A summing amplifier or adder is an analog amplifier circuit of an operational amplifier. As can be seen from the name, the level of several input signals is added and then the sum signal is amplified. The output voltage is proportional to the sum of all input voltages.
In terms of circuitry, a summing amplifier or adder is an operational amplifier at whose inverted input the levels of the individual signals are summed. In contrast to this, full adders or half adders are digital basic circuits of dual arithmetic with which binary states are added. A summing amplifier can weight and add several input signals differently via upstream resistors in the input circuits.
The resistor R(G) in the feedback loop forms a voltage divider with each input resistor, with which the input voltage is divided accordingly. The voltage dividers R(G)/R1 or R(G)/R2 represent the respective gain. These voltage dividers can be used to define different sum functions for the various input signals. The summed output voltage is calculated from the respective voltage divid ers multiplied by the corresponding input voltage. The number of inputs is arbitrary.
Summing amplifiers are used in audio mixing consoles where they mix two or more analog signals together. They are operational amplifiers whose output signal is formed from the sum of the input signals. If the operational amplifier has identical resistors, then the gain is identical and the output voltage is equal to the sum of the input voltages. By selecting the resistor values, the gain of the individual inputs can be changed.