Patent Publication Number: US-7903063-B2

Title: Liquid crystal panel capable of controlling viewing angle and liquid crystal display device with the same

Description:
This application claims the benefit of Korean Patent Application No. 10-2005-0135083, filed on Dec. 30, 2005, and Korean Paten Application No. 10-2006-0008737, filed on Jan. 27, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     A liquid crystal panel that can control a viewing angle of an image and a liquid crystal display device (LCD) with the liquid crystal panel is provided. 
     2. Related Art 
     A liquid crystal display device (LCD) displays an image by controlling the strength of an electric field applied to a liquid crystal panel such that the quantity of light penetrating the liquid crystal panel is adjusted. The liquid crystal panel is the main component of the LCD. The liquid crystal panel uses external light to display an image, and thus has a limited viewing angle. An in-plane switching (IPS) mode that uses an horizontal electric field, a mode that uses a compensation film, and a multi-domain mode that uses a protrusion or an opening pattern on a transparent electrode are introduced to enhance the limited viewing angle of the liquid crystal panel. 
     Users of data terminals, for example, portable phones, personal digital assistants (PDAs) and computers desire that the displayed data is prevented from being viewed by others. To meet such a demand, an LCD used as a display device of the data terminals needs to provide a narrow viewing angle mode as well as a wide viewing angle mode. 
     A dual-structure liquid crystal panel has been proposed to meet the need for the multiple viewing angle mode. 
       FIG. 1  is a sectional view of a related art dual-structure liquid crystal panel capable of controlling a viewing angle. Referring to  FIG. 1 , the related art dual-structure liquid crystal panel includes a normal panel  10  and an interference panel  12  disposed on the normal panel  10 . The normal panel  10  displays an image, while the interference panel  20  causes light traveling in the side directions to be interfered with. This dual-structure liquid crystal panel can change a viewing angle mode using the light interference operation of the interference panel  12 . 
     An LCD including the dual-structure liquid crystal panel selectively drives the interference panel  12  to provide both a wide viewing angle mode and a narrow viewing angle mode. That is, the interference panel  12  is turned on or off to provide the narrow viewing angle mode or the wide viewing angle mode. 
     In the dual-structure liquid crystal panel, an external light must penetrate two liquid crystal layers and thus the brightness of an image is greatly reduced. Also, the dual-structure liquid crystal panel is thicker and heavier than a single-structure liquid crystal panel. Moreover, even in the narrow viewing angle mode, an image viewed from the front side, as illustrated in  FIG. 2A , is also viewed dimly at the left and right sides, as illustrated in  FIGS. 2B and 2C . This makes it difficult to ensure the secrecy of a user. 
     SUMMARY 
     A liquid crystal panel that can limit a viewing angle and an LCD with the same is provided. 
     A liquid crystal panel includes a plurality of color pixels, wherein each color pixel includes red (R), green (G) and blue (B) sub-pixels. A plurality of interference (E) sub-pixels are included in each of the color pixels and disposed on any one of the same plane and layer as the color pixels to limit light that penetrates the liquid crystal panel and travels in both side directions of the liquid crystal panel, except from the front direction thereof. 
     The sub-pixels included in each of the color pixels are connected to a pair of gate lines and a pair of data lines. The sub-pixels included in each of the color pixels are connected commonly to one gate line and connected respectively to four data lines. 
     The R, G and B sub-pixels are driven by a horizontal electric field and the interference sub-pixels may be driven by a vertical electric field. 
     Each of the R, G and B sub-pixels may include at least one or more band-shaped common electrodes that alternates with at least one or more band-shaped pixel electrodes. Each of the interference sub-pixels may include a plate-shaped pixel electrode and a plate-shaped common electrode that face each other. 
     In another embodiment, an LCD includes the above liquid crystal panel. A data driver pixel drives signals to the sub-pixels of the liquid crystal panel on a line basis. An interference data generator generates interference data to be supplied to the sub-pixels. A video data combiner adds the interference data to video data supplied to the data driver. 
     The interference data generator includes a memory that stores interference sub-pixel data that forms an image with an interference pattern. A memory controller that controls a read operation of the memory. 
     The interference data generator further include an offset sub-pixel data generator that generates offset sub-pixel data with a logic value corresponding to an offset voltage. A selector selectively transferring the offset sub-pixel data from the offset sub-pixel data generator and the interference sub-pixel data from the memory to the video data combiner in response to a wide/narrow mode control signal. 
     The offset sub-pixel data generator includes either a register or a switch. 
     The memory may further store offset sub-pixel data with a logic value corresponding to an offset voltage. The memory controller control the memory according to a wide/narrow mode control signal such that the offset sub-pixel data and the interference sub-pixel data stored in the memory are selectively read and transmitted to the video data combiner. 
     The interference data generator includes a data combiner that combines R, G and B sub-pixel data contained in the video data. An operation unit that calculates interference sub-pixel data on the basis of the combined sub-pixel data and supplies the calculated interference sub-pixel data to the video data combiner. 
     The operation unit may perform an operation such that a luminance value of the interference sub-pixel data is distributed at a reference gray scale level. 
     The operation unit calculates the interference sub-pixel data by setting the sum of R, G, B and E sub-pixel data with a gray scale level lower than the maximum gray scale level to a reference luminance data and subtracting the sum of the combined R, G and B sub-pixel data from the data combiner from the reference luminance data. 
     The operation unit includes either a processor that performs an operation on the interference sub-pixel data using the combined R, G and B sub-pixel data from the data combiner or a look-up table configured to supply the interference sub-pixel data to the video data combiner using the combined R, G and B sub-pixel data from the data combiner. 
     The interference data generator may further include an offset sub-pixel data generator that generates offset sub-pixel data with a logic value corresponding to an offset voltage. A selector that selectively transfers the offset sub-pixel data from the offset sub-pixel data generator and the interference sub-pixel data from the operation unit to the video data combiner in response to a wide/narrow mode control signal. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide explanation. 
    
    
     
       DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding and are incorporated in and constitute a part of this application, illustrate embodiment(s) that serve to explain the principles of this application. In the drawings: 
         FIG. 1  is a sectional view of a related art liquid crystal panel capable of controlling a viewing angle; 
         FIGS. 2A to 2C  illustrate the states of an image depending on viewing angles when the liquid crystal panel of  FIG. 1  operates in a narrow viewing angle mode; 
         FIG. 3  is a plan view of a liquid crystal panel that limits a viewing angle; 
         FIG. 4  is a plan view of a liquid crystal panel that limits a viewing angle according to another embodiment; 
         FIG. 5  is a sectional view taken along a line A-A′ in  FIGS. 3 and 4 ; 
         FIGS. 6A to 6C  are graphs that illustrate the polarization characteristics of the liquid crystal panel in  FIG. 5 ; 
         FIG. 7  is a block diagram of an LCD that limits a viewing angle; 
         FIGS. 8A and 8B  illustrate the states of an image on a liquid crystal panel of the LCD of  FIG. 7 , which are viewed from the side in wide and narrow viewing angle modes, respectively; 
         FIG. 9  is a detailed block diagram that illustrates an embodiment of an interference data generator in  FIG. 7 ; 
         FIG. 10A  illustrates the characteristics of reference luminance data used in an operation unit of  FIG. 9 ; 
         FIGS. 10B and 10C  illustrate examples of interference sub-pixel data outputted from the operation unit of  FIG. 9 ; 
         FIG. 11  is a flow diagram that illustrates an operation of the interference data generator in  FIG. 9 ; 
         FIG. 12  is a detailed block diagram that illustrates another embodiment of an interference data generator in  FIG. 7 ; 
         FIG. 13  illustrates an example of a memory map of a memory in  FIG. 12 ; 
         FIG. 14  is a detailed block diagram that illustrates another embodiment of an interference data generator in  FIG. 7 ; 
         FIG. 15  is a flow diagram that illustrates an operation of a memory controller in  FIG. 14 ; and 
         FIG. 16  is a block diagram of an LCD that limits a viewing angle according to another embodiment. 
     
    
    
     DESCRIPTION 
       FIG. 3  is a plan view of a liquid crystal panel that limits a viewing angle. 
     Referring to  FIG. 3 , in a liquid crystal panel  30 , a plurality of sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn, BSP 11 ˜BSPmn, and ESP 11 ˜ESPmn are disposed in a plurality of regions that are divided by a plurality of horizontally-arranged data lines DL 1 ˜DL 2 m and a plurality of vertically-arranged gate lines GL 1 ˜GL 2 n. Each of the sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn, BSP 11 ˜BSPmn, and ESP 11 ˜ESPmn includes a liquid crystal cell CLC connected to a common electrode Vcom. A thin film transistor (TFT) MN that switches a sub-pixel that drives a signal transmitted from the data line DL to the liquid crystal cell CLC in response to a scan signal on a gate line GL. 
     The sub-pixels are classified into red (R) sub-pixels RSP 11 ˜RSPmn, green (G) sub-pixels GSP 11 ˜GSPmn, blue (B) sub-pixels BSP 11 ˜BSPmn, and interference (E) sub-pixels ESP 11 ˜ESPmn. The R sub-pixels RSP 11 ˜RSPmn are connected to the corresponding odd-numbered gate lines GL 1 ˜GL 2 n−1 and the corresponding odd-numbered data lines DL 1 ˜DL 2 m−1. The G sub-pixels GSP 11 ˜GSPmn are connected to the corresponding odd-numbered gate lines GL 1 ˜GL 2 n−1 and the corresponding even-numbered data lines DL 2 ˜DL 2 m. The B sub-pixels BSP 11 ˜BSPmn are connected to the corresponding even-numbered gate lines GL 2 ˜GL 2 n and the corresponding even-numbered data lines DL 2 ˜DL 2 m. The E sub-pixels ESP 11 ˜ESPmn are connected to the corresponding even-numbered gate lines GL 2 ˜GL 2 n and the corresponding odd-numbered data lines DL 1 ˜DL 2 n−1. In addition, the respective E sub-pixels ESP 11 ˜ESPmn are grouped together with the corresponding R, G and B sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn and BSP 11 ˜BSPmn that are adjacent to the top and right sides thereof, thereby forming color pixels PXC 11 ˜PXCmn that limit a viewing angle of an image. 
     The first color pixel PXC 11  of a first line includes the R and G sub-pixels RSP 11  and GSP 11  that are connected commonly to the first gate line GL 1  and connected respectively to the first and second data lines DL 1  and DL 2 . The E and B sub-pixels ESP 11  and BSP 11  are connected commonly to the second gate line GL 2  and connected respectively to the first and second data lines DL 1  and DL 2 . 
     The last color pixel PXCmn of the last line includes the R and G sub-pixels RSPmn and GSPmn that are connected commonly to the (2n−1)th gate line GL 2 n−1 and connected respectively to the (2m−1)th and (2m)th data lines DL 2 m−1 and DL 2 m. The E and B sub-pixels ESPmn and BSPmn are connected commonly to the (n)th gate line GL 2 n and connected respectively to the (2m−1)th and (2m) data lines DL 2 m−1 and DL 2 m. 
     The R, G and B sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn and BSP 11 ˜BSPmn are driven in an in-plane switching (IPS) mode, such that an image is displayed at a wide viewing angle. On the contrary, the E sub-pixels ESP 11 ˜ESPmn are driven in a vertical alignment (VA) mode, such that an image to be viewed in a side direction is selectively interfered with according to an interference sub-pixel signal. An image displayed on the liquid crystal panel  30  is viewed only within the range of a small angle with respect to the front of the liquid crystal panel  30 . In other words, when an image interference occurs due to the E sub-pixels ESP 11 ˜ESPmn, an image of a narrow viewing angle mode is displayed on the liquid crystal panel  30 . When no image interference occurs, an image of a wide viewing angle mode is displayed on the liquid crystal panel  30 . 
       FIG. 4  is a plan view of a liquid crystal panel that limits the viewing angle according to another embodiment. 
     Referring to  FIG. 4 , in a liquid crystal panel  30 A, a plurality of sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn, BSP 11 ˜BSPmn, and ESP 11 ˜ESPmn are disposed in a plurality of regions that are divided by a plurality of horizontally-arranged data lines DL 1 ˜DL 4 m and a plurality of vertically-arranged gate lines GL 1 ˜GLn. Each of the sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn, BSP 11 ˜BSPmn, and ESP 11 ˜ESPmn includes a liquid crystal cell CLC connected to a common electrode Vcom. A thin film transistor (TFT) MN switches a sub-pixel driving signal to be transmitted from the data line DL to the liquid crystal cell CLC in response to a scan signal on a gate line GL. The sub-pixels are classified into red (R) sub-pixels RSP 11 ˜RSPmn, green (G) sub-pixels GSP 11 ˜GSPmn, blue (B) sub-pixels BSP 11 ˜BSPmn, and interference (E) sub-pixels ESP 11 ˜ESPmn. The R sub-pixels RSP 11 ˜RSPmn are connected to the corresponding (4k−3)th data lines DL 1 ˜DL 4 m−1. The G sub-pixels GSP 11 ˜GSPmn are connected to the corresponding (4k−2)th data lines DL 2 ˜DL 4 m−2. The B sub-pixels BSP 11 ˜BSPmn are connected to the corresponding (4k−1)th data lines DL 3 ˜DL 4 m−1. The E sub-pixels ESP 11 ˜ESPmn are connected to the corresponding (4k)th data lines DL 4 ˜DL 4 m. 
     The respective E sub-pixels ESP 11 ˜ESPmn are grouped together with the corresponding R, G and B sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn and BSP 11 ˜BSPmn that are successively adjacent to the left side thereof, thereby forming color pixels PXC 11 ˜PXCmn that limit a viewing angle of an image. Accordingly, the first color pixel PXC 11  of a first line includes the R, G, B and E sub-pixels RSP 11 , GSP 11 , BSP 11  and ESP 11  that are connected commonly to the first gate line GL 1  and connected respectively to the first to fourth data lines DL 1 ˜DL 4 . The last color pixel PXCmn of the last line includes the R, G, B and E sub-pixels RSPmn, GSPmn, BSPmn and ESPmn that are connected commonly to the (n)th gate line GLn and connected respectively to the (4m−3)th to (4m)th data lines DL 4 m−3˜DL 4 m. 
     The R, G and B sub-pixels RSP 11 ˜RSPmn, GSP 11 ˜GSPmn and BSP 11 ˜BSPmn are driven in an IPS mode, such that an image is displayed at a wide viewing angle. The E sub-pixels ESP 11 ˜ESPmn are driven in a VA mode, such that an image to be viewed in a side direction is selectively interfered with according to an interference sub-pixel signal. An image displayed on the liquid crystal panel  30 A is viewed only within the range of a small angle with respect to the front of the liquid crystal panel  30 A. In other words, when an image interference occurs due to the E sub-pixels ESP 11 ˜ESPmn, an image of a narrow viewing angle mode is displayed on the liquid crystal panel  30 A. When no image interference occurs, an image of a wide viewing angle mode is displayed on the liquid crystal panel  30 A. 
       FIG. 5  is a sectional view taken along a line A-A′ in  FIGS. 3 and 4 . 
     Referring to  FIG. 5 , the liquid crystal panels  30  or  30 A includes a liquid crystal layer CL that is disposed between a lower glass layer  31  and an upper glass layer  36 . A gate insulating layer  32 , a data line DL and a passivation layer  33  are sequentially formed on the lower glass substrate  31 . Although not illustrated, a TFT and a gate line are formed between the gate insulating layer  32  and the lower glass substrate  31 . The data line DL is electrically connected through the gate insulating layer  32  to the TFT. A region located to the left of the data line DL corresponds to a blue (B) sub-pixel BSP, while a region located to the right of the data line DL corresponds to an interference (E) sub-pixel ESP. First pixel electrodes  34 A and common electrodes  35 A are alternately formed on the passivation layer  33  located to the left of the data line DL. A second pixel electrode  34 B is formed on the passivation layer  33  located to the right of the data line DL. The first pixel electrodes  34 A and the common electrodes  35 A are formed, for example, in the shape of a band, while the second pixel electrode  34 B is formed, for example, in the shape of a plate with the same size as a sub-pixel region. 
     A black matrix  37  is formed on the bottom surface of the upper glass substrate  36  to divide sub-pixel regions. A color filter  38  is formed in each of color sub-pixel regions among the sub-pixel regions divided by the black matrix  37 . That is, a blue color filter is formed in a blue sub-pixel region BSP located to the left of the data line DL. An overcoat layer  39  is formed on the black matrix  37  and the color filter  38 . A second common electrode  35 B with the same size as a sub-pixel region is formed on the right half of the overcoat layer  39  in the region located to the right of the data region DL. 
     In the blue sub-pixel BSP, a horizontal electric field is applied to the liquid crystal layer CL by the first pixel electrodes  34 A and the first common electrodes  35 A that are alternately arranged on the lower glass substrate  31 . Liquid crystal molecules CLCM in the blue sub pixel BSP, which responds to a voltage applied between the first pixel electrodes  34 A and the first common electrodes  35 A, polarize a penetrating light such that the quantity of light decreases as a viewing angle increases from the front to the side of the liquid crystal panel, as illustrated in  FIG. 6A . An image displayed on the liquid crystal panel  30  or  30 A can be viewed also in the side direction that is greatly inclined from the front direction of the liquid crystal panel. That is, the liquid crystal panel  30  or  30 A displays an image of a wide viewing angle mode. 
     In the interference sub-pixel ESP, a vertical electric field is applied to the liquid crystal panel CL by the second pixel electrode  34 B and the second common electrode  35 B that are disposed respectively on the lower and upper glass substrates  31  and  36  to face each other. Liquid crystal molecules CLCE in the interference sub pixel ESP, which responds to the size of a vertical electric field applied between the second pixel electrode  34 B and the second common electrode  35 B, polarize light such that the quantity of light is maximized in both side directions that are inclined by about 40° with respect to the front direction of the liquid crystal panel, as illustrated in  FIG. 6B . That is, the liquid crystal molecules CLCE in the interference sub-pixel ESP polarize light such that the light travels in both side directions, except the front direction. Accordingly, the liquid crystal panels  30  and  30 A can control a viewing angle. 
     Since the interference sub-pixel ESP and the color sub-pixels RSP, GSP and BSP are disposed on the same plane or on the same layer, the thickness and weight of the liquid crystal panel do not increase. The viewing angle can be limited by only one liquid crystal layer, and the decrease of the light quantity and the degradation of the brightness can be prevented. 
       FIG. 7  is a block diagram of an LCD that limits a viewing angle. 
     Referring to  FIG. 7 , an LCD according to another embodiment includes a liquid crystal panel  30 . A interference data generator  40  generates interference data IFD to be supplied to the interference sub-pixels ESP 11 ˜ESPmn on the liquid crystal panel  30 . A video data combiner  42  adds the interference data IFD to external video data VD. As illustrated in  FIG. 3 , the liquid crystal panel  30  includes m×n number of color pixels PXC 11 ˜PXCmn that include the red (R) sub-pixels RSP 11 ˜RSPmn connected to the odd-numbered gate lines GL 1 ˜GL 2 n−1 and the odd-numbered data lines DL 1 ˜DL 2 m−1. The green (G) sub-pixels GSP 11 ˜GSPmn are connected to the odd-numbered gate lines GL 1 ˜GL 2 n−1 and the even-numbered data lines DL 2 ˜DL 2 m. The blue (B) sub-pixels BSP 11 ˜BSPmn are connected to the even-numbered gate lines GL 2 ˜GL 2 n and the odd-numbered data lines DL 1 ˜DL 2 m−1. The interference sub-pixels ESP 11 ˜ESPmn are connected to the even-numbered gate lines GL 2 ˜GL 2 n and the even-numbered data lines DL 2 ˜DL 2 m. 
     In response to a wide/narrow mode control signal WIN from an external video source (e.g. a graphic card of a computer), the interference data generator  40  supplies the interference data IFD for switching W/N modes of a viewing angle of the liquid crystal panel  30  to the video data combiner  42 . When the wide/narrow mode control signal W/N has a specific logic level (e.g., a “high” logic level or a “low” logic level) that designates a narrow viewing angle mode, the interference data IFD includes interference (E) sub-pixel data Ed that form an image of a fixed interference pattern, which allows interference light to be added in the both side directions with respect to the front direction of the liquid crystal panel  30 . Alternatively, the interference data IFD may include interference sub-pixel data Ed that forms an interference pattern that varies per image. To generate the interference data IFD with the interference pattern that varies per image, the interference data generator  40  receives the external video data VD from the external video source (e.g., a graphic card of a computer). On the other hand, when the wide/narrow mode control signal W/N has an initialization logic level (e.g., a “low” logic level or a “high” logic level) that designates a wide viewing angle mode, the interference data IFD includes offset sub-pixel data Eoff with an offset value, which prevents interference light from traveling in the both side directions with respect to the front direction of the liquid crystal panel  30 . 
     The video data combiner  42  receives a video data VD that includes color sub-pixel data for the R, G and B sub-pixels RSP, GSP and BSP from the external video source (not illustrated). The video data combiner  42  adds the interference data IFD from the interference data generator  40  to the video data VD. Also, the video data combiner  42  rearranges the color sub-pixel data and the interference (or offset) sub-pixel data Ed (or Eoff) in accordance with the arrangement state of the sub-pixels on the liquid crystal panel  30 , thereby generating combined video data CVD. When the R and G sub-pixels RSP and GSP connected to the odd-numbered gate lines GL 1 ˜GL 2 n−1 are scanned, the combined video data CVD includes a sub-pixel data stream in which R and G sub-pixel data Rd and Gd alternate with each other. When the E and B sub-pixels ESP and BSP connected to the even-numbered gate lines GL 2 ˜GL 2 n are scanned, the combined video data CVD includes a sub-pixel data stream in which interference (or offset) and B sub-pixel data Ed (or Eoff) and Bd alternate with each other. 
     The LCD according to the embodiment of the present invention further includes a gate driver  44  sequentially drives the gate lines GL 1 ˜GL 2 n. A data driver  46  sequentially drives the data lines DL 1 ˜DL 2 m. A timing controller  48  controls the operation timing of the gate and data drivers  44  and  46 . In response to a gate timing signal GTS from the timing controller  48 , the gate driver  44  generates 2n number of scan signals that sequentially enables the gate lines GL 1 ˜GL 2 n. 
     In response to a data timing signal DTS from the timing controller  48 , the data driver  46  supplies sub-pixel driving signals to the data lines DL 11 ˜LL 2 m every time any one of the gate lines GL 1 ˜GL 2 n is enabled. The data driver  46  receives the combined video data CVD that is serially transferred from the video data combiner  42 . When lines of the R and G sub-pixels RSP and GSP that are connected to any one of the odd-numbered gate lines GL 1 ˜GL 2 n−1 are scanned, the data driver  46  receives the sub-pixel data stream in which R and G sub-pixel data Rd and Gd alternate with each other, such that an R sub-pixel driving signal and a G sub-pixel driving signal are supplied to the odd-numbered data lines DL 1 ˜DL 2 m−1 and the even-numbered data lines DL 2 ˜DL 2 m, respectively. When lines of the E and B sub-pixels ESP and BSP connected to any one of the even-numbered gate lines GL 2 ˜GL 2 n are scanned, the data driver  46  receives the sub-pixel data stream in which interference (or offset) and blue sub-pixel data Ed (or Eoff) and Bd alternate with each other, such that an interference sub-pixel driving signal and a blue sub-pixel driving signal are supplied to the odd-numbered data lines DL 1 ˜DL 2 m−1 and the even-numbered data lines DL 2 ˜DL 2 m, respectively. 
     When the wide/narrow mode control signal W/N has the specific logic level that designates the narrow viewing angle mode, the interference sub-pixel driving signal has a voltage level that allows the interference sub-pixel ESP to transmit interference light in the both side directions with respect to the front direction of the liquid crystal panel  30 . The quantity of this interference light is adjusted according to the voltage level of the interference sub-pixel driving signal. This quantity of the interference light is added to the quantity of light that travels through the R, G and B sub-pixels RSP, GSP and BSP in both side directions, such that luminance components at both sides interfere with each other. 
     As illustrated in  FIG. 8B , an image that cannot be viewed in the side direction is displayed on the liquid crystal panel  30 . Also, the interference sub-pixel driving signals have different voltage levels at positions of the interference sub-pixels ESP 11 ˜ESPmn, and thus the color pixels PXC have different interference amounts of luminance. An image displayed on the liquid crystal panel  30  cannot be recognized in both side directions. Consequently, the secrecy in the narrow viewing angle mode is further enhanced. 
     When the wide/narrow mode control signal W/N has the initialization logic level that designates the wide viewing angle mode, the interference sub-pixel ESP responds to an offset sub-pixel driving signal with an offset voltage level that prevents interference light from traveling in the front and both side directions of the liquid crystal panel  30 . Due to this offset sub-pixel driving signal, light only travels through the R, G and B sub-pixels in the front and both side directions of the liquid crystal panel  30 . As illustrated in  FIG. 8A , an image displayed on the liquid crystal panel  30  can be viewed in the side direction as well as the front direction. 
     The timing controller  48  receives sync signals (i.e., vertical and horizontal sync signals and a data clock) from the external video source. Using the sync signals, the timing controller  48  generates the gate timing signal GTS that is supplied to the gate driver  44  the data timing signal DTS that is supplied to the data driver  46 . The timing controller  48  generates an interference control signal ECS that controls the data generating operation of the interference data generator  40  and a combination control signal CCS that controls the data combining operation of the video data combiner  42 . 
       FIG. 9  is a detailed block diagram that illustrates an embodiment of the interference data generator  40  in  FIG. 7 . 
     Referring to  FIG. 9 , the interference data generator  40  includes a register  50 , a data combiner  52 , an operation unit  54  and a selector  56  that operate to reply sequentially to the video data VD from the external video source (i.e., a graphic card of a computer). The register  50  stores the offset sub-pixel data Eoff corresponding to an offset value. The register  50  can be replaced by a plurality of switches that can generate the offset sub-pixel data Eoff. 
     The data combiner  52  sequentially receives the R, G and B sub-pixel data Rd, Gd and Bd and simultaneously transfers them to the operation unit  54 . The data combiner  52  responds to a first interference control signal ECS 1  from the timing controller  48  of  FIG. 7 . The first interference control signal ECS 1  is preferably a data clock having the same period as the sub-pixel data. The data combiner  52  is preferably a shift register that sequentially shifts the R, G and G sub-pixel data Rd, Gd and Bd from the external video source in response to the first interference control signal ECS 1 . 
     Using the combined R, G and B sub-pixel data Rd, Gd and Bd from the data combiner  52 , the operation unit  54  generates the interference sub-pixel data Ed. The operation unit  54  that receives the combined R, G and B sub-pixel data Rd, Gd and Bd and responds to a second interference control signal ECS 2  from the timing controller  48 . The second interference control signal ECS 2  has ⅓ times the frequency (i.e., 3 times the period) of the first interference control signal ECS 1 . The second interference control signal ECS 2  is preferably a ⅓-divided data clock. For calculation of the interference sub-pixel data Ed, the operation unit  54  subtracts the combined R, G and B data Rd, Gd and Bd from a reference luminance data Yd according to Equation (1) below. As illustrated in  FIG. 10A , the reference luminance data Yd is determined to be the sum of R, G, B and E sub-pixel data Rref, Gref, Bref and Eref with a reference gray scale level REL that is lower than the maximum gray scale level HGL of the R, G, B and E sub-pixel data Rd, Gd, Bd and Ed. The reference gray scale level REL is preferably an intermediate gray scale level of each of the sub-pixel data. 
     
       
         
           
             
               
                 
                   
                     
                       
                         Ed 
                         = 
                           
                         ⁢ 
                         
                           Yd 
                           - 
                           
                             ( 
                             
                               Rd 
                               + 
                               Gd 
                               + 
                               Bd 
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               Rref 
                               + 
                               Gref 
                               + 
                               Bref 
                               + 
                               Eref 
                             
                             ) 
                           
                           - 
                           
                             ( 
                             
                               Rd 
                               + 
                               Gd 
                               + 
                               Bd 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     According to Equation (1), when the respective gray scale levels of the combined R, G and B sub-pixel data Rd, Gd and Bd become lower than the reference gray scale level REL and thus approach a base gray scale level (See  FIG. 10B ), the interference sub-pixel data Ed has a gray scale level close to the maximum gray scale level HGL. When the respective gray scale levels of the combined R, G and B sub-pixel data Rd, Gd and Bd become higher than the reference gray scale level REL and thus approach the maximum gray scale level HGL (See  FIG. 10B ), the interference sub-pixel data Ed has a gray scale level close to the base gray scale level. 
     Since the interference sub-pixel data Ed has a gray scale level contrary to those of the R, G and B sub-pixel data Rd, Gd and Bd as stated above, the luminance at the side of the color pixel PXC is distributed near a reference value (e.g., an intermediate luminance value). Since the luminance at the side of the color pixel PXC maintains the reference value, an image displayed on the liquid crystal panel  30  in the narrow viewing angle mode cannot be recognized at all from the side direction, as illustrated in  FIG. 8B . Consequently, the secrecy in the narrow viewing angle mode can be further enhanced. 
     The operation unit  54  that calculates the interference sub-pixel data Ed may be a processor with an operation function. The operation unit  54  may be a look-up table. That is, using the combined R, G and B sub-pixel data Rd, Gd and Bd as one address, the interference sub-pixel data Ed stored at an address corresponding to the logic value of the sub-pixel data is read out from the look-up table. Every time when the R, G and B sub-pixel data Rd, Gd and Bd are received in response to the second interference control signal, the look-up table performs a read operation one time. 
     Depending on the logic value of the wide/narrow mode control signal W/N from the external video source, the selector  56  selects the offset sub-pixel data Eoff from the register  50  or the interference sub-pixel data Ed from the operation unit  54  as an interference data IFD, and transfers the interference data IFD to the video data combiner  42  of  FIG. 7 . When the wide/narrow mode control signal W/N has the specific logic level (i.e., a “high” logic level or a “low” logic level) that designates the narrow viewing angle mode, the selector  56  selects the interference sub-pixel data Ed from the operation unit  54  as an interference data IFD and transfer the interference data IFD to the video data combiner  42 . When the wide/narrow mode control signal WIN has the initialization logic level (i.e., a “low” logic level or a “high” logic level) that designates the wide viewing angle mode, the selector  56  selects the offset sub-pixel data Eoff from the register  50  as an interference data IFD and transfer the interference data IFD to the video data combiner  42 . 
       FIG. 11  is a flow diagram that illustrates an operation of the interference data generator  40  in  FIG. 9 . 
     Referring to  FIG. 11 , the interference data generator  40  determines whether the wide/narrow mode control signal WIN has the specific logic level (i.e., a “high” logic level or a “low” logic level) that designates the narrow viewing angle mode (operation S 10 ). When the wide/narrow mode control signal W/N has the specific logic level (i.e., a “high” logic level or a “low” logic level) that designates the narrow viewing angle mode, the interference data generator  40  sequentially receives R, G and B sub-pixel data Rdi, Gdi and Bdi from the external video source (operation S 12 ) and combines the R, G and B sub-pixel data Rdi, Gdi and Bdi (operation S 14 ). 
     The interference data generator  40  calculates an interference sub-pixel data Edi by Equation (1) using the combined R, G and B sub-pixel data Rdi, Gdi and Bdi (operation S 16 ), and selects the calculated interference sub-pixel data Edi as an interference data IFD to supply the interference data IFD to the video data combiner  42  (operation S 18 ). When the wide/narrow mode control signal WIN has the initialization logic level (i.e., a “low” logic level or a “high” logic level) that designates the wide viewing angle mode, the interference data generator  40  selects the offset sub-pixel data Eoff as an interference data IFD and supplies the interference data IFD to the video data combiner  42  (operation S 20 ). After operations S 18  and S 20 , the interference data generator  40  returns to operation S 10 . 
       FIG. 12  is a detailed block diagram that illustrates another embodiment of the interference data generator  40  in  FIG. 7 . Unlike the interference data generator  40  of  FIG. 9 , the interference data generator  40  of  FIG. 12  uses a memory  58  and a memory controller  60  instead of the data combiner  52  and the operation unit  54 . Descriptions about the same elements as in  FIG. 9  will be omitted for conciseness. 
     Referring to  FIG. 12 , the memory  58  stores the interference sub-pixel data Ed corresponding to the interference sub-pixels ESP 11 ˜ESPmn on the liquid crystal panel  30 . The memory  58  may be nonvolatile memory such as an ROM and an EEPROM. The ROM can retain the interference sub-pixel data Ed even when no power is supplied thereto. The EEPROM can update the interference sub-pixel data Ed, and can retain the interference sub-pixel data Ed even when no power is supplied thereto. The memory  58  that stores the interference sub-pixel data Ed with a specific interference pattern includes as many storage regions as the interference sub-pixels ESP 11 ˜ESPmn of the liquid crystal panel  30 . Some of the storage regions store interference sub-pixel data with a specific gray scale level, while the other of the storage regions store interference sub-pixel data with gray scale levels lower or higher than the specific gray scale level. For example, when interference sub-pixel data Ed that form an “L”-shaped black pattern shown in  FIG. 13  are stored in the memory  58 , storage regions that are second and third column lines while being second to (n−1)th row lines and storage regions that are (n−2)th and (n−1)th row lines while being third to (m−1)th column lines store interference sub-pixel data Ed with a gray scale level corresponding to a black color, while the other storage regions store interference sub-pixel data Ed with a gray scale level corresponding to a white color. The memory  58  may store as many interference sub-pixel data Ed as the number of the interference sub-pixel ESP 11 ˜ESPmn that form a non-“L” shaped interference pattern. 
     When compared to the use of the interference sub-pixel data Ed calculated from the R, G and B sub-pixel data Rdi, Gdi and Bdi contained in the video data VD, the use of the interference sub-pixel data Ed stored in the memory  58  to form an image of a specific interference pattern simplifies a processing path of video data. Accordingly, the response speed of the video data combiner  42  can be enhanced. 
     The memory controller  60  controls the memory  58  using the interference control signal ECS from the timing controller  48  of  FIG. 7 , such that the interference sub-pixel data Ed corresponds to one image that is sequentially read out from the memory  58 . The interference control signal ECS supplied to the memory controller  60  includes a read mode control signal that periodically designates a read operation period. A read clock that allows all of the interference sub-pixel data Ed to be read one time during the read operation period. The memory controller  60  may respond to the wide/narrow mode control signal WIN. The memory controller  60  performs a read operation only when the wide/narrow mode control signal W/N has a specific logic level that designates the narrow viewing angle mode, thereby preventing unnecessary power consumption. 
     Depending on the logic value of the wide/narrow mode control signal W/N from the external video source, the selector  56  selects the offset sub-pixel data Eoff from the register  50  or the interference sub-pixel data Ed from the memory  58  as an interference data IFD, and transfers the interference data IFD to the video data combiner  42  of  FIG. 7 . When the wide/narrow mode control signal W/N has the specific logic level (i.e., a “high” logic level or a “low” logic level) that designates the narrow viewing angle mode, the selector  56  selects the interference sub-pixel data Ed from the memory  58  as an interference data IFD and transfer the interference data IFD to the video data combiner  42 . On the contrary, when the wide/narrow mode control signal W/N has the initialization logic level (i.e., a “low” logic level or a “high” logic level) designating the wide viewing angle mode, the selector  56  selects the offset sub-pixel data Eoff from the register  50  as an interference data IFD and transfer the interference data IFD to the video data combiner  42 . 
       FIG. 14  is a detailed block diagram that illustrates an another embodiment of the interference data generator  40  in  FIG. 7 . 
     Referring to  FIG. 14 , the interference data generator  40  includes a memory  70  and a memory controller  72  that controls a read operation of the memory  70 . The memory  70  stores as many interference sub-pixel data Ed as the number of the interference sub-pixel ESP 11 ˜ESPmn of the liquid crystal panel  30 , which form an image with a specific interference pattern. An image with a specific interference pattern stored in the memory  70  can be mapped in the same manner as for an image with an interference pattern stored in the memory  58  of  FIG. 12 . The memory  70  stores the offset sub-pixel data Eoff that corresponds to an offset value. The memory  70  may be a nonvolatile memory such as an ROM and an EEPROM. The ROM can retain data even when no power is supplied thereto. The EEPROM can update data, and can retain data even when no power is supplied thereto. The interference sub-pixel data Ed or the offset sub-pixel data Eoff read from the memory  70  is selected as an interference data IFD, and the interference data IFD is supplied to the video data combiner  42  of  FIG. 7 . 
     The memory controller  72  controls a successive read operation of the memory  70  using the interference control signal ECS from the timing controller  48  of  FIG. 7 , such that the offset sub-pixel data Eoff stored in the memory  70  are repeatedly read or the interference sub-pixel data Ed that forms an image of a specific interference pattern that are sequentially read. In response to the wide/narrow mode control signal WIN, the memory controller  72  performs a control operation such that the offset sub-pixel data Eoff stored in the memory and the interference sub-pixel data Ed forms an image of a specific interference pattern that are selectively read. When the wide/narrow mode control signal WIN has a specific logic level that designates the narrow viewing angle mode, the memory controller  72  performs a control operation such that the stored interference sub-pixel data Ed forms an image of a specific interference pattern that are sequentially read out from the memory  70  and the interference data IFD that correspond to the read interference sub-pixel data Ed that are transferred to the video data combiner  42  of  FIG. 7 . When the wide/narrow mode control signal WIN has the initialization logic level that designates the wide viewing angle mode, the memory controller  72  performs a control operation such that the offset sub-pixel data Eoff are repeatedly read out from the memory  70  and the interference data IFD that corresponds to the read offset sub-pixel data Eoff are transferred to the video data combiner  42  of  FIG. 7 . 
     The interference data generator  40  of  FIG. 14  has a simpler circuit structure than the interference data generator  40  of  FIG. 12 . 
       FIG. 15  is a flow diagram that illustrates an operation of the memory controller  40  in  FIG. 14 . 
     Referring to  FIG. 15 , the memory controller  40  checks and determines whether the wide/narrow mode control signal WIN has a specific logic level that designates the narrow viewing angle mode or an initialization logic level that designates the wide viewing angle mode (operation S 30 ). 
     When the wide/narrow mode control signal W/N has the specific logic level (e.g., a “high” logic level or a “low” logic level) that designates the narrow viewing angle mode, the memory controller  72  sets an interference sub-pixel data flag allocated to one of its resisters to “1” to set a read mode of the interference sub-pixel data Ed (operation S 32 ). The memory controller  72  sequentially designates storage regions of the memory  70  that stores an image of a specific interference pattern, such that the interference sub-pixel data Ed forming the image of a specific interference pattern are sequentially read (operation S 34 ). These sequentially-read interference sub-pixel data Ed, which are determined to be the interference data IFD, are supplied to the video data combiner  42  of  FIG. 7 . 
     On the contrary, when the initialization logic level (e.g., a “low” logic level or a “high” logic level) that designate the wide viewing angle mode, the memory controller  72  resets an interference sub-pixel data flag that is allocated to one of its resisters to “0” to set a read mode of the offset sub-pixel data Eoff (operation S 36 ). The memory controller  72  repeatedly designates storage regions of the memory  70  that stores the offset sub-pixel data Eoff, such that the offset sub-pixel data Eoff are repeatedly read (operation S 38 ). These sequentially-read the offset sub-pixel data Eoff, which are determined to be the interference data IFD, are supplied to the video data combiner  42  of  FIG. 7 . 
       FIG. 16  is a block diagram of an LCD that limits the viewing angle according to another embodiment. 
     Referring to  FIG. 16 , an LCD according to another embodiment includes a liquid crystal panel  30 A. A interference data generator  40  generates interference data IFD to be supplied to the interference sub-pixels ESP 11 ˜ESPmn on the liquid crystal panel  30 . A video data combiner  42 A adds the interference data IFD to external video data VD. As illustrated in  FIG. 4 , the liquid crystal panel  30 A includes m×n number of color pixels PXC 11 ˜PXCmn that include the red (R) sub-pixels RSP 11 ˜RSPmn connected to the (4k−3)th data lines DL 1 ˜DL 4 m−3. The green (G) sub-pixels GSP 11 ˜GSPmn are connected to (4k−2)th data lines DL 2 ˜DL 4 m−2. The blue (B) sub-pixels BSP 11 ˜BSPmn are connected to (4k−1)th data lines DL 3 ˜DL 4 m−1. The interference sub-pixels ESP 11 ˜ESPmn are connected to (4k)th data lines DL 4 ˜DL 4 m. 
     In response to a wide/narrow mode control signal W/N from an external video source (e.g. a graphic card of a computer), the interference data generator  40  supplies the interference data IFD for switching W/N modes of a viewing angle of the liquid crystal panel  30 A to the video data combiner  42 A. When the wide/narrow mode control signal W/N has a specific logic level (e.g., a “high” logic level or a “low” logic level) that designates a narrow viewing angle mode, the interference data IFD includes interference (E) sub-pixel data Ed that forms an image of a fixed interference pattern, which allows interference light to be added in the both side directions with respect to the front direction of the liquid crystal panel  30 A. The interference data IFD may include interference sub-pixel data Ed that forms an interference pattern that varies per image. The interference data generator  40  may receive the external video data VD from the external video source (e.g., a graphic card of a computer) that generates the interference data IFD with the interference pattern that varies per image. When the wide/narrow mode control signal W/N has an initialization logic level (e.g., a “low” logic level or a “high” logic level) that designates a wide viewing angle mode, the interference data IFD includes offset sub-pixel data Eoff with an offset value, which prevents interference light from traveling in the both side directions with respect to the front direction of the liquid crystal panel  30 A. 
     The video data combiner  42 A receives a video data VD that includes color sub-pixel data for the R, G and B sub-pixels RSP, GSP and BSP from the external video source (not illustrated). The video data combiner  42 A adds the interference data IFD from the interference data generator  40  to the video data VD. The video data combiner  42 A rearranges the R, G, B and E (or offset) sub-pixel data Rd, Gd, Bd and IFD (i.e., Ed or Eoff) in accordance with the arrangement state of the sub-pixels on the liquid crystal panel  30 A, thereby generating combined video data CVD. 
     The LCD according to another embodiment includes a gate driver  44 A that sequentially drives the gate lines GL 1 ˜GLn of the liquid crystal panel  30 A. A data driver  46 A sequentially drives the data lines DL 1 ˜DL 4 m of the liquid crystal panel  30 A. A timing controller  48 A controls the operation timing of the gate and data drivers  44 A and  46 A. In response to a gate timing signal GTS from the timing controller  48 A, the gate driver  44 A generates n number of scan signals that sequentially enables the gate lines GL 1 ˜GLn. 
     In response to a data timing signal DTS from the timing controller  48 A, the data driver  46 A supplies sub-pixel that drives signals to  4 m number of data lines DL 1 ˜LL 4 m every time when any one of the gate lines GL 1 ˜GLn is enabled. To this end, the data driver  46 A receives the combined video data CVD that is serially transferred from the video data combiner  42 A. Whenever any one of the gate lines GL 1 ˜GLn are enabled, the data driver  46 A receives sub-pixel data streams in which R, G, B and E (or offset) sub-pixel data Rd, Gd, Bd, IFD (Ed or Eoff) are arranged sequentially and alternately, such that the R sub-pixel data stream, the G sub-pixel data stream, the B sub-pixel data stream, and the E (or offset) sub-pixel data stream are applied to the (4k−3)th data lines DL 1 ˜DL 4 m−3, the (4k−2)th data lines DL 2 ˜DL 4 m−2, the (4k−1)th data lines DL 3 ˜DL 4 m−1, and the (4k)th data lines DL˜DL 4 m, respectively. 
     When the wide/narrow mode control signal W/N has the specific logic level that designates the narrow viewing angle mode, the interference sub-pixel driving signal has a voltage level that allows the interference sub-pixel ESP to transmit interference light in both side directions with respect to the front direction of the liquid crystal panel  30 A. The quantity of this interference light is adjusted according to the voltage level of the interference sub-pixel driving signal. This quantity of the interference light is added to the quantity of light that travels through the R, G and B sub-pixels RSP, GSP and BSP in the both side directions, such that luminance components at the both sides interfere with each other. As illustrated in  FIG. 8B , an image that cannot be viewed in the side direction is displayed on the liquid crystal panel  30 A. The interference sub-pixel that drives signals have different voltage levels at positions of the interference sub-pixels ESP 11 ˜ESPmn, and thus the color pixels PXC have different interference amounts of luminance. An image displayed on the liquid crystal panel  30 A cannot be recognized at all in the both side directions. Consequently, the secrecy in the narrow viewing angle mode is further enhanced. 
     When the wide/narrow mode control signal W/N has the initialization logic level that designates the wide viewing angle mode, the interference sub-pixel ESP responds to an offset sub-pixel driving signal with an offset voltage level that prevents interference light from traveling in the front and both side directions of the liquid crystal panel  30 A. Due to this offset sub-pixel driving signal, there only exists light that travels through the R, G and B sub-pixels in the front and both side directions of the liquid crystal panel  30 A. As illustrated in  FIG. 8A , an image displayed on the liquid crystal panel  30 A can be viewed in the side direction as well as the front direction. 
     The timing controller  48 A receives sync signals (i.e., vertical and horizontal sync signals and a data clock) from the external video source. Using the sync signals, the timing controller  48 A generates the gate timing signal GTS to be supplied to the gate driver  44 A the data timing signal DTS to be supplied to the data driver  46 A. The timing controller  48 A generates an interference control signal ECS that controls the data generating operation of the interference data generator  40  and a combination control signal CCS that controls the data combining operation of the video data combiner  42 A. 
     As described above, the liquid crystal panel includes the interference sub-pixels as well as the color sub-pixels, thereby limiting the viewing angle thereof. Since the interference sub-pixels and the color sub-pixels are disposed on the same plane or on the same layer, the thickness and weight of the liquid crystal panel do not increase. The viewing angle can be controlled by only one liquid crystal layer, and the decrease of the light quantity and the degradation of the brightness can be prevented. 
     The interference sub-pixels are driven by the interference sub-pixel data that form an image with an interference pattern. An image to be viewed in the side direction of the liquid crystal panel is changed. Consequently, the LCD according makes it possible to enhance the secrecy of a user thereof. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in light of the description above. Thus, it is intended that the description cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.