Summing Amplifier
Table of Contents
Summing Amplifier, Inverting, Non-Inverting
Summing Amplifier
A circuit whose output is the sum of several input signals can be designed using an op-amp. A summing amplifier, also known as a summer, is a circuit like this.
An inverting summer or a non-inverting summer may be discussed now.
Inverting Summing Amplifier
Figure 2 depicts an example of a typical summer with three input voltages V1, V2 and V3, three input resistors R1, R2, and R3, and a feedback resistor Rf.
The following analysis is carried out assuming that the op-amp is an ideal one, that is, AOL = ∞. Since the input bias current is assumed to be zero, there is no voltage drop across the resistor Rcomp and hence the non-inverting input terminal is at ground potential.
To find Rcomp, make all inputs V1 = V2 = V3 = 0. So the effective input resistance Ri = R1 || R2 || R3. Therefore, Rcomp = Ri || Rf = R1 || R2 || R3 || R,f.
Non-Inverting Summing Amplifier
The non-inverting summer of figure 3 produces a non-inverted sum. Let Va represent the voltage at the (-) input terminal.
which is a non-inverting weighted sum of inputs.
Let R1 = R2 = R3 = R = Rf/2, then Vo = V1+V2+V3