VNA-based fixture adapters for wideband accurate impedance extraction of single-phase EMI filtering chokes

Abstract

Differential-mode and common-mode chokes (DMC and CMC) are key components of electromagnetic interference filters. Accurate impedance knowledge of these chokes allows optimal EMI filter design to meet the conducted emission requirements. An impedance analyzer or vector network analyzer with a fixture adapter is commonly adopted for impedance measurement of a passive component. Usually, the non-standard terminals of both DMC and CMC make them incompatible for direct mounting on commercially available fixture adapters. Relying on additional interconnects to the fixture adapters introduce inherent parasitic effects that limit measurement accuracy up to several megahertz. This article proposes a design method of customized fixture adapters which are specifically tailored for impedance measurement of single-phase DMC and CMC. Through a systematic parasitic de-embedding process, the choke impedance can be extracted with excellent accuracy up to 120 MHz.