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single ended and differential outputs

Discussion in 'Electronic Design' started by rick, Feb 21, 2004.

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  1. rick

    rick Guest

    I need to provide single ended and differential +/- 5 volt signals from a DAC.
    So, my connector will have three signals on it, Vout+, Gnd, and Vout-, where
    Vout+ will go from +5V to -5V and Vout- will be the inverse of Vout+. I am
    sorry for explaining that..I know you guys know what differential signals are, I
    just wanted to be clear and complete.

    So...I have seen a comercial product that I believe does this differential
    output using two DACs, but I was wondering if a cheaper solution would be to
    just use an inverting op amp with a gain of 1 that samples Vout+ and whose
    output is directed to Vout-. What would be the downside of doing things this
    way? Perhaps at some DAC bit precision, the resistors in the unity gain
    inverting amplifier would have to be extremely precise? Is there a way to do
    this design, say for a 12 bit DAC using only 1% resistors and get the same
    results as using two 12 bit DACs.


  2. The way you described is certainly possible. Note that the accuracy
    depends on the resistor ratio, not the absolute resistor accuracy. In
    other words you need a matched resistor pair. Either you buy a suitably
    matched pair or you include a possibility to trim the value, if the
    accuracy of the resistors is not sufficient.

    Whether your solution works is also dependent on other factors, such as
    bandwidth required, what kind of load to drive (i.e. long cable), etc.

    There are OpAmps with differential outputs which you can use in more
    demanding cases.
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