Patent Application
20110100727
This relates generally to touch sensitive devices and, more particularly, to a touch sensitive device with a dielectric layer.
Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch sensitive devices, such as touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. A touch sensitive device can include a touch sensor panel, which can be a clear or opaque panel with a touch-sensitive surface. In some instances, the touch sensitive device can also include 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 or that can be remote from the panel so that the touch-sensitive surface can interface with the viewable area of the display device. The touch sensitive device can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, the touch sensitive device 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.
When the object touching the touch sensitive device is poorly grounded, touch output values indicative of a touch event can be erroneous or otherwise distorted. The possibility of such erroneous or distorted values can further increase when two or more simultaneous touch events occur at the device.
This relates to a touch sensitive device having a dielectric layer between a cover layer and a touch sensor layer. The dielectric layer can reduce a negative pixel effect associated with poor grounding of an object touching the device. To achieve this reduction, the dielectric layer can reduce a capacitance per unit area of the device to less than about 0.0305 picofarads per square millimeter. The dielectric layer can have a thickness of about 0.50 millimeters or more and/or a dielectric constant of about 2.3 or less. The ability to reduce a negative pixel effect in a touch sensitive device can advantageously provide faster and more accurate touch detection, as well as power savings, by not having to repeat measurements subject to poor grounding conditions. Additionally, the device can more robustly adapt to various grounding conditions of a user or other objects.
In the following description of various embodiments, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific embodiments which can be practiced. It is to be understood that other embodiments can be used and structural changes can be made without departing from the scope of the various embodiments.
This relates to a touch sensitive device having a dielectric layer between a cover layer and a touch sensor layer. The dielectric layer can reduce a negative pixel effect associated with poor grounding of an object touching the device. In some embodiments, the dielectric layer can reduce a capacitance per unit area of the device to less than about 0.0305 picofarads per square millimeter, thereby reducing the negative pixel effect. In some embodiments, the dielectric layer can have a thickness of about 0.50 millimeters or more to decrease capacitive coupling between the touch sensor layer and the poorly grounded object, thereby reducing the negative pixel effect. In some embodiments, the dielectric layer can have a dielectric constant of about 2.3 or less to reduce the negative pixel effect.
The ability to reduce a negative pixel effect in a touch sensitive device can advantageously provide faster and more accurate touch detection, as well as power savings, by not having to repeat measurements subject to poor grounding conditions. Additionally, the device can more robustly adapt to various grounding conditions of a user or other objects.
The terms “poorly grounded,” “ungrounded,” “not grounded,” “partially grounded,” “not well grounded,” “improperly grounded,” “isolated,” and “floating” can be used interchangeably to refer to poor grounding conditions that can exist when an object is not making a low impedance electrical coupling to the ground of the touch sensitive device.
The terms “grounded,” “properly grounded,” and “well grounded” can be used interchangeably to refer to good grounding conditions that can exist when an object is making a low impedance electrical coupling to the ground of the touch sensitive device.
The dielectric layer 120 can include a firm polymer material, such as polypropylene, to act as a dielectric. Alternatively, the dielectric layer 120 can include a porous polymer material, such as polyethylene plastic, to act as a dielectric. Alternatively, the dielectric layer 120 can include a composite material, such as a ceramic mixture, to act as a dielectric. Other suitable materials can also be used as a dielectric. In some embodiments, the dielectric layer 120 can have a thickness of about 0.50 mm to about 0.60 mm or more. In some embodiments, the dielectric layer 120 can have a dielectric constant of about 2.3 or less or, more preferably, about 1.5 or less. The dielectric layer 120 can be attached, assembled, or otherwise disposed between the cover layer 110 and the touch sensor layer 130. In some embodiments, the dielectric layer 120 can be non-deformable so as to maintain a substantially constant distance between the cover layer 110 and the touch sensor layer 130. Adhesive layers (not shown) can be applied to opposite surfaces of the dielectric layer 120 to adhere the dielectric layer to the cover layer 110 on one surface and to the touch sensor layer 130 on an opposite surface. The adhesive layers can include a pressure sensitive adhesive, an epoxy, a bubble free laminate, and the like. In some embodiments, the adhesive layers can each have a thickness of about 50 μm.
It is to be understood that a stackup of a touch sensitive device is not limited to that illustrated in
It is to be understood that fabrication of a touch sensitive device having a dielectric layer is not limited to that illustrated in
A dielectric layer as in
As a result, instead of the mutual capacitance Csig at the stimulated pixel 326-a being reduced by a desirable amount ΔCsig, Csig can only be reduced by (ΔCsig−Cneg), where Cneg (a function of Cfa and Cfb) can represent a so-called “negative capacitance” resulting from the charge from the blocked electric field lines being undesirably coupled into the touch sensor layer 330 due to the poor grounding of the user. Touch signals can still generally indicate a touch at the stimulated pixel 326-a, but with an indication of a lesser amount of touch than actually occurred.
Similarly, the finger 350-b at the unstimulated pixel 326-b can undesirably increase that pixel's capacitance by Cneg to a capacitance above that of a no-touch condition to give the appearance of a so-called “negative pixel” or a theoretical negative amount of touch at the unstimulated pixel.
Pixels adjacent to pixels 326-a and 326-b can also experience this negative pixel effect due to the capacitances Cfa and Cfb to give the appearance of a theoretical negative amount of touch thereat.
The net result of the user being poorly grounded can be that the touch signal of the stimulated pixel being touched (e.g., pixel 326-a) can be attenuated and the adjacent pixels (e.g., pixel 326-b and others) can have negative touch signals.
To reduce this negative pixel effect, dielectric layer 320 can be attached, assembled, or otherwise disposed between cover layer 310 and touch sensor layer 330, as illustrated in
Table 1 shows examples of capacitances per unit area for touch sensitive devices having and not having dielectric layers according to various embodiments.
As shown in Table 1, the capacitance per unit area of a touch sensitive device having a dielectric layer (which can be the series capacitance per unit area of the cover layer and the dielectric layer) can be significantly reduced over that of a touch sensitive device without a dielectric layer (which can be the capacitance per unit area of the cover layer). For example, the touch sensitive device having only a 0.55 mm cover layer can have a capacitance per unit area (0.121 picofarads per square millimeter (pF/mm2)) approximately 6.5 times that of the touch sensitive device having a dielectric porous polyethylene layer (0.0187 pF/mm2) and approximately 4.0 times that of the touch sensitive device having a dielectric firm polypropylene layer (0.0305 pF/mm2). The touch sensitive device having only a 1.15 mm cover layer can have a capacitance per unit area (0.0577 pF/mm2) that is approximately 2.0 times lower than that of the touch sensitive device having only a 0.55 mm cover layer. However, the touch sensitive device having only a 1.15 mm cover layer can still have a capacitance per unit area approximately 3.0 times that of the touch sensitive device having a dielectric porous polyethylene layer and approximately 2.0 times that of the touch sensitive device having a dielectric firm polypropylene layer. The reduced capacitance per unit area in the presence of a dielectric layer can lead to a reduced negative pixel effect.
It is to be understood that the touch sensitive device according to various embodiments is in no way limited by the examples shown in Table 1, but can include different and/or additional metrics and values for reducing the negative pixel effect. For example, the thickness and/or the dielectric constant of the dielectric layer can be varied according to the needs of the device to decrease the capacitive coupling between a touching finger and a touch sensor layer, to achieve a reduced capacitance per unit area, and to reduce the negative pixel effect. Similar variations can be made in the cover layer in conjunction with the dielectric layer according to the needs of the device. Additionally, the capacitance per unit area can vary depending on whether the touch sensor layer is formed in a continuous plane or in a pattern with gaps between sensor electrodes and/or whether the touching finger (or object) forms a continuous conductive plane.
The cover layer 410, dielectric layer 420, touch sensor layer 430, and first base layer 440 can correspond to the cover layer 110, dielectric layer 120, touch sensor layer 130, and base layer 140, respectively, as described in
As shown in Table 1, the dielectric layer 420 can reduce the capacitance per unit area of the touch sensitive device 400 to less than about 0.0305 picofarads per square millimeter and, more preferably, to less than about 0.0187 picofarads per square millimeter, thereby reducing a negative pixel effect in the device.
It is to be understood that a stackup of a touch sensitive device is not limited to that illustrated in
The touch controller 506 can also include charge pump 515, which can be used to generate the supply voltage for the transmit section 514. The stimulation signals 516 can have amplitudes higher than the maximum voltage by cascading two charge store devices, e.g., capacitors, together to form the charge pump 515. Therefore, the stimulus voltage can be higher (e.g., 6V) than the voltage level a single capacitor can handle (e.g., 3.6 V). Although
Touch sensor panel 524 can include a dielectric layer to reduce a negative pixel effect according to various embodiments. The dielectric layer can be disposed on a capacitive sensing medium of the panel 524 having row traces (e.g., drive lines) and column traces (e.g., sense lines), although other sensing media and other physical configurations can also be used. The row and column traces can be formed from a substantially transparent conductive medium such as Indium Tin Oxide (ITO) or Antimony Tin Oxide (ATO), although other transparent and non-transparent materials such as copper can also be used. The traces can also be formed from thin non-transparent materials that can be substantially transparent to the human eye. In some embodiments, the row and column traces can be perpendicular to each other, although in other embodiments other non-Cartesian orientations are possible. For example, in a polar coordinate system, the sense lines can be concentric circles and the drive lines can be radially extending lines (or vice versa). It should be understood, therefore, that the terms “row” and “column” as used herein are intended to encompass not only orthogonal grids, but the intersecting or adjacent traces of other geometric configurations having first and second dimensions (e.g. the concentric and radial lines of a polar-coordinate arrangement). The rows and columns can be formed on, for example, a single side of a substantially transparent substrate separated by a substantially transparent dielectric material, on opposite sides of the substrate, on two separate substrates separated by the dielectric material, etc.
Where the traces pass above and below (intersect) or are adjacent to each other (but do not make direct electrical contact with each other), the traces can essentially form two electrodes (although more than two traces can intersect as well). Each intersection or adjacency of row and column traces can represent a capacitive sensing node and can be viewed as picture element (pixel) 526, which can be particularly useful when the touch sensor panel 524 is viewed as capturing an “image” of touch. (In other words, after the touch controller 506 has determined whether a touch event has been detected at each touch sensor in the touch sensor panel, the pattern of touch sensors in the multi-touch panel at which a touch event occurred can be viewed as an “image” of touch (e.g. a pattern of fingers touching the panel).) The capacitance between row and column electrodes can appear as a stray capacitance Cstray when the given row is held at direct current (DC) voltage levels and as a mutual signal capacitance Csig when the given row is stimulated with an alternating current (AC) signal. The presence of a finger or other object near or on the touch sensor panel can be detected by measuring changes to a signal charge Qsig present at the pixels being touched, which can be a function of Csig. The signal change Qsig can also be a function of a capacitance Cbody of the finger or other object to ground.
Computing system 500 can also include host processor 528 for receiving outputs from the processor subsystems 502 and performing actions based on the outputs that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device coupled to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user's preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. The host processor 528 can also perform additional functions that may not be related to panel processing, and can be coupled to program storage 532 and display device 530 such as an LCD display for providing a UI to a user of the device. In some embodiments, the host processor 528 can be a separate component from the touch controller 506, as shown. In other embodiments, the host processor 528 can be included as part of the touch controller 506. In still other embodiments, the functions of the host processor 528 can be performed by the processor subsystem 502 and/or distributed among other components of the touch controller 506. The display device 530 together with the touch sensor panel 524, when located partially or entirely under the touch sensor panel or when integrated with the touch sensor panel, can form a touch sensitive device such as a touch screen.
Note that one or more of the functions described above can be performed, for example, by firmware stored in memory (e.g., one of the peripherals) and executed by the processor subsystem 502, or stored in the program storage 532 and executed by the host processor 528. The firmware can also be stored and/or transported within any computer readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer readable storage medium” can be any medium that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like.
The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium.
It is to be understood that the touch sensor panel is not limited to touch, as described in
It is further to be understood that the computing system is not limited to the components and configuration of
Although embodiments have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the various embodiments as defined by the appended claims.
