Welcome to the experiment for IIR Filter Design

Here we see an example to demonstrate the use of the IIR filter design functions of MATLAB

If you are looking only for the CODE: CLICK HERE

You can even find the CODE on GITHUB HERE

If you are looking only for FINAL RESULT: CLICK HERE

Working of CODE

Infinite Impulse Response Filter Design. This code will prove to be classic example for proper use of the given functions for Butterworth filter, Chebyshev Type 1 filter and Chebyshev Type 2 Filter Design

Inputs Provided

Passband Attenuation

Ap = 3;

Sampling Frequency

Fs = 500;

Stopband Attenuation

As = 60;

Passband Frequency

Wp = 40;

Dividing by Sampling Frequeny

Wp = Wp / Fs;

Stopband Frequency

Ws = 150;

Dividing by Sampling Frequeny

Ws = Ws / Fs;

Derivation of order by butterord

[n,Wn] = buttord(Wp,Ws,Ap,As);

Formula for Order n of Butterworth filter

OR another simplified version will be

Applying the Butterworth filter function

[b,a] = butter(n,Wn);

Converting to frequency domain.

[h,w] = freqz(b,a);

Since the obtained input was in Normalized Form we get it back by multiplying with Sampling Frequency

W = w*Fs/pi;

To remove the negative values of h we take absolute

h = abs(h);

The PLOT for Butterworth Filter

figure();
plot(W,h);
title('Butterworth Filter')

Butterworth Filter Characteristics

Derivation of order

[n,Wp] = cheb1ord(Wp,Ws,Ap,As);

Applying the Chebyshev Type I filter function

[b,a] = cheby1(n,Ap,Wp);

Converting to frequency domain.

[h,w] = freqz(b,a);

Again since the obtained input was in Normalized Form we get it back by multiplying with Sampling Frequency

W = w*Fs/pi;

Again to remove the negative values of h we take absolute

h = abs(h);

The PLOT for Chebyshev Type I Filter

figure();
plot(W,h);
title('Chebyshev Type I Lowpass Filter')

Derivation of order

[n,Wp] = cheb2ord(Wp,Ws,Ap,As);

Applying the Chebyshev Type II filter function

[b,a] = cheby2(n,As,Wp);

Converting to frequency domain.

[h,w] = freqz(b,a);

Again since the obtained input was in Normalized Form we get it back by multiplying with Sampling Frequency

W = w*Fs/pi;

Again to remove the negative values of h we take absolute

h = abs(h);

The PLOT for Chebyshev Type II Filter

figure();
plot(W,h);
title('Chebyshev Type II Lowpass Filter')

Author: Kaustubh Shivdikar, Mohit Srinivasan :: MATLAB Lab Experiment.