A Noise Source Impedance Extraction Method for Operating SMPS Using Modified LISN and Simplified Calibration Procedure

A noise source impedance extraction method for switched-mode power supply (SMPS) under operating condition is proposed and validated in this letter. First, a simplified precalibration method using several known impedances is introduced to eliminate the influence of measurement instruments and other parasitic effects. Second, the configuration of the proposed method is presented and the calculation methods of common-mode and differential-mode noise source impedances using microwave transmission analysis are described, respectively. The experimental results show that the proposed method can extract the noise source impedance of SMPS in wide frequency band with sufficient accuracy. Compared with traditional methods, the complex calibration process can be simplified, and no more additional equipment is required. Moreover, a novel multiple-function line impedance stabilization network (MF-LISN) with the function of electromagnetic interference measurement and noise source impedance extraction is designed according to the proposed method. Since only MF-LISN is used, it can be more convenient to extract the noise source impedance of SMPS for electromagnetic compatibility pretest.