clc;
1.8 Design a butterworth analog bandstop
filter with specifications
fp1 35 fp2 215 fs1 100 fs2 150
rp =-3db rs=-15db
clear all;
close all;
% ap=-3;%%db
% as=-40;%%db
% fp=1000;%%Hz
% fs=2000;%%Hz
ap=input('Enter the pass band ripple (in dB)');
as=input('Enter the stop band ripple (in dB)');
fp1=input('Enter the lower pass band frequency (in Hz)fp1=');
fp2=input('Enter the upper pass band frequency (in Hz)fp2=');
fs1=input('Enter the lower stop band frequency (in Hz)fs1=');
fs2=input('Enter the upper stop band frequency (in Hz)fs2=');
op1=2*pi*fp1; %%angular freq in rad/sec
op2=2*pi*fp2; %%angular freq in rad/sec
os1=2*pi*fs1; %%angular freq in rad/sec
os2=2*pi*fs2; %%angular freq in rad/sec
op=[op1 op2];
os=[os1 os2];
[N oc]=buttord(op,os,ap,as,'s');
disp('Orderofthefilter,N=');
disp(N);
% oc=op/((10^(-ap/10)-1)^(1/(2*N))); %or
% oc=or/((10^(-as/10)-1)^(1/(2*N)));
disp('Cutoff freq,oc=');
disp(oc);
Mohammed
Zaki Salman
Pes2201800
186
ece 4 A
[b,a]=butter(N,oc,'stop','s');
fr=0:100:4000;
wr=2*pi*fr;
[H,w]=freqs(b,a,wr);
f=w/(2*pi);
H_mag=20*log10(abs(H));
figure;
plot(f,H_mag);
grid on;
xlabel('Frequency in Hz');
ylabel('Magnitude in dB');
title('Magnitude Response');
Transferfunc=tf(b,a)
o/p:
Orderofthefilter,N=
2
Cutoff freq,oc=
1.0e+03 *
0.4841 1.2232
Transferfunc =
s^4 + 1.184e06 s^2 + 3.507e11
-----------------------------------------------------
s^4 + 1045 s^3 + 1.731e06 s^2 + 6.189e08 s + 3.507e11
Continuous-time transfer function.