Overview

Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.

Touch sensor panels can, in some embodiments, be formed from a matrix of drive lines (e.g., row traces) separated by a dielectric material from a plurality of sense lines (e.g., column traces), with sensors or pixels created at each crossing point of the drive and sense lines. Touch sensor panels can alternatively be arranged in any number of orientations or dimensions, including, but not limited to, diagonal, concentric circles, spiral, three-dimensional, or random orientations. In order to detect and identify the location of a touch on a touch sensor panel, stimulation signals are provided to the drive lines causing the sense lines to generate signals indicative of touch output values. By knowing the timing of the stimulation signals to specific drive lines relative to the signals read out of the sense lines, processor(s) can be used to determine where on the touch sensor panel a touch occurred.

When the object touching the touch sensor panel is poorly grounded, touch output values read out of the sense lines may be erroneous, false, or otherwise distorted. The possibility of such erroneous, false, or otherwise distorted signals is further increased when two or more simultaneous touch events occur on the touch sensor panel.

Apple's patent generally relates to multi-touch sensor panels that utilize an array of capacitive sensors (pixels) to detect and localize touch events, and more particularly, to the correction of pixels having distorted readings when touch events are generated by a poorly grounded object.

Two-Layer Electrode Touch Sensor Panel

Embodiments of the invention relate to correction of erroneous detection of touch event(s) on a touch sensor panel. Erroneous detection of what appears to be negative touch event(s) (e.g., so-called "negative pixels") may occur when a user is touching one or more locations on the touch sensor panel but fails to also be in good contact with another part of the device including the touch sensor panel. To compensate for these erroneous readings, sense lines of the touch sensor panel can include reverse driving circuits to facilitate calculation of an object-to-ground capacitance. This capacitance is periodically calculated during normal operation of the touch sensor panel to identify when the touch sensor panel is being touched under poor grounding conditions. If the calculated object-to-ground capacitance indicates the presence of a poor grounding condition, then the object-to-ground capacitance and detected pixel touch output values are used to estimate new pixel touch output values in an iterative manner. These new values represent estimates of the actual pixel touch output values and are used in place of the detected pixel touch output values to actually determine touch event(s). Accordingly, improved accuracy is provided for determining touch event(s) on a touch sensor panel.

 
Apple's patent FIG. 1 illustrates an exemplary touch sensor panel 100. The touch sensor panel includes an array of pixels 106 that can be formed by a two-layer electrode structure separated by a dielectric material. One layer of electrodes comprises a plurality of drive lines 102 positioned perpendicular to another layer of electrodes comprising a plurality of sense lines 104. The pixels 106 (also referred to as sensors) can be formed at the crossing points of the drive lines and sense lines, with each of the pixels having an associated mutual capacitance 114 (also referred to as coupling capacitance).

The drive lines (also referred to as rows, row traces, or row electrodes) can be activated by stimulation signals provided by respective drive circuits 108. Each of the drive circuits 108 includes an alternating current (AC) voltage source referred to as a stimulation signal source. The stimulation signals from the drive circuits may also be referred to as forward driving signals or forward stimulation signals. The sense lines (also referred to as columns, column traces, or column electrodes) can be activated by stimulation signals provided by respective reverse voltage sources 112 coupled to an input of its respective sense amplifier 110. Such stimulation signals may also be referred to as reverse driving signals or reverse stimulation signals. The reverse voltage sources comprise AC voltage sources. The sense amplifiers may also be referred to as charge amplifiers or trans-conductance amplifiers.

To sense touch event(s) on the touch sensor panel, each of the drive lines can be sequentially stimulated by the drive circuits, and the sense amplifiers detect the resulting voltage values from the sense lines. The detected voltage values are representative of pixel touch output values, indicating the pixel location(s) where the touch event(s) occurred and the amount of touch that occurred at those location(s).

Apple's technology, as noted in the patent figures above, applies to Apple's iPhone, future Classic or nano model iPods and future notebook-tablets that incorporate a multi-touch display.

Apple's patent FIG. 2 illustrates a close-up of a single exemplary pixel 106 with an impending touch event by a finger 200. When the pixel is not touched by an object, an electric field (shown as fringing electric field lines 202) can be formed between the drive line and the sense line via a dielectric material. Some of the electric field lines can extend above the drive and sense lines 102, 104 and even above a cover 204 located over the touch sensor panel. When an object, such as the finger, touches the pixel (or a location near the pixel 106), the object blocks some of the electric field lines extending above the cover. Such blockage or interruption of the electronic field lines changes the capacitance associated with the pixel 106, which changes the current flow from the drive line to the sense line (current is proportional to capacitance), and which in turn changes the voltage value (or charge coupling) detected at the sense line.

A Simultaneous Multiple Touch Event Occurring on the Touch Sensor Panel

 
If you're a glutton for punishment or happen to be one who dreams in electric mathematical equations, then you could read more about Apple's patent using this temporary link. Apple credits Marduke Yousefpor as the sole inventor of patent application 20100060608. Also see our related report that was published in January 2010.

The other three multi-touch related patents published yesterday: Phase Compensation for Multi-Stimulus Controller 20100060593, Bandwidth Enhancement for a Touch Sensor Panel 20100059294 and Single-Chip Multi-Stimulus Sensor Controller 20100059295 (see graphic below). Use our handy search engine link below to view these patents.

 
With Apple's law suit against HTC reportedly shaking their faith in Google and Whiny former Sun CEO recently whinging on about Apple threatening Sun over their Looking Glass OS, we now see Battleship Apple going on the offensive and will continue to do so going forward. This isn't the last we'll hear of Apple's legal actions – that's for sure. In truth, the patent wars have only begun.

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