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What is Active Filters and types of active filters:

Active Filters is a circuit that is designed to pass a specified band frequencies while attenuating all the signals outside that band. It is a frequency selective circuit.

The filter are basically classified as active filter and passive filter. The passive filter networks use only passive elements such as resistors, inductors and capacitors. On the other hand, active filter circuits use the active elements such as op-amps, transistors along with the resistors, inductors and capacitors. Modern active filter do not use inductors as the inductors are bulky, heavy and nonlinear. The inductors generate the stray magnetic fields. The inductors dissipate considerable amount of power.

Advantages of Active Filters:

Overall the active filter using resistors, capacitors and op-amps has following advantages over the passive filter

i) Flexibility in Gain and Frequency Adjustment : The op-amp gain can be easily controlled in the closed loop fashion, hence active filter input signal is not attenuated. The passive filter need the attenuation. The active filter can be easily tuned.

ii) No Loading Effect : The op-amp has high input impedance and low output impedance. Hence, the active filter using op-amp does not cause loading of the source or load.

iii) Cost : Due to availability of modern ICs, a variety of cheaper op-amps are available. The inductors are absent which makes the modern active filter more economical than passive filters.

Types of Active Filters:

The most commonly used types are :

1) Active Low Pass Filter

2) Active High Pass Filter

3) Active Band Pass Filter

4) Active Band Stop Filter. This is also called as Band Elimination filter.

Each of these filter use op-amp as an active element and resistors and capacitors.