Improvement of EMI Filter Performance With Parasitic Coupling Cancellation

TLDR

The study identifies critical parasitic couplings in EMI filters and proposes cancellation methods to enhance filter performance. A cancellation inductor is integrated with capacitors to null mutual coupling between capacitors and ESL, applied to rectangular and tubular capacitors, with two integration approaches compared and prototypes built for one‑stage and two‑stage filters. Experimental results demonstrate that the mutual coupling cancellation technique markedly improves high‑frequency EMI filter performance.

Abstract

In this paper, critical parasitic couplings in EMI filters are first identified. Based on the understanding of filter parasitics, methods are proposed to improve EMI filter performance by canceling critical couplings. A cancellation inductor is then integrated with capacitors to cancel the mutual coupling between two capacitors and the equivalent series inductance (ESL) of the integrated capacitor. The proposed method is applied to both rectangular and tubular capacitors. Two different integration approaches are also compared. Finally, prototypes are built and tested for both one-stage and two-stage EMI filters. Experimental results show the proposed mutual coupling cancellation technique can drastically improve EMI filter high frequency performance.