Editing Touchpad (section)

== Theory of operation ==
There are two principal means by which touchpads work: the matrix approach and the capacitive shunt method.{{citation needed|date=March 2011}} In the matrix approach, a series of [[Electrical conductor|conductors]] are arranged in an array of parallel lines in two layers, separated by an [[Insulator (electrical)|insulator]] and crossing each other at [[right angle]]s to form a grid. A high frequency signal is applied sequentially between pairs in this two-dimensional grid array. The current that passes between the nodes is proportional to the [[capacitance]]. When a [[virtual ground]], such as a finger, is placed over one of the intersections between the conductive layer some of the electrical field is [[Shunt (electrical)|shunted]] to this ground point, resulting in a change in the apparent capacitance at that location. This method received {{US patent|5305017}} awarded to George Gerpheide in April 1994.

The capacitive shunt method, described in an application note by manufacturer [[Analog Devices]],<ref name="capacitiveshunt">{{cite web |url=http://www.analog.com/media/en/technical-documentation/data-sheets/AD7142.pdf |title=Analog Devices' Capacitive Shunt Method| publisher= analog.com}}</ref> senses the change in [[capacitance]] between a transmitter and receiver that are on opposite sides of the sensor. The transmitter creates an electric field which oscillates at 200–300&nbsp;kHz. If a ground point, such as the finger, is placed between the transmitter and receiver, some of the field lines are shunted away, decreasing the apparent capacitance.

[[Optical trackpad|Trackpads]] such as those found in some Blackberry smartphones work optically, like an optical [[computer mouse]].