isolating digital and analog grounds
Your question is tricky. It applies many assumptions
(1) Digital ground and analog ground are already shorted if it is a common substrate, unless you have deep NWELL in process to isolate different grounds
(2) Even if u have common substrate, solid connection between them should be made as late as possible, like in PADs or in PCB level
(3) Anyhow, PCB will short them together, ppl always use ferite beads to separate grounds from one ground and then distribute to chips