Computer graphics processing and selective visual display system – Display driving control circuitry – Intensity or color driving control
Reexamination Certificate
1997-09-24
2001-11-27
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Intensity or color driving control
C345S063000, C345S060000
Reexamination Certificate
active
06323880
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gray scale expression method for use in a display device and, particularly, to a gray scale expression method adequate to suppress pseudo contours of moving images in displaying gray scale on a flat type display device such as plasma display panel and a gray scale display device using the same method.
In general, a plasma display panel (referred to as “PDP”, hereinafter) has many merits such as thin structure, free from flicker, large display contrast ratio, possibility of providing a relatively large screen, high response speed and possibility of multi-color emission by utilizing fluorescent material of self emission type, etc., and, recently, its use in such fields as display devices related to computer and color image display is becoming popular.
The PDP can be classified, according to an operation system thereof, to an AC discharge type in which electrodes are coated with dielectric material and are operated in an indirect AC discharging state and a DC discharge type in which electrodes are exposed in a discharge space and operated in a direct discharge state. The AC discharge type PDP is further classified, according to a drive system, to a memory operation type which utilizes a discharge cell memory and a refresh operation type which does not utilize such memory. Incidentally, light intensity of the PDP is substantially proportional to a discharge frequency, that is, a repetition frequency of pulse voltage. Since light intensity of the refresh type PDP is lowered when its display capacity becomes large, the refresh type PDP is mainly used for small display capacity.
FIG. 14
is a cross section of an example of the A.C. discharge memory operation type PDP, showing a construction of a display cell schematically. The display cell a rear insulating substrate
1
and a front insulating substrate
2
, both of which are of glass, a transparent scan electrode
3
formed on an inner surface of the front insulating substrate
2
, a transparent sustaining electrode
4
also formed on the inner surface of the front insulating substrate
2
, trace electrodes
5
and
6
formed on surfaces of the scan electrode
3
and the sustaining electrode
4
in order to reduce electrode resistances, respectively, a data electrode
7
formed on an inner surface of the rear insulating substrate
1
perpendicularly to the scan electrode
3
and the sustaining electrode
4
, a discharge gas space
8
provided between the insulating substrates
1
and
2
and filled with a discharge gas such as helium, neon or xenon or a mixture of them, partition walls
9
for maintaining the discharge gas space
8
and partitioning between display cells, a fluorescent material
11
for converting ultra-violet ray generated by a discharge of the discharge gas in the space
8
into a visible light
10
, a dielectric member
12
covering the scan electrode
3
and the sustaining electrode
4
, a protective layer
13
formed of magnesium oxide, etc., for protecting the dielectric member
12
against discharge and a dielectric member
14
covering the data electrode
7
.
A discharge operation of a selected display cell will be described with reference to FIG.
14
. When a discharge is started by applying a pulse voltage exceeding a discharge threshold value across the scan electrode
3
and the data electrode
4
, positive and negative electric charges are attracted to the respective dielectric members
12
and
14
and accumulated thereon correspondingly to the polarity of this pulse voltage. Since an internal voltage equivalent to the accumulated charge, that is, the wall voltage, has a polarity opposite to the polarity of the pulse voltage, an effective voltage within the cell is lowered with growth of discharge and it becomes impossible to sustain the discharge even when the pulse voltage is kept constant. Thus, the discharge is ultimately stopped. Thereafter, when a sustaining pulse which is a pulse voltage having the same polarity as that of the wall voltage is applied across the scan electrode
3
and the sustaining electrode
4
, it is possible to discharge even if the voltage amplitude of the sustaining pulse is small, since the wall voltage is added to the sustaining pulse voltage as an effective voltage, resulting in a drive voltage exceeding the discharge threshold value.
Therefore, it becomes possible to maintain discharge by continuously applying the sustaining pulse across the scan electrode
3
and the sustaining electrode
4
. This function is the above mentioned memory function. Further, it is possible to stop the sustaining discharge by applying a low voltage pulse having large width or an erase pulse having a small width similar to the sustaining pulse voltage across the scan electrode
3
and the sustaining electrode
4
such that the wall voltage is neutralized.
FIG. 15
shows conventional drive waveforms such as disclosed in SOCIETY FOR INFORMATION DISPLAY INTERNATIONAL SYMPOSIUM DIGEST OF TECHNICAL PAPERS VOLUME XXVI, pp807, for driving a plasma display panel having a structure such as shown in FIG.
16
.
The panel shown in
FIG. 16
is for a dot matrix display panel including j (column electrodes)×k (line electrodes). That is, the panel includes scan electrodes Sc
1
, Sc
2
, . . . , Scj and sustaining electrodes Su
1
, Su
2
, . . . , Suj arranged in parallel to the respective scan electrodes, as the column electrodes and data electrodes D
1
, D
2
, . . . , Dk arranged perpendicularly to each of the column electrodes, as the line electrodes.
In
FIG. 15
, a sustaining electrode drive waveform Wu applied commonly to the sustaining electrodes Su
1
, Su
2
, . . . , Suj, scan electrode drive waveforms Ws
1
, Ws
2
, . . . , Wsj applied to the respective scan electrodes Sc
1
, Sc
2
, . . . , Scj and a data electrode drive waveform Wd applied to the data electrode Di are shown, where 1≦i≦k. A drive period includes a preliminary discharge period A, a write discharge period B and a sustaining discharge period C and a desired image display is obtained by repeating the drive period.
The preliminary discharge period A includes a preliminary discharge pulse Pp for discharging all of the display cells of the PDP panel
15
and preliminary discharge erase pulses Pp
e
for extinguishing charges among the wall charges produced by the application of the preliminary discharge pulse, which impedes the write discharge and the sustaining discharge. In the preliminary discharge period A, active particles and the wall charges which are necessary to obtain a stable write discharge characteristics in the write discharge period B are produced in the discharge gas space.
In the sustaining discharge period C, in order to obtain desired light intensity of the display cells which are subjected to the write discharge in the write discharge period B, the discharges of the display cells are sustained.
In the preliminary discharge period A, the preliminary discharge pulse Pp is supplied to the sustaining electrodes Su
1
, Su
2
, . . . , Suj to discharge all of the display cells. Then, the erase pulses Pp
e
are applied to the scan electrodes Sc
1
, Sc
2
, . . . , Scj to produce erase discharges therein to thereby erase the wall charges accumulated by the preliminary discharge pulse.
Thereafter, in the write period B, the scan pulse Pw is applied to the scan electrodes Sc
1
, Sc
2
, . . . , Scj in line-sequence and the data pulse Pd is selectively applied to the data electrodes Di correspondingly to video display data, to produce discharges in the display cells to be displayed to thereby produce the wall charges.
Finally, in the sustaining discharge period C, the discharges of only the display cells in which the write discharges occur are sustained by the sustaining pulses Pc and Ps, completing a light emitting operation of the whole PDP panel.
A conventional sub-field display scheme for 64 gray levels, in which the scanning and sustaining drives are performed separately and which is utilized in an AC color plasma display, will be briefly described with ref
Dinh Duc Q.
Foley & Lardner
Hjerpe Richard
NEC Corporation
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