WO2018234749A1

WO2018234749A1 - Device for processing signals from a pressure-sensing touch panel

Info

Publication number: WO2018234749A1
Application number: PCT/GB2018/051598
Authority: WO
Inventors: Babak Bastani
Original assignee: Cambridge Touch Technologies, Ltd
Priority date: 2017-06-19
Filing date: 2018-06-12
Publication date: 2018-12-27
Also published as: GB2563601A; GB201709757D0; GB2563601B

Abstract

A device (44) for processing signals from a projected capacitance touch panel (43) is described. The touch panel (43) including a layer of piezoelectric material (9) disposed between a plurality of first electrodes (7) and at least one second electrode (8). The device includes a multiplexer (49) comprising a plurality of inputs and an output. The device also includes a plurality of amplification stages (50), each amplification stage including an input configured to receive signals from a corresponding first electrode, and an output coupled to a corresponding input of the multiplexer. The device also includes at least one signal splitter stage (12, 13), each signal splitter stage configured to generate, based on signals received from a given first electrode, a pressure signal (15) indicative of a pressure applied to the touch panel proximate to the given first electrode and a capacitance signal (16) indicative of a capacitance of the given first electrode.

Description

Device for processing signals from a pressure-sensing touch panel Field of the invention

The present invention relates to a device for processing signals from a pressure-sensing projected capacitance touch panel, and to a touch panel system including the device.

Background

Resistive and capacitive touch panels are used as input devices for computers and mobile devices. One type of capacitive touch panel, projected capacitance touch panels, is often used for mobile devices because an exterior layer may be made of glass, providing a hard surface which is resistant to scratching. An example of a projected capacitance touch panel is described in US 2010/0079384 Ai.

Projected capacitance touch panels operate by detecting changes in electric fields caused by the proximity of a conductive object. The location at which a projected capacitance touch panel is touched is often determined using an array or grid of capacitive sensors. Although projected capacitance touch panels can usually differentiate between single-touch events and multi-touch events, they suffer the drawback of not being able to sense pressure. Thus, projected capacitance touch panels tend to be unable to distinguish between a relatively light tap and a relatively heavy press. A touch panel which can sense pressure can allow a user to interact with a device in new ways by providing additional information to simply position of a touch.

Different approaches have been proposed to allow a touch panel to sense pressure. One approach is to provide capacitive sensors which include a gap whose size can be reduced by applied pressure, so as to produce a measureable difference in the mutual capacitance. For example, US 2014/043289 A describes a pressure sensitive capacitive sensor for a digitizer system which includes an interaction surface, at least one sensing layer operable to sense interaction by mutual capacitive sensing, and an additional layer comprising resilient properties and operable to be locally compressed responsive to pressure locally applied during user interaction with the capacitive sensor. However, the need for a measureable displacement may make it more difficult to use a glass touch surface and may cause problems with material fatigue after repeated straining.

Other pressure sensitive touch panels have proposed using one or more discrete force sensors supporting a capacitive touch panel, such that pressure applied to the capacitive touch panel is transferred to one or more sensors located behind the panel or disposed around the periphery. For example, US 2013/0076646 Ai describes using strain gauges with a force sensor interface which can couple to touch circuitry.

WO 2012/031564 Ai describes a touch panel including a first panel, a second panel, and a displacement sensor sandwiched between the first panel and the second panel. The displacement sensors, such as capacitive or piezoresistive sensors, are placed around the edge of the second panel. However, it may be difficult to distinguish the pressure of multiple touches using sensors located behind a touch panel or disposed around the periphery.

Other pressure sensitive touch panels have been proposed which attempt to combine capacitive touch sensing with force sensitive piezoelectric layers. For example, WO 2009/ 150498 A2 describes a device including a first layer, a second layer, a third layer, a capacitive sensing component coupled to the first layer, and a force sensing component coupled to the first layer and the third layer and configured to detect the amount of force applied to the second layer. WO 2015/046289 Ai describes a touch panel formed by stacking a piezoelectric sensor and an electrostatic sensor. The piezoelectric sensor is connected to a pressing force detection signal generation unit, and the electrostatic sensor is connected to a contact detection signal generation unit. However, systems which use separate electronics to sense changes in capacitance and pressures may make a touch panel more bulky and expensive. Systems in which electrodes are directly applied or patterned onto a piezoelectric film can be more complex and expensive to produce. WO 2016/ 102975 A2 describes apparatus and methods for combined capacitance and pressure sensing in which a single signal is amplified then subsequently separated into pressure and capacitance components. GB 2544353 A describes apparatus and methods for combined capacitance and pressure sensing in which a single signal is separated into a capacitance signal and a pressure signal which is amplified. Summary

According to a first aspect of the invention there is provided a device for processing signals from a projected capacitance touch panel including a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode. The device includes a multiplexer comprising a plurality of inputs and an output. The device also includes a plurality of amplification stages, each amplification stage including an input configured to receive signals from a corresponding first electrode, and an output coupled to a corresponding input of the multiplexer. The device also includes at least one signal splitter stage, each signal splitter stage configured to generate, based on signals received from a given first electrode, a pressure signal indicative of a pressure applied to the touch panel proximate to the given first electrode and a capacitance signal indicative of a capacitance of the given first electrode.

Each amplification stage may include a charge amplifier.

At least one signal splitter stage may include a signal splitter stage connected to the multiplexer output and configured to split signals received from the multiplexer output into first and second signals, to pass the first signal to a first frequency dependent filter configured to attenuate the pressure signal and pass the capacitance signal, and to pass the second signal to a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal. The first and second frequency dependent filters may include active or passive filter circuits.

The signal splitter stage may include a data processing device configured to apply the first and second frequency dependent filters to signals received from the multiplexer output.

At least one signal splitter stage may include a plurality of signal splitter stages, each signal splitter stage configured to receive signals from a corresponding first electrode and split the received signals into first and second signals, to pass the first signal to a first frequency dependent filter configured to attenuate the pressure signal and pass the capacitance signal, and to pass the second signal to a corresponding amplification stage.

Each signal splitter stage may be further configured to pass the second signal to a corresponding amplification stage via a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal.

Each amplification stage may include a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal.

Each amplification stage may include an amplifier having a frequency bandwidth configured to attenuate the capacitance signal.

A touch panel system may include the device and a projected capacitance touch panel which includes a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode. The device may be connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding first electrode. The touch panel system may also include a second device. The projected capacitance touch panel may also include a plurality of third electrodes separated from the at least one second electrode by the layer of piezoelectric material. The second device may be connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding third electrode. Each first electrode may extend in a first direction and the plurality of first electrodes may be disposed in an array spaced apart in a second, different direction. Each third electrode may extend in the second direction and the plurality of third electrodes may be disposed in an array spaced apart in the first direction. The touch panel system may also include a second device. At least one second electrode may include a plurality of second electrodes. The second device may be connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding second electrode. Each first electrode may extend in a first direction and the plurality of first electrodes may be disposed in an array spaced apart in a second, different direction. Each second electrode may extend in the second direction and the plurality of second electrodes may be disposed in an array spaced apart in the first direction.

A touch panel system may include the device which includes a plurality of signal splitter stages, and a projected capacitance touch panel which includes a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode. The touch panel system may also include a capacitive touch controller. The device maybe connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding first electrode. The device may be connected to the capacitive touch controller such that the capacitive touch controller may transmit and/or receive capacitance signals to and/or from each first electrode through a corresponding signal splitter stage.

The touch panel system including the device which includes a plurality of signal splitter stages may also include a second device. The projected capacitance touch panel may also include a plurality of third electrodes separated from the at least one second electrode by the layer of piezoelectric material. The second device may be connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding third electrode. The second device may be connected to the capacitive touch controller such that the capacitive touch controller may transmit and/or receive capacitance signals to and/or from each third electrode through a corresponding signal splitter stage. Each first electrode may extend in a first direction and the plurality of first electrodes may be disposed in an array spaced apart in a second, different direction. Each third electrode may extend in the second direction and the plurality of third electrodes may be disposed in an array spaced apart in the first direction.

The touch panel system including the device which includes a plurality of signal splitter stages may also include a second device. At least one second electrode may include a plurality of second electrodes. The second device may be connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding second electrode. The second device maybe connected to the capacitive touch controller such that the capacitive touch controller may transmit and/or receive capacitance signals to and/or from each second electrode through a corresponding signal splitter stage. Each first electrode may extend in a first direction and the plurality of first electrodes maybe disposed in an array spaced apart in a second, different direction. Each second electrode may extend in the second direction and the plurality of second electrodes may be disposed in an array spaced apart in the first direction. The capacitive touch controller, the device and, optionally the second device are integrated within a single package.

According to a second aspect of the invention there is provided a method of processing signals from a projected capacitance touch panel. The touch panel includes a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode. The method includes controlling a multiplexer to select a given one of a plurality of inputs. Each input of the multiplexer is coupled to an output of a corresponding amplification stage and each amplification stage is configured to receive signals from a corresponding first electrode. The method also includes generating, based on signals received from the first electrode corresponding to the selected input, a pressure signal indicative of a pressure applied to the touch panel proximate to the given first electrode. The method also includes generating, based on signals received from the first electrode corresponding to the selected input, a capacitance signal indicative of a capacitance of the given first electrode.

Brief Description of the drawings

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

Figure 1 illustrates a first apparatus for combined capacitive and pressure sensing; Figure 2 illustrates a second apparatus for combined capacitive and pressure sensing; Figure 3 illustrates an electronic device incorporating a touch panel;

Figure 4 illustrates separation of a single signal into pressure and capacitance signals; Figure 5 illustrates a first touch panel system;

Figure 6 is a circuit diagram for an example of charge amplifiers for use in the first touch panel system;

Figure 7 illustrates a second touch panel system;

Figure 8 is a plan view of an alternative electrode layout;

Figure 9 is a plan view of a third touch panel;

Figure 10 is a plan view of a patterned electrode;

Figure 11 is a plan view of a fourth touch panel;

Figure 12 is a cross-sectional view of a fourth touch panel;

Figure 13 illustrates a third apparatus for combined capacitive and pressure sensing; Figure 14 illustrates a third touch panel system;

Figure 15 is a circuit diagram for an example of a charge amplifier for use in the third touch panel system;

Figure 16 is a cross-sectional view of a first display stack-up;

Figure 17 is a cross-sectional view of a second display stack-up;

Figure 18 is a cross-sectional view of a third display stack-up;

Figure 19 is a cross-sectional view of a fourth display stack-up;

Figure 20 is a cross-sectional view of a fifth display stack-up;

Figure 21 is a cross-sectional view of a sixth display stack-up;

Figure 22 is a cross-sectional view of a seventh display stack-up;

Figure 23 is a cross-sectional view of an eighth display stack-up;

Figure 24 is a cross-sectional view of a first embedded stack-up;

Figure 25 is a cross-sectional view of a second embedded stack-up;

Figure 26 is a cross-sectional view of a third embedded stack-up;

Figure 27 is a cross-sectional view of a fourth embedded stack-up;

Figure 28 is a cross-sectional view of a fifth embedded stack-up;

Figure 29 is a cross-sectional view of a sixth embedded stack-up;

Figure 30 is a cross-sectional view of a seventh embedded stack-up;

Figure 31 is a cross-sectional view of an eighth embedded stack-up; Figure 32 is a cross-sectional view of a ninth embedded stack-up; and Figure 33 is a cross-sectional view of a tenth embedded stack-up.

Detailed description

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

First combined capacitance and pressure sensing apparatus and first touch sensor Figure 1 schematically illustrates a first apparatus 1 for combined capacitive and pressure sensing which includes a first touch sensor 2, a front end module 3 and a controller 19.

The first touch sensor 2 includes a layer structure 4 having a first face 5 and a second, opposite, face 6, a first electrode 7 and a second electrode 8. The layer structure 4 includes one or more layers, including at least a layer of piezoelectric material 9. Each layer included in the layer structure 4 is generally planar and extends in first x and second y directions which are perpendicular to a thickness direction z. The one or more layers of the layer structure 4 are arranged between the first and second faces 5, 6 such that the thickness direction z of each layer of the layer structure 4 is perpendicular to the first and second faces 5, 6. The first electrode 7 is disposed on the first face 5 of the layer structure 4, and the second electrode 8 is disposed on the second face 6 of the layer structure 4. The first electrode 7 is electrical coupled to a terminal A and the second electrode 8 is coupled to a terminal B.

Preferably, the layer of piezoelectric material 9 is a piezoelectric polymer such as polyvinylidene fluoride (PVDF) or polylactic acid. However, the piezoelectric material may alternatively be a layer of a piezoelectric ceramic such as lead zirconate titanate (PZT). Preferably, the first and second electrodes are indium tin oxide (ITO) or indium zinc oxide (IZO). However, the first and second electrodes 7, 8 may be metal films such as aluminium, copper, silver or other metals suitable for deposition and patterning as a thin film. The first and second electrodes 7, 8 may be conductive polymers such as polyaniline, polythiphene, polypyrrole or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). The first and second electrodes 7, 8 may be formed from a metal mesh; nanowires, optionally silver nanowires; graphene; and carbon nanotubes. The front end module 3 is coupled to the first touch sensor 2 via terminal A in order to receive an input signal 10 from the first electrode 7. The front end module 3 includes a first stage 11 in the form of an amplification stage, and a second stage in the form of a first frequency-dependent filter 12 and a second frequency-dependent filter 13. The first stage 11 receives the input signal 10 from the first electrode 7, and provides an amplified signal 14 based on the input signal 10. The first frequency-dependent filter 12 receives and filters the amplified signal 14 to provide a first filtered signal 15 having a first frequency bandwidth. The second frequency-dependent filter 13 receives and filters the amplified signal 14 to provide a second filtered signal 16 having a second frequency bandwidth. The second frequency bandwidth has a relatively higher start- frequency than the first frequency bandwidth.

The first stage 11 may receive an alternating signal 17, V_Si_g(t) supplied by a signal source 18. The amplified signal 14 may be based on the input signal 10 and the alternating signal 17. In general, the alternating signal 17 may be any alternating signal which is suitable for use in determining the self-capacitance or mutual capacitance of an electrode of a projected capacitance touch panel.

The first and second frequency dependent filters 12, 13 may be hardware filters such as, for example, active or passive filtering circuits. Alternatively, the amplified signal 14 may be converted into a digital signal by an analog-to-digital converter 55a, 55b (Figure 7) and the first and second frequency dependent filters 12, 13 may be implemented in the digital domain using, for example, one or more microprocessors, microcontrollers, field programmable gate arrays or other suitable data processing devices.

The input signal 10 is produced in response to a user interaction with the touch sensor 2 or with a layer of material overlying the touch sensor 2. In the following description, reference to a "user interaction" shall be taken to include a user touching or pressing a touch sensor, a touch panel or a layer of material overlying either. The term "user interaction" shall be taken to include interactions involving a user's digit or a stylus (whether conductive or not). The term "user interaction" shall also be taken to include a user's digit or conductive stylus being proximate to a touch sensor or touch panel without direct physical contact.

The terminal B may couple the second electrode 8 to ground, to a common mode voltage VCM, to a signal source 18 providing an alternating signal 17, V_Si_g(t) or to another front end module 3 (not shown in Figure 1). Alternatively, the terminal B may be connected to the same front end module 3, such that the front end module 3 is connected across the terminals A and B.

The terminals A, B, and other terminals denoted herein by capitalised Latin letters are used as reference points for describing electrical coupling between electrodes and other elements of an apparatus. Although the terminals A, B may actually be physical terminals, the description that an element, for example a front end module 3, is coupled to a terminal, for example, the terminal A shall be taken to also encompass that the front end module may be directly coupled to the first electrode 8. Similarly for other elements and other terminals denoted by capitalised Latin letters.

A controller 19 receives the first and second filtered signals 15, 16. In some examples, the controller 19 may also serve as the signal source 18 providing an alternating signal 17, V_Sig(f). The controller 19 calculates pressure values 20 based on the first filtered signal 15 and capacitance values 21 based on the second filtered signal 16. The pressure values 20 depend upon a deformation, which may be a strain, applied to the layer of piezoelectric material 9 and corresponding to a user interaction. The capacitance values 21 depend upon the self-capacitance of the first electrode 7 and/or a mutual capacitance between the first and second electrodes 7, 8. The capacitance values 22 vary in response to a user interaction involving a digit or a conductive stylus.

In this way, pressure and capacitance measurements may be performed using the touch sensor 2 without the need for separate pressure and capacitance electrodes. A single input signal 10 is received from the first electrode 7 which includes pressure and capacitance information. Additionally, the input signal 10 may be amplified and processed using a single front end module 3. This can allow the apparatus 1 to be more readily integrated into existing projected capacitance touch panels.

The layer structure 4 may include only the layer of piezoelectric material 9 such that the first and second opposite faces 5, 6 are faces of the piezoelectric material layer 9.

Alternatively, the layer structure 4 may include one or more dielectric layers which are stacked between the layer of piezoelectric material 9 and the first face 5 of the layer structure 4. The layer structure 4 may include one or more dielectric layers stacked between the second face 6 of the layer structure 4 and the layer of piezoelectric material 9. Preferably, one or more dielectric layer(s) include layers of a polymer dielectric material such as polyethylene terephthalate (PET), or layers of pressure sensitive adhesive (PSA) material. However, one or more dielectric layer(s) may include layers of a ceramic insulating material such as aluminium oxide.

In Figure 1, the first and second faces 5,6 and the layers of the layer structure 4 are shown extending along orthogonal axes labelled x and y, and the thickness direction of each layer of the layer structure 4 is aligned with an axis labelled z which is orthogonal to the x and y axes. However, the first, second and thickness directions need not form a right handed orthogonal set as shown. For example, the first and second directions x, y may intersect at an angle of 30 degrees or 45 degrees or any other angle greater than o degrees and less than 90 degrees.

Second combined capacitance and pressure sensing apparatus and second touch sensor Referring also to Figure 2, a second apparatus 22 is shown which includes a second touch sensor 23, a first front end module 3a, a second front end module 3b and a controller 19.

The second touch sensor 23 is similar to the first touch sensor 2, except that the second touch sensor 23 also includes a second layer structure 24 having a third face 25 and a fourth, opposite, face 26, and a third electrode 27. The second layer structure 24 includes one or more dielectric layers 28. Each dielectric layer 28 is generally planar and extends in first x and second y directions which are perpendicular to a thickness direction z. The one or more dielectric layers 28 of the second layer structure 24 are arranged between the third and fourth faces 25, 26 such that the thickness direction z of each dielectric layer 28 of the second layer structure 24 is perpendicular to the third and fourth faces 25, 26. The third electrode 27 is disposed on the third face 25 of the second layer structure 24, and the fourth face 26 of the second layer structure 24 contacts the first electrode 7.

Preferably, the dielectric layer(s) 28 include layers of a polymer dielectric material such as PET or layers of PSA materials. However, the dielectric layer(s) 28 may include layers of a ceramic insulating material such as aluminium oxide. Preferably, the third electrode 27 is made of indium tin oxide (ΓΓΟ) or indium zinc oxide (IZO). However, the third electrode 27 may be a metal mesh film such as aluminium, copper, silver or other metals suitable for deposition and patterning as a thin film. The third electrode 27 may be made of a conductive polymer such as polyaniline, polythiphene, polypyrrole or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). The first and second front end modules 3a, 3b are the same as the front end module 3. The first front end module 3a is coupled to the second touch sensor 23 via a terminal D in order to receive a first input signal 10a from the first electrode 7. The second front end module 3b is coupled to the second touch sensor 23 via a terminal C in order to receive a second input signal 10b from the third electrode 27. A terminal E may couple the second electrode 8 to ground, to a common mode voltage VCM, or to a signal source 18 providing an alternating signal 17, V_Si_g(t). Alternatively, the terminal E may be coupled to the first front end module 3a such that the first front end module 3a is connected across the terminals D and E, and the terminal E may also be coupled to the second front end module 3b such that the second front end module 3b is connected across the terminals C and E. One or both of the first and second front end modules 3a, 3b may be connected to a signal source 18 in order that the corresponding first stage(s) 11 may receive an alternating signal 17, !¾,(£)■

The controller 19 receives first and second filtered signals 15a, 16a from the first front end module 3a and first and second filtered signals 15b, 16b from the second front end module 3b. The controller 19 calculates first pressure values 20a based on the first filtered signal 15a from the first front end module 3a and second pressure values 20b based on the first filtered signal 15b from the second front end module 3b. The content of pressure values 21 depends on a measurement mode of the controller 19. The controller 19 may be operable in a self-capacitance measurement mode or a mutual capacitance measurement mode, and may be switchable between measurement modes. When self-capacitances of the first and third electrodes 7, 27 are measured, the controller 19 calculates self-capacitance values for the first electrode 7 based on the second filtered signal 16a from the first front end module 3a and self-capacitance values for the third electrode 27 based on the second filtered signal 16b from the second front end module 3b. When a mutual capacitance between the first and third electrodes 7, 27 is measured, the controller 19 calculates the mutual capacitance based on the second filtered signals 16a, 16b from both first and second front end modules 3a, 3b.

The pressure values 20a, 20b depend upon a deformation applied to the layer of piezoelectric material 9 by a user interaction. The capacitance values 21 may include self-capacitances of the first and third electrodes 7, 27, or a mutual capacitance measured between the first and third electrodes 7, 27, depending on the operation mode of the controller 19. The capacitance values 21 vary in response to a user interaction involving a digit or a conductive stylus.

The second layer structure 24 may include only a single dielectric layer 28, such that the third and fourth opposite faces 25, 2 are faces of a single dielectric layer 28.

Alternatively, a second layer structure 24 need not be used, and the third electrode 27 may be disposed on the first face 5 along with the first electrode 7. In Figure 2, the third and fourth faces 25, 26 and the dielectric layers 28 of the second layer structure 24 are shown extending along orthogonal axes labelled x and y, and the thickness direction of each dielectric layer 28 of the second layer structure 24 is aligned with an axis labelled z which is orthogonal to the x and y axes. However, the first, second and thickness directions need not form a right handed orthogonal set as shown.

Electronic device

Referring also to Figure 3, an electronic device 29 may include a touch panel 30 and a touch controller 31 for providing combined capacitive and pressure sensing.

The electronic device 29 may be a relatively immobile electronic device such as, for example a desktop computer, an automated teller machine (ATM), a vending machine, a point of sale device, or a public access information terminal. Alternatively, an electronic device 29 may be a portable electronic device such as a laptop, notebook or tablet computer, a mobile phone, a smart phone, a personal data assistant or a music playing device. The electronic device 29 includes a touch panel 30 including one or more touch sensors 2, 23. The touch panel 30 is coupled to a touch controller 31 including, for example, one or more front end modules 3 by a link 32. In a case where the link 32 is a multiplexed link, one front end module 3 may receive input signals 10 from multiple touch sensors 2, 23. For example, using a multiplexed link 32 the touch controller 31 may include one front end module and the touch panel 30 may include two, four, eight, sixteen, thirty two, sixty four, one hundred and twenty eight, two hundred and fifty six or more touch sensors 2, 23. The number of touch sensors 2, 23 coupled to a front end module 3 by a multiplexed link 32 need not be a power of two.

The electronic device 29 may include a processor 33 for executing programs and processing information. The electronic device 29 may include a memory 34 such as a volatile random access memory for temporarily storing programs and information, and/or storage 35 such as non-volatile random access memory (NVRAM) or a hard disc drive (HDD) for long term storage of programs and information. The electronic device

29 may include a network interface 36 for transmitting and/or receiving information from wired or wireless communication networks. The electronic device 29 may include a removable storage interface 37 which can interface with removable storage media to read and/ or write programs and information. The electronic device 29 may include output means such as a display 38 and/or speaker(s) 39. The display 38 may be any type of display such as, for example, an liquid crystal display (LCD), a light emitting diode display (LED), an organic LED display, an electrophoretic display or other type of electronic-ink display.

The touch controller 31 provides input information to the electronic device 29 which corresponds to user interactions with the touch panel 30. For example, input information may be the locations and/or pressures of one or more user interactions. The electronic device may include other input means such as a microphone 40, or other input devices 41 such as, for example, a keyboard, keypad, mouse or trackball. When the touch panel 30 includes a plurality of touch sensors 2, 23, the touch controller 31 may provide positional information in the form of coordinates and/or pressures corresponding to one user interaction or two or more simultaneous user interactions with the touch panel 30.

The touch panel 30 may be provided overlying the display 38, such that the touch panel

30 and display 38 provide a touch screen. Alternatively, the touch sensors 2, 23 of the touch panel 30 may be integrated into or embedded within the display 38. When the touch panel 30 is used overlying or integrated into the display 38, the layer structure(s) 4, 24 and electrodes 7, 8, 27 may be transparent or substantially transparent. For example, the layer structure(s) 4, 24 and electrodes 7, 8, 27 may transmit 50% or more, preferably at least 75 %, preferably at least 90% of light in visible wavelengths. For example, the piezoelectric material may be PVDF, dielectric layers included in the layers structures 4, 24 may be PET or an optically transparent or substantially transparent PSA, and the electrodes 7, 8, 27 may be ITO. Alternatively, the electrodes 7, 8, 27, and any connections thereto, may be opaque and sufficiently thin in a direction perpendicular to the thickness direction z that they are not immediately noticeable to the human eye, for example, electrodes, and any connections thereto, may be less than 100 micrometers (lx io ⁴ m) wide, less than 10 micrometers (lx io ⁵ m) wide or thinner. Operation of the first and second apparatuses

Referring also to Figure 4, separation of pressure and capacitance signals will be explained. The layer of piezoelectric material 9 is poled such that a polarisation P of the layer of piezoelectric material 9 will be generated by the application of a pressure (or stress or force) applied in the thickness direction z which results from a user interaction with the touch sensor 2, 23. The polarisation P of the layer of piezoelectric material results in an induced electric field E_p, which has a component E_z in the thickness direction. The deformation which produces the polarisation P may result from a compression or a tension. The deformation which produces the polarisation P may include an in-plane stretching of the piezoelectric material layer 9 in response to the applied pressure.

The induced electric field E_p produces a potential difference between the first and second electrodes 7, 8 of the first or second touch sensors 2, 23. The induced electric field Ep produces a potential difference between the third and second electrodes 27, 8 of the second touch sensor 23. If a conductive path is provided between the first or third electrodes 7, 27 and the second electrode 8, charges will flow between them until the induced electric field E_p is cancelled by an electric field E_q produced by the charging of the electrodes 7, 8, 27. Intimate contact between the layer of piezoelectric material 9 and the electrodes 7,8, 27 is not required, provided that intervening layers of the layer structures 4, 24 are not excessively thick. A potential difference may be produced between the third and second electrodes 27, 8 of the second touch sensor 23 provided that the first electrode 7 is arranged such that the third electrode 27 is not entirely screened from the induced electric field E_p.

The input signal 10 received from the first electrode 7 or the third electrode 27 includes a current signal I_Pi_ez0{t) which depends upon the induced electric field E_p. Generally, a greater deformation applied to the layer of piezoelectric material 9 will result in a greater magnitude of I_Pi_ez0{t). The first stage 11 includes a circuit providing an integrating amplifier which integrates the current signal I_Pi_ez0{t) and multiplies by a gain G in order to provide an integrated output voltage signal V_Pi_ez0(t). The gain G need not be fixed, and in general maybe by a function of time, frequency and/or the electrical parameters of a feedback network included in the first stage 11. The amplified signal 14 is a superposition of the integrated output voltage signal

Vpiezoit and a capacitance measurement voltage signal V_cap(t). The capacitance voltage signal V_cap(t) is an alternating signal having a basic frequency oifd. The capacitance voltage signal V_cap(t) is based on the capacitance of the touch sensor 2, 23 and an alternating signal 17, V_s¾,(t) provided by a signal source 18.

For the first touch sensor 2, a signal source 18 may be coupled to the front end module 3 or to the second electrode 8 via terminal B. For the second touch sensor 23, signal source(s) 18 may be coupled to one or both of the first and second front end modules 3a, 3b, or to the second electrode 8 via terminal E. The signal source 18 may be a voltage controlled source. The signal source 18 may be the controller 19, or a driving output of a separate projected capacitive touch controller.

The signal source 18 may provide an alternating signal 17, V_Si_g(t) having a sinusoidal, square, triangular or saw-toothed waveform. The signal source 18 may provide a periodic signal comprising a superposition of two or more sinusoidal waveforms having different frequencies. The alternating signal 17, V_Si_g(t) may be any signal suitable for measuring the self-capacitance or mutual capacitance of an electrode of a projected capacitance touch panel.

Preferably, the front end module 3 receives the alternating signal 17, V_Si_g(t) and the first stage 11 provides the amplified signal 14 based on the input signal 10 and the alternating signal 17, V_Si_g(t). The amplified signal 14 is a superposition of the integrated output voltage signal V_Pi_ezo(t) and the capacitance measurement voltage signal V_cap(t). However, the integrated output voltage signal V_Pi_ez0(t) and the capacitance

measurement voltage signal V_ca (t) generally have distinctly different frequency contents, which facilitates separation using the first and second frequency-dependent filters 12, 13. Where a user interaction does not apply a pressure to the layer of piezoelectric material the contribution of the integrated output voltage signal V_Pi_ez0(t) to the amplified signal 14 may be zero or negligible.

Self capacitances of the first or third electrodes 7, 27, or mutual capacitances between any pair of the first, second or third electrodes 7, 8, 27 may typically fall within the range of 0.1 to 3000 pF or more, and preferably 100 to 2500 pF. In order to effectively couple to capacitances in this range, the alternating signal 17, V_Si_g(f) may typically have a base frequency of greater than or equal to 10 kHz, greater than or equal to 20 kHz, greater than or equal to 50 kHz or greater than or equal to 100 kHz.

By contrast, the integrated output voltage signal V_Pi_ez0(t) typically includes a broadband frequency content spanning a range from several Hz to several hundreds or thousands of Hz. This is at least in part because the integrated output voltage signal V_Pi_ez0(t) arises from user interactions by a human user.

Preferably, the first frequency-dependent filter 12 attenuates the capacitance measurement voltage signal V_ca (t) such that the first filtered signal 15 is not based on the alternating signal 17, V_Si_g(t). Preferably, the first filtered signal 15 is substantially equal to the integrated output voltage signal V_Pi_ez0(t), or at least is primarily based on the piezoelectric current I_Pi_ez0{t). Preferably, the second frequency-dependent filter 13 selects the capacitance

measurement voltage signal V_ca (t) such that the second filtered signal 16 is based on the alternating signal 17, V_Si_g(t) and the capacitance of the touch sensor 2, 23.

Preferably, the second filtered signal 16 is substantially equal to the capacitance measurement voltage signal V_ca (t), or is at least primarily based on the alternating signal 17, V_sig{t).

In this way, the amplitude of the first filtered signal 15 is dependent upon a pressure applied to the layer of piezoelectric material 9 by a user interaction, and the amplitude of the second filtered signal 16 is dependent upon a capacitance of a the touch sensor 2, 23 as modified by the proximity of a user's digit or conductive stylus.

The first stage 11 has a frequency response having a low frequency cut-off// and a high frequency cut-off f_u. Below the low frequency cut-off// and above the high frequency cut-off/, the gain G of the first stage 11 drops rapidly so that frequencies outside the range between/ and/, are blocked. The high frequency cut-off/, is greater than the base frequency// of the alternating signal 17, V_Si_g(t) for capacitance measurements. The low-frequency cut-off/ is preferably at least 1 hertz, or at least sufficiently high to substantially block voltage signals resulting from a pyroelectric effect in the layer of piezoelectric material 9 which result from the body temperature of a user's digit. For application in an industrial or domestic environment, the low frequency cut-off/ may be at least 50 Hz, at least 60 Hz or at least sufficiently high to reject noise pick-up at a frequency of a domestic of industrial power distribution network and resulting from ambient electric fields. The low frequency cut-off// may be at least 100 Hz. The low frequency cut-off// may be at least 200 Hz. For application in aircraft, the low frequency cut-off/ may be at least 400 Hz. Frequency cut-offs may corresponds to 3 dB attenuation.

The first frequency-dependent filter 12 may be a low-pass filter having a cut-off frequency f₀jf which is lower than the base frequency// of the alternating signal 17, Vsig(f), and the second frequency-dependent filter 13 may be a band-pass filter having a pass-band including the base frequency//.

Alternatively, the first frequency-dependent filter 12 may be a band- reject filter having a stop-band including the base frequency//, and the second frequency-dependent filter 13 may be a band-pass filter having a pass-band including the base frequency//.

Alternatively, the first frequency-dependent filter 12 may be a low-pass filter having a cut-off frequency f₀jf which is lower than the base frequency// of the alternating signal 17, V_Sig(t , and the second frequency-dependent filter 13 may be a high-pass filter having a cut-off frequency f_on which is lower then the base frequency// of the alternating signal 17, V_Si_g(t) and higher than the cut-off frequency /, of the first frequency-dependent filter 12.

The first and second frequency-dependent filters 12, 13 may be provided by active filter circuits. The first and second frequency-dependent filters 12, 13 may be provided by passive filter circuits. The first and second frequency-dependent filters 12, 13 may be provided by single stage filters or multiple stage filters. The first and second frequency- dependent filters 12, 13 may be Butterworth filters, Chebyshev filters, Gaussian filters and Bessel filters. The first frequency-dependent filter 12 may be of different type to the second frequency-dependent filter.

Alternatively, the second stage of the front end module 3 and the first and second frequency-dependent filters 12, 13 may be provided by a suitably programmed information processing device such as a microprocessor or a microcontroller. First touch panel system

Touch panel systems including touch panels including multiple touch sensors 2, 23 combined with apparatus for combined capacitance and pressure sensing have been described in WO 2016/102975 A2, in particular with reference to Figures 15 to 18, 21, and 25 to 29 of this document.

In the touch panel systems described in WO 2016/102975 A2, each front end module 3 is connected to a number of electrodes using a multiplexer. In other words, electrode input signals 10 are multiplexed before amplification. Such systems are simple in that large numbers of front end modules 3 and first stages 11 are not required. In this way, multiplexing the electrode input signals 10 before amplification allows the size and complexity of an apparatus for connection to a touch panel to be minimised.

However, it has been surprisingly realised that, despite increasing the overall size and complexity of an apparatus for combined capacitance and pressure sensing, multiplexing the amplified signals 15 instead of the input signals 10 may provide improved performance, as described hereinafter.

Referring also to Figure 5, a first touch panel system 42 includes a first touch panel 43 and a first touch controller 44 for combined pressure and capacitance sensing.

The first touch panel 43 includes first and second layer structures 4, 24 which are generally the same as the layer structures 4, 24 of the second touch sensor 23, except that multiple first electrodes 7 are disposed on the first face 5 of the first layer structure 4 and that multiple third electrodes 27 are disposed on the third face 25 of the second layer structure 24.

The first electrodes 7 each extend in the second direction y and the first electrodes 7 are disposed in an array evenly spaced in the first direction x. The third electrodes 27 each extend in the first direction x and the third electrodes 27 are disposed in an array evenly spaced in the second direction y. Each first electrode 7 and each third electrode 27 is coupled to a corresponding conductive trace 45. The second electrode 8 is disposed on the second face 6 of the first layer structure 4 and is extensive such that the second electrode 8 at least partially underlies each first electrode 7 and each third electrode 27. The second electrode 8 may be substantially coextensive with the second face 6 of the first layer structure 4. The second electrode 8 is connected to a common mode voltage VCM-

In this way, the area around each intersection of a first electrode 7 with a third electrode 27 effectively provides a second touch sensor 23.

The first touch panel 43 may be bonded overlying the display 38 of an electronic device 29. In this case, the materials of the first touch panel 43 should be substantially transparent as described hereinbefore. A cover lens 46 (Figure 16) may be bonded overlying the first touch panel 43. The cover lens 46 (Figure 16) is preferably glass but may be any transparent material. The cover lens 46 (Figure 16) may be bonded to the first touch panel 43 using a layer of pressure sensitive adhesive (PSA) material 106 (Figure 17). The layer of PSA material 106 (Figure 17) may be substantially transparent. The first and third electrodes 7, 27 may be fabricated using index matching techniques to minimise visibility to a user.

The first touch controller 44 includes a controller 47, a pair of amplifier modules 48a, 48b a pair of multiplexers 49a, 49b, and a pair of second stages, each second stage including a first frequency dependent filter 12a, 12b and a second frequency dependent filter 13a, 13b. The controller 47 may communicate with the processor 33 of the electronic device 29 using a link 32. The first touch controller 44 include a signal source 18 for providing the alternating signal 17, V_Si_g(f) to one or both of the first stages 48a, 48b. The amplifier modules 48a, 48b are similar to the first stage 11, except that each amplifier module 48a, 48b includes a number of separate charge amplifiers 50. Each charge amplifier 50 of the first amplifier module 48a is connected to a corresponding third electrode 27 via a respective terminal Ci, C5 and conductive trace 45. The output of each charge amplifier 50 of the first amplifier module 48a is connected to a corresponding input of the first multiplexer 49a. In this way, the first multiplexer 49a may output an amplified signal 15 corresponding to an addressed third electrode 27 for separation and filtering by the corresponding frequency dependent filters 12a, 13a. The controller 47 receives first and second filtered signals 15a, 16a corresponding to a given third electrode 27 addressed by the first multiplexer 49a. Similarly, each charge amplifier 50 of the second amplifier module 48b is connected to a corresponding first electrode 7 via a respective terminal Di, D5 and conductive trace 45, and the output of each charge amplifier 50 of the second amplifier module 48b is connected to a corresponding input of the second multiplexer 49b. In this way, the second multiplexer 49b may output an amplified signal 15 corresponding to an addressed first electrode 7 for separation and filtering by the corresponding frequency dependent filters 12b, 13b. The controller 47 receives first and second filtered signals 15b, 16b corresponding to a given first electrode 7 addressed by the second multiplexer 49b.

The controller 47 may provide a synchronisation signal 51 to the multiplexers 49a, 49b and amplifiers 50. The synchronisation signal 51 may cause the multiplexers 49a, 49b to address each combination of first and third electrodes 7, 27 according to a sequence determined by the controller 47. In this way, the first touch controller 44 may receive amplified signals 15 from each pairing of first and third electrodes 7, 27 according to a sequence determined by the controller 47. The sequence may be pre-defined, for example, the sequence may select each pair of a first electrode 7 and a third electrode 27 once before repeating. The sequence may be dynamically determined, for example, when one or more user interactions are detected, the controller 47 may scan the subset of first electrodes 7 and third electrodes 27 adjacent to each detected user interaction in order to provide faster and/or more accurate tracking of user touches. The sequence may be arranged so that the multiplexors 49a, 49b address each pair of first and third electrodes 7, 27 during a quiet period or blanking period of the display 38. The sequence may be provided to the controller 47 by the processor 33 via the link 32. Alternatively, the processor 33 may directly control the sequence via the link 32.

Based on the received first filtered signals 15a, 15b the controller 47 may calculate first pressure values 20a corresponding to the addressed third electrode 27 and second pressure values 20b corresponding to the addressed first electrode 7. The pressure values 20a, 20b are output via the link 32.

When the first touch controller 44 is operated in a self-capacitance mode, the controller 47 may provide suitable alternating signals 17, \¾,(t) to each amplifier 50 of the first and second amplifier modules 48a, 48b. Based on the received second filtered signals 16a, 16b, the controller 47 may calculate first capacitance values 21a corresponding to a self-capacitance of the addressed third electrode 27 and second capacitance values 21b corresponding to a self-capacitance of the addressed first electrode 7. The capacitance values 21a, 21b are output via the link 32.

When the first touch controller 44 is operated in a mutual-capacitance mode, the controller 47 may provide suitable alternating signals 17, \¾,(t) to each amplifier 50 of the first amplifier module 48a. In this way, the third electrodes 27 may be

transmitting, or Tx, electrodes and the first electrodes 7 may be receiving, or Rx, electrodes. Based on the received second filtered signals 16a, 16b, the controller 47 calculates capacitance values 21 corresponding to a mutual-capacitance between the addressed third electrode 27 and the addressed first electrode 7. The capacitance values 21 are output via the link 32. Alternatively, alternating signals 17, V_Si_g(t) may be provided to the second amplifier module 48b, the first electrodes 7 may be

transmitting, or Tx, electrodes and the third electrodes 27 may be receiving, or Rx, electrodes.

The processor 33 of the electronic device 29 receives the pressure values 20a, 20b and capacitance values 21a, 21b, 21 and may use these to determine a location and an applied force corresponding to one or more user interactions with the first touch panel 43. Alternatively, the locations and applied forces corresponding to user interactions may be determined by the controller 47 and communicated to the processor 33 via the link 32.

The controller 47 and/ or the processor 33 may be calibrated to convert the first filtered signals 15 into applied forces or pressures by applying known pressures to known locations so that the accuracy of calculated positions and/ or pressures of one or more user interactions may be optimised and/ or verified.

Compared to the touch panel systems described with reference to Figures 15 to 18, 21, and 25 to 29 of WO 2016/102975 A2, the first touch panel 42 differs primarily in that the amplified signals 15 are multiplexed instead of the input signals 10. As described hereinbefore, a consequence of providing a separate charge amplifier for each first and third electrode 7, 27 of the first touch panel 43 is that the size, complexity and cost of the first touch controller 44 is increased relative to the touch panel systems described with reference to Figures 15 to 18, 21, and 25 to 29 of WO 2016/102975 A2. It might be considered that it would make little difference whether signals are multiplexed before or after amplification, so that multiplexing before amplification would always be preferred due to the reduction in size, complexity and cost possible when fewer charge amplifiers are required.

However, in the specific application of combined pressure and capacitive sensing by separating a single signal, it has been surprisingly realised that multiplexing the amplified signals 15 instead of the input signals 10 may provide improved performance.

In particular, multiplexing the amplified signal 15 may improve the capture of charges induced in response to straining of the piezoelectric material layer 9 at times when a particular electrode 7, 27 is not being addressed. In other words, charges induced whilst other electrodes 7, 27 are being read out. When the input signals 10 are multiplexed, any charge induced on a non-addressed electrode will be stored on the input capacitance of the multiplexer. An input capacitance of a multiplexer is typically small, and may show variations between different inputs which may be significant in comparison to charges generated in response to straining of the piezoelectric material layer 9. By contrast, when the amplified signals 15 are multiplexed instead, charges induced when an electrode 7, 27 is not being addressed may be stored in a capacitance of an amplifier 50 feedback network (see Figure 6), which may be both larger and more consistent. In this way, the first touch controller 44 may have improved accuracy in detecting the pressures of user interactions regardless of the timing of the user interaction with respect to a scanning/addressing sequence of the first and third electrodes 7, 27.

Additionally, multiplexing the amplified signal 15 instead of the input signals 10 may avoid problems with leakage current. In particular, the off-state switches of a multiplexer will, in practice, leak small currents over time. These small leakage currents corresponding to all of the inputs not being addressed by a multiplexor may add up and be integrated by a charge amplifier, and the overall effect may be comparable to the charge or current corresponding to a user interaction proximate to an addressed electrode 7, 27. Such leakage currents may degrade the sensitivity to applied pressures, and may also limit scalability, since a larger touch panel having a greater number of electrodes will need a correspondingly greater number of

multiplexer channels, increasing the leakage current. By contrast, when multiplexing the amplified signals 15 the charge amplifiers 50 do not receive such residual currents. In addition, it has been surprisingly realised that, in application to combined pressure and capacitance sensing based on separating a single signal, multiplexing the amplified signals 15 may allow each charge amplifier 50 to require a lower bandwidth and lower current capacity, as compared to the requirements for charge amplifiers when the input signals 10 are multiplexed.

Retaining multiplexing before filtering by the frequency dependent filters 12, 13 and/or conversion to the digital domain by an analog-to-digital convertor (ADC) permits the first touch controller 44 to still be smaller and less complex than providing a wholly separate channel for each first and third electrode 7, 27, since the ADC and frequency dependent filters 12, 13 do not need to be duplicated for each electrode 7, 27.

Example of charge amplifiers

Referring also to Figure 6, an example of one configuration of charge amplifiers 50a, 50b of the first and second amplifier modules 48a, 48b is shown.

In one configuration, each charge amplifier 50a, 50b includes an operational amplifier OP having an inverting input, a non-inverting input and an output. For example, each charge amplifier 50a forming part of the first amplifier module 48a includes an operational amplifier OP having an inverting input coupled to a corresponding terminal C via an input resistance ¾ and a first switch SWi connected in series. The non- inverting input of the operational amplifier OP is connected to an alternating signal 17, V_Sig(t). The alternating signal 17, V_Si_g(t) may be provided by the controller 47, by a separate module of the first touch controller 44, or may be received into the first touch controller 47 from an external source. A feedback network of the charge amplifier 50a includes a feedback resistance Rf, a feedback capacitance and a second switch SW2 connected in parallel between the inverting input and the output of the operational amplifier OP. The output of the operational amplifier V_out provides the amplified signal 15·

In the example shown in Figure 6, the first touch controller 44 is configured for mutual capacitance measurements between each pair of first and third electrodes 7, 27. Each charge amplifier 50b forming part of the second amplifier module 48b is the same as each charge amplifier 50a of the first amplifier module 48a, except that the non- inverting input of the operational amplifier OP is coupled to a common mode voltage VCM instead of the alternating signal 17, V_Si_g(t), and in that the inverting input is connected to a terminal D instead of a terminal C.

Other terminals of the operational amplifiers OP, such as power supply terminals, may be present, but are not shown in this or other schematic circuit diagrams described herein.

The second switches SW2 permit the corresponding feedback capacitors C/to be discharged. The opening and closing of the second switches SW2 may be governed by a synchronisation signal 51 provided by the controller 47. In this way, the feedback capacitors of each charge amplifier 50 may be periodically discharged in order to reset the feedback network of the operational amplifier OP to prevent excessive drift. Similarly, the first switches SWi may be controlled by a synchronisation signal 51 provided by the controller 47 to enable an amplifier 50a, 50b to be connected or disconnected from the corresponding electrode 7, 27 if required.

Second touch panel system

Referring also to Figure 7, a second touch panel system 52 includes a second touch panel 53 and a second touch controller 54 for combined pressure and capacitance sensing.

The second touch panel 53 includes a layer structure 4 which is generally the same as the first layer structures 4 of the first touch sensor 2, except that multiple first electrodes 7 are disposed on the first face 7 of the first layer structure 7 and that multiple second electrodes 8 are disposed on the second face 6 of the first layer structure 4.

The first electrodes 7 each extend in the first direction x and the first electrodes 7 are disposed in an array evenly spaced in the second direction y. The second electrodes 8 each extend in the second direction y and the second electrodes 8 are disposed in an array evenly spaced in the first direction x. Each first electrode 7 and each second electrode 8 is coupled to a corresponding conductive trace 45.

In this way, the area around each intersection of a first electrode 7 with a second electrode 8 effectively provides a first touch sensor 2. The second touch panel 53 may be bonded overlying the display 38 of an electronic device 29. In this case, the materials of the second touch panel 53 should be

substantially transparent as described hereinbefore. A cover lens 46 (Figure 16) may be bonded overlying the second touch panel 53. The cover lens 46 (Figure 16) is preferably glass but may be any transparent material. The cover lens 46 (Figure 16) may be bonded to the second touch panel 53 using a layer of pressure sensitive adhesive (PSA) material not shown. The layer of PSA material (not shown) may be substantially transparent. The first and second electrodes 7, 8 may be fabricated using index matching techniques to minimise visibility to a user.

The second touch controller 54 is similar to the first touch controller 44, except that the amplified signals 15 from the first and second multiplexers 49a, 49b are provided directly to corresponding first and second analog-to-digital converters (ADCs) 55a, 55b, and that the resulting digital amplified signals 56 are filtered by frequency dependent filters 12, 13 applied in the digital domain by the controller 47. Another difference to the first controller 44 is that the second touch controller 54 is used to measure mutual capacitances between a pair of a first electrode 7 and a second electrode 8. Each charge amplifier 50 of the first amplifier module 48a is connected to a corresponding first electrode 7 via a terminal Αι, ..., A5 and receives an alternating signal 17, V_Si_g(t). Each charge amplifier 50 of the second amplifier module 48b is connected to a

corresponding second electrode 8 via a terminal Βι, ..., B5 and does not receive the alternating signal 17, V_Si_g(t).

The second touch controller 54 may instead be coupled to the first and third electrodes 7, 27 of the first touch panel 43. Equally, the first touch controller 44 may instead be coupled to the first and second electrodes 7, 8 of the second touch panel 53.

The ADCs 55a, 55b may receive the synchronisation signal 51 to prevent sampling concurrent with switching between addressed electrodes 7, 27.

Alternative electrode geometries

In the first touch panel 43, the first and third electrodes 7, 27 have been shown in the form of elongated rectangular electrodes. However, other shapes may be used. Referring also to Figure 8, an alternative geometry of the first and third electrodes 7, 27 is shown. Instead of being rectangular, each first electrode 7 may include several pad segments 57 evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrow bridging segments 58. Similarly each third electrode 27 may comprise several pad segments 59 evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrow bridging segments 60. The pad segments 57 of the first electrodes 7 are diamonds having a first width Wi in the second direction y and the bridging segments 58 of the first electrodes 7 have a second width W2 in the second direction y. The pad segments 59 and bridging segments 60 of the third electrodes 27 have the same respective shapes and widths Wi, W2 as the first electrodes 7.

The first electrodes 7 and the third electrodes 27 are arranged such that the bridging segments 60 of the third electrodes 27 overlie the bridging segments 58 of the first electrodes 7. Alternatively, the first electrodes 7 and the third electrodes 27 may be arranged such that the pad segments 59 of the third electrodes 27 overlie the pad segments 57 of the first electrodes 7. The pad segments 57, 59 need not be diamond shaped, and may instead be circular. The pad segments 57, 59 may be a regular polygon such as a triangle, square, pentagon or hexagon. The pad segments 57, 59 may be I shaped or Z shaped.

The alternative geometries of first and third electrodes 7, 27 of the first touch panel 43 are equally applicable to the first and second electrodes 7, 8 of the second touch panel 53·

Third touch panel

Referring also Figure 9, a third touch panel 61 may be included in the first or second touch panel system 42, 52 instead of the first touch panel 43. The third touch panel 61 is substantially the same as the first touch panel 43 except that the third touch panel 61 does not include the second layer structure 24 and the third electrodes 27 are disposed on the first face 5 of the first layer structure 4 in addition to the first electrodes 7. Each first electrode 7 is a continuous conductive region extending in the first direction x. For example, each first electrode 7 may include several pad segments 62 evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrow bridging segments 63. Each third electrode 27 may comprise several pad segments 64 evenly spaced in the second direction y. However, the pad segments 64 of the third touch panel 61 are disposed on the first face 5 of the first layer structure 4 and are interspersed with, and separated by, the first electrodes 7. The pad segments 64 corresponding to each third electrode 27 are connected together by conductive jumpers 65. The jumpers 65 each span a part of a first electrode 7 and the jumpers 65 are insulated from the first electrodes 7 by a thin layer of dielectric material (not shown) which may be localised to the area around the intersection of the jumper 65 and the first electrode 7. Alternatively, a dielectric layer (not shown) may overlie the first face 5 of the first layer structure 4 and the first and third electrodes 7, 27. Conductive traces (not shown) extending in the second direction y may be disposed over the dielectric layer (not shown), each conductive trace (not shown) overlying the pad segments 64 making up one third electrode 27. The overlying conductive traces (not shown) may connect the pad segments 64 making up each third electrode 27 using vias (not shown) formed through the dielectric layer (not shown).

Patterned second electrode

Referring also to Figure 10, a patterned second electrode 66 is in the form of a

Cartesian grid. The conductive region of the patterned second electrode 66 includes struts 67 extending in the first direction x and having a width W in the second direction y, and struts 68 extending in the second direction y and having a width W in the first direction x. The struts 67 extending in the first direction x are evenly spaced in the second direction y with a spacing S, and the struts 68 extending in the second direction y are evenly spaced in the first direction x with the same spacing S. The struts 67, 68 are joined where they intersect such that the patterned second electrode 66 is formed of a single region of conductive material.

The patterned second electrode 66 may be arranged such that the magnitude of a mutual capacitance between the first electrode 7 and the second electrode 8 is reduced in the first touch panel 43. This may increase the relative size of changes in the mutual capacitance between the first electrode 7 and the second electrode 8 resulting from a users touch, making such changes easier to detect.

Additionally or alternatively, the patterned second electrode 66 may be placed between the first and/or third electrodes 7, 27 and a user's digit or stylus without entirely screening the first and/ or third electrodes 7, 27 from electrostatic interactions with the user's digit or stylus.

Fourth touch panel

Referring also to Figures 11 and 12, a fourth touch panel 69 is shown.

The fourth touch panel 69 includes the first layer 4, a plurality of first electrodes 7 disposed on the first face 5 of the first layer structure 4, a plurality of third electrodes 27 disposed on the second face 6 of the first layer structure 4 and a plurality of second electrodes 8 disposed on the second face 6 of the layer structure 4 in the form of a plurality of separated second electrodes 70.

The first electrodes 7 extend in the first direction x and are spaced apart in the second direction y. The third electrodes 27 extend in the second direction y and are spaced apart in the first direction x. The separated second electrodes 70 extend in the second direction y are spaced apart in the first direction x. The separated second electrodes 70 and the third electrodes 27 are interleaved and do not contact one another. The separated second electrodes 70 and the third electrodes 27 could also be described as interdigitated. The separated second electrodes 70 and third electrodes 27 may be read using conductive traces (not shown) which exit the fourth touch panel 69 on different edges. Each first electrode 7 may take the form of several pad segments 71 evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrow bridging segments 72. Similarly, each third electrode 27 may include several pad segments 73 evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrow bridging segments 74. The pad segments 71 of the first electrodes 7 may be diamond shaped. The pad segments 73 and bridging segments 74 of the third electrodes 27 may have the same respective shapes and widths as the first electrodes 7. Each separated second electrode 70 may include several pad segments 75 evenly spaced in the second direction y and connected to one another in the second direction y by relatively narrow bridging segments 76. The pad segments 75 and bridging segments 76 of the separated second electrodes 70 may have the same respective shapes and widths as the first and third electrodes 7, 27.

Alternatively, the pad segments 71 of the first electrodes 7 may be larger or smaller than the pad segments 71 of the separated second electrodes 70. The first electrodes 7 and the third electrodes 27 are arranged such that the bridging segments 74 of the third electrodes 27 overlie the bridging segments 72 of the first electrodes 7. The first electrodes 7 and the third electrodes 27 are arranged such that the respective pad segments 71, 73 do not overlap. Instead, the separated second electrodes 70 are arranged such that the pad segments 75 of the separated second electrodes 70 overlap the pad segments 71 of the first electrodes 7. The pad segments 7 73, 75 need not be diamond shaped, and may instead be circular. The pad segments 7 73, 75 may be a regular polygonal shape such as a triangle, square, pentagon or hexagon.

The fourth touch panel 69 may be used in, for example, the first or second touch panel systems 42, 52 to measure mutual capacitance between a pair of first and third electrodes 7, 27. The separated second electrodes 70 may be coupled to each another, for example using external traces (not shown) and addressed collectively to measure pressure values between a first electrode 7 and the separated second electrodes 70. Alternatively, the separated second electrodes 70 may be individually addressable to measure pressure values using a pair of first and separated second electrodes 7, 70.

Pre-amplification signal separation

In the first and second touch panel systems 42, 52, a single input signal 10 including both pressure and capacitance information is received from an electrode 7, 27, before being amplified to generate an amplified signal 14 which is subsequently filtered by the first and second frequency dependent filters 12, 13 to separate the pressure and capacitance information.

In an alternative approach to combined pressure and capacitance sensing, a single input signal 10 including pressure and capacitance information may be separated into pressure and capacitance components before or concurrent with amplification of the pressure signal. Touch panel systems employing post separation amplification can also benefit from many of the improvements provided by multiplexing amplified signals from a plurality of amplifiers.

Referring also to Figure 13, a third apparatus 77 for combined pressure and capacitance sensing is shown. The third apparatus 77 includes a first touch sensor 2 and an alternative front end module 78. The alternative front end module 78 includes a signal separation stage 79 and an amplification stage 80. The alternative front end module 78 is connected to the touch sensor 2, a capacitive touch controller 81 and a pressure signal processing module 82. The alternative front end module 78 allows capacitance and pressure measurements to be made from the first touch sensor 2 concurrently using one pair of electrodes 7, 8.

The alternative front end module 78 includes a first input/output terminal A for connecting to the touch sensor 2 and a second input/output terminal F for connecting to the capacitive touch controller 81. The signal separation stage 79 includes a first, capacitance signal filter 83. The signal separation stage 79 connects the first input/ output terminal A to the second input/ output terminal F via the capacitance signal filter 83. The capacitance signal filter 83 filters signals between the second input/ output terminal F and the first input/ output terminal A. The signal separation stage 79 also connects the amplification stage 80 to the first input/output terminal A. Signals between the first input/output terminal A and the amplification stage 80 are not filtered by the capacitance signal filter 83. The amplification stage 80 is connected to the first input/ output terminal A through the signal separation stage 79. The amplification stage 80 includes a second, pressure signal filter 84 and an amplifier 85. The pressure signal filter 84 receives an input signal 86 from an electrode 7 of the touch sensor 2 and filters it to produce a pressure signal 87. The amplifier 85 receives the pressure signal 87 and amplifies it to output an amplified signal 88. The amplifier 85 may provide additional frequency dependent filtering. The amplifier 85 is a charge amplifier.

Alternatively, the pressure signal filter 84 may be integrated as a single unit with an amplifier 85 in the form of, for example, an operational amplifier and a resistance- capacitance feedback network. In this case, the amplifier 85 receives the input signal 86 directly and the amplified signal 88 is based on the touch sensor signal 86.

Alternatively, the pressure signal filter 84 may be included in the signal separation stage 79 instead of the amplification stage 80. When the pressure signal filter 84 is included in the signal separation stage 79, the pressure signal filter 84 filters signals between the first input/output terminal A and the amplification stage 80. Signals between the first and second input/output terminals A, F are not filtered by the pressure signal filter 84.

The pressure signal filter 84 and/or the amplifier 85 may have a low-frequency cut-off configured to reject a pyroelectric response of the layer of piezoelectric material 9. The low frequency cut-off may take a value between 1 Hz and 7 Hz. The pressure signal filter 84 and/or the amplifier 85 may include a notch filter configured to reject a mains power distribution frequency, for example, 50 Hz or 60 Hz. Alternatively, the mains power notch filter may be a separate filter stage (not shown) disposed before or after the pressure signal filter 84 and/ or the amplifier 85.

The capacitive touch controller 81 is, in general, a conventional capacitive touch controller capable of measuring the self-capacitance or mutual capacitance of a projected capacitance touch panel electrode. For example, the capacitive touch controller may be a commercially available touch controller such as an Atmel (RTM) MXT224 touch controller. For example, for a mutual capacitance measurement, the capacitive touch controller 81 outputs a capacitance measurement drive signal 89 which drives the second electrode 8 as a transmitting or Tx electrode. The first electrode 7 serves as a receiving or Rx electrode and picks up a received signal 90 based on the drive signal 89 and a mutual capacitance between the first and second electrodes 7, 8. The drive and received signals 89, 90 typically have the same frequency contents. The capacitance signal filter 83 has a frequency response which passes the

drive/received signals 89, 90 without attenuation, or with minimal attenuation. Based on the transmitted drive signal 89 and the received signal 90, the capacitive touch controller 81 calculates a mutual capacitance value and provides an output comprising capacitance values 91.

The specific method and the specific waveforms of the capacitance measurement drive signals 89 depend on the particular capacitive touch controller 81 used. However, any capacitive touch controller 81 may be used with the alternative front end module 78 by adjusting the bandwidth of the capacitance signal filter 83 to pass the capacitance measurement drive signals 89 produced by a particular capacitive touch controller 81 and picked up as received signal 90. The input signal 86 may differ slightly from the received signal in response to a user interaction with the first touch sensor 2, or with a layer of material overlying the first touch sensor 2, which produces a piezoelectric response from the layer of piezoelectric material 9. In this way, the input signal 86 is approximately a superposition of a received signal 90 and a piezoelectric response I_Pi_ezo{t) which is approximately the same as the pressure signal 87. Because the capacitance signal filter 83 is adapted to pass the received signal 90, the capacitive touch controller 81 may communicate with the touch sensor 2 and receive the received signal 90 with no, or minimal, interference from the pressure signal. In this way, a capacitive touch controller 81 suitable for use with a conventional projected capacitance touch panel can be used with the alternative front end module 78. The pressure signal filter 84 is adapted to reject, or at least attenuate, the received signals 90. In this way, the amplified signal 88 may be based on the pressure signal 87 corresponding to a piezoelectric response I_Pi_ezo{t) produced by straining the layer of piezoelectric material 9.

The separation of the received signals 90 and the pressure signals 87 is possible because, as described hereinbefore, these signals have dissimilar and generally separable frequency bandwidths. Consequently, the capacitance signal filter 83 maybe adapted to pass the received signals 90 having relatively higher frequency content, and the pressure signal filter 84 may be adapted so that the pressure signal 87 is

substantially based on the relatively lower frequency piezoelectric response I_Pi_ezo{t). For example, the capacitance signal filter 83 may be a high-pass filter and the pressure signal filter 84 may be a low-pass filter. In this way, the amplitude of the amplified signal 88 is dependent upon a pressure applied to the first touch sensor 2. The pressure signal processing module 82 receives the amplified signals 88, determines pressure values 92 and provides the pressure values 92 as an output. The pressure signal processing module 82 may determine the pressure value 92 corresponding to a given amplified signal 88 using, for example, a pre-calibrated empirical relationship, or by interpolation of a pre-calibrated look-up table.

In practice, the pressure signal 87 will not be identical to the piezoelectric response Ipiezoi , and may include attenuated high frequency components of the received signals 90. Such attenuated high frequency components may be compensated/ removed by subsequent digital signal processing of the amplified signal 88, for example in the pressure signal processing module 82 or in the processor 33 of an electronic device 29. In this way, the third apparatus 77 may be used for combined pressure and capacitance sensing, although in a different way to the first or second apparatus 1, 22 or first or second touch panel systems 42, 52. Compared to the first or second apparatus 1, 22 or first or second touch panel systems 42, 52, the third apparatus 77 allows the separation and amplification of pressure and capacitance signals in a way which may be readily integrated with existing projected capacitance touch panels and capacitive touch controllers 81.

The capacitance and pressure signal filters 83, 84 need not be high-pass and low-pass filters respectively. Instead, the capacitance signal filter 83 may be a band-pass filter having a pass-band covering the driving and received signals 89, 90 and the pressure signal filter 84 may be a low-pass filter with a cut-off frequency below a base frequency fd of the driving and received signals 89, 90. Alternatively, the capacitance signal filter

83 maybe a band-pass filter having a pass-band covering the driving and received signals 89, 90 and the pressure signal filter 84 may be a band-stop filter having a stop- band covering the driving and received signals 89, 90. Band-pass or band-stop filters may be notch filters when the driving and received signals 89, 9ohave narrow frequency bandwidths, or comb filters if the power of the driving and received signals 89, 90 is predominantly at the base frequency fd and harmonics thereof. The filters 83,

84 may be passive or active, for example, the capacitance signal filter 83 may simply be a capacitance, or the pressure signal filter 84 maybe provided by a resistance- capacitance feedback network of an operational amplifier providing the amplifier 85. Alternatively, more complex passive filters may be used, for example Butterworth filters, Chebyshev filters, Gaussian filters or Bessel filters.

Alternatively, the third apparatus 77 maybe used with a capacitive touch controller 81 which measures self-capacitances, in which case the self-capacitance measurement signal (not shown) would be provided to the first electrode 7 via the signal separation stage 79 and capacitance signal filter 83. In this case, the capacitive touch controller 81 may also output a biasing signal to the second electrode 8 to screen out the mutual capacitance between the first and second electrodes 7, 8.

The third apparatus 77 may also be used with the second touch sensor 23, for example a third apparatus 77 may be connected to each of the first and third electrodes 7, 27.

Third touch panel system

Touch panel systems including touch panels including multiple touch sensors 2, 23 combined with apparatus for combined capacitance and pressure sensing employing pre-amplification signal separation have been described in GB 2544353 A, in particular with reference to Figures 5, 10 to 12, 15 and 19 to 23 of this document.

In the touch panel systems described in GB 2544353 A, an amplifier was provided corresponding to each electrode, or several electrodes were connected to a smaller number of amplifier by an impedance network to produce aggregated pressure signals.

The multiplexing of amplified signals described in relation to the first and second touch panel systems 42, 52 may be employed in the context of pre-amplifi cation signal separation and may obtain many of the same effects. In particular, multiplexing of amplified signals allows a reduction in the number of ADCs required.

Referring also to Figure 14, a third touch panel system 93 includes the first touch panel 43 and a third touch controller 94 for combined pressure and capacitance sensing.

The first touch panel 43 may be bonded overlying the display 38 of an electronic device 29. In this case, the materials of the first touch panel 43 should be substantially transparent as described hereinbefore. A cover lens 46 (Figure 16) may be bonded overlying the first touch panel 43. The cover lens 46 (Figure 16) is preferably glass but may be any transparent material. The cover lens 46 (Figure 16) may be bonded to the first touch panel 43 using a layer of pressure sensitive adhesive (PSA) material not shown. The layer of PSA material (not shown) may be substantially transparent. The first and third electrodes 7, 27 may be fabricated using index matching techniques to minimise visibility to a user.

The third touch controller 94 includes a capacitive touch controller 81, a number of signal separation stages 79, an amplifier module 95, a multiplexer 96, an ADC 97 and a controller 98. The controller 98 may communicate with the processor 33 of the electronic device 29 using a link 32.

Each separation stage 79 includes a capacitance signal filter 83. The amplifier module 95 includes a number of charge amplifiers 99. The pressure signal filters 84 may be included in the separation stages 79 or integrated with the amplifiers 99. Each charge amplifier 99 of the amplifier module 95 is connected to a corresponding first electrode 7 via a respective terminal Di, D5 and conductive trace 45. The outputs of the charge amplifiers 99 of the amplifier module 95 are each connected to a corresponding input of the multiplexer 96. In this way, the multiplexer 96 may output an amplified signal 88 corresponding to an addressed first electrode 7. The amplified signal 88 is converted into a digital signal by the ADC 97 before processing by the controller 98, which provides the functions of the pressure signal processing module. The ADC 97 may be integrated with the controller 98. The controller 98 determines pressure values 92 and outputs the pressure values 92 via the link 32. The controller 98 may perform additional filtering to remove and residual components of the received signal 90.

The capacitive touch controller 81 is connected to each third electrode 27 via a respective terminal Ci, C5 to supply capacitance measurement driving signals 89 to the third electrodes 27. In the example shown in Figure 14, the third electrodes 27 serve as transmitting, Tx, electrodes and the first electrodes serve as receiving, Rx, electrodes for mutual capacitance measurements. If the capacitive touch controller 81 has fewer driving outputs than there are third electrodes 27, a further multiplexer (not shown) may be included to enable driving of each third electrode 27. The capacitive touch controller 81 outputs capacitance values to the controller 98 for output via the link 32.

The controller 98 may provide a synchronisation signal 100 to the multiplexer 96, amplifiers 99 and/ or ADC 97. The synchronisation signal 100 may cause the multiplexer 96 to address each first electrode 7 according to a sequence determined by the controller 98. The controller 98 may also provide the synchronisation signal 100 to the capacitive touch controller 81 to cause the capacitive touch controller 81 to drive each third electrode 27 according to a sequence determined by the controller 98. In this way, the third touch controller 94 may obtain pressure and capacitance

information corresponding to each pairing of a first electrode 7 and a third electrode 27 according to a sequence which maybe predetermined or dynamically determined in the same way as for the first and second touch controllers 44, 54. In the example shown in Figure 14, the third touch panel system 93 allows

measurements of two-dimensional mutual capacitance information in the first and second directions x, y, and one-dimensional pressure information in the first direction x. In alternative examples, a second pressure measurement channel including signal separation stages 79, an amplifier module 95 and a multiplexer 96 may be provided for the third electrodes 27 to add another dimension of pressure sensing. In this latter case, the capacitive touch controller 81 may drive the third electrodes 27 through signal separation stages 79 of the second pressure measurement channel.

In the example shown in Figure 14, the capacitive touch controller 81 performs mutual capacitance measurements. Alternatively, the capacitive touch controller 81 may perform self-capacitance measurements of the first and third electrodes 7, 27 individually.

The capacitive touch controller 81 does not need to be a separate module within the third touch controller 94, and alternatively may be integrated with the controller 98. In other examples, the capacitive touch controller 81 may be provided separately from the third touch controller 94, which may facilitate augmenting an existing projected capacitance touch system with pressure sensing on one or both of x- and y-electrodes.

Multiplexing of the amplified signals 88 may provide some or all of the same effects as in the first and second touch systems 42, 52.

The third touch controller 94 may also be used with the second, third or fourth touch panels 53, 61, 69 instead of the first touch panel 43.

Example of charge amplifiers

Referring also to Figure 15, an example of one configuration of the charge amplifiers 99 and signal separation stages 79 of the amplifier module 95 is shown.

In one configuration, each charge amplifier 99 includes an operational amplifier OP having an inverting input, a non-inverting input and an output. Each charge amplifier 99 forming part of the amplifier module 95 includes an operational amplifier OP having an inverting input coupled to a corresponding terminal D via an input resistance R₂ and a first switch SWi connected in series. The non-inverting input of the operational amplifier OP is connected to a common mode voltage VCM- A feedback network of the charge amplifier 99 includes a feedback resistance Rf, a feedback capacitance and a second switch SW2 connected in parallel between the inverting input and the output of the operational amplifier OP. The output of the operational amplifier V_out provides the amplified signal 88. The capacitive touch controller 81 is connected to a node 101 between the input resistance R₂ and the terminal D via a resistance Ri and capacitance d connected in series. The resistances Ri, R₂, capacitance G and node 101 together form the signal separation stage 79 in the example shown in Figure 15. The capacitance signal filter 83 takes the form of the capacitance Ci. The feedback resistance and capacitance Rf, Cf, in combination with the input resistance R₂, control the frequency dependence of the amplifier 99, and are selected to provide the pressure signal filter 84 and attenuate the drive/received signals 89, 90. Other terminals of the operational amplifier OP, such as power supply terminals, may be present, but are not shown in this or other schematic circuit diagrams described herein.

The second switches SW2 permit the corresponding feedback capacitors C/to be discharged. The opening and closing of the second switches SW2 may be governed by a synchronisation signal 100 provided by the controller 98. In this way, the feedback capacitors of each charge amplifier 99 may be periodically discharged in order to reset the feedback network of the operational amplifier OP to prevent excessive drift. Similarly, the first switches SWi may be controlled by a synchronisation signal 100 provided by the controller 98 to enable connected or disconnected from the

corresponding first electrode 7 if required.

Touch display stack-ups

The first, second and third touch controllers 44, 54, 94 may be used in combination with a variety of different touch display stack-ups. The following examples are intended to demonstrate the versatility of the first, second and third touch controllers 44, 54, 94 and the following examples are not exhaustive.

Referring also to Figure 16, a first display stack-up 102 is shown.

The first display stack-up 102 includes a display 38, the second electrode 8, the layer of piezoelectric material 9, a first dielectric layer 103, the first electrodes 7, a second dielectric layer 104, the third electrodes 27 and a cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46. The first layer structure 4 includes the layer of piezoelectric material 9 and the first dielectric layer. The second layer structure 24 corresponds to the second dielectric layer 104. The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on the first dielectric layer 103. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on the second dielectric layer 104. The second electrode 8 takes the form of a conductive material region disposed on the layer of piezoelectric material 9 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27.

The cover lens 46 is made of glass, or PET or any other substantially transparent material. The cover lens 46 may be up to about 20 mm thick and may be at least 0.05 mm thick. Preferably, the cover lens 46 is up to about 2 mm thick and may be at least 0.05 mm thick. The layer of piezoelectric material 9 is made of PVDF or any other substantially transparent piezoelectric material. An alternative material is polylactic acid. The layer of piezoelectric material may be up to about 110 μπι thick, and may be at least 0.5 μπι or at least 1 μπι thick. The dielectric layers 103, 104 may be PET or any other substantially transparent polymer. The dielectric layers 103, 104 may be between 10 μπι and 100 μπι thick, for example, around 20 to 25 μπι thick. Preferably the dielectric layers 103, 104 are in the range of about ιο-ιοομπι thick. The conductive regions providing the electrodes 7, 8, 27 may be ITO, IZO or any other substantially transparent conductive material. The conductive regions providing the electrodes 7, 8, 27 may be applied to the dielectric layers 103, 104 and/ or the layer of piezoelectric material 9 using lithography, printing or other suitable methods. The shapes of the conductive regions providing the first, second and third electrodes 7, 8, 27 may be any suitable electrode shape described in relation to the first or second touch panels 43, 53. The sheet resistance of conductive regions providing electrodes may be between 1 and 200 Ω/ sq. The sheet resistance may be below 10 Ω/ sq. Preferably, the sheet resistance is as low as is practical.

Referring also to Figure 17, a second display stack-up 105 is shown.

The second display stack-up 105 is the same as the first display stack-up 102, except that elements of the second display stack-up 105 are bonded to one another using layers of pressure sensitive adhesive (PSA) material 106 extending in the first x and second y directions. Referring also to Figure 18, a third display stack-up 107 is shown.

The third display stack-up 107 includes a display 38, a PSA layer 106, the second electrode 8, the layer of piezoelectric material 9, the first electrodes 7, a PSA layer 106, a first dielectric layer 103, the third electrodes 27, a PSA layer 106 and the cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46.

The first electrodes 7 take the form of conductive regions extending in a second direction y and spaced apart in the first direction x, and are disposed on a face of the layer of piezoelectric material 9. The second electrode 8 takes the form of a conductive material region and is disposed on the opposite face of the layer of piezoelectric material 9 to the first electrodes 7. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on the first dielectric layer 103. The second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27.

The first layer structure 4 includes the layer of piezoelectric material 9 and the second layer structure 24 includes the first dielectric layer 103 and a PSA layer 106.

Referring also to Figure 19, a fourth display stack-up 108 is shown.

The fourth display stack-up 108 includes a display 38, a first dielectric layer 103, the second electrode 8, a PSA layer 106, the layer of piezoelectric material 9, a PSA layer 106, a second dielectric layer 104, the first electrodes 7, a PSA layer 106, a third dielectric layer 109, the third electrode 27, a PSA layer 106 and a cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46.

The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on the second dielectric layer 104. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on the third dielectric layer 109. The second electrode 8 takes the form of a conductive material region which is disposed on the first dielectric layer 103 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27. The first layer structure 4 includes the layer of piezoelectric material 9, the second dielectric layer 104 and two PSA layers 106. The second layer structure 24 includes the third dielectric layer 109 and a PSA layer 106.

Thus, in the fourth display stack-up 108, the layer of piezoelectric material 9 does not have any electrodes disposed thereon. This may simplify the fabrication of the fourth stack-up substantially because processing steps to deposit electrodes on the layer of piezoelectric material 9 are not required.

Referring also to Figure 20, a fifth display stack-up 110 is shown.

The fifth display stack-up 110 includes a display 38, a PSA layer 106, the second electrode 8, the layer of piezoelectric material 9, a PSA layer 106, the first electrodes 7, a first dielectric layer 103, the third electrodes 27, a PSA layer and the cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46.

The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on a face of the first dielectric layer 103. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on the opposite face of the first dielectric layer 103 to the first electrodes 7. The second electrode 8 takes the form of a conductive material region which is disposed on the layer of piezoelectric material 9 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27.

The first layer structure 4 includes the layer of piezoelectric material 9 and a PSA layer 106. The second layer structure 24 includes the first dielectric layer 103. The second electrode 8 need not be disposed on the layer of piezoelectric material 9. Alternatively, the fifth display stack-up 110 may include an additional dielectric layer (not shown) supporting the second electrode 8.

Referring also to Figure 21, a sixth display stack-up 111 is shown. The sixth display stack-up 111 includes a display 38, a PSA layer 106, the second electrode 8, the layer of piezoelectric material 9, a PSA layer 106, a first dielectric layer 103, the first and third electrodes 7, 27, a PSA layer 106, and the cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46.

The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on a face of the first dielectric layer 103. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on the same face of the first dielectric layer 103 as the first electrodes 7. Each first electrode 7 is a continuous conductive region and each third electrode is made up of a number of separate conductive regions connected by jumpers 65. Each jumper spans a portion of a conductive region belonging to a first electrode 7. The first and third electrodes 7, 27 may be substantially the same as the first and third electrodes 7, 27 of the third touch panel 61. The second electrode 8 takes the form of a conductive material region which is disposed on the layer of piezoelectric material 9 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27 region. The first layer structure 4 includes the layer of piezoelectric material 9, a layer of PSA material 106 and the first dielectric layer 103. The sixth display stack-up 111 does not include a second layer structure 24.

The second electrode 8 need not be disposed on the layer of piezoelectric material 9. Alternatively, the sixth display stack-up 111 may include an additional dielectric layer (not shown) supporting the second electrode 8.

Referring also to Figure 22, a seventh display stack-up 112 is shown. The seventh display stack-up 112 includes a display 38, a PSA layer 106, the second electrode 8, the layer of piezoelectric material 9, a PSA layer 106, a first dielectric layer 103, the first electrodes 7, a PSA layer 106, the third electrodes 27, and the cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46. The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on the first dielectric layer 103. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are disposed on an interior face of the cover lens 46. The second electrode 8 takes the form of a conductive material region which is disposed on the layer of piezoelectric material 9 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27 region.

The first layer structure 4 includes the first dielectric layer 103, the layer of piezoelectric material 9 and a PSA layer 106. The second layer structure 24 includes a PSA layer 106.

The second electrode 8 need not be disposed on the layer of piezoelectric material 9. Alternatively, the seventh display stack-up 112 may include an additional dielectric layer (not shown) supporting the second electrode 8. Referring also to Figure 23, an eighth display stack-up 113 is shown.

The eighth display stack-up 113 includes a display 38, a PSA layer 106, a first dielectric layer 103, the second electrode 8, a PSA layer 106, the layer of piezoelectric material 9, a PSA layer 106, the first and third electrodes 7, 27, and the cover lens 46, stacked in the thickness direction z from the display 38 to the cover lens 46.

The first electrodes 7 take the form of a set of conductive regions extending in the second direction y and spaced apart in the first direction x, and are disposed on an interior face of the cover lens 46. The third electrodes 27 take the form of a set of conductive regions extending in the first direction x and spaced apart in the second direction y, and are also disposed on the same face of the cover lens 46 as the first electrodes 27. Each first electrode 7 is a continuous conductive region and each third electrode 27 is made up of a number of separate conductive regions connected by jumpers 65. Each jumper 65 spans a portion of a conductive region belonging to a first electrode 7. The first and third electrodes 7, 27 may be substantially similar to the first and third electrodes 7, 27 of the third touch panel 61. The second electrode 8 takes the form of a conductive material region which is disposed on the first dielectric layer 103 such that the second electrode 8 at least partially overlaps each first electrode 7 and each third electrode 27. The second electrode 8 need not be disposed on the first dielectric layer 103.

Alternatively, the eighth display stack-up 113 may include a layer of piezoelectric material 9 having the second electrode 8 disposed on the layer of piezoelectric material 9-

Embedded stack-ups

The first to eighth display stack-ups 102, 105, 107, 108, 109, 110, 111, 112, 113 are bonded overlying a display 38 of an electronic device 29. Alternatively, the first, second and third touch controllers 44, 54, 94 may equally be used with touch panels which are embedded or integrated within the structure of a display 38 such as, for example, an LCD display, an OLED display, a plasma display or an electrophoretic display.

Referring also to Figure 24, a first embedded stack-up 114 includes a pixel array 115 of a display 38, a colour filter glass 116, first and third electrodes 7, 27, a first layer structure 4, a patterned second electrode 66, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed on the same face of the first layer structure 4 in

substantially the same way as the third touch panel 61. In this way, the first embedded stack-up 114 can be used in combination with the first, second or third touch controllers 44, 54, 94 to provide a touch panel with combined capacitive and pressure sensing embedded within an LCD display. This may allow the total thickness of the display 38 and touch panel to be reduced compared to a touch panel stack-up overlying the display 38.

Referring also to Figure 25, a second embedded stack-up 118 includes a pixel array 115 of a display 38, third electrodes 27, a colour filter glass 116, first electrodes 7 a first layer structure 4, a patterned second electrode 66, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed in substantially the same way as the first touch panel 43, except that the first and third electrodes 7, 27 are disposed on opposite sides of the colour filter glass 116 instead of the second layer structure 24.

Referring also to Figure 26, a third embedded stack-up 119 includes a pixel array 115 of a display 38, third electrodes 27, a second layer structure 24, first electrodes 7, a colour filter glass 116, a first layer structure 4, a patterned second electrode 66, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed in substantially the same way as the first touch panel 43. In the third embedded stack-up 119, the first and third electrodes 7, 27 are separated by the second layer structure 24. However, the third embedded stack-up 119 may alternatively omit the second layer structure 124 and include first and third electrodes 7, 27 disposed in substantially the same way as the third touch panel 61. Referring also to Figure 27, a fourth embedded stack-up 120 includes a pixel array 115 of a display 28, a colour filter glass 116, first and third electrodes 7, 27, a polariser 117, a first layer structure 4, a patterned second electrode 66, and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed on the same face of the colour filter glass 116 in substantially the same way as the third touch panel 61.

Referring also to Figure 28, a fifth embedded stack-up 121 includes a pixel array 115 of a display 38, third electrodes 27, a colour filter glass 116, first electrodes 7, a polariser 117, a first layer structure 4, a patterned second electrode 66, and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed in substantially the same way as the first touch panel 43, except that the first and third electrodes 7, 27 are disposed on opposite sides of the colour filter glass 116. Referring also to Figure 29, a sixth embedded stack-up 122 includes a pixel array 115 of a display 38, third electrodes 27, a second layer structure 24, first electrodes 7, a first layer structure 4, a colour filter glass 116, a patterned second electrode 66, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27are disposed in substantially the same way as the first touch panel 43.

Referring also to Figure 30, a seventh embedded stack-up 123 includes a pixel array 115 of a display 38, third electrodes 27, a second layer structure 24, first electrodes 7, a first layer structure 4, a patterned second electrode 66, a colour filter glass 116, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed in substantially the same way as the first touch panel 43.

Referring also to Figure 31, an eighth embedded stack-up 124 includes a pixel array 115 of a display 38, third electrodes 27, a second layer structure 24, first electrodes 7, a colour filter glass 116, a polariser 117, a first layer structure 4, a patterned second electrode 66 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The first and third electrodes 7, 27 are disposed in substantially the same way as the first touch panel 43.

The sixth, seventh and eighth embedded stack-ups 122, 123, 124 have been described with the first and third electrodes 7, 27 separated by the second layer structure 24. However, the sixth, seventh and eighth embedded stack-ups 122, 123, 124 may alternatively omit the second layer structure 24 and include first and third electrodes 7, 27 disposed in substantially the same way as the third touch panel 61.

The first to eighth embedded stack-ups 114, 118, 119, 120, 121, 122, 123, 124 have been described as including the patterned second electrode 66. However, the patterned second electrode 66 need not be used and the first to eighth embedded stack-ups 114, 118, 119, 120, 121, 122, 123, 124 may instead include un-patterned second electrodes 8.

Referring also to Figure 32, a ninth embedded stack-up 125 is shown. The ninth embedded stack-up 125 includes a pixel array 115 of a display 38, a colour filter glass 116, first electrodes 7, a first layer structure 4, third electrodes 27, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46. The third electrodes 27 may be disposed on the first layer structure 4 and the first electrodes 7 may be disposed on the colour filter glass 116. Alternatively, the third electrodes 27 may be disposed on the first face 5 of the first layer structure 4 and the first electrodes 7 may be disposed on the second face 6 of the first layer structure 4. In some examples, the first layer structure 4 may include only the layer of piezoelectric material 9, in which case the first and third electrodes 7, 27 may be disposed on opposite faces of the layer of piezoelectric material 9.

By omitting the second electrode 9, 66, the display stack-up may be simplified and may also be thinner as fewer layers are required. Additionally, even a patterned second electrode 66 will partially shield the first and third electrodes 7, 27, and thus reduce the sensitivity of capacitive touch measurements, if located between a user and the first and third electrodes 7, 27. Such problems maybe avoided using the ninth embedded stack- up 125.

Referring also to Figure 33, a tenth embedded stack-up 126 is shown. The tenth embedded stack-up 126 is the same as the ninth embedded stack-up 125, except that the order of the first electrodes 7 and the colour filter glass 116 is reversed, so that the tenth embedded stack-up 126 includes a pixel array 115 of a display 38, first electrodes 7, a colour filter glass 116, a first layer structure 4, third electrodes 27, a polariser 117 and a cover lens 46 stacked in the thickness direction z from the pixel array 115 to the cover lens 46.

Modifications

It will be appreciated that many modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of pressure-sensing projected capacitance touch panels and which maybe used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicant hereby gives notice that new claims may be formulated to such features and/ or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

1. A device for processing signals from a projected capacitance touch panel, the touch panel comprising a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode, the device comprising:

a multiplexer comprising a plurality of inputs and an output;

a plurality of amplification stages, each amplification stage comprising an input configured to receive signals from a corresponding first electrode, and an output coupled to a corresponding input of the multiplexer;

at least one signal splitter stage, each signal splitter stage configured to generate, based on signals received from a given first electrode, a pressure signal indicative of a pressure applied to the touch panel proximate to the given first electrode and a capacitance signal indicative of a capacitance of the given first electrode.

2. A device according to any preceding claim, wherein each amplification stage comprises a charge amplifier.

3. A device according to claim 1 or claim 2, wherein at least one signal splitter stage comprises a signal splitter stage connected to the multiplexer output and configured to split signals received from the multiplexer output into first and second signals, to pass the first signal to a first frequency dependent filter configured to attenuate the pressure signal and pass the capacitance signal, and to pass the second signal to a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal.

4. A device according to claim 3, wherein the first and second frequency dependent filters comprise active or passive filter circuits.

5. A device according to claim 3, wherein the signal splitter stage comprises a data processing device configured to apply the first and second frequency dependent filters to signals received from the multiplexer output.

6. A device according to claim 1 or claim 2, wherein at least one signal splitter stage comprises a plurality of signal splitter stages, each signal splitter stage configured to receive signals from a corresponding first electrode and split the received signals into first and second signals, to pass the first signal to a first frequency dependent filter configured to attenuate the pressure signal and pass the capacitance signal, and to pass the second signal to a corresponding amplification stage.

7. A device according to claim 6, wherein each signal splitter stage is further configured to pass the second signal to a corresponding amplification stage via a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal.

8. A device according to claim 6, wherein each amplification stage comprises a second frequency dependent filter configured to attenuate the capacitance signal and pass the pressure signal.

9. A device according to claim 6, wherein each amplification stage comprises an amplifier having a frequency bandwidth configured to attenuate the capacitance signal.

10. A touch panel system comprising:

a device according to any preceding claim; and

a projected capacitance touch panel comprising a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode;

wherein the device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding first electrode.

11. A touch panel system according to claim 10, further comprising a second device according to any one of claims 1 to 9;

wherein the projected capacitance touch panel further comprises a plurality of third electrodes separated from the at least one second electrode by the layer of piezoelectric material;

wherein the second device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding third electrode;

wherein each first electrode extends in a first direction and the plurality of first electrodes are disposed in an array spaced apart in a second, different direction, and wherein each third electrode extends in the second direction and the plurality of third electrodes are disposed in an array spaced apart in the first direction.

12. A touch panel system according to claim 10, further comprising a second device according to any one of claims l to 9;

wherein at least one second electrode comprises a plurality of second electrodes; wherein the second device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding second electrode;

wherein each first electrode extends in a first direction and the plurality of first electrodes are disposed in an array spaced apart in a second, different direction, and wherein each second electrode extends in the second direction and the plurality of second electrodes are disposed in an array spaced apart in the first direction.

13. A touch panel system comprising:

a device according to any one of claims 6 to 9;

a projected capacitance touch panel comprising a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode; and a capacitive touch controller;

wherein the device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding first electrode, and wherein the device is connected to the capacitive touch controller such that the capacitive touch controller may transmit and/ or receive capacitance signals to and/ or from each first electrode through a corresponding signal splitter stage.

14. A touch panel system according to claim 13, further comprising a second device according to any one of claims 6 to 9;

wherein the second device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding third electrode, and wherein the second device is connected to the capacitive touch controller such that the capacitive touch controller may transmit and/or receive capacitance signals to and/or from each third electrode through a corresponding signal splitter stage;

15. A touch panel system according to claim 13, further comprising a second device according to any one of claims 6 to 9;

wherein at least one second electrode comprises a plurality of second electrodes; wherein the second device is connected to the projected capacitance touch panel such that each amplification stage input may receive signals from a corresponding second electrode, and wherein the second device is connected to the capacitive touch controller such that the capacitive touch controller may transmit and/ or receive capacitance signals to and/or from each second electrode through a corresponding signal splitter stage;

16. A touch panel system according to any one of claims 13 to 15, wherein the capacitive touch controller, the device and, optionally the second device are integrated within a single package.