Editing Ground plane (section)

== Printed circuit boards ==
[[Image:TerraTec G3 circuit board 2.jpg|thumb|The large light-green areas on this [[printed circuit board]] are the ground plane]]

A ''ground plane'' on a [[printed circuit board]] (PCB) is a large area or layer of copper foil connected to the circuit's [[ground (electricity)|ground]] point, usually one terminal of the [[power supply]].  It serves as the return path for [[electric current|current]] from many different components.

A ground plane is often made as large as possible, covering most of the area of the PCB which is not occupied by circuit traces. In multilayer PCBs, it is often a separate layer covering the entire board.  This serves to make circuit layout easier, allowing the designer to ground any component without having to run additional traces; component leads needing grounding are routed directly through a hole in the board to the ground plane on another layer.  The large area of copper also conducts the large return currents from many components without significant voltage drops, ensuring that the ground connection of all the components are at the same reference potential.

In digital and [[radio frequency]] PCBs, the major reason for using large ground planes is to reduce [[electrical noise]] and interference through [[ground loop (electricity)|ground loop]]s and to prevent [[crosstalk]] between adjacent circuit traces.  When digital circuits switch state, large current pulses flow from the active devices (transistors or integrated circuits) through the ground circuit.  If the power supply and ground traces have significant impedance, the voltage drop across them may create noise voltage pulses that disturb other parts of the circuit (ground bounce).  The large conducting area of the ground plane has much lower impedance than a circuit trace, so the current pulses cause less disturbance.

In addition, a ground plane under printed circuit traces can reduce crosstalk between adjacent traces. When two traces run parallel, an electrical signal in one can be coupled into the other through [[electromagnetic induction]] by magnetic field lines from one linking the other; this is called [[crosstalk]].  When a ground plane layer is present underneath, it forms a [[transmission line]] with the trace.  The oppositely-directed return currents flow through the ground plane directly beneath the trace.  This confines most of the electromagnetic fields to the area near the trace and consequently reduces crosstalk.

A [[power plane]] is often used in addition to a ground plane in a multilayer circuit board, to distribute DC power to the active devices.   The two facing areas of copper create a large parallel plate [[decoupling capacitor]] that prevents noise from being coupled from one circuit to another through the [[power supply]].

{{anchor|Split ground}}Ground planes are sometimes split and then connected by a thin trace.  This allows the separation of analog and digital sections of a board or the inputs and outputs of amplifiers.  The thin trace has low enough [[Electrical impedance|impedance]] to keep the two sides very close to the same potential while keeping the ground currents of one side from coupling into the other side, causing [[ground loop (electricity)|ground loop]].