A novel common-mode filter (CMF) design based on signal interference technique

The signal interference technique is firstly employed to design the common-mode filter (CMF) for differential digital circuit applications. Using the network analysis, design curves for three common-mode transmission zeros are available by simple steps. A test sample is realized in two-layer PCB. The fractional bandwidth of common-mode suppression band (|S_cc21| <; -10 dB) is 63 %, from 3.85 GHz to 7.4 GHz. The transmission coefficient of differential mode (|S_dd21|) is better than -3 dB from DC up to 10 GHz in measurement. The flat differential-mode group delay implies this CMF can preserve good signal integrity, which is obvious by eye diagram measurement in time domain.