Why ACE FFT Peak Power is Different from Graph (off by 4dB)

Question

I'm observing fft peak power on ACE being different from when it gets exported & plotted. Follow graph is a 1kHz signal measurement using AD4630-24. 
 ACE measures fundamental power -0.491dBFS. 
 When exported in csv file, the FFT plot (done in matlab) show fundamental power is -4.81dBFS. Then I came back to ACE plot and noticed that dot on fundamental, lying somewhere around 0dB (full scale), whereas the tone below it has a peak at around -4dB, which aligns with MATLAB plot. Why the small gap and difference?

NathanT · Accepted Answer

Hi gaoxiaom , 
 
 Can you try putting a ground connection between the ground pin from the signal generator to the ground pins of your board? On the other hand, are you using our evaluation board for the AD4630? And what are your inputs to the ADC? 
 
 Warm regards, Jo)

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Why ACE FFT Peak Power is Different from Graph (off by 4dB)

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