WO2016114123A1 - A Capacitive Touch Panel with Matrix Electrode Pattern - Google Patents

Abstract

A capacitive touch sensor has at least a sensing column (410) comprising a plurality of sensing elements (420a-420g). The touch sensor comprises a substrate (10), and a conductive layer (11) disposed over the substrate. The sensing column comprises n first electrodes (D₁ - D₇), wherein n ≧ 2, and at least a second electrode (S_j). The first electrodes and the second electrode are defined in the conductive layer and extend generally parallel to a first direction. The first electrodes comprise a plurality of first electrode unit areas (440) disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer. The sensing elements (420a-420g) extend generally in a second direction crossed with the first direction, each sensing element of the sensing column including a respective first electrode unit area of at least two of the first electrodes of the sensing column and a portion of the second electrode of the sensing column.

Description

A Capacitive Touch Panel with Matrix Electrode Pattern

The present invention relates to touch panel devices. In particular, this invention relates to capacitive type touch panels. Such a capacitive type touch panel device may find application in a range of consumer electronic products including, for example, mobile phones, tablet and desktop PCs, electronic book readers and digital signage products.

Touch panels have become widely adopted as the input device for a range of electronic products such as smart-phones and tablet devices. Although, a number of different technologies can be used to create these touch panels, capacitive systems have proven to be the most popular due to their accuracy, durability and ability to detect touch input events with little or no activation force.

The most basic method of capacitive sensing for touch panels is the surface capacitive method - also known as self-capacitance - for example as disclosed in US4293734 (Pepper, October 6, 1981). A typical implementation of a surface capacitance type touch panel is illustrated in FIG.1 and comprises a transparent substrate 10, the surface of which is coated with a conductive material that forms a sensing electrode 11. One or more voltage sources 12 are connected to the sensing electrode, for example at each corner, and are used to generate an electrostatic field above the substrate. When an input object 13 that is electrically conductive - such as a human finger - comes into close proximity to the sensing electrode, a capacitor 14 is dynamically formed between the sensing electrode 11 and the input object 13 and this field is disturbed. The capacitor 14 causes a change in the amount of current drawn from the voltage sources 12 wherein the magnitude of current change is related to the distance between the finger location and the point at which the voltage source is connected to the sensing electrode. Current sensors 15 are provided to measure the current drawn from each voltage source 12 and the location of the touch input event is calculated by comparing the magnitude of the current measured at each source. Although simple in construction and operation, surface capacitive type touch panels are unable to detect multiple simultaneous touch input events as occurs when, for example, two or more fingers are in contact with the touch panel.

Another well-known method of capacitive sensing applied to touch panels is the projected capacitive method - also known as mutual capacitance. In this method, as shown in FIG.2, a drive electrode 20 and sense electrode 21 are formed on a transparent substrate (not shown). A changing voltage or excitation signal is applied to the drive electrode 20 from a voltage source 22. A signal is then generated on the adjacent sense electrode 21 by means of capacitive coupling via the mutual coupling capacitor 23 formed between the drive electrode 20 and sense electrode 21. A current measurement means 24 is connected to the sense electrode 21 and provides a measurement of the size of the mutual coupling capacitor 23. When the input object 13 is brought to close proximity to both electrodes, it forms a first dynamic capacitor to the drive electrode 27 and a second dynamic capacitor to the sense electrode 28. If the input object is connected to ground, as is the case for example of a human finger connected to a human body, the effect of these dynamically formed capacitances is manifested as a reduction of the amount of capacitive coupling in between the drive and sense electrodes and hence a reduction in the magnitude of the signal measured by the current measurement means 24 attached to the sense electrode 21.

As is well-known and disclosed, for example, in US 5,841,078 (Bisset et al, October 30, 1996), by arranging a plurality of drive and sense electrodes in a grid pattern to form an electrode array, this projected capacitance sensing method may be used to form a touch panel device. An advantage of the projected capacitance sensing method over the surface capacitance method is that multiple simultaneous touch input events may be detected.

In order to form the electrode grid array in a projected capacitance type touch panel device, a manufacturing process is typically used in which two layers of conductive material are deposited on the touch panel substrate with an electrically insulating layer deposited between them. The sense electrodes and drive electrodes may be formed entirely in separate conductive layers with the insulating layer preventing electrical contact between them at points in the array where they intersect. Alternatively, as disclosed in US 8,274,486 (Atmel, 2008) the sense electrodes and drive electrodes may be substantially formed in the same conductive layer and the other conductive layer used merely to provide bridges at the intersection points to prevent electrical contact. A disadvantage of the projected capacitance sensing method compared to the surface capacitance method is therefore the increased cost of manufacture. Consequently, it is desirable to provide a means of reducing the cost of manufacture of projected capacitance touch screen devices whilst maintaining the performance advantages of the method.

A means of manufacturing a projected capacitance type touch panel device using only a single conductive layer is disclosed, for example, in US 8,319,747 (Apple, 2008). However, although the cost of manufacture is reduced in this device the performance of the sensor is also reduced. Specifically, the accuracy at which the location of objects touching the surface can be calculated is decreased and the minimum size of object that can be detected is increased. A means to reduce the cost of manufacture of touch panel devices without reducing the performance is therefore sought.

US 2014/0340354 proposes a mutual capacitive touch control device that includes a sensing electrode and driving electrode that extend generally parallel to one another. The sensing electrode includes a main stem with strip-a shaped planar contour and a longer side parallel to a first direction, first electrode fingers that extend from the main stem toward a second direction perpendicular to the first direction and second electrode fingers that extend from the main stem toward opposite the second direction. A first driving electrode includes a main body having recesses corresponding to and interleaved with the first electrode fingers of the sensing electrode, and the second driving electrode includes a main body having recesses corresponding to and interleaved with the second electrode fingers of the sensing electrode. Sensing regions are formed between the sensing electrode and the first or second driving electrode, and these sensing regions extend parallel to the sensing and driving electrodes.

A first aspect of the present invention provides a capacitive touch sensor having at least a first sensing column comprising a plurality of sensing elements; the touch sensor comprising: a substrate; and a conductive layer disposed over the substrate; wherein the first sensing column comprises n first electrodes, wherein n ≧ 2, and at least a second electrode, the first electrodes and the second electrode defined in the conductive layer and extending generally parallel to a first direction; wherein the first electrodes each comprise a plurality of first electrode unit areas disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer; wherein the sensing elements extend generally in a second direction crossed with the first direction, each sensing element of the first sensing column including a respective first electrode unit area of at least two of the first electrodes of the first sensing column and a portion of the second electrode of the first sensing column.. The touch sensor comprises a drive circuit for applying drive voltages sequentially to successive groups of one or more first electrodes of the sensor column in successive sampling periods and a sensing circuit for measuring a current supplied by the second electrode of the sensor column. The touch sensor is adapted to compute K = R.(G.D)^-1, where:
K is a matrix representation of capacitances in the first sensing column,
R is a matrix representation of the currents measured from the second electrode of the first sensing column in respective sampling periods of one frame period;
G is a matrix representation of the sensing elements of a sensing column against the first electrodes of the sensing column, in which a row of the matrix representation G represents the relative areas of first electrode unit areas present in a respective sensing element and a column of the matrix representation G represents the relative areas of first electrode unit areas of a respective first electrode included in the sensing elements of the sensing column; and
D is a matrix representation of the sequence of drive voltages applied by the drive circuit, in which each column represents the relative magnitude of voltages applied to the first electrodes during a respective sampling period and each row represents the relative magnitude of voltages applied to respective first electrode in successive sampling periods of one frame period.

The invention may also be applied in a touch sensor having multiple sensing columns. In principle the touch sensor may compute K_i = R_i.(G_i.D_i)^-1 separately for individual sensing columns, where K_i, R_i, G_i, D_i are the matrix representation for the ith sensing column. This may be done where, for example, different sensing columns are driven with different voltage sequences so that D_i is not the same for all sensing columns and/or where different sensing columns have different electrode arrangements so that G_i is not the same for all sensing columns. Alternatively, if a touch sensor has multiple identical sensing columns, where two sensing columns are considered “identical” to one another if the matrix representation G₁ for one sensing column is identical to the matrix representation G₂ for the other sensing column, which are driven with the same sequence of drive voltages so that the multiple sensing columns all have the same matrix representation D of drive voltages, the touch sensor may compute C = S.(G.D)^-1, where
S is a matrix representation of the measured currents from the sensing columns, where a row of the matrix representation S represents the currents measured from the second electrode of a sensing column in respective sampling periods (that is, corresponds to the matrix representation R for that sensing column), and a column of the matrix representation S represents the currents measured from the second electrodes of respective sensing columns during one sampling period;
and C is a matrix representation of mutual capacitances, in which a row represents the relative mutual capacitances in a sensing element between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element (that is, corresponds to the matrix representation K for that sensing column). This has the advantage that the drive circuit need supply only one sequence of drive voltages.

The method may further include determining the location of one or more touches on the touch panel from the matrix representation K or from the matrix representation C.

In general, C is a p x m matrix, where p is the number of sensing columns in the sensor and m is the number of sensing elements in a sensing column. A row of C corresponds to the representation K of the mutual capacitances for the sensing elements of a sensing column ― that is, the k^th element of a row of C represents the total capacitance between the second electrode and all first electrode unit areas that are included in the k^th sensing element in that sensing column. In general S is a p x t matrix, where t is the number of sampling periods in a frame period. If the sensor includes only one sensing column, p = 1 so that C and S are both row matrices. G is an m x n matrix, and D is an n x t matrix.

It will be understood that, since G and D need represent, respectively, only relative areas of first electrode unit areas and relative magnitude of voltages applied to the first electrodes rather than the absolute values of first electrode unit areas and voltages, that the matrix representation C of the capacitances will represent relative mutual capacitances for the sensing elements of a sensing column rather than absolute values of the mutual capacitances. However, determination of the location of a touch on the touch panel requires only relative mutual capacitances and does not require absolute values of the capacitances. Thus the touch sensor, or a user, may use C to determine the location of one or more touches on the touch panel.

It will be appreciated that computing K = R.(G.D)^-1 or C = R.(G.D)^-1 or requires that the inverse matrix product (G.D)^-1 exists (formally, this means that the matrix product (G.D) must be “invertible” or pseudo-invertible) and can be calculated either exactly or to any desired degree of accuracy. One way of ensuring that (G.D) is invertible is to ensure that G and D are both individually invertible, but the invention is not limited to this.

Unlike in US 2014/0340354, the invention does not require the electrodes to be provided with electrode fingers or for the electrodes to be interdigitated with one another. This simplifies the process of defining the electrodes in the conductive layer.

A second aspect of the invention provides a method of determining capacitances in a sensor having p sensing columns, a sensing column comprising a plurality of sensing elements, each sensing element including respective portions of two or more first electrodes and a portion of a second electrode, the method comprising: applying a sequence of drive voltages to the first electrodes; measuring a sequence of currents supplied by the second electrodes of the sensing columns as a consequence of the application of the drive voltages to the first electrodes; and, for one or more sensing elements, determining capacitances between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element according to:
C = D.(G.S)^-1, where
D is a matrix representation of the sequence of drive voltages;
G is a matrix representation of the sensing elements, in which a row of the matrix representation G represents relative areas of the portions of the first electrodes present in a respective sensing element and a column of the matrix representation G represents relative areas of the portions of a respective first electrode included in the sensing elements;
S is a matrix representation of the currents measured from the second electrodes of the sensing columns in respective sampling periods;
and C is a matrix representation of relative mutual capacitances for the sensing elements of the first sensing column.

This aspect is generally complementary to the first aspect. In the first aspect the multiple first electrodes (n first electrodes) of a sensor column are used as drive electrodes to apply drive signals to a sensor column and a resultant current is sensed via the second electrode of the sensor column, whereas in the second aspect the multiple first electrodes (n first electrodes) are used as sense electrodes to sense currents generated when a drive voltage is applied to a sensor column via the second electrode.

FIG. 1 shows a typical implementation of a surface capacitance type touch panel device; FIG. 2 shows a typical implementation of a projected capacitance type touch panel device; FIG.3 shows the mathematical matrix representation of the signals generated in a touch panel device; FIG.4 shows an electrode arrangement in accordance with a first embodiment of the invention; FIG.5 shows a mathematical matrix representation of an electrode arrangement in accordance with a first embodiment of the invention; FIG. 6 shows a sensing circuit for measurement of the capacitances in a touch panel device; FIG.7 shows a waveform diagram illustrating the operation of a sensing circuit for measurement of the capacitances in a touch panel device; FIG.8 shows a block diagram of a system incorporating a touch panel device; FIG.9 shows an electrode arrangement in accordance with a third embodiment of the invention; FIG.10 shows a mathematical matrix representation of an electrode arrangement in accordance with a third embodiment of the invention; FIG.11 shows an electrode arrangement in accordance with a fourth embodiment of the invention; FIG.12 shows an electrode arrangement in accordance with a fifth embodiment of the invention; FIG.13 shows a mathematical matrix representation of an electrode arrangement in accordance with a fifth embodiment of the invention; FIG.14 shows a mathematical matrix representation of an electrode arrangement in accordance with a sixth embodiment of the invention FIG.15 shows an electrode arrangement in accordance with a seventh embodiment of the invention;

The present invention provides a capacitive touch sensor that may be used, for example in touch panel display systems or the like. The touch sensor includes a sensor substrate and an array of electrodes formed in a single layer of conductive material on the sensor substrate.

In accordance with a first and most general embodiment of the present invention, the touch sensor comprises a plurality of sensing columns each of which comprises a plurality of first electrodes (in this example drive electrodes) and at least one second electrode (in this example at least one sense electrode). The first and second electrodes are defined in a conductive layer that is disposed over a substrate. The plurality of drive electrodes and at least one sense electrode are formed into sensing elements wherein each sensing element includes areas of at least two drive electrodes from the plurality of drive electrodes and a portion of the at least one sense electrode. As is described herein, each drive electrode may contain drive electrode areas in at least two sensing elements and the selection of drive electrode areas present in each sensing element may be unique amongst all sensing elements in a sensing column. The physical area of all drive electrode areas in the sensing column may be the same. Further, the pattern of drive electrode areas in each sensing element may be expressed mathematically by an element vector E that represents the physical area of each drive electrode in the respective sensing element. The element vector E has dimension n wherein n denotes the number of drive electrodes in the sensing column. Each element Ei of the element vector E may be an integer or non-integer value. The value may represent an absolute area or a relative area with respect to a known reference area.

The total pattern of drive electrode areas in each sensing column may be represented as a geometry matrix G of dimension m x n wherein m represents the number of sensing elements in a sensing column. A row of the geometry matrix G represents one element vector E. A column of the geometry matrix describes the pattern of electrode areas of a single drive electrode across all sensing elements in one sensing column. The pattern of drive electrodes may be chosen across all sensing elements to form a geometry matrix G that is invertible, although this is not necessary provided that the matrix product (G.D) is invertible. Each sensing column in the sensing array may have the same pattern of drive electrodes. Similar drive electrodes from each sensing column may be connected to each by means external to the sensor substrate.

Within each sensing element each drive electrode area forms a mutual capacitor with the sense electrode. The capacitances of all mutual capacitors in one sensing column may therefore be represented by a capacitance vector K of dimension m wherein each element Km is the total capacitance between all drive electrode areas and the sense electrode in the mth sensing element. Further, the capacitances of all mutual capacitors in the sensing array may be represented as a capacitance matrix C of dimension p x m where p is the number of sensing columns in the sensing array. A row of the capacitance matrix represents one capacitance vector K. (If there is only one sensing column then p = 1 and the capacitance matrix C includes only one capacitance vector K.)

The capacitance of the mutual capacitors in a sensing element may be changed by the presence of an object in close proximity to or touching the surface of the touch panel device in the region of said sensing element. Measurements of the capacitance of the mutual capacitors in each sensing element of the sensing array may therefore be used to determine the location of any objects touching the surface of the device.

In order to measure the capacitance of each mutual capacitor in the sensing array, voltage excitation signals may be applied to the drive electrodes and the currents that are generated in each sense electrode as a result are measured. A sequence of voltage excitation signals may be time sequentially applied to the drive electrodes in successive sampling periods such that the capacitance of each mutual capacitor in the touch panel may be uniquely measured in one frame period of operation. The sequence of voltage excitation signals may be mathematically represented as a drive matrix D wherein a row of the matrix represents the relative magnitude of the voltage excitation signal applied to each drive electrode during one sample period. Each column of the drive matrix D represents the voltage excitation signals applied in sequential sampling periods to a drive electrode during one frame period. The dimension of the drive matrix D may be n x t wherein t is the number of sample periods in one frame period. In order to uniquely measure the capacitance of all mutual capacitors in the sensing array the minimum value of t must be equal to m such that the minimum dimension of drive matrix D is n x m. In a simple example the voltage excitation signals may be chosen to form a drive matrix D that is the identity matrix. This simple example corresponds to the case where m = n and a voltage excitation signal is time sequentially applied to each drive electrode in turn during one frame period.

The signal currents that are measured from the sense electrode in one sensing column during the frame period may be represented by a signal vector R of dimension t wherein each element Rt corresponds to the current measured in the t^th sampling period. Where the invention is applied with a touch sensor having multiple sensing columns, the signal currents that are measured from all sensing columns in the sensing array during one frame period may therefore be expressed as a signal matrix S of dimension p x t. A row of the signal matrix represents one signal vector R. A column of the signal matrix represents the signal currents measured from all sense electrodes in the sensing array during one sample period. In a case where the touch sensor has multiple sensing columns that are identical to one another in that they have the same geometry matrix G, and the touch sensor applies the same sequence of drive voltage to each of these multiple sensing columns, the signal matrix is therefore given by S = C.G.D as illustrated in FIG 3. Accordingly, it is possible to compute the capacitance matrix C from the measured signal matrix S and the known geometry matrix G and drive matrix D. In particular, the capacitance matrix C = S.(G.D)^-1. As a consequence, the matrix product (G.D) must be invertible to allow C to be determined.. Alternatively, as noted above, the touch sensor may determine K = R.(G.D)^-1 for an individual sensing column, where K represents capacitances of all mutual capacitors in one sensing column and R represents the signal currents measured from the sense electrode in one sensing column during a frame period.

Once K or C has been determined, it is possible to determine the location of one or more touches on the touch panel from the matrix representation K or from the matrix representation C.

The requirement for the matrix product G.D to be invertible imposes some restrictions on the properties of the matrices G and D. Matrix G has dimensions m x n; to guarantee invertibility it is necessary that n ≧ m - this means that the number of sensing elements in a sensing column must be equal or less than the number of drive electrodes in the sensing column. Matrix D has dimensions n x t where, as explained above, the value of t is equal to or greater than m ― so that D has n rows and at least m columns. It is possible for matrix D to have more than m columns, which would imply that there were more sample periods than strictly required. This option may be adopted if signals are weak, and there is a wish to increase the SNR of the measurements by taking additional samples. If additional sampling periods are provided, the matrix product G.D would be an (n x t) matrix where t > m, and C could be approximately obtained by multiplying S by a pseudoinverse of (G.D), for example using singular value decomposition.

For clarity, the structure and operation of a touch panel device in accordance with the present embodiment is described for an exemplary arrangement of the array of electrodes and an exemplary sequence of voltage excitation signals. As shown in FIG 4, the sensing array 400 in this exemplary arrangement consists of seven sensing columns 410. Each sensing column contains a plurality (in this example seven) drive electrodes 435 (which correspond to the “first electrodes” of claim 1) and at least one (in this example one) sense electrode 430 (which correspond to the “at least a second electrode” of claim 1. Each sensing column is arranged into multiple (in this example seven) sensing elements E₁ to E₇, 420a to 420g. The sensing elements E₁ to E₇ extend generally in a direction (the “second direction” of claim 1) that is crossed with the direction in which the drive and sense electrodes extend, and that may be at 90° or approximately 90° to the direction in which the drive and sense electrodes extend. (The drive electrodes extend parallel or generally parallel to one another, and the drive electrodes extend parallel or generally parallel to the sense electrode(s).)

At least one and preferably each sensing element includes electrode unit areas 440 from less than all of the drive electrodes of the sensing column, for example includes electrode unit areas 440 from w drive electrodes where 2 ≦ w < n (where n is the number of drive electrodes in the sensing column. In the example of figure 4 each sensing element comprises a selection of drive electrode areas 440 from four out of the seven drive electrodes in each column (that is w = 4, n = 7). Each sensing element also comprises a respective portion of the sense electrode 430. In the example of figure 4 the sensing elements include drive electrode areas from drive electrodes that are not all adjacent to one another (for example sensing element 420a includes drive electrode areas from drive electrodes D₁, D₂, D₄ and D₇), but in alterative embodiments one or more sensing elements may include drive unit areas from w adjacent first electrodes.

The selection of drive electrode areas present in each sensing element may be unique amongst all sensing elements in a sensing column. Thus, for example sensing element 420a includes drive electrode areas from drive electrodes D₁, D₂, D₄ and D₇ and no other sensing element 420b-420g includes drive electrode areas from this combination of drive electrodes. Sensing element 420b includes drive electrode areas from a different combination of drive electrodes, namely D₁, D₂, D₃ and D₅, and no other sensing element includes drive electrode areas from this combination of drive electrodes, and so on.

The physical area occupied by each of the drive electrode areas is the same. Narrow drive interconnection tracks 450 connect electrode areas 440 of the same drive electrode 435 together across different sensing elements 420. Thus, a drive electrode comprises a plurality of drive electrode areas 440 that are disposed along the direction in which the drive electrodes extend, and that are electrically connected with one another by the conductive tracks 450. The electrode areas 440 and conductive tracks 450 are defined in a conductive layer disposed over a substrate. The drive electrodes are connected to respective voltage supply lines by further conductive tracks.

In order to reduce the number of conductive lines that need be provided, the n drive electrodes may be common to the sensing columns (so that the first drive electrode D₁ of one sensing column is electrically connected to the first drive electrodes D₁ of all other sensing columns, and similarly for the other drive electrodes).

Each sensing element may optionally include a ground electrode, N 460. The purpose of the ground electrode 460 is to electrically isolate the drive electrodes of one sensing column from the sense electrode of the neighbouring sensing column, and the sensing column is therefore preferably arranged such that the drive electrodes are all located between the sense electrode and the ground electrode (that is, the drive electrodes and the ground electrode are all located on the same side of the sense electrode as one another). The geometry matrix G associated with the sensing array 400 depicted in FIG 4 is shown in FIG 5. In this exemplary geometry matrix the values in the matrix are expressed as a relative value. Each row of the geometry matrix G shown in figure 5 constitutes an element vector E relating to one sensing element of the sensing array 400 of figure 4, that represents the physical area of each drive electrode in that sensing element.

FIG. 6 shows a schematic diagram of a sensing circuit 600 that may be used to measure the signal currents generated on any one of the sense electrodes in the sensing array during each sampling period. The circuit described herein is provided as an example of a capacitance measurement circuit using a charge transfer technique as is well-known in the field. Alternatively, other known circuits and techniques for capacitance measurement may be used. During one sampling period, in one example a voltage excitation waveform is applied to one drive electrode of the sensing array. A voltage pulse generator 605 supplies the excitation waveform, a series of voltage pulses to the active drive electrode 610, whilst a charge integrator circuit 630 holds the sense electrode 620 at a constant voltage, V_REF. Such charge integrator circuits 630 will be well known to one skilled in the art, and typically comprise an operational amplifier 631, an integration capacitor 632 and a reset switch 633. The sensing circuit 600 may additionally have a switching circuit 640 containing a first input switch 641 and a second input switch 642. The first and second input switches are operated so as to accumulate charge onto the integration capacitors 632 over the course of multiple voltage pulses as a result of current coming from the sense electrode.. The amount of charge accumulated on each integration capacitor is indicative of the capacitance of the mutual capacitor 615 between the active drive electrode and the respective sense electrode. An analog-to-digital converter 650 is provided to convert the integrator circuit output voltage to a digital signal at the end of the sampling period.

The operation of the capacitance measurement circuit shown in FIG. 6 during one sample period is now described with reference to the waveform diagram of FIG. 7. The reset switch 633 is firstly closed under the control of a reset switch control signal RST so that the output voltage V_OUT begins at a known voltage, V_REF, such as the system ground potential. The second input switch 642 is closed under the control of a second input switch control signal S2 at the same time as the reset switch 633 such that the sense electrode 620 is set to a known initial voltage, such as the system ground potential. The second input switch 642 is then opened and the first input switch 641 is subsequently closed under the control of a first input switch control signal S1. The voltage pulse generator 605 now raises the voltage of the drive electrode 610 to a high voltage level causing charge to be injected across mutual capacitor 615 and accumulate on the integration capacitor 632. This causes the output voltage of each integrator circuit V_OUT to rise by an amount that corresponds to the capacitance of mutual capacitor 615 between the active drive electrode and the relevant sense electrode. Next, the first input switch 641 is opened and the second input switch 642 is closed. The voltage pulse generator 605 now returns the voltage of the drive electrode 610 to a low voltage level whilst the output voltage of the integrator circuit, which is isolated from the sense electrode 620, is maintained at a constant level. This operation of applying a voltage pulse to the drive electrode 610 and cycling the first and second input switches may be repeated many times (for example 20 times) in order to generate a measurable voltage at the output of each integration circuit.

Another drive electrode may then be selected as the new active drive electrode, and the voltage pulse generator 605 may supply an excitation waveform to the new drive electrode so that the sensing circuit can determines the capacitance of the mutual capacitor between the new active drive electrode and the respective sense electrode. This may be repeated for each drive electrode so that excitation waveforms are supplied to each drive electrode in sequence to obtain a sequence of currents supplied by the second electrode as a consequence of the application of the excitation voltage waveforms to the first electrodes.

The capacitive touch panel of the present embodiment may form part of a touch screen system. The system may include a touch sensor panel 800, a connector 810, a touch panel controller 820, a display device 830, a display controller 840 and a host 850. The touch sensor panel may include the sensing array 400 described above and be may be mounted on the display device 830. Electrical connections are made between the touch panel 800 and the touch panel controller 820 via the connector 810. The sense electrodes 802 from each sensing column 410 are routed directly to the sense unit (or sense circuit) 822 in the touch panel controller 820 via the connector 810. The drive electrodes 804 are routed from the drive unit (or drive circuit) 824 in the touch panel controller 820 to the sensing array 400 via the connector 810 such that all drive electrodes are connected to each sensing column. Specifically, the drive electrodes 804 are routed so that similar drive electrodes in each sensing column are connected together.

The sensing unit 822 may contain sensor circuits 600 to measure the currents generated on each sense electrode during operation. The drive unit 824 may contain voltage pulse generators 605 to provide voltage excitation signals to each drive electrode as described above. The measured capacitance values are conveyed by the interface unit 826 of the touch panel controller 820 to the host 850 which determines the position and type of input objects touching the surface of the sensor and outputs the result. Alternatively, the calculation of input object position and type may be accomplished within the controller circuit 820, and the calculation result passed to the host electronics 850. The host electronics may generate a video image in response to detected objects, and may pass this video image to the display controller 840 for display on the display device 830.

In general the performance of a touch sensor is related to its signal-to-noise ratio (SNR) which is limited by the frequency at which the excitation signal may be applied. Specifically, as the SNR is decreased, the accuracy at which the location of objects touching the surface of the sensor may be determined is reduced and the minimum size of object that can be detected is increased. The frequency at which the excitation signal may be applied is, in turn, limited by the resistance of the touch panel electrodes. Due to the distribution of wide drive electrode areas along the length of the sensing column, the total resistance of the drive electrode may be reduced compared to conventional means. An advantage of the sensing array of the present embodiment is therefore that the SNR may be increased and the performance improved.

In accordance with a second embodiment of the invention the pattern of drive electrode areas in each sensing column may be arranged so as to form a geometry matrix G that is orthogonal. Examples of orthogonal matrices that may be used are a Hadamard matrix or a Maximum length sequence (M-Sequence) matrix. An advantage of an orthogonal matrix is that the inverse may be simply computed by the matrix transpose. As a result it is computationally cheap to compute the capacitance matrix from the measured signal matrix.

A sensing column of a sensing array in accordance with a third embodiment of the invention is illustrated in FIG 9. Each sensing element 920a-g of the sensing column 910 comprises a respective portion of the sense electrode 930 a first drive electrode area 940 and a second drive electrode area 945. The first drive electrode area 940 may be arranged to be adjacent to the sense electrode 930 and the second drive electrode area 945 may be arranged to be adjacent to the first drive electrode area 940 and separated from the sense electrode 930 by it. The first and second drive electrode areas in one sensing element may be from two adjacent drive electrodes 935 - in the example shown sensing element 920a includes drive electrode areas from drive electrodes D₁ and D₂ which are two adjacent drive electrodes, sensing element 920f includes drive electrode areas from drive electrodes D₆ and D₇, etc. (For the purposes of this example, drive electrode D₇ is considered as adjacent to drive electrode D₁.) The drive electrode areas 940, 945 of each successive sensing element 920 may be from each successive drive electrode. The geometry matrix G corresponding to the sensing array of FIG 9 is shown in FIG 10.

In accordance with a fourth embodiment of the invention the physical area of each of the drive electrode areas in a sensing element may be arranged to have the same baseline mutual capacitance. The baseline mutual capacitance is the capacitance of the mutual capacitor between a drive electrode area and a sense electrode in a sensing element when there is no object present in the vicinity of the sensing element. As shown in the exemplary arrangement of FIG 11 which is based on the arrangement shown in FIG 10, each sensing element 1120a-f of the sensing column 1110 comprises a respective portion of sense electrode 1130 a first drive electrode area 1140 and a second drive electrode area 1145. Since the first drive electrode area 1140 is closer to the sense electrode 1130 than the second drive electrode area 1145, the baseline mutual capacitance per unit area of the first drive electrode area 1140 will be higher than that of the second drive electrode area 1145. The physical area of the first drive electrode 1140 may therefore be chosen to be smaller than the second drive electrode area 1145 such that the baseline mutual capacitance of each is equal.

In accordance with a fifth embodiment of the invention the physical area of the drive electrode areas of each sensing element may be different for each sensing element in a sensing column. In particular, the drive electrode areas may be arranged so as to occupy as much area as possible in the sensing element and hence maximise the signal-to-noise ratio. Due to the presence of the drive electrode interconnecting tracks the available area for the drive electrode areas is different in each sensing element in the sensing column. This is illustrated in the exemplary arrangement of FIG 12 which is based on the arrangement of FIG 11, but in which the overall area of the drive electrode unit areas in a sensing element 1120a-g increases along the sensing column. For example, the physical area occupied by the drive electrode areas 1140, 1200a in sensing element 1120a is limited by the presence of the drive electrode interconnecting tracks from drive electrodes D₂ to D₇. On the other hand, the lack of other drive electrode interconnecting tracks in sensing element 1120g allows the area occupied by the corresponding drive electrode areas 1140, 1200g to be enlarged. FIG 12 shows an arrangement in which the physical area occupied by the first drive electrode areas 1140 is the same in each sensing element while the physical area occupied by the second drive electrode areas 1200a-g is different in each sensing element 1120a-g, but this embodiment is not limited to this and a change in overall area of the drive electrodes from one sensing element to another may be effected by a change in the physical area of all, or any selection of, the drive electrodes. For example the physical area occupied by the first drive electrode areas might vary from one sensing element to another sensing element while the physical area occupied by the second drive electrode areas was the same in each sensing element, and as a further example it would be possible for the physical area occupied by each drive electrode are to vary from one sensing element to another sensing element.

The different sizes of second drive electrode areas may be encoded in the geometry matrix. An example of a geometry matrix, G, corresponding to the arrangement illustrated in FIG 12 is shown in FIG 13. Entries in the matrix may be non-integer values that correspond to the baseline capacitances between the drive electrode areas and the sense electrode. Entries in the matrix that correspond to the second drive electrode areas 1200a-g have different values for each sensing element due to the different physical areas occupied. Values of the entries may be absolute values corresponding to the physical size of the drive electrode area or, as shown in FIG 13, may be values relative to the size of the smallest drive electrode area in the sensing column. Accordingly, it is possible to maximise the signal-to-noise ratio whilst maintaining a consistent response across the sensing column in response to the presence of an object.

In accordance with a sixth embodiment of the invention the mutual capacitance between the drive electrode interconnecting tracks and the sense electrode may be encoded into the geometry matrix. An example of a geometry matrix, G, corresponding to the arrangement illustrated in FIG 12 and including entries in the matrix corresponding to the drive electrode interconnecting tracks is shown in FIG 14. Where a drive electrode interconnecting track of drive electrode Dj is present in a sensing element Ei a non-zero entry is made in the matrix at matrix element Gi,j. Entries in the matrix may be values relative to the smallest drive electrode area in the sensing column. In a conventional touch panel device the mutual capacitance associated with the drive electrode tracks is unwanted and acts to lower the signal-to-noise ratio. However, by encoding the mutual capacitances of the drive electrode tracks into the geometry matrix, such capacitances form part of the desired signal and the signal-to-noise ratio may be increased.

Further, since the mutual capacitances associated with the drive electrode interconnecting tracks now form part of the desired measurement signal it is possible to increase their width without introducing unwanted signal artefacts. This may bring an additional advantage as is now described. As stated above, the frequency of the excitation signal applied to the touch panel drives electrodes, and hence the signal-to-noise ratio of the capacitance measurement, may be limited by the resistance of the touch panel electrodes. Also, the drive electrode interconnecting tracks may form the major component of the drive electrode resistance. Accordingly, by increasing the width of the drive electrode interconnecting tracks the signal-to-noise ratio of the capacitance measurement may be further increased.

In accordance with a seventh embodiment of the invention, each sensing element includes two sense electrodes that extend generally parallel to one another. Fig 15 illustrates an exemplary arrangement of a sensing column 1510 in accordance with the present embodiment. The sensing column comprises a plurality of sensing elements 1520. Each sensing element comprises portions of a first sense electrode, SA 1530, portions of a second sense electrode, SB 1532 and first and second drive electrode areas 1540, 1545 chosen from amongst a plurality of drive electrodes 1535. The first sense electrode, SA 1530, is arranged to be adjacent to the first drive electrode areas 1540 and the second sense electrode, SB 1532, may be arranged to be adjacent to the first sense electrode, SA 1530 and separated from the first drive electrode areas 1530 by it. Within each sensing element, a first set of capacitors is formed between the first sense electrode, 1530, and the drive electrode areas and a second set of capacitors is formed between the second sense electrode, 1532, and the drive electrode areas. The capacitances of said capacitors may be independently measured using the aforementioned methods. For example, separate sensing circuits 600 may be connected to each of the first sense electrode, 1530, and the second sense electrode 1532, such that both sets of capacitances may be measured simultaneously. From these capacitance measurements, it is possible to compute a first and second capacitance matrix C for the first and second set of capacitances respectively in one sensing column. Since the first and second capacitors have different separations between the drive and sense electrodes it is possible to use the respective capacitance measurements to measure additional properties of the input object. For example, by comparing the first and second capacitance matrices it is possible to measure the height of objects above the surface of the touch panel, as disclosed in US 20140009428 (to Coulson et al, July 3, 2014) which is hereby incorporated in full by reference. Alternatively or additionally, it is possible to use the first and second capacitance matrices to detect input events from non-conductive objects, as disclosed in US Patent Application No. 14/135,639 (to Brown et al, December 20, 2013) which is hereby incorporated in full by reference.

The invention has been described above with respect to embodiments in which a sensing column includes a plurality of drive electrodes and one or more sense electrodes. The invention may however be implemented using a plurality of sense electrodes and a single drive electrode (or two or more drive electrodes). In essence this would require no change in the electrode structure, but what has been described as a “drive electrode” in the above embodiments would be used as a sense electrode and what has been described as a “sense electrode” in the above embodiments would be used as a drive electrode. Thus, in the embodiment of figures 4 and 6, for example, the voltage pulse generator 605 would be arranged to apply a voltage pulse to the electrode line S_j in each sampling period of a time frame (so that the electrode line S_j acted as the drive electrode). The sensing circuit 600 would be arranged to, in each sampling period, sample the current generated by the electrodes D₁ to D₇ (so that the electrodes D₁ to D₇ acted as sense electrodes), such that the capacitance of each mutual capacitor in the sensing column may be measured over one frame period. In a simple example, the sensing circuit 600 could be arranged to time-sequentially sample the current generated by each of the electrodes D₁ to D₇ in turn during a frame period. Alternatively, each electrode D₁ to D₇ could be provided with a separate sensing circuit, so that the currents generated by each of the electrodes D₁ to D₇ could be sensed simultaneously.

In more detail, the touch panel has p sensing columns. In a panel where the p sensing columns all have the same electrode arrangement as one another, each sensing column has:
1 drive electrode;
n sense electrodes;
m sensing elements.

In order to reduce the number of conductive lines that need be provided, the n sense electrodes may be common to the p sensing columns (so that the first sense electrode of one sensing column is electrically connected to the first sense electrodes of all other sensing columns, and similarly for the other sense electrodes. Hence, to determine the capacitances from currents sensed from the p different sensing columns, we need a sequence of readings over different sampling time periods. In matrix notation:
D(p,t) = C(p,m) * G(m,n) * S(n,t)
which has a similar structure to the equation for n drive lines and a single sense line. D is a matrix of dimensions p x t, and the columns of the drive matrix D represent the signals ( for example drive / no drive) applied to each of the p drive electrodes of the touch panel in one sampling period - as the n sense electrodes are shared by all the sensing columns, only one drive electrode is preferably be driven in each of the t time steps, i.e. preferably only one element of each column is non-zero. The rows of the drive matrix D represent the signals (eg drive / no drive) applied to one drive electrode in different sampling periods of a time frame.

S is a matrix of dimensions n x t. The columns of the sense matrix S represent the currents supplied by each of the n sense electrodes in one sampling period and the rows of the sense matrix S represent the currents supplied by one of the n sense electrodes in different sampling periods of a time frame.

To obtain the capacitance information:
C(p,m) = D(p,t) * [G(m,n) * S(n,t)]^-1
Thus, in this case the requirement is that [G.S] is invertible rather than [G.D]. As before, this requires that n ≧ m.

In the embodiments described above the drive and sense electrodes of a sensor column, and the ground electrode where present, may be defined in a conductive layer disposed on a substrate (not shown in the figures). Preferably all electrodes of all sensing columns of the touch sensor are defined in the same conductive layer - using only a single conductive layer reduces the cost of manufacture of the touch sensor.

In a touch sensor according to the present invention, each first electrode of the sensing column may have first electrode unit areas included in at least two sensing elements in the sensing column.

A sensing element may include first electrode unit areas from less than all of the first electrodes of the sensing column.

Each sensing element in the sensing column may include first electrode unit areas from w first electrodes, where 2 ≦ w < n.

A sensing element in the sensing column may include drive unit areas from w adjacent first electrodes. Preferably this is the case for all sensing elements in the sensing column, however if the term “adjacent” is interpreted as meaning physically adjacent it will be understood that there will be one sensing element that cannot incorporate this feature (although the first and last of the first electrodes may be understood as “adjacent” to one another in that, in a drive scheme in which voltages are applied to the first electrodes in a repeating sequence, application of a voltage to the last electrode may be followed by application of a voltage to the first electrode).

The value of w may be 2 and n may be greater than 2.

The i^th sensing element in the sensing column may include first electrode unit areas from an i^th selection of the first electrodes of the sensing column, the i^th selection being unique in the sensing column.

In the sensing column, the first electrodes may be located to one side of the second electrode, so that all first electrodes are one the same side of the second electrode as one another.

The sensing column may further comprise a ground electrode. If so, the first electrodes may be provided between the second electrode and the ground electrode.

The ground electrode may extend generally along the first direction.

All first electrode unit areas in a sensing element may have the same nominal area as one another, where the term “nominal area” is to be understood as not precluding variations in area that arise from normal manufacturing tolerances.

Alternatively, in a sensing element, a first first electrode unit area nearer the second electrode may have a smaller area than a second first electrode unit area further from the second electrode. The area of the first first electrode unit area and the area of the second first electrode unit area may be selected such that the baseline mutual capacitance between the first first electrode unit area and the second electrode is approximately equal to the baseline mutual capacitance between the second first electrode unit area and the second electrode.

The overall area of the first electrode unit areas in a sensing element in the sensing column may increase with distance of the sensor element from the voltage supply line. As the distance of a sensor element from the voltage supply line increases the number of conductive tracks passing through the sensor element generally decreases so that more of the area of the of the sensor element is available for the first electrode unit areas to occupy. Arranging for the first electrode unit areas to occupy as much area of the sensing element as possible maximises the signal-to-noise ratio. In one example, a sensing element in the sensing column may include at least an ith first electrode unit area and a jth first electrode unit area, the ith first electrode unit area having the same area in all sensing elements of the sensing column and the area of the jth first electrode unit area increasing with distance of the sensor element from the voltage supply line.

The first sensing column of the touch sensor may comprise another second electrode extending generally parallel to the first direction, and each sensing element of the sensing column may further include a portion of the another second electrode.

The matrix representation G of the sensing elements of the sensing column against the first electrodes of the sensing column may an invertible matrix.

The matrix representation G may be an orthogonal matrix.

The matrix representation G of the sensing elements of the sensing column against the first electrodes of the sensing column may further represent the relative areas of the interconnecting tracks present in a respective sensing element. Mutual capacitances formed by the interconnecting tracks thus form part of the desired signal, and their width may be increased, thereby reducing their electrical resistance, without introducing unwanted signal artefacts. This in turn increases the possible frequency range of the drive signals.

The matrix representation D of the sequence of drive voltages may be an invertible matrix.

The touch sensor may further comprise a second drive circuit for applying a drive voltage to the second electrode of the sensing column and a sensing circuit for measuring a current generated by one or more selected first electrodes of the sensing column. In this embodiment the sensing circuit may be adapted to measure a current generated by successive groups of first electrodes in successive sampling periods of one frame period.

The touch sensor may comprise a plurality of identical sensing columns; the drive circuit may be adapted to apply the same sequence of drive voltages to the sensing columns; and the touch sensor may be adapted to compute C = S.(G.D)^-1, where S is a matrix representation of the measured currents from the sensor columns, where a row of the matrix representation S represents the currents measured from the second electrode of a sensor column in respective sampling periods, and a column of the matrix representation S represents the currents measured from the second electrodes of respective sensing columns during one sampling period; and C is a matrix representation of mutual capacitances, in which a row represents the relative mutual capacitances in a sensing element between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element.

The capacitive touch sensor of the present invention provides a means of reducing the cost of manufacture of touch panel devices whilst improving (or at least not worsening) the sensor performance compared to the background art.

The touch sensor includes a sensor substrate and an array of electrodes formed in a single layer of conductive material on the sensor substrate. The array of electrodes is arranged in columns of sensing elements with each sensing element including at least one of a first electrode group comprising at least two drive electrodes and at least one sense electrode, or a second electrode group comprising at least two sense electrodes and at least one drive electrode. Where two or more sense electrodes are provided, the outputs from different sense electrodes, or from different groups of sense electrodes, may be sensed at different time period. Alternatively, the outputs from different sense electrodes may be sensed simultaneously.

The pattern of drive electrode areas in each sensing column may be mathematically represented as a geometry matrix G. The capacitances of all mutual capacitors in the sensing array may be mathematically represented as a capacitance matrix C. The sequence of voltage excitation signals applied to the drive electrodes in order to measure the capacitances of the mutual capacitors may be mathematically represented as a drive matrix D. The signal currents that are measured on the sense electrodes as a result of application of the voltage excitation signals in one frame period of operation may be mathematically represented as a signal matrix S.

In order to compute the capacitance matrix C a decoding matrix U is computed as the inverse of the matrix multiple of the drive matrix and geometry matrix, U=(D.G)^-1. The capacitance matrix is then computed in each frame period as the matrix multiple of the signal matrix and the decoding matrix, C = S.U. The capacitance matrix is processed to determine the presence and location of one or more objects touching the surface of the touch panel device.

Advantageously, the present invention enables the signal-to-noise ratio of the capacitance measurements to be increased. As a consequence, the accuracy at which the location of an object touching the surface of the touch panel device may be calculated is increased and the minimum size of object that may be detected is decreased.

In a method of the second aspect, the matrix representation G of the sensing elements may further represent relative areas of interconnecting tracks present in a respective sensing element.

A method of the second aspect may be applied with a sensing circuit that is constituted by a capacitive touch sensor of the first aspect.

A further aspect of the invention provides a capacitive touch sensor having p sensing column, a sensing column comprising a plurality of sensing elements;
the touch sensor comprising: a substrate; and a conductive layer disposed over the substrate;
wherein a sensing column comprises n first electrodes, wherein n ≧ 2, and at least a second electrode, the first electrodes and the second electrode defined in the conductive layer and extending generally parallel to a first direction; wherein the first electrodes comprise a plurality of first electrode unit areas disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer;
wherein the sensing elements extend generally in a second direction crossed with the first direction, each sensing element of the sensing column including a respective first electrode unit area of at least two of the first electrodes of the sensing column and a portion of the second electrode of the sensing column;
wherein the touch sensor comprises a drive circuit for applying drive voltages sequentially to the second electrodes of the sensor in successive sampling periods and a sensing circuit for measuring currents supplied by the first electrodes of the sensor;
and wherein the touch sensor is adapted to, for at least one sensing element, determine capacitances between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element according to C = D.(G.S)^-1, where
D is a matrix representation of the sequence of drive voltages;
G is a matrix representation of the sensing elements, in which a row of the matrix representation G represents relative areas of the portions of the first electrodes present in a respective sensing element and a column of the matrix representation G represents the relative areas of the portions of a respective first electrode included in the sensing elements;
S is a matrix representation of the currents measured from the second electrodes of the sensor in respective sampling periods;
and C is a matrix representation of mutual capacitances. This aspect corresponds to the first aspect except that, as described above, it uses a plurality of sense electrodes and a single drive electrode rather than a plurality of drive electrodes and a single sense electrode.

A further aspect of the invention provides a method of determining capacitances in a sensor having p sensing columns, a sensing column comprising a plurality of sensing elements, each sensing element of sensing column including respective portions of two or more first electrodes and a portion of a second electrode, the method comprising:
applying a sequence of drive voltages to the second electrodes of the sensor;
measuring a sequence of currents supplied by the first electrodes of the sensor as a consequence of the application of the drive voltages to the second electrodes; and
for one or more sensing elements, determining capacitances between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element according to C = D.(G.S)^-1, where
D is a matrix representation of the sequence of drive voltages;
G is a matrix representation of the sensing elements, in which a row of the matrix representation G represents relative areas of the portions of the first electrodes present in a respective sensing element and a column of the matrix representation G represents the relative areas of the portions of a respective first electrode included in the sensing elements;
S is a matrix representation of the currents measured from the second electrodes of the sensor in respective sampling periods;
and C is a matrix representation of mutual capacitances.

A further aspect of the invention provides a capacitive touch sensor having at least a first sensing column comprising a plurality of sensing elements; the touch sensor comprising: a substrate; and a conductive layer disposed over the substrate; wherein the first sensing column comprises n first electrodes, wherein n ≧ 2, and at least a second electrode, the first electrodes and the second electrode defined in the conductive layer and extending generally parallel to a first direction; wherein the first electrodes comprise a plurality of first electrode unit areas disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer; wherein the sensing elements extend generally in a second direction crossed with the first direction, each sensing element of the sensing column including a respective first electrode unit area of at least two of the first electrodes of the sensing column and a portion of the second electrode of the sensing column;
whereby, in use, application of a drive voltage sequentially to successive groups of first electrodes of the first sensing column in successive sampling periods generates currents in the second electrode of the first sensing column; and whereby K = R.(G.D)^-1, where:
G is a matrix representation of first electrode portions in each sense element of the first sensing column; D is a matrix representation of the sequence of drive voltages, in which each column represents the relative magnitude of voltages applied to the first electrodes of the first sensing column during a respective sampling period and each row represents the relative magnitude of voltages applied to a respective first electrode of the first sensing column in sequential sampling periods of one frame period; R is a matrix representation of the currents supplied by the second electrode of the first sensing column, and K is a matrix representation of mutual capacitances in the first sensing column. When applied to a touch sensor having p identical sensing columns, this aspect may alternatively determine an overall capacitance matrix C as described above.

A further aspect of the invention provides a capacitive touch sensor having at least a sensing column comprising a plurality of sensing elements; the touch sensor comprising: a substrate; and a conductive layer disposed over the substrate; wherein the sensing column comprises n first electrodes, wherein n ≧ 2, and at least a second electrode, the first electrodes and the second electrode defined in the conductive layer and extending generally parallel to a first direction; wherein the first electrodes each comprise a plurality of first electrode unit areas disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer; wherein the sensing elements extend generally in a second direction crossed with the first direction, each sensing element of the sensing column including a respective first electrode unit area of at least two of the first electrodes of the sensing column and a portion of the second electrode of the sensing column.

A further aspect of the invention comprises a method of representing the sensing elements of a sensing circuit having at least a sensing column comprising a plurality of sensing elements, each sensing element including respective portions of two or more first electrodes and a portion of a second electrode, the method comprising providing a matrix representation G of the sensing elements in which a row of the matrix representation G represents relative areas of portions of the first electrodes present in a respective sensing element and a column of the matrix representation G represents relative areas of the portions of a respective first electrode included in the sensing elements, and further comprising including in the matrix representation G relative areas of interconnecting tracks present in a respective sensing element.

10 Transparent substrate
11 Sensing electrode
12 Voltage source
13 Conductive object
14 Capacitor
15 Current sensor
20 Drive electrode
21 Sense electrode
22 Voltage source
23 Mutual coupling capacitor
24 Current measurement means
27 Drive electrode capacitor
28 Sense electrode capacitor
400 sensing array
410 sensing column
420 sensing element
430 sense electrode
435 drive electrode
440 drive electrode area
450 drive electrode interconnecting track
460 ground electrode
600 sensing circuit
605 voltage pulse generator
610 active drive electrode
615 mutual capacitor
620 sense electrode
630 integrator circuit
631 operational amplifier
632 integration capacitor
633 reset switch
640 switching circuit
641 first input switch
642 second input switch
650 analog-to-digital converter
800 touch sensor panel
802 sense electrodes
804 drive electrodes
810 connector
820 controller
822 sense unit
824 drive unit
826 interface unit
830 display device
840 display controller
850 host
910 sensing column
920 sensing element
930 sense electrode
935 drive electrode
940 first drive electrode area
945 second drive electrode area
1110 sensing column
1120 sensing element
1130 sense electrode
1135 drive electrodes
1140 first drive electrode area
1145 second drive electrode area
1200 second drive electrode area
1510 sensing column
1520 sensing element
1530 first sense electrode
1532 second sense electrode
1535 drive electrodes
1540 first drive electrode area
1545 second drive electrode area

Claims (24)

1. A capacitive touch sensor having at least a first sensing column comprising a plurality of sensing elements;
   the touch sensor comprising: a substrate; and a conductive layer disposed over the substrate;
   wherein the first sensing column comprises n first electrodes, wherein n ≧ 2, and at least a second electrode, the first electrodes and the second electrode defined in the conductive layer and extending generally parallel to a first direction; wherein the first electrodes comprise a plurality of first electrode unit areas disposed along the first direction and electrically connected with one another and to a voltage supply line by conductive tracks defined in the conductive layer;
   wherein the sensing elements extend generally in a second direction crossed with the first direction, each sensing element of the first sensing column including a respective first electrode unit area of at least two of the first electrodes of the first sensing column and a portion of the second electrode of the first sensing column;
   wherein the touch sensor comprises a drive circuit for applying drive voltages sequentially to successive groups of one or more first electrodes of the first sensor column in successive sampling periods and a sensing circuit for measuring a current supplied by the second electrode of the first sensor column;
   and wherein the touch sensor is adapted to compute K = R.(G.D)^-1, where:
   K is a matrix representation of capacitances in the first sensing column,
   R is a matrix representation of the currents measured from the second electrode of the first sensor column in respective sampling periods of one frame period;
   G is a matrix representation of the sensing elements of the first sensing column against the first electrodes of the first sensing column, in which a row of the matrix representation G represents the relative areas of first electrode unit areas present in a respective sensing element and a column of the matrix representation G represents the relative areas of first electrode unit areas of a respective first electrode included in the sensing elements of the first sensing column; and
   D is a matrix representation of the sequence of drive voltages applied by the drive circuit, in which each column represents the relative magnitude of voltages applied to the first electrodes during a respective sampling period and each row represents the relative magnitude of voltages applied to a respective first electrode in successive sampling periods of one frame period.
2. A touch sensor as claimed in claim 1 wherein the first electrodes of the first sensing column have first electrode unit areas included in at least two sensing elements in the sensing column.
3. A touch sensor as claimed in claim 1 or 2 wherein a sensing element in the first sensing column includes first electrode unit areas from less than all of the first electrodes of the sensing column.
4. A touch sensor as claimed in claim 1, 2 or 3 wherein each sensing element in the first sensing column includes first electrode unit areas from w first electrodes, where 2 ≦ w < n.
5. A touch sensor as claimed in claim 4 wherein a sensing element in the first sensing column includes drive unit areas from w adjacent first electrodes.
6. A touch sensor as claimed in claim 4 or 5 wherein w = 2 and n > 2.
7. A touch sensor as claimed in any preceding claim wherein the i^th sensing element in the first sensing column includes first electrode unit areas from an i^th selection of the first electrodes of the sensing column, the i^th selection being unique in the sensing column.
8. A touch sensor as claimed in any preceding claim wherein, in the first sensing column, the first electrodes are located to one side of the second electrode.
9. A touch sensor as claimed in any preceding claim wherein the first sensing column further comprises a ground electrode.
10. A touch sensor as claimed in claim 9 wherein the first electrodes are provided between the second electrode and the ground electrode.
11. A touch sensor as claimed in any preceding claim wherein all first electrode unit areas in a sensing element have the same area as one another.
12. A touch sensor as claimed in any one of claims 1 to 10 wherein, in a sensing element, a first first electrode unit area nearer the second electrode has a smaller area than a second first electrode unit area further from the second electrode.
13. A touch sensor as claimed in claim 12 wherein the area of the first first electrode unit area and the area of the second first electrode unit area are selected such that the baseline mutual capacitance between the first first electrode unit area and the second electrode is approximately equal to the baseline mutual capacitance between the second first electrode unit area and the second electrode.
14. A touch sensor as claimed in any preceding claim wherein the overall area of the first electrode unit areas in a sensing element in the sensing column increases with distance of the sensor element from the voltage supply line.
15. A touch sensor as claimed in any preceding claim wherein the first sensing column further comprises another second electrode extending generally parallel to the first direction, each sensing element of the or each sensing column further including a portion of the another second electrode.
16. A touch sensor as claimed in any preceding claim wherein the matrix representation G of the sensing elements of the first sensing column against the first electrodes of the sensing column is an invertible matrix.
17. A touch sensor as claimed in claim 16 wherein the matrix representation G is an orthogonal matrix.
18. A touch sensor as claimed in any one of claims 1 to 17 wherein the matrix representation G of the sensing elements of the first sensing column against the first electrodes of the sensing column further represents the relative areas of the interconnecting tracks present in a respective sensing element.
19. A touch sensor as claimed in any preceding claim in which the matrix representation D of the sequence of drive voltages is an invertible matrix.
20. A touch sensor as claimed in any preceding claim and further comprising a second drive circuit for applying a drive voltage to the second electrode of the first sensing column and a second sensing circuit for measuring a current generated by one or more selected first electrodes of the first sensing column.
21. A touch sensor as claimed in claim 20 wherein the second sensing circuit is adapted to measuring a current generated by successive groups of first electrodes in successive sampling periods of one frame period.
22. A touch sensor as claimed in any preceding claim and having a plurality of identical sensing columns;
    wherein the drive circuit is adapted to apply the same sequence of drive voltages to the sensing columns;
    and wherein the touch sensor is adapted to compute C = S.(G.D)^-1, where
    S is a matrix representation of the measured currents from the sensor columns, where a row of the matrix representation S represents the currents measured from the second electrode of a sensor column in respective sampling periods, and a column of the matrix representation S represents the currents measured from the second electrodes of respective sensing columns during one sampling period;
    and C is a matrix representation of mutual capacitances, in which a row represents the relative mutual capacitances in a sensing element between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element.
23. A method of determining capacitances in a sensor having at least a first sensing column comprising a plurality of sensing elements, each sensing element of sensing column including respective portions of two or more first electrodes and a portion of a second electrode, the method comprising:
    applying a sequence of drive voltages to the first electrodes of the first sensing column;
    measuring a sequence of currents supplied by the second electrode of the first sensing column as a consequence of the application of the drive voltages to the first electrodes of the first sensing column; and
    for a sensing element, determining capacitances between the portions of the first electrodes in the sensing element and the portion of the second electrode in the sensing element according to K = R.(G.D)^-1, where
    D is a matrix representation of the sequence of drive voltages applied by the drive circuit, in which each column represents the relative magnitude of voltages applied to the first electrodes of the first sensing column during a respective sampling period and each row represents the relative magnitude of voltages applied to a respective first electrode of the first sensing column in successive sampling periods of one frame period ;
    G is a matrix representation of the sensing elements of the first sensing column against the first electrodes of the first sensing column, in which a row of the matrix representation G represents relative areas of the portions of the first electrodes present in a respective sensing element and a column of the matrix representation G represents the relative areas of the portions of a respective first electrode included in the sensing elements;
    R is a matrix representation of the currents measured from the second electrode of the first sensing column in respective sampling periods;
    and K is a matrix representation of mutual capacitances t.
24. A method as claimed in claim 23 wherein the matrix representation G of the sensing elements further represents relative areas of interconnecting tracks present in a respective sensing element.

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