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    integrator

    whats the significance of positive feedback in op-amp based non-inverting integrators?

    please explain the functioning

    thank you

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    integrator

    I'm not aware of positive feedback in non-inverting integrators. You should show a schematic for reference.



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    Re: integrator




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    Re: integrator

    Quote Originally Posted by juglers
    whats the significance of positive feedback in op-amp based non-inverting integrators?

    please explain the functioning

    thank you
    You are referring to the so called "NIC integrator" that consists of an RC low pass which is connected to an NIC (negativ impedance converter) which has a negative input resistor. The NIC-block needs a positive feedback. This negativ resistor acts as a current source - thus you load the capacitor with a current source (instead a voltage source through a resistor).
    This yields an (ideal) noninverting integrator.



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    Re: integrator

    A Google search found this circuit (from the german text book "Aktive Filter und Oszillatoren")



    There's no overall positive feedback in the said circuit. In the general feedback amplifier scheme, the contributions of multiple parallel feedback pathes are added to form an effective feedback factor k. It can be expected negative for an integrator.

    Of course the NIC building block superimposes positive and negative feedback pathes.

    In any case, there are also non-inverting integrators without positive feedback pathes. So I prefer to see a schematic that clarifies the original question.

    P.S.: I found a (german) lecture paper also discussing the NIC integrator (see page 12/13) http://www.krucker.ch/Skripten-Uebun...ELA5-OpAmp.pdf

    LvW, do you know a link to an english paper presenting the topic?



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    Re: integrator

    Quote Originally Posted by FvM
    P.S.: I found a (german) lecture paper also discussing the NIC integrator (see page 12/13) http://www.krucker.ch/Skripten-Uebun...ELA5-OpAmp.pdf

    LvW, do you know a link to an english paper presenting the topic?

    Hi FvM,
    yes, there are a few. However, you will find some papers applying this scheme under the name "Deboo integrator" - named after its inventor DEBOO in 1967 !!
    (Electronic design, vol 15, June 1967, page 90.)
    In most cases , this circuit will be used for quadrature oscillators in conjunction with an inverting Miller integrator. See for example the attached pdf paper.
    LvW



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