Interaction between passive common mode noise cancellation and conservative passive filtering

Passive cancellation of common mode (cm) noise is a very promising alternative to conservative cm filtering. The basic idea has already been described in literature. A thorough analysis of parasitic effects as well as the effects of a finite differential mode (dm) filter shows that a significant reduction of cm noise is achievable. However, in a lot of applications the electromagnetic compatibility (EMC) standard has not yet been fulfilled and an additional compact conservative cm filter is necessary. These two filters interact. Hence, a detailed investigation of the resulting circuit with both filters is essential. An analysis based on the frequency-response allows quantifying the influences of different design parameters and optimizing the circuit. Finally, the theoretical results are verified in a test set-up.