Stepped-impedance common-mode filter in differential lines

High speed digital systems require differential lines for chip-to-chip links. A common concern in differential lines is the presence of common-mode noise, which can also be converted to differential mode, affecting the signal integrity of the differential channel. This paper presents a methodology based on varying the common-mode impedance of a differential line, while keeping the differential-mode constant. The variation in impedance results in a filter response solely for the common-mode signals, improving the noise immunity of the differential pair.