JP2000206922A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a reversal of gradation in gradation transition of one level and to perform an excellent gradation display by deciding a temporal division ratio of a field so as to divide further the time width of the high-order field with a specified expression. SOLUTION: When the number of sub-pixels constituting one pixel is defined N pieces, and areal rations of respective sub-pixels are 1:S2:S3:...:SN, and the number of fields is N, and the temporal division rations of the fields are 1:T2:T3:...:TN, a control means performs a multilevel display with the temporal division ratio TA becoming a second field < an A-th field < an N-th field decided in the expression. For instance, in the temporal division ratios of T1:T2:T3=1:4:16, the highest rank T3 is divided equally such as T3=T4=8 (that is, T1:T2:T3:T4=1:4:8:8). Further, simultaneously, respective gradation displays are made controllable independently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a panel in which a plurality of pixels are arranged in a matrix and each pixel is divided into a plurality of sub-pixels.
The present invention relates to a display device using a digital gradation display driving method in which the sub-pixels are turned on by combining an area division driving method and a time division driving method.

[0002]

2. Description of the Related Art In addition to a phase change type liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. Hei 5-107521, a matrix type display device having a memory function is disclosed in Japanese Patent Application Laid-Open No. HEI 3-20715. Liquid crystal display device, JP-A-6-43
No. 829 discloses a plasma display device and the like.

In general, a matrix type display device has a feature that a plurality of scanning electrodes cannot be selected at the same time because an independent selection period is required for each scanning electrode in common.

[0004] As the gray scale display method of the display device as described above, there are typically (1) a time division driving method, (2) a pixel division driving method, (3) a time division driving method and a pixel division driving method. Are combined. Hereinafter, each driving method will be described.

In the driving method of (1), 2 ^N levels can be realized by dividing one frame into a plurality of fields evenly and performing display independently in each field based on binary data ( See JP-A-5-88646. Also, one frame is 1: 2: 4:...: 2 ^N-1 (N
There is also a driving method in which the field is divided into a plurality of fields at a time interval of (a natural number) (see JP-A-6-18854). In such a time-division driving method, the same scan electrode is independently scanned N times in one frame. Therefore, each field for selecting one scan electrode is reduced to 1 / N of one frame.
The selection period for selecting one scanning period is also shortened. Accordingly, there is an inconvenience that the frequency of data becomes N times.

As another time division driving method, among a plurality of subfields, the uppermost subfield having the longest and almost equal light emission time width is four, and the uppermost subfield is two or two. There is a driving method of controlling light emission of a subfield in accordance with an image signal with a regularity of not emitting light continuously when three lights are emitted (see JP-A-9-107512). In this driving method,
For example, if the number of subfields is 10, the ratio of the light emission time width of each subfield is 1: 2: 4: 8: 16: 3.
2: 48: 48: 48: 48. This gives 1
Light emission in the field can be dispersed, and noise (moving image false contour) peculiar to digital gradation can be reduced.

In the driving method (2), one pixel is 1: 2: 4:
..: By dividing into sub-pixels having an area ratio of 2 ^{N -1} and independently driving each sub-pixel based on binary data, a 2 ^N level can be realized. In order to apply this pixel division driving method, one pixel must be divided into a plurality of pixels in a display cell, which has a disadvantage that the structure of the display cell becomes complicated. For example, when one pixel is divided at a division ratio of 1: 2: 4, it is necessary to provide an electrode corresponding to each sub-pixel in order to not only divide the pixel but also drive the divided sub-pixels independently. There is. However, it is very difficult to manufacture a liquid crystal cell capable of performing high-definition display using only such an electrode structure because the electrode structure becomes complicated.

The driving method (3) is disclosed in Japanese Patent Laid-Open No. 7-15201.
No. 7, for example. Hereinafter, such a driving method will be described in detail.

In the driving method described here, one frame is divided into three frames.
Time division for dividing into two and pixel division for dividing one pixel into two are used. FIG. 3 shows a gradation display pattern when 64 levels are displayed by this driving method. Hereinafter, each field in the time division is represented by T _n (n = 1,
2, 3...), And each sub-pixel in the pixel division is S _m (m
= 1, 2, 3 ...).

In the time division, 1: 4: 16 = T ₁ :
One frame is divided at a ratio of T ₂ : T ₃ .
One pixel is divided at a ratio of 1: 2 = S ₁ : S ₂ . FIG.
Shows three pixels for each level, but these represent the display pattern of the same pixel in each of the three divided periods. Therefore, the three pixels are 1:
Display is performed at a luminance of 4:16. One pixel is 1: 2
Are divided into two sub-pixels, and each sub-pixel is simultaneously scanned and driven independently.

[0011] For example, when all the pixels are non state levels of gradation "0" to lighting, if only S ₁ at T ₁ is turned on is level "1", S ₂ in Subsequently T ₁ only Is the level “2”. Further, the level “3” indicates that both S ₁ and S _{2 at} T ₁ are turned on. In T _2, since the display at four times the luminance of T _1, the level "4", by only S ₁ is turned on, display is possible at higher level "3" brightness.

As described above, the time division ratio is set to T ₁ : T ₂ : T
_{When 3} = 1: 4: 16, the number of gradations (the number of gradation levels) does not overlap each other depending on the display pattern. Therefore, a maximum of 64 levels (2 ^{2 3} = 2 ⁶ = 64 levels) can be displayed by 2-bit pixel division and 3-bit time division. Such a time division ratio T _A is calculated by the following equation.

[0013]

(Equation 3)

However, the above equation is a general equation, and the time division number is N bits, the pixel division number is M bits, and 2 ≦ A ≦ N.

[0015]

However, when the driving method (3) described above is used, that is, when displaying multiple gradations using time division and area division as shown in FIG. The divisional area error has a large effect on the luminance error in one-level gradation transition.

For example, consider the relationship between the gradation display pattern shown in FIG. 3 and the luminance expected for the gradation display pattern. In this case, as shown in FIG. 9 or FIG.
When the horizontal axis indicates the number of levels (levels) of the gray scale display pattern and the vertical axis indicates the above relationship using a gray scale linearity graph indicating the luminance expected for the gray scale display pattern, the area is as follows. The division ratio and the time division ratio are ideally 1: 2, 1: 4:
If it is divided into 16, it should be a straight line from gradation 0 to gradation 63.

However, the ideal area ratio of the divided sub-pixels is S ₁ : S ₂ = 1: 2, but in actuality, for example, the area is such that S ₁ : S ₂ = 1: 2 ± d. An error d occurs. In this case, as shown in FIG. 9 or FIG.
The inversion of the gradation is observed at 6, 42, and 48 levels. The graph of FIG. 9 shows the area error d = ± 0.13.
, And the graph of FIG. 10 shows the gradation linearity when the area error d = ± 0.3.

The cause of the inversion of the gradation will be described.
For example, when attention is paid to the gradation transition from the 31st level to the 32nd level, the relationship between the area error d and the gradation error D accompanying the one-level gradation transition will be considered. First, FIG.
In a horizontally long gradation display pattern as shown in (a) and (b), level display of 31 levels and 32 levels is expressed. The gradation display patterns of FIGS. 11 (a) and 11 (b) are for clearly expressing the length of time in the gradation display pattern as shown in FIG.

In FIGS. 11A and 11B, the horizontal axis represents the length of time, and is divided into T ₁ : T ₂ : T ₃ = 1: 4: 16. In the vertical direction, S ₁ :
It is divided into S ₂ = 1: 2. The divided rectangular or square area represents a gradation display element. Also,
The number described therein is obtained by multiplying any of S ₁ and S ₂ in the gradation display element and any of T _{1 to} T ₃ and indicates the level of luminance in the gradation display element. . The shaded gray scale display elements indicate the lighting state, while the shaded gray scale display elements indicate the non-lighted state.

For example, the 31st level is the state shown in FIG. 11A, and its luminance is the sum of the areas of the respective gray-scale display elements which are blank. That is, the luminance G ₃₁ 31 level is expressed as follows.

G ₃₁ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ = {(1 × 1) + (2 × 1)} + {(1 × 4) + (2 × 4)} + ｛(1 × 16) + (2 × 0) } = 1 + 2 + 4 + 8 + 16 + 0 = 31 [level] Meanwhile, 32 level is in the state shown in FIG. 11 (b), the luminance G ₃₂ is expressed as follows.

G ₃₂ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ = {(1 × 0) + (2 × 0)} + {(1 × 0) + (2 × 0)} + ｛(1 × 0) + (2 × 16) ｝ = 0 + 0 + 0 + 0 + 0 + 32 = 32 [level] As described above, when the area division ratio is ideally divided at S ₁ : S ₂ = 1: 2, there is no problem and the inversion of the gradation does not occur.

On the other hand, as shown in FIGS. 12A and 12B, consider a case where an area error + d occurs in the area division ratio. Assuming that the area error + d occurs in S ₂ , the area division ratio is S ₁ : S ₂ = 1: 2 + d.
In this case, 31 levels (see FIG. 12A) and 32 levels
The luminances G ₃₁ and G _{32 at the} level (see FIG. 12B) are expressed as follows.

G ₃₁ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ = [(1 × 1) + {(2 + d) × 1}] + [(1 × 4) + {(2 + d) × 4}] + [(1 × 16) + ｛ (2 + d) × 0}] = 1+ (2 + d) +4+ (8 + 4d) + 16 + 0 = 31 + 5d [level] G ₃₂ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + ｛(S ₁ · T ₂ ) + (S ₂ · T ₂ )｝ + {(S ₁ · T ₃ ) + (S ₂ · T ₃ )} = {(1 × 0) + {(2 + d) × 0}] + ｛(1 × 0 ) + {(2 + d) × 0}] + {(1 × 0) + {(2 + d) × 16}] = 0 + 0 + 0 + 0 + 0 + (32 + 16d) = 32 + 16
a luminance difference d [level] Therefore G ₃₁ and G ₃₂ are as follows.

G ₃₂ −G ₃₁ = (32 + 16d) − (31 + 5d) = 1 + 11d [level] In other words, an 11d grayscale error D occurs at the one-level grayscale transition from the 31st level to the 32nd level. Therefore, if d = 0.3, for example, the gradation error D will be 11d = 11 × 0.3 = 3.3 levels. As a result, the reversal of the gradation as seen near the 32 levels shown in FIGS. 9 and 10 is observed.

The gradation error D in the one-level gradation transition depends on the area error d in the pixel division and can be expressed by the following equation. Here, α is an arbitrary coefficient.

D = α · d [level]... As can be seen from this equation, the area error d when the pixel is divided and the coefficient α are greatly affected.

The coefficient α for each one-level gradation transition corresponding to the 64-level gradation display pattern shown in FIG.
Is shown in Table 1.

[0029]

[Table 1]

In Table 1, the leftmost column indicates the gradation level, and the rightmost column indicates the actual value of the coefficient α. In addition, S ₁ in each column of T _{1 to} T ₃
The sub-column of S ₂ is the same as that shown in FIGS.
Shows the lighting state of the gradation display element shown in FIG. 1, where 0 is a non-lighting state and 1 is a lighting state.

As can be seen from Table 1, the coefficient α is approximately 0
.Alpha. = 11 in the gradation transition from the 31st level to the 32nd level, and
Α = −5 in the gradation transition to the level and the gradation transition from the 47th level to the 48th level. That is, since the gradation error D increases in the three one-level gradation transitions, the gradation is inverted as shown in FIGS.

The value of the coefficient α becomes larger as the time division ratio increases. For example, the pixel area division ratio S ₁ : S ₂ = 1: 2 is the same as the above-mentioned condition, and the time division ratio of one frame is set as T ₁ : T ₂ : T ₃ : T ₄ = 1:
Assuming 4:16:64, as shown in Table 2, a maximum of 25
Six-level gradation display is possible.

[0033]

[Table 2]

In Table 2, it is shown that the basic transition pattern 3 for every 16 levels shown in FIG. 14 (c) enters the portion (3) shown in the columns of T ₁ and T ₂ . . In addition, "0 ... 0" in T ₃ and T ₄ each column
Or, “1... 1” indicates that all “0” or “1” is entered.

In the case of the 256-level gradation display pattern as shown in Table 2, as can be seen from the column of the coefficient α, a large numerical value of the coefficient α = 11 or α = −21 is observed. In the gradation transition to, a very large numerical value of α = 43 is seen. As a result, for example, if the area error d = 0.3, the gradation error D = 43 × 0.3 = 12.9 levels, and an extremely large gradation error D occurs at the time of one-level gradation transition. Become.

Further, when looking at the relationship between the luminance and the gradation in the 256-level gradation display pattern, it can be seen that the luminance is largely reversed as shown in FIG. Therefore, good gradation expression cannot be performed.

As described above, the reversal of the gradation which occurs in the relationship between the luminance and the gradation is greatly affected by the area error d and its coefficient α. Actually, the area error d always occurs in producing a panel. In particular, as the pixel pitch is reduced in pursuit of a high-definition image and the production process becomes more complicated, The area error d tends to increase. Furthermore, when the upper and lower panels are bonded, different errors may occur at each location in the panel due to misalignment of the bonding and the like.

Therefore, it is practical to eliminate the gradation error D by using a gradation display pattern that reduces the coefficient α instead of eliminating the area error d. Therefore, there is a need for a multi-gradation display technique that uses a gradation display pattern that makes the coefficient α as small as possible so that there is no inversion of the gradation even if a certain area error d occurs.

The higher time division ratio disclosed in Japanese Patent Application Laid-Open No. 9-107512 is divided into two,
In addition, if a technique of independent control is used, it is possible to avoid inversion of the gradation even if an area error d occurs in the division of the pixel. The technique disclosed in the above publication is for achieving an object different from that of the present invention, but as a result, even if an area error d occurs, the inversion of the gradation can be avoided. However, the technology disclosed in the above publication is a technology corresponding only to the time division driving method, and cannot be applied to a gradation display technology combining the area division driving method and the time division driving method as in the present invention. .

The present invention has been made in view of the above problems, and in a display device using a gradation driving method in which different methods are combined, an appropriate selection period is secured according to the gradation driving method. It is another object of the present invention to provide a display device which realizes a multi-gradation display and realizes a multi-gradation display in which the inversion of the gradation due to the cumulative response is eliminated.

[0041]

According to a first aspect of the present invention, there is provided a display device, in which a plurality of pixels are arranged in a matrix and one pixel is divided into a plurality of sub-pixels. And a control means for controlling one sub-pixel to be turned on for a predetermined time based on one of a plurality of fields obtained by dividing a time width in one frame of an image signal. And the control means further comprises:
One sub-pixel that is turned on in a time width of one field is used as one gradation display element, so that one pixel is configured in a display device that performs multi-gradation display by combining a plurality of these gradation display elements. , The area ratio of each sub-pixel is 1: S ₂ : S ₃ :...: S _N , the number of the fields is N, and the time division ratio of the field is 1 : T ₂ : T ₃ :...: T _N , the above-mentioned control means uses the following equation:

[0042]

(Equation 4)

The multi-gradation display is performed by the time division ratio T _A of the A-th field, which is the second to N-th field determined in the above, and each gradation display element can be controlled independently. Features.

Conventionally, when the time width of one frame is divided into a plurality of fields, if the time division ratio of the upper field is too large, a gradation error at the time of one-level gradation transition of the gradation increases. Was. This is because the luminance corresponding to the area error is amplified by the field due to the area error generated in the sub-pixel.

On the other hand, according to the configuration of the first aspect, the time division ratio of the field is determined so as to further divide the time width of the upper field by the above equation, so that one-level gradation transition is performed. Can be reduced. Therefore, it is possible to prevent the reversal of the gradation at the one-level gradation transition, and to realize a more excellent gradation display.

According to a second aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first aspect, the control means further comprises:

[0047]

(Equation 5)

[0048] determined at, it is characterized by performing multi-gradation display with the time division ratio T _B field to be a second or more A-1 th or less.

According to the second aspect of the present invention, the time width of the field is not limited unless the magnitude of the gradation error has a significant effect on the multi-gradation display. Can be suppressed, and a significant reduction in the number of gradations that can be expressed (the number of gradation levels) can be avoided.

According to a third aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first or second aspect, the control means includes a combination of a plurality of gradation display elements. The time division ratio of the field is determined so that when the displayed gray level transitions to the next level, the gray level error caused by the luminance difference between the levels is less than one level. Features.

According to the configuration of the third aspect, the gradation error at one-level gradation transition is less than one level, so that the effect obtained in the display device of the first or second aspect is further enhanced. Can be improved.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first or second aspect, the control means further comprises a control unit for setting the field from Ath to Nth. Are all set to the same time width.

According to the configuration of the fourth aspect, since the time widths of the A-th to N-th fields are all the same, the number of gradations that can be expressed is increased while suppressing an increase in the gradation error. It becomes possible.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first, second or fourth aspect, the control means further comprises one gradation display element. When transitioning the gradation from the level in the lighting state to the level in which the gradation display element is in the non-lighting state, if the field of the gradation display element is nth (1 ≦ n <N),
In the (n + 1) th or more fields, the gradation display element including the same sub-pixel as the gradation display element is changed from the non-lighting state to the lighting state.

According to the fifth aspect of the present invention, the luminance error of the gradation display element is shifted by one level so as to be moved in parallel to another gradation display element which is newly turned on. A gradation transition is performed. Therefore, it is possible to more effectively suppress the increase in the gradation error at the one-level gradation transition.

According to a sixth aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the fourth or fifth aspect, the number of the sub-pixels constituting one pixel is two. The area ratio of each sub-pixel is 1: 2, the number of the fields is 4, and the time division ratio of the fields is 1: 4: 8: 8.

According to the configuration of the sixth aspect, the effect obtained by the configuration of the fourth or fifth aspect can be further improved.

[0058]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The following will describe one embodiment of the present invention with reference to FIG. As shown in FIG. 2A, the display device according to the present invention includes a plurality of scanning electrodes 2 and a plurality of signal electrodes 3 which intersect each other, and is arranged in a matrix at each of the intersections to form an image signal. The panel 5 includes a plurality of pixels 4 that are turned on within a time width of one frame.

Each of the pixels 4 is composed of a plurality of sub-pixels 6 as shown in FIG. In other words, one pixel 4 is divided into a plurality of sub-pixels 6. Note that FIG.
In (b), there are two sub-pixels 6.

The pixel 4 is turned on within the time width of one frame of the image signal. At this time, each of the sub-pixels 6 is divided into a plurality of fields formed by dividing the time width of the one frame. The control means 7 as shown in FIG. 2A controls the lighting state for a predetermined time according to one of them.

Further, the control means 7 performs multi-gradation display by combining a plurality of the gradation display elements with the lighting state of one sub-pixel 6 in the time width of one field as one gradation display element. . That is, since a plurality of gradation levels can be displayed by a combination of gradation display elements, multi-gradation display can be realized.

Here, the control by the control means 7, that is, the method of driving gray scale display for multi-gray scale display in the display device according to the present invention, is a method of dividing one pixel 4 into M pixels ( The number of divisions (Mbit) and the time division for dividing one frame into N (the number of divisions Nbit) are used. Hereinafter, each sub-pixel 6 and its area ratio in the pixel division are represented by S
_m (1 ≦ m ≦ M, m is an integer), and each field in the time division and its time division ratio are represented by T _n (1 ≦ n ≦
N and n are integers). Also, S ₁ = 1 and T ₁ = 1.

For example, one pixel 4 is represented by S ₁ and S ₂
(M = 2), and the pixel division ratio (sub-pixel area ratio) is set to S ₁ : S ₂ = 1: 2. at the same time,
If one frame is divided into three (N = 3) and the time division ratio is divided into T ₁ : T ₂ : T ₃ = 1: 4: 16, multi-gradation display is possible.

That is, in each of T _{1 to} T ₃ ,
The luminance when S ₁ and S ₂ are all non-lighting state 0
And then, 1 each level increases the brightness, the luminance when ultimately all lighting state S ₁ and S ₂ and up. Therefore, under the above conditions, the brightness when all are in the non-lighting state is set to the 0 level, and S ₁ , S ₂ , or S ₁ and S ₂ are lit in each of T _{1 to} T _3. The gradation transitions for each level, and display of up to 64 levels is possible.

In the above-described multi-tone display, the m-th sub-pixel that is lit in the n-th field is used as a tone display element. Later, to express the gradation display element and S _m · T _n. For example, under the condition of M = 2 and N = 3, the gradation display elements are S ₁ · T ₁ , S ₂ · T ₁ , S ₁ · T ₂ , S
There are six, ₂ · T ₁ , S ₁ · T ₃ , and S ₂ · T ₃ .
The gradation display elements can be independently controlled. That is, the sub-pixel 6 in the panel 5 is
Are controlled to be turned on independently of each other.

Here, in the above-mentioned 64-level multi-gradation display, an arbitrary gradation level is changed to a K level (0 ≦ K <63, K
Is an integer), the gradation error D of the luminance generated when the gradation transition of one level from the K level to the K + 1 level is performed.
Is defined by the following equation: Here, the luminance at the K level is G _K [level], and the luminance at the K + 1 level is G
_{K + 1} [level].

D = | (G _{K + 1} −G _K ) −1 level |... The gradation error D depends on an area error generated in the pixel division. That is, the pixel division ratio is ideally S
_1: Even 2, in _{fact, S 1:: S 2 =} 1 S 2 =
1: 2 + d, an area error d occurs. Therefore, the tone error D is represented by the following equation by the area error d.
Here, α is an arbitrary coefficient.

D = α · d [level]... If such an area error d occurs, inversion of luminance occurs in multi-tone display combining pixel division and time division. Therefore, in order to realize the gradation transition without the inversion of the luminance, according to the conventional technique, the condition of the time division is that one frame is divided into two (N = 2), and the time division ratio is T _1. : T ₂ = 1: 4 only. Therefore, only 16 levels of expressible gradations are obtained,
Sufficient multi-gradation display cannot be realized.

Therefore, in the present invention, the driving method is controlled so as to suppress the coefficient α at the time of one-level gradation transition in multi-gradation display, in order to avoid the area error d in the pixel division. Specifically, it is preferable that the driving method is such that the coefficient α ≦ 1 / d from the above equation.

[0070] In the conventional driving method, as larger causes the coefficient alpha, the point time division ratio T _A of the A-th field is large and the like. When the time division ratio T _A is too large, when one level gradation transition, when the lighting T _A from the gradation display element that does not include the gradation display element containing a T _A state changes, a very large factor α May occur.

For example, in the sub-pixels S ₁ and S ₂ , S ₂ has an area error d and the gradation display element S ₁ · T _A
S but the K level is lit, S ₁ · T _A is off
₂ · T _A is the gradation transition to K + 1 level to be turned. When this time _{T 1 = 1, T A =} 16, the error of the luminance of S ₂ · T _A based on the area error d having the S ₂ is compared with the gradation display element S ₁ · T ₁ containing T ₁ 16 times. This causes the coefficient α to increase.

Therefore, in the present invention, the control means 7 executes control for further dividing the highest time division ratio.
For example, in the above-described time division ratio of T ₁ : T ₂ : T ₃ = 1: 4: 16, the uppermost T ₃ is further replaced by T ₃ = T ₄ =
8 (ie, T ₁ : T ₂ : T ₃ : T ₄ = 1: 4: 8:
8) or T ₃ = T ₄ = T ₅ = 6 (that is, T ₁ :
T ₂ : T ₃ : T ₄ : T ₅ = 1: 4: 6: 6: 6) or equally divided such as T ₃ = 6 and T ₄ = 10. By further dividing the uppermost time division ratio, it is possible to further reduce the luminance error in the gradation display element based on the area error d. As a result, an increase in the gradation error D can be suppressed.

In the conventional driving method, the A-th (2 ≦ A ≦ n)
The time-division ratio T _A of the field is determined by the following equation.

[0074]

(Equation 6)

[0075] In the display device according to the present invention, the right-hand side of equation further 1/2 or less, and by enabling control each gradation display element independently, the time width of the field T _A time division ratio too large Split. That is, the control means 7 controls the driving of the panel 5 by limiting the time width of the field T _A where the time division ratio is too large, and performs multi-gradation display. Such control is hereinafter referred to as first means. In this case, the time division ratio T _A of the A-th field is determined by the following equation.

[0076]

(Equation 7)

As a result, the coefficient α of the gradation error D at the one-level gradation transition is reduced, the occurrence of the inversion of the gradation at the one-level gradation transition is prevented, and more excellent gradation display is achieved. Realize.

For example, as an example of multi-tone display to which the first means is applied, one frame is divided into four (N = 4).
From the above equation, the time division ratio can be expressed as T ₁ : T ₂ : T ₃ : T ₄ =
1: 2: 4: 8. By this, time division is 4bit
Thus, gradation display of a maximum of 46 levels can be realized. Tables 3 and 4 show the gradation display patterns at this time.

[0079]

[Table 3]

[0080]

[Table 4]

As can be seen from Tables 3 and 4, this 46
In the gradation display of the level, the coefficient α is almost 0 or ± 1, and α3 is 7 in the gradation transition from the 13th level to the 14th level, and α = 7 in the gradation transition from the 29th level to the 30th level. It can only be seen. That is, by using the first means, the maximum value of the coefficient α can be suppressed to 7.

Further, when the first means is used or when the second means described in detail in the second embodiment is used, the control means 7 always sets the gradation error D defined by the above equation to 1 determine the time division ratio of the field T _n to be less than the level, and it is preferable to control each gradation display element independently.

That is, when the gradation level displayed by the combination of the plurality of gradation display elements transitions to the next level, the gradation error D caused by the difference in the luminance of each level is reduced by one.
As the level below, it is preferable to determine the time-division ratio of the field T _n. This control is hereinafter referred to as a third
Means. Thereby, the effects of the first means and the second means can be further improved.

For example, the coefficient α in the equation is set to be smaller than the reciprocal (1 / d) of the area error d. Specifically, if the surface error d = 0.3, α <1 / 0.3, that is, α <3. As a result, the gradation error D is always 1
Since the level is lower than the level, the reversal of the gray scale does not occur, and good gray scale display can be performed.

As described above, the maximum value of the coefficient α can be suppressed by applying the first means, preferably the third means. As a result, it is possible to avoid an increase in the gradation error D and realize a more excellent multi-gradation display.

[Second Embodiment] The following will describe another embodiment of the present invention. Note that the configuration and control conditions of the display device according to the present embodiment are the same as those in the first embodiment unless otherwise specified, and thus detailed description thereof will be omitted.

In the first embodiment described above, the maximum value of the coefficient α can be suppressed to 7, but when the time division ratio of all the fields T _{2 to} T _N except T ₁ = 1 is determined by the equation, the actual The number of gray scales that can be expressed in a single pixel may be smaller than the number of gray scales that can be originally expressed based on the number of bits for time division and the number of bits for pixel division.

More specifically, since the number of pixel divisions is 2 bits and the number of time division ratios is 4 bits, under the conditions of the first embodiment, a maximum of 2 ^{2 4} = 2 ⁸ = 256 levels of gray scale display Becomes possible. However, since the time width of the fields T _{2 to} T _N is limited by the above equation, in practice, 4
Only six levels can be expressed, and the number of gray levels that can be expressed is small.

Therefore, in the display device according to the present invention, 1
When the gradation error D in the gradation transition of the level is small, the control unit 7 controls the driving of the panel 5 so that the first unit is not applied. Specifically, the control unit 7, the field T _B from the second to be lower than the field T _A with a limited duration by the formula in the first embodiment to the A-1 th (2 ≦ B ≦ A-1 ) Is determined by the following equation, which is the same equation as the above equation. Such control is hereinafter referred to as a second means.

[0090]

(Equation 8)

In other words, in order to increase the number of gradations that can be expressed as much as possible, the fields T _{2 to} T _{A-1 which} are lower than the A-th among the time division ratios T _{1 to} T _n are the same as those in the conventional equation. Is used to determine the time division ratio.
The time division ratio is determined using the equation for the fields T _{A to} T _N.

For example, the pixel division ratio S ₁ : S ₂ = 1: 2+
In the case of d, a case is considered where the gradation transitions from 7 levels to 8 levels in the conventional gradation display pattern (see Table 1). At this time, the seven-level luminance G ₇ and the eight-level luminance G ₈ are as follows.

G ₇ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ = [(1 × 1) + {(2 + d) × 1}] + {(1 × 4) + {(2 + d) × 0}] + {(1 × 0) + ｛ (2 + d) × 0}] = 1+ (2 + d) + 4 + 0 + 0 + 0 = 7 + d [level] G ₈ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + ｛(S ₁ · T ₂ ) + (S ₂ · T ₂ )｝ + {(S ₁ · T ₃ ) + (S ₂ · T ₃ )} = [(1 × 0) + {(2 + d) × 0}] + {(1 × 0) + ｛( the difference in brightness between the 2 + d) × 4}] + {(1 × 0) + {(2 + d) × 0} ] = 8 + 4d [level] therefore G ₇ and G ₈ are as follows.

G ₈ −G ₇ = 8 + 4d− (7 + d) = 1 + 3d [level] Therefore, since the gradation error D = 3d level, the coefficient α = 3 (see Table 1). That is, in the gradation transition from the 7th level to the 8th level, the gradation error D can be kept sufficiently small without using the first means.

Therefore, it is determined that the gradation error D generated in the gradation transition between the levels composed of the gradation display elements including only T ₁ and T ₂ is sufficiently small, and the gradation display element including T ₃ is included. The above-described first means is used only in gradation transition between levels. This is the second means in the present embodiment.

Specifically, in the first embodiment,
As in the conventional case, one frame is divided into three (N = 3), and the time division ratio is set to T ₁ : T ₂ :
T ₃ = 1: 4: 8. In other words, the conventional T
_{From 1 to} T ₃ , the time division ratio is determined using a conventional equation for the second to the third, and the time division ratio is determined using the equation from the third. This allows time division of 3
Up to 40 levels of gray scale display can be realized with bits. Table 5 shows the gradation display patterns at this time.

[0097]

[Table 5]

As can be seen from Table 5, in this 40-level gradation display, the coefficient α is almost 0 or ± 1, and the coefficient α is 0 in the gradation transition from the 7th level to the 8th level.
= 3, only α = 7 is found in the gradation transition from the 23rd level to the 24th level. That is, similarly to the first means, the maximum value of the coefficient α can be suppressed to 7.

In the first means, a maximum of 256
Although 46-level gray scale display is realized by 4-bit time division capable of level gray scale display, the second means in the present embodiment employs 3 levels capable of displaying a maximum of 64 levels of gray scale.
40-level gray scale display is possible by bit time division. Therefore, by using the second means, it is possible to avoid a significant reduction in the number of gradations that can be expressed.

[Embodiment 3] Another embodiment of the present invention will be described below with reference to FIGS. 1, 3 to 6, 9, 10, and 13. In addition,
The configuration of the display device and each control condition in the present embodiment are as follows:
Unless otherwise specified, this is the same as Embodiments 1 and 2, and a detailed description thereof will be omitted.

In this embodiment, the second embodiment described above is used.
In addition to controlling the further, as with all time equal width fields T _A through T _N which is a A-th or N-th or less, the control unit 7 controls the driving of the panel 5. Such control is hereinafter referred to as fourth means.

For example, using the first and second means, preferably the third means, the A-th and higher fields T _E (A ≦ E ≦ N) so that the coefficient α is kept below a certain value.
If the restricted time range, the number of gradations that can be time width limit (time-division ratio determination) simultaneously with representation of the T _E is also determined. However, depending on the situation, the determined number of gradations may not reach the desired number of gradations. therefore,
In such a case, the field _{TE + 1} must be newly added.

[0103] However, the maximum value of the coefficient α in order to time-dependent width of principle above T _E, the value of the coefficient α The addition of T _{E + 1} having a longer width than the T _E is greater As a result, the gradation error D also increases. Therefore, it is desirable that the time width of T _{E + 1 be} equal to or less than T _E. Further, it is desirable that the time width of _{TE + 1} is as long as possible to secure the number of gradations. For the above reasons, it is preferable that the same length and the time width and T _{E + 1} of the time width of T _E.

If the number of gradations is small even in the case of adding T _{E + 1} , T _{E + 2} is further added. Duration the T _{E + 2} is also the same length as the T _E. Thus field T _{E + k} having the time width of the same length as the T _E; With the fourth means for adding (k 1 or more integer), to the area error d, the reversal of the gradation It is possible to secure the number of gradations most efficiently with respect to the number of bits of the time division ratio with no gradation transition.

The method of determining the time division ratio using the fourth means will be described below with reference to specific examples, including the first to third means.

As in the first embodiment, one pixel 4
Is divided into _two , S ₁ and S ₂ (M = 2), and the pixel division ratio (area ratio of sub-pixels) is S ₁ : S ₂ = 1:
Let it be 2. Here, for example, one frame is divided into three (N = 3), and the time division ratio is set to T ₁ : T ₂ : T ₃
Assuming that = 1: 4: 16, the gradation display pattern in this case enables 64-level gradation display as shown in FIG.

Here, at a pixel division ratio of S ₁ : S ₂ = 1: ₂ , the area error d = ± 0.13 (〜1 / 7) in S ₂
Is assumed to have occurred. In this case, the maximum value of the coefficient α is set to 7 or less (d = the reciprocal of 1/7) in order to more effectively avoid the inversion of the gray scale generated at the time of the one-level gray scale transition. It is highly preferable to apply the third means.

Conventionally, under the above-described conditions of pixel division and time division, as shown in Table 1, the coefficient α of the area error d is obtained by one-level gradation transition from the 31st level to the 32nd level. Becomes as large as α = 11.

As shown in the gray scale linearity graph of FIG. 9, the gray scale is inverted at the gray level transition from the 31st level to the 32nd level. The graph of FIG. 9 shows that the area error d = ± 0.1 in the gradation display pattern of Table 1.
3 shows the gradation linearity in the case of No. 3.

As shown in the first embodiment, in the conventional technique capable of eliminating the gradation error D, the time division ratio is up to T ₁ : T ₂ = 1: 4. However, in this case, there are only 16 levels of gray levels that can be expressed (the number of gray levels). Therefore, one frame is divided into four (N = 4) by using the first means and the second means.
From the above equation, the time division ratio is calculated as T ₁ : T
₂ : T ₃ : T ₄ = 1: 4: 8: 8.

That is, by setting the field T _A-1 not determined by the above equation to T ₂ (A = 3), the third to N-th fields T _E (A ≦ E ≦ N) are all set to the same value. I have. As a result, a maximum of 64 levels of gray scale display can be realized while the time division is 4 bits and the maximum value of the coefficient α is kept at 7. Table 6 shows the gradation display pattern at this time.
And 7.

[0112]

[Table 6]

[0113]

[Table 7]

As can be seen from Tables 6 and 7, this 64
In the gradation display of the level, the coefficient α is almost 0 or ± 1, and in the gradation transition from the 7th level to the 8th level, α = 3, the gradation transition from the 23rd level to the 24th level, and 47 Only α = 7 is found in the gradation transition from the level to the 48th level.

Further, as shown in the gradation linearity graph of FIG. 4, there is almost no reversal of gradation as compared with FIG. It can be seen that linearity is ensured. In this way, if the fourth means is used, with the maximum value of the coefficient α suppressed,
It is possible to increase the number of gradations that can be expressed.

The graph of FIG. 4 shows the gradation linearity when the area error d = ± 0.13 in the gradation display patterns of Tables 6 and 7, and the horizontal axis indicates the gradation display pattern. The vertical axis represents the luminance expected for the gradation display pattern.

FIG. 1A shows the application of the fourth means.
-It will be described in more detail based on (b).

As shown in FIG. 1A, the 23 levels are S ₁ · T ₁ , S ₂ · T ₁ , S ₁ · T ₂ , S ₂ ·
The gradation display elements of T ₂ and S ₁ · T ₃ are in the lighting state. Luminance G ₂₃ at this time is as follows.

G ₂₃ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ + {(S ₁ · T ₄ ) + (S ₂ · T ₄ )} = [(1 × 1) + {(2 + d) × 1}] + [(1 × 4) + {(2 + d) × 4}] + [(1 × 8) + {(2 + d) × 0}] + [(1 × 0) + {(2 + d) × 0}] = 1+ (2 + d) +4+ (8 + 4d) + 8 + 0 + 0 + 0 = 23 + 5d [level] Here, when the gradation transitions to the 24th level, as shown in FIG. 1B, S ₁ · T ₁ , S ₂ · T ₁ , S ₁ · T ₂ and S ₁ · T ₃ Is turned off, and S ₂ · T ₃ is turned on instead. That is, S ₂ · T ₂ and S ₂ · T ₃ are turned on. Luminance G ₂₄ at this time is as follows.

G ₂₄ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ + {(S ₁ · T ₄ ) + (S ₂ · T ₄ )} = [(1 × 0) + {(2 + d) × 0}] + [(1 × 0) + {(2 + d) × 4}] + [(1 × 0) + {(2 + d) × 8}] + [(1 × 0) + {(2 + d) × 0}] = 0 + 0 + 0 + (8 + 4d) +0+ (16 + 8d) the difference in luminance between + 0 + 0 = 24 + 12d [level] therefore G ₂₃ and G ₂₄ is as follows.

G ₂₄ −G ₂₃ = 24 + 12d− (23 + 5d) = 1 + 7d [Level] That is, since the gradation error D = 7d level, the coefficient α
Will be reduced to 7.

In particular, under the condition that the pixel division ratio is S ₁ : S ₂ = 1: 2, the above-mentioned time division ratio is set to T ₁ : T ₂ : T
₃ : T ₄ = 1: 4: 8: 8, that is, when one frame is time-divided, the field T
₂ = 4, and fields T _{3 to} T _N exceeding T ₂
Is limited to 8 in all cases, it is possible to realize better multi-tone expression.

In the present embodiment, since the third means is used, in the gradation display patterns of Tables 6 and 7, when the area error d = ± 0.13 (（1/7), The maximum value of the coefficient α is set to 7 or less. Therefore, in the graph shown in FIG. 4, the gradation linearity can be substantially secured.

On the other hand, for example, the area error d = ±
In the case of 0.3, if the third means is applied, the coefficient α
Must be less than or equal to about 3. However, in Tables 6 and 7 above, where the maximum value of the coefficient α is 7,
In the gray scale display pattern of FIG. 5, even if the area error d = ± 0.3, as shown in the graph of FIG. 5, although the gray scale is partially reversed, the gray scale linearity is considerably improved. ing.

More specifically, in the conventional gradation display pattern as shown in FIG. 10 (Table 1 of the first embodiment), the gradation linearity when the area error d = ± 0.3 is shown. Compared to the graph of FIG. 5 and the conventional graph of FIG. 10, even when the third means is not used,
The improvement in gradation linearity is obvious.

FIG. 6 shows a graph of gradation linearity in the case where the fourth means is applied without applying the third means.
Although this graph is not shown in the table, S ₁ : S ₂ = 1:
2. By setting A = 4 under the condition of an area error d = ± 0.3, the fourth to Nth fields T _E (A ≦ E ≦ N) in the time division ratio are all equal. The time division ratio at this time is T ₁ : T ₂ : T ₃ : T ₄ :
T ₅ = 1: 4: 16: 32: 32. As a result, the inversion of the gradation cannot be completely eliminated, but the gradation linearity can be improved.

On the other hand, in the conventional gradation linearity graph shown in FIG. 13, the gradation linearity is clearly inferior when compared with the graph of FIG.

Therefore, if it is not necessary to completely eliminate the reversal of the gradation, a good multi-gradation display can be achieved without necessarily using the third means.

[Embodiment 4] Another embodiment of the present invention will be described below with reference to FIGS. 7, 8 and 14. Note that the configuration and control conditions of the display device according to the present embodiment are the same as those in Embodiments 1 to 3 unless otherwise specified, and thus detailed description thereof is omitted.

[0130] In the first to third embodiments described above, by avoiding the point time division ratio of the A-th field T _A is larger in the conventional driving method, has been to reduce the value of the coefficient alpha. On the other hand, in the present embodiment, the value of the coefficient α is reduced by suppressing the point where the difference of the gradation error D in the one-level gradation transition caused by the large time division ratio of T _A is too large. I'm making it smaller.

For example, at the K level, T _A−1 · S ₁ ,
It is assumed that three gradation display elements T _A-1 · S ₂ and T _A · S ₁ are turned on, and at the K + 1 level, only T _A · S ₂ is turned on. Here, at the K level, the gradation display element of T _A-1 · S ₂ includes a luminance error based on the area error d.
At the +1 level, T _A · S ₂ includes a luminance error based on the area error d. However, T _A-1 =
Assuming that 4, T _A = 16, the above-described luminance error is the 4d level at the K level, while the luminance error is 16d level at the K + 1 level, which is four times the K level. This causes the coefficient α to increase.

Therefore, in this embodiment, the control means 7
However, in addition to the above-mentioned first, second or fourth means, 1
In the transition of the gradation of the level, the driving of the panel 5 is controlled so that the change of the lighting state of the gradation display element constituting the gradation display pattern is devised. As a result, the value of the coefficient α decreases. Such control is hereinafter referred to as fifth means.

More specifically, it is assumed that a gradation transition has been made from the K level in which the gradation display element S _m · T _n is in the lighting state to the K + 1 level in which the S _m · T _n is in the non-lighting state. If S _m · T _n is turned off by this gradation transition, at the K + 1 level, the (n + 1) to N-th fields T _C (n +
Gradation display elements S _m · T _C containing either 1 ≦ C ≦ N) to always be at on state.

[0134] That is, the control unit 7, a tone to K + 1 levels from K level gradation display elements S _m · T _n is in the lighting state grayscale display element S _m · T _n in a non-lighting state At the time of transition, _if the field of the gradation display element S _m · T _n is the n-th field (1 ≦ n <N), the field T _c (n + 1 ≦ C ≦ N) becomes the (n + 1) -th or more field. and lighting state gradation display elements S _m that contains the same sub-pixel as the tone display elements S _m · T _n from the non-lighting state.

FIG. 7A shows the fifth means.
This will be described with reference to FIG. Conventionally, for example, the pixel division ratio is S ₁ : S ₂ = 1: 2, and the time division ratio is T ₁ :
It is assumed that T ₂ : T ₃ = 1: 4: 16. In this case, as described above, the coefficient α is 11 in the gradation transition from the 31st level to the 32nd level (see Table 1). therefore,
Good multi-tone display cannot be performed.

Therefore, the time division ratio is set to T ₁ : T ₂ : T ₃ : T ₄ = 1: 4: 8: 8 by using the second means.
Further, in the gradation transition from the 31st level to the 32nd level, the fifth means is applied.

At the 31st level, as shown in FIG. 7A, all the gradation display elements including S ₁ and S ₂ · T ₁ and S ₂ · T ₂ are in a lighting state. The luminance G _{31 at} this time
Is as follows.

G ₃₁ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ + {(S ₁ · T ₄ ) + (S ₂ · T ₄ )} = [(1 × 1) + {(2 + d) × 1}] + [(1 × 4) + {(2 + d) × 4}] + [(1 × 8) + {(2 + d) × 0}] + [(1 × 8) + {(2 + d) × 0}] = 1+ (2 + d) +4+ (8 + 4d) + 8 + 0 + 8 + 0 = 31 + 5d [level] here, although the gradation transition S ₂ · T ₂ is turned off in 32 levels, by applying the fifth means, in the 32 level S ₂
-Either T ₃ or S ₂ · T ₄ is turned on. In this case, S ₂ · T ₃ as shown in FIG. 7 (b)
Is turned on. Luminance G ₃₂ at this time is as follows.

G ₃₂ = {(S ₁ · T ₁ ) + (S ₂ · T ₁ )} + {(S ₁ · T ₂ ) + (S ₂ · T ₂ )} + ｛(S ₁ · T ₃ ) + (S ₂ · T ₃ )｝ + {(S ₁ · T ₄ ) + (S ₂ · T ₄ )} = [(1 × 0) + {(2 + d) × 0}] + [(1 × 0) + {(2 + d) × 0}] + [(1 × 8) + {(2 + d) × 8}] + [(1 × 8) + {(2 + d) × 0}] = 0 + 0 + 0 + 0 + 8 + (16 + 8d) + 8 + 0 = 32 + 8d [ difference in luminance between the level] and hence G ₃₂ G ₃₁ is as follows.

G ₃₂ −G ₃₁ = 32 + 8d− (31 + 5d) = 1 + 3d [level] That is, the gradation error D = 3d level, and the coefficient α is suppressed to 3.

In the fifth means, the gradation transition is such that the luminance error 4d of S ₂ · T ₂ at the 31st level is shifted in parallel to S ₂ · T ₃ at the 32nd level. Therefore, it is possible to effectively suppress an increase in the coefficient α in one-level gradation transition. Tables 8 and 9 show the gradation display patterns at this time.

[0142]

[Table 8]

[0143]

[Table 9]

The same time division ratio (T ₁ : T ₂ : T ₃ : T ₄
= 1: 4: 8: 8), when compared with Tables 6 and 7 in Embodiment 3 above, the coefficient α is 7 at the maximum in Tables 6 and 7. On the other hand, in the present embodiment, as shown in Tables 8 and 9, 8 levels to 8 levels
Level transition from level 15 to level 16; level transition from level 23 to level 24;
In the gradation transition from the level 32 to the level 32 and the gradation transition from the level 55 to the level 56, the coefficient α is 3 which is the maximum value.

Further, when the fifth means is used, as shown in the gradation linearity graph of FIG.
It can be seen that the gradation linearity in the multi-gradation display is almost secured. The graph of FIG. 8 shows the gradation linearity when the area error d = ± 0.3 in the gradation display patterns of Tables 8 and 9.

Therefore, by using the fifth means, more excellent multi-tone display can be realized. In particular, under the condition that the pixel division ratio is S ₁ : S ₂ = 1: 2, the above-described time division ratio is set to T ₁ : T ₂ : T ₃ : T ₄
= 1: 4: 8: 8, that is, if the condition is limited to the field T ₂ = 4 when one frame is divided in time, the effect obtained by the fifth means is further improved. be able to.

Another example using the fifth means will be described below. Pixel division ratio S _1: S ₂ = _1: 2, the time division ratio _{T 1: T 2: T 3} : T 4: T 5 = 1: 4: 8: 1
Assuming that the ratio is 6:16, as shown in Table 10, 136-level gradation display (corresponding to 128 levels) is possible.

[0148]

[Table 10]

In Table 10, it is shown that the basic transition pattern 1 for every 16 levels shown in FIG. 14A is inserted into the portion (1) shown in the columns of T ₁ and T ₂ . . In addition, "0 ... 0" in T ₃ and T ₄ each column
Or, “1... 1” indicates that all “0” or “1” is entered.

In the case of a 136-level gradation display pattern as shown in Table 10, the maximum value of the coefficient α is 3, as can be seen from the column of the coefficient α. Therefore, no reversal of the gradation is observed, and the gradation linearity in the multi-gradation display can be substantially ensured, so that good multi-gradation display can be performed.

Similarly, when the pixel division ratio is S ₁ : S ₂ = 1: 2
And the time division ratio is T ₁ : T ₂ : T ₃ : T ₄ : T ₅ =
Assuming 1: 4: 8: 16: 32, as shown in Table 11, display at 184 levels is possible.

[0152]

[Table 11]

In Table 11, it is shown that the basic transition pattern 1 for every 16 levels shown in FIG. 14A is inserted in the portion (1) shown in the columns of T ₁ and T ₂ . . Further, it is shown that the basic transition pattern 2 for every 16 levels shown in FIG. 14B enters the portion (2) shown in the columns T _{1 to} T ₃ . Furthermore, T ₃ and T ₄ "0 ... 0" in each column or "1 ... 1"
Indicates that "0" or "1" is all entered.

In the case of a gradation display pattern of 184 levels as shown in Table 11, the maximum value of the coefficient α is 3, as can be seen from the column of the coefficient α. Therefore, no reversal of the gradation is observed, and the gradation linearity in the multi-gradation display can be substantially secured, so that good multi-gradation display can be performed.

In the above example, the pixel division ratios are all S ₁ :
Although the condition of S ₂ = 1: 2 was satisfied, the pixel division ratio was S ₁ : S
The application of the fifth means under the condition of ₂ = 1: 4 will be described below.

The pixel division ratio is S ₁ : S ₂ = 1: 4,
The time division ratio is T ₁ : T ₂ : T ₃ : T ₄ = 1: 2: 16:
32, conventionally, as shown in Table 12, 256
The level can be displayed.

[0157]

[Table 12]

In Table 12, it is shown that the basic transition pattern 3 for every 16 levels shown in FIG. 14 (c) enters the portion (3) shown in the columns of T ₁ and T ₂ . . In addition, "0 ... 0" in T ₃ and T ₄ each column
Or, “1... 1” indicates that all “0” or “1” is entered.

In the case of the conventional gradation display pattern as shown in Table 12, as can be seen from the column of the coefficient α, the coefficient α indicates the maximum value of 13 in the gradation transition from the 191 level to the 192 level. As a result, for example, the area error d
= 0.3, the gradation error D = 13 x 0.2 =
This is 2.6 levels, and a large gradation error D occurs at the time of one-level gradation transition.

The fifth means is applied to such a gradation display pattern. The pixel division ratio is S ₁ : S ₂ = 1: 4,
Time division ratio _{T 1: T 2: T 3} : T 4: T 5 = 1: 2:
Assuming that the ratio is 8:16:32, as shown in Tables 13 and 14, 296 levels of display are possible.

[0161]

[Table 13]

[0162]

[Table 14]

In Tables 13 and 14, it is shown that the basic transition pattern 3 for every 16 levels shown in FIG. 14 (c) is inserted into the part (3) shown in the columns of T ₁ and T ₂ . ing. Furthermore, T ₃ and T ₄ "0 ... 0" in each column or "1 ... 1" indicates that all "0" or "1" is entered.

In the case of the 296-level gradation display pattern as shown in Tables 13 and 14, the maximum value of the coefficient α is 5, as can be seen from the column of the coefficient α.
It can be seen that it is sufficiently lower than 13. Therefore, good multi-tone display can be realized.

[0165]

According to the display device of the first aspect of the present invention, a plurality of pixels are arranged in a matrix as described above.
One sub-pixel is lit for a predetermined time based on a panel in which one pixel is divided into a plurality of sub-pixels and one of a plurality of fields obtained by dividing a time width in one frame of an image signal. Control means for controlling the sub-pixels, which are turned on in a time width of one field, as one gradation display element. In a display device that performs multi-gradation display by combining a plurality of sub-pixels, the number of the sub-pixels constituting one pixel is N and the area ratio of each sub-pixel is 1: S ₂ : S
₃ : ...: S _N and the number of the above fields is N
And the time division ratio of the field is 1: T ₂ : T ₃ :
...: T _N , the control means calculates the following equation:

[0166]

(Equation 9)

The multi-gradation display is performed by the time division ratio T _A of the A-th field which is the second to N-th field determined in the above, and each gradation display element can be controlled independently. is there.

Therefore, in the above configuration, the gradation error at one-level gradation transition can be reduced.
It is possible to prevent the inversion of the gray scale and prevent the gray scale from being displayed.

As described above, in the display device according to the second aspect of the present invention, in addition to the configuration according to the first aspect, the control means includes:

[0170]

(Equation 10)

[0171] determined at, with a time-division ratio T _B field as a second or more A-1 th or less is configured to perform multi-gradation display.

Therefore, the above configuration has an effect that it is possible to suppress an increase in the gradation error and to avoid a drastic reduction in the number of gradations that can be expressed.

As described above, in the display device according to the third aspect of the present invention, in addition to the configuration according to the first or second aspect, the control means includes a display device which is displayed by a combination of a plurality of gradation display elements. When the tone level shifts to the next level, the time division ratio of the field is determined so that the tone error caused by the difference in luminance between the levels is less than one level.

Therefore, the above configuration has an effect that the effect obtained in the display device of the first or second aspect can be further improved.

According to the display device of the fourth aspect of the present invention, as described above, in addition to the configuration of the first or second aspect, the control means may control that all the fields from the Ath to the Nth have the same time. It is a configuration with a width.

Therefore, the above configuration has an effect that it is possible to increase the number of expressible gradations while suppressing an increase in the gradation error.

As described above, the display device according to the fifth aspect of the present invention has the structure according to the first, second, or fourth aspect.
The above-mentioned control means, when transitioning the gradation from a level at which one gradation display element is turned on to a level at which the gradation display element is turned off, sets the field of the gradation display element to the n-th field. If (1 ≦ n <N), the gray scale display element including the same sub-pixel as the gray scale display element is changed from the non-lighting state to the lighting state in the (n + 1) th or more field.

Therefore, the above configuration has an effect that the increase in the gradation error at the one-level gradation transition can be more effectively suppressed.

As described above, the display device according to claim 6 of the present invention has two sub-pixels forming one pixel in addition to the configuration according to claim 4 or 5, Is 1: 2, the number of the fields is 4, and the time division ratio of the field is 1: 4: 8: 8.
The configuration is as follows.

Therefore, the above configuration has an effect that the effect obtained by the configuration of claim 4 or 5 can be further improved.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram showing a gray scale display element in a 23-level display in a gray scale display driving method of a display device according to an embodiment of the present invention, and FIG. It is explanatory drawing which shows the gradation display element in 24 level display in the drive method shown to (a).

2A is a schematic explanatory view showing a configuration of a panel included in the display device, and FIG. 2B is a schematic explanatory view showing a configuration of a pixel included in the panel shown in FIG.

FIG. 3 is an explanatory diagram showing a gradation display pattern in the driving method shown in FIGS. 1 (a) and 1 (b).

FIG. 4 is a graph showing gradation linearity when the area error d = ± 0.13 in the gradation display patterns shown in Tables 6 and 7.

FIG. 5 is a graph showing gradation linearity when an area error d = ± 0.3 in the gradation display patterns shown in Tables 6 and 7.

FIG. 6 is a graph showing gradation linearity in a gradation display pattern not shown in the table.

FIG. 7A is an explanatory view showing a gradation display element in 31-level display in a gradation display driving method of a display device according to another embodiment of the present invention, and FIG. , (A)
FIG. 4 is an explanatory diagram showing gradation display elements in 32-level display in the driving method shown in FIG.

FIG. 8 is a graph showing gradation linearity in gradation display patterns shown in Tables 8 and 9.

FIG. 9 is a graph showing gradation linearity in the conventional gradation display pattern shown in Table 1.

FIG. 10 is a graph showing gradation linearity in the conventional gradation display pattern shown in Table 1.

FIG. 11A is an explanatory diagram showing ideal gray scale display elements for 31-level display in a conventional gray scale display driving method of a display device, and FIG. It is explanatory drawing which shows the gradation display element in the 32 level display in the driving method shown.

12A is an explanatory diagram showing actual gray scale display elements in 31-level display in a conventional gray scale display driving method of a display device, and FIG. 12B is a diagram showing FIG. It is explanatory drawing which shows the gradation display element in the display of 32 levels in a drive method.

FIG. 13 is a graph showing gradation linearity in the conventional gradation display pattern shown in Table 2.

FIGS. 14 (a) to (c) show Table 2 and Tables 10 to 14;
FIG. 9 is a diagram showing a transition pattern repeated in the gradation display pattern shown in FIG.

[Explanation of symbols]

4 pixel 5 panel 6 sub-pixel 7 control means _Sm sub-pixel _Tn field _Sm - _Tn gradation display element

Claims (6)

[Claims] A plurality of pixels arranged in a matrix,
One sub-pixel is lit for a predetermined time based on a panel in which one pixel is divided into a plurality of sub-pixels, and one of a plurality of fields obtained by dividing a time width in one frame of an image signal. And a control means for controlling the sub-pixel which is turned on in a time width of one field as one gradation display element. In a display device performing multi-gradation display by combining a plurality of sub-pixels, the number of the sub-pixels constituting one pixel is N, and the area ratio of each sub-pixel is 1: S ₂ : S ₃ :...: S _N. In addition, assuming that the number of the fields is N and the time division ratio of the fields is 1: T ₂ : T ₃ :...: T _N , the control means calculates the following equation: The multi-gradation display is performed using the time division ratio T _A of the A-th field which is the second to N-th determined in the above, and each gradation display element can be controlled independently. Display device. 2. The control means according to the following equation: 2. The display device according to claim 1, wherein the multi-gradation display is performed using the time division ratio TB of the second to A-1st fields determined in step ( _b ). 3. The control means according to claim 1, wherein, when a gradation level displayed by a combination of a plurality of gradation display elements transitions to the next level, a gradation error occurring in a difference in luminance of each level is determined. 3. The display device according to claim 1, wherein a time division ratio of the field is determined so as to be less than one level. 4. The display device according to claim 1, wherein said control means sets all the fields from Ath to Nth in equal time width. 5. The grayscale display element according to claim 1, wherein said grayscale display element shifts from a level at which one grayscale display element is lit to a level at which said grayscale display element is turned off. Is the nth field (where 1 ≦ n <N), n
5. The display device according to claim 1, wherein a gradation display element including the same sub-pixel as the gradation display element is turned from a non-lighting state to a lighting state in a field of +1 or more. 6. The method according to claim 1, wherein the number of the sub-pixels constituting one pixel is two, the area ratio of each sub-pixel is 1: 2, the number of the fields is four, and the time division ratio of the field is four. The ratio is 1: 4: 8: 8.
Or the display device according to 5.