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%-------------------------------------------------------------------------- 
% exa070302 , for example 7.3.2 and fig 7.3.6; 
% 说明如何设计椭圆滤波器及计算和显示功率互补IIR滤波器的频率响应 
% ------------------------------------------------------------------------- 
clear; 
 
wp=0.42;ws=1-wp;Fs=1; 
delta2=0.023; 
delta1=0.5-0.5*sqrt(1-delta2*delta2) 
 
rp=-20*log10(1-2*delta1) 
rs=-20*log10(delta2) 
[n,wn]=ellipord(wp,ws,rp,rs) 
[b,a]=ellip(n,rp,rs,wn) 
 
[H0,w]=freqz(b,a,256,Fs); 
absH0=abs(H0); 
subplot(221) 
plot(w,absH0);grid; 
 
subplot(222) 
zplane(b,a) 
 
[h0]=impz(b,a,125); 
h1=qmf(h0,1); 
 
[H1,F]= freqz(h1,1,256,Fs); 
absH1=abs(H1); 
 
subplot(223) 
ah0=20*log10(absH0); 
ah1=20*log10(absH1); 
plot(F,ah0,'k-',F,ah1,'b-'); 
grid on; 
 
sumh=absH0.*absH0+absH1.*absH1; 
sum=10*log10(sumh); 
subplot(224) 
plot(w,sum);grid; 
 
 
[z,p,k]=tf2zp(b,a)