Fast Circuit Boards

Energy Management

Ralph Morrison

• Publisher: Wiley
• Year: 2017
• Print ISBN:
  9781119413905
• Edition: 1
• eBook ISBN:
  9781119413998
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

An essential guide to modern circuit board design based on simple physics and practical applications 

The fundamentals taught in circuit theory were never intended to work above a few megahertz, let alone at a gigahertz. While electronics is grounded in physics, most engineers' education in this area is too general and mathematical to be easily applied to the problem of high speed circuits. Left to their own devices, many engineers produce layouts that require expensive revisions in order to finally meet specifications.

Fast Circuit Boards fills the gap in knowledge by providing clear, down-to-earth guidance on designing digital circuit boards that function at high clock rates. By making the direct connection between physics and fast circuits, this book instills the fundamental universal principles of information transfer to give engineers a solid basis for hardware design. Using simple tools, simple physics, and simple language, this invaluable resource walks through basic electrostatics, magnetics, wave mechanics, and more to bring the right technology down to the working level.

Designed to be directly relevant and immediately useful to circuit board designers, this book:

• Properly explains the problems of fast logic and the appropriate tools
• Applies basic principles of physics to the art of laying out circuit boards
• Simplifies essential concepts scaled up to the gigahertz level, saving time, money, and the need for revisions
• Goes beyond circuit theory to provide a deep, intuitive understanding of the mechanisms at work
• Demonstrates energy management's role in board design through step function-focused transmission line techniques

Engineers and technicians seeking a more systematic approach to board design and a deeper understanding of the fundamental principles at work will find tremendous value in this highly practical, long-awaited text.

1
Electric and Magnetic Fields

Buildings have walls and halls.
People travel in the halls, not the walls.
Circuits have traces and spaces.
Energy travels in the spaces, not the traces.

Ralph Morrison

1.1 Introduction

I have written many books that discuss electricity. The sixth edition to my Grounding and Shielding was published in 2016. Each time I start to write, it is because I have added to my understanding and I feel I can help others solve practical problems. The digital age is upon us and it is making demands on design that are not covered by circuit theory. In one sense, logic is easier to handle than sine waves as there is no phase shift to consider. As clock rates rise there are a host of other problems that must be considered. The tools of circuit theory are in many ways a mismatch for fast circuits and some new methods need to be introduced. Circuit theory does not consider time of transit and this is a key issue in logic design.

The insight that has led me to write this book involves one key word and that word is energy. Engineers are taught that stored energy can do work and that there is conservation of energy. What I want to point out is that all electrical phenomena is the movement or conversion of energy. When a logic signal is placed on a trace, the voltage that is present means that energy was placed on a capacitance. This energy had to be moved into position and it had to be done in a hurry. It cannot be done in zero time as this would take infinite power. The movement of voltage in circuit theory does not mention moving energy and that one fact leads to many difficulties. For example, energy is not carried or stored in conductors. It is carried and stored in spaces. This requires a different point of view. Providing this insight is the reason for writing this book.

I am writing this book to help you avoid problems when laying out digital circuit boards. This first chapter is about the fundamentals of electricity. You may opt to skim over this material but I would hope to change your mind. I want to show you how electricity works but not from a circuit theory viewpoint. I want to show you how to use the spaces that carry energy between components. This may be a new way for you to view electricity. Circuit theory pays little attention to spaces. Conductors outline the spaces used by nature to move field energy.

I am writing this book to describe the role fields play in moving energy on transmission lines. Most of the literature relating to transmission lines revolves around sine waves. There are insights to be gained when step functions are applied to moving energy. These insights can help you in today’s designs and prepare you for the future which is headed in the direction to move more and more digital data. Whatever the future holds, fundamentals apply.

This opening chapter will help to set the stage for discussing transmission lines. Once you see how nature really works, you will find it easy to accept the material in the later chapters. I have spent my career learning and applying this material and I know why basics come first. What is even more important is connecting these basics to real issues and that is not always easy. That is my objective in writing this book.

It is worth a moment to describe a problem in understanding. In reading posted online material, the language that is used often implies a picture of electrical behavior that is invalid. A writer may say that “—the return path impedance is too high.” The impedance of a transmission path is really the ratio of electric and magnetic fields involving the space between the forward and return current conductors. It is incorrect to treat the forward and return paths this way. It takes care in the use of language and a clear understanding of basics to communicate clearly. In this book I have chosen my words carefully and I hope they are read with the same care. I realize there are strange explanations that must be unlearned and that is not always easy to do. Currents do not travel one way on the surface of a conductor and return down the middle of that same conductor. I will not spend time trying to argue this point.

There are many ways to learn electronics. Diagrams that include connections between components are common. These diagrams make no attempt to suggest that energy is flowing in the spaces between the connections. It is through experience that an engineer learns that component locations and wiring methods are important. Understanding the mechanisms involved is presented in this book. What is hard to accept is that there are a lot of habit patterns that develop over the years. Some of these patterns may work at the time but lead to problems as the logic speeds increase. Looking back, I can say that many published application notes I tried to apply were invalid.

A good example of the problem ex...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• 1 Electric and Magnetic Fields
• 2 Transmission Lines—Part 1
• 3 Transmission Lines—Part 2
• 4 Interference
• 5 Radiation
• Appendix A: Sine Waves in Circuits
• Appendix B: Square‐Wave Frequency Spectrum
• Appendix C: The Decibel
• Appendix D: Abbreviations and Acronyms
• Index
• End User License Agreement