Varicap

A varicap diode, varactor diode or tuning diode is a type of diode Diode

In electronics [i], a diode is a component [i] that restricts the direction of mov ...

used in electronic Electronics

The field of electronics comprises the study and use of systems that operate by controlling the flow of ...

circuits.

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Encyclopedia

A varicap diode, varactor diode or tuning diode is a type of diode Diode

In electronics [i], a diode is a component [i] that restricts the direction of mov...

used in electronic Electronics

The field of electronics comprises the study and use of systems that operate by controlling the flow of ...

circuits.

Applications

Varactors are commonly used in parametric amplifiers, parametric oscillators and voltage-controlled oscillators as part of phase-locked loop Phase-locked loop

In electronics, a phase-locked loop is a closed-loop feedback [i] control system that generates and out ...

s and frequency synthesiser Frequency synthesiser

A frequency synthesizer is an electronic [i] system for generating any of a range of frequencies [i] ...

s.It is principally used as a voltage-controlled capacitor Capacitor

A capacitor is an electric [i]al device that can store energy [i] in the electric field [i] between a pair of ...

, and its diode function is secondary.

Operation

Varactors are operated reverse-biased Reverse-biased

Reverse-biased usually refers to how a diode [i] is used in a circuit [i]. ...

so no current flows , but since the width of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region width is proportional to the square root Square root

In mathematics [i], a square root of a number x is a number whose square [i] is x. ...

of the applied voltage; and capacitance is inversely proportional to the depletion region width. 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.

Non diode varicaps

Not all varactors are formed by diodes. In CMOS CMOS

Complementary metaloxidesemiconductor , is a major class of integrated circuit [i]s. ...

processes, varactors can be formed by placing a heavily positively-doped region inside a lightly positively-doped region The capacitance of these junctions behaves similarly to that of an NMOS transistor, which has an N+ implant inside a lightly negatively-doped region - which also forms a P-N junction device.

External links

Calculation of the characteristics of a varactor diode for various doping profiles