Investigation on common-mode noise for differential lines crossing other differential lines

Abstract

This work investigates the common-mode noise (CMN) for a weakly coupled differential microstrip lines (WCDMLs) that crosses a weakly coupled differential embedded microstrip lines (WCDEMLs) with different degrees. Time- and frequency-domains analyses of the proposed structure are performed to investigate the CMN by studying the differential-to-common mode conversion and the time-domain CMN waveform using the 3-D full-wave simulator HFSS and CST. According to analyzed results, the magnitudes of time- and frequency- domains near-end CM crosstalk are both large than far-end CM crosstalk for a weakly coupled differential microstrip lines (WCDMLs) that crosses a weakly coupled differential embedded microstrip lines (WCDEMLs). In addition, the amount of far-end CMN is small and almost independent of the crossing angle. For a small crossing angle, the very asymmetrical crossing area causes the differences between the propagation times of the two signals on the differential traces and the coupling noises on the other two differential traces to both are large.