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ARE WE THERE YET?Page 30

SORTING OUT

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Teardown:The power

inverterfromsunlight topower grid

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VOICE OF THE ENGINEER

EMI problems?Just the facts,please Pg 18

EDN.comment Pg 10

Pulse-widthmodulation Pg 20

Design IdeasPg 45

Copy that Pg 54

Issue 4/2012

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Mouser and Mouser Electronics are registered trademarks of Mouser Electronics, Inc. *2011 e-Legacy Award for Contribution to Sustainability.

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EDN (ISSN# 0012-7515) is published semimonthly by UBM Electronics, 600 Community Drive, Manhasset, NY 11030-3825. Periodicals

postage paid at Manhasset, NY, and at additional mailing office s. SUBSCRIPTIONSFree to qualified subscribers as defined on the sub scrip-

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Rich Hill. ON L4B 4R6. Copyright 2012 by UBM. All rights reserved. Reproduction in whole or part without written permission is prohibited.

Volume 57, Number 4 (Printed in USA).

contents

DEPARTMENTS & CO LUMNS

2.16.12

51

pulse

12Car-door-controller ICintegrates window control14 Meter reference design enables

secure purchase of energycredits

14MEMS-optical-IC platformallows the creation of customstructures

16 Wideband I/Q demodulatorimproves receiver performance

16Coventor automatesMEMS design

16 Automotive varistors havelow leakage current

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[www.edn.com]

54

9 EDN online: Join the conversation; Content; Engineering Community

10 EDN.comment: Qualcomm offers $10 million for a real-life tricorder,

not a moment too soon

18 Bakers Best: EMI problems? Just the facts, please

20 Mechatronics in Design: Pulse-width modulation

51 Product Roundup:Switches and Relays

54 Tales from the Cube: Copy that

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mouser.comSemiconductors and electroniccomponents for design engineers.

Mouser and Mouser Electronics are registered trademarks of Mouser Electronics, Inc.

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online

ENGINEERING COMMUNITYOpportunities to get involved and show your smarts

JOIN THE CONVERSATIONComments, thoughts, and opinions shared by EDNs community

CONTENTCant-miss content on EDN.com

THRUN SAYS GOODBYE

TO STANFORD, HELLO TO A

WORLD UNIVERSITY

Higher education is way past due fora change. Sebastian Thrun, Googlefellow and research professor atStanford University, is taking steps tomake that change. He has decidedto quit Stanford, giving up his tenure,to start a new online university.Thrun wants to empower an entireworld of people who understandtechnology and will tackle the big,hairy problems the world faces. Andthats a big, hairy, audacious goal.

http://bit.ly/yiRrcH

In response to Noise wars:Projected capacitance strikesback against internal noise, anarticle by John Carey of CypressSemiconductor, http://bit.ly/

yyXkWK, Bill Bohan comments:

I believe you have solved the issue.

Right off the bat, you cited inferiorpower-supply designs as the source ofnoise. Just dont buy them! Ive beendesigning dc/dc and universals for

years. You can get good, clean power supplies or design your own! Thosenoise levels are so outrageous, why do you accept that [situation]? It isgood that you cover the downstream effects as a result of inferior powermanagement. Take the battle back upstream; put an American to workdesigning one.

In response to The red-cableblues, a Tales from the Cubecolumn by Larry Goga, http://bit.ly/

A7qAhq, Sujit Liddle comments:

LOL. This brings back memories.I once traced poor video quality in

a video-capture system to the newbatch of S-video cables that lookedgreat but had been made usingunshielded four-core wire instead ofthe expected dual coaxial cables.

EDNinvites all of its readers to constructively and creatively comment

on our content. Youll find the opportunity to do so at the bottom of each

article and blog post. To review current comment threads on EDN.com,

visit http://bit.ly/EDN_Talkback.

FEBRUARY 16, 2012 | EDN 9[www.edn.com]

CALIFORNIA PASSES NEW

REGULATIONS FOR BATTERY-

CHARGING SYSTEMSThe California Energy Commissionreleased a new standard for personal-electronics equipment soldin California that targetsenergy efficiency in battery-charging systems. Werethese regulations necessary,and how do they play withDepartment of Energy regulations,which would pre-empt them?

http://bit.ly/xxAYvj

The Oscars celebrate Hollywood. The Super Bowl celebrates athletics. We celebrate engineering. New thisyear, EE TimesACE (Annual Creativity in Electronics) Awards and EDNs Innovation Awards are joiningforces to honor the people and companiesthe creatorsbehind the technologies and products that arechanging the world of electronics and shaping the way we work, live, and play. Join us and network withyour peers at the 2012 UBM Electronics ACE Awards taking place on March 27, 2012, during Design West,as we celebrate the industrys best of the best. Find out more at http://ubm-ace.com.

DANIELVASCONCELLOS

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E D N . C O M M E N T

10 EDN | FEBRUARY 16, 2012 [www.edn.com]

Youve probably heard of hospitalsthat remarkably improved their suc-cess rates by implementing checklists

for procedures. Atul Gawande, MD,author of The Checklist Manifesto and acontributor to The New Yorker, initiatedand champions the concept of check-lists in hospitals. Gawande begins bymaking a distinction between errors ofignorance (mistakes we make becausewe dont know enough) and errors ofineptitude (mistakes we made becausewe dont make proper use of what weknow), writes Malcolm Gladwell in areview of the book. Failure in the mod-

ern world, he writes, is really about thesecond of these errors, and he walks usthrough a series of examples from medi-cine showing how the routine tasks ofsurgeons have now become so incrediblycomplicated that mistakes ... are virtuallyinevitable. Its just too easy for an oth-erwise-competent doctor to miss a step,or forget to ask a key question, or, in thestress and pressure of the moment, failto plan properly for every eventuality.

Computers competently keep trackof what we know and follow checklists.

Combine these characteristics with

some clever sensor systems, and you justmight come up with a tricorderandnot a moment too soon.

Qualcomm is offering a $10 millionprize, the Tricorder X-Prize, for the firstnoninvasive health-diagnostic tool. Forthose of you who are rusty on your StarTrekplot lines, the tricorder is a pieceof equipment that takes a quick scan ofan injured or sick patient and instantlyboth diagnoses the problem and pre-scribes a treatment.

The winning team will be the onewith the technology that most accu-rately diagnoses a set of diseases without

using input from a doctor or a nurse andthat provides the best user experiencethus most likely eliminating the use ofinvasive probes that play such promi-nent roles in alien-abduction stories. Itwill capture metrics for patient health.These metrics could include blood pres-sure, respiratory rate, and temperature.The device can, however, use sensors orelectrodes that attach to the skin.

Looking toward the future, Qual-comm sees this tool collecting largevolumes of data from ongoing measure-

ment of health states through a com-

bination of wireless sensors; imagingtechnologies; and portable, noninvasivelaboratory replacements. Noninvasivemeans that the treatment would requireneither biopsies nor blood tests. Theonly limitation is that the weight ofboth the tool and any components itrequires must total 5 lbs or less.

Qualcomm implies that the benefits

of having a tricorder-like device are tobypass the personnel shortage and thussave time and money. I think theresanother benefit that could be just asgreat: The diagnosis and ensuing carefrom a computer could be much betterthan that from a human. Paraphrasingfrom the Qualcomm site, a tricorder-like device will go a long way towardtransforming health care by turning theart of medicine into a science.

Bones, were ready.EDN

Contact me at [email protected].

Qualcomm offers $10 millionfor a real-life tricorder, not amoment too soon

D

uring the past month, I have visited three hospitals forvarious family members, and, in each case, human error

caused some severe mistakes: misread charts, incorrect drugprescriptions, and incorrect surgical procedures. Yet, thesemedical professionals are perfectly competent individuals.They are humans dealing with an extremely complicated

system. When aspirin and morphine were among the only available drugsand patients were receiving treatment for one of the few diseases thatmedical science was able to treat, mere humans could track complex druginteractions, surgical procedures, and the likenowadays, not so much.

The routine tasksof surgeons havenow become socomplicated that

mistakes are virtu-ally inevitable.

BY MARGERY CONNER, TECHNICAL EDITOR

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BRAND DIRECTOR, EDN

Jim Dempsey1-440-333-3040;

[email protected]

DIRECTOR OF CONTENT,

EDNAND DESIGNLINES

Patrick Mannion1-631-543-0445;

[email protected]

EXECUTIVE EDITOR,

EDNAND DESIGNLINES

Rich PellConsumer

1-516-474-9568;[email protected]

MANAGING EDITOR

Amy NorcrossContributed technical articles


MANAGING EDITOR, ONLINE

Suzanne DeffreeElectronic Business, Distribution


TECHNICAL EDITOR

Margery ConnerDesign Ideas, Power Sources,

Components, Green Engineering1-805-461-8242;

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SENIOR ASSOCIATE EDITOR

Frances T Granville1-781-869-7969;

[email protected]

ASSOCIATE EDITOR

Jessica MacNeil1-781-869-7983;

[email protected]

COLUMNISTS

Howard Johnson, PhD,Signal Consulting

Bonnie Baker,Texas InstrumentsPallab Chatterjee,

SiliconMapKevin C Craig, PhD,

Marquette University

CONTRIBUTING TECHNICAL EDITORS

Dan Strassberg,[email protected]

Stephen Taranovich,[email protected]

Brian Bailey,[email protected]

Robert Cravotta,[email protected]

VICE PRESIDENT/DESIGN DIRECTOR

Gene Fedele

CREATIVE DIRECTOR

David Nicastro

ART DIRECTOR

Giulia Fini-Gulotta

PRODUCTION

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[email protected]

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[email protected] Wu

Associate [email protected]

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[email protected] Lu, Executive [email protected]

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MANAGEMENT TEAM

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[www.edn.com]

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STMicroelectronics new L99DZ80 car-door-controller IC removes the need

for mechanical relays in car-window

control, reducing component costs and elimi-

nating the need for expensive EMC counter-

measures. The door-zone driver supports

adjustable window speeds related to the

position of the window, soft start and shut-

down, and reduced noise levels, thanks to the

removal of the relay. The device embeds an

SPI-programmable slew-rate-control capabil-

ity that can drive four external MOSFETs in a

half-bridge configuration dedicated to PWM-

driven electric-window applications.Other features include six bridges, includ-

ing one full bridge for a 6A load with an on-

resistance of 150 m, two half-bridges for

a 3A load with an on-resistance of 300 m,two half-bridges for a 0.5A load with an on-

resistance of 1600 m, and one high-side

driver for a 5A load. The device supports

double door-lock control; mirror-folding and

mirror-axis control; and a high-side driver

for a mirror defroster, bulbs, and LEDs. The

device also integrates a control block with

an external MOS transistor for charging and

discharging of electrochromic, dimmable

mirror glasses. Standby current consump-

tion is less than 6 A, and junction tempera-

ture is 85C or less. The device comes in a

TQFP-64 package in tray and tape-and-reeloptions. Price is $2.50 (25,000).

by Fran Granville

STMicroelectronics , www.st.com.

Car-door-controller IC integrateswindow control

TALKBACK

1

7

4

1

The lesson whenit comes to propos-

als to introducenew tech thatundermines exist-ing product lines:It's better to shootyourself in the footthan have a com-petitor shoot youin the head.EDNreader Dirk Bruere, in EDNs

Talkback section, at http://bit.ly/

yvokLS. Add your comments.

STMicros L99DZ80 car-

door-controller IC has six

bridges for mirror-fold and

mirror-axis control and a

high-side driver for a mirror

defroster, bulbs, and LEDs.

pulseINNOVATIONS & INNOVATORS

EDITED BY FRAN GRANVILLE


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>>Find out how LabVIEW can make you better at ni.com/labview/better 800 453 6202

10 National Instruments. A ll rights reserved. LabVIEW, National Instruments, NI, and ni.com are trademarks of National Instruments.

r product and company names listed are trademarks or trade names of their respective companies. 2807

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Smart meters promise to

eliminate energy inef-ficiencies by allowing

users to remotely monitor, con-

trol, and optimize their energy

usage. Unfortunately, those

benefits come at the expense of

reduced security, leaving doors

open for hackers to snoop,

commit fraud, and criminally

tamper with safety systems. To

remedy these concerns, Fre-

escale Semiconductor has part-

nered with Inside Secure on a

prepaid smart-meter referencedesign that cures these security

ills with proven NFC technology.

At the recent 28C3 (28th

Chaos Communication Con-

gress), which took place in

December in Berlin, hack-

ers demonstrated how smart

meters allow unauthorized intru-

sions that can remotely control

meters, the devices they control,

and even the safety systems

that households depend on toprevent burglaries. Fortunately,

with proper designsand a few

extra security protocolssmart-

meter designers can avoid these

problems. The smart-meter ref-

erence design enables secure

mechanical meters that are vir-

tually tamperproof, says Olivier

Debelleix, Inside Secures busi-

ness-line manager for embed-

ded security.

Freescales secure-smart-

meter design enlists banking-industry-proven NFC protocols,

using a smartphone or a smart-

card with NFC to load prepaid

credits. Key to the secure smart

meter is Inside Secures VaultIC

chip, which uses the compa-

nys MicroRead NFC technol-

ogy. The technology allows

users to purchase energy cred-

its with their smartphones or

smartcards and then securely

load them into the smart meterusing the same technology that

allows users to make banking-

card purchases using NFC.

The secure-smart-meter ref-

erence design uses the crypto-

graphic hardware on Freescales

Kinetis MK30 microcontroller,

employing the ARM Cortex-M4

core, which operates at speeds

as high as 100 MHz with 1.25

DMIPS/MHz. The device uses

mutual authentication, verifi-

cation, security certificates,encryption/decryption, and on-

chip management of secure

cryptographic keys. The secure

smart meter uses the MK30s

built-in segment-LCD controller

to drive the display of metering

values at the push of a button

and runs on Freescales MQX

real-time operating system. The

system meets the requirements

of Federal Information Process-ing Standard FIPS140-2 Level

3, a US-government computer-

security standard to accredit

cryptographic systems.

by R Colin Johnson

Freescale

Semiconductor,

www.freescale.com.

Inside Secure,

www.insidesecure.com.

DILBERT By Scott Adams

Meter reference design enablessecure purchase of energy credits

A smart-meter reference de-

sign combines Inside Secures

contactless-NFC-chip

technology with Freescales

secure-microcontroller tech-

nology to enable virtually tam-

perproof secure mechanical

meters (courtesy Freescale).


pulse

Si-Ware Systems Ltd, a

fabless chip and design-

service company, has

announced its SiMOST (sil-

icon-integrated-micro-opti-

cal-system) platform for the

creation of single-chip opti-

cal systems. SiMOST allows

the integration of optical-

MEMS elements to create

custom structures. Manu-

facturers can pattern and etch

multiple optical-MEMS struc-

tures on SOI (silicon-on-insu-

lator) wafers using DRIE (deep

reactive ion etching). The manu-

facturer then packages the

structures at the wafer level and

dices them to create a one-chip

optical system.

Si-Ware has created a library

of building blocks for the plat-

form. Optical components

include flat, cylindrical, and

spherical collimating mirrors;

wide-bandwidth beam split-

ters; optical filters; and mov-

ing-corner cube reflectors.

MEMS components include

long-travel-range microactu-

ators and micromotors. The

components are lithographi-

cally aligned on the chip.

Si-Ware has already used

the SiMOST system to create a

monolithic infrared spectrom-

eter and swept-laser source.

Designers can complement

such optical-MEMS mono-

lithic-workbench ICs with elec-tronic interface-and-control

ICs from Si-Wares ASIC divi-

sion. These ASICs handle the

MEMS control, current, voltage

and capacitive sensing, data

conversion using ADCs and

DACs, and data processing.

The systems can rival micro-

electronics in economies of

scale in size and cost.

by Peter Clarke

Si-Ware Systems Ltd,

www.si-ware.com.

MEMS-optical-IC platform allowsthe creation of custom structures

8/12/2019 EDN febrero 2012

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Strange stories from the call logs of Analog Devices

To Learn More About

High-Speed Layouthttp://dn.hotims.com/40993-100

A.Part 1 of this seriesdiscussed why splittingAGND and DGND isnot necessary unless circum-stances within the design forceyou to make that choice. Part 2discussed the design of the powerdelivery system (PDS), and how squeez-ing the power and ground planes togetherprovide added capacitance. Part 3discussed how wise design of the E-Padgets the best performance and most heatout of your signal chain design. Part 4 will

make light of cross coupling betweenlayers and planes within the PCB.

It is inevitable that some high-speedconverter layouts will have a circuit planeoverlapping another within the PCB design.In some cases, a sensitive analog plane(power, ground, or signal) might be directlyabove a noisy digital plane. Most designerswouldnt think that this would matter, as theplanes are on different layers. So, heres asimple test:

Choose one of the adjacent layers andinject a signal on that plane. Next,connect the cross-coupled layer to aspectrum analyzer. Can you see how muchsignal is coupling through to the adjacentlayer? Even though they might beseparated by 40 mils, adjacent layers stillform a capacitor in some sense, and willtherefore still couple signal from one planeto another at some frequency.

Lets say a noisy digital plane on one layer

has a 1-V signal that switches at a highspeed. With 60-dB isolation between the

layers, the non-driven layer will see1 mV of coupling from the driven layer. Toa 12-bit analog-to-digital converter (ADC)with a 2-V p-p full-scale swing, this is 2 LSBs

(least significant bits) of coupling. Thismay be fine for your particular system, butkeep in mind that as you increase theresolution from 12 bits to 14 bits, thesensitivity quadruples, so the errorincreases to 8 LSBs.

Ignoring cross-plane/cross-layer couplingwill probably neither make the systemfail nor cripple the design, but be aware,because more coupling exists between twoplanes than what might be imagined.

Keep this in mind when noise spurs areseen coupling in the frequency spectrumof interest. Sometimes layouts dictate thatunintended signals or planes be cross-coupled to a different layer. Remember thiswhen debugging your sensitive systems:the issue may lie one layer below.

Considerations on High-Speed ConverterPCB Design, Part 4: Plane Coupling

Q. What are someimportant PCB layoutrules when using ahigh-speed converter?

SPONSORED BY

Have a question

involving a perplex-

ing or unusual analog

problem? Submit

your question to:

www.analog.com/

askrob

For Analog Devices

Technical Support,

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R A Q s

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ball with his two boys.
http://dn.hotims.com/40993-100http://www.analog.com/askrobhttp://www.analog.com/askrobhttp://www.analog.com/askrobhttp://www.analog.com/askrobhttp://dn.hotims.com/40993-100

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Linear Technologys new

ultrawide-bandwidth,d i r e c t - c o n v e r s i o n

LTC5585 I/Q demodulator

features an IIP3 and an IIP2 of

25.7 dBm and 60 dBm, respec-

tively, at 1.95 GHz. The demod-

ulator provides baseband

output-demodulation band-

width of more than 530 MHz,

which can support new-gen-

eration wideband LTE-multi-

mode and digital-predistortion

receivers. It operates over a

frequency range of 700 MHzto 3 GHz, covering virtually all

cellular-base-station frequency

bands.

The dev ice includes bui lt-

in calibration circuitry that

enables designers to improve

the receivers IIP2 performance

from a nominal 60 dBm to 30

dBm or higher. On-chip cali-

bration circuitry nulls out the

dc-offset voltages at the I and

the Q offsets. Output power

at 1-dB compression is 16

dBm. The LTC5585 offerstypical amplitude mismatch

of 0.05 dB and phase error of

0.7at 1.95 GHz, producing a

receiver-image-rejection capa-

bility of 43 dB.

The demodulator suits use

in multi mode LTE, WCDMA,

and TDSCDMA base-station

digital-predistortion receivers

and main receivers. It also tar-

gets use in military receivers,

broadband communications,

point-to-point microwave datalinks, image-rejection receiv-

ers, and long-range RFID

readers.

The LTC5585 has an on-

chip RF transformer to reduce

the need for external compo-

nents; comes in a 24-lead,

44-mm QFN package; and

operates over a temperature

range of 40 to +105C. It

operates from one 5V supply,

drawing a supply current of

200 mA. The device providesa digital input to enable or dis-

able the chip. When disabled,

the IC typically draws 11 A of

leakage current. The demodu-

lators turn-on time of 200 nsec

and turn-off time of 800 nsec

enable its use in burst-mode

receivers. Prices start at $5.98

(1000).by Fran Granville

Linear Technology

Corp,www.linear.com/product/LTC5585.

Wideband I/Q demodulator improvesreceiver performance

With the market for

MEMS chips grow-

ing at a 50% annual-

growth rate, according to Gold-

man Sachs, EDA-tool vendor

Coventor Inc aims to speed

up MEMS-chip design by add-

ing scripted automation and

by dramatically expanding thesize of the devices it can simu-

late. Coventor users can now

use the Python scripting lan-

guage to automate the process

of changing test parameters

and then running simulations

to make sure MEMS devices

meet their design specifications

under all operating conditions,

says Stephen Breit, vice presi-dent of product development

at Coventor.

Coventor also expanded the

resolution of its models from 32

to 64 bits, removing the 3-Gbyte

limit on simulation sizes that had

previously slowed the design

process. Now, our users can

focus on solving even the most

complex MEMS-design and

-simulation problems without

worrying about running out of

memory space, says Breit. Its

just a matter of how much simu-

lation memory you can afford,

rather than how much our tools

can access.

CoventorWare also sports

a new hex-dominant extrude-

meshing capability, which auto-

matically generates meshes of

uniform density and quality.Previously, inefficient tetrahe-

dryl meshes were necessary for

stacked layers of materials that

are perforated with release etch

holes. Coventor claims that its

new meshes use 20 to 40%

fewer elements, enabling the

simulation of multiaxis MEMS

sensors with hundreds of elec-

trostatic comb fingers.

by R Colin Johnson

Coventor Inc,

www.coventor.com.

Coventor automates MEMS design


pulse

AUTOMOTIVEVARISTORS HAVELOW LEAKAGECURRENT

02.1

6.1

2

The AEC Q200-qualified

automotive StaticGuard

series varistors de-

liver capacitance of

40 to 200 pF at 0.5V

and leakage current of

10 A, providing ESD

protection in CMOS,

bipolar, and SiGe-based

circuits. The varistors

provide bidirectional

transient-voltage pro-

tection in the on stateand EMI/RFI attenuation

in the off state, along

with an ESD rating as

high as 15 kV.

Typical ESD failure

voltage for CMOS and

bipolar parts is 200V

or greater, and the de-

vices comply with IEC

1000-4-2, Level 4, with

15-kV ESD pulse (air

discharge) and generate

less than 20 mJ of en-

ergy. The devices come

in 0402, 0603, and 0805

case sizes for use in

general-purpose drives

and logic, transceiver

chips, and sensor appli-

cations. Typical prices

range from 4 to 9 cents

(volume quantities).

by Ismini Scouras

AVX Corp,

www.avx.com.

AVXs StaticGuard varistors

provide transient-voltage

and signal suppression for

automotive applications.

Coventor claims its new hex-

dominant meshes use 20 to

40% fewer elements, enabling

the simulation of multiaxis

MEMS sensors with hundreds

of electrostatic comb fingers.

Linear Technologys wideband

LTC5585 I/Q demodulator

features an IIP3 and an IIP2

of 25.7 dBm and 60 dBm, re-

spectively, at 1.95 GHz.

8/12/2019 EDN febrero 2012

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Dell Precisionworkstations provide high speed and maximum power

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BY BONNIE BAKER

B A K E R S B E S T

[www.edn.com]

The hearts input signal to the sys-tem is approximately 0.25 mV p-p. Thissmall signal requires an instrumenta-tion amplifiers gain of approximately6000V/V. The good news is that theresults inFigure 1do not represent theperformance of a doctors office ECG-measurement tool. This measurement

was actually taken in an engineers labfrom the board inFigure 2.

Dont fall into this EMI trap. Takecare to create boards and use compo-nents that are EMI-resilient, regardlessof your analog or digital circuits band-

width. When an EMI source is pres-ent in the vicinity of your applicationcircuit, it may create a response to theradiating source.

How did the radiated noise from thephone get into the measurement withsuch a low-frequency board? In EMIterms, three elements are at work with

this type of problem: a radiation source,a coupling path for the radiation signalto travel through, and a receptor. Theradiation source in this example is thecell phone. The EMI signals may comethrough the air or be conducted across

your PCB andoriginate fromu n e x p e c t e dsources. EMI, orRFI, surrounds

a receptor either by direct conductionor through fields. These fields coupledirectly into the circuits connecting

wires and PCB traces, where they areconverted to conducted RFI.The conditions that create physi-

cal forces between charges are electric,magnetic, and electromagnetic radia-tion. An electric field describes a forcethat an uneven charge distribution cre-ates between two physical points. Forcedevelops between charges in an effortto balance the charge distribution.Moving charges or current flow createsa magnetic field, exerting a force on allother charges around them. This field,

or force, falls off rapidly with distance.Note that the electric and magneticfields interrelate, and a change in oneresults in a simultaneous change in theother. The acceleration of an electron,or charge, creates an electromagneticfield. This electromagnetic field is mostoften responsible for the propagationof EMI.

To tackle this problem, read my nextcolumn, which will examine the char-acteristics of the radiating sources thatcan cause EMI problems, along with

some tips on how to minimize theirtransmissions.EDN

ACKNOWLEDGMENT

Special thanks to John Brown for the ECGboard and data.

Bonnie Baker is a senior applications en-gineer at Texas Instruments and author ofA Bakers Dozen: Real Analog Solu-tions for Digital Designers.

EMI problems?Just the facts, please

The proliferation of intentional and unintentional EMI radia-

tors can wreak havoc on your circuits. The signals from these

radiators are not out to contaminate your circuits, but you

may want to keep your low-noise systems out of harms way.

Imagine a doctor using an ECG (electrocardiogram) diagnos-

tic tool to get a good look at your heart. This high-precision

measurement is also low-frequency, so the electronics dont extend past1 MHz. However, if you are connected to an ECG tool with a poor EMI

design and your physician answers his cell phone during the test, you may

have cause for concern (Figure 1).

Figure 1 EMI from a cell phone can cause a 1.5V change from

normal on an ECG. The ECG diagnostic tool senses a heart while

a 0.5W, 470-MHz transmitter turns on and off just one and a half

feet away.

Figure 2An engineers precision, low-level ECG cardiota-

chometer board took the measurements for Figure 1.

18 EDN | FEBRUARY 16, 2012

17 Hz2 Hz

AC COUPLED

GT=6 kV/V

ECG FULL

SCALE 1V P-P

0.5V/DIV

EMI NOISE

ON ECG

TRANSMITTER

KEYED 6 SEC

4V

OFFSET

1.5V

CHANGE

DUE TO

EMI

2.5V

NORMAL

OFFSET

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More Flexibility

vicorpower.com/rp/flexibility/edn

Vicor gives power system architects the flexibility to choose from modular,

plug-and-play components, ranging from bricks to semiconductor-centric solutions

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MECHATRONICSIN DESIGN

D

E

F

ENSES

YS

TEM

S

CON SUM E R P R O D U C TS

MA

NU

FAC

TUR

ING

ControlSystems

Software ElectronicSystems

MechanicalSystems

Digital Control

Systems

Control

Electronics

Mechanical

CAD

Electro-

mechanics

MA

T

E

R

I

A

L

S

PRO

CESSI N

G

AU

T OM O

T I V E A ERO SPAC

E

MED

IC

AL

XE

RO

G

R

A

P

H

Y

mechatronics

FRESH IDEAS ON INTEGRATINGMECHANICAL SYSTEMS,ELECTRONICS, CONTROL SYSTEMS,AND SOFTWARE IN DESIGN

As engineers, you use many components and devicesevery day that you treat as black boxes. You are con-cerned only about the inputs and outputs of the black

box, and that approach is acceptable provided that you know

the operating range and limitations of the device. The samecan be said about certain concepts and techniques. Youroutinely use them, and they work, but you may not totallyunderstand why they work. As fundamental performancelimitations and safety come into question, a deeper under-standing becomes necessary. In addition, innovation demandsunderstanding. The widely used PWM technique may fallinto this category. Most engineers use it every day to drive avariety of devices, but only a few know why they use it andhow it works.

A pulse signal is defined by its amplitude and pulse width.A periodic pulse train has a frequency, or pulse-repetitionrate, and a duty cyclethe ratio of pulse width to repeti-tion period, varying between 0 and 100%. PWM modulatesthe duty cycle and keeps the period fixed. Microcontrollers,which operate in the digital domain, can generate a PWMsignal. Although an analog signal is continuous in both timeand amplitude, a digital signal is discrete in timethat is, it issampled at a certain rateand quantized in amplitude using afinite number of bits. The output of a microcontroller is typi-cally either digital or PWM. The PWM signal typically ranges

from 0 to 5V; thus, you can use it to turn an electronic powerswitch, a transistor, on and off and to control the amount ofpower a load receives.

Why would anybody be interested in this type of signal?PWM avoids losses normally incurred when a power sourceis limited by resistive means. In PWM, the average deliveredpower is proportional to the modulation duty cycle. Thus,the switched circuits to control the voltage across or currentthrough a load have low power loss because the switchingdevices are either offand no current yields no power lossor on, with low power loss due to low voltage drop. You canaugment the PWM signal, with a sufficiently high modula-tion frequency, using a lowpass filter to smooth the pulse

train and recover an average analog waveform. Some people

refer to PWM as a poor mans DAC.What should the frequency of

the PWM signal be? First, considerthe case in which you are using the

PWM signal as a DAC. Many micro-controller applications need analogoutput but do not require high-res-olution DACs. In a typical PWMsignal, the frequency is constant, butthe pulse width, or duty cycle, is avariable, directly proportional to theamplitude of the original unmodu-lated signal. The bandwidth of thelowpass filter should equal the band-width of the unmodulated signal.Choose the PWM frequency to givean acceptable ripple magnitude in

the analog signal. For example, if youuse an RC lowpass filter, you derivethe amplitude attenuation using thefollowing equation:

ATTENUATION (dB)=20log101

(FPWM/FBW)2+1.

To increase the attenuation, and thus reduce the ripple,you may need to use a higher-order filter or a higher PWMfrequency.

Many devices inherently average an on/off signal tocontrol their operation, based on the duty cycle. Examples

include LEDs that humans and inductive loads view, such asmotors and solenoids. For an inductive load, such as an LRcircuit, you can derive the PWM voltage frequency so thatthe current waveform is within a certain percentage of theanalog step response. A fundamental analysis of an LR circuitcalculates the frequency according to the following equation:

FREQUENCY (Hz)=R

2L1N 1P

100

,

where P is percentage.A shroud of mystery often envelops devices and concepts,

which can often lead to avoidance or misuse. Focusing on the

fundamentals removes that mystery.EDN

Pulse-width modulationAll engineers need to know what PWM is and why it is so common.

Kevin C Craig, PhD,

is the Robert C Greenheck

chairman in engineering

design and a professor of

mechanical engineering at

the College of Engineering

at Marquette University.

For more mechatronic

news, visit mechatronicszone.com.

Some people refer to PWM as a

poor mans DAC.


8/12/2019 EDN febrero 2012

21/56

YourFIRSTCHOICE

forPerformance

for more information call 1.800.981.8699 or visit us at www.irf.com

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8/12/2019 EDN febrero 2012

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IM

AGE:JAMESTHEW/SHUTTERSTOCK

PROTECT

POE SYSTEMS

POE (power over Ethernet) has been rapidly gainingpopularity because it eliminates the requirements forseparate power supplies and power cables for con-nected equipment and for locating equipment nearan ac outlet. Recent increases have occurred in theamount of power that POE PSE (power-supply equip-

ment) can deliverfrom 15.4W for POE to 30W for POE+.These increases have in turn increased the number of potentialapplications. Ethernet now delivers sufficient power for VOIPtelephony, to power extended-range wireless-access points, andto operate surveillance cameras, for which it can also power pan

and tilt functions.

THE INCREASED USE OF POE

BROADENS THE RANGE OF

LOCATIONS IN WHICH YOU

CAN USE ETHERNETFROM

INDOORS TO CAMPUS LAYOUTS

OR FIRST- AND LAST-MILE TELE-

PHONY APPLICATIONS. THESE

USES INCREASE EXPOSURE TO

LIGHTNING-INDUCED SURGES,

ESD, AND ACCIDENTAL POWER

FAULTS. PROPER DESIGN PRO-

TECTS POE EQUIPMENT FROM

THESE HAZARDS.

PHILLIP HAVENS AND CHAD MARAK LITTELFUSE INC

FROM LIGHTNINGSURGES AND OTHERELECTRICAL HAZARDS


8/12/2019 EDN febrero 2012

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BASICS OF POE

In POE, PSE feeds power into the cable,either through a switch, also called anend span, or through a midspan, if itresides anywhere other than at the endof the cable. PDs (powered devices) onthe cable consume power.

The IEEE 802.af POE standard lim-

its PD power consumption to 12.95W,or 360 mA, which corresponds to a PSEoutput limit of 15.4W, or 400 mA, perport after accounting for cable losses.This standard takes into account linelosses for maximum loops as long as100m, thereby allowing as much as 57Vdc from the PSE. The nominal level is48V dc.

The POE+standard, IEEE 802.at,allows the PSE to deliver as much as30W and the PD to accept as much as25.5W for Type 2 equipment; POE+

Type 1 is equivalent to POE. The PSEsupplies a maximum of 600 mA. POE+also requires the use of wiring, suchas Category 5e or 6, with impedancethat is less than or equal to 12.5perloop pair, compared with 20per looppair for POE.

Companies are working to further

increase this maximum power limit.PSEs that promise 60W per port areavailable, and one vendor sells mid-

span PSEs that the company claimsprovides 95W per port using a propri-etary discovery process. This limit maybe approaching the physical boundariesof Category 5 cable, however, whichmeans that, for higher power, designersmust find a way around this bound-ary. One simple approach is to increase

separation between bundled cables toallow for improved heat dissipation.Power usage beyond the limit wouldrequire cable with heavier-gauge con-ductors. These higher voltages complywith neither IEEE 802.3af nor IEEE802.3at.

It is important for the PSE to deliv-

er the amount of power for the PDsit feeds without causing damage. Todetermine the required power level,the PSE and PD engage in a back-and-forth signaling-handshake rou-tine at turn-on that involves voltagepulses from the PSE that determine theimpedance signature of the connectedPDs. This discovery process sets thesystem to one of five classes (Table 1).Table 2shows the POE-PD classifica-tions for POE+.

POE MODESPSE can provide power over theEthernet cable in one of two ways.In Mode B, the PSE applies powerover the spare data pairs 4, 5 and 7,8 in 10BaseT or 100BaseTX systemsbecause only RJ-45 pins 1 through 2and 3 through 6 provide data delivery.Thus, RJ-45 pins 4 through 5 and 7through 8 are available for power deliv-ery (Figure 1). Notice that POE usesa phantom powering technique sothat a single pair carries a 0V-dc poten-

tial difference between its leads. Thepower-supply voltage is the differencebetween the two center-tap connec-tions of the wire pairs.

In a 1000BaseT application, thereis no spare pair; therefore, two of theactive data pairs, Mode A or Mode B,must supply power. Mode A combinesthe dc voltage with the signal over thedata pairs 1, 2 and 3, 6, respectively(Figure 2). An isolation transformerconnects across data pair 1, 2, and a

separate isolation transformer connectsacross data pair 3, 6 with a center tap.These two center taps provide accessto the dc power, and the voltage acrossany pair remains at 0V dc. This phan-tom-power technique for both Mode Aand Mode B helps to prevent accidentalshock hazards when users are handlingsingle pairs.

You can use either Mode A or ModeB connections with any Ethernetapplication, including 10, 100, and1000BaseT. The PSE cannot simulta-

neously provide power in both Mode

AT A GLANCE

Higher POE (power-over-Ether-

net) power levels allow use of equip-

ment outdoors, increasing exposure

to lightning strikes and other electri-

cal hazards.

Include a series-current-limiting

device in your equipment so that it

can resume operation after a light-ning-surge event.

Bidirectional surge-protection

devices, TVS (transient-voltage-sup-

pression) diodes, fuses, and PTCs

(positive-temperature-coefficient)

devices can help ensure reliable

operation despite hazards.


TABLE 1POE-PD POWER SPECIFICATIONS

Class Power range (W)

0 (default) 0.44 to 12.95

1 0.44 to 3.84

2 3.84 to 6.49

3 6.49 to 12.95

4 Reserved for future use

SPARE PAIR

4

5

4

5

SPARE PAIR

7

8

7

8

SIGNAL PAIR

11

22

RECEIVETRANSMIT

SIGNAL PAIR

33

66

TRANSMITRECEIVE

DC/DCCONVERTER

POWERED DEVICE

48V

POWER-SOURCING EQUIPMENT

Figure 1Apply POE Mode B power over the spare data pairs in 10 or 100BaseTX

systems or over pairs 4 to 5 and 7 to 8 of a 1000BaseT system. POE uses the phan-

tom powering technique so that a pair carries a 0V potential difference between its

leads; power-supply voltage is the difference between two wire pairs.

8/12/2019 EDN febrero 2012

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Stay connected and informed with EDNonLinkedIn, Facebook, and Twitter.

EDNs Electronics Design Network groupis the essential LinkedIn group for the full spectrum of information

needed by design engineers, engineering managers, and upper management through each phase of

the design cycle, from product-concept development to the manufacturing of electronics.

Become a fan of EDNon Facebookand join in discussions with your peers, keep track of industry events,

and stay on top of news and trends.

Follow EDNon Twitterfor real-time news updates, technical analysis, and quick tweets on our blogs, editors,

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@EDNmagazine

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A and Mode B, but the PD must besimultaneously compatible with bothMode A and Mode B powering tech-niques because you cannot predeter-mine which PSE mode will connect tothe PDs.

The details of the protective devic-es and how they connect depend on

the power mode and data rate of theEthernet system. Both the PSE andPD must be able to continue opera-tion after a lightning surge and alsosafely handle power-fault events asdefined in UL 60950-1 or EN 60950-1, although these standards do notrequire that the equipment operatesafter such a test.

Figure 2 Mode A POE uses the data-signaling pairs 1, 2 and 3, 6, thereby combining

the dc voltage with the signal over these data pairs.

TABLE 2POE-PD POWER CLASSIFICATIONS

Class Conditions (V) Classification current (mA) Average PD power (W) PD type

0

14.5 to

20.5 0 to 4 13 11 14.5 to 20.5 9 to 12 3.84 1

2 14.5 to 20.5 17 to 20 6.49 1

3 14.5 to 20.5 26 to 30 13 1

41 14.5 to 20.5/6.9 to 10.1 36 to 44 25.5 2

1POE+ Type 2 returns a Class 4 class ification signature.

SPARE PAIR

4

5

4

5

SPARE PAIR

7

8

7

8

SIGNAL PAIR

11

22

RECEIVETRANSMIT

SIGNAL PAIR

33

66

TRANSMITRECEIVE

DC/DCCONVERTER

POWERED DEVICE

48V

POWER-SOURCING EQUIPMENT

8/12/2019 EDN febrero 2012

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To meet this requirement, youmust include a series-current-limitingdevice, such as a fuse, which does notopen during lightning-surge testingbut opens appropriately for long-termac-power-fault conditions, or a PTCdevice, as long as it can operationallysurvive the lightning-surge testing.

PTC devices can self-recover aftera power fault but are incompatiblewith 100 and 1000BaseT Ethernetsystems due to their off-state resis-tance and hysteresis-recovery char-acteristics. PTCs will not remainperfectly matched after multipleoperations.

LIGHTNING PROTECTION

The choice of lightning protectiondepends on the expected exposurefor the application. For an indoor,


B B

IC1

2 7

81

63

4 5

DATA PAIR

B B

B

24V

24V

B

IC2

2 7

81

63

4 5

F3

DATA PAIR

B B

IC3

2 7

81

63

4 5

DATA PAIR

B B

IC4

2 7

81

63

4 5

DATA PAIR

VCC

DC

R110

DC

R2

10

BIAS-SUPPLY SUGGESTIONS:

NOTES:IC

1THROUGH IC

4ARE BIDIRECTIONAL

THYRISTOR-SURGE-PROTECTION DEVICES.

F1THROUGH F

8ARE 1.25A TELECOM FUSES.

TVS3

1000BASET

ETHERNET

PHY

F4

F5

F6

F7

F8

F1

F2

Figure 4A GR-1089-compliant approach for overvoltage and overcurrent events for 10, 100, and 1000BaseT applications in an

outdoor environment is subject to both lightning-surge and power-fault events. For 10 and 100BaseT, only the two data-wire

pairs would require this protection.

F1J1

J8

CASE GROUND

OUTSIDEWORLD

RJ-45 CONNECTOR TVS1

TVS2

VCC

PHY GROUND

TRANSMIT

TRANSMIT

RECEIVE

RECEIVE

NOTE:F1THROUGH F4ARE TELECOM FUSES.

F2

F3

F4

ETHERNET PHY

Figure 3 Lightning protection for 10 and 100BaseT applications uses a combina-

tion of clamping devices. A lightning-induced surge activates TVS1in the secondary

position, providing a clamping function that routes the offending surge away from

the sensitive Ethernet circuit. The tertiary device, TVS2, then provides another level

of protection on the line-driver side of the transformer. Power-fault events, char-

acterized as long-term 50- to 60-Hz waveshapes, activate fuses F1through F

4. A

1000BaseT system uses the same schematic for the other two data-signaling pairs.

8/12/2019 EDN febrero 2012

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Pulse Transformers10 Nanoseconds to 100 Microseconds.ET Rating to 150 Volt Microsecond,Manufactured and tested to MIL-PRF-21038.

Multiplex Data BusPulse TransformersPlug-In units meet the requirementsof QPL-MIL-PRF 21038/27.Surface units are electrical equivalentsof QPL-MIL-PRF 21038/27.

DC-DC ConverterTransformersInput voltages of 5V, 12V, 24V And 48V.Standard Output Voltages to 300V (Specialvoltages can be supplied). Can be used as selfsaturating or linear switching applications. Allunits manufactured and tested to MIL-PRF-27.

400Hz/800HzPower Transformers0.4 Watts to 150 Watts. Secondary Voltages 5Vto 300V. Units manufactured to MIL-PRF-27Grade 5, Class S (Class V, 1550C available).

SurfaceMount

(andPlugIn)

Transformersand

Inductors

SeePicosfull

Catalogimmed

iately

www.picoelec

tronics.com

Delivery-Sto

cktoonew

eek

forsample

quantities

less-severe application, you can useTVS-diode arrays between the RJ-45connector and the Ethernet PHYchip set in both the secondary posi-tion and the tertiary position (Figure3). A lightning-induced surge eventactivates TVS

1 within nanoseconds,

providing a clamping function that

routes the offending surge away fromthe sensitive Ethernet-line-driver cir-cuit. TVS

2clamps any residual surge

that couples across the transformer. Fora more robust approach, you can usea TVS-diode array for each wire pair;otherwise, one TVS array can protecttwo wire pairs, as TVS

2does. Power-

fault events, which involve long-term50- and 60-Hz waveshapes, activate1.25A fuses F

1through F

4after a TVS

device provides a current path.

PD PROTECTIONBecause you have no way of knowingwhether a PSE will use Mode A orMode B on an Ethernet installation,you must provide 57 to 90V protectionfor all wire pairs at the PD end, witheverything hardened to more than100V. The surge-protection deviceshould have a trigger voltage greaterthan any steady-state voltage likelyto appear on the cable. POE voltagescan reach 57V, so the device must nottrigger at or below this voltage.

This approach also prevents thesurge protector from turning on dur-ing power-classification testing orduring the resistive-power-discoverytest. Further, some power systems sup-ply 48V, whereas others supply 48V,so the protection device must not bepolarity-sensitive. Designers typicallyuse bidirectional thyristor-surge-pro-tection devices in this case. The solid-state crowbar devices reset only whenthe available current falls below its

holding-current parameter. This setupis not a problem because it draws excesscurrent from the PSE, which temporar-ily shuts down during an overcurrent-load condition, and it allows the thyris-tor surge protector to reset.

Figure 4shows a GR-1089-com-pliant approach for overvoltageand overcurrent events for 100 and1000BaseT applications in an outdoorenvironment subject to both lightning-surge and power-fault events. The fusesin both data-pair leads provide the nec-

essary overcurrent protection that is

insensitive to lightning-induced over-voltage surges for first-level GR-1089events. The bidirectional thyristor-surge-protection devices, IC

1 through

IC4, or SIDACtor (silicon-diode-

alternating-current) devices, providean overvoltage-crowbar-protectionapproach that complies with both first-

and second-level lightning surges ofGR-1089, Issue 6, port types 3 and 5.The two bias leads for IC

1through

IC4connect to any available voltage

rails that are less than the turn-onthreshold voltage of the protectivedevices, which stabilizes their off-statecapacitance and helps preserve signalintegrity. The bidirectional thyristor-surge-protection devices IC

1through

IC4can have a 58V minimum thresh-

old for a 48V POE. NoncompliantIEEE 802.3 systems that have a POE

voltage higher than 57V would requirea higher-minimum-threshold protec-tion device.

The tertiary, or chip-side, approachis a TVS-diode rail-clamp array, TVS

3,

which provides additional protectionafter the coupling transformer. You canuse Bob Smith terminations, whichSmith described in a US patent. BobSmith termination is a method ofreducing the longitudinal or common-mode current on multipair conductorsystems in which the pairs interrelate

in a uniform manner. If you use thismethod, you should capacitively iso-late the terminations so that they donot load the POE power supply. Thiscombined metallic/differential andlongitudinal/common-mode-protec-tion approach requires a fuse on bothleads of the transmitting and receiv-ing pair. An approach without thelongitudinal mode may require onlyone fuse per pair for lower-data-rateEthernet, such as 10BaseT. For 100

and 1000BaseT systems, it is prudentto place the identical fuse element inboth legs of a pair to maintain loopbalance (Figure 4).

The single-fuse approach is permis-sible if pins 3 and 6 of the protectivethyristor device do not connect toground but instead remain open fora 10BaseT Ethernet system. BecauseIEEE 802.3 does not strictly allow forcommon-mode protection on the pri-mary side of the coupling transformerfor cable-discharge-event-protection

reasons, the thyristor-surge-protec-

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IC1

2 7

81

63

4 5

F5

F6

F7

NOTES:

IC1THROUGH IC4ARE BIDIRECTIONALTHYRISTOR-SURGE-PROTECTION DEVICES.F1THROUGH F13ARE 1.25A TELECOM FUSES.

10M 10M

VPORTN VPORTP

IC2

2 7

81

63

4 5

10M 10M

VPORTN VPORTP

VPORTN

VPORTP

IC3

2 7

81

63

4 5

10M 10M

VPORTN

VPORTP

IC4

2 7

81

63

4 5

10M 10M

VPORTN

VPORTP

1

2

4

5

7

8

3

6

RJ-45

OUT

RJ-45

IN

TO SIGNAL PAIR 2

TO SIGNAL PAIR 3

C1

100 nF

100V

TVS DIODE

RATED 400W OR

HIGHER

F1

F2

F3

F4

TRANSMIT

RECEIVE

1

2

4

5

7

8

3

6

CABLE

SIGNAL PAIR 1

SPARE PAIR 2

SPARE PAIR 3

SIGNAL PAIR 4

F8

F10

F11

F12

F13

Figure 5A POE-system-protection example includes both data-pair protection and PD power-connection protection. The TVS

protection for the PD ends power-supply portion complies with both Mode A and Mode B POE power. Typical TVS devices for this

type of circuit are available in 400, 600, 1500, and 3000W ratings. Fuses F1through F

4provide overcurrent protection compliant with

GR-1089, Issue 6, and UL 60950-1.

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tion devices usually do not connectto ground. Therefore, most Ethernetapproaches depend on the isolationrating of the coupling transformer forlongitudinal/common-mode protec-tion on the line side, whereas the ter-tiary position on the secondary side ofthe coupling transformer may connect

to the Ethernet line drivers groundreference.TVS

3, a 2.5V TVS-diode array, pro-

vides tertiary protection on the chipside of the coupling transformer. Thisapproach complies with the surge andpower-fault requirements of GR 1089-Core, Issue 6, for intrabuilding andinterbuilding POE. You can substitute a0.3A PTC device for the fuses for com-pliance with ITU K.20/21 enhancedand basic, which contain coordina-tion clauses for 10BaseT Ethernet.

However, for 100 and 1000BaseT, youwould use a pair of appropriately sized,precision, 1% resistors to force coordi-nation between the secondary and theprimary protectors.

Fi gure 5 shows both data-pairprotection and PD center-tap power-connection protection that complywith both Mode A and Mode B POEpower for the PD end of the system.Both PD Mode A and Mode B POEare protected by a diode bridge and a1000W TVS device. More robust, 1500

and 3000W, approaches are also avail-able for harsher surge environments,such as those that regulatory standardsITU K.20 Enhanced or GR-1089 PortType 5 describe.

As the power POE systems deliverhas increased, developers are installingEthernet equipment in areas that exposeit to increased hazards from lightning-induced overvoltages and 50- to 60-Hzpower-line faults. Judicious use of bi-directional surge-protection devices,

TVS diodes, fuses, and PTC devicescan help ensure reliable operationdespite these hazards.EDN

AUTHORS BIOGRAPHIES

Phillip Havens is the technical-marketingand application manager at Littelfuse andbrings a wide range of electronics engineer-ing expertise. He earned both bachelorsand masters degrees in electrical engineer-ing from Louisiana Tech University (Rus-ton, LA), is a licensed professional engi-neer, and interfaces extensively with the

technical teams of many leading electron-

ics manufacturers to develop circuit pro-tection for specialized applications. Havensrepresents Littelfuse at electronics-safety,circuit-protection, and telecom-related in-dustry associations and helps define, di-rect, and support the companys silicon-based-protection-product lines. You canreach him at [email protected].

Chad Marak is a product-marketing man-ager in the semiconductor-business unit ofLittelfuse Inc. His responsibilities include

providing strategic direction for the growthof the TVS-diode-array product line andmanaging the North America field-appli-cation-engineering team. Marak receiveda bachelors degree in electrical engineer-ing from Texas A&M University (CollegeStation, TX) and a masters degree in elec-trical engineering from Santa Clara Uni-

versity (Santa Clara, CA). He has beenin the semiconductor industry for 10 yearsand holds four US patents. You can reachhim at [email protected].

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30 EDN | FEBRUARY 16, 2012

ARE WE THERE

SORTING OUT

YET?30 EDN | FEBRUARY 16, 2012 [www.edn.com]

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IMAGES:SHUTTERSTOCK


BY JANINE LOVE CONTRI BUTING TECHNICAL EDI TOR

CAN WE ACHIEVE THEPERFORMANCE LEVELS OF THEIMT-ADVANCED GLOBAL STANDARD

FOR INTERNATIONAL MOBILE

TELECOMMUNICATIONS?

hanks to clever marketing campaignsand branding, the general public believesthat 4G has arrived. The performanceof 4G/LTE mobile handsets has cer-

tainly improved, and designers arepushing the outer limits of performancein all parts of the handset to inch closer

to the rates that the IMT (InternationalMobile Telecommunications)-Advancedstandard dictates. In many cases, the limita-tion is available spectrum, so designers mustdevelop creative approaches until govern-ments act, preferably by making contiguousspectra available.

Riding the leading edge of what is pos-sible, engineers are turning to new technol-ogies, materials, and techniques, and theyare taxing the upper limits of their simu-

lation and test-and-measurement tools.On the bright side, all of the engineeringcommunities seem to be working togeth-er to squeeze the most performance fromlow-power handsets and the most diversewireless networks. With users download-ing more than 1 billion apps a month andsending 8 trillion texts in 2011, the surgein mobile usage will need all the support itcan get (Reference 1).

T

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IMT-ADVANCED

The ITU-R (International Telecommu-nications Union-Radio CommunicationSector) manages IMT-Advanced, whosefeatures enable worldwide usability. Thestandards targeted data rates of 100Mbps for high mobility and 1 Gbps forstationary use get the most attention,

however (Reference 2). For the physi-cal-layer requirements, IMT-Advancedcalls for a bandwidth exceeding 40MHz, peak downlink spectral efficiencyof better than 15 bps/Hz and uplinkefficiency of 6.75 bps/Hz, and latency ofless than 100 msec for users and 10 msecfor control.

Although the latest commercialLTE, HSPA (high-speed-packet-access)+,and EVDO (evolution-data-optimized) Revision B services providehigher data throughputs than do tra-

ditional wireless services, they still donot provide a high enough data rate tomeet IMT-Advanced requirements. Awider bandwidth and as much as 44[four antennas at the transmitter andfour antennas at the receiver] MIMO[multiple input/multiple output] forthe downlink are essential for achiev-ing the IMT-Advanced requirement,says Jung-ik Suh, wireless-marketing-program lead at Agilent Technologies.Suh notes, however, that researchers areaiming for a 100-MHz bandwidth with

as much as 88 MIMO for the down-link. Unfortunately, wireless-serviceproviders will be unlikely to achievethis goal in real-world conditions.

One approach to the bandwidthproblem is to use carrier aggregation,

which requires the deployment of paral-lel receivers. There are still many othertechnical hurdles to overcome to reachIMT-Advanced, says Suh. It is hardto say if we are now at either true-4Gperformance or [at] LTE-Advanced, butlots of technical research and efforts

will keep closing the gap to reach IMT-Advanced.

Developers of the 3GPP (third-gen-eration partnership project) in 1998created a global initiative to developspecifications to satisfy the latestmobile standards. To address the IMT-Advanced requirements, 3GPP hasintroduced LTE-A (LTE-Advanced).Initially part of Release 10 of the 3GPPspecifications, LTE-A is the new targetfor mobile developers (Reference 3).A main advantage of LTE-A over any

other proposal is the backward compat-ibility with LTE Release 8, says MarkusWillems, PhD, senior manager of prod-uct-marketing system-level solutionsat Synopsys. [LTE-As] being an evolu-tion rather than a revolution [should]

result in [its] widespread adoption.According to Chris Pearson, presi-

dent of 4G Americas, a wireless-indus-try trade association representing the3GPP family of technologies, somecarriers will deploy LTE-A in 2013. Inthe meantime, he notes, HSPA+andLTE now include tremendous technical

advancements, providing subscriberswith fast mobile. There are now 173HSPA+deployments in 86 countries,with peak speeds ranging from 21 to 42Mbps; 39 operators in 25 countries com-mercially deploy LTE, which has morethan 250 commitments for deploymentin the coming years.

For Pearson, the major hurdles forLTE-A are not of a technical nature.He notes, however, that the mobile-broadband industry is growing at a fastrate and that customers are using large

amounts of data (figures 1 and 2).There is a major concern and oppor-tunity for governments throughout theAmericas to act soon to plan, reserve,allocate, and auction additional inter-nationally harmonized spectra to theindustry, he says. The 3GPP standardswill offer substantial gains in spectralefficiency as they evolve; however,the current rate of mobile-data growthdemands additional spectrum resourcesglobally.

DEFINING THE CHALLENGES

Despite Pearsons faith in the engineer-ing community, real technical challeng-es remain for achieving the performancethat the IMT-Advanced standard out-lines. According to Madan Jagernauth,

AT A GLANCE

A surge in mobile traffic

demands evolution to higher data

rates.

LTE-A (Advanced) is the next

step toward IMT (International

Mobile Telecommunications)-

Advanced. Spectrum challenges are a limit-

ing factor to closing the gap be-

tween LTE-A and IMT-Advanced.

Figure 1As modern wireless standards evolve, data rates continue to climb (courtesy 4G Americas).


EDGE

DOWNLINK: 474 kBPSUPLINK: 474 kBPS

DOWNLINK: 42 MBPSUPLINK: 11.5 MBPS5/5 MHz

EVOLVED EDGE

DOWNLINK: 1.89 MBPSUPLINK: 947 kBPS

RELEASE 8 HSPA+

DOWNLINK: 84 MBPSUPLINK: 23 MBPS10/10 MHz

RELEASE 9 HSPA+


RELEASE 8 LTE

RELEASE 9 LTE


DOWNLINK: 1.2 GBPSUPLINK: 568 MBPS40/40 MHz

RELEASE 10 HSPA+

RELEASE 10 LTE


DOWNLINK: GREATERTHAN 1.2 GBPS

RELEASE 11 HSPA+

RELEASE 11 LTE

EDGE

HSPA

LTE

YEAR

2010 2011 2012 2013 2014

NOTE:THROUGHPUTS ARE PEAK THEORETICAL NETWORK RATES. FUTURE DATES ARE EXPECTED INITIAL COMMERCIAL-NETWORK DEPLOYMENTS(COURTESY RYSAVY RESEARCH/4G AMERICAS).

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vice president of mobile broadbandsolutions for Huawei TechnologiesUSA, those challenges include the useof multiple antennas in smartphones.Consumers desire for larger screens isdriving bigger form factors, which easesthis challenge. However, when deploy-ing MIMO in the device side of the

link, form factor is not the only con-cern. According to Jagernauth, man-ufacturers will not deploy 44 trans-mission in smartphones because of itsdrain on battery life. He does, however,expect to see virtual MIMO, in whichtwo subscribers can transmit simulta-neously on the same time slot and inwhich the base station can decode it.This approach enables higher networkusage. Huawei provides equipment onboth the infrastructure and the terminalsides of the link, including a number of

Android devices.According to Synopsys Willems,

when it comes to chip design, the mainhurdles are in the RF part. Carrier aggre-gation as a key concept requires runningmultiple transceivers in parallel, he says.Balancing area, power, and performanceis a key challenge. Synopsys offers theLTE-A library with a simulation setupthat allows users to run all the tests asspecified in the 3GPP standard docu-ments, thereby serving as an executablespecification. The product is currently

undergoing verification against equip-ment from Rohde & Schwarz.

BUILDING APPROACHES

Although manufacturers are on theverge of deploying LTE-based products,a lot of work still remains, according toManfred Schlett, vice president of mar-keting at RMC (Renesas Mobile Corp),a division that Renesas formed after itacquired Nokias wireless-modem busi-ness. Despite the availability of chip

sets from multiple vendors, both powerconsumption and costs are high. Schlettsees the chip sets, definitions, and bandallocations in the market as immature.Band fragmentation, which makes itchallenging to define chip sets, furthercomplicates these issues. RMC is nowlaunching a dual-mode HSPA+/LTEplatform, and it plans to launch LTE-focused parts this spring (Figure 3).

Power efficiency is crucial for themodem because of the need for moreoperations due to MIMO schemes.

Selecting smart algorithms for the

receiver part directly affects power effi-ciency, says Synopsys Willems. Thereis a dedicated need to explore algorithmalternatives that allow the system tostay close to the optimum maximumin throughput but that are less com-putationally intensive, he explains.According to Willems, using software-

defined approaches with multiple DSPcores is becoming the norm becauseit allows the reuse of functional unitsacross a variety of standards.

One of the key [remaining techni-cal hurdles] is achieving capacity gainsto users that are farther from the celltower, says YJ Kim, general managerof the infrastructure-processor group atCavium Networks. A heterogeneousnetwork consisting of macrocells andsmall cells somewhat solves this [prob-

lem] at a higher level. Once you peelthe onion, however, there is the issue ofinterference. The base stations need tobe capable of achieving error-free high

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throughput to all users that demandit. Kim adds that sophisticated inter-

ference-cancellation algorithms, whichdemand high processing power, canachieve that throughput. Throughputis important in both macrocells andsmall cell base stations. Effectively builtmulticore-base-station SOCs enablethese approaches without consum-ing much power, he says. Cavium isaddressing the needs of 4G with itsmulticore Octeon processors, whichtarget power management.

MEETING THE CHALLENGES

Systems implementing 4G involve amultitude of design challenges, includ-ing dealing with multiple channelbandwidths, transmission schemes foruplink and downlink, frequency- andtime-domain transmission modes, bat-tery-life management, and backwardcompatibility with 2 and 3G technolo-gies. To address the limited-bandwidth

issues, designers have developed carrieraggregation and MIMO techniques, but

these technologies, in turn, bring theirown challenges.

With the possibility of the emergenceof 20 LTE bands worldwide, the issueof coexistence also arises. Coexistencegives rise to a number of issues, includ-ing board area, antenna design, sensitiv-ity, configurability, and cost, accordingto RMCs Schlett. In response, RMChas designed its RF platform to supportseven LTE, five HSPA, and four GSMbands. These products underscore theneed for design-simulation tools and

robust virtual prototyping for analyzingthe real-time interaction between theprotocol stack and the modem.

Carrier aggregation requires devel-opers to pay more attention to con-trol channels, cell edge, power man-agement, spur management, andself-blocking, whereas MIMO designpresents interference issues, especial-ly on the terminal side, according toAgilents Suh. On the user-equipmentside of the link, designers are consider-

ing multistandard radios, which canhelp reduce the number of RF compo-nents by supporting multiple wirelesstechnologies on one chip.

Unlike with previous generations,however, 4G designs have many com-plex considerations, so designers havemore issues to address before moving toa prototype, says Suh. He points to toolssuch as Agilents SystemVue, which canhelp to overcome the challenges during4G user-equipment design before thespecifications are defined. The tool also

offers functional tests, such as a battery-

drain test that can help designers solvebattery issues using the terminals status

(sleep, standby, or call).Power-consumption issues also lead

to heat-dissipation problems, and theissue for 4G stems primarily from theneed for multiple CPU cores in the RFsection and the need to thermally man-age the baseband chip. Some designersare addressing the power issue by usingnew process technologies. For instance,process technologies are now at 28 nm,with 20 nm on the horizon. As theydesign new architectures, developersare finding that traditional spreadsheet-

based analysis is no longer enoughbecause it lacks sufficient support fordynamic-use case scenarios, accordingto Willems. Designers need simulation-based analysis of what-if scenarios.

Willems says that hardware- andsoftware-development engineers aremoving to prototyping as early as pos-sible, and virtual prototyping, whichgained favor with 3G design, hasbecome the mainstream approach assystems advance. High-performance

simulation is also critical for algorithmdesign in modems, which allows design-ers to explore alternatives and maintainstandards compliance. Synopsys offerssimulation and prototyping tools fromIP (intellectual property) and architec-ture to chip implementation (Figure 4).

WHATS NEXT?

Although much work remains, the pathto true 4G performance seems achiev-able, and the popularity of smartphonesand tablets is creating a huge market

demand for improvements. In the mean-


Figure 2 Traffic growth has exploded as manufacturers develop new mobile terminals. In 2000 (a), traffic included 50-kbps GPRS

(general-packet-radio service) and RTT (radio-transmission technology). By 2010, with approximately 500 million deployed smart-

phones, traffic had moved to 5- to 7-Mbps HSPA+and EVDO (b). By 2020, traffic will move at 1 Gbps (c), with LTE-A, 4 billion new

smartphones, 10 billion new smart devices, millions of new apps, and video- and cloud-based services (courtesy 4G Americas).

(c)(b)(a)

Figure 3 Renesas Mobile Corp has

released the SP2531 integrated triple-

mode LTE slim modem.

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time, the wireless industry continues totake defined steps toward the goals ofIMT-Advanced, leaning on the improve-ments from HSPA+ and evolving LTEto LTE-A. Although a disconnectionremains between the theoretical, such as88 MIMO, and the achievable, todays

wireless networks have significantlyhigher performance than their prede-cessors. Look for dramatic improvementsover the next two years. To address thespectrum crunch, you are likely to con-tinue to see interest in heterogeneousnetworks combining macrocell and

microcell deployments. Until blocks ofcontiguous spectra become available,however, you can expect to see morecreative design approaches to boostingdata rates and maintaining battery lifein next-generation mobile phones.EDN

REFERENCES1

Love, Janine, 2011: the year mobiletook over the world, EE Times RF and

Microwave Designline, Dec 15, 2011,

http://bit.ly/ymHvER.2 ITU global standard for international

mobile telecommunications IMT-

Advanced, http://bit.ly/f5FqtH.3 Rumney, Moray, Introducing LTE-

Advanced, EE Times RF and Micro-

wave Designline, Feb 5, 2011, http://

bit.ly/i4Fx6k.

You can reach JanineLove, senior editor, Test

& Measurement World,

and managing editor,

Test & Measurement

Designline,at janine.

[email protected].

Figure 4 The Synopsys LTE-A physical-layer-simulation library allows users to run tests

that the 3GPP standard documents specify.


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