Model weighted signal summing with resistor-based inversion. Compare channel contributions, gains, and net output quickly. Export clean results for reports, checks, records, and testing.
The calculator uses the ideal inverting summing amplifier relation:
Vout = -Rf × [(V1 / R1) + (V2 / R2) + ... + (Vn / Rn)]
Each channel gain is:
Gain(i) = -Rf / Rin(i)
Each output contribution is:
Contribution(i) = Vin(i) × Gain(i)
If all input resistors are equal, the circuit becomes a simple inverting voltage adder with equal weighting.
| Channel | Vin (V) | Rin (Ω) | Rf (Ω) | Contribution (V) |
|---|---|---|---|---|
| Input 1 | 1.0000 | 10000 | 10000 | -1.0000 |
| Input 2 | 2.0000 | 20000 | 10000 | -1.0000 |
| Input 3 | -0.5000 | 10000 | 10000 | 0.5000 |
| Ideal output | -1.5000 V | |||
An inverting voltage adder is a classic op-amp circuit. It combines several input signals at one summing node. Each source passes through its own resistor. The feedback resistor sets the overall scale. The calculator on this page helps you estimate the output voltage fast. It also shows channel gain, node current, and each weighted contribution. This makes design checks easier during analysis, troubleshooting, and lab preparation.
Input resistors define how strongly each source affects the output. A smaller input resistor gives that channel more weight. A larger resistor reduces its influence. The feedback resistor controls total amplification of the summed current. When all input resistors match, the circuit behaves like a simple inverting summer. When they differ, the circuit becomes a weighted adder. This is useful for sensor fusion, audio mixing, level shifting, and analog control systems.
The ideal output follows the summing amplifier equation. The result is negative because the amplifier is inverting. If the computed output exceeds the supply rails, a real device will saturate. The calculator compares the ideal result with your positive and negative rails. It then reports whether the design is inside limits. This helps you catch clipping before building the circuit. You can also export the result table for documentation or team review.
Real circuits are not perfectly ideal. Op-amp bandwidth, slew rate, input bias current, offset voltage, and output swing limits all matter. Resistor tolerance also changes the final sum. For precision work, use matched resistors and a suitable amplifier. Keep source impedance in mind. Confirm that the chosen op-amp can handle your required rail range and load. For fast signals, review stability and frequency response. Use this calculator as a strong first step, then verify with simulation and bench measurements.
This tool works well for homework checks, prototype planning, and engineering estimates. It is also useful when comparing weighted channels before choosing resistor values. By reviewing contributions, you can balance sources with trial and error during circuit refinement.
It sums several input voltages through separate resistors and produces one inverted output. The feedback resistor sets the overall scaling of that summed signal.
The circuit uses the inverting input of the op-amp. That topology introduces a sign reversal, so a positive weighted sum becomes a negative output.
Yes. Different input resistors create weighted summing. Smaller resistors increase a channel’s effect. Larger resistors reduce its effect on the final output.
A real op-amp cannot swing beyond its available supply limits. The output clips or saturates near the rails, so the ideal equation stops matching hardware behavior.
It is accurate for the ideal equation. Real accuracy depends on resistor tolerance, op-amp output swing, bandwidth, offset, bias current, and load conditions.
Equal resistors are useful when every input should have the same weight. That makes the circuit a straightforward inverting summer for clean signal addition.
Yes. Negative inputs are valid. Their contribution is still weighted by the resistor ratio, and the final sign depends on the inverting summing equation.
Exporting helps with reports, lab notes, design reviews, and quick sharing. It also gives you a simple record of the chosen resistors and computed output.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.