JP4165108B2 - Plasma display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma display device that displays an image by controlling discharge.
[0002]
[Prior art]
FIG. 5 is a perspective view showing the main part of the plasma display panel. As shown in FIG. 5, a scanning electrode 3 and a sustaining electrode 4 covered with a dielectric layer 2 are attached in parallel to each other on the first glass substrate 1, and the dielectric layer 2 A protective layer 5 is formed on the top. A data electrode 8 covered with an insulator layer 7 is provided on the second glass substrate 6, and a partition wall 9 is provided in parallel with the data electrode 8 on the insulator layer 7 between the data electrodes 8. . In addition, the phosphor 10 is provided on the surface of the insulator layer 7 and the side surface of the partition wall 9, and the first glass substrate 1 and the second glass substrate so that the scan electrode 3, the sustain electrode 4, and the data electrode 8 are orthogonal to each other. 6 is arranged to face each other. A discharge space 11 is formed between the first glass substrate 1 and the second glass substrate 6, and a discharge gas is sealed in the discharge space 11. A discharge cell is formed at the intersection of the data electrode 8, the scan electrode 3, and the sustain electrode 4, sandwiched between two adjacent barrier ribs 9.
[0003]
Since such a plasma display panel uses the discharge phenomenon, the discharge cell has only two states of lighting and non-lighting. Therefore, in order to perform halftone gradation expression, one field is divided into a plurality of subfields weighted corresponding to light emission luminance, and gradation expression is performed by controlling the presence or absence of light emission in each subfield. Yes. FIG. 6 shows a conventional gradation display method for a plasma display. SF1 to SF8 represent eight subfields constituting one field. The light emission luminance weights of the subfields SF1 to SF8 are “1”, “2”, “4”, “8”, “16”, “32”, “64”, and “128”, respectively. The left column represents the number of gradations, and “◯” in the table represents a subfield in which the light emission maintaining operation is performed when displaying an image with each gradation number. For example, when expressing the gradation “15”, by performing a writing operation in the writing period in the subfields SF1 to SF4, the respective weights “1”, “2”, and “4” of the subfields SF1, SF2, SF3, and SF4 are displayed. The light emission maintaining operation corresponding to “4” and “8” is performed, and the gradation “15” is expressed. Further, when expressing the gradation “16”, the light emission maintaining operation corresponding to the gradation “16” is performed by performing the writing operation only in the subfield SF5.
[0004]
7 and 8 show a driving timetable configuration and driving signals in one field for driving the plasma display panel. As shown in FIGS. 7 and 8, when one field is composed of a plurality of subfields, for example, eight subfields SF1 to SF8, the subfields SF1 to SF8 are processed in order, and all the processes are performed in a period of one field. Done within.
[0005]
The drive timetable configuration and drive signals will be described with reference to FIG. Each of the eight subfields SF1 to SF8 includes a writing period, a sustain period, and an erase initialization period, and one field includes an initializing period that is first followed by a plurality of subfields SF1 to SF8. Next, processing in each subfield will be described.
[0006]
In the writing period, the horizontal scanning electrodes 3 are sequentially scanned, and a predetermined writing operation is performed only on the discharge cells that have received pulses from the data electrodes 8. For example, when processing the subfield SF1, the write operation is performed in the discharge cells indicated by “◯” in the subfield SF1 shown in FIG. 6, and the write operation is performed in the discharge cells displayed in the blank. I will not.
[0007]
In the sustain period, a sustain pulse for sustaining light emission corresponding to a value weighted in each subfield is alternately applied to scan electrode 3 and sustain electrode 4. In the discharge cell indicated by “◯” in FIG. 6 and performing the writing operation, a discharge occurs for each sustain pulse to maintain light emission, and a predetermined luminance is obtained for a predetermined discharge cell by one discharge. Can do. In the subfield SF1, the weight is “1”, and by applying one sustain pulse to each of the scan electrode 3 and the sustain electrode 4 in the sustain period, a luminance of “1” level is obtained. In the subfield SF2, the weighting is “2”. By applying two sustain pulses to the scan electrode 3 and the sustain electrode 4 in the sustain period, a luminance of “2” level is obtained.
[0008]
As described above, the writing period is a period for selecting a discharge cell that emits light, and the sustain period is a period in which light emission is maintained a number of times according to the weighting of each subfield. That is, the subfields SF1 to SF8 shown in FIG. 7 are weighted with “1”, “2”, “4”, “8”, “16”, “32”, “64”, and “128”, respectively. In this case, the luminance level in each discharge cell can be adjusted in 256 steps from 0 to 255.
[0009]
By the way, a bright image can be obtained even if the sustain pulse obtained from the video signal is used as it is on an overall bright screen, but in the case where the sustain pulse obtained from the video signal is used as it is on an entirely dark screen. Becomes a very dark screen, resulting in poor video expression. According to the structure of the human eye, the pupil becomes smaller and the amount of light entering is reduced in bright places, but when it gets darker, the pupil becomes larger continuously and tries to capture more light. In order to obtain the same effect, if the entire screen becomes dark, the number of sustain pulses is increased at the same rate on the entire screen, so that the entire screen is brightened and a dark image is maintained while obtaining a solid image expression. Are known. For example, when the brightness of the entire screen is divided into three levels: “bright”, “slightly bright”, and “dark”, the number of sustain pulses in the case of “bright” is used as it is, and the mode is “slightly bright”. Uses a 2 × mode in which the number of sustain pulses is doubled, and in the case of “dark”, uses a 3 × mode in which the number of sustain pulses is tripled. FIG. 7 shows the case of the 1 × mode, and FIG. 8 shows the case of the 2 × mode.
[0010]
FIG. 9 shows a table relating to the correspondence between the emission luminance weighting of each subfield and the number of sustain pulses. As shown in FIG. 9, for example, when the maximum multiple is set to 3, the brightness is changed in multiple stages from 1 to 3 times in order to continuously change the brightness. In order to change continuously, the sustain pulse is changed not only by an integral multiple but also by a multiple including a decimal point. In principle, the number of sustain pulses is obtained by multiplying the weight of each subfield by a multiple. However, when the multiple includes a decimal point, the number of sustain pulses is not an integer value but a value including a decimal point. In this case, the value after the decimal point of the number of sustain pulses is rounded as shown in FIG. 9, so that the number of sustain pulses, that is, the number of times of sustaining light emission is always an integer value. Note that the value after the decimal point of the number of sustain pulses may be rounded down or rounded up.
[0011]
In this way, by changing the number of sustain pulses stepwise and further increasing the number of steps, it is possible to adjust the brightness without making the person watching the screen feel a change in brightness.
[0012]
[Problems to be solved by the invention]
However, when expressing a gradation close to black according to the table shown in FIG. 9, the number of times of maintaining the light emission in the 1 × mode used when the entire screen is bright is “1” at the next lowest gradation after black. “2” at a low gradation, and “3”, “4”, “5” as the gradation becomes higher. On the other hand, the number of times of sustaining light emission in the triple mode used when the entire screen is dark Even when expressing the next lowest gradation after black, it becomes “3”, and the amount of change in luminance with respect to black, that is, the luminance difference becomes larger than in the 1 × mode. Thereby, for example, even when the gradation near black is expressed using an error diffusion method or the like, the discharge cell expressed by the darkest luminance next to black is expressed by the number of times of light emission maintenance “3”. The discharge cell has a brightness that can be clearly confirmed, and there is a problem that the image quality particularly in the vicinity of black deteriorates.
[0013]
The present invention has been made to solve such a problem, and in the case of displaying an image in a plurality of multiple modes, the luminance of black and the luminance of a discharge cell expressing the next lowest gradation after black are calculated. An object of the present invention is to provide a plasma display device capable of preventing an increase in luminance difference and preventing image quality deterioration near black.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the plasma display apparatus of the present invention has a plurality of subfields weighted corresponding to the light emission luminance in one field, and the light emission luminance in each subfield in one field is a video signal. In a plasma display device that displays an image by changing the level according to the level, in the subfield weighted corresponding to the minimum light emission luminance among the plurality of subfields controlled to emit light according to the video signal . The light emission luminance is not changed in accordance with the video signal level. As a result, it is possible to achieve the minimum luminance that can set the next lowest gradation after black regardless of the video signal level.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the first aspect of the present invention, one field has a plurality of weighted subfields corresponding to the light emission luminance, and the light emission luminance in each subfield within one field is changed according to the video signal level. In the plasma display device that performs video display , the light emission luminance in the subfield weighted corresponding to the minimum light emission luminance among the plurality of subfields controlled to emit light according to the video signal, The plasma display device is characterized in that it is not changed in accordance with the video signal level.
[0016]
According to the invention of claim 2, one field has a plurality of subfields weighted corresponding to the light emission luminance and the number of times of maintaining the light emission is set according to the weighting, and the light emission in each subfield in one field. In a plasma display device that displays an image by multiplying the number of times of maintenance by a predetermined number according to the video signal level, among a plurality of subfields that are controlled to emit light according to the video signal, corresponding to the minimum light emission luminance The plasma display apparatus is characterized in that the number of times of light emission maintenance in the weighted subfield is not changed in accordance with the video signal level.
[0017]
Thereby, even when the sum of the luminances of a plurality of subfields that emit light increases, it is possible to prevent the luminance difference between the luminance of black and the luminance of the discharge cell expressing the next lowest gradation from black from increasing. Image quality deterioration near black can be prevented.
[0018]
According to the invention of claim 3, the video signal level is set to the value of the average luminance of the entire display screen. Thereby, it is possible to prevent the entire screen from becoming dark and poor even in a dark scene.
[0019]
According to a fourth aspect of the present invention, the video signal level is a value of an average luminance in a predetermined range including the central portion of the display screen. In the fifth aspect of the invention, the video signal level is set to the display screen. This is the value of the peak luminance at a predetermined one pixel. Thereby, it is possible to easily detect the video signal level.
[0020]
Furthermore, in the invention of claim 6, when displaying an image with a gradation higher than a predetermined gradation , the minimum light emission luminance among the plurality of subfields controlled to emit light according to the video signal. According to the seventh aspect of the present invention, the light emission maintaining operation is not performed in the subfields weighted corresponding to the above, and the predetermined gradation is set to the next lowest gradation after black display. Thereby, it is possible to reduce the power consumption of the data driver by the write operation for lighting the discharge cells without greatly degrading the gradation characteristics.
[0021]
Hereinafter, a plasma display device according to an embodiment of the present invention will be described with reference to the drawings.
[0022]
FIG. 1 is a configuration diagram of a plasma display device according to an embodiment of the present invention. This plasma display device includes a plasma display panel 20, a data driver 21, a scan driver 22, a sustain driver 23, a signal level detection means 24, and a sustain. Pulse number setting means 25 and subfield conversion means 26 are provided.
[0023]
The plasma display panel 20 has the same configuration as that of the conventional plasma display panel shown in FIG. 5, and a substrate on which a plurality of scan electrodes 3 and sustain electrodes 4 are formed and a substrate on which a plurality of data electrodes 8 are formed are opposed to each other. In addition, a discharge space is formed between the substrates. A discharge gas made of neon, xenon, or the like is sealed in the discharge space. Scan electrode 3, sustain electrode 4, and data electrode 8 are arranged to be orthogonal to each other, and discharge cell 27 is formed at the intersection of scan electrode 3, sustain electrode 4, and data electrode 8.
[0024]
A signal level detection unit 24, a sustain pulse number setting unit 25, and a subfield conversion unit 26 are sequentially arranged from the input side of the video signal. The subfield conversion unit 26 is connected to the data driver 21, the scan driver 22, and the sustain driver 23. Yes. The signal level detection means 24 detects the video signal level of the input video signal and outputs it to the sustain pulse number setting means 25. The sustain pulse number setting means 25 determines a multiple for the weighting of each subfield according to the video signal level and outputs it to the subfield conversion means 26 at the subsequent stage. The subfield conversion means 26 determines a subfield to be written according to the gradation and outputs it to the data driver 21 and outputs the number of sustain pulses in each subfield to the scan driver 22 and the sustain driver 23. The data driver 21, scan driver 22 and sustain driver 23 are connected to the data electrode 8, scan electrode 3 and sustain electrode 4 of the plasma display panel 20, respectively, and generate voltages to be applied to the respective electrodes.
[0025]
FIG. 2 is an explanatory diagram showing a driving timetable configuration and driving signals of the plasma display device according to one embodiment of the present invention. As shown in FIG. 2, one field includes an initializing period followed by eight subfields SF1 to SF8, and each subfield includes a writing period, a sustaining period, and an erasing initializing period. Has been. The subfields SF1 to SF8 are processed in order, and all the processes are performed within a period of one field.
[0026]
During the writing period in each subfield, a scan pulse is sequentially applied to each scan electrode 3 and a data pulse is applied to a desired data electrode 8 to thereby apply the scan electrode 3 to which the scan pulse is applied and the data electrode to which the data pulse is applied. An address operation is performed in the discharge cells 27 at the eight intersections. By applying sustain pulses alternately to the scan electrodes 3 and the sustain electrodes 4 in the sustain period following the write period, the light emission sustain operation is performed in the discharge cells 27 in which the write operation has been performed. For example, as shown in FIG. 2, four sustain pulses are applied to scan electrode 3 and sustain electrode 4 in the sustain period of subfield SF2, and each time sustain pulse is applied, scan electrode 3 and sustain electrode 4 When the light emission sustaining discharge occurs, a luminance of “4” corresponding to the number of times of the light emission sustaining discharge is obtained. Similarly, luminance of level “8” is obtained in subfield SF3.
[0027]
As described above, the writing period is a period for selecting a discharge cell that emits light, and the sustain period is a period in which a predetermined number of light emission sustain discharges are performed based on the weighting for each subfield. In the erase initialization period following the sustain period, the light emission sustain discharge generated in the sustain period is stopped and the discharge cells are initialized. The operation in the next subfield is affected by the light emission state of each discharge cell. Do not.
[0028]
FIG. 3 is a table showing the weighting of each subfield and the relationship between the weighting multiple and the number of sustain pulses. SF1 to SF8 in the left half represent the weights corresponding to the light emission luminances in the subfields SF1 to SF8. SF1 to SF8 represent the number of sustain pulses in each of the subfields SF1 to SF8. Here, when the sustaining operation is performed by applying the same number of sustain pulses as the weighting given to each subfield to the scan electrode 3 and the sustain electrode 4 to perform the light emission sustaining operation, the number of sustaining pulses in the 1 × mode is set. A case where n times the number of sustain pulses is applied is referred to as an n-fold mode, and n is referred to as a weighted multiple.
[0029]
As shown in FIG. 3, when the maximum weighting factor is 3, the weighting factor is changed by a number including a decimal point between 1 and 3 in order to continuously change the brightness. The number of sustain pulses in each subfield, that is, the number of times of sustaining light emission, is set according to the weight corresponding to the light emission luminance in the 1 × mode, and in the n × mode, the number is multiplied by the weighted multiple and the weight of each subfield. However, when the weighting multiple includes a decimal point, the number of sustain pulses is set by rounding down or rounding up to the whole number by rounding down or rounding up the number obtained by multiplying the weighting by the weighting multiple.
[0030]
In the present embodiment, as shown in FIG. 3, the number of sustain pulses in subfields SF2 to SF8 is set to a value obtained by multiplying the weighting multiple by the weight of each subfield. The number of sustain pulses in the weighted subfield SF1 is fixed to 1 which is the number of sustain pulses in the 1 × mode so as not to change depending on the weighting multiple. That is, the number of sustain pulses applied to scan electrode 3 and sustain electrode 4 is always 1 in subfield SF1. FIG. 2 shows the case of the double mode.
[0031]
When video display is performed according to the table of FIG. 3, the mode is switched between the 1 × mode and the 3 × mode according to the brightness of the entire screen. In other words, when the entire screen is bright, video display is performed in the 1 × mode, and when the entire screen is dark, video display is performed in the 3 × mode. Thereby, even in a scene where the entire screen is dark, it is possible to obtain a firm image while maintaining a dark atmosphere, and it is possible to adjust the brightness without making the viewer looking at the brightness change.
[0032]
In addition, since the number of sustain pulses in subfield SF1 is fixed so as not to change depending on the weighting multiple, even when the entire screen is a dark scene, that is, in a driving condition with a large weighting multiple and a large total number of sustain pulses, The luminance difference between the luminance of the discharge cell and the luminance of the discharge cell expressing the next lowest gray level can always be minimized. Therefore, when the weighting multiple is increased, the luminance of black is higher than that in the conventional case where the number of times of light emission sustaining discharge in the subfield SF1 used for expressing the next lower gradation after black increases as the weighting multiple increases. Therefore, it is possible to reduce the luminance difference between the luminance of the discharge cell that expresses the next lowest gray level and the luminance of black, so that it is possible to prevent image quality deterioration near black.
[0033]
In this embodiment, the weighting multiple is changed according to the brightness of the entire screen, but the brightness of the entire screen is a value of the average luminance of the entire display screen, and the signal level detection means 24 is determined from the input video signal. This is obtained as a video signal level. That is, in the present embodiment, video display is performed by changing the light emission luminance in each subfield in accordance with the video signal level, and the light emission luminance in subfield SF1 weighted corresponding to the minimum light emission luminance is displayed as video. It does not change according to the signal level.
[0034]
Further, the video signal level may be a value of average luminance in a predetermined range including the central portion of the display screen. In this case, since the range for obtaining the average luminance is narrower than that for obtaining the average luminance of the entire display screen, the video signal level can be easily detected.
[0035]
Further, the video signal level can be a peak luminance value at a predetermined pixel of the display screen, for example, a pixel at the center of the display screen. In this case, it is possible to easily detect the video signal level as compared with the case where the entire display screen and a predetermined range including a plurality of pixels are evaluated.
[0036]
Next, an embodiment of a gradation expression method in the plasma display apparatus of the present invention will be described with reference to FIG.
[0037]
FIG. 4 shows a case where the weighting factor used when the entire screen is dark is 3 (3 times mode). One field is divided into eight subfields, and weighting corresponding to the light emission luminances of the subfields SF1 to SF8 is shown. Are arranged as “1”, “2”, “4”, “8”, “16”, “32”, “64”, and “128”, respectively. As described above, the number of sustain pulses in the subfield SF1 is 1, and the number of sustain pulses in the subfields SF2 to SF8 is a number obtained by multiplying the weighting multiple corresponding to the light emission luminance. The left column of the table in FIG. 4 represents the number of gradations, and “◯” in the table represents a subfield in which the light emission maintaining operation is performed when an image with each gradation number is displayed. For example, when the gradation “1” is expressed, by performing the writing operation only in the writing period in the subfield SF1, the light emission maintaining operation corresponding to the weight “1” of the subfield SF1 is performed, and the gradation “1” is performed. 1 "is expressed. When expressing the next gradation “2”, the light emission maintaining operation corresponding to the gradation “2” is performed by performing the writing operation only in the subfield SF2. Then, as shown in FIG. 4, the light emission maintaining operation in the subfield SF1 is not performed in the gradation of gradation “3” or higher.
[0038]
For example, when the gradation “37” is expressed, the gradation “37” is expressed by performing the light emission maintaining operation in the subfield SF3 and the subfield SF6, and the light emission maintaining operation is not performed in the subfield SF1. In this case, since the number of sustain pulses is the same as when expressing gradation “36”, the light emission amount of the subfield to emit light is the same between gradation “36” and gradation “37”, and the number of sustain pulses The size corresponds to “108”. In addition, the amount of light emitted when the gradation “38” is expressed has a magnitude corresponding to the number of sustain pulses “114”.
[0039]
Here, if the light emission sustaining operation is performed in the subfield SF1 when the gradation “37” is expressed, the light emission amount has a magnitude corresponding to the sustain pulse number “109”, but the gradation “36” is obtained. The luminance difference between the gradation “36” and the gradation “37” is very small compared to the difference in light emission amount between the gradation “38”, that is, the luminance difference. For this reason, when the gradation “37” is expressed, there is almost no influence on the display even if the light emission maintaining operation of the subfield SF1 is not performed. In this embodiment, the light emission maintaining operation of the subfield SF1 is not performed. Yes. The effect of hardly affecting the display in this way is recognized as more prominent when the weighting factor is increased in order to display a higher luminance. The power consumption of the data driver increases in proportion to the number of write operations performed during the write period of each subfield that emits light. In the present embodiment, however, the subfield SF1 is used at the gray scale of “3” or higher. Since the light emission maintaining operation is not performed in step S1, the writing operation in the subfield SF1 is not performed, and the power consumption of the data driver can be reduced.
[0040]
When displaying a gradation having a large weighting factor and higher than a predetermined gradation in this way, a large gradation deterioration occurs without performing the light emission maintaining operation of the subfield SF1 weighted corresponding to the minimum light emission luminance. In addition, the power consumption of the data driver due to the writing operation in the writing period of the subfield SF1 can be reduced.
[0041]
Note that the maximum value of the weighting multiple does not need to be tripled as shown in the above embodiment, and the present invention can be applied to values including a decimal point, such as 5, 10, or 6.5 times. Can be applied. Further, the step size of the weighted multiple need not be equal to 0.125, but may be other values or not equal. Further, the number of subfields and the weighting value of each subfield do not necessarily have to be the values used in the above embodiment, but are weighted so that gradation can be expressed by the combination of light emission maintenance in the sustaining period of each subfield. If it is, the same effect can be acquired.
[0042]
【The invention's effect】
As described above, according to the present invention, the light emission luminance in each subfield is imaged by not changing the light emission luminance in the subfield weighted corresponding to the minimum light emission luminance according to the video signal level. In a plasma display device that displays an image by changing the signal level according to the signal level, it is possible to prevent the deterioration of the image quality in the vicinity of black.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a plasma display device according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a driving timetable configuration and driving signals for one field in the plasma display device. FIG. 4 is an explanatory view showing a subfield weighting and the number of sustaining light pulses. FIG. 4 is an explanatory view showing a gradation expression method in the plasma display device. FIG. 5 is a perspective view showing a main part of a conventional plasma display panel. FIG. 7 is an explanatory diagram showing a gradation expression method in a conventional plasma display device. FIG. 7 is an explanatory diagram showing a driving timetable configuration and a driving signal for one field in a conventional plasma display device. FIG. 9 is a diagram illustrating a driving timetable configuration and driving signals. Explanatory view showing weighting the number of light emission sustain pulses of each subfield in the plasma display device [Description of symbols]
3 Scan electrode 4 Sustain electrode 8 Data electrode 20 Plasma display panel 21 Data driver 22 Scan driver 23 Sustain driver 24 Signal level detection means 25 Sustain pulse number setting means 26 Subfield conversion means 27 Discharge cell

Claims (7)

One field has a plurality of subfields weighted to correspond to the emission luminance in the plasma display apparatus displaying a picture by changing accordance with luminance of each sub-field in one field in the video signal level, video Among the plurality of subfields whose presence or absence is controlled according to the signal, the emission luminance in the subfield weighted corresponding to the minimum emission luminance is not changed according to the video signal level. A plasma display device. One field has a plurality of subfields weighted corresponding to the light emission luminance and set the number of times of light emission maintenance according to the weighting, and the number of times of light emission maintenance in each subfield within one field is determined according to the video signal level. The number of times of sustaining light emission in the subfield weighted corresponding to the minimum light emission luminance among the plurality of subfields whose presence or absence of light emission is controlled according to the video signal in the plasma display device that displays the video at a predetermined magnification. Is not changed in accordance with the video signal level.   3. The plasma display device according to claim 1, wherein the video signal level is a value of an average luminance of the entire display screen.   3. The plasma display device according to claim 1, wherein the video signal level is a value of average luminance in a predetermined range including a central portion of the display screen.   3. The plasma display device according to claim 1, wherein the video signal level is a value of peak luminance in a predetermined pixel of the display screen. When displaying a video image with a gradation higher than a predetermined gradation, the subfield weighted corresponding to the minimum light emission luminance among the plurality of subfields controlled to emit light according to the video signal. 3. The plasma display device according to claim 1, wherein the operation of maintaining the light emission is not performed.   7. The plasma display apparatus according to claim 6, wherein the predetermined gradation is set to a gradation next to black display.

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