Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-07-21
2001-04-24
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S104000, C345S103000, C345S208000, C345S210000
Reexamination Certificate
active
06222517
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a matrix-type liquid crystal apparatus, more particularly to a driving method for a liquid crystal apparatus using a liquid crystal device having two stable states.
Hitherto, there has been a liquid crystal display device comprising a liquid crystal cell formed of a pair of substrates including one having thereon a group of scanning electrodes and the other having thereon a group of data electrodes, and a liquid crystal material disposed between the electrodes so as to form a matrix of pixels for displaying picture data. Particularly, extensive research and development have been made on a ferroelectric liquid crystal device using a liquid crystal having a spontaneous polarization and capable of responding to electric fields applied thereto at high speeds to realize two stable liquid crystal molecular alignment states since the year of 1980, e.g., as disclosed in Japanese Laid-Open Patent Application (JP-A) 56-107216.
In various driving methods for ferroelectric liquid crystal devices proposed heretofore, scanning lines are selected one by one for writing. A set of drive signal waveforms used in a representative conventional drive scheme is shown in FIG.
16
. In
FIG. 16
, at (A) is shown a scanning signal waveform at the time of selection; (B), a scanning signal waveform at the time of non-selection; (C), a data signal waveform for writing “white” (W) or a bright state; and (D), a data signal waveform for writing “black” (B) or a dark state. The drive signal waveform set is for a line-sequential writing scheme, wherein pixels on scanning lines are driven line by line, i.e., erased or reset into “black” by application of a V
1
pulse as shown at FIG.
16
(A), and then supplied selectively with either a pulse V
3
at (C) or a pulse V
4
at (D) to be written into “white” or to retain “black” without being written into “white” depending on the magnitude of a voltage difference with a V
2
pulse at (A). In a specific example, the voltages may be set to satisfy V
3
=−V
4
=V
5
, V
2
=2.V
4
and V
1
=V
2
, and the pulse widths may be set at ratios of V
1
:V
2
:V
5
:V
4
(C):V
3
(D):V
3
(C):V
4
(D)=5:2:1:1:1:2:2. The setting of more specific voltages and pulse widths may be varied depending on a cell gap between electrodes, a temperature and a liquid crystal material used in the device.
A ferroelectric liquid crystal device described above has a memory characteristic so that a black or a white display state can be sufficiently held even when an interval until a subsequent writing becomes long according to a lowering in frame frequency. Accordingly, a large panel having an increased number of scanning signal lines can be realized, but the image quality is inevitably lowered due to the lowering in frame frequency.
In order to provide an improvement to the above-mentioned problem, JP-A 63-155032 has proposed to scan a plurality of lines for realizing a high-speed drive. However, in the plural line scanning scheme described in JP-A 63-155032, each scanning signal is caused to have a pulse width of ½M in the case of scanning M lines at a time, and thus the pulse width becomes shorter corresponding to the number of scanning lines selected simultaneously, so that it is impossible to realize a substantially higher speed drive.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal apparatus using a polarity-driven liquid crystal as represented by a ferroelectric liquid crystal and capable of realizing a high-speed drive and a large display area without causing a lowering in picture quality due to a lowering in frame frequency.
According to the present invention, there is provided a liquid crystal apparatus, comprising:
(A) a liquid crystal device comprising a group of scanning electrodes, a group of data electrodes intersecting the scanning electrodes, and a liquid crystal disposed so as to form a matrix of pixels each at an intersection of the scanning electrodes and the data electrodes, said liquid crystal having at least two stable states so as to be written into one stable state when supplied with a voltage of one polarity exceeding a threshold, and
(B) drive means for driving the liquid crystal device by selectively applying scanning signals and data signals to the scanning electrodes and the data electrodes so as to selectively apply a combined voltage to each pixel; said drive means comprising means for:
simultaneously selecting M scanning electrodes (M being an integer of at least 2), and
applying scanning signals to the simultaneously selected scanning electrodes and data signals to the data electrodes so as to apply writing pulses for determining states of pixels to pixels at the intersections of the selected scanning electrodes and the data electrodes and so that each pixel on the selected scanning electrodes is supplied with writing pulse(s) of a writing polarity having a time-integrated voltage value which is larger than that of writing pulse(s) of an anti-writing polarity, if any.
Herein, a time-integrated voltage value of a polarity of writing pulse(s) refers to a value determined by
∫
0
t
V dt (wherein V is a voltage value in a writing or anti-writing polarity of writing pulse(s)) and is determined by
∑
n
(
Vn
)
×
(
Δ
tn
)
in the case of a plurality (n) of rectangular pulses in the writing or anti-writing polarity having voltage amplitudes V
1
, . . . Vn and pulse widths &Dgr;t, . . . &Dgr;n, respectively.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
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Iba Jun
Inaba Yutaka
Tsuboyama Akira
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kovalick Vincent E.
Shalwala Bipin
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