NMOS or PMOS when using MOS transistor as capacitance?

[gekk]

i want to ask which select is better with nmos or pmos when use mos transistor as capacitance?

 

[anades]

mos capacitance

Ideally, it sould not make a difference as long as you keep your MOS well biased (i.e. deep into accumulation). But, still PMOS can be preffered owing to its relatively low process variation which gives you a more defined cap across corners.

 

[Fom]

Re: mos capacitance

It depends on your process. For example: p-substrate PMOS capacitor can be implemented with floating pins.

 

[northeast1]

Re: mos capacitance

i want to ask which select is better with nmos or pmos when use mos transistor as capacitance?

PMOS has large cap, you can use varator cap base on PMOS

 

[hung_wai_ming@hotmail.com]

mos capacitance

Fom,

can u elaborate more with the floating pin PMOS cap? I am curious why we need to make it float?

Added after 2 minutes:

anades,

Why PMOS well controlled? Because it's having a separate NWELL for itself? If so, what about deep NWELL surrounding the NMOS?

 

[mkhafaji]

mos capacitance

When you have a PMOS transistor inside N-Well region your substrate for this transistor is also isolated from substrate of other noisy spaces. This help you when you connect your source terminal to substrate. The other thing is that the NPN transistor (a very weak transistor in the structure of CMOS circuits) does not turned on this way.