Abstract:
An exemplary liquid crystal display includes a substrate, a light source, and a color feedback system. The light source includes light emitting diodes. The color feedback system includes either one color sensor or plural color sensors. In one example, a single color sensor is disposed on the substrate and samples the light at the substrate. The color feedback system adjusts the brightness of the light emitting diodes according to the sampling signals of the color sensor.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to liquid crystal displays (LCDs), and particularly to an LCD with a color sensor on a substrate. 
       GENERAL BACKGROUND 
       [0002]    In various display technologies, a required color can be obtained by mixing primary colors. For example, white can be obtained by mixing red (R), green (G), and blue (B) in an optical mixing cavity of a display device. The mixing cavity has many applications. For example, the mixing cavity combined with a suitable light guide plate can be used as a backlight for an LCD. In this case, it is very important to mix the primary colors thoroughly. Thus, a color feedback system is needed in the LCD. 
         [0003]      FIG. 8  is a schematic view of a conventional LCD. The LCD  10  includes a mixing cavity  11  and a color feedback system  12 . The color feedback system  12  includes a color sensor  121 , an analog to digital (AID) converter  122 , a color controller  123 , and a light emitting diode (LED) driver  124 . The mixing cavity  11  includes a plurality of red LEDs (R), green LEDs (G), and blue LEDs (B). 
         [0004]    The red LEDs, the green LEDs, and the blue LEDs emit red light, green light, and blue light, respectively. The red light, the green light, and the blue light are sufficiently mixed into white light in the mixing cavity  11 . The color sensor  121  samples the white light and then outputs three individual analog signals V R , V G , V B  to the A/D converter  122 . The analog signal V R  represents a red component of the white light, the analog signal V G  represents a green component of the white light, and the analog signal V B  represents a blue component of the white light. The A/D converter  122  converts the three individual analog signals V R , V G , V B  into three individual digital signals R MEAS , G MEAS , B MEAS , respectively. The color controller  123  receives the three individual digital signals R MEAS , G MEAS , B MEAS , and outputs three individual control signals R CON , G CON , B CON , correspondingly. The LED driver  124  receives the three control signals R CON , G CON , B CON , and outputs three individual drive voltages R DRV , G DRV , B DRV , correspondingly. The drive voltage R DRV  is used to control the brightness of the red LEDs, the drive voltage G DRV  is used to control the brightness of the green LEDs, and the drive voltage B DRV  is used to control the brightness of the blue LEDs. 
         [0005]    In fact, the analog signals V R , V G , V B  outputted from the color sensor  121  vary with the ambient temperature of the color sensor  121 , as shown in  FIG. 9 . In  FIG. 9 , the left graph illustrates a functional relation between the analog signal V R  and an intensity of the red component of the white light I R  when the ambient temperature of the color sensor  121  is 25° C., and the right graph illustrates a functional relation between the analog signal V R  and the intensity I R  when the ambient temperature of the color sensor  121  is 125° C. As seen, the analog signals V R  are different at any same point of intensity I R  when the ambient temperature varies. The above kind of functional relation also exists between the analog signal V G  and an intensity I G  of the green component of the white light, and between the analog signal V B  and an intensity I B  of the blue component of the white light. 
         [0006]    In practice, the temperature of the mixing cavity  11  tends to increase with the continuous operation of the LCD  10  over a period of time. The main reason for this is the heat that is generated by the LEDs of the mixing cavity  11 . Typically, the ambient temperature of the color sensor  121  correspondingly increases. The analog signals outputted from the color sensor  121  vary when the ambient temperature increases. That is, the accuracy of the color sensor  121  declines, and the accuracy of the color feedback system  12  declines correspondingly. Because of the above problem, the display quality of the LCD  10  is liable to be adversely affected. 
       SUMMARY 
       [0007]    In accordance with one embodiment of the present invention, a liquid crystal display includes a transparent substrate, a light source, and a color feedback system. The light source includes a plurality of light emitting diodes. The color feedback system includes at least one color sensor. The substrate is capable of transmitting light originating from the light source, the at least one color sensor is disposed on the substrate and is configured to sample the light at the substrate and generate corresponding sampling signals, and the color feedback system is configured to adjust the brightness of the light emitting diodes according to the sampling signals of the at least one color sensor. 
         [0008]    Other novel features and advantages 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 
         [0009]      FIG. 1  is a side, cross-sectional view of an LCD according to a first embodiment of the present invention, the LCD including a light source and a color feedback system. 
           [0010]      FIG. 2  is a plan view of the light source of  FIG. 1 . 
           [0011]      FIG. 3  is a block diagram of the color feedback system of  FIG. 1 , also showing LEDs of the light source. 
           [0012]      FIG. 4  is a plan view of an LCD according to a second embodiment of the present invention, the LCD including a light source and a color feedback system. 
           [0013]      FIG. 5  is a block diagram of the color feedback system of  FIG. 4 , also showing LEDs of the light source. 
           [0014]      FIG. 6  is a plan view of an LCD according to a third embodiment of the present invention. 
           [0015]      FIG. 7  is a plan view of an LCD according to a fourth embodiment of the present invention. 
           [0016]      FIG. 8  is a block diagram of a conventional LCD, the LCD including a color sensor. 
           [0017]      FIG. 9  illustrates a functional relation between an analog signal V R  and an intensity of a red component of white light I R  when the ambient temperature of the color sensor of  FIG. 8  is respectively 25° C. and 125° C. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0018]    Reference will now be made to the drawings to describe various embodiments of the present invention in detail. 
         [0019]      FIG. 1  is a schematic, side cross-sectional view of an LCD according to a first embodiment of the present invention. The LCD  200  includes an LCD panel  20 , a backlight module  28 , and a color feedback system  30  (see  FIG. 3 ). The backlight module  28  is disposed at a rear side of the LCD panel  20 . The LCD panel  20  includes a color filter substrate (CF substrate)  21 , a thin film transistor substrate (TFT substrate)  23 , and a liquid crystal layer  22  interposed therebetween. The TFT substrate  23  is a transparent substrate. The LCD panel  20  also includes a flexible printed circuit (FPC)  233 . The color feedback system  30  includes a color sensor  230  connected to an indium tin oxide (ITO) circuit (not shown) on the TFT substrate  23  via anisotropic conductive films  231 . One terminal of the FPC  233  is connected to the ITO circuit on the TFT substrate  23  via one or more anisotropic conductive films  231 . The other terminal of the FPC  233  is connected to a circuit board (not shown) of the LCD  200 . The backlight module  28  includes a diffusion sheet  24 , a light guide plate  25 , a reflective sheet  26 , and a light source  27 . The light guide plate  25  includes a top light emitting surface  252 , a bottom surface  253 , and a light incident surface  251  adjoining the light emitting surface  252  and the bottom surface  253 . The light source  27  is located adjacent to the light incident surface  251 . The diffusion sheet  24  is disposed on the light emitting surface  252 , and the reflective sheet  26  is disposed on the bottom surface  253 . 
         [0020]    Referring also to  FIG. 2 , the light source  27  includes a mixing cavity  270  and a plurality of red LEDs (R), green LEDs (G), and blue LEDs (B). The red LEDs, the green LEDs, and the blue LEDs emit red light, green light, and blue light, respectively. The red light, the green light, and the blue light are sufficiently mixed into white light in the mixing cavity  270 . The white light enters the light guide plate  25  via the light incident surface  251 . Part of the white light emits from the light emitting surface  252  directly, and the other part of the white light is reflected by the reflective sheet  26  before emitting from the light emitting surface  252 . As a result, almost all the light from the light source  27  passes through the light guide plate  25 , and is diffused by the diffusion sheet  24  before entering the TFT substrate  23 . 
         [0021]      FIG. 3  is a block diagram of the color feedback system  30 , also showing a block for the LEDs of the light source  27 . The color feedback system  30  includes the color sensor  230 , an A/D converter  32 , a color controller  33 , and an LED driver  34 . The A/D converter  32 , the color controller  33 , and the LED driver  34  are disposed on the circuit board of the LCD device  200 . 
         [0022]    The color sensor  230  samples the white light and then outputs three individual analog signals V R , V G , V B  to the A/D converter  32 . The analog signal V R  represents a red component of the white light, the analog signal V G  represents a green component of the white light, and the analog signal V B  represents a blue component of the white light. The A/D converter  32  converts the three individual analog signals V R , V G , V B  into three individual digital signals R MEAS , G MEAS , B MEAS , respectively. The color controller  33  receives the three individual digital signals R MEAS , G MEAS , B MEAS , and outputs three individual control signals R CON , G CON , B CON , correspondingly. The LED driver  34  receives the three control signals R CON , G CON , B CON , and outputs three individual drive voltages R DRV , G DRV , B DRV , correspondingly. The drive voltage R DRV  is used to control the brightness of the red LEDs, the drive voltage G DRV  is used to control the brightness of the green LEDs, and the drive voltage B DRV  is used to control the brightness of the blue LEDs. 
         [0023]    Because the light source  27  does not contact the TFT substrate  23 , the ambient temperature of the light source  27  has little influence on the TFT substrate  23 . Correspondingly, the light source  27  has little or no effect on the ambient temperature of the color sensor  230 . Accordingly, the accuracy of the color sensor  230  can be improved. Thus, the accuracy of the color feedback system  30  is also improved. Furthermore, the location of the color sensor  230  as illustrated in  FIG. 1  enables the LCD  200  to have a compact configuration. 
         [0024]      FIG. 4  is a plan view of an LCD  300  according to a second embodiment of the present invention. The LCD  300  is generally similar to the LCD  200 . However, a TFT substrate  23  of the LCD  300  includes a first color sensor  331  and a second color sensor  332 . The first color sensor  331  and the second color sensor  332  are disposed on opposite edge portions of a major surface of the TFT substrate  23 . For example, the second color sensor  332  is adjacent to the light source  27 , and the first color sensor  331  is far from the light source  27 . 
         [0025]      FIG. 5  is a block diagram of a color feedback system of the LCD  300 , also showing a block for the LEDs of the light source  27 . The color feedback system  40  includes the first color sensor  331 , the second color sensor  332 , a first A/D converter  321 , a second A/D converter  322 , a first averaging circuit  41 , a second averaging circuit  42 , a third averaging circuit  43 , a color controller  45 , and an LED driver  46 . The first color sensor  331  samples the white light emitting from the TFT substrate  23 , and outputs individual analog signals V R1 , V G1 , V B1 . The second color sensor  332  samples the white light emitting from the TFT substrate  23 , and outputs individual analog signals V R2 , V G2 , V B2 . The first A/D converter  321  receives the analog signals V R1 , V G1 , V B1  and outputs digital signals R MEAS1 , G MEAS1 , B MEAS1 ; and the second A/D converter  322  receives the analog signals V R2 , V G2 , V B2  and outputs digital signals R MEAS2 , G MEAS2 , B MEAS2 . The first averaging circuit  41  averages the digital signals R MEAS1 , R MEAS2 , and outputs the mean value           The second averaging circuit  42  averages the digital signals G MEAS1 , G MEAS2 , and outputs the mean value           The third averaging circuit  43  averages the digital signals B MEAS1 , B MEAS2 , and outputs the mean value           The color controller  45  receives the mean values           and correspondingly outputs control signals R CON , G CON , B CON . The LED driver  46  receives the control signals R CON , G CON , B CON , and correspondingly outputs drive voltages R DRV , G DRV , B DRV . The drive voltage R DRV  is used to control the brightness of the red LEDs, the drive voltage G DRV  is used to control the brightness of the green LEDs, and the drive voltage B DRV  is used to control the brightness of the blue LEDs. 
         [0026]    The color feedback system  40  samples the white light at different positions and averages the sample signals to control the brightness of the light source  27 . Therefore, the accuracy of the color feedback system  40  is further improved. 
         [0027]    Referring to  FIG. 6 , in a third embodiment, the color feedback system includes four color sensors  601 . The four color sensors  601  can be disposed on four corner areas of the major surface of the TFT substrate  23 . In other embodiments, the color feedback system can include N color sensors  701  (where N is a natural number). Referring to  FIG. 7 , in an exemplary fourth embodiment, N is equal to six. In further or alternative embodiments, the color sensor(s) of any of the above embodiments can be disposed on the CF substrate  21 . In such cases, each color sensor may be disposed on a selected one of an upper major surface of the CF substrate  21  and a lower major surface of the CF substrate  21 . 
         [0028]    It is to be further understood that even though numerous characteristics and advantages of various embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.