KR100349030B1 - Plasma Display Panel and Method of Driving the Same - Google Patents

Abstract

The present invention relates to a plasma display panel and a driving method thereof for improving the brightness of a screen through high speed addressing.

The plasma display panel of the present invention is formed on a scan electrode and a sustain electrode which are formed side by side on an upper substrate, and a lower substrate facing the upper substrate with a discharge space therebetween to generate an address discharge with the scan electrode in an address period. A data electrode and an upper electrode are formed in parallel with the data electrode, and an auxiliary electrode for generating an auxiliary discharge with one of the scan electrode and the data electrode in an address period.

According to the present invention, the pulse is applied to the auxiliary electrode during the address discharge to cause the auxiliary discharge between the data electrode and the scan electrode. Since the charged discharge is sufficiently generated during the address discharge by the auxiliary discharge, the pulse width of the address discharge pulse can be greatly shortened and driven at a low voltage.

Description

Plasma Display Panel and Method of Driving the Same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display panel and a driving method thereof, and more particularly, to a plasma display panel and a driving method thereof capable of improving brightness of a screen through high speed addressing.

Plasma Display Panel (hereinafter referred to as "PDP") is a display device using visible light generated from a phosphor when ultraviolet light generated by gas discharge excites the phosphor. PDP is thinner and lighter than Cathode Ray Tube (CRT), which has been the mainstay of display means, and has the advantage of being able to realize high-definition large screen. PDP is composed of a plurality of discharge cells arranged in a matrix form, one discharge cell constitutes a pixel of the screen.

1 is a perspective view showing a discharge cell structure of a typical AC surface discharge PDP.

Referring to FIG. 1, the upper plate 20 and the lower plate 22 are provided in parallel with a predetermined distance. An AC driving signal is supplied to the rear surface of the upper substrate 24 constituting the upper plate 20 so that the scan electrode 26 and the sustain electrode 27 forming a sustain surface discharge are formed side by side. The scan electrode 26 and the sustain electrode 27 are transparent electrodes formed transparently from indium tin oxide (ITO). The bus electrodes 30 are formed side by side on each of the scan electrodes 26 and the sustain electrodes 27. Since ITO has a high resistance value, a uniform voltage is applied to each discharge cell by supplying an AC signal through the bus electrode 30. An upper dielectric layer 28 is formed on the front surface of the upper substrate 24 on which the scan electrodes 26 and the sustain electrodes 27 are formed. The upper dielectric layer 28 has a function of accumulating charges during discharge. The protective layer 31 coated on the entire upper dielectric layer 28 protects the upper dielectric layer 28 from sputtering during discharging, thereby extending the life of the pixel cell and increasing discharge efficiency of secondary electrons to improve discharge efficiency. . On the lower substrate 32 constituting the lower plate 22, a data electrode 34 for address discharge is formed to cross at right angles with the scan electrode 26 and the sustain electrode 27. The lower dielectric layer 36 is entirely coated on the lower substrate 32 and the data electrode 34 to form wall charges during discharge. In addition, the partition wall 42 is vertically formed between the upper plate 20 and the lower plate 22. The partition wall 42 forms the discharge space 38 of the cell together with the upper plate 20 and the lower plate 22, and blocks electrical and optical mutual interference between neighboring discharge cells. Phosphor 40 is applied to the surfaces of the lower dielectric layer 36 and the partition 42. The discharge space 38 is filled with a mixed gas of He + Xe or Ne + Xe.

The overall structure of the electrode lines and discharge cells of the AC surface discharge PDP is as shown in FIG.

Referring to FIG. 2, the discharge cells 44 are positioned at portions where the data electrode line X, the scan electrode line Y, and the sustain electrode line Z cross each other. The data electrode line X is divided into odd-numbered lines and even-numbered lines to be driven up and down.

Briefly describing the light emission process, an address discharge occurs between the scan electrode 26 and the data electrode 34 to form wall charges in the upper and lower dielectric layers 28 and 36. The formed wall charges lower the discharge voltage required for surface discharge. In the cells selected by the address discharge, a sustain discharge occurs between the two electrodes 26 and 27 by an alternating current signal supplied alternately to the scan electrode 26 and the sustain electrode 27. At this time, ultraviolet rays are generated in the discharge space 38 in the process of transition after the discharge gas is excited. The generated ultraviolet rays excite the phosphor 40 to generate visible light, thereby realizing an image of the PDP. The AC surface discharge PDP displays an image by an ADS (Addressing Display Separated: "ADS") driving method.

3 is a diagram illustrating an ADS driving method for expressing a gray level of one frame in the PDP. One frame for 16.67 ms is time-divided into eight subfields SF1 to SF8 according to the gradation to be driven. Each of the subfields SF1 to SF8 is largely divided into a reset and address period in which screen initialization and address discharge are performed, and a sustain period in which sustain discharge is performed. In each subfield, the widths of the preset reset and address periods are the same while the widths of the sustain periods are different. The sustain period is set in advance so as to increase at a rate of 2 ⁿ (n = 0,1,2,3,4,5,6,7) in each subfield according to the luminance relative ratio.

4 is a waveform diagram showing driving waveforms supplied to each electrode line of the PDP in each subfield in the conventional driving method.

Referring to FIG. 4, one subfield includes a priming and reset period for initializing the full screen, an address period for writing data while scanning the full screen in a linear order manner, and a sustain period for maintaining the light emission state of the cells in which the data is written. And an erasing period for erasing the sustain discharge. First, during the reset period, the discharge cells are initialized and discharged by discharge pulses applied to the scan electrode line (Y) and the sustain electrode line (Z) to help address discharge, thereby forming priming charged particles and wall charges in the discharge cells. Let's do it. In the address period, scan pulses (-Vs) are sequentially applied to the scan electrode lines Y of each scan line of the PDP, and the data pulses Vd are supplied to each data electrode line X in synchronization with the scan pulses. . At this time, a DC voltage of a predetermined level is supplied to the sustain electrode lines Z, and the DC voltage enables stable address discharge between the data electrode line X and the scan electrode line Y. In the conventional driving method, the pulse width Td of the discharge pulse for causing the address discharge is relatively long, which is 2.5 kHz or more. In the sustain period, a sustain pulse Vsus having the same pulse width and voltage is alternately applied to the scan electrode line Y and the sustain electrode line Z to cause sustain surface discharge in discharge cells selected by the address discharge. In the erase period, the charged particles are extinguished by an erase pulse supplied to the sustain electrode line Z, and the sustain discharge is erased.

In the conventional AC surface discharge PDP driven as described above, in order to obtain stable discharge characteristics during address discharge, a method of increasing the address discharge pulse width Td to 2.5 m or more for each subfield or increasing the voltage level of the discharge pulse is used. have. When the voltage level of the address discharge pulse is lowered, the intensity of the discharge and the amount of charged particles generated are reduced. When the voltage level of the address discharge pulse is shortened to the pulse width Td, there is a possibility that erroneous discharge may occur due to the discharge delay phenomenon inherent in the PDP. This problem can be solved by increasing the pulse width Td of the discharge pulse. However, when the pulse width Td of the address discharge pulse is longer than 2.5 ms, the actual duration of one frame is fixed to 16.67 ms. The sustain period that determines the brightness of the screen occupies 30% or less in one frame, and the brightness of the screen is lowered. In addition, in the current PDP driving method, the number of subfields during one frame is increased from 8 to 10 to 12 in order to reduce contour noise, which is an inherent image quality degradation phenomenon of the PDP. However, when the number of subfields increases during a fixed frame period, the period of each subfield is shortened by that much. Even in this case, the address period is fixed for each subfield for stable discharge, and only the sustain period is shortened, thereby lowering the brightness of the screen. In high-resolution PDPs with an increased number of scan lines, the sustain period becomes too short and the display itself becomes impossible. In the high resolution PDP, since the number of scan lines is much larger, the address period in which the scan lines are sequentially driven in each subfield is longer. Accordingly, the sustain period is inevitably reduced during the fixed one frame period and the luminance is lowered. In order to solve this problem, high speed addressing is required, and in the related art, a method of dividing and driving a scan line of a panel up and down is used. In the split driving method of the scan line, scan lines are divided up and down in order to shorten an address period in each subfield, and the upper scan line and the lower scan line are separately scanned simultaneously by two different scan drivers. As a result, the scan period or the address period is doubled, and the sustain period is sufficiently secured in each subfield, thereby preventing the screen brightness from being lowered. However, the conventional split driving method has a disadvantage in that the manufacturing cost of the PDP is increased by doubling the number of scan and data driver ICs.

Accordingly, it is an object of the present invention to provide a plasma display panel and a driving method thereof capable of improving the brightness of a screen through high speed addressing.

1 is a perspective view showing a discharge cell structure of a conventional AC surface discharge plasma display panel.

FIG. 2 is a plan view showing an arrangement structure of electrode lines and discharge cells in a conventional AC surface discharge plasma display panel. FIG.

3 is a diagram illustrating an ADS driving method for expressing a gray level of one frame in a plasma display panel;

FIG. 4 is a waveform diagram showing driving waveforms supplied to respective electrode lines of a plasma display panel for each subfield in the conventional plasma display panel driving method. FIG.

5 is a perspective view illustrating a discharge cell structure of an AC surface discharge plasma display panel according to a first embodiment of the present invention.

6 is a plan view of a panel showing the overall electrode arrangement structure of the AC surface discharge plasma display panel according to the first embodiment of the present invention.

7 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of the plasma display panel according to the first embodiment of the present invention;

8 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of the plasma display panel according to the second exemplary embodiment of the present invention.

9 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of a plasma display panel according to a third exemplary embodiment of the present invention.

10 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of a plasma display panel according to a fourth exemplary embodiment of the present invention.

11 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of the plasma display panel according to the fifth embodiment of the present invention;

12 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of a plasma display panel according to a sixth exemplary embodiment of the present invention.

FIG. 13 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of a plasma display panel according to a seventh exemplary embodiment of the present invention. FIG.

14 is a perspective view illustrating a discharge cell structure of an AC surface discharge plasma display panel according to an eighth embodiment of the present invention;

15 is a block diagram of a driving apparatus for driving an AC surface discharge plasma display panel according to the first to eighth embodiments of the present invention.

<Description of Symbols for Main Parts of Drawings>

20,50: top plate 22,52: bottom plate

24,54: upper substrate 26,56: scan electrode

27,57: sustain electrode 28,58: upper dielectric layer

30,60 bus electrode 31,61 protective layer

32,62: lower substrate 34,64,69: data electrode

36,66: lower dielectric layer 38,68: discharge space

40,70 Phosphor 42,72 Bulkhead

44,74 discharge cell 104 plasma display panel

65, 67: auxiliary electrode 100: image signal processing unit

102: frame memory 106: data driver

108: scan driver 110: discharge sustain electrode driver

112: auxiliary electrode driver 114: waveform generator

116 control unit 120 130 second dielectric layer

In order to achieve the above object, a plasma display panel of the present invention is formed on a scan electrode and a sustain electrode which are formed side by side on an upper substrate, and a lower substrate facing the upper substrate with a discharge space therebetween, so that the scan electrode is formed in an address period. And a data electrode for causing an address discharge, and an upper electrode formed in parallel with the data electrode, and an auxiliary electrode for generating an auxiliary discharge with one of the scan electrode and the data electrode in an address period.

In the method of driving a plasma display panel according to the present invention, a data pulse is supplied to a data electrode and a scan pulse is supplied to the scan electrode to cause an address discharge between the data electrode and the scan electrode, and parallel to the data electrode with a discharge space therebetween. The auxiliary pulse is supplied to the formed auxiliary electrode to generate an auxiliary discharge with any one of the scan electrode and the data electrode during address discharge. Other objects and features of the present invention in addition to the above object are described with reference to the accompanying drawings. Will be made apparent through.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 to 15.

5 is a perspective view illustrating a discharge cell structure of an AC surface discharge PDP according to a first embodiment of the present invention.

Referring to FIG. 5, the AC surface discharge PDP according to the first exemplary embodiment of the present invention includes an auxiliary electrode 65 formed in the second dielectric layer 130 with the discharge space 68 interposed therebetween with the data electrode 64. ). The auxiliary electrode 65 generates an auxiliary discharge together with the scan electrode 56 during the address discharge, thereby generating sufficient charged particles on the discharge space 68. Except that the auxiliary electrode 65 is formed, other configurations and features are the same as in the case of the conventional AC surface discharge PDP shown in FIG. The second dielectric layer 130 for forming the auxiliary electrode 65 is formed on the rear surface of the upper substrate 54 constituting the upper plate 50. The auxiliary electrode 65 formed on the second dielectric layer 130 is formed to be parallel to the scan electrode 56 and the sustain electrode 57 in a direction orthogonal to each other. The scan electrode 56 and the sustain electrode 57 are transparent electrodes formed of indium tin oxide (ITO). Bus electrodes 60 are formed in parallel on each of the scan electrodes 56 and the sustain electrodes 57. A protective layer 61 is formed on an entire surface of the upper dielectric layer 58 on which the scan electrode 56 and the sustain electrode 57 are formed. On the lower substrate 62 constituting the lower plate 52, a data electrode 64 for address discharge is formed in parallel with the scan electrode 56 and the sustain electrode 57. The lower dielectric layer 66 is entirely coated on the lower substrate 62 on which the data electrodes 64 are formed. The partition wall 72 is vertically formed between the upper plate 50 and the lower plate 52. Phosphor 70 is coated on the surfaces of the lower dielectric layer 66 and the partition wall 72. The discharge space 68 is filled with a mixed gas of He + Xe or Ne + Xe.

6 is a plan view of a panel showing an overall electrode arrangement structure of a PDP according to a first embodiment of the present invention.

Referring to FIG. 6, data electrode lines X1 to Xm and auxiliary electrode lines A1 to Am are formed in the column direction of the panel, and scan electrode lines Y1 to Yn and sustain electrode lines Z1. To Zn are formed in the row direction of the panel. The data electrode lines X1 to Xm and the auxiliary electrode lines A1 to Am vertically overlap each other. The discharge cells 74 are positioned at portions where the data electrode lines X1 to Xm and the auxiliary electrode lines A1 to Am cross the scan electrode lines Y1 to Yn and the sustain electrode lines Z1 to Zn.

FIG. 7 is a waveform diagram illustrating a driving waveform supplied to each electrode line of the PDP in each subfield in the method of driving an AC surface discharge PDP according to the first embodiment of the present invention.

Referring to FIG. 7, one subfield includes a priming and reset period for initializing a full screen, an address period for writing data while scanning the full screen in a sequential manner, and a light emission state of cells in which data is written. Is divided into a sustain period for maintaining and an erase period for canceling the sustain discharge. First, in the reset period, the discharge cells are initialized and discharged by discharge pulses applied to the scan electrode line (Y) and the sustain electrode line (Z) to form the charged particles and the wall charges in the discharge cells. . In the address period, scan pulses (-Vs) are sequentially applied to scan electrode lines (Y) for each scan line of the PDP, and data pulses (Vd) are applied to each data electrode line (S) to be synchronized with the scan pulse (-Vs). Supply to X). At this time, an address discharge occurs in the discharge cell in which the data pulse Vd and the scan pulse (-Vs) exist at the same time. However, in the present invention, the auxiliary pulse (-Va) is supplied to the auxiliary electrode line (A) parallel to the data electrode line (X) when the address discharge occurs. In the discharge cell supplied with the auxiliary pulse -Va, auxiliary discharge occurs between the data electrode line X and the auxiliary electrode line A. FIG. Sufficient charged particles are generated in the discharge space of the discharge cell during the auxiliary discharge to assist the address discharge. As a result, stable address discharge characteristics can be obtained while shortening the pulse width Td of the discharge pulses during the address discharge and lowering the voltage level. Through the auxiliary discharge, the pulse width Td of the address discharge pulse can be shortened to about 1 ms. Although the pulse width Td and the voltage level Vd of the discharge pulse are reduced, the charged particles are sufficiently generated through the auxiliary discharge, so that the discharge delay phenomenon and the misdischarge phenomenon do not occur. As the pulse width of the address discharge pulse is shortened, the address period in each subfield is significantly shortened by more than twice the conventional one. On the other hand, in the present invention, the auxiliary pulse (-Va) is supplied only to the discharge cells in which the data pulse (Vd) is present. In this way, the auxiliary discharge during address discharge occurs only in the discharge cells to which data is written. Thus, the contrast of the screen is prevented from being lowered by the micro light emission generated during the auxiliary discharge. In addition, in the present invention, since the auxiliary discharge is generated only in the discharge cell in which the data pulse Vd and the scan pulse (-Vs) exist at the same time, an addressing error does not occur. In the sustain period, the sustain pulse Vsus is alternately applied to the scan electrode line Y and the sustain electrode line Z to cause sustain surface discharge in the discharge cells selected by the address discharge. In the erase period, the charged particles are erased by the erase pulse supplied to the sustain electrode line Z, and the sustain discharge is erased.

On the other hand, the pulse width Ta and position of the auxiliary pulse in the PDP according to the present invention is not limited to the case of the first embodiment of the present invention shown in FIG. In order to improve the discharge characteristic, the position of the auxiliary pulse or the pulse width Ta may be varied. 8 to 12 are waveform diagrams showing driving waveforms supplied to electrode lines of the PDP for each subfield in the method for driving an AC surface discharge PDP according to the second to sixth embodiments of the present invention.

8 illustrates a driving waveform according to a second embodiment of the present invention.

Referring to FIG. 8, unlike in the case of the first embodiment of the present invention, the pulse width Ta of the auxiliary pulse is widened. When the pulse width Ta of the auxiliary pulse becomes wider, in the discharge cell supplied with the auxiliary pulse (-Va), an auxiliary discharge occurs between the data electrode line X and the auxiliary electrode line A, and the discharge is continued to be sufficient. Characteristics can be obtained. Other features and driving methods are the same as in the first embodiment of the present invention, and thus description thereof will be omitted.

9 and 10 illustrate driving waveforms according to third and fourth embodiments of the present invention.

9 and 10, unlike the first and second exemplary embodiments of the present invention, the auxiliary pulse -Va is applied before the data pulse Vd for a predetermined time. When the auxiliary pulse (-Va) is applied before the data pulse (Vd), charged particles are generated in the discharge space of the discharge cell to help address discharge. As a result, stable address discharge characteristics can be obtained while shortening the pulse width Td of the discharge pulses during the address discharge and lowering the voltage level. 10 shows sufficiently wide pulse width Ta of the auxiliary pulse to generate charged particles and to sustain the discharge to obtain sufficient discharge characteristics.

11 and 12 illustrate driving waveforms according to fifth and sixth embodiments of the present invention.

11 and 12, the auxiliary pulse -Va is applied simultaneously with the data pulse Vd. When the auxiliary pulse (-Va) is applied simultaneously with the data pulse (Vd), sufficient charged particles are generated in the discharge space of the discharge cell to help address discharge. As a result, stable address discharge characteristics can be obtained while shortening the pulse width Td of the discharge pulses during the address discharge and lowering the voltage level. Other features and driving methods are the same as those of the first to fourth embodiments of the present invention, and thus description thereof will be omitted. On the other hand, the position and voltage level of the auxiliary electrode 65 in the PDP according to the present invention is not limited only to the case of the first to sixth embodiments of the present invention shown in Figs.

FIG. 13 is a waveform diagram illustrating driving waveforms supplied to respective electrode lines of the PDP for each subfield in the AC surface discharge PDP driving method according to the seventh embodiment of the present invention.

Referring to FIG. 13, unlike the first to sixth exemplary embodiments, the auxiliary pulse Va of the auxiliary electrode line A has a positive polarity. Thus, in the seventh embodiment of the present invention, an auxiliary discharge is caused between the scan electrode line Y and the auxiliary electrode line A when the address discharge of the data electrode line X and the scan electrode line Y is performed. In addition, as in the first to sixth embodiments, the pulse width Ta and the position of the auxiliary pulse may vary. Other features and driving methods are the same as those of the first and sixth embodiments of the present invention, and thus description thereof will be omitted.

14 is a perspective view illustrating a discharge cell structure of an AC surface discharge PDP according to an eighth embodiment of the present invention.

Referring to FIG. 14, in the PDP according to the eighth embodiment of the present invention, an upper dielectric layer 58 is formed on the second dielectric layer 120 on which the auxiliary electrode 67 is formed. In addition, a protective layer 61 is formed on the rear surface of the second dielectric layer 120. Other structural and discharge characteristics are the same as those of the first to seventh embodiments of the present invention, and thus description thereof will be omitted.

15 is a block diagram of a driving device for driving an AC surface discharge PDP according to the first to eighth embodiments of the present invention. Referring to FIG. 15, an apparatus for driving a PDP according to the present invention includes an image signal processor 100 for processing image data and a frame memory 102 for storing image data supplied from the image signal processor 100 in prime units. And a data driver 106 for sequentially supplying the image data Vd transmitted from the frame memory 102 to the data electrode line X of the PDP 104 one by one scan line and the data driver 106. And a scan driver 108 and a sustain electrode line Z for sequentially supplying scan pulses (-Vs) to the scan electrode lines Y of the PDP 104 at every horizontal period and supplying a sustain pulse Vsus. A discharge sustain electrode driver 110 for supplying a sustain pulse Vsus and an auxiliary electrode driver 112 for supplying auxiliary pulses -Va and Va to the auxiliary electrode line A are provided. In addition, the driving apparatus of the present invention generates a waveform waveform and supplies the waveform generator 114 to each driver, and the frame memory 102 and the scan driver 108 to control the application time of the pulse supplied to each electrode line And a controller 116 for controlling the waveform generator 114. The controller 116 controls the waveform generator 114 to supply the auxiliary pulse (-Va) to the auxiliary electrode line only in the discharge cells in which the data pulse Vd and the scan pulse (-Vs) are present at the same time in each subfield. ) And the auxiliary electrode driver 112.

As described above, in the plasma display panel and the driving method thereof, the auxiliary electrode is formed in a direction parallel to the data electrode in the discharge cell with the discharge space therebetween, and the pulse is applied to the auxiliary electrode during the address discharge. An auxiliary discharge is caused between the electrodes or the scan electrodes. Since the charged discharge is sufficiently generated during the address discharge by the auxiliary discharge, the pulse width of the address discharge pulse can be greatly shortened and driven at a low voltage. As a result, the address period for each subfield is drastically shortened by more than twice as compared with the conventional one, and the sustain period is increased by that amount, thereby greatly improving the brightness of the screen. In addition, in the present invention, high-speed addressing is possible without dividing the scan lines of the panel, so that the number of subfields can be increased to 10 or more even when driving a high-resolution panel, thereby preventing the deterioration of image quality. In addition, since the number of driver integrated circuits does not need to be increased for split driving, manufacturing costs can be reduced.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (11)

A plasma display panel comprising an address period for selecting a discharge cell, the plasma display panel comprising: A scan electrode and a sustain electrode formed side by side on the upper substrate; A data electrode formed on a lower substrate facing the upper substrate with a discharge space therebetween to cause the scan electrode and the address discharge in the address period; And an auxiliary electrode formed on the upper substrate to be parallel to the data electrode and to generate an auxiliary discharge with any one of the scan electrode and the data electrode in the address period. The method of claim 1, And the auxiliary electrode is formed on the scan electrode with a dielectric layer interposed therebetween. The method of claim 1, And the auxiliary electrode is formed under the scan electrode with a dielectric layer interposed therebetween. Supplying a data pulse to a data electrode and supplying a scan pulse to the scan electrode to cause an address discharge between the data electrode and the scan electrode; And supplying an auxiliary pulse to an auxiliary electrode formed to be parallel to the data electrode with a discharge space therebetween to cause an auxiliary discharge with any one of the scan electrode and the data electrode during the address discharge. How to drive The method of claim 4, wherein And wherein the auxiliary pulse is supplied only to discharge cells selected during address discharge. The method of claim 4, wherein And the auxiliary pulse is applied before a predetermined time in advance of the data pulse. The method of claim 4, wherein And the auxiliary pulse is applied simultaneously with the data pulse. The method of claim 4, wherein And the auxiliary pulse is applied after a predetermined time after the data pulse. The method according to any one of claims 6 to 8, And the width of the auxiliary pulse is set to be smaller than the width of the data pulse. The method according to any one of claims 6 to 8, And the width of the auxiliary pulse is set equal to the width of the data pulse. The method according to any one of claims 6 to 8, The width of the auxiliary pulse is set to be wider than the width of the data pulse.