High-speed common-mode prediction method for PCBs having a signal line close to the ground edge

Evaluation of common-mode excitation is important to efficiently reduce the EMI radiated from printed circuit boards (PCBs). We have focused on the excitation mechanisms of the common-mode current flowing on a PCB. In a previous paper, we explained a mechanism of common-mode excitation in terms of the current division factor, which expresses the degree of imbalance of a transmission line. The calculation is two-dimensional so the evaluation time is much shorter than that of FDTD or other 3D full-wave simulations. The calculated reduction of common-mode radiation from simple PCBs agreed well with the measured value. In this paper, to demonstrate the effectiveness of this approach, we apply it to various PCBs, such as one that has a signal trace close to a board edge or one with guard bands, and evaluate the effectiveness of the common-mode reduction. Our calculated and experimental results are in good agreement.