EMC in digital circuit design

Abstract

Digital circuits are finding increasing use in equipment design. Unlike analog circuits, digital circuits do not degrade gracefully in the presence of electromagnetic interference. The user of equipment including digital circuits generally faces a 'go'-'no-go' situation. Further, digital circuits are major polluters of the electromagnetic environment (EME). A digital circuit designer faces a large number of choices; from the choice of logic families available for design to selection of clock rates and PCB design options. The paper provides a digital circuit designer with various design guidelines to achieve immunity enhancement of digital circuits from both internal and external interference, and also to reduce electromagnetic pollution of the EME. Circuit techniques assume importance because it is the logic on the board which is the ultimate culprit or victim in a given EMI situation. Good circuit techniques do not cost much and will ultimately reduce the dependence on traditional electromagnetic compatibility (EMC) techniques like grounding, shielding and filtering.