Description PLASMA DISPLAY APPARATUS

Technical Field

[I] Exemplary embodiments relate to a plasma display apparatus. Background Art

[2] A plasma display apparatus includes a plasma display panel.

[3] The plasma display panel includes a phosphor layer inside discharge cells partitioned by barrier ribs and a plurality of electrodes.

[4] When driving signals are applied to the electrodes of the plasma display panel, a discharge occurs inside the discharge cells. In other words, when the plasma display panel is discharged by applying the driving signals to the discharge cells, a discharge gas filled in the discharge cells generates vacuum ultraviolet rays, which thereby cause phosphors positioned between the barrier ribs to emit light, thus producing visible light. An image is displayed on the screen of the plasma display panel due to the visible light.

Disclosure of Invention Brief Description of the Drawings

[5] FIG. 1 illustrates a configuration of a plasma display apparatus according to an exemplary embodiment;

[6] FIG. 2 illustrates a structure of a plasma display panel;

[7] FIG. 3 illustrates a frame for achieving a gray level of an image in the plasma display apparatus;

[8] FIG. 4 illustrates an example of an operation of the plasma display apparatus;

[9] FIG. 5 illustrates an exemplary method for changing a structure of a frame;

[10] FIGs. 6 to 9 are diagrams for explaining a reason to change a structure of a frame;

[I I] FIGs. 10 and 11 illustrate changes in the image quality of an image depending on changes in a length of a subfield group;

[12] FIG. 12 are a diagram for explaining the number of subfields belonging to a subfield group; [13] FIG. 13 illustrates another exemplary method for changing a structure of a frame; and [14] FIG. 14 illustrates another exemplary method for changing a structure of a frame.

Mode for the Invention [15] FIG. 1 illustrates a configuration of a plasma display apparatus according to an

exemplary embodiment.

[16] As shown in FIG. 1, the plasma display apparatus according to the exemplary embodiment includes a plasma display panel 100 and a driver 110.

[17] The plasma display panel 100 includes scan electrodes Yl to Yn and sustain electrodes Zl to Zn positioned parallel to each other, and address electrodes Xl to Xm positioned to intersect the scan electrodes Yl to Yn and the sustain electrodes Zl to Za

[18] The driver 110 supplies driving signals to at least one of the scan electrodes Yl to

Yn, the sustain electrodes Zl to Zn, or the address electrodes Xl to Xm to thereby display an image on the screen of the plasma display panel 100.

[19] Although FIG. 1 has shown a case where the driver 110 is formed in the form of a signal board, the driver 110 may be formed in the form of a plurality of boards depending on the electrodes on the plasma display panel 100. For example, the driver 110 may include a first driver (not shown) for driving the scan electrodes Yl to Yn, a second driver (not shown) for driving the sustain electrodes Zl to Zn, and a third driver (not shown) for driving the address electrodes Xl to Xm.

[20] FIG. 2 illustrates a structure of a plasma display panel.

[21] As shown in FIG. 2, the plasma display panel may include a front substrate 201, on which a scan electrode 202 and a sustain electrode 203 are positioned parallel to each other, and a rear substrate 211 on which an address electrode 213 is positioned to intersect the scan electrode 202 and the sustain electrode 203.

[22] An upper dielectric layer 204 may be positioned on the front substrate 201, on which the scan electrode 202 and the sustain electrode 203 are positioned, to limit a discharge current of the scan electrode 202 and the sustain electrode 203 and to provide electrical insulation between the scan electrode 202 and the sustain electrode 203.

[23] A protective layer 205 may be positioned on the front substrate 201, on which the upper dielectric layer 204 is positioned, to facilitate discharge conditions. The protective layer 205 may be formed of a material having a high secondary electron emission coefficient, for example, magnesium oxide (MgO).

[24] A lower dielectric layer 215 may be positioned on the rear substrate 211, on which the address electrode 213 is positioned, to cover the address electrode 213 and to provide electrical insulation of the address electrodes 213.

[25] Barrier ribs 212 of a stripe type, a well type, a delta type, a honeycomb type, and the like, may be positioned on the lower dielectric layer 215 to partition discharge spaces, i.e., discharge cells. Hence, a red discharge cell R, a green discharge cell G, and a blue

discharge cell B, and the like, may be positioned between the front substrate 201 and the rear substrate 211.

[26] Widths of the red, green, and blue discharge cells R, G, and B may be substantially equal to one another. However, a width of at least one of the red, green, and blue discharge cells R, G, and B may be different from widths of the other discharge cells.

[27] The barrier rib 212 may have various forms of structures as well as a structure shown in FIG. 2. For example, the barrier rib 212 includes a first barrier rib 212b and a second barrier rib 212a. The barrier rib 212 may have a differential type barrier rib structure in which heights of the first and second barrier ribs 212b and 212a are different from each other, a channel type barrier rib structure in which a channel usable as an exhaust path is formed on at least one of the first barrier rib 212b or the second barrier rib 212a, a hollow type barrier rib structure in which a hollow is formed on at least one of the first barrier rib 212b or the second barrier rib 212a, and the like.

[28] In the differential type barrier rib structure, a height of the first barrier rib 212b may be smaller than a height of the second barrier rib 212a. In the channel type barrier rib structure, a channel may be formed on the first barrier rib 212b.

[29] Each of the discharge cells partitioned by the barrier ribs 212 may be filled with a discharge gas.

[30] A phosphor layer 214 may be positioned inside the discharge cells to emit visible light for an image display during an address discharge. For example, red, green, and blue phosphor layers may be positioned.

[31] A thickness of at least one of the red, green, and blue phosphor layers 214 may be different from thicknesses of the other phosphor layers. For example, a thickness of the green phosphor layer or the blue phosphor layer may be larger than a thickness of the red phosphor layer. The thickness of the green phosphor layer may be substantially equal to or different from the thickness of the blue phosphor layer.

[32] While the address electrode 213 may have a substantially constant width or thickness, a width or thickness of the address electrode 213 inside the discharge cell may be different from a width or thickness of the address electrode 213 outside the discharge cell. For example, a width or thickness of the address electrode 213 inside the discharge cell may be larger than a width or thickness of the address electrode 213 outside the discharge cell.

[33] When a predetermined signal is supplied to at least one of the scan electrode 202, the sustain electrode 203, and the address electrode 213, a discharge occurs inside the discharge cell. Hence, ultraviolet rays are generated by the discharge gas filled in the

discharge cell because of the discharge, and are emitted on phosphor particles of the phosphor layer 214. Then, the phosphor particles emit visible light to thereby display an image on the screen of the plasma display panel.

[34] FIG. 3 illustrates a frame for achieving a gray level of an image in the plasma display apparatus.

[35] As shown in FIG. 3, a frame may include a plurality of subfields. Each subfield may be divided into an address period and a sustain period. During the address period, the discharge cells not to generate a discharge are selected or the discharge cells to generate a discharge are selected. During the sustain period, gray levels are achieved depending on the number of discharges.

[36] For example, as shown in FIG. 3, if an image with 256-level gray scale is to be displayed, a frame may be divided into 8 subfields SFl to SF8. Each of the 8 subfields SFl to SF8 may be subdivided into an address period and a sustain period.

[37] The number of sustain signals supplied during the sustain period determines gray level weight in each of the subfields. For example, in such a method of setting gray level weight of a first subfield to 2° and gray level weight of a second subfield to 2 \ the sustain period increases in a ratio of 2 ⁿ (where, n = 0, 1, 2, 3, 4, 5, 6, 7) in each of the subfields. Hence, various gray levels of an image can be achieved by controlling the number of sustain signals supplied during the sustain period of each subfield depending on the gray level weight of each subfield.

[38] In FIG. 3, while one frame includes 8 subfields, the number of subfields constituting one frame may vary. For example, one frame may include 12 subfields or 10 subfields. Further, in FIG. 3, while the subfields of one frame are arranged in increasing order of gray level weight, the subfields may be arranged in decreasing order of gray level weight, or may be arranged regardless of gray level weight.

[39] At least one of the plurality of subfields of one frame may be a selective write subfield SW, and at least one of the other subfields may be a selective erase subfield SE.

[40] If a frame includes at least one selective write subfield and at least one selective erase subfield, it may be preferable that a first subfield of a plurality of subfields of the frame is a selective write subfield and the other subfields are selective erase subfields. Or, all the subfields of the frame may be selective erase subfields.

[41] The selective erase subfield is a subfield in which the discharge cell where a data signal is supplied to the address electrode during an address period is turned off during a sustain period following the address period. The selective write subfield is a subfield

in which the discharge cell where a data signal is supplied to the address electrode during an address period is turned on during a sustain period following the address period.

[42] FIG. 4 illustrates an example of an operation of the plasma display apparatus.

Driving signals to be described with reference to FIG. 4 are supplied by the driver 110 shown in FIG. 1.

[43] As shown in FIG. 4, during a reset period RP for initialization, a reset signal is supplied to the scan electrode Y. The reset signal includes a rising signal RU and a falling signal RD. The reset period is further divided into a setup period SU and a set- down period SD.

[44] IVbre specifically, during the setup period SU, the rising signal RU is supplied to the scan electrode Y. The rising signal RU rises from a voltage Vl to a voltage V2, and then gradually rises from the voltage V2 to a voltage V3. The supplying of the rising signal RU generates a weak dark discharge (i.e., a setup discharge) inside the discharge cells. Hence, a proper amouit of wall charges are accumulated inside the discharge cells.

[45] During the set-down period SD, the falling signal RD with a polarity opposite a polarity of the rising signal RU is supplied to the scan electrode Y. The falling signal RD gradually falls from a voltage V4 lower than the peak voltage V3 of the rising signal RU to a voltage V5. The supplying of the falling signal RD generates a weak erase discharge (i.e., a set-down discharge) inside the discharge cells. Hence, the remaining wall charges are irdform inside the discharge cells to the extent that an address discharge can stably occur inside the discharge cells.

[46] During an address period AP following the reset period RP, a scan bias signal Sbias, which is substantially hold at a voltage V6 higher than the lowest voltage V5 of the falling signal RD, is supplied to the scan electrode Y. A scan signal Scan falling from the scan bias signal Sbias is supplied to the scan electrode Y.

[47] A pulse width of a scan signal supplied to the scan electrode during an address period of at least one subfield may be different from pulse widths of scan signals supplied during address periods of the other subfields. A pulse width of a scan signal in a subfield may be larger than a pulse width of a scan signal in a next subfield in time order. For example, a pulse width of the scan signal may be gradually reduced in the order of 2.6 βs , 2.3 βs , 2.1 βs , 1.9 βs , etc., or may be reduced in the order of 2.6 βs , 2.3 βs, 2.3 βs, 2.1 βs 1.9 βs, 1.9 βs, etc. in the successively arranged subfields.

[48] When the scan signal Scan is supplied to the scan electrode Y, a data signal Data cor-

responding to the scan signal Scan is supplied to the address electrode X. As the voltage difference between the scan signal Scan and the data signal Data is added to the wall voltage produced during the reset period RP, the address discharge occurs inside the discharge cell to which the data signal Data is supplied.

[49] During the address period AP, a sustain bias signal Zbias is supplied to the sustain electrode Z so as to prevent the address discharge from uistably occurring by interference of the sustain electrode Z. The sustain bias signal Zbias may be substantially hold at a sustain bias voltage Vz. The sustain bias voltage Vz is smaller than a sustain voltage Vs of a sustain signal SUS and is larger than a grouid level voltage GND.

[50] During a sustain period SP for an image display, the sustain signal SUS may be supplied to at least one of the scan electrode Y or the sustain electrode Z. For example, the sustain signal SUS is alternately supplied to the scan electrode Y and the sustain electrode Z.

[51] As the wall voltage inside the discharge cell selected by performing the address discharge is added to the sustain voltage Vs of the sustain signal SUS, every time the sustain signal SUS is supplied, a sustain discharge, i.e., a display discharge occurs between the scan electrode Y and the sustain electrode Z.

[52] A plurality of sustain signals are supplied during a sustain period of at least one subfield, and a pulse width of at least one of the plurality of sustain signals may be different from pulse widths of the other sustain signals. For example, a pulse width of a first supplied sustain signal among the plurality of sustain signals may be larger than pulse widths of the other sustain signals. Hence, a sustain discharge can more stably occur.

[53] As shown in (a) of FIG. 5, one frame may be divided into two subfield groups. IVbre specifically, a first frame Fl may include a 1-1 subfield group A and a 1-2 subfield group B each including at least one subfield. A second frame F2 immediately following the first frame Fl may include a 2-1 subfield group C and a 2-2 subfield group D each including at least one subfield.

[54] The 1-1 subfield group A and the 1-2 subfield group B correspond to a vertical sync signal Vsync of 1 period, and the 2- 1 subfield group C and the 2-2 subfield group D correspond to a vertical sync signal Vsync of 1 period. In other words, the 1-1 subfield group A and the 1-2 subfield group B are included in the same frame, and the 2-1 subfield group C and the 2-2 subfield group D are included in the same frame.

[55] At least one of the subfields belonging to the 1-1 subfield group A may be identical to at least one of the subfields belonging to the 1-2 subfield group B, and at least one

of the subfields belonging to the 2- 1 subfield group C may be identical to at least one of the subfields belonging to the 2-2 subfield group D. Preferably, the 1-1 subfield group A and the 1-2 subfield group B are partially identical, and the 2-1 subfield group C and the 2-2 subfield group D are partially identical. For example, a first subfield "a" of the 1-1 subfield group A is identical to a first subfield "a"' of the 1-2 subfield group B, and a first subfield "k ¹ " of the 2-1 subfield group C is identical to a fifth subfield "k" of the 2-2 subfield group D.

[56] All the subfields belonging to the 1-2 subfield group B may be identical to some subfields of the 1-1 subfield group A, and all the subfields belonging to the 2-1 subfield group C may be identical to some subfields of the 2-2 subfield group D. Further, some subfields of the 1-2 subfield group B may be identical to some subfields of the 1-1 subfield group A, and the remaining subfields of the 1-2 subfield group B may not be identical to the remaining subfields of the 1-1 subfield group A Some subfields of the 2-1 subfield group C may be identical to some subfields of the 2-2 subfield group D, and the remaining subfields of the 2-1 subfield group C may not be identical to the remaining subfields of the 2-2 subfield group D.

[57] The fact that two subfields are identical may mean that data in the two identical subfields are identical. In other words, the two identical subfields have identical data. The fact that two subfields are identical may mean that two address periods of the two identical subfields are identical. In other word, signal operations during the two address periods of the two identical subfields are identical. The fact that two subfields are identical may mean that the number of sustain signals supplied during each of two sustain periods of the two identical subfields are equal to each other. The fact that two subfields are identical may mean signal operations during reset periods, address periods, and sustain periods of the two identical subfields are identical.

[58] As shown in (a) of FIG. 5, all the subfields a', b', c' and d' of the 1-2 subfield group B are identical to some subfields a, b, c and d of the 1-1 subfield group A, respectively. All the subfields k ¹ and 1' of the 2- 1 subfield group C are identical to some subfields k and 1 of the 2-2 subfield group D, respectively.

[59] As shown in (b) of FIG. 5, an effect, in which the first frame Fl and the second frame F2 are divided into 1st, 2nd, 3rd sub-frames subFl, subF2 and subF3, can be obtained. IVbre specifically, the 1st sub-frame subFl includes the 1-1 subfield group A, the 2nd sub-frame subF2 includes the 1-2 and 2-1 subfield groups B and C, the 3rd sub-frame subF3 includes the 2-2 subfield group D.

[60] As a result, a viewer can perceive an image displayed in two frames as an image

displayed in three frames. For example, if a length of each of the first and second frames Fl and F2 is 20 ms, a total of 50 images are displayed for 1 second. However, when a structure of the frame changes as shown in FIG. 5, an effect, in which a total of 75 images are displayed for 1 second, can be obtained. Hence, the image quality can be improved.

[61] A reason to change a structure of a frame is described with reference to FIGs. 6 to 9.

[62] FIG. 6 illustrates a case where a frame is not divided into two subfields groups. For example, first and second frames Fl and F2 each have a length of 20 ms.

[63] In this case, an afterglow time of a phosphor may be shorter than a vertical frequency of the frame, i.e., a frequency of a vertical sync signal Vsync. Hence, a phenomenon whereby a display screen appears to flicker may occur. When the vertical frequency of the frame is 50 Hz as in FIG. 6, the flicker phenomenon may worsea

[64] When the viewer watches an image, the viewer perceives a time direction as well as a spatial direction of the image. For example, if a car displayed on the plasma display panel moves from left to right, the viewer perceives a movement of the car as well as a position of the car on the plasma display panel.

[65] Accordingly, as shown in FIG. 6, if a moving image is displayed in the first and second frames Fl and F2 each having the length of 20 ms, there are a spatial difference and a time difference between the first and second frames Fl and F2. If the images are successively displayed in the first and second frames Fl and F2, as shown in FIG. 7, the viewer watches the image in the second frame F2 as if the image in the first frame Fl and the image in the second frame F2 overlap. Hence, an interface between the images may be inclear. For example, the viewer may perceive an image shown in (a) of FIG. 8 as an image shown in (b) of FIG. 8. This is referred to as a false contour noise. The false contour noise may be a cause reducing the image quality of the image. However, if the structure of the frame changes as shown in FIG. 5, an effect in which the first and second frames Fl and F2 are divided into three sub-frames can be obtained as shown in FIG. 9.

[66] In FIG. 5, in the second sub-frame subF2 between the first sub-frame subFl and the third sub-frame subF3, the 1-2 subfield group B is identical to a portion of the 1-1 subfield group A of the first sub-frame subFl, and the 2-1 subfield group C is identical to a portion of the 2-2 subfield group D of the third sub-frame subF3. Hence, the second sub-frame subF2 may have a middle value of the first sub-frame subFl and the third sub-frame subF3. Accordingly, because the viewer can watch the images in the first and second frames Fl and F2 as if the images are successively displayed in the

three sub-frames, the generation of the false contour noise can be reduced. Further, the viewer can watch 75 images for 1 second. Hence, because an effect in which the frame frequency increases from 50 Hz to 75 Hz can be obtained, the generation of the flicker can be reduced.

[67] When a frame length is about 1/50 sec, it is advantageous that two frames are divided into three sub-frames. Although the two frames are divided into the three sub-frames, each of the three sub-frames can have a sufficient time required to drive.

[68] In terms of video data, video data of the 1-2 and 2-1 subfield groups B and C may have a middle value of video data of the 1-1 subfield group A and video data of the 2-2 subfield group D. In other words, video data of the second sub-frame subF2 may have a middle value of video data of the first sub-frame subFl and video data of the third sub-frame subF3.

[69] As above, it may be preferable that the 1-2 subfield group B is produced from the 1-1 subfield group A and the 2- 1 subfield group C is produced from the 2-2 subfield group D so that the video data of the second sub-frame subF2 have the middle value of the video data of the first sub-frame subFl and the video data of the third sub-frame subF3.

[70] As above, when the video data of the second sub-frame subF2 have the middle value of the video data of the first sub-frame subFl and the video data of the third sub-frame subF3, the viewer perceives images in two frames as images in three frames. Hence, the image quality can be improved. Further, because the images are successively displayed in the three frames, the image quality can be further improved.

[71] FIGs. 10 and 11 illustrate a length of a subfield group.

[72] As shown in FIG. 10, a first frame Fl includes a 1-1 subfield group A and a 1-2 subfield group Ej and a second frame F2 includes a 2- 1 subfield group C and a 2-2 subfield group D. The 1-1 subfield group A includes subfields a, b, c, d, e, and f, and the 2-2 subfield group D includes g, h, i, j, k and 1. The 1-2 subfield group B includes subfields a' and b' identical to the subfields a and b. The 2-1 subfield group C includes a subfield 1' identical to the subfield 1. In other words, a second sub-frame subF2 includes a total of 3 subfields a', b' and 1'.

[73] In this case, a length of the second sub-frame subF2 corresponding to a sum of a length of the 1-2 subfield group B and a length of the 2-1 subfield group C may be excessively short. Hence, the viewer may perceive an image as if the image is achieved in only first and third sub-frames subFl and subF3. As a result, a reduction effect in the flicker may be small, and the false contour noise may occur frequently.

[74] As shown in FIG. 11, a first frame Fl includes a 1-1 subfield group A and a 1-2 subfield group Ej and a second frame F2 includes a 2- 1 subfield group C and a 2-2 subfield group D. The 1-1 subfield group A includes subfields a, b, c, d, and e, and the 2-2 subfield group D includes f, g, h, i, and j. The 1-2 subfield group B includes subfields a', b', c', d' and e' identical to the subfields a, b, c, d, and e. The 2-1 subfield group C includes subfields h', i' and j' identical to the subfields h, i, and j. In other words, a second sub-frame subF2 includes a total of 8 subfields.

[75] In this case, a length of the second sub-frame subF2 corresponding to a sum of a length of the 1-2 subfield group B and a length of the 2-1 subfield group C may be excessively long. Hence, an image may be remarkably displayed in the second sub-frame subF2. As a result, the image quality of the image may be reduced, and the false contour noise may occur frequently.

[76] Preferably, the length of the second sub-frame subF2 corresponding to the sum of the length of the 1-2 subfield group B and the length of the 2-1 subfield group C may be 1/100 sec to 1/80 sec in consideration of the above description IVbre preferably, the sum of the length of the 1-2 subfield group B and the length of the 2-1 subfield group C may be approximately equal to a length of the first sub-frame subFl (i.e., a length of the 1-1 subfield group A) or a length of the third sub-frame subF3 (i.e., a length of the 2-2 subfield group D). Further, a sum of the number of subfields belonging to the 1-2 subfield group B and the number of subfields belonging to the 2-1 subfield group C may be equal to the number of subfields belonging to the 1-1 subfield group A or the number of subfields belonging to the 2-2 subfield group D. For example, as shown in FIG. 12, a sum of the number of subfields belonging to a 1-2 subfield group B and the number of subfields belonging to a 2-1 subfield group C may be set at 6, and the number of subfields belonging to a 1-1 subfield group A or the number of subfields belonging to a 2-2 subfield group D may be set at 6. Hence, it can be easier that a sum d2 of a length of the 1-2 subfield group B and a length of the 2-1 subfield group C may be approximately equal to a length dl of the 1-1 subfield group A or a length d3 of the 2-2 subfield group D.

[77] Further, when a sum of the number of subfields belonging to the 1-2 subfield group

B and the number of subfields belonging to the 2-1 subfield group C is equal to the number of subfields belonging to the 1-1 subfield group A or the number of subfields belonging to the 2-2 subfield group D, it can be easier that image data of the 1-2 and 2-1 subfield groups B and C has a middle value of image data of the 1-1 subfield group A and image data of the 2-2 subfield group D.

[78] It may be preferable that the 1-2 subfield group B and the 2-1 subfield group C are successively arranged so as to prevent the generation of flicker and efficiently reduce the generation of false contour noise.

[79] FIG. 13 illustrates another exemplary method for changing a structure of a frame.

[80] In FIG. 13, a vertical frequency of a frame is 75 Hz. The above method for changing the structure of the frame whose the vertical frequency is 50 Hz may be used to change a structure of the frame whose the vertical frequency is 75 Hz. In other words, the above method may be used to change the structure of the frame whose a length is 1/75 sec (about 13.34 ms).

[81] As shown in FIG. 13, it is assumed that first, second, and third frames Fl, F2, and F3 are successively arranged in the order named. At least one of a plurality of subfields of the second frame F2 may be identical to at least one of a plurality of subfields of the first frame Fl, or may be identical to at least one of a plurality of subfields of the third frame F3. For example, the first frame Fl includes subfields a, b, c, d, e and f, and the third frame F3 includes subfields g, h, i, j, k and 1. The second frame F2 includes subfields a', b', c' and d' identical to the subfields a, b, c and d of the first frame Fl and subfields k ¹ and 1' and identical to the subfields k and 1 of the third frame F3.

[82] The second frame F2 between the first frame Fl and the third frame F3 may have a middle value of the first frame Fl and the third frame F3. Hence, a frame memory for storing video data of the second frame F2 is not necessary. Accordingly, the manufacturing cost can be reduced, and image processing can be simpler.

[83] As shown in FIG. 13, the first frame Fl may include a 1-1 subfield group A and a

1-2 subfield group B each including at least one subfield, the second frame F2 may include a 2- 1 subfield group C and a 2-2 subfield group D each including at least one subfield, and the third frame F3 may include a 3-1 subfield group E and a 3-2 subfield group F each including at least one subfield.

[84] At least one subfield group of the second frame F2 may be substantially identical to at least one subfield group of the first frame Fl or at least one subfield group of the third frame F3. For example, the 2-1 subfield group C of the second frame F2 may be substantially identical to the 1-1 subfield group A of the first frame Fl, and the 2-2 subfield group D of the second frame F2 may be substantially identical to the 3-2 subfield group F of the third frame F3.

[85] FIG. 14 illustrates another exemplary method for changing a structure of a frame. In

FIG. 14, a length of each of first, second and third frames Fl, F2 and F3 is 1/75 sec.

[86] As shown in FIG. 14, the first frame Fl includes subfields a, b, c, d, e and f, and the

third frame F3 includes subfields g, h, i, j, k and 1. The second frame F2 includes subfields a', c' and e' identical to the subfields a, c and e of the first frame Fl and subfields h', j' and 1' and identical to the subfields h, j and 1 of the third frame F3. Hence, the second frame F2 between the first frame Fl and the third frame F3 can have a middle value of the first frame Fl and the third frame F3 without adding a frame memory.

[87] The first frame Fl may include a 1-1 subfield group including the subfields a, c and e and a 1-2 subfield group including the subfields b, d and f, the second frame F2 may include a 2-1 subfield group including the subfields a', c' and e' and a 2-2 subfield group including the subfields h', j' and 1' and the third frame F3 may include a 3-1 subfield group including the subfields g, i and k and a 3-2 subfield group including the subfields h, j and 1.