Abstract:
A liquid crystal display has a plurality of image elements, all the image elements are subdivided identically into at least two zones, the zones being formed so that they have different liquid crystal structures, each of the zones of a respective one of the image elements being electrically controllable.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a liquid crystal display with a switchable view angle. 
     The publication “Development of a Dual Domain TFT-LCD Biocomptable Paterning” (H Klausmann, et al, SID Digest of Technical Papers, 1998 Anaheim, USA), discloses a liquid crystal display with dual-domain liquid crystal cells. With this dual domain liquid crystal cells, an individual viewpoint element is subdivided into two zones. In these zones, the liquid crystal has a different orientation. Thereby the view angle region of the liquid crystal display is expanded. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a liquid crystal display which has advantage that the individual zones of an image point element which have different orientation are controllable electrically separately. Therefore for the liquid crystal display, uniformly designed image point elements are arranged near one another. 
     Identically oriented zones of an image point element have the same view angle. This view angle is limited only right with an orientation direction of the liquid crystals. This means however that from different image angle regions of the inventive liquid crystal display, exclusively one image is visible, which is produced by the image element zones of only one liquid crystal orientation. In accordance with the present invention, in contrast to the prior art, these individual zones are controlled electronically separately. Thereby it is possible to make visible simultaneously different images in different image angle regions. 
     The possibility to perform the electrical control via different column conductors, different line conductors or via a subdivision of the front plane electrode allows an adaptation of the desired layout of the image element. Further, an adaptation of the use driver and the control circuit is possible. It should be also noted that the line driver as a rule is more favorable than the column driver. 
     It is further advantageous that, in addition to the possibility to see two different images simultaneously from two different viewing directions, there are other illustration possibilities. On the one hand, it is possible to switch the liquid crystal display for one view direction to be dark or bright, or in other words to show no image information. From the other image direction an image information can be recognized. Further, there is a possibility for both viewing directions to show the same image information. 
     In a limiting view angle region, in which at least two different image informations are visible, there is firstly the possibility to provide a stereoscopic image information. This is advantageous for example for the three dimensional representation of a land map, for example for the use in connection with a navigation system. 
     The rear illumination through two correspondingly modified light conductors, with two different light sources provides the advantage of a separated rear illustration for individual image point elements. It is therefore for example possible that each observer of the can individually regulate the display brightness for its view angle region. 
    
    
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a liquid crystal display in accordance with the present invention, formed as a passive liquid crystal display; 
     FIG. 2 is a view showing an inventive liquid crystal display formed as an active-matrix liquid crystal display with different column conductors for each zone of an image point element; 
     FIG. 3 is a view showing a liquid crystal display in accordance with the present invention with different line conductors for each zone of an image point element; 
     FIG. 4 is a view showing a liquid crystal display in accordance with the present invention with a subdivision of a front plane electrode; 
     FIG. 5 is a view showing a variant of the embodiment of FIG. 4; and 
     FIG. 6 is a view showing a liquid crystal display with the use of two light guides and two light sources for separate rear illumination of different image angle regions. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The liquid crystals in the liquid crystal display are located between two glass plates, on which additional layers, for example orientation layers, can be applied. On one glass side, in immovable condition all elongated liquid crystal molecules are oriented with their longitudinal axes parallel to the glass outer surface. All liquid crystal molecules extend with their longitudinal axes in one direction. Over the line distance, the direction of the longitudinal axes of the liquid crystal molecules changes, so that over the line distance a turning of the molecule by 90° is performed. 
     One possibility to produce zones of different orientation is to orient the liquid crystal so that in one zone a turning by the angle +90° and in another zone a turning by the angle of −90° is performed. Furthermore, it is also possible to change over the line distance, the angle of the longitudinal axis with the glass outer surface. A different photo orientation is obtained in that in one zone the longitudinal axes of the liquid crystal molecules on one glass side enclose with the glass surface an angle plus θ and in another zone enclose an angle minus θ. This angle is identified as a tilting angle of the liquid crystal. Its value is preferable located between 0° and 30°. In the following examples only the second type of liquid crystal orientation, which is provided by the orientation by different tilting angles is described. 
     FIG. 1 shows a liquid crystal display which is formed as an X-Y matrix. The display is controlled via column conductors  1 , and line conductor  2 ,  3 , which are arranged perpendicularly to one another. The column or line conductors are located on different glass substrates, between which the not shown liquid crystal is located. The addressing of the image screen is passive. In other words, it provides no active switching (for example a thin film transistor) on each image point. Instead, the information is inscribed by corresponding signals on the line and column conductors in line sequence in the image screen. An individual image element is formed from the intersection of a column  1  and two line conductors  2 ,  3 . Only for this selected image element important conductors are marked. 
     As line and column electrode material, transparent zinc-indium oxide (ITO) is used. An image element  4  is selected in FIG.  3  and for better illustration is encircled with a broken line. It is subdivided in a two zones  5 ,  6 . In this example as in the following examples, the different zones are selected to have identical sizes. In one zone  5 , for example by photo orientation of the liquid crystal, or by a different, comparable method, the liquid crystal structure is tilted by the angle +θ. In the other zone  6 , the liquid crystal structure to the contrary is tiled by the angle −θ. Each of the two zones is associated with one line conductor  2  or  3 , while neighboring image point halves are covered with the same tilting of the liquid crystal. Since the different tilting of the liquid crystal causes the change of the view angle, the view angle regions associated with the angle +θ and angle −θ are controllable by different line conductors separately. 
     FIG. 2 shows a further embodiment of the inventive liquid crystal display. The liquid crystal display is here formed as an active matrix. An image element  20  is selected. The control is performed through a line conductor  21  and through column conductors  22 ,  23 . The image element  20  is subdivided into two zones  24  and  25 , each having its own control transistor  26  or  27 . It has a joint storage conductor  28 . In the upper zone  24  the liquid crystal structure is tiled by the angle +θ and in the lower zone  25  it is tiled by the angle −θ. During one line cycle X, the zone  24  and a zone  31  of the upper limiting image element are controlled simultaneously. During the subsequent line cycles X+1 the zone  25  and a zone  32  of the downwardly adjoining image element are controlled simultaneously. As a result, the column information for all lower image element zones  25 ,  31 , etc. are displaced by one line cycle relative to the information for the upper image element zones  24 ,  32 , etc., when the information is inscribed linewise in the display. 
     The image information for the upper and lower image element zones can be different. The separate storage conductor  28  acts, in addition to its storage function, also as a black matrix between the zones. Some aperture loss due to the double number of the column conductors can be compensated by a more intensive rear illumination. In particular with the use in motor vehicles, in which a sufficient current source is always available, a higher power reception of the rear illumination causes no problems. 
     FIG. 3 shows another embodiment of the inventive liquid crystal display. It is also an active matrix liquid crystal display with a selected image element  40 . The control of this image element is performed via a column conductor  41  and via line conductors  42  and  43 . The control of an upper image point zone  44  is performed through the transistor  46  and the control of a lower image point zone  45  is performed through the transistor  47 . The orientation of the liquid crystals differs from one line to another. This guarantees the possibility to represent different images in different view angle regions. In contrast to the illustration in FIG. 2, per image element only one column and two line conductors are needed. This is advantageous since the line drivers are less expensive than column drivers. 
     FIG. 4 shows a further inventive arrangement. The liquid crystal display is here also formed as an active matrix. An image element  50  is selected. It is controlled via a line conductor  51  and a column conductor  52  with the transistor  53 . The image point element  50  is subdivided into two zones with different liquid crystal structures. The liquid crystal in the zone  54  has the tilting angle +θ, the liquid crystal in the zone  55  has the tilting angle −θ. Between the transparent front plane electrode  55 ,  56  and the matrix with transistors, line and column conductors, the not shown liquid crystal which is enclosed by two glass plates is located. The front plane electrodes  55  and  56  are finger shaped, so that they do not intersect. They are electrically separated. The front plane electrode  60  covers the lower zone of the image point element, all liquid crystals with the tilting angle −θ, for example  55 . The front plane electrode  61  overlaps the upper zone of the image point element, all with tilting angle +θ of the liquid crystal, for example  54 . 
     Two control types are proposed. In accordance with a first control type, a rectangular alternating voltage is applied to both front plane electrodes. Additionally, one of the both front plane electrodes, for example the front plane electrode  60  obtains an alternating signal with the image repeat frequency to avoid a flickering. The voltage of this alternating signal is selected so that for example all image point zones which belong to the front plane electrode  60  are switched to be dark. The second control type is to apply rectangular alternating voltages of different amplitudes to both front plane electrodes  60  and  61 . The voltages are selected so that with a lowering amplitude the standard image representation is obtained and with a higher amplitude the corresponding zones of the image element are made dark. 
     With this two control types, three operational types are possible: 
     Both line electrodes are operated parallel and the information is well read from both sides; 
     Only one of the both lines is controlled, and the image is recognized only from one side (only from right or only from left side) 
     Different column signals are applied during controlling of each of a front plane electrode. In this case two different images are recognized from separate view positions. With the alternating current applied to the front plane electrodes, the turns in a view angle region correspondingly from bright to dark switching of the display in an image representation. 
     FIG. 1 shows a special variation of this embodiment, in which the finger-shaped front plane electrodes are replaced by electrodes in line form  70 ,  71 . They are joined with thin conductive connections  80 ,  81 , for example low ohmic metal layers. In FIG. 5 the front plane electrodes  70 ,  71  and the conductive connections  80 ,  81  are shown. In the control, there are no differences from the arrangement shown in FIG.  4 . 
     FIG. 6 shows a further embodiment of the inventive liquid crystal display. Here it is of a special rear light type with two bar-shaped light sources  90  and  91 , for example cold cathode fluorescent lamps (CFL), with reflectors  92  and  93 . The light of the light sources  90  and  91  is coupled through the reflectors  92  and  93  into two light guides  94  and  95  which are provided on their outer surface with a prism structure. The prism structure is designed so that the light is emitted only in a selected view angle region. Due to the separated control of both light sources  90  and  91 , for each view angle region a separate brightness control is possible. In motor vehicles it is possible therefore that the driver and the passenger individually adjust their brightness. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in liquid crystal display with switchable view angle, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
     What is claimed as new and desired to be protected by letters patent is set forth in the appended claims.