Yawei,

  Sorry, to clarify

1) From the discussion, I can not visualize the issue you are having.
   In the past, I have seen tones in the response of a DAC and I
   re-created the conditions. Is this frequency spectrum similar to the
   the frequency spectrum you are seeing?

2) If this frequency spectrum is similar to your frequency spectrum,
   then the tones can be eliminated by modifying the input source
   being sampled by the ADC.

3) My apologizes, the meaning of default and smoothed are not
   clear. The intent was
     - default, the setup I would typically use for testing an ADC
     - smoothed, modified setup for DAC to eliminate concentrating
       quantitazation energy in a few frequency bins.

4) In this case, the input source was changed to make sure that
   that each DAC state gets exercised, or to prevent the quantitazation
   noise from being concentrated in a few frequency bins.

                                                           Best Regards,

                                                               Sheldon

Hi, Sheldon,

Quote:

I am sorry that I cannot put a waveform here because all the workstations are in a private network in my company. I take a look at my simulation results, they look similar as smoothed in your graph.

Quote:

Do you mean modify the input source to ensure a coherent sampling? Then a sine wave or other periodic signal are sampled at the codes which are evenly distributed. So the quantization noise looks like a white noise in the spectrum, NOT concentrate on some frequency points like default. The point 3) and 4) are tightly related to 2). Right?


Thank you
Yawei