sy22.m

数字信号处理工具箱

%Impulse response invariance method
Wp=2*pi*100;Ws=2*pi*300;
Rp=1;Rs=25;fs=1000;T=1/fs;
[n,Wn]=buttord(Wp,Ws,Rp,Rs,'s')
[c,d]=butter(n,Wn,'s');
[b,a]=impinvar(c,d,fs)
[db,mag,pha,grd,w]=freqz_m(b,a);
subplot(2,2,1);plot(w/pi,db);axis([0,1,-50,5]);
subplot(2,2,2);plot(w/pi,pha);
%Bilinear transformation method
Wp1=(2/T)*tan(Wp*T/2);Ws1=(2/T)*tan(Ws*T/2);
[n,Wn]=buttord(Wp1,Ws1,Rp,Rs,'s')
[c,d]=butter(n,Wn,'s');
[b,a]=bilinear(c,d,fs);
[db,mag,pha,grd,w]=freqz_m(b,a);
subplot(2,2,3);plot(w/pi,db);axis([0,1,-50,5]);
subplot(2,2,4);plot(w/pi,pha)