afd_elip.m

来自「很多matlab的源代码」· M 代码 · 共 30 行

function [b,a] = afd_elip(Wp,Ws,Rp,As)
% Analog Lowpass Filter Design:Elliptic
% -------------------------------------------
% [b,a] = afd_elip(Wp,Ws,Rp,As);
% b = Numerator coefficients of Ha(s)
% a = Denomintor coefficients of Ha(s)
% Wp = Passband edge frequency in rad/sec;Wp>0
% Ws = Stopband edge frequency in rad/sec;Ws>Wp>0
% Rp = Passband ripple in +dB:(Rp>0)
% As = stopband attenuation in +dB;(As>0)
%
if Wp <= 0
error('Passband edge must be large than 0')
end
if  Ws <= Wp
error('Stopband edge must be larger than Passband edge')
end
if (Rp<=0)|(As<0)
error('PB ripple and/or SB attenuation ust be larger than 0')
end
ep = sqrt(10^(Rp/10)-1);
A = 10^(As/20);
OmegaC = Wp;
k = Wp/Ws;
k1 = ep/sqrt(A*A-1);
capk = ellipke([k.^2 1-k.^2]);
capk1 = ellipke([(k1.^2) 1-(k1.^2)]);
N = ceil(capk(1)*capk1(2)/(capk(2)*capk1(1)));
fprintf('\n*** Elliptic Filter ORder = % 2.of\n',N)
[b,a] = u_elipap(N,Rp,As,OmegaC);