Abstract:
A system and method for compensating for non-uniform illumination from a light guide for a display in an electronics device is provided. The system comprises: a memory device storing a data representing a first compensation pattern for generation on the display to block light from a first portion of the light guide relative to light from a second portion of the light guide; a first module to incorporate the stored representation into an image to be displayed on the display; and a second module to generate the image with the stored representation for display on the display. In the system, when the first module generates the first compensation pattern on the display, the first compensation pattern aligns with the first and second portions to reduce an intensity of light from a light source passing through the first compensation pattern from the first portion relative to an intensity of light passing through the first compensation pattern from the second portion from the light source.

Description:
RELATED APPLICATIONS 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 12/168,093, filed on Jul. 4, 2008, which is a continuation of U.S. Pat. No. 7,415,176, issued on Aug. 19, 2008, which is a continuation application of U.S. Pat. No. 7,113,670, issued on Sep. 26, 2006. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to the field of liquid crystal displays and, particularly, to the field of backlighting for liquid crystal displays and/or keypads. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Liquid crystal displays are often illuminated by a backlight. When developing an LCD or keypad lighting system, many challenges are encountered that limit the ability to provide a uniformly lit light source to the display or keypad. For example, constraints on the x, y, and z size of the backlight system require tradeoffs or compromises in achieving proper and sufficient optical performance. Especially in those cases where there is little space in the x or y directions (the planar extensions of the light guide), the light guide providing light to the display from a light source (e.g., light emitting diodes—LEDs) or a light source directly illuminating a display may illuminate areas of the display (or keypad) more strongly than other areas. The more strongly lit areas are often referred to as “hot spots” or “bright spots.” Currently, the options to compensate for hot spots in LED illuminated LCDs and keypads are 1) moving the LEDs farther away from the light guide; 2) increasing the number of LEDs; or 3) creating a complex and difficult to tool optical dispersion patterns on the light guide plastic surface. The current methods have shortcomings. If x, y space is critical, then option (1) is not possible. Option (2) may be cost prohibitive. Option (3) in which creating a complex pattern is formed on the light guide, using current techniques, may increase the price of the light guide, extend the development time, and require difficult and/or expensive tooling for manufacture. Thus, there is a need to provide an effective and cost effective method for eliminating hot spots from an illuminated light guide in a space constrained arrangement. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    This disclosure addresses the problem of making light to a keypad or display uniform in a space constrained device or system. In the present disclosure, a simple light guide and hot spot filter are presented. The hot spot filter may be a separate layer, a display device, or patterns simply applied through a mask to the light guide surface. In creating the hot spot filter, an image from the illuminated light guide is captured to show precisely how the uniformity varies in the x and y directions. Then, the measured data is used to create a mask that is applied above or directly to the surface of the side of the light guide facing the display or keypad. This may be accomplished by creating a film that locally filters the hot spot and non-uniform regions. For example, if there are two strongly lit areas at the top of a module, the mask may be a transparent piece of material with grey printing placed on the transparent piece to correspond to the hot spots of the light guide. The net effect would be a uniform light output from the top surface of the light guide module. Alternatively, the image content of the LCD may be dynamically changed to cover up or compensate for hot spots. That is, in the case where there are multiple hot spots, if a white screen were requested by applications software, a white screen with grey regions corresponding to the hot spots would be formed to reduce hot spot brightness and provide a uniform image. 
         [0005]    Other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the disclosure in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments as provided in the present disclosure will now be described by way of example with reference to attached figures, wherein: 
           [0007]      FIG. 1  is a block diagram that illustrates pertinent components of a wireless communications device that communicate within a wireless communication network according to the present disclosure; 
           [0008]      FIG. 2  is a more detailed diagram of a preferred wireless communications device of  FIG. 1  according to the present disclosure; 
           [0009]      FIG. 3  illustrates an embodiment of a backlit liquid crystal display of the present disclosure; 
           [0010]      FIG. 4  illustrates an embodiment of a transparent sheet with filters to correct for the hot spots of the light guide; 
           [0011]      FIG. 5  illustrates an embodiment of an image capture method for capturing an image from which a filter is formed; 
           [0012]      FIG. 6  illustrates an embodiment of a method for forming a hot spot filter; and 
           [0013]      FIG. 7  illustrates an embodiment of a method for forming a hot spot compensation map for light sources of different colours. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The present disclosure relates to a method and apparatus, especially a mobile station such as a handheld communications device, that eliminates bright spots (or hot spots) in the light output pattern from a light guide that illuminates a display. Preferably, the light guide is illuminated by a light source that includes one or more light emitting diodes (LEDs). The LEDs of the light source preferably will include red, green, and blue colours. Other colour schemes, such as cyan, magenta, and yellow, are contemplated by the present disclosure. Although the present disclosure is directed to a liquid crystal display per se, the preferred use of the LCD is in a mobile station, such as a wireless portable handheld communications device. Cell phones and pagers are amongst the many handheld devices contemplated by the present disclosure. Aside from illuminating a display, the method may be used to illuminate a keypad or keyboard, such as a keypad found on a mobile station, or other illuminable device or layer. 
         [0015]      FIG. 1  is a block diagram of a communication system  100  that includes a mobile station  102  that communicates through a wireless communication network. Mobile station  102  preferably includes a visual display  112 , a keyboard  114 , and perhaps one or more auxiliary user interfaces (UI)  116 , each of which is coupled to a controller  106 . Controller  106  is also coupled to radio frequency (RF) transceiver circuitry  108  and an antenna  110 . 
         [0016]    Typically, controller  106  is embodied as a central processing unit (CPU) which runs operating system software in a memory component (not shown). Controller  106  will normally control overall operation of mobile station  102 , whereas signal-processing operations associated with communication functions are typically performed in radio frequency (RF) transceiver circuitry  108 . Controller  106  interfaces with device display  112  to display received information, stored information, user inputs, and the like. Keyboard  114 , which may be a telephone type keypad or full alphanumeric keyboard, is normally provided for entering data for storage in mobile station  102 , information for transmission to network, a telephone number to place a telephone call, commands to be executed on mobile station  102 , and possibly other or different user inputs. 
         [0017]    Mobile station  102  sends communication signals to and receives communication signals from the wireless network over a wireless link via antenna  110 . RF transceiver circuitry  108  performs functions similar to those of a base station and a base station controller (BSC) (not shown), including for example modulation/demodulation and possibly encoding/decoding and encryption/decryption. It is also contemplated that RF transceiver circuitry  108  may perform certain functions in addition to those performed by a BSC. It will be apparent to those skilled in art that RF transceiver circuitry  108  will be adapted to particular wireless network or networks in which mobile station  102  is intended to operate. 
         [0018]    Mobile station  102  includes a battery interface (IF)  134  for receiving one or more rechargeable batteries  132 . Battery  132  provides electrical power to electrical circuitry in mobile station  102 , and battery IF  134  provides for a mechanical and electrical connection for battery  132 . Battery IF  134  is coupled to a regulator  136  which regulates power to the device. When mobile station  102  is fully operational, an RF transmitter of RF transceiver circuitry  108  is typically keyed or turned on only when it is sending to network, and is otherwise turned off to conserve resources. Similarly, an RF receiver of RF transceiver circuitry  108  is typically periodically turned off to conserve power until it is needed to receive signals or information (if at all) during designated time periods. 
         [0019]    Mobile station  102  operates using a Subscriber Identity Module (SIM)  140  which is connected to or inserted in mobile station  102  at a SIM interface (IF)  142 . SIM  140  is one type of a conventional “smart card” used to identify an end user (or subscriber) of mobile station  102  and to personalize the device, among other things. Without SIM  140 , the mobile station terminal is not fully operational for communication through the wireless network. By inserting SIM  140  into mobile station  102 , an end user can have access to any and all of his/her subscribed services. SIM  140  generally includes a processor and memory for storing information. Since SIM  140  is coupled to SIM IF  142 , it is coupled to controller  106  through communication lines  144 . In order to identify the subscriber, SIM  140  contains some user parameters such as an International Mobile Subscriber Identity (IMSI). An advantage of using SIM  140  is that end users are not necessarily bound by any single physical mobile station. SIM  140  may store additional user information for the mobile station as well, including datebook (or calendar) information and recent call information. 
         [0020]    Mobile station  102  may consist of a single unit, such as a data communication device, a multiple-function communication device with data and voice communication capabilities, a personal digital assistant (PDA) enabled for wireless communication, or a computer incorporating an internal modem. Alternatively, mobile station  102  may be a multiple-module unit comprising a plurality of separate components, including but in no way limited to a computer or other device connected to a wireless modem. In particular, for example, in the mobile station block diagram of  FIG. 1 , RF transceiver circuitry  108  and antenna  110  may be implemented as a radio modem unit that may be inserted into a port on a laptop computer. In this case, the laptop computer would include display  112 , keyboard  114 , one or more auxiliary UIs  116 , and controller  106  embodied as the computer&#39;s CPU. The display may be a liquid crystal display (LCD), such as an LCD with colour filters or a field sequential LCD. It is also contemplated that a computer or other equipment not normally capable of wireless communication may be adapted to connect to and effectively assume control of RF transceiver circuitry  108  and antenna  110  of a single-unit device such as one of those described above. Such a mobile station  102  may have a more particular implementation as described later in relation to mobile station  202  of  FIG. 2 . 
         [0021]      FIG. 2  is a detailed block diagram of a preferred mobile station  202 . Mobile station  202  is preferably a two-way communication device having at least voice and advanced data communication capabilities, including the capability to communicate with other computer systems. Depending on the functionality provided by mobile station  202 , it may be referred to as a data messaging device, a two-way pager, a cellular telephone with data messaging capabilities, a wireless Internet appliance, or a data communication device (with or without telephony capabilities). Mobile station  202  may communicate with any one of a plurality of fixed transceiver stations  200  within its geographic coverage area. 
         [0022]    Mobile station  202  will normally incorporate a communication subsystem  211 , which includes a receiver, a transmitter, and associated components, such as one or more (preferably embedded or internal) antenna elements and, local oscillators (LOs), and a processing module such as a digital signal processor (DSP) (all not shown). Communication subsystem  211  is analogous to RF transceiver circuitry  108  and antenna  110  shown in  FIG. 1 . As will be apparent to those skilled in field of communications, particular design of communication subsystem  211  depends on the communication network in which mobile station  202  is intended to operate. 
         [0023]    Network access is associated with a subscriber or user of mobile station  202  and therefore mobile station  202  requires a Subscriber Identity Module or “SIM” card  262  to be inserted in a SIM IF  264  in order to operate in the network. SIM  262  includes those features described in relation to  FIG. 1 . Mobile station  202  is a battery-powered device so it also includes a battery IF  254  for receiving one or more rechargeable batteries  256 . Such a battery  256  provides electrical power to most if not all electrical circuitry in mobile station  202 , and battery IF  254  provides for a mechanical and electrical connection for it. The battery IF  254  is coupled to a regulator (not shown) which provides power V+ to all of the circuitry. 
         [0024]    Mobile station  202  includes a processor  238  (which is one implementation of controller  106  of  FIG. 1 ) which controls overall operation of mobile station  202 . Communication functions, including at least data and voice communications, are performed through communication subsystem  211 . Processor  238  may be an integrated circuit such as a microprocessor, a processing core on an integrated circuit, a processor of a system on a chip, or the like. Processor  238  also interacts with additional device subsystems such as a display  222 , a flash memory  224 , a random access memory (RAM)  226 , auxiliary input/output (I/O) subsystems  228 , a serial port  230 , a keyboard  232 , a speaker  234 , a microphone  236 , a short-range communications subsystem  240 , and any other device subsystems generally designated at  242 . Some of the subsystems shown in  FIG. 2  perform communication-related functions, whereas other subsystems may provide “resident” or on-device functions. Notably, some subsystems, such as keyboard  232  and display  222 , for example, may be used for both communication-related functions, such as entering a text message for transmission over a communication network, and device-resident functions such as a calculator or task list. Operating system software used by processor  238  is preferably stored in a persistent store such as flash memory  224 , which may alternatively be a read-only memory (ROM) or similar storage element (not shown). Those skilled in the art will appreciate that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile store such as RAM  226 . 
         [0025]    Processor  238 , in addition to its operating system functions, preferably enables execution of software applications on mobile station  202 . A predetermined set of applications which control basic device operations, including at least data and voice communication applications, will normally be installed on mobile station  202  during its manufacture. A preferred application that may be loaded onto mobile station  202  may be a personal information manager (PIM) application having the ability to organize and manage data items relating to the user such as, but not limited to, instant messaging (IM), e-mail, calendar events, voice mails, appointments, and task items. Naturally, one or more memory stores are available on mobile station  202  and SIM  262  to facilitate storage of PIM data items and other information. 
         [0026]    The PIM application preferably has the ability to send and receive data items via the wireless network. In a preferred embodiment, PIM data items are seamlessly integrated, synchronized, and updated via the wireless network, with the mobile station user&#39;s corresponding data items stored and/or associated with a host computer system thereby creating a mirrored host computer on mobile station  202  with respect to such items. This is especially advantageous where the host computer system is the mobile station user&#39;s office computer system. Additional applications may also be loaded onto mobile station  202  through network  200 , an auxiliary I/O subsystem  228 , serial port  230 , short-range communications subsystem  240 , or any other suitable subsystem  242 , and installed by a user in RAM  226  or preferably a non-volatile store (not shown) for execution by processor  238 . Such flexibility in application installation increases the functionality of mobile station  202  and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using mobile station  202 . 
         [0027]    In a data communication mode, a received signal such as a text message, an e-mail message, or web page download will be processed by communication subsystem  211  and input to processor  238 . Processor  238  will preferably further process the signal for output to display  222 , to auxiliary I/O device  228  or both as described further herein below with reference to  FIGS. 3 and 4 . A user of mobile station  202  may also compose data items, such as e-mail messages, for example, using keyboard  232  in conjunction with display  222  and possibly auxiliary I/O device  228 . Keyboard  232  is preferably a complete alphanumeric keyboard or keypad and/or telephone-type keypad. These composed items may be transmitted over a communication network through communication subsystem  211 . 
         [0028]    For voice communications, the overall operation of mobile station  202  is substantially similar, except that the received signals would be output to speaker  234  and signals for transmission would be generated by microphone  236 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on mobile station  202 . Although voice or audio signal output is preferably accomplished primarily through speaker  234 , display  222  may also be used to provide an indication of the identity of a calling party, duration of a voice call, or other voice call related information, as some examples. 
         [0029]    Serial port  230  in  FIG. 2  is normally implemented in a personal digital assistant (PDA)-type communication device for which synchronization with a user&#39;s desktop computer is a desirable, albeit optional, component. Serial port  230  enables a user to set preferences through an external device or software application and extends the capabilities of mobile station  202  by providing for information or software downloads to mobile station  202  other than through a wireless communication network. The alternate download path may, for example, be used to load an encryption key onto mobile station  202  through a direct and thus reliable and trusted connection to thereby provide secure device communication. 
         [0030]    Short-range communications subsystem  240  of  FIG. 2  is an additional optional component which provides for communication between mobile station  202  and different systems or devices, which need not necessarily be similar devices. For example, subsystem  240  may include an infrared device and associated circuits and components, or a Bluetooth™ communication module to provide for communication with similarly-enabled systems and devices. Bluetooth™ is a registered trademark of Bluetooth SIG, Inc. 
         [0031]    In accordance with an embodiment of the disclosure, mobile station  202  is a multi-tasking handheld wireless communications device configured for sending and receiving data items and for making and receiving voice calls. To provide a user-friendly environment to control the operation of mobile station  202 , an operating system resident on station  202  (not shown) provides a graphical user interface (GUI) having a main screen and a plurality of sub-screens navigable from the main screen. 
         [0032]    A preferred embodiment of the liquid crystal display cell  222  is shown in greater detail in  FIG. 3  in which a light source formed from multiple LEDs  322 ,  324 ,  326  is used as a backlight. The LCD may be a passive matrix or active matrix device. Preferably, the LCD is a full colour device. More preferably, the LCD is a field sequential LCD (FS LCD)—an LCD that obviates a need for colour filters. Alternatively, the LCD may contain colour filters in which case a white light source may be used. LCD controller  316  provides a voltage to the common electrode(s)  308  and the active elements  310  of the active matrix. The active elements are preferably thin film transistors. The common electrode(s)  308  and active elements of the LCD are supported on substrates  306  and  312 , respectively. The LCD preferably contains a brightness enhancing film or layer  340  to optimize the distribution of light for a viewer. As the preferred liquid crystal material is super twisted nematic, polarizers  302  and  314  are used. The LCD controller  316  sets the pixel grey scale of the LCD. An optional processor  318  may coordinate synchronization of the LCD controller  316  with the light source controller  320 . Preferably, the LCD controller  316  and the processor  318  are integrated into a single device  317 , which may simply be referred to as an LCD controller that has the capability of controlling a light source controller  320 . The light source may be implemented by using red, green, and blue LEDs  322 ,  324 ,  326 . In a specific embodiment, four green, four red, and two blue LEDs are used to provide full colour and/or black and white display. Other combinations of LEDs are contemplated by the present disclosure. The LED controller  320  may sequence the three colours or may simultaneously energize LEDs of all the colours and terminate power to the LEDs simultaneously. The light guide  328  may have a tapered block construction and may have approximately a trapezoidal form to more evenly distribute the light into the LCD. The light guide may also have uneven areas  332  that scatter the light so as to avoid shadowing effects in the LCD image. Although uneven area  332  is shown to project inward to the surface of the light guide  328 , the uneven areas may be arranged differently so long as the arrangement effectively scatters the light from the LEDs  322 ,  324 ,  326 . The uneven areas may be abraded, molded, corrugated, chemically etched, or the like. Preferably, to maximize the utilization of light, the LEDs  322 ,  324 ,  326  and the light guide  328  are partially enclosed by a reflector such that the only opening is fully bounded by the light transmissive area of the LCD. 
         [0033]      FIG. 4  illustrates an exemplary embodiment of a light guide and a compensation sheet. The left image of  FIG. 4  shows hot spots as seen from the LCD side of the light guide. The hot spot image may be captured directly from the light guide when the light guide is illuminated from its light source or may be captured through a filter. A mask is formed from the captured image in a pattern that mirrors the pattern of light from an illuminated light guide. The mask, shown in the centre image of  FIG. 4 , may be a sheet or film with apertures. The hot spot filter may be a transparent sheeting with printing or coating in select areas corresponding to the hot spots. The printing or coating may be light absorptive or partially light reflective. Light absorbing pigments may offer lower cost in making. Partially light reflective (and partially light transmissive) coatings aid to recycle light and so reduce power consumption since less power needs to be expended for illumination. The degree of reflectivity/transmissivity of a hot spot compensating region on a hot spot filter may be adjusted according to the particular application. Alternative to a transparent sheet with printing or coating, a bitmap correction filter may be applied for a software solution to the LCD image such as when a shutter (e.g., another LCD) is used to establish lowered transmissivity regions over the hot spots. The end result of the hot spot compensation layer or shutter is a uniform planar light to the LCD. 
         [0034]      FIG. 5  illustrates an exemplary embodiment of an optical system that captures the light distribution from a light guide  506  when illuminated by a light source  508 . The light source may include one or more light emitting diodes. For a full colour liquid crystal display, an image may be captured for each colour of light. Capturing an image for each colour of light allows for a more accurate hot spot filtering pattern to account for physical offsets in location for the light emitting diodes of each colour. For example, because a red LED is not located where a green LED is, the light output pattern from a light guide illuminated by the red LED is not likely to be identical to the light output pattern from the light guide illuminated by the green LED. Furthermore, a light guide image may be obtained from each individual LED of the backlight. This is especially useful where more than one LED is used per colour. The light output pattern from the light guide  506  may be optically processed through an optical system  504  that transfers to appropriately scaled imaged to a receiving sensor array with a camera  502 . In an embodiment, the optical system  504  may include one or more lenses. The camera  502  may, for example, include a charge-coupled device (CCD). 
         [0035]      FIG. 6  illustrates an embodiment of a method for creating a hot spot filter for the light guide. The light guide is illuminated to provide a light output pattern by an individual LED (e.g., white, red, green, or blue) or a group of LEDs representing a colour in step  602 . The light output pattern may be optically processed. This light output pattern is captured as an image by a light-capturing device, such as a camera  604 . The captured image may be used to make a mask  606 . This mask, in turn, is used to form the hot spot filter  608 . For example, the mask may contain apertures shaped and sized to conform to the hot spots. The mask may be laid over or upon a substrate, such as a plastic or glass film, and a coating or printing process deposits reflective and/or absorptive material onto the substrate through these apertures. After further processing (e.g., heating, drying, ultraviolet or infrared curing), the substrate is ready for disposition over the light guide in the finished product. The image capturing process may be performed from an actual handheld wireless device that is opened to expose the light guide. In such case, the camera may be disposed at a distance corresponding to that of the LCD&#39;s location within the finished product. This image capturing process may be performed once per batch or at a designated sampling rate to account for component devices from batch to batch. 
         [0036]      FIG. 7  illustrates another method for creating a hot spot filter. In  FIG. 7 , a colour grey scale compensation map is created for each colour of light illuminating the LCD. First, one of the colours is selected  702  in which light of that colour illuminates the light guide  706 . The image from the light guide for that colour is captured  708 . The captured image is processed to form a compensation map  710  to eliminate hot spots through use of the hot spot filter. In this case, the hot spot filter may be a film or layer ( 350  of  FIG. 3 ) upon which printing or coating of the hot spot areas is performed, may be such printing or coating directly upon the light guide, may be another liquid crystal display that is able to alter the pixel by pixel grey scale to compensate for any hot spots, or may be the primary LCD (defined by substrates  312  and  306  in  FIG. 3 ) in which certain pixels are given an added darkened grey scale value for compensation. The grey scale compensation map for the colour is stored in a suitable memory (e.g., the flash memory). The method determines if another colour of LED is to be processed  714 ,  704 . In this way, distinct image patterns may be obtained for each colour of light generated by the light source. 
         [0037]    The above-described embodiments of the present application are intended to be examples only. Those of skill in the art may effect alterations, modifications and variations to the particular embodiments without departing from the scope of the application. Instead of a liquid crystal display, a keypad or keyboard may be illuminated using the disclosed techniques. The disclosure described herein in the recited claims intends to cover and embrace all suitable changes in technology.