Design of Low-Loss Transmission Lines with Common Mode Suppression for Packages

Increasing data rates of high speed serial interfaces forces the insertion loss and common mode (CM) noise requirements to be tighter. This paper addresses both of these challenges by introducing a new low-loss transmission line design with simultaneous common mode filtering property. The line is composed of periodical repetitions of narrow and wide sections, which generates a CM impedance contrast to filter out the CM noise, while differential impedance is kept constant by locally voiding the planes below and above the wide trace sections. As a result of the wider sections, the loss is also smaller.