function [b,a] = u_chb2ap(N,As,Omegac);
% 未歸一化的切比雪夫-2型模擬低通濾波器原型
% --------------------------------------------------------
% [b,a] = u_chb2ap(N,As,Omegac);
%   b = Ha(s) 分子多項式的系數(shù)
%   a = Ha(s) 分母多項式的系數(shù)
%   N=濾波器的階數(shù) 
%   As = 阻帶波動dB數(shù); As > 0
% Omegac = 以弧度/秒的截止頻率
%
[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;