Difference Between Real Ground and Virtual Ground

What is the Difference Between Real Ground and Virtual Ground?

Real ground refers to a physical connection between the metallic body of a device to the earth or ground through ECG and GEC or Earth continuity conductor. In contrast, virtual ground is a concept used in operational amplifiers (op-amps), where a node is assumed to have the same potential as the ground terminal, even though it is not physically connected to it.

Real Ground

A real ground (also called actual ground or earth ground) is a direct physical connection to the Earth or a common reference point in an electrical system. It is typically used for safety, providing a return path for fault currents and preventing electrical shocks. In circuit schematics, it is represented by the ground symbol (⏚ or ⏋).

For example, as required by the National Electrical Code (NEC) Article 250, all metallic and exposed parts must be connected to a ground rod via an Equipment Grounding Conductor (EGC) and a Grounding Electrode Conductor (GEC). Similarly, the neutral wire in an electrical panel is often bonded to the earth ground. In electrical wiring installations, a green or bare conductor is used for grounding.

In IEC and BS 7671 standards, the concept and purpose of earthing are the same as grounding in the NEC and CEC, but different terminology is used. For instance, the metallic parts of equipment are connected to an earth plate via an Earth Continuity Conductor (ECC). A green or green-with-yellow-stripe wire is used for Protective Earth (PE).

• Good to Know: Grounding systems are required in both AC and DC systems according to NEC Article 250, NEC 690.41, NEC 690.47, IEC 60364, BS 7430, and IEEE 80.

Virtual Ground

A virtual ground is a point in a circuit that is maintained at a fixed reference voltage (often 0V) but is not actually connected to the Earth. It is commonly used in op-amp circuits, where one input is held at a constant voltage to create a stable reference.

Unlike real ground, virtual ground does not absorb current directly but serves as a potential reference. For example, In an op-amp inverting amplifier, the non-inverting terminal is grounded, and the inverting terminal becomes a virtual ground due to negative feedback.

In negative feedback configurations, the virtual ground concept is only applicable when both terminals have the same voltage, and neither terminal acts as an actual ground.

For instance, in operational amplifiers (op-amps), the virtual ground concept applies only to negative feedback configurations. In other words, virtual ground is not applicable in positive feedback configurations, such as a Schmitt trigger. Instead, it is observed in negative feedback op-amp circuits like inverting and non-inverting amplifiers, voltage followers, etc.

As shown in the figure below of a non-inverting op-amp (with negative feedback), V₁ is connected to the real ground, which has zero potential, allowing current to flow to the negative terminal of the supply source. V₂ is connected to the virtual ground, which maintains zero potential. However, while current flows to other nodes, it does not pass to the negative terminal of the supply source.

In short, V₂ does not sink current because the current at node V₂ flows through the feedback resistor (R_f) and V_OUT due to the high resistance of “R” in the op-amp. Therefore, the V₂ node acts as a virtual ground, while V₁ is connected to the real ground.

Key Differences Between Real and Virtual Ground

The following comparison table shows the main differences between virtual and real ground.

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