MATLAB Program for IIR Butterworth Filter

The function buttord(), is used to find the filter order and center frequency . Function butter() is used to find the filter coefficients.A low pass filter is implemented.


%Program to design an IIR Butterworth filter


clear all;
close all;
fp=input('Enter the pass band frequency fp   = ');
fs=input('Enter the stop band frequency fs   = ');
rp=input('Enter the pass band attenuation rp = ');
rs=input('Enter the stop band attenuation rs = ');
f=input ('Enter the sampling frequency f     = ');


wp=2*fp/f;
ws=2*fs/f;


[n,wn]=buttord(wp,ws,rp,rs);


[b,a]=butter(n,wn,'low');


freqz(b,a,500,f);
TITLE ('Magnitude and phase respose of the IIR butterworth filter');


%output
%Enter the pass band frequency fp   = 1000
%Enter the stop band frequency fs   = 1200
%Enter the pass band attenuation rp = .2
%Enter the stop band attenuation rs = 45
%Enter the sampling frequency f     = 3000