GUNN Diode Basics: Operation, Advantages, and Applications

The GUNN diode is a popular microwave semiconductor device. This page covers the fundamentals of GUNN diodes and their applications.

Image alt: Gunn diode

It exhibits a negative resistance property, allowing it to function as an oscillator. To achieve oscillation, the capacitance and shunt load resistance need to be tuned, ensuring they are not greater than the negative resistance.

The equivalent circuit of a GUNN diode consists of an active region approximately 6-18 μm long, featuring a negative resistance of around 100 Ohms and a parallel capacitance of about 0.6 pF.

GUNN diodes typically have a low efficiency, often only a few percent. Commercial GUNN diodes require a supply voltage of about 9V with an operating current of 950mA, and they are available for frequencies ranging from 4GHz to 100GHz. They are often placed in a resonant cavity. The GUNN diode is fundamentally a Transferred Electron Device (TED) capable of oscillating in different modes. In an unresonant transit time mode, radio frequencies of up to 1-18 GHz with a power output of up to 2 watts can be achieved. In a resonant limited space charge mode, radio frequencies of up to 100 GHz with about 100 watts of pulsed power can be achieved.

Refer to the operation principle of Gunn Diode for more details.

GUNN Diode Advantages

Here are the key advantages of GUNN diodes:

• High frequency stability
• Higher bandwidth and reliability
• Smaller size
• Ruggedness in operation
• Low supply voltage
• Noise performance similar to klystron
• Low manufacturing cost

GUNN Diode Disadvantages

Here are some of the disadvantages of GUNN diodes:

• High turn-on voltage
• Low efficiency below 10GHz
• Poor bias and temperature stability
• Small tuning range
• Higher spurious FM noise
• Higher device operating current, leading to more power dissipation
• Lower efficiency and power at millimeter bands

GUNN Diode Applications

• Used as low and medium power oscillators in microwave instruments and receiver circuits
• As pump sources in parametric amplifiers
• Used in police radars and 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.