A Novel Fractional Frequency Filtering Method Based on Double-Side Small EMI Inductors

Traditional Passive EMI filtering components suffered from poor high-frequency insertion loss, large size and weight. Developing active EMI filters still have issues like inconvenient in power supply, op-amp saturation, limited gain bandwidth product. This paper proposes a novel fractional frequency filtering method to improve high frequency performance of conventional passive EMI filters. It is achieved by tailored design of double-side EMI inductor high frequency performance. One is on line impedance stabilization network (USN) side. The other is on equipment under test (EUT) side. For the first fractional frequency (F2) design, traditional common mode inductor high frequency performance is corrected by a small F2 inductor located at USN-side. For the second fractional frequency (F2) design, EUT high frequency impedance is corrected by another small F2 inductor at EUT-side. By means of these double-side F2 inductors, EMI filter high frequency insertion loss can be improved a lot. Design process of these double-side F2 inductors are discussed in detail. Experimental results show the proposed F2 filtering method could have maximum 28dB insertion loss improvement at 20MHz.