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icekalt Community Member Offline Posts: 36 Aalen, Germany	How to determine SNR, SNDR and SFDR of 8-bit ADC Sep 11^th, 2009, 1:41am hello, I am currently measuring the dynamic perfomance of my ADC. What is really annoying me is i cannot get the spectrum or even the output of DAC. When i connect my ADC to a ideal DAC and simulate them, i got a constant value of output of DAC instead of a sinusoidal signal. Can anyone help me on this?
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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: How to determine SNR, SNDR and SFDR of 8-bit ADC Reply #1 - Sep 11^th, 2009, 2:34am Nobody can help you without details like schematic, simulation setup, tools, stimulus, and so on.
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icekalt

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Posts: 36
Aalen, Germany

Re: How to determine SNR, SNDR and SFDR of 8-bit ADC
Reply #2 - Sep 11^th, 2009, 4:53am

ywguo wrote on Sep 11^th, 2009, 2:34am:

Nobody can help you without details like schematic, simulation setup, tools, stimulus, and so on.

Sorry for the vague question. I' simulating my ADC in LTSpice and now i don't know how to determine the dynamic perfomance of it. I have done static performance and the result is good where all codes are presents and monotonous. I have just found a matlab code to convert the the .raw waveform and i have successfully convert it and read it in matlab. The problem is i don't know whether i should take the output waveform directly from my ADC or should i connect my ADC into an ideal DAC then use the output of DAC in matlab. Another issues is i need a matlab code where i can use directly. i really never use matlab before. Help is really appreciated

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ywguo

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Posts: 943
Shanghai, PRC

Re: How to determine SNR, SNDR and SFDR of 8-bit ADC
Reply #3 - Sep 12^th, 2009, 1:11am

Hi icekalt,

One point you must have in mind, what we expect at the ADC output is discrete signal. So be careful don't make FFT to the continuous waveform. I don't know LTSpice. It seems to be a SPICE like simulator. Now that you simulate with LTSpice, print every sample of the ADC output. If you don't have any other tool at hand, you have to write a matlab program to process the printed results.

Try to print the ADC output with the following command in SPICE file.
.tran step start stop $ set step = sample time
.print D_7 D_6 D_5 D_4 D_3 D_2 D_1 D_0 $ print the voltages of ADC output

Best Regards,
Yawei

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