Working with integrators

Discussion in 'General Electronics Chat' started by pwnt141, Apr 11, 2010.

  1. pwnt141

    Thread Starter New Member

    Apr 11, 2010
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    0
    when working with standard op amp circuits im fine with finding worst case offsets, but when working with integrators i get stuck.

    how exactly do you find worst case with the capacitor at work? the current across it always ruins my equations
    can someone provide an example (any numbers will do, or even just formulae ) on finding worst case with integrators?

    lets say, you were given the values of R, C, and all input bias current, offset current, and offset voltage figures.

    after grounding the input, and attaching imperfections, my equations (that work fine with standard amplifiers) usually end up extremely messy (due to the capacitor) and finding any worstcase numbers gets incredibly tedious and also look wrong. whats the correct procedure on this?

    ive considered removing the capacitor (as it IS dc after all) but then my answers get .. really small.
     
    Last edited: Apr 11, 2010
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    In the days of analog computers, opamp integrators were controlled by imposing initial conditions on the capacitor. That usually entailed closing a relay across the capacitor in the case of the initial condition being 0V across the capacitor. Some simulations using analog computers involved a non-zero DC voltage. Here again the relay came to the rescue. The relay would switch a specific voltage source across the capacitor. Another thing that we often did was to put a very large resistor in parallel with the capacitor to provide a DC current feedback path.

    hgmjr
     
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