Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-05
2004-01-06
Shankar, Vijay (Department: 2871)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S095000
Reexamination Certificate
active
06674421
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a driving method for a liquid crystal display device for use in a liquid crystal display apparatus, etc.
In recent years, liquid crystal display devices have been commercialized in various fields including monitors for personal computers, view finders for video camcorders and projectors. Most of these liquid crystal display devices employ twisted nematic (TN) liquid crystals.
However, the TN-type liquid crystal display devices have a problematic slower response speed and narrower viewing angle.
Incidentally, a color liquid crystal display device with no color filters driven according to a so-called field-sequential scheme has been proposed.
According to the field-sequential scheme, such a color filterless liquid crystal display device is used in combination with, e.g., three light sources of red (R), green (G) and blue (B), which are sequentially turned on to provide the color filterless liquid crystal display device with corresponding color images to be color-mixed in time sequence to form a desired color image. Accordingly, a liquid crystal used is required to possess such a response characteristic that its optical response is completed in each field period for a corresponding color in order to ensure the display of the desired color. As a result, the liquid crystal used for the field-sequential scheme is required to exhibit a higher response speed than ever.
In order to solve the above-mentioned problems, Yoshida et al have proposed a driving method using a combination of a mono-stabilized ferroelectric liquid crystal and a plurality of active (matrix) elements arranged in a matrix form (e.g., Japanese Patent No. 2681528). Such a mono-stabilized ferroelectric liquid crystal provides an electrical optical response characteristic such that the liquid crystal responds to the application of a voltage of one polarity to provide a V-T (voltage-transmittance) curve in a half-V character shape (i.e., a shape given by cutting V-character in half), as shown in
FIG. 2
(referred to as a “half-V character-mode liquid crystal”). On the other hand, a TN liquid crystal having an electrical optical characteristic with respect to both a positive polarity voltage and a negative polarity voltage and a liquid crystal as proposed in Japanese Laid-Open Patent Application (JP-A) 9-50049 show an optical response (V-T characteristic) such that the liquid crystal substantially equally responds to both the positive polarity voltage and the negative polarity voltage to provide a V-T curve like a V character (referred to as a (“V character-mode liquid crystal”).
FIG. 3
is a sequence (time chart) for driving a liquid crystal display device using a half-V character-mode liquid crystal by using active matrix elements, each adapted for a drive circuit unit as shown in FIG.
4
.
Referring to
FIG. 4
, the drive circuit unit comprises a gate line drive circuit
41
, a gate line (row electrode)
42
, a source line (column electrode)
43
, a source line drive circuit
44
, a storage (retention) capacitor Ccs and a liquid crystal capacitor Clc.
According to the driving sequence (time chart) shown in
FIG. 3
, the entire picture area (panel plane) of the liquid crystal display device is scanned (for writing) six times (first to sixth scannings) in one frame period (e.g., {fraction (1/60)} sec). Specifically, in each frame period, the first scanning (+(R) scanning) is effected for writing (supplying) a data voltage for a red (R) picture (image) of positive (+) polarity, and the second scanning (−(R) scanning) is effected for writing a data voltage for R picture of negative (−) polarity. Thereafter, the third scanning (+(G) scanning) is effected for writing a data voltage for a green (G) picture of (+) polarity, and the fourth scanning (−(G) scanning) is effected for writing a data voltage for G picture of (−) polarity. Further, the fifth scanning (+(B) scanning) is effected by writing a data voltage for a blue (B) picture of (+) polarity, and the sixth scanning (−(B) scanning) is effected for writing a data voltage of (−) polarity. On the other hand, a light source unit comprising three light sources of red (R), green (G) and blue (B) is turned on in such a manner that the R light source is turned on over the first and second scanning periods (for +(R) scanning and −(R) scanning), the G light source is turned on over the third and fourth scanning periods (for +(G) and −(G) scannings), and the B light source is turned on over the fifth and sixth scanning periods (for +(B) and −(B) scannings) sequentially in this order. These scannings are repeated in a succession of frame periods.
In the above sequence, the liquid crystal (half-V character-mode liquid crystal) provides an optical response (V-T characteristic) shown in
FIG. 2
, so that a color picture (image) display comprising R display state (based on the R data voltage), black state, G display state (based on the G data voltage), black state, B display state (based on the B data voltage), and black state in succession in each frame period is sequentially repeated, thus allowing full-color image display without using color filters.
However, the above-mentioned drive sequence (
FIG. 3
) is accompanied by problematic crosstalk, since the sequence is performed in a field-inversion drive scheme, wherein the polarity of the applied voltage to each pixel is inverted for each (one) picture scanning period ((+)→(−)→(+)→(−)→(+)→(−)).
More specifically, as shown in
FIG. 5
, pixel electrodes (defining the pixels) are accompanied by several parasitic (coupled) capacitances. Particularly, coupling the pixel electrode with the source line (data electrode)
43
causes an application of a voltage depending on a display picture (image) to the source line
43
, so that a field-through phenomenon attributable to a fluctuation of voltage at the source line
43
occurs, thus leading to a potential fluctuation of the pixel electrodes. As a result, a transmittance (transmitted light quantity) of the liquid crystal display device is also changed, thus failing to obtain a desired gradational characteristic, i.e., the crosstalk phenomenon described below with reference to
FIGS. 6 and 7
.
FIG. 6
is a plan view for illustrating a mechanism of the crosstalk phenomenon, and
FIG. 7
is a time chart for the quantitative explanation thereof.
Referring to
FIG. 6
, in this embodiment, a white display of a rectangular portion at pixel a and a rectangular portion at a region ranging from pixel b to pixel d is performed on a white background portion on the panel plane of the liquid crystal display device. A gate line I is disposed along the pixels a and b, and a gate line II is disposed along pixels c and d. On the other hand, a source line A is disposed along the pixels a and c, and a source line B is disposed along the pixels b and d. The gate lines I and II are successively scanned in this order.
For the scanning operation, referring to
FIG. 7
, the gate line I disposed along the pixels a and b is selected at times t
3
and t
3
′, and the gate line II disposed along the pixels c and d is selected at times t
5
and t
5
′. On the other hand, a voltage applied to the source line A disposed along the pixels a and c is +Vw ((+) polarity voltage for writing white data) at a time t
2
, 0 V at a time t
4
, −Vw ((−) polarity voltage for writing white data having an absolute value identical to +Vw) at a time t
2
′, and 0 V at a time t
4
′. Similarly, a voltage applied to the source line B disposed along the pixels b and d is +Vw ((−) polarity voltage for writing white data) at a time t
1
, 0 V at a time t
6
, −Vw ((−) polarity voltage for writing white at having an absolute value identical to +Vw) at a time t
1
′, and 0 V at a time t
6
′.
Then, a change in pixel potential with time will be desc
Miura Seishi
Mori Hideo
Togano Takeshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Drive method for liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drive method for liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drive method for liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261780