Active stylus differential synchronization

A touch-sensing system is disclosed. The system includes a display device including a touch sensor having a plurality of electrodes, and drive logic coupled to the plurality of electrodes and configured to drive the plurality of electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame during which the drive logic drives at least some of the plurality of electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms that are communicated electrostatically to cause synchronization of the display device with an active stylus. For each of the stylus sync sub-frames, the drive logic may be configured to differentially drive the sync-driven electrodes of such stylus sync sub-frame, such that a first synchronization waveform used to drive one of the sync-driven electrodes is different than a second synchronization waveform used to drive another of the sync-driven electrodes.

BACKGROUND

Some touch sensors are configured to detect touch input by sensing changes in capacitance at electrode locations in an electrode matrix. Touch inputs may be from a user's body (e.g., a finger) and, in some cases, a passive or active stylus. In active-stylus implementations, the stylus may be synchronized with the touch sensor to achieve a shared sense of time between the stylus and touch sensor. This may, among other things, facilitate determinations of stylus position relative to the touch sensor.

Multiple electrodes of the matrix may be driven simultaneously with a synchronization waveform. Via capacitive coupling, this causes current to flow into a tip electrode of the stylus. The current pattern is processed in receive logic of the stylus to achieve synchronization. Current flowing into the stylus tip may be affected by various capacitances and other conditions.

DETAILED DESCRIPTION

Some touch sensors are configured to detect touch input by sensing changes in capacitance in an electrode matrix. As used herein, “matrix” refers to, among other things, intersections between elongate row and column electrodes at which mutual capacitance is measured by driving at one, and receiving at the other, of the row and column electrodes. In other examples, “matrix” also refers to an array of locations where the self-capacitance of electrodes is measured, with both driving and receiving occurring at the electrodes. Indeed, “matrix” is applicable to any electrode scheme in which capacitance measurements are localized to XY coordinates across a touch-sensitive display or other expanse. In the examples herein, touch inputs may be detected from contact and/or hover of a user's body (e.g., a finger) and an active stylus over the electrode matrix. The stylus may be synchronized with the touch sensor to achieve a shared sense of time between the stylus and touch sensor (and/or a display device incorporating the touch sensor). Among other things, the shared sense of time facilitates determinations of relative stylus position.

Synchronization typically is performed every touch-sensing frame during a sub-frame referred to as a stylus sync sub-frame. During a stylus sync sub-frame, electrodes are driven with synchronization waveforms. For a given stylus sync sub-frame, the activated electrodes are referred to as sync-driven electrodes. Via capacitive coupling of sync-driven electrodes with a tip electrode in the active stylus, synchronization signals are received into receive logic of the stylus, in the form of current patterns flowing into the stylus tip (e.g., time varying current waveform). The inbound current pattern is processed in the receive logic to perform synchronization. In the examples herein, electrodes spanning the matrix (e.g., a subset of electrodes) are activated as sync-driven electrodes, allowing the stylus to achieve synchronization regardless of its vertical coordinate relative to the electrodes.

Current flowing into the stylus tip may be affected by various capacitances and other conditions. One challenge in particular may occur when the user's body comes into contact with the matrix. Even when such contact is relatively small (e.g., a fingertip as opposed to a resting palm), the contact patch will typically result in a relatively large increase in capacitance between the user's body and activated sync-driven electrodes. For example, as compared to the relatively small stylus tip, the user's body may overlap a greater number of sync-driven electrodes, and/or over a greater portion of the overlapped electrodes. Accordingly, the increase in body-to-matrix capacitance resulting from body contact may be significantly larger than the increase in stylus-to-matrix capacitance resulting from stylus tip contact. This may produce a change at various voltage nodes to cause a current flow into the user's body of sufficient magnitude to undesirably degrade current flow into the stylus tip, thereby reducing synchronization performance.

Accordingly, the disclosure contemplates differential driving of sync-driven electrodes within stylus sync sub-frames. Specifically, at least some different synchronization waveforms are used for different sync-driven electrodes. One sync-driven electrode might be driven with one waveform, while another, different synchronization waveform is used for another sync-driven electrode. In some cases, two waveforms may be used (e.g., two waveforms of inverse polarity) to drive sync-driven electrodes. In other cases, three or more different waveforms may be used. In some examples, two-value pulse trains are employed (e.g., binary waveforms). In other cases, employed waveforms may include digital waveforms taking on a greater range of values, analog waveforms, or any other type of waveforms.

Differential waveforms may be employed to provide cancellation to reduce current into a user's body. For example, within a given spatial grouping of sync-driven electrodes, differential waveforms may be employed so as to produce at least partially cancelling electrical conditions. Therefore, for a user body contact patch over that spatial grouping, current flowing into the user's body is reduced relative to what would occur with undifferentiated driving (using the same waveform on all of the sync-driven row electrodes in the grouping).

In some examples, different sets of sync-driven electrodes may be employed for different stylus sync sub-frames, with different synchronization waveforms being used in each set. In other words, one set of sync-driven electrodes might be employed for one sub-frame, with a second, different set of sync-driven electrodes employed for the next sub-frame. Any number of sets may be employed. Typically, the sets differ in that one or more electrodes function as sync-driven electrodes in one set, but not in another set. Reasons for omitting some electrodes from being activated during a sync sub-frame will be explained in detail below. For a given stylus contact point, shifting synchronization waveforms via use of different sets from frame-to-frame changes the distance between those waveforms and the stylus contact point, which affects the signals received into the stylus. One of the sets may be preferred for a given contact point, in that it brings a useful waveform close to the stylus, while having potentially canceling waveforms further away from the stylus. In such a setting, position information of the stylus may be used to select a particular set for an upcoming sync sub-frame (i.e., selecting a set which results in a desired waveform being positioned as close as possible to the current stylus location).

Approaches to differentially driving electrodes in a touch sensor are disclosed herein for both sensors that employ mutual capacitance sensing in a row/column electrode matrix, and for sensors that employ self-capacitance sensing in an electrode matrix. In particular,FIGS. 2-6depict examples that relate to mutual capacitance sensing, whereasFIGS. 8-10depict examples that relate to self-capacitance sensing. It will be understood that at least some of the approaches to differential electrode driving described with reference to mutual capacitance sensing may be employed in connection with self-capacitance sensing, and that at least some of the approaches to differential electrode driving described with reference to self-capacitance sensing may be employed in connection with mutual capacitance sensing, where adjustment may be potentially made when translating a differential driving method from one sensor type to another.

FIG. 1shows a touch interactive display system100including a display device102that has a touch sensor104. In some examples, display device102may be a large format display with a diagonal dimension D greater than 1 meter, though the display may assume any suitable size. Display device102may be configured to sense one or more sources of input, such as touch input imparted via a digit106of a user and/or input supplied by an input device108, shown inFIG. 1as a stylus. Digit106and input device108are provided as non-limiting examples and any other suitable source of input may be used in connection with display device102. Display device102may be configured to receive input from styluses and digits in contact with the display and/or “hovering” over the display surface. “Touch input” as used herein refers to both digit and non-digit (e.g., stylus) input, and to input supplied by input devices both in contact with, and spaced away from but proximate to, display device102. In some examples, display device102may be configured to receive input from two or more sources simultaneously, in which case the display may be referred to as a multi-touch display.

Display device102may be operatively coupled to an image source110, which may be, for example, a computing device external to, or housed within, the display. Image source110may receive input from display device102, process the input, and in response generate appropriate graphical output112for the display. In this way, display device102may provide a natural paradigm for interacting with a computing device that can respond appropriately to touch input. Details regarding an example computing device are described below with reference toFIG. 13.

FIG. 2is a cross-sectional view of an optical stack200of display device102(FIG. 1). Optical stack200includes a plurality of components configured to enable the reception of touch input and the generation of graphical output. As shown inFIG. 2, optical stack200may include an optically clear touch sheet202having a top surface204for receiving touch input, and an optically clear adhesive (OCA)206bonding a bottom surface of the touch sheet to a top surface of a touch sensor208, which may be touch sensor104(FIG. 1), for example. Touch sheet202may be comprised of any suitable materials, such as glass or plastic. As used herein, “optically clear adhesive” refers to a class of adhesives that transmit substantially all (e.g., about 99%) of incident visible light.

As described in further detail below with reference toFIG. 3, touch sensor208includes a matrix of electrodes that form capacitors whose capacitances may be evaluated in detecting touch input. As shown inFIG. 2, the electrodes may be formed in two separate layers: a receive electrode layer (Rx)210and a transmit electrode layer (Tx)212positioned below the receive electrode layer. Receive and transmit electrode layers210and212may each be formed on a respective dielectric substrate comprising materials including but not limited to glass, polyethylene terephthalate (PET), or cyclic olefin polymer (COP) film. Receive and transmit electrode layers210and212may be bonded together by a second optically clear adhesive211. OCA211may be an acrylic pressure-sensitive adhesive film, for example. The touch sensor configuration illustrated inFIG. 2is provided as an example; alternative arrangements are within the scope of this disclosure. In other implementations, for example, layers210,211, and212may be integrally formed as a single layer with electrodes disposed on opposite surfaces of the integral layer. Further, touch sensor208may alternatively be configured such that transmit electrode layer212is provided above, and bonded to via OCA211, with receive electrode layer210being positioned therebelow.

Receive and transmit electrode layers210and212may be formed by a variety of suitable processes. Such processes may include deposition of metallic wires onto the surface of an adhesive, dielectric substrate; patterned deposition of a material that selectively catalyzes the subsequent deposition of a metal film (e.g., via plating); photoetching; patterned deposition of a conductive ink (e.g., via inkjet, offset, relief, or intaglio printing); filling grooves in a dielectric substrate with conductive ink; selective optical exposure (e.g., through a mask or via laser writing) of an electrically conductive photoresist followed by chemical development to remove unexposed photoresist; and selective optical exposure of a silver halide emulsion followed by chemical development of the latent image to metallic silver, in turn followed by chemical fixing. In one example, metalized sensor films may be disposed on a user-facing side of a substrate, with the metal facing away from the user or alternatively facing toward the user with a protective sheet (e.g., comprised of PET) between the user and metal. Although transparent conducting oxide (TCO) is typically not used in the electrodes, partial use of TCO to form a portion of the electrodes with other portions being formed of metal is possible. In one example, the electrodes may be thin metal of substantially constant cross section, and may be sized such that they may not be optically resolved and may thus be unobtrusive as seen from a perspective of a user. Suitable materials from which electrodes may be formed include various suitable metals (e.g., aluminum, copper, nickel, silver, gold), metallic alloys, conductive allotropes of carbon (e.g., graphite, fullerenes, amorphous carbon), conductive polymers, and conductive inks (e.g., made conductive via the addition of metal or carbon particles).

Continuing withFIG. 2, touch sensor208may be bonded, at a bottom surface of transmit electrode layer212, to a display stack214via a third optically clear adhesive216. Display stack214may be a liquid crystal display (LCD) stack, organic light-emitting diode (OLED) stack, or plasma display panel (PDP), for example. Display stack214is configured to emit light L through a top surface of the display stack, such that emitted light travels in a light emitting direction through layers216,212,211,210,206, touch sheet202, and out through top surface204. In this way, emitted light may appear to a user as an image displayed on top surface204of touch sheet202.

Further variations to optical stack200are possible. For example, implementations are possible in which layers211and/or216are omitted. In this example, touch sensor208may be air-gapped and optically uncoupled to display stack214. Further, layers210and212may be laminated on top surface204. Still further, layer210may be disposed on top surface204while layer212may be disposed opposite and below top surface204.

FIG. 2also shows a controller218operatively coupled to receive electrode layer210, transmit electrode layer212, and display stack214. Controller218is configured to drive transmit electrodes in transmit electrode layer212, receive signals resulting from driven transmit electrodes via receive electrodes in receive electrode layer210, and locate, if detected, touch input imparted to optical stack200. Controller218may further drive display stack214to enable graphical output responsive to touch input. Two or more controllers may alternatively be provided, and in some examples, respective controllers for each of receive electrode layer210, transmit electrode layer212, and display stack214. In some implementations, controller218may be implemented in image source110(FIG. 1).

FIG. 3shows an example touch sensor matrix300. Matrix300may be included in touch sensor208of optical stack200(FIG. 2) to bestow touch sensing functionality to display device102(FIG. 1), for example. Matrix300includes a plurality of row electrodes and column electrodes. In the present example, the electrodes are shown in the form of row electrodes302vertically separated from column electrodes304. As described below, the row electrodes may be transmitters/drivers, with voltage waveforms (also referred to as “excitation waveforms”) being used to stimulate them via operation of drive logic. This in turn affects electrical conditions on the column electrodes (e.g., the excitation waveform produces a time-varying current on the column electrode), and the column electrodes operate in a receive mode with accompanying circuitry to process the induced electrical conditions. Referring again toFIG. 2, row electrodes302and column electrodes304may be respectively formed in transmit electrode layer212and receive electrode layer210of optical stack200, for example. Each intersection of row electrodes302with column electrodes304forms a corresponding node whose electrical properties (e.g., capacitance) may be measured to detect touch input. Three row electrodes302and three column electrodes304are shown inFIG. 3for the purpose of clarity, though matrix300may include any suitable number of row electrodes and column electrodes, which may be on the order of one hundred or one thousand, for example. Any suitable number of electrodes may be employed, depending on the setting.

While a rectangular grid arrangement is shown inFIG. 3, matrix300may assume other geometric arrangements—for example, the matrix may be arranged in a diamond pattern. Alternatively or additionally, individual electrodes in matrix300may assume nonlinear geometries—e.g., electrodes may exhibit curved or zigzag geometries, which may minimize the perceptibility of display artifacts (e.g., aliasing, moiré patterns) caused by occlusion of an underlying display by the electrodes. In addition, “row” and “column,” as used herein, does not imply any particular orientation relative to the display or to the floor/ground. In other words, relative to the display device or floor/ground, rows may be horizontal, vertical or in any other orientation. Typically, however, all of the rows will be parallel to one another, as will all of the columns.

The depicted system may also include drive logic306coupled to the row electrodes302and receive logic308coupled to the column electrodes304. Drive logic306and receive logic308may perform a variety of functions, and may, as in the present example, be interconnected in order to coordinate activity, exchange data, etc. In general, drive logic306is involved in causing excitation waveforms to be applied to row electrodes302, while receive logic308is involved in processing and interpreting signals on column electrodes304.

Each row electrode302in matrix300may be coupled to a respective driver310(included in drive logic306) configured to drive its corresponding row electrode with an excitation waveform (e.g., a time-varying voltage). In some implementations, drivers310of matrix300may be driven by a micro-coded state machine implemented within a field-programmable gate array (FPGA) forming part of controller218(FIG. 2), for example. Each driver310may be implemented as a shift register having one flip-flop and output for its corresponding row electrode, and may be operable to force all output values to zero, independently of register state. The inputs to each shift register may be a clock, data input, and a blanking input, which may be driven by outputs from the micro-coded state machine. Signals may be transmitted by filling the shift register with ones on every output to be excited, and zeroes elsewhere, and then toggling the blanking input with a desired modulation to create a transmitted waveform for exciting a row electrode. The excitation waveforms may be time-varying voltages that, when digitally sampled, comprise a sequence of pulses—e.g., one or more samples of a relatively higher (or lower) digital value followed by one or more samples of a relatively lower (or higher) digital value. If a shift register is used in this fashion, waveforms may take on only two digital values—e.g., only binary waveforms can be transmitted. In other implementations, drivers310may be configured to transmit non-binary waveforms that can assume three or more digital values. Non-binary excitation waveforms may enable a reduction in the harmonic content of driver output and decrease the emissions radiated by matrix300. In still other examples, non-quantized waveforms may play a role in row electrode excitation. Any practicable method may be employed by drive logic306to generate appropriate excitation waveforms on the row electrodes302.

In some implementations, matrix300may be configured to communicate and interact with an active stylus320(e.g., corresponding to input device108ofFIG. 1), which may include a tip electrode322(also referred to as the stylus electrode or stylus tip); drive logic324responsible for applying waveforms to tip electrode322for transmission to matrix300; and receive logic326responsible for processing waveforms received from matrix300(e.g., as a result of drive logic306exciting a row electrode302in close proximity to the stylus tip). In the context ofFIG. 1, use of a stylus such as active stylus320may at least partially enable touch sensitive display device102to communicate with input device108when matrix300is implemented in display device102. Specifically, an electrostatic link may be established between tip electrode322and one or more row electrodes302or one or more column electrodes304, along which data may be transmitted.

In one example, electrostatic communication is conducted via transmission of a synchronization waveform from matrix300to the active stylus320. The synchronization waveform may enable matrix300and stylus322to obtain a shared sense of time. In some examples, synchronization waveforms may be transmitted via multiple row electrodes302simultaneously so that the active stylus can receive the synchronization waveform regardless of the active stylus's position relative to the matrix. In the case that waveforms are transmitted by multiple row electrodes302simultaneously, different waveforms may be used on different row electrodes302, as explained in detail below. In some cases, synchronization may be performed via correlation operations, in which received waveforms are processed using reference waveforms that are based on the synchronization waveforms.

The shared sense of time may facilitate the correlation of a time at which the stylus detects a signal transmitted on row electrodes302to a location on matrix300. Such correlation may enable the stylus to determine at least one coordinate (e.g., its row coordinate) relative to matrix300, which may be transmitted back to the matrix (e.g., via the electrostatic link) or to an associated display via a different communication protocol (e.g., radio, Bluetooth). To determine a second coordinate (e.g., a column coordinate) of the stylus, all row electrodes302may be held at a constant voltage, and the stylus may transmit a time-varying voltage to matrix300, which may measure currents resulting from the stylus voltage in each column electrode304to ascertain the second coordinate.

Each column electrode304in matrix300may be coupled to a respective receiver312configured to analyze received signals resulting from the transmission of waveforms on row electrodes302. During touch detection, matrix300may hold all row electrodes302at a constant voltage except for an active row electrode302along which an excitation waveform is transmitted. During transmission of the excitation sequence, all column electrodes304may be held at a constant voltage (e.g., ground). With the excitation waveform applied to the active row electrode302and all column electrodes304held at the constant voltage, a current may flow into each of the receivers312as a result of application of the excitation waveform. This current is proportional to the capacitance. Touch detection is achieved as a result of the change in capacitance produced, for example, by the presence of a user's finger. Matrix300may be repeatedly scanned at a frame rate (e.g., 60 Hz, 120 Hz) to persistently detect touch input, where a complete scan of a frame comprises applying an excitation sequence to each transmit row302, and for each driven transmit row, collecting output from all of the receive columns304. However, in other examples, a complete scan of a frame may be a scan of a desired subset, and not all, of one or both of transmit row electrodes302and receive column electrodes304.

Higher resolution positional determinations of both a user's finger and an active stylus may be achieved via interpolation methods. Using the above example of determining a stylus's row coordinate, measurements for rows on either side of a highest-signal row may be assessed. Assuming the stylus detects a highest signal strength at time t(K), corresponding to the excitation of row K, the system may also take readings from any number or distribution of neighboring row electrodes. In one non-limiting example, measurements are assessed for rows K−2, K−1, K+1 and K+2. The distribution of received signal strength across these rows enables the system to increase the positional resolution. Similarly, when the stylus is transmitting through operation of drive logic324, one of the column electrodes304receives the strongest signal (i.e., the nearest column to the stylus). Signal strength at nearby columns can be used for interpolation. Similar interpolation methods may be used for determining finger/hand position (i.e., measure strength of signals neighboring the highest-signal column or highest-signal row).

From the above, it will be appreciated that touch functionality (from user's body and stylus) occurs over an ongoing series of touch-sensing frames, during which drive logic in matrix300or stylus320drive electrodes therein to transmit waveforms to receiving electrodes, where the received signals are processed by receive logic (e.g., receive logic308or receive logic326).FIG. 4depicts an example touch-sensing frame400. Each touch-sensing frame400includes a number of different sub-frames. One sub-frame is a stylus sync sub-frame (SSSF)402, during which, as described above, row electrodes302on matrix300transmit synchronization waveforms to enable stylus320and display device102to gain/maintain a shared sense of time.

During any given stylus sync sub-frame (SSSF)402, the specific row electrodes302being driven with synchronization waveforms are referred to, for that stylus sync sub-frame (SSSF)402, as sync-driven row electrodes. The specific sync-driven row electrodes being used may vary from one stylus sync sub-frame (SSSF)402to the next. In some cases, multiple different sets of sync-driven row electrodes may be employed, each of which omits some row electrodes302(e.g., two out of every three). In other words, a given row electrode302may be a sync-driven row electrode in one set, but not in another. In some examples, a set of sync-driven row electrodes may use differing synchronization waveforms (i.e., a waveform used on one sync-driven row electrode differs from that used on another in the set). Sync-driven row electrodes and the synchronization waveforms employed with them will be discussed in more detail below.

Two other sub-frames, also discussed above, which may be employed, are (1) a row-drive sub-frame (RDSF)404during which row electrodes are driven sequentially to support determination of a row coordinate of stylus320and row and column coordinates of user's body106; and (2) a stylus-drive sub-frame (SDSF)406during which stylus320is driven to facilitate determination of its column coordinate. Touch-sensing frames typically repeat at relatively high frequencies to support rapidly updated touch detection with minimal lag (e.g., between finger movement and a line being drawn under the user's finger). In one example, a frame rate of 120 Hz may be employed.

During the stylus sync sub-frames (SSSFs)402, gaining and maintaining proper synchronization may depend upon whether a current having sufficient magnitude is flowing into stylus electrode322. Current flowing into stylus electrode322may depend on various capacitances during the stylus sync sub-frames (SSSFs)402. The most relevant capacitances may be (1) Cts—capacitance from the stylus electrode322to row electrodes302being driven with synchronization waveforms; (2) Ctg—capacitance from stylus electrode322to a chassis ground of display device102or equivalent (e.g., receive column electrodes304or inactive row electrodes302); (3) Cbs—capacitance from the user's body106to row electrodes302being driven with synchronization waveforms (i.e., sync-driven row electrodes); and (4) Cbg—capacitance from the user's body106to a chassis ground of display device102or equivalent.

Three conditions will now be described, along with their potential effect upon current flowing into stylus electrode322in the case of undifferentiated driving of the sync-driven row electrodes. The first condition may be described as:
Cts/(Cts+Ctg)>>Cbs/(Cbs+Cbg)

Under these circumstances (equation 1 above), synchronization waveforms on row electrodes302may cause sufficient current to flow into stylus electrode322(e.g., of sufficient SNR to derive useful synchronization information from the inbound waveform).

The second condition may be described as:
Cts/(Cts+Ctg)≈Cbs/(Cbs+Cbg)  (2)

Under these circumstances (equation 2 above), synchronization waveforms on row electrodes302may cause negligible current to flow into stylus electrode322. As a result, stylus320is not able to receive a sufficiently strong signal to support synchronization.

The third condition may be described as:
Cts/(Cts+Ctg)<<Cbs/(Cbs+Cbg)  (3)

Under these circumstances (equation 3 above), synchronization waveforms on row electrodes302may cause current to flow out of stylus electrode322. Such reverse polarity/phase current may also hinder synchronization.

In many cases, capacitance of the user's body to driven rows of matrix300(Cbs) will have the strongest effect on which of the above three conditions exist during any given stylus sync sub-frame. Specifically, when the user touches display device102over matrix300, Cbs increases. The increase may be substantial, particularly in the not-infrequent case of a large contact patch (e.g., user rests their palm on the display while holding the stylus). In such a case, the user's body significantly covers sync-driven row electrodes during a series of stylus sync sub-frames (SSSFs)402. Relative to when the stylus contacts the display, the user's body overlaps more sync-driven row electrodes, and overlaps them along a greater length. As a result of the relatively large increase in Cbs and the associated change at various voltage nodes, increased current may flow into the user's body, thereby reducing current into the stylus electrode, in turn hindering the ability of the stylus to obtain a sufficiently strong synchronization signal.

As will now be described, the compromising of stylus current may in some examples be improved by differentially driving sync-driven row electrodes in touch-sensing frames400. In other words, within a given stylus sync sub-frame (SSSF)402, drive logic306may use one synchronization waveform on some sync-driven row electrodes, and another, different, synchronization waveform on other sync-driven row electrodes. Any number and type of different synchronization waveforms may be used in a given stylus sync sub-frame (SSSF)402. As described in detail below, the different synchronization waveforms are configured to create at least partially cancelling electrical conditions to reduce current flowing into a user's body that would undesirably affect synchronization current flowing into stylus electrode322.FIG. 5shows an example of such differential driving. The figure shows twelve row electrodes302, as driven during three successive stylus sync sub-frames (SSSFs)402. In this example, every nth electrode (n=3 here, but could be any other practicable number) is a sync-driven row electrode. One such sync-driven row electrode is indicated at502in the figure. Different sets of sync-driven row electrodes may be employed; three sets504are depicted. In the first stylus sync sub-frame, the set of sync-driven row electrodes (Set A) includes electrodes001,004,007,010. In the figure, sync-driven row electrodes502are distinguished from inactive row electrodes in that they are labeled with a synchronization waveform that is used on the electrode for synchronization (waveform labels in the figure are an encircled “P” and an encircled “N,” to be explained). In Set B, the sync-driven row electrodes are rows002,005,008,011; in Set C, the sync-driven row electrodes are rows003,006,009,012. When referring to a “set” of sync-driven row electrodes302, or “set information,” this disclosure is referring to the specific row electrodes that are being driven during sync, and to the specific differential waveforms that are used for sync. In the example ofFIG. 5, varied use of the three different sets cause the deployed waveforms to spatially shift in terms of row coordinate from frame to frame. This in turn, will cause the deployed respective waveforms to vary in distance to a given stylus contact point from frame to frame.

As mentioned above, different waveforms may be employed on the sync-driven row electrodes502in each set. Specifically, in any given stylus sync sub-frame (SSSF)402, drive logic306(FIG. 2) may be configured to use two or more different waveforms on different sync-driven row electrodes for synchronization. In this example, reverse polarity waveforms are used (positive waveform indicated with an encircled “P” and negative waveform indicated with an encircled “N”). As shown in the figure, Sets A, B and C differ from one another in that the spatial distribution of sync-driven row electrodes, inactive row electrodes (i.e., not driven with synchronization waveforms) and specific synchronization waveforms are the same but shifted by one row electrode302from one set to the next. The different waveforms yield at least partially cancelling electrical conditions (e.g., when two inverse waveforms are close to one another) to reduce current flowing into the user's body and thereby avoid adverse impacts upon current flowing into the stylus electrode. In all three sets, a one-by-one alternating polarity scheme is employed, in which every sync-driven row electrode is driven with a synchronization waveform that is inverted with respect to that used on the adjacent sync-driven row electrodes.

Current reduction/cancellation into the user's body may be considered in terms of “spatial groupings” of sync-driven row electrodes. Referring to the first stylus sync sub-frame (Set A), the sync-driven row electrodes502may be grouped into various spatial groupings. One such spatial grouping is indicated at505, and includes two sync-driven row electrodes502(rows004and007). Two-row groupings may also be formed from the following sync-driven row electrode pairs in Set A:001/004and007/010. Alternatively, a spatial grouping may include more than two row electrodes302(e.g., all four sync-driven row electrodes in Set A). Any practicable number of sync-driven row electrodes may comprise a spatial grouping.

When a user's body contacts display device102, a contact patch may cover a spatial grouping of sync-driven row electrodes. Such a contact patch is shown at506, and sits over spatial grouping505so as to overlap sync-driven row electrodes at rows004and007. In many cases, the contact patch will cover a larger number of row electrodes302; four electrodes, two of which are sync-driven row electrodes, are used here for clarity. As indicated above, a contact patch with significant electrode overlap can potentially produce a significant change in capacitance which can reduce current into a stylus tip. The opposite polarity waveforms on electrodes004and007may produce at least partially cancelling electrical conditions. This can reduce the current into the user's body, in some cases reducing it to zero, thereby avoiding some current reduction into the stylus electrode.

It will be appreciated that these partially cancelling conditions would occur in Sets A, B and C in the event of any contact patch overlapping any number of sync-driven row electrodes302. Overlap of an even number of electrodes potentially would allow for greater cancellation, though even where an odd number of sync-driven row electrodes are overlapped, sufficient cancellation may be achieved. Typically, and as in the present example, a plurality of spatial groupings exist across the span of the matrix, each one including differentially driven sync-driven row electrodes, such that current into a user's body would be reduced relative to that which would occur if the same waveforms were used. In some examples, current-reducing spatial groupings may be sized based on an expected minimum size of a body contact patch. For example, the grouping may be sized based on a patch size that would provide a particular level of synchronization interference in the event of undifferentiated driving of sync-driven row electrodes.

It will be appreciated that any number, type and placement of different synchronization waveforms may be used within a spatial grouping/contact patch. The above example contemplates opposite polarity waveforms (e.g., binary pulse train), alternating at every other drive electrode. A different distribution might involve clustering of similar polarities (e.g., clusters of two or more positive waveforms spatially interleaved with clusters of two or more negative waveforms). More than two different waveforms may be employed. Digital waveforms taking on more than two values may be employed. Analog waveforms may be employed. Different frequencies, phases and amplitudes may be employed. In general, any synchronization waveform configuration may be used where the different waveforms under a body contact patch provide some cancellation to reduce into-body current.

In certain settings, synchronization performance may be affected by the spacing between sync-driven row electrodes. For example, a higher density of electrodes providing cancelling waveforms may more effectively provide cancellation for a variety of different size contact patches. A relatively high density would ensure, for example, that a sufficient number of varied waveforms are driven underneath an expected smallest contact patch, i.e., sufficient to achieve a desired level of cancellation. Additionally, a high-density scheme may decrease the number of sets of sync-driven row electrodes, thereby reducing the latency for the stylus gaining the shared sense of time.

Referring to the depiction ofFIG. 5, a high-density scheme potentially could entail all twelve row electrodes302being sync-driven row electrodes, and altering one-by-one between positive “P” synchronization waveform and negative “N” synchronization waveform (e.g., even rows positive, odd rows negative). In such a case, for any given contact point of stylus electrode322on the matrix, the stylus tip would be close enough to both waveforms that they potentially would cancel/reduce current flowing into the stylus, thereby weakening the received synchronization signal.

Accordingly, in some cases it will be desirable to have an increased distance between sync-driven row electrodes, as in the every-nth example ofFIG. 5. Therefore, when the stylus is close to a particular sync-driven row electrode, the distance to neighboring sync-driven row electrodes is sufficiently large so as to reduce the capacitance from the stylus tip to those electrodes. The stylus therefore receives a strong synchronization signal, without interference from synchronization waveforms on adjacent sync-driven row electrodes that would potentially reduce the strength of the synchronization signal.

Regardless of whether sync-driven row electrodes are closely or distantly spaced, it may be desirable to employ different sets of sync-driven row electrodes. When employed, the different sets may be configured so that, for any given point on an operative portion of a touch-sensing matrix, using at least one of the sets will cause a reduction in distance, to below a threshold, between such point and a closest sync-driven row electrode, relative to another set of the sync-driven row electrodes. For example, assuming a minimum desired threshold distance between a sync-driven row electrode502and where stylus electrode322is contacting matrix300, different sync-driven row electrode sets may be employed so that at least one of them includes a sync-driven row electrode that will be within that threshold distance from the stylus electrode322, to thereby provide a sufficiently strong signal with minimized interference from other synchronization waveforms. In other words, the different sets of sync-driven row electrodes may be constructed such that cycling through them causes frame-to-frame variation between a stylus contact point and a closest sync-driven row electrode.

Referring to point508on the matrix (e.g., a contact point where stylus electrode322might contact matrix300), it will be seen that performance may vary between Sets A, B and C. Cycling through the sets from stylus sync sub-frame to the next causes the distance between point508and the closest sync-driven row electrodes to vary. As indicated above, it will normally be desirable that, for at least one of the sets, the stylus tip is relatively close to one sync-driven row electrode and relatively distant from any sync-driven row electrode that would produce cancellation (e.g., close to a one waveform and far from an inversion of that waveform). Referring specifically toFIG. 5, Set C provides the best performance in this regard. In Set A and Set B, the stylus electrode would be (1) either too far from the neighboring sync-driven row electrodes; and/or (2) the proximity to each sync-driven row electrode would be sufficient, but the nearby inverted waveforms would reduce the signal received by the stylus.

More generally, different sets of sync-driven row electrodes, and the differential waveforms used to drive them, may be used to provide, for a stylus electrode contact point on a matrix, varied positioning of the following relative to that contact point: (1) a synchronization waveform or waveforms that cause receipt of a synchronization signal into the stylus; and (2) a synchronization waveform or waveforms that counter the effect of (1). As indicated above, using different sets increases the potential that the distance of (1) will be relatively small while the distance of (2) will be relatively large.

Referring to the example ofFIG. 5, drive logic306may selectively apply the different sets in any order over successive stylus sync sub-frames. In one example, the drive logic306cycles through them repeatedly in the same sequence: ABCABCABC etc. In other examples, the sets are chosen randomly. In other examples, only some of the sets are used over a given period of time, with some being omitted.

In other examples, sets of sync-driven row electrodes are chosen selectively, rather than cycling through them in a predetermined order, to achieve a performance benefit. In some cases, the benefit is as described above, namely placing a particular synchronization waveform close to the stylus electrode, while ensuring that interfering waveforms are farther away. Accordingly, the drive logic306may select from a plurality of different sets of sync-driven row electrodes based on position information associated with an active stylus.

Position information used for set selection may be stored in various places, for example as position information330in drive logic306(FIG. 3). With regard to stylus320, position information330can take a wide variety of forms, including (1) current, past or predicted row and column coordinates of the stylus; (2) speed of stylus movement over past touch-sensing frames; (3) direction of stylus movement over past touch-sensing frames; (4) indicators affecting the ability to predict future position of the stylus; etc. In general, position information can include any type of information that may be useful in determining where stylus electrode322will be in a future touch-sensing frame. Position information may be performed in any suitable manner, including via the non-limiting examples described above, in which row drive sub-frames (RDSFs)404and stylus drive sub-frames (SDSFs)406(FIG. 4) are used to establish row coordinates and column coordinates for stylus320.

When predictive-quality exceeds a threshold (e.g., relatively high confidence in future position of stylus), drive logic may enter a mode where sync-driven row electrode sets are chosen based on the position information. Referring again to the example ofFIG. 5, if the system is able to predict, with sufficient accuracy, that the stylus electrode will be very close to point508in an upcoming touch-sensing frame, then drive logic306may employ Set C of sync-driven row electrodes for synchronization.

The drive logic may switch into and out of position-based selection. For example, prior to selecting based on position, the drive logic may be operating in a cycling mode, in which a defined sequence of sets is used, or a random cycling is used. These less-selective approaches may be employed when the system is not able to sufficiently assess whether one set will outperform another, in terms of its ability to effectively position synchronization waveforms around the stylus electrode. For example, if the stylus electrode is moving quickly, beyond a velocity threshold, then the drive logic may revert to a cycling mode (e.g., an ABCABCABCABC . . . set selection fromFIG. 5). In addition to or instead of velocity thresholds, any type of threshold associated with the position information may be used to mode switch into and out of selecting sets of sync-driven row electrodes based on position information330.

In typical implementations, receive logic, whether in matrix300or stylus320, includes specific circuitry tuned to account for the properties of the excitation signal it receives. In some examples, receive processing is performed via correlation operations using a reference signal, which typically is based off of, and in many cases identical to, the excitation waveform. For example, if a synchronization waveform on a sync-driven row electrode is a 50% duty cycle square wave, a phase-aligned 50% duty cycle square wave may be used in receive circuitry for correlation purposes (e.g., in receive logic326of stylus320). A high positive value in the correlation receiver indicates affirmative presence of the excitation signal. In the inversion examples mentioned above (one synchronization waveform is the inversion of the other), it will often be possible to use a single receiver (i.e., one reference waveform). In more complicated examples, multiple different receivers may be employed, one for each different excitation waveform.

The present disclosure does contemplate examples where multiple different waveforms are used in a set of sync-driven row electrodes. For example, given a minimum expected size of a body contact patch occurring anywhere on matrix300, a set of sync-driven row electrodes might be constructed so that four different synchronization waveforms are positioned underneath the contact patch. The waveforms would be designed so that they collectively at least partially cancel one another, thereby reducing current into the user's body and maintaining current into stylus electrode322. Use of this many waveforms may provide various benefits, though at the expense of configuring and operating four receivers within receive logic326of stylus320.

In some circumstances in the above example, all four receivers must operate simultaneously. This might occur, for example, if the stylus does not know its row coordinate on the matrix. Not knowing that, the stylus cannot know what the nearby synchronization waveforms will be, and thus must attempt detection on all four of the different synchronization waveforms. On the other hand, the stylus may know its position, but not have knowledge of where the different synchronization waveforms will be placed along the row electrodes302of the matrix.

Accordingly, in some examples, operation of receive logic326in stylus320may be controlled based on position information (e.g., stylus coordinates) and set information for the sync-driven row electrodes (i.e., what row electrodes302will be activated and what synchronization waveforms will be used). For example, via some type of communication from matrix300(e.g., radio or electrostatic), or through another method, stylus320may learn of the various sets of sync-driven row electrodes that are employed. More specifically, the stylus may know that a particular set will be used in a specific upcoming touch-sensing frame, and that in that set, the row electrode302closest to its current position will be activated with a particular synchronization waveform. This may then enable the receive logic326to run only a receiver (e.g., correlation operation) particular to that synchronization waveform, instead of a less-targeted approach where multiple receivers are active. In other words, selective activation and deactivation of receivers may be based upon knowledge of the different sets of sync-driven row electrodes and which of such sets will be deployed by the drive logic during an upcoming stylus sync sub-frames.

Referring now toFIG. 6, the figure depicts a touch-sensing method600for a display device having a touch sensor with a matrix of row electrodes and column electrodes. The method may be employed in connection with the systems shown inFIGS. 1-3, or with differently-configured systems. At602, the method includes driving the row electrodes during a plurality of touch-sensing frames, e.g., in order to determine row/column coordinates of a user's finger and an active stylus. Each of the touch-sensing frames includes a stylus-sync sub-frame. At604, the method includes driving, differentially, during each stylus sync sub-frame, at least some of the row electrodes, referred to for that stylus sync sub-frame as sync-driven row electrodes with synchronization waveforms. The synchronization waveforms are communicated electrostatically to an active stylus to synchronize the active stylus and the display device. The driving includes differentially driving the sync-driven row electrodes of the stylus sync sub-frame, such that a synchronization waveform used to drive one of the sync-driven row electrodes is different than a synchronization waveform used to drive another of the sync-driven row electrodes.

As shown at606, the differential driving indicated at604may further include using two or more different synchronization waveforms to drive sync-driven row electrodes in each of a plurality of spatial groupings of sync-driven row electrodes. The two or more different synchronization waveforms may be configured to produce at least partially cancelling electrical conditions. This may reduce, in the event of a user's body part touching the display device on a contact patch over the spatial grouping of sync-driven row electrodes, current flowing into the user's body part, relative to current which would flow in the case of undifferentiated driving of the sync-driven row electrodes in the spatial grouping. In some examples, a spatial grouping may include synchronization waveforms of opposite polarity to provide cancellation, though this is but one example. Any size spatial groupings may be employed and, as described above, a wide range of different types and numbers of waveforms may be used to achieve cancelling electrical conditions. Such cancellation may, as described above, reduce current flowing into the user's body to avoid compromising current needed by the stylus for synchronization.

Method600may further include selecting from among a plurality of different sets of sync-driven row electrodes to use during stylus sync sub-frames. Typically, each set will omit some of the row electrodes of the matrix and will differ from the other sets (e.g., a row electrode is sync-driven for one set and not for another). In some cases, the sets may be constructed so that, for any given point on an operative portion of the matrix (i.e., a stylus contact point), using the different sets causes variation of distance between the closest sync-driven row electrode and the stylus contact point. Typically, one of the sets will cause a reduction in distance between the stylus contact point and a closest sync-driven row electrode, relative to another set of the sync-driven row electrodes. The sets may be constructed so that this is below a threshold distance to provide desired synchronization signal strength to the stylus. The method may also include selecting from among the different sets based on position information associated with the active stylus. In one example, a set is selected to place a sync-driven row electrode as close as possible to the current row coordinate of the stylus, to thereby improve the strength of the synchronization signal. A variety of other position-based selections may be employed, as described above with reference toFIGS. 3 and 5.

The approaches described above for increasing the strength of electrostatic signals transmitted to a stylus electrode may be applicable to capacitive touch sensors other than those described above. For example, differential waveforms may be utilized in so-called “in-cell” touch sensor matrices, in addition to so-called “mutual capacitance” touch sensor matrices, of which touch sensor matrix300ofFIG. 3may be considered an example. It will be appreciated that, inFIG. 3, “matrix” refers to, among other things, the intersections between the elongate transmitting and receiving row/column electrodes, where mutual capacitance is measured at those intersections via transmitting on one electrode and receiving on the other. In the in-cell and on-cell examples below, “matrix” refers also to an array of locations where capacitance is measured (and/or the electrodes themselves), but the measurement locations instead are individual electrodes (instead of electrode intersections), with self-capacitance measurements occurring by both transmitting and receiving at each electrode to establish, for example, x/y location of finger touch on the matrix. It will further be appreciated that in-cell display implementations are but one example setting in which the to-be-described self-capacitance methods may be employed.

FIG. 7shows an example touch-sensitive display device700, including a display702and a touch sensor704to enable graphical output and touch input (e.g., from a stylus or finger). Display702is operable to emit light in an upward direction to yield viewable imagery at a top surface706of the display device or other locations. Display702may assume the form of a liquid crystal display (LCD), organic light-emitting diode display (OLED), or any other suitable display. To effect display operation,FIG. 7shows display702coupled to a controller708, which may control pixel operation, refresh rate, drive electronics, operation of a backlight if included, and/or other aspects of the display. A suitable image source, which may be integrated with, or provided separately from, controller708, may provide graphical content for output by display702. The image source may be a computing device external to, or integrated within, display device700, for example.

Touch sensor704is operable to receive input, which may assume various suitable form(s). As examples, touch sensor704and associated componentry may detect (1) touch input applied by a human digit710in contact with top surface706of display device700; (2) a force and/or pressure applied by the human digit to the top surface; (3) hover input associated with a human digit near but not in contact with top surface706; (4) a height of the hovering human digit from the top surface, such that a substantially continuous range of heights from the top surface can be determined; and/or (5) input from a non-digit input device such as an active stylus712. As described in further detail below, touch sensor704may receive position, tip force, button state, and/or other information from stylus712, and in some examples may transmit information to the stylus. Touch sensor704may be operable to receive input from multiple input devices (e.g., digits, styluses, other input devices) simultaneously, in which case display device may be referred to as a “multi-touch” display device. To enable input reception, touch sensor704may be configured to detect changes associated with the capacitance of a plurality of electrodes, as described in further detail below.

Inputs received by touch sensor704are operable to affect any suitable aspect of display702and/or a computing device operatively coupled to display device700, and may include two or three-dimensional finger inputs and/or gestures. As an example,FIG. 7depicts the output of graphical content by display702in spatial correspondence with paths traced out by digit710and stylus712proximate to top surface706. WhileFIG. 7shows controller708as effecting operation of both display702and touch sensor704(e.g., electrode drive/receive operation), separate display and touch sensor controllers may be provided.

Display device700may be implemented in a variety of forms. For example, display device700may be implemented as a so-called “large-format” display device with a diagonal dimension of approximately 1 meter or greater, or in a mobile device (e.g., tablet, smartphone) with a diagonal dimension on the order of inches. Other suitable forms are contemplated, including but not limited to desktop display monitors, high-definition television screens, tablet devices, etc.

Display device700may include other components in addition to display702and touch sensor704. As an example,FIG. 7shows the inclusion of an optically clear touch sheet714providing top surface706for receiving touch input as described above. Touch sheet714may be comprised of any suitable materials, such as glass or plastic. Further, an optically clear adhesive (OCA)716bonds a bottom surface of touch sheet714to a top surface of display702. As used herein, “optically clear adhesive” refers to a class of adhesives that transmit substantially all (e.g., about 99%) of incident visible light. Alternatively or additionally, display device700may include any suitable components not shown inFIG. 7, including but not limited to various optical elements (e.g., lens, diffuser, diffractive optical element, waveguide, filter, polarizer).

FIG. 7depicts the integration of touch sensor704within display702in a so-called “in-cell” touch sensor implementation. In this example, one or more components of display device700may be operated to perform both display output and input sensing functions. As a particular example in which a display702is an LCD, the same physical electrode structures may be used both for capacitive sensing and for determining the field in the liquid crystal material that rotates polarization to form a displayed image. Alternative or additional components of display device700may be employed for display and input sensing functions, however.

Other touch sensor configurations are possible. For example, touch sensor704may alternatively be implemented in a so-called “on-cell” configuration, in which the touch sensor is disposed directly on display702. In an example on-cell configuration, touch sensing electrodes may be arranged on a color filter substrate of display702. Implementations in which touch sensor704is configured neither as an in-cell nor on-cell sensor are possible, however. In such implementations, an optically clear adhesive (OCA) may be interposed between display702and touch sensor704, for example.

Touch sensor704may be configured in various structural forms and for different modes of capacitive sensing. In a self-capacitance mode, the capacitance and/or other electrical properties (e.g., voltage, charge) between touch sensing electrodes and ground may be measured to detect inputs. In other words, properties of the electrode itself are measured, rather than in relation to another electrode in the capacitance measuring system. Additional detail regarding self-capacitance touch sensing is described below with reference toFIG. 8, which shows an example self-capacitance touch sensor that can be implemented in an in-cell or on-cell fashion.

In a mutual capacitance mode, the capacitance and/or other electrical properties between electrodes of differing electrical state may be measured to detect inputs. When configured for mutual capacitance sensing, and similar to the above examples, touch sensor704may include a plurality of vertically separated row and column electrodes that form capacitive, plate-like nodes at row/column intersections when the touch sensor is driven. The capacitance and/or other electrical properties of the nodes can be measured to detect inputs.

Touch sensor704may include a plurality of electrodes that are configured to detect input in response to applied drive signals. In some cases, the drive signals are applied at the same electrode(s) at which the capacitance measurements are made. In other cases, the drive signals are applied at one or more electrodes near the receiving electrode. The electrodes may assume a variety of suitable forms, including but not limited to (1) elongate traces, as in row/column electrode configurations, where the rows and columns are arranged at substantially perpendicular or oblique angles to one another; (2) substantially contiguous pads, as in mutual capacitance configurations in which the pads are arranged in a substantially common plane and partitioned into drive and receive electrode sets, or as in in-cell or on-cell configurations; (3) meshes; and (4) an array of point electrodes arranged at specific x/y locations, as in in-cell or on-cell configurations.

In some scenarios, touch sensor704may identify the presence of an input mechanism by driving at least a set of electrodes, and analyzing output resulting from such driving at the same or different set of electrodes. For mutual capacitance implementations, a drive signal (also referred to herein as an “excitation waveform”) such as a time-varying voltage may be applied to a first set electrodes (e.g., “drive” electrodes), thus influencing an output signal at a second set of electrodes (e.g., “receive” electrodes). The presence of an input mechanism may then be ascertained by analyzing the output signal as described below.

For self-capacitance implementations, one or more electrode characteristics may be analyzed to identify the presence of an input mechanism. Typically, this is implemented via driving an electrode with a drive signal, and observing the electrical behavior with receive circuitry attached to the electrode. For example, charge accumulation at the electrodes resulting from drive signal application can be analyzed to ascertain the presence of the input mechanism as described below. In these example methods, input mechanisms of the types that influence measurable properties of electrodes can be identified, such as human digits, which may affect electrode conditions by providing a capacitive path to ground for electromagnetic fields. Other methods may be used to identify different input mechanism types, such as those with active electronics.

In both mutual and self-capacitance implementations, touch sensor704may employ a correlation-based approach in analyzing output signals to perform input mechanism detection, among other potential tasks. In this approach, a given output signal may be correlated with one or more reference sequences using a suitable correlation operation (e.g., cross-correlation) to obtain correlated output with a sufficient signal-to-noise ratio. The correlation operation may yield a number that can be compared to a threshold such that, if the number meets or exceeds the threshold, touch sensor704determines that an input mechanism is present, and if the number falls below the threshold, the touch sensor determines that an input mechanism is not present. In some examples, a drive signal used to drive electrodes may form the basis for a reference sequence. Further, one or more reference sequences may be designed to mitigate noise for certain operating conditions, noise sources, and/or wavelength bands.

FIG. 8shows an example touch sensor800. Touch sensor800includes a plurality of electrodes, such as electrode802, which are configured to receive, via capacitance measurements, input in one or more of the forms described above—e.g., touch, hover, force/pressure, and/or stylus/active input device.FIG. 8is described in the context of an in-cell implementation, in which touch sensor800is configured as an in-cell sensor in combination with a display as described above. As such, touch sensor800may be touch sensor704of touch-sensitive display device700, both ofFIG. 7. However, touch sensor800may be implemented as an on-cell touch sensor, or as neither an in-cell nor on-cell sensor that is discrete and separate from a display. For in-cell and on-cell implementations, the plurality of electrodes is referred to herein as a plurality of “sensels”.

To enable sensel charging and the reception of resulting output, the sensels are operatively coupled to drive logic804and receive logic806. One or both of the drive logic and receive logic may be implemented into a controller, such as controller708ofFIG. 7. Via drive logic804, each sensel may be selectively driven with one or more drive signals, and, via receive logic806, one or more electrical characteristics (e.g., capacitance, voltage, charge) of the sensels influenced by such driving are monitored to perform input sensing. Input sensing may also be performed at the sensels in response to drive signals applied from an active stylus, such as active stylus712. Receive logic806may perform correlation operations to perform sensing, as described above with reference toFIG. 7. In one example, output from a given sensel may be used in a correlation operation after charging of the sensel for an integer number of iterations in an integration period. Alternatively or additionally, the sensel may be continuously monitored during charging and/or discharging. In either case, self-capacitance of the plurality of sensels is measured for input sensing.

Due to the relatively large number of sensels included in a typical implementation of touch sensor800, a limited number of sensels are shown inFIG. 8for simplicity/clarity. Examples described below contemplate a particular configuration in which touch sensor800includes 20,000 sensels—e.g., when implemented in a large-format display device. Touch sensor800may include any suitable number of sensels, however.

In an example such as that referenced above with20,000sensels, the sensels may be arranged in 100 rows and 200 columns. While it may be desirable to maximize sensing frequency by simultaneously measuring capacitance at each sensel, this would entail provision of significant processing and hardware resources. In particular, 20,000 receivers (e.g., analog-to-digital converters) in receive logic806would be needed to perform full-granularity, simultaneous self-capacitance measurements at each sensel. As such, partial-granularity, multiplexed approaches to self-capacitance measurement may be desired to reduce the volume of receive logic806. Specifically, as described below, receive logic capable of servicing only a portion of the touch sensor at one time may be successively connected to different portions of the touch sensor over the course of a touch frame, via time multiplexing, in order to service the entire touch sensor.

FIG. 8illustrates one example approach to partial-granularity self-capacitance measurement in touch sensor800. In this approach, the sensels are grouped into horizontal bands810A-810J, each having ten rows of sensels. In this approach, self-capacitance measurements are temporally multiplexed via a multiplexer812, with a respective measurement time slot in a touch frame being allocated for each band810. Accordingly, receive logic806may include a number of receivers equal to the number of sensels in a given band810—e.g., 2,000 receivers. For example, the receivers may be connected to one band in a first time slot, then to another in the next time slot, and so on. It will be appreciated that the above groupings, bands, number of sensels, etc. reflect but one of many possible implementations. Different numbers of sensels may be employed; shapes and arrangements of groupings may differ from the depicted example; etc.

Touch sensor800may employ a variety of drive modes to effect sensel operation. In one drive mode, all sensels may be driven to perform input sensing, which may simplify drive logic804. It may be desirable to employ such an approach even when only a portion of the touch sensor is read at any given time, as in the multiplexing scheme described above. Drive logic804may apply a single drive signal during a drive mode, differing drive signals during the drive mode, or may employ multiple drive modes with differing drive signals. Further, drive logic804may switch among two or more drive modes to alter input mechanism detection and/or to facilitate communication with an active input mechanism such as a stylus. “Drive mode” may also refer to periods in which one or more sensels are not driven but instead are receiving input from driven electrodes of an active stylus, as described elsewhere in more detail.

In some implementations, touch sensor800may be selectively operated in a “full search” mode and a “local search mode.” Full search refers to operations, within the course of a single touch-sensing frame, that cause the entirety of the touch sensor to be scanned for inputs. In some examples, the touch sensor is placed into full search mode during multiple different intervals to scan the entire sensor. For example, in the banded approach described above, ten different intervals could be used for full search, that is, full search mode would be employed during ten different sub-frames of the touch-sensing frame. During each full search mode interval, one of the ten bands would be scanned. Still further, two or more full search intervals could be allocated for each of the ten bands, thus resulting in twenty or more full search intervals.

Local search refers to performing an operation for only a portion of the touch sensor in a given touch-sensing frame. In other words, for a given touch-sensing frame, the operation is localized to a specific location (or locations) on the touch sensor, and the operation is not performed during that frame for the remainder of the touch sensor. In one example, as will be discussed in detail below, full search mode is used to scan the entire touch sensor for inputs, with local search being employed in the touch-sensing frame only in a region where an active stylus is detected (e.g., to receive electrostatic communication of pressure values from the stylus).

Referring again to full search, and in the context of the time multiplexing of receive logic806, full search mode intervals may be used successively for each band810in each touch-sensing frame. Thus, in each touch-sensing frame, the full search periods collectively enable detection of finger touches and other input mechanisms, such as an active or passive stylus, across the entire touch sensor.

In some examples, a local search period or periods may be performed to receive stylus state information from an active stylus at touch sensor800. The stylus state information may include information regarding battery level, firmware version, tip force/pressure values, and/or button state, among other potential data. In typical implementations, this local search activity also informs/confirms stylus position, since the strongest signals on the touch sensor will occur at the x/y stylus location. During full search, some stylus location functionality may also occur—e.g., the stylus sending a locating drive signal indicating a band810of touch sensor800that corresponds to the active stylus location. As such, the indication of a band810corresponding to the active stylus location may prompt a subsequent local search in that band to thereby receive stylus state information from the stylus and potentially a confirmation or further pinpointing of stylus location.

Touch sensor800may perform multiple local searches in a single touch frame to receive stylus state information at multiple times within the touch frame. In this way, an increased frequency of receiving stylus state information may reduce the latency of active stylus operation. Other uses for local searching are possible. For implementations in which full search reveals an indeterminate location of the active stylus, such as a band810and not a particular x/y location, a local search may be performed following a rough position determination via a full search, to resolve location to a desired degree of accuracy. This scheme may be desirable in terms of time efficiency. Specifically, to achieve a high overall frame rate in an active stylus implementation, it may be desirable to conduct the full search periods at a speed that does not allow for full resolution of stylus position. Targeted work is then done at a specific location (local search) to pinpoint stylus location.

Referring to active stylus814, the stylus includes electrode tip820through which signals can be transmitted (e.g., electrostatically) to and/or received from touch sensor800(in combination with suitable drive logic and a power source not shown inFIG. 8). Stylus814may include one or more additional electrodes for various purposes, for example to enable enhanced information about stylus position. In some examples, stylus814transmits a drive signal to touch sensor800to enable location sensing of the stylus during full search periods. Typically, this drive signal is selected so that the receive logic806can distinguish stylus inputs from finger inputs. In some examples, the stylus electrode drive signal is selected so that the receive logic sees an output similar to that produced by a finger, but opposite in polarity. This can simplify the receive circuitry in some cases while still allowing simultaneous sensing of stylus and finger inputs.

Generally, electrostatic interaction between stylus814and touch sensor800can be used to (1) determine the location of the stylus relative to the touch sensor; (2) send/receive synchronization signals to establish/maintain a shared sense of time between the stylus and the touch sensor; (3) communicate state/status between the stylus and display such as identifiers, stylus button state, battery level and the like; and/or (4) transmit various other data, such as force determined in the stylus tip, firmware updates, encryption keys/information, time at which various events occur, etc. While not shown inFIG. 8, touch sensor800and stylus814may include components configured to enable radio communication therebetween, which may perform one or more of the functions described above and/or other functions.

As mentioned above, one or more synchronization periods may be employed to enable temporal synchronization between touch sensor800and stylus814. Any synchronization period within a touch-sensing frame shall be referred to herein as a “stylus sync sub-frame”, and sensels driven as a part of the sync-frame are referred to herein as “sync-driven” sensels or electrodes.

To illustrate the use of full searches, local searches, and synchronization periods,FIG. 9shows an example touch-sensing frame900according to which touch sensor800may be operated. Touch-sensing frame900begins with a stylus synchronization sub-frame902in which touch sensor800transmits a synchronization beacon to stylus814. However, one or more synchronization beacons maybe employed at different locations within the touch-sensing frame. When the stylus is in range, it receives the synchronization beacon and thereby synchronizes timing with the display, which, due to the designed communication protocol, enables the stylus to know the exact timing of all of the sub-frames of touch-sensing frame900. Sync sub-frame902is followed by a full search sub-frame904A. Full search sub-frame904A is denoted inFIG. 9as FS(bandA), indicating that, while all sensels of touch sensor800may be driven during the full search sub-frame, output reception and input sensing is limited to band810A due to the multiplexing of receive logic806to the sensels of that band. In this example, results from the full search sub-frame904A indicate the presence/location of stylus814in a band810N. As such, full search sub-frame904A is followed by a local search sub-frame906A, denoted inFIG. 9as LS(bandN), indicating local searching in the band810N identified by full search sub-frame904A.

As described above, local search sub-frame906A may be allocated for receiving data from stylus814, such as data relating to battery level, identification information, button state, force at electrode tip820, and/or other stylus data described above. As local searches in general may be allocated for receiving stylus data beyond the approximately locating drive signal, it is desirable for touch sensor800to identify the particular band810in which stylus814is located. To this end, stylus814may transmit the approximately locating drive signal described above during portions of full searches (and/or potentially portions of local searches—e.g., during times other than those at which stylus data beyond the drive signal is transmitted).

FIG. 9also depicts additional full search sub-frames interspersed with local search sub-frames centered on the bands where the stylus is found as a result of the full search intervals. As depicted, the intervals are as follows in sequence:

(1) a full search sub-frame904B in band810B;

(2) a local search sub-frame906B at the stylus's band location;

(3) a full search sub-frame904C in band810C;

(4) a local search sub-frame906C at the stylus's band location;

(5) a full search sub-frame904D in band810D; and

(6) a local search sub-frame906D at the stylus's band location;

In the depicted example, the above sequence would continue through to band810J for each touch-sensing frame900. From the above, it will be understood that the band810multiplexed to receive logic806may vary between full and local search sub-frames—e.g., the band810at which a local search is performed may differ from the band investigated during the immediately preceding full search interval.

The execution of full searches in each of bands810A-J may be considered a complete touch-sensing frame. Thus, in the depicted example, the full search intervals identify finger touch inputs and active stylus location over the entire panel. The local search intervals may enable other interaction such as communication of data from the stylus to the touch sensor/display.

Touch sensor800and/or stylus814may vary the number, inclusion, sequence, structure, duration, etc. of the various sub-frames on a frame-to-frame basis, based on operation conditions and/or other factors. For example, signal-to-noise conditions may influence adjustments to the duration of various sub-frames. In another example, local search intervals may be omitted from the touch-sensing frame when the stylus is not present and interacting with the display, thus increasing the frame rate for sensing finger touch. The specific application being controlled by touch input may influence dynamic adjustment to the configuration of the touch-sensing frame. These and other potential adjustments may be made to minimize the duration of input sensing and maximize frame rate to enhance performance.

As described above, a single band810identified by a full search may be selected for subsequent local searching. However, relatively rapid full searching may reduce uncertainty to a point where two or more bands must be searched locally. For example, local searching may additionally be performed in one or more bands adjacent a band in which the input mechanism location is most strongly suspected. The selection of multiple bands810may be desired even if the input mechanism location can be sufficiently narrowed to a single band, e.g., to accommodate the potential for rapid stylus movement over the tough sensor surface. Searching multiple bands requires additional time and it may therefore be desirable to enhance estimations of stylus location via use of motion data.

Specifically, in one example, location data for an input mechanism may be updated for each frame of touch sensor800. Historical location data may be used to determine a stylus motion vector to future location of the stylus, which may or may not correspond to the location which would be identified absent the motion data (i.e., using only the most recent snapshot of stylus location). Motion prediction along these lines may potentially limit the need to query multiple bands during local search intervals of the touch-sensing frame.

As described above, drive logic804may apply a common drive signal to the plurality of sensels. One issue potentially associated with the application of a common drive signal to the plurality of sensels is the insufficient transmission of signals from touch sensor800to stylus814. For example, insufficient signal transmission may occur in the case of a user being capacitively coupled to touch sensor800and poorly grounded (e.g., by placing a body part in contact with a display device in which the sensor is housed). The diminished signal transmission to stylus814may be worsened in some cases as the contact patch between the user and display device increases. Thus, a similar issue may arise from the use of the common drive signal in touch sensor800as in touch sensor matrix300ofFIG. 3. Synchronization in particular may be affected when insufficient current flows into the stylus tip electrode820.

To address the issues described above in connection with the use of a common, undifferentiated, drive signal, drive logic804may apply differential excitation waveforms to at least a set of the sensels. To this end,FIG. 10shows an example sensel grouping1000that may be implemented in touch sensor800. In grouping1000, the sensels are arranged in rectangular sets that alternate with respect to excitation waveforms in both the row and column directions. For example, a first excitation waveform (represented by diagonal shading) is applied to a first set1002A, whereas a second excitation waveform (represented by a lack of shading) is applied to a second set1002B and a third set1002C, which are adjacent to the first set in the row and column directions, respectively. Grouping1000, and the other groupings shown inFIGS. 10 and 11, generally represent example spatial arrangements of sensels that may be employed with the use of differential waveforms in an in-cell touch sensor. The sensel sets included in a spatial sensel grouping may include any suitable number of individual sensels—e.g., a single sensel; two or more sensels; tens, hundreds, or thousands of sensels; all sensels within a given column section of a band810, such that the number of rows within the sensel set is equal to the number of sensel rows in that band. With reference to touch sensor800, the sensel sets shown inFIGS. 10 and 11may cover the entire touch sensor, or in other examples may cover merely a portion of the touch sensor, in which case the sets and/or groupings may be at least partially repeated. Sensel numbers in a given sensel set may be equal or unequal in the row and column directions, and set numbers in a given spatial grouping may be equal or unequal. Rectangular, Euclidean, non-Euclidean, and/or other geometries may be employed in arranging sensels, sensel sets, and spatial groupings of sensels. Further, sensel sets and/or spatial groupings of sensel sets may be chosen as a function of an expected contact patch (e.g., minimum size) of an input mechanism, such as the contact patch of a human digit or heel of a human palm.

As additional examples,FIG. 10shows spatial groupings1004and1006. In spatial grouping1004, the first excitation waveform is applied to a first set1004A, and the second excitation waveform is applied to a second set1004B adjacent to the first set in the column direction. In spatial grouping1006, the first excitation waveform is applied to a first set1006A, and the second excitation waveform is applied to a second set1006B adjacent to the first set in the row direction. It will be understood that the designation between “row” and “column” is arbitrary in that the row and column directions described herein can be reversed, such that the row direction (e.g., horizontal direction) becomes the column direction (e.g., vertical direction) and the column direction becomes the row direction. In the sensel groupings shown inFIGS. 10 and 11, for example, the row/column directions can be reversed such that the spatial alternation between waveforms also reverses with respect to the row/column directions.

The first and second excitation waveforms may assume any suitable form. In some examples, the first excitation waveform may be a substantial inverse of the second excitation waveform to enable at least partial cancellation of current flowing into a user's body, as described above. Further, three or more excitation waveforms, at least partially cancelling each other and/or to varying degrees, may be employed with the groupings shown inFIGS. 10 and 11. Still further, the excitation waveform applied to a given grouping may be alternated over time. Generally, the groupings described herein may be configured or modified to support any suitable set of excitation waveforms, which may include any suitable number, type, and/or spatial arrangement of waveforms across the sensels. In this way, the current flowing into a user's body part capacitively coupled to touch sensor800may be reduced as compared to non-differential driving schemes, thus ensuring desired current flow into stylus electrode(s).

As another example,FIG. 11shows an example sensel grouping1100that may be implemented in touch sensor800. In grouping1100, the sensels are arranged in rectangular sets that alternate with respect to excitation waveforms in successive sets of four in the row direction, and alternate back-to-back in the column direction. For example, a first excitation waveform (represented by diagonal shading) is applied to a successive set of four sets1102A-D, whereas a second excitation waveform (represented by a lack of shading) is applied to a successive set of four sets1104A-D following the four sets1102A-D in the row direction. The second excitation waveform is applied to a set1106A adjacent to the set1102A. As described above with reference toFIG. 10, the first and second excitation waveforms may be substantial inverses, and in some examples three or more excitation waveforms may be employed with grouping1100. Further, the excitation waveform applied to one or more sets in grouping1100may be alternated over time (e.g., frame-to-frame to provide varying performance at a given location, as discussed with reference toFIG. 5). Generally, grouping1100may be configured or modified to support any suitable set of excitation waveforms, which may include any suitable number, type, and/or spatial arrangement of waveforms across the sensels. In this way, the current flowing into a user's body part capacitively coupled to touch sensor800may be reduced as compared to non-differential driving schemes, such that desired current flow into stylus electrode(s) is enabled.FIG. 11also shows the application of spatial groupings1000,1004, and1006relative to the differential driving scheme shown therein.

Attributes of groupings may be varied over time, including but not limited to grouping number, sensel number, and grouping geometry, as described above. In some examples, a set of sensels, and not all of the sensels of a touch sensor, may be driven at any given time. The set of driven sensels may be varied over time. Further, the approaches described above for reducing the attenuation of capacitive communication between a stylus and in-cell touch sensor may be applied to any suitable type of signal transmission, including stylus synchronization signals as well as non-synchronization signals. Generally, differential driving of an in-cell touch sensor may be employed during scenarios in which capacitive communication with a stylus may be adversely affected by the presence of a user's body.

Drive logic804may be configured to enable the selected grouping applied to touch sensor800. For example, the sensels in each spatial grouping set may be commonly coupled to drive logic804and isolated from other sets to enable the selective driving of each set in the spatial groupings. Similarly common couplings may be employed to achieve other groupings. In yet other examples, one or more (e.g., all) of the sensels may be individually coupled to drive logic804to enable each sensel to be uniquely and selectively driven, which may afford greater flexibility in the selection of sensel groupings. In some examples in which partial-granularity self-capacitance measurement is employed as described above, the number of rows in each grouping set may be equal to the number of rows in each horizontal band.

Drive logic804may select a spatial grouping to achieve a distance between the location of stylus814and a closest driven sensel that is below a threshold distance. For example, assuming a minimum desired threshold distance between a driven sensel and stylus814contact point on touch sensor800, different spatial groupings may be employed so that at least one grouping includes a driven sensel (or sensel set) that is within the threshold distance from the stylus contact point, to thereby provide a sufficiently strong signal with minimized interference from other waveforms. In other words, the different spatial groupings may be constructed such that cycling through the groupings causes frame-to-frame variation between a stylus contact point and a closest driven sensel. Further, drive logic804may select a spatial grouping, sensel set, or any other hierarchical arrangement of sensels for alternative or additional purposes (e.g., to minimize signal attenuation, increase SNR of stylus communication, increase SNR of sensing, reduce power consumption). In some examples, stylus814may include receive logic configured to selectively activate and deactivate multiple different receivers within the receive logic based on knowledge of differential synchronization forms to be deployed by drive logic814during an upcoming stylus sync sub-frame. For example, the stylus receive logic may have knowledge of one or more of a spatial grouping of sensels, sensel set, or other hierarchical arrangement of sensels to be used by touch sensor800.

The following example spatial sensel groupings are further contemplated: (1) a grouping alternating between first and second excitation waveforms in the diagonal direction, (2) successive sets of five (or any other suitable integer number) sensel sets alternating between first and second excitation waveforms in the row direction, (3) sets that alternate in one of the row/column directions and not in the other of the row/column directions, (4) sets that alternate in some regions of touch sensor800but not in others, and (5) sets in which only some, and not all, of the sensels in the set are differentially driven (e.g., the non-differentially driven sensels are not driven).

FIG. 12shows a flowchart illustrating an example touch-sensing method1200for a display device having a touch sensor with a plurality of electrodes. The plurality of electrodes may be a plurality of sensels. Method1200may be executed on touch sensor800ofFIG. 8, for example.

At1202, method1200includes driving the plurality of electrodes during a plurality of touch-sensing frames, e.g., in order to determine x/y coordinates of a user's finger and an active stylus. Each of the touch-sensing frames includes a stylus-sync sub-frame. At1204, method1200includes driving, differentially, during each stylus sync sub-frame, at least some of the plurality of electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes with synchronization waveforms. The synchronization waveforms are communicated electrostatically to an active stylus to synchronize the active stylus and the touch sensor. The driving includes differentially driving the sync-driven electrodes of the stylus sync sub-frame, such that a synchronization waveform used to drive one of the sync-driven electrodes is different than a synchronization waveform used to drive another of the sync-driven electrodes.

As shown at1206, the differential driving indicated at1204may further include using two or more different synchronization waveforms to drive sync-driven electrodes in each of a plurality of spatial groupings of sensels. The two or more different synchronization waveforms may be configured to produce at least partially cancelling electrical conditions. This may reduce, in the event of a user's body part touching the display device on a contact patch over the spatial grouping of sync-driven electrodes, current flowing into the user's body part, relative to current which would flow in the case of undifferentiated driving of the sync-driven electrodes in the spatial grouping. In some examples, a spatial grouping may include synchronization waveforms of opposite polarity to provide cancellation, though this is but one example. Any size spatial groupings may be employed and, as described above, a wide range of different types and numbers of waveforms may be used to achieve cancelling electrical conditions. Such cancellation may, as described above, reduce current flowing into the user's body to avoid compromising current needed by the stylus for synchronization.

Method1200may further include selecting from among a plurality of different sets of sync-driven electrodes to use during stylus sync sub-frames. Typically, each set will omit some of the electrodes of the touch sensor and will differ from the other sets (e.g., an electrode is sync-driven for one set and not for another). In some cases, the sets may be constructed so that, for any given point on an operative portion of the touch sensor (i.e., a stylus contact point), using the different sets causes variation of distance between the closest sync-driven electrode and the stylus contact point. Typically, one of the sets will cause a reduction in distance between the stylus contact point and a closest sync-driven electrode, relative to another set of the sync-driven electrodes. The sets may be constructed so that this is below a threshold distance to provide desired synchronization signal strength to the stylus. The method may also include selecting from among the different sets based on position information associated with the active stylus. In one example, a set is selected to place a sync-driven electrode as close as possible to the current y-coordinate of the stylus, to thereby improve the strength of the synchronization signal. A variety of other position-based selections may be employed.

FIG. 13schematically shows a non-limiting embodiment of a computing system1300, one or more aspects of which may be used to implement the touch-sensing systems and methods described above. Computing system1300is shown in simplified form. Computing system1300may take the form of one or more personal computers, server computers, tablet computers, home-entertainment computers, network computing devices, gaming devices, mobile computing devices, mobile communication devices (e.g., smart phone), wearable devices, and/or other computing devices.

Computing system1300includes a logic machine1302and a storage machine1304. Computing system1300may optionally include a display subsystem1306, input subsystem1308, communication subsystem1310, and/or other components not shown inFIG. 13.

The logic machine may correspond to one or more of the various drive logic and receive logic described above. For example, logic and associated instructions may be implemented to select and apply waveforms to drive electrodes to achieve synchronization; process inbound signals induced as a result of excitation of capacitively coupled electrodes; determine position of an active stylus; select from different sets of sync-driven electrodes; etc.

Storage machine1304includes one or more physical devices configured to hold instructions executable by the logic machine to implement the methods and processes described herein. When such methods and processes are implemented, the state of storage machine1304may be transformed—e.g., to hold different data.

Aspects of logic machine1302and storage machine1304may be integrated together into one or more hardware-logic components. Such hardware-logic components may include field-programmable gate arrays (FPGAs), program- and application-specific integrated circuits (PASIC/ASICs), program- and application-specific standard products (PSSP/ASSPs), system-on-a-chip (SOC), and complex programmable logic devices (CPLDs), for example.

The terms “module,” “program,” and “engine” may be used to describe an aspect of computing system1300implemented to perform a particular function. In some cases, a module, program, or engine may be instantiated via logic machine1302executing instructions held by storage machine1304. It will be understood that different modules, programs, and/or engines may be instantiated from the same application, service, code block, object, library, routine, API, function, etc. Likewise, the same module, program, and/or engine may be instantiated by different applications, services, code blocks, objects, routines, APIs, functions, etc. The terms “module,” “program,” and “engine” may encompass individual or groups of executable files, data files, libraries, drivers, scripts, database records, etc.

When included, display subsystem1306may be used to present a visual representation of data held by storage machine1304. This visual representation may take the form of a graphical user interface (GUI). As the herein described methods and processes change the data held by the storage machine, and thus transform the state of the storage machine, the state of display subsystem1306may likewise be transformed to visually represent changes in the underlying data. Display subsystem1306may include one or more display devices utilizing virtually any type of technology. Such display devices may be combined with logic machine1302and/or storage machine1304in a shared enclosure, or such display devices may be peripheral display devices.

When included, communication subsystem1310may be configured to communicatively couple computing system1300with one or more other computing devices. Communication subsystem1310may include wired and/or wireless communication devices compatible with one or more different communication protocols. As non-limiting examples, the communication subsystem may be configured for communication via a wireless telephone network, or a wired or wireless local- or wide-area network. In some embodiments, the communication subsystem may allow computing system1300to send and/or receive messages to and/or from other devices via a network such as the Internet.

Another example provides a touch sensing system comprising a display device including a touch sensor having a plurality of electrodes, and drive logic coupled to the plurality of electrodes and configured to drive the plurality of electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame during which the drive logic drives at least some of the plurality of electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms that are communicated electrostatically to cause synchronization of the display device with an active stylus, where for each of the stylus sync sub-frames, the drive logic is configured to differentially drive the sync-driven electrodes of such stylus sync sub-frame, such that a first synchronization waveform used to drive one of the sync-driven electrodes is different than a second synchronization waveform used to drive another of the sync-driven electrodes. In such an example, the drive logic may be configured to, for each stylus sync sub-frame, differentially drive sync-driven electrodes during that sub-frame such that, for a plurality of spatial groupings of sync-driven electrodes, two or more different synchronization waveforms are used to drive the sync-driven electrodes in the spatial grouping, the two or more different synchronization waveforms being configured to produce at least partially cancelling electrical conditions to reduce, in the event of a user's body part touching the display device on a contact patch over the spatial grouping of sync-driven electrodes, current flowing into the user's body part, relative to current which would flow in the case of undifferentiated driving of the sync-driven electrodes in the spatial grouping. In such an example, the drive logic may be configured, for any given one of the stylus sync sub-frames, to select from among a plurality of sets of sync-driven electrodes and differentially drive sync-driven electrodes in that set of sync-driven electrodes during the stylus sync sub-frame. In such an example, the spatial groupings may be distributed over a plurality of electrode sets that alternate in a row direction and in a column direction with respect to the two or more different synchronization waveforms. In such an example, the electrode sets that alternate in the column direction may be longer than the electrode sets that alternate in the row direction. In such an example, the drive logic may switch into and out of position-based selection of the plurality of spatial groupings of sync-driven electrodes. In such an example, the touch-sensing system alternatively or additionally may comprise an active stylus having receive logic configured to selectively activate and deactivate multiple different receivers within the receive logic based on knowledge of differential synchronization forms to be deployed by the drive logic during an upcoming stylus sync sub-frame. In such an example, within each spatial grouping, the drive logic may drive sync-driven electrodes using synchronization waveforms of opposite polarity. In such an example, the spatial groupings may be sized based on an expected minimum size of the contact patch. In such an example, the touch sensor may be an in-cell touch sensor.

Another example provides a touch-sensing method for a display device having a touch sensor with a matrix of electrodes comprising driving the electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame, and during each stylus sync sub-frame, driving at least some of the electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms configured to be electrostatically communicated to an active stylus to synchronize the display device and the active stylus, where such driving during each stylus sync sub-frame includes differentially driving the sync-driven electrodes of that stylus sync sub-frame, such that a first synchronization waveform used to drive one of the sync-driven electrodes is different than a second synchronization waveform used to drive another of the sync-driven electrodes. In such an example, for each stylus sync sub-frame, differentially driving the sync-driven electrodes in that stylus sync sub-frame may include, for each of a plurality of spatial groupings of sync-driven electrodes in that stylus sync sub-frame, using two or more different synchronization waveforms to drive the sync-driven electrodes in the spatial grouping, the two or more different synchronization waveforms being configured to produce at least partially cancelling electrical conditions to reduce, in the event of a user's body part touching the display device on a contact patch over the spatial grouping of sync-driven electrodes, current flowing into the user's body part, relative to current which would flow in the case of undifferentiated driving of the sync-driven electrodes in the spatial grouping. In such an example, synchronization waveforms of opposite polarity may be used on sync-driven electrodes within each of the spatial groupings. In such an example, the differential driving of the sync-driven electrodes during each of the stylus sync sub-frame may include, for any given stylus sync sub-frame, selecting from among a plurality of sets of sync-driven electrodes and differentially driving the sync-driven electrodes in that set during the stylus sync sub-frame. In such an example, the spatial groupings may be distributed over a plurality of electrode sets that alternate in a row direction and in a column direction with respect to the two or more different synchronization waveforms. In such an example, the electrode sets that alternate in the column direction may be longer than the electrode sets that alternate in the column direction.

Another example provides a touch-sensing system comprising a display device including a touch sensor having a matrix of electrodes, drive logic coupled to the electrodes, where the drive logic is configured to drive the electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame during which the drive logic drives at least some of the electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms to facilitate synchronization of the display device with an active stylus, where the drive logic is configured, for any given one of the stylus sync sub-frames, to select from among a plurality of sets of sync-driven electrodes and differentially drive sync-driven electrodes in that set of sync-driven electrodes during the stylus sync sub-frame, and where for each of the sets of sync-driven electrodes, the differential driving includes, for each a plurality of spatial groupings of sync-driven electrodes in the set, using two or more different synchronization waveforms in the spatial grouping which are configured to produce at least partially cancelling electrical conditions to reduce, in the event of a user's body part touching the display device on a contact patch over the spatial grouping, current flowing into the user's body part, relative to current which would flow in the case of undifferentiated driving of the sync-driven electrodes in the spatial grouping. In such an example, within each spatial grouping, the drive logic may drive sync-driven electrodes using synchronization waveforms of opposite polarity. In such an example, the electrode sets that alternate in the column direction may be longer than the electrode sets that alternate in the row direction. In such an example, the spatial groupings may be distributed over a plurality of electrode sets that alternate in a row direction and in a column direction with respect to the two or more different synchronization waveforms.