JPH04204628A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which can display moving pictures and medium contrasts by executing the initialization to put liquid crystals into a scattering state by moving the same by one line each in precedence to a display data writing line, successively writing the display data from the initialized line, then holding thereof. CONSTITUTION:An initializing means 12 subjects a liquid crystal display panel 11, which is regularly arranged with the plural phase transition type liquid crystals respectively as picture element cells, to the initialization to put the respective liquid crystals on the line precedent for the time longer than the response time until the liquid crystals attain the scattered state from the transparent state for the writing line. A writing and display means 13 executes writing by impressing the driving voltages of the levels meeting the display gradations to the respective liquid crystals of the writing of the already initialized display data and holdss the same. The display data by one line each can be written in such a manner; in addition, the display data to be written is made into the data of the arbitrary positions in the voltage-transmittance characteristics of the liquid crystal and, therefore, the moving the picture display and the medium contrast display are respectively executed.

Description

[Detailed Description of the Invention] [Summary] Regarding a liquid crystal display device that drives a phase change type liquid crystal panel, for the purpose of displaying moving images and halftones, a plurality of phase change type liquid crystals are arranged regularly as pixel cells. In a liquid crystal display device that performs display using a liquid crystal display panel, one of the plurality of phase change liquid crystals precedes a writing line of display data by a time equal to or longer than a response time for the liquid crystal to change from a transparent state to a scattering state. an initialization means for initializing each liquid crystal on the line to a scattering state, and an initialization means for initializing each liquid crystal on the line for writing display data, which has already been initialized by the initialization means, according to the display gradation. It is configured to have a write and hold means for applying a drive voltage of a certain level to perform writing and then holding the data.

[Industrial application field]

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that drives a phase change type liquid crystal panel.

A phase change type liquid crystal display device performs display in two states: a cholesteric phase, which is a light scattering state, and a nematic phase, which is a light transmitting state. The driving method is different from the refresh driving method that uses cumulative response such as twisted nematic liquid crystal, in which all cells in the screen are initialized at the same time, and then writing is performed line-sequentially, and writing is performed by selective scanning for l frames. Complete. Thereafter, by applying a sustain voltage to all cells, the two display states are maintained and display is performed. Therefore, phase change type liquid crystal display devices are capable of large-capacity display without decreasing contrast even when the number of display lines increases, and because they utilize light scattering, they can display images without a polarizing plate, unlike other liquid crystals. It has the characteristic of being visible.

For this reason, liquid crystal display devices such as dot matrix liquid crystal displays (LCDs) using this phase change type liquid crystal have been put into practical use as projection type LCDs because the light utilization rate of the light source is extremely high and bright display is possible. There is.

In such a phase change type liquid crystal display device, since it takes a long time to write one screen, it is difficult to display a moving image, and therefore a moving image display is desired.

[Conventional technology]

FIG. 6 shows a configuration diagram of an example of a conventional liquid crystal display device. In the figure, 1 is a simple matrix liquid crystal panel, and phase change type liquid crystal cells are arranged and displayed in a matrix (Y1 to Yfil in the horizontal direction and X, to X in the vertical direction). In addition, 2 is a scan driver, and 3 is a data driver, which are used in the horizontal direction (
drive each liquid crystal cell in the line direction) and vertical direction. A control circuit 4 controls the scan driver 2 and data driver 3, respectively, and causes the liquid crystal panel I to display a desired image.

Next, the operation of the plurality of phase change type liquid crystal cells constituting this liquid crystal panel 1 will be explained. First, initialization is performed. That is, this initialization is performed by repeatedly applying a pulse with a period of, for example, 4 ms at a peak value of 2 Vd (where Vd is the center voltage of hysteresis) in 10 cycles as shown in FIG. The transparent state is shown as H in Fig. 8.

Next, a write operation is performed. For this writing, OV is applied to the cell in which black is to be written, and F is shown in FIG. The cell is brought into a cloudy state as shown in FIG. 2, and a pulse with a peak value of 2 Vd is applied to the cell where white is to be written to maintain the previous transparent state. This is repeated for all scan lines to complete writing. The writing time is determined by the phase transition time (H-F,) of the liquid crystal. After selection, a non-selection voltage of <Vd is applied to the liquid crystal cell as shown in FIG. 7, so the cloudy cell transitions to the state shown by F in FIG. The state has transitioned to the state indicated by H'' in the figure.

Next, memory driving is performed. As shown in FIG. 7, this is done by applying Vd to all cells from the scan driver 2,
Keep visible.

In this manner, in the conventional liquid crystal display device, as shown in FIG. 9, the states of initialization a, writing, and memory drive C are repeated to display one screen.

[Problem to be solved by the invention]

However, in the above-mentioned conventional liquid crystal display device, a writing time of several ms per line is required, so the writing time is 40 ms.
When attempting to display a screen with approximately 0 lines, it takes more than one second, making it impossible to display fast-moving moving images. Furthermore, since the conventional device performs memory drive using hysteresis characteristics, it is not possible to display halftones.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device capable of displaying moving images and halftones.

[Means to solve the problem]

FIG. 1 shows a basic configuration diagram of the present invention. In the figure, reference numeral 11 denotes a liquid crystal display panel in which a plurality of phase change liquid crystals are regularly arranged as pixel cells. Reference numeral 12 denotes an initializing means which initializes each liquid crystal on a line preceding the writing line by a time equal to or longer than the response time for the liquid crystal to change from a transparent state to a scattering state to a scattering state. Reference numeral I3 denotes a write and hold means which applies a drive voltage at a level corresponding to the display gradation to each liquid crystal in the write line of display data that has already been initialized, performs writing, and then holds the data.

[Effect]

Phase change type liquid crystals generally have voltage-transmittance characteristics or hysteresis characteristics, and as shown by ■ in Figure 2, when the applied voltage (cell voltage) is increased from v0 to bring about the light scattering state. The change in transmittance is a cumulative response and requires a response time of several tens of milliseconds to several tens of milliseconds. On the other hand, 2Vd
etc., when the voltage is lowered from the applied voltage (cell voltage) that makes the phase change liquid crystal sufficiently transparent, and it reaches Vo, which makes the liquid crystal a scattering state, the transmittance is instantaneous as shown by ■ in Figure 2. It is a value response and changes in an extremely short response time of several ms.

The present invention focuses on the hysteresis characteristic of the voltage-transmittance characteristic, and the initializing means I2 sets the liquid crystal in a scattering state by the number of scanning lines corresponding to the instantaneous value response time, prior to the display data writing line. That is, the initialization to black is performed by moving one line at a time, and the display data is sequentially written by the holding means 13 from the line that has been sufficiently initialized using the characteristics based on the cumulative response, and then held.

Therefore, in the present invention, display data can be written line by line, and the written display data can be data at any position in the voltage-transmittance characteristic.

〔Example〕

FIG. 3 shows a configuration diagram of an embodiment of the present invention. In the same figure, 2
Reference numeral 1 denotes an active matrix liquid crystal panel (corresponding to the liquid crystal display panel 11 in FIG. 1), in which phase change type liquid crystals are arranged in a matrix as pixel cells, n pieces in the vertical direction and m pieces in the horizontal direction; Each of the above phase change liquid crystals (pixel cells) is a thin film transistor (TFT: Th1n Film) as a switching transistor.
Transistor) 23 source. In FIG. 3, 22j indicates a pixel cell in the 1st row and 1st column among the plurality of pixel cells arranged in the matrix, and 23''l indicates the TPT 23 connected to this pixel cell 23jA.

The control signal generating circuit 24 generates a vertical synchronizing signal Vs and a vertical synchronizing signal Vs as shown in FIG.
A horizontal synchronizing signal Hs shown in A) is input, and a control signal Cdi as shown in FIG. 4B is generated in synchronization with these signals. This control signal Cdi is generated during one horizontal scanning period r/! IPjI
The high level period is a display data period, and the low level period is an initialization data period.

The data driver 25 is a circuit that applies display data or initialization voltage to the active matrix liquid crystal panel 21, and has m switches 25" (2511 in FIG. indicates the first switch 251), and m output amplifiers 25
2 (2521 in FIG. 3 indicates the first output amplifier 252). The output terminals of the m output amplifiers 252 are connected to the T terminals of m columns of phase change liquid crystal groups (pixel cell groups) of the active matrix liquid crystal panel 21 via data lines such as Dl.
Connected to the drain of PT. m switches 25
1 is the voltage Vi required for initialization and the display data voltage V
One of da is selected and output.

The scan driver 26 includes registers Ri and Rs, and a switch 261 that selects the output of one of the registers R1 and Rs.
．． -261n and output amplifiers 262, -262, which amplify and output the outputs of switches 2611-261,
, and a control terminal IS. The initialization line selection signal Hi from the control signal generation circuit 24 is written into the register Ri and is shifted every l horizontal scanning period, and the display line selection signal Hi from the control signal generation circuit 24 is written into the register Rs. and shifted every horizontal scanning period.

Switch 261. ~26]. is switched in accordance with the control signal Cdi input to the control terminal Is, and the register Ri
One of the initialization line selection signal from the register Rs and the display line selection signal from the register Rs is selected.

In addition, the output amplifier 262. 262o are connected to the gates of the TFTs 23 in rows 1 to n of the active matrix liquid crystal panel 21 via signal lines 81 to S0. The data driver 25 and the scan driver 26 are connected to the initialization means 12 and the write and hold means 1.
3.

Next, the operation of this embodiment will be explained using the pixel cell 22jl of the 3rd row and 1st column of the active matrix liquid crystal panel 21 as an example. The data driver 25 has an input control signal Cdi.
During the high level period, the display data voltage Vda is output, and C
During the low level period of di, the initialization voltage Vi is connected to the data line DI.
Output to. FIG. 4(C) shows the voltages sent to the data line DI, where the initialization voltage Vi is a constant low voltage that causes the pixel cell 22jl to be in a scattering state, while the display data voltage Vda is a constant value that changes the display gradation. It is a voltage whose level changes accordingly.

The scan driver 26 outputs a signal (shown in FIG. 4(D)) that makes the line Sj active during the display data period of the line Sj, and turns on the TPT 23jA. As a result, during the ON period of the TPT23jl, the display data voltage Vda input via the data line D7 is
It is applied to the pixel cell 22j1 through the drain and source of 1.

Thereby, the pixel cell 22jj7 performs gradation display according to the voltage Vda.

In the initialization data period following the display data period of line Sj in which TFT 23j is turned on, the scan driver 26
outputs a signal (shown in FIG. 4 (G)) that activates the line Sk, turns on each TPT on this line Sk, and applies the initialization voltage Vi to the pixel cell through the drain and source of the turned-on TPT. is applied to perform initialization to write black into those pixel cells. Note that, compared to line Sj, line Sk is a scanning line of the spectrum corresponding to the instantaneous value response time. Furthermore, after this initialization data period, until the next initialization of line Sj, the TFT 23jf
fi is turned off, so that the charge charged by the voltage Vda is held in the pixel cell 22jl. In the next horizontal scanning period, the scan driver 26 outputs a signal (fourth
After outputting the signal (shown in Figure 4(E)), the signal that activates the line Sk++ in the latter half of the initialization data period (shown in Figure 4(E)) is output.
Furthermore, in the display data period in the first half of the next horizontal scanning period, a signal (shown in FIG. 4F) for activating line SJ+2 is output. In addition, the fourth
In the figure, in order to simplify the explanation, only the case where the voltage applied to the cell has one voltage polarity is explained. Thereafter, the same operation as above is repeated, display data is sequentially written line by line, and the pixel cells of the preceding line are also initialized line by line.

To explain the operation of the above-mentioned embodiment together with the display mode, for example, assuming that there are n display lines as shown in FIGS. During the data period, the first line (here, j=1) is written as shown in FIG. 5(A). At this point, lines from the second line to the (k-1)th line are already displayed in black due to initialization. Note that from the th line to the nth line
Display data from one frame before is displayed on the line.

Then - the fifth data period in the second half of the horizontal scanning period.
As shown in Figure (B), the line is first initialized,
First, each pixel cell of the line is all in a scattered state and displayed as black.

In the display data period in the first half of the next horizontal scanning period, the fifth
As shown in Figure (C), display data is written into each pixel cell of the second line that has already been initialized.

Thereafter, the same operation as above is repeated.

Here, H8 and V are not necessarily limited to the cycles of current televisions.

According to this embodiment, since the display data is rewritten one after another line by line, a moving image can be displayed. Further, since a voltage at any level of the cumulative response can be applied as display data, it is possible to display halftones.

〔Effect of the invention〕

As described above, according to the present invention, display data can be written line by line, and the written display data can be data at any position in the voltage-transmittance characteristic of the liquid crystal, so Features include the ability to display moving images and halftones without sacrificing the advantage of bright display without the need for a polarizing plate, which is a characteristic of transition type liquid crystals, which greatly contributes to improving display quality. It has the following.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle configuration of the present invention, Fig. 2 is an explanatory diagram of the operation of the present invention, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a signal waveform diagram for explaining the operation of Fig. 3. , Figure 5 is the third
Figure 6 is a configuration diagram of a conventional example; Figure 7 is a time chart for explaining the operation of Figure 6; Figure 8 is a drive principle diagram of the conventional device; Figure 9 is a diagram of the conventional device. It is a drive procedure explanatory diagram. In the figure, 11 is a liquid crystal display panel, 12 is an initialization means, 13 is a writing and holding means, 21 is an active matrix liquid crystal panel, 24 is a control signal generation circuit, 25 is a data driver, and 26 is a scan driver. Figure 11 shows the principle structure of the present invention Figure 2 (A) illustrates the action of the present invention! Writing of the line Figure 3: Explanation of display operation Figure 5: Configuration diagram of a conventional example Figure 6

Claims (3)

[Claims] (1) In a liquid crystal display device that performs display using a liquid crystal display panel (11) in which a plurality of phase change liquid crystals are regularly arranged as pixel cells, a writing line for display data among the plurality of phase change liquid crystals is provided. initializing means (12) for initializing each liquid crystal on a line preceding the line by a time equal to or longer than the response time for the liquid crystal to change from a transparent state to a scattering state to a scattering state; writing and holding means (13) for applying a drive voltage at a level corresponding to the display gradation to each liquid crystal in the writing line of the display data that has already been initialized by (12) to perform writing and then holding the liquid crystal; A liquid crystal display device comprising: (2) The liquid crystal display panel (11) has a plurality of switching transistors (23) connected to each of the plurality of phase change liquid crystals in a one-to-one correspondence, and the initialization means (12) is an initialization voltage that is turned on for a first predetermined period within one horizontal scanning period for the switching transistors (23) connected to each liquid crystal on the line to be initialized among the plurality of switching transistors (23). is applied to each liquid crystal on the line to be initialized through the turned-on switching transistor, and the writing and holding means (13) is a means for applying the voltage to each liquid crystal on the line to be initialized through the turned-on switching transistor, and the writing and holding means (13) is a means for applying The switching transistors connected to each liquid crystal on the write line are turned on only for a second predetermined period within one horizontal scanning period and then turned off, and the display data is transferred onto the write line through the switching transistors that have been turned on. 2. The liquid crystal display device according to claim 1, further comprising means for applying a driving voltage to each liquid crystal. (3) The initialization voltage applied to the plurality of switching transistors (23) and the display data are synthesized in time series for each of the first and second predetermined periods within one horizontal scanning period. The liquid crystal display device according to claim 2, characterized in that: