JPH10307562A - Plasma display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display an image having the gradation corresponding to a video signal by controlling writing operations of frame memories with an input vertical synchronizing signal as a reference, and controlling reading operations of the frame memories with a display vertical synchronizing signal as a reference. SOLUTION: A frame memory writing control part 7 controls respective writing operations of a first frame memory 4 and a second frame memory 5 with an input vertical synchronizing signal as a reference. On the other hand, a frame memory reading control part 8 controls respective reading operations of the first frame memory 4 and the second frame memory 5 with a display vertical synchronizing signal as a reference. As a result, an image having the gradation corresponding to a video signal is displayed on a PDP 16 on the basis of data read out by the first frame memory 4 and the second frame memory 5. Therefore, a plasma display is driven by a vertical synchronizing frequency different from a frequency of the input vertical synchronizing signal of the video signal, and the image having the gradation corresponding to the video signal is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a plasma display device capable of coping with a change in the vertical scanning frequency of a video signal.

[0002]

2. Description of the Related Art Generally, a plasma display device is
The drive input voltage and the display output show non-linear characteristics. Therefore, a video signal having a luminance gradation corresponding to the input signal cannot be displayed in gradation by the driving input voltage.

Therefore, in a plasma display device,
One frame of the screen is divided into multiple sub-frames (hereinafter,
It is called "SF". ), The discharge light emission time of each SF is weighted, and the discharge light emission of each SF is turned ON / OFF.
The gray scale is displayed by changing the number of times of discharge emission of each SF by performing the OFF control.

[0004]

However, when gradation display is performed by SF processing as in the above-described plasma display device, when the vertical frequency of the video signal changes, especially when the vertical frequency of the video signal becomes high, the write pulse becomes low. There is a problem that the frequency and the frequency of the sustaining pulse also change, and the operation becomes unstable. In order to cope with such a problem, various plasma display devices have been proposed which can cope with a change in the vertical scanning frequency of a video signal.

[0005] As this type of plasma display device, Japanese Patent Laid-Open Publication No. 8-76716 discloses a method of adjusting the number of discharge light emission of each SF for performing gradation display based on a vertical synchronizing frequency of a video signal. An arrangement for stabilizing the level is disclosed. However, when adjusting the number of times of discharge emission of each SF for performing gradation display based on the vertical synchronization frequency of a video signal as in the plasma display device according to the above-mentioned publication, the number of times of discharge emission of each SF is reduced. In many cases, the number cannot be set to a number proportional to the power of two. For this reason, there is a problem that the linearity of gradation is lost.

In order to cope with such a problem, the inventor of the present application generates a reference vertical synchronizing signal separately from an input vertical synchronizing signal of a video signal, and uses a frame memory necessary for performing SF processing to discharge and emit light. Display the reference vertical sync signal for the input vertical sync frequency in the region where the operation of
I imagined that it would be better to perform so-called frame rate conversion.

Further, the inventor of the present application has conceived that the number of SFs may be changed with respect to an input vertical synchronization frequency in a region where the operation of discharge light emission becomes unstable. The present invention
Based on the above idea, a plasma display that can operate within a stable range of discharge light emission operation without deteriorating the linearity of gradation even if the frequency of an input vertical synchronization signal of a video signal changes. It is intended to provide a device.

[0008]

According to a first aspect of the present invention, there is provided a plasma display apparatus comprising: a plurality of subfields having different relative ratios of luminance; A gradation image corresponding to a gradation image signal is displayed on a plasma display panel, and is used for generating the subfield. The image signal writing operation is performed for each one field. And two frame memories for alternately performing a read operation of the video signal and frame memory write control means for controlling a write operation of the frame memory with reference to an input vertical synchronization signal of the video signal; The frame memory is read based on a display vertical synchronization signal for displaying the image on the panel. Is characterized in that comprises a frame memory readout control means for controlling the operation out.

According to a second aspect of the present invention, there is provided a plasma display apparatus according to the first aspect, further comprising a display vertical synchronizing signal generating means for generating the display vertical synchronizing signal. The vertical synchronizing signal generating means compares the frequency of the input vertical synchronizing signal with the frequency of a reference vertical synchronizing signal serving as a reference for display. As a result of the comparison, the frequency of the input vertical synchronizing signal is The reference vertical synchronizing signal is output to the frame memory read control means as the display vertical synchronizing signal on condition that the frequency is higher than the above frequency.

According to a third aspect of the present invention, there is provided the plasma display apparatus according to the first aspect, further comprising a display vertical synchronizing signal generating means for generating the display vertical synchronizing signal. The vertical synchronizing signal generation means obtains a difference between the frequency of the input vertical synchronizing signal and the frequency of a reference vertical synchronizing signal serving as a display reference, and if the obtained difference is within a predetermined range,
The input vertical synchronizing signal is output as the display vertical synchronizing signal to the frame memory read control means. If the input vertical synchronizing signal is out of a predetermined range, the reference vertical synchronizing signal is used as the display vertical synchronizing signal. The data is output to the memory read control means.

According to a fourth aspect of the present invention, in the plasma display device according to any one of the first to third aspects, when the frame memory is performing a read operation, a next frame is read. By overwriting the data, it is possible to prevent an overtaking phenomenon that an image relating to a different frame is displayed on the plasma display panel even though an image relating to the same frame is displayed on the plasma display panel. The overtaking phenomenon occurrence prediction means for predicting, wherein the frame memory writing control means inhibits the writing operation of the frame memory when the overtaking phenomenon is predicted by the overtaking phenomenon occurrence prediction means. Is what you do.

According to a fifth aspect of the present invention, in the plasma display device according to the fourth aspect, the overtaking phenomenon occurrence predicting means includes:
A counter that counts a clock signal and is initialized by the input vertical synchronization signal, a first latch that latches a count value of the counter based on the reference vertical synchronization signal, and an output value of the first latch. A comparator for comparing a preset reference value and predicting the occurrence of the overtaking phenomenon based on the comparison result, a second latch for latching an output value of the comparator based on the input vertical synchronization signal, A logic gate for determining whether to mask the output signal of the second latch based on a comparison result between the frequency of the input vertical synchronization signal and the frequency of the reference vertical signal. is there.

According to a sixth aspect of the present invention, there is provided a plasma display apparatus comprising a plurality of sub-fields having different relative ratios of luminance, and forming an image having a gradation corresponding to a multi-gradation image signal into a plasma. A vertical synchronization frequency measuring means for measuring a frequency of an input vertical synchronization signal of the video signal, and a frequency measurement by the vertical synchronization frequency measuring means when generating a subfield. And a subfield generating means for changing the number of subfields to be generated based on the result.

According to a seventh aspect of the present invention, there is provided a plasma display apparatus comprising a plurality of sub-fields having different relative ratios of luminance, and forming an image having a gradation corresponding to a multi-gradation video signal into a plasma. A motion detection means for comparing a current image with a past image and detecting whether or not the image has a motion based on a result of the comparison; When generating a signal, a display vertical synchronizing signal generating means for lowering and outputting a frequency of a display vertical synchronizing signal to be generated, on condition that the motion detecting means detects no motion in the video. When generating a subfield, on the condition that a display vertical synchronization signal having a lower frequency than the display vertical synchronization signal generation means is output,
And a subfield generating means for increasing the number of subfields to be generated.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration of a plasma display device according to a first embodiment of the present invention.

Referring to FIG. 1, the plasma display device according to the first embodiment forms a single field from a plurality of subfields (hereinafter, referred to as “SF”) having different relative ratios of luminance, thereby forming a multi-level display. An image of a gradation corresponding to a video signal of a tone is displayed on a plasma display panel (hereinafter, referred to as “PDP”) 16, and a video signal input from a video signal input terminal 1 is A / A. An A / D converter 2 for D-conversion, and used for generating SF;
A first operation of alternately performing a writing operation of a video signal digitized by the A / D conversion unit 2 and a reading operation of a video signal digitized by the A / D conversion unit 2 for each field.
Frame memory 4 and second frame memory 5
A write selection switch 3 for selecting a frame memory for performing a write operation from the first frame memory 4 and the second frame memory 5; and a write selection switch 3 for selecting a frame memory from the first frame memory 4 and the second frame memory 5. The PDP 16 is based on a read selection switch 6 for selecting a frame memory for performing a read operation from a vertical synchronizing signal input terminal 9 and a vertical synchronizing signal (hereinafter referred to as “input vertical synchronizing signal”) of a video signal input from the vertical synchronizing signal input terminal 9. A display vertical synchronizing signal generating unit 13 for generating a display vertical synchronizing signal for displaying an image on the display unit;
Frame memory writing control unit 7 for controlling the writing operation of the frame memory 4 and the second frame memory 5 and the switching operation of the writing selection switch 3
And a read operation of the first frame memory 4 and the second frame memory 5 and a switching operation of the read selection switch 6 with reference to the display vertical synchronization signal generated by the display vertical synchronization signal generator 13. , A subfield generator 14 for generating an SF based on data read from the first frame memory 4 or the second frame memory 5, Drive control unit 15 that controls the drive of PDP 16 based on the output signal
And

The video signals include, for example, NTSC signals (vertical synchronization frequency is 60 Hz), PAL / SECAM
(The vertical synchronization frequency is 50 Hz), or a video signal having various vertical synchronization frequencies such as a personal computer.

The display vertical signal generator 13 generates a reference vertical sync signal generator 10 for generating a reference vertical sync signal serving as a display reference, and a frequency of the input vertical sync signal and the reference vertical sync signal generator 10. A frequency comparing section 11 for comparing the frequency of the reference vertical synchronizing signal and a synchronizing signal changeover switch 1 for selecting either an input vertical synchronizing signal or a reference vertical synchronizing signal as a display vertical synchronizing signal.
2. The frequency of the input vertical synchronization signal is compared with the frequency of the reference vertical synchronization signal, and as a result of the comparison, on the condition that the frequency of the input vertical synchronization signal is higher than the frequency of the reference vertical synchronization signal. The reference vertical synchronizing signal is output to the frame memory read control unit 8 as a display vertical synchronizing signal.

The reference vertical synchronizing signal generator 10 is, for example,
It is composed of a crystal oscillator, a counter for dividing the frequency of a clock generated thereby, and the like. Frequency comparison unit 11
Is composed of, for example, two counters initialized with an input vertical synchronization signal and a reference vertical synchronization signal and counting the same clock, or an arithmetic device such as a microcontroller.

Here, the operation of the plasma display device will be described. The video signal is supplied from the video signal input terminal 1 to the A / D converter 2. Then, A /
The D conversion unit 2 A / D converts the video signal and supplies the digitized video signal to the write selection switch 3.

On the other hand, an input vertical synchronizing signal of a video signal is supplied from a vertical synchronizing signal input terminal 9 to a frame memory writing control section 7 and a display vertical synchronizing signal generating section 13. Then, the frame memory write control unit 7
Each write operation of the first frame memory 4 and the second frame memory 5 is controlled based on the input vertical synchronization signal. Specifically, every time an input vertical synchronization signal is input, the frame memory write control unit 7 switches the contacts a and b to the write selection switch 3 so as to switch the frame memory for performing the write operation. And a write control signal for controlling whether or not to perform a write operation is output to the first frame memory 4 and the second frame memory 5, respectively. As a result, the first frame memory 4 and the second frame memory 5 are switched each time an input vertical synchronization signal is input, and alternately perform a writing operation of a digitized video signal (data).

The display vertical synchronizing signal generation unit 13
A display vertical synchronization signal is generated based on the input vertical synchronization signal. Specifically, the frequency comparison unit 11 compares the frequency of the input vertical synchronization signal with the frequency of the reference vertical synchronization signal generated by the reference vertical synchronization signal generation unit 10. As a result of the comparison, when the frequency of the input vertical synchronizing signal is higher than the frequency of the reference vertical synchronizing signal, the frequency comparing section 11 outputs to the synchronizing signal changeover switch 12 a contact switching signal for urging the switching to the contact e. . Then,
The contact of the synchronization signal switch 12 is switched to e. As a result, the display vertical synchronization signal generation unit 13
The reference vertical synchronization signal is output to the frame memory read control unit 8 as a display vertical synchronization signal. On the other hand, when the frequency of the input vertical synchronizing signal is lower than the frequency of the reference vertical synchronizing signal, the frequency comparing section 11 outputs a contact switching signal to the synchronizing signal switch 12 to urge the switching to the contact f. Then, the contact of the synchronization signal changeover switch 12 is switched to f. As a result, the display vertical synchronization signal generator 13 outputs the input vertical synchronization signal to the frame memory read controller 8 as a display vertical synchronization signal.

Then, the frame memory read control unit 8 controls each read operation of the first frame memory 4 and the second frame memory 5 based on the display vertical synchronization signal. More specifically, every time the display vertical synchronization signal is input, the frame memory read control unit 8 switches the contact c,
A contact switching signal for prompting the switching of d is output, and a write control signal for prompting the start of the read operation is output to the first frame memory 4 and the second frame memory 5, respectively. As a result, the first frame memory 4 and the second frame memory 5 are switched each time the display vertical synchronizing signal is input, and the read operation of the already stored video signal (data) is alternately performed. Do. The data read from the first frame memory 4 or the second frame memory 5 is provided to the subfield generator 14.

Then, the subfield generator 14
Generates a first subfield (SF1) based on data of a first bit (MSB) read from the first frame memory 4 or the second frame memory 5,
The second subfield (SF2) is generated based on the second bit data, and the eighth subfield (SF8) is generated based on the eighth bit data.

The drive controller 15 drives the PDP 16 based on the output signal from the subfield generator 14. Specifically, the drive control unit 15 causes the subfield generation unit 14 to set the relative ratio of the luminance of each SF to 12
8 (SF1): 64 (SF2): 32 (SF3): 16
(SF4): 8 (SF5): 4 (SF6): 2 (SF
7): Since 1 (SF8) is set, the discharge of each SF is performed for each cell of the PDP 16 based on the data read from the first frame memory 4 or the second frame memory 5. By controlling the light emission, an image having a gradation corresponding to the video signal is displayed on the PDP 16.

That is, in the first embodiment, the write operation of the first frame memory 4 or the second frame memory 5 is controlled on the basis of the input vertical synchronizing signal. The control of the read operation of the second frame memory 5 is performed based on the display vertical synchronization signal. Therefore, the plasma display device can be driven at a vertical synchronization frequency different from the frequency of the input vertical synchronization signal of the video signal, and an image having a gradation corresponding to the video signal can be displayed.

When the display vertical synchronizing signal is generated, the frequency of the input vertical synchronizing signal is compared with the frequency of the reference vertical synchronizing signal. On condition that the frequency is higher than the frequency of the signal, the reference vertical synchronization signal is output to the frame memory read control unit 8 as a display vertical synchronization signal.

Therefore, the image can be displayed by driving the PDP 16 based on the reference vertical synchronization signal only when a high vertical synchronization frequency at which the discharge light emission operation becomes unstable is input. As a result, it is possible to obtain a plasma display device that operates within a range where the discharge light emission operation is stable.

In the first embodiment, the selection of the write operation and the selection of the read operation of the first frame memory 4 and the second frame memory 5 are respectively performed by the write selection switch 3 and the read selection switch. 6, the write enable signal to the frame memories 4 and 5 and the read enable signal may be used.

(Embodiment 2) FIG. 2 is a block diagram showing a configuration of a plasma display device according to Embodiment 2 of the present invention. Referring to FIG. 2, the feature of the plasma display device according to the second embodiment is that the display vertical synchronization signal generation unit 13 determines the difference between the frequency of the input vertical synchronization signal and the frequency of the reference vertical synchronization signal, If the obtained difference is within a predetermined range, the input vertical synchronization signal is output to the frame memory read control unit 8 as a display vertical synchronization signal, and if the difference is outside the predetermined range, the reference vertical synchronization signal is output. The configuration is such that a signal is output to the frame memory read control unit 8 as a display vertical synchronization signal.

More specifically, the display vertical synchronizing signal generator 1
Reference numeral 3 denotes a reference vertical synchronizing signal generator 10 and a difference between the frequency of the input vertical synchronizing signal and the frequency of the reference vertical synchronizing signal generated by the reference vertical synchronizing signal generator 10, and the obtained difference is a predetermined constant. A frequency difference calculating unit 20 for determining whether the input signal is within the range, and one of an input vertical synchronization signal and a reference vertical synchronization signal as a display vertical synchronization signal based on the determination result of the frequency difference calculation unit 20. And a synchronizing signal changeover switch 12 for selecting the

Other configurations are the same as those of the first embodiment. Here, an operation of the plasma display device for generating a display vertical synchronization signal will be described.

In the display vertical synchronizing signal generator 13,
When generating the display vertical synchronization signal, first, the frequency difference calculation unit 20 calculates the difference between the frequency of the input vertical synchronization signal and the frequency of the reference vertical synchronization signal generated by the reference vertical synchronization signal generation unit 10. Then, it is determined whether or not the obtained difference is within a predetermined range. As a result of this determination, if the obtained difference is within a predetermined range, the frequency difference calculation unit 2
0 outputs a contact switch signal to the synchronous signal switch 12 to prompt the switch to the contact f. Then, the contact of the synchronization signal changeover switch 12 is set to f
Is switched to. As a result, the display vertical synchronization signal generator 13 outputs the input vertical synchronization signal to the frame memory read controller 8 as a display vertical synchronization signal. On the other hand, if the obtained difference is out of the predetermined range, the frequency difference calculator 20 outputs a contact switching signal to the synchronization signal switch 12 to prompt the switching to the contact e. Then, the synchronization signal switch 12
Is switched to e. As a result, the display vertical synchronization signal generator 13 outputs the reference vertical synchronization signal to the frame memory read controller 8 as a display vertical synchronization signal.

That is, in the second embodiment, the difference between the frequency of the input vertical synchronizing signal and the frequency of the reference vertical synchronizing signal is obtained, and if the obtained difference is within a predetermined range, the input vertical synchronizing signal is obtained. The signal is output to the frame memory readout control unit 8 as a display vertical synchronization signal. If the signal is out of a predetermined range, the reference vertical synchronization signal is output to the frame memory readout control unit 8 as a display vertical synchronization signal. It has become so.

Therefore, when the discharge light emission operation is stable or the luminance level change due to the vertical synchronization frequency is within a permissible range, the display is driven at the input vertical synchronization frequency, and the operation is unstable or the luminance level change is unacceptable. Thus, the driving display can be performed based on the reference vertical synchronization signal. As a result, it is possible to operate within a range where the discharge light emission operation is stable, and to reduce the change in the luminance level due to the vertical synchronization frequency.

(Third Embodiment) In the first and second embodiments, when the frame memories 4 and 5 are performing a read operation, the data is rewritten to the data of the next frame. Although an image related to the same frame is displayed on the PDP 16, an image related to a different frame is displayed on the PDP 16.
So-called overtaking phenomenon may be generated.

FIG. 3 shows how the overtaking phenomenon occurs.
Shown in FIG. 3 is a timing chart showing a control state of the frame memories 4 and 5 when the vertical synchronization frequency for writing to the frame memories 4 and 5 is higher than the vertical synchronization frequency for reading. In FIG. 3, triangular waveforms for writing to and reading from the frame memories 4 and 5 indicate that the address of the frame memory has changed.

Referring to FIG. 3, when an overtaking phenomenon appears when the input vertical synchronization signal writes the third frame,
While the PDP 16 is displaying the image related to the first frame, the image related to the third frame is displayed.
As a result, scratches appear on the display screen.

In the third embodiment, the frame memories 4 and 5
Due to the difference between the vertical synchronizing frequency to be written to and the vertical synchronizing frequency to be read out, that is, due to the above-mentioned overtaking phenomenon that occurs when performing frame rate conversion, one display screen is divided into upper and lower parts, and images related to different frames are displayed. In order to prevent the occurrence of scratches on the display screen, the present invention has been proposed.

FIG. 4 is a block diagram showing the configuration of the plasma display device according to the third embodiment of the present invention.
Referring to FIG. 4, the features of the plasma display device according to the third embodiment are that an overtaking phenomenon occurrence prediction unit 17 for predicting the occurrence of an overtaking phenomenon is provided, and a frame memory writing control unit 8 is When the overtaking phenomenon prediction unit 17 predicts that an overtaking phenomenon will occur, the overwriting phenomenon prediction unit 17 is configured to prohibit the write operation of the frame memories 4 and 5, and the other configuration is the same as that of the first embodiment. is there.

Here, the operation of predicting the occurrence of the overtaking phenomenon of the plasma display device and the write control operation of the frame memories 4 and 5 will be described.

When the input vertical synchronizing signal and the reference vertical synchronizing signal are input, the overtaking phenomenon occurrence predicting unit 17 calculates the comparison result between the frequency of the input vertical synchronizing signal of the frequency comparing unit 13 and the frequency of the reference vertical synchronizing signal. Based on this, it is predicted that an overtaking phenomenon will occur. Specifically, when a comparison result signal indicating that the frequency of the input vertical synchronization signal is higher than the reference vertical synchronization frequency is input from the frequency comparison unit 13, the overtaking phenomenon occurrence prediction unit 17 determines that the overtaking phenomenon occurs. And outputs an overtaking phenomenon occurrence prediction signal to the frame memory writing control unit 7.

Then, the frame memory write controller 7 outputs a write control signal to the frame memories 4 and 5 so as to inhibit the write operation of the frame memories 4 and 5. As a result, the frame memories 4 and 5 do not perform the write operation.

FIG. 5 shows a state in which the write operation of the frame memories 4 and 5 is prohibited when the occurrence of the overtaking phenomenon is predicted. FIG. 5 shows a case where the overtaking is predicted so that the writing to the frame memories 4 and 5 is prohibited so that the overtaking phenomenon is not caused.
5 is a timing chart showing a control state of No. 5; In FIG. 5, triangular waveforms for writing to and reading from the frame memories 4 and 5 indicate that the addresses of the frame memories have changed.

Referring to FIG. 5, when the input vertical synchronizing signal of the third frame in which overtaking occurs is input, a frame memory is provided to prevent a flaw from being displayed on the screen due to overtaking. The writing operation of the frame memory 5 is controlled so that 5 does not write the data of the third frame. When the input vertical synchronizing signal of the ninth frame where overtaking occurs is input, the frame memory 4 stores the data of the ninth frame so as to prevent a scratch from being displayed on the screen due to the overtaking. Is written, the writing operation of the frame memory 4 is controlled.

As described above, the image related to the third frame and the image related to the ninth frame are completely PDPs.
Although not displayed on the screen 16, the scratches caused by the overtaking phenomenon become less noticeable, which is preferable in terms of image quality.

That is, in the fourth embodiment, when the overtaking phenomenon is predicted by the overtaking phenomenon prediction unit 17, the frame memory writing control unit 8 prohibits the writing operation of the frame memories 4 and 5. Has become.

Therefore, the occurrence of the overtaking phenomenon can be prevented. Therefore, one display screen is divided into upper and lower parts, and images relating to different frames are not displayed on the PDP 16. As a result, no scratch occurs on the display screen.

In the fourth embodiment, the example in which the overtaking phenomenon prediction unit 17 is added to the configuration of the first embodiment has been described. However, even if the overtaking phenomenon prediction unit 17 is added to the configuration of the second embodiment. The same effect is achieved.

(Embodiment 4) FIG. 6 is a diagram showing a configuration of an overtaking phenomenon occurrence predicting section of a plasma display device according to Embodiment 4 of the present invention. Referring to FIG. 6, a feature of the plasma display device of the fourth embodiment is that the overtaking phenomenon occurrence predicting unit 17 is connected to the clock signal input terminal 2.
6, the counter 21 is initialized by the input vertical synchronization signal input from the vertical synchronization signal input terminal 27, and the count value of the counter 21 is input from the reference vertical synchronization signal input terminal 27. A first latch 22 for latching based on the reference vertical synchronization signal, a reference value setting unit 29 for setting a reference value in advance, and an output value of the first latch 22 and an output from the reference value setting unit 29. And a comparator 23 for predicting the occurrence of an overtaking phenomenon based on the comparison result and a second latch for latching the output value of the comparator 23 based on the input vertical synchronization signal.
And whether or not to mask the output signal of the second latch 24 based on the comparison result signal between the frequency of the input vertical synchronization signal and the frequency of the reference vertical signal input from the frequency result signal input terminal 30 AND gate 25 that determines
The other configuration is the same as that of the third embodiment.

Here, the clock signal is generated, for example, in order to take timing to output a write signal or a read signal to the frame memories 4 and 5. Note that the clock signal may be obtained by other means. The reference value set in advance by the reference value setting unit 29 is set based on the difference between the frequency of the input vertical synchronization signal and the frequency of the reference vertical synchronization signal and the relationship between the frequency of the clock signal.

Here, the operation of the overtaking phenomenon occurrence predicting section 17 of the plasma display device will be described.

The counter 21 counts clocks and outputs the counted value to the first latch 22. The counter 21 is initialized (cleared) when the input vertical synchronization signal 27 is input.

Then, the first latch 22 latches the count value of the counter 21 based on the reference vertical synchronization signal. Here, as the value latched by the first latch 22 is higher, the reference vertical synchronization signal is closer to the next input vertical synchronization signal 27, so that the overtaking phenomenon may occur. Get higher. Also, when the value latched by the first latch 22 is close to “0”, the reference vertical synchronization signal is approaching the immediately preceding input vertical synchronization signal. However, the reference vertical synchronization signal is input later than the input vertical synchronization signal. It is also assumed that the input vertical synchronization frequency is higher than the frequency of the reference vertical synchronization signal. Therefore, when the latched value is close to "0", the overtaking phenomenon does not occur even though the reference vertical synchronization signal is approaching the next input vertical synchronization signal.

The comparator 23 compares the reference value set by the reference value setting section 29 with the output value of the first latch 22. As a result of the comparison, when the output value of the second latch 22 is larger than the reference value, the comparator 23
Predicts that an overtaking phenomenon will occur, for example, "1"
Is output.

Next, the second latch 24 latches the output value "1" of the comparator 23 based on the input vertical synchronizing signal and synchronizes with the input vertical synchronizing signal. Then AND
The gate 25 determines whether to mask the output signal of the second latch 24 based on a comparison result signal between the frequency of the reference vertical synchronization signal and the frequency of the input vertical synchronization signal 27.
Specifically, when a comparison result signal indicating that the frequency of the input vertical synchronization signal is higher than the frequency of the reference vertical synchronization signal is input, the AND gate 25 does not mask the output signal of the second latch 24. And outputs an overtaking phenomenon occurrence prediction signal to the frame memory write control unit 7. On the other hand, when a comparison result signal indicating that the frequency of the reference vertical synchronization signal is higher than the frequency of the input vertical synchronization signal is input, AN
The D gate 25 masks the output signal of the second latch 24 and does not output the overtaking phenomenon occurrence prediction signal to the frame memory write control unit 7.

That is, in the first embodiment, the overtaking phenomenon occurrence predicting unit 17 transmits the clock signal for generating the write signal or the read signal to the frame memories 4 and 5 input from the clock signal input terminal 26. The counter 21 is counted and initialized by the input vertical synchronization signal input from the vertical synchronization signal input terminal 27, and the count value of the counter 21 is calculated based on the reference vertical synchronization signal input from the reference vertical synchronization signal input terminal 27. A first latch 22 to be latched, a reference value setting unit 29 for setting a reference value in advance, an output value of the first latch 22 and a reference value setting unit 2
The comparator 23 compares the reference value output from the comparator 9 with the reference value and predicts the occurrence of the overtaking phenomenon based on the comparison result.
A second latch 24 that latches the output value of the comparator 23 based on the input vertical synchronization signal, and a second latch 24 that latches the frequency of the input vertical synchronization signal and the frequency of the reference vertical synchronization signal input from the frequency result signal input terminal 30. Based on the comparison result signal,
And an AND gate 25 for determining whether or not to mask the output signal of the second latch 24. On the condition that the frequency of the input vertical synchronizing signal is higher than the frequency of the reference vertical synchronizing signal, the generation of the overtaking phenomenon is prevented. To predict.

Therefore, the occurrence of the overtaking phenomenon can be predicted only by comparing the value of the counter 21 with the reference value according to the temporal position of the reference vertical synchronization signal.
As a result, the overtaking phenomenon occurrence prediction unit 17 can be realized by a simple circuit.

(Fifth Embodiment) Referring to FIG. 7, the operation principle of the plasma display device of the fifth embodiment will be described. FIG. 7A shows an example of a subfield operation when the vertical synchronization frequency is 60 Hz, such as when the input video signal is NTSC. In FIG. 7A, 1
The field is 1/60 second and 8 of SF1 to SF8
It is composed of SFs. Each SF is composed of an address period and a display period.

Referring to FIG. 7A, during the address period of each SF, a write pulse is applied to the address electrodes of PDP 16 based on the display data read from frame memories 4 and 5. Then, the PD corresponding to this
Wall charges are formed in each cell of P16. In a subsequent display period (sustain period), sustain discharge is performed in each cell of the PDP 16 based on a required sustain pulse, and an image is displayed. At this time, if the write pulse and the sustain pulse do not have a certain pulse width or more, the operation of writing and discharge light emission is not stable. Therefore, like a personal computer, it has various kinds of vertical synchronizing frequencies. For example, when the vertical synchronizing frequency is 72 Hz, the time of one field is shortened. In this case, as in FIG. 7A, eight SFs
If one field is to be constituted by the above, the pulse width of the write pulse or the sustain pulse must be reduced. As a result, the operations of writing and discharge light emission are not stable.

Thus, for example, as shown in FIG.
By setting the number of SFs to 6, the pulse widths of the write pulse and the sustain pulse can be made the same as those in FIG. As a result, the writing and discharge light emission operations can be stabilized.

As shown in FIG. 7C, when the video signal has a low vertical synchronizing frequency of 50 Hz, such as PAL, the time of one field becomes long. Therefore, more SFs can be generated than in FIG. However, in FIG. 7C, eight or more SF gradations are practically unnecessary. Therefore, the eight SFs are left as they are.
In FIG. 7C, the number of SFs is kept at eight, but if it is necessary to increase the number of SFs for some reason, the number of subfields can be increased.

That is, in the fifth embodiment, the input vertical synchronizing frequency in the region where the operation of discharge light emission becomes unstable is
By changing the number of SFs, a plasma display apparatus capable of operating within a stable range of discharge light emission operation without deteriorating the linearity of gradation even if the frequency of an input vertical synchronization signal of a video signal changes. Propose technology to provide.

FIG. 8 is a block diagram showing a configuration of a plasma display device according to the fifth embodiment of the present invention.

Referring to FIG. 8, the feature of the plasma display device of the fifth embodiment is that the vertical synchronization signal generator 13 for display is eliminated and the vertical synchronization for measuring the frequency of the input vertical synchronization signal of the video signal is performed. The point that the frequency measurement unit 41 is provided, and that the subfield generation unit 14 is configured to change the number of SFs to be generated based on the frequency measurement result by the vertical synchronization frequency measurement unit 41,
Other configurations are the same as those of the first embodiment.

Here, the subfield generating operation of the plasma display device will be described. The vertical synchronization frequency measuring section 41 measures the frequency of the input vertical synchronization signal. Then, when the frequency of the input vertical synchronizing signal is increasing, the subfield generator 14 decreases the number of SFs accordingly. On the other hand, if the frequency of the input vertical synchronization signal is decreasing,
No. 4 increases the number of SFs accordingly.

That is, in the fifth embodiment, when generating an SF, the number of SFs to be generated is changed based on the measurement result of the frequency of the input vertical synchronization signal. Therefore, when the frequency of the input vertical synchronization signal is low, the number of SFs is increased to increase the number of gray scale steps to be displayed. On the other hand, when the frequency of the input vertical synchronization signal is high, the number of SFs is reduced. Thus, a stable discharge light emission operation can be performed.

(Embodiment 6) FIG. 9 is a block diagram showing a configuration of a plasma display device according to Embodiment 6 of the present invention. Referring to FIG. 9, the feature of the plasma display device of the sixth embodiment is that a third frame memory 51 that stores one frame of video signal converted into a digital signal by A / D converter 2, A motion detection unit 52 that reads out the content stored in the third frame memory 51, compares the current video with the past video, and detects whether or not the video has a motion based on the comparison result. When the display vertical synchronizing signal generation unit 13 generates the display vertical synchronizing signal, on the condition that the motion detecting unit 52 detects that there is no motion in the video, When the frequency is lowered and the SF is generated by the subfield generator 14, the display vertical sync signal generator 13 outputs a lower frequency display vertical sync signal from the display vertical sync signal generator 13 by the vertical sync frequency measuring unit 41. Was possible on condition that is measured, there the to be generated SF in that are configured to increase, other configurations are similar to that of the fifth embodiment.

The display vertical synchronizing signal generator 13 generates a reference vertical synchronizing signal having a frequency lower than that of the input vertical synchronizing signal. A synchronization signal changeover switch 12 for selecting one of an input vertical synchronization signal and a reference vertical synchronization signal as a vertical synchronization signal is provided, and the selected signal is transmitted to the frame memory read control unit 8 as a display vertical synchronization signal. Output.

Here, the subfield generating operation of the plasma display device will be described. The third frame memory 51 stores the video signal for one frame converted into a digital signal by the A / D converter 2. The motion detection unit 52 reads the content stored in the third frame memory 51, compares the current video with the past video, and detects whether or not the video has a motion based on the comparison result. This detection result is output to the display vertical synchronization signal generator 1.
3 given.

Then, the display vertical synchronizing signal generator 1
3 selects one of the input vertical synchronizing signal and the reference vertical synchronizing signal based on the detection result of the motion detecting section 52 and outputs the selected signal to the frame memory read control section 8 as a display vertical synchronizing signal. I do. Specifically, when the motion of the video is not detected by the motion detection unit 52 and the video to be displayed is a still image, the contact of the synchronization signal switch 12 is switched to e. As a result, the display vertical synchronization signal generator 13 outputs a reference vertical synchronization signal having a low frequency as the display vertical synchronization signal.

When the vertical synchronizing frequency measuring section 41 measures that the display vertical synchronizing signal generating section 13 outputs the low-frequency reference vertical synchronizing signal as the display vertical synchronizing signal, the subfield generating section 14 sets The SF to be generated is increased accordingly.

That is, in the sixth embodiment, the present video is compared with the past video, and based on the result of the comparison, it is detected whether or not the video has motion, and the display vertical synchronizing signal is generated. Sometimes, on the condition that it is detected that there is no motion in the video, the frequency of the display vertical synchronization signal to be generated is reduced and output, and when generating SF, the display vertical synchronization signal having a lower frequency is output. On the condition that the number of SFs to be generated is increased, the number of SFs to be generated is increased.

Therefore, for a motionless image,
By increasing the number of SFs, the number of gradation steps to be displayed can be increased. It should be noted that the present invention is not limited to the above embodiments, and various design changes and modifications may be made within the scope of the present invention.

[0075]

As is apparent from the above description, claim 1
According to the invention described in the above, control of the write operation of the frame memory is performed based on the input vertical synchronization signal, and control of the read operation of the frame memory is performed based on the display vertical synchronization signal. By driving the plasma display device at a vertical synchronizing frequency different from the frequency of the input vertical synchronizing signal, an image having a gradation corresponding to the video signal can be displayed.

According to the second aspect of the present invention, when the display vertical synchronizing signal is generated, the frequency of the input vertical synchronizing signal is compared with the frequency of the reference vertical synchronizing signal. On the condition that the frequency of the synchronization signal is higher than the frequency of the reference vertical synchronization signal, the reference vertical synchronization signal is output to the frame memory read control means as a display vertical synchronization signal, so that the discharge light emission operation becomes unstable. Only when the vertical synchronization frequency is input, the plasma display panel can be driven and an image can be displayed based on the reference vertical synchronization signal. As a result, a plasma display device that operates within a range where the discharge light emission operation is stable can be realized. Obtainable.

According to the third aspect of the present invention, the difference between the frequency of the input vertical synchronizing signal and the frequency of the reference vertical synchronizing signal is obtained, and if the obtained difference is within a predetermined range, the input vertical synchronizing signal is obtained. The synchronization signal is output to the frame memory readout control means as a display vertical synchronization signal, and if it is outside a predetermined range, the reference vertical synchronization signal is output to the frame memory readout control means as a display vertical synchronization signal. Therefore, as long as the discharge light emission operation is stable or the change in the luminance level due to the vertical synchronization frequency is within the allowable range,
Drive and display at the input vertical synchronization frequency, and at frequencies where operation is unstable or changes in luminance level are unacceptable, driving and display can be performed based on the reference vertical synchronization signal.
The operation can be performed within a range where the discharge light emission operation is stable, and a change in the luminance level due to the vertical synchronization frequency can be reduced.

According to the fourth aspect of the present invention, when the overtaking phenomenon is predicted by the overtaking phenomenon predicting means,
Since the frame memory writing control means prohibits the writing operation of the frame memory, it is possible to prevent an overtaking phenomenon from occurring, so that one display screen is divided into upper and lower parts, and images relating to different frames are displayed on the plasma display. As a result, no scratch is generated on the display screen.

According to the fifth aspect of the present invention, the overtaking phenomenon occurrence predicting unit counts a clock signal for generating a write signal or a read signal to the frame memory, and is initialized by the input vertical synchronization signal. A counter, a first latch for latching the count value of the counter based on the reference vertical synchronization signal, and comparing the output value of the first latch with a preset reference value. And a second latch that latches an output value of the comparator based on an input vertical synchronization signal.
And a logic gate that determines whether or not to mask the output signal of the second latch based on a comparison result signal between the frequency of the input vertical synchronization signal and the frequency of the reference vertical signal. According to the temporal position of the reference vertical synchronizing signal, it is possible to predict the occurrence of the overtaking phenomenon simply by comparing the counter value with the reference value. As a result, the overtaking phenomenon occurrence prediction means is realized by a simple circuit. be able to.

According to the sixth aspect of the present invention, when generating a subfield, the number of subfields to be generated is changed based on the measurement result of the frequency of the input vertical synchronization signal. If the frequency is low, the number of subfields is increased to increase the number of gradation steps to be displayed, while if the frequency of the input vertical synchronization signal is high, the number of subfields is reduced to achieve stable discharge. A light emitting operation can be performed.

According to the seventh aspect of the present invention, the present image is compared with the past image, and based on the result of the comparison, it is detected whether or not the image has movement, and the display vertical synchronizing signal is generated. When the sub-field is generated, the frequency of the display vertical synchronizing signal to be generated is reduced and output on the condition that it is detected that there is no motion in the video. The number of subfields to be generated is increased on the condition that is output, so that the number of grayscale steps to be displayed can be increased by increasing the number of subfields for an image without motion. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a plasma display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a plasma display device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing how an overtaking phenomenon occurs.

FIG. 4 is a block diagram showing a configuration of a plasma display device according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a state in which a write operation of the frame memories 4 and 5 is prohibited when occurrence of an overtaking phenomenon is predicted.

FIG. 6 is a diagram showing a configuration of an overtaking phenomenon occurrence predicting unit of a plasma display device according to a fourth embodiment of the present invention;

FIG. 7 is a diagram for explaining the operation principle of the plasma display device according to the fifth embodiment.

FIG. 8 is a block diagram showing a configuration of a plasma display device according to a fifth embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a plasma display device according to a sixth embodiment of the present invention.

[Explanation of symbols]

 4, 5 frame memory 7 frame memory write control unit 8 frame memory read control unit 10 reference vertical synchronization signal generation unit 11 frequency comparison unit 13 display vertical synchronization signal generation unit 14 subfield generation unit 15 drive control unit 16 plasma display panel ( PDP) 17 Overtaking phenomenon occurrence predicting unit 20 Frequency difference calculating unit 41 Vertical synchronization frequency measuring unit

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[Procedure amendment]

[Submission date] March 20, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

FIG. 4 is a block diagram showing the configuration of the plasma display device according to the third embodiment of the present invention.
Referring to FIG. 4, the features of the plasma display device according to the third embodiment are that an overtaking phenomenon occurrence prediction unit 17 for predicting the occurrence of an overtaking phenomenon is provided, and a frame memory writing control unit 8 is The overwriting phenomenon occurrence prediction unit 17 is configured to prohibit the writing operation of the frame memories 4 and 5 when the occurrence of the overtaking phenomenon is predicted. This is the same as in the first embodiment.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

[0042] When the input vertical synchronizing signal, and a reference vertical synchronizing signal is inputted, overtaking phenomenon occurrence prediction unit 17, the comparison result between the frequency of the reference vertical synchronizing signal of the frequency comparison unit 1 1 of the input vertical synchronizing signal Based on the above, it is predicted that an overtaking phenomenon will occur. Specifically, when the comparison result signal indicating that the frequency of the input vertical synchronizing signal from the frequency detector 1 1 is higher than the reference vertical synchronizing frequency is inputted, overtaking phenomenon occurrence prediction unit 17, overtaking phenomenon occurs And outputs an overtaking phenomenon occurrence prediction signal to the frame memory writing control unit 7.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction contents]

[0047] That is, in the third embodiment, when the occurrence of the overtaking phenomenon in overtaking phenomenon occurrence prediction unit 17 is predicted, the frame memory writing control unit 7, so as to inhibit writing operation of the frame memory 4 and 5 It has become.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0049

[Correction method] Change

[Correction contents]

In the third embodiment, the overtaking phenomenon
Although the example in which the occurrence prediction unit 17 is added to the configuration of the first embodiment has been described, the overtaking phenomenon occurrence prediction unit 17 is replaced with the second embodiment.
The same effect can be obtained by adding to the configuration described above.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction contents]

(Embodiment 4) FIG. 6 is a diagram showing a configuration of an overtaking phenomenon occurrence predicting section of a plasma display device according to Embodiment 4 of the present invention. Referring to FIG. 6, a feature of the plasma display device of the fourth embodiment is that the overtaking phenomenon occurrence predicting unit 17 is connected to the clock signal input terminal 2.
Counting the input clock signal from the 6, the counters 21 are initialized by the input vertical synchronization signal inputted from the vertical synchronization signal input terminal 27, the count value of the counters 21 from the reference vertical synchronizing signal input terminal 27 A first latch 22 for latching based on the input reference vertical synchronization signal, a reference value setting unit 29 for setting a reference value in advance, an output value of the first latch 22 and a reference value setting unit 29 And a second latch 24 for comparing the output value of the comparator 23 with an output value of the comparator 23 based on the input vertical synchronizing signal. Frequency comparison result signal input terminal 30
And an AND gate 25 that determines whether or not to mask the output signal of the second latch 24 based on a comparison result signal between the frequency of the input vertical synchronization signal and the frequency of the reference vertical signal input from The other configuration is the same as that of the third embodiment.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

[0053] counters 21 counts the clock and outputs this count value to the first latch 22. Note that counter <br/> te 21, when the input vertical synchronizing signal 27 is inputted is initialized (cleared).

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0055

[Correction method] Change

[Correction contents]

The comparator 23 compares the reference value set by the reference value setting section 29 with the output value of the first latch 22. As a result of this comparison, when the output value of the first latch 22 is larger than the reference value, the comparator 23
Predicts that an overtaking phenomenon will occur, for example, "1"
Is output.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0057

[Correction method] Change

[Correction contents]

That is, in the fourth embodiment, the overtaking phenomenon occurrence predicting unit 17 transmits the clock signal for generating a write signal or a read signal to the frame memories 4 and 5 input from the clock signal input terminal 26. counted, and counters 21 to be initialized in the input vertical synchronization signal inputted from the vertical synchronization signal input terminal 27, is input the count value of the count <br/> printer over 21 from a reference vertical synchronizing signal input terminal 27 A first latch 22 for latching based on a reference vertical synchronization signal, a reference value setting unit 29 for setting a reference value in advance, and an output value of the first latch 22 and an output from the reference value setting unit 29 And a comparator 23 for predicting the occurrence of an overtaking phenomenon based on the comparison result, and latching the output value of the comparator 23 based on the input vertical synchronization signal. A second latch 24 that has been inputted from the frequency comparison result signal input terminal 30, based on the comparison result signal between the frequency of the reference vertical synchronizing signal of the input vertical synchronizing signal, the output signal of the second latch 24 An AND gate 25 for determining whether or not to mask is provided, and on the condition that the frequency of the input vertical synchronizing signal is higher than the frequency of the reference vertical synchronizing signal, the occurrence of an overtaking phenomenon is predicted.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0058

[Correction method] Change

[Correction contents]

[0058] Thus, in accordance with the temporal position of the reference vertical synchronizing signal, only compares the value with the reference value of the counters 21, it is possible to predict the occurrence of overtaking phenomenon. As a result, the overtaking phenomenon occurrence prediction unit 17 can be realized by a simple circuit.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0081

[Correction method] Change

[Correction contents]

According to the seventh aspect of the present invention, the present image is compared with the past image, and based on the result of the comparison, it is detected whether or not the image has movement, and the display vertical synchronizing signal is generated. When the sub-field is generated, the frequency of the display vertical synchronizing signal to be generated is reduced and output on the condition that it is detected that there is no motion in the video. Subject to the this but output, because it increases the number of subfields to be generated, for no motion picture, that by increasing the number of subfields and increases the number of gradation steps of displaying Can be.

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Description of Signs] 4, 5 frame memory 7 frame memory write control unit 8 frame memory read control unit 10 reference vertical synchronization signal generation unit 11 frequency comparison unit 13 display vertical synchronization signal generation unit 14 subfield generation unit 15 drive control unit 16 plasma display panel (PDP) 17 overtaking phenomenon occurs prediction unit 20 frequency difference calculation unit 41 vertical synchronizing frequency measurement unit

Claims (7)

[Claims] 1. A plasma display panel in which one field is constituted by a plurality of sub-fields having different relative ratios of luminance, and an image of a gradation corresponding to a multi-gradation video signal is displayed on a plasma display panel. , Used to generate the subfield,
Two frame memories for alternately performing the video signal writing operation and the video signal reading operation for each field, and controlling the writing operation of the frame memory based on an input vertical synchronization signal of the video signal. Frame memory write control means; and frame memory read control means for controlling a read operation of the frame memory based on a display vertical synchronization signal for displaying the image on the plasma display panel. Plasma display device. 2. The plasma display device according to claim 1, further comprising display vertical synchronizing signal generating means for generating said display vertical synchronizing signal, wherein said display vertical synchronizing signal generating means includes said input vertical synchronizing signal. Is compared with the frequency of a reference vertical synchronization signal serving as a reference for display, and as a result of this comparison, on the condition that the frequency of the input vertical synchronization signal is higher than the frequency of the reference vertical synchronization signal, A plasma display device, wherein a vertical synchronization signal is output to the frame memory read control means as the display vertical synchronization signal. 3. The plasma display device according to claim 1, further comprising display vertical synchronizing signal generating means for generating said display vertical synchronizing signal, wherein said display vertical synchronizing signal generating means comprises said input vertical synchronizing signal. The difference between the frequency of the reference and the frequency of the reference vertical synchronization signal as a display reference, if the obtained difference is within a predetermined range, the input vertical synchronization signal as the display vertical synchronization signal, A plasma display for outputting to the frame memory readout control means, and outputting the reference vertical synchronization signal to the frame memory readout control means as the display vertical synchronization signal if it is outside a predetermined range. apparatus. 4. The plasma display device according to claim 1, wherein, when the frame memory is performing a read operation, an image relating to the same frame is rewritten by data of a next frame. Includes overtaking phenomenon occurrence predicting means for predicting that an overtaking phenomenon that an image relating to a different frame is displayed on the plasma display panel even though the image is displayed on the plasma display panel, A plasma display device, wherein the memory writing control means inhibits the writing operation of the frame memory when the overtaking phenomenon occurrence prediction means predicts the occurrence of the overtaking phenomenon. 5. The plasma display device according to claim 4, wherein the overtaking phenomenon occurrence predicting means counts a clock signal, and initializes the counter with the input vertical synchronization signal; A first latch that latches based on a reference vertical synchronization signal, a comparator that compares an output value of the first latch with a preset reference value, and predicts the occurrence of the overtaking phenomenon based on the comparison result A second latch for latching an output value of the comparator based on the input vertical synchronization signal; and a second latch based on a comparison result between a frequency of the input vertical synchronization signal and a frequency of the reference vertical signal. And a logic gate for determining whether to mask the output signal of the plasma display device. 6. A plasma display panel in which one field is composed of a plurality of subfields having different relative ratios of luminance, and an image of a gradation corresponding to a multi-gradation video signal is displayed on a plasma display panel. A vertical synchronization frequency measuring means for measuring a frequency of an input vertical synchronization signal of the video signal; and when generating a subfield, the number of subfields to be generated is determined based on a frequency measurement result by the vertical synchronization frequency measuring means. A plasma display device, comprising: a subfield generating means for changing the subfield. 7. A plasma display panel wherein one field is composed of a plurality of subfields having different relative ratios of luminance, and an image having a gradation corresponding to a multi-gradation video signal is displayed on a plasma display panel. A motion detecting means for comparing the current video with the past video and detecting whether or not the video has a motion based on the comparison result; and when generating the display vertical synchronizing signal, the motion detecting means Display vertical synchronizing signal generating means for lowering and outputting the frequency of the display vertical synchronizing signal to be generated, on condition that it is detected that there is no motion in the video; and Sub-field generating means for increasing the number of sub-fields to be generated on condition that a display vertical synchronizing signal having a lower frequency than the vertical synchronizing signal generating means has been output. A plasma display device characterized by the above-mentioned.