Op-Amp Differential Amplifier

Subtract two input voltages with a matched four-resistor network.

V1 is a 0.5 V peak, 100 Hz signal on a 1 V offset. V2 supplies a steady 1 V. R1 and R3 are 10 kΩ; RF and R4 are 20 kΩ. The matched ratios make the output depend primarily on the difference between V1 and V2.

$$V_{\mathrm{out}}\approx2(V_1-V_2)$$ $$V_{\mathrm{diff,pk}}=0.5\,\mathrm{V},\qquad V_{\mathrm{out,pk}}\approx1\,\mathrm{V}$$

Vdiff is the green differential measurement between the two source outputs, identified by its reference marker. Vout is red and Iload blue. Adding the same DC voltage to both inputs should leave the result nearly unchanged. Real common-mode rejection depends strongly on resistor matching and amplifier input limits.

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 offset and V2 DC voltage both to 2 V; the difference and output stay the same. Restore the original values after comparing the results.