Filters : Active Versus Passive Filters

In electronics, filters are the circuits which removes the unwanted part from the information which is being provided to it at input.

Also, in electronics, there are two classes of devices, namely Active devices and Passive devices.

Active Devices: Simply, the active device or circuits are which , who requires or who can store energy in them example, semiconductor devices.

Passive Devices:
Passive devices are the devices which do not require any power input or they can not store any power in them, for example, a simple resistor.

The circuits which is made of passive elements is called passive circuits and the one which is made of active elements is called active circuits.

Now let us discuss the advantages and disadvantages of Active filter circuits and passive filter circuits.

Advantages of active filters

the active filters consisting of an opamnp and passive component such as resistors,capacitors and inductors have following advantages over the passive filters:

Flexibility in gain and frequency adjustment

In passive filters the input signal is attenuated while passing though the filter. But in active filters as an opamnp can provide a gain, the inputs signal is not attenuated. In addition, the active filter is easy to tune.

2>No loading problem:
the opamp has a high input resistance and low put resistance there active filters using opamp do not lead the input source or load.

3>low cost:
due to easy of a variety of cheaper opams and due to the absence of inductors in the active filters, the active filters are more economical than the passive filters.

No insertion loss
The active filters do not exhibit any insertion loss, whereas the passive filters always show some loss of signal in their pass band.

5>pass band gain
the active filter can be designed to provide some pass band gain, this is not possible for the passive filters

7>small component size
the components required for the active filters are of smaller size as compared to those used for the passive filters

use of inductors can be avoided
It is possible to avoid the use of inductors filters. This reduces the size of the filters to a great extent.

Now, lets us look over the Disadvantages of Active Filters.

active filters requires dc power supply for their operation, while passive filters do not.

Active filters are limited in their frequency range. This is because an op-amp has a finite gain bandwidth product. The passive filters do not have this limitation.

Active filters can no handle large amounts of power, Passive filters can handle hundreds of pass

The active filters are suitable for low or moderate frequencies
(upto 1MHz for typical devices) and they cannot handle larger power.