The present invention relates to a plasma method for driving a plasma display panel. More particularly, the present invention relates to a method for driving an AC-driven plasma display panel (referred to as an AC-driven PDP hereinafter) that has a three-electrode structure and performs memory display.
FIG. 1 is a diagram that shows the general structure of an AC-driven PDP.
A PDP 1 comprises a pair of substrates arranged opposite to each other and a discharge gas sealed therebetween. On one of the substrates, sustain electrodes (X1 to X3) and scan electrodes (Y1 to Y3) arranged in parallel to each other are provided, and on the other substrate, address electrodes (A1 to A4) arranged in the direction perpendicular to the sustain electrodes and the scan electrodes and partitions 2 arranged in parallel to the address electrodes to define a discharge space are provided. Although only the three sustain electrodes, three scan electrodes and four address electrodes are shown in FIG. 1 for simplicity, many electrodes are actually used according to the resolution of the PDP 1.
A display line L is formed between a sustain electrode and a scan electrode adjacent to each other. In the example in FIG. 1, the X1 electrode and the Y1 electrode form a display line L1, the X2 electrode and the Y2 electrode form a display line L2, and the X3 electrode and the Y3 electrode form a display line 3. On the other hand, adjacent pairs of the sustain electrode and the scan electrode that form the display lines form a non-display line therebetween. In the example in FIG. 1, the non-display lines are formed between the Y1 electrode and the X2 electrode, and between the Y2 electrode and the X3 electrode. In order to prevent an erroneous discharge from occurring in the adjacent display lines L1 to L3, the interval between neighboring electrodes that form a non-display line is made wider than the interval between neighboring electrodes that form a display line. Moreover, a discharge cell is formed in an area defined by a pair of the neighboring sustain electrode and the scan electrode and the address electrode that is perpendicular thereto, and a phosphor is provided in the discharge cell in order to obtain visible light.
FIG. 2 is a block diagram that shows the general structure of the PDP apparatus shown in FIG. 5.
The PDP apparatus in FIG. 2 comprises the PDP 1, a data (address) driver 22, a sustain driver 23, a first (odd-numbered) scan driver 24a, a second (even-numbered) scan driver 24b, a scan pulse generation circuit 25 and an interface circuit 26 (for example, refer to Japanese Unexamined Patent Publication (Kokai) No. 10-39834).
The display data and the control signal from the outside of the apparatus are converted properly in the interface circuit 26 and supplied to the data (address) driver 22, the sustain driver 23, the first (odd-numbered) scan driver 24a and the second (even-numbered) scan driver 24b. The scan pulse and the sustain pulse to be applied to the scan electrode Y are generated in the scan pulse generation circuit 25 and their timings are controlled in the first (odd-numbered) scan driver 24a and the second (even-numbered) scan driver 24b by the signal from the interface circuit 26.
Similarly, the sustain pulse and the erasure pulse to be applied to the sustain electrode X are generated in the sustain driver 23 while being controlled by the interface circuit 26.
A description about a method for driving the above-mentioned AC-driven PDP is given below with reference to drawings.
A gradated display in the PDP 1 shown in FIG. 1 is performed by using the subfield driving method in which a frame is divided into a plurality of subfields and driven.
FIG. 3 is a diagram that shows the structure of a field in the PDP shown in FIG. 1. FIG. 3 shows an example of the subfield driving method in which a field is divided into eight subfields SF1 to SF8 for a gradated display. The luminance of each field is weighted by two to the n-th power and it is possible to perform a gradated display of any level by combining proper subfields.
In this method, each subfield is divided into a write period (address period), a sustain discharge period and an erasure period (reset period).
FIG. 4 is a diagram that shows the waveforms that illustrate the method for driving the PDP shown in FIG. 1. FIG. 4 shows the waveforms at the address electrode, the sustain electrodes X1 to Xn and the scan electrodes Y1 to Yn in an arbitrary subfield in a field, and each subfield is composed of the write period (address period), the sustain discharge period and the erasure period (reset period). When the scan electrode is scanned and display data is written during the write discharge period (address period), subsequent scanning is performed not to the next but the following scan electrode so that a write discharge (address discharge) is prevented from being caused to occur in the adjacent pixel successively with respect to time, and all the discharges are maintained at a time in the sustain discharge period for a light emitted display (for example, refer to Japanese Unexamined Patent Publication (Kokai) No. 2001-13915).
As shown in FIG. 4, in the write action (addressing) in the first half of the write period (address period), a voltage Vx is applied to the odd-numbered X electrodes X1, X3, . . . , a voltage 0V is applied to the even-numbered X electrodes X2, X4, . . . , and a scan pulse voltage −Vsc is applied to the odd-numbered Y electrodes Y1, Y3, . . . At this time, the voltage 0V is applied to the even-numbered Y electrodes. In concurrence with this, an address pulse having a voltage Va is applied selectively to the address electrode and a first discharge is caused to occur between the address electrode and the Y electrode in the selected cell in the odd-numbered display lines (L1, L3, . . . ) to be lit. Then with this discharge serving as a priming, a second discharge is immediately caused to occur between the X electrode and the Y electrode. “Address discharge” is a general term for the first discharge and the second discharge. Due to this, wall charges that enable a sustain discharge to occur are accumulated on the X electrode and the Y electrode in the selected cell in the odd-numbered display lines. When the above action is performed as far as the last odd-numbered Y electrode (Yn−1), the writing (addressing) of the selected cells in the odd-numbered display lines is completed in the first half of the write address (address period).
Next, in the second half of the write period (address period), the voltage Vx is applied to the even-numbered X electrodes X2, X4, . . . , the voltage 0V is applied to the odd-numbered X electrodes Y1, Y3, . . . , and the scan pulse voltage −Vsc is applied to the even-numbered Y electrodes Y2, Y4, . . . , sequentially. In this way, the writing (addressing) of the selected cells in the even-numbered display lines is completed. As described above, the writing (addressing) of the selected cells in all of the display lines is completed in the first half and the second half of the write period (address period).
In the next sustain discharge period, a sustain pulse having a (alternating) voltage Vs is applied alternately to the Y electrode and the X electrode, a sustain discharge is caused to occur (only in the selected cells in the display lines in which the address discharge has been formed) according to the wall charges written (addressed) during the write period, as described above, and the image of a subfield in a field is displayed.
In the erasure period (reset period), an erasure pulse voltage VB is applied to all the sustain electrodes (X1 to Xn) to cause an erasure discharge to occur and the wall charges in the (lit) cells in the display lines, in which the sustain discharge has been caused to occur in the previous sustain period, are reduced or erased.
However, in the driving method described above, the address discharge is weak in the skipped display lines (even-numbered lines in this case). As a result, a problem occurs that the light emitted display in the display line flickers or the lines appear dim.
Concerning this problem, a description is given below with reference to FIG. 4 and FIG. 5.
FIG. 5 is a diagram that shows how an address discharge is caused to occur when the driving method described in FIG. 4 is applied to the PDP shown in FIG. 1. For simplicity, only four sustain discharge electrodes and four scan electrodes are shown and the X1 electrode and the Y1 electrode form the display line L1, the X2 electrode and the Y2 electrode form the display line L2, the X3 electrode and the Y3 electrode form the display line L3, and the X4 electrode and the Y4 electrode form the display line L4 as shown schematically.
As described above, in the first half of the write period (address period), the first discharge is caused to occur between the address electrode and the Y electrode (Y1 and Y3) in the selected cell in the odd-numbered display lines (L1 and L3) to be lit, and with the first discharge serving as a priming, the second discharge is immediately caused to occur between the scan electrode Y and the sustain electrode X (between the X1 and the Y1 electrodes, and between the X3 and the Y3 electrodes).
However, as the above-mentioned address discharge propagates while extending along the address electrode, it may happen that an erroneous discharge (referred to as a first erroneous discharge hereinafter) is caused to occur in the X electrode (X2) in the adjacent display line L2 adjacent to the Y1 electrode during the period of the address discharge in the odd-numbered line L1 in the first half of the write period (address period), as shown by the dotted line in the figure.
As a result, the address discharge during the scanning of the even-numbered line L2 in the second half of the write period (address period), which follows the scanning of the odd-numbered line L1 in the first half of the write period (address period), becomes weak and unstable, therefore, a problem occurs that the light emitted display of the display line (the even-numbered line L2) in the subsequent sustain discharge period flickers or the line appears dim.
The reason may be that the wall charges, which tend to decrease the potential of the sustain electrode X2 with respect to the scan electrode Y2 and the address electrode, are formed on the sustain electrode X2 due to the erroneous discharge (the first erroneous discharge), the voltage between the scan electrode Y2 and the sustain electrode X2 in the even-numbered line L2 is reduced, and the address discharge during the scanning of the even-numbered line L2 becomes weaker than the address discharge during the scanning of the odd-numbered line L1.
In Japanese Unexamined Patent Publication (Kokai) No. 2001-13915, a driving method has been proposed, as an improved method for driving an AC-driven PDP, in which the above-mentioned problems have been solved, the object of which is to stabilize the address discharge in the second half of the write period (address period) by increasing the voltage to be applied to the sustain electrode in the second half of the write period (address period) to recover the internal voltage that has been lowered due to the excessive wall charges caused to form by the erroneous discharge in the first half of the write period (address period), using a driving method in which either one of the odd-numbered lines and the even-numbered lines are scanned in the first half of the write period (address period) and the others are scanned in the second half of the write period (address period).
FIG. 6 is a diagram that shows the waveforms illustrating the method for driving the PDP shown in FIG. 1. FIG. 6 shows the driving method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-13915, described above, wherein a voltage Vy to be applied to the sustain electrodes (X2, X4, . . . ) during the scanning of the even-lines in the second half of the write period (address period) is set to a value larger than the voltage Vx (Vx<Vy) to be applied to the sustain electrodes (X1, X3, . . . ) during the scanning of the odd-numbered lines in the first half of the write period (address period).
As described above, when the scanning of the odd-numbered lines and the even-numbered lines is performed separately in the first half and the second half of the write period (address period), it is possible to compensate for the amount of decrease in the potential of the sustain electrodes (X2, X4, . . . ) due to the wall charges formed on the sustain electrodes (X2, X4, . . . ) in the even-numbered lines by the erroneous discharge of the address discharge during the scanning of the odd-numbered lines in the first half of the write period (address period) by increasing the potential of the sustain electrode X with respect to the scan electrode Y and the address electrode. In this way, the address discharge can stably be caused to occur during the scanning of the even-numbered lines.
FIG. 7 is a diagram that shows how the address discharge is caused to occur when the driving method described in FIG. 6 is applied to the PDP shown in FIG. 1.
As described above, the voltage Vy to be applied to the X2 electrode during the scanning of the even-numbered line L2 in the second half of the write period (address period) becomes larger than the voltage Vx to be applied to the X1 and X3 electrodes during the scanning of the odd-numbered lines L1 and L3 in the first half of the address period (Vx<Vy), therefore, the potential difference Vy+Vs between the X2 and Y2 electrodes in the even-numbered line L2 becomes larger than the potential difference Vx+Vs between the X1 and Y1 electrodes in the odd-numbered display line L1 and between the X3 and Y3 electrodes in the odd-numbered display line L3 (Vx+Vs<Vy+Vs). Due to this, the scale of the address discharge in the even-numbered line L2 becomes greater than that in the odd-numbered line L1 (by the amount of the potential difference Vy−Vx>0).
As a result, when the sustain discharge is caused to occur in the subsequent sustain discharge period, the scale of the sustain discharge in the even-numbered line L2 is increased by the alternating sustain pulse voltage Vs to be applied to cause the sustain discharge to occur in the selected cells in all of the display lines, and the discharge propagates to the odd-numbered line L3 adjacent to the Y2 electrode in the even-numbered line L2, as shown in FIG. 7 (a second erroneous discharge is caused to occur). This is because the wall charges, which tend to decrease the potential of the sustain electrode X3 with respect to the scan electrode Y3 and the address electrode, are formed on the sustain electrode X3 in the odd-numbered line L3 due to the second erroneous discharge, as is the same in the first erroneous discharge described above, the voltage between the scan electrode Y3 and the sustain electrode X3 in the even-numbered line L3 is reduced, and the sustain discharge in the even-numbered line L3 becomes weak and unstable. As a result, a problem occurs that the light emitted display in the display line flickers or the line appears dim.