JP5076286B2 - Image display device - Google Patents

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 for 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. There has been proposed a display device (for example, see Patent Document 1) provided with a control means for controlling the drive means. 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 continuous discharges, in particular 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 discharge. Moreover, even if the lighting rate is the same, if the lighting pattern is different, the path through which the discharge current flows is also different, so it is difficult to stably control the two discharges using only the lighting rate.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image display apparatus that stably generates two continuous discharges, improves luminous efficiency, and reduces power consumption.

  An image display apparatus according to the present invention includes a panel including a plurality of discharge cells having a pair of display electrodes, and a sustain pulse generator for applying a sustain pulse for generating a sustain discharge to the display electrode. The generator 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 clamp unit that applies the voltage by connecting to a predetermined power source or ground potential. A voltage is applied to one of the display electrodes using a power recovery unit corresponding to the display electrode, a voltage is applied using a clamp unit corresponding to the display electrode, and then the display is displayed on the other display electrode. A first sustaining step of applying a voltage using a power recovery unit corresponding to the electrode and then applying a voltage using a clamp unit corresponding to the display electrode to generate one discharge; and one of the display electrodes A voltage is applied using the power recovery unit corresponding to the display electrode, and a voltage is applied to the other display electrode using the power recovery unit corresponding to the display electrode, and one of the display electrodes corresponds to the display electrode. A second voltage is generated by applying a voltage using the clamp unit to generate a first discharge and then applying a voltage to the other display electrode using the clamp unit corresponding to the display electrode to generate a second discharge. And applying a voltage to each of the display electrodes using a power recovery unit corresponding to the display electrode, and then applying a voltage using a clamp unit corresponding to the display electrode to generate one discharge. And a third maintenance step. With this configuration, it is possible to provide an image display device that can stably generate two continuous discharges, improve luminous efficiency, and reduce power consumption.

  In the image display device of the present invention, one field period is divided into a plurality of subfields having an initialization period, an address period, and a sustain period, and the sustain pulse generator performs the first sustain step after the first sustain step in the sustain period. Two maintenance steps may be performed.

  In the image display device of the present invention, the third sustain step is inserted after at least one of the sustain pulse generators continuously performs the first sustain step or the second sustain step a predetermined number of times during the sustain period. You may do it.

  The image display device of the present invention further includes a lighting rate calculation unit that calculates the lighting rate of the discharge cells based on the image signal to be displayed, and the sustain pulse generation unit performs the second sustaining step in the subfield having a low lighting rate. The first maintenance step and the second maintenance step so that the ratio of the first maintenance step to the second maintenance step is low in the subfield having a high lighting rate. The ratio may be changed.

  The sustain pulse generator of the image display device of the present invention increases the ratio of the third sustain step to the sustain period in the subfield with a low lighting rate, and the third sustain step with respect to the sustain period in the subfield with a high lighting rate. The third maintenance step may be inserted so that the ratio of the above is low.

  Further, in the image display device of the present invention, each clamp unit of the sustain pulse generation unit applies the voltage by discharging the display electrode and the inductance of the power recovery inductor when charging the display electrode and applying the voltage. The display electrode is charged and discharged using the power recovery inductor having a small inductance when the voltage is applied to the display electrode using the power recovery unit in the second maintenance step, unlike the inductance of the power recovery inductor at the time The voltage application may be started prior to the voltage application of the display electrode that is charged and discharged using the power recovery inductor having a large inductance.

  According to the present invention, it is possible to provide an image display device that stably generates two continuous discharges, improves luminous efficiency, and reduces power consumption.

  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 the image display apparatus according to the 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 a panel used in the image display apparatus. 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 in the row direction, 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 a 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. Cp exists.

  FIG. 3 is a circuit block diagram of the image display apparatus according to the embodiment of the present invention. The 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 circuit 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 three types of sustain pulses: a first sustain pulse, a second sustain pulse, and a third sustain pulse.

  The lighting rate calculation circuit 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 circuit 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, the scan electrode drive circuit 13 and the sustain electrode drive circuit 14 are controlled.

  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, and the sustain period generates the first sustain pulse. 1 sustain period and a second sustain period for generating a second sustain pulse. FIG. 4 is a diagram showing drive voltage waveforms applied to the respective electrodes of the panel used in the image display apparatus according to the embodiment of the present invention.

  In the first half of the initialization period, data electrodes D1 to Dm and sustain electrodes SU1 to SUn are held at 0 (V), and discharge starts from voltage Vi1 (V) that is equal to or lower than the discharge start voltage with respect to scan electrodes SC1 to SCn. A ramp voltage that gradually increases toward the voltage Vi2 (V) exceeding the 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 the dielectric layer or the phosphor layer covering the electrode.

  Thereafter, in the second half of the initialization period, sustain electrodes SU1 to SUn are maintained at positive voltage Vh (V), and gradually decrease from scan voltage SC1 to SCn toward voltage Vi4 (V) from voltage Vi3 (V). Apply lamp voltage. 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.

  Depending on the subfield, the first half of the initializing period may be omitted. In this case, an initializing discharge is generated in a discharge cell that has undergone a sustaining discharge in the sustaining period of the immediately preceding subfield.

  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). Exceeding the discharge start voltage. 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.

  Among the subsequent sustain periods, the first sustain step and the third sustain step are performed in the first sustain period, and the second sustain step and the third sustain step are performed in the second sustain period. The discharge cell in which the wall charge is formed by is selectively discharged to emit light. At this time, the waveform of the sustain pulse applied between scan electrodes SC1 to SCn and sustain electrodes SU1 to SUn and the details of the discharge associated therewith will be described later, and the outline of the operation in the sustain period will be described here.

  First, sustain electrodes SU1 to SUn are returned to 0 (V), 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 equal to sustain pulse voltage Vs (V), which is the magnitude of the wall voltage on scan electrode SCi and sustain electrode SUi. Exceeds the discharge start voltage. Then, a sustain discharge occurs between scan electrode SCi and sustain electrode SUi, 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, scan electrodes SC1 to SCn are returned to 0 (V), 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. Although the interelectrode capacitance Cp is also shown in FIG. 5, a circuit for generating a scan pulse is omitted. 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 power recovery inductors L11 and L12. Here, the inductance of the inductor L11 is set to a value slightly larger than the inductance of L12. 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 which is one end of the interelectrode capacitance Cp of the panel 1 via a scan pulse generation circuit (not shown because it is in a short circuit state during the sustain period). ing. The capacitor C10 has a sufficiently large capacity compared to the interelectrode capacity Cp, and is charged to approximately Vs / 2 (V) so as to function 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 a power recovery capacitor C20, switching elements Q21 and Q22, backflow prevention diodes D21 and D22, and power recovery inductors L21 and L22. The power recovery unit 210 includes a power source VS, and a clamp unit 220 including switching elements Q23 and Q24. The output of sustain pulse generator 200 is connected to sustain electrode 5 of interelectrode capacitance Cp of panel 1. Also here, the inductance of the inductor L21 is set to a value slightly larger than the inductance of L22.

  Next, a sustain pulse used for the first sustain step in the first sustain period (hereinafter abbreviated as “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.

(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 L12, the diode D12, and the switching element Q12, and the voltage of the scan electrode 4 starts to decrease.

(Period T2)
Since the inductor L12 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the scan electrode 4 decreases to near 0 (V) at time t2 after the lapse of half the resonance period. 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, current starts to flow from the power recovery capacitor C20 through the switching element Q21, the diode D21, and the inductor L21, and the voltage of the sustain electrode 5 starts to rise.

(Period T3)
Since the inductor L21 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 a time ½ 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 turned off immediately before time t4.

(Period T4-T6)
Since the first sustain pulse applied to scan electrode 4 and the first sustain pulse applied to sustain electrode 5 have the same waveform, the operation from period T4 to period T6 is the operation from period T1 to period T3. Thus, the operation is the same as the operation in which the scan electrode 4 and the sustain electrode 5 are interchanged, and the description thereof is omitted.

  As described above, 1/2 of the resonance period of the resonance circuit formed by the inductors L11, L12, L21, and L22 and the interelectrode capacitance Cp, that is, the time periods T1, T2, T4, and T5 are set to be sufficiently long. . In this embodiment, the periods T1 and T4 are set to 1050 ns, and the periods T2 and T5 are set to 1000 ns. Therefore, the characteristics of the first sustain pulse are that the power recovery efficiency of the power recovery units 110 and 210 is high, and the reactive power can be greatly reduced. On the other hand, the time periods T3 and T6 are shortened, and the sustain pulse voltage required for continuing the sustain discharge tends to be higher than that of a second sustain pulse described later. In particular, this tendency becomes remarkable when the lighting rate increases and the discharge current increases.

  Next, the second sustaining step for stably generating two continuous discharges in the second sustaining period will be described in detail. FIG. 7 shows an operation for generating a sustain pulse (hereinafter abbreviated as “second sustain pulse”) used in the second sustain step of sustain pulse generating units 100 and 200 of the image display apparatus according to the embodiment of the present invention. It is a timing chart for explaining. One period of the second sustain pulse is divided into eight periods indicated by T1 to T8, and each period will be described.

(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 L12, the diode D12, and the switching element Q12, and the voltage of the scan electrode 4 starts to decrease. Here, since the inductor L12 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, current starts to flow from the power recovery capacitor C20 through the switching element Q21, the diode D21, and the inductor L21, and the voltage of the sustain electrode 5 starts to rise. Also here, since the inductor L21 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 time ½ of the resonance period has elapsed.

(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 scan electrode 4 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 a certain 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 is generated. Since the second discharge is generated while sufficient priming due to the first discharge remains, the second discharge becomes a stable discharge. Further, at the time of 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, so that the discharge current is not limited and becomes a sufficiently strong discharge, which 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 preferably turned off immediately before time t5.

  Since the second sustain pulse applied to scan electrode 4 and the second sustain pulse applied to sustain electrode 5 have the same waveform, the operation from period T5 to period T8 is performed from period T1 to period T4. This is the same as the operation in which the scan electrode 4 and the sustain electrode 5 are interchanged in the operation described above, and thus the description thereof is omitted.

  Although the mechanism by which the light emission efficiency is improved by the sustain discharge using the second sustain step has not been completely elucidated, since the amount of ultraviolet radiation is not saturated with respect to the first discharge, and with respect to the second discharge, Since discharge is generated at an effective low voltage, it can be considered that the light emission efficiency is improved.

  In order to improve the light emission efficiency of the sustain discharge in the second sustain step, it is desirable to generate the second discharge by raising the output voltage again after the first discharge is weakened. In the case of the panel used in the embodiment, 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, it is desirable that the time interval between the first discharge peak and the second discharge peak be 50 ns or more and 400 ns or less. Furthermore, when the time interval between the peaks of the two discharges is set to 100 ns or more and 250 ns or less, the light emission efficiency by the first discharge can be almost maximized and the light emission efficiency by the second discharge can be sufficiently increased. Can do. In the present embodiment, the sustain pulse repetition period is set to 5.4 μs, and the time interval between the two discharge peaks is set to 150 ns. Further, by setting the inductances of the inductors L11 and L21 to be approximately 2.5% larger than the inductances of the inductors L12 and L22, 1/2 of the resonance period of the power recovery units 110 and 210 at the rising edge of the sustain pulse is approximately 1000 ns. In addition, the falling time was set to 1050 ns.

  FIG. 8 is a diagram showing an applied voltage waveform of the second sustain pulse and an actually measured value of the emission intensity at that time. Thus, the actual measurement values of the applied voltage waveforms at the electrode terminal portions of scan electrode 4 and sustain electrode 5 are different from the voltage waveforms shown in FIG. In particular, the rising time of the sustain pulse seems to be greatly delayed from t2 or t6. This is because the interelectrode capacitance Cp is driven simultaneously from both sides of the scan electrode 4 side and the sustain electrode 5 side, so that the voltage changes first and is pulled by the drive waveform on the electrode side where the voltage change is large. This is because the change in the drive waveform on the electrode side that changes and the voltage change is small appears to be 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-sustain electrode” in FIG. 8), it is sufficient between scan electrode and sustain electrode. In the discharge cell in which a large voltage is applied and the address discharge is caused, the first discharge is stably generated at the time t3 or the time t7 after exceeding the discharge start voltage. As described above, the first discharge is generated after the voltage between the display electrodes of the discharge cell to be sustained discharge exceeds the discharge start voltage between the display electrodes. Therefore, the first discharge is not a so-called erasing discharge generated between the data electrode and the scan electrode. It can be seen that the sustain discharge is generated between the display electrodes. Then, the second discharge is stably generated after 150 ns.

  In general, as in the second sustain step, the drive waveform on the scan electrode side and the drive waveform on the sustain electrode side are changed simultaneously, and the interelectrode capacitance Cp is simultaneously driven from both sides of the scan electrode 4 side and the sustain electrode 5 side. In this case, the drive waveform tends to become unstable due to the influence of a change in the display image. However, in the present embodiment, the inductances of the inductors L11 and L21 that determine the resonance period at the rising edge of the sustain pulse are set larger than the inductances of the inductors L12 and L22 that determine the resonance period at the time of falling. The voltage change at the time is larger than the voltage change at the rise. Furthermore, by setting the period T1 to about 150 ns and generating the sustain pulse fall before the sustain pulse fall, the drive waveform can be reliably pulled to the electrode side where the sustain pulse falls, A stable drive waveform can be obtained as shown in FIG. 8 without being affected by the display state or the like. It has also been experimentally confirmed that pulling the drive waveform to the electrode side where the sustain pulse falls has the effect of widening the sustain pulse voltage margin.

  Thus, it is desirable that the light emission efficiency of the sustain discharge in the second sustain step is stably set to an optimal value for the time interval between the two discharge peaks. In particular, the first discharge, which is the first discharge, is easily affected by individual discharge characteristics, and is also easily affected by driving conditions such as the lighting rate, so that the first discharge can be generated accurately at a desired time. Although it is not easy, in the embodiment of the present invention, the rise of the sustain pulse applied to the scan electrode and the sustain electrode and the fall of the sustain pulse applied to the other electrode are overlapped in time, By clamping the electrode to the power supply voltage or the ground potential to generate the first discharge, the first discharge can be stably generated at a desired time. Thereafter, the second discharge can be controlled by clamping the other electrode to the ground potential or the power supply voltage to generate the second discharge. As a result, the time interval between the two discharges can be set as desired. It can be generated stably at time intervals.

  As described above, the characteristic of the sustain discharge by the second sustain step is that the luminous efficiency is higher than that of the sustain discharge by the first sustain step. Furthermore, since the discharge current is dispersed in the sustain discharge in the second sustain step, there is an advantage that the sustain pulse voltage necessary for continuing the sustain discharge becomes 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 generates a sustain discharge using the first sustain step and the sustain period in order to take advantage of the advantages of the first sustain step and the second sustain step described above. A first sustain period to be generated and a second sustain period to generate a sustain discharge using the second sustain step, the lighting rate in each subfield is calculated, and the first sustain when the lighting rate is low The period is set longer, and the second sustain period is set longer as the lighting rate becomes higher. FIG. 9 is a diagram illustrating an example of a ratio of the first sustain period and the second sustain period to the lighting rate in the image display device according to the embodiment of the present invention. In the present embodiment, the last several pulses of the sustain period are always set as the second sustain period, and the first sustain step is used for the remaining sustain period in the subfield where the lighting rate is 0% to 43.9%. Sudden discharge is performed. In the subfield having the lighting rate of 43.9% to 44.7%, the first sustain step is used in the first 3/4 period of the remaining sustain period, and the second sustain step is performed in the remaining 1/4 period. Sustain discharge using In the sustain period of the subfield having the lighting rate of 44.7% to 45.5%, the first sustain step is used in the first half period, and the second sustain step is used in the remaining half period. Sudden discharge is performed. In the sustain period of the subfield having the lighting rate of 45.5% to 46.2%, the first sustain step is used in the first 1/4 period, and the second sustain step is performed in the remaining 3/4 period. Sustain discharge using Further, the sustain discharge using the second sustain step is performed in the sustain period of the subfield where the lighting rate is 46.2% to 100%.

  In this way, the sustain period is divided into two according to the lighting rate, and the first sustain pulse is divided into scan electrodes SC1 to SCn and the sustain electrodes in the first sustain period, and the second sustain pulse in the second sustain period. By applying the sustain discharge between SU1 and SUn to generate the sustain discharge, the ratio of the two sustain pulses can be changed without any visual discomfort. In addition, by making the last several sustain pulses the second sustain pulse at all times, the last sustain discharge in the sustain period can be stabilized, and the subsequent initialization operation can also be stabilized.

  As described above, according to the sustain discharge using the first sustain step and the second sustain step, it is possible to generate an efficient discharge utilizing the advantages of the respective sustain steps. However, when the wall voltage on the display electrode varies for some reason, there is a risk that the luminance varies due to the wall voltage variation. In the embodiment of the present invention, even if the wall voltage varies, the sustain pulse (hereinafter referred to as “the third sustain step” for stabilizing the wall voltage and stably maintaining the sustain discharge). (Abbreviated as “third sustain pulse”) is inserted into the first and second sustain pulse trains. Then, every time the first maintenance step or the second maintenance step is continuously performed a predetermined number of times on at least one of the display electrodes, the third maintenance step is inserted.

  Next, the third sustain pulse will be described. FIG. 10 is a timing chart showing details of the third sustain pulse in the embodiment of the present invention. The third sustain pulse has an effect of stabilizing the wall voltage only by being inserted at a rate of once per several times of the first sustain pulse or the second sustain pulse. In FIG. 10, the following explanation will be given assuming that one third pulse is inserted into the second sustain pulse train on the sustain electrode side. Of course, the third sustain pulse train includes the third sustain pulse in the first sustain pulse train. The sustain pulse may be inserted, and the same effect can be obtained on the scan electrode side by inserting the third sustain pulse.

(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 L12, the diode D12, and the switching element Q12, and the voltage of the scan electrode 4 starts to decrease. Here, since the inductor L12 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, current starts to flow from the power recovery capacitor C20 through the switching element Q21, the diode D21, and the inductor L21, and the voltage of the sustain electrode 5 starts to rise. Also here, since the inductor L21 and the interelectrode capacitance Cp form a resonance circuit, the voltage of the sustain electrode 5 rises to near Vs (V) after a time ½ of the resonance period has elapsed. The process up to this point is the same as the second sustain pulse.

(Period T3)
The third sustain pulse is greatly different from the second sustain pulse in that switching element Q23 and switching element Q14 are turned on before sustain discharge is generated between scan electrode 4 and sustain electrode 5. In the present embodiment, switching element Q23 is turned on without waiting until time t4. That is, at time t3, the switching element Q14 is turned on and the switching element Q23 is turned on. When switching element Q14 is turned on at time t3, scan electrode 4 is directly grounded through switching element Q14, so the voltage of scan electrode 4 is forcibly reduced to 0 (V). At the same time, switching element Q23 is turned ON, so that sustain electrode 5 is directly connected to power supply VS through switching element Q23, and the voltage of sustain electrode 5 is forcibly increased to Vs (V). Then, the voltage drop of the scan electrode 4 and the voltage rise of the sustain electrode 5 are triggered, and the discharge cell exceeding the discharge start voltage is generated in the discharge cell which has caused the address discharge. Since the sustain discharge at this time is very strong and the pulse duration (the period T3 in FIG. 10) is long, wall charges that can relax the electric field inside the discharge cell are accumulated. Therefore, even if the wall voltage varies for some reason, the wall voltage can be stabilized by generating a discharge using the third sustain pulse.

  Here, the switching element Q12 may be turned off after time t3 and before time t6, and the switching element Q21 may be turned off after time t3 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 preferably turned off immediately before time t5.

  Note that the timing for controlling switching element Q21 and switching element Q23 is not limited to that described above, and switching element Q23, switching element Q14, and switching element Q14 are switched before the sustain discharge is generated between scan electrode 4 and sustain electrode 5. Can be turned on. FIG. 11 is a timing chart showing a third sustain pulse in another embodiment. FIG. 11A shows a case where the switching element Q12 is turned on at the time t1 and the switching element Q21 is turned on at the same time, and the switching element Q14 and the switching element Q23 are turned on at the time t3 'before the time t3. By controlling in this way, the pulse duration can be further increased and the wall voltage can be further stabilized. In FIG. 11B, the time at which the switching element Q12 is turned on and the time at which the switching element Q21 is turned on are not simultaneous, and the time at which the switching element Q14 is turned on and the time at which the switching element Q23 is turned on are not simultaneous. Before the discharge occurs, switching element Q23 and switching element Q14 are turned on. Sustain pulses with timings other than these are possible, but in any case, switching element Q23 and switching element Q14 are turned on before sustain discharge is generated between scan electrode 4 and sustain electrode 5. Therefore, unlike the discharge by the second sustain pulse, the sustain discharge by the third sustain pulse becomes one strong discharge.

  As described above, even if the wall voltage varies for some reason when the sustain discharge is generated using the first sustain step or the second sustain step, the third sustain is performed. The wall voltage can be stabilized by generating a discharge using steps. On the other hand, since the third sustain pulse forcibly clamps the voltage using the clamp units 120 and 220, the power recovery rate is low, and the reactive power tends to increase compared to the first sustain pulse.

  Next, a specific method for inserting the third maintenance step into the first maintenance step or the second maintenance step will be described. For example, the third maintenance step is inserted once for the first maintenance step four times, or the third maintenance step is inserted once for the second maintenance step three times. May be inserted at a constant ratio. However, when the lighting rate of the discharge cells in the sustain period increases, the wall voltage variation increases and the luminance variation tends to be noticeable. Therefore, it is effective to control the ratio of the third sustain step according to the lighting rate. . That is, the ratio of the third sustain step inserted in the first or second sustain step is high in the subfield with a high lighting rate, and the ratio of the third sustain step is low in the subfield with a low lighting rate. To control. FIG. 12 is a diagram schematically showing the sustain pulse of the image display device according to the embodiment of the present invention. FIG. 12A shows the ratio of the second sustain step to 1/3, that is, the predetermined number of times = 2. FIG. 12B shows the ratio when the step ratio is 1/4, ie, the predetermined number of times = 3, and FIG. 12C shows the case where the ratio of the step is 1/6, ie, the predetermined number of times = 5. A pulse is shown. For example, when the lighting rate is 0% to 5%, the ratio of the third maintenance step is 0, when the lighting rate is 5% to 20%, the ratio of the same step is 1/6, and when the lighting rate is 20% to 50%, the same. When the step ratio is 1/4 and the lighting rate is 50% or more, the step ratio is controlled to be 1/3. Although FIG. 12 shows a voltage waveform in which the third sustain pulse is inserted into the second sustain pulse train, the same applies to the case where the third sustain pulse is inserted into the first sustain pulse train.

  As described above, according to the sustain discharge using the first sustain step and the second sustain step, it is possible to generate an efficient sustain discharge that takes advantage of the advantages of the respective sustain steps. Furthermore, even if the wall voltage on the display electrode varies for some reason by inserting the third maintenance step into the first maintenance step or the second maintenance step according to the lighting rate. The wall voltage can be stabilized and the sustain discharge can be continued stably.

  The image display device of the present invention is useful as an image display device using a panel because it can stably generate two continuous discharges and perform discharge control according to the lighting rate to improve the light emission efficiency.

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 Drive voltage waveform diagram applied to each electrode of the panel used in the image display device Circuit diagram of sustain pulse generator of image display device Timing chart showing details of first sustain pulse of image display device Timing chart showing details of second sustain pulse of image display device The figure which shows the applied voltage waveform of the 2nd sustain pulse of the image display apparatus, and the measured value of the emitted light intensity at that time The figure which shows an example of the ratio of the 1st maintenance period and the 2nd maintenance period with respect to the lighting rate of the image display apparatus Timing chart showing details of third sustain pulse of image display device Timing chart showing third sustain pulse in another embodiment The figure which shows typically the sustain pulse of the image display apparatus in embodiment of this invention

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 15 Timing generation circuit 18 Image signal processing circuit 20 Lighting rate calculation circuit 100,200 Sustain pulse generation part 110,210 Power recovery part 120,220 Clamp part

Claims (6)

A plasma display panel having a plurality of discharge cells having a pair of display electrodes, and a sustain pulse generator for applying a sustain pulse for generating a sustain discharge to the display electrode, the sustain pulse generator, A power recovery unit that charges and discharges the display electrodes by resonance between the capacitance between the display electrodes and a power recovery inductor, and a clamp unit that applies a voltage by connecting to a predetermined power supply or ground potential And applying a voltage to one of the display electrodes using a power recovery unit corresponding to the display electrode to discharge the display electrode, and then applying a ground voltage using a clamp unit corresponding to the display electrode At the same time, after applying a voltage to the other display electrode using a power recovery unit corresponding to the display electrode to charge the display electrode, a clamp unit corresponding to the display electrode is provided. A first maintenance step of generating a single discharge by applying a predetermined power supply had,
A voltage is applied to one of the display electrodes using a power recovery unit corresponding to the display electrode to discharge the display electrode, and a voltage is also applied to the other display electrode using a power recovery unit corresponding to the display electrode. The display electrode is charged, and a ground voltage is applied to one of the display electrodes using a clamp portion corresponding to the display electrode to generate a first discharge, and then the display electrode is applied to the other display electrode. A second sustaining step of generating a second discharge by applying a predetermined power using a clamp portion corresponding to
A voltage is applied to each of the display electrodes using a power recovery unit corresponding to the display electrode to discharge the display electrode, and then a ground voltage is applied using a clamp unit corresponding to the display electrode. And a third sustaining step for generating discharges of times.   One field period is divided into a plurality of subfields having an initialization period, an address period, and a sustain period, and the sustain pulse generator performs a first sustain step in the sustain period, and then performs a second sustain step. The image display device according to claim 1, wherein: One field period is divided into a plurality of subfields having an initialization period, an address period, and a sustain period , and at least one of the sustain pulse generators performs the first sustain step or the second sustain step in the sustain period. The image display device according to claim 1, wherein a third maintenance step is inserted after the predetermined number of consecutive times.   A lighting rate calculation unit that calculates the lighting rate of the discharge cells based on an image signal to be displayed is further provided, and the sustain pulse generator has a ratio of the first sustaining step to the second sustaining step in a subfield having a low lighting rate. The ratio of the first maintenance step to the second maintenance step is changed so that the ratio of the first maintenance step to the second maintenance step is low in the subfield having a high lighting rate. The image display device according to any one of claims 1 to 3, wherein the image display device is characterized. The sustain pulse generating unit, in the low lighting rate subfield lower the ratio of the third sustain step for sustaining period, the high lighting rate subfield such that the ratio of the third sustain step for sustaining period increases The image display device according to claim 1, wherein the third maintaining step is inserted into the image display device. Each of the sustaining pulse generators includes a clamp unit for charging the display electrode and applying a voltage to the inductance of the power recovery inductor, and for discharging the display electrode and applying a voltage. Unlike the inductance of the inductor,
In the second maintaining step, when a voltage is applied to the display electrode using a power recovery unit to discharge the display electrode, a voltage applied to the display electrode that is charged / discharged using a power recovery inductor having a small inductance is applied. The image display device according to claim 1, wherein the image display device is started prior to voltage application of a display electrode that is charged and discharged using a power recovery inductor having a large inductance.

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