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capacitance in device models (Read 2542 times)

c1000

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capacitance in device models
Aug 04^th, 2010, 1:29pm

In physics-based device models, like BSIM models, �the parasitic capacitance is evaluated by the derivative of charge with respect to corresponding terminal voltage.
If the device is modeled as a current source and 16 or less capacitors, why not using capacitance directly but calculating charge for caps?
does charge must be evaluated for circuit simulation?

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Geoffrey_Coram

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Re: capacitance in device models
Reply #1 - Aug 5^th, 2010, 6:48am

c1000 wrote on Aug 4^th, 2010, 1:29pm:

does charge must be evaluated for circuit simulation?

Yes.

Ken's book (Designer's Guide to Spice & Spectre) shows why -- charge conservation. BSIM3/4 model the device as currents and charges -- four, one for each terminal. I suppose you could count it differently: channel charge (split into four components), plus junction and overlap caps (which are two-terminal capacitors).

Not sure what you meant by "parasitic capacitance" -- the channel charge is not parasitic.

If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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