Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-03-17
2001-09-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S060000, C345S063000, C345S055000, C315S169400
Reexamination Certificate
active
06288495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving voltage control system for a plasma display panel, and more particularly to a plasma display panel driving apparatus wherein selective discharging of cells is performed in an optimum state to display an image in an optimum voltage condition.
2. Description of the Related Art
Normally, a plasma display panel of the type mentioned performs selective discharge and light emission of pixels making use of a characteristic that there is a difference between a discharge starting voltage and a discharge maintaining voltage of gas filled between two glass plates.
For example, if a certain cell is selected so as to emit light, discharging for writing is performed for the cell in advance so that charge called wall charge is stored in a wall in the inside of the cell.
On the other hand, if a cell is selected so as not to emit light, discharging for writing is not performed, and consequently, wall charge is not accumulated.
After, from among cells of all of pixels of a plasma display panel, those cells which are to emit light depending upon presence of wall charge are selected in this manner, a discharge maintaining pulse is applied at a time to all cells.
Generally, since discharge gas used for a plasma display panel has a discharge starting voltage set higher than its discharge maintaining voltage as seen in
FIG. 1
, to those cells which have wall charge because a discharge maintaining pulse has been applied thereto, that is, to those cells with which writing discharging has been performed in advance, a voltage corresponding to the wall charge is applied in addition to the discharge maintaining voltage. Consequently, those cells begin to discharge and emit light.
However, those cells to which no wall charge has been given cannot enter a light emitting state only with the discharge maintaining voltage.
While light emission control of a plasma display panel conventionally makes use of presence or absence of wall charge and a difference between a discharge maintaining voltage and a discharge starting voltage in this manner, it is sometimes difficult to control all cells in an optimum state against a secular change or a temperature variation.
An exemplary one of conventional driving apparatus for a plasma display panel is shown in FIG.
5
. Referring to
FIG. 5
, the driving apparatus for a plasma display panel shown includes a scanning electrode driver
16
, a write electrode driver
11
and a common electrode driver
12
for a main scanning electrode set
50
, a write electrode set
51
and a common electrode set
52
of a plasma display panel PDP, respectively. The scanning electrode set
16
includes a pulse generator
13
for generating various pulse signals, a maintaining pulse generator
14
for generating a maintaining pulse signal, and a switching circuit
15
for selectively outputting one of an output pulse signal of the pulse generator
13
and the maintaining pulse signal from the maintaining pulse generator
14
. The scanning electrode set
50
is driven by a maintaining voltage (Vs) power supply
2
and drives the scanning electrode set
50
in accordance with the pulse signal selected by the switching circuit
15
. Meanwhile, the write electrode driver
11
is driven by a discharging voltage (Vd) power supply
5
and drives the write electrode set
51
in accordance with a normal signal (normal image signal) originated from a normal signal inputting section
6
and processed by a signal processing circuit
10
.
Consequently, depending upon a cell, if such a phenomenon occurs that, although wall charge is not formed therein, the cell discharges when only the discharge maintaining voltage is applied thereto, or although the cell has wall charge and must emit light, discharge and emission of light does not occur, this cannot be observed. In this instance, it is normally the actual state of things that it is confirmed through visual observation if those cells in the screen which should emit light do not emit light or if those cells which should not emit light emit light, and the setting of the discharge maintaining voltage or the writing voltage is adjusted manually.
Therefore, where it is necessary to adjust the discharge maintaining voltage or the writing voltage in accordance with the necessity upon manufacture of the product or when the situation of a discharging phenomenon varies because of a secular change or from some other reason, the adjustment operation is cumbersome and besides requires long time.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a plasma display panel driving apparatus which achieves equation of adjustment operation and reduction of the adjustment time to reduce the number of steps of adjustment upon manufacture of the product and is easy to maintain the display quality when a secular change occurs with the product.
In order to attain the object described above, according to the present invention, confirmation of those cells which should emit light and those cells which should not emit light is automatically performed making use of discharge current and adjustment of a discharge maintaining voltage or a writing voltage is performed automatically.
More particularly, according to the present invention, there is provided a driving apparatus for a plasma display panel wherein discharging gas is filled and enclosed between two glass plates and a plurality of scanning electrodes are provided in a horizontal direction while a plurality of write electrodes are provided in a vertical direction on inner faces of the glass plates and wherein a voltage is selectively applied between the electrodes to cause cells defined by the scanning electrodes and the write electrodes to discharge and emit light, comprising discharging situation detection means for detecting a variation of a state of each of the cells which has an influence on a display quality such as a temperature, an elapsed time or the like of the cell, and control means for calculating an optimum driving voltage for the scanning electrode or the write electrode of the cell in response to the discharging situation of the cell detected by the discharging situation detection means and causing the optimum driving voltage to be applied to the scanning electrode or the write electrode of the cell to cause the cell to discharge.
Where the discharging situation detection means varies a discharge voltage for light emission of the scanning electrode to detect the light emitting discharging situation, the control means may calculate an optimum voltage necessary to drive the scanning electrode and apply the optimum voltage to the scanning electrode. In this instance, the discharging situation detection means may include a current detection circuit for detecting current to flow to the scanning electrode and an integration circuit for integrating the detection current of the current detection circuit, and the control means may include a microcomputer which calculates the optimum voltage necessary to drive the scanning electrode from an output of the integration circuit and controls a voltage of a power supply for the scanning electrode.
Alternatively, where the discharging situation detection means varies a discharge voltage for the write electrode to detect the light emitting discharging situation, the control means may calculate an optimum voltage necessary to drive the write electrode and applies the optimum voltage to the write electrode. In this instance, the discharging situation detection means may include a current detection circuit for detecting current to flow to the scanning electrode and an integration circuit for integrating the detection current of the current detection circuit, and the control means may include a signal switching circuit for first inputting an all-black signal and then inputting an all-white signal as a testing signal for detection of the discharging situation to a driver for the write electrode, and a microcomputer for calculating an optimum voltage necessary to d
NEC Corporation
Vo Tuyet T.
Wong Don
Young & Thompson
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