JP2006171180A - Image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display apparatus that is improved in luminous efficiency, by generating two continuous stable discharges and performing discharge control, according to the turn-on ratio. <P>SOLUTION: The image display apparatus comprises a plasma display panel with two or more discharge cells, having a pair of display electrodes; a pair of sustain pulse generating part for applying to the pair of display electrodes a 1st sustain pulse for generating one time sustain discharge in the discharge cells, when the voltage applied across the display electrodes changes, or a 2nd sustain pulse generating part for generating two-time continuous sustain discharges in the discharge cells, when the voltage applied across the pair of the display electrodes changes; and an turn-on ratio calculation part for calculating the discharge cell turn-on ratio, based on the image signal to be displayed, and the sustain pulse generating part generates the 1st sustain pulse, when the turn-on ratio is less than a prescribed threshold, and generates the 2nd sustain pulse when the turn-on ratio is not less than the prescribed value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image display apparatus using a plasma display panel that selectively discharges a plurality of discharge cells to display an image.

  2. Description of the Related Art In recent years, a plasma display panel (hereinafter abbreviated as “panel”), which has rapidly expanded the market scale, is a display device with excellent visibility characterized by a large screen, a thin shape, and a light weight. However, its luminous efficiency is still low, and various techniques for improving luminous efficiency and reducing power consumption have been proposed.

As a method of increasing the light emission efficiency by the panel driving method and reducing the power consumption, for example, a driving pulse is applied to a selected discharge cell in the display panel to generate a first discharge and then a second discharge. The driving means for generating, the detecting means for detecting the lighting rate of the discharge cells, and the timing for generating the second discharge after the first discharge is generated according to the lighting rate detected by the detecting means is changed. In addition, a display device (see Patent Document 1) including a control unit that controls a driving unit is proposed. According to this display device, it is possible to stably discharge even if the lighting rate changes, and to improve the light emission efficiency with respect to the input power and reduce the power consumption.
Japanese Patent No. 3242097

  However, these two consecutive discharges, particularly the first discharge, are easily affected by the discharge characteristics and discharge conditions of the individual discharge cells, variations in the circuit components of the drive circuit, and the like. It was not easy to generate a single discharge.

  The present invention has been made in view of the above problems, and provides an image display device that stably generates two continuous discharges and performs discharge control according to the lighting rate to improve luminous efficiency. With the goal.

  The image display device of the present invention includes a panel having a plurality of discharge cells having a pair of display electrodes, and a first sustain that generates one sustain discharge in the discharge cells when a voltage applied between the display electrodes changes. A pair of sustain pulse generators for applying to the display electrode a second sustain pulse for generating two continuous sustain discharges in the discharge cell when a pulse or a voltage applied between the display electrodes changes; A lighting rate calculator that calculates the lighting rate of the cell based on the image signal to be displayed, and the sustain pulse generator generates a first sustain pulse when the lighting rate is less than a predetermined threshold, The second sustain pulse is generated when the threshold value is exceeded. With this configuration, it is possible to provide an image display device that can stably generate two continuous discharges, perform discharge control according to the lighting rate, and improve luminous efficiency.

  Each of the sustain pulse generators of the image display device of the present invention includes a power recovery unit that charges and discharges the display electrodes by resonance between the capacitance between the display electrodes and the power recovery inductor, and a predetermined voltage. And a clamp portion for applying a voltage to a power source or a ground potential. With this configuration, it is possible to stably generate two consecutive discharges.

  The first sustain pulse of the image display device according to the present invention is applied by applying a voltage to one of the display electrodes using a power recovery unit corresponding to the display electrode and then using a clamp unit corresponding to the display electrode. A voltage is applied, a voltage is applied to the other display electrode using a power recovery unit corresponding to the display electrode, and then a voltage is applied using a clamp unit corresponding to the display electrode. With this configuration, it is possible to suppress the reactive power of the sustain pulse generation unit when the first sustain pulse is applied.

  In addition, the second sustain pulse of the image display device of the present invention is applied to one of the display electrodes using a power recovery unit corresponding to the display electrode and to the other display electrode corresponding to the display electrode. A voltage is applied using the power recovery unit, a voltage is applied to one of the display electrodes using a clamp unit corresponding to the display electrode, and a first discharge is generated, and then the display is applied to the other display electrode. A voltage is applied using a clamp portion corresponding to the electrode to generate and execute a second discharge. With this configuration, it is possible to improve the light emission efficiency when the second sustain pulse is applied.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the image display apparatus which generated the continuous two times of discharge stably, performed discharge control according to the lighting rate, and improved luminous efficiency.

  Hereinafter, an image display device according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 is an exploded perspective view showing a structure of a panel used in an image display apparatus according to an embodiment of the present invention. The panel 1 is configured such that a glass front substrate 2 and a back substrate 3 are disposed to face each other and a discharge space is formed therebetween. On the front substrate 2, a plurality of scanning electrodes 4 and sustaining electrodes 5 constituting display electrodes are formed in parallel with each other. A dielectric layer 6 is formed so as to cover the scan electrode 4 and the sustain electrode 5, and a protective layer 7 is formed on the dielectric layer 6. A plurality of data electrodes 9 covered with an insulator layer 8 are formed on the back substrate 3, and a partition wall 10 is provided in parallel with the data electrodes 9 on the insulator layer 8 between the data electrodes 9. Yes. A phosphor layer 11 is provided on the surface of the insulator layer 8 and the side surfaces of the partition walls 10. The front substrate 2 and the rear substrate 3 are arranged to face each other in the direction in which the scan electrodes 4 and the sustain electrodes 5 and the data electrodes 9 intersect, and in the discharge space formed between them, for example, neon And a mixed gas of xenon.

  FIG. 2 is an electrode array diagram of the panel. In the row direction, n scan electrodes SC1 to SCn (scan electrode 4 in FIG. 1) and n sustain electrodes SU1 to SUn (sustain electrode 5 in FIG. 1) are alternately arranged, and m data electrodes in the column direction. D1 to Dm (data electrodes 9 in FIG. 1) are arranged. A discharge cell is formed at a portion where the pair of scan electrode SCi and sustain electrode SUi (i = 1 to n) and one data electrode Dj (j = 1 to m) intersect, and the discharge cell is in the discharge space. m × n are formed. As shown in FIGS. 1 and 2, since the scan electrode 4 and the sustain electrode 5 are formed in parallel with each other, a large interelectrode capacitance is formed between the scan electrode 4 and the sustain electrode 5. Exists.

  FIG. 3 is a circuit block diagram of the image display apparatus according to the embodiment of the present invention. This image display device includes a panel 1, a data electrode drive circuit 12, a scan electrode drive circuit 13, a sustain electrode drive circuit 14, a timing generation circuit 15, an image signal processing circuit 18, a lighting rate calculation unit 20, and a power supply circuit (not shown). ).

  The image signal processing circuit 18 converts the image signal sig into image data for each subfield. The data electrode driving circuit 12 converts the image data for each subfield into signals corresponding to the data electrodes D1 to Dm, and drives the data electrodes D1 to Dm. The timing generation circuit 15 generates various timing signals based on the horizontal synchronization signal H and the vertical synchronization signal V and supplies them to each circuit block. Scan electrode drive circuit 13 supplies a drive voltage waveform to scan electrodes SC1 to SCn based on the timing signal, and sustain electrode drive circuit 14 supplies a drive voltage waveform to sustain electrodes SU1 to SUn based on the timing signal. Here, scan electrode drive circuit 13 includes sustain pulse generation unit 100 for generating a sustain pulse, which will be described later, and sustain electrode drive circuit 14 also includes sustain pulse generation unit 200. As will be described in detail later, sustain pulse generators 100 and 200 can generate two types of sustain pulses, a first sustain pulse and a second sustain pulse.

  The lighting rate calculation unit 20 calculates the lighting rate for each subfield based on the image data of the image signal processing circuit 18, that is, the ratio of the number of discharge cells to be lit to the total number of discharge cells. The lighting rate of each subfield calculated by the lighting rate calculation unit 20 is sent to the timing generation circuit 15, and the timing generation circuit 15 switches between the first sustain pulse and the second sustain pulse based on the lighting rate. Further, sustain pulse generating units 100 and 200 of scan electrode drive circuit 13 and sustain electrode drive circuit 14 are controlled. Specifically, the lighting rate is compared with a predetermined threshold. When the lighting rate is smaller than the threshold, the first sustain pulse is generated from the sustain pulse generators 100 and 200, and the lighting rate is equal to or higher than the threshold. The timing generator 15 controls the sustain pulse generators 100 and 200 so as to generate the second sustain pulse.

  Next, a driving voltage waveform for driving the panel and its operation will be described. In the embodiment of the present invention, one field is divided into a plurality of subfields, and each subfield has an initialization period, an address period, and a sustain period. FIG. 4 is a diagram showing drive voltage waveforms applied to the respective electrodes of the panel according to the embodiment of the present invention.

  In the initializing period of the first subfield, the data electrodes D1 to Dm and the sustain electrodes SU1 to SUn are held at 0 (V), and from the voltage Vi1 (V) that is lower than the discharge start voltage with respect to the scan electrodes SC1 to SCn. A ramp voltage that gradually increases toward the voltage Vi2 (V) exceeding the discharge start voltage is applied. Then, the first weak initializing discharge is caused in all the discharge cells, negative wall voltages are stored on scan electrodes SC1 to SCn, and positive walls on sustain electrodes SU1 to SUn and data electrodes D1 to Dm. The voltage is stored. Here, the wall voltage on the electrode refers to a voltage generated by wall charges accumulated on a dielectric layer or a phosphor layer covering the electrode. Thereafter, sustain electrodes SU1 to SUn are maintained at positive voltage Vh (V), and a ramp voltage that gradually decreases from voltage Vi3 (V) to voltage Vi4 (V) is applied to scan electrodes SC1 to SCn. Then, the second weak initializing discharge is caused in all the discharge cells, the wall voltage on scan electrodes SC1 to SCn and the wall voltage on sustain electrodes SU1 to SUn are weakened, and the wall voltage on data electrodes D1 to Dm is reduced. Is also adjusted to a value suitable for the write operation.

  In the subsequent address period, scan electrodes SC1 to SCn are temporarily held at Vr (V). Next, a positive address pulse voltage Vd (V) is applied to the data electrode Dk (k = 1 to m) of the discharge cell to be displayed in the first row among the data electrodes D1 to Dm, and the first row is scanned. Scanning pulse voltage Va (V) is applied to electrode SC1. At this time, the voltage at the intersection between the data electrode Dk and the scan electrode SC1 is obtained by adding the wall voltage on the data electrode Dk and the wall voltage on the scan electrode SC1 to the externally applied voltage (Vd−Va) (V). And the discharge start voltage is exceeded. Then, an address discharge occurs between data electrode Dk and scan electrode SC1 and between sustain electrode SU1 and scan electrode SC1, and a positive wall voltage is accumulated on scan electrode SC1 of this discharge cell, and on sustain electrode SU1. And a negative wall voltage is also accumulated on the data electrode Dk. In this manner, an address operation is performed in which address discharge is caused in the discharge cells to be displayed in the first row and wall voltage is accumulated on each electrode. On the other hand, since the voltage at the intersection of data electrodes D1 to Dm and scan electrode SC1 to which positive address pulse voltage Vd (V) is not applied does not exceed the discharge start voltage, address discharge does not occur. The above address operation is sequentially performed until the discharge cell in the nth row, and the address period ends.

  In the subsequent sustain period, scan electrodes SC1 to SCn and sustain electrodes SU1 to SUn receive the first sustain pulse in the subfield where the lighting rate is lower than the threshold, and the second sustain pulse in the subfield where the lighting rate is equal to or higher than the threshold. The discharge cell which has been applied during the period and has formed wall charges by address discharge is selectively discharged to emit light. The waveforms of the two sustain pulses at this time and the details of the discharge associated therewith will be described later, and an outline of the operation in the sustain period will be described here.

  First, 0 (V) is applied to sustain electrodes SU1 to SUn, and positive sustain pulse voltage Vs (V) is applied to scan electrodes SC1 to SCn. In the discharge cell in which the address discharge has occurred at this time, the voltage between scan electrode SCi and sustain electrode SUi is the sustain pulse voltage Vs (V), the wall voltage on scan electrode SCi and the wall voltage on sustain electrode SUi. Exceeds the discharge start voltage. Then, a sustain discharge occurs between scan electrode SCi and sustain electrode SUi, and phosphor layer 11 emits light by the ultraviolet rays generated at this time. Then, a negative wall voltage is accumulated on scan electrode SCi, and a positive wall voltage is accumulated on sustain electrode SUi. At this time, a positive wall voltage is also accumulated on the data electrode Dk. In the discharge cells in which no address discharge has occurred during the address period, no sustain discharge occurs, and the wall voltage state at the end of the initialization period is maintained. Subsequently, 0 (V) is applied to scan electrodes SC1 to SCn, and positive sustain pulse voltage Vs (V) is applied to sustain electrodes SU1 to SUn. Then, in the discharge cell in which the sustain discharge has occurred, since the voltage between sustain electrode SUi and scan electrode SCi exceeds the discharge start voltage, a sustain discharge occurs again between sustain electrode SUi and scan electrode SCi, and the sustain cell is maintained. Negative wall voltage is accumulated on electrode SUi, and positive wall voltage is accumulated on scan electrode SCi. Thereafter, similarly, by applying sustain pulses of the number corresponding to the luminance weight alternately to scan electrodes SC1 to SCn and sustain electrodes SU1 to SUn, the sustain discharge continues in the discharge cells that have caused the address discharge in the address period. Done. Thus, the maintenance operation in the maintenance period is completed.

  The operations in the initialization period, address period, and sustain period in the subsequent subfield are substantially the same as those in the first subfield, and thus description thereof is omitted.

  Next, details of sustain pulse generators 100 and 200 will be described. FIG. 5 is a circuit diagram of sustain pulse generators 100 and 200 of the image display apparatus according to the embodiment of the present invention. Sustain pulse generation unit 100 includes power recovery unit 110 and clamp unit 120. The power recovery unit 110 includes a power recovery capacitor C10, switching elements Q11 and Q12, backflow prevention diodes D11 and D12, and a power recovery inductor L10. The clamp unit 120 includes a power source VS having a voltage value of Vs (V), and switching elements Q13 and Q14. The power recovery unit 110 and the clamp unit 120 are connected to the scan electrode 4 that is one end of the interelectrode capacitance Cp of the panel 1. The capacitor C10 has a sufficiently large capacity compared to the interelectrode capacity Cp, and functions as a power source for the power recovery unit 110.

  Sustain pulse generator 200 has the same circuit configuration as sustain pulse generator 100, and includes power recovery capacitor C20, switching elements Q21 and Q22, backflow prevention diodes D21 and D22, and power recovery inductor L20. A recovery unit 210 and a clamp unit 220 having a power source VS and switching elements Q23 and Q24 are provided, and the output of the sustain pulse generator 200 is connected to the sustain electrode 5 of the interelectrode capacitance Cp of the panel 1.

  Next, the first sustain pulse will be described in detail. FIG. 6 is a timing chart for explaining the operation of generating the first sustain pulse of sustain pulse generating units 100 and 200 of the image display device according to the embodiment of the present invention. One period of the first sustain pulse is divided into six periods indicated by T1 to T6, and each period will be described. Since the first sustain pulse applied to scan electrode 4 and the first sustain pulse applied to sustain electrode 5 have the same waveform but different phases, the operation from period T4 to period T6 is performed during period T1. Is equivalent to the operation in which the scan electrode 4 and the sustain electrode 5 are replaced in the operation from the period T3 to the period T3.

(Period T1)
At time t1, switching element Q12 is turned on. Then, the charge on the scan electrode 4 side starts to flow to the capacitor C10 through the inductor L10, the diode D12, and the switching element Q12, and the voltage of the scan electrode 4 starts to decrease.

(Period T2)
Since the inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the scan electrode 4 drops to near 0 (V) at time t2 after the time ½ of the resonance period has elapsed. However, due to the power loss due to the resistance component of the resonance circuit, the voltage of the sustain electrode 5 cannot be lowered to 0 (V). At time t2, switching element Q14 is turned on. Then, since scan electrode 4 is directly grounded through switching element Q14, the voltage of scan electrode 4 is forcibly lowered to 0 (V).

  Further, the switching element Q21 is turned ON at time t2. Then, a current starts to flow from the power recovery capacitor C20 through the switching element Q21, the diode D21, and the inductor L20, and the voltage of the sustain electrode 5 starts to rise.

(Period T3)
Since the inductor L20 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the sustain electrode 5 rises to near Vs (V) at time t3 after ½ time of the resonance period has elapsed. Therefore, the voltage of the sustain electrode 5 does not rise to Vs (V). At time t3, the switching element Q23 is turned on. Then, since sustain electrode 5 is directly connected to power supply VS through switching element Q23, the voltage of sustain electrode 5 is forcibly increased to Vs (V). Then, in the discharge cell in which the address discharge has occurred, the voltage between scan electrode 4 and sustain electrode 5 exceeds the discharge start voltage, and a sustain discharge occurs.

  Switching element Q12 may be turned off after time t2 and before time t5, and switching element Q21 may be turned off after time t3 and before time t4. In order to lower the output impedance of sustain pulse generating units 100 and 200, switching element Q14 is preferably turned off immediately before time t5, and switching element Q23 is preferably turned off immediately before time t4.

(Period T4)
At time t4, switching element Q22 is turned on. Then, the charge on the sustain electrode 5 side starts to flow to the capacitor C20 through the inductor L20, the diode D22, and the switching element Q22, and the voltage of the sustain electrode 5 starts to decrease.

(Period T5)
The voltage of sustain electrode 5 decreases to near 0 (V) at time t5 after the time ½ of the resonance period of inductor L20 and interelectrode capacitance Cp has elapsed. Switching element Q24 is turned on at time t5. Then, since sustain electrode 5 is directly grounded through switching element Q24, the voltage of sustain electrode 5 is forcibly reduced to 0 (V).

  Further, the switching element Q11 is turned ON at time t5. Then, current starts to flow from the power recovery capacitor C10 through the switching element Q11, the diode D11, and the inductor L10, and the voltage of the scan electrode 4 starts to rise.

(Period T6)
Since the inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the scan electrode 4 rises to near Vs (V) at time t6 after the time ½ of the resonance period has elapsed. Then, switching element Q13 is turned on at time t6. Then, since scan electrode 4 is directly connected to power supply VS through switching element Q13, the voltage of scan electrode 4 is forcibly increased to Vs (V). Then, in the discharge cell in which the address discharge has occurred, the voltage between scan electrode 4 and sustain electrode 5 exceeds the discharge start voltage, and a sustain discharge occurs.

  Switching element Q22 may be turned off by time t5 and after time t2, and switching element Q11 may be turned off by time t6 and after time t1. Further, it is desirable that the switching element Q24 is turned off immediately before time t2, and the switching element Q13 is turned off immediately before time t1.

  In the embodiment of the present invention, the resonance period of the resonance circuit formed by the inductor L10 or L20 and the interelectrode capacitance Cp, that is, so as to increase the recovery efficiency of the power recovery units 110 and 210, that is, The time of the periods T1, T2, T4, and T5 is set to 900 ns, which is twice as long as the conventional driving waveform, and the reactive power of the sustain pulse generators 100 and 200 when the first sustain pulse is generated is greatly reduced. ing. It has been known for some time that reactive power can be reduced by increasing the resonance period of the power recovery unit. However, when the repetition period of the sustain pulse is fixed, if the resonance period is set longer, the pulse duration will be shortened, and the sustain pulse voltage (hereinafter referred to as “minimum sustain pulse voltage”) required for continuing the sustain discharge. (Abbreviated) There is a tendency that Vpd tends to be high, and particularly when the lighting rate becomes high and the discharge current increases, this tendency becomes prominent and the discharge itself becomes unstable. However, in the embodiment of the present invention, since the first sustain pulse is used only during the sustain period of the subfield with a low lighting rate, 1/2 of the resonance period of the power recovery units 110 and 210 is set to 2 It is possible to set the time to about twice, that is, about 500 ns to 1200 ns, and the reactive power can be greatly reduced.

  Next, the second sustain pulse will be described in detail. FIG. 7 is a timing chart for explaining the operation of generating the second sustain pulse of sustain pulse generating units 100 and 200 of the image display device according to the embodiment of the present invention. One period of the second sustain pulse is divided into eight periods indicated by T1 to T8, and each period will be described. Since the second sustain pulse applied to scan electrode 4 and the second sustain pulse applied to sustain electrode 5 have the same waveform but different phases, the operation from period T5 to period T8 is performed in period T1. Is equivalent to the operation in which the scan electrode 4 and the sustain electrode 5 are replaced in the operation from the period T4 to the period T4.

(Period T1)
At time t1, switching element Q12 is turned on. Then, the charge on the scan electrode 4 side starts to flow to the capacitor C10 through the inductor L10, the diode D12, and the switching element Q12, and the voltage of the scan electrode 4 starts to decrease. Here, since the inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the scan electrode 4 decreases to near 0 (V) at time t3 after the time ½ of the resonance period has elapsed.

(Period T2)
At time t2, switching element Q21 is turned on. Then, a current starts to flow from the power recovery capacitor C20 through the switching element Q21, the diode D21, and the inductor L20, and the voltage of the sustain electrode 5 starts to rise. Again, since the inductor L20 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the sustain electrode 5 rises to near Vs (V) at time t4 after the lapse of half the resonance period.

(Period T3)
As described above, at time t3, the voltage of scan electrode 4 drops to near 0 (V). However, due to the power loss due to the resistance component of the resonance circuit, the voltage of the sustain electrode 5 cannot be lowered to 0 (V). At time t3, switching element Q14 is turned on. Then, since scan electrode 4 is directly grounded through switching element Q14, the voltage of scan electrode 4 is forcibly lowered to 0 (V). At this time, since the voltage of the sustain electrode 5 is also sufficiently increased, the decrease in the voltage of the scan electrode 4 is triggered to generate the first discharge. When the first discharge becomes large to some extent and the amount of ultraviolet light emission accompanying the discharge begins to saturate, the current required for the discharge exceeds the current supply capability of the power recovery unit 210 on the sustain electrode 5 side, and the first discharge starts to weaken. For this reason, the amount of ultraviolet rays emitted with respect to the discharge current is not saturated, and the light emission efficiency is improved.

(Period T4)
Switching element Q23 is turned on at time t4. Then, since sustain electrode 5 is directly connected to power supply VS through switching element Q23, the voltage of sustain electrode 5 is forcibly increased to Vs (V). Then, the voltage rise at this time becomes a trigger, and the second discharge occurs. Since the second discharge is generated while sufficient priming from the first discharge remains, the discharge is stable. In the second discharge, the scan electrode 4 is connected to the ground potential, and the sustain electrode 5 is connected to the power source VS. Therefore, the discharge current is not limited, and the discharge is sufficiently strong, and is necessary for continuing the sustain discharge. Can store a large wall voltage. In the second discharge, since the effective voltage applied to the discharge space is relaxed by the first discharge, that is, in a state where the voltage is relatively low, the light emission efficiency is improved.

  Switching element Q12 may be turned off after time t3 and before time t6, and switching element Q21 may be turned off after time t4 and before time t5. In order to lower the output impedance of sustain pulse generating units 100 and 200, switching element Q14 is preferably turned off immediately before time t6 and switching element Q23 is turned off immediately before time t5.

(Period T5)
At time t5, switching element Q22 is turned on. Then, the charge on the sustain electrode 5 side starts to flow to the capacitor C20 through the inductor L20, the diode D22, and the switching element Q22, and the voltage of the sustain electrode 5 starts to decrease. Here, since the inductor L20 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the sustain electrode 5 decreases to near 0 (V) at time t7 after a time ½ of the resonance period has elapsed.

(Period T6)
At time t6, switching element Q11 is turned on. Then, current starts to flow from the power recovery capacitor C10 through the switching element Q11, the diode D11, and the inductor L10, and the voltage of the scan electrode 4 starts to rise. Also here, since the inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the scan electrode 4 rises to near Vs (V) at time t8 after a time ½ of the resonance period has elapsed.

(Period T7)
Switching element Q24 is turned on at time t7. Then, since sustain electrode 5 is directly grounded through switching element Q24, the voltage of sustain electrode 5 is forcibly reduced to 0 (V). Then, the decrease in the voltage of the sustain electrode 5 is triggered to generate the first discharge. When the first discharge becomes large to some extent and the amount of ultraviolet rays emitted due to the discharge begins to saturate, the current required for the discharge exceeds the current supply capability of the power recovery unit 110 on the scan electrode 4 side, and the first discharge starts to weaken. For this reason, the amount of ultraviolet rays emitted with respect to the discharge current is not saturated, and the light emission efficiency is improved.

(Period T8)
Switching element Q13 is turned on at time t8. Then, since scan electrode 4 is directly connected to power supply VS through switching element Q13, the voltage of scan electrode 4 is forcibly increased to Vs (V). Then, the voltage rise at this time becomes a trigger, and the second discharge occurs. Since the second discharge is generated while sufficient priming due to the first discharge remains, the discharge is stable. In the second discharge, the sustain electrode 5 is connected to the ground potential, and the scan electrode 4 is connected to the power source VS, so that the discharge is strong enough to store the necessary wall voltage. In addition, the second discharge is a discharge with a very low effective voltage applied to the discharge space and high luminous efficiency.

  Note that the switching element Q22 may be turned off after time t7 and before time t2, and the switching element Q11 may be turned off after time t8 and before time t1. Further, it is desirable that the switching element Q24 is turned off immediately before time t2, and the switching element Q13 is turned off immediately before time t1.

  As described above, the sustain discharge by the second sustain pulse has higher luminous efficiency than the sustain discharge by the first sustain pulse. Furthermore, since the discharge current is dispersed in the sustain discharge by the second sustain pulse, there is an advantage that the sustain pulse voltage necessary for continuing the sustain discharge is relatively low. On the other hand, since the outputs of sustain pulse generating unit 100 and sustain pulse generating unit 200 interfere with each other, reactive power tends to increase as compared with the case where the first sustain pulse is generated.

  The image display device according to the embodiment of the present invention calculates the lighting rate in each subfield in order to take advantage of each of the first sustain pulse and the second sustain pulse, and the subfield whose lighting rate is lower than the threshold value. In FIG. 2, a sustain discharge is generated using the first sustain pulse, and a sustain discharge is generated using the second sustain pulse in a subfield having a lighting rate higher than the threshold value.

  FIG. 8 is a conceptual diagram for explaining a method of determining the threshold value in the image display apparatus according to the embodiment of the present invention. The reactive power of the first sustain pulse is smaller than the reactive power of the second sustain pulse, and any reactive power is almost constant regardless of the lighting rate. On the other hand, the light emission power of the first sustain pulse is larger than the light emission power of the second sustain pulse, and increases substantially in proportion to the lighting rate. Therefore, when the lighting rate is low, the total power of the first sustain pulse is smaller than the total power of the second sustain pulse, and when the lighting rate is high, the total power of the first sustain pulse is equal to the second sustain pulse. It becomes larger than the total power. Therefore, this characteristic is experimentally obtained for the panel to be used, and the lighting rate at which the total power of the two sustain pulses is equal may be set as a predetermined threshold value. Note that the above-described characteristics, particularly reactive power, greatly depend on the resonance period of the power recovery unit. When the resonance period is lengthened, the minimum sustain pulse voltage Vpd increases, and the first sustain pulse is generated in the subfield having a high lighting rate. Therefore, in setting the threshold value, it is desirable to consider the resonance period and the minimum sustain pulse voltage Vpd.

  FIG. 9 is a conceptual diagram for explaining another method for setting a threshold value. The first sustain pulse has a larger discharge current peak value and a shorter pulse duration of the sustain pulse than the second sustain pulse. Therefore, the minimum sustain pulse voltage Vpd of the first sustain pulse is larger than the minimum sustain pulse voltage Vpd of the second sustain pulse, and increases rapidly with respect to the lighting rate. In FIG. 9, when the first sustain pulse is used in the range of the lighting rate in which the minimum sustain pulse voltage Vpd of the first sustain pulse is smaller than the minimum sustain pulse voltage Vpd at the lighting rate of 100% of the second sustain pulse, There is no possibility that the discharge of the first sustain pulse becomes unstable.

  Therefore, the upper limit value of the threshold value can be determined by the method shown in FIG. 9 using the resonance period of the power recovery unit as a parameter, and the threshold value can be determined by the method shown in FIG.

  Although the mechanism by which the light emission efficiency is improved by the sustain discharge using the second sustain pulse has not been completely elucidated, since the amount of ultraviolet radiation is not saturated in the first discharge, the second discharge is performed again. With respect to, since discharge occurs at an effective low voltage, it is considered that the luminous efficiency is improved.

  In order to improve the light emission efficiency of the first discharge, it is desirable to increase the output voltage again after the first discharge has weakened to generate the second discharge, which is used in this embodiment. In the case of a panel, it is desirable that the time interval between the first discharge peak and the second discharge peak be 50 ns or more. Further, in order to generate the second discharge at a low voltage, it is desirable to increase the voltage applied to the electrode while the priming effect by the first discharge is obtained, thereby generating the second discharge. In the case of the panel used in this embodiment, the time interval between the first discharge peak and the second discharge peak is preferably 400 ns or less.

  Therefore, the time interval between the first discharge peak and the second discharge peak is preferably 50 ns or more and 400 ns or less. Furthermore, when the time interval of the peak of the second discharge is set to 100 ns or more and 250 ns or less, the light emission efficiency by the first discharge can be increased to the maximum, and the light emission efficiency by the second discharge is sufficiently increased. be able to. In the present embodiment, the sustain pulse period is set to 5.4 μs, the time interval between the two discharge peaks is set to 150 ns, and half of the resonance period of the power recovery units 110 and 210 is set to about 900 ns.

  FIG. 10 is a diagram showing a voltage waveform applied to the second sustain pulse and the light emission intensity at that time in the image display device according to the embodiment of the present invention. Thus, the actual measurement values of the applied voltage waveforms of scan electrode 4 and sustain electrode 5 are different from the voltage waveforms shown in FIG. In particular, the rise time of the sustain pulse seems to be greatly delayed from t2 or t6. Since this is driven simultaneously from both sides of the scan electrode 4 side and the sustain electrode 5 side of the interelectrode capacitance Cp, it is pulled by the drive waveform on the electrode side where the voltage changes first, and the drive on the electrode side where the voltage changes later. This is because the change in waveform appears delayed. However, looking at the voltage difference between the voltage applied to scan electrode 4 and the voltage applied to sustain electrode 5 (the voltage indicated by “scan electrode 4-sustain electrode 5” in FIG. 10), scan electrode 4-sustain electrode It can be seen that the first discharge is stably generated at the time t3 or t7 after the discharge start voltage is exceeded for 5 hours. After 200 ns, the second discharge is stably generated.

  As described above, it is desirable that the second sustain pulse is stably set to an optimal value for the time interval between the two discharge peaks. In particular, the first discharge is easily affected by individual discharge characteristics, and is also easily influenced by driving conditions such as the lighting rate. Conventionally, it is not easy to generate the first discharge accurately at a desired time. There wasn't. However, in the embodiment of the present invention, in periods T2 and T6, a voltage is applied to one of the display electrodes using the power recovery unit corresponding to the display electrode, and the power corresponding to the display electrode is applied to the other display electrode. A voltage is applied using the recovery unit, and a first discharge is generated by applying a voltage to one of the display electrodes using a clamp unit corresponding to the display electrode at time t3 and t7 to generate a first discharge. Can be stably generated at a desired time. Then, after the first discharge, the second discharge is generated by applying a voltage to the other of the display electrodes using a clamp portion corresponding to the display electrode at times t4 and t8 to generate the second discharge. As a result, the time interval between two successive discharges can be stably generated at a desired time interval.

  As described above, since the first and second discharges are continuously performed, the light emission efficiency can be improved. Therefore, the light emission efficiency with respect to the input power can be improved and the power consumption can be reduced. Alternatively, the power saved by improving the light emission efficiency can be used to improve display luminance by increasing the number of times of light emission.

  In the embodiment of the present invention, first, the voltage of one display electrode is forcibly lowered to 0 (V) to generate the first discharge, and then the voltage of the other display electrode is forcibly set. Although it has been described that the second discharge is generated by raising the voltage to Vs (V), first, the voltage of one display electrode is forcibly raised to Vs (V) to generate the first discharge, and then Even if the voltage of the other display electrode is forcibly lowered to 0 (V) to generate the second discharge, the same effect as in the present invention can be obtained.

  The image display device of the present invention can stably generate two continuous discharges and perform discharge control according to the lighting rate to improve the light emission efficiency, so that a plurality of discharge cells can be selectively discharged to generate an image. It is useful as an image display device that displays

1 is an exploded perspective view showing a structure of a panel used in an image display device in an embodiment of the present invention. Electrode array diagram of panel used in the image display device Circuit block diagram of the image display device The figure which shows the drive voltage waveform applied to each electrode of the panel used for the image display apparatus Circuit diagram of sustain pulse generator of image display device Timing chart for explaining the operation of generating the first sustain pulse of the sustain pulse generator of the image display device Timing chart for explaining the operation of generating the second sustain pulse of the sustain pulse generator of the image display device Conceptual diagram for explaining a method of determining a threshold value of the image display device The conceptual diagram for demonstrating the other method for setting the threshold value of the image display apparatus The figure which shows the applied voltage waveform of the 2nd sustain pulse of the image display apparatus, and the emitted light intensity at that time

Explanation of symbols

1 Panel 2 Front substrate 3 Back substrate 4 Scan electrode (display electrode)
5 Maintenance electrode (display electrode)
DESCRIPTION OF SYMBOLS 9 Data electrode 12 Data electrode drive circuit 13 Scan electrode drive circuit 14 Sustain electrode drive circuit 20 Lighting rate calculation part 100,200 Sustain pulse generation part 110,210 Power recovery part 120,220 Clamp part

Claims (4)

A plasma display panel comprising a plurality of discharge cells having a pair of display electrodes;
A first sustain pulse for generating one sustain discharge in the discharge cell when the voltage applied between the display electrodes changes, or a continuous in the discharge cell when the voltage applied between the display electrodes changes A pair of sustain pulse generators for applying the second sustain pulse for generating the two sustain discharges to the display electrodes;
A lighting rate calculator that calculates the lighting rate of the discharge cells based on an image signal to be displayed;
The sustain pulse generating unit generates a first sustain pulse when the lighting rate is less than a predetermined threshold value, and generates a second sustain pulse when the lighting rate is equal to or higher than the predetermined threshold value. Display device. Each of the sustain pulse generators includes a power recovery unit that applies a voltage by charging and discharging the display electrodes by resonance between a capacitance between the display electrodes and a power recovery inductor, and a predetermined power source or ground potential. The image display device according to claim 1, further comprising a clamp unit that connects and applies a voltage. The first sustain pulse is applied by applying a voltage to one of the display electrodes using a power recovery unit corresponding to the display electrode and then using a clamp unit corresponding to the display electrode, 2. The method according to claim 1, wherein a voltage is applied to the other of the display electrodes using a power recovery unit corresponding to the display electrode and then a voltage is applied using a clamp unit corresponding to the display electrode. Item 3. The image display device according to Item 2. The second sustain pulse is applied by applying a voltage to one of the display electrodes using a power recovery unit corresponding to the display electrode and using the power recovery unit corresponding to the display electrode for the other display electrode. And applying a voltage to one of the display electrodes using a clamp portion corresponding to the display electrode to generate a first discharge, and then corresponding to the display electrode on the other display electrode. The image display device according to claim 1, wherein a voltage is applied using a clamp unit to generate a second discharge and execute the discharge.

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