JPH09211423A - Driving method of active matrix liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving method of a large size liquid crystal display capable of displaying without luminence flickering by using no field memory but using NTSC TV signal as it is, and further capable of being employed even when an auxiliary storage capacity is formed between each pixel and an adjacent scanning electrode. SOLUTION: In m-th field, driving pulse is applied to an n-th line and (n+2)th line during a certain horizontal scanningperiod, and the driving pulse is applied to a (n+1)-th and (n+3)th lines during the following horizontal scanning period, and it is repeated every four scanning lines to apply the driving pulse in such a sequence. And in the following (m+1) field, the driving pulse is impressed on a (n+2)th and a (n+4)th lines during a certain horizontal scanning period, and the driving pulse is impressed on a (n+5)th and a (n+3)th lines during the following horizontal scanning period, and it is repeated every four scanning lines to impress the driving pulse in such a sequence.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display in which an image signal is applied to each pixel electrode via a TFT (thin film transistor) connected to each intersection of a scan electrode and a source electrode formed in a matrix. Driving method.

[0002]

2. Description of the Related Art An active matrix liquid crystal display using a TFT is superior in image quality to a simple matrix type liquid crystal display. FIG. 3 schematically shows the structure of an active matrix liquid crystal display. The scan electrodes 3 and the data electrodes 2 are formed in a matrix on the substrate 1, and thin film transistors (TF) are formed at respective intersections thereof.
T) 4 is arranged. The gate 9 of each TFT is the scan electrode 3, the source (or drain) 8 is the data electrode 2, and
The drain (or source) 10 is connected to the pixel electrode 5. With such a configuration, the TFT connected to the scan electrode 3 to which the drive pulse is applied is turned on, and the TF
The signal voltage on the data electrode 2 is applied to the pixel electrode via T. In addition, 6 is a transparent conductive film serving as a counter electrode,
7 is the substrate.

Driving of such an active matrix liquid crystal display will be described with reference to the equivalent circuit of FIG. As shown in the figure, TFTs arranged at respective intersections of the matrix-shaped data electrode lines A1, A2, ..., An and the scanning electrode lines B1, B2 ,.
Sources (or drains) of Q11 to Qnm are connected to the data electrode lines A1, A2, ..., An, and gates are connected to the scan electrode lines B1, B2 ,. The drain (source) of each TFT is connected to one electrode of a liquid crystal cell forming each pixel, and the other electrode of the liquid crystal cell is connected to a common counter electrode T. The image signal is applied to the data electrode lines A1, A2, ..., An.
Then, drive pulses Φ1, Φ2, ...
.., Bm are sequentially applied to the scanning electrode lines B1, B2, ..., Bm, so that the TFTs are turned on one scanning line at a time, and an image signal is written in a liquid crystal cell (pixel) connected to each TFT.

The image signal written in each pixel in this way is held by the storage capacitance of the pixel itself until a drive pulse is newly applied in the next field.
However, since it is structurally difficult to sufficiently secure the storage capacitance, it is generally performed to form the auxiliary storage capacitance by using the overlapping portion of the pixel electrode and the adjacent scanning electrode.
For example, as described above, the scan electrode lines B1, B2, ...
, Bm are sequentially applied to the scan electrodes Bk connected to a certain pixel electrode via the TFT, the drive pulse is applied to the scan electrode Bk connected to a certain pixel electrode via the TFT. The scan electrode Bk-1 is connected to the GND potential or a predetermined fixed potential, and this state continues until a drive pulse is applied in the next field, so that the auxiliary storage capacitance effectively acts.

The above liquid crystal display has the NTSC
In the case of displaying an image by the television broadcasting of the method, it is necessary to change the driving method depending on the number of pixels in the vertical direction of the liquid crystal display. In the NTSC system, the number of scanning lines is 525,
Interlaced scanning with a frame frequency of 30 Hz is performed, the field frequency is 60 Hz, and the number of scanning lines per field is 262.5 (525/2).

The number of pixels in the vertical direction of the liquid crystal display is 26
In the case of 2 or less, for example 240, the image signal of each field may be written in the pixel (liquid crystal cell) by sequentially scanning the pixels of the liquid crystal display for each field. At this time, by inverting and writing the polarity for each field, the DC component of the effective voltage applied to the liquid crystal cell can be made zero, and at the same time, the polarities of the adjacent upper and lower lines can be made different. That is, since the voltage change of each pixel is performed every 30 Hz of the frame frequency, the flicker due to the change is invisible to human eyes.

However, when the number of pixels in the vertical direction of the liquid crystal display becomes 263 or more, for example, 480, it is not possible to cover all the pixels in the vertical direction with the image signal of one field by performing sequential scanning as described above. On the other hand, CR
When the interlaced scanning similar to T is performed, the writing operation for each pixel is every 30 Hz, and the polarity of the signal is inverted for each writing to make the DC component of the effective voltage applied to the liquid crystal cell zero. Because you need to
A frequency component of 15 Hz will appear. This is shown in FIG. FIG. 5 shows the pixel potential at the center of the screen when the diagonal line from the upper left to the lower right is displayed on the screen for each field (m, m + 1, m + 2, m + 3). The black circles are the pixels that make up the diagonal lines,
+ And-indicate the polarities of the signals applied to the pixels. () Indicates that the pixel is not a target for interlaced scanning. As can be seen from this figure, the polarities between the adjacent upper and lower lines can be made different by two, but not by one. Thus, if a frequency component of 15 Hz appears on the liquid crystal display, it will appear as flicker to the human eye.

As a method for solving such a problem, n
There is a driving method in which the 1st and n + 1th scanning electrodes are always set as one set and are driven at the same time, and an image signal whose polarity is inverted is written in each field, but in this case, the resolution is sacrificed. Therefore, in one field, the n-1 and n-th scan electrodes are simultaneously turned on, and in the next field, n and n + 1.
A driving method for simultaneously turning on the second scan electrode (line complementary sequential scanning), or driving a scan electrode at every 60 Hz while correcting a movement between fields using a field memory to write a signal whose polarity is alternately inverted. There is a driving method (motion adaptive progressive scanning). These driving methods are described, for example, on page 83 of the 1989 National Conference of the Television Society of Japan.

[0009]

However, in the method of simultaneously driving the adjacent scan electrodes as described above, the auxiliary storage capacitor is formed by using the overlapping portion of the pixel electrode and the adjacent scan electrode as described above. It cannot be applied to the liquid crystal display having the structure. This is because the adjacent scan electrodes must be connected to the GND potential or a predetermined fixed potential until the drive pulse is applied in the next field in order for the auxiliary storage capacitance to work effectively. Further, the method of using the field memory such as the motion adaptive progressive scanning inevitably increases the cost of the liquid crystal display due to the complicated circuit configuration.

Therefore, according to the present invention, in a large-sized liquid crystal display, it is possible to display an image without flicker by directly using an NTSC type television signal without using a field memory, and further, to display each pixel and an adjacent scanning electrode. It is an object of the present invention to provide a driving method that can be adopted even when an auxiliary storage capacitor is formed between the two.

[0011]

In order to achieve the above object, a driving method of an active matrix liquid crystal display according to the present invention is to apply a driving pulse to two scanning electrodes separated by one horizontal scanning line at the same time to polarize an image signal. Is inverted for each scanning period and is inverted for each field.

Specifically, when m and n are natural numbers,
In the m-th field, a driving pulse is applied to the nth line and the (n + 2) th line in a certain horizontal scanning period, and a driving pulse is applied to the (n + 1) th line and the (n + 3) th line in the next horizontal scanning period. The pulse application is repeated for every four scanning lines, and in the next m + 1-th field, a driving pulse is applied to the n + 2th line and the n + 4th line in a certain horizontal scanning period, and the n + 3th line in the next horizontal scanning period.
A driving method in which a driving pulse is applied to the line and the (n + 5) th line, and such driving pulse application is repeated for every four scanning lines is preferable.

According to such a driving method, it is possible to display an image without flicker by using an NTSC television signal as it is on an active matrix liquid crystal display having 263 or more vertical pixels.
Moreover, it can be applied to an active matrix liquid crystal display in which an auxiliary storage capacitor is formed between each pixel electrode and its adjacent scanning electrode.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows pulse signals applied to scan electrodes in the driving method according to the present invention. In FIG. 1, n, n + 1, n + 2, ... Represents arbitrarily picked consecutive scanning line numbers, and the driving pulse signal in each scanning line is set to an arbitrary m-th field and the next m-th field.
The +1 field is shown side by side. When a positive drive pulse is applied, the TFT connected to the scan electrode (line) is turned on, and the voltage forming the image is applied to the corresponding pixel.

According to the driving method of the present invention, the driving pulse is simultaneously applied to the two scanning electrodes separated by one line to turn them on. For example, as shown in FIG. 1, when m and n are natural numbers, a drive pulse is applied to the nth line and the (n + 2) th line at a certain horizontal scanning start timing t1 in the mth field, and the next horizontal scanning is performed. At the start timing t2, the drive pulse is applied to the (n + 1) th line and the (n + 3) th line. Hereinafter, at t3, the n + 4th line and the n + th line
6th line, at t4, the n + 5th line and the n + 7th line,
As described above, the scanning in the vertical direction of the screen is performed while repeating the driving pulse application order in the four scanning lines from the nth line to the (n + 3) th line for every four scanning lines.

In the next (m + 1) th field, a combination different from that in the mth field is used, and two lines separated by one line are used.
A driving pulse is applied to the scanning lines of the book at the same time. That is, the drive pulse is applied to the n + 2th line and the n + 4th line at t2, and the drive pulse is applied to the n + 3th line and the n + 5th line at t3. Hereinafter, at t4, the n + 6th line and the n + 8th line, and at t5, the n + 7th line and the n + th line.
The scanning pulse is applied in the vertical direction of the screen by repeating the driving pulse application order in the four scanning lines from the (n + 2) th line to the (n + 5) th line for every four scanning lines.

FIG. 2 shows the state of each pixel when the above driving is performed. This figure is arranged in a matrix of 8 in the vertical direction (vertical scanning direction) and 3 in the horizontal direction (horizontal scanning direction) at the center of the screen when diagonal lines from the upper left to the lower right are displayed on the screen. Pixels are shown side by side for the m-th field and the m + 1-th field that follows it. The black circles are the pixels that make up the diagonal lines,
+ And-indicate the polarities of the signals applied to the pixels.

As can be seen from FIG. 2, according to the driving method of the present invention, the polarities of the pixels are always inverted between the adjacent scanning lines. Then, the polarity of each scanning line changes for each field. Therefore, line flicker does not occur. Since the driving pulse is simultaneously applied to the two scanning lines separated by one line, as shown in FIG. 2, for example, the pixels forming the shaded display portion are set to 1 at the same timing.
Although the lines are separated from each other, they appear as one diagonal line in the actual averaged display pattern with almost no problem, and it is possible to obtain the same resolution as that of the conventional line complementary sequential scanning.

Further, in the driving method of the present invention, since the scanning lines which are turned on at the same time are not adjacent to each other, it is applied to an active matrix liquid crystal display in which an auxiliary storage capacitor is formed between a pixel electrode and an adjacent scanning electrode. be able to. Therefore, the driving method of the present invention can be used for a liquid crystal display having a large aperture ratio.

[0020]

As described above, according to the liquid crystal display driving method of the present invention, in a large active matrix liquid crystal display in which an auxiliary storage capacitor is formed between a pixel electrode and an adjacent scanning electrode, a line memory is provided. It is possible to display a high-resolution image without flicker without requiring.

[Brief description of drawings]

FIG. 1 is a timing chart of driving pulses showing a driving method of an active matrix liquid crystal display according to the present invention.

FIG. 2 is a diagram showing a state of each pixel in a display example of a liquid crystal display by the driving method of FIG.

FIG. 3 is a block diagram of an active matrix liquid crystal display.

FIG. 4 Equivalent circuit of active matrix liquid crystal display

FIG. 5 is a diagram showing a state of each pixel when interlaced scanning is applied as it is.

Claims (4)

[Claims] 1. A driving method of an active matrix liquid crystal display, wherein an image signal is applied to each pixel electrode via a TFT connected to each intersection of a scan electrode and a data electrode formed in a matrix, and A drive pulse is applied simultaneously to two scan electrodes separated by a horizontal scan line to invert the polarity of the image signal every scan period, and
A method for driving an active matrix liquid crystal display, characterized by inverting each field. 2. When m and n are natural numbers, in the m-th field, the n-th line and the (n +) th line in a certain horizontal scanning period.
A drive pulse is applied to 2 lines, and a drive pulse is applied to the (n + 1) th line and the (n + 3) th line in the next horizontal scanning period,
The driving pulse application in this order is repeated for every four scanning lines, and in the next m + 1-th field, the driving pulse is applied to the (n + 2) th line and the (n + 4) th line in a certain horizontal scanning period, and in the next horizontal scanning period, 2. The method of driving an active matrix liquid crystal display according to claim 1, wherein a driving pulse is applied to the (n + 3) th line and the (n + 5) th line, and such driving pulse application is repeated for every four scanning lines. 3. The driving method according to claim 1, wherein the driving method is applied to an active matrix liquid crystal display in which an auxiliary storage capacitor is formed between each pixel electrode and its adjacent scanning electrode. 4. The driving method according to claim 1, wherein the driving method is applied to an active matrix liquid crystal display in which the number of pixels in the vertical direction is 263 or more.