u_elipap.m

西交大刘树棠写的《数字信号处理》那本书的所有源代码

function [b,a]=u_elipap(N,Rp,As,Omegac);
%    b=numerator polynomial coefficients
%    a=denominator polynomial coefficients
%    N=Order of the Elliptic Filter
%    Rp=Passband Ripple in dB;Rp>0
%    As=Stopband Attenuation in dB;As>0
%    Omegac=Cutoff frequency in radians/sec
     [z,p,k]=ellipap(N,Rp,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;