How to calculate the 4 MOS caps for a given bias point?

[A_U_J]

measuring MOS caps

hi all,
I am trying to figure out how to calculate the 4 MOS caps(Cgd,Cgs, Cdb,Cbs) for a given bias point using transient or AC simulations.
Any i/ps or comments greatly appreciated.

thanks

 

[milkdragon]

Re: measuring MOS caps

If you are using spectre, DC analysis may give you those values by PRINT

 

[A_U_J]

Re: measuring MOS caps

Hi,
thanks for the reply,but we are expected to find it by performing simulations rather than by taking the output of the simulator.

 

[A_U_J]

Re: measuring MOS caps

Here's the method..
we need to short out one cap @ a time in AC analysis using Vac source and calculate the pole and/or zero locations from transfer function obtained by hand analysis.
Next from the bode plot of the transfer function generated by the simulator find the pole and zero/or locations.
Equating the results from hand analysis and simulator we can find values of one cap @ a time.
eg to find Cgs, get rid of Cgd by applying an AC short b/w G and D.

 

[Sadegh.j]

Re: measuring MOS caps

In ADS, you can use Zin.

You can use a current source, measure the voltage and divide the two.

Cheers

 

[shqzhao]

Re: measuring MOS caps

I need same too