Variable capacitor circuits

[walters]

What circuits or a network act like a variable capacitor?

I know some circuits produces like if its a variable capacitor
where can i find these circuits and whats the theory behind them?

 

[Davood Amerion]

One of them are varcap diode.
If any diode biased in revers direction,it act like capacitor, and it's capacity varies with reverse voltage.

 

[airman]

where can i find these circuits and whats the theory behind them?

the theory behind it is mentioned by Davood Amerion

this concept is mainly used in the ICs or VLSI so that it is not practical to integrate a FM radio in one IC and to connect the IC by a variable cap. at the same size as the hole device :?:. So that we should replace it by a varactor or reversed diode in the IC chip.

 

[Kral]

Walters,
In the "old days" of radio, a circuit called a "reactance tube" was used to provide variable capacitance to produce FM. A similar circuit called a reactance modulator, using transistors, employs roughly the same principle. See the following article
~ h**p://www.tpub.com/neets/book12/49d.htm
Scroll down to the section entitled "Semiconductor Reactance Modulator".
Regards,
Kral

 

[gunsuresh]

Any ckt having a barrier can act as a varactor diode but the magnitude og capacitance differs.

 

[A.Anand Srinivasan]

varicap diode can act as a electrically controlled variable capacitor owing to the fact that the depletion region width varies in reverse bias and acts as a dielectric between P layer and N layer