range of varactor capacitance

[Taherinia]

Hi
i used NMOS transistor as varactor. drain and source is connected to each other and voltage on varactor is changed between 2 various values but i don't exactly know what is changed range of varactor capacitance?is it in

 

[erikl]

Without knowing your process details, I think you can calculate with about a 1:4 range in accumulation, s. the following examples:

 

[Taherinia]

Thanks for your help
How can plot c-v curve for varactor in ADS or cadence?

 

[kenambo]

You can plot it from calculater op function..

you can take the variable cgg and plot in parametric analysis..

 

[Taherinia]

can you explain about variable cgg more?i don't know exactly what's that?

 

[erikl]

cgg is the total gate capacitance, including intrinsic and all overlap and fringing components.

 

[kenambo]

can you explain about variable cgg more?i don't know exactly what's that?

hi,

As erikl said.. Cgg is the total gate capacitance.. which represents the Varactor capacitance value mostly..

it can be obtained using output parameter function of that varactor from calculator..

 

[dick_freebird]

MOS varactor can swing between Cox(W,L) and
(Cgso+Cgdo+Cgbo) if you can push the silicon depletion
that far without gate ox rupture (or on thin enough SOI).

It will not act entirely the same as a PIN varactor as you
have a compound capacitor (oxide cap in series with
junction cap).