1. Field of the Invention
The present invention relates to a method of driving a plasma display panel including discharge cells arranged in a matrix fashion.
2. Description of the Related Art
In recent years, a plasma display panel (referred to as “PDP”) in which a number of discharge cells are arranged in a matrix has been drawn attention as a two-dimensional image display panel. The PDP is directly driven by a digital image signal and the number of gradation levels (gradation sequence) of luminance (the number of luminance levels) expressable by the PDP is decided by the number of bits of an image data for each pixel included in the digital image signal. A sub field method is known as a gradation sequence display method for the PDP. The sub field method divides a display period of one field into a plurality of sub fields, and drives each cell for each sub field. One method for driving the PDP is disclosed in Japanese Patent Kokai No. 2001-312244.
In the sub field method, a display period of one field is divided into a plurality of sub fields. Each sub field includes an address period for setting each pixel in a lighting mode or a light extinguishing mode in accordance with the image data and a luminance maintaining period for only lighting a pixel in the lighting mode for a period corresponding to weighting of the sub field concerned. In other words, whether or not a discharge cell is illuminated within each sub field (address period) is decided, and only the discharge cell in the lighting mode is illuminated for a period (i.e., a luminance maintaining period) allocated to this sub field. Accordingly, one field may include one or more sub fields in a luminance state and one or more sub fields in a light extinguishment (nonluminance) state. Therefore, an intermediate luminance is created for that one field in accordance with a sum of the luminance periods of all the sub fields in that one field.
First, in the initial reset stage RC of the sub field SF1, a reset pulse RPX having a negative polarity is applied to row electrodes X1 to Xn. In parallel with application of such a reset pulse RPX, a reset pulse RPY having a positive polarity is applied to row electrodes Y1 to Y2. As a result of application of the reset pulses RPx and RPY, all discharge cells of the PDP are reset-discharged, so that wall electric charge of a certain amount is equally formed within each discharge cell. All the discharge cells are therefore initialized into the lighting mode (illumination mode).
Next, at the address stage Wc of each sub field, a pixel data pulse DP having a voltage corresponding to a logical level of a pixel driving data bit DB (DB1 to DB12) is generated. The pixel driving data bits DB1 to DB12 correspond to the first to twelfth bits of the pixel driving data GD. For example, at the address stage WC of the sub field SF1, a part corresponding to a first row within the pixel driving data bit DB1 is picked out and a pixel data pulse group DP11 including m pixel data pulses corresponding to the logical levels of the picked up part is applied to column electrodes D1 to Dm. By executing the same operation on and after the second row of the pixel driving data bit DB1, a pixel data pulse group DP1i (DP11 to DP1n) for each row is sequentially applied to column electrodes D1 to Dm in the address stage Wc of the sub field SF1.
Also in the address stage Wc, a scan pulse SP with a negative polarity is sequentially applied to row electrodes Y1 to Yn at the same timing as each application timing of the pixel data pulse DP. In this case, discharge (selected light-extinction discharge) occurs only in a discharge cell at a crossing of the row electrode to which the scan pulse SP is applied and the column electrode to which the high voltage pixel data pulse is applied, and then the wall electric charge remaining in this discharge cell is eliminated.
According to such selected light-extinction discharge, the discharge cell that is initialized in the lighting mode at the reset stage RC shifts to the light extinguishing mode. On the other hand, the discharge cell, in which the above described selected light-extinction discharge does not occur, maintains a condition that it is initialized in the reset stage Rc, namely, the lighting mode.
Next, at the luminance maintaining stage Ic of each sub field, as shown in
SF1:SF2:SF3 . . . =2:4:6: . . .
A discharge cell in which the wall electric charge is remaining, namely, the discharge cell set in the lighting mode at the address stage Wc only performs the maintaining-discharge upon every application of the maintaining pulses IPX and IPY. Accordingly, the discharge cell set in the lighting mode maintains the light emitting condition (emission maintaining-discharge) for a period corresponding to the numbers of the discharging, which is allocated to each sub field as described above.
Then, only in the sub field SF12 at the rear end of the field, a light extinction stage E is executed. At this light extinction stage E, a light extinction pulse AP with a positive polarity (not illustrated) is generated and this light extinction pulse AP is applied to the column electrodes D1 to Dm. In parallel with the application of the light extinction pulse AP, another light extinction pulse EP with a negative polarity is generated and is applied to each of the row electrodes Y1 to Yn. The simultaneous application of the light extinction pulses AP and EP causes the light extinction discharge within all the discharge cells in the PDP, so that the wall electric charges remaining in all the discharge cells are eliminated. As a result of such light extinction discharge, all the discharge cells in the PDP are set in the light extinction mode.
In the above described driving method, only a discharge cell in the light emitting state in the immediately preceding sub field is selectively eliminated and discharged at a selected light extinction address stage of the subject sub field only. Thus, the N (e.g., twelve) sub fields are sequentially lighted from the front (head) sub field, so that N+1 (thirteen) gradation sequence display is created. By summing up the numbers of the illumination of the maintaining-discharge in each sub field, the gradation sequence display is created in accordance with the input image signal.
Since a visual property of a human being has a logarithmic property, human's eyes are sensitive to variation in the gradation sequence (sequence of gradation levels) in a low luminance area. In the above described driving method, the number of the maintaining light emissions (i.e., the number of the maintaining pulses) in the sub field SF1 used for the lowest gradation level should be at least twice because the negative wall electric charge is needed to be formed on a row electrode Y, to which the scan pulse SP is applied at the selected light extinction address in the next sub field. Accordingly, a finer gradation sequence display is difficult. For example, it is impossible to reduce to the number of the maintaining light emissions to once.
An object of the present invention is to provide a plasma display panel (PDP) driving method that can improve a gradation sequence display ability in a low luminance area.
According to one aspect of the present invention, there is provided a method of driving a plasma display panel for each of a plurality of sub fields. The sub fields are arranged from a head sub field to a tail sub field. Each of a plurality of fields which define a picture signal is divided into the sub fields. The plasma display panel includes a plurality of discharge cells formed at a plurality of crossing portions of a plurality of row electrodes corresponding to a plurality of display lines respectively and a plurality of column electrodes arranged to crisscross the plurality of row electrodes. The method comprises the steps of providing a sub field group which includes the head sub field and at least one subsequent sub field, such that each sub field of the sub field group includes a selected writing address stage for selectively discharging a discharge cell in question so as to set the discharge cell into a lighting mode in accordance with the picture signal; and providing at least one sub field subsequent to the sub field group such that the at least one sub field includes a light emission maintaining stage for repeatedly maintaining discharge of the discharge cell in only the lighting mode for a number of times in accordance with weighting of the plurality of sub fields, wherein one of the at least one sub field includes a selected light extinction address stage for selectively discharging only a discharge cell which undergoes the light emission maintaining stage in an immediately preceding sub field, in accordance with the picture signal so as to set the discharge cell in a light extinguishing mode.
Embodiments according to the present invention will be described with reference to the accompanying drawings.
First Embodiment
Referring to
The display unit shown in
The PDP 10 includes column electrodes D1 to Dm (address electrodes) and row electrodes X1 to Xn and row electrodes Y1 to Yn that are arranged orthogonally to the column electrodes. In the PDP 10, an effective row electrode corresponding to one display row is formed by a pair of a row electrode X and a row electrode Y. The column electrodes D1 to Dm are sectionalized into column electrodes D1, D4, D7, . . . , Dm−2 serving to emit red light, column electrodes D2, D5, D8, . . . , Dm−1 serving to emit green light and column electrodes D3, D6, D9, . . . , Dm serving to emit blue light. At each crossing of each of the column electrodes D1, D4, D7, . . . , Dm−2 and each of the row electrodes X and Y, a red discharge cell for discharging to emit red is formed. At each crossing of each of the column electrodes D2, D5, D8, . . . , Dm−1 and each of the row electrodes X and Y, a green light emission cell for discharging to emit green is formed. At each crossing of each of the column electrodes D3, D6, D9, . . . , Dm and each of the row electrodes X and Y, a blue light emission cell for discharging to emit blue is formed. Three discharge cells abutting with each other in a display line direction, namely, a red discharge cell, a green discharge cell and a blue discharge cell define one pixel.
The synchronization detecting circuit 11 generates a vertical synchronization signal V when the synchronization detecting circuit 11 detects a vertical synchronization signal in an analog picture signal. The synchronization detecting circuit 11 generates a horizontal synchronization signal H when the synchronization detecting circuit 11 detects a horizontal synchronization signal in the analog picture signal. The synchronization detecting circuit 11 supplies the vertical synchronization signal V and the horizontal synchronization signal H to the drive control circuit 12 and a multi gradation sequence processing circuit 31 (
The multi gradation processing circuit 31 applies an error diffusion processing and a dither processing to the pixel data PD of eight bits. For example, in the error diffusion processing, the multi gradation processing circuit 31 defines the upper six bits of the pixel data PD as the display data and defines the remaining lower two bits thereof as the error data. Then, the multi gradation processing circuit 31 weight-adds each error data of the pixel data PD in connection with each of peripheral (surrounding/neighboring) pixels and reflects the result on the display data. According to such operation, the pseudo luminance for the lower two bits in an original pixel is expressed by the circumferential pixels. Therefore, the display data for six bits (not eight bits) can express the luminance gradation sequence equivalent to the 8-bit pixel data. Then, the multi gradation processing circuit 31 performs the dither processing to the error-diffusion-processed pixel data of six bits that is obtained by the error diffusion processing.
In the dither processing, a plurality of pixels abutting with each other are defined as one pixel unit, and dither coefficients including different coefficient values are allocated and added to the error diffusion processed pixel data corresponding to the pixels within this one pixel unit, respectively. In this manner, the multi gradation processing circuit 31 obtains the dither-added pixel data. As a result of such addition of the dither coefficients, if viewed as the pixel unit, the upper four bits of the dither-added pixel data is sufficient to express the luminance equivalent to the eight-bit pixel data. Thus, the multi gradation processing circuit 31 supplies the upper four bits of the dither-added pixel data, as the multi-gradation image data PDS, to the drive data generation circuit 32.
The drive data generation circuit 32 converts the multi-gradation (grayscale) image data PDS of four bits into the pixel driving data GD including the first to twelfth bits in accordance with a conversion table shown in
In this way, the multi-gradation (halftone) processing circuit 31 and the driving data generation circuit 32 can convert the pixel data PD, capable of expressing 256 gradation levels in eight bits, into the pixel driving data GD of twelve bits including thirteen patterns in total as shown in
In response to a write signal supplied from the driving control circuit 12, the memory 15 sequentially writes and stores the pixel driving data GD. When the writing of the pixel driving data GD11 to GDnm for one screen (n rows, m columns) is complete, and the memory 15 receives a read signal from the driving control circuit 12, then the memory 15 sequentially reads each of the pixel driving data GD11 to GDnm at the same bit digit for each row and supplies the pixel driving data GD11 to GDnm to the address driver 16. In other words, the memory 15 divides the twelve-bit pixel driving data GD11 to GDnm for one screen into twelve pixel driving data bits GD111-nm to GD1211-nm as shown below:
DB111-nm: first bit of the pixel driving data GD11-nm
DB211-nm: second bit of the pixel driving data GD11-nm
DB311-nm: third bit of the pixel driving data GD11-nm
DB411-nm: fourth bit of the pixel driving data GD11-nm
DB511-nm: fifth bit of the pixel driving data GD11-nm
DB611-nm: sixth bit of the pixel driving data GD11-nm
DB711-nm: seventh bit of the pixel driving data GD11-nm
DB811-nm: eighth bit of the pixel driving data GD11-nm
DB911-nm: ninth bit of the pixel driving data GD11-nm
DB1011-nm: tenth bit of the pixel driving data GD11-nm
DB1111-nm: eleventh bit of the pixel driving data GD11-nm and
DB1211-nm: twelfth bit of the pixel driving data GD11-nm.
Then, the memory 15 sequentially reads each of the DB111-nm, DB211-nm, . . . , DB1211-nm for each row in response to a read signal from the driving control circuit 12, and supplies them to the address driver 16.
The driving control circuit 12 generates a clock signal for the A/D converter 14 and the write and read signals for the memory 15 in synchronization with the horizontal synchronization signal H and vertical synchronization signal V.
In accordance with a light emitting driving format shown in
In the light emission driving format shown in
First, in the all reset stage Rc of the sub field SF1, the second sustain driver 18 applies a reset pulse RPY having a positive polarity as shown in
Next, in the selected writing address stage WO of the sub field SF1, a predetermined voltage of positive polarity is applied to the row electrodes X1 to Xn by the first sustain driver 17. Then, the address driver 16 generates a pixel data pulse having a voltage corresponding to a logical level of the pixel driving data bit DB that is supplied from the memory 15. For example, the address driver 16 generates a high voltage pixel data pulse if the logical level of the pixel driving data bit DB is “1”, and the address driver 16 generates a low voltage (0 volt) pixel data pulse if the logical level of the pixel driving data bit DB is “0”. The address driver 16 applies the pixel data pulse group DP, including the pixel data pulse for one row, to the column electrodes D1 to Dm. In the selected writing address stage WO of the sub field SF1, a portion corresponding to the first row in the pixel driving data bits DB111-nm, i.e., the DB111-1m, is first extracted. Then, the pixel data pulse group DP11 including m pixel data pulses corresponding to respective logical levels of the DB111-nm is applied to the column electrodes D1 to Dm. Next, a portion corresponding to the second row in the pixel driving data bits DB111-nm, namely the DB121-2m, is picked up, and the pixel data pulse group DP12 including m pixel data pulses corresponding to respective logical levels of the DB121-2m is applied to the column electrodes D1 to Dm. Subsequently, in the address stage Wc of the sub field SF1, the pixel data pulse groups DP13 to DP1n for each row are sequentially applied to the column electrodes D1 to Dm in the same manner.
In the address stage WO, the second sustain driver 18 generates scan pulses SP of a negative polarity as shown in
After the address stage WO is complete, the complete (all-surface) light extinction stage E is executed. In the light extinction stage E, the first sustain driver 17 applies a certain voltage EX of a positive polarity to the row electrodes X1 to Xn, and the second sustain driver 18 applies a light extinction pulse EPY of a positive polarity to each of row electrodes Y1 to Yn. By the application of the light extinction pulses, the light extinction discharge PE occurs in all the discharge cells of the PDP 10, and all the wall electric charge remaining in the discharge cells is eliminated. According to such light extinction discharge, all the discharge cells in the PDP 10 are set in the light extinguishing mode.
As described above, in the sub field SF1, the writing-discharge light-emission PW for one time is used as a light emission of the gradation sequence display.
In the sub field SF2, the selected writing address stage WO is first executed, like the sub field SF1. If the pixel driving data bit DB has a light emission logical level (“1”) for designating the lighting of the pixel, the light emission PW is generated by the selected writing discharge.
Next, the light emission maintaining stage Ic is executed. The second sustain driver 18 applies the light emission maintaining pulse (i.e., the sustain pulse) IPY of a positive polarity once to the row electrodes Y1 to Yn substantially at the same time. The discharge cells in which the wall electric charge remains, namely, the discharge cells that are set in the lighting mode in the address stage WO, only maintain the discharging of electricity by the application of the maintaining pulse IPY, so that the light emission (PW) is generated.
After the light emission maintaining stage Ic, the first sustain driver 17 applies a light extinction pulse EPX of a positive polarity to the row electrodes X1 to Xn, so that the complete light extinction stage E is executed. Thus, all the discharge cells are set in the light extinguishing mode.
As described above, in the sub field SF2, two discharge light emissions in total, namely, the writing-discharge light emission PW for one time and a maintaining-discharge light emission PS for one time, are used as the light emission of the gradation sequence display.
In the sub field SF3, like the sub field SF1 and the sub field SF2, the selected writing address stage WO is executed, so that the light emission PW is generated by the selected writing discharge. Then, the emission maintaining stage Ic is executed. In other words, as shown in
As understood from the above, in the sub field SF3, the discharge light emission four times in total (namely, the writing discharge light emission PW for one time, and the maintaining discharge light emission Ps for three times) are used as the light emission of the gradation sequence display.
In the sub fields SF4 to SF12, as described above, the selected light extinction address stage W1 and the emission maintaining stage Ic are executed. More in detail, the voltage is not applied to the row electrodes X1 to Xn, but the scan pulse SP of a negative polarity is sequentially applied to the row electrodes Y1 to Yn at the same timing as each application timing of the pixel data pulse DP. In this case, a very weak discharge (namely, a selected light extinction discharge PI) is generated only in a discharge cell at a crossing of the row electrode to which the scan pulse SP is applied and the column electrode to which the high voltage pixel data pulse is applied. Thus, the wall electric charge remaining within this discharge cell is (selectively) eliminated. According to such selected light extinction discharge, the discharge cells in the lighting mode shift to the light extinguishing mode. On the other hand, the discharge cells, in which the selected extinguishment discharge does not occur, maintain the lighting mode.
In the light emission maintaining stage Ic of each sub field, as shown in
It should be noted that how many times the maintaining pulse IP should be applied to the sub fields SF2, SF3, SF4 to SF12 respectively are not limited to the above example, and it may be appropriately decided depending on various conditions.
The discharge cells in which the wall electric charge remains namely, the discharge cells maintained in the lighting mode, only keep discharging the electricity upon every application of the maintaining pulses IPx and IPY. Accordingly, the discharge cells set in the lighting mode maintain the lighting emission condition based on this emission maintaining discharge for the number of times allocated to the respective sub fields.
Only in the sub field SF12 at the rear end (not illustrated), the light extinguishing stage E is executed. In such light extinguishing stage E, a light extinguishment pulse AP of a positive polarity is generated and applied to the column electrodes D1 to Dm. At the same time as the application timing of this light extinguishment pulse AP, a light extinguishment pulse EP of a negative polarity is also generated and applied to the row electrodes Y1 to Yn, respectively. By the simultaneous application of the light extinguishment pulses AP and EP, the light extinguishment discharge occurs in all the discharge cells in the PDP, so that all the wall electric charge remaining in the discharge cells is eliminated. According to such light extinction discharge, the all discharge cells in the PDP are set in the light extinguishing mode.
According to the above described driving method, therefore, in the sub fields SF4 to SF12 in which the selected light extinction address stage WI is executed, only the discharge cells maintained in the lighting mode repeat the light emissions for the above described number of times in the subsequent light emission maintaining stage Ic. Whether or not the discharge cell in question is set into the light extinguishing mode is determined by the pixel driving data GD. If a certain bit of the pixel driving data GD is a logical level “0”, which represents the light extinguishment, then the selected light extinction discharge takes place in the address stage WI of the sub field corresponding to its bit digit, and the discharge cells are set into the light extinguishing mode. On the other hand, if a logical level of this bit is “1”, the selected light extinction discharge does not take place, so that the discharge cells are maintained in the present mode. There is no chance of shifting the discharge cells from the light extinguishing mode to the lighting mode within the sub fields SF4 to SF12. Thus, once the discharge cells shifts to the light extinguishing mode, the discharge cells do not shift back to the lighting mode at any one of the address stages WI in the sub fields SF4 to SF12. Accordingly, after the sub field SF4, the lighting mode is only maintained till the selected light extinction discharge occurs in the sub fields shown by black circles in
For instance, the pixel driving data GD having thirteen data patterns as shown in
Therefore, it is possible to not only maintain the advantages of the one reset and one address method (namely, low electric power consumption, high contrast, and no fake outline), but also finely adjust the gradation levels in the low luminance area to improve the gradation sequence display capability.
A second embodiment of the present invention will be described with reference to
The second embodiment is different from the first embodiment in that, as shown in
In the above described embodiments, the address stage in the sub fields SF1 to SF3 or the sub fields SF1 and SF2 is defined as the selected writing address. However, it should be noted that only the address stage of the sub field SF1 may be defined as the selected writing address. In this case, the sub field SF1 includes only the reset stage Rc (the complete writing+the complete light extinguishment), the selected writing address stage and the emission maintaining stage Ic (the number of the maintaining pulses is two).
In the above described embodiments, the reset stage Rc is provided preceding the address stage of the head sub field SF1 in one field. However, it may be provided for each plurality of fields, not for each field. Alternatively, the reset stage may not be provided. In this case, the number of times of the discharge light emissions that are not directly related to the gradation sequence display decreases, so that contrast is improved more.
In the first and second embodiments, since the rising and falling edges of the reset pulse or the rising and falling edges of the light extinction pulse have more gradual slopes than the maintaining discharge pulse, the complete writing discharge and the complete light extinction discharge in the reset stage or the light extinction discharge after the address stage is very weak. As a result, the discharge light emissions do not adversely influence the gradation sequence display even in the low luminance area.
Various modifications and changes may be made to the illustrated and described embodiments by those skilled in the art without departing from the spirit and scope of the present invention. Such modifications and changes are encompassed by the present invention defined by the appended claims.
This application is based on a Japanese patent application No. 2002-5537, and the entire disclosure thereof is incorporated herein by reference.
Number | Date | Country | Kind |
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2002-005537 | Jan 2002 | JP | national |
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Number | Date | Country |
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2001-312244 | Nov 2001 | JP |
Number | Date | Country | |
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20030132897 A1 | Jul 2003 | US |