Noise can propagate in two major ways: Differential Mode (DM) Noise occurs between two conductors carrying opposing currents, such as the positive and negative lines in a DC circuit. Common Mode (CM) Noise appears in the same direction on both conductors relative to ground. Each sort of noise behaves differently, requiring a specific filtering technique.
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This EMI filter consists of a common-mode filter and a differential-mode filter. Differential mode filters typically filter noise below 30 MHz, while common mode filters filter noise between 30 MHz and 100 MHz. Both filters affect the entire frequency range where EMI needs to be limited.
