An alternating high‐low impedance common‐mode filter for differential striplines

Abstract

The conventional quarter/half-wavelength common-mode filter (CMF) cannot work well for a differential stripline when there is no ground via. A new and effective viafree CMF design for the differential striplines is proposed in this study. An alternating high-low impedance structure is developed to increase the coupling between the stripline and the CMF, thus achieving a good filtering effect. A cascaded CMF design is further studied to enhance the stopband without deterioration of the differential signals. Both simulation and measurement results demonstrate the effectiveness of the proposed high-low impedance CMF. The significant advantage of the proposed CMF is its compactness and simplicity, which has almost no impact on the original layout of differential striplines.