Right the first time; A PRACTICAL HANDBOOK ON HIGH-SPEED PCB AND SYSTEM DESIGN

639 Pages·021.588 MB·English

by  LEE W. RITCHEY

1
This book is dedicated to the memory of the
late Dan Murphy. He paved the way for many of us.
Library of Congress Control Number:
2003109272
ISBN-0-9741936-0-7
Right the First Time—A Practical Handbook on High-speed
PCB and System Design. Copyright © 2003 by Speeding
Edge. All rights reserved. No part of this book may be used
or reproduced in any manner whatsoever without written
permission, except in the case of brief quotations
embodied in critical articles and reviews.
2
RIGHT THE FIRST TIME
A PRACTICAL HANDBOOK ON
HIGH-SPEED PCB AND SYSTEM DESIGN
AUTHOR LEE W. RITCHEY
POWER SECTION BY JOHN ZASIO
EDITED BY KELLA J. KNACK
SPEEDING EDGE SUMMER 2003
COPYRIGHT 2003 BY Speeding Edge
Revised 9/06/03 and 01/15/08
Revised 6/2/03
Revised and edited 6/11/03
Revised and edited 8/14/03
Revised and edited 9/15/08
3
ACKNOWLEDGEMENTS
As with all books, this one is the result of the work of many
people. At the top of the list are the many students who have
attended my “High Speed PCB and System Design” classes over
the last ten years. There have been more than 5000 of you.
You have challenged me with your questions, prompted me to
go back and study topics I had long forgotten and pushed me
for better answers. Even more, you have continually asked me
when I was going to write the book that goes with the class.
Without that continual prompting, this book might still be just
a promise. To all of you, thanks for your encouragement and
prompting.
The next group of people who played a big role in making
this book a reality are all of the senior engineers who taught me
when I was a young engineer. They took their time to explain
diffi cult concepts to me; to prepare lectures and classes that I at-
tended at conferences and to write articles and papers that have
been in my reference library throughout my career and from
which I drew upon for this book. As I went through my career,
I vowed that if ever I had the opportunity, I would give back to
my profession as it gave to me and all of the other young en-
gineers that started out with me. More of the senior, seasoned,
experienced engineers need to stay in the industry and share
what they have learned with new engineers. If ever there was
a time when this was needed, it is now because of the rapidly
changing technologies with which we work.
I have worked with hundreds of very good engineers and
designers. From each of them, I have learned things. Many of
them have participated in experiments that were aimed at refi n-
ing the rules I used to do design and to demonstrate concepts.
Many of those experiments are in this book.
4
RIGHT THE FIRST TIME
Early in my career, I switched from microwave and RF de-
sign to computer design. When this happened, I was privileged
to work with two very good engineers at Amdahl Corporation,
Dan Murphy and John Zasio.
With Dan, I later founded a design company known as
Shared Resources. Dan was a great router developer and we used
his skills to put together a design company and a PCB router
that set the standards for how to route high speed PCBs. Many
of the features in today’s PCB routers came from the work that
Dan did. He made it possible for Shared Resources to design
PCBs that could not be attempted with any of the then available
design tools. Many of the design concepts in this book came
from the work we did designing hundreds of high speed PCBs.
With John, I was able to work on many high-speed designs
and to see how he performed analysis of some fairly complex
problems. He has always had a design and analytical discipline
that stands out among all the engineers I have known and with
whom I have worked. I could always count on him to put to-
gether good analyses and to perform measurements with the
rigor necessary to prove concepts in a conclusive way. He has
been working at engineering since the early sixties and is still
actively working on new and more complex designs. Whenever
I needed a reliable ear to explore an idea, John has been there.
For this book, he did the lab experiments that support the state-
ments about bypass capacitors and he also wrote the section on
that topic. We still fi nd new things to explore.
In the fall of 1989, I was writing design articles for the early
version of Printed Circuit Design magazine. A new editor came
on the scene who did major damage to the articles I submitted.
Some of them were sent back to me with so much red ink, it
looked as though someone had been slain on them. This editor
was Kella Knack who had come from Martin Marrietta where
5
ACKNOWLEDGEMENTS
she had been a technical writer. I got used to her style and wrote
many articles for the magazine. Time went by and Kella moved
to the west coast to edit other magazines. We met, I found out
she could talk techie talk, she had a sense of humor and liked
to sail and backpack. One thing led to another and we became
each other’s signifi cant other. She has been my sounding board
for this book. She is its editor and, in the end, she is the one who
kept after me to get it fi nished. Without her, the book might
have happened but it would not have the quality it does.
6
RIGHT THE FIRST TIME
7
FOREWORD
There were two engineers, a civil engineer, and an electrical
engineer who worked together. A mechanical engineer came to
visit their project. During a day off, these three colleagues de-
cided to go fi shing. They went to a local lake and set out in a
small boat.
After a while, the civil engineer said he had to take care of
a little personal business. He stepped out of the boat, walked
across the lake to shore, did his business, walked back, got in
the boat, sat down and continued fi shing. A little while later,
the electrical engineer said he had to take care of some personal
business, got up, stepped out of the boat, walked to shore, took
care of business, returned and continued to fi sh.
The mechanical engineer watched all this in amazement,
scarcely believing that the other two had walked to shore and
back without getting wet. Wanting to demonstrate that his skill
set was as powerful as the other two, he announced that he, too,
had to take care of some personal business. As he stepped out of
the boat, he promptly sunk out of sight.
Seeing the mechanical engineer sink out of sight, the civil
engineer turned to the electrical engineer and said, “Do you
suppose we should tell him where the rocks are?”
Like getting to shore without getting wet, high speed de-
sign is about knowing where the rocks are. If you do, it’s pret-
ty easy to get to shore without getting wet. If you don’t, you
and your project are bound to sink out of sight. The problem is
compounded by the enormous amount of fake rocks that are in
print as rules of thumb and philosophical rules.
The intent of this book is to show the reader where the rocks
are so that a high-speed design can be successfully realized in a
straight forward and relatively easy manner. Along the way, the
8
RIGHT THE FIRST TIME
rules of thumb often presented as the “correct way” will be ex-
amined to see if they are valid or are the product of someone’s
imagination.
The subject matter involved in high-speed design is quite
large. So large, in fact, that one book does not and cannot ad-
equately cover it all. There have been many books written at
the theoretical level on this topic. Among these are “High Speed
Signal Propagation” by Howard Johnson and Martin Graham
(Prentice Hall, 2003), and “Introduction to Fields and Waves”
by Holt, Wiley and Sons, 1963.
This book will not attempt to repeat the information in
these books. Instead, where appropriate, I will refer the reader
to the appropriate book to learn more. The reader is advised to
obtain copies of these books, or their equal, as part of his or her
technical library.
This book will focus on the practical business of turning
theoretical concepts into fi nished PCBs that work right the fi rst
time. It is based on more than thirty years experience designing
high-speed products ranging from microwave transponders to
super computers to terabit routers to network interface cards.
What has been learned designing hundreds of high speed PCBs
and dozens of high performance systems will be shared with the
reader. Not to leave out the other end of the high-speed spec-
trum, I have worked on elevator controllers, hand held comput-
ers, cell phones and PCs that have needed the same design tech-
niques. High speed is high speed, no matter what the product.
As this book is being written, I am actively engaged in the
design of next generation products. On the one end are net-
working products that have 4.8 GB/s and higher data paths in
the backplane and at the other are the next round of handheld
computers. The knowledge gained working on these products is
shared as well.
9
FOREWORD
Many of the illustrations in this book have been taken di-
rectly from the screens of oscilloscopes and spectrum analyz-
ers. The intention is to show actual waveforms of real circuits,
both failing and functioning properly. This has been done to
make it easier for the reader to see how to set up instruments to
make measurements and to see what real waveforms look like.
The intent is to get as close to the work bench with real PCBs
as possible. Some of these measurements were only days old
when this book went to press. As a result, their formats may
be varied and look like they have been hastily done. In some
cases they have been, so that the latest information is avail-
able to the reader. I feel that accuracy and timeliness should
win over fi nesse in presentation. For those who are bothered by
the changing styles from illustration to illustration, I apologize.
This is a practical handbook aimed at those who must get re-
sults immediately and is aimed at helping them along the way.
Perhaps, someday it may be a textbook. When that happens, it
won’t be as current as it should be and will be of less use to the
reader. It will be more like a history book. I will try to make sure
this never happens.
Note to the reader concerning current fl ow. When Ben
Franklin did his experiments on current fl ow, he estimated that
current fl owed from positive to negative. Later it was demon-
strated that current was electron fl ow, moving from negative to
positive. The former is called conventional current. The power
section of this book discusses current in this manner. The rest
of the book refers to current fl ow as electron fl ow from negative
to positive.
As we got deep into covering the important topics of high
speed PCB and system design, it became readily apparent that
there was too much information to cover in a single volume.
Therefore, this book constitutes Volume 1 and covers all the
10