1. Field of the Invention
This invention relates to touch sensors, and more particularly to capacitive touchscreens and to circuits for use and methods for use in capacitive touchscreens that can provide a control signal providing information about the location of a touch on the sensor.
2. Introduction to the Invention
Touchscreens are commonly used as interfaces for computers and other electronic devices, such as hand held personal digital assistants, kiosks, games, point-of-sale devices, etc.
A capacitive touchscreen sensor is one type of sensor for a touchscreen that operates by capacitive shunting of current through a dielectric layer to a user's finger and then through the user's body to ground. Other grounded elements, such as a grounded stylus, may also be used. This type of sensor typically includes a capacitive sensing circuit with multiple electrodes, each producing an electric field across a touch sensitive area of the sensor. The sensing circuit can be adjacent to a transparent protective sensor substrate, e.g., glass. A touch near an electrode affects the electric field and creates a signal that can be detected by the sensing circuit. A set of electrical connections is made between the sensing circuit and a controller that resolves the signals to determine the location of the touch on the sensor. The coordinates of the location may then be communicated to another processor such as a host computer for further processing.
In a typical capacitive sensor, a stack including multiple transparent layers is used, including a substrate layer, a resistive layer, e.g., indium tin oxide (ITO), on top of the substrate, and a layer acting as a shield on the bottom of the substrate. Silver frit traces are a commonly used element to couple the resistive layer to detection electronics.