Fast Circuit Boards

1Electric 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. ...