Summing Amplifier Calculator

A summing amplifier is an operational amplifier circuit that adds multiple input voltages together with individual gains determined by input and feedback resistor ratios. The output voltage is the inverted sum of all weighted input voltages.

The gain for each input channel is calculated as the negative ratio of feedback resistor to input resistor: Gain = -RF/Rin. The negative sign indicates signal inversion in the inverting summing amplifier configuration.

Different input resistor values create different gains for each channel, allowing you to weight the contributions of each input signal differently in the final sum. Smaller input resistors create higher gains and larger contributions to the output.

The output is negative because summing amplifiers typically use the inverting configuration of an op-amp. The virtual ground at the inverting input and feedback resistor arrangement naturally inverts the signal polarity while performing the summing operation.

Choose input resistor values based on desired gain ratios and input impedance requirements. The feedback resistor determines overall circuit gain. Keep resistor values in the kΩ range to minimize current consumption while avoiding noise issues from very high resistances.

Real op-amps have finite gain, input bias currents, and offset voltages that affect accuracy. The circuit also has bandwidth limitations and may require compensation for stability with certain resistor combinations or capacitive loads.

Yes, you can add as many inputs as needed by connecting additional input resistors to the inverting input of the op-amp. Each additional input follows the same gain calculation: -RF/Rin for that specific input channel.