A novel wideband common-mode suppression filter for differential signal transmission

A novel wideband filter is designed for common mode noise (CMN) suppression in high-speed differential signaling. The dumbbell-shaped defected ground structure (DGS) is periodically etched in the return path of differential line to suppress CMN. In order to improve the signal quality of the differential transmission, a periodic stub-loaded structure is designed to compensate the discontinuity of the odd-mode characteristic impedance. Furthermore, a slow-wave structure is employed to decrease the Bragg frequency and then enhance the bandwidth of CMN suppression effectively without enlarging the circuit size. The simulated and measured results of the prototype indicate that the CMN can be suppressed over 20 dB from 3.2 to 8.6 GHz by the filter, while good transmission characteristic can be achieved for the differential signals.