Abstract:
The disclosed embodiments relate to a system and method for projecting video onto a screen. A video unit ( 10 ) may comprise a plurality of light emitting diodes ( 40   a,    40   b , and  40   c ) disposed in an annular formation ( 41 ) and configured to produce light ( 44 ), a reflector configured to reflect the produced light from at least one of the plurality of light emitting diodes ( 40   a,    40   b , and  40   c ), and a plurality of optical components disposed in an annular formation, wherein each of the optical components corresponds to one of the light emitting diodes ( 40   a,    40   b , and  40   c ), wherein each of the optical components is configured to focus the produced light at the reflector.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to projecting video images onto a screen. More specifically, the present invention relates to a system and method for projecting video images using multiple light emitting diodes. 
     BACKGROUND OF THE INVENTION 
     This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Projection televisions create video images by varying the color and shade of projected light. One example of a projection television system is a Digital Light Processing (“DLP”) system. DLP systems employ an optical semiconductor, known as a Digital Micromirror Device (“DMD”) to project video onto a screen. DMDs typically contain an array of at least one million or more microscopic mirrors mounted on microscopic hinges. Each of these mirrors is associated with a point on the screen, known as a pixel. By varying the amount of light that is reflected off each of these mirrors, it is possible to project video images onto the screen. 
     Specifically, by electrically actuating each of these hinge-mounted microscopic mirrors, it is possible to either illuminate a point on the screen (i.e., “turn on” a particular micromirror) or to leave that particular point dark by reflecting the light somewhere else besides the screen (i.e., “turn off” the micromirror). Further, by varying the amount of time a particular micromirror is turned on, it is possible to create a variety of gray shades. For example, if a micromirror is turned on for longer than it is turned off, the pixel that is associated with that particular micromirror, will have a light gray color; whereas if a particular micromirror is turned off more frequently than it is turned on, that particular pixel will have a darker gray color. In this manner, video can be created by turning each micromirror on or off several thousand times per second. Moreover, by shining colored light at the micromirrors instead of white light, it is possible to generate millions of shades or color instead of shades of gray. 
     Conventionally, there are two main techniques to produce the light used in a projection television or video projector. First, the light may be created by a conventional lamp, such as an incandescent lamp or a halogen lamp. Second, the light may be produced by one or more light emitting diodes (“LEDs”). There are many advantages to using LEDs instead of incandescent or halogen lamps. Specifically, LEDs are solid state components, and thus are typically more robust and more efficient than incandescent or halogen lamps, because they operate at lower temperatures. Moreover, because LEDs can generate specific colors of light, projection televisions employing LEDs do not use a color wheel. Unfortunately, a single LED cannot presently produce enough light to continuously project large video images, and conventional techniques for harnessing the light from multiple LEDs are extremely inefficient. An efficient method for harnessing light from multiple LEDs to project a video image is desirable. 
     SUMMARY OF THE INVENTION 
     The disclosed embodiments relate to a system and method for projecting video onto a screen. A video unit ( 10 ) may comprise a plurality of light emitting diodes ( 40   a ,  40   b , and  40   c ) disposed in an annular formation ( 41 ) and configured to produce light ( 44 ), a plurality of optical components disposed in an annular formation, wherein each of the optical components corresponds to one of the light emitting diodes ( 40   a ,  40   b , and  40   c ), and a reflector configured to reflect light from at least one of the plurality of light emitting diodes ( 48 ), wherein each of the optical components is configured to focus the produced light at the reflector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a block diagram of a video unit employing an LED light engine in accordance with embodiments of the present invention; 
         FIG. 2  is a diagram of one embodiment of the LED light engine comprising an LED ring and a static reflector in accordance with embodiments of the present invention; 
         FIG. 3  is a diagram of another embodiment of the LED light engine comprising an LED ring and a rotating reflector in accordance with embodiments of the present invention; and 
         FIG. 4  is a diagram of another embodiment of the LED light engine comprising an LED ring and an ellipsoidal reflector in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
       FIG. 1  is a block diagram of a video unit  10  employing a Light Emitting Diode (“LED”) light engine  12  in accordance with embodiments of the present invention. In one embodiment, the video unit  10  comprises a Digital Light Processing (“DLP”) projection television. In another embodiment, the video unit  10  may comprise a DLP-based video or movie projector. In still another embodiment, the video unit  10  may comprise another form of projection television. 
     The LED light engine  12  comprises multiple LEDs that are configured to project, shine, or focus colored light  14  at a digital micromirror device (“DMD”)  18 . In alternate embodiments, such as a black and white video system or a color wheel based system, the LED light engine  12  may be configured to produce a single color of light. As will be described in greater detail below in regard to  FIGS. 2 ,  3 , and  4 , embodiments of the present invention enable multiple LEDs within the LED light engine  12  to be efficiently employed in combination with each other to create light to project large video images. 
     As illustrated, the LED light engine  12  projects, shines, or focuses colored light  14  at the DMD  18 . The DMD  18  may be located on a digital light processing (“DLP”) circuit board  16  arrayed within an optical line of sight of the LED light engine  12 . The DLP circuit board  16  may comprise the DMD  18  and a processor  20 . As described above, the DMD  18  may comprise up to one million or more micromirrors mounted on microscopic, electrically-actuated hinges that enable the micromirrors to tilt between a turned on position and turned off position. In the illustrated embodiment, the DMD  18  is coupled to the processor  20 . In one embodiment, the processor  20  receives a video input and directs the micromirrors on the DMD  18  to turn on or off, as appropriate to create the video image. In alternate embodiments the processor  20  may be located elsewhere in the video unit  10 . 
     The colored light  14  that reflects off a turned on micromirror (identified by a reference numeral  24 ) is reflected to a projecting lens  26  and then projected on to a screen  28  for viewing. On the other hand, the colored light  14  that reflects off of a turned off micromirror (identified by a reference numeral  30 ) is directed somewhere else in the video unit  10  besides the screen  28 , such as a light absorber  22 . In this way, the pixel on the screen  28  that corresponds to a turned off micromirror does not receive the projected colored light  14  while the micromirror is turned off. 
     In one embodiment, the colored light  14  from the LED light engine  12  rapidly changes from red to green to blue and then back to red many times per second. When the DMD  18  receives this stream of rapidly changing colored light  14 , the micromirrors on the DMD  18  are directed rapidly turn on or off to create the video images. In one embodiment, this direction is provided by the processor  20 . This rapid turning on and off of the micromirrors is coordinated to match the sequence of colors in the colored light  14 . For example, when the colored light  14  is red, the micromirrors turn on or off as appropriate to generate the shades of red for a particular frame of video. Specifically, one micromirror may turn on for 25 microseconds to contribute one shade of red to its associated pixel while another one of the micromirrors may turn on for 30 microseconds to contribute another shade of red to a different pixel while still another micromirror may turn off completely for some period of time if no red light is to be projected to a particular one of the pixels during a particular frame. In a similar fashion, the micromirrors generate shades of green and blue, if needed, when the colored light  14  is green or blue, respectively. Those skilled in the art will appreciate that in alternate embodiments other colors of light may be employed besides or in addition to red, green, and blue. 
     Because these different colors of light are rapidly changing (e.g. 30 times per second), the viewer sees a cohesive image formed from the three colors of light on the screen  28 . For example, to create a particular shade for a particular pixel, the micromirror corresponding to that particular pixel may turn on for 20 microseconds of red light, 22 microseconds of green light, and 17 microseconds of blue light. Alternately, the micromirror may turn on for 20 microseconds of red light and 20 microseconds of blue light, but remain turned off for green light. Those skilled in the art will appreciate that millions of color combinations can be projected by varying the lengths of time that the micromirrors are turned on. 
     The video unit  10  may also comprise the projection lens  26  to project the light reflected from the DMD  18  onto the screen  28 . In one embodiment, the projecting lens  26  facilitates the projection of turned-on light  24  by expanding the turned-on light  24  to cover the relatively large area of the screen  28 . In an alternate embodiment, the screen  28  may not be a part of the video unit  10 . For example, the screen  28  may be mounted on a wall and the video unit  10  may comprise a projector configured to project video across a room to the screen  28 . 
       FIG. 2  is a diagram of one embodiment of the LED light engine  12  comprising an LED ring  41  and a static reflector  46  in accordance with embodiments of the present invention. As illustrated, the LED light engine  12  is comprised of a plurality of LEDs  40   a ,  40   b , and  40   c  oriented in an angular configuration to form the LED ring  41 . The embodiment illustrated in  FIG. 2  comprises  15  LEDs  40   a ,  40   b , and  40   c . While only three of the LEDs  40   a ,  40   b , and  40   c  are specifically labeled in  FIG. 2 , it will be appreciated that the discussion below may refer to all of the LEDs in the LED ring  41 . Alternate embodiments of the LED ring  41  may comprise either more LEDs  40   a ,  40   b , and  40   c  or less LEDs  40   a ,  40   b , and  40   c  depending on the design of the video unit  10 . Moreover, those skilled in the art will appreciate that the LED ring  41  is merely one exemplary configuration of LEDs in the LED light engine  12 . In alternate embodiments, other configurations besides the LED ring  41  may be employed with the LED light engine  12 . 
     Each of the LEDs  40   a ,  40   b , and  40   c  may comprise any one of a number of standard, projection quality LEDs, as known to those of ordinary skill in the art. In one embodiment, the LEDs  40   a ,  40   b , and  40   c  may comprise a variety of different colors of LED  40   a ,  40   b , and  40   c . For example, the embodiment illustrated in  FIG. 2  comprises five red LEDs  40   a , five green LEDs  40   b , and five blue LEDs  40   c . In alternate embodiments, different colored LEDs  40   a ,  40   b , and  40   c  may be used. 
     The LED light engine  12  may also comprise a static reflector  46 . In the embodiment illustrated in  FIG. 2 , the static reflector  46  is a conical prism. In alternate embodiments, different forms of reflectors, optics, or prisms may be employed to reflect light  44  from the LEDs  40   a ,  40   b , and  40   c  in the manner described below. 
     The LED light engine  12  may also comprise a plurality of lenses  42 . In the illustrated embodiment, the lenses  42  are arrayed in an annular configuration between each of the LEDs  40   a ,  40   b  and  40   c  in the LED ring  41  and the static reflector  46 . Each of the lenses  42  is configured to focus light from one of the LEDs  40   a ,  40   b , and  40   c  at the static reflector  46 . For example, each of the lenses  42  may be configured such that one of the LEDs  40   a ,  40   b , and  40   c  is at a focal point on one side of the lens  42  and the static reflector  46  is at the focal point on the other side of the lens  42 . Those of ordinary skill in the art will appreciate that the location and configuration of the plurality of lenses  42  and the static reflector  46  may be altered to accommodate design considerations of various systems, such as the locations of the LEDs  40   a ,  40   b , and  40   c.    
     The LED light engine  12  may also comprise an integrator  48 , which is also referred to as a light tunnel. The integrator  48  is configured to spread out, focus, or align the light generated by the LEDs  40   a ,  40   b , and  40   c  to evenly reflect off the DMD  18  ( FIG. 1 ). 
     In turning to operation of the LED light engine  12 , when the LEDs  40   a ,  40   b , and  40   c  emit the light  44 , the lenses  42  focus the light  44  at the static reflector  46 . Most of the light  44  is reflected off the static reflector  46  into the integrator  48 . The light  44  that enters the integrator  48  is spread out, focused or aligned, as appropriate, to create the colored light  14 . Those skilled in the art will appreciate that from the perspective of the integrator  48 , all of the light  44  that enters the integrator  48  appears to be being generated at a point directly below or behind the static reflector  46 . In other words, the static reflector  46  combines the light produced by the LEDs  40   a ,  40   b  and  40   c  (and focused by the lenses  42 ) into what appears from the integrator&#39;s  48  perspective to be a single light source that is produces as much a light as multiple LEDs  40   a ,  40   b , and  40   c  from the LED ring  41 . 
     Those skilled in the art will appreciate that different colors of the LED  40   a ,  40   b , and  40   c  may be used to produce the alternating red, green, and blue light that typically comprises the colored light  14 . As described above in the embodiment illustrated in  FIG. 2 , five of the fifteen LEDs  40   a ,  40   b  and  40   c  may be red LEDs  40   a , five of the fifteen LEDs  40   a ,  40   b , and  40   c  may be green LEDs  40   b , and five of the fifteen LEDs  40   a ,  40   b , and  40   c  may be blue LEDs  40   c . In this embodiment, to create the colored light  14  that alternates from red to green to blue, the red LEDs are turned on momentarily (flashed) then the green LEDs are flashed, then the blue LEDs are flashed, then the red LEDs are flashed, and so forth. In this embodiment, the LEDs  40   a ,  40   b , and  40   c  alternate in color red, green, and blue around the LED ring  41 . In alternate embodiments, the color distribution of the LEDs  40   a ,  40   b , and  40   c  may differ depending upon design considerations. For example, in one embodiment, there may be fewer green LEDs  40   b  in the LED ring  41  because green light has higher luminance than red light or blue light. 
     As described above, single conventional LEDs  40   a ,  40   b , and  40   c  cannot be used to project large video images because a single conventional LEDs  40   a ,  40   b , and  40   c  do not typically produce enough light to project a large, continual video image. One of ordinary skill in the art, however, will appreciate that the light output from one of the LEDs  40   a ,  40   b , and  40   c  is generally inversely proportional to the ratio of the time that the LED  40   a ,  40   b , and  40   c  is turned on versus the time that the LED  40   a ,  40   b , and  40   c  is turned off. This ratio is known as the duty cycle. For example, conventional LED-based projection systems comprise one red LED  40   a , one green LED  40   b , and one blue LED  40   c . To create a sequence of colored light each of these LEDs is turned on for one third of the time (i.e., the red LED flashes red, then the green LED flashes green, then the blue LED flashes blue, then the red LED flashes red again, and so on). For this reason, each of these LEDs is deemed to have a ⅓ duty cycle. Operating with a ⅓ duty cycle, single conventional LEDs simply do not typically produce enough light to project a large video image. 
     However, if the duty cycle of the LED is decreased (i.e., the LED has more time to “rest” between flashes), a single individual LED can produce enough light to project a large video image. In one embodiment, a duty cycle of less than ⅓ is employed. For example, with a duty cycle of 1/15 (i.e., turned on approximately 6.5% of the time), a single LED can project a large video image. Those skilled in the art, however, will appreciate that with a duty cycle of 1/15, it takes approximately 15 LEDs to produce a continuous video image. 
       FIG. 3  is a diagram of another embodiment of the LED light engine  12  comprising an LED ring  41  and a rotating reflector  50  in accordance with embodiments of the present invention. For simplicity, like reference numerals have been used to designate those features previously described in reference to  FIG. 2 . Similar to the embodiment of the LED light engine  12  illustrated in  FIG. 2 , the embodiment of the LED light engine  12  illustrated in  FIG. 3  comprises a plurality of LEDs  40   a ,  40   b , and  40   c  arranged in the LED ring  41  around a plurality of lenses  42 , also arranged in a ring in the illustrated embodiment. This embodiment of the LED light engine  12  also comprises the integrator  48 , as described above. 
     The embodiment illustrated in  FIG. 3  comprises a rotating reflector  50  that rotates in a clockwise direction  52 . In one embodiment, the rotating reflector  50  comprises a parabolic mirror. Whereas the static reflector  46  is placed at a location within the LED light engine  12  that is amenable to simultaneously reflecting light from all of the LEDs  40   a ,  40   b , and  40   c , the rotating reflector  50  is configured to sequentially focus the light from each particular one of the LEDs  40   a ,  40   b , and  40   c  in the LED ring  41  as the rotating reflector  50  rotates in the counter clockwise direction  52 . 
     By synchronizing the rotation of the rotating reflector  50  with the highly bright (low duty cycle) flashes of the LEDs  40   a ,  40   b , and  40   c , sufficient light is reflected from the LEDs  40   a ,  40   b , and  40   c  to project a large continuous video image. For example, the rotating reflector  50  may begin facing a first red LED  40   a . While the rotating reflector  50  is pointed at the first red LED  40   a , the first red LED  40   a  will produce a flash of red light bright enough to project the video image. Most of this red light will reflect off the rotating reflector  50  and into the integrator  48 . The rotating reflector  50  will then rotate to face the first green LED  40   b  and reflect the green light produced by the first green LED  40   b . Next, the rotating reflecting will rotate to face the first blue LED  40   c  and so forth around the LED ring  41 . Those skilled in the art will appreciate that from the perspective of the integrator  48 , there will appear to be a single light source producing a sequence of red, green, and blue light with sufficient brightness to project a large video image. 
       FIG. 4  is a diagram of another embodiment of the LED light engine  12  comprising an LED ring and an ellipsoidal reflector  52  in accordance with embodiments of the present invention. For simplicity, like reference numerals have been used to designate those features previously described in reference to  FIGS. 2 and 3 . The embodiment of the LED light engine  12  illustrated in  FIG. 4  comprises the LEDs  40   a ,  40   b , and  40   c  disposed in the LED ring  41 , a plurality of ellipsoidal reflectors  52 , a reflector  54 , and the integrator  48 . 
     Each of the LEDs  40   a ,  40   b , and  40   c  is configured to produce the light  44  which reflects off the ellipsoidal reflectors  52  towards the reflector  54 . Those skilled in the art will appreciate that the ellipsoidal reflectors  52  have two focal points. In one embodiment, as illustrated, the LEDs  40   a ,  40   b , and  40   c  will be placed at one of the focal points and the reflector  54  will be placed at the other focal point. The ellipsoidal reflectors  52  may achieve a result similar to the lenses  42  that were described above. In one embodiment, the ellipsoidal reflectors  52  are comprised of a plastic shell with a reflective paint or coating. In alternate embodiments, the ellipsoidal reflectors  52  may be constructed from any other suitable materials, as known to those of ordinary skill in the art. 
     The embodiment of the LED light engine  12  depicted in  FIG. 4  may function similarly to either the embodiment depicted in  FIG. 2  or the embodiment depicted in  FIG. 3 . Specifically, in one embodiment, the reflector  54  comprises a stationary reflector and the LEDs  40   a ,  40   b , and  40   c  are configured to operate in combination to produce enough light to project a large video image, as described in relation to  FIG. 2 . In another embodiment, however, the reflector  54  comprises a rotating reflector and the LEDs  40   a ,  40   b , and  40   c  are configured to operate with a lower duty cycle (e.g., 1/15). In this embodiment, each individual LED  40   a ,  40   b , and  40   c  is configured to produce enough light to project a large video image, as outline above in regard to  FIG. 3 . 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.