Hybrid differential transmission line bend to suppress common-mode noise

A new type of differential transmission line with a bend is proposed to reduce differential-to-common-mode conversion noise for high-speed digital circuits. The hybrid structure consists of alternating edge-coupled and broadside-coupled transmission line sections which has the effect of reducing the mode conversion noise by at least 20 dB up to 10 GHz, whereas the differential insertion loss remains low. In addition, in the time domain, the common-mode noise is lower than the conventional edge-coupled differential transmission line bend. The performance of the proposed structure with a bend is demonstrated both numerically and experimentally. The measurement results agree very well with the simulation results from the three-dimensional full-wave solver.