Gate (electrical engineering)

In electrical engineering, a gate is a connection to a component. Reducing a component to its behavior at the connections facilitates calculations and simulations or makes them possible in the first place.

Goal in low frequency technology

If at the frequencies used the voltage ${\ displaystyle u _ {\ mathrm {AB}}}$

{\ displaystyle u _ {\ mathrm {AB}} = \ int _ {A} ^ {B} {\ vec {E}} \ cdot \ mathrm {d} {\ vec {s}}}

between two terminals A and B is practically independent of the chosen path, these two terminals of the component can be understood as a gate. This does not have to be real contacts . Parts of a circuit can also be picked out for an analytical consideration and connections that were separated on paper for this purpose can be combined in pairs to form gates.

A voltage in volts can be measured or calculated at a gate . In reality, this can be read off by applying a voltmeter to both contacts. Since the sign of the voltage depends on how the voltmeter is applied, the orientation in which the voltage is measured must be specified when describing the gate. This definition is shown in a circuit diagram by a counting arrow .

The gate condition

A current can flow through the connections of a gate . The decisive property of the gate is that the current through both connections must be opposite. This means that both currents must have the same amount and different sign at every moment. For example, if a current I flows into one connection (e.g. 3 amps ), then -I (i.e. −3 A) must flow into the other connection . The measurement of the current also depends on the direction in which an intended measuring device is used. This is why counting arrows are shown in circuit diagrams for electricity .

These properties place some theoretical and practical conditions on the component whose doors are to be examined and described. As a rule, there must not be any connections that are not part of a gate, otherwise it would not be possible to ensure that the current flowing into a gate is the same as the current flowing out . It may e.g. B. do not accumulate any load carriers.

A gate is thus completely described by two quantities, the current and the voltage.

Goal in high frequency and optical communications engineering

In high-frequency technology , it is often impossible to assign a clear voltage meaningfully. For example, this is impossible with waveguides . In optical communications technology , the components under consideration do not even have conductive contacts. During a transition from one component to another, it is not electrical voltages that are considered, but the corresponding electrical and magnetic fields. In high-frequency technology, there are also the location-dependent currents.

use

A two-port , called four-pole in older literature, describes components with four connections or with two ports. Most of the elementary components of electrical engineering can be fully described with two goals.

literature

Karl Küpfmüller, Wolfgang Mathis, Albrecht Reibiger: Theoretical Electrical Engineering - An Introduction . 18th edition. Springer, 2008, ISBN 978-3-540-78589-7 .