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bandgap voltages

Discussion in 'Electronic Design' started by John Larkin, Mar 4, 2008.

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  1. John Larkin

    John Larkin Guest

    Why are all the bandgap pseudo-zeners 1.25 volts or more? Is there
    something in the physics that prevents them from being any lower?

    John
     
  2. linnix

    linnix Guest

    The AVR internal bandgap is 1.1V. So it should be possible with a
    discrete.
     
  3. Possibly the band gap of silicon (1.12eV)?

    A Ge one should be possible at around 0.7V.

    The reference in the LM10 is about 200mV but it requires a higher
    voltage to power it (about 1.1V).

    http://www.national.com/rap/Application/0,1570,24,00.html
    Best regards,
    Spehro Pefhany
     
  4. Jim Thompson

    Jim Thompson Guest

    A (standard) straight vbe + NkT/q stack always gives around 1.25V ±

    However, if you have a low-VDD/low-current requirement (as I often
    do), you can make them anything you want by doing current mirror
    tricks.

    But there's still the limitation that it takes around 1.4V VDD to run
    it.

    ...Jim Thompson
     
  5. Phil Hobbs

    Phil Hobbs Guest

    That's where the Vbe drift cancels out the PTAT drift. It varies a bit
    with the current density in the Vbe.

    Cheers,

    Phil Hobbs
     
  6. Robert Baer

    Robert Baer Guest

    As i understand it, yes; it is the "definition" (actually an
    un-achieveable limit point) that "sets" that value.
    Mr Pease has an elegant explaination.
     
  7. John Larkin

    John Larkin Guest


    One of my guys just pointed this out to me:

    http://www.analog.com/en/prod/0,,769_838_ADR510,00.html

    I wonder how they do it.

    John
     
  8. Interesting. The usual parabolic tempco curve for a bandgap is
    inverted. Looks like it would overcorrect a bit if you put it in
    series with the output of a TL431 to get 1.5V.


    Best regards,
    Spehro Pefhany
     
  9. Fred Bloggs

    Fred Bloggs Guest

  10. John Larkin

    John Larkin Guest

    That appears to describe 3-terminal refs that need about 1.2 volts to
    power them. The ADI thing is a 2-terminal, 1-volt shunt reg.

    CMOS? SiGe? Some new trick?

    They may have a patent, too.

    John
     
  11. MooseFET

    MooseFET Guest

    The noise number makes it look like a bandgap reference based design.
    1V is enough that an op-amp of sorts can be used. I remember reading
    a paper on a topology that leads to "op-amps" down to 0.8V The op-amp
    was really a Norton amplifier with resistors built in.
     
  12. Jim Thompson

    Jim Thompson Guest

    Perhaps, but I doubt that Analog Devices has that particular
    configuration.

    Note the 100uA _minimum_ current... there's a lot of circuitry in
    there.

    "Shunt" allows the lower voltage operation.

    ...Jim Thompson
     
  13. James Arthur

    James Arthur Guest

    I'm surprised no one's mentioned the LM10 -- 200mV:

    http://www.national.com/ds.cgi/LM/LM10.pdf

    One of the Bobs wrote it up somewhere, I think.

    Cheers,
    James Arthur
     
  14. Fred Bartoli

    Fred Bartoli Guest

    James Arthur a écrit :
    I think Spehro did.
     
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