Virtual Ground – OpampLigo George
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.
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
Using Infinite Input Impedance
We know that an ideal opamp will have infinite input impedance. For real opamps also the input impedance will be very high such that we can consider it as infinite for calculation purposes.
Due to this infinite input impedance, current flowing into the terminals will be zero. Thus, as per ohms low the voltage drop across the input impedance will be zero. Thus V2 = 0.
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.
Virtual Ground vs Real Ground
|Virtual Ground||Real 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 Zero||Voltage is Zero|
|Not able to sink infinite current||It is an infinite current sink|
|Not electrically connected to Ground||Electrically connected to Ground|
Above concept is valid only when negative feedback is applied to opamp like in inverting ampliers.