Capacitive touch sensor

• US 20050162408A1
• Filed: 01/27/2005
• Published: 07/28/2005
• Est. Priority Date: 01/27/2004
• Status: Active Grant

• Current Assignee: Elo Touch Solutions, Inc.
• Original Assignee: Elo Touchsystems Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Martchovsky, Detelin
• Granted Patent: US 7,307,626 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

A method for determining the location of a touch made to a capacitive touchscreen in which the touchscreen includes a plurality of electrodes distributed around a touch sensitive area of the touchscreen, and a control circuit connected to the plurality of electrodes. The control circuit includes circuitry for measuring capacitance on the sensor, and provides a control signal indicating coordinates of a touch position on the screen, and includes multiple input/output connections, and multiple sub-circuits, where one sub-circuit is associated with one electrode. The method includes using a first switching element of each sub-circuit, when closed, to connect an electrode to an energy storage element which is in turn connected to a reference or ground, and using a second switching element, when closed, to connect the energy storage element to a detector. The method includes charging an electrode to a set voltage level when the associated first and second switching elements are closed and opened, respectively, and measuring energy in the energy storage element with the detector when the first and second switching elements are opened and closed, respectively.

Claims

1. A method for determining the location of a touch made to a capacitive touchscreen sensor which sensor comprises

(1) a touchscreen comprising a touch-sensitive region comprising a resistive layer,

(2) a plurality of electrodes distributed around the touch sensitive region, and

(3) a control circuit for charging the resistive layer, sensing capacitance on the resistive layer, and providing a control signal indicating coordinates of touch position on the touchscreen, said circuit

(a) being connected to the plurality of electrodes, and

(b) comprising multiple input/output connections to the touchscreen and multiple sub-circuits, each sub-circuit (i) being associated with one electrode, and (ii) comprising first and second switching elements, an energy storage element, a detector for measuring charge, and an analog to digital converter for digitizing the output of the detector, arranged such that for each sub-circuit, the first switching element, when closed, connects an electrode to the energy storage element and the second switching element, when closed, connects the energy storage element to the detector,

said method comprising

(A) closing a first switching element of each sub-unit while a second switch element is open so as to connect an electrode to an energy storage element, thus charging the electrode to a set voltage level,

(B) opening the first switching element while closing the second switching element to connect the energy storage element to a detector, thus transferring energy from the detector to the energy storage element in an amount equal to that used to charge the electrode,

(C) repeating steps (A) and (B) until saturation of a detector in one sub-unit occurs, thus stopping the charging of the detectors in all sub-units,

(D) measuring accumulated energy in the detector of each sub-circuit, and

(E) using the measurement of accumulated energy to determine coordinates of a touch position on the touchscreen.

2. The method of claim 1 wherein the set voltage level is a virtual ground.

3. The method of claim 2 wherein the electrodes are charged to a specified potential relative to a reference.

4. The method of claim 3 wherein the specified potential is +2.5V.

5. The method of claim 1 wherein a gain control is automatically set by using a plurality of most significant bits of the analog to digital converter to determine saturation of the detector.

6. The method of claim 1 wherein in each sub-circuit the first switching element and the second switching element are electrically connected in series and to a capacitor which is connected to ground.