%雙線性變換法設計ButterWorth帶通數字濾波器
wp1=0.25*pi; 
wp2=0.45*pi;
wp=[wp1,wp2];
ws1=0.15*pi;  
ws2=0.55*pi;
ws=[ws1,ws2];
Ap=3;
As=15;
Fs=1;
[n,Wc]=buttord(wp,ws,Ap,As,'s')
[b,a]=butter(n,Wc,'s')
[bz,az]=bilinear(b,a,1)
freqz(bz,az)