Patent Publication Number: US-2010117945-A1

Title: Color sequence offset modulation method and device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a display method and device of a color liquid crystal display, particularly to a color sequence offset modulation method and device, which can prevent from color mixing-induced color deviation and present the designed colors correctly. 
     BACKGROUND OF THE INVENTION 
     In FSC LCD (Field Sequential Color Liquid Crystal Display), multi-color backlights are sequentially emitted and pass through optical liquid crystal gates. FSC LCD opens and closes the liquid crystal optical gates to sequentially generate pure-color fields, and then the visual persistence of human eyes mixes the pure colors to present various colors. Refer to  FIG. 1 . The timing signal  1  is used to open and close the liquid crystal optical gates. However, the light transmission curve  2  cannot fully reflect the timing signal  1  because the delayed response of liquid crystal molecules. Thus, there are open delays  3  and close delays  4  appearing in the light transmission curve  2 . 
     Refer to  FIG. 2 . The multi-color backlights  5  includes a red backlight (R)  6 , a green backlight (G)  7  and a blue backlight (B)  8 , which are sequentially emitted. The liquid crystal optical gate has three light transmission curves  2  (designated by r, g, and b) corresponding to the sequentially-emitted red backlight (R)  6 , green backlight (G)  7  and blue backlight (B)  8 . The close delays  4  of the light transmission curves  2  extend to the time intervals for the latter-color backlight. In other words, the green backlight  7  appears in a portion of the time interval for the red backlight  6 ; the blue backlight  8  appears in a portion of the time interval for the green backlight  7 ; the red backlight  6  appears in a portion of the time interval for the blue backlight  8 . Thus, color deviations appear in human eyes. When the liquid crystal optical gate generates other light transmission curves  2  (designated by c, m, and y) to mix two pure color lights, the close delays  4  of the light transmission curves  2  (c, m, and y) also extend to the time intervals for the latter-color backlight. Thus, color deviations also appear in human eyes in the color-mixing case. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide an offset modulation method and device to eliminate color difference and retain the purity of colors, whereby the problem of color deviation is solved. 
     The present invention proposes a color sequence offset modulation method and device. The device of the present invention comprises a multi-color backlight source, a liquid crystal optical gate and a controller. 
     The method of the present invention comprises steps: 
     providing a multi-color backlight source sequentially emitting at least two colored backlights with a dark interval therebetween; 
     providing a liquid crystal optical gate illuminated by said colored backlights and having a light blocking state and a light permeable state; 
     providing a timing signal to switch the liquid crystal optical gate into the light blocking state or the light permeable state, whereby the liquid crystal optical gate has a light transmission curve, wherein the light transmission curve has an open delay interval or a close delay interval in the transitions of the light blocking state and the light permeable state, and wherein the timing signal makes the close delay interval coincide with the dark interval lest the latter colored backlight mix with the former colored backlight during the close delay interval. 
     Therefore, the present invention can prevent from the color difference caused by color mixing during the close delay interval. In a case of needing pure colors, the present invention can avoid the color deviation caused by color mixing. In a case of needing mixed colors, the present invention can present the designed colors correctly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the timing signal and transmission curve of a conventional technology; 
         FIG. 2  is a diagram showing the timing charts of a conventional FSC LCD. 
         FIG. 3  is a diagram schematically showing a color sequence offset modulation device according to a first embodiment of the present invention; 
         FIG. 4  is a diagram showing the timing charts of a FSC LCD using a color sequence offset modulation device according to a first embodiment of the present invention; and 
         FIG. 5  is a diagram showing the timing charts of a FSC LCD using a color sequence offset modulation device according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, the technical contents of the present invention are described in detail in cooperation with the drawings. 
     Refer to  FIG. 3  and  FIG. 4 . In a first embodiment, the device of the present invention comprises a multi-color backlight source  10 , a liquid crystal optical gate  20  and a controller  30 . The multi-color backlight source  10  is arranged near the liquid crystal optical gate  20 , and the controller  30  is electrically coupled to the liquid crystal optical gate  20 . 
     The multi-color backlight source  10  emits at least two colored backlights  11  with a dark interval  12  therebetween. The colored backlights  11  include a red backlight  111 , a green backlight  112  and a blue backlight  113 . The colored backlight  11  may have the dark interval  12  at the instant that the multi-color backlight source  10  begins to emit the colored backlight  11 . 
     The colored backlights  11  are projected onto the liquid crystal optical gate  20 . The liquid crystal optical gate  20  has a light blocking state and a light permeable state. The controller  30  generates a timing signal  31 . The timing signal  31  may be an alternating signal. The time interval of two opposite phases of the timing signal  31  is equal to the time interval to emit the red backlight  111 , green backlight  112  and blue backlight  113  once. The timing signal  31  switches the liquid crystal optical gate  20  into the light blocking state or the light permeable state, whereby the liquid crystal optical gate  20  has a light transmission curve  21 . The light transmission curve  21  has an open delay interval  211  and a close delay interval  212  in the transitions of the light blocking state and the light permeable state. The timing signal  31  makes the close delay interval  212  coincide with the dark interval  12 . 
     When the present invention generates pure-color lights with the light transmission curve  21  designated by r, g and b in  FIG. 4 , or when the present invention generates mixed-color lights with the light transmission curve  21  designated by c, m and y in  FIG. 4 , the latter colored backlight is not emitted during the close delay interval  212  because the close delay interval  212  coincides with the dark interval  12 . Therefore, the latter colored backlight does not mix with the former colored backlight. 
     Refer to  FIG. 5 . In a second embodiment, the time point of switching two opposite phases of the timing signal  31  is identical to the time point of sequentially shifting the colored backlights  11 . In such a mode, the three colored backlights  11  have almost identical light flux loss in the open delay interval  211  and close delay interval  212 . Thus, no matter whether the present invention generates pure-color lights or mixed-color lights, the ratio of the component lights is almost identical to the ratio of the original design. Therefore, the present invention can present the designed colors correctly. 
     As described above, when generating pure-color lights the present invention can prevent the active colored backlight from mixing with another colored backlight  11  and avoids color deviation. When generating mixed-color lights, the present invention can present the designed colors correctly.