Hi Meir, I am increasingly convinced of your hypothesis that it might be analog. I need a few more pieces of information, though: I want to verify that the issue is indeed an analog issue and not a digital capture issue: Try another test pattern like toggle mode to verify that all bits are working as expected. Vary the gain and capture data to see if the oscillation is amplified. Is it possible to remove or power down in the ADC input clock and not power down the ADC? Layout Concerns Are the analog and digital grounds combined or separate? Do you see the same oscillations on the analog power supplies going into the device pins, AVDD_5V, AVDD_3V. You mention that you are probing at the ADC input. Do you mean the AFE input? Which pins, INP, INM or ACT? What are the bypass capacitors on the power supply pins and how many? Are the caps close to the pins. For the INP and INM pins, are there any vias going through a ground plane or near a PS plane? Is there sufficient isolation of power planes (clearance)? How are the power supplies isolated from each other. My suspicion is that the second harmonic is generated in the ADC and feeding into the AFE inputs through a GND, Power or close proximity plane.
↧
