polyam wrote on Nov 1st, 2020, 7:45pm:Are you sure you are correctly DACing the output signal ? Clearly the amplitude of your output signal is being modulated. Maybe you need to check your demux. I am guessing there is something wrong with the demux. I did a quick simulation for a TI-ADC. Please see the input and output of the ADC. You should be able to see your input signal (of course with a delay) when you DAC the output of the ADC.
Since I'm doing the sampling in Nyquist frequency, I think I should see the modulation. If you decrease the sampling frequency to less than half you should see the same thing. Let's say you have Nfft=64 Cycles=31 then if your sampling frequency is 800M S/s your input frequency must be 800*31/64 which is 387.5M Hz. If you run the simulation for at least Nfft*(1/Fs) seconds then you will see the same thing.
I have also done the simulation for less than Nyquist frequency (1/10), and my DAC output looks more like yours.