% 用PM算法進(jìn)行的低通濾波器設(shè)計
%
wp = 0.2*pi; ws = 0.3*pi; Rp = 0.25; As = 50;
delta1 = (10^(Rp/20)-1)/(10^(Rp/20)+1)
delta2 = (1+delta1)*(10^(-As/20))
deltaH = max(delta1,delta2); deltaL = min(delta1,delta2);
weights = [delta2/delta1 1]
deltaf = (ws-wp)/(2*pi)
M = ceil((-20*log10(sqrt(delta1*delta2))-13)/(14.6*deltaf)+1)
f = [0 wp/pi ws/pi 1]
m = [1 1 0 0];
h = remez(M-1,f,m,weights);
[db,mag,pha,grd,w] = freqz_m(h,[1]);
delta_w = 2*pi/1000; wsi=ws/delta_w+1; wpi = wp/delta_w;
Asd = -max(db(wsi:1:501))
M = M+1;
h = remez(M-1,f,m,weights);
[db,mag,pha,grd,w] = freqz_m(h,[1]);
Asd = -max(db(wsi:1:501))
M = M+1;
h = remez(M-1,f,m,weights);
[db,mag,pha,grd,w] = freqz_m(h,[1]);
Asd = -max(db(wsi:1:501))
M = M+1;
h = remez(M-1,f,m,weights);
[db,mag,pha,grd,w] = freqz_m(h,[1]);
Asd = -max(db(wsi:1:501))
M = M+1;
h = remez(M-1,f,m,weights);
[db,mag,pha,grd,w] = freqz_m(h,[1]);
Asd = -max(db(wsi:1:501))
M
[Hr,omega,P,L] = ampl_res(h);
%
% 畫圖
figure(1); subplot(1,1,1)
subplot(2,2,1); stem([0:1:M-1],h); title('實(shí)際脈沖響應(yīng)')
axis([0 M-1 -0.1 0.3]); ylabel('h(n)');text(M,-0.1,'n')
set(gca,'XTickMode','manual','XTick',[0,M-1])
set(gca,'YTickMode','manual','YTick',[-0.1:0.1:0.3])
subplot(2,2,2);plot(w/pi,db);title('幅度響應(yīng)（單位：dB）');
axis([0,1,-80,10]); xlabel(''); ylabel('分貝數(shù)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1])
set(gca,'YTickMode','manual','YTick',[-50,0]);
set(gca,'YTickLabelMode','manual','YTickLabels',['50';' 0']);grid
subplot(2,2,3);plot(omega/pi,Hr);title('振幅響應(yīng)');
axis([0 1 -0.1 1.1]); xlabel('頻率（單位：pi）'); ylabel('Hr(w)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1])
set(gca,'YTickMode','manual','YTick',[0,1]);grid
subplot(2,2,4);
pbw = omega(1:1:wpi+1)/pi; pbe = Hr(1:1:wpi+1)-1;
sbw = omega(wsi+1:501)/pi; sbe = Hr(wsi+1:501);
plot(pbw,pbe,sbw,sbe);
axis([0,1,-deltaH,deltaH]);title('誤差響應(yīng)');
xlabel('頻率（單位：pi）'); ylabel('Hr(w)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1])
set(gca,'YTickMode','manual','YTick',[-deltaH,-deltaL,0,deltaL,deltaH]);
set(gca,'XGrid','on')