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Consider the figure above how Rcomp was choosen. I know for simpler circuits like inverting amplifier and ideal integrator how Rcomp was calculated but following same procedure (that's using superposition principle for Ip and In and then convert to Ibias and Ioffset) here gives a time variant equation of single time constant circuit I don't know how one can cancel offset due to Bias current in such equation.

  • \$\begingroup\$ If you haven't already, watch this EEVBlog video where Dave explains about opamp's input bias currents: youtube.com/watch?v=TxBJb-Z0XFI&t=1s \$\endgroup\$ Commented Jun 21, 2019 at 21:21
  • \$\begingroup\$ DC bias not not time variant, but for AC, CMRR from external components demands matched differential source Impedances. \$\endgroup\$ Commented Jun 21, 2019 at 22:39

1 Answer 1


Bias current and offset are both DC phenomenon. The way to deal with a capacitor for DC analysis is to treat it as an open circuit (and in the unlikely event that you have any coils in an op-amp circuit, you treat them as short circuits, or as the coil's DC resistance only).

In that event, the given expression for \$R_{comp}\$ is correct.


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