JP2009186807A - Plasma display device and driving method for plasma display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the quality of an image display device, without increasing the noise, even for a plasma display panel which is refined into high definition. <P>SOLUTION: The plasma display device comprises: an APL detection circuit for detecting the average brightness level of an input image signal; a maintaining pulse generator circuit for generating the maintaining pulses for the number of times of the product of luminance weight and prescribed luminance magnification, alternately applying it to the pair of display electrode, in the maintaining periods set for each subfield; and a drive circuit for driving the plasma display panel with a maintaining pulse generator. In an APL circuit, the luminance magnification and the luminance weighings are varied according to the detected average brightness, and the total sum of the luminance weights is made larger, by enlarging the luminance weight of subfields which is originally large, when the average luminance level detected in the APL detection circuit, is set smaller than a previously determined first threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plasma display device and a plasma display panel driving method used for a wall-mounted television or a large monitor.

  A typical AC surface discharge type panel as a plasma display panel (hereinafter abbreviated as “panel”) has a large number of discharge cells formed between a front plate and a back plate arranged to face each other. In the front plate, a plurality of display electrode pairs each consisting of a pair of scan electrodes and sustain electrodes are formed in parallel with each other on the front glass substrate, and a dielectric layer and a protective layer are formed so as to cover the display electrode pairs. Yes. The back plate has a plurality of parallel data electrodes on the back glass substrate, a dielectric layer so as to cover them, and a plurality of barrier ribs in parallel with the data electrodes formed on the back glass substrate. A phosphor layer is formed on the side walls of the barrier ribs. Then, the front plate and the back plate are arranged opposite to each other so that the display electrode pair and the data electrode are three-dimensionally crossed and sealed, and a discharge gas containing, for example, 5% xenon is enclosed in the internal discharge space. Has been. Here, a discharge cell is formed at a portion where the display electrode pair and the data electrode face each other. In the panel having such a configuration, ultraviolet rays are generated by gas discharge in each discharge cell, and the phosphors of red (R), green (G) and blue (B) colors are excited and emitted by the ultraviolet rays, thereby performing color display. It is carried out.

  As a method of driving the panel, a subfield method, that is, a method of performing gradation display by combining subfields to emit light after dividing one field period into a plurality of subfields is generally used.

  Each subfield has an initialization period, an address period, and a sustain period. During the initializing period, initializing discharge is generated, and wall charges necessary for the subsequent addressing operation are formed on each electrode, and priming particles (excited particles for generating addressing discharge) for stably generating the address discharge. ).

  In the address period, a scan pulse is sequentially applied to the scan electrodes (hereinafter, this operation is also referred to as “scan”), and an address pulse corresponding to an image signal to be displayed is applied to the data electrodes (hereinafter, these operations are performed). Are collectively referred to as “writing”). Thereby, an address discharge is selectively generated between the scan electrode and the data electrode, and a wall charge is selectively formed.

  In the subsequent sustain period, a predetermined number of sustain pulses corresponding to the luminance to be displayed are alternately applied to the display electrode pair composed of the scan electrode and the sustain electrode. Thereby, a discharge is selectively caused in the discharge cell in which the wall charge is formed by the address discharge, and the discharge cell is caused to emit light. Thereby, an image is displayed.

  In addition, among the subfield methods, initializing discharge is performed using a slowly changing voltage waveform, and further, initializing discharge is selectively performed on discharge cells that have undergone sustain discharge. A driving method is disclosed in which the light emission that is not generated is reduced as much as possible to improve the contrast ratio.

  Specifically, among the plurality of subfields, in the initialization period of one subfield, an all-cell initializing operation for generating an initializing discharge in all discharge cells is performed, and in an initializing period of the other subfield. Performs a selective initializing operation in which initializing discharge is generated only in the discharge cells that have undergone sustain discharge in the immediately preceding sustain period. By driving in this way, the luminance of the black display area that changes depending on the light emission not related to the image display (hereinafter abbreviated as “black luminance”) is only weak light emission in the all-cell initialization operation, High-contrast image display is possible (see, for example, Patent Document 1).

  In a plasma display device incorporating such a panel, various power consumption reduction techniques have been proposed in order to reduce power consumption.

  Focusing on the fact that the panel is a capacitive load as one of the technologies to reduce power consumption, LC resonance between the inductor and the load capacity of the panel is performed by a resonance circuit including the inductor as a component, and the load capacity of the panel In other words, a so-called power recovery circuit is disclosed in which the power stored in is recovered in a power recovery capacitor and the recovered power is reused for driving the panel (see, for example, Patent Document 2).

  In this technology, for example, the power recovered from the PDP is reused to apply the sustain pulse voltage to the scan electrode and the sustain electrode in the sustain period, and the power consumed in the sustain period is reduced, thereby reducing the power consumption. Can be realized.

  On the other hand, in the PDP, it is important to display an image in an easy-to-view manner as well as to reduce power consumption, and various proposals have been made regarding techniques for brightly displaying an image for easy viewing.

  As a technique for brightly displaying an image, a technique for controlling the number of sustain pulses in the sustain period is disclosed. In the panel, the brightness (light emission luminance) of one light emission generated by one discharge in the sustain period is substantially the same, but the light emission period is short, so that the display cell having a larger number of light emission in one field period It appears to be brightly lit. In this technique, this principle is used. For example, one field is referred to as a first subfield to an eighth subfield (hereinafter, the first subfield is referred to as “first SF”, and the second subfield is referred to as “second SF”). The number of sustain pulses in the first SF is 1, the number of sustain pulses in the second SF is 2, and the number of sustain pulses from the 3rd SF to the 8th SF is 4, 8, 16, respectively. When the number of sustain pulses is 32, 64, and 128, the number of sustain pulses from the first SF to the eighth SF is doubled to 2, 4, 8, 16, 32, 64, 128, and 256, respectively. The number of sustain pulses up to 8SF is tripled by 3 times, and the number of sustain pulses in the subfield is changed from 1 to 2 times, 3 times, and 4 times. Hereinafter referred to a the sustain pulse number ratio to as "luminance magnification") by controlling the number of light emission in the sustain period to adjust the brightness of the screen by. By using this technique, an average luminance level (APL: Average Picture Level) of an image signal is detected, a luminance magnification is switched based on the detected APL, and a dark image is increased by increasing the luminance magnification when the APL is low. It becomes possible to display brighter (see, for example, Patent Document 3).

In addition, a technique is disclosed in which the number of sustain pulses in the sustain period can be performed not only for an integral multiple but also for multiples of a numerical value after the decimal point so that the change in brightness is smoother (for example, see Patent Document 4) ).
JP 2000-242224 A Japanese Examined Patent Publication No. 7-109542 JP-A-8-286636 Japanese Patent Laid-Open No. 11-231833

  In recent years, with an increase in screen size and definition, a further improvement in display quality in a plasma display device is desired.

  On the other hand, the higher definition of the panel increases the number of scan electrodes that must be scanned, so that the time required for one address period is increased and the length of the subfield period is increased. For example, if the length of the subfield period is increased and the upper limit of the number of subfields constituting one field period is suppressed, the gradation that can be used for displaying an image is limited, the gradation becomes rough, and noise is reduced. May increase.

  The present invention has been made in view of the above problems, and provides a plasma display device and a panel driving method capable of improving image display quality without increasing noise even in a high-definition panel. The purpose is to provide.

  A plasma display device according to the present invention includes a panel including a plurality of discharge cells each having a display electrode pair including a scan electrode and a sustain electrode, an APL detection circuit that detects an average luminance level of an input image signal, an initialization period, and writing A plurality of subfields each having a period and a sustain period are provided in one field period, and a sustain pulse is generated a number of times obtained by multiplying a luminance weight set for each subfield in the sustain period by a predetermined luminance magnification, thereby generating a display electrode pair. A drive circuit for driving the panel having sustain pulse generation circuits applied alternately, the drive circuit changing the luminance magnification and the luminance weight according to the average luminance level detected in the APL detection circuit, and the APL When the average luminance level detected by the detection circuit is less than a predetermined first threshold value, the luminance weight is large. There was a larger luminance weights of the subfields, characterized in that increasing the sum of the luminance weight.

  As a result, when displaying a dark image with a low APL, it is possible to smoothly display an area with a low gradation value without increasing noise, and an improvement in image display quality can be realized.

  Further, in this plasma display device, the drive circuit has a luminance so that power consumption in the plasma display device is constant when the average luminance level detected by the APL detection circuit is equal to or higher than a predetermined second threshold value. The total number of sustain pulses in one field period is changed by controlling the magnification and the luminance weight. This makes it possible to display a dynamic and powerful image while keeping power consumption constant when displaying an image with a high APL.

  Further, in this plasma display device, the drive circuit has a luminance magnification according to the total number of luminance weights in one field period when the average luminance level detected by the APL detection circuit is less than a predetermined first threshold value. And the total number of sustain pulses may be kept substantially constant. As a result, the luminance magnification can be decreased in accordance with the increase in the total number of luminance weights, and the total number of sustain pulses can be kept almost constant, so that the time that can be allocated to the sustain period is limited. Desirable when driving a panel.

  Also, the panel driving method of the present invention provides a panel having a plurality of discharge cells each having a display electrode pair composed of a scan electrode and a sustain electrode, and a subfield having an initialization period, an address period, and a sustain period in one field. Drive using a sustain pulse generator circuit that generates multiple sustain pulses by multiplying the brightness weight set for each subfield in the sustain period by a predetermined brightness magnification and alternately applies it to the display electrode pairs. A panel driving method for detecting an average luminance level of an input image signal, changing a luminance magnification and a luminance weight according to the detected average luminance level, and determining the detected average luminance level in advance. When it is less than the first threshold, the luminance weight of the subfield having a large luminance weight is increased to increase the sum of the luminance weights. And butterflies.

  As a result, when displaying a dark image with a low APL, it is possible to smoothly display an area with a low gradation value without increasing noise, and an improvement in image display quality can be realized.

  According to the present invention, it is possible to provide a plasma display apparatus and a panel driving method capable of improving the image display quality without increasing noise even in a panel with high definition.

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

(Embodiment)
FIG. 1 is an exploded perspective view showing the structure of panel 10 according to an embodiment of the present invention. A plurality of display electrode pairs 24 each including a scanning electrode 22 and a sustain electrode 23 are formed on a glass front plate 21. A dielectric layer 25 is formed so as to cover the scan electrode 22 and the sustain electrode 23, and a protective layer 26 is formed on the dielectric layer 25.

  The protective layer 26 has been used as a panel material in order to lower the discharge start voltage in the discharge cell, and has a large secondary electron emission coefficient and durability when neon (Ne) and xenon (Xe) gas is sealed. It is formed from a material mainly composed of MgO having excellent properties.

  A plurality of data electrodes 32 are formed on the back plate 31, a dielectric layer 33 is formed so as to cover the data electrodes 32, and a grid-like partition wall 34 is formed thereon. A phosphor layer 35 that emits light of each color of red (R), green (G), and blue (B) is provided on the side surface of the partition wall 34 and on the dielectric layer 33.

  The front plate 21 and the back plate 31 are arranged to face each other so that the display electrode pair 24 and the data electrode 32 intersect with each other with a minute discharge space interposed therebetween, and the outer periphery thereof is sealed with a sealing material such as glass frit. Has been. A mixed gas of neon and xenon is sealed as a discharge gas in the internal discharge space. In the present embodiment, a discharge gas having a xenon partial pressure of about 10% is used in order to improve luminous efficiency. The discharge space is partitioned into a plurality of sections by barrier ribs 34, and discharge cells are formed at portions where display electrode pairs 24 and data electrodes 32 intersect. These discharge cells discharge and emit light to display an image.

  Note that the structure of the panel 10 is not limited to the above-described structure, and for example, the panel 10 may include a stripe-shaped partition wall. Further, the mixing ratio of the discharge gas is not limited to the above-described numerical values, and may be other mixing ratios.

  FIG. 2 is an electrode array diagram of panel 10 according to the embodiment of the present invention. The panel 10 includes n scan electrodes SC1 to SCn (scan electrodes 22 in FIG. 1) and n sustain electrodes SU1 to SUn (sustain electrodes 23 in FIG. 1) that are long in the row direction. M data electrodes D1 to Dm (data electrodes 32 in FIG. 1) that are long in the column direction are arranged. A discharge cell is formed at a portion where one pair of scan electrode SCi (i = 1 to n) and sustain electrode SUi intersects one data electrode Dj (j = 1 to m), and the discharge cell is in the discharge space. M × n are formed. A region where m × n discharge cells are formed becomes a display region of the panel 10.

  Next, a driving voltage waveform for driving the panel 10 and an outline of the operation will be described. The plasma display device according to the present embodiment performs gradation display by subfield method, that is, by dividing one field period into a plurality of subfields and controlling light emission / non-light emission of each discharge cell for each subfield. Each subfield has an initialization period, an address period, and a sustain period.

  In each subfield, initializing discharge is generated in the initializing period, and wall charges necessary for subsequent address discharge are formed on each electrode. In addition, it has a function of generating priming particles (priming for discharge = excited particles) for reducing discharge delay and generating address discharge stably. The initializing operation at this time is an all-cell initializing operation in which initializing discharge is generated in all discharge cells, and an initializing discharge is selectively generated only in the discharge cells that have undergone sustain discharge in the immediately preceding subfield. There is a selective initialization operation.

  In the address period, an address discharge is selectively generated in the discharge cells to emit light in the subsequent sustain period to form wall charges. In the sustain period, a number of sustain pulses proportional to the luminance weight are alternately applied to the display electrode pair 24 to generate a sustain discharge in the discharge cells that have generated the address discharge, thereby causing light emission. The proportionality constant at this time is “luminance magnification”.

  In the present embodiment, one field is composed of nine subfields (first SF, second SF,..., Ninth SF), and each subfield is, for example, (1, 2, 4, 7, 13, 24). , 41, 64, 100). Then, the all-cell initialization operation is performed in the initialization period of the first SF, and the selective initialization operation is performed in the initialization period of the second SF to the ninth SF. As a result, the light emission not related to the image display is only the light emission due to the discharge of the all-cell initialization operation in the first SF, and the black luminance that is the luminance of the black display area that does not generate the sustain discharge is weak in the all-cell initialization operation. Only the emission of light makes it possible to display an image with high contrast. In the sustain period of each subfield, the number of sustain pulses obtained by multiplying the luminance weight of each subfield by a predetermined luminance magnification is applied to each display electrode pair 24.

  Note that the luminance weight value of each subfield described above is merely an example in the present embodiment. In this embodiment, the average luminance level (hereinafter abbreviated as “APL”) of the image signal is detected, and the luminance weight value is changed based on the detected APL. Details of this will be described later.

  FIG. 3 is a drive voltage waveform diagram applied to each electrode of panel 10 in one embodiment of the present invention. FIG. 3 shows a driving voltage waveform of two subfields, that is, a first subfield (first SF) of a subfield performing an all-cell initializing operation (hereinafter referred to as “all-cell initializing subfield”), A second subfield (second SF) of a subfield (hereinafter referred to as “selective initialization subfield”) for performing a selective initialization operation is shown, but the drive voltage waveforms in the other subfields are substantially the same. is there. Further, scan electrode SCi, sustain electrode SUi, and data electrode Dk in the following represent electrodes selected from the respective electrodes based on image data.

  First, the first SF, which is an all-cell initialization subfield, will be described.

  In the first half of the initializing period of the first SF, 0 (V) is applied to data electrode D1 to data electrode Dm and sustain electrode SU1 to sustain electrode SUn, respectively, and sustain electrode SU1 to sustain is applied to scan electrode SC1 to scan electrode SCn. A ramp waveform voltage (hereinafter referred to as “up-ramp waveform voltage”) that gently rises from voltage Vi1 that is equal to or lower than the discharge start voltage to voltage Vi2 that exceeds the discharge start voltage is applied to electrode SUn.

  In the present embodiment, this up-ramp waveform voltage is generated with a slope of about 1.3 V / μsec.

  While the rising ramp waveform voltage rises, weak initializing discharges are continuously generated between scan electrode SC1 through scan electrode SCn, sustain electrode SU1 through sustain electrode SUn, and data electrode D1 through data electrode Dm. Negative wall voltage is accumulated above scan electrode SC1 through scan electrode SCn, and positive wall voltage is accumulated above data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn. The wall voltage above the electrode represents a voltage generated by wall charges accumulated on the dielectric layer covering the electrode, the protective layer, the phosphor layer, and the like.

  In the latter half of the initialization period, positive voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, 0 (V) is applied to data electrode D1 through data electrode Dm, and scan electrode SC1 through scan electrode SCn. , A ramp waveform voltage that gradually falls from voltage Vi3 that is equal to or lower than the discharge start voltage to sustain voltage SUn with respect to sustain electrode SU1 to voltage Vi4 that exceeds the discharge start voltage (hereinafter referred to as “down-ramp waveform voltage”). Is applied. During this time, weak initializing discharges are continuously generated between scan electrode SC1 through scan electrode SCn, sustain electrode SU1 through sustain electrode SUn, and data electrode D1 through data electrode Dm. Then, the negative wall voltage above scan electrode SC1 through scan electrode SCn and the positive wall voltage above sustain electrode SU1 through sustain electrode SUn are weakened, and the positive wall voltage above data electrode D1 through data electrode Dm is used for the write operation. It is adjusted to a suitable value. Thus, the all-cell initializing operation for performing the initializing discharge on all the discharge cells is completed.

  Note that, as shown in the initialization period of the second SF in FIG. 3, a drive voltage waveform in which the first half of the initialization period is omitted may be applied to each electrode. That is, 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, respectively, and voltage that is equal to or less than the discharge start voltage (for example, 0) is applied to scan electrode SC1 through scan electrode SCn. (V)) is applied to the ramp-down waveform voltage that gradually falls toward the voltage Vi4. As a result, a weak initializing discharge is generated in the discharge cell in which the sustain discharge has occurred in the sustain period of the previous subfield, and the wall voltage above scan electrode SCi and sustain electrode SUi is weakened. Further, in a discharge cell in which a sufficient positive wall voltage is accumulated on the data electrode Dk (k = 1 to m) by the last sustain discharge, an excessive portion of the wall voltage is discharged, and the wall voltage suitable for the address operation is obtained. Adjusted to On the other hand, the discharge cells that did not cause the sustain discharge in the previous subfield are not discharged, and the wall charges at the end of the initialization period of the previous subfield are maintained as they are. Thus, the initializing operation in which the first half is omitted is a selective initializing operation in which initializing discharge is performed on the discharge cells in which the sustaining operation has been performed in the sustain period of the immediately preceding subfield.

  In the subsequent address period, a scan pulse voltage is sequentially applied to scan electrode SC1 through scan electrode SCn, and data electrode Dk (k = 1) corresponding to a discharge cell to emit light is applied to data electrode D1 through data electrode Dm. To m), a positive address pulse voltage Vd is applied to selectively generate an address discharge in each discharge cell.

  In the address period, voltage Ve2 is first applied to sustain electrode SU1 through sustain electrode SUn, and voltage Vc is applied to scan electrode SC1 through scan electrode SCn.

  The negative scan pulse voltage Va is applied to the scan electrode SC1 in the first row, and the data electrode Dk (k = 1 to m) of the discharge cell that should emit light in the first row among the data electrodes D1 to Dm. A positive write pulse voltage Vd is applied to. At this time, the voltage difference at the intersection between the data electrode Dk and the scan electrode SC1 is the difference between the wall voltage on the data electrode Dk and the wall voltage on the scan electrode SC1 due to the difference in externally applied voltage (Vd−Va). It becomes the sum and exceeds the discharge start voltage. As a result, a discharge is generated 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 the difference between the externally applied voltages (Ve2-Va) and sustain electrode SU1. The difference between the upper wall voltage and the wall voltage on the scan electrode SC1 is added. At this time, by setting the voltage Ve2 to a voltage value that is slightly lower than the discharge start voltage, the sustain electrode SU1 and the scan electrode SC1 are not easily discharged but are likely to be discharged. Can do. Thereby, the discharge generated between data electrode Dk and scan electrode SC1 can be triggered to generate a discharge between sustain electrode SU1 and scan electrode SC1 in the region intersecting with data electrode Dk. Thus, an address discharge occurs in the discharge cell to emit light, a positive wall voltage is accumulated on scan electrode SC1, a negative wall voltage is accumulated on sustain electrode SU1, and a negative wall voltage is also accumulated on data electrode Dk. Accumulated.

  In this manner, an address operation is performed in which an address discharge is caused in the discharge cells to be lit in the first row and wall voltage is accumulated on each electrode. On the other hand, the voltage at the intersection of data electrode D1 to data electrode Dm to which scan pulse SC1 is not applied with address pulse voltage Vd does not exceed the discharge start voltage, so that address discharge does not occur. The above address operation is performed until the discharge cell in the nth row, and the address period ends.

  In the subsequent sustain period, first, positive sustain pulse voltage Vs is applied to scan electrode SC1 through scan electrode SCn, and the ground potential serving as the base potential, that is, 0 (V), is applied to sustain electrode SU1 through sustain electrode SUn. Then, in the discharge cell in which the address discharge has occurred, the voltage difference between scan electrode SCi and sustain electrode SUi is the difference between the wall voltage on scan electrode SCi and the wall voltage on sustain electrode SUi. Exceeds the discharge start voltage.

  Then, a sustain discharge occurs between scan electrode SCi and sustain electrode SUi, and phosphor layer 35 emits light by the ultraviolet rays generated at this time. Then, a negative wall voltage is accumulated on scan electrode SCi, and a positive wall voltage is accumulated on sustain electrode SUi. Further, a positive wall voltage is accumulated on the data electrode Dk. In the discharge cells in which no address discharge has occurred during the address period, no sustain discharge occurs, and the wall voltage at the end of the initialization period is maintained.

  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. Then, in the discharge cell in which the sustain discharge has occurred, the voltage difference between the sustain electrode SUi and the scan electrode SCi exceeds the discharge start voltage, so that the sustain discharge occurs again between the sustain electrode SUi and the scan electrode SCi. A negative wall voltage is accumulated on SUi, and a positive wall voltage is accumulated on scan electrode SCi. Thereafter, similarly, sustain electrodes of the number obtained by multiplying the luminance weight by the luminance magnification are applied alternately to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and a potential difference is given between the electrodes of display electrode pair 24. As a result, the sustain discharge is continuously performed in the discharge cells that have caused the address discharge in the address period.

  At the end of the sustain period, the ramp waveform voltage gradually increases (for example, with a gradient of about 10 V / μsec) from 0 (V), which is the base potential, to voltage Vers at scan electrode SC1 through scan electrode SCn. (Hereinafter referred to as “erasing ramp waveform voltage”). As a result, a weak discharge is continuously generated, and some or all of the wall voltages on scan electrode SCi and sustain electrode SUi are erased while the positive wall voltage on data electrode Dk remains. The last discharge in the sustain period generated by the erase ramp waveform voltage is referred to as “erase discharge”.

  Subsequent subfield operations are substantially the same as those described above except for the number of sustain pulses in the sustain period, and thus description thereof is omitted. The above is the outline of the drive voltage waveform applied to each electrode of panel 10 in the present embodiment.

  Next, the configuration of the plasma display device in the present embodiment will be described. FIG. 4 is a circuit block diagram of the plasma display device in one embodiment of the present invention. The plasma display device 1 includes a panel 10, a drive circuit that drives the panel 10, and a power supply circuit (not shown) that supplies power necessary for each circuit block. As a drive circuit, an image signal processing circuit 41, a data electrode drive circuit 42, a scan electrode drive circuit 43, a sustain electrode drive circuit 44, and a timing generation circuit 45 are provided.

  The image signal processing circuit 41 converts the input image signal sig into image data indicating light emission / non-light emission for each subfield in the discharge cell.

  The timing generation circuit 45 generates various timing signals for controlling the operation of each circuit block based on the horizontal synchronization signal H and the vertical synchronization signal V, and supplies them to the respective circuit blocks.

  Scan electrode drive circuit 43 includes an initialization waveform generation circuit (not shown) for generating an initialization waveform voltage to be applied to scan electrode SC1 through scan electrode SCn in the initialization period, and scan electrode SC1 through scan electrode in the sustain period. A sustain pulse generating circuit 70 for generating a sustain pulse to be applied to SCn, a scan pulse generating circuit having a plurality of scan ICs and generating a scan pulse voltage to be applied to scan electrode SC1 to scan electrode SCn in the address period (FIG. Not shown). Then, each scan electrode SC1 to scan electrode SCn is driven based on the timing signal.

  The data electrode driving circuit 42 outputs subfield data output from the image signal processing circuit 41 (data obtained by converting an image signal into a signal indicating lighting / non-lighting in each subfield of each data electrode D1 to data electrode Dm). And the data electrodes D1 to Dm are driven based on the timing signal.

  Sustain electrode drive circuit 44 includes sustain pulse generation circuit 80 and a circuit (not shown) for generating voltage Ve1 and voltage Ve2, and drives sustain electrode SU1 through sustain electrode SUn based on a timing signal.

  FIG. 5 is a circuit block diagram of the image signal processing circuit 41 according to the embodiment of the present invention. FIG. 5 shows circuit blocks related to luminance magnification control and luminance weight control in this embodiment, and other circuit blocks are omitted.

  The image signal processing circuit 41 includes an A / D conversion circuit 60, a gamma correction circuit 61, an APL detection circuit 62, an error diffusion circuit 63, a multiplication circuit 64, a subfield data creation circuit 65, a memory 66, And a luminance magnification setting circuit 67.

  The A / D conversion circuit 60 performs generally known A / D conversion (Analog Digital Conversion), and converts an analog image signal input to the image signal processing circuit 41 into, for example, a 10-bit digital image signal. .

  The gamma correction circuit 61 performs gamma correction generally performed in the processing of a television signal on the digital image signal output from the A / D conversion circuit 60. In gamma correction, a process of multiplying an image signal by a correction value that changes according to a gradation value called a gamma curve is performed. At this time, the digital image signal is expanded to digital data (for example, 16-bit data) larger than the uncorrected image signal (for example, 10-bit data) by multiplication processing by gamma correction and output from the gamma correction circuit 61. The

  The APL detection circuit 62 detects the average brightness (APL) of the image signal by a generally known calculation method such that the luminance signal of the image signal is cumulatively added over one field period (or one frame period). To do. For example, the detected APL may be normalized to a numerical value from 0% to 100% and output.

  When there is a difference between the gradation value of the image signal and the gradation value for display, the error diffusion circuit 63 diffuses the difference to surrounding pixels, thereby converting the displayed gradation value to the image signal. A generally known error diffusion process such as approaching the gradation value is performed. The error diffusion circuit 63 converts the image signal (for example, 16-bit data) output from the gamma correction circuit 61 into an image signal (for example, 9-bit data) with a limited number of gradations, and outputs the image signal.

  In the memory 66, a plurality of pieces of subfield information (hereinafter referred to as “subfield configuration”) having different combinations of luminance weights in each subfield in one field period and a plurality of coding data corresponding to the subfield configuration are stored in advance. It is remembered. The coding data is data that predetermines which gradation value is used for image display and how to combine a subfield to be lit and a non-lighting subfield to display the gradation value. That is, under one subfield configuration, there are a plurality of coding data predetermined based on the subfield configuration, and such a plurality of coding data is set in each subfield configuration and stored in the memory 66. Is remembered. Then, the memory 66 outputs internal data to the subfield data creation circuit 65 under the control of the subfield data creation circuit 65.

  In the present embodiment, the plurality of subfield configurations stored in memory 66 include subfield configurations with different sums of luminance weights in one field period.

  The subfield data creation circuit 65 selects one subfield configuration according to the APL detected by the APL detection circuit 62, and from among a plurality of coding data created under the subfield configuration, Coding data corresponding to the gradation value is selected and read from the memory 66. The data read in this way is output to the data electrode drive circuit 42 as subfield data (signals indicating lighting / non-lighting of each data electrode D1 to data electrode Dm in each subfield). Also, luminance weight information of each subfield in the selected subfield configuration is output to the timing generation circuit 45.

  In the present embodiment, as described above, a plurality of subfield configurations include subfield configurations in which the sum of luminance weights in one field period is different. Therefore, the image signal must be changed to digital data corresponding to the sum of luminance weights. Therefore, the multiplication circuit 64 performs a process of changing the number of gradations of the image signal based on the sum of luminance weights of the subfield configuration selected by the subfield data creation circuit 65. For example, when the sum of the luminance weights of the subfield configuration selected by the subfield data creation circuit 65 is 256, the multiplication circuit 64 outputs the image signal (for example, 9-bit, 512-gradation digital signal) output from the error diffusion circuit 63. Data) is changed to 256 gradation digital data, and when the sum of luminance weights is 322, the image signal output from the error diffusion circuit 63 is changed to 322 gradation digital data.

  The luminance magnification setting circuit 67 sets the luminance magnification according to the APL detected by the APL detection circuit 62 and outputs the luminance magnification to the timing generation circuit 45. Thus, in this embodiment, based on the APL detected by the APL detection circuit 62, the subfield data creation circuit 65 changes the subfield configuration (in this case, the luminance weight of each subfield), and sets the luminance magnification. In the circuit 67, the luminance magnification is changed.

  The data electrode drive circuit 42 performs a write operation based on the subfield data output from the subfield data generation circuit 65, and the timing generation circuit 45 performs luminance weight information and luminance output from the subfield data generation circuit 65. Based on the luminance magnification output from magnification setting circuit 67, the number of sustain pulses generated in the sustain period of each subfield is controlled.

  Next, the relationship between the APL detected by the APL detection circuit 62 in this embodiment, the subfield configuration selected by the subfield data creation circuit 65, and the luminance magnification set by the luminance magnification setting circuit 67 will be described. First, the relationship between the total number of sustain pulses generated in one field period and APL will be described. Note that the APL used in the following description is an APL detected by the APL detection circuit 62.

  FIG. 6 is a characteristic diagram showing an example of the relationship between the APL, the total number of sustain pulses generated in one field period, and the power consumption in one embodiment of the present invention. FIG. 6A is a characteristic diagram showing an example of the relationship between the APL and the total number of sustain pulses generated in one field period in the present embodiment, and the horizontal axis indicates the APL detected by the APL detection circuit 62. The vertical axis represents the total number of sustain pulses generated in one field period (hereinafter simply referred to as “total number of sustain pulses”). FIG. 6B is a characteristic diagram showing an example of the relationship between APL and power consumption in the present embodiment. The horizontal axis indicates the APL detected by the APL detection circuit 62, and the vertical axis indicates the plasma display device. 1 represents power consumption.

  In the present embodiment, as shown in FIG. 6A, when displaying an image with APL less than 24%, which is the second threshold value, APL is 100 so that the total number of sustain pulses is about 918. When displaying images of%, the total number of sustain pulses is 239, and when displaying images whose APL is the second threshold value of 24% or more, from APL 24% to APL 100%, The subfield configuration and the luminance magnification are changed according to APL so that the total number gradually decreases from 918 to 239. At this time, in this embodiment, from APL 24% to APL 100%, the total number of sustain pulses is controlled so that the power consumption is constant as shown in FIG. 6B. In the present embodiment, the change at this time is performed in 120 stages.

  As described above, when the APL of the image to be displayed is low, the total number of sustain pulses is increased because a dark image is displayed brighter by increasing the total number of sustain pulses generated when the APL is low. This is because it becomes possible. In an image with a low APL, the luminance value is generally low, or the image is often an image in which a region with a high luminance value exists while the luminance value is generally low. Thus, the luminance difference between the dark portion and the bright portion can be further increased, and a more dynamic and powerful image can be displayed.

  On the other hand, since an image with a high APL is an image with a high luminance value as a whole, even if the total number of sustain pulses is increased to increase the luminance, the dynamics of the image do not change so much only by increasing the overall luminance. . Furthermore, when the luminance is further increased in an image having a high APL, there is a problem that the power consumption increases accordingly. Therefore, when the APL of the image to be displayed is high, the total number of sustain pulses is reduced, and driving is performed with priority on reducing power consumption.

  Thus, by adopting a configuration in which the total number of sustain pulses is changed according to APL, it is possible to display a dynamic and powerful image while suppressing power consumption.

  Here, when the definition of the panel 10 is increased and the number of scan electrodes to be scanned increases, the time required for one address period increases, and the length of the subfield period may increase. If the length of the subfield period is increased and the number of subfields constituting one field period is limited, the gradation value that can be used for image display is limited, which may increase the noise of the display image. is there. For example, when one field period must be composed of 9 subfields, there is a risk that the noise of the display image will increase as compared to when one field period is composed of 12 subfields.

  On the other hand, the present inventor has a rough gradation value change in a region having a high gradation value by suppressing the ratio of the luminance weight of the subfield having a large luminance weight to the sum of the luminance weights in a bright image having a high APL. It was confirmed that noise can be reduced. In addition, it was confirmed that in a dark image with a low APL, an area with a low gradation value can be smoothly displayed by reducing the ratio of the luminance weight of the subfield with a small luminance weight to the total luminance weight. Thus, it has been found that the image display quality can be improved by changing the subfield configuration in accordance with the APL.

  Therefore, in this embodiment, the subfield configuration is changed according to APL, and in a bright image with high APL, the ratio of the luminance weight of the subfield with large luminance weight to the sum of the luminance weights is suppressed, and an image with low APL is selected. When displaying, the sum of the luminance weights is increased to reduce the ratio of the luminance weights of the subfields with the smaller luminance weights to the total luminance weights.

  FIG. 7 is a characteristic diagram showing an example of the relationship between the APL, the luminance weight, and the sum of the luminance weight in one field period in the embodiment of the present invention. FIG. 7A is a characteristic diagram showing an example of the relationship between APL and luminance weight in the present embodiment. The horizontal axis indicates APL detected by the APL detection circuit 62, and the vertical axis indicates luminance magnification. To express. FIG. 7B is a characteristic diagram showing an example of the relationship between the APL and the sum of luminance weights in one field period in the present embodiment, and the horizontal axis indicates the APL detected by the APL detection circuit 62. The vertical axis represents the sum of luminance weights in one field period (hereinafter simply referred to as “sum of luminance weights”). FIG. 7C is a table summarizing the relationship between APL, luminance magnification, luminance weight sum, and total number of sustain pulses. FIG. 8 is a diagram showing an example of the distribution of luminance weights of sub-fields in each APL according to an embodiment of the present invention.

  In this embodiment, when displaying an image with a high APL, the luminance weight of each subfield is set so that the ratio of the luminance weight of the subfield having a large luminance weight to the total luminance weight is suppressed. Specifically, as shown in FIGS. 7 and 8, the luminance weight of each subfield (first SF to ninth SF) is set to (1, 2, 4, 7, 13, 24, 41, 64, APL 24% or more). 100), the sum of the luminance weights is set to 256, and the luminance weights of the subfields having a large luminance weight, for example, the eighth SF and the ninth SF are suppressed to a relatively small numerical value of (64, 100).

  Thereby, it is possible to suppress a change in gradation value from becoming rough in a region having a high gradation value, and to reduce noise when an image having a high APL is displayed. In this embodiment, when displaying an image with a high APL, the luminance magnification is gradually decreased from 3.561 to 0.93 in accordance with the APL, and the total number of sustain pulses is decreased from 908 to 239. As shown in FIG. 6, the power consumption is controlled to be constant at APL 24% or more.

  Further, when displaying an image with a low APL, the subfield configuration is switched in accordance with the APL so that the ratio of the luminance weight of the subfield with a small luminance weight to the sum of the luminance weights becomes smaller. Specifically, as shown in FIGS. 7 and 8, when the APL is less than the first threshold value of 17%, the total number of luminance weights is gradually increased from 259 to 322. At this time, the luminance weights of the subfields with small luminance weights (here, the first SF to the fifth SF) are not changed, and the luminance weights of the subfields with large luminance weights (here, the eighth SF and the ninth SF) are increased more. Each luminance weight is set so that For example, the luminance weights from the first SF to the fifth SF remain constant at (1, 2, 4, 7, 13), and the luminance weights from the eighth SF and the ninth SF are (65 to 82) and (102 to 142, respectively). ).

  In this way, by changing the ratio of the luminance weight of the subfield having a small luminance weight with respect to the sum of the luminance weights, the change in the gradation value in the region having a low gradation value is made relatively fine, and the APL It is possible to display more smoothly an area with a low gradation value that occupies most of the display image with a low image. In addition, in a dark image with a low APL, noise in a region with a high gradation value is relatively inconspicuous, so even if the luminance weight of a subfield with a large luminance weight is increased, the influence on the display image is very small. It will not be. Therefore, by increasing the luminance weight of the subfield having a large luminance weight to increase the sum of the luminance weights, it is possible to smoothly display a region having a low gradation value without increasing noise.

  In FIGS. 7 and 8, the luminance weight of each subfield (first SF to ninth SF) is set to (1, 2, 4, 7, 13, 25, 46, 82, 142) in the region where APL is less than 10%. The sum of the luminance weights is made constant at 322, and the luminance weight of each subfield (first SF to ninth SF) is set to (1, 2, 4, 7, 13, 24, 41) in an area of APL 17% or more and less than APL 24%. , 64, 100), and the sum of luminance weights is made constant at 256, this is merely one setting example. Also, the numerical values and the number of subfields constituting one field are merely examples, and are not limited to these numerical values. These numerical values and settings may be optimally set according to the characteristics of the panel and the specifications of the plasma display device.

  In this embodiment, when displaying an image with a low APL, the total number of luminance weights is increased. However, if the luminance magnification is fixed, the total number of sustain pulses increases according to the total number of luminance weights. , The duration of the maintenance period increases. Accordingly, when the time that can be allocated to the sustain period is limited, the luminance magnification is decreased in accordance with the increase in the total number of luminance weights, and the total number of sustain pulses is kept almost constant. desirable. 7 and 8 in the present embodiment, the luminance magnification is decreased from 3.60 to 2.862 in accordance with the total number of luminance weights in the region where APL is less than the first threshold value of 24%. In this configuration, the total number of sustain pulses is maintained at about 918. However, this configuration is merely an example, and is not limited to this configuration.

  As described above, according to the present embodiment, the subfield configuration is changed according to the APL, and in a bright image with a high APL, the ratio of the luminance weight of the subfield having a large luminance weight to the sum of the luminance weights is suppressed. When displaying an image with a low APL, the luminance weight of the subfield with a large luminance weight is increased to increase the luminance weight sum, and the ratio of the luminance weight of the subfield with a small luminance weight to the luminance weight sum is decreased. The configuration. As a result, in a bright image with a high APL, the change in the gradation value in a region with a high gradation value is suppressed to reduce noise, and in a dark image with a low APL, the gradation value is increased without increasing the noise. Therefore, it is possible to smoothly display an area with a low image quality, so that the image display quality can be improved without increasing noise. Further, by adopting a configuration in which the total number of sustain pulses is changed according to APL, it is possible to display a dynamic and powerful image while keeping power consumption constant when displaying an image with a high APL. .

  In the embodiment of the present invention, scan electrode SC1 to scan electrode SCn are divided into a first scan electrode group and a second scan electrode group, and an address period is a scan electrode belonging to the first scan electrode group. Of a panel by so-called two-phase driving, which includes a first address period in which a scan pulse is applied to each of the first and second address periods in which a scan pulse is applied to each of the scan electrodes belonging to the second scan electrode group. The present invention can also be applied to a driving method, and the same effect as described above can be obtained.

  In the embodiment of the present invention, the scan electrode and the scan electrode are adjacent to each other, and the sustain electrode and the sustain electrode are adjacent to each other. , Scan electrode, sustain electrode, sustain electrode, scan electrode, scan electrode,... ”Is also effective in a panel having an electrode structure (hereinafter referred to as“ ABBA electrode structure ”).

  It should be noted that the specific numerical values shown in the present embodiment are set based on the characteristics of a 50-inch panel with 1080 display electrode pairs, and are merely examples of the embodiment. The present invention is not limited to these numerical values, and is desirably set optimally according to the characteristics of the panel, the specifications of the plasma display device, and the like. Each of these numerical values is allowed to vary within a range where the above-described effect can be obtained.

  The present invention is useful as a plasma display device and a panel driving method because the image display quality can be improved without increasing noise even if the panel has a high definition.

The disassembled perspective view which shows the structure of the panel in one embodiment of this invention. Electrode arrangement of the panel Drive voltage waveform diagram applied to each electrode of the panel The circuit block diagram of the plasma display apparatus in one embodiment of the present invention 1 is a circuit block diagram of an image signal processing circuit according to an embodiment of the present invention. The characteristic view which shows an example of the relationship between the total number of sustain pulses generated in one field period and power consumption in an embodiment of the present invention The characteristic view which shows an example of the relationship between APL, luminance weight, and the total of the luminance weight in 1 field period in one embodiment of this invention The figure which shows an example of distribution of the luminance weight of each subfield in each APL in one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma display apparatus 10 Panel 21 Front plate (made of glass) 22 Scan electrode 23 Sustain electrode 24 Display electrode pair 25, 33 Dielectric layer 26 Protection layer 31 Back plate 32 Data electrode 34 Partition 35 Phosphor layer 41 Image signal processing circuit 42 data electrode drive circuit 43 scan electrode drive circuit 44 sustain electrode drive circuit 45 timing generation circuit 60 A / D conversion circuit 61 gamma correction circuit 62 APL detection circuit 63 error diffusion circuit 64 multiplication circuit 65 subfield data creation circuit 66 memory 67 brightness Magnification setting circuit 70, 80 Sustain pulse generation circuit

Claims (4)

A plasma display panel having a plurality of discharge cells each having a display electrode pair consisting of a scan electrode and a sustain electrode;
An APL detection circuit for detecting an average luminance level of the input image signal;
A plurality of subfields each having an initialization period, an address period, and a sustain period are provided in one field period, and sustain pulses are generated by multiplying a luminance weight set for each subfield in the sustain period by a predetermined luminance magnification. A sustaining pulse generating circuit that alternately applies to the display electrode pair, and a driving circuit that drives the plasma display panel,
The drive circuit changes the luminance magnification and the luminance weight in accordance with the average luminance level detected in the APL detection circuit, and the average luminance level detected in the APL detection circuit is determined in advance. The plasma display device is characterized in that, when the value is less than the threshold value, the luminance weight of the subfield having a large luminance weight is increased to increase the sum of luminance weights. When the average luminance level detected by the APL detection circuit is greater than or equal to a predetermined second threshold value, the driving circuit is configured to increase the luminance magnification and the luminance so that power consumption in the plasma display device is constant. The plasma display apparatus according to claim 1, wherein the total number of sustain pulses in one field period is changed by controlling the weight. When the average luminance level detected by the APL detection circuit is less than the first threshold, the driving circuit changes the luminance magnification according to the total number of luminance weights in one field period, and maintains a sustain pulse. 2. The plasma display device according to claim 1, wherein the total number of the plasma display devices is kept substantially constant. A plasma display panel comprising a plurality of discharge cells having a display electrode pair consisting of a scan electrode and a sustain electrode,
A plurality of subfields each having an initialization period, an address period, and a sustain period are provided in one field period, and sustain pulses are generated by multiplying a luminance weight set for each subfield in the sustain period by a predetermined luminance magnification. A method of driving a plasma display panel that is driven using a sustain pulse generating circuit that alternately applies to the display electrode pairs,
An average luminance level of the input image signal is detected, the luminance magnification and the luminance weight are changed according to the detected average luminance level, and the detected first luminance level is a predetermined first threshold. When the value is less than the value, the luminance weight of the subfield having a large luminance weight is increased to increase the sum of the luminance weights.

Images