3.1 Introduction

The waves found in logic are step functions and the radiating geometries are certainly not simple dipoles. Most of the literature that is available on radiation discusses sinusoidal wave patterns from antenna or wave guide type structures. Circuit board radiation does not result from a recognized structure, and the wave forms are not sinusoidal. To discuss radiation and field coupling, we will use the accepted terminology although it may not be a good fit. For example, the term wave impedance applies to sine waves and not step functions.

Interference on a circuit board can result from external fields in the environment or from fields that originate on the circuit board. Cables that interconnect circuit boards or hardware can carry interference fields into the circuitry. This is sometimes called conducted interference. When these fields couple into logic signal paths, they take up a part of the available noise budget.