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AD7626 EVAL unstable noise floor

Question asked by zimingw on May 3, 2017
Latest reply on May 8, 2017 by Gnib

Hi,

 

I am using AD7626 + SDP-H1 as part of my test bench.

 

I use a clean signal generator with a balun to generate the differential test signal.

I found there is some problem that the captured signal is really not stable after powering on 1 min. 

Two figures are the single tone captured directly after power on and the signal captured after 1 min power on.

The ADC were very unstable. Sometimes the FFT looks correct, sometimes not.

I used 'Continuous Capture', and the noise floor were jumping up and down.

 

 

If I keep the input port open, I got a noise floor about -120dB.

But if I put 50 Ohm load to each differential input port. And I got figure below that the noise floor is only -50dB.

 

 

Could you please help me on that?

 

Thanks very much

Ziming

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