Varactor Diode

Varactor diodes or varicap diodes are semiconductor devices that are widely used in the electronics industry. They are also used within the RF design arena. In this article, we will learn about the characteristics and applications and uses of varactor diode in a detailed manner.

How frequently do we use electrical gadgets and switches in a day to day activities? Some of the basic components include capacitors, resistors, transistors, transformers and so on. Let’s consider a solid semiconductor electronic device with two terminals. The diode shows nonlinear V-I characteristics and allows the current to flow in a single direction in forward bias and offers less resistance. Similarly, it blocks the current flow in the other direction during reverse bias where it offers high resistance. Varactor diode

What is Varactor diode?

Varactor diode got its name due to its variable reactor or variable capacitor of diodes. It is a special kind of diode and widely used in the electronics industry along with different electronics applications. These diodes are also named as varicap diodes.

The varactor diode is also a solid semiconductor microwave and used in applications where the variable capacitance is obtained by controlling voltage.

Following is the table of links related to diode:

Varactor diode Symbol

Since Variable capacitor is the primary function of this diode, the circuit symbol is represented like this. the Varactor diode circuit symbol is given below.

Varactor diode Symbol

Varactor Diode Characteristics

Varactor diodes are mostly operated under reverse bias conditions and therefore there is no conduction. They are voltage controlled capacitors and sometimes known as varicap diodes, although the word varactor is widely used.

Variable Capacitance Characteristics

Variable capacitance effect is shown by normal diodes, but varactor diodes are preferred for providing the required capacitance changes. The diodes are uniquely optimized and manufactured such that they enable high range changes in capacitance. Varactor diodes are categorized based on the properties of diode junction.

Varactor diode Applications

Some applications of varactor diode are given in the points mentioned below.

  • They are used in RF design arena and provide a method of varying the capacitance within a circuit by the application of control voltage. It provides them with special capability due to which varactor diodes are used in the RF industry.
  • These diodes are used in many circuits and find applications in two main sectors.
  • FR filters – It is possible to tune filters by using varactor diodes. Tracking filters can be required in front-end receiver circuits wherein the filters are enabled to track the frequency of incoming received signals.
  • Voltage controlled oscillators (VCOs) – VCOs are used for many applications and oscillator within a phase locked loop is the major region. VCOs are present in almost all wireless receivers and radio.

Varactor Diode Formula

Varactor capacitance \(C_{j}=\frac{CK}{(V_{b}-V)^{m}}\)
Dependence of varactor diode on series resistance and diode capacitance \(F=\frac{1}{2*p_{i}*R_{s}*C_{j}}\)
Quality factor \(Q=\frac{F}{f}\)

Notations Used In The Varactor Formula

  • Cj is the diode capacitance
  • C is the diode capacitance when the device is unbiased
  • V is the applied voltage
  • Vb is the barrier voltage at the junction
  • m is the constant depending upon the material
  • K is the constant equal to 1
  • F is the maximum operating frequency
  • Rs is the series resistance
  • f is the operating frequency

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Important Questions On Varactor Diode

Q1. How is varactor diode categorised?

Ans: Varactor diode can be categorised as abrupt and hyperabrupt varactor diode.

Q2. What is abrupt varactor diode?

Ans: Abrupt varactor diode exhibits the inverse square of C-V function and the doping concentration is constant.

Q3. What is a hyperabrupt varactor diode?

Ans: Hyperabrupt varactor diode is used as it has greater capacitance for the given change of voltage.

Q4. In varactor diode which layer can be used for the detection of bad frames?

Ans: Link layer is used for the detection of bad frames.

Q5. What is the major use of varactor diode?

Ans: The major use of varactor diode is for tuning of the circuit.

Q6. What happens to plate separation when the depletion region in the varactor diode widens?

Ans: As the depletion region in the varactor diode widens, the plate separation increases.

Q7. What is the key feature of the varactor diode?

Ans: The key feature of the varactor diode is that it exhibits variable capacitance.

Q8. What is the reason behind the usage of back-to-back varactor diode?

Ans: The reason behind the usage of the back-to-back varactor diode is to eliminate harmonic distortion.

Q9. Which type of diode is commonly used in electronic tuners in TVs?

Ans: Varactor diode is the commonly used diode in electronic tuners in TVs.

Q10. Varactor diode operates in which bias?

Ans: Varactor diode operates in reverse bias.

Q11. Which diode is associated with voltage-controlled capacitance?

Ans: Varactor diode is associated with voltage-controlled capacitance.


Practise This Question

An electric  bulb consumes 7.2 kJ of electrical energy in 2 minutes. What is the power of the electric bulb?