A tunnel diode can be used for oscillation when operated in its negative resistance region.
From the diagram above, a tank circuit is the RLC circuit. When the tank circuit is set into oscillation by applying voltage without the tunnel diode a damped oscillation is produced.
This is where application of a tunnel diode is very important. If a tunnel diode is placed in series with the tank circuit and biased at the centre of the negative resistance region, undamped oscillations are produced as you can see in the diagram above.
This is possible because the negative resistance characteristics of the tunnel diode suppresses or rather counteracts the positive characteristics of the tank (RLC) circuit.
Tunnel diode oscillator can also be called negative resistance oscillator.
The tunnel diode oscillator has one big setback which is that it does not work efficiently at low frequencies.
Although the tunnel diode does not work well or efficiently at low frequencies, it does work well at high frequencies.
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