JPH0423244B2 - - 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 change type liquid crystal.

[Prior Art] For example, 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. 4, as the applied voltage increases, the voltage response characteristic transitions from the grunge-uan state G, which has a 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, when the applied voltage is suddenly reduced to 0 from the H _n state, the state does not change to the F _p state, 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 2 V _n ) is applied to the entire screen to bring the entire screen into the H state, and then a signal as shown in Figure 5 is applied to the voltage O, 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 disadvantage 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 of 2V _n only to the display area you want to rewrite to bring this area into the H state, then change it to 0V to transition to the F state, and keep the other areas at the memory voltage V. A method of applying _n has been proposed. However, according to this method, even if the memory voltage V _n is applied,
After 30 seconds, a transition occurs from the H _n state to the F state, 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. This is what we provide.

[Means for Solving the Problem] The present invention sequentially supplies a display initialization signal and a subsequent selection signal to each scanning electrode, and when the initialization signal and selection signal are not supplied, a non-selection signal is supplied. On the other hand, by supplying a data signal specifying the display state of each pixel to the selection electrode, the pixel is initialized to a homeotropic state, and then that state is maintained or transitioned to a focal conic state. After that, it maintains a focalonic or homeotropic state.
The above problem is solved by applying an alternating current pulse consisting of a positive polarity pulse and a negative polarity pulse having the same waveform to the liquid crystal.

[Example] In FIGS. 1 and 2, a selection signal S consisting of an initialization signal RS of a voltage V (V≧V _H ) and subsequent memory voltages V _n and -V _n is output from the scanning circuit SE. is generated and sequentially supplied to scanning electrodes L ₁ to _{L n} . When the initialization signal RS and selection signal S are not supplied, a non-selection signal NS of voltage O is supplied.

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

By supplying the above signals, the following pulses are applied to the liquid crystal. First, the first AC pulse P ₁ or P ₂ is applied according to the initialization signal RS to initialize it to the H _n state. However, the application time of the initialization signal is determined by the voltage and number of times required to transition from the F state to H _n , and is approximately inversely proportional to the square of the effective voltage value. For example, if 200 ms is required when the voltage effective value is 2V _n , 50 ms is required when the voltage effective value is 4V _n .

Next, depending on the selection signal S, the voltage O or the voltage
A second AC pulse P ₃ of 2V _n is applied. Voltage O
By applying , the liquid crystal enters the F state, and the pulse P ₃
By applying , the liquid crystal is maintained in the H _n state. In other words, the pixel to which the data signal V _F is supplied is F
Pixels that have transitioned to the H n state and are supplied with the data signal V _H are held in the H _n state.

Then, by supplying the non-selection signal NS, a third alternating current pulse P ₄ or P ₅ consisting of the memory voltage V _n is generated.
is applied. This maintains the display state of the liquid crystal.

Note that the selection signal application time is determined by the OV application time required to transition from the H _n state to the F state, and is approximately 10 ms or less.

The above-mentioned first, second and third alternating current pulses all consist of a positive polarity pulse and a negative polarity pulse having the same waveform.

FIG. 3A shows a pulse waveform applied to the liquid crystal to be brought into the F state. That is, after initialization is performed by applying the pulse _P1 or _P2 according to the initialization signal RS, the applied voltage becomes 0, and then the state is changed to the F state by the subsequent pulse _P4 or _P5 . , the state is maintained.

FIG. 3B shows a pulse waveform applied to the liquid crystal to be brought into the H _n state. In this case as well, after initialization is performed by applying pulse P ₁ or P ₂ according to the initialization signal RS, pulse P ₃ is applied to maintain the H _n state, and then pulse P ₄ or P ₅ maintains that state.

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

[Effects of the Invention] According to the present invention, since the initialization signal and the selection signal are sequentially supplied to each scanning electrode to sequentially perform initialization and display writing, the entire screen is not covered when rewriting the display as in the conventional case. It does not disappear and the display can be made easier to see. Moreover, since the display is written using the transition from the H _n state to the F state as in the conventional case, the writing time is short and the number of driving digits can be increased. Furthermore, since the display is refreshed at regular intervals, the contrast will not deteriorate even after a long period of time.

Furthermore, since the pulse applied to the liquid crystal is an alternating current pulse consisting of a positive pulse and a negative pulse with the same waveform, deterioration of the liquid crystal, darkening of the electrodes, etc. can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the display device of the present invention, FIG. 2 is a waveform diagram showing the signal waveform supplied to the electrodes and the pulse waveform applied to the liquid crystal according to the present invention, and FIG. 3 is the F state. and a waveform diagram showing the pulse waveform applied to the pixel to be in the H _n state,
FIG. 4 is a characteristic diagram showing the characteristics of a phase change type liquid crystal, and FIG. 5 is a waveform diagram showing an example of a conventional drive waveform. SE...scanning circuit, L ₁ ~L _n ...scanning electrode, DR
...Drive control circuit, R ₁ ~ R _o ...Selection electrode, RS...
...Initialization signal, S...Selection signal, _VF ...Data signal, _VH ...Data signal, _P1 , _P2 ...First AC pulse, _P3 ...Second AC pulse, _P4 , _P5 ...
...Third AC pulse.

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. In this method of driving a matrix type liquid crystal display device, a display initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, and when the initialization signal and selection signal are not supplied, a non-selection signal is supplied. , A data signal specifying the display state of each pixel is supplied to each selection electrode, and a first alternating current pulse is applied to the pixel to bring the liquid crystal into a homeotropic state based on the potential difference between the data signal and the initialization signal. A second alternating current pulse that maintains the liquid crystal in a homeotropic state or a voltage O that transitions the liquid crystal to a focal conic state is applied to the pixel due to the potential difference between the data signal and the selection signal, and the data signal and the non-selection signal are Due to the potential difference between
A third alternating current pulse that maintains the liquid crystal in a focal conic state or a homeotropic state is applied to the pixel, and the first, second, and third alternating current pulses are a positive polarity pulse and a negative polarity pulse with the same waveform, respectively. 1. A method of driving a matrix liquid crystal display device, characterized in that the method comprises a pulse of: