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ex8_17.cem

/*   Chapter 8: Example 8.17            
BiLinear Transformation:
Butterworth Lowpass Filter Design
*/
 
 /* Digital Filter Specifications: */
 wp = 0.2*pi;                          /* digital Passband freq in Hz */
 ws = 0.3*pi;                          /* digital Stopband freq in Hz */
 Rp = 1;                               /* Passband ripple in dB */
 As = 15;                              /* Stopband attenuation in dB */
 
 /* Analog Prototype Specifications: Inverse mapping for frequencies */
 T = 1; Fs = 1/T;                      /* Set T=1 */
 OmegaP = (2/T)*tan(wp/2);             /* Prewarp Prototype Passband freq */
 OmegaS = (2/T)*tan(ws/2);             /* Prewarp Prototype Stopband freq */
 
 /* Analog Butterworth Prototype Filter Calculation: */
 [cs,ds] = butlpf(OmegaP,OmegaS,Rp,As);
 
 
 /* Bilinear transformation: */
 [b,a] = bilinear(cs,ds,T);
 [C,B,A] = drt2cas(b,a) 
 
% Plotting
figure;
subplot(1,1,1)[db,mag,pha,grd,w] = mfreq_z(b,a);
subplot(2,2,1); plot(w/pi,mag);
title("Magnitude Response")xtitle("frequency in pi units"); ytitle("|H|");
 
subplot(2,2,3); plot(w/pi,db);
title("Magnitude in dB");
xtitle("frequency in pi units"); ytitle("decibels");
 
subplot(2,2,2); plot(w/pi,pha/pi);
title("Phase Response")xtitle("frequency in pi units"); ytitle("pi units");
 
subplot(2,2,4); plot(w/pi,grd);
title("Group Delay")xtitle("frequency in pi units"); ytitle("Samples");