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OP, inverting or non-inverting?

Discussion in 'Electronic Design' started by Elektro, Feb 16, 2006.

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  1. Elektro

    Elektro Guest

    If I want to amplify a signal and signal phase doesn't matter. What
    alternative is the best to select, a inverting OP circuit or a non
    inverting?

    And why?
     
  2. Guest

    As usual, it depends. If you just want to get the most bandwidth out of
    your amplifier, opt for non-inverting - an inverting amplifer with a
    gain of -1 has a "noise gain"of 2, and thus half the bandwidth of a
    non-inverting amplifier with a gain of one.

    This advantage becomes negligible at high gains.

    If you are worried about distortion, opt for inverting - the amplifier
    input then stays at an almost constant voltage independent of the
    excursions of the input signal, thus pretty much eliminating any
    moduation of the base-width with changing collector-to-base voltage
    (Early effect). FET-input amplifiers are subject to a similar sort of
    problem.
     
  3. Phil Hobbs

    Phil Hobbs Guest


    Jim Williams gives "Williams' Law": Always invert, except when you can't.

    Keeping the inputs nearly still helps with all sorts of bias-related
    problems, such as common mode range limitations and startup problems.
    The gain of an op amp isn't exactly constant over its common mode range,
    so that noninverting amps tend to have more distortion.

    It's also quite common for an op amp to have an output voltage swing
    that's wider than the input common mode range--which means that stage 1
    is liable to wake up with its output outside stage 2's CMR, so that
    stage 2's input stage is turned off. This can lead to latching
    problems, especially if you have a circuit like a PLL, where there's
    feedback from stage 2 to stage 1. (That one bit me many moons ago when
    I first started using the late lamented MC34084 quad FET op amp.)

    Inverting amplifiers are more or less immune to these sorts of troubles.

    Cheers,

    Phil Hobbs
     
  4. Good advice for logic designers too.

    <snip>
     
  5. Pooh Bear

    Pooh Bear Guest

    Inverting configurations using an op-amp are invariably noisier than
    non-inverting.

    Graham
     
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