Patent Publication Number: US-2012026123-A1

Title: Compensation for Capacitance Change in Touch Sensing Device

Description:
FIELD 
     This relates generally to touch sensing devices and, more particularly, to compensation for undesirable capacitance changes in a touch sensing device. 
     BACKGROUND 
     Touch sensitive devices have become quite popular as input devices to computing systems 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 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. 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. 
     At times, environmental conditions and device operations can adversely affect the touch sensitive device&#39;s ability to recognize a touch event. For example, capacitance changes due to a change in the device temperature caused by either an ambient temperature change or heat from device components can mask a real touch event or erroneously indicate a false touch event. Because a touch sensitive device cannot avoid generating some heat during operation and cannot control the outside environment, it can be difficult to prevent errors in touch event recognition. 
     SUMMARY 
     This relates to compensation for undesirable capacitance changes in a touch sensing device. The capacitance changes, which can be caused by environmental changes and/or device operating changes and not by a touch, can mask an actual touch at the device and/or erroneously indicate a false touch. To compensate for such capacitance changes, the touch sensing device can include one or more reference conductive traces decoupled from touch sensors of the device to measure non-touch capacitance. The touch sensing device can then adjust a touch signal with the non-touch capacitance measurement to substantially reduce or eliminate the non-touch capacitance from the signal. In one example, the reference trace can be disposed on a flexible circuit of the touch sensing device parallel to a conductive trace that transmits the touch signal from a touch sensor panel of the device, thereby giving an indication of the non-touch capacitance introduced by the conductive trace. In another example, the reference trace can be extended onto the touch sensor panel parallel to a touch sensor trace that transmits the touch signal from a touch sensor to the conductive trace on the flexible circuit, thereby giving an indication of the non-touch capacitances introduced by the touch sensor trace and the conductive trace. In still another example, the reference trace can be extended further onto the touch sensor panel to couple to a conductive element on the panel that measures non-touch capacitance of the touch sensor, thereby giving an indication of the non-touch capacitances introduced by the touch sensor, the touch sensor trace, and the conductive trace. In another example, the reference trace coupled to a touch controller of the touch sensing device (to which the reference trace transmits the non-touch capacitances of the touch sensor, the touch sensor trace, and/or the conductive trace) can give an indication of the non-touch capacitance introduced by various components on the touch controller. Compensation for undesirable capacitance changes in the touch sensing device can advantageously provide a more accurate and reliable touch signal regardless of the conditions and circumstances in which the device operates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary touch sensing device that can compensate for capacitance changes according to various embodiments. 
         FIG. 2  illustrates another exemplary touch sensing device that can compensate for capacitance changes according to various embodiments. 
         FIG. 3  illustrates another exemplary touch sensing device that can compensate for capacitance changes according to various embodiments. 
         FIG. 4  illustrates another exemplary touch sensing device that can compensate for capacitance changes according to various embodiments. 
         FIG. 5  illustrates an exemplary method to compensate for capacitance changes in a touch sensing device according to various embodiments. 
         FIG. 6  illustrates an exemplary computing system that can compensate for capacitance changes according to various embodiments. 
         FIG. 7  illustrates an exemplary mobile telephone that can compensate for capacitance changes according to various embodiments. 
         FIG. 8  illustrates an exemplary digital media player that can compensate for capacitance changes according to various embodiments. 
         FIG. 9  illustrates an exemplary personal computer that can compensate for capacitance changes according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     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 compensation for undesirable capacitance changes in a touch sensing device, where the capacitance changes are not indicative of a touch at the device, but of environmental changes or device operating changes. Environmental changes can include ambient temperature, humidity, and barometric pressure changes. Device operating changes can include start-up, shutdown, and prolonged operation of device components. To compensate for such capacitance changes, the touch sensing device can include one or more reference conductive traces decoupled from touch sensors of the device to measure non-touch capacitances in the device. The touch sensing device can then adjust a touch signal from the touch sensors using the non-touch capacitance measurements to substantially reduce or eliminate the non-touch capacitances from the signal. 
     The touch sensing device can include a touch sensor panel having one or more touch sensors for sensing a touch at the panel, a flexible circuit for transmitting the sensed touch signal from the panel, and a touch controller for receiving and processing the transmitted signal. In one embodiment, the reference trace can be disposed on the flexible circuit parallel to a conductive trace that transmits the touch signal from the touch sensor panel to the touch controller, thereby giving an indication of the non-touch capacitance introduced by the conductive trace. One end of the reference trace can be coupled to the touch controller to transmit the non-touch capacitance thereto. The other end of the reference trace can be free on the flexible circuit. 
     In another embodiment, the reference trace can be extended onto the touch sensor panel parallel to a touch sensor trace that transmits the touch signal from a touch sensor to the conductive trace on the flexible circuit, thereby giving an indication of the non-touch capacitances introduced by the touch sensor trace and the conductive trace. One end of the reference trace can be coupled to the touch controller to transmit the non-touch capacitances thereto. The other end of the reference trace can be free on the touch sensor panel. 
     In still another embodiment, the reference trace can be extended further onto the touch sensor panel to couple to a conductive element on the panel that measures non-touch capacitance of the touch sensor, thereby giving an indication of the non-touch capacitances introduced by the touch sensor, the touch sensor trace, and the conductive trace. One end of the reference trace can be coupled to the touch controller to transmit the non-touch capacitances thereto. The other end of the reference trace can be coupled to the conductive element on the panel. 
     In another embodiment, the reference trace coupled to the touch controller can give an indication of the non-touch capacitance introduced by various components on the touch controller along with non-touch capacitances of the conductive trace, the touch sensor trace, and/or the touch sensor. 
     Compensating for undesirable capacitance changes can advantageously realize more accurate and reliable touch measurements regardless of the conditions and circumstances in which the touch sensing device operates. 
       FIG. 1  illustrates an exemplary touch sensing device that can compensate for undesirable capacitance changes according to various embodiments. In the example of  FIG. 1 , touch sensing device  100  can include touch sensor panel  120 , flexible circuit  130 , and touch controller  140  to sense a touch or near-touch (hover) at the device. As an object approaches the panel  120 , a small capacitance can form between the object and capacitive touch sensors  122  proximate to the object. Touch signals indicating changes in capacitance caused by this small capacitance and the position of the touch sensor  122 - a  sensing the object can be transmitted along sensor trace  126  through the flexible circuit  130  to the touch controller  140  for processing. The capacitive touch sensors  122  can be based on self capacitance. 
     In a self capacitance sensor panel, the self capacitance of a touch sensor can be measured relative to some reference, e.g., ground. The touch sensors  122  can be spatially separated electrodes. The touch sensors  122  can be indium-tin-oxide (ITO) or any suitable conductive material. Each electrode can define a touch sensor  122 . The electrodes can be coupled to driving circuitry via conductive traces (not shown) and to sensing circuitry, e.g., the touch controller  140 , via sensor traces  126 . The sensor traces  126  can be silver, copper, or any suitable conductive material. Each touch sensor electrode  122  can have a sensor trace  126 . Touches, near-touches (hovers), and gestures can be detected at the panel  120  by measuring changes in the capacitance of the electrode forming the touch sensor  122 . 
     During operation, the total capacitance along a sensing path can be measured from the touch sensors  122  to the touch controller  140 . Under normal conditions, in some embodiments, the capacitance of the touch sensors  122  can be approximately 12 picofarads (pF), the sensor traces  126  approximately 2 pF, the conductive traces  132  approximately 8-10 pF, and various components at the touch controller  140  about 2 pF. In some embodiments, a touch at the touch sensors  122  can increase the total capacitance by 0.3 to 1.5 pF. Upon measuring this increase, the touch controller  140  can deduce that there has been a touch at the panel  120  and perform further processing accordingly. 
     However, when the device experiences environmental changes or device operating changes that cause the device temperature, for example, to increase, the dielectric constants and/or the geometry of the device materials can change, thereby increasing the capacitances of proximate conductive components. In some instances, the capacitance change due to environmental changes or device operating changes can exceed the capacitance change due to a touch. Some materials can be more sensitive to environmental or device changes than others and therefore more prone to change their dielectric constants. For example, the touch sensor panel substrate can be glass or like substrates, which can be less sensitive to changes; whereas the flexible circuit substrate can be polyimide or like flexible polymers, which can be more sensitive to changes. In some instances, the flexible circuit&#39;s conductive components can contribute a majority of the increase in capacitance when there are environmental or device operating changes. Therefore, eliminating or reducing the contributions from at least the flexible circuit&#39;s components can substantially reduce or eliminate the effects of the changes. 
     To do so, referring again to  FIG. 1 , reference trace  134  can be disposed on the flexible circuit  130  parallel to the conductive trace  132 , but decoupled from the touch sensor  122 - a . As such, the reference trace  134  can provide the same or a similar capacitance as the conductive trace  132 . When there is an environmental or device operating change that causes a temperature increase, for example, in the flexible circuit  130 , the capacitance of the reference trace  134  and the conductive trace  132  can increase or otherwise change in a similar manner. The amount of the increase may not be readily apparent on the conductive trace  132  because the trace may also include a touch signal. However, since the reference trace  134  is decoupled from the touch sensor  122 - a , the reference trace can have just the capacitance measurement. Therefore, the amount of the capacitance increase can be measured from the reference trace  134  and applied to the transmitted touch signal to substantially reduce or eliminate the conductive trace&#39;s capacitance increase from the signal. This can provide a more accurate touch measurement despite the undesirable capacitance change. 
     Similarly, a hover measurement can be adjusted by applying the capacitance measurement from the reference trace  134  to the transmitted hover signal to substantially reduce or eliminate the conductive trace&#39;s capacitance increase from the signal. A touch and hover measurement can be similarly adjusted to substantially reduce or eliminate the conductive trace&#39;s capacitance increase from the transmitted touch and hover signal. 
     In alternate embodiments, one or more additional reference traces can be disposed on the flexible circuit parallel to the conductive trace, but decoupled from the touch sensors. Capacitances can vary somewhat by location on the flexible circuit according to the number of neighboring traces, which can parasitically couple with a trace. As such, a reference trace can be placed in the middle of the flexible circuit, while another reference trace can be placed at an edge of the flexible circuit. The appropriate edge and/or center reference trace can then be used to correspondingly compensate neighboring conductive traces that are either edge or center races. Alternatively, an average capacitance from the reference traces can be calculated and applied to the touch measurement to compensate for the undesirable capacitance changes. Or the capacitance(s) of the reference trace(s) closest to the conductive trace can be applied to the touch measurement. 
     It is to be understood that the touch sensor arrangement is not limited to that illustrated herein, but can be a radial, circular, diamond, diagonal, and like arrangements according to the needs of the device. 
     It is to be further understood that the touch sensing device is not limited to self capacitance, but can be based on mutual capacitance as well. In a mutual capacitance sensor panel, the mutual capacitance of a touch sensor can be measured between two conductors. The touch sensors can be formed by the crossing of patterned conductors forming spatially separated drive and sense lines, or by placing the drive and sense lines adjacent to each other. Driving circuitry can be coupled to the drive lines and sensing circuitry can be coupled to the sensing lines. Touches, near-touches (hovers), and gestures can be detected at the panel by measuring changes in the capacitance between the drive and sense lines associated with the touch sensor. 
       FIG. 2  illustrates another exemplary touch sensing device that can compensate for undesirable capacitance changes according to various embodiments. The device of  FIG. 2  is the same as the device of  FIG. 1  except for the following addition. In the example of  FIG. 2 , reference trace  234  can extend onto touch sensor panel  220  to be proximate to sensor trace  226 . As a result, the reference trace  234  can have a same or similar capacitance as the sensor trace  226  in addition to having a same or similar capacitance as the conductive trace  232 . While the flexible circuit  230  can contribute to an undesirable capacitance change, the touch sensor panel  220  can also contribute, such that eliminating or substantially reducing the effects of the panel can likewise be helpful. When there is an environmental or device operating change that causes a temperature increase, for example, in touch sensor panel  120 , the capacitance of the reference trace  134  and the sensor trace  126  can increase. The amount of the increase may not be readily apparent on the sensor trace  226  because the trace may also include a touch signal. However, since the reference trace  234  is decoupled from the touch sensor  222 - a , the reference trace can just have the capacitance measurement. The amount of the increase can therefore be measured from the reference trace  234  and applied to the transmitted touch signal to substantially reduce or eliminate the sensor trace&#39;s capacitance increase from the signal. As described in  FIG. 1 , the amount of the increase in the conductive trace&#39;s  232  capacitance can also be measured from the reference trace  234  and applied to the transmitted touch signal to substantially reduce or eliminate the conductive trace&#39;s capacitance increase from the signal. Application of the reference trace capacitance measurement can provide a more accurate touch measurement despite the undesirable capacitance changes. 
       FIG. 3  illustrates another exemplary touch sensing device that can compensate for capacitance changes according to various embodiments. The device of  FIG. 3  is the same as the device of  FIG. 2  except for the following addition. In the example of  FIG. 3 , reference trace  334  can extend further onto touch sensor panel  320  to be coupled to conductive element  328 . The conductive element  328  can be ITO similar to the touch sensors  322 . As a result, the conductive element  328  can have a same or similar capacitance as the touch sensors  322 . When there is an environmental or device operating change that cause a temperature increase, for example, in the touch sensor panel  320 , the capacitance of the conductive element  328  and the touch sensors  322  can increase or otherwise change in a similar manner. The amount of the increase may not be readily apparent on the touch sensors  322  because the sensors may also include a touch signal. However, since the conductive element  328  is not coupled to the touch sensor  322 - a , the conductive element can have just the capacitance measurement associated with an environmental or device operating change. The amount of the increase can therefore be measured from the conductive element  328  and therefore the reference trace  324  and applied to the transmitted touch signal to substantially reduce or eliminate the touch sensors&#39; non-touch capacitance increase from the signal. As described in  FIG. 2 , the amount of increase in the sensor trace&#39;s  326  and the conductive trace&#39;s  332  capacitances can also be measured from the reference trace  324  and applied to the transmitted touch signal to substantially reduce or eliminate the sensor trace&#39;s and the conductive trace&#39;s capacitance increases from the signal. Application of the reference trace capacitance measurement can provide a more accurate touch measurement despite the undesirable capacitance changes. 
     In an alternate embodiment, the reference trace can couple to the conductive element without following the sensor trace such that the reference trace can provide capacitance increases of the touch sensor on the touch sensor panel and the conductive traces on the flexible circuit. This embodiment may be useful when the sensor traces&#39; capacitance increases are not very significant, when space is limited on the panel, or for any suitable reason. 
       FIG. 4  illustrates another exemplary touch sensing device that can compensate for undesirable capacitance changes according to various embodiments. The device of  FIG. 4  is the same as the device of  FIG. 1  except for the following. In the example of  FIG. 4 , reference trace  434  can extend only part of the length of conductive trace  432 . This arrangement can be useful when the flexible circuit  430  is space-limited. Similar to reference trace  134  of  FIG. 1 , the reference trace  434  of  FIG. 4  can transmit a capacitance measurement indicative of a capacitance change in the conductive trace  432  caused by environmental or device operating changes affecting the flexible circuit  430 . The amount of the increase can therefore be measured from the reference trace  434  and applied to the transmitted touch signal to substantially reduce or eliminate the conductive trace&#39;s  432  capacitance increase from the signal. The amount of capacitance applied to the transmitted touch signal can be scaled either proportionally or otherwise to more closely approximate the conductive trace&#39;s  432  capacitance with the reduced reference trace  434 . Application of the reference trace capacitance measurement can provide a more accurate touch measurement despite the undesirable capacitance change. 
     As illustrated in  FIGS. 1 through 4 , the reference trace can be coupled to the touch controller to transmit capacitance measurements thereto. Various components of the touch controller can also introduce undesirable capacitance changes into the touch sensing device. Accordingly, the reference trace can measure capacitance changes of these components, which can be used along with the measurements associated with the conductive traces on the flexible circuit, the sensor traces on the touch sensor panel, and/or the conductive elements on the touch sensor panel to adjust touch measurements. 
       FIG. 5  illustrates an exemplary method to compensate for undesirable capacitance changes in a touch sensing device according to various embodiments. In the example of  FIG. 5 , a touch controller can measure a touch signal from a touch sensor that is transmitted to the controller through a conductive trace on a flexible circuit coupled to the touch sensor ( 510 ). The touch signal can include a first capacitance indicative of a touch at the touch sensor and a second capacitance indicative of an environmental or device operating change affecting the flexible circuit. The touch controller can measure the second capacitance from a reference trace on the flexible circuit parallel and proximate to the conductive trace, but decoupled from the touch sensor ( 520 ). The touch controller can then adjust the touch measurement based on the second capacitance measurement to compensate the touch measurement for the undesirable capacitance change ( 530 ). The result can be a more accurate touch measurement despite the capacitance change. 
     In alternate embodiments, the touch controller can measure the second capacitance from a reference trace on the touch sensor panel and the flexible circuit, where a portion of the reference trace is parallel and proximate to a sensor trace on the panel and another portion of the reference trace is parallel and proximate to a conductive trace on the flexible circuit ( 520 ). 
     In alternate embodiments, the touch controller can measure the second capacitance from a reference trace coupled to a conductive element on the touch sensor panel in addition to being parallel and proximate to the sensor trace on the panel and/or the conductive trace on the flexible circuit ( 520 ). 
     The method of  FIG. 5  can be implemented according to various embodiments. In one embodiment, the method can account for a change in measured touch sensor capacitance by measuring the change in the reference trace on the flexible circuit and scaling the result accordingly. 
     This method can start with the assumption that the untouched sensor capacitance is made up of the flexible circuit substrate capacitance, C flex , plus the touch sensor panel substrate capacitance, C panel , and that the flexible circuit capacitance is fully known from measurements of the reference trace on the flexible circuit. 
         C   sensor   =C   panel   +C   flex .  (1)
 
     In order to measure capacitance changes, baseline values can be known for the flexible circuit (the reference trace) and overall touch sensor (panel+flexible circuit). These values can be obtained anytime when the sensor is untouched, such as during a factory calibration. Considering the example of temperature compensation, suppose the calibration measurement was taken at temperature T 1  and the current measurement is at temperature T 2 . As such, the change in capacitance for the flexible circuit can be 
       Δ C   flex   =C   flex     —     T2   −C     —     flex     —     T1   (2)
 
     and for the sensor, 
       Δ C   sensor   =C   sensor     —     T2   −C   sensor     —     T1 .  (3)
 
     Using Equations (1), (2), and (3), the change in capacitance for the panel substrate can be 
       Δ C   panel   =C   panel     —     T2   −C   panel     —     T1 .  (4)
 
     The panel substrate capacitance can track the flexible circuit capacitance and can be scaled according to the ratio of the capacitances (i.e., the percent capacitance change can track) and can additionally have a scaling factor α if the temperature coefficients of the panel substrate and the flexible circuit are different. This can be expressed as 
     
       
         
           
             
               
                 
                   
                     
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     If the original values of C flex     —     T1  and C sensor     —     T1  are known at temperature T 1 , and the change of the flexible circuit capacitance is known from the reference trace, then a sensor measurement at temperature T 2  can be scaled back to the reference temperature T 1 , using the formula 
         C   sensor     —     comp   =C   sensor     —     T2   −ΔC   flex   −ΔC   panel   (6)
 
     where ΔC panel  can be estimated from Equation (5) and the measured ΔC flex . Substituting from Equation (5) into Equation (6), the compensated sensor measurement can be expressed as 
     
       
         
           
             
               
                 
                   
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     Here, the change in flexible circuit capacitance and the change in panel substrate capacitance can be subtracted from the sensor measurement to provide the compensated sensor measurement. The scaling factor α can typically vary from 0.5 to 2, but can span an even larger range if the panel substrate and the flexible circuit are vastly different in temperature sensitivity, one being more temperature sensitive than then other. 
     If the reference trace is shorter than the conductive traces, as shown in  FIG. 4 , the capacitance change can first be scaled by the length of the conductive trace  432  to the reference trace  434  prior to applying the above method. 
     An alternative method can simply assume that the overall sensor measurement tracks proportionally with the flexible circuit capacitance, according to 
     
       
         
           
             
               
                 
                   
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                     sensor_comp 
                   
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     Here, it can be assumed that the panel substrate temperature coefficient matches the flexible circuit temperature coefficient and, therefore, has additional error taken into account. 
     Although these example methods address temperature compensation, they can apply equally well to other environmental changes, e.g., humidity and pressure, and to design operating changes. 
     It is to be understood that the method of  FIG. 5  is not limited to these embodiments, but can include other methods suitable for compensating a touch measurement for environmental or device operating changes. 
       FIG. 6  illustrates an exemplary computing system  600  that can compensate for an undesirable capacitance change in a touch sensing device according to various embodiments described herein. In the example of  FIG. 6 , computing system  600  can include touch controller  606 . The touch controller  606  can be a single application specific integrated circuit (ASIC) that can include one or more processor subsystems  602 , which can include one or more main processors, such as ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the processor functionality can be implemented instead by dedicated logic, such as a state machine. The processor subsystems  602  can also include peripherals (not shown) such as random access memory (RAM) or other types of memory or storage, watchdog timers and the like. The touch controller  606  can also include receive section  607  for receiving signals, such as touch signals  603  of one or more sense channels (not shown), other signals from other sensors such as sensor  611 , etc. The touch controller  606  can also include demodulation section  609  such as a multistage vector demodulation engine, panel scan logic  610 , and transmit section  614  for transmitting stimulation signals  616  to touch sensor panel  624  to drive the panel. The panel scan logic  610  can access RAM  612 , autonomously read data from the sense channels, and provide control for the sense channels. In addition, the panel scan logic  610  can control the transmit section  614  to generate the stimulation signals  616  at various frequencies and phases that can be selectively applied to rows of the touch sensor panel  624 . 
     The touch controller  606  can also include charge pump  615 , which can be used to generate the supply voltage for the transmit section  614 . The stimulation signals  616  can have amplitudes higher than the maximum voltage by cascading two charge store devices, e.g., capacitors, together to form the charge pump  615 . 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  FIG. 6  shows the charge pump  615  separate from the transmit section  614 , the charge pump can be part of the transmit section. 
     Touch sensor panel  624  can include a capacitive sensing medium having electrodes for detecting a touch at the panel. The electrodes can be formed from a 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. Each electrode can represent a capacitive sensing node and can be viewed as picture element (pixel)  626 , which can be particularly useful when the touch sensor panel  624  is viewed as capturing an “image” of touch. (In other words, after the touch controller  606  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 panel at which a touch event occurred can be viewed as an “image” of touch (e.g. a pattern of fingers touching the panel).) 
     Computing system  600  can also include host processor  628  for receiving outputs from the processor subsystems  602  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&#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. The host processor  628  can also perform additional functions that may not be related to panel processing, and can be coupled to program storage  632  and display device  630  such as an LCD display for providing a UI to a user of the device. In some embodiments, the host processor  628  can be a separate component from the touch controller  606 , as shown. In other embodiments, the host processor  628  can be included as part of the touch controller  606 . In still other embodiments, the functions of the host processor  628  can be performed by the processor subsystem  602  and/or distributed among other components of the touch controller  606 . The display device  630  together with the touch sensor panel  624 , 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. 
     Compensation for a capacitance change can be determined by the processor in subsystem  602 , the host processor  628 , dedicated logic such as a state machine, or any combination thereof according to various embodiments. 
     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  602 , or stored in the program storage  632  and executed by the host processor  628 . 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. 
       FIG. 7  illustrates an exemplary mobile telephone  700  that can include a display  736  and a touch sensor panel  724  that can compensate for capacitance changes according to various embodiments. 
       FIG. 8  illustrates an exemplary digital media player  800  that can include a display  836  and a touch sensor panel  824  that can compensate for capacitance changes according to various embodiments. 
       FIG. 9  illustrates an exemplary personal computer  900  that can include a touch sensitive display  936  and a touch sensor panel (trackpad)  924 , where the touch sensitive display and the trackpad can compensate for capacitance changes according to various embodiments. 
     The mobile telephone, media player, and personal computer of  FIGS. 7 through 9  can advantageously adapt to various operating conditions to provide more accurate touch sensing with a touch sensor panel that can compensate for capacitance changes according to various embodiments. 
     Although embodiments describe touch sensors, it is to be understood that proximity and other types of sensors can also be used. It is to be further understood that the touch sensing device according to various embodiments can be used to compensate hover measurements, combined touch and hover measurements, and the like for undesirable capacitance changes. 
     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.