18 Mar 2004
20 Jun 2009)
Interactive simulation of a PID with autotuning.
function [B,A] = butterdesign(N,Wc)
%BUTTERDESIGN Butterworth analog lowpass filter design.
% [B,A] = BUTTERDESIGN(N,Wc) returns the numerator and denominator for an
% N-th order Butterworth analog with a bandwith Wc.
% The resulting filter has N poles around the circle of radius Wn in the
% left half plane, and no zeros.
% Author: William Spinelli (email@example.com)
% Copyright 2004 W.Spinelli
% $Revision: 1.0 $ $Date: 2004/02/27 12:00:00 $
% Poles are on the circle of radius Wn in the left-half plane.
p = Wc*exp(i*(pi*(1:2:N-1)/(2*N) + pi/2));
p = [p; conj(p)];
p = p(:);
if rem(N,2)==1, p = [p; -Wc]; end
A = poly(p);
B = real(prod(-p));