Patent Publication Number: US-2013234986-A1

Title: Stylus adapted for low resolution touch sensor panels

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of touch detection. More particularly, the present invention is directed in one exemplary aspect to providing a stylus adapted for use with a capacitive touch sensor panel optimized for finger detection. 
     BACKGROUND OF THE INVENTION 
     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 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 are typically fabricated as one or more layers of thin film deposited and patterned into conductive regions upon at least one layer of a transparent substrate. The conductive regions include a number of capacitive elements arranged into a plurality of rows and columns. When a user&#39;s finger contacts a specific region of the touch surface, the approximate location of the user&#39;s finger can be determined based upon analysis of one or more sensed signals. 
     A low resolution array of row and column elements is usually sufficient for finger detection. This is because the width of the typical human finger is relatively large (roughly 10 mm) in relation to at least one dimension of a capacitive element. Therefore, if it is known in advance that the touch sensor panel will primarily be driven by finger input, fewer capacitive elements can be built into the touch sensor panel. Additionally, the rows and columns can be separated at a greater distance. 
     However, when a stylus is subsequently employed on a touch sensor panel optimized for finger input, the stylus&#39;s small tip can often contact a region of the touch surface that is between adjacent capacitive elements (e.g., as between adjacent column sensors). Since the tip of the stylus is not sufficiently wide so as to guarantee the level of electrical interaction necessary for it to be sensed by at least one capacitive element, many situations exist where the touch sensor panel will not be able to identify an input even if the stylus is making contact with the touch surface. 
     SUMMARY OF THE INVENTION 
     In many conventional touch sensor panels, capacitive elements are arranged into a plurality of rows and columns so as to service an entire region of a touch surface. By analyzing the state of each column sensor after a particular row has been driven, a centroid can be calculated indicating the approximate position of a contacting entity upon the touch surface. 
     In many cases, however, the small tip of a stylus will contact a region of the touch surface that is between adjacent sensors (for example, as in certain low resolution touch sensor panels that are adapted for finger input). Without sufficient electrical interaction with at least one sensory element, a centroid may not be properly identified, and hence the input will not be recognized. Various examples of the present invention therefore ensure that contact from the stylus will be detected on a low resolution touch sensor panel irrespective of the location of the region of contact upon the touch surface. 
     In some examples, a metallic or otherwise conductive disk may be attached to one end of the stylus. The disk may be sized so as to guarantee sufficient electrical interaction with at least one sensory element of the touch sensor panel. In some examples, the disk may be attached to one end of the stylus via a pivotal connector. This increases the likelihood that the disk will remain flush with the touch surface as the user applies different combinations of directional forces to the stylus. 
     In some examples, the stylus may be powered so as to provide a stimulus signal to the capacitive elements. In this manner, the capacitive elements do not need to be driven continuously within a host device. Optionally, one or more force and/or angle sensors disposed within the stylus can supply additional data to the touch panel. This additional data can be used for selecting various features in an application executing on the host device (e.g., selecting various colors, brushes, shading, line widths, etc.). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary stylus adapted for use with a host device according to one example of the present invention. 
         FIG. 2  is a diagram illustrating components of an exemplary stylus according to one example of the present invention. 
         FIG. 3  is a diagram illustrating how an exemplary stylus including a rigid tip can yield a non-uniform signal. 
         FIG. 4A  is a diagram illustrating an exemplary disk pivot adapted to ensure that a conductive disk remains flush with a touch surface according to one example of the present invention. 
         FIG. 4B  is a diagram illustrating an exemplary disk pivot adapted to ensure that a conductive disk remains flush with a touch surface according to one example of the present invention. 
         FIG. 4C  is a diagram illustrating an exemplary disk pivot adapted to ensure that a conductive disk remains flush with a touch surface according to one example of the present invention. 
         FIG. 5  is a diagram illustrating an exemplary stylus including a conductive disk emanating a set of fringe fields according to one example of the present invention. 
         FIG. 6  is a diagram illustrating components of an exemplary stylus according to another example of the present invention. 
         FIG. 7  is a diagram illustrating an exemplary single-sided indium tin oxide circuit  700  adapted to detect stimulus signals generated by a powered stylus according to one example of the present invention. 
         FIG. 8  is a flow diagram illustrating an exemplary method of automatically selecting a mode of operation for input detection according to one example of the present invention. 
         FIG. 9  is a block diagram illustrating an exemplary computing system including a touch sensor panel adapted for use with one example of the present invention. 
         FIG. 10A  is a block diagram illustrating an exemplary mobile telephone having a touch sensor panel adapted for use with a powered stylus according to one example of the present invention. 
         FIG. 10B  is a block diagram illustrating an exemplary digital media player having a touch sensor panel adapted for use with a powered stylus according to one example of the present invention. 
         FIG. 10C  is a block diagram illustrating an exemplary personal computer having a touch sensor panel (trackpad) and/or display adapted for use with a powered stylus according to one example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EXAMPLES 
     In the following description of preferred examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples in which the invention can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the examples of this invention. 
     As used herein, the term “application” includes without limitation any unit of executable software which implements a specific functionality or theme. The unit of executable software may run in a predetermined environment; for example, a downloadable Java Xlet™ that runs within the JavaTV™ environment. 
     As used herein, the terms “computer program” and “software” include without limitation any sequence of human or machine cognizable steps that are adapted to be processed by a computer. Such may be rendered in any programming language or environment including, for example, C/C++, Fortran, COBOL, PASCAL, Perl, Prolog, Python, MATLAB, assembly language, scripting languages, markup languages (e.g., HTML, SGML, XML, VoXML), functional languages (e.g., APL, Erlang, Haskell, Lisp, ML, F# and Scheme), as well as object-oriented environments such as the Common Object Request Broker Architecture (CORBA), Java™ (including J2ME, Java Beans, etc.). 
     As used herein, the term “display” includes any type of device adapted to display information, including without limitation cathode ray tube displays (CRTs), liquid crystal displays (LCDs), thin film transistor displays (TFTs), digital light processor displays (DLPs), plasma displays, light emitting diodes (LEDs) or diode arrays, incandescent devices, and fluorescent devices. Display devices also include less dynamic devices such as printers, e-ink devices, and other similar structures. 
     As used herein, the term “memory” includes any type of integrated circuit or other storage device adapted for storing digital data including, without limitation, ROM, PROM, EEPROM, DRAM, SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, “flash” memory (e.g., NAND/NOR), and PSRAM. 
     As used herein, the term “module” refers to any type of software, firmware, hardware, or combination thereof that is designed to perform a desired function. 
     As used herein, the terms “processor,” “microprocessor,” and “digital processor” include all types of digital processing devices including, without limitation, digital signal processors (DSPs), reduced instruction set computers (RISC), general-purpose (CISC) processors, microprocessors, gate arrays (e.g., FPGAs), programmable logic devices (PLDs), reconfigurable compute fabrics (RCFs), array processors, and application-specific integrated circuits (ASICs). Such processors may be contained on a single unitary IC die or distributed across multiple components. 
     As used herein, the term “network” refers generally to any type of telecommunications or data network including, without limitation, cable networks, satellite networks, optical networks, cellular networks, and bus networks (including MANs, WANs, LANs, WLANs, internets, and intranets). Such networks or portions thereof may utilize any one or more different topologies (e.g., ring, bus, star, loop, etc.), transmission media (e.g., wired/RF cable, RF wireless, millimeter wave, hybrid fiber coaxial, etc.) and/or communications or networking protocols (e.g., SONET, DOCSIS, IEEE Std. 802.3, ATM, X.25, Frame Relay, 3 GPP, 3 GPP2, WAP, SIP, UDP, FTP, RTP/RTCP, TCP/IP, H.323, etc.). 
     As used herein, the term “wireless” refers to any wireless signal, data, communication, or other interface including, without limitation, Wi-Fi, Bluetooth, 3 G, HSDPA/HSUPA, TDMA, CDMA (e.g., IS-95A, WCDMA, etc.), FHSS, DSSS, GSM, PAN/802.15, WiMAX (802.16), 802.20, narrowband/FDMA, OFDM, PCS/DCS, analog cellular, CDPD, satellite systems, millimeter wave or microwave systems, acoustic, and infrared (i.e., IrDA). 
     In many conventional touch sensor panels, capacitive elements are arranged into a plurality of rows and columns so as to service an entire region of a touch surface. By analyzing the state of each column sensor after a particular row has been driven, a centroid can be calculated indicating the approximate position of a contacting entity upon the touch surface. 
     In many cases, however, the small tip of a stylus will contact a region of the touch surface that is between adjacent sensors (for example, as in certain low resolution touch sensor panels that are adapted for finger input). Without sufficient electrical interaction with at least one sensory element, a centroid may not be properly identified, and hence the input will not be recognized. Various examples of the present invention therefore ensure that contact from the stylus will be detected on a low resolution touch sensor panel irrespective of the location of the region of contact upon the touch surface. 
     In some examples, a metallic or otherwise conductive disk may be attached to one end of the stylus. The disk may be sized so as to guarantee sufficient electrical interaction with at least one sensory element of the touch sensor panel. In some examples, the disk may be attached to one end of the stylus via a pivotal connector. This increases the likelihood that the disk will remain flush with the touch surface as the user applies different combinations of directional forces to the stylus. 
     In some examples, the stylus may be powered so as to provide a stimulus signal to the capacitive elements. In this manner, the capacitive elements do not need to be driven continuously within a host device. Optionally, one or more force and/or angle sensors disposed within the stylus can supply additional data to the touch panel. This additional data can be used for selecting various features in an application executing on the host device (e.g., selecting various colors, brushes, shading, line widths, etc.). 
     Although examples of the invention may be described and illustrated herein in terms of touch sensor panels, it should be understood that examples of this invention are not so limited, but are additionally applicable to any module adapted to determine input via capacitive sensing. Furthermore, although examples of the invention may be described and illustrated herein in terms of indium tin oxide (ITO) touch sensor panels, it should be understood that examples of the invention are not so limited, but are also applicable to other conductive media as well. This includes, without limitation, amorphous silicon, copper indium diselenide, cadmium telluride, and film crystalline silicon. 
       FIG. 1  illustrates an exemplary stylus  200  adapted for use with a host device  100  according to one example of the present invention. As shown by the figure, the host device  100  includes a touch surface  102  that is serviced by a plurality of capacitive elements  104  arranged into a plurality of rows  106  and columns  108 . Note, however, that even though  FIG. 1  depicts the capacitive elements  104  arranged in this particular manner, other configurations of capacitive elements  104  are also possible according to examples of the present invention. 
     When the stylus  200  makes contact with the touch surface  102 , one or more capacitive elements  104  undergo a change in capacitance that can be detected by charge amplifier circuitry. These sensors define a crude two-dimensional “patch” which represents the “image” of the touch provided by the stylus. From the shape and dimensions of the patch, a centroid can be calculated which represents an approximate center of the touch area. Once the centroid has been calculated, its position can then be transmitted to an application resident on the host device  100  for input processing. 
     As shown by  FIG. 1 , the stylus  200  includes a conductive disk  208  with a diameter  204  large enough to ensure sufficient electrical interaction with a minimum number of capacitive elements  104  for the purposes of centroid calculation. In this manner, a centroid may be calculated irrespective of the position of the conductive disk  208  upon the touch surface  102 . 
       FIG. 2  is a diagram illustrating components of an exemplary stylus  200  according to one example of the present invention. As shown by the figure, the exemplary stylus  200  of  FIG. 2  includes a shaft  202 , a replacement tip  204 , and a conductive disk  208  attached to a disk pivot  206  that is connected to the replacement tip  204 . 
     In one example, the shaft of the stylus  200  has a length of approximately 130 millimeters and a diameter of approximately 8 millimeters, although any set of dimensions may be utilized according to examples of the present invention. Additionally, the shape of the shaft may be of any shape or geometry including, for example, rectangular and cylindrical shapes. 
     In some examples, the shaft  202  contains a conductive material such as a metal or a metal alloy (e.g., aluminum or copper). The conductive material in the shaft  202  allows the user&#39;s body to extend the conductor upon contact with the shaft  202 , thus facilitating current flow from the user&#39;s body to the conductive disk  206  and providing a ground path for charge coupled onto the conductive disk from the touch sensor panel. In some examples, this allows for stronger signal detection at the touch sensor panel. 
     In other examples, the shaft  202  contains an insulating material such as plastic or glass. In some examples, the insulating material in the shaft  202  serves to prevent electrical noise picked up by the user&#39;s body from being transmitted to the touch surface. This electrical noise can interfere with the input detection mechanism of the touch sensor panel. 
     In some examples, a detachable replacement tip  204  may be attached to one end of the shaft  202 . The replacement tip  204  includes a disk pivot  206  and a conductive disk  208 . Since the diameter of the conductive disk is optimized for a particular spatial resolution of a touch sensor panel (as discussed in further detail below), replacement tips  204  having conductive disks  208  of different diameters  204  enable a single stylus  200  to operate on a variety of touch sensor panels with different spatial resolutions. Additionally, the shafts  202  of styli  100  can be manufactured independently from the replacement tips  204 , thereby reducing the costs of manufacture. 
     In several examples, a disk pivot  206  increases the likelihood that the conductive disk  208  will remain flush with the touch surface  102  as various directional forces are applied to the stylus  200  during operation. In some examples, the disk pivot  206  can provide a uniform interaction with sensory elements for the purposes of centroid calculation. If the conductive disk  208  were instead rigidly attached to the shaft  202 , then the varying distances between each region of the conductive disk  208  and each corresponding capacitive element could in some cases result in inaccurate touch detection and a shifted centroid. 
       FIG. 3  is a diagram illustrating this phenomenon. As the stylus  200  is oriented at an angle  304  relative to the touch surface  102 , a set of distances  302 ( 1 ),  302 ( 2 ), and  302 ( 3 ) separate regions of the conductive disk  208  from the corresponding capacitive elements  300 ( 1 ),  302 ( 2 ), and  303 ( 3 ) beneath them. As  FIG. 3  indicates, the distance from the conductive disk  208  to each capacitive element  300 ( 1 ),  300 ( 2 ), and  302 ( 3 ) progressively decreases as the disk approaches the touch surface  102 . Since the conductive disk  208  is rigidly connected to the shaft  202 , one side of the conductive disk  208  will elevate from the touch surface  102  as the angle  304  formed between the shaft  202  and the touch surface  102  approaches 0 degrees from the vertical position. 
       FIGS. 4A-4C  are diagrams illustrating an exemplary disk pivot  206  that increases the likelihood that the conductive disk  208  will remain flush with the touch surface  102  according to one example of the present invention. As shown by the figure, the replacement tip  204  rotates about the disk pivot  206  as the angle of application  400  changes from  400 ( 1 ) to  400 ( 2 ) and  400 ( 3 ). In this manner, amount of charge is greatest at the electrodes situated closest to the center of the disk, thus ensuring proper centroid calculation. 
     As illustrated by  FIG. 2 , a conductive disk  208  may be attached to one side of the disk pivot  206 . Note that even though a conductive disk  208  is depicted in  FIG. 2 , the contact member may include other surface shapes and/or geometries according to various examples of the present invention. This includes without limitation elliptical and polygonal surfaces (e.g., square and rectangular surfaces). In one example, the contact member includes a conductive sphere adapted to simultaneously serve as the disk pivot  206 . 
     The conductive disk  208  (or other such contact member) is adapted to electrically interact with one or more electrodes disposed within a touch sensor panel. In order to ensure sufficient electrical interaction with enough electrodes so as to generate a centroid, the conductive disk  208  may appropriately sized. The size of the disk  208  or other contact member depends in part upon the size of each electrode in the touch sensor panel and the distance between adjacent electrodes. For example, in touch sensor panels with higher spatial resolutions (i.e., with less space separating each adjacent electrode) the conductive disk  208  may have a smaller diameter (e.g., four millimeters). By contrast, in touch sensor panels with lower spatial resolutions (i.e. with more space separating each adjacent electrode), the conductive disk  208  may have a greater diameter (e.g., seven millimeters). 
     According to certain examples, the size of the conductive disk  208  depends on other factors as well. For example,  FIG. 5  illustrates an exemplary stylus  200  including a conductive disk  208  with an associated set of fringe fields  500 ( 1 ) and  500 ( 2 ). In some examples, the fringe fields  500  are sufficiently strong so as to charge capacitive elements adjacent to those situated beneath the region of contact. In this manner, the strength and spread of the fringe fields  500  may be taken into account when calculating the size of the conductive disk  208  or other contact member. 
     In some examples, the size of the conductive disk  208  or other contact member also depends upon additional functionality supported by the stylus  200 . For example, in some examples, the stylus  200  includes one or more embedded accelerometers adapted to transmit positional information to the touch sensor panel. Positional information generated by the capacitive elements  300  may be synthesized with the accelerometer data by a processor in the host device in order to derive the precise region of contact upon the touch surface  102 . In some of these examples, the capacitive touch circuitry is required only to generate a rough indication of the location of the conductive disk  208  upon the touch surface  102 , while the high precision information is provided by the one or more accelerometers. Thus, the conductive disk  208  need not electrically interact with as many capacitive elements as would be necessary to calculate a high precision centroid using the capacitive elements alone. In this manner, the conductive disk  208  may be sized so as to take this into account. 
       FIG. 6  is a diagram of components of an exemplary stylus  600  according to another example of the present invention. The stylus  600  includes a shaft  202  and a conductive member  604  with a conductive tip  606 . A power connector  608  such as a conductive cable may be adapted to transmit current to the stylus  600 , thereby increasing the voltage between the conductive tip  606  and capacitive elements situated behind the touch surface  102 . The strength of the electric field  610  generated is a function of the applied voltage. Note that the power supplied to the stylus  600  via the power connector  608  can be specified according to the power necessary for a designated number of capacitive elements to be able to sufficiently detect the generated electric field  610 . 
     The spread of the electric field  610  is a function of the shape and/or sharpness of the conductive tip  606 . In some examples, a sharp tip may be utilized in order to increase the spread of the electric field  610  such that it is detected by some predetermined number of capacitive elements (e.g., at least three capacitive elements). In this manner, a powered stylus  600  can generate an electric field  610  both strong enough and wide enough so as to enable calculation of a high precision centroid. Note also that any number of tip shapes and/or geometries may be used according to examples of the present invention. Additionally, any number of conductive materials may be used within the power connector  608 , the shaft  202 , and/or the conductive member  604 . This includes without limitation metallic substances such as aluminum, gold, silver and copper. 
       FIG. 7  is a diagram illustrating an exemplary single-sided indium tin oxide (SITO) circuit  700  adapted to detect stimulus signals generated by a powered stylus according to one example of the present invention. As shown by the figure, the SITO circuit  700  includes a number of row electrodes  702  and a number of column electrodes  704  adapted to service a certain region of a touch sensor panel. Note that the connections between adjacent row electrodes are shown symbolically as dashed lines in  FIG. 7 . The actual connections may take on any number of configurations, including, for example, connecting traces that are routed to metal traces in the border areas of the panel, or vias that allows the connections to pass over or under the column electrodes in a different layer. For simplicity of illustration, not all row and column electrodes included within the SITO  700  circuit are illustrated in  FIG. 7 ; in some examples, for example, the SITO circuit  700  includes ten columns and fifteen rows. Note, however, that any number of rows electrodes  702  and column electrodes  704  may be utilized according to examples of the present invention. Additionally, the size of each electrode as well as the spacing between each electrode may vary across examples. 
     In many conventional SITO circuits, the rows are progressively driven while the columns are set to sense signals. The column electrodes may be connected to a set of column charge amplifiers adapted to amplify sensed signals. Charge coupled from the driven row to the sense column can be detected by the charge amplifiers. Touch events cause a change in the charge coupling, and this change can be detected by the charge amplifier as a touch event. The locations (and optionally the magnitudes) of the sensed changes in charge coupling at a particular instant in time are then used for centroid calculation by a processor in the host device. Note that in some SITO circuits, all electrodes are scanned in order to process simultaneous contacts upon the touch surface (for example, as in the case of multi-touch applications adapted to calculate a plurality of centroids from a number of interactions with the touch surface  102 ). 
     With a powered stylus, however, it becomes unnecessary to continuously drive the row electrodes since the stylus can provide the requisite stimulus signals. As such, the row electrodes can be provided a set of row charge amplifiers  706  in addition to the conventional column charge amplifiers  708  associated with the column electrodes  704 . In this manner, both the row electrodes  702  and the column electrodes  704  can be set to sense changes in charge coupling, where the stimulus signal is provided by the powered stylus. 
     Additionally, according to certain examples, only a single region of contact  710  (i.e., calculation of a single centroid) may be necessary for an application executing on the host device  100 . This is because many applications adapted to receive input from a stylus do not require multi-touch capability. In some of these examples, since there is no frame scanning as would be the case in finger tracking acquisition mode, the signal recording rate can be greatly increased so as to allow more signal averaging or to track very fast motion. The data processing burden may also be reduced since there may be a smaller number of signals to analyze (n+m signals as compared to n*m signals, where n is the number of rows and m is the number of columns in the touch panel). In addition to these computational efficiencies, power may also be preserved. 
     In some examples, the SITO circuit  700  may be adapted to automatically switch modes of operation (for example, as between a stylus mode, where both the rows and columns are set to sense, and a finger mode, where either the rows or the columns are set to drive, while the other is set to sense). 
       FIG. 8  is a flow diagram illustrating an exemplary method of automatically selecting a mode of operation for input detection according to one example of the present invention. At block  802 , a first mode of operation is selected. In some examples, the mode of operation defaults to the first mode of operation when the host device  100  is powered on. 
     At block  804 , a processor within the host device continuously determines whether the second mode of operation has been triggered. In some examples, this may be accomplished by determining whether one or more parameters of a detected centroid satisfy certain criteria. For example, in one example, if a detected centroid corresponds to a region of contact  710  with an estimated diameter of approximately ten millimeters, the system may assume that a finger is presently contacting the touch surface  102  and adjust the mode of operation accordingly. Alternatively, if the detected centroid corresponds to a region of contact  710  with a smaller estimated diameter, the system may assume that a stylus is contacting the touch surface  102 . 
     In alternative examples, other techniques may be employed. For example, in some examples, the presence of multiple contacts upon the touch surface  102  may be used to support a determination that the first mode of operation should be retained. In some examples, mode selection may be based in part upon the strength of the signal detected by one or more sense electrodes. Other techniques may also be utilized according to examples of the present invention. 
     Once the second mode of operation has been triggered, it is correspondingly selected at block  806 . The system then continuously detects whether the first mode of operation has been triggered at block  808  and the process repeats per step  802 . Note that in some examples, the criteria used to determine whether the first mode is triggered at step  808  is different than the criteria used at step  804 . Note also that one or more temporal values may be used for restoring a prior selected mode of operation. For example, in one example, a finger mode may be automatically restored one minute from the time that a stylus mode is selected. 
     In several examples, a powered stylus may be further adapted to provide additional information to the host device  100  for subsequent processing. For example, in certain examples, the stylus includes one or more squeeze (force) sensors, switches, buttons and/or other toggles adapted to allow a user to quickly select among various types of associated functionality (for example, selecting colors, brush sizes, shading, line width, eraser functionality, etc.). 
     In some examples, stylus functionality may be determined based upon output from one or more sensory modules adapted to estimate at least one angle of inclination. The sensory modules include, without limitation, accelerometers, force sensors, motion sensors, pressure sensors, and other similar devices. In some examples, the angle of inclination is an estimated angle of the position of the shaft  202  relative to the touch surface  102 . Note that in some examples, angles may be estimated about more than one axis. 
     In some examples, stylus functionality may be automatically selected based upon one or more estimated angles of inclination. For example, in one example, if a stylus is oriented at an angle smaller than 45 degrees or at an angle greater than 225 degrees relative to the touch surface  102  about at least one axis, a larger brush size is automatically selected. Alternatively, a stylus  200  contacting a touch surface  102  may be adapted to navigate among a plurality of selections upon a display screen, thus functioning in a manner similar to a joystick. 
     In some examples, stylus functionality may be determined based upon output from one or more sensory modules adapted to estimate the amount of force applied in a direction that is perpendicular to the touch surface  102 . Any number or combination of modules may be used for this purpose, including, for example, force sensors, pressure sensors, accelerometers, strain gauges, piezoelectric sensors, etc. 
     In one example, for example, the width of the line output on an associated display screen is a function of the amount of force applied to the stylus  200  against the touch surface  102 . Thus, if a small amount of dynamic force is applied to the stylus in a direction perpendicular to the touch surface  102 , an application resident on the host device  100  may generate a thin line on an associated display screen. Conversely, if a large amount of dynamic force is applied to the stylus, the application may output a thicker line. 
     In another example, the amount of force applied to the stylus  200  against the touch surface  102  is adapted to trigger one or more power states of the stylus  200 . For example, a stylus  200  operating in a low power state may automatically switch to a higher power state upon detecting an inertial force exerted upon the conductive disk  208  or other contact member. The low power state may subsequently be restored when the inertial force is no longer detected. 
     A variety of information transfer methods may be used to convey functional information associated with a particular configuration of the stylus  200  to an application resident in the host device  100 . This information includes, without limitation, the state of one or more buttons, switches or other similar toggles; data indicating the output from one or more sensory modules (e.g., estimated angles of inclination, data generated by squeeze sensors, estimated forces applied in a direction perpendicular to the touch surface  102 , etc.); and fine positional data adapted to complement data generated by the capacitive elements disposed within the SITO circuit  700 . In some examples, a stylus stimulus frequency may be used to select one or more stylus functions. For example, in one example, toggling a particular setting in the stylus  200  modulates the frequency of the stimulating signal. One or more modules resident in the host device  100  may then be used to determine the function based upon the detected frequency. 
     In other examples, the stylus  200  communicates to the system by stimulation voltage levels. In some examples, for example, analog stimulation voltage levels are utilized. In this manner, the specific function selected may be predicated on the applied voltage at a given instant or over a given period of time. In other examples, the stylus  200  communicates to the system using a digital stimulation voltage stream. In one example, for example, a stimulation pattern of high and low voltage pulses is adapted to transmit information to the host device  100 . In another example, a simulation pattern of single-level voltage pulses is adapted to convey this information. One or more demodulation and analysis modules resident in the host device  100  may then be used to derive the selected function from detected voltage conditions. These modules may include any combination of hardware, software, and/or firmware. 
     In still other examples, information may be conveyed to the host device  100  via one or more wireless network connections. For example, in some examples, one or more embedded accelerometers provide fine resolution information to the host device  100  for the purposes of centroid calculation. As the stylus  200  kinetically contacts the touch surface, the capacitive position information may be integrated with the accelerometer data in order to maintain a high-resolution position of the region of contact  710 . This enables a sharper end stylus to operate with the SITO circuit  700  while simultaneously providing positional information which significantly exceeds the spatial resolution capability of the capacitive touch sensor panel. 
     In some examples, one or more accelerometers allow tracking of the conductive disk  208  or conductive tip  606  above the touch surface (i.e., Z direction tracking). The Z-directional information determined by the accelerometers may be used, for example, to verify whether there is contact with the touch surface  102 , to determine whether a gesture-based function has been performed by a user, to select a particular setting on the host device  100 , to navigate among a plurality of display screens, or to transition between power states. Other functions are also possible according to examples of the present invention. Note that one or more wireless connections may be used to convey the Z-directional information to the host device  100 . 
       FIG. 9  illustrates exemplary computing system  900  adapted for use with one or more of the examples of the invention described above. Computing system  900  can include one or more panel processors  902  and peripherals  904 , and panel subsystem  906 . Peripherals  904  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Panel subsystem  906  can include, but is not limited to, one or more sense channels  908 , channel scan logic  910  and driver logic  914 . Channel scan logic  910  can access RAM  912 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  910  can control driver logic  914  to generate stimulation signals  916  at various frequencies and phases that can be selectively applied to drive lines of touch sensor panel  924 . In some examples, panel subsystem  906 , panel processor  902  and peripherals  904  can be integrated into a single application specific integrated circuit (ASIC). 
     Touch sensor panel  924  can include a capacitive sensing medium having a plurality of drive lines and a plurality of sense lines, although other sensing media can also be used. Additionally, one or more of the drive lines may be adapted to operate in sense mode according to various examples of the invention. Each intersection of drive and sense lines can represent a capacitive sensing node and can be viewed as picture element (pixel)  926 , which can be particularly useful when touch sensor panel  924  is viewed as capturing an “image” of touch. (In other words, after panel subsystem  906  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).) Each sense line of touch sensor panel  924  can drive sense channel  908  (also referred to herein as an event detection and demodulation circuit) in panel subsystem  906 . 
     Computing system  900  can also include host processor  928  for receiving outputs from panel processor  902  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 connected 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&#39;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. Host processor  928  can also perform additional functions that may not be related to panel processing, and can be connected to program storage  932  and display device  930  such as an LCD display for providing a UI to a user of the device. Display device  930  together with touch sensor panel  924 , when located partially or entirely under the touch sensor panel, can form touch screen  918 . 
     Note that one or more of the functions described above can be performed by firmware stored in memory (e.g. one of the peripherals  904  in  FIG. 9 ) and executed by panel processor  902 , or stored in program storage  932  and executed by host processor  928 . The firmware can also be stored and/or transported within any computer-readable 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 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 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 readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
       FIG. 10A  illustrates exemplary mobile telephone  1036  that can include touch sensor panel  1024  and display device  1030 , the touch sensor panel adapted for use with a stylus according to examples of the invention. 
       FIG. 10B  illustrates exemplary digital media player  1040  that can include touch sensor panel  1024  and display device  1030 , the touch sensor panel adapted for use with a stylus according to examples of the invention. 
       FIG. 10C  illustrates exemplary personal computer  1044  that can include touch sensor panel (trackpad)  1024  and display  1030 , the touch sensor panel and/or display of the personal computer (in examples where the display is part of a touch screen) adapted for use with a stylus according to examples of the invention. The mobile telephone, media player and personal computer of  FIGS. 10A ,  10 B and  10 C can increase computational efficiency and preserve power by utilizing the stylus to provide stimulus signals for one or more sensory electrodes. 
     Although examples of this invention 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 examples of this invention as defined by the appended claims.