High Speed Digital Design: A Handbook of Black Magic
by: Howard W. Johnson
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This book focuses on a combination of digital and analog circuit theory. Helps engineers who work with digital systems, shorten their product development cycles and fix their latest high-speed design problems. DLC: Digital electronics. From the publisher, Prentice-Hall ECS Professional: Focused on the field of knowledge lying between digital and analog circuit theory, this new text will help engineers working with digital systems shorten their latest design problems. The scope of the material covered includes signal reflection, crosstalk, and noise problems which occur in high speed digital machines ( above 10 megahertz). This volume will be of practical use to digital logic designers, sstaff and senior communitions scientist, and all those interested in digital design. The text concentrates on a combination of digital and analog circuit theory, this comprehensive volume will help engineers who work with digital systems, shorten their product development cycles, and fix their latest high-speed design problems. Topics covered include: signal reflection, crosstalk, and noise problems that occur in high-speed digtal machines (above 10 megahertz). lncludes checklists that ask the questions an experienced designer would about a new system. Offers useful formulas for inductance, capacitance, resistance, rise time, and Q. Explains the trade-offs between signal cross talk, mechanical fabrication of tolerances, and trace routing density. Presents a methodology for determining how many layrs will be required to route a printed circuit board. Howard W. Johnson is president of Olympic Technology Group, Inc., of Redmond, Washington, a digital electronic design and consulting organization. Before founding the firm, he was Manager of Technology and Advanced Development at Ultra Network Technologies, a manufacturer of gigabit-per-second local area networks for supercomputers. Since obtaining his Ph.D. in 1982 from Rice University, he has specialized in the design of high-speed digital communications and digital signal processing systems. Martin Graham has been a Professor of Electrical Engineering and Computer Sciences at the University of California at Berkeley since 1966, where he teaches the design of reliable and manufacturable electronic systems. Excerpt from this book: Preface This is a book for digital designers. It highlights and explains analog circuit principles relevant to high-speed digital design. Teaching by example, the authors cover ringing, crosstalk, and radiated noise problems which commonly beset high-speed digital machines. None of this material is new. On the contrary, it has been handed down by word of mouth and passed along through application notes for many years. This book simply collects together that wisdom. Because much of this material is not covered in standard college curricula, many practicing engineers view high-speed effects as somewhat mysterious, ominous, or daunting. For them, this subject matter has earned the name "black magic." The authors would like to dispel the popular myth that anything unusual or unexplained happens at high speeds. It's simply a matter of knowing which principles apply, and how. Digital designers working at low speeds do not need this material. In low-speed designs, signals remain clean and well behaved, conforming nicely to the binary model. At high speeds, where fast signal rise times exaggerate the influence of analog effects, engineers experience a completely different view of logic signals. To them, logic signals often appear hairy, jagged, and distorted. For their products to function, high-speed designers must know and use analog principles. This book explains what those principles are and how to apply them. 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 may comprehend this material at a deeper level. Chapters 1-3 introduce analog circuit terminology, the high-speed properties of logic gates, and standard high-speed measurement techniques, respectively. These three chapters form the core of the book and should be included in any serious study of high-speed logic design. The remaining chapters, 4-12, each treat specialized topics in high-speed logic design and may be studied in any order. Appendix A collects highlights from each section, listing the most important ideas and concepts presented. It can be used as a checklist for system design or as an index to the text when facing a difficult problem. Appendix B details the mathematical assumptions behind various forms of rise time measurement. This section helps relate results given in this book to other sources and standards of nomenclature. Appendix C lists standard formulas for computing the resistance, capacitance, and inductance of physical structures. These formulas have been implemented in MathCad and are available from the authors in magnetic form.
Reviews:
An overview/summary with little theoretical development: An overview/summary of many basic concepts but with little theoretical development based on physical models. For example, the authors discuss transmission lines but don't trouble themselves to show the incremental circuit model of a transmission line or the differential circuit equations, they simply state the solution of the differential equations. Likewise the authors inadequately discuss how terminations affect transmission lines and fail to show how the reflection coefficient follow from the physical model. The point of showing the theoretical underpinnings is to make clear when the stated solutions are valid and more importantly, not valid. In ignoring the physical models, the authors do a disservice to their readers. An altogether disappointing book.
Mostly a very solid book:
A disservice to an important and beautiful subject: Superficially this books appears to be a treatise on the subject. But a more careful look reveals a lack of motivation, justification, or proof for any idea presented. Indeed there are no direct references to other authorities so as to allow the reader to either confirm a purported fact or take a deeper look at a particular point. What results, instead, is a compilation of alleged "facts" (none are proved and all are stated without proof) in cook book style. Even more, some of the formulas are not verifiable by spice simulation, and even conflict with other formulas bearing on the same issue. The overall impression of this book is that it is a hodge podge of ideas drawn from other sources, without any coherent theme. In the end Johnson performs a disservice to his readers by promoting the idea that the subject is nothing more than "black magic." It is not, and there are many other books and application notes stretching back decades which bear testimony to this fact. The very essence of the subject is a study of the effects of parasitic elements which become dominant in the presence of high edge rate signals. In this regard high speed digital design draws more heavily upon analog design, with a particular emphasis on rf design techniques. By leaving out all derivations, the reader is never truly educated on this subject and is thereby left in the dark.
Useful textbook if you need a cook book, but.......This book is useful if you want to have a long series of equations available in one place to jog your memory. But if you want to learn something useful and practical- and real-world - then perhaps you would be better off doing a web search for application notes, tutorial papers, and articles, particularly from semiconductor manufacturers, and vendors of high-performance test equipment such as Agilent, Tektronix, and others. To take one example (page 134,) Johnson purports to describe problems associated with a wire-wrapped prototype processor board containing TTL devices operating at high edge rates ( 2 ns.) According to Johnson, the design engineers failed to realize that the circuits would ring excessively, making the board unusable. To "prove" this he posits a model consisting of a 30 ohm TTL driver, with a 2 ns rise time, a 4" length of wire with 89 nH of self inductance, and a 15pf load - a series LRC circuit. Yes, this circuit will ring wildly, but the model is totally incorrect. The TTL input is not considered, which has a relatively low input impedance in the low state since it is current operated. This circuit -effectively a parallel LRC - does not ring nearly as much, as any experienced engineer knows. As a reality check, remember that wire wrap was successfully used for years by thousand of engineers. To listen to Johnson, though, this technology is almost unusable. Wire wrap circuits do ring, but under his example, the real amount of overshoot/undershoot is well within the limits of TTL. Further, no real circuit produces textbook looking traces, so the role of experience is to learn what worst-case design means, and what is acceptable for good manufacturing yield. Lesson: real experience teaches you how to produce correct, functional models. An incorrect model will cause you grief. Much could have been done here, to be useful, by way of analysis and of recommendation. The wire should have been modeled as part of a transmission line, not as a lumped element, which any high speed digital design engineer would know, and the idea of terminating a transmission line should have been introduced. This is standard fare. Even with the series LRC, instead of deriving the formula for critical damping, he instead says: "This approximation (reduce Q to .5) is derived from the solution to a second order linear differential equation describing an RLC low pass filter. First find the point at which the derivative of the solution passes through zero (a maximum point) and then evaluate the solution at that point." Got that? Take the derivative of a solution you want to find? Any book on circuits will reduce this to the solution of a quadratic equation. Obfuscating something that's really elementary does not help produce genuine insight. But this is what Johnson does throughout the book. Isn't it simpler to say that if you have fast rise time signals, treat most connections as transmission lines, and add termination resistors? As for a series RLC, use the formula for critical damping: R = 1/2 (sqrt(L/C))