Noninverting Summer

This is a Noninverting Summer an op-amp circuit which combines and amplifies the input signals with no phase reversal. For the general case, calculation of the resistances is somehow laborious. On the other hand, when the input resistances (R1, R2, and R3) are made equal, the design process is easier. The output voltage is then Vout = [(1 + Rf/Rg)/n](Vin1 + Vin2 + ...) where n is the number of input signals. In this circuit the overall gain is (1 + 15 kΩ / 3 kΩ) / 3 = (6) / 3 = 2 Feedback action amplifies the voltage at the noninverting terminal by 6 but the input signals are attenuated by 3 in the resistive combiner. Compared with the inverting summer, providing a weight for each input requires more work in this circuit. The virtual ground in the inverting summer aids in making the design process easier.