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Reach 0V with single-supply op-amps

Discussion in 'Electronic Design' started by Marco Trapanese, Aug 26, 2011.

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  1. Hello,

    I'd like to achieve a 0V output (say < 10 mV) from an op-amp. I'd prefer
    a single-supply design. As far as I know most rail-to-rail op-amps can
    swing about some hundreds mV above the negative rail.

    OPAx330 should do the trick using a local negative voltage applied
    through a resistor to the output of the op-amp.

    What do you suggest to generate such a negative, low-noise voltage?

    Marco
     
  2. Rich Webb

    Rich Webb Guest

    National's single-supply LM6132/6134 has a guaranteed maximum output low
    of 19 mV into a 100 K load, although that guaranteed max goes up as the
    output current (which you need to specify) increases, with a "typical"
    max low of 7 mV into 100K ohms. Might work?
     
  3. What is the load? If it's a resistor to 0V then many CMOS opamps will do
    it. If the opamp output has to sink current then you need to say how
    much.
    I posted a circuit here not too long ago that used an opto-isolator in a
    novel way to generate a negative current (not my idea, Bob Pease (RIP) I
    think.

    <http://ee.devereux.me.uk/opto-current-source-2.jpg>

    The boring way would be a switched capacitor converter and RC filter if
    needed.
     
  4. Joerg

    Joerg Guest

    This, doesn't get much cheaper:

    http://www.national.com/ds/LM/LMC7660.pdf
     
  5. Jamie

    Jamie Guest

    THe old LM324 would do 0 volts if I remember..

    Jamie..
     
  6. I notice Linear have just released an all-in-one version if you are
    feeling really lazy:

    <http://www.linear.com/product/LTC6360>
     
  7. Jamie

    Jamie Guest

    Are you a circus wannabe left behind? What a wanker!

    Goes to show just how much actual hands on you have with
    components. You're no better than the bible thumpers, just
    believe what the good book says, even though most of them
    create their own version of what you read. Sort of like you,
    read a data sheet and create your own version of it says and
    means.

    Jamie
     
  8. Il 29/08/2011 02:32, Bill Sloman ha scritto:

    Thus, it could be done only if it's recommended in the datasheet, like
    OPAx330 does.

    Marco
     
  9. Il 26/08/2011 15:27, John Devereux ha scritto:

    You're right. I forgot to mention.
    The op-amp output feeds the on-board ADC of xmega. The ADC acquires at 1
    kHz.


    Very interesting. Do you have any hint how to find the app-note where
    it's described in detail, if any?

    Marco
     
  10. Il 27/08/2011 13:59, John Devereux ha scritto:

    Great! :)

    Marco
     
  11. OK I don't know much about that ADC - most of them can source or sink a
    current that increases with sample rate, and 1kHz is not very high.
    I never saw it. James Arthur posted the original suggestion, the thread
    is:

    <http://groups.google.com/group/sci....-8&q=opamp+buffer+and+transistor+buffer&pli=1>

    (Sorry don't know how to post a concise link to the thread in google
    groups. If that link also exposes my amazon login and credit card
    details buy me something nice while you're there...)
     
  12. Il 29/08/2011 16:57, John Devereux ha scritto:

    Use tinyurl:

    http://tinyurl.com/3kcj3jn

    Marco
     
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