We all are known with the word filter. Filter is a thing that removes the unwanted objects or particles from some desired thing and provide only the desired thing. The concept of electronic filter is same. It does the same thing. It removes the unwanted frequency components from electrical signal and provide the desired electrical signal. So, we can define Electronic Filter like this:
‘Electronic filters are electronic circuit that performs signal processing functions like removing unwanted frequency components from signal, enhancing the desired signal, splitting the different frequency component embedded in a signal etc.’
Electronic Filter can be different in type. It can be:
- Passive Electronic Filter
- Active Electronic Filter
- High-Pass Electronic Filter
- Low-Pass Electronic Filter
- Band Pass Electronic Filter
- Band Reject Electronic Filter
- All Pass Filter
and so on.
Passive Filter:
Passive filters are the electronic filters which are constructed using the combination of passive circuit elements. Passive circuit elements are resistors, capacitors and inductors. These components are called passive element because they do not require any external power source to keep themselves active. All the operations they do, they do it from the main power source of the circuit.
There are some disadvantage of passive filters. They are:
- The gain of passive filter is always less than unity. That means the magnitude of the output signal is always less than the input signal.
- When inductors are used, the passive filter becomes bulky. If inductors are not used, then the output response curve goes far away from the ideal response curve.
Active Filter:
Active filters are the electronic filters which have some active component like transistor, Op-Amp in circuit assembly. Actually the only difference between active filter and passive filter is amplifier. When amplifier is implemented in passive filter to restore the attenuated signal, the filter becomes active filter. Active filters are very popular because of its advantages.
The advantages of active filter are:
- The gain of active filter is always greater than or equal to unity. So, there is no distorted signal in the output. The desired signal can be obtained in its original shape using active filters.
- Active filter can modify the output signal if necessary. It can modify the magnitude and time duration of the signal.
- Active filters are not bulky. Because no inductor is needed to implement active filters.
However, active filters has some disadvantages too.
The disadvantages of active filters are:
- Unlike passive filters, active filters have finite bandwidth.
- Sometimes active filters becomes unstable or stop working at high frequency
- Active components of the active filters requires DC power supply to stay on in the circuit.
- Power consumption rate is another major disadvantage of active filters