Most ADC datasheets recommend a single unbroken ground plane right under the device and connect the DGND and AGND to this plane with the least possible inductance.
such sa Techniques for High Speed ADC PCB Layout_AN-1142
but the article GROUNDING IN MIXED SIGNAL SYSTEMS by Walt Kester, James Bryant
talk more about tie AGND and DGND under the converter.
I have Multiple AD7606 connect with FPGA,
should I use unbroken ground or seperate ground connected at some point?