afd_chb2.m

Digital signal processing using Matlab一書之範例程式

function [b,a] = afd_chb2(Wp,Ws,Rp,As);
% Analog Lowpass Filter Design: Chebyshev-2
% -----------------------------------------
% [b,a] = afd_chb2(Wp,Ws,Rp,As);
%  b = Numerator 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 attenuation ust be larger than 0')
end

ep = sqrt(10^(Rp/10)-1);
A = 10^(As/20);
OmegaC = Wp;
OmegaR = Ws/Wp;
g = sqrt(A*A-1)/ep;
N = ceil(log10(g+sqrt(g*g-1))/log10(OmegaR+sqrt(OmegaR*OmegaR-1)));
fprintf('\n*** Chebyshev-2 Filter Order = %2.0f \n',N)
[b,a]=u_chb2ap(N,As,Ws);