Signal Integrity - Simplified
by: Eric Bogatin
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Back Cover
The complete guide to understanding and designing for signal integrity
Suitable for even non-specialists, Signal Integrity?Simplified offers a comprehensive, easy-to-follow look at how physical interconnects affect electrical performance. World-class engineer Eric Bogatin expertly reviews the root causes of the four families of signal integrity problems and offers solutions to design them out early in the design cycle. Coverage includes:
An introduction to signal integrity and physical design
A fundamental understanding of what bandwidth, inductance, and characteristic impedance really mean
Analysis of resistance, capacitance, inductance, and impedance
The four important practical tools used to solve signal integrity problems: rules of thumb, analytic approximations, numerical simulation, and measurements
The effect of the physical design of interconnects on signal integrity
Solutions that do not hide behind mathematical derivations
Recommendations for design guidelines to improve signal integrity, and much more
Unlike related books that concentrate on theoretical derivation and mathematical rigor, this book emphasizes intuitive understanding, practical tools, and engineering discipline. Specially designed for everyone in the electronics industry, from electrical engineers to product managers, Signal Integrity?Simplified will prove itself an invaluable resource for helping you find and fix signal integrity problems before they become problems.
About the Author
ERIC BOGATIN, Chief Technology Officer at GigaTest Labs, has over 23 years of experience in the microelectronics industry. Before joining GigaTest, he worked with AT&T Bell Labs, Raychem Corporation, Sun Microsystems, and other leading microelectronics manufacturers. He received his B.S. degree in physics at MIT and his M.S. and Ph.D. degrees from the University of Arizona, Tucson, in 1980. Over the years, he has taught over 3,000 engineers and authored over 100 technical articles and books on signal integrity and interconnect design.
Preface
Printed circuit-board and IC-package design used to be a field that involved expertise in layout, CAD, logic design, heat transfer, mechanical engineering, and reliability analysis. With modern digital electronic systems pushing beyond the 1-GHz barrier, packaging and board designers must now balance signal integrity and electrical performance with these other concerns.
Everyone who touches the physical design of a product has the potential of affecting the performance. All designers should understand how what they do will affect signal integrity or, at the very least, be able to talk with engineers who are responsible for the signal integrity.
The old design methodology of building prototypes, hoping they work, and then testing them to find out is no longer cost effective when time to market is as important as cost and performance. If signal integrity is not taken into account from the beginning, there is little hope a design will work the first time.
In our new "high-speed" world, where the packaging and interconnect are no longer electrically transparent to the signals, a new methodology for designing a product right the first time is needed. This new methodology is based on predictability. The first step is to use established design guidelines based on engineering discipline. The second step is to evaluate the expected performance by "putting in the numbers." This is what distinguishes engineering from guesswork. It takes advantage of four important tools: rules of thumb, analytic approximations, numerical simulation tools, and measurements. With an efficient design and simulation process, many of the trade-offs between the expected performance and the ultimate cost can be evaluated early in the design cycle, where the time, risk, and cost savings will have the biggest impact. The way to solve signal integrity problems is to first understand their origin and then apply all the tools in our toolbox to find and verify the optimum solution.
The design process is an intuitive one. The source of inspiration for a new way of solving a problem is that mysterious world of imagination and creativity. An idea is generated and the analytical powers of our technical training take over to massage the idea into a practical solution. Though computer simulations are absolutely necessary for final verification of a solution, they only rarely aid in our intuitive understanding. Rather, it is an understanding of the mechanisms, principles and definitions, and exposure to the possibilities, that contribute to the creation of a solution. Arriving at that initial guess and knowing the places to look for solutions require understanding and imagination.
This book emphasizes the intuitive approach. It offers a framework for understanding the electrical properties of interconnects and materials that apply across the entire hierarchy from on-chip, through the packages, circuit boards, connectors, and cables.
Those struggling with the confusing and sometimes contradictory statements made in the trade press will use this book as their starting place. Those experienced in electrical design will use this book as the place to finally understand what the equations mean.
In this book, terms are introduced starting at the ground floor. For example, the impedance of a transmission line is the most fundamental electrical property of an interconnect. It describes what a signal will see electrically and how it will interact with the interconnects. For those new to signal integrity, most of the problems arise from confusion over three terms: the characteristic impedance, the impedance, and the instantaneous impedance a signal sees. This distinction is even important for experienced engineers. This book introduces the reader to each of these terms and their meanings, without complex mathematics.
New topics are introduced at a basic level; most are not covered in other signal integrity books at this level. These include partial inductance (as distinct from loop inductance), the origin of ground bounce and EMI, impedance, transmission line discontinuities, differential impedance, and attenuation in lossy lines affecting the collapse of the eye diagram. These topics have become critically important for the new high-speed serial links.
In addition to understanding the basic principles, leveraging commercially available tools is critical for the practicing engineer who wants to find the best answer in the shortest time. Tools for solving signal integrity problems fall in two categories: analysis and characterization. Analysis is what we usually refer to as a calculation. Characterization is what we usually refer to as a measurement. The various tools, guidelines on when they should be used, and examples of their value are presented throughout the book.
There are three types of analysis tools: rules of thumb, analytic approximations, and numerical simulation. Each has a different balance between accuracy and effort to use. Each has a right and a wrong place for its appropriate use. And each tool is important and should be in the toolbox of every engineer.
Rules of thumb, such as "the self inductance of a wire is about 25 nH/inch," are important when having a quick answer NOW! is more important than having an accurate answer late. With very few exceptions, every equation used in signal integrity is either a definition or an approximation. Approximations are great for exploring design space and balancing design and performance trade-offs. However, without knowing how accurate a particular approximation really is, would you want to risk a $10,000 board-fabrication run and four weeks of your schedule based on an approximation?
When accuracy is important, for example, when signing off on a design, numerical simulation is the right tool to use. In the last five years, a whole new generation of tools has become available. These new tools have the powerful combination of being both easy to use and accurate. They can predict the characteristic impedance, cross talk, and differential impedance of any cross-section transmission line and simulate how a signal might be affected by any type of termination scheme. You don't have to be a Ph.D. to use this new generation of tools so there is no reason every engineer can't take advantage of them.
The quality of the simulation is only as good as the quality of the electrical description of the components (i.e., the equivalent circuit models). Engineers are taught about circuit models of gates that perform all the information processing, but rarely are the circuit models of the interconnects reviewed. Fifteen years ago, when interconnects looked transparent to the signals, all interconnects were considered as ideal wires--no impedance and no delay. When these terms were added, they were lumped together as "parasitics."
Today, in a high-speed digital system with a clock frequency above about 100 MHz, it is the real wires--the wire bonds, the package leads, the pins, the circuit board traces, the connectors, and the cabling--that create signal-integrity problems and can prevent products from working correctly the first time. Understanding these "analog" effects, designing for them, specifying correct values for them, and including them in the system simulations before the design is committed to hardware, can enable moving a more robust product to market more quickly.
This book provides the tools to enable all engineers and managers involved in chip packaging and board, connector and interconnect design, to understand how these passive elements affect the electrical performance of a system and how they can be incorporated in system simulation. It illustrates how to perform engineering estimates of important electrical parameters and evaluate technology trade-offs. Examples are selected from a wide variety of common systems, including on-chip interconnects, wire bonds, flip chip attach, multilayer circuit boards, DIPs, PGAs, BGAs, QFPs, MCM connectors, and cables.
While most textbooks emphasize theoretical derivation and mathematical rigor, this book emphasizes intuitive understanding, practical tools, and engineering discipline. We use the principles of electrical engineering and physics and apply them to the world of packaging and interconnects to establish a framework of understanding and a methodology of solving problems. The tools of time- and frequency-domain measurement, two- and three-dimensional field solvers, transmission-line simulations, circuit simulators, and analytical approximations are introduced to build verified equivalent circuit models for packages and interconnects.
There are two important questions that all designers should ask of any model they use: How accurate is it? And what is the bandwidth of the model? The answers to these questions can come only from measurements. Measurements play the very important role of risk reduction.
The three generic measurement instruments, the impedance analyzer, the vector-network analyzer (VNA) and the time-domain reflectometer (TDR) are introduced and the interpretation of their data explained. Examples of measurements from real interconnects such as IC packages, printed circuit boards, cables, and connectors are included throughout this book to illustrate the principles and, by example, the value of characterization tools.
This book has been designed for use by people of all levels of expertise and training: engineers, project managers, sales and marketing managers, technology developers, and scientists. We start out with an overview of why designing the interconnects for high-speed digital systems is difficult and what major technical hurdles must be overcome to reach high-frequency operation.
We apply the tools of electrical engineering and physics to the problems of signal integrity in digital signals through the entire range of interconnects. The concept of equivalent circuit models is introduced to facilitate the quantified prediction of performance. The rest of the book describes how the circuit models of interconnects affect the electrical perf...
Excellent book for establishing fundamentals of SI: I have read Black Magic by Johnson and believe that Bogatin's book is superior. I bought this book as a beginner hardware engineer and this book does a wonderful job of explaining and integrating different concepts I learned as an undergrad. Universities don't stress SI enough (even at my school, electromagnetics was optional), and Bogatin's book does an great job of integrating and enhancing what one is taught at the unversity level. The reason I prefer this book over Black Magic is that it puts more effort into explaining the fundamentals of Signal Integrity (what causes it, how to fix, etc) rather than going in depth into the mathematical theory and calculations behind the phenomena. As engineers, we have computer programs that do much of this calculating for us and we need to understand "rules of thumb" that will help us design/test better in the future. I believe this book is an excellent addition into any hardware engineer's library, as well as for students intersted in hardware design/test as a career.
Reviews:
Pretty much everything you wanted to know about high-speed design practices:
For a designer it is critically important to maintain a correct mental image of the electromagnetic effects that the design must take into account. Without a clear and balanced mental image flaws might be introduced in the design; corrective measures may not work as anticipated, and may even worsen the situation as is too often the case in the field of high-speed design and EMI control.
Contrary to many who focus on the algebraic developments without guiding the reader through the actual physical meaning of these developments, this book contributes to the establishment of a clear and solid mental image. I especially appreciated the treatment of inductance in chapter 6, as well as the use of field-solver images throughout the book, which help a great deal in visualizing the electromagnetic effects.
Even though it tackles an admitedly difficult subject, the book is actually very easy to read. It explains modern design practices with great clarity.
Superb Practical Information for Signal Integrity Designers: I work in test and measurement as an Application Engineer and assist with Signal Integrity issues/solutions often. "Signal Integrity - Simplified", by Eric Bogatin, is one of the best fundamental overview books on Signal Integrity I have seen.
SI is a growing and vastly misunderstood segment of measurement and Dr. Bogatin does an excellent job at covering the fundamentals in a clear, concise and easy to understand fashion. His coverage of the core of SI is very thorough with entire chapters dedicated to Time and Frequency Domains, Impedance, Transmission Lines, Cross Talk as well as Differential Signals.
Unlike most engineering texts, "Signal Integrity - Simplified" covers key topics with a style that is more intuitive than mathematical. This is refreshing since, for complex topics, mathematical equations do not always speak to every engineer to clarify the issue. Dr. Bogatin uses a variety of word pictures as well as easily understandable diagrams to make his points. This is not to say the book is not technical, it is very technical (he introduces Maxwell's Equations) yet easier to understand than most for complex topics.
Each chapter provides a "Bottom Line" rather than a summary. These are numbered points of one or two sentences reinforcing the key concepts of the chapter. This makes for convenient and easy referral after reading the text. Throughout each chapter, Dr. Bogatin also provides "tips" to drive home a basic point and supply help or insight for the designer. These tips are easy to spot in the book as they are separated from the main text and labeled "tips". The tips alone are worth the price of the book.
Since Signal Integrity is an area effecting engineers working on high-speed products who have not typically had to deal with traditional RF/microwave effects, Dr. Bogatin does an excellent job presenting these rather daunting concepts simply so the designer is up to speed quickly.
The value this text brings is in its
-Intuitive style
-Tips
-Bottom Lines
-General Design Guidelines
-Rules of Thumb
-Appendixes with the Collected Guidelines and Rules of Thumb
This book is a must for your technical library and essential for SI engineers.
Superb introductory book: This is a real book. It is not one of those cut and paste jobs where "authors" throw together material covered in other places. This author has gone through pains to simplify things, explain common misconceptions, and add his own insights. All books should be written like this. I have read many books covering Signal Integrity and yet I still learned a few new ideas and it clarified things for me. It was a joy to read. There are a few things that could have been done better including some of the figures which look like they have been created by an amateur, but these don't take away from the overall good effort.
This book is vastly superior to some highly praised books on Signal Integrity like Hall, Hall, and McCall's book or like Dally's book. It might be too basic to compete with such "distinguished" books but those books can't touch this one in terms of being a real effort to explain things. If you want to progress to more advanced material I recommend the books by Bakoglu, H.B.; Howard Johnson; Brian Young; Ott, Henry; and Paul Clayton. Of course, signal integrity is no black magic and if you really want to progress you can read books on Microwaves ---a field where transmission lines and impedance matching networks were used long before signal integrity books became so popular.
The author puts a lot of practical advice and details into this book. He goes down into the device physics of the circuit elements, in order to derive fundamental formulae for such quantities as the loop inductance of a circular loop. The text also explains ideas like a ground plane and power plane, and why you need to maximise the decoupling capacitance between power and ground. Don't forget that this book is about chip design. So there is advice included on topics like via placements to minimise inductance. And practical tips on understanding lossy transmission lines. The book does exhibit a US engineering bias. The units of measurement often include imperial units, like lengths in mils, or capacitance per length in pFarads per inch. Miserable choices. But if you use metric units, as you should, converting will be straightforward.
Practical advice with just enough theory: I had the excellent book High-Speed Digital Design A Handbook of Black Magic by Johnson and Graham but went ahead and bought this book. I'm glad I did. The two books cover the same subject quite differently and I think they are complementary. Signal Integrity Simplified has many great layout/note tidbits mentioned by other reviewers but the one thing I really liked is that below each formula is an explaination of each variable in the formula, even if you should already know what the variable is from previous formulas and text. This makes it a good reference that doesn't have to be read linearly. In addition, the author gives an example of when each esoteric formula applies and I found myself saying over and over, "Oh, I do have that case in my design." In other words, the examples were exactly what layout or frequency range I was dealing with. "Everyone" knows there are 3 basic circuit elements: resistors, capacitors, and inductors. But this book refers to the fourth, the transmission line. Much of the book is dedicated to this element, as it should be for a signal integrity book. This book focuses on 100 Mhz to 4 Ghz designs. Any modern digital signal has rising/falling edge frequency components in that range. If you are doing board design, don't let the price scare you away, you need this or one of the other signal integrity books. Geez, I sound like one of those glowing fake reviews but I can assure you I've no interest in the sales of this book and have been doing real circuit design for 25 years.