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In electronics
Electronics

Electronics refers to the flow of charge through nonmetal electrical conductor , whereas electrical refers to the flow of charge through metal electrical conductor....
, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
 which has a variable capacitance
Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge.Capacitance is also a measure of the amount of electric charge stored for a given electric potential....
 that is a function of the voltage impressed on its terminals.

ctors are principally used as a voltage-controlled capacitor
Capacitor

A capacitor or condenser is a Passive component electronic component consisting of a pair of electrical conductor separated by a dielectric....
, rather than as rectifier
Rectifier

A rectifier is an electrical device that converts alternating current to direct current , a process known as rectification. Rectifiers have many uses including as components of power supply and as detector s of radio signals....
s.






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Varicap Symbol
In electronics
Electronics

Electronics refers to the flow of charge through nonmetal electrical conductor , whereas electrical refers to the flow of charge through metal electrical conductor....
, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
 which has a variable capacitance
Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge.Capacitance is also a measure of the amount of electric charge stored for a given electric potential....
 that is a function of the voltage impressed on its terminals.

Applications

Varactors are principally used as a voltage-controlled capacitor
Capacitor

A capacitor or condenser is a Passive component electronic component consisting of a pair of electrical conductor separated by a dielectric....
, rather than as rectifier
Rectifier

A rectifier is an electrical device that converts alternating current to direct current , a process known as rectification. Rectifiers have many uses including as components of power supply and as detector s of radio signals....
s. They are commonly used in parametric amplifiers, parametric oscillator
Parametric oscillator

A parametric oscillator is a simple harmonic oscillator whose parameters vary in time.Another intuitive way of understanding a parametric oscillator is as follows: a parametric oscillator is a device that oscillates when one of its "parameters" is changed....
s and voltage-controlled oscillator
Voltage-controlled oscillator

A voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage, while Modulation signals may also be fed into the VCO to cause frequency modulation or phase modulation ; a VCO with digital pulse o...
s as part of phase-locked loop
Phase-locked loop

A phase-locked loop or phase lock loop is a control system that generates a Signal that has a fixed relation to the phase of a "reference" signal....
s and frequency synthesizer
Frequency synthesizer

A frequency synthesizer is an electronics system for generating any of a range of frequency from a single fixed quartz clock or electronic oscillator....
s.

Operation

Varactor
Varactor Function
Varactors are operated reverse-biased so no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region thickness is proportional to the square root
Square root

In mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x....
 of the applied voltage; and capacitance
Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge.Capacitance is also a measure of the amount of electric charge stored for a given electric potential....
 is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage.

All diodes exhibit this phenomenon to some degree, but specially made varactor diodes exploit the effect to boost the capacitance and variability range achieved - most diode fabrication attempts to achieve the opposite.

External links

  • Calculation of the characteristics of a varactor diode for various doping profiles
  • Trimless IF VCO: Part 1: Design Considerations from Maxim.


Further reading

  • Mortenson, Kenneth E. (1974). Variable capacitance diodes: the operation and characterization of varactor, charge storage and PIN diodes for RF and microwave applications. Dedham, Mass.: Artech House.
  • Penfield, Paul and Rafuse, Robert P. (1962). Varactor applications. Cambridge, M.I.T. Press.