%% Copyright (C) 2021 Tony Richardson %% %% This program is free software: you can redistribute it and/or modify %% it under the terms of the GNU General Public License as published by %% the Free Software Foundation, either version 3 of the License, or %% (at your option) any later version. %% %% This program is distributed in the hope that it will be useful, %% but WITHOUT ANY WARRANTY; without even the implied warranty of %% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the %% GNU General Public License for more details. %% %% You should have received a copy of the GNU General Public License %% along with this program. If not, see . %% -*- texinfo -*- %% @deftypefn {} {@var{[bt, at]} =} lp3hp (@var{b}, @var{a}, @var{Wo}) %% @deftypefnx {}{@var{[At,Bt,Ct,Dt]} =} lp3hp (@var{A}, @var{B}, @var{C}, @var{D}, @var{Wo}) %% %% [bt, at] = lp3hp(b, a, Wo) transforms an analog lowpass filter in transfer %% function form to an analog highpass filter with a different cutoff frequency (Wo). %% %% [At,Bt,Ct,Dt] = lp3hp(A, B, C, D, Wo) transforms an analog lowpass filter in state %% space form to an analog highpass filter with a different cutoff frequency (Wo). %% @seealso{lp2lp, lp2bp, lp2bs} %% @end deftypefn %% Author: Tony Richardson %% Created: 2021-04-09 function [BT AT XO1 XO2] = lp3hp(BP, AP, Wo, XI1, XI2) if (nargin == 5) Wo = XI2; [BP AP] = ss2tf(BP, AP, Wo, XI1); elseif nargin!=3 print_usage; end [BT AT] = tftrans(BP, AP, Wo, true); if (nargout == 4) [BT AT XO1 XO2] = tf2ss(BT, AT); end end %!demo %! f = 100; %! [ze pe ke] = ellipap(5, 3, 30); %! [be ae] = zp2tf(ze, pe, ke); %! %! w = logspace(-2, 1, 501); %! H = freqs(be, ae, w); %! figure(1) %! clf %! semilogx(w, 20*log10(abs(H))) %! grid %! %! [bh ah] = lp3hp(be, ae, 2*pi*f); %! %! f = logspace(1, 3, 501); %! H = freqs(bh, ah, 2*pi*f); %! figure(2) %! clf %! semilogx(f, 20*log10(abs(H))) %! grid