Abstract:

The Source and load impedances of filter vary in practical applications, so, it is very important to optimize the design of filter under impedances-mismatch conditions. The influence that the source and load impedances has on the insertion loss of filters is analyzed in detail. A method of calculating the minimum insertion loss of electromagnetic interference (EMI) filters under impedance-mismatch conditions is presented. The result indicates that the parasitic capacitance and parasitic inductance cause deviation of insertion loss between results of theoretical calculation and measurements in high frequency. So,the model of a typical kind of EMI filter is modified in high frequency by optimization method. Finally, the modified model and the method to calculate the minimum insertion loss is verified to be true.

Key words: electromagnetic interference filter, insertion loss, impedance-mismatch