avalanche transit – time devices
DESCRIPTION
transit time devicesTRANSCRIPT
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Avalanche Transit Time Devices.TRAPATT & BARITT DIODES.
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Avalanche OperationAvalanche breakdown is caused by impact ionization of electron-hole pairs.When applying a high electric field, carriers gain kinetic energy and generate additional electron-hole pairs through impact ionization.
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Transit TimeThe time taken by the electron to travel into the repeller space and back to the gap.
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TRAPATT DIODETrapped Plasma Avalanche Triggered Transit.Its a high-efficiency microwave generator capable of operating from several hundred megahertz to several gigahertz.Basic operation p-n junction reverse biased to current densities well in excess of those encountered in normal avalanche operation.
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DimensionsN-type width 2.5 12.5 umP-type width 2.5 7.5 umTRAPATT Diode dia 50 70 um for CW operation @ lower frequency for high peak-power devices.
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TRAPATT Diode
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Principle of operationAs soon as the diode is excited, the charge is accumulated in the depletion region at the junction & the electric field across the junction increases linearly.When sufficient carriers are generated, it then depress throughout the depletion region, causing voltage to fall down.During this interval, plasma formation takes place.
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Principle of operationVoltage & current continue to decrease to residual value & the plasma is extracted from the region.As the residual charge is removed, the voltage increases further & the diode charges again.At some point, the diode is charged fully & maintains a constant voltage across it while current drops down.When current comes back, the cycle is repeated.
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Voltage & Current waveforms for TRAPATT Diode
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Mathematical expressions
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Mathematical expressions
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Mathematical expressions
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Typical Parameters
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ApplicationsThe applications area)Phased-array Radar systemsb)Intermediate frequency transmitters.c)Proxity fuse sourcesd)Radio altimeterse)Microwave landing systems.f)Air borne & marine radars.
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Negative ResistanceNegative resistance is defined as that property of a device which causes the current through it to be 180 degree out of phase with the voltage across it.
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BARITT DIODEBarrier Injected Transit Time DiodeThe BARITT diode uses injection and transit time characteristics of minority charge carriersto generate a negative resistance at microwave frequencies.About the biased in the forward direction boundary layer, the minority charge carriers are injected.The charge carriers have a low unsaturated drift velocity.This causes the carriers in BARITT diodes to have a large transit time leading to oscillation only @ low microwave frequencies.
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BARITT DIODE - Principle of operation
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BARITT DIODE - Principle of operation
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BARITT DIODE - Principle of operation
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I - V Characteristics of BARITT Diode.