JPH1138928A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the generation of false noises and false contours accompanying time-shared gradation display supprescible to the minimum by increasing the number of gradations with a minimized number of the sub-fields as many as possible. SOLUTION: One field is constructed by, e.g. 8 sub-fields, SF1 to SF8. The time width ratios of the display periods corresponding to the sub-field periods, SF1 to SF8, are made 1:2:4:7:14:28:56:112. This time, when a level 112 is to be displayed, whether the preceding display level was 111 or less or 113 or more, is judged. In the former case, the redundant luminescent pattern(b) is used and in the latter case, the conventional luminescence pattern(c) is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a display device such as a plasma display panel or a ferroelectric liquid crystal display device using a time division gray scale display method.

[0002]

2. Description of the Related Art In a display device such as a plasma display panel (hereinafter abbreviated as PDP) or a ferroelectric liquid crystal display device (hereinafter abbreviated as FLCD), which performs essentially binary display, it takes one field period. A time division gray scale display method in which a plurality of sub-field (or sub-frame) scans are performed during (or one frame period) and gray scale display is performed by the cumulative effect is adopted.

For example, in a PDP, one field period is divided into eight subfield periods SF as shown in FIG.
1 to SF8, and each subfield period SF1 to S8
F8 is further divided into an address period and a display period.
Then, the time width ratio of the display period corresponding to each of the subfield periods SF1 to SF8 is set to 1: 2: 4: 8: 16: 3.
2: 64: 128, and each subfield period SF1 to SF1
By turning on / off the display of SF8 independently, 256 gradation display is realized.

However, in such a time division gray scale display method, when 127 levels are displayed as shown in FIG. 13, the 127 level light emission period of the PDP is concentrated in the first half of one field period, and 128 levels are displayed. If you want to concentrate on the second half. Note that, in the figure, hatched portions indicate light emission of the PDP.

Accordingly, a certain pixel is shifted from 127 level to 12 level.
When the level changes to eight levels, there is a non-light-emission period in which the PDP does not emit light for one field period at that moment, resulting in dark pixels appearing in the image and deteriorating the image quality. Also, although not shown, there is a problem that the moment when the level changes from the 128th level to the 127th level, a bright line appears on the image and the image quality is impaired.

[0006] Such a phenomenon occurs when the brightness of a still image is 1 unit.
When the 27th level and the 128th level are alternately present (for example, when the brightness to be displayed is between the 127th level and the 128th level, the same pixel has the 127th level due to the analog / digital conversion noise of the A / D conversion circuit). The moment when the level changes from the 127 level to the 128 level and the moment when the level changes from the 128 level to the 127 level are recognized as noise, which leads to a significant loss of image quality. Hereinafter, such a phenomenon is abbreviated as pseudo noise.

In addition, as shown in FIG. 14, when an object 102 having a brightness of 128 moves in a background 101 having a brightness of 127, the moving object 102 having a brightness of 128 is visually observed. It will be. Therefore, for example, when the object 102 moves from the image 102a to the image 102b, the object 102 having the original brightness of 128 levels is changed from the portion of the brightness 0 level, the portion of the brightness 128 level, and the portion of the brightness 255 level. Is recognized as being configured,
The image quality may be significantly impaired. Hereinafter, such a phenomenon is abbreviated as false contour.

As a method for solving the above-mentioned problem, the first one of the time width ratio “128” of the conventional method shown in FIG.
A method of subdividing bits into two subfields SF8-1 and SF8-2 of 64:64 as shown in FIG.
No. 5439.

The time width ratio "64" shown in FIG.
A method of subdividing two subfields of “128” into four subfields of 48: 48: 48: 48 as shown in FIG. 16 and rearranging each subfield in the first half and the second half of one field period (hereinafter, referred to as “subfield”) , Abbreviated as subfield rearrangement method) is “Dynamic False Contours on PDPs-F
atal or Curable? ”IDW'96 Workshop on Plasma
Displays pp 251-254 described by Mikoshiba of the University of Electro-Communications. At this time, the four subfields having the time width ratio “48” are sequentially illuminated from the time center of one field period, and are lit so that the time center of the light emission period does not move remarkably.

[0010] As shown in FIG. 17, another subfield having a time width ratio “1” corresponding to the least significant bit has another one.
Japanese Patent Application Laid-Open No. 8-278767 discloses a gradation display method for providing a subfield having a time width ratio of “1” (hereinafter, abbreviated as a least significant field addition method). At this time, the movement of the time center of the light emission period of one pixel is large 2 ⁿ
Only when the level changes from -1 (for example, when n = 4, 15) level to 2 ⁿ (for example, 16) level, the newly added least significant bit is turned on to suppress the movement of the time center of the light emission period. .

[0011]

Conventionally, the above-mentioned problems of false noise and false contour have been recognized as problems peculiar to PDPs. It has been found that this problem is common to display devices that perform divided gray scale display.

For example, in an FLCD, like a PDP, FIG.
, One field period is divided into three subfield periods SF1 to SF3, and each subfield period SF1 to SF3 is further divided into an erasing period and a display period.
The time width ratio of the display period corresponding to each of the subfield periods SF1 to SF3 is 1: 2: 4, and the display of each of the subfield periods SF1 to SF3 is independently turned ON / OFF to realize eight gradation display. ing. However, this F
It has recently been found that false noise and false contours occur in LCDs as well as in PDPs as long as time-division gradation display is performed.

In view of the above, the use of an upper bit division method, a subfield rearrangement method, or a least significant field addition method which can mitigate a false noise or a false contour conventionally proposed has been examined. A problem arises that the number of required subfields increases.

This is a fatal drawback in a display device that drives a capacitive load (ie, ferroelectric liquid crystal) such as an FLCD. In other words, the FLCD applies the scan voltage shown in the first stage of FIG. 11, which is an explanatory diagram of the present invention, to the scan electrode L of the FLCD (see FIG. 10, which is an explanatory diagram of the present invention), and The data voltage shown in FIG.
11), and the pixel voltage shown in the third row of FIG. 11 which is the difference voltage is applied to the ferroelectric liquid crystal (hereinafter abbreviated as FLC) 6 between the scan electrode L and the data electrode S (see FIG. 10). )
To drive the FLC, the higher the driving frequency, the more the waveform distortion at the terminal of the electrode and the problem of heat generation due to the current flowing through the electrode occur.

In a FLCD or PDP, a scanning period is determined by one scanning period = 1 field period / (the number of scanning lines × the number of subfields). Is too short to secure the number of subfields.

For example, when the number of subfields is set to 8 in all the methods due to the limitation of the scanning period, the time width ratio is 1: 2: 4: 8: 16: 32: 64: 1 in the conventional method.
In the case where 256 gradations can be displayed by 28 time division gradation display, the time width ratio is 1: 2: 4:
8: 16: 32: 32: 32 time division gray scale display of 12
In the 8-gradation display and the subfield rearrangement method, the time width ratio is 1
6: 16: 1: 2: 4: 8: 16: 16 time-division gradation display with 64 gradations, and even with the least significant field addition method, a time width ratio of 1: 1: 2: 4: 8: 16: 32: With 64 time division gray scale displays, only 129 gray scale displays are possible.

The present invention has been made in order to solve the above-mentioned conventional problems. The object of the present invention is to provide a floor which can be displayed in comparison with the above-mentioned three methods when the same number of subfields is maintained as in the conventional method shown in FIG. It is an object of the present invention to provide a display device having a large number of tones and capable of alleviating the problem of false noise and the problem of false contours associated with time division gray scale display.

[0018]

In order to achieve the above object, a display device according to a first aspect of the present invention is characterized in that one field is constituted by a plurality of subfields having different display duration time width ratios. in the display device which performs multi-gradation display, the time width ratio of the display period for each subfield, 1:, ...,: 2 m:, ..., :( 2 a -B) × 2 k:, ... Here, m is a variable from 1 to A-1, k is a variable from 0 to n-A-1, n is the number of subfields, A is an integer of 2 or more, and B
Is an integer of 1 or more.

According to the above configuration, in a display device in which one pixel is a binary display, each subfield period is independently turned ON.
/ OFF enables time division gray scale display. At this time, if the ON / OFF of the subfield period is appropriately controlled in accordance with the change in the brightness of the image in the time axis direction, when the number of subfields is the same, the number of gradations is remarkably larger than that of the related art. By the number, the problem of the false noise and the false contour associated with the time division gray scale display method can be solved. In particular, the movement of the time center during the display period in which the image is bright is large (2 ^A− B) × 2 ^k −B level to (2 ^A− B) ×
When changing from the 2 ^k level or (2 ^A− B) × 2 ^k + B level to the (2 ^A− B) × 2 ^k level, it is possible to effectively suppress the occurrence of false noise and false contour. .

According to a second aspect of the present invention, there is provided a display device which performs multi-gradation display by forming one field by a plurality of subfields having different time width ratios of a display period. The time width ratio of the corresponding display period is 1: (M ^A -B) × M ^k :, or 1 ::...: M ^m :,...,: (M ^A −B) × M ^k :, ..., where M (M is an integer of 3 or more) is the number of gray levels that can be displayed in a subfield period corresponding to each bit other than the least significant bit, m is a variable from 1 to A-1, and k is 0 ~ N-A-
1 variable, n is the number of subfields, A is an integer of 1 or more,
And B is an integer of 1 or more.

According to the above configuration, in a display device in which one pixel displays M values, the same operation and effect as the configuration according to the first aspect can be obtained.

According to a third aspect, in the display device according to the second aspect, a plurality of scanning electrodes arranged in parallel with each other and a plurality of scanning electrodes arranged in parallel with each other in a direction orthogonal to the scanning electrodes. A data electrode and a liquid crystal layer comprising a ferroelectric liquid crystal disposed between the scanning electrode and the data electrode, each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode, Preferably, the sub-pixels include a plurality of sub-pixels.

According to the above arrangement, since one pixel is divided into a plurality of sub-pixels, three or more gradations can be displayed for one pixel. Therefore, the value of M can be set freely, and it is possible to obtain the number of gradations according to the purpose.

According to a fourth aspect of the present invention, in the display device according to the second aspect, a plurality of scan electrodes arranged in parallel with each other and a plurality of data arranged in parallel with each other in a direction orthogonal to the scan electrodes. An electrode, disposed between the scanning electrode and the data electrode, including a liquid crystal layer made of ferroelectric liquid crystal,
It is preferable to change the brightness of each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode by controlling the pulse voltage applied to the data electrode.

According to the above configuration, the ratio between the bright domain region and the dark domain region in one pixel can be changed, so that three or more gradations can be displayed for one pixel. Therefore, the value of M can be set freely, and it is possible to obtain the number of gradations according to the purpose.

According to a fifth aspect of the present invention, in the display device according to the second aspect, a plurality of scan electrodes arranged in parallel with each other and a plurality of data arranged in parallel with each other in a direction orthogonal to the scan electrodes. An electrode, disposed between the scanning electrode and the data electrode, including a liquid crystal layer made of ferroelectric liquid crystal,
Each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode is composed of a plurality of sub-pixels, and the brightness of each pixel is changed by controlling a pulse voltage applied to the data electrode. Is preferred.

According to the above configuration, since the configurations of the third and fourth aspects are combined, the same effect as that of the configuration can be obtained, and the number of gradations can be further increased. It is possible to set the key number.

As set forth in claim 6, claims 1 to 5
, SPi,..., SPi, respectively.
.., SPn (i is an integer from A + 1 to n), the display periods SP2 to SPi are bright and the display period S
P1, SP (i + 1) to SPn are the dark first display state and the next brightness level after the first display state, the display periods SP1 to SPi are bright and the display period SP (i
+1) to SPn are the dark second display state and the same brightness level as the second display state, and the display period SP (i +
1) is bright and the display periods SP1 to SPi, SP (i
+2) to SPn are the dark third display state and the next brightness level after the third display state, and the display periods SP1, S
P (i + 1) is bright and the display periods SP2 to SPi,
It is desirable that SP (i + 2) to SPn have a dark fourth display state.

According to the above configuration, since there are two display states having the same brightness level, if the two display states are appropriately selected according to the change in the brightness of the image, the display state at the time center of the display period can be obtained. Movement can be minimized.

According to a seventh aspect of the present invention, in the display device according to the sixth aspect, when selecting the brightness level of the second or third display state, the display state of one pixel before one field of each pixel is changed. When the brightness is equal to or lower than the brightness level of the first display state, the second display state is selected as the next display state, and when the brightness level is equal to or higher than the brightness level of the fourth display state, the next display state is selected. It is preferable to select the third display state.

According to the above configuration, a dark image or a bright line does not appear over one field, so that it is possible to prevent the image quality from deteriorating.

As described in the eighth aspect, in the display device according to the sixth aspect, it is preferable that the display states of adjacent pixels are made different from each other by using the second display state and the third display state.

According to the above configuration, the pixel in the second display state and the pixel in the third display state are adjacent to each other. Movement can be suppressed.

According to a ninth aspect, in the display device according to the sixth aspect, when the display state of a certain pixel is set to the second or third display state, the display state of the pixels surrounding the pixel is changed. When the brightness is equal to or lower than the brightness level of the first display state, the display state of the surrounding pixels is set to the second display state. It is preferable that the display state of the pixel is set to the third display state.

According to the above configuration, since the display state of the pixel is selected after referring to the surrounding pixels, it is possible to suppress the movement of the time center of the display period when a plurality of pixels are viewed as a unit. Become.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIG. 1 shows an embodiment of the present invention.
The following is a description based on FIGS. 10 and 11. In the present embodiment, a case where a ferroelectric liquid crystal display device (hereinafter abbreviated as FLCD) is applied as a display device will be described.

[Basic Configuration of FLCD] The FLCD according to the present embodiment has a liquid crystal panel 1 as shown in FIG. The liquid crystal panel 1 includes two light-transmitting substrates 2a and 2b made of, for example, glass and opposed to each other.

On the surface of the substrate 2a, a plurality of transparent data electrodes S made of, for example, indium tin oxide (hereinafter abbreviated as ITO) are arranged in parallel with each other. These data electrodes S are made of, for example, silicon oxide (SiO ₂ ).
Covered with a transparent insulating film 3a made of

On the other hand, on the surface of the substrate 2b, for example, ITO
Are arranged in parallel with each other so as to be orthogonal to the data electrodes S. These scanning electrodes L are covered with a transparent insulating film 3b made of the same material as the insulating film 3a.

A plurality of pixels are formed in a matrix by the orthogonal intersection of the scanning electrodes L and the data electrodes S.

On the insulating films 3a and 3b, there are formed alignment films 4a and 4b which have been subjected to a uniaxial alignment process such as a rubbing process. As the alignment films 4a and 4b, polyvinyl alcohol or the like is used.

The ferroelectric liquid crystal 6 is formed on the substrates 2a and 2a bonded together with the sealing agent 5 so that the alignment films 4a and 4b face each other.
The space between 2b is filled to form a liquid crystal layer.
The ferroelectric liquid crystal 6 is injected from an injection port (not shown) provided in the sealing agent 5, and is sealed by sealing the injection port.

The substrates 2a and 2b are further sandwiched between two polarizing plates 7a and 7b arranged so that the polarization axes are orthogonal to each other.

[Driving Method of FLCD] FIG. 1 shows a case where the above FLCD is driven by using the blanking driving method.
1 will be described.

The top row of FIG. 11 shows the waveform of the scanning voltage applied to the scanning electrode L in this blanking drive method. As is apparent from this waveform, in the blanking drive method, one slot is two slots (2τ _s ) during one field period.
And a 2-slot erasing period having a length equal to the selecting period before the selecting period.

The peak value of the first slot in the above selection period is 0
A V, the second slot strobe pulse peak value V _s is applied as the scan voltage. During the erasing period, a strobe pulse having a polarity opposite to that of the above strobe pulse, a pulse width of 2 slots, and a peak value _Vb is applied.

The data voltage applied to the data electrode S is
As shown in an example in the middle part of FIG.
It is represented by a bipolar pulse with a period. The data voltage is for a write first slot -V _d, the second slot is + V _d, and when the non-write, the first slot is + V _d, the second slot becomes -V _d.

The potential difference between the scanning voltage and the data voltage is applied to the pixel. The lowermost part of FIG. 11 shows a waveform of a pixel voltage generated in the pixel by the scanning voltage and the data voltage.

[Time-Division Grayscale Display Method of FLCD] In this embodiment, the weighting factor of the time-division grayscale display, that is, the number of grayscales (M that can be displayed in the subfield period corresponding to each bit other than the least significant bit) ) Is 2, that is, a case in which one pixel performs binary display will be described.

Here, one field period is divided into n subfield periods SF1 to SFn, and each of the subfield periods SF1 to SFn includes an erasing period and a display period.

Each of the above subfield periods SF1 to SFn
The time width ratio of the corresponding display period SP1~SPn to, 1:, ...,: 2 m:, ..., :( 2 A -B) × 2 k:, ... ··· (1) where, m is 1 -A-1 variables, k is a variable of 0-n-A-1, n is the number of subfields, A is an integer of 2 or more, and B
Is an integer of 1 or more.

FIG. 1 is an explanatory diagram of the time division gray scale display when n = 8, A = 3, and B = 1. From the above equation (1), the time width ratio of the display periods SP1 to SP8 corresponding to the respective subfield periods SF1 to SF8 is 1: 2: 2 ² : (2 ³ -1) :( 2 ³ -1) × 2. : (2
^{3 -1) × 2 2: (} 2 3 -1) × 2 3: (2 3 -1) ×
2 ⁴ = 1: 2: 4: 7: 14: 28: 56: 112. At this time, the number of gradations is 225 gradation display.

In this case, the movement of the time center during the bright display period is large because the display level is from 2 + 2 ² = 6 levels to (2 ³ -1).
= 7 levels, or 1 + 2 + 2 ² = 7 levels to 1+
When the display level changes to (2 ³ -1) = 8 levels: from 2 + 2 ² + (2 ³ -1) = 13 levels to (2 ³ -1) × 2 = 14 levels, or 1 + 2 + 2
² + (2 ³ -1) = 14 levels from 1+ (2 ³ -1) ×
2 = 15 Reberuhe change when the display level is 2 + ² 2 + (2 ³ -1) + (2 ³ -
1) × 2 = 27 levels to (2 ³ −1) × 2 ² = 28 levels, or 1 + 2 + 2 ² + (2 ³ −1) + (2 ³ −
From 1) × 2 = 28 levels, 1+ (2 ³ −1) × 2 ² = 2
When changing to 9 levels: Display level is 2 + 2 ² + (2 ³ -1) + (2 ^3-
1) × 2 + (2 ³ −1) × 2 ² = 55 levels to (2 ³
-1) × 2 ³ = 56 levels, or 1 + 2 + 2 ² + (2
³ -1) + (2 ³ -1) × 2 + (2 ³ -1) × 2 ² = 5
When the level changes from 6 levels to 1+ (2 ³ -1) × 2 ³ = 57 levels The display level is 2 + 2 ² + (2 ³ -1) + (2 ³ −
1) × 2 + (2 ³ -1) × 2 ² + (2 ³ -1) × 2 ³ =
(2 ³ -1) × 2 ⁴ = 112 levels from 111 levels,
Or 1 + 2 + 2 ² + (2 ³ -1) + (2 ³ -1) × 2
A case where the level changes from + (2 ³ -1) × 2 ² + (2 ³ -1) × 2 ³ = 112 levels to 1+ (2 ³ -1) × 2 ⁴ = 113 levels may be considered.

Among these, the movement of the center of time during the brightest display period is large when the display level changes from 111 level to 112 level or from 112 level to 113 level.

In the example of FIG. 1, in the display state of level 111, each display period in the subfield periods SF2 to SF7 is bright (see FIG. 1A), and the display state of level 113 is in the subfield period. SF1 / SF8
Is brighter in each display period (see FIG. 1D).

The display state of 112 levels is as follows.
The display state shown in FIG. 1B (hereinafter abbreviated as a redundant light emission pattern) and the display state shown in FIG. 1C (hereinafter abbreviated as a conventional light emission pattern) exist. In the above-described redundant light emitting pattern, each display period in the subfield periods SF1 to SF7 is bright, and in the conventional light emitting pattern, the display period in the subfield period SF8 is bright.

Thus, in the above case, the movement of the time center of the brightest display period is large when the level changes from the 111 level to the 112 level of the conventional light emitting pattern and when the level changes from the 112 level of the redundant light emitting pattern to the 113 level. It can be seen that it is.

Therefore, when the same 112 levels are displayed, whether the previous display state was at a level of 111 or less or 11
It is determined whether the level is 3 or more. If the level is 111 or less, the redundant light emission pattern of FIG.
At the above level, the conventional light emitting pattern of FIG. 1C is used. This suppresses the movement of the display period around the time.

Here, A in the above equation (1) determines the number of gradations. When the values of M (here, 2) and B are fixed, the larger the value of A, the more the number of gradations. Becomes larger.

For example, when A = 2 and B = 1, the time width ratio is 1: 2: (2 ² -1) :( 2 ² -1) × 2: (2 ^2-
1) × 2 ² : (2 ² -1) × 2 ³ : (2 ² -1) ×
2 ⁴ : (2 ² -1) × 2 ⁵ = 1: 2: 3: 6: 12: 2
4:48:96, and the number of gradations is 193 gradation display.

When A = 4 and B = 1, the time width ratio is 1: 2: 2 ² : 2 ³ : (2 ⁴ -1) :( 2 ⁴ -1) ×
2: (2 ⁴ -1) × 2 ² : (2 ⁴ -1) × 2 ³ = 1
2: 4: 8: 15: 30: 60: 120, and the number of gradations is 241 gradation display.

B determines a level interval having two patterns of a conventional light emitting pattern and a redundant light emitting pattern. When the values of M and A are fixed, the level interval becomes larger as the value of B becomes larger. Becomes smaller. For example, B
In the case of = 1, the level having the conventional light emitting pattern and the redundant light emitting pattern is 1 level every 1 + 2 + 2 ² = (2 ³ −1) = 7 levels, but when B = 2, 2 + 2 ² = (2
³ -2) = can 6 level every two levels. Therefore,
By increasing the value of B, it is possible to further alleviate the problem of the false noise and the problem of the false contour accompanying the time division gray scale display.

For example, when A = 3 and B = 2, the time width ratio is 1: 2: 2 ² : (2 ³ -2) :( 2 ³ -2) × 2: (2
^{3 -2) × 2 2: (} 2 3 -2) × 2 3: (2 3 -2) ×
2 ⁴ = 1: 2: 4: 6: 12: 24: 48: 96, and the level interval is 6.

[0064] In the case of A = 3, B = 3, the time width ^{ratio, 1: 2: 2 2:} (2 3 -3) :( 2 3 -3) × 2: (2
^{3 -3) × 2 2: (} 2 3 -3) × 2 3: (2 3 -3) ×
2 ⁴ = 1: 2: 4: 5: 10: 20: 40: 80, and the level interval is 5.

As described above, in the display device according to the present embodiment, one field is constituted by a plurality of subfields having different time width ratios of the display period. Is a configuration in which the time width ratio of the display period corresponding to.

According to this configuration, for example, n = 8, A =
3, when B = 1, the number of displayable gradations is 225 gradation display, and the problem of false noise and the problem of false contour accompanying the time division gradation display can be mitigated. When the number of subfields is the same (n = 8), the number of gradations is 128 in the conventional upper bit division method, 64 in the subfield rearrangement method, and 129 in the least significant field addition method. Since the gradation display is performed, it can be seen that the number is significantly increased as compared with those.

The display periods corresponding to the n subfield periods are denoted by SP1,..., SPi,.
When (i is an integer from A + 1 to n), the display periods SP2 to SPi are bright and the display periods SP1, SP1
(I + 1) to the first display state where SPn is dark (for example, 1
11 levels) and the next brightness level after the first display state, the second display state (for example, redundant light emission) in which the display periods SP1 to SPi are bright and the display periods SP (i + 1) to SPn are dark. (112 levels of the pattern) and the same brightness level as in the second display state, and the display period SP
(I + 1) is bright and the display periods SP1 to SPi, S
A third display state in which P (i + 2) to SPn are dark (for example,
(112 levels of the conventional light emission pattern) and the next brightness level of the third display state, and the display periods SP1 and SP
(I + 1) is bright and the display periods SP2 to SPi, S
A fourth display state in which P (i + 2) to SPn is dark (for example,
113 levels).

Further, when the brightness level of the second or third display state is selected, if the display state one field before of each pixel is lower than the brightness level of the first display state, While the second display state is selected as the next display state, when the brightness is equal to or higher than the brightness level of the fourth display state, the third display state is selected as the next display state.

Therefore, since a dark image or a bright line does not appear over one field, it is possible to prevent the image quality from deteriorating.

In the present embodiment, the order of the subfields on the time axis starts from the subfield corresponding to the smaller bit, but is not limited to this. That is, the order of the subfields on the time axis may start from the subfield corresponding to the larger bit, or may be arranged in any order.

[Embodiment 2] The following will describe Embodiment 2 of the present invention with reference to FIGS. For the sake of convenience of explanation, the same members as those shown in the drawings of the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the present embodiment, essentially, the FLCD or the like
A case will be described in which a weighting coefficient for time division gray scale display, that is, the number of gray scales (M) that can be displayed in a subfield period corresponding to each bit other than the least significant bit is 3 or more in a display device that performs value display.

Here, one field period is divided into n subfield periods SF1 to SFn, and each of the subfield periods SF1 to SFn is composed of an erasing period and a display period.

Each of the above subfield periods SF1 to SFn
The time width ratio of the corresponding display period SP1~SPn ^{to, 1: (M A -B)} × M k:, ... ··· (2) or, 1:, ...,: M m:, ..., :( M ^A −B) × M ^k :, (3) where m is a variable of 1 to A−1, k is a variable of 0 to n−A−1, n is the number of subfields, and A is 1 An integer greater than or equal to B
Is an integer of 1 or more.

As a method of determining M, a first method of dividing one pixel into a plurality of sub-pixels (pixel division gray scale display method) and a method of controlling a pulse voltage applied to a data electrode to control the brightness of a pixel There is a second method of changing

The first method will be described for the case of the FLCD shown in FIG. This FLCD has a liquid crystal panel 11 having the same configuration as the liquid crystal panel 1 of the first embodiment except for the data electrodes S. That is, the liquid crystal panel 11
Has a plurality of scanning electrodes L and a plurality of data electrodes S ′ orthogonally intersecting the scanning electrodes L. Further, the liquid crystal panel 11 is connected to a scan electrode drive circuit 12 for applying a scan voltage to the scan electrodes L and a data electrode drive circuit 13 for applying a data voltage to the data electrodes S ′.
An I / O converter 14 is connected to the data electrode drive circuit 13.

Here, the data electrode S 'is connected to three sub-data electrodes S1, S2, S with an electrode width ratio of 1: 2: 4, for example.
Divide into three. As described above, by dividing one pixel into three sub-pixels, as shown in FIGS.
Eight gradation displays from 0 to 7 are obtained in each subfield period. In the same figure, the hatched portion indicates a bright state.

As a second method, for example, as shown in FIG. 4, in an FLCD, a pulse voltage applied to a data electrode may be changed. Note that, in the figure, the vertical axis is a relative value when the light transmittance at the pulse height is set to 1.

As a result, for example, as shown in FIGS. 5A to 5E, the ratio of the bright domain region 22 to the dark domain region 21 in one pixel can be changed. A tone display is obtained.

FIG. 6 shows that, using an FLCD that has obtained an 8-gradation display (M = 8) by the first method, n = 3, A = 1,
FIG. 4 is an explanatory diagram of time division gray scale display when B = 1.
From the above equation (2), each subfield period SF1 to SF
The time width ratio of the display periods SP1 to SP3 corresponding to 3 is 1: 8-1: (8-1) × 8 = 1: 7: 56. The number of gradations at this time is 512 gradation display.

In this case, the movement of the center of time during the bright display period is large because the display level changes from 6 to 7 levels, or from 7 to 8 levels, and the display level changes from 55 to 56 levels or 5 levels.
A case where the level changes from 6 to 57 is considered.

Of these, the movement of the center of time during the brightest display period is large when the display level changes from 55 level to 56 level or from 56 level to 57 level.

In the example of FIG. 6, the 55-level display state is as follows.
Each of the display periods SP1 and SP2 in the subfield periods SF1 and SF2 is in the ON state (see FIG. 6A).
Display periods SP1 and SP3 in F1 and SF3 are ON
State (see FIG. 6D). As the 56-level display state, there are a redundant light emitting pattern shown in FIG. 6B and a conventional light emitting pattern shown in FIG. 6C. In the figure, the numerical value on the vertical axis indicates the pixel division gray scale ratio. For example, in the subfield period SF1 of FIG. 6A, the pixel is in the state of FIG. Is shown.

Thus, in the above case, the movement of the time center of the brightest display period is large when the level changes from the 55 level to the 56 level of the conventional light emitting pattern and when the level changes from the 56 level of the redundant light emitting pattern to the 57 level. It is.

Therefore, when displaying the same 56 levels,
It is determined whether the previous display state was at a level of 55 or less or at a level of 57 or more. If the level is 55 or less, the redundant light emitting pattern shown in FIG. The conventional light emitting pattern of c) will be used. This suppresses the movement of the display period around the time.

Although not shown, similarly, n = 3 and A =
When 2, B = 1, the display periods SP1 to SP3 corresponding to the subfield periods SF1 to SF3 are obtained from the above equation (3).
The time width ratio of SP3 is 1: 8: (8 ² -1) = 1: 8: 63. When the display state changes from 62 level to 63 level or from 63 level to 64 level, the same result is obtained. can get.

Next, FIG. 7 is an explanatory diagram of the time division gray scale display when the first method and the second method are combined. That is, in this case, the data electrodes are connected at an electrode width ratio of 1: 2.
A second technique is used in which the brightness of a pixel is changed by controlling a pulse voltage applied to the data electrode only during a subfield period corresponding to the least significant bit. In this case, only the 4-gradation display is performed in the subfield period corresponding to the bits excluding the least significant bit, and only the 19th gradation display of 0 to 18 is performed in the subfield period corresponding to the least significant bit.

In the case of the example shown in FIG. 7, only four gradations can be displayed in a subfield period corresponding to bits other than the least significant bit, so that M = 4, n = 3, A = 1, and B =
It is set to 1. Note that, in the figure, SD1 (area ratio =
One circle of 1) represents seven gradations of “0, 1, 2, 3, 4, 5, 6”, and one circle of SD2 (area ratio = 2) represents “0,
2, 4, 6, 8, 10, 12 ".
In total, 19 gradation display of 0 to 18 is shown.

From the above equation (2), the time width ratio of the display period corresponding to each of the subfield periods SF1 to SF3 is as follows: 1: (4-1) :( 4-1) × 4 = 1: 3: 12 Become. The number of gradations at this time is 49 gradation display (289 gradation display in consideration of the gradation number of the least significant bit).

In this case, the movement of the time center during the bright display period is large because the display level is 17 to 18 levels or 1 level.
When the level changes from level 8 to level 19, the display level changes from level 71 to level 72, or 7
When the display level changes from level 2 to level 73 The display level changes from level 141 to level 142 or level 142 to level 143.

Among these, the movement of the center of time during the brightest display period is large when the display level changes from the 71st level to the 72nd level or from the 72nd level to the 73rd level.

In the example of FIG. 7, the display state of the 71 level is
The display periods SP1 and SP2 are in the ON state (FIG. 8)
, The display state of the 73 level is the display period S
P1 and SP3 are in the ON state (see the lower left part of FIG. 8). As the 72-level display state, there are a conventional light emitting pattern shown in the middle right of FIG. 8 and a redundant light emitting pattern shown in the middle left of FIG.

Thus, in the above case, the movement of the time center during the brightest display period is large when the level changes from the 71 level to the 72 level of the conventional light emitting pattern and when the level changes from the 72 level of the redundant light emitting pattern to the 73 level. It is.

Therefore, when displaying the same 72 levels,
It is determined whether the previous display state was a level of 71 or less or a level of 73 or more. If the level is 71 or less, the redundant light emission pattern in the middle left of FIG. A conventional light emission pattern in the middle right is used. This suppresses the movement of the display period around the time.

As described above, in the display device according to the present embodiment, one field is composed of a plurality of subfields having different display time width ratios. Is a configuration in which the time width ratio of the display period corresponding to the above satisfies the relationship of the above equation (2) or (3).

According to this configuration, for example, n = 3, A =
When 1, B = 1, the number of displayable gradations is 512 gradation display, and the problem of false noise and the problem of false contour accompanying the time division gradation display can be alleviated. When the number of subfields is the same (n = 3), the time width ratio is 1:
The time division ratio display of 8:64 was used to display 584 gradations, but the time division ratio of 1: 4: 4 is used in the upper bit division method.
72 time gray scale display in the time division gray scale display, 72 gray scale display in the time division gray scale display with the time width ratio of 4: 1: 4 in the subfield rearrangement method, and 1: 1 time width ratio in the lowest field addition method. In the present embodiment, it is possible to display 512 gray scales in the time division gray scale display with the time width ratio of 1: 7: 56, although the time division gray scale display of: 8 is only capable of displaying 80 gray scales. Therefore, it can be seen that when the number of subfields is the same, the number of gradations is much larger than that of the upper bit division method, the subfield rearrangement method, or the least significant field addition method.

Further, for example, M = 4, n = 3, A = 1,
When B = 1, the number of displayable gradations is 16 × 3 + 1 =
49 gray scale display (considering the number of gray scales of the least significant bit, 1
(6 × 3 × 6 + 1 = 289 gradation display), it is possible to alleviate the problem of false noise and the problem of false contour accompanying the time division gradation display. When the number of subfields is the same (n =
3) In the conventional method, 21 × 3 + 1 = 64 gradations could be displayed by the time division gradation display with the time width ratio of 1: 4: 16, but in the upper bit division method, the time width ratio was 1: 2: 2. 5 × 3 + 1 = 16 gray scale display in divided gray scale display, 16 gray scale display in time division gray scale display with a time width ratio of 2: 1: 2 even in the subfield rearrangement method, and time width ratio of 1 in the lowest field addition method 6 × 3 + 1 = 1 in 1: 4 time division gray scale display
Although only nine gray scales can be displayed, in the present embodiment, 49 gray scales can be displayed by the time division gray scale display with a time width ratio of 1: 3: 12. Therefore, if the number of subfields is the same,
It can be seen that the number of gradations increases in each stage as compared with the upper bit division method, the subfield rearrangement method, or the least significant field addition method.

The display periods corresponding to the n subfield periods are denoted by SP1,..., SPi,.
When (i is an integer from A + 1 to n), the display periods SP2 to SPi are bright and the display periods SP1, SP1
(I + 1) -first display state where SPn is dark (for example, 5
5 or 71 level), which is the next brightness level after the first display state. The second display state (for example, the display periods SP1 to SPi are bright and the display periods SP (i + 1) to SPn are dark). 56 or 7 of redundant light emission pattern
(2 levels) and the same brightness level as that of the second display state. The third display period SP (i + 1) is bright, and the display periods SP1 to SPi and SP (i + 2) to SPn are dark.
(For example, 56 or 72 levels of the conventional light emission pattern) and the next brightness level of the third display state, and the display periods SP1 and SP (i + 1) are bright.
And display periods SP2 to SPi, SP (i + 2) to SPn
Has a dark fourth display state (for example, 57 or 73 levels).

Further, when the brightness level of the second or third display state is selected, if the display state one field before of each pixel is lower than the brightness level of the first display state, While the second display state is selected as the next display state, when the brightness is equal to or higher than the brightness level of the fourth display state, the third display state is selected as the next display state.

Therefore, a dark image or a bright line does not appear over one field, so that deterioration of the image quality can be prevented.

In this embodiment, the data electrode is divided into three or two sub-data electrodes. However, the present invention is not limited to this, and the division number may be selected as needed.

In the first and second embodiments, 1
Although the description has been given of the case where attention is paid to the pixels, when the plurality of pixels are viewed as a whole, the following configuration can further suppress the movement of the display period around the time.

That is, as shown in FIG. 9, a certain level (for example, 112 level, 56 level, 7 level,
When displaying (two levels), a redundant light emitting pattern (corresponding to ● in the figure) and a conventional light emitting pattern (corresponding to ○ in the figure) are alternately changed for each of the upper, lower, left and right pixels.
According to this, it is possible to suppress the movement of the time center in the display period when a plurality of pixels are viewed as a unit.

Further, an arbitrary level having two patterns of a redundant light emitting pattern and a conventional light emitting pattern (for example,
When displaying the above-mentioned 112 levels, 56 levels, and 72 levels), the brightness level of the surrounding pixels is referred to, and when the brightness level is equal to or lower than the arbitrary level, the display state of the surrounding pixels is redundant. On the other hand, when the brightness level is equal to or higher than the arbitrary level, the display state of the surrounding pixels is preferably the conventional light emission pattern. According to this, it is possible to suppress the movement of the time center in the display period when a plurality of pixels are viewed as a unit.

In the first and second embodiments, the FLCD
However, the same effect can be obtained by similarly setting the time width ratio of the display period in the PDP.

[0106]

As described above, in the display device according to the first aspect of the present invention, the time width ratio of the display period corresponding to each subfield period is 1 :,...,: 2 ^m :,. ^{: (2 a -B) × 2} k:, ... where, m is 1 to a-1 variable, k is 0 to n-a-1 variable, n represents the number of sub-fields, a is an integer of 2 or more, And B
Is a configuration that is an integer of 1 or more.

Further, in the display device according to the second aspect, the time width ratio of the display period corresponding to each subfield period is 1: (M ^A -B) × M ^k :,. ,: M ^m :,...: (M ^A -B) × M ^k :,... Where M (M is an integer of 3 or more) can be displayed in a subfield period corresponding to each bit other than the least significant bit. M is a variable of 1 to A-1 and k is 0 to nA-
1 is a variable, n is the number of subfields, A is an integer of 2 or more,
And B have a structure of an integer of 1 or more.

According to the structure of the first or second aspect, in a display device in which one pixel is a binary display or a ternary display or more, the subfield period is appropriately adjusted according to a change in brightness of an image in a time axis direction. By controlling ON / OFF of
When the number of subfields is the same, the effect of eliminating false noise and false contour associated with the time division gray scale display method can be achieved with a significantly larger number of gray levels than in the past.

According to a third aspect of the present invention, in the display device according to the second aspect, a plurality of scanning electrodes arranged in parallel with each other and a plurality of scanning electrodes arranged in parallel with each other in a direction orthogonal to the scanning electrodes. A data electrode and a liquid crystal layer comprising a ferroelectric liquid crystal disposed between the scanning electrode and the data electrode, each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode, This is a configuration including a plurality of sub-pixels.

According to a fourth aspect of the present invention, in the display device according to the second aspect, a plurality of scanning electrodes arranged in parallel with each other and a plurality of data arranged in parallel with each other in a direction orthogonal to the scanning electrodes. An electrode, disposed between the scanning electrode and the data electrode, including a liquid crystal layer made of ferroelectric liquid crystal,
By controlling the pulse voltage applied to the data electrode, the brightness of each pixel formed in a matrix by the intersection of the scan electrode and the data electrode is changed.

According to the configuration of the third or fourth aspect, it is possible to display three or more levels of gradation for one pixel, so that the value of M can be set freely and the gradation corresponding to the purpose can be set. This has the effect of being able to obtain numbers.

According to a fifth aspect of the present invention, in the display device according to the second aspect, a plurality of scanning electrodes arranged in parallel with each other and a plurality of data arranged in parallel with each other in a direction orthogonal to the scanning electrodes. An electrode, disposed between the scanning electrode and the data electrode, including a liquid crystal layer made of ferroelectric liquid crystal,
Each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode is composed of a plurality of sub-pixels, and the brightness of each pixel is changed by controlling a pulse voltage applied to the data electrode. Configuration.

As a result, the same effects as those of the third and fourth aspects are obtained, and the number of options of the number of tones is further increased. This has the effect of making it possible to

As set forth in claim 6, claims 1 to 5
, SPi,..., SPi, respectively.
.., SPn (i is an integer from A + 1 to n), the display periods SP2 to SPi are bright and the display period S
P1, SP (i + 1) to SPn are the dark first display state and the next brightness level after the first display state, the display periods SP1 to SPi are bright and the display period SP (i
+1) to SPn are the dark second display state and the same brightness level as the second display state, and the display period SP (i +
1) is bright and the display periods SP1 to SPi, SP (i
+2) to SPn are the dark third display state and the next brightness level after the third display state, and the display periods SP1, S
P (i + 1) is bright and the display periods SP2 to SPi,
SP (i + 2) to SPn have a dark fourth display state.

As a result, since there are two display states having the same brightness level, if the two display states are appropriately selected according to the change in the brightness of the image, the movement of the time center of the display period can be minimized. The effect that it becomes possible to suppress it is achieved.

According to a seventh aspect of the present invention, in the display device according to the sixth aspect, when the brightness level of the second or third display state is selected, the display state one field before of each pixel is changed. When the brightness is equal to or lower than the brightness level of the first display state, the second display state is selected as the next display state, and when the brightness level is equal to or higher than the brightness level of the fourth display state, the next display state is selected. And the third display state is selected.

As a result, a dark image or a bright line does not appear over one field, so that it is possible to prevent the image quality from being deteriorated.

According to an eighth aspect, the display device according to the sixth aspect has a configuration in which display states of adjacent pixels are made different from each other by using the second display state and the third display state.

According to a ninth aspect, in the display device according to the sixth aspect, when the display state of a certain pixel is set to the second or third display state, the display state of pixels surrounding the pixel is changed to the second or third display state. When the brightness is equal to or lower than the brightness level of the first display state, the display state of the surrounding pixels is set to the second display state. Is set to the third display state.

According to the configuration of the eighth or ninth aspect, there is an effect that it is possible to suppress the movement of the time center of the display period when a plurality of pixels are viewed as a unit.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory diagrams showing time-division gray scale display in a display device according to a first embodiment of the present invention, wherein FIG. 1A shows 111 levels, FIG.
(C) is the 112 level of the conventional light emission pattern, and (d) is 1 level.
13 levels are shown.

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

FIGS. 3A to 3H are explanatory diagrams showing gradation display by data electrode division in the display device. FIGS.

FIG. 4 is a graph showing a relationship between a pulse voltage applied to a data electrode and light transmittance in the display device.

FIGS. 5A to 5E are explanatory diagrams showing gradation display by a pulse voltage change in the display device. FIGS.

FIG. 6 is an explanatory diagram showing a case where pixel division gray scale display is combined with time division gray scale display.

FIG. 7 is an explanatory diagram showing a case where time division gradation display is combined with pixel division gradation display and gradation display based on pulse voltage change.

FIG. 8 is an explanatory diagram showing three levels in the time division gray scale display of FIG. 7;

FIG. 9 is an explanatory diagram showing spatial dispersion in time division gray scale display.

FIG. 10 is a configuration diagram showing a ferroelectric liquid crystal device according to the first embodiment.

FIG. 11 is a waveform chart showing a driving method of the ferroelectric liquid crystal device.

FIG. 12 is an explanatory diagram showing a time division 256 gray scale display of a conventional method on a plasma display panel.

FIG. 13 is an explanatory diagram showing a problem in a still image of the time division 256 gradation display.

FIG. 14 is an explanatory diagram showing a problem in a moving image of the time division 256 gradation display.

FIG. 15 is an explanatory diagram showing a time division 256 gradation display of the upper bit division method in the plasma display panel.

FIG. 16 is an explanatory diagram showing time division 256 gray scale display of a subfield rearrangement method in a plasma display panel.

17 (a) and (b) show plasma display devices.
Time division 2 of the lowest field addition method in the panel
It is explanatory drawing which shows 56 gradation display.

FIG. 18 is an explanatory diagram showing a time division 256 gray scale display of a conventional method in a ferroelectric liquid crystal device.

[Explanation of symbols]

 6 Ferroelectric liquid crystal L Scan electrode S Data electrode S1 to S3 Sub data electrode

 ──────────────────────────────────────────────────の Continuation of the front page (71) Applicant 390040604 United Kingdom THE SECRETARY OF STATE FOR DEFENSE IN HER BRITANNIC MAJES TY'S GOVERNMENT OF THE THE UNTERED KINGDOM OF GREEN REGISTER MONEY REGISTER MAN Borrow Ivey Road (without address) Defence Evaluation and Research Agency (72) Koji Numa Inventor Sharp Corporation

Claims (9)

[Claims] 1. A display device which performs multi-gradation display by forming one field with a plurality of subfields having different display period time width ratios, wherein a display period corresponding to each subfield period has a time width ratio of: 1 :,...,: 2 ^m :,...,: (2 ^A -B) × 2 ^k :, where m is a variable from 1 to A-1, k is a variable from 0 to n-A-1, n Is the number of subfields, A is an integer of 2 or more, and B
Is a whole number of 1 or more. 2. A display device which performs multi-gradation display by forming one field with a plurality of subfields having different display period time width ratios, wherein a display period corresponding to each subfield period has a time width ratio of: 1: (M ^A -B) × M ^k :, or 1 :,...,: M ^m :,...,: (M ^A −B) × M ^k :,. (Integer) is the number of gray scales that can be displayed in the subfield period corresponding to each bit other than the least significant bit, m is a variable of 1 to A-1, and k is 0 to n-A-
1 variable, n is the number of subfields, A is an integer of 1 or more,
And B is an integer of 1 or more. 3. A plurality of scan electrodes arranged in parallel with each other, a plurality of data electrodes arranged in parallel with each other in a direction perpendicular to the scan electrodes, and arranged between the scan electrodes and the data electrodes; 3. The liquid crystal display according to claim 2, further comprising a liquid crystal layer made of a ferroelectric liquid crystal, wherein each pixel formed in a matrix by the intersection of the scan electrode and the data electrode comprises a plurality of sub-pixels. Display device. 4. A plurality of scanning electrodes arranged in parallel with each other, a plurality of data electrodes arranged in parallel with each other in a direction orthogonal to the scanning electrodes, and arranged between the scanning electrodes and the data electrodes; A liquid crystal layer comprising a ferroelectric liquid crystal, and controlling a pulse voltage applied to the data electrode to change the brightness of each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode. The display device according to claim 2, wherein: 5. A plurality of scan electrodes arranged in parallel with each other, a plurality of data electrodes arranged in parallel with each other in a direction orthogonal to the scan electrodes, and arranged between the scan electrodes and the data electrodes; A liquid crystal layer comprising a ferroelectric liquid crystal, wherein each pixel formed in a matrix by the intersection of the scanning electrode and the data electrode comprises a plurality of sub-pixels, and controls a pulse voltage applied to the data electrode. The display device according to claim 2, wherein the brightness of each pixel is changed by doing so. 6. A display period corresponding to n sub-field periods is represented by SP1,..., SPi,..., SPn (i is an integer from A + 1 to n). And display period SP
1, SP (i + 1) to SPn are the dark first display state, and the next brightness level after the first display state, the display periods SP1 to SPi are bright and the display period SP (i +
1) to SPn are dark second display states, the same brightness level as the second display state, the display period SP (i + 1) is bright, and the display periods SP1 to SP
i, SP (i + 2) to SPn are the third display state which is dark, and the next brightness level after the third display state, display periods SP1 and SP (i + 1) are bright and display period SP
The display device according to any one of claims 1 to 5, wherein 2 to SPi and SP (i + 2) to SPn have a dark fourth display state. 7. When the brightness level of the second or third display state is selected, if the display state one field before of each pixel is equal to or less than the brightness level of the first display state. The second display state is selected as the next display state, and when the brightness is equal to or higher than the brightness level of the fourth display state, the third display state is selected as the next display state. 7. The display device according to 6. 8. The display device according to claim 6, wherein display states of adjacent pixels are made different from each other by using the second display state and the third display state. 9. When the display state of a certain pixel is set to the second or third display state, and the display state of pixels surrounding the pixel is lower than the brightness level of the first display state, The display state of the surrounding pixels is set to a second display state, and the display state of the surrounding pixels is set to a third display state when the brightness level is equal to or higher than the brightness level of the fourth display state. The display device according to claim 6.