Controlling Radiated Emissions by Design

301 Pages·1992·11.53 MB·English

by  Michel Mardiguian (auth.)

Controlling
Radiated Emissions by
Design
Contro Hing
Radiated Emissions by
Design
Michel Mardiguian
SPRINGER-SCIENCE+BUSINESS MEDIA, B.Y.
Library of Congress Cataloging-in-Publication
Mardiguian, Michel.
Controlling radiated emissions by design / Michel Mardiguian.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4613-6356-9 ISBN 978-1-4615-3102-9 (eBook)
DOI 10.1007/978-1-4615-3102-9
1. Electronic circuits--noise. 2. Elecromagnetic interference.
3. Electronic circuit design. 4. Sheilding (Electricity).
I. Title.
TK7867.5.M37 1992 92-10392
621.382'24--dc 20 CIP
Copyright © 1992 Springer Science+Business Media New York
Originally published by Van Nostrand Reinhold Inc. 1992
Softcover reprint ofthe hardcover 1st edition 1992
All rights reserved. No part of this publication may be reproduced, stored in a retrieval
system or transmitted in any form or by any means, mechanical, photo-copying, recording,
or otherwise, without the prior written permission of the publisher, Kluwer Academic
Publishers, 101 Philip Drive, Assinippi Park, NorweU, Massachusetts 02061
Printed on acid-free paper.
Contents
Foreword ix
1. Generalities on Radiated Interference 1
1.1 The Problem of Radiated EMI 1
1.2 Basic Understanding of Radiated EMI 2
1.3 EMI Tenninology and Units 4
1.4 U.S. and Worldwide Regulatory Approach Against Radiated EMI 7
2. Electric and Magnetic Fields from Simple Circuit Shapes 16
2.1 Fields Radiated by a Loop 17
2.2 Fields Radiated by a Straight Wire 20
2.3 Extension to Practical, Real-Life Circuits 24
2.4 Differential-Mode Radiation from Simple Circuits 29
2.5 Common-Mode Radiation from External Cables 35
3. Fields Radiated by Nonsinusoidal Sources 48
3.1 Frequency Spectrum, and Radiation from Periodic Pulses 48
3.2 Spectrum and Radiation from Broadband Sources 56
3.3 Random versus Periodic Spectra 60
4. General Strategy for Designing a Low-Radiation Product 64
4.1 Basic System Decisions that Impact EMI Control 64
4.2 Design Control Areas for Radiated Emission Reduction 66
4.3 Design Milestones for Radiated EMI Control 67
S. ControUing Radiated Emissions at the Chip and Integrated Circuit
Level 73
5.1 Logic Families 73
5.2 Calculation of an Ideal Decoupling Capacitor 78
5.3 Influence of the IC Package 82
5.4 Summary of Radiation Control at the Chip and IC Level 83
6. Printed Circuit Board Design 87
6.1 Board Zoning 88
6.2 Single-Layer Boards 88
6.3 Multilayer Boards 99
6.4 Crosstalk 107
v
vi Controlling Radiated Emissions by Design
6.5 Impedance Matching 112
6.6 Card Connector Pin Assignment 116
6.7 Grounding ofOv Reference to Chassis 120
6.8 Summary of Radiation Control at PCB Level 123
7. Emission Control in Mother Boards and Backplanes 124
7.1 Wire-Wrapped Backplanes 126
7.2 Single or Multilayer Mother Boards with Vee and Ground
Planes 126
7.3 Crosstalk and Impedance Matching 126
7.4 Connector Areas at Backplane Interfaces 128
8. Controlling Radiated Fields from Switch-Mode Power Supplies 130
8.1 Basic Radiating Sources 131
8.2 Effect of Actual Current Wave Forms 135
8.3 Packaging and Circuit Layout 135
8.4 Shielding the Power Supply Module 144
8.5 Effect of the Power Supply Filter on Radiated EMI 146
9. Reducing Radiated EMI via Internal Cabling and Packaging 152
9.1 Card-ta-Card and Backplane Interconnects 153
9.2 Internal Coaxial and Shield Cables 155
9.3 Some Hidden Radiating Antennas 160
9.4 Internal Connection ofO Reference and Corresponding Ground
y
Loops 163
9.5 I/O Connector Areas 165
9.6 A Few Other Radiated EMI Sources 179
10. Box Shielding 180
10.1 How to Determine Box Attenuation Requirements 181
10.2 Some Shielding Basics: Shielding Effectiveness of Materials 184
10.3 Shielding Effectiveness of Conductive Plastics 189
10.4 Field Attenuation through Apertures 192
10.5 Effect of Source Proximity on Aperture Leakage 197
10.6 Methods of Leakage Reduction and Aperture Treatment 198
10.7 Specially Hardened Equipment Housings 215
10.8 Application Example: Box Design for a Given SE Objective 218
10.9 Summary of Radiation Control via Box Shielding 220
11. Controlling Radiation from External Cables 221
11.1 Advantages of Balanced Interfaces 221
11.2 Line Balancing Devices 222
11.3 Reducing CM Radiation by Ferrite Loading 228
Contents vii
11.4 Reducing OM Radiation by Twisting 235
11.5 Reducing Cable Radiation by Shielding 237
11.6 Eliminating Cable Radiation by Fiber Optics 255
12. Principal Radiated Emission Specifications and Test Methods 256
12.1 MIL-Standards 461-C and 462 256
12.2 CISPR International Limits, Test Instrumentation and Methods 259
12.3 FCC Part 15-J 261
12.4 European Norm (EN) 55022 261
12.5 German VDE 871 261
12.6 German VDE 875 and EN 55014 263
12.7 Japanese Voluntary Council for the Control of Interference
(VCCI) 263
12.8 FCC Part 18 263
12.9 RTCAJDO-160.B 265
13. Troubleshooting Radiated EMI Problems 267
13.1 Cable Radiation vs. Box Radiation in Specification
Compliance 267
13.2 Strategy when a Product Fails Radiated Emission Tests: Quantifying
the dB Reduction 268
13.3 Approximation of Radiated RFI levels from 110 Cable CM Currents
(VHF Region) 275
Appendix A: The Modified Dipole Model 279
Appendix B: Some Validation Results Supporting the Simplified
Radiation Model 285
Index 291
Foreword
Something over a year ago, I was fortunate enough to preview another VNR
book, Controlling Conducted Emissions by Design, by John Fluke. My
assessment at the time was that Mr. Fluke had written a very good and useful
volume, its only flaw being that it focused on just half of the EMI emissions
problem. This, of course, was also its strength; although radiated and conducted
emissions do not exist in separate worlds, it can be useful, at least as a point of
departure, to look at them as distinct phenomena. Expanding the scope of the
conducted emissions book therefore would have served mostly to dilute its
purpose and compromise its clarity.
After some informal discussions with the publisher on that subject, it was de
cided to correct the sin of omission by recruiting an author for a companion vol
ume, to be titled Controlling Radiated Emissions by Design. I am gratified to have
played a minor role in making that happen.
Many EMC engineers with whom I have worked over the years are capable of
writing a good radiated emissions book, but few can match Michel Mardiguian's
combination of practical engineering experience and proficiency with the pen. On
the engineering side, he has worked on such diverse projects as the Mirage V ver
tical-takeoff jet fighter, computer-controlled PBX systems and, most recently, the
renowned tunnel that stretches beneath the English channel to join England with
France.
In terms of academic credentials, the author has written or coauthored at least
half a dozen earlier books, including a highly durable and well respected one on
electrostatic discharge. He has taught the principles of electromagnetic compati
bility throughout the United States and Europe, and IEEE symposium records
contain many of his short works.
Michel's books typically have several characteristics:
1. They are aimed at practical applications but provide enough theoretical ma
terial to support the suggested design and retrofit solutions.
2. They rely heavily on visual material, allowing the reader to "see" the EMI
problems and solutions.
3. They omit everything that is not essential to the subject under scrutiny.
This third quality is less common that one might expect-many authors feel an
irresistible urge to stuff everything they know into one volume. But Michel avoids
ix
x Controlling Radiated Emissions by Design
egocentric dissertations on marginal subjects, preferring to approach each book
simply as ajob that needs to be done.
With this book, the author follows his usual pattern but with perhaps a greater
refinement. Mathematical material is largely confined to two chapters, allowing
the book to look mostly at real-world applications. More than 175 tables and illus
trations provide information in a highly accessible format. This type of book is dif
ficult for the editors and expensive for the publisher, but the reader should benefit.
Some subjects (e.g., EMC testing) are covered very briefly, but the reader is re
ferred to other sources of pertinent information.
It would be premature and presumptuous to call this book a classic in EMC lit
erature, but it does display some of the characteristics of enduring works. Control
ling Radiated Emissions by Design constitutes a cohesive and clear examination
of the subject and is perhaps the author's best work to date.
Jeffrey K. Eckert
1. K. Eckert & Company
Gainesville, Virginia
1
Generalities on Radiated
Interference
1.1 The Problem of Radiated EMI
1.2 Basic Understanding of Radiated EMI
1.3 EMI Terminology and Units
1.4 U.S. and Worldwide Regulatory Approach Against Radiated EMI
1.1 THE PROBLEM OF RADIATED EMI
During the first part ofthe twentieth century, electromagnetic interference (EMI)
was primarily a concern for telecommunications via wire and radio. In these spe
cific engineering communities, highly qualified engineers developed quite sophis
ticated analytical approaches to predict interference levels, taking into consider
ation the sources' parameters, the propagation media and the sensitivity of the
pertinent telephone or radio receivers. The typical sources of EMI until the 1960s
were natural atmospheric noise, motor commutators, fluorescent lights, automo
bile ignition systems and 50/60 Hz overhead lines (unintentional sources), plus
jamming by other authorized (and sometimes unauthorized) radio transmitters.
The results of such interference ranged from a mere annoyance, such as poor
telephone and radio audibility and disrupted TV reception, to a serious danger if
the interfered transmission was critical, as in the case of an emergency service, an
air navigation system, etc.
But let us say that, with proper handling ofthe frequency allocations and some
rather simple constraints applied at national and international levels, the problem
was acceptably under control. The "policing of the air waves" was a manageable
task.
2 Controlling Radiated Emissions by Design
In the latter half of the century, an incredible proliferation of new RF sources
has developed, including all computing and digitally operated devices (today it is
very difficult to find a simple electrical home appliance that does not incorporate
at least an 8-bit microprocessor), medical electronics, power switchers, machine
tools, remote control systems, local area networks (LANS), etc. Most of these de
vices produce signal trains of discrete frequencies that can be a stable, continuous
threat for radio communication.
At the same time, the legitimate users of the radio spectrum have grown in num
ber and types of service. From a limited, identified number of radio, TV, naviga
tion and safety services before 1950, the number of RF spectrum users is still in
creasing, comprising satellite data transmission, telemetry and radio telescopes,
CB and cellular telephones, vehicle positioning systems, etc.
As the number and variety of potential offenders increases, so does the number
and variety of potential victims, and all growths are approximately exponential.
Accordingly, the risk of interference increases astronomically, and it is little won
der that specifications and regulations have become more and more precise and
stringent in an attempt to hold the problem to a manageable scale.
Equally serious is the problem of a system interfering with itself. This occurs
due to ignorance or negligence regarding the EMI problem created by multiple
sources and victims packed in close proximity.
Therefore, the subject of controlling interference, and more specifically radi
ated interference (which is the focus of this book), becomes both a matter of sat
isfactory performance of an equipment as well as its compliance with the non
interfering norms of the military or civilian world. EMI control must be incorpo
rated in the design stage of a product rather than postponed until the day of the
prequalification or final acceptance testing. The latter invariably results in late
and expensive fixes and retrofits.
This book will provide the necessary background and step-by-step procedures
to design a product that neither radiates undesired signals in excess of the appli
cable specifications nor interferes with itself or other equipments in its vicinity.
This desirable condition is known as electromagnetic compatibility (EMC).
1.2 BASIC UNDERSTANDING OF RADIATED EM!
Three players are needed for the interference act:
1. a source, or emitter
2. a victim, or receiver
3. a coupling path between the two