# Virtuoso: Value of Capacitances

1. ## Virtuoso: Value of Capacitances

Hello
Dear All
I am working on designing Opamp in my course When I started to work with frequency response and I have three questions ( attached two photos one for DC operating and another for Model parameters)
1- The two lists give values for internal capacitances which one should I use?
2- In DC operating list there are capacitances for any MOSFET with negative value what does that mean?
3- for units "aF" does it mean Angstrom unit with 10^(-10) and fF for Femto Farad (10^-15) ??
Best Regards,

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2. ## Re: Virtuoso: Value of Capacitances

Originally Posted by MahmoudHassan
1- The two lists give values for internal capacitances which one should I use?
Depends on what for. If you need the total capacitance of a node, use those with double characters: cgg , css ... It's always meant as capacitance against the "0" node, mostly GND .

Originally Posted by MahmoudHassan
2- In DC operating list there are capacitances for any MOSFET with negative value what does that mean?
I guess victoriya's answer is the best I've seen.

Originally Posted by MahmoudHassan
3- for units "aF" does it mean Angstrom unit with 10^(-10) and fF for Femto Farad (10^-15) ??
The "a" means "atto", which is 10-18, whereas 1 ångström means 10-10 m = 10-4 µm , it is only used as a length unit. femto is correct: f = 10-15 .

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