Effects of parasitic parameters on EMI filter performance

Two filters with identical topologies and components can exhibit a significant difference in filter effectiveness when the layouts are different. The goal of this paper is to examine the effects of parasitic couplings among the filter components and the coupling between the filter components and the ground plane of printed circuit board (PCB). Specifically, six different coupling effects are investigated: the couplings between the inductor and capacitors, a filter inductor and trace loops, two filter inductors, two capacitor parasitic inductances, a filter inductor and ground plane, and two trace loops. Experiments were performed, theories were developed to investigate and characterize these parasitic couplings.