In
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
, 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 amplifier 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 circui ...
, 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 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 in ...
, 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 high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to c ...
or some other circuit element that has gain. Since an
operational amplifier
An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to c ...
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) ...
, the potential difference between its inputs tend 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 electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
is a differential quantity, which appears between two points. In order to deal only with a voltage (an
electrical potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
) 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 having steady voltage with respect 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 reciproca ...
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 multipl ...
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
Rail Splitter, from Abraham Lincoln to Virtual Ground
Application note on creating an artificial virtual ground as a reference voltage (Archived from original).
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