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current output vs voltage output

Discussion in 'Electronic Basics' started by axr0284, Feb 21, 2007.

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  1. axr0284

    axr0284 Guest

    Hi,
    I would like to know why some DACs have current output instead of
    voltage output. Is there any advantage with one or the other. Thanks.
    Amish
     
  2. John  Larkin

    John Larkin Guest

    The usual situation is that

    1. The dac uses an inverted ladder architecture, where each bit switch
    steers current into one node or into another. So the output is
    inherently differential currents. Some architectures, like resistor
    strings and delta-sigma, are inherently voltage generators, but are
    usually slow.

    2. The dac technology (say, cmos switches and thinfilm resistors)
    isn't suitable for growing good opamps on the same chip. So they bring
    out the differential currents so good, fast external bipolar opamps
    can do the current-to-voltage conversion.

    Current output DACs cn be very fast, gigasamples per second.

    John
     
  3. axr0284

    axr0284 Guest

    2. The dac technology (say, cmos switches and thinfilm resistors)

    Thanks for your answer. I was wonmdering if you could explain the
    above in more detail or maybe steer me towards a website that has more
    information on this. Thanks,
    Amish
     
  4. Rich Grise

    Rich Grise Guest

    Sure!
    http://www.google.com/search?q=How+does+a+DAC+work?
    :)

    Cheers!
    RIch
     
  5. axr0284

    axr0284 Guest

    I was asking more info on the following particular subject:
    The dac technology (say, cmos switches and thinfilm resistors) isn't
    suitable for growing good opamps on the same chip.
    Amish
     
  6. John Larkin

    John Larkin Guest

    I'm not an IC designer, so I can't say a lot more. But bipolar
    processing makes fast, precise opamps, and CMOS makes good switches.

    There are some mixed-process dacs with cmos switches and internal
    opamps, but they tend to be lower, specifically slower, performance
    parts.

    Are there any ic design newsgroups?


    John
     
  7. axr0284

    axr0284 Guest

    I'll do more research. Thanks for your time.
    Amish
     
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