function [sv,sx,sigma_se,max_sx,max_sy] = simulateESL(v,mtf,M,dw,sx0)%[sv,sx,sigma_se,max_sx,max_sy] = simulateESL(v,mtf,M=16,dw=[1..],sx0=[0..])%Simulate the Element Selection Logic for a multi-element DAC.%Outputs:% sv	is an MxN matrix whose columns are the selection vectors.% sx	is an orderxM matrix containing the final state of the ESL.% sigma_se	is the rms value of the selection error.% max_sx	is the maximum absolute value of the state for all modulators.% max_sy	is the maximum absolute value of the input to the VQ.%Inputs:% v	is a vector of the digital (positive integer) input values.% mtf	is the mismatch-shaping transfer function, given in zero-pole form.% M	is the number of elements.% sx0	is a matrix whose columns are the initial states of the ESL.% dw	is a vector of dac element weights%% For a brief description of the theory of mismatch-shaping DACs, see% R. Schreier and B. Zhang "Noise-shaped multibit D/A convertor employing% unit elements," Electronics Letters, vol. 31, no. 20, pp. 1712-1713,% Sept. 28 1995.%% Handle the input argumentsif nargin < 2    fprintf(1,'simulateESL needs at least two input arguments\n');    returnendparameters = {'v' 'mtf' 'M' 'dw' 'sx0'};defaults = { NaN NaN 16 NaN NaN };for i=1:length(defaults)    parameter = char(parameters(i));    if i>nargin | ( eval(['isnumeric(' parameter ') '])  &  ...     eval(['any(isnan(' parameter ')) | isempty(' parameter ') ']) )        eval([parameter '=defaults{i};'])    endendif isobject(mtf)     if ~strcmp(class(mtf),'zpk')	error('The mtf is an unsupported type of object.')    end    tmp = mtf;	clear mtf;    mtf.form = 'zp';    mtf.k = tmp.k;    mtf.zeros = tmp.z{:};    mtf.poles = tmp.p{:};    form = 2;elseif isstruct(mtf)    if strcmp(class(mtf),'zpk')    end    if ~any(strcmp(fieldnames(mtf),'zeros'))	error('No zeros field in the MTF.')    end    if ~any(strcmp(fieldnames(mtf),'poles'))	error('No poles field in the MTF.')    endelseif isnan(mtf)    mtf.form = 'zp';    mtf.k = 1;    mtf.zeros = 1;    mtf.poles = 0;elseif isnumeric(mtf)    if size(mtf,2) == 2		% Probably old (ver. 2) ntf form	fprintf(1,'You appear to be using the old-style form of MTF specification.\n Automatic converstion to the new form will be done for this release only.\n');	tmp.form = 'zp';	tmp.k = 1;	tmp.zeros = mtf(:,1);	tmp.poles = mtf(:,2);	mtf = tmp;    endendorder = length(mtf.poles);if isnan(sx0)    sx0 = zeros(order,M);endif isnan(dw)    dw = ones(M,1);end% B/A = MTF-1num = poly(mtf.zeros);den = poly(mtf.poles);A = real(-den(2:order+1));B = real(num(2:order+1)+A);N = length(v);sv = zeros(M,N);sx = sx0;max_sx = max(max(abs(sx)));max_sy = 0;sum_se2 = 0;for i=1:N    % Compute the sy vector.    sy = B*sx;    % Normalize sy for a minimum value of zero.    sy = sy - min(sy);    % Pick the elements that have the largest desired_usage (sy) values.    sv(:,i) = ESLselect(v(i),sy,dw);    % Compute the selection error.    se = sv(:,i)' - sy;    % Compute the new sx matrix    sxn = A*sx + se;    sx = [ sxn; sx(1:order-1,:)];    % Keep track of some statistics.    sum_se2 = sum_se2 + sum((se-mean(se)).^2);    max_sx = max([max_sx abs(sxn)]);    max_sy = max([max_sy abs(sy)]);endsigma_se = sqrt(sum_se2/(M*N));