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Design >> RF Design >> Error in Modeling varactors paper
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Message started by City on Dec 22^nd, 2004, 2:14am

Title: Error in Modeling varactors paper
Post by City on Dec 22^nd, 2004, 2:14am

Hi,

FYI there is an error in the white paper "Modeling varactors" eqts (21) states that q(v)=C0*v+C1*v1*ln(cosh((v-v0)/v1)). There is a missing term because clearly if v=0 there is still a charge in the capacitor which is physically wrong the correct integral is q(v) =c0*v+v1*c1*( ln(cosh((v-v0)/v1)) - ln(cosh(v0/v1)) ).
The error does not appear if you are interested in the current because of the derivative, but the charge in the capacitor is wrong.

City

Title: Re: Error in Modeling varactors paper
Post by Mighty Mouse on Dec 22^nd, 2004, 9:14am

City,
There is no reason why the charge of a nonlinear capacitor must be zero when the voltage across it is zero. Furthermore, the absolute charge on a capacitor is of no consequence, only the change of charge is important. So the only practical effect of adding the constant term is to slow the evaluation of the model.

- MM -