Varactor Diode

A varactor diode is a reverse-biassed p-n junction diode with electrically variable capacitance. Varactor, tuning diodes, voltage variable capacitor diodes, parametric diodes, and variable capacitor diodes are all terms used to describe these diodes. The varactor diode has a symbol that is comparable to the PN-junction diode. Anode and cathode are the two terminals of the diode. The diode is on one end of the symbol, while the capacitor’s conducting plates are represented by two parallel lines on the other. The dielectric properties of the plates may be seen in the space between them.

Varactor diode

Now we will learn more about diodes, how a varactor diode works and finally we will look at the varactor diode formula.

Diode

A diode is an electrical component having two terminals that exclusively conducts electricity in one direction (so long as it is operated within a specified voltage level). In one direction, a perfect diode will have zero resistance, while in the other, it will have infinite resistance.

Diodes cannot attain zero or infinite resistance in the actual world. A diode, on the other hand, will have extremely low resistance in one direction (to enable current flow) and very high resistance in the other (to prevent current flow). A diode is an electrical circuit’s equivalent of a valve.

The most common kind of diode is a semiconductor diode. Only when a specified threshold voltage is present in the forward direction (i.e., the “low resistance” direction) do these diodes begin to conduct electricity. When current flows in this direction, the diode is said to be “forward biassed.” The diode is considered to be “reverse biassed” when it is linked in the opposite way (i.e., the “high resistance” direction) inside a circuit.

How does varactor diode work

Varactor diodes function on the premise of altering the breadth of the depletion area of the P-N junction to change capacitance. The capacitor effect is created by the P-N Junction diode. The capacitance is regulated by the voltage supplied to it. It operates in a backward biassed mode.

The term Varactor is made from the words Variable reactance and Variable resistor. As a result, it is known as a varactor diode because it delivers changing resistance, reactance, or capacitance. The varactor diode has the same symbol as a normal diode, with the exception that the capacitor sign is merged with the diode symbol to illustrate the capacitance effect.

Working-

1.A basic diode is made up of conducting plates made up of p-type and n-type materials.

2.The depletion zone is referred to as the dielectric.

3.The depletion region is a crucial component in determining the capacitance value. As a result, this idea is comparable to that of a capacitor.

4.The applied reverse voltage is proportional to the increase or decrease in the depletion area.

5.As the reverse voltage is applied, the depletion area expands, and vice versa.

6.The capacitance may be changed depending on the reverse voltages used.

Or we can also say this, we can do this. The breadth of the depletion layer grows when a reverse bias is given to the P-N junction. And when the reverse voltage is increased, the depletion layer expands even further. Transition capacitance is created as a result of the depletion area.

Varactor Diode benefits- 

1.Low Noise: When compared to other P-N junction diodes, it produces less noise. As a result, the power loss due to noise in varactor diodes is minimal.

2.Portability: Because of its tiny size and low weight, it is easily transportable.

3.Reliability: It outperforms other P-N junction diodes in terms of reliability.

4.Economical: Because it is a low-cost diode, it is cost-effective to employ in a variety of applications.

Varactor Diode disadvantages-

These are specifically engineered to function in the reverse biassed mode; when used in the forward biassed mode, they have the least impact.

Varactor diode formula

CT =  ɛA/W

CT stands for transition capacitance, ɛ is the dielectric constant, A is the capacitor’s plate area, and W is the depletion layer’s width.

The above relationship shows that transition capacitance is inversely related to depletion layer width. As a result, if we desire a large capacitance magnitude, the width should be minimal. And if we use a low reverse voltage, the width will be minimal.

Conclusion

In this article we have read about diodes, varactor diodes, its working, advantages or disadvantages too and read about its formula too, in short it is a device that allows a circuit to have a voltage-controlled variable capacitance. Varactor diodes are used to produce voltage controlled variable capacitance in radio frequency or RF circuits. When compared to other diodes, these diodes produce substantially less noise. These diodes are offered at a reduced cost and are also more dependable. These diodes are very tiny and low in weight. When it’s set to advancing bias, it’s useless.