Abstract:
A viewing-angle adjustable liquid crystal display includes a display panel, a backlight unit, and a sidelight unit. The backlight unit is located under the sidelight unit, and the sidelight unit is disposed under the display panel. The sidelight unit includes a first sidelight source and a light-guide plate. The first sidelight source is disposed at one end of the light-guide plate. The displaying method includes providing direct light to the display panel in response to the narrow-viewing-angle-mode signal; and providing scattering light to the display panel in response to the wide-viewing-angel-mode signal.

Description:
This application claims the benefit of Taiwan application Ser. No. 93135766, filed Nov. 19, 2004, the subject matter of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates in general to a viewing-angle adjustable liquid crystal display and method for adjusting same, and more particularly to a viewing-angle adjustable liquid crystal display, which can provide the required viewing-angle mode for the user by electrical signal switching, and method for adjusting same. 
   2. Description of the Related Art 
   As technology makes progress, consumers have more opportunities of using mobile devices equipped with liquid crystal displays, such as mobile phones or notebook computers, in public regions. As using the mobile device in a public region, the consumers often need the mobile device to have a viewing-angle adjustable display so as to keep his/her secret. At present, there are three kinds of well-known liquid crystal display viewing-angle control methods. 
     FIG. 1  is a schematic diagram of using shutter structure to adjust the liquid crystal display viewing-angle. Referring to  FIG. 1 , the shutter structure  110  is disposed in front of the liquid crystal display  100  and has the shutters arranged in parallel. By adjusting the height h of the shutter structure  110  and the distance I between two adjacent shutters, the light L emitted by the display  100  can be restricted to reach eyes of the observers at some specific viewing-angles. Therefore, only within the viewing angle region spreading the angle ⊖ as shown in the figure, the light L can pass the absorbing materials  110  and the observer at these viewing angles can thus see the images on the display  100  while the light L emitted beyond the viewing-angle region of the angle ⊖, will be absorbed by the absorbing materials  110 . 
   However, the viewing-angle control method has the following disadvantages. The shutter structure  110 , as used, should be additionally configured at the exterior of the display, thereby causing the inconvenience in usage. Since a part of the light L is absorbed by the shutter structure  110 , the display luminance will be lowered down at least a half. Moreover, the shutter structure  110  can only provide a left side viewing-angle mode or a right side viewing-angle mode, which will not meet the user&#39;s requirement of various view-angle modes, for example, only the users at the front view and the left-side view can observe the displayed images. 
     FIG. 2A  and  FIG. 2B  are schematic diagrams of using a light scattering device to adjust the liquid crystal display viewing-angle in prior art. The light scattering device  210 , such as a polymer dispersed liquid crystal (PDLC) layer, in which light scattering features can be adjusted, is disposed between the parallel backlight (Lb) device (not shown in the figure) and the liquid crystal cell  200 . By adjusting the voltage applied to the light scattering device  210 , the narrow viewing-angle mode and the wide viewing-angle mode can be provided. As shown in  FIG. 2A , under the narrow viewing-angle mode, the light scattering device  210  is in the power on state, and appears transparent so that the backlight Lb is maintained parallel after passing the light scattering device  210  to reach the liquid crystal cell  200 . Therefore, only the front view observer can see the displayed images. As shown in  FIG. 2B , under the wide viewing-angle mode, the light scattering device  210  is in the power off state, the backlight Lb is scattered to form the scattering light Ls and enter the liquid crystal layer  200  so that the observers at every viewing angle can see the displayed images. 
   However, this viewing angle control method has the following disadvantages. When the light scattering device  210  is switched to the power on state, a part of the backlight Lb will be reflected as passing the light scattering device  210 , thereby reducing the luminance of the liquid crystal panel  200 . In addition, as the above-mentioned example, this viewing angle control method can only provide the narrow viewing angle mode for front view observers, but not for the user at any other viewing angle, thereby reducing the available options in viewing-angle adjusting. 
     FIG. 3A  and  FIG. 3B  are schematic diagrams of controlling viewing angles by using an extra alignment layer in the prior art. By adjusting the rubbing direction of the alignment layer additionally disposed on the liquid crystal display, a wide viewing angle mode and a narrow viewing angle mode can be provided. As shown in  FIG. 3A , under the narrow viewing-angle mode, the front view observer can see the displayed image  300  while the side view observer cannot distinguish the display image  300  for a specific picture  310  having bright and dark stripes in turn covers the image  300  as shown in  FIG. 3B . By doing so, the viewing-angle adjusting purpose can be achieved. 
   However, as shown in the above-mentioned three examples, the present viewing angle adjustable liquid crystal display structures have the disadvantage of the luminance and bright contrast deviation as the viewing angle modes are switched. Also they cannot provide the narrow viewing angle mode for users at other viewing-angles except the front view ones. Therefore, such viewing angle adjusting methods are not satisfied. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide a viewing-angle adjustable liquid crystal display and method for adjusting same. The light valve is disposed between the backlight module and the liquid crystal panel and a sidelight unit is disposed between the light valve and the liquid crystal panel. As the display operates in the wide viewing-angle mode, the backlight module and the sidelight unit are powered on while in the narrow viewing-angle mode only the backlight module or the sidelight unit is powered on. Therefore, the display can provide the required viewing-angle mode for the user. 
   The invention achieves the above-identified object by providing a viewing angle adjustable liquid crystal display including a display panel, a sidelight unit, and a backlight unit. The sidelight unit, disposed under the display panel, includes a light guide plate and a first sidelight source. The first sidelight source is disposed at one end of the light guide plate. The backlight unit is disposed under the sidelight unit. 
   The invention achieves the above-identified object by providing a method for adjusting the viewing angle of a liquid crystal display. The method includes providing direct light to the display panel in response to a narrow-viewing-angle-mode signal; and providing scattering light to the display panel in response to a wide-viewing-angle-mode signal. 
   Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of using shutter structure to adjust the liquid crystal display viewing-angle. 
       FIG. 2A  and  FIG. 2B  are schematic diagrams of using light scattering device to adjust the liquid crystal display viewing-angle. 
       FIG. 3A  and  FIG. 3B  are schematic diagrams of controlling viewing angles by using an extra alignment layer. 
       FIG. 4A  is a schematic cross-sectional view of the liquid crystal display according to the first embodiment of the invention. 
       FIG. 4B  is a flow chart of the method for adjusting the viewing angle of the liquid crystal display according to the first embodiment of the invention. 
       FIG. 4C  is a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode in  FIG. 4A . 
       FIG. 4D  is a schematic cross-sectional view of the liquid crystal display operating under the wide viewing-angle mode in  FIG. 4A   
       FIG. 5A  is a schematic cross-sectional view of the liquid crystal display according to the second embodiment of the invention. 
       FIG. 5B  is a schematic diagram of geometrical structure of the light-guide plate in  FIG. 5A . 
       FIG. 5C  is a flow chart of the method for adjusting the viewing angle of the liquid crystal display according to the second embodiment of the invention. 
       FIG. 5D  is a schematic cross-sectional view of the liquid crystal display operating under the wide viewing-angle mode in  FIG. 5A . 
       FIG. 5E  is a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode whose images can only be seen by the front-view and left-side view observers in  FIG. 5A . 
       FIG. 5F  is a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode whose images can only be seen by the left-side view observers. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, two embodiments are taken as examples for the viewing angle adjustable liquid crystal display of the invention. 
   Embodiment One 
   Referring to  FIG. 4A , a schematic cross-sectional view of the liquid crystal display according to the first embodiment of the invention is shown. The liquid crystal display  400  includes a backlight module  410 , a light valve  420 , a sidelight unit  430 , and a display panel  440 . The backlight module  410  can be a bottom lighting backlight module or a side lighting backlight module. The light valve  420  can be shutter structure made of light absorbing materials for confining the passing light within a specific region to generate approximately parallel light. The sidelight unit  430  includes a transparent light-guide plate  432  and a sidelight source  434 , such as lamps or light emitting diodes. The scattering light-guide plate  432  can be passed by the backlight generated from the backlight module  410  and can be used to scatter the light generated from the sidelight unit  434  to the display panel  440 . 
   Referring to  FIG. 4B , a flow chart of the method for adjusting the viewing angle of the liquid crystal display according to the first embodiment of the invention is shown. First, in step  450 , switch off the sidelight source  434  and provide the approximately parallel backlight to the display panel  440  by using the backlight module  410  and the light valve  420  in response to a narrow-viewing-angle-mode signal. In step  460 , provide scattering light to the display panel  440  by using the light-guide plate  432  to scatter the sidelight generated from the sidelight source  434  in response to a wide-viewing-angle-mode signal. 
   Referring to  FIG. 4C , a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode in  FIG. 4A  is shown. Under the narrow viewing-angle mode, the sidelight source  434  is switched off while the backlight module  410  is switched on. When the backlight Lb emitted from the backlight module  410  enters the light valve  420 , only the backlight Lb within a small viewing-angle region can pass the light valve  420  to form the approximately parallel backlight Lp. Therefore, only the front-view observer can see the information on the display  400  while observers at two sides cannot see anything. 
   Referring to  FIG. 4D , a schematic cross-sectional view of the liquid crystal display operating under the wide viewing-angle mode in  FIG. 4A  is shown. Under the wide viewing-angle mode, the backlight module  410  and the sidelight unit  434  are both switched-on. The backlight Lb passes the light valve  420  to form the approximately parallel backlight Lp while the light emitted by the sidelight source  434  is scattered by the light-guide plate  432  to form the scattering light Ls and enter the observer&#39;s eyes via the display panel  440 . Therefore, no matter at the front view or at the side view, observers can see the information on the display  400 . 
   Furthermore, when the display  400  is operated at the narrow viewing-angle mode, for only the backlight module  410  is powered on, the luminance of the display  400  will be lower than that in wide viewing-angle mode. The luminance of the display  400  in the narrow viewing-angle mode can be adjusted to be the same with that in the wide viewing-angle mode by increasing the operation currents of the backlight module  410  so that users will not feel apparent luminance difference between these two modes. 
   Embodiment Two 
   Referring to  FIG. 5A , a schematic cross-sectional view of the liquid crystal display according to the second embodiment of the invention is shown. The liquid crystal display  500  includes a backlight module  510 , a light valve  520 , a sidelight unit  530 , and a display panel  540 . The backlight module  510  can be a bottom lighting backlight module or a side lighting backlight module. The light valve  520  is shutter structure made of light absorbing materials for confining the passing light within a specific region to form approximately parallel light. The sidelight unit  530  includes a transparent and directional light-guide plate  532 , a first sidelight source  534 , and a second sidelight source  536 . The first and the second sidelight sources  534  and  536  are such as lamps or light emitting diodes. The light emitted from the backlight module  510  can pass through the light-guide plate  532 . Moreover, as shown in  FIG. 5B , the light-guide plate  532  includes a first thin film  531  and a second thin film  533 . By using the specific geometric structure of the first and the second thin films  531  and  533 , the light L 1  emitted from the first sidelight source  534  can be guided to enter the display panel  540  at a direction deviated left from the vertical while the light L 2  emitted from the second sidelight source  536  be guided to enter the display panel  540  at a direction deviated right from the vertical. 
   Referring to  FIG. 5C , a flow chart of the method for adjusting the viewing angle of the liquid crystal display according to the second embodiment of the invention is shown. First, in step  550 , provide the approximately parallel backlight, the sidelight L 1  and L 2  to the display panel  540  by respectively using the backlight module  510 , the light valve  520 , and the first sidelight source  534 , the second sidelight source  536  in response to a wide-viewing-angle-mode signal. In step  560 , provide the approximately parallel backlight, and in step  570 , provide the sidelight L 1 , or the sidelight L 2  to the display panel  540  by using the backlight module  510  and the light valve  520 , the first sidelight source  534 , or the second sidelight source  536  in response to a narrow-viewing-angle-mode signal. 
   Referring to  FIG. 5D , a schematic cross-sectional view of the liquid crystal display operating under the wide viewing-angle mode in  FIG. 5A  is shown. Under the wide viewing-angle mode, the backlight module  510 , the first sidelight source  534  and the second sidelight source  536  are all powered on. The backlight Lb emitted from the backlight module  510  passes the light valve  520  to form the approximately parallel backlight Lp, and the backlight Lp further passes through the transparent light-guide plate  532  to enter the display panel  540 . The light L 1  emitted from the first sidelight source  534  is guided by the light-guide plate  532  to enter the display panel  540  at a direction deviated left from the vertical while the light L 2  emitted from the second sidelight source  536  is guided by the light-guide plate  532  to enter the display panel  540  at a direction deviated right from the vertical. Therefore, the observers at the front view, the left-side view, and the right-side view, can see the information on the display  500  at the same time, thereby achieving the wide viewing-angle purpose. 
   Referring to  FIG. 5E , a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode whose images can only be seen by the front-view and left-side view observers in  FIG. 5A  is shown. Under the narrow viewing-angle mode, the backlight module  510 , the first sidelight source  534 , and the second sidelight source  536  are not switched on at the same time. As shown in  FIG. 5E , the backlight module  510  and the first sidelight source  534  are switched on while the second sidelight source  536  is switched off. Therefore, as mentioned above, it can be similarly reasoned that only the light L 1  emitted from the first sidelight source  534  and the backlight Lp passing the light valve  520  can pass the display panel  540 , and thus only the front-view and the left-side view observers can see the display images while the right-side view observer cannot see anything. 
   Referring to  FIG. 5F , a schematic cross-sectional view of the liquid crystal display operating under the narrow viewing-angle mode whose images can only be seen by the left-side view observers is shown. The backlight module  510  and the second sidelight source  536  are switched off while the first sidelight source  534  is switched on. As a result, as mentioned above, only the light L 1  emitted from the first sidelight source  534  can pass the display panel  540 , and thus only the left-side view observer can see the displayed images while the front-view and the right-side view observers cannot see anything. Therefore, the display  500  can provide the required viewing angle mode for the user by switching the backlight module  510 , the first sidelight source  534 , and the second sidelight source  536 . 
   In addition, when the display  500  is operated under the narrow viewing-angle mode, for the backlight module  510 , the first sidelight source  534 , and the second sidelight source  536  are not switched on at the same time, the luminance of the display  500  will be lower than that under the wide viewing-angle mode. The luminance of the display  500  in the narrow viewing-angle mode can be adjusted to be the same with that in the wide viewing-angle mode by increasing the operation currents of the backlight module  510 , the first sidelight source  534  or the second sidelight source  536 . Therefore, the observers will not feel apparent display luminance difference between two modes. 
   As mentioned above, although the backlight module equipped with the light valve to generate the approximately parallel light is taken as an example in the invention, the liquid crystal display of the invention can also use other kinds of backlight device to generate the approximately parallel light. Moreover, the relative configuration of the backlight device and the sidelight unit is not restricted to be that the sidelight unit is disposed above the backlight device as shown in  FIG. 4A  and  FIG. 5A . The sidelight unit can also be disposed under the backlight device. Since the approximately parallel light and the sidelight can be selectively generated to provide the required narrow and wide viewing angle modes and achieve the viewing angle adjusting purpose, it will not be deviated from the scope of skills in the invention. 
   The liquid crystal display of the invention disclosed by the above-mentioned two embodiments has the following advantages. The sidelight unit can not only provide the backlight to pass and enter the display panel but also guide the sidelight to reach observers at various viewing angles. Therefore, under the wide viewing-angle mode, the front-view and two-side view observers can see the information on the display while under the narrow viewing-angle mode only the front-view, the left-side view, or the right-side view observer can see the displayed information, thereby effectively achieving the viewing angle adjusting purpose. 
   While the invention has been described by way of example and in terms of two preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.