PATENT DOCUMENT

Publication Number: US-9557868-B2
Application Number: US-201414550784-A
Country: US
Kind Code: B2

Title: Noise reduction for touch sensor system with active stylus

Abstract:
A touch sensor may overlap a display. A transparent shield layer that is grounded around its edges may be interposed between the display and the touch sensor to help prevent noise from display data lines from reaching the touch sensor. The data lines may extend along a first dimension. The touch sensor may have first elongated electrodes that extend along the first dimension and second elongated electrodes that extend along a second dimension that is perpendicular to the first dimension. The second electrodes may be interposed between the first electrodes and the data lines. Pen present electrodes may be used to gather pen present data associated with a stylus on the touch sensor. Adjacent noise sensors may collect noise data that is removed from the pen present data.

Claims:
What is claimed is: 
     
       1. Apparatus that is responsive to input from a stylus, comprising:
 a touch sensor having edges and having a plurality of electrodes; and 
 touch sensor circuitry that processes signals from the plurality of electrodes, wherein the touch sensor circuitry obtains signal data from the plurality of electrodes including pen present data from pen present electrodes where the stylus is located on the touch sensor and noise data from noise electrodes adjacent to the pen present electrodes, wherein the touch sensor circuitry includes a processor that removes the noise data from the pen present data to produce noise-removed pen present data, wherein the noise electrodes include at least four electrodes adjacent to the pen present electrodes, and wherein the processor includes a noise correction module that removes the noise data from the pen present data by computing a mean of the noise data on the noise electrodes. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the touch sensor circuitry is configured to compute position data for the stylus based on the noise-removed pen present data. 
     
     
       3. The apparatus defined in  claim 2  wherein the touch sensor circuitry includes front-end circuitry that obtains the signal data from the plurality of electrodes. 
     
     
       4. The apparatus defined in  claim 3  wherein the pen present electrodes are formed from a set of at least three electrodes among the plurality of electrodes. 
     
     
       5. The apparatus defined in  claim 4  wherein the noise correction module is configured to subtract a value equal to the mean of the noise data multiplied by a noise data scaling factor from the pen present data to produce the noise-removed pen present data. 
     
     
       6. The apparatus defined in  claim 5  further comprising:
 a display, wherein the touch sensor overlaps the display. 
 
     
     
       7. The apparatus defined in  claim 6  wherein the plurality of electrodes includes first elongated transparent electrodes that extend along a first dimension, the touch sensor further comprising second elongated transparent electrodes that extend along a second dimension that is perpendicular to the first dimension. 
     
     
       8. The apparatus defined in  claim 7  wherein the display has a plurality of data lines that extend along the first dimension and wherein the second elongated transparent electrodes are interposed between the first elongated transparent electrodes and the plurality of data lines. 
     
     
       9. The apparatus defined in  claim 8  wherein the noise correction module is configured to select a value for the noise data scaling factor based on how far the pen present electrodes are located from one of the edges. 
     
     
       10. A touch sensor display that receives input from a stylus, comprising:
 display layers that produce images, wherein the display layers include data lines and have edges; 
 a conductive transparent shield layer that overlaps the display layers and that is grounded at the edges; 
 touch sensor electrodes on the display layers that receive noise from the data lines; and 
 touch sensor circuitry that processes signals from the electrodes, wherein the touch sensor circuitry obtains pen present data from pen present electrodes associated with presence of the stylus and noise data from noise electrodes adjacent to the pen present electrodes and that removes the noise data from the pen present data, wherein the pen present electrodes have first and second opposing sides, wherein there are at least two adjacent noise electrodes on the first side of the pen present electrodes when the pen present electrodes are located away from the edges of the display layers, and wherein there are at least two adjacent noise electrodes on the second side of the pen present electrodes when the pen present electrodes are located away from the edges of the display layers. 
 
     
     
       11. The touch sensor display defined in  claim 10  wherein there are three pen present electrodes. 
     
     
       12. The touch sensor display defined in  claim 10  wherein the touch sensor circuitry removes the noise data based at least partly on how far the pen present electrodes are from the edges. 
     
     
       13. The touch sensor display defined in  claim 12  wherein the touch sensor electrodes include first elongated transparent electrodes that extend along a first dimension and second elongated transparent electrodes that extend along a second dimension that is perpendicular to the first dimension, wherein the data lines extend along the first dimension, and wherein the second elongated transparent electrodes are interposed between the first elongated transparent electrodes and the data lines. 
     
     
       14. The touch sensor display defined in  claim 10  wherein there are two pen present electrodes. 
     
     
       15. The touch sensor display defined in  claim 10 , wherein there are less than two noise electrodes on the first side of the pen present electrodes when the pen present electrodes are located near the edges of the display layers, and wherein there are at least three noise electrodes on the second side of the pen present electrodes when the pen present electrodes are located near the edges of the display layers. 
     
     
       16. A method of determining where a stylus is located on a touch sensor, comprising:
 with front end circuitry in a touch sensor circuit, measuring pen present data on at least one pen present touch sensor electrode associated with a presence of the stylus on the touch sensor and measuring noise data on first and second sets of touch sensor noise electrodes that are adjacent to the at least one pen present touch sensor electrode and that are located on opposing sides of the at least one pen present touch sensor electrode, wherein the first and second sets of adjacent touch sensor noise electrodes each include fewer than four touch sensor noise electrodes; and 
 with the touch sensor circuit, removing noise from the pen present data based on the measured noise data. 
 
     
     
       17. The method defined in  claim 16  wherein removing the noise comprises removing the noise with a noise correction module in the touch sensor circuit based at least partly on how far the at least one pen present touch sensor electrode is from edges of the touch sensor. 
     
     
       18. The method defined in  claim 17  wherein removing the noise comprises applying a scaling factor to the measured noise data based on how far the at least one pen present touch sensor electrode is from the edges of the touch sensor. 
     
     
       19. The method defined in  claim 16  wherein removing the noise comprises removing the noise in phase with the pen present data. 
     
     
       20. The method defined in  claim 16  wherein the at least one pen present touch sensor electrode comprises more than one pen present touch sensor electrode and fewer than three pen present touch sensor electrodes. 
     
     
       21. The method defined in  claim 16 , wherein the first set of adjacent touch sensor noise electrodes includes two touch sensor noise electrodes when the pen present electrodes are located a first distance from an edge of the touch sensor, wherein the first set of adjacent touch sensor noise electrodes includes one touch sensor noise electrode when the pen present electrodes are located a second distance from the edge of the touch sensor, wherein the first set of adjacent touch sensor noise electrodes includes zero touch sensor noise electrodes when the pen present electrodes are located a third distance from the edge of the touch sensor, wherein the first distance is greater than the second distance, and wherein the second distance is greater than the third distance. 
     
     
       22. The method defined in  claim 21 , wherein the second set of adjacent touch sensor noise electrodes includes two touch sensor noise electrodes when the first set of adjacent touch sensor noise electrodes includes two touch sensor noise electrodes, wherein the second set of adjacent touch sensor noise electrodes includes three touch sensor noise electrodes when the first set of adjacent touch sensor noise electrodes includes one touch sensor noise electrode, and wherein the second set of adjacent touch sensor noise electrodes includes four touch sensor noise electrodes when the first set of adjacent touch sensor noise electrodes includes zero touch sensor noise electrodes.

Description:
BACKGROUND 
     This relates generally to touch sensors and, more particularly, to reducing noise in touch sensors. 
     Electronic devices such as tablet computers and cellular telephones often include capacitive touch sensors. A capacitive touch sensor has an array of electrodes that can be used to measure the position of a user&#39;s finger or an external device such as a touch sensor stylus. In an active stylus design, circuitry in a stylus emits signals that are detected by the touch sensor electrodes. The use of active stylus designs can help improve stylus performance. 
     There are challenges associated with using capacitive touch sensors to gather stylus input. Touch sensors are often mounted over displays to form touch sensitive displays. Displays have signal lines such as data lines that can emit noise. The noise can interfere with the operation of the touch sensor and can make it difficult to obtain accurate position information for a stylus. Unless care is taken, stylus data may be inaccurate or may require overly complex signal processing operations. 
     It would therefore be desirable to be able to provide an improved touch sensor system for an electronic device. 
     SUMMARY 
     An electronic device may have a display. The display may have an array of pixels to produce images for a user. Data lines in the display may distribute data to the pixels. A touch sensor may overlap the display. 
     The data lines and other signal lines in the display have a potential to produce electrical noise that can be coupled into the touch sensor. A transparent shield layer may be interposed between the display and the touch sensor to help suppress this noise. The shield may be grounded along the edges of the touch sensor. 
     The data lines may extend along a first dimension. The touch sensor may have first elongated electrodes that extend along the first dimension and second elongated electrodes that extend along a second dimension that is perpendicular to the first dimension. The second electrodes may be interposed between the first electrodes and the data lines. 
     In the presence of a stylus at a location on the surface of the touch sensor, some of the touch sensor electrodes will pick up signals from the stylus. These pen present electrodes may be used to gather pen present data associated with the stylus. Noise from the display may be assessed by making noise data measurements using noise electrodes that are adjacent to the pen present electrodes. 
     During operation, touch sensor circuitry may identify the pen present electrodes and gather pen present data. Adjacent noise electrodes to the left and right of the pen present electrodes may be used to measure noise data. The noise data can be averaged to assess how much noise is present on the pen present electrodes, so that corrective processing may be performed. The amount of noise on the noise electrodes can be affected by the distance from the grounded edges of the shield and therefore the edges of the touch sensor. To ensure that pen present data is processed accurately, the averaged noise data can be scaled based on how far the pen present electrodes are from the edge of the touch sensor. In the center of the sensor, no scaling is needed. At the edge of the display, the pattern of noise electrodes that are used in gathering noise data may be reconfigured and scaling operations may be used to take account of the noise electrode configuration and position dependence of the noise. 
     The scaled noise data can be removed from the pen present data to produce noise-removed (corrected) pen present data. This data may be processed to produce information on the current location of the stylus on the surface of the touch sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of an illustrative electronic device with a touch sensitive display and an associated stylus for providing touch input in accordance with an embodiment. 
         FIG. 2  is a top view of an illustrative touch sensor in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative touch sensor and display in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of a touch sensor and display showing how touch sensor electrodes may interact with a stylus and may overlap signal lines such as data lines in a display in accordance with an embodiment. 
         FIG. 5  is a diagram of a touch sensor and associated touch sensor circuitry in accordance with an embodiment. 
         FIG. 6  is diagram of touch sensor circuitry in accordance with an embodiment. 
         FIG. 7  is a graph showing how touch sensor noise may vary as a function of distance across a touch sensor in accordance with an embodiment. 
         FIG. 8  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in a configuration in which the stylus is not near the edge of a touch sensor in accordance with an embodiment. 
         FIG. 9  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in a configuration in which the stylus is within one electrode of the edge of the touch sensor in accordance with an embodiment. 
         FIG. 10  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in a configuration in which the stylus is adjacent to the edge of the touch sensor in accordance with an embodiment. 
         FIG. 11  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in another configuration in which the stylus is not near the edge of a touch sensor in accordance with an embodiment. 
         FIG. 12  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in a configuration of the type shown in  FIG. 11  where the stylus is within one electrode of the edge of the touch sensor in accordance with an embodiment. 
         FIG. 13  is a diagram showing sets of sensor electrodes that may be used for measuring stylus signals and noise in a configuration of the type shown in  FIGS. 11 and 12  where the stylus is adjacent to the edge of the touch sensor in accordance with an embodiment. 
         FIG. 14  is an illustrative look-up table that may be used to store scaling factor information for a noise correction module in accordance with an embodiment. 
         FIG. 15  is a flow chart of illustrative steps involved in processing stylus data in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device such as electronic device  10  of  FIG. 1  may be provided with a touch sensor. The touch sensor may be integrated with a display to form a touch screen display or may be incorporated into a component without a display such as a touch pad. Configurations in which the touch sensor forms part of a display are sometimes described herein as an example. A stylus such as stylus  18  may be used to provide touch input to the touch sensor. 
     Electronic device  10  may be computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14  mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. The use of transparent structures in forming the electrodes for the touch sensor of display  14  allows light from an array of pixels within display  14  to be used to display images for a user. The touch sensor may, as an example, be mounted on the outside of display  14  (e.g., on the underside of a display cover layer or other protective layer). During operation, the light from display  14  may pass through the touch sensor for viewing by a user. 
     Display  14  may include an array of pixels formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma pixels, an array of organic light-emitting diode pixels or other light-emitting diodes, an array of electrowetting pixels, or pixels based on other display technologies. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16 . An opening may also be formed in the display cover layer to accommodate ports such as speaker ports. Openings may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.), to form openings for buttons, to form media card slots, etc. For example, an opening may be formed at the end of housing  12  to accommodate a data port. 
     During operation, a user of device  10  may supply input to device  10  using stylus  18 . Stylus  18 , which may sometimes be referred to as a computer stylus or pen, may have a tip such as tip  20 . Circuitry within stylus  18  may be used to emit electrical signals that are detected by the capacitive touch sensor electrodes of the touch sensor of device  10  (e.g., the touch sensor of touch screen display  14 ). Device  10  may contain touch sensor circuitry that detects and processes the emitted electromagnetic signals to determine the position of stylus  18  (i.e., to determine the position of tip  20  on display  14  relative to lateral dimensions X and Y). 
       FIG. 2  is a top view of an illustrative capacitive touch sensor. As shown in  FIG. 2 , touch sensor  22  may have electrodes  24 . Electrodes  24  may be formed from metal, transparent conductive materials such as indium tin oxide, or other conductive material. When mounting touch sensor  22  of  FIG. 2  over the front of a display, electrodes  24  are preferably formed from a transparent conductive material such as indium tin oxide. 
     Electrodes  24  may have any suitable shape and layout. For example, electrodes  24  may be formed from horizontal conductive strips  24 - 2  and vertical conductive strips  24 - 1  (i.e., elongated electrodes  24 - 1  and  24 - 2  may run perpendicular to each other). There may be multiple rows of strips  24 - 2  and multiple rows of strips  24 - 1  in sensor  22 . Touch sensors with larger numbers of rows and columns of electrodes  24  exhibit greater spatial resolution than touch sensors with fewer electrodes, but can be more complex and costly than simpler touch sensors. Touch sensor circuitry  26  may be coupled to electrodes  24 - 1  and  24 - 2  (e.g., to supply drive signals to electrodes  24 - 2  while sensing signals on electrodes  24 - 1 ). Electrodes  24  may, if desired, have other shapes. The use of overlapping rows and columns of capacitive touch sensor electrodes is merely illustrative. 
       FIG. 3  is a cross-sectional side view of display  14 . As shown in  FIG. 3 , display  14  may include display cover layer  32 . Display cover layer  32  may be formed from transparent plastic, clear glass, a clear ceramic, a clear crystalline material such as sapphire, or other transparent material. Touch sensor electrodes  24  may be mounted under display cover layer  32 . Touch sensor circuitry  26  may supply signals to touch sensor electrodes  24  and may process signals received from the touch sensor formed by touch sensor electrodes  24  to determine the position of the tip of stylus (pen)  18  on display  14  (i.e., the position of stylus  18  in dimensions X and Y). Display  14  may have display layers  38  (e.g., a display module or other display structures) that emit light  43  for images. User  30  may observe the images produced by display module  38  when viewing display  14  in direction  40 . Touch sensor electrodes  24  may be transparent so that light  43  from display module  38  passes through touch sensor electrodes  24  and cover layer  32 . Display module  38  may be a liquid crystal display module, an organic light-emitting diode display module, may be based on electrophoretic display structures, or may be based on any other suitable display layers. 
     Display module  38  may have signal lines that convey data and control signals produced by display driver circuitry  28  to an array of pixels in display module  38 . These signals in display module  38  have the potential to create electromagnetic signal noise that affects the operation of the touch sensor. For example, data line signals can create noise in electrodes  24 . To help shield touch sensor electrodes  24  from noise produced by display module  38 , the upper surface of display module  38  (e.g., the upper surface of a color filter layer) or other layer in display  14  may be provided with a transparent shield layer such as shield layer  34 . Shield layer  34  may be formed from a transparent conductive material such as indium tin oxide and may be grounded along its peripheral edges  42  (i.e., shield  34  may be shorted to ground  36  along the edges of display  14  and the touch sensor of display  14  that is formed by touch sensor electrodes  24 ). The presence of shield layer  34  may help prevent noise from signals such as data line signals in display module  38  from interfering with the operation of the touch sensor. There is some resistance associated with conductive shields formed from indium tin oxide shielding layers, so shielding effectiveness may be greatest near grounded edges  42 . 
       FIG. 4  is a cross-sectional side view of an illustrative touch screen display to which touch input is being provided by stylus  18 . As shown by electromagnetic field lines  44 , electromagnetic signals from stylus  18  may be detected by one or more touch sensor electrodes  24 - 1  in the touch sensor of display  14 . In the example of  FIG. 4 , signals  44  are being detected by four of electrodes  24 - 1  that are in the vicinity of the tip of stylus  18 , but are not detected by other electrodes  24 - 1  (i.e., electrodes that are adjacent to the main four electrodes) because those electrodes are too far away from the tip. Touch sensor circuitry  26  can monitor the signals on electrodes  24  and can use the presence of signals  44  on certain electrodes  24  to determine the location of stylus  18  in lateral dimensions X and Y. 
     Touch sensor electrodes  24  of  FIG. 4  may be formed on the upper and lower surfaces of a sheet of polymer or other dielectric support structure (i.e., touch sensor  22  may be use a two-sided electrode pattern). The upper electrodes (electrodes  24 - 1  in the example of  FIG. 4 ) may run into and out of the page along the Y axis. The lower electrodes (electrodes  24 - 2 ) may run along the X axis. Display module  38  may have signal lines such as data lines  46  that emit noise. To help reduce spatial variations in the electromagnetic noise signals from data lines D that are coupled onto electrodes  24 , the lower electrodes (i.e., electrodes  24 - 2 ) can be configured to run perpendicular to data lines  46 . If, for example, data lines  46  run along axis Y, lower electrodes  24 - 2  may be formed from elongated strips of indium tin oxide or other conductive material that run along perpendicular dimension X. 
     Signals in the touch sensor that are associated with electrodes  24  that are not in the immediate vicinity of stylus  18  (e.g., electrode  24 - 1 ′ in the example of  FIG. 4 ) may not receive significant electrical signals  44  from stylus  18 . Noise (e.g., electrical noise from data lines  46  or other signal sources in display module  38 ) may be produced uniformly across display  14  and may therefore be coupled onto both the electrodes that are in the vicinity of stylus  18  and electrodes that are not in the vicinity of stylus  18  (e.g., electrode  24 - 1 ′). To remove noise data from the electrodes that have stylus signals, noise signals can be measured using one or more electrodes such as electrode  24 - 1 ′ that are not receiving significant stylus data and this noise data can be subtracted or otherwise removed from the stylus data on  24 - 1 . 
     Touch sensor signal processing can be performed using touch sensor circuitry  26 . As shown in  FIG. 5 , touch sensor circuitry  26  may include front-end circuitry  50  and processor circuitry  52 . Front-end circuitry  50  and processor circuitry  52  may be implemented on one or more integrated circuits and may be used to convert raw analog touch sensor data into digital position data. System-on-chip circuitry  48  or other control circuitry in device  10  may use position information from touch sensor circuitry  26  in controlling the operation of device  10 . 
       FIG. 6  is a diagram showing how touch sensor circuitry  26  may process analog signals from capacitive touch sensor electrodes  24 . As shown in  FIG. 6 , touch sensor circuitry  26  may include front-end circuitry  50  and processing circuitry  52 . Front-end circuitry  50  may include band pass filter and transimpedance amplifier  60  and demodulator  62  for converting analog signals from electrodes  24  into digital electrode signals. 
     Stylus  18  may emit electromagnetic signals that are modulated using any suitable modulation scheme. For example, stylus  18  may use quadrature amplitude modulation. Demodulator  62  may include circuitry for demodulating the signals emitted by stylus  18 . For example, demodulator  62  may be a quadrature demodulator that demodulates the signals from circuitry  60  and that produces corresponding in-phase (I) and quadrature phase (Q) signals as outputs. Circuitry  50  may be implemented in hardwired circuitry in touch sensor circuit  26 . 
     If desired, stylus  18  may have multiple electrodes (e.g., two stylus electrodes, three or more stylus electrodes, etc.). Stylus electrodes in stylus  18  emit signals that are detected by touch sensor electrodes  24  and may therefore sometimes be referred to as drive electrodes or pen drive electrodes. Stylus  18  may have a tip electrode located at the tip of end  20  of stylus  18 , may have a ring electrode (e.g., a drive electrode with the shape of a ring that encircles stylus  18 ), and/or other drive electrodes. 
     In configurations for stylus  18  with multiple pen drive electrodes, each of the drive electrodes may be modulated differently. For example, stylus  18  may have a pair of pen drive electrodes (e.g., tip and ring electrodes) and a first of the electrodes may be modulated using quadrature amplitude modulation at a first frequency whereas a second of the electrodes may be modulated using quadrature amplitude modulation at a second frequency that is different form the first frequency. Frequency division multiplexing or time division multiplexing may be used to drive the tip and ring electrodes simultaneously. 
     Front-end circuitry  50  can receive and process the signals from each of the stylus electrode separately, albeit simultaneously. If desired, information that is gathered in connection with one stylus electrode may be used in connection with the other stylus electrode. For example, information associated with operation of one stylus electrode may, if desired, be used when performing noise correction operations on signals associated with operation of another stylus electrode. 
     Processor  52  may perform noise correction operations (see, e.g., noise correction module  64 ) and position determination operations (see, e.g., position determination module  66 ). During noise correction operations, digital noise signals that are gathered using electrodes  24  and circuitry  50  may be removed from digital stylus signals that are gathered using electrodes  24  and circuitry  50 . Noise correction operations may involve removing noise from digital stylus signals associated with one or more distinct stylus electrodes. Each stylus electrode may have a different profile and different noise correction factors may be used in connection with each stylus electrode. For example, the tip electrode may be associated with a 2-4 touch sensor electrode profile while the ring electrode may be associated with an 8-12 touch sensor electrode profile. 
     During position determination operations, the corrected noise-removed touch sensor signals (i.e., the touch sensor data from which display noise has been removed) may be processed to produce position data (i.e., X-Y coordinates specifying the location of the tip of stylus  18 ). Noise correction operations may, if desired, be performed in phase with the received signals (e.g., by performing subtraction operations and other correction operations on the I and Q signals from demodulator  62 ). 
     As described in connection with  FIG. 4 , display signal lines such as data lines  46  produce noise that is coupled into touch sensor electrodes  24 . Display noise tends to be produced uniformly by all of lines  46 . However, because shield  34  is grounded along edges  42 , shielding effectiveness tends to be largest at the edges of display  14 . As a result, the amount of noise that is coupled into electrodes  14  tends to increase near the center of display  68  and tends to be minimized near edges  42 . Touch sensor electrode noise magnitude for an illustrative touch sensor has been plotted as a function of distance X across the surface of display  14  in the graph of  FIG. 7 . As shown by curve  68 , noise is largest near the center of the touch sensor and display and is lowest near edges  42 . 
     When stylus  18  is placed in the vicinity of electrodes  24 , a set of N electrodes  24 - 1  will receive significant stylus signals from electrodes and circuitry in stylus  18 . The value of N may vary as a function of touch sensor size, electrode size, and other parameters. As an example, the value of N may be 1, 2, 3, 4, or 5. The electrodes that receive significant stylus data from stylus  18  are sometimes referred to as “pen present” electrodes. Sets of electrodes that are adjacent to the pen present electrodes pick up primarily noise and may therefore sometimes be referred to as adjacent noise electrodes or noise electrodes. Because the amount of electrode noise varies as a function of distance X, the noise on the electrodes that are immediately to the left and right of the pen present electrodes is closest in magnitude to the noise on the pen present electrodes themselves. Accordingly, the amount of noise on the pen present electrodes can be accurately estimated (with minimal processing complexity) by gathering noise data from the electrodes to the immediate right and left of the pen present electrodes. As an example, noise data can be gathered for M electrodes that are located immediately to the left of the pen present electrodes and M electrodes that are located immediately to the right of the pen present electrodes. The value of M may vary as a function of touch sensor size, electrode size, and other parameters. As an example, the value of M may be 2, 3, or 4 (so that the total number of noise electrodes 2 M is 4, 6, or 8). 
     In a typical noise correction scenario, pen present data can be gathered from the pen present electrodes and noise data can be gathered from electrodes adjacent to the pen present electrodes. Processor  52  (i.e., noise correction module  64  of  FIG. 6 ) produces pen present electrode data from which the noise data has been removed (sometimes referred to as noise-removed pen present data or corrected stylus data). The corrected stylus data can then be used to produce position information. 
     When the pen present electrodes are located in the center of the display, symmetrical sets of the noise electrodes can be located to the left and right of the pen present electrodes. In situations in which the pen present electrodes are near to the edges  42  of display  14 , the noise electrodes at the display will not all be available. To compensate for the loss of edge-side noise electrodes, the number of noise electrodes that are used on the inner side of the pen present electrodes may be expanded. This helps ensure that a sufficient amount of noise data is sampled. 
     Electrode sampling configurations of the type that may be used for touch sensor electrodes  24  of display  14  are shown in  FIGS. 8, 9, 10, 11, 12, and 13 . 
       FIGS. 8, 9, and 10  show how pen present and noise signals can be gathered in a configuration in which pen present data is collected from three electrodes.  FIG. 8  shows how data may be measured in a configuration in which pen present electrodes  76  are located in the center of display  14 . In this type of situation, noise sampling electrodes  74  and  78  are not located at the edge of display  14  and are therefore not pinched off by the presence of the display (and touch sensor) edge  42 . Accordingly, pen present data  70  can be sampled from a set of electrodes such as electrodes  76  among electrodes  24  and noise samples  72  can be taken from noise sample electrodes  74  (on the left of pen present electrodes  76 ) and from noise sample electrodes  78  (on the right of pen present electrodes  76 ). There are three pen present electrodes  76 , two left noise electrodes  74 , and two right noise electrodes  78  in the example of  FIG. 8 , but other numbers of pen present electrodes and/or noise electrodes may be used to collect data if desired. For example, there may be only one pen present electrode, may be only two pen present electrodes (i.e., more than one and fewer than three), may be three or more pen present electrodes, may be only three pen present electrodes, may be three or four pen present electrodes, may be four or more pen present electrodes, etc. 
     Touch sensor circuitry  26  can identify which of electrodes  24  correspond to the presence of active stylus data (i.e., which electrodes are the pen present electrodes) by identifying which electrodes have the largest signal strengths, by comparing signal strengths to threshold values, and/or other signal processing techniques. Once the electrodes with the largest signal strengths have been identified, the position of the pen present electrodes relative to edges  42  may be determined. When the stylus is near the edge of display  14 , the pattern of noise electrodes that is used in gathering noise data  72  can be adjusted to accommodate the display edge. 
     In the example of  FIG. 8 , pen present electrodes  76  are located in the center of display  14 , so the noise electrodes from which noise signals  72  are measured are equally spaced about pen present electrodes  76 . Two electrodes are located in left-side noise electrodes  74  and two electrodes are located in right-side noise electrodes  78 . In the example of  FIG. 9 , stylus  18  is located near display edge  42 , so that pen present electrodes  76  are separated from edge  42  of display  14  by only a single electrode  24  (i.e., left side noise electrodes  74  contain only a single electrode). As a result, the number of right-side noise electrodes  78  that are being used has been expanded from two electrodes to three electrodes. In the example of  FIG. 10 , stylus  18  is located even nearer display edge  42 , so that no noise electrodes  74  are interposed between pen present electrodes  76  and edge  42 . In this scenario, there are four right-side noise electrodes  78 . The expansion of the number of right-side noise electrodes as the left-side electrodes become pinched off helps to avoid situations in which too little noise data is being collected. Both left-edge pinch-off and right-edge pinch-off conditions for electrodes  24 - 1  may be treated in the same way. The use of a left-hand pinch-off condition in the example of  FIGS. 8, 9, and 10  is merely illustrative. Because there are two electrodes  74  and two electrodes  78  in the arrangement of  FIG. 8 , configurations of the type shown  FIG. 8  in which none of the noise electrodes are pinched off may sometimes be referred to as 2/2 configurations. There is one electrode  74  and three electrodes  78  in the configuration of  FIG. 9 , so the configuration of  FIG. 9  may be referred to as a 1/3 configuration.  FIG. 10  is an example of a 0/4 configuration (0 electrodes  74  and 4 electrodes  78  are being used for noise data collection). 
       FIGS. 11, 12, and 13  show how pen present data and noise data can be gathered in a configuration in which pen present data is collected from four electrodes.  FIG. 11  shows how data may be measured in a configuration in which pen present electrodes  76  are located in the center of display  14  (i.e., a 2/2 configuration).  FIG. 12  shows an illustrative 1/3 configuration with four electrodes  76 , whereas  FIG. 13  shows and illustrative 0/4 configuration with four electrodes  78 . In general, any suitable number N of pen present electrodes and any suitable number 2 M of noise electrodes may be used. For example, there may be only one pen present electrode (N may be one), may be only two pen present electrodes (i.e., N may be two), may be three or more pen present electrodes, may be only three pen present electrodes, may be three or four pen present electrodes, may be four or more pen present electrodes, etc. The number 2 M may be two or more, four or more, six or more, seven or more, eight or more, nine or more, ten or more, 5-15, less than 15, more than two, less than eight, or any other suitable number. The arrangements of  FIGS. 8, 9   10 ,  11 ,  12 , and  13  are merely illustrative. 
     As shown by curve  68  in  FIG. 7 , noise decreases in magnitude near edges  42 . The downward slope of noise curve  68  creates larger noise signals on the inner side of pen present pixels  76  than on the outer side of pen present pixels  76  when stylus  18  is near edge  42 . As a result, the noise measured from the noise electrodes in the 1/3 scenario and in the 0/4 scenario will be larger than actual noise on the pen present electrodes, because the noise samples are effectively being spatially weighted towards the noisier side of the pen present electrodes. This can be accommodating by using a noise scaling factor K when removing noise from pen present data when stylus  18  is near edges  42 . 
       FIG. 14  is a look-up table showing how noise scaling factor K may be adjusted by touch sensor circuitry  26  as a function of noise electrode configuration. In unpinched configurations (i.e., 2/2 configurations), there is no scaling (i.e., K is one), because noise signals  72  for both electrodes  74  and  78  are relatively equal (and are equal to the noise signals on electrodes  76 ). In slightly pinched-off configurations (e.g., 1/3 configurations on both the left and right edges), the value of K may be decreased to 0.75 or other suitable value. In completely pinched-off configurations (e.g., 0/4 configurations on both the left and right edges), the value of K may be decreased further to 0.6 or other suitable value. Other types of scaling function may be used by touch sensor circuitry  26  if desired. The use of a look-up table to store values of a linear noise data scaling parameter that varies as a function of distance between stylus  18  and display edge  42  is merely illustrative. 
     A flow chart of illustrative steps involved in processing touch sensor data (e.g., touch sensor data gathered from touch sensor electrodes  24  in display  14 ) is shown in  FIG. 15 . 
     At step  90 , touch sensor circuitry  26  (e.g., bandpass filter and transimpedance amplifier  60  and demodulator  62 ) may gather signal data from electrodes  24 . 
     Steps  92 ,  94 ,  96 ,  98 , and  100  may be performed using noise correction module  64  ( FIG. 6 ). 
     At step  92 , touch sensor circuitry  26  may identify the main signals on sensors  24 . In particular, touch sensor circuitry  26  may identify the pen present signals  70  on pen present electrodes  76 . 
     At step  94 , touch sensor circuitry  26  may determine whether stylus  18  is close to display (and sensor) edge  42 , so that noise electrodes are being pinched off. In configurations in which stylus  18  is located near the center of display  14 , the noise electrodes will not be pinched off and scaling factor K may be set to 1 at step  96  (i.e., scaling is disabled). In configurations in which stylus  18  is near edge  42 , the value of K may be determined based on how far pen present electrodes  76  are from edge  42  (step  98 ). For example, the look-up table of  FIG. 14  may be used to determine K in response to determining whether the noise sampling electrodes are in a 1/3 or 0/4 configuration (in a four noise electrode example). 
     After determining K, touch sensor circuitry  26  may remove noise from the raw pen present signals  70  gathered using pen present electrodes  76  (step  100 ). During the operations of step  100 , noise correction module  64  of processor  52  may compute the average noise signal on the noise electrodes (i.e., the value of mean(S i,n ), where signals S i,n  represent sampled noise data—see, e.g., signals  72  of  FIGS. 8, 9, 10, 11, 12, and 13 ). Scaling factor K may be multiplied against this value to scale the noise appropriately (i.e., to scale the noise data based on the distance of pen present electrodes  76  from edge  42 ). Noise correction module  64  may then compute noise-removed pen present signal values (i.e., signals S i,c ) by subtracting {K mean(S i,n )} from raw pen present signals S i,m  (signals  70 ). If desired, noise correction operations may be performed in phase with the received signals (e.g., by performing subtraction operations and other correction operations in phase with raw pen present signals such as I and Q signals from demodulator  62 ). 
     Other types of noise removal process may be used to remove noise from the pen present data on the pen present electrodes. The use of subtraction to remove a scaled version of the average value of the noise measured with 2 M adjacent noise electrodes is merely illustrative. 
     At step  102 , position determination module  66  may determine the position of stylus  18  (i.e., stylus coordinates in dimensions X and Y). Processing may then loop back to step  90 , as shown by line  104 . During the operations of step  102 , control circuitry such as system-on-chip processor  48  may take suitable action based on the stylus coordinates. For example, control circuitry in device  10  may draw a line on display  14  using display driver circuitry  28 , may determine whether a user has made a selection of an on-screen option and respond appropriately, or may take other suitable action in connection with an operating system, application program, or other code running on device  10 . 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20141121
Publication Date: 20170131
Grant Date: 20170131
Priority Date: 20141121
Inventors: AGARWAL MANU
SHAHPARNIA SHAHROOZ
PANT VIVEK
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 56010162