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.

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.

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.

John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.