Op-amp Summing Amplifier

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Op-amp summing amplifier and op-amp non inverting summing amplifier are analog circuits for analog summing of the input signals.

Simulate op-amp summing amplifier.
Simulate op-amp non inverting summing amplifier.

Op-amp summing amplifier is given in figure bellow.

op-amp-summing-amplifier

By using superposition theorem, it can be obtained:

op-amp-sum-eq01

If R1=R2=R, then the output voltage from op-amp summing amplifier is

op-amp-sum-eq02

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.

op-amp-summing-amplifier-non-inv

Again, by using superposition theorem it can be obtained:

op-amp-sum-eq03

i.e.

op-amp-sum-eq04

If

op-amp-sum-eq05

we obtain

op-amp-sum-eq06

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.

Simulate op-amp summing amplifier.
Simulate op-amp non inverting summing amplifier.

External links:

Op-amp Summing Amplifier on Electronics-tutorials
Op-amp non Inverting Summing Amplifier on Masteringelectronicsdesign

 

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