Nevertheless, if all the inputs have the same resistive values, then the maths involved will be a lot less. However, there is more maths involed in selecting the weighted gains for each individual input at the summing junction especially if there are more than two inputs each with a different weighting factor. Besides the most obvious fact that the op-amps output voltage V OUT is in phase with its input, and the output voltage is the weighted sum of all its inputs which themselves are determined by their resistance ratios, the biggest advantage of the non-inverting summing amplifier is that because there is no virtual earth condition across the input terminals, its input impedance is much higher than that of the standard inverting amplifier configuration.Īlso, the input summing part of the circuit is unaffected if the op-amps closed-loop voltage gain is changed. So what’s the advantage of the non-inverting configuration compared to the inverting summing amplifier configuration. Then the equation would have to be modified to: Likewise, when the summing point is connected to the non-inverting input of the op-amp, it will produce the positive sum of the input voltages.Ī Scaling Summing Amplifier can be made if the individual input resistors are “NOT” equal. Note that when the summing point is connected to the inverting input of the op-amp the circuit will produce the negative sum of any number of input voltages. A direct voltage addition can also be obtained when all the resistances are of equal value and Rƒ is equal to Rin. This is because the input signals are effectively isolated from each other by the “virtual earth” node at the inverting input of the op-amp. We can also add more inputs if required as each individual input “sees” their respective resistance, Rin as the only input impedance. We now have an operational amplifier circuit that will amplify each individual input voltage and produce an output voltage signal that is proportional to the algebraic “SUM” of the three individual input voltages V 1, V 2 and V 3.

4 1000 amplifier schematic