Parasitic capacitance cancellation of integrated EMI filter by splitting ground windings

High-frequency (HF) attenuation of integrated electromagnetic interference (EMI) filter is determined by parasitics. The split ground structure is applied in this paper to realize parasitic capacitance cancellation, which resulted in expanded effective frequency range in common mode (CM) noise suppression. A simplified equivalent circuit is firstly derived and investigated to demonstrate the parasitic capacitance cancellation mechanism. Then design procedure with considered structural constraints is presented. Prototype of an integrated CM filter with split ground layers is finally designed and constructed. Experimental results show the resonance frequency of filter inductor is effectively shifted; hence better filtering characteristics can be achieved.