与有源共模滤波器相比,无源共模滤波器具有结构简单、成本低廉等优点,但其滤波性能易受元件寄生参数和饱和特性影响。该文针对一个LC二阶无源共模滤波器,分别基于离线测量和在线测量提取了其电感和电容的寄生参数,分析了离线参数与在线参数的异同。对插入损耗进行了离线测量和在线测量。结果表明:离线测量能反映磁心材料的频率特性,但不能反映饱和特性;而在线测量受制于测量仪器的性能,很难反映宽频率范围的频率特性。因此,对无源共模滤波器,离线测量所得滤波性能不能充分反映在线测量的滤波性能。 Compared with the active common mode filter, the passive common mode filter has the advantages of simple structure and low cost, but its filtering performance is easily affected by parasitic parameters and saturation characteristics of the device. In this paper, an LC second-order passive common-mode filter is used to extract parasitic parameters of inductance and capacitance based on off-line measurement and on-line measurement respectively. The similarities and differences between off-line parameters and on-line parameters are analyzed. Insertion loss was measured offline and online. The results show that the off-line measurement can reflect the frequency characteristics of the magnetic core material, but can not reflect the saturation characteristics. However, the on-line measurement is limited by the performance of the measuring instrument and it is difficult to reflect the frequency characteristics of the wide frequency range. Therefore, for passive common mode filter, the performance of the offline measurement can not fully reflect the performance of online measurement.