Adding Circuit

The output voltage UO of the adding circuit is the weighted sum of N input voltages UI1, UI2...UIN. Its basic function can be expressed by the mathematical expression Y=A1*1+A2*2...+AN*N, as shown in Figure 5.4-1.

It is the schematic diagram of the adding circuit. Figure 5.4-1A is the inverting input adding circuit. UI1, UI2, UI3 are the input signals to be added to the inverting input terminal of the op amp. As an adding circuit, the number of input terminals can be arbitrarily expanded according to the number of signals to be added. The ∑ point in the figure is a virtual ground point, IF=I1+I2+I3, and the output voltage

In order to ensure that the circuit has a balanced and symmetrical structure (to eliminate the influence of input bias current and its temperature drift), the resistor R should satisfy RP||R1=R1||R2||R3||R

The adding circuit composed of operational amplifiers is divided into inverting and non-inverting. Compared with the two, the inverting input adding circuit has no cross-interference problem between its inputs, no common-mode voltage interference, and is easy to adjust. Therefore, the operational amplifier is usually used in an inverted state as a summing (addition) circuit.