cheby1_3db_lp.m

编写一个函数

function [b,a] = cheby1_3db_lp(N,Fc,Ap)
% CHEBY1_3DB Design a lowpass Chebyshev Type I filter given a 3 dB point.
%   Inputs:
%       N  - Filter order
%       Fc - 3 dB cutoff frequency (0 to 1)
%       Ap - Passband attenuation (dB)

% Compute cutoff frequency of analog lowpass filter
Wc = tan(pi*Fc/2); 

% Find corresponding analog passband-edge frequency
Wp = Wc/cosh(1/N*acosh(1/sqrt(10^(Ap/10)-1)));

% Convert analog passband-edge frequency to digital
Fp = 2*atan(Wp)/pi;

% Use classic design technique
[b,a] = cheby1(N,Ap,Fp)
fvtool(b,a);