Varactor Diodes, high-frequency circuit, communication circuit, television receiver PCB, China PCBA manufacturer, China PCB manufacturer, Shenzhen PCBA manufacturer, Shenzhen SMT process, Shenzhen PCB assembly, Shenzhen PCB factory
Varactor Diodes

Varactor diodes, also known as "variable reactance diodes", are made by using the characteristic that the junction capacitance changes with the applied voltage when the pN junction is reverse biased. When the reverse bias voltage increases, the junction capacitance decreases, and conversely, when the reverse bias voltage decreases, the junction capacitance increases. The capacitance of the varactor diode is generally small. The maximum value is tens of picofarads to hundreds of picofarads, and the ratio of maximum capacitance to minimum capacitance is about 5:1. It is mainly used in high-frequency circuits as automatic tuning, frequency modulation, equal modulation, for example, as a variable capacitor in the tuning loop of a television receiver.

Working principle

Varactor diode is a kind of special diode. When a forward bias is applied, a large amount of current is generated, the depletion region of the PN (positive and negative) junction becomes narrower, and the capacitance becomes larger, resulting in a diffusion capacitance effect; when a reverse bias is applied, a transition capacitance effect will occur. However, due to the leakage current generated when the forward bias is applied, so the reverse bias is supplied in applications.

In fact, we can think of it as a PN junction. We think that if a reverse voltage V (Varactor diode is used in reverse) is added to the PN junction, the electrons in the N-type semiconductor are led to the positive pole, the holes in the T-type semiconductor are led to the negative electrode, and then a depletion layer with neither electrons nor holes is formed. The width of the depletion layer is set to d, which changes with the change of the reverse voltage V. As a result, when the reverse voltage V increases, the depletion layer d becomes wider, and the capacitance C of the diode decreases (according to C=kS/d), while the reverse voltage decreases, the depletion layer width d becomes narrower, the capacitance of the diode becomes larger. The change of the reverse voltage V causes the change of the depletion layer, thereby changing the junction capacity C of the voltage-controlled varactor. Achieved the goal.


The function of the varactor diode is to use the principle of variable capacitance between PN junctions to make semiconductor devices, which are used as variable capacitors in high-frequency tuning, communication and other circuits.