JPH0423243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a matrix type liquid crystal display device using a nematic-cholesteric phase transition type liquid crystal.

[Prior Art] A phase change liquid crystal is known as a display element suitable for large-capacity displays such as computer terminal displays. As shown in Fig. 5, as the applied voltage increases, the voltage response characteristic transitions from the grunge-uan state G, which has relatively high transmittance, to the cloudy focal conic state F, and exceeds the memory voltage V _n . The transmittance increases again, and when the saturation voltage V _H is exceeded, the transparent homeotropic state H is reached.

On the other hand, when the applied voltage is lowered, the homeotropic state H _n is maintained until near the memory voltage V _n , and after the memory voltage V _n is exceeded, the focal conic state F _p appears again.

Further, if the applied voltage is suddenly reduced to 0 from the H _n state, the state does not change to F _p but changes to the G state.

When displaying using this H _n state and F state,
The transition from the H _n state to the F state takes about 10 ms, and the transition from the F state to the H _n state via the H state takes about 200 ms, with the former having a much faster response speed. Therefore, in the conventional driving method, first, a voltage higher than the saturation voltage V _H (usually 2V _n ) is applied to the entire screen to bring the entire screen into the H state, and then a signal as shown in Fig. 6 is used to reduce the voltage to 0, H _n The display was performed by transitioning the state to the F state.

[Problems to be Solved by the Invention] In the above driving method, each time the screen is rewritten, it is necessary to bring the entire screen into the H state. It had the drawback of being stored away.

Moreover, when data is typed in at high speed, such as in a word processor, if the number of lines on the entire screen is large, the maximum amount of time it will take from when new data is typed in until the display is rewritten.
Time for one period of time division (for scanning one line)
Even if 10 ms is required, it may take several seconds to scan the entire line, which is not desirable.

To solve this problem, apply a high voltage (2V _n ) only to the display area you want to rewrite to bring this area into the H state, then reduce it to 0V to transition to the F state, and keep the other areas in the memory at all times. A method of applying a voltage V _n has been proposed. However, according to this method, even if the memory voltage V _n is applied,
After 20 to 30 seconds have elapsed, a transition from the H _n state to the F state occurs, causing problems such as a decrease in contrast.

Due to the above-mentioned problems and the fact that no decisive driving method has been established, it has not been possible to put it into practical use until now.

The present invention provides a driving method for a matrix type liquid crystal display device in which the entire screen does not disappear when the display is rewritten, the display can be rewritten immediately, the number of driving digits can be increased, and the contrast does not deteriorate even after a long period of time. It is for providing.

[Means for Solving the Problems] The present invention provides a method for driving a matrix liquid crystal display device comprising a nematic-cholesteric phase transition type liquid crystal, in which the display state of each pixel is sequentially rewritten when the display does not need to be rewritten. However, when rewriting the display state of pixels in a part of the area, the above objective is achieved by interrupting the rewriting and rewriting the pixels in the part of the area.

Further, when rewriting the partial area, the rewriting time can be further reduced by initializing the pixels of the partial area in parallel with the rewriting.

[Example] In FIG. 1, the scanning circuit SE receives the output from the rewriting area specifying circuit A, and supplies the initialization signal RS ₁ consisting of the voltage 2V _n in FIG. 2 to the first area to be rewritten. After that, a scanning signal S ₁ consisting of a memory voltage V _n is supplied, and thereafter a signal consisting of a voltage 0 is supplied.
Supply NS ₁ . Further, to the second area where rewriting is not performed, the scanning signal S ₂ having a voltage of 2V _n shown in FIG. 3 is supplied, and then the signal NS ₂ having a voltage of 0 is supplied to perform rewriting. This rewriting operation for the first area is performed by interrupting the rewriting operation for the second area.

On the other hand, a data signal V _F or a data signal V _H is selectively generated from the drive control circuit DR to the selected electrode.
It is supplied to R ₁ to R _o .

Next, the operation will be explained. First, a case where there is no area to be rewritten and rewriting is performed over the entire area will be described. In this case, since no output is generated from the rewriting area specifying circuit A, the scanning signal _S2 shown in _{FIG .} Ru.
When the scanning signal S ₂ is not supplied, the signal NS ₂ is supplied. By supplying the scanning signal _S2 , a voltage is applied to the pixel.
A pulse P ₆ consisting of a voltage of V _n or a pulse P ₇ consisting of a voltage of 3 V _n is applied. That is, the pixel in the H _n state is rewritten to the H _n state by applying pulse P ₇ , and
A pulse _P6 is applied to the pixels in the F state to maintain the F state. When the signal NS ₂ is supplied, a pulse P ₈ or P ₉ is applied to maintain the state of the pixel.

Next, the operation when rewriting a specific area will be explained. For example, a case will be described in which the pixels in rows L _i-1 to _{L i+1} in FIG. 1 are rewritten, and the other pixels are not rewritten. In this case, from rewrite area designation circuit A
An instruction signal is generated that designates the lines L _i-1 to _{L i+1} as the first area, and the initialization signal RS ₁ in FIG. 2 is supplied to these three lines at the first timing, and then the L _i The scanning signal S ₁ is sequentially supplied from _{the −1} row to the L _i+1 row, and the signal NS ₁ is supplied at other times. Also the second
At the timing shown in FIG. 3, the scanning signals shown in FIG. 3 are sequentially supplied starting from the _L1 row. The first timing and the second timing appear alternately. That is, at the first timing, the initialization signal RS ₁ is supplied from the L _i-1 row to the L _i+1 row, and then the scanning signal S ₁ is sequentially supplied from the L _i-1 row to the L _i+1 row. When these three rows are rewritten, the scanning signal S ₂ of FIG. 3 is sequentially supplied from row _L1 at the next second timing, and rewriting is performed up to a predetermined row L _o (not shown).

In this way, each row of the first region and each row of the second region are alternately selected and driven. Therefore, while rewriting scanning is performed at short intervals, rewriting scanning of the second area is performed at several timings, and the entire screen does not disappear, and rewriting is performed quickly.

Note that the rewriting scan may be performed only on the second area excluding the first area, or may be performed on the entire area including the first area.

Here, the rewriting operation of the first area will be explained in more detail. First, when the initialization signal RS ₁ shown in FIG. 2 is supplied, a pulse P ₁ consisting of a voltage V _n or a pulse P ₂ consisting of a voltage 3V _n is applied. Since the liquid crystal changes to the H state by the pulse _P2 and initialization is performed, the data signal _VH is supplied only to the pixels to be rewritten. However, the application time of the initialization signal is determined by the voltage required to transition from the F state to the H _n state, and is approximately inversely proportional to the square of the effective voltage value. For example, if the effective voltage value is
If 200ms is required when the voltage is 2V _n , approximately 100ms is required when the effective voltage value is 3V _n .

Next, depending on the scanning signal _S1 , the voltage is 0 or the voltage is
A pulse P ₃ of 2V _n is applied. When a voltage of 0 is applied, the liquid crystal is brought into the F state by the subsequent pulse P ₄ or P ₅ , and the liquid crystal is maintained in the H state by the application of the pulse P ₃ . i.e. data signal
Pixels supplied with V _F transition to the F state, while pixels supplied with the data signal V _H are held in the H state and rewritten.

Note that the application time of the scanning signal is determined by the application time of 0 V necessary for transitioning from the H _n state to the F state, and is approximately 10 ms or less.

Further, the rewriting scan does not need to have the same period as the rewriting scan, and it is sufficient that the H _n state can be maintained with the pulse _P7 , and the period may be about twice that of the rewriting scan.

Next, an example will be described in which the rewrite time is further shortened by initializing the area to be rewritten during the rewrite operation. In this case, the initialization signal RS ₂ shown in FIG. 4 is used instead of the initialization signal RS ₁ shown in FIG. 2. A pulse P ₁₀ or P ₁₁ is applied to the pixels in the row to which this initialization signal P ₂ has been supplied, and each pixel is temporarily changed to the H state to perform initialization. This initialization signal RS ₂ is supplied at a timing when the second rewrite operation is being performed. Then, the rewriting is performed by supplying the scanning signal S ₁ and the signal NS ₁ alternately with the rewriting operation. That is, among the pixels that have been initialized to the H state, the data signal VF is supplied to the pixel that is desired to be put into the F state, the applied voltage is set to 0, and the pixel is caused to transition to the F state. Note that the scanning signal for rewriting in this example is the same as in the example of FIG. 3, and is performed in the same manner.

Note that the present invention is not limited to scattering mode liquid crystals;
It can be similarly applied to a guest-host type to which a chromatic dye is added or a type in which display is performed using depolarization caused by scattering between crossed nicols.

[Effects of the Invention] According to the present invention, the rewriting operation of the area to be rewritten is performed by interrupting the rewriting operation of each pixel, which eliminates the drawback that the entire screen disappears during rewriting, and a new The time from when data is input until it is rewritten is shortened, and an easy-to-read display can be achieved. Furthermore, since rewriting is performed sequentially in areas other than the area to be rewritten, the contrast does not deteriorate even after a long period of time.

Furthermore, by initializing the area to be rewritten while rewriting, the rewriting time can be further shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the display device of the present invention, FIGS. 2 and 3 are waveform diagrams showing signal waveforms supplied to the electrodes and pulse waveforms applied to the liquid crystal according to the present invention, and FIG. The figure is a waveform diagram showing another example of the signal waveform supplied to the electrodes, Figure 5 is a characteristic diagram showing the characteristics of a phase change type liquid crystal, and Figure 6 is a waveform diagram showing an example of a conventional drive waveform. be. SE...scanning circuit, L ₁ ~L _n ...scanning electrode, DR
... Drive control circuit, R ₁ ~ R _o ... Selection electrode, A...
...Rewriting area designation circuit, RS ₁ , RS ₂ ... Initialization signal, S ₁ ... Scanning signal, V _F , V _H ... Data signal,
S ₂ ...Scanning signal.

Claims (1)

[Claims] 1. A nematic-cholesteric phase transition type liquid crystal is interposed between a plurality of scanning electrodes and a plurality of selection electrodes, and a plurality of pixels are formed at the intersections of each scanning electrode and each selection electrode, A scanning signal is sequentially supplied to the scanning electrodes, and a data signal is selectively supplied to the selected electrode in synchronization with this scanning signal, and each pixel is set in a desired display state based on this data signal. In a method of driving a matrix liquid crystal display device in which a memory voltage is applied to each pixel to maintain its display state, when rewriting the display is not necessary, a scanning signal is sequentially supplied to each of the scanning electrodes, and a data signal is supplied to the selected electrode. is supplied to rewrite the display state, and upon the arrival of an instruction signal to rewrite the display state of pixels in a part of the area, the rewriting is interrupted,
Rewriting is performed by sequentially supplying scanning signals to the scanning electrodes of the partial area and data signals to the selected electrodes, and after the rewriting of the partial area is completed, the rewriting is resumed. A method for driving a matrix type liquid crystal display device. 2 A nematic-cholesteric phase transition type liquid crystal is interposed between a plurality of scanning electrodes and a plurality of selection electrodes, and a plurality of pixels are formed at the intersections of each scanning electrode and each selection electrode, and scanning signals are sequentially applied to the scanning electrodes. At the same time, a data signal is selectively supplied to the selected electrode in synchronization with this scanning signal, and each pixel is set to a desired display state based on this data signal, and a memory voltage is applied to each pixel when the scanning signal is not supplied. In a method for driving a matrix type liquid crystal display device in which the display state is maintained by applying voltage, when the display does not need to be rewritten, a scanning signal is sequentially supplied to each of the scanning electrodes, and a data signal is supplied to the selected electrode to change the display state. In parallel with the above rewriting, due to the arrival of an instruction signal to rewrite the display state of pixels in some areas,
An initialization signal is supplied to the scanning electrodes in the partial area to bring it into a homeotropic state, and then the rewriting is interrupted, and a scanning signal is sequentially supplied to the scanning electrodes of the pixels in the partial area, and the pixel is selected. A method for driving a matrix type liquid crystal display device, comprising performing rewriting by supplying a data signal to an electrode, and restarting the rewriting after the rewriting of the partial area is completed.