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Simple question about inverting and noninverting op amp amplifiers

  1. Oct 26, 2004 #1

    learningphysics

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    Hi. I've always seen inverting amplifiers with the input going to the negative terminal of the op amp, and noninverting amplifiers with the input going to the positive terminal. However I don't see any reason why the inverting amplifier couldn't be used exactly the same way with the input going to the positive terminal, and noninverting with the input going to the negative terminal (but I've never seen it like this). Am I wrong?

    Is there a reason the design is the way it is? Thanks.
     
  2. jcsd
  3. Oct 27, 2004 #2

    NoTime

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    I am not entirely sure what your question is.
    For the - input the phase of the output is 180 degrees from the input.
    For the + input the phase is the same.

    If you do not care about the phase then either the + or - terminal can be used.
    If you do not care about the phase then you do not care about inverting or noninverting.

    For a digital NOT gate phase of the output is 180 degrees from the input.
    This is the meaning of inverting.
     
  4. Oct 27, 2004 #3

    learningphysics

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    By inverting amplifiers, I was referring to this circuit:http://cnx.rice.edu/content/m0055/latest/
    not the inverting terminal. I was wondering if the circuit would work if you had the positive terminal at the top and negative at the bottom. Anyway I think I found the answer, it won't work. The loop gain BA must be >0 to ensure negative feedback. If the terminals are switched BA becomes <0 which means positive feedback and instability.
     
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