Plasma display panel

The invention provides a plasma display panel having an improved light emission contrast. The plasma display panel includes a plurality of discharge sustaining electrode pairs X.sub.n and Y.sub.n each comprising discharge sustaining electrodes x'.sub.n and x.sub.n, and y.sub.n and y'.sub.n, respectively, which are electrically isolated from each other and which extend in a direction along the scanning lines. The plasma display panel also includes discharging cells in which a discharge occurs within a region limited between the discharge sustaining electrodes x.sub.n and y.sub.n in the first and second priming periods, small-width erasing periods, and writing periods. The black-level intensity can be reduced without causing an increase in the power dissipation and a significant decrease in the normal light emission intensity. Thus, the light emission contrast is improved to a great extent without having to increase the maximum light emission intensity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relate to a plasma display panel provided with 
electrodes having a structure bringing about an improvement in the 
contrast of light emission on the display screen. 
2. Description of the Related Art 
FIG. 3 illustrates the structure of a plane-emission plasma display panel 
according to a conventional technique. 
In FIG. 3, there are provided stripe-shaped discharge-sustaining electrodes 
X.sub.n and Y.sub.n formed on a front glass plate 1. Although discharge 
sustaining electrodes are disposed in the order . . . , X.sub.n, Y.sub.n, 
X.sub.n+1, Y.sub.n+1, . . . in the specific example shown in FIG. 3, they 
may also be disposed in the order such as . . . , Y.sub.n, X.sub.n, 
Y.sub.n+1, X.sub.n+1, . . . to achieve the same functions. The discharge 
sustaining electrodes X.sub.n and Y.sub.n each comprise a transparent 
electrode 2 and a bus electrode 3 for supplying electric power to the 
transparent electrode 2. The discharge sustaining electrodes X.sub.n and 
Y.sub.n are covered with a dielectric layer 4 on which there is provided a 
cathode film 5 made up of a MgO film serving as a discharging cathode. 
On the cathode film 5, there are provided partition walls 7 extending in a 
direction perpendicular to the discharge sustaining electrodes X.sub.n and 
Y.sub.n so that discharging spaces 6 are isolated from each other by the 
partition walls 7. Address electrodes 8 for selecting a light emission 
region in the discharging spaces 6 are formed between adjacent partition 
walls 7 in such a manner that the address electrodes 8 extend in a 
direction parallel to the partition walls 7. Each discharging spaces 6 are 
filled with a mixed gas of Ne and Xe. 
Furthermore, three-color phosphors 9 are disposed periodically in the order 
red 9R, green 9G and blue 9B on the surfaces, on the sides facing the 
respective discharging spaces, of the partition walls and the address 
electrodes 8. Furthermore, as shown in FIG. 3, there is also provided a 
back side glass plate 10 on the partition walls and the address electrodes 
8. 
An nth scanning line is formed by the discharge sustaining electrodes 
X.sub.n and Y.sub.n. In the discharging spaces 6, a discharging cell in 
which a discharge occurs is formed at each intersection of the scanning 
lines and the address electrodes. That is, the plasma display panel has 
the structure in which discharging cells are disposed in a matrix fashion. 
FIG. 4 illustrates a cross section of the conventional plasma display 
panel, taken along a plane perpendicular to the scanning lines. For 
simplicity, the partition walls 7, the address electrodes, 8, the 
phosphors 9R, 9G, and 9B, and the back side glass plate 10 are not shown 
in FIG. 4. 
In FIG. 4, by way of example, dimensions typical for a 40 inch VGA-type 
plasma display panel are also shown, wherein the values are expressed in 
.mu.m. As shown in FIG. 4, the nth scanning line is located at the center 
between a pair of discharge sustaining electrodes X.sub.n and Y.sub.n. 
The operation of the conventional plasma display panel is described below. 
FIG. 5 illustrates an example of the manner in which a frame is divided 
into a plurality of fields so that a color image with 256 halftone levels 
is represented therein. 
In this example, one main frame consists of eight subfields (first SF to 
eighth SF). Each subfield consists of a first priming period (I), a second 
priming period (II), a small-width erasing period (III), a writing period 
(IV), and a discharge sustaining period (V). 
In any subfield, the periods I-IV are equal in length of time. However, the 
discharge sustaining period (V) varies in accordance with the rank defined 
for each subfield. The discharge sustaining period (V) of the (N+1)th 
subfield is about twice that of the nth subfield (wherein N is a natural 
number). In the writing period (IV) of each subfield, a desired cell is 
selected by applying a pulse-shaped voltage to a corresponding address 
electrode 8. During the following discharge sustaining period (V), a 
sustaining discharge occurs as many times as the number of sustaining 
pulses applied during the discharge sustaining period (V). Therefore, the 
length of the discharge sustaining period (V) is proportional to the 
number of sustaining pulses. 
As a result, the intensity of light emission which occurs in the cell 
selected in the writing period (IV) increases about twice at each 
transition from any subfield to the following subfield. In the main frame, 
the respective subfields are either selected or not selected so as to 
achieve any arbitrary halftone level selected from 2.sup.8 =256 levels. 
FIG. 6 is a timing chart illustrating an example of a sequence of pulses 
applied, in each subfield, to the address electrodes (W electrodes) and 
the discharge sustaining electrodes X.sub.n and Y.sub.n. 
After passing through the first priming period (I) and further the second 
priming period (II), a priming discharge occurs between the discharge 
sustaining electrodes X.sub.n and Y.sub.n in all discharging cells. In the 
subsequent small-width erasing period (III), an erasing discharge occurs 
between the discharge sustaining electrodes X.sub.n and Y.sub.n. thereby 
removing most of charges present on the surface of the cathode film 5 at 
locations above the discharge sustaining electrodes X.sub.n and Y.sub.n. 
As a result, information stored in the discharging cell selected in the 
previous subfield is reset. 
In the following writing period (IV), the voltage of the discharge 
sustaining electrode Y.sub.n is swung from one scanning line to another. 
In synchronization therewith, a selected/non-selected image signal is 
applied to the W electrode of the respective cells so that a writing 
discharge occurs between Xn and Y.sub.n in the selected cells. In the 
discharging cells in which the writing discharge has occurred, a 
sustaining discharge occurs as many times as the number of sustaining 
pulses applied to the discharge sustaining electrodes X.sub.n and Y.sub.n 
during the following discharge sustaining period (V). On the other hand, 
in the discharging cells which were not selected in the writing period 
(IV), no sustaining discharge occurs during the sustaining period (V). By 
properly selecting discharging cells in the manner described above, a 
desired image is produced. 
In the plasma display panel, the discharging cells which were not selected 
during the writing period (IV) have no discharge during the discharge 
sustaining period (V) as described above, and thus black is displayed in 
these non-selected discharging cells. 
The image becomes sharper and clearer with the ratio (light emission 
contrast) of the light emission intensity (maximum brightness) of the 
discharge in the discharging cells selected in the writing period (IV) to 
the black-level intensity of the discharging cells which were not selected 
in the writing period (IV). In other words, to improve the image quality 
of the plasma display panel, it is required to increase the light emission 
contrast. 
One possible way of increasing the light emission contrast is to generally 
increase the number of sustaining pulses applied during the discharge 
sustaining period (V) thereby increasing the maximum light emission 
intensity thus increasing the contrast. However, this technique results in 
an increase in the power dissipation and also an increase in the amount of 
heat generated in the plasma display panel. Therefore, this technique has 
a limitation in the maximum light emission contrast. 
In the operating sequence described above, "black" is displayed by not 
selecting the discharging cell of interest during the writing period (IV) 
in any subfield. However, even in the discharging cells which were not 
selected during the writing period (IV), a priming discharge and erasing 
discharge still occur in the first and second priming periods (I, II) and 
the erasing period (III), respectively. This makes it difficult to 
decrease the black-level intensity. 
Furthermore, as shown in FIG. 4, the priming discharge and the erasing 
discharge during the first and second priming periods (I, II) and the 
small-width erasing period (III) occur over the entire width of the 
discharge sustaining electrodes X.sub.n and Y.sub.n as in the case of the 
sustaining discharge during the discharge sustaining period (V). In 
particular, in the second priming period (II) and the small-width erasing 
period (III), pulses with a large amplitude are applied between the 
discharge sustaining electrodes X.sub.n and Y.sub.n, and thus the 
intensity of light emission generated by one discharge during these 
periods is generally greater than the intensity of light emission 
generated by one discharge in the discharge sustaining period. 
For the above reason, the maximum light emission contrast practically 
achieved in the conventional plasma display panel is about 50:1. However, 
the light emission contrast of 50:1 is not high enough to represent fine 
difference in the light emission intensity in the low halftone-level 
range. As described above, the conventional plasma display panel has the 
problem that it is difficult to achieve a high enough light emission 
contrast without causing an increase in the power dissipation or an 
increase in heat generated in the plasma display panel. 
Thus, it is an object of the present invention to provide a plasma display 
device having an improved light emission contrast without encountering a 
significant increase in the power dissipation and heat generation. 
SUMMARY OF THE INVENTION 
According to an aspect of the present invention, there is provided a plasma 
display panel comprising: a back side glass plate on which there is 
provided an address electrode; a front glass plate located opposite to the 
back side glass plate; andapluralityofdischarge sustaining electrode pairs 
provided on the front glass plate in such a manner that they extend along 
scanning lines perpendicular to the address electrode, wherein the 
discharge sustaining electrodes X.sub.n and Y.sub.n of each discharge 
sustaining electrode pair comprise discharge sustaining electrodes 
x'.sub.n and x.sub.n, and y.sub.n and y'.sub.n, respectively, which are 
electrically isolated from each other and which extend in a direction 
along the scanning lines. 
In a preferred form of the invention, the discharge sustaining electrodes 
x.sub.n and y.sub.n have the property of blocking light, and the discharge 
sustaining electrodes x'.sub.n and y'.sub.n are provided with a 
transparent electrode. 
In accordance with another aspect of the present invention, the 
electrically isolated discharge sustaining electrodes are disposed in the 
order x'.sub.n, x.sub.n, y.sub.n, y'.sub.n or in the order y'.sub.n, 
y.sub.n, x.sub.n, x'.sub.n, in a direction in which the scanning line 
number n increases (where n is a natural number). 
In accordance with a further aspect of the present invention, when a 
priming pulse and an erasing pulse are applied to the discharge sustaining 
electrodes x.sub.n and y.sub.n in driving operation, the priming pulse and 
the erasing pulse are not always applied to the discharge sustaining 
electrodes x'.sub.n and y'.sub.n. 
In a further preferred form of the present invention, no erasing pulse is 
applied to the discharge sustaining electrodes x'.sub.n and y'.sub.n. 
In a still further preferred form of the present invention, a priming pulse 
is applied to the discharge sustaining electrodes x'.sub.n and y'.sub.n 
only in one subfield of each main frame consisting of a plurality of 
subfields. 
In accordance with a still further aspect of the invention, a series of 
main frames each consisting of a plurality of subfields is constructed so 
that in some of the main frames no priming pulse is applied to the 
discharge sustaining electrodes x'.sub.n and y'.sub.n. 
In accordance with a yet further aspect of the present invention, when 
image data is written via the address electrode while sequentially 
scanning the scanning lines, a discharge occurs only in the region limited 
between the discharge sustaining electrodes x.sub.n and y.sub.n and the 
discharge sustaining electrodes x'.sub.n and y'.sub.n make no contribution 
to the discharge. 
In a further preferred formof the present invention, the plasma display 
panel further includes a dielectric layer covering the discharge 
sustaining electrode pair X.sub.n and Y.sub.n ; and a protective film 
covering the dielectric layer, wherein passivation films are formed of a 
material passive to discharging on the back-side surface of the protective 
film in such a manner that each passive film extends along each boundary 
between adjacent scanning lines. 
In a further preferred form of the present invention, first types of 
scanning lines and second types scanning lines are alternately disposed 
wherein each first type of scanning line comprises electrically isolated 
discharge sustaining electrodes disposed in the order x'.sub.n, x.sub.n, 
y.sub.n in a direction in which the scanning line number n increases and 
wherein each second type of scanning line comprises electrically isolated 
discharge sustaining electrodes disposed in the order y'.sub.n, y.sub.n, 
x.sub.n, and x'.sub.n in the direction in which the scanning line number n 
increases. 
In a further preferred form of the present invention, at least either 
discharge sustaining electrode x'.sub.n or y'.sub.n includes a part 
located at the boundary between adjacent scanning lines and shared by the 
adjacent scanning lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
FIG. 1 is a cross-sectional view schematically illustrating the structure 
of a plasma display device according to a first embodiment of the present 
invention. 
As shown in FIG. 1, there are provided a plurality of pairs of discharge 
sustaining electrodes X.sub.n and Y.sub.n on a front glass plate 1. The 
discharge sustaining electrodes X.sub.n and Y.sub.n comprise discharge 
sustaining electrodes x'.sub.n and x.sub.n and y.sub.n and y'.sub.n, 
respectively, each extending in a direction along the scanning line, 
wherein x.sub.n and y.sub.n are electrically isolated from each other and 
x'.sub.n and y'.sub.n are also electrically isolated from each other. 
Although in the present embodiment the electrically isolated discharge 
sustaining electrodes are disposed in the order x.sub.n, x'.sub.n, 
y.sub.n, and y'.sub.n in a direction toward a greater value of scanning 
line number n, they may also be disposed in the order y'.sub.n, y.sub.n, 
x.sub.n, and x'.sub.n to achieve the same functions. 
As shown in FIG. 1, the discharge sustaining electrodes x.sub.n and y.sub.n 
are spaced 75 .mu.m apart from each other via the nth scanning line. At 
locations which are 50 .mu.m apart, in a direction opposite to the nth 
scanning line, from the respective discharge sustaining electrodes x.sub.n 
and y.sub.n, there are provided discharge sustaining electrodes x'.sub.n 
and y'.sub.n, respectively. The discharge sustaining electrodes x.sub.n 
and y.sub.n each consist of an opaque bus electrode 11 formed of metal. 
The discharge sustaining electrodes x'.sub.n and y'.sub.n each consist of 
a transparent electrode 12 and an opaque bus electrode 13 formed of metal, 
wherein the bus electrode 13 is located on the side, opposite to the nth 
scanning direction, of the transparent electrode 12. 
These discharge sustaining electrodes X.sub.n and Y.sub.n are covered with 
a dielectric layer 4 on which there is formed a cathode film 5 made of 
MgO. 
On the cathode film 5, although not shown in FIG. 1, there are also 
provided, as in the conventional plasma display panel, partition walls for 
isolating discharging spaces from each other, address electrodes disposed 
between adjacent partition walls, three-color phosphors (red, green, 
blue), and a back side glass plate. In FIG. 1, by way of example, 
dimensions typical for 40 inch VGA-type plasma display panels are also 
described, wherein the values are all expressed in .mu.m. Dimensions 
described elsewhere in this invention are also in .mu.m. 
FIG. 2 is a time chart representing a time sequence of pulse voltages which 
are applied to the respective electrodes so as to drive the plasma display 
panel according to the first embodiment of the invention. The image frame 
is divided into a plurality of fields in the same manner as in the 
conventional plasma display panel (refer to FIG. 5). 
As shown in FIG. 2, the sequence of pulse voltages applied to the address 
electrode 8 are similar to those employed in the conventional technique 
(described earlier with reference to FIG. 6). The sequence of pulse 
voltages applied to the discharge sustaining electrodes x.sub.n and yn are 
also similar to those applied to the discharge sustaining electrodes 
X.sub.n and Y.sub.n of the conventional plasma display panel (refer to 
FIG. 6). On the other hand, to the discharge sustaining electrodes 
x'.sub.n and y'.sub.n, a sequence of pulse voltages are applied 
independently of those applied to the discharge sustaining electrodes 
x.sub.n and y.sub.n. 
The operation of the plasma display panel according to the first embodiment 
of the invention is described below. 
During the first priming period (I) and the second priming period (II) in 
the first subfield, the voltages of the discharge sustaining electrodes 
x'.sub.n and y'.sub.n vary in the same manner as those of the discharge 
sustaining electrodes x.sub.n and y.sub.n as represented by the alternate 
long and short dash line in FIG. 2 (the voltages applied to the discharge 
sustaining electrodes x'.sub.n vary in the manner described by the 
alternate long and short dash line only in the first subfield, and they 
vary in the manner described by the solid line in the second subfield and 
other subfields following that). 
In this situation, because the discharge sustaining electrodes x'.sub.n and 
y'.sub.n have the same voltage as those of the discharge sustaining 
electrodes x.sub.n and y.sub.n, respectively, and because the gap between 
the discharge sustaining electrodes x.sub.n and y.sub.n is as small as 50 
.mu.m, the potential of the surface of the cathode film 5 at the locations 
above the discharge sustaining electrodes x.sub.n and x'.sub.n and that at 
the locations above the discharge sustaining electrodes y.sub.n and 
y'.sub.n are determined mainly by the potential of the discharge 
sustaining electrodes x.sub.n and x'.sub.n and that of the discharge 
sustaining electrodes y.sub.n and y'.sub.n without having substantially no 
influence of the potential of the address electrode 8 separated by the 
discharging space 6 from the discharge sustaining electrodes. 
As a result, the voltages of the discharge sustaining electrodes x.sub.n 
and x'.sub.n become greater than those of the discharge sustaining 
electrodes y.sub.n and y'.sub.n. Thus, an electric field is developed 
between the discharge sustaining electrodes x.sub.n and y.sub.n and the 
discharge sustaining electrodes x'.sub.n and y'.sub.n in a direction from 
the discharge sustaining electrodes x.sub.n and x'.sub.n toward the 
discharge sustaining electrodes y.sub.n and y'.sub.n. 
In this situation, if a priming discharge starts, in the first and second 
priming periods (I, II) of the first subfield, at the location above the 
gap (75 .mu.m) between the discharge sustaining electrodes x.sub.n and 
y.sub.n where a highly concentrated electric field is developed, the 
discharge grows into a greater size extending over the entire width of the 
discharge sustaining electrodes X.sub.n and Y.sub.n. The size of a grown 
discharge is schematically illustrated at the (n-1)th scanning line in 
FIG. 1. 
In this case, as described above, the priming discharge during the second 
priming period occurs in the great region in which the discharge 
sustaining electrodes x'.sub.n and y'.sub.n also make a contribution to 
the priming discharge. The surface areas of the discharge sustaining 
electrodes X.sub.n and Y.sub.n are nearly equal to those of the 
conventional discharge sustaining electrodes X.sub.n and Y.sub.n, and thus 
the discharge grown into the great size has an intensity similar to that 
which occurs between the conventional discharge sustaining electrodes 
X.sub.n and Y.sub.n. 
The major part of the width of each discharge sustaining electrode x'.sub.n 
and y'.sub.n is occupied by the transparent electrode 12. Therefore, light 
emitted from the phosphor 9 excited by the discharge passes through an 
aperture having a size similar to that of the conventional discharge 
sustaining electrodes X.sub.n and Y.sub.n. This means that the intensity 
of visible light emission is as large as that achieved by the discharge 
sustaining electrodes constructed into the conventional structure. 
At the end of the second priming period of the first subfield, there is a 
negative charge stored on the surface of the cathode film at the location 
above the discharge sustaining electrodes X.sub.n and x'.sub.n, and a 
positive charge above the discharge sustaining electrodes y.sub.n and 
y'.sub.n. 
After that, the operation proceeds to the small-width erasing period (III) 
of the first subfield. As described above, the sequence of pulses similar 
to that shown in FIG. 6 is input to the address electrodes 8, and the 
sequence of pulses similar to that applied to the conventional discharge 
sustaining electrodes X.sub.n and Y.sub.n is applied to the discharge 
sustaining electrodes x.sub.n and yn, respectively. Thus, an erasing 
discharge occurs between the discharge sustaining electrodes x.sub.n and 
y.sub.n thereby erasing most of charges which have been stored, through 
the first and second priming periods (I, II), on the surface of the 
cathode film 5 at the locations above the discharge sustaining electrodes 
x.sub.n and y.sub.n. 
The erasing discharge occurs when a small-width erasing pulse applied to 
the discharge sustaining electrodes x swings from the highest voltage to 
the GND voltage in the small-width erasing period (III) shown in FIG. 2. 
In order for the erasing discharge to occur, the discharge sustaining 
electrode y.sub.n needs to be at an intermediate voltage. To meet this 
requirement, the voltage applied to the discharge sustaining electrode 
y.sub.n is increased from GND to the intermediate voltage prior to 
applying the small-width erasing pulse. On the other hand, when the 
small-width erasing pulse is applied to the discharge sustaining electrode 
x.sub.n, the discharge sustaining electrode y'.sub.n is at GND while the 
discharge sustaining electrode x'.sub.n, to which the small-width erasing 
pulse is not applied, remains at the intermediate voltage. Therefore, the 
discharge sustaining electrodes x'.sub.n and y'.sub.n make no contribution 
to the erasing discharge. As a result, the erasing discharge occurs in a 
small region limited between the discharge sustaining electrodes x.sub.n 
and y.sub.n (as illustrated at the nth scanning line in FIG. 1). 
This small discharge occurs at a low intensity level and thus light 
emission from the phosphor 9 occurs at a corresponding low level. Besides, 
most of light emitted from the phosphor 9 is blocked by the opaque bus 
electrodes 11 made of metal forming the discharge sustaining electrodes 
x.sub.n and y.sub.n. As a result, the intensity of light arising from the 
erasing discharge, which is visible from the front side of the plasma 
display panel, becomes very low. Thus, the influence of the erasing 
discharge on the light emission contrast becomes extremely small. 
The negative and positive charges, which have been stored, through the 
first and second priming periods (I, II), on the surface of the cathode 
film 5 at the locations above the discharge sustaining electrodes x'.sub.n 
and y'.sub.n, respectively, remain there at the end of the small-width 
erasing period (III) of the first subfield. 
Then the operation proceeds to the writing period (IV) of the first 
subfield. In this writing period (IV), a sequence of pulse voltages is 
applied to the address electrode 8 in a similar manner to the conventional 
technique, and a sequence of pulse voltages is applied to the discharge 
sustaining electrodes x.sub.n and y.sub.n in a similar manner to that 
applied to the discharge sustaining electrode X.sub.n and Y.sub.n having 
the conventional structure. In response to an image signal applied to the 
address electrode 8, a light emission region is selected and a writing 
discharge occurs selectively between the discharge sustaining electrodes 
x.sub.n and y.sub.n. However, the voltage of the discharge sustaining 
electrode y'.sub.n is maintained at GND and there is a positive charge on 
the surface of the cathode film 5 at the corresponding location, and the 
voltage of the discharge sustaining electrode x'.sub.n is maintained at 
the intermediate voltage and there is a negative charge on the surface of 
the cathode film 5 at the corresponding location. Therefore, the discharge 
sustaining electrodes x'.sub.n and y'.sub.n make no contribution to the 
writing discharge. 
As a result, the writing discharge occurs in a small region limited between 
the discharge sustaining electrodes x.sub.n and y.sub.n. Thus, at the end 
of the writing period (IV) of the first subfield, negative and positive 
charges remain on the surface of the cathode film 5 at the locations above 
the discharge sustaining electrodes x.sub.n and y.sub.n in the discharging 
cell in which the writing discharge occurred in response to the image 
signal (i.e., in the discharge cell selected by the address electrode). On 
the other hand, in the discharge cells in which no writing charge occurred 
(i.e., in the discharge cells which were not selected by the address 
electrode), there is no such charge remaining on the surface of the 
cathode film 5 at the locations above the discharge sustaining electrodes 
x.sub.n and y.sub.n. 
On the other hand, at locations above the discharge sustaining electrodes 
x'.sub.n and y'.sub.n, almost all the negative and positive charges which 
have been stored through the first and second priming periods (I, II) 
remain on the surface of the cathode film 5 in all discharge cells 
regardless of whether the image signal was applied or not. 
Then the operation proceeds to the discharge sustaining period (V) of the 
first subfield. At the beginning of the discharge sustaining period (V), 
the discharge sustaining electrodes x.sub.n, y.sub.n, x'.sub.n, and 
y'.sub.n are all at the GND voltage. In the discharge cells in which the 
writing discharge occurred in the writing period (IV), the negative charge 
remains at the locations above the discharge sustaining electrodes x.sub.n 
and x'.sub.n, and the positive charge remains at the locations above the 
discharge sustaining electrodes y.sub.n and y'.sub.n. If the voltage of 
the discharge sustaining electrodes y.sub.n and y'.sub.n is increased to 
the intermediate voltage, the application of the intermediate voltage in 
addition to the presence of the remaining charge results in creation of a 
strong electric field in the discharging space at the location above the 
gap between the discharge sustaining electrodes x.sub.n and y.sub.n. As a 
result, a first large-size discharge occurs between the discharge 
sustaining electrodes X.sub.n and Y.sub.n. 
The above discharge occurs in the same manner as that in the first and 
second priming periods (I, II) of the first subfield, and thus the 
discharge occurs in a large region over the entire width of the discharge 
sustaining electrodes x.sub.n, x'.sub.n, y.sub.n, and y'.sub.n (i.e., over 
the entire width of the discharge sustaining electrodes X.sub.n and 
Y.sub.n). This first sustaining discharge ends when a certain among of 
positive charge has been stored at the location above the discharge 
sustaining electrode X.sub.n through the discharge and a certain amount of 
negative charge has been stored at the location above the discharge 
sustaining electrode Y.sub.n. Thus, certain amounts of positive and 
negative charges remain at the locations above the discharge sustaining 
electrodes x.sub.n and x'.sub.n, and y.sub.n and y'.sub.n, respectively. 
After that, the voltage of the discharge sustaining electrode Y.sub.n is 
returned to GND, and then the voltage of the discharge sustaining 
electrode X.sub.n is swung to the intermediate voltage. At this stage, the 
charges on the cathode film 5 and the voltages of the respective 
sustaining electrodes all become opposite in polarity to those in the 
first sustaining discharge. That is, there is a positive charge stored at 
the location above the discharge sustaining electrodes x.sub.n and 
x'.sub.n, and a negative charge stored at the location above the discharge 
sustaining electrodes y.sub.n and y'.sub.n. If the voltages of the 
discharge sustaining electrodes x.sub.n and x'.sub.n are both increased to 
the intermediate voltage while maintaining the discharge sustaining 
electrodes y.sub.n and y'.sub.n at GND, the application of the 
intermediate voltage in addition to the presence of the stored charge 
results in creation of a strong electric field in the discharging space at 
the location above the gap between the discharge sustaining electrodes 
x.sub.n and y.sub.n. Thus, following the first discharge, a second 
large-size discharge occurs between the discharge sustaining electrodes 
X.sub.n and Y.sub.n. 
The second sustaining discharge ends when a certain amount of negative 
charge has been stored at the location above the discharge sustaining 
electrode X.sub.n through the discharge and a certain amount of positive 
charge has been stored at the location above the discharge sustaining 
electrode Y.sub.n. The above operation is performed repeatedly so that a 
large-size sustaining discharge occurs each time a pulse is applied 
alternately to the discharge sustaining electrodes X.sub.n and Y.sub.n. 
In the discharging cells in which no writing discharge occurred in the 
writing period (IV), there are no similar charges at the locations above 
the discharge sustaining electrodes x.sub.n and y.sub.n. Therefore, when 
the voltages of the discharge sustaining electrodes y.sub.n and y'.sub.n 
are both increased to the intermediate voltage, the electric field does 
not become strong enough to start a discharge in the discharging space at 
the location above the gap between the discharge sustaining electrodes 
x.sub.n and y.sub.n. As a result, no sustaining discharge occurs in these 
discharging cells,. In these cells, no discharge occurs when a pulse is 
applied to the discharge sustaining electrode X.sub.n or Y.sub.n in the 
following operation steps. 
As a result of generating large-size discharges in the above-described 
manner during the discharge sustaining period (V) of the first subfield, a 
desired light emission image is created. At the end of the discharge 
sustaining period (V) of the first subfield, there are negative and 
positive charges stored at the locations above the discharge sustaining 
electrodes x.sub.n and y.sub.n, respeectively, in the discharging cells in 
which the sustaining discharge occurred. However, in the discharging cells 
in which no sustaining discharge occurred, there are no such charges at 
the location above the discharge sustaining electrodes x.sub.n, and 
y.sub.n. On the other hand, at the locations above the discharge 
sustaining electrodes x'.sub.n and y'.sub.n, there are negative and 
positive charges remaining on the surface of the cathode film 5 regardless 
of the occurrence of the sustaining discharge. This is a situation at the 
end of the first subfield. 
In the second subfield and the subfields following that, a similar sequence 
of operations is performed repeatedly. In the first priming period (I) of 
the second subfield, a discharge occurs in the small region limited 
between discharge sustaining electrodes x.sub.n and y.sub.n only in the 
discharging cells in which neither a writing discharge nor a sustaining 
discharge occurred in the first subfield. Also in this case, the discharge 
sustaining electrodes x'.sub.n and y'.sub.n make no contribution to the 
priming discharge during the first priming period (I) for the same reason 
described above with reference to the writing period (IV) in the first 
subfield. 
As described above, in the second and following subfields, the sequence of 
operations are performed in a similar manner to the first subfield, and 
thus a great reduction is achieved in the intensity of light emission 
during the erasing discharge. As a result, the light emission contrast is 
improved. 
Second Embodiment 
This second embodiment is concerned with the technique to decrease the 
light emission intensity during the second priming period (II) of the 
second and following subfields in the operation of the plasma display 
panel. 
In the first embodiment described above, the reduction in the intensity of 
light emission during the second priming period (II) is not achieved in 
the first subfield. Thus, no reduction is achieved in the second and 
following subfield. in this second embodiment, to solve the above problem, 
the voltage of the discharge sustaining electrode x'.sub.n is not swung to 
the highest voltage but is maintained at the intermediate voltage, as 
represented by the solid line in FIG. 2, during the second priming period 
(II) in the second and following subfields. Instead, the voltage of the 
discharge sustaining electrode y'.sub.n is swung from the GND voltage to 
the intermediate voltage. 
In this technique, when a priming discharge occurs between the discharge 
sustaining electrodes x.sub.n and y.sub.n in the second priming period 
(II), the discharge no longer grows into the region between the discharge 
sustaining electrodes x'.sub.n and y.sub.n or into the region between the 
discharge sustaining electrodes x.sub.n and y'.sub.n. 
Therefore, in the second and following subfields, the discharge sustaining 
electrodes x'.sub.n and y'.sub.n make no contribution to the discharge 
during the second priming period (II) and the discharge is confined in the 
region limited between the discharge sustaining electrodes x.sub.n and 
y.sub.n and thus the discharge occurs in a small-size form unlike the 
discharge in the first subfield. 
As described above, in the second and following subfields, the intensity of 
light emission due to the priming discharge in the second priming period 
(II), which is perceived by a user watching the plasma display panel, is 
reduced to a very low level and thus the influence of the light emission 
due to the priming discharge during the second priming period on the light 
emission contrast is suppressed. In this technique, therefore, the 
discharge sustaining electrodes x'.sub.n and y'.sub.n make no contribution 
to the discharge during the periods from the first priming period (I) to 
the writing period (IV) in the second and following subfields. At the 
beginning of the discharge sustaining period (V), therefore, the discharge 
sustaining electrodes x'.sub.n and y'.sub.n still hold the negative and 
positive charges which had been stored at the location above the discharge 
sustaining electrodes x'.sub.n and y'.sub.n at the end of the discharge 
sustaining period (V) in the previous subfield. 
In this second embodiment, therefore, a desired image is created by the 
large-size sustaining discharges also in the second and following 
subfields based on the same principle as that described above with 
reference to the writing period (V) in the first subfield. 
Third Embodiment 
The third embodiment is concerned with the operation of the plasma display 
panel, at the stage where the second main frame starts after completion of 
all subfields (SF1-SF8) of the first main frame. 
When the first subfield of the next main frame starts, the voltages to the 
discharge sustaining electrodes x'.sub.n and y'.sub.n during the second 
priming period (II) are applied in the manner represented by the alternate 
long and short dash lines in FIG. 2 as in the second priming period of the 
first main frame. However, such a large-size priming discharge in the 
second priming period (II) is undesirable because it has a bad influence 
on the light emission contrast, although it occurs only once in each main 
frame. In this third embodiment, to ease the above problem, the frequency 
of generating large-size priming discharges is decreased such that a 
discharge occurs every two or more main frames instead of every main frame 
thereby achieving an improvement in the light emission contrast. 
Fourth Embodiment 
The fourth embodiment is concerned with a particular operation of the 
plasma display panel in which the negative and positive charges, present 
on the surface of the cathode film 5 at the locations above the discharge 
sustaining electrodes x'.sub.n and y'.sub.n in discharging cells in which 
no discharge occurs in a decaying thereby ensuring that a discharge can 
occur in a correct fashion when the discharge is required. 
If no discharge occurs at a particular pair of discharge sustaining 
electrodes x'.sub.n and y'.sub.n in the second priming period (II) over a 
very long succession of main frames, negative and positive charges at the 
locations above x'.sub.n and y'.sub.n are lost in a rather long time in 
those discharging cells in which no sustaining discharge occurs in the 
discharge sustaining period (V). This can produce a problem, because the 
software program controlling the operation of displaying an image on the 
plasma display panel has not the capability of dealing with such a loss of 
charge. 
If the amount of the charge drops below a certain level, it becomes 
impossible for the discharge sustaining electrodes x'.sub.n and y'.sub.n 
to make contribution to the discharge in the discharge sustaining period 
(V) when such a cell is selected in the subsequent writing period (IV). In 
the case where the frequency of the priming discharge operations in the 
second priming period (II) is reduced, the priming discharge frequency 
becomes lower than the main frame frequency, and thus flicker noise 
becomes perceptible in particular at low halftone levels. 
To improve the image quality, it is desirable to generate at least one 
priming discharge in the second priming period (II) in each main frame. 
Depending on a particular application in which the plasma display panel is 
used, it may be determined whether the light emission contrast or the 
image quality is considered as a more important factor in the design. 
Fifth Embodiment 
FIG. 7 is a cross-sectional view schematically illustrating the structure 
of a plasma display panel according to a fifth embodiment of the 
invention. 
As shown in FIG. 7, on the back surface (the upper surface in FIG. 7) of a 
cathode film 5 uniformly formed over the entire surface of a dielectric 
layer 4 so that it serves as a protective film, there are provided 
discharge passivation films 14 extending along the respective boundaries 
between adjacent scanning lines so that the respective boundaries are 
prevented from being exposed directly to the discharge. The discharge 
passivation film 14 is formed mainly of a material such as Al.sub.2 
O.sub.3 or TiO.sub.2 which is passive to discharging and transparent to 
light. In the areas along the respective boundaries between the adjacent 
scanning lines, the dielectric films 4 are protected from the gas 
discharging space by a two-layer film consisting of the discharge 
passivation film 14 and the cathode film 5. 
Instead of employing the structure shown in FIG. 7, the discharge 
passivation film 14 may be formed directly on the dielectric layer 4 over 
its entire surface before forming the cathode film 5, and then the cathode 
film 5 maybe formed on the discharge passivation film 14 and patterned so 
that there is no cathode film 5 in the areas along the respective 
boundaries between adjacent scanning lines. 
In this case, the passivation film is formed on the plasma display panel in 
such a manner that a two-layer protective film is provided at the central 
part of each scanning line and the discharge passivation film serving as a 
single-layer protective film is provided at each respective boundary 
between adjacent scanning lines. 
In the plasma display panel according to the present invention, each 
discharge sustaining electrode X.sub.n or Y.sub.n is divided into two 
parts unlike the conventional structure in which each discharge sustaining 
electrode X.sub.n or Y.sub.n consists of one part, and thus the density of 
patterns such as discharge sustaining electrodes is twice that of the 
conventional structure. 
In the structure having a high density of discharge sustaining electrodes, 
it becomes difficult to have wide enough spaces between the discharge 
sustaining electrodes x'.sub.n+1 and y' located at both sides of the 
boundary between adjacent scanning lines so that there is no interference 
between adjacent discharges. However, the above problem can be avoided by 
employing the discharge passivation film 14, since this film has, as 
described in detail in previous patents (Japanese Patents Laid-Open Nos. 
7-256262, 9-102280) filed by the same applicant for the present invention, 
the ability of suppressing the interference between adjacent discharges 
occurring at the boundary between adjacent scanning lines. That is, the 
above structure with the discharge passivation film 14 is particularly 
useful to achieve a high density of scanning lines. 
Sixth Embodiment 
FIG. 8 is a cross-sectional view schematically illustrating the structure 
of a plasma display device according to a sixth embodiment of the present 
invention. 
As described in FIGS. 1 and 7, each scanning line consists of 
electrically-isolated discharge sustaining electrodes located in the order 
x'.sub.n, x.sub.n, y.sub.n, and y'.sub.n or y'.sub.n, y.sub.n, x.sub.n, 
and x'.sub.n in a direction toward a greater value of scanning line number 
n. 
It is generally required to form terminals on the front glass substrate 1 
so that the discharge sustaining electrodes are connected to the external 
electrodes through the terminals. To prevent the adjacent terminals from 
having a voltage difference at a high frequency, it is desirable that 
electrodes {x'.sub.n } and {x.sub.n } extend in parallel along the same 
direction and that electrodes {y.sub.n } and {y'.sub.n } extend in 
parallel in the direction different from the direction of {x'.sub.n } and 
{x.sub.n }. 
However, in the structures of discharge sustaining electrodes shown in 
FIGS. 1 and 7, the density of the terminal patterns is also twice that of 
the conventional structure. Therefore, the increase in the scanning line 
density brings about difficulty in making connections of the high-density 
terminals in the assembling process. 
In this sixth embodiment of the plasma display panel, to avoid the above 
problem, electrically isolated discharge sustaining electrodes are 
disposed in one scanning line in the order x'.sub.n, x.sub.n, y.sub.n, and 
y'.sub.n in the direction in which the scanning line number n increases, 
while electrodes are disposed in the order y'.sub.n, y.sub.n, x.sub.n, and 
x'.sub.n in an adjacent scanning line. Scanning lines having these two 
different arrangements of the discharge sustaining electrodes are 
alternately disposed. 
In this structure, the discharge sustaining electrodes {x'.sub.n } and 
{x.sub.n } extend toward the terminals in the order . . . , x.sub.n-1, 
x'.sub.n-1, x'.sub.n, x.sub.n, x.sub.n+1, x'.sub.n+1, . . . and thus it is 
possible to connect adjacent discharge sustaining electrodes x' together 
and connect adjacent discharge sustaining electrodes x together. As a 
result, the density of terminals can be reduced to a similar to that of 
the conventional structure (half that of the structure shown in FIGS. 1 or 
7). 
Similarly, the discharge sustaining electrodes {y'.sub.n } and {y.sub.n } 
extend toward the terminals in the order . . . , y'.sub.n-1, y.sub.n-1, 
y.sub.n, y'.sub.n, y'.sub.n+1, y.sub.n+1, . . . and thus it is possible to 
connect adjacent discharge sustaining electrodes y' together thereby 
reducing the terminal density to a level about 1.5 times that of the 
conventional structure (3/4 times that of the structure shown in FIGS. 1 
or 7). 
As described above, in the sixth embodiment of the plasma display panel 
according to the invention, the pattern density is increased without 
causing a significant increase in the terminal density thereby achieving a 
high-performance plasma display panel which can be easily produced. 
Seventh Embodiment 
FIG. 9 is a cross-sectional view schematically illustrating the structure 
of a plasma display device according to a seventh embodiment of the 
present invention. 
As shown in FIG. 9, there is provided an electrode x' serving as a common 
discharge sustaining electrode 15 disposed between adjacent discharge 
sustaining electrodes x.sub.n and x.sub.n-1, and there is provided an 
electrode y' also serving as a common discharge sustaining electrode 
disposed between adjacent discharge sustaining electrodes y.sub.n and 
y.sub.n-1, wherein common bus electrodes 15 (x', y') are formed on a 
transparent electrode 16 which is formed at a boundary between adjacent 
scanning line so that it is shared by the adjacent scanning lines. 
In contrast to the structure shown in FIG. 8 in which x'.sub.n and 
x'.sub.n-1 are adjacent to each other via a boundary of adjacent scanning 
lines and y'.sub.n and y'.sub.n-1 are adjacent to each other via a 
boundary of adjacent scanning lines, the present embodiment has the 
structure in which the electrode x' or y' is formed at the boundary 
between adjacent scanning lines so that it is shared by the adjacent 
scanning lines. However, as described in detail in a previous patent 
(Japanese Patent Laid-Open No. 9-60930) filed by the same applicant for 
the present invention, this structure is not effective enough to prevent 
discharging interference from occurring at the boundary between adjacent 
scanning lines. To ensure that the discharging interference is prevented, 
there is provided, as in the fifth embodiment (refer to FIG. 7), a 
discharge passivation film 14 made of a material passive to discharging, 
disposed on the back side of the cathode film 5 at the locations 
corresponding to the boundaries between adjacent scanning lines. 
In contrast to the structures according to the first to sixth embodiments 
in which the pattern density of the bus electrodes 15 is twice that of the 
conventional structure, the seventh embodiment has a bus electrode pattern 
density reduced to a level about 1.5 times that of the conventional 
structure. 
Thus, the structure according to the seventh embodiment is useful to 
achieve a high density of scanning lines. 
If the ratio of the area occupied by the bus electrodes which block the 
light emitted from the phosphors 8 to the total area increases with the 
increase in the density of the scanning lines, the light emission 
efficiency decreases. This problem can also be suppressed to a great 
extent in this seventh embodiment. 
That is, in this structure according to the seventh embodiment in which the 
common bus electrodes 15 (x', y') shared by adjacent scanning lines are 
disposed at the boundaries between adjacent scanning lines, the presence 
of the common bus electrodes 15 (x', y') does not cause a significant 
reduction in the light transmission efficiency because the common bus 
electrodes 15 (x' y') are disposed at locations where light emission from 
the phosphor 8 is weak. Furthermore, the presence of the single line of 
the large-width common bus electrode 15 (x', y'), which is opaque and 
disposed at each boundary, blocks the light at boundaries, and thus light 
emission cells are physically isolated from each other. This results in an 
improvement in isolation among picture elements of an image and thus an 
improvement in the image quality. 
Furthermore, the width of the common bus electrodes 15 can be increased by 
an amount corresponding to the lost gap at the boundary between adjacent 
discharge sustaining electrodes, and more specifically to twice that of 
the bus electrodes 13 employed in the first to sixth embodiments. The bus 
electrodes with the increased width are suitable for use in the discharge 
sustaining electrodes x' and y' which need to pass a greater amount of 
current than the discharge sustaining electrodes x and y. 
As described above the present invention provides the plasma display panel 
having the following advantages. That is, the plasma display panel 
comprises: a back side glass plate on which there is provided an address 
electrode; a front glass plate located opposite to the back side glass 
plate; and a plurality of discharge sustaining electrode pairs provided on 
the front glass plate in such a manner that they extend along scanning 
lines perpendicular to the address electrode, wherein the discharge 
sustaining electrodes X.sub.n and Y.sub.n of each discharge sustaining 
electrode pair comprise discharge sustaining electrodes x'.sub.n and 
x.sub.n, and y.sub.n and y'.sub.n, respectively, which are electrically 
isolated from each other and which extend in a direction along the 
scanning lines. In this structure, a discharge occurs basically in a small 
region limited between the discharge sustaining electrodes x.sub.n and 
y.sub.n in the priming and erasing discharge periods thereby reducing the 
intensity of black level thus improving the light emission contrast. 
Furthermore, the power dissipation is also reduced. 
Furthermore, since the discharge sustaining electrodes x.sub.n and y.sub.n 
have the property of blocking light and the discharge sustaining 
electrodes x'.sub.n and y'.sub.n are provided with a transparent 
electrode, when a discharge occurs only in the small region limited 
between the discharge sustaining electrodes x.sub.n and y.sub.n, the light 
emitted from the phosphor in response to such a discharge is blocked by 
the electrode having the property of blocking light. On the other hand, 
when a discharge occurs over the entire region including all discharge 
sustaining electrodes x.sub.n, x'.sub.n, y.sub.n, and y'.sub.n, it is 
possible to achieve as high a visible light intensity level as obtained in 
the conventional technique. 
Furthermore, the electrically isolated discharge sustaining electrodes are 
disposed in the order x'.sub.n, x.sub.n, y.sub.n, y'.sub.n or in the order 
y'.sub.n, y.sub.n, x.sub.n, x'.sub.n in a direction in which the scanning 
line number n increases (where n is a natural number). This makes it 
possible to generate a discharge in either mode. That is, it is possible 
to generate a discharge within a small region limited between the 
discharge sustaining electrodes x.sub.n and y.sub.n and also possible to 
generate a discharge over the entire region including all discharge 
sustaining electrodes x.sub.n, x'.sub.n, y.sub.n, and y'.sub.n. 
Furthermore, when a priming pulse and an erasing pulse are applied to the 
discharge sustaining electrodes x.sub.n and y.sub.n in driving operation, 
the priming pulse and the erasing pulse are not always applied to the 
discharge sustaining electrodes x'.sub.n and y'.sub.n. As a result, 
priming and erasing discharges occur in a small region, which results in 
an improvement in the light emission contrast. 
In the preferred mode of the invention, no erasing pulse is applied to the 
discharge sustaining electrodes x'.sub.n and y'.sub.n. As a result, 
erasing discharges occur in a small region, and thus the light emission 
contrast is improved. 
Furthermore, in the preferred mode in which a priming pulse is applied to 
the discharge sustaining electrodes x'.sub.n and y'.sub.n only in one 
subfield of each main frame consisting of a plurality of subfields, the 
light emission contrast is improved without causing degradation in the 
image quality. 
In the preferred mode in which a series of main frames each consisting of a 
plurality of subfields is constructed so that in some of the main frames 
no priming pulse is applied to the discharge sustaining electrodes 
x'.sub.n and y'.sub.n, the light emission contrast is further improved. 
Furthermore, when image data is written via the address electrode while 
sequentially scanning the scanning lines, a discharge occurs only in the 
region limited between the discharge sustaining electrodes x.sub.n and 
y.sub.n and the discharge sustaining electrodes x'.sub.n and y'.sub.n make 
no contribution to the discharge. This allows a reduction in the power 
dissipation. 
In the preferred mode in which the plasma display panel further includes a 
dielectric layer covering the discharge sustaining electrode pair X.sub.n 
and Y.sub.n ; and a protective film covering the dielectric layer, wherein 
passivation films are formed of a material passive to discharging on the 
back-side surface of the protective film in such a manner that each 
passive film extends along each boundary between adjacent scanning lines, 
it is possible to suppress interference between adjacent dischargers. 
Furthermore, it is also possible to ease the increase in the density of 
terminals connected to the discharge sustaining electrodes. 
In another preferred mode, first types of scanning lines and second types 
scanning lines are alternately disposed, wherein each first type of 
scanning line comprises electrically isolated discharge sustaining 
electrodes disposed in the order x'.sub.n, x.sub.n, y.sub.n in a direction 
in which the scanning line number n increases and wherein each second type 
of scanning line comprises electrically isolated discharge sustaining 
electrodes disposed in the order y'.sub.n, y.sub.n, x.sub.n, and x'.sub.n 
in the direction in which the scanning line number n increases. This 
structure is useful to suppress discharging interference between adjacent 
scanning lines and also to deal with the increase in the density of 
scanning lines. 
In the preferred mode in which at least either discharge sustaining 
electrode x'.sub.n or y'.sub.n includes a part located at the boundary 
between adjacent scanning lines and shared by the adjacent scanning lines, 
it is possible to ease the increase in the pattern density of bus 
electrodes. Furthermore, the light emission efficiency is improved, and 
picture elements are clearly isolated from each other. Still furthermore, 
it is possible to increase the maximum allowable current passing through 
x' and y'.