Patent Application
20090146922
The present invention relates to an image display device with a plasma display panel.
Plasma display panels (hereinafter, abbreviated as “panels”) expanding market size rapidly in recent years are display devices with the advantages of being large, thin, lightweight, and highly visible. The panels, however, are low in emission efficiency, so that various techniques are being developed to improve emission efficiency and to reduce power consumption.
As an example to improve emission efficiency and hence to reduce power consumption by devising a method of driving the panel, the following display device has been developed which includes a first drive part and a second drive part. The first drive part generates a first discharge in a plurality of discharge cells in the display panel by applying a drive pulse to the discharge cells. The second drive part generates a second discharge subsequent to the first discharge by applying a current from a power supply to the discharge cells so as to increase the voltage of the drive pulse which has been decreased along with the first discharge.
In this display device, the first discharge is supplied with minimum electric power necessary for the discharge, so that when the first discharge begins to weaken, the current supply can be limited to reduce ultraviolet saturation, thereby improving the emission efficiency in the first discharge. As a result, the first discharge is generated to have high emission efficiency and is followed by the second discharge in all the discharge cells to be turned on, thereby improving the emission efficiency of the discharge cells. The technical contents are disclosed in Japanese Patent No. 3242096.
However, these consecutive discharges, especially the first discharge, are susceptible to the characteristics and conditions of discharge of each discharge cell and to variations in the component properties of the driving circuits. This makes it uneasy to stably generate the two discharges in all the discharge cells.
The present invention, which has been devised to solve the aforementioned problems, provides an image display device with emission efficiency improved by stably generating two consecutive discharges.
The image display device of the present invention comprises: a panel including a plurality of discharge cells each having a pair of display electrodes; and a pair of sustain pulse generators applying one of a first sustain pulse and a second sustain pulse to the pair of display electrodes, the first sustain pulse generating a sustain discharge twice in the plurality of discharge cells when a voltage applied between the pair of display electrodes changes, and the second sustain pulse generating a sustain discharge once in the plurality of discharge cells when the voltage applied between the pair of display electrodes changes, wherein each of the pair of sustain pulse generators includes: an electric power recovery part for applying a voltage by charging and discharging the pair of display electrodes by a resonance between an inductor for electric power recovery and an electrostatic capacitance between the pair of display electrodes; and a clamp for applying a voltage by being connected to one of a predetermined power supply and a ground potential, the application of the first sustain pulse is performed by applying a voltage to one of the pair of display electrodes using the electric power recovery part corresponding to the one of the pair of display electrodes; by applying a voltage to an other of the pair of display electrodes using the electric power recovery part corresponding to the other of the pair of display electrodes; by applying a voltage to the one of the pair of display electrodes using the clamp corresponding to the one of the pair of display electrodes so as to generate a first discharge, and later by applying a voltage to the other of the pair of display electrodes using the clamp corresponding to the other of the pair of display electrodes so as to generate a second discharge, the application of the second sustain pulse is performed by applying a voltage to each of the pair of display electrodes using the electric power recovery parts corresponding to each of the pair of display electrodes, and by applying a voltage using the clamps corresponding to each of the pair of display electrodes so as to generate a first discharge. This structure enables the image display device to stably generate the two consecutive discharges so as to improve emission efficiency.
In the image display device of the present invention, it is preferable that the first sustain pulse is applied a predetermined number of times in succession to at least one of the pair of display electrodes, and that the second sustain pulse is applied by being added to the predetermined number of the first sustain pulses. In this structure, when wall voltages have variations for some reason, the wall voltages can be stabilized by generating a discharge with the second sustain pulse.
In the image display device of the present invention, the predetermined number of times can be controlled based on an image signal to be displayed. As a result, the image display device can be driven by an optimum sustain pulse in accordance with the image signal.
Thus, the present invention can provide an image display device with improved emission efficiency by stably generating the two consecutive discharges.
An image display device of embodiments of the present invention will be described with reference to drawings.
Image signal processing circuit 18 converts an image signal “sig” to image data for each subfield. Data electrode driving circuit 12 converts the image data for each subfield to a signal corresponding to each of data electrodes D1 to Dm and drives data electrodes D1 to Dm. Timing generating circuit 15 generates various timing signals based on a horizontal synchronizing signal H and a vertical synchronizing signal V and supplies them to each circuit block. Scan electrode driving circuit 13 provides scan electrodes SC1 to SCn with drive voltage waveforms based on a timing signal, and sustain electrode driving circuit 14 provides sustain electrodes SU1 to SUn with drive voltage waveforms based on another timing signal. Scan electrode driving circuit 13 includes sustain pulse generator 100 for generating a sustain pulse, which will be described later, and similarly, sustain electrode driving circuit 14 includes sustain pulse generator 200. Sustain pulse generators 100 and 200 can generate several kinds of sustain pulses which will be detailed later. Sustain pulse generators 100 and 200 each include an electric power recovery part in order to recover the electric power due to the charge and discharge of the interelectrode capacitance between scan electrodes 4 and sustain electrodes 5.
The following is a description of the drive voltage waveforms to drive the panel and the driving operation. In the first embodiment of the present invention, one field is divided into a plurality of subfields each having an initialization period, a write period, and a sustain period.
In the subsequent write period, scan electrodes SC1 to SCn are once held at a voltage Vr (V). Then, of data electrodes D1 to Dm, data electrode Dk (k=1 to m) of the discharge cell to be displayed on the first row is subjected to a positive write pulse voltage Vd (V), and scan electrode SC1 on the first row is subjected to a scan pulse voltage Va (V). In this case, the intersection point of data electrode Dk and scan electrode SC1 has a voltage which is equal to the total of an externally applied voltage (Vd−Va) (V), the wall voltage on data electrode Dk, and the wall voltage on scan electrode SC1, and the total exceeds the starting voltage. A write discharge is generated between data electrode Dk and scan electrode SC and between sustain electrode SU1 and scan electrode SC1. A positive wall voltage is accumulated on scan electrode SC1 of this discharge cell, and a negative wall voltage is accumulated on sustain electrode SU1 and on data electrode Dk. Thus, the write discharge is generated in the discharge cell to be displayed on the first row, thereby performing a writing operation to accumulate the wall voltage on each electrode. On the other hand, the intersection points of data electrodes D1 to Dm that have not been subjected to the positive write pulse voltage Vd (V) and scan electrode SC1 have a voltage not exceeding the starting voltage, so that no write discharge is generated. The above-described writing operation is applied up to the discharge cells on the nth row so as to terminate the write period.
In the subsequent sustain period, a sustain pulse voltage Vs (V) is applied between scan electrodes SC1 to SCn and sustain electrodes SU1 to SUn so as to generate a discharge and to emit light selectively in the discharge cell which has formed a wall charge due to the write discharge. The sustain pulse and the sustain discharge in this case will be briefly described as follows and in detail later. First, sustain electrodes SU1 to SUn are subjected to a voltage of 0 (V), and scan electrodes SC1 to SCn are subjected to the positive sustain pulse voltage Vs (V). In the discharge cell in which the write discharge has occurred, the voltage between the top of scan electrode SCi and the top of sustain electrode SUi is equal to the total of the sustain pulse voltage Vs (V), the wall voltage on scan electrode SCi, and the wall voltage on sustain electrode SUi, and the total exceeds the starting voltage. Scan electrode SCi and sustain electrode SUi generate a sustain discharge therebetween, and the ultraviolet light generated in this case allows phosphor layers 11 to emit light. As a result, a negative wall voltage is accumulated on scan electrode SCi, and a positive wall voltage is accumulated on sustain electrode SUi. In addition, a positive wall voltage is also accumulated on data electrode Dk. In the discharge cells in which no write discharge has occurred in the write period, no sustain discharge occurs, so that the wall voltage condition at the end of the initialization period is maintained. Then, scan electrodes SC1 to SCn are subjected to a voltage of 0 (V), and sustain electrodes SU1 to SUn are subjected to the positive sustain pulse voltage Vs (V). In the discharge cell in which the sustain discharge has occurred, the voltage between the top of sustain electrode SUi and the top of scan electrode SCi exceeds the starting voltage. This causes another sustain discharge between sustain electrode SUi and scan electrode SCi. A negative wall voltage is accumulated on sustain electrode SUi, and a positive wall voltage is accumulated on scan electrode SCi. Hereinafter, in the same manner, the number of sustain pulses corresponding to the luminance weight is applied alternately to scan electrodes SC1 to SCn and sustain electrodes SU1 to SUn. This allows the sustain discharge to be continued in the discharge cell in which the write discharge has occurred in the write period. Thus, the sustain operation in the sustain period is terminated.
In the subsequent subfield, the operations in the initialization period, the write period, and the sustain period will not be described because they are equal to those in the first subfield.
Sustain pulse generators 100 and 200 of scan electrode driving circuit 13 and sustain electrode driving circuit 14, respectively, generate the above-described sustain pulse in the sustain period and apply the pulse to scan electrodes 4 and sustain electrodes 5, respectively.
The sustain pulse voltage and the sustain discharge will be described in detail as follows. In the first embodiment of the present invention, a sustain discharge is performed using two kinds of sustain pulses: a first sustain pulse which can stably generate two consecutive discharges and a second sustain pulse which can stably continue the sustain discharge by stabilizing the wall voltages.
At time t1, switching element Q12 is turned on. This causes the charge on the scan electrode 4 side to flow to capacitor C10 via inductor L10, diode D12, and switching element Q12, making the voltage of scan electrodes 4 begin to fall. Since inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of scan electrodes 4 falls to around 0 (V) at time t3 when ½ of the resonance period has elapsed.
At time t2, switching element Q21 is turned on. This causes a current to flow from capacitor C20 for electric power recovery via switching element Q21, diode D21, and inductor L20, making the voltage of sustain electrodes 5 begin to rise. Since inductor L20 and the interelectrode capacitance Cp form a resonance circuit, the voltage of sustain electrodes 5 rises to around a Vs (V) at time t4 when ½ of the resonance period has elapsed.
At time t3, the voltage of scan electrodes 4 falls to around 0 (V) as described above, but not reach 0 (V) due to the power loss of the resistance component of the resonance circuit and the like. At time t3, switching element Q14 is turned on. This allows scan electrodes 4 to be directly grounded via switching element Q14, so that their voltage is forced to 0 (V). At this moment, the voltage of sustain electrodes 5 rises sufficiently and exceeds the starting voltage in the discharge cell in which the write discharge has occurred. The voltage drop in scan electrodes 4 triggers the generation of a first discharge. When the first discharge reaches a certain intensity and the amount of ultraviolet light generated by the discharge begins to saturate, the current required for the discharge exceeds the current capability of electric power recovery part 210 on the sustain electrode side. As a result, the first discharge begins to weaken, so that the amount of ultraviolet light generated by the discharge current does not reach saturation, thereby improving emission efficiency.
At time t4, switching element Q23 is turned on. This allows sustain electrodes 5 to be directly connected to power supply VS via switching element Q23, so that their voltage is forced to the Vs (V). The voltage rise triggers the generation of a second discharge. The second discharge can be stable because it is generated when a sufficient priming of the first discharge is still left. The second discharge can also be strong with no limitation on the amount of the discharge current so as to accumulate a wall voltage required to continue the sustain discharge. This is because scan electrodes 4 are connected to the ground potential, and sustain electrodes 5 are connected to power supply VS. Furthermore, the second discharge has a high emission efficiency because it is performed when the effective voltage applied on the discharge space is reduced by the first discharge, that is, when the voltage is comparatively low.
Switching element Q12 has only to be turned off after time t3 and before time t6, and switching element Q21 has only to be turned off after time t4 and before time t5. In order to reduce the output impedances of sustain pulse generators 100 and 200, it is preferable to turn off switching element Q14 immediately before time t6 and switching element Q23 immediately before time t5.
The mechanism that the sustain discharge generated by the first sustain pulse can improve emission efficiency is not elucidated completely. However, as described above, the improvement seems to be achieved by the absence of the saturation of the ultraviolet light in the first discharge and the generation of the second discharge at an effectively low voltage.
In order to improve the emission efficiency of the first discharge, the second discharge is preferably generated by increasing the output voltage again after the first discharge is weakened. In the panel used in the present embodiment, the peak of the first discharge and the peak of the second discharge are preferably not less than 50 ns apart from each other. On the other hand, in order to generate the second discharge at a low voltage, the second discharge is preferably generated by increasing the voltage applied on the electrodes when the priming effect of the first discharge is still left. In the panel used in the present embodiment, the peak of the first discharge and the peak of the second discharge are preferably not more than 400 ns apart from each other.
Therefore, the peak of the first discharge and the peak of the second discharge are preferably not less than 50 ns and not more than 400 ns apart from each other. Furthermore, setting the time interval between the peaks of the two discharges not less than 100 ns and not more than 250 ns apart from each other can almost maximize the emission efficiency of the first discharge and can also make the emission efficiency of the second discharge sufficiently large. In the present embodiment, the repetition period of the sustain pulse is set to 5.4 μs, the time interval of the peaks of the two discharges is set to 150 ns, and ½ of the resonance period of electric power recovery parts 110 and 210 is set to 900 ns.
As described hereinbefore, the sustain discharge using the first sustain pulse allows the stable generation of the two discharges with high emission efficiency. However, the two discharges may lose balance and have variation in luminance when the wall voltages on the display electrodes have variations for some reason. In the first embodiment of the present invention, the first sustain pulse train has a second sustain pulse added thereto for stably continuing the sustain discharge by stabilizing the wall voltages if the wall voltages have variations. The second sustain pulse is added and applied every time the first sustain pulse is applied a predetermined number of times in succession to at least one of the display electrodes.
The second sustain pulse will be described as follows.
At time t1, switching element Q12 is turned on. This causes the charge on the scan electrode 4 side to flow to capacitor C10 via inductor L10, diode D12, and switching element Q12, making the voltage of scan electrodes 4 begin to fall. Since inductor L10 and the interelectrode capacitance Cp form a resonance circuit, the voltage of scan electrodes 4 falls to around 0 (V) at time t3 when ½ of the resonance period has elapsed.
At time t2, switching element Q21 is turned on. This causes a current to flow from capacitor C20 for electric power recovery via switching element Q21, diode D21, and inductor L20, making the voltage of sustain electrodes 5 begin to rise. Since inductor L20 and the interelectrode capacitance Cp form a resonance circuit, the voltage of sustain electrodes 5 rise to around the Vs (V) when ½ of the resonance period has elapsed. The operation described so far is the same as that of the first sustain pulse.
The second sustain pulse greatly differs from the first sustain pulse in that switching elements Q23 and Q14 are turned on before a sustain discharge is generated between scan electrodes 4 and sustain electrodes 5. In the first embodiment, switching element Q23 is turned on before time t4. More specifically, not only switching element Q14 but also switching element Q23 is turned on at time t3. When switching element Q14 is turned on at time t3, scan electrodes 4 are directly grounded via switching element Q14 and therefore the voltage of scan electrodes 4 is forced to 0 (V). Since switching element Q23 is turned on at the same time, sustain electrodes 5 are directly connected to power supply VS via switching element Q23, so that the voltage of sustain electrodes 5 is forced to the Vs (V). The voltage drop in scan electrodes 4 and the voltage rise in sustain electrodes 5 trigger the voltage difference between scan electrodes 4 and sustain electrodes 5 to exceed the starting voltage so as to generate a sustain discharge in the discharge cell in which a write discharge has occurred. In this case, the sustain discharge is very strong and the pulse duration (the length of period T4′ shown in
Switching element Q12 has only to be turned off after time t3 and before time t6, and switching element Q21 has only to be turned off after time t3 and before time t5. In order to reduce the output impedances of sustain pulse generators 100 and 200, it is preferable to turn off switching element Q14 immediately before time t6 and switching element Q23 immediately before time t5.
The timing of controlling switching elements Q21 and Q23 is not limited to the aforementioned one, but can be performed by turning switching elements Q23 and Q14 on before a sustain discharge is generated between scan electrodes 4 and sustain electrodes 5.
b are timing charts showing details of a second sustain pulse in other embodiments.
As described above, the first sustain pulse in the first embodiment of the present invention generates the first discharge by forcibly reducing the voltage of the display electrodes on one side to 0 (V) first, and then generates the second discharge by forcibly increasing the voltage of the display electrodes on the other side to the Vs (V). However, it is alternatively possible to generate the first discharge by forcibly increasing the voltage of the display electrodes on one side to the Vs (V) first and then to generate the second discharge by forcibly decreasing the voltage of the display electrodes on the other side to 0 (V).
Similar to the first embodiment, in a second embodiment of the present invention, a sustain discharge is performed using two kinds of sustain pulses: a first sustain pulse which can stably generate two consecutive discharges and a second sustain pulse which can stably continue the sustain discharge by stabilizing the wall voltages. The second embodiment differs from the first embodiment in that the rate of the second sustain pulse added to the first sustain pulse train is controlled in accordance with the image signal to be displayed. More specifically, the second sustain pulse is added to the first sustain pulse train after the first sustain pulse is applied a predetermined number of times in succession to the display electrodes, and the predetermined number of times is controlled in accordance with the image signal.
As the lighting rate of the discharge cells in the sustain period is larger, the wall voltages tend to have more variations, making the luminance variation noticeable. Therefore, in the present second embodiment, the proportion of the second sustain pulse is controlled to increase with increasing lighting rate.
As described hereinbefore, the sustain discharge using the first sustain pulse can stably generate two discharges with high emission efficiency. Adding the second sustain pulse to the first sustain pulse train can stabilize the wall voltages on the display electrodes when the wall voltages have variation for some reason, thereby stably continuing the two consecutive sustain discharges. The proportion of the second sustain pulse is controlled to increase with increasing lighting rate. Therefore, the proportion of the first pulse can be increased when the wall voltages are unlikely to decrease so as to improve emission efficiency, and the proportion of the second pulse can be increased when the wall voltages are likely to have more variations so as to stabilize the wall voltages. As a result, the image display device can be driven by an optimum sustain pulse in accordance with the image signal.
The present invention is useful as an image display device and other similar devices which can improve emission efficiency by stably generating two consecutive discharges.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-143777 | May 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/309632 | 5/15/2006 | WO | 00 | 2/26/2007 |
