Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-06-21
2002-07-02
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S211000
Reexamination Certificate
active
06414655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma address display apparatus for selectively controlling a pixel by using a plasma switch and a constant-current control apparatus for use in the plasma address display apparatus.
2. Description of the Related Art
As a flat display apparatus, a liquid crystal display apparatus has already been put into practical use in a number of fields, and enlargement of the liquid crystal display apparatus has been actively developed. In order to allow a liquid crystal display apparatus to have a high resolution and a high contrast, a method for providing an active element such as a transistor in each display pixel and driving it is generally used. However, when it is attempted to enlarge a liquid crystal display apparatus, the number of active elements is remarkably increased, which results in a decrease in a production yield.
In order to solve the above-mentioned problem, Japanese Laid-Open Publication No. 1-217396 discloses a method utilizing plasma discharge, instead of semiconductor elements such as MOS transistors and thin film transistors. Hereinafter, a structure of a liquid crystal display apparatus in which liquid crystal is driven by utilizing plasma discharge (hereinafter, referred to as a “plasma address display apparatus) will be briefly described.
As shown in
FIG. 7
, in a plasma address display apparatus, a liquid crystal layer
103
which is an electrooptical material layer and plasma chambers P
1
to P
n
are disposed adjacent to each other via a thin dielectric sheet
104
. Each of the plasma chambers P
1
to P
n
is surrounded by partition walls
105
parallel to each other and the dielectric sheet
104
on a plasma substrate
102
. In each plasma chamber, ionizable gas such as He, Ne, Ar, Kr, and Xe, or mixed gas thereof is sealed. Furthermore, electrodes
106
are formed in each plasma chamber on the plasma substrate
102
, and the electrodes
106
function as an anode electrode and a cathode electrode for ionizing gas in each plasma chamber to generate plasma discharge.
On the other hand, the liquid crystal layer
103
is interposed between the dielectric sheet
104
and a transparent substrate
101
, and the periphery of the liquid crystal layer
103
is sealed with a sealant
108
. On the surface of the transparent substrate
101
on the liquid crystal layer side, stripe-shaped signal electrodes
107
are formed. The signal electrodes
107
cross the plasma chambers P
1
to P
n
, and each crossed portion of the signal electrodes
107
and the plasma chambers P
1
to P
n
correspond to each display pixel.
In the plasma address display apparatus, the plasma chambers P
1
to P
n
in which plasma is discharged are scanned successively in this order, and in synchronization with this, the signal electrodes
107
on the liquid crystal layer
103
side are supplied with a signal voltage, whereby the signal voltage is held by each pixel, and the liquid crystal layer
103
is driven. Thus, each of the plasma chambers P
1
and P
n
correspond to one scanning line. The adjacent plasma chambers of the plasma chambers P
1
to P
n
are separated by a partition wall.
FIG. 8
schematically shows a pixel. In
FIG. 8
, reference
110
denotes an anode electrode,
111
denotes a cathode electrode,
112
denotes a plasma switch operated by plasma discharge, and
113
denotes a signal electrode. The plasma switch
112
is turned on when a desired voltage is applied to the cathode electrode
111
, and is turned off when the voltage of the cathode electrode
111
becomes equal to that of the anode electrode
110
.
A capacitor C
t
corresponds to a capacitance of the dielectric sheet
104
in
FIG. 7
, and a capacitor C
LC
corresponds to a capacitance of the liquid crystal layer
103
in FIG.
7
. By applying a desired voltage to the signal electrode
113
when the plasma switch
112
is turned on, an voltage between the anode electrode
110
and the signal electrode
113
is divided by the capacitors C
t
and C
CL
, and a desired voltage is applied to the liquid crystal layer
103
. If the plasma switch
112
is turned off in this state, the voltage applied to the liquid crystal layer
103
is held until the plasma switch
112
is turned on again.
FIG. 9
is a schematic circuit diagram of a plasma address display apparatus. In this figure, each pixel pix is further simplified, compared with FIG.
5
.
A plurality of pixels are arranged in a matrix. Anode electrodes
120
and cathode electrodes
121
are arranged in rows, and signal electrodes VL
1
, VL
2
, . . . , VL
n
are arranged in columns. The anode electrodes
120
are commonly fixed at the identical voltage, and the cathode electrodes
121
are independently connected to switches S
1
, S
2
, . . . , S
n
. The switches S
1
, S
2
, . . . , S
n
are for switching an voltage of the cathode electrodes
121
.
Next, driving of the plasma address display apparatus will be briefly described.
Under the condition that plasma discharge is not generated, the dielectric sheet
104
is electrically insulated from the anode electrode
120
and the cathode electrode
121
. When an voltage which is negative to the anode electrode
120
is applied to the cathode electrode
121
, plasma discharge is generated.
Due to the plasma discharge, space charges of ions and electrons is generated in the plasma chamber, whereby the voltage in the plasma chamber becomes equal to that of the anode electrode
120
. At this time, the voltage of the lower surface of the dielectric sheet
104
becomes equal to that of the anode electrode
120
, which means that a virtual electrode is formed. When a data voltage is applied to the signal electrode
107
based on the voltage of the anode electrode
120
, the data voltage is divided in accordance with a ratio between the capacitance of the dielectric sheet
104
and that of the liquid crystal layer
103
. As a result, desired data is written in a display pixel.
When the voltage of the cathode electrode
121
is returned to be equal to that of the anode electrode
120
, the plasma discharge is finished. After the plasma discharge is finished, the space charges are decayed gradually, and the plasma chamber returns to an insulated state. This state is the same as the state where the plasma switch
112
is turned off, and a voltage is not applied to the liquid crystal layer
103
. However, the charge accumulated on the surface of the dielectric sheet
104
is held in the liquid crystal until the subsequent discharge is generated. Because of this operation, a sample-and-hold drive which is similar to that of a liquid crystal apparatus using ordinary active elements is conducted.
It is more advantageous in terms of desirably writing data in a pixel that the data voltage applied to the signal electrode
107
continues to be applied until the plasma chamber returns to an insulated state. However, as the period of applying a data voltage is extended, crosstalk in the vertical direction becomes more likely to occur. This is a trade-off relationship. Thus, the applied voltage is reset slightly before the plasma chamber returns to an insulated state. As a result, the charge held in the liquid crystal layer
103
is slightly changed; however, this change is suppressed to such a degree that no substantial problem arises.
Among the space charges, some particles are excited in a metastable state, and thereafter, returns to the basic state. Therefore, even after the plasma discharge is finished, such metastable atoms remain for a relatively long period of time, and generate a trace amount of paired ions and electrons. Thus, the plasma switch
112
holds a conductive state for a while after the finish of the plasma discharge. The plasma switch
112
returns to a non-conductive state only when the metastable atoms substantially completely return to the basic state. Therefore, the charge eventually written in each display pixel depends upon a decay time &tgr; 1 from the time when the plasma discharge is finished to the time when the metastable atom
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Wu Xiao
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