Lambda diode

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An n-channel JFET (top) and a p-channel JFET combine to form a lambda-diode circuit

A lambda diode is an electronic circuit that combines a complementary pair of field-effect transistors into a two-terminal device that exhibits an area of differential negative resistance much like a tunnel diode. The term refers to the shape of the VI curve of the device, which resembles the Greek letter λ (lambda).

Lambda diodes work at higher voltage than tunnel diodes. Whereas a typical tunnel diode[1] may exhibit negative differential resistance approximately between 70 mV and 350 mV, this region occurs approximately between 1.5 V and 6 V in a lambda diode due to the higher pinch-off voltages of typical JFET devices. A lambda diode therefore cannot replace a tunnel diode directly.

Moreover, in a tunnel diode the current reaches a minimum of about 20% of the peak current before rising again towards higher voltages. The lambda diode current approaches zero as voltage increases, before rising quickly again at a voltage high enough to cause gate–source Zener breakdown in the FETs.

It is also possible to construct a device similar to a lambda diode by combining an n-channel JFET with a PNP bipolar transistor.[2] A suggested modulatable variant but is a bit more difficult to build uses a PNP based optocoupler and can be tweaked by using its IR diode. This has the advantage that its properties can be fine tuned with a simple bias driver and used for high sensitivity radio applications, sometimes a modified open can PNP transistor with IR LED can be used instead.

Applications[edit]

Like the tunnel diode, the negative resistance aspect of the lambda diode lends itself naturally to application in oscillator circuits[3] and amplifiers. In addition, bistable circuits such as memory cells have been described.[4]

References[edit]

Literature[edit]

  • Graf, Rudolf F. (1999). Modern Dictionary of Electronics, 7th ed. Boston [etc.]: Newnes Press. p. 411. ISBN 0-7506-9866-7.