Intra-pair Length Matching by Asymmetric Dual Bend to Reduce Mode Conversion

Asymmetric dual bend (ADB) technique for intra-pair length matching of differential routing is proposed in this paper, to reduce the differential mode to common mode conversion in system. This layout technique helps in achieving lower EMI without impacting SI performance and with insignificant effect on PCB cost. Three types of asymmetric dual bend designs are evaluated in this paper, by simulating the EMI and SI performance in two layout scenarios i.e. fixed length and fixed location routing. The results illustrate that the asymmetric dual bend scheme can provide 10+ dB improvement for Scd21 in stripline layout and nearly 5dB improvement for microstrip layout. Several PCB coupons were also made, and the results match quite well between simulation and measurement.