A method of common-mode reduction based on imbalance difference model for differential transmission line bend

A differential transmission line bend generates a large common mode due to its asymmetry, and it leads signal integrity problems. In this paper, the imbalance difference model, which was proposed by the authors for estimation of common-mode radiation, is extended to apply to the differential signaling systems. An equivalent circuit model based on the imbalance difference model is proposed for estimation of the common-mode excitation at the bent area. Simulation results of mode conversion from the differential mode to the common mode calculated by the proposed model are in good agreement with those using a three-dimensional electromagnetic solver. In order to reduce the common mode, a guard trace is added near the narrowed inner signal line at the bent area and it gives 15 dB of reduction of the common mode.