第六版《电路与干扰接地与屏蔽指南》：电磁理论与设计实践

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《接地与屏蔽：电路与干扰》第六版是一本专门针对电子设计中电磁兼容（EMC）和电磁干扰（EMI）问题的权威指南。该书由Ralph Morrison撰写，版权归属于John Wiley & Sons, Inc.，2016年出版。本书将电磁理论基础与实际电路设计中的接地与屏蔽需求和技术相结合，旨在帮助电路设计工程师和技术人员理解和解决现代电子设计中遇到的各种干扰挑战。在第六版中，作者对原有的内容进行了更新，增加了关于通孔、场控制、电容器作为传输线的新材料，以及第一级能源源和使用只有两层的高速设计等主题。这些新增内容紧跟技术发展，帮助读者更好地理解如何处理高速信号传输中的噪声问题，特别是在多层板设计中。书中深入探讨了电路几何如何控制从直流到吉赫兹频率范围内的性能，强调了正确接地和屏蔽对于确保电路稳定性和抗干扰能力的重要性。作者还特别关注了在清洁电源系统中使用多屏蔽变压器的应用，并提供了有效的策略来应对模拟和数字电路中的噪声问题。作者还讲解了如何通过调整导体形状来优化性能，减少辐射，并降低硬件和系统对各种外部干扰的敏感性。这本书不仅适用于电路设计工程师，也对半导体设备行业的工程师具有参考价值。《接地与屏蔽：电路与干扰》第六版是一本实用且全面的工具书，它不仅涵盖了基本的电磁理论，还提供了最新的实践技巧和标准，有助于设计师们在复杂电磁环境中实现高效、可靠的电路设计。

k k

xiv PREFACE TO THE SIXTH EDITION

of my background and describe a few of my experiences to illustrate

why this basic physics is critical to an understanding of grounding and

shielding. So stay with me as I go back in time. I think the history is both

interesting and insightful.

ALPH MORRISONJuly 1, 2015

San Bruno, CA

k k

A HISTORICAL PERSPECTIVE INTO GROUNDING

AND SHIELDING

As a teenager, in 1940, I built my own crystal set. I remember connect-

ing the circuit common (ground) to a water pipe some 20 ft away from

my set. The conductor went out through a hole in a wire mesh window

screen. I found out that routing the antenna made a difference, so I kept

trying different approaches to receive more radio stations. Little did I

know of the complex nature of coupling to a transmitted radio signal.

This was my rst association with grounding (making an earth connec-

tion).

My interest in electronics extended to how a radio works and before

long I was spending time in the neighborhood radio repair shop, where

I learned how to test vacuum tubes. I was given a discarded radio

as a present because the plastic case had been smashed. I freed the

speaker cone and I had my own working radio. The radio had a ground

clip that suggested that a grounding wire might improve reception.

As a teenager, I spent time with several classmates that had acquired

the skills needed to be amateur radio operators. They were always

discussing their antennas and the grounding of their transmitters.

I borrowed a copy of the ARRL handbook to get some idea of their

hobby and what it meant to be a ham radio operator. I was an observer

as I did not have the resources to enter this hobby.

I was drafted into the army in WW2 at age 18. Eventually, I became a

radio repairman in the infantry and xed radios in Patton’s third army as

it crossed Germany. The radios I serviced had no connections to earth

as they had to be very mobile. I never gave grounding a second thought.

After I returned home, the GI bill gave me the opportunity to go to

Caltech and get a BS degree in physics. I remember taking courses in

electricity and magnetism, not realizing the impact this subject would

have on my future. I remember solving differential equations and fum-

bling through systems of units. I was introduced to Maxwell’s equations.

At the time, I had no way of assigning signicance to this information.

It was as if I was reading the rst paragraph of many different chapters

in many different books.

k k

xvi A HISTORICAL PERSPECTIVE INTO GROUNDING

After graduation in 1949, I started working as an electronics engi-

neer at a company called Applied Physics Corporation located in

Pasadena, CA. My rst boss was George W. Downs, a well-respected

entrepreneur. During the war, he had worked as a high-level consultant

and was associated with the Atomic Energy Commission. I had a lot

to learn. The company products included oscillographs, electrometers,

and spectrophotometers. I was impressed with the beautiful packaging

and the fact they were so well respected by their customers. All of their

products used vacuum tubes and I saw “grounding” for the rst time.

They explained to me how they used a grounding stud that collected all

the common leads used in the instrument. This included the metal case,

the equipment ground, the centertap on the secondary of the power

transformer, the transformer shield, and the various circuit commons.

There was no explanation given to me as to why this was the best

solution. I was told that the order used in placing these conductors on

the stud was important, and they had found a solution that made the

instrument free of noise. In later years, this star-grounding congura-

tion would appear in very unusual places. At the time, I had no basis

to be critical of star-grounding methods. The products worked well

and engineers with years of experience had spoken. Do not mistake

me. A grounding stud was a valid approach to building this product.

It is not however a solution to grounding in general. Asking questions

did not yield useful answers and I did what everyone else did – I used

common sense, I copied the procedures used in other products, and I

experimented when I could. I was a part of the work force.

My rst assignment as an engineer was to design a dc instrumentation

amplier. This type of instrument was needed in conditioning signals

from strain gages, position sensors, and thermocouples. I was shown a

circuit approach that had been developed by RCA that used a mechan-

ical chopper to correct for dc drift. I was soon immersed in regulated dc

power supplies, transformers, laments, tube type selections, and feed-

back. I managed a design one channel of dc amplier including a power

supply that weighed over 70 lb. Do not forget that vacuum tubes take

several hundred volts to operate and these voltages had to be very care-

fully regulated. When I look back at those early days, I can see how

far electronic instrumentation has come and in particular how much I

had to learn. At the beginning, there were no shielded transformers,

feedback techniques were primitive, noise and hum were problems, and

there was a limited understanding of signal isolation. There were sele-

nium rectiers that did not work very well. Dc ampliers and vacuum

tubes are a denite mismatch. In those days, that was all there was.

k k

A HISTORICAL PERSPECTIVE INTO GROUNDING xvii

The techniques of differential amplication and common-mode rejec-

tion had not yet entered my understanding. My boss was learning from

me. We had to start somewhere.

The period after WW2 saw the growth of the aerospace industry. I was

project engineer on several analog computers that were sold to Dou-

glas, Northrup, and Lockheed. These computers helped in the design

of the rst commercial jet aircraft. The computer design was based on

work done at Caltech and included some dc ampliers I had developed.

After this project was completed, our instrumentation group was sold to

a company in the transformer business. Our rst project was to develop

a high-speed recording oscillograph. The photographic paper speed in

this machine was over 200 ft/s. Needless to say, Kodak appreciated our

business. Getting the paper up to speed in milliseconds was no small

task.

I designed the ampliers that drove the galvanometers. I found

out about the limitations imposed by using a common power supply to

power a group of single-ended instruments. It was obvious that there

was a lot to be gained by using a separate power supply for each signal

channel. To meet this challenge, I began working on new techniques to

reduce cost and size and avoid the use of common supplies. I invented a

method of using AC coupling and a parallel feedback network to make

a dc instrument. The company rejected my proposals for a new prod-

uct line. I recognized the relevance of my new ideas, and I talked with

two other engineers to leave and form a new company. George actually

helped us make the transition.

The new company was called Dynamics Instrumentation. We manu-

factured instrumentation ampliers for aerospace. The product line was

based on the design ideas I had proposed. I could now contact users

directly and I began to understand their dilemma. In rocket test stands,

vacuum tube electronics had to be mounted in a blockhouse hundreds

of feet away from the rocket engines and any sensors. This meant long

input cables had to carry millivolt signals between structures. This raised

issues of where to connect the input and output signal cable shields. I

had some ideas on how to handle these issues and wrote some articles on

the subject. I passed these articles out to potential customers. I was sur-

prised at the reception these articles received. It was obvious there was

very little information available on where to connect shields on large

systems. Years later, engineers would pull these articles out of their les

to show them to me. Now, when I look back at that period, I too had a

The mechanical engineer was William McLellan also a Caltech graduate. He was the

engineer that took the challenge from Dr. Richard Feynman to build a working motor

1/64 of an inch on a side. This motor is on exhibit at Caltech.

k k

xviii A HISTORICAL PERSPECTIVE INTO GROUNDING

lot to learn. I could tell that this was a difcult problem and the size of a

company had nothing to do with understanding the issues. Rocketdyne

was interested in designing rocket engines not where to connect shields.

I found out that interference resulted from the ow of power

current in input conductors. Remember there were hundreds of volts

on the secondary coils of the power transformers. Simply put, I was

the culprit. This current could be limited by the use of transformer

shields. I built my own power transformers and played with the

shielding until I understood what was happening. My competition

built a carrier-type differential dc amplier that used a mechanical

modulator/demodulator and a multishielded input transformer. Being

differential allowed input and output commons to be grounded sepa-

rately without creating a ground loop. I tried to duplicate this approach,

but I had problems building the input transformers. Instead, I built a

postmodulator/demodulator around a postcarrier transformer using

newly available transistors and managed in effect to build a wide-band

differential amplier. The mechanical modulator approach had 100 Hz

bandwidth and the post-transistor modulator instrument I built had

10 kHz bandwidth. I had a new product and I had a new denition of

the word differential as applied to instrument amplier.

I needed three shields in the power transformers I used in this design.

I got a company in San Diego to build them for me. I noticed one day in

an electronics magazine that this company was offering what it called

“isolation” transformers with four shields. On my next visit, I asked

the company owner what his recommendation was for using a fourth

shield. He did not know. I then asked why he offered it. The answer

was simple: “They sell better.” I had aided in the formation of a new

business based on adding multiple shields to distribution transformers.

I had used shields to make one instrument work and the industry had

decided to use these same methods to “clean up” systems. To me, they

had a solution looking for a problem. To me, the multishield solution

only worked for one instrument. Later, I would take a broader view of

this shielding. I also saw marketing at work.

I began to feel I had something important to offer other engineers.

I saw a pattern in how shields worked and how they controlled the ow

of interfering current. It was all tied to the electrostatics I had studied in

school. So in the days of ribbon typewriters and carbon paper I started

the task of writing a book. I showed the manuscript to Dr Ernst Guille-

man of MIT and he was enthusiastic. I then submitted a manuscript to

George Novotny the editor at John Wiley, where, much to my surprise, it

was accepted for publication. The rst edition of Grounding and Shield-

ing was published in 1967.

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