An ESL-Cancelling Circuit for a Shunt-Connected Film Capacitor Filter Using Vertically Stacked Coupled Spiral Loops

This article reports an ESL-canceling circuit using vertically stacked coupled spiral loops for a shunt-connected film capacitor filter. The proposed circuit is applicable to shunt-connected capacitor filters, where the equivalent series inductance (ESL) in the shunt path deteriorates filter performance above the self-resonant frequency. Previously reported ESL cancellation techniques are employed magnetically coupled loops. These loops equivalently add negative inductance into the shunt path, canceling ESL and improving filter performance. However, a major challenge in ESL cancellation circuits employing windings or loops is the miniaturization of the coupled elements. To overcome this limitation, it is necessary to develop a more efficient magnetically coupled structure to achieve a compact filter design. In this article, an ESL-canceling circuit for a film capacitor was designed based on the Biot–Savart law and electromagnetic analysis. A prototype of the circuit was fabricated and measured. The measurement results confirmed that the filter performance improved by 20 dB above the self-resonant frequency, as designed. A comparison between the spiral loop configuration and the conventional square loop configuration was conducted. The results showed that the spiral loop configuration reduced the area of the square loops by 40% . This result indicates that applying the spiral loop configuration enables the miniaturization of the ESL-canceling circuit.