Active filters - Synthesis and fabrication

Active filters are filters with active components: MOS transistors (metal oxide semiconductor), amplifiers, electronic switches...

However, the term is almost exclusively reserved for filters consisting solely of resistors, capacitors and linear active elements. These are mainly operational amplifiers, but also amplifiers made with MOS transistors. Inductors, which are difficult to integrate, are in principle excluded.

The main advantage of active filters is their low cost and the fact that they can be produced in very small volumes, often in fully integrated form.

The disadvantage is that they have to be powered and can only filter signals whose amplitude is limited by the strength of the active components. The noise level and the presence of offset voltages can also limit the range of applications, which in any case lie within the operating frequency ranges of the active components used [1] [2] [3].

Finally, it should be noted that the active power filters widely used in electrical distribution networks will not be covered in this article. These are generally hybrid topologies combining an active and a passive filter [4].