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Favourite low offset op-amp

Discussion in 'Electronic Design' started by Pooh Bear, May 17, 2005.

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  1. Pooh Bear

    Pooh Bear Guest

    Hi all,

    I have an application where I'm looking for a low input voltage offset
    op-amp. I'd like 100uV or so typical and don't want to pay much. Lowish
    input current is desirable too.

    Speed isn't an issue, nor is very low noise or single supply operation.
    In fact I *want* to run it off +/- 17V.

    It's not an area I'm intimately familiar with.

    Anyone got any suggestions ? Low cost remember !

    Cheers, Graham
  2. Pooh Bear

    Pooh Bear Guest

    That's > 10x what I want to pay ! I could live with 100kHz GBWP - lol !

    My idea of low cost is around 15 cents per dual op-amp in quantity !

  3. Guest

    Pooh Bear a écrit :
    One of my favourite opamps is the OPA227. It has an offset of < 75 uV,
    is reasonable fast (8MHz, 2 V/us Slew Rate, but the OPA228 is faster),
    and runs off +/- 18 V max. It's a low cost opamp with good
    characteristics, IMHO. But look out for its input bias, it is around 10
    or 100 nA.

  4. Guest

    Sounds like a job for an auto-zeroing op amp. Linear Technology have
    been making them for many years, though National Semiconductor and
    Analog Devices also introduced useful products some years ago.

    +/-17V is a bit high for this sort of amplifier - the Linear Technology
    LTC1150 is the only one I know of that comes close, with a maximum
    supply voltage of +/-16V. It isn't cheap - at about $5 in small
    quantities, while the lower supply voltage parts come in under a
    dollar. and the input currents aren't all that low, at around a
    nanoamp, while the lower supply voltage parts claim tens of picoamps,
    but the input offset voltage is 0.5uV typical, +/-10uV worst case.
  5. Pooh Bear (Graham) wrote...
  6. Pooh Bear

    Pooh Bear Guest

    That's consumer product for you !

    You want to see an itemised BOM ?

  7. Pooh Bear wrote...
    If you wish, but it'd be better to discuss your application and
    circuit, to see why you need 0.1mV, and if there's a workaround
    that'll allow you to use cheaper opamps.
  8. There's no contest, use an OP-07D

    Best regards,
    Spehro Pefhany
  9. Spehro Pefhany wrote...
    TI's OP07DD, 60uV typ, 32.5 cents qty 2500, not bad, good call Spef!
  10. John  Larkin

    John Larkin Guest

    Is that term in the Dictionary of Electronics?

  11. Joerg

    Joerg Guest

    Hello Graham,

    If you can afford to do auto-zero as Bill suggested and your opamp
    budget really is 15 cents for a dual: Why not use ye olde LM324 and
    clamp to zero? Ok, you'd have to spring another 5c or so for a BSS123 to
    do the clamping but a quad LM324 can be had for around 10c.

    Regards, Joerg
  12. Joerg

    Joerg Guest

    Hello Winfield,
    Yes. I wish they were teaching this kind of thinking at universities (at
    least at mine they didn't). There is almost always a chance to do even
    the most challenging designs with jelly bean components. Even though I
    prefer M&Ms over jelly beans.

    Regards, Joerg
  13. Jim Thompson

    Jim Thompson Guest

    Bill? Did I miss an actual technical contribution by Sloman ?:)

    I love auto-zeroing.

    Once upon a time, I even built a micro-voltmeter, using LM324's, to
    measure voltage drop on PCB tracks, to locate shorts.

    Zero, measure, zero, measure....

    ...Jim Thompson
  14. Joerg

    Joerg Guest

    Hello Jim,
    Yes, although he was suggesting the use of an LTC auto-zero amp which
    are expensive.
    Me, too. But I like the old fashioned word "clamping" better. Even the
    vintage tube TV sets did that already to set the proper black level.
    Way to go. It'll even work with a crude transistor amp.

    Regards, Joerg
  15. Jim Thompson

    Jim Thompson Guest

    Ah, yes. DC restorers. I grew up in a radio/TV repair shop ;-)
    I used 'HC4016's to do the work. Actually left out a step above,
    should be...

    Zero, measure, hold, zero, measure, hold....

    With non-overlap between each, to keep caps from getting tweaked.

    ...Jim Thompson
  16. It actually works *better* with a crude transistor amplifier.

    Best regards,
    Spehro Pefhany
  17. John  Larkin

    John Larkin Guest

    Double-emitter choppers.

  18. Tis now


    After the first death, there is no other.
    (Dylan Thomas)
  19. Jim Thompson

    Jim Thompson Guest

    You're showing your age, John. And they weren't all that wonderful...
    CMOS is MUCH better.

    ...Jim Thompson
  20. John  Larkin

    John Larkin Guest

    Varicap parametric bridges.

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