JPH1152913A - Plasma display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma display device superior in gradation characteristic over the range from low luminance to high luminance and fine in the adjustment step of contrast. SOLUTION: When a time division driving method is selected, a contrast adjustment is conducted by the number of sustaining pulses, the number of sustaining pulses in the subfield(SF) corresponding to the same bit of digital video signals is set to the different value. For example, the sustaining pulse number of a first SF of a contract adjustment level 2 is set to 1.5 and the sustaining pulse numbers of a first SF of first and second fields 100 and 200 are set to/and 2. Moreover, the gradation display of the fields 100 and 200 are alternatively conducted for every field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device, and more particularly to a plasma display device, which divides one field into a plurality of sub-fields weighted by luminance and selects an arbitrary sub-field in accordance with a video signal to obtain a halftone image. The present invention relates to a plasma display device that performs display.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram schematically showing a conventional AC type plasma display device 20. As shown in FIG. The plasma display device 20 includes a display panel 21, an address pulse output circuit 22, a scan and sustain pulse output circuit 23 for driving an address electrode 26, a scan electrode 27, and a sustain electrode 28 included in the display panel 21, and a sustain pulse. It comprises an output circuit 25 and a signal processing circuit 24 for controlling the output circuits 22, 23 and 25.

The display panel 21 has two glass plates (not shown), an address electrode 26, a scanning electrode 27, a sustain electrode 28, and a partition for partitioning a space between the glass plates. The storage electrode 28 is covered with a dielectric (not shown). Pixels displayed on the display panel 21 are formed by discharge cells that are spaces sandwiched between two glass plates and separated by partition walls.

[0004] For example, He-Xe, Ne-
A rare gas such as Xe is sealed, and the address electrode 2
6. When a voltage is applied between the scanning electrodes 27, a discharge occurs,
Ultraviolet light is generated. The partition walls are coated with a phosphor, and emit light when excited by ultraviolet rays. Color display can be performed by separately coloring the emission color of the phosphor into red, green, and blue for each discharge cell and selecting the color according to an image signal.

The electrodes are driven in a line-sequential manner, and an address pulse is applied to the address electrode 26 in accordance with an image signal. On the other hand, a scanning pulse is sequentially applied to the scanning electrodes 27 from the first row. In a cell to which the address voltage and the scanning voltage are simultaneously applied, the voltage between the electrodes exceeds the discharge starting voltage and discharges. This discharge is referred to as an address discharge. In the cell where the discharge has occurred, the charge is accumulated on the dielectric covering the electrode
The discharge can be started again at a voltage lower than the discharge start voltage within a certain period thereafter.

In the example shown in FIG. 6, the scan electrode 27 also serves as a sustain electrode, and a sustain discharge is generated by alternately applying a sustain pulse to the scan electrode 27 and the sustain electrode 28. At this time,
The direction of discharge between scan electrode 27 and sustain electrode 28 alternates. Such a driving method is called a memory driving method.

Next, a description will be given of a halftone display method by a time-division driving method (hereinafter, a subfield method) utilizing the memory effect. With the subfield method, halftone display is realized by dividing one field into a plurality of subfields weighted by the difference in light emission luminance and selecting an arbitrary subfield for each pixel according to the signal amplitude How to Here, the field indicates a vertical scanning period, and may be replaced with a frame subframe.

The driving sequence 60 shown in FIG. 7 is an example of a case where 16 gradations are displayed by four subfields SF1 to SF4. The scanning period 61 indicates a period for selecting a light emitting cell in the first subfield, and the sustain period 62 indicates a period during which the selected cell emits light. The sustain periods of the subfields SF1 to SF4 are weighted with a luminance ratio of 8: 4: 2: 1. If these subfields are arbitrarily selected according to the level of the video signal, 2 4 = 1
Display of six gradations becomes possible.

This type of apparatus is described in, for example, IEICE Technical Report EID92-86 (1993-3, pp. 7-11).

[0010]

In a display device, contrast adjustment is an essential function. As the contrast adjustment method in the time-division driving method,
Two methods are conceivable: (1) changing the amplitude of the video signal, and (2) adjusting the total number of pulses without changing the luminance ratio for each subfield.

The former method has been conventionally used. However, when this method is used for a digital signal, as the luminance is reduced, the number of displayable gradations is reduced, and deterioration of the image quality is inevitable. On the other hand, in the latter method, if the luminance ratio for each subfield can be kept constant, there is no deterioration in gradation display due to contrast adjustment. However, if an attempt is made to increase the number of contrast adjustment steps while maintaining the number of display gradations, the luminance ratio for each subfield cannot be kept constant, and it becomes difficult to secure a sufficient number of contrast adjustment steps. . The reason is as follows.

In the plasma display, the period of the sustain pulse for controlling the brightness needs to secure at least several microseconds in order to maintain an efficient and stable discharge. Also, considering the time related to the address,
In general, the ratio of the sustain period in one field is set to about 30%. Therefore, the number of sustain pulses per field cannot be increased beyond a certain level.
For example, assuming that the field frequency is 60 Hz, the sustain period per field is 30%, and the period of the sustain pulse is 10 μs, the maximum number of sustain pulses per field is 500.

On the other hand, as shown in FIG. 8, when the number of gradations to be displayed is increased and the number of subfields is set to 6 (64 gradation display), the luminance ratio for each subfield is 1: 2:
4: 8: 16: 32, and 63 pulses are required to accurately display 64 gradations. When performing accurate contrast adjustment, the number of sustain pulses is n times this (n is a positive integer). However, as described above, since the maximum number of sustain pulses per field is about 500, n is a maximum. n = 8, and an adjustment range of only about eight steps can be secured.

Therefore, in order to make the contrast adjustment step larger than eight steps, the maximum number of pulses corresponding to the maximum luminance of the luminance ratio is arbitrarily determined, and the number of sustain pulses in each frame becomes closest to the luminance ratio. With this setting, a luminance error at a certain gradation corresponds to the luminance of one pulse at the maximum. For example, as shown in FIG. 9, when the number of steps of adjusting the contrast is increased to 29, a small number of pulses is generated in the second, third, and fourth steps of contrast, but the number of pulses is an integer. When the decimal number is replaced by an integer, the luminance error becomes a luminance of one pulse at the maximum. These characteristics are hardly satisfactory in performance as compared with the CRT (cathode ray tube) type display which is most widely used today.

An object of the present invention is to eliminate the above-mentioned problems of the prior art, maintain a sufficient number of display gradations, secure a sufficient number of contrast adjustment steps, and realize a plasma capable of realizing a highly accurate display gradation. It is to provide a display device. In other words, it is an object of the present invention to provide a plasma display device capable of reducing a luminance error of each display gradation even if a sufficient number of contrast adjustment stages is secured.

[0016]

In order to achieve the above object, the present invention provides a method in which one field is divided into a plurality of subfields, and each subfield is weighted by a luminance controlled by the number of sustain pulses. In a plasma display apparatus that performs halftone display by arbitrarily selecting the subfield according to a digital video signal composed of a plurality of bits according to a video signal level, the luminance ratio of the halftone display does not apply. The subfield is characterized in that the number of sustain pulses is set to a different value over a plurality of subfields.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. First, the principle of the present invention will be described with reference to FIGS. FIG. 1 is a diagram illustrating a driving sequence of a plasma display device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating the principle of the present invention. Although FIG. 2 shows four subfields as an example for simplicity, the present invention is not limited to this.

A driving sequence 100 shown in FIG. 1 represents a driving sequence in the case of 4 subfields and 16 gradations, and the luminance ratio of the first subfield (first SF) to the fourth subfield (fourth SF) is as follows. Basically 1: 2:
4: 8. Each of the first to fourth subfields has scanning periods 111 to 114 and sustain periods 101 to 104. The pixels correspond to the least significant bit to the most significant bit of the 4-bit digital video signal in this order, and the pixel selected in the address period emits light in the sustain period.

Next, as shown in FIG. 2 (a), the principle of the present invention is that the contrast adjustment level at which the number of sustain pulses in the sub-field has a decimal number, as shown in FIG.
, The number of sustain pulses in a subfield is set to a different number between a plurality of fields (for example, the first field 100 and the second field 200).

FIG. 2B is a diagram showing the relationship between the contrast adjustment level and the sustain pulse in each subfield. When the contrast level is 1, the number of sustain pulses in the fourth sub-field is set to 8. If the ratio of the number of sustain pulses in each sub-field is 1: 2: 4: 8, the number of pulses is 1st sub-field. The numbers are 1, 2, 4, and 8 in order from the field. In the case of this contrast level 1, since the number of sustain pulses in each subfield does not appear as a decimal, the number of sustain pulses is the same in both the first field and the second field.

On the other hand, at contrast adjustment level 2, the number of sustain pulses in the fourth subfield is set to 12, and the ratio of the number of sustain pulses in each subfield is 1: 2:
Assuming 4: 8, the number of pulses is 1.5, 3, 6, and 12, respectively, in order from the first subfield, and a fractional number appears in the number of sustain pulses in the first subfield. However, in practice, the number of 0.5 pulses cannot be realized.

Therefore, in the present invention, the number of pulses in the sustain period of the first subfield of the first field is one, and the number of pulses in the sustain period of the first subfield of the second field is two.
And Visually, light emission of a plurality of fields is integrated and captured, so that gradation display using the number of sustain pulses in the first field and gradation display using the number of sustain pulses in the second field are performed for each field. When done alternately,
As a result, for the first subfield, a luminance equivalent to 1.5 pulses per subfield can be obtained.

In the case of the contrast adjustment level 3, since the number of sustain pulses in each subfield does not appear as a decimal, the number of sustain pulses is the same in both the first field and the second field.

Next, at contrast adjustment level 4, the number of sustain pulses in the fourth subfield is set to 20, and the ratio of the number of sustain pulses in each subfield is 1: 2:
If the ratio is 4: 8, the number of pulses is 2.5, 5, 10, and 20 in order from the first subfield, and a fractional number appears in the number of sustain pulses in the first subfield.

Therefore, in the present invention, the number of pulses in the sustain period of the first subfield of the first field is two, and the number of pulses in the sustain period of the first subfield of the second field is three.
And Visually, light emission of a plurality of fields is integrated and captured, so that gradation display using the number of sustain pulses in the first field and gradation display using the number of sustain pulses in the second field are alternately performed. As a result, the first
For subfields, one per subfield 2.
Brightness equivalent to 5 pulses can be obtained.

According to the principle of the present invention, an error in gradation display when an arbitrary contrast level is set is reduced from the conventional brightness corresponding to a maximum of one pulse to the brightness corresponding to a maximum of 0.5 pulses. be able to. That is, it is possible to greatly improve the accuracy of the luminance of each display gradation when adjusting the contrast. In addition, by improving the accuracy, a sufficient number of steps for contrast adjustment can be set, and a plasma display device excellent in usability can be provided.

In the principle of the present invention, 4
In the subfield, the luminance ratio of each subfield is 1: 2:
The example of 4: 8 has been described, but the number of subfields,
The correspondence with each bit of the digital video signal, the weighting of the luminance of each subfield, the order thereof, and the like may be arbitrary.
For example, in this embodiment, the subfields are arranged in ascending order of the luminance weight, but as shown in FIG.
They may be arranged in descending order of weight.

The number of sustain pulses may be set to an arbitrary number instead of a two-field unit. For example, if a unit of three fields is used, the gradation error can be reduced to a luminance equivalent to a maximum of 0.33 pulses, and if a unit of four fields is used, the gradation error can be reduced to a luminance equivalent to a maximum of 0.25 pulses.

FIG. 3 is a block diagram showing a driving circuit of a plasma display device for realizing the principle of the present invention. FIG. 4 is a timing chart of the signal of the main part. The driving circuit includes a video signal processing circuit 301, a microcomputer 30
2. ROM 303 for storing a table in which the number of sustain pulses in each subfield is set for each contrast level (for example, the table in FIG. 2B), and a control signal generation circuit 30
4, an address pulse output circuit 305, a scan pulse output circuit 306, and a sustain pulse output circuit 307.

The video signal v is rearranged by a video signal processing circuit 301 having a field memory (or a frame memory) into sub-field data, for example, 4-bit data, and sent to the address pulse output circuit 305 as data v '. Can be The control signal generation circuit 304
As shown in FIG. 4, a scan period signal b is generated based on a synchronization signal a from the video signal processing circuit 301, and data of the number of sustain pulses is read out from the ROM 303 to generate a sustain pulse output circuit. Then, a control signal c at 307 is generated. The scanning period signal b is sent to the video signal processing circuit 301. Note that the control signal c in FIG. 3 is schematically shown. Further, the control signal generation circuit 304 generates control signals d and e, which are signals for instructing output permission of the address pulse output circuit 305 and the scan pulse output circuit 306.

The control signal generation circuit 304 includes a ROM 303
For example, by accessing the contrast adjustment level and the first and second fields as an address f,
From 303, data g corresponding to the address f is read. The microcomputer 302 and the control signal generation circuit 304
And the video signal processing circuit 301, respectively.
Control signals h and j are input and output.

With respect to the setting of the number of sustain pulses, as described above, a table in which the number of sustain pulses of each subfield is stored in a storage device such as the ROM 303 for each contrast level (for example, the table of FIG. 2B) ) Can be prepared. In this case, the microcomputer 302 switches the read address f of the ROM 303 via the control signal generation circuit 304 according to the input signal i of the contrast level set by the user or the like, and outputs the data g and c relating to the number of pulses to the sustain pulse output circuit. A method for reading the data into 307 is conceivable. Alternatively, the microcomputer 302 may calculate the number of sustain pulses according to the contrast level and directly transfer data on the number of pulses to the sustain pulse output circuit 307 without having a storage unit such as the ROM 303.

Also, when the luminance is high, flicker is relatively easy to feel, so that the number of fields to be adjusted can be switched between when the luminance is high and when the luminance is low. For example, a method of detecting the average level of a signal and performing adjustment in units of two fields when the level is high, that is, when the entire screen is bright, and performing adjustment in units of four fields when the average level of the signal is relatively low, or the like. Conceivable. Specifically, for example, the video signal processing circuit 301 can send information on the level of the video signal v to the microcomputer 302 by the control signal j and reflect the information on the number of sustain pulses.

Further, from the viewpoints of reducing power consumption and suppressing a rise in the temperature of the panel, it is one of effective means to monitor the power of the sustain pulse output circuit 307 and reflect it on the luminance of the panel. For example, the sustain pulse output circuit 3
A power detection signal k of 07 is sent to the microcomputer 302, and when the power detection signal k is large, the number of sustain pulses can be reflected in the number of sustain pulses, such as reducing the number of sustain pulses by one contrast level.

FIG. 5 is a circuit diagram showing a specific example of the sustain pulse output circuit 307.
7b, a resistor 307c and a level conversion circuit 307d. When the power consumption of the output circuit 307a increases, the current supplied from the power supply 307b increases, and the voltage drop of the resistor 307c increases. The signal obtained by level-converting the voltage drop by the level conversion circuit 307d in accordance with the input specification is the power detection signal k.

[0036]

As is apparent from the above description, according to the present invention, the accuracy of contrast adjustment by adjusting the number of sustain pulses can be greatly improved. In addition, by improving the accuracy, a sufficient number of adjustment steps can be set, and a plasma display device excellent in usability can be provided.

According to the present invention, the gradation characteristics are good.
Since the contrast adjustment step can be finely and smoothly adjusted, a plasma display which is natural in appearance and has high image quality can be provided.

Further, as compared with the conventional signal level adjustment, particularly the adjustment of the analog signal level, not only the performance improvement that the number of gradations can be maintained even at low luminance, but also the improvement of the noise immunity and the reduction of the circuit scale are realized. This can greatly contribute to improving reliability.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a driving sequence of a plasma display according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a contrast adjustment level and a sustain pulse in each subfield according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a driving circuit of the plasma display device according to one embodiment of the present invention.

FIG. 4 is a timing chart of signals of main parts of the circuit of FIG. 3;

FIG. 5 is a block diagram showing a specific example of a sustain pulse output circuit of FIG. 3;

FIG. 6 is a configuration diagram of a conventional three-electrode AC type plasma display device.

FIG. 7 is a diagram illustrating a driving sequence according to a conventional time division driving method.

FIG. 8 is a diagram showing a relationship between a conventional contrast adjustment level and a sustain pulse of each subfield.

FIG. 9 shows a case where the contrast adjustment level is increased.
FIG. 7 is a diagram illustrating a relationship between a contrast adjustment level and a sustain pulse of each subfield.

[Explanation of symbols]

301: video signal processing circuit, 302: microcomputer, 303
... ROM, 304, a control signal generation circuit, 305, an address pulse output circuit, 306, a scan pulse output circuit, 30
7. Sustain pulse output circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichiro Kimura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi, Ltd. Home Appliances and Information Media Division

Claims (6)

[Claims] A digital signal comprising a plurality of bits corresponding to a video signal level, wherein one field is divided into a plurality of subfields, and each subfield is weighted by luminance controlled by the number of sustain pulses. In a plasma display device that performs halftone display by arbitrarily selecting the subfield according to a video signal, a plurality of fields may be configured such that the number of sustain pulses in a subfield corresponding to the same bit of the digital video signal is different among a plurality of fields. A plasma display device characterized in that: 2. The plasma display apparatus according to claim 1, wherein a plurality of fields in which the number of sustain pulses of the subfield is set to different numbers are cyclically selected at the time of driving. 3. The plasma display apparatus according to claim 1, further comprising storage means for storing the number of sustain pulses corresponding to each of the plurality of digitized bits according to the contrast adjustment level of the display. 4. The plasma display apparatus according to claim 1, further comprising a calculating means for calculating the number of sustain pulses corresponding to a plurality of digitized bits according to a contrast adjustment level of the display. 5. The plasma display device according to claim 1, further comprising a power consumption detecting means of the sustain pulse output circuit, wherein the contrast is adjusted based on information obtained from the power consumption detecting means. . 6. An average level of a video signal is detected, and when the average level is higher than a predetermined value, contrast adjustment is performed in units of p fields (p is an integer of 2 or more), and when the average level is lower than the predetermined value. 5. The plasma display device according to claim 1, wherein the contrast is adjusted in units of q fields (q is an integer greater than p).