Summing Amplifier: Circuit Diagram and Its Applications.


The summing amplifier is an another type of amplifiers circuit combination that are use to combine voltage present two or more than two inputs voltages into a single voltage at output terminal. That operational amplifier add more than two input voltages are called summing amplifier or voltage adder.


An operational amplifier an amplifier which can perform various types of operations like invert input signal, summing, integrating and differentiating operations. In this tutorial we are going to study about summing amplifier. What are the circuit configurations and applications of summing amplifier?

What is summing amplifier?

In electronics circuit, most of the time required two or more than two voltage required to add these voltages into a single signal. One of the best examples to add two input voltages is summing amplifier. The best example of use of summing amplifier is the Music Recording and Broadcasting applications.

This is where the Summing Amplifier comes handy, as it combines several inputs into one common signal without noise or interference. For this reason, the Summing Amplifier is also called as Voltage Adder as its output is the addition of voltages present at its input terminal.

Summing Amplifier Circuit diagram


As we know that the inverting operational amplifier has single input voltage (Vin) at inverting input. If we add more input resistance, each resistance have same value to the original input resistance (Rin) we end up with another operational amplifier circuit called a Summing Amplifier, “summing inverter” or even a “voltage adder” circuit as shown above.

Summing Amplifier Equation

From the circuit diagram, the output voltage is proportional to the sum of inputs voltage V1, V2, V3, etc. than we can modify the original equation of inverting amplifier to take account of these new inputs thus:


If all input resistance is equal we can simplify the output voltage of:


We have an operational amplifier circuit that will amplify each individual voltage and produce an output voltage which is proportional to algebraic sum of the individual voltage of the three individual input voltages V1, V2 and V3. We can also add more voltage as per required.

The input voltages are effectively isolated from each other by the “virtual earth” node at the inverting input of the op-amp. A direct voltage addition can also be obtained when all the resistances are of equal value and Rƒ is equal to Rin.

Note when the summing point is connected to the inverting input of operational amplifiers the circuit output will produce negative sum of any number of input voltage. Likewise, when the summing point is connected to the non-inverting input of operational amplifier the circuit output will be positive sum of input voltage.

The scaling summing amplifier can be made, if individual input voltage is not equal than the summing equation would have to be modified to:


We can rearrange the above formula, the output voltage is



Audio Mixer

The summing amplifiers is very useful of when two or more signal needs to added or combine like in audio mixing applications. The sounds have a different musical instrument can be converted in a specific voltage level using transducer, and connected as a input to a summing amplifiers.
These different signals are combining in summing amplifier and sent to audio amplifier. Below the circuit is shown the a summing amplifiers as audio mixer


Digital to Analog Converter (DAC)

Digital to analog is use to converts the binary data to its analog voltage output. Now a day, industry use for control application is microcomputer. These microcomputers are digital data needs to convert to an analog voltage to drive the motors, relays, actuators, etc.
The circuit diagram of digital to analog convert using summing amplifier and weighted resistor network are shown below.


The circuit has four inputs QA, QB, QC and QD, the 5v represents the logic 1 and 0v shows the logical 0.

Level Shifter

The summing amplifiers is also use for level shifter. The two inputs summing amplifiers is act as a level shifter, which one is AC and another input is DC.

The AC Signal will be offset by the input DC Signal. One of the major applications of such level shifter is in Signal Generators for DC Offset Control.

people also ask

What is a summing?

The summing amplifiers is the type of operational amplifiers that are use to combine two or more than two signal into a single output signal.

What is summing inverting ?

The summing amplifiers is a type of operational amplifiers that combine the two or more the two inputs voltage over a single output voltage. If we provide the input at the inverting terminal of summing amplifiers the output will be phase shift of 180 degree of input signal.

What is the output of a summing ?

The output of summing is the combinations of two or more than two outputs. The phase shift of output will be depends upon the which terminal we applied input i.e. Inverting or non inverting terminal.

When would you use a summing?

The summing is use for various types of application like audio signal processing, digital to analog converter and level shifter.

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