EMI measurements in pseduo-differential signaling for SDRAM interface

Abstract

Near-field EMI measurements were successfully performed by using an H-field probe for a differential and a single-ended microstrip transmission line on FR4 PCB; empirical equations were derived for H_r and H_θ w.r.t. the distance from the transmission line by applying a 3 GHz clock signal to the terminated microstrip lines. The comparison of the near-field EMI measured at 1 mm from the transmission line for a single-ended, a differential and a pseudo-differential signaling showed that the differential EMI was lower than the single-ended EMI by 28 dB, and the pseudo-differential EMI was lower than the single-ended EMI by 10 dB when the delay mismatch between the two clock signals was 5 % of the clock period. This EMI measurement of the pseudo-differential signaling can provide the EMI criterion for the maximum delay mismatch between two strobe clock signals used in the SDRAM interface.