Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-12-01
2001-09-11
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S209000, C345S060000
Reexamination Certificate
active
06288693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to flat panel display devices and, more particularly, to a method of driving a plasma display panel (PDP) among the flat panel display devices.
2. Discussion of Related Art
Generally, cells forming a pixel of PDP are discharging regions insulated by a spacer between upper layer and lower layer. These cells perform discharging by controlling voltages applied to horizontal and vertical electrodes formed on each of the upper and lower layers. An amount of discharged light is controlled according to the variation of the discharging time in the cell. The cells are arranged horizontally and vertically according to a specific size, forming the total field of PDP. The PDP displays digital video signals to a specific video field with a scanning driver and an addressing driver. That is, the addressing driver is connected to the vertical electrode, and the scanning driver is connected to the horizontal electrode. The former applies a write pulse for inputting the digital video signal and an erase pulse for stopping the cell discharged by the video signal. The latter realizes a matrix type field by applying the scan pulse for causing discharge according to the video signal and the sustain pulse for sustaining the discharge caused the scan pulse for a predetermined time to the cell on the corresponding horizontal line. To make a continuous image, the following operations are repeated: the scan and write pulses are applied to PDP at the same time in order to discharge; the field is sustained at the discharged state for a predetermined time by the sustain pulse; the field is erased by the erase pulse to display the next field. That is, the preceding discharging, sustaining and erasing operations are repeated to display the next field.
As described above, eight sub-fields are overlapped and sequentially displayed as one field by controlling the scanning and addressing drivers. The method is called sub-field driving method.
In this sub-field driving method, eight sub-fields should be sequentially concentrated to make one image. An one-bit digital image signal corresponds to each of the cells and is applied to each of the 960 lines, thereby forming one PDP sub-field having equal brightness. Therefore, when the eight sub-fields each having different brightness are collected by the digital video signals of eight bits, they make one image. Theses images continuously arranged form the moving picture. That is, the eight sub-fields are classified into sub-fields having different brightness. A first sub-field is formed of digital video signal of most significant bit (MSB), which has highest brightness among those digital signals of eight bits. Each of second through seventh sub-fields has the differentially lower brightness than the first sub-field. An eighth sub-field is made of the digital signal of least significant bits (LSB).
A method of operating these sub-fields is to display eight sub-fields having the digital signals of eight bits from first LSB to last LSB. In other words, those eight sub-fields are formed by scanning the first sub-field for the discharging time T, and another second through eight sub-fields for T/2, T/4, T/8, T/16, T/32, T/64 and T/128. In this way, a complete video field is displayed by a persistence of vision with respect to light emitted from each of the sub-field. To form the sub-field, a predetermined period of time is needed to scan all of the horizontal electrodes. Each of the cells can maintain discharging only during the predetermined period of time, that is, the average time exclusive of scanning time, the average time being allocated to each sub-field. The scanning time increases in proportion to the number of the horizontal electrodes. As one cannot maintain the discharging during the scanning time, contrast and brightness of PDP may be decreased, so that the scanning time should be reduced.
In addition, as the difference of discharging time between the upper bits and the lower bits in forming the sub-field and the sub-fields are formed sequentially, a flickering occurs due to the difference of discharging time. To reduce the flickering, it is needed to arrange the sub-field of upper bit requiring the long discharging time and the other sub-field of lower bit requiring the short discharging time in the appropriate order.
In the sub-field operating method, a gradual gray scale required for displaying image realizes the length of time in which each cell is discharged and maintained differently within the predetermined period of time ({fraction (1/30)} sec. in case of NTSC TV) given to display total image. Here, the brightness of the field is determined by the gray scale when each cell is operated maximally. To increase this brightness, the operating circuit should be designed to maximally maintain the cell discharging time with the time given for structuring one field. The contrast, the difference in tone between dark area and bright area, can be controlled by the brightness determined. To increase the contrast, it is needed to darken the background and increase the brightness. Specifically, in case of flat display panel devices for high resolution television, as the gray scale should be 256 units, the resolution should be 1280×1024 and contrast should be more than 100:1 under the light of 200 Lux, 8 bits of R. G. B. data are respectively required for the video digital signals for displaying the gray scale of 256 units, and the discharging time of the cell should be maximally maintained to gain the required brightness and contrast.
An conventional PDP operating method will be described below.
FIG. 1
is a sectional view of an surface discharged cell of AC PDP having the three electrodes typically used.
A spacer
10
maintains first and second insulting layers
1
and
2
, and insulates the gap among cells. Row electrodes are made of a scan electrode
11
and a common electrode
12
and arranged on the first insulating layer
1
in parallel.
The column electrode
4
is arranged on the second insulating substrate
2
to oppose to the row electrode, keeping a matrix shape. The first and second insulating layers
5
and
6
respectively covers the row electrode and the column electrode
4
, protecting the electrodes. As the electrodes are covered with the insulating layers, if a series voltage is applied between the electrodes to discharge, the discharging is erased instantly. In case of the PDP having the thus-structured electrodes, a parallel voltage whose polarity is continuously inverted should be applied between electrodes to maintain the discharging.
A passivation layer
7
is deposited on the second insulating layer
5
. The passivation layer
7
is typically made of thin film of MgO in order to protect the insulating layer
5
, enlarge its lifetime, increase the efficiency of emitting second electrons and reduce the variation in the discharging characteristics caused by the contamination of oxide in refractory metals.
A fluorescent layer
9
is deposited on the second insulating layer
2
including the spacer
10
, and excited by ultraviolet rays generated due to the discharging, generating visible rays of R. G. B. colors. A discharge space
8
is the cell space in which the discharging is performed. To increase the ultraviolet ray emitting efficiency, a mixture of Ar and Xe is filled in the space.
FIG. 2
shows an arrangement of the conventional AC PDP electrodes.
Each of the cells
13
is formed at the intersecting point where the column electrode intersects with the row electrode. The row electrode has scan electrode group S
1
through S
m
mainly used for scanning field, and common electrode group C
1
through C
m
mainly used for maintaining the discharging. The group of the row electrode is made of the address electrodes D
1
through D
n
used for data input.
A sealing region
14
is used for maintaining vacuum state of the entire PDP, and formed by inserting the spacer
10
between the first and second insulating layers
1
and
2
and sealing the edge of the PDP
Jung Sung Wook
Kang Bong Koo
Kim Byeong Cheol
Kim Young Hwan
Lee Nam Kyu
Alphonse Fritz
Fleshner & Kim LLP
LG Electronics Inc.
Saras Steven
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