1.  Field of the Invention
The present invention relates to an AC-type ((Alternating Current type) plasma display panel (PDP) and a method for driving the AC-type PDP and more particularly to the matrix-type AC-type PDP to perform display in a form of a matrix and the method for driving the matrix-type AC-type PDP. 
The present application claims priority of Japanese Patent Application No.  2001-398402 filed on Dec. 27, 2001, which is hereby incorporated by reference. 
2.  Description of the Related Art
A PDP can be classified from a viewpoint of its structure into two types, one type being a DC (Direct-current)-type PDP in which electrodes are exposed in a discharging gas and another type being an AC (Alternating Current)-type PDP in which electrodes are covered with a dielectric and not exposed directly to the discharging gas.  Furthermore, the AC-type PDP can be classified into two types, one type being a memory-operated-type AC-type PDP in which a memory function based on an electric charge accumulating action on the dielectric is used and another being a refresh-operated-type AC-type PDP in which such the memory function is not used. 
A generic memory-operated-type and AC-type PDP and its driving method are described by referring to FIG.  8.  FIG.  8 is an exploded perspective view of the conventional AC-type PDP.  The conventional AC-type PDP shown in FIG.  8 has an insulating substrate 101a on a front surface and an insulating substrate 101b on a rear surface.  On the insulating substrate 101a are arranged, at specified intervals, scanning electrodes 109 and sustaining electrodes 110 in parallel to each other and in such a manner that each of the scanning electrodes 109 pairs up with each of the sustaining electrodes 110.  Each of the scanning electrodes 109 and each of the sustaining electrodes 110 are made up of a bus electrode 103 to possess electrical conductivity and a main discharge electrode 102 to cause discharge to occur.  In FIG.  8, though a transparent electrode is used as the main discharge electrode 102 to prevent a decrease in transmittancy, use of the transparent electrode is not always necessary.  The scanning electrodes 109 and sustaining electrodes 110 are covered with a dielectric layer 104a on which a protective film 105 made of magnesium oxide is formed that serves to protect the dielectric layer 104a from discharging. 
On the insulating substrate 101b are placed data electrodes 106 in such a manner that each of the data electrodes 106 and each of the scanning electrodes 109 intersect at right angles and that each of the data electrodes 106 and each of the sustaining electrodes 110 also intersect at right angles.  The data electrodes 106 are covered with a dielectric layer 104b.  On the dielectric layer 104b are formed first partition walls (ribs) 107 each being used to secure discharging space and to partition a display cell.  On the dielectric layer 104b on which the first partition walls 107 are not formed and on sides of the first partition walls 107 is applied a phosphor 108 used to convert ultraviolet rays generated by discharge into visible light.  By applying the phosphor 108 so as to assign, for example, each color out of three primary colors consisting of a red color, a green color, and a blue color to a different cell, color display can be achieved.  Space being put between the insulating substrates 101a and 101b and being partitioned by each of the first partition walls 107 is hermetically filled with discharging gas selected from the group consisting of helium, neon, xenon, Argon or a like. 
FIG.  9A is a plan view of the conventional AC-type PDP when seen from a side of its display surface.  Each of the scanning electrodes (Si) 109 and each of the sustaining electrodes (C) 110 are arranged, in parallel to each other and in a row direction, so as to pair up with each other.  Out of gaps formed between the scanning electrodes 109 and the sustaining electrodes 110, the gap having a shorter distance is called “discharging space” in which surface discharge occurs between each of the scanning electrodes 109 and each of the sustaining electrodes 110, which makes up a display line.  On the other hand, the gap having a larger size and in which discharge does not occur is called “non-discharging space”. 
Next, a method for driving the conventional memory-operated-type and AC-type PDP is described by referring to FIG.  10.  FIG.  10 is a timing chart showing pulses of voltages applied to each electrode which explains driving waveforms employed in the conventional method.  In FIG.  10, “Si” denotes one of the scanning electrodes 109 which is scanned “i-th” time. “ C” denotes one of the sustaining electrodes 110. “ D” denotes one of the data electrodes 106.  As shown in FIG.  10, a basic cycle of the driving of the conventional AC-type PDP is made up of an initializing period during which a display cell is initialized to cause discharge to occur readily, a scanning period during which a display cell to be used for displaying is selected, and a sustaining period during which the display cell selected during the scanning period is made to emit light.  First, during the initializing period, an erasing pulse is applied to all the scanning electrodes (Si) 109 to stop discharge of a display cell having emitted light due to sustaining discharge before the initializing period shown in FIG.  10, thereby putting all the display cells into an erased state.  Next, a pre-discharging pulse is applied to all the scanning electrodes (Si) 109 to cause all the display cells to forcedly emit light and further a pre-discharge erasing pulse is applied to all the scanning electrodes (Si) 109, thereby stopping discharge of all display cells.  Such the pre-discharging and pre-discharge erasing operations cause subsequent writing discharge to occur readily. 
During the scanning period during which discharge for selection of the display cell occurs, the scanning pulse is sequentially applied to each of the scanning electrodes (Si) 109 by deviating timing with which the scanning pulse is applied and a data pulse is applied, with timing with which the scanning pulse is applied to each of the scanning electrodes (Si) 109, to the data electrodes (D) 106 according to display data.  In a display cell to which the data pulse has been applied while the scanning pulse was applied, discharge occurs between each of the scanning electrodes (Si) 109 and each of the data electrodes (D) 106 and the discharge induces another discharge to occur between each of the scanning electrodes (Si) 109 and each of sustaining electrodes (C) 110.  A series of these operations is called “writing discharge”.  When the writing discharge occurs, positive charges are accumulated on the dielectric layer 104a on each of the scanning electrodes (Si) 109, negative charges are accumulated on the dielectric layer 104a on each of the sustaining electrodes (C) 110 and negative charges are accumulated on the dielectric layer 104b on each of the data electrodes (D) 106
During the sustaining period, when the writing discharge occurred during the scanning period and a voltage produced by electric charges accumulated on the dielectric layer 104a has been superimposed on a sustaining voltage, surface discharge occurs between each of the scanning electrodes (Si) 109 and each of the sustaining electrodes (C) 110.  When the writing discharge does not occur during the scanning period and no wall charges are formed on the dielectric layer 104a, the sustaining voltage is set so as not to exceed an initiating voltage at which surface discharge occurs.  Therefore, the sustaining discharge required for display occurs only in display cells selected during the scanning period. 
When a first-time sustaining discharge occurs, negative charges are accumulated on the dielectric layer 104a on the scanning electrodes (Si) 109 and positive charges are accumulated on the dielectric layer 104a on the sustaining electrodes (C) 110.  A polarity of a voltage of a second-time sustaining pulse to be applied to the scanning electrode (Si) 109 and the sustaining electrode (C) 110 is reverse to a voltage of the first-time sustaining pulse, a voltage produced by charges accumulated on the dielectric layer 104a is superimposed on the voltage of the second sustaining pulse, which causes second-time discharge to occur.  Thereafter, occurrence of the sustaining discharge continues in the same manner as above.  If no surface discharge occurs by the first-time pulse, no discharge occurs by subsequent sustaining pulses. 
The above-described three periods including the initializing period, scanning period, and sustaining period makes up one sub-field and an image is displayed by ON/OFF operations in a plurality of the sub-fields.  According to the conventional method for driving described above, light-emitting luminance in the conventional AC-type PDP is represented by a product of a number of sustaining pulses, that is, a number of times of light-emission and luminance provided by one-time light-emission during the sustaining period.  Therefore, enhancement of the luminance can be achieved by increasing either of the number of times of light-emission or luminance to be produced by one-time light-emission during the sustaining period. 
However, since an increase in the number of times of light emission causes the sustaining period to increase, thus tending to shorten the scanning period, there is a limit to the increase.  On the other hand, by shortening a width of a sustaining pulse, while a length of the sustaining period is being kept, a number of sustaining pulses can be increased.  However, if the pulse width is shortened too much, since formation of the wall charge becomes insufficient, as a result, making it difficult to perform normal light emission, excessive shortening of the pulse width is not allowed.  To solve this problem, it is desirous to enhance luminance to be provided by one-time light emission. 
One method for enhancing luminance to be provided by one-time light emission is to make large an electrode being used for sustaining discharge which serves to widen the area in which discharge occurs.  However, as is apparent from FIG.  9A, it is impossible to make the width wider in a row direction.  Though it is possible to extend the width more in a column direction, since non-discharging space becomes narrower, discharge leak (crosstalk) among display cells existing in the column direction tends to readily occur.  In some cases, as shown in FIG.  11, erroneous discharge is prevented physically by inserting second partition walls (ribs) 107′ into the non-discharge space to form a display cell so as to have a sealed-type structure.  FIG.  9B shows a plan view of the conventional AC-type PDP when seen from a side of its display surface.  To make narrow the non-discharging space, two pieces of the scanning electrodes (Si, Si+1) 109 and two pieces of the sustaining electrodes C and C are alternately arranged, as shown in FIG.  9C, so that the non-discharging space is put between the scanning electrodes (Si, Si+1) 109 and between the sustaining electrodes (C) 110, thus enabling reduction of electrostatic capacity, which causes a load during the sustaining period, between electrodes.  The conventional AC-type PDP having such the display cell structure as described above can be driven by the method shown in FIG.  10. 
Next, stability of driving the conventional AC-type PDP during the scanning period is described.  During the scanning period, some periods of time are needed before writing discharge occurs after application of the scanning pulse.  The time is called “discharging delay time”.  The discharging delay time is determined, based on various parameters of the conventional AC-type PDP, as a value of probability.  An important index representing the discharging delay time includes density of a charged particle, a metastable particle, or a like existing in discharging space.  The charged particle and the metastable particle in totality are called as “priming particle”.  These particles are originally produced when pre-discharge during the initializing period or sustaining discharge occurred.  Existence of these particles causes discharge to readily occur and the probability of discharge to increase. 
In the driving method shown in FIG.  10, selection of display cells to be used for display is performed, sequentially in order of display lines, on each of display rows during the scanning period. 
As a result, if a same sub-field in display cells existing in the column direction is selected, immediately after occurrence of writing discharge, writing discharge occurs also in display cells adjacent to each other in the column direction.  A great number of priming particles are produced when writing discharge occurs and, if discharging space portions are connected to each other among display cells existing in the column direction, the priming particles are dispersed into display cells adjacent to the display cell where writing discharge occurred, thereby raising the probability of discharge in display cells adjacent to the display cell where writing discharge occurred.  Immediately after the dispersion of priming particles into the display cells, writing discharge occurs in display cells adjacent to the display cell where writing discharge occurred.  At this point, the priming particles has not almost decreased in an existing number since no time elapsed after the occurrence of the priming particles and the probability of discharge become very large, which serves to shorten the discharging delay time and thus causes writing discharge to occur in a reliable manner, as a result, preventing a failure in light emission.  Therefore, the priming particles produced when writing discharge occurs has a great influence on operations of the conventional AC-type PDP. 
If a number of electrodes used to cause sustaining discharge to occur in the column direction is increased, non-discharging space becomes narrow and, as a result, discharge leak occurs in the column direction.  At the time of occurrence of writing discharge, since the discharge occurs not only between each of the scanning electrodes 109 and each of the sustaining electrodes (C) 110, but also between each of the scanning electrodes 109 and each of the data electrodes 106, discharge leak tends to occur more often.  Moreover, in the conventional AC-type PDP in which two scanning electrodes 109 being adjacent to each other and two sustaining electrodes (C) 110 being adjacent to each other are alternately arranged and a display line is formed by the scanning electrodes 109 and sustaining electrodes (C) 110 being adjacent to each other, during the scanning period, since a scanning pulse is applied only to the scanning electrodes 109 being scanned, a difference in potential is always provided between scanning electrodes 109 being adjacent to each other.  However, since the sustaining electrodes (C) 110 are always kept at a same potential and there is no difference in potential between the sustaining electrodes (C) 110 being adjacent to each other, discharge leak tends to occur more often, thus resulting in reduction of operating range. 
Therefore, as shown in FIG.  9B and FIG.  9C, by placing the first partition wall in the space, serving as the non-discharging space, between display cells in the column direction to construct the display cell in a sealed form, the discharging space has to be partitioned.  However, if such the first partition wall is placed, an area in which light is intercepted increases, as a result, reducing luminance.  In this case, since a sealing characteristic of each display cell is large, the priming particles cannot be captured from display cells being adjacent to each other and, even when the display cell is consecutively selected in the column direction, improvement in the discharging delay time cannot be expected, thus causing a failure in lighting in some cases. 
Furthermore, before the conventional AC-type PDP is filled with discharging gas, the conventional AC-type PDP has to be evacuated once and unwanted gas has to be exhausted from the PDP.  However, since, at the time of the evacuation, exhausting time is determined depending on exhaust conductance, if the conventional AC-type PDP has such the highly-sealed type of cell structure, much time is required for exhausting the unwanted gas. 
To solve this problem, a trial to improve operating range by forming a groove in a transverse wall in such a manner to surround a discharging occurring area is disclosed in Japanese Patent Application Laid-open No.  2001-189133.  However, an experiment made by the inventors showed that, even when a non-discharging space was made narrow by the disclosed trial, discharge leak was not inhibited sufficiently and operating range is reduced much.  Therefore, since the number of electrodes used to cause discharge to occur is not allowed to increase, an increase in luminance was impossible. 
Another trial is disclosed in Japanese Patent Application Laid-open No.  2000-123747 in which a protrusion being lower than a first partition wall placed in space between display cells in a column direction is formed.  However, this trial presents a problem in that, due to a difference in height of the first partition walls placed in space between display cells, manufacturing processes for forming the first partition walls are made complicated.