Varactor diodes

when a diode is operated inthe reverse biased condition, the width of the depletion region increases as voltage that is applied increases. Varying the width of the depletion region is equivalent to varying the plate separation of a very small capacitor such that the relationship between junction capacitance & applied reverse voltage will look something like that presented in figure below. The typical variation of capacitance supplied by a varactor is from about 50pF to 10pF as the reverse voltage goes up from 2V to 20V. The symbol used for a varactor diode has been shown above.