Inverting Summing Amplifier using Operational Amplifier

From the different modes of operational amplifier series, today will see how this inverting summing amplifier works, as many tutorials, videos, books are out there to know about this concept. Very few people provide a satisfactory description about this concept using operational amplifier.

inverting summing amplifier using op amp


It may also be termed as widely used operational amplifier circuit. This above circuit shows two input summing amplifier circuit, its output voltage is proportional to the reverse polarity of the summing of input voltages, why is it proportional and not equal, because each voltages are multiplied by a common gain factor.

In simple terms, every input adds a voltage to its output multiplied by a separate constant gain multiplier.

The output of the inverting summing amplifier using operational amplifier is

Vout = -(Rf / R1 Vin1 + Rf / R2 Vin2)

And not only two inputs, more and more no of inputs can be added which will eventually add up to the output with its particular constant gain multiplier.

This can be more easily understood by the concept of infinite input impedance and virtual ground. The inverting input (-) of the operational amplifier is almost 0 volts and there is no current at the input. And non-inverting input (+) of the operational amplifier is connected to ground.

Well, now comes the main part, where do we use this circuit, as I said before, it is the widely used operational amplifier circuit. Let me state it one by one

  • Audio Mixer (Remember all DJ’s move up and down a button which will eventually mix the essentials needed for that song)
  • LED Modulation circuit to keep the operating range linear
  • Bipolar to uni-polar Converter and
  • Digital to Analog Converter and many others.
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Author: JAY

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