Liquid crystal display

Abstract

To reduce viewing angle dependence of γ characteristics in a normally black liquid crystal display. Each pixel 10 has a first sub-pixel 10 a and a second sub-pixel 10 b which can apply mutually different voltages to their respective liquid crystal layers. Relationships ΔV 12 (gk)>0 volts and ΔV 12 (gk)≧ΔV 12 (gk+1) are satisfied at least in a range 0<gk≦n−1 if it is assumed that ΔV 12 =V 1 −V 2, where ΔV 12 is the difference between root-mean-square voltage V 1 applied to the liquid crystal layer of the first sub-pixel 10 a and root-mean-square voltage V 2 applied to the liquid crystal layer of the second sub-pixel 10 b.

What is claimed is: 
     
       1. A liquid crystal display used in normally black mode, comprising a plurality of pixels each of which has a liquid crystal layer and a plurality of electrodes for applying voltage to the liquid crystal layer, wherein:
 each of the plurality of pixels comprises a first sub-pixel and a second sub-pixel which can apply mutually different voltages to their respective liquid crystal layers; and   when each of the plurality of pixels displays a grayscale gk which satisfies 0≦gk≦n, where gk and n are integers not less than zero and a larger value of gk corresponds to higher brightness, n represents the highest grayscale, and at least the range of 0<gk≦n−1 includes gk which satisfies relationships ΔV 12  (gk)>0 volts and ΔV 12  (gk)≦ΔV 12  (gk+1) if it is assumed that ΔV 12  (gk)=V 1  (gk)−V 2  (gk), where V 1  (gk) and V 2  (gk) are root-mean-square voltages applied to the liquid crystal layers of the first sub-pixel and the second sub-pixel, respectively.   
     
     
       2. The liquid crystal display according to  claim 1 , wherein:
 each of the plurality of pixels comprises a third sub-pixel which can apply a voltage different from those of the first sub-pixel and the second sub-pixel to its liquid crystal layer; and   when each of the plurality of pixels displays a grayscale gk, a relationship 0 volts<ΔV 13  (gk)<ΔV 12  (gk) is satisfied if the root-mean-square voltage applied to the liquid crystal layer of the third sub-pixel is V 3  (gk) and ΔV 13  (gk)=V 1  (gk)−V 3  (gk).   
     
     
       3. The liquid crystal display according to  claim 1 , wherein a relationship ΔV 12  (gk)≧ΔV 12  (gk+1) is satisfied at least in a range 0<gk≦n−1. 
     
     
       4. The liquid crystal display according to  claim 2 , wherein a relationship ΔV 13  (gk)≧ΔV 13  (gk+1) is satisfied at least in a range 0<gk≦n−1. 
     
     
       5. The liquid crystal display according to  claim 1 , wherein:
 the first sub-pixel and the second sub-pixel each comprise:   a liquid crystal capacitor formed by a counter electrode and a sub-pixel electrode opposing the counter electrode via the liquid crystal layer, and   a storage capacitor formed by a storage capacitor electrode connected electrically to the sub-pixel electrode, an insulating layer, and a storage capacitor counter electrode opposing the storage capacitor electrode via the insulating layer; and   the counter electrode is a single electrode shared by the first sub-pixel and the second sub-pixel, and the storage capacitor counter electrodes of the first sub-pixel and the second sub-pixel are electrically independent of each other.   
     
     
       6. The liquid crystal display according to  claim 5 , comprising two switching elements provided for the first sub-pixel and the second sub-pixel, respectively,
 wherein the two switching elements are turned on and off by scan line signal voltages supplied to a common scan line; display signal voltages are applied to the respective sub-pixel electrodes and storage capacitor electrodes of the first sub-pixel and the second sub-pixel from a common signal line when the two switching elements are on; voltages of the respective storage capacitor counter electrodes of the first sub-pixel and the second sub-pixel change after the two switching elements are turned off; and the amounts of change defined by the direction and magnitude of the change differ between the first sub-pixel and the second sub-pixel.   
     
     
       7. The liquid crystal display according to  claim 6 , wherein the liquid crystal layer is a vertically aligned liquid crystal layer and contains nematic liquid crystal material with negative dielectric anisotropy. 
     
     
       8. The liquid crystal display according to  claim 7 , wherein the liquid crystal layers of the first sub-pixel and the second sub-pixel each contain four domains which are approximately 90 degrees apart in azimuth direction in which their liquid crystal molecules incline when a voltage is applied. 
     
     
       9. The liquid crystal display according to  claim 8 , wherein:
 the first sub-pixel and the second sub-pixel are placed on opposite sides of the common signal line;   the first sub-pixel and the second sub-pixel each have, on the counter electrode side, a plurality of ribs protruding towards the liquid crystal layer and the plurality of ribs include a first rib extending in a first direction and a second rib extending in a second direction approximately orthogonal to the first direction; and   the first rib and the second rib are placed symmetrically with respect to a center line parallel to the common scan line in each of the first sub-pixel and the second sub-pixel and the arrangement of the first rib and the second rib in one of the first and second sub-pixels is symmetrical with respect to the arrangement of the first rib and the second rib in the other sub-pixel.   
     
     
       10. The liquid crystal display according to  claim 9 , wherein the areas of the first sub-pixel and the second sub-pixel are practically equal and the center line parallel to the common scan line in each of the first sub-pixel and the second sub-pixel is placed at an interval equal to approximately one half of an array pitch of the scan lines in both the first sub-pixel and the second sub-pixel. 
     
     
       11. The liquid crystal display according to  claim 1 , wherein the area of the first sub-pixel is equal to or smaller than the area of the second sub-pixel. 
     
     
       12. A liquid crystal display used in a normally black mode, comprising:
 a plurality of pixels, each pixel including a first sub-pixel electrode and a second sub-pixel electrode forming a first sub-pixel and a second sub-pixel respectively;   a counter electrode;   a first liquid crystal capacitor formed by the first sub-pixel electrode, the counter electrode and a liquid crystal layer therebetween; and   a second liquid crystal capacitor formed by the second sub-pixel electrode, the counter electrode and a liquid crystal layer therebetween,   a circuit configured to apply voltages to the first sub-pixel electrode and the second sub-pixel electrode,
 wherein when voltages V1 and V2 are respectively applied across the liquid crystal layers of the first and second sub-pixels, such that the first sub-pixel and the second sub-pixel display one of a plurality of grayscales in cooperation with each other, a ratio of V2/V1 for a first value of V1, which is accompanied by a first value of V2, is less than the ratio of V2/V1 at a second relatively greater value of V1, which is accompanied by a second relatively greater value of V2, and 
 wherein, at least at the second relatively greater value of V1, values of V1 and V2 are mutually different, and the value of V1 is larger than the value of V2. 
   
     
     
       13. The liquid crystal display according to claim 12, wherein a first switching element and a second switching element are respectively connected to the first and second sub-pixel electrodes and wherein a single scan line is commonly connected to the first and second switching elements. 
     
     
       14. The liquid crystal display according to claim 12, wherein the each of the plurality of pixels includes four domains which are approximately 90 degrees different in azimuth direction in which their liquid crystal molecules incline when a voltage is applied across the liquid crystal layers. 
     
     
       15. The liquid crystal display according to claim 14, wherein the azimuth directions of the four domains are upper right, upper left, lower left, and lower right. 
     
     
       16. The liquid crystal display according to claim 12, further comprising:
 a first switching element and a second switching element respectively connected to the first and second sub-pixel electrodes;   at least one scan line connected to the first and second switching elements; and   a first signal line and a second signal line respectively connected to the first and second switching elements.   
     
     
       17. The liquid crystal display according to claim 13, further comprising:
 a first signal line and a second signal line respectively connected to the first and second switching elements.   
     
     
       18. The liquid crystal display according to claim 12, wherein as a value of V1 increases above a voltage value of V1, a difference between values of V1 and V2 decreases. 
     
     
       19. The liquid crystal display according to claim 12, wherein as a value of V1 increases below a voltage value of V1, a difference between values of V1 and V2 remains constant. 
     
     
       20. A display method for a liquid crystal display used in a normally black mode, the method comprising:
 supplying a scan signal voltage to at least one scan line to turn on a first and a second switching element connected to the at least one scan line, the first switching element and second switching element respectively being further connected to a first sub-pixel electrode forming a first sub-pixel of a pixel and a second sub-pixel electrode forming a second sub-pixel of the pixel, the first sub-pixel electrode and the second sub-pixel electrode forming a pixel, wherein a first liquid crystal capacitor is formed by the first sub-pixel electrode, a counter electrode and a liquid crystal layer therebetween and wherein a second liquid crystal capacitor is formed by the second sub-pixel electrode, the counter electrode and a liquid crystal layer therebetween; and   respectively applying voltages V1 and V2 across the liquid crystal layers of the first and second sub-pixels such that the first sub-pixel and the second sub-pixel display one of a plurality of grayscales in cooperation with each other, a ratio of V2/V1 for a first value of V1, which is accompanied by a first value of V2, is less than the ratio of V2/V1 at a second relatively greater value of V1, which is accompanied by a second relatively greater value of V2, and such that, at least at the second relatively greater value of V1, values of V1 and V2 are mutually different, and the value of V1 is larger than the value of V2.   
     
     
       21. The display method according to claim 20, wherein the scan signal voltage is applied to a single scan line commonly connected to the first and second switching elements. 
     
     
       22. The display method according to claim 20, wherein the liquid crystal display includes a plurality of pixels, and wherein each of the plurality of pixels includes four domains which are approximately 90 degrees different in azimuth direction in which their liquid crystal molecules incline when a voltage is applied across the liquid crystal layers. 
     
     
       23. The display method according to claim 22 wherein the azimuth directions of the four domains are upper right, upper left, lower left, and lower right. 
     
     
       24. The display method according to claim 20, wherein as V1 increases above a voltage value of V1, a difference between values of V1 and V2 decreases. 
     
     
       25. The display method according to claim 20, wherein as V1 increases below a voltage value of V1, a difference between values of V1 and V2 remains constant.