Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-04-19
2002-03-26
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S062000, C345S063000, C345S065000, C345S066000, C345S067000, C345S068000, C345S077000, C345S080000, C313S582000, C313S583000, C313S585000, C313S631000
Reexamination Certificate
active
06362799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma display, and more particularly to the structure and drive of an AC memory type plasma display.
2. Description of the Related Art
A DC plasma display and an AC (AC memory type) plasma display are known conventionally. In particular, an AC memory type plasma display is widely used as a color display.
FIG. 9
illustrates the structure of a conventional AC memory type plasma display panel in cross section. As illustrated, this type of plasma display panel has a front substrate
41
and a rear substrate
45
which face each other and which are made of insulating material such as glass.
A plurality of transparent scanning electrodes
42
a
and maintaining electrodes
42
b
, formed from an ITO (Indium Tin Oxide) or Nesa film, are provided on the front substrate
41
. Each of the scanning electrodes
42
a
and its corresponding one of the maintaining electrodes
42
b
form a surface discharge electrode
42
. In order to reduce the resistances of the scanning and maintaining electrodes
42
a
and
42
b
, trace electrodes
43
are formed one on each of them. Normally, Cr/Cu/Cr (chrome/copper/chrome) stacked thin film electrodes or Ag (silver) thick film electrodes are employed as the trace electrodes
43
.
A dielectric layer
44
is formed on the scanning electrodes
42
a
, the maintaining electrodes
42
b
and the trace electrodes
43
. In general, lead glass having a low melting point is used to form the dielectric layer
44
. An MgO film (not shown), having a thickness of approximately 0.5 &mgr;m to 1 &mgr;m, is formed on the dielectric layer
44
by vacuum vapor deposition, in order to prevent the dielectric layer
44
from being damaged by minus and plus ions and electrons, which are generated due to a gas discharge, and in order to lower a discharge voltage.
A plurality of data electrodes
46
, which face the scanning and maintaining electrodes
42
a
and
42
b
and which are substantially perpendicular to the scanning and maintaining electrodes
42
a
and
42
b
, are formed on the rear substrate
45
. Ag thick film electrodes are employed as the data electrodes
46
. A white dielectric layer
47
is formed on the data electrodes
46
. The white dielectric layer
47
is formed by printing and sintering glass paste prepared by mixing powder of white oxide (alumina, titanium oxide or the like), powder of lead glass having a low melting point, etc. The white dielectric layer
47
has the function of reflecting light emitted from phosphor layers
48
and directing the light toward the front substrate
41
.
The phosphor layers
48
are formed on the white dielectric layer
47
. The phosphor layers
48
are separate coatings of three phosphor materials applied onto the white dielectric layer
47
by thick film printing techniques and which respectively emit red, green and blue visible light when they are excited by ultraviolet rays generated due to the gas discharge.
The front and rear substrates
41
and
45
are arranged facing each other with a gap of 100 &mgr;m to 200 &mgr;m in between and with partition walls (not shown) in a lattice or stripe pattern being provided therebetween. The partition walls are made of a mixture of lead glass and one of magnesia oxide, titanium oxide, etc. A discharge gas, which essentially consists of a mixture of rare gases such as He (helium), Ne (neon) and Xe (xenon) gases, is filled in the gap between the front and rear substrates
41
and
45
, and the peripheral portions of those substrates are sealed by a seal member. Employing the above-described structure, discharge cells
49
are formed between the front and rear substrates
41
and
45
.
A drive method for the plasma display panel illustrated in
FIG. 9
will now be described. This type of plasma display panel is driven by a subfield drive method such as that shown in FIG.
10
. According to this drive method, a field which constitutes a single image is repeated about 50 to 70 times per second. Due to the afterimage effect, each field image displayed successively stays in the viewer's eyes, which ensures a flicker-free natural image displayed on the plasma display panel.
A field is divided into a plurality of subfields. The subfields differ from each other in the number of maintaining pulses (the number of discharge times) generated during a maintaining period which will be described later. A multi-gradation image is displayed by combining the subfields into one field. For example, in the case of displaying a 64-gradation image, a field (F) is divided into 6 subfields (SF
1
to SF
6
) as illustrated in FIG.
10
. In each of the subfields SF
1
to SF
6
, a preliminary lighting period, a preliminary erasing period and a writing period come in sequence, and a maintaining period follows. During the maintaining period, a surface discharge is caused between the scanning and maintaining electrodes
42
a
and
42
b
. The number of times the surface discharge is caused in the subfield SF
1
is 32n (n: a positive integer). This number is progressively reduced by ½ at a time in the sequence of the subfield SF
2
to the subfield SF
6
, whereby each subfield is weighted.
The drive operation of the above-described plasma display panel during one subfield period, more specifically, the discharge operation of a discharge cell
19
, will now be explained with reference to
FIGS. 11A
to
11
D illustrating the waveforms of drive voltage pulses. In
FIGS. 11A
to
11
D, reference character D represents a train of data pulses to be applied to the data electrodes
46
. Reference symbol SO denotes a train of drive voltage pulses to be applied to the 0
th
scanning electrode
42
a
. Reference symbol Sm represents a train of drive voltage pulses to be applied to the m
th
scanning electrode
42
a
. Reference character C denotes a train of drive voltage pulses to be applied to the maintaining electrodes
42
b.
In the preliminary lighting period which comes first, a preliminary discharge pulse P
P
is applied to all scanning electrodes
42
a
in order to cause a surface discharge between the electrodes
42
a
and
42
b
. In the next preliminary erasing period, pulses P
E1
, P
E2
and P
E3
are sequentially applied to the scanning and maintaining electrodes
42
a
and
42
b
in order to erase wall charges which have been generated between the electrodes
42
a
and
42
b
during the preliminary lighting period.
In the writing period, a writing pulse P
W
is applied to the selected scanning electrodes
42
a
of the plasma display panel so as to sequentially scan them. In synchronization with this, data pulses P
D
according to the display data are applied to the data electrodes
46
. By so doing, a discharge between the selected scanning electrodes
42
a
and the data electrodes
46
supplied with the predetermined data pulses P
D
is caused at the opposite surfaces of those electrodes
42
a
and
46
such that wall charges are generated in the pixels supplied with the predetermined data pulses P
D
. In the next maintaining period, maintaining pulses P
SUS
are applied to the scanning electrodes
42
a
and the maintaining electrodes
42
b
so as to be superimposed on the wall charges. By thus superimposing the maintaining pulses P
SUS
, the discharge caused during the writing period is maintained as a surface discharge between the scanning and maintaining electrodes
42
a
and
42
b.
As explained above, according to the conventional AC memory type plasma display panel, the discharge caused between the opposite surfaces of the scanning and data electrodes
42
a
and
46
is utilized to write the display data in each pixel. The scanning electrodes
42
a
are covered with a magnesia oxide film which has excellent properties as discharge proof material, while the data electrodes
46
are covered with the phosphor layers
48
.
Owing to the above structure, the potential of the scanning electrodes
42
a
is lower than that of the data electrodes
46
at the time of writing display data, as shown also in FIGS,
11
B to
Takada Hidekazu
Ueoka Mitsuo
Hjerpe Richard
NEC Corporation
Zamani Ali
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