% Chapter 8: Example 8.20%            BiLinear Transformation:%                Elliptic Lowpass Filter Design%% Digital Filter Specifications:wp = 0.2*pi;                         % digital Passband freq in Hzws = 0.3*pi;                         % digital Stopband freq in HzRp = 1;                              % Passband ripple in dBAs = 15;                             % Stopband attenuation in dB% Analog Prototype Specifications: Inverse mapping for frequenciesT = 1; Fs = 1/T;                     % Set T=1OmegaP = (2/T)*tan(wp/2);            % Prewarp Prototype Passband freqOmegaS = (2/T)*tan(ws/2);            % Prewarp Prototype Stopband freqep = sqrt(10^(Rp/10)-1);             % Passband Ripple parameterRipple = sqrt(1/(1+ep*ep));          % Passband RippleAttn = 1/(10^(As/20));               % Stopband Attenuation% Analog Elliptic Prototype Filter Calculation:[cs,ds] = afd_elip(OmegaP,OmegaS,Rp,As);%%*** Elliptic Filter Order =  3 % Bilinear transformation:[b,a] = bilinear(cs,ds,T);[C,B,A] = dir2cas(b,a)%%C = 0.1214%%B = 1.0000   -1.4211    1.0000%%    1.0000    1.0000         0%%A = 1.0000   -1.4928    0.8612%%    1.0000   -0.6183         0% Plottingfigure(1); subplot(1,1,1)[db,mag,pha,grd,w] = freqz_m(b,a);subplot(2,2,1); plot(w/pi,mag); title('Magnitude Response')xlabel('frequency in pi units'); 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]); gridsubplot(2,2,3); plot(w/pi,db); title('Magnitude in dB');xlabel('frequency in pi units'); ylabel('decibels'); 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]); gridset(gca,'YTickLabelMode','manual','YTickLabels',['50';'15';' 1';' 0'])subplot(2,2,2); plot(w/pi,pha/pi); title('Phase Response')xlabel('frequency in pi units'); ylabel('pi units'); axis([0,1,-1,1]);set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);set(gca,'YTickmode','manual','YTick',[-1,0,1]); gridsubplot(2,2,4); plot(w/pi,grd); title('Group Delay')xlabel('frequency in pi units'); ylabel('Samples'); 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