US 8,941,394 B2 · Capacitive sensor system with noise reduction

Abstract

A system for reducing noise when detecting the capacitance value of a capacitor in a touch display that operates in a potentially noisy environment. A capacitance sensor is provided for determining the size of the capacitor in the touch screen display and includes a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero. A control circuit controls the capacitance sensor and the operation of the charge and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation. The operation of the control circuit and the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value. A noise reduction circuit is provided to modify the operation of the control circuit to reduce noise.

Drawings

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Drawings

Claims11

Dependent claims

A system for reducing noise when detecting a capacitance value of a capacitor in a touch display that operates in a potentially noisy environment, comprising:

a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero;
a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation;
wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value;
and
noise reduction circuitry for modifying the operation of the control circuit to reduce noise without repeating the charge and discharge of the capacitor.

2 more elements

A system disposed on an integrated circuit for reducing noise when detecting a capacitance value of a capacitor external to the integrated circuit in a touch display that operates in a potentially noisy environment, comprising:

a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero;
a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation;
wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value;
and
noise reduction circuitry for modifying the operation of the control circuit to reduce noise;
wherein the charging and discharge circuits operate to deliver a bit value in a SAR operation in accordance with the SAR algorithm of the ADC having a fixed bit length and resolution, the control circuit operable to control the charging circuit and the discharge circuit to successively charge and discharge the capacitor in accordance with a SAR operation and the noise reduction circuitry is operable to vary the resolution of the SAR operation as a function of noise.

3 more elements

a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero;
a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation;
wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value;
and
noise reduction circuitry for modifying the operation of the control circuit to reduce noise,
wherein the discharge circuit includes:
a first discharge circuit for discharging the capacitor through a low impedance path to ground;
a second discharge circuit for discharging the capacitor through a high impedance path to ground;
and
the noise reduction circuitry including timing circuitry to control the first and second discharge circuitry to first discharge the capacitor during a discharge operation through the low impedance path to remove a substantial portion of charge therefrom followed by discharging the capacitor through the high impedance path such that the second discharge circuit operates as a low pass filter to remove high frequency external noise from the capacitor.

7 more elements

Dependencies are inferred from the claim text.

Description23,611 words

Summary330 words

#The present invention relates to noise reduction in a touch capacitive sensing system, and more particularly, to a system and method for reducing noise from various sources that may affect touch capacitor sensing.

#Electronic circuit design often requires the use of various interface circuitries such as capacitive sensor arrays that enable the user to interact with or receive information from an electronic circuit. Typically, dedicated sensing circuitry may be used to detect the activation of various capacitive switches within a capacitive sensor array enabling a user to input particular information into a circuit.

#Within a capacitive sensor array there is needed the ability to detect differences in the capacitance value of a capacitive switch responsive to the placement of an object upon or in the proximity of the capacitive switch. Current technologies lack the ability to adequately reduce noise that may affect such detection and improvements are needed. Further, the displays that incorporate such capacitive switches are subject to various noise sources that can affect the capacitance measurement.

Brief description of the drawings46 figures

#For a more complete understanding, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:

#FIG. 1A illustrates an overall diagram of a scan control IC interface with a touch screen;

#FIG. 1B illustrates a more detailed diagram of the scan control IC illustrating the two scan functions;

Detailed description22,250 words

#Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout, the various views and embodiments of a capacitive touch sensor are illustrated and described, and other possible embodiments are described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations based on the following examples of possible embodiments.

#Referring now to FIG. 1A, there is illustrated a diagrammatic view of a scan control IC 102 that is interfaced with a touch screen 104 that can be used by itself or in conjunction with a display as an overlay. The touch screen 104 is a touch screen having a plurality of distributed capacitors 401 disposed at intersections of columns and rows. There are a plurality of rows 108 and a plurality of columns 110 interfaced with the scan control IC. Thus, a row line will be disposed across each row which intersects with a column line on the touch screen surface and these are interfaced with the scan control IC 102. It should be understood that a capacitive touch pad refers to an area on the touch screen, but will be used to refer to an intersection between a row line and a column line. The term “touch pad” and “intersection” shall be used interchangeably throughout.

#As will be described herein below, the self capacitance of a particular row or a particular column in one mode is evaluated by determining the capacitance that is associated with a particular row or column line, this being an external capacitance. Any change to this capacitance will be sensed and evaluated, this change being due to such things as a finger touching an area of the touch screen 104. By sensing both the row and the column lines and determining the self capacitance associated therewith, the particular capacitive touch pad 106 (or area of the touch screen) touched can be determined which will be indicated by an increase in capacitance on a row and a column line (for a single touch). In another mode, mutual capacitance between the intersection of a row and a column is determined.

Facts

Application

12/895,087Filed 30 Sep 2010 · continuation in part

Priority

31 Dec 2009

Published

US 2011/0156839 A130 Jun 2011

Granted

27 Jan 2015

Term ends

14 Feb 2033

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment, including 1,141 days of adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification6 codes

G06F 3/0418
Control or interface arrangements specially adapted for digitisers: for error correction or compensation, e.g. based on parallax, calibration or…
G06F 3/044
Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means: by capacitive means
G06F 3/0446
By capacitive means: using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
G01R 27/2605
Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric…:…

Timeline

31 Dec 2009Priority claimedParent application 12/650,748
30 Sep 2010Application filedUS 12/895,087
2 Nov 2010Assigned to Silicon Laboratories Inc.assignment of assignor's interest
30 Jun 2011PublishedUS 2011/0156839 A1
27 Jan 2015GrantedUS 8,941,394 B2
12 Oct 2026TodayWithin its term
14 Feb 2033Term endsEstimated, includes 1,141 days of adjustment

Capacitive sensor system with noise reduction

Life of this patent

Capacitive sensor system with noise reduction

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims11

Description23,611 words

Drawings

Classification6 codes

Life of this patent

Description23,611 words