Capacitor within NWELL good or surround with NWELL good? ( d

[boki]

Dear All,


Could you please tell me layout capacitor within NWELL good or
surround with NWELL good? ( double poly)


Best regards,

Boki.

 

[G Vandevalk]

boki wrote:

Dear All,


Could you please tell me layout capacitor within NWELL good or
surround with NWELL good? ( double poly)


Best regards,

Boki.


You could connect the NWELL to a quiet supply. (AGND !?)

OR you could let it float and get some extra isolation from a noisy chip
substrate.

The concept of letting it float will mess up some verification systems
and simulators
so it is a bad idea in practice. (but may acually work!)

The concept of placing it inside an area surrounded by an NWELL do-nut shape
is simply to physically separate it from the (supposedly noisy )
substrate to some degree.

The concepts that are understood about substrate noise are modeled
weakly in this area.

YMMV

- Gerry