afd_butt.m

butterworth+chebcv的matlab 程序

%Butterworth模拟滤波器原型设计子程序afd_buff.m
function[b,a]=afd_butt(Wp,Ws,Rp,As,fs);
%Analog lowpass filter design:butterworth
%[b,a]=afd(Wp,Ws,Rp,As)
%b=Numberator coefficients of Ha(s)
%a=Denominator 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 attanuation 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=%2.0f\n',N)
OmegaC=Wp/((10^(Rp/10)-1)^(1/(2*N)));
[b,a]=g_bilinear(N,OmegaC,fs);