how to write the instruction to declare the "plus minus" 1V?

The sample-and-hold and the residue generators are used in a 100Ms/s, 10-bit pipeline converter with a "plus minus" 1V reference made by 9stages with 1.5-bit per stage and a final 1-bit stage.

Below is the code that i took from SD toolbox and how i declare the Vref. hope someone can tell me the correct way to do it.

                                                                                           function [snrdB,ptotdB,psigdB,pnoisedB] = calcSNR(vout,f,fB,w,N,Vref)
% SNR calculation in the time domain (P. Malcovati, S. Brigati)
% vout: Sigma-Delta bit-stream taken at the modulator output
% f:    Normalized signal frequency (fs -> 1)
% fB:  Base-band frequency bins
% w:  windowing vector
% N:    samples number
% Vref: feedback reference voltage
%
% snrdB:    SNR in dB
% ptotdB:    Bit-stream power spectral density (vector)
% psigdB:   Extracted signal power spectral density (vector)
% pnoisedB:  Noise power spectral density (vector)
%

                                                                                         Vref=-1|1
fB=ceil(fB);
signal=(N/sum(w))*sinusx(vout(1:N).*w,f,N);  % Extracts sinusoidal signal
noise=vout(1:N)-signal;                  % Extracts noise components
stot=((abs(fft((vout(1:N).*w)'))).^2);    % Bit-stream PSD
ssignal=(abs(fft((signal(1:N).*w)'))).^2;  % Signal PSD
snoise=(abs(fft((noise(1:N).*w)'))).^2;    % Noise PSD
pwsignal=sum(ssignal(1:fB));                  % Signal power
pwnoise=sum(snoise(1:fB));            % Noise power
snr=pwsignal/pwnoise;
snrdB=dbp(snr);
norm=sum(stot)/Vref^2;              % PSD normalization
if nargout > 1
  ptot=stot/norm; 
  ptotdB=dbp(ptot);
end

                                                                                                             if nargout > 2
  psig=ssignal/norm;
  psigdB=dbp(psig);
end

                                                                                                                   if nargout > 3
  pnoise=snoise/norm;
  pnoisedB=dbp(pnoise);
end