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ex8_22.cem

/*   Chapter 8: Example 8.22            
Butterworth Lowpass Filter Design:
Use of the CHEBY1 function
*/
 
 /* 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: */
 T = 1;                                /* Set T=1 */
 OmegaP = (2/T)*tan(wp/2);             /* Prewarp Prototype Passband freq */
 OmegaS = (2/T)*tan(ws/2);             /* Prewarp Prototype Stopband freq */
 
 /* Analog Prototype Order Calculation: */
 ep = sqrt(10^(Rp/10)-1);               /* Passband Ripple Factor */
 A = 10^(As/20);                        /* Stopband Attenuation Factor */
 OmegaC = OmegaP;                  	/* Analog Prototype Cutoff freq */
 OmegaR = OmegaS/OmegaP;           	/* Analog Prototype Transition Ratio */
 g = sqrt(A*A-1)/ep;                    /* Analog Prototype Intermediate cal. */
 N = ceil(log10(g+sqrt(g*g-1))/log10(OmegaR+sqrt(OmegaR*OmegaR-1)));
 msgprint("*** Chebyshev-1 Filter Order = ") N
 
 
 /* Digital Chebyshev-I Filter Design: */
 wn = wp/pi;                          /* Digital Passband freq in pi units */
 [b,a]=cheby1(N,Rp,wn);
 [b0,B,A] = drt2cas(b,a)