ms21r3.m

《数字信号处理实验(MATLAB版)》这

%双线性变换法设计数字带通
%数字滤波器指标
fp1=200;fp2=300;fs1=150;fs2=350;
Fs=1000;T=1/Fs;
wp1=fp1/Fs*2*pi;wp2=fp2/Fs*2*pi;  %数字滤波器的通带截止频率
ws1=fs1/Fs*2*pi;ws2=fs2/Fs*2*pi;  %数字滤波器的阻带截止频率
Rp=1;As=20;             %输入滤波器的通阻带衰减指标
%转换为模拟滤波器指标
Omgp1=(2/T)*tan(wp1/2);Omgp2=(2/T)*tan(wp2/2);
Omgp=[Omgp1,Omgp2];           %模拟滤波器的通带截止频率
Omgs1=(2/T)*tan(ws1/2);Omgs2=(2/T)*tan(ws2/2);
Omgs=[Omgs1,Omgs2];           %模拟滤波器的阻带截止频率
bw=Omgs2-Omgs1;w0=sqrt(Omgs1*Omgs2);%模拟通带带宽和中心频率
%模拟原型滤波器计算
[n,Omgn]=cheb2ord(Omgp,Omgs,Rp,As,'s') %计算阶数n和截止频率
[z0,p0,k0]=cheb2ap(n,As);     %设计归一化的模拟原型滤波器
ba1=k0*real(poly(z0));        %求原型滤波器系数b
aa1=real(poly(p0));           %求原型滤波器系数a
[ba,aa]=lp2bp(ba1,aa1,w0,bw); %变换为模拟带通滤波器
%用双线性变换法计算数字滤波器系数
[bd,ad]=bilinear(ba,aa,Fs)
%求数字系统的频率特性
[H,w]=freqz(bd,ad);   
dbH=20*log10((abs(H)+eps)/max(abs(H))); %化为分贝值
%
subplot(2,2,1),plot(w/2/pi*Fs,abs(H),'k'); 
ylabel('|H|');title('幅度响应');axis([0,Fs/2,0,1.1]);
set(gca,'XTickMode','manual','XTick',[0,fs1,fp1,fp2,fs2,Fs/2]);
set(gca,'YTickMode','manual','YTick',[0,Attn,ripple,1]);grid
subplot(2,2,2),plot(w/2/pi*Fs,angle(H)/pi*180,'k');
ylabel('\phi');title('相位响应');axis([0,Fs/2,-180,180]);
set(gca,'XTickMode','manual','XTick',[0,fs1,fp1,fp2,fs2,Fs/2]);
set(gca,'YTickMode','manual','YTick',[-180,0,180]);grid
subplot(2,2,3),plot(w/2/pi*Fs,dbH,'k');
title('幅度响应(dB)');axis([0,Fs/2,-40,5]); 
ylabel('dB');xlabel('频率(\pi)');
set(gca,'XTickMode','manual','XTick',[0,fs1,fp1,fp2,fs2,Fs/2]);
set(gca,'YTickMode','manual','YTick',[-50,-20,-1,0]);grid
subplot(2,2,4),zplane(bd,ad);
axis([-1.1,1.1,-1.1,1.1]);title('零极图');