Patent Application
20090244040
The present application claims priority from Japanese Patent Application No. JP 2008-085752 filed on Mar. 28, 2008, the content of which is hereby incorporated by reference into this application.
The present invention relates to a display device utilizing discharge such as a plasma display panel (PDP), and more particularly to a structure of a cell (discharge cell) and a countermeasure against voltage drop or the like.
In a PDP, a pulse-like discharge current is supplied as a drive waveform for display discharge (sustain discharge) or the like from a drive control circuit side via a bus electrode. Such a phenomenon as voltage drop (discharge drop) of the bus electrode occurs due to the concentration (peak value increase) of discharge current.
Regarding the above, Japanese Patent No. 3547267 describes a technique of varying the width of electrodes (projecting portions) or the like in the respective cells in a bus electrode extending direction for the purpose of reducing a peak value of discharge current.
Also, Japanese Patent No. 3864204 describes a technique of varying the electrode area or the like in the respective cells of each color R, G, and B for the purpose of adjusting a color temperature of white display.
Due to the increase of wiring resistance resulting from a panel size increase, voltage drop of a bus electrode or the like caused by the concentration (peak value increase) of discharge current is increased. As a result, luminance unevenness occurs due to the difference in discharge timing caused by minute difference in cell discharge characteristics.
The details thereof are as follows. For example, in a cell (average cell) which discharges (lights up) at the same timing as an average cell, the luminance is lowered because the voltage drop is occurring therein. On the other hand, since a cell which discharges at a timing earlier than or later than the average cell is not influenced by the voltage drop or influence thereto is small, luminance of the cell is higher than that of the average cell (
It is considered that such a difference in discharge timing (difference in cell discharge characteristics) is caused from the difference in panel manufacture characteristics, namely, a minute structural difference formed in the course of panel manufacture, a material characteristic difference and others.
The present invention has been made in view of the problem as described above, and a principal object thereof is to provide a technique relating to a PDP and capable of canceling or reducing luminance unevenness due to the voltage drop or the like and improving the display quality.
The typical ones of the inventions disclosed in this application will be briefly described as follows. In order to achieve the above object, a representative embodiment of the present invention is directed to a technique for a PDP, a PDP driving method and a PDP apparatus and is characterized by including a configuration described below.
A PDP according to the present embodiment is provided with plural types of cells intentionally designed to have a discharge characteristic with a predetermined difference so that the discharge timing thereof differs with respect to the discharge timing obtained by the application of a drive waveform to a cell to be a reference (average). In the plural types of cells, discharge timing is varied by controlling the characteristics (length, position and others) of the discharge gap by changing the electrode shapes of respective cells.
Further, the plural types of cells are distributed and arranged in a predetermined pattern in a screen of the PDP. This arrangement pattern is set to a pattern obtained by spatial frequency hardly recognized as noises (unevenness) visually by human eyes in a plane including an electrode extending direction (lateral direction) and a direction orthogonal thereto (vertical direction) of a screen. More specifically, for example, the plural types of cells are arranged in a sequentially repetitive pattern so that cells of different types are arranged adjacent to each other. For example, two types of cells are arranged in a zigzag pattern (alternately).
Alternatively, arrangement patterns other than a completely regular arrangement pattern can be adopted. For example, plural types of cells are arranged on a screen in a regular pattern so that cells of the same type are arranged adjacent to each other in some parts and cells of different types are arranged in a sequentially repetitive manner as far as possible in other parts, or arranged in a pattern obtained by a known error diffusion processing. In this case, it is visually preferable to adopt the pattern where a portion where cells of the same type are arranged adjacent to each other is contained in a block with a size of 2×2 at a maximum.
Also, it is preferable to design so that the discharge timings of respective cells in the plural types of cells vary by about a half-height full-width of the discharge current.
With the configuration mentioned above, design characteristics based on the arrangement pattern (discharge timing (luminance) dispersion characteristics) are superimposed on the panel manufacture characteristics (random and minute cell discharge characteristic difference and luminance unevenness due to that), and the luminance unevenness due to the causes mentioned above is reduced in the display characteristics at the time of the utilization of this panel. Difference in discharge timing occurs between cells at the time of display discharge and discharge currents are dispersed by the superimposition thereof. Accordingly, a degree of vertical fluctuation such as voltage drop is reduced as compared with the conventional art, so that the luminance unevenness is reduced.
For example, in the PDP of the present invention, plural types of cells different in discharge timing with respect to a reference waveform application are provided, the plural types of cells have different discharge timings because lengths of discharge gaps are varied by electrode shapes of the respective cells, and the plural types of cells are arranged on a screen in a sequentially repetitive pattern so that cells of different types are arranged in adjacent cells.
Also, in a PDP driving method and a PDP apparatus according to the embodiment, in the application of drive waveforms to electrodes used for display discharge, a first drive waveform which generates rising to a predetermined voltage and overshoot at a first timing coinciding with a discharge timing of the first cell and a second drive waveform which generates rising to a predetermined voltage and overshoot at a second timing coinciding with a discharge timing of the second cell are applied in a switched manner.
An effect obtained by the representative ones of the inventions disclosed in this application will be briefly described below. According to the representative embodiments of the present invention, in a PDP, luminance unevenness due to voltage drop or the like is cancelled or reduced and display quality can be improved.
Especially, the maximum amount of the voltage drop is reduced by the difference (dispersion) in discharge timings, and the luminance difference in respective cells is reduced. Also, even if there is a panel manufacture characteristic difference, it is possible to make it hard to see the luminance unevenness due to the difference.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference numbers throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.
<Conventional Art>
A conventional art (basic mechanism of voltage drop or the like) will be briefly described with reference to
In (A), the waveform rises up to a predetermined voltage Vs from a timing t1, and after maintaining the voltage Vs, it falls down by a timing t5.
In the discharge drive to the display electrode pair (Y-X), since all cells of the electrode pair discharge approximately at the same time and large current flows instantaneously, the voltage drop or the like occurs due to the wiring resistance of electrodes. Fluctuation (ringing) occurs in a voltage of a bus electrode as a whole due to the concentration of discharge current. More specifically, the voltage fluctuates up and down from a reference (Vs) as shown by “a”, “b” and “c”. Note that this example shows a case of three stage change of “a”, “b” and “c” for simplification.
Differences in discharge timing occur in respective cells on a screen due to discharge characteristic differences as shown in (B), (C) and (D), so that luminance unevenness is generated due to differences in discharge light emission amount. It is considered that the discharge characteristic difference is caused by a minute structural difference, a material characteristic difference and the like formed in the course of panel manufacture.
Specifically, since the cell which discharges (lights up) at a timing t2 as shown by (B) is in an overshoot state, namely, a voltage exceeds the reference value (Vs) as shown by “a” of the waveform of (A), the light emission is accordingly larger than the reference, and the luminance becomes high.
Also, since the cell which discharges at a timing t3 as shown by (C) is in a voltage drop state, namely, a voltage is lower than the reference value (Vs) as shown by “b”, the light emission is accordingly smaller than the reference, and the luminance becomes low.
Further, since the cell which discharges at a timing t4 as shown by (D) is also in the overshoot state as shown by “c”, the light emission is accordingly larger than the reference, and the luminance becomes high.
<PDP Apparatus>
In light of the above, embodiments of the present invention will be described. A background configuration is first described, and then a characteristic configuration will be described. Note that an x direction (first direction, horizontal direction in the screen), a y direction (second direction, vertical direction in the screen), and a z direction (third direction, vertical direction to a panel plane) are provided for description.
In the PDP 10, pairs of sustain electrodes (represented by symbol X) and scan electrodes (represented by symbol Y) are formed in parallel to the x direction of the screen as the electrodes (display electrodes) used for sustain discharge (display discharge), and the display lines are configured by the electrode pairs. Also, address electrodes (represented by symbol A) are formed in parallel to the y direction of the screen so as to intersect these electrode pairs, and the display columns are configured by the electrodes. Also, on the screen (display region) of the PDP 10, cells (discharge cells) are configured in a matrix manner so as to correspond to intersecting regions of these electrode groups (X, Y and A).
For example, data showing luminance levels of three colors of red (R), green (G) and blue (B), various synchronous signals (clock signal, horizontal synchronization signal and vertical synchronization signal) and others are input to the PDP apparatus from an external apparatus such as a TV tuner or a computer. Also, the control circuit 110 generates and outputs control signals suitable for respective drivers based on the data and signals. In accordance with the input, the drivers drive corresponding electrode groups by the application of voltages (waveforms). In this manner, a video image is displayed on the screen of the PDP 10 in accordance with a predetermined method.
As an example of an electrode arrangement of the PDP 10, sustain electrodes X (X1 to Xn) and scan electrodes Y (Y1 to Yn) are alternately and repeatedly arranged in the y direction in the case of a normal method, and display lines formed by the display electrode pairs (X-Y) are sequentially arranged. Also, cells are configured by the address electrodes (A1 to Am) intersecting the display lines.
<Drive Method>
In a drive method of the present PDP apparatus, a field associated with the screen of the PDP 10 is driven by a sub-field method, an address display separation method, and the like. In the drive sequence, the field (or frame) includes a plurality of sub-fields (or sub-frames) each having predetermined weight of luminance applied thereto. Grayscale expression is performed for each cell by selection and combination of lighting-up of respective sub-fields (SF) of the field. Each SF period has respective operation periods such as a reset period, an address period, and a sustain (display) period. A ratio of the number of sustain discharges during the sustain period varies in accordance with the weight of SF.
In an example of the SF drive sequence, states of all cells in SF are initialized in the reset period to prepare for the address period. Specifically, by applying a reset waveform from a reset circuit to the display electrode (X, Y) group, discharge for charge adjustment is generated. In the next address period, cells to be lit (ON)/unlit (OFF) in the SF are selected. Specifically, the Y scan driver 123 performs an operation (scan) for controlling the individual scan electrodes Y (display line) to sequentially select them. Simultaneously therewith, the address driver 124 performs an operation for controlling the individual address electrodes A to select them. By these operations, cell selection discharges (address discharges) are generated at the pair of (between) the address electrode A and the scan electrode Y to be selected. In the next sustain period, the cells which have been selected in the previous address period are lit by sustain discharge light emission. Specifically, the X sustain driver 121 and the Y sustain driver 122 apply a number of sustain waveforms corresponding to the weight to the display electrode (X, Y) group. By this means, a number of sustain discharges corresponding to the weight are generated in the selected cells.
<PDP>
The PDP 10 is configured by combining two structures (11, 12) mainly formed of two glass substrates 1 and 5 positioned on a front side and a back side. A discharge space 30 is formed by sealing the outer peripheral portions of these structures (11, 12), degassing a region (inside) between the structures, and filling discharge gas in the region.
In the first structure (front substrate structure) 11, display electrodes (X, Y) are formed on the glass substrate 1 so as to extend in parallel to the x direction. The sustain electrodes X for sustain drive and the scan electrodes Y for both sustain drive and scan drive are provided. The display electrodes (X, Y) are formed of, for example, transparent electrodes 2a and bus electrodes 2b. End portions of the bus electrodes 2b are connected to a driver side. The display electrodes (X, Y) are covered with a dielectric layer 3 and a protective layer 4.
In the second structure (back substrate structure) 12, address electrodes A for address drive are formed on the glass substrate 5 so as to extend in parallel to the y direction. The address electrodes A are covered with a dielectric layer 7, and barrier rib portions (vertical ribs) 8a extending in the y direction and barrier rib portions (lateral ribs) 8b extending in the x direction are formed on the dielectric layer 7 as barrier ribs 8. The barrier rib 8 in this case has a box (grid) shape. The barrier rib 8 partitions the discharge space 30 so as to correspond to the cells (discharge regions). Phosphors 9 (9R, 9G and 9G) of respective colors are separately formed in the regions partitioned by the barrier rib 8 on the dielectric layer 7 so as to be exposed to the discharge space 30.
Other than the structure of the PDP 10 described above, various specific structures can be adopted in accordance with a drive method. For example, in the case of the so-called ALIS method, display lines are configured by all the adjacent pairs of display electrodes (X, Y), and an image displayed on the screen is displayed by the interlace drive of odd fields which drive the odd display lines and even fields which drive the even display lines.
<Characteristic Configuration>
A characteristic configuration (basic design concept, operation effect, and others) in the PDP according to an embodiment (first embodiment and others) of the present invention will be described with reference to
In
In
Note that, in the example of discharge current of FIGS. 3A and 4A, the total height is about 1.0, the width is about 2.0 (timing of i=1.0 to m=3.0 and center timing k=2.0), and the half-height full-width thereof is w (about 1.0 or less). On the other hand, in “a” and “b” in
In
By adopting a structure in which respective cells (A, B) in the PDP are intentionally designed to have different discharge timings as shown in
In the conventional art of
On the other hand, the present PDP shown in
In the correlation between the timings of the phenomena of “a”, “b” and “c” shown in
In
In the panel manufacture characteristic (random and minute unevenness of panel) shown by (A) of
Next, a cell structure (including electrode structure and the like) in a screen (x-y plane) of the PDP 10 according to a first embodiment is shown in
The first cell A is a cell which discharges at an early timing, and the second cell B is a cell which discharges at a late timing. The cell A has a short discharge gap length (Ga), and the cell B has a long discharge gap length (Gb). In other words, both the sustain electrode X and the scan electrode Y (transparent electrode 2a) have large areas in the cell A, and both the sustain electrode X and the scan electrode Y (transparent electrode 2a) have small areas in the cell B.
In the zigzag arrangement pattern, the cells A and the cells B are alternately arranged in both the x direction and the y direction, and different types of cells are arranged in adjacent cells, respectively. An arrangement ratio of the first cells A and the second cells B in a screen is set to 1:1 (each 50%) for the average dispersion.
Note that, in the example of the present cell structure, the electrode pairs of X-Y positioned reversely are repeatedly arranged in the barrier rib 8 of a box type similar to that shown in
In a region of the discharge space 30 corresponding to a screen, each cell (A, B) is configured as a closed discharge light emission region surrounded by the barrier rib 8 of the box type and the bus electrode 2b. In this case, the bus electrode 2b of the display electrode (X, Y) is arranged so as to slightly project in a cell inner side direction with respect to the lateral rib 8b. The bus electrode 2b is formed in a thin linear shape continuous over a whole length in the x direction and is made of metal with low electric resistance. In each of the display electrodes (X, Y), the transparent electrode 2a is overlapped on and connected to the bus electrode 2b, and a portion of the transparent electrode 2a projects in a rectangular shape from the bus electrode 2b in the cell inner side direction. The transparent electrode 2a is made of a transparent material such as ITO and discharge gaps (Ga, Gb) are defined by rectangular distal ends of the transparent electrodes 2a of X-Y in the cell. The transparent electrode 2a is connected commonly to the cells in the x direction, but it may be separated for each cell.
In the cell A, the lengths of the rectangular projections (y direction) of the transparent electrodes 2a of X and Y are relatively large, and a relatively short discharge gap Ga is configured. On the contrary, in the cell B, the lengths of the rectangular projections (y direction) of the transparent electrodes 2a of X and Y are relatively small, and a relatively long discharge gap Gb is configured.
As described above, according to the PDP 10 of the present embodiment, by adopting the structure of the zigzag arrangement pattern of the two types of cells (A, B), luminance unevenness due to voltage drop can be cancelled or reduced, and the display quality can be improved. Especially, by the difference (dispersion) in discharge timing in the cells (A, B), the maximum amount of the voltage drop or the like is reduced, and the luminance difference between respective cells having different discharge timings with respect to a predetermined waveform (sustain pulse) is reduced. Even if there is a panel manufacture characteristic difference, it is possible to make it hard to see the luminance unevenness due to the characteristic difference.
Next,
The first cell A has a large electrode area of X and a small electrode area of Y. The second cell B has a small electrode area of X and a large electrode of Y. These cells (A, B) take a zigzag arrangement pattern. For example, discharge gap lengths of respective cells are uniform.
When electrode areas of X and Y in the cell are varied like in this configuration, a difference in discharge timing due to polarity of discharge occurs from the difference in diffusion speed between ions and electrons.
Also, when the discharge gap lengths of respective cells are made uniform like in this configuration, the firing voltages become equal, and such an effect can be obtained that the adverse effect to a reset operation caused by the difference in firing voltage or the like can be suppressed to the minimum.
In
In a PDP according to a third embodiment, an error diffusion processing pattern is used as an applicable structure other than the zigzag arrangement pattern shown in the first and second embodiments. For example, two types of cells (A, B) are provided like in the first embodiment and others. Then, in the third embodiment, the respective cells (A, B) are arranged by using a pattern determined by a predetermined (known) error diffusion processing so that they are equal in number on a screen. For example, a predetermined error diffusion processing is performed with setting the cell A as a numeral value 1 and the cell B as a numeral value 0. The cells A and the cells B are arranged in a display region in accordance with the pattern of bitmap data obtained by the processing.
Note that, in this pattern, cells of the same type are arranged in adjacent cells in some parts. It is visually preferable to adopt the arrangement in which the cells of the same type are contained in a block with a size of 2×2 in the vertical and horizontal directions.
As described above, various arrangement patterns in which luminance unevenness is hardly recognized as noise visually can be used.
In a PDP according to a fourth embodiment, in addition to the structures according to the first and second embodiments and others described above, luminance gradient (shading structure) is provided in a screen by means of arrangement pattern. For example, two types of cells (A, B) are provided like the above, they are arranged on a screen in accordance with the error diffusion processing pattern or the like in the same manner as the third embodiment, and the luminance gradient in the screen is provided in accordance with a ratio in the arrangement (the number of cells per unit area). For example, the ratio of the cells B is made high at a central portion of the screen so that an average value of discharge gap lengths is made large (light emission and luminance are relatively reduced), and the ratio of cells A is made high in a peripheral portion of the screen so that the average value is made small (light emission and luminance are relatively increased). The cells are arranged so that the luminance gradient varies continuously from the central portion of the screen toward the peripheral portion thereof.
Also, the structure having a luminance gradient reverse to the above (structure where luminance is large in the central portion and luminance is small in the peripheral portion) can be adopted.
As described above, not only the luminance unevenness reduction effect can be obtained, but also shading structure and the like can be added in accordance with the arrangement pattern.
Next, a PDP, a PDP apparatus and a PDP driving method according to a fifth embodiment will be described. In the fifth embodiment, a drive waveform applied from a drive control circuit to electrodes of the PDP 10 is ingeniously controlled. Drive waveforms of corresponding types are applied from the control circuit 110 and the respective drivers shown in
The PDP 10 according to the fifth embodiment can use a structure similar to that of each of the above-mentioned embodiments. For example, a zigzag arrangement pattern of two types of cells (A, B) similar to that of the first embodiment can be adopted. Then, in the PDP driving method and the PDP apparatus according to the fifth embodiment, the two types of drive waveforms A and B are used in combination in the sustain drive waveforms to the display electrode pairs (X, Y) of the PDP 10. Specifically, a first drive waveform A of (A) including overshoot at the same timing (T1) as the cell (cell A) discharging early as shown by (C) in
In the present PDP driving method, sustain drive operation is performed to the display electrode pairs (X, Y) by using the drive waveforms (A, B) approximately equal in number in accordance with the arrangement pattern of the PDP 10. In the example shown in
According to this configuration, it is possible to reduce luminance difference due to a fixed arrangement pattern owned by the PDP 10 of the respective embodiments.
In the foregoing, the invention made by the inventors of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention. For example, it is also possible to provide three or more types of cells instead of two types of cells.
The present invention can be utilized in a display device such as a PDP.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-085752 | Mar 2008 | JP | national |
