to 
500-MHz bandwidth 

The general-purpose DS4000 
series of digital oscilloscopes fea- 
tures bandwidths of 100, 200, 350, or 
500 MHz; two or four analog channels; 
a real-time sampling rate of 4G samples/ 
sec; a memory depth of 140 million 
points; and a waveform-acquisition rate 
of 1 10,000 waveforms/sec. The vendor's 
UltraVision technology and a 9-in. 
WVGA display offer an intensity-grad- 
ing, real-time waveform recording. 
Waveform visualization and replay and 
customizable real-time hardware filters 
are available. Targeting applications in 
communications, defense, aerospace, 
industrial electronics, R&D, and educa- 



tion, the units cost $1999 to $4699. 
Rigol Technologies Inc, 
www.rigolna.com 



ADVERTISER INDEX 



Company 


Page 


Agilent Technologies 


C-3 


Centellax 


8 


Coilcraft 


3 


Digi-Key Corp 


C-l.C-2 


Emulation Technology 


23 


IMS 2012 


19 


International Rectifier 


C-4 


Linear Technology 


34A-34B, 
42 


Maxim Integrated Products 


45 


Mill-Max Manufacturing 


11 


Mouser Electronics 


4,6 


National Instruments 


13 


Pico Electronics Inc 


7,39 


Rohde & Schwarz GmbH 
&Co KG 


29 


UBM EDN 


37,49 


Vicor Corp 


15 


EDN provides this index as an additional service.The 
publisher assumes no liability for errors or omissions. 



UBM Z^rl 

Electronics voice of the engineer 



Customize Your Reprints! 



EDN EDN REPRINTS 

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[www.edn.com] 



MARCH 1, 2012 | EDN 49 



TALES FROM THE CUBE 



DAN DULL • NOVO ENGINEERING 



Printer parking brake 




About 15 years ago, I was working for a wide-format- 
ink- jet-printer company in the San Diego area. The 
printers we designed could print on rolls of paper 
that were 5 feet wide and several hundred feet long. 
Needless to say, we needed to send an enormous 
amount of data to these printers to keep the print 
heads moving and the paper advancing. One of the key product 
requirements was throughput, specified in square feet per hour. 
Ideally, the print head's firing rate governed the throughput. The 
rest of the system had to ensure that the print heads were always 
squirting ink onto the paper. If the print heads were not squirting, 
we were wasting time. Our customers tended to get upset when 
their expensive printer paused and hesitated while printing post- 
ers because they charge their customers by the square foot. The 
longer it takes to print the poster, the less money they make. 



My primary jobs were to design the 
controller board for these printers, 
design the FPGA that was on the con- 
troller board, and write the low-level 
firmware that interfaced with the hard- 
ware. Each new product we developed 
was roughly twice as fast as the previous 
product, so I constantly had to find new 
ways to process the image data faster. I 
started evaluating new microprocessors 
because the one we were currently using 



was occasionally making the printer 
hesitate after each pass of the print 
heads and would definitely not be suf- 
ficient for the next-generation product. 

After doing some research and anal- 
ysis, I found a microprocessor that I felt 
could handle our processing needs for 
at least several more future products. I 
designed a controller board using this 
part, designed the FPGA logic, and 
wrote the device drivers and some test 



code. Everything seemed to be going 
well. All of the major functional blocks 
appeared to be working correctly. 

The firmware team started work- 
ing on the project, and, once the team 
had written enough firmware to make 
the printer function, it was apparent 
that this microprocessor appeared sig- 
nificantly slower than the old one. It 
should have been at least 10 times faster 
based on clock rate alone, but it also had 
caches and a DMA controller to further 
speed things up. The board had copi- 
ous amounts of high-speed memory, and 
the FPGA had logic to offload some of 
the data-processing tasks from the main 
microprocessor. Something was horribly 
wrong, and, because I had designed the 
system, I was the only one who could 
fix it. 

The user's manual for the micropro- 
cessor comprised two books with more 
than 1000 pages each. I grabbed both 
books and started reading. This incident 
occurred before PDF files were com- 
mon, so searching was a manual process. 
While reading through the debugging 
section, I came across an interesting 
feature. This feature set the level of 
detail about the microprocessor's core 
and instruction pipeline that is reported 
to an external debugger. 

As I read more about this debug- 
ging feature, I discovered that it 
affects the microprocessor's perform- 
ance. If you want more detail about 
what is happening internally, the core 
slows down. I checked to see what the 
default setting was and was pleased to 
discover that maximum detail, slowest 
core was the reset value. I modified the 
firmware to turn this feature completely 
off, and the microprocessor started run- 
ning at full speed. The printer ran at 
full speed with no hesitation. My co- 
workers and I then decided to call this 
feature the parking brake.EDN 

Dan Dull currently works as an electrical 
engineer for Novo Engineering, a product- 
development company in Vista, CA. 



This Tale is a runner-up in EDN's Tales from the 
Cube: Tell Us Your Tale contest, sponsored by 
Tektronix. Read the other finalists' entries at http:// 
b it . ly/Talesf inal_ED N . 



50 EDN | MARCH 1, 2012 



[www.edn.com] 



I need a function generator that generates confidence, too. 





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