What is an Active Filter? Explain Types, Applications & Advantages

The Active filters are a group of electronic filters that utilizes only its active components for its functioning as an amplifier. To enhance the predictability and performance of filters we use amplifiers in it for designing. In this way, there is no need for inductors.

Usually, the characteristics of a filter can be determined by using an amplifier. The various types of active filters will have a large capacity and will signify the future technology than it has at the present.

What is an Active Filter?

The filter is electric equipment used in any circuit theory, which is used to change either phase or amplitude of signal characteristics with respect to its frequency. Ideally, this will not include any new frequency signal to the input nor it will change the frequency component of that signal.

The Active Filter utilizes the operational amplifiers along with various electronic components like capacitors, resistors that use for the filtering. Operational Amplifier is used to allow working easily to make many different types of active filters. An Amplifier stops the impedance of a load from affecting the filter characteristics.

The form of the response, tuned frequency and duality factor and can often set with special variable resistors.In these filter circuits we can change one parameter without damaging the other parameter.

Active Filter Design

Types of Active Filters

The most common types of active filters are classified into four groups.

  • Butterworth

  • Chebyshev

  • Bessel

  • Elliptical

There are various different kinds of filters are available, but most of the applications can be resolved with these implementations.

Types of Active Filters

Butterworth Active Filter

It is also called a flat filter.

By using the Butterworth active filter guarantees to give a flat response in the pass band and have enough roll-off.

These filters approximate the perfect filter that fits in the pass band.

The frequency response curves of different kinds of filters are shown below.

This filter includes a perfect flat amplitude, frequency response up to the cutoff frequency.

frequency response curves

These kinds of filters are good and very easy to understand. These filters are  excellent for audio processing applications.

Butterworth Active Filter

Chebyshev Filter

It is also named as an equal ripple filter.

In the pass band it gives a sharp cutoff than the Butterworth filter.

Both Butterworth and Chebyshev filters show large degree phase shifts closer to the cutoff frequency.

A main disadvantage of the Chebyshev filter is the gain of the exterior is minima and maxima below the cutoff frequency.

The gain ripple is expressed in dB.

minima and maxima below the cutoff frequency.

The implementation of these filters gives a lot of hurdles roll-off, but it has a ripple in the pass-band, so Chebyshev Filter is not used in audio systems.

But it is better in some applications where there is only one frequency signal is available in the pass band, but other frequencies are required to eliminate.

Chebyshev Filter


Bessel Filter

It gives an ideal phase characteristic with a linear phase response that is almost to the cutoff frequency.

It includes a linear phase response but having a quite gentle skirt slope.

The applications of this filter are used where the phase characteristic is very significant.

It has a small phase shift even though its cutoff characteristics are not very good.

It is mostly used for pulse applications.

input frequency spectrum of Bessel Filter

It exhibits a stable propagation delay across the input frequency spectrum.

When we applying a square wave to the input of a filter will give a square wave on the output with no exceed Further, any other filter will wait for various frequencies by various different amounts.

This will clear itself as exceed on the output waveform.

Bessel Filter Design

Elliptical Filter

It is a very complicated filter like the Chebyshev.

In the pass band It includes a ripple and sharp roll-off at the cost of ripple in the stop band.

This filter has important characteristics of every filter in the conversion region, but it has both regions of the pass band and stop band.

Elliptical Filter Design

It can be designed to have a high sensitivity of particular frequencies in the stop band, which decreases the effect of further frequencies in the stop band.

decreases the effect of further frequencies in the stop band


Advantages of Active filters

The advantages of active filters are as following

  • The Active filters are more reasonable than passive filters.
  • The apparatus that are used in these filters is smaller than the components used in passive filters.
  • The active filter does not show any internal loss.
  • It also permits internal isolation for controlling input and output impedance.


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