There is a huge importance of electronic filter in engineering. In electronics engineering, it is generally used to eliminate unwanted parts of an input signal. In other words, the electronic filter is normally used to suppress interfering signals. It is used to selectively pass or stop (reject) frequency band. The main function of the electronic filter is to pass all the wanted signals with very less attenuation. It also reduces background noise.
Types of Electronic Filter
There are various types of filter available for various purposes. They are termed as low pass filter, high pass filter, band pass filter, band stop filter, all-pass filter, notch filter, comb filter, etc.In low pass filter, only the low frequencies signals are passed whereas the high-frequency signals are suppressed. In high pass filter, only the high frequencies signals are passed whereas the low-frequency signals are suppressed. The bandpass and bandstop filters are quite different than the low pass and high pass filters. In the bandpass filter, only the signal frequency in a certain frequency band is passed. In the band stop filter, only the signal frequency in a certain frequency band is suppressed.
One of the types of band stop filter is a notch filter. It is a type of band filter which rejects or suppress only one specific frequency signal. Also, one of the important types of the bandpass filter is the comb filter. And, in all pass filter, the signals having all types of frequency are passed. It doesn't suppress any frequency signals. In the all-pass filter, the phase of the passed signal is modified. It is normally used for the delay equalization purpose. The all-pass filter is realized only in the infinite networks.
There are also other types of filter such as active filter, passive filter, waveguide filter, etc. In an active filter, the components such as the operational amplifier and transistors are used. It is normally of small in size as compared to the passive filter. It is also cheaper in price. Normally active filter is preferred because it provides much greater amplification as compared to other types of filter.
Similarly, the passive filter consists of passive elements like an inductor, capacitor, and resistor. Among inductor, capacitor, and resistor; only the inductor and capacitor are called as filter components. In the waveguide filter, the waveguide components are basically used for the signal transmission purpose. Generally, the waveguide filter is designed implementing waveguide technology where directly coupled resonator filters are used. It is easy to build such types of filter.
In electronic filter design, other important filters known are the Butter-worth filter, Bessel filter, elliptic filter, etc.
In Butter-worth filter, the used filter normally has a maximum flat frequency response. The Butter-worth function used in the Butter-worth filter has no amplitude ripple.
Similarly, the Bessel filter normally has a maximum flat phase delay. In other words, the Bessel filter is also known as a constant delay filter. In Bessel filter, the Bessel function (which has low pass magnitude characteristic) is carried out with the delay constant as the objective because the denominator of the Bessel function tends to be large at high frequencies.
And, the elliptic filter has a steepest cut-off frequency for a particular ripple. The ripple is normally seen in the bandpass filter. Ripple is defined as the variation of the filter insertion loss seen in some types of the filter.
Characteristics of a filter
The electronic filter should have the following characteristics:1. The filter network should be simple. Complex or complicated filter network is very hard to realize and analysis.
2. Another important factor to be considered while designing filter is the transition band ratio. Hence, the transition band ratio of the filter should be low.
3. There should be small passband ripple. In other words, the passband variation shouldn't be large.
4. While designing filter, large band reject attenuation is normally preferred. The stop band attenuation shouldn't be small.