Abstract:
A liquid crystal display device includes an array of pixels each including a plurality of sub-pixels, a plurality of pixel electrodes disposed in the respective sub-pixels, and a plurality of common electrodes disposed in the respective sub-pixels. The common electrode disposed in each of the sub-pixels in one of the pixels on each row is connected to the common electrodes disposed in the corresponding sub-pixels in the others of the pixels on the each row, to form a group of common electrodes connected together.

Description:
[0001]    This application is based upon and claims the benefit of priority from Japanese patent application No. 2007-133431 filed on May 18, 2007, the disclosure of which is incorporated herein in its entirety by reference. 
       FIELD OF THE INVENTION  
       [0002]    The present invention relates to a liquid crystal display (LCD) device and a terminal unit and, more particularly, to LCD device including a plurality of sub-pixels in each pixel and a terminal unit including the LCD device. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is known a LCD device including a plurality of sub-pixels in each pixel of the LCD device. Examples of such a LCD device include a transflective LCD device wherein each pixel includes a sub-pixel corresponding to a transmissive area and a sub-pixel corresponding to a reflective area. In the transflective LCD device, if a lateral electric field mode, such as an IPS (in-plane-switching) mode or FFS (fringe-field-switching) mode is adopted, a black-white inversion problem is known, wherein display of a dark state and display of a bright state are reversed between the transmissive area and the reflective area such that the transmissive area assumes a normally black mode and the reflective area assumes a normally white mode, as described in Patent Publication JP-2003-344837A, for example. In a typical longitudinal (vertical alignment) mode, the problem of black-white inversion is optically solved by inserting a λ/4 film. However, in the lateral electric field mode, the technique of inserting the λ/4 film cannot be adopted. 
         [0004]    Patent Publication JP-2007-041572A describes a technique for solving the above black-white inversion problem without inserting a λ/4 film. In the technique of this publication, the black-white inversion problem is solved in a specific drive scheme by applying voltages that provide reversed gray-scale levels to the reflective area and the transmissive area.  FIG. 15  shows the circuit configuration of a pixel in the LCD device described in JP-2007-041572A. Each pixel  50  includes a first common electrode  53  corresponding to the reflective area  51 , second common electrode  54  corresponding to the transmissive area  52 , and pixel electrodes  55  and  56  in the reflective area  51  and the transmissive area  52 , respectively, to which a common data signal is applied. The liquid crystal (LC) layer in the reflective area  51  is driven by the electric field generated between the pixel electrode  55  and the first common electrode  53 , whereas the LC layer in the transmissive area  52  is driven by the electric field generated between the pixel electrode  56  and the second common electrode  54 . 
         [0005]    In the technique of JP-2007-041572A, the signal applied to the first common electrode  53  and the signal applied to the second common electrode  54  are reversed. For example, when 5V is applied to the pixel electrodes  55  and  56 , 0V and 5V are applied to the first common electrode  53  and the second common electrode  54 , respectively. In this configuration, 5V is applied to the LC layer in the reflective area  51 , whereas 0V is applied to the LC layer in the transmissive area  52 . Thus, LC molecules in the LC layer are turned only in the reflective area  51 , whereby the problem of black-white inversion is solved. 
         [0006]    JP-2007-041572A describes the relationship of potential inversion between the first common-electrode signal and the second common-electrode signal in each pixel; however, the publication is silent to the relationship in the common-electrode signal between adjacent rows of the pixels in the whole display area of the LCD device. In addition, there is no teaching as to the technique for generating the common-electrode signal and as to the electric connection in the display area. 
       SUMMARY OF THE INVENTION  
       [0007]    It is an object of the present invention to provide a LCD device including a plurality of sub-pixels in a pixel of the LCD device wherein the electric connection for the common electrodes have a specific configuration for solving the problem of black-white inversion. 
         [0008]    The present invention provides, in a first aspect thereof, a liquid crystal display device including: an array of pixels each including a plurality of sub-pixels; a plurality of pixel electrodes each disposed in corresponding one of the sub-pixels; and a plurality of common electrodes each disposed in a corresponding one of the sub-pixels to oppose a corresponding one of the pixel electrodes, wherein: one of the common electrode disposed in each of the sub-pixels in one of the pixels on each row is connected to others of the common electrodes disposed in corresponding sub-pixels in the others of the pixels arranged on the each row, to form a group of common electrodes connected together. 
         [0009]    The present invention provides, in a second aspect thereof, a liquid crystal display device including: an array of pixels each including first and second sub-pixels; first and second pixel electrodes each disposed in the first and second the sub-pixels, respectively; and first and second common electrodes disposed in the first and second sub-pixels, respectively, to oppose the first and second pixel electrodes, respectively, wherein: the first common electrodes in the pixels arranged on an odd-numbered row are connected to the second common electrodes in the pixels arranged on an even-numbered row to form a first group of common electrodes connected together, the second common electrodes in the pixels arranged on the odd-numbered row are connected to the first common electrodes in the pixels arranged on the even-numbered row to form a second group of common electrodes connected together. 
         [0010]    The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a sectional view of a LCD device according to a first embodiment of the present invention. 
           [0012]      FIG. 2  is a schematic circuit diagram of a pixel in of the LCD device of the first embodiment. 
           [0013]      FIG. 3  is a schematic circuit diagram of the LCD device of the first embodiment including a LC driver. 
           [0014]      FIGS. 4A and 4B  are a schematic operation diagram of the LCD device of the first embodiment. 
           [0015]      FIG. 5  is a schematic circuit diagram of the common electrodes in the LCD device of the first embodiment. 
           [0016]      FIG. 6  is a graph showing the relationship between the time constant of the common electrodes and the lateral cross talk. 
           [0017]      FIG. 7  is a timing chart showing the drive signals. 
           [0018]      FIG. 8  is a schematic circuit diagram of a LCD device according to a second embodiment of the present invention. 
           [0019]      FIG. 9  is a schematic circuit diagram of a LCD device according to a modification of the second embodiment. 
           [0020]      FIGS. 10A and 10   b  are schematic operation diagram of the LCD device of the second embodiment. 
           [0021]      FIGS. 11A and 11B  are schematic operation diagram of a LCD device according to a third embodiment of the present invention. 
           [0022]      FIG. 12  is a sectional view of a LCD device according to a modification of the embodiment. 
           [0023]      FIG. 13  is a schematic circuit diagram of a pixel in of the LCD device of  FIG. 12 . 
           [0024]      FIG. 14  is front view of a portable terminal including a LCD device according to an example of the present invention. 
           [0025]      FIG. 15  is a schematic circuit diagram of a LCD device described in a patent publication. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Before describing exemplary embodiments of the present invention, investigation of LCD devices conducted by the present inventors will be described for a better understanding of the present invention. As described before, there arises a black-white inversion problem in a lateral-electric-field mode transflective LCD device. This problem results from the fact that reflective area assumes a normally white mode, wherein the reflective area represents a bright state (white) upon absence of an applied voltage whereas the reflective area represents a dark state (black) upon presence of the applied voltage, and that the transmissive area assumes a normally black mode, wherein the transmissive area represents a dark state upon absence of the applied voltage whereas the transmissive area represents a bright state upon presence of the applied voltage. 
         [0027]    It may be considered that the above black-white inversion problem is solved using different drive voltages to the transmissive area and the transmissive area, wherein the transmissive area is applied with a specific voltage when the reflective area is not applied the specific voltage. The present invention modifies this technique wherein the reflective area is applied with a specific voltage simultaneously with application of another specific voltage to the transmissive area. More specifically, in an example of the present invention, a gate-line-inverting drive scheme is adopted, and a common-electrode signal (COM signal) and an inverted COM signal (COM signal) are generated. These common-electrode signals are applied to the common electrodes in a pixel disposed in an m-th row and an n-th column, i.e., pixel (m, n), wherein the reflective-area common electrodes, comr(n), and transmissive-area common electrodes, comt(n), are connected in a specific configuration. The present invention is based on a specific circuit configuration of the common electrodes and the technique for generating those common-electrode signals. 
         [0028]    Now, exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein similar constituent elements are designated by similar reference numerals for a better understanding of the present invention. It should be noted that IPS-mode LCD devices are exemplified as the most of the following embodiments, the present invention can be applied to lateral-electric-filed mode LCD devices including a FES-mode LCD device. 
         [0029]      FIG. 1  shows the sectional structure of a transflective LCD according to a first embodiment of the present invention. The LCD device  10  includes a first polarizing film  11 , a counter substrate  12  mounting thereon color layers if the LCD device is a color LCD device, an LC layer  13 , a TFT (thin-film-transistor) substrate  14  on which an array of pixels each associated with two TFTs are defined, and a second polarizing film  15 . The polarization direction (direction of optical transmission axis or optical absorption axis) of the first polarizing film  11  and the polarization direction of the second polarizing film  15  are perpendicular to each other. The LC molecules in the LC layer  13  have a major axis aligned with the polarization direction of the first polarizing film  11  or second polarizing film  15  upon absence of the applied voltage. It is assumed here that the optical transmission axis direction of the first polarizing film  11  is at 90 degrees (upward in the figure), the optical transmission axis direction of the second polarizing film is at 0 degree (left in the figure), the direction of the major axis of the LC molecules is at 90 degrees, and these angles are expressed in terms of a clockwise direction. In  FIG. 1 , the arrow attached to the polarizing film denotes the optical transmission axis direction of the corresponding polarizing film, In the LCD device  10 , a pixel  20  is divided into a plurality (two in this example) of sub-pixels each corresponding to a reflective area  21  or a transmissive area  22 . On the TFT substrate  14 , there are provided a reflection film  16  and an insulating layer  17  in the reflective area  21 . The reflection film  16  reflects the light incident through the first polarizing-film  11 . Generally, in order to raise the light dispersion function of the reflection film  16 , the surface thereof has convex and concave portions. In the reflective area  21 , a pixel electrode  35  receiving a drive signal and a common electrode  36  receiving a reference potential are formed on the insulating layer  17  for driving an LC layer  13 . A pixel electrode  36  and a common electrode  38  are also formed in the transmissive area  22  on the TFT substrate  14 . The pixel electrodes  35 ,  36  and common electrodes  37 ,  38  have a shape of comb teeth as viewed from the above in the figure, and may be referred to as comb-teeth electrodes. 
         [0030]    The reflective area  21  uses the light reflected by the reflection film  16  as a light source for display. The LCD device  10  includes a backlight source (not shown) at the rear side of the second polarizing film  15 , and the transmissive area  22  uses the backlight as a light source for display. In the transmissive area  22 , the gap distance between both the substrates  12 ,  14  is adjusted so that the retardation of the LC layer  13  assumes around λ/2. The reason for expressing “around λ/2” is as follows. When a voltage is applied to the LC layer  13  to turn the major axis of the LC molecules, the LC molecules in the intermediate portion of the cell gap are turned whereas the LC molecules in the LC layer  13  in the vicinity of the substrates  12 ,  14  are suppressed for the turn. For this reason, the LC layer  13  has physically an actual retardation of (λ/2)+α to achieve an effective retardation of λ/2. 
         [0031]    On the other hand, in the reflective area  21 , the cell gap is adjusted by controlling the thickness of the insulating film  17  so that the effective retardation of the LC layer  13  assumes λ/4 upon presence of the voltage applied to the LC layer  13 . 
         [0032]      FIG. 2  is a top plan view of the pixel on the TFT substrate in the LCD device of  FIG. 1 .  FIG. 3  shows the schematic circuit configuration of the LCD device  10  including a LC driver for driving the LC layer. On the TFT substrate  14 , there are provided a plurality of gate lines  31  extending in the row direction of the display area  24 , and a plurality of data lines  32  extending in the column direction. Each pixel  20  is associated with a TFT  33  for the reflective area  21  and a TFT  34  for the transmissive area  22 , both the TFTs  33 ,  34  being located in the vicinity of an intersection of a corresponding gate line  31  and a corresponding data line  32 . A first common electrode  37  is provided in the reflective area  21 , and a second common electrode  38  is provided in the transmissive area  22 . 
         [0033]    Now, the drive signal supplied to a pixel (m, n) will be described, the pixel (m, n) being located in the m-th row and the n-th column and including the first common electrode or reflective-area common electrode com(m,n)  37  and the second common electrode or transmissive-area common electrode comt(m,n)  38 . Common electrode signal lines include a COM_ 1 ( m ) line supplying a COM signal to the reflective-area common electrode of the pixels on the m-th row, and a COM_ 2 ( m ) line supplying an inverted COM signal, or ˜COM signal, to the transmissive-area common electrode of the pixels on the m-th row. The COM_ 1 ( m ) line and COM_ 2 ( m ) line provided for the pixels on the m-th row are connected to a first peripheral common-electrode signal line (Peripheral_COM_ 1  line)  25 , and a second peripheral common-electrode signal line (Peripheral_COM_ 2  line)  26 , respectively, which extend in the peripheral area of the LCD device  10  outside the display area  24  thereof. 
         [0034]    The LC driver  41  generates a gate signal supplied to the gate line  31 , a data signal supplied to the data line  32 , and a common-electrode signal, COM signal, based on the pixel signal input thereto and a timing signal. The common-electrode signal, COM signal, is delivered to a VCOM-IC  42 , which inverts the COM signal to generate an inverted COM signal, or ˜COM signal. The COM signal is supplied to the Peripheral_COM_ 1  line  25 , whereas the ˜COM signal is supplied to the Peripheral_COM_ 2  line  26 . The data signal is a gate-line inverted signal that is inverted gate line by gate line, whereas the COM signal and ˜COM signal are also a gate-line inverted signal that is inverted gate line by gate line. 
         [0035]    The technique for driving the LC device  10  as a whole will be described for the case where the common-electrode lines are connected a for the array of pixels such that: 
         [0036]    COM_ 1 ( m ) line is connected to comt(m,n), comt(m,n+1), . . . of the pixels on the m-th row: and 
         [0037]    COM_ 2 ( m ) lines is connected to comr(m,n), comr(m,n+1), . . . .  FIGS. 4A and 4B  exemplify the pixel voltage and COM signal in the reflective area and transmissive area of each pixel, upon display of a bright state and a dark state, respectively, in the LCD device  10 . The pixel voltage is inverted every row by using a gate-line inversion technique, and COM signal and ˜COM signal are also inverted every-row by using a gate-line inversion technique. More specifically, in a single frame of the LCD operation, the COM signal is inverted every row selection period so that potentials 5V, 0V, 5V, 0V, . . . appear in sequence. Similarly, the ˜COM signal is inverted every row selection period so that 0V, 5V, 0V, 5V, . . . appear in sequence, assuming an inverted potential of the COM signal. 
         [0038]    Upon display of a bright state, as shown in  FIG. 4A , the pixel-electrode potential of the reflective area  21  and the transmissive area  22  in the pixels on the m-th row assumes 5V. In this description n is an arbitrary number of the column. The reflective-area common electrode, comr(m,n), of the pixels on the m-th row is connected to the COM electrode line, COM_ 2 ( m ), which supplies the ˜COM signal and assumes 5V upon selection of the m-th line. The transmissive-area common electrode, comt(m,n), of the pixels on the m-th row is connected to the COM_ 1 (m) line, which supplies the COM signal and assumes 0V upon selection of the m-th row. In this case; the LC layer in the reflective area is applied with a voltage equal to |(reflective-area pixel-electrode potential)−(reflective-area common-electrode potential)|=0V, whereas the LC layer in the transmissive area is applied with a voltage equal to |(transmissive-area pixel-electrode potential)−(transmissive-area common-electrode potential)|=5V, whereby both the areas  21 ,  22  represent a bright state. 
         [0039]    On the other hand, upon selection of a (m+1)th row, since the pixel-electrode potential and the common-electrode potential are driven by the gate-line inverting drive scheme, both the reflective-area pixel-electrode potential and transmissive-area pixel-electrode potential are 0V. The reflective-area common electrode, comr(m+1,n), of the reflective area on the (m+1)th row is connected to the COM_ 2 (m+1) line which supplies the ˜COM signal and assumes 0V upon selection of the (m+1)th row. The transmissive-area common electrode, comt(m+1,n) of the transmissive area of the pixels on the (m+1)th row is connected to the COM_ 1 (m+1) line, which supplies the COM signal and assumes 5V upon selection of the (m+1)th row. In this case, the LC layer in the reflective area is applied with 0V, whereas the LC layer in the transmissive area is applied with 5V, whereby both the areas represent a bright state. All the rows including the (m+2)th row and subsequent rows operate similarly to the above m-th row or (m+1)th row, whereby all the pixels on the screen represent a bright state. 
         [0040]    Upon display of a dark state, as shown in  FIG. 4l , the reflective-area pixel-electrode potential and the transmissive-area pixel-electrode potential of the pixels on the m-th row assume 0V. The reflective-area common electrode, comr(m,n), of the pixels on the m-th row is connected to the common-electrode line, COM_ 2 ( m ), which supplies the ˜COM signal and assumes 5V upon selection of the m-th row. The transmissive-area common electrode, comt(m,n), of the pixels on the m-th row is connected to the COM_ 1 ( m ) line, which supplies the COM signal and assumes 0V upon selection of the m-th row. In this case, the LC layer in the reflective area is applied with a voltage equal to |(reflective-area pixel-electrode potential)−(reflective-area common-electrode potential)|=5V, whereas the LC layer in the transmissive area is applied with a voltage equal to |(transmissive-area pixel-electrode potential)−(transmissive-area common-electrode potential)|=0V, whereby both the areas represent a dark state. 
         [0041]    On the other hand, for the pixels connected to the (m+1)th row, since both the pixel-electrode potential and the common-electrode potential are driven by a gate-line inverting drive scheme, the reflective-area pixel-electrode potential and transmissive-area pixel-electrode potential assume 5V. The reflective-area common electrode, comr(m+1,n) of the (m+1)th row is connected to the COM_ 2 (m+1) line, which supplies the COM signal and assumes 0V upon selection of (m+1)th row. The transmissive-area common electrode, comt(m+1, n), of pixels on the (m+1)th row is connected to the COM_ 1 (m+1) line, which supplies the COM signal and assumes 5V upon selection of the (m+1)th row. In this case, the LC layer in the reflective area is applied with 5V, whereas the LC layer in the transmissive area is applied with 0V whereby both the areas of the (m+1)th row represent a dark state. Operation of (m+2)th row is similar to that of the m-th row. 
         [0042]    Detail of the circuit configuration of the common-electrode lines including the Peripheral_COM_ 1  line  25  and Peripheral_COM_ 2  line  26  will be exemplified hereinafter.  FIG. 5  shows an example of connection for the common-electrode lines in the LCD device  10 . The COM signal output from the LC driver  41  is supplied to the Peripheral_COM_ 1  line  25 , which supplies the COM signal for the transmissive area. The COM signal is also input to the inverting amplifier VCOM-IC  42 , which generates the ˜COM signal and supplies the ˜COM signal to the Peripheral_COM_ 2  line  26 . The VCOM-IC  42  raises the signal amplitude of the ˜COM signal to increase the drive voltage for the reflective area. The reason for using a higher signal amplitude in the reflective area compared to the transmissive area is that an ON-OFF control of the comb-teeth electrodes of the pixel electrode and common electrode is not performed in the reflective area, and thus for achieving a higher contrast ratio in the transmissive area, a larger distance should be adopted between the pixel electrode and the common electrode in the reflective area, which reduces the electric field per voltage therebetween. 
         [0043]    As to the layout configuration of the Peripheral_COM_ 1  line  25 , a plurality of gate lines  31 , and the Peripheral_COM_ 2  line  26 , it is preferable that the layout of these lines outside the display area  24  follows in the order of the Peripheral_COM_ 1  line  25 , gate lines  31  and the Peripheral_COM_ 2  line  26  as viewed from the display area  24  of the LCD device  10 . The reason for disposing the Peripheral_COM_ 1  line.  25  nearest to the display area  24  is that the Peripheral_COM_ 1  line  25  supplies a signal to the transmissive area, which requires a higher image quality compared to the transmissive area, and thus it is desirable that the Peripheral_COM_ 1  line  25  have a lower resistance and thus a smaller time constant. The smaller time constant suppresses distortion of the lo signal waveform of the COM signal and also reduces the lateral cross talk. 
         [0044]    Detail of the layout of Peripheral COM lines will be described. In general, the LC driver  41  has a pair of COM terminals at both the ends of the LC driver  41  attached to the LCD panel of the LCD device  10  at one side thereof Thus, in the present embodiment, the Peripheral_COM_ 1  line  25  extends from the COM terminals of the LC driver  41  and configures a loop extending along the three sides of the display area  24 . The loop of the Peripheral COM lines lowers the voltage drop of the COM lines and thus suppresses distortion of the signal waveform of the COM signal and ˜COM signal applied to the pixels. In the present embodiment, the Peripheral_COM_ 1  line  25  is formed from a gate (G) layer which is configured to form the gate lines  31 , and enters from the LC driver  41  to the display area  24  after crossing a seal member  27  which defines the outer periphery of the display area  24 . The seal member  27  is used for sealing the LC layer between the TFT substrate and the counter substrate. After crossing the seal member  27 , the Peripheral COM_ 1  line is connected via through-holes  23  to a data (D) layer which is also configured to form data lines, and extends along the outer periphery of the display area  24  inside the seal member  27 . This configuration is adopted because the gate layer is covered by a gate insulation layer and an overcoat layer, whereas the data layer is covered only by the overcoat layer, and thus the gate layer is less likely to be corroded by ingress of water compared to the data layer outside the seal member  27 . The gate lines extend from the LC driver  41  and enter the display area  24  after crossing the seal member  27 . The gate lines  31  cross the Peripheral_COM_ 1  line  25  after the Peripheral COM_ 1  line  25  is configured by the data layer. That is, in this configuration, the Peripheral_COM_ 1  line  25  can intersect the gate lines  31  at any position within the display area  24 . 
         [0045]    On the other hand, since the Peripheral_COM_ 2  line  26  extends from the VCOM_IC  42 , the Peripheral_COM_ 2  line  26  is arranged outside the COM terminals and gate terminals of the LC driver  41 . Therefore, the Peripheral_COM_ 2  line  26  is disposed outside the peripheral gate line as viewed from the display area  24 . Since the location outside the gate line  31  means outside the seal member  27 , the Peripheral_COM_ 2  line  26  is configured by the gate layer. The Peripheral_COM_ 2  line  26  extends to the peripheral position opposite to the LC driver  41 , is subjected to G/D conversion at the through-holes and then again extends toward the LC driver  41  as the data layer within the display area  24  inside the seal member  27 . The Peripheral_COM_ 2  line  26  is introduced into the display area  24  after this G/D conversion. 
         [0046]      FIG. 6  shows the relationship between the time constant of COM line and the lateral cross talk. This figure exemplifies a chrome (Cr) metal extending as the Peripheral_COM_ 1  line  25  on a 3.5″ QVGA (240×320) panel. If the Peripheral_COM_ 1  line  25  extends outside the Peripheral_COM_ 2  line, the time constant may assume 35 microseconds as indicated by “B” in the graph, which cause a 4%-level cross talk. On the other hand, as shown by “A” in the graph, if the Peripheral_COM_ 1  line  25  extends inside the Peripheral_COM_ 2  line, the time constant may assume 20 microseconds, which reduces the cross talk down to a 2% level. 
         [0047]    By the way, the reason for using the driver COM output signal as the transmissive-area COM signal and generating the inverted COM signal, ˜COM, by using the driver COM signal as an input is as follows. In the case of lateral-electric-field mode, since the gap distance between the reflective area and the transmissive area varies from the location to th location and a compensation film is not used therein, VT (voltage-transmittance) and VR (voltage-reflectance) characteristics of the LCD device do not coincide with each other. Thus, it is determined that the amplitude of the driver output voltage be 5V, and the amplitude of the output voltage of the VCOM-IC  42  be 8V. 
         [0048]      FIG. 7  shows the drive voltage waveform having an offset voltage in this case. The term “offset voltage” is a deviation of the center value of the amplitude of the voltage with respect to 0V. It is assumed here that the potential of the Peripheral_COM_ 2  line  26 , i.e., the reflective-area common-electrode potential (R-COM potential) is varied within an amplitude of 8V between −3V and 5V. It is also assumed that the potential of the Peripheral_COM_ 1  line  25 , i.e., the transmissive-area common-electrode potential (T-COM potential) is varied within an amplitude of 5V between −1.5V and 3.5V. In this case, the reflective area is driven in an offset drive of (8-5)V/2=1.5V. By using this configuration, the VT characteristic of the reflective area (inverted VR characteristic) and the VT characteristic of the transmissive area can be adjusted to have an offset voltage. 
         [0049]    The VCOM-IC  42  eliminates the DC component of the transmissive-area COM signal by using a capacitor, then inverts the same, and amplifies in voltage if needed. The VCOM-IC  42  is configured so that the center value of the inverted COM signal may be adjusted in an offset control circuit. In general, if the center value of the transmissive-area and reflective-area COM signals is deviated from a flicker minimum voltage, a flicker is generated. In addition, the flicker minimum value is generally different between the reflective area and the transmissive area depending on the way of TFT leakage current and the storage capacitance of the reflective/transmissive area. By inputting the transmissive-area COM signal after eliminating the DC component thereof, and adjusting the center value of the inverted COM signal in an off adjusting circuit, it is possible to suppress the flicker in both the reflective area and transmissive area. The suppression of the flicker eliminates the DC component from the LC, thereby achieving a transflective LCD having a higher resistance against both burning and stain. 
         [0050]    In the description of the present embodiment, the technique for supplying the common-electrode signal to the reflective area and transmissive area of the pixels arranged in a plurality of rows is detailed. This technique achieves an effective drive of a lateral-electric-field-mode transflective LCD device. In addition, use of the COM signal output from the LC driver as the transmissive-area common-electrode signal, and generation of the amplified inverted common-electrode signal, ˜COM, from the COM signal provides an effective technique for allowing coincidence of the VT characteristic between the reflective area and the transmissive area, and eliminating the factor impeding a display quality, such as cross talk or flicker. Further, by optimizing the extension of the two COM lines in the peripheral area, the transmissive LCD device has an improved image quality substantially without incurring a cross talk. 
         [0051]    A second embodiment of the present invention will be described hereinafter. The sectional view and optical arrangement of the LCD device are similar to those of the first embodiment, and are omitted for description and depiction thereof  FIG. 8  shows a sectional view of the LCD device of the present embodiment including a driver for driving the LC. The TFT substrate  14  mounts thereon a plurality of gate lines  31  extending in a row direction, a plurality of data lines  32  extending in a column direction, and an array of pair of TFTs disposed in the vicinity of an intersection of a gate line and a data line. The pair of TFTs are disposed for a single pixel, and include a first TFT  33  for a reflective area and a second TFT  34  for a transmissive area. The TFTs  33 ,  34  are connected to the reflective-area pixel electrode and transmissive-area pixel electrode, respectively. The reflective area  21  includes a first common electrode, and the transmissive area  22  includes a second common electrode. 
         [0052]    A pixel (m,n) located on a m-th row and n-th column includes a reflective-area common electrode, comr(m,n), and a transmissive-area common electrode, comt(m,n). A COM_ 1 ( m ) line extends on the m-th row for supplying the common-electrode signal, COM, to the reflective area, and a COM_ 2 ( m ) line extends on the m-th row for supplying the inverted common-electrode signal, ˜COM, to the transmissive area. The COM_ 1 (2m) line is connected to the transmissive-area common electrodes comt(2m,n), comt(2m,n+1), on the 2m-th row, whereas a COM_ 2 (2m+1) line is connected to the transmissive-area common electrodes comt(2m+1,n), comt(2m+1,n), . . . on the (2m+1)th row. The COM_ 2 (2m) line is connected to the reflective-area common electrodes comr(2m,n), comr(2m,n+1), . . . , whereas the COM_ 1 (2m+1) line is connected to the reflective-area common electrodes comt(2m+1,n), comt(2m+1n+1), . . . . In short, the pixels on the even-numbered row has a connection configuration opposite to the connection configuration of the pixels on the odd-numbered row as to the relationship between the COM_ 1  and COM_ 2  lines. 
         [0053]    The LC driver  41  generates a gate signal supplied to the gate lines  31 , a data signal supplied to the data line  32 , and a common-electrode signal, COM signal, supplied to the common electrodes, based on the input pixel signal and a timing signal. The VCOM-IC  42  receives the common-electrode signal, COM, and generates therefrom an inverted COM signal. Although COM_ 1 (2m+1) and COM_ 1 (2m) signals are separately generated in  FIG. 8 , the COM_ 1 (2m+1) signal is the same as the COM_ 1 (2m) signal, and thus the signal lines for these signals may be integrated, as shown in  FIG. 9 . That is, the transmissive-area common-electrode signal, COM 1 (2m), for the pixels on the 2m-th row is the same as the reflective-area common-electrode signal, COM_ 1 (2m+1), for the pixels on the adjacent (2m+1)th row. 
         [0054]      FIGS. 10A and 10B  are an operation diagram showing the drive voltage for the pixels upon display of a bright state and a dark state, respectively, associated with a waveform signal of the pixel signals and the COM signals. The LCD device uses a gate-line inverting drive scheme for the pixel signals, whereas the LCD device uses a frame inverting drive scheme for the COM signal and ˜COM signal pixel. More specifically, in a frame, COM 1  signal is constant at 5V, and COM 2  signal is constant at 0V. Since COM 1 (2m) signal and COM 1  (2m+1) signal have the same potential, the signal lines for supplying COM_ 1 (2m) and COM_ 1 (2m+1) signals are shown as an integrated line in  FIG. 10 . 
         [0055]    Upon display of a bright state, as shown in  FIG. 10A , the reflective-area pixel-electrode potential and the transmissive-area pixel-electrode potential on the 2m-th row are at 5V The common electrode, comr(2m,n) of the reflective-area of the pixels on the 2m-th row is connected to the common-electrode line, COM_ 2 (2m), which receives inverted COM signal and assumes 5V upon selection of the 2m-th row. On the other hand, the transmissive-area common electrode, comt(2m,n), of the pixels on the 2m-th row is connected to the COM_ 1 (2m) line, which receives the COM signal and assumes 0V upon selection of the 2m-th row. Thus, the LC layer in the reflective area is applied with 0V, whereas the LC layer in the transmissive area is applied with 5V, whereby LC layer in both the areas represents a bright state. 
         [0056]    The reflective-area pixel-electrode potential and the transmissive-area pixel-electrode potential on the (2m+1)th row assume 0V, due to the gate-line inverting drive scheme. The reflective-area common electrode, comr(2m+1,n), of the pixels on the (2m+1)th row is connected to the COM_ 1  (2m+1) line, which receives the COM signal and assumes 0V due to the frame inverting drive scheme. The transmissive-area common electrode of the pixels on the (2m+1)th row is connected the COM_ 2 (2m+1) line, which receives the inverted COM signal, COM signal, and assumes 5V upon selection of the (2m+1)th row. Thus, the LC layer in the reflective area is applied with 0V, and the LC layer in the transmissive area is applied with 5V, whereby the LC layer in both the areas represent a bright state. The COM signals of the pixels on the (2m+2)-th row is similar to the COM signals of the pixels on the 2m-th row. 
         [0057]    Upon display of a dark state, as shown in  FIG. 10B , the reflective-area pixel-electrode potential and transmissive-area pixel-electrode potential on the m-th row is 0V. The reflective-area common electrode, comr(2m,n), is connected to the common-electrode line, COM_ 2  (2m), of the 2m-th row, which receives the inverted COM signal, ˜COM, and assumes 5V upon selection of the 2m-th row. The transmissive-area common electrode, comt(2m,n), of the pixels on the 2m-th row is connected to COM_ 1 (2m) line, which receives the COM signal and assumes 0V upon selection of the 2m-th row. Therefore, the LC layer in the reflective area is applied with 5V, and the LC layer in the transmissive area is applied with 0V, whereby the LC layer in the reflective area and transmissive area represents a dark state. 
         [0058]    The reflective-area pixel-electrode potential and transmissive-area pixel-electrode potential of the pixels on the (2m+1)th row is 5V due to the gate-line inverting drive scheme. The reflective-area common electrode, comr(2m+1,n) of the pixels on the (2m+1)th row is connected to the COM_ 1 (2m+1) line, which receives the COM signal and assumes 0V upon selection of the (2m+1)th row due to the frame inverting drive scheme. The transmissive-area pixel electrode of the pixels on the (2m+1)th row is connected to the COM_ 2 (2m+1) line, which receives the inverted COM signal, COM, and assumes 5V upon selection of the (2m+1)th row. Therefore, the LC layer in the reflective area is applied with 5V, and the LC layer in the transmissive area is applied with 0V, whereby the LC layer in the reflective area and transmissive area represents a dark state. The subsequent (2m+2)th row is similar to the 2m-th row. 
         [0059]    In the present embodiment, the COM signal driven by the frame inverting drive scheme reduces the power dissipation. In addition, as shown in  FIG. 9 , the reflective-area common-electrode line of the pixels on the 2m-th row can be integrated with the transmissive-area common-electrode line of the pixels on the (2m+1)th row, to thereby increase the aperture ratio of the LCD device, which is defined by an effective display area to the total display area. 
         [0060]    The method of driving the LC layer is not limited to the above embodiments. For example, the COM potential and inverted COM potential may be driven in a frame inverting drive scheme, whereas the pixel-electrode potential is driven in the frame inverting drive scheme.  FIGS. 11A and 11B  show a bright state and a dark state, respectively, in which both the pixel-electrode potential and the COM potential are driven by a frame inverting drive scheme. This configuration further reduces the power dissipation. 
         [0061]    In the above embodiments, each pixel includes a reflective area corresponding to a first sub-pixel, and a transmissive area corresponding to a second sub-pixel; however, each pixel in the LCD device of the present invention may include two or more sub-pixels. In such a case the term “odd-numbered row” and “even-numbered row” may be replaced by m-th row, (m+1)th row and (m+2)th row where m is an integer equal to or more than zero. 
         [0062]      FIG. 12  is sectional view of a LCD device according to a modification of the first embodiment. This modification is an example of the FFS-mode LCD device to which the first embodiment of the present invention is applied. In both the reflective area  21  and transmissive area  22 , the common electrode  35 ,  36  are formed on the TFT substrate  14 , and are isolated from each other by an intervening insulation film  17 . Electric field for the LC layer  13  is generated between the fringe of the pixel electrode  35 ,  36  and the common electrode  37 ,  38 . The first common electrode  37  functions as a reflector in the reflection area  21 . 
         [0063]      FIG. 13  is a schematic circuit diagram of a pixel in of the LCD device of  FIG. 12 .  FIG. 13  corresponds to  FIG. 2  showing the circuit configuration of the pixel in the LCD device of the first embodiment. Both the first and second pixel electrodes  35 ,  36  are configured as a comb-shaped electrode, whereas the first and second common electrodes  37 ,  38  are of a flat shape. Other configurations of the LCD device of the modification are similar to those of the LCD device of the first embodiment. 
         [0064]      FIG. 14  shows a front view of a portable terminal including a LCD device according to an example of the present invention The portable device  60  includes the LCD device  10  as a display unit for the portable device. Other constituent elements of the portable device  10  are configured by typical devices, and thus are omitted for detailed description. 
         [0065]    While the invention has been particularly shown and described with reference to exemplary embodiment and modifications thereof, the invention is not limited to these embodiment and modifications. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined in the claims,