High-Speed Circuit Board Signal Integrity

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3 High-Speed Circuit Board Signal Integrity

4 For a listing of recent titles in the Artech House Microwave Library, turn to the back of this book.

5 High-Speed Circuit Board Signal Integrity Stephen C. Thierauf Artech House, Inc. Boston London

6 Library of Congress Cataloguing-in-Publication Data A catalog record for this book is available from the U.S. Library of Congress. British Library Cataloguing in Publication Data A catalog record for this book is available from the British Library. Cover design by Igor Valdman 2004 ARTECH HOUSE, INC. 685 Canton Street Norwood, MA All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. International Standard Book Number:

7 To Ann, Christopher, and Kevin

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9 Contents Preface xiii CHAPTER 1 Characteristics and Construction of Printed Wiring Boards Introduction Unit System PWB Construction Resins Alternate Resin Systems Reinforcements Variability in Building Stackups Mixing Laminate Types PWB Traces Copper Cladding Copper Weights and Thickness Plating the Surface Traces Trace Etch Shape Effects Vias Via Aspect Ratio Surface Finishes and Solder Mask Summary 14 References 15 CHAPTER 2 Resistance of Etched Conductors Introduction Resistance at Low Frequencies Loop Resistance and the Proximity Effect Resistance Matrix Proximity Effect Resistance Increase with Frequency: Skin Effect Hand Calculations of Frequency-Dependent Resistance Return Path Resistance Conductor Resistance Total Loop Resistance Resistance Increase Due to Surface Roughness Summary 30 vii

10 viii Contents References 30 CHAPTER 3 Capacitance of Etched Conductors Introduction Capacitance and Charge Dielectric Constant Parallel Plate Capacitor Self and Mutual Capacitance Capacitance Matrix Dielectric Losses Reactance and Displacement Current Loss Tangent Calculating Loss Tangent and Conductance G Environmental Effects on Laminate ε r and Loss Tangent Temperature Effects Moisture Effects Summary 45 References 45 CHAPTER 4 Inductance of Etched Conductors Introduction Field Theory Permeability Inductance Internal and External Inductance Partial Inductance Reciprocity Principal and Transverse Electromagnetic Mode Circuit Behavior of Inductance Inductive Voltage Drop Inductive Reactance Inductance Matrix Using the Reciprocity Principle to Obtain the Inductance Matrix from a Capacitance Matrix Mutual Inductance Coupling Coefficient Beneficial Effects of Mutual Inductance Deleterious Effects of Mutual Inductance Hand Calculations for Inductance Inductance of a Wire Above a Return Plane Inductance of Side-by-Side Wires Inductance of Parallel Plates Inductance of Microstrip Inductance of Stripline Summary 64 References 65

11 Contents ix CHAPTER 5 Transmission Lines Introduction General Circuit Model of a Lossy Transmission Line Relationship Between ωl and R Relationship Between ωc and G Impedance Calculating Impedance Traveling Waves Propagation Constant Phase Shift, Delay, and Wavelength Phase Constant at High Frequencies When R and G Are Small Attenuation Neper and Decibel Conversion Summary and Worked Examples 82 References 86 CHAPTER 6 Return Paths and Power Supply Decoupling Introduction Proper Return Paths Return Paths of Ground-Referenced Signals Stripline Stripline Routed Between Power and Ground Planes When Power Plane Voltage Is the Same as Signal Voltage When Power Plane Voltage Differs from Signal Voltage Power System Inductance Split Planes, Motes, and Layer Changes Motes Layer Changes Connectors and Dense Pin Fields Plane Perforation Antipads Nonfunctional Pads Guidelines for Routing Through Dense Pin Fields Power Supply Bypass/Decoupling Capacitance Power Supply Integrity Distributed Power Supply Interconnect Model Connecting to Decoupling Capacitors Via Inductance Summary 114 References 115 CHAPTER 7 Serial Communication, Loss, and Equalization Introduction Harmonic Contents of a Data Stream 117

12 x Contents Line Spectra Combining Harmonics to Create a Pulse The Fourier Integral Rectangular Pulses with Nonzero Rise Times Line Codes Bit Rate and Data Rate Block Codes Used in Serial Transmission ISI Dispersion Lone 1-Bit Pattern Eye Diagrams Equalization and Preemphasis Preemphasis Passive Equalizers Passive RC Equalizer DC-Blocking Capacitors Calculating the Coupling Capacitor Value Summary 145 References 146 CHAPTER 8 Single-Ended and Differential Signaling and Crosstalk Introduction Odd and Even Modes Circuit Description of Odd and Even Modes Coupling Coefficient Stripline and Microstrip Odd- and Even-Mode Timing Effects of Spacing on Impedance Multiconductor Transmission Lines Bus Segmentation for Simulation Purposes Switching Behavior of a Wide Bus Simulation Results for Loosely Coupled Lines Simulation Results for Tightly Coupled Lines Data-Dependent Timing Jitter in Multiconductor Transmission Lines Differential Signaling, Termination, and Layout Rules Differential Signals and Noise Rejection Differential Impedance and Termination Reflection Coefficient and Return Loss PWB Layout Rules When Routing Differential Pairs Crosstalk Coupled-Line Circuit Model NEXT and FEXT Coupling Factors Using K b to Predict NEXT Using K f to Predict FEXT Guard Traces Crosstalk Worked Example 180

13 Contents xi Crosstalk Summary Summary 182 References 183 CHAPTER 9 Characteristics of Printed Wiring Stripline and Microstrips Introduction Stripline Time of Flight Impedance Relationship Between Trace Width, Thickness, and Plate Spacing Mask Biasing to Obtain a Specific Impedance Hand Calculation of Z o Stripline Fabrication Microstrip Exposed Microstrip Solder Mask and Embedded Microstrip Losses in Stripline and Microstrip Dielectric Loss Conductor Loss Microstrip and Stripline Differential Pairs Broadside Coupled Stripline Edge-Coupled Stripline Edge-Coupled Microstrip Summary 206 References 207 CHAPTER 10 Surface Mount Capacitors Introduction Ceramic Surface Mount Capacitors Dielectric Temperature Characteristics Classification Body Size Coding Frequency Response Inductive Effects: ESL Dielectric and Conductor Losses: ESR Leakage Currents: Insulation Resistance Electrical Model MLCC Capacitor Aging Capacitance Change with DC Bias and Frequency MLCC Usage Guidelines SMT Tantalum Capacitors Body Size Coding Frequency Response Electrical Model Aging Effects of DC Bias, Temperature, and Relative Humidity 225

14 xii Contents Failure of Tantalum Capacitors ESR and Self Heating: Voltage and Temperature Derating Usage Guidelines Replacing Tantalum with High-Valued Ceramic Capacitors 228 References 230 Appendix: Conversion Factors 231 About the Author 233 Index 235