Bypass Capacitor Design for Wideband Impedance Measurements of Inductive Coupling Approaches

In-circuit impedances of power converters are pivotal for the prediction and mitigation of electromagnetic interference (EMI) in power electronics applications. Inductive coupling approaches, favored for their safety and non-intrusive nature, are the preferred solutions for in-circuit measurements. Given that the power converters are operational under test, a set of capacitors is essential to show low impedances at a frequency of interest and bypass the effects of loads. Owing to inherent parasitics in capacitors, their performance deviates from ideal and produces inductive behavior at high frequencies, ultimately constraining the usable frequency range of inductive coupling approaches. In this paper, an innovative strategy for wideband bypass capacitor design is proposed and illustrated. Several individual film capacitors are paralleled and packaged in a printed circuit board to form the bypass capacitor. Their impedance frequency responses are measured through the two-port circuit de-embedding method and the parasitics of PCB are extracted via the boundary element analysis. Consequently, an equivalent circuit model of this bypass capacitor is constructed, enabling the impedance derivation grounded in circuit theory. The experiment validates the efficacy of the proposed capacitor, showcasing consistently low impedances spanning a wideband frequency range from 100 kHz to 1 GHz.