3. Filter structures

The primary purpose of a filter is to attenuate disturbances generated by electronic equipment. The idea is to create an impedance break. Indeed, if input and output impedances are low, the aim is to obtain a high impedance filter to effectively filter the system, and vice versa for high input and output impedances. Typically, inductors and common-mode cores (CMTs) are of high impedance, while capacitors are of low impedance (depending on the frequency range).

Depending on the type of disturbance, filtering must be oriented either towards the differential mode, the common mode or both. The structures presented in this section can be used alone or in combination to act on the 2 modes simultaneously.

The filter structure must be chosen according to the desired attenuation and the source and load impedances. The more cascaded filter cells there...