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inverting op amp

Discussion in 'Electronic Basics' started by smokie, Apr 2, 2005.

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  1. smokie

    smokie Guest

    Ri = 1K Rf = 10K and a 910 ohm from the non-inverting input to
    ground.

    how would the output be afffected if i swapped the 910 ohm with a 10K
    resistor?
     
  2. Andrew Holme

    Andrew Holme Guest

    Depends on the input bias current - a (very) small current which flows out
    of op-amp inputs. For a JFET-input op-amp, with a bias current of 200pA, it
    would shift the ground reference level by (10e3-910) * 200e-12 = 1.8
    micro-volts ! I leave it for the student to calculate the effect of this on
    output voltage (of a x10 amplifier) ...
     
  3. Ban

    Ban Guest

    There would be a change in offset voltage by offset current x 9090.
    There would be also an increase in noise voltage by around 3-5dB, depending
    on the current- and voltage noise figures of the opamp.
    The lowest noise would be achieved with the +input grounded.
     
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