WO2015005845A1

WO2015005845A1 - Touch-sensing apparatus suitable for mass production using optical data communication

Info

Publication number: WO2015005845A1
Application number: PCT/SE2014/050699
Authority: WO
Inventors: Ivan Karlsson; David SERNELIUS
Original assignee: Flatfrog Laboratories Ab
Priority date: 2013-07-12
Filing date: 2014-06-10
Publication date: 2015-01-15

Abstract

A touch-sensing apparatus operates by transmitting light by total internal reflection (TIR) inside a planar light guide (1). Light emitters (2) and light detectors (3) are optically connected to the planar light guide (1) to define a grid of light propagation paths inside planar light guide (1). A plurality of electronic circuitry units (12) are electrically connected to a respective component group comprising one of the light emitters (2) and one of the light detectors (3). The respective electronic circuitry unit (12) is operable to generate a set of projection values (DPV) representing the measurement light received by said one of the light detectors (3) on a subset of the light propagation paths. The respective electronic circuitry unit (12) is further arranged to optically transmit the set of projection values (DPV) to an optical signal receiver (103', 8) which is arranged to provide the set of projection values (DPV) to a touch controller (24) for determining a property of objects on the planar light guide (1).

Description

TOUCH-SENSING APPARATUS SUITABLE FOR MASS PRODUCTION USING OPTICAL DATA COMMUNICATION Cross-reference to Related Applications

The present application claims the benefit of Swedish patent application No. 1350872-6, filed 12-M-2013.

Technical Field

The present invention relates to a touch-sensing apparatus, and in particular to touch-sensing apparatus that operates by propagating light by total internal reflection (TIR) inside a planar light guide.

Background Art

Touch-sensing systems ("touch systems") are in widespread use in a variety of applications. Touch systems are actuated by a touching object such as a finger or stylus, either in direct contact or through proximity (i.e. without contact) with a touch surface. Touch systems are for example used as touch pads of laptop computers, in control panels, and as overlays to displays on e.g. hand held devices, such as mobile telephones or tablet computers. A touch panel that is overlaid on or integrated in a display is also denoted a "touch screen". Many other applications are known in the art.

There are numerous known techniques for providing touch sensitivity, e.g. by incorporating resistive wire grids, capacitive sensors, strain gauges, etc into a touch panel. There are also various types of optical touch systems, which e.g. detect shadows cast by touching objects onto a touch surface, or detect light scattered off the point(s) of touching objects on a touch panel.

One specific type of optical touch system uses projection measurements of light that is transmitted on a plurality of optical paths inside a planar light guide across a touch surface on the light guide. The light propagates in the light guide by internal reflections, and specifically by total internal reflections (TIR) in the touch surface. An object (e.g. a finger) that is brought into contact with the touch surface will interact with the propagating light and cause the light on one or more of the optical paths to be attenuated. This phenomenon is commonly referred to as FTIR (Frustrated TIR). The projection measurements quantify the amount of light received on each of the optical paths downstream of the touch surface, and allow the position of the object to be determined by analyzing the attenuation of light on the respective optical path.

One example of this projection-type optical touch system is disclosed in

WO2011/028170, in which individual light emitters and light detectors are disposed along the perimeter of a planar panel of light transmissive material. The light emitters are optically coupled to the panel to inject diverging beams of light for propagation by TIR inside the panel, and the light detectors are optically coupled to the panel to receive light from the light emitters on a plurality of optical paths that extend across a touch surface on the panel. The system includes a common illumination control unit which is electrically connected to all of the light emitters to control the activation of the light emitters, by controlling the supply of power to the respective emitter. The system also includes a common detection control unit which is electrically connected to all of the light detectors and operable to read measurement data from the respective light detector. The operation of the illumination control unit and the detection control unit is in turn controlled by a central control unit, which retrieves the measurement data from the detection control unit and computes the location of objects on the touch surface of the panel.

WO2010/015410 discloses a control system that may be used for operating optical touch systems of the projection-type as described above. The control system includes a central microprocessor which is electrically connected to an emitter register, which in turn is electrically connected to all of the light emitters. By supplying dedicated control signals for setting the emitter register, the microprocessor is operable to selectively control the activation of individual light emitters. The central microprocessor is also electrically connected to the output of a common analog-to-digital converter (ADC). The input of the ADC is electrically connected to an analog multiplexer, which in turn is electrically connected to all of the light detectors. The analog multiplexer is controlled by the central microprocessor to selectively supply an analog measurement signal from the respective light detector to the common ADC for conversion into a digital signal. The digital signal from the ADC is acquired by the microprocessor and processed for touch determination.

In order for these optical touch systems of projection-type to be commercially relevant, in particular on a mass market, they need to be optimized for production at high volumes and low cost. For example, the optical touch systems may need to be designed to facilitate assembly, to reduce the impact of assembly tolerances on the performance of the optical touch system, and to reduce the rejection rate in production. It may also be desirable to reduce the impact of subsequent failure of one or more components in the optical touch system. If the optical touch system is to be integrated in a handheld or portable device, the optical touch system may need to be designed to survive vibrations, drops, blows, etc. If the optical touch system is to be integrated into a host device, be it a mobile handset, laptop, tablet computer, computer display, television set, gaming console etc, it may also be important to ensure that the optical touch system is electromagnetically compatible with the host device, i.e. that the operation of the host device does not disturb the operation of the optical touch system, and vice versa. Many host devices include components known to generate significant electromagnetic interference (EMI), e.g. mobile transceivers and antennas in mobile handsets, and clocks and busses in computers, as well as the embedded wireless data transceivers that are becoming pervasive in portable electronic devices. Also the electronic displays that typically are placed behind the optical touch system may generate significant electromagnetic interference.

The prior art also comprises touch systems configured to propagate light in free space above a touch surface. One such touch system is disclosed in EP2350780, in which a plurality of integrated T/R modules are disposed around the touch surface, each T/R module consisting of a light emitting unit stacked on a light detecting unit. A central controller is electrically connected to all light emitting units and light detecting units. The central controller activates the light emitting units one by one and receives analog signals from the light detection units. By detecting blocked light paths between pairs of light emitting units and light detecting units, the central controller calculates a user touch location on the touch surface.

EP0520669 also discloses a touch system that propagates light in free space above a touch surface in an orthogonal grid. A single emitter is optically coupled to a plurality of input ports along the perimeter of the touch surface by a fiber-optic bundle, and a single light detector is optically coupled to a plurality of output ports opposite to the input ports along the perimeter. An LCD mask is arranged along the perimeter of the touch surface to block the input and output ports and is controlled by multiplexor circuitry to selectively open opposite input and output ports, such that light from the light source propagates across the touch surface and is received by the light detector.

A similar touch system is disclosed in US6181842, in which a bundle of send waveguides are embedded in a substrate to direct light from a common light source to the perimeter of a touch surface and a bundle of receive waveguides are embedded in the substrate to direct light from the perimeter of a touch surface to individual detector elements of a single detector array.

Summary

It is an objective of the invention to at least partly overcome one or more limitations of the prior art.

Another objective is to provide a touch-sensing apparatus with improved electromagnetic compatibility when installed in an electronic host device. One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by means of a touch-sensing apparatus according to the independent claims, embodiments thereof being defined by the dependent claims.

A first aspect of the invention is a touch-sensing apparatus, comprising: a planar light guide having a front surface, forming a touch-sensing region, and an opposite rear surface; light emitters operable to introduce measurement light into the planar light guide for propagation by internal reflections between the front surface and the rear surface; light detectors optically connected to the planar light guide and operable to detect the measurement light on a grid of light propagation paths between pairs of the light emitters and the light detectors; and a plurality of electronic circuitry units electrically connected to a respective component group comprising one of the light emitters and one of the light detectors, wherein the respective electronic circuitry unit is operable to generate a set of projection values representing the measurement light received by said one of the light detectors on a subset of the light propagation paths.

The respective electronic circuitry unit is further arranged to optically transmit the set of projection values to an optical signal receiver which is arranged to provide the set of projection values to a touch controller for determining a property of objects on the touch-sensing region. The property may be any of a location, a shape or an area of the object(s).

By providing a plurality of electronic circuitry units and by transmitting the projection values optically from these electronic circuitry units, an improved robustness to electromagnetic interference can be attained. In an optical touch system of conventional type, which transports electric analog signals from individual detectors to the touch controller or to a centralized analog-to-digital converter, the extent of the electric conductors for the analog signals may be excessive. Analog signals are generally sensitive to disturbances, and this may impose strict requirements on the quality of the electric conductors. Furthermore, long electric conductors may lead to ground currents and other parasite signal and power issues. All of these issues will increase cost and put constraints on the design of the system. The use of optical data transmission from the plurality of electronic circuitry units thus enables the touch- sensing apparatus to be designed with electric pathways for the analog signals that are shorter and/or easier to shield from electromagnetic interference. Optical data transmission as such is inherently immune to electromagnetic interference and does not lead to issues with ground currents, parasite signals, etc.

It is to be understood that the respective component group may contain more than one of the light emitters for generating measurement light and/or more than one of the light detectors that are optically connected to the planar light guide for receiving the measurement light. Further, the touch sensing apparatus may include component groups containing different numbers of light emitters and light detectors. The component groups are mutually exclusive, i.e. each light emitter and each light detector is only included in one component group.

In one embodiment, a dedicated waveguide is arranged to extend between each electronic circuitry unit and the optical signal receiver. The dedicated waveguide forms an extraneous optical channel and may be implemented by an optical fiber, a strip waveguide, a rib waveguide, etc. The respective electronic circuitry unit may be electrically connected to a dedicated communication emitter, which is optically coupled to the dedicated waveguide, and be operable to emit communication light that encodes the set of projection values.

In another embodiment, the respective electronic circuitry unit is arranged to optically transmit the set of projection values through the planar light guide or through a secondary planar light guide which is mounted behind the rear surface of the planar light guide, and the optical signal receiver is optically coupled to the planar light guide or the secondary planar light guide. By optically transmitting the projection values through the planar light guide or the secondary planar light guide, it is possible to reduce the mechanical complexity of the touch-sensing apparatus since there is no need to install electric wiring or optical fibers to transport the projection values from the electronic circuitry units to the touch controller. This advantage increases in importance with increasing number of electronic circuitry units. The reduced mechanical complexity will facilitate the assembly of the touch-sensing apparatus, and possibly reduce both cost and weight. Further, the optical communication of projection values inside the planar light guide or the secondary planar light guide may enable a more compact design of the touch-sensing apparatus. In one specific implementation, the secondary planar light guide forms a functional part of a display unit which is mounted behind the rear surface of the planar light guide. The secondary planar light guide is a "functional part" of the display unit in the sense that the secondary planar light guide is installed to perform a function related to the operation of the display unit as combined with the planar light guide. In one example, the secondary planar light guide is a diffuser included in a backlight of the display unit. In another example, the secondary planar light guide is a connecting layer between the display unit and the planar light guide.

In one embodiment, the respective electronic circuitry unit comprises an optical communication unit for encoding and communicating the set of projection values according to a predefined protocol for digital data communication. The electronic circuitry unit may implement any conceivable communication protocol, including a protocol based on PPM (Pulse-Position Modulation), OOK (On-Off Keying), PIM (Pulse-Interval Modulation), FSK (Frequency- Shift Keying), and Thunderbolt™.

The respective electronic circuitry unit may be electrically connected to a dedicated communication light emitter which is optically coupled to either the planar light guide or the secondary planar light guide and is operable to emit communication light that encodes the set of projection values.

In one embodiment, however, the respective electronic circuitry unit is configured to operate said one of the light emitters to optically transmit the set of projection values through the planar light guide. Thus, the light emitter is used for the dual purpose of generating measurement light and optically transmitting the set of projection values. This embodiment obviates the need to install and electrically connect the electronic circuitry unit to a dedicated communication light emitter for optically transmitting the projection values. This may lead to cost savings and may also reduce the complexity of the electronic circuitry units.

In one embodiment, the touch-sensing apparatus further comprises a sequencer which is operable to trigger the electronic circuitry units to perform a predefined sequence of measurement phases, wherein a unique subset of the light emitters is activated during each measurement phase to introduce the measurement light on a unique subset of the light propagation paths, and wherein the predefined sequence of measurement phases results in projection values being generated by the plurality of electronic circuitry units to represent a complete set of light propagation paths in the grid of light propagation paths. Each unique subset may include one or more light emitters. In one specific implementation, a single light emitter is activated during each measurement phase, whereby the light emitters are activated one-by-one in sequence.

The optical transmission of the projection values may be timed in different ways with respect to the measurement phases. A few "timing embodiments" are presented in the following.

In one timing embodiment, the respective electronic circuitry unit is configured to optically transmit the set of projection values separated in time from the measurement phases. This means that no measurement light is propagated in the planar light guide while the set of projection values is optically transmitted from the electronic circuitry units. The time-separation is simple and cost-effective to implement and puts low demands on the electronic circuitry units. Further, a light emitter that is electrically connected to the electronic circuitry unit may be used for both generating measurement light and optically transmitting the set of projection values. In one timing embodiment, each measurement phase is followed by a

communication phase, wherein the respective electronic circuitry unit is configured to optically transmit, during the communication phase, the set of projection values generated during the most recent measurement phase. This embodiment provides for a low latency or time delay between a measurement phase and the time point when the touch controller receives the projection values. It should be noted that even if this embodiment may be implemented with the above-mentioned time-separation, it is also possible that the communication phase of one module (partly) coincides with the measurement phase of another electronic circuitry unit.

In one timing embodiment, the respective electronic circuitry unit is configured to optically transmit the set of projection values at least partly during one or more measurement phases. In one implementation, the respective electronic circuitry unit is operable to transmit the set of projection values as encoded in communication light emitted by a dedicated communication light emitter which is electrically connected to the respective electronic circuitry unit, wherein the communication light is distinct from the measurement light by frequency modulation and/or by spectral separation. This implementation enables a low latency between the measurement phase and the receipt of projection values by the touch controller. In another implementation, the respective electronic circuitry unit is configured to encode the set of projection values in the measurement light generated by said one of the light emitters when activated during a given measurement phase in the predefined sequence of measurement phases, wherein the set of projection values is generated to represent the measurement light received by said one of the light detectors during preceding measurement phases since the latest activation of said one of the light emitters, such that the set of projection values represent the light propagation paths that extend to said one of the light detectors. This implementation with data-encoded measurement light enables a low energy

consumption, since the measurement light serves the additional function of conveying the set of projection values, and it also provides the advantage of using the same light emitter to both generate measurement light and optically transmit the projection values.

In one embodiment, the respective electronic circuitry unit is configured to generate, irrespective of the encoded set of projection values, the same amount of measurement light during a given time period. This embodiment may facilitate the processing of the projection values in the touch controller or improve the result of this processing, since the encoded information does not affect the amount of emitted measurement light. Uncontrolled variations in the amount of emitted measurement light might cause the touch controller to erroneously identify touching objects on the touch- sensing region. This embodiment may be achieved by encoding the set of projection values using a protocol that yields the same amount of light irrespective of information content. One such type of protocol is based on Pulse-Position Modulation (PPM).

Alternatively, this embodiment may be achieved by controlling the light emitter to generate both encoded and non-encoded measurement light during the given time period, where the amount of light in the non-encoded measurement light is adapted to yield the same total amount of measurement light during the given time period.

In one embodiment, the respective electronic circuitry unit comprises a data buffer which is configured for intermediate storage of the projection values generated by the respective electronic circuitry unit during the predefined sequence of measurement phases. The provision of a data buffer in the electronic circuitry units makes it possible to configure the electronic circuitry units with any timing scheme between the measurement phases and the optical communication. For example, the data buffer enables the above-mentioned generation of data-encoded measurement light.

In one embodiment, the sequencer is configured to embed a synchronization signal in an electric power signal which is supplied to the electronic circuitry unit. This embodiment is simple to implement and obviates the need to install a separate data line for the synchronization signals or to configure the sequencer to transmit the

synchronization signal together with control signals for the electronic circuitry units.

In one embodiment, the sequencer is configured to generate an optical

synchronization signal inside the planar light guide or the secondary planar light guide, and the respective electronic circuitry unit is operable to receive the optical

synchronization signal via said one of the light detectors or via a dedicated

communication light detector which is optically coupled the secondary planar light guide and electrically connected to the electronic circuitry unit. This embodiment is simple to implement and is robust to electromagnetic interference. It also obviates the need to install a separate data line for the synchronization signals or to configure the sequencer to transmit the synchronization signal together with control signals for the electronic circuitry units.

In one embodiment, the sequencer is configured to optically transmit, inside the planar light guide or the secondary planar light guide, control signals for controlling the operation of the electronic circuitry units, wherein the respective electronic circuitry unit is operable to receive the control signals via said one of the light detectors or via a dedicated communication light detector which is electrically connected to the electronic circuitry unit. This embodiment will further reduce the mechanical complexity of the touch-sensing apparatus, which in turn facilitates the assembly of the touch-sensing apparatus and may reduce cost. It may also enable a further improved robustness to electromagnetic interference. Further, the optical communication of control signals inside the planar light guide or the secondary light guide may enable a more compact design of the touch-sensing apparatus.

In one embodiment, the electronic circuitry unit is implemented by an integrated circuit (IC), such as an ASIC. The IC is a compact component which can be

manufactured at low cost in mass production and its functionality may be separately tested. The IC may also be tailored for power efficient operation. The use of an IC facilitates assembly of the touch-sensing apparatus. The IC may also include at least one of the light emitter and the light detector.

In one embodiment, the set of the projection values represents energy of the measurement light received by said one of the light detectors during a given time period for each light propagation path that extends to the light detector. In this context, "energy" is equivalent to the power or the intensity of the measurement light.

In one embodiment, the respective component group contains one and only one light emitter for generating the measurement light and one and only one light detector for receiving the measurement light. The provision of a single emitter and a single detector for measurement light may reduce the complexity of the electronic circuitry unit and its control. Further, the impact of the component group on the operation of the touch-sensing apparatus is relatively low, and if a electronic circuitry unit, or its emitter or detector, operates badly or not at all will only affect a small subset of the available light propagation paths. This embodiment does not exclude that the respective electronic circuitry unit is electrically connected to an additional light detector or light emitter exclusively used for optical data communication to or from the electronic circuitry unit.

In one embodiment, the touch-sensing apparatus comprises a plurality of identical, unitary emitter-detector modules which are disposed in optical contact with the planar light guide, wherein each emitter-detector module comprises one of the electronic circuitry units and the component group which is electrically connected to the electronic circuitry unit. The provision of unitary emitter-detector modules generally allows for greater precision in the coupling of measurement light into and out of the light guide. The modules may be separately designed and optimized with respect to optical properties for generating and detecting the measurement light, e.g. with respect to achieving desired signal levels for the emitted measurement light and adequate signal- to-noise ratio (S R) for the detected measurement light. Also, the modules enable an improved accuracy in the positioning of the emitters and detectors with respect to the light guide, since each module defines the relative locations of its included emitter(s) and detector(s) irrespective of the accuracy with which the modules are mounted to the light guide. The provision of modules will also facilitate assembly of the touch-sensing apparatus, by reducing the number of individual components that need to be handled and assembled with the planar light guide. The modules may form integrated optical units that may be separately tested before being installed in the touch-sensing apparatus. Since the modules incorporate also the electronic circuitry units for generating the set of projection values, this testing corresponds to testing a major part of the functionality of the touch-sensing apparatus. If all modules that are installed in the touch-sensing apparatus have passed a functionality test, it is relatively likely that the resulting apparatus will perform properly. It is thus realized that the provision of emitter-detector modules may serve to enable production of the touch-sensing apparatus with a low rejection ratio. Further, since the respective module contains an electronic circuitry unit which is operable to generate the set of projection values, the analog measurement signals that are generated by the light detectors are contained within the modules. By containing the analog signals within the modules, it is possible to improve the immunity of the touch-sensing apparatus as a whole to electromagnetic interference by optimizing the design of the individual modules and/or by integrating dedicated shielding into the modules, rather than shielding the entire touch-sensing apparatus from the

electromagnetic interference.

By using a plurality of identical modules, it is possible to reduce the cost for producing the touch-sensing apparatus. The logistics will be improved, since fewer number of components need to be manufactured and kept in stock. The manufacturing cost per module can be reduced through economies of scale when a large number of identical modules is to be produced.

In one embodiment, the respective emitter-detector module comprises a common mounting structure for the electronic circuitry unit and the component group. The common mounting structure may improve the stability of the module and its robustness to stress and vibrations. Also, it may facilitate accurate positioning of light detector and the light emitter during assembly. The common mounting structure may e.g. be a PCB.

In one embodiment, the respective emitter-detector module further comprises one or more optical components for directing the measurement light from said one of the light emitters into the planar light guide and/or for directing light from the planar light guide onto said one of the light detectors. By including such optical components in the modules, the sources of error in manufacture of the touch-sensing apparatus are reduced even further. A module may be tested also to ensure that the optical components function properly and are properly located with respect to the emitter or detector.

Further, if the optical component needs to be accurately positioned with respect to the light emitter or the light detector, this is easier to achieve during manufacture of the module. In one embodiment, the respective emitter-detector module comprises a housing which contains the component group and the electronic circuitry and which defines a front face that is transparent to the measurement light, the front face being attached to the planar light guide. The housing will protect the light emitter, light detector and electronic circuitry unit during shipping, handling and assembly of the touch-sensitive apparatus. The housing will also shield these components, e.g. from dust, when the modules have been installed in the touch-sensing apparatus, and it may also be implemented to shield the detector from ambient light. The housing may also shield electromagnetic interference. Further, the front face of the housing may be tailored to ensure proper attachment and optical coupling to the planar light guide.

In one embodiment, each of the light emitters is optically coupled to the planar light guide at an incoupling port so as to generate an individual beam of measurement light that diverges in the plane of the planar light guide while it propagates away from the incoupling port inside the planar light guide by internal reflections between the front and rear surfaces.

In one embodiment, each of the light detectors is optically coupled to the planar light guide at an outcoupling port to receive measurement light from a plurality of the light emitters.

In one embodiment, the respective electronic circuitry unit comprises a detector driver operatively connected to said one of the light detectors for generating an analog measurement signal in response to impinging light on the light detector, an analog-to- digital converter for converting the analog measurement signal into a digital signal, and a projection value generator for generating the set of projection values based on the digital signal.

Still other objectives, features, aspects and advantages of the present invention will appear from the following detailed description, from the attached claims as well as from the drawings.

Brief Description of Drawings

Embodiments of the invention will now be described in more detail with reference to the accompanying schematic drawings. Throughout the description, the same reference numerals are used to identify corresponding elements.

Fig. 1 is a side view of a light projection system coupled to a planar waveguide. Figs 2A-2B are top plan views of a light projection system during activation of two different emitters.

Fig. 3 shows an example of a reconstructed attenuation pattern.

Fig. 4 is a bottom plan view of a touch system according to a first embodiment. Figs 5 A-5B exemplify the operation of the first embodiment in Fig. 4 during light generation by two different ED modules.

Fig. 6 illustrates overall operation of the light projection system in Fig. 4.

Fig. 7 illustrates operation of an ED module in the touch system of Fig. 4.

Fig. 8 illustrates detection lines extending to one of the ED modules from the other ED modules in the touch system of Fig. 4.

Figs 9A-9E are signal timing diagrams to illustrate encoding of digital projection values into measurement light emitted by the ED modules.

Figs 10-11 are block diagrams of an ED module and a main controller, respectively, for use in the touch system of Fig. 4.

Fig. 12 illustrates operation of the main controller in the touch system of Fig. 4.

Fig. 13 is a schematic block diagram of a light projection system connected for data transmission in a token ring.

Fig. 14 is a bottom plan view of a touch system according to a second

embodiment.

Figs 15-16 are block diagrams of an ED module and a main controller, respectively, for use in the touch system of Fig. 14.

Fig. 17 is a perspective view of ED modules attached to the rear side of a planar waveguide.

Figs 18A-18B are plan views of two different configurations of electronic components in an ED module.

Figs 19 A, 19C and 19E are perspective views of different implementations of an ED module, and Figs 19B, 19D and 19F are side views of the respective ED module as mounted to a planar waveguide.

Figs 20A-20C are side views of touch-sensitive display systems containing ED modules.

Fig. 21 is a section view of a touch-sensitive display system with optical communication through a backlight unit.

Detailed Description of Example Embodiments

Fig. 1 illustrates the principle of propagating light inside a light transmissive panel 1 while enabling the light to interact with objects that are brought into contact with the panel. In the example of Fig. 1, light emitters 2 (one shown) are optically coupled to the panel 1 to inject light for propagation inside the panel 1 and light detectors or sensors 3 (one shown) are optically coupled to the panel 1 to detect propagating light. The panel 1 is made of solid material in one or more layers and may have any shape. The material of the panel 1 is transmissive to the light generated by the emitters 2, e.g. in the NIR (near infrared) or IR (infrared) wavelength region. The panel 1 is also referred to as a "planar light guide" or "planar waveguide" herein. The panel 1 defines an internal propagation channel, in which the light propagates by internal reflections. In Fig. 1, the propagation channel is defined between two boundary surfaces 5, 6 of the panel 1, viz. a top (front) surface 5 and a bottom (rear) surface 6, where the top surface 5 allows the propagating light to interact with touching objects 7 and thereby defines a touch surface 4. This is achieved by injecting the light into the panel 1 such that the light is reflected by total internal reflection (TIR) in the touch surface 4 as it propagates through the panel 1. The light may be reflected by TIR in the bottom surface 6 or against a reflective coating thereon. It is also conceivable that the propagation channel is spaced from the bottom surface 6, e.g. if the panel 1 comprises multiple layers of different materials. In Fig. 1, the emitters 2 and detectors 3 are coupled to the panel 1 via the edge surface that connects the top and bottom surface 5, 6. In variants, the emitters 2 and detectors 3 are instead attached to the top surface 5 or the bottom surface 6. The panel 1 may be designed to be overlaid on or integrated into a display device or monitor.

Each object 7 that is brought into close vicinity of, or in contact with, the touch surface 4 scatters and/or absorbs part of the propagating light, while the remainder of the light continues to propagate in its original direction across the panel 1. Thereby, when an object 7 touches the top surface 5, the total internal reflection is disrupted, or "frustrated", and the energy (or equivalently, the power or intensity) of the transmitted light is decreased, as indicated by the thinned lines to the right of the object 7. This phenomenon is commonly denoted FTIR (Frustrated Total Internal Reflection) and a corresponding touch-sensing apparatus is referred to as an "FTIR system".

Figs 2A-2B are top plan views of an example embodiment of the panel 1 in an FTIR system. Emitters 2 (represented by circles) and detectors 3 (represented by squares) are dispersed along and optically coupled to the perimeter of the panel 1 to define a frame of incoupling and outcoupling ports where light is injected into and coupled out of the panel, respectively. The touch surface 4 (indicated by dashed frame) is defined within this perimeter. Each emitter 2 is arranged to generate and inject a diverging beam of light into the panel 1, i.e. a beam that diverges in the plane of the panel 1 while it propagates by internal reflections inside the panel 1. In Figs 2A-2B, the outer boundaries of the diverging beam is indicated by B. Each detector 3 is arranged to detect light from a range of angles in the plane of the panel 1. When an emitter 2 is activated, as indicated by a filled circle, the injected light propagates to and is received by a number of detectors 3, as indicated by a shading of the squares that represent the detectors 3. Thus, a plurality of light propagation paths are defined from each emitter 2 to a set of detectors 3. Each of the light propagation paths, as projected onto the touch surface 4, forms a detection line D. In Fig. 2A and Fig. 2B dashed lines illustrate the detection lines D that are generated when two different emitters 2 are activated.

The FTIR system is operated according to an activation scheme that defines the order in which the emitters 2 are activated. The activation scheme may cause the emitters 2 to be activated in any order, but for the following discussions it is assumed that the emitters 2 are activated sequentially in clockwise succession starting from a given emitter. The activation scheme may also indicate the detectors 3 that are to be activated to measure the light received from each emitter 2, so as to generate a measurement value (also denoted "energy value" or "projection value" herein) for each detection line D. For example, detectors 3 that do not receive light from a particular emitter need not be activated. In a variant, all detectors 3 are activated for all emitters, by default, and the projection values that correspond to detection lines D are extracted in a post-processing step. Even if it is not further discussed herein, the activation scheme may alternatively cause more than one emitter to be activated at the same time, e.g. using the techniques disclosed in WO2010/064983 which is incorporated herein in its entirety.

When all emitters have been activated according to the activation scheme, the system has generated one projection value for each detection line D that extends across the touch surface 4. The projection values are then processed for touch determination, which involves detecting objects on the touch surface 4 and determining a property of these objects, such as a position (e.g. in the x,y coordinate system shown in Fig. 2), a shape, or an area. The touch determination may involve detecting detection lines that are attenuated and triangulating the touching objects based on the attenuated detection lines, e.g. as disclosed in US7432893 and WO2010/015408. Alternatively, the touch determination may involve advanced signal processing to recreate a distribution of attenuation values (for simplicity, referred to as an "attenuation pattern") across the touch surface 4, where each attenuation value represents a local degree of light attenuation. An example of such an attenuation pattern is given in the 3D plot of Fig. 3, where the peaks of increased attenuation represent touching objects. The attenuation pattern may be further processed for determination of a position, shape or area of touching objects. The attenuation pattern may be generated by any available algorithm for image reconstruction based on projection signal values, including tomographic reconstruction methods such as Filtered Back Projection, FFT-based algorithms, ART (Algebraic Reconstruction Technique), SART (Simultaneous Algebraic Reconstruction Technique), etc. Alternatively, the attenuation pattern may be generated by adapting one or more basis functions and/or by statistical methods such as Bayesian inversion.

Examples of such reconstruction functions designed for use in touch determination are found in WO2009/077962, WO201 1/049511, WO2011/139213, WO2012/050510, WO2013/062471, WO2013/133756, WO2013/133757, WO2013/165305, and

WO2013/165306, all of which are incorporated herein by reference.

Based on the foregoing, a few definitions will be given for terms used in the following description.

An "activation scheme" represents a series of "exposures" or "measurement phases" and identifies, for each exposure, one or more emitters to be activated

(energized) to emit light for propagation inside the panel. The activation scheme may also identify a respective set of detectors to be activated (energized) for each exposure.

A "frame" corresponds to an execution of an activation scheme and thus involves activation of the emitters to generate light on the detection lines of the touch system, and activation of the detectors to generate projection values for these detection lines.

A "detection line" is a light propagation path from an incoupling port to an outcoupling port on the panel, as projected onto the touch surface. An "incoupling port" denotes the location on the panel where light from an emitter enters the panel, and an "outcoupling port" denotes the location on the panel where the light that strikes a detector leaves the panel. The location of the incoupling and outcoupling ports may, but need not, be defined by dedicated light coupling structures attached to the panel.

"Measurement light" is light generated to propagate on the light propagation paths in the panel for the purpose of producing projection values for the detection lines, a "measurement emitter" is an emitter that generates the measurement light, a

"measurement detector" is a detector that detects the measurement light.

An "emitter driver" is an electronic circuit which is operable to energize an emitter to generate light.

A "detector driver" is a electronic circuit which is operable to energize a detector to produce an analog signal that represents a property of the light that impinges on a light-sensitive surface of the detector.

An "integrated circuit", IC, is a set of electronic circuits integrated on one unitary small plate ("chip") of semiconductor material, e.g. silicon.

A "communication emitter" is an emitter that is installed for the exclusive purpose of transmitting light encoded with information, a "communication detector" is a detector that is installed for the exclusive purpose of receiving light encoded with information, and "communication light" is the encoded light that is generated by the communication emitter.

Fig. 4 is a plan view of a touch system according to a first embodiment. The touch system includes a panel 1 and a plurality of identical ED modules 10 ("modules") which are attached to the bottom surface 6 in optical contact with the panel 1. Each ED module 10 is a unitary structure that contains one emitter 2, one detector 3, and an electronic circuitry unit (EC) 12 connected to the emitter 2 and the detector 3. The EC 12 is configured to receive digital control signals, from a main controller 14, and to control the operation of the ED module 10 based on the control signals, e.g. the operation of the emitter 2 and the detector 3. The EC 12 is also configured to acquire an analog energy signal from the detector 3 and generate digital projection values (DPVs) that represent measured energy (or power or intensity) for the detection lines D that extend to the detector 3 from the different emitters 2 in the touch system.

The EC 12 is further configured to encode the DPVs according to a predefined protocol and to communicate the encoded DPVs optically inside the panel 1 for receipt by the main controller 14. Thus, the DPVs are optically communicated inside an existing light transmissive structure in the touch system, which obviates the need to install dedicated pathways for transmission of the DPVs from each module 10. This may reduce cost, weight and size, as well as facilitate the assembly of the touch system. By the optical communication, the transmission of DPVs is immune to electromagnetic interference. Also, known complications of electric data transmission become more manageable or are avoided all together, such as ground currents, parasitic signals, overhearing, etc. The EC 12 may be configured to transmit further data with the DPVs, such as a unique ID or address for the ED module in the touch system, parity bits enabling error detection at the receiving end, synchronization bits for use at the receiving end if the optical data transmission is asynchronous, etc.

The EC 12 may also implement additional functions, such as filtering of the analog signal for noise suppression, correction of the DPVs for influence of ambient light, intermediate storage of DPVs in a local memory in the ED module 10, formatting of the DPVs before output, etc.

In certain embodiments, the EC 12 may be responsive to control signals generated by the main controller 14, e.g. to set a mode of operation for the ED module 10. Such modes may include an emission mode, in which the ED module 10 activates the emitter 2 to generate measurement light for propagation in the panel 1, and a detection mode, in which the ED module 10 activates the detector 3 to detect measurement light and generate a DPV. Another mode may enable the main controller 14 to configure the respective ED module 10, e.g. to set the exposure time of the emitter, the exposure time of the detector, and control parameters for the correction for ambient light, etc.

As understood, the main controller 14 is arranged to communicate with the modules 10. The main controller 14 includes a module sequencer (MS) 16 for generating the control signals for the modules 10, a digital data receiver (DDR) 18 for receiving and checking the DPVs from the modules 10, and an oscillator (clock) 20 that generates clock pulses for use by the MS 16 and the DDR 18 to synchronize their operation. A data line 22 A connects the main controller 14 to the modules 10, such that main controller 14 is operable to electrically transmit the control signals to the modules 10. In the illustrated example, the modules 10 are connected to a common data line 22A, but it is also conceivable to arrange separate data lines from the main controller 14 to each module 10. In a variant, the control signals are communicated optically in one or more optical fibers that extend between the main controller 14 and the modules 10. By using optical communication for the control signals, the robustness to signal

interferences may be improved.

In the embodiment in Fig. 4, the main controller 14 is electrically connected to two communication detectors 103' by a respective data line 22B. The communication detectors 103' are attached in optical contact with the bottom surface 6 of the panel 1. As will be further explained below, the communication detectors 103' are arranged to intercept encoded light emitted by the modules 10, i.e. light containing the encoded DPVs. Thereby, the DDR18 is operable to receive the DPVs from the modules 10.

The main controller 14 also comprises a power supply (not shown) and is arranged to supply power to the modules 10 via a power transmission line (not shown). The modules 10 may be connected either in series or in parallel to the power

transmission line.

A touch controller 24 is connected to the main controller 14 to receive digital output data from the DDR 18. This digital output data may include at least a subset of the DPVs that are generated and output by the modules 10, or a formatted version of these DPVs. The touch controller 24 is configured to process the DPVs for touch determination, e.g. using any of the above-mentioned techniques, such as triangulation or image reconstruction.

In the embodiment of Fig. 4, the main controller 14 and the modules 10 may be regarded to jointly define a light projection system that operates to transmit light inside the panel 1, to detect the propagating light, and to generate and output the DPVs for individual light propagation paths D across the panel 1. The light projection system operates according to a predefined activation scheme, such that the emitters 2 are sequentially activated while the detectors 3 are operated to measure the received light from each activated emitter. The light projection system operates in a repeating sequence of frames, where each frame results in DPVs being generated for the detection lines D in the system.

Fig. 5 A illustrates the system in Fig. 4 when one module has activated its emitter

2 (black circle) to generate measurement light that propagates on a respective detection line D to detectors 3 (shaded squares) in other modules, which generate a respective DPV based on the received light. In the example of Fig. 5 A, each module 10 is also configured to operate the emitter 2 to transmit light with optically encoded data, which represents one or more of the DPVs generated by the module 10. Since the emitted light propagates in the panel 1 as a diverging beam, the encoded light will be received by one of the communication detectors 103' (shaded square) on a communication path C. Fig. 5B illustrates the activation of the emitter 2 in another module to generate measurement light that propagates on detection lines D to detectors 3 in a set of modules. Fig. 5B also illustrates how the emitter 2 is activated (black circle) to optically transfer digitally encoded data to the detector 103' on communication path C.

The light projection system in Fig. 4 includes two communication detectors 103' since the diverging beams from all the modules 10 cannot be intercepted by a single detector 103'. However, a single detector 103' may be used for other placements of the modules 10 or if the modules 10 are configured to emit light with such divergence in the plane of the panel 1 that the single detector 103' receives light from all modules in the system. In other variants, the system includes more than two communication detectors 103'.

In a variant (not shown), the communication detector 103' is located in the main controller 14 and is optically coupled to the panel 1 by an optical fiber. The optical fiber is thus attached to or defines an outcoupling port on the panel 1 and directs light from the panel 1 to the detector 103' in the main controller 14. In analogy with Fig. 4, one or more detectors 103' in the main controller 14 may be coupled by optical fibers to a plurality of different locations on the panel 1.

In a further variant, the detector 103' is located in the main controller 14 which is implemented as a module for attachment to the panel 1, e.g. to the bottom surface 6. The detector 103' is arranged to be in optical contact with the panel 1 when this modular main controller 14 is attached to the panel 1.

An example of the combined operation of the main controller 14 and the modules 10 in Fig. 4 during a frame is shown in Fig. 6. Each frame starts by concurrently activating a first emitter (steps 60-61) and the detectors (step 62) that are arranged to receive light from the activated emitter. In step 63, the ED modules 10 generate one DPV for each detection line D that extends from the activated emitter to the respective detector in the system. Then, steps 61-63 are repeated, subject to steps 64-65, until all emitters have been activated according to the activation scheme and DPVs have been generated for all detection lines D in the system.

Different schemes may be implemented for optically transferring the encoded data from the modules 10 to the detector 103' and the main controller 14, with respect to the timing between the measurement phases and communication phases, in which the modules optically communicate the DPVs in the planar light guide 1.

According to one scheme, denoted "time separation scheme", the optical communication of the DPVs and the generation of the measurement light are time- separated. This means that the modules 10 are operable to transmit the DPVs during periods ("OFF periods") when no measurement light is transmitted in the panel 1. In one example, each sequence of steps 61-65 in Fig. 6 may include an OFF period during which the modules 10 optically transmit the DPVs that were generated in step 63. The modules 10 may be activated one by one, according to a predefined sequence, to transmit the light with a respective encoded DPV during the OFF period. In another example, each module 10 stores the DPVs in local memory and transfers the DPVs once during every frame. In this example, the modules 10 may sequentially transmit the stored DPVs during a common OFF period, or they may transmit the stored DPVs during different time-separated OFF periods such that each module 10 transmits its stored DPVs during a dedicated OFF period. The use of time-separation may, depending on implementation, provide a low latency between data capture and the receipt of DPVs by the touch controller. On the other hand, the energy consumption may increase since the emitter in each module is activated twice during each frame: to generate measurement light and to communicate the DPVs.

According to another scheme, denoted "embedded scheme", the DPVs that are generated by the respective module 10 are encoded in the measurement light that is subsequently generated by this module 10. Thus, the DPVs are embedded in and transmitted as part of the measurement light, i.e. the light that is emitted for the purpose of enabling other modules to generate DPVs for the set of detection lines that extend from the activated module. This means that the respective module 10 stores the generated DPVs in local memory until it is time for this module 10 to transmit measurement light according to the activation scheme. The embedded scheme has an inherent latency of one frame since the respective module buffers its generated DPVs, but provides the benefit of a low energy consumption. Furthermore, there is no need to provide for OFF periods that are extended to enable data transfer. Examples of the embedded scheme are discussed below with reference to Figs 7-9.

In other schemes (not shown), the respective module 10 includes a dedicated communication emitter and an associated emitter driver, which are operable to transmit dedicated communication light which is distinguished from the measurement light by either frequency modulation ("frequency separation scheme") or by optical wavelength ("wavelength separation scheme"). These schemes allow the communication light, with encoded DPVs, to be transmitted independently of the measurement light. This comes at the cost of an additional emitter and emitter driver for each module. The communication emitter is arranged in the module 10 such that the communication light is coupled into the panel 1 for propagation to the communication detector 103'. It should be noted that the communication emitters may generate a diverging beam in the panel 1 similarly to the emitters 2.

Fig. 7 is an example of a process in a module 10 that operates according to the embedded scheme to embed the DPVs in the measurement light. Initially, the module is in a state where it waits for a control signal (step 110). The control signal may direct the module to perform either a detection event (step 111) or an emission event (step 112). If the module is directed to perform a detection event (step 111), the module activates the detector driver to generate an analog measurement signal from the detector (step 113) and operates on the analog measurement signal to generate a current DPV, which represents received light energy on a specific detection line (step 114). Then, the module operates to store the current DPV in local memory (step 115). It is realized that DPVs for different detection lines D will be accumulated in the local memory as the module is sequentially activated to receive measurement light from other modules in the system. This is illustrated in Fig. 8, which represents the modules in Fig. 4 as rectangular boxes M1-M18 and illustrates the detection lines D that extend to module Ml from the other modules M2-M18 in the system. As modules M2-M18 are activated in sequence to emit measurement light, module Ml will store DPVs for these detection lines in local memory.

Reverting to the process in Fig. 7, if the module is directed to perform an emission event (step 112), i.e. to generate measurement light, the module operates to retrieve all DPVs from local memory (step 116). The module then encodes the DPVs according to a predefined protocol (step 117) and operates the emitter driver to transmit the encoded DPVs as part of the measurement light (step 118).

The DPVs may be encoded into the measurement light using any available optical data communication protocol, although it is preferable that the protocol is robust to disturbances caused by ambient light. The protocol preferably also has a low complexity such that it does not require significant processing for data encoding in the modules. One such protocol which is used in wireless optical communication, e.g. within the IrDA standard, is Pulse-Position Modulation (PPM), in which M message bits are encoded by transmitting a single pulse in one of 2^M possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second. There are a number of variants and extensions of the PPM protocol, e.g. 4-PPM, 4-PPM+, MPPM, OPPM, DPPM, dicode PPM, EPM, DAPPM, etc. It may also be desirable that the protocol results in the same total energy of the measurement light for all possible values of the DPVs ("energy invariant encoding"), i.e. irrespective of the encoded data. Many PPM protocols provide such energy invariant encoding. Thus, using a PPM protocol, each DPV may be encoded by the position of a single pulse of light within a given time window. It is to be understood that there are many other protocols that may be used, including OOK (On-Off Keying), PIM (Pulse-Interval Modulation), Frequency Shift Keying (FSK) and Thunderbolt™.

The use of PPM encoding will be further described with reference to timing diagrams for the emitter activation in Figs 9A-9E. Fig. 9A is a plot of a sequence of frames F with sequential activation of the emitters el -el 8 in the system of Fig. 8, where the emitters are enumerated according to the modules in which they are located. Thus, each vertical bar in Fig. 9A represents the total measurement light that is generated by the respective emitter during a frame. Although not shown, each vertical bar includes a plurality of pulses for data encoding. Fig. 9B is an enlarged view of the activation of emitters el-e3 in Fig. 9A, where each vertical bar comprises a plurality of sub-bars. Each sub-bar represents an individual "word" of M bits that is encoded in the measurement light. Thus, the sub-bars in Fig. 9B correspond to encoded DPVs and comprises a pulse of light. This is further illustrated in Fig. 9C, which is an enlarged view of the sub-bars for emitter el . As explained above, module Ml has recorded and stored DPVs for the detection lines in Fig. 8 in the time period since emitter el was last activated. These DPVs are now encoded in sequence into the measurement light, as indicated by the encircled numbers. Thus, in Fig. 9C, the first sub-bar encodes the DPV for the light received from module M5, the second sub-bar encodes the DPV for the light received from module M6, and so on. Fig. 9D is a further enlarged view of the first and second sub-bars in Fig. 9C and illustrates the actual encoding of the respective DPV by the position of a single light pulse within the time window defined by the sub-bar.

It can be noted that the PPM protocol has been developed to optimize data transfer for a given amount of energy, i.e. to minimize the duty cycle of the respective emitter. In FTIR-based touch systems, it is generally more critical to ensure that sufficient light reaches all detectors in the system. To improve the light budget it may be advantageous to implement the PPM protocol with inverted duty cycle of the emitters. In practice, this means that the DPVs are encoded by the position of a temporary absence of light, i.e. an OFF pulse, during the given time window. Fig. 9E illustrates the inverted duty cycle for the regular PPM encoding in Fig. 9D.

In a variant, each module 10 is operated to generate measurement light that includes both encoded and non-encoded portions. For example, the module may generate non-encoded portions of measurement light to achieve a given total energy of the emitted measurement light and/or to compensate for differences in total energy if the data protocol does not provide an energy invariant encoding. It is also conceivable that the modules implement a compensation scheme to adapt the magnitude of the pulses so as to compensate for differences in emitted total energy caused by the data protocol.

Fig. 10 is a block diagram of an ED module 10 which may be used in the embodiment in Fig. 4 and which is operable to embed DPVs in the measurement light. The module 10 is configured to receive electric control signals ("CTRL") from the main controller 14 and/or other ED modules 10. The module 10 has a local processor 30 that controls the operation of the module 10, based on the control signals. The detector 3 is connected to a detector driver 32 which is operable to retrieve and amplify an analog measurement signal from the detector 3. The analog measurement signal is received by a DPV block 60, which includes an analog-to-digital converter (ADC) 61 that converts the analog measurement signal to a stream of digital values, a DPV generator 62 that processes the stream of digital values to generate a DPV, and a local memory 35 that forms a data buffer for intermediate storage of the DPV. The operation of the detector driver 32 and the DPV block 60 is controlled by the local processor 30, based on the control signals. The module 10 also includes a data receiver 34 that receives the control signals ("CTRL"). In the illustrated example, the data receiver 34 includes a clock recovery block 64 which recovers global clock pulses from the control signals in a manner known to the skilled person. The control signals are passed to the processor 30, and the global clock pulses are passed to the processor 30 and to an encoder block 65. As indicated in Fig. 10, the module 10 may include a local oscillator 36 which synchronizes with the global clock pulses and generates local clock pulses that control the operation of the local processor 30 and the encoder block 65. The encoder block 65 retrieves the DPVs from the memory 35 and encodes the DPVs according to a predefined protocol, e.g. a PPM protocol. The encoder block 65 generates a stream of bits that are received by the emitter driver 31 which is operated to generate the measurement light based on the stream of bits, e.g. by generating light pulses as shown in Fig. 9D or 9E. The encoder 65 and the emitter driver 31 forms a communication unit for encoding and communicating the DPVs from the modules 10. The operation of the encoder block 65 and the emitter driver 31 is controlled by the processor 30.

The DPV generator 62 may perform additional functions. One such function is to generate a digital OFF value by processing the stream of digital values that is received from the ADC 61 when the detector driver 32 is operated to generate an analog measurement signal when all emitters in the system are turned off. The DPV generator 62 may generate the DPV by subtracting this OFF value from a digital measurement value generated when the detector 3 receives measurement light from an emitter in the system. Another function of the DPV generator 62 may be to apply a logarithm to the DPV value before it is stored in the memory 35.

Fig. 11 is a block diagram of a main controller 14 which may be used in the embodiment in Fig. 4 and which is operable to decode DPVs from measurement light which is intercepted by the communication detector 103'. The main controller 14 is configured to receive instructions ("DATA IN") from and to output DPVs ("DATA OUT") to the touch controller 24 as shown in Fig. 4. The main controller includes a module sequencer (MS) 16 which generates the control signals ("CTRL") for the ED modules 10, and a digital data receiver (DDR) 18 which processes an analog

measurement signal from a communication detector 103' to retrieve and output the DPVs. Of course, the DDR18 may be adapted to operate with more than one

communication detector 103'. A global oscillator 20 generates global clock pulses which are used by the MS 16 and the DDR18 to operate in synchronization. The MS 16 may also include at least one global clock pulse in the control signals during each frame (for use by the clock recovery block 64 in the modules 10). In the illustrated example, the DDR 18 includes a detector driver 70 that implements a high-pass filter combined with automatic gain adjustment. The detector driver 70 generates an analog

measurement signal which is received by a decoder 71. The decoder 71 operates to convert the analog signal into a DPV, by applying the predefined protocol. For example, if the modules 10 encode the DPVs by the PPM protocol, the decoder 71 will identify a sequence of pulses in the analog signal and decode, based on the global clock pulses, the sequence of pulses into DPVs. A DPV processor 72 receives the decoded DPVs and other data that may have been generated by the decoder 71 (e.g. parity bits, module ID, etc) and verifies the accuracy of the data, e.g. by parity check. The DPV processor 72 also signals to the MS 16 when the receipt of a batch of DPVs is completed, allowing the MS 16 to track the progress of the activation scheme and generate appropriate control signals for the ED modules 10.

Fig. 12 is a flow chart that exemplifies the operation of the main controller 14 in Fig. 11. The main controller 14 initiates a series of exposures given by the activation scheme, by repeating steps 121-126, starting from a first exposure (step 120). During a frame, the main controller 14 iterates over a series of n exposures, with n being equal to the number of modules. In step 121, the MS 16 generates a control signal that causes the modules to activate a given emitter and a given set of detectors. Then the detector driver 70 in the DDR 18 retrieves the analog measurement signal from the communication detector 103' (step 122) and the decoder 71 decodes the batch of DPVs that are transmitted by the given emitter during the exposure (step 123). The DPV processor 72 checks the batch of DPVs (step 124), which are then transmitted from the main controller 14 to the touch controller (step 125).

It should be understood that the main controller 14 may be more or less involved in controlling the operation of the modules 10. In one implementation, the control of the system is centralized. For example, the main controller 14 may send control signals for activating the emitter 2 and detector 3 in the respective module 10 and for causing the respective module 10 to generate and transmit the DPVs. Thus, the main controller 14 directly controls when the respective emitter 2 and detector 3 is to be activated and when DPVs are to be generated and transmitted. In another implementation, the control of the system is distributed. For example, the main controller 14 may trigger pre-defined events or modes that are locally defined in each module 10. These events may be triggered by dedicated commands that are encoded in the control signals. One event may be to activate the emitter 2 during a given exposure time. Another event may be to activate the detector 3 during a given exposure time and to generate the DPV. Yet another event may be to transmit one or more DPVs to the main controller 14, etc. In yet another example with distributed control, the main controller 14 merely sends a frame start command to the modules 10, which triggers each module 10 to operate according to the predefined activation scheme. Thus, the modules 10 are pre-configured to collectively and in synchronization execute the activation scheme once the frame start command is received.

In all of these examples, the operation of the modules 10 may be synchronized across the system by a global clock signal ("synchronization signal") which is transmitted by the main controller 14 to the modules 10. The global clock signal comprises clock pulses generated by the oscillator 20 in the main controller 16. The internal operation of the modules 10 may also be controlled by this global clock signal. In an alternative, each module 10 includes a local oscillator (clock) which generates clock pulses that are used for the internal operation of the modules 10. The local oscillator may be intermittently synchronized with the global clock signal, e.g. once every frame.

Fig. 13 shows a non-limiting example of an embodiment with distributed control, using a token ring or daisy chain architecture. The ED modules, represented by reference numerals Ml to Mn, are connected in series along the data line 22A. The data line 22 A extends in a ring from the MS 16 in the main controller 14 to the DDR 18. Depending on implementation, the main controller 14 may be connected to directly transmit a control signal to all modules, or the modules may be configured to sequentially relay such a control signal from one module to the next along the data line 22 A. Every module stores two identifiers in internal memory: one ID number and one Token number. The ID number may be pre-assigned or assigned by the main controller 14 at start-up of the touch system. Before a frame has started, the Token number is zero in all modules (as shown in Fig. 13). To start a frame, the main controller 14 sends a trigger signal (control signal) via data line 22A to the modules 10. The trigger signal initiates a first exposure (measurement phase) according to the activation scheme. The trigger signal causes the respective module to increment its Token number by 1, compare the incremented Token number with the ID number and take dedicated action based on the outcome. If the Token number matches the ID number, the module has the "token" and activates its emitter for a given exposure time. Alternatively, the module that has the token enables its emitter driver to receive a dedicated control signal from the main controller 14, whereby the main controller 14 will control when the emitter is activated. Given the notation in Fig. 13, module Ml will emit light during the first exposure. On the other hand, if the Token number does not match the ID number, the module activates its detector for a given exposure time. Alternatively, the module enables the detector driver to receive a dedicated control signal from the main controller 14, whereby the main controller 14 will control when the detector is activated. Given the notation in Fig. 13, modules M2-Mn will detect light and generate corresponding DPVs during the first exposure. The next exposure (measurement phase) according to the activation scheme is then initiated by a trigger signal which, depending on implementation, is generated by the main controller 14 or by the module that has the token. The trigger signal again causes the modules to increment their Token number by 1, which in turn triggers module M2 to activate its emitter and the remaining modules to activate their detectors. The process proceeds until the frame is completed, i.e. until all emitters have been activated. When the last emitter has been activated, the Token number is incremented to exceed n. When this happens, the modules are configured to set the Token number back to zero and wait for another trigger signal.

The skilled person realizes that the modules Ml-Mn may be configured to transmit the DPVs according to any of the time separation scheme, the embedded scheme, the frequency separation scheme and the wavelength separation scheme.

A second embodiment will now be described with reference to Figs 14-16, in which not only the DPVs but also the control signals are communicated optically inside the panel 1. The following description focuses on differences compared to the first embodiment. Unless stated otherwise, it can be assumed that the foregoing description of the first embodiment is equally applicable to the second embodiment as exemplified in Figs 14-16.

As seen in the plan view of Fig. 14, each module 10 includes a communication detector 103 in addition to the measurement emitter 2 and the measurement detector 3. The communication detector 103 is in optical contact with the panel 1. Further, the main controller 14 is not only electrically connected to two communication detectors 103' but also to two communication emitters 102'. Each communication emitter 102' is arranged to generate a diverging beam in the panel 1 similarly to the emitters 2. Thereby, the communication emitters 102' are operable to transmit communication light that propagates inside the panel 1 and is intercepted by the communication detectors 103 in the modules 10. It is to be understood that any number of communication emitters 102' and communication detectors 103' may be installed in the system.

As an alternative to mounting the communication emitter(s) 102' and the communication detector(s) 103' in optical contact with the panel 1, as shown in Fig. 14, the communication emitter 102' and/or the communication detector 103' may be located in the main controller 14 and be optically coupled to the panel 1 by optical fiber. In a further alternative, the communication emitter 102' and the communication detector 103' is located in the main controller 14 which is implemented as a module for attachment to the panel 1 with the communication emitter 102' and the communication detector 103' in optical contact with the panel 1.

The main controller 14 may be operated to transmit the communication light with a time-shift to the measurement light that is generated by the modules 10. Alternatively, the communication light may be generated independently of the measurement light, e.g. if the communication light is distinguished from the measurement light by either frequency modulation or by optical wavelength.

Irrespective of implementation, the second embodiment is operable to optically communicate control signals from the main controller 14 to the modules 10 on communication paths inside the panel 1, from one of the communication emitters 102' to the respective communication detector 103 in the modules 10. The second embodiment simplifies the manufacture of the touch system considerably, by removing the need to install data lines from the main controller 14 to each module 10. The second embodiment also improves the ability to shield the control signals from electromagnetic interference.

In an alternative, not further illustrated herein, the modules 10 are configured to receive the communication light by the measurement detector 3. Thus, the modules 10 lack a dedicated communication detector 103, and the EC 12 is operable to both generate DPVs from measurement light received by the detector 3 and retrieve the control signals from communication light received by the detector 3.

Fig. 15 is a block diagram of an ED module 10 which may be used in the embodiment in Fig. 14. Except as described in the following, the module 10 is identical to the one in Fig. 10. The module 10 includes an optical data receiver which comprises the communication detector 103, a detector driver 80, a decoder 81 and a clock recovery block 64. The communication detector 103 and the driver 80 may be identical to the communication detector 103' and the driver 70 as described above for the main controller in Fig. 11. The communication detector 103 is installed in the module 10 so as to be brought into optical contact with the panel when the module 10 is mounted on the panel 1. The detector driver 80 is operated to generate an analog measurement signal that represents the communication light that is received by the detector 103. The analog signal is received by the decoder 81, which is operated to convert the analog signal into a digital control signal by applying a predefined protocol, e.g. a PPM protocol. As in Fig. 10, the clock recovery block 64 is operated to recover global clock pulses that are included in the analog signal, and these global clock pulses are used by the decoder 81 to generate the digital control signal, which is supplied to the local processor 30. As in Fig. 10, the global clock pulses and/or local clock pulses generated by a local clock 36 are supplied to the processor 30.

Fig. 16 is a block diagram of a main controller 14 which may be used in the embodiment in Fig. 14. Except as described in the following, the main controller 14 is identical to the one in Fig. 10. The main controller 14 includes an optical data transmitter, which comprises an encoder block 82, an emitter driver 83 and the communication emitter 102'. The communication emitter 102' and the driver 83 may be identical to the emitter 2 and the driver 32 as described above for the module 10 in Fig. 10. The operation of the MS 16 is controlled by a local processor 84. The encoder block 82 receives digital control signals from the processor 84 and encodes the control signals according to a predefined protocol, e.g. a PPM protocol. The encoder block 82 may also receive global clock pulses from the oscillator 20. The encoder block 85 generates a stream of bits that represent the control signals, possibly including the global clock pulses. The stream of bits is received by the emitter driver 83 which is operated to generate encoded communication light based on the stream of bits.

In the following, different embodiments of the ED module 10 and its coupling to the panel 1 will be described with reference to Figs 17-20. Fig. 17 illustrates a set of modules 10 attached to the bottom surface 6 of the panel 1 by an optically clear fixture 26, such as adhesive, glue, tape, gel or a silicone compound. When the module 10 is attached to the panel 1, its emitter 2 is operable to generate a diverging beam of measurement light that is captured inside the panel and propagates across the touch surface 4, as described in relation to Fig. 2 above. Likewise, the detector 3 is arranged to receive measurement light from the panel 1, from a number of different emitters 2, and is operable to measure the energy of the measurement light from each emitter. It is conceivable that one of more additional elements for coupling light into and out of the panel 1 are arranged intermediate the modules 10 and panel 1, e.g. an optically active component for shaping or re-directing the light from or to the module 10, an angular filter, an optical filter, etc.

The ED module 10 may be formed by separate components that are attached to a common mounting structure, e.g. a PCB or a non-conducting substrate. An example is shown in Fig. 18A for the module in Fig. 10. In this example, the electronic circuit (EC) 12 of the module 10 is formed by a local controller (processor) 30 for controlling the local operation of the module 10, an emitter driver 31, a detector driver 32, a digital data receiver 34 for receiving the control signals ("CTRL"), a local electronic memory 35 and a local oscillator 36, which are all electrically connected to a PCB 37. An emitter 2 and a detector 3 are also physically attached to the PCB 37 and electrically connected to the emitter driver 31 and the detector driver 32, respectively. The emitter 2 and the detector 3 may be powered by the respective driver 31, 32 or via the PCB 37. The PCB 37 includes connectors for receiving electric power ("POWER"), which is distributed to the components on the PCB 37. In a variant, the EC 12 is instead embodied as an integrated circuit (IC), such as an ASIC. Thereby, it is possible to dispense with the PCB, if desired, and directly interconnect the EC 12, the emitter 2 and the detector 3. In a variant, the integrated circuit may also include the emitter 2 or the detector 3. Fig. 18B illustrates an embodiment in which both the emitter 2 and the detector 3 are included in the integrated circuit.

Figs 19A-19F show examples of modules 10 that have an outer casing 40 that encloses the EC 12, the emitter 2 and the detector 3. The casing 40 may serve to protect the components 2, 3, 12 from dust and other contaminants during transport and handling, e.g. if the modules 10 are manufactured separately and shipped to an assembly line for attachment to the panel 1. The casing 40 may also serve to isolate the components from electric shocks, e.g. electrostatic discharges. The casing defines a mounting surface for mounting the module 10 on the panel 1. The casing 40 may be blocking to all light except the light generated by the emitters 2, so as to reduce the amount of ambient light that reaches the detectors 3. In the illustrated example, the casing 40 is totally blocking to all light, and a light transmissive window 42 is formed in the mounting surface. Fig. 19A shows an example of a module 10 that has a top- emitting emitter 2 and a top-detecting detector 3. In this example, the window 42 is arranged directly above the light-emitting and light-sensing surfaces 2', 3'. Fig. 19B illustrates the module 10 in Fig. 19A when attached to the bottom surface 6 of the panel 1. Fig. 19C shows an example of a module 10 that has a side-emitting emitter 2 and a side-detecting detector 3. The window 42 is aligned with the surfaces 2', 3'. Fig. 19D illustrates the module 10 in Fig. 19C when mounted on the bottom surface 6 of the panel 1. Fig. 19E shows another example of a module 10 with a side-emitting emitter 2 and a side-detecting detector 3, where the window 42 is arranged at right angles to and is displaced from the surfaces 2', 3'. This embodiment may serve to reduce the impact of ambient light, i.e. light emanating from the surroundings of the touch system, since the light-sensing surface 3' is arranged at right angles to the top and bottom surfaces 5, 6 and is shielded by the non-transmissive casing 40 from a large portion of the ambient light that impinges onto the top surface 5, as understood from Fig. 19F. Further, this embodiment may serve to increase the amount of light that is captured by internal reflections in the panel 1, since a larger portion of the light from the emitter 2 will strike the bottom surface 6 at large angles to its normal. Further reference is given to US provisional application No. 61/738044, filed on December 17, 2012, which is incorporated herein in its entirety.

The casing 40 may be filled with a light transmissive material, e.g. silicon, at least in the space between the surfaces 2', 3' and the window 42, so as to achieve an efficient coupling of light into the panel 1 at angles that sustain propagation by total internal reflection.

Although not shown on the drawings, the casing 40 may contain optically active components, such as lenses for re-directing or shaping the emitted and/or received measurement light, optical filters for suppressing ambient light and/or for hiding the interior of the module 10 from view through the top surface 5. The casing may also include an angular filter for controlling the angles of the light entering and/or leaving the panel, as described in Applicant's US provisional application No. 61/740093, filed on December 20, 2012, which is incorporated herein in its entirety.

In a further variant, the casing 40 may include a partition (not shown) that defines two physically separated compartments inside the module 10 beneath the window 42, one containing the emitter 2 and one containing the detector 3.

Figs 20A-20C show examples of how the panel 1 and the modules 10 may be combined with a display unit 90 to form an integrated touch-sensitive display. In Fig. 20A, the modules 10 are attached to the bottom surface 6 of the panel 1, and the display unit 90 is fitted within the perimeter of modules and is attached to the bottom surface 6. A spacer 91 of transmissive material connects the display unit 90 to the panel. The transmissive material has a lower index of refraction than the panel 1. Alternatively, the spacer 91 is replaced by an air gap. In Fig. 20B, the display unit 90 is instead mounted onto the rear side of the modules 10, which are mounted to the bottom surface 6 of the panel 1. In Fig. 20C, the modules 10 are mounted in optical contact with the edge surface that connects the top and bottom surfaces 5, 6 of the panel 1, and the display unit 90 is attached to the bottom surface 6. As an alternative to optically communicating encoded data inside the light transmissive panel 1, it is conceivable to use an existing planar waveguide in the display unit 90 as a channel for transmitting communication light. Many display units, e.g. LCDs, are illuminated from behind by a backlight to produce a visible image. The backlight may be formed by a transparent planar waveguide ("backlight panel") of plastic material which is patterned on one of its planar surfaces. One or more light sources are installed on its edge(s) to inject light into the backlight panel. The patterning causes the light from the light source to leak across planar surface of the backlight panel. Such a backlight panel is also known as a "diffuser". The display unit 90 may also include other layers of light transmissive material suitable for conducting light by internal reflections, e.g. a layer that is bounded by materials of lower index of refraction. Such layers may also be used as a channel for transmitting communication light.

Fig. 21 shows an example of an integrated touch-sensitive display system which includes a light transmissive panel 1 in combination with an LCD display 90. The LCD display 90 comprises an LCD panel 92 and a diffuser 93. ED modules 10 (one shown) are attached in optical contact with the panel 1 to inject measurement light which propagates by internal reflections inside the panel 1 for detection downstream of the touch surface. In the illustrated example, the modules 10 are configured to optically transmit the DPVs via the diffuser 93, which is a planar light guide that forms a functional part of the display 90. In this example, the module 10 includes a dedicated communication emitter 102 which is optically coupled to generate communication light that propagates in the diffuser 93. Although not shown in Fig. 20, light sources are coupled to the diffuser to inject light that is leaked towards the LCD panel 92 (vertical arrows). The communication emitter 102 may be implemented and controlled similar to the emitter 2 in Fig. 10. The main controller 14 is arranged to retrieve the DPVs by means of a communication detector 103' which is arranged in optical contact with the diffuser 93 to intercept the communication light. The control signals may similarly be optically transmitted inside the diffuser 93 from the main controller 14 to the modules 10, by the main controller 14 operating a communication emitter (cf. 102' in Figs 14 and 16) arranged in optical contact with the diffuser 93 and the modules 10 operating a respective communication detector (cf. 103 in Figs 14 and 15) arranged in optical contact with the diffuser 93.

In a further alternative (not shown), the measurement emitter 2 or a

communication emitter 102 is arranged to transmit data-encoded light through the spacer 91, which is a functional part of the display 90 as attached to the light transmissive panel 1. The spacer 91 thus forms a planar light guide for the data-encoded light.

In yet another alternative (not shown), the data-encoded light is transmitted through a planar light guide which is installed behind the panel 1 (e.g. behind the display 90) without forming a functional part of the display 90 as attached to the panel 1. Thus, such a planar light guide is added to the combination of the panel 1 and the display 90 for the dedicated purpose of transporting the data-encoded light.

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 to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims.

For example, each ED module 10 may comprise more than one emitter 2 of measurement light and/or more than one detector 3 of measurement light. The skilled person can readily design the EC 12 in the ED module 10 to generate and output DPVs for all detection lines that extend to such an ED module 10.

Furthermore, it is not necessary that all ED modules 10 in the touch system are identical. For example, it is conceivable that the touch system is formed by installing different types of ED modules 10 in optical contact with the light transmissive panel 1.

It is conceivable that the touch system includes more than one main controller 14, where the respective main controller 14 is configured for communication with a subset of the ED modules 10 in the touch system, and where all main controllers 14 are arranged for communication with the touch controller 24.

It is also conceivable that the main controller 14 and the touch controller 24 are integrated in a single unit, which is thus arranged for communication with the ED modules 10.

It is also conceivable to omit the distribution of global clock signals if the control signals and the DPVs are encoded and decoded using a protocol that does not require synchronization between the ED modules 10 and main controller 14. In another alternative, the global clock pulses are transmitted from the main controller 14 to the ED modules 10 via the power transmission lines.

The emitters 2, 102, 102' may be any device capable of emitting radiation in a desired wavelength range, for example an LED (light-emitting diode), a diode laser, a VCSEL (vertical-cavity surface-emitting laser), etc. Likewise, the detectors 3, 103, 103' may be any device capable of converting light into an electric signal, such as a photo- detector, a CCD device, a CMOS device, etc. It is also to be understood that the blocks that are shown on block diagrams herein are functional blocks that may each be implemented by electronic hardware, electronic software instructions loaded into a RAM and executed by a processor, or a combination thereof.

It is also conceivable to implement the optical communication according to the first and second embodiments without using unitary ED modules 10. Instead, the functionality of the ED modules 10 may be provided by separate components installed in the touch system. For example, discrete emitters 2, 102 and detectors 3, 103 may be mounted onto the panel 1 and be electrically connected to separate ECs 12. These ECs 12 may, but need not, be mounted on the panel 1 and may be implemented by an IC or by an assembly of discrete analog and/or digital components. It is to be understood that the detailed description of example embodiments given hereinabove is applicable also to touch systems that do not contain separate, unitary ED modules, as long as the touch systems includes a plurality of ECs 12 that are electrically connected to a respective ED group, i.e. a group comprising at least one emitter 2 and one detector 3, to implement the functionality of the ED modules.

It is also conceivable to optically communicate the DPVs and/or the control signals via optical fibers or other types of dedicated waveguides that are installed in the optical touch system for the purpose of transmitting communication light, generated by communication emitters under control of the ECs 12, to an optical signal receiver in the main controller 16.

Claims

1. A touch-sensing apparatus, comprising:

a planar light guide (1) having a front surface (5), forming a touch-sensing region (4), and an opposite rear surface (6);

light emitters (2) operable to introduce measurement light into the planar light guide (1) for propagation by internal reflections between the front surface (5) and the rear surface (6);

light detectors (3) optically connected to the planar light guide (1) and operable to detect the measurement light on a grid of light propagation paths between pairs of the light emitters (2) and the light detectors (3); and

a plurality of electronic circuitry units (12) electrically connected to a respective component group comprising one of the light emitters (2) and one of the light detectors (3), wherein the respective electronic circuitry unit (12) is operable to generate a set of projection values (DPV) representing the measurement light received by said one of the light detectors (3) on a subset of the light propagation paths (D), wherein the respective electronic circuitry unit (12) is further arranged to optically transmit the set of projection values (DPV) to an optical signal receiver (103', 18) which is arranged to provide the set of projection values (DPV) to a touch controller (24) for determining a property of objects on the touch-sensing region (4).

2. The touch-sensing apparatus of claim 1, wherein the respective electronic circuitry unit (12) is arranged to optically transmit the set of projection values (DPV) through the planar light guide (1) or through a secondary planar light guide (93) which is mounted behind the rear surface (6) of the planar light guide (1), and wherein the optical signal receiver (103', 18) is optically coupled to the planar light guide (1) or the secondary planar light guide (93).

3. The touch-sensing apparatus of claim 2, wherein the secondary planar light guide (93) forms a functional part of a display unit (90) which is mounted behind the rear surface (6) of the planar light guide (1).

4. The touch-sensing apparatus of claim 2 or 3, wherein the respective electronic circuitry unit (12) is configured to operate said one of the light emitters (2) to optically transmit the set of projection values (DPV) through the planar light guide (1).

5. The touch-sensing apparatus of any one of claims 2-4, further comprising a sequencer (16) which is operable to trigger the electronic circuitry units (12) to perform a predefined sequence of measurement phases, wherein a unique subset of the light emitters (2) is activated during each measurement phase to introduce the measurement light on a unique subset of the light propagation paths (D), and wherein the predefined sequence of measurement phases results in projection values (DPV) being generated by the plurality of electronic circuitry units (12) to represent a complete set of light propagation paths (D) in the grid of light propagation paths (D).

6. The touch-sensing apparatus of claim 5, wherein the respective electronic circuitry unit (12) is configured to optically transmit the set of projection values (DPV) separated in time from the measurement phases.

7. The touch-sensing apparatus of claim 5 or 6, wherein each measurement phase is followed by a communication phase, wherein the respective electronic circuitry unit (12) is configured to optically transmit, during the communication phase, the set of projection values (DPV) generated during the most recent measurement phase.

8. The touch-sensing apparatus of claim 7, wherein the respective electronic circuitry unit (12) is configured to optically transmit the set of projection values (DPV) at least partly during one or more measurement phases.

9. The touch-sensing apparatus of claim 8, wherein the respective electronic circuitry unit (12) is operable to transmit the set of projection values (DPV) as encoded in communication light emitted by a dedicated communication light emitter (102) which is electrically connected to the respective electronic circuitry unit (12), wherein the communication light is distinct from the measurement light by frequency modulation and/or by spectral separation.

10. The touch-sensing apparatus of claim 8, wherein the respective electronic circuitry unit (12) is configured to encode the set of projection values (DPV) in the measurement light generated by said one of the light emitters (2) when activated during a given measurement phase in the predefined sequence of measurement phases, wherein the set of projection values (DPV) is generated to represent the measurement light received by said one of the light detectors (3) during preceding measurement phases since the latest activation of said one of the light emitters (2), such that the set of projection values (DPV) represent the light propagation paths (D) that extend to said one of the light detectors (3).

1 1. The touch-sensing apparatus of claim 10, wherein the respective electronic circuitry unit (12) is configured to generate, irrespective of the encoded set of projection values (DPV), the same amount of measurement light during a given time period.

12. The touch-sensing apparatus of any one of claims 5-1 1, wherein the respective electronic circuitry unit (12) comprises a data buffer (35) which is configured for intermediate storage of the projection values (DPV) generated by the respective electronic circuitry unit (12) during the predefined sequence of measurement phases.

13. The touch-sensing apparatus of any one of claims 5-12, wherein the sequencer (16) is configured to embed a synchronization signal in an electric power signal which is supplied to the electronic circuitry unit (12).

14. The touch-sensing apparatus of any one of claims 5-12, wherein the sequencer (16) is configured to generate an optical synchronization signal inside the planar light guide (1) or the secondary planar light guide (93), and wherein the respective electronic circuitry unit (12) is operable to receive the optical synchronization signal via said one of the light detectors (3) or via a dedicated communication light detector (103) which is optically coupled the secondary planar light guide (93) and electrically connected to the electronic circuitry unit (12).

15. The touch-sensing apparatus of any one of claims 5-13, wherein the sequencer (16) is configured to optically transmit, inside the planar light guide (1) or the secondary planar light guide (93), control signals for controlling the operation of the electronic circuitry units (12), and wherein the respective electronic circuitry unit (12) is operable to receive the control signals via said one of the light detectors (3) or via a dedicated communication light detector (103) which is electrically connected to the electronic circuitry unit (12).

16. The touch-sensing apparatus of any preceding claim, wherein the respective electronic circuitry unit (12) is configured to optically encode the set of projection values using Pulse-Position Modulation (PPM).

17. The touch-sensing apparatus of any preceding claim, wherein the respective electronic circuitry unit (12) comprises a detector driver (32) operatively connected to said one of the light detectors (3) for generating an analog measurement signal in response to impinging light on the light detector (3), an analog-to-digital converter (61) for converting the analog measurement signal into a digital signal, and a projection value generator (62) for generating the set of projection values based on the digital signal.

18. The touch-sensing apparatus of any preceding claim, wherein the electronic circuitry unit (12) is implemented by an integrated circuit, such as an ASIC.

19. The touch-sensing apparatus of any preceding claim, wherein the respective component group contains one and only one light emitter (2) for generating the measurement light and one and only one light detector (3) for receiving the

measurement light.

20. The touch-sensing apparatus of any preceding claim, which comprises a plurality of identical, unitary emitter-detector modules (10) which are disposed in optical contact with the planar light guide (1), wherein each emitter-detector module (10) comprises one of the electronic circuitry units (12) and the component group which is electrically connected to the electronic circuitry unit (12).

21. The touch-sensing apparatus of claim 20, wherein the respective emitter- detector module (10) comprises a common mounting structure (37) for the electronic circuitry unit (12) and the component group.

22. The touch-sensing apparatus of claim 20 or 21, wherein the respective emitter- detector module (10) further comprises one or more optical components for directing the measurement light from said one of the light emitters (2) into the planar light guide (1) and/or for directing light from the planar light guide (1) onto said one of the light detectors (3).

23. The touch-sensing apparatus of claim 20, 21 or 22, wherein the respective emitter-detector module (10) comprises a housing (40) which contains the component group and the electronic circuitry (12) and which defines a front face that is transparent to the measurement light, the front face being attached to the planar light guide (1).

24. The touch-sensing apparatus of any preceding claim, wherein each of the light emitters (2) is optically coupled to the planar light guide (1) at an incoupling port so as to generate an individual beam of measurement light that diverges in the plane of the planar light guide (1) while it propagates away from the incoupling port inside the planar light guide (1) by internal reflections between the front and rear surfaces (5, 6).

25. The touch-sensing apparatus of any preceding claim, wherein each of the light detectors (3) is optically coupled to the planar light guide (1) at an outcoupling port to receive measurement light from a plurality of the light emitters (2).

26. The touch-sensing apparatus of any preceding claim, wherein the set of the projection values (DPV) represents energy of the measurement light received by said one of the light detectors (3) during a given time period for each light propagation path (D) that extends to the light detector (3).