Combined touch and displacement sensing

Abstract

Described is a capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus. The capacitive sensing apparatus includes a base, a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base, a first electrode positioned adjacent the displacement element, a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode, measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode, and control circuitry. The control circuitry is configured to: operate the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operate the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode. Also described is an apparatus comprising the sensing apparatus and a method for operating a capacitive sensing apparatus.

Description

[0001] TITLE OF THE INVENTION

[0002] COMBINED TOUCH AND DISPLACEMENT SENSING

[0003] BACKGROUND OF THE INVENTION

[0004] The present invention relates to combined touch and displacement sensing, e.g. using capacitive sensing techniques.

[0005] Capacitive sensing techniques have become widespread for providing touch-sensitive inputs, for example in computer tablets, mobile phones, and in many other applications. Touch sensitive input devices are generally perceived to be more aesthetically pleasing than input devices that are based on mechanical switches. Nonetheless, the present inventors have recognised there are still situations in which a user-interface that is responsive to mechanical input may be desired. In particular, the inventors have recognised there are situations in which there is a desire to measure the physical displacement of a displacement element, for example to provide the equivalent of a "click" when navigating a cursor across a display screen using a touch sensor. Furthermore, the inventors have recognised it can be desirable to provide such functionality using capacitive sensing techniques rather than mechanical switching techniques. Not only can capacitive sensing techniques provide for more reliable sensors (as they are less prone to mechanical wear), there may be situations in which displacement sensing is desired in conjunction with other sensors based on capacitive sensing (for example to measure the displacement of a capacitive touch screen), and so it can be convenient to adopt the same sensing technologies for both touch position and displacement sensing aspects.

[0006] Such combined capacitive touch and displacement sensors often comprise a capacitive touch sensor element and a separate displacement sensor element. While this arrangement provides each of the abovementioned capacitive touch and capacitive displacement sensing, the combined capacitive touch and displacement sensors can be considered expensive and complex to manufacture and are often bulkier due to the presence of separate sensor elements. Such sensors may not be considered suitable for all applications, particularly those where there is a desire to minimise the thickness of such sensors (e.g., such as on thin screen displays or the like).

[0007] There is therefore a desire for apparatus and methods that can help to address these kinds of issues. SUMMARY OF THE INVENTION

[0008] According to a first aspect of certain embodiments there is provided a capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus. The capacitive sensing apparatus includes a base, a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base, a first electrode positioned adjacent the displacement element, a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode, measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode, and control circuitry. The control circuitry is configured to: operate the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operate the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode.

[0009] According to a second aspect of certain embodiments there is provided an apparatus comprising the sensing apparatus of the first aspect.

[0010] According to a third aspect of certain embodiments there is provided a method for operating a capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus, the capacitive sensing apparatus including a base, a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base, a first electrode positioned adjacent the displacement element, a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode, measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode, and control circuitry. The method includes operating the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operating the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode.

[0011] It will be appreciated that features and aspects of the invention described above in relation to the first and other aspects of the invention are equally applicable to, and may be combined with, embodiments of the invention according to other aspects of the invention as appropriate, and not just in the specific combinations described above.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is now described by way of example only with reference to the following drawings in which:

[0014] Figure 1 schematically represents a sensor element and controller element of a sensing apparatus according to certain embodiments of the invention;

[0015] Figure 2 schematically shows in cross-section a portion of the sensing apparatus of Figure 1 in a non-displaced state;

[0016] Figure 3 schematically shows in cross-section a portion of the sensing apparatus of Figure 1 in a displaced state;

[0017] Figure 4 is a flow chart showing an example method for operating the sensing apparatus Figures 1 to 3, in particular to obtain a capacitance measurement of the displacement and a capacitance measurement of a touch as sensed by the sensing apparatus;

[0018] Figure 5 shows a modification to the flow chart of Figure 4 additionally including the step of determining if the displacement load is applied via a conductive object;

[0019] Figure 6 shows a modification to the flow chart of Figure 4 additionally including the step of verifying the displacement capacitance measurement in view of the touch capacitance measurement;

[0020] Figure 7 shows a modification to the flow chart of Figure 4 additionally including the step of determining a compensation factor for applying to the displacement capacitance measurement; Figure 8 schematically represents a modification to the sensor element of Figures 1 to 3 where a conductive trace for supplying a driving signal to the deformable electrode is shown deposited on the frame element of the sensing apparatus;

[0021] Figures 9a and 9b schematically and in perspective view show example arrangements of the reference electrode according to a first and second implementation, where Figure 9a shows the reference electrode as a series of concentric electrode rings and Figure 9b shows a series of linear electrodes in a sunburst pattern;

[0022] Figures 10a and 10b schematically and in perspective view show example arrangements of the deformable electrode according to a first and second implementation, where Figure 10a shows the deformable electrode comprising an opening for allowing the passing of light through the deformable electrode and Figure 10b shows a plurality of discrete deformable electrodes arranged with a gap therebetween for allowing the passing of light around the deformable electrode;

[0023] Figure 11 schematically represents a sensor element and controller element of a sensing apparatus according to a modification in which a plurality of deformable electrodes and reference electrodes are provided to allow for determination of a position of a touch relative to the sensing surface to be determined; and

[0024] Figure 12 schematically represents a sensor element of a sensing apparatus according to a further embodiment of the invention.

[0025] DETAILED DESCRIPTION

[0026] Aspects and features of certain examples and embodiments of the present invention are discussed I described herein. Some aspects and features of certain examples and embodiments may be implemented conventionally and these are not discussed I described in detail in the interests of brevity. It will thus be appreciated that aspects and features of apparatus and methods discussed herein which are not described in detail may be implemented in accordance with any conventional techniques for implementing such aspects and features.

[0027] Figures 1, 2 and 3 schematically represent various aspects of a sensing apparatus 1 in accordance with certain embodiments of the invention.

[0028] Overall the sensing apparatus 1 comprises two main functional parts, namely a sensor element 6, comprising a displacement element 3 that is movably mounted with respect to a frame element 2 and associated components used for capacitively measuring displacements of the displacement element 3 relative to the frame element 2 and objects (e.g., a human finger) touching or in the vicinity the displacement element 3, and a controller element 4 (or control circuitry) comprising displacement capacitance measurement circuitry 4A and touch capacitance measurement circuitry 4B for measuring capacitances indicative of displacements and touches applied to the sensor element 6 respectively, and processor circuitry 4C for processing the obtained capacitance measurements.

[0029] The sensing apparatus 1 is operable to measure both a displacement of the displacement element 3 and the presence of an object over I touching the displacement element 3 using capacitive sensing techniques. As will be described in more detail below, the sensing apparatus 1 according to the present disclosure utilises a pair of electrodes to provide both the touch sensing functionality (i.e., whether an object is over or touches the displacement element 3) and the displacement sensing functionality (i.e., the displacement of the displacement element 3 towards or away from the frame element 2). In this way, the sensing apparatus 1 of the present disclosure avoids the necessity to implement separate electrodes for providing the touch sensing functionality and separate electrodes for providing the displacement sensing functionality, thereby reducing the number of parts required (e.g., such as further electrodes as well as any insulating material) and reducing the thickness of the corresponding sensing apparatus 1).

[0030] Figure 1 schematically represents the sensor element 6 in plan view and the controller element 4 in highly schematic form (i.e. as a functional block). Figures 2 and 3 respectively show portions of the sensor element 6 of the sensing apparatus 1 in cross-section (taken on the line A-A represented in Figure 1), with Figure 2 showing the sensing apparatus 1 in a non-displaced (rest) state and Figure 3 showing the sensing apparatus 1 in a displaced state.

[0031] The sensor element 6 comprises a displacement element 3 that is movably mounted with respect to a frame element 2. In particular, the displacement element 3 is mounted such that it is capable of moving along a direction towards or away from a base 2a of the frame element 2 (along the direction indicated by h in Figure 2). The sensor element 6 further comprises a first electrode 5, which in this implementation is a deformable electrode 5, and a second electrode 12, which in this implementation is also referred to as a reference electrode 12. In the implementation of Figures 1 to 3, the displacement element 3 is mounted to the frame element 2 using one or more support elements 8.

[0032] The displacement element 3 comprises a substrate, such as a dielectric substrate, e.g. formed from glass or plastic. The displacement element 3 is, or forms part of, the surface of the sensing apparatus 1 that the user interacts with, and thus can be considered to provide a sensing or interaction surface. In some implementations, one or more additional layers, such as a protective layer, may be provided adjacent the substrate, but in other implementations only the substrate is provided. When reference is made to a user interacting with the displacement element 3, it should be appreciated that interacting encompasses an object physically contacting the interaction or sensing surface (e.g., a user’s finger physically touches the substrate or protective layer), but also encompasses an object being in proximity of the displacement element 3 (e.g., a user’s finger hovers over the substrate or protective layer within a certain detectable distance from the substrate or protective layer).

[0033] The displacement element 3 in this example is in the form of a planar rectangle, but other shapes may be used. The size of the displacement element 3 may be chosen according to the implementation at hand to provide the desired area over which sensing is to be provided. Purely for the sake of a specific example, it will be assumed here the displacement element 3 has a size of around 10 cm (width) x 5 cm (height) x 0.2 cm (thickness). The displacement element 3 may be transparent or opaque according to the application at hand. For example, in some implementations a display screen or backlight may be provided below the sensor element 6. In this case the displacement element 3 (and any parts of the frame element 2 overlying the display screen) should be transparent, at least to some extent, to allow a user to see the display screen I light through the sensor element 6. In other cases there may be a desire from a design perspective to hide what is behind the displacement element 3 (for example because there is internal wiring or structural elements of an apparatus in which the sensor element 6 is mounted which are not intended to be visible to the user for aesthetic reasons). In this case the displacement element 3 and I or frame element 2 may be opaque. In such cases, the displacement element 3 may include markings or other form of indicia representing certain functions associated with the device in which the sensing apparatus 1 is to be used, e.g., the letters of the alphabet at positions on the displacement element 3 corresponding to a conventional keyboard layout.

[0034] When a user desires to press the displacement element 3, e.g., to perform a “click” function as described above, the displacement element 3 is the part of sensor apparatus 1 to which a load may be applied during normal use. The application of an example load during use, e.g. corresponding to a user pressing a finger on the displacement element 3, is schematically shown in Figure 3 by the arrow labelled "LOAD". For ease of explanation, the side of the displacement element 3 to which the load is applied in normal use may sometimes be referred to herein as the "upper" or "outer" side of the displacement element 3 (or similar terminology such as "top"), with the other side being referred to as "lower" or "inner" (or similar terminology, such as "bottom"). Thus, the surface of the displacement element 3 shown uppermost in the orientation of Figures 2 and 3 may sometimes be referred to as the upper I outer I top surface of the displacement element 3. Likewise, the lowermost surface of the displacement element 3 for the orientation of Figures 2 and 3 may sometimes be referred to as the bottom I lower I inner surface. Corresponding terms may similarly be used in respect of other parts of the sensing apparatus 1 in accordance with the orientation shown in the relevant figures. However, it will be appreciated this terminology is used purely for convenience of explanation and is not intended to suggest a particular orientation of the sensing apparatus 1 should be adopted in normal use. For example, although in the orientation of Figures 2 and 3 the upper surface of the sensor element 6 is shown uppermost, the sensor element 6 could equally be used in a downward facing configuration, or facing outwards from a vertical surface, according to the implementation at hand. More generally, the sensing apparatus 1 may be incorporated in a portable device (such as a tablet computer or mobile telephone), and in that case the orientation in use will vary according to how a user happens to be holding the device.

[0035] The frame element 2 provides a structural support for the displacement element 3 and will typically be connected to, or comprise an integral part of, an apparatus in which the sensing apparatus 1 is provided. The frame element 2 may comprise any suitable structural material, for example it may be formed from metal or plastic. The frame element 2 in this example defines a recess I opening into which the displacement element 3 is received and moveably supported therein by a support element 8 arranged around a peripheral part of the displacement element 3. In this example the movable mounting of the displacement element 3 relative to the frame element 2 is provided by virtue of the support element 8 comprising a resiliently compressible material. An upper edge of the support element 8 is bonded to the underside of the displacement element 3 and a lower edge of the support element 8 is bonded to the frame element 2. Conventional bonding techniques can be used for bonding the support element 8 to the other parts of the sensing apparatus 1 , for example having regard to bonding techniques appropriate for the materials involved. However, it should be appreciated that, more generally, the displacement element 3 may be coupled to the frame element 2 in a fixed or freely moveable manner. That is, the displacement element 3 may be alternatively be rigidly fixed to the frame element 2 and displacement or movement of the displacement element 3 is caused by deflection (e.g., bending or flexing) of parts of the displacement element 3. In other implementations, such as the one described, the displacement element 3 may be arranged such it is able to freely move, albeit supported in some way such as by the support element 8, relative to the frame element 2 upon displacement of the displacement element 3. In some implementations, where the displacement element 3 is freely moveable with respect to the frame element 2, displacement may be a combination of both the free movement and deflection of the displacement element 3.

[0036] The support element 8 in this example is thus generally in the form of a rectangular ring arranged around a peripheral part of the displacement element 3. The support element 8 has a generally rectangular cross-section when in its relaxed state (as shown in Figure 2), although when the support element 8 is compressed by virtue of a load being applied to the displacement element 3, its sides may bow out to accommodate the movement, as schematically indicated in Figure 3. It will, however, be appreciated that other shapes could be used in accordance with established mounting practices. For example, more complex shapes for the support element 8 may be chosen to provide different degrees of compressibility according to the degree to which the support element is already compressed. The frame element 2 may include a stop to limit the extent to which the support element 8 may be compressed (i.e. to limit the extent to which the displacement element may be displaced relative to the frame element 2). In this example such a stop is provided by a suitably arranged protrusion 10 from a side wall of the recess defined by the frame element 2. This protrusion 10 may extend all around the recess or may be provided at a number of discrete locations around the periphery of the recess.

[0037] The sensing apparatus 1 further comprises the deformable electrode 5 and the reference electrode 12. Together, these electrodes 5, 12 may be referred to as sensing electrodes as the deformable electrode 5 and the reference electrode 12 are capable of providing both a touch sensing functionality and a displacement sensing functionality, as described in more detail below.

[0038] With reference to Figures 2 and 3, the deformable electrode 5 is arranged between the displacement element 3 and the base 2a of the frame element 2. The deformable electrode 5 has a generally "D" shaped cross-section with a lower curved wall 7, which may also be referred to as a contact surface 7 for the deformable electrode 5. In the example described in Figures 1 to 3, the deformable electrode 5 has a circular cross-section (when viewed from above in Figure 1) and is arranged such that the centre of the circular cross-section is approximately aligned with the centre point of the rectangular displacement element 3. However, the specific geometry of the deformable electrode 5, e.g. in terms of its cross- sectional size, position relative to a reference point of the displacement element 3, and its areal extent, is not significant to the principles described herein and may vary depending on the specific construction of the sensing apparatus 1. The deformable electrode 5 may be formed in a number of different ways. In this example the deformable electrode 5 comprises a suitably profiled elastomeric conductive foam; however, other materials may also be used.

[0039] Between the deformable electrode 5 and the base 2a of the frame element 2 is the reference electrode 12. The reference electrode 12 is generally provided to align with the deformable electrode 5 to some extent. In the present implementation, the reference electrode 12 is provided directly below the deformable electrode 5, and is configured to have a horizontal I longitudinal extent that is less than the corresponding dimensions of the deformable electrode 5. Put another way, when viewed in the direction from the displacement element 3 to the base 2a of the frame element 2, the areal extent of the deformable electrode 5 covers the areal extent of the reference electrode 12. An upper surface of the reference electrode 12 is provided with an electrical insulator layer 14 (shown schematically in the magnified parts of Figures 2 and 3). The insulator layer 14 prevents the overlying deformable electrode 5 from coming into direct electrical (galvanic) contact with the reference electrode 12.

[0040] The reference electrode 12 may be provided in a number of different ways, for example as a conductive trace deposited on the frame element 2. The insulator layer 14 may also be provided in a conventional manner, for example comprising a plastic film or layer of plastic I resin encapsulant over the reference electrode 12. It will, however, be appreciated that different techniques can be used in different implementations. Although the reference electrode 12 is schematically represented in Figures 2 and 3 as being disposed on top of the frame element 2, in other examples the reference electrode may be embedded within the frame element 2. If the frame element 2 is conductive, the reference electrode 12 may be insulated therefrom. It will be appreciated the reference electrode 12 and insulator layer 14 might typically be relatively thin compared to the other elements of the sensor element 6 shown in Figures 2 and 3, but these figures are not drawn to scale with the reference electrode 12 (and its layer of insulation 14) shown with exaggerated thickness in the crosssections of Figures 2 and 3 for ease of representation.

[0041] As noted above, Figure 2 schematically represents the sensor element 6 in a rest state with no displacement load applied to the displacement element 3. In this example the gap between the upper surface of the base 2a of the frame element 2 and a lower surface of the displacement element 3 is, as indicated in Figure 2, h. This gap, h, corresponds with the height of the support element 8 in its relaxed state. In this example the support element 8 is sized to provide a gap, h, that is slightly less than the height of the deformable electrode 5, such that the deformable electrode 5 is in slight compression so there is a portion of its contact surface 7 for which there is no free space (air gap) between the deformable electrode 5 and the frame element 2, even when in the rest (non-displaced) state.

[0042] Figure 3 schematically represents the sensor element 6 in a displaced state in which a displacement load is applied to the displacement element 3. The displacement load may, for example, be provided by a user's finger pressing on the outer surface of the displacement element 3 or by a user pressing a stylus on the outer surface of the displacement element 3. The support element 8 and the deformable electrode 5 are both compressed under the action of the displacement load allowing the displacement element 3 to move along a displacement direction towards the base 2a of the frame element 2 by an amount, d. The magnitude of the displacement, d, will be a function of the force (load) applied and the combined resilience of the support element 8 and the deformable electrode 5. The displacement element 3 in Figure 3 is schematically shown as remaining parallel to the frame element when displaced, but in general it may be expected the displacement element 3 may be tilted depending on the location of the load (i.e. the value of d may be different at different positions across the displacement element 3). In this example the magnitude of the displacement is assumed to be around 0.1 cm.

[0043] As noted above, the sensing apparatus 1 is capable of capacitively detecting the displacement of the displacement element 3 using the sensing electrodes 5, 12 as will be explained herein. The sensing apparatus 1 may be configured to detect displacement of the displacement element 3 in one of two ways.

[0044] In one implementation, the sensing apparatus 1 is configured to measure the selfcapacitance of the reference electrode 12. More particularly, the controller element 4, via suitable circuitry, is configured to cause a drive signal to be applied to the reference electrode 12 and cause associated measurement circuitry (specifically, displacement capacitance measurement circuitry 4A) to obtain a measurement of the self-capacitance of the reference electrode 12.

[0045] In accordance with conventional techniques, measuring the self-capacitance of the reference electrode 12 may be performed by applying an electrical stimulus (drive signal) to the reference electrode 12 that varies in time relative to system ground (or other reference potential) and by determining the extent to which the drive signal is capacitively coupled to system ground via conductive paths in the vicinity of the reference electrode 12 that are connected to the system ground potential. In particular, applying the drive signal to the reference electrode 12 causes an electric field to form around the reference electrode 12. This field couples through the space around the reference electrode 12 back to the displacement capacitance measurement circuitry 4A via numerous conductive return paths that are part of the nearby circuitry of the sensor element 6 and any housing (e.g., such as the frame element 2) or physical elements from the nearby surroundings, etc., so completing a capacitive circuit. The overall sum of return paths is typically referred to as the “free space return path” in an attempt to simplify an otherwise hard-to-visualize electric field distribution. The important point to realise is that the drive signal is only applied to the reference electrode 12 from a single explicit electrical terminal; the other terminal is the capacitive connection via this “free space return path”. The capacitance measured by the displacement capacitance measurement circuitry 4A is the “self-capacitance” of the reference electrode 12 that is being driven relative to free space (or Earth as it is sometimes called).

[0046] In the example sensing apparatus 1 of Figures 1 to 3, the presence of the deformable electrode 5 provides a significant contribution to the extent to which the reference electrode 12 is capacitively coupled to the reference potential. The magnitude of this capacitive coupling depends on the separation between the different parts of the reference electrode 12 and the deformable electrode 5. Consequently, the magnitude of the capacitive coupling between the reference electrode 12 and the deformable electrode 5 depends on the volume between them, and therefore, this self-capacitance of the reference electrode 12 changes when the displacement element 3 is displaced under load thereby compressing the deformable electrode 5 towards the reference electrode 12. That is to say, as a consequence of the deformable electrode 5 being squashed under the displacement load, the curved contact surface 7 is pressed harder against the underlying insulator layer 14. This causes the contact surface 7 to flatten against the insulator layer 14, thereby reducing the overall volume between the deformable electrode 5 and the reference electrode 12 as compared to the rest state represented in Figure 2. The space between the deformable electrode 5 and the reference electrode 12 is schematically shown with shading in Figures 2 and 3, and it can be seen how the shading in Figure 3 occupies a smaller area than the shading in Figure 2.

[0047] When the sensing apparatus 1 is arranged to measure the self-capacitance of the reference electrode 12, the deformable electrode 5 may be coupled to a reference potential, such as the system ground or another reference potential. Specifically, the reference potential is a potential that is seen, in effect, as a DC potential to the displacement capacitance measurement circuitry 4A connected to the reference electrode 12. The reference potential could take the form of a DC potential or it could be a time-varying signal that is "out of band" with respect to the displacement capacitance measurement circuitry 4A, therefore the deformable electrode 5 feels like a return path to ground as far as the displacement capacitance measurement circuitry 4A is concerned, For simplicity the system reference potential may sometimes be referred to herein as a system ground or earth, but it will be appreciated the actual value of the potential itself may be arbitrary and is not significant (e.g. it could be 0V, 5V or 12V, or any other value according to the implementation at hand).

[0048] The specific nature of the signalling and the manner in which it indicates a degree of capacitive coupling will depend on the sensing technology adopted. The textbook "Capacitive Sensors: Design and Applications" by Larry K. Baxter, August 1996, Wiley-IEEE Press, ISBN: 978-0-7803-5351-0 [1] summarises some of the principles of conventional capacitive sensing techniques that may be used for measuring capacitance characteristics in accordance with various implementations.

[0049] In another implementation, the sensing apparatus 1 is configured to measure the mutualcapacitance between the deformable electrode 5 and the reference electrode 12. More particularly, the controller element 4 is configured to apply a drive signal (which may be different to the drive signal described above in the self-capacitance measurement implementation) to the deformable electrode 5 and cause associated measurement circuitry (specifically, displacement capacitance measurement circuitry 4A) to obtain a measurement of the mutual-capacitance between the deformable electrode 5 and the reference electrode 12.

[0050] In these implementations, the controller element 4, via suitable circuitry, is configured to cause a time-varying drive signal to be applied to the deformable electrode 5 and to measure the extent to which the drive signal is capacitively coupled to the reference electrode 12. The resulting electric field generated by applying the drive signal to the deformable electrode 5 is now directly coupled from the deformable electrode 5 to the reference electrode 12 (the “free space” return path discussed above plays a negligible part in the overall coupling back to the displacement capacitance measurement circuitry 4A when the sensing apparatus 1 is not being touched). The magnitude of the mutual capacitive coupling between the deformable electrode 5 and the reference electrode 12 similarly depends on the separation between the different parts of the reference electrode 12 and the deformable electrode 5, corresponding with the volume between them. Thus, the mutual-capacitance between the reference electrode 12 and the deformable electrode 5 changes when the deformable electrode 5 is compressed towards the reference electrode 12 under the application of a displacement load to the displacement element 3. Coupling the displacement capacitance measurement circuitry 4A to the reference electrode 12 (otherwise referred to as a receiver electrode) allows for the displacement capacitance measurement circuitry 4A to measure the mutual capacitance between the deformable electrode 5 and the reference electrode 12. Regardless of whether the sensing apparatus 1 is configured to utilise the self-capacitance measurement technique or the mutual capacitance measurement technique, the displacement capacitance measurement circuitry 4A is configured to sense the change in capacitance (either self- or mutual capacitance) resulting from a change in the relative distance I volume between parts of the deformable electrode 5 and the reference electrode 12. Accordingly, when a displacement load is applied to the displacement element 3, which causes the displacement element 3 to move towards the base 2a of the frame element 2, the displacement capacitance measurement circuitry 4A is capable of outputting a measurement of the capacitance that is dependent on the separation distance'd’ between the displacement element 3 and the base 2a of the frame element 2.

[0051] The displacement capacitance measurement circuitry 4A outputs a measure of this capacitance to the processing circuitry 4C of the controller element 4. In some cases, the processing circuitry 4C may be configured to determine an absolute value for a displacement, for example by converting an individual capacitance measurement (or average of several capacitance measurements) to a displacement (‘d’) based on a calibration function which relates capacitance measurements to displacements. The calibration function may, for example, be based on modelling or established in an initial setup procedure in accordance with conventional capacitance measurement techniques. In particular, a baseline value (corresponding to a measurement of the relevant capacitance characteristic of the reference electrode 12 when there is no displacement) may be established at various times, for example when the sensing apparatus 1 is initially turned on. The calibration function may then be used to convert differences in capacitance measurement from the baseline measurement to corresponding displacements of the displacement element 3 (i.e., corresponding displacements ‘d’). In other cases, the processing circuitry 4C may be configured to in effect provide a binary indication as to whether or not there has been a displacement greater than a threshold displacement. For example, the processing circuitry 4C may be configured to identify when there has been a change in measured capacitance that is greater than a pre-defined trigger threshold, and to determine that this corresponds with a displacement by more than an amount corresponding to the pre-defined threshold displacement. An appropriate value for the pre-defined trigger threshold in any given implementation can be established empirically having regard to the extent of displacement which is desired to trigger a determination that displaced has occurred, and may be dynamically chosen to suit a given application.

[0052] In accordance with the principles of the present disclosure, the sensing apparatus 1 is configured to use the sensing electrodes 5, 12 not only to determine the displacement of the displacement element 3 relative to the frame element 2, but also to determine the presence of an object adjacent or on the sensing surface of the displacement element 3. That is to say, the sensing apparatus 1 is configured to detect the presence of objects adjacent or touching the displacement element 3 using the sensing electrodes 5, 12.

[0053] When providing the touch sensing functionality, the controller element 4 is configured to measure the self-capacitance of the deformable electrode 5. In a similar manner to as described above with regards to sensing the self-capacitance of the reference electrode 12 as part of the displacement sensing functionality, the controller element 4 is configured to cause a drive signal to be applied, in this case, to the deformable electrode 5 and associated measurement circuitry (in this case, touch capacitance measurement circuitry 4B) to obtain a measurement of the self-capacitance of the deformable electrode 5. Measuring the selfcapacitance of the deformable electrode 5 may be performed by applying an electrical stimulus (drive signal, which may be the same or different to the drive signal applied to the reference electrode 12 when measuring the self-capacitance of the reference electrode 12 when measuring the displacement of the displacement element 3) to the deformable electrode 5 that varies in time relative to system ground (or other reference potential) and by determining the extent to which the drive signal is capacitively coupled to system ground via conductive paths in the vicinity of the deformable electrode 5 that are connected to the system ground potential. The touch capacitance measurement circuitry 4B is configured to measure the “self-capacitance” of the deformable electrode 5 that is being driven relative to free space.

[0054] Touching or approaching the deformable electrode 5 with a conductive element, such as a user’s finger or a stylus, causes some of the electric field generated by the drive signal applied to the deformable electrode 5 to couple via the object through the connected user’s body, through free space and back to the touch capacitance measurement circuitry 4B. This extra return path can be relatively strong for large objects (such as a human body), and so can give a stronger coupling of the deformable electrode’s field back to the touch capacitance measurement circuitry 4B; touching or approaching the deformable electrode 5 hence increases the self-capacitance of the deformable electrode 5. The increase is strongly proportional to the area of the applied touch and is normally weakly proportional to the touching body’s size (the latter typically offering quite a strong coupling and therefore not being the dominant term in the sum of series connected capacitances). That is, the magnitude of the capacitive coupling to the object may depend on the distance of the object and / or parts of the object to the deformable electrode 5; for example, a light touch in which a user’s finger is only just touching the sensing surface couples relatively less than a heavy touch in which the user’s finger is compressed by and spreads across the sensing surface, much like the deformable electrode 5 in respect of the reference electrode 12 in Figures 2 and 3. The touch capacitance measurement circuitry 4B is configured to sense this increase in capacitance.

[0055] In this implementation, the processing circuitry 4C is configured to receive the measured capacitance from the touch capacitance measurement circuitry 4B. In some cases, the processing circuitry 4C may be configured to determine an absolute value for the magnitude of touch, for example by converting an individual capacitance measurement (or average of several capacitance measurements) to a magnitude based on a calibration function which relates capacitance measurements to a degree of touch (for example, the extent that the user’s finger spreads across the sensing surface). The calibration function may, for example, be based on modelling or established in an initial setup procedure in accordance with conventional capacitance measurement techniques. In particular, a baseline value (corresponding to a measurement of the relevant capacitance characteristic of the deformable electrode 5 when there is no touch) may be established at various times, for example when the sensing apparatus 1 is initially turned on. The calibration function may then be used to convert differences in capacitance measurement from the baseline measurement to corresponding degrees of touch on the displacement element 3. In other cases, the processing circuitry 4C may be configured to in effect provide a binary (or ternary, etc.) indication as to whether or not there has been a displacement greater than one or more touch detection thresholds. For example, the processing circuitry 4C may be configured to identify when there has been a change in measured capacitance that is greater than a predefined trigger threshold, and to determine that this corresponds with a touch by more than an amount corresponding to the pre-defined threshold touch. An appropriate value for the pre-defined trigger threshold in any given implementation can be established empirically having regard to the extent of touch which is desired to trigger a determination that a touch has occurred, and may be dynamically chosen to suit a given application. In addition, it should be appreciated that the principles above can be used to, in effect, qualify detected touches based on their magnitude relative to one or more touch detection thresholds. For example, in some implementations, the processing circuitry 4C may be capable of distinguishing between a heavy touch and a light touch based on defining a touch detection threshold (i.e., corresponding to a capacitance measurement) corresponding to a heavy touch and a touch detection threshold corresponding to a light touch (which may be a selfcapacitance value less than the touch detection threshold corresponding to a heavy touch). In other implementations, the processing circuitry 4C may be capable of distinguishing between a light touch and a hovering touch (i.e., an object adjacent, but not contacting, the sensing surface) based on defining a touch detection threshold corresponding to a light touch and a touch detection threshold corresponding to a hovering touch (which may be a selfcapacitance value less than the touch detection threshold corresponding to a light touch).

[0056] It should be appreciated from the above that the sensing apparatus 1, or more specifically the processing circuitry 4C, is capable of providing an output that corresponds to a displacement of the displaceable element 3 and an output that corresponds to the presence of a touch at or in the vicinity of the sensing surface of the displacement element 3. Broadly speaking, the processing circuitry 4C may be capable of providing either or both of these outputs as absolute values for displacements or extents of touches or as binary / ternary outputs which may be provided to an associated apparatus which the sensing apparatus 1 is provided in conjunction with (where the associated apparatus may utilise these outputs as appropriate depending on the application at hand).

[0057] In some conventional sensing apparatuses, separate electrodes or electrode arrays are provided for the purposes of sensing whether a touch is present at, or in the vicinity of, the sensing surface of the displacement element 3 and whether there is displacement of the displacement element 3. For example, an electrode or electrode array in some conventional sensing apparatuses 1 may be provided in or on a surface of the displacement element 3. However, the inventor has recognised that the sensing apparatus 1 can be constructed at a lower cost and at lower complexity by utilising the same electrodes for both touch sensing and displacement sensing functionality.

[0058] In this regard, the controller element 4 is configured to operate the sensing apparatus 1 according to the present disclosure in a touch sensing mode in which the sensing apparatus 1 is capable of sensing an object touching or in proximity of the displaceable element 3 by obtaining the self-capacitance of the deformable electrode 5, and to operate the sensing apparatus 1 in a displacement sensing mode in which the sensing apparatus 1 is capable of sensing a displacement of the displaceable element 3 relative to the base 2a by sensing at least one of the self-capacitance of the reference electrode 12 and the mutual capacitance between the deformable electrode 5 and the reference electrode 12.

[0059] Figure 4 shows an example method for operating the sensing apparatus 1 according to the present disclosure.

[0060] Figure 4 shows the method starting at step S1 where a drive signal is applied to a first electrode, such as the deformable electrode 5. As described above, the controller element 4 is configured to cause a drive signal to be applied to the deformable electrode 5, e.g., via controlling associated circuitry to generate and supply the drive signal to the deformable electrode 5. The drive signal may take any suitable form and be applied using conventional circuitry.

[0061] At step S2, a measure of the self-capacitance of the first electrode, e.g., the deformable electrode 5, is obtained. In particular, the control element 4 is configured to cause the touch capacitance measurement circuitry 4B to obtain a self-capacitance measurement of the deformable electrode 5 while the drive signal is applied to the deformable electrode at step S1. That is to say, steps S1 and S2 may be performed substantially at the same time. A plurality of self-capacitance measurements may be obtained during step S2 over a discrete time period and an average may be determined for the time period.

[0062] Steps S1 and S2 of the method define the touch sensing mode of the sensing apparatus 1 and, as described above, it should be appreciated that the self-capacitance measurement of the deformable electrode 5 is sensitive to touches on or in the vicinity of the sensing surface of the displacement element 3. Accordingly, in the presence of a touch, the measured selfcapacitance varies (in particular, increases) when a conductive object such as a user’s finger approaches or contacts the sensing surface of the displacement element 3 relative to a baseline value of the self-capacitance of the deformable electrode 5 obtained in the absence of a touch.

[0063] Figure 4 shows the method branching to either step S3a or step S3b after step S2.

[0064] At step S3a, a drive signal is applied to a first electrode, such as the deformable electrode 5. As described above, the controller element 4 is configured to cause a drive signal to be applied to the deformable electrode 5, e.g., via controlling associated circuitry to generate and supply the drive signal to the deformable electrode 5. The drive signal may take any suitable form and be applied using conventional circuitry.

[0065] After step S3a, the method proceeds to step S4a. At step S4a, a measure of the mutualcapacitance between the first electrode, e.g., the deformable electrode 5, and a second electrode, e.g., the reference electrode 12 is obtained. In particular, the control element 4 is configured to cause the displacement capacitance measurement circuitry 4A to obtain a mutual capacitance measurement between the deformable electrode 5 and the reference electrode 12 while the drive signal is applied to the deformable electrode at step S3a. That is to say, steps S3a and S4a may be performed substantially at the same time. A plurality of mutual capacitance measurements may be obtained during step S4a over a discrete time period and an average may be determined for the time period.

[0066] At step S3b, a drive signal is applied to the second electrode, such as the reference electrode 12. As described above, the controller element 4 is configured to cause a drive signal to be applied to the reference electrode 12, e.g., via controlling associated circuitry to generate and supply the drive signal to the reference electrode 12. The drive signal may take any suitable form and be applied using conventional circuitry.

[0067] After step S3b, the method proceeds to step S4b. At step S4b, a measure of the selfcapacitance of the second electrode, e.g., the reference electrode 12, is obtained. In particular, the control element 4 is configured to cause the displacement capacitance measurement circuitry 4A to obtain a self-capacitance measurement of the reference electrode 12 while the drive signal is applied to the reference electrode 12 at step S3b. That is to say, steps S3b and S4b may be performed substantially at the same time. A plurality of self-capacitance measurements may be obtained during step S4b over a discrete time period and an average may be determined for the time period.

[0068] Steps S3a and S4a, or steps S3b and S4b of the method define the displacement sensing mode of the sensing apparatus 1 and, as described above, it should be appreciated that the mutual capacitance measurement between the deformable electrode 5 and the reference electrode 12 (as obtained at step S4a) or the self-capacitance measurement of the reference electrode 12 (as obtained at step S4b) is sensitive to the displacement of the displacement element 3 relative to the frame element 2. Accordingly, when the displacement element 3 is displaced from an at rest state (e.g., as in Figure 3), the measured mutual capacitance or measured self-capacitance varies relative to a baseline value of the mutual capacitance between the deformable electrode 5 and reference electrode 12 or of the self-capacitance of the reference electrode 12 obtained in the absence of any displacement of the displacement element 3.

[0069] After step S4a or S4b, the method proceeds to step S5 where the outputs of the respective capacitance measurement circuitries 4A, 4B are provided to the processing circuitry 4C. The processing circuitry 4C as described above is configured to process the obtained capacitance measurements and provide an output to the associated apparatus. In particular, the processing circuitry 4C is configured to receive the measured capacitance from the displacement capacitance measurement circuitry 4A and the touch capacitance measurement circuitry 4B, and perform suitable processing on these measured capacitances dependent on the implementation at hand. As described above, this may involve converting the capacitance measurements to corresponding displacements of the displacement element 3 or degrees of touch at or on the sensing surface, or providing a binary (or ternary, etc.) output of whether there is determined to be displacement of the displacement element 3 or whether there is determined to be a touch. The output is provided to an associated apparatus which is configured to use the output from the processing circuitry 4C as an input for one or more functions implemented by the associated apparatus. The associated apparatus may be configured to utilise the outputs from the processing circuitry 4C in any suitable way. For example, certain functions may be implemented when the displacement is determined to exceed a threshold or when a displacement is determined, by the processing circuitry 4C, to have occurred. In other instances, certain functions may be controlled based on the magnitude of the displacement and I or extent of the touch.

[0070] In some implementations, the controller element 4 is configured to sequentially operate in the touch sensing mode and the displacement sensing mode. That is, for a first time period, the controller element 4 is configured to operate the sensing apparatus in the touch sensing mode by causing a drive signal to be applied to the deformable electrode 5 and by causing the touch capacitance measurement circuitry 4B to obtain the self-capacitance of the deformable electrode 5 (i.e. , to perform steps S1 and S2), and for a second time period, the controller element 4 is configured to operate the sensing apparatus in the displacement sensing mode either by causing a drive signal to be applied to the reference electrode 12 and by causing the displacement capacitance measurement circuitry 4A to obtain the selfcapacitance of the reference electrode 12 (i.e., to perform steps S3a and S3b), or by causing a drive signal to be applied to the deformable electrode 5 and by causing the touch capacitance measurement circuitry 4B to obtain the mutual capacitance between the driven deformable electrode 5 and the receiver reference electrode 12 (i.e., to perform steps S3b and S4b).

[0071] The first time period and second time period need not be identical and may be set based upon certain performance characteristics for the sensing apparatus 1 including the responsiveness (i.e., how quickly the sensing apparatus 1 is capable of detecting when a touch I displacement is applied) and the sensitivity (i.e., how reliably the sensing apparatus 1 determines a touch I displacement occurs, which may be based in part on the signal to noise ratio for the respective capacitance measurements). Typically, responsiveness varies inversely with the length of the time period, while sensitivity varies proportionally with the length of the time period. In some implementations, a balance may need to be struck between these different performance characteristics in order to provide a sensing apparatus 1 with acceptable performance characteristics. When the controller element 4 is configured to sequentially operate in the touch sensing mode and the displacement sensing mode, the drive signal applied to the deformable electrode 5 in the first time period at step S1 (herein a first drive signal) may be the same or different to the drive signal applied to the reference electrode 12 during the second time period at step S3b (herein second drive signal) or the same or different to the drive signal applied to the deformable electrode 5 in the second time period at step S3a (herein third drive signal). In particular, the first and second drive signals may be selected (e.g., in terms of amplitude, frequency, waveform shape) to be suitable for obtaining the self-capacitances of the deformable electrode 5 and reference electrode 12, respectively, and may take account of other factors of the sensing apparatus 1 , such as sources of noise or the like. Suitable parameters for the first and second drive signals may be found through modelling or empirical testing. Equally, the third drive signal applied to the deformable electrode 5 in the second time period may be suitably selected for obtaining the mutual capacitance between the deformable electrode 5 and reference electrode 12. The precise parameters of the first to third drive signals may depend on the application at hand.

[0072] In accordance with some implementations, the sensing apparatus 1 is simultaneously operated in the touch sensing mode and displacement sensing mode. In particular, the controller element 4 in some implementations is configured to cause a drive signal to be applied to the deformable electrode 5 and cause the touch capacitance measurement circuitry 4B to obtain the self-capacitance of the deformable electrode 5 at step S1 and S2, while simultaneously causing the touch capacitance measurement circuitry 4B to obtain the mutual capacitance between the driven deformable electrode 5 and the receiver reference electrode 12 at steps S3a and S4a. That is to say, by applying a suitable drive signal to the deformable electrode 5, both the self-capacitance of the deformable electrode 5 (indicative of a touch) and the mutual capacitance between the deformable electrode 5 and the reference electrode 12 (indicative of a displacement) can be obtained by the respective capacitance measurement circuitries 4A, 4B. In this regard, the displacement capacitance measurement circuitry 4A is controlled, e.g., by the controller element 4, to obtain the self-capacitance measurement of the deformable electrode 5, while the touch capacitance measurement circuitry 4B is controlled, e.g., by the controller element 4, to obtain the mutual-capacitance measurement between the deformable electrode 5 and reference electrode 12 (e.g., by being controlled to couple to the reference electrode 12).

[0073] Not only does this approach avoid the need to compromise between responsiveness and sensitivity, as described in the case of sequentially operating in the touch sensing mode and displacement sensing mode above, but the sensing apparatus 1 is capable of concurrently measuring any displacement and any touch. For instance, sequentially operating in the touch sensing mode and displacement sensing mode means that any displacement that is obtained is actually indicative of the displacement in the second time period, not the first time period when the controller element 4 is operating in the touch sensing mode, meaning there may be degree of extrapolation (i.e. , prediction) required to determine the displacement at the time when a touch is detected, which may bring about some errors. This may substantially be avoided by operating the sensing apparatus 1 simultaneously in the touch sensing mode and displacement sensing mode. That is to say, the sensing apparatus 1 is capable of obtaining the self-capacitance of the deformable electrode 5 at the same time, or substantially the same time (e.g., within the same time period) as obtaining the mutual capacitance between the deformable electrode 5 and the reference electrode 12.

[0074] In such implementations, the parameters of the drive signal applied to the deformable electrode 5 may be selected to be suitable for determining the self-capacitance of the deformable electrode 5 and for determining the mutual-capacitance between the deformable electrode 5 and the reference electrode 12. Again, the properties of the drive signal may be found through modelling or empirical testing.

[0075] As noted above, the processing circuitry 4C is configured to receive the measured capacitance from the displacement capacitance measurement circuitry 4A and the touch capacitance measurement circuitry 4B, and perform suitable processing on these measured capacitances dependent on the implementation at hand. In some implementations, either the processing circuitry 4C or suitable circuitry of the associated apparatus is configured to distinguish between displacement loads applied by a non-conductive object and those applied by conductive objects (such as a stylus or user’s finger).

[0076] Figure 5 represents a modification to Figure 4 showing this modification in the context of the processing circuitry 4C. Figure 5 shows a part of the method of Figure 4 and thus will be understood from Figure 4.

[0077] In Figure 5, after step S4a or S4b, the processing circuitry 4C is configured to receive the outputs of the respective capacitance measurement circuitries 4A, 4B. In this modification, the processing circuitry 4C is capable of determining at step S4c whether any detected displacement, on the basis of the output of the displacement capacitance measurement circuitry 4A, is applied by a conductive object. In particular, it should be appreciated that when a displacement load is applied by a conductive object, which is capable of capacitively coupling to the deformable electrode 5 when the sensing apparatus 1 is operated in a touch sensing mode, the touch capacitance measurement circuitry 4B obtains a self-capacitance measurement from the deformable electrode 5 that is proportional to the coupling between the deformable electrode 5 and the conductive objection. Conversely, in cases where a non- conductive object applies the displacement load, the non-conductive object does not capacitively couple to the deformable electrode 5 and thus the touch capacitance measurement circuitry 4B obtains a self-capacitance measurement from the deformable electrode 5 that is, in effect, invariant to the presence of the non-conductive object. In either case, however, the displacement load causes the displaceable element 3 to move towards the frame 2, and this displacement is sensed via the displacement capacitance measurement circuitry 4A. Accordingly, in this example, at step S4c, the processing circuitry 4C (or in other implementations, suitable circuitry of the associated apparatus) is capable of determining whether the displacement, as sensed by the displacement capacitance measurement circuitry 4A, is due to a conductive or non-conductive object based on whether or not the touch capacitance measurement circuitry 4B also senses a change in capacitance when the displacement is detected. The processing circuitry 4C may be configured, at step S5, to output an indication indicating whether the detected displacement is caused by a conductive or non-conductive object to the associated apparatus. (Or alternatively, in other implementations, after step S5, the associated apparatus may be configured to perform similar determination on receiving the outputs from the processing circuitry 4C in Figure 4.)

[0078] In other implementations, the processing circuitry 4C is configured to verify the detected displacement of the displacement element 3 (as determined from the obtained selfcapacitance of the reference electrode 12 or the obtained mutual capacitance between the deformable electrode 5 and the reference electrode 12) based on the obtained selfcapacitance of the deformable electrode 5.

[0079] Figure 6 represents a modification to Figure 4. Figure 6 shows a part of the method of Figure 4 and thus will be understood from Figure 4.

[0080] In Figure 6, after step S4a or S4b (and also, in some implementations, after step S4c of Figure 5), the method proceeds to step S4d. At step S4d, the processing circuitry 4C is configured to verify the obtained displacement capacitance measurement in view of the obtained touch capacitance measurement. In this regard, it should be appreciated that when an object, such as a human finger or stylus, applies a displacement load to the displacement element 3, not only does the displacement element 3 become displaced from its at rest state as described above, but additionally the contact surface of the human finger or stylus spreads out across the sensing surface of the displacement element under the applied load. As described above, this can give rise to varying degrees of touch (e.g., light or heavy touch) or differing magnitudes of the capacitive coupling between the object and deformable electrode 5 when the sensing apparatus 1 is operating in the touch sensing mode.

[0081] Accordingly, the processing circuitry 4C can be configured to provide a verification of the obtained displacement capacitance measurement by comparing any determined displacement to the determined magnitude of the capacitive coupling of the object to the deformable electrode 5 (i.e., on the basis of the touch capacitance measurement). For example, if the processing circuitry 4C determines there is a relatively large displacement of the displacement element 3 (i.e., the displacement d is large) but determines there is a relatively light touch applied to the displacement element 3 based on the output of the touch capacitance measurement circuitry 4B, the processing circuitry 4C determines that the two conditions do not tally. That is, one would expect a significantly greater magnitude I extent of a touch (e.g., a relatively heavier touch) for a large amount of displacement d, as one would expect the user to apply a larger force to cause the displacement element 3 to be displaced by a larger amount and the same force to cause a user’s finger or stylus applying the force to also spread out more on the sensing surface of the displacement element 3.

[0082] Hence, based on comparing the determined displacement with the determined touch, the processing circuitry 4C is capable of verifying whether the determined displacement is consistent with the determined degree / magnitude of the touch (or alternatively, whether the determined degree / magnitude of the touch is consistent with the determined displacement). In the event that the processing circuitry 4C determines the determined displacement is consistent with the determined degree / magnitude of the touch or vice versa, then the method proceeds to step S5, substantially as described above and the obtained capacitance measurements are processed (to the extent they have not been already) and suitable signals are output from the processing circuitry 4C. In other implementations, instead of or in parallel with step S5, when the processing circuitry 4C determines the determined displacement is not consistent with the determined degree / magnitude of the touch or vice versa, then the processing circuitry 4C may output a signal indicating that the determined displacement is not consistent with the determined degree / magnitude of the touch or vice versa.

[0083] It should be appreciated that in this modification, the processing circuitry 4C may compare either the outputs from the displacement and touch capacitance measurement circuitries 4A, 4B before performing any processing and thus verify the respective capacitance measurements or the processing circuitry 4C may perform processing on the outputs from the displacement and touch capacitance measurement circuitries 4A, 4B (e.g., to determine the displacement and / or extent or magnitude of the touch) before performing the verification of the determined displacement / extent of touch.

[0084] Figure 7 is a further modification to the method of Figure 6, and subsequently will be understood from Figure 6. In Figure 7, after step S4a or S4b (and also, in some implementations, after step S4d of Figure 6), the method proceeds to step S4e. At step S4e, the processing circuitry 4C is configured to determine a correction factor which is to be applied to either the output of the displacement capacitance measurement circuitry 4A or the processed output of the displacement capacitance measurement circuitry 4A (i.e., the determined displacement ‘d’). In this regard, the processing circuitry 4C is configured to determine a correction factor which, when applied to the displacement capacitance measurement, brings the displacement capacitance measurement more into line with an expected value of the displacement capacitance measurement in view of the obtained touch capacitance measurement. For example, in some implementations, there may be nonintended changes in the force sensing measurement caused by a touch on the displacement element 3, which could be caused by imperfections in the driving of the deformable electrode 5 e.g., such as source impedance. Thus, this may result in a larger indicated change in the self-capacitance measurement of the deformable electrode 5 (i.e., the displacement capacitance measurement), and thus this affect may be compensated for by calculating a correction factor to be applied to the displacement capacitance measurement. Put another way, the processing circuitry 4C may be provided with relationship data that provides an expected relationship between measured touch capacitance measurements and a corresponding expected displacement capacitance measurement. On the basis of the obtained touch capacitance measurement, the processing circuitry 4C may identify the corresponding expected displacement capacitance measurement. Comparing the expected displacement capacitance measurement with the actual displacement capacitance measurement may reveal that there is some deviation between these two values, and thus the processing circuitry 4C may determine a corresponding correction factor (which may be an absolute value or a function dependent on one or more variables) which is to be applied to the obtained displacement capacitance measurement. This can be thought of as effectively performing a calibration I compensation during use of the sensing apparatus 1.

[0085] The processing circuitry 4C may apply the correction factor to each of the displacement capacitance measurements once calculated, but in some implementations, the processing circuitry 4C does not calculate a correction factor each time a touch capacitance measurement is obtained. For example, periodically, such as once an hour, once a day, etc. the processing circuitry 4C is configured to determine the correction factor which may be subsequently applied to future measurements of the displacement capacitance measurement until the subsequent calculation of the correction factor. Alternatively, the correction factor may be determined each time the verification step S4d reveals that the displacement is not consistent with the determined degree / magnitude of the touch.

[0086] It should be appreciated that in this modification, the processing circuitry 4C may determine the corrector factor either from the outputs of the displacement and touch capacitance measurement circuitries 4A, 4B (i.e., prior to performing any processing on the respective capacitance measurements) or the processing circuitry 4C may determine the correction factor based on the processed outputs from the displacement and touch capacitance measurement circuitries 4A, 4B (e.g., to determine the displacement and / or extent or magnitude of the touch). Correspondingly, the correction factor may be applied to the obtained capacitance measurements from the respective capacitance measurement circuitries 4A, 4B or the processed capacitance measurements accordingly.

[0087] As described above, the deformable electrode 5 and reference electrode 12 are configured to sense both a displacement and the presence of a touch via capacitive sensing.

[0088] However, it should be understood that the capacitance measurements of displacement may be affected by the presence of a touch at or on the displacement element 3 and, equally, the capacitance measurements in respect of sensing a touch at the sensing surface may be affected by the displacement of the displacement element 3 relative to the frame element 2. For example, as noted above, the presence of a user’s finger affects the self-capacitance or mutual capacitance of a driven electrode, and equally, the distance between a driven electrode and a reference electrode may also affect the measurement of self-capacitance of the driven electrode.

[0089] For example, in order to help reduce or eliminate the impact of a change in capacitance resulting from a touch I object on the measured change in capacitance caused by displacement of the displacement element 3, or vice versa, the touch apparatus 1 may be configured as follows. In some implementations, the geometry of the deformable electrode 5 is such that the deformable electrode 5 covers (i.e., extends across) the reference electrode 12 as viewed from above (e.g., as viewed in Figure 1). In this way, the capacitance measurement made by the displacement capacitance measurement circuitry 4A is unaffected by any changes in capacitance caused by a touch I object on or in the vicinity of the displacement element 3. That is to say, the capacitance measurement made by the displacement capacitance measurement circuitry 4A does not react or change due to touch, but only due to displacement of the displacement element 3. In other implementations, these cross-couplings may be compensated for using a driven shield, thereby acting to isolate the two capacitance measurements from each other.

[0090] For example, when operating in the touch sensing mode, in some cases, there may be a change in the self-capacitance measurement of the deformable electrode 5 caused purely by displacement of the displaceable element 3. In some cases, this may mean that the sensing apparatus 1 cannot differentiate between pushing the displacement element 3 with a non- conductive object, and a pushing the displacement element 3 with a user’s finger (both can create similar changes in self-capacitance and mutual-capacitance). To help counteract this, the deformable electrode 5 may be surrounded with another electrode (not shown) that is driven with a duplicate of the drive signal (i.e. , it has substantially the same amplitude, same frequency, and same waveform, where substantially means, e.g., within a 5% deviation) applied to the deformable electrode 5. This another electrode acts as a driven shield, which is known in the field. This driven electrode serves to effectively neutralise parasitic capacitances between the deformable electrode 5 and its environment (because the driven shield surrounds the deformable electrode 5 except on the surface facing towards the displaceable element 3, and it is driven with a substantially similar drive signal to the deformable electrode 5 which hence causes little or no current to flow even under deformation of the deformable electrode 5).

[0091] Alternatively or additionally, the reference electrode 12 may be driven with such a drive signal that is the same or similar to the drive signal applied to the deformable electrode 5 (i.e., it has substantially the same amplitude, same frequency, and same waveform, where substantially means, e.g., within a 5% deviation). In this way, the reference electrode 12 acts as a driven shield for the deformable electrode 5 effectively causing the deformable electrode 5 to be isolated from changes caused by movement (i.e., applied pressure to the displacement element 3). Hence, the self-capacitance measurement of the deformable electrode 5 serves to detect a touch or the proximity of an object but to be mostly immune to changes caused by the applied load.

[0092] The deformable electrode 5 could potentially adopt any of many different shapes. In some cases it may be helpful if the face that overlaps the reference electrode 12 does so with a relatively shallow (but non-zero, for example greater than 5 degrees) angle of incidence, for example, at an angle less than 45 degrees, such as an angle less than 40 degrees, less than 35 degrees, less than 30 degrees, less than 25 degrees, less than 20 degrees, less than 15 degrees, less than 10 degrees. This can help mean that a small vertical displacement is translated to a relatively large change in overlap area by virtue. It may also include “side walls” that run substantially vertically so that a small vertical displacement is transmitted in a direct way to the inclined surface(s) (between the deformable electrode 5 and reference electrode 12) so causing the desired change in surface area.

[0093] The deformable electrode 5 may be supplied with the corresponding drive signal in any suitable manner. Figure 8 schematically shows one such example where the sensing apparatus 1 is provided with a drive signal supply track 5a provided on the base 2a of the frame element 2. Figure 8 is based on Figure 2 and will be understood therefrom. Only the differences with respect to Figure 2 are described herein.

[0094] As can be seen in Figure 8, directly below the contact surface 7 of the deformable electrode 5, the drive signal supply track 5a is provided on the surface of the frame element 2. The drive signal supply track 5a is provided in direct electrical contact with the deformable electrode 5. The drive signal supply track 5a is electrically coupled at the other end to circuitry capable of generating the drive signal form the deformable electrode 5. Hence, it should be appreciated that the drive signal supply track 5a is capable of supplying the generated drive signal to the deformable electrode 5. Providing this configuration is advantageous as the drive signal supply track 5a is provided on the frame element 2, which already comprises the reference electrodes 12, as opposed to the displacement element 3. In particular, this may mean that the displacement element 3 can be kept relatively free of electrodes.

[0095] As also seen in Figure 8, the reference electrode 12 is split into a plurality of parts, namely a first reference electrode 12a and a second reference electrode 12b, provided either side of the drive signal supply track 5a. In a broadly similar manner to Figures 1 to 3, the first and second reference electrodes 12a, 12b are electrically isolated from the deformable electrode 5 by an insulating layer 14, but in this implementation the first and second reference electrodes 12a, 12b are also electrically isolated from the drive signal supply track 5a via the insulating layer 14. The operation of the sensing apparatus of Figure 8 is broadly similar to the operation as described above. That is, the displacement measurement circuitry 4A is configured to either measure the self-capacitance of one or both the first and second reference electrodes 12a, 12b (and, e.g., sum the contributions from each electrode) or to measure the mutual capacitance of one or both the first and second reference electrodes 12a, 12b (and, e.g., sum the contributions from each electrode) in the displacement sensing mode.

[0096] In the described implementations, such as Figures 1 to 3, the reference electrode 12 is shown as being located, in effect, as a rectangular block or blocks below the deformable electrode 5. However, the reference electrode 12 may be shaped in such a way to maximise a range of overlap with the deformable electrode 5 as the displacement element 3 is moved relative to the frame element 2.

[0097] Figures 9a and 9b show, schematically and in perspective view, two example arrangements of the reference electrode(s) 12 of the sensing apparatus 1. It should be appreciated that Figures 9a and 9b are shown with several aspects of the sensing apparatus 1 omitted for clarity. In fact, Figures 9a, 9b show only the deformable electrode 5, the drive signal supply track 5a, the base of the frame 2a and the two reference electrode patterns 12c, 12d as will be explained below.

[0098] In Figure 9a, the reference electrode 12c is formed of a plurality of ring or annular electrodes 12c of varying diameters provided concentrically about an axis of the deformable electrode 5 and an axis of the drive signal supply track 5a (which in this implementation is a circular contact pad). In this regard, the deformable electrode 5 is shown as a hemi-spherical dome, where it should be appreciated that the circular face of the deformable electrode 5 is provided adjacent the underside or lower surface of the displacement element 3. The ring or annular electrodes 12c are provided concentrically with the axis defining the radius of curvature of the deformable electrode 5 that is perpendicular to the plane of the base 2a of the frame element 2. Each of the ring or annular electrodes 12c may be electrically coupled (either individually or in series) to the displacement capacitance measurement circuitry 4A.

[0099] In Figure 9b, the reference electrode 12d is formed of a plurality of linear electrodes 12d extending from a point directly below the axis of the deformable electrode 5 and centred on the axis of the drive signal supply track 5a (which in this implementation is a circular contact pad). The linear electrodes 12d are arranged in a “sunburst” type pattern whereby the separation distance between two adjacent electrodes 12d increases the further from the point along the direction of extent of the electrodes 12d. Each of the linear electrodes 12d may be electrically coupled (either individually or in series) to the displacement capacitance measurement circuitry 4A.

[0100] In other implementations, the reference electrode 12 may be in the form of a zig-zag trace, or a linked set of diamond shapes. However, any suitable arrangement of the reference electrode 12 may be applied in accordance with the principles of the present disclosure.

[0101] By arranging the reference electrode 12 as described in Figures 9a or 9b, the overall capacitance of the reference electrode 12 can be minimized (compared to just using a wide plain strip trace), whilst achieving a wider range of operation as the deformable electrode 5 squashes down onto the surface. This may also be significant for implementations where a display or light-emitting element is provided below the base 2a of the frame element 2, such that the reference electrode 12 provided in one of the aforementioned patterns may offer greater flexibility to designers of the sensing apparatus 1 (that is, the reference electrode 12 need not be formed of a transparent material, such as transparent indium tin oxide (ITO), but instead the reference electrodes 12 may be arranged in a pattern which can reduce the presence of visual interference I visual artefacts).

[0102] In respect of configurations of the sensing apparatus 1 where a backlight or display element is provided below the deformable electrode 5 (and optionally below the base 2a of the frame element 2), the deformable electrode 5 may be configured to permit light either from the light emitting element or the display element to pass to (and through) the displacement element 3.

[0103] In some implementations, the deformable electrode 5 may be formed from a suitable transparent and electrically conductive material, for example, such as transparent indium tin oxide (ITO). Other transparent and electrically conductive materials may be employed in other implementations.

[0104] However, in some implementations, it may not be practical or feasible to form the deformable electrode 5 from a conductive and transparent material. Figures 10a and 10b schematically illustrate two example arrangements where the deformable electrode 5 is structurally configured to permit light to pass from the direction of the base 2a of the frame element toward the underside of the displacement element 3. Figures 10a and 10b schematically show, in perspective view, two example arrangements of the deformable electrode 5 of the sensing apparatus 1. It should be appreciated that Figures 10a and 10b are shown with several aspects of the sensing apparatus 1 omitted for clarity. In fact, Figures 9a, 9b show only the deformable electrode and the base 2a of the frame 2.

[0105] In Figure 10a, the deformable electrode 5b is formed with a central hole or opening 51 provided therein which extends along an axis of the deformable electrode 5b parallel to the direction from the base 2a of the frame towards the displacement element 3. The central opening 51 extends completely through the deformable electrode 5b from one side to the other, thereby providing a pathway for light to pass through the deformable electrode 5b and to the displacement element 3.

[0106] In Figure 10b, the deformable electrode is formed from a plurality of discrete deformable electrodes 5c to 5f. The plurality of discrete deformable electrodes 5c to 5f in this example together have approximately the same shape as the deformable electrode 5 of Figure 9a or 9b (i.e., a hemispherical dome), and thus individually comprise a segment of this shape. Each of the plurality of discrete deformable electrodes 5c to 5f are spaced apart from each other to define a gap therebetween (in this example, a cross-shaped gap). The gap defined between the plurality of discrete deformable electrodes 5c to 5f allows light to pass to the displacement element 3. That is, the gap provides a pathway for light to pass through the gap and around the plurality of discrete deformable electrodes 5c to 5f to the displacement element 3.

[0107] It should be appreciated that Figures 10a and 10b are examples only and the configuration of the deformable electrode 5, 5b, 5c-5f may differ depending on the application at hand.

[0108] It should be appreciated from the above that the sensing apparatus 1 is configured to sense both the displacement of the displacement element 3 and the presence (or absence) of a touch on or above the sensing surface of the displacement element 3 using the sensing electrodes 5, 12. In respect of the touch sensing functionality, it has been described above that the self-capacitance of a deformable electrode 5 is used to signify whether a touch is detected or not, and optionally a magnitude or classification (i.e., light, heavy, or hovering) of the touch. However, the sensing apparatus 1 as described above is unable to determine where on the sensing surface of the displacement element 3 the touch is applied. That is to say, the sensing apparatus 1 as described above is only capable of detecting the present or absence, and optionally the strength, of a touch, but not the relative position thereof.

[0109] Furthermore, whereas the above-described embodiments have focused on arrangements in which the reference electrode 12 is underneath the deformable electrode 5 from the point of view of the direction from which the load is applied, in another configuration the reference electrode 12 could be on top of the deformable electrode 5 (i.e. on the same side as that from which the load is applied). For example, the reference electrode 12 may be provided on an underside of the displacement element 3 in a configuration that is otherwise in accordance with represented that in Figures 1 to 3.

[0110] In some implementations, the sensing apparatus 1 is configured so as to comprise a plurality of deformable electrodes 5, for example arranged in a matrix or grid type arrangement, in conjunction with a plurality of reference electrodes 12 (or reference electrode patterns) correspondingly arranged.

[0111] Figure 11 schematically shows a configuration of a sensing apparatus T according to an implementation in which a plurality of deformable electrodes 5 are provided in a matrix or grid-type arrangement relative to the displacement element 3. Figure 11 will be understood from Figure 1, and like components are shown with corresponding reference signs. A description thereof will not be repeated. Not shown in Figure 11 are a plurality of reference electrodes 12 corresponding to each of the deformable electrodes 5. The reference electrodes 12 are provided in a similar manner to the reference electrode 12 of Figure 1. That is, the deformable electrode 5 is provided overlapping (i.e., having a greater areal extent than) the reference electrode 12 when viewed from a direction parallel to the normal of the sensing surface of the displacement element 3.

[0112] In such configurations, the controller element 4 is capable of receiving capacitance measurements in respect of each combination of the deformable electrode 5 and reference electrode 12. That is to say, in the example above, the displacement element 3 is a rectangular shape, and ten deformable electrodes 5 are provided, in each of ten different regions of the displacement element 3, and the controller element 4 is configured to obtain capacitance measurements from each of the ten regions.

[0113] In this regard, when operating in the touch sensing mode, the touch capacitance measurement circuitry 4B is configured to obtain the self-capacitance measurements for each of the plurality of deformable electrodes 5. The touch capacitance measurement circuitry 4B may be provided with a plurality of channels to receive self-capacitance measurements from each of the individual deformable electrodes in parallel, or alternatively the touch capacitance measurement circuitry 4B may be configured to sequentially obtain a self-capacitance measurement from each of the deformable electrodes 5 in discrete time periods. In some implementations, it may be necessary to couple those deformable electrodes that are not currently being sensed by the touch capacitance measurement circuitry 4B to ground or the system potential.

[0114] When operating in the displacement sensing mode, the displacement capacitance measurement circuitry 4A is configured to obtain either the self-capacitance measurements for each of the respective reference electrodes 12 or the mutual capacitance measurements between each of the plurality of deformable electrodes 5 and the respective reference electrodes. The displacement capacitance measurement circuitry 4A may be provided with a plurality of channels to receive self-capacitance measurements I mutual capacitance measurements from each of the reference electrodes 12 in parallel, or alternatively the displacement capacitance measurement circuitry 4A may be configured to sequentially obtain a self-capacitance measurement or mutual-capacitance measurement from each of the reference electrodes 12 in discrete time periods. In some implementations, it may be necessary to couple those deformable electrodes and / or reference electrodes 12 that are not currently being sensed by the displacement capacitance measurement circuitry 4A to ground or the system potential.

[0115] Accordingly, it should be appreciated that by providing a plurality of deformable electrodes 5 and reference electrodes 12 that are spatially arranged across the sensing surface of the displacement element 3, the controller element 4 is capable of determining relative locations of a detected touch at or adjacent the sensing surface and / or of displacements of the displacement element 3. For example, if a touch and displacement are determined to be present in one of the ten regions of the sensing surface, the processing circuitry 4C can be configured to output not only an indication that a touch and a displacement are detected, but additionally that the touch and displacement are detected in a particular location (e.g., region). The associated apparatus receiving this output from the controller element 4 may be arranged to perform different functions depending on the locations of the identified touch and / or displacement. (For example, the displacement element 3 may be used as a keypad, and thus different numbers or keys corresponding to a user’s input may be identified by the associated apparatus based on the location of the detected touch and / or displacement.)

[0116] It should be appreciated that the principles described above may be extended to systems having more than ten deformable electrodes 5 and having more complex shapes than a rectangular sensing surface.

[0117] Figure 12 represents an alternative configuration of a sensing apparatus. The alternative sensing apparatus comprises an alternative sensor element 106 and the controller element 4 as described previously. Figure 12 schematically shows, in cross-section, the alternative configuration for the sensor element 106 of the sensing apparatus.

[0118] The alternative sensor element 106 of Figure 12 is broadly similar to the sensor element 6 described above but has some structural differences. In particular, instead of the frame element 2 and displacement element 3, the sensor element 106 comprises a flexible substrate 101 , such as a flexible PCB, having a longitudinal extent and which is arranged (e.g., folded or bent) such that a first part or region (herein referred to as a base 102) is overlapped with a second part or region (herein referred to as a displacement part 103).

[0119] A reference electrode 112 is provided on a surface of the first part 102 of the substrate 101. The reference electrode 112 is, functionally, the same as reference electrode 12 of the sensing apparatus 1 although the reference electrode 112 may have a different structural configuration. A second electrode 105 is provided on a surface of the second part 103 of the substrate 101. The second electrode 105 is, functionally, the same as the deformable electrode 5 of the sensing apparatus 1 although the second electrode 105 has a different structural configuration. In particular, in this implementation, the second electrode 105 is a flat plate-like electrode 105 disposed on the surface of the substrate 101.

[0120] The reference electrode 112 and the second electrode 105 are provided on the same surface of the substrate 101 but spaced in the longitudinal direction of the substrate. (That is to say, the first part 102 and the second part 103 define longitudinally separated parts of the substrate.) Between the first part 102 comprising the reference electrode 112 and the second part 103 comprising the second electrode 105, a bending or folding axis may be defined, which is perpendicular to the longitudinal extent of the substrate 101.

[0121] Accordingly, it should be understood that when the substrate is bent or folded about the bending or folding axis, the first part 102 and the second part 103 are able to be provided in an overlapping configuration, as shown in Figure 12. In addition, the substrate 101 is bent or folded such that the reference electrode 112 and the second electrode 105 face each other. To prevent the reference electrode 112 and the second electrode 105 from electrically contacting one another, a compressible insulating substrate 114, such as a non-conductive polymer foam, air, gel or the like, is disposed between the reference electrode 112 and the second electrode 105.

[0122] Optionally, the sensor element 106 comprises a cover or protective layer 120 which is disposed adjacent to the surface of the second part 103 of the substrate 101 opposite to the surface that comprises the second electrode 105. The cover or protective layer 120 may be provided if the surface of the substrate 101 opposite to the surface that comprises the second electrode 105 is not suitable for contacting an object, such as a user’s finger, in operation, or simply to provide better rigidity or protection for the sensor element 106.

[0123] The operation of the sensing apparatus is broadly similar to the operation of the sensing apparatus 1 described above. A user may apply a displacement load to the second part 103 of the substrate 101 , either directly to the substrate 101 or via the optional cover layer 120, in a similar manner to a user applying a displacement load to the displacement element 3 in sensing apparatus 1. In this example, the second part 103 is arranged to move relative to the first, base part 102 by virtue of the flexibility that is provided by the bent or folded section of the substrate 101. That is to say, the folded or bent section enables relative movement of the first part 102 and second part 103 (specifically toward and away from each other) under application of a force I displacement load. The insulating layer 114 may deform (squash) as the displacement load is applied to the second part 103 of the substrate 101. In a similar manner to as described above, the controller element 4 is configured to operate the sensing apparatus according to the present disclosure in a touch sensing mode in which the sensing apparatus is capable of sensing an object touching or in proximity of the second electrode 105 / second part 103 of the sensor element 106 by obtaining the self-capacitance of the second electrode 105, and to operate the sensing apparatus in a displacement sensing mode in which the sensing apparatus is capable of sensing a displacement of the second part 103 relative to the first or base part 102 by sensing at least one of the selfcapacitance of the reference electrode 112 and the mutual capacitance between the second electrode 105 and the reference electrode 112. In the alternative sensor element 106, the self-capacitance of the reference electrode 112 or the mutual-capacitance between the reference electrode 112 and the second electrode 105 varies based on the separation distance between the reference electrode 112 and the second electrode 105.

[0124] Additionally shown for completeness in Figure 12 is an optional third electrode 130 which is configured to act as a driven shield behind the reference electrode 112 to isolate the second electrode 105 from any changes that might be induced from the behind the sensor element 106, e.g., mechanical movements or distortions, as described above.

[0125] The alternative sensor element 106 of Figure 12 provides a more simple construction of the sensor element, and therefore may further reduce costs, materials, and manufacturing complexity.

[0126] Thus there has been described a capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus. The capacitive sensing apparatus includes a base, a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base, a first electrode positioned adjacent the displacement element, a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode, measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode, and control circuitry. The control circuitry is configured to: operate the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operate the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode. Also described is an apparatus comprising the sensing apparatus and a method for operating a capacitive sensing apparatus. Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. It will be appreciated that features of the dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claims.

[0127] REFERENCES

[0128] [1] Capacitive Sensors: Design and Applications by Larry K. Baxter, August 1996, Wiley- IEEE Press, ISBN: 978-0-7803-5351-0

Claims

CLAIMS1. A capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus, the capacitive sensing apparatus comprising: a base; a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base; a first electrode positioned adjacent the displacement element; a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode; measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode; and control circuitry, wherein the control circuitry is configured to: operate the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operate the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the selfcapacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode.

2. The capacitive sensing apparatus of claim 1 , wherein, in the touch sensing mode, the control circuitry is configured to cause a first drive signal to be applied to the first electrode and to cause the measurement circuitry to obtain the self-capacitance of the first electrode.

3. The capacitive sensing apparatus of claim 2, wherein, in the touch sensing mode, the control circuitry is configured to cause a second drive signal to be applied to the second electrode, the second drive signal being the same or close to the first drive signal, the second electrode acting as a driven shield for the first electrode.

4. The capacitive sensing apparatus of any of the preceding claims, wherein, in the displacement sensing mode, the control circuitry is configured to couple the first electrode to ground or a constant potential, and to cause a third drive signal to be applied to the second electrode and to cause the measurement circuitry to obtain the self-capacitance of the second electrode.

5. The capacitive sensing apparatus of claim 1 or 2, wherein, in the displacement sensing mode, the control circuitry is configured to cause a fourth drive signal to be applied to the first electrode and to cause the measurement circuitry to obtain the mutualcapacitance between the first electrode and the second electrode.

6. The capacitive sensing apparatus of any of the preceding claims, wherein the control circuitry is configured to sequentially operate the capacitive sensing apparatus in the touch sensing mode for a first time period and to operate the capacitive sensing apparatus in the displacement sensing mode for a second time period.

7. The capacitive sensing apparatus of claim 5, wherein the control circuitry is configured to simultaneously operate the capacitive sensing apparatus in the touch sensing mode and the displacement sensing mode, wherein the control circuitry is configured to cause the measurement circuitry to obtain the self-capacitance of the first electrode and simultaneously the mutual-capacitance between the first electrode and second electrode.

8. The capacitive sensing apparatus of any of the preceding claims, wherein the control circuitry is configured to determine whether a displacement, as sensed by at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode, occurs from an electrically conductive or electrically non- conductive object based on the obtained self-capacitance of the first electrode.

9. The capacitive sensing apparatus of any of the preceding claims, wherein the control circuitry is configured to use the obtained self-capacitance of the first electrode obtained in the touch sensing mode to verify the at least one of the obtained self-capacitance of the second electrode and the obtained mutual capacitance between the first electrode and the second electrode.

10. The capacitive sensing apparatus of claim 9, where on the basis of the verification, the control circuitry is configured to apply a correction factor to the at least one of theobtained self-capacitance of the second electrode and the obtained mutual capacitance between the first electrode and the second electrode and use at least one of the corrected self-capacitance of the second electrode and the corrected mutual capacitance between the first electrode and the second electrode to determine the displacement of the displacement element.

11. The capacitive sensing apparatus of any of the preceding claims, wherein the first electrode is positioned so as to overlie the second electrode.

12. The capacitive sensing apparatus of any of the preceding claims, wherein the first electrode is configured to permit light to pass to the displacement element, wherein either: the first electrode is configured to comprise an opening through which light is able to pass to the displacement element; the first electrode is formed from a transparent material through which light is able to pass to the displacement element; or the first electrode comprises a plurality of discrete electrodes, each of the plurality of discrete electrodes spaced apart from each other and defining a gap therebetween through which light is able to pass to the displacement element.

13. The capacitive sensing apparatus of any of the preceding claims, wherein the first electrode is a deformable electrode, wherein the deformable electrode has a surface facing toward the base insulated from the second electrode by an insulator layer, and wherein at least part of the surface is inclined relative to an opposing surface of the base such that when the deformable electrode is compressed along the displacement direction there is a reduction in volume between the surface and the opposing surface of the base.

14. The capacitive sensing apparatus of any of claims 1 to 13, wherein the capacitive sensing apparatus comprises a substrate, the substrate having a longitudinal extent and comprising a first region comprising the first electrode and a second region, spaced in the longitudinal direction from the first region, comprising the second electrode, and wherein the substrate is folded or bent along an axis perpendicular to the longitudinal extent of the substrate and between the first region and the second region, such that the first region is arranged to overlie the second region, and wherein the second region of the substrate is adjacent to, or forms, the base.

15. An apparatus comprising the sensing apparatus of any preceding claim.

16. A method for operating a capacitive sensing apparatus for sensing an object touching or in proximity of the capacitive sensing apparatus and for sensing a displacement of a displacement element of the capacitive sensing apparatus, the capacitive sensing apparatus comprising, a base, a displacement element movably mounted relative to the base and capable of moving, under application of a force, along a displacement direction towards or away from the base, a first electrode positioned adjacent the displacement element, a second electrode positioned adjacent the base, wherein the second electrode is positioned closer to the base than the first electrode and spaced apart from the first electrode, measurement circuitry, for obtaining capacitance measurements from the first electrode and the second electrode, and control circuitry, wherein the method comprises: operating the capacitive sensing apparatus in a touch sensing mode in which the capacitive sensing apparatus is capable of sensing an object touching or in proximity of the displacement element by obtaining the self-capacitance of the first electrode, and operating the capacitive sensing apparatus in a displacement sensing mode in which the capacitive sensing apparatus is capable of sensing a displacement of the displacement element relative to the base by sensing at least one of the self-capacitance of the second electrode and the mutual capacitance between the first electrode and the second electrode.

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