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10mv Resolution

Discussion in 'Electronic Design' started by tt, Mar 14, 2005.

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  1. tt

    tt Guest

    Hi, All

    My boss want a DDS signal generator having 10mv resolution output. Does that
    kind of stuff exist on the world? D/A Vref error, INL DNL error, amp op
    error and system noise would make 10mv not available. How could precise
    instrument achieve that kind of resolution?

  2. PeteS

    PeteS Guest

    Without wishing to seem pedantic, resolution and precision are not the
    same thing, although they can overlap.

    The resolution of a system may be millivolts, but it's overall error
    much larger, where the error is precision.

    Perhaps a better question for you is:

    Do you need 10mV of differential resolution (and what precision) or do
    you need 10mV of precision?

  3. John Larkin

    John Larkin Guest

    10 mv out of what?

  4. tt wrote...
    I've been using AD's nice 14-bit DDS chips, a pair of balanced
    10mA fs current-source outputs with 14-bit resolution, which is
    500mV fs, and 61uV or so lsb into 50 ohms.
  5. Adam Kumpf

    Adam Kumpf Guest

    Hi tt,

    10mV is not that difficult to achieve if you get it indirectly.

    Imagine that you a 50ohm output impedance is desired. (as with most signal
    generators) Now produce a 1Vpeak-to-peak output, pass it through a voltage
    divider (say.. 10k on top, and 10ohm to ground) and at that midpoint, you
    have a 1mV signal and the output impedance is parallel combination of the
    two resistances to AC ground. (10 // (10k + 50) if the original signal
    generator had 50 ohm output). Then put a 40 ohm in series with the center
    tap and, there you have it.. a 50ohm impedance signal generator with a 1mV
    signal output and a relatively easy to create 1V signal input.

    These kinds of attenuators are used all of the time when testing high
    gain circuits. I don't see any reason why it couldn't help you out here..
    unless you want to go so low that you are greatly affected by thermal noise.

    This does limit the upper range of your signal generator (you would need
    1000V for a 1V output), so perhaps voltages this low may require a special
    mode to be used. Depending on the frequency ranges you are looking at, a
    relay could switch between the modes fairly easily.

    I hope that helps a bit.

    Best Regards,
    Adam Kumpf
  6. Winfield Hill wrote...
    Right, 50 ohms ... These parts use 400MHz clocks.
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