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0V reference

Discussion in 'Electronic Design' started by Fred Bear, May 14, 2006.

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  1. Fred Bear

    Fred Bear Guest

    Can anyone help with designing a 0V reference?
    FB
     
  2. The intended accuracy and drift ?
    :)

    Rene
     
  3. Fred Bear

    Fred Bear Guest

    Thanks for the reply, Rene.
    100% accuracy, 0% drift - It is critical that this is a 0.0000V reference.
    FB
     
  4. Fred Bear

    Fred Bear Guest

    I was told that a resistor to ground would do it, with a capacitor to 0V to
    stabilise the voltage. What values of resistor and capacitor would you
    recommend for 1 amp?
    Fred
     
  5. Slurp

    Slurp Guest

    For your quoted 0.0000V reference at 1A the resistor needs to be <100 micro
    ohms. -- but is in conflict with your required 100% accuracy.

    Ideally you need a 1 * 10 ^(-(infinity -1)) femto ohm resistor and an
    (infinity - 1) Farad capacitor.

    BTW - Do you know what the capacitance is between two pinheads 1 light year
    apart?

    Slurp
     
  6. John_H

    John_H Guest

    0V relative to what?
     
  7. 0.0000V is trivial. 0.0000000 is more difficult.



    Best regards,
    Spehro Pefhany
     
  8. Joerg

    Joerg Guest

    Hello Spehro,
    Nah, replace the bolts with marine grade stainless and give it some more
    torque :)

    Regards, Joerg
     
  9. Nah, stainless is a bad conductor, worse then steel.
    Copper is what you need ;)
    If its a audio application, you will need a 101%
    super-duper-ultra-OFC-OMG-WTCF-STFU plated bolt made from 50 year old
    5-times refined silver from a certain mine in england that was processed
    by a tibetian monk.Othwerise it will sound rough, cold, shady and dark.
    ;)
     
  10. John Fields

    John Fields Guest

     
  11. Guest

    Even marine-grade stainless steel is stainless by virtue of a thin and
    cohernet layer of chromium oxide - I don't know which one - which has
    an appreciable electrical resistance.

    My conductivity meter stopped using stainless steel electrodes - a bad
    idea that I'd inherited - at the point where I could prove that the
    oxide film had an appreciable electrical resistance by changing that
    resistance by exposing the film to 2% aqueous sodium hydroxide (whose
    conductivity the meter had to monitor, along with that of the tap water
    that washed it away).
     
  12. would -273.16 degrees C help?


    martin
     
  13. Lots of unpleasant ways for 100nV to crop up..


    Best regards,
    Spehro Pefhany
     
  14. You left out "Dank" ;-)


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  15. Joerg

    Joerg Guest

    Well, guys, this was meant as a joke...

    Ok then, how 'bout a nice thick gold plating on everything? Of course
    only gold mined from a particular mine here in California in 1850.

    Regards, Joerg
     
  16. A reference has never 1 amp. References just
    supply the voltage, not power. Lookup
    "supply" or "voltage regulator"

    Rene
     
  17. How pure? Gold-copper doesn't have much thermocouple voltage, but a
    couple tenths of a degree C would be enough to swamp 100nV. Galvanic
    action might be possible too.

    Of course the advantage of selling such a 'reference' to
    unsophisticated customers would be that few would be able to test it
    sufficiently accurately to complain.



    Best regards,
    Spehro Pefhany
     
  18. Pooh Bear

    Pooh Bear Guest

    In that case the reference has appreciable resistance / impedance.

    An ideal reference would have zero impedance and laugh at an Amp.

    Graham
     
  19. Pooh Bear

    Pooh Bear Guest

    You've been looking at some schematics that have 0Vref on them haven't you ? (
    blushes )

    Graham
     
  20. An ideal reference yes, but actual references
    only supply a few mA at close to zero ohms

    Rene
     
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