How should I power an ADC?
My thoughts on the matter:

*Make sure you have proper bypassing on VDD of the ADC. Close to the package as possible. On the other side of the board is usually nice. Combination of both large and small (10u &amp; 0.1u).

*If you can separate the AGND and DGND, you'll see less ground noise from the digital circuits being injecting into the analog signals. You can use an isolator to bring signals between separate ground planes. That may be overkill though.

*Connecting AGND and DGND planes with a ferrite bead can help remove high frequency noise.

*Regarding power, I think either switching regulators or linear regulators are fine, just make sure you have appropriate filtering on the switching regulators and bypass caps on either type of supply.

Some extra links for reading:
TI Application Note on grounding in mixed signal. Part 1 Part 2