A new common-mode noise reduction scheme for weakly coupled differential serpentine delay microstrip lines

This work proposes a new common-mode noise (CMN) reduction scheme that involves different-layers-routing turned traces to reduce the CMN in weakly coupled differential serpentine delay microstrip lines (DSDMLs). The purpose of using different-layers-routing turned traces instead of same-layer-routing coupled turned traces (CTTs) (conventional scheme) is to cause the difference between the delay times of the two traces of the turn-traces section to approach zero to minimize the CMN. Moreover, the CMNs in weakly coupled DSDMLs achieved using various reduction schemes are compared. The proposed solution obtains a peak-to-peak amplitude of CMN in the time domain simulation that is more than 90 % with respect to the corresponding value obtained using the conventional scheme. The proposed reduction scheme in DSDMLs reduces the differential-to-common mode conversion (|S_cd21|) by more than 20dB in the range 4.5GHz~16GHz. The range of frequencies over which CMN is reduced is very wide, being almost the full band (DC~16GHz). The reduction using the proposed reduction scheme exceeds those achieved using previous reduction schemes, strongly coupled turned-traces and guard traces.