Digital Circuit Boards: Mach 1 GHz

1.2 Why the Field Approach is Important

All electrical behavior from dc to light can be described in terms of the electric and magnetic fields. For many reasons, a field approach to circuit function is very impractical. This is why engineers heavily rely on circuit theory as a working tool. Our understanding of how a circuit functions is closely related to the circuit symbols we have created and to the language we use. When we use capacitors and inductors in our analysis we think of reactances and we generally ignore the fields and energy storage that are inside of these components. In a typical circuit design, the energy that is moved and stored between traces or between traces and a conducting plane is not considered. In high speed logic, this movement of energy must be considered. In fact, this energy must be controlled and dissipated so that the logic can function. The dissipation of this energy can be a serious problem as it can cause board overheating.

Every component is a conductor geometry of some sort. Fields inside the components determine their performance. In a FET (field-effect transistor), there is an electric field between the source and drain. Fields carry operating power and signals to the components over the connecting traces. Getting these fields to the components on a timely basis is handled by traces. The rou4ing of traces is a problem, and we discuss this in great detail later.

Nature does not read our circuit diagrams or symbols. She approaches a circuit ...