In this paper, the power plane resonance problem in a multi-layered PCB is numerically analyzed by applying the alternating-direction implicit (ADI) FDTD method. This method is extremely suitable for analyzing the power plane resonance problems having locally fine structures of two closely located planes. This paper also analyzes the effect of the decoupling capacitor, which is one of the solutions for reducing the resonance problem. The results of the ADI-FDTD agree well with those of the conventional FDTD and the analytic solutions, and the computational CPU time is reduced to about a half of that of the conventional FDTD.

This paper presents a new decoupling circuit for suppressing radiated emissions due to power plane resonance in multilayer printed circuit boards (PCBs). This circuit is based on transmission line theory, and consists of two decoupling capacitors and one power trace. The two capacitors, one mounted on the power pin of an IC and the other mounted on the common power distribution bus in a board, are connected through the power trace. The characteristic impedance of the trace is much higher than the impedance of the capacitors. In addition, the length of the trace between the capacitors is less than 1/4 the effective wavelength for high frequency (e.g., 1 GHz). Tests we performed on simple PCBs confirm that our decoupling circuit suppresses radiated emissions due to power plane resonance.