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Deep N-Well is of greater use when there is power switches in ur analog ckts.since the power swiches generates both the lateral and vertical currents .gaurdrings will collect the lateral currents effectively where as the Deep N-well collects the vertical currents .The depth of Deep N-well depends on the depeth of penetration of the vertical current carriers.
Also some people wrap noise sensitive circuits with Deep Nwell.
Upto ~10MHz it's said to be effective.
Practically, it's not easy to completely wrap big piece of analog circuit blocks
by deep Nwell
since some designers tend to deploy Nwell not tighted to AVDD.
Some foundry does has certain "Isolation measurement report"
in their technical information center. You might want to take a look.
The isolation should be similar even if you use very different generation
Deep Nwell is used only when u require high threshold transistors.It is not like it is better or that is better it depends on the design requirements.If the designer says to use deepnwell then u hav to use deep N-well.
deepNwell serves needy when the transistors inside are very sensitive to the substrate noise or if there is lot of fluctuations in the power . deep nwell penetrates deep into the substrate almost cutting of the substrate. it also depends on the placement of the transistors, suppose if the transistors are placed near to photodoide then its almost compulsory to use deep nwell to avoid the heavy flow of electrons in the substrate generated due to the photo emission.