[[Image:Lambda diode.svg|thumb|right|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 junction gated 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 ''V''–''I'' 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<ref>[https://www.elfa.se/Web/Downloads/_t/ds/1n37xx_eng_tds.pdf?mime=application%2Fpdf 1N3712 data sheet].</ref> 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.<ref>[https://www.cxi1.co.uk/Theory/neg_resistance/negres.htm Oscillations and Regenerative Amplification using Negative Resistance].</ref> 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==
Like the tunnel diode, the negative resistance aspect of the lambda diode lends itself naturally to application in oscillator circuits<ref>[https://www.ahars.au/vk5br/NegativeResistance/NegResDipMeter.html ''A Dip Meter Using the Lambda Negative Resistance Circuit'']. Lloyd Butler, ''Amateur Radio'', January 1997.</ref> and amplifiers. In addition, bistable circuits such as memory cells have been described.<ref>United States Patent 4376986: Double Lambda diode memory cell; http://www.wipo.int/pctdb/images4/PCT-PAGES/1983/091983/83001335/83001335.pdf.</ref>
==References== {{Reflist}}
==Literature== * {{cite book|first=Rudolf F.|last=Graf|title=Modern Dictionary of Electronics, 7th ed.|page=411|location=Boston [etc.]|publisher=Newnes Press|year=1999|isbn=0-7506-9866-7}}
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Category:Analog circuits
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