Gunn diodes and IMPATT diodes use high field effects in semiconductor materials to drive a negative resistance mode of operation. Gunn diodes use the Gunn effect to produce microwave oscillations when a constant voltage is applied. Gunn diodes are a type of transferred electron device (TED). They generate relatively low-power microwave radio signals at frequencies from a few GHz up to 200 GHz. As a discrete component, a Gunn diode can be used as an oscillator or amplifier in applications that require low-power radio frequency (RF) signals, such as proximity sensors and wireless local area networks (LAN). IMPATT diodes are semiconductor devices that generate relatively high-power microwave signals at frequencies between about 3 GHz and 100 GHz or more. IMPATT is an abbreviation for impact avalanche transit time. IMPATT diodes are used in low-power radar systems and alarms. The main drawback of using an IMPATT diode is the high level of phase noise that the device generates.
Gunn diodes and IMPATT diodes are similar, but not interchangeable. Gunn diodes that are made from gallium arsenide can operate at frequencies up to 200 GHz. A Gunn diode made from gallium nitride can reach 3 THz. Specifications for Gunn diodes include frequency range, minimum power, typical operating voltage, operating current, and packaging. For higher output power, a Gunn diode can be pulsed or stacked. Specifications for IMPATT diodes include frequency range (GHz), bandwidth range (GHz), power output (W), breakdown voltage, and gain (dB). To help maintain frequency and power stability over wide temperature ranges, the diode manufacturer can supply heatsink stands and temperature controllers. An IMPATT diode can be stable (linear) or injection-locked. A pulsed IMPATT diode operates with short bias current pulses and low duty cycles, and can produce higher output power than a continuous wave (CW) IMPATT diode.
Gunn diodes and IMPATT diodes can be manufactured to U.S. federal standards as described in MIL-STD 750 (Test Method Standard for Semiconductor Devices) and MIL-HDBK-6100 (Military Handbook, List of Case Outlines and Dimensions for Discrete Semiconductor Devices). Both Gunn diodes and IMPATT diodes are covered by the International Electrotechnical Commission (IEC) standard IEC 60747.
