JPH0830238A - Driving method for image display device - Google Patents

Abstract

(57) [Abstract] [Purpose] In a driving method of a liquid crystal display device for simultaneously selecting a plurality of rows, display unevenness due to the presence of virtual rows is suppressed. [Configuration] A screen is divided into two upper and lower screens and independently driven, and at least a part of a set of row electrodes that are simultaneously selected includes a virtual row electrode, and a row electrode including the virtual electrode is It is characterized by arranging them at the top and bottom of the screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device suitable for a liquid crystal which responds at high speed. In particular, the present invention relates to a driving method of a simple matrix type liquid crystal display device which performs multiplex driving by the MLS method (multiple line simultaneous selection method, see JP-A-6-27907, USP5262881).

[0002]

2. Description of the Related Art Hereinafter, in the present specification, scan electrodes are referred to as row electrodes, and data electrodes are also referred to as column electrodes.

With the progress in the advanced information age, the need for information display media is ever increasing. Liquid crystal displays have advantages such as thinness, light weight, and low power consumption, and are considered to be more and more popular because of their compatibility with semiconductor technology. On the other hand, with the spread, the demand for larger screens and higher definition has started, and the search for a method for large-capacity display has begun. Among them, the STN (super twisted nematic) method is the TFT (thin film transistor).
The manufacturing process is simpler than that of the conventional method, and it can be produced at low cost, so it is expected to become the mainstream of future liquid crystal displays.

In order to display a large capacity in the STN system, line sequential multiplex driving has been conventionally performed. This method selects each row electrode one by one, and selects the column electrodes corresponding to the pattern to be displayed.
The display of one screen is completed by selecting all the row electrodes.

However, it is known that the line-sequential driving method causes a problem called frame response as the display capacity increases. In the line-sequential driving method, a relatively high voltage is applied to the pixels when selected, and a relatively low voltage is applied when the pixels are not selected. This voltage ratio generally increases as the number of row lines increases (higher duty driving). Therefore, when the voltage ratio is small, the liquid crystal that responds to the voltage effective value responds to the applied waveform. That is,
The frame response is a phenomenon in which the transmittance at the time of OFF increases because the amplitude of the selection pulse is large, and the transmittance at the time of ON decreases as the cycle of the selection pulse is long, resulting in a decrease in contrast.

A method is known in which the frame frequency is increased in order to suppress the occurrence of the frame response, and thereby the period of the selection pulse is shortened, but this has a serious drawback. That is, when the frame frequency is increased, the frequency spectrum of the applied waveform becomes high, which causes non-uniformity of display and increases power consumption. In addition, the upper limit of the frame frequency is limited to prevent the selection pulse width from becoming too narrow.

In order to solve this problem without increasing the frequency spectrum, a new driving method has recently been proposed. A method such as an MLS (multiple line simultaneous selection) method for simultaneously selecting a plurality of row electrodes (selection electrodes). This method is a method in which a plurality of row electrodes can be simultaneously selected and the display pattern in the column direction can be independently controlled, and the frame period can be shortened while keeping the selection width constant. That is, high contrast display with suppressed frame response can be performed.

In the MLS method, in order to control the column display pattern independently, a constant voltage pulse train is applied to each row electrode applied simultaneously. In the driving method in which a plurality of lines are selected at the same time, voltage pulses are simultaneously applied to a plurality of row electrodes. At this time, in order to control the display pattern in the column direction simultaneously and independently, it is necessary to apply pulse voltages having different polarities to the row electrodes. A pulse having a polarity is applied to the row electrode several times, and an effective voltage corresponding to ON / OFF is applied to each pixel in total.

The selection pulse voltage group applied to each row electrode can be expressed as a matrix of L rows and K columns (hereinafter, referred to as a selection matrix (A)). Since the selected pulse voltage series can be represented as mutually orthogonal vector groups, a matrix including these as column elements is an orthogonal matrix. At this time, the row vectors in the matrix are orthogonal to each other. The number L of rows corresponds to the number of simultaneous selections, and each row corresponds to each line. For example, the first row element of the selection matrix (A) is applied to the line 1 of the L selection lines, and the selection pulse is applied in the order of the first column element and the second column element. In the present specification, in the notation of the selection matrix (A), 1 means a positive selection pulse, and −1 means a negative selection pulse.

A voltage level corresponding to each column element of this matrix and a column display pattern is applied to the column electrode. That is, the column electrode voltage series is determined by the matrix and the display pattern that determine the row electrode voltage series.

The sequence of voltage waveforms applied to the column electrodes is determined as follows. FIG. 9 is an explanatory diagram showing the concept. A Hadamard matrix of 4 rows and 4 columns will be described as an example. It is assumed that the display data of the column electrode i and the column electrode j are as shown in FIG. The column display pattern is represented as a vector (d) as shown in FIG. 9 (b). Here, when the column element is -1, it indicates ON display,
1 represents the off display. Assuming that the row electrode voltages are sequentially applied to the row electrodes in the order of the columns of the matrix, the column electrode voltage level becomes a vector (v) shown in FIG. 9B, and its waveform is shown in FIG. 9C. become that way. In FIG. 9C, the vertical axis and the horizontal axis are arbitrary units.

The waveform of FIG. 9 (c) shows the case where each time a selection pulse is applied to one subgroup, the next subgroup is selected. The selection pulse to be applied to each subgroup is selected. The case of shifting in the matrix is shown. If the selection pulse sequence is different,
The sequence of column voltages is also different.

[0013]

[Problems to be Solved by the Invention] In the MLS method,
In many cases, driving is performed assuming a virtual row electrode other than the row electrode actually existing on the substrate. One reason is that when performing the simultaneous selection of a smaller number of electrodes than all the lines, the number of all row electrodes is not always divisible by the number of row electrodes to be selected at the same time. This is because the number of electrodes may be the same. That is, the column electrode signal is calculated and driven assuming that the row electrode subgroup in which the actual number of row electrodes is insufficient has virtual row electrodes.

However, as the inventors proceeded with the development, it has been found that display irregularities may occur in the vicinity of such virtual row electrodes. Particularly, when the screen is divided into upper and lower parts and the two screens are driven independently, this display unevenness often causes a problem. This is because when the virtual electrode is arranged in the center of the screen, display unevenness appears as black stripes or white stripes along the row direction, which is noticeable on the display.

[0015]

According to the present invention, in a driving method for simultaneously selecting and driving a plurality of row electrodes of an image display device having a plurality of row electrodes and a plurality of column electrodes, the screen is divided into two screens. Of at least a part of a set of row electrodes that are independently driven and simultaneously selected include a virtual row electrode, and the virtual electrode is arranged at a screen end portion. In a driving method and a driving method of simultaneously driving a plurality of row electrodes of an image display device having a plurality of row electrodes and a plurality of column electrodes, a screen is divided into two screens and driven independently, and simultaneous selection is performed. At least a part of the set of row electrodes to be included includes a virtual row electrode, and
A method for driving an image display device, characterized in that a set of row electrodes including the virtual electrodes is arranged at an end portion of a screen. In particular, the above method for driving an image display device is provided, wherein each screen is scanned from a boundary between the two screens toward an end of the screen.

That is, by arranging the virtual row electrodes in a portion where the display unevenness on the screen is inconspicuous, as a whole,
The display unevenness can be greatly reduced.

The virtual row electrode does not actually exist, but in reality, its position is often fixed on the display screen. In many cases, in order to make the circuit design advantageous, the selection pulse sequence is applied with a certain regularity, and the row electrodes simultaneously selected have a certain regularity on the real screen. Because they are arranged.

For example, FIG. 2 shows an example in which row electrodes that are selected at the same time are collectively arranged on the actual screen.
It is shown in (a). The figure shows a case where there are 14 actual scanning lines, the number of row electrodes that are simultaneously selected is 3, and the number of independent selection pulses is 4 (A _{1 to} A ₄ ). In the figure, 1, 2, 3,
Reference numerals 4 and 5 are row electrode subgroups, and reference numerals 1-1 to 5-5 are row electrodes (including virtual row electrodes).

In the case of FIG. 2 (a), row selection proceeds from the top of the screen by advancing the selection pulse by one in the selection matrix each time a row subgroup is selected.
The selection pulse is applied to the sub-group 3 in the order of A ₃ , A ₄ , A ₁ , A ₂ . By comparing this with the actually applied selection waveform, it is possible to recognize at which position the row electrode is treated as a virtual electrode. Then, considering that the row electrodes that are simultaneously selected are collectively arranged on the actual screen as a group, the virtual row electrodes 3-3 are
It can be considered that they are arranged between the 8th and 9th lines from the top on the real screen.

Similarly, FIG. 2 (b) shows the row electrodes selected at the same time distributedly arranged on the actual screen. In this case as well, by performing the same consideration,
It can be considered that a virtual electrode is inserted between the third and the third position.

In the present invention, when the two screens are driven, the positions of the virtual row electrodes specified in this way are arranged above and below the screen, so that display unevenness due to the positions of the virtual row electrodes is substantially caused. It is possible to reduce.

Specifically, in order to arrange the virtual row electrodes at the edges of the screen, for example, in the case of FIG. 2A, the virtual electrodes are included in the first sub-group, and the row electrodes 1-1. It is sufficient to drive in a sequence so that becomes a virtual electrode. Figure 2
Also in the case of (b), similarly, it is sufficient that the first subgroup includes the virtual electrodes and the 1-1 row electrodes are driven in a sequence so as to become the virtual electrodes.

In the present invention, since the virtual electrodes are distributed to the plurality of row electrode subgroups, the display unevenness due to the presence of the virtual electrodes is distributed, so that the display quality can be expected to be improved.

Further, as shown in FIG. 2A, when the row electrodes to be simultaneously selected are grouped together, the row electrode subgroup including the virtual electrodes is simply arranged at the edge (upper and lower) of the screen. , Has a considerable effect in reducing display unevenness.

Further, in the present invention, each screen is preferably scanned from the boundary between the two screens toward the end of the screen. That is, when upper and lower halves are divided, it is preferable to scan the upper screen from top to bottom and scan the lower screen from bottom to top. This is because the column voltage fluctuation caused by the virtual electrode often affects the subgroup to be scanned next, so that it is advantageous to position it at the end of scanning. The column voltage fluctuation also affects the subgroup to be scanned next. In the next subgroup, a new waveform distortion is generated in a direction to restore the waveform distortion generated in the subgroup including the virtual electrode. This is because there are many cases.

The driving method in the present invention is disclosed in JP-A-6-27.
It can be realized by using a circuit as described in Japanese Patent Application No. 907, USP5262881 as a basis.

A block diagram of an example of the circuit configuration is shown in FIG. This is a circuit for displaying 16 gradations for each of RGB. Data signal, 16 gradation signal MSB
To LSB are input to the data preprocessing circuit 51 as 4-bit signals. The data preprocessing circuit 51 is a circuit for outputting a data signal input to the column signal generation circuit 52 with a format and timing suitable for forming a column signal in the subsequent stage. The column signal generation circuit 52 includes a data preprocessing circuit 51.
The data signal output from the input terminal and the orthogonal function signal output from the orthogonal function generation circuit 55 are input.

The column signal generation circuit 52 performs a predetermined operation using both signals to form a column signal, and then outputs the column signal to the column driver 53. The column driver 53 uses a predetermined reference voltage to form a column electrode voltage applied to the column electrode of the liquid crystal panel 56 from the input column signal and outputs the column electrode voltage to the liquid crystal panel 56. On the other hand, the orthogonal function generating circuit 5 is connected to the row electrodes of the liquid crystal panel 56.
A row electrode voltage obtained by converting the orthogonal function signal output by the row driver 54 is applied. These circuits are provided with a timing circuit and the like as necessary, and are controlled and operated at a predetermined timing.

The orthogonal function used in the present invention is generated by the orthogonal function generating circuit 55. Orthogonal function generating circuit 55
Can also perform calculation every time an orthogonal function signal is generated to form a signal. However, it is preferable in terms of simplicity that the orthogonal function signal to be used is stored in the ROM in advance and the signal is read out at an appropriate timing. That is, the pulses that define the voltage application timing to the liquid crystal panel 56 are counted, and the orthogonal function signals in the ROM are sequentially read using the counted value as an address signal.

The data preprocessing circuit 51 is specifically constructed as shown in FIG. The signal processing is performed by dividing 4-bit image data having gradation information into 4 sets of R, G, and B 3 bits. That is, MSB (2 ³ ), 2ndMSB
4 of (2 ² ), 3rdMSB (2 ¹ ), LSB (2 ⁰ ).
The signals are divided into sets and parallel processing is performed.

The input 3-bit data is converted into 15-bit data by the 5-stage serial / parallel converter 11 and is stored in the memory 12.
Sent to Specifically, serial data is input to the input terminal of the 5-stage shift register, and each of the five tap outputs is input to the memory 12.

As the memory 12, a VRAM having a data width of 16 bits was used. Writing to the memory 12 is performed as follows using the direct access mode. That is, the data on the row electrodes corresponding to the same column electrode is stored in seven adjacent addresses for the seven row electrodes selected at the same time. By doing so, reading from the memory in the subsequent stage can be performed at high speed, and the operation becomes easy.

Reading from the memory 12 is performed in a high-speed sequential access mode in accordance with the LCD drive timing.
The four sets of 15-bit data are sent to the data format conversion circuit 16.

The data format conversion circuit 16 converts the data sent in parallel with a 15-bit width for each gradation into RGB.
This is a circuit for rearranging parallel signals each having a 20-bit width, and it is usually sufficient to perform appropriate wiring on the circuit board.

The data format conversion circuit 16 outputs RGB
After being converted into three sets of 20-bit data, the data is sent to the gradation determining circuit 15. The gradation determination circuit 15 converts 4-bit gradation data per dot into ON / OFF 1-bit data to form a video signal for a sub-screen, and the sub-screen is subjected to, for example, 15 cycles to perform frame modulation for realizing gradation display. Circuit.

Specifically, a demultiplexer for distributing 20-bit width data into 5-bit width data at a predetermined timing is used. Which bit corresponds to which sub-screen is determined by counting by the frame counter. In this way, the 20-bit data corresponding to the gradation data for 5 dots is converted into 5-bit serial data without gradation and is output to the vertical / horizontal conversion circuit 13.

The vertical-to-horizontal conversion circuit 13 is a circuit which transfers display data of 5 pixels seven times and stores the display data, and reads this as data of 7 pixels in five times. 2 sets of 5x
It consists of a 7-bit register. Vertical-to-horizontal conversion circuit 13
To the column signal generation circuit 52.

The column signal generation circuit 52 has the structure shown in FIG. Exclusive OR gate 2 for 7-bit data signal
Input to 3, 23, .... Exclusive OR gate 23
A signal from the orthogonal function generating circuit 5 is also input to each. The outputs of the exclusive OR gates 23 are added to the row electrodes simultaneously selected by the adder 21.

The column driver 53 has a structure as shown in FIG. It comprises a shift register 31, a latch 32, a decoder 33, and a voltage divider 34.
A demultiplexer is used as the voltage level selector 33, and when the data for one row is sent to the shift register 31, the display data is converted into the column voltage.

Further, the row driver 54 has a structure as shown in FIG. It includes a drive pattern register 41, a selection signal register 42, and a decoder 43. The contents of the selection signal register 42 determine the simultaneously selected rows, and the contents of the drive pattern register 41 determine which polarity the selection signal is output to. 0V is output to the non-selected rows.

4 to 8 are shown as an example of a circuit, and various circuits can be adopted without impairing the essence of the present invention.

[0042]

EXAMPLE A liquid crystal display panel was driven in the following manner using the circuits shown in FIGS. The liquid crystal display panel is 9.
4-inch VGA module (number of pixels 480 x 640 x
3 (RGB)) with a back backlight. The response time of the liquid crystal display panel is 60 ms on average of rising and falling. The 480 row electrodes were divided into upper and lower 240 electrodes to drive two screens. A method in which seven rows are selected simultaneously, row electrodes to be simultaneously selected are arranged so as to be adjacent to each other in a lump on the screen, and the selection matrix is advanced by one column in each selection (method 1) Driven by. Since two screens were driven (vertical division), the number of subgroups was 35, and 5 of them were treated as virtual electrodes. The bias was adjusted so that the contrast ratio became almost maximum, and the display contrast ratio was 30: 1 and the maximum brightness was 100 cd / m ² .

As Example 1, driving was performed in a virtual row electrode arrangement and sequence as shown in FIG. That is,
In the upper screen, 1-1 to 1 of row electrode subgroup 1
The row electrode of -5 is used as a virtual electrode, and the row electrodes of row electrode subgroups 35-3 to 35-7 are used as virtual electrodes in the lower screen, and scanning is performed from the smallest row electrode subgroup number to the largest row electrode subgroup number. I went.

As Example 2, driving was performed in a virtual row electrode arrangement and sequence as shown in FIG. Both the upper screen and the lower screen are 1-1 to 1-of the row electrode subgroup 1.
The row electrode of No. 5 was used as a virtual electrode, and scanning was performed from the smallest row electrode subgroup number to the largest row electrode subgroup number.

As a comparative example, driving was performed in a virtual row electrode arrangement and sequence as shown in FIG. 35-3 to 35-7 of the row electrode subgroup 35 for both the upper screen and the lower screen
The row electrodes were used as virtual electrodes, and scanning was performed from the smallest row electrode subgroup number to the largest row electrode subgroup number.

As a result, the display unevenness in the vicinity of the boundaries between the upper and lower screens was the smallest in Example 2, the next was Example 1, and the comparative example had the largest display unevenness.

[0047]

According to the present invention, it is possible to suppress display unevenness due to the presence of virtual rows in a driving method of a liquid crystal display element in which a plurality of rows are simultaneously selected and two screens are driven.

[Brief description of drawings]

FIG. 1A is an explanatory view for explaining the arrangement and sequence of virtual row electrodes on the screen of Embodiment 1, and FIG. 1B is an explanatory view for explaining the arrangement and sequence of virtual row electrodes on the screen of Embodiment 2. Figure

2A and 2B are explanatory views for explaining the arrangement of virtual row electrodes on the screen.

FIG. 3 is an explanatory diagram illustrating the arrangement and sequence of virtual row electrodes on the screen of a comparative example.

FIG. 4 is a circuit diagram showing an example of a drive circuit for realizing the drive method of the present invention.

FIG. 5 is a block diagram showing a data preprocessing circuit 1.

FIG. 6 is a block diagram showing a column signal generation circuit 2.

FIG. 7 is a block diagram showing a column driver 3.

FIG. 8 is a block diagram showing a row driver 4.

9A to 9C are conceptual diagrams and waveform diagrams for explaining a voltage application method in the MLS method.

[Explanation of symbols]

 21: Column signal generation circuit 22: Column signal generation circuit 31: Latch circuit 32: Selection circuit 51: Data preprocessing circuit 52: Column signal generation circuit 53: Column driver 54: Row driver 55: Orthogonal function generation circuit 56: Liquid crystal panel

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takeshi Kuwata 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory

Claims (3)

[Claims] 1. A driving method for simultaneously selecting and driving a plurality of row electrodes of an image display device having a plurality of row electrodes and a plurality of column electrodes, wherein a screen is divided into two screens and independently driven, and simultaneous selection is performed. A method for driving an image display device, characterized in that a virtual row electrode is included in at least a part of a set of row electrodes to be formed, and the virtual electrode is arranged at an end portion of a screen. 2. A driving method for simultaneously selecting and driving a plurality of row electrodes of an image display device having a plurality of row electrodes and a plurality of column electrodes, wherein a screen is divided into two screens and driven independently, and simultaneous selection is performed. Driving method for an image display device, characterized in that a virtual row electrode is included in at least a part of the set of row electrodes, and the set of row electrodes including the virtual electrode is arranged at an end portion of the screen. . 3. Each screen, from the boundary between the two screens,
The driving method for an image display device according to claim 1, wherein scanning is performed toward an end portion of the screen.