What is a Filter ?

The circuit that is designed to modify or reject all frequencies of the signal which are not required at the output of the circuit and accept or pass only those frequencies which are required at the output .

Let’s take an example. There are various radio station which broadcast their signals over the air. Each station has different carrier frequency. If we want a listen to a particular station the radio has to select a particular frequency while reject all others. At that time we can use a filter to listen to particular station by using a filter that allows only the frequency that you want listen to.

Capacitor, Resistor and Inductor are “Passive Components”.

The Filter Designed using passive components are known are known as “Passive Filters”.

It is important to note that the passive filters have no amplifying elements like transistors, op-amps, etc so have no signal gain, therefore their output level is always less than the input.

The filters are named in accordance with the frequencies they allow to pass through them. There are mainly there types of filters

1.   Low Pass Filters

2.   High Pass Filters

3.   Band Pass Filters