Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-04-15
2001-12-11
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C349S129000, C349S134000
Reexamination Certificate
active
06329972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive method of a liquid crystal display and, more particularly, to a method for driving an antiferroelectric liquid crystal display.
2. Description of Related Art
Generally, in a conventional antiferroelectric liquid crystal display, a white mode is realized when liquid crystal molecules undergo a phase-transition into one of a positive ferroelectric phase (hereinafter, referred to as “F+phase”) by positive voltage and a negative ferroelectric phase (hereinafter, referred to as “F−phase”) by negative voltage, while a black mode is realized when the liquid crystal molecules undergo a phase-transition into an antiferroeletric phase (hereinafter, referred to as “AF phase”) when no voltage is applied.
Describing more in detail, to realize the white mode, the liquid crystal molecules alternately undergo a phase-transition into the F+phase and the F−phase by one frame cycle, and the time for one frame cycle is set at less than 30 ms, at which the frame is invisible, to prevent the flicker of images.
However, in the above described antiferroelectric liquid crystal display, if a viewing angle is inclined from a direction normal to an activated pixel on a screen, since directions of the F−phase and the F+phase are different from each other as shown in
FIG. 1
, light transmittance with respect to the viewing angle becomes different, causing flicker of images on he screen.
To prevent flicker, the time for two frame cycles for repeating the +phase and the F−phase should be set at less than 30 ms. That is, one frame cycle should take less than 15 ms.
However, since present technology cannot increase a drive frequency of a drive device of the liquid crystal display above tens of MHz, it is impossible to realize a high color moving picture. Therefore, it is very costly and time-consuming to develop a drive device that can realize 15 ms frame cycle.
Therefore, the conventional antiferroelectric liquid crystal display displaying an image using the F+phase and the F−phase cannot solve the flicker problem unless the frame cycle is reduced to less than 15 ms.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in an effort to solve the above-described problems.
It is an objective of the present invention to provide a method for driving an antiferroelectric liquid crystal display in which a display quality can be improved by preventing a flicker effect at all viewing angles without reducing frame cycle times.
To achieve the above objective, the present invention provides a method for driving an antiferroelectric liquid crystal display, comprising the steps of causing antiferroelectric liquid crystal molecules to undergo a phase-transition into only one of positive and negative ferroelectric phases, and causing the antiferroelectric liquid crystal molecules to undergo a phase-transition into an antiferroelectric phase.
Preferably, the step of causing the antiferroelectric liquid crystal molecules to undergo a phase-transition into only one of positive and negative ferroelectric phases comprises the steps of applying a selection voltage, which is higher than a threshold selection voltage by which the liquid crystal molecules undergo the phase-transion into one of the positive and negative ferroelectric phases, to the antiferroelectric liquid crystal molecules and applying a sustain voltage to the liquid crystal molecules to sustain the phase-transition state of the molecules into one of the positive and negative ferroelectric phases.
Preferably, the step of causing the antiferroelectric liquid crystal molecules to undergo a phase-transition into the antiferroeletric phase comprises the step of applying a direct compensating voltage to the antiferroelectric liquid crystal molecules, the direct compensating voltage having a potential opposite to the threshold selection voltage and the sustain voltage, and an absolute value lower than that of the threshold selection voltage.
A total value of the selection voltage, the sustain voltage, and the direct compensating voltage in a unit frame becomes zero.
The absolute value of the threshold selection voltage is higher than that of a threshold non-selection voltage by which the liquid crystal molecules undergo the phase-transition into the antiferroelectric phase.
An effective absolute value of the direct compensating voltage in a unit frame is equal to the sum of an effective absolute value of the selection voltage and an effective absolute value of the sustain voltage.
The selection voltage has a positive and negative level. And a negative level selection voltage initially applied in the unit frame may be omitted.
An absolute value of the sustain voltage is lower than that of the threshold selection voltage but higher than that of a threshold non-selection voltage by which the liquid crystal molecules undergo the phase-transition into the antiferroelectric phase.
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Bushnell , Esq. Robert E.
Nelson Alecia D.
Samsung SDI & Co., Ltd.
Saras Steven
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