The gigahertz two-band common-mode filter for 10-Gbit/s differential signal lines

In addition to the desired differential signals, the undesired and EMI harmful common-mode noise may propagate along differential signal lines. Conventional common-mode filters such as ferrite chokes - which work well in lower frequencies below 1 GHz - have limited effectiveness in the gigahertz frequency range. To suppress critical common-mode in this frequency range without degrading the quality of the differential signals, the gigahertz common-mode filter structure is proposed herein. This design is directed to a compact-size electromagnetic band gap (EBG) structure suitable for placement in a multilayer PCB, individual IC chip package, or in an optical transceiver module. The filter provides common-mode suppression at 10-Gbit/s differential signal lines for the frequencies 10.3125 GHz and 20.625 GHz, where common-mode noise is highly problematic.