Patent Grant
8384623
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP2008/003274.
The present invention relates to a plasma display device used in a wall-hanging television (TV) or a large monitor, and a driving method for a plasma display panel.
A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:
A subfield method is generally used as a method of driving the panel. In this method, one field is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display.
Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge is caused, a wall charge required for a subsequent address operation is formed on each electrode, and a priming particle (an excitation particle for causing address discharge) for stably causing address discharge is generated.
In the address period, address pulse voltage is selectively applied to a discharge cell where display is to be performed to cause address discharge, thereby forming a wall charge (hereinafter, this operation is referred to as “address”). In the sustain period, sustain pulse voltage is alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustain discharge is caused in the discharge cell having undergone address discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
In this subfield method, the following operations are performed. In the initializing period of one of a plurality of subfields, the all-cell initializing operation of causing discharge in all discharge cells is performed. In the initializing period of other subfields, the selection initializing operation of selectively causing initializing discharge in the discharge cell having undergone sustain discharge is performed. Thus, light emission that is not related to the gradation display is minimized, and the contrast ratio can be improved.
As a circuit for applying a sustain pulse to a display electrode pair, the so-called electric power recovering circuit capable of reducing power consumption is generally used (e.g. patent document 1). Patent document 1 discloses an electric power recovering circuit, focusing attention on a fact that each display electrode pair is a capacitive load having an inter-electrode capacity of the display electrode pair. The disclosed electric power recovering circuit LC(inductance-capacitance)-resonates an inductor and the inter-electrode capacity using a resonance circuit including the inductor as a component, recovers the electric power stored in the inter-electrode capacity in a capacitor for electric power recovery, and recycles the recovered electric power for driving the display electrode pair.
Recently, the screen size and definition of the panel have been further increased, and hence various studies of improving the luminous efficiency of the panel and improving the luminance have been performed. For example, a study of largely increasing the luminous efficiency by increasing the xenon partial pressure has been performed. When the xenon partial pressure is increased, however, variation in timing of causing discharge increases, the light emission intensity in each discharge cell varies, and the display luminance can become un-uniform. In order to improve the un-uniformity of the luminance, a driving method is disclosed in which the rising period is shortened once per a plurality of times in the sustain period, for example, a sustain pulse whose rising is steep is inserted, the timing of the sustain discharge is aligned, and the display luminance is uniformed (e.g. patent document 2).
A technology is disclosed where, in the sustain period, the switch timing from the electric power recovering circuit to a clamping circuit of a sustain pulse that belongs to a first group including the firstly applied sustain pulse is delayed comparing with sustain pulses that belong to the other groups, thereby suppressing the variation in light emission intensity in each discharge cell to improve the display quality (e.g. patent document 3).
Recently, the screen size and luminance of the panel have been increased, and hence power consumption of the panel is apt to increase. Recent increase in definition of the panel increases the number of electrodes to be driven, and hence further increases the power consumption. Therefore, the power consumption is desired to be further reduced.
Regarding a panel whose screen size and definition are increased, the load during driving of the panel increases, so that the discharge is apt to become unstable and hence it is further important to cause stable sustain discharge.
In the technology disclosed in patent document 2, for example, a sustain pulse having steep rising can suppress variation in light emission intensity in each discharge cell and cause stable sustain discharge. However, the recovery efficiency in the electric power recovering circuit decreases, and hence it is difficult to reduce the power consumption.
In the technology disclosed in patent document 3, a sustain pulse whose rising is moderated by delaying the switch timing from the electric power recovering circuit to the clamping circuit comparing with the sustain pulses that belong to the other groups can produce the following effects:
However, the sustain pulse whose rising is moderated has a discharge intensity lower that that of the sustain pulse whose rising is steep, and hardly produces sufficient wall charge in the discharge cell. In the technology disclosed in patent document 3, disadvantageously, this sustain pulse continuously occurs and hence the sustain discharge hardly occurs.
The plasma display device of the present invention has the following elements:
Thus, even in the panel whose screen size, luminance, and definition are increased, sustain discharge can be stably caused while the power consumption is reduced, and the image display quality of the panel can be improved.
A plasma display device in accordance with an exemplary embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.
Protective layer 26 is actually used as a material of the panel in order to reduce the discharge start voltage in a discharge cell. Protective layer 26 is made of material that is mainly made of MgO and has a large secondary electron discharge coefficient and high durability when neon (Ne) and xenon (Xe) gases are filled.
A plurality of data electrodes 32 are formed on back plate 31, dielectric layer 33 is formed so as to cover data electrodes 32, and mesh barrier ribs 34 are formed on dielectric layer 33. Phosphor layers 35 for emitting lights of respective colors of red (R), green (G), and blue (B) are formed on the side surfaces of barrier ribs 34 and on dielectric layer 33.
Front plate 21 and back plate 31 are faced to each other so that display electrode pairs 24 cross data electrodes 32 with a micro discharge space sandwiched between them, and the outer peripheries of them are sealed by a sealing material such as glass frit. The discharge space is filled with mixed gas of neon and xenon as discharge gas. In the present embodiment, discharge gas where xenon partial pressure is set at about 10% is employed for improving luminous efficiency. The discharge space is partitioned into a plurality of sections by barrier ribs 34. Discharge cells are formed in the intersecting parts of display electrode pairs 24 and data electrodes 32. The discharge cells discharge and emit light to display an image.
The structure of panel 10 is not limited to the above-mentioned one, but may be a structure having striped barrier ribs, for example. The mixing ratio of the discharge gas is not limited to the above-mentioned value, but may be another mixing ratio.
Next, a driving voltage waveform and its operation for driving panel 10 are described. The plasma display device of the present embodiment performs gradation display by a subfield method. In this method, one field is divided into a plurality of subfields, and emission and non-emission of light of each display cell are controlled in each subfield. Each subfield has an initializing period, an address period, and a sustain period.
In the initializing period in each subfield, initializing discharge is caused to produce a wall charge required for a subsequent address discharge on each electrode. The initializing operation has a function of generating a priming particle (an excitation particle as a detonating agent for discharge) for reducing the discharge delay and stably causing the address discharge. The initializing operation at this time includes an all-cell initializing operation of causing initializing discharge in all discharge cells, and a selection initializing operation of selectively causing initializing discharge only in a discharge cell that has undergone sustain discharge in the adjacently previous subfield.
In the address period, address discharge is selectively caused in a discharge cell to emit light in a subsequent sustain period, thereby producing a wall charge. In the sustain period, as many sustain pulses as the number proportional to luminance weight are alternately applied to display electrode pairs 24, and sustain discharge is caused in the discharge cell having undergone address discharge, thereby emitting light. The proportionality constant at this time is called “luminance magnification”.
In the present embodiment, one field is formed of 10 subfields (first SF, second SF, . . . , 10th SF), and respective subfields have luminance weights of 1, 2, 3, 6, 11, 18, 30, 44, 60 and 80, for example. The all-cell initializing operation is performed in the initializing period of the first SF, and the selection initializing operation is performed in the initializing period of each of the second SF through 10th SF. Thus, the light emission that is not related to the image display is only light emission caused by discharge in the all-cell initializing operation in the first SF. Therefore, luminance of black level, which is the luminance in a black display region where sustain discharge is not caused, is determined only by weak light emission in the all-cell initializing operation, and image display of sharp contrast is allowed. In the sustain period of each subfield, as many sustain pulses as the number derived by multiplying the luminance weight of each subfield by a predetermined luminance magnification are applied to respective display electrode pairs 24.
In the present embodiment, the number of subfields and luminance weight of each subfield are not limited to the above-mentioned values. The subfield structure may be changed based on an image signal or the like.
In the present embodiment, the length of the period (hereinafter referred to as “rising period”) when an after-mentioned electric power recovering circuit is operated in order to raise a sustain pulse is changed to generate the sustain pulse. Specifically, in the sustain period, the following three kinds of sustain pulses are switched and generated so that the second sustain pulse does not continue. The three kinds of sustain pulses include a first sustain pulse serving as a reference, a second sustain pulse whose rising is moderated by making the “rising period” longer than that of the first sustain pulse, and a third sustain pulse whose rising is sharpened by making the “rising period” shorter than that of the first sustain pulse. Thus, the sustain discharge is stabilized to uniform the display luminance of each discharge cell while the power consumption of panel 10 is reduced, thereby improving the image display quality of panel 10.
Next, the outline of a driving voltage waveform and the configuration of the driving circuit are firstly described, then the operation in the sustain period is described in detail.
First, a first SF as the all-cell initializing subfield is described.
In the first half of the initializing period of the first SF, 0 (V) is applied to data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn, and a ramp voltage (hereinafter referred to as “up-ramp voltage”) is applied to scan electrode SC1 through scan electrode SCn. Here, the up-ramp voltage gradually increases from voltage Vi1, which is not higher than a discharge start voltage, to voltage Vi2, which is higher than the discharge start voltage, with respect to sustain electrode SU1 through sustain electrode SUn.
While the up-ramp voltage increases, feeble initializing discharge continuously occurs between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and feeble initializing discharge continuously occurs between scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm. Negative wall voltage is accumulated on scan electrode SC1 through scan electrode SCn, and positive wall voltage is accumulated on data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn. Here, the wall voltage on the electrodes means the voltage generated by the wall charges accumulated on the dielectric layer covering the electrodes, the protective layer, and the phosphor layer.
In the last half of the initializing period, positive voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, and 0 (V) is applied to data electrode D1 through data electrode Dm. A ramp voltage (hereinafter referred to as “down-ramp voltage”) is applied to scan electrode SC1 through scan electrode SCn. Here, the down-ramp voltage gradually decreases from voltage Vi3, which is not higher than the discharge start voltage, to voltage V14, which is higher than the discharge start voltage, with respect to sustain electrode SU1 through sustain electrode SUn. While the down-ramp voltage decreases, feeble initializing discharge continuously occurs between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and feeble initializing discharge continuously occurs between scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm. The negative wall voltage on scan electrode SC1 through scan electrode SCn and the positive wall voltage on sustain electrode SU1 through sustain electrode SUn are reduced, positive wall voltage on data electrode D1 through data electrode Dm is adjusted to a value suitable for the address operation. Thus, the all-cell initializing operation of applying initializing discharge to all discharge cells is completed.
As shown in the initializing period of the second SF of
In the subsequent address period, voltage Ve2 is firstly applied to sustain electrode SU1 through sustain electrode SUn, and voltage Vc is applied to scan electrode SC1 through scan electrode SCn.
Negative scan pulse voltage Va is applied to scan electrode SC1 in the first column, positive address pulse voltage Vd is applied to data electrode Dk (k is 1 through m), of data electrode D1 through data electrode Dm, in the discharge cell to emit light in the first column. At this time, the voltage difference in the intersecting part of data electrode Dk and scan electrode SC1 is derived by adding the difference between the wall voltage on data electrode Dk and that on scan electrode SC1 to the difference (Vd−Va) of the external applied voltage, and exceeds the discharge start voltage. Discharge thus occurs between data electrode Dk and scan electrode SC1. Since voltage Ve2 is applied to sustain electrode SU1 through sustain electrode SUn, the voltage difference between sustain electrode SU1 and scan electrode SC1 is derived by adding the difference between the wall voltage on sustain electrode SU1 and that on scan electrode SC1 to the difference (Ve2−Va) of the external applied voltage. At this time, by setting voltage Ve2 at a voltage value slightly lower than the discharge start voltage, a state where discharge does not occur but is apt to occur can be caused between sustain electrode SU1 and scan electrode SC1. Therefore, the discharge occurring between data electrode Dk and scan electrode SC1 can cause discharge between sustain electrode SU1 and scan electrode SC1 that exist in a region crossing data electrode Dk. Thus, address discharge occurs in the discharge cell to emit light, positive wall voltage is accumulated on scan electrode SC1, negative wall voltage is accumulated on sustain electrode SU1, and negative wall voltage is also accumulated on data electrode Dk.
Thus, an address operation of causing address discharge in the discharge cell to emit light in the first column and accumulating wall voltage on each electrode is performed. The voltage in the intersecting parts of scan electrode SC1 and data electrode D1 through data electrode Dm to which address pulse voltage Vd is not applied does not exceed the discharge start voltage, so that address discharge does not occur. This address operation is repeated until it reaches the discharge cell in the n-th column, and the address period is completed.
In the subsequent sustain period, positive sustain pulse voltage Vs is firstly applied to scan electrode SC1 through scan electrode SCn, and the ground potential as a base potential, namely 0 (V), is applied to sustain electrode SU1 through sustain electrode SUn. In the discharge cell having undergone the address discharge, the voltage difference between scan electrode SCi and sustain electrode SUi is obtained by adding the difference between the wall voltage on scan electrode SCi and that on sustain electrode SUi to sustain pulse voltage Vs, and exceeds the discharge start voltage.
Sustain discharge occurs between scan electrode SCi and sustain electrode SUi, and ultraviolet rays generated at this time cause phosphor layer 35 to emit light. Negative wall voltage is accumulated on scan electrode SCi, positive wall voltage is accumulated on sustain electrode SUi. Positive wall voltage is also accumulated on data electrode Dk. In the discharge cell where address discharge has not occurred in the address period, sustain discharge does not occur and the wall voltage at the end of the initializing period is kept.
Subsequently, 0 (V) as the base potential is applied to scan electrode SC1 through scan electrode SCn, and sustain pulse voltage Vs is applied to sustain electrode SU1 through sustain electrode SUn. In the discharge cell having undergone the sustain discharge, the voltage difference between sustain electrode SUi and scan electrode SCi exceeds the discharge start voltage. Therefore, sustain discharge occurs between sustain electrode SUi and scan electrode SCi again, negative wall voltage is accumulated on sustain electrode SUi, and positive wall voltage is accumulated on scan electrode SCi. Hereinafter, similarly, as many sustain pulses as the number derived by multiplying the luminance weight by luminance magnification are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn to cause potential difference between the electrodes of display electrode pairs 24. Thus, sustain discharge is continuously performed in the discharge cell where the address discharge has been caused in the address period.
As discussed above, the present embodiment has the configuration where three kinds of sustain pulses are switched and generated so that the second sustain pulse does not continue. Here, the three kinds of sustain pulses include a first sustain pulse serving as a reference, a second sustain pulse whose rising is made gentler than that of the first sustain pulse, and a third sustain pulse whose rising is made steeper than that of the first sustain pulse. Thus, the sustain discharge is stabilized to uniform the display luminance of each discharge cell while the power consumption of panel 10 is reduced, thereby improving the image display quality of panel 10.
At the end of the sustain period, a ramp voltage (hereinafter referred to as “erasing ramp voltage”) is applied to scan electrode SC1 through scan electrode SCn. Here, the erasing ramp voltage gradually increases from 0 (V) as the base potential to voltage Vers. Thus, feeble discharge is continuously caused, and a part or the whole of the wall voltages on scan electrode SCi and sustain electrode SUi is erased while positive wall voltage is left on data electrode Dk.
Specifically, sustain electrode SU1 through sustain electrode SUn are returned to 0 (V), then the erasing ramp voltage, which increases from 0 (V) as the base potential to voltage Vers higher than the discharge start voltage, is applied to scan electrode SC1 through scan electrode SCn. Then, feeble discharge occurs between sustain electrode SUi and scan electrode SCi in the discharge cell having undergone the sustain discharge. This feeble discharge is continuously caused while the voltage applied to scan electrode SC1 through scan electrode SCn increases.
At this time, charged particles generated by the feeble discharge are accumulated on sustain electrode SUi and scan electrode SCi to form wall charge so as to reduce the voltage difference between sustain electrode SUi and scan electrode SCi. Thus, while positive wall charge is left on data electrode Dk, the wall voltage between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn is decreased to the extent of the difference between the voltage applied to scan electrode SCi and the discharge start voltage, namely (voltage Vers—discharge start voltage). The last discharge in the sustain period caused by the erasing ramp voltage is called “erasing discharge”.
The operation of the subsequent subfield is substantially similar to the above-mentioned operation except for the number of sustain pulses in the sustain period, and is not described. The outline of the driving voltage waveform to be applied to each electrode of panel 10 of the present embodiment has been described.
Next, a configuration of the plasma display device of the present embodiment is described.
Image signal processing circuit 41 converts input image signal sig into image data that indicates emission or non-emission of light in each subfield. Data electrode driving circuit 42 converts the image data in each subfield into a signal corresponding to each of data electrode D1 through data electrode Dm, and drives each of data electrode D1 through data electrode Dm.
Timing generating circuit 45 generates various timing signals for controlling operations of respective circuit blocks based on horizontal synchronizing signal H and vertical synchronizing signal V, and supplies them to respective circuit blocks. In the present embodiment, as discussed above, timing generating circuit 45 switches the “rising period” in rising of the sustain pulse among three different lengths, and outputs a timing signal responsive to the switched length to scan electrode driving circuit 43 and sustain electrode driving circuit 44. Thus, the power consumption is reduced and the sustain discharge is stabilized.
Scan electrode driving circuit 43 has the following elements:
Next, the detail and the operation of sustain pulse generating circuit 50 and sustain pulse generating circuit 60 are described.
Sustain pulse generating circuit 50 has electric power recovering circuit 51 and clamping circuit 52. Electric power recovering circuit 51 and clamping circuit 52 are connected to scan electrode SC1 through scan electrode SCn, which are one end of inter-electrode capacity Cp of panel 10 via the scan pulse generating circuit (not shown because it comes into a short circuit state during the sustain period).
Electric power recovering circuit 51 has capacitor C10 for recovering electric power, switching element Q11, switching element Q12, diode D11 for preventing back flow, diode D12 for preventing back flow, and inductor L10 for resonance Electric power recovering circuit 51 LC-resonates inter-electrode capacity Cp and inductor L10 to raise and fall the sustain pulse. Thus, electric power recovering circuit 51 drives scan electrode SC1 through scan electrode SCn by LC-resonance without power from the power supply, so that the power consumption is 0 ideally. Capacitor C10 for recovering electric power has a capacity sufficiently larger than inter-electrode capacity Cp, and is charged up to about Vs/2, namely a half voltage value Vs, so as to work as the power supply of electric power recovering circuit 51.
Clamping circuit 52 has switching element Q13 for clamping scan electrode SC1 through scan electrode SCn on voltage Vs, and switching element Q14 for clamping scan electrode SC1 through scan electrode SCn on 0 (V) as the base potential. Clamping circuit 52 clamps scan electrode SC1 through scan electrode SCn on voltage Vs by connecting them to power supply VS via switching element Q13, and clamps scan electrode SC1 through scan electrode SCn on 0 (V) by grounding them via switching element Q14. Therefore, the impedance during voltage application by clamping circuit 52 is small, and large discharge current by strong sustain discharge can be stably made to flow.
Sustain pulse generating circuit 50 switches conduction and breaking of switching element Q11, switching element Q12, switching element Q13, and switching element Q14 in response to the timing signal output from timing generating circuit 45, thereby operating electric power recovering circuit 51 and clamping circuit 52 and generating a sustain pulse.
For example, in raising a sustain pulse, switching element Q11 is set at ON to resonate inter-electrode capacity Cp and inductor L10, and electric power is supplied from capacitor C10 for recovering electric power to scan electrode SC1 through scan electrode SCn via switching element Q11, diode D11, and inductor L10. When the voltage of scan electrode SC1 through scan electrode SCn approaches voltage Vs, switching element Q13 is set at ON, a circuit for driving scan electrode SC1 through scan electrode SCn is switched from electric power recovering circuit 51 to clamping circuit 52, and scan electrode SC1 through scan electrode SCn are clamped on voltage Vs. In the present embodiment, the rising of the sustain pulse is controlled by controlling the driving time by electric power recovering circuit 51.
While, in falling a sustain pulse, switching element Q12 is set at ON to resonate inter-electrode capacity Cp and inductor L10, and electric power is recovered from inter-electrode capacity Cp to capacitor C10 for recovering electric power via inductor L10, diode D12, and switching element Q12. When the voltage of scan electrode SC1 through scan electrode SCn approaches 0 (V), switching element Q14 is set at ON, a circuit for driving scan electrode SC1 through scan electrode SCn is switched from electric power recovering circuit 51 to clamping circuit 52, and scan electrode SC1 through scan electrode SCn are clamped on voltage 0 (V) as the base potential.
Thus, sustain pulse generating circuit 50 generates a sustain pulse. These switching elements can be formed of a generally known element such as a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).
Sustain pulse generating circuit 60 has a configuration substantially the same as that of sustain pulse generating circuit 50. Sustain pulse generating circuit 60 has the following elements:
At the timing when voltage Ve1 is applied in
The circuit for applying voltage Ve1 and voltage Ve2 is not limited to the circuit shown in
Next, the driving voltage waveform in the sustain period is described in detail.
In the following description, the operation of conducting a switching element is denoted with ON, and the operation of breaking it is denoted with OFF. In the drawings, a signal for setting a switching element at ON is denoted with “ON”, and a signal for setting a switching element at OFF is denoted with “OFF”.
(Time Period T1)
Switching element Q12 is set at ON at time t1. At this time, charge on the side of scan electrode SC1 through scan electrode SCn starts to flow to capacitor C10 via inductor L10, diode D12, and switching element Q12, and the voltage of scan electrode SC1 through scan electrode SCn starts to decrease. Inductor L10 and inter-electrode capacity Cp form a resonance circuit, so that the voltage of scan electrode SC1 through scan electrode SCn decreases to a voltage close to 0 (V) at time t2 after a lapse of a half the resonance cycle (here, it is set at 2000 nsec). However, due to electric power loss by a resonance component or the like of the resonance circuit, the voltage of scan electrode SC1 through scan electrode SCn does not decrease to 0 (V).
During this operation, switching element Q24 is kept at ON, and sustain electrode SU1 through sustain electrode SUn are clamped on 0 (V).
(Time period T2)
Switching element Q14 is set at ON at time t2. Then, scan electrode SC1 through scan electrode SCn are directly grounded via switching element Q14, so that the voltage of scan electrode SC1 through scan electrode SCn is clamped on 0 (V) as the ground potential.
Simultaneously, switching element Q21 is set at ON at time t2. Then, current starts to flow from capacitor C20 for recovering electric power to sustain electrode SU1 through sustain electrode SUn via switching element Q21, diode D21, and inductor L20, and the voltage of sustain electrode SU1 through sustain electrode SUn starts to increase. Inductor L20 and inter-electrode capacity Cp form a resonance circuit, so that the voltage of sustain electrode SU1 through sustain electrode SUn increases to a voltage close to Vs at time t3 after a lapse of a half the resonance cycle (here, it is set at 2000 nsec). Due to the output impedance of the driving circuit or an effect of the driving load, however, the voltage of sustain electrode SU1 through sustain electrode SUn does not increase to Vs.
In the present embodiment, the rising of the sustain pulse is controlled by controlling the lengths of time period T2 and time period T5, and the first sustain pulse, the second sustain pulse, and the third sustain pulse are generated.
(Time Period T3)
Switching element Q23 is set at ON at time t3. Then, sustain electrode SU1 through sustain electrode SUn are directly connected to power supply VS via switching element Q23, so that the voltage of sustain electrode SU1 through sustain electrode SUn is clamped on voltage Vs and forcibly increased to voltage
Vs. In time period T3, the voltage of sustain electrode SU1 through sustain electrode SUn is kept at voltage Vs.
(Time Periods T4 Through T6)
The sustain pulse applied to scan electrode SC1 through scan electrode SCn has the same waveform as that of the sustain pulse applied to sustain electrode SU1 through sustain electrode SUn. The operation from time period T4 to time period T6 is the same as the operation obtained by interchanging scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn in the operation from time period T1 to time period T3, and is not described.
In the present embodiment, time period T1 and time period T4 are set as “falling period”, time period T2 and time period T5 are set as “rising period”, and the lengths of these time periods are set at required values. Thus, “rising period” and “falling period” are set.
Switching element Q12 is simply required to be set at OFF after time t2 before time t5, and switching element Q21 is simply required to be set at OFF after time t3 before time t4. Switching element Q22 is simply required to be set at OFF after time t5 before time t2 of the next cycle, and switching element Q11 is simply required to be set at OFF after time t6 before time t1 of the next cycle. In order to decrease the output impedance of sustain pulse generating circuit 50 and sustain pulse generating circuit 60, preferably, switching element Q24 is set at OFF immediately before time t2, switching element Q13 is set at OFF immediately before time t1, switching element Q14 is set at OFF immediately before time t5, and switching element Q23 is set at OFF immediately before time t4.
In the sustain period, the operation of time period T1 through time period T6 is repeated in response to the number of required pulses. Thus, sustain pulse voltage varying from 0 (V) as the base potential to voltage Vs is alternately applied to display electrode pairs 24 to cause sustain discharge in the discharge cells.
The cycle (hereinafter referred to as “resonance cycle”) of the LC resonance of inductor L10 of electric power recovering circuit 51 and inter-electrode capacity Cp of panel 10 and the cycle of the LC resonance of inductor L20 of electric power recovering circuit 61 and inter-electrode capacity Cp can be determined using expression “2π√(LCp)” when the inductance of each of inductor L10 and inductor L20 is denoted with L. In the present embodiment, inductor L10 and inductor L20 are set so that the resonance cycle of electric power recovering circuit 51 and electric power recovering circuit 61 is 2000 nsec.
Next, three kinds of sustain pulses of the present embodiment are described. The waveforms of the three kinds of sustain pulses are firstly described, and the reason for performing the driving using the three kinds of sustain pulses is then described.
In the present embodiment, as shown in
Specifically, the first sustain pulse as the reference sustain pulse is generated while “rising period” is set at about 800 nsec as shown in
In the present embodiment, the reason why three kinds of sustain pulses having different rising waveforms are generated is described below.
When the driving load is increased by increasing the screen size and definition of panel 10, the rising waveform of the sustain pulse is apt to vary and the timing (discharge start time) of causing the discharge between discharge cells can vary.
While, in a panel where the xenon partial pressure is increased in order to improve the luminous efficiency, the discharge start voltage between display electrode pairs also increases and hence the variation in timing of causing the discharge is apt to further increase.
When the timing of causing the discharge varies between adjacent discharge cells, the light emission intensity in the discharge cell having undergone discharge ahead differs from that in the discharge cell having undergone discharge later, and hence the light emission luminance on the display surface of the panel can vary. This phenomenon occurs for the following reasons, for example. The wall charge of the discharge cell undergoing discharge later is reduced due to the effect of the discharge cell undergoing discharge ahead to slightly weaken the discharge. Alternatively, the discharge started once is temporarily stopped by the effect of the discharge of an adjacent discharge cell and then the discharge is caused again by increase in applied voltage, thereby weakening the discharge.
The luminance of the discharge cell has a correlation to the number of sustain discharges in one field and light emission intensity in one sustain discharge, so that the above-mentioned phenomena causes the luminance to vary between discharge cells.
In order to solve this problem, it is effective to cause discharge in a state where the variation in voltage is steep. Here, “rising period” of the sustain pulse and variation in discharge are described with reference to the drawings.
In each of
For example, when the “rising period” is set at 400 nsec, which is relatively short, and the rising of the sustain pulse is made steep, it is recognized that most of the discharge cells emit light at substantially the same time and variation in discharge is suppressed.
When the rising of the sustain pulse is made steep and discharge is caused in a state of steep voltage variation, the variation in discharge start voltage is absorbed, variation in timing of causing discharge between discharge cells can be reduced and occurrence of variation in luminance can be suppressed.
When discharge is caused in a state of steep voltage variation, strong sustain discharge occurs to produce sufficient wall charge in the discharge cell and hence subsequent sustain discharge can be caused stably.
In the present embodiment, the “rising period” of the third sustain pulse is shortened to a length that allows light emission having one peak shown in
When the “rising period” of the sustain pulse is shortened to make the rising steep, however, the following problems occur. The operation period of the electric power recovering circuit decreases correspondingly to the shortening, the recovery efficiency of the electric power decreases, and power consumption increases.
The power consumption and the “rising period” are described hereinafter. The luminous efficiency and reactive power are considered as main items affecting the power consumption, so that the relations between these items and the “rising period” are sequentially described.
In
According to
In order to reduce the power consumption by increasing the recovery efficiency of the electric power in the electric power recovering circuit, the period when the electric power recovering circuit is operated is required to be as long as possible. In other words, the “rising period” of the sustain pulse is made as long as possible to moderate the rising.
When the “rising period” is made longer (here, it is set at 500 nsec longer by 100 nsec) than the “rising period” (400 nsec) of the sustain pulses used for measuring the characteristic of
When the “rising period” is further made longer (here, it is set at 550 nsec further longer by 50 nsec) than the “rising period” (500 nsec) of the sustain pulses used for measuring the characteristic of
According to this experiment, sufficiently moderating the rising of the sustain pulse can suppress the variation in discharge similarly to the sustain pulse whose rising is made steep. In other words, the variation in discharge can be reduced by extending the “rising period” in the sustain pulse to a length at which light emission having one peak can be caused in most discharge cells so as to provide the characteristic of
In the present embodiment, the “rising period” of the generated second sustain pulse is extended to a length at which light emission having one peak can be caused in the discharge cells so as to provide the characteristic of
However, the discharge caused by gentle voltage increase is relatively weak and sufficient wall charge is hardly produced in the discharge cells disadvantageously, though the sustain pulse whose rising is steep causes relatively strong discharge by the steep voltage variation. In the sustain period, the wall voltage produced by a sustain discharge is used for its subsequent sustain discharge, thereby continuously causing the sustain discharge. The light emission intensity in the subsequent sustain discharge depends on the wall voltage produced by the sustain discharge immediately before it. In other words, when the sustain pulses whose rising is gentle are continuously generated, sufficient wall voltage cannot be produced and generation of sustain discharge gradually becomes difficult, disadvantageously. This is clear also from the characteristic diagram showing the relation between the “rising period” of the sustain pulses and sustain pulse voltage Vs required for stably causing the sustain discharge in
According to
In the present embodiment, the first sustain pulse serving as the reference is generated as a sustain pulse having the following feature.
In other words, the first sustain pulse occurs as a sustain pulse where the power recovery efficiency in the electric power recovering circuit can be increased to some extent and somewhat strong sustain discharge can be caused. Here, “the power recovery efficiency in the electric power recovering circuit can be increased to some extent” means that the power recovery efficiency can be made higher than that of the sustain pulse of steep rising that causes light emission having one peak in the discharge cells (
In the present embodiment, as shown in
The second sustain pulse of
The third sustain pulse of
In the present embodiment, the first sustain pulse, the second sustain pulse, and the third sustain pulse are switched and generated so that the second sustain pulse does not continue. Thus, the power consumption is reduced and sustain discharge is stabilized.
In the present embodiment, as shown in
In the first sustain pulse as the reference, the power recovery efficiency can be made higher than that of the third sustain pulse, and the wall charge accumulated in the discharge cells can be made more than the discharge by the second sustain pulse. While, the length of the “rising period” is set to be between the lengths of the “rising period” of the second sustain pulse and the “rising period” of the third sustain pulse, so that light emission having two peaks is apt to occur in the discharge cells and variation in discharge is apt to increase, as shown in
In the present embodiment, however, one of three caused sustain discharges is sustain discharge for causing light emission having one peak in the discharge cells using the second sustain pulse and the third sustain pulse. Thus, discharge variation that can be caused by the first sustain pulse can be suppressed, and the variation in luminance between the discharge cells can be reduced to achieve stable light emission.
Next, the rising of the second sustain pulse is set to be gentler than that of the other sustain pulses by making the “rising period” longer, so that the recovery efficiency of the electric power recovering circuit can be improved and the reduction effect of the power consumption can be improved. In addition, light emission having one peak can be caused in the discharge cells, so that the variation in timing of causing discharge between the discharge cells can be suppressed. However, the rising is gentler than that of the other sustain pulses. Therefore, the caused discharge becomes weak, and only small amount of wall charge can be produced in the discharge cells.
In the present embodiment, however, the second sustain pulse does not occur continuously, and five of six caused sustain discharges are caused by the first sustain pulse capable of causing discharge stronger than that by the second sustain pulse, and the third sustain pulse capable of causing further stronger discharge. Thus, sufficient wall charge can be accumulated in the discharge cells, and stable sustain discharge can be caused continuously.
In the third sustain pulse, the “rising period” is set to be shorter than that of the other sustain pulses, and the rising is set to be steeper. Therefore, sufficient wall charge can be produced in the discharge cells by strong discharge, and the variation in timing of causing discharge between the discharge cells can be suppressed by causing light emission having one peak in the discharge cells. While, the period when the electric power recovering circuit is operated is shorter than that of the other sustain pulses, and hence the power recovery efficiency reduces.
In the present embodiment, however, five of six caused sustain discharges are caused by the first sustain pulse of high power recovery efficiency and the second sustain pulse of higher power recovery efficiency. Thus, the power recovery efficiency is comprehensively improved, and the power consumption can be reduced.
Thus, in the present embodiment, three kinds of sustain pulses are switched and generated so that the second sustain pulse does not continue. The three kinds of sustain pulses include the first sustain pulse serving as the reference, the second sustain pulse whose rising is gentler than that of the first sustain pulse, and the third sustain pulse whose rising is steeper than that of the first sustain pulse. Thus, even in the panel whose screen size, luminance, and definition are increased, sustain discharge can be stably caused while the power consumption is reduced, and the image display quality can be improved.
In the present embodiment, the “rising periods” of the first sustain pulse, the second sustain pulse, and the third sustain pulse are set at 800 nsec, 850 nsec, and 650 nsec for resonance cycle 2000 nsec, respectively. However, the present embodiment is not limited to these numerical values. The relation between each of the above-mentioned effects and the length of the “rising period” depends on the resonance cycle, so that it is preferable to optimally set the length of the “rising period” in response to the resonance cycle. In order to obtain the effects, preferably, the three-kinds of sustain pulses are generated on the following conditions. The first sustain pulse is generated while the “rising period” is set at 80% or higher and lower than 85% of a half the resonance cycle. The second sustain pulse is generated while the “rising period” is set at 85% or higher and 100% or lower of a half the resonance cycle. The third sustain pulse is generated while the “rising period” is set at 65% or higher and lower than 80% of a half the resonance cycle. The “rising periods” of the first sustain pulse, the second sustain pulse, and the third sustain pulse are set different from each other by 50 nsec or longer.
The generation frequency and generation order of the sustain pulses are not limited to the above-mentioned frequency and order.
In the first exemplary embodiment, the first sustain pulse, the second sustain pulse, and the third sustain pulse are switched and generated, thereby producing effects of reducing the discharge variation and reducing the power consumption. However, these effects depend on the rate of discharge cells to be lighted (lit cell), namely light-emitting rate.
This is for the following reason. The output impedance of the electric power recovering circuit is larger than that of the clamping circuit, so that the waveform of the “rising period” varies when the light-emitting rate of the discharge cells varies dependently on the display image and the load during driving varies.
Therefore, the following method may be employed during the driving. The all-cell light-emitting rate showing the ratio of the lit cells to all discharge cells of panel 10 is detected, the numbers of generations of the second sustain pulse and the third sustain pulse are varied in response to the detection result, and the generation frequencies of the second sustain pulse and the third sustain pulse are varied. For example, in a subfield of low all-cell light-emitting rate, it is considered that the driving load is relatively small and the variation in waveform is relatively small, so that the number of generations of the second sustain pulse is increased to increase the generation frequency of the second sustain pulse. In a subfield of high light-emitting rate, it is considered that the driving load is relatively large and the waveform is relatively apt to vary, so that the number of generations of the third sustain pulse is increased to increase the generation frequency of the third sustain pulse.
Thus, the above-mentioned effects can be further improved by varying the number of generations of each sustain pulse in response to the detected all-cell light-emitting rate.
Even when the all-cell light-emitting rate is constant, the number of lit cells occurring on one display electrode pair 24 significantly varies and the driving load of each display electrode pair 24 also varies in response to the pattern of an image to be displayed, namely in response to distribution of the lit cells.
For example, when the lit cells are distributed in the longitudinally extending shape (in the drawing) as shown in the upper part of
Thus, even when the all-cell light-emitting rate is constant, the driving load partially varies in response to the pattern, and a display electrode pair where driving load is large can occur partially dependently on the pattern.
In the present embodiment, the following configuration may be employed. The all-cell light-emitting rate is detected, the light-emitting rate in each of a plurality of regions that are obtained by dividing the display region of the panel is also detected as a partial light-emitting rate, and the occurrence rate of each sustain pulse is varied in response to these detection results.
All-cell light-emitting rate detecting circuit 46, based on the image data of each subfield, detects the ratio of the number of discharge cells to be lighted to the number of all discharge cells, namely the all-cell light-emitting rate, in each subfield. All-cell light-emitting rate detecting circuit 46 compares the detected all-cell light-emitting rate with a predetermined light-emitting rate threshold (for example, 50%), and outputs a signal showing the comparison result to timing generating circuit 45.
Partial light-emitting rate detecting circuit 47 divides the display region of the panel into a plurality of regions, and detects, based on the image data of each subfield, the ratio of the number of discharge cells to be lighted to the number of discharge cells, namely the partial light-emitting rate, in each region and subfield.
Maximum value detecting circuit 48 compares the partial light-emitting rates detected by partial light-emitting rate detecting circuit 47 with each other, and detects the maximum value in each subfield. Maximum value detecting circuit 48 then compares the detected maximum value with a predetermined maximum value threshold (for example, 60%), and outputs a signal showing the comparison result to timing generating circuit 45.
Timing generating circuit 45 generates various timing signals for controlling operations of respective circuit blocks based on horizontal synchronizing signal H, vertical synchronizing signal V, and the outputs from all-cell light-emitting rate detecting circuit 46 and maximum value detecting circuit 48, and supplies them to respective circuit blocks. Timing generating circuit 45 varies the number of generations of each of the sustain pulses based on the outputs from all-cell light-emitting rate detecting circuit 46 and maximum value detecting circuit 48, and outputs a timing signal responsive to it to scan electrode driving circuit 43 and sustain electrode driving circuit 44.
Plasma display device 2 having such a configuration can change the number of generations of each sustain pulse in response to the all-cell light-emitting rate and the maximum value of the partial light-emitting rates. For example, the following driving may be employed. In a subfield where both the all-cell light-emitting rate and the maximum value of the partial light-emitting rates are smaller than the set thresholds, it is considered that the driving load is relatively small and the variation in waveform is relatively small, so that the number of generations of the second sustain pulse can be increased to increase the generation frequency of the second sustain pulse. In a subfield where both the all-cell light-emitting rate and the maximum value of the partial light-emitting rates are the thresholds or larger, it is considered that the driving load is relatively large and the waveform is relatively apt to vary, so that the number of generations of the third sustain pulse can be increased to increase the generation frequency of the third sustain pulse. A specific example of this control is described.
For example, as shown in
Thus, by detecting the all-cell light-emitting rate and the maximum value of the partial light-emitting rates and changing the number of generations of each sustain pulse in response to these detection results, control corresponding to the pattern of the display image can be achieved and the effect of reducing the power consumption and the effect of stably causing the sustain discharge can be further improved.
As discussed above, in the present embodiment, the all-cell light-emitting rate, the partial light-emitting rates, and the maximum value of the partial light-emitting rates are detected, and the generations of each sustain pulse in response to the detection results can be controlled. Therefore, control responsive to the display image can be performed more finely, and the effect of stably causing the sustain discharge while reducing the power consumption can be further improved.
The light-emitting rate threshold is set at 50% and the maximum value threshold is set at 60% in the present embodiment; however, the present invention is not these numerical values. Preferably, these thresholds are set at the optimum values based on the characteristic of the panel and the specification of the plasma display device. Alternatively, a plurality of values may be set as each of the light-emitting rate threshold and the maximum value threshold, and the change or the like of the number of generations of each sustain pulse may be performed more finely.
In the present embodiment, the display region of panel 10 is divided into eight regions. However, this value is simply one example. This value is required to be set at the optimum value in response to the characteristic of the panel and the specification of the plasma display device. For example, the region may be divided in response to the specification of the integrated circuit (IC) used for driving the display electrode pair. As one specific example, in the plasma display device configured so as to drive 108 scan electrodes or sustain electrodes with one IC, 108 display electrode pairs may be set as one region in response to the IC, and the panel of 1080 display electrode pairs may be divided into 10 regions. Alternatively, the number of display electrode pairs may be set to be the same as the number of regions, and the light-emitting rate may be detected for each display electrode pair.
The present embodiment of the present invention is effective also in a panel of an electrode structure where a scan electrode is adjacent to another scan electrode and a sustain electrode is adjacent to another sustain electrode, namely an electrode structure where the arrangement of the electrodes disposed on front plate 21 is “—scan electrode, scan electrode, sustain electrode, sustain electrode, scan electrode, scan electrode,—” (hereinafter referred to as “ABBA electrode structure”).
In the panel having the ABBA electrode structure, the variation in sustain pulse voltage between adjacent discharge cells can be in the same phase, and hence the reactive power can be reduced. In the discharge cells in the ABBA electrode structure, however, discharge is apt to vary. This is for the following reason. The same kind of electrodes are adjacent to each other (scan electrode—scan electrode, or sustain electrode—sustain electrode) in the ABBA electrode structure, so that the applied sustain pulses are in the same phase, and hence the reactive power can be reduced. However, the electric field applied between the discharge cells adjacent to each other in the row direction in this electrode structure is smaller than that between the discharge cells in a usual electrode structure where scan electrodes are arranged alternately (hereinafter referred to as “ABAB electrode structure”). Therefore, in the ABBA electrode structure, the charge easily moves to the discharge cells adjacent to each other in the column direction to increase the amount of the charge moving between the discharge cells, and hence the variation in wall charge increases. In the embodiment of the present invention, the power consumption can be reduced and stable sustain discharge can be caused even in a panel where discharge is apt to vary.
Numerical values shown in the embodiment of the present invention, for example, specific numerical values of “rising period”, resonance cycle, light-emitting rate threshold, and maximum value threshold, are set based on the characteristic of a 42-inch panel having 1080 display electrode pairs. These numerical values are simply one example in the embodiment. The present invention is not limited to these numerical values. Preferably, these numerical values are set optimally based on the characteristic of the panel and the specification of the plasma display device. These numerical values are allowed to vary within the range capable of producing the above-mentioned effects.
The embodiment of the present invention can be applied to a panel driving method by the so-called two-phase driving, and the effects similar to the above-mentioned effects can be obtained. The two-phase driving is described below. Scan electrode SC1 through scan electrode SCn are divided into first and second scan electrode groups. The address period consists of a first address period when scan pulses are sequentially applied to scan electrodes belonging to the first scan electrode group, and a second address period when scan pulses are sequentially applied to scan electrodes belonging to the second scan electrode group. In at least one of the first address period and second address period, scan pulses that change from a second voltage, which is higher than the scan pulse voltage, to the scan pulse voltage and change to the second voltage again are sequentially applied to scan electrodes that belong to the scan electrode group to be applied with the scan pulses. One of a third voltage higher than the scan pulse voltage and a fourth voltage higher than the second voltage and the third voltage is applied to the scan electrodes belonging to the scan electrode group to which the scan pulses are not applied. While the scan pulse voltage is applied to at least adjacent scan electrodes, the third voltage is applied.
In the embodiment of the present invention, the erasing ramp voltage is applied to scan electrode SC1 through scan electrode SCn. However, the erasing ramp voltage may be applied to sustain electrode SU1 through sustain electrode SUn. Alternatively, erasing discharge may be caused by not the erasing ramp voltage but the so-called narrow-width erasing pulse.
In the embodiment of the present invention, electric power recovering circuits 51 and 61 use one inductor commonly in rising and falling of the sustain pulse. However, electric power recovering circuits 51 and 61 may use a plurality of inductors and use different inductors in rising and falling of the sustain pulse.
In the present invention, even in the panel whose screen size, luminance, and definition are increased, sustain discharge can be stably caused while the power consumption is reduced, and the image display quality can be improved. Therefore, the present invention is useful as a plasma display device and a driving method for the panel.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-296518 | Nov 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003274 | 11/12/2008 | WO | 00 | 5/17/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/063622 | 5/22/2009 | WO | A |
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