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E ENGINEER 




Tales fronn the Cube 

Pg 56 

EDN.connnnent: Robots, 
jobs, and war Pg 6 

Baker's Best Pg 18 

Tapeout Pg 20 

Prying Eyes: 

T-Mobile'sGl Pg22 

Design Ideas Pg 45 



PF SWITCHINC^ OPTIONS: 

THE RIGHT FIT MIGHT COME WITH A LOSS 



Page 30 



BREAKING DOW 

THE SENSOR-SIGNAL PA 



IN SEARCH OF 
A BEHER DRAM: 

EVOLVING TO 
FLOATING B 




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EDN 9,17,09 

contents 




RF switching options: 
The right fit might 
come with a loss 

Manufacturers are 
I 1 offering SOI and 

MEMS alternatives 
to PIN-diode, GaAs, and electro- 
mechanical switches for a variety 
of RF applications, but you need 
to understand RF-switch specs 
before you commit to a new 
technology 

by Rick Nelson, Editor-in-Chief 



Breaking down the 
sensor-signal path 

O pr By understanding the 
^ vJ stages of an analog-signal 
path, digital-system developers 
can more accurately capture 
sensor data for a variety of appli- 
cations, by Aaron GL Podbelski, 
Cypress Semiconductor 




Osram develops direct-emit- 
ting green-laser diode 

13 1-GHz Cortex-A8 maintains 
cycle-accurate operation 

14 Versatile audio analyzer eas- 
ily quantifies performance of 
audio components, products 

14 Mentor unveils strategy 
at DAC 



15 Quad 1 2-bit DAC has internal 
reference and EEPROM 

Workshop addresses 
LED challenges 



Voices: Newark/Premier 
Farnell's Gary Nevison: 
scoping out the Environmental 
Design of Electrical 
Equipment Act 



DESIG 



IDEAS 




In search of a better 
DRAM: evolving 
to floating bodies 

O QWidely investigated float- 
O vl/ing-body memories appear 
to be compelling replacements 
for conventional DRAMs. A new 
floating-body memory uses the 
intrinsic bipolar transistor to store 
significantly greater charge. 

by Serguei Oktionin, PhD, 
Innovative Silicon 



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contents 91709 




DEPARTMENTS & COLUMNS 

6 EDN.comment: Robots, jobs, and war 

1 8 Baker's Best: A designer's guide to op-annp gain error 

20 Tapeout: Reference-tool flows and process-design kits, part one 

22 Prying Eyes: T-Mobile's G1 : Google's Android OS emerges 

53 Product Roundup: Power Sources, Integrated Circuits 

56 Tales from the Cube: Lightning strikes sewage setup 



online contents 



www.edn.com 



EDN TECH CLIPS 

In ED/V Tech Clips, we showcase video 
versions of our popular Design Ideas, 
instructional clips from signal-integrity 
guru Howard Johnson, PhD, and other 
short videos on various tech topics. 

Here's a sample of what you might find: 

Video Design Ideas: Set your lights to 
music. Microcontroller drives 20 LEDs, 
Diagnose setup and hold times, and more. 

Howard Johnson: Blocking capacitor 
layout. Signal dispersion, PCB-trace 
losses, and more. 



www.edn.com/techclips 



ONLINE ONLY 

Check out this Web-exclusive article: 

Implementing power-factor correction 
with frequency-clamp-critical-conduction 
mode 

An innovative power-factor-correction design, 
frequency-clamp-critical-conduction mode 
clamps the frequency with a near-unity power 
factor and keeps the simple control scheme 
of a critical-conduction-mode design. 
www.edn.com/article/CA6677288 



HOT TOPICS 

Have you looked at EDM's Hot Topics 
pages recently? Hot Topics pages 
deliver continuously updated, subject- 
specific links from not only EDA/ but 
also the entire electronics-industry 
Web. New listings include aerospace, 
industrial, and mobile. 
►www.edn.com/hottopics 



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E D N . C O M M E N T 




BY RICK NELSON, EDITOR-IN-CHIEF 



Robots, jobs, and war 

Robotics was a focus of attention at National Instruments' 
N I Week event in Austin, TX, last month, when presenters 
discussed the technical capabilities and ethical consider- 
ations surrounding robot use. Although the technical is- 
sues got most of the attention, it may be the ethical ones 
that prove to be more difficult. Consider mining accidents. 
Six miners died tragically in the 2007 Crandall Canyon Mine disas- 
ter. The loss 10 days later of three would-be rescuers compounded the 

tragedy. Could the use of robots to In a recent article, Gregory Clark, 
perform the rescue reconnaissance a professor of economics at the Uni- 
have averted those three deaths? 

At N I Week, Thomas Bewley, a pro- 
fessor at the University of California — 
San Diego, described the challenges 
robots can face. Those small enough 
to access a collapsed mine tend to be 
too small to climb over the debris they 
encounter once inside. That problem 
is one Bewley and his students are ad- 
dressing by finding ways to have small 
robots climb over large obstacles. A 
robot should roll when possible, he 
says, but use multifunction mecha- 
nisms, including plungers, for exam- 
ple, when necessary. 

It would clearly be ethical to have 
robots search for survivors in col- 
lapsed mines, sparing rescue workers 
the risk. If such robots can reconnoiter 
collapsed mines, however, they could 
take over mining it- 
self. Mining is 
a dangerous 
job, but is it better 
than no job at all? In 
less dangerous occu- 
pations, is it ethical 
to substitute robots 



versity of California — Davis, doesn't 
discuss the ethics of the situation 
but rather the consequences of what 
he takes to be the inevitable (Refer" 
ence 1). Clark writes that the current 
downturn is a minor blip in technol- 
ogy-driven economic growth, and, he 
cautions, "The economic problems of 
the future will not be about growth 
but about . . . the ineluctable increase 
in the number of people with no mar- 
ketable skills and technology's role 
not as the antidote to social conflict, 
but as its instigator" as machines dis- 
place people. 

In a keynote address at N I Week, Da- 
vid Barrett, PhD, director of SCOPE 
(Senior Capstone Program in Engi- 
neering) at Eranklin W Olin College 
of Engineering (Needham, MA), de- 
scribed robots that are or will be taking 
over human tasks, including mining, 
industry, construction, and agriculture. 
It won't just be unskilled workers who 
might have something to fear. Barrett 
also described various medical robots, 
including ones that perform surgery. 

What should we do about robots' 
displacement of people? Clark pic- 



tures a dystopia: "We could imagine 
cities where entire neighborhoods are 
populated by people on state support. 
In Erance, generous welfare has al- 
ready produced huge suburban hous- 
ing estates, les hanlieues, populated 
with a substantially unemployed and 
immigrant population, parts of which 
have periodically burst into violent 
protest." To support such populations, 
he says, "you tax the winners — those 
with the still uniquely human skills 
and those owning the capital and 
land — to provide for the losers." 

Perhaps the most difficult prob- 
lem of ethics centers on robots' use in 
the military. In another recent article 
(Reference 2), James Carroll writes, 
"When will the unempathetic Ameri- 
cans imagine what it feels like to have 
a robot monster bolt from the sky — the 
drones of August — and, in one strike, 
turn a wedding feast into a funeral?" 
On the ethics of using robots in war- 
fare, scope's Barrett said that, if we 
don't do it, our enemies will. 

It's inevitable that robots will take 
on more and more roles. The true eth- 
ical question comes into play in how 
we address the consequences, and so 
far we have fallen short. We cannot 
continue turning weddings into funer- 
als and turning middle-class neighbor- 
hoods into violent hanlieues of disaf- 
fected, unemployed losers meagerly 
supported by taxing the winners. EDN 

REFERENCES 

9 Clark, Gregory, "Tax and Spend, 
or Face The Consequences," The 
Washington Post, Aug 9, 2009, 
www.washingtonpost.conn/ 
wp-dyn/content/article/2009/08/07/ 
AR2009080702043.html. 
3 Carroll, James, "In search of em- 
pathy," The Boston Globe, Aug 1 7, 
2009, www.boston.com/boston 
globe/editoriaLopinion/oped/ 
articles/2009/08/1 7/in_search_of_ 
empathy. 

Contact me at rnelson@reedhusiness . 
com. 



6 EDN I SEPTEMBER 17, 2009 




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EDITED BY FRAN GRANVILLE 




INNOVATIONS & INNOVATORS 



Osram develops direct-emitting 
green-laser diode 



Osram Opto Semiconductors announced 
lab results for a direct-emitting green- 
InGaN (indium-gallium-nitride)-laser 
diode. In pulsed-mode operation at room tem- 
perature, the laboratory prototype achieved an 
optical output of 50 mW, with a threshold-cur- 




This lab prototype of Osram's direct-emitting green-lnGaN- 
laser diode achieved an optical output of 50 mW in pulsed 
mode operation at room temperature. 



rent density of approximately 9 kA/cm^, emit- 
ting light in true green-defined by the spectral 
range of 5 1 5 to 535 nm-with a wavelength of 
515 nm. The current technology for green semi- 
conductor lasers is to double the frequency of a 
material capable of lasing at 1060 nm to pro- 
duce a green laser at 531 nm. 
The highest output power for a 
frequency-doubling green laser 
is currently about 1 .5W. 

Osram developed the green- 
laser diode in conjunction 
with the German Ministry for 
Education and Research (www. 
bmbf.de/en) MOLAS research 
project, which involves tech- 
nologies for ultracompact and 
mobile-laser-projection sys- 
tems; green lasers also find 
use in a range of medical and 
research applications. 

—by Margery Conner 
Osram Opto Semicon- 
ductors, www.osram-os.com. 



m FEEDBACK LOOP 
"Einstein, IVIozart, 
and every otiier 
genius had con- 
temporaries (and 
quite smart ones 
at that) whom 
they were able to 
bounce ideas off 
of and refine their 
best worlc. ... Very 
little would have 
been discovered 
if that so-called 
'genius' were 
locked in a cell 
by himself." 

—Design engineer CInris 
Gannmell, in EDN's Feedback 
Loop, at www.edn.conn/article/ 
CA6666234. Add your connnnents. 



1-GHz Cortex-A8 maintains cycle-accurate operation 



Samsung Electronics and 
Intrinsity have worked together 
to produce an ARM (www.arm. 
com) Cortex-A8 processor, 
Hummingbird, that can oper- 
ate at 1 GHz in a 45-nm, low- 
power process and maintain 
the same cycle-accurate and 
Boolean-equivalent opera- 
tion as the original Cortex-A8 
RTL (register-transfer-level) 
specification. The compa- 
nies attained this clock rate 



by applying custom-designed 
circuit/memory structures 
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FastCore and Fasti 4 high- 
speed domino logic to timing- 
critical paths in the Cortex-A8 
RTL core. The latest genera- 
tion of Intrinsity's NDL (one- 
of-N-domino-logic) implemen- 
tation now supports seamless 
mixing between domino and 
static logic in a standard-cell- 
synthesized design. This fea- 



ture enables the core to use 
only those NDL gates that are 
25 to 50% faster than static- 
logic gates in those critical- 
path circuits in which they 
affect the overall clock rate. 
This mixing enables the sys- 
tem to consume less static 
and dynamic power than ear- 
lier implementations of other 
cores that used the NDL gates 
throughout the entire core. 
The core includes 32-kbyte 



instruction and data caches, 
512 kbytes of L2 memory 
and an ARM Neon multimedia 
extension. The core supports 
multiple drain-to-drain-voltage 
and frequency operation that 
includes a minimum supply 
voltage of 1 V so that the core 
can target mobile devices. 

—by Robert Cravotta 
t>lntrinsity, www.intrinsity 
com. 

Samsung Electronics, 

www.samsung.com. 



SEPTEMBER 17, 2009 | EDN 13 



MENTOR UNVEILS 
STRATEGY AT DAC 

Mentor Graphics (www. 
mentor.com) announced 
its acquisition of Embed- 
ded Alley Solutions as a 
key component of its An- 
droid and embedded-Linux 
strategy last month at the 
Design Automation Con- 
ference in San Francisco. 
Mentor also announced the 
integration of its Nucleus 
graphical-user-interface 
tool with the ARM (www. 
arm.com) Mali graph- 
ics-processing unit; it an- 
nounced the availability of 
a Linux/Nucleus operating- 
system combination for 
the Marvell (www.marvell. 
com) Sheeva MV78200 du- 
al-core embedded proces- 
sor; and it plans to extend 
Embedded Alley's Android 
mobile-applications plat- 
form to support Freescale 
Semiconductor's (www. 
freescale.com) QorlQ and 
PowerQUiCC (quad-inte- 
grated-communications- 
controller) ill processors. 

Mentor plans to com- 
bine its Nucleus RTOS (re- 
al-time operating system) 
and associated tools and 
services with Embedded 
Alley's Android and Linux 
development systems to 
offer device manufactur- 
ers one source for the 
operating systems they 
need for embedded-sys- 
tem designs. The goal is 
to support Mentor's cus- 
tomers in supplying com- 
plete systems-not just 
silicon-to their own cus- 
tomers. For more news on 
DAC, go to www.edn.com/ 
090917pulsea. 

-by Rick Nelson 

Design Automation 
Conference, www.dac.com. 



)Lise 



Versatile audio analyzer easily quantifies 
performance of audio components, products 

a You can 
purchase 
a two-channel 
analyzer for 
the price of 
a typical single- 
channel unit. 



Agilent Technologies 
has introduced the 
U8903A audio ana- 
lyzer, a single unit that incor- 
porates the broad range of ca- 
pabilities you need to quantify 
the characteristics that affect 
sound quality in audio devic- 
es. The instrument is also the 
manufacturer's next-genera- 
tion replacement for its wide- 
ly used legacy audio analyzer, 
the 8903B. The new, scalable, 
two-channel unit includes 
several measurement func- 
tions and test signals, pow- 
erful analysis functions, and 
industry-standard balanced 
and single-ended connectors. 
At dc and from 1 Hz to 1 00 
kHz, the analyzer helps you to 
measure performance in such 
applications as consumer and 
wireless audio and analog- 
component and -IC test. In ad- 



dition, the manufacturer plans 
to soon offer upgrades that will 
equip the instrument with as 
many as eight input channels. 

The U8903A offers in- 
creased capabilities, wider fre- 
quency coverage, and great- 
er dynamic range than the 
8903B. The new model also 
includes a graphical user in- 
terface with a 5.7-in. color dis- 
play and one-button selection 
of major operating modes. For 
automated operation, an appli- 
cation note describes equiva- 
lent software commands and 
provides sample test programs 
that substitute the new unit's 
SCPI (standard commands for 
programmable instruments) in- 
structions for the older instru- 
ment's commands. 

The U8903A is avail- 
able now at a US list price of 
$12,000. For a limited time. 



the manufacturer is offering 
the new instrument at a 20% 
discount when you trade in 
an 8903B. With this arrange- 
ment, you can purchase a two- 
channel analyzer for the price 
of a typical single-channel 
unit. Find further information 
about the discount program at 
www.agilent.com/find/audio 
analyzerpromo. 

-by Dan Strassberg 
Agilent Technologies, 
www.agilent.com/find/audio 
analyzer. 



1.000 kHz * 
970.635 mV 



1^^^^^ Dkt SMS Mu.1kKSBiTiKl Ca^ 

^^^M ^ Rw-io 5.000 kHz 
^^^^Ji 4S5.793 mV 




The compact U8903A audio analyzer integrates a range of single-ended and differential source and 
measurement capabilities that enable you to perform extensive testing of components and systems 
at dc and at frequencies from 1 Hz to 1 00 kHz. 



DILBERT By Scott Adams 



JOB INTERVIEU 



WE NEED SOtAEONE 
UHO CAN SOLVE THE 
BIGGEST ENGINEERING 
PROBLErA UJE HAVE EVER 
ENCOUNTERED. 




JUST DISTRIBUTE THE 
POUER SUPPLY ACROSS 
BOTH FUNCTIONS AND 
DOUBLE THE FAN SIZE. 




THANKS. IF I NEED 
ANYTHING ELSE. I^L 
INTERVIEUJ YOU 
AGAIN. 




14 EDN I SEPTEMBER 17, 2009 



Quad 1 2-bit DAC has 

internal reference and EEPROM 



Microchip Technol- 
ogy has announced 
a quad 12-bit DAC 
that remembers its settings 
in an internal EEPROM. The 
MCP4728 has a ±2%, 2.048V 
voltage reference, but you can 
also use an external reference. 
The reference has a 1.2-[xV/ 
VHz noise floor with a 400-Hz 
flicker-noise corner. You com- 
municate with the part over an 
PC (inter-integrated-circuit) 
bus in standard 1 00-kbps, fast 
400-kbps, and high-speed 
3.4-Mbps modes. 

You can individually shut 
down each DAC; total shut- 
down current is 0.04 |jlA. You 
can set the outputs to go to a 
low-, medium-, or high-imped- 
ance state during shutdown. 
Operating current is 800 jjlA. 

The devices features rail-to- 
rail outputs over the 2.7 to 5.5V 
power-supply range. Typical 
DNL (differential nonlinearity) 




The MPC4728EV evaluation 
board interfaces with the $49 
PICkit serial analyzer, which 
converts your computer's USB 
bus to PC, SMBus, SPI, or 
USART protocols. You can 
also use your own PC inter- 
face board. 

is ±0.2 LSB with a maximum of 
±0.75 LSB, which ensures that 
the device remains monotonic 
across all input codes. The DAC 

LDAC 



contains a power-on circuit for 
predictable operation. 

The device has applica- 
tions in consumer products, 
such as personal media play- 
ers, digital cameras, and GPS 
(global-positioning-system) 
devices. Medical applications 
include portable glucose me- 
ters, blood-pressure monitors, 
and heart-rate monitors. It also 
finds use in industrial products, 
such as handheld instruments, 
motor-control applications, and 
temperature and light control. 
The unit's wide temperature 
range also makes it suitable for 
automotive applications. 

The MCP4728EV evalu- 
ation board is available now 
and costs $15. The $1.36 
(10,000) MPC4728 operates 
from -40 to +125°C and 
comes in a 10-pin MSOP 

-by Paul Rako 

Microchip Technology, 
www.microchip.com. 




Vppp POWER-DOWN 
CONTROL 



Q] FEEDBACK LOOP 
"If people want 
to play In the 
open-hardware 
sandbox, they 
have to share 
their toys." 

—Roboticist Zach Hoeken 
Smith, in EDN's Feedback 
Loop, at www.edn.conn/ 
articie/CA6676166. Add your 
connments. 



WORKSHOP 
ADDRESSES LED 
CHALLENGES 

I 

The US Department of 
Energy recently invested 
$6.4 million in LED design 
to encourage innovation 
in solid-state lighting (see 
www.edn.com/article/ 
CA6685811). But solid-state 
lighting is as much about 
the surrounding electronic- 
power-control circuitry, 
thermal management, and 
optics as it is about the 
basic LED devices. EDyv is 
hosting a free "Designing 
with LEDs" workshop on 
Oct 6 at theWestin Lom- 
bard hotel near Chicago. 
The workshop will focus 
on the electronic-circuit, 
thermal, and optical-design 
challenges of designing 
with solid-state lighting, as 
well as other LED-based 
lighting applications. You 
can register at the Web site 
below.-by Margery Conner 
►www.edn.com/leds. 



*CHANNELS Vmix B AND Vmix C NOT SHOWN. 



You control tlie Microcliip i\/IPC4728 quad DAC witli tlie PC bus. The device's nonvolatile memory 
allows it to power up without microprocessor supervision. 



Designing 



In October, EDN will host a 
workshop on designing with 
LEDs. 



SEPTEMBER 17, 2009 | EDN 1 



pulse 



VOICES 



NEWARK/PREMIER FARNELL'S 
GARYNEVISON: 

scoping out the 
Environmental Design of 
Electrical Equipment Act 

As a proposed amendment to the 1 976 Toxic Substances 
Control Act, the Environmental Design of Electrical 
Equipment Act (Bill HR2420) has stirred much contro- 
versy within the electronics supply chain about whether a US 
version of the EU (European Union) ROHS (restriction-of-haz- 
ardous-substances) directive is coming. Gary Nevison, legisla- 
tion and environmental-affairs manager at global Premier Farnell 
(www.farnell.com) and its US business Newark, recently dis- 
cussed the bill and compared it with ROHS. The following text 
includes excerpts from that conversation. 



Is the Environmental De- 
sign of Electrical Equipment 
Act (H R2420), along with the 
US Toxic Substances Con- 
trol Act, similar to a US ver- 
sion of ROHS for electronics 
designers? 

First, this new legisla- 
tion is clearly not ROHS. 
It would be misleading to talk 
about US ROHS compliance. 
The proposed HR2420 is dif- 
ferent from EU ROHS, and, 
although it is claimed to be 
legislation designed to control 
hazardous substances, its main 
aim appears to be preventing 
states from imposing sub- 
stance restrictions on products 
within the scope of this legis- 
lation. It would introduce some 
limited restrictions, but the ex- 
emptions list is so comprehen- 
sive that these [restrictions] 
would be few. 

So, this act is not the US 
ROHS that many members 
of the electronics supply 
chain have been waiting for? 



Initially, this [act] might 
appear to be so; howev- 
er, closer scrutiny of the scope 
and structure of HR2420 re- 
veals that it is ... an effort to 
limit uncoordinated piecemeal 
legislation on this issue by indi- 
vidual states. At present, there 
is no federal US equivalent 
to EU ROHS, although some 
states have introduced limited 
ROHS-like laws. Many manu- 
facturers would welcome a 
single uniform US ROHS law, 
as this [law] would remove the 
need to meet multiple, chang- 
ing requirements across US 
states, although others, which 
predominantly sell internally, 
may be concerned about this 
extra restriction. 

The main implications of 
H R2420 are for new chemicals 
or major new uses of existing 
ones. For example, products 
containing substances that are 
not included in the TSCA [Toxic 
Substances Control Act] regis- 
ter require certification before 
they can be imported. TSCA 




currently imposes very few re- 
strictions on substances, but it 
does affect lead-based paints, 
asbestos, and polychlorinated 
biphenyls. 

Please elaborate on how 
HR2420 differs from ROHS. 

Although the bill propos- 
es to restrict the same 
six substances as EU ROHS 
at the same concentration val- 
ues in homogeneous materials, 
there are no apparent equiva- 
lents to 17 EU ROHS exemp- 
tions, and there is no use of the 
EU ROHS product categories. 
The product scope appears 
quite different from EU ROHS, 
as it seems to exclude house- 
hold or consumer products and 
include products not covered 
by EU ROHS, such as electric- 
ity-distribution equipment. An- 
other significant difference is 
that EU ROHS excludes prod- 
ucts designed for use with 
voltages above 1000V ac or 
1500V dc, whereas HR2420 
has a limit of 300V. The re- 
strictions would apply to prod- 
ucts manufactured after July 1 , 
2010. 

So, in summary the scope 
of the bill is quite limited and 
is clearly different from EU 
ROHS and mainly consists 
of a detailed list of exclusions 
and exemptions. As the scope 
includes many items current- 
ly excluded from EU ROHS, 
HR2420 does not appear to 
be a federal ROHS bill-more 



an attempt to avoid disjointed 
ROHS requirements emerging 
for products currently outside 
or on the fringe of the scope 
of EU ROHS. 

Many engineers think that, 
once the original ROHS 
hubbub concluded, all of 
the environmental compli- 
ance issues were behind us. 
Why is it important for engi- 
neers and OEMs to continue 
to work with distributors on 
environmental compliance 
issues? 

That [ending of contro- 
versy] was never the 
case. Under the original ROHS 
scope, it was always going to 
be reviewed, there were always 
going to be more substances, 
product categories, etcetera. 
And now we have the REACH 
[registration/evaluation/au- 
thorization-of-chemicals] di- 
rective. There will be more and 
more and more products and 
substance [limitations] in the 
short, medium, and long term, 
[which] will probably be the big- 
gest issue for design engineers 
around the world. They will have 
to seek suitable alternatives to 
these ever-increasing [number 
of] substances. This [situation] 
is kind of a nightmare. It is go- 
ing to roll and roll and roll for 
many years. 

Sure, engineers could look 
at all of this on the Web, but 
there is so much information 
and so much misinformation 
that is now dated that a dis- 
tributor is a good route to take. 
There are good distributors do- 
ing this [work] and there are not 
so good, but one of the biggest 
issues for me is whether things 
ever get deleted from the Web. 
For the designer, the simple 
reason would be getting the 
latest information, providing the 
distributor is doing the job well, 
-interview conducted and 
edited by Suzanne Deffree 



16 EDN I SEPTEMBER 17, 2009 



Special Advertising Section 



Rarely Asked Questions 



What^s the (Converter) Frequency Kenneth? 



Q. How Do I Design a Converter 
Front-end without Connpronnising 
the Perfornnance? 

A» Designers that employ a converter 
for high-frequency sampling have to face 
many challenges. Designing a front-end 
isn't simple, but the following comments 
can guide the designer to a solution. 

Designers can choose amongst three 
types of front-ends: baseband, narrow- 
band, or wideband; the application deter- 
mines which should be applied. 

Baseband applications require bandwidth 
from dc or the low MHz to the Nyquist 
frequency of the converter. In terms of 
relative bandwidth, this implies about 100 
MHz or less. These designs can employ 
either an amplifier or a transformer (balun). 

Narrowband applications (narrow being 
relative to the ADC's full Nyquist band- 
width) usually operate at high intermedi- 
ate frequencies (IF). They typically use 
only 5 to 20 MHz of bandwidth in the 2nd 
or 3rd Nyquist zone, with a center fre- 
quency >190 MHz. The design only needs 
a portion of the Nyquist bandwidth, but 
the unused bandwidth is often needed to 
implement an anti aliasing filter. A trans- 
former or balun is typically used for these 
applications, but an amplifier can be used 
if its performance is adequate at these 
frequencies. 

Wideband designs need it all, with the 
user taking as much as the converter 
will supply. These designs have the 
widest bandwidth, making the front- 
end design the most challenging of 
the three types. These applications 
require bandwidth from dc or low MHz 
to several GHz. Currently, these designs 




typically employ a wideband balun, but 
amplifiers are catching up in bandwidth 
and performance. 

After choosing the converter, choose 
the front-end amplifier (active) or trans- 
former (passive). The tradeoffs between 
the two are many and depend on the 
application, but can be distilled to a few 
points. Amplifiers add noise, require a 
power supply, and burn power, but they 
are not gain bandwidth dependent like a 
transformer. Also, they have better gain 
flatness within the pass band region. 
Transformers are passive, so they don't 
add noise or burn power, but their asym- 
metrical behavior can cause spurious 
issues. Transformers are not ideal devices; 
if not used properly their parasitics can 
undermine any design, particularly at 
higher frequencies (>100 MHz). 

Hopefully, this advice will keep the 
design on track. For additional informa- 
tion, please refer to the references or 
send me an email. 



To Learn More About 
Front-end Design 

http : //designne ws . hotims . com/2 3118-101 




Contributing Writer 
Rob Reeder is a senior 
converter applications 
engineer working in 
Analog Devices high- 
speed converter group 
in Greensboro, NC since 
1998. Rob received 
his MSEE and BSEE 
from Northern Illinois 
University in DeKalb, 
IL in 1998 and 1996 
respectively. In his 
spare time he enjoys 
mixing music, art, and 
playing basketball with 
his two boys. 



Have a question 
involving a perplex- 
ing or unusual analog 
problem? Submit 
your question to: 
raq@reedbusiness.com 



For Analog Devices' 
Technical Support, 
Call 800-AnalogD 



SPONSORED BY 




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DEVICES 



SEPTEMBER 17, 2009 | EDN 17 




BAKER'S BEST 




BY BONNIE BAKER 



A designer's guide 
to op-amp gain error 

As you sit down to select the proper operational amplifier 
for your circuit, the first order of business is to determine 
the signal bandwidth that your system will send through 
that amplifier. Once you settle on this parameter, you 
can start to look for the right amplifier. The high-speed- 
op -amp gurus warn that you should avoid using analog 
devices that are too fast for your application. So you try to pick an am- 
plifier with a closed-loop bandwidth just a little higher than the maxi- 
mum frequency of your signal. 



of lOV/V, or 20 dB, out to 1 MHz, but 
look a little closer. The gain of the 
open-loop gain curve at the signal's 
bandwidth is 



A 



OL-SBW 



GBWP 
SBW ' 



VOLTAGE 60 
GAIN 



(dB) 



This strategy may sound 
like a good product-selection 
recipe, but it will probably 
bring disaster to your appli- 
cation board. In the lab, you 
may find that, when you put 
an input-sine-wave signal at 
the application's maximum 
frequency into your system, 
the output signal from your 
amplifier does not go across 
the expected full-scale ana- 
log range. The gain on the 
signal is much less than you 
would expect. If the slew- 
rate magnitude of your am- 
plifier is more than adequate 
and you are not driving the 
amplifier output into the power-sup- 
ply rails, then what has gone wrong? 

Stop double-checking your resistor 
values! When designing an amplifier 
into a gain cell, you must know your 
signal's maximum bandwidth, the am- 
plifier's closed-loop noise gain, the 
amplifier's gain-bandwidth product, 
and how much gain error your design 
can tolerate. The closed-loop noise 
gain is the amplifier's gain, as if a small 
voltage source were in series with the 



140 



120 



100 



80 



40 



20 



-20 



I III i I II I I MUM III I I I 

OPEN-LOOP GAIN OF AMPLIFIER " 




1k 10k 100k 
FREQUENCY (Hz) 



Figure 1 The open- and closed-loop gain of this voltage-feed- 
back amplifier has a gain-bandwidth product of 1 6 MHz and a 
circuit noise gain of 10V/V. 



op amp s noninverting input. 

You can work this problem through 
by example. For instance, start with 
a signal bandwidth of 1 MHz. The 
amplifier's circuit noise gain in Fig^ 
ure 1 is lOV/V. Figure 1 also shows 
the open-loop frequency response 
of an amplifier that has just enough 
bandwidth for this circuit — or so you 
think. The amplifier has a 16-MHz 
gain-bandwidth product. The op amp 
looks as though it can support a gain 



where A^^ is the open- loop gain of 
the amplifier, SBW is the signal band- 
width, and GBWP is the gain-band- 
width product. 

In this case, the amplifier's open- 
loop gain, is l6VfV at 1 MHz. 
But here's the kicker: The closed- 
loop gain error in this circuit is NG/ 
(AQ^_gg^+NG), where NG is the 
noise gain. The closed-loop gain error 
at 1 MHz in this example is 0.385, or a 
gain error of 38.5%. 

For this circuit, if you are willing to 
tolerate a gain error of 0.05 from your 
amplifier and you understand that the 
GBWP of an amplifier can change 
a maximum of 30% from product to 
product and over tempera- 
ture, you need an amplifi- 
er that has a GBWP greater 
than 246 MHz. The guid- 
ing formula is 

GBWPopA = l-30x 

NGxSBWx(l-ERROR) 
ERROR 
where GBWP, 
op amp's 
product. 

Use this formula dur- 
ing your first pass when you 
choose an amplifier for your 
circuit. After you determine 
the amplifier's bandwidth, 
you can start to delve into 
the other important amplifier charac- 
teristics for your application. EDN 

REFERENCES 

n Bendaoud, Soufiane "Gain error af- 
fects op annp choices," Planet Analog, 
July 14, 2006, www.planetanalog. 
conn/features/analog/showArticle. 
jhtml?articlelD= 1 90400337. 
aMancini, Ron, "Op-amp-gain error 
analysis," EDA/, Dec 7, 2000, www. 
edn.com/article/CA561 90. 



CPA is the 
gain-bandwidth 



100M 



18 EDN I SEPTEMBER 17, 2009 




THREE AIRCRAFT, A SINGLE MODEL, 

AND 80% COMMON CODE. 



THAT'S MODEL-BASED DESIGN. 



To develop the unprecedented 
three-version F-35, engineers 
at Locicheed Martin created a 
common system model to 
simulate the avionics, propulsion, 
and other systems and 
to automatically generate 
final flight code. 
The result: reusable designs, 
rapid implementation, and 
global teamwork. To learn more, 
visit mathworks.com/mbd 



TheMathWorks™ 

Accelerating the pace of engineering and science 



matlab* 

^IMULINK' 



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TAPED UT 




BY PALLAB CHATTERJEE, CONTRIBUTING TECHNICAL EDITOR 



Reference-tool flows and 
process-design kits, part one 

est of the advanced process technologies from wafer 
foundries include RTFs (reference-tool flows) to aid in 
tool selection. In addition, PDKs (process-design kits) 
describe the electrical, yield, and performance aspects 
of the process. These two pieces of support documenta- 
tion have been the basis of chip design since the start 
of the semiconductor industry. Although these files provided adequate 
information for engineers to complete designs on process geometries as 
small as 0.25 micron, they alone do not represent all of the issues that 
lithographic and advanced processing variation introduces. 




An RTF is usually a sequence of 
recommended tools that identify all of 
the steps — with the associated EDA 
tools — you need to verify that a phys- 
ical-design view of a circuit meets all 
of the quality criteria to ensure man- 
ufacturability The RTF also ensures 
that the chosen EDA tool will oper- 
ate with the information the foundry 
provides and produce a "correct" re- 
sult. Most of these tool flows involve 
timing closure and detailed placement 
and routing of the circuits — capabil- 
ities that all of the major EDA ven- 
dors provide. Supplementary tools in- 
clude device simulators; parasitic RC 
( resistance/ capacitance ) extractors ; 
physical verification, including DRC 
(design-rule checking), D/S (layout 
versus schematic), and ERC (electri- 
cal-rule checking); package model- 
ing; high-capacity simulation; noise 
modeling; power analysis; and custom 
layout. The addition of these supple- 
mentary tools allows customers who 
want analysis outside their all-in-one 
flow to add independent checks or ad- 
vanced analysis. 



Most fabs try to 
maintain more than 
2000 control files 
for a commercial- 
foundry offering, so 
updates take time, 
and the customer 
must verify them. 



A key misunderstanding about the 
tools in RTFs is that the foundry advo- 
cates them. Rather, the RTF is a list of 
tools with known interoperability with 
each other. Furthermore, the foundry 
believes that these tools can produce 
a result from a certain level of public- 
ly released information on the process 
within an acceptable amount of error 
that the wafer foundry determines. 
Participation in an RTF does not guar- 
antee correct answers from any EDA 
tool for an arbitrary circuit application, 
so don't blindly trust the tools on the 
I list. As a corollary, omission from the | 



list merely indicates that the found- 
ry has not established vendor-to-ven- 
dor interoperability from a menu level 
or that, to achieve higher accuracy or 
performance, the tool requires supple- 
mental information that is not avail- 
able to the general design communi- 
ty but may be available on a case-by- 
case basis. Typically, mixed-signal, RE, 
memory, imaging, telecom, very-high- 
speed, multiprocessor-core, DSP, and 
low-power designs do not use RTFs. 

The basics of RTFs are the tech- 
nology files that describe the mask- 
ing and design layers for the process 
and their functions. This technolo- 
gy also contains a naming convention 
and information for operating a cus- 
tom physical-design tool, or layout ed- 
itor. The technology file also has the 
rudimentary minimum-design-rule in- 
formation for the process, so physical- 
system designers can use the rules as 
guidelines. There is also a place-and- 
route control file, which dictates de- 
vice-to-device and wire-to-wire spac- 
ing on the design and is written in the 
dialect of the EDA vendor's tools. 

The last major component is the 
physical-verification files. These files 
include the DRC deck, which com- 
prises minimum rules, recommended 
rules, DEM (design-for-manufacturing) 
"increased-yield" rules, memory rules, 
I/O rules, power-supply rules, ESD 
(electrostatic-discharge) rules, analog 
rules, and special-device rules. A sim- 
ilar format is available for ERC-, LVS-, 
and parasitic-extraction-rule decks. As 
a result, most fabs try to maintain more 
than 2000 control files for a commer- 
cial-foundry offering, so updates take 
time, and the customer must verify 
them.EDN 

Contact me at pallahc@siliconmap.net. 



\±} Go to www.edn.com/09091 7pc 
and click on Feedback Loop to post 
a comment on this column. 

\±} www.edn.com/tapeout 



20 EDN I SEPTEMBER 17, 2009 



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Agilent Technologies 



BRIAN DIPERT SENIOR TECHNICAL EDITOR 



T-Mobile's G1 : Google's Android OS emerges 

The myTouch 3G (also known as the HTC Magic), T-Mobile's second Google Android-OS-based and HTC-designed 
handset, recently became available for purchase- More svelte and with a more responsive touchscreen than its prede- 
cessor, the Gl (also known as the HTC Dream), the myTouch 3G conversely relies exclusively on an on-screen virtual 
keyboard- After peeling away the Gl's oft-preferred physical keyboard, my Prying Eyes partners at phone Wreck discovered 
some interesting facts about the two primary PCBs (printed-circuit boards) inside the premier Google Android offering. 



T-Mobile's UMTS (Universal Mobile 
Telecommunications System) cellular-data 
network leverages the WODMA (wide- 
band-code-division/multiple-access), 1 700- 
and 2100-MHz bands in the United States, 
whereas GSM (global-system-for-mobile)- 
communication competitor AT&T, which 
currently touts a more extensive 3G cover- 
age footprint, employs 850- and 1 900- 
MHz spectrum slices. You'll therefore 
see some unique pieces of silicon in the 
01 versus, say, the BlackBerry Bold (see 
"Trolling for gold in the BlackBerry Bold," 
EDA/, May 28, 2009, pg 20, www.edn. 
com/article/CA665941 5). Avago's ACPM- 
7381 andACPM-7391 UMTS power 
amplifiers, along with TriQuint's ALM-1 41 2 
quadband power-GSM amplifier, together 
mate to Qualcomm's RTR6285 RF trans- 
ceiver and PM7540 power-management 
IC. Avago also supplies the ALM-1 41 2 
GPS (global-positioning-system) amplifier. 



The multidie, single-package memory subsystem sandwiches | 
256 Mbytes of Samsung's NAND flash memory and 1 28 
Mbytes of that company's DDR SDRAM. T-Mobile bundles 
a 1-Gbyte microSD (secure-digital) card with the handset; 
the memory-module interface is higher-capacity microSDHG 
(secure-digital-high-capacity)-compatible. 




AKM's AK- 
7986A six- 
axis electronic 
compass sup- 
plements the 
Gl 's accel- 
erometer and 
GPS capabili- 
ties to provide 
the handset 
with a rich set 
of location, 
motion, and 
direction 
statistics. 




1 



Qualcomm's 528-MHz 
MSM7201 A baseband processor, 
which embeds GPS and audio 
DAG/ADC functions, acts as the 
brains of the Gl . Curiously, HTC 
augmented the Gl 's logic with 
a Xilinx XC2C1 28 CoolRunner- 
II CPLD, which HTC has also 
employed in past PDA and smart- 
phone designs. Although the 
CPLD seemingly runs counter to 
the integration- and cost-optimized 
focus of a high-volume consumer- 
electronics device, it also enables 
HTC to easily augment and update 
hardware capabilities both on the 
manufacturing line and in the field. 



22 EDN I SEPTEMBER 17, 2009 





[+] Go to www.edn.com/ 
pryingeyes for past Prying 
Eyes write-ups. 




Not shown are the 
G1's 3.2M-pixel still- 
mage-only camera 
based on Aptina's 
(formerly Micron's) 
MT9T013D sensor 
and Analog Devices' 
AD5398 autofocus- 
capable lens-coil driver 
the Sharp-supplied 
3.2-in, 320X480-pixel 
resolution and 65,536 
color LCD; and the 
1150-mAhr battery. 



For those of 
you who prefer 
old-fashioned 
but reliable 
wires, SMSC's 
(Standard 
Microsystems 
Corp's) 
USB3316 
USB (Universal 
Serial Bus) 
controller has 
you covered. 



The device has 
802.11 b/g 
Wi-Fi- and 
Bluetooth-con- 
nectivity options, 
The Texas 
Instruments 
WL1251B 
transceiver and 
companion 
WL1251FE 
power amplifier 
handle Wi-Fi, 
and the compa- 
ny's BRF6300 
chip handles 
Bluetooth. 





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PATH, DIGITAL-SYSTEM DEVELOPERS CAN MORE ACCURATELY 
CAPTURE SENSOR DATA FOR A VARIETY OF APPLICATIONS. 

BREAKING DOWN 

THE SENSOR-SIGNAL PATH 

BY AARON GL PODBELSKI • CYPRESS SEMICONDUCTOR 

Sensors are increasingly finding use in embed- 
ded systems. Although industrial products have 
long used them for manufacturing-control sys- 
tems, consumer devices are now starting to em- 
ploy them, as well Manufacturers are integrat- 
ing sensors into consumer products to create 
better user experiences — ranging from adding 
accelerometers in mobile phones to adding wa- 
ter-vapor sensors in microwave ovens. System 
designers, who previously worked only in the digital domain, are 
now finding themselves having to interface with analog sensors. 

You must digitize a sensor's analog signal so that the sys- 
tem can use it, and the signal path goes through amplification, 

filtering, and digitization stages (Figure a control system on the microcontroller 

!)♦ Each stage usually involves a com- or massage the data and pass it to a host 

ponent with passives around it to per- processor through a communication 

form properly for an application. Once protocol. The protocol can use the sen- 

you digitize the signal, you can pass it to sor data as necessary. 



Every sensor has a different output 
signal and range. The output signal can 
be voltage-, current-, resistive-, capaci- 
tive-, or frequency-based, but few stan- 
dards exist, and only specific industrial 
systems use them. Even similar sensors 
from the same manufacturer can have 
different outputs, and these differences 
can create problems for system design- 
ers. A designer must select a sensor that 
meets the requirements for the system. If 
the requirements change during the de- 
sign, however, a sensor change may al- 
so be in order. In addition, a new sensor 
with a slightly different output would 
necessitate altering the amplification 
and filtering stages. 

Most sensors output a low-level cur- 
rent- or voltage-based signal, so a sim- 
ple resistive network adapts any current- 
based signal into a voltage. This article 



SEPTEMBER 17, 2009 | EDN 25 




simplifies some concepts and the com- 
ponent'Selection process. 

AMPLITUDE 

The output of a sensor can be as small 
as several millivolts or as large as sever- 
al volts- For proper digitization, the sig- 
nal must be large enough for the ADC 
to effectively read it- In most cases, the 
sensor signal requires amplification. For 
example, a typical type-K thermocou- 
pie outputs 41 |JlV/°C, which you must 
greatly amplify if your design requires 
1°C granularity. Thus, you must take 
ADC resolution into account to ensure 
that you sufficiently amplify the signal 
to obtain the desired granularity. 

You base the selection of an amplifier 
mainly on the type you need — be it an 
instrumentation amplifier, a differential 
amplifier, an operational amplifier, or a 
PGA (programmable-gain amplifier). 
You also must determine the amount 
of gain your amplifier requires. A resis- 
tive network, with feedback, around the 
amplifier sets the amplifier's gain. The 
maximum gain for standard amplifiers is 
ideally limitless. A digital signal to the 
device usually sets the gain for a PGA. 
This signal alters an internal resistive 
network. The maximum possible gain 
for a PGA is 0.5 to 1000 times less than 
that of a traditional amplifier, but this 
range is more than acceptable in most 



AT A GLANCE 

□ Even similar sensors from the 
same manufacturer can have differ- 
ent outputs, and these differences 
can create problems for system 
designers. 



□ Noise arises from a number of 
sources, including board layout, 
radios, thermal components, and 
even the sensor itself. 



□ To use the sensor's filtered sig- 
nal, you must quantify the analog 
signal into the digital domain using 
an ADC. 



El You have the choice of using an 
external ADC or a microcontroller 
with an integrated ADC. External 
ADCs tend to have higher accuracy 
and higher performance in both 
I speed and resolution. 

With amplifiers, you must take into 
account another key specification: offset 
voltage. Offset voltage is the amount of 
alteration in volts of a signal that pass- 
es through the amplifier. For example, if 
you put a 500-mV signal into an ampli- 
fier with unity gain, or a gain of one, and 
an offset voltage of 10 mV, the resulting 
output would be 510 mV. If the output 
range of the sensor is to 900 mV and 
the system does not need a very granu- 
lar reading of the sensor, this offset may 
be negligible. If the range of the sensor 























SENSOR 




AMP -► 


FILTER 


ADC 


PROCESSING 
CORE 




DIGITAL 
INTERFACE 




HOST 























ACTUATOR 
CONTROL 



Figure 1 A sensor's analog-signal path goes through several stages: amplification, filtering, 
and digitization. 



is 450 to 550 mV, this offset is probably 
unacceptable. The smaller the offset 
voltage, the more costly the amplifier 
is. All amplifiers have an offset, but you 
need to know whether the system can 
tolerate it. You can reduce or eliminate 
the offset voltage using correlated dou- 
ble sampling. 

FILTERING 

All systems impart some noise on the 
sensor's signal. Noise arises from a num- 
ber of sources, including board layout, 
radios, thermal components, and even 
the sensor itself. Signal noise causes the 
ADC to make inaccurate and unstable 
readings, and the noise level increases 
through the amplification stage, which 
exaggerates the error in the signal. You 
can qualify signal noise as low frequen- 
cy, high frequency, or a known frequen- 
cy. You most often need to address high- 
frequency-noise issues. 

You can filter noise using passive an- 
alog filters, filter ICs, and digital filters 
(Figure 2). The most common method, 
passive filtering, involves creating a pas- 
sive network of resistors, capacitors, and 
inductors. You must design passive fil- 
ters, however, and you cannot easily al- 
ter them. Filter design can be as cumber- 
some as the order of the filter you need; 
a first-order Chebyshev filter takes much 
less effort to design than an eighth-order 
Bessel filter. So you should determine 
the order of the filter you need before 
selecting the method of filtering you 
will employ. 

Some ICs allow you to digitally 
program the type of filter you need. 
These ICs use internal analog cir- 
cuitry to create the filter and may 
have offset voltages associated with 
them. They also allow you to move 
the filter process after quantifica- 
tion with the ADC. Digital-filter 
design can be complex, but many 



RAW SIGNAL AMPLIFIED SIGNAL FILTERED SIGNAL 





















AMP 




FILTER 






ADC 



























Figure 2 The sensor-signal path includes amplifiers, filters, and an ADC. You design the filter to remove noise and limit the bandwidth 
of the signal. 



26 EDN I SEPTEMBER 17, 2009 





Figure 3 Combining INL error (a), DNL error (b), gain error (c), offset error (d), and total error (e) provides an understanding of the 
ADC in use compared with an ideal ADC (f). 



tools allow for the easy design of high- 
order filters. Digital filtering can be an 
ideal means of removing noise; howev- 
er, it often requires many CPU cycles, 
increasing power consumption. The 
system normally incurs high-frequency 
noise, necessitating the use of a lowpass 
filter. This filter attenuates any part of 
the signal that is higher frequency than 
the set cutoff frequency. Some sensor 
signals require the use of several types 
of filters in tandem with each other. 
Most sensor data sheets specify a ba- 
sic interface circuit but do not mention 
the necessary filtering. System design- 
ers must create the system before fully 



understanding how much filtering is 
necessary. 

DIGITAL CONVERSION 

To use the sensor's filtered signal, you 
must quantify the analog signal into the 
digital domain using an ADC. Selection 
of an ADC mainly concerns the system's 
requirements for sampling speed and res- 
olution. The necessary sampling speed 
relates to the sensor's bandwidth or how 
often the system needs updating. Resolu- 
tion depends on the granularity you need 
for the ADC to react to the sensor's in- 
formation. The system's usage model de- 
fines this speed and resolution require- 



ment. For example, a generic gyroscope 
measures 360° of rotation at 0.67 mV/°, 
resulting in an output range of 241 mV. 
To remain upright, a hobbyist's helicop- 
ter might need information from a gy- 
roscope at a granularity of 1° but with 
a throughput of 10k samples/sec. This 
requirement would necessitate a 10-bit 
ADC, which would provide 0.357bit. 
Note that the signal still has noise on it, 
however, and ± 1 bit is acceptable. Con- 
versely, a digital camera with image sta- 
bilization might require a granularity of 
0.02° but with a throughput of 5k sam- 
ples/sec to adjust the image sensor as a 
camera shakes. This requirement would 
necessitate the use of a 16-bit ADC, 
which would provide 0.005°/bit. 
Manufacturers measure the accu- 
I racy of ADCs in terms of INL (inte- 
I gral nonlinear ity), DNL (differential 
' nonlinearity), offset error, gain er- 
ror, and SNR (signal-to-noise ratio). 
When you combine these terms, they 
offer an understanding of the ADC's 
total error (Figure 3). For most ap- 
plications, it is not necessary to look 
into these ADC specifications, but 
engineers should have a thorough 
understanding of these values for the 
ADC in use. You have the choice of 
using an external ADC or a micro- 
- controller with an integrated ADC. 



I — AMP 




ADC 



ACTUATOR 
CONTROL 



PROCESSING 
CORE 



DIGITAL 
INTERFACE 



STANDARD 
MICROCONTROLLER 



PSOC 

Figure 4 Developers can implement the amplification and filtering stages, integrati 
entire analog-signal chain onto one device. 



ng the 



SEPTEMBER 17, 2009 | EDN 27 




External ADCs tend to have higher ac- 
curacy and higher performance in both 
speed and resolution. Most sensor-appli- 
cation requirements align well with inte- 
grated-microcontroller ADCs, however. 

Another option is to use configurable 
ADCs, which comprise programmable- 
logic blocks within a microcontroller. In- 
tegrated digital and analog programma- 
ble blocks allow for the dynamic defini- 
tion of configurable peripherals for each 
sensor application. These blocks include 
counters, PWMs (pulse-width modula- 
tors), UARTs, SPIs (serial-peripheral in- 
terfaces), amplifiers, filters, ADCs, and 
DACs. Developers can also implement 
the amplification and filtering stages, in- 
tegrating the entire analog- signal chain 
onto one device (Figure 4)- Using con- 
figurable ADCs can result in cleaner de- 
signs than those using passive compo- 
nents. In addition, you can dynamically 
reconfigure these blocks, so you have the 
option of reusing these system resources 
for other functions. 

Sensors continue to penetrate a range 
of markets, bringing you more control 



SENSORS CONTINUE 
TO PENETRATE A 
RANGE OF MARKETS, 
BRINGING YOU 
MORE CONTROL AND 
GREATER FLEXIBILITY. 



and greater flexibility. Sensors increase 
reliability through management of the 
environment, including, for example, 
temperature monitoring; improved per- 
formance through feedback mechanisms; 
and enabling new types of user interfac- 
es. For many of these designs, the inte- 
grated ADCs on microcontrollers pro- 
vide sufficient granularity and accuracy. 
Developers who are unfamiliar with an- 
alog design may encounter pitfalls along 
the analog-signal chain between the 
sensor and the microprocessor. 

Implementing the multiple stages of 
the analog-signal path can seem con- 
voluted, especially to engineers accus- 
tomed to designing primarily in the digi- 



tal domain. However, by breaking down 
the analog-signal path into the various 
amplification, filtering, and ADC stag- 
es, digital-system developers can more 
easily and accurately capture sensor data 
for a variety of industrial and consumer 
applications. In addition, readily avail- 
able ICs, configurable ADCs, and filter- 
design tools can greatly simplify sensor 
design. EDN 

AUTHOR'S BIOGRAPHY 

Aaron GL Podhelski is a project manager at 
Cypress Semiconductor. He manages sev- 
eral of the company's PSoC (programma- 
hle-sy stem-on-chip) products and focuses 
on marketing the PSoC's analog capabilities 
for customers using sensors. Podhelski has 
a bachelors degree in computer engineering 
from Marquette University (Milwaukee, 
Wl). His personal interests include playing 
the guitar and drums, snowhoarding, surf- 
ing, playing with tech gadgets, and smiling. 

A version of this article appeared in 
a May 2009 supplement published by 
EDN's sister publication Design News, 




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RF 



SWITCHING OPTIONS: 

THE RIGHT FIT MIGHT COME WITH A LOSS 




MANUFACTURERS ARE OFFERING SOI AND MEMS ALTER- 
NATIVES TO PIN-DIODE, GaAs, AND ELECTROMECHANI- 
CAL SWITCHES FOR A VARIETY OF RF APPLICATIONS, 
BUT YOU NEED TO UNDERSTAND RF-SWITCH SPECS 
BEFORE YOU COMMIT TO A NEW TECHNOLOGY 



BY RICK NELSON • EDITOR-IN-CHIEF 



Whether you are building "big-iron" RF- 
test equipment or tiny, muhiband mo- 
bile devices, you need to route RF and 
microwave signals among instruments 
and devices under test or between an- 
tennas and amplifiers. To accomplish 
that task, you can turn to various sol- 
id-state implementations, including 
SOI (silicon-on-insulator) devices and 
MEMS (microelectromechanical-system) switches, both of which 
vendors were touting at the June IEEE MTT-S (Microwave Theory 
and Techniques) International Microwave Symposium. Highly inte- 
grated bulk-CMOS devices represent another alternative. However, 



you need to know when those options 
make sense as alternatives to the more 
traditional electromechanical, PIN-di- 
ode, and GaAs (gallium-arsenide) FET 
versions- Solid-state and MEMS switch- 
es take up much less real estate and have 
longer lifetimes than do electromagnetic 
switches. Further, SOI and MEMS devic- 
es can be easier to integrate than GaAs 
devices with other components- Before 
embarking on switch selection, howev- 
er, you need to understand whether the 
specs of the device you select will meet 
your application requirements- 

GETTING TO KNOW SPECS 

You need to consider switch band- 
width. The switch you choose must, at its 
maximum operating frequency, conduct 
a signal Unfortunately, when choosing 
a switch, you can't rely on the "3-dB- 
down" — that is, noise that is 3 dB lower 
than peak noise — rule of thumb that you 
might use to determine the upper oper- 
ating limit of an amplifier, for example- 
You need to determine the acceptable 



performance with respect to bandwidth 
in the context of the other specifications, 
including characteristic impedance and 
VSWR (voltage-standing- wave ratio), 
crosstalk, and isolation (Reference 1). 

You should also consider whether you 
need to transmit low frequencies or dc- 
Electromechanical and FET switches 
generally pass low frequencies; PIN-diode 
switches and capacitive MEMS switches 
generally do not (Reference 2). 

Other RF-switch specifications include 
characteristic impedance. You typically 
use a lumped-element model to represent 
transmission lines (Figure !)♦ In these 
models, successive infinitesimal segments 
of the line, which ideal transmission lines 
interconnect, have series resistance R, se- 
ries inductance L, shunt conductance G, 
and shunt capacitance C- Characteristic 
impedance, then, is 



Zo= 



R + jcoL 



|G + jcoC 

For zero resistance and zero conduc- 
tance, characteristic impedance is 



Any switch you select should pres- 
ent the same characteristic impedance 
your system exhibits to prevent signal 
reflections- The reflection coefficient 
quantifies reflections. This coefficient is 
equivalent to the s^^ S parameter (Ref- 
erence 3), which can contribute to a 
poor VSWR. With regard to VSWR, 
you want to know whether you are se- 
lecting an absorptive switch or a reflec- 
tive switch. Absorptive versions apply a 
resistive shunt to ground in the off state 
to provide a good impedance match and 
minimize VSWR, regardless of switch 
position; reflective versions serve appli- 
cations in which VSWR doesn't matter 
or in which you control impedance else- 
where (Reference 4). 

INSERTION LOSS, ISOLATION 

Other key specs include isolation, 
crosstalk, and insertion loss: 



IL = 101og 



10- 



Pin ' 



where IL is insertion loss and P^^^ and 
Pj^ are output power and input power, 
respectively. 

You can also represent insertion loss 
in terms of S parameters: 

f Q ^ 

IL^lOlogio 



S21 



1- 



■sil 



The S-parameter notation to the 
right of the equal sign shows that the 
switch's insertion loss is inherent to the 
switch and does not depend on input 
mismatches. The 1 ~s^^ denominator in- 
dicates that you subtract any reflected 



SEPTEMBER 17, 2009 | EDN 31 



a 



signal that the s^^ term represents from 
the normalized input-signal level before 
you calculate insertion loss- 
Insertion loss is critical, says David 
Hall, an RF-product manager for Na- 
tional Instruments, which uses RF 
switches in its lineup of RF-switch-ma- 
trix test-and-measurement products- A 
switch must transmit your signal with- 
out undue attenuation at the frequen- 
cy or frequencies of operation. If you 
choose a switch with too much insertion 
loss, he says, you may have to amplify a 
switched signal to make it usable, add- 
ing to system complexity and potential- 
ly introducing linearity errors- 

SPECIFYING LINEARITY 

A switch can exhibit linearity errors 
even in the absence of amplification. 
Specs that indicate linearity include 
the 1-dB compression point and the IP3 
(third-order intercept point). Measur- 
ing the 1 -dB compression point involves 
a power sweep on the input to a device 
under test; when the output drops 1 dB 
from the level you would expect based 
on the small-signal response, you've 
reached the 1-dB compression point. IP3 
measurements involve applying closely 
spaced tones to a nonlinear device un- 
der test, which generates third-order in- 
termodulation products. The IP3 point 
is typically hypothetical because it might 
lie outside the safe operating region of 
the device under test. You obtain the IP3 
using extrapolation. It occurs when the 
power of the third-order intermodula- 
tion products would equal that of the de- 
sired signal (Reference 5). 

Other specs include crosstalk and iso- 
lation. Crosstalk represents the mag- 
nitude of a signal that couples from an 
active switch to an adjacent inactive 
switch, and isolation represents the mag- 

R L R L 



G > -T- C 



AT A GLANCE 

□ You need to determine the 
acceptable performance with respect 
to bandwidth in the context of the 
other specifications, including inser- 
tion loss, crosstalk, and isolation. 



□ Absorptive versions apply 
a resistive shunt to ground 
in the off state to provide good 
impedance match and minimize 
VSWR (voltage-standing-wave ratio) 
regardless of switch position. 



□ Bulk-CMOS devices offer cost 
advantages and fit within a small 
footprint. 



□ One MEMS (microelectrome- 
chanical-system) switch is rated for 
100 million operations and can work 
for 1 billion cycles. 



□ The handset market offers high- 
volume opportunities for nine-throw 
switches going into pentaband 
phones. 



nitude of a signal that a switch transmits 
from its input to its output when in the 
open position. A switch can be subject 
to various deleterious effects, including 
impedance mismatch, insertion loss, 
crosstalk, and isolation (Figure 2). 

Electromechanical switches as well 
as PIN diodes and GaAs FET switches 
traditionally have excelled at meeting 
these specs, but each offers drawbacks. 
Electromechanical switches are large 
and can occupy significant amounts of 
PCB (printed-circuit-board) real estate. 
PIN diodes include a high-resistivity in- 
trinsic region between their P- and N- 
type semiconductor regions (Reference 
6). The intrinsic region becomes con- 
ductive when you forward-bias the de- 
vice, essentially closing the switch to al- 
low RF signals to pass. PIN diodes are 
rugged, compact devices that can handle 

R L 



1- C 



G > n-C 



Figure 1 Lumped-element models typically represent transmission lines, with succes- 
sive infinitesimal segments, interconnected by an ideal transmission line, having series 
resistance R, series inductance L, shunt conductance G, and shunt capacitance C, 
from which you can calculate characteristic impedance. Your switch should offer the 
same characteristic impedance. 



high voltages and currents; drawbacks 
include the need for external bias cir- 
cuitry and the fact that the required dc 
bias current — and the higher the bias, 
the lower the insertion loss — makes 
them problematic for use in power-sen- 
sitive battery-operated system. 

GaAs DEVICES ARRIVE 

GaAs devices remain popular. NEC 
markets the devices for wireless applica- 
tions (Reference 7). At the June Interna- 
tional Microwave Symposium, RF Micro 
Devices introduced its 6-GHz RF3021, 
RF3023, RF3024, and RF3025 switches, 
which it fabricated in its GaAs PHEMT 
(pseudomorphic-high-electron-mobil- 
ity-transistor) technology. The symmet- 
ric SPDT (single-pole/double-throw) 
RF3021 and RF3025 switches feature 
high isolation; the RF3023 and RF3024 
symmetric SPDT switches feature low in- 
sertion loss and moderate isolation. This 
year, Skyworks Solutions Inc introduced 
its Skyl3317-373LF, a PHEMT GaAs 
SP3T (single-pole/three-throw) antenna 
switch that operates from 0.1 to 6 GHz. 
Last month, Hittite Microwave Corp 
introduced its GaAs PHEMT, MMIC 
(monolithic-microwave-integrated-cir- 
cuit), SP4T (single-pole/four- throw), 
nonreflective HMC-C071 switch mod- 
ule, which targets microwave radio, 
VSAT (very-small-aperture- terminal), 
military and aerospace, fiber-optic, and 
broadband-test applications requiring 
operation from dc to 20 GHz. 

GaAs FET switches have their draw- 
backs, however, in that they require ex- 
ternal components in the form of block- 
ing capacitors, and they can be difficult 
to integrate with other components 
(Reference 8). Alternatives to GaAs 
switches, as well as to electromechanical 
switches and PIN diodes, include bulk- 
CMOS, MEMS, and SOI switches. 

BULK-CMOS SWITCHES 

Analog Devices touts its ADG9XX- 
family submicron, 1-GHz bulk-CMOS 
switches (Figure 3), which the company 
offers for use in the 900-MHz ISM (in- 
dustrial/scientific/medical) band (Refer^ 
ence 9). Ray Goggin, staff design engi- 
neer, and John Quill, engineering man- 
ager, both of Analog Devices' switches- 
and multiplexer-product line, cite sever- 
al advantages of the devices. For exam- 



32 EDN I SEPTEMBER 17, 2009 




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COUPLED SIGNAL 
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Figure 2 A switch can be subject to various deleterious effects. An impedance mis- 
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Goggin and Quill note that bulk- 
CMOS switches have lower band- 
width and maximum switched-RF 
power than do other switches, but, 
for applications whose require- 
ments fall within bulk-CMOS 
limitations, the bulk-CMOS de- 
vices offer cost advantages- They 
also note that each device exhibits 
a footprint as small as 9 mm^ in a 
CSP (chip-scale package) and can 
integrate driver circuitry, thereby 
eliminating the need for separate 
ICs. 



MEMS AND SOS DEVICES 

If your application requires per- 
formance levels that lie beyond 
what bulk-CMOS devices can pro- 
vide, you might consider a MEMS 

switch. Omron's 2SMES-01, for 

example, operates to 10 GHz, of- 
fering 30-dB isolation and 1-dB insertion 
loss (Figure 4)- It offers maximum power 
consumption of 10 fxW, which, accord- 
ing to Donna Sandfox, product manager 
at Omron Electronic Components LLC, 
is about one ten-thousandth that of an 
equivalent electromagnetic relay- 

The device targets high- throughput 
ATE (automated-test-equipment) ap- 
plications- An electrostatic-drive system 
powers the device, which performs 100 
million operations switching a resistive 
load at 0.5 mA and 0.5V dc. Sandfox 
says the company has tested the device 
over 1 billion cycles. Each switch con- 



RFC Q 



ctrlQ 




RF 1 



QrF2 



Figure 3 The Analog Devices SPOT ADG91 8 
absorptive switch has 50n-ternninated shunt 
resistors to ground, minimizing reflections back to 
the RF source. It is available in a 3X3-mm chip- 
scale package. 



sists of two normally open SPST (sin- 
gle-pole/single-throw) silicon switches 
in a 5.2X3.0X 1.8-mm housing offer- 
ing SPDT or DPST (double-pole/single- 
throw) normally open operation. 

Peregrine Semiconductor addresses 
the RF-switch market with its Ultra- 
CMOS SOS (silicon-on-sapphire) tech- 
nology, which integrates ultrathin-sili- 
con-CMOS circuitry on an insulating 
dielectric sapphire substrate. Peregrine 
also targets ATE and other applications, 
including digital TV, cable and satel- 
lite set-top boxes, game consoles, and 
cellular communications. For RF trans- 



INPUT 1 Q 



INPUT 2 O 




Orfi 



Qrfcom 



0RF2 



DRIVER IC 



Figure 4 An electrostatic-drive system powers Omron's 2SMES-01 , which operates to 1 
GHz, offering 30-dB isolation and 1-dB insertion loss. It performs 1 00 million operations 
switching a resistive load. 



EDN I SEPTEMBER 17, 2009 



LOW-NOISE 
AMP 



V 



SWITCH 




Figure 5 For RF-transceiver applications, Peregrine Semiconductor complements its 
switches with UltraCMOS quad MOSFETs, PLLs, and prescalers. 



ceivers, the company complements its 
switches with UltraCMOS quad MOS- 
FETs, PLLs, and prescalers (Figure 5), 
enabling Peregrine parts to make up 
a substantial portion of the RF-signal 
chain. Rodd Novak, vice president of 
sales, marketing, and business deveL 
opment, says that the handset market 
offers high'volume opportunities, with 
the company's nine-throw switches go- 
ing into pentaband phones- 

For ATE applications. Peregrine offers 
the PE42552 absorptive SPDT device, 
which operates to 7-5 GHz with a 1-dB 
compression point of 34-5 dBm. Inser- 
tion loss is 0.65 dB at 3 GHz. Also for 
ATE applications, the company com- 
plements the PE42552 switch with the 
PE43703 7 -bit digital step attenuator. 

Mark Schrepferman, director of sales 
and marketing for communications and 
industrial markets at Peregrine, says that 
Peregrine has learned a lot about how to 
serve the test-equipment market from 
looking at its own test needs. Chris- 
tian Steele, product-development sec- 
tion manager at Peregrine, recounts one 
major problem. Big-box ATE systems, 
he says, often include one or two sourc- 
es and one or two receivers and rely on 
electromechanical switches to route sig- 
nals among the available instruments 
and the multiport devices under test. "A 
lot of those mechanical switches have a 
reliability of very few throws — often less 
than 2 million," he explains. "At the 
volumes in which we are shipping our 
handset switches, we would be replacing 
very expensive mechanical switches in 



less than a month." The cover story of 
the October issue of EDN's sister pub- 
lication Test & Measurement World will 
describe how Peregrine engineers per- 
form engineering characterization and 
production test of SOS devices. 

Schrepferman says he has learned a lot 
from Steele and colleagues involved in 
test at Peregrine and has put the infor- 



mation to good use. He notes that, even 
in the down economy, the company has 
seen "a tremendous number of design 
wins" in the test-equipment market. 

As RF-switch technology advances, 
there is unlikely to be a clear-cut winner 
serving all applications, and Peregrine 
is evaluating multiple technologies. At 
Peregrine, there is one restriction. Ron 
Reedy, co-founder and chief technolo- 
gy officer, says that he put one edict in 
place when he founded the company: 
"Don't get in front of the CMOS steam- 
roller." If you can implement something 
in bulk silicon CMOS, which he calls 
mankind's greatest volume accomplish- 
ment by any standard, then that's how 
you should implement it. 

Reedy says that Peregrine is investi- 
gating MEMS, noting that, "from a per- 
formance point of view, it's pretty hard 
to beat metal contact." It's counterpro- 
ductive, however, to put a high-perform- 
ance switch on a lossy substrate, and 
work is under way to see whether MEMS 
belong on sapphire. "We would not say 
there is a single technical solution that 
covers all applications," he adds.EDN 



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REFERENCES 

m Rowe, Martin, "Get to know RF 
switch specifications," Test & Measure- 
ment World, October 2007, www. 
tmworld.com/article/CA648291 1 . 
3 "Microwave switches," Microwaves- 
101 Microwave Encyclopedia, www. 
microwaves 1 01 .com/encyclopedia/ 
switches.cfm. 



a Nelson, Rick, "What are S-param- 
eters, anyway?" Test & Measurement 
World, February 2001, www.tmworld. 
com/article/CAl 87307. 
El Corrigan, Theresa, "Ask the Ap- 
plication Engineer-34: Wideband 
CMOS Switches," Analog Dialogue, 
October 2004, Analog Devices, www. 
analog.com/library/analogDialogue/ 



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archives/38-1 0/wideband_switch.htnnl. 
3 Kundert, Ken, "Accurate and Rapid 
Measurement of and IP3," The De- 
signer's Guide Community, May 2002, 
www.designers-guide.org/Analysis/ 
intercept-point.pdf. 
3 The PIN Diode Circuit Designers' 
Handbook, Microsemi Corp, 1 998, 
www.ieee.li/pdf/pin_diode_handbook. 
pdf. 

a Iwata, N, and M Fujita, "GaAs Switch 
ICs for Cellular Phone Antenna Im- 
pedance Matching," NEC Technical 
Journal, March 2009, www.nec.co.jp/ 
techrep/en/journal/g09/n01/090108. 
html. 

[H "RF Switch Performance Advantages 
of UltraCMOS Technology over GaAs 
Technology," Application Note AN 18, 
Peregrine Semiconductor, 2007, www. 
psemi.com/pdf/app_notes/an 1 8.pdf. 
3 Corrigan, Theresa, "ADG9xx Wide- 
band CMOS Switches: Frequently 
Asked Questions," Application Note 
AN-952, Analog Devices, 2008, www. 
analog.com/static/imported-files/ 
application_notes/AN_952.pdf. 



\±\ Go to www.edn.com/09091 7cs 
and click on Feedback Loop to post 
a comment on this article. 

[±] For more technical articles, go to 
www.edn.com/features. 



FOR MORE I 

Analog Devices 

www.analog.conn 

Hittite Microwave 
Corp 

www.hittite.com 

National Instruments 

www. ni. com 

NEC 

www.nec.com 

Omron Electronic 
Components 

www.components. 
omron.com 



You can reach 
Editor-in-Chief , 



Rick Nelson 

at 1-781-734-84U 



and rnelson® 
reedbusiness.com 



NFORMATION 

Peregrine 
Semiconductor 

www.psemi.com 

RF Micro Devices 

www.rfmd.com 

Skyworks Solutions 
Inc 

www.skyworksinc.conn 




36 EDN I SEPTEMBER 17, 2009 



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max. 


(on) 
VGS^ 
typ. 


zlOV 
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(nC) 


% 

(nC) 




RJK03C0DPA 


30 


+20/-20V 


70 


65 


1.8 


2.5 


1.5 


2.0 


13.7 


66 


0.75 


RJK0390DPA 


65 


60 


2.1 


2.9 


1.7 


2.2 


11.3 


54 


0.8 


RJK0391DPA 


50 


50 


2.8 


3.9 


2.2 


2.9 


7.4 


34 


0.95 


RJK0392DPA 


45 


45 


3.4 


4.8 


2.7 


3.5 


5.9 


26 


0.8 


RJK0393DPA 


40 


40 


4.2 


5.9 


3.3 


4.3 


4.7 


21 


1.4 


RJK0394DPA 


35 


35 


5.3 


7.4 


4.1 


5.3 


3.7 


15.5 


1.4 


RJK0395DPA 


30 


30 


7.6 


10.6 


5.9 


7.7 


2.6 


11.0 


2.2 


RJK0396DPA 


30 


28 


9.0 


12.6 


6.9 


9.0 


2.2 


9 


2.5 


RJK0397DPA 


30 


25 


10.4 


14.6 


7.8 


10.1 


1.9 


7.4 


2.5 


RJK03B7DPA 


30 


30 


7.7 


10.7 


6.0 


7.8 


2.6 


11.0 


1.0 


RJK03B8DPA 


30 


28 


9.3 


12.9 


7.0 


9.3 


2.2 


9 


1.2 


RJK03B9DPA 


30 


25 


10.9 


15.1 


8.3 


10.6 


1.9 


7.4 


1.2 



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In search of a better DRAM 
evolving to floating bodies 

WIDELY INVESTIGATED FLOATING-BODY MEMORIES APPEAR TO 
BE COMPELLING REPLACEMENTS FOR CONVENTIONAL DRAMs. 
A NEW FLOATING-BODY MEMORY USES THE INTRINSIC BIPOLAR 
TRANSISTOR TO STORE SIGNIFICANTLY GREATER CHARGE. 



MOS TRANSISTOR 



The memory industry has 
crammed more and more mem- 
ory bits onto ever smaller die 
and is selling those slivers of sil- 
icon for a few cents each. Cur- 
rently, 1-Gbit and even 4'Gbit 
DRAMs (dynamic random-access memo- 
ries) are available- Process engineers have 
been able to achieve these goals, especially 
with respect to the capacitor element, which 
has become more difficult to scale, a problem 
that gets worse as device geometries shrink. 
These advances employ the basic one- tran- 
sistor DRAM, which Robert H Dennard, 

PhD, a fellow at the IBM Thomas J Watson 

Research Center (www.watson.ibm.com), 
created in 1966. In 1970, Intel (www.intel.com) released the 
first DRAM chip, a 1-kbit PMOS device. Since that time, the 
basic DRAM building block has comprised a single transistor 
and an increasingly complex capacitor. 

Scaling introduces yet another major problem for DRAM 
manufacturers: leakage current. In both the bit cell and its sup- 
porting circuitry, leakage becomes more significant as CMOS 
(complementary metal-oxide-semiconductor) processing nodes 
progress from 90 nm through 78, 50, and 45 nm. Manufacturers 
are now discussing building memory chips at the 32-nm node. 
At this point, leakage in traditional designs will become a diffi- 
cult problem and prohibitively expensive to counteract, requir- 
ing new architectures, changes to standard operating specifica- 
tions, and significant process evolutions. 

The problems of scaling and leakage, as well as device size, 
rest fundamentally with the basic transistor-plus-capacitor 




Figure 1 The use of an intrinsic 
bipolar transistor results in a supe 
rior floating-body-memory design. 



building block. Although the transistor ele- 
ment is theoretically infinitely scalable, at 
least for the foreseeable future, the capacitor 
is not. Manufacturers can fabricate capacitors 
as either high stacks or deep trenches. How- 
ever, if the overall bit cell shrinks due to in- 
creased density or a smaller process node, the 
capacitor must become higher or deeper to 
maintain the minimum charge necessary for 
reliable operation. 

The memory industry is fast approach- 
ing the scaling limits for the capacitor ele- 
ment, and it is therefore time for a new ap- 
proach. There appears to be a groundswell 
of opinion in the commercial world and the 
analyst community that floating-body-based 
memories may provide the answer. The floating-body effect 
is the dependence of the body potential of a transistor, using 
the SOI (silicon-on-insulator) technology, on the history of 
its biasing and the carrier-recombination processes. The tran- 
sistor's body forms a capacitor against the insulated substrate. 
The charge accumulates on this capacitor and may cause ad- 
verse effects — for example, opening parasitic transistors in the 
structure and causing off-state leakages, resulting in higher 
current consumption and, in DRAM, the loss of information 
from the memory cells. 

Multiple significant companies, notably Samsung (www. 
samsung.com), Intel, and STMicroelectronics (www.st.com), 
have published work on the subject, and at least three pa- 



s 

1 




D 
1 










BOX 



S 
1 




D 
1 




+ + + + + 










BOX 



Figure 2 The write cycle for 
a one data pattern gener- 
ates current flow through 
the transistor body. 



Figure 3 A read-cycle 
mechanism senses bipolar 
current flow. 



! 




















1 




. 


WRITE 


ONE 


READ 


ONE 












































^ i 










r 


















: WRITE 


ZERO 


READ 


ZERO 






I 








^ 



























Figure 4 Read and write currents are nearly identical. 



SEPTEMBER 17, 2009 | EDN 39 



pers presented at the International Electron Devices Meet- 
ing, which took place in December 2008 in San Francisco, 
addressed floating bodies- Equally significant, at least one ma- 
jor stand-alone-memory maker, Hynix (www-hynixxom), and 
one processor company, AMD (www.amd.com), have signed 



300 



200 



CURRENT 

((jlA/ijlM) 150h 



100 



TEMPERATURE: 85°C 
LENGTH: 290 nm 



GENERATION 2 



50% 



GENERATION 1 



50% 



(a) 



10-5 0.0001 0.001 0.01 0.1 1 

RETENTION TIME (SEC) 



CURRENT. 

(m-A/i^M) 




(b) 



-2 -1.5 -1 -0.5 0.5 

GATE-VOLTAGE READ (V) 



99.99 
99.9 



99 

95 
90 
80 

70 

IMPROVEMENT 50 

{%) 30 
20 
10 
5 

1 

0.1 



LENGTH: 290 nm TEMPERATURE: 85°C 



{GENERATION 1 
25X 



^GENERATION 2 



0.001 



0.01 0.1 
RETENTION TIME (SEC) 



(c) 

Figure 5 A retention-measurement comparison of first-generation 
(MOS-transistor element only) and second-generation (added 
bipolar element) floating-body memories reveals the second 
generation's superiority (a). The bipolar-inclusive floating-body 
approach also delivers a more substantial programming window 
(b), along with a 25-fold improvement in retention time (c). 



licenses with a floating-body-memory company to develop 
products. 

The floating-body effect naturally occurs in transistors fabri- 
cated on SOI substrates, leading to the accumulation of charge 
in the transistor body. Recently introduced device types such 
as FinFETs (fin-shaped field-effect transistors) and surround- 
gate, or pillar, transistors also demonstrate a floating-body 
effect, even when you implement them on traditional bulk- 
CMOS substrates. For these reasons, engineers no longer re- 
gard the floating-body effect as a parasitic nuisance. Many en- 
gineers have tried to manipulate and enhance the body charge 
so that they can use it to reliably store a logical "state" and 
function as a memory element. The objective is a memory bit 
cell that comprises only one transistor, fundamentally the sim- 
plest and most scalable of all semiconductor devices. 

Although a number of companies have investigated float- 
ing-body memories, the conventional approach is unlikely 
to lead to a manufacturable product. A second generation 
of floating-body memory must be able to store a significantly 
larger charge in a smaller transistor. This increased amount of 
charge greatly improves the amount of time the memory can 
retain its state as well as the signal margin between a one state 
and a zero state. Other improvements include faster reads and 
writes and reduced write power consumption. 

PRINCIPLES OF OPERATION 

Early attempts at realizing usable floating-body memories 
employed a MOS transistor to pass current and create charge 
in the body using impact ionization. Although you can dem- 
onstrate memory performance using such a technique, the 
amount of charge you create with this method is insufficient 
to create a robust and manufacturable memory device. A su- 
perior approach is to use the bipolar transistor intrinsic in 




Figure 6 A FinFET design is amenable to floating-body techniques. 



40 EDN I SEPTEMBER 17, 2009 



the SOI'MOS structure to create charge (Figure !)♦ This ap- 
proach allows the creation of a much larger charge and the 
ability to store more charge because of the increased capaci- 
tance of the memory cell. 

If you consider an N-channel device, the N+ source, the 
type body, and the N+ drain form the emitter, base, and col- 
lector, respectively, of anNPN (negative-positive-negative) bi- 
polar transistor. The body of the MOS transistor is the base 
of the bipolar transistor and acts as a storage node. Writing a 
one into a second-generation bipolar floating-body-memory 
cell triggers the intrinsic bipolar transistor, causing current to 
flow throughout the transistor body. This approach differs sig- 
nificantly from the behavior of MOS, in which current flows 
only at the interface. Charge collects at the interface due to the 
slight bias at the gate. The impact- ionization effect that creates 
an excess of majority carriers in the floating body is more ef- 
ficient in this bipolar bit-cell structure, quickly charging the 
body and therefore resulting in rapid writes (Figure 2). 

You can read a floating-body memory using a similar mecha- 
nism, which senses the bipolar current through the transistor 
(Figure 3). Write current is close in value to the read current, 
and the latch-up characteristic of the intrinsic bipolar quality 
causes the behavior of the memory cell to appear nearly digital 
(Figure 4). 

CELL MARGIN AND SCALABILITY 

Bipolar floating-body memories have a significantly higher 
operating margin than traditional floating-body devices, al- 



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1 

\ 
1 
I 








1 

.p _ _ _ 















500 M.V/DIV 
200 NSEC/DIV 



Figure 7 The read and write currents for a FinFET with a length 
of 55 nm and width of 1 1 nm reveal its robust capabilities. 



lowing them to create faster memory bit cells. The operating 
margin is better for two reasons: The storage charge is higher, 
and the difference between the one and the zero states is much 
larger because the bipolar element is a better amplifier than a 
MOS device (Figure 5). A high cell margin eases sensing us- 
ing a simple sensing scheme. The approach also simplifies the 
sense amplifier's design. When you implement floating-body 
memories with conventional planar transistors, the memories' 



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large voltage margin helps to miti- 
gate the negative effects of process 
fluctuations, which become increas- 
ingly significant at smaller process 
geometries- Perhaps just as impor- 
tant, the new bipolar floating-body- 
memory designs are compatible with 
advanced, nonplanar devices, such as 
FinFET, multigate FET, and gate-all- 
around FET Older floating-body de- 
signs work on only thin-film planar 
devices. 

FINFETs AND ARRAYS 

FinFETs, surround-gate transis- 
tors, and other similar 3-0 structures 
should provide the basis for future 
stand-alone memories as the industry 
scales to ever smaller process geom- 
etries- Working at the 54'nm node, 
some DRAM companies are using 
FinFET designs, and most suppliers 
should follow in the next five years. 
Manufacturers can fabricate Fin- 
FETs and pillar transistors on both 
SOI and conventional bulk sub- 
strates. In a FinFET or trigate-based 
Z'RAM (zero'capacitor RAM), the 




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42 EDN I SEPTEMBER 17, 2009 



charge accumulates under the transistor gate, and 
the current flows in the middle of the fin struc- 
ture. The fin stores charge throughout the struc- 
ture, permitting excellent control of the bipolar 
current (Figure 6)- Bipolar floating-body-memo- 
ry implementations using FinFET structures tend 
to exhibit an approximately 30'fold increase in 
margin, leading to a proportional increase in sig- 
nal and device speed- Figure 7 shows the cell cur- 
rent during write and read- Fven an undoped cell 
with an 11 -nm fin shows clean digital behavior and a good 
margin. Floating-body memory continues to scale with tech- 
nology whether you fabricate on planar or 3-D structures- 

For the successful implementation of floating-body memo- 
ries, it is crucial to create memory-bit-cell arrays- Original float- 
ing-body implementations, due to the limited possible margin 
between the one and the zero states, are relatively slow and 
therefore unsuitable for combining into useful arrays- However, 
new bipolar floating-body-memory cells, which produce supe- 
rior signal margins due to the large current gain available from 
the bipolar device, enable more robust arrays (Figure 8). 

The macro for these memories supports a 2-nsec read laten- 
cy and a 4'nsec write latency- It also implements a high-speed 
page mode to read a 140-bit word during every 2-GHz-proces- 
sor clock cycle, using a shared-I/O bus and data latches at the 
interface. This macro supports consecutive memory operations 
at 4 nsec and a burst of four words during page mode- The 4- 
Mbit memory macro comprises 16 subarrays of 256X 1024-'bit, 



\±} Go to www.edn. 
com/ms4332 and click 
on Feedback Loop to 
post a comment on 
this articie. 



[±] For more tectinicai 
articles, go to www. 
edn.com/features. 



or 25 6 -kbit, cells (Figure 8)- The exact imple- 
mentation, 260X1120 bits, includes redundancy 
and FCC (error-correcting code). Subarrays share 
two banks of sense amplifiers at each end of every 
subarray and each bank with adjacent subarrays. 
A combination of column and row operations al- 
lows the access of four 140-bit words by simulta- 
neously activating two subarrays on the right and 
left sides of a shared block of row drivers. 
A subset of combined read- and write-restore op- 
erations constitutes a refresh operation. A control block outside 
the 4'Mbit macro initiates refresh. A low-power refresh mode 
minimizes the voltage swings on inactive bit lines between the 
read- and write-restore operations of the refresh cycle. The 
memory macro has a refresh cycle of 1 msec at 105°C, along 
with three external power supplies of 1.1, 2.6, and 0.5 V. A dedi- 
cated on-chip voltage-generation block attaches to the memory 
macro and supplies the required operational voltages.EDN 



AUTHOR'S BIOGRAPHY 

Serguei Okhonin, PhD, is co-founder and chief sci- 
entist of Innovative Silicon, where he has worked for 
six years. He has a masters degree in physics from 
Novosibirsk State University (Novosibirsk, Russia) 
and a doctorate from the Swiss Federal Institute of 
Technology (Zurich, Switzerland). His personal interests include 
skiing, rock climbing, and mountaineering. You can reach him at 
sokhonin@z-ram . com . 



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READERS SOLVE DESIGN PROBLEMS 



Missing pulse detects position 
or produces a delay 



Michael C Page, Chelmsford, MA 

MH Consider an application that 

KM needs a series of pulses to indi- 
cate position in which the lack of a 
pulse "indexes" the count. To achieve 
that goal, the application uses a rotat- 
ing, 3 6' tooth sprocket with one miss- 
ing tooth. Rotational speed ranges 
from 500 to 7000 rpm. The mecha- 
nism uses an inductive pickup to sense 
the sprocket's teeth. With one of the 
sprocket's 36 teeth missing, the detec- 
tor senses 35 pulses, and then a pulse 
disappears. 

Unfortunately, the mechanism fre- 
quently breaks down or simply breaks 



apart. Because the application uses 
this wheel just to trick the computer 
by simulating an operating engine, 
the application's designers replaced 
the rotating gear with a simulator cir- 
cuit (Figure 1). Given the rotational 
speed and number of teeth, the maxi- 
mum pulse frequency is 1000/60X36, 
or 4200 Hz. The circuit works well 
from single stepping to more than 1 
MHz before starting to break down. 
The maximum frequency depends 
on the logic family and construction 
methods you use. 
Figures 2 and 3 show the outputs 



DIs Inside 

47 Emulate SPI signals 
with a digital-l/O card 

48 Resistive DAC and op amp 
form hybrid divider 

49 Connect two buttons 
with just two wires 

►To see all of EDA/'s Design 
Ideas, visit www.edn.com/design 
ideas. 



running at 100 Hz and 1 MHz, respec- 
tively. At power-up, capacitor re- 
mains the same, which forces RST on 




OSIGNALIN 



CLOCK 



BZD23-4V7 



D1N4148 



CLK 
RST 



IC2 
4024 



Q5 



QO 
Q1 
Q2|-0 
Q3 — O 
Q4 — O 



D2 

D1N4148 



32 



D1N4148 

H— 



Q6 — O 



IC4A 
HC08 



IC1B 
HC14 



R2 
Ik 



D SET Q 
> 4013 



QN 



RST 



IC4B 
HC08 



SENSE 

— o 



'^4C R, ^ 

HC08 3 9 DETECT 



R5 

6.8k 



1 



POWER 
RESET 



1k 



"1 nF 



5V 



Figure 1 combines with three diodes to produce a stream of 36 pulses before resetting. 



SEPTEMBER 17, 2009 | EDN 45 



designideas 



VOLTAGE 3 

(V) 




200 
TIME (mS EC) 



400 
50 mSEC/DIV 



Figure 2 Operating at 100 Hz, the circuit signals include the clock-sine-wave signal (red), the sense-square-wave signal 
(green), and the detect signal (blue), which indicates the missing pulse. 



(v) 




40 

5 jjlSEC/DIV 



Figure 3 The pulse train at a clock frequency of 1 MHz still shows the missing 36th pulse along with the power-reset 
signal (blue). 



IC^^ low. That action puts the D flip- 
flop into a known state. As charges 
through Rp the voltage at the power 
reset falls, letting clock pulses set IC3^'s 
outputs. You must keep the small vah 
ue for the C^R^ combination if you 
use a high input frequency with a low 
count rate. As Figure 3 shows, the de- 
sired count must exceed the duration 
of the power reset. The values in Fig- 
ure 1 provide a time of approximate- 
ly 0.66 X 1 kfl (the value of R^) X 1 nF 
(the value of C^), or 0.66 fxsec, leav- 
ing a minimum count of approximately 
three at 1 MHz. 

For the clock signal, the circuit 
uses a sine-wave signal with an am- 
plitude of 5 to lOV from the system. 
The clock signal goes through R^ to 
and IC^^ to produce a 5V square- 
wave signal. The signal goes to coun- 
ter IC^ and to one input of AND gate 
IC^g. With the other input of IC^g 
coming from IC^^'s QN output, which 
is high from power reset at start-up, 
the input-pulse train passes through 
IC^g, which simulates sprocket teeth 
at the sensor. Resistors R^ and R^ 
halve the clock-signal amplitude just 
to make the graphics clear at "signal | 



in." Diodes D^ D^, and D^ pull up to 
5 V through R^ and form an AND gate 
to select the desired count. Coun- 
ter IC^'s outputs are binary, so, for a 
36-tooth sprocket with one missing 
tooth, outputs QO, Ql, and Q5 cor- 
respond to 1 + 2+32=35. 

You can produce any count as high 
as 128 by adding the appropriate di- 
odes on the Q outputs on IC^. In oth- 
er words, you need to generate one 
missing pulse of 36 to simulate the 
36-tooth sprocket. Thus, you select a 
count of 35; the circuit automatically 
adds a count of one due to the one- 
clock delay of the counter. Because 
you reset IC^ at power-up, all outputs 
are low, keeping the D input of IC^^ 
low, with a count of zero. 



THE CIRCUIT AUTO- 
MATICALLY ADDS A 
COUNT OF ONE DUE 
TO THE ONE-CLOCK 
DELAY OF THE 
COUNTER. 



As clock pulses continue into IC^ 
and when outputs QO, Ql, and Q5 are 
all high, with a count of 35, IC^^'s D 
pin pulls high through R^. On the next 
clock pulse, the Q output of IC^^ goes 
high and the QN output goes low, stop- 
ping the pulses from passing through 
IC^g. This action indicates the missing 
tooth and produces the sense condition 
(the missing pulses in figures 2 and 3 ). 
Meanwhile, the Q output of IC^^'s out- 
put goes high, yielding a single detect 
pulse at IC^^^ through R^ and R^. On 
the next clock pulse, with IC^^'s Q 
output high, IC^ resets logic zero and is 
ready for the next count cycle. R^ and 
R^ halve the clock signal just to make 
the graphics clear at "detect." 

The 4024 is an eight-stage binary- 
ripple counter. You can replace it with 
a 4040 counter to achieve a count of 
2048, and you can cascade counters to 
get longer counts or delays. The 4040's 
pinout differs from that of the 4024, 
but their operation is identical. Some 
systems have an extra tooth instead of 
a missing tooth, and some have mul- 
tiple missing teeth at odd locations 
around the sprocket, all waiting for re- 
placement by this simple circuit.EDN 



46 EDN I SEPTEMBER 17, 2009 



Emulate SPI signals 
with a digital-l/O card 

Andy Street, Autoliv Electronics, Lowell, MA 



A design-verification tester for 
millimeter-wave SOC (system- 
on-chip) devices needed to combine 
switching, electrical measurements, 
temperature measurement, a parallel- 
digital interface, and a serial-digital in- 
terface into one instrument- To mini- 
mize rack space, the circuit uses an Agi- 
lent Technologies (www-agilentxom) 
3 4980 A multifunction mainframe be- 
cause its plug- in cards could support a 
force/sense dc matrix and multiplexed 
temperature measurements- The ad- 
dition of an Agilent 34950A 64'bit 
digital-I/O card formed the basis of a 
system that could provide both an SPI 
(serial-peripheral- interface) bus and a 
simple parallel bus. The 34950A groups 
its I/O lines into two banks of four 8- 
bit channels- It provides 64 kbytes of 
memory per bank for pattern genera- 
tion or signal capture- It also has three 
I/O lines per bank for handshaking. 



YOU CAN STORE 
A MAXIMUM OF 32 
TRACES IN THE PAT- 
TERN RAM PER BANK. 



However, the card's handshake lines 
provide insufficient control for imple- 
menting SPI transactions. To get ade- 
quate control, you can emulate the SPI 
bus using three of the data- I/O lines. 

Motorola (www.motorola.com) 
microcontrollers first used the SPI 
master-slave protocol. Today, it's be- 
come the control interface in a va- 
riety of ICs, including PLLs (phase- 
locked loops) and RF ASICs (refer- 
ences 1 and 2). The SPI bus uses the 
clock, SS (slave-select), MOSI (mas- 
ter-out/slave-in), and MISO (master- 



34950A 
BANK1 



DOO 




CH01 




D07 




DOS 




CH02 




D15 




.„..„. 




OH 03 




D23 




□ 24 




OH 04 




D31 




HO 




HI 




H2 







34950A SYNCHRONOUS BUFFERED OUTPUT 



HO 

START/ 
STOP 



H1 

STROBE 





h 


DATA INVALID^ 


|vALID^ 


1 VALID j^VALID^VALID^VALID^VALID^ 


^VALID^ VALID 



Figure 1 The 34950A synchronous buffered output uses the falling edge, making it unsuited to 
rising-edge SPI implementations. 



in/slave-out) lines. The clock line is a 
signal from the master to the slave. All 
SPI signals are synchronous with this 
clock. The SS line selects the slave for 
communication. The SPI specification 
defines four modes of operation, which 
effectively specify the clock edges for 
toggling and sampling and the clock- 
idle level. The specification makes no 
requirements on voltage levels or data 
rates, and many SPI implementations 
can clock in excess of 10 MHz. Fig^ 
ure 1 shows a block and timing dia- 
gram of the 34950A's Bank 1, config- 
ured for synchronous, buffered output. 
HO through H2 denote the handshake 
lines. The figure also shows an 8-bit 
SPI transaction for reference. 

You cannot use the 3 495 OA's hand- 
shake lines to emulate all modes of the 
SPI bus because the bus latches data 
on the falling edge of the clock, mak- 
ing the bus unsuitable for slaves that 
use the rising edge. Inverting the clock 
polarity is not a solution because you 
may lose the last data bit. Furthermore, 
if you write a number of transactions 
to a slave, you must store each trans- 
action as a separate 
trace memory in the 
34950A. Although 
each bank supports 
64kX8 bits, you can 
store a maximum of 
32 traces in the pat- 
tern RAM per bank, 
thereby limiting the 
number of SPI trans- 
actions. In addition, 
the card lacks a se- 
quencer, so you can- 
not download a num- 
ber of bit patterns and 
then play them in se- 
quence. You must load 
each pattern into the 
I/O card's memory 
and then play each 
pattern under SCPI 
(standard commands 
for programmable in- 
struments) from a 
host computer, slow- 
ing transactions. 
I Instead of using the 
handshake lines, this 
J solution uses three da- 



SEPTEMBER 17, 2009 



EDN 47 



designideas 



ta-I/O lines to emulate the SPI clock, 
SS, and MOSL The software driver for 
the I/O cards then has the responsibil- 
ity of translating the data to be sent 
into an SPI-compatible bit stream. 
Listing 1, which is available at www- 
edn.com/090917dia, contains the algo- 



rithm in pseudocode, which translates 
a hexadecimal string, DH, of characters 
to an SPI signal LD, LSS, and LCLK 
are integers to define which data out- 
puts represent the MOSI, CLK, and SS, 
respectively- 
Assuming a 24'bit register write 



'!Cr Agilent Technologies 



SAT MAR 14 00:14:15 2009 
)!( 8.400y 2.000y/ Stop t |i| 1.50V 























~cs 












1 






i 












CLK 


1 




■ 


i 


■ 


11 


■ 


■ 


1 


1 


lU 


■ 


1 


■ 


1 




i 


■ 


DATA 




n 








U 












1 




1 


































































SPI 




16 C 


LKS 


16 CL 


<5 1 


i CLKS 




24 CL 


KS 




(' 


D 


7X0 





eX9 


> eX 


4 





4X0 


) 4 



[Freq(D, ): 5.0MHz 



1"-^ Print to E 
<None> I 



O Options 



1^ Palette 
<None> 



Figure 2 An MSO screen shows the SPI transactions using the digital-l/O lines. 



with two bits of overhead for the SS 
prefix and postfix, the 64'kbyte mem- 
ory can support more than 1000 SPI 
transactions. The approach has two 
additional advantages: The three lines 
that form the SPI bus are under soft- 
ware control, which provides cabling 
flexibility, and the implementation 
can support multiple slaves through 
the use of additional SS lines- Fig- 
ure 2 shows an MSO (mixed-signal- 
oscilloscope) screen that shows the 
SPI transaction. The SPI clock rate is 
5 MHz, which the 34950A's internal 
lO-MHz clock limits. The different 
payload sizes correspond to writing 
data to 16" and 24'bit registers within 
the slave. EDN 

REFERENCES 

tl Leans, Frederic, "An Introduction 
to I^C and SPI Protocols," IEEE In- 
strumentation & Measurement, 
Volunne 1 2, No. 1 , February 2009, 
pg 8, www.innnn.ieee-inns.org/docs/ 
ColunnnsFebruary2009.pdf. 
a "SPI Block Guide V04.01 ," Freescale 
Semiconductor, July 2004, www. 
freescale.com/files/microcontrollers/ 
doc/ref_manual/S1 2SPIV4.pdf. 



Resistive DAC and op amp 
form hybrid divider 

Marian Stofka, Slovak University of Technology, Bratislava, Slovakia 



A resistive DAC in a resistive- 
feedback loop of an op amp lets 
you create an analog-digital-analog 
divider. The resistance, R^^, between 
the W and A terminals of the Analog 
Devices (www.analog.com) AD5293 
(Figure 1 ) decreases linearly with in- 
creasing the digital-control data, D: 

^WA (D) = \q2^ ^ ^ AB ' 

and the value of the R^g, the resistance 
between the W and B terminals of the 
DAC, rises proportionally to D as 

R^g is a constant value of resistance be- 



tween the ends of the digital potenti- 
ometer. The circuit uses resistance R^^ 
as a feedback resistor, and resistance 
R^g connects between the inverting 
input of the op amp and ground. The 
voltage gain of the noninverting am- 
plifier becomes 

RwA _ 1024 



Ax 



R 



WB 



D 



The output voltage is 



1024 
D 



Both the input voltage and the digital- 
input data can be time variables, and 
the clock frequency for fetching digital- 
input data can be as high as 50 MHz. 



The potentiometer's data sheet pro- 
vides the ground-referred parasitic ca- 
pacitances at the A, B, and W termi- 
nals of the potentiometer. Thorough 
measurement of the capacitances at 
these terminals provides enough data 
to determine capacitances between the 
terminals. An evaluation of the mea- 
sured data shows that the direct capaci- 
tance between the A and W terminals 
at the midscale position of the wiper is 
just 2.4 pF: 

Caw(X = '/2) = 2.4 pF, 

If you assume that the five segments 
of the potentiometer are ordered topo- 
logically into a chain, then the direct 
intercapacitance between the A and B 
ends of potentiometer is 

Cab(X = Vi) - i/2Caw(X = - 1.2 pF. 

The capacitance per segment of the 
five segments of the potentiometer is 



48 EDN I SEPTEMBER 17, 2009 



Csegm=5Cab(X = '/2) = 6pF, 

where X=K2 denotes the midscale of 
the resistive DAC. 

The five-step distributed RC line of 
the potentiometer has a time constant 
of 



'^SEGM 



R 



AB 



5 

Cab '■ 



xC 



SEGM - ^AB X 



: 24 NSEC, 



where R^g is 20 kll. The ground-re- 
ferred wiper capacitance, C^, of 40 pF 
is much higher than the intercapaci- 
tances and creates a time constant: 

I^W '^RWBXC^^• 

The feedback network of the amplifier 
is frequency-compensated for Tg^^j^^ 
Thus, you can calculate the value 
of R^g as 600n, meaning that the volt- 
age gain of the amplifier, is 323. 
For gains higher than 323, the effect of 
becomes negligible, and you need 
not bother about amplifier stability- To 
suppress the derivative behavior of the 
amplifier for gain values of two to 323, 
you can add a 40-pF compensating ca- 
pacitor in parallel to feed back part of 
the potentiometer. The amplifier thus 
has an integrating character for all 
gains down to a value of two. 

You fetch the divisor, Y, which is a 
digital-data word, D, through a stan- 



AD5293 
5 OR 3.3V 
? V 

V LOGIC 



AD8677 



15V 
Q 



DIGITAL INPUT 

o— 



I SPI 



Lo- 



EXT_CAP 



NCO- 



1 |xF=^100 nF=;= 



o^^o^ 

^SDIN V, 
11 ■ 



RESET 



pSYNC 
;)SDO 



=p47 pF 



14 a 

— H^RDY 



I 
I 
I 

W'4 



|~ 1 V GND Vgg 

-'-inn^c-'- ' ■Q--Q 



I 
I 

B I 



ANALOG INPUT 
O 



i 



-L Or - 




-OOUT 



Figure 1 The resistive DAC-potentiometer forming the feedback for an op amp 
controls the op amp's gain as inversely proportional to the digital-input-data 
word. The circuit thus becomes a two-quadrant divider. 



dard SPI (serial-peripheral interface). 
After power-on, you must initially neu- 
tralize the write-in protection of the 
resistive DAC. You have to first pro- 
gram the control bit to the value of 
one, whereas it is zero by default. You 
achieve this task by clocking in the 
word containing C^, C^, and C^, 



which equals 0110, and you put the 
desired and values at data po- 
sitions and D^. After performing 
these steps, you change the wiper posi- 
tion in which the control bit is 0^,0^, 
C^, and Cq, which equals 0001, and the 
data bits, to D^, represent the gain 
as 1024/D.EDN 



Connect two buttons 
with just two wires 

Fikret Yilmaz, Mobil Elektronik, Istanbul, Turkey 

HH Sometimes, you need to read the status of 
pushbuttons that are as much as 5 m away 
from your electronic circuit. That task is easy if 
you have just one button. You simply design a 
constant'Current source, connect the current line 
from your button, and measure the current in the 
line. If you press the button, current flows through 
it. Otherwise, current does not flow. 

Problems occur, however, when you need to 
read two or more buttons. Several approaches 
to this problem are available. For example, you 
could use an RS'485 interface with two wires 
for communication and two for power. Alterna- 
tively, you could use a single-wire connection 




1k 



R2 
1k 



T ^ 1 N4004 



D2 
1 N4004 



IC1 
4N35 



IC2 
4N35 



10k >10k 



-O Dqutsi 

~0 '-*0UTS2 



Figure 1 You can connect two buttons using diodes. 



SEPTEMBER 17, 2009 | EDN 



49 



designideas 




ODq, 



Figure 2 By adding a third wire, you can connect four pushbutton switches. 



with one wire for communication and 
two for power. Another option is to 
use separate wires for each button. 
In that case, you would use one more 
wire than there are buttons. Finally, 
you could use a POE (power-over- 
Ethernet) approach, employing four 
wires for communication and power. 
All of these approaches require a but- 
ton reader or a controller, which you 
must program, adding complexity and 
cost. 

The circuit in Figure 1 shows you 
how to connect two buttons using di- 
odes. Because the diodes steer the cur- 
rent, the circuit needs just two wires. 
On a positive cycle from the trans- 
former secondary and with switch 
closed, current flows through IC^ R^, 
and D^. Thus, output Dqutsz P^^^^ 
Conversely, if closes on a negative 
cycle, then current flows through 
to and IC^, which pulls Dqutsi 
The circuit in Figure 2 extends the 
concept to four pushbutton switches 
by adding a third wire.EDN 



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Impedance Levels 10 ohms to 
250k ohms, Power Level to 3 
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manufactured and tested to 
MIL-PRF-27. QPL units available. 
Special order class V (155°C). 

POWER & EMI INDUCTORS 

Ultra- Miniature inductors are 
ideal for Noise, Spike and 
Power Filtering Applications 
in Power Supplies, DC-DC 
Converters and Switching 
Regulators. All units 
manufactured and tested 
to MIL-PRF-27. QPL units 
available. Special order 
class V(155°C). 

PULSE TRANSFORMERS 

10 Nanoseconds to 100 
Microseconds. ET Rating to 
150 Volt-Microsecond. All 
units manufactured and tested to 
MIL-PRF-21038. QPL units 
available. Special order class V 
(155°C). 

400HZ TRANSFORMERS 

115 volt or 26 volt primary. 
Split secondary voltages, 5 volt 
to 310 volts, 150VA, Manufactured 
and test to MIL-PRF-27. Special 
order class V (155°C) 





These pulse transformers manufactured to 
MIL-STD-1553. COMMAND/ RESPONSE 
MULTI-PLEX DATA BUS requirements. 
They also are manufactured to MIL-PRF- 
21038/27 specifications and are designed 
to meet MAC AIR SPECIFICATIONS 
A3818, A5690, A5232, and A4905. 
All of these trasformers exhibit superior 
electrical performance. Common mode 
rejection ratio is greater than 45dB at 1 
MHz. Input impedance is greater than 
3000 ohms over the band from 75 kHz to 
1MHz at IV rms. This series possesses 
exceptional waveform integrity: Rise time 
and fall time is less than 100 nanosec- 
onds. Overshoot and ringing is less than 
±1V peak. Droop is less than 20%. 



Surface Mount 



M electrical equivalents 
of QPL-IVIIL-PRF-21 038/27 



DC-DC CONVERTER TRANSFORMERS 
POWER INDUCTORS 
COMMON MODE EMI INDUCTORS 

These units have gull wing construc- 
tion which is compatible with tube fed 
automatic placement equipment or 
pick and place manufacturing tech- 
niques. Transformers can be used for 
self-saturating or linear switching appli- 
cations. The Inductors are ideal for 
noise, spike and power filtering appli- 
cations in Power Supplies, DC-DC 
Converters and Switching Regulators. 




J LEAD 
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for sample quantities 



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PICO Electronics^ inc. 

I www.picoelectronics.com 



Call Toll Free... 800-431-1064 • FAX: 914-738-8225 
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Call toll Free 1-800-431-1064 
I or send direct for FREE 178 pg. 
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QPL Units 

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MIL-PRF-27/97 

MIL-PRF-27/103 

MIL-PRF-27/277 

MIL-PRF-27/290 

MIL-PRF-27/357 

MIL-PRF-27/358 

MIL-PRF-27/359 

MIL-PRF-27/172 



productroundup 



POWER SOURCES 

Offline BCM arrays 
include a vertically 
mounted heat sink 

Claiming 95 % efficiency, the 65 OW, 
vertically mounted VI Brick BCM 
arrays provide isolation and conver- 
sion from 380V to 12 or 48V Aiming at 
front-end applications, the devices have 
352 and 384V nominal voltages and 11, 
12, 44, and 48V'dc output voltages- The 
modules yield 290W/in.^ power density 
and fast transient response- The BCM 
buses offline power to the motherboard 
and converts it to 12 or 48V, minimiz- 
ing distribution losses and reducing con- 
version steps and overall cost- Devices 
in the VI Brick BCM -array family cost 
$109 each. 

Vicor Corp, www.vicorpower.com 



Triple-output dc/dc module includes 
switch-mode and linear regulators 

The LTM4615 triple-output dc/dc fJuModule regulator 
system contains two 4A switch-mode regulators and 
a 1.5 A low-dropout linear regulator. The switching regula- 
tors have an adjustable 0.8 to 5V output voltage and regu- 
late three outputs at 1.5, 4, and 4A or two outputs at 1.5 and 
8A while operating from one, two, or three input supplies. 
The regulator system features short-circuit and overtemper- 
ature protection and provides a ±2% total dc-output error 
for switch-mode regulators and ±1% error for low-dropout 
linear regulators. Claiming 90% efficiency, the device oper- 
ates over a —40 to +125°C temperature range. Available in 
a 15 X 15 X2.8-mm LGA package, the LTM4615 triple-output 
regulator costs $17.20 (1000). 
Linear Technology Corp, www.linear.com 

Switching regulator provides 
alternative to linear regulators 

The 96%-efficient, 0.5A V78XX-500-SMT dc-switch- 
ing-regulator series provides a high-performance alter- 
native to linear regulators. Features include a 4-5 to 28V-dc 
input range; 3.3, 5, 12, and 15V-dc regulated output voltage; 
500-mA output current; —40 to +75°C temperature range at 
100% load; and 60% load derating at 85 °C. The converter pro- 
vides short-circuit protection, thermal shutdown, 10-mV p-p 




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SEPTEMBER 17, 2009 | EDN 53 



productroundup 

POWER SOURCES 



typical ripple and noise, and a 2 million- 
hour MTBE Measuring 15.24X8.5x7 
mm, devices in the surface-mount 
V78XX-500-SMT dc-switching-regula- 
tor series cost $8-24 each. 
V- Infinity, www.v-infinity.com 

1 0A synchronous 
buck converter has 
integrated FETs 

□ Combining a lOA synchronous 
buck converter with integrat- 
ed FETs, the 1-MHz TPS51315 dc/dc 
switcher uses a D-Cap Mode control 
scheme, allowing fast transient response 
and reducing the required number of ex- 
ternal output capacitors by 32%. The 
converter meets Energy Star/90 Plus 



guidelines using an auto-skip mode and 
an Eco-mode light-load-control scheme, 
achieving an improved efficiency across 
the entire load range. Additional fea- 
tures include a 3 to 14V input voltage, 
and a 0.75 to 5.5V output- voltage range 
enables flexible design in 3.3, 5, and 
12V power systems. Available in a 5 X 7- 
mm QEN package, the TPS51315 dc/dc 
switcher costs $3.80 (1000). 
Texas Instruments, www.ti.conn 

240W one-eighth-brick 
module provides 
digital interface 

□ Allowing monitoring using a PM- 
Bus interface, the BMT454 eighth- 
brick family delivers 240 W and a 36 to 




75V input-voltage range. The devices are 
95% efficient at 53V input and 12V out- 
put at 20 A full loads. They target infor- 
mation- and communication- technology 
applications requiring 48V power. These 
applications include radio base stations, 
servers, and routers. The devices also suit 
use as intermediate-bus converters with 
regulators or as dc/dc modules powering 
hard drives and fans. The modules feature 
a 1 500 V-dc input- to-output isolation fig- 




MPD offers a wide diversity of popular sizes, styles, terminations, 
options and accessories. The fact is, our website features the 
industry's largest array of battery holders, including extensive 
medical and military types. 

Key Features • Engineered designs assure optimum battery 
tightness • Low contact resistance • Accepts NiCd, Carbon 
Zinc, & Alkaline batteries • Molded of flammability rated high 
impact resistant plastic • Broad temperature service range 
• Molded-in contacts for PC board wave soldering • 6" UL-CSA 
rated wire • Male/Female 9V snap fastener terminals 

For details: write, call, fax or visit our website 

: MPD 

■ MEMORY PROTECTION DEVICES, INC. 

200 BROAD HOLLOW RD., FARMINGDALE, NY 11735 
TEL (631) 249-0001 / FAX (631) 249-0002 

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54 EDN I SEPTEMBER 17, 2009 




This advertising is for new 
and current products. 



ure, allow output- voltage adjustments 
between 8.1 and 13.2V with a ±2% 
output tolerance, and have 18W/cm^ 
power density. Available in 9V/20A, 
12V/20A, and 12V/2A models with- 
out a digital interface, the BMR454 
costs $37 (10,000). 
Ericsson Power Modules, 
www.ericsson.com 

1 5W converters come in 
open-frame and shield- 
ed-metal-case options 

The fully isolated, 15W PXA 
open-frame and PXB shielded- 
metal-case dc/dc converters provide 
88% efficiency and have a —40 to 
+ 85°C operating temperature. The 



PXA series has single-output models 
with 24V nominal inputs and 48V 
dc in 2-to-l and wide 4'to-l versions. 
The PXB series comes in single- and 
dual-output models with 12V-dc nom- 
inal inputs in a 2-to-l version and 24 
and 48V-dc inputs in 2-to-l and wide 
4'to-l versions. Single-output voltages 
include 3.3, 5, 12, and 15V dc, and the 
PXB series offers dual-output models 
providing ±5, ±12, and ± 15V-dc out- 
puts. Standard models include remote 
on/off and output adjustment; single- 
output models and devices with over- 
voltage and overcurrent/short-circuit 
protection are also available. Measur- 
ing 1 X 1 in. each, devices in the PXA 
and PXB series cost $28 (500). 
TDK-Lambda Corp, 
www.us.tdk-lambda.com 



INTEGRATED CIRCUITS 

Op amp uses EMI- 
suppression filters 

□ Consuming 560 nW, the LPV52 1 
op amp suits wireless remote 
sensors, power-line monitoring, and 
micropower oxygen and gas sensors. 
Features include a 1.6 to 5.5V voltage 
range with a 0.4- fx A maximum supply 
current, a maximum 1-mV input offset 
voltage, and a 3.5-|jlV/°C input offset- 
voltage drift. The op amp comes with 
EMI-suppression filters, reducing RFI 
from external sources. Available in a 
five-pin SC-70 package, the LPV521 
op amp costs 65 cents (1000). 
National Semiconductor, 
www.national.com 



Voltage-reference ICs 
come in multiple 
accuracy grades 

□ The CAT8900 voltage refer- 
ence aims at handheld medi- 
cal devices, high-resolution ADCs 
and DACs, and precision-regula- 
tor systems. The device offers 1.024, 
1.2, 1.25, 1.8, 1.048, 1.5, 2.6, 3, and 
3.3V voltage-reference options; cus- 
tom voltages are available on request. 
The device provides 0.02% initial ac- 
curacy at ±0.5 mV, a 20-ppm/°C tem- 



perature coefficient, and an 800-nA 
maximum supply current. The voltage 
reference sources or sinks as much as 
10 mA of load current with 50 mV of 
dropout; the devices require no out- 
put-bypass capacitor for most applica- 
tions. The devices have an eight- to 
12-week leadtime and come in three- 
lead SOT-23 packages. The CAT8900 
voltage reference comes in ±5-, ±2.5-, 




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±1-, and ±0.5-mV initial accuracy 
grades and costs 60 cents, 92 cents, 
$1.55, and $2.44 (1000), respectively. 
On Semiconductor, 
www.onsemi.com 



ADVERTISER INDEX 



Company 




Company 


Page 1 


Achronix Semiconductor 


C-3 


Mentor Graphics 


12 J 


Agilent Technologies 


C-2 


Micro Crystal 


35 1 




21,29 


Mill Max Manufacturing Corp 


9 1 


1 Analog Devices Inc 


17 


Mouser Electronics 


4 1 


austriamicrosystems AG 


50 


Notional Instruments 


2 1 


Bergquist Co 


24 


National Semiconductor 


44 1 


Coilcraft 


7 


Pico Electronics 


23 1 


Digi-Key Corp 


1 




34, 52I 


Express PCB 


54 


Renesos Technology Corp 




International Rectifier Corp 


5 


Samsung Electro-Mechanics 




Keil Software 


33 


Silicon Lobs 




Linear Technology Corp 


C^ 


Todiron Electronic Industries 


8 1 


LPKF Loser & Electronics 


36 


Trilogy Design 


55 1 


LS Research 


53 


Vicor 


41,431 


Magna-Power Electronics Inc 


28 


Xilinx Inc 


51 1 


MathWorks Inc 


19 


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


Maxim Integrated Products 


10,11 


Memory Protection Devices 


54 









SEPTEMBER 17, 2009 | EDN 55 



TALES FROM THE CUBE 



JACOB BRODSKY • WASHINGTON SUBURBAN SANITARY COMMISSION 



Lightning strikes sewage setup 




In early 1988, we had finished the start-up of a brand-new 
SCADA (supervisory-controhand-data-acquisition) system 
at the water-and-sewer utility where I work. It was sum- 
mer, and we were busy repairing the damage from frequent 
thunderstorms, A co-worker, George, was supposed to pro- 
vide postmortem repair and analysis of the RTU (remote- 
telemetry-unit) processor boards. Most of the 1 -foot-square, 
multilayer processor boards had obvious scorch marks from 

lightning damage. We'd typically see a just repaired this one over here," he 



burned switching-power- supply mod- 
ule, PCB (printed'Circuit'board) burns 
at the phone-line interface, or burns on 
an analog' input card- We'd then take 
a closer look at each of the sites where 
these boards originated and try to im- 
prove the situation through more care- 
ful grounding, better surge suppressors, 
or another means. 

One morning, I noticed that George 
had set aside a few RTU processor cards. 
When I asked about it, he told me that 
they were malfunctioning but that he'd 
been having a hard time with figuring 
out what was wrong, so he'd set them 
aside to work on when he had time. "I 



said. "It was a single blown 74HC00 
gate; the other three in the same chip 
were just fine." I asked where another 
similar card had come from. "You're go- 
ing to love this," he said, "All of these 
problem cards, except for one, are from 
the Cabin John interceptor." I walked 
away, befuddled. 

I made a detour in my travels later 
that week to take a look at the Cabin 
John interceptor, a waste-water meter- 
ing vault. Resembling a small brick out- 
house, it sat at the bottom of a valley in 
the woods. The RTU processor's only 
purpose at that site was to gather flow 
data from a large venturi tube, which 



measures fluid pressures and velocities, 
in the vault below the building. This 
flow meter was important because it 
was a change-of'Custody billing meter. 
The saying "sewage flows downhill" 
isn't just an expression; it's also a fact of 
life. The sewage in this area was headed 
for a plant in another jurisdiction. 

The only two points of data coming 
from the site were flow and a loss-of-ac- 
power alarm. The RTU processor was 
in a robust fiberglass box. At the back 
of the box, all the PCBs mounted flat 
on a grounded steel plate with 14 -in. 
standoffs and isolated screws. The setup 
also included an I/O card, the proces- 
sor card, a battery-charge controller 
board, some terminal strips, an ac cir- 
cuit breaker, and the 928/95 Z-MHz te- 
lemetry radio. A lOO-foot tower stood 
next to the building to get the antenna 
above the tree line. 

The installation gathered the flow 
data from a 4- to ZO-mA-current-loop 
pressure transmitter next to the cabinet. 
The pressure- transducer electronics, 
batteries, and PCBs were isolated from 
ground. Sure that George must have 
been wrong about something, I went 
back to his shop. He had set aside a few 
more cards, all with different failures. 

The next morning, as I stumbled 
into the shower, I had a flash of insight: 
Maybe lightning was striking the tower 
and causing the ground potential of 
the backplate to rise. The board was 
quite close to the backplate. Perhaps a 
static charge was forming between the 
grounded metal backplate and the iso- 
lated RTU processor. A small arc could 
be destroying the weakest chips. 

I got to work early and snagged some 
I'in.'long nylon screws and standoffs 
from the maintenance shop. Replacing 
the ^'in. screws with the longer ones 
protected the isolated board from ran- 
dom chip damage, fixing the problem, 
and we haven't seen failures of this sort 
since.EDN 

Jacob Brodsky is a controh system en- 
gineer with the Washington Suhurhan 
Sanitary Commission (Laurel, MDj, 



El www.edn.com/tales 



56 EDN I SEPTEMBER 17, 2009 




Breaking Through Performance Barriers 



Speedster is the 
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Breaking through the speed barriers of traditional FPGAs, 
fully reprogrammable Speedster devices from Achronix 
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Speedster's unique 40 lanes of 10.3 Gbps embedded SerDes 
and four independent 1066 Mbps DDR2/DDR3 controllers 
enable extremely high I/O throughput to match the device's 
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opens up new worlds of application design previously 
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Familiar Silicon. Familiar Tools. Fast Time-to-IVIarket. 

Speedster uses familiar LUT-based fabric and standard 
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High-Performance Applications 

• Networking 

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See what's possible: 
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©2008 Achronix Semiconductor Corporation. All rights reserved. 



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