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Low voltage rectification

Discussion in 'Electronic Design' started by James, Jul 20, 2007.

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  1. James

    James Guest

    Hi All,
    I would like to rectify a signal with peak voltages in the range of
    50mV to 100mV. Are there any diodes that will start to conduct in
    this voltage range? Any other options besides a diode, I need it to
    be a passive device.
  2. Winfield

    Winfield Guest

    You could step up the voltage with a transformer and rectify it.
  3. Mook Johnson

    Mook Johnson Guest

    How do you define a passive device. Since a diode is a considered a passive
    device is a transistor a passive device too.

    An opamp based active rectifier circuit would fit the bill perfectly.

    Otherwide gain the signal up with transistors (common emitter,etc) and
    rectifiy that, then attenuate to the original levels.
  4. If it is not to power something, then use active rectifier:

    Uin ----------- + diode
    out ----a k----------------- peak rectified
    ---- - |
    | |
    | |
    [ ] R === C
    | ---
    | |
    /// ///

    The voltage on C will equal the posivie peak voltage of Uin.
  5. feebo

    feebo Guest

    I would say you need to abandon the idea of doing this "on the cheap"
    with a passive setup.

    Even though you seem to class diodes as active components, I don't
    know of any that will conduct this low - let alone what you are going
    to do with the signal once you have removed the diode "voltage".
    Chances are anything that will is gonna be mil-spec and/or hideously
    expensive/unobtainable. Germanium stuff can come down as low as 180mv
    but this is still way over what you are after.

    google "precision rectifier" there's plenty out there and depending on
    the opamp, they can work in this formation (i.e as a rectifier) down
    to a few micro-volts (some even lower)

    the first thing that came up for me here was

    which gives a nice precision full wave rectifier circuit which you
    could construct for <$5 at a one-off price - Pay attention to the
    conclusion on this page - I think you will find it encoraging.
  6. MooseFET

    MooseFET Guest

    The "backwards diode" conducts at very low voltages. Nobody makes
    them any more because active rectifiers are commonly used today.

    You can bias a normal silicon diode part way on and rectify small
    waveforms that way. The result is not very accurate.

    An ALD110800 with its gate hooked to the drain is fairly nonlinear
    near zero volts so it would also rectify.
  7. Eeyore

    Eeyore Guest

    Copper oxide rectifiers used to be fitted to the likes of VU meters.

    What kind of reverse voltage does it need to withstand ?

  8. feebo

    feebo Guest

    further browsing turned up this very concise little page on precision
    rectifiers with single opamps which further reduces your

    hant tried any of these - experienced eyes in this group will no doubt
    be able to comment on particular solutions to greater improve
    everyone's knowledge... gentlmen; the floor is yours.
  9. John Larkin

    John Larkin Guest

    "no forward tunnel current" is not exactly correct. A back diode is a
    tunnel diode with a low Ip.
    Several people still make back diodes. They are photolithographically
    fabbed on germanium, unlike the classic/horrible tunnel diode fab.
    Back diodes are still the lowest noise unbiased RF detectors.

    (I think the Ip's are uA, not mA)

  10. The first question is what is this for? Is it RF detector or something
    else? Is it a measurement circuit? How accurate?
    50...100mV is not a very small voltage per se. A conventional small
    signal Shotky diode will have the impedance at the order of 100k at this

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
  11. There are some diodes that have significant rectification in
    this voltage range. These include some very low voltage
    Schottky types.

    Here are some data sheets for low forward drop Schottkys, as
  12. Jim Thompson

    Jim Thompson Guest

    With lower resistance values and high GBW OpAmps I've used the
    following up into the MHz range...

    ...Jim Thompson
  13. Use a synchronous rectifier.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  14. Eeyore

    Eeyore Guest

    Wow ! Some of those have useful reverse breakdown voltages.

    Whereas those don't. The usual problem with them it seems.

  15. They are all just nonlinear resistors. Changes to the
    process move the nonlinearities around a bit.
  16. Eeyore

    Eeyore Guest

    Since when is synchronous rectification passive ?

  17. Jim Thompson

    Jim Thompson Guest

    I know. But, as most posters here, he probably doesn't know what he
    really wants, or couldn't find a canned solution in AoE ;-)

    ...Jim Thompson
  18. Spajky

    Spajky Guest

    look at this mine first upper schematics (slide C); it is a 70Khz IF
    amp for measuring signal strenght. (for TDA7000 IC)

    Last half of the schematic- passive part at the end:
    The right last 2 resistors provide current biasing two germanium point
    glass demodulator type diodes to the knee of conducting signal ..
    So, you can measure from few mV & up to 2V RMS signals..
  19. Robert Baer

    Robert Baer Guest

    The Esaki (tunnel) diode is the closest passive device able to do that.
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