Operational Amplifier Fundamentals Unit 5 – The Inverting Summer
Input impedance for each circuit input voltage equals the value of the respective input resistor.
The impedance is based upon a virtual ground at the circuit summing junction.
If the input and feedback resistors equal each other, the circuit performs a summing (algebraic
addition) operation.
VO = -(V1 + V2 + V3)
In a scaling, or weighted configuration, if R1, R2, and RF equal each other but not R3, V3 is
scaled (or weighted) differently than V1 and V2. Scaling can be similarly applied to R1 or R2.