Non-Inverting Summing Amplifier

Summing amplifier can be constructed using a non-inverting configuration. The summing amplifier below shows V1 and V2 are connected to the non-inverting input (V+) of the op-amp. We can apply superposition theory to calculate the V+, then use standard non-inverting feedback gain equation to evaluate the output voltage, VOUT.

Example:
The circuit example below shows V1 connects to a 2 kΩ resistor and V2 connects to a 3 kΩ resistor, which connects to the V+ of the op-amp. The 9 kΩ feedback and the 1 kΩ resistors are arranged in standard inverting configurations.

Answer:
Apply superposition theory, first let V1 = 0 (ground), we then get V+ = (2/5)V2, based on voltage divider rule.
VO1 = (1 + 9 kΩ/1 kΩ)V+ = 4(V2)
We then let V2 = 0 (ground), we get V+ = (3/5)V1
VO2 = (1 + 9 kΩ/1 kΩ)V+ = 6(V1)

Hence, V_OUT = VO1 + VO2 = 6(V1) + 4(V2)

For V1 = 3 V and V2 = -4 V
We get V_OUT = (6 X 3 V) - (4 X 4 V) = 2 V