Tunnel Diode Oscillator

Tunnel Diode Oscillators and Self-Capacitance

A tunnel diode oscillator is a circuit that utilizes the unique properties of a tunnel diode to generate high-frequency electronic oscillations. Here's a breakdown:

• Tunnel Diodes:  These are special semiconductor diodes with heavily doped p and n regions, allowing for a quantum mechanical tunneling effect. This effect creates a characteristic current-voltage (I-V) curve with a negative resistance region.

• Oscillation Principle: The negative resistance region of the tunnel diode is crucial for oscillation. In a circuit with a tank circuit (inductor and capacitor) and the tunnel diode biased in this region, the negative resistance can overcome losses in the circuit, leading to sustained oscillations at a specific frequency.

Impact of Tunnel Diode Self-Capacitance:

• Self-capacitance:  Every tunnel diode has a small inherent capacitance due to its physical construction. This capacitance acts in parallel with the negative resistance of the diode.

• Frequency Limitation:  As the operating frequency increases, the effect of the self-capacitance becomes more prominent. It acts like a shunt, diverting current away from the negative resistance path and reducing its effective value. This ultimately limits the maximum achievable oscillation frequency in the circuit.

• Frequency Drift: Changes in temperature or supply voltage alter the self-capacitance. This alters the resonant frequency of any LC resonance circuit the tunnel diode is connected to. A solution is to connect the tunnel diode to a tap in the inductor rather than across the entire inductor.