Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-04-18
2002-10-29
Wong, Don (Department: 2628)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S066000
Reexamination Certificate
active
06472825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for driving a plasma display panel.
2. Description of the Related Art
As a thin display device, at present, there has been placed in the market an AC discharge type plasma display panel. The plasma display panel emits light by utilizing the discharge phenomenon and assumes only two states, i.e., a light emitting state corresponding to a maximum brightness level and a non-light emitting state corresponding to a minimum brightness level. In order to obtain a display brightness of a half tone corresponding to a video signal, therefore, a gradation drive is effected for the plasma display panel based upon a sub-field method. In the sub-field method, a display period of a field is divided into N sub-fields to meet the bit digits of pixel data of N bits corresponding to the video signal. A number of times of emitting light (light emitting period) corresponding to the weighting of each bit digit of pixel data is assigned to each of the N sub-fields. The discharge cells are selected to emit light in response to the pixel data bit in each sub-field.
FIG. 1
is a diagram schematically illustrating the construction of a plasma display apparatus for gradation-driving the plasma display panel relying upon the sub-field method.
In
FIG. 1
, the plasma display panel PDP
10
includes column electrodes D
1
to D
m
of a number of m, row electrodes X
1
to X
n
of a number of n and row electrodes Y
1
to Y
n
of a number of n arranged to intersect the column electrodes. Each pair of row electrodes X and Y produce a display line on the PDP
10
. The column electrodes D and the row electrodes X and Y are covered with a dielectric layer for discharge space. A discharge cell that works as a pixel is formed at every portion where a pair of row electrodes intersect a column electrode.
A drive unit
100
gradation-drives the PDP
10
in compliance with a light emission drive format shown in FIG.
2
.
In the drive according to the light emission drive format shown in
FIG. 2
, a display period of a field is divided into six sub-fields SF
1
to SF
6
. A simultaneous resetting step Rc, a pixel data writing step Wc, a light emission-sustaining step Ic and an erasing step E are executed in each sub-field.
FIG. 3
is a timing diagram (in a sub-field) for applying drive pulses to the column electrodes and to the pairs of row electrodes in the PDP
10
by the drive unit
100
to execute the above steps.
In the simultaneous resetting step Rc, first, the drive unit
100
applies a reset pulse RP
X
of the negative polarity and a reset pulse RP
Y
of the positive polarity to the row electrodes X
1
to X
n
and Y
1
to Y
n
, simultaneously. In response to the application of these reset pulses RP
X
and RP
Y
, the discharge cells in the PDP
10
all undergo a reset discharge. At this moment, a wall charge of a predetermined quantity is formed uniformly in each discharge cell. Accordingly, every discharge cell is once initially set to be a “light emitting cell”.
Next, in the pixel data writing step Wc, the drive unit
100
, first, converts the video signal that is received into pixel data of 6 bits for each of the pixels. A first bit of the pixel data is used in the pixel data writing step Wc in a sub-field SF
1
, a second bit is used in the pixel data writing step Wc in a sub-field SF
2
, a third bit is used in the pixel data writing step Wc in a sub-field SF
3
, a fourth bit is used in the pixel data writing step Wc in a sub-field SF
4
, a fifth bit is used in the pixel data writing step Wc in a sub-field SF
5
and a sixth bit is used in the pixel data writing step Wc in a sub-field SF
6
. The drive unit
100
generates a pixel data pulse corresponding to the logic level of each bit in the pixel data, and applies it to the column electrodes D
1
to D
m
. For example, in the pixel data writing step Wc in the sub-field SF
1
, the drive unit
100
gives attention to a first bit only of the pixel data, and generates a pixel data pulse of a high voltage when the first bit has a logic level “1” and generates a pixel data pulse of a low voltage (0 bolt) when the first bit has a logic level “0”. The drive unit
100
applies pixel data pulse groups DP
1
, DP
2
, DP
3
, . . . , DP
n
to the column electrodes D
1
to D
m
successively as shown in
FIG. 3
, each of the pixel data pulse groups DP
1
, DP
2
, DP
3
, . . . , DP
n
consisting of m pixel data pulses and corresponding to each of the first to n-th display lines in the PDP
10
. The drive unit
100
further applies the scanning pulses SP of the negative polarity shown in
FIG. 3
successively to the row electrodes Y
1
to Y
n
at the same timings as the timings of applying the pixel data pulse groups DP. Here, a discharge (selectively erasing discharge) takes place in only the discharge cells at portions where the “rows” to which the scanning pulse SP is applied are intersecting the “columns” to which the pixel data pulse of a high voltage is applied, and the wall charge remaining in the discharge cells is erased. Due to the selectively erasing discharge, the discharge cells initialized to the state of “light emitting cells” in the simultaneously resetting step Rc turn into the “non-light emitting cells”. The selectively erasing discharge does not occur in the discharge cells to which the pixel data pulse of a low voltage is applied simultaneously with the application of the scanning pulse SP. Therefore, the discharge cells are maintained in a state of “light emitting cells”.
Next, in the light emission-sustaining step Ic, the drive unit
100
alternately applies the sustain pulses IP
X
and IP
Y
shown in
FIG. 3
to the row electrodes X
1
to X
n
and Y
1
to Y
n
. Here, the number of times (period) of applying the sustain pulses IP
X
and IP
Y
in each light emission-sustaining step Ic, is set depending upon the weighting of each of the sub-fields. That is, as shown in
FIG. 2
, the sustain pulses IP
X
and IP
Y
are repetitively applied numbers of times (periods) for example:
SF
1
: 1
SF
2
: 2
SF
3
: 4
SF
4
: 8
SF
5
: 16
SF
6
: 32
After the pixel data writing step Wc has been finished, only those discharge cells in which the wall charge is remaining undergo the sustain discharge, i.e., only those discharge cells in a state of “light emitting cells” undergo the sustain discharge every time when the sustain pulses IP
X
and IP
Y
are applied. Therefore, the discharge cells in the state of “light emitting cells”, emit light accompanying the discharge the above-mentioned numbers of times (periods). In the discharge cells in the state of “non-light emitting cells”, on the other hand, the above-mentioned discharge does not occur even when, for example, a sustain pulse is applied, and the discharge cells stay in the non-light emitting state.
Next, in the erasing step E, the drive unit
100
applies the erasing pulse EP shown in
FIG. 3
to the row electrodes Y
1
to Y
n
, whereby the discharge cells all undergo an erase discharge simultaneously to thereby erase the wall charge remaining in the discharge cells.
In the above gradation drive, when a video signal corresponding to, for example, a brightness level “18” (corresponding to pixel data “101101”) is fed, light is emitted in the light emission-sustaining step IC in the sub-fields SF
2
and SF
5
among the sub-fields SF
1
to SF
6
. Therefore, light is emitted a total of 18 times in a field, i.e., 2 times in SF
2
and 16 times in SF
5
, and a half brightness corresponding to the brightness “18” is seen. According to the gradation drive using the above six sub-fields SF
1
to SF
6
, therefore, a half bright display of 64 gradations can be realized in a brightness range of from a brightness level “0” to brightness level “63”.
According to the sub-field method, the number of gradations increase with an increase in the number of the sub-fields, and a picture is displayed in a higher quality. Further, the display is obtained in a higher brightness if the number of times of emitting light is increased in the light emission-sust
Honda Hirofumi
Nagakubo Tetsuro
Shigeta Tetsuya
Minh D A
Pioneer Corporation
Sughrue & Mion, PLLC
Wong Don
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