Improving EMI filter design with in circuit impedance mismatching

This paper discussed improving EMI design based on propagation path impedance. The way conventionally used in EMI filter design barely includes information on propagation path impedances, although this information is well known as important to filter topology selection and its in-circuit attenuation; besides, filters attenuation is usually measured by small signal insertion gain, which is different from real in-circuit attenuation. This paper starts from the propagation path impedance characterization, and then it investigates into the impacts of the propagation path impedance on the in-circuit filter attenuation. Parasitic effects of the filter are included in the analysis. Parasitics creates multiply resonances and anti-resonances in the propagation path, which can be reflected in filter in-circuit attenuation. By accurate control and design of these parasitic, we can take the advantage of parasitics to improve the filter performance. Furthermore, knowing the relationship between filter impedances and propagation path gives better understanding of how to design an effective filter for noise reduction.