MATLAB CODE TO DESIGN A BUTTERWORTH HIGHPASS FILTER

CODE:

clear all

alphap=.4;  %passband attenuation in dB

alphas=30; %stopband attenuation in dB

fp=400; %passband freq. in hz

fs=800; %stopband freq. in hz

F=2000; %sampling freq. in hz

omp=2*fp/F;oms=2*fs/F; % To find cutoff freq. and order of the filter

[n,wn]=buttord(omp,oms,alphap,alphas) %syatem function of the filter

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

w=0:.01:pi;

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

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

an=angle(h);

subplot(2,1,1);plot(om/pi,m);grid;

ylabel('gain in dB');

Xlabel('NORMALISED FREQUENCY')

subplot(2,1,2);plot(om/pi,an);grid

ylabel('phase in radians')

xlabel('noramlised frequency')

OUTPUT:

n =   4

wn =0.5821

b =  0.0535   -0.2139    0.3209   -0.2139    0.0535

a =  1.0000    0.6418    0.6165    0.1449    0.0259