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Digital Signal Processing Using MATLAB

Digital Signal Processing Using MATLAB

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21 Aug 2002 (Updated )

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cheb1hpf(wp,ws,Rp,As)
function [b,a] = cheb1hpf(wp,ws,Rp,As)

% IIR Highpass filter design using Chebyshev-1 prototype

% [b,a] = cheb1hpf(wp,ws,Rp,As)

%   b = Numerator polynomial of the highpass filter

%   a = Denominator polynomial of the highpass filter

%  wp = Passband frequency in radians

%  ws = Stopband frequency in radians

%  Rp = Passband ripple in dB

%  As = Stopband attenuation in dB

%

% Determine the digital lowpass cutoff frequecies:

wplp = 0.2*pi;

alpha = -(cos((wplp+wp)/2))/(cos((wplp-wp)/2));

wslp = angle(-(exp(-j*ws)+alpha)/(1+alpha*exp(-j*ws)));

%

% Compute Analog lowpass Prototype Specifications:

T = 1; Fs = 1/T;

OmegaP = (2/T)*tan(wplp/2);

OmegaS = (2/T)*tan(wslp/2);



% Design Analog Chebyshev Prototype Lowpass Filter:

[cs,ds] = afd_chb1(OmegaP,OmegaS,Rp,As);



% Perform Bilinear transformation to obtain digital lowpass

[blp,alp] = bilinear(cs,ds,Fs);



% Transform digital lowpass into highpass filter

Nz = -[alpha,1]; Dz = [1,alpha];

[b,a] = zmapping(blp,alp,Nz,Dz);

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