Abstract:
A light emitting flat-panel display includes a plurality of light emitting diodes; a sensor for sensing the light output of at least one of the light emitting diodes to produce a light output signal; and a display controller responsive to the light output signal for producing a signal representing the remaining useful life of the display.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to light emitting flat-panel displays, and more particularly to means for signaling the remaining useful life of such displays.  
         BACKGROUND OF THE INVENTION  
         [0002]    Emissive flat-panel display devices are widely used in conjunction with computing devices and in particular with portable devices. Over time, the efficiency and effectiveness of the displays change and the quality of the displays, particularly for sensitive applications such as imaging, declines. This decrease in quality can be due to changes in the materials comprising the display, degradation in electronic components, and the like.  
           [0003]    In particular, organic light emitting diode (OLED) display devices suffer from changes in the organic light emitting materials within the display. The changes affect the efficiency and brightness of the display. These changes may also be color dependent, that is, the changes affect the different colors in the display device in different ways so that over time not only does the power efficiency of the display device decrease but the color balance changes. These changes result in an inferior display with poor image and color rendition.  
           [0004]    Some imaging applications are critical, that is, they cannot be allowed to fail. For example, some applications within the military and medical fields fall into this critical category. Moreover, within large systems, regular maintenance is often used to replace components, such as display devices, at fixed intervals whether or not the device is about to fail. Unnecessary replacement wastes resources. To address these concerns, some imaging systems, such as white-light projectors, utilizing radiation sources measure the time that the radiation source is turned on. Comparing this measurement to known life times allows a system to recommend maintenance or replacement. However, this approach is not useful for displays with light emitting elements and variable display content since the degradation of the light emitting elements is dependent on the exercise of each element.  
           [0005]    There is a need therefore for an improved emissive flat-panel display system that improves the maintainability and reduces the operational costs of the display system.  
         SUMMARY OF THE INVENTION  
         [0006]    The need is met according to the present invention by providing a light emitting flat-panel display that includes a plurality of light emitting diodes; a sensor for sensing the light output of at least one of the light emitting diodes to produce a light output signal; and a display controller responsive to the light output signal for producing a signal representing the remaining useful life of the display. In a preferred embodiment, the display is an organic light emitting diode display.  
         ADVANTAGES  
         [0007]    The present invention has the advantage that it reduces the life-cycle costs and improves the reliability of an emissive flat-panel display device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic block diagram of a light emitting display according to the present invention;  
         [0009]    [0009]FIG. 2 is a flow chart showing the operation of the display shown in FIG. 1;  
         [0010]    [0010]FIG. 3 is a schematic block diagram of a light emitting display according to a further embodiment of the present invention where the controller is integrated on the same substrate as the display; and  
         [0011]    [0011]FIG. 4 is a graph useful in describing the calculation of remaining useful life of the display.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Flat-panel display devices degrade over time as they are used. In particular, the light emitting or controlling materials become less effective and accurate, resulting in a loss of brightness and accuracy in color rendition. For those flat-panel display devices for which the brightness of each light emitting or controlling element can be detected and measured, the present invention provides a system wherein a detector supplies a light output signal to a controller. The controller processes the light output signal and calculates an estimated lifetime for the display device. This estimated lifetime may be made accessible to an external system or the controller may signal an external system when particular display device lifetime parameters are met.  
         [0013]    Referring to FIG. 1, a flat-panel display system  10  includes a flat-panel display  12  with light emitting diodes  14 , a display controller  18  includes a storage device  20 , a sensor  24  (such as a photo diode) to produce a light output signal, and produces a signal  28  representing the remaining useful life of the display. The controller  18  signals the light emitting diode  14  to produce a desired light output value. The sensor  24  detects the light emitted by the light emitting diode  14  in the display and provides this information to the controller  18 . The controller  18  then calculates an estimate of the lifetime of the display by comparing the light output value to the desired value originally sent to the display element by extrapolating the comparison according to known degradation rates. This estimate is stored in the storage device  20 . This storage device may be accessible from an external system using traditional read and write signals  22  applied to the storage device  20 . Alternatively, when a particular lifetime parameter is exceeded, the controller may signal an external system with the signal  28 .  
         [0014]    Referring to FIG. 2, the operation of the display device will be described. The controller first signals  40  a light emitting diode to produce a desired light output value. The light emitting diode emits  42  an amount of light in response to the signal. The sensor detects  44  the emitted light and provides  46  a light output signal to the controller. The controller compares  48  the light output signal to the desired light output value and calculates  50  an estimate of the remaining lifetime of the display. The estimate is stored  52  in the memory device and is available for access  54  by an external system (not shown). Alternatively, when the estimate of the remaining useful lifetime is zero  56 , the controller generates  58  a signal that is supplied to an external system (not shown).  
         [0015]    As shown in FIG. 3, the sensor  24  and controller  18  can be integrated on a common substrate or contained within a common package with the display  12 . Alternatively, the sensor and/or controller may be implemented externally to the display on a separate integrated circuit or printed circuit board as was shown in FIG. 1. By including the sensor  24  and controller  18  within a common package or upon a common substrate with the flat-panel display  12 , the number of electrical signal leads necessary for the flat-panel display can be minimized.  
         [0016]    In a preferred embodiment, the display device is an Organic Light Emitting Diode (OLED) display which is composed of small molecule polymeric OLEDs as disclosed in but not limited to U.S. Pat. No. 4,769,292, issued Sep. 6, 1988 to Tang et al., and U.S. Pat. No. 5,061,569, issued Oct. 29, 1991 to VanSlyke et al. Many combinations and variations of organic light emitting displays can be used to fabricate such a device.  
         [0017]    Referring to FIG. 4, a graph  60  of the efficiency of an OLED display vs. time used is shown. The graph can be generated empirically by measuring the decrease in efficiency of a number of diodes over time and averaging the results. The remaining useful life of an OLED display can be calculated, for example, by taking the ratio of the signal S from the sensor with an expected signal S N  that would be produced if the display was new to produce an efficiency value E. When the efficiency value E reaches a predetermined threshold  62  (e.g. 50%), the display is said to have reached the end of its useful life (EOL). The remaining useful life of the display is calculated using the efficiency function  60 . The remaining useful life δt is the difference between the measured efficiency  64  and the threshold efficiency  62 .  
         [0018]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0019]    [0019] 10  flat panel display system  
         [0020]    [0020] 12  flat-panel display  
         [0021]    [0021] 14  light emitting diodes  
         [0022]    [0022] 18  display controller  
         [0023]    [0023] 20  storage device  
         [0024]    [0024] 22  read and write signals  
         [0025]    [0025] 24  sensor  
         [0026]    [0026] 28  signal  
         [0027]    [0027] 40  signal step  
         [0028]    [0028] 42  emitting step  
         [0029]    [0029] 44  detecting step  
         [0030]    [0030] 46  providing step  
         [0031]    [0031] 48  comparing step  
         [0032]    [0032] 50  calculating step  
         [0033]    [0033] 52  storing step  
         [0034]    [0034] 54  access step  
         [0035]    [0035] 56  comparison step  
         [0036]    [0036] 58  generating step  
         [0037]    [0037] 60  graph of efficiency vs. time  
         [0038]    [0038] 62  efficiency at end of useful life of display  
         [0039]    [0039] 64  measured efficiency