varactor diode amar.ppt

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  • Microwave Semiconductor Devices

  • 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.