Page "Touchpad" Paragraph 18

There are two principal means by which touchpads work.

In the matrix approach, a series of conductors are arranged in an array of parallel lines in two layers, separated by an insulator and crossing each other at right angles 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 shunted to this ground point, resulting in a change in the apparent capacitance at that location.

This method received awarded to George Gerpheide in April 1994.