VARACTOR DIODEThe term varactor is shortened form of variable
reactor.Also called a parametric diode, tuning diodes or varicap
diodes.Provides a voltage-dependent variable capacitance. Commonly
used symbols
TYPES OF VARACTOR DIODESAbrupt and hyper abrupt type : When the
changeover p-n junction is abrupt then it is called abrupt type.
When change is very abrupt, they are called hyper abrupt type. They
are used in oscillators to sweep for different frequencies.
Gallium-arsenide varactor diodes : The semiconductor material
used is gallium arsenide. They are used for frequencies from 18 GHz
up to and beyond 600 GHz.
DescriptionAs already said varactor diode is a semiconductor
device in which the junction capacitance can be varied as a
function of the reverse voltage.
When we are applying the voltage to the junction the dielectric
is acting as capacitor.Cj Vr
-n
Capacitance : Capacitance of the device. Capacitance from a few
picoFarads to hundreds of picoFarads is provided.Capacitance range
: Range of capacitance produced when voltage is varied.
CHARACTERISTICS
Notice the nonlinear increase in capacitance as the reverse
voltage is decreased.
OPERATIONIt has a p-n junction of semiconducting
material and is always reverse biased.
The depletion zone width depends on the applied voltage and this
makes the capacitance vary with the applied voltage.
APPLICATIONSFREQUENCY MULTIPLIERS - used in applications where
its difficult to generate microwave signalsProducing relatively
high power outputs at frequencies up to 100GHzOutput can be as high
as 80% of the inputTUNING - Since the frequency can be made to vary
they are used as electronic tuning devices in tuners for
television, mobiles.PARAMETRIC AMPLIFIERS. - named for the
time-varying parameter, or value of capacitance, associated with
the operation.
