A novel differential serpentine delay line to reduce differential to common mode conversion and impedance discontinuity

Abstract

A novel differential serpentine delay line is proposed in this paper for intra-pair (positive and negative trace) length matching as well as inter-pair skew between other pairs simultaneously. It contains several differential U-turn structure in which each U-turn has two different kinds of corners (e.g. two corners are 45 degree while the other two are round). Full-wave simulation was done between traditional length matching scheme and the novel one, which indicates that novel serpentine delay line has nearly 5-15dB reduction in differential to common mode conversion below 14GHz in microstrip application and almost 10dB reduction at full frequency range in stripline application, additionally impedance continuity can be improved from 108Ω to 102Ω, several print circuit board (PCB) were made and tested, the test result matched with simulation.