Op-Amp Feedback

Connect the output back to the inverting input and observe how negative feedback makes the output track the input.

The output is wired directly to the inverting input. V1 is a ±1 V, 100 Hz sine wave. If the output rises above the input, the resulting negative differential error drives it back down; the opposite happens if it falls below the input.

$$V_{\mathrm{out}}=A_{\mathrm{OL}}(V_{\mathrm{in}}-V_{\mathrm{out}})$$ $$\frac{V_{\mathrm{out}}}{V_{\mathrm{in}}}=\frac{A_{\mathrm{OL}}}{1+A_{\mathrm{OL}}}\approx1$$

The input and output traces nearly overlap. Their small difference is the error needed to produce the output with finite gain. RL = 10 kΩ draws roughly ±100 µA. Negative feedback works while the amplifier remains within its output range and bandwidth.

Read the results. The saved transient chart uses separate voltage and current panels; the table provides numerical samples. 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 V1 peak voltage to 2 V; negative feedback preserves unity gain. Restore the original values after comparing the results.