RIGHT THE FIRST TIME 09-15-08 - Kyaw Soe Hein

[Pages:295]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 0/15/08

Revised 6/2/03 Revised and edited 6/11/03 Revised and edited 8/14/03 Revised and edited 9/15/08

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This book is dedicated to the memory of the late Dan Murphy. He paved the way for many of us.

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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.

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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 difficult concepts to me; to prepare lectures and classes that I attended 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 engineers 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 refining the rules I used to do design and to demonstrate concepts. Many of those experiments are in this book.

Early in my career, I switched from microwave and RF design 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 together 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 statements about bypass capacitors and he also wrote the section on that topic. We still find 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 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 significant 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 finished. Without her, the book might have happened but it would not have the quality it does.

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FORWARD TO RIGHT THE FIRST TIME BOOK

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 decided to go fishing. 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 fishing. 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 fish.

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 design is about knowing where the rocks are. If you do, it's pretty 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 rules of thumb often presented as the "correct way" will be examined 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 adequately 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 finished PCBs that work right the first 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 spectrum, I have worked on elevator controllers, hand held computers, cell phones and PCs that have needed the same design techniques. 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 networking 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.

Many of the illustrations in this book have been taken directly from the screens of oscilloscopes and spectrum analyzers. 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 available to the reader. I feel that accuracy and timeliness should win over finesse 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 results 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 flow. When Ben Franklin did his experiments on current flow, he estimated that current flowed from positive to negative. Later it was demonstrated that current was electron flow, 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 flow as electron flow from negative to positive.

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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 fundamentals. Volume 2 will cover all the advanced topics and will be available sometime in 2004.

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TABLE OF CONTENTS

CHAPTER 1: INTRODUCTION......................................................................................................................... 14 CHAPTER 1: INTRODUCTION......................................................................................................................... 14 CHAPTER 2: THE ELECTRICAL ENGINEERING PROBLEM........................................................................ 18 CHAPTER 3: MAJOR ELEMENTS IN AN ELECTRONIC SYSTEM ............................................................... 21 CHAPTER 4: ASSUMPTIONS OFTEN MADE ABOUT ELECTRONIC SYSTEMS ........................................ 23 CHAPTER 5: HOW DIFFERENT FROM IDEAL REAL SYSTEMS AND THEIR COMPONENTS ARE ......... 24 CHAPTER 6: TRANSMISSION LINES ............................................................................................................. 25 CHAPTER 7: WHAT'S MOVING ON A TRANSMISSION LINE? .................................................................... 26 CHAPTER 8: BASICS OF ELECTROMAGNETIC FIELDS ............................................................................. 30 CHAPTER 9: DIGITAL vs. RF/MICROWAVE vs. ANALOG ........................................................................... 32 CHAPTER 10: TIME AND DISTANCE ............................................................................................................. 33 CHAPTER 11: INDUCTANCE .......................................................................................................................... 36 CHAPTER 12: CAPACITANCE ......................................................................................................................... 39 CHAPTER 13: RESISTANCE ........................................................................................................................... 41 CHAPTER 14: FUNDAMENTALS OF TRANSMISSION LINES...................................................................... 43 CHAPTER 15: THE CONCEPT OF GROUND AND POWER PLANES .......................................................... 45 CHAPTER 16: IMPEDANCE............................................................................................................................. 47 CHAPTER 17: REFLECTIONS--WHAT CAUSES THEM, WHAT THEY DO TO A SIGNAL.......................... 50 CHAPTER 18: WHAT IS MEANT BY SIGNAL INTEGRITY ENGINEERING.................................................. 57 CHAPTER 19: WHEN IS A DESIGN HIGH SPEED?....................................................................................... 59 CHAPTER 20: CONTROLLING REFLECTIONS BY USING TERMINATIONS .............................................. 61 CHAPTER 21: TERMINATOR TYPE, TERMINATOR PLACEMENT AND NET SEQUENCING ................... 69 CHAPTER 22: STUBS ON TRANSMISSION LINES? ..................................................................................... 78 CHAPTER 23: PROPERTIES OF TRANSMISSION LINES THAT AFFECT IMPEDANCE............................ 80 CHAPTER 24: METHODS FOR CALCULATING AND MEASURING IMPEDANCE...................................... 83 CHAPTER 25: RIGHT ANGLE BENDS AND VIAS POTENTIAL SOURCES OF REFLECTIONS AND OTHER PROBLEMS .......................................................................................................................................... 90 CHAPTER 26: TYPES OF DRIVERS OR SOURCES ...................................................................................... 96 CHAPTER 27: TYPES OF LOADS................................................................................................................... 98 CHAPTER 28: BUS PROTOCOLS................................................................................................................... 99 CHAPTER 29: CROSSTALK OR COUPLING ............................................................................................... 103 CHAPTER 30: SINGLE ENDED SIGNALING ................................................................................................ 112 CHAPTER 31: DIFFERENTIAL SIGNALING ................................................................................................. 114 CHAPTER 32: THE POWER SUBSYSTEM .................................................................................................... 122 CHAPTER 33: POWER DISTRIBUTION DC DROP ...................................................................................... 127 CHAPTER 34: DECOUPLING CAPACITORS ............................................................................................... 132 CHAPTER 35: POWER SUBSYSTEM INDUCTANCE .................................................................................. 140 CHAPTER 36: POWER DISSIPATION ESTIMATE ....................................................................................... 152

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CHAPTER 37: EXAMPLE POWER SUBSYSTEM DESIGN.......................................................................... 164 CHAPTER 38: IC PACKAGES--Vcc AND GROUND BOUNCE OR SSN..................................................... 176 CHAPTER 39: NOISE MARGINS ................................................................................................................... 183 CHAPTER 40: DESIGN RULE CREATION USING NOISE MARGIN ANALYSIS ........................................ 185 CHAPTER 41: PCB FABRICATION PROCESS ............................................................................................ 196 CHAPTER 42: PCB MATERIALS .................................................................................................................. 201 CHAPTER 43: CREATING PCB STACKUPS................................................................................................ 207 CHAPTER 44: TYPES OF VIAS ..................................................................................................................... 211 CHAPTER 45: PCB DESIGN PROCESS ....................................................................................................... 214 CHAPTER 46: PCB ROUTING ....................................................................................................................... 221 CHAPTER 47: DOCUMENTATION ................................................................................................................ 226 CHAPTER 48: THE IDEAL COMPONENT DATA SHEET ............................................................................ 229 GLOSSARY...................................................................................................................................................... 231 APPENDIX 1: BIBLIOGRAPHY ..................................................................................................................... 264 APPENDIX 2: ANATOMY OF A PLATED THROUGH HOLE ....................................................................... 270 APPENDIX 3: SELECTING PCB SUPPLIERS .............................................................................................. 275 APPENDIX 4: A PAGE OF USEFUL EQUATIONS ....................................................................................... 287 APPENDIX 5: TECHNOLOGY TABLE EXPLANATION................................................................................ 288 APPENDIX 6: DRILL TABLE.......................................................................................................................... 294 APPENDIX 7: CONVERSION TABLES ......................................................................................................... 295

Figures, Tables and Equations

Figure 1.1. Golden Gate Bridge

Figure 1.2. Boeing 777 .................................. 14

Table 2.1. Characteristics of Two General Classes of High Speed PCBs .......................................................................... 18

Figure 2.1. A Typical Microwave PCB Surface Layer ....................................................................................................... 19

Table 3.1. Major Elements in an Electronic System........................................................................................................... 21

Table 3.2. Types of Signal Sources or Voltage Waveform Generators............................................................................... 21

Table 3.3. Methods of Moving A Voltage Waveform or Electromagnetic Field From Its Source to its User .................... 21

Table 3.4. Types of Loads................................................................................................................................................... 21

Table 3.5. Power Sources .................................................................................................................................................. 22

Table 6.1. Examples of Transmission Lines ....................................................................................................................... 25

Figure 7.1. A Mechanical Transmission Line .................................................................................................................... 26

Figure 7.2. Potential Energy Stored in Elevated Ball ........................................................................................................ 27

Figure 7.3. Kinetic Energy From Falling Ball Transferring into Transmission Line ........................................................ 27

Figure 7.4. Kinetic Energy Transferring to Ball at Far End of Transmission Line ........................................................... 28

Figure 7.5. Absorbing the Acoustic Energy at the Load Using a "Parallel" Termination ................................................. 28

Figure 7.6. Absorbing the Acoustic Energy at the Source with a "Series" Termination .................................................... 29

Figure 8.1. An End-on View of a Stripline Transmission Line Showing the Electromagnetic Field Traveling on It ......... 30

Table 8.1. Examples of Electromagnetic Energy Moving from One Place to Another Without Electrons in the Path ...... 31

Equation 10.1. Velocity vs. Material Relative Dielectric Constant .................................................................................... 33

Figure 10.1. Rise and Fall Time......................................................................................................................................... 34

Table 10.1. Several Logic Families, Their Rise Time and the Length in a PCB ................................................................ 35

Equation 11.1. Voltage Drop Across an Inductance .......................................................................................................... 36

Table 11.1. Parasitic Inductance of Some Typical Components ........................................................................................ 36

Equation 11.2. Inductive Reactance Equation.................................................................................................................... 36

Table 11.2. Impedance, in Ohms, of the Parasitic Inductances of Table 11.1 Components at Several Frequencies ......... 37

Figure 11.1. Typical Ideal Inductor Symbol....................................................................................................................... 37

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