% A/D Converter Spectrum
% -----------------------

clear;clf;clc;

% Set Input Parameters

N=2048;		  % Sample Points
f=80;    	  % Hz
b=[3 5];	  	  % Quantizing Bits	

% Define Time Vector

t=(10/f)*(1:N)/N;

for k=1:2;

% Define Input Signals

Em=2^b(k);
xn=(Em/2)*sin(2*pi*f*t);

% Quantize Signal - Mid-point Quantizer

qn=(2*floor(xn-1e-6)+1)/Em;
  if xn<0;qn=(2*floor(xn+1e-6)+1)/Em;end;

qn=qn/max(qn);

% Store Quantized Signal

xx(:,k)=qn';

% Find Quantized Signal Spectrum

X=fft(qn,N);
X=fftshift(X);
Pxx=X.*conj(X);
Pxx=Pxx/max(Pxx);
Pz=10*log10(Pxx+1e-6);

% Store Quantized Signal Spectrum

yy(:,k)=Pz';

end;

% Plot Quantized Signal

subplot(221);
plot(t,xx(:,1));grid;
axis([0 .04 -1.25 1.25]);
xlabel('Time - sec');
ylabel('Voltage');
title(['Quantized Sine Wave (3 bits)']);

% Plot Quantized Signal Spectrums

fx=(f/10)*(-N/2:N/2-1);
subplot(223);
plot(fx,yy(:,1));grid;
axis([0 2500 -60 0]);
xlabel('Frequency - Hz');
ylabel('Power - db');
title(['Quantize Signal Spectrum (3 bits)']);

subplot(222);
plot(fx,yy(:,2));grid;
axis([0 2500 -60 0]);
xlabel('Frequency - Hz');
ylabel('Power - db');
title(['Quantized Signal Spectrum (5 bits)']);

% Find Two Tone Signal Spectrum

Em=2^b(2);
f1=80;f2=200;	  % Hz
xn=(Em/4)*(sin(2*pi*f1*t)+sin(2*pi*f2*t));
qn=(2*floor(xn-1e-6)+1)/Em;
if xn<0;qn=(2*floor(xn-1e-6)+1)/Em;end;
qn=qn/max(qn);
X=fft(qn,N);X=fftshift(X);
Pxx=X.*conj(X);
Pxx=Pxx/max(Pxx);
Pz=10*log10(Pxx+1e-6);

subplot(224);
plot(fx,Pz);grid;
axis([0 2500 -60 0]);
xlabel('Frequency - Hz');
ylabel('Power - db');
title(['Two Tone Power Spectrum (5 bits)']);