Performance improvement of CM/DM noise separator with impedance matching approach

Noise separators have been wildly used in separating the common mode and differential mode signals in conducted EMI measurements. The high frequency performance of a single phase noise separator is improved in this paper. It is realized by a detailed calculation of the impedance characterization of the transmission line transformer. Then an impedance matching capacitance is added at the output terminal of the transmission line transformer. The main advantages of the proposed method are twofold. On one hand, compared to traditional noise separator, it can acquire better high frequency performance. On the other hand, the principle to obtain the impedance matching capacitance is very simple and easy to implement. The presented simulation results and laboratory tests validate the effectiveness of the proposed method.