Hi Javad, Most likely, there is some noise that is injected onto the ground plane from the Xilinx Chipscope that is coupling onto the ADC board and onto the oscilloscope. Make sure you have a good connection between the ground planes of each board and between the oscilloscope ground. The results above do not appear to be sampled at a consistent sampling rate. For AC applications, it is more appropriate to use RDATAC mode and ensure you can read all the data between samples. Start with a slow data rate at first. Best Regards,
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