%例程4－5    基于巴特沃斯模擬濾波器設(shè)計(jì)數(shù)字帶阻濾波器

Wp=[0.4*pi,0.7*pi];
Ws=[0.2*pi,0.8*pi];
Ap=1;
As=30;
[N,wn]=buttord(Wp/pi,Ws/pi,Ap,As); %計(jì)算巴特沃斯濾波器階次和截止頻率
[b,a]=butter(N,wn,'stop');      %頻率變換法設(shè)計(jì)巴特沃斯帶通濾波器
[db,mag,pha,grd,w]=freqz_m(b,a);   %數(shù)字濾波器響應(yīng)
plot(w/pi,mag);
Title('數(shù)字濾波器幅頻響|H(ejOmega)|')