JP2008185758A - Liquid crystal device, method for driving the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a response time in motion picture display by applying a second reference voltage which is lower than a first reference voltage to a liquid crystal element in a third period. <P>SOLUTION: The liquid crystal device is driven by repeating first to third periods T1 to T3. In the first period T1, a gradation voltage Vb is applied to the liquid crystal element. In the second period T2, a first reference voltage Vb required to maintain a bend state is applied to the liquid crystal element. In the third period T3, a second reference voltage Vw which is lower than the first reference voltage Vb is applied to the liquid crystal element. A backlight is turned on in the first period T1 and turned off in the second period T2 and in the third period T3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal device using a liquid crystal having a bend state and a splay state as an alignment state, a driving method thereof, and an electronic apparatus.

  A liquid crystal device that performs display by changing the transmittance of liquid crystal is widely used as a display device such as an information processing device or a television. In this display device, pixel electrodes are formed corresponding to the intersections of scanning lines extending in the row direction and data lines extending in the column direction. In addition, a pixel switch such as a thin film transistor (hereinafter referred to as a TFT: Thin Film Transistor) that is turned on and off according to a scanning signal supplied to the scanning line is interposed between the pixel electrode and the data line at the intersection. It is. Further, a counter electrode is provided so as to face the pixel electrode through the liquid crystal. The alignment state of the liquid crystal changes according to the applied voltage between the pixel electrode and the counter electrode. As a result, the amount of transmitted light in the pixel changes, and a predetermined display becomes possible.

An OCB (Optical Compensated Bend) liquid crystal has a splay state and a bend state. Compared with TN (Twisted Nematic) liquid crystal in the bend state, high-speed response is possible. In the initial state, that is, the state where the applied voltage is 0 V continues for a long time, the OCB liquid crystal is in the splay state. In order to shift from the splay state to the bend state, it is necessary to apply a high voltage for a certain period of time. Although a high-speed response is possible in the bend state, the alignment state returns to the splay state unless a voltage of a predetermined level or higher is applied for a certain period of time. Therefore, a technique is known in which a voltage of a predetermined level or higher is applied to a normally white OCB liquid crystal at a predetermined cycle and the backlight is turned off at this time (for example, Patent Document 1).
JP 2002-31790 A

By the way, in the normally white OCB liquid crystal, the response time when changing from black display (predetermined voltage application) to white display (application voltage 0 V) is compared with the response time when changing from white display to black display. long.
For this reason, when black is written in the OCB liquid crystal at a predetermined cycle, the alignment state does not immediately change even when a voltage corresponding to the gradation to be displayed is applied to the OCB liquid crystal. That is, there is a problem that it takes time for the response and the advantage of the high-speed response is not sufficiently brought out.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid crystal device capable of high-speed response in OCB liquid crystal, a driving method thereof, and an electronic apparatus.

  In order to solve the above-described problem, a driving method of a liquid crystal device according to the present invention includes a pixel electrode, a counter electrode, a bend state and a splay state as an alignment state sandwiched between the pixel electrode and the counter electrode. A liquid crystal device including a liquid crystal panel including a liquid crystal element including a liquid crystal is driven repeatedly in a first period, a second period, and a third period, and display is performed in the first period. A gradation voltage corresponding to a power gradation is applied to the liquid crystal element, and a first reference voltage necessary to maintain a bend state is applied to the liquid crystal element in the second period, and in the third period, A second reference voltage lower than the first reference voltage is applied to the liquid crystal element.

  In a liquid crystal having a bend state and a splay state, the transition time from the high voltage transmittance to the low voltage transmittance is longer than the time required to change from the low voltage transmittance to the high voltage transmittance. According to the present invention, since the second reference voltage lower than the first reference voltage is applied to the liquid crystal element in the third period, the transmittance of the liquid crystal can be changed before the first period is started. . As a result, the response characteristic of the transmittance can be improved, and even a fast-moving image can be displayed with a high quality image with reduced blur.

  Here, when the liquid crystal device includes a light source that emits light toward one surface of the liquid crystal panel, the light source is turned on in the entire first period, and a part of the third period or In all, it is preferable to turn off the light source. In the third period, the transmittance increases because a low voltage is applied to the liquid crystal. However, since the light source is turned off at this time, the influence on the gradation display can be reduced.

Next, a liquid crystal device according to the present invention includes a liquid crystal panel having a plurality of scanning lines, a plurality of data lines, and a plurality of pixel circuits provided corresponding to intersections of the scanning lines and the data lines. ,
Data obtained by time-division-multiplexing a gradation voltage corresponding to a gradation to be displayed, a first reference voltage necessary for maintaining a bend state, and a second reference voltage lower than the first reference voltage in one horizontal scanning period Data line driving means for supplying a signal to the plurality of data lines, and a period of one frame is divided into a first period, a second period, and a third period, and in each horizontal scanning period of the first period, the gray level A period in which the plurality of scanning lines are sequentially selected in a period in which a voltage is supplied to the plurality of data lines, and a period in which the first reference voltage is supplied to the plurality of data lines in each horizontal scanning period in the second period. The plurality of scanning lines are sequentially selected, and in each horizontal scanning period of the third period, the plurality of scanning lines are sequentially selected in a period in which the second reference voltage is supplied to the plurality of data lines. Drive means Each of the plurality of pixel circuits includes a pixel electrode, a counter electrode, and a liquid crystal element including a liquid crystal sandwiched between the pixel electrode and the counter electrode and having a bend state and a splay state as an alignment state; The gradation voltage is applied to the pixel electrode in the first period and the gradation voltage is applied to the pixel electrode in the first period by electrically connecting the data line and the pixel electrode in the period in which the scanning line is selected. A switching element that applies a first reference voltage to the pixel electrode and applies the second reference voltage to the pixel electrode in the third period. According to the present invention, since the second reference voltage lower than the first reference voltage is applied to the liquid crystal element in the third period, the transmittance of the liquid crystal can be changed before the first period is started. . As a result, the response characteristic of the transmittance can be improved, and even a fast-moving image can be displayed with a high quality image with reduced blur.

  As a more specific aspect of the liquid crystal device, a light source that emits light toward one surface of the liquid crystal panel, and selection of scanning lines of the scanning line driving means in the second period and the third period It is preferable to include a control unit that turns off the light source in synchronization. In the third period, the transmittance increases because a low voltage is applied to the liquid crystal. However, since the light source is turned off at this time, the influence on the gradation display can be reduced.

  Further, the light source can control lighting / extinction for each of a plurality of individual regions divided for each predetermined number of rows, and the control means is configured to control the lighting in the second period and the third period. It is preferable to control the light source so that a plurality of individual regions are sequentially turned off. In this case, the configuration of the light source can be simplified.

  In addition, it is preferable that the first reference voltage is a voltage corresponding to black display, and the second reference voltage is a voltage corresponding to white display. Thereby, since the black display is performed in the second period, it is possible to approach so-called impulse driving, and it is possible to reduce the influence of afterimages on the human retina and improve the motion blur.

  Next, an electronic apparatus according to the present invention includes the above-described liquid crystal device, and corresponds to a so-called liquid crystal display, a mobile phone, a personal computer, and the like.

<1. Embodiment>
FIG. 1 shows a block diagram of a liquid crystal device according to the embodiment. The liquid crystal device 700 uses liquid crystal as an electro-optic material. The liquid crystal device 700 includes a liquid crystal panel AA as a main part. In the liquid crystal panel AA, an element substrate on which a TFT is formed as a switching element and a counter substrate are pasted with their electrode forming surfaces facing each other with a certain gap therebetween, and liquid crystal is sandwiched between the gaps. The liquid crystal in this example is an OCB liquid crystal.

  The liquid crystal device 700 includes a timing generation circuit 300, an image processing circuit 400, a main control circuit 500, and a backlight 600. An image display area A, a scanning line driving circuit 100, and a data line driving circuit 200 are formed on the element substrate of the liquid crystal panel AA. The main control circuit 500 converts an input image signal Vin supplied from an external device in an analog format into a digital signal, and supplies it to the image processing circuit 400 as input image data Din. The main control circuit 500 performs lighting control of the backlight 600. In the present embodiment, the backlight 600 is provided on the opposite side of the image display surface of the liquid crystal panel AA, and can be turned on / off in a plurality of regions obtained by dividing the liquid crystal panel AA in the scanning line direction. It is configured as follows. The lighting control of the backlight 600 will be described later.

  Next, the input image data Din is in a 24-bit parallel format, for example. The timing generation circuit 300 is synchronized with a control signal such as a horizontal scanning signal and a vertical scanning signal supplied from the image processing circuit 400, and generates a Y clock signal YCK, an X clock signal XCK, a Y transfer start pulse DY, and an X transfer start. A pulse DX is generated and supplied to the scanning line driving circuit 100 and the data line driving circuit 200. The timing generation circuit 300 generates various timing signals for controlling the image processing circuit 400 and outputs them.

Here, the Y clock signal YCK specifies a period for selecting the scanning line 20, and the X clock signal XCK specifies a period for selecting the data line 10. The Y transfer start pulse DY is a pulse for instructing the start of selection of the scanning line 20, while the X transfer start pulse DX is a pulse for instructing the start of selection of the data line 10.
Next, the image processing circuit 400 performs gamma correction and the like on the input image data Din in consideration of the light transmission characteristics of the liquid crystal panel AA, and then D / A converts the image data of each RGB color to obtain the image signal VID. Generated and supplied to the liquid crystal panel AA.

FIG. 2 shows a detailed configuration of the image display area A. In the image display area A, m (m is a natural number of 2 or more) scanning lines 20 are formed in parallel along the X direction, while n (n is a natural number of 2 or more) data. Lines 10 are formed in parallel along the Y direction. Then, m × n pixel circuits P are arranged corresponding to the intersection of the data line 10 and the scanning line 20.
As shown in the figure, the pixel circuit P includes a liquid crystal element 60 and a TFT 50. The liquid crystal element 60 is configured by sandwiching an OCB liquid crystal between a pixel electrode 61 and a counter electrode 62. A common potential Vcom is supplied to the counter electrode 62. The gate electrode of the TFT 50 is electrically connected to the scanning line 20, one of its drain electrode or source electrode is electrically connected to the data line 10, and the other is electrically connected to the pixel electrode 61.

  The data line driving circuit 200 shown in FIG. 1 outputs data signals X1 to Xn to n data lines 10. If the polarity of the signal is determined based on the common potential Vcom of the counter electrode 62 as a high potential, the low potential is defined as a negative polarity, the polarity of the data signal is positive in the odd-numbered frame and the data signal in the even-numbered frame. The polarity is negative. This inverts the voltage applied to the liquid crystal on a frame basis. Note that the voltage applied to the liquid crystal may be inverted in units of lines, or the voltage applied to the liquid crystal may be inverted in units of dots.

  Further, scanning signals Y1, Y2,..., Ym are applied to each scanning line 20 from the scanning line drive circuit 100 in a line-sequential manner in a pulse manner. For this reason, when a scanning signal is supplied to a certain scanning line 20, the TFT 50 is turned on in the pixel circuit P in the row, and the data signal supplied via the data line 20 is written into the liquid crystal element 60. Since the orientation and order of liquid crystal molecules change according to the voltage level applied to each pixel, gradation display by light modulation becomes possible. For example, in the normally white mode, the amount of light passing through the liquid crystal is limited as the applied voltage increases. In the normally black mode, the amount of light is reduced as the applied voltage increases. As a whole, light having contrast according to the image signal is emitted for each pixel. The liquid crystal device 700 in this example is normally white. Note that a storage capacitor may be added in parallel with the liquid crystal capacitor formed between the pixel electrode 61 and the counter electrode 62 in order to prevent the stored image signal from leaking.

  Next, FIG. 3 shows an explanatory diagram of area division of the backlight 600. As shown in this figure, the backlight 600 is divided into f (f is a natural number of 2 or more) blocks B [1] to B [f], and one block B has k (k is a natural number) rows. Pixel circuit P is included. For example, the block B2 includes pixel circuits P from k + 1 rows to 2k rows. The main control circuit 500 controls the blocks B [1] to B [f] to be sequentially turned off in synchronization with the selection of the scanning line 20 of the scanning line driving circuit 100.

  Next, the operation of the liquid crystal device 700 will be described with reference to FIG. In this example, the liquid crystal device 700 is driven by dividing one frame period 1F into a first period T1, a second period T2, and a third period T3. Here, if the data signal supplied to the jth data line 10 (j is an integer satisfying 1 ≦ j ≦ n) is the data signal Xj, the data signal Xj should be displayed in one horizontal scanning period 1H. A gradation voltage Vd corresponding to the gradation, a first reference voltage Vb corresponding to black display, and a second reference voltage Vw corresponding to white display are time-division multiplexed. As described above, in order to maintain the bend state in the OCB liquid crystal, it is necessary to apply a voltage higher than a predetermined voltage to the liquid crystal at a predetermined cycle. The first reference voltage Vb is a voltage sufficient to maintain the bend state. On the other hand, the second reference voltage Vw is a voltage lower than the first reference voltage Vb, and in this example, is a voltage (0 V) corresponding to white display. In the present embodiment, the voltage means a voltage applied to the liquid crystal element 60, that is, a potential difference between the pixel electrode 61 and the counter electrode 62.

  Next, the scanning signals Y1, Y2,... Ym are sequentially activated in the period Td in which the gradation voltage Vd is supplied in the first period T1, and the period Tb in which the first reference voltage Vb is supplied in the second period T2. In the third period T3, it becomes active in the period Tw in which the second reference voltage Vw is supplied. As a result, the gradation voltage Vd is written to the pixel circuit P in the first period T1, the first reference voltage Vb is written to the pixel circuit P in the second period T2, and the second reference voltage Vw is written to the pixel in the third period T3. It is written in the circuit P.

For example, focusing on the pixel circuit P in the first row and jth column, the gradation voltage Vd is applied to the OCB liquid crystal in the first period T1, the first reference voltage Vb is applied to the OCB liquid crystal in the second period T2, and In the third period T3, the second reference voltage Vw is applied to the OCB liquid crystal.
At this time, the transmittance of the pixel circuit P in the first row and jth column changes as shown in the figure. That is, when the gradation voltage Vd is applied in the first period T1, the transmittance does not immediately change to the transmittance Qd corresponding to the gradation voltage Vd, but gradually changes from the initial value Qi of the transmittance to the transmittance Qd. Change. On the other hand, in the second period T2, the transmittance Qd changes to the transmittance Qb corresponding to the first reference voltage Vb in a short time. The OCB liquid crystal has the property that the rise time and fall time of the transmittance are different.

Further, in the third period T3, since the second reference voltage Vw corresponding to white display is applied to the OCB liquid crystal, the transmittance changes from the transmittance Qb to the transmittance Qw. Thus, by providing the third period T3, the transmittance can be increased to some extent at the start of the first period T1. For this reason, compared with the case where the third period T3 is not provided, the transmittance of the OCB liquid crystal can be set to a transmittance corresponding to the gradation voltage Vd in a shorter time.
Here, since the transmittance changes from Qb to Qw in the third period T3, when the backlight 600 is turned on, the display luminance shifts in the white direction. Therefore, the main control circuit 500 controls the backlight 600 to be turned off in the second period T2 and the third period T3. As a result, as shown in the figure, in the second period T2 and the third period, the luminance is black and the transmittance is not changed in the third period T3. In this example, the backlight 600 is turned off in the second period T2 and the third period T3. However, in the second period T2, the transmittance decreases and black display is performed. It is not always necessary to control the backlight 600 to be turned off.

  If one frame period 1F is 16.7 ms, for example, 60% is allocated to the first period T1 to 10.1 ms, 20% is allocated to the second period T2 to 3.3 ms, and the third period T3 20% may be allocated to 3.3 ms. According to the experiment, the time for the OCB liquid crystal to transition from black display to white display is 5.3 ms, and the time for the OCB liquid crystal to transition from white display to black display is 0.8 ms. Therefore, if the gradation to be displayed in the next frame is white display, the target gradation can be displayed in 2 ms from the start of the first period T1. On the other hand, if the gradation to be displayed in the next frame is black display, the target gradation can be displayed within 0.8 ms from the start of the first period T1.

  As shown in FIG. 5, the backlight 500 is turned off for each block B in the second period T2 and the third period T3 in synchronization with the driving of the OCB liquid crystal. In this case, since turning on and off of the backlight 500 is controlled in units of blocks, in the pixel circuit P connected to the scanning line 20 selected first in the block B [2], the second period T2 and the second period Although the backlight 500 is turned off in the third period T3, the pixel circuit P connected to the scanning line 20 selected last in the block B [2] is shifted by a period of scanning the scanning line 20 of one block. . For example, if the number of scanning lines 20 is 768 and the number of scanning lines 20 per block B is 50, the scanning period for one row is 20 μs, and the scanning period for one block B is 1 ms. In this case, luminance that is not originally displayed is displayed for a period of 1 ms. However, if the number of scanning lines 20 included in the block B is reduced, the period is shortened and the image quality is not greatly affected. Further, since the luminance in the period is determined by the response characteristic of the OCB liquid crystal, this may be predicted and the input image data Din corrected by the main control circuit 500 may be generated.

  As described above, according to the present embodiment, since the third period T3 for white display is provided in one frame period 1F, the responsiveness of transmittance can be improved. As a result, moving image blur can be greatly improved when displaying fast-moving images such as sports. Further, since black display is performed in the second period T2, it is possible to approach so-called impulse driving, and the afterimage of the human retina can be reduced to further improve the motion blur. Furthermore, since the backlight 600 is controlled to be turned off during part or all of the third period T3 for white display, image quality deterioration can be reduced.

In the above-described embodiment, the white display voltage is adopted as the second reference voltage Vw. However, since the second reference voltage Vw is applied to improve the response time, the first reference voltage Vb is used. Any voltage may be used as long as the voltage is lower.
Further, the number of scanning lines 20 included in the block B is arbitrary, and may be one, for example. In this case, since the relationship between the turn-off of the backlight 600 and the applied voltage is completely synchronized, a high-quality image can be displayed.
Further, the backlight 600 may be any light source as long as it can emit light to one surface of the liquid crystal panel AA. For example, it may be composed of a fluorescent tube or an organic light emitting diode. In this case, organic light emitting diodes may be arranged in a strip shape to control lighting / extinguishing for each row.

<2. Electronic equipment>
Next, electronic equipment using the liquid crystal device 700 according to the present invention will be described. FIG. 6 is a perspective view showing the configuration of a mobile personal computer that employs the liquid crystal device 700 according to any one of the embodiments described above as a display device. The personal computer 2000 includes a liquid crystal device 700 as a display device and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the liquid crystal device 700 can reduce moving image blur, the display quality of an image can be improved.

  FIG. 7 shows a configuration of a mobile phone to which the liquid crystal device 700 according to the embodiment is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and a liquid crystal device 700 as a display device. By operating the scroll button 3002, the screen displayed on the liquid crystal device 700 is scrolled. According to the liquid crystal device 700, since the response time of a moving image is short, characters can be read even during scrolling.

  FIG. 8 shows a configuration of a personal digital assistant (PDA) to which the liquid crystal device 700 according to the embodiment is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and a liquid crystal device 700 as a display device. When the power switch 4002 is operated, various kinds of information such as an address book and a schedule book are displayed on the liquid crystal device 700.

  Electronic devices to which the liquid crystal device according to the present invention is applied include projectors, televisions, video cameras, car navigation devices, pagers, electronic notebooks, electronic papers, calculators, word processors in addition to those shown in FIGS. , Workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices with touch panels, and the like.

1 is a block diagram of a liquid crystal device according to an embodiment of the present invention. It is a block diagram which shows the detailed structure of the image display area of the same apparatus. It is explanatory drawing of the backlight used for the apparatus. It is a timing chart which shows operation | movement of the apparatus. It is explanatory drawing which shows operation | movement of the backlight used for the apparatus. It is a perspective view of the personal computer which is an example of an electronic device. It is a perspective view of the mobile telephone which is an example of an electronic device. It is a perspective view of the portable information terminal which is an example of an electronic device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Data line, 20 ... Scan line, 50 ... TFT (switching element), 60 ... Liquid crystal element, 61 ... Pixel electrode, 62 ... Counter electrode, Vcom ... Common potential, 100 ... Scan line Drive circuit 200... Data line drive circuit 500... Main control circuit 600. Backlight X1 to Xn Data signal Y1 Ym Scan signal P Pixel circuit

Claims (7)

A liquid crystal device including a liquid crystal panel including a pixel electrode, a counter electrode, and a liquid crystal element including a liquid crystal having a bend state and a splay state as an alignment state sandwiched between the pixel electrode and the counter electrode. In contrast, a driving method of a liquid crystal device that repeatedly drives a first period, a second period, and a third period,
In the first period, a gradation voltage corresponding to a gradation to be displayed is applied to the liquid crystal element,
In the second period, a first reference voltage necessary to maintain a bend state is applied to the liquid crystal element,
Applying a second reference voltage lower than the first reference voltage to the liquid crystal element in the third period;
A driving method of a liquid crystal device. The liquid crystal device includes a light source that emits light toward one surface of the liquid crystal panel,
In all of the first period, turn on the light source,
Turning off the light source during part or all of the third period;
The method for driving a liquid crystal device according to claim 1. A liquid crystal panel having a plurality of scanning lines, a plurality of data lines, and a plurality of pixel circuits provided corresponding to intersections of the scanning lines and the data lines;
Data obtained by time-division-multiplexing a gradation voltage corresponding to a gradation to be displayed, a first reference voltage necessary for maintaining a bend state, and a second reference voltage lower than the first reference voltage in one horizontal scanning period Data line driving means for supplying a signal to the plurality of data lines;
A period of one frame is divided into a first period, a second period, and a third period. In each horizontal scanning period of the first period, the plurality of gradation voltages are supplied to the plurality of data lines. The scanning lines are sequentially selected. In each horizontal scanning period of the second period, the plurality of scanning lines are sequentially selected in a period in which the first reference voltage is supplied to the plurality of data lines. In each horizontal scanning period, a scanning line driving unit that sequentially selects the plurality of scanning lines in a period in which the second reference voltage is supplied to the plurality of data lines,
Each of the plurality of pixel circuits is
A liquid crystal element comprising a pixel electrode, a counter electrode, and a liquid crystal sandwiched between the pixel electrode and the counter electrode and having a bend state and a splay state as an alignment state;
By electrically connecting the data line and the pixel electrode in a period in which the scanning line is selected, the gray scale voltage is applied to the pixel electrode in the first period, and the second voltage period is applied to the pixel electrode. A switching element that applies one reference voltage to the pixel electrode and applies the second reference voltage to the pixel electrode in the third period;
Liquid crystal device. A light source that emits light toward one surface of the liquid crystal panel;
Control means for turning off the light source in synchronization with selection of the scanning line of the scanning line driving means in the second period and the third period;
The liquid crystal device according to claim 3. The light source can control lighting / extinguishing for each of a plurality of individual areas divided for each predetermined number of rows,
The control means controls the light source so as to sequentially turn off the plurality of individual regions in the second period and the third period.
The liquid crystal device according to claim 4.   The liquid crystal device according to claim 3, wherein the first reference voltage is a voltage corresponding to black display, and the second reference voltage is a voltage corresponding to white display. . An electronic apparatus comprising the liquid crystal device according to claim 3.

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