WO2015118297A1

WO2015118297A1 - Touch sensors and touch sensing methods

Info

Publication number: WO2015118297A1
Application number: PCT/GB2015/050118
Authority: WO
Inventors: Stephen William Roberts
Original assignee: Touchnetix Limited
Priority date: 2014-02-07
Filing date: 2015-01-20
Publication date: 2015-08-13
Also published as: GB201402074D0; GB2522875A

Abstract

A touch-sensitive position sensor comprises an array of sensing nodes defined by electrodes arranged in columns across a sensing surface and a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface. The traces for the sensing nodes in a particular column run between the column and a neighbouring column on one or other side of the column. For at least a subset of the columns the number of traces for the sensing nodes in a particular column which run to one side of the column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are different for different columns.

Description

TITLE OF THE INVENTION

TOUCH SENSORS AND TOUCH SENSING METHODS BACKGROUND OF THE INVENTION

The present invention relates to the field of touch sensors, including touch screens and touch pads. In particular, embodiments of the invention relate to designs for electrode patterns for such sensors for sensing the presence of one or more touching objects within a two-dimensional sensing area (which may comprise a flat or curved surface).

A capacitive touch sensor can be generalised as one that uses a physical sensor element comprising an arrangement of electrically conductive electrodes extending over a touch sensitive area (sensing area) to define sensor nodes and a controller chip connected to the electrodes and operable to measure changes in the electrical capacitance of each of the electrodes or the mutual-capacitance between combinations of the electrodes. The electrodes are typically provided on a substrate. In some configurations electrodes are provided on both sides of a substrate, and these may be referred to as two-sided (two-layer) designs. In other configurations electrodes are provided on a single side of a substrate, and these may be referred to as single-sided (single-layer) designs. Single-sided designs are sometimes preferred because they have reduced manufacturing costs as compared to multi- layered designs. However, single-layer designs can be more challenging from a design point of view because of the restricted topology, principally because it is not possible for electrode interconnections to cross within a single layer design.

Figure 1 schematically shows some principal components of a generic two-sided capacitive touchscreen comprising a physical sensor element 100. The touch screen is represented in plan view (to the left in the figure) and also in cross-sectional view (to the right in the figure).

The touch screen is configured for establishing the position of a touch within a two- dimensional sensing area by providing Cartesian coordinates along an X-direction (horizontal in the figure) and a Y-direction (vertical in the figure). In this example the sensor element 100 is constructed from a substrate 103 that could be glass or plastic or some other insulating material and upon which is arranged an array of electrodes consisting of multiple laterally extending parallel electrodes, X-electrodes 101 (row electrodes), and multiple vertically extending parallel electrodes, Y-electrodes 102 (column electrodes), which in combination allow the position of a touch 109 to be determined. To clarify the terminology, and as will be seen from Figure 1 , the X-electrodes 101 (row electrodes) are aligned parallel to the X- direction and the Y-electrodes 102 (column electrodes) are aligned parallel to the Y-direction. Thus the different X-electrodes allow the position of a touch to be determined at different positions along the Y-direction while the different Y-electrodes allow the position of a touch to be determined at different positions along the X-direction. That is to say in accordance with the terminology used herein, the electrodes are named (in terms of X- and Y-) after their direction of extent rather than the direction along which they resolve position. Furthermore, the electrodes may also be referred to as row electrodes and column electrodes. It will however be appreciated these terms are simply used as a convenient way of distinguishing the groups of electrodes extending in the different directions. In particular, the terms are not intended to indicate any specific electrode orientation. In general the term "row" will be used to refer to electrodes extending in a horizontal direction for the orientations represented in the figures while the terms "column" will be used to refer to electrodes extending in a vertical direction in the orientations represented in the figures.

In some cases, each electrode may have a more detailed structure than the simple "bar" structures represented in Figure 1 , but the operating principles are broadly the same. The sensor electrodes are made of an electrically conductive material such as copper or Indium Tin Oxide (ITO). The nature of the various materials used depends on the desired characteristics of the touch screen. For example, a touch screen may need to be transparent, in which case ITO electrodes and a plastic substrate are common. On the other hand a touch pad, such as often provided as an alternative to a mouse in laptop computers is usually opaque, and hence can use lower cost copper electrodes and an epoxy-g lass-fib re substrate (e.g. FR4). Referring back to Figure 1 , the electrodes are electrically connected via circuit conductors 104 to a controller chip 105, which is in turn connected to a host processing system 106 by means of a communication interface 107. The host 106 interrogates the controller chip 105 to recover the presence and coordinates of any touch or touches present on, or proximate to the sensor 103. In the example, a front cover (also referred to as a lens or panel) 108 is positioned in front of the sensor 103 and a single touch 109 on the surface of the cover 108 is schematically represented.

Note that the touch itself does not generally make direct galvanic connection to the sensor 103 or to the electrodes 102. Rather, the touch influences the electric fields 110 that the controller chip 105 generates using the electrodes 102. With appropriate analysis of relative changes in the electrodes' measured capacitance / capacitive coupling, the controller chip 105 can thus calculate a touch position on the cover's surface as an XY coordinate 1 11. The host system can therefore use the controller chip to detect where a user is touching, and hence take appropriate action, perhaps displaying a menu or activating some function.

There are many different material combinations and electrode configurations to allow creation of a touch screen and the example discussed above is just one. A further aspect of capacitive touch sensors relates to the way the controller chip uses the electrodes of the sensor element to make its measurements. There are two main classes of controller in this regard.

A first class is known as a "self-capacitance" style. Reference is made to Figure 2. In this design of a capacitive sensor, the controller 201 will typically apply some electrical stimulus (drive signal) 202 to each electrode 203 which will cause an electric field to form around it 204. This field couples through the space around the electrode back to the controller chip via numerous conductive return paths that are part of the nearby circuitry 205, product housing 206, physical elements from the nearby surroundings 207 etc., so completing a capacitive circuit 209. The overall sum of return paths is typically referred to as the "free space return path" in an attempt to simplify an otherwise hard-to-visualize electric field distribution. The important point to realise is that the controller is only driving each electrode from a single explicit electrical terminal 208; the other terminal is the capacitive connection via this "free space return path". The capacitance measured by the controller is the "self-capacitance" of the sensor electrode (and connected tracks) relative to free space (or Earth as it is sometimes called) i.e. the "self-capacitance" of the relevant sensor electrode. Touching or approaching the electrode with a conductive element 210, such as a human finger, causes some of the field to couple via the finger through the connected body 213, through free space and back to the controller. This extra return path 211 can be relatively strong for large objects (such as the human body), and so can give a stronger coupling of the electrode's field back to the controller; touching or approaching the electrode hence increases the self-capacitance of the electrode. The controller is configured to sense this increase in capacitance. The increase is strongly proportional to the area 212 of the applied touch and is normally weakly proportional to the touching body's size (the latter typically offering quite a strong coupling and therefore not being the dominant term in the sum of series connected capacitances).

In a classic two-layer self-capacitance sensor the electrodes are arranged on an orthogonal grid, generally with a first set of electrodes on one side of a substantially insulating substrate and the other set of electrodes on the opposite side of the substrate and oriented at nominally 90° to the first set. There are also structures where the grid is formed on a single side of the substrate and small conductive bridges are used to allow the two orthogonal sets of electrodes to cross each other without short circuiting. However, these designs are more complex to manufacture and less suitable for transparent sensors. There are also known designs where the electrode pattern is formed on a single side of a substrate and external connections are used to allow the respective electrodes to be appropriately connected, as discussed further below. One set of electrodes is used to sense touch position in a first axis that we shall call "X" and the second set to sense the touch position in the second orthogonal axis that we shall call "Y".

In a self-capacitance touch sensor, the controller can either drive each electrode in turn (sequential) with appropriate switching of a single control channel or it can drive them all in parallel with an appropriate number of separate control channels. In the former sequential case, any neighbouring electrodes to a driven electrode are sometimes grounded by the controller to prevent them becoming touch sensitive when they are not being sensed (remembering that all nearby capacitive return paths will influence the measured value of the actively driven electrode). In the case of the parallel drive scheme, the nature of the stimulus applied to all the electrodes is typically the same so that the instantaneous voltage on each electrode is approximately the same. The drive to each electrode is electrically separate so that the controller can discriminate changes on each electrode individually, but the driving stimulus in terms of voltage or current versus time, is the same. In this way, each electrode has minimal influence on its neighbours (the electrode-to-electrode capacitance is non-zero but its influence is only "felt" by the controller if there is a voltage difference between the electrodes).

The second class of controller is known as a "mutual-capacitance" style. Reference is made to Figure 3. In this design of a capacitive sensor the controller 301 will sequentially stimulate each of an array of transmitter (driven/drive) electrodes 302 that are coupled by virtue of their proximity to an array of receiver electrodes 303. The resulting electric field 304 is now directly coupled from the transmitter to each of the nearby receiver electrodes; the "free space" return path discussed above plays a negligible part in the overall coupling back to the controller chip when the sensor is not being touched. The area local to and centred on the intersection of a transmitter and a receiver electrode is typically referred to as a "node". Now, on application or approach of a conductive element 305 such as a human finger, the electric field 304 is partly diverted to the touching object 305. An extra return path to the controller 301 is now established via the body 306 and "free-space" in a similar manner to that described above. However, because this extra return path acts to couple the diverted field directly to the controller chip 301 , the amount of field coupled to the nearby receiver electrode 303 decreases. This is measured by the controller chip 301 as a decrease in the "mutual-capacitance" between that particular transmitter electrode and receiver electrodes in the vicinity of the touch. The controller senses this change in capacitance of one or more nodes. For example, if a reduction in capacitive coupling to a given Y-electrode is observed while a given X-electrode is being driven, it may be determined there is a touch in the vicinity of where the given X-electrode and given Y-electrode cross within the sensing surface. The magnitude of a capacitance change is nominally proportional to the area 307 of the touch (although the change in capacitance does tend to saturate as the touch area increases beyond a certain size to completely cover the nodes directly under the touch) and weakly proportional to the size of the touching body (for reasons as described above). The magnitude of the capacitance change also reduces as the distance between the touch sensor electrodes and the touching object increases.

In a classic two-sided mutual-capacitance sensor the transmitter electrodes and receiver electrodes are arranged as an orthogonal grid, with the transmitter electrodes on one side of a substantially insulating substrate and the receiver electrodes on the opposite side of the substrate. This is as schematically shown in Figure 3. In Figure 3 a first set of transmitter electrodes 303 is shown on one side of a substantially insulating substrate 308 and a second set of receiver electrodes 302 is arranged at nominally 90° to the transmitter electrodes on the other side of the substrate. There are also structures where the grid is formed on a single side of the substrate and small insulating bridges, or as discussed below external connections, are used to allow the transmitter and receiver electrodes to be connected to in rows and columns without short circuiting.

By using interpolation between adjacent nodes for both types of capacitive touch sensor a controller chip can typically determine touch positions to a greater resolution than the spacing between electrodes. Also there are established techniques by which multiple touches within a sensing area, and which might be moving, can be uniquely identified and tracked, for example until they leave the sensing area.

Figure 4 schematically represents a conventional single-sided (single-layer) electrode pattern for a capacitive touch sensor 40. The sensor 40 comprises an array of sensing nodes 42 arranged in a plurality of rows and columns across a two-dimensional sensing surface. In this example there are five rows schematically labelled R1 to R5 (running horizontally for the orientation represented in the figure) and six columns schematically labelled C1 to C6 (running vertically for the orientation represented in the figure). Thus the sensing surface extends horizontally from a first (left) edge 47A adjacent column C1 to a second (right) edge 47B adjacent column C6 and extends vertically from a third (top) edge 47C adjacent row R1 to a fourth (bottom) edge 47D adjacent row R5.

Each sensing node 42 comprises a first electrode 43 and a second electrode 44. The first electrodes are schematically represented in Figure 4 with darker shading than the second electrodes. A plurality of traces 45 connect respective ones of the first electrodes 43 to a perimeter of the sensing surface, in this case down to the fourth (bottom) edge 47D adjacent row R5. There is a separate trace 45 for each of the first electrodes 43. The respective first electrodes 43 of each row R1 to R5 are electrically connected together outside the surface of the sensing area by external wiring (not shown) connecting to the respective traces 45 at the perimeter of the sensing area. A plurality of further traces 46 interconnect respective ones of the second electrodes 44 in the same column, and the respective further traces also extend down to the perimeter of the sensing area along the fourth edge 47D. Ground traces 48 (schematically represented in Figure 4 with dotted lines) are provided at locations where traces 45 connecting to the first electrodes 43 and further traces 46 connecting to the second electrodes 46 would otherwise be adjacent.

Thus, in the arrangement represented in Figure 4 the first electrodes 43 in each row are interconnected (via their respective traces 45 and external wiring) and the second electrodes in each column are interconnected (by the further traces 46) within the sensing area. In this regard the arrangement of electrodes in Figure 4 provides an array of interconnected rows and columns defining a two-dimensional array of sensing nodes. In effect the sensing nodes 43 of Figure 4 correspond to the sensing nodes at the crossing points in the two-layer designs of Figures 1 to 3, but with electrodes provided on only a single layer of a substrate. Thus, the approach of Figure 4 can be advantageous in certain circumstances, for example because of simpler manufacturing and / or higher transparency.

The sensing element represented in Figure 4 can be connected to conventional drive circuitry for establishing the position of an object adjacent the sensing surface in accordance with conventional techniques such as discussed above with reference to Figures 1 to 3. Thus the sensing element can be used in a mutual-capacitance mode in which capacitive coupling between the respective first electrodes and the second electrodes are measured to identify which sensing nodes are associated with a change in mutual capacitance caused by a proximate object. The sensing elements can also be used in a self-capacitance mode in which the self-capacitance of the respective electrodes are separately measured to identify which sensing nodes are associated with a change in mutual capacitance. In this regard, the interconnection of the electrodes into rows and columns provides a matrix approach which reduces the number of control channels required (as compared to approaches where the individual sensing nodes are coupled to separate measurement channels).

Whilst a single-layer design of the type represented in Figure 4 can be advantageous from a manufacturing point of view, it requires additional trace circuitry within the sensing surface to provide the connections between the electrodes comprising the respective sensor nodes and the associated control circuitry. One drawback of this is the introduction of areas of varying sensitivity to touch within the sensing area. For example, referring to Figure 4, the area to the right of column C6 can be expected to have lower sensitivity to reliable touch determination because the area comprises traces connecting to the second electrodes of the sensor nodes in column C6 without any additional column of sensor nodes to the right to allow for interpolation in conjunction with measurements from the sensor nodes of column C6.

As a consequence of this it would be common for the region to the right of column C6 to in effect be considered a non-usable part of the sensing surface. In some situations this is not considered problematic and a bezel or other cover associated with a device in which the sensor is mounted may simply overlay this region so that it does not form part of the active sensing surface. However, there can in some circumstances be a desire for an active sensing surfaces to be as large as possible and extend as close as possible to the edge of a device in which the sensor comprising the sensing surface is mounted, i.e. to provide what might be termed an "edgeless" electrode pattern. In this situation the "dead" area to the right of column C6 is problematic because it restricts how close the sensing area can extend towards the edge of a device in which the sensing areas provided.

There is therefore a desire for touch sensitive position sensors with reduced areas of low sensitivity in the vicinity of their edges.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a touch-sensitive position sensor comprising: an array of sensing nodes defined by electrodes arranged in rows and columns across a sensing surface; and a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface, wherein the traces for the sensing nodes in a given column run between the given column and a neighbouring column to one or other side of the given column; and wherein for at least a subset of the columns the number of traces for the sensing nodes in a given column that run to one side of the given column and the number of traces for the sensing nodes in the given column that run to the other side of the given column are different for different columns, wherein each sensing node is associated with a first electrode and a second electrode, and wherein the traces for each sensing node are associated with the respective first electrodes, and wherein the second electrodes for the sensing nodes in the same column are connected together within the sensing area by further traces.

In accordance with some embodiments the number of traces for the sensing nodes in a given column which run to one side of the given column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are selected according to the position of the column within the sensing area.

In accordance with some embodiments a first edge of the sensing area is defined by a first column of sensing nodes and a second edge of the sensing area is defined by a final column of sensing nodes, and wherein within the at least a subset of the columns, the number of traces for the sensing nodes in a given column which run to one side of the given column increase with increasing distance from the first edge of the sensing area to the second edge of the sensing area and the number of traces for the sensing nodes in a given column which run to the other side of the given column decrease with increasing distance from the first edge of the sensing area to the second edge of the sensing area.

In accordance with some embodiments a first edge of the sensing area is defined by a first column of sensing nodes and a second edge of the sensing area is defined by a final column of sensing nodes, and wherein at least a majority of the traces for the sensing nodes in the first column of sensing nodes run to a side of the first column which is away from the first edge of the sensing area and at least a majority of the traces for the sensing nodes in the final column of sensing nodes run to a side of the first column which is away from the second edge of the sensing area.

In accordance with some embodiments a third edge of the sensing area is defined by a first row of sensing nodes and a fourth edge of the sensing area is defined by a final row of sensing nodes, and wherein for each column having sensing nodes associated with traces running on both sides of the column, the sensing nodes associated with traces on one side of the column are between the third edge of the sensing surface and a switch-over point for the column and the sensing nodes associated with traces on the other side of the column are between the switch-over point for the column and the fourth edge of the sensing surface.

In accordance with some embodiments for each column within the at least a subset of the columns the switch-over point is between sensing nodes in a different pair of adjacent rows.

In accordance with some embodiments the traces for sensing nodes in the same row of different columns are connected together outside the sensing surface.

In accordance with some embodiments the traces associated with the first electrodes and the further traces associated with the second electrodes are connected to their respective sensing nodes from opposite sides of the respective columns in which the sensing nodes are arranged.

In accordance with some embodiments a third edge of the sensing area is defined by a first row of sensing nodes and a fourth edge of the sensing area is defined by a final row of sensing nodes, and wherein for each column having sensing nodes associated with traces running on both sides of the column, the sensing nodes associated with traces on one side of the column are between the third edge of the sensing surface and a switch-over point for the column and the sensing nodes associated with traces on the other side of the column are between the switch-over point for the column and the fourth edge of the sensing surface, and wherein the further traces connecting the second electrodes of the sensing nodes in each column together pass from one side of their respective column to the other side of their respective column between sensing nodes on either side of the switch-over point for the column.

In accordance with some embodiments the touch-sensitive position sensor further comprises a controller coupled to respective ones of the sensing nodes via the traces and arranged to measure changes in a capacitive coupling associated with the respective electrodes comprising the sensing nodes.

In accordance with some embodiments the controller is further operable to determine the position of an object adjacent the sensing surface based on the measured changes in the capacitive coupling associated with the respective electrodes comprising the sensing nodes.

According to a second aspect of the invention there is provided a method of sensing a position of an object adjacent a sensing surface comprising: providing an array of sensing nodes defined by electrodes arranged in rows and columns across a sensing surface and a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface, wherein the traces for the sensing nodes in a given column run between the given column and a neighbouring column to one or other side of the given column; and wherein for at least a subset of the columns the number of traces for the sensing nodes in a given column which run to one side of the given column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are different for different columns; measuring changes in a capacitive coupling associated with the respective electrodes comprising the sensing nodes; and determining the position of the object adjacent the sensing surface based on the measured changes in the capacitive coupling associated with the respective electrodes comprising the sensing nodes, wherein each sensing node is associated with a first electrode and a second electrode, and wherein the traces for each sensing node are associated with the respective first electrodes, and wherein the second electrodes for the sensing nodes in the same column are connected together within the sensing area by further traces.

It will be appreciated that features and aspects of the invention described above in relation to the first and other aspects of the invention are equally applicable to, and may be combined with, embodiments of the invention according to other aspects of the invention as appropriate, and not just in the specific combinations described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example only with reference to the following drawings in which:

Figure 1 illustrates a typical touchscreen / touch sensor system;

Figure 2 illustrates a typical self-capacitance type touchscreen system;

Figure 3 illustrates a typical mutual-capacitance type touchscreen system; Figure 4 schematically illustrates a conventional single-sided electrode pattern for a two-dimensional capacitive sensor;

Figure 5 schematically illustrates a modified single-sided electrode pattern for a two- dimensional capacitive sensor;

Figures 6 to 9 schematically illustrate single-sided electrode patterns for two- dimensional capacitive sensors according to various example embodiments of the invention; and

Figure 10 schematically shows some components of a touch sensor according to an embodiment of the invention.

DETAILED DESCRIPTION

Figure 5 schematically represents a single-sided (single-layer) electrode pattern for a capacitive touch sensor 50 which can provide sensitivity at locations closer to its edge than existing designs. In many respects the sensor 50 of Figure 5 is similar to, and will be understood from, the sensor 40 of Figure 4. Aspects of the sensor 50 and its operation to provide position measurements which are not described in detail herein may be implemented in accordance with any conventional techniques.

The sensor 50 comprises an array of sensing nodes 52 arranged in a plurality of rows and columns across a two-dimensional sensing surface. In this example there are five rows schematically labelled R1 to R5 (running horizontally for the orientation represented in the figure) and six columns schematically labelled C1 to C6 (running vertically for the orientation represented in the figure). Thus the sensing surface extends horizontally from a first (left) edge 57A adjacent column C1 to a second (right) edge 57B adjacent column C6 and extends vertically from a third (top) edge 57C adjacent row R1 to a fourth (bottom) edge 57D adjacent row R5.

Each sensing node 52 comprises a first electrode 53 and a second electrode 54. The first electrodes are schematically represented in Figure 5 with darker shading than the second electrodes. A plurality of traces 55 connect respective ones of the first electrodes 53 to a perimeter of the sensing surface, in this case down to the fourth (bottom) edge 57D adjacent row R5. There is a separate trace 55 for each of the first electrodes. The respective first electrodes 53 of each row R1 to R5 are electrically connected together outside the surface of the sensing area by external wiring (not shown) connecting to the respective traces 55 at the perimeter of the sensing area. In principle the first electrodes in the sensing nodes in columns C5 and C6 in row R1 could be connected together within the sensing area and share a common trace down to the lower edge 47D. A plurality of further traces 56 interconnect respective ones of the second electrodes 54 which are in the same column. The further traces also extend down to the perimeter of the sensing area along the fourth (bottom) edge 57D. Ground traces 58 (schematically represented in Figure 5 with dotted lines) are provided at locations where traces 55 connecting to the first electrodes 53 and further traces 56 connecting to the second electrodes 56 would otherwise be adjacent.

Thus, and in a manner similar to the design of Figure 4, in the arrangement represented in Figure 5 the first electrodes 53 in each row are interconnected (via their respective traces 55 and external wiring) and the second electrodes in each column are interconnected (by the further traces 56) within the sensing area. In this regard the arrangement of electrodes in Figure 5 again provides an array of interconnected rows and columns defining a two-dimensional array of sensing nodes. In effect the sensing nodes of Figure 5 again correspond to the sensing nodes at the crossing points in the two-layer designs of Figures 1 to 3, but with electrodes provided on only a single layer of a substrate.

The sensing element (sensing surface) represented in Figure 5 can be connected to conventional drive circuitry for establishing the position of an object adjacent the sensing surface in accordance with conventional techniques such as discussed above with reference to Figures 1 to 3. Thus the sensing element can be used in a mutual-capacitance mode in which capacitive coupling between the respective first electrodes and the second electrodes are measured to identify which sensing nodes are associated with a change in mutual capacitance caused by a proximate object. The sensing elements can also be used in a self- capacitance mode in which the self-capacitance of the respective electrodes are separately measured to identify which sensing nodes are associated with a change in mutual capacitance. In this regard it will be appreciated the interconnection of the electrodes into rows and columns provides a matrix approach which reduces the number of control channels required in accordance with conventional touch-sense of techniques.

The design of the sensor 50 of Figure 5 differs from the design of the sensor 40 of Figure 4 in that the first electrodes 53 and second electrodes 54 of the sensor nodes 52 in column C6 and their associated traces 55 and further traces 56 are "mirrored" in the design of Figure 5 relative to the arrangement of the corresponding elements in the design of Figure 4. Thus in Figure 5 the traces 55 connecting to the respective first electrodes 53 (shown darker than the second electrodes 54) in the column C6 run to the left-hand side of the column (for the orientation shown in the figure), as opposed to the right-hand side of the column. In effect, the relative positions of the first and second electrodes and associated trace circuitry are reversed in column C6 as compared to the corresponding elements in the other columns C1 to C5 in the design of Figure 5. A consequence of this approach is the sensing area provided by the electrode pattern represented in Figure 5 provides sensitivity closer to both left and right edges of the sensing area than the sensor design represented in Figure 4. This is because the sensing nodes associated with column C6 are closer to the edge of the sensing surface. However, a drawback of the modified design of Figure 5 is a reduction in sensitivity in the region between columns C5 and C6 due to a greater separation between these columns of sensing nodes to allow room for the traces 55 connecting to the first electrodes 53 of the fifth and sixth columns (C5 and C6) to be provided within the sensing area.

Figure 6 schematically represents a single-sided (single-layer) electrode pattern for a capacitive touch sensor 60 in accordance with an embodiment of the invention. In many respects the sensor 60 of Figure 6 is similar to, and will be understood from, the sensors 40, 50 of Figures 4 and 5. Aspects of the sensor 60 and its operation to provide position measurements which are not described in detail herein may be implemented in accordance with any conventional techniques.

The sensor 60 comprises an array of sensing nodes 62 arranged in a plurality of rows and columns across a two-dimensional sensing surface. In this example there are five rows schematically labelled R1 to R5 (running horizontally for the orientation represented in the figure) and six columns schematically labelled C1 to C6 (running vertically for the orientation represented in the figure). Thus the sensing surface extends horizontally from a first (left) edge 67A adjacent column C1 to a second (right) edge 67B adjacent column C6 and extends vertically from a third (top) edge 67C adjacent row R1 to a fourth (bottom) edge 67D adjacent row R5.

Each sensing node 62 comprises a first electrode 63 and a second electrode 64. The first electrodes 63 are schematically represented in Figure 6 with darker shading than the second electrodes 64. A plurality of traces 65 connect respective ones of the first electrodes 63 to a perimeter of the sensing surface, in this case down to the fourth (bottom) edge 67D adjacent row R5. There is a separate trace 65 for each of the first electrodes. The respective first electrodes 63 of each row R1 to R5 are electrically connected together outside the surface of the sensing area by external wiring (not shown) connecting to the respective traces 65 at the perimeter of the sensing area. (In principle the first electrodes in the sensing nodes in columns C1 and C2 in row R1 could be connected together within the sensing area and share a common trace down to the lower edge 47D.) A plurality of further traces 66 interconnect respective ones of the second electrodes 64 which are in the same column as each other. The further traces also extend down to the perimeter of the sensing area along the fourth (bottom) edge 67D. In this regard, and in addition to being differently shaded in the figure, the respective first electrodes 63 and second electrodes 64 can also be distinguished from one another in that the first electrodes are each associated with an individual connecting trace 65 down to the bottom edge 67D whereas the second electrodes are all connected to at least one other second electrode within the sensing area. Ground traces 68 (schematically represented in Figure 6 with dotted lines) are provided at locations where traces 65 connecting to the first electrodes 63 and further traces 66 connecting to the second electrodes 66 would otherwise be adjacent.

Thus, and in a manner similar to the designs of Figures 4 and 5, in the arrangement represented in Figure 6 the first electrodes 63 in each row are interconnected (via their respective traces 65 and external wiring) and the second electrodes 64 in each column are interconnected (by the further traces 66) within the sensing area. In this regard the arrangement of electrodes in Figure 6 again provides an array of interconnected rows and columns defining a two-dimensional array of sensing nodes. In effect the sensing nodes of Figure 6 again correspond to the sensing nodes at the crossing points in the two-layer designs of Figures 1 to 3, but with electrodes provided on only a single layer of a substrate.

The sensing element (sensing surface) represented in Figure 6 can be connected to conventional drive circuitry for establishing the position of an object adjacent the sensing surface in accordance with conventional techniques such as discussed above with reference to Figures 1 to 3. Thus the sensing element can be used in a mutual-capacitance mode in which capacitive coupling between the respective first electrodes and the second electrodes are measured to identify which sensing nodes are associated with a change in mutual capacitance caused by a proximate object. The sensing elements can also be used in a self- capacitance mode in which the self-capacitance of the respective electrodes are separately measured to identify which sensing nodes are associated with a change in mutual capacitance. In this regard it will be appreciated the interconnection of the electrodes into rows and columns provides a matrix approach which reduces the number of control channels required in accordance with conventional touch-sense of techniques.

The design of the sensor 60 of Figure 6 differs from the design of the sensor 40 of Figure 4 in that the number of traces 65 associated with the first electrodes for the sensing nodes in a given column that run to one side of the given column and the number of traces for the sensing nodes in the given column that run to the other side of the given column are different for different columns. For example, for column C1 the traces 65 associated with the first electrodes 63 of all five sensing nodes in the rows R1 to R5 pass to the right of the column C1. However, for column C2 the traces 65 associated with the first electrodes 63 of the four sensing nodes in the rows R2 to R5 pass to the right of the column C2 while the trace 65 associated with the first electrode 63 of the sensing node in the rows R1 passes to the left of the column C2. For column C3 the traces 65 associated with the first electrodes 63 of the three sensing nodes in the rows R3 to R5 pass to the right of the column C3 while the traces 65 associated with the first electrodes 63 of the sensing nodes in the rows R1 and R2 pass to the left of the column C3. This changing number in the traces 65 associated with the first electrodes 63 passing on the different sides of the respective columns when moving from left to right across the sensor continues to the last column C6. Thus, for column C6 the traces 65 associated with the first electrodes 63 of all five sensing nodes in the rows R1 to R5 pass to the left of the column C6.

A consequence of this approach is that the sensing nodes of the sixth column C6 in Figure 6 are relatively close to the edge of the sensing area (similar to the design of Figure 5), thereby providing improved performance towards the sensing area edge relative to the design of Figure 4. However, unlike the design of Figure 5, the sensing nodes are more uniformly spaced, thereby avoiding the relatively reduced sensitivity in the region between columns C5 and C6 which might be expected with the design of Figure 5. In effect extra space needed within the sensing area to accommodate the five traces 65 associated with the first electrodes 63 of the sensing nodes in column C6 which are no longer to the right of this column is shared among the gaps between all the other columns.

Ignoring the ground traces which are not directly involved in the capacitance measurements, the example configuration of 5 rows by 6 columns of sensing nodes represented in Figures 4 to 6 relies on a total of 36 traces leading down to the bottom edge of the respective sensing areas.

In the conventional design of Figure 4 there are six traces running between each pair of adjacent columns, with a single trace running to the left of column C1 and five traces running to the right of column C6. It is these five columns running to the right of column C6 which can be problematic in some limitations as discussed above. In the conventional design of Figure 4 there are six traces running between each pair of adjacent columns, with a single trace running to the left of column C1 and five traces running to the right of column C6. It is these five traces running to the right of column C6 which can be problematic in some implementations as discussed above.

In the modified design of Figure 5 there are six traces running between each pair of adjacent columns up to column C5, with a single trace running to the left of column C1 and a single trace running to the right of column C6. However, there are 10 traces running between columns C5 and C6. It is the 10 traces running between columns C5 and C6 which can be problematic in some implementations as discussed above.

In the design of Figure 6 the number of traces between the respective columns are more uniform than for Figure 5. Thus, there are seven traces running between each pair of adjacent columns up to column C5, with a single trace running to the left of column C1. There are 6 traces running between columns C5 and C6 and a single trace running to the right of column C6. Although there is one fewer trace between columns C5 and C6 than between the other columns in the design of Figure 6, a uniform pitch of sensing nodes (column separations) can readily be provided by having a slightly larger gap between columns C5 and C6 than is strictly necessary to fit the number of traces.

Because the sensor design represented in Figure 6 is an example that relies on sensing nodes comprising first and second electrodes, the "reversing" of the first electrode wiring for different numbers of the sensing nodes in the different columns impacts the manner in which the second electrodes can be interconnected within the sensing area. In particular, the traces 66 connecting the respective second electrodes within each column switch from one side of their column to the other side between the rows where the first and second electrodes are "reversed" - this point may be referred to as a "switch-over" point for the column. This can be seen in Figure 6, for example, between rows R1 and R2 in column C2, between rows R2 and R3 in column C3, between rows R3 and R4 in column C4 and between rows R4 and R5 in column C5. As explained further below, some embodiments of the invention may rely on sensing nodes provided by single electrodes, and in which case the issue of interconnecting second electrodes of sensing nodes in a column does not arise.

Another consequence of the design of Figure 6 in which the sensing nodes in different columns within a given row can have their first and second electrodes opposite ways around (resulting in the associated traces 65 for the first electrodes of the sensing nodes in the given row running down different sides of the respective columns for different columns) is that the locations where traces associated with a first electrode and traces associated with a second electrode are adjacent are modified. This means the locations of ground traces 68 might also be modified in the design of Figure 6 relative to the design of Figure 5. In particular, between columns which both have the electrode configuration reversed for at least one sensing node relative to the others (i.e. between columns C2 and C3, between columns C3 and C4, and between columns C4 and C5 in the example of Figure 6) there are two ground traces 68 which are not connected to one another within the sensing area. The respective ground traces may be interconnected to the other ground traces outside the sensing area. For examples, as is common with capacitive sensing elements, an ground region may run around the perimeter of the sensing area (except where the traces 65, 66 exit the perimeter). Thus, the ground traces are shown in Figure 6 as extending to the upper edge 67C may connect to this ground trace. Alternatively, these traces may connect down to the bottom edge 67D by in effect extending the relevant ground traces to run between the traces 65 connecting to the first electrodes of the neighbouring columns. Thus Figure 6 represents a two-dimensional capacitive touch sensor comprising a single-sided design (i.e. having an sensing electrode and trace pattern that may be formed in a single layer of conductive material) in which sensing nodes are provided closer to the edge of the sensing surface then for the conventional design represented in Figure 4 and with an improved uniformity in sensor node separation than for the design represented in Figure 5.

The respective first and second electrodes comprising the respective sensing nodes of the sensor 60 represented in Figure 6 are schematically shown as simple rectangles for ease of representation. It will, however, be appreciated that in general the design of the electrodes may be made in accordance with conventional techniques for designing electrodes to define sensing nodes in a capacitive touch sensor. Furthermore, it will be appreciated the specific electrode design considerations may be different depending on whether the control circuitry for the capacitive sensor is based on mutual-capacitance sensing techniques or self-capacitance sensing techniques. In any event, these design considerations may follow established techniques. One established design technique is for the electrodes defining a sensing node to comprise a pattern of interdigitated fingers / branches to increase the interaction region between the respective electrodes and / or their surroundings. An example of this is shown in Figure 7.

Figure 7 schematically represents a single-sided (single-layer) electrode pattern for a capacitive touch sensor 70 in accordance with an embodiment of the invention. In essence the sensor 70 of Figure 6 is the same as the sensor 60 Figure 6 with corresponding elements being identified by corresponding the reference numerals. The only significant difference for the sensor 70 in Figure 7 is that the respective first electrodes 63 and the respective second electrodes 64 comprise interdigitated designs as opposed to the highly schematic rectangle designs of Figure 6. The topology of the electrodes and their associated traces in Figure 7 is otherwise the same as that of Figure 6. The design of Figure 7 also shows the inclusion of an ground region 69 at the perimeter of the sensing area of the kind mentioned above. In all other regards the design of Figure 7 is based on the same principles as the design of Figure 6 and may be operated in the same manner.

Figure 8 schematically represents a variation on the single-sided electrode pattern design of Figure 7. One difference in the design of Figure 8 is the introduction of an additional row R6 and an additional column C7 of sensing nodes. However, this increase in the number of sensing node does not impact the underlying design principles or operation. A further difference in the design of Figure 8 as compared to the design of Figure 7 is that the sensing nodes in the first column (column C1) and the sensing nodes in the last column (column C7) are of around half-width as compared to the other sensing nodes. The provision of narrower sensing nodes at the edges of a sensing area is an established technique in capacitive sensing for improving linearity in these regions.

The above-described sensors have all been based on what might be termed a matrix approach in which electrodes are arranged into interconnected rows and interconnected columns with sensing nodes corresponding to the locations where the electrodes comprising the rows and columns come into proximity. This matrix arrangement of rows and columns allows for a reduced number of capacitance measurement channels as compared to a configuration in which each sensing node is individually connected to its own sensing channel. Nonetheless, capacitive sensors in which each sensing node is connected to its own sensing channel (as opposed to being interconnected into rows and columns) can also implement techniques in accordance with the principles described above.

Thus, Figure 9 schematically represents a single-sided (single-layer) electrode pattern for a capacitive touch sensor 90 in accordance with an embodiment of the invention.

Aspects of the sensor 90 and its operation to provide position measurements which are not described in detail herein may be implemented in accordance with any conventional techniques.

The sensor 90 comprises an array of sensing nodes 92 arranged in a plurality of rows and columns across a two-dimensional sensing surface. In this example there are five rows schematically labelled R1 to R5 (running horizontally for the orientation represented in the figure) and six columns schematically labelled C1 to C6 (running vertically for the orientation represented in the figure). Thus the sensing surface extends horizontally from a first (left) edge 97A adjacent column C1 to a second (right) edge 97B adjacent column C6 and extends vertically from a third (top) edge 97C adjacent row R1 to a fourth (bottom) edge 97D adjacent row R5.

Each sensing node 92 comprises a single electrode 93. A plurality of traces 95 connect respective ones of the electrodes 93 to a perimeter of the sensing surface, in this case down to the fourth (bottom) edge 97D adjacent row R5. There is a separate trace 95 for each of the electrodes. The respective first electrodes 93 are electrically connected to control circuitry configured to measure the capacitance of the respective electrodes 93. There are a total of 30 electrodes 93 comprising the sensing surface and these may, for example, be coupled to 30 separate measurement channels or time-multiplexed to a single measurement channel.

The sensing element (sensing surface) represented in Figure 9 can be connected to conventional drive circuitry for establishing the position of an object adjacent the sensing surface in accordance with conventional self-capacitance measuring techniques. The design of the sensor 90 of Figure 9 differs from the design of the sensor 60 of Figure 6 in being based on sensing nodes comprising a single electrode in which the capacitance is individually measured. However, the considerations regarding the manner in which the traces 95 connect to the respective electrodes 93 in the design of Figure 9 are in essence the same as the considerations regarding the manner in which the traces 65 connects to the respective first electrodes 63 in the design of Figure 6. Thus, and in a manner to similar to that described above Figure 6, the arrangement of Figure 9 also adopts an approach in which the number of traces 95 associated with the sensing nodes 92 in a given column that run to one side of the given column and the number of traces for the sensing nodes in the given column that run to the other side of the given column are different for different columns. Thus, Figure 9 provides another example of a single-sided capacitive sensor having sensing nodes in close proximity to the sensing surface edges in conjunction with a uniform separation between columns of sensing nodes.

Thus, sensor designs in accordance with embodiment of the invention may comprise an array of sensing nodes defined by electrodes arranged in rows and columns across a sensing surface. These electrodes may comprise the electrodes in single-electrode based sensing nodes or one of the electrodes in two-electrode based sensing nodes. A plurality of traces may be arranged to provide electrical connections from the electrodes to a perimeter of the sensing surface. For example, the traces may run between the columns to a single edge of the sensing area to simplify connectivity to external circuitry. The traces associated with the sensing nodes in a given column may run between the given column and a neighbouring column to one or other side of the given column. For at least a subset of the columns the number of traces for the sensing nodes in a given column that run to one side of the given column and the number of traces for the sensing nodes in the given column that run to the other side of the given column may be different for different columns. This approach in effect allows the number of traces for the columns of electrodes to be gradually moved from one side to the other side of the columns when moving across the sensing area, thereby allowing the wiring for the columns at the edges of the sensing area to in effect be reversed relative to one another, thereby allowing the respective sensing nodes to be placed in close proximity to the edge.

In the examples described above, the number of columns was one more than the number of rows and this was sufficient to allow a complete reversal of the wiring associated with each of the rows by reversing the wiring of one additional sensing node for each column step across the sensing surface.

In examples where there are a greater number of columns, some of the columns will have the same arrangement of traces as other columns (i.e. not all columns need have a different number of traces on different sides of the column). For example, if a design similar to that of Figure 6 were required to have five rows and 12 columns, the electrode pattern corresponding to that represented in Figure 6 might be arranged towards the middle of the plurality of columns with three additional columns provided to the left and the right. The three columns to the left may have a pattern of electrodes and traces which matches that of column C1 and the three columns to the right may have a pattern of electrodes and traces which matches that of column C6.

Conversely, in examples where there are a greater number of rows, a complete reversal of the wiring associated with each of the rows may be achieved by reversing the wiring of more than one additional sensing node for each column step across the sensing surface. For example, if a design were required to have five rows but only four columns, the electrode pattern corresponding to that represented in Figure 8 may be modified to in effect delete the electrode patterning associated with columns C2, C4 and C6 with the electrode patterning of the remaining columns shunted together to remove the resulting gaps. In this case there would be reversals of wiring for two sensing nodes for each column step across the sensing surface. As an alternative to increasing the number of wiring reversals per column step, a different approach would be to in effect delete columns from the ends of the designs described above, and accept this means the edge-most sensing nodes are not as close to the edge of the sensing area as they could otherwise be because additional trace circuitry is required at the edges. For example, a five row by four column design could be provided by in effect deleting the electrode patterning associated with columns C1 and C6 in the design of Figure 6.

In general the number of traces for the sensing nodes in a given column which run to one side of the given column and the number of traces for the sensing nodes in the given column which run to the other side of the given column may be selected according to the position of the column within the sensing area. That is to say, the numbers may change with increasing position across the sensing area, for example with the trace for one additional sensing node being switched from one side of the column to the other side of the column for each column step across the sensing surface. Thus the number of traces for the sensing nodes in a given column which run to one side of the given column may increase with increasing distance from a first edge of the sensing area to a second edge of the sensing area while the number of traces for the sensing nodes in a given column which run to the other side of the given column decrease with increasing distance from the first edge of the sensing area to the second edge of the sensing area. In this way, the total number of traces between the different columns (i.e. comprising traces associated with both columns of a neighbouring pair) may remain more consistent than for other designs. As noted above, it will be appreciated the electrodes may be referred to herein as row electrodes and column electrodes to provide a convenient way of distinguishing the groups of electrodes extending in the different directions and these terms are not intended to indicate any specific electrode orientation while a sensor is in use. In general the term "row" will be used to refer to electrodes extending in a horizontal direction for the orientations represented in the figures while the terms "column" will be used to refer to electrodes extending in a vertical direction in the orientations represented in the figures. However, if a sensor in accordance with an embodiment of the invention is rotated relative to the representation identified in the figures, what are referred to herein as rows will in effect become vertical, and what are referred to herein as columns will in effect become horizontal, but it will of course be appreciated this will have no impact on the operation of the sensor. It will further be appreciated that whilst the described embodiments have adopted a regular square array of sensing nodes, the same principles apply for non-regular arrays of sensing nodes. For example, the same principles would apply for a sensor in which the two directions along which position is resolved are not orthogonal - that is to say, the row and column electrodes need not be at 90° to another and the notes need not be regularly spaced. Furthermore, the plane of the sensing surface need not be flat, and the sensing surface may instead be conformed to a three-dimensional surface.

Figure 10 schematically shows some components of a touch sensor 1300 according to an embodiment of the invention. The sensor 1300 comprises a sensing surface 1302, for example in accordance with any of the embodiments of the invention such as discussed above, coupled to a controller chip 1304. The controller chip 1304 may, for example, be a conventional "off the shelf controller chip configured to determine the occurrence of and report a location of a touch using conventional capacitive sensing techniques. The sensor 1300 further comprises a processor 1306 arranged to receive a reported position estimate from the controller 1304 and to convert the reported position estimate to a physical position estimate in accordance with the above-describe techniques. The processor 1306 may, for example, comprise a suitably programmed general purpose microprocessor, or field programmable gate array, or an application specific integrated circuit. Furthermore, although presented in Figure 13 as two separate elements, it will be appreciated the functionality of the controller 1304 and the processor 1306 may be provided in a single element, for example, a single suitably-programmed microprocessor.

Thus there has been described a touch-sensitive position sensor comprising an array of sensing nodes defined by electrodes arranged in columns across a sensing surface and a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface. The traces for the sensing nodes in a particular column run between the column and a neighbouring column on one or other side of the column. For at least a subset of the columns the number of traces for the sensing nodes in a particular column which run to one side of the column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are different for different columns.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. It will be appreciated that features of the dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claims.

Claims

1. A touch-sensitive position sensor comprising:

an array of sensing nodes defined by electrodes arranged in rows and columns across a sensing surface; and

a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface, wherein the traces for the sensing nodes in a given column run between the given column and a neighbouring column to one or other side of the given column; and wherein for at least a subset of the columns the number of traces for the sensing nodes in a given column that run to one side of the given column and the number of traces for the sensing nodes in the given column that run to the other side of the given column are different for different columns, wherein each sensing node is associated with a first electrode and a second electrode, and wherein the traces for each sensing node are associated with the respective first electrodes, and wherein the second electrodes for the sensing nodes in the same column are connected together within the sensing area by further traces.

2. The touch-sensitive position sensor of claim 1 , wherein the number of traces for the sensing nodes in a given column which run to one side of the given column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are selected according to the position of the column within the sensing area.

3. The touch sensitive position sensor of any preceding claim, wherein a first edge of the sensing area is defined by a first column of sensing nodes and a second edge of the sensing area is defined by a final column of sensing nodes, and wherein within the at least a subset of the columns, the number of traces for the sensing nodes in a given column which run to one side of the given column increase with increasing distance from the first edge of the sensing area to the second edge of the sensing area and the number of traces for the sensing nodes in a given column which run to the other side of the given column decrease with increasing distance from the first edge of the sensing area to the second edge of the sensing area.

4. The touch sensitive position sensor of any preceding claim, wherein a first edge of the sensing area is defined by a first column of sensing nodes and a second edge of the sensing area is defined by a final column of sensing nodes, and wherein at least a majority of the traces for the sensing nodes in the first column of sensing nodes run to a side of the first column which is away from the first edge of the sensing area and at least a majority of the traces for the sensing nodes in the final column of sensing nodes run to a side of the first column which is away from the second edge of the sensing area.

5. The touch sensitive position sensor of any preceding claim, wherein a third edge of the sensing area is defined by a first row of sensing nodes and a fourth edge of the sensing area is defined by a final row of sensing nodes, and wherein for each column having sensing nodes associated with traces running on both sides of the column, the sensing nodes associated with traces on one side of the column are between the third edge of the sensing surface and a switch-over point for the column and the sensing nodes associated with traces on the other side of the column are between the switch-over point for the column and the fourth edge of the sensing surface.

6. The touch sensitive position sensor of claim 5, wherein for each column within the at least a subset of the columns the switch-over point is between sensing nodes in a different pair of adjacent rows.

7. The touch sensitive position sensor of any preceding claim, wherein the traces for sensing nodes in the same row of different columns are connected together outside the sensing surface.

8. The touch sensitive position sensor of claim 1 , wherein the traces associated with the first electrodes and the further traces associated with the second electrodes are connected to their respective sensing nodes from opposite sides of the respective columns in which the sensing nodes are arranged.

9. The touch sensitive position sensor of claim 1 , wherein a third edge of the sensing area is defined by a first row of sensing nodes and a fourth edge of the sensing area is defined by a final row of sensing nodes, and wherein for each column having sensing nodes associated with traces running on both sides of the column, the sensing nodes associated with traces on one side of the column are between the third edge of the sensing surface and a switch-over point for the column and the sensing nodes associated with traces on the other side of the column are between the switch-over point for the column and the fourth edge of the sensing surface, and wherein the further traces connecting the second electrodes of the sensing nodes in each column together pass from one side of their respective column to the other side of their respective column between sensing nodes on either side of the switchover point for the column.

10. The touch-sensitive position sensor of any preceding claim, further comprising a controller coupled to respective ones of the sensing nodes via the traces and arranged to measure changes in a capacitive coupling associated with the respective electrodes comprising the sensing nodes.

11. The touch-sensitive position sensor of 10, wherein the controller is further operable to determine the position of an object adjacent the sensing surface based on the measured changes in the capacitive coupling associated with the respective electrodes comprising the sensing nodes.

12. A method of sensing a position of an object adjacent a sensing surface comprising: providing an array of sensing nodes defined by electrodes arranged in rows and columns across a sensing surface and a plurality of traces arranged to provide electrical connections from the respective sensing nodes to a perimeter of the sensing surface, wherein the traces for the sensing nodes in a given column run between the given column and a neighbouring column to one or other side of the given column; and wherein for at least a subset of the columns the number of traces for the sensing nodes in a given column which run to one side of the given column and the number of traces for the sensing nodes in the given column which run to the other side of the given column are different for different columns;

measuring changes in a capacitive coupling associated with the respective electrodes comprising the sensing nodes; and

determining the position of the object adjacent the sensing surface based on the measured changes in the capacitive coupling associated with the respective electrodes comprising the sensing nodes, wherein each sensing node is associated with a first electrode and a second electrode, and wherein the traces for each sensing node are associated with the respective first electrodes, and wherein the second electrodes for the sensing nodes in the same column are connected together within the sensing area by further traces.

13. A touch-sensitive position sensor substantially as hereinbefore described with reference to Figures 6 to 8 and 10 of the accompanying drawings.

14. A method of sensing a position of an object substantially as hereinbefore described with reference to Figures 6 to 8 and 10 of the accompanying drawings.