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GUNN diode basics

GUNN diode is one of the many microwave semiconductor devices in use today. This page covers GUNN diode basics and its applications.

Gunn diode

It has negative resistance property by which gunn diode act as oscillator. To achieve this capacitance and shunt load resistance need to be tuned but not greater than negative resistance. The figure describes GUNN diode equivalent circuit. Here active region is about 6-18 μm long. It has negative resistance of about 100 Ohm with parallel capacitance of about 0.6 PF. Gunn diode will have efficiency of only few percentage.

Commercial GUNN didoe need supply of about 9V with operating current of 950mA and available from 4GHz to 100GHz frequency band. It is preferably placed in a resonant cavity.

The GUNN diode is basically a TED i.e. Transferred Electron Device capable of oscillating based on different modes.
In a unresonant transit time mode, radio frequencies of upto 1-18 GHz with power of upto 2 watt can be achieved. In a resonant limited space charge mode, radio frequencies of upto 100 Ghz with about 100watts of pulsed power can be achieved. Also refer operation principle of Gunn Diode>>.

Gunn diode advantages

Following are major advantages of the Gunn diode.
•  High frequency stability
•  Higher bandwidth and reliability
•  Smaller size
•  Ruggedness in operation
•  low supply voltage
•  noise performance similar to klystron
•  low cost of manufacturing

Gunn diode disadvantages

•  High turn on voltage
•  low efficiency below 10GHz
•  Poor bias and temperature stability
•  Small tuning range
•  Higher spurious FM noise
•  higher device operating current and hence more power dissipation
•  Lower efficiency and power at millimeter band

GUNN Diode Applications

•  Gunn didoe is used as low and medium power oscillators in microwave instruments and receiver circuits
•  As pump sources in parametric amplifiers
•  Used in police radars and also in CW doppler radars
•  Gunn diode oscillators are used to generate power at microwave frequencies for various applications such as automatic door openers, traffic gates, traffic signal controllers etc.

Application Note-Gunn diode as Oscillator

Refer application note on Gunn diode used as Oscillator.

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