A variable capacitance, variously called a varicap diode, is a type of electronic semiconductor diode device which is specifically designed to work in reverse bias p-n junction. The device is capable of storing the electrical charge and exploiting the voltage-dependent capacitance. The internal capacitance of a varicap diode characteristically varies based on the variation of the reverse voltage. A variable capacitance diode is thus also known as a varactor diode, a variable reactance diode, or a tuning diode in electronics.
The variable capacitance diode has similar basic characteristics to a p-n junction since it is formed from it. However, there are certain characteristic specifications of a varicap diode that further defines its performance and importance in electronics. These include the diode's capacitance value, capacitance-voltage change behaviour, reverse breakdown, and quality factor or Q. For instance, the Q or the quality factor of the variable capacitance diode is very critical for the overall performance of the circuit.
Variable capacitance diodes have extensive uses. These include: