Summing Amplifier

Add a sinusoidal signal and a DC offset at an inverting summing node.

V1 supplies a ±1 V sine wave at 100 Hz. V2 supplies +0.5 V. Each source feeds the inverting summing node through 10 kΩ, and RF is also 10 kΩ. The grounded noninverting input establishes a virtual-ground summing node.

$$V_{\mathrm{out}}=-R_F\left(\frac{V_1}{R_1}+\frac{V_2}{R_2}\right)$$ $$V_{\mathrm{out}}\approx-V_1-0.5\,\mathrm{V}$$

The red output spans approximately −1.5 V to +0.5 V. It is inverted and shifted downward relative to the green sine-wave input. Different resistor ratios give different weights to each source.

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 V2 DC voltage to 1 V; the output shifts downward by another 0.5 V. Restore the original values after comparing the results.