Diagnosis network performance for conducted EMI measurement

Currently the most common test instrument for conducted electromagnetic interference (EMI) measurement is an EMI test receiver with a line impedance stabilization network (LISN). However, it can only measure total conducted EMI on the power lines, and cannot detect the common-mode (CM) and differential mode (DM) components. Paul and Hardin presented a CM/DM discriminating network that uses a pair of identical 1:1 transformers to add or subtract two voltages. The add/subtract function is achieved by reversal of one of the transformer secondary windings through a mechanical switch. We presented another network which employs two 2:1 transformers with center-tapped secondaries to realize the function, without use of a switch. Mardiguian proposed a much simpler version of network that uses only one 2:1 center-tapped transformer. Gun presented another style that uses two combiners instead of transformers to achieve a similar function. In order to have a compete knowledge of the discrimination capability of these networks, they are constructed and their CM/DM insertion losses and mode rejection abilities are measured.