PresentationTopic: Varactor Diode

Name: Abdul MohizRoll No: CS-15-41

Varactor diodeo A varactor is a diode that always works /operates

in reverse bias and is doped to maximize the inherent capacitance of depletion region.

o The Depletion region act as a capacitor di-electric because of its non conductive characteristic.

o The P and N region are conductive and acts as the capacitor plates.

Capacitance varies with reverse voltage

Basic OperationRecall that capacitance is determined by the parameters of plate area (A), dielectric constant( ), and plate separation (d), as expressed in the following formula:

BasicsVaractor Diode are also referred to as Varicaps or Tuning Diodes and they are commonly Used in Communication Systems.

Information About Varactor Diode

A tuning diode, also known as a varactor

diode, variable capacitance diode, varicap diode or

variable reactance diode, is a diode that

has a variable capacitance which is

a function of the voltage that is

impressed on its terminals.

Tuning / varactor diodes are operated reverse-biased, and therefore no current

flows. However, since the thickness

of the depletion zone varies with the

applied bias voltage, the capacitance of the diode can be

made to vary.

The symbol of varactor diode is

shown in the figure. The varactor diode symbol consists of

the capacitor symbol at one end of the

diode that represents the

variable capacitor characteristics of

the varactor diodes.

Defining Varactor Diode

Meaning of Varactor

Symbol For Varactor Diode:

In general, it looks like a normal PN- junction diode in which one terminal is termed as the cathode and the

other terminal is termed as anode. Here, varactor diode consists of two lines at one end (cathode end of

normal diode) that indicates the capacitor symbol. 

P-N JUNCTION:

Operation :Varactors are operated in a reverse-biased state, so no DC current flows through the device. The amount of reverse bias controls the thickness of the depletion zone and therefore the varactor's junction capacitance. Generally, the depletion region thickness is proportional to the square root of the applied voltage, and capacitance 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 variable junction capacitance, but varactors are manufactured to exploit the effect and increase the capacitance variation.

Usage

Characteristic

Varactor Diode Example

The body plotters show the frequency

response at 0V and 20V reverse bias.The center of the 0V bias response curve is at

553.64 KHz and the center of the 20V bias response curve at 1.548 MHz

Any Questions About Varactor Diode

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