Application Note 389 Follow PC-Board Design Guidelines for Lowest CMOS EMI Radiation

The need to reduce a logic system’s noise emission is becoming ever more apparent with the increased use of high-speed electronics, and with the progressive tightening of regulations covering the amount of permissible radiated system noise. This article presents empirical and analytical techniques for effective EMI control of 54HC/74HC high-speed CMOS-logic circuitry. Several sources conduct or radiate EMI from electronic apparatus. Among these are • antenna loops formed by ICs and their decoupling capacitors • pc-board traces carrying driving-and driven-chip currents • common-impedance coupling and crosstalk. To minimize EMI-related problems, you must reduce all extraneous system noise, reduce the effects of parasitic pc-board trace antennas, and employ effective system shielding. The following sections examine these EMI sources and present techniques of minimizing them for high-speed CMOS logic.