u_chb2ap.m

Digital signal processing using Matlab一書之範例程式

function [b,a] = u_chb2ap(N,As,Omegac);
% Unnormalized Chebyshev-2 Analog Lowpass Filter Prototype
% --------------------------------------------------------
% [b,a] = u_chb2ap(N,As,Omegac);
%      b = numerator polynomial coefficients
%      a = denominator polynomial coefficients
%      N = Order of the Elliptic Filter
%     As = Stopband Ripple in dB; As > 0
% Omegac = Cutoff frequency in radians/sec
%
[z,p,k] = cheb2ap(N,As);
      a = real(poly(p));
    aNn = a(N+1);
      p = p*Omegac;
      a = real(poly(p));
    aNu = a(N+1);  
      b = real(poly(z));
      M = length(b);
    bNn = b(M);  
      z = z*Omegac;
      b = real(poly(z));
    bNu = b(M);
      k = k*(aNu*bNn)/(aNn*bNu);
     b0 = k;
      b = k*b;