Tunnel Diode Oscillator

A tunnel diode is always operate in the negative resistance region. When operated in this re-gion, it works very well in an oscillator. Fig.1 (i) shows a parallel resonant circuit. Note that RPis the parallel equivalent of the series winding resistance of the coil. When the tank circuit is set intooscillations by applying voltage as show in Fig.1 (ii), damp oscillations are produce. It isbecause energy is lose in the resistance RP of the tank circuit.

f a tunnel diode is place in series with the tank circuit and biase at the centre of the negative-resistance portion of its characteristic as show in Fig.2, undamped oscillations are produce atthe output. It is because the negative-resistance characteristic of the tunnel diode counteracts thepositive-resistance characteristic of the tank circuit.The circuit shown in Fig. 2 is calledtunnel diode oscillatorornegative resistance oscillator.The tunnel negative resistance oscillator has one major drawback. While the circuit works very well atextreme high frequencies (upper mega hertz range), it cannot be use efficiently at low frequencies.Low-frequency diode oscillators generally use transistors.

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