JPH05188351A - Device and method for driving liquid crystal display element - Google Patents

Abstract

PURPOSE:To allow visibility and durability of an animated picture displayed on the liquid crystal display element to be compatible with each other. CONSTITUTION:In the driving device and the driving method of a liquid crystal display element 1 formed by inserting and holding a liquid crystal between a pair of substrates 11 provided with a matrix electrode formed of a scanning electrode and an information electrode, it is detected that a change has been executed to image information to be displayed on a display element 1, and in order to change a frame frequency in accordance with a result of detection, a driving condition is controlled so that the frame frequency becomes high in the case a change is executed to the image information to be displayed on the display element 1, and in the case in which no change has been executed to the image information, the driving condition is controlled so that the frame frequency becomes lower than the case when the change has been executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device and a driving method for a liquid crystal display device such as a display panel using a ferroelectric liquid crystal, and more particularly to a driving device for improving the visibility of a moving image of a ferroelectric liquid crystal display device. And a driving method.

[0002]

2. Description of the Related Art Conventionally, a refresh scan type CRT is mainly used for a display device as a computer terminal device, and a frame frequency of 60 Hz or more is used from the viewpoint of preventing flicker (flicker of the screen) and the screen. A non-interlaced method is used to improve the visibility of the internal information movement display (movement of mouse, icon, etc.). For this reason, this CRT requires higher power as the display resolution becomes higher, and the drive control device becomes larger and the cost becomes higher. The TV employs a 1/2 interlace system with a field frequency of 60 Hz and a frame frequency of 30 Hz from the viewpoint of moving image display and simplification of the drive control system.

In recent years, due to the inconvenience of increasing the size and power of this CRT, attention has been paid to flat panel displays.

Currently, there are several types of flat panel displays. For example, the twisted nematic liquid crystal high time division method (STN), a modification of the method for aiming at monochrome display (NTN), and the plasma display method are all the same image data transfer methods as the CRT. The screen changing method also uses a non-interlaced method with a frame frequency of 60 Hz or higher. The reason for this is that these display panels do not have a memory property in view of the display principle, so that a refresh cycle of a frame frequency of 60 Hz or higher is necessary from the viewpoint of flicker prevention. Further, even in a method (TFT, MIM, TFD method, etc.) in which a switching transistor or a non-linear element is formed in each pixel of the twisted nematic liquid crystal, it is possible to retain image information within a maximum of one frame. As with each method, a refresh cycle of 60 Hz or higher is required.

On the other hand, since the ferroelectric liquid crystal display device has a feature that it can hold image information once displayed (memory property), it has a large-screen and high-definition display far surpassing the above-mentioned various display devices. Is possible.

[0006]

However, in such a ferroelectric liquid crystal display device, when the display panel has a large screen, the frame frequency is inevitably lowered, and as a result, particularly the visibility of moving images is lowered. There was a problem.

As a method for solving the above problem, a driving condition that shortens one line scanning time, that is, a driving voltage Vo
It is conceivable to increase p to increase the frame frequency. On the other hand, when the ferroelectric liquid crystal display panel is driven for a long time, a frame display area outside the information display area (hereinafter referred to as a frame display section) As described above, there is a phenomenon that liquid crystal molecules move in a region where a fixed pattern is displayed. The movement phenomenon of the liquid crystal molecules largely depends on the driving voltage Vop,
Since the moving phenomenon becomes more remarkable as the value of V becomes higher, there is a drawback that Vop cannot be made higher in terms of durability performance. As a measure against the movement of the liquid crystal molecules, it is possible to use the characteristic of the ferroelectric liquid crystal to refresh only when the screen is updated, and to drive it in the memory state when it is not updated, but the memory property of the liquid crystal element is not semi-permanent. , A new problem in image quality will occur.

As described above, with the increase in the screen size of the display panel, there has been a problem that both the visibility and durability of moving images cannot be satisfied at the same time.

The present invention has been made in view of the problems in the above-mentioned conventional example, and provides a driving device and a method for achieving both visibility and durability of a moving image displayed on a liquid crystal display element. To aim.

[0010]

In order to achieve the above object, the present invention provides a liquid crystal display device in which a liquid crystal is sandwiched between a pair of substrates having matrix electrodes formed of scanning electrodes and information electrodes. In the driving device and the driving method, the change in the image information to be displayed on the display element is detected, and the frame frequency is changed according to the detection result. The drive conditions are controlled so that the frame frequency becomes higher when the image information that should be changed is made, and when the image information is not changed, the frame frequency becomes higher than that when the change is not made. The driving condition is controlled so as to be low.

The present invention is suitable for application to a ferroelectric liquid crystal panel which is a ferroelectric liquid crystal display device using a ferroelectric liquid crystal as the liquid crystal.

In a preferred embodiment of the present invention, two kinds of the frame frequencies are prepared, and after it is detected that the image information to be displayed on the display device is changed, the liquid crystal display device is switched to the liquid crystal display device. The liquid crystal display element is driven at the high frame frequency only in the frame until the display image is updated to the changed image, and the other is driven at the low frame frequency.

[0013]

According to the present invention, a display panel comprising a ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having a matrix electrode formed of scanning electrodes and information electrodes is driven. In doing so, it is possible to detect that the image information to be displayed on the display panel has been changed, and to control the drive condition of the display panel according to the detection result.

That is, when the image information is not changed, the frame frequency is lowered so that the driving voltage Vop is low in consideration of durability, and when the image information is changed. In consideration of visibility, the driving voltage Vop is increased so that the frame frequency becomes high.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a liquid crystal display device according to an embodiment of the present invention. In Figure 1, 1 is the scanning electrode S ₁ as shown in FIG. 2, S _2, ‥‥, S glass substrate formed with _m and data electrodes I _1, I _2, ‥‥, glass formed a I _n A ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sandwiched between a pair of substrates 11 and 11 with a substrate, 2 is a driver IC board for driving scan electrodes, and 3 is a driver IC board for driving information electrodes. .. Further, in the liquid crystal display element 1, 12 is a sealing portion, 13 is a sealing portion, 14 is an information display area, and 15 is a frame display area.

The specifications of the liquid crystal display element (liquid crystal panel) 1 are shown below. Number of information display pixels: 480 (number of scanning electrodes) × 640 (number of information electrodes) (m = 480, n = 64 in the electrode plan view of FIG. 2)
0) Liquid crystal: Pyrimidine liquid crystal Phase change As shown in Table 1.

[0018]

[Table 1] -2.8 ° C 60.0 ° C 79.7 ° C 86.1 ° C Cryst ⇒ SmC * ⇒ SmA ⇒ Ch ⇒ Iso Spontaneous polarization (Ps) 4.8 nc / cm ² (40 ° C) Cell thickness (pair) (Space between the substrates): 1.2 μm Alignment treatment The polyimide films provided on the pair of substrates 11 and 11 (see FIG. 1) were rubbed to make their directions parallel to each other. The rubbing direction was parallel to the scanning electrodes. In FIG. 1, arrow A indicates the rubbing direction.

For the liquid crystal display element as described above, the 15-line scanning method (1 /
15 interlace system) and a scanning system in which a scanning selection signal is applied to non-adjacent scanning electrodes in at least two consecutive field scans, the surface temperature of the liquid crystal display device is set to 40 ° C., and display is performed on the entire surface of the device. The possible driving voltage Vop and the drivable area of one line scanning time 1H were measured. FIG. 4 is a graph showing the measurement results, and the area between the two straight lines is the drivable area.

According to the above result, the drive voltage Vop is 10
When V, 1H (horizontal scanning time) is 120 to 130 μse
c, 1H is 45 to 60 μ when the driving voltage Vop is 20V
sec. Since the liquid crystal display element used in this embodiment has 480 scanning electrodes, the frame frequency is about 17 Hz when the driving voltage Vop = 10 V, and the frame frequency is about 40 Hz when Vop = 20 V.

Under the conditions within the drivable area, a schematic pattern of cursor movement as shown in FIG. 5 is displayed, the cursor is sequentially moved from the top to the bottom of the panel as indicated by arrow B in FIG. A test was repeated such that positive display and negative display were repeated every time, and the visibility and durability of the moving cursor were confirmed. In this case, the frame display is always white.

The ratio of the time the cursor is moving to the time the cursor is stopped is about 1: 1.

In the display pattern shown in FIG. 5, Vop = 20V, 1H = 52 μsec and frame frequency = 40 Hz are set under the condition that the cursor is stopped, that is, the display pattern, when the cursor is moved and when negative or positive is reversed, that is, when the display is rewritten. When not changing, Vop = 10V, 1H = 12
As a condition of 5 μsec and frame frequency = 17 Hz,
The visibility of the moving cursor and the durability performance for a predetermined time were confirmed.

As a result, good visibility and durability were obtained, and there was no problem in practical use as a display device.

Comparative Example 1 In the display pattern shown in FIG. 5, Vop = 10V, 1H = 125 μse both when the screen is updated and when the screen is not updated.
Under the conditions of c and frame frequency = 17 Hz, the visibility of the moving cursor and the durability for a predetermined time were confirmed in the same manner as in the example.

As a result, the durability was good, but the phenomenon in which the display when the cursor was moved looked different due to the low frame frequency was a practical problem.

Comparative Example 2 In the display pattern shown in FIG. 5, Vop = 20V, 1H = 52 μse both when the screen is updated and when the screen is not updated.
Under the condition of c and frame frequency = 40 Hz, the visibility of the moving cursor and the durability for a predetermined time were confirmed in the same manner as in the example. As a result, contrary to Comparative Example 1, good visibility was obtained when the screen was updated. After endurance, a part 61 of the frame display portion above the display element as shown in FIG.
It was observed that 62 was colored yellow. this is,
Since the frame display is always fixed in white, the liquid crystal molecules move,
This is due to the increased cell thickness. Therefore, as in Comparative Example 1, there was a problem in practical use.

[0028]

As described above, according to the present invention, the driving condition is set so that the frame frequency becomes faster when the screen display is updated, and the frame frequency is made slower when the image display is not updated. By performing the drive control, it is possible to realize a display device in which the visibility and durability of a moving image are practically unproblematic.

[Brief description of drawings]

FIG. 1 is a plan view of a ferroelectric liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view of electrodes of the liquid crystal display element used in FIG.

FIG. 3 is a drive voltage waveform diagram used for driving the liquid crystal element of FIG.

4 is a relationship diagram between a drive voltage and one line scanning time when the display element shown in FIG. 1 is driven by using the drive voltage waveform of FIG.

FIG. 5 is a display pattern diagram used in Examples and Comparative Examples.

6 is a plan view of a liquid crystal element after a durability test of Comparative Example 2. FIG.

[Explanation of symbols]

1: Ferroelectric liquid crystal display device, 2: Scan electrode driver IC board, 3: Information electrode driver IC board, 1
1: glass substrate, 12: sealing part, 13: sealing part, 14:
Information display area, 15: Frame display area, S ₁ , S ₂ , ...
S _m: scanning _{electrodes, I 1, I 2, ‥‥} , I n: data electrodes.

Claims (4)

[Claims] 1. A device for driving a liquid crystal display device comprising a pair of substrates each having a matrix electrode composed of a scanning electrode and an information electrode, the liquid crystal being sandwiched between the substrates. Detecting means for detecting that the image information to be changed is detected, and if the image information to be displayed on the liquid crystal display element is changed according to the detection result, the image information is not changed. A driving device comprising: a control unit that controls a driving condition of the liquid crystal display element so that a frame frequency becomes higher. 2. The liquid crystal is a ferroelectric liquid crystal.
The drive device described. 3. The control means sets 2 as the driving condition.
It is possible to set different kinds of frame frequencies, and after the detection means detects that the image information to be displayed on the liquid crystal display element has been changed, the image displayed on the liquid crystal display element is the image after the change. 2. The drive device according to claim 1, wherein the liquid crystal display element is driven at a high-side frame frequency and the other portions are driven at a low-side frame frequency until it is updated. 4. A method of driving a ferroelectric liquid crystal display device, comprising a ferroelectric liquid crystal sandwiched between a pair of substrates having a matrix electrode formed of scanning electrodes and information electrodes,
It is characterized in that a change in the image information to be displayed on the display element is detected and the frame frequency is changed according to the detection result, and the image information to be displayed on the display element is changed. Drive conditions are controlled so that the frame frequency becomes higher, and when the image information is not changed, the drive conditions are controlled so that the frame frequency becomes lower than when the change is not made. A driving method characterized by: