HELP : Isoalted substrate

[hauntedhunter]

Hi,

In an interview i was asked about isolated substrate.Can anyoe please tell me what it is?

 

[swkimaz]

Main idea is coming from mixed signal implemented in same die.
Digital circuit is very noisy and is coupled to analog side through substrate.
So, we need analog circuit, esp. references to be isolated from substrate.
The ways are dependent on technology. For example, we are using CMOS Nwell processing and then we can surrond Nwell to analog circuit to protect noise.