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logaritmic R-?R ladder?

Discussion in 'Electronic Design' started by Tenho Hätönen, Apr 21, 2004.

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  1. The R-2R ladder is the well known network used in (linear)DA converters, but
    is it possible to construct such a R-?R ladder that would give a logaritmic
    Digital to Analog conversion?

    Tenho Hatonen
  2. Jim Thompson

    Jim Thompson Guest

    I've done it with a custom designed (by me) potentiometric DAC, to get
    a gain control in dB's.

    An R-2R ladder is an ADDITIVE process, so, off-hand, I don't think it
    can be made to be logarithmic.

    ...Jim Thompson
  3. Tim Wescott

    Tim Wescott Guest

    There are (or were) specialty audio chips that would provide digitally
    controlled attenuation -- with a DC input one of these could be
    considered a "logarithmic DAC". A google search with those keywords
    might be useful.

    Or you could just use a really high bit count DAC and feed it
    logarithmic data.
  4. I read in that Tenho Hätönen
    Yes. IIRC, the range to be covered affects the resistance ratios in a
    way that, in practice, prevents a universal solution. But for a given
    range, it's just arithmetic.
  5. Joerg

    Joerg Guest

  6. Tim Wescott

    Tim Wescott Guest

    Every time I think that some part is a weird niche, corner-case kind of
    part that only crazies would buy (sorry, OP), Analog Devices has it.
    Worse, I never learn to just look there first.
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