In the Passive filters we have learnt about the simple passive filters designed using simple passive components.The passive components are Capacitor, Resistor and Inductor.

We learnt that the passive filters never amplifies the signal i.e. the gain of the signal is never greater than the unity gain. The signal is at the output is always lower than the signal applied to the input i.e. there is always some attenuation due to the circuit. This is the main disadvantage of the Passive filter. With passive filter circuits containing multiple stages, this kind of signal loss is called “Attenuation” can become quite severe. One way of restoring or controlling this loss of signal is by using amplification through the use of Active Filters.

Components such as operational amplifiers, transistors or FET’s are Active components. The Filter Circuit Designed using the active components are known as Active Filters.

They draw their power from an external power source and use it to boost or amplify the output signal. Op-amp has a high input impedance, a low output impedance and a voltage gain determined by the resistor network within its feedback loop.