%a22.m
wp=0.2*pi;wr=0.3*pi;Ap=1;Ar=15;
T=1;
Omegap=(2/T)*tan(wp/2);Omegar=(2/T)*tan(wr/2);
ep=sqrt(10^(Ap/10)-1);
Ripple=sqrt(1/(1+ep*ep));
Attn=1/(10^(Ar/20));
%雙線性變換法設計Chebshev 2型數字低通濾波器
[cs,ds]=afd_chb2(Omegap,Omegar,Ap,Ar);
[b,a]=bilinear(cs,ds,T);
[C,B,A]=dir2cas(b,a)
[db,mag,pha,w]=freqz_m(b,a);
subplot(2,2,1);plot(w/pi,mag);
title('數字濾波器幅度響應|H(w)|');axis([0,1,0,1.1]);
subplot(2,2,2);plot(w/pi,db);
title('數字濾波器衰減響應(dB)');axis([0,1,-40,5]);
subplot(2,2,3);plot(w/pi,pha/pi);title('數字濾波器相位響應');
%雙線性變換法設計Chebshev 2型模擬低通濾波器
[b,a]=afd_chb2(wp,wr,Ap,Ar)
[C,B,A]=sdir2cas(b,a)
[db,mag,pha,w]=freqs_m(b,a,pi);
subplot(2,2,4);plot(w/pi,mag);
title('模擬濾波器幅度響應|H(Omega)|');axis([0,1,0,1.1]);