JPH02207296A - Liquid crystal driving system and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To enable a half-tone gradational display and AC driving without increasing a frame frequency by switching a write voltage between the positive and negative polarities alternately at intervals of two frames and writing a white level in one frame and a black level in the other frame corresponding to the half- tone gradational display. CONSTITUTION:Unit signal line driving circuits DV1 - DVn output selectively voltages corresponding to picture element data corresponding to white and black outputted from latch circuits FF1 - FFn in parallel according to an AC converted signal M supplied from a timing control circuit TG for the AC driving of liquid crystal. Then positive writing and negative writing are performed at intervals of two frames and when the half-tone gradational display is made, a white display and a black display are inputted alternately at intervals of one frame as the picture element data to write the white level in one frame and the black level in the other frame. Consequently, the half-tone gradational display and AC driving are enabled without increasing the frame frequency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal driving method and a liquid crystal display device using the same, and for example, a liquid crystal display method having an intermediate gradation display function and a color liquid crystal display using the same. It relates to techniques that are effective for use in devices.

[Conventional technology]

Regarding a liquid crystal device having an active matrix structure equipped with a TPT (thin film transistor), there is, for example, "Nikkei Electronics", page 211, published by Nikkei McGraw-Hill, September 10, 1984.

[Problem to be solved by the invention]

TPT liquid crystal display devices are used as monitors in microcomputer systems as small, low-power consumption display devices, but in the future there will be strong demand for multi-gradation and multi-color displays as display devices in office automation equipment. .

In a TPT liquid crystal display device, since the voltage applied to the liquid crystal must not have a DC component, AC driving is performed in which the polarity of the write voltage is alternately reversed between positive and negative polarity every frame. For example, as shown in FIG. 5, the alternating current signal M is set to 1 (positive polarity) in frame I, 0 (negative polarity) in frame 2, and 1 (negative polarity) in odd-numbered frames.
In addition, it is set to 0 for even frames.

In the case of multicolor display, intermediate gradation display of color pixels is required. Therefore, when displaying an intermediate gradation, it is possible to make the voltage applied to the color pixel equal to an intermediate voltage by alternately displaying a binary value of bright and dark in the color pixel. However, due to the AC driving operation of the liquid crystal as described above, bright display is performed in the first and second frames and dark display is performed in the third and fourth frames as shown in FIG. This results in 4 frames being spent on intermediate gradations.

In the above-mentioned halftone display, the display frequency (lowest frequency) is reduced to 1/4 of the frame frequency.

Since flicker is noticeable when the display frequency is about 50 Hz or less, if the above-mentioned halftone display is to be performed, the frame frequency must be as high as about 200 Hz. However, with current technology, the switching characteristics of TPT and the performance of the drive circuit are limited.
The above-mentioned intermediate gradation display is practically impossible without a very high frame frequency.

An object of the present invention is to provide a liquid crystal driving method that realizes intermediate gradation display without increasing the frame frequency, and a liquid crystal driving device using the same.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

In other words, the write voltage supplied to the liquid crystal pixels is alternately switched between positive and negative polarity every two frames, and the white level is written in one of the two frames, corresponding to the intermediate gradation display, and the white level is written in the other frame. Write the black level.

For this reason, the signal line drive circuit alternately switches the polarity of the write voltage supplied to the pixels by the alternating current signal between positive and negative every two frames, and selects one of the two frames according to the display data of the intermediate gradation. In the frame, a white level is written, and in the other frame, a voltage for writing a black level is output.

[For production]

According to the above-mentioned means, white and black display, which is not halftone display, is performed for each frame, and halftone display and AC drive of the liquid crystal can be realized without increasing the frame frequency.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of a liquid crystal display device to which the present invention is applied.

The latch circuits FFI to FFn serially take in pixel data from the input terminal Din and output it in parallel. That is, the latch circuits FFI to FFn constitute a shift register and launch having a serial/parallel conversion function.

The pixel data serially captured in each of the latch circuits FFI to FFn is output in parallel from each of the latch circuits FFI to FFn, and is transmitted to the input of each unit circuit DVI to DVn constituting the signal line drive circuit (driver). . Unit signal line drive circuit DVI to D
Vn is set to a positive polarity, for example, according to pixel data corresponding to white/black output from the latch circuits FF1 to FFn in parallel in accordance with an AC conversion signal M supplied from the timing control circuit TG for AC driving of the liquid crystal. Three voltages are selectively output: a negative white level V1 is +IV, a black level V2 is approximately -7V, and a negative white level V3 is approximately -15V.

On the other hand, the launch circuits FFI to FFn are
Since it handles binary pixel data such as +5V and 0, an appropriate level conversion circuit is provided at the input section of the unit signal line drive circuits D1 to DVn, and a level conversion circuit corresponding to the above output operation is provided. The level is converted to the same level.

A scanning line drive circuit (driver) GDV selects scanning lines of the liquid crystal display panel LCD in order from the top.

Although the details of the scanning line driving circuit GDV are not shown in the drawings, the scanning line driving circuit GDV includes a signal generating circuit consisting of a shift register or counter that performs a shift operation in response to a horizontal synchronizing signal and its decoder circuit;
In response to the output, a drive signal is generated to sequentially drive the scanning lines G1 to Gm of the liquid crystal display panel LCD.

The timing generation circuit TG uses the basic clock pulse CLK.
For example, as shown in the representative example, the shift clock SK is sent to the latch circuits FFI to FFn constituting the shift register, and the alternating current signal M is sent to the signal line drive circuits DVI to DVn, horizontally. A synchronizing signal HK is supplied to the scanning line drive circuit GDV. In addition, necessary timing signals and control signals are generated.

A color liquid crystal display device performs color display by providing a color filter for each pixel PX. Therefore, there are two types of liquid crystal: white (bright) and black (dark).
Value display is still performed, and multicolor display is realized by adding an intermediate gradation display function as described later. For example, when color filters of three primary colors of red, green, and blue are used, a total of eight colors can be displayed when combined with a binary liquid crystal display as described above. If halftone display is added to each of the three primary colors red, green, and blue, a color display of as many as 27 colors can be realized.

In this example, without increasing the frame frequency,
In order to realize intermediate gradation display of pixels, the alternating current signal M is switched between 1 and O every two frames. That is, as shown in the operational relationship diagram of FIG. 2, the AC conversion signal M is set to 1 in frames 1 and 2, and is changed to 0 in frames 3 and 4. And frames 5 and 6
When this happens, the alternating current signal M is returned to its original value of 1. Thereafter, the alternating current signal M is similarly switched between 1 and 0 every two frames. In other words, as an AC drive system for the liquid crystal display panel, positive polarity writing and negative polarity writing are performed every two frames.

When displaying an intermediate gradation, pixel data such as 1, which does not indicate white display, and O, which indicates black display, are alternately input for each frame. That is, in frame 1, the voltage 1 (IV) of the own level is written to the liquid crystal pixel with positive polarity, and in frame 2, the voltage of the black level V2 (-7V) is written to the liquid crystal pixel with the same positive polarity. Then, in frame 3, the voltage V3(
-15V) is written to the liquid crystal pixel, and in frame 4, the voltage of the black level V2 (-7V) is written to the liquid crystal pixel under the same negative polarity. In addition, the common electrode of the liquid crystal has a voltage of -7V.
A reference voltage of is applied.

In this type of liquid crystal drive system, it is possible to display halftones by having the liquid crystal pixels for halftone display display white (bright) and black (dark) for each frame, and smoothing the results. . With this method, even when achieving a display frequency of approximately 50 Hz as described above, the frame frequency can be as low as 100 Hz.

As a result, gradation display using the so-called frame thinning method as described above can be realized using the switching characteristics of the current TPT and the operating speed of the signal line drive circuit constituted by a semiconductor integrated circuit. In this gradation method, the generation timing of the alternating current signal and the input pixel data are processed and formed in accordance with the gradation display while using the existing drive circuit without changing the configuration of the drive circuit itself. By means of software, so to speak, it becomes possible to realize intermediate gradation display on a liquid crystal.

If the liquid crystal display panel displays in color, the application of the present invention makes it possible to display as many as 27 colors.

FIG. 3 shows a screen configuration diagram of an embodiment of the method for setting the alternating current signal.

In this embodiment, a case is shown in which the alternating current signal M is set fixedly during one frame.

That is, in the first frame F1, the alternating current signal M is fixed at 1, and in other words, white/black writing is performed with positive polarity to all the liquid crystal pixels constituting the liquid crystal screen. In this embodiment, since the alternating current signal M is switched every two frames as described above,
Also in the second frame F2, the alternating current signal M is fixed to 1,
Similarly to the above, white or black is written to all the liquid crystal pixels constituting the liquid crystal screen according to the pixel data using positive polarity. However, pixel data corresponding to halftone display is set to 1 and 0 between two frames. For example, in the first frame F1, white (or black) can be written with positive polarity, and in the second frame, black can be written with positive polarity. (or white) is written.

Next, in the third frame F3, the alternating current signal M is switched to 0 and fixed for that period, in other words, all the liquid crystal pixels constituting the liquid crystal screen are set to white or white according to the pixel data by applying negative polarity to This is for writing in black. In this embodiment, since the alternating current signal M is switched every two frames as described above, the alternating current signal M is still fixed at 0 in the fourth frame F4, and the liquid crystal screen is changed as described above. White or black is written to all the liquid crystal pixels in accordance with the pixel data using negative polarity. However, pixel data corresponding to halftone display is set to 1 and O between two frames, and for example, the third
In frame F3, white (or black) writing is performed with negative polarity, and in the fourth frame, black (or white) writing is performed with negative polarity.

FIG. 4 shows a screen configuration diagram of another embodiment of the setting direction of the alternating current signal.

In this embodiment, the alternating current signal M is switched for each scanning line. That is, in the first line (scanning line Gl) of the first frame F1, the alternating current signal M is set to 1, and the white/black color is set to one line of liquid crystal pixels connected to the scanning line G1 by positive polarity. This is for writing. In the second line (scanning line G2), the alternating current signal M is switched to O, and white/black writing is performed with negative polarity to one line of liquid crystal pixels connected to the scanning line G2. Similarly, the alternating current signal M is switched to 1 for odd lines and to 0 for even lines. In this configuration, the alternating current signal M is alternately switched between 1 and 0 for each line within one frame. In this embodiment, as described above, the alternating current signal M
, so even in the second frame F2,
The alternating current signal M is set to 1 on odd-numbered lines, and set to 0 on even-numbered lines. As a result, when focusing on pixels in a certain line, writing with positive polarity or negative polarity is performed twice in succession in both the first frame F1 and the second frame F2.

Next, in the third frame F3, the alternating current signals M for each line are reversely switched. That is, in the first line (scanning line Gl) of the third frame F3, contrary to the above case, the alternating current signal M is set to 0, and a negative polarity is applied to one line of liquid crystal pixels connected to the scanning line G1. white/
This is for writing in black. 2nd line (scanning line G
In 2), contrary to the above case, the alternating current signal M is switched to 1, and white/black writing is performed with positive polarity to one line of liquid crystal pixels connected to the scanning line G2. Similarly, the alternating current signal M is switched to O for odd lines and to 1 for even lines. In this configuration, the alternating current signal M is alternately switched between 0 and 1 for each line within one frame. In this embodiment, since the alternating current signal M is switched every two frames as described above, the fourth frame F4
However, the alternating current signal M is set to 0 on odd-numbered lines, and set to 1 on even-numbered lines. As a result, when focusing on pixels in a certain line, writing with positive polarity or negative polarity is performed twice in succession in both the third frame F3 and the fourth frame F4.

As a modification of the embodiment described in 1 above, the scanning line of the liquid crystal display panel may be divided into a plurality of blocks, and the alternating current signal may be designated for each block.

As mentioned above, as in the embodiment shown in FIGS. 3 and 4,
The designation of the alternating current signal M can be set on a frame-by-frame basis, or on a line-by-line basis. Therefore, it goes without saying that the switching of the alternating current signal every two frames in this embodiment focuses on a specific pixel.

The effects obtained from the above examples are as follows. In other words, (1) The write voltage supplied to the liquid crystal pixels is alternately switched between positive and negative polarity every two frames, and the white level is changed in one of the two frames in 1. By writing the black level in the other frame, white and black display for halftone display is performed for each frame. This provides the effect of realizing intermediate gradation display and alternating current driving of the liquid crystal without increasing the frame frequency.

(2) According to (1) above, even if halftone display is performed at a display frequency of approximately 50H2, the frame frequency will be reduced to 100H2.
Since it can be made as low as Hz, it is possible to achieve the effect of realizing gradation display by the so-called frame thinning method as described above using existing TPT liquid crystal display panels and semiconductor integrated circuits.

(3) According to (2) above, the generation timing of the alternating current signal and the input pixel data can be changed without changing the configuration of the liquid crystal display panel or the drive circuit itself, in other words, while using the existing liquid crystal display device. By processing and forming according to the tone display, so to speak, by software means,
The effect of realizing intermediate gradation display of liquid crystal can be obtained.

(4) According to (3) above, if the liquid crystal display panel performs color display, it is possible to easily realize a multi-color display of as many as 27 colors.

Although the invention made by the present inventor has been specifically explained based on Examples above, this invention is not limited to the above-mentioned Examples, and it should be noted that various changes can be made without departing from the gist of the invention. Not even. For example, as a color liquid crystal display panel, there are 1 horizontal strip to live type, and 1 vertical strip.
Various embodiments can be adopted, such as a helical shape or a diagonal mosaic shape having various color filters. When realizing the above diagonal mosaic color filter, the diagonal mosaic color pixels of the same color may be connected by signal lines or scanning lines. In this case, the signal lines or scanning lines are arranged in a wavy manner in accordance with the arrangement of pixels of the same color. By adopting the above configuration, it is sufficient to supply color pixel signals corresponding to the same color at a certain timing, thereby facilitating driving of the signal line.

The specific structure of the signal line drive circuit may be of any type as long as the write signal to be transmitted to the signal line is as in the embodiment described above based on the pixel data and the alternating current signal.

Note that the pixel data may have a 2-bit configuration per pixel, and 1 and 0 for intermediate gradation display may be generated within the drive circuit. In this case, a three-value display decoder is also provided in the signal line drive circuit.

INDUSTRIAL APPLICABILITY The present invention can be widely used in liquid crystal drive systems including intermediate gradation display and liquid crystal display devices using the same.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. That is, the write voltage supplied to the liquid crystal pixels is alternately switched between positive polarity and negative polarity every two frames, and
By writing the white level in one of the above two frames and writing the black level in the other frame in correspondence with the intermediate gradation display, white and black display for the intermediate gradation display can be performed for each frame. conduct. As a result, it is possible to realize intermediate gradation display and AC drive of the liquid crystal without increasing the frame frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a liquid crystal display device to which the present invention is applied, FIG. 2 is an operation-related diagram for explaining the display operation, and FIG. 3 is an AC signal setting. FIG. 4 is a screen configuration diagram showing another embodiment of the method for setting an AC signal; FIG. 5 is a diagram for explaining the display operation of a liquid crystal according to the prior art. FIG. FFI~FFn...Shift register & launch circuit, DV
1-DVn...Signal line drive circuit, I-CD...Liquid crystal display panel, GDV...Scanning line drive circuit, TG...Timing control circuit F1-F4...Frame.

Claims (1)

[Claims] 1. The write voltage supplied to the pixel is set to positive/positive every two frames.
A liquid crystal driving method characterized in that the polarity is alternately switched to negative polarity, and a white level is written in one of the two frames, and a black level is written in the other frame to pixels corresponding to intermediate gradation display. 2. Receives an alternating current signal that instructs to alternately switch the polarity of the write voltage supplied to pixels between positive and negative every two frames and pixel data including intermediate gradation, and supplies it to the signal line of the liquid crystal display panel. It is provided with a signal line drive circuit that switches the polarity of the write voltage according to the alternating current signal, and writes a white level in one of the two frames and writes a black level in the other frame according to the intermediate gradation display data. A liquid crystal display device featuring: 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display panel is a color liquid crystal display panel having an active matrix structure using thin film transistors.