Patent Publication Number: US-2005134526-A1

Title: Configurable tiled emissive display

Description:
FIELD OF THE INVENTION  
      The present invention relates to a modular large-screen emissive display such as an organic light-emitting diode (OLED) display. In particular, this invention relates to a scalable display composed of autonomous and interchangeable tiles. The present invention also provides a method for automatic configuration of a tiled emissive display such as an OLED display, and a method for replacing tiles in a tiled emissive display such as an OLED display.  
     BACKGROUND OF THE INVENTION  
      OLED technology incorporates organic luminescent materials that, when sandwiched between electrodes and subjected to a DC electric current, produce intense light of a variety of colours. These OLED structures can be combined into the picture elements, or pixels, that comprise a display or a tile of a complete display. OLEDs are also useful in a variety of applications as discrete light-emitting devices or as the active element of light-emitting arrays or displays, such as flat-panel displays in watches, telephones, laptop computers, pagers, cellular phones, calculators, and the like. To date, the use of OLED light-emitting arrays or displays has been largely limited to small-screen applications such as those mentioned above.  
      The market is now, however, demanding larger displays with the flexibility to customise display sizes. For example, advertisers use standard sizes for marketing materials; however, those sizes differ based on location. Therefore, a standard display size for the United Kingdom differs from that of Canada or Australia. Additionally, advertisers at trade shows need bright, eye-catching, flexible systems that are easily portable and easy to assemble and disassemble. Still another rising market for customisable large display systems is the control room industry, in which maximum display quantity, quality, and viewing angles are critical. Demands for large-screen display applications possessing higher quality and higher light output has led the industry to turn to alternative display technologies that replace older LED and liquid crystal displays (LCDs). For example, LCDs fail to provide the bright, high light output, larger viewing angles, and high resolution and speed requirements that the large-screen display market demands. By contrast, OLED technology promises bright, vivid colours in high resolution and at wider viewing angles. However, the use of OLED technology in large-screen display applications, such as outdoor or indoor stadium displays, large marketing advertisement displays, and mass-public informational displays, is only beginning to emerge.  
      Large screen displays are often modular or tiled displays made from smaller modules or displays that are then combined into larger tiles. These tiled displays are manufactured as a complete unit that can be further combined with other tiles to create displays of any size and shape. However, the individual tiles forming a tiled display are typically not capable to operate as a full display alone. What is needed is an OLED tile that may operate standing alone as an autonomous display or alternatively may operate within a set of tiles to form a larger tiled display. Consequently, what is further needed is a scalable OLED display tile that reduces system architecture complexity and a method of associating and configuring an OLED tile automatically upon installation. Lastly, what is needed is a scalable OLED display tile that allows distributed and parallel processing, thereby reducing the complexity of the overall system processing requirements.  
      An example tiled display is described in WO 99/41732, entitled, “Tiled electronic display structure.” The &#39;732 patent application describes a tiled display device that is formed from display tiles having pixel positions defined up to the edge of the tiles. Each pixel position has an OLED active area that occupies approximately twenty-five percent of the pixel area. Each tile includes a memory that stores display data and pixel driving circuitry that controls the scanning and illumination of the pixels on the tile. The pixel driving circuitry is located on the back side of the module and connections to pixel electrodes on the front side of the tile are made by vias that pass through portions of selected ones of the pixel areas that are not occupied by the active pixel material. The tiles are formed in two parts—an electronics section and a display section. Each of these parts includes connecting pads that cover several pixel positions. Each connecting pad makes an electrical connection to only one row electrode or column electrode. The connecting pads on the display section are electrically connected and physically joined to corresponding connecting pads on the electronics section to form a complete tile. Each tile has a glass substrate on the front of the tile. Black matrix lines are formed on the front of the glass substrate and the tiles are joined by mullions that have the same appearance as the black matrix lines.  
      Although the tiled display described in the &#39;732 patent application provides a means for interconnecting tiles to create a large display system, &#39;732 patent application fails to provide a scalable OLED display tile that reduces system architecture complexity and a method of associating and configuring an OLED tile automatically upon installation.  
      Furthermore, the tiled OLED display needs a high bandwidth for calculations done in a central processor.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide an emissive display that is scalable and reduces the complexity of the overall system processing requirements as well as a method of operating the same.  
      It is another object of this invention to provide a scalable emissive display tile that reduces system architecture complexity as well as a method of operating the same.  
      It is yet another object of this invention to provide a way of associating and configuring an emissive tile, e.g. an OLED tile, automatically upon installation.  
      The above objectives are accomplished by a method and device according to the present invention.  
      In a first aspect, the present invention relates to a tiled emissive, e.g. an OLED display for displaying an image. The tiled emissive, e.g. OLED display comprises a plurality of OLED tile assemblies mechanically coupled together, and a processing means for performing real-time calculations with respect to the image to be displayed. The processing means according to the present invention is a distributed processing means which is distributed over the plurality of emissive display, e.g. OLED tile assemblies, so that each emissive display, e.g. OLED tile assembly is suitable for handling a different portion of the image for performing real-time calculations. A tile can automatically configure its operational characteristics, and the tiles associate/communicate with one another upon installation, to form an integral display. The tiles have electrical connections for access to the distributed processing means.  
      The tiled emissive, e.g. OLED display can have distributed processing means which are suitable for performing image upscaling or downscaling as necessary at each emissive display, e.g. OLED tile assembly. For the image upscaling or downscaling a high-level scaling algorithm can be used. This high-level scaling algorithm may be a 100% accurate scaling algorithm.  
      The distributed processing means of the plurality of emissive display, e.g. OLED tile assemblies comprise processing elements operating in parallel.  
      An emissive display, e.g. OLED tile assembly may be provided with a data input and/or a data output connection for receiving data from or transmitting data to another emissive display, e.g. OLED tile assembly via any of suitable connection topology, e.g. a feed-and-drop line, a multi-line connection, a daisy chain connection or a star connection. Furthermore, the emissive display, e.g. OLED tile assemblies may be provided with a power input and/or a power output connection for receiving power from or transmitting power to another emissive display, e.g. OLED tile assembly via any of a feed-and drop line, a multi-line connection, a daisy chain connection or a star connection or there may be a separate power connection.  
      The emissive display, e.g. OLED tile assemblies may be provided with a single connector allowing to combine both power and data transmission.  
      The emissive display, e.g. OLED tile assemblies may furthermore be provided with a local memory means for storing configuration data. The memory means is preferably a non-volatile memory. The emissive display, e.g. OLED tile display may furthermore be adapted so that the emissive display, e.g. OLED tile assemblies can be repaired while the other tiles continue working, i.e. the tiles may be hot-swap enabled. This can mean that e.g. the controller or the power supply in a tile may be replaced without disconnecting the power and data connectors. In this way the internal parts of the tile may be replaced without the other tiles having to cease their operation.  
      Furthermore, the tiled emissive display, e.g. OLED display according to the invention may have an adjustable size, e.g. by addition or subtraction of tiles.  
      In a second aspect, the invention relates to a method of automatically configuring a tiled emissive display, e.g. OLED display comprising a plurality of emissive display, e.g. OLED tile assemblies mechanically coupled together, whereby the tiled emissive display, e.g. OLED display is intended for displaying an image. The method comprises assigning to each emissive display, e.g. OLED tile assembly a unique address for use in steering content and communication data, distributing to each emissive display, e.g. OLED tile assembly display co-ordinates that designate which portion of the image to be displayed it will show, configuring the emissive display, e.g. OLED tile assemblies by reading, for each emissive display, e.g. OLED tile assembly, configuration data stored in a memory device local to the emissive display, e.g. OLED tile assembly, and using this information in a distributed processing means local to the emissive display, e.g. OLED tile assembly to configure the resolution of the emissive display, e.g. OLED tile assembly.  
      The method furthermore may comprise, before assigning to each emissive display, e.g. OLED tile assembly a unique address, detecting the presence of the emissive display, e.g. OLED tile assemblies in the tiled emissive display, e.g. OLED display.  
      Additionally, calibrating the emissive display, e.g. OLED tile assemblies to match overall display brightness and/or to correct individual pixel non-uniformity may be performed.  
      Furthermore, the method may comprise, before assigning to each emissive display, e.g. OLED tile assembly a unique address, mechanically assembling and activating the tiled emissive display, e.g. OLED display. This mechanical assembling may include providing a feed-and-drop line, a daisy chain connection, a multi-line connection or a star connection for data and/or power from one emissive display, e.g. OLED tile assembly to another.  
      In a third aspect, the present invention relates to a method of replacing at least one emissive display, e.g. OLED tile assembly in a tiled emissive display, e.g. OLED display intended for displaying an image. The method comprises mechanically replacing at least one emissive display, e.g. OLED tile assembly in the tiled emissive display, e.g. OLED display, assigning to the at least one replaced emissive display, e.g. OLED tile assembly a unique address for use in steering content and communication data, assigning to the at least one replaced emissive display, e.g. OLED tile assembly display co-ordinates that designate which portion of the image to be displayed it will show, configuring the at least one replaced emissive display, e.g. OLED tile assembly by reading, for each replaced emissive display, e.g. OLED tile assembly, configuration data stored in a memory device local to the at least one emissive display, e.g. OLED tile assembly, and using this information in a distributed processing means local to the replaced emissive display, e.g. OLED tile assembly to configure the resolution of the emissive display, e.g. OLED tile assembly. The method may also include the step of detecting that a display tile has been removed from the tiled display and storing information with respect to that part of the image which the removed tile displayed. It further includes assigning to a new tile, the part of the image which was displayed by the removed tile.  
      The method furthermore may comprise calibrating the at least one replaced emissive display, e.g. OLED tile assembly to match overall display brightness and/or to correct individual pixel non-uniformity.  
      Before assigning the unique address, the method may include determining whether the number or arrangement of tiles has been altered. If the number or arrangement of the tiles has been altered, the method may furthermore comprise configuring the tiled emissive display, e.g. OLED display according to the above mentioned methods of configuring.  
      The method furthermore may include mechanically replacing at least one emissive display, e.g. OLED tile assembly whereby the connection of the different emissive display, e.g. OLED tile assemblies is restored, for data and/or power from or to at least one other emissive display, e.g. OLED tile assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a perspective view of a viewable side of an OLED tile assembly in accordance with an embodiment of the present invention.  
       FIG. 1B  is a perspective view of a non-viewable side of an OLED tile assembly in accordance with an embodiment of the present invention.  
       FIG. 1C  is an exploded view of an OLED tile assembly in accordance with an embodiment of the present invention.  
       FIG. 2  is a cross-sectional drawing of the OLED tile assembly taken along line A-A of  FIG. 1B .  
       FIG. 3  is a cross-sectional drawing of a Detail A of  FIG. 1C .  
       FIG. 4  is a perspective view of a single mask for use with an OLED tile assembly of the present invention.  
       FIG. 5A  schematically illustrates a tiled OLED display and a multi-line method of signal and power distribution in accordance with an embodiment of the present invention.  
       FIG. 5B  schematically illustrates a tiled OLED display and a daisy-chain method of signal and power distribution in accordance with an embodiment of the present invention.  
       FIG. 6  illustrates a functional block diagram of an OLED tile control system for use in an OLED tile assembly in accordance with an embodiment of the present invention.  
       FIG. 7  illustrates the overall architecture of an OLED tile control system in accordance with an embodiment of the present invention.  
       FIG. 8  is a flow diagram of a method of initial assembly, automatic configuration, and calibration of a tiled OLED display in accordance with an embodiment of the present invention.  
       FIG. 9  is a flow diagram of a method of replacing, adding, or removing one or more OLED tile assemblies in a tiled OLED display. 
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS  
      The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.  
      The present invention will be described with reference to an OLED display, especially an OLED tiled display but the present invention is not limited to OLED displays but may be used with any emissive displays, especially tiled emissive displays. Emissive displays generally comprise an array of emissive pixel elements, each pixel element or group of pixel elements being individually addressable so as to display an arbitrary image. Such displays are often described as fixed format displays to distinguish them over CRT displays. The term “fixed format” refers to the fact that addressable pixel elements at fixed positions are used to display the image. Fixed format does not mean that the displays cannot be made scalable, e.g. tiled. Suitable emissive displays include Light Emitting Diode (LED) displays, electroluminescent displays such as EL displays, Plasma displays, etc.  
      In the following reference will be made to OLED displays but such reference applies equally well to any emissive display. Accordingly in one aspect of the present invention, a configurable OLED display tile and associated methods for use in a tiled large-screen display application are provided. The OLED display tile according to an embodiment of the present invention is capable of operating either as an autonomous display or alternatively of operating within a set of OLED display tiles forming a larger tiled display. The present invention may also include assemblies of pixel arrays, e.g. they may be tiled displays and may comprise modules made up of tiled arrays which are themselves tiled into supermodules. Thus, the word display relates to a set of addressable pixels in an array or in groups of arrays. Several display units or tiles may be located adjacent to each other to from a larger display, i.e. multiple display elements are physically arranged side-by-side so that they can be viewed as a single image. The physical hardware implementation of the OLED display tile or OLED tile assembly of the present invention and the architecture of a larger tiled display formed by an k by l array of OLED tile assemblies provide distributed processing that has the result of a less complex display hardware and software system, thereby avoiding the need for high-bandwidth calculations by a central processor.  
       FIG. 1A  is a perspective view of a viewable side of an OLED tile assembly  100  in accordance with an embodiment of the invention. OLED tile assembly  100  is suitable for use as an autonomous display or alternatively may operate within a set of OLED tile assemblies  100  to form a larger tiled display. OLED tile assembly  100  includes a precision frame  110 ; a plurality of masks  112 ; an enclosure  114 ; a plurality of positioning plates and pins  116  (e.g., positioning plate and pin  116   a , positioning plate and pin  116   b , positioning plate and pin  116   c , and positioning plate and pin  116   d ), and a plurality of clamp elements  118  (e.g., alignment tab  118   a  and alignment tab  118   b ) disposed within precision frame  110 , as shown in  FIG. 1A .  
       FIG. 1B  is a perspective view of a non-viewable side of OLED tile assembly  100  in accordance with an embodiment of the invention. In this view, it is apparent that OLED tile assembly  100  further includes a plurality of positioning plates and holes  120  (e.g., positioning plate and hole  120   a , positioning plate and hole  120   b ), and a plurality of alignment slots  122  (e.g., alignment slot  122   a ), all disposed within precision frame  110 . Disposed within enclosure  114  is an air inlet  124 , a first air outlet  126 , a second air outlet  128 , a data input connector  130 , a data output connector  132 , a power input connector  134 , and a power output connector  136 , as shown in  FIG. 1B .  
       FIG. 1C  is an exploded view of OLED tile assembly  100  in accordance with an embodiment of the invention. In this view, it is apparent that OLED tile assembly  100  includes, in order from front to back, the front side being the side suitable for displaying the image, an array of OLED module assemblies  138 , each further including a mask  112 , a substrate  140 , an OLED board  142 , optionally a quantity of underfill material  144 , a cooling block  146 , a quantity of potting material  148 , and a circular polariser  150 ; a plurality of connectors  152 ; precision frame  110 ; a control board  154 ; an assembly bracket  156 ; a power supply (P/S)  158  and a plurality of cooling fans  160 , both of which are mounted upon assembly bracket  156 ; an insulation sheet  162  for P/S  158 , and enclosure  114 , as shown in  FIG. 1C . With reference to  FIG. 1A ,  FIG. 1B , and  FIG. 1C , it is noted that OLED tile assembly  100  is sized according to the array of OLED module assemblies  138 . In this example, a 3×3 array of OLED module assemblies  138  is illustrated. However, OLED tile assembly  100  is not limited to this example: the physical size of OLED tile assembly  100  and its elements may vary depending upon the configuration of an n by m array of OLED module assemblies  138 , which is selectable.  
      With reference to  FIG. 1A ,  FIG. 1B , and  FIG. 1C , the elements of OLED tile assembly  100  are described as follows.  
      Precision frame  110  serves as the primary mechanical structure upon and within which all other elements of OLED tile assembly  100  are mounted. Precision frame  110  is formed of any suitably strong material, such as light metal alloys, that will support the structure of OLED tile assembly  100 . Precision frame  110  is sized according to a predetermined array configuration of OLED module assemblies  138  housed within the precision frame  110 . Mounted upon a first side of precision frame  110  are a first positioning plate and pin  116   a  and a second positioning plate and pin  116   b , with a first alignment tab  118   a  positioned therebetween. Mounted upon a second side (adjacent to the first side) of precision frame  110  are a third positioning plate and pin and a fourth positioning plate and pin, with a second alignment tab positioned therebetween. These, however, are not visible in the perspective view of  FIG. 1C . Similarly, mounted upon a third side of precision frame  110  are a first positioning plate and hole  120   a  and a second positioning plate and hole  120   b , with a first alignment slot  122   a  positioned therebetween. Mounted upon a fourth side (adjacent to the third side, and not visible in  FIG. 1C ) of precision frame  110  are a third positioning plate and hole and a fourth positioning plate and hole, with a second alignment slot positioned therebetween.  
      Enclosure  114  also can comprise 2 separate parts: i.e. one part with the air inlet and outlets and one part with the data and power input and output connectors. This feature combined with the correct internal arrangements in the tile allows to replace e.g. the controller or the power supply in a tile, without disconnecting the power and data connectors. When the internal parts of the tile that has to be repaired are replaced, all the other tiles will continue working. This feature of the display is called “hot swap capability”. The hot swap capability is not shown in any of the drawings.  
      Positioning plates and pins  116 , clamp elements  118 , positioning plates and holes  120 , and alignment slots  122  are typically formed of stainless steel. Positioning plates and pins  116 , clamp elements  118 , positioning plates and holes  120 , and alignment slots  122  serve as alignment and locking mechanisms for use when a plurality of OLED tile assemblies  100  are assembled in the k by l array to form a larger tiled display. More specifically, positioning plates and pins  116  and clamp elements  118  of one OLED tile assembly  100  align and mechanically couple to positioning plates and holes  120  and alignment slots  122 , respectively, of an adjacent OLED tile assembly  100 .  
      Each mask  112  is sized accordingly and placed on the viewable side of each respective OLED module assembly  138 . Collectively, masks  112  are used to hide the seams between substrates  140  within OLED tile assembly  100  when assembled. Furthermore, masks  112  are used to hide the seams between OLED tile assemblies  100  within the k by l array of OLED tile assemblies  100  that form a larger tiled display. Each mask  112  forms a grid of dark lines; thus, physical gaps between elements become impossible to see because they disappear among the other lines. The pitch of the dark lines in the mask is usually equal to the pixel pitch or to a multiple of the pixel pitch. Further details of mask  112  are found in reference to  FIG. 4 .  
      Enclosure  114  forms the structure of the non-viewable side of OLED tile assembly  100 . Enclosure  114  is formed of any suitably strong material, such as light metal alloy, and is mechanically attached to one side of precision frame  110 . Disposed within enclosure  114  are air inlet  124 , first air outlet  126 , and second air outlet  128 , as shown in  FIG. 1B . Air inlet  124 , first air outlet  126 , and second air outlet  128  are formed of any suitable material that is permeable to air, such as an iron or aluminium grid. Air inlet  124  serves as the ambient air intake to OLED tile assembly  100 , for cooling the OLED tile assembly  100 . By contrast, first air outlet  126  and second air outlet  128  serve to exhaust warm air generated by OLED tile assembly  100  during operation. The movement of air into and out of OLED tile assembly  100  is due to the action of cooling fans  160 . Further details of the airflow within OLED tile assembly  100  are illustrated in reference to  FIG. 2 .  
      Also disposed within enclosure  114  are data input connector  130 , data output connector  132 , power input connector  134 , and power output connector  136 , as shown in  FIG. 1B .  
      Data input connector  130  and data output connector  132  are conventional signal connectors, such as MOLEX, DVI-digital 74320-3004. Data input connector  130  provides an electrical connection for receiving serial video data signals containing the current video frame information to be displayed on OLED tile assembly  100  and for receiving serial control data signals from a general processor (not shown). If applicable, OLED tile assembly  100  subsequently re-transmits serial video and control data signals to a next, preferably adjacent, OLED tile assembly  100  via data output connector  132 . Power input connector  134  and power output connector  136  are conventional power connectors capable of handling up to e.g. 265 AC volts and 10 amps, such as power input connector IEC60320-C14 or power output connector IEC60320-C13. Power input connector  134  provides an electrical connection for receiving AC input power to OLED tile assembly  100 . If applicable, OLED tile assembly  100  subsequently transmits this AC power to a next, preferably adjacent, OLED tile assembly  100  via power output connector  136 . The AC voltage from power input connector  134  is bussed directly to power output connector  136 . An illustration of distribution methods of signal and power distribution within a tiled OLED display is found with reference to  FIG. 5A  and  FIG. 5B . For compactness issues, the data and power connections can also be integrated in one connector block.  
      Each OLED module assembly  138 , which includes mask  112 , substrate  140 , OLED board  142 , optional underfill material  144 , cooling block  146 , potting material  148 , and circular polariser  150 , is representative of a structure for forming a common-anode, passive-matrix, OLED array with associated drive circuitry. In the common-anode configuration, a current source is arranged between each individual cathode of the OLED devices and ground, while the anodes of the OLED devices are electrically connected in common to a positive power supply. As a result, the current and voltage are completely independent of one another and small voltage variations do not result in current variations eliminating light output variations due to voltage variations. Its elements are described as follows.  
      Substrate  140  of OLED module assembly  138  is formed of a non-conductive, transparent material, such as glass for example. Deposited upon substrate  140  is a pixel array formed of a plurality of addressable discrete OLED devices or pixels. Those skilled in the art will appreciate that the OLED devices for forming graphics display are typically arranged logically in rows and columns to form an OLED array or matrix. The term “logically arranged in rows and columns” refers to the fact that the actual display does not have to be formed in Cartesian co-ordinates but may be provided in other co-ordinate systems such as polar. However, in all of these systems there are equivalents to rows and columns, e.g. arcs of circles and radii. These are therefore logically arranged in rows and columns even if they are not physically arranged in such a manner. Substrate  140  further includes electrical contacts to and from anode and cathode lines, which respectively are electrically connected to the anodes of a row of OLED pixels and to the cathodes of a column of OLED pixels.  
      OLED board  142  of OLED module assembly  138  is a conventional printed circuit board (PCB) formed of a material such as ceramic or FR4 or FR5, i.e. known glass laminates widely used for subtractive printed circuit board fabrication because of their ability to meet a wide variety of processing conditions. On the printed circuit board are mounted the drive circuitry devices. A functional block diagram of OLED board  142  is described in reference to  FIG. 6 . OLED board  142  includes wiring to facilitate electrical signal and power connections to and from the pixel array upon substrate  140 . OLED board  142  further includes a set of counter contacts for providing electrical connections to substrate  140 , for example via well-known solder bump technology (not shown). Through an alignment procedure, substrate  140  is placed on top of the prepared OLED board  142 . Substrate  140  and OLED board  142  are subsequently placed into an oven, thereby melting the solder and forming a solder joint between substrate  140  and OLED board  142 .  
      Optionally, underfill material  144  is used in OLED module assembly  138 , which is electrically non-conductive and thermally conductive material, such as liquid epoxy material, that is inserted between substrate  140  and OLED board  142 . Underfill material  144  can be applied as a liquid after substrate  140  and OLED board  142  have been connected to each other by solder joints. Underfill material  144  can be used to remove the air gap between these solder joints, thereby increasing the heat transfer between substrate  140  and OLED board  142  and thus improving the cooling. After application as a liquid, underfill material  144  is cured, thereby forming a solid material. Furthermore, due to the presence of underfill material  144 , thermal stresses on the solder joints are redistributed among substrate  140 , OLED board  142 , underfill material  144 , and the solder, thereby increasing the life of the solder joints by mitigating fatigue. Although the presence of underfill material  144  improves the performance of OLED module assembly  138 , underfill material  144  is optional and, thus, may be omitted from the structure of OLED module assembly  138 .  
      Cooling block  146  of OLED module assembly  138  is a conventional heat sink device formed of thermally conductive material, such as aluminium, that is thermally bonded to OLED board  142  via potting material  148 . Potting material  148  is a thermally conductive material, such as Loctite product Hysol EE1087 in combination with the hardener HD  3561 . Potting material  148  is injected between OLED board  142  and cooling block  146  in order to improve the heat transfer and thus the cooling therebetween. Potting material  148  is injected as a liquid and is then cured to form a solid material. Further details of cooling block  146  and potting material  148  are found in reference to  FIG. 3 .  
      Circular polariser  150  of OLED module assembly  138  is mounted between substrate  140  and mask  112 . Circular polariser  150  is a well-known optical device formed of a material, such as e.g. polycarbonate. Circular polariser  150  is an absorptive polariser that allows one type of circular polarisation (left or right) to transmit largely unattenuated, while it will absorb the other circular polarisation (right or left). Circular polariser  150  is used to reduce the amount of ambient light reflections on substrate  140 . The ambient light is unpolarised and therefore part of it is directly absorbed by the circular polariser and the other part is converted into left (or right) circular polarised light by circular polariser  150 . This transmitted left (or right) circular polarised light reflects on substrate  140  and is converted into right (or left) circular polarised light. This right (left) circular polarised light is absorbed by circular polariser  150 . Circular polariser  150  increases the contrast of the display. An example of an absorbing circular polariser  150  is a Nitto Denko model SEG1425DU+NRF QF01A.  
      Connectors  152  are standard connectors for transferring signals and power from control board  154  to the plurality of OLED boards  142 . There is one connector  152  per OLED module assembly  138 . Connectors  152  must be dimensioned to span the distance between OLED boards  142  and control board  154  while taking into account the thickness of cooling blocks  146 . In doing so, clearance holes are provided within precision frame  110  and cooling blocks  146  to allow connectors  152  to pass therethrough. An example of connector  152  is a BergStak Connector, product number: 61082-06YABC.  
      Control board  154  is a conventional printed circuit board (PCB) formed of a material such as ceramic or FR4, upon which are mounted the local processing and control devices needed to operate the n by m array of OLED module assemblies  138 . In general, control board  154  performs pre-processing tasks, such as gamma correction, gamma adjustment of the incoming signal, colour and light calibration according to measurements done at manufacture with a spectral camera and a colour meter, and image scaling algorithms. A functional block diagram of control board  154  is described in reference to  FIG. 6 .  
      Assembly bracket  156  is a mechanical structure for supporting both control board  154 , P/S  158  and cooling fans  160  within OLED tile assembly  100 , as shown in  FIG. 1C . Assembly bracket  156  is formed of any suitably strong material, such as steel.  
      P/S  158  is a conventional power supply that includes a programmable AC-to-DC converter (not shown) and a programmable voltage regulator (not shown). The voltage is regulated per OLED tile assembly  100 . An AC input voltage of between 170 and 265 volts is supplied to P/S  158  via power input connector  134  (see  FIG. 1B ). A DC output voltage of 5 to 25 volts at a maximum current of 7 amps is provided to control board  154  and to OLED module assemblies  138 . Furthermore, the DC power from P/S  158  is bussed to OLED module assemblies  138  in a passive manner by control board  154 .  
      Cooling fans  160  are conventional DC fans capable of providing a volume rate of airflow of between 2 and 5 cubic feet per minute (cfm) in order to maintain an operating temperature within OLED tile assembly  100  of between 10 and 50° C. An example of cooling fan  160  is a Delta Electronics model BFB0505M. The number of cooling fans  160  mounted within OLED tile assembly  100  depends upon the n by m array configuration of OLED module assemblies  138  and the associated control board  154  and P/S  158  requirements. P/S  158  provides DC power to cooling fans  160 . P/S  158  also controls cooling fans  160 .  
      Insulation sheet  162  is an insulation sheet for the power supply, as shown in  FIG. 1C . Insulation sheet  162  is formed of a suitable material, such as mica.  
       FIG. 2  is a cross-sectional drawing of OLED tile assembly  100  taken along line A-A of  FIG. 1B .  FIG. 2  is intended to illustrate the airflow within OLED tile assembly  100  and shows that air is drawn into OLED tile assembly  100  via air inlet  124  as a result of the action of cooling fans  160 . The airflow subsequently passes over cooling blocks  146  (see  FIG. 3 ) and subsequently exhausts via first air outlet  126  and second air outlet  128  as shown in  FIG. 2 . In this way, heat generated by the active components of OLED module assemblies  138 , control board  154 , and P/S  158  is removed.  
       FIG. 3  is a cross-sectional drawing of a Detail A of  FIG. 1C .  FIG. 3  is intended to illustrate the injection process of potting material  148  between OLED board  142  and cooling block  146 . Detail A illustrates that cooling block  146  further includes a plurality of fins  310  that are typical of a heat-removing device. Also included within cooling block  146  is a plurality of injection points  312  that inject potting material  148  in liquid form. A potting calibre  314  is mounted along the perimeter edge of cooling block  146  and serves as a form for containing potting material  148 . Lastly, Detail A illustrates a plurality of components  316  mounted upon OLED board  142 . Components  316  are active and/or passive electrical components that generate heat when operating, such as the OLED devices and switches for example. Upon injection, potting material  148  fills the gap between cooling block  146  and OLED board  142  as well as the gaps between components  316 , thereby forming a heat transfer medium for efficiently transferring heat away from OLED board  142  and components  316 .  
       FIG. 4  is a perspective view of a single mask  112  with OLED tile assembly  100  of the present invention. Mask  112  is a custom made device that is sized according to the size of its associated OLED module assembly  138 . Mask  112  may be formed of polyamide or polycarbonate, and the grid pattern formed therein is determined by the pixel pitch of its associated OLED module assembly  138 . In this example, the grid of mask  112  is designed for use with a 24×32 pixel array.  
       FIG. 5A  and  FIG. 5B  illustrate two possibilities for signal distribution in a tiled OLED display  500 .  FIG. 5A  shows a multi-line distribution method of signal and power distribution in accordance with the invention. Tiled OLED display  500  is representative of a k by l array of OLED tile assemblies  100 . In this example, a 3×3 array is pictured. More specifically,  FIG. 5A  illustrates that tiled OLED display  500  includes, for example, OLED tile assemblies  100   a ,  100   b ,  100   c ,  100   d ,  100   e ,  100   f ,  100   g ,  100   h , and  100   j . It is further illustrated that each OLED tile assembly  100  includes its associated data input connector  130 , data output connector  132 , power input connector  134 , and power output connector  136 . Lastly, tiled OLED display  500  further includes a plurality of data reclockers  510 , for example, data reclocker  5100   a , data reclocker  5100   b , and data reclocker  5100   c.    
      The multi-line distribution method of signal distribution is described as follows. A DATA IN signal  505  from a central processing unit (not shown) is supplied to an input of data reclocker  5100   a . DATA IN signal  505  is representative of serial video and control data.  
      Data reclocker  5100   a  subsequently re-transmits this serial video and control data to one OLED tile assembly  100  as well as to a next data reclocker  510 , i.e., in the example given, to an input of data reclocker  5100   b  and to data input connector  130  of OLED tile assembly  100   g . Similarly, data reclocker  5100   b  transmits the received serial video and control data signal to an input of data reclocker  5100   c  and to data input connector  130  of OLED tile assembly  100   h . Finally, data reclocker  5100   c  transmits the received serial video and control data to data input connector  130  of OLED tile assembly  100   j . This way, the DATA IN signal  505  is distributed to all OLED tiles assemblies  100  of one row of the tiled OLED display  500 . It is to be noted that the data links in the tiled OLED display  500  are bidirectional, so it is also possible to place data reclockers  5100   a ,  5100   b , and  5100   c  on top of tiled OLED display  500 , instead of placing them at the bottom, thus feeding the DATA IN signal  505  to data input connectors  130  of OLED tile assemblies  100   a ,  100   b ,  100   c . These bidirectional links also make it possible to pass the DATA IN signal  505  from the end of one column to the beginning of the neighbouring column. It is likewise to be noted that the terms “row” and “column” are interchangeable, meaning that the data reclockers may distribute the DATA IN signal  505  to all OLED tiles assemblies  100  of one column of the tiled OLED display  500 .  
      Subsequently, the serial video and control data is transferred from one OLED tile assembly  100  to the next OLED tile assembly  100  along a same column if the DATA IN signal  505  was fed to all OLED tile assemblies  100  of a row, or to the next OLED tile assembly  100  along a same row if the DATA IN signal  505  was fed to all OLED tile assemblies  100  of a column. Hereinafter, the situation of  FIG. 5A  is further described, i.e. the case in which the DATA IN signal  505  was fed to all OLED tile assemblies  100  along a same row. For example and with reference to  FIG. 5A , the serial video and control data is transferred from OLED tile assembly  100   g  to OLED tile assembly  100   d  via an electrical connection between data output connector  132  of OLED tile assembly  100   g  and data input connector  130  of OLED tile assembly  100   d , then from OLED tile assembly  100   d  to OLED tile assembly  100   a  via an electrical connection between data output connector  132  of OLED tile assembly  100   d  and data input connector  130  of OLED tile assembly  100   a . Likewise, the serial video and control data is transferred from OLED tile assembly  100   h  to OLED tile assembly  100   e  via an electrical connection between data output connector  132  of OLED tile assembly  100   h  and data input connector  130  of OLED tile assembly  100   e , then from OLED tile assembly  100   e  to OLED tile assembly  100   b  via an electrical connection between data output connector  132  of OLED tile assembly  100   e  and data input connector  130  of OLED tile assembly  100   b . Lastly, the serial video and control data is transferred from OLED tile assembly  100   j  to OLED tile assembly  100   f  via an electrical connection between data output connector  132  of OLED tile assembly  100   j  and data input connector  130  of OLED tile assembly  100   f , then from OLED tile assembly  100   f  to OLED tile assembly  100   c  via an electrical connection between data output connector  132  of OLED tile assembly  100   f  and data input connector  130  of OLED tile assembly  100   c . In each case, the serial video and control data is retransmitted by control board  154  of each OLED tile assembly  100 .  
      The multi-line distribution method of power distribution is accomplished by AC power connections from one OLED tile assembly  100  to the next OLED tile assembly  100  along the same column or row as follows. A POWER INPUT signal  520   a  from a mains power supply (not shown) is supplied to OLED tile assembly  100   g  via an electrical connection to power input connector  134  of OLED tile assembly  100   g . AC power is then transferred from OLED tile assembly  100   g  to OLED tile assembly  100   d  via an electrical connection between power output connector  136  of OLED tile assembly  100   g  and power input connector  134  of OLED tile assembly  100   d . AC power is then subsequently also transferred from OLED tile assembly  100   d  to OLED tile assembly  100   a  via an electrical connection between power output connector  136  of OLED tile assembly  100   d  and power input connector  134  of OLED tile assembly  100   a . Likewise, a POWER INPUT signal  520   b  from the mains power supply (not shown) is supplied to OLED tile assembly  100   h  via an electrical connection to power input connector  134  of OLED tile assembly  100   h . AC power is then transferred from OLED tile assembly  100   h  to OLED tile assembly  100   e  via an electrical connection between power output connector  136  of OLED tile assembly  100   h  and power input connector  134  of OLED tile assembly  100   e . AC power is then transferred from OLED tile assembly  100   e  to OLED tile assembly  100   b  via an electrical connection between power output connector  136  of OLED tile assembly  100   e  and power input connector  134  of OLED tile assembly  100   b . Lastly, a POWER INPUT signal  520   c  from the mains power supply (not shown) is supplied to OLED tile assembly  100   j  via an electrical connection to power input connector  134  of OLED tile assembly  100   j . AC power is then transferred from OLED tile assembly  100   j  to OLED tile assembly  100   f  via an electrical connection between power output connector  136  of OLED tile assembly  100   j  and power input connector  134  of OLED tile assembly  100   f . AC power is then transferred from OLED tile assembly  100   f  to OLED tile assembly  100   c  via an electrical connection between power output connector  136  of OLED tile assembly  100   f  and power input connector  134  of OLED tile assembly  100   c . As mentioned previously, the AC input voltage from a power input connector  134  is simply bussed directly to power output connector  136 . Equally to the distribution of the DATA IN signal  505  over the OLED tile assemblies  100 , the power distribution may be performed either column-wise or row-wise.  
      An alternative distribution method for signal distribution is a star distribution (not represented in the drawings). The wording star distribution refers to the fact that the distribution of data signals or power occurs from the centre to the edge of the tiled OLED display  500  or vice versa. In this distribution method, the signals are transferred by a data reclocker  510  to several central OLED tile assemblies  100 , each of them further transferring the data signals to tiles at further distance of the centre or the edge respectively of the tiled OLED display  500 . In this way, distribution of serial video data and control data is obtained between the OLED tile assemblies from the centre assemblies  100  of the OLED tile display  500  to the edge assemblies  100  or vice versa, so that all OLED tile assemblies  100  obtain their part of the serial video data and control data. If preferred, it is also possible to obtain serial video data and control data transfer from edge assemblies to centre assemblies, i.e. starting at some of the edge assemblies and transferring to neighbouring assemblies ending in or around the centre of the display, so that all OLED tile assemblies  100  obtain their part of the serial video data and control data. In similar way, it is possible to obtain this method of distribution, i.e. star distribution, for the power distribution.  
      A third distribution method of both serial video and control data and power is illustrated in  FIG. 5B . It shows a daisy-chain method of distribution for a tiled OLED display  500 . The tiled OLED display  500  is representative of a k by l array of OLED tile assemblies  100 . In this example, a 3×3 array is pictured. More specifically,  FIG. 5B  illustrates that tiled OLED display  500  includes, for example, OLED tile assemblies  100   a ,  100   b ,  100   c ,  100   d ,  100   e ,  100   f ,  100   g ,  100   h , and  100   j . It is further illustrated that each OLED tile assembly  100  includes its associated data input connector  130 , data output connector  132 , power input connector  134 , and power output connector  136 .  
      The daisy-chain distribution method of signal distribution is described as follows. A DATA IN signal  505 , representative of serial video and control data, from a central processing unit (not shown) is supplied to an input of one OLED tile assembly  100 , i.e. in the example given to data input connector  130  of OLED tile assembly  100   g . Subsequently, the serial video and control data is transferred from one OLED tile assembly  100  to a next, neighbouring OLED tile assembly  100 . For example and with reference to  FIG. 5B , the serial video and control data is transferred from OLED tile assembly  100   g  to OLED tile assembly  100   d  via an electrical connection between data output connector  132  of OLED tile assembly  100   g  and data input connector  130  of OLED tile assembly  100   d , then from OLED tile assembly  100   d  to OLED tile assembly  100   a  via an electrical connection between data output connector  132  of OLED tile assembly  100   d  and data input connector  130  of OLED tile assembly  100   a . The serial video and control data is then further transferred from OLED tile assembly  100   a  to OLED tile assembly  100   b , via an electrical connection between data output connector  132  of OLED tile assembly  100   a  and data input connector  130  of OLED tile assembly  100   b . In similar way, the serial video data and control data are subsequently transferred from OLED tile assembly  100   b  to OLED tile assembly  100   e , from OLED tile assembly  100   e  to OLED tile assembly  100   h , from OLED tile assembly  100   h  to OLED tile assembly  100   j , from OLED tile assembly  100   j  to OLED tile assembly  100   f  and from OLED tile assembly  100   f  to OLED tile assembly  100   c . In similar way, the daisy-chain method of power distribution is accomplished by AC power connections from one OLED tile assembly  100  to the next OLED tile assembly  100 .  
      Although the latter method does not allow parallel distribution of the serial video and control data, i.e. distributing of serial video and control data occurs subsequently to a neighbouring tile, it can allow parallel, i.e. simultaneous, processing by the different OLED tile assemblies.  
      In  FIGS. 5A and 5B , the same distribution method is used to distribute the power and the data. There is however no need to use the same method for data and power distribution.  
      The central system controller is aware of the X and Y configuration of each OLED tile assembly  100 , i.e. its location in the array, in the tiled OLED display  500 . High-level software addresses each OLED tile assembly  100  uniquely. At set-up, each OLED tile assembly  100  is assigned a unique number in the chain and picture co-ordinates are assigned accordingly. Once the configuration of tiled OLED display  500  is established at set-up, each OLED tile assembly  100  stores its information locally and thus the configuration process need not be repeated with each cycle of power. Only when the user reconfigures tiled OLED display  500  is it necessary to reassign OLED tile assemblies  100  to re-establish the picture co-ordinates.  
       FIG. 6  illustrates a functional block diagram of an OLED tile control system  600  for use in an OLED tile assembly  100  in accordance with an embodiment of the present invention. OLED tile control system  600  performs the local processing and control functions needed to operate the n by m array of OLED module assemblies  138 .  FIG. 6  illustrates the physical distribution of the active functions across the combination of substrates  140 , OLED boards  142 , and control board  154 , along with their electrical interconnections. More specifically,  FIG. 6  illustrates that: a substrate  140   a  further includes an OLED array  612 ; an OLED board  142   a  further includes a plurality of bank switches  613 , a plurality of current sources  614 , an analog-to-digital (A/D) converter  622 , an EEPROM  624 , and a temperature sensor  628 ; and control board  154  further includes a tile processing unit  610 , a bank switch controller  616 , a constant current driver (CCD) controller  618 , a pre-processor  620 , and a module interface  626 . Substrate  140   a  and OLED board  142   a  shown in  FIG. 6  are representative of one of n by m substrates  140  and one of n by m OLED boards  142 , as shown in  FIG. 7 .  
      The physical implementation of the functional blocks of each OLED board  142  and control board  154  may be via a custom application-specific integrated circuit (ASIC) device or a field-programmable gate array (FPGA) device, as is well known.  
       FIG. 6  illustrates that tile processing unit  610  is fed by an incoming red, green, blue data signal RGB DATA IN that is a serial data signal containing the current video frame information to be displayed on OLED tile assembly  100 . Tile processing unit  610  subsequently buffers the incoming data signal RGB DATA IN and supplies an output data signal RGB DATA OUT of tile processing unit  610 . Additionally, control data CNTL DATA from a general processor (not shown), such as a personal computer (PC) for example, that functions as the system-level controller of the OLED tile assembly  100  is supplied to tile processing unit  610  via a CNTL DATA bus. The CNTL DATA bus is a serial data bus that provides control information to OLED tile assembly  100 , such as colour temperature, gamma, and imaging information. Tile processing unit  610  subsequently buffers the control data from the CNTL DATA bus for supplying an output control data signal to an outgoing CNTL DATA bus of tile processing unit  610 . Tile processing unit  610  re-transmits the data signal RGB DATA IN and the control data on the CNTL DATA bus to the next OLED tile assembly  100  of a tiled OLED display  500 , as shown in  FIG. 5A  and  FIG. 5B .  
      Using the imaging information from the control data signal on the CNTL DATA bus, tile processing unit  610  stores the serial data signal RGB DATA IN for that particular frame that corresponds to either OLED tile assembly  100  being used as an autonomous display or by the physical position of a given OLED tile assembly  100  being used within a larger tiled display, such a tiled OLED display  500  of  FIG. 5A  or  FIG. 5B .  
      In the case of tiled OLED display  500 , tile processing unit  610  of each OLED tile assembly  100  associated with an OLED array in a tiled display  500  receives the data signal RGB DATA IN and subsequently parses this information into specific packets associated with the location of a given OLED tile assembly  100  within tiled OLED display  500 . Algorithms running on tile processing unit  610  of each OLED tile assembly  100  facilitate the process of identifying the portion of the serial input data signal RGB DATA IN that belongs to its physical portion of tiled OLED display  500 . Subsequently, tile processing unit  610  distributes a serial RGB signal RGB (x)  to pre-processor  620 , which RGB signal RGB (x)  belongs to a physical portion of the tiled OLED display  500 .  
      Similarly, tile processing unit  610  receives the control data on the control data bus CNTL DATA and subsequently parses this information into specific control buses associated with the location of a given OLED tile assembly  100  within tiled OLED display  500 . Subsequently, tile processing unit  610  distributes a control signal CONTROL (X)  that provides control information, such as colour temperature, gamma, and imaging information, to OLED tile control system  600 .  
      The elements of OLED tile control system  600  are electrically connected as follows. The RGB signal RGB (X)  from tile processing unit  610  feeds pre-processor  620 ; a control bus output BANK CONTROL of pre-processor  620  feeds bank switch controller  616 ; a control bus output CCD CONTROL of pre-processor  620  feeds CCD controller  618 ; a control bus output V OLED  CONTROL of bank switch controller  616  feeds bank switches  613  that are connected to the row lines of OLED array  612 ; and a pulse width modulation control bus output PWM CONTROL of CCD controller  618  feeds current sources  614  that are connected to the column lines of OLED array  612  via conventional active switch devices, such as MOSFET switches or transistors. A bus output ANALOG VOLTAGE of OLED array  612  feeds A/D converter  622 ; a bus output DIGITAL VOLTAGE of A/D converter  622  feeds module interface  626 ; and a bus output TEMPERATURE DATA of temperature sensor  628  feeds module interface  626 . The control bus output CONTROL (X)  of tile processing unit  610  also feeds module interface  626 . Furthermore, an input/output bus EEPROM I/O exists between EEPROM  624  and module interface  626 ; an input/output bus DATA I/O exists between pre-processor  620  and module interface  626 ; and, lastly, module interface  626  drives a data bus MODULE DATA (X)  to tile processing unit  610 . Critical diagnostic information, such as temperature, ageing factors, and other colour correction data, is available to tile processing unit  610  via the data bus MODULE DATA (X) .  
      A summary of the elements in the OLED tile control system  600  and their functions is provided below:  
      OLED array  612  includes a plurality of addressable discrete OLED devices, i.e., pixels. Those skilled in the art will appreciate that the OLED devices for forming a graphics display are typically arranged logically in rows and columns, as explained above, to form an OLED array, as is well known. OLED array  612  may be configured as a common-anode, passive-matrix OLED array. Bank switches  613  may be conventional active switch devices, such as MOSFET switches or transistors. Bank switches  613  connecting positive voltage sources to the rows of OLED array  612  are controlled by the control bus V OLED  CONTROL of bank switch controller  616 . Current sources  614  may be conventional current sources capable of supplying a constant current, typically in the range of 5 to 50 mA. Examples of constant current devices include a Toshiba TB62705 (8-bit constant current LED driver with shift register and latch functions) and a Silicon Touch ST2226A (PWM-controlled constant current driver for LED displays). The active switches connecting current sources  614  to the columns of OLED array  612  are controlled by the control bus PWM CONTROL of CCD controller  618 . OLED array  612  also provides feedback of the cathode voltages via the ANALOG VOLTAGE bus. OLED array  612  also provides feedback of the voltage value across each current source  614  via the bus ANALOG VOLTAGE.  
      Bank switch controller  616  contains a series of latches that store the active state of each bank switch  613  for a given frame. In this manner, random line addressing is possible, as opposed to conventional line addressing, which is consecutive. Furthermore, pre-processor  620  may update the values stored within bank switch controller  616  more than once per frame in order to make real-time corrections to the positive voltage +V OLED  driving a line of OLED pixels based on temperature and voltage information received during the frame. For example, an increase in temperature during a frame output may trigger a voltage reading command where bank switch controller  616  enables the positive voltage +V OLED  to the requested OLED devices within OLED array  612 .  
      CCD controller  618  converts data from pre-processor  620  into PWM signals, i.e., the signals on the control bus PWM CONTROL, to drive current sources  614  that deliver varying amounts of current to the OLED devices or pixels within OLED array  612 . The width of each pulse within the control bus PWM CONTROL dictates the amount of time a current source  614  associated with a given OLED device will be activated and deliver current. Additionally, CCD controller  618  sends information to each current source  614  regarding the amount of current to drive, which is typically in the range of 5 to 50 mA. The amount of current is determined from the brightness value, Y, for a given OLED device, which brightness value is calculated in pre-processor  620 .  
      Pre-processor  620  develops local colour correction, ageing correction, black level, and gamma models (correction values may be stored in internal look-up tables (not shown) or in EEPROM  624 ) for the current video frame using information from module interface  626 . Pre-processor  620  combines the RGB data of the RGB signal RGB (X)  describing the current frame of video to display with the newly developed colour correction algorithms and produces digital control signals, i.e., the signals on the buses BANK CONTROL and CCD CONTROL, for bank switch controller  616  and CCD controller  618 , respectively. These signals dictate exactly which OLED devices within OLED array  612  to illuminate and at what intensity and colour temperature in order to produce the desired frame at the required resolution and colour-corrected levels. In general, the intensity, or greyscale value, is controlled by the amount of current used to drive an OLED device. Similarly, the colour temperature of the emitted light is controlled by the greyscale colour value and the relative proximity of each sub-pixel required to produce the desired colour. For example, a bright orange colour is produced by illuminating a green sub-pixel in close proximity to a brightly lit red sub-pixel. Therefore, it is important to have precise control over the brightness and the amount of time an OLED device is lit.  
      A/D converter  622  uses the analog voltage values, i.e., signals on the bus ANALOG VOLTAGE, from OLED array  612  to feed the voltage information back to module interface  626  via the bus DIGITAL VOLTAGE. The voltages across each OLED device within OLED array  612  (i.e., power supply voltage minus the cathode voltages) are monitored so that correct aging factors and light output values may be calculated in order to further produce the correct amounts of driving current through each OLED device within OLED array  612 . Pre-processor  620  compares a pre-stored threshold voltage level for each OLED device within OLED array  612  with the voltage value measured by A/D converter  622  to determine whether digital voltage correction is plausible. If the voltage across a specific OLED device is below a maximum threshold voltage, digital correction may be implemented through colour correction algorithms. However, if the voltage is greater than the maximum threshold voltage, an adjustment must be made to the overall supply voltage. Digital voltage correction is preferred to supply voltage correction because it allows finer light output control for specific OLED devices within OLED array  612 .  
      EEPROM  624  may be any type of electronically erasable storage medium for pervasively storing diagnostic and colour correction information. For example, EEPROM  624  may be a Xicor or Atmel model 24C16 or 24C164. EEPROM  624  holds the most recently calculated colour correction values used for a preceding video frame, specifically, gamma correction, ageing factor, colour co-ordinates, and temperature for each OLED module assembly  138 . All factory and calibration settings may be stored in EEPROM  624  as well.  
      The gamma curves (either full gamma curves or parameters that define the curves in order to conserve storage space) for both light and dark values are stored in EEPROM  624  at start-up from the system-level controller via the control bus CONTROL (X)  from tile processing unit  610 . Colour co-ordinates for each OLED device within OLED array  612  are also stored in EEPROM  624  in the form of (x,y,Y), where x and y are the co-ordinates of the primary emitters and Y is defined as the brightness.  
      The ageing factor of an OLED device is a value based on the total ON time, the temperature during that ON time, and total amount of current through each OLED device within OLED array  612 . Other information may be stored in EEPROM  624  at any time without deviating from the spirit and scope of the present invention. Communication to EEPROM  624  is accomplished via the input/output bus EEPROM I/O. An advantage to locally storing colour correction and additional information specific to an OLED module assembly  138  on EEPROM  624  is that when new OLED module assemblies  138  are added to OLED tile assembly  100 , or when OLED module assemblies  138  are rearranged within OLED tile assembly  100 , valuable colour correction, ageing factors, and other details regarding the operation of OLED module assemblies  138  are also transported. Therefore, the new tile processing unit  610  is able to read the existing colour correction information specific to that OLED module assembly  138  from its local EEPROM  624  at any time and is able to make adjustments to the overall control of OLED tile assembly  100 . This allows thus switching the OLED tiles without losing the necessary correction information.  
      Module interface  626  serves as an interface between tile processing unit  610  and all other elements within OLED boards  142 . Module interface  626  collects the current temperature data from temperature sensor  628  and the current colour co-ordinate information (tri-stimulus values in the form of x,y,Y), ageing measurements, and runtime values from EEPROM  624  for each OLED device within OLED array  612 . In addition, module interface  626  collects the digital voltage values during the ON time of each OLED device within OLED array  612  from A/D converter  622 . Module interface  626  also receives control data, i.e., the signal on the control bus CONTROL (X) , from tile processing unit  610 , which dictates to pre-processor  620  how to perform colour correction (from a tile-level point of view) for the current video frame.  
      Temperature sensor  628  may be a conventional sensing device that takes temperature readings within OLED module assembly  138  to determine the temperature of the OLED devices within OLED module assembly  138 . Accurate temperature readings are critical in order to correctly adjust for colour correction. Based on the temperature of each OLED device within OLED array  612 , the current may be adjusted to compensate for the variation in light output caused by temperature. Temperature information from temperature sensor  628  is sent to module interface  626  for processing via the data bus TEMPERATURE DATA. An example temperature sensor  628  is an Analog Devices AD7416 device.  
      Embedded in an OLED tile assembly  100 , the OLED tile control system  600 —as well as other parts in the OLED tile assembly  100 , e.g. the power supply of the OLED tile assembly  100  and additional cooling blocks provided as heat sinks e.g. at the back of the OLED array  612 —are cooled by a cooling fluid, e.g. by airflow, as a result of the action of one or more cooling fans. These cooling fans can be conventional DC fans capable of providing a volume rate of airflow of between 2 and 5 cubic feet per minute (cfm) in order to maintain an operating temperature within the OLED tile assembly of between 10 and 50° C. An example of a cooling fan that can be used is a Delta Electronics model BFB0505M. The power supply of the OLED tile assembly  100  provides DC power to the cooling fans.  
       FIG. 7  illustrates the overall architecture of OLED tile control system  600  in accordance with the invention.  FIG. 7  illustrates that a single control board  154  is designed to handle n by m OLED boards  142   a  to  142   n  and substrates  140   a  to  140   n . Control board  154  is therefore customised depending upon the specific n by m configuration of OLED module assemblies  138  within a given OLED tile assembly  100 . More specifically, a single control board  154  provides the signal fanout associated with the control bus V OLED  CONTROL, the control bus PWM CONTROL, the bus DIGITAL VOLTAGE, the data bus TEMPERATURE DATA, and the input/output bus EEPROM I/O to OLED boards  142   a  to  142   n  via connectors  152   a  to  152   n , respectively.  
      With reference to  FIGS. 1A through 7 , the features and operation of OLED tile assembly  100  are generally described as follows.  
      Firstly, functionality is built into OLED tile assembly  100  that allows it to operate autonomously as a single display unit or alternatively within a set of OLED tile assemblies  100  forming a larger tiled display, such as tiled OLED display  500 , all under the control of a central control system. To achieve this flexibility, each OLED tile assembly  100  includes, for example: 
          A digital video interface (i.e., tile processing unit  610 ) to handle all content (i.e., video) and communications information received. Content generation is e.g. via a DVI data stream of 24-bit RGB data (i.e., signal RGB DATA IN). Tile processing unit  610  handles the transfer of content data to each OLED module assembly  138 . The communication link between OLED tile assembly  100  and the central control system is provided via standard RS-485 protocol (i.e., CNTL DATA bus).     An automatic addressing system, which is software based. Each OLED tile assembly  100  receives the same content data stream, but due to the addressing scheme, each OLED tile assembly  100  decodes which portion of the data to use and displays only that portion thereof based upon a predetermined co-ordinate address that is stored locally via each EEPROM  624 .     A power supply (i.e., P/S  158 ) with a programmable regulated DC output.     A processor (i.e., tile processing unit  610 ) for performing real-time calculations for the various pixels, such as upscaling, downscaling, ON time calculations, light output calculation, lifetime correction, colour correction, pre-charge control, etc.; all to achieve a uniform image at the OLED module assembly  138  level.     A cooling system (i.e., see  FIG. 2 ). More specifically, each OLED tile assembly  100  includes a set of cooling fans  160  and cooling blocks  146 .     A diagnostic system, within which tile processing unit  610  handles the transfer of data to each OLED module assembly  138 . For example, A/D converter  622  is used to monitor voltage thresholds (i.e., power supply voltage minus the cathode voltages) across each OLED device within OLED array  612 , and temperature sensor  628  is used to measure the temperature within an OLED module assembly  138  or OLED tile assembly  100 .        

      A first key aspect of OLED tile assembly  100  for use autonomously or alternatively within a set of OLED tile assemblies  100  is that distributed processing performs image upscaling or downscaling as necessary at each OLED tile assembly  100 , rather than having a single central processor performing all of the scaling tasks. For example, instead of one central processor handling a 4K×4K resolution image and running all of the image scaling algorithms, each tile processing unit  610  (a simple video processor) of each OLED tile assembly  100  handles a small resolution image, such as 100×100 pixels. Furthermore, each tile processing unit  610  of each respective OLED tile assembly  100  is operating in parallel, thereby achieving very time-efficient processing. The parallel processing allows much more time for each OLED tile assembly  100  to calculate the image scaling, typically a 50 or 60 Hz timeframe. Thus, a very high-level scaling algorithm, e.g. bilinear or bicubic interpolation, is implemented very cost-effectively, which provides added value to the overall display system. Furthermore, instead of doing linear interpolation, this distributed processing technique allows the use of a slower 100% accurate scaling algorithm. An example calculation illustrating a comparison between non-distributed processing via a central processor and distributed processing via OLED tile assemblies  100  is as follows:  
      Real-time ON time calculation using non-distributed processing via a central processor 
          Supposing incoming active data: 1600×1200 pixels at 50 Hz.     PixelRate=50*1600*1200=96 MHz (minimum because of reduced blanking signal).     For real-time ON time calculations, a [3×3]×[3×1] matrix calculation for every pixel is performed. This [3×3]×[3×1] requires 3×3=9 multiplications and 3×3=9 additions, thus totalling 18 mathematical calculations.     Supposing every calculation requires one clock cycle, a calculation speed of 96 MHz×18=1.72 GHz is needed.        

      Real-time ON time calculation using distributed processing via OLED tile assemblies  100  
          Supposing each OLED module assembly  138  comprises 96×72 pixels.     A display of 1600×1200 pixels can be split into (1600/96)×(1200/72)=277 OLED tile assemblies  100 .     Each OLED tile assembly  100  has to process 96×72=6912 pixels in one frame of 50 Hz, resulting in a processing speed of 6912×50=345 kHz.     Taking into account the multiplication of the matrix, a calculation speed of 345 kHz×18=6.2 MHz is needed.        

      A second key aspect of OLED tile assembly  100  for use autonomously or alternatively within a set of OLED tile assemblies  100  is that, because video stream is known, once the image scaling has been calculated, the ON time for each OLED may be calculated for a given OLED module assembly  138 . This ON time is stored locally within EEPROM  624 . This ON time in combination with the temperature measurement of OLED module assembly  138  and the voltage measurement of the OLED itself may be used to derive the lifetime of each OLED within a given OLED module assembly  138 .  
      In summary, within OLED tile assembly  100 , the information to potentially provide a 100% lifetime guarantee for OLED tile assembly  100  is available locally. The physical hardware implementation of OLED tile assembly  100  and the architecture of tiled OLED display  500  formed by a k by l array of OLED tile assemblies  100  provides distributed processing that has the result of a less complex display hardware and software system, thereby avoiding the need for high-bandwidth calculations by a central processor.  
       FIG. 8  is a flow diagram of a method  800  of initial assembly, automatic configuration, and calibration of tiled OLED display  500  in accordance with an embodiment of the present invention.  FIGS. 1A through 7  are referenced throughout the steps of method  800 . Method  800  includes the following steps:  
      Step  810 : Assembling and Activating Tiled Display System  
      In this step, a plurality of OLED tile assemblies  100  are mechanically assembled in a k by l array, thereby forming a tiled OLED display such as tiled OLED display  500 . Examples of data signal and power distribution methods are shown in  FIG. 5A  and  FIG. 5B . Power is subsequently applied to each OLED tile assembly  100  of tiled OLED display  500 . Method  800  proceeds to step  812 .  
      Step  812 : Assigning Chain Address  
      In this step, a central processor detects the presence of OLED tile assemblies  100  by systematically opening and closing switches to detect the presence and location of each OLED tile assembly  100  within tiled OLED display  500 . The identification information of the OLED tile assembly  100  is read by an identification information determining means, such as e.g. an RS232 data interface. The switches used represent e.g. digital ‘AND’ functions. These are located in the data reclockers. The central processor subsequently assigns each OLED tile assembly  100  a unique address for use in steering content and communications data to each. Method  800  proceeds to step  814 .  
      Step  814 : Assigning Display Co-Ordinates  
      In this step, each OLED tile assembly  100  receives the display co-ordinates that designate what portion of the overall display it will show. Tile processing unit  610  of each OLED tile assembly  100  uses its display co-ordinates to automatically scale the incoming data to the resolution of OLED tile assembly  100 . Method  800  proceeds to step  816 .  
      Step  816 : Configuring Tiles  
      In this step, the configuration data contained in EEPROM  624  within each OLED module assembly  138  is read by its associated tile processing unit  610 . Each tile processing unit  610  uses this information to configure the resolution of its associated OLED tile assembly  100  according to the characteristics of its associated OLED module assemblies  138 . Method  800  proceeds to step  818 .  
      Step  818 : Calibrating OLED Modules  
      In this step, each OLED module assembly  138  within each OLED tile assembly  100  is calibrated by setting the brightness value Y of each sub-pixel to the appropriate value, i.e. the value that allows realising the desired colour temperature and brightness. Calibration factors are set within each OLED tile assembly  100  so that every pixel within each OLED tile assembly  100  matches the overall display brightness and is colour-compensated to correct individual pixel non-uniformity. Method  800  proceeds to step  820 .  
      Step  820 : Entering Operation Mode  
      In this step, each tile processing unit  610  of each OLED tile assembly  100  within tiled OLED display  500  now receives global display parameters for normal operation from the central processor, thereby entering operation mode. Method  800  ends.  
       FIG. 9  is a flow diagram of a method  900  of replacing, adding, or removing one or more OLED tile assemblies  100  in tiled OLED display  500 .  FIGS. 1A through 7  are referenced throughout the steps of method  900 . Method  900  includes the following steps:  
      Step  910 : Adding, Removing, or Replacing Tiles  
      In this step, one or more OLED tile assemblies  100  of an existing tiled OLED display  500  are mechanically replaced, added, or removed. Additionally, existing OLED tile assemblies  100  within an existing tiled OLED display  500  may be reconfigured to form a tiled OLED display  500  of different dimensions than the original. Method  900  proceeds to step  912 .  
      Step  912 : Detecting Display Tiles  
      In this step, a central processor detects the presence of OLED tile assemblies  100  by systematically opening and closing switches to detect the presence and location of each OLED tile assembly  100  with tiled OLED display  500 . Method  900  proceeds to step  914 .  
      Step  914 : Reconfigure Display? 
      In this decision step, using the information about OLED tile assemblies  100  detected in step  912 , the central processor determines whether the number and arrangement of tiles has been altered. If yes, method  900  ends and method  800  is performed; if no, tiles have only been replaced and method  900  proceeds to step  916 .  
      Step  916 : Assigning Chain Address  
      In this step, the central processor detects the presence and location of each replacement or repositioned OLED tile assembly  100  and assigns a unique chain address for use in steering content and communications data to each. Method  900  proceeds to step  918 .  
      Step  918 : Assigning Display Co-Ordinates  
      In this step, each replacement OLED tile assembly  100  receives the display co-ordinates that designate what portion of the overall display it will show. Tile processing unit  610  of each OLED tile assembly  100  uses its display co-ordinates to automatically scale the incoming data to the resolution of OLED tile assembly  100 . Method  900  proceeds to step  920 .  
      Step  920 : Configuring Replacement Tiles  
      In this step, the configuration data contained in EEPROM  624  in each tile processing unit  610  contained in each replacement OLED tile assembly  100  is read by tile processing unit  610 . Each tile processing unit  610  uses this information to configure the resolution of its associated OLED tile assembly  100  according to the characteristics of its associated OLED module assemblies  138 . Method  900  proceeds to step  922 .  
      Step  922 : Calibrating OLED Modules  
      In this step, each tile processing unit  610  within each replacement OLED tile assembly  100  is calibrated by setting the brightness value Y of each sub-pixel to the appropriate value, i.e. the value that allows realising the desired colour temperature, the desired brightness level and uniformity and the desired colour uniformity. Calibration factors are set within each OLED tile assembly  100  so that every pixel within each OLED tile assembly  100  matches the overall display brightness and is colour-compensated to correct individual pixel non-uniformity. Method  900  proceeds to step  924 .  
      Step  924 : Entering Operation Mode  
      In this step, each tile processing unit  610  of each OLED tile assembly  100  within tiled OLED display  500  now receives global display parameters for normal operation from the central processor, thereby entering operation mode. Method  900  ends.