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ADC TEST[Matlab code] using Logic Analyzer

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ljy4468

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maxim adc logic analyzer

Hi all
I've a question about ADC TEST.
I received Matlab code for logic analyzer's data in MAXIM Homepage.
But I'm confused about that.

In code...
.
.
.

figure;
plot([1:numpt],code);
title('TIME DOMAIN')
xlabel('SAMPLES');
ylabel('DIGITAL OUTPUT CODE');
Dout=code-(2^numbit-1)/2; %Re-center the digitized sinusoidal input
Doutw=Dout;
Dout_spect=fft(Doutw);
Dout_dB=20log10(abs(Dout_spect));
figure;
maxdB=max(Dout_dB(1:numpt/2));
plot([0:numpt/2-1].fclk/numpt,Dout_dB(1:numpt/2)-maxdB);
grid on;
title('FFT PLOT');
xlabel('ANALOG INPUT FREQUENCY (MHz)');
ylabel('AMPLITUDE (dB)');
.
.
.

I'm wondering this.-->
Dout=code-(2^numbit-1)/2; %Re-center the digitized sinusoidal input

code meaning digital output code..
Example, In 3bit ADC, there are only 9code.(0,1,2,3,4,5,6,7,8)
Am I Right????

Then Why Re-center the digitized sinusoidal input???
output code must be centered around 0??

Anyone help me
 

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