Abstract:
A method of implementing global illumination in an organic light emitting diode (OLED) display device utilizing an external shutter to reduce visual artifacts and motion blurring. The display device has a screen for displaying image data and a plurality of pixels each including an organic light-emitting diode. The method includes controlling emission of light from each light emitting diode along a path from the pixel to the screen. The shutter is coupled to the display device and has an on-time state, permitting light to pass therethrough, and an off-time state, blocking light from passing therethrough. The method includes loading image data into the plurality of pixels in raster scan order while the shutter is in the off-time state. The shutter is then switched to the on-time state to simultaneously allow emission of light from each pixel to pass therethrough. During the brief on-time state, image data is simultaneously displayed on the screen for the plurality of pixels thereby displaying the full image all at once.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional patent application Ser. No. 62/138,679 filed in the United States Patent and Trademark Office on Mar. 26, 2015, the entire disclosure and drawings of which are incorporated in their entirety by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an electronic display device and operation method thereof, and more particularly, to a method for implementing global illumination with an organic light emitting diode (OLED) display or microdisplay utilizing an external shutter to reduce visual artifacts and motion blurring in high speed video applications and head-mounted cockpit displays. 
       BACKGROUND OF THE INVENTION 
       [0003]    In conventional displays, pixel data is scanned into the displays in a time sequential pattern because the video source transmits pixel data in a stream. It has been discovered for certain applications that it is unfavorable for these changes to be visible over time. Specifically, fast moving objects on an electronic display exhibit visual artifacts and motion blurring due to persistence of the image from the previous frame. This can occur within a scene or due to background change. Rolling shutter techniques have been used to partially compensate the effect when an object is moving at a high rate within a relatively fixed non-moving background. However, in situations where the background is also moving at a fast rate, for example, high speed video applications, video games, head-mounted cockpit displays, and the like, visual artifacts and motion blur are still perceived and distracting to the user. 
         [0004]    For such applications, it has been discovered that the best technique is to utilize global illumination (also known as low persistence, global shutter design, global shutter technique, or global display). In contrast to rolling shutter techniques, in a global shutter technique all pixels integrate light simultaneously. For high-speed video applications, a global shutter technique minimizes the motion distortion otherwise formed by rolling shutter techniques. In particular, the global shutter technique scans the full frame until all pixel data has been loaded, and then enable all pixels in the active array to illuminate simultaneously for a short fraction of the frame time. Thereby allowing the human eye response to relax in between frames, which provides the perception of a smooth continuous motion. 
         [0005]    However, because a display device implementing a global illumination technique will only turn on for a portion of the frame time, the brightness of the display device is affected. Adjustments are therefore required in order to maintain the same average brightness as a conventional raster-scanned display. It has been found that the brightness during the on-time must be inversely proportional to the ratio of on-time to frame time. However, this leads to significantly higher peak operating current, requiring not only adequate power routing in the display but also bias levels that allow this peak brightness to be reached. The power constraint leads to larger silicon die sizes, which not only drives the cost but also impacts the total system design. The bias level constraint leads to having to operate at a higher voltage bias, which may not be available at the technology node being considered for the design. In addition, limitations within the display technology including transparent electrode impedance and display array total capacitance, impact the effective and consistent control of the on-time parameter. 
         [0006]    The present invention aims at circumventing these constraints by providing a display device having an external shutter. According to various embodiments of the invention, organic light emitting diode (OLED) displays are one type of popular display device that may be so adapted. As used herein, “OLED” refers to the underlying screen of a display device, for example, active (or passive) matrix OLED. It should be understood, however, that various embodiments of the present disclosure may be implemented on other types of transmissive or emissive displays, including, but not limited to, Organic Light Emitting Diode (OLED), LCD, devices incorporating certain microelectromechanical systems (MEMS), plasma display panels (PDP), and the like. 
         [0007]    It is, therefore, a primary object of the present invention to provide a method for implementing global illumination with a display device utilizing an external shutter to reduce visual artifacts and motion blurring in high speed video applications and head-mounted cockpit displays. 
         [0008]    It is another object of the present invention to provide a display device having an external shutter used with a conventional raster-scanned display to provide the capability of global illumination. 
         [0009]    It is another object of the present invention to provide a method for implementing global illumination using a conventional raster-scanned display without placing power or bias constraints on the display device. 
         [0010]    It is another object of the present invention to provide a method for implementing global illumination with a conventional active or passive matrix OLED display device having an electro-mechanical light shutter. 
         [0011]    It is another object of the present invention to provide a method for implementing global illumination with a conventional active or passive matrix OLED display device having an electro-optical light shutter, which may include a liquid crystal light valve. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention cures some of the deficiencies in the prior art by providing a method for implementing global illumination with a display device utilizing an external shutter to reduce visual artifacts and motion blurring in high speed video applications and head-mounted cockpit displays. 
         [0013]    In an illustrative embodiment of the present invention, a method of controlling emission of light in a display device which receives image data from a video source is provided. The display device has a screen and comprises a plurality of pixels each including a light emitting element configured to emit light along a path from the pixel to the screen. The method steps include providing a shutter disposed on the display device and operated to block emission of light from all pixels during a first portion video frame. The steps then include loading image data into each one of the plurality of pixels and controlling the light emitting element of each pixel based on the image data received during the first portion video frame. Lastly, the steps include simultaneously enabling emission of light from each pixel through the shutter during a second portion video frame. The light-emitting element may comprise an organic light emitting diode. The shutter may be a mechanical light shutter or an electro-optical light shutter. The electro-optical light shutter may be a liquid crystal light valve, which may further include a ferroelectric liquid crystal light valve. The shutter includes an off-time state during the first portion video frame and an on-time state during the second portion video frame. The on-time state of the shutter is transparent or open, while the off-time state of the shutter is non-transparent or closed. The display may be a microdisplay. The display may be active matrix or passive matrix. The image data loaded into the pixels may be in raster scan order. The first and second portion video frames together comprise a frame. The frame may be 1/60 of a second. 
         [0014]    In an alternate embodiment of the present invention, a method of operating a display system in communication with a video source for receiving image data is provided. The method steps include providing a display device having a screen for displaying image data, the display device having a plurality of pixels each including a light-emitting diode. The method includes emitting light from each light emitting diode along a path from the pixel to the screen, and providing a shutter coupled to the display device having an on-time state and an off-time state, wherein the on-time state allows transmission of light to pass therethrough and the off-time state blocks transmission of light from passing therethrough. The method includes loading image data into the plurality of pixels in raster scan order until the image is loaded. Then, switching the shutter to simultaneously allow emission of light from each pixel to pass through the shutter. The full image is then displayed by simultaneously displaying image data for each of the plurality of pixels. The plurality of pixels may comprise active-matrix organic light-emitting diodes. The shutter may be a mechanical light shutter or an electro-optical light shutter. The electro-optical light shutter may be a liquid crystal light valve. The liquid crystal light valve may be a ferroelectric liquid crystal light valve. 
         [0015]    These advantages of the present invention will be apparent from the following disclosure and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic diagram of a display system in accordance with an illustrative embodiment of the present invention. 
           [0017]      FIG. 2A  is a side elevation view of a light emitting panel in a display device in accordance with an illustrative embodiment of the present invention. 
           [0018]      FIG. 2B  is a plan view of a base plate having a plurality of light emitting elements mounted thereon in accordance with an illustrative embodiment of the present invention. 
           [0019]      FIG. 3  is a portion of an idealized AMOLED microdisplay having an active matrix of OLED pixels generating light through an external shutter to a display screen in accordance with an alternate embodiment of the present invention. 
           [0020]      FIG. 4  is a cross-sectional view of a liquid crystal light valve of the display device in accordance with an alternate embodiment of the present invention. 
           [0021]      FIG. 5  is a timing diagram of the operation of the shutter in accordance with an illustrative embodiment of the present invention. 
           [0022]      FIG. 6  is a schematic diagram of the timing scheme of the display device in accordance with an illustrative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The present invention is method for implementing global illumination with a display device to reduce visual artifacts and motion blurring in high speed video applications and head-mounted cockpit displays. It should be noted that the display devices described in the various embodiments of the invention are for illustrative purposes and the present invention is not limited to the specific devices described herein. 
         [0024]      FIG. 1  illustrates a display system  100  according to an illustrative embodiment of the present invention, which includes a display device  102  in communication with a video source  104  for providing images to be displayed by the display device. The display device  102  is based on a conventional raster-scanned display. In its broadest context, the display device  102  includes a controller  106  coupled to a light source  110  for emanating light to a display screen  114 . The display screen  114  includes a plurality of picture elements (i.e. pixels) each adapted to display a portion of an image underlying the display screen  114 , such that the image is viewed by a user  116  on the display screen  114 . The light source  110  provides light through an external shutter  112  for controlling the passage of light to the display screen  114 . The controller  106  may control both the light source  110  and shutter  112 . A memory  108  may be in communication with the controller  106  for receiving and storing image data from the video source  104  and sending image data to the controller  106 . The controller  106  is adapted to control the rate at which data is accessed from the memory  108 , thus avoiding frame latency. 
         [0025]    According to an illustrative embodiment of the present, the controller  106  receives a signal from the video source  104 . The video signal may include 2D and/or 3D image or video data and frame synchronization information (i.e. frame data). The controller  106  uses the video signal to update each of the picture elements (i.e. pixels) of the display screen  114 . The controller  106  uses the synchronization information to synchronize the illumination provided by the light source  110  to provide an update scan of the display screen  114 , preferably by loading frame data using conventional line at a time techniques (i.e. raster scanning technology). The controller  106  uses the synchronization information to synchronize the operation of the shutter  112 , such that once the display screen  114  has been fully scanned, the shutter  112  is turned on for a predetermined amount of time, allowing the light of pixels to emanated therethrough and present the full field image on the display screen  114  at once rather than on a line at a time basis. 
         [0026]    The shutter  112  used herein is an external shutter, which can be an electro-optical light shutter or an electro-mechanical light shutter. The shutter  112  has a transparent or on-time state allowing light to pass therethrough, and a non-transparent or off-time state blocking passage of light therethrough. The electro-optical light shutter is configured as a liquid crystal light valve, a ferroelectric light valve, or other array controlled light valve that is broken into elements. The ferroelectric light valve is optically bonded to the display device in such a manner as to minimize coupling and resolution losses. It should be understood by those skilled in the art that several techniques can be used to achieve this, such as for example, replacing the top cover glass of the display device with the light valve or by using an intermediate fiberoptic faceplate as a coupling element. The electro-mechanical shutter  112   b  is equivalent to that of a high-speed camera shutter. It should be understood, however, that various embodiments of the present disclosure may be implemented with other types of shutters known to those skilled in the art. 
         [0027]      FIG. 2A  illustrates display device  102 A according to an illustrative embodiment of the present invention. The display device  102 A includes a transparent base panel  200  and an electro-optical shutter  210  disposed on the base panel  200 . The base panel  200  includes an outer surface  202  opposite an inner surface  204 . The base panel  200  includes a plurality of light emitting elements or pixels  206  which generate an image on the display screen. Preferably, the pixels include active-matrix organic light-emitting diodes. When the base panel  200  is shuttered or blocked by the electro-optical light shutter  210 , the image data being loaded into the pixels is obscured from view. 
         [0028]    According to an illustrative embodiment, the electro-optical light shutter  210  is a voltage controlled light valve  210 . The light valve  210  has an inner surface  212  opposite an outer surface  214 . In the exemplary embodiment, an adhesive layer  220  is disposed between the transparent base panel  200  and the light valve  210 , such that the inner surface  212  of the light valve  210  is adhered to the inner surface  204  of the base panel  200 . The adhesive layer  220  may be an intermediate fiber-optic faceplate. In other embodiments, the inner surface  212  of the light valve  210  may be disposed directly onto the inner surface  204  of the base panel  200 . 
         [0029]      FIG. 2B  illustrates a plan view of the base plate  200  according to an illustrative embodiment of the present invention. The light emitting elements  206  on the base plate  200  may include one or more light emitting diodes  230  (LEDs), such as organic LEDs (OLEDs), red-green-blue (RGB) LEDs, white phosphor based LEDs, or other electronic light sources. The LEDs  230  are mounted to the transparent base panel  200  and arranged in a plurality of columns  232  and rows  234 . It should be understood that alternative LED arrangements and patterns are possible. It should also be understood that the light source may be arranged in an indirect, edge-lit configuration, where the LEDs may be positioned above, below, to the side of, or behind the display screen  114  with respect to the viewer of the light emanating from system  100 , or that the light source may include a plurality of LEDs arranged in a direct back-lit configuration and configured to illuminate different portions of the display screen. 
         [0030]    According to the illustrative embodiment, a printed circuit board (not shown) is connected to the base panel  200  for enabling the wiring of the light emitting elements  206  to a power source. The light emitting elements  206  are electrically coupled to drive circuitry (not shown) which provides the necessary electric current to the light emitting elements  206 . It will be clear to those skilled in the art how to make and use the printed circuit board, it will also be clear to those skilled in the art that alternative power configurations are possible. 
         [0031]      FIG. 3  illustrates display device  102 B according to an alternate embodiment of the present invention. The device  102 B is an idealized structure of an active matrix organic light emitting diode (AMOLED) microdisplay fabricated onto circuitry that controls and processes the video signal from the video source  104 . The shutter  112 , preferably a liquid crystal light valve, is coupled to the AMOLED microdisplay  102 B. The device  102 B uses an organic compound to produce the light when power is applied, and because the OLEDs produce their own light, there is no need for additional back-lighting as with LCD systems. 
         [0032]    The device  102 B includes a single crystal silicon substrate layer with integrated active matrix drives  302 , a polarized insular layer with vias  304  above the substrate layer, and individual anode electrodes  306  for each color subpixel positioned above the insular layer  304 . A white light emitting OLED layer  308  is deposited onto the anode layer  306 , followed by a cathode layer  310  deposited on the OLED layer  308 . One or more transparent seal layers  312  cover the cathode layer  310 . The black matrix stripes  314 , and color filter strips  316  (red, green, blue), are deposited onto the seal layers  312  and covered by a transparent protective layer or antireflective layer  318 . The liquid crystal light valve  112  is coupled to the device  102 B either by replacing the transparent protective layer  318  or by using an intermediate fiberoptic faceplate (not shown) as a coupling element. 
         [0033]      FIG. 4  illustrates the liquid crystal light valve of the display device in accordance with various embodiment of the present invention. The liquid crystal light value  400  includes a first substrate layer  402 , a first conductive layer positioned on the first substrate layer  404 , a liquid crystal layer  406 , a second conductive layer  408 , and a second substrate  410  position on the second conductive layer  408 , between the second conductive layer  408  and the base panel. Specifically, the second substrate is positioned adjacent the inner surface  204  of base panel  200  in the illustrative embodiment (shown in  FIGS. 2A and 2B ) and adjacent the protective layer  318  in the alternate embodiment (shown in  FIG. 3 ). The first and second substrate layers  402  and  410  are transparent and may include, for example, material such as glass, plastic, quartz, or the like, which allows the liquid crystal light valve  400  to maintain a transparent state as desired. 
         [0034]    The liquid crystal layer  406  is disposed between the first and second conductive layers  404  and  408  and includes a plurality of liquid crystal molecules  412 . The liquid crystal light valve  400  is switched from the transparent to the non-transparent state by controlling the rotation of the liquid crystal molecules  412  within the liquid crystal layer  406 . In particular, the transparency of the liquid crystal light valve  400  is controlled by adjusting the voltage differential of the driving means (not shown) between the first and second conductive layers  404  and  408  sandwiching the liquid crystal layer  406 . 
         [0035]    The liquid crystal light valve  400  may also include first and second alignment films  414  and  416 , which provide alignment functionality to align the liquid crystal molecules  412  within the liquid crystal layer  406 . The liquid crystal light valve  400  may also include first and second polarization layers  418  and  420 . It should be clear to those skilled in the art that the alignment directions of the first and second alignment films  414  and  416  and the polarization directions of the first and second polarization layers  418  and  420  can be adjusted as required in order to allow the liquid crystal light valve  400  to be in the transparent state or non-transparent state according to the driving means. It should also be noted that the light valve described in the various embodiment of the invention is for illustrative purposes and the present invention is not limited to the specific light valve arrangement or configuration described herein. 
         [0036]      FIG. 5  illustrates a simplified timing diagram  500  of the exemplary operation of the display device implementing global illumination in accordance with the present invention. The shutter has an on-time state (transparent) and an off-time state (non-transparent), which is controlled and set by a synchronizing circuit that is programmed to turn on the shutter for a predetermined amount of time after the display has been fully scanned and loaded. As illustrated, the on-time period occurs after the image data has been loaded into the display using a conventional raster scanned technique, and prior to the start of the next frame. 
         [0037]    The timing diagram  500  illustrates the timing of a synchronous signal (Vsync), the timing of video data being loaded into the display device, and the timing of the shutter operation over a time interval  508  (e.g. frame, single frame period, frame time, or 1/60 of a second). Line  502  illustrates the synchronous signal (Vsync). Line  504  illustrates the timing of loading video or image data. Line  506  illustrates the on-time and off-time of the shutter. The time interval  508  is a frame, which includes a first portion video frame and a second portion video frame. The on-time of the shutter occurs during the second portion video frame. The off-time of the shutter occurs during the first portion video frame. In the exemplary implementation, the image data is received by the controller  106  and loaded to the array by a sequential addressing of individual rows, also referred to as scan lines, according to conventional raster-scanned techniques. Once all image data has been loaded for all rows in the array, the shutter is turned on for a pre-determined amount of time (e.g. a fraction of the frame time or fraction of 1/60 of a second). During the on-time state, the shutter is transparent allowing light to pass and image data is not loading. One the shutter is switched to the off-time state, light is no longer allowed to pass therethrough and the image data is loaded into the array in accordance with conventional techniques. 
         [0038]      FIG. 6  illustrates a schematic diagram of the timing scheme  600  of the display device implementing global illumination. The timing diagram  600  illustrates line  602  as the timing of a synchronous signal (Vsync), line  604  as video data signal, line  606  as the OLED emission under normal operation, and line  608  as the shutter operation. The image or frame data is loaded into the display in accordance with line  604 , while the shutter operation shown by line  608  is in the off-time. Once the frame data is completely loaded the shutter is switched to the on-time according to line  608 . During the on-time state of the shutter, the video data signal is blank (i.e. not updating) and light is permitted to pass through the shutter. Once the shutter is switched to the off-time state, light is no longer permitted to pass therethrough and the image data continues loading into the array in accordance with conventional techniques. 
         [0039]    It is to be understood that the disclosure describes a few embodiments and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.