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THE FIELDS OF ELECTRONICS THE FIELDS OF ELECTRONICS Understanding Electronics Using Basic Physics Ralph Morrison A Wiley-Interscience Publication JOHN WILEY & SONS, INC " This book is printed on acid-free paper ! c 2002 by John Wiley & Sons, Inc., New York All rights reserved Copyright ! Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744 Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY 10158-0012, (212) 850-6011, fax (212) 850-6008, E-Mail: PERMREQ@WILEY.COM For ordering and customer service, call 1-800-CALL-WILEY Library of Congress Cataloging-in-Publication Data Is Available ISBN 0-471-22290-9 Printed in the United States of America 10 CONTENTS Preface xi The Electric Field 1.1 Introduction 1.2 Charge 1.3 Electrical Forces on Charged Bodies 1.4 Electric Field 1.5 Work 1.6 Voltage 1.7 Charges on Surfaces 1.8 Equipotential Surfaces 1.9 Field Units 1.10 Batteries—A Voltage Source 10 1.11 Current 11 1.12 Resistors 12 1.13 Resistors in Series or Parallel 13 1.14 E Field and Current Flow 15 1.15 Problems 15 1.16 Energy Transfer 16 1.17 Resistor Dissipation 17 1.18 Problems 17 1.19 Electric Field Energy 18 1.20 Ground and Ground Planes 19 1.21 Induced Charges 20 1.22 Forces and Energy 20 1.23 Problems 21 1.24 Review 21 Capacitors, Magnetic Fields, and Transformers 2.1 Dielectrics 23 2.2 Displacement Field 23 23 vi 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 CONTENTS Capacitance 25 Capacitance of Two Parallel Plates 25 Capacitance in Space 26 Current Flow in Capacitors 27 RC Time Constant 28 Problems 29 Shields 30 Magnetic Field 31 Solenoids 32 Ampe` re’s Law 32 Problems 34 Magnetic Circuit 34 Induction or B Field 34 Magnetic Circuit without a Gap 36 Magnetic Circuit with a Gap 38 Transformer Action 39 Magnetic Field Energy 40 Inductors 41 L=R Time Constant 42 Mutual Inductance 43 Problems 44 Review 44 Utility Power and Circuit Concepts 3.1 Sine Waves 46 3.2 Reactance and Impedance 47 3.3 Problems 50 3.4 Resonance 50 3.5 Phase 52 3.6 Parallel RL and RC Circuits 53 3.7 Problems 54 3.8 RMS Values 54 3.9 Problems 55 3.10 Transmission Lines 56 3.11 Poynting’s Vector 57 3.12 Transmission Line over an Equipotential Surface 58 3.13 Transmission Lines and Sine Waves 59 3.14 Coaxial Transmission 61 3.15 Utility Power Distribution 62 46 CONTENTS 3.16 3.17 3.18 3.19 3.20 3.21 Earth as a Conductor 64 Power Transformers in Electronic Hardware 65 Electrostatic Shields in Electronic Hardware 67 Where to Connect the Metal Box 69 Problems 73 Review 74 A Few More Tools 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 vii Introduction 75 Resistivity 75 Inductance of Isolated Conductors 76 Ohms per Square 77 Problems 77 Radiation 77 Half-Dipole Antennas 78 Current Loop Radiators 80 Field Energy in Space 82 Problems 82 Reflection 83 Skin Effect 84 Problems 84 Surface Currents 85 Ground Planes and Fields 86 Apertures 86 Multiple Apertures 87 Waveguides 88 Attenuation of Fields by a Conductive Enclosure 88 Gaskets 89 Honeycombs 89 Wave Coupling into Circuits 90 Problems 91 Square Waves 91 Harmonic Content in Utility Power 94 Spikes and Pulses 95 Transformers 96 Eddy Currents 98 Ferrite Materials 99 75 viii CONTENTS 4.30 Problems 99 4.31 Review 100 Analog Design 5.1 Introduction 101 5.2 Analog Signals 101 5.3 Common-Mode Interference 102 5.4 Common-Mode Rejection in Instrumentation 106 5.5 Problems 107 5.6 Voltage Measurement: Oscilloscopes 107 5.7 Microphones 108 5.8 Resistors 109 5.9 Guard Rings 110 5.10 Capacitors 111 5.11 Problems 112 5.12 Feedback Processes 113 5.13 Problems 115 5.14 Miller Effect 115 5.15 Inductors 116 5.16 Transformers 117 5.17 Problems 119 5.18 Isolation Transformers 120 5.19 Solenoids and Relays 121 5.20 Problems 122 5.21 Power Line Filters 123 5.22 Request for Energy 124 5.23 Filter and Energy Requests 125 5.24 Power Line Filters above MHz 125 5.25 Mounting the Filter 125 5.26 Optical Isolators 127 5.27 Hall Effect 127 5.28 Surface Effects 127 5.29 Review 127 101 Digital Design and Mixed Analog/Digital Design 6.1 Introduction 129 6.2 Logic and Transmission Lines 129 6.3 Decoupling Capacitors 130 6.4 Ground Planes 131 129 CONTENTS 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.21 6.22 6.23 6.24 6.25 6.26 6.27 6.28 6.29 6.30 6.31 6.32 6.33 ix Power Planes 132 Decoupling Power Geometries 132 Ground Plane Islands 133 Radiation from Loops 133 Problems 133 Leaving the Board 134 Ribbon Cable and Common-Mode Coupling 135 Braided Cable Shields 135 Transfer Impedance 137 Mechanical Cable Terminations 138 Problems 138 Mounting Power Transistors 139 Electrostatic Discharge 139 ESD Precautions 141 Zapping 141 Product Testing: Radiation 142 Military Testing 142 Chattering Relay Test 143 Euro Standards 143 LISN 144 Sniffers 144 Simple Antenna 145 Peripherals 145 Problems 146 Lightning 146 Problems 147 Mixing Analog and Digital Design 147 Ground Bounce 148 Review 148 Facilities and Sites 7.1 Introduction 149 7.2 Utility Power 149 7.3 Floating Utility Power 151 7.4 Isolated Grounds 152 7.5 Single-Point Grounding 153 7.6 Ground Planes 155 7.7 Alternative Ground Planes 156 7.8 Power Centers 157 149 x 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 CONTENTS Lightning Protection 158 Surge Suppression 160 Racks 161 Magnet Fields around Distribution Transformers 161 Monitor Fields 162 Motor Controllers 162 Screen Rooms 163 Review 164 Appendix I: Solutions to Problems 165 Appendix II: Glossary of Common Terms 177 Appendix III: Abbreviations 183 Index 187 PREFACE This book provides a new way to understand the subject of electronics The central theme is that all electrical phenomena can be explained in terms of electric and magnetic fields Beginning students place their faith in their early instruction They assume that the way they have been educated is the best way Any departure from this format just adds complications This book is a departure—hopefully, one that helps There are many engineers and scientists struggling to function in the real world Their education did not prepare them for handling most of the practical problems they encounter The practitioner in trouble with grounds, noise, and interference feels that something is missing in his education The new engineer has a very difficult time ordering, specifying, or using hardware correctly Facilities and power distribution are a mystery Surprisingly, all these areas are accessible once the correct viewpoint is taken This book has been written to provide a better introduction to the field of electronics so that the parts that are often omitted can be put into perspective The book uses very little mathematics It helps to have some background in electronics, but it is not necessary The beginning student may need some help from an instructor to fill in some of the blanks The practicing engineer will be able to read this book with ease Field phenomena are often felt to be the domain of the physicist In a sense this is correct Unfortunately, without a field-based understanding, many electronic processes must remain mysteries It is not necessary to solve difficult problems to have an appreciation of how things work It is only necessary to appreciate the fundamentals and understand the true nature of the world To illustrate the problem, consider an electric field that is constant everywhere Place a conducting loop of wire at some crazy angle in this field and ask a question: What is the shape of the new field? This is a very difficult problem even with a great deal of computing power Now, have the field change sinusoidally and consider current flow and skin effect and the problem really gets difficult The ideas are important, but the exact answer is not worth worrying about Connecting wires and components to form circuits is standard practice These conductors modify the fields around them This is the same nasty problem, and again it does not need an exact solution What is needed is an understanding of what actually takes place Circuit theory does not consider this type of problem xii PREFACE Most students in electronics spend a great deal of time with circuit theory The viewpoint of circuit theory is to treat lumped-parameter models Circuit theory provides an excellent way to predict the behavior of a group of components The mathematics is very straightforward Field theory, on the other hand, provides very little in terms of simple answers Most practical problems cannot be approached by field theory, and yet circuit theory and field theory are inseparable Circuit theory has no way to handle component size or orientation Circuit theory, with its zero-ohm connections, avoids any reference to loop area, common-impedance coupling, or common-mode coupling It fails to reference radiated energy from any source Circuit theory has its successes, but it also has its failures Field theory has its place, too, and yet it fails, as there is no convenient methodology Educators are oriented toward problem-solving courses Circuit theory fits this model, as it lends itself to solving many practical problems Electricity and magnetism courses are more difficult, and only very simple geometries can be approached The mathematics of vector fields, complex variable, and partial differential equations are not for the faint of heart This leaves the practicing engineer with one solution Drop physics and concentrate on circuit theory to provide answers The circuit diagram of a building or the grounding diagram of a power grid is of no help in analyzing interference These diagrams can be attempted, but they fail to provide a useful approach They not fit the textbook models, as they are not lumped-parameter circuits The engineer is at a loss This book allows the student to solve problems by means of simple ratios In each area, typical practical problems are solved in the text The student is expected to use this information to work the problem sets The answers are all worked out in Appendix I This makes it possible for the engineer or technician out of school to use the book for self-study It also makes it possible to use the text in school, where problems can be assigned The teacher can modify the parameters in the problems so that the student must work out the details rather than copy the answers This book is not intended to teach circuit theory It is not a substitute for teaching physics It is a tool that can be used to connect the two subjects There is a need to establish an elementary understanding in both areas so that the reader can understand the things that occur in the real world This is done in the early chapters The problems that are discussed throughout the book occur frequently Exact solutions are not attempted The simplifications that are applied are brought out in the text These simple approaches provide insight into what can be done to handle practical situations If students want to study physics or expand their knowledge of circuit theory, many texts and courses are available This book takes the liberty of choosing important features from both areas in order to provide students with a different view of the electrical world—a view from the bridge between electrical behavior and physics Redwood City, CA February 14, 2001 Ralph Morrison