Common-mode noise reduction schemes for differential serpentine delay microstrip line in high-speed digital circuits

Abstract

This work proposes two noise reduction schemes that use strongly coupled vertical-turn traces as substitute for weakly coupled vertical-turn traces and added guard traces to reduce the common-mode noise in a weakly differential serpentine delay microstrip line. The peak-to-peak amplitude of common-mode noise in the time-domain is reduced by bout 65% using the two methods, according to simulation results. The simulation results demonstrate that the frequency range over which the magnitude of differential-to-common mode conversion is reduced for a differential serpentine delay line with is wide band in the range 0.1∼2.7GHz and 3.2∼10GHz. Furthermore, the differential reflection loss for additional guard traces is only slightly reduced at the frequency of interest, but when strongly coupled vertical-turn traces are used. However, the differential insertion loss achieved using the two improved schemes is almost the same as that of the traditional pattern.