20 March 2019

What is varactor diode

Meaning of varactor diode:

A varactor diode is one kind of semiconductor microwave solid-state device. A varactor diode is a PN junction diode whose capacitance is varied by varying the reverse voltage. These diodes are also named as varicap diodes. A varactor diode is specifically fabricated and optimized such that they permit a high range of changes in capacitance. Before we learn about varactor diode first let us understand the topic of the capacitor.

What is a capacitor?

A capacitor is an electronic component that stores electrical energy or electronic charge in the form of an electric field. The basic capacitor is made up of two parallel conductive plates separated by a dielectric. The two conductive plates act like electrodes and the dielectric act like an insulator. This capacitor, the voltage-dependent device means the output of the diode depends on their input voltage. The varactor diode is used in a place where the variable capacitance is required, and that capacitance with the help of the voltage. This diode also called a volt cap, varicap, voltage variable capacitance or tuning diode. Here first show the figure of the capacitor.

Capacitor symbol

Symbol of varactor diode:

In general, it looks like or similar to that a normal PN junction diode in which one terminal is termed as the cathode and the other terminal is termed as an anode. Here the varactor diode consists of two lines at one end cathode end of normal diode that indicates the capacitor symbol. The one end of a symbol consists of the diode and their other end has two parallel lines.

 varactor diode symbol

Working of varactor diode:

We know that the capacitance of the capacitor is directly proportional to the region of the terminals as the region of the terminals increases the capacitance of capacitor increases when in this mode diode is in the reverse bias mode. The varactor diode is basically made for n-type and p-type of a semiconductor. In n-type semiconductor material the free electrons are the majority carriers while in holes are minority carriers but in p-type of semiconductor holes are the majority carriers and free electrons are the minority carriers. So here when p-type and n-type material are joined together or contact them the PN junction.

This PN junction separates the p-type and n-type semiconductors and the depletion region is created at the PN junction side.  The positive and negative ions make the depletion region. A depletion region is a region where the mobile charge carrier is absent. so diode in reverse bias mode current does not flow. When the diode is connected in forward biasing move the current start flowing through the diode and their depletion region becomes decreases. The depletion region mode does not move from one side to another side. The depletion region blocks free electron from the n-side and hole from the p side region. The depletion-mode region blocks electric current across the PN junction

Depletion region in reverse bias PN junction

Characteristics of the varactor diode

The characteristics of the varactor diode have the following:
  • These diodes are significantly generated less noise compared to other diodes
  • The cost of these diodes is available at lower or more reliable also
  • These diodes are very small in size and very lightweight compared to other diodes
  • There is no use when it is operated in forwarding bias
  • In reverse bias mode, this diode enhanced the capacitance as shown in the graph below

Characteristics of a varactor diode

More detailed information

Advantages and disadvantages of varactor diode:

Advantages of varactor diode:
  • Less noise 
  • The power loss due to noise is low 
  • It is portable due to the small size  
  • Lightweight
  • Reliability
  • It is economical
  • Low cost
  • Small size 
Disadvantages of varactor diode:
  • These diodes are specially designed to work in the reverse biased mode. Hence they are not useful when operating them in the forward bias mode
More detailed information
Read more >> Advantages and disadvantages of a varactor diode

Application of varactor diode:
  • To set LO signal
  • A variable resonant tank LC circuit
  • Electronic application
  • Ultra-high-frequency television sets
  • Harmonic generators
  • Frequency control circuits
  • High-frequency radios
  • Frequency modulator
  • RF phase shifter
  • Frequency multiplier
  • Radio receiver for tunning the circuit
  • Parametric amplifier
  • Bandpass filters
  • Voltage controlled oscillators
More detailed information