Take a six layer PCB with lots of circuitry, smaller than you'd like, parts on both sides, with very sensitive amplifiers looking for RF signals in the 100nV range, and digital circuitry.
Top layer, parts and short tracks. L2 Ground L3 long tracks L4 long tracks L5 Ground Bottom Parts and short tracks.
The digital section is running, and there are plenty of bypass caps etc, but in the end there will always be currents running around. The low noise sections are laid out very tightly, and as far away from the digital as possible. For mechanical reasons, I don't have the option of just placing circuitry where I'd like to, many part locations are dictated.
If L2 and L5 are solid ground, then current between any two points will take all possible paths, the majority will take the most direct paths and a small part of the digital noise currents will end up running through the analog sections.
If I carefully "moat" the analog sections, I think that I would get lower noise because that current would be prevented from running through my analog.
Obviously I still need to make a connection, but power in and ground can then be restricted to a single point.
Am I thinking about this correctly?
Experience in support or against? Authoritative documentation in support or against?