PATENT DOCUMENT

Publication Number: US-10459546-B2
Application Number: US-201313830127-A
Country: US
Kind Code: B2

Title: Channel aggregation for optimal stylus detection

Abstract:
A touch input device configured to detect stylus signals generated by an external stylus is provided. The touch input device includes a plurality of stylus signal detectors that receive at its input a combination of stylus receive channels that are combined in a manner to minimize noise while at the same time keeping the stylus signal strength uniform independent of the position of the stylus on the device.

Claims:
What is claimed is: 
     
       1. A stylus detection apparatus for detecting an asynchronous active stylus, the apparatus comprising:
 a plurality of sense channels, each sense channel including an amplifier, wherein the plurality of sense channels are configured to sense signals at a plurality of electrodes of a touch sensor panel, the signals including one or more stylus signals generated by the asynchronous active stylus; 
 a channel aggregator coupled to receive outputs of the plurality of sense channels and configured to generate one or more aggregated signals based on combinations of the outputs of the plurality of sense channels, wherein the channel aggregator is configured to sum at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and 
 one or more stylus signal detectors, each stylus signal detector configured to:
 receive one of the aggregated signals from the channel aggregator; 
 detect one of the stylus signals based on the received aggregated signal; and 
 estimate a start time and an end time for the detected stylus signal. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein the plurality of first electrodes are chosen such that a detected signal strength of the stylus signal is uniform and independent of the active stylus&#39; position on the touch sensor panel. 
     
     
       3. The apparatus of  claim 1 , wherein the channel aggregator is further configured to subtract one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously. 
     
     
       4. The apparatus of  claim 3 , wherein the one or more second electrodes are chosen such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes. 
     
     
       5. The apparatus of  claim 3 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive. 
     
     
       6. The apparatus of  claim 1 , wherein a number of the stylus signal detectors is based in part on a spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel. 
     
     
       7. A method for detecting an asynchronous active stylus, the method comprising:
 sensing, by a plurality of sense channels, one or more active stylus signals at a plurality of electrodes of a touch sensor panel, the one or more active stylus signals generated by the asynchronous active stylus, wherein each sense channel includes an amplifier; 
 generating one or more aggregated signals based on combinations of outputs of the plurality of sense channels, wherein generating the one or more aggregated signals includes summing at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and 
 at a stylus signal detector:
 detecting one of the stylus signals based on the received aggregated signal; and 
 estimating a start time and an end time for the detected stylus signal. 
 
 
     
     
       8. The method of  claim 7 , further comprising choosing the plurality of first electrodes such that the detected signal strength of the stylus signal is uniform and independent of the active stylus&#39; position on the touch sensor panel. 
     
     
       9. The method of  claim 7 , wherein generating the one or more aggregated signals further includes subtracting one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously. 
     
     
       10. The method of  claim 9 , further comprising choosing the one or more second electrodes such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes. 
     
     
       11. The method of  claim 9 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive. 
     
     
       12. The method of  claim 7 , wherein a number of the stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel. 
     
     
       13. A non-transitory computer readable storage medium having stored thereon a set of instructions for detecting an asynchronous active stylus that when executed by a processor causes the processor to:
 sense, by a plurality of sense channels, one or more active stylus signals at a plurality of electrodes of a touch sensor panel, the one or more active stylus signals generated by the asynchronous active stylus, wherein each sense channel includes an amplifier; 
 generate one or more aggregated signals based on combinations of outputs of the plurality of sense channels, wherein generating the one or more aggregated signals includes summing at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and 
 at a stylus signal detector:
 receive one of the aggregated signals; 
 detect one of the stylus signals based on the received aggregated signal; and 
 estimate a start time and an end time for the detected stylus signal. 
 
 
     
     
       14. The non-transitory computer readable storage medium of  claim 13 , wherein the processor is further caused to choose the plurality of first electrodes such that the detected signal strength of the stylus signal is uniform and independent of the active stylus&#39; position on the touch sensor panel. 
     
     
       15. The non-transitory computer readable storage medium of  claim 13 , wherein generating the one or more aggregated signals further includes subtracting one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously. 
     
     
       16. The non-transitory computer readable storage medium of  claim 15 , wherein the processor is further caused to choose the one or more second electrodes such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes. 
     
     
       17. The non-transitory computer readable storage medium of  claim 15 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive. 
     
     
       18. The non-transitory computer readable storage medium of  claim 13 , wherein a number of the stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel. 
     
     
       19. The apparatus of  claim 1 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for at least one of the stylus signal detectors. 
     
     
       20. The method of  claim 7 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for the stylus signal detector. 
     
     
       21. The non-transitory computer readable storage medium of  claim 13 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for the stylus signal detector. 
     
     
       22. The apparatus of  claim 1 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal. 
     
     
       23. The method of  claim 7 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal. 
     
     
       24. The non-transitory computer readable storage medium of  claim 13 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal.

Description:
FIELD 
     This relates generally to touch sensitive devices and, more specifically, to touch sensitive devices which can also accept input from a stylus. 
     BACKGROUND 
     Touch sensitive devices have become popular as input devices to computing systems due to 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 or integrated with 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. 
     As touch sensing technology continues to improve, touch sensitive devices are increasingly being used to compose and mark-up electronic documents. In particular, styli have become popular input devices as they emulate the feel of traditional writing instruments. Most conventional styli simply include a bulky tip made of a material capable of interacting with the touch sensitive device and resembling a user&#39;s finger. As a result, conventional styli lack the precision and control of traditional writing instruments. A stylus capable of receiving stimulation and force signals and generating stylus stimulation signals that can be transmitted to the touch sensitive device can improve the precision and control of the stylus. However, such a stylus can present demodulation challenges to the touch sensitive device due to the asynchronous interaction between the stylus and the device. 
     SUMMARY 
     A stylus signal detection technique and apparatus that can facilitate synchronous demodulation on a touch input device is disclosed. 
     In one example, a stylus signal can be detected and the detector can estimate the start and end time of the stylus signal. The estimated start and end time of the stylus signal can then be used to generate a window to be used by a digital demodulator to effectively and efficiently demodulate the stylus signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary touch sensor that can be used with a touch sensitive device according to various examples. 
         FIG. 2  illustrates a block diagram of an exemplary stylus according to various examples. 
         FIG. 3  illustrates a control system for a touch sensor that can detect both a user&#39;s touch and signals from a stylus according to disclosed examples. 
         FIG. 4  illustrates an example stylus signal waveform according to examples of the disclosure. 
         FIG. 5  illustrates an example touch/stylus demodulation circuit according to examples of the disclosure. 
         FIG. 6  illustrates a method of detecting the beginning and the end of a stylus signal waveform according to examples of the disclosure. 
         FIG. 7  illustrates an example stylus signal detector, integrated into a demodulation circuit according examples of the disclosure. 
         FIG. 8  illustrates an example concept for a stylus signal detector according to examples of the disclosure. 
         FIG. 9  illustrates an example implementation of an envelope detector according to examples of the disclosure. 
         FIG. 10  illustrates an exemplary centroid peak detection method according to examples of the disclosure. 
         FIG. 11 a    illustrates an example stylus detector aggregation scheme according to examples of the disclosure. 
         FIG. 11 b    illustrates a corresponding detector chart to the aggregation scheme of  FIG. 11   a.    
         FIG. 12 a    illustrates another exemplary stylus detector aggregation scheme according to examples of the disclosure. 
         FIG. 12 b    illustrates the corresponding detector chart of  FIG. 12 a    according to examples of the disclosure. 
         FIG. 13 a    represents yet another exemplary stylus detector aggregation scheme according to examples of the disclosure. 
         FIG. 13 b    illustrates a detector chart corresponding to the example of  FIG. 13 a    according to examples of the disclosure 
         FIG. 14  illustrates an exemplary detector chart of a stylus detector aggregation scheme according to examples of the disclosure. 
         FIG. 15 a    illustrates an exemplary detector aggregation scheme according to examples of the disclosure. 
         FIG. 15 b    illustrates a corresponding detector chart to the aggregation schemed depicted in  FIG. 15 a    according to examples of the disclosure. 
         FIG. 16  illustrates an aggregation scheme that uses only two detectors according to examples of the disclosure. 
         FIG. 17  illustrates an exemplary aggregation scheme according to examples of the disclosure. 
         FIG. 18  is a block diagram of an example computing system that illustrates one implementation of a touch sensor panel display with stylus signal noise correction according to examples of the disclosure. 
         FIG. 19  illustrates an exemplary system for generating or processing a stylus stimulation signal according to examples of the disclosure. 
         FIG. 20 a - d    illustrate exemplary personal devices that include a touch sensor according to various examples. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that 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 various examples. 
     This relates to synchronizing a detected stylus signal with a windowing function in order to facilitate efficient demodulation of a stylus. In one example, a stylus signal can be processed by a detector which can detect an end point of a stylus signal in the time domain, and based on the end point can estimate the beginning of the stylus signal. After obtaining the start and end times of a stylus signal, the demodulator can then synchronize the signal to an appropriately sized windowed demodulation scheme in order to achieve efficient demodulation of the stylus signal on a touch sensor panel. 
     In some examples, the detectors used to determine the beginning and end of a stylus signal can be aggregated in various architectures throughout the touch sensor panel in order to efficiently detect stylus signals while at the same time providing a robust detection scheme that protects against common mode noise. 
       FIG. 1  illustrates touch sensor  100  that can be used to detect touch events on a touch sensitive device, such as a mobile phone, tablet, touchpad, portable computer, portable media player, or the like. Touch sensor  100  can include an array of touch regions or nodes  105  that can be formed at the crossing points between rows of drive lines  101  (D0-D3) and columns of sense lines  103  (S0-S4). Each touch region  105  can have an associated mutual capacitance Csig  111  formed between the crossing drive lines  101  and sense lines  103  when the drive lines are stimulated. The drive lines  101  can be stimulated by stimulation signals  107  provided by drive circuitry (not shown) and can include an alternating current (AC) waveform. The sense lines  103  can receive touch signals  109  indicative of a touch at the touch sensor  100  to sense circuitry (not shown), which can include a sense amplifier for each sense line, or a fewer number of sense amplifiers that can be multiplexed to connect to a larger number of sense lines. 
     To sense a touch at the touch sensor  100 , drive lines  101  can be stimulated by the stimulation signals  107  to capacitively couple with the crossing sense lines  103 , thereby forming a capacitive path for coupling charge from the drive lines  101  to the sense lines  103 . The crossing sense lines  103  can output touch signals  109 , representing the coupled charge or current. When an object, such as a passive stylus, finger, etc., touches the touch sensor  100 , the object can cause the capacitance Csig  111  to reduce by an amount ΔCsig at the touch location. This capacitance change ΔCsig can be caused by charge or current from the stimulated drive line  101  being shunted through the touching object to ground rather than being coupled to the crossing sense line  103  at the touch location. The touch signals  109  representative of the capacitance change ΔCsig can be received by the sense lines  103  to the sense circuitry for processing. The touch signals  109  can indicate the touch region where the touch occurred and the amount of touch that occurred at that touch region location. 
     While the example shown in  FIG. 1  includes four drive lines  101  and five sense lines  103 , it should be appreciated that touch sensor  100  can include any number of drive lines  101  and any number of sense lines  103  to form the desired number and pattern of touch regions  105 . Additionally, while the drive lines  101  and sense lines  103  are shown in  FIG. 1  in a crossing configuration, it should be appreciated that other configurations are also possible to form the desired touch region pattern. While  FIG. 1  illustrates mutual capacitance touch sensing, other touch sensing technologies may also be used in conjunction with examples of the disclosure, such as self-capacitance touch sensing, resistive touch sensing, projection scan touch sensing, and the like. Furthermore, while various examples describe a sensed touch, it should be appreciated that the touch sensor  100  can also sense a hovering object and generate hover signals therefrom. 
       FIG. 2  illustrates a block diagram of an exemplary stylus  200  that can be used with a touch sensitive device, such as a mobile phone, touchpad, portable computer, or the like. Stylus  200  can generally include tip  201 , ring  203 , body  207 , and multiple stylus stimulation signal circuitry  205  located within body  207 . As will be described in greater detail below, stylus stimulation signal circuitry  205  can be used to generate a stimulation signal that can be transmitted to a touch sensitive device through tip  201 . Tip  201  can include a material capable of transmitting the stylus stimulation signal from stylus stimulation signal circuitry  205  to the touch sensitive device, such as a flexible conductor, a metal, a conductor wrapped by a non-conductor, a non-conductor coated with a metal, a transparent conducting material (e.g., indium tin oxide (ITO)) or a transparent non-conductive material (e.g., glass) coated with a transparent (e.g., ITO) (if the tip is also used for projection purposes) or opaque material, or the like. In some examples, tip  201  can have a diameter of about 1.5 mm or less. Tip  201 , used to transmit stimulus signals from the stylus can be implemented using ring  203 . Ring  203  can include a conductive material, such as a flexible conductor, a metal, a conductor wrapped by a non-conductor, a non-conductor coated with a metal, a transparent conducting material (e.g., ITO) or a transparent non-conductive material (e.g., glass) coated with a transparent (e.g., ITO if the tip is used for projection purposes) or opaque material, or the like. Ring  203  can serve other purposes, such as providing an alternative means for transmitting the stylus stimulation signal from the stylus to the touch sensitive device. Similarly, tip  201  or ring  203  can also be used to sense the touch drive signal from the touch sensitive device. Both tip  201  and ring  203  can be segmented and each segment can be independently controlled according to the description above. 
       FIG. 3  illustrates a control system for a touch sensor that can detect both a user&#39;s touch or proximity and signals from a stylus according to disclosed examples. The sensor panel  314  of the touch sensor may be configured to detect touches on, or hovering over, the surface of the touch screen by changes in capacitance as described above in reference to  FIG. 1 . With reference to  FIG. 3 , a sensing node  344  formed by one or more electrodes (explained below) may form a first electrically conductive member and an object, such as a finger of the user, may form a second electrically conductive member. The sensor panel  314  of the touch screen may be configured as in a self-capacitance arrangement or in a mutual capacitance arrangement. 
     In the self-capacitance arrangement, electrodes may include a single layer of a plurality of electrodes spaced in a grid or other arrangement where each electrode may form a node  344 . The sensing circuit  350  can monitor changes in capacitance that may occur at each node  344 . These changes can typically occur at a node  344  when a user places an object (e.g., finger or tip  201  of the stylus  200 ) in close proximity to the electrode. 
     With continued reference to  FIG. 3 , in a mutual capacitance system, the electrodes may be separated into two layers forming drive lines  342  and sense lines  340 . The drive lines  342  may be formed on a first layer and the sense lines  340  may be formed on a second layer. The nodes  344  for the sensor panel  314  may be defined at locations where the drive lines  342  may cross over or under the sense lines  340  (although they are typically placed in different layers). The sense lines  340  may intersect the drive lines  342  in a variety of manners. For example, in one example, the sense lines  340  can be perpendicular to the drive lines  342 , thus forming nodes  344  with x and y coordinates. However, other coordinate systems can also be used, and the coordinates of the nodes  344  may be differently defined. 
     A drive controller  346  can be connected to each of the drive lines  342 . The drive controller  346  can provide a stimulation signal (e.g., voltage) to the drive lines  342 . The sensing circuit  350  can be connected to each of the sense lines  340  and the sensing circuit  350  can act to detect changes in capacitance at the nodes  344  in the same manner as described in  FIG. 1 . During operation, the stimulation signal can be applied to the drive lines  342  and due to the capacitive coupling between the drive lines  342  and sensing rows  340 , a current can be carried through to the sense lines  340  at each of the nodes  344 . The sensing circuit  350  can then monitor changes in capacitance at each of the nodes  344 . In some examples each drive line can be switchably configured to operate as sense lines, and thus a sensing circuit and multiplexer similar to  350  and  354  can be connected to the drive lines similar to the sense lines depicted in  FIG. 3 . 
     In either the self-capacitance or mutual capacitance arrangements discussed above, the sensing circuit  350  can detect changes in capacitance at each node  344 . This may allow the sensing circuit  350  to determine when and where a user has touched various surfaces of the touch screen  306  with one or more objects, or has come in close proximity to the various surfaces of the touch screen. The sensing circuit  350  may include one more sensors for each of the sense lines  340  and may then communicate data to a processor  348 . In one example, the sensing circuit  350  may convert the analog capacitive signals to digital data and then transmit the digital data to the processor  348 . In other examples, the sensing circuit  350  may transmit the analog capacitance signals to the processor  348 , which may then convert the data to a digital form. Further, it should be noted that the sensing circuit  350  may include individual sensors for each sensing line  342  or a single sensor for all of the sense lines  340 . The sensing circuit  350  may report a location of the node  344 , as well as the intensity of the capacitance (or changed thereof) at the node  344 . 
     In some examples, the touch screen may include one or more multiplexers. For example, during touch or proximity operation, the sensing circuit  350  may also include a multiplexer configured to perform time multiplexing for the sense lines  340 . For example, the sensing circuit  350  may receive signals from each of the nodes  344  along the sense lines  340  at approximately the same time, the multiplexer stores the incoming signals and then may release the signals sequentially to the processor  348  one at a time. As discussed above in some examples that are not pictured, the drive lines can be configured to also act as sense lines and thus can be configured with multiplexers and sense circuitry similar to the sense lines as described above. 
     In addition to the multiplexers that may be used to during a touch mode to process touch signals, the touch screen may also include a drive multiplexer  352  and/or a sense multiplexer  354 . These two input device multiplexers  352 ,  354  may be in communication with the respective set of lines  342 ,  344  to switch between a touch mode and a stylus or input device mode. As will be discussed in more detail below, during a stylus mode, in which the sensing circuit  350  is configured to detect input from a stylus or other input device, the touch screen may selectively scan the sense lines  340 , as well as the drive lines  342 , in order to receive data transmitted from the tip  202  of the stylus  200 . In these examples, the drive controller  346  may further be configured to sense for signals on the drive lines  342  in order to detect a signal transmitted from the tip  202  of the stylus  200 . In this manner, the drive lines  342  may be configured to act as sense lines  340  and interact with the tip  202  of the stylus  200  to receive one or more signals (e.g., voltage signals). In other words, rather than providing a stimulation signal to the drive lines  342 , during a stylus scan, if the stylus is transmitting, the stylus may apply a stimulation signal to the drive lines  342  (in the form of a data transmission signal). 
     In some examples, the drive lines  342  may be scanned after the input device has been detected by the sense lines. These examples may reduce the scanning time required for the touch screen to detect the input device, as the drive lines  342  may only be scanned in instances where the input device is actually present. Thus, if the input device is not detected, the touch screen may more quickly return to scanning for touch inputs. That said, it should be noted that when driving, the stylus  200  may provide a stimulation signal to both the sense and drive lines simultaneously and so in some instances both lines may be scanned simultaneously. However, in some examples, the sense lines  340  and drive lines  342  are scanned and demodulated sequentially (when the input device is detected) as this type of scanning may allow the touch screen to re-use the same touch hardware for both scanning and drive line scanning. That is, the sense circuitry may be multiplexed to the drive lines, to reduce the separate components that may be required by the touch screen. 
     Additionally, in some examples, the touch controller, such as the sense circuitry  350  and/or drive controller may analyze the input or stimulation signal transmitted from the input device in order to detect the position of the input device, as well as to receive data communication. In other words, the input signal may be used to detect location, and the same signal may be encoded with data from the input device. 
       FIG. 4  illustrates an example stylus signal waveform according to examples of the disclosure. In this example, stylus signal  400  can contain multiple steps  402 . Each step can be of a pre-determined time period T. A grouping of steps can be called a burst. For instance, as illustrated, a stylus burst  404  can be made up of 3 stylus steps. 
       FIG. 5  illustrates an example touch/stylus demodulation circuit according to examples of the disclosure. The circuit of  FIG. 5  shows an example implementation of a digital phase demodulation, known in the art. As illustrated, sense or drive line  502  can be inputted into detection circuitry  504 . The detection circuitry can provide buffering and other pre-detection signal processing needs. The analog signal output from the detection circuitry  504  can then be converted to digital samples via analog-to-digital converter (ADC)  506 . The output signal of ADC  506  can then be split into an I channel stream  508 , and a Q channel stream  510 , where they can each be multiplied by an in-phase and quadrature phase carrier, respectively. After being mixed with the in-phase and quadrature phase carrier, each stream can then be filtered using a matched filter  512  and  514 . 
     Matched filter  512  and  514  can be implemented digitally by employing a windowing function that can be synchronized with the start time of incoming signal and the end time of an incoming signal. Thus in order to implement an efficient digital matched filter, the demodulator may need to have prior knowledge of the start time of a signal and the end time of the signal. In a touch detection mode, knowledge of the start time and end time of a signal can be readily accessed since the signal transmission on the drive line and the demodulation of the touch signal can be performed by the same touch controller. The touch controller can know at what time the signal started transmission and at what time the transmission ended. However, in stylus detection mode, the system may not have knowledge of the start and end time of a signal due to the fact that the stylus generates signals outside of the touch sensor panel, and there may be no communication of the start and stop time of a stylus signal between the stylus and the demodulator, thus making implementation of a windowed demodulation function difficult. Thus, in order to implement a windowed digital demodulation on a stylus signal, the demodulator may need to ascertain the beginning and end of a signal, in order to create an appropriate window. 
       FIG. 6  illustrates a method of detecting the beginning and the end of a stylus signal waveform according to examples of the disclosure. In this example method, at step  600 , the end of the stylus step can be detected. A method of detecting the end of the stylus step is discussed further below. At step S 602 , based on the detected end time of the stylus signal, the beginning time of the stylus step can be estimated. Since a stylus step is of a pre-determined duration, by determining the end of the stylus signal, the beginning time can be known. At step S 604 , the information of the beginning and end time of the stylus step can be sent to the demodulators which can then employ a synchronized window function to perform the demodulation of the stylus signal as described above. 
       FIG. 7  illustrates an example stylus signal detector integrated into a demodulation circuit according examples of the disclosure. The circuit  700  can include an ADC  702  that digitizes the signals received from a touch/stylus sense channel. The digitized data can be fed into a first-in-first-out (FIFO) buffer  704  and detector  706 . FIFO buffer  704  can create a time delay between the time a signal enters the buffer, and the time that the signal exits the buffer. FIFO buffer  704  can store values of the signal outputted by ADC and can subsequently output the signals after a pre-determined amount of time has passed. Detector  706  (described in further detail below) can detect the presence of a stylus signal, determine the starting time of the stylus signal, and determine the end time. When detector  706  determines the beginning and end of the stylus signal, it can assert a signal on its output to enable multiplier  712  so that the output of the FIFO buffer  704  and demodulation waveform generator  708  can be multiplied together. Detector  706 , upon determining the beginning time of a stylus signal can enable multiplier  712  at the same time that FIFO buffer  704  begins to output the portion of the signal in the buffer corresponding to the beginning of the stylus signal. Detector  706  can then terminate the signal at its output, when the end of the stylus signal has passed out of FIFO buffer  704 . In this way, the detector can act to “window” the stylus signal, in order to effectuate efficient digital demodulation as described above. 
       FIG. 8  illustrates an example concept for a stylus signal detector according to examples of the disclosure.  FIG. 8  represents a time domain analysis of the stylus signal&#39;s interaction with an envelope detector. The detector  706  of  FIG. 7  in one example can act as envelope detector that integrates a signal over a specific window of time. The detector  706  can be represented by window  802 . The energy contained in window  802  at any given time can be represented by graph  804 , which is a plot of the energy in the window as a function of time. For example, at t1 on plot  806 , the stylus signal  814  has yet to enter the window  802 . Thus, the energy in the window  802  as plotted on graph  804  can be zero as shown at the t1 mark on  804 . At t2 on plot  808 , the beginning edge of the stylus signal  814  begins to appear in the window. At corresponding t2 of plot  804  the magnitude of the signal within the window begins to rise. As signal  814  moves further into the window the detected energy within the window. At t3 on plot  810  the entire stylus signal can be contained within the window. 
     As shown in plot  804  at t3, the energy reaches a peak value. At t4, as the stylus signal moves out of the window, the energy in the window corresponding to t4 diminishes. Finally as the stylus signal moves completely out of the window, the energy in the window can return to a minimal value. The length of window  802  can be pre-determined and can correspond to the length in time of a stylus step signal. So, for instance, if a stylus step is 140 μs long, the window of the envelope detector can be set to 140 μs long. Correlating the length of the envelope detector to the length in time of the stylus signal can ensure that when the entire stylus signal is within the window  802 , it can correspond to the peak of the signal plotted on graph  804 . The length of the window however can be of a different size than the length in time of a stylus signal in other examples. 
     The stylus detector can thus determine the end of the stylus signal by detecting the peak signal generated by the envelope detector. As shown in  FIG. 8 , when the peak of signal on graph  804  is reached, it can correspond to the time when the stylus signal is fully encapsulated within the window. By detecting the peak, the detector can thus ascertain the end time of the stylus signal, and since the stylus signal is of a pre-determined duration, the detector can then know the beginning time of the stylus signal. 
     A stylus detector as described above can, in some examples, be implemented as a single frequency discrete Fourier transfer that integrates the energy of a signal over a specific duration of time. The discrete Fourier transfer can be implemented using various methods known in the art, for instance a fast Fourier transform, a zero crossing detection or a Goertzl Algorithm.  FIG. 9  illustrates an example implementation of an envelope detector according to examples of the disclosure. The circuit depicted in  FIG. 9  is known in the art as a circuit implementation of a sliding I/Q demodulator that can perform a single frequency discrete time Fourier transform. The output  902  of the circuit can be sent to a peak detector  904 . 
     Peak detector  904  can be implemented using many methods known in the art. For instance, a threshold method can be employed in which the peak of the signal is detected when the signal crosses a pre-determined threshold. This method can, however, be susceptible to corruption from noise, since noise can cause the signal to prematurely exceed the threshold, thus causing the time estimates for the peak to be erroneous. Centroid detection (i.e., detecting the geometric center of a shape) can be employed in the time domain to find the peak of a signal.  FIG. 10  illustrates an exemplary centroid peak detection method according to examples of the disclosure. As illustrated in  FIG. 10 , two pre-determined thresholds A h  and A 1  can be pre-determined. A h  can be the initial threshold encountered in time, and A 1  can be the second threshold encountered in time. The thresholds can be set such that they give the peak detector hysteresis, thus making the detector more robust to noise. In other words the thresholds can be set so that they are not equal. The peak detector can record the time at which the thresholds are crossed by the signal. Thus, T h  can correspond to the time when the first threshold is crossed and T 1  can correspond to the time when the second threshold is crossed. Once T h  and T 1  are obtained by the peak detector, the centroid in time can be calculated using the following equation. 
     
       
         
           
             
               T 
               p 
             
             = 
             
               
                 ( 
                 
                   
                     
                       T 
                       h 
                     
                     · 
                     
                       A 
                       h 
                     
                   
                   + 
                   
                     
                       T 
                       l 
                     
                     · 
                     
                       A 
                       l 
                     
                   
                 
                 ) 
               
               
                 ( 
                 
                   
                     A 
                     h 
                   
                   + 
                   
                     A 
                     l 
                   
                 
                 ) 
               
             
           
         
       
     
     The equation above relates to a 2 point centroid calculation. The equation above can be generalized to a multi-point centroid calculation using the equation below: 
     
       
         
           
             
               T 
               p 
             
             = 
             
               
                 
                   ∑ 
                   i 
                   
                       
                   
                 
                 ⁢ 
                 
                   
                     T 
                     i 
                   
                   · 
                   
                     A 
                     i 
                   
                 
               
               
                 ∑ 
                 
                   A 
                   i 
                 
               
             
           
         
       
     
     As discussed above, Tp can be equivalent to the time when the end of the stylus signal occurs. Since the stylus signal is of a pre-determined duration, the beginning of the stylus signal can be calculated and the information used to generate the window and enable proper demodulation of the stylus signal. 
     Stylus detectors can be aggregated amongst the stylus sense channels in various ways in order to create a uniform signal to noise ratio, while at the same time minimizing the effects of common mode noise on a stylus detector. Aggregation can refer to the distribution of detectors amongst the stylus sense channels and can also refer to how stylus sense channels are combined at each detector to determine the beginning and end of a stylus signal. Stylus detector aggregation schemes can be evaluated using at least two metrics. First, the minimum signal level into each detector can be monitored as the stylus moves across the sense channels. This can be important due to the fact that the detected signal power level can effect signal to noise ratios. Aggregation can be used to maximize the signal and keep it as uniform as possible as the stylus moves across the touch screen. Second, aggregation can be used to minimize the number of detectors used on the touch screen. 
       FIG. 11 a    illustrates an example stylus detector aggregation scheme according to examples of the disclosure. In this example, each stylus sense channel can have a dedicated detector coupled to it. As illustrated, each sense channel  1102  can have a stylus detector  1104  as described above coupled to it. For instance channel i can have detector i coupled to it. Channel i+1 can have detector i+1 attached to it, and so on and so forth. While only 4 channels are shown, the disclosure is not so limited and there can be as many channels as necessary to cover the area of a touch screen. Also illustrated in  FIG. 11 a    are stylus touches  1106  and  1108 . Stylus touch  1106  can represent a stylus that touches the touch screen directly on top of a stylus signal sense channel. Stylus touch  1108  can represent a stylus that touches the touch screen in between two stylus signal sense channels. 
       FIG. 11 b    illustrates an example detector chart corresponding to the aggregation scheme of  FIG. 11 a   . The chart can be read as follows. The rows of the chart can represent stylus sense channels depicted in  FIG. 11 a   . For instance, C(i) can represent channel i+1, c(ii) channel i+2, etc. The columns of the chart can represent stylus detectors depicted in  FIG. 11 b   . For instance d(i) can represent detector i+1, etc. As shown at cell (c(i), d(i)), a plus (+) symbol can indicate that a particular channel is connected to a detector. For instance, at (c(i), d(i)), the plus symbol indicates that channel (i) is connected to detector (i). At (c(i), d(i+1)) there is no symbol, thus indicating that there is no connection between channel i and detector i+1. The chart of  FIG. 11 b    can be helpful in analyzing the effectiveness of a particular aggregation scheme. For instance, the aggregation scheme of  FIG. 11 a    can have non-uniform SNR as the stylus signal moves across the touch screen. At touch  1106 , depicted in  FIGS. 11 a  and 11 b   , the stylus can transmit its entire energy into the detector (i) since it is directly on top of channel i. However, touch  1108 , depicted at  1108 , is located partially between channel i and channel i+2. This can mean that detector i will only receive about half of the energy from the stylus signal, while detector i+1 can receive the other half. This can mean that each detector may have a smaller SNR since each only receives only half of the energy from the stylus. 
       FIG. 12 a    illustrates another exemplary stylus detector aggregation scheme according to examples of the disclosure. The stylus detector aggregation scheme of  FIG. 12 a    can be described as a paired aggregation. As illustrated, detector i can be coupled to two channels i and i+1. Specifically, channels i and i+1 are summed together and the summed signal in then inputted into detector i. Channels i+1 and i+2 are summed together and the summed signal is then inputted into detector i+2 and so on. Also, stylus touches  1202  and  1206  can represent the stylus touching the touch screen. Stylus touch  1202  can represent the instance when the stylus is directly touching and is on top of channel i. Stylus touch  1206  can represent when the stylus is in between channel i and channel i+1. 
       FIG. 12 b    illustrates the corresponding detector chart of  FIG. 12 a   . As illustrated, detector i can be coupled to sense channels i and i+1. The + symbol corresponding to the channels i and i+1 can represent the fact that each channel is summed together into the detector. By having two adjacent channels summed together and then fed into the detector, the issue of non-uniform SNR can be mitigated. For instance, when the stylus is in between two channels as is stylus touch  1206 , detector i can receive the full signal since detector i receives the sum of channel i (which receives half the stylus signal) and channel i+1 (which receives the other half of the stylus signal). Thus, the aggregation scheme of  FIG. 12 a    can produce a uniform SNR despite is the location of the stylus, whether it is directly on top of a sense channel or in between sense channels. 
     The aggregation scheme depicted in  FIG. 12 a    however can produce a signal to the stylus detector that has more common mode noise than the aggregation scheme depicted in  FIG. 11 a   . If each channel contains a certain amount of common mode noise, by summing the channels together and then inputting the sum into a detector, the noise on each channel can also be summed. This can increase the magnitude of the noise seen by the detector and can create a diminished SNR. 
       FIG. 13 a    represents yet another exemplary stylus detector aggregation scheme according to examples of the disclosure. In this example, the signal on channel i can be subtracted from the signal on channel i+2 and the result inputted into detector i. The signal on channel i+1 can be subtracted from the signal on channel i+3 and the result inputted into detector i+1. This pattern can be repeated for each detector. By subtracting one signal from another, the common mode noise present in the signal inputted into the stylus detector can be minimized, since the noise signals will be also subtracted from each other. The noise signals present on each channel can be correlated with each other in order to ensure that when subtracted from each other, they effectively cancel each other out. In order to ensure that the noise signals are correlated, channels that are in spatial proximity to each other can be chosen to be subtracted from each other. However, having the channels too close to each other can mean that if a stylus signal is present on both channels, the stylus signals may also cancel or partially cancel each other out. If the stylus signals are subtracted from each other, the SNR into the stylus detector may be diminished. In the example of  FIG. 13 a   , detector i, for instance, is fed channel i subtracted from channel i+2. In this example, the subtracted channel is in close proximity to the other channel while at the same time not being so close in proximity that stylus signals maybe subtracted from each other. Thus, if a stylus touch is applied at  1302 , which is directly on top of a stylus channel, the common mode noise can be minimized by the subtraction. If a stylus touch is applied at  1304 , which is in between two sense channels, the subtraction will not result in the cancellation of the stylus signals because the stylus signal would be present on two channels. However, if the stylus tip were to be larger, such that it could occupy two sense channels, then the aggregation scheme illustrated in  FIG. 13 a    may not be adequate in ensuring that stylus signals don&#39;t get canceled out as a result of the subtraction. 
       FIG. 13 b    illustrates a detector chart corresponding to the example of  FIG. 13 a   . As discussed above, the example of  FIG. 13 a    uses non-adjacent channels to perform subtraction in order to mitigate common mode noise. However, as shown in  FIG. 13 b   , this detector aggregation scheme can lead to a non-uniform SNR as the stylus moves across the panel. For instance, at stylus touch  1302 , the stylus is directly on top of a channel and thus the detector can receive a full signal. However at stylus touch  1304 , the detector may only receive half of the stylus signal and thus the SNR can vary depending on the location of the stylus. 
       FIG. 14  illustrates an exemplary detector chart of a stylus detector aggregation scheme according to examples of the disclosure. In this example, as illustrated, detector i receives the sum of channel i+1 and channel i+2, subtracted by the sum of channel i and channel i+3. Detector i+1 receives the sum of channel i+2 and channel i+3, subtracted by the sum of channel i+1 and i+4. This pattern can continue for each detector. The aggregation scheme depicted in  FIG. 14  can provide a uniform stylus signal independent of position of the stylus, because no matter whether the stylus is directly on a channel or between channels, its total energy can be received by one detector. Furthermore, the aggregation scheme depicted in  FIG. 14  can provide good common mode noise suppression since the channels in close proximity to the summed channels are used to subtract out any potential common mode noise. The proximity of the channels used to subtract noise can provide good noise correlation to the noise encountered by the channels that contain stylus signals. 
     While various aggregation schemes can be used to ensure a uniform SNR and minimized common mode noise as the stylus moves across the panel, another goal of aggregation can be to reduce the number of detectors needed by the sensor panel. 
       FIG. 15 a    illustrates an exemplary detector aggregation scheme according to examples of the disclosure. The aggregation scheme depicted in  FIG. 15 a    is nearly identical to aggregation scheme depicted in  FIG. 13  except that only half of the detectors are used for detection. In other words, the detectors are spaced farther apart, meaning that there are fewer detectors on the panel. 
       FIG. 15 b    illustrates a detector chart corresponding to the aggregation schemed depicted in  FIG. 15 a   . As illustrated, by spacing the detectors farther apart, the stylus signal can be non-uniform as it moves across the panel. This result may be acceptable, however, if the common mode noise has good suppression due to the differential inputs to the detectors. 
     In the absence of noise, the panel would only require one solitary detector. All of the channels could be summed, and the result could be received by one detector. The number of detectors required by the panel to ensure common mode suppression can be a function of how correlated the noise is across the panel. For instance, if the noise on the touch sensor panel was globally correlated (in other words, the noise received by each channel is correlated to the noise received by all of the other channels), the panel could only use two detectors.  FIG. 16  illustrates an aggregation scheme that uses only two detectors according to examples of the disclosure. The aggregation scheme depicted in  FIG. 16  can work to ensure uniform SNR as the stylus moves across the panel; however common mode noise suppression can only be adequate if the noise is globally correlated across the entire panel. 
     If the noise is not globally correlated across the panel and instead is correlated within regions of the panel, the panel can be split into parts and the aggregation scheme of  FIG. 16  can be applied. For instance, if the noise on the panel were correlated within halves of the screen, such that the noise on one half of the screen was correlated, while the noise on the other half of the screen was globally correlated, then the panel could be sectioned off into halves, and each half could have the detector scheme of  FIG. 15  applied to it.  FIG. 17  illustrates an exemplary aggregation scheme according to examples of the disclosure. As illustrated, detectors 1 and 2 are used to detect stylus signals in the upper half of the panel, while detectors 3 and 4 are used to detect stylus signals in the lower half of the panel. 
       FIG. 18  is a block diagram of an example computing system that illustrates one implementation of a touch sensor panel display with stylus signal noise correction according to examples of the disclosure. Computing system  1800  could be included in, for example, mobile telephone  136 , digital media player  140 , personal computer  144 , or any mobile or non-mobile computing device that includes a touch screen. Computing system  1800  can include a touch sensing system including one or more touch processors  1802 , peripherals  1804 , a touch controller  1806 , and touch sensing circuitry. Peripherals  1804  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  1806  can include, but is not limited to, one or more sense channels  1809 , channel scan logic  1810  and driver logic  1814 . Channel scan logic  1810  can access RAM  1812 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  1810  can control driver logic  1814  to generate stimulation signals  1816  at various frequencies and phases that can be selectively applied to drive regions of the touch sensing circuitry of touch screen  1820 , as described in more detail below. In some examples, touch controller  1806 , touch processor  102  and peripherals  1804  can be integrated into a single application specific integrated circuit (ASIC). 
     Computing system  1800  can also include a host processor  1829  for receiving outputs from touch processor  1802  and performing actions based on the outputs. For example, host processor  1829  can be connected to program storage  1832  and a display controller, such as an LCD driver  1834 . Host processor  1829  can use LCD driver  1834  to generate an image on touch screen  1820 , such as an image of a user interface (UI), and can use touch processor  1802  and touch controller  1806  to detect a touch on or near touch screen  1820 , such a touch input to the displayed UI. The touch input can be used by computer programs stored in program storage  1832  to perform actions 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  1829  can also perform additional functions that may not be related to touch processing. 
     Integrated display and touch screen  1820  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  1822  and a plurality of sense lines  1823 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  1822  can be driven by stimulation signals  1816  from driver logic  1814  through a drive interface  1824 , and resulting sense signals  1817  generated in sense lines  1823  can be transmitted through a sense interface  1825  to sense channels  1809  (also referred to as an event detection and demodulation circuit) in touch controller  1806 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive sensing nodes, which can be thought of as touch picture elements (touch pixels), such as touch pixels  1826  and  1827 . This way of understanding can be particularly useful when touch screen  1820  is viewed as capturing an “image” of touch. In other words, after touch controller  1806  has determined whether a touch has been detected at each touch pixel in the touch screen, the pattern of touch pixels in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g. a pattern of fingers touching the touch screen). 
     One or more of the functions relating to the generation or processing of a stylus stimulation signal described above can be performed by a system similar or identical to system  1900  shown in  FIG. 19 . System  1900  can include instructions stored in a non-transitory computer readable storage medium, such as memory  1903  or storage device  1901 , and executed by processor  1905 . The instructions can also be stored and/or transported within any non-transitory 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 “non-transitory 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 non-transitory 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 instructions 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 system is not limited to the components and configuration of  FIG. 19 , but can include other or additional components in multiple configurations according to various examples. Additionally, the components of system  1900  can be included within a single device, or can be distributed between multiple devices. 
       FIGS. 20A-20D  show example systems in which touch sensor panels according to examples of the disclosure may be implemented.  FIG. 20A  illustrates an example mobile telephone  2036  that includes a touch sensor panel  2024 .  FIG. 20B  illustrates an example digital media player  2040  that includes a touch sensor panel  2026 .  FIG. 20C  illustrates an example personal computer  2044  that includes a touch sensor panel  2028 .  FIG. 20D  illustrates an example tablet computing device  2048  that includes a touch sensor panel  2030 . 
     Therefore, according to the above, some examples of the disclosure are directed to a stylus detection apparatus for detecting contacts from a stylus, the apparatus comprising a touch sensor panel comprising a plurality of electrodes, each electrode configured to receive and transmit one or more signals from a stylus, a channel aggregator configured to combine the signals transmitted by the plurality of electrodes to create a plurality of aggregated signals, and one or more stylus signal detectors, each detector configured to receive one of the aggregated signals of the plurality of aggregated signals from the channel aggregator and determine a presence and signal strength of a stylus signal based on the received signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the channel aggregator is configured to separate one or more signals transmitted by the plurality of electrodes into a first group, and further configured to sum the one or more signals of the first group to generate an aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more of the electrodes of the first group are chosen such that a detected signal strength of the stylus is uniform and independent of the stylus&#39; position on the touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the channel aggregator is further configured to separate the one or more signals transmitted by the plurality of electrodes into a second group, and further configured to subtract the one or more signals from the aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more of the electrodes of the second group of the electrodes are chosen such that a noise signal transmitted by second group of electrodes is correlated to a noise signal transmitted by the first group of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first group and the second group are mutually exclusive. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a number of the stylus signal detectors is based in part on a spatial correlation of a plurality of noise signals transmitted on the plurality of electrodes of the touch sensor panel. 
     Some examples of the disclosure are directed to a method for detecting contacts from a stylus signal, the method comprising receiving one or more stylus signals on a plurality of electrodes of a touch sensor panel, combining the signals transmitted by the plurality of electrodes to create a plurality of aggregated signals, and inputting the one more aggregated signals into one more stylus signal detectors, each detector configured to receive one of the aggregated signals of the plurality of aggregated signals from the channel aggregator and determine the presence and signal strength of a stylus signal based on the received signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, combining the signals includes separating the one or more signals transmitted by the plurality of electrodes into a first group and summing the one more signals of the first group to generate an aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises choosing the one or more of the electrodes of the first group such that a detected signal strength of the stylus is uniform and independent of the stylus&#39; position on the touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, combining the signals further includes separating the one or more signals transmitted by the plurality of electrodes into a second group, and subtracting the one or more signals from the aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises choosing the one or more electrodes of the second group of electrodes such that a noise signal transmitted by second group of electrodes is correlated to a noise signal transmitted by the first group of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first group and the second group are mutually exclusive. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a number of stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals transmitted on the plurality of electrodes of the touch sensor panel. 
     Some examples of the disclosure are directed to a non-transitory computer readable storage medium having stored thereon a set of instructions for detecting contacts from a stylus signal that when executed by a processor causes the processor to receive one or more stylus signals on a plurality of electrodes of a touch sensor panel, combine the signals transmitted by the plurality of electrodes to create a plurality of aggregated signals, and input the one more aggregated signals into one more stylus signal detectors, each detector configured to receive one of the aggregated signals of the plurality of aggregated signals from the channel aggregator and determine the presence and signal strength of a stylus signal based on the received signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, combining the signals includes separating the one or more signals transmitted by the plurality of electrodes into a first group and summing the one more signals of the first group to generate an aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processor is further caused to choose the one or more of the electrodes of the first group such that a detected signal strength of the stylus is uniform and independent of the stylus&#39; position on the touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, combining the signals further includes separating the one or more signals transmitted by the plurality of electrodes into a second group, and subtracting the one or more signals from the aggregated signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processor is further caused to choose the one or more electrodes of the second group of electrodes such that a noise signal transmitted by second group of electrodes is correlated to a noise signal transmitted by the first group of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first group and the second group are mutually exclusive. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a number of stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals transmitted on the plurality of electrodes of the touch sensor panel. 
     Although examples 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 examples as defined by the appended claims.

Metadata:
Filing Date: 20130314
Publication Date: 20191029
Grant Date: 20191029
Priority Date: 20130314
Inventors: SHAHPARNIA, SHAHROOZ
WHITE, KEVIN J.
AGARWAL, MANU
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/041", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/046", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/046", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/046", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 50382597