Patent Application
20120287181
The present invention relates to a plasma display apparatus and a driving method of a plasma display panel that are used in a wall-mounted television or a large monitor.
An alternating-current surface discharge type panel typical as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front substrate and a rear substrate that are faced to each other.
The front substrate has the following elements:
The rear substrate has the following elements:
The front substrate and rear substrate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon with a partial pressure ratio of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color image display.
A subfield method is generally used as a method of driving the panel. In this subfield method, one field is divided into a plurality of subfields, and light is emitted or light is not emitted in each discharge cell in each subfield, thereby performing gradation display. Each subfield has an initializing period, an address period, and a sustain period.
In the initializing period, an initializing waveform is applied to each scan electrode, and initializing discharge is caused in each discharge cell. Thus, wall charge required for a subsequent address operation is produced in each discharge cell, and a priming particle (an excitation particle for causing address discharge) for stably causing address discharge is generated.
In the address period, a scan pulse is sequentially applied to scan electrodes (hereinafter, this operation is also referred to as “scan”), and an address pulse is selectively applied to data electrodes based on an image signal to be displayed. Thus, address discharge is caused between the scan electrode and the data electrode of the discharge cell to emit light, thereby producing wall charge in the discharge cell (hereinafter, this operation is also collectively referred to as “address”).
In a sustain period, as many sustain pulses as a number determined for each subfield are alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes. Thus, sustain discharge is caused in the discharge cell having undergone address discharge, thereby emitting light in the phosphor layer of this discharge cell (hereinafter, light emission by sustain discharge in a discharge cell is referred to as “lighting”, and no light emission is referred to as “no-lighting”). Thus, light is emitted in each discharge cell at a luminance corresponding to the luminance weight that is determined for each subfield. Thus, light is emitted in each discharge cell of the panel at a luminance corresponding to the generation value of the image signal, and an image is displayed on the image display surface of the panel.
As one of subfield methods, the following driving method is used. In the initializing period of one of a plurality of subfields, an all-cell initializing operation of causing initializing discharge in all discharge cells is performed. In the initializing periods of other subfields, a selective initializing operation of causing initializing discharge only in the discharge cell having undergone sustain discharge in the sustain period immediately before it is performed. Thus, the luminance (hereinafter, referred to as “luminance of black level”) in a black displaying region that does not cause sustain discharge is only weak light emission in the all-cell initializing operation. Therefore, light emission that is not related to the gradation display can be minimized, and the contrast ratio of the display image can be increased.
When the driving load (impedance when a driver circuit applies driving voltage to an electrode) differs between display electrode pairs, voltage drop of the driving voltage differs between them, and the emission luminance can differ between discharge cells though image signals have the same luminance. A technology is therefore disclosed where the lighting pattern is made to differ between subfields in one field when the driving load differs between display electrode pairs (for example, Patent Literature 1).
Recently, as the screen of the panel is enlarged and the definition is enhanced, the driving load of the panel is apt to increase. In such a panel, the difference in driving load between display electrode pairs is apt to increase, and the difference in voltage drop of the driving voltage is also apt to increase.
When the driving load differs between subfields, emission luminance caused by one sustain discharge differs between the subfields. When the panel is driven by the subfield method, as discussed above, one field period is divided into a plurality of subfields, and gradation display is performed by combination of the subfields to emit light. Therefore, when the emission luminance caused by one sustain discharge differs between subfields, the linearity of the gradation can be damaged.
In the panel where the driving load is increased by the enlargement of the screen and the enhancement of the definition, the difference in driving load between subfields is apt to increase and the difference in emission luminance between subfields is apt to occur, so that the linearity of the gradation is apt to be damaged. On such a panel, in order to display an image where the linearity of the gradation is kept, it is preferable that the luminance of each subfield is controlled optimally in response to the difference in emission luminance between subfields.
In the panel where the screen is enlarged and the definition is enhanced, it is desired that the image display quality of the plasma display apparatus is further improved. The brightness of the image to be displayed on the panel is one factor for determining the image display quality. Therefore, preferably, variation in brightness of the display image is minimized when correction such as alteration of the lighting pattern of a subfield is performed.
PTL 1
Unexamined Japanese Patent Publication No. 2006-184843
A plasma display apparatus of the present invention includes the following elements:
Thus, variation in emission luminance between subfields can be accurately estimated by detecting the all-cell light-emitting rate and the partial light-emitting rates. And, the number of generated sustain pulses set based on the input image signal and luminance weigh can be corrected using the first correction coefficient responsive to the all-cell light-emitting rate and the partial light-emitting rates. The number of generated sustain pulses can be controlled using the common correction coefficient that can make the estimated value of the power consumption in one field period before the correction equivalent to that after the correction. Thus, even in the panel where the screen is enlarged and the definition is enhanced, the linearity of the gradation in the display image can be kept, and the brightness of the display image can be controlled while the increase in power consumption is suppressed, so that the image display quality of the plasma display apparatus can be improved.
In a driving method of a panel of the present invention, the panel emits light in discharge cells by disposing a plurality of subfields, each of which has a luminance weight in one field and applying as many sustain pulses as the number corresponding to the luminance weight to the discharge cells in the sustain period.
The driving method includes the following steps:
Thus, variation in emission luminance between subfields can be accurately estimated by detecting the all-cell light-emitting rate and the partial light-emitting rates, and the number of generated sustain pulses set based on the input image signal and luminance weigh can be corrected using the first correction coefficient responsive to the all-cell light-emitting rate and the partial light-emitting rates. The number of generated sustain pulses can be controlled using the common correction coefficient that can make the estimated value of the power consumption in one field period before the correction equivalent to that after the correction. Thus, even in the panel where the screen is enlarged and the definition is enhanced, the linearity of the gradation in the display image can be kept, and the brightness of the display image can be controlled while the increase in power consumption is suppressed, so that the image display quality of the plasma display apparatus can be improved.
A plasma display apparatus in accordance with exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
A plurality of data electrodes 32 is formed on rear substrate 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 light of each of red color (R), green color (G), and blue color (B) are formed on the side surfaces of barrier ribs 34 and on dielectric layer 33.
Front substrate 21 and rear substrate 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, for example. In the present exemplary embodiment, discharge gas with a xenon partial pressure of 10% is used for improving the 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. Then, discharge is caused and light is emitted (lighting) in the discharge cells, thereby displaying a color image on panel 10.
In panel 10, one pixel is formed of three consecutive discharge cells arranged in the extending direction of display electrode pairs 24. The three discharge cells are a discharge cell for emitting light of red color (R), a discharge cell for emitting light of green color (G), and a discharge cell for emitting light of blue color (B). Hereinafter, a discharge cell for emitting light of red color is called an R discharge cell, a discharge cell for emitting light of green color is called a G discharge cell, and a discharge cell for emitting light of blue color is called a B discharge cell.
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 one, but may be another mixing ratio.
Next, a driving voltage waveform and operation for driving panel 10 are described schematically. The plasma display apparatus of the present exemplary embodiment performs gradation display by a subfield method. In this subfield method, the plasma display apparatus divides one field into a plurality of subfields on the time axis, and sets luminance weight for each subfield. An image is displayed on panel 10 by controlling light emission and no light emission in each discharge cell of each subfield.
The luminance weight means the ratio between the luminances displayed in respective subfields, and as many sustain pulses as the number corresponding to the luminance weight are generated in each subfield in the sustain period. For example, in the subfield of luminance weight “8”, as many sustain pulses as the number eight times that in the subfield of luminance weight “1” are generated in the sustain period, and as many sustain pulses as the number four times that in the subfield of luminance weight “2” are generated in the sustain period. Therefore, in the subfield of luminance weight “8”, light is emitted at a luminance about eight times that in the subfield of luminance weight “1” and light is emitted at a luminance about four times that in the subfield of luminance weight “2”. As a result, various gradations can be displayed by selectively emitting light in each subfield using a combination corresponding to the image signal, and an image can be displayed.
In the present exemplary embodiment, a structure example is described where one field is formed of 8 subfields (first SF, second SF, . . . , eighth SF), and the respective subfields have luminance weights of (1, 2, 4, 8, 16, 32, 64, 128) so that the luminance weights sequentially increase as subfields are sequentially generated. In this structure, each of the R signal, G signal, and B signal is displayed at 256 gradations (0 through 255).
In the initializing period of one of a plurality of subfields, an all-cell initializing operation of causing initializing discharge in all discharge cells is performed. In the initializing periods of the other subfields, a selective initializing operation of selectively causing initializing discharge in the discharge cell having undergone sustain discharge in the sustain period in the immediately preceding subfield is performed. Thus, the light emission related to no gradation display is minimized, the emission luminance in a black region that does not cause sustain discharge is reduced, and the contrast ratio of the image displayed on panel 10 can be improved. Hereinafter, the subfield for performing the all-cell initializing operation is referred to as “all-cell initializing subfield”, and the subfield for performing the selective initializing operation is referred to as “selective initializing subfield”.
In the present exemplary embodiment, an example is described where the all-cell initializing operation is performed in the initializing period of the first SF and the selective initializing operation is performed in the initializing periods of the second SF through eighth SF. Thus, the light emission related to no image display is only light emission following the discharge of the all-cell initializing operation in the first SF. Therefore, the luminance of black level, which is luminance in a black displaying region that does not cause sustain discharge, is therefore determined only by weak light emission in the all-cell initializing operation. An image of sharp contrast can be displayed on panel 10.
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 proportionality constant are applied to each of display electrode pairs 24. This proportionality constant is luminance magnification.
In the present exemplary embodiment, when the luminance magnification is one, four sustain pulses are generated in the sustain period of the subfield of luminance weight “2”, and two sustain pulses are applied to each of scan electrode 22 and sustain electrode 23. In other words, in the sustain period, as many sustain pulses as the number derived by multiplying the luminance weight of each subfield by a predetermined luminance magnification are applied to each of scan electrode 22 and sustain electrode 23. Therefore, when the luminance magnification is two, the number of sustain pulses generated in the sustain period of the subfield of luminance weight “2” is eight. When the luminance magnification is three, the number of sustain pulses generated in the sustain period of the subfield of luminance weight “2” is 12.
In the present exemplary embodiment, however, the number of subfields constituting one field and the luminance weight of each subfield are not limited to the above-mentioned numerical values. The subfield structure may be changed based on an image signal or the like.
In the present exemplary embodiment, the number of generated sustain pulses is altered in response to the light-emitting rates of each subfield detected by all-cell light-emitting rate detecting circuit 46 and partial light-emitting rate detecting circuit 47 that are described later. Here, each of the light-emitting rates means the ratio of the number of discharge cells to be lit to a predetermined number of discharge cells. Thus, the linearity of the gradation in the display image on panel 10 is kept, and the image display quality is improved. Hereinafter, the outline of the driving voltage waveforms and the configuration of driver circuits are firstly described, and then a configuration for controlling the number of generated sustain pulses in response to the light-emitting rates is described.
SC1 for firstly performing an address operation in the address period, scan electrode SCn for finally performing the address operation in the address period, sustain electrode SU1 through sustain electrode SUn, and data electrode D1 through data electrode Dm.
First, the first SF, which is an all-cell initializing subfield, is described.
In the first half of the initializing period of the first SF, voltage 0 (V) is applied to data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn. Voltage Vi1 is applied to scan electrode SC1 through scan electrode SCn. Voltage Vi1 is set at a voltage lower than the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn. Then, a ramp waveform voltage, which gently increases from voltage Vi1 to voltage Vi2, is applied to scan electrode SC1 through scan electrode SCn. Hereinafter, the ramp waveform voltage is referred to as “up-ramp voltage L1”. Voltage Vi2 is set at a voltage exceeding the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn. As one example of the gradient of up-ramp voltage L1, a numerical value of about 1.3 V/μsec can be used.
While up-ramp voltage L1 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. Then, 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. The wall voltage on the electrode means voltage generated by the wall charge accumulated on the dielectric layer for covering the electrodes, the protective layer, or the phosphor layers.
In the latter half of the initializing period, positive voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, and voltage 0 (V) is applied to data electrode D1 through data electrode Dm. Ramp waveform voltage, which gently decreases from voltage Vi3 to negative voltage Vi4, is applied to scan electrode SC 1 through scan electrode SCn. Hereinafter, this ramp waveform voltage is referred to as “down-ramp voltage L2”. Voltage Vi3 is set at a voltage lower than the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn, and voltage Vi4 is set at a voltage exceeding the discharge start voltage. As one example of the gradient of down-ramp voltage L2, a numerical value of about −2.5 V/μsec can be used.
While down-ramp voltage L2 is applied to scan electrode SC1 through scan electrode SCn, feeble initializing discharge occurs between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and feeble initializing discharge occurs between scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm. Then, the negative wall voltage accumulated on scan electrode SC1 through scan electrode SCn and the positive wall voltage accumulated on sustain electrode SU 1 through sustain electrode SUn are reduced, and the positive wall voltage accumulated on data electrode D1 through data electrode Dm is adjusted to a value suitable for an address operation. Thus, the all-cell initializing operation of causing initializing discharge in all discharge cells is completed.
In the subsequent address period, scan pulses of voltage Va are sequentially applied to scan electrode SC 1 through scan electrode SCn. An address pulse of positive voltage Vd is applied to data electrode Dk corresponding to the discharge cell to emit light, of data electrode D1 through data electrode Dm. Thus, address discharge is selectively caused to each discharge cell.
Specifically, 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. Then, a scan pulse of negative voltage Va is applied to scan electrode SC1 in the first row, and an address pulse of positive voltage Vd is applied to data electrode Dk of the discharge cell to emit light in the first row, of data electrode D1 through data electrode Dm. 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 (voltage Vd−voltage Va) of the external applied voltage. Thus, the voltage difference between data electrode Dk and scan electrode SC1 exceeds the discharge start voltage, and discharge 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 (voltage Ve2−voltage 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, the address operation is performed where address discharge is caused in the discharge cell to emit light in the first row and wall voltage is accumulated on each electrode. The voltage in the part where scan electrode SC1 intersects with data electrode 32 to which no address pulse has been applied does not exceed the discharge start voltage, so that address discharge does not occur. This address operation is performed until it reaches the discharge cell in the n-th row, and the address period is completed.
In the subsequent sustain period, as many sustain pulses as the number derived by multiplying the luminance weight by a predetermined luminance magnification are alternately applied to display electrode pairs 24, sustain discharge is caused in the discharge cell having undergone the address discharge, and light is emitted in the discharge cell.
In the sustain period, firstly, a sustain pulse of positive voltage Vs is applied to scan electrode SC1 through scan electrode SCn, and ground potential as base potential, namely 0 (V), is applied to sustain electrode SU1 through sustain electrode SUn. In the discharge cell having undergone 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 voltage Vs of the sustain pulses.
Thus, the voltage difference between scan electrode SCi and sustain electrode SUi exceeds the discharge start voltage, and sustain discharge occurs between scan electrode SCi and sustain electrode SUi. Ultraviolet rays generated by this discharge cause phosphor layer 35 to emit light. By this discharge, negative wall voltage is accumulated on scan electrode SCi, and positive wall voltage is accumulated on sustain electrode SUi. Positive wall voltage is also accumulated on data electrode Dk. In the discharge cell having undergone no address discharge in the address period, sustain discharge does not occur, and the wall voltage at the completion of the initializing period is kept.
Subsequently, 0 (V) as base potential is applied to scan electrode SC1 through scan electrode SCn, and a sustain pulse 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. Thus, 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 the luminance magnification are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn. Thus, sustain discharge is continuously caused in the discharge cell having undergone the address discharge in the address period.
After generation of a sustain pulse in the sustain period, in the state where voltage 0 (V) is applied to sustain electrode SU1 through sustain electrode SUn and data electrode D1 through data electrode Dm, ramp waveform voltage, which gently increases from 0 (V) to voltage Vers, is applied to scan electrode SC1 through scan electrode SCn. Hereinafter, the ramp waveform voltage is referred to as “erasing ramp voltage L3”.
The gradient of erasing ramp voltage L3 is set to be steeper than that of up-ramp voltage L1. As one example of the gradient of erasing ramp voltage L3, a numerical value of about 10 V/μsec can be used. When voltage Vers is set at a voltage exceeding the discharge start voltage, feeble discharge occurs between sustain electrode SUi and scan electrode SCi in the discharge cell having undergone sustain discharge. This feeble discharge continuously occurs while the voltage applied to scan electrode SC1 through scan electrode SCn increases beyond the discharge start voltage.
Charged particles generated by the feeble discharge are accumulated on sustain electrode SUi and scan electrode SCi so as to reduce the voltage difference between sustain electrode SUi and scan electrode SCi. Therefore, in the discharge cell having undergone the sustain discharge, a part or the whole of the wall voltages on scan electrode SCi and sustain electrode SUi is erased while the positive wall voltage is left on data electrode Dk. In other words, the discharge caused by erasing ramp voltage L3 works as “erasing discharge” for erasing unnecessary wall charge in the discharge cell having undergone the sustain discharge.
When the increasing voltage arrives at predetermined voltage Vers, the voltage applied to scan electrode SC 1 through scan electrode SCn is decreased to 0 (V) as base potential. Thus, the sustain operation in the sustain period is completed.
In the initializing period of the second SF, the driving voltage waveform where the first half of the initializing period of the first SF is omitted is applied to each electrode. Voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, and voltage 0 (V) is applied to data electrode D1 through data electrode Dm. Down-ramp voltage L4, which gently decreases from voltage Vi3′ (e.g. voltage 0 (V)) lower than the discharge start voltage to negative voltage Vi4 exceeding the discharge start voltage, is applied to scan electrode SC1 through scan electrode SCn. As one example of the gradient of down-ramp voltage L4, a numerical value of about −2.5 V/μsec can be used.
Thus, feeble initializing discharge occurs in the discharge cell having undergone the sustain discharge in the sustain period of the immediately preceding subfield (first SF in
In the address period and sustain period of the second SF, driving voltage waveforms similar to those in the address period and sustain period of the first SF are applied to each electrode except for the number of generated sustain pulses. In each of the third SF and later, a driving voltage waveform similar to that in the second SF is applied to each electrode except for the number of generated sustain pulses.
The driving voltage waveform applied to each electrode of panel 10 of the present exemplary embodiment has been described schematically.
Next, the configuration of the plasma display apparatus of the present exemplary embodiment is described.
Image signal processing circuit 41 assigns a gradation value to each discharge cell based on input image signal sig. Then, image signal processing circuit 41 converts the gradation value into image data that indicates light emission or no light emission in each subfield.
For example, when input image signal sig includes an R signal, G signal, and B signal, image signal processing circuit 41 assigns each gradation value of R, G, and B to each discharge cell based on the R signal, G signal, and B signal. Alternatively, when input image signal sig includes a luminance signal (Y signal) and a chroma signal (C signal, R-Y signal and B-Y signal, or u signal and v signal), image signal processing circuit 41 calculates the R signal, G signal, and B signal based on the luminance signal and chroma signal, and then assigns each gradation value (gradation value represented in one field) of R, G, and B to each discharge cell. Image signal processing circuit 41 converts each gradation value of R, G, and B assigned to each discharge cell into image data that indicates light emission or no light emission in each subfield.
Based on the image data for each subfield, all-cell light-emitting rate detecting circuit 46 detects, as “all-cell light-emitting rate”, the ratio of the number of discharge cells to be lit to the total number of discharge cells in the image display surface of panel 10 in each subfield. All-cell light-emitting rate detecting circuit 46 outputs a signal indicating the detected all-cell light-emitting rate to timing generation circuit 45.
Partial light-emitting rate detecting circuit 47 divides the image display surface of panel 10 into a plurality of regions and detects, as “partial light-emitting rate”, the ratio of the number of discharge cells to be lit to the number of discharge cells in each region in each subfield based on the image data in each subfield. Partial light-emitting rate detecting circuit 47 may be configured to detect the partial light-emitting rate while the region constituted by a plurality of scan electrodes 22 that is connected to one of integrated circuits (ICs) (hereinafter referred to as “scan ICs”) for driving scan electrodes 22 is set as one region, for example. In the present exemplary embodiment, however, the partial light-emitting rate is detected while one display electrode pair 24 is considered as one region.
Partial light-emitting rate detecting circuit 47 includes average value detecting circuit 48. Average value detecting circuit 48 compares the partial light-emitting rate detected by partial light-emitting rate detecting circuit 47 with a predetermined threshold. Hereinafter, the predetermined threshold is referred to as “partial light-emitting rate threshold”. Then, average value detecting circuit 48 calculates, in each subfield, the average value of the partial light-emitting rates in display electrode pairs 24 other than display electrode pairs 24 where the partial light-emitting rate is the partial light-emitting rate threshold or lower, namely in display electrode pairs 24 where the partial light-emitting rate exceeds the partial light-emitting rate threshold. Then, average value detecting circuit 48 outputs a signal that indicates the result to timing generation circuit 45. For example, it is assumed that the number of display electrode pairs 24 disposed on panel 10 is 1080 and the partial light-emitting rates of 200 display electrode pairs 24 are the partial light-emitting rate threshold or lower in a certain subfield. In this case, in the certain subfield, average value detecting circuit 48 calculates the average value of the partial light-emitting rates of 880 display electrode pairs 24 where the partial light-emitting rate exceeds the partial light-emitting rate threshold.
In the present exemplary embodiment, the partial light-emitting rate threshold is set at “0%”. The purpose of this setting is to omit display electrode pairs 24 where a discharge cell to be lit does not substantially occur when an average value of the partial light-emitting rates is calculated.
However, the partial light-emitting rate threshold of the present invention is not limited to the above-mentioned numerical value. Preferably, the partial light-emitting rate threshold is set at the optimal value based on the characteristics of panel 10 and the specification of plasma display apparatus 1.
In the present exemplary embodiment, a normalizing operation for percentage notation (% notation) is performed when the all-cell light-emitting rate and partial light-emitting rates are calculated. However, the normalizing operation is not necessarily required. For example, the calculated number of discharge cells to be lit may be used instead of the all-cell light-emitting rate and partial light-emitting rates. Hereinafter, a discharge cell to be lit is referred to as “lit cell”, and a discharge cell that is not to be lit is referred to as “unlit cell”.
Timing generation circuit 45 generates various timing signals for controlling the operation of each circuit block based on horizontal synchronizing signal H, vertical synchronizing signal V, and outputs from all-cell light-emitting rate detecting circuit 46 and partial light-emitting rate detecting circuit 47. Then, timing generation circuit 45 supplies the generated timing signals to respective circuit blocks (image signal processing circuit 41, data electrode driver circuit 42, scan electrode driver circuit 43, and sustain electrode driver circuit 44).
In the present exemplary embodiment, as discussed above, the number of generated sustain pulses is altered in response to the all-cell light-emitting rate and the average value of the partial light-emitting rates. Specifically, the number of generated sustain pulses, which is set by timing generation circuit 45 based on the input image signal and the luminance weight set for each subfield, is altered by correcting the number of generated sustain pulses using a correction coefficient that is determined based on the all-cell light-emitting rate and the average value of the partial light-emitting rates. For this purpose, timing generation circuit 45 has a number-of-sustain-pulses correcting section (not shown) capable of correcting the number of generated sustain pulses based on the all-cell light-emitting rate and the average value of the partial light-emitting rates.
In the present exemplary embodiment, the number-of-sustain-pulses correcting section has a look-up table that can previously store a plurality of different correction coefficients in association with the all-cell light-emitting rate and the partial light-emitting rates, and can read one of the correction coefficients in response to the all-cell light-emitting rate and the average value of the partial light-emitting rates. The details of these configurations are described later. However, the present invention is not limited to these configurations. Any configuration may be employed as long as it performs the same operation.
Scan electrode driver circuit 43 has an initializing waveform generation circuit (not shown), sustain pulse generation circuit 50, and a scan pulse generation circuit (not shown). The initializing waveform generation circuit generates an initializing waveform to be applied to scan electrode SC1 through scan electrode SCn in the initializing period. Sustain pulse generation circuit 50 generates a sustain pulse to be applied to scan electrode SC1 through scan electrode SCn in the sustain period. The scan pulse generation circuit has a plurality of scan electrode driver ICs (scan ICs), and generates a scan pulse to be applied to scan electrode SC1 through scan electrode SCn in the address period. Scan electrode driver circuit 43 drives each of scan electrode SC1 through scan electrode SCn based on the timing signal supplied from timing generation circuit 45.
Data electrode driver circuit 42 converts the data, which constitutes image data, of each subfield into a signal corresponding to each of data electrode D1 through data electrode Dm. Data electrode driver circuit 42 drives each of data electrode D1 through data electrode Dm based on the converted signal and the timing signal supplied from timing generation circuit 45.
Sustain electrode driver circuit 44 has sustain pulse generation circuit 80 and a circuit (not shown) for generating voltage Ve1 and voltage Ve2. Sustain electrode driver circuit 44 drives sustain electrode SU1 through sustain electrode SUn based on the timing signal supplied from timing generation circuit 45.
Next, the details and operation of scan electrode driver circuit 43 are described. In the following description, an operation of turning on a switching element is denoted as “ON”, and an operation of turning off it is denoted as “OFF”. A signal for setting the switching element at ON is denoted as “Hi”, and a signal for setting it at OFF is denoted as “Lo”.
Initializing waveform generation circuit 53 generates initializing waveforms of
Sustain pulse generation circuit 50 includes power recovery circuit 51 and clamping circuit 52.
Power recovery circuit 51 includes capacitor C10 for power recovery, switching element Q11, switching element Q12, diode D11 for back flow prevention, diode D12 for back flow prevention, and inductor L10 for resonance. Power recovery circuit 51 raises and drops a sustain pulse by LC-resonance between inter-electrode capacity Cp and inductor L10.
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 base potential. Clamping circuit 52 connects scan electrode SC1 through scan electrode SCn to power supply VS via switching element Q13, thereby clamping them on voltage Vs. Clamping circuit 52 connects scan electrode SC1 through scan electrode SCn to the ground potential to clamp them on 0 (V) via switching element Q14. Sustain pulse generation circuit 50 generates a sustain pulse by operating power recovery circuit 51 and clamping circuit 52 by switching each of switching element Q11, switching element Q12, switching element Q13, and switching element Q14 between turn on and turn off in response to the timing signal output from timing generation circuit 45.
For example, for raising a sustain pulse, switching element Q11 is set at ON to cause resonance between inter-electrode capacity Cp and inductor L10, and supplies electric power from capacitor C10 for power recovery 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. Thus, a circuit for driving scan electrode SC1 through scan electrode SCn is switched from power recovery circuit 51 to clamping circuit 52, and scan electrode SC1 through scan electrode SCn are clamped on voltage Vs.
Conversely, for dropping a sustain pulse, switching element Q12 is set at ON to cause resonance between inter-electrode capacity Cp and inductor L10, and recovers electric power from inter-electrode capacity Cp to capacitor C10 for power recovery 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. Thus, a circuit for driving scan electrode SC1 through scan electrode SCn is switched from power recovery circuit 51 to clamping circuit 52, and scan electrode SC1 through scan electrode SCn are clamped on 0 (V) as base potential.
These switching elements can be formed using a generally known element such as a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).
Sustain pulse generation circuit 54 includes the following elements:
When initializing waveform generation circuit 53 or sustain pulse generation circuit 50 is being operated, by setting switching element QH1 through switching element QHn at OFF and setting switching element QL1 through switching element QLn at ON, an initializing waveform or sustain pulse is applied to each of scan electrode SC1 through scan electrode SCn via switching element QL1 through switching element QLn.
Sustain electrode driver circuit 44 has sustain pulse generation circuit 80 having a configuration similar to that of sustain pulse generation circuit 50. Sustain pulse generation circuit 80 includes power recovery circuit 81 and clamping circuit 82, and is connected to sustain electrode SU1 through sustain electrode SUn of panel 10. Thus, the output voltage of sustain electrode driver circuit 44 is applied to all of sustain electrodes 23 in parallel, and sustain electrode driver circuit 44 drives all of sustain electrodes 23 collectively. This is because, in either of the address period and sustain period, individual driving of sustain electrodes 23 is not required differently from scan electrodes 22 and driving voltage is applied to all of sustain electrodes 23 collectively.
Power recovery circuit 81 includes capacitor C20 for power recovery, switching element Q21, switching element Q22, diode D21 for back flow prevention, diode D22 for back flow prevention, and inductor L20 for resonance. Clamping circuit 82 has switching element Q23 for clamping sustain electrode SU1 through sustain electrode SUn on voltage Vs, and switching element Q24 for clamping sustain electrode SU1 through sustain electrode SUn on ground potential (0 (V)).
Sustain pulse generation circuit 80 generates a sustain pulse while switching each switching element between ON and OFF based on the timing signal output from timing generation circuit 45. The operation of sustain pulse generation circuit 80 is similar to that of sustain pulse generation circuit 50, and hence is not described.
Sustain electrode driver circuit 44 includes the following elements:
Next, the difference in emission luminance caused by variation in driving load is described.
When light is emitted on panel 10 while the area of the lit region is altered as shown in
Display electrode pairs 24 are extended in the row direction as discussed above. Therefore, when light is emitted on panel 10 while the lit region is altered as shown in
In other words, in order to accurately estimate the variation in emission luminance in lit cells, preferably, both the all-cell light-emitting rate and the partial light-emitting rates on panel 10 are detected.
Thus, in the present exemplary embodiment, the all-cell light-emitting rate and the partial light-emitting rates are detected for each subfield. In the present exemplary embodiment, the average value of the partial light-emitting rates is detected. In other words, in the present exemplary embodiment, the all-cell light-emitting rate and the average value of the partial light-emitting rates are detected for each subfield.
The number of generated sustain pulses in the sustain period of the subfield having undergone the detection is altered based on the detection result, and the luminance generated in the sustain period is controlled. This luminance means the luminance obtained by accumulating the emitted light generated by sustain discharge in the sustain period. The luminance in each subfield is thus kept at a predetermined brightness. Thus, the linearity of the gradation in the display image is kept, and the image display quality can be improved.
In the present exemplary embodiment, the number of generated sustain pulses set based on the input image signal and luminance weight is corrected using a correction coefficient that is set based on the all-cell light-emitting rate and the average value of the partial light-emitting rates. In the sustain period, as many sustain pulses as the number after the correction are generated. Thus, the number of generated sustain pulses is controlled.
Next, one example of a setting method of the correction coefficient is described.
For example, an image is displayed where the length of the row direction (horizontal direction in
Next, an image is displayed where the length of the row direction of the lit region is 10% of that of the image display surface of panel 10 and the length of the column direction of the lit region is 20% of that of the image display surface, and the emission luminance of the lit region is measured. Thus, the emission luminance of the image where the all-cell light-emitting rate is 2% and the average value of the partial light-emitting rates is 10% can be acquired.
Similarly, the emission luminance is measured while the lit region is gradually enlarged. By repeating the measurement, respective emission luminances of a plurality of images having different all-cell light-emitting rate and different average value of partial light-emitting rates can be acquired.
Then, a reference emission luminance is set at “1”, and each emission luminance is normalized. For example, the emission luminance of the image where the all-cell light-emitting rate and the average value of the partial light-emitting rates are 100% is assumed to be the reference emission luminance, and each emission luminance is normalized. The inverse of each numerical value is then calculated. In the present exemplary embodiment, the calculation result is set as the correction coefficient. For example, it is assumed that the emission luminance of the image where the all-cell light-emitting rate and the average value of the partial light-emitting rates are 100% is set at “1”. When the emission luminance of an image where the all-cell light-emitting rate is 5% and the average value of the partial light-emitting rates is 40% is “1.25”, the inverse of “1.25”, namely “0.80”, is set as the correction coefficient when the all-cell light-emitting rate is 5% and the average value of partial light-emitting rates is 40%.
As shown in
Number-of-sustain-pulses correcting section 61 has look-up table 62 (“LUT” in
Then, timing generation circuit 45 generates a timing signal for controlling each circuit block so that as many sustain pulses as the number of sustain pulses after correction output from after-correction number-of-sustain-pulses setting section 63 are output from sustain pulse generation circuit 50 and sustain pulse generation circuit 80.
In
In the present exemplary embodiment, as shown in
For example, it is assumed that the number of generated sustain pulses set based on the input image signal and luminance weight in the sixth SF is “128”. It is also assumed that the all-cell light-emitting rate in the sixth SF is 5% and the average value of the partial light-emitting rates is 45%. In this case, the correction coefficient acquired from the data of look-up table 62 of
In the present exemplary embodiment, thus, the luminance of each subfield can be always equal to a predetermined luminance regardless of the lit state of the discharge cell, by correcting the number of generated sustain pulses set based on the input image signal and luminance weight by using a correction coefficient that is determined based on the all-cell light-emitting rate and the average value of the partial light-emitting rates in each subfield. For example, the predetermined luminance is the luminance when the all-cell light-emitting rate is 100%.
As discussed above, in the present exemplary embodiment, the all-cell light-emitting rate and the average value of the partial light-emitting rates are detected in each subfield. One correction coefficient is read from look-up table 62 based on the all-cell light-emitting rate and the average value of the partial light-emitting rates that are detected for each subfield. Here, look-up table 62 previously stores a plurality of preset correction coefficients in association with the all-cell light-emitting rate and the average value of the partial light-emitting rates. Then, after-correction number-of-sustain-pulses setting section 63 corrects the number of generated sustain pulses set based on the input image signal and luminance weight by using the correction coefficient. Thanks to such a configuration, the variation in emission luminance occurring in each subfield can be estimated accurately, and the luminance of each subfield can be always kept at a predetermined luminance (for example, the luminance when the all-cell light-emitting rate is 100%) based on the estimation result. Therefore, the linearity of gradation in the display image can be kept and the image display quality can be enhanced.
In the present exemplary embodiment, the configuration has been described where each correction coefficient is set while the maximum value of the correction coefficients is assumed to be “1”. In this case, the number of sustain pulses after correction is equal to or smaller than the number of sustain pulses before correction. This configuration is simply one example that is effective when the total period required for each subfield arrives at about one-field period and it is therefore difficult to increase the number of sustain pulses by extending the sustain period. The present invention is not limited to this configuration. In a case where the total period required for each subfield is shorter than one-field period and the number of sustain pulses can be increased by extending the sustain period, for example a case where the luminance magnification is small, plasma display apparatus 1 may have the following configuration:
In the first exemplary embodiment, the configuration has been described where each correction coefficient is set so that the maximum value of the correction coefficients is “1”. In this case, the number of sustain pulses after correction is equal to or smaller than the number of sustain pulses before correction. When the number of sustain pulses after correction is smaller than that before correction, the luminance of a display image decreases. In the second exemplary embodiment, the configuration is described where, after the correction of the first exemplary embodiment, new correction is performed where the total number of sustain pulses generated in one field period is equivalent to that before the former correction. In the present exemplary embodiment, in order to differentiate between these corrections, the correction of the first exemplary embodiment is called “first correction” and the correction coefficient used for “first correction” is called “first correction coefficient”. The new correction of the present exemplary embodiment is called “second correction” and the correction coefficient used for “second correction” is called “second correction coefficient”. “First correction coefficient” is set for each subfield, and “second correction coefficient” is commonly set for all subfields in one field.
In
After-first-correction number-of-sustain-pulses summarizing section 68 accumulates the numbers of sustain pulses after “first correction” in respective subfields output from after-first-correction number-of-sustain-pulses setting section 63 for one field period. Thus, when “first correction” is performed, the total number of sustain pulses generated in one field period is calculated.
Before-correction number-of-sustain-pulses summarizing section 69 accumulates the numbers of sustain pulses in respective subfields set based on the input image signal and luminance weight for one field period. Thus, when “first correction” is not performed (hereinafter referred to as “before “first correction””), the total number of sustain pulses generated in one field period is calculated.
Second-correction-coefficient calculating section 71 divides the numerical value output from before-correction number-of-sustain-pulses summarizing section 69 by the numerical value output from after-first-correction number-of-sustain-pulses summarizing section 68. In other words, the total number of sustain pulses generated in one field period when “first correction” is not performed is divided by the total number of sustain pulses generated in one field period when “first correction” is performed. This operation result is “second correction coefficient” in the present exemplary embodiment.
After-second-correction number-of-sustain-pulses setting section 73 multiplies the numerical value output from after-first-correction number-of-sustain-pulses setting section 63 by “second correction coefficient” output from second-correction-coefficient calculating section 71. In other words, the number of sustain pulses after “first correction” in each subfield is multiplied by “second correction coefficient” output from second-correction-coefficient calculating section 71. This multiplication result is “number of sustain pulses after second correction”. After-second-correction number-of-sustain-pulses setting section 73 outputs the number of sustain pulses after second correction.
Timing generation circuit 60 generates a timing signal for controlling each circuit block so that, in each subfield, as many sustain pulses as the number of sustain pulses after second correction output from after-second-correction number-of-sustain-pulses setting section 73 are output from sustain pulse generation circuit 50 and sustain pulse generation circuit 80.
Next, “second correction” of the present exemplary embodiment is described using a specific numerical value.
For example, when the number of sustain pulses generated based on the input image signal and luminance weight is (4, 8, 16, 32, 64, 128, 256, and 512) in the first SF through eighth SF, respectively, the total number of sustain pulses in one field period calculated by before-correction number-of-sustain-pulses summarizing section 69 is “1020”.
It is assumed that “first correction coefficient” read from look-up table 62 based on the all-cell light-emitting rate and the average value of the partial light-emitting rates is (1.00, 0.98, 0.92, 0.90, 0.85, 0.80, 0.74, and 0.70) in the first SF through eighth SF, respectively. In this case, the number of sustain pulses after “first correction” calculated by after-first-correction number-of-sustain-pulses setting section 63 is (4, 8, 15, 29, 54, 102, 189, and 358) (the fractional portion is rounded) in the first SF through eighth SF, respectively.
Therefore, the total number of these numerical values, namely the numerical value output from after-first-correction number-of-sustain-pulses summarizing section 68, is “759”. According to these results, the number of sustain pulses generated in one field period after “first correction” is “759”, which is “261” smaller than the number (“1020”) of sustain pulses generated in one field period before “first correction”.
Next, second-correction-coefficient calculating section 71 divides “1020” calculated by before-correction number-of-sustain-pulses summarizing section 69 by “759” calculated by after-first-correction number-of-sustain-pulses summarizing section 68, and obtains “second correction coefficient”=“1.344”.
Then, after-second-correction number-of-sustain-pulses setting section 73 multiplies “1.344” obtained as “second correction coefficient” by the numbers (4, 8, 15, 29, 54, 102, 189, and 358) of sustain pulses in the first SF through eighth SF calculated by after-first-correction number-of-sustain-pulses setting section 63.
Thus, the number of sustain pulses generated after “second correction” is (5, 11, 20, 39, 73, 137, 254, and 481) (the fractional portion is rounded) in the first SF through eighth SF, respectively. The total number of these numerical values is “1020”. Therefore, thanks to “second correction”, the number of sustain pulses generated in one field period can be made equal to the total number “1020” of sustain pulses before “first correction”.
As discussed above, in the present exemplary embodiment, “second correction” capable of making the total number of sustain pulses in one field period equivalent to that before “first correction” is performed, in addition to “first correction” of the first exemplary embodiment. Thanks to such a configuration, the linearity of gradation in the display image can be kept, the reduction in brightness of the display image can be prevented, and hence the image display quality can be improved.
In the configuration of the present exemplary embodiment, the total number of sustain pulses in one field period after “second correction” can be made equivalent to that before “first correction”. Therefore, even when the total period required for each subfield arrives at about one-field period and increase of the number of sustain pulses by extension of the sustain period is difficult, the maximum value of the correction coefficients stored on look-up table 62 by “first correction” can be made larger than “1”. Therefore, the degree of freedom of the setting range of the correction coefficient can be increased.
In the second exemplary embodiment, the configuration has been described where “second correction” for making the total number of sustain pulses generated in one field period equivalent to that before “first correction” is performed. In this configuration, however, the power consumption after “second correction” can be larger than that before “first correction”. In the third exemplary embodiment, the configuration is described where, after “first correction” of the first exemplary embodiment, another new correction is performed where the estimated value of the power consumption in one field period is equivalent to that when “first correction” is not performed. In the present exemplary embodiment, in order to differentiate between these corrections, the new correction of the third exemplary embodiment is called “third correction” and the correction coefficient used for “third correction” is called “third correction coefficient”. “Third correction coefficient” is commonly set for all subfields in one field.
In
Multiplying section 74 multiplies the number of sustain pulses set for each subfield based on the input image signal and the luminance weight by the all-cell light-emitting rate of the subfield. Thus, the estimated value of the power consumption in each sustain period when an image is displayed without “first correction” is calculated.
Sum total calculating section 76 calculates the sum total in one field period of the multiplication results output from multiplying section 74. Thus, sum total calculating section 76 calculates the sum total in one field period of the estimated values of the power consumption in respective sustain periods when an image is displayed without “first correction”.
Multiplying section 75 multiplies the number of sustain pulses after “first correction” of each subfield output from after-first-correction number-of-sustain-pulses setting section 63 by the all-cell light-emitting rate of the subfield. Thus, the estimated value of the power consumption in each sustain period when an image is displayed only through “first correction” is calculated.
Sum total calculating section 77 calculates the sum total in one field period of the multiplication results output from multiplying section 75. Thus, sum total calculating section 77 calculates the sum total in one field period of the estimated values of the power consumption in respective sustain periods when an image is displayed only through “first correction”.
The numerical values calculated by sum total calculating section 76 and sum total calculating section 77 indicate the estimated values of the power consumption in the sustain period, but do not indicate the power consumption in a strict sense. These estimated values are just approximate values that are determined by using the following phenomenon:
Third-correction-coefficient calculating section 78 divides the numerical value output from sum total calculating section 76 by the numerical value output from sum total calculating section 77. In other words, third-correction-coefficient calculating section 78 divides the estimated value of the power consumption when an image is displayed without “first correction” by that when an image is displayed only through “first correction”. This operation result is “third correction coefficient” of the present exemplary embodiment.
After-third-correction number-of-sustain-pulses setting section 79 multiplies the numerical value output from after-first-correction number-of-sustain-pulses setting section 63 by “third correction coefficient” output from third-correction-coefficient calculating section 78. In other words, the number of sustain pulses after “first correction” in each subfield is multiplied by “third correction coefficient” output from third-correction-coefficient calculating section 78. This multiplication result is “number of sustain pulses after third correction”. After-third-correction number-of-sustain-pulses setting section 79 outputs the number of sustain pulses after third correction.
Timing generation circuit 70 generates a timing signal for controlling each circuit block so that, in each subfield, as many sustain pulses as the number of sustain pulses after third correction output from after-third-correction number-of-sustain-pulses setting section 79 are output from sustain pulse generation circuit 50 and sustain pulse generation circuit 80.
Next, “third correction” of the present exemplary embodiment is described using a specific numerical value.
It is assumed that the all-cell light-emitting rate is (95%, 85%, 35%, 45%, 25%, 15%, 10%, and 5%) in the first SF through eighth SF, respectively. In this case, the numerical multiplication value calculated by multiplying the number of sustain pulses before “first correction” by the all-cell light-emitting rate with multiplying section 74 is (3.8, 6.8, 5.6, 14.4, 16, 19.2, 25.6, and 25.6) in the first SF through eighth SF, respectively.
Therefore, the total number of these numerical values, namely the numerical value output from sum total calculating section 76, is “117”. The total number (appropriate value) of power consumption in each sustain period when an image is displayed without “first correction” is “117”.
Similarly, the numerical multiplication value calculated by multiplying the number of sustain pulses after “first correction” by the all-cell light-emitting rate with multiplying section 75 is (3.8, 6.8, 5.25, 13.05, 13.5, 15.3, 18.9, and 17.9) in the first SF through eighth SF, respectively.
Therefore, the total number of these numerical values, namely the numerical value output from sum total calculating section 77, is “94.5”. The total number (appropriate value) of power consumption in each sustain period when an image is displayed only through “first correction” is “94.5”.
According to these results, the total number (appropriate value) of power consumption in each sustain period when an image is displayed only through “first correction”, namely “94.5”, is smaller than that when an image is displayed without “first correction”, namely “117”.
Next, third-correction-coefficient calculating section 78 divides “117” calculated by sum total calculating section 76 by “94.5” calculated by sum total calculating section 77, and obtains “third correction coefficient”=“1.238”.
Then, after-third-correction number-of-sustain-pulses setting section 79 multiplies “1.238” obtained as “third correction coefficient” by the numbers (4, 8, 15, 29, 54, 102, 189, and 358) of sustain pulses in the first SF through eighth SF calculated by after-first-correction number-of-sustain-pulses setting section 63.
Thus, the number of sustain pulses generated in each subfield after “third correction” is (5, 10, 19, 36, 67, 126, 234, and 443) (the fractional portion is rounded) in the first SF through eighth SF, respectively. The result obtained by multiplying the number of sustain pulses in each subfield after “third correction” by the all-cell light-emitting rate is (4.75, 8.5, 6.65, 16.2, 16.75, 18.9, 23.4, and 22.15) in the first SF through eighth SF, respectively, and the sum total of these values is “117.3”. Therefore, by “third correction”, the power consumption in one field period can be made equivalent to the power consumption before “first correction”. The total number of sustain pulses in one field can be made larger than that when only “first correction” is performed, so that reduction in brightness of the display image can be prevented to improve the image display quality.
As discussed above, in the present exemplary embodiment, “third correction” capable of making the power consumption in one field period equivalent to the power consumption before “first correction” is performed, in addition to “first correction” of the first exemplary embodiment. Thanks to such a configuration, the linearity of gradation in the display image can be kept and reduction in brightness of the display image can be prevented while increase in power consumption is suppressed.
In the present exemplary embodiment, the estimated value of the power consumption in one field period after “third correction” can be made equivalent to that before “first correction”. Therefore, this configuration can be used for a configuration where the maximum value of the correction coefficients stored on look-up table 62 is larger than “1” and the estimated value of the power consumption in one field period after “first correction” is larger than that before “first correction”.
In the second exemplary embodiment, the configuration has been described where “second correction” for making the total number of sustain pulses generated in one field period equivalent to that before “first correction” is performed. In this configuration, however, the power consumption after “second correction” can be larger than that before “first correction”.
This is for the following reason: “first correction coefficient” is set for each of subfields as shown in the first exemplary embodiment, and “first correction coefficient” increases as the all-cell light-emitting rate increases or decreases as the all-cell light-emitting rate decreases, as shown in
Therefore, when the maximum value of “first correction coefficient” is set at “1”, the following phenomenon occurs:
When the maximum value of “first correction coefficient” is set at “1”, “first correction coefficient” of each subfield is “1” or smaller. Therefore, the total number of sustain pulses in one field period after “first correction” is not higher than that before “first correction”. As a result, “second correction coefficient” is “1” or larger.
“Second correction coefficient” is set commonly for all subfields in one field as discussed in the second exemplary embodiment. Therefore, in a subfield of a high all-cell light-emitting rate (for example, first SF through sixth SF of
The number of discharge cells to be lit is larger in a subfield of a high all-cell light-emitting rate than in a subfield of a low all-cell light-emitting rate, so that the electric power consumed by one sustain discharge also increases.
In other words, in a subfield where the electric power consumed by one sustain discharge is large (the all-cell light-emitting rate is high), the number of sustain pulses after “second correction” is apt to be larger than that before “first correction”. In a subfield where the electric power consumed by one sustain discharge is small (the all-cell light-emitting rate is low), the number of sustain pulses after “second correction” is apt to be smaller than that before “first correction”. As a result, it is considered that the power consumption after “second correction” can be larger than that before “first correction”.
However, the power consumption of plasma display apparatus 1 is smaller when the average picture level (APL) of an image signal is low than when the APL is high. Therefore, even if the power consumption is somewhat increased by “second correction”, a significant problem does not occur. In order to improve the image display quality, it is preferable that an image of a low APL can be displayed more brightly. When the APL is high, the power consumption of plasma display apparatus 1 increases, and hence “third correction” capable of preventing reduction in brightness of the display image while suppressing increase in power consumption is more preferable than “second correction” where the power consumption increases.
In the present exemplary embodiment, a configuration is described where “fourth correction” using “fourth correction coefficient” is performed after “first correction” of the first exemplary embodiment. “Fourth correction coefficient” is obtained by mixing “second correction coefficient” and “third correction coefficient” at a ratio corresponding to the magnitude of the APL, and is set commonly for all subfields in one field.
Plasma display apparatus 2 includes the following elements:
APL detecting circuit 49 detects the APL using a generally known method of accumulating the luminance value of an input image signal for one field period, and transmits the detection result to timing generation circuit 91.
In
Fourth-correction-coefficient calculating section 93 mixes “second correction coefficient” output from number-of-sustain-pulses correcting section 83 and “third correction coefficient” output from number-of-sustain-pulses correcting section 90 in response to the APL. Specifically, when the APL is lower than a first threshold (e.g. 20%), “second correction coefficient” is output as “fourth correction coefficient” in order to place a high priority on luminance improvement of a display image. When the APL is not lower than a second threshold (e.g. 30%), which is higher than the first threshold, “third correction coefficient” is output as “fourth correction coefficient” in order to place a high priority on suppression of power consumption. When the APL is the first threshold or higher and lower than the second threshold, “second correction coefficient” and “third correction coefficient” are mixed at a ratio corresponding to the magnitude of the APL, and the mixing result is output as “fourth correction coefficient”.
As a method of calculating “fourth correction coefficient”, for example, a method using variable k can be used.
For example, k=“0” when the APL is lower than the first threshold, k=“1” when the APL is not lower than the second threshold, and k=(APL−first threshold)/(second threshold−first threshold) when the APL is the first threshold or higher and lower than the second threshold.
Then, “fourth correction coefficient” is calculated by substituting variable k obtained from the above-mentioned calculation equation into the following calculation equation:
“fourth correction coefficient”=(1−k)דsecond correction coefficient”+kדthird correction coefficient”.
For example, such a calculation method can be used as one example of a method of calculating “fourth correction coefficient”.
In the present invention, however, the method of calculating “fourth correction coefficient” is not limited to the above-mentioned method. “Fourth correction coefficient” may be calculated in another method, for example, by raising variable k to the power of 2 or raising variable k to the power of ½.
After-fourth-correction number-of-sustain-pulses setting section 94 multiplies the number of sustain pulses after first correction output from after-first-correction number-of-sustain-pulses setting section 63 (not shown in
Then, timing generation circuit 91 generates a timing signal for controlling each circuit block so that, in each subfield, as many sustain pulses as the number of sustain pulses after fourth correction output from after-fourth-correction number-of-sustain-pulses setting section 94 are output from sustain pulse generation circuit 50 and sustain pulse generation circuit 80.
As discussed above, in the present exemplary embodiment, when the APL of the input image signal is low (APL is lower than the first threshold), “second correction” that places a high priority on the brightness of the display image is performed in addition to “first correction” of the first exemplary embodiment. When the APL of the input image signal is high (APL is the second threshold or higher), “third correction” capable of preventing the reduction in brightness of the display image while suppressing the increase in power consumption is performed. When the APL is the first threshold or higher and lower than the second threshold, “fourth correction” is performed where “fourth correction coefficient” is obtained by mixing “second correction coefficient” and “third correction coefficient” at a ratio corresponding to the magnitude of the APL. In such a configuration, the linearity of the gradation in the display image can be kept, and the reduction in brightness of the display image can be prevented while the increase in power consumption is suppressed.
In the third exemplary embodiment, the following configuration has been described: after “first correction” of the first exemplary embodiment, “third correction” that makes the estimated value of the power consumption in one field period equivalent to that before “first correction” is performed. The configuration has been also described where, in each subfield, the number of sustain pulses is multiplied by the all-cell light-emitting rate, the sum total of the multiplication results in one field period is calculated, thereby calculating the estimated value of the power consumption in one field period. However, the estimated value of the power consumption can be calculated at an increased accuracy, and the accuracy of “third correction” can be increased. In the fifth exemplary embodiment, a configuration where the accuracy of the estimated value of the power consumption is further increased is described.
Correction using “third correction coefficient” is a correction commonly set for each subfield, and “third correction coefficient” is “common correction coefficient” used commonly for each subfield.
When panel 10 is driven, electric power generally called “reactive power” that is consumed ineffectively without contributing on the light emission is generated. This reactive power is considered to be generated by the following factor, for example:
In the present exemplary embodiment, offset value OFST based on the reactive power is set, and an estimated value of power consumption is calculated using offset value OFST. Specifically, offset value OFST preset for the all-cell light-emitting rate in each subfield is added. The addition result is multiplied by the number of sustain pulses in each subfield, and the sum total of the multiplication results in one field period is calculated. Thus, the estimated value of power consumption in one field period is calculated. Thus, the estimated value of the power consumption can be calculated in consideration of the reactive power, and the accuracy of the estimated value of power consumption can be increased.
In the present exemplary embodiment, offset value OFST based on the reactive power is set as below.
When the characteristics of
Next, the measurement result is plotted on the graph of
Next, the straight line obtained by plotting is extended until it crosses the horizontal axis. This extended line is shown by a broken like, and the intersection point of the extended line and the horizontal axis is denoted as “-OFST”. The intersection point of the extended line and the horizontal axis can be considered as a rough estimated value obtained by converting the reactive power into the all-cell light-emitting rate. In the present exemplary embodiment, the absolute value of the intersection point is used as offset value OFST.
For example, when the intersection point exists at a position of “−30%” on the horizontal axis, offset value OFST is “30%”. In the present exemplary embodiment, the offset value is set in this manner.
Adding section 85 adds offset value OFST previously determined by the above-mentioned method to the all-cell light-emitting rate detected by all-cell light-emitting rate detecting circuit 46. The addition result is output to multiplying section 74 and multiplying section 75.
Multiplying section 74 multiplies the number of sustain pulses in each subfield set based on the input image signal and luminance weight by the result obtained by adding the offset value OFST to the all-cell light-emitting rate of the subfield. Thus, in the present exemplary embodiment, the estimated value of the power consumption in each sustain period when an image is displayed without “first correction” can be calculated as an accurate estimated value considering the reactive power.
Multiplying section 75 multiplies the number of sustain pulses after “first correction” in each subfield output from after-first-correction number-of-sustain-pulses setting section 63 by the result obtained by adding the offset value OFST to the all-cell light-emitting rate of the subfield. Thus, in the present exemplary embodiment, the estimated value of the power consumption in each sustain period when an image is displayed only through “first correction” can be calculated as an accurate estimated value considering the reactive power.
For example, it is assumed that offset value OFST is 30%, and the all-cell light-emitting rate is (95%, 85%, 35%, 45%, 25%, 15%, 10%, and 5%) in the first SF through eighth SF, respectively. In this case, the numerical values “after OFST addition” are (125%, 115%, 65%, 75%, 55%, 45%, 40%, and 35%). Therefore, the numerical multiplication value calculated by multiplying the number of sustain pulses before “first correction” by “after OFST addition” is (5.0, 9.2, 10.4, 24.0, 35.2, 57.6, 102.4, and 179.2) in the first SF through eighth SF, respectively.
Therefore, the sum total of them, namely the numerical value output from sum total calculating section 76, is “423”. In other words, the sum total (estimated value considering reactive power) of the power consumption in each sustain period when an image is displayed without “first correction” is “423”.
Similarly, the numerical multiplication value calculated by multiplying the number of sustain pulses after “first correction” by “after OFST addition” with multiplying section 75 is (5.0, 9.2, 9.75, 21.75, 29.7, 45.9, 75.6, and 125.3) in the first SF through eighth SF, respectively.
Therefore, the sum total of them, namely the numerical value output from sum total calculating section 77, is “322.2”. In other words, the sum total (estimated value considering reactive power) of the power consumption in each sustain period when an image is displayed only through “first correction” is “322.2”.
According to these results, the sum total (estimated value considering reactive power) of the power consumption in each sustain period when an image is displayed only through “first correction”, namely “322.2”, is smaller than that when an image is displayed without “first correction”, namely “423”. These estimated values of power consumption are numerical values calculated in consideration of the reactive power as discussed above, and hence are more accurate than the similar numerical values of the third exemplary embodiment. Next, third-correction-coefficient calculating section 78 divides “423” calculated by sum total calculating section 76 by “322.2” calculated by sum total calculating section 77, and obtains “third correction coefficient”=“1.313”.
Then, after-third-correction number-of-sustain-pulses setting section 79 multiplies “1.313” obtained as “third correction coefficient” by the numbers (4, 8, 15, 29, 54, 102, 189, and 358) of sustain pulses in the first SF through eighth SF calculated by after-first-correction number-of-sustain-pulses setting section 63.
Thus, the number of sustain pulses generated after “third correction” is (5, 11, 20, 38, 71, 134, 248, and 470) (the fractional portion is rounded) in the first SF through eighth SF, respectively. The result obtained by multiplying the number of sustain pulses in each subfield after “third correction” by each numerical value of “after offset addition” is (6.25, 12.65, 13, 28.5, 39.05, 60.3, 99.2, and 164.5) in the first SF through eighth SF, respectively, and the sum total of these values is “423.45” (not shown). Therefore, the estimated value of the power consumption in one field period after “third correction” becomes substantially equivalent to that before “first correction”.
In the present exemplary embodiment, when “third correction” is performed, an estimated value of power consumption is calculated in each subfield using offset value OFST set based on the reactive power, as discussed above. Thanks to such a configuration, the estimated value of power consumption can be calculated at an increased accuracy, and the accuracy of “third correction” can be further increased.
The exemplary embodiments of the present invention can be applied to a panel driving method by the so-called two-phase drive. In this driving method, scan electrode SC1 through scan electrode SCn are classified into a first scan electrode group and a second scan electrode group, and the address period is constituted by a first address period and a second address period. Here, in the first address period, a scan pulse is applied to each scan electrode belonging to the first scan electrode group. In the second address period, a scan pulse is applied to each scan electrode belonging to the second scan electrode group. Also in this case, an effect similar to the above-mentioned effect can be produced.
The exemplary embodiments of the present invention are also useful for a panel having 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 (referred to as “ABBA electrode structure”) where the electrode array disposed on the front substrate is “ . . . , scan electrode, scan electrode, sustain electrode, sustain electrode, scan electrode, scan electrode, . . . ”.
Each circuit block shown in the exemplary embodiments of the present invention may be configured as an electric circuit for performing each operation shown in the exemplary embodiments, or may be configured using a microcomputer or the like programmed so as to perform a similar operation.
In the exemplary embodiments of the present invention, an example where one pixel is formed of discharge cells of three colors R, G, and B has been described. However, also in a panel where one pixel is formed of discharge cells of four or more colors, the configurations shown in the present exemplary embodiments can be applied and a similar effect can be produced.
Each specific numerical value shown in the exemplary embodiments of the present invention is set based on the characteristics of panel 10 having a screen size of 50 inches and having 1080 display electrode pairs 24, and is simply one example in the embodiments. The present invention is not limited to these numerical values. Numerical values are preferably set optimally in response to the characteristics of the panel or the specification of the plasma display apparatus. These numerical values can vary in a range allowing the above-mentioned effect. The number of subfields and the luminance weight of each subfield are not limited to the values shown in the exemplary embodiments of the present invention, but the subfield structure may be changed based on an image signal or the like.
Even in a panel where the screen is enlarged and the definition is enhanced, the variation in luminance weight caused in each subfield can be estimated accurately, the linearity of the gradation in the display image can be kept, and reduction in brightness of the display image can be prevented, so that the image display quality can be improved. Therefore, the present invention is useful as a plasma display apparatus and a driving method of a panel.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-003748 | Jan 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/000083 | 1/12/2011 | WO | 00 | 6/26/2012 |
