Abstract:
In one embodiment, a liquid crystal display assembly comprises a liquid crystal module, a backlight assembly comprising an array of light emitting diodes, a detector to detect an optical output of at least one light emitting diode, and a controller coupled to the detector wherein the controller comprises logic to record in a memory location a first output value from the detector at a first point in time for a plurality of light emitting diodes in the array of light emitting diodes, measure a second output value from the detector at a second point in time for the plurality of light emitting diodes in the array of light emitting diodes, and adjust at least one input value to the plurality of light emitting diodes based on a relationship between the first output value and the second output value.

Description:
BACKGROUND 
     Many electronic devices include color liquid crystal displays (LCDs). Some LCDs utilize a white backlight, which is passed through at least one color filter to make different colors available to the LCD screen. In some devices, pixels on the LCD screen are assigned to groups of three, which include a red pixel, a green pixel, and a blue pixel. By managing the intensity of the red, green, and blue pixels, a range of colors are presented on the screen. 
     LCD displays may utilize arrays of light emitting diodes (LEDs) as an illumination source. The output of an LED may vary as a function of multiple factors including age of the LED and the operating temperature of the LED. Such variation can cause the output quality of a display to degrade over time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic, front view of a display assembly, according to an embodiment. 
         FIG. 1B  is an exploded, side view of a display assembly, according to an embodiment. 
         FIGS. 2A and 2B  are schematic illustrations of an illumination timing sequence, according to embodiments. 
         FIGS. 3 and 5  are flowcharts illustrating operations in embodiments of a method to operate a display. 
         FIG. 4  is a schematic illustration of a data table, according to embodiments. 
         FIG. 6  is a schematic illustration of a computing system, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a schematic, front view of a display assembly, according to an embodiment, and  FIG. 1B  is an exploded, side view of a liquid crystal display assembly, according to an embodiment. Referring to  FIG. 1A , a display assembly  100  comprises a base  110  and a monitor assembly  120  coupled to the base. Monitor assembly  120  comprises a housing  122 , which houses a LCD assembly  150 . 
     Referring to  FIG. 1B , liquid crystal display assembly  150  comprises a controller  152 , a memory module  154 , a backlight assembly  160 , a diffuser/polarizer  168 , a liquid crystal (LC) module  170 , and may include a light directing film  172 . Display assembly  100  may be embodied as any type of color graphics display. In one embodiment, LC module  170  may comprise a thin film transistor (TFT) assembly. In other embodiments, the LC module  170  may embodied as a different type of LC, e.g., a diode matrix or another capacitively driven LC, a digital mirror assembly, or the like. 
     Backlight assembly  160  comprises one or more arrays of light emitting diodes (LEDs). In some embodiments the one or more arrays of light emitting diodes may include, e.g., an array of red LEDs  162 , an array of green LEDs  164 , and an array of blue LEDs  166 . In some embodiments, backlight assembly  160  may include one or more reflecting cups  174  positioned adjacent a light emitting diode to reflect light from the diode toward a diffuser  168  positioned adjacent the backlight assembly  160 . In some embodiments, diffuser  168  may also act as a polarizer to polarize light emitted by the arrays of LEDs  162 ,  164 ,  166 . 
     In some embodiments the backlight assembly may implement alternate illumination techniques. For example, in some embodiments the backlight assembly  160  may include an array of white LEDs and one or more color filters to generate colors from the white light emitted by the LEDs. In alternate embodiments the backlight assembly  160  may include an array of blue LEDs accompanied by a diffusing layer and a photon conversion material to convert the blue light to shades of green and red. In still alternate embodiments the backlight assembly  160  may include LEDs that generate ultraviolet (UV) radiation and a filter assembly to shift the wavelength of the UV radiation to visible light of varying colors. 
     An LC module  170  is positioned adjacent diffuser  168 . In some embodiments, LC module may be a twisted nematic LC, an in-plane switching LC, or a vertical alignment (VA) LC. In some embodiments, a light directing film  172  may be positioned adjacent the LC to enhance the brightness of the display. 
     In some embodiments, a light director  158  is disposed adjacent backlight assembly  160  to direct light emitted by the LED arrays  162 ,  164 ,  166  onto a detector  156 . Like director  158  may be embodied as a focusing lens, a Fresnel lens, one or more mirrors, one or more light pipes, or a collector such as, for example, in integrating sphere. Detector  156  generates an electrical signal in response to a characteristic of the light incident upon the detector  156 . For example, some embodiments detector one or 56 may be embodied as a photodiode, a quadrant detector, or another suitable optical detector. 
     In some embodiments, the LED arrays  162 ,  164 ,  166  may be illuminated in sequence to create a color image on LCD assembly  150 .  FIGS. 2A and 2B  are schematic illustrations of an illumination timing sequence, according to embodiments. The timing sequence may be managed by the controller  152 . 
       FIG. 2A  illustrates a timing sequence for the presentation of a single color image on the LCD assembly  150 . In the embodiment depicted in  FIG. 2A , the timing controller implements a multi-step process to display a full-color image on the LCD assembly  150 . The multi-step process successively generates a single color component image of a full-color image, then illuminates the screen with the color component. This process is repeated with each color component of a full-color image. When implemented at a sufficiently fast cycle rate, the successive single color component images appear as a full-color image. 
     Referring to  FIG. 2A , initially the LCD assembly is synchronized at time T 1 . A red component of a full-color image is generated on LCD assembly  150 , and then the array of red LEDs  162  is illuminated. A green component of a full-color image is generated on LCD assembly  150 , and then the array of green LEDs  164  is illuminated. Finally, a blue component of a full-color image is generated on LCD assembly  150 , and then the array of blue LEDs  166  is illuminated. The combination of the red, green, and blue images generate a full color image on display assembly  150 . 
     Many display assemblies operate using a 60 Hz image refresh rate. In some embodiments the controller  152  operates such that each refresh cycle is subdivided into (n+1) different cycles, where n corresponds to the number of component color images presented on the display assembly  150 . For example, in an embodiment which uses red, green, and blue LEDs, the 60 Hz refresh rate may be divided into four different cycles. In some embodiments a white illumination cycle may be added to the backlight assembly, (e.g., by the addition of a white LED array or by the contemporaneous illumination of the red, green, and blue LED arrays) to increase the luminance of the screen, such that each refresh cycle is subdivided into five different cycles. 
       FIG. 2B  illustrates a timing cycle of controller  152  in an embodiment that utilizes a three-cycle illumination scheme. Referring to  FIG. 2B , after the initial synchronization period, a voltage is applied to the array of red LEDs  162 , then the voltage is removed from array of red LEDs  162 . A delay is introduced before a voltage is applied to the array of green LEDs  164 . The voltage is maintained for a time period, then the voltage is removed from array of green LEDs  164 . Another delay is introduced before a voltage is applied to the array of blue LEDs  166 . The voltage is maintained for a time period, then the voltage is removed from array of blue LEDs  166 . Another delay second is introduced before a voltage is applied to the array of red LEDs  162 , and the cycle continues. Other embodiments of the display assembly may implement illumination timing sequences different from the sequences depicted in  FIGS. 2A and 2B . 
     In some embodiments, a liquid crystal display assembly may implement techniques to compensate for changes in the optical characteristics of the light emitting diodes used as an illumination source in the display. For example, in some embodiments the display assembly may establish a baseline measurement for one or more optical characteristics of the light emitting diodes when the display assembly is properly calibrated. The optical characteristic measurements may be stored in a memory modules such as, for example, the memory  154 . Subsequently, a recalibration routine may be implemented in which optical characteristic measurements are collected from the light emitting diodes and one or more operating parameters of the light emitting diodes may be adjusted based upon relationship between the optical characteristics collected during the initial baseline measurement and the subsequent recalibration measurement. 
     One example of such a technique is described with reference to  FIGS. 3-5 .  FIGS. 3 and 5  are flowcharts illustrating operations in embodiments of a method to operate a display, and  FIG. 4  is a schematic illustration of a data table, according to embodiments. In some embodiments, the operations depicted in  FIGS. 3 and 5  may be implemented by the controller  152  and the data table depicted in  FIG. 4  may be stored in the memory module  154 . 
     Referring to  FIG. 3 , at operation  310  one or more initial operating conditions are established for the display assembly. For example, in some embodiments the display assembly may be calibrated by using a camera or charge coupled device (CCD) coupled to a computing device to view the display. One or more operating parameters associated with the light emitting diodes may be adjusted until the display assembly exhibits a desired color temperature (e.g., 6500K). 
     At operation  315 , one or more of the operating parameters associated with the light emitting diodes are recorded. For example, in one embodiment the controller maintains a data table  400  ( FIG. 4 ) in memory module  154 . Referring to  FIG. 4 , the data table  400  may be organized as a series of columns and rows. The table  400  may include a row for each light emitting diode. In the embodiment depicted in  FIG. 4 , each light emitting diode may be uniquely identified by its Cartesian coordinate position (x,y) in the array of light emitting diodes. 
     In the embodiment depicted in  FIG. 4  data table  400  includes an entry for the operating voltage of each light emitting diode. At operation  315  the operating voltage for a plurality of light emitting diodes, and in some embodiments for each light emitting diode, in the display is recorded in the data table  400 . 
     At operation  320  an output parameter of one or more light emitting diodes is measured using an integrated detector, such as the detector  156 . For example, in some embodiments each light emitting diode in the LCD assembly  150  is a separately addressable by the controller  152 . During the initial calibration process depicted in  FIG. 3 , the controller may activate individual light emitting diodes, applying the voltage V(T 0 ) depicted in  FIG. 4  to the diode. At operation  325  an output parameter from the light emitting diode is recorded in the data table  400 . For example, in some embodiments the detector  156  produces an output signal, such as an output voltage VD(T 0 ) in response to an optical input from the light emitting diode. The output voltage associated with each light emitting diode when operated at the initial calibration voltage is recorded in the data table  400 . Thus, the data table  400  provides a correlation between the driving voltage of each light emitting diode and an output signal generated by the detector  156  in response to the driving voltage. 
       FIG. 5  depicts operations in a process that may be used to recalibrate the liquid crystal display. At operation  510  the recalibration process is initiated. In some embodiments, the recalibration process may be initiated by a user through a user interface, such as, for example to a software interface or a hardware interface coupled to the liquid crystal display assembly  150 . In other embodiments the recalibration process may be implemented periodically through time. In still other embodiments, the recalibration process may be implemented based on temperature variation in the region proximate the liquid crystal display assembly  150 . For example, a thermocouple or other thermoelectric detection device may detect when a change in temperature in the liquid crystal device assembly exceeds a threshold and may trigger a recalibration process in response to the temperature change. 
     At operation  515  one or more output parameters associated with the light emitting diodes are measured using the integrated detector  156 . As described above, in some embodiments each light emitting diode in the LCD assembly  150  is a separately addressable by the controller  152 . During recalibration process depicted in  FIG. 5 , the controller may activate individual light emitting diodes, again applying the voltage V(T 0 ) depicted in  FIG. 4  to the diode. At operation  515  an output parameter from the light emitting diode is measured. For example, in some embodiments the detector  156  produces an output signal, such as an output voltage VD(T R ) in response to an optical input from the light emitting diode. The output voltage associated with each light emitting diode when operated at the initial calibration voltage may be recorded in the data table  400 . 
     If, at operation  520  the difference between the output parameter measured during the recalibration process and the output parameter measured during the initial calibration process exceeds a threshold and control passes to operation  525  and one or more operating parameters associated with the light emitting diode is adjusted. For example, using the embodiment depicted in  FIG. 4 , is the difference between the output detector voltage measured during the calibration process and the output detector voltage measured during the recalibration process exceeds a threshold than the operating voltage of the light emitting diode may be adjusted. 
     In some embodiments, the operating voltage may be adjusted as a function of a difference between the output voltage generated by the detector  156 . For example, the operating voltage of the light emitting diode may be adjusted as by a factor of the ratio of the voltages measured during the initial calibration process and the recalibration process, respectively. Thus, V new =V(T 0 )*(VD(T 0 )/VD(T R )). In alternate embodiments a quadratic approximation technique may be applied. 
     If, at operation  530 , they are more light emitting diodes to evaluate the control passes to operation  535  in the controller activates a next light emitting diode in the array. Control in passes back to operation  515  in the selected light emitting diode is evaluated. Thus, operations  515  through  535  may be repeated in a loop such that all light emitting diodes in the array, or a subset thereof, may be evaluated and if necessary adjusted during the recalibration process. 
     In some embodiments, a liquid crystal display assembly  150  may be distributed as a component of a computer system.  FIG. 6  is a schematic illustration of a computing system, according to an embodiment. The components shown in  FIG. 6  are only examples, and are not intended to suggest any limitation as to the scope of the functionality of the display assembly; the display assembly is not necessarily dependent on the features shown in  FIG. 6 . In the illustrated embodiment, computer system  600  may be embodied as a hand-held or stationary device for accessing the Internet, a desktop PCs, notebook computer, personal digital assistant, or any other processing devices that have a basic input/output system (BIOS) or equivalent. 
     The computing system  600  includes a computer  608  and one or more accompanying input/output devices  606  including a display  602  having a screen  604 , a keyboard  610 , other I/O device(s)  612 , and a mouse  614 . The other device(s)  612  may include, for example, a touch screen, a voice-activated input device, a track ball, and any other device that allows the system  600  to receive input from a developer and/or a user. 
     The computer  608  includes system hardware  620  commonly implemented on a motherboard and at least one auxiliary circuit boards. System hardware  620  including a processor  622  and a basic input/output system (BIOS)  626 . BIOS  626  may be implemented in flash memory and may comprise logic operations to boot the computer device and a power-on self-test (POST) module for performing system initialization and tests. In operation, when activation of computing system  600  begins processor  622  accesses BIOS  626  and shadows the instructions of BIOS  626 , such as power-on self-test module, into operating memory. Processor  622  then executes power-on self-test operations to implement POST processing. 
     Computer system  600  further includes a file store  680  communicatively connected to computer  608 . File store  680  may be internal such as, e.g., one or more hard drives, or external such as, e.g., one or more external hard drives, network attached storage, or a separate storage network. In some embodiments, the file store  680  may include one or more partitions  682 ,  684 ,  686 . 
     Memory  630  includes an operating system  640  for managing operations of computer  608 . In one embodiment, operating system  640  includes a hardware interface module  654  that provides an interface to system hardware  620 . In addition, operating system  640  includes a kernel  644 , one or more file systems  646  that manage files used in the operation of computer  608  and a process control subsystem  648  that manages processes executing on computer  608 . Operating system  640  further includes one or more device drivers  650  and a system call interface module  642  that provides an interface between the operating system  640  and one or more application modules  662  and/or libraries  664 . The various device drivers  650  interface with and generally control the hardware installed in the computing system  600 . 
     In operation, one or more application modules  662  and/or libraries  664  executing on computer  608  make calls to the system call interface module  642  to execute one or more commands on the computer&#39;s processor. The system call interface module  642  invokes the services of the file systems  646  to manage the files required by the command(s) and the process control subsystem  648  to manage the process required by the command(s). The file system(s)  646  and the process control subsystem  648 , in turn, invoke the services of the hardware interface module  654  to interface with the system hardware  620 . The operating system kernel  644  can be generally considered as one or more software modules that are responsible for performing many operating system functions. 
     The particular embodiment of operating system  640  is not critical to the subject matter described herein. Operating system  640  may be embodied as a UNIX operating system or any derivative thereof (e.g., Linux, Solaris, etc.) or as a Windows® brand operating system or another operating system. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an implementation. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     Thus, although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that claimed subject matter may not be limited to the specific features or acts described. Rather, the specific features and acts are disclosed as sample forms of implementing the claimed subject matter.