Lattice touch-sensing system

[0001] The present invention relates to a lattice touch-sensing system. More particularly, the present invention relates to a touch-sensing system with a touch-sensitive surface that includes sensor bars laid out in a lattice.

[0002] As computers and other electronic devices become more ubiquitous, touch-sensing systems are becoming more prevalent as a means for inputting data. For example, touch-sensing systems may now be found in workshops, warehouses, manufacturing facilities, restaurants, on hand-held personal digital assistants, automatic teller machines, casino game-machines, and the like.

[0003] Capacitive touch sensing is one of the most widely used techniques in touch screen industries. Capacitive touch sensors are mainly divided in two groups, namely, the continuous capacitive sensors, and discontinuous (patterned) capacitive sensors. In a continuous capacitive sensor, the sensor consists of a sheet of conducting thin film that is excited from four corners. The signals induced by a touch are transmitted from the corners to a controller, where they are decoded and translated to coordinates. In a typical patterned capacitive touch screen the sensor consists of a series of parallel conductive bars that are driven from both ends with an excitation signal from the controller. The signals induced by a touch are transmitted to the controller with the same lead lines that excite the sensor bars. These signals are then decoded in the controller and the touch coordinates are reported to a computer. For examples of this type of sensor refer to U.S. Pat. No. 5,650,597, and U.S. patent application Ser. No. 10/176,564.

[0004] In patterned capacitive screens different methods are used to calculate the touch coordinates. For example, in capacitive screens using near field imaging (NFI) the coordinate along the parallel bars, the X-axis, is determined by ratio of the voltage drops on left and right of the touch. The coordinate in the direction perpendicular to the bars, the Y-axis, is determined by finding the location of the touched bar combined by interpolation methods.

[0005] Touch sensors utilizing more than one patterned sensing layer can be used to determine the coordinates of a touch with high accuracy in both directions, provided that the sensing layers have the proper pattern geometry. Examples of multi-layered capacitive touch sensors are U.S. Pat. No. 4,686,332, and U.S. Pat. No. 6,137,427. The challenge of capacitively coupling to more than one sensing layer has forced the designers either to use very narrow conducting bars, or to use bars with vastly different widths on the two layers. The former design suffers from a very low signal level, and the latter design has significant error due to sparse distribution of the bars.

[0006] This invention is directed to a touch-sensing system for detecting a position of a touch on a touch-sensitive surface. The touch-sensing system comprises at least two layers of unidirectional capacitive sensor bars where each sensor bar is electrically connected at one or both ends to a lead line. According to one example, the other end of the sensor bar may be left open, which enables the area on that side of the touch sensor to be as small as possible. In another example, one or more layers may be connected at both ends so that weaker touches or multiple touches may be sensed. The sensor bars of the layers are disposed in a lattice configuration such that the sensor bars of one layer are disposed in a different direction from the sensor bars of the other layer. A touch on the touch-sensing system is located in one direction by signals from one layer of sensor bars, and in another direction by signals from the other layer of sensor bars.

[0007] In one aspect of the invention, the lattice touch-sensing system includes a surface and a lattice touch-sensing circuit. The sensing circuit comprises two sets of parallel and unidirectional capacitive sensor bars where the sensor bars of the first set are not parallel to the sensor bars of the second set. Each sensor bar of a given set of sensor bars is electrically connected to a lead line of a corresponding set of lead lines.

[0008] In another aspect of the invention, the lattice touch-sensing system includes a surface, a lattice touch-sensing circuit with two sets of parallel and unidirectional capacitive sensor bars and two corresponding sets of lead lines, and a control circuit. The control circuit provides an excitation signal to both set of sensor bars through the corresponding set of lead lines, receives sensing signals produced when a touch on the surface occurs, and determines the position of the touch from the sensing signals.

[0009] In yet another aspect of the invention, the lattice touch-sensing system includes a touch pane, two sensor planes separated by a sheet of dielectric material, and a control circuit. Each of the two sensor planes includes parallel and unidirectional capacitive sensor bars, which are electrically connected to corresponding lead lines. The lead lines are electrically connected to the control circuit, which provides an excitation signal to the sensor bars through the lead lines, receives sensing signals produced when a touch on the surface occurs, and determines a position of the touch from the sensing signals.

[0010] In still another aspect of the invention, the lattice touch-sensing system includes a touch surface and a lattice touch-sensing circuit. The sensing circuit includes two layers of unidirectional capacitive sensor bars where the sensor bars of the first layer are not parallel to the sensor bars of the second layer. More than one sensor bar of a given layer of the touch-sensing circuit is electrically connected to the same lead line of a corresponding set of lead lines. A signal-processing scheme is then used to distinguish which of the sensor bars experience the touch.

[0011] In still another aspect of the invention, the lattice touch-sensing system includes a touch surface and a lattice touch-sensing circuit. The sensing circuit includes two layers of unidirectional capacitive sensor bars where the sensor bars of the first layer are not parallel to the sensor bars of the second layer. Each sensor bar of one or both layers of the touch-sensing circuit is electrically connected at both ends to a lead line, wherein the resultant touch sensing system has improved multiple-touch recognition and/or rejection characteristics over a similar single-ended system.

[0018] The invention enables a touch-sensing system capable of detecting a position of a touch on a touch-sensitive surface. The touch-sensing system enabled by the invention includes a first layer of sensor bars arranged in a first direction, and a second layer of sensor bars arranged in a second direction. The first and second directions may be substantially orthogonal to each other. In this configuration, a touch to the touch-sensitive surface creates a signal on at least one sensor bar in each layer. The position of the touch is then determined by locating the touch on each of the two sensor bars. The first layer of sensor bars is used to identify the location of a touch along one axis, and the second layer of sensor bars is used to identify the touch location along another axis.

[0019] In one embodiment, the invention is implemented in a touch-sensitive screen in which multiple sensor bars arranged in a lattice configuration are embedded in the screen. Each of the sensor bars is electrically connected at least at one end to a lead line. The particulars of this invention will become apparent from the following detailed discussion of embodiments of the invention.

[0020] FIG. 1 is a schematic representation of one implementation of the present invention, showing an exemplary touch-sensing system 110 that includes a touch-sensitive screen 120, a control circuit 130, and a computer 140. In operation, the touch-sensing screen 120 generates signals in response to a touch on the screen. The signals are transmitted to the control circuit 130, which processes the signals. The control circuit 130 then transmits the results from processing the signals to computer 140 for further processing.

[0021] Touch-sensitive screen 120 is a capacitive touch screen that generates signals when it is touched. The components of touch-sensitive screen 120 will be discussed in detail in conjunction with FIG. 2. Briefly stated, touch-sensitive screen 120 has two layers of capacitive sensor bars. Each sensor bar in each layer is connected to a lead line at least at one end.

[0022] Control circuit 130 is a circuit that provides excitation current to the capacitive sensor bars in touch-sensitive screen 120. Control circuit 130 also detects and processes signals generated by the capacitive sensor bars. While driving and sensing signals on one layer, the control circuit 130 could put the other layer in any appropriate state, such as float the other layer or drive the other layer with a known signal or guard signal. Control circuit 130 may be of any type of electronic circuit, such as an integrated circuit. Control circuit 130 may be installed by itself or integrated into a computer, such as computer 140.

[0023] FIG. 2 is an exploded view of an exemplary embodiment of touch-sensitive screen 210. FIG. 2 only illustrates the principle components in touch-sensitive screen 210. Other components may be added without deviating from the principles of the invention.

[0024] Touch-sensitive screen 210 is made up of a series of layers laminated together. In this embodiment, touch-sensitive screen 210 includes a touch pane 220 and a lattice touch-sensing element 230. The lattice touch-sensing element 230 includes a first sensor layer 240, a second sensor layer 260, and an intermediate dielectric layer 250 disposed between the first sensor layer 240 and the second sensor layer 260.

[0025] The touch pane 220 is the uppermost layer of the touch-sensitive screen 210. The touch pane 220 may be made of an optically clear substance. The touch pane 220 may be manufactured from a chemically strengthened glass, transparent plastic, or any other acceptable dielectric material. One side of the touch pane 220 serves as the touch surface of the touch-sensitive screen 210, while the other side of the touch pane 220 is attached to the lattice touch-sensing element 230. The touch pane 220 provides the necessary dielectric material between the touching object and the sensing element, as well as protecting the touch-sensing element 230 from environmental hazards.

[0026] The top layer of the lattice touch-sensing element 230 is the first sensor layer 240. The first sensor layer 240 includes a plurality of capacitive touch-sensitive sensor bars 270 arranged substantially parallel to each other in a unidirectional manner. They are preferably constructed of indium tin oxide (ITO) for optical transparency, but may be constructed of any conductive transparent material for transparent applications, such as other transparent conductive oxides as well as transparent conductive polymers. Alternatively, the sensor bars may be constructed from conductive non-transparent material for applications that do not require transparency.

[0027] The second sensor layer 260 also includes a plurality of capacitive touch-sensitive sensor bars 290 arranged substantially parallel to each other in a unidirectional manner. The sensor layers 240 and 260 are parallel to each other with the sensor bars 290 of the second sensor layer 260 being oriented substantially orthogonal to the sensor bars 270 of the first sensor layer 240. As used herein, the terms “orthogonal” or “perpendicular” shall have their ordinary meanings but that the elements referred to as orthogonal or perpendicular do not actually intersect because they lie in different planes. The term intersection shall be used to mean an intersection of bars when projected onto an imaginary plane parallel to the touch sensing planes 240 and 260, even though the bars do not actually join.

[0028] In accordance with the invention, one end of each first-layer sensor bar 270 is electrically connected to one end of a corresponding lead line in a plurality of lead lines 280. Likewise, one end of each second-layer sensor bar 290 is connected to one end of a corresponding lead line in a plurality of lead lines 285. The other ends of the lead lines 280/285 are coupled to a control circuit 130 (FIG. 1). The lead lines 280/285 are electrical conduits that allow signals to travel between control circuit 130 and sensor bars 270/290. The lead lines 280/285 are illustrated in FIG. 2 as a single line for simplicity of illustration only. It should be appreciated that each lead line may individually extend from the sensor bars 279/290 to the control circuit 130, or that more than one sensor bar 270/290 may be connected to the same lead line 280/290 if an alternative addressing mechanism is used to uniquely identify each sensor bar on a particular layer. Lead lines 280 may be made of any conductive material, such as copper, silver, gold, or the like.

[0029] The dielectric layer 250 is a non-conductive layer that separates the first sensor layer 240 and the second sensor layer 260. The dielectric layer 250 may be an adhesive manufactured from any non-conductive, transparent material. The dielectric layer 250 serves as electrical insulator, which prevents sensor bars 270 of the first sensor layer 240 and sensor bars 290 of the second sensor layer 260 from coming into direct contact.

[0030] Briefly stated here, and described in greater detail in conjunction with FIGS. 3 and 4, the sensor bars 270/290 receive an excitation signal via the lead lines 280/285 from the control circuit 130. The excitation signal sets up an electric field on each sensor bar 270/290. A touch to the touch-sensitive screen 210 results in a capacitive coupling between the touching object and the sensor bars 270/290 of both layers in the area proximate to the touch. The capacitive coupling between the touching object and the sensor bars near the touch causes an AC current to flow from the controller via the lead lines through the coupled sensor bars to ground. Since the magnitude of the current on each lead line depends on the extent of the coupling of the touching object with the bar (or bars) connected to that lead line, the controller can accurately determine the touched bars on each sensing layer by determining which bar on each sensor layer has the highest signal. The touch position on each layer may be further refined by also examining the strength of the signals on the lead lines connected to the bars in the immediate neighborhood of the sensor bars having the highest signal. The inventors have determined that interpolating between two or more strong signals on each sensing layer can improve the accuracy of the coordinate determination. The signals from each sensing layer determine the touch position along an axis perpendicular to the bars in that layer. Since the bars on the two sensing layers are perpendicular to each other the axes on which the touch position are calculated are also perpendicular to each other. Therefore, the touch position is uniquely determined by knowing the touch coordinates on the two orthogonal axes.

[0031] FIG. 2 illustrates an exemplary touch-sensitive screen 215 in which only one end of first-layer sensor bar 270 is electrically connected to one end of a corresponding lead line in a plurality of lead lines 280, and one end of each second-layer sensor bar 290 is connected to one end of a corresponding lead line in a plurality of lead lines 285. In an alternative example, either first-layer sensor bar 270, second-layer sensor bar 290, or both, could be electrically connected at both ends. With both ends of one or both sensor bars electrically connected, extra information can be obtained. For example, electrically connecting both ends of the sensor bars could be used for greater resolution. Alternatively, electrically connecting to both ends of the sensor bars could be used for the recognition of multiple touches. Recognition of multiple touches could be used in a gaming application, for example. In another alternative, electrically connecting both ends of the sensor bar could be used in the rejection of multiple touches.

[0032] FIG. 3 is a simplified schematic representation of one embodiment of sensor bars 315 in a first layer 305 and sensor bars 320 in a second layer 310 of a touch-sensitive screen, configured as described in conjunction with FIG. 2, to further illustrate the concepts of this invention. In this implementation, the sensor bars 315 of the first layer 305 and the sensor bars 320 of the second layer 310 are oriented substantially orthogonal to each other. Other orientations may be used without deviating from the principles of the invention. To facilitate discussion, the sensor bars 315 of the first layer 305 are parallel to an arbitrarily drawn X-axis 323. The sensor bars 320 of the second layer 310 are parallel to an arbitrarily drawn Y-axis 325.

[0033] Each of the sensor bars 315 and sensor bars 320 has one end electrically connected to corresponding lead lines 330 and lead line 335, respectively. In the example illustrated in FIG. 3, sensor bars 315 and sensor bars 320 may or may not be electrically connected at the other end. Lead lines 330 and lead lines 335 may be connected to a control circuit, such as the control circuit 130 shown in FIG. 1. It should be appreciated that the number of lead lines on each layer is always less than or equal to the number of sensor bars on that layer.

[0034] When in operation, the control circuit 130 sets up an electric potential on sensor bars 315 and sensor bars 320 via the corresponding lead lines 330 and 335. The excitation signal electrically energizes sensor bars 315 and sensor bars 320. The excitation of the sensing layers may be simultaneous or sequential. In another embodiment, the sensing bars of each layer may be excited one at a time, while the sensing bars of the other layer are kept at a fixed potential or driven with some other signal, such as a guard signal.

[0035] FIG. 3 illustrates an example in which the sensor bars of each layer are electrically connected at one end. However, in another embodiment, the sensor bars of one or both layers may be electrically connected at both ends. Having the sensor bars connected at both ends in one or both layers provides certain benefits over the single-ended embodiments. Each sensor layer could provide more detailed information, including the touch location in both directions. This extra information could greatly improve multiple touch rejection, or, conversely, to enable multiple touch recognition. For instance, a two-layer touch sensor could be used in combination with a gaming application that allowed two players to simultaneously touch the touch sensor. In addition, the improved performance of a dual-layer double-end-connected design would allow weaker signals to be accurately detected, such as those experienced by users wearing gloves or the like. These and other advantages and applications will be apparent to those skilled in the art.

[0036] FIG. 4 is a simplified schematic representation of the touch-sensitive screen of FIG. 3 in operation responding to a touch. To illustrate the principles of this invention, assume that a user touches a touch-sensitive screen with an object or a finger at position 410, which is experienced by both sensor bar 415 and sensor bar 420. As shown in FIG. 4, sensor bar 415 is oriented parallel to the X-axis 323, which is orthogonal to the Y-axis 325. The location of sensor bar 415 on Y-axis 325 may be represented by Y1 425. Similarly, sensor bar 420 is oriented parallel to Y-axis 325, which is orthogonal to X-axis 323. The location of sensor bar 420 on X-axis 323 may be represented by X1 430. By touching the touch sensitive screen at position 410, which corresponds to the intersection of sensor bar 415 and sensor bar 420, the object or the finger becomes capacitively coupled to both energized sensor bars, producing a response signal 435 on lead line 445 and a response signal 440 on lead line 450. Both signals are provided to the control circuit 130 (FIG. 1), where they are received and processed by the control circuit 130.

[0037] It should be appreciated that only one response signal from each layer is shown for simplicity of illustration. In actual operation, a touch may produce signals of various strengths on multiple sensor bars of a single sensor layer. The control circuit may determine the touch position by taking into account the signals from multiple bars in the immediate neighborhood of the touched bars. A linear or non-linear interpolation of the multiple signals from each layer may be used to accurately determine the touch position.

[0038] FIG. 5 is a schematic illustration of another embodiment in which the sensor bars are not rectangular as shown in FIGS. 2 through 4. In this embodiment, there are two sensor layers, a first layer 501 and a second layer 502. Each row of conducting elements (e.g., element 503) of each sensor layer includes a series of diamond-shaped patches that are connected to each other with short pieces of relatively narrow rectangles (e.g., connector 504). One advantage of this sensor geometry is that if both sensing layers are excited simultaneously the top layer (second layer 502) shields the bottom layer (first layer 501) except for the deletion areas between the bars, where the bars of the first layer 501 can be capacitively coupled. In this embodiment, it is possible to have a significant amount of coupling on points on both sensor layers even when both sensor layers are excited simultaneously. It should be mentioned that the patches in the conducting elements may have shapes other than diamond. For example the patches may be hexagons or the like. The size and aspect ratios of the conductive patches may be chosen such that a typical finger would cover at least a portion of a diamond on each layer.

[0039] It may be highly desirable to minimize the area occupied on the sides of touch sensors for routing lead lines. There are several possible ways of reducing this area. For instance, the lattice touch sensor envisioned by the present invention may use sensor bars connected to lead lines only at one end. This effectively reduces the lead line routing area around the touch screen. Another example is to connect more than one bar to each lead line, and use signal-processing schemes to distinguish the touched bars. In this embodiment, each lead line is shared by an equal number of bars as the other lead lines. For example, if a lead line in a sensor layer is connected to 3 bars, the other lead lines on that sensor layer are attached to 3 bars. One of the possible methods that may be applied to determine which of the bars, sharing the same lead line, has actually been touched is that reported in co-pending U.S. patent application Ser. No. 09/998,614.

[0040] FIG. 6 shows an alternative embodiment of the invention that reduces the area around the sensor. A sensor layer is shown in which there are eight bars that are uniquely addressed by their individual lead lines (a discrete design). In this embodiment each sensing layer forms a discrete capacitive touch sensor, such as the one described in co-pending U.S. patent application Ser. No. 10/176,564. A discrete pattern is used in FIG. 6 for simplicity. Other connection schemes may be used without deviating from the spirit of this particular embodiment.

[0041] The lead lines on each sensor layer are divided in two groups, each group running along a different edge of the sensor. The first group 603 is connected to Indium Tin Oxide (ITO) bars 605 on the top half of the sensor. This group of lead lines runs along the left edge and goes straight to tail connection pads. The second group 607 is connected to ITO bars 609 in the bottom half of the sensor. The lead lines of this second group 607 are connected to the opposite end of the bars 609 at the right side, and run along the right edge and then along the bottom edge of the sensor to go to their corresponding contact pads. In this embodiment, three edges of the sensor are occupied by the space required for four lead lines. This is half of the space that would have been necessary for a conventional design with eight lead lines on each side of the sensor. The saving on the lead line routing area in this embodiment may be used to minimize the overall size of the sensor, or it could be used to keep the same overall sensor size but increase the active area of the sensor.

[0042] In accordance with the invention, the coordinates are determined by finding the bars carrying the peak signal and their immediate neighbors on each layer. One of the advantages of this method is that the accuracy of the coordinates determined is neither dependent on the uniformity of the sheet resistance of the conductive bars, nor is it affected by any possible imbalances caused by the sensor circuit configuration. This eases the stringent uniformity requirement that applies in conventional capacitive touch sensors, and allows the use of less expensive transparent conductive thin films in the sensor element. In other words, if the sensor bars are used to locate a touch in only one direction, the ratio of signal strength on each side is not important. Thus, the resistance uniformity of the sensor bars is much less important, thus simplifying the manufacturing process and reducing the cost of the touch sensor.

[0043] In addition, implementations of the present invention are not strongly affected by far field effects. Thus, another advantage of the invention is that simpler control circuits may be used that do not include the elements for countering far field effects. This further lowers the cost of manufacturing such touch screens.