Patent Grant
8212746
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP2008/000931.
The present invention relates to a driving method of a plasma display panel that is used in a wall-hanging television (TV) or a large monitor.
A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has a plurality of display electrode pairs each of which is formed of a pair of scan electrode and sustain electrode. The back plate has a plurality of parallel data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in the discharge cells. The ultraviolet rays excite respective phosphor layers of red, green, and blue to emit light, and thus provide color display.
A subfield method is generally used as a method of driving the panel. In this method, one field period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display. Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge occurs, and a wall charge required for a subsequent address operation is formed. In the address period, address discharge is selectively caused in a discharge cell where display is to be performed, thereby forming a wall charge. In the sustain period, a sustain pulse is alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustain discharge is caused, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
Of the subfield method, a new driving method is disclosed where light emission that is not related to gradation display is minimized and the contrast ratio is improved (patent document 1, for example). In this driving method, the initializing discharge is performed using a gradually varying voltage waveform, and the initializing discharge is selectively applied to the discharge cell having performed sustain discharge.
The screen size and definition of the panel have been recently increased, and the discharge cells have been further fined. As the discharge cells are fined, it becomes difficult to control the wall charge of the discharge cells, and an operation failure, such as a failure that address discharge does not occur in the discharge cell where an address operation is to be performed, occurs, and the image display quality can be reduced.
[Patent document 1] Japanese Patent Unexamined Publication No. 2000-242224
The present invention provides a driving method of the panel in order to address the above-mentioned problems. This driving method uses a panel having a plurality of discharge cells. Each discharge cell has a data electrode and a display electrode pair that is formed of a scan electrode and a sustain electrode. In the driving method, one field period is formed by arranging a plurality of subfields. Each of the subfields has the following periods:
Thus, a driving method of the panel can be provided that allows high-quality image display without causing an operation failure even when a high-definition panel is used.
A plasma display device in accordance with an exemplary embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.
(Exemplary Embodiment)
Front substrate 21 and back substrate 31 are faced to each other so that display electrode pairs 24 cross data electrodes 32 with a minute discharge space sandwiched between them. The outer peripheries of front substrate 21 and back substrate 31 are sealed by a sealing material such as glass frit. The discharge space is filled with discharge gas, for example, mixed gas of neon and xenon. Here, the xenon partial pressure is set at 10%, for example. The discharge space is partitioned into a plurality of sections by barrier ribs 34. Discharge cells are formed in the intersecting parts of display electrode pairs 24 and data electrodes 32. The discharge cells discharge and emit light to display an image.
The structure of panel 10 is not limited to the above-mentioned one, but may be a structure having striped barrier ribs, for example.
Image signal processing circuit 51 converts an input image signal into image data that indicates emission or non-emission of light in each subfield. Data electrode driving circuit 52 converts the image data of each subfield into a signal corresponding to each of data electrodes D1 through Dm, and drives each of data electrodes D1 through Dm.
Timing generating circuit 55 generates various timing signals for controlling the operation of each circuit block based on a horizontal synchronizing signal and a vertical synchronizing signal, and supplies them to respective circuits. Scan electrode driving circuit 53 drives each of scan electrodes 22 based on the timing signal. Sustain electrode driving circuit 54 drives sustain electrodes 23 based on the timing signal.
Next, a driving voltage waveform for driving panel 10 and its operation are described. Plasma display device 100 performs gradation display by a subfield method. In this method, one field period is divided into a plurality of subfields, and emission and non-emission of light of each discharge cell are controlled in each subfield. Each subfield has an initializing period, an address period, and a sustain period.
In the initializing period, initializing discharge is performed to form, on each electrode, a wall charge required for a subsequent address discharge. In the initializing period, a priming (excitation particle as a detonating agent for discharge) for reducing discharge delay and stably causing address discharge is generated. The initializing operation at this time includes an all-cell initializing operation and a selection initializing operation. In the address period, address discharge is caused in a discharge cell to emit light, thereby forming a wall charge. In the sustain period, as many sustain pulses as the number corresponding to luminance weight are alternately applied to display electrode pairs 24, and sustain discharge is caused in the discharge cell having caused address discharge, thereby emitting light.
Details on the subfield structure are described later. A driving voltage waveform to be applied to each electrode is firstly described.
In the first half of the initializing period, voltage Vw is applied to data electrodes D1 through Dm, and voltage 0 (V) is applied to sustain electrodes SU1 through SUn. A gradually increasing ramp waveform voltage is applied to scan electrodes SC1 through SCn. Here, the ramp waveform voltage gradually increases from voltage Vi1, which is not higher than a discharge start voltage, to voltage Vi2, which is higher than the discharge start voltage, with respect to scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn. The gradient of the ramp waveform voltage is set at 1.3 V/μsec, for example. While this ramp waveform voltage increases, feeble initializing discharge occurs between scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn, and feeble initializing discharge occurs between scan electrodes SC1 through SCn and data electrodes D1 through Dm. Negative wall voltage is accumulated on scan electrodes SC1 through SCn, and positive wall voltage is accumulated on data electrodes D1 through Dm and sustain electrodes SU1 through SUn. Here, the wall voltage on the electrodes means the voltage generated by the wall charges accumulated on the dielectric layer covering the electrodes, the protective layer, and the phosphor layer.
In the last half of the initializing period, voltage 0 (V) is applied to data electrodes D1 through Dm, and positive voltage Ve1 is applied to sustain electrodes SU1 through SUn. A gradually decreasing ramp waveform voltage is applied to scan electrodes SC1 through SCn. Here, the ramp waveform voltage gradually decreases from voltage Vi3, at which the voltage difference between scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn is not higher than the discharge start voltage, to voltage Vi4, at which the voltage difference is higher than the discharge start voltage. While the ramp waveform voltage decreases, feeble initializing discharge occurs between scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn, and feeble initializing discharge occurs between scan electrodes SC1 through SCn and data electrodes D1 through Dm. Then, the negative wall voltage on scan electrodes SC1 through SCn and the positive wall voltage on sustain electrodes SU1 through SUn are reduced, positive wall voltage on data electrodes D1 through Dm is adjusted to a value suitable for the address operation. Thus, the all-cell initializing operation in which the initializing discharge is carried out in all discharge cells is completed.
In an odd period of the subsequent address period, voltage Ve2 is applied to sustain electrodes SU1 through SUn, second voltage Vs2 is applied to each of odd-numbered scan electrode SC1, scan electrode SC3, . . . , and scan electrode SCn−1, and fourth voltage Vs4 is applied to each of even-numbered scan electrode SC2, scan electrode SC4, . . . , and scan electrode SCn. Here, fourth voltage Vs4 is higher than second voltage Vs2.
Next, scan pulse voltage Vad is applied in order to apply a negative scan pulse to first scan electrode SC1. Positive address pulse voltage Vw is applied to data electrode Dk (k is 1 through m), of data electrodes D1 through Dm, in the discharge cell to emit light in the first column. At this time, in the present embodiment, third voltage Vs3 lower than fourth voltage Vs4 is applied to a scan electrode adjacent to scan electrode SC1, namely second scan electrode SC2. This prevents excessive voltage difference from being applied between adjacent scan electrode SC1 and second scan electrode SC2.
The voltage difference in the intersecting part of data electrode Dk of the discharge cell to which address pulse voltage Vw is applied and scan electrode SC1 is obtained by adding the difference between the wall voltage on data electrode Dk and that on scan electrode SCI to the difference (Vw−Vad) of the external applied voltage. The obtained voltage difference exceeds the discharge start voltage. Address discharge occurs between data electrode Dk and scan electrode SC1 and between sustain electrode SU1 and scan electrode SC1. Positive wall voltage is accumulated on scan electrode SC1, negative wall voltage is accumulated on sustain electrode SU1, and negative wall voltage is also accumulated on data electrode Dk. Thus, an address operation is performed that causes address discharge in the discharge cell to emit light in the first column and accumulates wall voltage on each electrode. The voltage in the intersecting parts of scan electrode SC1 and data electrodes D1 through Dm to which address pulse voltage Vw is not applied does not exceed the discharge start voltage, so that address discharge does not occur.
Regarding odd-numbered scan electrode SC3, scan electrode SC5, . . . , and scan electrode SCn−1, an address operation is performed similarly. Third voltage Vs3 is also applied to even-numbered scan electrode SCp (p is even number, 1<p<n) and scan electrode SCp+2 that are adjacent to the odd-numbered scan electrode SCp+1 where the address operation is performed at this time.
In a subsequent even period, second voltage Vs2 is applied to even-numbered scan electrode SC2, scan electrode SC4, . . . , and scan electrode SCn while second voltage Vs2 is applied to odd-numbered scan electrode SC1, scan electrode SC3, . . . , and scan electrode SCn−1.
Next, scan pulse voltage Vad is applied in order to apply a negative scan pulse to second scan electrode SC2. Positive address pulse voltage Vw is applied to data electrode Dk, of data electrodes D1 through Dm, in the discharge cell to emit light in the second column. The voltage difference in the intersecting part of data electrode Dk of the discharge cell and scan electrode SC2 exceeds the discharge start voltage, and causes address discharge in the discharge cell to emit light in the second column, thereby performing an address operation of accumulating wall voltage on each electrode.
Regarding even-numbered scan electrode SC4, scan electrode SC6, . . . , and scan electrode SCn, an address operation is performed similarly.
In the subsequent sustain period, positive sustain pulse voltage Vm is firstly applied to scan electrodes SC1 through SCn, and voltage 0 (V) is applied to sustain electrodes SU1 through SUn. In the discharge cell having caused the address discharge, the voltage difference between scan electrode SCi and sustain electrode SUi is obtained by adding the difference between the wall voltage on scan electrode SCi and that on sustain electrode SUi to sustain pulse voltage Vm. The obtained voltage difference exceeds the discharge start voltage. Sustain discharge occurs between scan electrode SCi and sustain electrode SUi, and ultraviolet rays generated at this time cause phosphor layer 35 to emit light. Negative wall voltage is accumulated on scan electrode SCi, and positive wall voltage is accumulated on sustain electrode SUi. Positive wall voltage is also accumulated on data electrode Dk. In the discharge cell where address discharge does not occur in the address period, sustain discharge does not occur, and the wall voltage at the completion of the initializing period is kept.
Subsequently, voltage 0 (V) is applied to scan electrodes SC1 through SCn, and sustain pulse voltage Vm is applied to sustain electrodes SU1 through SUn. In the discharge cell having caused the sustain discharge, the voltage difference between sustain electrode SUi and scan electrode SCi exceeds the discharge start voltage. Therefore, sustain discharge occurs between sustain electrode SUi and scan electrode SCi again. Negative wall voltage is accumulated on sustain electrode SUi, and positive wall voltage is accumulated on scan electrode SCi. Hereinafter, similarly, as many sustain pulses as the number corresponding to the luminance weight are alternately applied to scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn, and potential difference is caused between the electrodes of display electrode pairs 24. Thus, sustain discharge occurs continuously in the discharge cell that has caused the address discharge in the address period.
At the end of the sustain period, ramp waveform voltage gradually increases to voltage Vr that is equal to sustain pulse voltage Vm or higher than Vm is applied to scan electrodes SC1 through SCn. While the positive wall voltage is kept on data electrode Dk, wall voltages on scan electrode SCi and sustain electrode SUi are reduced. The gradient of the ramp waveform voltage is preferably set at 2 V/μsec-20 V/μsec, and is set at 10 V/μsec, for example. Thus, the sustain operation in the sustain period is completed.
In the initializing period of the second SF in which the selection initializing operation is performed, voltage Ve1 is applied to sustain electrodes SU1 through SUn, voltage 0 (V) is applied to data electrodes D1 through Dm, and a ramp waveform voltage gradually decreasing to voltage Vi4 is applied to scan electrodes SC1 through SCn. Thus, in the discharge cell that has caused the sustain discharge in the sustain period of the preceding subfield, feeble initializing discharge occurs, and the wall voltage on scan electrode SCi and sustain electrode SUi is reduced. Regarding data electrode Dk, sufficient positive wall voltage is accumulated on data electrode Dk by the immediately preceding sustain discharge, so that the wall voltage is discharged by the excessive amount and is adjusted to a wall voltage appropriate for the address operation. While, in the discharge cell that has not caused the sustain discharge in the preceding subfield, discharge is not performed and the wall charge at the completion of the initializing period of the preceding subfield is kept. Such selection initializing operation is an operation of selectively performing the initializing discharge in the discharge cell where a sustain operation is performed in the sustain period of the immediately preceding subfield.
The operation in the subsequent address period is similar to that in the address period of the first SF, so that the description of it is omitted. The operation in the subsequent sustain period is similar to that in the sustain period of the first SF except for the number of sustain pulses.
Next, the subfield structure of a plasma display device of the present exemplary embodiment is described.
In the subfield structure of the present embodiment, first SF through seventh SF belong to a first subfield group, eighth SF through 12th SF belong to a second subfield group, and the subfields are arranged in each subfield group so that the luminance weights of the subfields monotonically increase. In other words, the luminance weights of first SF through seventh SF monotonically increase, the luminance weight of eighth SF decreases, and the luminance weights of eighth SF through 12th SF monotonically increase. Such an arranging method is effective in suppressing occurrence of flicker in an image signal of low field frequency, for example, in an image signal of a PAL (Phase Alternation by Line) method.
A holding period when discharge is not caused is disposed before the head subfield belonging to the second subfield group. The all-cell initializing operation is performed in the initializing period of the first SF, and the selection initializing operation is performed in the initializing period of the second SF through 12th SF.
Next, a display method of the gradation of the present embodiment is described.
In the present embodiment, as shown in
Next, the reason for this is described. Generally, occurrence of discharge generates positive and negative charged particles in discharge space. When the charged particles adhere to a wall of a discharge cell, the wall voltage is varied, the electric field strength inside the discharge space is varied to affect the discharge phenomenon. For example, when address discharge occurs in a discharge cell adjacent to the discharge cell where an address operation is not performed, a charged particle generated at this time can fly to the discharge cell where an address operation is not performed, and can reduce the wall voltage. This phenomenon is referred to as “charge drop off phenomenon”. When the positive wall voltage on the data electrode required for the address operation excessively decreases, an operation failure that further address operation cannot be performed occurs, and the image display quality can be reduced.
The inventors experimentally verify that a charge drop off phenomenon is apt to occur in the address period after the all-cell initializing operation. Here, in the all-cell initializing operation, initializing discharge is generated by applying high voltage to all discharge cells. The sustain discharge is not caused in the subfield of a large luminance weight of the first subfield group in the discharge cell showing not so large gradation, so that the priming decreases in the head subfield of the second subfield group and the address margin decreases. Therefore, the charge drop off phenomenon is apt to occur also in the head subfield of the second subfield group. In addition, firstly, a gradually increasing ramp waveform voltage is applied to the scan electrode at the end of the sustain period. Secondly, the selection initializing operation of applying a gradually decreasing ramp waveform voltage is performed to a scan electrode. Finally it is experimentally verified that charge drop off phenomenon hardly occurs in the address period.
It is verified that the charge drop off phenomenon is apt to occur as the definition of the panel increases. That is considered to be because the size of the discharge cells is small and the amount of wall charge defining the wall voltage is also small in the high-definition panel, and hence the wall voltage significantly decreases even when the wall charge amount decreases slightly.
According to the coding of the present embodiment, when the address operation has not been performed in the head subfield of each subfield group, the address operation is not performed either in the subfield following the head subfield of the subfield group. Therefore, even when the wall voltage of the discharge cell where the address operation has not been performed in head address period of the subfield group decreases, the address operation is not performed in the subsequent subfield and hence the display image is not affected.
According to the coding of
In the present embodiment, a holding period where discharge is not caused is disposed before the eighth SF as the head subfield of the second subfield group.
According to the measurement result, amplitude Vscn of the scan pulse can be reduced by extending holding duration Ts. Specifically, as holding duration Ts is extended in the range of 0 μs to 300 μs, amplitude Vscn of the scan pulse can be reduced. However, even when holding duration Ts is extended beyond 400 μs, amplitude Vscn of the scan pulse can be hardly reduced. Therefore, it is preferable that holding duration Ts is set at 300 μs or longer. In the present embodiment, holding duration Ts is set at 400 μs. However, preferably, holding duration Ts is set appropriately in response to the discharge characteristic of the panel.
The reason why the selection initializing operation is stabilized by setting holding duration Ts in this manner is not completely understood, but can be considered as below. A gradually decreasing ramp waveform voltage is simply applied to scan electrodes SC1 through SCn in the selection initializing operation, so that only reduction of the positive wall voltage on data electrodes D1 through Dm is allowed. In the selection initializing operation, initializing discharge is caused in a localized region near the discharge gap between data electrodes D1 through Dm and scan electrodes SC1 through SCn or between scan electrodes SC1 through SCn and sustain electrodes SU1 through SUn. Therefore, when unnecessary wall charge is accumulated on the periphery of a discharge cell for some reason, the unnecessary wall charge can remain.
In the selection initializing operation, the wall voltage accumulated by the sustain discharge in the immediately preceding subfield is adjusted, and wall voltage required for the subsequent address operation is obtained. Whether appropriate wall voltage can be formed in the selection initializing operation largely depends on the state of the wall charge accumulated by the last discharge (erasing discharge) of the sustain period. After the completion of the erasing discharge, however, many primings of the sustain discharges occurring before then remain. As a result, if the selection initializing operation is performed at this time, the selection initializing operation cannot be always performed normally for the following reasons:
Therefore, when one field period is formed by arranging a plurality of subfield groups having a plurality of subfields whose luminance weight monotonically increases, the possibility that the address operation is not stably performed in the head subfield of the second subfield group or later, namely in the eighth SF in the present embodiment, becomes high.
In the present embodiment, however, after the completion of the erasing discharge in the immediately preceding subfield of the head subfield of the second subfield group, namely in the seventh SF, voltages applied to data electrodes D1 through Dm, scan electrodes SC1 through SCn, and sustain electrodes SU1 through SUn are kept for predetermined holding duration Ts. The gradually decreasing ramp waveform voltage is applied to scan electrodes SC1 through SCn after disappearance of the priming by the sustain discharge in the seventh SF, so that stable selection initializing operation is considered to be allowed without being affected by the sustain discharge in the immediately preceding subfield.
As shown in
Similarly, a pause period is disposed at the beginning of the initializing period of the sixth SF, and a pause period is disposed at the beginning of the initializing period of the seventh SF. Also in the second subfield group, a pause period is disposed at the beginning of the initializing period of the 10th SF, a pause period is disposed at the beginning of the initializing period of the 11th SF, and a pause period is disposed at the beginning of the initializing period of the 12th SF. Thus, a pause period is disposed in at least one subfield of the subfields that constitute one field period and do not include the head subfields of the first subfield group and the second subfield group. In this pause period, similarly in the holding period, discharge does not occur.
By disposing such a pause period, an advantage similar to that obtained by disposing the holding period can be obtained. As shown in
Thus, in the present embodiment, one field period is formed by arranging a plurality of subfield groups having a plurality of subfields that are arranged so that the luminance weight monotonically increases. In the discharge cell for causing address discharge in some subfield other than the head subfield in each subfield group, address discharge is caused even in the head subfield. A holding period when discharge is not caused is disposed before the head subfield belonging to at least one subfield group of the plurality of subfield groups. In the initializing period of the head subfield belonging to at least one subfield group, an initializing operation of causing initializing discharge is performed in the discharge cell where the sustain discharge has been performed in the sustain period of the immediately preceding subfield. Thus, even a high-definition panel can display a high-quality image without causing an operation failure.
Various specific numerical values used in the present embodiment are just one example, and are appropriately set at the optimal values in response to the characteristic of the panel, the specification of the plasma display device, and the like.
Industrial Applicability
The present invention is useful as a driving method of a panel that does not cause an operation failure even in the high-definition panel and allows high-quality image display.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-108888 | Apr 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/000931 | 4/10/2008 | WO | 00 | 11/11/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/129871 | 10/30/2008 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20030218580 | Yokoyama et al. | Nov 2003 | A1 |
| 20040032533 | Correa et al. | Feb 2004 | A1 |
| 20050264230 | Kim et al. | Dec 2005 | A1 |
| 20050264483 | Jeong | Dec 2005 | A1 |
| 20060227075 | Kim | Oct 2006 | A1 |
| 20060227076 | Kim | Oct 2006 | A1 |
| 20060227253 | Kim | Oct 2006 | A1 |
| 20070030214 | Kim | Feb 2007 | A1 |
| 20090015520 | Akamatsu et al. | Jan 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 1 710 775 | Oct 2006 | EP |
| 1 710 777 | Oct 2006 | EP |
| 1 715 469 | Oct 2006 | EP |
| 1 729 278 | Dec 2006 | EP |
| 2000-242224 | Sep 2000 | JP |
| 2004-157291 | Jun 2004 | JP |
| 2006-293303 | Oct 2006 | JP |
| 2006-293318 | Oct 2006 | JP |
| 2006-301571 | Nov 2006 | JP |
| 2007-078946 | Mar 2007 | JP |
| WO 0245062 | Jun 2002 | WO |
| WO 2006112233 | Oct 2006 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20090179877 A1 | Jul 2009 | US |
