Patent Publication Number: US-2009231234-A1

Title: Plasma display apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a plasma display apparatus. To be more precise, preferred embodiments of the present invention provide a plasma display apparatus of which unevenness in luminance between electrode lines of a plasma display panel has been reduced. 
     BACKGROUND ART 
     Conventionally, in the technological field of a plasma display apparatus, there are known devices of an Alternate Lighting of Surfaces (hereinafter, abbreviated as ALIS) method of adjacently placing multiple first and second electrodes and forming display lines among all the electrodes (refer to Patent Document 1 below). 
     A plasma display panel of the ALIS method performs a so-called interlaced scan. The interlaced scan adjacently and alternately places n (512 for instance) odd-numbered electrodes and even-numbered electrodes of Y electrodes (first electrodes) and n+1 odd-numbered electrodes and even-numbered electrodes of X electrodes (second electrodes) and performs display emission among all display electrodes (Y and X electrodes) so as to perform display dividedly timewise between even-numbered lines and odd-numbered lines by forming 2n display lines with 2n+1 display electrodes. 
       FIG. 6  is a diagram showing an overview of a drive circuit of a conventional plasma display panel of the ALIS method. The X electrodes and Y electrodes are alternately placed in parallel, and address electrodes are placed in a vertical direction thereto. Reference character Y 1  denotes an odd-numbered Y electrode, Y 2  denotes an even-numbered Y electrode, X 1  denotes an odd-numbered X electrode, and X 2  denotes an even-numbered X electrode. The Y electrodes are connected to a scan driver SD. The scan driver SD is provided with a switch SW, which is switched to sequentially apply scan pulses in an address period. In a sustain discharge period, it is switched so that the odd-numbered Y electrode Y 1  is connected to a first Y sustain circuit, and the even-numbered Y electrode Y 2  is connected to a second Y sustain circuit. The odd-numbered X electrode X 1  is connected to a first X sustain circuit, and an even-numbered X electrode X 2  is connected to a second X sustain circuit. The address electrodes are connected to an address driver. 
       FIGS. 7 and 8  are diagrams showing drive waveforms of the conventional plasma display panel of the ALIS method.  FIG. 7  shows the drive waveforms of odd-numbered fields, and  FIG. 8  shows the drive waveforms of even-numbered fields. As shown in  FIG. 7 , in a reset period, voltage pulses are applied between all the X electrodes and Y electrodes, and initialization discharge is performed on all the display lines. The address period is divided into a first half and a second half. In the odd-numbered fields, the scan pulses are sequentially applied to the odd-numbered Y electrode (Y 1 ) in the first half of the address period. In this case, a positive voltage is applied to the odd-numbered X electrodes (X 1 , X 3 ), the even-numbered X electrode (X 2 ) is put to a ground level, and a small negative voltage is applied to the even-numbered Y electrode (Y 2 ). Therefore, address discharge is only performed on address lines where address pulses are applied between the odd-numbered X electrodes and the odd-numbered Y electrodes so as to accumulate wall charges. In the second half of the address period of the odd-numbered fields, the scan pulses are sequentially applied to the even-numbered Y electrode (Y 2 ). The positive voltage is applied to the even-numbered X electrode (X 2 ), the odd-numbered X electrodes (X 1 , X 3 ) are put to the ground level, and the small negative voltage is applied to the odd-numbered Y electrode (Y 1 ). Therefore, the address discharge is only performed between the even-numbered X electrodes and the even-numbered Y electrodes. Similarly, in the even-numbered fields, the address discharge is performed between the odd-numbered Y electrodes and the even-numbered X electrodes in the first half of the address period, and between the even-numbered Y electrodes and the odd-numbered X electrodes in the second half of the address period as shown in  FIG. 8 . Thus, the charges corresponding to display data are accumulated on odd-numbered display lines. In the sustain discharge period, reversed-phase sustain pulses are applied between the odd-numbered X electrodes and the odd-numbered Y electrodes and between the even-numbered X electrodes and the even-numbered Y electrodes so as to perform the sustain discharge, that is, the display emission on the odd-numbered display lines. 
     As a conventional technology relating to the plasma display apparatus, Patent Document 2 described below discloses a plasma display apparatus which suppresses unevenness in voltage drops generated according to wiring length from an electrode drive circuit to the electrodes for equalizing discharge currents flowing to the odd-numbered electrodes and the even-numbered electrodes so as to improve image quality. 
     Patent Document 1: Japanese Patent Publication No. 2801893 
     Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-196719 
     As for the conventional plasma display apparatus for supplying the discharge currents to the odd-numbered electrodes and the even-numbered electrodes, there was a problem that the lines corresponding to the odd-numbered electrodes are dark and the lines corresponding to the even-numbered electrodes become dark so that a difference in luminance arises between the lines. 
     As a result of considering the unevenness in luminance, the following was clarified. On resistance of a power MOSFET used for an output element of the sustain circuit changes according to temperature. When the temperature becomes high, the on resistance becomes high. In the case of mounting a sustain substrate having the sustain circuit placed thereon, placing sustain output elements for the odd-numbered electrodes on the upper side of the sustain substrate and placing the sustain output elements for the even-numbered electrodes on the lower side of the sustain substrate, ambient temperature rises around the sustain output elements for the odd-numbered electrodes placed on the upper side so that temperature resistance of the sustain output elements becomes higher. As a result of this, a gas discharge current does not easily pass through the sustain output elements for the odd-numbered electrodes placed on the upper side in comparison with the sustain output elements for the even-numbered electrodes placed on the lower side. Thus, the gas discharge currents supplied to the odd-numbered electrodes are different from the gas discharge currents supplied to the even-numbered electrodes. Due to the difference in the gas discharge currents passing through them, the lines corresponding to the odd-numbered electrodes are dark and the lines corresponding to the even-numbered electrodes become dark so that a difference in luminance arises between the lines. 
     The difference in luminance is referred to as 2-line unevenness. According to the conventional example, no consideration was given to a cause of the problem or a method for solving the problem of the 2-line unevenness. 
     The problem to be solved by the present invention is to reduce the 2-line unevenness correspondingly to clarification of the cause of the difference in luminance. 
     DISCLOSURE OF THE INVENTION 
     Of multiple electrode groups such as odd-numbered electrode drive circuits and even-numbered electrode drive circuits for supplying discharge currents to the odd-numbered electrodes and even-numbered electrodes, a plasma display apparatus of the present invention increases impedance of the drive circuits placed on a lower side, reduces unbalance of the discharge currents due to temperature and improves 2-line unevenness. To be more precise, the plasma display apparatus of the present invention is most characterized by detecting the temperature of output elements of the drive circuits and controlling the discharge currents so as to evenly supply gas discharge currents flowing to multiple electrode groups such as those flowing to the odd-numbered electrodes and those flowing to even-numbered electrodes. 
     According to the present invention, it is possible to equalize the gas discharge currents flowing to the odd-numbered electrodes and the even-numbered electrodes and reduce the 2-line unevenness for instance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sustain circuit of a plasma display apparatus of the present invention (first embodiment); 
         FIG. 2  is a sustain circuit of the plasma display apparatus of the present invention (second embodiment); 
         FIG. 3  is a sustain substrate of the plasma display apparatus of the present invention (second embodiment); 
         FIG. 4  is a sustain circuit of the plasma display apparatus of the present invention (third embodiment); 
         FIG. 5  is a sustain substrate of the plasma display apparatus of the present invention (third embodiment); 
         FIG. 6  is a diagram showing an overview of a drive circuit for a plasma display apparatus of the ALIS method in a conventional example; 
         FIG. 7  is a diagram showing drive waveforms of odd-numbered fields of a plasma display panel of the ALIS method in a conventional example; and 
         FIG. 8  is a diagram showing the drive waveforms of even-numbered fields of the plasma display panel of the ALIS method in a conventional example. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           1  Plasma display panel 
           2  Sustain substrate 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereunder, embodiments of the present invention will be described by using the drawings. 
     First Embodiment 
       FIG. 1  shows a first embodiment of a sustain circuit of a plasma display apparatus according to the present invention. Reference character PD 1  of  FIG. 1  denotes a pre-drive circuit for odd-numbered electrodes. PD 1  supplies drive pulses for driving output elements Q 1 , Q 2 , Q 3  and Q 4 . Reference character PD 2  denotes a pre-drive circuit for even-numbered electrodes. PD 2  supplies the drive pulses for driving output elements Q 21 , Q 22 , and Q 24 . 
     In the circuit shown in  FIG. 1 , reference characters T 1  and T 2  denote temperature detection means which are configured by using diodes, thermistors and the like. Reference character A 1  denotes a temperature difference detection circuit which detects, from a signal corresponding to the temperature difference detected by T 1  and T 2 , a temperature difference between the two and forms a control signal. Based on the control signal outputted from the temperature difference detection circuit A 1 , amplitude is changed as to the drive pulses for driving the output elements Q 1 , Q 2 , Q 3  and Q 4  supplied by the pre-drive circuit for odd-numbered electrodes. 
     The amplitude is increased as to the drive pulses for driving the output elements Q 1 , Q 2 , Q 3  and Q 4  supplied by the pre-drive circuit for odd-numbered electrodes. It is thereby possible to reduce on resistance of the output elements Q 1 , Q 2 , Q 3  and Q 4  and increase gas discharge currents to be supplied to an odd-numbered electrode Cp 1  of a plasma display  1 . As a result of this, even when the temperature of the output elements Q 1 , Q 2 , Q 3  and Q 4  becomes higher than the temperature of the output elements Q 21 , Q 22 , Q 23  and Q 24 , it is possible to equalize the gas discharge currents to be supplied to the odd-numbered electrodes and even-numbered electrodes and reduce the 2-line unevenness. 
     The output elements Q 1 , Q 2 , Q 3  and Q 4  and the output elements Q 21 , Q 22 , Q 23  and Q 24  are mounted on heat sinks F 1  and F 2  respectively. Therefore, it is possible, by providing the temperature detection means T 1  and T 2  on the heat sinks F 1  and F 2 , to detect the temperature of the output elements Q 1 , Q 2 , Q 3  and Q 4  and the output elements Q 21 , Q 22 , Q 23  and Q 24 . 
     According to the first embodiment, it detects the temperature difference, forms the control signal to be supplied to the pre-drive circuit for odd-numbered electrodes and increases the amplitude of the drive pulses outputted by the pre-drive circuit for odd-numbered electrodes. It is thereby possible to reduce on resistance of the output elements Q 1 , Q 2 , Q 3  and Q 4  and increase the gas discharge currents to be supplied to an odd-numbered electrode Cp 1  of the plasma display  1 . Therefore, it is possible to replenish the gas discharge currents of the output elements where the gas discharge currents became less passable due to temperature rise, equalize the gas discharge currents in a stable form and reduce the 2-line unevenness. 
     Second Embodiment 
       FIG. 2  shows a second embodiment of the sustain circuit of the plasma display apparatus according to the present invention.  FIG. 3  shows an embodiment of a sustain substrate on which the circuit shown in  FIG. 2  is mounted. 
     Reference character PD 1  of  FIG. 2  denotes a pre-drive circuit for odd-numbered electrodes. PD 1  supplies drive pulses for driving the output elements Q 1 , Q 2 , Q 3  and Q 4 . Reference character PD 2  denotes a pre-drive circuit for even-numbered electrodes. PD 2  supplies the drive pulses for driving the output elements Q 21 , Q 22 , Q 23  and Q 24 . 
     In the circuit shown in  FIG. 2 , reference characters T 1  and T 2  denote temperature detection means which are configured by using diodes, thermistors and the like. Reference character Z 2  denotes a discharge current control means for controlling the gas discharge currents flowing to an even-numbered electrode Cp 2  of the plasma display panel  1 . Reference character A 1  denotes a temperature difference detection circuit which detects, from a signal corresponding to the temperature difference detected by T 1  and T 2 , a temperature difference between the two and forms a control signal to be supplied to the discharge current control means Z 2 . 
     Based on the control signal outputted from the temperature difference detection circuit A 1 , the discharge current control means Z 2  exerts control to change the gas discharge currents flowing to the even-numbered electrode Cp 2  of the plasma display panel  1  so that the gas discharge currents flowing to the odd-numbered electrode Cp 1  of the plasma display panel  1  and the gas discharge currents flowing to the even-numbered electrode Cp 2  become almost equal. 
     The sustain circuit shown in  FIG. 2  is mounted on the sustain substrate  2  shown in  FIG. 3 , and the heat sinks F 1  and F 2  are mounted on the sustain substrate  2 . The output elements Q 1 , Q 2 , Q 3  and Q 4  and the output elements Q 21 , Q 22 , Q 23  and Q 24  are mounted on the heat sinks F 1  and F 2  respectively. Therefore, it is possible, assuming that the temperature in the heat sinks F 1  and F 2  is almost constant, to detect the temperature difference in the temperature difference detection circuit A 1  from outputs of the temperature detection means T 1  and T 2  provided on the heat sinks F 1  and F 2  and use it as a signal corresponding to the temperature difference between the output elements Q 1 , Q 2 , Q 3  and Q 4  and the output elements Q 21 , Q 22 , Q 23  and Q 24  so as to exert control so that the gas discharge currents flowing to the odd-numbered electrode Cp 1  and the even-numbered electrode Cp 2  of the plasma display panel  1  become almost equal. 
     The sustain circuit shown in  FIG. 2  may be used to equalize the gas discharge currents flowing to the odd-numbered electrodes and the gas discharge currents flowing to the even-numbered electrodes so as to reduce the 2-line unevenness. 
     According to the second embodiment, it directly controls the gas discharge currents flowing to the even-numbered electrode Cp 2  of the plasma display panel  1  from the output elements Q 21 , Q 22 , Q 23  and Q 24  by the control signal supplied from the discharge current control means Z 2 . Therefore, it is possible to promptly and accurately control the gas discharge currents by electrical control means. 
     Third Embodiment 
       FIG. 4  shows a third embodiment of the sustain circuit of the plasma display apparatus according to the present invention.  FIG. 5  shows an embodiment of a sustain substrate on which the circuit shown in  FIG. 4  is mounted. Reference character H 2  of  FIG. 5  denotes heating means which is configured by using a heater and the like. In  FIG. 5 , reference character A 1  denotes a temperature difference detection circuit which detects, from a signal corresponding to the temperature difference detected by T 1  and T 2 , a temperature difference between the two and forms a control signal to be supplied to the heating means H 2 . Based on the control signal inputted from the above A 1 , the heating means performs a function of heating the heat sink F 2  to set its temperature equal to the heat sink F 1 . As a result of this, the temperature of the output elements Q 1 , Q 2 , Q 3  and Q 4  mounted on the heat sink F 1  becomes equal to the temperature of the output elements Q 21 , Q 22 , Q 23  and Q 24  mounted on the heat sink F 2 . Thus, it is possible to equalize the gas discharge currents supplied to the odd-numbered electrodes and the even-numbered electrodes and reduce the 2-line unevenness. 
     According to the third embodiment, it detects the temperature difference of the output elements and equalizes the temperature by using the heating means. Therefore, it is possible to realize discharge current control means for controlling the discharge currents from the output elements in a simple configuration. 
     According to the above embodiments, it is described that the present invention is intended to solve unevenness in luminance of odd-numbered electrode lines and even-numbered electrode lines of a conventional plasma display apparatus of the ALIS method. However, the present invention is not limited to the above method but is also applicable, for the sake of solving the unevenness in luminance due to the temperature difference, to the plasma display apparatus which divides the first electrode or the second electrode into multiple electrode groups to supply driving power respectively. 
     Other Embodiments 
     The present invention has various configuration examples according to differences in configurations of the X electrode and Y electrode and configurations of a temperature detection element and discharge current limiting means. Hereunder, the configuration examples of the present invention will be described as additional statements. 
     Additional Statement  1   
     A plasma display apparatus including: 
     multiple X electrodes; 
     multiple Y electrodes alternately placed adjacently to the multiple X electrodes and generating discharge between themselves and the multiple X electrodes; 
     a first X electrode drive circuit for applying discharge voltage to odd-numbered electrodes of the multiple X electrodes; 
     a second X electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple X electrodes; 
     a first Y electrode drive circuit for applying the discharge voltage to odd-numbered electrodes of the multiple Y electrodes; and 
     a second Y electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple Y electrodes, 
     characterized in that: 
     the apparatus is provided with: 
     first temperature detection means for detecting temperature of a heat sink mounted on an output element of the first X electrode drive circuit; 
     second temperature detection means for detecting temperature of a heat sink mounted on an output element of the second X electrode drive circuit; 
     first temperature difference detection circuit connected to the first temperature detection means and the second temperature detection means; and 
     first discharge current control means connected to the first temperature difference detection circuit. 
     Additional Statement  2   
     A plasma display apparatus including: 
     multiple X electrodes; 
     multiple Y electrodes alternately placed adjacently to the multiple X electrodes and generating discharge between themselves and the multiple X electrodes; 
     a first X electrode drive circuit for applying discharge voltage to odd-numbered electrodes of the multiple X electrodes; 
     a second X electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple X electrodes; 
     a first Y electrode drive circuit for applying the discharge voltage to odd-numbered electrodes of the multiple Y electrodes; and 
     a second Y electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple Y electrodes, 
     characterized in that: 
     the apparatus is provided with: 
     third temperature detection means for detecting temperature of a heat sink mounted on an output element of the first Y electrode drive circuit; 
     fourth temperature detection means for detecting temperature of a heat sink mounted on an output element of the second Y electrode drive circuit; 
     second temperature difference detection circuit connected to the third temperature detection means and the fourth temperature detection means; and 
     second discharge current control means connected to the second temperature difference detection circuit. 
     Additional Statement  3   
     A plasma display apparatus including: 
     multiple X electrodes; 
     multiple Y electrodes alternately placed adjacently to the multiple X electrodes and generating discharge between themselves and the multiple X electrodes; 
     a first X electrode drive circuit for applying discharge voltage to odd-numbered electrodes of the multiple X electrodes; 
     a second X electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple X electrodes; 
     a first Y electrode drive circuit for applying discharge voltage to odd-numbered electrodes of the multiple Y electrodes; and 
     a second Y electrode drive circuit for applying the discharge voltage to even-numbered electrodes of the multiple Y electrodes, 
     characterized in that: 
     the apparatus is provided with: 
     first temperature detection means for detecting temperature of a heat sink mounted on an output element of the first X electrode drive circuit; 
     second temperature detection means for detecting temperature of a heat sink mounted on an output element of the second X electrode drive circuit; 
     first temperature difference detection circuit connected to the first temperature detection means and the second temperature detection means; 
     first discharge current control means connected to the first temperature difference detection circuit; 
     third temperature detection means for detecting temperature of a heat sink mounted on an output element of the first Y electrode drive circuit; 
     fourth temperature detection means for detecting temperature of a heat sink mounted on an output element of the second Y electrode drive circuit; 
     second temperature difference detection circuit connected to the third temperature detection means and the fourth temperature detection means; and 
     second discharge current control means connected to the second temperature difference detection circuit. 
     Additional Statement  4   
     The plasma display apparatus according to the additional statements  1  to  3 , characterized in that: 
     the discharge current control means is impedance control means capable of changing impedance by a supplied voltage or current. 
     Additional Statement  5   
     The plasma display apparatus according to the additional statement  4 , characterized in that: 
     the discharge current control means is configured by using semiconductor devices. 
     Additional Statement  6   
     The plasma display apparatus according to the additional statements  1  to  5 , characterized in that: 
     the discharge current control means controls a discharge current passing through the output element placed on a downside of a plasma display panel out of the first X electrode drive circuit and the second X electrode drive circuit. 
     Additional Statement  7   
     The plasma display apparatus according to the additional statements  1  to  5 , characterized in that: 
     the discharge current control means controls a discharge current passing through the output element placed on the downside of the plasma display panel out of the first Y electrode drive circuit and the second Y electrode drive circuit. 
     Additional Statement  8   
     The plasma display apparatus according to the additional statements  1  to  7 , characterized in that: 
     the discharge current control means controls amplitude of drive voltage supplied to the output element placed on an upside of the plasma display panel out of the first X electrode drive circuit and the second X electrode drive circuit. 
     Additional Statement  9   
     The plasma display apparatus according to the additional statements  1  to  7 , characterized in that: 
     the discharge current control means controls amplitude of drive voltage supplied to the output element placed on the upside of the plasma display panel out of the first Y electrode drive circuit and the second Y electrode drive circuit. 
     Additional Statement  10   
     The plasma display apparatus according to the additional statements  1  to  3 , characterized in that: 
     the discharge current control means is heating means for increasing temperature of the heat sink of the output element placed on the downside of the plasma display panel. 
     Additional Statement  11   
     The plasma display apparatus according to the additional statement  1 , characterized in that: 
     the heat sink mounted on the output element of the first X electrode drive circuit and the heat sink mounted on the output element of the second X electrode drive circuit are different heat sinks; and 
     the heat sink mounted on the output element of the first X electrode drive circuit and the heat sink mounted on the output element of the second X electrode drive circuit are placed on the same printed board. 
     Additional Statement  12   
     The plasma display apparatus according to the additional statement  2 , characterized in that: 
     the heat sink mounted on the output element of the first Y electrode drive circuit and the heat sink mounted on the output element of the second Y electrode drive circuit are different heat sinks; and 
     the heat sink mounted on the output element of the first Y electrode drive circuit and the heat sink mounted on the output element of the second Y electrode drive circuit are placed on the same printed board. 
     Additional Statement  13   
     The plasma display apparatus according to the additional statement  3 , characterized in that: 
     the heat sink mounted on the output element of the first X electrode drive circuit and the heat sink mounted on the output element of the second X electrode drive circuit are different heat sinks; and 
     the heat sink mounted on the output element of the first X electrode drive circuit and the heat sink mounted on the output element of the second X electrode drive circuit are placed on the same printed board, and further, 
     the heat sink mounted on the output element of the first Y electrode drive circuit and the heat sink mounted on the output element of the second Y electrode drive circuit are different heat sinks; and 
     the heat sink mounted on the output element of the first Y electrode drive circuit is placed on the same printed board. 
     Additional Statement  14   
     The plasma display apparatus according to the additional statements  1  to  3 , characterized in that: 
     the temperature detection means are configured by using diodes. 
     Additional Statement  15   
     The plasma display apparatus according to the additional statements  1  to  3 , characterized in that: 
     the temperature detection means are configured by using thermistors. 
     Additional Statement  16   
     The plasma display apparatus according to the additional statements  1  to  3 , characterized in that: 
     the temperature difference detection circuit compares output signals of multiple temperature detection means, and supplies a control signal based on information obtained as a result thereof the discharge current control means. 
     Additional Statement  17   
     The plasma display apparatus according to the additional statement  16 , characterized in that: 
     the temperature difference detection circuit supplies a control signal to the discharge current control means based on a voltage difference generated at both ends of multiple diodes used as the temperature detection means. 
     Additional Statement  18   
     The plasma display apparatus according to the additional statement  16 , characterized in that: 
     the temperature difference detection circuit supplies a control signal to the discharge current control means based on a voltage difference generated at both ends of multiple thermistors used as the temperature detection means. 
     Additional Statement  19   
     A plasma display apparatus characterized in that: 
     the configuration of the additional statement  1  is provided to a plasma display apparatus of the ALIS method. 
     Additional Statement  20   
     A plasma display apparatus characterized in that: 
     the configuration of the additional statement  2  is provided to a plasma display apparatus of the ALIS method. 
     Additional Statement  21   
     A plasma display apparatus characterized in that: 
     the configuration of the additional statement  3  is provided to a plasma display apparatus of the ALIS method.