JP2012053479A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device that can reduce pseudo contour while suppressing the increase in the number of sub-frames.SOLUTION: A display device expresses grayscale by dividing one frame into plural sub-frames. The plural sub-frames include M (M is an integer of 2 or more) normal sub-frames necessary for expressing predetermined grayscale and further include N (N is a natural number) additional sub-frames. At least the following two sub-frame lighting patterns are set: a first sub-frame lighting pattern in which only the normal sub-frame is used with respect to at least one grayscale number among the predetermined grayscale and a second sub-frame lighting pattern in which the additional sub-frame and the normal sub-frame are used with respect to at least one grayscale number among the predetermined grayscale.

Description

  The present invention relates to a display device, and more particularly to a display device using a time gray scale method.

In recent years, active matrix display devices using digital video signals have been actively researched and developed. Such active matrix display devices include a light receiving display device such as a liquid crystal display (LCD) and a self-luminous display device such as a plasma display. As a light emitting element used in a self-luminous display device, an organic light emitting diode (
Organic Light Emitting Diode (OLED) is attracting attention. OLED is also called an organic EL element, an electro luminescence (EL) element, or the like (a display using the EL element is called an EL display). A self-luminous display device using an OLED has advantages such as higher pixel visibility than a liquid crystal display, no need for a backlight, and high response speed. The luminance of the light emitting element is controlled by the value of current flowing therethrough.

It is known that a time gray scale method is used as a method of performing gray scale display using a digital video signal in such an active matrix display device.

The time gradation method is a method of expressing gradation by controlling the length of a light emitting period and the number of times of light emission. In other words, one frame period is divided into a plurality of subframe periods, and each subframe is weighted such as the number of times of light emission and the time of light emission, and the total amount of weighting (total number of times of light emission and total time of light emission) is assigned for each gradation. The gradation is expressed by making a difference in. As an example, FIG.
One frame is divided into five subframes SF1 to SF5, and the weighting is performed so that the ratio of the lighting periods of these subframes is 2 ⁰ : 2 ¹ : 2 ² : 2 ³ : 2 ⁴ . Also,
FIG. 32 shows the relationship between the selection pattern of lighting / non-lighting of these subframes and the number of gradations. As can be seen from these figures, by controlling lighting / non-lighting of the subframes SF1 to SF5, 32 gradations of 0 to 31 can be displayed (the gradation number 1 represents the minimum unit of gradation change). . Since 1 bit is required to instruct lighting / non-lighting of each subframe, a 5-bit digital signal is required to control the five subframes SF1 to SF5. In general, M subframes weighted according to a binary number (power of 2) are controlled using an M-bit digital video signal to display 2 ^M gradations (ie, 0 to 2 ^M −1). It can be carried out. In this specification, a time gray scale method for performing gray scale display using a plurality of subframes (typically according to the binary system) weighted differently in this way is referred to as a binary code time gray scale method. Call. Also, a bit of a digital signal that controls a large weight subframe (for example, SF5) is referred to as an upper bit, and a bit of a digital signal that controls a small weight subframe (for example, SF1) is referred to as a lower bit. Note that the weights of subframes do not necessarily follow binary numbers, and all subframes do not necessarily have different weightings. The weight (lighting period or number of blinks) of a certain subframe may be equal to or less than a value obtained by adding 1 to the sum of the weights of subframes with smaller weights (that is, lower-order). Thereby, all gradations can be expressed continuously. For example, if the ratio of the lengths of the lighting periods of the subframes is 1: 1: 2: 3, all gradations from 0 to 7 can be expressed continuously.

In a display device using such a binary code time gradation method, when displaying a moving image,
There are cases where a false contour (or pseudo contour) is perceived at a portion where the gradation changes smoothly without causing a boundary. In such a pseudo contour, one of adjacent pixels has a gradation number of 1
It is known that this is likely to occur when pixels with greatly different lighting patterns are adjacent, such as 5 and the other having 16 gradations. Further, one of the adjacent pixels has a gradation number that is a multiple of 4 (for example, 4
, 8, 16), and the other is one smaller number of gradations (for example, 3, 7, 15), the pseudo contour can be perceived. Various measures have been proposed to reduce such pseudo contours (see Patent Documents 1 to 7).

For example, in Patent Document 2, seven subframes (upper subframes) having substantially equal weights are controlled by the upper 7 bits of, for example, a 12-bit digital signal representing gradation, and the remaining five lower bits are converted into a binary system. It is disclosed to control a plurality of sub-frames according to the weighting. In this device, the seven upper subframes are continuously arranged in one frame period, and the upper subframes are sequentially and cumulatively lit as the gradation increases. That is, the upper subframe that is lit at a small gradation is also lit at a larger gradation. Such a gradation method is called a superposition time gradation method. That is, Patent Document 2 can be said to be a combination of the superimposition time gradation method using the upper bits and the binary code time gradation method using the lower bits.

Japanese Patent No. 2903984 Japanese Patent No. 3075335 Japanese Patent No. 2639311 Japanese Patent No. 3322809 JP-A-10-307561 Japanese Patent No. 3585369 Japanese Patent No. 3489884 JP 2001-324958 A

As described above, various methods for reducing pseudo contours have been proposed, but the effect of pseudo contour reduction is not yet sufficient.

For example, the invention described in Patent Document 2 is used to represent 32 gradations, and adjacent pixels A and B
FIG. 33 shows the case of representing the number of gradations 15 and the number of gradations 16 respectively. In this figure, subframes SF1 to SF7 have the same weight (4) and are used for the superposition time gray scale method, and subframes SF8 to SF9 have weights according to binary numbers (1: 2),
Used in the binary code time gray scale method (such a subframe is referred to herein as a binary code subframe). As shown in the figure, the subframes SF1 to SF3, SF8, and SF9 are turned on in the pixel A representing the gradation number 15, and the subframes SF1 to SF4 are turned on in the pixel B representing the gradation number 16. At this time, if the line of sight does not move, the gradation number 15 (4 + 4 + 4 + 1 + 2) is perceived in the pixel A, and the gradation number 16 (4 + 4 + 4 + 4) is perceived in the pixel B, and no pseudo contour is generated.

On the other hand, it is assumed that the line of sight moves from the pixel A to the pixel B or from the pixel B to the pixel A. Such a case is shown in FIG. In this case, depending on how the line of sight moves, in some cases, the number of gradations is 12 (4
+ 4 + 4), and in some cases, the number of tones is 19 (4 + 4 + 4 + 4 + 1 + 2). Originally, the number of gradations should be 15 and 16, but the number of gradations is about 12 to 19, which is an improvement over the binary code time gradation method alone, A pseudo contour is generated.

Increasing the number of subframes used in the superposition time gray scale method and shortening the lighting period of each subframe (that is, reducing the weighting) can reduce the pseudo contour, but the number of subframes As it increases, the number of bits of the digital signal to control it increases,
There is a problem that the device scale increases or the frequency increases and the power consumption increases.

In view of such problems, it is a primary object of the present invention to provide a display device capable of reducing pseudo contours while suppressing an increase in the number of subframes as much as possible.

In order to solve the above-described problem, according to the present invention, a display device that expresses gradation by dividing one frame into a plurality of subframes, and the plurality of subframes is necessary for expressing a predetermined gradation. It has M (M is an integer of 2 or more) normal subframes and N (N is a natural number) additional subframes, and the normal subframes for at least one gray level within a predetermined gray level. A display device, wherein at least two subframe lighting patterns are set: a first subframe lighting pattern using only a frame, and a second subframe lighting pattern using an additional subframe and a regular subframe. Is provided.

The number of gradations for which at least two subframe lighting patterns are set may be the number of gradations in which the subframe lighting pattern changes greatly between adjacent gradation numbers when no additional subframe is used.

According to the preferred embodiment of the present invention, the M regular subframes have r (2 ≦ r ≦ M, r is an integer) binary code subframes having different weights and used in the binary code time gray scale method. And the number of gradations for which the at least two subframe lighting patterns are set may include the number of gradations represented only by the subframe with the highest weighting when no additional subframe is used. Here, weighting means relative luminance with respect to a subframe corresponding to the minimum luminance, and is determined by the lighting period and the number of blinks of each subframe. Note that the binary code subframe weighting preferably conforms to a binary number, but does not necessarily conform to a binary number. Weight of a subframe (
The lighting period and the number of blinks) may be equal to or less than a value obtained by adding 1 to the sum of the weights of subframes with smaller weights (that is, lower-order). Thereby, all gradations can be expressed continuously.

According to another preferred embodiment of the present invention, t (2 ≦ t) used in the overlay time gray scale method.
≦ M, t is an integer), and the number of gradations for which at least two subframe lighting patterns are set is lit compared to the one lower gradation number when no additional subframe is used. It is possible to include the number of gradations in which the superimposed subframe increases by one. According to this, for example, if t overlapping subframes have a weight of 4,
If an additional subframe is not used, one of t subframes is additionally lit every time the gray level increases by 4. Therefore, a lighting pattern using only regular subframes for a gray level that is a multiple of 4 At least two subframe lighting patterns of the lighting pattern using the additional subframe are set. Note that superimposed subframes usually have approximately the same weighting,
It is possible to have different weights.

According to a preferred embodiment of the present invention, the M regular subframes include three subframes having weights of 1, 2, and 4, and the number of gradations for which at least two subframe lighting patterns are set is 4 The number of gradations can be a multiple of. The number of gradations for which at least two subframe lighting patterns are set may further include the number of gradations obtained by adding 1 to a multiple of 4 or the number of gradations obtained by adding 2 to a multiple of 4. It is also possible to set at least two sub-frame lighting patterns for all the gradation numbers of 4 or more.

Preferably, at least one of the N additional subframes has the same weight as the subframe having the smallest weight among the M regular subframes.

Further, the number N of additional subframes may be 2 or more. In that case, two or more additional subframes may include different weighted subframes, and / or two or more additional subframes may include the same weighted subframes.

Preferably, the display device is an EL display, a plasma display, a digital micromirror device (DMD), a field emission display (FED), a surface electric field display (SED), or a ferroelectric liquid crystal display.

According to the present invention, one or more additional subframes are provided in addition to the regular subframe for expressing a desired gradation, and a plurality of additional gradations can be obtained for the desired number of gradations by using the additional subframe. Since the sub-frame lighting pattern is set, the pseudo contour can be reduced by selectively switching the plurality of sub-frame lighting patterns according to the number of gradations of adjacent pixels.

The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. The figure explaining the drive method of the display apparatus based on the preferred Example of this invention. 4A and 4B illustrate a structure of a driving method of a display device of the present invention. 4A and 4B illustrate a structure of a driving method of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. 4A and 4B illustrate a structure of a driving method of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. 4A and 4B illustrate a structure of a driving method of a display device of the present invention. 4A and 4B illustrate a structure of a driving method of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 14 illustrates an electronic device to which the present invention is applied. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 14 illustrates an electronic device to which the present invention is applied. FIG. 6 illustrates a structure of a display device of the present invention. FIG. 14 illustrates an electronic device to which the present invention is applied. 8A and 8B illustrate a structure of a conventional display device driving method. 10A and 10B illustrate a driving method of a conventional display device. 8A and 8B illustrate another example of a conventional display device driving method. 8A and 8B illustrate another example of a conventional display device driving method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of this embodiment mode.

(Embodiment 1)
FIG. 1 is a diagram illustrating a lighting pattern of a subframe according to a preferred embodiment of the present invention. As in the prior art, this embodiment has five subframes that are weighted according to binary numbers to represent 32 (2 ⁵ ) gradations with gradation numbers 0 to 31 and driven in a binary code time gradation method. SF1 ~
Has SF5. A subframe necessary for representing such a predetermined gradation is called a normal subframe. In the embodiment of FIG. 1, it is necessary that all the regular subframes SF1 to SF5 are lit when the maximum number of gradations 31 among the predetermined gradations is represented. In the embodiment of FIG. 1, as in the conventional example, various gradation numbers can be expressed by selectively lighting the regular subframes SF1 to SF5. In addition, the lighting order of the regular subframes in one frame may be changed for each frame, from the smallest weight to the largest, or vice versa, or randomly, and may take various forms. Further, for example, the subfield SF5 having the maximum weight may be divided into two or more and arranged separately within one frame period (
Patent Document 1).

According to the present invention, the additional subframe SF6 is provided in addition to the regular subframes SF1 to SF5. As a result, six subframes are included in one frame. Since a bit (additional bit) for driving the additional subframe 6 is necessary in addition to the five bits for driving the regular subframes SF1 to SF5, the digital signal that defines the luminance in one frame of each pixel is 6 bits. The number of regular subframes is not limited to 5, but can include M (M is an integer of 2 or more) regular subframes, and the number of additional subframes is limited to 1. Instead, it may include N (N is an arbitrary natural number) additional subframes. In the embodiment of FIG. 1, the additional subframe SF6 has the same weight (1) as the subframe SF1 having the smallest weight (1) among the regular subframes. Accordingly, the number of gradations that is a multiple of 4 (ie, the number of gradations 4, 8, 12, 16, 20, 24,
28), it is possible to set a subframe lighting pattern similar to the lighting pattern of the next lower subframe using the additional subframe SF6. For example, the number of gradations is 4
Can be represented by two subframe lighting patterns: lighting of only SF3 that does not light the additional subframe SF6 (4), and lighting of subframes SF1, SF2, and SF6 that light the additional subframe SF6 (4 '). The sub-frame lighting pattern (4 ′) using the additional sub-frame SF6 is similar to the sub-frame lighting pattern with the gradation number 3 below. The number of gradations 8 is represented by two patterns: lighting of only SF4 that does not light the additional subframe SF6 (8), and lighting of subframes SF1, SF2, SF3, and SF6 that light the additional subframe SF6 (8 '). The sub-frame lighting pattern (8 ′) using the additional sub-frame SF6 is similar to the sub-frame lighting pattern with the gradation number 7 below. The same applies to the number of gradations of multiples of 4.

Thereby, for example, when the pixel B adjacent to a certain pixel A has the gradation number 15 (SF1 to SF4 are lit), and represents the gradation number 16 in the pixel A, the additional subframe SF6 is used for the SF.
1 to SF4 and SF6 are turned on (that is, 16 ′ lighting pattern), the number of gradations is 1
Since it is similar to the lighting pattern 5, the pseudo contour can be reduced. Similarly, with respect to the other gradation numbers for which two lighting patterns are set, a lighting pattern can be selected according to the gradation number of adjacent pixels, and the pseudo contour can be reduced.

In the above embodiment, a plurality of gradation numbers (4, 8, 12, 16, 20, 24) that are multiples of 4 are used.
28), the subframe lighting pattern using the additional subframe SF6 is set, but the number of gradations 16 that is most likely to generate a pseudo contour (generally, a normal subframe having the largest weighting when no additional subframe is used) The sub-frame lighting pattern using the additional sub-frame SF6 may be set only for the number of gradations represented by only lighting), whereby a predetermined pseudo contour reduction effect can be obtained.

As described above, according to the present invention, M pieces (5 in the embodiment of FIG.
In addition to the regular subframes, N additional subframes (one in the embodiment of FIG. 1) are provided, and only the regular subframe is used for at least one gradation number within a predetermined gradation. 1
At least two subframe lighting patterns of the second subframe lighting pattern using the additional subframe and the regular subframe are set, and the at least two subframe lighting patterns are selectively used. Therefore, for example, one of a plurality of sub-frame lighting patterns can be selectively used so that the pseudo contour is reduced as much as possible in accordance with the brightness of adjacent pixels, and so on, which has a great effect on the pseudo contour reduction. . In addition, a significant increase in the number of subframes can be avoided by reducing the number of additional subframes to 1 bit or 2 bits. The subframe lighting pattern using only the regular subframe means a subframe lighting pattern in which the additional subframe is not lit, and the subframe lighting pattern using the additional subframe and the regular subframe is:
It means a subframe lighting pattern in which at least one of the additional subframes and at least one of the regular subframes are lit.

FIG. 2 is a diagram showing another embodiment of the display device driving method using the additional subframe according to the present invention. In the embodiment of FIG. 2, there are six subframes S that are weighted according to a binary number to represent 64 (2 ⁶ ) gradations with gradation numbers 0 to 63 and driven in a binary code time gradation method.
F1 to SF6 and one additional subframe SF7 having a weight of 1. In this embodiment, a subframe lighting pattern using only regular subframes and additional subframes for gradation numbers 4 (2 ² ), 8 (2 ³ ), 16 (2 ⁴ ), and 32 (2 ⁵ ) And two lighting patterns of lighting patterns using regular subframes are set. Thereby, when displaying these gradation numbers with a certain pixel, a pseudo contour can be reduced by selecting a lighting pattern according to the gradation number of an adjacent pixel, for example. In general, M regular subframes are weighted according to a binary number and used in the binary code time gray scale method. R (2 ≦ r ≦ M, M and r are natural numbers. In the embodiment of FIG. r = M = 6) in the case of having a binary code subframe, a subframe lighting pattern using only regular subframes for the gradation number 2 ^s (2 ≦ s <r, s is a natural number), and an additional subframe And at least two subframe lighting patterns of subframe lighting patterns using regular subframes may be set. In the embodiment of FIG. 2, similarly to the embodiment of FIG. 1, the subframe lighting pattern using only the regular subframe for the number of gradations that is a multiple of 4, the additional subframe, and the regular subframe are used. Of course, it is also possible to set two lighting patterns.

FIG. 3 is a diagram illustrating another embodiment of a display device driving method using an additional subframe according to the present invention. The embodiment of FIG. 3 is different from the embodiment of FIG. 1 in that two subframes SF6 and SF7 each having a weight of 1 are used as additional subframes. That is, in the embodiment of FIG. 3, the number of additional subframes N = 2. Thus, the number of additional subframes is not limited to one. As shown in FIG. 3, the number of gradations is 4, 8, 12, 16, 20, 2
In addition to 4 and 28, the additional subframes SF6 and SF7 are not used for the gradation numbers 5, 9, 13, 17, 21, 25, and 29 (that is, 5, 9, 13, 17, 21, 25). And 2
9) and additional subframes SF6 and SF7 (ie, 5 ', 9', 13 ', 1)
Two sub-frame lighting patterns 7 ', 21', 25 'and 28') are assigned. In general, two subframe lighting patterns can be assigned to the number of gradations that is a multiple of 4 and the number of gradations that is a multiple of 4 + 1. Thus, for example, when the pixel B adjacent to a certain pixel A has the gradation number 15 (SF1 to SF4 are lit) and the pixel A represents the gradation number 16 (or 17), the additional subframe SF6 is used to select SF1. When SF4 and SF6 (or SF1 to SF4, SF6, and SF7) are turned on, they are similar to the subframe lighting pattern with the number of gradations of 15, so that the pseudo contour can be reduced. In the embodiment of FIG. 3, the additional subframes SF6 and SF7 have the same weight and are used in the superposition time gray scale method (for example, when the gray scale number 4 'is compared with the gray scale number 5'). The additional subframe SF6 is lit at the gradation number 4 ', and the additional subframe SF7 is additionally lit at the gradation number 5', and as a result, both the additional subframes SF6 and SF7 are lit). As a result, pseudo contours due to these additional subframes are less likely to occur.

FIG. 4 is a diagram showing still another embodiment of a display device driving method using additional subframes according to the present invention. In the embodiment of FIG. 4, a subframe SF6 having a weight of 1 and a subframe SF7 having a weight of 2 are used as additional subframes. Thus, when it has a some additional sub-frame, those weights may differ. When the weights of the additional subframes are different in this way,
More gradations can be represented by a small number of additional subframes (for example, since the two additional subframes have the same weight in the embodiment of FIG. 3), the combination of these two additional subframes The gradations that can be represented by 3 are 0, 1, and 2, but FIG.
In this embodiment, since the two additional subframes have different weights from 1 and 2, the gradation that can be expressed by the combination of these two additional subframes is 0, 1, 2, 3 Street). As shown in FIG. 4, the number of gradations is 4-6, 8-10, 12-14, 1
When the additional subframes SF6 and SF7 are not used for each of 6 to 18, 20 to 22, and 24 to 26 (that is, 4 to 6, 8 to 10, 12 to 14, 16 to 18, 20 to 22 and 24)
26) and the additional subframes SF6 and / or SF7 (ie, 4 'to 6)
', 8'-10', 12'-14 ', 16'-18', 20'-22 'and 24'-26
2) sub-frame lighting patterns are assigned. In general, two subframe lighting patterns can be assigned to the number of gradations that is a multiple of 4, the number of gradations that is a multiple of 4 + 1, and the number of gradations that is a multiple of 4 + 2. In this case, when displaying the number of gradations having these two subframe lighting patterns in a certain pixel, the pseudo contour can be reduced by selecting the subframe lighting pattern according to the subframe lighting pattern of the adjacent pixel. Can do.

FIG. 5 is a diagram showing still another embodiment of a display device driving method using additional subframes according to the present invention. In the embodiment of FIG. 5, a subframe SF6 having a weight of 1 is used as an additional subframe, a subframe SF7 having a weight of 2 and a subframe SF8 having a weight of 3. Generally, when there are N (N is a natural number) additional subframes, the weights of these subframes are set to 1, 2, 3,. . . , N can be used. In the embodiment of FIG. 3, since there are three additional subframes SF6, SF7, and SF8 with weights 1, 2, and 3, respectively, eight combinations of 0 to 7 can be obtained by combining these three additional subframes. The number of gradations can be expressed. As shown in FIG. 5, when the additional subframes SF6, SF7, and SF8 are not used for each of the gradation numbers 4 to 31, that is, when the additional subframes SF6, SF7, and / or Or when using SF8 (
That is, two subframe lighting patterns 4 'to 31') are assigned. Generally, at least two subframe lighting patterns can be assigned to each gradation number. In the embodiment of FIG. 5 as well, when displaying the number of gradations having two subframe lighting patterns in a certain pixel, pseudo contour can be obtained by selecting an appropriate subframe lighting pattern in accordance with the subframe lighting pattern of the adjacent pixel. Can be reduced.

When there are a plurality of additional subframes, their weighting pattern is not limited to the above embodiment, and other patterns are possible. For example, if there are N additional subframes, 1, 2, 4, 8,. . . 2 ^N-1 may have a weight according to a binary number. Or 1, 2, 2, 2,. . . And 1, 1, 2, 2, 2,. . . Or 1, 1, 1, 2, 2, 2,. . . As described above, the weighting of an arbitrary number of subframes among the N additional subframes can be set to 1, and the weighting of other additional subframes can be set to 2.

Further, the subframe lighting pattern using the additional subframe is not limited to the above embodiment. For example, in the embodiment of FIG. 3, the number of gradations is 4, 5, 8, 9, 12, 13, 16, 17, 20,
Subframe lighting patterns using the additional subframes SF6 and SF7 are set for 21, 24, 25, 28, and 29. For example, the gradation number 3 is set to the subframes SF1, SF6, and SF.
A sub-frame lighting pattern using additional sub-frames can be set for the number of gradations other than that shown in the above-described embodiment, as represented by lighting 7. In addition, for example, in the embodiment of FIG. 3, the sub-frame lighting pattern for lighting the sub-frames SF2, SF6, and SF7 is additionally set for the number of gradations 4 so that a total of three sub-patterns for the number of gradations 4 is provided. A frame lighting pattern can also be set. Thus, the number of different subframe lighting patterns that can be assigned to a certain number of gradations is not limited to two. Further, as described above, the number of gradations having a plurality of subframe lighting patterns (two in the above embodiment) for each row,
The sub-frame lighting pattern can be changed for each column, each pixel, each frame, and the like.
Further, the lighting position of the additional sub-frame in one frame may be anywhere after the regular frame, before, or among the regular frames.

In the above embodiment, the regular subframes SF1 to SF5 have a weighting (lighting period or number of times of lighting) according to a binary number, and are used in the binary code time gray scale method. However,
The present invention can also be effectively applied when some of the subframes are used in the superposition time gray scale method. FIG. 6 shows such a preferred embodiment of the present invention.

The embodiment of FIG. 6 includes seven subframes SF1 to SF7 having the same weighting (4) as normal subframes, and two subframes SF8 having weights (1, 2) according to binary numbers.
, SF9. The upper seven subframes SF1 to SF7 are used for superposition time gradation (these are referred to as superposition subframes). That is, every time the number of gradations increases by 4, the lights are sequentially accumulated in the order of SF1, SF2, SF3. The lower two subframes are used for binary code time gray scale. As a result, the regular subframe S
By changing the lighting pattern of F1 to SF9, 32 gradation display of 0 to 31 is possible.

Further, in the embodiment of FIG. 5, the additional subframe SF10 having a weight of 1 is added as the additional subframe.
Have As a result, the number of gradations is 4, 8, 12, 16, 20, 24, 28 (that is, when the additional subframe SF10 is not used, the number of superimposed subframes to be lit increases by one compared to the number of gradations one lower The number of gradations to be used) when the additional subframe SF10 is not used (that is, 4, 8, 12, 16, 20, 24, 28) and when the additional subframe SF10 is used (that is, 4 ', 8', 12 ', 16', 20 ', 24', 28 ') are assigned two subframe lighting patterns. Thus, when displaying the number of gradations having a plurality of (two in this example) sub-frame lighting patterns in a certain pixel, the sub-frame lighting pattern is selected according to the sub-frame lighting pattern of the adjacent pixel. The pseudo contour can be reduced. For example, a pixel B adjacent to a certain pixel A has a gradation number 15 (S
When the gradation number 16 is expressed in the pixel A when F1 to SF3, SF8, and SF9 are turned on), SF1 to SF3, SF8, SF9, and SF10 are turned on using the additional subframe SF10 (that is, 16 'is turned on) Pattern) is similar to the sub-frame lighting pattern having the number of gradations of 15, and the pseudo contour can be reduced.

In general, M (M = 9 in the example of FIG. 6) t sub-frames (2 ≦ t <M
, T is an integer. In the embodiment of FIG. 5, when there is a subframe (superposition subframe) used in the superposition time gray scale method of t = 7), as described above, one lower gray scale when no additional subframe is used. Since pseudo contours are likely to occur at the number of gradations where the number of superimposed subframes that are lit increases by one compared to the number of subframes, a subframe lighting pattern that uses only regular subframes for such gradations and the addition It is preferable to set at least two subframe lighting patterns of subframe lighting patterns using subframes and regular subframes. Thereby, pseudo contour can be reduced by switching and using at least two subframe lighting patterns.

FIG. 7 illustrates yet another preferred embodiment of the present invention. The embodiment of FIG. 7 is different from the embodiment of FIG. 6 in that two subframes SF10 and SF11 each having a weight of 1 are used as additional subframes. That is, in the embodiment of FIG. 7, the number of additional subframes N = 2. As shown in FIG. 7, in addition to the number of gradations 4, 8, 12, 16, 20, 24 and 28, it is added to the gradation numbers 5, 9, 13, 17, 21, 25 and 29. Subframe SF
6. When SF7 is not used (that is, 5, 9, 13, 17, 21, 25, and 29) and when additional subframes SF6 and SF7 are used (that is, 5 ', 9', 13 ', 17') , 21 '
, 25 ', and 28'). Thus, for example, a pixel B adjacent to a certain pixel A has a gradation number 15 (SF1 to SF3 and SF8,
In the case where the gradation number 16 (or 17) is expressed in the pixel A when SF9 is lit), SF1 to SF3 and SF10 (or SF1 to SF) are used using the additional subframes SF10 and SF11.
3. When SF10 and SF11) are turned on, the pseudo contour can be reduced because it is similar to the subframe lighting pattern with 15 gradations. In the embodiment of FIG. 3, the additional subframes SF10 and SF11 have the same weight and are used in the superposition time gray scale method (for example, when the gray scale number 4 'is compared with the gray scale number 5'). The additional subframe SF10 is lit at the gradation number 4 ', and the additional subframe SF11 is additionally lit at the gradation number 5', so that both the additional subframes SF10 and SF11 are lit. As a result, pseudo contours due to these additional subframes are less likely to occur.

FIG. 8 illustrates yet another preferred embodiment of the present invention. In the embodiment of FIG. 8, a subframe SF10 having a weight of 1 and a subframe SF11 having a weight of 2 are used as additional subframes. Thus, when it has a some additional sub-frame, those weights may differ. When the weights of the additional subframes are different as described above, a larger number of gradations can be expressed by a small number of additional subframes. As shown in FIG. 8, the number of gradations is 4 to 6, 8 to 10, 12 to 14, 16 to 18, 20 to 22, and 24 to
When the additional subframes SF10 and SF11 are not used for each of 26 (ie, 4 to 6)
8-10, 12-14, 16-18, 20-22, and 24-26) and additional subframes SF10 and / or SF11 (ie, 4'-6 ', 8'-10', 12
'-14', 16'-18 ', 20'-22' and 24'-26 ') are assigned. In this case, when displaying the number of gradations having these two sub-frame lighting patterns in a certain pixel, the pseudo contour can be reduced by appropriately selecting the sub-frame lighting pattern according to the sub-frame lighting pattern of the adjacent pixel. Can be planned. Even when the present invention is applied to the overlapping time gray scale method, the number of additional subframes is not limited to 1 or 2, and the weighting pattern in the case of having a plurality of additional subframes is shown in FIGS. Various patterns other than those shown are possible as described above.

FIG. 9 illustrates yet another preferred embodiment of the present invention. In the embodiment of FIG. 9, there are three subframes SF8 to SF10 having the same weight (1) as the lower subframes, and the superimposition time gray scale method is also applied to the lower subframes (or lower bits). This is different from the embodiment of FIG. As shown in the drawing, the number of gradation levels 4, 8, 12, 16, 2 is also applied to the embodiment of FIG.
0, 24, 28 (that is, 4 which is the weighting of the upper superimposed subframes SF1 to SF7)
In the case where the additional subframe SF10 is not used (that is, 4, 8, 12, 1).
6, 20, 24, 28) and additional subframe SF10 (ie, 4 ', 8',
12 ', 16', 20 ', 24', 28 ') are assigned, and the same effects as in the embodiment of FIG. 6 can be obtained.

As described above, according to the present invention, one or more additional subframes are included in addition to the regular subframe necessary for expressing a desired gradation, and the desired subframe can be obtained by using the additional subframe. The number of gradations can be represented by a plurality of subframe lighting patterns, and the pseudo contour can be reduced by selectively switching the plurality of subframe lighting patterns according to the number of gradations of adjacent pixels. it can.

So far, the case where the lighting period increases linearly in proportion to the number of gradations has been described. Next, an embodiment in which the present invention is applied when gamma correction is performed will be described. The gamma correction refers to a non-linear lighting period that increases as the number of gradations increases. Even if the luminance increases linearly in proportion, the human eye does not feel that it is brighter in proportion. The higher the brightness, the less the difference in brightness is felt. Therefore, in order for the human eye to feel the difference in brightness, as the number of gradations increases,
It is necessary to take a longer lighting period, that is, to perform gamma correction.

The simplest method is to enable display with a larger number of bits (number of gradations) than the actual number of bits (number of gradations) to be displayed. For example, when displaying with 6 bits (64 gradations), in reality, 8 bits (256 gradations) can be displayed. Then, when actually displaying, the luminance of the number of gradations is made non-linear so that 6 bits (64
(Gradation). Thereby, gamma correction can be realized.

As an example, FIG. 10 and FIG. 11 show a subframe selection method in which gamma correction is performed and display is performed with 5 bits (32 gradations) so that the display can be performed with 6 bits (64 gradations). . The embodiment of FIG. 10 has subframes SF1 to SF6 having weights according to binary numbers as normal subframes. In the 6-bit display, these subframes SF1
By selectively lighting up .about.SF6, it is possible to display 64 (2 ⁶ ) gradations having 0 to 63 gradations. In the embodiment of FIG. 11, the normal subframe includes seven upper subframes SF1 to SF7 having a weight of 8, and three lower subframes SF8 to SF10 having a weight (1, 2, 4) according to a binary number. In 6-bit display, these subframes SF1 to SF10 are displayed.
Is selectively lit to display 64 (2 ⁶ ) gradations with 0 to 63 gradations. The gamma correction in the 5-bit display is realized by assigning the gradation numbers from 0 to 63 in the 6-bit display to the gradation numbers 0 to 31 in the 5-bit display. In other words, in FIGS. 10 and 11, the number of gradations in 5 bits up to 12 is the same as the number of gradations in 6 bits. However, when the number of gray scales with 5 bits after gamma correction is 13, light is actually turned on by a subframe selection method with 14 bits of gray scale levels. Similarly, when the number of gradations with 5 bits after gamma correction is 14, display is actually performed with 16 gradations with 6 bits, and when gradation number with 5 bits after gamma correction is 15, Actually, the display is performed with 18 bits of 6-bit gradation. In this way, a correspondence table between the number of gradations of 5 bits after gamma correction and the number of gradations of 6 bits may be created and displayed accordingly. Thereby, gamma correction can be realized.

It should be noted that the correspondence table between the number of gradations of 5 bits after gamma correction and the number of gradations of 6 bits can be changed as appropriate. Therefore, it is possible to easily change the degree of gamma correction by changing the correspondence table.

Also, how many bits (for example, p bits, where p is a natural number) can be displayed, and how many bits (for example, q bits, where q is a natural number) after gamma correction is displayed. It is not limited. When displaying with gamma correction, it is desirable to increase the number of bits p as much as possible in order to express gradation smoothly. However, if it is made too large, there will be adverse effects such as an increase in the number of subframes. Therefore, it is desirable that the relationship between the number of bits q and the number of bits p is q + 2 ≦ p ≦ q + 5.
As a result, it is possible to realize that the number of subframes does not increase too much while the gradation is expressed smoothly.

In the embodiment of FIG. 10, according to the present invention, an additional subframe SF8 having a weight of 1 is provided, and among the number of gradations in 5 bits, the number of gradations in the corresponding 6 bits is a multiple of 4 (ie, A sub-frame lighting pattern for lighting the additional sub-frame SF8 is set for gradation numbers of 4, 8, 12, 14, 16, 18, 20, 22, and 26). The embodiment of FIG. 11 is provided with an additional subframe SF11 having a weight of 1 according to the present invention, and the number of gradations corresponding to 6 bits out of the number of gradations of 5 bits is a multiple of 4 ( That is,
Sub-frame lighting patterns for lighting the additional sub-frame SF11 are set for gradation numbers of 4, 8, 12, 14, 16, 18, 20, 22, and 26). Thereby, when displaying the number of gradations with a certain pixel, the pseudo contour can be reduced by appropriately selecting the subframe lighting pattern. Thus, the present invention can also be applied when gamma correction is performed.

So far, the gradation expression method, that is, the subframe selection method has been described. Next, the appearance order of subframes will be described.

As an example, FIG. 12 shows a pattern example of the appearance order of subframes in the case of FIG. In FIG. 12, subframes SF8 and SF9 in the binary code time gray scale method are used.
The additional subframe SF10 is indicated by shading.

As the first pattern, SF1, SF2, SF3, SF4, SF5, SF6, SF
7, SF8, SF9, and SF10. The subframes SF8 and SF9 and the additional subframe SF10 in the binary code time gray scale method are arranged together at the end.

As the second pattern, SF8, SF9, SF10, SF1, SF2, SF3, S
F4, SF5, SF6, and SF7. The subframes SF8 and SF9 and the additional subframe SF10 in the binary code time gray scale method are first arranged together.

The third pattern is SF1, SF2, SF3, SF4, SF8, SF9, SF
10, SF6, SF7, SF5. The subframes SF8 and SF9 and the additional subframe SF10 in the binary code time gray scale method are arranged together in the middle.

As the fourth pattern, SF1, SF2, SF8, SF3, SF4, SF9, SF
5, SF6, SF10, SF7. The subframes SF1 to SF7 in the overlapping time gray scale method are arranged in order. The subframes SF8 and SF9 and the additional subframe SF10 in the binary code time gray scale method are also arranged in order. Then, after two subframes in the overlapping time gray scale method are arranged, one subframe or additional subframe in the binary code time gray scale method is arranged.

As the fifth pattern, SF1, SF2, SF9, SF3, SF4, SF8, SF
5, SF6, SF10, SF8. In this case, the order of appearance of subframes and additional subframes in the binary code time gray scale method is made random with respect to the fourth pattern.

As the sixth pattern, SF1, SF5, SF8, SF2, SF7, SF9, SF
3, SF6, SF10, SF4. In this case, the appearance order of the subframes in the overlapping time gray scale method is made random with respect to the fourth pattern.

As the seventh pattern, SF1, SF5, SF9, SF2, SF7, SF8, SF
3, SF6, SF10, SF4. This is a random pattern of the subframe appearance order in the superposition time gradation method and the appearance order of the subframes and additional subframes in the binary code time gradation method for the fourth pattern. .

As the eighth pattern, SF1, SF2, SF8, SF3, SF9, SF4, SF
5, SF6, SF10, SF7. This is because, after two subframes in the superimposition time gray scale method are arranged, one subframe in the binary code time gray scale method is arranged, and one subframe in the superposition time gray scale method is arranged. One subframe in the code time gray scale method is arranged, three subframes in the superposition time gray scale method are arranged, and one additional subframe is arranged.

As the ninth pattern, SF1, SF2, SF3, SF4, SF8, SF9, SF
5, SF6, SF7, SF10. This is because, after four subframes in the overlay time gray scale method are arranged, two subframes in the binary code time gray scale method are arranged, and three subframes in the overlay time gray scale method are arranged. Subframes are arranged.

In this way, it is desirable to arrange subframes and additional subframes in the binary code time gray scale method between subframes in the superposition time gray scale method so that the subframes are not unevenly distributed. As a result, the eyes are deceived and pseudo contours can be reduced.

Note that the appearance order of the subframes may change depending on the time. For example, the appearance order of subframes may change between the first frame and the second frame. Further, the appearance order of subframes may vary depending on the location. For example, the appearance order of the subframes may be changed between the pixel A and the pixel B. In addition, by combining them, the appearance order of the subframes may change with time and change with place.

The normal frame frequency is 60 Hz, but is not limited to this. The pseudo contour may be reduced by further increasing the frame frequency. For example, the operation may be performed at a frequency that is about twice that of a normal frequency of 120 Hz.

(Embodiment 2)
In this embodiment, an example of a timing chart is described. As an example, the subframe selection method shown in FIG. 1 is used. However, the subframe selection method is not limited to this, and the method can be easily applied to other subframe selection methods and other gradation numbers.

The order in which the subframes appear is, for example, SF1, SF2, SF3, SF4.
SF5 and SF6 are not limited to this, but can be easily applied to other orders.

First, FIG. 13 shows a timing chart in the case where a period for writing a signal to a pixel and a lighting period are separated. First, in a signal writing period, a signal for one screen is input to all pixels. During this time, the pixels are not lit. After the signal writing period ends, the lighting period starts and the pixels are lit. The length of the lighting period at that time is 1. Next, the next subframe starts, and a signal for one screen is input to all pixels in the signal writing period. During this time, the pixels are not lit. After the signal writing period ends, the lighting period starts and the pixels are lit. The length of the lighting period at that time is 2.

By repeating the same, the lighting periods are arranged in the order of 1, 2, 4, 8, 16, 1.

As described above, the driving method in which the signal writing period and the lighting period are separated from each other is preferably applied to the plasma display. In the case of using for a plasma display, an initialization operation or the like is required. However, it is omitted for simplicity.

This driving method is also preferably applied to an organic EL display, a field emission display, a display using a digital micromirror device (DMD), and the like.

FIG. 14 shows a pixel configuration in that case. The gate line 1607 is selected, the selection transistor 1603 is turned on, and a signal is input from the signal line 1605 to the storage capacitor 1602. Then, the current of the drive transistor 1603 is controlled according to the signal, and the first power line 16
A current flows from 06 to the second power supply line 1608 through the display element 1604.

Note that in the signal writing period, the potential of the first power supply line 1606 and the second power supply line 1608 is controlled so that no voltage is applied to the display element 1604. As a result, the display element 1604 can be prevented from being lit during the signal writing period.

Next, FIG. 15 shows a timing chart in the case where the period for writing a signal to the pixel and the lighting period are not separated. When a signal writing operation is performed in each row, the lighting period starts immediately.

In a certain row, a signal is written, and after a predetermined lighting period ends, a signal writing operation in the next subframe is started. By repeating this, the length of the lighting period is arranged in the order of 1, 2, 4, 8, 16, 1.

This makes it possible to arrange many subframes in one frame even if the signal writing operation is slow.

Such a driving method is preferably applied to a plasma display. In the case of using for a plasma display, an initialization operation or the like is necessary, but it is omitted for simplicity.

This driving method is also preferably applied to an organic EL display, a field emission display, a display using a digital micromirror device (DMD), and the like.

FIG. 16 shows a pixel configuration in that case. The first gate line 1807 is selected, the first selection transistor 1801 is turned on, and a signal is input from the first signal line 1805 to the storage capacitor 1802. Then, the current of the driving transistor 1803 is controlled according to the signal, and current flows from the first power supply line 1806 through the display element 1804 to the second power supply line 1808. Similarly, the second gate line 1817 is selected, the second selection transistor 1811 is turned on, and a signal is input from the second signal line 1815 to the storage capacitor 1802. Then, the current of the driving transistor 1803 is controlled according to the signal, and current flows from the first power supply line 1806 through the display element 1804 to the second power supply line 1808.

The first gate line 1807 and the second gate line 1817 can be controlled separately. Similarly, the first
The signal line 1805 and the second signal line 1815 can be controlled separately. Accordingly, it is possible to input signals to pixels for two rows at the same time, so that a driving method as shown in FIG. 15 can be realized.

Note that the driving method shown in FIG. 15 can be realized by using the circuit shown in FIG. FIG. 17 shows a timing chart in that case. As shown in FIG. 17, one gate selection period is divided into a plurality (two in FIG. 17). Then, each gate line is selected within the divided selection period, and a corresponding signal is input to the signal line 1605 at that time. For example, in one gate selection period, the first half selects the i-th row and the second half selects the j-th row. Then, it is possible to operate as if two rows are selected at the same time in one gate selection period.

  Such a driving method can be applied in combination with the present invention.

Next, FIG. 18 shows a timing chart in the case of performing an operation of erasing a pixel signal. In each row, a signal writing operation is performed, and the pixel signal is erased before the next signal writing operation is performed. In this way, the length of the lighting period can be easily controlled.

In a certain row, a signal is written, and after a predetermined lighting period ends, a signal writing operation in the next subframe is started. If the lighting period is short, a signal erasing operation is performed to turn off the light. By repeating such an operation, the length of the lighting period becomes 1
2, 4, 8, 16, 1 are arranged in this order.

In FIG. 18, the signal erasing operation is performed when the lighting periods are 1 and 2.
It is not limited to this. The erase operation may be performed in other lighting periods.

This makes it possible to arrange many subframes in one frame even if the signal writing operation is slow. Further, when performing an erasing operation, it is not necessary to acquire erasing data in the same manner as a video signal, so that the driving frequency of the source driver can be reduced.

Such a driving method is preferably applied to a plasma display. In the case of using for a plasma display, an initialization operation or the like is necessary, but it is omitted for simplicity.

This driving method is also preferably applied to an organic EL display, a field emission display, a display using a digital micromirror device (DMD), and the like.

FIG. 19 shows a pixel configuration in that case. The first gate line 2107 is selected, the selection transistor 2101 is turned on, and a signal is input from the signal line 2105 to the storage capacitor 2102. Then, the current of the driving transistor 2103 is controlled according to the signal, and current flows from the first power supply line 2106 through the display element 2104 to the second power supply line 2108.

When it is desired to erase the signal, the second gate line 2117 is selected and the erase transistor 211 is selected.
1 is turned on so that the driving transistor 2103 is turned off. Then
Current does not flow from the first power supply line 2106 to the second power supply line 2108 through the display element 2104. As a result, a non-lighting period can be created and the length of the lighting period can be freely controlled.

In FIG. 19, the erase transistor 2111 is used, but another method may be used. This is because it is only necessary to forcibly create a non-lighting period, so that no current is supplied to the display element 2104. Therefore, the display element 21 is connected from the first power supply line 2106.
A switch may be arranged somewhere along the path through which the current flows through the second power supply line 2108 through 04 and the on / off state of the switch is controlled to create a non-lighting period. Alternatively, the gate-source voltage of the drive transistor 2103 may be controlled so that the drive transistor is forcibly turned off.

FIG. 20 shows an example of a pixel configuration in the case where the driving transistor is forcibly turned off. Select transistor 2201, drive transistor 2203, erase diode 2211, display element 22
04 is arranged. The source and drain of the selection transistor 2201 are respectively connected to the signal line 2
205 and the gate of the driving transistor 2203 are connected. Select transistor 220
1 gate is connected to the first gate line 2107. The source and drain of the driving transistor 2203 are connected to the power supply line 2206 and the display element 2204, respectively. The erasing diode 2211 is connected to the gate of the driving transistor 2203 and the second gate line 2217.

The storage capacitor 2202 serves to hold the gate potential of the driving transistor 2203. Therefore, although connected between the gate of the driving transistor 2203 and the power supply line 2206, the invention is not limited to this. It is only necessary that the gate potential of the driving transistor 2203 be arranged so as to be held. In the case where the gate potential of the driving transistor 2203 can be held using the gate capacitance of the driving transistor 2203 or the like, the holding capacitor 2202 may be omitted.

As an operation method, the first gate line 2207 is selected, the selection transistor 2201 is turned on, and a signal is input from the signal line 2205 to the storage capacitor 2202. Then, the current of the driving transistor 2203 is controlled according to the signal, and current flows from the first power supply line 2106 to the second power supply line 2108 through the display element 2104.

When the signal is to be erased, the second gate line 2117 is selected (here, a high potential is set).
Then, the erasing diode 2211 is turned on so that a current flows from the second gate line 2117 to the gate of the driving transistor 2203. As a result, the driving transistor 2203 is turned off. Then, no current flows from the first power supply line 2206 to the second power supply line 2208 through the display element 2204. As a result, a non-lighting period can be created,
The length of the lighting period can be freely controlled.

When it is desired to hold the signal, the second gate line 2117 is not selected (here, set to a low potential). Then, since the erasing diode 2211 is turned off, the gate potential of the driving transistor 2203 is held.

The erasing diode 2211 may be anything as long as it has a rectifying property. A PN-type diode, a PIN-type diode, a Schottky diode, or a Zener-type diode may be used.

Alternatively, a transistor may be used by diode connection (gate and drain connected). A circuit diagram in that case is shown in FIG. As the erasing diode 2211, a diode-connected transistor 2311 is used. Here, an N-channel type is used, but the present invention is not limited to this. A P-channel type may be used.

As another circuit, the driving method as shown in FIG. 18 can be realized by using the circuit shown in FIG. FIG. 17 shows a timing chart in that case. As shown in FIG. 17, one gate selection period is divided into a plurality (two in FIG. 17). Then, each gate line is selected within the divided selection period, and a signal (a video signal and a signal for erasing) corresponding to the gate line is input to the signal line 1605 at that time. For example, in one gate selection period, the first half is i
Select the line, and select the j line in the second half. When the i-th row is selected, such a video signal is input. On the other hand, when the j-th row is selected, a signal that turns off the driving transistor is input. Then, it is as if 2 at the same time in one gate selection period.
It is possible to operate as if a line is selected.

  Such a driving method can be applied in combination with the present invention.

Note that the timing chart, the pixel configuration, and the driving method shown in this embodiment mode are examples, and the present invention is not limited to this. The present invention can be applied to various timing charts, pixel configurations, and driving methods.

Note that the appearance order of the subframes may change depending on the time. For example, the appearance order of subframes may change between the first frame and the second frame. Further, the appearance order of subframes may vary depending on the location. For example, the appearance order of the subframes may be changed between the pixel A and the pixel B. In addition, by combining them, the appearance order of the subframes may change with time and change with place.

Note that although a lighting period, a signal writing period, and a non-lighting period are arranged in one frame period in this embodiment mode, the present invention is not limited to this. Other operation periods may be arranged. For example, a period in which the voltage applied to the display element has a polarity opposite to that of the normal voltage, that is, a so-called reverse bias period may be provided. By providing the reverse bias period, the reliability of the display element may be improved.

Note that the pixel structure described in this embodiment is not limited thereto. Any structure can be applied as long as it has a similar function.

Note that the description in this embodiment can be implemented in free combination with the content described in Embodiment 1.

(Embodiment 3)
In this embodiment mode, an example of a display device using the driving method of the present invention will be described.

The most typical display device is a plasma display. A pixel of a plasma display can take only two states of light emission and non-light emission. Therefore, the time gray scale method is used as one of means for increasing the gray scale. Therefore, the present invention can be applied to that portion.

Note that in a plasma display, it is necessary to initialize a pixel in addition to writing a signal to the pixel. Therefore, it is desirable that the subframes are arranged in order in the portion using the overlapping time gray scale method, and that no subframe in the binary code time gray scale method is inserted between them. By arranging subframes in this way, the number of pixel initializations can be reduced. As a result, the contrast can be improved.

However, if subframes in the binary code time gray scale method are arranged together, a pseudo contour is generated due to the portion. Therefore, it is desirable to arrange the subframes in the binary code time gray scale method so as to be dispersed within one frame as much as possible. When subframes in the binary code time gray scale method are used, it is necessary to perform initialization corresponding to each subframe. Therefore, even if the subframes in the binary code time gray scale method are distributed and arranged, it does not cause a big problem. On the other hand, in the case of the superframe time gray scale subframe, if the lit subframes are arranged continuously,
There is no need to initialize. Therefore, it is desirable to arrange them in order as much as possible.

Therefore, in the case of using a combination of the superimposing time gray scale subframe and the binary code time gray scale subframe, the subframe appearing in the superposition time gray scale is turned on as the order of appearance of the subframes. It is desirable that the subframes in the binary code time gray scale method are distributed and arranged between the subframes in the superposition time gray scale method. As a result, the number of initializations can be reduced, the contrast can be improved, and the occurrence of pseudo contours can be reduced.

Examples of display devices other than plasma displays include organic EL displays, field emission displays, displays using digital micromirror devices (DMD), ferroelectric liquid crystal displays, and bistable liquid crystal displays. These are all display devices that can use the time gray scale method. By applying the present invention to these display devices, pseudo contour can be reduced while using the time gray scale method.

For example, in the case of an organic EL display, it is not necessary to initialize pixels. Therefore, it does not happen that light is emitted during initialization and the contrast is reduced.
Therefore, the appearance order of subframes can be set arbitrarily. It is desirable to arrange them so that pseudo contours do not occur as much as possible.

Therefore, the superframe time gray scale subframes are arranged so that the lit subframes are continuous, and the binary code time grayscale subframes are arranged between the superposition time grayscale subframes. It may be arranged in a distributed manner. As a result, the overlapping time gray scale subframes are arranged to some extent within one frame. Therefore, when changing from the first frame to the second frame, it is possible to reduce the occurrence of a pseudo contour at the switching point. So-called moving image pseudo contour can be reduced. In addition, since the subframes in the binary code time gray scale method are arranged in a distributed manner, pseudo contour can be reduced.

In addition, the subframes of the overlapping time gray scale method may be arranged separately, and the subframes of the binary code time gray scale method may be arranged separately. As a result, the pseudo contour caused by the binary code time gray scale method is mixed with the superframe time gray scale subframe, so that the effect of reducing the pseudo contour as a whole is enhanced.

Note that the description in this embodiment can be implemented in free combination with the contents described in Embodiments 1 and 2.

(Embodiment 4)
In this embodiment, structures and operations of a display device, a signal line driver circuit, a gate line driver circuit, and the like are described.

As shown in FIG. 22, the display device includes a pixel array 2401, a gate line driver circuit 2402, and a signal line driver circuit 2410. The gate line driver circuit 2402 sequentially outputs a selection signal to the pixel array 2401. The gate line driver circuit 2402 includes a shift register, a buffer circuit, and the like.

In addition, the gate line driver circuit 2402 often includes a level shifter circuit, a pulse width control circuit, and the like. The shift register outputs pulses that are sequentially selected. The signal line driver circuit 2410 sequentially outputs video signals to the pixel array 2401.
The shift register 2403 outputs pulses that are sequentially selected. Pixel array 24
In 01, an image is displayed by controlling the state of light according to the video signal. A video signal input from the signal line driver circuit 2410 to the pixel array 2401 is often a voltage. In other words, the display elements arranged in each pixel and the elements that control the display elements change states according to the video signal (voltage) input from the signal line driver circuit 2410. Examples of the display element arranged in the pixel include an EL element, an element used in an FED (field emission display), a liquid crystal, a DMD (digital micromirror device), and the like.

Note that a plurality of gate line driver circuits 2402 and signal line driver circuits 2410 may be provided.

The signal line driver circuit 2410 is divided into a plurality of parts. In general, as an example, a shift register 2403, a first latch circuit (LAT1) 2404, a second latch circuit (LAT2)
2405 and the amplifier circuit 2406. The amplifier circuit 2406 may have a function of converting a digital signal into analog or a function of performing gamma correction.

Further, the pixel has a display element such as an EL element. A circuit that outputs a current (video signal) to the display element, that is, a current source circuit may be provided.

Therefore, the operation of the signal line driver circuit 2410 will be briefly described. The shift register 2403 receives a clock signal (S-CLK), a start pulse (SP), and a clock inversion signal (S-CLKb), and sequentially outputs sampling pulses according to the timing of these signals.

The sampling pulse output from the shift register 2403 is supplied to the first latch circuit (LAT
1) Input to 2404. The first latch circuit (LAT1) 2404 has a video signal line 24
From 08, the video signal is input, and the video signal is held in each column according to the timing at which the sampling pulse is input.

When the first latch circuit (LAT1) 2404 completes holding the video signal up to the last column, a latch pulse (Latch Pulse) is input from the latch control line 2409 during the horizontal blanking period, and the first latch circuit (LAT1) The video signals held in 2404 are transferred to the second latch circuit (LAT2) 2405 all at once. After that, the video signal held in the second latch circuit (LAT2) 2405 is input to the amplifier circuit 2406 for one row at the same time. And
A signal output from the amplifier circuit 2406 is input to the pixel array 2401.

While the video signal held in the second latch circuit (LAT2) 2405 is input to the amplifier circuit 2406 and is input to the pixel 2401, the shift register 2403 outputs a sampling pulse again. That is, two operations are performed simultaneously. Thereby, line-sequential driving becomes possible. Thereafter, this operation is repeated.

Note that the signal line driver circuit and a part thereof (such as a current source circuit and an amplifier circuit) are included in the pixel array 2401.
For example, an external IC chip may be used.

Note that the structures of the signal line driver circuit, the gate line driver circuit, and the like are not limited to those in FIGS. For example, a signal may be supplied to the pixel by dot sequential driving. The signal line driver circuit 2510 in that case
An example of this is shown in FIG. A sampling pulse is output from the shift register 2503 to the sampling circuit 2504. A video signal is input from the video signal line 2508, and the video signal is output to the pixel 2501 in accordance with the sampling pulse.

Note that as described above, the transistor in the present invention may be any type of transistor, and may be formed on any substrate. Therefore, the circuits as shown in FIGS. 22 and 23 may all be formed on a glass substrate, may be formed on a plastic substrate, or may be formed on a single crystal substrate. It may be formed on an SOI substrate or on any substrate. Alternatively, FIG.
Alternatively, part of the circuit in FIG. 23 may be formed on a certain substrate, and another part of the circuit in FIG. 22 or FIG. 23 may be formed on another substrate. That is, all the circuits in FIGS. 22 and 23 may not be formed on the same substrate. For example, in FIG. 22 and FIG.
The pixel 2401 and the gate line driver circuit 2402 are formed using a TFT over a glass substrate, and the signal line driver circuit 2410 (or part thereof) is formed over a single crystal substrate.
You may connect by COG (Chip On Glass) and arrange | position on a glass substrate. Alternatively, the IC chip may be connected to the glass substrate using TAB (Tape Auto Bonding) or a printed board.

Note that the contents described in the present embodiment correspond to those using the contents described in the first to third embodiments. Therefore, the contents described in Embodiments 1 to 3 can be applied to this embodiment.

(Embodiment 5)
Next, a pixel layout in the display device of the present invention will be described. As an example, see FIG.
A layout diagram of the circuit diagram shown in FIG. 1 is shown in FIG. Note that the circuit diagrams and layout diagrams are not limited to FIGS. 21 and 24.

A selection transistor 2601, a driving transistor 2603, an erasing diode 2611, and a display element power 2604 are arranged. The source and drain of the selection transistor 2601 are connected to the signal line 2605 and the gate of the driving transistor 2603, respectively. The gate of the selection transistor 2601 is connected to the first gate line 2107. The source and drain of the driving transistor 2603 are connected to the power supply line 2606 and the display element 2604, respectively. The diode-connected erasing transistor 2611 includes a driving transistor 2603.
Are connected to the second gate line 2617. The storage capacitor 2602 is connected between the gate of the driving transistor 2603 and the power supply line 2606.

The signal line 2605 and the power supply line 2606 are formed by the second wiring, and the first gate line 210 is formed.
7. The second gate line 2617 is formed by the first wiring.

In the case of the top gate structure, the substrate, the semiconductor layer, the gate insulating film, the first wiring, the interlayer insulating film,
A film | membrane is comprised in order of a 2nd wiring. In the case of the bottom gate structure, the film is formed in the order of the substrate, the first wiring, the gate insulating film, the semiconductor layer, the interlayer insulating film, and the second wiring.

Note that the contents described in this embodiment can be implemented by being freely combined with the contents described in Embodiments 1 to 4.

(Embodiment 6)
In the present embodiment, hardware for controlling the driving method described in the first to fifth embodiments will be described.

A rough block diagram is shown in FIG. A pixel array 2704 is arranged on the substrate 2701. In many cases, a signal line driver circuit 2706 and a gate line driver circuit 2705 are provided. In addition, a power supply circuit, a precharge circuit, a timing generation circuit, and the like may be arranged. In some cases, the signal line driver circuit 2706 and the gate line driver circuit 2705 are not provided. In that case, what is not arranged on the substrate 2701 is often formed in an IC. In many cases, the IC is disposed on the substrate 2701 by COG (Chip On Glass). Alternatively, an IC may be arranged on the connection board 2707 that connects the peripheral circuit board 2702 and the board 2701.

A signal 2703 is input to the peripheral circuit board 2702. And the controller 270
8 controls and the signal is stored in the memory 2709, the memory 2710, or the like. Signal 2703
Is an analog signal, after analog-to-digital conversion, and then the memory 2709
Or the memory 2710 or the like. Then, the controller 2708 outputs a signal to the substrate 2701 using a signal stored in the memory 2709, the memory 2710, or the like.

In order to realize the driving method described in Embodiment Modes 1 to 5, the controller 2708 controls the appearance order of subframes and outputs a signal to the substrate 2701.

Note that the contents described in this embodiment mode can be implemented by being freely combined with the contents described in Embodiment Modes 1 to 5.

(Embodiment 7)
An example of a structure of a mobile phone having a display portion using the display device of the present invention and a display device using the driving method thereof is described with reference to FIG.

The display panel 5410 is incorporated in a housing 5400 so as to be detachable. Housing 54
00 can be changed as appropriate in accordance with the size of the display panel 5410. A housing 5400 to which the display panel 5410 is fixed is fitted into a printed board 5401 and assembled as a module.

The display panel 5410 is connected to the printed board 5401 through the FPC 5411. A printed board 5401 includes a speaker 5402, a microphone 5403, and a transmission / reception circuit 54.
04, a signal processing circuit 5405 including a CPU and a controller is formed. Such a module is combined with an input means 5406 and a battery 5407 to form a housing 5409.
And 5412. The pixel portion of the display panel 5410 is arranged so as to be visible from an opening window formed in the housing 5409.

In the display panel 5410, a pixel portion and some peripheral driver circuits (a driver circuit having a low operating frequency among a plurality of driver circuits) are formed over a substrate using TFTs, and some peripheral driver circuits (a plurality of driver circuits) are formed. A driving circuit having a high operating frequency among the circuits) may be formed over the IC chip, and the IC chip may be mounted on the display panel 5410 by COG (Chip On Glass). Or its IC
The chip may be connected to the glass substrate using TAB (Tape Auto Bonding) or a printed board. Note that FIG. 27A shows an example of a structure of a display panel in which some peripheral drive circuits are formed integrally with a pixel portion on a substrate and an IC chip on which other peripheral drive circuits are formed is mounted by COG or the like. is there. Note that the structure of the display panel in FIG. 27A includes a substrate 5300 and a signal line driver circuit 530.
1, a pixel portion 5302, a scan line driver circuit 5303, a scan line driver circuit 5304, and an FPC 530
5, an IC chip 5306, an IC chip 5307, a sealing substrate 5308, and a sealant 5309. With such a structure, low power consumption of the display device can be achieved, and the use time by one charge of the mobile phone can be extended. In addition, the cost of the mobile phone can be reduced.

In addition, by performing impedance conversion of a signal set to the scanning line or the signal line using a buffer, the pixel writing time for each row can be shortened. Therefore, a high-definition display device can be provided.

Further, in order to further reduce power consumption, a pixel portion is formed on a substrate using TFTs as shown in FIG. 27B, and all peripheral drive circuits are formed on an IC chip. You may mount in a display panel by COG (Chip On Glass). 26B includes a substrate 5310, a signal line driver circuit 5311, a pixel portion 5312, a scan line driver circuit 5313, a scan line driver circuit 5314, an FPC 5315, an IC chip 5316, and an IC.
A chip 5317, a sealing substrate 5318, and a sealant 5319 are included.

Then, by using the display device of the present invention and its driving method, it is possible to view a clear image with reduced pseudo contour. Therefore, even an image whose gradation changes slightly like human skin can be displayed neatly.

Further, the configuration shown in this embodiment is an example of a mobile phone, and the display device of the present invention is not limited to the mobile phone having such a configuration, and can be applied to mobile phones having various configurations.

(Embodiment 8)
FIG. 28 shows an EL module in which a display panel 5701 and a circuit board 5702 are combined. A display panel 5701 includes a pixel portion 5703, a scan line driver circuit 5704, and a signal line driver circuit 5705. The circuit board 5702 includes, for example, a control circuit 570.
6 and a signal dividing circuit 5707 are formed. Display panel 5701 and circuit board 570
2 are connected by a connection wiring 5708. An FPC or the like can be used for the connection wiring.

The control circuit 5706 corresponds to the controller 2708, the memory 2709, the memory 2710, and the like in the seventh embodiment. Mainly in the control circuit 5706,
Controls the appearance order of subframes.

In the display panel 5701, a pixel portion and some peripheral driver circuits (a driver circuit having a low operating frequency among a plurality of driver circuits) are integrally formed using a TFT on a substrate, and some peripheral driver circuits (a plurality of driver circuits) are formed. A driving circuit having a high operating frequency) is formed on the IC chip, and the IC chip is formed on the C chip.
It may be mounted on the display panel 5701 by OG (Chip On Glass) or the like. Or its IC
The chip may be mounted on the display panel 5701 using TAB (Tape Auto Bonding) or a printed board. FIG. 27A shows an example of a configuration in which some peripheral drive circuits are formed integrally with a pixel portion on a substrate and an IC chip on which other peripheral drive circuits are formed is mounted by COG or the like.
With such a structure, low power consumption of the display device can be achieved, and the use time by one charge of the mobile phone can be extended. In addition, the cost of the mobile phone can be reduced.

In addition, by performing impedance conversion of a signal set to the scanning line or the signal line using a buffer, the pixel writing time for each row can be shortened. Therefore, a high-definition display device can be provided.

In order to further reduce power consumption, a pixel portion is formed on a glass substrate using a TFT, all signal line driver circuits are formed on an IC chip, and the IC chip is formed on a COG (Chip On Glass).
) It may be mounted on a display panel.

Note that a pixel portion is formed using a TFT over a substrate, all peripheral driver circuits are formed over an IC chip, and the IC chip is mounted on a display panel by COG (Chip On Glass). Note that an IC chip in which a pixel portion is formed on a substrate and a signal line driver circuit is formed on the substrate is COG.
An example of the configuration implemented by the above is shown in FIG.

With this EL module, an EL television receiver can be completed. FIG.
It is a block diagram which shows the main structures of L television receiver. A tuner 5801 receives video signals and audio signals. The video signal includes a video signal amplifying circuit 5802, a video signal processing circuit 5803 that converts a signal output from the video signal into a color signal corresponding to each color of red, green, and blue, and uses the video signal as input specifications of the drive circuit. Processing is performed by a control circuit 5706 for conversion. The control circuit 5706 outputs a signal to each of the scan line side and the signal line side. In the case of digital driving, a signal dividing circuit 5707 may be provided on the signal line side, and an input digital signal may be divided into m pieces and supplied.

Of the signals received by the tuner 5801, the audio signal is sent to the audio signal amplifier circuit 5804, and the output is supplied to the speaker 5806 via the audio signal processing circuit 5805. The control circuit 5807 receives control information on the receiving station (reception frequency) and volume from the input unit 5808 and sends a signal to the tuner 5801 and the audio signal processing circuit 5805.

A television receiver can be completed by incorporating an EL module into a housing. A display portion is formed by the EL module. In addition, speakers, video input terminals, and the like are provided as appropriate.

Of course, the present invention is not limited to a television receiver, and is applied to various uses as a display medium of a particularly large area such as a monitor of a personal computer, an information display board in a railway station or airport, an advertisement display board in a street, etc. can do.

As described above, by using the display device of the present invention and its driving method, it is possible to view a beautiful image with reduced pseudo contour. Therefore, even an image whose gradation changes slightly like human skin can be displayed neatly.

(Embodiment 9)
Electronic devices to which the present invention can be applied include desktop, floor-standing, or wall-mounted displays, video cameras, digital cameras, goggles-type displays (head-mounted displays), navigation systems, sound playback devices (car audio, audio components, etc.), Computer, game device, portable information terminal (mobile computer, cellular phone, portable game machine, electronic book, etc.), and image playback device (specifically Digital
And a device equipped with a display capable of reproducing and displaying video and still images recorded on a recording medium such as Versatile Disc (DVD). Specific examples of these electronic devices are shown in FIG.
0 (A) to 30 (H).

FIG. 30A shows a desktop, floor-standing, or wall-mounted display.
1, a support base 302, a display unit 303, a speaker unit 304, a video input terminal 305, and the like. The present invention can be used for a display device constituting the display unit 303. Such a display can be used as an arbitrary information display device such as a personal computer, a TV broadcast receiver, and an advertisement display. As a result, it is possible to provide a display that can perform a clean display without false contours.

FIG. 30B illustrates a digital camera, which includes a main body 311, a display portion 312, an image receiving portion 313, operation keys 314, an external connection port 315, a shutter 316, and the like. The present invention relates to the display unit 31.
2 can be used. As a result, it is possible to provide a digital camera that can display cleanly without false contours.

FIG. 30C illustrates a computer, which includes a main body 321, a housing 322, a display portion 323, a keyboard 324, an external connection port 325, a pointing mouse 326, and the like. The present invention can be used for a display device constituting the display portion 323. As a result, it is possible to provide a computer that can perform clean display without false contours. The computer has
A so-called notebook computer in which a central processing unit (CPU), a recording medium, and the like are integrated, and a so-called desktop computer separated from each other are included.

FIG. 30D illustrates a mobile computer, which includes a main body 331, a display portion 332, and a switch 3.
33, an operation key 334, an infrared port 335, and the like. The present invention can be used for a display device constituting the display portion 332. As a result, it is possible to provide a mobile computer that can perform a clean display without false contours.

FIG. 30E shows a portable image reproducing device (specifically, a DVD reproducing device) provided with a recording medium.
A main body 341, a housing 342, a first display portion 343, a second display portion 344, a recording medium (D
VD or the like) includes a reading unit 345, operation keys 346, a speaker unit 347, and the like. Although the first display unit 343 mainly displays image information and the second display unit 344 mainly displays character information, the present invention can be used for display devices that constitute the first and second display units 343 and 344. . As a result, it is possible to provide an image reproducing apparatus that can perform a clear display without false contours. Note that an image reproducing device provided with a recording medium includes a home game machine and the like.

FIG. 30F illustrates a goggle type display (head mounted display), which includes a main body 351, a display portion 352, and an arm portion 353. The present invention can be used for a display device constituting the display portion 352. As a result, it is possible to provide a goggle type display that can perform a clean display without false contours.

FIG. 30G shows a video camera, which includes a main body 361, a display portion 362, a housing 363, an external connection port 364, a remote control receiving portion 365, an image receiving portion 366, a battery 367, an audio input portion 368, operation keys 369, and the like. . The present invention can be used for a display device constituting the display portion 362. As a result, it is possible to provide a video camera that can perform a clean display without false contours.

FIG. 30H illustrates a mobile phone, which includes a main body 371, a housing 372, a display portion 373, a voice input portion 374, a voice output portion 375, operation keys 376, an external connection port 377, and an antenna 378.
Etc. The present invention can be used for a display device constituting the display portion 373. as a result,
It is possible to provide a mobile phone that can perform clean display without false contours.

The display unit of the electronic device as described above may be a self-luminous type using a light emitting element such as an LED or an organic EL for each pixel, or may use another light source such as a backlight like a liquid crystal display. It can also be, but in the case of a self-luminous type, no backlight is needed,
The display portion can be thinner than the liquid crystal display.

In addition, the electronic device often displays information distributed through an electronic communication line such as the Internet or CATV (cable television), or is used as a TV receiver, and in particular, the opportunity to display moving image information increases. It is coming. If the display is self-luminous, organic E
Since the response speed of the light emitting material such as L is much faster than that of the liquid crystal, it is suitable for such moving image display. Moreover, it is preferable also in performing time-division driving. If the light emission luminance of the light emitting material is increased in the future, the light including the output image information can be enlarged and projected by a lens or the like and used for a front type or rear type projector.

In the self-luminous display unit, the light emitting part consumes power, and thus it is desirable to display information so that the light emitting part is minimized. Therefore, when a display unit mainly including character information such as a portable information terminal, particularly a mobile phone or a sound reproducing device is a self-luminous type, the character information is formed by the light emitting part with the non-light emitting part as the background. It is desirable to drive.

As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields.

Claims (1)

A display device that expresses gradation by dividing one frame into a plurality of subframes,
The plurality of subframes have M (M is an integer of 2 or more) normal subframes necessary for representing a predetermined gradation, and N (N is a natural number) additional subframes,
A first subframe lighting pattern that uses only the regular subframe for at least one grayscale level within the predetermined gradation, and a second subframe lighting pattern that uses the additional subframe and the regular subframe. A display device, wherein at least two subframe lighting patterns are set.

Images