# Low Pass IIR butterworth digital filter MATLAB source code

This section of MATLAB source code covers BUTTERWORTH IIR digital filter matlab code.It describes Low Pass IIR filter.

IIR digital filter works on digital samples. It uses current input sample,previous input samples as well as previous output samples to produce current output sample.

## IIR Filter Specifications

Following points are usually considered to design FIR filter other the window type.
INPUT:
• Passband and stopband ripples
• passband and stopband edge frequencies
• sampling frequency
• order of the filter
• filter coefficients
OUTPUT:
• magnitude and phase responses

## Entering Input parameters

clc;close all;clear all;
format long
rp=input('enter the passband ripple(Example:0.5):');
rs=input('enter the stopband ripple(Example:60):');
wp=input('enter the passband freq(Example:1300):');
ws=input('enter the stopband freq(Example:2600):');
fs=input('enter the sampling freq(Example:10000):');

## IIR MATLAB Function main part

w1=2*wp/fs;w2=2*ws/fs;
[n,wn]=buttord(w1,w2,rp,rs);
[b,a]=butter(n,wn);
w=0:.01:pi;
[h,om]=freqz(b,a,w);
m=20*log10(abs(h));
an=angle(h);

figure;plot(om/pi,m);title('IIR Filter magnitude Response');ylabel('Gain in dB');xlabel('Normalised frequency');
figure;plot(om/pi,an);title('IIR Filter phase Response');xlabel('Normalised frequency');ylabel('Phase in radians');

## Useful Links to MATLAB codes

Refer following as well as links mentioned on left side panel for useful MATLAB codes.
OFDM Preamble generation  Time off estimation corr  Freq off estimation corr  channel estimation  11a WLAN channel  PN sequence generation  OFDMA Tx Rx  AES DES  carrier aggregation  CCDF  FIR Filter  IIR Filter  Low Pass FIR  Viterbi decoder  CRC8 CRC32