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What is an adc with pseudo-differential inputs?

Discussion in 'Electronic Basics' started by [email protected], Jul 5, 2007.

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  1. Guest

    Hi. I've done some reading (eg Horowitz & Hill and other books), but I
    can't find an explanation to what pseudo-differential inputs is. Could
    someone explain or direct me to an application note?

    Thanks

    Juan Herrera
     
  2. Chris

    Chris Guest

    Hi, Juan. Pseudo-differential inputs means the ADC actually has two
    inputs. The ADC measures both inputs, then calculates and gives you
    the difference between the two.

    You have to be aware that pseudo-differential input range doesn't mean
    the same thing as input range. You can have single supply +5V ADCs
    which advertise an input range of +5V to -5V. This merely means the
    difference between the two inputs -- you're still limited to a 0 to
    +5V amplitude on either input.

    Good luck
    Chris
     
  3. Bob Masta

    Bob Masta Guest

    Maxim has a discussion of differential and pseudo-differential inputs
    at:
    http://www.maxim-ic.com/appnotes.cfm/an_pk/1108

    Note that the advantage of true differential inputs is that any
    common mode noise is removed automatically by the implicit
    subtraction of the + and - inputs. Pseudo-differential typically
    doesn't do that (or at least, not as well) since the + and - channels
    are independent and are typically not converted at the same time.
    So only low frequencies and DC are removed by this method...
    but that's still useful for devices that have DC common mode
    present, like strain gages, etc.

    Best regards,


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
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