The present invention relates to a method for driving a surface discharge type plasma display panel and a display device using the method.
A surface discharge type AC plasma display panel is used for displaying color pictures. The surface discharge type mentioned here has a structure in which first electrodes and second electrodes for generating display discharge are arranged in parallel on a front substrate or a rear substrate, and third electrodes are arranged so as to cross the first electrodes and the second electrodes. The display discharge determines light emission quantity of a cell that is a display element. In general, the first electrodes and the second electrodes are row electrodes that define rows of a matrix display while the third electrodes are column electrodes that define columns thereof. One of the first electrode and the second electrode (the second electrode in this description) is used as a scan electrode for row selection in addressing.
A typical surface discharge AC type plasma display panel has a cell structure as shown in
The plasma display panel includes the front plate 10, the rear plate 20 and discharge gas (not shown). The front plate 10 includes a glass substrate 11, first row electrodes X, second row electrodes Y, a dielectric film 17 and a protection film 18. Each of the row electrodes X and the row electrodes Y is a laminate of a patterned transparent conductive film 14 and a metal film 15. The rear plate 20 includes a glass substrate 21, column electrodes A, a dielectric film 22, a plurality of partitions 23, a red (R) fluorescent material 24, a green (G) fluorescent material 25, and a blue (B) fluorescent material 26.
The row electrodes X and the row electrode Y are arranged alternately as display electrodes for generating surface discharge on the inner surface of the glass substrate 11 and are covered with the dielectric film 17 and the protection film 18. The dielectric film 17 is an essential element for the AC plasma display panel. The coating with the dielectric film 17 enables surface discharge to be generated repeatedly by utilizing wall charge accumulated in the dielectric film 17. The protection film 18 is made of a material that has good resistance to sputtering and a large secondary electron emission coefficient (in general, magnesia), and it has a function of preventing sputtering to the dielectric film 17 and a function of decreasing display discharge start voltage.
Since the plasma display panel reproduces a color display by a binary control of lighting, each of time sequence of frames Fk-2, Fk-1, Fk and Fk+1 (hereinafter, subscripts indicating input orders are omitted) that are input images is divided into a predetermined number N of sub frames SF1, SF2, SF3, SF4, . . . SFN-1 and SFN (hereinafter, subscripts indicating display orders are omitted) as shown in
Furthermore, in case of an interlace display like a television display in which the frame is divided into a plurality of fields, each of the fields is replaced with a plurality of sub fields. In this case, the “frame” should be read as the “field” while the “sub frame” should be read as the “sub field”. In addition, it is possible to divide the screen into a plurality of parts so that the reset, the addressing and the sustaining are performed individually for each of the parts.
As a related-art document about the drive sequence described above, there is Japanese unexamined patent publication No. 2004-302134. This publication discloses typical drive waveforms, which are shown in
In the reset period, so-called obtuse wave reset is performed. In the obtuse wave reset, an obtuse wave pulse like a ramp waveform pulse shown in
In the address period, a scan pulse is applied to each of the row electrodes Y one by one. In other words, the row selection is performed. In synchronization with the row selection, an address pulse is applied to the column electrode A corresponding to the cell to be energized in the selected row. Address discharge is generated in the cell to be energized that is selected by the row electrode Y and the column electrode A so that predetermined wall charge is formed there.
In the sustain period, a sustain pulse is applied to the row electrode Y and the row electrode X alternately. The display discharge is generated between the row electrodes of the cell to be energized (hereinafter, this is referred to as an interelectrode XY) by each application.
Hereinafter, the reset operation that is deeply connected to the present invention will be described more.
In the reset operation as shown in
However, in the combination of the opposed discharge and the opposed discharge, the column electrode becomes a cathode either in the first discharge or in the second discharge. Since a value of a secondary electron emission coefficient γ of a fluorescent material covering the cathode is smaller than that of a protection film covering an anode, electron supply quantity by the fluorescent material is little. Therefore, the opposed discharge in which the column electrode becomes a cathode is apt to be unstable.
Therefore, a drive voltage in the reset period shown in
[Patent Document 1] Japanese unexamined patent publication No. 2004-302134
The obtuse wave pulse is applied for the purpose of generating the feeble discharge that changes the wall charge quantity gradually. Here, a ramp wave is exemplified as a typical obtuse wave. If a gradient of the ramp wave is steep, strong discharge will be generated so that the wall charge quantity cannot be adjusted to a desired value. In contrast, if the gradient of the ramp wave is sufficiently gentle, a pulse width of the obtuse wave pulse should be large for changing the wall charge quantity to be a desired value though the feeble discharge can be generated. Therefore, a turnaround time for the reset operation is increased. If the reset period is increased, time that can be assigned to the sustain period is decreased. As a result, luminance of the display is decreased.
An object of the present invention is to decrease a turnaround time for the adjustment of the wall charge quantity as a preprocess of the addressing operation.
A plasma display panel, for which the driving method for achieving the above-mentioned purpose is used, includes a first substrate and a second substrate that sandwich a discharge gas space in between the first substrate and the second substrate, first electrodes and second electrodes both arranged on the first substrate, a first insulator intervening between the first electrode and the discharge gas space as well as between the second electrode and the discharge gas space, third electrodes arranged on the second substrate, and a second insulator intervening between the third electrode and the discharge gas space. The first insulator emits secondary electrons more readily than the second insulator.
An experiment of changing a gradient of a ramp wave pulse (a rate of a voltage change) for generating discharge is carried out on the plasma display panel having the typical structure described above. The experiment showed that the discharge operation has tendencies (1) and (2) as follows.
(1) Even if the gradient is steep, strong discharge is less prone to be generated in the case where the discharge starts from the opposed discharge, compared to the case where the discharge starts from the surface discharge.
(2) Even if the discharge starts from the surface discharge, strong discharge is less prone to be generated in the case where a ramp wave pulse having a positive polarity is applied to the first electrode or the second electrode, compared to the case where a ramp wave pulse having a negative polarity is applied to the same.
More specifically, as to an example of a plasma display panel that can generate desired feeble discharge starting from the surface discharge by applying a ramp wave pulse having a negative polarity with a gradient of 1 V/μs or smaller, an upper limit of the gradient was 3 V/μs in the case where the feeble discharge starting from the surface discharge is generated by the ramp wave pulse having a positive polarity. Furthermore, in this plasma display panel, an upper limit of the gradient was 5 V/μs in the case where the feeble discharge starting from the opposed discharge is generated.
Concerning the tendency (1), the wall charge before the adjustment remaining at a position away from the electrode gap probably induces the strong discharge since the surface discharge expands from a vicinity of the electrode gap toward a far position. In contrast, the opposed discharge expands uniformly in the region where the electrodes are opposed, so that an offset of adjustment of the wall charge is hardly generated. Therefore, strong discharge is probably hardly generated in the opposed discharge.
Concerning the tendency (2), a potential of the third electrode has a negative polarity with respect to a potential of the first electrode or the second electrode when the ramp wave pulse having a positive polarity is applied. In this relationship between the potentials, strong discharge is probably hardly generated since there are few secondary electrons emitted from the second insulator disposed between the third electrode and the discharge gas space.
Based on the tendencies, it is advantageous to generate feeble discharge starting from the opposed discharge in order that the desired charge adjustment by the feeble discharge can be finished in a shorter time. In addition, if it is necessary to generate feeble discharge starting from the surface discharge, it is advantageous to generate the discharge by applying the obtuse wave pulse having a positive polarity to the first electrode or the second electrode.
The driving method for achieving the above-mentioned purpose includes the steps of performing an addressing operation that forms a state in which wall charge is accumulated that is necessary for energizing a cell to be energized, performing a sustaining operation that generates discharge between the first electrode and the second electrode in the cell to be energized, and performing a reset operation that forms a state in which wall charge of the first insulator in every cell is initialized. In the addressing operation, address discharge of an opposed discharge form is generated with the second electrode used as a cathode between the second electrode and the third electrode in a cell to be energized or a cell not to be energized, and in the reset operation, an obtuse wave pulse having a negative polarity is applied to the second electrode, so that charge adjustment discharge starting from the discharge of an opposed discharge form with the second electrode used as a cathode is generated between the second electrode and the third electrode.
A preferred example of the present invention is a typical three-electrode surface discharge type plasma display panel shown in
In addition, a method of replacing a frame F with a plurality of sub frames SF shown in
In the following description, driving of the plasma display panel shown in
The first substrate corresponds to the glass substrate 11, and the second substrate corresponds to the glass substrate 21. The first electrode corresponds to the row electrode X, the second electrode corresponds to the row electrode Y, and the third electrode corresponds to the column electrode A. The first insulator corresponds to the protection film 18, and the second insulator corresponds to the fluorescent materials 24, 25 and 26.
With reference to
Purposes of the reset operation as a preprocess of the addressing operation is to cancel a binary set state of quantity of the wall charge formed in the previous addressing and to optimize wall charge quantity of every cell, so that the address discharge can be generated easily in the next addressing. In order to make the address discharge be generated easily, it is necessary that the discharge just before the address period should be the discharge having the same polarity as the address discharge. Since the scan pulse that is applied to the row electrode Y in the addressing operation has a negative polarity, the final discharge in the reset period is the discharge with the row electrode Y being a cathode. Furthermore, it is desirable that the final discharge should be the discharge starting from the opposed discharge for adjusting the wall charge precisely.
This example will be described more specifically with reference to a cell voltage plane.
An operation of the plasma display panel having the three-electrode structure can be analyzed in a geometric manner with reference to a cell voltage plane and a discharge start threshold value closed curve as disclosed in the above-mentioned document. The cell voltage plane that is used here is a rectangular coordinate plane in which the horizontal axis is a cell voltage of the interelectrode XY while the vertical axis is a cell voltage of the interelectrode AY as shown in
The discharge with the row electrode Y being a cathode includes A-Y discharge that is the opposed discharge and X-Y discharge that is the surface discharge. In the expression of the “A-Y discharge” and the “X-Y discharge”, the upper case letter before “-” (A or X) indicates an anode while the upper case letter after the same (Y) indicates a cathode. Hereinafter, a discharge start threshold value of the X-Y discharge is represented by Vt(XY), and a discharge start threshold value of the A-Y discharge is represented by Vt(AY). In addition, applying a voltage between an electrode and a reference potential line is expressed like “applying a voltage to an electrode” or “applying a pulse to an electrode” for convenience sake. As to the polarity of the obtuse wave pulse, a polarity that decreases electrode potential is referred to as a negative polarity while a polarity that increases electrode potential is referred to as a positive polarity.
When the obtuse wave pulse having a negative polarity is applied to the row electrode Y for generating the discharge with the row electrode Y being a cathode, potential of the row electrode X and potential of the column electrode A increase in the same manner relatively to potential of the row electrode Y. Therefore, the application is represented by a vector having a gradient “1” in the cell voltage plane as shown in
This first example satisfies the above-mentioned condition by applying a rectangular pulse prior to the application of the obtuse wave pulse having a negative polarity. As shown in
In
A second example is a variation of the first example. As shown in
According to this example, the charge adjustment discharge starting from the opposed discharge can be generated more securely. It is because that a start point of a vector having a gradient “1” corresponding to the obtuse wave pulse Pr1 having a negative polarity is shifted from the origin of the cell voltage plane toward the left (the negative side of the horizontal axis) by the bias of the row electrode X as shown in
Since the Y-X discharge in response to the sustain pulse Ps forms the wall charge that cancels an applied voltage, the state when the Y-X discharge is finished corresponds to the origin on the cell voltage plane ideally. However, there is the case where the state is shifted to the right from the origin because of some error actually. In this case, as shown in
In other words, tolerance of the cell state (the start point of the vector) when the application of the obtuse wave pulse Pr1 having a negative polarity is started as well as tolerance of a variation of the Vt closed curve is large in the second example.
In a third example, application of the obtuse wave pulse is performed two times as the reset operation. As shown in
If the wall charge state just before the application of the obtuse wave pulse Pr1 in the reset period is uncertain, or if the wall charge quantity when the sustain period is finished is excessively large or small, it is necessary to generate discharge for charge adjustment before the application of the obtuse wave pulse Pr1. In this discharge, the row electrode Y must be an anode. The opposed discharge with the row electrode Y being an anode is unstable because of a small quantity of secondary electron emission as described above. Therefore, the surface discharge is generated before the application of the obtuse wave pulse Pr1.
Since the obtuse wave pulse Pr2 that generates the surface discharge has a positive polarity, the gradient can be steeper than the case where it has a negative polarity. However, it is necessary to prevent the surface discharge from being generated in the pre-extinguished cell. The waveform of the obtuse wave pulse Pr2 (including the gradient and the pulse width) is set so that the above-mentioned constraint can be satisfied. It is because that if the reset operation includes only two obtuse wave pulse application steps, the combination of the surface discharge and the surface discharge or the combination of the opposed discharge and the opposed discharge is necessary, so the driving sequence repeating the combination of the surface discharge and the opposed discharge will be unstable. For example, if a certain cell is not energized in a certain sub frame, neither the address discharge nor the display discharge is generated. Therefore, the discharge operation that is a combination of the surface discharge and the opposed discharge continues in the reset period of the current sub frame and in the reset period of the next sub frame. If the cell is energized, there is no problem because there is a display discharge operation between the reset operation and the next reset operation. If the surface discharge is not generated in the pre-extinguished cell during the reset period, the discharge operation that is a combination of the surface discharge and the opposed discharge does not continue.
In a fourth example, application of the obtuse wave pulse is performed three times as the reset operation. If each cell is not in the state where the reset operation has been performed like the state just after the power is turned on, it is necessary to generate the charge adjustment discharge with the row electrode X being an anode before the surface discharge of the third example described above. As shown in
As apparent from
The first to fourth examples can be carried out in the display device having the structure shown in
In
The screen 16 of the plasma display panel 2 is a set of cells having the structure shown in
The driving circuit 3 includes an X-driver 91 for applying the drive voltage to the row electrodes X, a Y-driver 92 for applying the drive voltage to the row electrodes Y, an A-driver 93 for applying the drive voltage to the column electrodes A, a controller 95 for controlling application of the drive voltages to the plasma display panel 1, and a power supply circuit 96.
The X-driver 91 includes a circuit 911 for applying the sustain pulse and a circuit 912 for applying a pulse for the reset. The Y-driver 92 has a circuit 921 for applying the scan pulse, a circuit 922 for applying the sustain pulse, and a circuit 923 for applying a pulse for the reset.
The driving circuit 3 is supplied with a color picture signal S1 having a frame rate of 1/30 seconds from an image output device such as a TV tuner, a computer or the like. This color picture signal S1 is converted into sub frame data for display of a plasma display panel 8 by a data processing block of the controller 95.
In the embodiments described above, the waveforms, the voltages, the driving sequence, the device structures and the like can be modified within the scope of the present invention without deviating from the spirit thereof, if necessary. For example, the reset of the fourth example may be performed just after the power is turned on or at a set timing of a predetermined interval, and the other reset is performed in accordance with any one of the first to the third examples.
The present invention can be used for a display device equipped with a surface discharge type plasma display panel, which includes a display of information processing equipment such as a personal computer or a workstation, a flat television set, a public display for advertisement or guide information.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2006/300544 | 1/17/2006 | WO | 00 | 3/30/2009 |