Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-09-20
2004-10-12
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S102000
Reexamination Certificate
active
06803894
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display apparatus and its displaying method to which a color field sequential driving method has been applied. More particularly, it relates to a liquid crystal display apparatus using the apparatus and method, such as a wearable display or a projection type display.
At present, as the methods of displaying a color image in a liquid crystal display, the following two methods can mainly be mentioned. One is a three-primary-colors color filter method, and the other is the color field sequential driving method (which is also referred to as a color frame sequential driving method).
The color filter method is as follows: One pixel is divided into three subpixels, and then the three-primary-colors color filter is located in each of the subpixels, and finally the luminance relationship among the respective colors is adjusted, thereby making it possible to implement the color display in the liquid crystal display. This method is the most common of the color display methods used at present. Meanwhile, the color field sequential driving method is as follows: Monochromatic images corresponding to the respective three primary colors are displayed in sequence in time-division at high-speed, thereby taking advantage of an afterimage effect of the eyes so as to cause the observer to visually recognize the image as a color image.
The color filter method requires that one pixel should include three subpixels in order to perform the color display. In contrast to this, the color field sequential driving method allows the color display to be performed with only one subpixel (Hereinafter, in the present specification, one subpixel in the color field sequential driving method is also represented as one pixel). Accordingly, in the color field sequential driving method, it is possible to reduce the number of the pixels down to one-third with the resolution maintained that is the same as the resolution in the color filter method. This condition makes it possible to reduce the driver circuit down to one-third, thereby allowing the power to be saved. Also, in aiming to downsize the display, for the above-described reason, the color field sequential driving method is more advantageous than the color filter method.
Moreover, in the color field sequential driving method, there is no need of using the color filter that absorbs light of unnecessary wavelength and permits light of necessary wavelength alone to pass through. Accordingly, the use of monochromatic light as the backlight makes it possible to obtain a light-utilization ratio that is even higher as compared with the case of the color filter method. Namely, there also exists an advantage that, in comparison with the color filter method, it becomes possible to exceedingly reduce the power consumption needed to achieve the same luminance.
Consequently, the color field sequential driving method having the above-described advantages is particularly important in a small-sized portable type color display required to operate with a low power consumption, such as the wearable display that is expected to become a next-generation portable type color display.
Incidentally as a literature concerning the above-described technologies, there exists Society for Information Display (SID) (99, pp. 1098-1101 N. Ogawa et al. Field-Sequential-Color LCD Using Switched Organic EL Backlighting).
FIGS. 1A
to
1
D illustrate data such as signal waveforms for explaining the prior arts in the color field sequential driving method.
FIGS. 1A
to
1
C are signal waveform diagrams for illustrating the following, respectively: FIG.
1
A: time variations in driving voltages to a liquid crystal pixel (cell), FIG.
1
B: time variations in driving voltages in the case where a direct voltage component is superimposed on the driving voltages to the liquid crystal pixel, FIG.
1
C: time variations in luminances of the liquid crystal pixel in the case where the driving voltages in
FIG. 1B
are applied to the liquid crystal pixel.
FIG. 1D
illustrates an applied voltage-luminance characteristic in the liquid crystal pixel.
Usually, when displaying an image in a liquid crystal display, an alternating voltage as illustrated in
FIG. 1A
is applied to an electrode of a liquid crystal pixel, thereby driving the liquid crystal pixel. In an example in
FIG. 1A
, driving voltages V
R
, V
G
, and V
B
, which cause colors of red (R), green (G), and blue (B) to be displayed respectively in this sequence during one frame time-period
102
, are applied to each liquid crystal pixel. Each of the driving voltages V
R
, V
G
, and V
B
is applied during a subframe time-period
103
. Incidentally, although the polarity of each of the driving voltages V
R
, V
G
, and V
B
is inverted between adjacent frames, the sequence of the colors remains the same in each frame.
However, when the driving is executed using the alternating signal in a transistor circuit in a liquid crystal pixel included in an actual active matrix type liquid crystal display, in, for example, the liquid crystal cell, there occurs a capacitive coupling attributed to a signal electrode and the pixel electrode. This capacitive coupling superimposes a direct voltage component V
DC
on the driving voltages V
R
, V
G
, and V
B
.
FIG. 1B
illustrates, as the concrete example, the case where the direct voltage component V
DC
(in the case in
FIG. 1B
, V
DC
>0) is superimposed on the driving voltages. Additionally, for your information, the case illustrated in
FIG. 1A
can be considered as an ideal case where V
DC
=0. In the example illustrated in
FIG. 1B
, the direct voltage component by the amount of V
DC
is added to the driving voltage waveforms illustrated in FIG.
1
A. Namely, the driving voltage waveforms in
FIG. 1B
are the same as those in
FIG. 1A
, but are shifted onto the plus side by the amount of V
DC
. Consequently, even when the same color is displayed in the same liquid crystal cell during a time-period of a certain plurality of frames, the absolute value of the driving voltage for displaying the same color turns out to become different between the adjacent frames between which the polarity of the driving voltage differs (in the case illustrated in
FIG. 1B
, the driving voltage differs by the amount of 2V
DC
). Eventually, towards the pixel having one and the same color, the absolute value of the driving voltage differs between the adjacent frames. This means that the luminance corresponding to the driving voltage differs between the adjacent frames as illustrated in the characteristic diagram in FIG.
1
D.
FIG. 1C
illustrates, introducing the difference in each luminance, a time variation in each luminance corresponding to each driving voltage waveform in FIG.
1
B. As is obvious from
FIG. 1C
, even when the same color is displayed continuously in the same liquid crystal cell, the next frame turns out to become distinguishable because the luminance differs between the adjacent frames. As a consequence of this, the two frames become one period, thus causing flicker (which, here, means a slight amount of blinking of the luminance) to occur. Here, the flicker is synchronized with a frequency that is equal to one-half of the frame frequency.
In order to prevent this flicker, in an ordinary liquid crystal display, the following driving is performed: Towards the pixel having one and the same color, the polarity of the driving voltage is inverted for each column and/or for each row.
SUMMARY OF THE INVENTION
Applying the above-described driving method, however, results in inverting polarities of the driving voltages to each other, the driving voltages occurring in two pixels existing in adjacent columns and/or adjacent rows. This causes a disturbance in an electric field to occur in proximity to the boundary of the pixels. As a result, there occurs a liquid crystal orientation failure in proximity to the boundary of the pixels. The region where the liquid crystal orientation failure has happened is recognized as a display failure. Concealin
Hirota Shoichi
Takemoto Iwao
Tsumura Makoto
Antonelli Terry Stout & Kraus LLP
Wu Xiao
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