We are working on an ADC that has maximum sampling rate of 2.5MSps at clock frequency of 40MHz and Vref of 2.5V. The architecture is SAR and it carries out the calibration internally. Currently we are running at clock frequency of 32MHz and sampling rate of 1.25MSps. We are reconstructing the analog waveform using MATLAB from the raw data collected and are observing a periodic noise. We are unable to comprehend the cause of this noise. The noise is approximately equal in amplitude ~80mV. We have also observed noise on power supply of the FPGA that is collecting the raw data but the frequency of the noise was very low. We need your help in troubleshooting this noise. Even if you could give us any pointers to look at, that would be greatly appreciated. Please let us know if you need further information regarding the setup of the system. EDIT: Schematic is attached below. Analog input is given to the "Input circuit". C42 is shown DNP but we have connected a capacitor of 1uF 16V. We are using Analog Discovery 2 as our signal source. Regards.
Do you need to read more than 1 byte in more than 1 read operation to read an ADC value?
If so, you need to synchronise reading correctly to ADC conversions.
If the ADC periodically samples between reading the MSB and the LSB, you will get periodic error that looks exactly like this.
For ADC samples 1.01 and 0.99, you can read 1, then .99, Put them together, guess what? 1.99.
I can't say this is exactly your problem because you don't tell us what the ADC is - resolution, interface typ, or link to the datasheet, and I can't enlarge those schematics in the middle of editing an answer. But it's one possible (likely) problem that has bitten someone here before.