A Common-Mode Filter with Three Alterable and Designable Transmission Zeroes

A common-mode suppressing circuit with three transmission zeroes is proposed to improve the electromagnetic compatibility (EMC) for high-speed digital circuits. A design method is also established for the proposed circuit to control the transmission zeroes. Based on the concept, a common-mode filter can be easily designed as broadband suppressing type or high-level suppressing type. Both of the two types are implemented in low-temperature co-fired ceramic (LTCC) fabrication as a component with a compact size of 3 ⨯ 2.3 mm2. The broadband one has a −10 dB stopband from 1.3 GHz to 5.25 GHz and the other one can reduce the common-mode noise over 20 dB from 2.25 GHz to 5.0 GHz. In addition, both of the two designs are with good signaling quality for differential mode.