Preface

Note from the Author

Even if you’re on the right track, you’ll get run over if you just sit there.

—Will Rogers (1879–1935)

Photo courtesy of Will Rogers Memorial Museums, Claremore, Oklahoma

Welcome, and thank you for your interest in High-Speed Signal Propagation: Advanced Black Magic. This is an advanced-level reference text for experienced digital designers who want to press their designs to the upper limits of speed and distance.

If you need to transmit faster and further than ever before, this book is here to help. You’ll find it packed with practical advice.

The material in this book has been honed during my many years of work as chief technical editor of standards for both Fast Ethernet and Gigabit Ethernet—projects which, I hope, have touched your life in a favorable way. During those and many other projects, the models and concepts described here have been of invaluable service to me. Now I’d like to pass them on to you.

When you are done reading, share your knowledge with those around you as my technical mentor, Martin Graham, has done with me. Educate your coworkers. Educate your management. Above all, continue to educate yourself. If this book inspires you to advance your understanding with even one laboratory measurement, then I will know you are on the right track.

I would also like to say it has been a great pleasure teaching and working with many of you through my classes and lectures. Above all, I appreciate those who take the time to share with me their thoughts, their concerns, their dreams, and their problems. It always interests me to hear about real experiences from real engineers.

I wish you the best of luck on your next design.

See you on the Internet,
Dr. Howard Johnson
www.sigcon.com

Topics Covered

Printed circuit traces	Limits to attainable speed and distance RC and LC mode propagation Skin effect and dielectric loss design charts and equations Proximity effect Surface roughness Non-TEM mode of propagation Step response Effect of vias
Differential signaling	Edge-coupled and broadside-coupled differential pairs Effect of bends Intrapair skew Differential trace geometry impedance Crosstalk Radiation
Inter-cabinet connections	Coaxial cables Twisted-pair cables Fiber optics Equalizers General building wiring for LAN applications
Clock distribution	Special requirements for clocks Clock repeaters Multidrop clock distribution Clock jitter Power filtering for clock sources
Simulation	Frequency-domain simulation method Applicability of Spice and IBIS

How This Book Is Organized

Each chapter in this book treats a specialized topic having to do with high-speed signal propagation. They may be studied in any order.

Chapters 1 and 2 present the underlying physical theory of various transmission-line parameters, including the skin effect, proximity effect, dielectric loss, and surface roughness.

Chapter 3 develops a generalized frequency-response model common to all conductive media.

Chapter 4 outlines the calculation of time-domain waveforms from frequency-domain transfer functions.

Chapters 5 through 11 discuss specific transmission media, including single-ended pcb traces, differential media, general building wiring standards, unshielded twisted-pair wiring, 150-Ω shielded twisted-pair wiring, coaxial cables, and fiber.

Chapter 12 addresses miscellaneous issues concerning clock distribution.

Chapter 13 explores the limitations of Spice and IBIS simulation methods.

Prerequisites

A basic understanding of the frequency domain representation of linear systems is assumed. Readers without the benefit of formal training in analog circuit theory can use and apply the formulas and examples in this book. Readers who have completed a first-year class in introductory linear circuit theory will comprehend the material at a deeper level.

Relation to Prior Books

This book is a companion to the original book by Johnson and Graham, High-Speed Digital Design: A Handbook of Black Magic, Prentice-Hall, 1993. The two books may be used separately or together. They cover different material.

The original book deals with a broad spectrum of high-speed phenomena. It builds a solid understanding of ringing, crosstalk, ground bounce, and power supply noise as they exist on printed circuit boards. It emphasizes basic circuit configurations where these effects may be easily understood and learned. It treats supplementary subjects including chip packages, oscilloscope probe, and power systems for high-speed digital products.

This High-Speed Signal Propagation book is more highly specialized, delving into issues relevant to transmission at the upper limits of speed and distance. If you need to transmit faster and further than ever before, this book shows you how.

High-Speed Digital Design and High-Speed Signal Propagation together comprise a good reference set for persons working with high-speed digital technology.

Those of you familiar with my other books will recognize similarities in style. Notably, I’ve tried to impart, as best I can, the same sense of realism born of long experience.

Acknowledgements

Literally thousands of people have taken the time to communicate with me about high-speed issues, either through email or in person at my seminars. These conversations have inspired me to investigate and collect together the material in this book. To all of you, I owe a debt of gratitude.

The following people contributed specific comments or questions that are discussed in the text (in alphabetical order): Sal Aguinaga, James C. Bach, Eric V. Berger, Raymond Bullington, Doug Butler, Tim Canales, Bruce Carsten, Code Cubitt, Dave Cuthbert, Bill Daskalakis, Martin Graham, Paul Greene, Gary Griffin, Bob Haller, John Lehew, John Lin, Raymond P. Meixner, Craig Miller, Mitch Morey, Dan Nitzan, Bhavesh Patel, Dipak Patel, Jim Rautio, Ravi, Boris Shusterman, Kevin Slattery, Bob Stroupe, Bill Stutz (twice), and Fabrizio Zanella. Thanks to all of you for many hours of good correspondence.

I especially thank those who volunteered for the difficult task of reviewing the text. This group of intrepid individuals spotted numerous errors and suggested many new topics for exploration. They deserve a large measure of credit for helping make this a more useful text (in alphabetical order): Jacob Ben Ary at Aquanet, Greg Dermer at Easystreet, Steve Ems at Lecroy, Alexandre Guterman at Nortel, Valery Kugel at Juniper, Professor Will Moore at Oxford University, Jose Moreira at Agilent, Gopa Parameswaran at Cisco, Bob Ross at Mentor Graphics, Bert Simonovich at Nortel, Palani Subbiah at Cypress, and Geoff Thompson at Nortel.

My editors at Prentice-Hall, Bernard Goodwin, Nicholas Radhuber, and Carol J. Lallier, have contributed their professional expertise (and patience) during the long process required to complete this project. Without my dutiful and highly accurate assistant Jennifer Epps this book would not have been possible.

Bob Ross, Mentor Graphics Corp., past chair of the EIA IBIS Open Forum, wrote a fine discussion about the future of IBIS modeling for Chapter 13. Bruce Archambeault contributed the article in Chapter 12 about reducing emissions, which I only edited. Brad Cole and Matt Hudale of Ansoft simulated the capacitance of many via configurations for Chapter 5. To Gopa Parameswaran at Cisco, thanks for your simulations of via capacitance, although your data did not appear in the final version of the book. Steve Ems and Robert Talambiras of Lecroy piqued my interest in non-TEM modes of propagation during a visit to my ranch in October of 2000. Roger Billings of Wideband Corporation deserves mention as the world record-holder for fastest data conveyed across barbed-wire cabling (Chapter 2). Jeff Sonntag at Accelerant Networks was the first to focus my attention on how backplane performance changes with temperature (Chapter 5). Thanks also to Jim Tavacoli at Accelerant for sending the cool pictures showing adaptive equalization at work in Chapter 3.

The discussions I have been privileged to hold with Michael King, Ed Sayre, and Doug Smith have been of enormous value to me. Thank you for your friendship.

My technical mentor Dr. Martin Graham of U.C. Berkeley has contributed his enduring support, encouragement, and technical assistance over the past twenty years, as well as having been the first to direct my attention toward the general features of transmission line attenuation and how it varies with frequency. Thank you, Martin.

To my wonderful and understanding wife Liz, thank you for taking care of all the details of my life so that I could have time to write a book like this.

Regardless of the assistance of others, any remaining errors are entirely mine.

Information contained in this work has been obtained by Prentice Hall from sources believed to be reliable. However, neither Prentice Hall nor its author guarantees the accuracy or completeness of any information published herein and neither Prentice Hall nor its authors shall be responsible for any errors, omission, or damages arising out of this information.

Notational Conventions

This book uses metric units, except for some common printed-circuit board dimensions, which are denoted in English units. Variables and general function names appear in italics. Constants, enumerators, and specific well-known functions appear in ordinary type (e.g., f(x) = 1 + sin x). Matrix and vector-field quantities occur in boldface type.

Contacting the Author

Should you spot something out of place in the text, or merely wish to discuss the finer points of transmission-line theory, I may be reached at my ranch high in the mountains near the town of Twisp, Washington: howiej@sigcon.com.

A great place to keep up with the latest developments in high-speed signaling is my web site, www.sigcon.com. At that site I maintain a growing collection of articles about high-speed digital phenomena, and information about my schedule of public seminars. If you would like to read even more about signal integrity issues, sign up to receive my newsletter. An errata page for this book is located on the site.

Howard Johnson, PhD, is the author of High-Speed Digital Design: A Handbook of Black Magic, Prentice-Hall, 1993, Fast Ethernet: Dawn of a New Network, Prentice-Hall, 1996, and the Signal Integrity columnist for EDN magazine. He frequently conducts technical workshops for digital engineers at Oxford University and other sites worldwide.