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lowest leakage, lowest Vf diode?

Discussion in 'Electronic Design' started by [email protected], Apr 24, 2007.

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  1. Guest

    I need a diode which leaks less than 100nA at 13V Vr from 25C to 50C,
    and whose foward voltage drop is less than 400mV at 100mA, any ideas?
  2. Charles

    Charles Guest

  3. John Larkin

    John Larkin Guest

    I'd guess impossible. You'd need a schottky for the forward drop, but
    they leak a lot. You might be able to fake it with a small mosfet,

  4. CW Northrop

    CW Northrop Guest

  5. Peltier cooled schottky?
  6. legg

    legg Guest

    Trouble is with leakage - the importance of sub-microamp drain leakage
    in mosfets not being specifiable.

  7. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
    You'll probably won't find one, but depending on what you're trying to
    do you might come up with something to do the trick.

    What is it for?
  8. John Larkin

    John Larkin Guest

    I've used some that were consistantly good. When what you want to do
    is impossible with guaranteed specs, you may have to settle for
    actuals. Many semi "max" parameters are set where they are just to
    speed up testing, so can often be finessed if one is careful.

    Anybody know typical Idss for a 2N7002? It's spec'd at 1 uA, but I
    suspect it's a lot less. I guess I could test a few. Gate leakage is
    spec'd in nA, but it should be spec'd in electrons per second.

  9. Robert Baer

    Robert Baer Guest

    Do you not mean "not in the datasheet"?
    The nanoamp region is very achieveable.
    Since the OP wanted a low Vf diode, the problem with FETS is that the
    gate control is sensitive to temperature, so a fixed bias scheme for
    enhancement *or* depletion mode FET is a bit iffy - especially in this
    case where the gate control voltage is going to change only a few
    hundred millivolts.
    Now that temperature sensitivity can be compensated some with a
    scheme similar to my first Codatron (TM) design; the patent for that has
    been released into the public domain - so feel free to use as you see fit.
    Be advised that there can be some mis-matching between FETS, so that
    for this "low Vf" application, that can have a large effect on the total
    operation if multiple composite devices are needed (read: volume
    production greater than 1000 per day).
    That can be mitigated to a degree by making it as IC, wafer testing
    offset before breakout and use.
    Shoot, one could even trim one of the FETs my having graded sizes for
    cutting out small areas; and the bias offset can also be trimmed (refer
    to the ALD110800 series).
  10. Robert Baer

    Robert Baer Guest

    Agree on the leakage spec; many devices are *at worst* orders of
    magnitude better than datasheet spec.
  11. John Larkin

    John Larkin Guest

    Last week's problem (the one MassivePratt squirmed out of addressing)
    was the opposite: nearly 200 uA of current coming out of the input of
    a cmos TinyLogic chip while the input voltage was well within the
    rails. We were impressed.

  12. Rich Grise

    Rich Grise Guest

    OK, Mr. Smartyboots, how many amps is(are?) one electron per second?

    Please show your work. ;-)

  13. John Larkin

    John Larkin Guest

    1.602e-19. It wasn't any work at all.

  14. Phil Hobbs

    Phil Hobbs Guest

    The mosfet sounds about right, but it'd have to be connected backwards
    on account of the source-drain diode, as in Bob Pease's polarity
    protection trick. Maybe the OP could use a lithium battery to get the
    gate bias right. It ought to be possible to power a comparator off
    wherever that 100 mA is coming from.


    Phil Hobbs
  15. Tim Williams

    Tim Williams Guest

    That's a good point- I was playing with a an, um, I think it was BS171, a
    few weeks ago, in the trudge through my parts bin for an analog switch (for
    which I eventually settled on a 2SK30 or something).

    After discovering it was in fact a MOSFET, I had it set up on the breadboard
    as a source follower into a 4.7kohm resistor from +12V or so. I connected
    the gate to a wire in air. While playing, I discovered that a plastic bag,
    charged with a stroke over my hair, switched it from two feet away, with no
    apparent drift in the potential (that is, the distance at which it
    saturates). Not bad at all. Probably, the adhesive label on the bottom of
    the protoboard has more leakage than that thing.

  16. oopere

    oopere Guest

    This makes an interesting shot noise then! One shot per second, exactly :)

  17. John Larkin

    John Larkin Guest

    It is possible to produce electrical currents that have little or no
    random shot noise, to literally dispense exactly one (or more!)
    electrons a second, rigidly periodically. SETs (single electron
    transistors) are one way to do this.

    But I guess that one electron a second does have a lot of shot noise
    in a 1 Hz bandwidth.

  18. What's it for indeed! Some special circuit configuration may be
    able to handle the problem. For example, two 1n5822 diodes in
    series will drop about 450mV at 100mA, and the connection node
    between the two diodes can be bypassed with a resistor to ground
    for the purpose of diverting most of the leakage current of the first
    diode with 13 volts across it. If the resistor is a low enough value
    the voltage drop across it from the first diode's leakage will be low
    enough to avoid creating much leakage across the second diode.
  19. Tim Williams

    Tim Williams Guest

    (Single Ended Triodes? ;-) )

    The gain on those things must be horrific. One electron admitted for -- how
    much capacitance to switch it?

  20. Mike Monett

    Mike Monett Guest

    A Radio Frequency Single Electron Transistor (RFSet) can have a
    bandwidth greater than 100MHz and extreme sensitivity. It is
    described as a fraction of the charge on an electron.

    Here's one that runs at 700MHz with a sensitivity of 3.63 * 10-5
    e/RootHz. They show how it is measured:

    Schoelkopf has a bunch of papers on them:

    Here's one that operates at 1.7GHz with a sensitivity of 1.2 * 10-5
    e/Roothertz. Fig. 1 shows a SEM photo of the device.

    Fig. 3 shows the time-domain response for a large (~5.5 electrons
    peak-to-peak) signal, 10 kHz triangle-wave applied to the gate. The
    SNR looks very good:

    These things fascinate me. I want one. No clue what I'd do with it,
    but it would be nice to have laying around just in case I found a
    use for it:)


    Mike Monett
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