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baab Senior Member Offline Posts: 178 EA	Cgs and Cgs vs Vgs Mar 14^th, 2014, 7:06pm Hi. I set up this circuit for simulation Cgs and Cgs as Vgs changes. Below are the curves Cgs and Cgs vs Vgs. (please see it in the second post. The forum doesn't allow to post two images in a single post) I have some questions, hope you can help. 1. Why Cgs and Cgs are negative? 2. Why Cgs and Csg are not equal? Thanks.
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baab Senior Member Offline Posts: 178 EA	Re: Cgs and Cgs vs Vgs Reply #1 - Mar 14^th, 2014, 7:07pm And this is the curves Cgs and Cgs vs Vgs:
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aaron_do

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Re: Cgs and Cgs vs Vgs
Reply #2 - Mar 16^th, 2014, 10:18pm

Hi baab,

I think this has been discussed more than once before, but you will need to do a search. I believe it is just something to do with the way capacitance is defined in the model which makes it a negative value. Also, Cgs and Csg may not be defined exactly symmetrically. For your purposes (matching I assume), I guess you're probably better off doing an AC or SP analysis to find the capacitance since all the capacitance will be lumped together...

regards,
Aaron

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there is no energy in matter other than that received from the environment - Nikola Tesla

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baab

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Re: Cgs and Cgs vs Vgs
Reply #3 - Mar 16^th, 2014, 10:38pm

Thanks, Aaron.

You are correct. Here is the link to the previous discussion.
http://www.designers-guide.org/Forum/YaBB.pl?num=1087411058

As I understand from the link, the capacitance between G and S will be -Csg in BSIM3V3 model.

I am going to post a new thread about LNA design procedure that is very confusing. Hope you could help.

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Andrew Beckett Senior Fellow Offline Life, don't talk to me about Life... Posts: 1742 Bracknell, UK	Re: Cgs and Cgs vs Vgs Reply #4 - Mar 18^th, 2014, 4:21pm See also my response to your identical question http://www.cadence.com/Community/forums/p/28791/1332097.aspx#1332097 - I'm assuming that's you, because it's an enormous coincidence otherwise. Andrew
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baab Senior Member Offline Posts: 178 EA	Re: Cgs and Cgs vs Vgs Reply #5 - Mar 20^th, 2014, 12:20am Thanks. yes, it is me.
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