Sensor pattern with signal-spreading electrodes

A capacitive sensor array may include a plurality of row sensor electrodes and a column sensor electrode capacitively coupled with each of the plurality of row sensor electrodes to form a plurality of unit cells. For each row sensor electrode, a unit cell that is associated with the column sensor electrode and the row sensor electrode comprises an area where a capacitance between the column sensor electrode and the row sensor electrode is greater than any other capacitance between the column sensor electrode and a different row sensor electrode. The capacitive sensor array further includes a first plurality of dummy electrodes, where each of the first plurality of dummy electrodes is capacitively coupled with the column sensor electrode and two adjacent row sensor electrodes of the plurality of row sensor electrodes.

TECHNICAL FIELD

This disclosure relates to the field of touch-sensors and, in particular, to capacitive touch-sensor arrays.

BACKGROUND

Computing devices, such as notebook computers, personal data assistants (PDAs), kiosks, and mobile handsets, have user interface devices, which are also known as human interface devices (HID). One user interface device that has become more common is a touch-sensor pad (also commonly referred to as a touchpad). A basic notebook computer touch-sensor pad emulates the function of a personal computer (PC) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. A touch-sensor pad replicates mouse X/Y movement by using two defined axes which contain a collection of sensor electrodes that detect the position of one or more conductive objects, such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touch-sensor pad itself. The touch-sensor pad provides a user interface device for performing such functions as positioning a pointer, or selecting an item on a display. These touch-sensor pads may include multi-dimensional sensor arrays for detecting movement in multiple axes. The sensor array may include a one-dimensional sensor array, detecting movement in one axis. The sensor array may also be two dimensional, detecting movements in two axes.

Another user interface device that has become more common is a touch screen. Touch screens, also known as touchscreens, touch windows, touch panels, or touchscreen panels, are transparent display overlays which are typically either pressure-sensitive (resistive or piezoelectric), electrically-sensitive (capacitive), acoustically-sensitive (surface acoustic wave (SAW)) or photo-sensitive (infra-red). The effect of such overlays allows a display to be used as an input device, removing the keyboard and/or the mouse as the primary input device for interacting with the display's content. Such displays can be attached to computers or, as terminals, to networks. Touch screens have become familiar in retail settings, on point-of-sale systems, on ATMs, on mobile handsets, on kiosks, on game consoles, and on PDAs where a stylus is sometimes used to manipulate the graphical user interface (GUI) and to enter data. A user can touch a touch screen or a touch-sensor pad to manipulate data. For example, a user can apply a single touch, by using a finger to touch the surface of a touch screen, to select an item from a menu.

DETAILED DESCRIPTION

In one embodiment, a capacitive sensor array used to track the movement of a contact, such as a finger or stylus touch, across its surface may include multiple signal-spreading dummy electrodes within its sensor pattern. The inclusion of such signal-spreading dummy electrodes increases linearity of the touch tracking relative to a sensor array that does not include signal-spreading dummy electrodes. As described herein, the term “dummy electrode” may refer to an electrode that is not conductively coupled with a row or column sensor electrode, but does not necessarily imply a lack of electrical function.

FIG. 1illustrates a block diagram of one embodiment of an electronic system100including a processing device110that may be configured to measure capacitances from a touch sensing surface116implemented using a capacitive sensor array that includes the signal-spreading dummy electrodes as described above. The electronic system100includes a touch-sensing surface116(e.g., a touchscreen, or a touch pad) coupled to the processing device110and a host150. In one embodiment, the touch-sensing surface116is a two-dimensional user interface that uses a sensor array121to detect touches on the surface116.

In one embodiment, the sensor array121includes sensor electrodes121(1)-121(N) (where N is a positive integer) that are disposed as a two-dimensional matrix (also referred to as an XY matrix). The sensor array121is coupled to pins113(1)-113(N) of the processing device110via one or more analog buses115transporting multiple signals. In this embodiment, each sensor electrode121(1)-121(N) is represented as a capacitor.

In one embodiment, the capacitance sensor101may include a relaxation oscillator or other means to convert a capacitance into a measured value. The capacitance sensor101may also include a counter or timer to measure the oscillator output. The processing device110may further include software components to convert the count value (e.g., capacitance value) into a sensor electrode detection decision (also referred to as switch detection decision) or relative magnitude. It should be noted that there are various known methods for measuring capacitance, such as current versus voltage phase shift measurement, resistor-capacitor charge timing, capacitive bridge divider, charge transfer, successive approximation, sigma-delta modulators, charge-accumulation circuits, field effect, mutual capacitance, frequency shift, or other capacitance measurement algorithms. It should be noted however, instead of evaluating the raw counts relative to a threshold, the capacitance sensor101may be evaluating other measurements to determine the user interaction. For example, in the capacitance sensor101having a sigma-delta modulator, the capacitance sensor101is evaluating the ratio of pulse widths of the output, instead of the raw counts being over or under a certain threshold.

In one embodiment, the processing device110further includes processing logic102. Operations of the processing logic102may be implemented in firmware; alternatively, it may be implemented in hardware or software. The processing logic102may receive signals from the capacitance sensor101, and determine the state of the sensor array121, such as whether an object (e.g., a finger) is detected on or in proximity to the sensor array121(e.g., determining the presence of the object), where the object is detected on the sensor array (e.g., determining the location of the object), tracking the motion of the object, or other information related to an object detected at the touch sensor.

In another embodiment, instead of performing the operations of the processing logic102in the processing device110, the processing device110may send the raw data or partially-processed data to the host150. The host150, as illustrated inFIG. 1, may include decision logic151that performs some or all of the operations of the processing logic102. Operations of the decision logic151may be implemented in firmware, hardware, software, or a combination thereof. The host150may include a high-level Application Programming Interface (API) in applications152that perform routines on the received data, such as compensating for sensitivity differences, other compensation algorithms, baseline update routines, start-up and/or initialization routines, interpolation operations, or scaling operations. The operations described with respect to the processing logic102may be implemented in the decision logic151, the applications152, or in other hardware, software, and/or firmware external to the processing device110. In some other embodiments, the processing device110is the host150.

In another embodiment, the processing device110may also include a non-sensing actions block103. This block103may be used to process and/or receive/transmit data to and from the host150. For example, additional components may be implemented to operate with the processing device110along with the sensor array121(e.g., keyboard, keypad, mouse, trackball, LEDs, displays, or other peripheral devices).

The processing device110may reside on a common carrier substrate such as, for example, an integrated circuit (IC) die substrate, or a multi-chip module substrate. Alternatively, the components of the processing device110may be one or more separate integrated circuits and/or discrete components. In one embodiment, the processing device110may be the Programmable System on a Chip (PSoC™) processing device, developed by Cypress Semiconductor Corporation, San Jose, Calif. Alternatively, the processing device110may be one or more other processing devices known by those of ordinary skill in the art, such as a microprocessor or central processing unit, a controller, special-purpose processor, digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable device. In an alternative embodiment, for example, the processing device110may be a network processor having multiple processors including a core unit and multiple micro-engines. Additionally, the processing device110may include any combination of general-purpose processing device(s) and special-purpose processing device(s).

In one embodiment, the electronic system100is implemented in a device that includes the touch-sensing surface116as the user interface, such as handheld electronics, portable telephones, cellular telephones, notebook computers, personal computers, personal data assistants (PDAs), kiosks, keyboards, televisions, remote controls, monitors, handheld multi-media devices, handheld video players, gaming devices, control panels of a household or industrial appliances, or other computer peripheral or input devices. Alternatively, the electronic system100may be used in other types of devices. It should be noted that the components of electronic system100may include all the components described above. Alternatively, electronic system100may include only some of the components described above, or include additional components not listed herein.

FIG. 2is a block diagram illustrating one embodiment of a capacitive touch sensor array121and a capacitance sensor101that converts changes in measured capacitances to coordinates indicating the presence and location of touch. The coordinates are calculated based on changes in measured capacitances relative to the capacitances of the same touch sensor array121in an un-touched state. In one embodiment, sensor array121and capacitance sensor101are implemented in a system such as electronic system100. Sensor array220includes a matrix225of N×M electrodes (N receive electrodes and M transmit electrodes), which further includes transmit (TX) electrode222and receive (RX) electrode223. Each of the electrodes in matrix225is connected with capacitance sensing circuit201through demultiplexer212and multiplexer213.

Capacitance sensor101includes multiplexer control211, demultiplexer212and multiplexer213, clock generator214, signal generator215, demodulation circuit216, and analog to digital converter (ADC)217. ADC217is further coupled with touch coordinate converter218. Touch coordinate converter218may be implemented in the processing logic102.

The transmit and receive electrodes in the electrode matrix225may be arranged so that each of the transmit electrodes overlap and cross each of the receive electrodes such as to form an array of intersections, while maintaining galvanic isolation from each other. Thus, each transmit electrode may be capacitively coupled with each of the receive electrodes. For example, transmit electrode222is capacitively coupled with receive electrode223at the point where transmit electrode222and receive electrode223overlap.

Clock generator214supplies a clock signal to signal generator215, which produces a TX signal224to be supplied to the transmit electrodes of touch sensor121. In one embodiment, the signal generator215includes a set of switches that operate according to the clock signal from clock generator214. The switches may generate a TX signal224by periodically connecting the output of signal generator215to a first voltage and then to a second voltage, wherein said first and second voltages are different.

The output of signal generator215is connected with demultiplexer212, which allows the TX signal224to be applied to any of the M transmit electrodes of touch sensor121. In one embodiment, multiplexer control211controls demultiplexer212so that the TX signal224is applied to each transmit electrode222in a controlled sequence. Demultiplexer212may also be used to ground, float, or connect an alternate signal to the other transmit electrodes to which the TX signal224is not currently being applied. In an alternate embodiment the TX signal224may be presented in a true form to a subset of the transmit electrodes222and in complement form to a second subset of the transmit electrodes222, wherein there is no overlap in members of the first and second subset of transmit electrodes222.

Because of the capacitive coupling between the transmit and receive electrodes, the TX signal224applied to each transmit electrode induces a current within each of the receive electrodes. For instance, when the TX signal224is applied to transmit electrode222through demultiplexer212, the TX signal224induces an RX signal227on the receive electrodes in matrix225. The RX signal227on each of the receive electrodes can then be measured in sequence by using multiplexer213to connect each of the N receive electrodes to demodulation circuit216in sequence.

The mutual capacitance associated with each intersection between a TX electrode and an RX electrode can be sensed by selecting every available combination of TX electrode and an RX electrode using demultiplexer212and multiplexer213. To improve performance, multiplexer213may also be segmented to allow more than one of the receive electrodes in matrix225to be routed to additional demodulation circuits216. In an optimized configuration, wherein there is a 1-to-1 correspondence of instances of demodulation circuit216with receive electrodes, multiplexer213may not be present in the system.

When an object, such as a finger, approaches the electrode matrix225, the object causes a change in the measured mutual capacitance between only some of the electrodes. For example, if a finger is placed near the intersection of transmit electrode222and receive electrode223, the presence of the finger will decrease the charge coupled between electrodes222and223. Thus, the location of the finger on the touchpad can be determined by identifying the one or more receive electrodes having a decrease in measured mutual capacitance in addition to identifying the transmit electrode to which the TX signal224was applied at the time the decrease in capacitance was measured on the one or more receive electrodes.

By determining the mutual capacitances associated with each intersection of electrodes in the matrix225, the presence and locations of one or more conductive objects may be determined. The determination may be sequential, in parallel, or may occur more frequently at commonly used electrodes.

In alternative embodiments, other methods for detecting the presence of a finger or other conductive object may be used where the finger or conductive object causes an increase in measured capacitance at one or more electrodes, which may be arranged in a grid or other pattern. For example, a finger placed near an electrode of a capacitive sensor may introduce an additional capacitance to ground that increases the total capacitance between the electrode and ground. The location of the finger can be determined based on the locations of one or more electrodes at which a change in measured capacitance is detected.

The induced current signal227is integrated by demodulation circuit216. The rectified current output by demodulation circuit216can then be filtered and converted to a digital code by ADC217.

A series of such digital codes measured from adjacent sensor or intersections may be converted to touch coordinates indicating a position of an input on touch sensor array121by touch coordinate converter218. In one embodiment, the touch coordinate converter218may be coupled with a lookup table (LUT)230. The LUT stores a number of correction vectors each corresponding to a different location on the capacitive sensor array. For example, each of the correction vectors may include correction values for adjusting along one or both of the x-axis and y-axis the touch coordinates calculated by the touch coordinate converter218. In one embodiment, the touch-coordinate converter218selects from the LUT230the appropriate correction vector corresponding to the location of the calculated touch coordinates, then adjusts the touch coordinates according to the correction vector. In one embodiment, the correction vectors compensate for any systematic displacement error affecting the calculated touch coordinates. The corrected touch coordinates may then be used to detect gestures or perform other functions by the processing logic102.

In one embodiment, the capacitance sensor101can be configured to detect multiple touches. One technique for the detection and location resolution of multiple touches uses a two-axis implementation: one axis to support rows and another axis to support columns. Additional axes, such as a diagonal axis, implemented on the surface using additional layers, can allow resolution of additional touches.

FIG. 3Aillustrates an embodiment of a capacitive touch sensing system300that includes a capacitive sensor array320. Capacitive sensor array320includes a plurality of row sensor electrodes331-340and a plurality of column sensor electrodes341-348. The row and column sensor electrodes331-348are connected to a processing device310, which may include the functionality of capacitance sensor101, as illustrated inFIG. 2. In one embodiment, the processing device310may perform TX-RX scans of the capacitive sensor array320to measure a mutual capacitance value associated with each of the intersections between a row sensor electrode and a column sensor electrode in the sensor array320. The measured capacitances may be further processed to determine higher resolution locations of one or more contacts at the capacitive sensor array320.

In one embodiment, the processing device310is connected to a host150which may receive the measured capacitances or calculate high precision locations from the processing device310.

The sensor array320illustrated inFIG. 3Aincludes sensor electrodes arranged in a diamond pattern. Specifically, the sensor electrodes331-348of sensor array320are arranged in a single solid diamond (SSD) pattern.FIG. 3Billustrates a capacitive sensor array321having an alternate embodiment of the diamond pattern, which is the dual solid diamond (DSD) pattern. Each of the sensor electrodes of capacitive sensor array321includes two rows or columns of electrically connected diamond shaped traces. Relative to the SSD pattern, the DSD pattern has improved signal disparity characteristics due to an increase in the coupling between TX and RX sensor electrodes while maintaining the same self-capacitance coupling possible between each sensor electrode and a conductive object near the sensor electrode. The DSD pattern may also provide higher sensitivity for tracking smaller objects, such as the point of a stylus, as compared to patterns having larger features, such as SSD. However, the DSD pattern also increases the number of bridges (such as bridge323) used to create the pattern, which may result in decreased manufacturing yield. The increased number of bridges may also be visible if metal bridges are used. For example, sensor array321includes four bridges within unit cell322.

FIGS. 4A and 4Billustrate embodiments of touch screen assemblies400and410, respectively, that include capacitive sensor arrays. Touch screen assembly400includes a liquid crystal display (LCD)401over which glass402is laid. A sensor pattern403is constructed on the surface of glass402. In one embodiment, the sensor pattern403is constructed on the surface of glass402that faces away from the LCD401. Optically clear adhesive (OCA)404may be used to bond glass405to the surface of glass402on which the sensor pattern403is constructed, thus protecting the sensor pattern403. The sensor pattern403may be a SSD pattern, a DSD pattern, or another pattern as described in the following figures.

Touch screen assembly410includes an LCD411, over which a glass412may be positioned. In one embodiment, sensor pattern413may be constructed on the surface of glass412that faces the LCD411. In one embodiment, an air gap414may separate the glass412from the LCD411.

In one embodiment, a capacitive sensor pattern such as the SSD pattern, DSD pattern, or other capacitive sensor pattern described herein may include row and column sensor electrodes that can be expressed as a matrix of the intersections between the row and column electrodes. Resolution of these sensor arrays may be represented as the product of the number of columns and the number of rows. For example, for a sensor array with N row electrodes and M column electrodes, the number of intersections would be N×M.

FIG. 5illustrates a capacitive sensor array500that includes signal-spreading dummy electrodes, according to an embodiment. Capacitive sensor array500includes row sensor electrodes501,502, and503, and column sensor electrodes511,512, and513. Each of the row sensor electrodes501-503is capacitively coupled with each of the column sensor electrodes511-513to form a grid of unit cells. In one embodiment, the row sensor electrodes501-503are formed from a single layer of conductive material and the column sensor electrodes are formed from another layer of conductive material.

Each unit cell is associated with a particular pairing of a row sensor electrode and a column sensor electrode, and corresponds to an area within which the capacitive coupling between the row sensor electrode and the column sensor electrode is greater than for any other pairing of sensor electrodes. For example, unit cell520includes an area where the capacitance between sensor electrodes502and512is greater than the capacitance between any other pair of electrodes.

In one embodiment, capacitance sensor101performs a scan of the sensor array500by applying a transmit (TX) signal to each of the row sensor electrodes501-503and measuring a resulting receive (RX) signal generated at each of the column sensor electrodes511-513. The sensor array500includes multiple signal-spreading dummy electrodes that are each capacitively coupled with at least two of the TX sensor electrodes. For example, each of the dummy electrodes531and532overlaps and is capacitively coupled with both of TX sensor electrodes501and502.

FIG. 6illustrates the signal-spreading dummy electrodes531and532in the sensor array500, according to an embodiment. As illustrated inFIG. 6, each of the dummy electrodes531and532is located over a gap between the adjacent TX row sensor electrodes501and502. Thus, each of the dummy electrodes531and532overlaps at least a portion of each of the row sensor electrodes501and502and is capacitively coupled with each of the sensor electrodes501and502.

Thus, each of the dummy electrodes531and532is situated at least partially within the area of two adjacent unit cells520and521. As illustrated inFIG. 6, the area of each dummy electrode531and532is approximately evenly divided between the unit cells520and521. In one embodiment, the dummy electrodes531and532each comprise two smaller portions that are electrically connected by a connecting trace that is narrower than either of the portions. For example, the dummy electrode532is made up of a first portion532aand a second portion532celectrically connected together by a connecting trace532b. The connecting trace532bis narrower than either of the portions532aand532cin terms of the widths of these elements, as measured perpendicular to the longitudinal axis601of the column sensor electrode512(i.e., along the x-axis indicated inFIG. 6).

In one embodiment, the connecting trace532boverlaps a gap between the adjacent row sensor electrodes501and502to mitigate the effects of lamination offset during the manufacturing process. For instance, a manufacturing process that positions a top layer of conductive material (including dummy electrode532) over a bottom layer (including row electrodes501and502) may result in an offset between the layers of as much as 0.2 millimeters in either direction along the y-axis from a nominal position which evenly divides the area of dummy electrode532between unit cells520and521. Accordingly, the length of the connecting trace532balong the longitudinal axis601of the column sensor electrode (i.e., parallel to the indicated y-axis) may be selected as 0.5 millimeters (at least double the tolerance of 0.2 millimeters). Since only the smaller area of the connecting trace532bis subject to unequal division between unit cells520and521due to lamination offset, the possible variation of the total area of dummy electrode532caused by lamination offset can be reduced, relative to embodiments where the dummy electrode is not narrower across the gap between row electrodes.

Additionally, each of the dummy electrodes531and532also capacitively coupled with the RX column sensor electrode512, illustrated inFIG. 6as three subtraces512a,512b, and512c, which are electrically coupled as can be seen inFIG. 5. In one embodiment, the width of the central subtrace512bis less than the width of either of the outer subtraces512aand512c. As the central trace, subtrace512bis nearer than the other subtraces512aand512cto a central longitudinal axis601of the column electrode512. The signal spreading dummy electrodes531and532are located between the subtraces512a-512cof the column electrode512. In alternative embodiments, the column electrode may include fewer or more than three subtraces, with correspondingly fewer or more signal-spreading dummy electrodes in between the subtraces. In one embodiment, the subtraces may become progressively wider the farther they are positioned away from the central longitudinal axis of the column sensor electrode.

FIG. 7Aillustrates a unit cell520of sensor array500, according to an embodiment. The unit cell520, as illustrated inFIG. 7A, includes only part of each of the signal-spreading dummy electrodes531,532,703, and704. Each of the dummy electrodes531,532,703, and704are located partially within unit cell520and partially within other unit cells adjacent to unit cell520. Unit cell520also includes optical dummy electrodes701and702, which are positioned in between the subtraces512a,512b, and512cof the columns sensor electrode512.

Optical dummy electrode701is positioned between the signal-spreading dummy electrodes531and703and optical dummy electrode702is positioned between the signal-spreading dummy electrodes532and704. In one embodiment, each of the optical dummy electrodes701and702is formed from the same layer of conductive material as the column sensor electrode512and the signal-spreading dummy electrodes531,532,703, and704. Optical dummy electrodes such as electrodes701and702may minimize the gaps between the column sensor electrode512and the signal-spreading dummy electrodes531,532,703, and704, to improve optical uniformity for applications such as, for example, touch screens or transparent touch-sensing surfaces.

The pattern of conductive material in unit cell520also includes isolation regions708a,708b,708c, and708dbetween the subtraces512a,512b, and512cof the RX column sensor electrode512and the dummy electrodes531,532, and701-704. As illustrated inFIG. 7A, these isolation regions708a-708dinclude additional optical dummy electrodes, such as706and707. In one embodiment, each of these optical dummy electrodes706and707may be formed from the same layer of conductive material as the column sensor electrode512and the signal-spreading dummy electrodes531,532,703, and704.

In one embodiment, the isolation regions708a-708dreduce crosstalk between the RX sensor electrode512and the signal-spreading dummy electrodes, while the optical dummy electrodes such as706and707occupy the space in the isolation regions708a-708dto improve optical uniformity in the isolation regions708a-708d. Accordingly, optical dummy electrodes may be positioned between a column sensor electrode and a signal-spreading dummy electrode; for example, dummy electrodes706are positioned between the column sensor electrode512and the signal-spreading dummy electrode532. Other dummy electrodes may be positioned between a column sensor electrode and an optical dummy electrode; for example, dummy electrodes707are positioned between column sensor electrode512and optical dummy electrode702. In an alternative embodiments, the isolation regions708a-708dmay not contain any dummy electrodes.

FIG. 7Billustrates a cross-section view of unit cell520along section line705, as illustrated inFIG. 7A. Section line705runs parallel to the y-axis and intersects the dummy electrodes531,701, and703, and the row sensor electrodes501,502, and503. As illustrated inFIG. 7B, the signal-spreading dummy electrode703comprises two portions703aand703cthat are electrically connected by a connecting trace703b. The connecting trace703bextends across the boundary of the unit cell520, and overlaps the gap between row sensor electrodes502and503. Similarly, the dummy electrode531comprises portions531aand531cconnected together by connecting trace531b. Trace531bextends across the boundary of the unit cell520and overlaps the gap between row sensor electrodes502and501.

In one embodiment, the length of each signal-spreading dummy electrode is at least half the length of the unit cell; for example, the length531dof the dummy electrode531along the y-axis is at least half the length of the unit cell520along the y-axis. In alternative embodiments, the lengths of the signal spreading dummy electrodes may be greater or less than half the length of the unit cell.

FIG. 8AandFIG. 8Billustrate cross sectional views of a sensor array without signal spreading dummy electrodes and a sensor array with signal-spreading dummy electrodes, respectively, along with their corresponding capacitance profiles, according to an embodiment.FIG. 8Aillustrates unit cells803,804, and805from a capacitive sensor array without signal-spreading dummy electrodes, such as a single solid diamond or dual solid diamond pattern.

When a stylus tip806moves over the three unit cells803,804, and805in a direction807parallel to the y-axis, the unit cells803,804, and805produce corresponding signal profiles803a,804a, and805a, respectively. As illustrated inFIG. 8A, a positive direction along the axis801corresponds to an increase in the signal, while the axis802indicates the position of the stylus tip806. For each of the signal profiles803a,804a, and805a, a maximum signal is observed when the stylus806is above a center of the unit cell. The signal descends quickly as stylus806is moved away from the center of the unit cell. When the signal strength falls below a noise level808, the signal cannot be used for position calculation. When fewer than three of the signals are discernable above the noise level808, the position of the stylus806may be inaccurately determined. A location within the unit cell where this tends to occur may be referred to as a “dead zone” in the unit cell. For example, such a “dead zone” may exist in the center of unit cell804, where the signal levels803aand805aare both below the noise level808.

FIG. 8Billustrates a cross-sectional view of TX row sensor electrodes501,502, and503, along with signal spreading dummy electrodes531,703,813, and814. When a stylus tip806moves over the three unit cells including sensor electrodes501,502, and503in a direction807parallel to the y-axis, the sensor electrodes501,502, and503produce corresponding signal profiles501a,502a, and503a, respectively. As illustrated inFIG. 8B, a positive direction along the axis811corresponds to an increase in the signal, while the axis812indicates the position of the stylus tip806.

A maximum signal for a sensor electrode is observed when the stylus806is above a center of the sensor electrode. The capacitive sensor array with signal-spreading dummy electrodes, such as electrodes531and703, widens the signal profiles501a,502a, and503a. In contrast with the signal profiles illustrated inFIG. 8A, the signal profiles501a,502a, and503ado not descend as quickly when the stylus806is moved away from the center of the corresponding electrode. With regard to the TX row sensor electrode502, for example, the electrode502is capacitively coupled with the signal-spreading dummy electrodes531and703. Thus, a TX signal applied to sensor electrode502is additionally applied to dummy electrodes531and703via the capacitive coupling. The resulting set of electrodes703,502, and531to which the TX signal is applied is physically wider than the sensor pitch (i.e., the distance between corresponding portions of adjacent row sensor electrodes). Accordingly, the stylus806may be sensed over a wider span, resulting in a wider signal profile502afor the sensor pattern with signal-spreading dummy electrodes, as compared to a sensor pattern without the signal-spreading dummy electrodes.

The adjacent TX row sensor electrodes501and503operate in similar fashion; for example, sensor electrode501is capacitively coupled with signal-spreading dummy electrodes531and814, while sensor electrode503is capacitively coupled with signal-spreading dummy electrodes813and703. This results in wider signal profiles501aand503acorresponding to the sensor electrodes501and503, respectively.

Provided the same sensor pitch as the sensor pattern illustrated inFIG. 8A, the wider signal profiles501aand503across at a higher point than the signal profiles803aand805a. As a result, all three signals are above the noise level808when the stylus806is at the center of electrode502. The unit cells of the sensor pattern inFIG. 8Btherefore do not have a dead zone at this noise level808. As described above, the sensor pitch can be measured between a center of one unit cell and a center of an adjacent unit cell. Alternatively, the sensor pitch can be measured from one edge of an electrode to the corresponding edge of the adjacent electrode to include the width of the electrode and the gap between the electrodes.

In one embodiment, signal spreading dummies widen the signal profile for a stylus or other conductive object moving along the y-axis, while the differences in widths of the RX subtraces widen the signal profile for conductive objects moving in the direction of the x-axis. With reference toFIG. 6, for example, the arrangement of wider subtraces512aand512cat the edges of sensor electrode512and a thinner subtrace512balong the center of electrode512provides for increased sensitivity at the edges and decreased sensitivity in the center, thus widening the overall signal profile.

FIG. 9illustrates signal-spreading dummy electrodes in a sensor array pattern, according to an embodiment. The signal-spreading dummy electrodes901and902function in similar fashion as the dummy electrodes531and532illustrated inFIG. 6. Each of the dummy electrodes901and902overlaps two adjacent row sensor electrodes921and922; however, in contrast with the electrodes531and532, the electrodes901and902lack a narrower connecting trace across the gap between the sensor electrodes921and922, which corresponds to a boundary between the unit cells911and912. Such signal-spreading dummy electrodes901and902lacking a narrow connecting trace may be used when the lamination offset tolerance is relatively small when compared to the size of the dummy electrodes901and902, or when the lamination offset is otherwise compensated.

FIG. 10illustrates a capacitive sensor pattern according to an embodiment, showing additional possible placements for dummy electrodes in the sensor pattern. The sensor array1000illustrated inFIG. 10includes signal spreading dummy electrodes1002-1006that are less than half the length of the unit cell, as measured along the y-axis. For example, the dummy electrodes1002-1006are slightly less than one-third the length of the unit cell1020, as measured along the y-axis.

Among the signal-spreading dummy electrodes1002-1006, electrodes1002-1004are located within the perimeter of the column sensor electrode1001, while electrodes1005and1006are located outside the perimeter of the column sensor electrode1001. In other words, electrodes1002-1004are located between the subtraces of sensor electrode1001, while electrodes1005and1006are not located between the subtraces of sensor electrode1001.

Sensor array1000additionally includes more than one optical dummy electrode1012and1013in between the subtraces of the column sensor electrode1001and between the signal-spreading dummy electrodes1002and1004. Additional optical dummy electrodes1014and1015are located outside the perimeter of the column sensor electrode1001, between the column sensor electrode1001and an adjacent column sensor electrode, and between the signal-spreading dummy electrodes1005and1006.

FIG. 11is a flow diagram of a sensing method1100of sensing a capacitive sensor array with signal-spreading dummy electrodes, according to an embodiment. The method1100may be performed by processing logic that may include hardware (circuitry, dedicated logic, etc.), software (such as is run on a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In one embodiment, the processing device110ofFIG. 1performs some or all of method1100. In another embodiment, the processing logic102ofFIG. 1orFIG. 2performs some or all of the operations of method1100. In other embodiments, the capacitance-sensing circuit101performs some of the operations of method1100. Alternatively, other components of the electronic system100ofFIG. 1perform some or all of the operations of method1100.

InFIG. 11, method1100begins at block1102with the processing logic applying a transmit (TX) signal on a first electrode of a first set of electrodes of a capacitive sensor array. For example, the TX signal may be applied to the row sensor electrode501illustrated inFIG. 5. At block1104, the processing logic measures a receive (RX) signal on a second electrode of a second set of electrodes. For example, the RX signal may be measured at column electrode511illustrated inFIG. 5. Each electrode of the first set of electrodes intersects each of the second set of electrodes to form unit cells each corresponding to an intersection of a pair of electrodes comprising one electrode from the first set and one electrode from the second set. At block1106, the processing logic converts the measured RX signal into a first digital value, which represents a first capacitance at the intersection between the first electrode and the second electrode. The operations of method1100may be repeated for each pair of sensor electrodes comprising one TX row sensor electrode and one RX column sensor electrode in order to detect one or more conductive objects at the surface of the capacitive sensor array.

In the foregoing embodiments, various modifications can be made; for example, row sensor electrodes and column sensor electrodes may be interchanged, and row or column sensor electrodes may be used as either TX or RX sensor electrodes. Furthermore, in some embodiments, intersections between row and column sensor electrodes may be replaced with conductive bridges. For example, bridges may be used to electrically connect portions of sensor electrodes when both row and column sensor electrodes are constructed from a single layer of conductive material. As described herein, conductive electrodes that are “electrically connected” or “electrically coupled” may be coupled such that a relatively low resistance conductive path exists between the conductive electrodes. The terms “substantially” and “approximately” may indicate values or characteristics that may deviate from a nominal value or ideal characteristic (where such deviation may result from manufacturing tolerances, rounding error, and the like) while the desired effect of the nominal value or ideal characteristic is preserved.

Embodiments of the present invention, described herein, include various operations. These operations may be performed by hardware components, software, firmware, or a combination thereof. As used herein, the term “coupled to” may mean coupled directly or indirectly through one or more intervening components. Any of the signals provided over various buses described herein may be time multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit components or blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be one or more single signal lines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program product that may include instructions stored on a computer-readable medium. These instructions may be used to program a general-purpose or special-purpose processor to perform the described operations. A computer-readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The computer-readable storage medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM); random-access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory, or another type of medium suitable for storing electronic instructions.

Additionally, some embodiments may be practiced in distributed computing environments where the computer-readable medium is stored on and/or executed by more than one computer system. In addition, the information transferred between computer systems may either be pulled or pushed across the transmission medium connecting the computer systems.