Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1996-12-06
1999-12-28
Mengistu, Amare
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
349174, G09G 336
Patent
active
060087870
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an antiferroelectric liquid crystal panel used for a liquid crystal display panel, a liquid crystal optical shutter array, and the like, and a method for driving the antiferroelectric liquid crystal panel, more particularly to an antiferroelectric liquid crystal panel using antiferroelectric liquid crystal and having matrix-forming pixels.
BACKGROUND ART
An antiferroelectric liquid crystal panel is known as having a wide angle of view, a capability of a high speed response, and a good multiplex characteristic, and the studies of the antiferroelectric liquid crystal panel have been energetically carried out. Reference can be made to Japanese Unexamined Patent Publication (Kokai) No. 2-173724.
An antiferroelectric liquid crystal panel has a hysteresis characteristic regarding light transmittance versus applied voltage. Accordingly, when a voltage is applied to an antiferroelectric liquid crystal panel, if the product of the applied voltage and the applied pulse width exceeds a threshold value, a ferroelectric state as the first stable state is selected, if the polarity of the applied voltage is changed, a ferroelectric state as the second stable state is selected, and if the product of the applied voltage and the applied pulse width is below the threshold value, an antiferroelectric state as the third stable state is selected. An example of the characteristic regarding light transmissivity versus applied voltage is shown in FIG. 1. An example of an electrode of an antiferroelectric liquid crystal panel having matrix-forming pixels is shown in FIG. 2. Generally in such an antiferroelectric liquid crystal panel, time-divisional driving is adopted in which the scanning voltages are successively cyclically applied to the scanning electrodes Y1 to Y128, predetermined signal voltages are applied in parallel in synchronization with the scanning voltages to the signal electrodes X1 to X160, and the liquid crystal molecules of the selected pixel are switched in correspondence with the display information.
Various methods of time-divisional driving have been proposed. Examples of the proposed methods are shown in FIGS. 3 and 4. To write one picture plane, the writing of two frames is carried out in which the voltage values of the waveforms of the first frame and the second frame are symmetrical regarding the zero voltage value, so that an alternation of the operation is achieved. The ON state is shown in FIG. 3, and the changes of the voltage and the light transmissivity of pixels at the time of setting the OFF state are shown in FIG. 4. The scanning voltage applied to the scanning electrode consists of three phases in which in the first phase resetting to the OFF state, i.e. the antiferroelectric state, is carried out, in the second phase the state in the first phase is maintained, and in the third phase selecting whether or not the setting to the ON state, i.e. the ferroelectric state is carried out. In the case of FIG. 3, the setting to the ON state, i.e. the ferroelectric state, is carried out, since the third phase of the resultant voltage as the difference between the scanning voltage and the signal voltage exceeds the threshold voltage, while in the case of FIG. 4, the OFF state, i.e. the antiferroelectric state, is maintained, since the third phase does not exceed the threshold voltage.
One of the problems in an antiferroelectric liquid crystal panel is that the response speed of switching from the ferroelectric state to the antiferroelectric state is twice as slow as that of switching from the antiferroelectric state to the ferroelectric state. Therefore, in the prior art method of driving, the period for resetting to the antiferroelectric state is made longer than the period for setting to the ferroelectric state or the antiferroelectric state. However, if the number of the scanning electrode is increased, an disadvantage will occur that the time for writing all the pixels is very much extended. An object of the present invention is to solve the disadvanta
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Citizen Watch Co. Ltd.
Mengistu Amare
Osorio Ricardo
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