Current-to-Voltage Converter

Convert an input current to an output voltage with a feedback resistor and a virtual-ground input.

I1 injects 100 µA into the inverting input. RF = 10 kΩ carries almost all of that current to the amplifier output. The noninverting input is grounded, so feedback keeps the summing node near zero.

$$V_{\mathrm{out}}\approx-I_{\mathrm{in}}R_F=-1\,\mathrm{V}$$ $$V_{\mathrm{sum}}\approx0\,\mathrm{V}$$

Summing is green, Vout red and input current through RF blue. A virtual ground is a controlled node voltage, not an actual ground wire. Sensor capacitance, amplifier input capacitance and bandwidth can require a feedback capacitor in a physical transimpedance amplifier.

Read the results. The saved operating-point table shows the probe values. The first voltage probe is green and the second red. The first current probe is blue; a second current probe is purple.

Model limits. The three-terminal op-amp model has implicit ±12 V output limits, 200,000 low-frequency gain and 10 MHz gain-bandwidth product. Supply pins are intentionally absent in this functional model. In Schmitt-trigger and relaxation/integrator oscillator examples, the switching amplifier uses a 100 kHz gain-bandwidth setting to resolve transitions cleanly at the saved time step. It omits detailed slew-rate, input common-mode, output-current and thermal limits.

Try it. Set I1 DC current to 200 µA; the output changes from about −1 V to −2 V. Restore the original values after comparing the results.