lp2bp.m

matlabDigitalSigalProcess内有文件若干

function [at,bt,ct,dt] = lp2bp(a,b,c,d,wo,bw)
%LP2BP Lowpass to bandpass analog filter transformation.
%   [NUMT,DENT] = LP2BP(NUM,DEN,Wo,Bw) transforms the lowpass filter
%   prototype NUM(s)/DEN(s) with unity cutoff frequency to a
%   bandpass filter with center frequency Wo and bandwidth Bw.
%   [AT,BT,CT,DT] = LP2BP(A,B,C,D,Wo,Bw) does the same when the
%   filter is described in state-space form.

%   Author(s): J.N. Little and G.F. Franklin, 8-4-87
%   Copyright (c) 1988-98 by The MathWorks, Inc.
%   $Revision: 1.11 $  $Date: 1997/12/02 19:16:59 $

if nargin == 4		% Transfer function case
    % handle column vector inputs: convert to rows
    if size(a,2) == 1
        a = a(:).';
    end
    if size(b,2) == 1
        b = b(:).';
    end
    % Transform to state-space
    wo = c;
    bw = d;
    [a,b,c,d] = tf2ss(a,b);
end

error(abcdchk(a,b,c,d));
[ma,nb] = size(b);
[mc,ma] = size(c);

% Transform lowpass to bandpass
q = wo/bw;
at = wo*[a/q eye(ma); -eye(ma) zeros(ma)];
bt = wo*[b/q; zeros(ma,nb)];
ct = [c zeros(mc,ma)];
dt = d;

if nargin == 4		% Transfer function case
    % Transform back to transfer function
    [z,k] = tzero(at,bt,ct,dt);
    num = k * poly(z);
    den = poly(at);
    at = num;
    bt = den;
end