MATLAB CODE FOR LOW PASS BUTTERWORTH IIR FILTER USING BILINEAR TRANSFORM TECHNIQUE.

clc;

clear all;

close all;

Ap=input('Enter the passband ripple in db:\n');

As=input('Enter the stopband attenuation in db:\n');

Wp=input('Enter the pass band edge frequency in rad:\n');

Ws=input('Enter the stop band edge frequency in rad:\n');

Fs=input('Enter sampling frequency in Hz:\n');

Omgp=2*Fs*tan(Wp/2);

Omgs=2*Fs*tan(Ws/2);                              

[N,W]=buttord(Omgp,Omgs,Ap,As,'s');      

[num,den]=butter(N,Ap,W,'low','s');      

[B,A]=bilinear(num,den,Fs);              

w=0:0.01:pi;

[h,ph]=freqz(B,A,w);                    

m=20*log(abs(h));

an=angle(h);

subplot(211);

plot(ph/pi,m);                            

grid;

xlabel('Frequency in Hz');

ylabel('Gain in db');

title('Frequency response of the Chebyshev filter');

subplot(212);

plot(ph/pi,an);                            

grid;

ylabel('Phase in rad');

xlabel('Frequency in Hz');