In
electronics
Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...
, a virtual ground (or virtual earth) is a node of a circuit that is maintained at a steady reference potential, without being connected directly to the reference potential. In some cases the reference potential is considered to be that of the surface of the earth, and the reference node is called "ground" or "earth" as a consequence.
The virtual ground concept aids circuit analysis in operational amplifiers and other circuits and provides useful practical circuit effects that would be difficult to achieve in other ways.
In
circuit theory
Circuit may refer to:
Science and technology
Electrical engineering
* Electrical circuit, a complete electrical network with a closed-loop giving a return path for current
** Analog circuit, uses continuous signal levels
** Balanced circu ...
, a
node
In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex).
Node may refer to:
In mathematics
* Vertex (graph theory), a vertex in a mathematical graph
*Vertex (geometry), a point where two or more curves, lines ...
may have any value of current or voltage but physical implementations of a virtual ground will have limitations in terms of current handling ability and a non-zero
impedance which may have practical side effects.
Construction
A
voltage divider
In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (''V''out) that is a fraction of its input voltage (''V''in). Voltage division is the result of distributing the i ...
, using two resistors, can be used to create a virtual ground node. If two voltage sources are connected in series with two resistors, it can be shown that the midpoint becomes a virtual ground if
:
An active virtual ground circuit is sometimes called a rail splitter. Such a circuit uses an
op-amp
An operational amplifier (often op amp or opamp) is a DC-coupled electronic voltage amplifier with a differential input, a (usually) single-ended output, and an extremely high gain. Its name comes from its original use of performing mathem ...
or some other circuit element that has gain. Since an
operational amplifier
An operational amplifier (often op amp or opamp) is a direct coupling, DC-coupled Electronic component, electronic voltage amplifier with a differential input, a (usually) Single-ended signaling, single-ended output, and an extremely high gain ( ...
has very high
open-loop gain The open-loop gain of an electronic amplifier is the gain obtained when no overall feedback is used in the circuit.
The open-loop gain of many electronic amplifiers is exceedingly high (by design) – an ''ideal'' operational amplifier (op-amp) h ...
, the potential difference between its inputs tends to zero when a feedback network is implemented.
This means that the output supplies the inverting input (via the feedback network) with enough voltage to reduce the potential difference between the inputs to microvolts. More precisely, it can be shown that the output voltage of the amplifier in the figure is approximately equal to
.
Thus, as far as the amplifier is working in its linear region (output not saturated, frequencies inside the range of the opamp), the voltage at the inverting input terminal remains constant with respect to the real ground, and independent from the loads to which the output may be connected.
This property is characterized a "virtual ground".
Applications
Voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
is a differential quantity, which appears between two points. In order to deal only with a voltage (an
electrical potential
Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work neede ...
) of a single point, the second point has to be connected to a reference point (
ground). Usually, the power supply terminals serve as steady grounds; when the internal points of compound power sources are accessible, they can also serve as real grounds.
If there are no accessible source internal points, external circuit points with steady voltage relative to the source terminals can serve as artificial ''virtual grounds''. Such a point has to have steady potential, which does not vary when a load is attached.
Designing Single Supply, Low-Power Systems
/ref>
See also
*Voltage-to-current converter
Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the recipro ...
and Current-to-voltage converter
In electronics, a transimpedance amplifier (TIA) is a current to voltage converter, almost exclusively implemented with one or more operational amplifiers. The TIA can be used to amplify the current output of Geiger–Müller tubes, photo multipli ...
show some typical virtual ground applications
* Miller theorem applications
References
External links
Create a Virtual Ground with the LT1118-2.5 Sink/Source Voltage Regulator
Application note on creating an artificial virtual ground as a reference voltage.
Creating a Virtual Power Supply Ground
shows the application of the virtual ground concept in an inverting amplifier (Archived)
{{DEFAULTSORT:Virtual Ground
Electrical circuits
Electricity concepts