Patent Publication Number: US-9905178-B2

Title: Liquid crystal display apparatus and method of driving thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-38819, filed on Feb. 28, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiment disclosed here relates to a liquid crystal display apparatus and a method of driving thereof. 
     BACKGROUND 
     An active matrix type liquid crystal display apparatus includes a pair of substrates opposing each other, a liquid crystal layer sandwiched between the pair of the substrates, and a display unit including a plurality of pixels arranged in a matrix pattern. One of the pair of the substrates includes scanning lines arranged along arrays of a plurality of pixel rows and signal lines arranged along arrays of a plurality of pixel columns in the display unit . The oriented state of liquid crystal molecules included in the liquid crystal layer is controlled by an electric field applied to the liquid crystal layer (JP-A-2009-296252 (KOKAI)). 
     Among others, liquid crystal display apparatuses of IPS (In-Plane Switching) system and FFS (Fringe Field Switching) system include a plurality of pixel electrodes arranged on one of the pair of the substrates in the matrix pattern and common electrodes opposing the plurality of the pixel electrodes, and are configured to control the oriented state of the liquid crystal molecules included in the liquid crystal layer by a lateral electric field generated between the pixel electrodes and the common electrodes. These liquid crystal display apparatuses have superior characteristics such as a wide view angle or low power consumption, and are widely applied to displays for TVs and mobile phones. 
     In recent years, there is an increasing demand for a user interface provided on a display surface such as a touch panel for improving operability, and products provided with a contact detecting element on the display surface of the liquid crystal apparatus are spreading in the market. For example, according to JP-A-2009-296252 (KOKAI), the contact detecting element and the liquid crystal display apparatus may be integrated, so that the liquid crystal display apparatus provided with a contact detecting function is provided at low costs. 
     In the above-described liquid crystal display apparatus, the orientation of the liquid crystal molecules included in the liquid crystal layer is controlled by voltages to be supplied to the common electrodes and video signals to be written in the pixel electrodes in sequence. In the configuration disclosed in JP-A-2009-296252 (KOKAI), the common electrodes also serve as wiring for detecting a change of electrostatic capacity caused by a contact on the display surface, and a plurality of the common electrodes are disposed electrically independently in the display surface. 
     The liquid crystal display apparatus and the method of driving the same of the related art will be described in detail below with reference to  FIG. 5  to  FIG. 8 , and the problems will be clarified. The liquid crystal display apparatus here is assumed to be normally black and of the FFS system. 
     (1) Structure of Liquid Crystal Display Apparatus of Related Art 
     The structure of the liquid crystal display apparatus of the related art will be described with reference to  FIG. 5 . 
     As illustrated in  FIG. 5 , the liquid crystal display apparatus of the related art includes a pair of an array substrate (which is not illustrated) and a counter substrate (which is not illustrated) opposing each other, a liquid crystal layer LQ sandwiched between the array substrate and the counter substrate, and a display unit (which is not illustrated) including pixels PX arranged in the matrix pattern. 
     The array substrate is formed of a transparent insulative substrate (which is not illustrated), and pixel electrodes PE arranged on the respective pixels PX, scanning lines GL (GL 1 , GL 2 , GL 3 , . . . ) extending along the rows of the pixel electrodes PE, a scanning line drive circuit GD, signal lines SL (SL 1 , SL 2 , SL 3 , . . . ) extending along the columns of pixel electrodes PE, pixel switches SWP arranged at positions in the vicinity of points of intersection of the scanning lines GL and the signal lines SL, and common electrodes COM arranged so as to oppose the plurality of the pixel electrodes PE via the pixel electrodes PE and the insulating layer (which is not illustrated) on the transparent insulative substrate. The common electrode COM includes column common electrodes arranged along the columns of the pixel electrodes PE (hereinafter referred to as “column common electrode”) COM_Column and row common electrodes COM_Row arranged along the rows of the pixel electrodes PE (hereinafter referred to as “row common electrode”). 
     The pixel switch SWP includes a TFT (Thin Film Transistor) as a switching element. A gate electrode of the TFT is electrically connected to or integrated with the corresponding scanning line GL. A source electrode of the TFT is electrically connected to or integrated with the corresponding signal line SL. A drain electrode of the TFT is electrically connected to or integrated with the corresponding pixel electrode PE. 
     When an ON voltage is applied to the gate electrode of the TFT, electricity is conducted between the source electrode and the drain electrode, and a video signal is supplied from the corresponding signal line SL to the pixel electrode PE. A liquid crystal capacity is formed by the video signal applied to the pixel electrode PE, and a common voltage applied to the common electrodes COM_(COM_Column, COM_Row). 
     The pixel electrodes PE includes, for example, slits at a predetermined interval, and a lateral electric field is generated between the pixel electrode PE and the common electrodes COM_(COM_Column, COM_Row) arranged via an insulating layer. The oriented state of the liquid crystal molecules included in the liquid crystal layer LQ is controlled by the lateral electric field. Each pixel PX further includes an auxiliary capacity CS configured to be coupled with the liquid crystal capacity. The liquid crystal capacity is accumulated in the liquid crystal layer by the electric field applied to the liquid crystal layer. The auxiliary capacity CS is a capacity generated between the pixel electrode PE and the common electrodes COM_(COM_Column, COM_Row). 
     The common electrodes COM_(COM_Column, COM_Row) are wiring of the plurality of the common electrodes which are electrically independent, and also serve as wiring for detecting a change in an electrostatic capacity caused by the contact on the display surface. 
     In a display period, a common voltage is commonly supplied to each of the plurality of common electrodes COM (COM_Column, COM_Row). In a period in which the contact on the display surface is to be detected, independent detecting signals are supplied to the common electrodes COM (COM 1 , COM 2 , COM 3 , . . . ) respectively. 
     In one frame, rewriting of the liquid crystal display is performed in the same manner as the normal liquid crystal display apparatus in sequence on the basis of row scanning, and the detection of the contact on the display surface is performed during a vertical blanking period, so that the display of the liquid crystal and the detection of the contact on the display surface are both achieved. The detection of the contact on the display surface is performed on the basis of the detection signals as described in JP-A-2009-296252 (KOKAI). 
     During the display period, a common voltage common to the column common electrode COM_Column and the row common electrodes COM_Row, is supplied thereto by a common electrode drive circuit COM_Dry. The common electrode drive circuit COM_Dry includes a buffer circuit  1  and an amplitude control circuit  2 . A high potential and a low potential of the common voltage are determined by the amplitude control circuit  2 , and the buffer circuit  1  amplifies a current and supplies the same to the common electrodes COM_(COM_Column, COM_Row) after an adequate amplitude A has been set. 
     A switching element DEMUX_SW includes a demultiplexer, is turned ON in sequence during one horizontal period, and supplies the video signals output from one output terminal of a signal line drive circuit (which is not illustrated) divided temporarily into three signal lines (SL 1 , SL 2 , and SL 3 ) to the same. The video signals supplied to each of the signal lines are supplied to the pixel electrode PE via a pixel switch SWP. 
     (2) Method of Driving Liquid Crystal Display Apparatus of Related Art 
     A method of driving the liquid crystal display apparatus of the related art will be described. In order to simplify the description of the problems of the related art, the driving method will be described in  FIG. 7  with reference to  FIG. 6 , which illustrates a configuration of  FIG. 5  simplified with a smaller number of pixels. 
     As illustrated in  FIG. 6 , the simplified liquid crystal display apparatus includes six scanning lines GL 1 , GL 2 , . . . GL 6 , and includes a column common electrode COM_Column, a row common electrode COM_Row 1 , a row common electrode COM_Row 2 , and a row common electrode COM_Row 3  having the arrayed pixel electrodes PE as a plurality of the common electrodes COM. 
     As illustrated in  FIG. 7 , the gate signal output from the scanning line drive circuit GD is supplied to the scanning lines GL 1 , GL 2 , . . . GL 6  to be driven in sequence by one horizontal period. 
     An AC driving of the liquid crystal is achieved by the signal line drive circuit (which is not illustrated) switching the polarity of the potential of the video signal to be charged to the pixel electrodes PE to positive and negative alternately for the common voltage from one frame to another. 
     When the potential of the video signal in the signal lines varies, in particular, when the video signal is charged by temporarily dividing the one horizontal period by a demultiplexer DEMUX_SW, a charging and discharging current is generated in the pixel electrodes PE of the selected scanning line, and hence the potential variation of the common electrode COM_occurs due to the capacity coupling. 
     However, the common electrodes COM_(COM_Row 1 , COM_Row 2 , COM_Row 3 , COM_Column) are provided as electrically independent wiring in the display surface as wiring for detecting the change of the electric static capacity caused by the contact on the display surface as described above, and hence have different and specific time constants, and the potential is converged independently according to the respective time constants. 
     Since the common electrodes COM_(COM_Row 1 , COM_Row 2 , COM_Row 3 , COM_Column) divide the display area in a plane, the potential variations thereof behave in conjunction with the scanning line included in the corresponding areas. 
     For example, the row common electrode COM_Row 1  includes the scanning lines GL 1  and GL 2  in an area  3  and an area  5 . Therefore, as illustrated in  FIG. 7 , between a period  1  (this period is one horizontal period) and a period  2 , the gate signals GL 1  and GL 2  are input in addition to the coupling between the signal line and the common electrode COM, and hence direct transmission of electric charge with respect to the pixel electrodes PE occurs. Therefore, the potential of the row common electrode COM_Row 1  notably varies. However, in other periods  3  to  6 , the potential variation of the row common electrode COM_Row 1  is caused only by the coupling between the signal line and the common electrode COM, and hence the potential variation is calm. 
     In the same manner, since the row common electrode COM_Row 2  includes the scanning liens GL 3  and GL 4  in an area  6  and an area  8  between the period  3  and the period  4 , direct transmission of the electric charge with respect to the pixel electrodes PE occurs in addition to the coupling between the signal line and the common electrode COM. Therefore, the potential of the row common electrode COM_Row 2  notably varies. However, in other periods  1 ,  2 ,  5 , and  6 , the potential variation thereof is caused only by the coupling between the signal line and the common electrode COM, and hence the potential variation is calm. 
     In the same manner, since the row common electrode COM__Row 3  includes the scanning liens GL 5  and GL 6  in an area  9  and an area  11  between the period  5  and the period  6 , direct transmission of the electric charge with respect to the pixel electrodes PE occurs in addition to the coupling between the signal lien and the common electrode COM. Therefore, the potential of the row common electrode COM_Row 3  notably varies. However, in other periods  1  to  4 , the potential variation of the row common electrode COM_Row 3  is caused only by the coupling between the signal line and the common electrode, and hence the potential variation is calm. 
     In contrast, since the column common electrode COM_Column includes all the scanning liens GL 1 , GL 2 , GL 3 , GL 4 , GL 5 , and GL 6  in the area  4 , the area  7 , and the area  10  in the period  1  to the period  6 , direct transmission of the electric charge with respect to the pixel electrodes PE occurs in addition to the coupling between the signal line and the common electrode COM, so that the potential of the column common electrode COM_Column varies notably and continuously. 
     (3) Problem of Related Art 
     As is clear from the description given above, an effective value of the voltage of the column common electrode COM_Column is smaller than effective values of the row common electrode COM_Row 1 , COM_Row 2 , and COM_Row 3 . Since the liquid crystal responds to the effective value of the AC electric field, the luminance of the pixels belonging to the areas of the column common electrode COM_Column is low. 
     In other words, as illustrated in  FIG. 8 , the area  4 , the area  7 , and the area  10  which belong to the column common electrode COM_Column are darker than other areas, and the display unevenness along the wiring of the column common electrode COM_Column occurs. In  FIG. 8 , the difference in luminance is indicated by a diagonal hatch and a cross hatch marked in the respective areas. 
     Although charging of the common electrodes in the display periods have been focused in the description here, the difference in effective value occurs from one display area to another even in a case where independent signals for inspection are applied to the column common electrode COM_Column and the row common electrodes COM_Row respectively in the vertical blanking period. 
     Accordingly, in view of such problems described above, it is an object of the invention to provide a liquid crystal display apparatus which prevents occurrence of display unevenness is avoided and achieves a desirable quality, and a method of driving the same. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for explaining a liquid crystal display apparatus according to an embodiment; 
         FIG. 2  is a drawing for explaining the liquid crystal display apparatus according to the embodiment; 
         FIG. 3  is a timing chart for explaining an example of a method of driving the liquid crystal display apparatus of the embodiment; 
         FIG. 4  is a drawing for explaining advantages of the liquid crystal display apparatus according to the embodiment; 
         FIG. 5  is a drawing for explaining a liquid crystal display apparatus of the related art; 
         FIG. 6  is a drawing for explaining the liquid crystal display apparatus of the related art; 
         FIG. 7  is a timing chart for explaining an example of a method of driving the liquid crystal display apparatus of the related art; and 
         FIG. 8  is a drawing for explaining problems of the liquid crystal display apparatus of the related art. 
     
    
    
     DETAILED DESCRIPTION 
     According to embodiments, there is provided a liquid crystal display apparatus including: a plurality of pixels arranged on a substrate in a matrix pattern; pixel electrodes arranged on the respective pixels; pixel switches arranged on the respective pixels; scanning lines extending along rows in which the plurality of pixels are arrayed; signal lines extending along columns in which the plurality of pixels are arrayed; a scanning line drive circuit configured to supply gate signals to the scanning lines; a signal line drive circuit configured to supply video signals to the signal lines; a plurality of common electrodes arranged in a display plane electrically independently via the pixel electrodes of the plurality of pixels arranged in a direction of the row and an insulating layer; a row common electrode drive circuit configured to supply a voltage to the common electrodes along the rows in which the pixels are arrayed; and a column common electrode drive circuit configured to supply a voltage to the common electrodes along the column in which the pixels are arrayed, wherein the scanning line drive circuit drives the pixel switches of the respective pixels by the gate signals to be supplied to the scanning lines, connects the signal lines and the pixel electrodes, and supplies the video signals to the respective pixels, and the row common electrode drive circuit and the column common electrode drive circuit control an effective value of a voltage to be applied to the common electrodes along the rows in which the pixels are arrayed and an effective value of a voltage to be applied to the common electrodes along the columns in which the pixels are arrayed. 
     According to the embodiment, there is provided a method of driving a liquid crystal display apparatus, the liquid crystal display apparatus including: a plurality of pixels arranged on a substrate in a matrix pattern; pixel electrodes arranged on the respective pixels; pixel switches arranged on the respective pixels; scanning lines extending along rows in which the plurality of pixels are arrayed; signal lines extending along columns in which the plurality of pixels are arrayed; a scanning line drive circuit configured to supply gate signals to the scanning lines; a signal line drive circuit configured to supply video signals to the signal lines; and a plurality of common electrodes arranged in a display plane electrically independently via the pixel electrodes of the plurality of pixels arranged in a direction of the row and an insulating layer, including driving the pixel switches of the respective pixels by the gate signals to be supplied to the scanning lines, connecting the signal lines and the pixel electrodes, and supplying the video signals to the respective pixels, and controlling an effective value of a voltage to be applied to the common electrodes along the rows in which the pixels are arrayed and an effective value of a voltage to be applied to the common electrodes along the columns in which the pixels are arrayed. 
     Referring now to the drawings, the liquid crystal display apparatus according to an embodiment and the method of driving the same will be described. 
     The liquid crystal display apparatus of the embodiment is also normally black and of the FFS system in the same manner as the related art. A different point of the liquid crystal display apparatus of the embodiment from the liquid crystal display apparatus of the related art is a common electrode drive circuit COM_Dry and an action thereof. Therefore, the same portions as in the related art are denoted by the same reference numerals and detailed description is omitted. 
     (1) Structure of Liquid Crystal Apparatus 
     The common electrode drive circuit COM_Dry of the liquid crystal display apparatus of the embodiment will be described with reference to  FIG. 1 . 
     As illustrated in  FIG. 1 , the common electrode drive circuit COM_Dry includes a buffer circuit  1 R, an amplitude control circuit  2 R, a buffer circuit  1 C and an amplitude control circuit  2 C. 
     The buffer circuit  1 R supplies a voltage to the common electrodes (hereinafter, referred to as “row common electrode”) COM_Row arranged along rows of the pixel electrodes. The amplitude control circuit  2 R determines the amplitude of the voltage that the buffer circuit  1 R supplies. The buffer circuit  1 R and the amplitude control circuit  2 R constitute a row common electrode drive circuit. 
     The buffer circuit  1 C supplies a voltage to the common electrodes (hereinafter, referred to as “column common electrode”) COM_Column arranged along the columns of the pixel electrodes. The amplitude control circuit  2 C determines the amplitude of the voltage that the buffer circuit  1 C supplies. The buffer circuit  1 C and the amplitude control circuit  2 C constitute a column common electrode drive circuit. 
     During the display period, common voltages COM_set individually by the independent buffer circuit  1 R, the amplitude control circuit  2 R, the buffer circuit  1 C and the amplitude control circuit  2 C are supplied to the column common electrode COM_Column and the row common electrodes COM_Row. 
     In other words, the amplitude control circuit  2 R determines a high potential and a low potential for determining the amplitude of the voltage to be applied to the row common electrodes COM_Row, and sets an adequate amplitude A, then the buffer circuit  1 R amplifies the current and supplies the same to the row common electrodes COM_Row. 
     Also, the amplitude control circuit  2 C determines the high potential and the low potential for determining the amplitude of the voltage to be applied to the column common electrodes COM_Column, and sets an adequate amplitude B, then the buffer circuit  1 C amplifies the current and supplies the same to the column common electrodes COM_Column. 
     (2) Method of Driving Liquid Crystal Display Apparatus of Embodiment 
     Subsequently, the method of driving the liquid crystal display apparatus of the embodiment will be described. In order to simplify the description, driving timing will be described in  FIG. 3  with reference to  FIG. 2 , which illustrates a configuration of  FIG. 1  simplified with a smaller number of the pixels. 
     As illustrated in  FIG. 2 , the simplified liquid crystal display apparatus includes six scanning lines GL 1 , GL 2 , . GL 6 , and a plurality of common electrodes COM, and the common electrode COM_includes a column common electrode COM_Column, a row common electrode COM_ROW 1 , a row common electrode COM_Row 2 , and a row common electrode COM_Row 3  as the plurality the common electrodes COM. 
     In the embodiment, when the potential of the video signal in the signal lines varies, in particular, when the video signal is charged by temporarily dividing the one horizontal period by the demultiplexer, a charging and discharging current is generated in the pixel electrodes PE of the selected scanning line, and hence the potential variation of the common electrode COM_occurs due to the capacity coupling, which is the same as in the related art. 
     In the embodiment, the common electrodes COM_(COM_Row 1 , COM_Row 2 , COM_Row 3 , and common electrode COM_Column) have specific time constants different from each other, the potentials are converged independently in accordance with the respective time constants, and the potential variations thereof behave in conjunction with the scanning line included in the corresponding areas in the same manner as the related art. 
     As described in the related art, in the common amplitude, an effective value of the voltage of the column common electrode COM_Column is smaller than effective values of the voltage of the row common electrodes COM_ROW 1 , COM_Row 2 , and COM_Row 3 , and the difference in effective value is generated. 
     Accordingly, in the driving method of the embodiment, the difference of the elective values is compensated in order to equalize the effective values of the respective voltages of the the row common electrodes COM_Row 1 , COM_Row 2 , and COM_Row 3  and the effective value of the column common electrode COM_Column. More specifically, the amplitude control circuit  2 C sets the amplitude of the voltage to be applied to the column common electrode COM_Column to B=A+a, and the smaller effective value of the voltage of the column common electrode COM_Column is inflated. The value of a is determined in advance by experiment or the like and is set to the amplitude control circuit  2 C. 
     (3) Advantages 
     According to the embodiment, as is clear from the description given above, the effective value of the voltage of the column common electrode COM_Column is the same as the effective values of the row common electrodes COM_ROW 1 , COM_Row 2 , and COM_Row 3 . Since the liquid crystal responds to the effective value of the applied AC electric field, such a phenomenon that the luminance of the pixels belonging to an area of the column common electrode COM_Column is lowered as in the related art may be suppressed. 
     In other words, as illustrated in  FIG. 4 , the same luminance as other areas is obtained even in the area  4 , the area  7 , and the area  10  which belong to the column common electrode COM_Column, the display unevenness along the wiring of the column common electrode COM_Column is avoided, and the liquid crystal display apparatus with a desirable quality is achieved.  FIG. 4  illustrates the luminance of the respective areas with a diagonal hatch. 
     (4) Modification 
     In the embodiment, although charging of the common electrodes in the display periods have been focused in the description here, display unevenness is avoided and a liquid crystal apparatus having a good quality is achieved by correcting and adjusting the difference of the effective values occurring from one display area to another by the same method as described above so as to obtain an uniform effective value in the plane also in the case where independent signals for inspection are applied to the column common electrode COM_Column and the row common electrodes COM_ROW respectively in the vertical blanking period. 
     In the embodiment described above, the FFS type liquid crystal display apparatus has been described. Instead, however, the same advantages may be achieved by applying the embodiment as long as the liquid crystal display apparatus is a liquid crystal display apparatus employing DC for the common voltage and configured to invert the polarity of the potential to be applied to the liquid crystal layer LQ by changing the potential of the pixel electrodes PE from frame to frame. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.