# Transimpedance amplifier with a non-ground reference

I'm studying for an exam and as a part of a question I am given a transimpedance amplifier and need to explain/show how the current gets converted to voltage.

That's fairly easy, however, the op-amp has a Vb connected to the non-inverting input, which makes my answer differ from the official one.

My logic says that the inverting input is virtually on Vb, and then when we add the voltage drop over R1, output is V1 = Vb - I * R1.

The official answer just says V1 = - I * R1.

Is my understanding flawed? Does the non-ground reference affect the output?

• Simplest answer is to specify that Vb is the reference point for measuring V1. Mar 28, 2016 at 21:11
• That is why the answers differ! Thanks! Due to a language barrier I didn't think that Vb was used as a reference to the answer as well. When I read the question again, it is oh-so clear :) Mar 28, 2016 at 21:16