AD7606 PCB Layout - separating Analog and Digital grounds when no dedicated pins are present?
Do NOT split the grounds underneath the IC. A single ground plane is fine. Instead, keep all analog components to the North and all digital components to the south west. That way, digital return currents are less likely to stray into the area where the analog return currents are circulating.



Is your issue cross talk with your ADC's own digital communications? Or cross talk from communications other devices sharing the same bus as the ADC?

If the problem is the latter, then the solution to this is to buffer the ADC from the rest of the digital bus with a transparent latch (sometimes even with two in cascade). The latch disconnects the ADC from the bus when the ADC is not communicating and thereby reduces crosstalk from the other devices on the bus.



https://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html

You should check out everything else in that link too.