JPS61138991A - Driving of phase shift type liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a display device composed of a cholesteric-nematic phase change type liquid crystal, which has a display memory function and is called a storage type liquid crystal.

[Conventional technology]

FIG. 7 is a flow chart for explaining the process of displaying using a phase change type liquid crystal.

As is clear from the figure, (11 initialization (2) Writing (3) Memory display This is done in the following order.

FIG. 8 is a diagram illustrating the relationship between the light transmittance of the liquid crystal cell and the voltage applied to the liquid crystal cell when performing the above display.

In the figure, the vertical axis represents transmittance, and the horizontal axis represents cell applied voltage.

First, when initializing, a voltage of 2Vo is applied to all cells to make them all transparent (H).

Next, when writing is to be performed, a voltage of 0 is applied to the cell to be clouded, that is, a cell to be written, and a voltage of 2■ is applied to the cell to be kept transparent. are applied respectively.

Next, when performing memory display, a memory voltage vo is applied to all cells.

In Figure 8, black circles (・) indicate transparent cells, and white circles (0)
represent cloudy cells.

Note that the relationship between ・ and ○ is the same in the following descriptions.

FIG. 9 is a diagram illustrating the main parts of four cells extracted from a liquid crystal panel in which cells are arranged in a matrix.

In the figure, Yl and Y2 indicate row lines (represented by Y), and XI and X2 indicate column lines (represented by X), respectively.

FIG. 10 is a timing chart of pulses applied to each cell when displaying as shown in FIG. 9.

Here again, the flow of (1) initialization, (2) writing, and (3) memory display remains unchanged, and the relationship between the voltages applied to each cell is also as described above. In FIG. 10, cells related to column line XI and row line Y, and cells related to column line X2 and row line Y1 are displayed as representing transparent and cloudy operations, respectively.

As is clear from the figure, during writing, after initialization, a voltage of 2V is applied to cells related to column line x1 and row line Y1 when selectively scanning row line Y. After that, voltage v0 is applied to shift to memory display, and column line Xz and row line Y
Once voltage 0 is applied to the cell related to 1, the cell becomes cloudy, and then voltage 2 is applied. It can be recognized that is applied and the display shifts to memory display.

[Problem that the invention seeks to solve]

For writing on the liquid crystal described above, - number of seconds per line [m seconds]
It takes about several tens of milliseconds, for example, 450 [pieces]
On an LCD panel with several scanning lines, it takes a long time, ranging from one second to several seconds, to rewrite one screen, and even when rewriting a part of the displayed screen, , requires a full screen rewrite.

Therefore, when it becomes necessary to rewrite a part of the displayed screen, if the entire screen is rewritten by following steps (11 to (3)), for example, in the case of keyboard input, the input will not be followed at all. The problem arises that it cannot be done.

In the present invention, when a part of the display screen of a phase change liquid crystal panel is rewritten, only the rows of the part that require rewriting are rewritten, thereby realizing high-speed and high-quality display.

[Means for solving problems]

In the method for driving a phase change type liquid crystal display device according to the present invention, when rewriting a display based on a phase change type liquid crystal, rewriting is performed line by line by selectively scanning only the lines that require rewriting. That's what I do.

[Effect]

In this way, it becomes possible to rewrite much faster than in the past.

〔Example〕

As a first example, in a phase change type liquid crystal panel consisting of 4x4 matrix cells shown in Fig. 1, the display in the area surrounded by the broken line is rewritten to the display shown in Fig. 2. Let us explain this with reference to the timing chart shown in FIG.

In FIGS. 1, 2, and 3, the same parts as those explained with respect to FIGS. 7 to 10 are indicated by the same symbols, and Y3 and Y4 are row lines, It goes without saying that Xff and X4 are column lines.

In this case as well, as in the conventional example described above, all cells are now at a voltage of 1 after going through the steps of (1) initialization = (2) writing - (3) memory display. is applied and static display is performed.

Next, in order to rewrite, (4) partial writing - (5)
The memory display process will be performed, but since the cells to be rewritten are on the row lines Y1 and Y2, selective scanning is performed only on these two scanning lines.
Predetermined signals are applied to all data lines such as column lines X1 and X2, and all cells on row lines Y and Y2 are written to the state shown in FIG.

At this time, since the cells on rows Y and Y4 are not rewritten, the voltage V0 continues to be applied as in the (3) memory display stage.

Figure 4 is a circuit diagram of the main part of the drive circuit used to actually output the voltage waveform shown in Figure 3, and Figure 5 shows the output voltage of each drive element in the drive circuit shown in Figure 4. Each represents a waveform diagram. In addition, in order to output the voltage waveform seen in Fig. 3, CMO3 (complementary
y metaloxide semiconductor
However, since the driving voltage of phase change liquid crystals is generally high, it is preferable to use a high voltage IC driver with on/off binary output. Here, also, an example using this configuration is shown.

In FIG. 4, 1 and 2 are the X-side IC driver which also includes a built-in circuit such as a shift register, and YO1! II
c driver, X I-X ) is an X-side electrode, Y1 to Y are Y-side electrodes, C0 to C are liquid crystal cells, The output voltage value is 2■. The high-voltage power supply of the X-side IC driver, vsl, has an output voltage value of ■. The power supply of the Y-side IC driver, . . . represents a reference voltage resistor whose output voltage value is vo and serves as the reference potential of the Y4iAIG driver. Note that IC drivers include shift registers, latch circuits,
It is assumed that the circuit is an integrated circuit including a high-voltage switching circuit and the like.

In Fig. 5, the waveform represented by the black part on the Y side is the voltage value output by the reference voltage pulser v5□, and a voltage whose value is Vo is periodically output, and the first On either side of the cycle, the power supply of the Y side IC driver ■Value from 1■
. By superimposing the voltages, a waveform identical to that seen in FIG. 3 can be obtained.

For example, in the selection period T+ of the electrode Y in the partial write section in FIG.
The output of driver 2 is on for electrode YI, therefore 2
■. Then, the output of the Y-side IC driver 2 is turned off for the electrode Yl, so it is set to O, and in the second half period Tlt, the output of the Y-side IC driver 2 is turned off for the electrode Yl, so it is set to O, and the output is set to O for the electrode Yz. is on, so it becomes vo. Furthermore, on the X side, depending on the display data, if electrode X is turned on in the first half period and turned off in the second half period, and vice versa for electrode
A voltage O and a voltage 2vo are applied to the liquid crystal cell C+Z associated with the electrode Y1 and the liquid crystal cell C+Z, respectively, so that the liquid crystal cell C+Z becomes cloudy and transparent. At this time, the voltage ■ is applied to the liquid crystal cell associated with the electrodes Y2 to Y4. Since only the current is applied, each liquid crystal cell continues to maintain its previous display. After this, the same operation as above is performed on the electrode Y2.
If this is also done for the electrodes Y and Y2, partial writing will be completed only for the liquid crystal cells related to the electrodes Y and Y2.

Note that when performing partial writing, it is sufficient to simply apply new display data to the X-side electrode, regardless of the previous display state, and the control circuit monitors which row (Y-side electrode) to perform partial writing. A waveform for partial writing can be obtained by applying a method such as leaving the Y-side data set in accordance with the Y-side data.

In the above embodiment, (4) selective scanning for partial writing is performed once for row lines Y and yz, but
If this is insufficient, it is preferable to repeat the selection scan a plurality of times, that is, Y+, Yz, Y+, Y2, . . .

FIG. 6 is a timing chart for explaining a second embodiment of the present invention in which the selective scanning is repeated.

The difference between this example and the previously described example is (4
) Writing is repeatedly performed at the partial writing stage.

In this embodiment, even if it takes a long time to write a scan line, that is, a row line, by appropriately increasing the number of selected scans, an effect similar to that obtained by applying a substantially wide pulse can be obtained. Therefore, it is possible to perform a good rewriting operation.

In any of the above embodiments, when rewriting, the address operation is only visible in a limited area of the screen, and unlike conventional methods, there is no phenomenon such as a white line running across the entire screen. does not appear, and the display quality is good.

In each of the embodiments described above, the waveform of the voltage applied to each cell is not limited to the illustrated example; for example, the voltage level is O, VO, or 2V. This is a combination of =■. ,0. ■. You may also change the order of the voltages to be applied when performing AC drive to (0,
■. ) instead of (V,,O).

〔Effect of the invention〕

In the method for driving a phase change type liquid crystal display device according to the present invention,
When rewriting the display, only the lines that need to be rewritten are selectively scanned and rewritten line by line.

Therefore, even when rewriting a part of the display, compared to the conventional driving method in which the entire screen is rewritten, it is possible to perform extremely high-speed rewriting, and the display quality at the time of rewriting is also good.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the main parts of the liquid crystal panel, Figure 3 is a timing chart of the voltage waveforms that drive the liquid crystal panel seen in Figures 1 and 2, and Figure 4 is the same as Figure 3. Figure 5 is a circuit diagram of the main part of the drive circuit for obtaining the voltage waveform shown in Figure 4. Figure 6 is a diagram of the output voltage waveform of each drive element in the drive circuit shown in Figure 4. Timing chart of the voltage waveform that drives the liquid crystal panel shown in Figure 7.
The figure is a flow chart of the process of displaying using a liquid crystal.
Figure 8 is a diagram showing the relationship between liquid crystal transmittance and cell applied voltage, Figure 9 is an explanatory diagram of the main parts of the liquid crystal panel, and Figure 10 is the timing of the voltage waveform that drives the liquid crystal panel seen in Figure 9.・Represents each chart. In the figure, x, , x, , x3. x, is column line, Y+
, Yz, Ys, Ya are row lines, l and 2 are X-side IC drivers with built-in shift registers, etc., and Y
(Ij IC driver, X1 to X are X side electrodes, Y, -Y
, are Y-side electrodes, CI I to Cij are liquid crystal cells, and VD is an output voltage value of 2■. The high voltage power supply of the X side IC driver is
vsl indicates the power supply of the Y (jlJIc driver) whose output voltage value is vo, and ■3□ indicates a reference voltage pulser whose output voltage value is vo and serves as the reference potential of the Y-side IC driver.

Claims (1)

[Claims] A method for driving a phase change type liquid crystal display device, characterized in that when rewriting a display based on a phase change type liquid crystal, rewriting is performed line by line by selectively scanning only the lines that require rewriting.