Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-05-12
2003-08-19
Hjerpe, Richard (Department: 2778)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S066000
Reexamination Certificate
active
06608609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology for driving a display panel constituted by a group of memory cells having a memory function as display elements. More particularly, the present invention relates to a method for driving a plasma display panel, which is directed to reducing background light emission of an alternating current (AC) type plasma display panel. (Generally, a plasma display apparatus, inclusive of the plasma display panel is referred to as a “PDP”.)
The AC type plasma display panel, of this kind sustains discharges and carries out light emission display by alternately applying voltage waveforms of a plurality of pulses to two electrodes for sustaining this discharge (i.e., sustain electrodes). A discharge (lighting) operation for every discharge period finishes within a few micro-seconds (is) after the application of pulses. Ions defined as positive charges that are generated by this discharge are accumulated over an insulating layer on the electrode to which a negative voltage is applied. Similarly, electrons as negative charges are accumulated over an insulating layer on the electrode to which a positive voltage is applied.
Therefore, when wall charges are generated by causing the discharges by the pulses, (write pulses) each having a relatively high voltage, (write voltage) and then the pulses (sustain discharge pulses, that is, “sustain pulses”), each having a voltage lower than that of each of the write pulses (sustain discharge voltage) and an opposite polarity to each of the write pulses, are applied to the electrodes, electric charges generated by the sustain pulses are superimposed on the wall charges previously accumulated by the write pulses so as to enhance the accumulated wall charges.* As a result, the potential of the wall charges with respect to a discharge space becomes large and, eventually the above voltage exceeds a discharge threshold voltage at which the discharge starts. In other words, given cells that once executed the write discharge and have formed the wall charges have characteristics such that of these cells sustain the discharge when the sustain discharge pulses are alternately applied thereto in the opposite polarities. A phenomenon having the above characteristics is referred to as a “memory effect”or “memory drive”. The AC type plasma display panel carries out display by utilizing this memory effect.
2. Description of the Related Art
The AC type plasma display panels can be Hi . *classified into a two-electrode type which executes selective discharge. (i.e., selective address discharge) and sustain discharge by two electrodes, and a three electrode type which executes the addressing discharge by Utilizing a third-electrode. In color plasma display panels for effecting multi-gradation display., a phosphor inside the cell is excited by ultra-violet rays generated by the discharge between different kinds of electrodes, but this phosphor involves the problem that it is extremely fragile against the impact of the ions defined as the positive charges that are generated simultaneously by the discharge (that is, the phosphor is sensitive to the impact of the ions). Since the former two-electrode type plasma display panel described above employs the construction in which the ions are allowed to-collide directly with the phosphor, the life of the phosphor is likely to become shorter. To avoid this problem, the latter three-electrode type plasma display panel utilizing a surface discharge (that is, a surface discharge type plasma display panel which is carried out between, different electrodes that are located in the same plane), has been used generally in the color plasma display panels.
Here, in order to enable the problems of the driving method of the plasma display panel, according to the prior art systems, to be more easily understood, the construction of a conventional plasma display panel and its driving method will be explained with reference to
FIGS. 1
to
3
of the later-appearing “Brief Description of the Drawings”.
An AC type color plasma display panel which is a three-electrode and a surface discharge type, such as the one shown in a schematic plan view of
FIG. 1
, has been known in the past., In
FIG. 2
, a schematic sectional view of cells shown in
FIG. 1
in a horizontal direction is illustrated.
A panel
1
comprises two glass substrates (that is, a front glass substrate
8
and a back glass substrate
9
). The front glass substrate
8
defined as the first glass substrate includes first and second electrodes (X electrodes
2
, Y electrodes
3
-
1
to
3
-N (where N is an arbitrary positive integer of 2 or more than 2)), which are both defined as parallel sustain electrodes. Each of these electrodes comprises a transparent electrode
14
and a bus electrode
13
.. The transparent electrode
14
is made of an ITO (a transparent conductive film consisting of indium oxide as the main component), etc., because it has a role of transmitting the reflected rays of light from the phosphor
12
. The bus electrode
13
must be fabricated with a low resistance value so as to prevent a voltage drop due to the resistance of these electrodes, and is usually made of Cr or Cu. These electrodes are covered with a dielectric layer (e.g., glass)
10
, and a MgO (magnesium oxide) film
11
is formed as a protective film on the discharge surface. Third electrodes (addressing electrodes A
1
to AM (where M is an arbitrary positive integer of 2 or more than 2) are formed on the back glass substrate
9
defined as the second glass substrate opposing the first glass substrate in such a manner as to orthogonally cross the sustain electrodes. The addressing electrodes A
1
to AM are covered with the dielectric layer
10
to form barriers
6
thereon, and phosphors
12
having red, green and blue light emission characteristics are formed between the barriers
6
. The two glass substrates are assembled in such a manner that the portions of ridges of the barriers
6
are in close contact with the surface of the MgO film
11
.
The selective address discharge for selecting cells
5
is executed by selecting the addressing electrodes and the Y electrodes. The sustain discharge is effected between the X electrode and the Y electrode. In the panel
1
having such a construction, the sustain discharge is effected in narrower gaps between the adjacent sustain electrodes (which gaps are referred to as “discharge slits”) but is not effected in the broader gaps between the adjacent sustain electrodes (which-are referred to as. “opposite slits”).
The sustain electrodes are arranged on the entire surface:in the sequence of the X electrode
2
of the first display line, the Y electrode
3
-
1
of the first display line, the X electrode
2
of the second display line, the Y electrode
3
-
2
of the second display line, the X electrode
2
of the third display line, the Y electrode
3
—
3
of the third display line, and so forth.
In
FIG. 3
, a timing chart useful for explaining the method for driving the plasma display panel according to the prior art when the-plasma display driving apparatus described above or the like is used, is illustrated.
The timing chart of
FIG. 3
shows typically the configuration of frames necessary for forming the display screen of the plasma display panel and voltage waveforms of various driving voltage pulses for each of the electrodes. Generally, each frame is divided into a plurality of subframes for effecting multi-gradation display by setting mutually different light emission periods (strictly speaking, sustain discharge periods). Each of these subframes includes an initialization period (reset period) of the wall charges, an addressing period (abbreviated to “addr. period” in
FIG. 3
) for executing selective write discharge (that is, selective address discharge) of display data for the selected cell after the execution of the reset period, and a sustain discharge period (abbreviated to “sust. discharge period” in
FIG. 3
) for repeatedly executing light emission disp
Asao Shigeharu
Kanazawa Yoshikazu
Setoguchi Noriaki
Fujitsu Limited
Hjerpe Richard
Nguyen Kevin M.
Staas & Halsey , LLP
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