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OPA2626: Impedance match for Input Bias current

user4090349
Intellectual 961 points
Part Number: OPA2626


Tool/software:

To minimize the input bias current impact on the output of OPA2626, I understand it is necessary to match the impedance.

For Invert Input Amplifier, I should add a R=RF//RG in the Non-invert Input to match the impedance.

And for Non-Invert Input Amplifier, is it necessary to put a R = RF//RG in the Non-Invert Input to match the impedance, especially when Input Bias Current is at uA level.

  • +1
    TI__Intellectual 2065 points

    Hi,

    Yes, you can put an R in series with the non-inverting input to reduce the effect of input bias current. The reason is the same regardless of the input given to inverting or non-inverting terminal. 

    In short, when we choose R = RF || RG, the error voltage at output due to bias current comes out to be RF * Ios, (Ios = Ib1 - Ib2, difference between bias currents of inv and non-inv terminal of OpAmp). Typically Ios or input offset current of OpAmp is very low, so the DC error voltage due to bias current also reduces. Thus adding a series R helps to reduce bias current effects of OpAmp.

    Thanks 

    Aditya Gosavi

  • 0 in reply to Aditya Gosavi
    Intellectual 961 points

    Thanks, it is very clear.