High speed signal transmission compatibility with noise suppression by common mode chokes

The technical issues about the common mode chokes to design the high-speed signal transmission that are compatible with the electromagnetic noise reduction are discussed. A conventional common mode choke cannot be used for high speed signal transmission because the waveform is degraded by the transmission characteristics at high frequencies. The common mode choke of shielded wire structure is proposed, which can realize the GHz class signal transmission without the degrading noise reduction characteristics ranging from low to high frequencies. Comparing the measurement results of the proposed common mode choke of shielded wire structure with the conventional common mode choke, it is confirmed that Sdd21 of the proposed choke is only -2dB at 4GHz, whereas the conventional choke is -10dB at 4GHz.