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Sample and hold and A/D

Discussion in 'Electronic Design' started by Mark, Sep 5, 2003.

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  1. Mark

    Mark Guest

    Do I need to use a sample-and-hold? I'm using a 12 bit
    successive-approximation A/D converter to read 0 - 10 volts from a
    pressure transducer. No large or "fast" changes are expected from the
    transduced output. I'm plan to sample the transduced output voltage at
    5 HZ.


  2. Mark

    Mark Guest

    I'm using an AD574A. I need to use this "Old technology" beacuse it is
    for a HI REL application. I need a QPL part and no CMOS because of
    radiation concerns. The 574 is an "old workhorse" available as a QPL
    part and is all bipolar. The conversion time is 35us. I plan to have a
    differential buffer amp ahead of the converter. This amp will have a
    simple RC low pass filter set at about 100Hz. This should slow things
    down alot. Unfortunally, I can't find an all bipolar (except for the
    hold cap) QPL A/D with the S&H built in. Also, fortunately, the
    application does not require high accuracy. The strain gage pressure
    transduced data sheet I'm looking at showns a 5.000 +/- 0.050 volts for
    a full scale output. That seem like a lot of "slop" to me. The system
    will be calibrated end-to-end using accurate pressure inputs and errors
    will be corrected in the software.

  3. If it was my job I'd get the pcb layout done exactly as per fig3
    of the AD574A data sheet, including the AD585 and an exact copy of
    AD's earthing layout. It could then be tried without a S/H, but at
    least there's an escape route already on the pcb if the conversion
    jitter is too large.
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