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Modeling >> Semiconductor Devices >> drain capacitance calculations
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Message started by jefkat on Nov 14^th, 2007, 5:23am

Title: drain capacitance calculations
Post by jefkat on Nov 14^th, 2007, 5:23am

Hi guys,
I am trying to calculate the total cap at drain. The spectre output parameters (that you get after the sim) have an element called 'cdd'.
According to definition this is dQd/dVd. So the change in drain charge to a change in drain voltage. If the definition is right then 'cdd' must be the
total cap at the drain node. However ac sims show that actual cap is somewhat bigger than this 'cdd'.
Would anyone please explain where is this comming from? has it to do with mutiterminal cap stuff (guessing)?
Thanks :)
Shaf

Title: Re: drain capacitance calculations
Post by Geoffrey_Coram on Nov 15^th, 2007, 8:40am

cdd usually refers only to the channel capacitance, so it excludes overlap and depletion capacitances.

Title: Re: drain capacitance calculations
Post by jefkat on Nov 16^th, 2007, 1:02am

Thanks much for your reply!