Current-to-voltage converter op-amp circuit with virtual ground [edited]

I understand that one of the input to the opamp is current , but what confuses me is that the other input is some voltage. I am trying to find the Voltage output, but the virtual earth theorem confuses me, because there are 2 different inputs. Could anyone help me to find the Vout of the circuit, please?

by muffintop94
June 04, 2020

1 Answer

Answer by mrobbins

I think the easiest way to think about this circuit is to remember two principles:

  1. No current flows into the +/- input terminals of an (ideal) op-amp
  2. The op-amp changes its output so as to make the voltage at the +/- input terminals equal.

Because of #1, the current through R1 is equal to the current through I1. And because of #2, the op-amp will adjust its output so that the inverting input equals the virtual ground.

I've copied and pasted your circuit here, and added node labels on the inverting and non-inverting inputs, and also set it up for DC Sweep simulation:

If we let $I = \text{I(I1)} = \text{I(R1)}$, then from Ohm's Law we have:

$$V_\text{out} - V_\text{inv} = I \cdot R_1$$

and from the ideal op-amp:

$$V_\text{inv} = V_\text{virtual_ground}$$

so

$$V_\text{out} = V_\text{virtual_ground} + I \cdot R_1$$

+2 votes
by mrobbins
June 04, 2020

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