@Tim Edwards Excuse me. In magic ,how can I separate ground of digital cell (DVSS) with the ground of the analog core (VSS) which is typically substrate contact. Thanks

Assuming that you really care about noise isolation of the analog part, the best way is to use a deep nwell structure, with the analog ground being tied to the pwell inside the deep nwell.

@Ahmed Reda If the regions are physically separated and you are not worried about the noise as @Tim Edwards mentioned, you can surround one (or both) of the regions with

subcut

81/53. This is what we do for the

user_project_wrapper

region when running LVS at the caravel level.

@Mitch Bailey: Yes, but I'm sure the application here is a noise-sensitive analog circuit.

@Ahmed Reda For reference, the SRAM macros have a 3 well structure where the deep nwell was added at higher level of the hierarchy. If you do use deep nwell, be sure to have the outer nwell guard ring fully closed at the level where you add the deep nwell.

Thanks @Tim Edwards @Mitch Bailey. I got it.