Overview
ABSTRACT
Active filters commonly refer to filters including active components such as resistors, capacitors, amplifiers, MOS (metal oxide semiconductor) transistors. The main interest of the active filters lies in their low cost and the possibility to fabricate them in a small volume; they are often completely integrated. The article starts by presenting the technologies used in the design of these components. The building block (integrator, adder-subtractor, voltage source, gyrator, etc.) allowing for the combination of these complex and precise active filters are then presented. It is highly essential that the variations of the values of the components do not significantly alter the performances of the filter.
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Gaëlle LISSORGUES: Professor at ESIEE, PhD in electronics - Agrégée in applied physics, former student at the École normale supérieure de Cachan - This edition is an update of Paul BILDSTEIN's 1997 article entitled Synthèse et réalisation des filtres actifs.
INTRODUCTION
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].
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