bp2ip3m.m

toolbox of sdt implementation

% 2nd Order Band-Pass Sigma-Delta Modulator Model with IP3 Calculation
% by S. Brigati, F. Francesconi, A. Fornasari, P. Malcovati
% The modulator structure is simulated using Simulink (BP2IP3.mdl).
% 1. Plots the Power Spectral Density of the bit-stream 
% 2. Calculates the SNR
% 2. Calculates the IP3
% 4. Calculates histograms at the integrator outputs

clear

t0=clock;

% ************************************************************************
% Variabili globali
% ************************************************************************
bw=200e3;					% Base-band
R=107;						% 42.8 MHz sampling rate
Fs=R*2*bw;                  % Oversampling frequency
Ts=1/Fs;
N=2^15;                     % Samples number
nper=32;
Fin1=(Fs/4)+ nper*Fs/N;     % Input signal frequency 
Fin2=(Fs/4)- nper*Fs/N;     % Input signal frequency 

Ampl=0.5-pi/256;			% Input signal amplitude [V]
Ntransient=0;
%
% kT/C noise and op-amp non-idealities
%
k=1.38e-23;             % Boltzmann Constant
Temp=300;				% Absolute Temperature in Kelvin
Cs=1e-12;				% Integrating Capacitance of the first integrator
alfa=(711-1)/711;       % A=Op-amp finite gain (alfa=(A-1)/A -> ideal op-amp alfa=1)
Amax=2;                 % Op-amp saturation value [V]
sr=280e6;				% Op-amp slew rate [V/s]
GBW=250e6;              % Op-amp GBW [Hz]
noise1=4.39e-3;         % 1st int. output noise std. dev. [V/sqrt(Hz)]
delta=0.1e-9;			% Random Sampling jitter (std. dev.) [s] (Boser, Wooley JSSC Dec. 88)
%
% Modulator coefficients
%
b=0.125;		% 1/8 gain of the first stage
b2=0.125;		% 1/8 gain of the second stage
b3=0.25;         % 1/4 additional gain of the second feedback loop
Vref=1;

finrad1=Fin1*2*pi;		% Input signal frequency in radians
finrad2=Fin2*2*pi;		% Input signal frequency in radians


s0=sprintf('** Simulation Parameters **');
s1=sprintf('   Fs(Hz)=%1.0f',Fs);
s2=sprintf('   Ts(s)=%1.6e',Ts);
s3=sprintf('   Fin1(Hz)=%1.4f',Fin1);
s4=sprintf('   Fin2(Hz)=%1.4f',Fin2);
s5=sprintf('   BW(Hz)=%1.0f',bw);
s6=sprintf('   OSR=%1.0f',R);
s7=sprintf('   Npoints=%1.0f',N);
s8=sprintf('   tsim(sec)=%1.3f',N/Fs);
s9=sprintf('   Nperiods=%1.3f',N*Fin1/Fs);
disp(s0)
disp(s1)
disp(s2)
disp(s3)
disp(s4)
disp(s5)
disp(s6)
disp(s7)
disp(s8)
disp(s9)
% ************************************************************************
% Open Simulink diagram first
% ************************************************************************
open_system('BP2IP3')

options=simset('InitialState', zeros(1,5), 'RelTol', 1e-3, 'MaxStep', 1/Fs);
sim('bp2IP3', (N+Ntransient)/Fs, options);	% Starts Simulink simulation

% ************************************************************************
%   Calculates PSD and IP3 of the bit-stream and of the signal
% ************************************************************************
w=hann_pv(N);
f=Fin1/Fs;						% Normalized signal frequency
fBL=N*(1/4-bw/(2*Fs));       	% Lower limit Base-band frequency bins
fBH=N*(1/4+bw/(2*Fs));       	% Higher limit Base-band frequency bins


yy1=zeros(1,N);
yy1=yout(2+Ntransient:1+N+Ntransient)';

ptot=zeros(1,N);
[snr,ptot]=calcSNR(yy1(1:N),f,fBL,fBH,w,N);


% Calculate intermodulation products
fip1=N*Fin1/Fs;
fip2=N*Fin2/Fs;
fip31=2*fip1-fip2;
fip32=2*fip2-fip1;

ampdb1=ptot(ceil(fip1));
ampdb2=ptot(ceil(fip31));
ampdb3=ptot(ceil(fip2));
ampdb4=ptot(ceil(fip32));

IP3=min(abs(ampdb2-ampdb1), abs(ampdb4-ampdb3))

% ************************************************************************
% Graphical output
% ************************************************************************

figure(1);
clf;
plot(linspace(0,Fs/2,N/2), ptot(1:N/2), 'r');
grid on;
title('PSD of a 2nd-Order Band-Pass Sigma-Delta Modulator')
xlabel('Frequency [Hz]')
ylabel('PSD [dB]')
axis([0 Fs/2 -100 0]);


% ************************************************************************
% Histograms of the integrator outputs
% ************************************************************************

figure(4)
nbins=200;
[bin1,xx1]=histo(y1, nbins);
[bin2,xx2]=histo(y2, nbins);
clf;
subplot(1,2,1), plot(xx1, bin1)
grid on;
title('First Integrator Output')
xlabel('Voltage [V]')
ylabel('Occurrences')
subplot(1,2,2), plot(xx2, bin2)
grid on;
title('Second Integrator Output')
xlabel('Voltage [V]')
ylabel('Occurrences')