Patent Publication Number: US-2013250194-A1

Title: Autostereoscopic display apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 101109605, filed on Mar. 21, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an autostereoscopic display apparatus, and more particularly to a parallax barrier cell of an autostereoscopic display apparatus. 
     2. Description of the Related Art 
     A three-dimensional (3D) image is formed according to the principle of autostereoscopic vision by the eyes of a human being. Binocular parallax, which is generated by the distance of about 65 mm between a human&#39;s left and right eyes, can be considered the most important factor inducing the perception of depth of field. 
     In recent years, 3D video content, in which video can be viewed in a three-dimensional manner, has attracted much development attention. There are two types of systems for viewing 3D video: a glasses system using polarizing filter glasses (passive polarized glasses) or shutter glasses; and a naked-eye system that does not require glasses, instead using other methods such as a lenticular system or a parallax barrier system. 
     In a two-dimensional/three-dimensional switchable display system that uses the parallax barrier method, Twisted Nematic (TN) liquid crystals are usually used to perform barrier switching. However, a transitive region between a black region and a white region is generated when the TN liquid crystals of a conventional barrier cell are driven. Furthermore, a tangle phenomenon caused by the twists of TN liquid crystals, can easily generate a larger value in brightness at two sides of the transitive region, thereby a discontinuous brightness phenomenon is generated. 
     Therefore, an autostereoscopic display apparatus that has a smaller transitive region and is able to avoid a discontinuous brightness phenomenon is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     Autostereoscopic display apparatus are provided. An embodiment of an autostereoscopic display apparatus is provided. The autostereoscopic display apparatus comprises a liquid-crystal panel and a barrier cell. The barrier cell comprises: a first substrate, comprising a first electrode; a second substrate, comprising a second electrode and a third electrode, wherein the second and third electrodes are separated from each other; and a liquid-crystal layer disposed between the first and second substrates. A first black region corresponding to the overlap of the first and third electrodes is formed when a first voltage is applied to the first and second electrodes and a second voltage is applied to the third electrode. 
     Furthermore, another embodiment of an autostereoscopic display apparatus is provided. The autostereoscopic display apparatus comprises a liquid-crystal panel and a barrier cell. The barrier cell comprises: a first substrate, comprising a first electrode; a second substrate, comprising a second electrode and a plurality of third electrodes, wherein the second electrode and the third electrodes are separated from each other, and each of the third electrodes is floating and is surrounded by the second electrode; and a liquid-crystal layer disposed between the first and second substrates. A black region corresponding to the overlap of the first and second electrodes is formed when a first voltage is applied to the first electrode and a second voltage is applied to the second electrode. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a two-dimensional/three-dimensional switchable autostereoscopic display apparatus according to an embodiment of the invention; 
         FIG. 2A  shows a barrier cell according to an embodiment of the invention; 
         FIG. 2B  shows a circuit schematic diagram illustrating a section line A-A′ of the barrier cell of  FIG. 2A ; 
         FIG. 3  shows a schematic diagram illustrating equal potential lines and liquid-crystal distribution of the circuit R 1  in the barrier cell of  FIG. 2B ; 
         FIG. 4A  shows a barrier cell according to another embodiment of the invention; 
         FIG. 4B  shows a circuit schematic diagram illustrating a section line B-B′ of the barrier cell of  FIG. 4A ; 
         FIG. 5  shows a simple circuit diagram of the electrodes of  FIG. 4B ; 
         FIG. 6A  shows a barrier cell according to another embodiment of the invention; 
         FIG. 6B  shows a circuit schematic diagram illustrating a section line C-C′ of the barrier cell of  FIG. 6A ; 
         FIG. 6C  shows a circuit schematic diagram illustrating a section line D-D′ of the barrier cell of  FIG. 6A . 
         FIG. 7A  shows a brightness schematic diagram of the barrier cell of  FIG. 6A ; 
         FIG. 7B  shows another brightness schematic diagram of the barrier cell of  FIG. 6A ; and 
         FIG. 8  shows a schematic illustrating an arrangement of a color filter and a barrier cell of a single pixel of an autostereoscopic display apparatus according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 1  shows a two-dimensional/three-dimensional switchable autostereoscopic display apparatus  100  according to an embodiment of the invention. The autostereoscopic display apparatus  100  comprises a polarizer  110 , a barrier cell  120 , a liquid-crystal panel  130 , and a back light  170 . The barrier cell  120  comprises an upper substrate  122 , a liquid-crystal layer  124  and a lower substrate  126 , wherein the liquid-crystal layer  124  comprises a plurality of Twisted Nematic (TN) liquid crystals. The liquid-crystal panel  130  comprises a polarizer  140 , a liquid-crystal array  150 , and a polarizer  160 . The liquid-crystal array  150  comprises a Thin Film Transistor (TFT) substrate (not shown), a color filter substrate (not shown) and a liquid-crystal layer (not shown) disposed between the TFT substrate and the color filter substrate, wherein the color substrate may be a glass substrate or a polymer substrate, and the liquid-crystal layer may be formed by TN liquid crystals, Vertical Alignment (VA) liquid crystals or In place Switch (IPS) liquid crystals. In the embodiment, the upper substrate  122  and the lower substrate  126  are the glass substrates. Furthermore, the upper substrate  122  and the lower substrate  126  may be the polymer substrates. Moreover, the polarizer  110  is an upper polarizer, the polarizer  140  is a middle polarizer and the polarizer  150  is a lower polarizer. In the three-dimensional mode of the autostereoscopic display apparatus  100 , the switching state of the barrier cell  120  is controlled by applying voltage to the barrier cell  120 , so as to selectively block the light from the back light  170  and limit the emergence direction of the light. Thus, the left and right eyes respectively receive the left eye image and the right eye image for generating stereo vision. In a two-dimensional mode of the autostereoscopic display apparatus  100 , no voltage is applied to the barrier cell  120 , so as to hold a normally white state for the TN liquid crystals. Therefore, an image of the liquid-crystal panel  130  is completely passed, so as to display a two-dimensional image. Furthermore, a wide-view file is further disposed on the polarizer  110 ,  140  or  160 , so that ISO CR range is spread to reach a contrast balance. 
       FIG. 2A  shows a barrier cell  200  according to an embodiment of the invention. The barrier cell  200  comprises three electrodes  210 ,  220  and  230 , wherein the electrodes  210 ,  220  and  230  are formed by transparent electrodes, e.g. Indium Tin Oxide (ITO). In the embodiment, the electrode  210  is disposed on an upper substrate of the barrier cell  200  (e.g.  122  of  FIG. 1 ), and the electrodes  220  and  230  are disposed on a lower substrate of the barrier cell  200  (e.g.  126  of  FIG. 1 ). It should be noted that the electrodes  220  and  230  are disposed on a common plane and separated from each other. In addition, finger parts of the electrodes  220  and  230  are mutually interlaced and separated by a slit S 1 . Furthermore, the electrodes  220  and  230  and the slit S 1  are entirely overlaid by the electrode  210 . In the three-dimensional mode of the embodiment, the barrier cell  200  is turned on when a common voltage V COM  is applied to the electrodes  210  and  220  and a driving voltage V D  is applied to the electrode  230 , wherein a difference between the common voltage V COM  and the driving voltage V D  is larger than a threshold voltage and is also larger than 90% level of grey scale. Thus, the TN liquid crystals between the electrodes  210  and  230  form a black region Z B  (the black region Z B  corresponds to the overlap of electrode  210  and  230 ), and the TN liquid crystals between the electrodes  210  and  220  form a white region Z W  (the white region Z W  corresponds to the overlap of electrode  210  and  220 ). The common voltage may be a DC grounding voltage (e.g. 0V), or a DC/AC low voltage (e.g. DC 5V, AC 2.5V). The black region Z B  and the white region Z W  are the optical results when light pass through polarizer and liquid crystal layer. Furthermore, the barrier cell  200  holds the normally white state of the TN liquid crystals as a two-dimensional mode when the driving voltage V D  is applied to the electrodes  220  and  230  simultaneously. In one embodiment, the electrode  210  is disposed on the lower substrate of the barrier cell  200 , and the electrodes  220  and  230  are disposed on the upper substrate of the barrier cell  200 . 
       FIG. 2B  shows a circuit schematic diagram illustrating a section line A-A′ of the barrier cell  200  of  FIG. 2A . In  FIG. 2B , the common voltage V com  is applied to the electrodes  210  and  220  and the driving voltage V D  is applied to the electrode  230 , such that the barrier cell  200  is switched to three-dimensional mode. An equivalent capacitor of the liquid-crystal layer between the electrodes  210  and  220  is C 1 , and an equivalent capacitor of the liquid-crystal layer between the electrodes  210  and  230  is C 2 , wherein the voltage difference of the equivalent capacitor C 1  is 0, thereby the capacitance of the equivalent capacitor C 1  is 0. Compared with a conventional barrier cell, the equivalent capacitor C 1  disposed on the barrier cell  200  can minimize the transitive region Z T  between the black region Z B  and the white region Z W  and improve image X-talk. In the embodiment, the transitive region Z T  is defined as a region between the 10% level and the 90% level on the grey scale.  FIG. 3  shows a schematic diagram illustrating equal potential lines and liquid-crystal distribution of the circuit R 1  in the barrier cell  200  of  FIG. 2B . Referring to  FIG. 2B  and  FIG. 3  together, in an electric field distribution diagram, the equivalent capacitor C 1  makes the equal potential lines concentrate in the white region Z W  and the transitive region Z T . In other words, an original state that no voltage is applied is held by the liquid crystals within a region of the equivalent capacitor C 1 , so that the transitive region Z T  between the white region Z W  and the black region Z B  is narrowed. Therefore, for a conventional barrier cell without the equivalent capacitor C 1 , the equal potential lines and the transitive region Z T  will extend to the white region Z W , thus the width of the transitive region Z T  is larger than that of the embodiment. 
       FIG. 4A  shows a barrier cell  300  according to another embodiment of the invention. The barrier cell  300  comprises an electrode  310 , an electrode  320  and a plurality of electrodes  330 , wherein the electrodes  310 ,  320  and  330  are formed by transparent electrodes. The electrode  310  is disposed on an upper substrate of the barrier cell  300  (e.g.  122  of  FIG. 1 ), and the electrodes  320  and  330  are disposed on a lower substrate of the barrier cell  300  (e.g.  126  of  FIG. 1 ). It should be noted that the electrodes  320  and  330  are disposed on a common plane and separated from each other. In addition, each of the electrodes  330  is a bar and is surrounded by the electrode  320 , wherein a slit between the electrode  320  and each electrode  330  is slit S 2 . Moreover, the electrodes  320  and  330  and the slit S 2  are entirely overlaid by the electrode  310 . It should be noted that each of the electrodes  330  is floating, i.e. not electrically connect to other conductor electrodes. In the three-dimensional mode of the embodiment, when the common voltage V com  is applied to the electrode  310  and the driving voltage V D  is applied to the electrode  320 , the barrier cell  300  is turned on. Thus, TN liquid crystals between the electrodes  310  and  320  form a black region Z B  corresponding to the overlap of electrode  310  and  320 , and the TN liquid crystals between the electrodes  310  and  330  form a white region Z W  corresponding to the overlap of the electrode  310  and  330 . In one embodiment, the electrode  310  is disposed on the lower substrate of the barrier cell  300 , and the electrodes  320  and  330  are disposed on the upper substrate of the barrier cell  300 . 
       FIG. 4B  shows a circuit schematic diagram illustrating a section line B-B′ of the barrier cell  300  of  FIG. 4A . In  FIG. 4B , the common voltage V com  is applied to the electrode  310  and the driving voltage V D  is applied to the electrode  320 , such that the barrier cell  300  is switched on. An equivalent capacitor of the liquid-crystal layer between the electrodes  310  and  320  is C 3 , and an equivalent capacitor of the liquid-crystal layer between the electrodes  310  and  330  is C 4 . Furthermore, an equivalent capacitor of the liquid-crystal layer between the electrodes  320  and  330  is C 5 , wherein a voltage V float  of the electrode  330  is determined by the equivalent capacitors C 4  and C 5 .  FIG. 5  shows a simple circuit diagram of the electrodes  310 ,  320  and  330  of  FIG. 4B  in order to simplify the description. In general, the capacity of a capacitor is in direct ratio to the area A of its metal plate and the dielectric constant ε, and is in an inverse ratio of the distance d between the two metal plates, i.e. 
     
       
         
           
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     Therefore, the equivalent capacitor C 4  is increased when the distance between the electrodes  310  and  330  is decreased. Moreover, the equivalent capacitor C 4  is also increased when the area of the electrode  330  is increased. In addition, the equivalent capacitor C 5  is decreased when the slit S 2  between the electrodes  320  and  330  is increased. Thus, the equivalent capacitor C 4  is much larger than the equivalent capacitor C 5  (i.e. C 4 &gt;&gt;C 5 ). Therefore, the equivalent capacitor C 5  is about equal to a total capacitor C total  according to the following formula: 
     
       
         
           
             
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     Furthermore, the voltage V float  of the electrode  330  is about 0V according to the following formula: 
     
       
         
           
             
               
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     Where Q represents the charges stored in the total capacitor C total . As describe above, when the voltage V float  of the electrode  330  is 0V, the equivalent capacitor C 4  of the barrier cell  300  can minimize a transitive region Z T  between the black region Z B  and the white region Z W  and improve image X-talk. 
       FIG. 6A  shows a barrier cell  400  according to another embodiment of the invention. An autostereoscopic display apparatus equipped with the barrier cell  400  can be implemented in a portable electronic product, such as a smart phone or a tablet. The autostereoscopic display apparatus is able to provide a three-dimensional image when the portable electronic product is operating in a landscape mode or a portrait mode. The barrier cell  400  comprises the electrodes  410 ,  420 ,  430  and  440 , wherein the electrodes  410 ,  420 ,  430  and  440  are formed by transparent electrodes. The electrodes  410  and  420  are disposed on an upper substrate of the barrier cell  400  (e.g.  122  of  FIG. 1 ), and the electrodes  430  and  440  are disposed on a lower substrate of the barrier cell  400  (e.g.  126  of  FIG. 1 ). It should be noted that the electrodes  410  and  420  are disposed on a common plane and separated from each other, and finger parts of the electrodes  410  and  420  are mutually interlaced and separated by a slit S 3 . In addition, the electrodes  430  and  440  are disposed on a common plane and separated from each other, and finger parts of the electrodes  430  and  440  are mutually interlaced and separated by a slit S 4 . According to various operation modes of the portable electronic product, the corresponding voltages are applied to the electrodes  410 - 440 , so as to control the switching state of the barrier cell  400 . For example, if the portable electronic product is operating in the three-dimensional display landscape mode, the barrier cell  400  is turned on when the common voltage V com  is applied to the electrodes  410 ,  420  and  430  and the driving voltage V D  is applied to the electrode  440 . Thus, TN liquid crystals between the electrodes  440  and  410  and between the electrodes  440  and  420  may form the black regions Z B  corresponding to the overlap of the electrode  440  and  420 , and the TN liquid crystals between the electrodes  430  and  410  and between the electrodes  430  and  420  may form the white regions Z W  corresponding to the overlap the of electrode  430  and  420 . If the portable electronic product is operating in three-dimensional display portrait mode, the barrier cell  400  is turned on when the common voltage V com  is applied to the electrodes  420 ,  430  and  440  and the driving voltage is applied to the electrode  410 . Thus, TN liquid crystals between the electrodes  410  and  430  and between the electrodes  410  and  440  form the black regions Z B  corresponding to the overlap of the electrode  410  and  440 , and the TN liquid crystals between the electrodes  420  and  430  and between the electrodes  420  and  440  form the white regions Z W  corresponding to the overlap of the electrode  410  and  440 . Furthermore, in the embodiment, the slits S 3  and S 4  have the same distance. In one embodiment, the electrodes  410  and  420  are disposed on the lower substrate of the barrier cell  400 , and the electrodes  430  and  440  are disposed on the upper substrate of the barrier cell  400 . 
       FIG. 6B  shows a circuit schematic diagram illustrating a section line C-C′ of the barrier cell  400  of  FIG. 6A . In  FIG. 6B , the common voltage V com  is applied to the electrodes  420  and  430  and the driving voltage V D  is applied to the electrode  440 , such that the barrier cell  400  is switched on. Similarly, a capacitor between the electrodes  420  and  430  can minimize the transitive region Z T  between the black region Z B  and the white region Z W  and improve image X-talk.  FIG. 6C  shows a circuit schematic diagram illustrating a section line D-D′ of the barrier cell  400  of  FIG. 6A . In  FIG. 6C , the common voltage V com  is applied to the electrodes  420  and  440  and the driving voltage V D  is applied to the electrode  410 , such that the barrier cell  400  is switched on. Similarly, a capacitor between the electrodes  420  and  440  can minimize the transitive region Z T  between the black region Z B  and the white region Z W  and improve image X-talk. 
     Referring back to  FIG. 6A , the light leak phenomenon (as shown in label  450 ) caused by a larger slit can be avoided by narrowing the distances of the slits S 3  and S 4 , for example, the slits S 3  and S 4  are smaller than 7 um. Thus, the discontinuous line within the black region also disappears. An overdriving voltage may be applied to the electrode except the narrower slit, i.e. the voltage levels of the common voltage V com  and the driving voltage V D  are increased, so as to avoid the light leak phenomenon. Furthermore, the overdriving manner can decrease the liquid-crystal tangle phenomenon and improve the discontinuous brightness phenomenon.  FIG. 7A  shows a brightness schematic diagram of the barrier cell  400  of  FIG. 6A . In  FIG. 7A , the liquid-crystal layer of the barrier cell  400  is formed by low driving voltage TN liquid crystals and the common voltage V com  is 0, wherein a curve  70  represents a brightness corresponding to the normal driving voltage (e.g. V D ±2.5V), and a curve  72  represents a brightness corresponding to the overdriving voltage (e.g. V D ±5V). Compared to the discontinuous brightness phenomenon of the curve  70  (as shown in an arrow R 2 ), the discontinuous brightness phenomenon of the curve  72  (as shown in an arrow R 3 ) is noticeably decreased.  FIG. 7B  shows another brightness schematic diagram of the barrier cell  400  of  FIG. 6A . In  FIG. 7B , the liquid-crystal layer of the barrier cell  400  is formed by normal TN liquid crystals and the common voltage V com  is 0, wherein a curve  74  represents a brightness corresponding to a normal driving voltage (e.g. V D ±5V), and a curve  76  represents a brightness corresponding to an overdriving voltage (e.g. V D ±7V). Compared to the discontinuous brightness phenomenon of the curve  74  (as shown in an arrow R 4 ), the discontinuous brightness phenomenon of the curve  76  (as shown in an arrow R 5 ) is noticeably decreased. 
       FIG. 8  shows a schematic illustrating the arrangement of a color filter  510  and the barrier cell  520  of a single pixel of an autostereoscopic display apparatus according to an embodiment of the invention, wherein the autostereoscopic display apparatus is implemented in a portable electronic product that is able to operate in a landscape mode and a portrait mode. In  FIG. 8 , the pixel  500  comprises three primary colors (e.g. red (R), green (G) and blue (B)). The color filter  510  comprises a 3×3 array formed by 9 sub-pixels  512 R,  512 G,  512 B,  514 R,  514 G,  514 B,  516 R,  516 G and  516 B. In the embodiment, the 9 sub-pixels are arranged in the array in a mosaic pattern. In the array of the color filter  510 , each row and each column has the 3 sub-pixels corresponding to the RGB primary colors, respectively. For example, the first row has the red color sub-pixel  512 R, the green color sub-pixel  512 G and the blue color sub-pixel  512 B, and the first column has the red color sub-pixel  512 R, the blue color sub-pixel  514 B and the green color sub-pixel  516 G. It should be noted that no sub-pixels with the same primary color are arranged in the same row and the same column. Furthermore, in response to the arrangement of the sub-pixel array of the color filter  510 , the barrier cell  520  also comprises 9 barrier sub-cells, wherein the structure of each sub-cell may be the barrier cell  200  of  FIG. 2A , the barrier cell  300  of  FIG. 4A  and the barrier cell  400  of  FIG. 6A . In one embodiment, the pixel  500  may comprise four primary colors (e.g. red (R), green (G), blue (B) and white (W)), and the color filter  510  may comprise a 4×4 array formed by 16 sub-pixels. Similarly, no sub-pixels with the same primary color are arranged in the same row and the same column. Therefore, the effects on color development are similar in landscape mode and portrait mode of the portable electronic product. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.