JPS63118128A - Driving method for active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a uniform image over the entire surface of the display part of a liquid crystal display device by making the application time of a scanning voltage applied to scanning electrodes shorter than the application time of a signal voltage applied to picture elements belonging to the scanning electrodes through the signal electrodes. CONSTITUTION:A pulse outputted from a controller 43 for liquid crystal driving, i.e. a start pulse S1 for the signal voltage and scanning voltage is inputted to a scanning electrode driver 45 and a signal electrode driver 47. At this time, the signal voltage and scanning voltage are applied to the signal electrodes and scanning electrodes respectively. The start pulse S1 is further inputted to a timer 61 as well, which outputs a signal S2 for turning off the scanning voltage to a scanning electrode driver 45 a time period equal to the scanning voltage application time tau after it is started with the start pulse S1. The time period wherein the scanning voltage is applied is controllable with the signal S2. This scanning is carried out for all the scanning electrodes (b1-bn) in order and a line sequential scan is made on condition that the scanning voltage application time is shorter than the signal voltage application time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for driving an active matrix liquid crystal display device.

(Prior art) A liquid crystal is provided between a first substrate having a large number of scanning electrodes and a large number of signal electrodes, and a large number of switching elements in the intersection area of these two electrodes, and a second substrate having a counter electrode. An active matrix liquid crystal display device (hereinafter sometimes abbreviated as a display device) is known as one of the devices that can display highly detailed images.

A suitable method for driving such a display device is line sequential scanning. This is done by selecting one line at a time a large number of scan electrodes to which many gate electrodes of a thin film transistor (TPT), for example, are connected, as a switching element, and making them conductive. A signal corresponding to each pixel belonging to the scanning electrode in a conductive state is written through the signal electrode.

FIGS. 5A to 5D are diagrams showing the waveforms of drive signals used in the conventional drive method using line sequential scanning, with voltage plotted horizontally and with time on the vertical axis, respectively.

In FIG. 5(A), the dashed line indicated by II is the voltage of the counter electrode of the second substrate, and the curve indicated by 13 is the signal waveform applied to the signal electrode. FIGS. 5(B) to 5(D) are diagrams showing the waveforms of the scanning voltages applied to the scanning electrodes in the first row, m-th row, and n-th row, respectively.

Moreover, in FIG. 5(A), the application time of a signal voltage to one pixel of a certain signal electrode is shown. In the conventional driving method using line sequential scanning, the time for applying a scanning voltage to a scanning electrode is equal to the time for applying a signal voltage to a pixel belonging to this scanning electrode via a signal electrode. . This τ is given by τ=1/f−n, where n is the number of scanning electrodes and f is the frame frequency.

In addition, in FIG. 5(A), the waveforms following the waveforms marked with τ are pixels that belong to the scan electrode and belong to the above-mentioned signal electrode each time the scan electrode is sequentially scanned. This indicates that a signal of either "0" or "1" is sequentially applied to the pixels. In line sequential scanning, generally, when one frame scanning (sequentially turning on all scan electrodes from the first row scan electrode to the nth row scan' electrode) is completed (see FIG. (A) At the time indicated by t), the polarity of the signal voltage is reversed from the next time onwards.

Here, the scanning electrodes will be explained. Scanning electrodes are generally made of a very thin metal film processed into an elongated strip. Then, one end of this electrode is connected to a driving means, for example, a driver IC.

By the way, when a scanning voltage is applied to such a scanning electrode from the driver side, the scanning voltage waveform at the part near the driving means of this scanning electrode is different from the scanning voltage waveform at the end part away from the driving means. Become something.

In Figure 6, time is plotted on the horizontal axis and voltage is plotted on the vertical axis.
FIG. 3 is a diagram showing the waveform of a scanning voltage at each part of a certain scanning electrode. In FIG. 6, a waveform 21 indicated by a broken line is a scanning voltage waveform in the vicinity of the driving means, and a waveform 23 indicated by a solid line is a scanning voltage waveform at an end portion away from the driving means. The time constant of this waveform 23 is expressed as the product of the load resistance of the scan electrode, which is determined by the specific resistance of the material of the scan electrode, its thickness, width, and distance from the drive means, and the load capacitance between it and the drive means. I can do it. Therefore, the scanning voltage waveform deforms more as the distance tIi from the driving means (distance from the input end of the scanning electrode) increases.

(Problems to be Solved by the Invention) However, in the conventional method of driving a liquid crystal display device by making the signal voltage application time equal to the scanning voltage application time in a state where the scanning voltage waveform is deformed in this way, When the voltage application to one scan electrode is stopped and the voltage is applied to the next scan electrode, this certain scan electrode is not completely turned off, and a certain voltage is applied to this scan electrode for a period of time due to waveform deformation. There was a problem in that a phenomenon in which the voltage was applied was caused to occur.

This phenomenon will be specifically explained below.

Consider the case where information is written to a pixel near the end of a scanning electrode. For example, the pixels in the end part are the pixels (first pixels) related to the scanning electrode in the first row and the signal electrode in the column 'fIJj, and the scanning electrode in the (i+1)th row and the signal electrode in the jth column.
The pixel (second pixel) is associated with the signal electrode in the column. Then, it is assumed that information of "0" is written to the first pixel and information of "1" is written to the second pixel.

Under these conditions, when a scanning voltage is applied to the (i+1)th row scanning electrode, the voltage corresponding to the falling portion 25 of the waveform 23 shown in FIG. 6 is applied to the first scanning electrode. It is still applied. Since the voltage 25 at this falling portion includes a voltage value sufficient to drive the liquid crystal, the scanning electrodes in the first row are in a so-called "r half-on" state. Therefore, the first (
When the scanning electrode in the i+1)th row is on and a voltage is applied to the second pixel to write information "1" to the second pixel via the signal electrode in the jth column (see FIG. ), a half-on voltage is applied to the first pixel (see FIG. 7(B)). Therefore, this first pixel is "0"
It becomes impossible to write. In such a case, for example, the contrast ratio of the image will be significantly reduced and this will cause
The closer to the end of the scanning electrode, the more blurring occurs in the image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving an active matrix liquid crystal display device that solves the above-mentioned problems and allows a uniform image to be obtained over the entire display area of the liquid crystal display device.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, a scanning voltage is applied to the scanning electrodes, a signal voltage is applied to the signal electrodes, and an active matrix type liquid crystal display device is manufactured. In line sequential scanning and driving, the application time of the scanning voltage applied to the scanning electrode is made shorter than the application time of the signal voltage applied to the pixels belonging to this scanning electrode via the signal electrode. Features.

(Function) According to such a configuration, after the scan voltage applied to a certain scan electrode substantially falls, the scan voltage is applied to the next scan electrode. Therefore, even if the waveform of the scan voltage is deformed at the end of a scan electrode and the fall of this voltage is delayed by a certain time constant, it will not be applied to the scan electrode in the next row. During the process of writing information to the pixels, the pixels belonging to the above-mentioned certain scan electrodes do not suffer any effects.

(Example) Hereinafter, an example of a method for driving an active matrix liquid crystal display device (hereinafter sometimes abbreviated as a display device) of the present invention will be described with reference to the drawings. Incidentally, these figures are shown schematically to the extent that the present invention can be understood.

Note that the display device used in the embodiment of the driving method of this invention is as follows:
This is a conventionally known active matrix liquid crystal display device as described above, and includes switching elements (for example, TPT).
) in a matrix form. However, the driving method of the present invention can be applied to display devices other than those using liquid crystal.

FIGS. 1A to 1D are diagrams showing waveforms of drive signals suitable for use in the drive method of the present invention, with time on the horizontal axis and voltage on the vertical axis, respectively.

FIG. 1(A) is similar to the drive signal already explained using FIG. 5(A). In this figure, the dashed-dot line indicated by 11 is the signal voltage of the counter electrode of the second substrate, and 1
The curve indicated by 3 is the signal waveform applied to the signal electrode.

Then, let τ be the application time of the signal voltage to one pixel of the signal electrode.

FIGS. 1(B) to (D) are diagrams showing the waveforms of the scanning voltages applied to the scanning electrodes in the first row, second row, and nth row, respectively. In the driving method of the present invention, when the application time of the scanning voltage is τg, τg×τ ......(1
) Set τg so that

Therefore, the voltage state of the scan electrode exhibits an on state until a time period τg has elapsed from the time the scan voltage is applied to this scan electrode, and then an off state for a time period between τg and τg. Become. Then, when the time τ has elapsed, a scan voltage is applied to the next scan electrode. As described above, the scanning voltage application time is shorter than the conventional driving method.

FIG. 2 is a diagram showing the waveform of the scanning voltage obtained as a result of setting τg so as to satisfy the above-mentioned equation (1) for the same signal voltage application time τ as in the prior art. Note that the horizontal axis represents time and the vertical axis represents voltage value.

In FIG. 2, a waveform 31 shown by a broken line is a scanning voltage waveform in the vicinity of the driving means of the scanning electrode, and a waveform 33 shown by a solid line is a scanning voltage waveform at the end portion of the same scanning electrode. In such a case, the waveform 33 in FIG.
The portion 35 that still shows a certain voltage after the time τ has passed becomes a voltage that turns pixels not belonging to this scan electrode into a half-on state when the scan voltage is applied to the next scan electrode. However, as is clear from a comparison between FIG. 2 and the above-mentioned FIG. You can see that it becomes smaller.

FIG. 3 shows that rQJ information is transmitted to the pixel (first pixel) in the i-th row and j-th column in a portion near the end of the scanning electrode by the driving method of the present invention. FIG. 4 is a waveform diagram showing a pixel voltage written to the first pixel when information "1" is given to the pixel (second pixel).

According to this invention, when the scanning voltage is applied to the scanning electrode of the (i+2)th row, the scanning voltage of the scanning electrode of the first row is applied to the falling portion 35 of the waveform 33 shown in FIG.
It is only the voltage corresponding to

Therefore, even if "1" is applied to the signal electrode in the third column, and thereby "1" is applied to the pixel in the i-th row and j-th column, this pixel will not be in a half-on state; The pixel voltage at the pixel becomes a very small value, which is essentially an off state, as shown in FIG.

FIG. 4 is a block diagram showing an example of a display device suitable for use in implementing the driving method of the present invention.

In FIG. 4, reference numeral 41 indicates a conventionally known driving section provided in the display device. Reference numeral 51 indicates a conventionally known display section provided in the display device. Further, 61 indicates a newly provided additional circuit for carrying out the driving method of the present invention. In the display device of this embodiment, this additional circuit 61 is configured with a timer (details will be described later).

The drive section 41 includes a liquid crystal drive controller 43, a scanning electrode driver 45, and a signal electrode driver 47.

The display section 51 is configured with a transistor matrix array including a large number of scanning electrodes (b+ to bo), a large number of signal electrodes (at to am), and a TPT formed at each intersection area of these two electrodes. It is.

In such a drive device, a pulse output from the liquid crystal drive controller 43, that is, a start pulse Sl of the signal voltage and scanning voltage, is input to the scanning electrode driver 45 and the signal electrode driver 47. At this time, a signal voltage and a scanning voltage are applied to the signal electrode and the scanning electrode, respectively. On the other hand, the start pulse S1 is also manually input to the timer 61. This timer 61 sends a signal S2 for turning off the scanning voltage to the scanning electrode driver 45 when a time period equal to the scanning voltage application time τg already explained using FIG. 1 has elapsed after being activated by the start pulse S. Output. The time period during which the scanning voltage is applied can be controlled by this signal S2.

The above scanning is performed sequentially on all the scanning electrodes (b+ to b,), and line sequential scanning can be performed under the condition that the scanning voltage application time is shorter than the signal voltage application time.

In the case of the above-mentioned display device, by changing the time setting of the timer 61, it is possible to set an arbitrary suitable scanning voltage application time depending on the degree of deformation of the scanning voltage waveform.

Next, an experimental example using the driving method of the present invention will be explained. Note that this experimental result is just an example, and the numerical values shown below vary depending on the liquid crystal material, the scale of the display device, etc. Therefore, it should be understood that the present invention is not limited to the numerical examples below.

The display device used had 200 scanning electrodes and a frame frequency of 60 Hz. Therefore, the signal voltage application time per pixel of 200 pixels belonging to the signal electrode is approximately 8
It becomes 3 μsec.

With respect to the signal voltage application time τ, the scanning voltage application time τg was set to be shorter than τ, and the display quality was confirmed.

As a result, when τg was set to a value shorter than about 77 μsec, no image blurring occurred at all.

Further, the τg value is set to an appropriate value that can prevent blurring of one image and prevent the display quality from being impaired by making τg too short.

In the above embodiment, the method for driving an active matrix liquid crystal display device of the present invention was explained as an example in which it was applied to a display device equipped with a TPT. Even if the invention is used, similar effects can be expected.

(Effects of the Invention) As is clear from the above description, according to the method for driving an active matrix liquid crystal display device of the present invention, after the scanning voltage applied to a certain scanning electrode substantially falls, A scan voltage can be applied to the next scan electrode. Therefore, it is possible to significantly reduce the blurring of the image caused by the deformation of the scanning voltage waveform at the end portion of the scanning electrode and the information (signal voltage) written to the pixels belonging to the scanning electrode of the next row.

Therefore, a uniform image can be obtained over the entire display section of the liquid crystal display device.

[Brief explanation of the drawing]

1(A) to (D) are waveform diagrams showing an example of a drive signal used in the driving method of an active matrix liquid crystal display device of the present invention. FIG. FIG. 3 is a diagram showing the waveform of the scanning voltage of each part. FIG. 3 is a diagram showing the waveform of the pixel voltage, which is used to explain the present invention. FIG. 4 is a block diagram showing a display device suitable for implementing the driving method of the present invention. , Figures 5(A) to (D) are diagrams showing the waveforms of drive signals to explain the conventional driving method, and Figure 6 shows the scanning voltages at various parts on the scanning electrode to explain the conventional driving method. Figures 7 (A) and (
B) is a diagram showing a waveform of a pixel voltage, which is used to explain the prior art. 11--Voltage of the counter electrode, 13--Signal voltage of the signal electrode 31--Scanning voltage waveform near the scanning electrode driver 33--Scanning voltage waveform of the end portion of the scanning electrode 35-...
Falling portion, 41--Drive unit 43--Liquid crystal drive controller 45--Scanning electrode driver, 47--Signal electrode driver 51--Display section, 61--Additional circuit (timer)... ...Signal voltage application time τg...Scanning voltage application time. Patent Applicant Oki Electric Industry Co., Ltd. 7 4 Kuzu No. I Binmanj Oshi Karo G Imhu 71 L/ Voltage 1-7 Mouth B Qiun ff Te 1 Hyakubuseo Electric Nagi 13 Ru No. 9 Bar Signal Flow ) This invention's p, a gravity movement 1: use, driving No. 1, the skin-shaped concave Fig. 1 Jf, upper 4, seven drags, high L4, the ultimate compensation of the body. Hikata 33 Tiger 1 n Raigon Song 4 Rei Fusuke's running 2 stitches Oka Nami Kata j
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Claims (1)

[Claims] When driving an active matrix liquid crystal display device by line-sequential scanning by applying a scanning voltage to the scanning electrode and applying a signal voltage to the signal electrode, the scanning voltage applied to the scanning electrode is A method for driving an active matrix liquid crystal display device, characterized in that the application time is shorter than the application time of a signal voltage applied to pixels belonging to the scanning electrode via a signal electrode.