Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-09-13
2002-06-18
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S492000
Reexamination Certificate
active
06407503
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plasma display panel (PDP) and, more particularly, to a PDP of a three-electrode AC discharge type which is capable of operating in a stable state.
DESCRIPTION OF A RELATED ART
In general, a PDP has a large number of advantages of smaller thickness, lower flicker, larger contrast, larger display area, quicker response etc., and thus is expected for use as a flat panel display unit in a personal computer system or a workstation system as well as a wall television.
PDPs are categorized by the operational principle thereof into two types: a DC discharge type wherein bare electrodes are exposed to a discharge space (or discharge gas) for operation at a DC driving voltage; and an AC discharge type wherein electrodes are insulated from the discharge gas by an insulating coat for operation at an AC driving voltage. The DC discharge type is such that the discharge in the display cell continues during the period wherein the DC driving voltage is applied, whereas the AC discharge type is such that the polarities of the driving voltage are switched for maintaining the discharge. The AC discharge type PDP referred to as AC-PDP hereinafter is categorized into two types: a two-electrode type and a three-electrode type.
The structure and driving method of a conventional three-electrode AC-PDP will be described with reference to
FIG. 1
showing a display cell of the conventional PDP in cross-section.
The AC-PDP includes a front substrate
11
and a rear substrate
12
opposed to each other, a plurality of electrodes disposed on the substrates
11
and
12
, an array of display cells disposed at intersections of the electrodes. The electrodes includes a plurality of scanning electrodes
13
and a plurality of common electrodes
14
extending in parallel to one another, and a plurality of data electrodes
21
extending in parallel to one another and in perpendicular to the scanning electrodes
13
and the common electrodes
14
.
The front substrate
11
is made of a glass plate mounting thereon the scanning electrodes
13
and the common electrodes
14
at a specified pitch. A dielectric film
15
and a protective film
16
for protecting the dielectric film
15
against the electric discharge are consecutively formed on the scanning electrodes
13
and the common electrodes
14
. The rear substrate
12
is also made of a glass plate mounting thereon the data electrodes
21
, on which a white dielectric film
10
and a fluorescent film
19
are consecutively formed. A plurality of ribs
17
are formed for defining a plurality of display cells and maintaining a specified gap between the glass substrates
11
and
12
.
Each display cell defined by the ribs
17
functions as a discharge space, which is filled with a discharge gas including He, Ne and Xe, for example. The structure of the PDP is described, for example, in a literature “Society for Information Display '98 Digest” pp279-281, May 1998.
FIG. 2
shows a schematic top plan view of a general three-electrode AC-PDP, wherein a plurality of scanning electrodes S
1
, S
2
, . . . and a plurality of common electrodes C
1
, C
2
, . . . extend in a row direction, one of the scanning electrodes and one of he common electrodes forming an electrode pair, whereas a plurality data electrodes D
1
, D
2
, . . . extend in the column direction. A display cell or pixel
23
is formed at each intersection between the electrode pair and the data electrodes, a plurality of display cells
23
forming an array.
A separate driving scheme is generally used in current driving techniques for driving the AC-PDP, wherein a scanning period and a sustaining discharge period are separately provided.
FIG. 3
shows a timing chart of driving signals used in the separate driving technique.
In
FIG. 3
, a first erasing pulse
31
is applied to each scanning electrode S
1
, S
2
, . . . for erasing the previous sustaining discharge in each cell, thereby effecting an initialization of all the cells. Subsequently, a preliminary discharge pulse
32
is applied to each common electrode C
1
, C
2
, . . . for conducting a preliminary discharge in each cell. The preliminary discharge functions for allowing a write discharge in each cell to start at a lower voltage.
Thereafter, a second erasing pulse
33
for erasing the preliminary discharge is applied to each scanning electrode S
1
, S
2
, . . . to control the wall charge in each cell generated on the dielectric film by the preliminary discharge. The period from the first erasing pulse to the second erasing pulse is called herein an erasing period. In the above description, although a single pulse is applied to electrodes at each of the first erasing voltage, preliminary discharge voltage and the second erasing voltage, a pulse train including a plurality of pulses may be applied in each driving voltages for achieving an even discharge in the cell area and suppressing the fluctuation of the electric load. Each driving pulse or pulse train may be applied to other electrodes other than those described above.
Subsequently, a scanning period is conducted by supplying a scanning pulse
34
consecutively to the scanning electrodes S
1
to Sn for consecutive selection of the scanning electrodes S
1
to Sn. In synchrony with supplying the scanning pulse
34
, data pulses
35
are supplied to the data electrodes D
1
to Dn depending on the display data. In each selected data electrode, to which a data pulse is supplied, a high voltage is applied for conducting a discharge between the scanning electrode
13
and the data electrode
21
to write the cell with the display data. Thus, each of the selected cells has larger positive wall charge generated by the high voltage near the scanning electrode
13
and negative wall charge generated by the high voltage near the data electrode
21
. On the other hand, in each non-selected data electrode
21
, to which a data pulse is not supplied, a discharge is not generated without changing the wall charge in the cell. In these procedures, a display data is stored in the display cells depending on the presence or absence of the data pulse.
After the scanning pulse
34
is supplied to all the scanning electrodes S
1
to Sn, the PDP shifts into a sustaining discharge period wherein a sustaining pulse train is supplied to each electrode pair, whereby the scanning electrode and the common electrode are alternately supplied with sustaining pulses. The voltage of the pulse train is selected such that the pulse train cannot start a discharge by itself in each display cell without the wall charge generated by the write operation.
In the display cell having the larger positive wall charge, the first sustaining pulse of the pulse train having a negative polarity and supplied to the common electrode
14
applies the display cell with a voltage higher than the break-down voltage, thereby starting a sustaining discharge in association with the positive wall charge in the cell. The sustaining discharge by the first sustaining pulse stores negative wall charge near the scanning electrode
13
and positive wall charge near the common electrode
14
.
A second sustaining pulse of the pulse train supplied to the scanning electrode
13
generates another sustaining discharge in association with the wall charge as generated by the first sustaining pulse, whereby wall charge having inverse polarities is stored near the scanning electrode
13
and the common electrode
14
. Thereafter, similar sustaining discharges are generated by the alternate sustaining pulses. In this sustaining discharge period, the wall charge generated by the previous sustaining pulse is used for generating the next sustaining discharge in association with the next sustaining pulse. The number of sustaining discharges effected in a display cell determines the luminance or brightness of the display cell.
A combination of the erasing period, scanning period and sustaining discharge period as described above defines a sub-field of the PDP. In a gray-scale display scheme, a field for displayin
Day Michael H.
McGinn & Gibb PLLC
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