Touchpad having increased noise rejection, decreased moisture sensitivity, and improved tracking

• US 6,730,863 B1
• Filed: 06/22/2000
• Issued: 05/04/2004
• Est. Priority Date: 06/22/1999
• Status: Active Grant

• Current Assignee: Cirque Corporation
• Original Assignee: Cirque Corporation
• Inventors: Taylor, Brian, Lee, Daniel, Gerpheide, George
• Primary Examiner(s): Awad, Amr Ahmed
• Application Number:
  US09/603,417
• Time in Patent Office: 1,412 Days
• Field of Search: 345/173-179, 178/18.01, 178/18.02, 178/18.03, 178/18.05, 178/18.06, 178/18.07, 178/18.08, 178/19.01, 178/19.03, 178/20.01, 178/20.02, 178/20.03, 178/20.04
• US Class Current: 178/18.02
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

An improved touchpad and measurement circuitry for enabling input to a computer or other electronic device. The system includes an X electrode, a Y electrode, a common sensing electrode, and a “water” electrode, wherein these four separate electrodes can be implemented in various physical configurations to obtain the desired effects, wherein moisture and water droplets can be identified and compensated for so as not to interfere with the input of data, wherein noise rejection is achieved by using a time aperture filtering method, wherein an improved scanning technique focuses scanning around an identified input object, wherein an adaptive motion filter responds to the speed and acceleration of an object being tracked, and wherein the measurement circuitry has an increased dynamic range enabling the touchpad to operate with greater tolerances to manufacturing variances.

Claims

1. A method for decreasing noise in a capacitance sensitive touchpad to thereby improve accuracy of operation, said method comprising the steps of:

(1) disposing a time aperture filter between at least one sense electrode and at least one measurement circuit, wherein the time aperture filter opens prior to an electrode transition of at least one sense electrode, and remains open for a selectable time aperture window period, and wherein a measurement time at which the time aperture window period begins is randomly varied to thereby avoid noise that may be synchronous with periodic events in the capacitance sensitive touchpad; and

(2) draining remaining charge from the time aperture filter after the time aperture filter closes, to a reference circuit, thereby preventing the remaining charge from reaching the at least one measurement circuit.

2. The method as defined in claim 1 wherein the method further comprises the steps of:

(1) utilizing at least one A/D converter as a portion of the at least one measurement circuit; and

(2) passing power that is in the time aperture filter during the selectable time aperture window period to the at least one A/D converter, wherein data from the at least one A/D converter is used to determine if an electrode event has occurred on the at least one sense electrode, wherein the time aperture filter is thereby capable of rejecting in-band noise.

3. The method as defined in claim 2 wherein the method further comprises the step of disposing the time aperture filter on a front end transconductance amplifier, thereby preventing most electrical charge that is noise related from reaching the at least one A/D converter of the at least one measurement circuit.

4. The method as defined in claim 3 wherein the method further comprises the step of decoupling an actual electrode frequency from the time aperture filter thereby making the at least one time aperture filter time dependent and not frequency dependent.

5. The method as defined in claim 4 wherein the method further comprises the step of continuously varying a drive frequency of the at least one sense electrode to thereby eliminate noise that is generated at generally fixed frequencies from reaching the at least one measurement circuit.

6. A capacitance sensitive touchpad that filters noise on a sense electrode from reaching measurement circuitry which detects an electrode event that is indicative of the presence of an object on a surface of the touchpad, said noise filtering touchpad comprising:

at least one sense electrode which is driven by at least one drive frequency, and which generates at least one electrode event when an object on the surface of the touchpad causes a change in capacitance on the at least one sense electrode;

at least one measurement circuit that receives an electrical signal from the at least one sense electrode, wherein the at least one measurement circuit is capable of detecting the at least one electrode event; and

a time aperture filter disposed between the at least one sense electrode and the at least one measurement circuit, wherein the time aperture filter is capable of passing the electrical signal that is indicative of the electrode event, while preventing noise on the at least one sense electrode from reaching the at least one measurement circuit by randomly varying a time at which the electrical signal is allowed to pass from the at least one sense electrode to the at least one measurement circuit to thereby avoid noise that may be synchronous with periodic events in the capacitance sensitive touchpad and thus improve performance by decreasing sensitivity of the measurement circuit to noise.

7. The capacitance sensitive touchpad as defined in claim 6 wherein the capacitance sensitive touchpad further comprises a reference circuit which is coupled to the time aperture filter, wherein an electrical charge can be drained from the time aperture filter to the reference circuit.

8. The capacitance sensitive touchpad as defined in claim 7 wherein the time aperture filter enables the electrical signal to reach the at least one measurement circuit when a selectable time aperture duration window is opened, and prevents the electrical signal from reaching the at least one measurement circuit when the selectable time aperture duration window is closed.

9. The capacitance sensitive touchpad as defined in claim 8 wherein the at least one measurement circuit further comprises:

at least one transconductance amplifier; and

at least one A/D converter which is coupled to the at least one transconductance amplifier via the time aperture filter.

10. The capacitance sensitive touchpad as defined in claim 9 wherein the time aperture filter is controlled by a timing circuit so as not to be dependent upon a drive frequency of the at least one sense electrode to thereby eliminate noise that is generated at generally fixed frequencies from reaching the at least one measurement circuit.

11. The capacitance sensitive touchpad as defined in claim 6 wherein the at least one sensor electrode is further comprised of:

a common sensing electrode in a first plane;

an array of first electrodes in the first plane, wherein the first electrodes in the array are arranged generally parallel to each other, and wherein the array of first electrodes is driven to the common sensing electrode; and

an array of second electrodes in a second plane, wherein the second electrodes in the array are arranged generally parallel to each other, wherein the second plane is parallel to the first plane, wherein the array of second electrodes is driven to the common sensing electrode, and wherein the array of second electrodes is disposed in a direction which is perpendicular to a direction of the array of first electrodes.