Patent Description:
Resistive and capacitive touch panels are used as input devices for computers and mobile devices. One type of capacitive touch panel, projected capacitance touch panels, is often used for mobile devices because an exterior layer may be made of glass, providing a hard surface which is resistant to scratching. An example of a projected capacitance touch panel is described in <CIT>.

Touch panels which use piezoelectric based force-detection have been proposed. For example <CIT> describes a touch panel which includes a piezoelectric body layer containing a polyvinylidene fluoride-ethylene tetrafluoride copolymer, a first electrode provided on one surface of the piezoelectric body layer, and a second electrode provided on the other surface of the piezoelectric body layer.

Examples of touch sensors combining capacitive sensing with piezoelectric based force-detection capabilities are described in <CIT>. Further examples of touch sensors combining capacitive sensing with piezoelectric based force-detection capabilities are described in <CIT>, <CIT> and <CIT>.

<CIT> discloses a touch panel using capacitive touch and force detection to discriminate between intended touches, including when the user is wearing gloves, and unintended touches or contamination of the touch panel caused by water.

<CIT> discloses a touch panel using acoustic touch and force detection that can detect touches even when the panel is wet or submerged.

According to a first aspect of the invention, there is provided apparatus which includes a touch panel. The touch panel includes a layer of piezoelectric material disposed between a number of sensing electrodes and at least one counter electrode. The apparatus also includes a touch controller connected to the touch panel. The touch controller is configured to determine, in response to receiving piezoelectric signals from one or more of the sensing electrodes, a location and an applied force corresponding to a user interaction with the touch panel. The touch controller is configured, in response to receiving piezoelectric signals and determining no changes in the capacitance values for any of the sensing electrodes, to operate in a force-based mode wherein the touch controller is configured to determine a location and an applied force corresponding to a user interaction based on the piezoelectric signals. The touch controller is configured, in response to determining changes in the capacitance values of one or more sensing electrodes and receiving no piezoelectric signals, to operate in a capacitance-based mode wherein the touch controller is configured to determine a location corresponding to a user interaction based on the determined changes in capacitance values. The touch controller is configured, in response to determining changes in the capacitance values of one or more sensing electrodes and receiving piezoelectric signals, to operate in a mixed force-capacitance mode wherein the touch controller is configured to determine a location corresponding to a user interaction based on the determined changes in capacitance values and to determine an applied force corresponding to the user interaction based on the piezoelectric signals.

Each sensing electrode may include one or more sensing pads. Each sensing pad may be opposed across the layer of piezoelectric material by a corresponding counter electrode pad of a counter electrode.

The touch controller may also be configured to determine a capacitance value of one or more of the sensing electrodes.

The touch controller may be configured to determine one or more capacitance values and to receive one or more piezoelectric signals concurrently.

The touch controller may be configured to determine one or more capacitance values and to receive one or more piezoelectric signals sequentially.

In the mixed force-capacitance mode, the touch controller may be configured to determine a location corresponding to a user interaction based on the determined changes in the capacitance values and the piezoelectric signals.

The touch controller may also be configured to determine whether the touch panel is wet or submerged based on the determined capacitance values of the sensing electrodes. The touch controller may also be configured, in response to determining that the touch panel is wet, to operate in the force-based mode.

The touch controller may also be configured to operate in the force-based mode in response to determining that a signal-to-noise ratio of the capacitance values is less than a pre-calibrated threshold.

The apparatus may also include a switch configured such that when the touch controller operates in the force-based mode, the switch connects each sensing electrode to a corresponding piezoelectric signal sensing circuit. The switch may be configured such that when the touch controller operates in the mixed force-capacitance mode, the switch connects two or more sensing electrodes to one piezoelectric signal sensing circuit.

The sensing electrodes may include a number of first electrodes and a number of second electrodes. Each first electrode may extend in a first direction, and the first electrodes may be spaced apart in a second direction which is perpendicular to the first direction. Each second electrode may extend in the second direction, and the plurality of second electrodes may be spaced apart in the first direction.

The first and second electrodes may be arranged on the same plane within the touch panel.

The first and second electrodes may be arranged on different, parallel planes within the touch panel.

The touch panel may have a circular or elliptical perimeter. The touch panel may have a square or rectangular perimeter.

The touch panel may be a button input panel. A button input panel may include one or more sensing electrodes in the form of discrete button electrodes. Button electrodes of the button input panel may have different sizes and/or shapes. The counter electrode of the button input panel may be uniform. The counter electrode of the button input panel may be patterned to match the shapes and positions of the button electrodes. Patterned counter electrodes may all be electrically connected to one another. Patterned counter electrodes may be connected to individual conductive traces to enable patterned counter electrodes to be addressed individually. The button input panel may include a light emitting diode layer including one or more light emitting diodes. Each light emitting diode may be disposed and configured to illuminate a corresponding button electrode.

A wearable device may include the apparatus. A wearable device may take the form of a watch, a smart watch, a bracelet, a belt, a buckle, glasses, lenses of glasses, frames of glasses, jewellery, and so forth.

According to a second aspect of the invention there is provided a method for processing signals from a touch panel. The touch panel includes a layer of piezoelectric material disposed between a plurality of sensing electrodes and at least one counter electrode. The method includes, in response to receiving piezoelectric signals from one or more of the sensing electrodes, determining a location corresponding to a user interaction with the touch panel based on the piezoelectric signals. The method also includes determining a capacitance value of one or more of the sensing electrodes. The method also includes, in response to receiving piezoelectric signals and determining no changes in the capacitance values for any of the sensing electrodes, determining, in a force-based mode, a location and an applied force corresponding to a user interaction based on the piezoelectric signals. The method also includes, in response to determining changes in the capacitance values of one or more sensing electrodes and receiving no piezoelectric signals, determining, in a capacitance-based mode, a location corresponding to a user interaction based on the determined changes in capacitance values. The method also includes, in response to determining changes in the capacitance values of one or more sensing electrodes and receiving piezoelectric signals, determining, in a mixed force-capacitance mode, a location corresponding to a user interaction based on the determined changes in capacitance values and determining an applied force corresponding to the user interaction based on the piezoelectric signals.

Determining capacitance values of one or more of the sensing electrodes may be performed concurrently with receiving piezoelectric signals from one or more of the sensing electrodes.

Determining capacitance values of one or more of the sensing electrodes may be performed sequentially with receiving piezoelectric signals from one or more of the sensing electrodes. Sequentially may include alternating between determining capacitance values and receiving piezoelectric signals.

In the mixed force-capacitance mode, the location corresponding to a user interaction may be determined based on the determined changes in capacitance values and the piezoelectric signals.

The method may also include determining whether the touch panel is wet or submerged based on the determined capacitance values of the sensing electrodes. The method may also include, in response to determining that the touch panel is wet, operating in the force-based mode.

The method may also include operating in the force-based mode in response to determining that a signal-to-noise ratio of the capacitance values is less than a pre-calibrated threshold.

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:.

In the following description, like parts are denoted by like reference numerals.

Projected capacitance touch panels operate by detecting changes in electric fields caused by the proximity of a conductive object. However, when a projected capacitance screen is wet, or fully submerged, the presence of water may cause the determination of a number of and locations of user touches based on capacitance values to become unreliable or entirely non-functional.

Touch panels which operate using combined force sensing and capacitance sensing may use the capacitance measurements to determine the locations of one or more touches. However, such measurements suffer the same issues as a pure capacitive touch panel when wet or submerged underwater. Furthermore, capacitance measurements will not detect a user touch using a non-conductive object, or through most conventional gloves.

The present specification concerns apparatuses and methods which may mitigate one or more of these issues.

Referring to <FIG>, a schematic cross section of a display stack-up including a first touch panel <NUM> is shown.

Referring also to <FIG>, a first apparatus <NUM> is shown.

The first apparatus <NUM> includes the first touch panel <NUM> and a touch controller <NUM>. In general, the touch panel <NUM> includes a layer of piezoelectric material <NUM> disposed between a number of sensing electrodes <NUM> and at least one counter electrode <NUM>. The touch controller <NUM> is electrically connected to the sensing electrodes <NUM> of the touch panel <NUM>. The touch controller <NUM> is configured to receive piezoelectric signals <NUM> from one or more of the sensing electrodes <NUM> via corresponding conductive traces <NUM>. In dependence on the received piezoelectric signals <NUM>, the touch controller <NUM> is configured to determine a location <NUM> and an applied force <NUM> corresponding to a user interaction <NUM> with the touch panel <NUM>. The touch controller <NUM> may be configured to amplify and/or filter the piezoelectric signals <NUM>. The touch controller <NUM> may determine a location <NUM> and an applied force <NUM> by interpolating values of the piezoelectric signals <NUM> to determine an implied position and magnitude of a peak piezoelectric signal, which may correspond to a location <NUM> between a pair of sensing electrodes <NUM>. The implied magnitude of a peak piezoelectric signal <NUM> may be mapped to an applied force using calibration data, and the mapping may depend on the location <NUM> of the user interaction <NUM>. The touch controller <NUM> may be configured to determine locations <NUM> and applied forces <NUM> corresponding to two or more simultaneous (or concurrent) user interactions <NUM>.

By determining locations <NUM> using only an applied force, the first apparatus <NUM> may continue to function without interruption even when the touch panel <NUM> is wet or submerged. Additionally or alternatively, the first apparatus <NUM> may continue to function even in environments which experience a relatively high level of electromagnetic interference. Such functionality may be particularly advantageous for wearable devices such as smart watches, which are more likely to be worn when swimming, or to become wet from, for example, rain, wet fingers, sweat and so forth. Although smart watches and other devices may be made waterproof, there has been little incentive to use them in wet environments such as, for example, a swimming pool, because a conventional projected capacitance touch panel does not function when wet or submerged.

The first touch panel <NUM> includes, stacked in a thickness direction z, the counter electrode <NUM>, a first layer structure <NUM> which includes the layer of piezoelectric material <NUM>, and the sensing electrodes <NUM>. The first layer structure <NUM> has a first face <NUM> and a second, opposite, face <NUM>. The first layer structure <NUM> includes one or more layers, including at least the layer of piezoelectric material <NUM>. Each layer included in the first layer structure <NUM> is generally planar and extends in first x and second y directions which are perpendicular to a thickness direction z. The one or more layers of the first layer structure <NUM> are arranged between the first and second faces <NUM>, <NUM> such that the thickness direction z of each layer of the first layer structure <NUM> is perpendicular to the first and second faces <NUM>, <NUM>.

The sensing electrodes <NUM> are disposed on the first face <NUM> of the first layer structure <NUM>, and the counter electrode <NUM> is disposed on the second face <NUM> of the first layer structure <NUM>. Each sensing electrode <NUM> takes the form of a conductive pad <NUM>. The conductive pads <NUM> are disposed on the first face <NUM> in an array extending in the first and second directions x, y. Each sensing electrode <NUM> in the form of a conductive pad <NUM> is coupled to a corresponding input of the touch controller <NUM> by a respective conductive trace <NUM>. The counter electrode <NUM> is disposed on the second face <NUM> and is extensive such that the counter electrode <NUM> at least partial underlies each sensing electrode <NUM> in the form of a conductive pad <NUM>. The counter electrode <NUM> may be substantially coextensive with the second face <NUM>. The counter electrode <NUM> is coupled to a common mode voltage Vcm, system ground and/or to the touch controller <NUM> via a return path (not shown).

The first touch panel <NUM> may be bonded overlying the display <NUM> of an electronic device such as, for example, a mobile phone, a tablet computer, a laptop computer, a smart watch or other wearable device, and so forth. In such contexts, the materials of the first touch panel <NUM> should be substantially transparent. A cover lens <NUM> is typically bonded overlying the first touch panel <NUM>. The cover lens <NUM> is preferably glass but may be any transparent material including transparent polymers. The cover lens <NUM> may be bonded to the first touch panel <NUM> using a layer of pressure sensitive adhesive (PSA) material <NUM>. The layer of PSA material <NUM> may also be substantially transparent. The array of sensing electrodes <NUM> and the corresponding conductive traces <NUM> may be fabricated using index matching techniques to minimise visibility to a user.

The layer of piezoelectric material <NUM> is a piezoelectric polymer such as polyvinylidene fluoride (PVDF) or or polylactic acid (PLLA). However, the layer of piezoelectric material <NUM> may alternatively be a layer of a piezoelectric ceramic such as lead zirconate titanate (PZT). The sensing electrodes <NUM> and counter electrode <NUM> may be formed from indium tin oxide (ITO) or indium zinc oxide (IZO). The sensing electrodes <NUM> and counter electrode <NUM> may be formed from metal films such as aluminium, copper, silver or other metals suitable for deposition and patterning as a thin film. The sensing electrodes <NUM> and counter electrode <NUM> may be formed from conductive polymers such as polyaniline, polythiphene, polypyrrole or poly(<NUM>,<NUM>-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). The sensing electrodes <NUM> and counter electrode <NUM> may be formed from a metal mesh; nanowires, for example silver nanowires; graphene; and/or carbon nanotubes.

The first layer structure <NUM> may include only the layer of piezoelectric material <NUM>, such that the first and second opposite faces <NUM>, <NUM> are faces of the layer of piezoelectric material <NUM>. Alternatively, the first layer structure <NUM> may include one or more dielectric layers <NUM> (<FIG>) stacked between the layer of piezoelectric material <NUM> and the first face <NUM> of the first layer structure <NUM>. The first layer structure <NUM> may include one or more dielectric layers <NUM> (<FIG>) stacked between the second face <NUM> of the first layer structure <NUM> and the layer of piezoelectric material <NUM>. One or more dielectric layer(s) <NUM> (<FIG>) may include layers of a polymer dielectric material such as polyethylene terephthalate (PET), or layers of pressure sensitive adhesive (PSA) material. However, one or more dielectric layer(s) <NUM> (<FIG>) may include layers of a ceramic insulating material such as aluminium oxide.

The conductive traces <NUM> may be made of the same material as the sensing electrodes <NUM>. Alternatively, the conductive traces <NUM> may be made of a material having a higher conductivity than the material used for the sensing electrodes <NUM>. The conductive traces <NUM> are generally much thinner in the plane defined by the first and second directions x, y than the corresponding sensing electrodes <NUM>.

In the example of the first touch panel <NUM> shown in <FIG>, the first and second faces <NUM>, <NUM> and the layers of the first layer structure <NUM> are shown extending along orthogonal axes labelled x and y, and the thickness direction of each layer of the first layer structure <NUM> is aligned with an axis labelled z which is orthogonal to the x and y axes. However, the first, second and thickness directions need not form a right handed orthogonal set as shown. For example, the first and second directions x, y may intersect at an angle of <NUM> degrees or <NUM> degrees or any other angle greater than <NUM> degrees and less than <NUM> degrees.

The touch controller <NUM> is further configured to determine one or more capacitance values <NUM>, each capacitance value <NUM> corresponding to one, or a pairing, of the sensing electrodes <NUM>. The touch controller <NUM> may determine a capacitance value <NUM> corresponding to each sensing electrode <NUM> and/or each pairing of sensing electrodes <NUM>.

The touch controller <NUM> may receive and measure piezoelectric signals <NUM> and capacitance values <NUM> concurrently. For example, as described in <CIT>, or as described in <CIT>. In particular, see the combined force and capacitance touch panel systems shown in, and described with reference to, <FIG> of <CIT>. Further, suitable combined force and capacitance touch panel systems are shown in, and described with reference to, Figures <NUM> and <NUM> of <CIT>.

Alternatively, the touch controller <NUM> may receive and measure piezoelectric signals <NUM> and capacitance values <NUM> sequentially, for example, as described in <CIT>. In particular, see the combined force and capacitance touch panel systems shown in, and described with reference to, <FIG> of <CIT>.

Referring to <FIG>, a schematic cross section of a second touch panel <NUM> is shown.

Referring also to <FIG>, a second apparatus <NUM> is shown.

The second apparatus <NUM> includes the second touch panel <NUM> and the touch controller <NUM>. The touch controller <NUM> is substantially the same as for the first apparatus <NUM>.

Compared to the first touch panel <NUM>, the sensing electrodes <NUM> of the second touch panel <NUM> are divided into first electrodes <NUM> and second electrodes <NUM>. Additionally, the second touch panel <NUM> also includes a second layer structure <NUM>. Stacked in the thickness direction, the second touch panel <NUM> includes the counter electrode <NUM>, the first layer structure <NUM>, the sensing electrodes <NUM> in the form of first electrodes <NUM>, the second layer structure <NUM> and the sensing electrodes <NUM> in the form of second electrodes <NUM>.

The second layer structure <NUM> has a third face <NUM> and a fourth, opposite, face <NUM>. The second layer structure <NUM> includes one or more dielectric layers <NUM>. Each dielectric layer <NUM> is generally planar and extends in first x and second y directions which are perpendicular to a thickness direction z. The one or more dielectric layers <NUM> of the second layer structure <NUM> are arranged between the third and fourth faces <NUM>, <NUM> such that the thickness direction z of each dielectric layer <NUM> of the second layer structure <NUM> is perpendicular to the third and fourth faces <NUM>, <NUM>.

The first electrodes <NUM> each extend in the first direction x and the first electrodes <NUM> are disposed in an array evenly spaced in the second direction y. The second electrodes <NUM> each extend in the second direction y and the second electrodes <NUM> are disposed in an array evenly spaced in the first direction x. Each first electrode <NUM> and each second electrode <NUM> are coupled to a corresponding input of the touch controller <NUM> by a respective conductive trace <NUM>. The first electrodes <NUM> may be disposed on the first surface <NUM> of the first layer structure <NUM>, or on the fourth surface <NUM> of the second layer structure <NUM>. The second electrodes <NUM> may be disposed on the third surface <NUM> of the second layer structure <NUM>, or on the underside of a cover lens <NUM> bonded over the second touch panel <NUM>. The counter electrode <NUM> is disposed on the second face <NUM> and is extensive such that the counter electrode <NUM> at least partially underlies each first electrode <NUM> and each second electrode <NUM>. The counter electrode <NUM> may be substantially coextensive with the second face <NUM>. The counter electrode <NUM> is coupled to a common mode voltage Vcm, system ground and/or the touch controller <NUM>.

The touch controller <NUM> may address each sensing electrode <NUM>, <NUM>, <NUM> according to a predetermined or dynamically determined sequence so as to perform a raster scan of the first and second electrodes <NUM>, <NUM>. This may enable the touch controller <NUM> to determine locations <NUM> and applied forces <NUM> corresponding to one or more user interactions <NUM>.

By determining locations <NUM> using only an applied force, the first apparatus may continue to function without interruption even when the second touch panel <NUM> is wet or submerged. Additionally or alternatively, the first apparatus <NUM> may continue to function even in environments which experience a relatively high level of electromagnetic interference. Such functionality may be particularly advantageous for wearable devices such as smart watches, which are more likely to be worn when swimming, or to become wet from, for example, rain, wet fingers, sweat and so forth. Although smart watches and other devices may be made waterproof, there has been little incentive to use them in wet environments such as, for example, a swimming pool, because a conventional projected capacitance touch panel does not function when wet or submerged.

The dielectric layer(s) <NUM> may include layers of a polymer dielectric material such as PET or layers of PSA materials. However, the dielectric layer(s) <NUM> may include layers of a ceramic insulating material such as aluminium oxide.

The second layer structure <NUM> may include only a single dielectric layer <NUM>, such that the third and fourth opposite faces <NUM>, <NUM> are faces of a single dielectric layer <NUM>. Alternatively, a second layer structure <NUM> need not be used, and the second electrodes <NUM> may be disposed on the first face <NUM> along with the first electrodes <NUM> (<FIG>).

In <FIG>, the third and fourth faces <NUM>, <NUM> and the dielectric layers <NUM> of the second layer structure <NUM> are shown extending along orthogonal axes labelled x and y, and the thickness direction of each dielectric layer <NUM> of the second layer structure <NUM> is aligned with an axis labelled z which is orthogonal to the x and y axes. However, the first, second and thickness directions x, y, z need not form a right handed orthogonal set as shown.

In the same way as the first apparatus <NUM>, the touch controller <NUM> of the second apparatus <NUM> may also determine capacitance values <NUM>. For the first apparatus <NUM>, the capacitance values <NUM> measured by the touch controller <NUM> correspond to self-capacitances of the conductive pads <NUM>. For the second apparatus <NUM>, the capacitance values <NUM> measured by the touch controller <NUM> may correspond to self-capacitances of the first and second electrodes <NUM>, <NUM> and/or mutual capacitances between pairings of a first electrode <NUM> and a second electrode <NUM>.

The touch controller <NUM> may receive and measure piezoelectric signals <NUM> and capacitance values <NUM> concurrently. For example, as described in <CIT>, or as described in <CIT>. In particular, see the combined force and capacitance touch panel systems shown in, and described with reference to, Figures <NUM> to <NUM> of <CIT>. Further, suitable combined force and capacitance touch panel systems are shown in, and described with reference to, <FIG> to <NUM> of <CIT>.

The second touch panel <NUM> may be bonded overlying the display <NUM> of an electronic device and a cover lens <NUM> may be bonded overlying the second touch panel <NUM> in the same way as for the first touch panel <NUM>.

Although the first and second electrodes <NUM>, <NUM> have been shown as being substantially rectangular, other shapes can be used.

For example, referring also to <FIG>, a third touch panel <NUM> having an alternative arrangement of the first and second electrodes <NUM>, <NUM> is shown.

Instead of being rectangular, each first electrode <NUM> may include several first pad segments <NUM> evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrower first bridging segments <NUM>. Similarly each second electrode <NUM> may comprise several second pad segments <NUM> evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrower second bridging segments <NUM>. The first pad segments <NUM> are diamonds having a first width W<NUM> in the second direction y and the first bridging segments <NUM> have a second width W<NUM> in the second direction y. The second pad segments <NUM> and second bridging segments <NUM> of the second electrodes <NUM> have the same respective shapes and widths W<NUM>, W<NUM> as the first electrodes <NUM>.

The first electrodes <NUM> and the second electrodes <NUM> are arranged such that the second bridging segments <NUM> overlie the first bridging segments <NUM>. Alternatively, the first electrodes <NUM> and the second electrodes <NUM> may be arranged such that the second pad segments <NUM> overlie the first pad segments <NUM>. The pad segments <NUM>, <NUM> need not be diamond shaped, and may instead be circular. The pad segments <NUM>, <NUM> may take the form of a regular polygon such as a triangle, square, pentagon or hexagon. The pad segments <NUM>, <NUM> may be I shaped or Z shaped. The first and second electrodes <NUM>, <NUM> may take the form of interdigitated, comb-like, snowflake or Manhattan layouts.

In the second apparatus <NUM>, the second touch panel <NUM> may be exchanged for the third touch panel <NUM>.

In the second and third touch panels <NUM>, <NUM>, the first and second electrodes <NUM>, <NUM> are arranged on different, parallel planes within the touch panels <NUM>, <NUM>. However, in some examples the first and second electrodes <NUM>, <NUM> may be disposed on substantially the same plane.

For example, referring also to <FIG>, a fourth touch panel <NUM> is shown.

The fourth touch panel <NUM> is substantially the same as the third touch panel <NUM> except that the fourth touch panel <NUM> does not include the second layer structure <NUM> and the second electrodes <NUM> are disposed on the first face <NUM> of the first layer structure <NUM> in addition to the first electrodes <NUM>. Each first electrode <NUM> is a continuous conductive region extending in the first direction x in the same way as the third touch panel <NUM>. For example, each first electrode <NUM> may include several first pad segments <NUM> evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrower first bridging segments <NUM>. Each second electrode <NUM> may comprise several second pad segments <NUM> evenly spaced in the second direction y in the same way as the third touch panel <NUM>. However, unlike the third touch panel <NUM>, the second pad segments <NUM> of the fourth touch panel <NUM> are disposed on the first face <NUM> of the first layer structure <NUM> and are interspersed with, and separated by, the first electrodes <NUM>. The second pad segments <NUM> are connected together by conductive jumpers <NUM>. The jumpers <NUM> each span a part of a first electrode <NUM> and the jumpers <NUM> are insulated from the first electrodes <NUM> by a thin layer of dielectric material (not shown) which may be localised to the area around the intersection of the jumper <NUM> and the first electrode <NUM>.

Alternatively, a thin dielectric layer (not shown) may overlie the first face <NUM> of the first layer structure <NUM> and the first and second electrodes <NUM>, <NUM>. Conductive regions (not shown) extending in the second direction y may be disposed over the dielectric layer (not shown), each conductive region (not shown) overlying the second pad segments <NUM> making up one second electrode <NUM>. The overlying conductive regions (not shown) may connect the second pad segments <NUM> making up each second electrode <NUM> using vias (not shown) formed through the dielectric layer (not shown).

In the second apparatus, the second touch panel <NUM> may be exchanged for the fourth touch panel <NUM>.

In the first to fourth touch panels <NUM>, <NUM>, <NUM>, <NUM>, the counter electrode <NUM> was disposed on, and substantially co-extensive with, the second surface <NUM> of the first layer structure <NUM>. However, in some examples the counter electrode <NUM> may be replaced with one or more patterned counter electrodes.

For example, referring also to <FIG>, a fifth touch panel <NUM> is shown.

Each sensing electrode <NUM>, <NUM>, <NUM> of the touch panel <NUM> takes the form of one or more sensing pads <NUM>, <NUM> , and each sensing pad <NUM>, <NUM> is opposed across the first layer structure <NUM> by a corresponding counter electrode pad 43a, 43b of a patterned counter electrode 39a, 39b.

Referring in particular to <FIG>, an arrangement of first electrodes <NUM> and a first patterned counter electrode 39a is shown.

The first electrodes <NUM> and first patterned counter electrode 39a are disposed on the second surface <NUM> of a first layer structure <NUM>. Each first electrode <NUM> includes several first sensing pads <NUM> evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrower first bridging segments <NUM>. The first patterned counter electrode 39a includes a number of first branches 42a. The first branches 42a each extend in the first direction x, and the first branches 42a are spaced apart in the second direction y and interdigitated with the first electrodes <NUM>. The first branches 42a are all electrically connected together, for example, the first branches 42a may all connect to a single conductive trace <NUM> along one or more peripheral edges of the fifth touch panel <NUM>. Each first branch 42a includes several first counter electrode pads 43a evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrower first bridging counter electrode segments 44a.

Referring in particular to <FIG>, an arrangement of second electrodes <NUM> and a second patterned counter electrode 39b is shown.

The second electrodes <NUM> and second patterned counter electrode 39b are disposed on the first surface <NUM> of the first layer structure <NUM>. Each second electrode <NUM> includes several second sensing pads <NUM> evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrower second bridging segments <NUM>. The second patterned counter electrode 39b includes a number of second branches 42b. The second branches 42b each extend in the second direction y, and the second branches 42b are spaced apart in the first direction x and interdigitated with the second electrodes <NUM>. The second branches 42b are all electrically connected together, for example, the second branches 42b may all connect to a single conductive trace <NUM> along one or more peripheral edges of the fifth touch panel <NUM>. Each second branch 42b includes several second counter electrode pads 43b evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrower second bridging counter electrode segments 44b.

Referring in particular to <FIG>, a plan view of the fifth touch panel <NUM> is shown.

The second electrodes <NUM> and the second patterned counter electrode 39b are arranged over the first electrodes <NUM> and the first patterned counter electrode 39a. The first layer structure <NUM> is not shown in <FIG> to aid visualisation of the relative positioning of the electrodes <NUM>, <NUM>, 39a, 39b. Each first sensing pad <NUM> is opposed to a second counter electrode pad 43b across the first layer structure <NUM>. Similarly, each second sensing pad <NUM> is opposed to a first counter electrode pad 43a across the first layer structure <NUM>.

In this way, the fifth touch panel <NUM> may be optimised for location sensing using only piezoelectric signals <NUM>, because the capacitance between sensing pads <NUM>, <NUM> and corresponding counter electrode pads 43a, 43b may be maximised. This may increase the relative size of piezoelectric signals <NUM>, compared to the second, third or fourth touch panels <NUM>, <NUM>, <NUM>. The relative strength of piezoelectric signals <NUM> may be further increased by using a first layer structure <NUM> which only includes the layer of piezoelectric material <NUM>.

The sensing pads <NUM>, <NUM> and the counter electrode pads 43a, 43b are diamond shaped in this example. However, the first sensing pads <NUM>, <NUM> and counter electrode pads 43a, 43b may alternatively be square, circular, or any other regular or irregular shape. Preferably the sensing pads <NUM>, <NUM> and the corresponding counter electrode pads 43a, 43b are the same shape. In the example shown in <FIG>, the counter electrode pads 43a, 43b have been drawn with slightly reduced areas compared to the sensing pads <NUM>, <NUM> for the purposes of visualisation. In examples in which capacitance values <NUM> are not obtained, each counter electrode pad 43a, 43b may have a shape and area matching the corresponding sensing pad <NUM>, <NUM> in order to maximise collection of piezoelectric induced charges. In examples in which capacitance values <NUM> are obtained, the counter electrode pads 43a, 43b which will be closest to an input surface in use may be made relatively smaller in order to reduce the effects of screening of electrical fringing fields between the first and second electrodes <NUM>, <NUM>.

In the second apparatus <NUM>, the second touch panel <NUM> may be exchanged for the fifth touch panel <NUM>.

In a modification (not shown) of the fifth touch panel <NUM>, the branches 42a, 42b of the patterned counter electrodes need not all be connected to a single conductive trace <NUM>. Instead, each branch 42a, 42b may be connected to the touch controller <NUM> using a separate conductive trace <NUM>. In such a modification (not shown), instead of measuring applied forces <NUM> only from the sensing electrodes <NUM>, applied forces <NUM> may additionally or alternatively be measured using the separately addressable patterned counter electrode branches 42a, 42b. In one example using such a modification (not shown) of the fifth touch panel <NUM>, if the first face <NUM> is closer to a user, then the second electrodes <NUM> and branches 42b supported on the first face <NUM> may be connected to system ground or common mode (to provide electrostatic shielding), whilst applied forces <NUM> are measured using the first electrodes <NUM> and branches 42a supported on the second face <NUM>.

Referring also to <FIG>, a first method of switching sensing modes is shown.

The first method is applicable to apparatuses <NUM>, <NUM> which implement force and capacitance sensing, whether concurrently or sequentially. The first method may be used in combination with any touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, which may be used for measurements of force and capacitance.

Measurements of applied force(s) <NUM> and capacitance values <NUM> are obtained by the touch controller (step S1). When the apparatus <NUM>, <NUM> measures force and capacitance concurrently, a single set of applied force(s) <NUM> and capacitance values <NUM> may be measured. When the apparatus <NUM>, <NUM> measures force and capacitance sequentially, one or more applied force(s) <NUM> may be measured, followed by measurements of the capacitance values <NUM>, or vice versa.

In response to receiving piezoelectric signals <NUM> (step S2, Yes), it is checked whether there are changes ΔC in the capacitance values <NUM> (step S3). The reception of piezoelectric signals <NUM> may correspond to piezoelectric signals <NUM> exceeding a pre-calibrated minimum piezoelectric signal threshold. As piezoelectric signals <NUM> are typically transient, checking whether piezoelectric signals <NUM> are received (step S2) may correspond to checking the time elapsed since piezoelectric signals <NUM> last exceeded the minimum piezoelectric signal. This condition checks for the application of a detectable force to the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Changes ΔC in the capacitance values <NUM> may correspond to differences between the capacitance values <NUM> and a set of baseline capacitance values which exceed minimum capacitance change thresholds. Minimum capacitance change thresholds may be determined upon start-up of the apparatus <NUM>, <NUM>, or may be pre-calibrated. This second condition checks for the presence of a conductive object close to, or touching, the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

If changes ΔC in capacitance values <NUM> are also detected (step S3, Yes), then the touch controller <NUM> operates in a mixed force-capacitance mode (step S4). In the mixed force-capacitance mode (step S4), the touch controller <NUM> is configured to determine a location <NUM> corresponding to a user interaction <NUM> based on the determined changes ΔC in capacitance values <NUM> (step S5), and to determine an applied force <NUM> corresponding to the user interaction <NUM> based on the piezoelectric signals. The mixed force-capacitance mode (step S4) corresponds to a user interaction <NUM> which applies force to a touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> using a conductive object such as a user's digit or a conductive stylus.

Whilst the first method continues (step S7, Yes), a further set of measurements is obtained (step S1).

Other outcomes are possible. For example, in response to in response to receiving piezoelectric signals (step S2, Yes) and determining no changes ΔC (at least no significant changes ΔC) in capacitance values <NUM> for any of the sensing electrodes <NUM> (step S3, No), the touch controller <NUM> operates in a force-based mode (step S8). In the force-based mode (step S8), the touch controller <NUM> is configured to determine both a location <NUM> (step S9) and an applied force <NUM> (step S10) corresponding to a user interaction <NUM> based on the piezoelectric signals <NUM>, without any input from capacitance values <NUM>. The force-based mode (step S8) corresponds to a user interaction <NUM> which applies force to a touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> using a non-conductive object such as a user's gloved digit or a non-conductive stylus.

In response to receiving no piezoelectric signals <NUM> (step S2, No), and also determining changes ΔC in capacitance values <NUM> of one or more sensing electrodes <NUM> (step S11, Yes), the touch controller <NUM> operated in a capacitance-based mode (step S12). In the capacitance based mode (step S12), the touch controller <NUM> is configured to determine a location <NUM> (step S13) corresponding to a user interaction <NUM> based on the determined changes ΔC in capacitance values <NUM>. The capacitance-based mode (step S12) corresponds to a user interaction <NUM> which applies no or negligible force to a touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> using a conductive object such as a user's digit or a conductive stylus.

In response to receiving no piezoelectric signals <NUM> (step S2, No), and also determining no changes ΔC in capacitance values <NUM> (step S11, No), there is no detectable user interaction <NUM> and the next set of measurements are obtained (step S1).

By differentiating between these different modes (steps S4, S8 or S12), the touch controller <NUM> may optimise signal processing for the conditions of ongoing user interactions <NUM>. For example, in the mixed force-capacitance mode (step S4), the processing of piezoelectric signals <NUM> may be optimised for maximum accuracy of determining applied force(s) <NUM>. This may include aggregating piezoelectric signals <NUM> from one or more groups of sensing electrodes <NUM>. However, in the force-based mode (step S8), the processing of the piezoelectric signals <NUM> may be optimised for accuracy in determining locations <NUM> of one or more user interactions <NUM>, for example by treating piezoelectric signal <NUM> from each sensing electrode <NUM> separately. In the capacitance-based mode (step S12), piezoelectric signals <NUM> may be ignored to save processing cycles/power.

In some examples, when the touch controller <NUM> operates in the mixed force-capacitance mode (step S4), the touch controller <NUM> may be configured to determine a location <NUM> corresponding to one or more user interactions <NUM> based on the determined changes ΔC in capacitance values <NUM>, additionally augmented by the piezoelectric signals <NUM>.

Referring also to <FIG>, a second method of switching sensing modes is shown.

The second method is the same as the first method, except that an additional check (step S14) is conducted before the touch controller <NUM> operates in mixed force-capacitance mode (step S4).

In particular, in response to receiving piezoelectric signals <NUM> (step S2, Yes) and measuring changes ΔC in the capacitance values <NUM> (step S3, Yes), the touch controller <NUM> also checks whether the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is wet or submerged (step S14). The touch controller <NUM> may determine whether the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is wet or submerged based on the measured changes ΔC in the capacitance values <NUM>. For example, when the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is wet or submerged, the fraction of sensing electrodes <NUM> registering changes ΔC and the magnitude of those changes ΔC may be inconsistent with even multiple user interactions <NUM>. Appropriate thresholds may be determined based on calibration experiments conducted by applying progressively more droplets of water to the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Alternatively, measured changes ΔC in the capacitance values <NUM> corresponding to wet and dry touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be used to train a neural network based classifier.

If the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is wet or submerged (step S14, Yes), the touch controller <NUM> operates in the force-based mode (step S8), despite the existence of measured changes ΔC in the capacitance values <NUM>. If the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is not wet or submerged (step S14, No), the touch controller <NUM> operates in the mixed force-capacitance mode (step S4).

In this way, in addition to the effects described hereinbefore in relation to the first method, a touch controller <NUM> carrying out the second method may avoid unreliable inputs when the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is wet or submerged by using the force-based mode to determine locations <NUM> of one or more user interactions <NUM> without relying on the measured changes ΔC in the capacitance values <NUM>.

In other examples, the test for the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> being wet or submerged (step S14) may be expanded to encompass further criteria. For example, the touch controller <NUM> may additionally or alternatively be configured to operate in the force-based mode (step S8) in response to determining that a signal-to-noise ratio for the capacitance values <NUM> is less than a pre-calibrated threshold. Such relatively high noise environments may be encountered in the in the presence of a high-frequency (<NUM> to <NUM>) electrical noise environment, for example caused by proximity to a poorly shielded switched-mode power supply.

As described hereinbefore, the touch controller <NUM> may process received piezoelectric signals <NUM> differently in the force-based and mixed force-capacitance modes. The differences in processing may be differences in processing of digital signals, but may additionally or alternatively correspond to changes in one or more physical connections between the sensing electrodes <NUM> and the touch controller <NUM>.

The touch controller <NUM> may include a switch <NUM> (<FIG>) configured so that:.

Each sensing electrode <NUM> remains coupled to a corresponding capacitance measurement channel <NUM> (<FIG>) at all times. The sensing electrodes <NUM> may be coupled to the capacitance measurement channels <NUM> (<FIG>) via high-pass filters, for example capacitances.

In this way, piezoelectric signals <NUM> from individual sensing electrodes <NUM> may be processed individually in the force-based mode (step S8) to provide the best possible accuracy in determining locations <NUM> corresponding to user interactions <NUM>. However, the piezoelectric signals <NUM> correspond to relatively low currents, and typically require amplification be a significant gain factor. High gain amplification may be relatively noisy and susceptible to interference from external electric fields. By contrast, in the mixed force-capacitance mode (step S4) changes ΔC in capacitance values <NUM> are available for determining locations <NUM>. Thus, piezoelectric signals <NUM> from two or more sensing electrodes <NUM> (typically adjacent to one another) may be combined in order to increase the relatiove strength of the signal. Potentially, the amplification gain used may also be decreased.

Referring also to <FIG>, a first exemplary switching configuration is shown.

The first switching configuration includes a number, N, of sensing electrodes <NUM><NUM>, <NUM><NUM>,. , <NUM>N which are connectable by a switch <NUM> to either a corresponding number N of piezoelectric signal sensing circuits <NUM><NUM>, <NUM><NUM>,. , <NUM>N, or to a total piezoelectric signal sensing circuit <NUM>. The switch <NUM> includes a number N of individual switch elements SW<NUM>, SW<NUM>,. The nth of N switch elements SWn may connect the corresponding nth sensing electrode <NUM>n to either the nth piezoelectric signal sensing circuit <NUM>n or to the total piezoelectric signal sensing circuit <NUM>. The capacitive coupling of each sensing electrode <NUM><NUM>, <NUM><NUM>,. , <NUM>N to a corresponding capacitance measurement channel <NUM><NUM>, <NUM><NUM>,. , <NUM>N is shown in <FIG> for reference, but is not drawn in <FIG> as the capacitive coupling does not vary with the mode of the touch controller <NUM>. The capacitance measurement channels <NUM><NUM>, <NUM><NUM>,. , <NUM>N are not used in the force-based mode (step S8).

Referring in particular to <FIG>, when the touch controller <NUM> operates in the force-based mode (step S8), the switch <NUM> according to the first exemplary switching configuration connects each sensing electrode <NUM>n to the corresponding piezoelectric signal sensing circuit <NUM>n.

Referring in particular to <FIG>, when the touch controller <NUM> operates in the mixed force-capacitance mode (step S4), the switch <NUM> according to the first exemplary switching configuration connects all of the sensing electrodes <NUM><NUM>, <NUM><NUM>,. , 5rr to the total piezoelectric signal sensing circuit <NUM>.

Preferably a significant resistance R (not shown in <FIG>) in the range from about <NUM> kΩ to about <NUM> kΩ should also be provided in series between each capacitance measurement channel <NUM><NUM>, <NUM><NUM>,. , <NUM>N and the corresponding switch elements SW<NUM>, SW<NUM>,. These resistances R may act to suppress or block high-frequency coupling of signals between capacitance measurement channels <NUM><NUM>, <NUM><NUM>,. , <NUM>N via the switch elements SW<NUM>, SW<NUM>,. As an alternative to additional resistances, whenever a particular capacitance measurement channel <NUM>n is read, the corresponding switch element SWn may be temporarily opened to isolate the electrode <NUM>n for the duration of measuring a capacitance value <NUM>. When the touch controller <NUM> performs mutual capacitance measurements, both a transmitting electrode <NUM>n and a receiving electrode <NUM>k (with k an integer <NUM>≤k≤N) may be temporarily isolated for the duration of the measurement using corresponding switch elements SWn, SWk.

Referring also to <FIG>, a second exemplary switching configuration is shown.

The second switching configuration includes a number, N, of sensing electrodes <NUM><NUM>, <NUM><NUM>,. , <NUM>N which are connectable either individually or in pairs to a corresponding number N of piezoelectric signal sensing circuits <NUM><NUM>, <NUM><NUM>,. , <NUM>N by a switch <NUM>. The switch <NUM> includes a number N/<NUM> of individual switch elements SW<NUM>,<NUM>, SW<NUM>,<NUM>,. , SWN-<NUM>,N. The switch element SWn-<NUM>,n may connect the n-<NUM>th and nth of N sensing electrodes 5n-<NUM>, 5n to the corresponding piezoelectric signal sensing circuits <NUM>n-<NUM>, <NUM>n, or the switch element SWn-<NUM>,n may connect both sensing electrodes <NUM>n-<NUM>, <NUM>n to the n-<NUM>th piezoelectric signal sensing circuit <NUM>n-<NUM>. The capacitive coupling of each sensing electrode <NUM><NUM>, <NUM><NUM>,. , 5rr to a corresponding capacitance measurement channel <NUM><NUM>, <NUM><NUM>,. , 49rr is not drawn in <FIG>.

In <FIG>, the switch <NUM> is shown corresponding to the force-based mode (step S8) of the touch controller <NUM>. The configuration of the switch elements SW<NUM>,<NUM>, SW<NUM>,<NUM>,. , SWN-<NUM>,N corresponding to the mixed force-capacitance mode (step S4) is indicated in <FIG> by dashed lines.

Examples of touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM> described hereinbefore have been illustrated with generally square shapes (square perimeters). However, touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may have other shaped perimeters, for example rectangular, circular, elliptical, or any other regular or irregular perimeter shape.

For example, referring also to <FIG> a sixth touch panel <NUM> is shown.

The sixth touch panel <NUM> is the same as the second touch panel <NUM>, except that the second touch panel <NUM> has a circular perimeter <NUM>. The second layer structure <NUM> is not drawn in <FIG>. The first and second sensing electrodes <NUM>, <NUM> are truncated at one end by the circular perimeter <NUM> of the sixth touch panel <NUM>.

Although illustrated as a modification of the second touch panel <NUM>, any hereinbefore described touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be modified to use a circular perimeter <NUM>, or other shaped perimeter.

First and second electrodes <NUM>, <NUM> extending in first and second perpendicular directions need not be used. Sensing electrodes <NUM> may be disposed according to any suitable coordinate system for determining locations <NUM> of user interactions <NUM> with the touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

For example, referring also to <FIG>, a seventh touch panel <NUM> is shown.

The seventh touch panel <NUM> is the same as the second to fourth or sixth touch panels <NUM>, <NUM>, <NUM>, <NUM>, except that the first and second electrodes <NUM>, <NUM> defining a Cartesian grid have been replaced with radial first electrodes <NUM> and circumferential second electrodes <NUM> defining a circular polar coordinate system (θ, r). The radial first electrodes <NUM> measure the angle θ of a location <NUM> with respect to the centre of the seventh touch panel <NUM>, and the circumferential second electrodes <NUM> measure the radius r of a location <NUM> with respect to the centre of the seventh touch panel <NUM>. The seventh touch panel <NUM> has a circular perimeter <NUM>.

With appropriate modifications to the first and second patterned counter electrodes 39a, 39b, the fifth touch panel <NUM> may be modified to employ radial first electrodes <NUM> and circumferential second electrodes <NUM>.

It will be appreciated that many modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of touch panels and which may be used instead of or in addition to features already described herein. Apparatuses <NUM>, <NUM> and touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> according to the present specification may be particularly advantageous when incorporated into a wearable device (not shown). For example, because apparatuses <NUM>, <NUM> and touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> according to the present specification may operate underwater or when wetted by rain, wet fingers and so forth. A wearable device (not shown) may take the form of a watch, a smart watch, a bracelet, a belt, a buckle, glasses, lenses of glasses, frames of glasses, jewellery, and so forth. When used, the first and second methods of switching sensing modes may allow a wearable device to better handle varied input methods and/or challenging environmental conditions such as, for example, a wet or submerged touch panel <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and so forth.

For example, a smart watch (not shown) may incorporate a sixth or seventh touch panel <NUM>, <NUM> and may include a touch controller <NUM> implementing the second method of switching sensing modes.

First to seventh touch panels <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have been described in which sensing electrode <NUM> are disposed in regular patterns or arrays. However, the touch controller <NUM> and associated methods may also be used with touch panels in which sensing electrodes <NUM> are not disposed in regular patterns or arrays. Instead, the sensing electrodes <NUM> may be used to provide one or more discrete buttons for use on a control panel of a device.

Referring also to <FIG>, a button input panel <NUM> is shown.

The button input panel <NUM> includes an outer layer <NUM> providing a user input surface <NUM>, and stacked behind the outer layer <NUM> are sensing electrodes <NUM>, a first layer structure <NUM>, a counter electrode layer <NUM> and a light emitting diode (LED) layer <NUM>. The button input panel <NUM> is a type of touch panel, and unless evidently incompatible, any description hereinbefore relating to touch panel(s) is equally applicable to the button input panel <NUM>.

Referring in particular to <FIG>, an example of a user input surface <NUM> is shown. The user input surface <NUM> shown in <FIG> is for a washing machine (not shown), although the button input panel <NUM> may be readily adapted and applied to any device or machinery which requires or receives user input. Graphics, text or other indicia are printed or otherwise applied to the user input surface <NUM> (or the other side of the outer layer <NUM> if transparent) to define regions where a user may interact with the button input panel <NUM>. A "Program" input area <NUM> is defined, including text corresponding to the different types of washing cycles which the washing machine can run. Each section of text is positioned over a corresponding sensing electrode <NUM> in the form of a first button electrode <NUM> belonging to a first group of buttons <NUM>.

Similarly, a "Temp" input area <NUM> is defined, containing text corresponding to different wash temperatures and overlying sensing electrodes <NUM> in the form of second button electrodes <NUM> belonging to a second group of buttons <NUM>. Additionally, a "Spin" input area <NUM> is defined, containing text corresponding to different spin speeds and overlying sensing electrodes <NUM> in the form of third button electrodes <NUM> belonging to a third group of buttons <NUM>. A power button electrode <NUM> is overlaid by a suitable graphic, as are a start button electrode <NUM> and a pause button electrode <NUM>.

The user input surface <NUM> may be generally opaque except for a transparent window <NUM> which is provided for viewing an underlying display <NUM>. The display <NUM> may be provided as part of the LED layer <NUM>, for example using one or more organic light emitting diodes (OLEDs), or the display <NUM> may be a separate device mounted to the underside of the button input panel <NUM>, for example a liquid crystal display or OLED display. Preferably the area corresponding to each button electrode <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is at least partially translucent to allow particular buttons to be individually illuminable using the LED layer <NUM>. This can allow the actuation status of the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to be visually indicated, for example, if the currently selected temperature is <NUM>, then the second button electrode <NUM> underlying the text "<NUM>" may be illuminated whilst all the other buttons electrodes <NUM> of the second group <NUM> are not illuminated. To provide these functions, the outer layer <NUM> may be transparent, and areas other than the transparent window <NUM> may be printed (for example on the opposite side to the user input surface) using opaque ink. Text or other indicia overlying button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be defined by omitting the opaque ink, or by using a different, translucent ink.

Referring in particular to <FIG>, the first face <NUM> of the first layer structure <NUM> underlying the outer layer <NUM> is shown. Each of the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is connected to the touch controller <NUM> via a corresponding conductive trace <NUM>. The operation of the touch controller <NUM> is the same as described hereinbefore. In particular the touch controller <NUM> measures forces <NUM> applied to the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, locations <NUM> in the form of the identities of any actuated button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and optionally self-capacitances of the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

Referring in particular to <FIG>, a cross-section of the button input panel <NUM> is shown corresponding to the line labelled B-B' in <FIG>. The button input panel <NUM> has a similar structure to the first touch panel <NUM>, except that the cover lens <NUM> is replaced by the outer layer <NUM>, the display <NUM> is replaced by the LED layer <NUM> and the sensing electrodes <NUM> have a different pattern. The LED layer <NUM> includes a light emitting diode (LED) <NUM> arranged to underlie each of the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in order to provide illumination indicative of actuating the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Consequently, the intervening layers of counter electrode <NUM>, first layer structure <NUM>, button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and pressure sensitive adhesive <NUM> should be transparent or at least translucent. In other examples where the buttons are not required to be illuminable, the LED layer <NUM> may be omitted. In further examples, a backlight (not shown) may be combined with a liquid crystal array (not shown) to provide selective illumination of the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and optionally the display <NUM>.

Each LED <NUM> may single or multi-coloured. When multi-coloured LEDs <NUM> are used, feedback of force values <NUM> from the touch controller <NUM> may be used to alter the colour emitted to illuminate a corresponding button electrode <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in dependence on the magnitude of a corresponding applied force <NUM>.

The button input panel <NUM> may employ any of the hereinbefore described methods of switching input modes between capacitance-based, force-based and mixed force-capacitance modes. This may be advantageous in the context of a washing machine, as a user's hands may often be wet, and the ambient environment may often be humid and prone to condensation (e.g. from a tumble dryer machine). In this environment, replacement of mechanical buttons with capacitive buttons alone may not be practical. The devices and methods of the present specification may be used in this environment because even if a user's hands are wet and/or a thin film of condensed water vapour has formed over the user input surface, the force sensing mode may still reliably detect user input.

Although illustrated using a single, continuous counter electrode <NUM>, in other examples a counter electrode layer may be patterned to correspond to the button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, for example the second face <NUM> may be patterned with a number of patterned counter electrodes having an identical layout to that shown in <FIG>. When such patterned counter electrodes (identical layout to <FIG>) are used, they may all be connected together so that forces may be measured between any button electrode <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the patterned counter electrodes (identical layout to <FIG>).

Alternatively, each patterned counter electrode (identical layout to <FIG>) may be connected to a separate conductive trace <NUM>, enabling differential force measurements to be obtained for each individual button electrode <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In a further example, the touch controller <NUM> may measure applied forces <NUM> using the patterned counter electrodes (identical layout to <FIG>), whilst connecting the corresponding button electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to system ground or common mode voltage to provide electrostatic shielding. Counter electrode measurement of force values <NUM> may be performed in the force-based mode, and/or time multiplexed with capacitance measurements in the mixed force-capacitance.

Other configurations of a counter electrode layer are possible, for example, a counter electrode layer may include separate electrodes (not shown) corresponding to each of the power, start and pause button electrodes <NUM>, <NUM>, <NUM>, and further electrodes (not shown) each of which is coextensive with one of the first, second and third groups <NUM>, <NUM>, <NUM> of electrodes. This latter approach represents a hybrid approach in which some button electrodes <NUM>, <NUM>, <NUM> are opposed by a matching counter electrodes (not shown), whereas each group <NUM>, <NUM>, <NUM> of electrodes is opposed by a common counter electrode (not shown). Counter electrode <NUM> measurements of applied force <NUM> would be possible using such a hybrid approach. For example, whilst an applied force <NUM> measurement made using a common counter electrode (not shown) for the "Spin" input area <NUM> could not distinguish between the various options, the touch controller <NUM> may be configured to cycle through the options each time the common counter electrode (not shown) is actuated. The currently selected option may be indicated by illumination from the LED layer <NUM>.

The display <NUM> of the button input panel <NUM> is optional, and in other example may be omitted.

Claim 1:
Apparatus comprising:
a touch panel (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) which comprises a layer of piezoelectric material (<NUM>) disposed between a plurality of sensing electrodes (<NUM>, <NUM>, <NUM>) and at least one counter electrode (<NUM>);
a touch controller (<NUM>) connected to the touch panel, and configured to determine, in response to receiving piezoelectric signals (<NUM>) from one or more of the sensing electrodes, a location (<NUM>) and an applied force (<NUM>) corresponding to a user interaction (<NUM>) with the touch panel;
wherein the touch controller is further configured to determine a capacitance value (<NUM>) of one or more of the sensing electrodes;
characterized in that the touch controller is configured to:
in response to receiving piezoelectric signals and determining no changes in the capacitance values for any of the sensing electrodes, to operate in a force-based mode wherein the touch controller is configured to determine a location and an applied force corresponding to a user interaction based on the piezoelectric signals;
in response to determining changes in the capacitance values of one or more sensing electrodes and receiving no piezoelectric signals, to operate in a capacitance-based mode wherein the touch controller is configured to determine a location corresponding to a user interaction based on the determined changes in the capacitance values;
in response to determining changes in the capacitance values of one or more sensing electrodes and receiving piezoelectric signals, to operate in a mixed force-capacitance mode wherein the touch controller is configured to determine a location corresponding to a user interaction based on the determined changes in the capacitance values and to determine an applied force corresponding to the user interaction based on the piezoelectric signals.