Touch-sensing display panel

A touch-sensing display panel, comprising a plurality of image-forming pixel elements; a planar light guide with a first refractive index, having a front surface forming a touch-sensing region and an opposite rear surface facing the pixel elements; a plurality of light emitters arranged at a peripheral region of the panel to emit light into the light guide for propagation therein through total internal reflection; a plurality of light detectors disposed at the peripheral region for receiving light from the light guide; and an optical layer disposed at the rear surface of the light guide to cover a plurality of the image-forming pixel elements in at least a central region of the panel, wherein said optical layer is configured to reflect at least a part of the light from the emitters impinging thereon from within the light guide.

TECHNICAL FIELD

The present invention relates to touch sensing systems and especially to display devices that offer touch sensitivity.

BACKGROUND ART

Display devices with touch sensitivity are used today in a wide variety of applications such as touch pads in laptop computers, all-in-one computers, mobile phones and other hand-held devices, etc. It is often a desire to provide these electronic devices with a relatively large touch sensing display and still let the devices be small and thin.

There are numerous techniques for providing a display device with touch sensitivity, e.g. by adding layers of resistive wire grids or layers for capacitive touch-sensing or by integrating detectors in the display device. The major drawback of these techniques is that they reduce the optical quality of the display device, by reducing the amount of light emitted from the display or by reducing the number of active pixels of the display device.

U.S. Pat. No. 7,432,893 discloses a touch sensing system that uses FTIR (frustrated total internal reflection) to detect touching objects. Light emitted by a light source is coupled into a transparent light guide by a prism, then propagates inside the light guide by total internal reflection where after the transmitted light is received at an array of light detection points. The light may be disturbed (frustrated) by an object touching the light guide, whereby a decrease in transmitted light is sensed at certain light detection points. Providing a display device with this touch sensing system would add an undesired thickness and complexity to the display device.

WO2009/077962 also discloses a touch sensing system that uses FTIR to detect touching objects. Disclosed is a light guide with a tomograph having signal flow ports adjacent the light guide, the flow ports being arrayed around the border of the light guide. Light is emitted into the light guide by the flow ports and propagates inside the light guide by total internal reflection where after the transmitted light is detected at a plurality of flow ports. The light may be disturbed by an object touching the light guide. Providing a display device with this touch sensing system would add an undesired thickness and complexity to the display device.

US20040140960 shows a system which makes use of a different type och touch-sensing mechanism, namely by allowing beams of light to pass over the top surface of an OLED display through a prism or mirror system, and detecting obstruction of those beams. This document also proposes to use OLEDs for the light emitters. Such a design will be comparatively thick and also sensitive to contamination at the edges of the light-deflecting mechanism.

US20080150848 discloses an OLED display combined with touch sensor. In this disclosure, a separate waveguide in which infrared (IR) light propagates by TIR is placed over the display light guide, and throughout the surface of the display light guide, IR-sensing OLED elements are dispersed. Upon touching the waveguide, some light will be scattered downwards and detected by the underlying OLED sensor element. Since this solution requires IR sensors throughout the light guide, the light sensors may occupy a significant part of the display surface, hence affecting the imaging capability. The stacked solution also adds thickness to the design.

SUMMARY

It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the prior art.

Another objective is to reduce the required thickness for providing touch sensitivity to a display device.

One or more of these objects, as well as further objects that may appear from the description below, are at least partly achieved by means of a touch-sensing display apparatus and an electronic device according to the independent claims, embodiments thereof being defined by the dependent claims.

A first aspect of the invention is a touch-sensing display panel, comprising a plurality of image-forming pixel elements; a planar light guide with a first refractive index, having a front surface forming a touch-sensing region and an opposite rear surface facing the pixel elements; a plurality of light emitters arranged at a peripheral region of the panel to emit light into the light guide for propagation therein through total internal reflection in at least the front surface; a plurality of light detectors disposed at the peripheral region for receiving light from the light guide; and an optical layer disposed at the rear surface of the light guide to cover a plurality of the image-forming pixel elements in at least a central region of the panel, wherein said optical layer is configured to reflect at least a part of the light from the emitters impinging thereon from within the light guide.

In one embodiment said optical layer has a second refractive index which is lower than the first refractive index.

In one embodiment an extension portion of the optical layer is disposed over the light emitters, said extension portion having a third refractive index which is higher than the second refractive index.

In one embodiment the third refractive index is equal to or higher than the first refractive index.

In one embodiment the extension portion of the optical layer covers said peripheral region.

In one embodiment the light emitters are coupled to emit light into the light guide, which light bypasses said main portion of the optical layer.

In one embodiment said light emitters and said image-forming pixel elements are OLED elements.

In one embodiment the light emitters are integrated with the image-forming pixel elements in the panel.

In one embodiment said light emitters are disposed behind one of the image-forming pixel elements, and configured to emit light through the image-forming pixel elements and into the light guide.

In one embodiment the extension portion of the optical layer is also disposed over the light detectors.

In one embodiment said light detectors are coupled to receive light from the light guide, which light bypasses said main portion of the optical layer.

In one embodiment said light detectors are OLED elements.

In one embodiment the light detectors are integrated with the image-forming pixel elements in the panel.

In one embodiment the light detectors are functionally arranged in a number of detector subsets, wherein the detectors of one subset are configured to operate as one larger area light detector.

In one embodiment said light detectors and said image-forming pixel elements are stacked OLEDs, wherein the light detectors are configured to detect light from the light guide through the image-forming pixel elements.

In one embodiment at least one of said light detectors is disposed behind a plurality of the image-forming pixel elements.

In one embodiment the touch-sensing display panel further comprises a light output mechanism arranged to lead out light from the light guide to the light detectors.

In one embodiment said light guide is a substrate of the panel on which said pixel elements are formed, and said light guide is sealed at an edge portion to a cover disposed on the opposing side of the pixel elements.

In one embodiment said pixel elements are formed on a substrate, which is sealed at an edge portion to a said light guide cover, which is disposed on the opposing side of the pixel elements.

In one embodiment said image forming pixel elements are configured to operate in the visible range, whereas the emitters and detectors are configured to operate in the IR range.

In one embodiment a grid of propagation paths is defined across the touch-sensing region between pairs of light emitters and light detectors.

In one embodiment the touch-sensing display panel comprises an LCD unit, of which a central region is controlled to operate as said image-forming pixels and a peripheral region is controlled to pass light from the light guide to the detectors.

In one embodiment the touch-sensing display panel comprises LCD unit including a backlight, wherein the LCD unit is controlled to emulate said emitters by passing light from the backlight through selected portions of the LCD unit.

According to a second aspect, the invention relates to an electronic device comprising the touch-sensing display panel of any preceding claim, and a controller for causing the image-forming elements to display information content within at least part of the touch surface while causing the touch-sensor elements to provide touch sensitivity within said at least part of the touch surface.

According to a third aspect, the invention relates to a method of producing a touch-sensing display panel, comprising the steps of:

providing a transparent substrate with a first refractive index;

providing an optical layer on a rear surface of the substrate, with a second refractive index which is lower than the first refractive index at a central region;

providing a matrix of pixels at the rear surface over the central region and over a peripheral region;

providing a cover sheet over the pixel matrix; and

sealing the cover sheet to the substrate.

According to a fourth aspect, the invention relates to a method of producing a touch-sensing display panel, comprising the steps of:

providing a carrier sheet;

providing a matrix of pixels on the carrier sheet;

providing a transparent substrate with a first refractive index over the pixels, with an intermediate optical layer with a second refractive index which is lower than the first refractive index at central region of the substrate within a peripheral region;

sealing the transparent substrate to the carrier sheet.

In one embodiment, the method comprises the steps of:

connecting a plurality of pixels in at least the central region to a control circuit configured to drive them to act as image-forming pixel elements;

connecting at least one pixel in the peripheral region to a control circuit configured to drive them to emit light into the transparent substrate for propagation by TIR therein; and

connecting at least one detector in the peripheral region to a control circuit configured to drive it to detect light from the transparent substrate, emanating from the emitter.

In one embodiment said pixels are OLEDs.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention relates to the use of optical techniques, specifically FTIR, for providing touch sensitivity to a display apparatus. More specifically, the invention provides a truly integrated touch-sensing display panel1, operating by means of FTIR. Example embodiments are mainly presented in relation to OLED displays but also to LCD, and throughout the description the same reference numerals are used to identify corresponding elements.

FIG. 1illustrates the operating principle of an touch-sensing FTIR system. In the side view ofFIG. 1, a beam of light is propagated by total internal reflection (TIR) inside a planar (two-dimensional) light guide2. The light guide2comprises opposing surfaces3,4which define a respective boundary surface of the light guide2. Each boundary surface3,4reflects light that impinges on the boundary surface from within the light guide2at an angle that exceeds the so-called critical angle, as is well-known to the skilled person. When an object5is brought sufficiently close to one of the boundary surfaces (here, the top surface3), part of the beam may be scattered by the object5, part of the beam may be absorbed by the object5, and part of the beam may continue to propagate in the light guide by TIR in the incoming direction. Thus, when the object5touches the top surface3, which forms a “touch surface”, the total internal reflection is frustrated and the energy of the transmitted light is decreased, as indicated by the thinned lines to the right of the object5. This phenomenon is known as FTIR (Frustrated Total Internal Reflection) and a corresponding touch-sensing device may be referred to as an “FTIR system”.

Although not shown inFIG. 1, the FTIR system typically includes an arrangement of emitters and detectors, which are distributed along the peripheral region of the touch surface3. Light from an emitter is introduced into the light guide2and propagates by TIR to one or more detectors. Each pair of an emitter and a detector defines a “detection line”, which corresponds to the propagation path from the emitter to the detector. Any object that touches the touch surface along the extent of the detection line will thus decrease or attenuate the amount of light received by the detector. The emitters and detectors are typically arranged to define a grid of intersecting detection lines on the touch surface, whereby each touching object is likely to cause an attenuation of several non-parallel detection lines.

The arrangement of detectors is electrically connected to a signal processor, which acquires and processes an output signal from the arrangement. The output signal is indicative of the power of transmitted light at each detector. The signal processor may be configured to process the output signal for extraction of touch data, such as a position (e.g. x, y coordinates), a shape or an area of each touching object.

WhileFIG. 1illustrates the working principle of FTIR touch as such, the invention relates to a touch-sensing display panel in which an FTIR touch-sensing mechanism is truly integrated with a display, as will be shown with reference to the subsequent drawings.

FIG. 2Ais a top plan view andFIG. 2Bis a side view of a touch-sensing display light guide1according to an embodiment of the invention. The touch-sensing display light guide1is implemented as a combination of a light transmissive light guide2that defines a front touch surface3, and a dual-function display pixel matrix6which is configured to both display images through the front surface3and provide touch sensitivity to the front surface3via FTIR.

As seen in the plan view ofFIG. 2A, a plurality of emitters7and detectors8(collectively referred to as “touch-sensor elements”) are arranged in interleaved fashion underneath a peripheral region of the light guide2. It should be noted, though, that interleaved arrangement is merely one example of positioning the emitters7and detectors. Another example may be to arrange emitters along two sides, and detectors along the other two sides, of the panel1. In the drawings, for illustrative purposes only, emitters7and detectors8are represented by circles and rectangles, respectively. Furthermore, a center region of the light guide2is aligned with a matrix of image-forming elements or picture elements (“pixels” or “pixel elements”)10that define a display area for displaying visual images in monochrome or color. The pixels10, which are indicated as a matrix of square elements inFIG. 2A, may be formed by any available integrated display technology, including but not limited to OLED (Organic Light-Emitting Diode), PLED (Polymer Light-Emitting Diode), LED (Light Emitting Diode), LCD (Liquid Crystal Display) with internal illumination (“backlighting”), TFT-LCD (Thin Film Transistor Liquid Crystal Display), ELD (Electroluminescent Display), etc. Below, embodiments of the invention will be further exemplified mainly with respect to OLED, but also to LCD.

Embodiments of the invention are based on the insight that the emitters7and detectors8may be integrated into the display unit6, and preferably be formed by the same technology as used for producing images in the display area. Furthermore, the transparent display cover, which covers the pixel elements, is also used as a light guide. As such, various embodiments of the invention may be realized with no addition of thickness or bulkiness at all. As used herein, an “integrated” emitter/detector7,8is to be construed as an emitter/detector7,8that is integrally formed on or in a substrate, which typically is a composite substrate comprising a plurality of layers. InFIG. 2B, the integration is indicated by dashed lines indicating that the display unit6is functionally (not physically) separated into a peripheral region11with emitters7and detectors8and a center region12with pixels10, where the emitters7, detectors8and pixels10are integrally formed in a common substrate. Each emitter7is configured to generate a cone of light in any suitable wavelength region. In one embodiment, the emitter7generates light that is invisible to the human eye, preferably in the infrared (IR) or possibly in the ultraviolet (UV) region. Each detector8is configured to be responsive to the light emitted by emitters7.

Compared to the prior art as described in the background section, embodiments of the invention make is possible to provide touch sensitivity to a display apparatus essentially without adding to the thickness of the display apparatus. Furthermore, the manufacturing cost may be reduced since there is no need for a separate mounting operation for attaching emitters7and detectors8. As will be further exemplified below, the emitters/detectors7,8may be formed from functional structures also present in the display unit for the operation of the pixels10. This means that the emitters7and detectors8may be manufactured by the same or a similar process as the pixels10, whereby the added manufacturing cost may be minimal. It is also to be noted that the number of emitters7and detectors8that need to be added is comparatively small compared to the number of pixels of a typical display apparatus. For example, a 3.5″ display may be provided with about 10-102emitters and detectors, while the number of pixels is typically in the order of about 105-106. Still further, the touch sensitivity may be added without impairing the quality of images displayed in the display area, since the need to add touch-sensing layer(s) to the display area or integrate light detectors among the pixels within the display area is obviated.

Furthermore, by integrating the emitters/detectors7,8at the peripheral region11of the display unit6, it is possible to omit separate contacting of the emitters/detectors7,8. Instead, they may be contacted and electronically controlled in the same way as the pixels10. For example, a data bus structure or an electronics backplane for supplying control signals to the pixels10, to selectively control the light emitted by the pixels10, may also be used to supply control signals to the individual emitters7and detectors8and/or to retrieve output signals from the individual detectors8.

FIG. 2Aindicates that the peripheral region11contains only emitters7and detectors8, and thus is free of pixels10. However, it is certainly possible to include pixels10also in the peripheral region11, if desired, as will be described further below.

FIG. 3is a top plan view to further illustrate the operation of the touch-sensing display light guide1. For reasons of clarity, the pixels have been omitted. As shown, one emitter7is activated to emit an expanding beam of light. The emitted beam, or at least part thereof, is coupled into the light guide2such that it propagates by TIR across the touch surface3, while expanding in the plane of the light guide2away from the emitter7(indicated by the hatched area). Such a beam is denoted a “fan beam” herein. Thus, each fan beam diverges from an entry or incoupling site, as seen on a top plan view. Downstream of the touch surface3, the propagating light is coupled out of the light guide2and received by a subset of the detectors8. As noted above, a detection line is formed between the emitter7and each of the detectors8that receive the fan beam. It is realized that a large number of detection lines may be generated by activating each of the emitters7and measuring the power of received light at the detectors8for each emitter7. Depending on implementation, the emitters7may be activated in sequence or concurrently, e.g. by implementing the coding scheme disclosed in WO2010/064983.

Reverting toFIGS. 2A-2B, the display pixel matrix6may be an optoelectronic device that makes use of organic materials for defining the pixels10, emitters7and detectors8. Examples of organic optoelectronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For further details regarding the structure and manufacture of organic optoelectronic devices, reference is made to WO2011/068761 and citations therein, all of which are incorporated herein by reference.

In the following, it is assumed that the display pixel matrix6inFIGS. 2A-2Bis based on OLEDs. The display device6comprises a rear electrode (e.g. an anode)15, and a front electrode (e.g. a cathode)16, and an intermediate organic structure17, which may be formed by one or plural organic layers, as is known in the art. The front electrode layer16is transparent and may e.g. be made of indium tin oxide (ITO). The pixels10of the display area may be defined by patterning of the electrode layers15,16, and optionally by patterning of the organic structure17. Each pixel10may include one or more sub-pixels (not shown), which may be formed by selective doping to generate different light emissive properties of the different sub-pixels, e.g. such that the sub-pixels emit red, green and blue light, respectively. Different designs of a combined thin film transistor (TFT) structure and OLED pixels are shown in US20080150848, which is incorporated herein by reference.

The emitters7and detectors8in the peripheral region11may also be defined by patterning of the electrode layers15,16and/or by patterning of the organic structure17. It is well-known that junction diodes, such as LEDs and OLEDs, are operable as both emitters and detectors by application of proper control voltages to the junction diodes. Thus, the emitters7and the detectors8may be implemented by the same or similar elements, whereby the emitters7, the detectors8and the pixels10are formed as portions in the organic structure17that are selectively and individually addressable via the electrode layers15,16. In this embodiment, the combination of electrode layers15,16and organic structure thus forms a composite substrate in which emitters7, detectors8and pixels10are integrated.

Preferably, the light guide2is included as a transparent substrate during manufacture of the display pixel matrix6, e.g. as a backing for supporting the front electrode16. Alternatively, the OLEDs may be built up from the side of the lower electrode layer15, and in that case the light guide2is a cover sheet that is nevertheless required for an OLED display, due to its sensitivity to moisture. Generally, the light guide2may be made of any material that transmits a sufficient amount of radiation in the relevant wavelength range to permit a sensible measurement of transmitted energy. Such material includes glass, poly(methyl methacrylate) (PMMA), polycarbonates (PC), PET (poly(ethylene terephthalate)) and TAC (Triallyl cyanurate). The light guide2may be flat or curved and may be of any shape, such as circular, elliptical or polygonal. It is possible that the light guide2is comprised of plural material layers, e.g. for the purpose of scratch-resistance, anti-fingerprint functionality, anti reflection or other functional purpose.

The use of OLED technology makes it possible to design the display unit6as a thin and flexible unit, if desired. It is also possible to design the emitters7and the pixels10with different emissive properties, if desired. For example, the wavelength(s) at which the organic structure17emits light may be readily tuned with appropriate dopants during manufacture. Furthermore, the display unit6does not need to have a backlight. Still further, the size and shape of the image-forming pixels10, emitters7and detectors8are readily set in manufacture. It may e.g. be advantageous to make the emitters7and detectors8larger than the pixels10. The amount of light emitted by an OLED element increases with its surface area, and it may thus be desirable to make the emitters7larger than the pixels10to increase the amount of emitted light from each emitter7. OLEDs are known to have small heat losses, which enables the use of large emitters7without a need for additional cooling measures. The detectors8may also be made larger than the pixels10in order to improve the light gathering ability of the detectors8. Another advantage of OLED technology is that OLEDs typically have a large index of refraction, typically in the range of 1.7-2 or even higher, whereby light is emitted in a large solid angle, which may serve to favorably increase the divergence angle of the respective fan beam inside the light guide2(cf.FIG. 3).

As noted above, it is conceivable that the light guide2is formed by a transparent substrate or backing for the front electrode layer16. It is realized that the process for manufacturing the display unit6may be adapted to add a layer of lower index of refraction between the electrode layer16and the transparent backing, i.e. the light guide2, if needed to sustain light propagation by TIR therein.FIG. 4shows an embodiment of the invention, wherein a cross-section of a touch-sensing display panel1is disclosed. In this drawing, the layering of the electrodes and the organic structure outlined with respect toFIG. 2Bare not shown in detail. However, separate pixel elements10are indicated at the central region of the panel. As is well known in the art, each pixel10may be configured to emit light in one color only, or may comprise several sub pixels configured to emit light in different colors, such as RGB (red, green, blue). Such sub pixels may be formed by stacking OLEDs, i.e. forming them on top of each other, or by placing them next to each other within the area of the pixel element10. So, each pixel10may include one or several OLEDs. At the peripheral region the emitters7and detectors8are arranged, one of each shown in the drawing. Preferably, as already described, also the emitter7and detector8are OLEDs, formed integrally with the image-forming pixels10. However, the purposive use of the emitter7and detector8on the one hand, and the image-forming pixel elements10on the other hand, are quite different. The image-forming pixels10, i.e. the display pixels, are configured to shine light out from the display panel1, preferably in a wide cone angle but most importantly straight up (in the drawing), which would normally represent the best viewing angle for an observer. The emitter7, however, will only be useful if its light is captured within the light guide2to propagate with TIR towards the detector8. As a consequence, the part of the light emanating from the emitter7that goes straight up will be lost. However, a good part of the light will impinge on the front surface3, from the inside of the light guide2, in a wide enough angle to be deflected by TIR. The problem is that since the refractive index of the image-forming pixels10normally is higher than the index of the light guide2, the light would escape downwards through the pixels10after reflection in the front surface3. For this purpose, an optical layer21is disposed between the rear surface4of the light guide2and the image-forming pixels10. In one embodiment this optical layer21is made from a material which has a refractive index n1which is lower than the refractive index n0of the light guide2. That way, there will be TIR in the light guide2in both the front surface3and the rear surface4, as indicated by the arrows, provided that the angle of incidence is wide enough. As an example, the optical layer21may be provided by means of a resin used as a cladding material for optical fibers. Such a resin lay may be provided on the substrate2before deposition of the electrode and organic layers. Alternatively, if the OLED structure is built from a bottom sheet or plate9, the optical layer21may be provided on the lower face4of the light guide2before attachment over the OLEDs, or over the OLEDs before attachment of the light guide2. Another example of an optical layer21with a lower refractive index is an air gap21, as will be described further below with reference toFIG. 15.

In another embodiment, the optical layer21is a wavelength-dependent reflector. Particularly, reflection of the emitter light in the rear surface4is obtained by providing an optical layer21which is at least partly reflective for the emitter light, while at the same time being highly transmissive for visible light. As an example, such an optical layer21may be provided by means of a commercially available coating called IR Blocker 90 by JDSU. This coating21has a reflectivity of up to 90% in the NIR, while at the same time being designed to minimize the effect on light in the visible (VIS) range to not degrade the display performance of the touch system, and offers a transmission of more than 95% in the VIS. It should be noted that there are also other usable available types of coatings, IR Blocker 90 being mentioned merely as an example. This type of wavelength-dependent reflectors are typically formed by means of multi-layer coatings, as is well known in the art. In an embodiment of this kind, light from the emitters7will propagate by TIR in the front surface3and by partial specular reflection in the rear surface4.

As is well known, OLEDs are sensitive to moisture, and the organic layers must therefore be encapsulated. Apart from the light guide2and the bottom sheet9, a hermetic peripheral seal91is therefore also provided on the panel, e.g. by means of a UV-curable epoxy.

It should be noted that the drawings here do not represent any realistic scale. The thickness of the light guide front glass2may be dependent on the size of the panel1and what it intended to be used for, i.e. the environment it will be used in. However, an OLED structure as such, with electrode layers and intermediate organic layers, may be very thin and even less than 1 μm. The substrate2or9and the cover9or2will add to the thickness considerably, though, in order to provide rigidity to a certain extent. In one embodiment, the light guide may be in the order of 200-500 μm thick. The optical layer21, though, need not be thicker than 1-5 μm to provide the cladding effect of realizing TIR in the rear surface4of the light guide2.

FIG. 5shows quite schematically a corner portion of a touch-sensing display panel1according to an embodiment of the invention. For the sake of simplicity, the peripheral seal91is left out in this drawing. The lower left corner in the drawing represents an outer corner of the panel1, whereas the right and upper edges are to be understood as cutout from a larger panel1. Emitters7and detectors8, shown in grey, are arranged along the peripheral region11, and the optical layer21is provided to cover the central region12of the panel1and the image-forming pixels10arranged at the central region12. In an alternative embodiment (as can be seen inFIG. 8), image-forming pixels10are also present in the peripheral region11among the emitters7and detectors8. Also, the peripheral region11may comprise more than one row of pixels. In addition, the optical layer21may cover also such image-forming pixel elements10provided in the peripheral region11, in addition to covering the central region12. It should be understood thatFIG. 5(andFIG. 7) only schematically show the different elements in a separated manner in order to clearly point out those elements, it shall not to be understood as an assembly instruction or the like.

FIGS. 6 and 7show an alternative embodiment, in which an extension portion21aof the optical layer21is provided over the emitters7and detectors8. The extension portion21apreferably has substantially the same thickness as the optical layer21, which will make it easier to make produce the OLEDs in the peripheral region11and in the central region12in the same process, since they will be provided at the same level. This extension portion21ahas a refractive index n2which is higher than the refractive index n1of the optical layer21. This way, light that is injected into the light guide2through the extension portion21amay still be reflected in the rear surface4where it faces the optical layer21, provided that the angle of incidence is large enough. The refractive index n2of the extension portion21amay e.g. be the same as the refractive index n0for the light guide2. Alternatively, a material for the extension portion21amay be chosen such that its refractive index lies between the refractive index for the light guide2and the refractive index for the emitter7and/or the detector8.

In the embodiment shown inFIG. 7, which also shows a cutout lower left corner portion of a panel1, the extension portion21aruns as a frame portion covering the entire peripheral region. As an alternative, where image-forming pixels10are disposed also in the peripheral region, the optical layer21may be disposed over such image-forming pixel elements in the peripheral region too.

FIG. 8schematically shows a top view of a lower left cutout corner portion of a panel1in accordance with an embodiment of the invention. In this embodiment, emitters7, preferably OLEDs, are shown in grey and are located in the peripheral region11. Detectors8, preferably also realized by means of OLEDs, are marked with a double frame. The optical layer21is not included in the drawing, but shall be understood to cover at least all of the image forming elements10in the central region12, and possibly also some or all of the image forming elements10in the peripheral region11. If devised in accordance with the embodiment described with reference toFIGS. 6 and 7, an extension portion21ais also employed to cover the emitters7and the detectors8.FIG. 8also illustrates how several detectors8can be functionally grouped (in the drawing also physically grouped) into a subset80to act as one larger detector. This way the light-sensing detector surface can be increased, and be operated as having its center between the detectors8of the subset80.FIG. 8also shows that the peripheral region11, in some embodiments, may include more than one row of pixels.

FIG. 9illustrates a variant of the embodiment ofFIG. 6. However, instead of arranging the emitters7and detectors8to take the place of respective image-forming elements10, they are instead configured together as stacked OLEDs. Also, as illustrated, the detector8may be realized as one larger surface OLED8, or as a grouped subset80of separate adjacent or dispersed OLED detectors8, each stacked with an image-forming element10. The drawing shows the emitter7and detector8stacked beneath a respective image-forming OLED element10. In an alternative design, the emitter7and/or the detector8may instead by stacked on top of the respective image-forming OLED element10.

FIG. 10shows an embodiment, which exhibits yet another type of detector arrangement. In this embodiment, the detector8is provided as a separate element, attached beneath the entire OLED structure of image-forming elements10. Such a design has a large degree of freedom for the placement and size of the detector element8, but requires that also the back panel9is transmissive to the operating wavelength range of the emitter7, which typically lies in the near IR (NIR). InFIG. 10this detector design is combined with an integrated OLED emitter7, corresponding to the disclosure ofFIG. 6. However, a stacked OLED emitter7, as inFIG. 9, may also be employed.

FIGS. 11-12outline some steps included in embodiments of a method of producing a touch-sensing display panel1in accordance with the invention.FIG. 11relates to a method of producing a pixel matrix that starts from anode side, andFIG. 12relates to a method of producing a pixel matrix starting at a cathode side, according to known alternative principles within the industry. In a preferred embodiment, those pixels are OLEDs.

Following the embodiment ofFIG. 11, step111involves providing a transparent substrate2with refractive index n0. This transparent substrate2will serve as the FTIR light guide in the final product, with a front surface3providing the touch-sensitive region, potentially with additional functional layers on it. The substrate2may e.g. be made of a suitable glass material, of PMMA, PC, or other transparent material.

In a subsequent step112, an optical layer21is provided on a rear surface4of the substrate with a refractive index n1<n0at a central region12. The optical layer21may e.g. be a resin or an adhesive attached to the rear surface4. Alternatively, the optical layer21may be formed in e.g. a vapor deposition process. The difference in refractive index need not be large. As a mere example, n0may be between 1.5 and 1.6, and n1may be between 1.4 and 1.5. With reference to the preceding disclosure, the optical layer21may be added with an extension portion21aat a peripheral region11around the central region12. In such an embodiment, the refractive index n2of the extension portion shall be higher than n1.

In a subsequent step113a matrix of pixel elements is provided at the rear surface4over the central region12and over a peripheral region11. According to processes well known in the art of OLED technology, such a process may include a TFT layer and possibly a TFT passivation layer thereon, before applying an anode layer. One or plural organic layers are then built up, typically including an emissive layer but selectively also transport layers and blocking layers. A cathode layer is then provided to create the polarity of the OLED cell.

In step114a cover sheet9is provided over the pixel matrix. This may be realized by means of an assembly of a rigid or flexible solid sheet9, by coating the pixel matrix with a curable liquid, or in a vapor deposition process.

In step115, the cover sheet9is sealed to the substrate2, so as to obtain a hermetic encapsulation. This sealing is made using a peripheral seal91, while still providing means for a galvanic connection to the pixel matrix, e.g. by means of a flex film connection. It should be noted that the steps of providing the cover sheet9and sealing it may at least to some extent be performed concurrently with each other.

The embodiment ofFIG. 12begins at the other end, with the step121of providing a carrier sheet9. This carrier sheet will form the backside of the touch-sensing display panel1, and while it therefore does not need not be transparent it may still be made of glass, a plastic material, a metal such as aluminum, etc.

Step122includes providing a matrix of pixels on the carrier sheet9. This will be a process which has a reversed order in comparison with the process ofFIG. 11, beginning with the cathode layer. Otherwise it may include the same type of electrode layers and organic layers, as is known in the art.

In step123, a transparent substrate2with refractive index n0over the pixels is then provided, which has an intermediate optical layer21with a refractive index n1<n0at a central region12of the substrate within a peripheral region11. As outlined above, the optical layer21may be applied to the backside4of the substrate2and then attached over the pixels. Alternatively, the optical layer21may first be coated onto the pixel matrix, after which the substrate2is attached. Also, as noted with reference toFIG. 11, an extension portion21amay be provided over the peripheral region11, adjacent to the optical layer21.

In step124, the transparent substrate is sealed to the carrier sheet. As for the embodiment ofFIG. 11, this will include a peripheral seal and the provision of a connector to the electrode layers for driving of the pixel matrix. Again, the steps of providing the substrate2and sealing it may at least to some extent be performed concurrently with each other.

The process step ofFIGS. 11 and 12, respectively, deal with the provision of the layered structure according to the invention. In order to become a final working product, the layered structure must also be connected and driven so as to enable the use of the panel1both for image reproduction and touch-sensing.

FIG. 13is a section view of a touch-sensing display apparatus40, which comprises the display panel1, including the light transmissive light guide2and a pixel matrix6, and a signal processor41, which are arranged in an enclosure42such that the light guide2forms a transparent front cover of the display apparatus40. The signal processor41is a processing element (or means) which is connected to the display panel1so as to transmit control signals to the pixels, the emitters and the detectors, as well as to acquire output signals from the detectors. The signal processor41is also operable to generate and output touch data calculated based on the output signals. It is to be understood that the signal processor41may alternatively be implemented as a dedicated controller for the pixels and a dedicated controller for the emitters and the detectors.

It is to be understood that the display apparatus/display unity may form part of any form of electronic device, including but not limited to a laptop computer, an all-in-one computer, a handheld computer, a mobile terminal, a gaming console, a television set, etc. Such an electronic device typically includes a processor or similar controller that may be connected to control the display panel1to display information content within at least part of the touch surface3and to provide touch sensitivity within the touch surface3. The controller may be implemented to control the display panel1via the signal processor41, or it may implement part or all of the functionality of the signal processor41.

FIG. 14shows a number of steps, which need not be provided in the given order, that may be included in any one of the embodiments ofFIGS. 11 and 12, so as to create a functional connection of the display panel1to a signal processor41.

In step141a plurality of pixels10in at least the central region12are connected to a control circuit41configured to drive them as image-forming pixel elements. As noted before, these image-forming elements are preferably all disposed under the optical layer21, and may to some extent also be provided in the peripheral region11. Collectively, the image-forming elements10form the display part of the panel1.

In step142at least one pixel7in the peripheral region11is connected to a control circuit41configured to drive the pixel7to emit light into the transparent substrate2for propagation by TIR therein. Preferably, a number of emitters7are connected this way, provided in the peripheral region along at least two sides of the panel1.

In step143at least one detector8in the peripheral region11is connected to a control circuit41configured to drive that detector8to detect light from the transparent substrate2, emanating from the emitter7. Correspondingly, a number of detectors8are preferably connected this way, provided in the peripheral region along at least two sides of the panel1. Together with the emitters7, they will form the touch-sensing detection grid of the touch surface3. With reference to the embodiments of e.g. FIGS.4and9-11, the detectors8may also be pixels8of a common matrix as the image-forming elements10and the emitters7, preferably OLEDs, or alternatively separate detector elements8applied below the pixel matrix. Also, the detectors8may be connected to the control circuit41so as to be controlled in subsets80, where each subset80has an aggregate detector surface of the combined surface areas of the included detectors8.

Reference will now be made to the embodiment ofFIG. 15, illustrating a side view of an FTIR system of a combined display and touch-sensing panel1, formed by attaching a light guide2to a display6. The light guide2may be bonded to the display unit6by means of an adhesive, such as an optical adhesive. In one embodiment, the light guide2is laminated onto the display unit6. To enable the light from the emitters7to be coupled into and out of the light guide2at the peripheral region11, while enabling the light to propagate by TIR across the light guide above the center region12, different adhesives may be used in the peripheral region11and the center region12, as indicated by reference numerals20,21. Specifically, the adhesive21in the center region12may be selected to have an lower index of refraction lower than the light guide2, while the adhesive20in the peripheral region11may be selected to have an index of refraction that is higher or substantially equal to the index of refraction of the light guide2.

In a variant, the light guide2is attached by an adhesive20to the display unit6at the peripheral region11only and arranged with an air gap21to the center region12of the display unit6. It is currently believed that an air gap of at least about 2-3 μm is sufficient to enable propagation by TIR in the light guide2. This variant may facilitate removal and replacement of the light guide2in the course of service and maintenance.

It is also conceivable that the light guide2is attached to the display unit6via a spacer20of solid transmissive material. The spacer may be bonded to the light guide2and the display unit6, respectively, by thin adhesive layers, such that the coupling of light is controlled by the index of refraction of the spacer20rather than the adhesive. In analogy with the above, the spacer20may be located at the peripheral region11only, or spacers20,21with different index of refraction may be located at both the peripheral region11and the center region12.

The combined touch-sensing display panel FTIR system1may also include structures configured to re-direct the light emitted by the emitters7, e.g. to reshape the emitted cone of light so as to increase the amount of light coupled into the light guide2in a desired fashion. For example, the emitted light may be redirected so as to form the fan beam in the plane of the light guide2, as shown inFIG. 3, and/or the emitted light may be redirected to increase the amount of light that is trapped by TIR in the light guide2. These light-directing structures may be included in the above-mentioned spacer20, or the portion of the surface4that faces the peripheral region11of the display unit6, or the peripheral region11of the display unit6itself. Similar light-directing structures may be included between the light guide2and the detectors8, so as to re-direct outcoupled light onto the detectors8. Generally, the light-directing structures may be said to define the field of view of the emitter/detector7,8inside the light guide2. The light-directing structures may be in the form of a micro-structured elements, such as but not limited to, reflectors, prisms, gratings or holographic structures. The micro-structured elements may be etched, printed, hot embossed, injection molded, pressure molded or otherwise provided between the emitters/detectors7,8and the light guide2. One approach for coupling the LEDs to the light guide panel is proposed in the article “Injecting Light of High-Power LEDs into Thin Light Guides”, by Cornelissen et al, published in Proc. SPIE 7652, International Optical Design Conference 2010, pp 7652121-7652126, 2010. According to this approach, the top surface of the LED is modified to have a rough surface behaving like a Lambertian reflector. A dielectric multilayer filter is deposited on the bottom of the light guide panel, and the top surface of the LED is optically coupled to the filter by a silicone adhesive. The filter is optimized to only transmit light emitted from the LED at angles larger than the critical angle at the interface between the light guide and its neighboring optical layer. The purpose of the multilayer is thus to only transmit light that can propagate in the light guide. The light emitted at smaller angles is reflected back toward the rough LED surface where it is subsequently recycled by reflection and redistribution.

The light-directing structures may be omitted, whereby part of the emitted light will pass through the light guide2without being trapped by TIR. Selected parts of the front surface3of the light guide2, e.g. above the peripheral region11, may be provided with a coating or cover22, as will be described in more detail below, to prevent such light from passing the front surface3.

With or without light-directing structures, it may be desirable to implement stray light reduction measures. In one example, the edge surface of the light guide2and/or the portion of the surface3above the peripheral region11may be provided with surface structures that prevent light from the emitters from being reflected back into the light guide2. Useful anti-reflective surface structures include diffusers and light-absorbing coatings.

In a variant, surface structures are provided on the edge surface of the light guide2and/or the portion of the surface3above the peripheral region11to re-direct light from the emitters into the light guide2for propagation by TIR. It is also possible that the edge surface is formed with a suitable bevel to re-direct the light. Such surface structures may include light-reflective coating(s) and/or micro-structured elements, and may implement or be part of the above-mentioned light-directing structures.

FIG. 15further illustrates a cover frame22, a feature which may be included in any one of the other described embodiments as well. The cover frame22is disposed to cover the peripheral region11, and possibly also extend a portion into the central region12. The cover frame22may fulfill one or more of three different purposes.

As noted above, a surface of the cover frame22, facing the light guide2, may be configured to reflect light from the emitter7such that it may propagate in the light guide2rather than escape. As an example, a diffuser may be used for this purpose, which will reflect a part of the emitter light in angle that may satisfy the requirements for TIR in the light guide2.

Secondly, the cover frame22may hide any structures in the peripheral region11from a user, particularly if only the central region12is used as an image display. For this purpose the cover frame22should be opaque to visible light.

As a third purpose, the cover frame22may be configured to block out ambient light from reaching the detectors8. For this purpose, the cover frame22should be opaque to the operating wavelength of the touch-sensing system, i.e. the light detected by the detectors8from the emitters7to determine the occurrence of a touch. As mentioned, also the FTIR system may make use of visible light, but in a preferred embodiment NIR radiation is employed.

The cover frame22may e.g. be provided by means of a thin metal sheet. It may be provided as a separate element or form part of a housing42or bracket for holding the display panel1. In another embodiment, the cover frame22may be implemented as a coating or film, in one or more layers, on the front surface3. For example, an inner layer facing the front surface3may provide specular and possibly partly-diffuse reflectivity, and an outer layer may block ambient and/or visible light. In one embodiment, the cover frame22may comprise a chromium layer provided onto the top surface3, to obtain a surface towards the panel light guide2which is at least partially specularly reflective to light in the emitter wavelength. In addition, the cover frame22may comprise an outer layer, which is substantially black to block visible light, by oxidizing the upper surface of the chromium layer. In other embodiments, other metals, with corresponding oxides, may be used, such as aluminum, silver etc. In yet other embodiments, the specularly reflecting lower layer may be provided by means of a metal, whereas an upper layer may be provided by means of paint, e.g. black paint. In any case, the cover frame22is preferably substantially flat, and should be as thin as possible while providing the desired benefits of blocking IR light and visible light. In yet another embodiment, the cover frame may be disposed as an opaque frame layer between two different layers of the light guide2, rather than on the front surface3. This way it may be possible to obtain a flush front surface3. In a further embodiment the cover frame22is disposed at the rear surface4of the light guide2, and is configured to block visible light but to transmit IR. This way, the peripheral region structures are covered but light from the emitters7may still pass through the cover frame22to the light guide2, and subsequently out through the cover frame to the detectors8.

FIG. 16is a section view of an embodiment in which the display unit6is based on liquid crystal technology, and specifically with the display unit6being a TFT-LCD. The display unit6comprises a rear electrode layer25, a front electrode layer26and an intermediate liquid crystal (LC) structure27. The electrode layers25,26are transparent and comprises a respective polarizer. The rear electrode layer25comprises a pixel-defining electrode structure and a TFT active matrix for pixel selection, whereby the polarization of the LC structure27may be selectively controlled (addressed) at the location of each pixel. The front electrode layer26may be implemented as a common electrode and may also comprise color filters, as is known in the art. In the illustrated embodiment, the display unit6further comprises a LED matrix backlight28, which projects light for transmission through the electrode layers25,26and the LC structure27. Like in the foregoing embodiments, a light transmissive light guide2is arranged to define a front touch surface3. In effect, the light guide2may be a sandwich structure including both color filters and polarizer, or simply be a planar cover lens, dependent on at which layer forms the rear surface4for reflection of the propagating light. In the illustrated embodiment, the rear electrode layer25is designed with detectors in its peripheral region11. The detectors may e.g. be integrated as light-sensitive TFTs. Further details on TFT-LCDs and light-sensitive TFTs are e.g. found in WO2007/058924 and US2008/0074401, which are incorporated herein by reference.

In one embodiment, the LC structure27does not extend into the peripheral region11, in order to avoid that the liquid crystal obstructs the detection of the light that is coupled out of the light guide2. In the example ofFIG. 16, the emitters are formed by dedicated LEDs in the peripheral region11of the backlight28. In this embodiment, the combination of backlight28, electrode layers25,26and LC structure27thus forms a composite substrate in which emitters7, detectors8and pixels10are integrated. Further, a light-coupling element30is arranged to direct the light from the emitters to the light guide2and from the light guide2to the detectors. The light-coupling element30may or may not include the above-mentioned light-directing structures.

In an alternative embodiment (not shown), all or part of the emitters are integrated in the rear electrode layer25, e.g. in the form of LEDs or light-emitting TFTs. In a further alternative embodiment (not shown), all or part of the detectors are integrated into the backlight28, e.g. in the form of light-sensing LEDs or TFTs. In all of these embodiments, the backlight28may instead be implemented to illuminate the electrode layers25,26and the liquid crystal structure27from the side, as is known in the art.

It is to be understood that the above discussion in relation toFIG. 15is equally applicable to the embodiment inFIG. 16.

FIG. 17shows another embodiment of the invention, implementing an LCD unit6. The drawing shows a corner portion of a touch-sensing display panel1, in which a number of elements have been vertically separated for the purpose of illustration only. Basically, the display panel1of this embodiment includes the LCD unit6and a light guide2which provides the touch-sensitive surface3. At the bottom of the drawing, a backlight28is disposed. Light is injected into the backlight28from a light source (not shown), preferably through an incoupling arrangement designed to spread light within the light guide, as is well known in the art. In this embodiment the backlight28includes a light guide with at least one structured surface281, functioning to lead out light upwards through the display layers. Typically it is the lower surface281which is structured, whereas light propagates by TIR in the upper surface of the backlight light guide28, and preferably also in the lower surface281between structured areas thereof. The backlight28may also include a rear side reflector (not shown) for reflecting light, which escapes through the structured surface281of the light guide, back into the backlight light guide. Further details with regard to embodiments of the backlight28will now be outlined below with reference toFIG. 18-20, before returning to the embodiment ofFIG. 17.

FIG. 18shows a plane view of the backlight28, whereasFIGS. 19 and 20shown perspective views of two different ways of realizing the backlight28. In the present embodiment, the backlight28is not only used for the image-forming pixels10, but also as the light source of the emitters7. For the first purpose, an area28arepresenting the central region12of the lower surface281of the backlight28is structured to evenly spread light up through the upper surface282of the backlight28. This is, as such, well-known technology frequently used in the art. Exact or detailed ways of structuring a surface of a backlight for this purpose will therefore not be outlined here, but typically the structured area28ais designed with respect to where light is injected, such that not all light is leaked close to the light source. In addition to the central region structured area28a, the backlight is also devised with a structured area28bin the peripheral region11. The structured area28bpreferably has a sequential design, such that light is leaked out at distinct places, where it is wanted, throughout the peripheral region11. This way less light is wasted. In an alternative embodiment (not shown) also the peripheral region11may be devised with a more evenly dispersed structured area28b, similar to the structured area28aof the central region12, and which light is to be led up is instead only defined by the pixel structure of the driving of the liquid crystals.

FIG. 19shows one way of realizing the backlight28. In this embodiment, the backlight28comprises two light guides; a central light guide283and a peripheral light guide284, one disposed over the other in a sandwich structure. The two light guides283,284may be configured with different refractive indexes for the wavelengths used, typically white light in the central region12and NIR in the peripheral region, so at to allow light to propagate by TIR in the respective light guides without leaking In the drawing, the central light guide283is only about as wide as the central region12, i.e. the imaging part of the display. In an alternative embodiment (not shown), the central light guide283may be just as wide as the peripheral light guide284, yet only provided with its structured area28aat the central region12. Correspondingly, it may be noted that the peripheral light guide284is illustrated as an entire sheet covering the central region12too. However, an alternative design (not shown) may include a peripheral light guide284that is frame-like, lacking a central portion. Such a frame-like light guide may be disposed around the central light guide283. Such an embodiment would thus mean an arrangement where the two light guides283and284are arranged in the same plane rather than being sandwiched, which theoretically could entail a lower profile to the entire display panel1. In the embodiment ofFIG. 19, separate light sources are employed for the different purpose; a VIS light source285for injecting white light into the central light guide283, and a NIR light source286for injecting NIR light into the peripheral light guide284. As is known by the skilled person, plural light emitters may be used for injecting light into a light guide, and the representation of one light source for each light guide shall therefore merely be seen as an example.

FIG. 20shows an alternative embodiment, where one and the same light guide287is configured to be used for both purposes. A single light source288is shown, but as already explained it may comprise plural emitters. In any case, light is injected in the light guide287within wavelength ranges for use both as imaging backlight via the central structured area28aand for FTIR purposes via the peripheral structured area28b. The light source288may comprise a broad spectrum emitter, or may comprise several emitters devised to inject light in different wavelengths, such as VIS and NIR.

Returning toFIG. 17, starting from the bottom this drawing shows a display panel1comprising an LCD unit6and a light guide2. The LCD unit6, in turn, comprises a backlight28, an electrode25including a lower polarizer, a liquid crystal layer27, and an upper electrode26with an upper polarizer and color filters. The peripheral structured area28bof backlight28is indicated, but the drawing leaves out the central structured area28afor the sake of clarity. As indicated by the dashed vertical arrows, the peripheral structured area28bserves to lead out light upwards in the structure. The backlight28may e.g. be designed in accordance with any of the embodiments described with reference toFIGS. 18-20. It should also be noted that the arrows are symbolic and that rather a cone of light will be led out in reality, as determined by the geometry of the backlight. The electrode25comprises a pixel-defining structure and a TFT active matrix. In operation together with the upper electrode26(indicated as a lower surface of the light guide2), the electrode25is configured to define pixels in the intermediate liquid crystal (LC) layer27. Also, the TFT active matrix connect to detectors8, to read out sensed received light. Such detectors may e.g. be photo detectors, OLEDs or similar, as previously discussed for other embodiments.

Preferably, the LC layer27is driven by a controller41using the electrodes25,26according to a predetermined scheme such that the LC layer is opened at portions271over the structured area28bin a certain pattern. In one embodiment, portions271are opened one by one in succession over each one structured area28b, such that each portion271will serve as, or emulate, one emitter7, which emitters7will act as flashed one by one. An incoupling arrangement71is configured at the rear surface4of the light guide, at which light is injected into the light guide2. Emitter light is indicated in the drawing by means of dashed vertical arrows, from the structured area28bto the light guide2.

Once injected in the light guide2, at least parts of the light will propagate by TIR in at least the front surface3to outcoupling structures81at the rear surface4. Furthermore, the LC layer27is preferably driven by the controller41over the electrodes25,26such that the LC layer27is held open, i.e. transmissive, at portions272over the detectors8, below the outcoupling structures81. This way, light coupled out from the light guide2is led to the detectors8, as indicated by the vertical dash-dotted arrows.

Although this is not shown in this drawing, it has been outlined with respect to other embodiments that incoupling and outcoupling may be achieved simply by bypassing an optical layer21disposed under the light guide2over the image-forming pixels10in the central region12. In addition, the incoupling and outcoupling structures may include diffusive and/or diffractive elements to direct light in or out of the light guide2. It may be noted that the size of the portions271and272of the LC layer27need not be equally large, even though the drawing indicates this. Also, each such portion271and272is preferably made up of a plurality of pixels of the TFT active matrix and the LC layer27.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. It should be noted that while certain features have been described in conjunction with different drawings, such features may well be combined in one and the same embodiment.

For example, it is conceivable that only the detectors8are integrated in the display unit6, while the emitters7are otherwise installed in the display apparatus40, e.g. as separate components. Likewise, it is conceivable that only the emitters7are integrated in the display unit6, while the detectors8are otherwise installed in the display apparatus40, e.g. as separate components.

In certain embodiments, the display unit6may comprise only one emitter7in combination with plural detectors8, or only one detector8in conjunction with plural emitters7. It is even conceivable that the display unit6has only one emitter7and one detector8, e.g. to detect the presence of a touching object5on the touch surface3.

Although it may be preferable that the emitter(s)7and the detector(s)8are implemented by the same technology as used for generating images in the display area, e.g. to have similar functional structure as the pixels10, it is also possible that the detector(s)7or the emitter(s)8, or both, are implemented by a different technology when integrated into the display unit6.

As noted above, it may be desirable that the surface area of the emitters and detectors is larger than the surface area of the pixels. It is to be understood that the emitters may be larger than the detectors, and vice versa, and also that the emitters and detectors may have any shape, including circular, elliptical, and polygonal.