Abstract:
An exemplary backlight module and a liquid crystal display device using the backlight module are provided. The backlight module includes a light beam generator and a reflector. The light beam generator includes a light source, a polygon mirror and an f-theta lens. The polygon mirror reflects light beams into a scanning light beam which can rotate at a certain speed. The scanning light beam transmits through the f-theta lens, and then it is transferred into parallel scanning beams. The parallel scanning beams reach the reflector. A light source device to produce a scanning light beam is also provided. The light source device can improve the uniformity of emission of the backlight module.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a backlight unit, and particularly a display system applied the backlight unit.  
         [0003]     2. General Background  
         [0004]     A liquid crystal display (LCD) is one kind of display system that cannot produce illumination for a displayed image by itself. Therefore in order to display images, a planar light source (e.g. a backlight unit) is usually provided with an LCD panel. The backlight unit is configured with the LCD panel so as to provide a bright and uniform planar light source. Two types of backlight unit (i.e. side edge type and direct type) are well-known in this field.  
         [0005]     Backlight unit of side edge type is illustrated below. The side edge type backlight is always in bright state and mounted aside to the light guide plate for the LCD module so as to transmit light beam to LCD panel. The LCD panel usually includes a so-called upper substrate and a lower substrate. The pixel electrode (at the lower substrate) and the common electrode (at the upper substrate) cooperatively constitute a capacitor. During display images, each scan signal coming from the corresponding gate electrode is proceeded a scan process upon each column of pixels sequentially. At the moment of changing different scanning columns, light beam cannot be exactly controlled due to the capacitor&#39;s effect according to the scanning signals applied to the corresponding pixels in a predetermined manner that the contrast of display images is decreased. Furthermore, due to mutually reinforcing of lower response time for liquid crystal molecules and the persistence of vision in human eyes, the blurred image of object movement of image display and the contrast in boundary shape of the displaying object became worse are occurred.  
         [0006]     In the other case, a typical direct type backlight unit is described as follows. Several cold cathode fluorescent lamps (CCFLs) are set under the light guide plate of the LCD module. In order to overcome the weakness of side edge type backlight, the timing signals from timing controller are used to turn on or turn off the foregoing CCFLs so as to control the light beams introduced to the LCD panel in accordance with the timing signals.  
         [0007]     Referring to  FIG. 6 , this is an exploded, side cross-sectional view of a conventional LCD device  1 . The LCD device mainly includes a backlight  10  and an LCD panel  17 . The backlight  10  generally includes a light guide plate (LGP)  11 , a plurality of CCFLs  12 , a reflector  13 , a light source cover  14 , a diffuser sheet  15  and a prism sheet  16 . The LGP  11  is a rectangle plate including a light entrance surface  111  and a light exit surface  112 . The CCFLs  12  are set uniformly under the light entrance surface  11  side of the LGP  11 . The light source cover  14  has an accommodating space which is to receive the CCFLs  12  and the reflector  13 . The reflector  13  is set between the light source cover  14  and the CCFLs  12 . The LGP  11  is set above the light source cover  14 . The diffuser sheet  15  and the prism sheet  16  are stacked on the light exit surface  112  side of the LGP  11 , in that order.  
         [0008]     The display process of the LCD device  1  is as follows. A timing signal is provided to control the turn on and turn off of the CCFLs  12 . The frequency of the timing signal synchronizes with the frequency of the gate scanning signal of the LCD panel  17 . The scan light beams are obtained from the scan process achieved by CCFLs  12 . The light beams transmit through the LGP  11 , the diffuser sheet  15  and the prism sheet  16  sequentially and eventually reach the LCD panel  17  so as to provide light for display.  
         [0009]     When the direct type of backlight is configured to introduce light for LCD panel  17  to display, the scan light beams vary with the scanning signal so as to increase the contrast of the LCD panel  17 . Therefore, some serious problems occurred in side edge type of backlight such as, the blurred image of object movement of image display and the contrast in boundary shape of the displaying object became worse can be reduced. However, each CCFLs  12  is corresponding many pixel regions that the dark state and bright state of the CCFLs  12  cannot match the status of pixel regions precisely. Therefore, this type of backlight still exhibits a contrast problem. Moreover, the brightness upon the area between each two CCFLs  12  is a little darker than other areas having CCFLs  12  below that the light uniformity of the LCD panel cannot be achieved.  
         [0010]     Furthermore, the starting voltage of the CCFL is higher than the normal work voltage thereof. Additionally, in order to meet the basic requirement of image display for the LCD device, the frequency of turning on and turning off of the CCFL might be higher than 25 times per second. This situation might reduce the life of the CCFLs.  
       SUMMARY  
       [0011]     An exemplary light beam generator is used in a backlight module for a display device. The light beam generator includes a light source, a multi-surface rotating mirror, a flattened lens (collimator lens), two optical detectors, a gray filter, and a lens array. The multi-surface rotating mirror (also known as a polygon mirror) is configured to provide a predetermined rotating frequency so as to reflect light beams from the light source. The flattened lens is adopted to transform the reflecting light beams to parallel light beams. In the exemplary embodiment, the two optical detector set on two end of the flattened lens, the optical detector is configured to detect light beams and generate feedback signals so as to control the rotating frequency of the multi-surface rotating mirror.  
         [0012]     An exemplary backlight module is configured to provide light to a display device. The backlight module usually includes a light beam generator, a gray filter, a lens array, a light guide plate (LGP), a diffuser sheet, a prism sheet, and a reflector. The light beam generator includes a light source, a multi-surface rotating mirror, a flattened lens, two optical detectors, a gray filter, and a lens array. The multi-surface rotating mirror (also known as a polygon mirror) is configured to rotate at a predetermined frequency so as to reflect light beams from the light source. The flattened lens is adapted to transform the reflecting light beams to parallel light beams. In the exemplary embodiment, the two optical detectors set on both end of the flattened lens, the optical detectors are configured to detect light beams and generate feedback signals to the PCB according to a scanning frequency of light beam reflecting from the multi-surface rotating mirror. Therefore, the frequency of the scanning light beams is corresponding to the frequency of the scanning signal. During the rotating process of the polygon mirror, when the scanning signal is applied to the LCD panel, the scanning light beams scan the LGP one or more than one time. By using this technique, the blurred image of object movement of image display and the contrast in boundary shape of the displaying object became worse can be reduced.  
         [0013]     An exemplary liquid crystal display (LCD) device includes an LCD panel, a backlight module and a printed circuit board (PCB). The PCB is at least mounted with a driving signal generator and a timing controller configured to provide scanning signals and timing signals. The backlight module usually includes a light beam generator, a gray filter, a lens array, a light guide plate (LGP), a diffuser sheet, a prism sheet, and a reflector. The light beam generator includes a light source, a multi-surface rotating mirror, a flattened lens, two optical detectors, a gray filter, and a lens array. The multi-surface rotating mirror (also known as a polygon mirror) is configured to rotate at a predetermined frequency so as to reflect light beams from the light source. The flattened lens is adapted to transform the reflecting light beams to parallel light beams. In the exemplary embodiment, the two optical detectors set on both end of the flattened lens, the optical detector is configured to detect light beams and generate feedback signals to the PCB according to a scanning frequency of light beam reflecting from the multi-surface rotating mirror. Therefore, the frequency of the scanning light beams is corresponding to the frequency of the scanning signal. During the rotating process of the polygon mirror, when the scanning signal is applied to the LCD panel, the scanning light beams scan the LGP one or more than one time. By using this technique, the blurred image of object movement of image display and the contrast in boundary shape of the displaying object became worse can be reduced.  
         [0014]     On the other hand, a total reflection prism can set to replace the aforesaid elements, the gray filter and the lens array. The total reflection prism can be set aside the light entrance surface of the LGP wherein the total reflection prism is figured as an isosceles right triangle and a bevel of the total reflection prism faces the light entrance surface of the LGP. Therefore, a parallel scanning light beam can be provided. Furthermore, the other type of light source can be adopted to provide polarized light beams. If the light source provides the polarized light beams, a polarized beam splitter and a beam combiner should be needed.  
         [0015]     Advantages and novel features of the above-described devices and systems will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a plan view of a liquid crystal display (LCD) device illustrating a first embodiment of the present invention.  
         [0017]      FIG. 2  is an enlarged, side plan view of a marked area III of  FIG. 1 .  
         [0018]      FIG. 3  is a plan view of an LCD device illustrating a second embodiment of the present invention.  
         [0019]      FIG. 4  is a plan view of an LCD device illustrating a third embodiment of the present invention.  
         [0020]      FIG. 5  is an exploded, side plan view of an LCD device illustrating a fourth embodiment of the present invention.  
         [0021]      FIG. 6  is an exploded, side cross-sectional view of a conventional LCD device. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  is a schematic plan view of a liquid crystal display (LCD) device illustrating a first embodiment of the present invention.  FIG. 2  is an enlarged, side plan view of a marked area III of  FIG. 1 . The LCD device  2  mainly includes an LCD panel  21 , a backlight module  23  and a printed circuit board (PCB)  25 . The LCD panel  21  and the backlight module  23  are stacked with each other and the PCB  25  electrically connects to the LCD panel  21  and the backlight module  23 .  
         [0023]     As shown in  FIG. 2 , the backlight module  23  usually includes a light beam generator  230 , a gray filter  231 , a lens array  233 , a light guide plate (LGP)  235 , a diffuser sheet  237 , a prism sheet  238 , and a reflector  239 . The LGP  235  can be a plastic plate with wedge shape, which includes a light entrance surface  2351 , a light exit surface  2352 , and a bottom  2353 . The LGP  235  is used to introduce light beams to transmit from the light entrance surface  2351  to the light exit surface  2352 .  
         [0024]     The light beam generator  230  can generate scanning light beams with specific scanning frequency, and includes a light source  2300 , a polygon mirror  2302 , two optical detectors  2303 , an f-theta lens  2304 , and a driving motor  2305 . In the exemplary embodiment, the light source  2300  can be a white light LED, which is set at a side of the polygon mirror  2302  and emits light directly toward the polygon mirror  2302 . The polygon mirror (i.e. a multi-surface rotating mirror)  2302  can be a polygon prism, with each surface of the polygon prism being a reflector. The polygon mirror  2302  can be driven by the driving motor  2305 . The f-theta lens (i.e. a flattened lens)  2304  can be a convex lens that is used to transform a dispersing light to a parallel light beam. The f-theta lens  2304  is set between the polygon mirror  2302  and the gray filter  231 . The optical detector  2303  is used to detect the strength of light and also generates a feedback signal. The two optical detectors  2303  are arranged on the two sides of the f-theta lens  2304  and are electrically connected to the PCB  25 .  
         [0025]     The gray filter  231  is used to uniform the strength of light when light passes through the gray filter  231 . The lens array  233  is also used to uniform the strength of light. When light passes through the lens array  233 , the brightness of light coming from the central region of the lens array  233  probably approaches the brightness of light coming from the peripheral region thereof so as to increase total brightness as much as about 40%.  
         [0026]     The optical transmission path of the backlight module  23  in the exemplary embodiment of the present invention is described as follows. The light source  2300  emits light beam  2300   a  to one surface of the polygon mirror  2302 . The polygon mirror  2302  rotates with a predetermined frequency under driving by the driving motor  2305 . The light beams  2300   a  are reflected through the polygon mirror  2302  with a specific angular velocity so as to emit scanning light beams  2302   a  to the f-theta lens  2304 . When the scanning light beams  2302   a  transmit from the f-theta lens  2304 , parallel scanning light beams  2304   a  are obtained. The parallel scanning light beams  2304   a  emit through the gray filter  231  and the lens array  233  sequentially and reach the light entrance surface  2351  of the LGP  235  uniformly. As shown in  FIG. 2 , when light transmits through the LGP  231 , a portion of light beams  2352   a  is obtained from the light exit surface  2352  of the LGP  235  and the other portion of light beams emit through the bottom  2353  to the reflector  239  then reflect back to the LGP  235  so as to emit through the light exit surface  2352  of the LGP  235  finally. The light beams  2352   a  emit through the diffuser sheet  237  and the prism sheet  238  so as to reach the LCD panel  21  and display images.  
         [0027]     Referring back to  FIG. 1 , the LCD panel  21  includes a plurality of pixel regions  211 . Each of the pixel regions  211  includes a thin film transistor (TFT)  212 . The TFT  212  includes a gate electrode  2121 , a source electrode  2122  and a drain electrode  2123 . The LCD panel  21  also includes a plurality of scan lines  2131 , a plurality of signal lines  2132 , and a plurality of pixel electrodes  2133 . The scan lines  2131  and the signal lines  2132  cross each other so as to define the pixels. Additionally, each gate electrode  2121  connects to the corresponding scan line  2131  and each source electrode  2122  and drain electrode  2123  individually connect to the signal line  2132  and the pixel electrode  2133 .  
         [0028]     Scanning signals  251  are generated from the PCB  25  so as to drive each gate electrode  2121  of the LCD panel  21  column by column. Simultaneously, a timing signal  252  is transmitted to the driving motor  2305  of the polygon mirror  2302  so as to control a rotating velocity of the polygon mirror  2302 . Additionally, the PCB  25  can receive the feedback signal  253  coming from the optical detectors  2303  so as to modify the rotation velocity of the polygon mirror  2302 . In order to coordinate the rotating frequency of the polygon mirror  2302  with the frequency of the scanning signal  251 , the feedback signal  253  is used to modify and correct the rotating velocity of the polygon mirror  2302  from time to time as necessary.  
         [0029]     In the aforesaid exemplary embodiment, the frequency of the scanning light beams  2302   a  are corresponding to the frequency of the scanning signal  251 . Therefore, during the rotating process of the polygon mirror  2302 , when the scanning signal  251  is applied to the LCD panel  21 , the scanning light beams  2302   a  scan the LGP  235  one or more than one time. By using this technique, the blurred image of object movement of image display and the contrast in boundary shape of the displaying object became worse can be reduced.  
         [0030]     In addition, scanning light beams  2302   a  are emitted from the rotating polygon mirror  2302 , during the light transmission process, light source  2300  is always turn on instead of changing from a turn on to a turn off state frequently. This protects the light source  2300  from premature aging.  
         [0031]     Referring to  FIG. 3 , this is a schematic plan view of an LCD device  3  illustrating a second embodiment of the present invention. The major difference between the second embodiment and the first embodiment is introducing a plane reflector  3301 . The plane reflector  3301  is located between the light source  3300  and the polygon mirror  3302 . The plane reflector  3301  is used to reflect light beams coming from the light source  3300  to the polygon mirror  3302 . This is because the light source  3300  usually has larger volume and is hard to move (in order to have a stable light emitting quality). Therefore, in this exemplary embodiment, the plane reflector  3300  is configured to adjust the incident light for the polygon mirror  3302  without moving the light source  3300 .  
         [0032]     Referring to  FIG. 4 , this is a schematic plan view of an LCD device  4  illustrating a third embodiment of the present invention. The major difference between the third embodiment and the first embodiment is the light source generator  430 . The light source generator  430  includes a polarized beam splitter  4301 , a beam combiner  4305 . The polarized beam splitter  4301  and the beam combiner  4305  are located between the light source  4300  and the polygon mirror  4302 . The light source  4300  is a polarized light source so as to generate polarized light beams. The polarized beam splitter  4301  can be a polarized beams transformer so as to use a polarize sheet to block polarized beams with predetermined direction. The beam combiner  4305  is configured to assemble light beams so as to increase the strength of light.  
         [0033]     Referring to  FIG. 5 , this is an exploded, side plan view of an LCD device  5  illustrating a fourth embodiment of the present invention. The backlight module  53  includes a light beam generator  530 , a total reflection prism  531 , a LGP  535 , a diffuser sheet  537 , a prism sheet  538 , and a reflector  539 . It should be noted that the light beam generator  530  is the same as the light beam generator  230  of the first embodiment. The total reflection prism  531  can be configured to replace the gray filter  231  and the lens array  233  of the first embodiment as shown in  FIG. 1 . The total reflection prism  531  is a triangular prism, wherein a cross-sectional view of the total reflection prism  531  is an isosceles right triangle. As shown in  FIG. 5 , the side opposite to the right angle of the isosceles right triangle is the bevel  5311  and the two sides adjacent the right angle are the first right angle bevel  5312  and the second right angle bevel  5313  separately. The total reflection prism  531  is located adjacent to the light entrance surface  5351  of the LGP  535 .  
         [0034]     In the preferred embodiment, the bevel  5311  is parallel to the entrance surface  5351  of the LGP  535  and the first right angle bevel  5312  face the light entrance surface  5351  of the LGP  535  that incident light beams can emit into the total reflection prism  531  from bevel  5311  and transmit out from the bevel  5311  to the LGP  535  by reflecting twice on both the first right angle bevels  5313  and  5312  sequentially. Therefore, the light beam generator  530  can be set under the reflector  539  so as to reduce the side volume of the LCD panel  51 .  
         [0035]     As would be understood by a person skilled in the art, the foregoing preferred and exemplary embodiments are provided in order to illustrate principles of the present invention rather than limiting the present invention. The above descriptions are intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which scope should be accorded the broadest interpretation so as to encompass all such modifications and similar structures and methods.