I'm trying to create an op-amp circuit that attenuates a 5 V input signal down to a 1 VRMS Vout signal (1.414 V Vout).

I need to shift the output signal by 2.5 V so that it can be fed into a unipolar ADC.

Below is my current inverting op-amp circuit in Multisim:

enter image description here

As can be seen above, the Vout signal amplitude is spot on: (4.6338 - 1.7895) / 2 = 1.422 V (roughly 1.414 V).

The problem is that the blue Vout signal appears to have shifted much further than expected. The midpoint should be on the purple 2.5 V line but it is actually at (4.6338 + 1.7895)/2 = 3.211V.

Does anyone have any idea what's causing the unexpected voltage shift, and how to fix it?

My circuit on Multisim

  • \$\begingroup\$ If you don't need to go down to DC, just use capacitative coupling with a suitable bias at the input to the ADC with a couple of resistors. No need for an opamp. \$\endgroup\$ Commented Mar 29, 2023 at 23:20

2 Answers 2


Your voltage divider applies 2.5V to the non-inverting input of the OpAmp. To see what's happening there, just set Vin=0 and draw the circuit again:


simulate this circuit – Schematic created using CircuitLab

It should be easy to see that this is a non-inverting OpAmp amplifier circuit with a gain of about 1.286. As a result, if you apply 2.5V DC to the non-inverting input, you get around 3.2V DC at the output. That's exactly what you're seeing in your simulation.

If you want 2.5V at the output, you have to apply 2.5V / 1.286 = 1.944V at the non-inverting input instead.


Mid-point of vout is (4.6338 + 1.7895)/2 = 3.211V which seems expected.

2.5V is the DC applied at the opamp +ve input. At output, it is 2.5*(1+1/3.5) which is what you got

  • \$\begingroup\$ Ah thanks. How did you arrive at the "2.5*(1+1/3.5)" equation? \$\endgroup\$
    – tpalmer345
    Commented Mar 29, 2023 at 17:59
  • \$\begingroup\$ @tpalmer345 That's the formula for calculating the gain of a non-inverting OpAmp stage. \$\endgroup\$ Commented Mar 29, 2023 at 18:06
  • \$\begingroup\$ That is basically the gain of the non-inverting amplifier (1+Rfb/Rin) multiplied with the DC voltage on the +ve terminal which is 2.5V \$\endgroup\$
    – sai
    Commented Mar 29, 2023 at 18:08
  • \$\begingroup\$ A brilliant thank you so much guys, really appreciate it! \$\endgroup\$
    – tpalmer345
    Commented Mar 29, 2023 at 18:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.