What is Active Filter?

An active filter is a special type of analog electronic filter which involves active electronic elements such as an amplifier, or OpAmp etc. In word active means the power of increasing the signal level, similarly an active filter is able to increase the signal gain along with the filtering. These active components like amplifiers or OpAmp have a unique feature that they are able to boost the signal level. Inclusion of those components in a filter design can be used to improve the performance and increase the versatility of the filter circuit. In frequency domain, the performance of these filters are observed and corrected by changing the overall gain of active elements. Inductors coils are also serve the same, but typically they are expensive compared to other components, so the filtering action is established with low cost electronic elements.

In active filters, the load impedance of the connected circuitry is freed from the voltage current or other characteristics of the filter, which means it is independent from the effect of varying load. Generally active filters are able to produce buffered output, and also able to notching of signals. It is quite cost effective solution for electronic filter circuit, because it serves two purposes, one is filtering the input and other is boosting the energy level. In this way it is able to tasks of two separate elements, they are filter and active source. Butterworth filter is instant of an active filter which is used as the model filter for design purposes.