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The Principle and Application of IMPATT Diode

The Impact Avalanche Transit Time (IMPATT) diode is a high power radio frequency (RF) generator that operates from 3 to 100 GHz. IMPATT diodes are manufactured from silicon, gallium arsenide or silicon carbide.

An IMPATT diode is reverse biased above the breakdown voltage. The high doping levels produce a thin depletion region.

Principle of IMPATT diode
Figure 1.0 Heavily doped P and N layers of IMPATT diode

The arising high electric field rapidly accelerates carriers which free other carriers in collisions with the crystal lattice. Holes are swept into the P+ region. Electrons drift toward the N regions. The cascading effect creates an avalanche current which increases even as voltage across the junction decreases. The pulses of current lag the voltage peak across the junction. A “negative resistance” effect in conjunction with a resonant circuit produces oscillations at high power levels.

Oscillator circuit with an IMPATT diode in use
Figure 1.1 Oscillator circuit with an IMPATT diode in use

The DC reverse bias is applied through a choke which keeps RF from being lost in the bias supply. Low power RADAR transmitters may employ an IMPATT diode as a power source.

Related: The Shockley Diode Features & Operation

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