Op-amp summing amplifier and op-amp non inverting summing amplifier are analog circuits for analog summing of the input signals.
Op-amp summing amplifier is given in figure bellow.
By using superposition theorem, it can be obtained:
If R1=R2=R, then the output voltage from op-amp summing amplifier is
It means that output voltage is proportional to sum of input voltages V1 and V2, with negative sign (opposite polarity). There can be added an arbitrary number of inputs, i.e. summands. Good feature of op-amp summing amplifier is that there is direct current path provided from every input to the output. For that reasons input voltage sources don’t need to have current sink capability.
Op-amp non inverting summing amplifier is given in figure bellow.
Again, by using superposition theorem it can be obtained:
Additional condition for op-amp non inverting summing amplifier to operate as summing circuit is that R4=R3. In that case output voltage is
Good feature of op-amp non inverting summing amplifier is that output voltage is proportional with the sum of the input signals, and with the same sign. Bad feature is that there is no direct current path from the inputs to the output, so input voltage sources must have sinking current capability.