Avalanche Transit Time Devices.TRAPATT & BARITT DIODES.

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.

Transit TimeThe time taken by the electron to travel into the repeller space and back to the gap.

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.

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.

TRAPATT Diode

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.

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.

Voltage & Current waveforms for TRAPATT Diode

Mathematical expressions

Mathematical expressions

Mathematical expressions

Typical Parameters

ApplicationsThe applications area)Phased-array Radar systemsb)Intermediate frequency transmitters.c)Proxity fuse sourcesd)Radio altimeterse)Microwave landing systems.f)Air borne & marine radars.

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.

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.

BARITT DIODE - Principle of operation

BARITT DIODE - Principle of operation

BARITT DIODE - Principle of operation

I - V Characteristics of BARITT Diode.