Virtual Ground – Opamp

Virtual Ground – Opamp

What is Virtual Ground ?

As the name indicates it is virtual, not real ground. For some purposes we can consider it as equivalent to ground. In opamps the term virtual ground means that the voltage at that particular node is almost equal to ground voltage (0V). It is not physically connected to ground. This concept is very useful in analysis of opamp circuits and it will make a lot of calculations very simple.

Virtual Ground – Opamp

Lets see how the virtual ground concept is employed in inverting amplier.

Virtual Ground - Inverting Amplifier using Opamp

Virtual Ground – Inverting Amplifier using Opamp

We can explain this concept in two different ways using two different characteristics of an ideal opamp.

Using Infinite Voltage Gain

We already know that an ideal opamp will provide infinite voltage gain. For real opamps also the gain will be very high such that we can consider it as infinite for calculation purposes.


  • Gain = Vo/Vin

As gain is infinite, Vin = 0

  • Vin = V2 – V1

In the above circuit V1 is connected to ground, so V1 = 0. Thus V2 also will be at ground potential.

  • V2 = 0
Virtual Ground - Inverting Amplifier using Opamp

Virtual Ground – Inverting Amplifier using Opamp

Why we need Virtual Ground ?

Virtual Ground concept is very useful in analysis of an opamp when negative feedback is employed. It will simply a lot of calculations and derivations.

Equivalent Circuit - Inverting Amplifier - Virtual Ground - Opamp

Equivalent Circuit – Inverting Amplifier – Virtual Ground – Opamp

Virtual Ground vs Real Ground

Virtual GroundReal Ground
Virtual Ground is a concept that made for easy explantaion and calculation purposes.Real Ground is a terminal which is physically connected to ground or earth which acts as the reference point for the entire circuit.
Voltage is approximately ZeroVoltage is Zero
Not able to sink infinite currentIt is an infinite current sink
Not electrically connected to GroundElectrically connected to Ground

Note

Above concept is valid only when negative feedback is applied to opamp like in inverting ampliers.



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