Integrating op amp question

  1. Hello,
    I'm having problem understanding the output of the integrating op amp.

    [​IMG]
    https://www.dropbox.com/s/djpg0uhi465ot86/download2.png

    [​IMG]
    https://www.dropbox.com/s/p9bp9tlyykhjtvf/download.png
    (hope you can see that, I can't see it on my preview)

    The blue line is input, orange is output. So if it's supposed to integrate, surely output signal has a wrong sign, doesn't it? If the integral is the area under the square signal, there should be linear increase when the signal is positive and linear decrease when it's negative, yet it's the other way around, why? I'd thought it was because my voltage had been applied to the inverting input of the op-amp, but even when I flipped it, it stays the same...
     
    Last edited: Mar 5, 2013
  2. jcsd
  3. jim hardy

    jim hardy 4,607
    Science Advisor
    Gold Member
    2014 Award

    Remember you have an inverting amplifier there.
    The opamp will hold its inputs equal, and +input is at zero.
    Therefore whatever current is pushed into summing junction through R1 must get pulled back out through C1&R2,,,,
    ,,,so an input to output reversal of polarity is nessary.

    After the initial transient (power up i presume?) , output looks like it moves in right direction.

    http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf
     
    Last edited: Mar 5, 2013
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