Noise reduction for touch sensor system with active stylus

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.

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'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.

DETAILED DESCRIPTION

An electronic device such as electronic device10ofFIG. 1may 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 stylus18may be used to provide touch input to the touch sensor.

Electronic device10may 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'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 ofFIG. 1, device10is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. Other configurations may be used for device10if desired. The example ofFIG. 1is merely illustrative.

In the example ofFIG. 1, device10includes a display such as display14mounted in housing12. Housing12, 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. Housing12may be formed using a unibody configuration in which some or all of housing12is 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.).

Display14may 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 display14allows light from an array of pixels within display14to be used to display images for a user. The touch sensor may, as an example, be mounted on the outside of display14(e.g., on the underside of a display cover layer or other protective layer). During operation, the light from display14may pass through the touch sensor for viewing by a user.

Display14may 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.

Display14may 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 button16. An opening may also be formed in the display cover layer to accommodate ports such as speaker ports. Openings may be formed in housing12to 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 housing12to accommodate a data port.

During operation, a user of device10may supply input to device10using stylus18. Stylus18, which may sometimes be referred to as a computer stylus or pen, may have a tip such as tip20. Circuitry within stylus18may be used to emit electrical signals that are detected by the capacitive touch sensor electrodes of the touch sensor of device10(e.g., the touch sensor of touch screen display14). Device10may contain touch sensor circuitry that detects and processes the emitted electromagnetic signals to determine the position of stylus18(i.e., to determine the position of tip20on display14relative to lateral dimensions X and Y).

FIG. 2is a top view of an illustrative capacitive touch sensor. As shown inFIG. 2, touch sensor22may have electrodes24. Electrodes24may be formed from metal, transparent conductive materials such as indium tin oxide, or other conductive material. When mounting touch sensor22ofFIG. 2over the front of a display, electrodes24are preferably formed from a transparent conductive material such as indium tin oxide.

Electrodes24may have any suitable shape and layout. For example, electrodes24may be formed from horizontal conductive strips24-2and vertical conductive strips24-1(i.e., elongated electrodes24-1and24-2may run perpendicular to each other). There may be multiple rows of strips24-2and multiple rows of strips24-1in sensor22. Touch sensors with larger numbers of rows and columns of electrodes24exhibit greater spatial resolution than touch sensors with fewer electrodes, but can be more complex and costly than simpler touch sensors. Touch sensor circuitry26may be coupled to electrodes24-1and24-2(e.g., to supply drive signals to electrodes24-2while sensing signals on electrodes24-1). Electrodes24may, if desired, have other shapes. The use of overlapping rows and columns of capacitive touch sensor electrodes is merely illustrative.

FIG. 3is a cross-sectional side view of display14. As shown inFIG. 3, display14may include display cover layer32. Display cover layer32may be formed from transparent plastic, clear glass, a clear ceramic, a clear crystalline material such as sapphire, or other transparent material. Touch sensor electrodes24may be mounted under display cover layer32. Touch sensor circuitry26may supply signals to touch sensor electrodes24and may process signals received from the touch sensor formed by touch sensor electrodes24to determine the position of the tip of stylus (pen)18on display14(i.e., the position of stylus18in dimensions X and Y). Display14may have display layers38(e.g., a display module or other display structures) that emit light43for images. User30may observe the images produced by display module38when viewing display14in direction40. Touch sensor electrodes24may be transparent so that light43from display module38passes through touch sensor electrodes24and cover layer32. Display module38may 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 module38may have signal lines that convey data and control signals produced by display driver circuitry28to an array of pixels in display module38. These signals in display module38have the potential to create electromagnetic signal noise that affects the operation of the touch sensor. For example, data line signals can create noise in electrodes24. To help shield touch sensor electrodes24from noise produced by display module38, the upper surface of display module38(e.g., the upper surface of a color filter layer) or other layer in display14may be provided with a transparent shield layer such as shield layer34. Shield layer34may be formed from a transparent conductive material such as indium tin oxide and may be grounded along its peripheral edges42(i.e., shield34may be shorted to ground36along the edges of display14and the touch sensor of display14that is formed by touch sensor electrodes24). The presence of shield layer34may help prevent noise from signals such as data line signals in display module38from 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 edges42.

FIG. 4is a cross-sectional side view of an illustrative touch screen display to which touch input is being provided by stylus18. As shown by electromagnetic field lines44, electromagnetic signals from stylus18may be detected by one or more touch sensor electrodes24-1in the touch sensor of display14. In the example ofFIG. 4, signals44are being detected by four of electrodes24-1that are in the vicinity of the tip of stylus18, but are not detected by other electrodes24-1(i.e., electrodes that are adjacent to the main four electrodes) because those electrodes are too far away from the tip. Touch sensor circuitry26can monitor the signals on electrodes24and can use the presence of signals44on certain electrodes24to determine the location of stylus18in lateral dimensions X and Y.

Touch sensor electrodes24ofFIG. 4may be formed on the upper and lower surfaces of a sheet of polymer or other dielectric support structure (i.e., touch sensor22may be use a two-sided electrode pattern). The upper electrodes (electrodes24-1in the example ofFIG. 4) may run into and out of the page along the Y axis. The lower electrodes (electrodes24-2) may run along the X axis. Display module38may have signal lines such as data lines46that emit noise. To help reduce spatial variations in the electromagnetic noise signals from data lines D that are coupled onto electrodes24, the lower electrodes (i.e., electrodes24-2) can be configured to run perpendicular to data lines46. If, for example, data lines46run along axis Y, lower electrodes24-2may 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 electrodes24that are not in the immediate vicinity of stylus18(e.g., electrode24-1′ in the example ofFIG. 4) may not receive significant electrical signals44from stylus18. Noise (e.g., electrical noise from data lines46or other signal sources in display module38) may be produced uniformly across display14and may therefore be coupled onto both the electrodes that are in the vicinity of stylus18and electrodes that are not in the vicinity of stylus18(e.g., electrode24-1′). To remove noise data from the electrodes that have stylus signals, noise signals can be measured using one or more electrodes such as electrode24-1′ that are not receiving significant stylus data and this noise data can be subtracted or otherwise removed from the stylus data on24-1.

Touch sensor signal processing can be performed using touch sensor circuitry26. As shown inFIG. 5, touch sensor circuitry26may include front-end circuitry50and processor circuitry52. Front-end circuitry50and processor circuitry52may 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 circuitry48or other control circuitry in device10may use position information from touch sensor circuitry26in controlling the operation of device10.

FIG. 6is a diagram showing how touch sensor circuitry26may process analog signals from capacitive touch sensor electrodes24. As shown inFIG. 6, touch sensor circuitry26may include front-end circuitry50and processing circuitry52. Front-end circuitry50may include band pass filter and transimpedance amplifier60and demodulator62for converting analog signals from electrodes24into digital electrode signals.

Stylus18may emit electromagnetic signals that are modulated using any suitable modulation scheme. For example, stylus18may use quadrature amplitude modulation. Demodulator62may include circuitry for demodulating the signals emitted by stylus18. For example, demodulator62may be a quadrature demodulator that demodulates the signals from circuitry60and that produces corresponding in-phase (I) and quadrature phase (Q) signals as outputs. Circuitry50may be implemented in hardwired circuitry in touch sensor circuit26.

If desired, stylus18may have multiple electrodes (e.g., two stylus electrodes, three or more stylus electrodes, etc.). Stylus electrodes in stylus18emit signals that are detected by touch sensor electrodes24and may therefore sometimes be referred to as drive electrodes or pen drive electrodes. Stylus18may have a tip electrode located at the tip of end20of stylus18, may have a ring electrode (e.g., a drive electrode with the shape of a ring that encircles stylus18), and/or other drive electrodes.

In configurations for stylus18with multiple pen drive electrodes, each of the drive electrodes may be modulated differently. For example, stylus18may 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 circuitry50can 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.

Processor52may perform noise correction operations (see, e.g., noise correction module64) and position determination operations (see, e.g., position determination module66). During noise correction operations, digital noise signals that are gathered using electrodes24and circuitry50may be removed from digital stylus signals that are gathered using electrodes24and circuitry50. 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 stylus18). 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 demodulator62).

As described in connection withFIG. 4, display signal lines such as data lines46produce noise that is coupled into touch sensor electrodes24. Display noise tends to be produced uniformly by all of lines46. However, because shield34is grounded along edges42, shielding effectiveness tends to be largest at the edges of display14. As a result, the amount of noise that is coupled into electrodes14tends to increase near the center of display68and tends to be minimized near edges42. Touch sensor electrode noise magnitude for an illustrative touch sensor has been plotted as a function of distance X across the surface of display14in the graph ofFIG. 7. As shown by curve68, noise is largest near the center of the touch sensor and display and is lowest near edges42.

When stylus18is placed in the vicinity of electrodes24, a set of N electrodes24-1will receive significant stylus signals from electrodes and circuitry in stylus18. 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 stylus18are 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. Processor52(i.e., noise correction module64ofFIG. 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 edges42of display14, 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 electrodes24of display14are shown inFIGS. 8, 9, 10, 11, 12, and 13.

FIGS. 8, 9, and 10show how pen present and noise signals can be gathered in a configuration in which pen present data is collected from three electrodes.FIG. 8shows how data may be measured in a configuration in which pen present electrodes76are located in the center of display14. In this type of situation, noise sampling electrodes74and78are not located at the edge of display14and are therefore not pinched off by the presence of the display (and touch sensor) edge42. Accordingly, pen present data70can be sampled from a set of electrodes such as electrodes76among electrodes24and noise samples72can be taken from noise sample electrodes74(on the left of pen present electrodes76) and from noise sample electrodes78(on the right of pen present electrodes76). There are three pen present electrodes76, two left noise electrodes74, and two right noise electrodes78in the example ofFIG. 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 circuitry26can identify which of electrodes24correspond 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 edges42may be determined. When the stylus is near the edge of display14, the pattern of noise electrodes that is used in gathering noise data72can be adjusted to accommodate the display edge.

In the example ofFIG. 8, pen present electrodes76are located in the center of display14, so the noise electrodes from which noise signals72are measured are equally spaced about pen present electrodes76. Two electrodes are located in left-side noise electrodes74and two electrodes are located in right-side noise electrodes78. In the example ofFIG. 9, stylus18is located near display edge42, so that pen present electrodes76are separated from edge42of display14by only a single electrode24(i.e., left side noise electrodes74contain only a single electrode). As a result, the number of right-side noise electrodes78that are being used has been expanded from two electrodes to three electrodes. In the example ofFIG. 10, stylus18is located even nearer display edge42, so that no noise electrodes74are interposed between pen present electrodes76and edge42. In this scenario, there are four right-side noise electrodes78. 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 electrodes24-1may be treated in the same way. The use of a left-hand pinch-off condition in the example ofFIGS. 8, 9, and 10is merely illustrative. Because there are two electrodes74and two electrodes78in the arrangement ofFIG. 8, configurations of the type shownFIG. 8in which none of the noise electrodes are pinched off may sometimes be referred to as 2/2 configurations. There is one electrode74and three electrodes78in the configuration ofFIG. 9, so the configuration ofFIG. 9may be referred to as a 1/3 configuration.FIG. 10is an example of a 0/4 configuration (0 electrodes74and 4 electrodes78are being used for noise data collection).

FIGS. 11, 12, and 13show how pen present data and noise data can be gathered in a configuration in which pen present data is collected from four electrodes.FIG. 11shows how data may be measured in a configuration in which pen present electrodes76are located in the center of display14(i.e., a 2/2 configuration).FIG. 12shows an illustrative 1/3 configuration with four electrodes76, whereasFIG. 13shows and illustrative 0/4 configuration with four electrodes78. 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 ofFIGS. 8, 910,11,12, and13are merely illustrative.

As shown by curve68inFIG. 7, noise decreases in magnitude near edges42. The downward slope of noise curve68creates larger noise signals on the inner side of pen present pixels76than on the outer side of pen present pixels76when stylus18is near edge42. 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 stylus18is near edges42.

FIG. 14is a look-up table showing how noise scaling factor K may be adjusted by touch sensor circuitry26as 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 signals72for both electrodes74and78are relatively equal (and are equal to the noise signals on electrodes76). 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 circuitry26if 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 stylus18and display edge42is merely illustrative.

A flow chart of illustrative steps involved in processing touch sensor data (e.g., touch sensor data gathered from touch sensor electrodes24in display14) is shown inFIG. 15.

At step90, touch sensor circuitry26(e.g., bandpass filter and transimpedance amplifier60and demodulator62) may gather signal data from electrodes24.

At step92, touch sensor circuitry26may identify the main signals on sensors24. In particular, touch sensor circuitry26may identify the pen present signals70on pen present electrodes76.

At step94, touch sensor circuitry26may determine whether stylus18is close to display (and sensor) edge42, so that noise electrodes are being pinched off. In configurations in which stylus18is located near the center of display14, the noise electrodes will not be pinched off and scaling factor K may be set to 1 at step96(i.e., scaling is disabled). In configurations in which stylus18is near edge42, the value of K may be determined based on how far pen present electrodes76are from edge42(step98). For example, the look-up table ofFIG. 14may 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 circuitry26may remove noise from the raw pen present signals70gathered using pen present electrodes76(step100). During the operations of step100, noise correction module64of processor52may compute the average noise signal on the noise electrodes (i.e., the value of mean(Si,n), where signals Si,nrepresent sampled noise data—see, e.g., signals72ofFIGS. 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 electrodes76from edge42). Noise correction module64may then compute noise-removed pen present signal values (i.e., signals Si,c) by subtracting {K mean(Si,n)} from raw pen present signals Si,m(signals70). 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 demodulator62).

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 step102, position determination module66may determine the position of stylus18(i.e., stylus coordinates in dimensions X and Y). Processing may then loop back to step90, as shown by line104. During the operations of step102, control circuitry such as system-on-chip processor48may take suitable action based on the stylus coordinates. For example, control circuitry in device10may draw a line on display14using display driver circuitry28, 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 device10.