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, comprising a plurality of pixels each of which has a liquid crystal layer and a plurality of electrodes for applying an electric field across the liquid crystal layer, wherein:
 the plurality of pixels are arranged in a matrix (rp, cq) with a plurality of rows (1 to rp) and plurality of columns (1 to cq) and each pixel is expressed as P (p, q), where 1≤p≤rp and 1≤q≤cq;   each of the plurality of pixels has at least two sub-pixels SPa (p, q), SPb (p, q), arranged in the column direction;   the at least two sub-pixels differ from each other in brightness when displaying an intermediate grayscale;   the at least two sub-pixels include two sub-pixels SPa (p, q) and SPb (p, q);   SPa (p, q) and SPb (p, q) 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 connected electrically to the liquid crystal capacitor and having a storage capacitor counter electrode;   the counter electrode is a single electrode shared by SPa (p, q) and SPb (p, q), and the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) are electrically independent of each other;   the liquid crystal display comprises two switching elements provided for SPa (p, q) and SPb (p, q), respectively;   the two switching elements are turned on and off by a common scan line signal voltage; a common display signal voltage is applied to the respective sub-pixel electrodes of SPa (p, q) and SPb (p, q) when the two switching elements are on; voltages of the respective storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) change after the two switching elements are turned off; and   the sub-pixels are arranged so that, in each vertical scanning period, any two sub-pixels which pertain to a same pixel or different pixels and which are adjacent to each other in the column direction differ from each other in terms of an exclusive disjunction of: a) the direction of the electric field applied across the liquid crystal layer; and b) the direction of the change of the voltage of the storage capacitor counter electrode, where a logical value of a) the direction of the electric field applied across the liquid crystal layer is true (T) if the direction is toward the counter electrode and false (F) if the direction is toward the sub-pixel electrode, and a logical value of b) the direction of the change of the voltage of the storage capacitor counter electrode is true (T) if the change is an increase and false (F) if the change is a decrease.    
     
     
       13. The liquid crystal display according to claim 12, wherein the position of the brightest of the at least two sub-pixels arranged in the column direction changes periodically in the row direction in the case of a pixel in an arbitrary row, but it is constant in the case of a pixel in an arbitrary column.  
     
     
       14. The liquid crystal display according to claim 13, wherein in each of the plurality of pixels, correspondence between the order of brightness of the at least two sub-pixels and position of the at least two sub-pixels arranged in the column direction changes in the row direction periodically in the case of a pixel in an arbitrary row, but it is constant in the case of a pixel in an arbitrary column.  
     
     
       15. The liquid crystal display according to claim 13, wherein when displaying an intermediate grayscale, the at least two sub-pixels in each of the plurality of pixels are placed such that sub-pixels equal in the order of brightness will not adjoin each other.  
     
     
       16. The liquid crystal display according to claim 12, wherein when displaying an intermediate grayscale:
 the brightest sub-pixel in a pixel P (p, q) in an arbitrary row is SPa (p, q) in the case where q is an odd number and SPb (p, q) in the case where q is an even number, or SPb (p, q) in the case where q is an odd number and SPa (p, q) in the case where q is an even number; and   the brightest sub-pixel in a pixel P (p, q) in an arbitrary column is either SPa (p, q) or SPb (p, q) regardless of whether p is an odd number.    
     
     
       17. The liquid crystal display according to claim 16, wherein when displaying an intermediate grayscale, the at least two sub-pixels in each of the plurality of pixels are placed such that the brightest sub-pixels form a checkered pattern.  
     
     
       18. The liquid crystal display according to claim 12, wherein:
 direction of the electric field applied across the liquid crystal layers in the plurality of pixels is reversed every vertical scanning period; and   when displaying an intermediate grayscale, the direction of the electric field is reversed periodically in the row direction in the case of pixels in an arbitrary row.    
     
     
       19. The liquid crystal display according to claim 18, wherein the direction of the electric field is reversed every pixel in the row direction in the case of pixels in an arbitrary row.  
     
     
       20. The liquid crystal display according to claim 18, wherein the direction of the electric field is reversed every two pixels in the row direction in the case of pixels in an arbitrary row.  
     
     
       21. The liquid crystal display according to claim 12, wherein:
 the liquid crystal display operates in normally black mode, 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, relationships ΔV12 (gk)>0 volts and ΔV12 (gk)≥ΔV12 (gk+1) are satisfied if it is assumed that ΔV12 (gk)=V1 (gk)−V2 (gk), where V1 (gk) and V2 (gk) are root-mean-square voltages applied to the liquid crystal layers of the first sub-pixel and the second sub-pixel, respectively.    
     
     
       22. The liquid crystal display according to claim 21, wherein a relationship ΔV12 (gk)≥ΔV12 (gk+1) is satisfied.  
     
     
       23. The liquid crystal display according to claim 12, wherein the changes in the voltages of the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) are equal in amount and opposite in direction.  
     
     
       24. The liquid crystal display according to claim 12, wherein the voltages of the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) are oscillating voltages 180 degrees out of phase with each other.  
     
     
       25. The liquid crystal display according to claim 24, wherein the oscillating voltages of the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) each have a period approximately equal to one horizontal scanning period.  
     
     
       26. The liquid crystal display according to claim 24, wherein the oscillating voltages of the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) each have a period shorter than one horizontal scanning period.  
     
     
       27. The liquid crystal display according to claim 24, wherein the oscillating voltages of the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) are approximately equal within any horizontal scanning period if averaged over the period.  
     
     
       28. The liquid crystal display according to claim 26, wherein the period of the oscillation is one-half of one horizontal scanning period.  
     
     
       29. The liquid crystal display according to claim 24, wherein the oscillating voltages are rectangular waves with a duty ratio of 1:1.  
     
     
       30. The liquid crystal display according to claim 12, wherein SPa (p, q) and SPb (p, q) have different areas, of which the smaller area belongs to SPa (p, q) or SPb (p, q) whichever has a larger root-mean-square voltage applied to its liquid crystal layer.  
     
     
       31. The liquid crystal display according to claim 12, wherein the area of SPa (p, q) and area of SPb (p, q) are practically equal.  
     
     
       32. The liquid crystal display according to claim 12, wherein the storage capacitor is formed by the storage capacitor counter electrode, an insulating layer, and a storage capacitor electrode opposing the storage capacitor counter electrode via the insulating layer and connected electrically to the sub-pixel electrode.  
     
     
       33. A liquid crystal display, comprising a plurality of pixels each of which has a liquid crystal layer and a plurality of electrodes for applying an electric field across the liquid crystal layer, wherein:
 the plurality of pixels are arranged in a matrix (rp, cq) with a plurality of rows (1 to rp) and plurality of columns (1 to cq) and each pixel is expressed as P (p, q), where 1≤p≤rp and 1≤q≤cq;   each of the plurality of pixels has at least two sub-pixels SPa (p, q), SPb (p, q), arranged in the column direction;   the at least two sub-pixels differ from each other in brightness when displaying an intermediate grayscale;   the at least two sub-pixels include two sub-pixels SPa (p, q) and SPb (p, q);   SPa (p, q) and SPb (p, q) 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 connected electrically to the liquid crystal capacitor and having a storage capacitor counter electrode;   the counter electrode is a single electrode shared by SPa (p, q) and SPb (p, q), and the storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) are electrically independent of each other;   the liquid crystal display comprises two switching elements provided for SPa (p, q) and SPb (p, q), respectively;   the two switching elements are turned on and off by a common scan line signal voltage; a common display signal voltage is applied to the respective sub-pixel electrodes of SPa (p, q) and SPb (p, q) when the two switching elements are on; voltages of the respective storage capacitor counter electrodes of SPa (p, q) and SPb (p, q) change after the two switching elements are turned off; and   in each vertical scanning period, any two sub-pixels which pertain to a same pixel or different pixels and which are adjacent to each other in the column direction are opposite in the direction of the electric field applied across the liquid crystal layer and equal in the direction of the change of the voltage of the storage capacitor counter electrode, or, equal in the direction of the electric field applied across the liquid crystal layer and opposite in the direction of the change of the voltage of the storage capacitor counter electrode.