In this video, five different types of filter approximations which are quite commonly used in the analog filter design have been discussed briefly.
What is Filter Approximation:
Ideal filters have brick wall type of frequency response. So, they have flat passband and monotonic stopband. And the transition from passband to stopband is very abrupt (vertical transition).
But in actual filter design, it is almost impossible to achieve frequency response like an ideal filter.
So, in filter design (particularly for higher order filter design), five different types of filter approximations are quite commonly used.
1. Butterworth Filter Approximation
2. Chebyshev Filter Approximation
3. Inverse Chebyshev (Chebyshev Type-II) Filter Approximation
4. Elliptic Filter Approximation
5. Bessel Filter Approximation
1. Butterworth Filter Approximation
This filter approximation is also known as the maximally flat response approximation as it provides the flat passband response.
It does not have any ripple in the stop band and the roll-off rate is 20n dB /decade. It is most often used in audio processing applications where flat passband response is necessary.
2. Chebyshev Filter
This filter has rippled passband and monotonic stopband, but the roll-off rate of this filter is faster than the Butterworth filter. It is also known as the equal ripple filter.
3. Inverse Chebyshev (Chebyshev Type -II) Filter Approximation
This filter has flat passband and rippled stop band, and the roll-off rate is same as the Chebyshev filter.
4. Elliptic filter approximation
This filter has rippled passband and stopband but it has fastest roll-off rate among all the filter approximations.
While it has very poor step response.
5. Bessel Filter Approximation
This filter has flat passband and monotonic stop band like Butterworth filter but the roll-off rate is slowest among all the filter approximations.
This filter has linear phase to frequency response, and hence very good step response.
Here are the timestamps for the different topics in the video:
0:48 What is Filter Approximation?
3:10 Butterworth Filter Approximation
4:04 Chebyshev Filter Approximation
5:13 Inverse Chebyshev Filter Approximation
6:07 Elliptic Filter Approximation
6:40 Bessel Filter Approximation
7:51 Comparision of different filter approximations
This video will be helpful to all students of science and engineering in understanding the concept of filter approximation and to get the overview of different filter approximations.
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Music Credit:
www.bensound.com/