Abstract:
The invention pertains to an improved LCOS microdevice that eliminates colored lights required generally in a prior art system. According to one aspect of the present invention, the LCOS structure uses color filters directly in the LCOS chip. Depending on the number of colors being used, the color filters are arranged repeatedly according to a predefined pattern across an entire LCOS chip to coincide with pixels in the microdevice. When a white light is focused onto the LCOS microdevice, it reflects a color image that is then magnified and projected onto a display screen.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to the area of display devices. More particularly, the present invention is related to Liquid Crystal on Silicon (LCOS) microdevice with color filters so that a corresponding reflective lighting optical system can be simplified. 
     2. Description of the Related Art 
     Instead of using liquid crystal between two polarized panels like an LCD (liquid crystal display), an LCOS (Liquid Crystal on Silicon) microdevice has a liquid crystal layer between one transparent thin-film transistor (TFT) and one silicon semiconductor. The semiconductor has a reflective and pixilated surface. The lamp shines light through a polarizing filter and onto the device, and the liquid crystals act like gates or valves, controlling the amount of light that reaches the reflective surface. The more voltage a particular pixel&#39;s crystal receives, the more light the crystal allows to pass. It takes several layers of different materials to do this. 
     In general, LCOS devices have only a very small gap between pixels. The pixel pitch—the horizontal distance between one pixel and the next pixel of the same color—is between 8 and 20 microns (10 −6 ). LCOS technology can produce much higher resolution images than liquid crystal display and plasma display technologies, which makes it less expensive to implement in such devices as televisions. 
     An LCOS microdevice has a liquid crystal layer between one transparent thin-film transistor (TFT) and one silicon semiconductor. The semiconductor has a reflective, pixilated surface. The lamp shines light through a polarizing filter and onto the device, and the liquid crystals act like gates or valves, controlling the amount of light that reaches the reflective surface. The more voltage the crystal of a particular pixel receives, the more light the crystal allows to pass. It takes several layers of different materials to do this. In general, there are a printed circuit board (PCB) carrying instructions and electricity from the television to the device, a silicon chip controlling the liquid crystal, generally with one transistor per pixel, using data from the television&#39;s pixel drivers, a reflective coating reflecting the light to create a picture, a liquid crystal layer controlling the amount of light that reaches and leaves the reflective coating, an alignment layer keeping the liquid crystals properly aligned so they can direct the light accurately, a transparent electrode completing the circuit with the silicon and the liquid crystal, and a glass cover protecting and sealing the entire microdevice. 
     There are in general two broad categories of LCOS displays: three-panel and single-panel. In three-panel designs, there is one display chip per color, and the images are combined optically. In single-panel designs, one display chip shows the red, green, and blue components in succession with the observer&#39;s eyes relied upon to combine the color stream. As each color is presented, a color wheel (or an RGB LED array) illuminates the display with only red, green or blue light. If the frequency of the color fields is lower than about 540 Hz, an effect called color breakup is seen, where false colors are briefly perceived when either the image or the observer&#39;s eye is in motion. While less expensive; single-panel projectors require higher-speed display elements to process all three colors during a single frame time, and the need to avoid color breakup makes further demands on the speed of the display technology. 
       FIG. 1  shows a prior art LCOS system  100  including three LCOS microdevices and an optical engine to form an image from the three LCOS microdevices. A lamp (not shown) produces a beam of white light that passes through a condenser lens. The light is focused and directed to pass through a filter  104  that only allows visible light to pass through, which helps protect the other components. The filtered white light passes through a series of dichroic mirrors  106  that reflect some wavelengths while allowing the rest of the light to pass through. For example, the dichroic mirror  106  can separate red light from the white light, leaving blue and green, and a second mirror can separate the green light, leaving only blue. The newly created beams of colored light simultaneously come into contact with one of three LCOS microdevices  108 ,  110  and  112 —one each for red, green and blue. The reflected lights from the respective microdevices  108 ,  110  and  102  pass through a prism  114  that combines the lights and creates a full-color image  114 . A projection lens  116  is provided and magnifies the image  114  and projects it on the screen  118 . 
     As shown in  FIG. 1 , the optical engine is mechanically complicated, requiring a lot of manual calibrations to ensure that three reflected images are precisely coincident. If one optical component is off some alignment, a distorted color could be perceived. 
     There is a need for LCOS microdevices that would require the optical engine less complicated. 
     SUMMARY OF THE INVENTION 
     This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract and the title may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
     The invention pertains to an improved LCOS microdevice that eliminates colored lights required generally in a prior art system. According to one aspect of the present invention, the LCOS structure uses color filers directly in the LCOS chip. Depending on the number of colors being used, the color filters are arranged repeatedly according to a predefined pattern across an entire LCOS chip in the microdevice. When a white light is focused onto the LCOS microdevice, it reflects a color image that is then magnified and projected onto a display screen. 
     According to another aspect of the present invention, a group pixel includes pixels covered by each set of the color filters. The sizes of the pixels (e.g., width and height) are limited by a predefined size of the group pixel. To compensate for the brightness of a display image due to the smaller pixels, a video or image controller is employed. The controller includes at least three buffers, each for driving one type of pixels. In one embodiment, a frame of video in three different colors is buffered respectively in three buffers that drive at the same time the LCOS chip more than once (e.g., twice or three times). As a result, the image being projected on the display screen is shown more than once, resulting in accumulatively brighter display perceived by human eyes. 
     The present invention may be implemented as a method, a system or part of a system. According to one embodiment, the present invention is an LCOS system comprising an LCOS microdevice including an array of group pixels, each of the group pixels including three pixels respectively covered by three types of color filters; and an optical engine receiving a white light and projecting the white light onto the LCOS microdevice that reflects a color image, the optical engine projecting the color image onto a display screen. 
     The foregoing and other objects, features and advantages of the invention will become more apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows a prior art LCOS system including three LCOS microdevices and an optical engine to form an image from the three LCOS microdevices; 
         FIG. 2A  shows an exemplary LCOS chip according to one embodiment of the present invention; 
         FIG. 2B  shows an exemplary structure of a pixel group that may be used in the chip of  FIG. 2A ; 
         FIG. 2C  shows an exemplary external layout of an LCOS microdevice according to one embodiment of the present invention, where an color image is directly produced via three types of color filters (e.g., red, green and blue); 
         FIG. 3  shows an exemplary LCOS system employing a single LCOS microdevice using the LCOS chip of  FIG. 2A  and an optical engine to form an image for projection onto a display screen; 
         FIG. 4  shows a controller including at least three buffers buffering data to drive the LCOS chip  200  of  FIG. 2A  more than once to increase brightness of perceived image projected on the display screen; 
         FIG. 5A  shows an exemplary layout of pixels according to another embodiment, wherein the rows of the pixels in each pixel group is shifted by a half of pixel size, compared to  FIG. 2A   
         FIG. 5B  shows an exemplary layout in consideration of increasing the display intensity without increasing the chip size or the size of individual pixels; and 
         FIG. 5C  shows a corresponding filter layer that is flexible enough to accommodate various sizes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description of the invention is presented largely in terms of procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
     Referring now to the drawings, in which like numerals refer to like parts throughout the several views.  FIG. 2A  shows an exemplary LCOS chip  200  according to one embodiment of the present invention. The chip  200  includes an array of group pixels, each of the group pixels includes three colored pixels referenced as R, G, and B. In other words, the pixels in a group pixel  202  are covered with corresponding color filters. In one embodiment, three primary colored filters Red (R), Green (G) and Blue (B) are used.  FIG. 2B  shows an exemplary structure  210  of a pixel group that may be used in the chip  200  of  FIG. 2A . Three pixels  214 ,  216  and  218  are layered on a substrate  212 , for example, formed through a CMOS process. On top of the three pixels  214 ,  216  and  218 , there are a filter layer  218 , a seal layer  220  and a liquid crystal layer  222 . The filter layer  218  includes three kinds of filters, red (R), green (G) and blue (B) filters respectively coincided with the three pixels  214 ,  216  and  218 , resulting in three pixels in a pixel group. 
     In one embodiment, the size of the pixels  214 ,  216  and  218  is made rectangular with width being one third of its height. As a result, three closely positioned pixels  214 ,  216  and  218  make a nearly squared group pixel. If it is for high-definition television (HDTV) with a resolution of 1920 by 1080, the LCOS chip in accordance with the present invention will have 1920×3 by 1080 pixels. By the LCOS chip, an optical engine designed therefor can be greatly simplified. Unlike the prior art system that would employ a complicated optical engine to produce three colored images for combination and projection, a television system employing the LCOS of the present invention needs an optical engine that requires no separated colored images for combination. 
       FIG. 2C  shows an exemplary external layout of an LCOS microdevice according to one embodiment of the present invention. With the on-chip colored filters (e.g., red, green and blue), a color image can be directly produced and projected onto a screen. 
       FIG. 3  shows an exemplary LCOS system employing a single LCOS microdevice using the LCOS chip of  FIG. 2A  and an optical engine to form an image for projection screen  318 . A lamp (not shown) produces a beam of white light that passes through a condenser lens. The light is focused and directed to pass through a filter  304  that only allows visible light to pass through. The filtered light is reflected by a reflector  306  onto an LCOS microdevice  310 . Because the LCOS microdevice  310  in accordance with the present invention reflects a full color image  314 , there would no need to split colored lights or combine colored images. A projection lens  316  is provided to magnify the image  314  and project it on the screen  318 . As a result, the light engine is greatly simplified. 
     Besides the overall cost of such a system is much lower than that of the corresponding one shown in  FIG. 1 , these is no required precise alignment of the optical components in such a system, the assembly of such a system is also simplified. 
     It is described above that the size of the individual pixels is somehow limited by the size of a group pixel. It is likely that the brightness of a projected image may not be as bright as that in the system of  FIG. 1 , if the same light source is used. To increase the brightness of the projected image, a controller designed to drive the LCOS chip  200  is shown in  FIG. 4  according to one embodiment of the present invention. The controller  400  includes three image buffers, one for one type of pixels in the LCOS chip. Thus there are three types of pixels in the exemplary LCOS chip  200  of  FIG. 2A . In operation, when video signals are processed and received in the controller  400 , the video signals are separated into three colored video signals (e.g., red, green and blue), if the video signals are not already separated. 
     As the LCOS chip  200  of  FIG. 2A  uses three types of color filters, there are three types of pixels. Although they are in general “red” pixels, “green” pixels, and “blue” pixels due to the corresponding color filters, other possible color filters may be used as well. To drive each type of pixels, the LCOS chip provides corresponding pins to receive proper signals. Collectively, the LCOS chip is assumed to have three types of pins, each designated to one type of signal (e.g., a signal to drive “red”, “green” or “blue” type of pixels). 
     For each frame, the corresponding image data is buffered in one of the image buffers for a predefined time. Unlike the prior art system in which an image buffer is used to buffer image data to drive a display device only once, the image buffer in the controller  400  is caused to drive the LCOS chip more than once. In other words, the same data is used more than once to drive the LCOS chip. The perceived result is an accumulatively brighter image as human eyes are accumulative in perception. In operation, three colored images are respectively stored in the three buffers in the controller  400 . These three buffers drive the LCOS chip at the same time more than once (e.g., twice or three times), essentially, the same signals are displayed more than once before flashed out by a next set of data or signal. 
       FIG. 5A  shows an exemplary layout  500  of the pixels according to another embodiment. Compared to  FIG. 2A , the rows of the pixels in each pixel group is shifted by a half of pixel size. As shown in  FIG. 5A , a group pixel is now made up with three pixels, one of which is being shared with an adjacent group pixel. For example, a group pixel  502  includes three pixels labeled respectively as R, G, and B, where the G pixel  504  is one of the three pixels in the group pixel  506 . Likewise, the G pixel in the group pixel  506  is one of the three pixels in the group pixel  508 . It can be appreciated that one of the advantages and benefits of the color filters as arranged in  FIG. 5A  is an increased spatial resolution an LCOS microdevice may offer. Given the same size of an LCOS microdevice, the spatial resolution is doubled. For example, an area of 4 by 4 group pixels of  FIG. 2A  may present 8 by 8 group pixels according to the filter arrangement in  FIG. 5A . In other words, an LCOS microdevice configured for a resolution of 640 by 360 or 1920 by 1080 may project a resolution of 1280 by 720 or 3840 by 2160 according to the filter arrangement in  FIG. 5A . 
     According to one embodiment, to maintain a resolution requirement but keep the same size of an LCOS chip, the size of the pixels may be enlarged by the filter arrangement in  FIG. 5A . As a result, the brightness of the resultant LCOS microdevice may be enhanced. 
     The layout  500  of  FIG. 5A  is disclosed in consideration of increasing display resolutions without increasing chip size.  FIG. 5B  shows an exemplary layout  520  in consideration of increasing the display intensity without increasing the chip size or the size of individual pixels. The filter pattern in the layout  520  is 50% green, 25% red and 25% blue, hence is also called RGBG or GRGB. In one embodiment, each of group pixels is formed by three of pixels in the layout  520 . For example, a first group pixel  522  is formed by three adjacent RGB pixels, a second group pixel  524  is formed by three adjacent RGB pixels, one of which is shared from the first group pixel  533 , and another one of which is share from a third group pixel  526  that is also formed by three adjacent RGB pixels. In a sense, a group pixel is enlarged three times by taking the advantages of two neighboring pixels. 
       FIG. 5C  shows an example of a filter layer  520  that may be cut to accommodate a specially required size. For example, the filter layer  520  is designed for a resolution of 1920 by 1080. The filter layer may be cut into 9 pieces of smaller filter layers, each for a resolution of 640 by 360. According to the filter arrangement of  FIG. 5A , the smaller filter layer can be used in a LCOS microdevice to provide a resolution of 1280 by 720. 
     The present invention has been described in sufficient detail with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. While the embodiments discussed herein may appear to include some limitations as to the presentation of the information units, in terms of the format and arrangement, the invention has applicability well beyond such embodiment, which can be appreciated by those skilled in the art. Accordingly, the scope of the present invention is defined by the appended claims rather than the forgoing description of embodiments.