实验七、用双线性变换法设计IIR数字滤波器

实验七、用双线性变换法设计IIR数字滤波器一、源程序程序一clc;clearall;closeall;wp=0.2;ws=0.3;Rp=1;Rs=10;Fs=1000;wp1=2*Fs*tan(wp/2);ws1=2*Fs*tan(ws/2);[N,Wn]=buttord(wp1,ws1,Rp,Rs,'s');[Z,P,K]=buttap(N);[Bap,Aap]=zp2tf(Z,P,K);[b,a]=lp2lp(Bap,Aap,Wn);[bz,az]=bilinear(b,a,Fs);[H,W]=freqz(bz,az);subplot(2,1,1);plot(W/pi,abs(H));grid;xlabel('频率');ylabel('幅度');subplot(2,1,2);plot(W/pi,20*log10(abs(H)));grid;xlabel('频率');ylabel('幅度(db)');程序二clc;clearall;closeall;wp=0.2*2*pi;ws=0.3*2*pi;Rp=1;Rs=25;Fs=1;wp1=2*Fs*tan(wp/2);ws1=2*Fs*tan(ws/2);[N,Wn]=buttord(wp1,ws1,Rp,Rs,'s');[Z,P,K]=buttap(N);[Bap,Aap]=zp2tf(Z,P,K);[b,a]=lp2lp(Bap,Aap,Wn);[bz,az]=bilinear(b,a,Fs);[H,W]=freqz(bz,az);subplot(2,1,1);plot(W/pi,abs(H));grid;xlabel('频率');ylabel('幅度');subplot(2,1,2);plot(W/pi,20*log10(abs(H)));grid;xlabel('频率');ylabel('幅度(db)');程序三clc;clearall;closeall;wp=0.2*2*pi;ws=0.3*2*pi;Rp=1;Rs=25;Fs=1;wp1=2*Fs*tan(wp/2);ws1=2*Fs*tan(ws/2);[N,Wn]=buttord(wp1,ws1,Rp,Rs,'s');[Z,P,K]=buttap(N);[Bap,Aap]=zp2tf(Z,P,K);[b,a]=lp2lp(Bap,Aap,Wn);[bz,az]=bilinear(b,a,Fs);[H,W]=freqz(bz,az,64);figure(1)subplot(2,1,1);plot(W/pi,abs(H));grid;xlabel('频率');ylabel('幅度');subplot(2,1,2);plot(W/pi,20*log10(abs(H)));grid;xlabel('频率');ylabel('幅度(db)');程序四：clc;clearall;closeall;wp=0.2*2*pi;ws=0.3*2*pi;Rp=1;Rs=25;Fs=1;wp1=2*Fs*tan(wp/2);ws1=2*Fs*tan(ws/2);[N,Wn]=buttord(wp1,ws1,Rp,Rs,'s');[Z,P,K]=buttap(N);[Bap,Aap]=zp2tf(Z,P,K);[b,a]=lp2lp(Bap,Aap,Wn);[bz,az]=bilinear(b,a,Fs);[H,W]=freqz(bz,az);figure(1)subplot(2,1,1);plot(W/pi,abs(H));grid;xlabel('频率');ylabel('幅度');subplot(2,1,2);plot(W/pi,20*log10(abs(H)));grid;xlabel('频率');ylabel('幅度(db)');bzaz运行结果：bz=0.01790.10720.26810.35750.26810.10720.0179az=1.0000-0.60190.9130-0.29890.1501-0.02080.0025三、实验总结：脉冲响应不变法和双线性变换法都是将模拟滤波器变换为数字滤波器，但前者不可避免的存在频谱混叠，后者能克服这一缺点，同时，不能用脉冲响应不变法将模拟高通和带阻滤波器转换为数字滤波器。双线性变换法不