Chapter 12 - Digital and analogue circuit design

Abstract

The control measures can be conceived at three levels—primary, secondary, and tertiary. Control at the primary level involves circuit design measures. This chapter discusses circuit design—both digital and analogue. Circuit design is an essential contributor to electromagnetic compatibility (EMC). In this area, the techniques used to control radio frequency emissions from an operating circuit can be distinguished from those used to control radio frequency and transient immunity of an operating circuit. The chapter discusses the design for emissions control. Digital circuits are prolific generators of electromagnetic interference. High-frequency square waves, rich in harmonics, are distributed throughout the system. Analogue circuits are in general much quieter because high-frequency square waves are not normally a feature. The chapter also explores the design for immunity. Analogue signals are more affected by continuous interference, which is rectified by nonlinear circuit elements and causes bias or signal level shifts. The immunity of analogue circuits is improved by minimizing amplifier bandwidth, maximizing the signal level, using balanced configurations, and electrically isolating I/O that will be connected to “dirty” external circuits.