Summing Amplifier : Circuit Diagram and Its Applications

The summing amplifier is a one kind of circuit and the configuration of this circuit is based upon the standard inverting op-amp. The name of this circuit suggests the summing amplifier, that is used to combine the voltage existing on many i/ps into a single o/p voltage. The inverting op-amp has a single i/p voltage applied to the i/p terminal. If we connect more resistors to the i/p terminal, each input value is equal to the input of the resistor. Input of the resistor will be end up with another op-amp circuit named as a summing amplifier.

Summing Amplifier

The term summing amplifier is also named as adder, which is used to add two signal voltages. The circuit of the voltage adder is so simple to construct and it enables to add many signals together. These kind of amplifiers is used in a wide range of electronic circuits. For instance, on a precise amplifier you have to add a small voltage to terminate the offset error of the operational amplifier. An audio mixer is another example to add the waveforms together from various channels before sending the mixed signal to a recorder. You can add or change the i/p or the gain without messing up with the i/ps of the gain. Just recollect that the circuit of the inverting summing amplifier changes the input signals.

Summing Amplifier
Summing Amplifier

Summing Amplifier Circuit

The summing amplifier circuit is shown below. In the circuit below Va, Vb and Vc are input signals. These input signals are given to the inverting terminal of the operational amplifier using input resistors like Ra, Rb and Rc. In the above manner, the number of input signals can be given to the inverting i/p. Here, Rf is feedback resistor and RL is the load resistor. Noninverting terminal of the operational amplifier is given to the ground terminal using Rm resistor. By applying KCL at node V2 we can get the following equation.

Summing Amplifier Circuit
Summing Amplifier Circuit

If + Ib= Ia + Ib + Ic

The input resistance of an ideal operational amplifier is near to infinity, so we can neglect V2 and Ib

If= la + lb + lc

The first equation can be written as

(V2-V0)/Rf = Va/Ra + Vb/Rb + Vc/ Rc

By neglecting V2 we can get the following equation

-V0/Rf = Va/Ra + Vb/Rb + Vc/ Rc

V0 = -Rf (Va/Ra + Vb/Rb + Vc/ Rc)

V0 = -(Rf/Ra)/Va + (Rf/Rb)Vb + (Rf/ Rc) Vc

If the values of resistors Ra, Rb and Rc are same then the above equation can be written as

Vo= ( Va + Vb + Vc) X –( Rf/R)

If the values of R and Rf are similar, then the equation becomes
V0 = -(Va + Vb + Vc)

Summing Amplifier Applications

Summing amplifier is a versatile device, used to combine the signals. These amplifiers add the signals directly or scale them to fit some prearranged combination rule.

  • These amplifiers are used in an audio mixer to add different signals with equal gains
  • There are various resistors are used at the input of the summing amplifier to give a weighted sum. This can be used to change a binary number to a voltage in an AC (digital to analog converter)
  • This amplifier is used to apply a DC offset voltage with an AC signal voltage. This process can be done in an LED modulation circuit to maintain the LED in its linear operating range.

Summing Amplifier based Audio Mixer

A summing amplifier is a one kind of circuit which is used to add when the two or more signals need to be combined like in audio mixing applications. The sounds from various musical devices can be changed to an exact voltage level by using transducers, and linked as i/p to a summing amplifier. These different signal sources will be added together by this amplifier, and the added signal is directed to an audio amplifier. The circuit diagram of audio mixer using a summing amplifier is shown below.

Summing Amplifier based Audio Mixer
Summing Amplifier based Audio Mixer

The working principle of the summing amplifier is like a multi-channel audio mixer for several audio channels. No interference will happen because each signal is given through a resistor, with its other end connected to GND terminal.

Summing Amplifier based DAC

A DAC converts the binary data which is applied to its input into an analogue voltage value. Digital to analog conversion is mainly used in Real-time industrial control applications like microcomputers. The o/p of the microcomputers is digital data that needs to be changed to an analogue voltage to drive the relays, actuators, motors, etc. The simplest DAC circuit includes a summing amplifier and also a weighted resistor n/w. The circuit diagram of the 4-bit digital to analog circuit using a summing amplifier is shown below.

Summing Amplifier based DAC
Summing Amplifier based DAC

The inputs of the summing amplifier circuit are QA, QB, QC and QD. These inputs represents 5V to logic 1 and Ov to logic 0

If the i/p resistors in each branch are selected, such that the i/p value of each resistor is twice the value of the resistor in earlier input branch, then a digital logical voltage at the i/p terminal will produce an o/p which is a weighted totality of the input voltages applied.

The exactness of such a DA (digital to analogue converter) circuit is imperfect by the accuracy of the values of the resistor employed and the differences in denoting the logic levels.

Thus, this is all about summing amplifier, summing amplifier circuit and its applications of op amp. We believe that you have got a better understanding about this concept. Furthermore, any queries regarding this concept or inverting summing amplifier and non inverting summing amplifier please give your suggestions by commenting in the comment section below. Here is a question for you, what is the main function of summing amplifier?

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