A Novel Compact Dual-Functional Circuit with Differential-Mode Equalization and Broadband Common-Mode Suppression Using Patterned Ground Plane

A new passive differential-mode equalizer equipped with the function of common-mode suppression is proposed by using differential shunt stubs and patterned ground structure. The differential shunt stub is mainly responsible for generating the high-pass response in differential mode to achieve the equalization effect with data rate up to 10 Gbps, while the patterned ground structure is responsible for creating the wideband common-mode suppression from 2 GHz to more than 10 GHz. The equivalent circuit model is constructed and frequency-domain analysis is applied to calculate the even-mode and odd-mode responses. The calculated responses are validated and then used to solve the approximated resonant frequencies and cut-off frequency of the common-mode response analytically. Additionally, time-domain eye simulation, full-wave simulation and measurement are performed to verify the effectiveness of differential-mode equalization and wideband common-mode suppression. Most crucially, this proposed circuit not only provides better performance on signal integrity, but features the most compact size in 2-layer PCB and the lowest frequency 2.1 GHz of the common-mode stopband, in contrast to the previous works.