% Chapter 8: Example 8.23%            Butterworth Lowpass Filter Design:%                Use of the CHEBY2 function%% 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:T = 1;                               %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 Prototype Order Calculation:ep = sqrt(10^(Rp/10)-1);             %Passband Ripple FactorA = 10^(As/20);                      %Stopband Attenuation FactorOmegaC = OmegaP;                     %Analog Prototype Cutoff freqOmegaR = OmegaS/OmegaP;              %Analog Prototype Transition Ratiog = sqrt(A*A-1)/ep;                  %Analog Prototype Intermediate cal.N = ceil(log10(g+sqrt(g*g-1))/log10(OmegaR+sqrt(OmegaR*OmegaR-1)));fprintf('\n*** Chebyshev-2 Filter Order = %2.0f \n',N)%%*** Chebyshev-2 Filter Order =  4 % Digital Chebyshev-II Filter Design:wn = ws/pi;                          %Digital Stopband freq in pi units[b,a]=cheby2(N,As,wn);[b0,B,A] = dir2cas(b,a)%%b0 = 0.1797%%B = 1.0000    0.5574    1.0000%%    1.0000   -1.0671    1.0000%%A = 1.0000   -0.4183    0.1503%%    1.0000   -1.1325    0.7183