Input Bias Compensation Resistor Calculation for an Integrator

Question

I have been reading the following tech note from Analog Devices that discusses designing an op amp circuit to compensate for the input bias current: https://www.analog.com/media/en/training-seminars/tutorials/MT-038.pdf

The example they provide to calculate the input bias current is an inverting op amp.

I would like to understand how to better calculate the value of a compensation resistor in an integrator op amp design:

As I understand it, input bias currents are what can lead to op amp saturation when nothing is connected to the input of an integrator. Is this correct? Is an input bias compensation resistor necessary in an integrator?

Answer 1

According to EEEguide, if you provide a resistor with equal resistance to the input resistor, you will be able to compensate for the current bias:

http://www.eeeguide.com/integrators/

Answer 2

If you have a perfect current source connected to "Signal" then you would need an infinite value resistor for R15 to compensate, because that current source has infinite output impedance.

In general that resistor is not particularly useful on an integrator. Many times the offset current is not all that significant and is not necessarily even lower than the bias current.

You could replace R15 with a capacitor equal to C5 and you would get less drift for a while, until the bias currents cause the inputs to go outside their common mode range. You could short out both caps momentarily and start again.

Integrators (unless you degrade them by paralleling the cap with a resistor) will always saturate given enough time.