Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-12-01
2001-03-27
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C345S068000, C345S090000
Reexamination Certificate
active
06208084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device comprising a display panel using ac discharge.
2. Description of the Background Art
As a conventional display panel using ac discharge, an ac plasma display panel (hereinafter referred to as a “PDP”) has been well known. The ac PDP includes a two-electrode opposite discharge type and a three-electrode surface discharge type. We will first describe the two-electrode opposite discharge type.
FIG. 17
is an exploded perspective view showing the structure of a conventional ac PDP, which is described for example in Owaki et. al., “Plasma Display”, Kyoritsu Publishing, p. 21 (hereinafter referred to as a “reference 1”). A conventional ac PDP
1
is produced by bonding two glass substrates
2
on which various members are formed. The two glass substrates
2
are provided in parallel with a predetermined gap therebetween. Assuming that the surface of the glass substrate
2
on the gap side is the inner surface and the surface on the opposite side is the outer surface, sealing glass
6
is formed on the inner periphery of the inner surface of the glass substrate
2
. A gap surrounded by the sealing glass
6
is sealed and filled with discharge gas. Hereinafter the glass substrate
2
closer to a display viewer is referred to as a front glass substrate
2
and the other as a rear glass substrate
2
. Strip electrodes
3
a
on the inner surface of the front glass substrate
2
are usually transparent electrodes. This is for the purpose of admitting light, which is produced in the gap between the two glass substrates
2
, to the front through the front glass substrate
2
. On the inner surface of the rear glass substrate
2
, strip electrodes
3
b
are formed which are orthogonal to the electrodes
3
a
when the glass substrate
2
is seen through from the front. The strip electrodes
3
a
formed in an area surrounded by the sealing glass
6
on the front glass substrate
2
are covered with a dielectric layer
4
, which is then covered with a protective layer
5
. Similarly, the rear glass substrate
2
is provided with a dielectric layer
4
which covers the electrodes
3
b
and a protective layer
5
which covers the dielectric layer
4
.
For monochrome display using emitted colors of discharge gas itself, discharge is induced at the intersections of the strip electrodes
3
a
,
3
b
in the above structure. Color display, on the other hand, requires additional three kinds of phosphors which emit red, green, and blue lights, respectively, depending on the light (e.g., ultraviolet ray) produced by discharge, besides the above structure. For color display, each intersection of the electrodes
3
a
,
3
b
is coated with a phosphor of one color and three emitted colors of adjacent phosphors are mixed to be a point (pixel) representing various colors. The combination of such points allows acquisition of any desired image in color display.
Now, we will describe the driving principle of a conventional two-electrode opposite discharge type ac PDP.
FIG. 18
shows variations in the voltage across electrodes, variations in the wall voltage, and the waveform of light emission, all in the two-electrode opposite discharge type ac PDP. These waveforms are disclosed for example in the above reference 1. The wall voltage is a voltage generated by charge accumulated on the walls of discharge cells. The voltage waveform across electrodes varies with three periods, i.e., address period (writing), sustained discharge period (sustaining), and reset period (erasing), even in one cycle of a driving sequence. The amplitude baselines of a write pulse WPu, a sustain voltage pulse SPu, and an erase pulse EPu in the address, sustain discharge, and reset periods, respectively, are 0V. The write pulse WPu has a write voltage Vwr larger than a firing voltage Vf in amplitude. The sustain voltage pulse SPu has a sustain voltage Vs larger than a discharge sustain voltage Vsm in amplitude. The erase pulse EPu has an erase voltage Ve in amplitude.
With the wall voltage brought to 0V by the erase pulse, a driving sequence starts with no discharge and no light emission. When the write pulse WPu larger in amplitude than the sustain voltage pulse SPu is applied across the electrodes
3
a
,
3
b
, discharge occurs in cells, which produces light. Then, charge is transferred to the surface of the dielectric layer
4
which covers the electrodes
3
a
,
3
b
, This causes charge-up and a reverse voltage in the cells, thus stopping discharge. At this time, the accumulated charge on the surface of the dielectric layer
4
generates a wall voltage Vw. In cells where no write pulse WPu is applied and no write discharge occurs, the wall voltage Vw does not appear.
After the address period, a sustain voltage pulse HPu (−Vs), opposite in polarity from the write pulse WPu, is applied across the electrodes
3
a
,
3
b
. This generates a voltage equal to a sum of the wall voltage Vw and the sustain voltage Vs from the outside, in the discharge cells. The reference Vw indicates the value of the wall voltage as well as the wall voltage itself. The resultant voltage (|Vw|+|Vs|) is large enough to induce discharge, so discharge occurs again to produce light. At this time, a wall voltage Vw, opposite in polarity from that in writing, is developed in the discharge cells.
Further, a sustain voltage pulse SPu (Vs), opposite in polarity from that before a half cycle, is applied across the electrodes
3
a
,
3
b
. This generates a voltage equal to the sum of the wall voltage Vw and the sustain voltage Vs (|Vw|+|Vs|), whereby discharge occurs again. During the sustain discharge period, every application of the sustain voltage pulse SPu generates a potential of |Vw|+|Vs| and discharge is repeated. The discharge repeated during the sustain discharge period is referred to as “sustain discharge”. The sustain discharge stops when the wall voltage Vw becomes almost 0 V due to weak discharge caused by the erase pulse EPu in the discharge cells. The erase pulse EPu includes two types: wide and low-voltage type which is large in width and small in amplitude; and narrow and high-voltage type which is small in width and large in amplitude. Here, high/low in the voltage indicates that the voltage is higher or lower than the sustain voltage Vs, respectively. The former type is the driving condition of the aforementioned two-electrode opposite discharge type ac PDP, and the latter type is the driving condition of a three-electrode surface discharge type ac PDP which will be described later.
It is found from the above description that it is important to erase the wall voltage down to 0V in all discharge cells before the address (write) discharge in the conventional display panels. If the wall voltage Vw in the discharge cells before the address discharge is not 0 V, undesirable discharge may occur in the unselected cells or necessary discharge may not occur in the selected cells. This insufficient erasing is one of the big factors behind reduction in the driving margin.
Now, we will describe a conventional driving principle of a three-electrode surface discharge type ac PDP.
FIG. 19
shows voltage waveforms across electrodes to explain how to drive the PDP, which is described for example in Japanese Patent Laid-open No. P07-160218A. As shown, voltages of different waveforms are applied to three types of electrodes to drive a PDP. The three types of electrodes include column electrodes Wj, row electrodes Yk, and a common row electrode X, where the subscripts j, k are natural numbers indicating the sequences of the column electrodes W and the row electrodes Y. The driving principle of the three-electrode surface discharge type ac PDP is identical to that of the aforementioned two-electrode opposite discharge type ac PDP, so it can be applied to the two-electrode opposite discharge type ac PDP without problems. Under the present circumstances, the three-electro
Hashimoto Takashi
Iwata Akihiko
Urakabe Takahiro
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Philogene Haissa
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