Patent Publication Number: US-2005128376-A1

Title: Liquid crystal display and the backlight module thereof

Description:
This application claims the benefit of Taiwan application Serial No. 92135467, filed Dec. 15, 2003, the subject matter of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates in general to a liquid crystal display (LCD) and the backlight module thereof, and more particularly to an LCD and the backlight module thereof which can regulate the luminance of at least one of a number of light sources.  
      2. Description of the Related Art  
      The conventional LCD uses a backlight module to provide the LCD panel with necessary light. The light source of the backlight module must have the characteristics of high luminance and long lifespan. The backlight module includes mainly a light source, a light guide panel, a diffuser, and a plastic frame. The light source is fixed onto the plastic frame. After the light emitted by the light source is processed by the light guide panel and the diffuser, uniform luminance light is generated to be emitted to the LCD panel. Currently, the most commonly adopted light sources include cold cathode fluorescent lamp (CCFL), hot cathode fluorescent lamp and light emitter diode (LED).  
      The backlight module can be classified as the edge-type backlight module and the back-type backlight module according to the disposition of the light source on the backlight module. As for the edge-type backlight module, the light source is disposed on lateral sides of the LCD panel, and the light emitted by the light source is transmitted to the central part of the light guide panel disposed at the rear of the LCD panel and is scattered through the light guide panel. As for the back-type backlight module, a number of light sources are disposed at the rear of the LCD panel in parallel to provide the LCD panel with necessary light when displaying.  
      After a long period of service, one of a number of light sources of the edge-type backlight module disposed on lateral sides of the LCD panel might be broken and cease to emit luminance. Meanwhile, if the broken light source is removed and replaced with a new light source, unbalanced luminance of the two lateral sides will occur and uniformity of LCD panel luminance will deteriorate because the luminance of the new light source is brighter than of the old light source. So, the edge-type backlight module might have unbalanced luminance and deteriorated level of uniformity of luminance.  
      The same problem might occur to a back-type backlight module, which uses a number of light sources. If one of the light sources of the back-type backlight module is broken and is replaced with a new light source, since the luminance of the new light source is brighter than that of an old light source, the back-type backlight module might still have the same problem of unbalanced and uneven luminance. If an I-shaped light tube is used as the light source, the uneven luminance of the light tube will cause the distribution of alternated bright bars and dark bars to occur on the LCD panel, greatly deteriorating display quality.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the invention to provide an LCD and the backlight module thereof, which regulates the luminance of one of the light source of the backlight module according to the invention through a signal-modulating device, so that the plural light sources with different luminance characteristics can generate substantially identical luminance enabling the LCD panel to achieve a high level of luminance uniformity.  
      According to the object of the invention, a backlight module, include a first light source, a printed circuit board, a first inverter, and a first signal-modulating device is provided. The first light source is disposed on the printed circuit board. The inverter is disposed on the printed circuit board for driving the first light source. By modulating the first signal-modulating device, which is disposed on printed circuit board and is electrically connected to the inverter, the luminance of the first light source can be adjusted.  
      According to another object of the invention, an LCD including a display housing, a signal-socket and a backlight module is provided. The display housing has a receiving space. The signal-socket, which is disposed at the receiving space, provides a first driving signal. The backlight module is removeably disposed at the receiving space. The backlight module includes a printed circuit board, a first light source and a first signal-modulating device. The printed circuit board is selectively electrically connected to the signal-socket for receiving the first driving signal. The first light source is disposed on the printed circuit board. The first driving signal is for driving the first light source. The first signal-modulating device, which is disposed on printed circuit board, is electrically connected to first light source. By modulating the first driving signal through the first signal-modulating device, the luminance of the first light source can be changed.  
      Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a three-dimensional diagram of a backlight module according to the first embodiment of the invention;  
       FIG. 2  is a three-dimensional decomposition diagram of an LCD with the application of the backlight module according to the first embodiment of the invention;  
       FIG. 3  is a side view of an LCD with the application of the backlight module according to the first embodiment of the invention;  
       FIG. 4  is a three-dimensional diagram of a backlight module according to the second embodiment of the invention;  
       FIG. 5  is a side view of a backlight module according to the third embodiment of the invention;  
       FIG. 6  is a side view of a backlight module according to the fourth embodiment of the invention;  
       FIG. 7  is a side view of an LCD with the application of the backlight module according to the fourth embodiment of the invention; and  
       FIG. 8  is a diagram of an edge-type backlight module according to the fifth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1 , a three-dimensional diagram of a backlight module according to a first embodiment of the invention is illustrated. The backlight module  100  includes light sources  102   a ˜ 102   e , a printed circuit board  104 , inverters  106   a ˜ 106   e , and a signal-modulating device. The light sources  102   a ˜ 102   e  are disposed on the printed circuit board  104 . The inverter  106  is disposed on the printed circuit board  104  for driving the light source  102   a . The signal-modulating device  108  is disposed on the printed circuit board  104  and is electrically connected to inverter  106   a . The luminance of the light source  102   a  can be adjusted through modulating the signal-modulating device.  
      Preferably, the signal-modulating device  108  is an adjustable resistor. The inverter  106   a  is serially connected to the adjustable resistor  108 . The inverter  106   a  outputs a current I 1  to drive the light source  102   a , and the strength of the current I 1  is related to the resistance of the adjustable resistor  108 . The light sources  102   a ˜ 102   e  are disposed on an upper surface  110   a  of the printed circuit board  104 , and so are the inverter  106   a ˜ 106   e  and adjustable resistor  108  disposed on the upper surface  110   a.    
      Besides, the lower part of the printed circuit board  104  has a connector  112 . The connector  112  can be a number of electrode pads formed at the lower part of the printed circuit board  104  with one of the plural electrode pads being electrically connected to the inverter  106   a.    
      Referring to  FIG. 2  and  FIG. 3 , a three-dimensional decomposition diagram and a side view of an LCD with the application of the backlight module according to the first embodiment of the invention are shown respectively. The LCD  201  includes a display housing  202 , a signal-socket  204 , a control printed circuit board  206 , an LCD panel  208 , and a backlight module  100 . The display housing  202  has a receiving space  202   a . The signal-socket  204 , which is disposed in the receiving space  202   a , is positioned at the bottom of the display housing  202 . The control printed circuit board  206  is electrically connected to the LCD panel  208  for driving the LCD panel  208  to display the image. The signal-socket  204  is disposed on the control printed circuit board  206  and is electrically connected to the control printed circuit board  206 . The backlight module  100  is removeably disposed in the receiving space  202   a . When the backlight module  100  moves downward to the bottom, the backlight module  100  is inserted onto the signal-socket  204 , enabling the connector  112  disposed on the bottom of the printed circuit board  104  to be electrically connected to the signal-socket  204 . By doing so, the printed circuit board  104  can be electrically connected to the control printed circuit board  206  for receiving the power transmitted from the control printed circuit board  206 .  
      Refer to  FIG. 1  and  FIG. 2  at the same time. When the light source  102   a  is the new light source to replace the broken light source while the light sources  102   b ˜ 102   e  are old light sources, the luminance of the new light source, i.e., the light source  102   a , will be brighter than that of the light sources  102   b ˜ 102   e  having been in service over a period of time. By adjusting the resistance of the adjustable resistor  108 , the strength of the current I 1  outputted by the inverter  106   a  will be changed. For example, if the resistance of the adjustable resistor  108  is increased, the current I 1  will be reduced. When the light source  102   a  is driven by a reduced current I 1 , the luminance of the light source  102   a  will be reduced to be close to that of the light sources  102   b ˜ 102   e . Therefore, the LCD  201  can achieve a high level of luminance uniformity.  
      On the other hand, if the light source  102   e  is the new light source to replace the broken light source originally disposed at the first left position of the diagram while the light sources  102   a ˜ 102   d  are old light sources, the light source  102   a , which is an old light source, will be moved to the first left position of the diagram while the light source  102   e , which is a new light source, will be moved to the first right position of the diagram. The above steps can be repeated. Through adjusting the adjustable resistor  108 , the luminance of the new light source can be reduced to be close to that of the old light sources. After the broken light source of the old light source is replaced with a new light source, the LCD  201  still achieves a high level of luminance uniformity.  
      Referring to  FIG. 4 , a three-dimensional diagram of a backlight module  400  according to a second embodiment of the invention is shown. The second embodiment differs with the first embodiment in that at least two light sources of the light sources  402   a ˜ 402   e  are electrically connected to the signal-modulating device.  FIG. 4  is an example when respective light source of the light sources  402   a ˜ 402   e  is electrically connected to a signal-modulating device. The signal-modulating device can be an adjustable resistor for instance. The inverters  406   a ˜ 406   e  and the adjustable resistors  408   a ˜ 408   e  are disposed on the upper surface  410   a  of the printed circuit board  404 , but are positioned between two adjacent light sources or besides the corresponding light source. The inverters  406   a ˜ 406   e , which are serially connected with the adjustable resistors  408   a ˜ 408   e  respectively, output currents I 1 ˜I 5  respectively for driving the light sources  402   a ˜ 402   e , wherein the strength of the currents I 1 ˜I 5  are related to the resistance of the adjustable resistors  408   a ˜ 408   e . Through modulating the resistance of the adjustable resistors  408   a ˜ 408   e , the luminance of the light sources  402   a ˜ 402   e  can be adjusted to be substantially identical.  
      In the second embodiment, the light sources  402   a ˜ 402   e  have different luminance characteristics. For example, the light sources might have different periods of service or their original luminance might be different as well. The backlight module  400  can be connected to a signal socket which simulates the signal-socket  204  of a factory or service center, then regulate the resistance of the adjustable resistors  408   a ˜ 408   e  until the luminance of light sources  402   a ˜ 402   e  are identical before inserting the backlight module  400  into the receiving space  202   a  to be connected with the signal-socket  204 , so that the LCD  201  can assure a high level of luminance uniformity.  
      Referring to  FIG. 5 , a side view of a backlight module according to a third embodiment of the invention is shown. The third embodiment differs with the first embodiment and the second embodiment in that, the inverter  506  and adjustable resistor  508  of a backlight module  500  according to the third embodiment are disposed on the lower surface  510   b  of the printed circuit board  504 , wherein the lower surface  510   b  is opposite to the upper surface  510   a . Such practice can save the size of the printed circuit board  504  effectively, or allow the light sources to be arranged and disposed on the upper surface  510   a more closely to improve luminance.  
      Refer to  FIG. 6  and  FIG. 7  at the same time, wherein  FIG. 6  is a side view of a backlight module  600  according to the fourth embodiment of the invention, while  FIG. 7  is a side view of an LCD  701  with the application of the backlight module according to the fourth embodiment of the invention. The LCD  701  includes a display housing  702 , a signal-socket  704 , a control printed circuit board  706 , an LCD panel  708 , and a backlight module  600 . The display housing  702  has a receiving space  702   a . The signal-socket  704  is disposed in the receiving space  702   a  for receiving a first driving signal DSI. The backlight module  600  is removeably disposed at the receiving space  702   a.    
      The backlight module  600  includes a printed circuit board  604 , light sources  602   a ˜ 602   e  and a signal-modulating device. The signal-modulating device can be an adjustable resistor  608   a  for instance. The printed circuit board  604  can be selectively electrically connected to signal-socket  704  for receiving the first driving signal DSI. The light source  602   a ˜ 602   e  are disposed on the printed circuit board  604 . The first driving signal DSI is for driving the light source  602   a . The adjustable resistor  608   a , which is disposed on the printed circuit board  604 , is electrically connected to the light source  602   a . The luminance of the light source  602   a  can be adjusted through modulating the first driving signal DSI by the adjustable resistor  608   a.    
      The adjustable resistor  608   a  can regulate the power of the first driving signal DSI inputted to the light source  602   a , so the strength of the current of the first driving signal DSI is related to the resistance of the adjustable resistor  608   a . Through modulating the resistance of the adjustable resistor  608   a , the current of the drive light source  602   a  can be adjusted, so that the light source  602   a  and the light sources  602   b ˜ 602   e , whose luminance characteristics were originally different, can generate substantially identical luminance.  
      The control printed circuit board  706  is for controlling the LCD panel  708 . The control printed circuit board  706  has an inverter  706   a , which is used for generating driving signal DSI. When the backlight module  600  is inserted into the signal-socket  704 , the connector  612  positioned at one side of the printed circuit board  604   a  is electrically connected to the signal-socket  704 , so that the driving signal DSI generated by the inverter  706   a  can be transmitted to the light source  602   a  through the adjustable resistor  608   a.    
      In the fourth embodiment, at least two light sources can be electrically connected to the adjustable resistor correspondingly to regulate the luminance of the light sources. Under this circumstance, the driving current for driving the light sources can also be provided by the control printed circuit board. The adjustable resistor of backlight module according to the fourth embodiment, like the backlight module  400   a  according to the second embodiment, can be disposed between two adjacent light sources or besides a corresponding light source. Besides, the adjustable resistor of backlight module according to the fourth embodiment, like the backlight module  500   a  according to the third embodiment, can be disposed on the lower surface of the printed circuit board  604 . The light sources  602   a ˜ 602   e  can be achieved by CCFL or hot cathode fluorescent lamp.  
      Moreover, if the light sources  602   a ˜ 602   e  adopt a light emitter diode (LED), the control printed circuit board  706  can be dispensed with the inverter  706   a  which is needed if a CCFL is adopted.  
      The backlight modules according to the first embodiment to the fourth embodiment of the invention are back-type backlight modules. Nonetheless, the spirit of the invention can be applied to the edge-type backlight module. Referring to  FIG. 8 , a diagram of an edge-type backlight module according to the fifth embodiment of the invention is shown. A light source  802   a , an inverter  806   a  and an adjustable resistor  808   a  are disposed on the printed circuit board  804   a . A light source  802   b , an inverter  806   b  and an adjustable resistor  808   b  are disposed on the printed circuit board  804   b . The adjustable resistor  808   a  and  808   b  are respectively electrically connected to the inverters  806   a  and  806   b . An edge-type backlight module  800  has a light guide panel  820 . The light sources  802   a  and  802   b  are respectively disposed at the two sides of the light guide panel  820 . When the light source  802   a  and  802   b  are having different luminance characteristics, by modulating the luminance of the light sources  802   a  and  802   b  through modulating the adjustable resistors  808   a  and  808   b , the luminance of the light source  802   a  and that of the light source  802   b  will be the same, so that the luminance of the light guide panel  820  will have a high level of uniformity.  
      The printed circuit boards  804   a  and  804   b  are not necessary to have the inverters  806   a  and  806   b  disposed thereon. When the printed circuit boards  804   a  and  804   b  are electrically connected the signal-sockets  805   a  and  805   b  respectively, the printed circuit boards  804   a  and  804   b  will receive respective driving signal for driving the light sources  802   a  and  802   b  respectively.  
      The backlight module of the invention can adopt a light source such as a CCFL, a hot cathode fluorescent lamp, an LED, or other light source whose luminance is adjustable. Any light source whose luminance can be changed through modulating the power of a driving signal adjusted through a signal-modulating device can be applied to the backlight module of the invention.  
      The LCD and the backlight module thereof disclosed in the above preferred embodiments of the invention, through a signal-modulating device, enable the light sources whose luminance characteristics are different to generate substantially identical luminance, so that the LCD panel can achieve a high level of luminance uniformity.  
      While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.