AD9265 board and help about ENOB

Hi every body

I have designed a board using AD9265 according to datasheet and its evaluation board but when I sampled 140MHz single tone signal with 80 MHz sampling frequency I got 8.5 bit ENOB. Also I have used AD9524 clock distributor for low jitter clock. I compared my result with its figures in datasheet and considered that in its data noise floor is on -120db but noise floor in my data is about -80db. So whhat can be the problem in this system?

I have designed a board using AD9265 according to datasheet and its evaluation board but when I sampled 140MHz single tone signal with 80 MHz sampling frequency I got 8.5 bit ENOB. Also I have used AD9524 clock distributor for low jitter clock. I compared my result with its figures in datasheet and considered that in its data noise floor is on -120db but noise floor in my data is about -80db. So whhat can be the problem in this system?

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Hi hamed
How is your PSU ? it can be because of the PSU and your grounding . check them out .

Best Wishes
Goldsmith

goldsmith said:

Hi hamed
How is your PSU ? it can be because of the PSU and your grounding . check them out .

Best Wishes
Goldsmith

Click to expand...

Dear Goldsmith

Thank you very much for your reply. Our board is multilayer board with 4 ground plane. I checked several analog device documents and found that for multilayer boards there is no need to separate analog and digital ground although in some documents they told that it is better to have individual ground for analog and digital part but in others it is mentioned that the effect will be less and here the problem is more than 4 bits or in other words 4*6 db = 24 db in SNR. I asked analog device and they sent a pdf to me regarding to analyzing ADC's . According to this document I should use a high precision source with good SNR and -120 db which is in datasheet is because of source signal generator.

Best,
Hamed