In this lecture, we will learn about the Virtual Short and Virtual Ground Concepts in op-amp in detail. So we will discuss virtual short in op amp and virtual ground in op amp in detail.
Virtual Short and Virtual Ground Concept
While analyzing the different circuits that include Op-amps, we need to use some important concepts for the betterment and easiness of the analysis of the circuit.
The concepts that we use for the analysis of op-amp are
- Virtual Short in Op Amp
- Virtual Ground in Op Amp
We are now discussing each concept in detail.
Also Read: what is Op-amp? Block diagram of op-amp
Virtual Short in Op Amp
According to the concept of virtual short in op-amp, the potential difference between the two input terminals of an op-amp is almost zero.
In other words, both the input terminals are approximately at the same potential.
The concept of Virtual short in Op-amp can be explained as follows:
The input impedance (Ri) of an op-amp is ideally infinite. Hence the current ‘I’ flowing from one input terminal to the other will be zero as shown in the below figure. Thus the voltage drop across Ri will be zero and both the input terminals will be at the same potential. In other words, they are virtually shorted to each other.
Another way of explaining this concept is as follows:
The output voltage of an op-amp is given by,
Vo = AV . Vd
Where, AV = Open loop gain and Vd = Differential input voltage
\therefore \mathbf{V_d=\frac{V_o}{A_V}}
But AV = ∞ for an ideal op-amp and AV = 2 x 105 for IC 741
∴ For ideal op-amp, Vd = 0. Thus the potential difference between the input terminals is zero.
When we short-circuit two points, they will have the same potential. Due to this reason, the two op-amp terminals which are almost equipotential are said to be virtually (not actually) short-circuited.
Also Read: What is CMRR? | Common Mode Rejection Ratio
Virtual Ground in Op Amp
If the non-inverting (+) terminal of the op-amp is connected to the ground as shown in the below figure, then due to the “virtual short” existing between the two input terminals, the inverting (-) terminal will also be at ground potential.
Hence it is said to be on virtual ground.
Similarly, if the inverting (-) terminal is connected to the ground, then the non-inverting (+) terminal will be at “virtual ground” potential.
The concept of virtual ground has been used extensively for amplifier analysis.
FAQs
What is virtual ground in opamp?
A virtual ground is a node of a circuit that is at a steady reference potential, without being directly connected to the reference potential.
What is meant by a virtual short in op-amp?
A virtual short-circuit (or simply virtual short) refers to a condition of a differential input amplifier such as an op-amp in which its noninverting and inverting inputs have almost the same voltage.
What is the principle of virtual short?
Virtual short means that under ideal conditions, the potentials of the two input terminals are equal.
Where is virtual ground used?
Virtual ground is a concept that is used in various applications, such as power electronics, microprocessors, and analog circuits.
