**Summing Amplifier** is an electronic circuit that produces output as a weighted sum of the applied inputs. It is also known as **Op-amp adder**. Basically it performs mathematical operation of addition. In this article, we will see the summing amplifier circuit, its working and its applications.

**Contents**show

## Summing Amplifier Circuit

The summing amplifier circuit is shown in figure 1. The input V_{1 }, V_{2}, and V_{3} are applied. V_{o} is the output voltage. The non-inverting terminal of the op-amp is connected to the ground. This means that the voltage of the non-inverting terminal is zero volts.

### Analysis

The analysis of the summing amplifier circuit is shown in figure 2. Since the op-amp is ideal and negative feedback is present, the voltage of the inverting terminal (V_{−}) is equal to the voltage of the non-inverting terminal (V_{+} = 0V), according to the **virtual short concept**.

V_{− }= V_{+} = 0V

The currents entering both terminals of the op-amp are zero since the op-amp is ideal.

The currents I_{1}, I_{2} and I_{3} flowing through resistances R_{1}, R_{2} and R_{3} respectively.

(1)

(2)

(3)

Apply KCL at node **Q**

(4)

Apply KCL at node **P**

(5)

(6)

From equations (4), (5) and (6), we have

putting values of I_{1}, I_{2} and I_{3} from equations (1), (2) and (3), we have

Therefore,

If

Then, we have