What Is a Tunnel Diode?
A tunnel diode (Esaki diode) is a very high-speed diode that works by quantum tunneling and has an interesting property: over a certain voltage range it shows negative resistance.
How Does It Work?
Thanks to its very heavily doped junction, electrons "tunnel" through the barrier in a way that isn't possible in a classic diode. This gives a very fast response and conduction at low voltage.
Negative Resistance Region
In normal components, current rises as voltage rises; but in one region of the tunnel diode, current falls as voltage rises. This "negative resistance" makes it suitable for building high-frequency oscillators.
| Region | Current as voltage rises |
|---|---|
| Normal | Rises |
| Negative resistance | Falls (inverted) |
| High voltage | Rises again |
Where Is It Used?
Very high-frequency oscillators, fast switching and microwave circuits. The negative resistance offsets the losses of a resonant circuit and keeps the oscillation going.
Limitations
It works at low power and low voltage; modern transistor-based solutions have replaced it in most places, but it remains valuable in special microwave applications.
Common Mistakes
- Choosing the wrong operating point: for oscillation the diode must be kept in the negative-resistance region.
- Expecting high power: the tunnel diode is a low-power component.
- Using it in place of an ordinary diode: it isn't suitable for jobs like rectification.
Frequently Asked Questions
What is negative resistance good for?+
Are tunnel diodes still used?+
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