function [b,a] = cheb1hpf(wp,ws,Rp,As)
% 用切比雪夫-1為原型設計IIR 高通濾波器
% [b,a] = cheb1hpf(wp,ws,Rp,As)
%   b = 高通濾波器的分子多項式
%   a = 高通濾波器的分母多項式
%  wp = 以弧度/秒為單位的通帶頻率
%  ws = 以弧度/秒為單位的阻帶頻率; 
%  Rp = 通帶中的振幅波動的+dB數; (Rp > 0)
%  As = 阻帶衰減的+dB數; (As > 0)
%
% 求出數字低通截止頻率:
wplp = 0.2*pi;
alpha = -(cos((wplp+wp)/2))/(cos((wplp-wp)/2));
wslp = angle(-(exp(-j*ws)+alpha)/(1+alpha*exp(-j*ws)));
%
% 求出模擬低通原型指標:
T = 1; Fs = 1/T;
OmegaP = (2/T)*tan(wplp/2);
OmegaS = (2/T)*tan(wslp/2);

% 設計模擬切比雪夫原型低通濾波器.:
[cs,ds] = afd_chb1(OmegaP,OmegaS,Rp,As);

% 實行雙線性變換以得到數字低通:
[blp,alp] = bilinear(cs,ds,Fs);

% 將數字低通變換為高通濾波器:
Nz = -[alpha,1]; Dz = [1,alpha];
[b,a] = zmapping(blp,alp,Nz,Dz);