gusucode.com > 信号处理工具箱 - signal源码程序 > signal\signal\signal\lp2lp.m
function [at,bt,ct,dt] = lp2lp(a,b,c,d,wo) %LP2LP Lowpass to lowpass analog filter transformation. % [NUMT,DENT] = LP2LP(NUM,DEN,Wo) transforms the lowpass filter % prototype NUM(s)/DEN(s) with unity cutoff frequency of 1 rad/sec % to a lowpass filter with cutoff frequency Wo (rad/sec). % [AT,BT,CT,DT] = LP2LP(A,B,C,D,Wo) does the same when the % filter is described in state-space form. % % See also BILINEAR, IMPINVAR, LP2BP, LP2BS and LP2HP % Author(s): J.N. Little and G.F. Franklin, 8-4-87 % Copyright (c) 1988-98 by The MathWorks, Inc. % $Revision: 1.3 $ $Date: 1998/07/13 19:02:11 $ if nargin == 3 % 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; [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 lowpass at = wo*a; bt = wo*b; ct = c; dt = d; if nargin == 3 % 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