Method of driving plasma display panel

A method of driving a plasma display panel including a plurality of scanning electrodes covered with a dielectric layer, and a plurality of sustaining electrodes covered with a dielectric layer, including the steps of (a) applying scanning pulses in time-division to the scanning electrodes in an addressing period in which a cell or cells emitting light is(are) selected, and applying sustaining pulses to the sustaining electrodes in a sustaining period for generating preliminary discharge and preliminary erasing discharge before the cell or cells emitting light is(are) selected, and (b) applying a serrate pulse to the scanning or sustaining electrodes when the preliminary erasing discharge is generated, the serrate pulse having an inclination smaller than 10 V/μs, wherein a period of time until the generation of the preliminary erasing discharge from the termination of the preliminary discharge is set shorter than 3T where T indicates a decay time constant of priming particles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of driving a plasma display panel (PDP) which is one of flat display panels which can be readily formed in a larger size, and more particularly to such a method which makes it possible, after priming discharge or preliminary discharge has been generated in all of cells, but prior to addressing action carried out for determining a cell or cells which emit(s) light, to generate priming erasing discharge for controlling wall charges generated by the preliminary discharge.

2. Description of the Related Art

A plasma display panel is presently used in various fields such as a personal computer, a display of a work-station, or a television set hung over a wall. A plasma display panel can be structurally grouped into a direct current (DC) type panel in which electrodes are exposed to discharge gas, and an alternate current (AC) type panel in which electrodes are covered with a dielectric film, and hence, are not exposed to discharge gas. An alternate current (AC) type panel is grouped further into a memory operation type panel which makes use of a memory function caused by a charge-accumulation function of the dielectric film, and a refresh operation type panel which does not make use of the memory function.

FIG. 1is a cross-sectional view of a conventional AC type plasma display panel.

The illustrated plasma display panel includes a front substrate1and a rear substrate2both of which are composed of glass.

On the front substrate1are formed a plurality of scanning electrodes3and a plurality of sustaining electrodes4all extending in a direction perpendicular to a plane ofFIG. 1. Each of the scanning electrodes3is equally spaced away from each of the sustaining electrodes4. A dielectric layer5ais formed on the front substrate1such that the dielectric layer5aentirely covers the scanning and sustaining electrodes3and4therewith. A protection layer6is formed entirely over the dielectric layer5a.The protection layer6is composed of magnesium oxide (MgO), and protects the dielectric layer5afrom discharge generated in a discharge space9defined between the front and rear substrates1and2.

On the rear substrate2is formed a plurality of data electrodes extending in a direction perpendicular to a direction in which the scanning and sustaining electrodes3and4extend. The data electrodes8are covered with a dielectric layer5b.Phosphor7is coated over the dielectric layer5bfor converting ultra-violet light generated by discharge, into visible light. A color plasma display panel is fabricated, if red, green and blue phosphors are coated in every three cells.

Between the dielectric layers5aand5bis formed a partition wall10for defining discharge spaces9and partitioning cells. A discharge gas composed of He, Ne and Xe is introduced into each of the discharge spaces9.

FIG. 2is a plan view of the scanning, sustaining and data electrodes3,4and8of the plasma display panel illustrated inFIG. 1.

As illustrated inFIG. 2, first to m-th scanning electrodes Si (i=1, 2, - - - , m) are formed to extend in a column direction, and first to n-th data electrodes Dj (j=1, 2, - - - , n) are formed to extend in a row direction. A cell is formed at each of intersections of the scanning and data electrodes. First to m-th sustaining electrodes are formed to extend in a column direction in parallel with the scanning electrodes Si. Each of the first to m-th scanning electrodes Si and each of the sustaining electrodes Ci make a pair.

FIG. 3is a timing chart showing waveforms of driving voltages to be applied to the scanning, sustaining and data electrodes3,4and8. Hereinbelow is explained a method of driving the AC type plasma display panel, with reference toFIG. 3.

First, a first preliminary discharge pulse11ahaving a sign which is negative with respect to a base voltage of a sustaining electrode is applied to the sustaining electrodes4, and a second preliminary discharge pulse11bhaving a sign which is positive with respect to a base voltage of a sustaining voltage is applied to the scanning electrodes3. As a result, a voltage difference exceeding a threshold voltage at which discharge starts is applied across the scanning electrodes3and the sustaining electrodes4, and thus, discharge is compulsorily generated in all cells.

The first preliminary discharge pulse11ais rectangular in shape. Hence, a voltage drastically varies at leading and trailing edges of the first preliminary discharge pulse11a.The second preliminary discharge pulse11bis serrate in shape, and hence, a voltage gently varies at a leading edge of the second preliminary discharge pulse11b.An inclination of the leading edge of the second preliminary discharge pulse11bis set smaller than about 10 V/μs.

Then, a preliminary erasing discharge pulse12having a sign which is negative with respect to a base voltage of a scanning electrode is applied to the scanning electrodes3for generating discharge in all cells to thereby put wall charges into an initial state for generating writing discharge afterwards.

The preliminary erasing discharge pulse12is serrate in shape, and hence, a voltage gently varies at a leading edge of the preliminary erasing discharge pulse12. An inclination of the leading edge of the preliminary erasing discharge pulse12is set smaller than about 10 V/μs.

Discharge generated by the first and second preliminary discharge pulses11aand11bis called preliminary discharge, and discharge generated by the preliminary erasing discharge pulse12is called preliminary erasing discharge. Subsequent writing discharge is stably generated by virtue of the preliminary discharge and preliminary erasing discharge.

After the preliminary discharge and preliminary erasing discharge have been generated, a scanning pulse13is applied to each of the scanning electrodes S1to Sm at different timings from one another. The scanning pulse13has a sign which is negative with respect to a base voltage of a scanning electrode.

In synchronization with the scanning pulse13, a data pulse14is applied to the data electrodes D1to Dn in accordance with image data. The data pulse14has a sign which is positive with respect to a base voltage of a data electrode. An oblique line in each of the data pulses14indicates whether presence or absence of the data pulse14is determined in accordance with presence or absence of image data for a cell.

In a cell in which the data pulse14is applied to the data electrode8while the scanning pulse13is being applied to the scanning electrode3, discharge is generated in the discharge space9defined between the scanning electrode3and the data electrode8. In contrast, if the data pulse14is not applied to the data electrode8while the scanning pulse13is being applied to the scanning electrode3, discharge is not generated in the discharge space9. Image data is written into a cell in accordance with presence or absence of the discharge, the discharge is called a writing discharge.

In the above-mentioned writing discharge, the discharge generated between the scanning electrode3and the data electrode8triggers discharge between the scanning electrode3and the sustaining electrode4. In order to cause the discharge between the scanning electrode3and the sustaining electrode4to be stably generated, a voltage difference between the scanning electrode3and the sustaining electrode4in the writing discharge may be increased by applying a bias voltage or scanning sub-pulse17to the sustaining electrodes4. The scanning sub-pulse17has a sign which is positive with respect to a base voltage of a sustaining electrode. In order to shorten an amplitude of the scanning pulse13, a bias voltage or scanning base pulse18may be applied to the scanning electrodes3. The scanning base pulse18has a sign which is negative with respect to a base voltage of a scanning electrode.

In a cell in which the writing discharge has been generated, positive charges called “wall charges” are accumulated on the dielectric layer5aabove the scanning electrodes3. In contrast, negative wall charges are accumulated on the dielectric layer5babove the data electrodes8. Thereafter, a positive voltage caused by the positive wall charges accumulated on the dielectric layer5aabove the scanning electrodes3, and a first sustaining pulse15ahaving a negative sign and applied to the sustaining electrodes4overlap each other with the result that first discharge is generated.

If discharge is generated also between the scanning electrode3and the sustaining electrode4during the wiring discharge, negative wall charges are accumulated on the dielectric layer5aabove the sustaining electrodes4by the writing discharge. As a result, a positive voltage caused by the positive wall charges accumulated on the dielectric layer5aabove the scanning electrodes3and a negative voltage caused by the negative wall charges caused by the dielectric layer5aabove the sustaining electrodes4are added to the first sustaining pulse15a,resulting in that first discharge is generated.

After the first discharge has been generated, positive wall charges are accumulated on the dielectric layer5aabove the sustaining electrodes4, and negative wall charges are accumulated on the dielectric layer5aabove the scanning electrodes3. A second sustaining pulse15bto be applied to the scanning electrodes3is added to a voltage difference between the above-mentioned positive and negative wall charges, resulting in that second discharge is generated.

In the same way as mentioned above, a voltage difference caused by positive and negative wall charges accumulated by n-th discharge is added to a (n+1)-th sustaining pulse15b,resulting in that discharge is kept generated. Hence, discharge caused by the above-mentioned action is called sustaining discharge. A luminance is dependent on the number of sustaining discharges.

If the sustaining pulses15aand15bare designed to have a voltage at which discharge is not generated merely by applying the sustaining pulses15aand15bto the sustaining and scanning electrodes4and3, first sustaining discharge is not generated even if the first sustaining pulse15ais applied to the sustaining electrodes4in a cell in which the writing discharge has not been generated, because a voltage caused by wall charges is not generated before applying the first sustaining pulse15ato the sustaining electrodes4. Accordingly, subsequent sustaining discharges are not generated.

After the sustaining pulses15aand15bhave been applied to the sustaining electrodes4and the scanning electrodes3, respectively, a sustaining erasing pulse16having a sign which is negative with respect to a base voltage of a scanning electrode is applied to all of the scanning electrodes3to thereby generate discharge in a cell in which the sustaining discharge has been kept generated. As a result, a wall charge profile is initialized. The sustaining erasing pulse16is a serrate pulse having a leading edge varying smaller than about 10 V/μs. Discharge caused by the sustaining erasing pulse16is called sustaining discharge erasion.

With reference toFIG. 3, a period in which the preliminary discharge pulses11aand11band the preliminary erasing discharge pulse12are applied to the sustaining electrodes4and the scanning electrodes3is called a preliminary discharge period, a period in which the scanning pulse13, the data pulse14, the scanning sub-pulse17(if necessary), and the scanning base pulse18(if necessary) are applied to the electrodes is called a scanning or addressing period, a period in which the sustaining pulses15aand15bare applied to the sustaining and scanning electrodes4and3is called a sustaining period, and a period in which the sustaining erasing pulse16is applied to the scanning electrodes3is called a sustaining erasing period. A combination of a preliminary discharge period, a scanning period, a sustaining period and a sustaining erasing period makes a sub-field.

A method of displaying images at a certain gray scale in a conventional plasma display panel is explained hereinbelow with reference toFIG. 4.

A field defined as a period in which one picture is to be displayed is divided into a plurality of sub-fields. For instance, a field is 1/60 seconds, and is divided into four sub-fields. Each of the sub-fields has such a structure as illustrated inFIG. 4, and is controlled to be turned on or off independently of other sub-fields. The sub-fields have sustaining periods different from one another. In other words, the sustaining pulses15aand15bare applied to the sustaining and scanning electrodes4and3in each of the sub-fields in the different numbers from one another, and hence, the sub-fields provide different luminances from one another.

When a field is divided into four sub-fields as illustrated inFIG. 4, it is assumed that a ratio in luminance obtained when light is emitted solely in each of the sub-fields is set 1:2:4:8, for instance. Thus, it would be possible to display images at sixteen (16) luminance ratios from zero (0) to fifteen (15) in accordance with a combination of four sub-fields in each of which light is emitted or not. Herein, if no light is emitted in all of the sub-fields, a luminance ratio would be zero, and if light is emitted in all of the sub-fields, a luminance ratio would be fifteen.

If a field is divided into N sub-fields, and a luminance ratio in the N sub-fields is set at 1 (=20): 2 (=21): - - - : 2(N−2): 2(N−1), it would be possible to display images at 2Ngray scales.

However, the above-mentioned conventional method of driving a plasma display panel is accompanied with a problem that excessively intensive discharge might be generated, when the preliminary erasing discharge pulse12having a leading edge varying at a rate smaller than 10 V/μs is applied to the scanning electrodes3, resulting in that sustaining discharge is generated regardless of whether the writing discharge has been generated, in a cell in which excessively intensive preliminary erasing discharge has been generated.

Japanese Patent Application Publication No. 2001-184023 has suggested a display unit including a plurality of first electrodes arranged in a first direction, a plurality of second electrodes arranged in a second direction perpendicular to the first direction, a plurality of third electrodes each of which makes a pair with each of the first electrodes, and a controller which adjusts a wall voltage difference between the first and third electrodes, and further adjusts a wall voltage difference between the first and second electrodes independently of the adjustment of the wall voltage difference between the first and third electrodes, before addressing discharge is generated between the first and second electrodes.

Japanese Patent Application Publication No. 2001-210238 has suggested an AC type plasma display panel including a first substrate, and a second substrate facing the first substrate with discharge space being sandwiched therebetween. On the first substrate are formed a first electrode, a second electrode extending in parallel with the first electrode, and a dielectric layer covering the first and second electrode therewith. On the second substrate is formed a third electrode extending in a direction perpendicular to a direction in which the first electrode extends. A distance between the first and second electrodes is set greater than a height of the discharge space.

Japanese Patent Application Publication No. 2001-242824 has suggested a method of driving a plasma display panel including a discharge cell which includes a first electrode and a second electrode and which can control whether discharge is generated in accordance with a voltage difference between the first and second electrodes, the method including the step of applying a pulse successively varying from a first voltage to a second voltage, to the first electrode. The step further includes the first step of forming a first region of the pulse in accordance with a first pulse-generation process, and the second step of forming a second region of the pulse in accordance with a second pulse-generation process.

Japanese Patent Application Publication No. 2002-14652 has suggested a method of driving a plasma display panel, in which images are displayed at a certain gray scale by means of a pulse having a increased-width portion, in a certain sub-field.

SUMMARY OF THE INVENTION

In view of the above-mentioned problem in the conventional method of driving a plasma display panel, it is an object of the present invention to provide a method of driving a plasma display panel which method is capable of preventing such erroneous discharge as mentioned above, and displaying images at high quality.

In one aspect of the present invention, there is provided a method of driving a plasma display panel including a plurality of scanning electrodes covered with a dielectric layer, and a plurality of sustaining electrodes covered with a dielectric layer, including the steps of (a) applying scanning pulses in time-division to the scanning electrodes in an addressing period in which a cell or cells emitting light is(are) selected, and applying sustaining pulses to the sustaining electrodes in a sustaining period for generating preliminary discharge and preliminary erasing discharge before the cell or cells emitting light is(are) selected, and (b) applying a serrate pulse to the scanning or sustaining electrodes when the preliminary erasing discharge is generated, the serrate pulse having an inclination smaller than 10 V/μs, wherein a period of time until the generation of the preliminary erasing discharge from the termination of the preliminary discharge is set shorter than 3T where T indicates a decay time constant of priming particles.

It is preferable that the priming particles are xenon (Xe) metastable level atoms, and the period of time is shorter than 58 microseconds.

There is further provided a method of driving a plasma display panel including a plurality of scanning electrodes covered with a dielectric layer, and a plurality of sustaining electrodes covered with a dielectric layer, including the steps of (a) applying scanning pulses in time-division to the scanning electrodes in an addressing period in which a cell or cells emitting light is(are) selected, and applying sustaining pulses to the sustaining electrodes in a sustaining period for generating preliminary discharge and preliminary erasing discharge before the cell or cells emitting light is(are) selected, and (b) applying a serrate pulse to the scanning or sustaining electrodes when the preliminary erasing discharge is generated, the serrate pulse having an inclination smaller than 10 V/μs, wherein in a period including a first period in which the serrate pulse is applied to one of the scanning and sustaining electrodes for generating the preliminary erasing discharge, a first pulse having a sign opposite to a sign of the serrate pulse with respect to a base voltage is applied to the other of the scanning and sustaining electrodes.

It is preferable that the serrate pulse is applied to the scanning electrodes and the first pulse is applied to the sustaining electrodes, and the first pulse has a voltage equal to a voltage of a pulse applied to the sustaining electrodes in the addressing period.

The method may further include the step of stopping applying a second voltage to the other of the scanning and sustaining electrodes for returning the other of the scanning and sustaining electrodes back to a base voltage, before the serrate pulse reaches a third voltage, wherein the second voltage is defined as a voltage having a sign opposite to a sign of the serrate pulse with respect to the base voltage to be applied to the other of the scanning and sustaining electrodes, the third voltage is defined as a voltage closer to the base voltage than a first voltage by a bias-voltage difference, the first voltage is defined as a voltage to which the serrate pulse finally reaches, and the bias-voltage difference is defined as a difference between the base voltage and the second voltage.

It is preferable that the first voltage is a ground (GND) voltage.

It is preferable that a first bias-voltage difference defined as a difference between a ground voltage and a first voltage is greater than a second bias-voltage difference between the base voltage and a second voltage, wherein the serrate pulse has a negative sign, the first voltage is defined as a voltage to which the serrate pulse finally reaches, and the second voltage is defined as a voltage which has a positive sign and is applied to the other of the scanning and sustaining electrodes.

It is preferable that a period of time until the generation of the preliminary erasing discharge from the termination of the preliminary discharge is set shorter than 3T where T indicates a decay time constant of priming particles.

It is preferable that a period of time until the generation of the preliminary erasing discharge from the termination of the preliminary discharge is set shorter than 58 microseconds.

It is preferable that a voltage to be applied to the scanning and sustaining electrodes is kept equal to a base voltage of the scanning and sustaining electrodes in a period between a period in which the preliminary discharge is generated and a period in which the next preliminary discharge is generated.

It is preferable that the base voltage is equal to a maximum or minimum of an amplitude of the sustaining pulse.

It is preferable that the maximum or minimum of an amplitude of the sustaining pulse is equal to a ground voltage.

There is still further provided a method of driving a plasma display panel including a plurality of scanning electrodes covered with a dielectric layer, and a plurality of sustaining electrodes covered with a dielectric layer, including the steps of (a) applying scanning pulses in time-division to the scanning electrodes in an addressing period in which a cell or cells emitting light is(are) selected, and applying sustaining pulses to the sustaining electrodes in a sustaining period for generating preliminary discharge and preliminary erasing discharge before the cell or cells emitting light is(are) selected, and (b) applying a serrate pulse to one of the scanning and sustaining electrodes when the preliminary erasing discharge is generated wherein the serrate pulse falls down to a first voltage from a base voltage at 100 V/μs or greater and falls down to a second voltage from the first voltage at 10 V/μs or smaller, or rises up to a first voltage from a base voltage at 100 V/μs or greater and rises up to a second voltage from the first voltage at 10 V/μs or smaller.

The advantages obtained by the aforementioned present invention will be described hereinbelow.

In accordance with the above-mentioned present invention, it is possible to prevent generation of intensive discharge in preliminary erasing discharge generated by using a serrate pulse having a leading edge gently varying. This ensures it possible to provide a plasma display panel in which erroneous discharge is not generated and which provides high quality in displaying images.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will be explained hereinbelow with reference to drawings.

Hereinbelow is explained a method of driving a plasma display panel, in accordance with the first embodiment of the present invention, with reference toFIGS. 5A to 5Din whichFIG. 5Aillustrates a waveform of a pulse to be applied to the sustaining electrode4in a preliminary discharge period,FIG. 5Billustrates a waveform of a pulse to be applied to the scanning electrode3in a preliminary discharge period,FIG. 5Cillustrates a voltage difference between the scanning electrode3and the sustaining electrode4, andFIG. 5Dillustrates a waveform of light emitted in a cell as a result of the voltage difference illustrated inFIG. 5C.

InFIGS. 5A to 5C, Vs indicates a base voltage of both a scanning electrode and a sustaining electrode, and further indicates a voltage amplitude of a sustaining pulse (not illustrated).

As illustrated inFIG. 5A, a preliminary discharge pulse11ato be applied to the sustaining electrode4falls down from the base voltage Vs to a ground voltage (GND) at a leading edge, is kept at the ground voltage GND for a certain period of time, and then, rises up from the ground voltage GND to the base voltage Vs at a trailing edge. As illustrated inFIG. 5B, a preliminary discharge pulse11bto be applied to the scanning electrode3gently rises up from the base voltage Vs to a voltage Vp at a leading edge, is kept at the voltage Vp for a certain period of time, and then, falls down from the voltage Vp to the base voltage Vs at a trailing edge. As illustrated inFIG. 5B, a preliminary erasing discharge pulse12to be applied to the scanning electrode3gently falls down from the base voltage Vs to a voltage Vp at a leading edge, is kept at the ground voltage GND for a certain period of time, and then, falls down from the ground voltage GND to the base voltage Vs at a trailing edge.

As illustrated inFIG. 5C, while a voltage difference between the scanning electrode3and the sustaining electrode4is gently increasing to the voltage Vp from the base voltage Vs, the preliminary discharge is generated, as illustrated inFIG. 5D. The preliminary discharge is kept generated while the voltage difference between the scanning electrode3and the sustaining electrode4is increasing. Thereafter, a sign of the voltage difference between the scanning electrode3and the sustaining electrode4is turned to negative one from positive one. Then, the preliminary erasing discharge is generated while the voltage difference is gently decreasing from 0 to −Vs. The preliminary erasing discharge is kept generated while the preliminary erasing discharge is generated while the voltage difference is gently decreasing from 0 to −Vs.

In the first embodiment, a period of time from termination of the preliminary discharge to generation of the preliminary erasing discharge is set shorter than 58 microseconds. Hereinbelow, a period of time from termination of the preliminary discharge to generation of the preliminary erasing discharge is referred to simply as “the period of time X”.

In a plasma display panel, when a voltage difference between electrodes is over a threshold voltage at which discharge is generated, discharge is generated between the electrodes, and, after discharge has been generated, wall charges start being accumulated on a dielectric film covering the electrodes therewith. A voltage caused by the wall charges cancels a voltage difference applied from an external circuit, and hence, a voltage difference between the electrodes gradually falls, and, if the voltage difference falls below the above-mentioned threshold voltage, generation of discharge stops.

However, once discharge has been generated, even if a voltage difference between the electrodes falls below the above-mentioned threshold voltage, discharge is kept generated for a few microseconds due to diffusion and/or recombination. Such phenomenon is called afterglow. In the first embodiment, such afterglow is ignored. Hence, termination of the preliminary discharge indicates a timing at which a discharge current or a power of emitted light in the preliminary discharge is reduced down to or below 1% of a peak, and hence, can be scarcely observed. This timing corresponds to a timing at which a voltage difference between the electrodes falls below the above-mentioned threshold voltage, and is almost identical with a timing at which the voltage difference starts being kept at a voltage (Vp+Vs) after the inclining leading edge has been terminated.

The first embodiment is identical with the conventional method with respect to a structure of the plasma display panel, and how the plasma display panel is driven in periods other than the preliminary discharge period, that is, waveforms of pulses to be applied to electrodes, and accordingly, they are not explained.

FIG. 6shows a relation between the period of time X, and a minimum voltage Vp at which excessively intensive discharge is not generated in the preliminary erasing discharge.

The plasma display panel having been used to measure the relation shown inFIG. 6had a cell having a size of 0.81 mm×0.27 mm, and includes discharge gas comprised of Ne at 96% and Xe at 4%, sealed into the discharge space9at 400 torr (53.3 kPa). The minimum voltage Vp linearly increases with the lapse of the period of time X, and if the period of time X is over 58 microseconds, it would not be possible to prevent generation of intensive discharge unless the minimum voltage Vp is set equal to or greater than 400 V. The minimum voltage Vp increases at a first rate before the period of time X is not over 58 microseconds, and at a second rate greater than the first rate if the period of time X is over 58 microseconds.

In the first embodiment, the period of time X is set smaller than 58 microseconds to thereby control generation of intensive discharge in dependence on the minimum voltage Vp equal to or smaller than 400 V, because the minimum voltage Vp is less dependent on the period of time X while the minimum voltage Vp is equal to or smaller than 400 V. Accordingly, it would be possible to design devices constituting a circuit for driving the plasma display panel, such as a diode or a field effect transistor (FET), to have a breakdown voltage equal to or smaller than 400 V.

In order to set the period of time X equal to or smaller than 58 microseconds, a period of time in which a voltage is kept equal to the voltage Vp in the waveform of a pulse to be applied to the scanning electrode3, illustrated inFIG. 5B, may be shortened, a period of time in which a voltage is kept equal to the voltage Vs in the waveform of a pulse to be applied to the scanning electrode3, illustrated inFIG. 5B, may be shortened, or the preliminary erasing pulse12may be designed to have a leading edge having steeper inclination. By designing the preliminary erasing pulse12to have a leading edge having steeper inclination, a pulse would reach a voltage difference caused by the preliminary erasing discharge, in a shorter period of time, resulting in that the period of time X is shortened.

Hereinbelow is explained mechanism which determines a relation between the minimum voltage Vp and the period of time X.

Various charged or excited particles are generated by generation of the preliminary discharge, and stay in the discharge space9. Most of the particles vanish at early time in the period of time X, however, some particles such as Xe metastable level atoms have long lifetime. Since Xe metastable level atoms provide electrons which act as a trigger for generation of discharge, discharge is likely to be generated, if a lot of Xe metastable level atoms exist in the discharge space9. This is one of phenomena called priming effect, and a particle acting as an electron source, such as Xe metastable level atom, is called priming particle.

In the plasma display panel having been used to measure the relation illustrated inFIG. 6, Xe metastable level atoms exponentially decay due to collision and/or diffusion when decay time constant τ=18.2 microseconds. As the period of time X becomes longer, the number of Xe metastable level atoms is reduced to a greater degree, resulting in that the preliminary erasing discharge becomes harder to be generated, that is, the priming effect becomes weaker. If the priming effect is weak, discharge which should be generated might not be generated, even if a voltage of the serrate pulse reaches a threshold voltage at which the preliminary erasing discharge is to be generated, in which case, discharge is suddenly generated when a voltage of the serrate pulse reaches a certain voltage quite higher than the threshold voltage. Such discharge is not weak discharge which should be originally generated, but intensive discharge which is erroneous discharge and hence causes a problem in driving a plasma display panel.

Herein, “weak discharge which should be originally generated” means discharge generated when a serrate pulse having a leading or trailing edge gently varying. Such weak discharge is kept generated while such a serrate pulse is applied to the electrode, forming wall charges little by little in dependence on an inclined voltage such that an effective voltage difference between the electrodes, partially caused by the wall charges, is kept equal to a voltage at which discharge is generated.

In contrast, intensive discharge forms wall charges in a greater amount than the weak discharge, resulting in that wall charges are formed such that an effective voltage difference between electrodes is significantly below a threshold voltage at which discharge is generated, and hence, discharge rapidly terminates. Herein, the first embodiment is on the assumption that preliminary erasing discharge is generated through the use of a serrate pulse.

As the voltage Vp becomes higher, Xe metastable level atoms are formed in preliminary discharge in a greater amount, resulting in that Xe metastable level atoms would be residual after termination of the preliminary discharge in a greater amount in the same period of time until generation of the preliminary erasing discharge from termination of the preliminary discharge. This ensures that the priming effect becomes intensive, and that it is possible to prevent intensive discharge from being generated, and hence, a problem of erroneous discharge can be solved. Thus, if the period of time X becomes longer, the voltage Vp becomes higher.

If a gas composition and/or a cell structure is varied, the longest period of time in which intensive discharge is not generated varies, as will be obvious in view of the above-mentioned mechanism, because a decay time constant of Xe metastable level atoms varies. If the decay time constant becomes higher, the period of time X has to be shorter.

A relation between the voltage Vp and the period of time X was measured to a gas composition and/or a cell structure other than those shown inFIG. 6. As a result, it was found out that the advantages obtained by the first embodiment could be obtained if the period of time X was smaller than 3T where T indicates a decay time constant τ. The above-mentioned 58 microseconds measured inFIG. 6is about 3.19 times greater than the decay time constant τ, 18.2 microseconds. That is, by setting the period of time X to be smaller than 3T where T indicates a decay time constant of Xe metastable level atoms, it would be possible to prevent intensive discharge from being generated by a low drive voltage Vp at the generation of the preliminary erasing discharge.

The above-mentioned 400 V below and above which the voltage Vp is dependent on the period of time X in different ways is just an example. If a discharge gas composition and/or a cell structure varies, such a threshold voltage also varies.

Hereinbelow is explained a method of driving a plasma display panel, in accordance with the second embodiment of the present invention, with reference toFIGS. 7A to 7Din whichFIG. 7Aillustrates a waveform of a pulse to be applied to the sustaining electrode4in a preliminary discharge period, FIG.7B illustrates a waveform of a pulse to be applied to the scanning electrode3in a preliminary discharge period,FIG. 7Cillustrates a voltage difference between the scanning electrode3and the sustaining electrode4, andFIG. 7Dillustrates a waveform of light emitted in a cell as a result of the voltage difference illustrated inFIG. 7C.

In the second embodiment, while the preliminary erasing discharge pulse12is applied to the scanning electrodes3, a voltage (Vs+Vpeb) greater than the voltage Vs is applied to the sustaining electrodes4.

As illustrated inFIG. 7C, the voltage difference gently falls down to apply a negative voltage difference across the scanning electrode3and the sustaining electrode4after the preliminary discharge has been terminated. Specifically, the voltage difference varies in the range of −Vpeb to −(Vs+Vpeb), whereas a voltage difference varies in the range of zero to −Vs in the conventional method.

In accordance with the second embodiment, it is possible to delete a period of time necessary for gently falling down a voltage difference from zero to −Vpeb, ensuring that the period of time X can be shortened. The period of time X can be shortened by newly introducing the voltage Vpeb, and it is also possible to suppress intensive discharge in the generation of the preliminary erasing discharge by means of a low drive voltage Vp.

It was found out that if preliminary erasing discharge was generated at a moment when the voltage difference became the voltage −Vpeb after termination of the preliminary discharge, the preliminary erasing discharge was generated as intensive discharge. Accordingly, the voltage Vpeb has to be determined such that discharge is not generated when the voltage difference becomes −Vpeb by combining the voltage Vpeb and a wall charge voltage formed by the preliminary discharge to each other. Hence, the voltage Vpeb is set smaller than a minimum voltage at which discharge is generated when a voltage of the sustaining electrodes4reaches the voltage (Vs+Vpeb) without applying the preliminary erasing pulse12to the scanning electrode3after application of the preliminary discharge pulses11aand11bto the sustaining and scanning electrodes4and3has been terminated.

The method in accordance with the second embodiment can be carried out without preparing a new power source, if a voltage of the scanning sub-pulse17to be applied to the sustaining electrodes4in a scanning period is designed equal to the voltage (Vs+Vpeb). Similarly, the method in accordance with the second embodiment can be carried out without preparing a new circuit, if a driver circuit for outputting the scanning sub-pulse17is designed to output a pulse having a voltage (Vs+Vpeb) in synchronization with the preliminary erasing discharge pulse12.

For simplification of description,FIGS. 7A and 7Billustrate that the pulse Vpeb is applied to the sustaining electrodes4at a timing at which the preliminary erasing discharge pulse12to be applied to the scanning electrodes3starts falling down. However, it should be noted that the pulse Vpeb may be applied to the sustaining electrodes4while the preliminary erasing discharge is being generated, that is, earlier than 3T where T indicates a decay time constant. Hence, the pulse Vpeb may be applied to the sustaining electrodes4before the preliminary erasing discharge pulse12to be applied to the scanning electrodes3starts falling down.

However, it is not preferable that the pulse Vpeb is applied to the sustaining electrodes4subsequently to a rising-up trailing edge of the preliminary discharge pulse11a.This is because a driver circuit for outputting a pulse (Vs+Vpeb) has to be designed to be able to output an intensive current in a short period of time in order to rise up a voltage from a ground level of the preliminary discharge pulse11ato the voltage (Vs+Vpeb).

It is preferable that the preliminary discharge pulse11ais kept at the voltage Vs for a certain period of time after risen up from a ground level to the voltage Vs, and thereafter, risen up to the voltage (Vs+Vpeb). A driver circuit which keeps a voltage at the Vs or ground voltage has to output a higher power than a driver circuit which outputs a voltage level other than the Vs or ground levels. Accordingly, if a voltage is first kept at the voltage Vs by a high-power driver circuit, and then, is risen up to the voltage (Vs+Vpeb), it would not be necessary for a circuit for rising a voltage up to the voltage (Vs+Vpeb) to be a high-power driver circuit.

Hereinbelow is explained a method of driving a plasma display panel, in accordance with the third embodiment of the present invention, with reference toFIGS. 8A to 8Din whichFIG. 8Aillustrates a waveform of a pulse to be applied to the sustaining electrode4in a preliminary discharge period,FIG. 8Billustrates a waveform of a pulse to be applied to the scanning electrode3in a preliminary discharge period,FIG. 8Cillustrates a voltage difference between the scanning electrode3and the sustaining electrode4, andFIG. 8Dillustrates a waveform of light emitted in a cell as a result of the voltage difference illustrated inFIG. 8C.

The third embodiment is different from the second embodiment in that a pulse (Vs+Vpeb) to be applied to the sustaining electrodes4in synchronization with the preliminary erasing discharge pulse12is terminated while the preliminary erasing discharge pulse12is falling down at its leading edge, and a pulse to be applied to the sustaining electrodes4is fallen down to the voltage Vs.

As illustrated inFIG. 7C, the final voltage difference in the second embodiment is equal to −(Vs+Vpeb) which is greater than −Vs in the conventional method. It was found out that if a final voltage difference during generation of the preliminary erasing discharge was too high, there was generated erroneous discharge which has not been found yet, specifically, sustaining discharge in a non-selected cell.

For instance, assuming that the pulses illustrated inFIGS. 7A and 7Bwere applied to a plasma display panel, erroneous discharge was generated though intensive discharge was not generated during generation of the preliminary erasing discharge, if the voltage Vpeb was over 30 V when the voltage Vs was equal to 165 V and the voltage Vp was equal to 320 V. In order to avoid such erroneous discharge, it is necessary for the voltage difference at the generation of the preliminary erasing discharge not to exceed the voltage (−Vs). Accordingly, in the third embodiment, a voltage of the sustaining electrodes4is fallen down to the voltage Vs from the voltage (Vs+Vpeb) before a leading edge of the preliminary erasing discharge pulse12to be applied to the scanning electrodes3reaches the voltage Vpeb.

In the third embodiment, as illustrated inFIGS. 8A to 8D, just when a leading edge of the preliminary erasing discharge pulse12reaches the voltage Vpeb, a voltage of the sustaining electrodes4is fallen down to the voltage Vs. The voltage difference between the scanning and sustaining electrodes3and4is equal to −Vs, when a leading edge of the preliminary erasing discharge pulse12applied to the scanning electrodes3is equal to the voltage Vpeb, and a voltage applied to the sustaining electrodes4is equal to the voltage Vs. However, by falling a voltage applied to the sustaining electrodes4down to the voltage Vs, the voltage difference can be reduced down to −(Vs−Vpeb). Since a voltage applied to the sustaining electrodes4is kept at the voltage Vs thereafter, the voltage difference would be −Vs, even if a leading edge of the preliminary erasing discharge pulse12applied to the scanning electrodes3gradually falls down, and finally reaches a ground voltage.

Thus, the voltage difference between the scanning and sustaining electrodes3and4is always smaller than −Vs.

In accordance with the third embodiment, it was possible to raise the voltage Vpeb up to 70V, when the pulses illustrated inFIGS. 7A to 7Cwere applied to a plasma display panel, the voltage Vs was set equal to 165V, and the voltage Vp was set equal to 320V.

The preliminary erasing discharge terminates when a voltage applied to the sustaining electrodes4is fallen down to the voltage Vs from the voltage (Vs+Vpeb).

In accordance with the third embodiment, it is possible to readily shorten the period of time X, and suppress intensive discharge during the preliminary erasing discharge by a low drive voltage. In addition, since the voltage difference between the scanning and sustaining electrodes3and4while the preliminary erasing discharge pulse12is being applied to the scanning electrodes3is in the range of 0 and −Vs, it is also possible the above-mentioned problem which was newly caused, because the voltage difference was over −Vs.

Hereinbelow is explained a method of driving a plasma display panel, in accordance with the fourth embodiment of the present invention, with reference toFIGS. 9A to 9Din whichFIG. 9Aillustrates a waveform of a pulse to be applied to the sustaining electrode4in a preliminary discharge period,FIG. 9Billustrates a waveform of a pulse to be applied to the scanning electrode3in a preliminary discharge period,FIG. 9Cillustrates a voltage difference between the scanning electrode3and the sustaining electrode4, andFIG. 9Dillustrates a waveform of light emitted in a cell as a result of the voltage difference illustrated inFIG. 9C.

The fourth embodiment is different from the second embodiment in that the preliminary erasing discharge pulse12finally reaches a voltage higher than the voltage Vpeb.

In the fourth embodiment, as illustrated inFIG. 9B, the preliminary erasing discharge pulse12is designed to finally reach the voltage Vpeb.

When a leading edge of the preliminary erasing discharge pulse12applied to the scanning electrodes3reaches the voltage Vpeb, a voltage (Vs+Vpeb) is applied to the sustaining electrodes4. Accordingly, the voltage difference between the scanning and sustaining electrodes3and4is equal to −Vs. Since a voltage of the preliminary erasing discharge pulse12is not smaller than the voltage Vpeb and a voltage applied to the sustaining electrodes4is not greater than the voltage (Vs+Vpeb), the voltage difference between the scanning and sustaining electrodes3and4is always smaller than −Vs.

Accordingly, similarly to the third embodiment, the fourth embodiment makes it possible to readily shorten the period of time X, and suppress intensive discharge during the preliminary erasing discharge by a low drive voltage. In addition, since the voltage difference between the scanning and sustaining electrodes3and4while the preliminary erasing discharge pulse12is being applied to the scanning electrodes3is in the range of 0 and −Vs similarly to the conventional method, it is also possible the above-mentioned problem which was newly caused, because the voltage difference was over −Vs.

Hereinbelow is explained a method of driving a plasma display panel, in accordance with the fifth embodiment of the present invention, with reference toFIGS. 10A to 10Din whichFIG. 10Aillustrates a waveform of a pulse to be applied to the sustaining electrode4in a preliminary discharge period,FIG. 10Billustrates a waveform of a pulse to be applied to the scanning electrode3in a preliminary discharge period,FIG. 10Cillustrates a voltage difference between the scanning electrode3and the sustaining electrode4, andFIG. 10Dillustrates a waveform of light emitted in a cell as a result of the voltage difference illustrated inFIG. 10C.

In the fifth embodiment, the preliminary erasing discharge pulse12to be applied to the scanning electrodes3steeply falls down to a voltage Vstep from the voltage Vs, and then, further gently falls down to a ground voltage from the voltage Vstep.

As illustrated inFIG. 10C, when a pulse having a negative sign is applied across the scanning and sustaining electrodes3and4after termination of the application of the preliminary discharge pulses11aand11b,a leading edge of the negative pulse varies to the voltage −Vs from the voltage −(Vs−Vstep), whereas a leading edge of the pulse varies to the voltage −Vs from zero (0) in the conventional method.

In accordance with the fifth embodiment, it is possible to delete a period of time necessary for the pulse to gently fall down to the voltage −(Vs−Vstep) from zero, ensuring that the period of time X can be shortened. The period of time X can be shortened by newly introducing the voltage Vpeb, and it is also possible to suppress intensive discharge during the generation of the preliminary erasing discharge by means of a low drive voltage Vp.

It was found out that if the preliminary erasing discharge was generated at a moment when the voltage difference reached the voltage −(Vs−Vstep) after the termination of the application of the preliminary discharge pulses11aand11b, the preliminary erasing discharge was generated as intensive discharge. Hence, the voltage Vstep has to be determined to be such a voltage that discharge is not generated when the voltage difference defined as a sum of the voltage Vstep and a wall charge voltage formed by the preliminary discharge reaches the voltage −(Vs−Vstep). Specifically, the voltage Vstep is set smaller than a minimum voltage at which discharge is generated when a voltage of the sustaining electrodes4is set equal to the voltage Vs and a voltage of the scanning electrode3is set equal to the voltage Vstep after termination of the preliminary erasing discharge pulse12. For instance, the voltage Vstep may be set smaller than 70V when the voltage Vs is set equal to 165V and the voltage Vp is set equal to 320V in the plasma display panel having the relation illustrated inFIG. 6.

It is not preferable that a trailing edge of the preliminary discharge pulse11bwhich falls down is continuous with a leading edge of the voltage Vstep which falls down. This is because a driver circuit for outputting a pulse Vpeb has to be designed to be able to output an intensive current in a short period of time in order to continuously fall down the voltage Vp of the preliminary discharge pulse11bto the voltage Vstep. It is preferable that the preliminary discharge pulse11bis kept at the voltage Vs for a certain period of time after fallen down from the voltage Vp, and thereafter, fallen down to the voltage Vstep.

The method in accordance with the fifth embodiment can be carried out without preparing a new power source, if a voltage of the scanning base pulse18to be applied to the scanning electrodes3in a scanning period is designed equal to the voltage Vstep. Similarly, the method in accordance with the fifth embodiment can be carried out without preparing a new circuit, if a driver circuit for outputting the scanning base pulse18is designed to output a pulse having the voltage Vstep.

Steep rising-up and falling-down of a pulse in the description having been made above means such a voltage change as being generated by digitally turning on a switching device such as a field effect transistor (FET). A plasma display panel has capacitive load therein, and thus, such steep rising-up and falling-down of a pulse take about 1 microsecond, particularly in a large-sized panel. If expressed in a rate per a unit time, the rate is equal to or greater than 100 V/μs. On the other hand, gentle rising-up and falling-down of a pulse in the description having been made above means such a voltage change as being generated by gradually varying an impedance of a switching device while the switching device is on. If expressed in a rate per a unit time, the rate is equal to or smaller than 10 V/μs.

Though Xe metastable level atoms are described as most primary priming particles in the above-mentioned first to fifth embodiments, charged or excited particles other than Xe metastable level atoms may be selected as priming particles, if a discharge gas composition is changed from the same used in the first to fifth embodiments. Even in such a case, it is possible to suppress intensive discharge similarly to the first to fifth embodiments by setting the period of time X to be shorter than 3T where T indicates a decay time constant of the most primary priming particle.

The entire disclosure of Japanese Patent Application No. 2002-097945 filed on Mar. 29, 2002 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.