Table of Contents

Title Page

Preface

A HISTORICAL PERSPECTIVE INTO GROUNDING AND SHIELDING

1 VOLTAGE AND CAPACITORS

1.1 INTRODUCTION
1.2 CHARGES AND ELECTRONS
1.3 THE ELECTRIC FORCE FIELD
1.4 FIELD REPRESENTATIONS
1.5 THE DEFINITION OF VOLTAGE
1.6 EQUIPOTENTIAL SURFACES
1.7 THE FORCE FIELD OR E FIELD BETWEEN TWO CONDUCTING PLATES
1.8 ELECTRIC FIELD PATTERNS
1.9 THE ENERGY STORED IN AN ELECTRIC FIELD
1.10 DIELECTRICS
1.11 THE D FIELD
1.12 CAPACITANCE
1.13 MUTUAL CAPACITANCE
1.14 DISPLACEMENT CURRENT
1.15 ENERGY STORED IN A CAPACITOR
1.16 FORCES IN THE ELECTRIC FIELD
1.17 CAPACITORS
1.18 DIELECTRIC ABSORPTION
1.19 RESISTANCE OF PLANE CONDUCTORS

2 MAGNETICS

2.1 MAGNETIC FIELDS
2.2 AMPERE'S LAW
2.3 THE SOLENOID
2.4 FARADAY'S LAW AND THE INDUCTION FIELD
2.5 THE DEFINITION OF INDUCTANCE
2.6 THE ENERGY STORED IN AN INDUCTANCE
2.7 MAGNETIC FIELD ENERGY IN SPACE
2.8 ELECTRON DRIFT
2.9 THE MAGNETIC CIRCUIT
2.10 A MAGNETIC CIRCUIT WITH A GAP
2.11 SMALL INDUCTORS
2.12 SELF- AND MUTUAL INDUCTANCE
2.13 TRANSFORMER ACTION
2.14 HYSTERESIS AND PERMEABILITY
2.15 EDDY CURRENTS

3 DIGITAL ELECTRONICS

3.1 INTRODUCTION
3.2 THE TRANSPORT OF ELECTRICAL ENERGY
3.3 TRANSMISSION LINES – INTRODUCTION
3.4 TRANSMISSION LINE OPERATIONS
3.5 TRANSMISSION LINE FIELD PATTERNS
3.6 A TERMINATED TRANSMISSION LINE
3.7 THE UNTERMINATED TRANSMISSION LINE
3.8 A SHORT CIRCUIT TERMINATION
3.9 THE REAL WORLD
3.10 SINE WAVES VERSUS STEP VOLTAGES
3.11 A BIT OF HISTORY
3.12 IDEAL CONDITIONS
3.13 REFLECTION AND TRANSMISSION COEFFICIENTS
3.14 TAKING ENERGY FROM AN IDEAL ENERGY SOURCE
3.15 A CAPACITOR AS A TRANSMISSION LINE
3.16 DECOUPLING CAPACITORS AND NATURAL FREQUENCIES
3.17 PRINTED CIRCUIT BOARDS
3.18 TWO-LAYER LOGIC BOARDS
3.19 VIAS
3.20 THE TERMINATION OF TRANSMISSION LINES
3.21 ENERGY IN THE GROUND/POWER PLANE CAPACITANCE
3.22 POYNTING'S VECTOR
3.23 SKIN EFFECT
3.24 MEASUREMENT PROBLEMS: GROUND BOUNCE
3.25 BALANCED TRANSMISSION
3.26 RIBBON CABLE AND CONNECTORS
3.27 INTERFACING ANALOG AND DIGITAL CIRCUITS

4 ANALOG CIRCUITS

4.1 INTRODUCTION
4.2 INSTRUMENTATION
4.3 HISTORY
4.4 THE BASIC SHIELD ENCLOSURE
4.5 THE ENCLOSURE AND UTILITY POWER
4.6 THE TWO-GROUND PROBLEM
4.7 INSTRUMENTATION AND THE TWO-GROUND PROBLEM
4.8 STRAIN-GAUGE INSTRUMENTATION
4.9 THE FLOATING STRAIN GAUGE
4.10 THE THERMOCOUPLE
4.11 THE BASIC LOW-GAIN DIFFERENTIAL AMPLIFIER (FORWARD REFERENCING AMPLIFER)
4.12 SHIELDING IN POWER TRANSFORMERS
4.13 CALIBRATION AND INTERFERENCE
4.14 The Guard Shield Above 100 kHz
4.15 SIGNAL FLOW PATHS IN ANALOG CIRCUITS
4.16 PARALLEL ACTIVE COMPONENTS
4.17 FEEDBACK STABILITY – INTRODUCTION
4.18 FEEDBACK THEORY
4.19 OUTPUT LOADS AND CIRCUIT STABILITY
4.20 FEEDBACK AROUND A POWER STAGE
4.21 CONSTANT CURRENT LOOPS
4.22 FILTERS AND ALIASING ERRORS
4.23 ISOLATION AND Dc-TO-DC CONVERTERS
4.24 CHARGE CONVERTER BASICS
4.25 DC POWER SUPPLIES
4.26 GUARD RINGS
4.27 THERMOCOUPLE EFFECTS
4.28 SOME THOUGHTS ON INSTRUMENTATION

5 UTILITY POWER AND FACILITY GROUNDING

5.1 INTRODUCTION
5.2 HISTORY
5.3 SEMANTICS
5.4 UTILITY POWER
5.5 THE EARTH AS A CONDUCTOR
5.6 THE NEUTRAL CONNECTION TO EARTH
5.7 GROUND POTENTIAL DIFFERENCES
5.8 FIELD COUPLING TO POWER CONDUCTORS
5.9 NEUTRAL CONDUCTORS
5.10 k Factor in Transformers
5.11 POWER FACTOR CORRECTION
5.12 UNGROUNDED POWER
5.13 A REQUEST FOR POWER
5.14 EARTH POWER CURRENTS
5.15 LINE FILTERS
5.16 ISOLATED GROUNDS
5.17 FACILITY GROUNDS – SOME MORE HISTORY
5.18 GROUND PLANES IN FACILITIES
5.19 OTHER GROUND PLANES
5.20 GROUND AT REMOTE SITES
5.21 EXTENDING GROUND PLANES
5.22 LIGHTNING
5.23 LIGHTNING AND FACILITIES
5.24 LIGHTNING PROTECTION FOR BOATS AND SHIPS
5.25 GROUNDING OF BOATS AND SHIPS AT DOCK
5.26 AIRCRAFT GROUNDING (FUELING)
5.27 GROUND FAULT INTERRUPTION (GFI)
5.28 ISOLATION TRANSFORMERS
5.29 GROUNDING AND THE PACIFIC INTERTIE
5.30 SOLAR WIND

6 RADIATION

6.1 HANDLING RADIATION AND SUSCEPTIBILITY
6.2 RADIATION
6.3 SINE WAVES AND TRANSMISSION LINES
6.4 APPROXIMATIONS FOR PULSES AND SQUARE WAVES
6.5 RADIATION FROM COMPONENTS
6.6 THE DIPOLE ANTENNA
6.7 WAVE IMPEDANCE
6.8 FIELD STRENGTH AND ANTENNA GAIN
6.9 RADIATION FROM LOOPS
6.10 E-FIELD COUPLING TO A LOOP
6.11 RADIATION FROM PRINTED CIRCUIT BOARDS
6.12 THE SNIFFER AND THE ANTENNA
6.13 MICROWAVE OVENS

7 SHIELDING FROM RADIATION

7.1 CABLES WITH SHIELDS
7.2 LOW-NOISE CABLES
7.3 TRANSFER IMPEDANCE
7.4 WAVEGUIDES
7.5 ELECTROMAGNETIC FIELDS OVER A GROUND PLANE
7.6 FIELDS AND CONDUCTORS
7.7 CONDUCTIVE ENCLOSURES – INTRODUCTION
7.8 COUPLING THROUGH ENCLOSURE WALLS BY AN INDUCTION FIELD
7.9 REFLECTION AND ABSORPTION OF FIELD ENERGY AT A CONDUCTING SURFACE
7.10 INDEPENDENT APERTURES
7.11 DEPENDENT APERTURES
7.12 HONEYCOMBS
7.13 SUMMING FIELD PENETRATIONS
7.14 POWER LINE FILTERS
7.15 BACKSHELL CONNECTORS
7.16 H-FIELD COUPLING
7.17 GASKETS
7.18 FINGER STOCK
7.19 GLASS APERTURES
7.20 GUARDING LARGE TRANSISTORS
7.21 MOUNTING COMPONENTS ON SURFACES
7.22 ZAPPERS
7.23 SHIELDED AND SCREEN ROOMS

APPENDIX A

Further Reading

Index

End User License Agreement

List of Illustrations

Chapter 1

Figure 1.1 The force field lines around a positively charged conducting sphere
Figure 1.2 Equipotential surfaces around a charged sphere
Figure 1.3 The force field between two conducting plates with equal and opposite charges and a spacing distance h
Figure 1.4 The electric field pattern of a circuit trace over a ground plane
Figure 1.5 The electric field pattern around two traces over a ground plane
Figure 1.6 Field configurations around a shielded conductor
Figure 1.7 The electric field pattern in the presence of a dielectric
Figure 1.8 The mutual capacitances between several traces on a ground plane
Figure 1.9 A capacitor driven from a constant current source
Figure 1.10 A typical wrap and foil capacitor

Chapter 2

Figure 2.1 The H field around a current-carrying conductor
Figure 2.2 The H field around a solenoid
Figure 2.3 A voltage induced into a moving coil
Figure 2.4 The inductance of round copper conductors
Figure 2.5 A coil wound on a toroidal core of magnetic material
Figure 2.6 A magnetic circuit with an air gap
Figure 2.7 The flux pattern for a square wave voltage applied to a transformer coil
Figure 2.8 A core with two coils that form a simple transformer. (a) Assembly, (b) symbol, and (c) winding arrangement
Figure 2.9 The equivalent circuit of a transformer
Figure 2.10 Typical hysteresis curves
Figure 2.11 Ferrite cup-core construction

Chapter 3

Figure 3.1 The electric and magnetic fields associated with a flashlight
Figure 3.2 A battery, a switch, and a transmission line
Figure 3.3 (a, b) The E and H field patterns around transmission lines
Figure 3.4 The wave associated with a transmission line terminated in its characteristic impedance
Figure 3.5 The voltage waveforms on an ideal open circuit transmission line for a step voltage
Figure 3.6 (a, b) The staircase current pattern for a short circuit termination of a transmission line
Figure 3.7 Waves that supply energy to a resistor over an impedance matching transmission line
Figure 3.8 The voltage at a termination resistor when there is a mismatch of impedances
Figure 3.9 A via geometry
Figure 3.10 Rise times and the reflections from an unterminated transmission line
Figure 3.11 Poynting's vector for parallel conductors carrying power
Figure 3.12 The termination of a balanced transmission line on a circuit board

Chapter 4

Figure 4.1 Parasitic capacitances in a simple circuit. (a) Field lines in a circuit, (b) mutual capacitance diagram, and (c) circuit representation
Figure 4.2 Grounding the shield to limit feedback
Figure 4.3 (a) The problem of bringing one lead out of a shielded region. Unwanted current circulates in the signal lead 2. (b) The E field circulates current in the shield, not in the signal conductor.
Figure 4.4 A power transformer added to the circuit enclosure
Figure 4.5 The two-circuit enclosures used to transport signals between grounds
Figure 4.6 The basic strain-gauge circuit
Figure 4.7 The low-gain differential amplifier applied to the two-ground problem
Figure 4.8 The basic low-gain differential amplifier
Figure 4.9 The single shield applied to a power transformer
Figure 4.10 The RC bypass on the input guard shield
Figure 4.11 Adding suppression resistors to parallel circuit elements
Figure 4.12 The basic feedback circuit
Figure 4.13 An LR-stabilizing network
Figure 4.14 Feedback around a power stage
Figure 4.15 Using a second transformer to isolate switching noise
Figure 4.16 A basic charge amplifier
Figure 4.17 The resistor feedback arrangement to control the low-frequency response

Chapter 5

Figure 5.1 Normal-mode and common-mode field coupling
Figure 5.2 The coupling in a transformer resulting from neutral voltage drop
Figure 5.3 Filter current flowing in signal interconnections
Figure 5.4 Typical ground plane in an electronic installation
Figure 5.5 A single-phase isolation transformer. (a) One shield, (b) two shields, and (c) three shields

Chapter 6

Figure 6.1 The harmonics that make up a square wave
Figure 6.2 The harmonics of a square wave plotted on logarithmic scales
Figure 6.3 The harmonics that make up a square wave with a finite rise time
Figure 6.4 The harmonics of a square with finite rise time plotted on logarithmic scales
Figure 6.5 The frequency spectrum for repetitive short pulses
Figure 6.6 The frequency spectrum of a single pulse with a finite rise time
Figure 6.7 A half-dipole antenna
Figure 6.8 The radiated field from a conducting loop
Figure 6.9 Electric field coupling to a pair of conductors
Figure 6.10 A sniffer and a test antenna

Chapter 7

Figure 7.1 (a, b) Characteristic impedance of a coaxial geometry
Figure 7.2 The characteristic impedance of parallel conductors
Figure 7.3 Transfer impedance test for a coaxial cable
Figure 7.4 The transfer impedance for a few standard cables
Figure 7.5 Diverting a magnetic field
Figure 7.6 The location of power conductors and a line filter
Figure 7.7 Methods of terminating the braided shield on a cable
Figure 7.8 A guard gasket applied to a transistor

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Preface to the Sixth Edition

Six editions of a book that spans 50 years is surely unique. I want to thank John Wiley for staying with me for all these decades. I want to thank Brett Kurzman, my new editor, for getting me a contract. I want to thank my wife Elizabeth for her continuous support. I want to thank all the readers that have supported me over the years. If it had not been for the urging of Dan Beeker of NXP Semiconductor, there would not have been a fifth edition. For this reason, I owe him a “thank you” for making a sixth edition possible. I have been puzzling how to make this edition more effective and I feel my opening statements are key. I need to tell the story so that the reader will appreciate my approach.

There are many meanings to the words grounding and shielding. To an English speaker, the nonengineering application of the word “ground” can include such diverse usage as coffee grounds, grounds for dismissal, playgrounds, ground round, or ground floor. The nonengineering use of shield can include such topics as windshield, police badge, metal armor, or protective clothing. In an electrical sense, ground can mean earth, the minus side of a battery, the conducting plane on a circuit board, the neutral power conductor, or a metal cabinet. People involved with electricity often associate these words with protection against electrical interference. The book title is intended to convey this meaning. Each reader of this book will start with a unique set of experiences associated with these words. I want to broaden that experience.

I have been involved in electrical grounding and shielding for over 50 years. My understanding comes from my experiences, my interests, and from my education. I have rewritten this book every 10 years since 1967 because the electrical world keeps changing. Also, I keep learning and the books do sell. Grounding and Shielding is an important topic as it relates to both cost and performance in about every aspect of our modern technology. The subject is difficult to present for many reasons. First, it is related more closely to conductor geometry than it is to circuit content. Next, a lot of the information that is passed on through usage is simply lore and some of it is wrong or misleading. This means that often engineers have preconceived ideas and need to do some unlearning to get things straight. In some cases, the grounding rules a user must follow are a part of a code or a regulation that leaves no choices. When the rules are printed on fancy paper, it is easy to assume they are valid. If the rules are in error, arguing against the establishment can be very frustrating. Unfortunately, not all rules are effective or practical. And finally, the subject is not taught in schools and engineers are often on their own to find answers. I have also found that quality control people will follow written rules rather than the opinion of one outside engineer or author. They respect authority, which is what they are expected to do. I have had some polite arguments that have lasted years, where my viewpoint keeps being questioned. From this fact alone, I know just how ingrained some viewpoints can become.

The subject of grounding and shielding comes up in most designs. Because it is not an exact science, there can be many opinions as to where to connect shields and reference signals. Some approaches are lore and are passed on by copying past designs or by word of mouth. In most cases, there is no simple test that tells if a viewpoint is valid. We may know how to test a piece of hardware but testing a building is another matter. There is an important question that must be asked. What measurements would you like to make? Where do I put my voltage probes? Even if tests could be made, making changes to a large system can be very expensive. In many cases, the ideas used in a design are valid but over some limited range. A person with a misconception may find it difficult to accept a different explanation. This is especially true when many different opinions have been expressed. I find that for good reason, engineers are very skeptical about an explanation that suggests a new viewpoint. They do not know what or whom to believe. Another problem is that the engineering idiom is constantly changing and sometimes valid explanations fail to communicate. The subject lies somewhere between trade practices and physics and this is a wide separation. It is a subject area that does not fit into academia. To some managers, grounding seems like a job for a technician. In reality, it is often a very sophisticated and complex issue. For these and many other reasons, it is time to write a sixth edition. I want to try to get the message across for today's designers. As much as possible, I want to keep opinions to a minimum and I want to focus on connecting this subject to basic principles. I want to use physics as the basis for explanations but without getting too mathematical.

I have taken what I feel is a unique position in discussing grounding and shielding. Circuit theory leaves the distinct impression that conductors carry signals. The fact is that conductors guide the flow of field energy and this field energy can carry signals, interference, and operate components. Nature does not distinguish between these three functions. We definitely need circuits to describe our intentions. We need circuit theory to analyze these circuits. We need to apply basic physics when circuit theory is not sufficient. We have to keep power, signals, and interference separated because nature is not going to offer any help. We need to appreciate that nearly all electrical activity takes place in the spaces between conductors. It is the intent of this book to clearly point out how this very key idea can solve problems. This field transport idea is covered in physics courses. The connection between these ideas and practical designing is usually missing in textbooks and in the classroom. The arrangement of the spaces between conductors can keep various fields separated. This control of conductor geometry is the job of the designer. This is the central theme of this book.

This book is not an introduction to circuit theory. I assume the reader is familiar with how a circuit works. It is also not an introduction to applied physics. It is about all the things that happen when an education meets the real world. The problems that are solved in a textbook are nothing like the problems that are faced by the new designer. After graduation, there are no teachers around to explain how to proceed.

I solved many problems using my intuition and my past experiences. Little by little my understanding grew. Over time, it became clear that I should have used more of my education and less of my intuition. This is easy to say and not very easy to do. In the real world, problems must be resolved not studied. Most problems are multidimensional and do not fit just one subject. Finding a way through a maze may not be very efficient but experimenting with the maze to learn more is not often done. That takes time and that means spending resources.

I was told about displacement current in college. I never appreciated the value of this concept until I began writing about digital circuits. Then I discovered this idea let me explain how current flows into the distributed capacitance of a transmission line. In reading the literature, I had never seen this explanation. I present this idea in this book and I hope it helps to explain the real world to others.

In looking back at the fifth edition, I noticed how austere Chapter 1 appeared. Reading this material seemed a little like taking medicine to get well. It is not fun. Even though I wrote it with good intentions and I was excited to tell this story, the material did not appear inviting. To correct this condition, I decided to open this sixth edition with some 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.

RALPH MORRISON

July 1, 2015

San Bruno, CA

Circuits and Interference