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.