I am using in my design the AD7656 and the AD5724.
At the AD7656 I saw a specific recommendation to use separate Ground planes for AGND pins and for DGND pins and to connect them with a resistor (under the chip itself).
However, in the Analog-Devices MT-031 app note, which examine this very issue, it states doing such a separation is a "disaster" !!
This app note demands both AGND and DGND pins to be connected to the same AGND plane.
Which concept should I follow?
Can it be that the MT-031 app note is not relevant for SAR ADC such as the AD7656?