Tutorial on Different Types of Active Filters and Their Applications

As the time moves forward and the study on the filters has increased, active filters have been a matter of discussion. Active filters are a group of electronic filters that utilizes active components like an amplifier for its functioning. Amplifiers are used in filters for designing to enhance the predictability and performance. This is all finished while keeping away from the need of the inductors. Usually, the filter characteristics can be determined by using an amplifier. This article presents a detailed study and usage of active filters in modern technology. In future, the various types of active filters will have a much wider capacity and will signify the future technology than it has at the present.

What is an Active Filter?

The filter is an electric n/w in any circuit theory, that used to change either phase or amplitude of signal characteristics with respect to its frequency. Ideally, this will not include any new frequency to the i/p nor it will alter the frequency component of that signal. An Active Filter utilizes an operational amplifiers along with various electronic components like resistors, capacitors for the filtering. Op-Amps are used to allow easily to make many types of active filters.

An Amplifier stops the load impedance from affecting the filter characteristics. The form of the response, duality factor and tuned frequency and can often set with inexpensive variable resistors. In these filter circuits we can alter one parameter without damaging the other. Since their basic return principles were projected around 1970, a lot of research has been done with these filters and their realistic applications.

Types of Active Filters

The most common types of active filters are classified into four such as

• Butterworth
• Chebyshev
• Bessel
• Elliptical

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

Chebyshev Filter

The Chebyshev active filter is also named as an equal ripple filter. It gives a sharper cutoff than a Butterworth filter in the pass band. Both Chebyshev and Butterworth filters show large phase shifts close to the cutoff frequency. A disadvantage of the Chebyshev filter is the exterior of gain minima and maxima below the cutoff frequency. The adjustable parameter in designing of filter, the gain ripple is expressed in dB.

The implementation of these filters gives a a lot steeper roll- off, but has ripple in the pass-band, so it is not used in audio systems. Though it is far better in some applications where there is only one frequency available in the pass band, but numerous other frequencies are required to eliminate.

Butterworth Active Filter

The Butterworth active filter is also named as flat filter. The implementation of the Butterworth active filter guarantees a flat response in the pass band and an ample roll-off. This group of filters approximates the perfect filter fit in the pass band. Frequency response curves of different kinds of filters are shown. This filter includes an essentially flat amplitude, frequency response up-to the cut¬-off frequency.

The roughness of the cutoff can be seen in the diagram. It is to be famous that all the three filters achieve a roll-off angle of -40db/decade at frequencies much superior than cutoff. This filter has a characteristic somewhere b/n Chebyshev and Bessel filters. It has a sensible roll-off of the skirt &a slightly non¬linear phase responses. This kind of filter is a good, very easy to understand and is excellent for audio processing applications.

Bessel Filter

The Bessel filter gives an ideal phase characteristic with an about linear phase response up to an almost cutoff frequency. Although, it includes a very linear phase response but a quite gentle skirt slope. The applications of this filter involve where the phase characteristic is significant. It is a small phase shift even though its cutoff characteristics are not very intelligent. It is well matched for pulse applications.

The Bessel filter exhibits a stable propagation delay across the i/p frequency spectrum. So applying a square wave to the input of a filter will give a square wave on the o/p with no exceed Further, any filter will wait various frequencies by various amounts. This will evident itself as exceed on the o/p waveform.

Elliptical Filter

The Elliptical Filter is a much more complicated filter like the Chebyshev. It includes a ripple in the pass band & severe roll-off at the cost of ripple in the stop band. This filter has the roll off of every filter in the conversion region, but it has both the regions of stop band and pass band. This filter can be designed to have high attention of particular frequencies in the stop band, which decreases the attenuation of further frequencies in the stop band.

Advantages of Active filters

The advantages of an active filters include the following

• These filters are more reasonable than passive filters.
• The apparatus used in these filters is smaller than the components used in passive filters.
• Active filter doesn’t show any insertion loss.
• It also permits the interstage isolation for controlling of i/p and o/p impedance.

Applications of Active filters

• Active filters are used in communication systems for suppressing noise, to isolate a communication of signal from various channels to improve the unique message signal from a modulated signal.
• These filters are used in instrumentation systems by the designers to choose a required frequency apparatus and detach unwanted ones.
• These filters can be used to limit the analog signal’s bandwidth before altering them to digital signals.
• Analog filters are used in audio systems by engineers to send various frequencies to various speakers. For example, in the music industry, record & playback applications are needed to control the frequency components.
• Active filters are used in biomedical instruments to interface psychological Sensors with diagnostic equipments & data logging.

Currently, numerous types of active filters are at the initial stage due to its short capacity. But, at present many engineers are designing it with large capacities. Effectiveness in the long run will not only pressure consumers with nonlinear load to employ these filters for preserving but also the quality of power at efficient. The configuration of huge number of active filters will be available to reimburse reactive power, harmonic current, unbalanced and neutral current. The customer can choose the active filter with preferred features in the near future as the technology moves on. Furthermore, any queries regarding this concept or to know about Butterworth filter construction and its applications, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the function of a filter?

Photo Credits:

• Bessel Filter circuitstoday
• Elliptical Filter ni