Patent Publication Number: US-8537084-B2

Title: Liquid crystal panel and display apparatus including liquid crystal panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and expressly incorporates by reference Chinese patent application No. 200810090489.0 filed Apr. 21, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of liquid crystal displays, and more particularly to a liquid crystal panel and a liquid crystal display apparatus having the same. 
     BACKGROUND OF THE INVENTION 
     With wide applications of the liquid crystal panel, there have been improvements in the development of liquid crystal panels. In order to improve display quality of the liquid crystal panel and decrease power consumption of a liquid crystal display, a conventional liquid crystal panel generally adopts a dot-inversion driving technology, which can improve the display quality of the liquid crystal panel but can increase power consumption of a source driver. 
       FIG. 1  is an equivalent circuit illustrating a part of a conventional liquid crystal panel. As shown in  FIG. 1 , the liquid crystal panel includes N×M pixel units (only 3×4 pixel units are shown in the Figure), where N is the number of columns of the pixel units and M is the number of rows of the pixel units. Each pixel unit  10  includes a gating line G 1 , a gating line G 2 , or a gating line G 3  . . . , a data line D 1 , a data line D 2 , or a data line D 3  . . . , a Thin Film Transistor  101 , a storage capacitor  102  and a liquid crystal capacitor  103 . A common line  11  is configured between the gating lines. One end of the storage capacitor  102  is a pixel electrode (not shown in the Figure); and the other end of the storage capacitor  102  is a storage electrode (not shown in the Figure). One end of the liquid crystal capacitor  103  is a pixel electrode (not shown in the Figure), and the other end of the liquid crystal capacitor  103  is a contraposition electrode (not shown in the Figure). The gate electrode of the Thin Film Transistor  101  (not shown in the Figure) is electrically connected with the gating line G 2 ; the source electrode of the Thin Film Transistor  101  (not shown in the Figure) is electrically connected with data line D 1 ; and the drain electrode of the Thin Film Transistor  101  (not shown in the Figure) is electrically connected with the pixel electrode (not shown in the Figure) through a through hole (not shown in the Figure). 
     In the liquid crystal panel shown in  FIG. 1 , the pixel units  10  with the same polarity in two adjacent columns are electrically connected with one data line. In one frame time, when gating pulses are inputted to different gating lines, i.e. different gating lines are scanned, the amplitude of a voltage applied to a single data line changes little because the pixel units electrically connected with the single data line have the same polarity, and thereby the power consumption of the source driver is decreased relatively. 
       FIG. 2  is a driving simulation chart of the conventional liquid crystal panel shown in  FIG. 1 . At the time of alternation between frames, a single data line provides each pixel unit  10  with a plurality of inverted data voltages. For example, in the n th  frame, a data voltage higher than a common voltage Vcom is applied to the pixel electrode, and the pixel unit has a positive polarity represented as “+”. In the (n+1) th  frame, a data voltage lower than the common voltage Vcom is applied to the pixel electrode, and the pixel unit has a negative polarity represented as “−”. When a gating pulse is applied to a corresponding gating line, the Thin Film Transistor  101  connected with the corresponding gating line is turned on, the data voltage is applied to the pixel electrode (not shown in the Figure), and the liquid crystal capacitor  103  and the storage capacitor  102  are charged. When the gating pulse applied to the corresponding gating line is off, the Thin Film Transistor  101  is disconnected with the corresponding gating line, and the pixel electrode (not shown in the Figure) keeps a voltage value after being charged until the Thin Film Transistor  101  is turned on again. 
     In the n th  frame, the data voltage of 15 V is applied to the data line. After a scanning start signal is applied to a gating line and when the gating line is on a high level, the Thin Film Transistor connected with the gating line is turned on. Through the Thin Film Transistor, the liquid crystal capacitor of the pixel unit is charged with the data voltage of 15V on the data line, and the pixel voltage on the pixel electrode reaches a voltage value equal to the destination data voltage. However, at the moment that the scanning signal is off, a decreasing feed-through voltage ΔVp is generated for the pixel voltage. After the scanning signal is off, the gating line is on a low level, the Thin Film Transistor is disconnected from the gating line, and the pixel electrode keeps the pixel voltage at about 12.5V. The common voltage Vcom is a constant 5V, and the liquid crystal voltage between the two ends of the liquid crystal capacitor maintains a positive voltage of about 7.5V. 
     In the (n+1) th  frame, after the scanning start signal is applied to the gating line and the gating line is on the high level, the Thin Film Transistor connected with the gating line is turned on. Through the Thin Film Transistor, the liquid crystal capacitor of the pixel unit is charged with the data voltage of 0V on the data line, and the pixel voltage on the pixel electrode reaches a voltage value equal to the destination data voltage. However, at the moment that the scanning signal is off, a decreasing feed-through voltage ΔVp is generated for the pixel voltage. After the scanning signal is off, the gating line is on a low level, the Thin Film Transistor is disconnected with the gating line, and the pixel electrode keeps the pixel voltage at about 2.5V. The common voltage Vcom is 5V, and the liquid crystal voltage between the two ends of the liquid crystal capacitor maintains a negative voltage of about 7.5V. 
     In the conventional driving circuit for the Liquid Crystal Display (LCD) apparatus with an In-Plane Switching (IPS) liquid crystal panel or a Fringe-Field Switching (FFS) liquid crystal panel, an invariable Direct Current (DC) voltage value is taken as the common voltage, data voltages with a positive or a negative polarity respectively are provided to the data line in different frames alternatively. The polarities and value of the liquid crystal voltage applied between the two ends of the liquid crystal capacitor in the pixel unit depend on the polarities and values of the data voltage as well as the value of the common voltage. In order to stabilize the liquid crystal voltage at a demanded value, a source driver with a higher output voltage difference must be used so as to apply a high voltage to the pixel unit  10 . This, however, increases the power consumption of the source driver and increases the costs of use of the liquid crystal panel. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention provide a liquid crystal panel, which can decrease power consumption of a source driver and lower cost of the liquid crystal panel. 
     In some examples, a liquid crystal panel includes multiple pixel units; each of the multiple pixel units comprises gating lines, data lines, a pixel electrode and a Thin Film Transistor (TFT). Common electrodes of the first pixel units in the same row of the liquid crystal panel are electrically connected via a first common line, while common electrodes of the second pixel units in the same row of the liquid crystal panel are electrically connected via a second common line. 
     The embodiments of the invention also provide a display apparatus including the above liquid crystal panel. 
     In the embodiments of the present invention, the first common line and the second common line are configured in the IPS liquid crystal panel; the common electrodes of the first pixel units are electrically connected through the first common line; and the common electrodes of the second pixel units are electrically connected through the second common line. When the data voltage is on the high level, the first common voltage Vcom 1  and the second common voltage Vcom 2  change to be on the low level. When the data voltage is on the low level, the first common voltage Vcom 1  and the second common voltage Vcom 2  change to be on the high level. Further, in combination with the change of the data voltage, the source driver with 10V voltage difference can apply 7.5V voltage to the liquid crystals. Comparatively, in the conventional technology, only the source driver with 15V voltage difference can apply 7.5V voltage to the liquid crystals. Therefore, the voltage difference outputted by the source driver in the embodiments of the present invention is smaller, which can decrease the power consumption of the source driver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an equivalent circuit illustrating a part of the conventional liquid crystal panel. 
         FIG. 2  is a driving simulation chart of the conventional liquid crystal panel shown in  FIG. 1 . 
         FIG. 3  is a plan view illustrating a part of a liquid crystal panel according to an embodiment of the invention. 
         FIG. 4  is a plan view illustrating an IPS liquid crystal panel according to a first embodiment of the invention. 
         FIG. 5  is a sectional view along an A-A′ direction after the combination of the upper and the lower substrates in  FIG. 4 . 
         FIG. 6  is an equivalent circuit illustrating a part of a liquid crystal panel according to the first embodiment of the invention. 
         FIG. 7  is a timing chart of common voltages according to the invention. 
         FIG. 8  is a driving simulation chart of the liquid crystal panel according to the invention. 
         FIG. 9  is a plan view illustrating an FFS liquid crystal panel according to a second embodiment of the invention. 
         FIG. 10  is a sectional view along a B-B′ direction after the combination of the upper and the lower substrates in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the invention are described hereinafter with reference to the accompanying drawings and detailed descriptions. 
       FIG. 3  is a plan view illustrating a part of a liquid crystal panel according to an embodiment of the invention. As shown in  FIG. 3 , the IPS liquid crystal panel includes first pixel units, second pixel units, a first common line and a second common line. The common electrodes of the first pixel units in each row are electrically connected via the first common line, and the common electrodes of the second pixel units in each row are electrically connected via the second common line. The first common line and the second common line are connected with a first common voltage and a second voltage respectively. The first common voltage and the second voltage are respectively applied with alternating current voltages with different polarities, so as to drive the pixel units in combination with the change of data signals. 
     For convenience, only an array substrate configured with gating lines, data lines, common lines and Thin Film Transistors is illustrated in  FIG. 3 , and a color filter substrate configured opposite to the array substrate is omitted. As shown in this figure, a first common line  41  is electrically connected with the first common voltage Vcom 1 ; and a second common line  42  is electrically connected with the second common voltage Vcom 2 . When the liquid crystal panel is on, in the n th  frame, the polarities of the pixel units electrically connected with the first common line  41  are opposite to those of the pixel units electrically connected with the second common line  42 . The first common line  41  is electrically connected with the common electrodes of the pixel units with positive polarities, and the second common line  42  is electrically connected with the common electrodes of the pixel units with negative polarities. In the (n+1) th  frame, the polarities of all the pixel units are inverted, the first common line  41  is electrically connected with the common electrodes of the pixel units with negative polarities, and the second common line  42  is electrically connected with the common electrodes of the pixel units with positive polarities. In the embodiments of the invention, with the change of the data signals, the first common voltage Vcom 1  and the second common voltage Vcom 2  also alternate voltages, so as to invert polarities of the pixel units. A specific embodiment illustrating the voltage alternation of the first common voltage Vcom 1  and the second common voltage Vcom 2  will be described in detail with reference to  FIG. 7  and  FIG. 8 . 
       FIG. 4  is a plan view illustrating an IPS liquid crystal panel according to a first embodiment of the invention. In  FIG. 4 , only a Black Matrix (BM) rather than the whole color filter substrate is shown. What is different from a general liquid crystal panel is that the pixel electrode and the contraposition electrode (called a common electrode in this embodiment) in the IPS liquid crystal panel are configured in parallel in the array substrate. Common electrodes  70  of the first pixel units in each row are connected via a first common line  71  and are applied with the first common voltage Vcom 1 . The common electrodes  70  of the second pixel units in each row are connected via a second common line  72  and are applied with the second common voltage Vcom 2 . A Thin Film Transistor  701  receives a scanning start signal from a gating line  74 , applies the data voltage of a data line  73  to a pixel electrode  75  of a liquid crystal capacitor (where the two electrodes of the liquid crystal capacitor in this embodiment are the common electrode  70  and the pixel electrode  75 , respectively), so that the liquid crystal capacitor is charged. The voltage between the two ends of the liquid crystal capacitor increases to be close to the data voltage. A horizontal electric field is formed between the pixel electrode and the common electrode  70  with the common voltage, and the liquid crystal molecules rotate to some angles according to the electric field intensity so that the transmitting light intensity is controlled and the gray scale is formed for display. In addition, each pixel unit further includes a storage capacitor which includes a storage electrode (not shown) and a pixel electrode. 
       FIG. 5  is a sectional view along an A-A′ direction in  FIG. 4 . As shown in  FIG. 5 , the liquid crystal panel includes an upper substrate, a lower substrate and a liquid crystal layer between both substrates. The upper substrate is a color filter substrate, which includes an upper glass substrate  80 , color filters  80   a  and  80   b  attached to the upper glass substrate (where the color filters have three primary colors, RED short for R represented by  80   a , GREEN short for G represented by  80   b , and BLUE not shown in the Figure), and a black matrix  81  configured between the color filters, and partially overlapping the color filters at the two sides thereof to prevent light leakage. 
     The lower substrate is an array substrate which includes a lower glass substrate  83 , a first metal layer, a gate insulation layer  85 , a second metal layer and a passivation layer  86 , where the first metal layer is covered with the gate insulation layer  85 , and the second metal layer is covered with the passivation layer  86 . 
     The first metal layer includes common electrodes  70  and the second common line  72 . The two ends of the second common line  72  are electrically connected with some branches of the common electrodes  70 , respectively. The central top of the second common line  72  corresponds to the black matrix  81  of the upper substrate, and is hidden entirely for preventing light leakage. The first metal layer is covered with the gate insulation layer  85  for preventing the electrical connection between the first metal layer and the second metal layer and the electrical connection among the common electrodes  70  of the first metal layer. 
     The second metal layer which includes pixel electrodes  75  and data lines  73  is configured on the gate insulation layer  85 . The second metal layer is covered with the passivation layer  86 . 
     After the combination of the upper substrate and the lower substrate, the position and characteristic of the first common line is similar to those of the second common line, which will not be described in detail again. 
       FIG. 6  is an equivalent circuit illustrating a part of a liquid crystal panel according to the first embodiment of the invention. As shown in  FIG. 6 , a gating line G 1 , a gating line G 2 , a gating line G 3  etc. intersect respectively a data line D 1 , a data line D 2 , a data line D 3  etc., where a first common line  31  and a second common line  32  are configured between two adjacent gating lines while the first common line  31  is connected with a first common voltage Vcom 1  and the second common line  32  is connected with a second common voltage Vcom 2 . When the pixel units are in the dot-inversion driving manner, each pixel unit  30  has a polarity opposite to polarities of its adjacent pixel units, in other words, the pixel units  30  with the same polarity are not adjacent to each other. The pixel unit  30  includes a Thin Film Transistor  301 , a storage capacitor  302  and a liquid crystal capacitor  303 . Each data line is electrically connected with the pixel units with the same polarity in two adjacent columns. In two adjacent rows, a gating line Gn is electrically connected with all the pixel units in odd/even columns while a gating line Gn+1 is electrically connected with all the pixel units in even/odd columns. For example, the data line D 2  is electrically connected with all the pixel units with the negative polarity in the first column and the second column, and the gating line G 2  is electrically connected with all the pixel units with the positive polarity in the first row and all the pixel units with the negative polarity in the second row. 
       FIG. 7  is a timing chart of common voltages according to the invention. As shown in  FIG. 7 , a first common voltage Vcom 1  and a second common voltage Vcom 2  are in rectangle square wave forms. In the same frame, the first common voltage Vcom 1  and the second common voltage Vcom 2  have opposite polarities. With changes of time sequences, the first common voltage Vcom 1  and the second common voltage Vcom 2  also change their own polarities respectively. For example, in the first frame, the first common voltage Vcom 1  is on the high level and the second common voltage Vcom 2  is on the low level. In the second frame, the first common voltage Vcom 1  is on the low level and the second common voltage Vcom 2  is on the high level. 
       FIG. 8  is a driving simulation chart of the liquid crystal panel according to the invention. The driving simulation chart in  FIG. 8  is obtained when the liquid crystal panel has the following parameters: the ratio of Width to Length of the Thin Film Transistor in each pixel unit is 17/5.3 μm, capacitance of the storage capacitor (Cst) is 479 fF, capacitance of the parasitic capacitor (Cgs) between the gate electrode and the source electrode of the Thin Film Transistor is 29.6 fF, and capacitance of the liquid crystal capacitor (Clc) is 85 fF. 
     In the n th  frame, the data voltages of 10.5V are applied to the data lines. After the scanning start signal is inputted to a gating line and the gating line is on the high level, the Thin Film Transistor electrically connected with the gating line is turned on. Via the Thin Film Transistor, the liquid crystal capacitor of the pixel unit is charged with 10.5V voltage on the data line, and the pixel voltage on the pixel electrode reaches a value equal to the destination data voltage. However, at the moment that the scanning signal is off, a decreasing feed-through voltage ΔVp is generated for the pixel voltage. After the scanning signal is off and when the gating line is on the low level, the Thin Film Transistor is disconnected with the gating line, and the pixel electrode keeps the pixel voltage about 7.5V. In this case, the first common voltage Vcom 1  is on the low level, which is about 0V, and the liquid crystal voltage between the two ends of the liquid crystal capacitor keep a positive voltage about 7.5V. 
     When the first common voltage Vcom 1  changes from the low level 0V to the high level 5V, the pixel voltage on the pixel electrode also changes from the original 7.5V to 12.5V (shown in the part of “Vcom 1  coupling” in  FIG. 8 ) because of the capacitor coupling effect, and the liquid crystal voltage between the two ends of the liquid crystal capacitor keeps a positive voltage about 7.5V. 
     In the (n+1) th  frame, after the scanning start signal is inputted to the gating line and the gating line is on the high level, the Thin Film Transistor connected with the gating line is turned on. Via the Thin Film Transistor, the liquid crystal capacitor of the pixel unit is charged with the 0.5V voltage on the data line, the pixel voltage on the pixel electrode reaches a value equal to the destination data voltage. However, at the moment that the scanning signal is off, a decreased feed-through voltage ΔVp is generated for the pixel voltage. After the scanning signal is off and the gating line is on the low level, the Thin Film Transistor is disconnected with the gating line, and the pixel electrode keeps a pixel voltage of about −2.5V. In this case, the first common voltage Vcom 1  is 5V, and the liquid crystal voltage between the two ends of the liquid crystal capacitor still keeps a negative voltage about 7.5V. 
     Similarly, the second common voltage Vcom 2  having the same high and low levels and the opposite polarity to the first common voltage Vcom 1 , in combination with the change of data voltage applied to the data line, can also make the two ends of the liquid crystals keep the demanded voltage by applying a lower voltage to the data line. 
     As can be seen from the above analysis, when the data voltage applied to the data line is on the high level, the first common voltage Vcom 1  and the second common voltage Vcom 2  of the invention change to be on the low level; when the data voltage applied to the data line is on the low level, the first common voltage Vcom 1  and the second common voltage Vcom 2  change to be on the high level, and further in combination with the change of the data voltage, the source driver with 10V voltage difference can apply 7.5V voltage to the liquid crystal layer. Comparatively, in the conventional technology, only the source driver with 15 voltage difference can apply 7.5V voltage to the liquid crystal layer (referring to  FIG. 2  for details). Therefore, the voltage difference outputted by the source driver in the invention is smaller, which can decrease the power consumption of the source driver. 
       FIG. 9  is a plan view illustrating an FFS liquid crystal panel according to a second embodiment of the invention. In order to clearly describe a pixel unit, only a Black Matrix (BM) of the color filter substrate rather than the whole color filter is shown in  FIG. 9 . Common electrodes  90  of the first pixel units in each row are connected via a first common line  91  and are applied with a first common voltage Vcom 1 ; common electrodes  90  of second pixel units in each row are connected via a second common line  92  and are applied with a second common voltage Vcom 2 . A Thin Film Transistor  901  receives a scanning start signal from a gating line  94 , applies data voltage of a data line  93  to a liquid crystal capacitor so that the liquid crystal capacitor is charged, and the voltage between the two ends of the liquid crystal capacitor increases to be close to the destination data voltage. A horizontal electric field is formed between a pixel electrode  95  and the common electrode  90  with the common voltage, and the liquid crystal molecules rotate to some angles according to the electric field intensity between the two electrodes, so that the transmitting light intensity is controlled and the gray scale is formed for display. 
       FIG. 10  is a sectional view along a B-B′ direction in  FIG. 9 . As shown in  FIG. 10 , the liquid crystal panel mainly includes an upper substrate, a lower substrate and a liquid crystal layer between the both substrates. The upper substrate is a color filter substrate, which includes an upper glass substrate  100 , color filters  100   a  and  100   b  attached to the upper glass substrate  100  (where the color filters have three primary colors, RED short for R represented by  80   a , GREEN short for G represented by  80   b , and BLUE not shown in the Figure), and a black matrix  110  configured between the color filters, and partially overlapping the color filters at the two sides thereof for preventing light leakage. 
     The lower substrate is an array substrate which includes a lower glass substrate  130 , a first metal layer, a gate insulation layer  150 , a second metal layer and a passivation layer  160 , where the first metal layer is covered with the gate insulation layer  150 , the second metal layer is covered with the passivation layer  160 . 
     The first metal layer includes common electrodes  90  and a second common line  92 . The two ends of the second common line  92  cover a part of the common electrodes  90  respectively. The central top of the second common line  92  corresponds to the black matrix  110  of the upper substrate, and is hidden entirely for preventing light leakage. The first metal layer is covered with the gate insulation layer  150  for preventing the electrical connection between the first metal layer and the second metal layer. 
     The second metal layer includes pixel electrodes  95  and data lines  93 . The data lines  93  are configured on the gate insulation layer  150  and are covered with the passivation layer  160 , and the pixel electrodes  95  are configured on the passivation layer  160 . 
     After the combination of the upper substrate and the lower substrate, the position and characteristic of the first common line is similar to those of the second common line, which will not be described in detail again. 
     The embodiments of the invention are described by taking the IPS and FFS liquid crystal panels as examples. However, according to the principle of the invention, the techniques may be applied to other types of liquid crystal panels, such as a Twisted Nematic (TN) liquid crystal panel and so on. The common electrodes of all the pixel units in the TN liquid crystal panel are electrodes forming storage capacitors&#39; electrodes and a third common voltage needs to be inputted to the contraposition electrode of the color filter substrate. The connections among the common electrodes of all the pixel units are similar to those in the IPS and FFS liquid crystal panels, which will not be described in detail again. 
     The foregoing describes the liquid crystal panel of the invention in detail, and several specific examples are used to describe the principle and implementation manners of the invention. The above embodiments are only for better understanding of the method of the invention and the core idea thereof. The protection scope of the invention, however, is not limited to the above description. Any change or substitution, easily occurring to those skilled in the art, should be covered by the protection scope of the present invention.