Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-02-05
2003-11-11
Nguyen, Chanh (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06646627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to liquid crystal display control devices and liquid crystal display apparatus.
2. Description of Related Art
The liquid crystal display is becoming popular for it's space saving characteristics and low power consumption in picture display devices. Research on liquid crystal displays is being done actively, and the performance of liquid crystal displays has improved remarkably in recent years.
Liquid crystals have a property of changing their molecular orientation when an electric field is applied. A vertical alignment-type liquid crystal is shown in FIGS.
5
(
a
) and
5
(
b
). FIG.
5
(
a
) shows a liquid crystal of a vertical alignment-type liquid crystal when an electric field is not applied. FIG.
5
(
b
) shows the same liquid crystal when an electric field is applied.
A negative dielectric anisotropic nematic liquid crystal molecule
2
, sandwiched between a pair of electrodes
1
, is oriented vertically with respect to the pair of electrodes
1
as shown in FIG.
5
(
a
) when no voltage is applied to the electrodes
1
. When a voltage is applied to the electrodes
1
, the orientation of the nematic liquid crystal molecule
2
changes to horizontal relative to the electrode
1
as shown in FIG.
5
(
b
). The liquid crystal illustrated in FIGS.
5
(
a
) and
5
(
b
) is called a vertical alignment type liquid crystal of an electric field effect-type.
Another type of liquid crystal is called a horizontal alignment liquid crystal of an electric field effect type. This type of liquid crystal molecule aligns in the horizontal direction when no voltage is applied to a pair of electrodes. When a voltage is applied to the electrodes, the liquid crystal molecule orientation changes to vertical relative to the electrodes. This type of liquid crystal aligns to an electric field orientation when a voltage is applied to the electrodes.
Liquid crystal displays using above-described electric field effect-type liquid crystal, include a pair of transparent electrodes and a pair of orientation films beneath the inner sides of the electrodes. The orientation film has a plurality of grooves and is arranged such that the directions of the grooves are different by 90 degrees from each other. Polarizing plates are disposed outside the transparent electrodes, respectively. The liquid crystal molecules are oriented by aligning to the grooves of the orientation film in the neighborhood of each orientation film. Between the orientation films, the liquid crystal molecules are twisted continuously by 90 degrees. The pair of polarizing plates controls the beam to pass through or be intercepted. A pair of polarizing plates can be arranged in the same direction, or in 90 degree direction, according to a design of the display apparatus.
Normally black systems employ intercepting beams when no voltage is applied, and passes through the beam when a voltage is applied. In contrast, normally white systems employ intercepting beams when a voltage is applied, and passes through the beam when no voltage is applied.
Presently, liquid crystal displays for notebook computers, normally white system with a horizontal alignment liquid crystal of an electric field effect-type are popular. For a projection display and a television display, it is important to have wide view-angle characteristics, normally black systems are becoming popular with a vertical alignment-type liquid crystal.
Liquid crystal displays are controlled by the supply voltage to an individual pixel. If a fixed voltage is applied to each pixel adopting the normally black system liquid crystal display, a fixed brightness is sure to be obtained on the liquid crystal display. If a fixed voltage is applied to each pixel adopting a normally white system liquid crystal display, a fixed darkness is sure to be obtained on the liquid crystal display. However, even if a fixed voltage is applied to a pixel, the brightness or the darkness of the pixel is not constant due to the effect of the darkness or the brightness of the surrounding pixels. In other words, the brightness or the darkness of a pixel is affected by voltages applied to the surrounding pixels. The phenomenon of having non-constant brightness or darkness regardless of the same supply voltage is called discrimination.
Recently, the size of pixels of liquid crystal displays has become smaller and smaller. As a result, controlling discrimination is becoming more important in order to obtain a good quality liquid crystal display.
FIGS. 6 and 7
show discrimination data measured on a conventional vertical alignment normally black-type liquid crystal display.
FIG. 6
shows image patterns for measurements of discrimination.
FIG. 7
shows the relationship between an applied voltage and a standardized mean brightness value of a pixel of the image patterns. Each image pattern has eight columns and plural rows and the same voltage is applied to the pixels in the same column. FIG.
6
(
a
) is a “1111” pattern. All pixels are applied voltage. FIG.
6
(
b
) is a “1110” pattern. Pixels in the left three columns are applied voltage and the pixels in the fourth column are not applied voltage. FIG.
6
(
c
) is a “1100” pattern. Pixels in the left two columns are applied voltage and the pixels in the third and forth columns are not applied voltage. FIG.
6
(
d
) is named“1000” pattern. Pixels in the first column are applied voltage and the pixels in the second through forth columns are not applied voltage. FIG.
6
(
e
) is named“0101” pattern. Pixels in the second and fourth columns are applied voltage and the pixels in the first and third columns are not applied voltage. In this measurement, the brightness of the entire image is measured changing the applied voltage to each pixel.
The processing for measured brightness values of one pixel is standardized as follows. First, the number of pixels to which the voltage is applied is counted for each image pattern. Next, all the measured brightness values of all image patterns are standardized using the highest brightness value. The measured brightness value at 3900 mV voltage of the “1111” pattern is set to be the standard 1.0. Finally, the standardized brightness values are divided by the number of voltage-applied pixels and the standardized brightness value for each image pattern is calculated.
The x-axis in the graph of
FIG. 7
is the voltage (mV) applied to a pixel, and the y-axis is the standardized brightness value of the pixel. The mean standardized brightness value of a pixel of the “1111” pattern is plotted by the symbol “♦” in this graph. Also the mean standardized brightness value of a pixel of the “1110” pattern is plotted by the symbol “▪”, the “1100” pattern is plotted by the symbol “&Dgr;”, the “1000” pattern is plotted by the symbol “X”, and the “0101” pattern is plotted by the symbol “∘”.
Originally, the mean standardized brightness value of each pixel is expected to be the same value as that of the “1111” pattern. However, because of discrimination, the mean standardized brightness value of a pattern having non-voltage applied pixels is lower than that of the “1111” pattern when the applied voltage is 200 mV and above. Moreover, the mean standardized brightness value of the “1100” pattern (FIG.
6
(
c
)) is higher than that of the “0101” pattern (FIG.
6
(
e
)), even though the total number of voltage applied pixels are equal. The mean standardized brightness value of the “0101” pattern (FIG.
6
(
e
)) is almost equal to that of the “1000” pattern (FIG.
6
(
d
)), even though the total number of voltage applied pixels are doubled.
It is understood that on a normally black type liquid crystal display, discrimination appears to have an influence of darkening a pixel by surrounding black pixels. Moreover, a pixel to which the voltage is applied is affected by the discrimination largely owing to the number of surrounding pixels to which no voltage applied.
The discrimination in normally black-type liquid crystal displays causes a white character in a black ba
Kawasaki Microelectronics Inc.
Nguyen Chanh
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