A difference amplifier / difference op amp amplifies the difference of two input signals. It functions as a subtractor. It has two inputs and one output, thus amplifies the difference between the voltages at the two inputs. The difference amplifier is useful for handling floating signal sources. The following schematic shows the Difference Op Amp Circuit Diagram. There are two resistors Rf and Rf ‘ as well as two Ri and Ri ‘ resistors.
For correct circuit operation, the two ratios p = Rf/Ri and q = Rf ‘/Ri ‘ must be precisely equal, then the Voutput will be calculated as:
vo = [q(p+1)/(q+1)]v2 – pv
If Ri = Ri ‘ and Rf = Rf ‘, the Voutput is:
vo = (v2 – v1) Rf/Ri