%数字滤波器指标;
wp=0.2*pi; %数字通带频率(弧度)
ws=0.3*pi; %数字阻带频率(弧度)
Rp=1; %通带波动(dB)
As=15; %阻带衰减(dB)
%模拟原型指标对频率的逆映射
T=1; %置T=1
OmegaP=wp*T; %原型通带频率
OmegaS=ws*T; %原型阻带频率
ep=sqrt(10^(Rp/10)-1);%通带波动参数
Ripple=sqrt(1/(1+ep*ep));%通带波动
Attn=1/(10^(As/20)); %阻带衰减
%模拟切比雪夫Ⅱ型原型滤波器计算:
[cs,ds]=afd_chb2(OmegaP,OmegaS,Rp,As);
%%***切比雪夫Ⅱ型滤波器阶次= 4
%脉冲恒等变换:
[b,a]=imp_invr(cs,ds,T);
[C,B,A]=dir2par(b,a)
%%C=0.1778
%%B=-0.0313 0.5760
%% -0.3901 0.152
%%A=1.0000 -0.5273 0.1348
%% 1.0000 -1.1386 0.6938
%绘图
figure(1);subplot(1,1,1)
[db,mag,pha,grd,w]=freqz_m(b,a);
subplot(2,2,1);plot(w/pi,mag);title('幅度响应');
xlabel('');ylabel('|H|');axis([0,1,0,1.1]);
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickmode','manual','YTick',[0,Attn,Ripple,1]);grid
subplot(2,2,2);plot(w/pi,db);title('幅度(单位:dB)');
xlabel('频率(单位:pi)');ylabel('分贝');axis([0,1,-40,5]);
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickmode','manual','YTick',[-50,-15,-1,0]);grid
set(gca,'YTickLabelMode','manual','YTickLabels',['50';'15';'1';'0']);
subplot(2,2,3);plot(w/pi,pha/pi);title('相位响应');
xlabel('');ylabel('单位:pi');axis([0,1,-1,1]);
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickmode','manual','YTick',[-1,0,1]);grid
subplot(2,2,4);plot(w/pi,grd);title('群延迟');
xlabel('频率(单位:pi)');ylabel('样本');axis([0,1,0,15]);
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickmode','manual','YTick',[0:5:15]);grid