Summing amplifier calculator

Calculate a two-input inverting summer, including each weighted contribution and the total output.

Schematic

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Results

Ideal output voltage-2 V

V1 contribution	-1 V
V2 contribution	-1 V

Advanced results

V1 gain	-10 V/V
V2 gain	-5 V/V
Ideal rail headroom	13 V

How summing amplifier works

Two input resistors feed a shared inverting summing node. Each input contributes its voltage multiplied by the negative ratio of feedback resistance to its own resistance. The output is the sum of those contributions. Set one source to zero to inspect the other input alone.

V_{out}=-R_3\left(\frac{V_1}{R_1}+\frac{V_2}{R_2}\right)

Ideal DC equations assume negative feedback and operation within the supply rails. The guest uses a generic op-amp model; finite gain, input loading, output current and saturation can change the simulated result.

Change the form inputs or click a component value on the schematic. Choose Try in CircuitSim to simulate the configured circuit.

Do the math

Selected input values
V1	100 mV
R1	10 kΩ
V2	200 mV
R2	20 kΩ
R3	100 kΩ
V3	15 V
V4	-15 V

First contribution: $V_{o1}=-\frac{R_3}{R_1}V_1$
$-\frac{100\,\mathrm{k\Omega}}{10\,\mathrm{k\Omega}}\times 100\,\mathrm{mV}$
≈ -1 V
Second contribution: $V_{o2}=-\frac{R_3}{R_2}V_2$
$-\frac{100\,\mathrm{k\Omega}}{20\,\mathrm{k\Omega}}\times 200\,\mathrm{mV}$
≈ -1 V
Summed output: $V_{out}=V_{o1}+V_{o2}$
$-1\,\mathrm{V}+(-1\,\mathrm{V})$
≈ -2 V

Summing amplifier calculator

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Schematic

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How summing amplifier works

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