Re: nonlinear capacitors

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

I never heard about varactors before. But reading about
them I realized that an electrostatic voltmeter (for example
a quadrant electrometer) is a nonlinear capacitor. In this
application the non-linearity is a tolerable nuisance.
Ludwik Kowalski

"John S. Denker" wrote:

> Ludwik Kowalski wrote:
> > I would not
> > be surprised by a "nonlinear capacitor." Does it exist?
>
> Sure.  One important family is called "varactor".
>   http://www.google.com/search?q=varactor
> e.g.
>   http://www.americanmicrosemi.com/tutorials/varactor.htm
>   http://www.tpub.com/neets/book11/45k.htm
>
> It's a back-biased PN junction.  Lightly doped.
> The depletion region grows as the stored Q increases,
> so the incremental capacitance dQ/dV goes down.
>
> If you put it in a suitable circuit so you can adjust
> the operating point, it makes a fine electronically-
> adjustable capacitor.  Useful as a tuning element.
>
> You can also use it as an out-and-out nonlinear
> element for mixers, parametric amplifiers, et cetera.
>
> > Since epsilon is likely to depend
> > of conditions, such as pressure or temperature
>
> That wouldn't normally be considered a "nonlinear"
> capacitor.  Variable capacitor, maybe.