Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-01-09
2001-01-23
Hjerpe, Richard A. (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S094000, C349S036000
Reexamination Certificate
active
06177914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma addressed electro-optical display having a flat panel structure formed of a liquid crystal cell and a plasma cell affixed together with a dielectric sheet interposed in between. More particularly, it relates to a technology to prevent crosstalk from occurring in a plasma addressed electro-optical display.
2. Description of the Related Art
A plasma addressed electro-optical display panel is disclosed for example in Japanese Patent Laid-open No. Hei 1-217396 and
FIG. 8
shows its structure. The plasma addressed electro-optical display panel has a flat structure formed of a liquid crystal cell
101
and a plasma cell
102
affixed together with a dielectric sheet
107
made of a thin glass plate or the like interposed in between. The plasma cell
102
is formed with a glass substrate
104
on the lower side and hermetically joined to the dielectric sheet
107
with a predetermined space in between. An ionized gas is contained in the hermetically sealed space. The glass plate
104
is provided on the lower side on the inner surface thereof, with a plurality of pairs of discharge electrodes
108
and
109
disposed parallel to each other. Each pair of the discharge electrodes
108
and
109
function as the anode and the cathode for ionizing the hermetically sealed-in gas to generate plasma discharge and, thus, they form a discharge channel. On the other hand, the liquid crystal cell
101
is provided with a liquid crystal layer
106
sandwiched between the dielectric sheet
107
and a glass substrate
103
on the upper side. The upper substrate
103
is provided, on the inner surface thereof, with signal electrodes
105
in a striped array. The signal electrodes
105
cross the above described discharge channels at right angles. The signal electrodes
105
function as column driving units and the discharge channels function as row scanning units and, at the intersections of them, there are defined pixels in a matrix array and an image is formed by the pixels in the matrix array.
The operating principle of the plasma addressed electro-optical display panel shown in
FIG. 8
will be briefly described with reference to FIG.
9
. In this panel, while the discharge channels in which plasma discharge takes place are selectively scanned in a line sequential manner over the screen, signal voltages are applied to the signal electrodes
105
on the liquid crystal cell side in synchronism with the selective scanning, and, thereby, a desired picture is displayed. To achieve this, a scanning circuit
201
is connected to the plasma cell side and a signal circuit
202
is connected to the liquid crystal cell side. When plasma discharge occurs in the discharge channel formed of an anode A and a cathode K, the potential therein is maintained virtually at the anode potential. When, in this state, a signal voltage is applied to the signal electrode
105
, a signal voltage is written into the liquid crystal layer
106
of each pixel through the dielectric sheet
107
. When the plasma discharge is ended, the discharge channel is left at a floating potential and the signal voltage written therein is held by each pixel. A so-called sampling is thus performed and, while the discharge channel functions as a sampling switch, the liquid crystal layer
106
functions as a sampling capacitor. The transmittance factor of the liquid crystal varies with the signal voltage used for the sampling and, thus, activating and extinguishing the plasma addressed electro-optical display panel is carried out by pixels as the units.
FIG. 10
is a drawing schematically showing only a portion of the signal electrodes
105
formed on the inner surface of the substrate
103
on the side of the liquid crystal cell
101
. Although a color filter is placed over or under the signal electrodes
105
in constructing a color plasma addressed electro-optical display panel, it is not shown in the drawing. However, for the sake of explanation, colors assigned to the signal electrodes
105
are denoted by “Red”, “Green”, and “Blue”. Now, if a cyan color is to be displayed in a normally white mode, the display of the color cyan can be achieved by applying a signal voltage, for example, of +70V to the signal electrode which is identified as Red, as shown in
FIG. 10
, and a signal for displaying the black image is applied to the Blue and Green electrodes. At this time, the adjoining Blue and Green signal electrodes receive horizontal electric fields as indicated by the arrows in the drawing. The liquid crystal existing between the signal electrode Red and the signal electrode Blue and between the signal electrode Red and the signal electrode Green receives the electric fields virtually in the horizontal direction and changes its molecular alignment. This phenomenon is called crosstalk. Since the liquid crystal at these portions is not necessary for the originally intended display of the color cyan, it is normally shut out from the visual field by placing black masks at the corresponding portions of the color filter. However, since, in the case of the plasma addressed electro-optical display panel, the electric field is applied to the liquid crystal through the dielectric sheet
107
(refer to FIG.
8
and FIG.
9
), the signal voltage applied to each signal electrode
105
is set high. Therefore, the amount of crosstalk becomes much greater than in a normal active matrix type liquid crystal display panel or the like. Accordingly, the horizontal electric fields not only affect the gap portions between the adjoining signal electrodes but also affect the effective edge portions of the signal electrodes beyond the gap portions. If it is attempted to cover such effects with black masks, a considerable quantity of light is shielded thereby and it becomes impossible to provide a sufficient quantity of light for the display. Since such crosstalk is caused by leakage of the signal voltage, crosstalk appears most conspicuously at the time of displaying of the gray image which is performed by driving the liquid crystal at the portion of the applied voltage/transmittance characteristic where the slope is steep, i.e., in the range where the liquid crystal is more sensitive to the applied voltage (the voltage at this time is called a half-tone voltage).
When a horizontal band in a gray color is to be displayed on a screen with a background of a cyan color as shown in
FIG. 11
, the scanning is started in turn from the top of the screen and the color cyan is written in first. At this time, the liquid crystal existing between the signal electrodes receives the horizontal electric field at a considerably high level. Then, in the period when the gray band is written, half tone voltages at equal levels are applied to the electrodes of all the three colors of Blue, Red, and Green, and therefore the electric field is not applied in the horizontal direction. Then, with the progression of the scanning, the color cyan is written in as the remaining portion of the background and, thus, one frame is projected. Since the liquid crystal is actuated by the effective value of the applied voltage, when such an image is displayed, the liquid crystal existing between the adjoining signal electrodes at the edge portions of the differently colored regions suffers changes in the molecular alignment because most portions of it have been driven by the color cyan. Consequently, in the edge portion of the gray band, there is made a display in a color different from that (gray) originally intended. In the ordinary plasma addressed electro-optical display panel, there are arranged a great number of signal electrodes at narrow intervals. In order to improve the transmittance of the incident light, it is preferred that the gap between the signal electrodes be as narrow as possible. However, the phenomenon of leakage of voltage between adjoining signal electrodes, called crosstalk, appears more conspicuously as the gap is narrowed. Due to such a phenomenon, not only is color reprodu
Abe Hironobu
Iwama Jun
Dinh Duc
Hill & Simpson
Hjerpe Richard A.
Sony Corporation
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