afd_butt.m

the file contain many matlab signal source code and many example .

function [b,a]=afd_butt(Wp,Ws,Rp,As);
% Analog Lowpass Filter Design:Butterworth
% --------------------
% [b,a]=afd_butt(Wp,Ws,Rp,As);
% b=Numberator coefficients of Ha(s)
% a=Denomimator 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 larger 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 must be larger than 0')
end
N=ceil((log10((10^(Rp/10)-1)/(10^(As/10)-1)))/(2*log10(Wp/Ws)));
fprintf('\n* * *Butterworth Filter Order=%2.of \n',N)
OmegaC=Wp/((10^(Rp/10)-1)^(1/(2*N)));
[b,a]=u_buttap(N,OmegaC);