# Total voltage error at the output of the Op-Amp

I have this circuit (shown below), I need to calculate the total error voltage at the output of the Op-Amp due to R3 and Vos.

U1 is the LM741, which has Vos = 5mV and ib = 80nA.

Till now I’ve calculated the error voltage contribution for Vos as following;

Vo = Vos * (1 + Rf/R1)

Vo = 5m * (1 + 47k/2k)

Vo = 122.5mV

How can I calculate the error voltage contribution for R3?

Thanks !

• What is the impedance of Vi ? The error contribution of R3 depends on this May 25, 2021 at 10:00
• @tobalt, I can assume that Vi is a high impedance source May 25, 2021 at 10:14
• so if Vi has a source impedance that is much larger than R3, then all of the input bias current of the + input flows where ? (However, in this case, the signal being fed via Vi would be also shunted to GND and the circuit makes no sense) May 25, 2021 at 10:17
• @tobalt, Thanks. What if Vi has a low impedance? May 25, 2021 at 10:23
• The same rationale. Consider where the input bias current would flow and what the associated voltage drop will be that is visible at IN+ May 25, 2021 at 10:26