Techniques to Reduce the Equivalent Parallel Capacitance for EMI Filters Integration

Abstract

One of the major goals in designing of the integrated EMI filters is to improve their highfrequency characteristics. To achieve this, special technologies need to be developed, including the mechanisms for suppression of the equivalent parallel capacitance (EPC) and of the equivalent series inductance (ESL), in spite of increasing the high-frequency losses. In this light, the main goal of the paper is to develop and analyse the effectiveness of several EPCreducing technologies. The study is performed using the numerical analysis software Maxwell Q2D Extractor that is able to give at the end of the numerical analysis process the values of the lumped per-unit-length capacitance or inductance of the geometrical structure proposed. There are calculated the EPC of the four single winding structures and of the coupled windings. The main component of an EMI filter is the low pass filter; therefore, in order to develop the integrated low pass filter, the integrated L-C structure must be carefully studied and modelled. The planar integrated L-C structure consists of alternating layers of conductors, dielectrics, insulation and ferrite materials that produce an integrated structure with similar terminal characteristics as the lumped components. The exploded view of an integrated L-C structure was shown in Figure 1 [WLD03]. The integrated L-C winding consists of a dielectric substrate with conductor windings directly deposited on both sides, thus resulting in a structure having both sufficient inductance and capacitance. This realizes the equivalent integrated capacitance as well as the inductance. By appropriately terminating the four terminals A, B, C and D of the integrated L-C winding, the same structure could be configured as equivalent L-C series resonator, parallel resonator or low pass filter. To integrate the EMI filter, the L-C low pass filter configuration is used, where AD is the input port and CD is the output.