example8_18.m

原名：数字信号处理基础及MATLAB实现,解压缩密码：[e-mail]

%例8-18程序:example8_18
Wp=0.2*pi;Ws=0.3*pi;Rp=1;Ar=15; T=1;    %数字滤波器设计指标
Fs=1/T;
OmegaP=(2/T)*tan(Wp/2);                 %修正的模拟原型滤波器通带截止频率
OmegaS=(2/T)*tan(Ws/2);                 %修正的模拟原型滤波器阻带截止频率
%模拟切比雪夫Ι型低通原型滤波器计算
[cs,ds]=afd_chb1(OmegaP,OmegaS,Rp,Ar);
[b2,a2]=bilinear(cs,ds,Fs);                       %用双线性变换法实现模拟滤波器到数字滤波器的变换
%画图
[db1,mag1,pha1,grd1,w1]=freqz_m(b2,a2);        %计算频率响应和相位响应
figure(1)
subplot(2,3,1)
plot(w1/pi,mag1);
axis([0 1 0 1.1]);
ylabel('(a)')
title('幅度响应');
subplot(2,3,2);
plot(w1/pi,db1);
axis([0 1 -40 5]);
title('幅度响应（dB）');
subplot(2,3,3);
plot(w1/pi,pha1/pi);
axis([0 1 -1 1]);
title('相位响应');
%双线性变换
[blp,alp]=bilinear(cs,ds,T);
wphp=0.6*pi;                            %数字高通滤波器通带截止频率
%数字低通到高通滤波器的频带变换
alpha=-(cos((Wp+wphp)/2))/(cos((Wp-wphp)/2));
Nz=-[alpha,1];Dz=[1,alpha];
[bhp,ahp]=zmapping(blp,alp,Nz,Dz);
[C,B,A]=dir2cas(bhp,ahp)
%画图
[db2,mag2,pha2,grd2,w2]=freqz_m(bhp,ahp);             %计算频率响应和相位响应
subplot(2,3,4)
plot(w2/pi,mag2);
axis([0 1 0 1.1]);
ylabel('(b)')
subplot(2,3,5);
plot(w2/pi,db2);
axis([0 1 -40 5]);
subplot(2,3,6);
plot(w2/pi,pha2/pi);
axis([0 1 -1 1]);