JP2007010945A - Liquid crystal display device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cancel image retention to display a clear image. <P>SOLUTION: A liquid crystal display device included; a plurality of scan lines and a plurality of data lines formed on a pair of substrates disposed with an electro-optical material between them; switching elements provided in a plurality of pixels arranged like a matrix correspondingly to respective intersections between the plurality of scan lines and the plurality of data lines; a scan signal supply means for supplying a selection signal to two scan lines out of the plurality of scan lines in one horizontal period of an image signal; and a data signal supply means which supplies a data signal based on the image signal, to pixels corresponding to one of two scan lines selected in one horizontal period by the scan signal supply means, through the data lines and supplies a data signal based on a fixed-level signal, to pixels corresponding to the other through the data lines. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and electronic equipment suitable for displaying moving images.

  The liquid crystal display device is configured by sealing liquid crystal between two substrates such as a glass substrate and a quartz substrate. Each substrate is provided with electrodes, and the optical characteristics of the liquid crystal between the electrodes of each substrate are changed by a drive signal applied to the electrodes. That is, by applying a voltage based on the image signal to the liquid crystal between the electrodes of each substrate, the light transmittance of each pixel is changed according to the image signal to perform image display.

  In an active matrix liquid crystal display device, a drive signal is supplied to an electrode on one substrate via a switching element. As a switching element, there is an element using a two-terminal nonlinear element having bidirectional diode characteristics such as an MIM driving element in addition to an element using a TFT (thin film transistor) driving element. Since the MIM driving element has a steep threshold value, it is advantageous in that it has fewer problems of crosstalk between pixels as compared with a simple matrix driving method that does not use a switching element. And the manufacturing process is relatively simple.

  For gradation display in a liquid crystal display panel using this type of MIM drive element or the like, a binary driver circuit is used as a data side driver circuit, and for example, a period in which each drive element is selected, such as PWM (pulse width modulation). In general, it is performed by controlling a time ratio of taking a binary value (ON or OFF) of a data signal during one selection period in accordance with the gradation level.

  In other words, a pulsed scanning signal VS having a predetermined voltage value (crest value) lower than the width defining the selection period and the threshold voltage of the MIM driving element is supplied to each scanning line (electrode). On the other hand, in this selection period, a data signal VD composed of a pulse having a predetermined voltage value (crest value) is supplied from the data line to the pixel electrode facing the scan line with the liquid crystal interposed therebetween via the MIM driving element. To do.

  If the difference (VS−VD) between these voltage values within the selection period is set so as to exceed the threshold voltage of the MIM drive element, the MIM drive element is turned on only in the pixel to which both are supplied. Is done. As a result, a voltage is charged between the scanning line (counter electrode) and the pixel electrode across the liquid crystal, that is, an applied voltage is applied to the liquid crystal.

  During a period other than the selection period, the MIM driving element is off, the resistances of the MIM driving element and the liquid crystal layer are sufficiently high, and the applied voltage of the liquid crystal layer is maintained. Therefore, it is only necessary to apply a charge to the liquid crystal layer of each pixel during a part of the period. Accordingly, in the liquid crystal display device, when pixels are configured in a matrix corresponding to the intersections of the scanning lines and the data lines extending in the horizontal and vertical directions, respectively, the scanning lines and the data lines are shared by a plurality of pixels. Divided drive is possible.

  That is, in the liquid crystal display device, among the plurality of pixel electrodes connected to the same data line, only the pixel electrode facing the selected scanning line is written during the selection period, and facing the other scanning line. The pixel electrode is in a non-selection period and holds the written voltage. By sequentially selecting the scanning lines, one screen can be displayed.

A method for driving such an MIM liquid crystal display device is described in detail in Patent Document 1 and the like.
Japanese Patent Laid-Open No. 2002-40978

  As described above, the liquid crystal electrically has a capacitive component and holds the applied voltage. Time-division driving is performed by holding the written voltage until the next selection period.

  However, the response speed of the liquid crystal is slow due to the capacitive component of the liquid crystal, and when a moving image is displayed, the written image of the previous frame is displayed as an afterimage. For this reason, the liquid crystal display device has a problem that a blurred image is easily displayed.

  The present invention has been made in view of such problems, and by writing an image and, for example, a black level on different lines in one horizontal period, the image is initialized by black display to remove an afterimage, and clear. An object of the present invention is to provide a liquid crystal display device and an electronic apparatus that can display an image.

  The liquid crystal display device according to the present invention includes a scanning line, a data line, a switching element provided in each pixel provided corresponding to the intersection of the scanning line and the data line, and two horizontal scanning periods. In one selection period of the scanning signal supply unit that supplies a selection signal with a predetermined scanning interval for each of the divided periods, and the scanning period divided by the scanning signal supply unit, A data signal supply means for supplying a data signal based on a gradation signal via the data line, and for supplying a data signal based on a signal of a fixed level via the data line in the other selection period. Features.

  According to such a configuration, the scanning signal supply means divides one horizontal scanning period into two, and supplies a selection signal with a predetermined scanning interval for each of the divided periods. The data signal supply means supplies a data signal based on the gradation signal to each pixel corresponding to one period divided by the scanning signal supply means via the data line, and each pixel corresponding to the other period. And supplying a data signal based on a fixed level signal. Thus, in the same horizontal period, gradation display is performed on each pixel corresponding to one of the two periods, and a fixed level display, for example, black display is displayed on each pixel corresponding to the other period. The By this black display, the previous video writing to each pixel corresponding to the scanning line on which the black display has been performed is erased, and the occurrence of an afterimage is prevented.

  Further, the scanning signal supply means shifts two scanning lines for supplying the selection signal by one line every horizontal period.

  According to such a configuration, the black display is sequentially shifted. Accordingly, the black display can be made inconspicuous on the screen, and the previous video writing can be erased in all the areas, and the afterimage can be prevented.

  Further, the data signal supply means sets a black level signal as the fixed level signal.

  According to such a configuration, the previously written video can be surely erased by the black display, and an afterimage can be prevented.

  The switching element supplies a data signal from the data line to a pixel electrode in the pixel.

  The switching element is a two-terminal element.

  In addition, an electronic apparatus according to the present invention is configured using the liquid crystal display device.

  According to such a configuration, it is possible to prevent the occurrence of an afterimage, and it is possible to display a clear image as well as a clear display of a fast moving image.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device in this embodiment uses a TFD (Thin Film Diode) which is a two-terminal switching element. FIG. 2 is a perspective view schematically showing the entire structure of the liquid crystal panel 10 in FIG. FIG. 3 is a perspective view showing the structure of two adjacent pixel regions.

<Configuration>
In FIG. 1, the liquid crystal panel 10 has a plurality of scanning lines (common electrodes) 21 extending in the row (X) direction in the display area, while data lines (segment electrodes) 31 are arranged in columns (Y). A plurality are formed extending in the direction. Pixels 40 are formed in an m × n matrix corresponding to each intersection of m (320 in FIG. 1) scanning lines 21 and n (160 in FIG. 1) data lines 31. .

  As shown in FIG. 2, the liquid crystal panel 10 has a configuration in which a pair of substrates 11 and 12 are arranged to face each other and a liquid crystal 13 is sealed between the substrates. That is, the counter substrate 12 positioned on the observer side and the element substrate 11 positioned on the back side thereof are bonded together with a predetermined gap by the sealing material 15 mixed with conductive particles serving also as a spacer. . For example, a TN (Twisted Nematic) type liquid crystal 13 is sealed in the gap between the substrates 11 and 12.

  A scanning line 21, a data line 31, and a TFD 41 are configured on each of the substrates 11 and 12. For example, as shown in FIG. 3, the data line 31 is formed on the element substrate 11, and the scanning line 21 is formed on the counter substrate 12. In FIG. 2, for the sake of simplification, the scanning lines 21 and the data lines 31 are indicated by broken lines having no width.

  On the liquid crystal facing surface of the counter substrate 12, in addition to m scanning lines 21 formed extending in the row (X) direction, an alignment film (not shown) is formed and subjected to a rubbing process in a predetermined direction. Yes. The scanning lines 21 formed on the counter substrate 12 are wirings 21c (see FIG. 2) corresponding to the respective scanning lines 21 through conductive particles (not shown) mixed in the sealing material 15 in one-to-one correspondence. Therefore, it is connected to one end of the wiring 21 c formed on the element substrate 11. That is, the scanning line 21 formed on the counter substrate 12 is configured to be drawn out to the element substrate 11 side through the conductive particles and the wiring 21c.

  A rectangular pixel electrode corresponding to the width of each scanning line 21 is adjacent to the n data lines 31 formed extending in the Y (column) direction on the liquid crystal facing surface of the element substrate 11. 43 (not shown in FIG. 2) is formed, and an alignment film (not shown) is formed and a rubbing process is performed in a predetermined direction.

  As shown in FIG. 3, TFDs 41, which are examples of switching elements, are formed between each data line 31 and the pixel electrode 43 adjacent to each data line 31. When the TFD 41 is turned on, a data signal is supplied to the m pixel electrodes 43 per column of each data line 31 through each data line 31.

  The TFD 41 is formed of a tantalum simple substance, a tantalum alloy, or the like, and includes a first conductor 41a connected to the data line 31, and an insulator 41b formed by anodizing the first conductor 41a. And a second conductor 41c such as chromium formed on the insulator 41b and connected to the pixel electrode. Thus, the TFD 41 has a conductor / insulator / conductor sandwich structure and has diode switching characteristics in which the current-voltage characteristics are nonlinear in both positive and negative directions.

  Each pixel electrode 43 on the element substrate 11 faces the scanning line (common electrode) 21 on the counter substrate 12 through the liquid crystal 13. The liquid crystal 13 can be electrically expressed as a liquid crystal capacitance. As shown in FIG. 1, the liquid crystal 13, the pixel electrode 43 (not shown in FIG. 1), and the TFD 41 are interposed between the scanning line 21 and the data line 31. In other words, from an electrical viewpoint, each pixel 40 is configured by a series connection of capacitors by the liquid crystal 13 and the TFD 41.

  The insulator 42 formed on the upper surface of the element substrate 11 has transparency and insulating properties. The reason why the insulator 42 is formed is to prevent the first conductor 41a from being peeled off by heat treatment after the deposition of the second conductor 41c, and to diffuse impurities into the first conductor 41a. This is to prevent it from happening. Therefore, when these do not cause a problem, the insulator 42 can be omitted.

  On the element substrate 11 constituting the liquid crystal panel 10, a Y driver 51 and an X driver 52 for driving the scanning lines 21 and the data lines 31 are formed in a region other than the display region where the pixels 40 are configured. . The X driver 51 as the scanning signal supply means and the Y driver 52 as the data signal supply means are mounted by COG (Chip On Glass) technology. The Y driver 51 supplies a scanning signal to the scanning line 21, and the X driver 52 supplies a data signal to the data line 31. FIG. 3 shows an example in which the Y driver 52 and the X driver 51 are mounted on the element substrate 11 as the driver unit 55.

  Further, an FPC (Flexible Printed Circuit) substrate 16 or the like is attached on the element substrate 11 so that various signals from the control circuit 53 and the drive voltage generation circuit 54 are supplied to the Y driver 51 and the X driver 52. It has become.

  The arrangement of the driver unit 55 (Y driver 51 and X driver 52) in FIG. 1 on the element substrate 11 is an example, and is not limited to the arrangement in FIG. Further, the Y driver 51 and the X driver 52 are not mounted on the element substrate 11 by COG, but, for example, a TAB (Tape Automated Bonding) technique is used to mount a TCP (Tape Carrier Package) on which each driver is mounted on the substrate. It may be configured to be electrically and mechanically connected by an anisotropic conductive film provided at a predetermined position.

  A polarizer (not shown) is attached to the outer (observation side) surface of the counter substrate 12, and its absorption axis is set corresponding to the direction of the rubbing process on the alignment film formed on the counter substrate 12. . A polarizer (not shown) is also attached to the outer surface (opposite the observation side) of the element substrate 11, and the absorption axis thereof corresponds to the direction of rubbing treatment on the alignment film formed on the element substrate 11. Is set.

  In FIG. 1, for the sake of simplicity, the total number of scanning lines 21 is 320, the total number of data lines 31 is 160, and the description will be made as a matrix display device of 320 rows × 160 columns. The present invention is not intended to be limited to this.

  The Y driver 51 supplies scanning signals Y1, Y2,..., Y320 to the scanning lines in the first to 320th rows, respectively. When the Y driver 51 uses the scanning signal as the selection voltage, the scanning line is selected, and the corresponding pixel enters the selection period. While the scanning signal in the selection period is the selection voltage, the scanning signal in the non-selection period (holding period) is set to the non-selection voltage (holding voltage).

  On the other hand, the X driver 52 applies the data signals X1 to X160 to the pixel 40 (pixel electrode 43) located on the selected scanning line 21 in the example of FIG. Supply through. Specifically, in the selection period, a data signal corresponding to each pixel is supplied to the pixel electrode 43 via the corresponding data line 31 and TFD 41.

  As the data signal, two voltages Von and Voff having a positive polarity or a negative polarity are used. Von is a voltage for turning on the TFD 41, and Voff is a voltage for turning off the TFD 41. When Von is given as a data signal when the scanning signal is a selection voltage, the pixel 40 is turned on (for example, black display in the normally white mode). Even when the scanning signal is a selection voltage, when the data signal is Voff, the pixel 40 is turned off (for example, color display in the normally white mode).

  Further, in consideration of polarity inversion driving, the voltage of the data signal in the quaternary driving method ((1/2) H selection, 1H inversion) is displayed when the pixel 40 is turned on when a positive selection voltage is applied ( For example, in the case of black display in the normally white mode), it is −Von, and in the case of displaying the pixel 40 off (white display in the normally white mode), it is + Voff, while a negative selection voltage is applied. When the pixel 40 is on-displayed, it is + Von, and when the pixel 40 is off-displayed, it is −Voff.

  The TFD 41 is turned on, a voltage based on the scanning signal and the data signal is applied to the pixel electrode 43, and the liquid crystal 13 changes to a transmittance based on the data signal. By performing PWM control on the pulse width of Von (Voff) according to the image, gradation display is possible by controlling the transmittance of the pixel 40.

  When the selection period ends, the Y driver 51 sets the scanning signal to the non-selection voltage (holding voltage) until the next selection period. In the non-selection period, the resistance of the TFD 41 is sufficiently large and the resistance of the liquid crystal 13 is also sufficiently large, so that the applied voltage of the liquid crystal 13 is held until writing in the next selection period.

  In the present embodiment, the Y driver 51 outputs a scanning signal for writing to two lines of pixels in the display area in one line image period (one horizontal period) of an image to be displayed. For example, the Y driver 51 uses a predetermined one scanning line (hereinafter referred to as a video writing scanning line) as a selection voltage in the first half of one horizontal period, and a scanning line different from the video writing scanning line in the second half of the horizontal period ( Hereinafter, the black writing scanning line) is set to the selection voltage.

  On the other hand, the X driver 52 corresponds to two voltages Von and Voff having a width based on the input video signal in the first half of one horizontal period in which the video writing scanning line becomes the selection voltage (hereinafter referred to as video writing period). The pixel data line 31 is supplied.

  Further, in the present embodiment, the X driver 52 has a predetermined fixed level (for example, black level) in the latter half of one horizontal period (hereinafter referred to as black writing period) in which the black writing scanning line becomes the selection voltage. Two voltages Von and Voff having a width based on the above are supplied to all the data lines 31. The X driver 52 may supply only the voltage Voff to supply the black level signal to the data line 31 during the black writing period, and set the pulse widths of the voltages Von and Voff as appropriate, thereby obtaining a predetermined gray level signal. May be supplied to the data line 31.

  The X driver 52 supplies a data signal based on the video signal to the data line 31 in the latter half of one horizontal period, thereby setting the latter half of the one horizontal period as the video writing period and the first half of the one horizontal period. In addition, the first half of one horizontal period may be set as the black writing period by supplying a data signal based on the black level to the data line 31.

  The time ratio between the video writing period and the black writing period can be set as appropriate.

  The control circuit 53 supplies various control signals and clock signals to the X driver 52 and the Y driver 51 to control them. The drive voltage generation circuit 54 generates a data signal, a voltage Von that is also used as a non-selection voltage among the scanning signals, and a voltage Vs that is used as a selection voltage among the scanning signals.

  In the present embodiment, the control circuit 53 supplies a data signal based on the video signal to the X driver 52 and also supplies a data signal for displaying a predetermined fixed level (for example, a black level). Be able to.

  Although the example in which the Y driver 51 enables video writing and black writing without increasing the circuit scale by setting the video writing period and the black writing period in a time-sharing manner has been described, two Y drivers are provided. Thus, these periods may be set simultaneously.

<Action>
Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 4 is a timing chart for explaining a scanning signal from the Y driver 51, and FIG. 5 is an explanatory diagram for explaining a screen display in the present embodiment.

  In the present embodiment, the Y driver 51 divides one horizontal period 1H into a first half and a second half, and applies a selection voltage Vs to two different scanning lines to make a selection period. The X driver 52 sets one selection period as a video writing period for writing a data signal based on a video signal, and sets the other selection period as a black writing period for writing a data signal based on a black level, for example.

  FIG. 4 shows this state. FIG. 4A shows an odd frame scan signal, and FIG. 4B shows an even frame scan signal. 4 indicate scanning signals Y1 to Y320 output from the Y driver 51, respectively.

  For example, as indicated by Line 2 in FIG. 4A, in a predetermined horizontal period h2 in which the scanning signal Y2 applied to the scanning line of the second line becomes the selection voltage Vs, the scanning signal Y2 is not detected in the first half of the horizontal period h2. It becomes a negative selection voltage. In the second half of the horizontal period h2, the scanning signal Y318 of the 318th line is a negative selection voltage as indicated by the Line 318 in FIG. That is, in the horizontal period h2, the scanning line of the second line becomes the selection period in the first half, and the scanning line of the 318th line becomes the selection period in the second half.

  In the example of FIG. 4A, in the horizontal period h2, the second line is a black writing period and the 318th line is a video writing period. That is, the X driver 52 supplies a data signal based on the video signal supplied from the control circuit 53 to each pixel 40 through the data line 31 in the first half of the horizontal period h2. The X driver 52 supplies a data signal based on the black level signal supplied from the control circuit 53 to each pixel 40 via the data line 31 in the latter half of the horizontal period h2.

  Therefore, in the horizontal period h2, display based on the video signal is performed on the second line, and black display is displayed on the 318th line. As shown in FIG. 4, the Y driver 52 sequentially shifts the selection voltage generated in the first half and the second half of one horizontal period by one line for each horizontal period. Accordingly, the lines for sequentially displaying the video are shifted by one line every horizontal period, and the lines for displaying the black display are also shifted by one line.

  Thus, in the display area, an image based on the input video signal is displayed and a black display (black band) is displayed with a predetermined line width in the display area. This black belt shifts line by line and is not visually observed.

  FIG. 5 is for explaining this display. In FIG. 5, the hatched portion indicates the area where the video is displayed, and the filled portion indicates the black display area.

  FIG. 5A shows that the first line is the video writing scanning line LP and the Nth line is the black writing scanning line LB. FIG. 5B shows a state in which the video writing scanning line LP has reached the (N-1) th line.

  In the next horizontal period of FIG. 5B, the video writing scanning line LP reaches the Nth line, and the black display is rewritten to the video display AP. On the other hand, the black writing scanning line LB reaches the 2N + 1th line and makes this line the black display AB. That is, the width of the black display AB remains the N line. Thereafter, the same operation is repeated, and the video display AP is displayed while the black display AB is shifted as shown in FIGS. 5 (c) to 5 (f).

  As shown in FIGS. 4 (a) and 4 (b), for each line, a black writing period is set to a predetermined period before a video writing period of an even frame in which video is written next from an odd frame video writing period. Has been. Similarly, the black writing period is set a predetermined period before the video writing period of the odd frame in which the video is written next from the video writing period of the even frame. Therefore, the voltage written in the liquid crystal in the video writing period is forcibly changed to a black level voltage in the black writing period slightly before the next writing period. That is, in each pixel, immediately before the next writing, the holding voltage of the previous writing is forcibly changed to the black level, and the afterimage is canceled.

  As described above, in the present embodiment, by writing an image and, for example, a black level on different lines in one horizontal period, the image is initialized by black display and an afterimage is removed. Thereby, a clear image can be displayed. In addition, clear display is possible even for fast moving images.

  It is obvious that the width of the black display is determined by the interval between the video writing scanning line and the black writing scanning line for starting the black display, and can be set as appropriate. In the above embodiment, an example in which a black level signal is supplied to a pixel during a black writing period has been described. However, it is not always necessary to supply a black level signal, and the same effect can be obtained even in gray display at a predetermined level. It is clear that it is obtained.

  In the above embodiment, the video writing period and the black writing period are both set to H / 2. However, the video writing period and the black writing period may be set within the same horizontal period. Can be set as appropriate. For example, the video writing period may be set longer than the black writing period. Further, the video writing period and the black writing period may be set in reverse order within the same horizontal period.

<Electronic equipment>
Further, an electronic device using the above-described liquid crystal display device is also included in the present invention. FIG. 6 is a perspective view showing an example of an electronic device, and shows the appearance of a mobile phone. As shown in FIG. 6, the above-described liquid crystal display device is used for the display unit 42 of the mobile phone 200 as an electronic device.

  In addition, as an electronic device, for example, a projection display device including a light source, a light valve that modulates light emitted from the light source, and an optical system for projecting light modulated by the light valve It is. In addition, other electronic devices include televisions, viewfinder type / monitor direct view type video tape recorders, car navigation devices, pagers, electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, digital Examples include a still camera and a device equipped with a touch panel. Needless to say, the liquid crystal display device according to the present invention is applicable to these various electronic devices.

1 is a block diagram illustrating a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing an overall structure of the liquid crystal panel 10 in FIG. 1. The perspective view which shows the structure of two adjacent pixel areas. 4 is a timing chart for explaining a scanning signal from a Y driver 51. Explanatory drawing for demonstrating the screen display in this Embodiment. The perspective view which shows the example of an electronic device.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 ... Liquid crystal panel, 21 ... Scan line, 31 ... Data line, 40 ... Pixel, 41 ... TFD, 13 ... Liquid crystal capacity, 43 ... Pixel electrode, 51 ... Y driver, 52 ... X driver, 53 ... Control circuit, 54 ... Drive voltage generation circuit.

Claims (6)

Scanning lines;
Data lines,
Switching elements respectively provided in pixels provided corresponding to intersections of the scanning lines and the data lines;
A scanning signal supply unit that divides one horizontal scanning period into two and supplies a selection signal with a predetermined scanning interval for each of the divided periods;
In one selection period of the scanning period divided by the scanning signal supply means, a data signal based on a gradation signal is supplied via the data line, and in the other selection period, a fixed level is supplied via the data line. Data signal supply means for supplying a data signal based on the signal;
A liquid crystal display device comprising:   2. The liquid crystal display device according to claim 1, wherein the scanning signal supply means shifts two scanning lines supplying the selection signal by one line every horizontal period.   The liquid crystal display device according to claim 1, wherein the data signal supply unit sets a black level signal as the fixed level signal.   The liquid crystal display device according to claim 1, wherein the switching element supplies a data signal from the data line to a pixel electrode in the pixel.   The liquid crystal display device according to claim 1, wherein the switching element is a two-terminal element. An electronic apparatus comprising the liquid crystal display device according to claim 1.

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