JP5392965B2 - Display device - Google Patents

Description

The present invention relates to a display device that performs display by a time gray scale method and a driving method of the display device.

A time scale in which gradation is displayed by using a binary voltage of a digital video signal as a driving method of a light emitting device which is one of display devices, and controlling a time during which a pixel emits light during one frame period. There is a law. In general, it can be said that the time gray scale method is more suitable because the electroluminescent material has a higher response speed than liquid crystal. Specifically, when display is performed by the time gray scale method, one frame period is divided into a plurality of subframe periods. Then, in accordance with the video signal, the pixels are caused to emit light or not in each subframe period. With the above structure, the total length of a period during which a pixel actually emits light during one frame period can be controlled by a video signal to display gradation.

However, when displaying by the time gray scale method, there is a problem that a pseudo contour is displayed in the pixel portion depending on the frame frequency. Pseudo contour is an unnatural contour line that is often seen when intermediate gray levels are displayed by the time gray scale method, and is mainly caused by fluctuations in perceived luminance caused by human visual characteristics. .

As a technique for preventing the above-described pseudo contour, Patent Document 1 below describes a plasma display driving method in which a subframe period in a light emission state appears continuously within one frame period. According to the above driving method, a situation in which a period in which light emission is performed and a period in which light emission is not performed in one frame period does not reverse each other between adjacent frame periods can be prevented, so that a pseudo contour can be suppressed. It is said that.
JP 2000-231362 A

However, in the driving method described in Patent Document 1, the total number of gradations matches the number of subframe periods that appear within one frame period. Therefore, if the number of subframe periods is increased in order to increase the total number of gradations, it is necessary to shorten each subframe period. However, in a normal display device, a video signal must be input to all rows of pixels every subframe period. Therefore, when the subframe period is too short, it is necessary to increase the drive frequency of the drive circuit. Therefore, considering the reliability of the drive circuit, it is not preferable to shorten the subframe period unnecessarily.

Note that each subframe period can be lengthened to some extent by lengthening the frame period. However, even if the frame period is lengthened, it is not possible to expect a dramatic increase in the total number of gradations, and it is not preferable because pseudo contours are more likely to occur.

Therefore, Patent Document 1 also describes a technique for performing pseudo image processing such as dithering and increasing the total number of gradations to be displayed in a pseudo manner without increasing the number of subframes. However, when image processing such as dithering is performed, a high total number of gradations can be displayed. However, since the image is displayed in a rough manner as if sand is sown, deterioration in image quality is inevitable.

In view of the above-described problems, an object of the present invention is to propose a driving method of a display device that can suppress the generation of a pseudo contour while suppressing the driving frequency of a driving circuit. Another object of the present invention is to propose a method for driving a display device that can suppress the occurrence of pseudo contours while suppressing deterioration in image quality.

Another object of the present invention is to propose a display device that can suppress the generation of pseudo contours while suppressing the drive frequency of the drive circuit. Another object of the present invention is to propose a display device that can suppress the occurrence of a pseudo contour while suppressing a decrease in image quality.

In view of the above problems, the present invention is characterized in that the display device is provided with tables each storing data defining subframes in a light emission state among a plurality of subframe periods. A plurality of subframe periods are determined for an arbitrary pixel from a plurality of pixels. Such a table is stored in a memory.

The specific configuration of the present invention is shown below.

According to one embodiment of the present invention, a plurality of tables storing data defining subframe periods in which light emission is performed, a controller that outputs a video signal according to the data, and a pixel gradation according to the output video signal The display device is characterized in that the plurality of tables differ between adjacent pixels in the pixel portion.

According to another aspect of the present invention, a plurality of tables storing data defining subframe periods in which light emission is performed, a controller that outputs a video signal according to the data, and a pixel gradation according to the output video signal A plurality of tables that are different between adjacent pixels in the pixel portion, and the tables for the pixels are different for each frame period having a sub-frame period. Device.

In the display device of the present invention, the number and length of the plurality of sub-frame periods, characterized in that it is determined in accordance with the sub-frame rate R _SF obtained by the sharing ratio R _sh.

In the display device of the present invention, a combination of subframe periods determined for displaying a certain gradation is different between a plurality of tables.

  The display device of the present invention includes a light emitting device including a light emitting element represented by an organic light emitting element (OLED), a liquid crystal display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), and an FED (Field Emission Display). ), And other display devices capable of displaying by the time gray scale method are included in the category. The light-emitting device refers to a state including a panel in which the light-emitting element is sealed and a module in which an IC or the like including a controller is mounted on the panel.

One embodiment of a display device driving method according to the present invention includes a plurality of tables that have at least adjacent first pixels and second pixels and store data defining subframe periods in which light emission is performed. The selected first table is provided for the first pixel, and the second table selected from the plurality of tables is provided for the second pixel.

Another embodiment of the method for driving a display device according to the present invention includes a plurality of tables having at least adjacent first pixels and second pixels and storing data defining subframe periods in which light is emitted. The selected first table is provided for the first pixel, the second table selected from the plurality of tables is provided for the second pixel, and a certain gradation is displayed between the plurality of tables. Therefore, the combinations of subframe periods determined for this purpose are different.

In the driving method of the display device of the present invention, the first table and the second table are exchanged for each frame period having a sub-frame period.

Thus, by providing a table for each of at least two or more pixels, the occurrence of pseudo contours can be reduced. Further, by changing the first table and the second table every frame period, the generation of pseudo contours can be further reduced.

Embodiments of the present invention will be described below 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. Note that in all the drawings for describing the embodiments, the same portions or portions having similar functions are denoted by the same reference numerals, and repetitive description thereof is omitted.

(Embodiment 1)
In this embodiment, a case where a plurality of tables are used between a plurality of pixels will be described.

As shown in FIG. 1, the pixel unit 100 includes a plurality of pixels 101. Among the pixels 101, different tables (Table a, b) are provided for arbitrary adjacent pixels (A) and (B). In other words, a table a and a table b selected from a plurality of tables storing data defining subframe periods in which light emission is performed are prepared, and a table a is provided for the adjacent pixel (A). A table b is provided for the pixel (B).

At this time, the arrangement of adjacent pixels (A) and (B) can be expressed as (m, n) (m, n + 1). Here, m is an arbitrary number of pixels in the row direction in the pixel portion, and n is an arbitrary number of pixels in the column direction in the pixel portion. At this time, in the next row (m + 1), the pixels (A) and (B) are arranged so as not to be adjacent vertically. That is, in the (m + 1) th row, the arrangement of the pixels (A) and (B) is (m + 1, n + 1) (m + 1, n). Looking at the arrangement of such pixels as a whole, the pixels (A) and (B) are diagonal.

The tables a and b provided for the pixels arranged in this way are set to display a certain gradation at different timings. In order to display gradations at different timings as described above, the length of the subframe period is determined in consideration of the sharing rate. Note that the sharing rate is a ratio of the length of a subframe period in which light is emitted in common in two frame periods in which gradation is different by one step.

The specific sharing rate is calculated by dividing the frame period into sub-frame periods SF _{1 to} SF ₃ , and emitting only SF _{3 in the} previous frame period, and all SF _{1 to} SF ₃ in the next frame period. In the case of emitting light, the sharing rate is SF ₃ / (SF ₁ + SF ₂ + SF ₃ ) × 100 (%).

In general, the length of the subframe period is set to be 2 ⁰ : 2 ¹ : 2 ² : 2 ³ :..., But in the present invention, the sharing rate is not limited to this. The length of the subframe period is determined in consideration of the above.

FIG. 16 shows an example of the configuration of the subframe period. FIG. 16 (A) shows the time for displaying the total gray scale level 2 ^4, the configuration of the sub-frame period of the gradation 7 according to the conventional method, the configuration of the sub-frame period of gradation 8. In FIG. 16A, four subframe periods SF _{1 to} SF ₄ are used, and the subframe period SF ₄ is further divided into two. The ratio of the lengths of the subframe periods SF _{1 to} SF ₄ is SF ₁ : SF ₂ : SF ₃ : SF ₄ = 1: 2: 4: 8. Further, the period indicated by BK corresponds to a period (non-display period) in which the light emitting element is forced to be in a non-light emitting state, and thus does not contribute to gradation.

In the case of displaying gradation 7 in FIG. 16A, the subframe periods in the light emitting state are SF ₁ , SF ₂ , SF ₃ , and the subframe periods in the non-light emitting state are SF ₄ . Then, when displaying a gradation 8, subframe periods in a state of light emission SF _4, subframe period in the non-emission state is _{SF 1, SF 2, SF 3} . Therefore, since there is no subframe period in which both are in a light emitting state, the sharing rate is 0%. In such a configuration of the subframe period shown in FIG. 16A, it can be said that a pseudo contour is likely to occur.

FIG. 16B shows a structure of a subframe period in consideration of the sharing rate, unlike FIG. 16A. Figure 16 (B), like the FIG. 16 (A), the shown configuration of the sub-frame period of the tone 7 in displaying the total gray scale level 2 ^4, the configuration of the sub-frame period of gradation 8 ing. In FIG. 16B, eight subframe periods SF _{1 to} SF ₈ are used. The ratio of the lengths of the subframe periods SF _{1 to} SF ₈ is as follows: SF ₁ : SF ₂ : SF ₃ : SF ₄ : SF ₅ : SF ₆ : SF ₇ : SF ₈ = 1: 1: 1: 2: 2: 2: 3: 3. Note that the period indicated by BK corresponds to a non-display period and thus does not contribute to gradation.

When gradation 7 is displayed in FIG. 16B, SF ₃ , SF ₇ , SF ₈ are in the subframe period in the light emission state, and SF ₁ , SF ₂ , SF ₄ are in the subframe period in the non-light emission state. , SF ₅ and SF ₆ . 16B, when gradation 8 is displayed, SF ₆ , SF ₇ , SF ₈ are in the sub-frame period in the light emission state, and SF ₁ , SF ₂ , in the sub-frame period in the non-light emission state. SF ₃ , SF ₄ , and SF ₅ . Therefore, since the subframe periods in which light is emitted in common are SF ₇ and SF ₈ , the sharing rate is (SF ₇ + SF ₈ ) × 100 / (SF ₆ + SF ₇ + SF ₈ ) = 75%. Therefore, it can be said that the configuration of the subframe period illustrated in FIG. 16B is less likely to generate a pseudo contour than the case of FIG.

Further, in the subframe period of the present invention, since a certain gradation such as gradations 7 and 8 is displayed, there are a plurality of combinations of subframe periods in which light emission occurs. For example, in FIG. 16B, when gradation 7 is displayed, subframe periods in a light emission state are (SF ₁ , SF ₇ , SF ₈ ), (SF ₂ , SF ₇ , SF ₈ ), or ( SF ₁ , SF ₄ , SF ₅ , SF ₆ ) and the like. In the case of displaying gradation 8, the subframe period in the light emission state is set to (SF ₆ , SF ₇ , SF ₈ ), (SF ₁ , SF ₂ , SF ₇ , SF ₈ ), or (SF ₁ , SF ₈ ). ₂ , SF ₄ , SF ₅ , SF ₆ ) and the like. Therefore, a different table can be provided for each pixel. The combination of subframe periods can be determined in consideration of the sharing rate. As a result, it is possible to provide a display device in which gradations that do not easily generate pseudo contours are determined according to the table.

Next, a method for determining the length of each subframe period of one frame period from the sharing rate R _sh and the total number of gradations will be specifically described.

First, the sharing rate R _sh is obtained from the frame frequency used for driving. The false contour is less likely to be generated as the frame frequency is higher, and conversely, it is more likely to be generated as the frame frequency is lower. For this reason, if the frame frequency is determined in advance, the lowest sharing rate that will be able to suppress the occurrence of the pseudo contour can be determined for each display device.

FIG. 5 shows an example of the relationship between the frame frequency (Hz) and the lowest sharing rate (%) that can suppress the occurrence of the pseudo contour.

As shown in FIG. 5, the lower the sharing rate, the higher the frame frequency is required to suppress the occurrence of pseudo contours. Note that since the practitioner can appropriately determine whether or not the pseudo contour is generated, the same numerical relationship as in FIG. 5 is not always derived. However, under a certain set criterion, the higher the frame frequency, the more the generation of pseudo contour can be suppressed, and the generation of the pseudo contour can be suppressed. The relationship with the lowest share (%) can be derived.

From the graph shown in FIG. 5, when the lowest sharing rate (%) that can suppress the occurrence of pseudo contours when a specific frame frequency is used is derived, it is equal to or higher than the sharing rate. A sharing rate R _sh having a value of can be determined. After determining the sharing rate R _sh , next, the length of each subframe period is determined from the sharing rate R _sh .

First, it is assumed that n subframe periods included in one frame period are SF _{1 to} SF _{n in} order from the shortest. It is assumed that gradation m (m <2 ⁿ ) can be displayed when all of SF _{1 to} SF _p (p <n) are emitted. In this case, the sub-frame periods SF ₁ - SF _p that emits light when displaying the gradation m, and the length of the total of the T _m, T _m can be expressed by Equation 1 below.

Next, consider the case of displaying gradation (m + 1). Since gradation m can be displayed when all of SF _{1 to} SF _p are emitted, it is necessary to use SF _{p + 1} longer than SF _{p in} order to display gradation (m + 1). is there. At the same time, _one or a plurality of subframe periods corresponding to a value obtained by subtracting a length corresponding to one gradation (for example, a length corresponding to SF ₁ ) from SF _{p + 1 is} excluded from SF _{1 to} SF _p. Need to be displayed. Therefore, if the total length of the subframe periods that emit light when displaying the gradation (m + 1) is T _{m + 1} , T _{m + 1} can be expressed by Equation 2 below.

Here, if the ratio of SF _{p + 1} to Σ (SF _{1 to} SF _{p + 1} ) is the subframe rate R _SF , R _SF can be expressed by the following Equation 3.

From Equation 3, the following Equation 4 can be derived.

Further, if the total length of the sub-frame periods in which both the gray scale m is displayed and the gray scale (m + 1) is displayed is W _{m / m + 1} , W _{m / m + 1} can be represented by the following formula 5.

Therefore, the following Expression 6 is derived from Expression 1, Expression 4, and Expression 5.

Further, the sharing rate R _sh of the sub-frame period in which both the gradation m is displayed and the gradation (m + 1) is displayed is expressed by the following Expression 7.

Therefore, the following Expression 8 is derived from Expression 2, Expression 4, Expression 6, and Expression 7.

Therefore, from Equation 8, the following Equation 9 can be derived.

Therefore, the value of the subframe rate R _SF can be derived by substituting the value of the sharing rate R _sh into Equation 9. Subframe ratio R _SF is the ratio of the SF _{p + 1} for _{Σ (SF 1 ~SF p + 1} ). By using the sub-frame rate R _SF, in order from the longest sub-frame period SF _n, it is possible to determine the length of each sub-frame period.

When the length of the subframe period is determined in consideration of the sharing rate in this way, as described above, a selection range appears in the subframe period in which light is emitted to display a certain gradation. That is, redundancy occurs between a plurality of tables in which data defining subframes in a light emission state is stored. Therefore, a certain table selected from a plurality of tables can be provided for each of the plurality of pixels.

In this way, by providing a table for each of at least two or more pixels, the pseudo contour can be made inconspicuous by distributing gradations at which pseudo contour is likely to occur.

Note that although cases have been described with the present embodiment where a table is provided for each of the pixels (A) and (B), the present invention is not limited to this. For example, when four tables are provided, the pixels provided with the respective tables may be arranged in a rectangular shape. That is, according to the present invention, by providing a table for each of at least two or more pixels, pseudo contours can be prevented as compared with the conventional method.

Note that in the display device that performs the driving method of the present invention described above, a table that outputs a signal determined in response to signal input is a kind of lookup table, and the hardware is a memory such as a ROM or a RAM. Remembered.

In the driving method described in this embodiment, the subframe period may be inverted. For example, within one frame period, a set of subframe periods is inverted at the end. As a result, it is possible to further prevent pseudo contours, particularly moving image pseudo contours.

(Embodiment 2)
In this embodiment, a specific example of a subframe period is shown.

Figure 6 shows a specific example of sub-frame periods in the state of light emission in displaying the total gray scale level is 2 ⁴ using 4-bit video signal. In FIG. 6, the horizontal axis corresponds to the total length (light emission period) of the subframe periods in which the gray scale is on the left and the left vertical axis is in the light emission state. FIG. 6 also shows the sharing rate R _sh (%) when compared with the case where the gradation is one step lower, along with the right vertical axis. FIG. 6 shows an example in which display is performed using _nine subframe periods SF _{1 to} SF ₉ . The ratio of the lengths of the subframe periods SF _{1 to} SF ₉ is 1: 1: 1: 1: 1: 2: 2: 3: 3 in order from SF ₁ .

In this subframe period, there are periods having the same length. Therefore, there are a plurality of combinations of subframe periods selected for displaying a certain gray scale, and different tables can be set according to the combinations.

Such a table is a kind of lookup table. The table is recorded in a memory such as a ROM or a RAM as hardware.

In FIG. 6, the length of each subframe period is determined so that the sharing rate R _sh (%) is maintained at 65% or more when the gradations 4 to 16 are displayed. Incidentally, the definition of the sharing ratio R _sh, the gradation 0,1, sharing ratio R _sh (%) is not satisfied. In FIG. 6, the sharing rate R _sh (%) is not satisfied at the relatively low gradation 2. This is because it is not always necessary to satisfy the sharing rate R _sh (%) because pseudo contours hardly occur at low gradations.

FIG. 17 shows a specific example of a subframe period in a light emission state when the total number of gradations ²⁶ is displayed using a 6-bit video signal. In FIG. 17, the horizontal axis corresponds to the total length of the subframe periods (light emission period) in which the gray scale is on the left and the left vertical axis is in the light emission state. The gradation to be displayed is determined by the length of the light emission period. Similarly, FIG. 17 also shows the sharing ratio R _sh (%) when compared with the case where the gradation is one step lower on the right vertical axis. FIG. 17 shows an example in which display is performed using _twelve subframe periods SF _{1 to} SF ₁₂ . The ratio of the lengths of the subframe periods SF _{1 to} SF ₁₂ is 1: 2: 3: 3: 4: 4: 5: 6: 7: 8: 9: 11 in order from SF ₁ .

In this subframe period, there are periods having the same length. Therefore, there are a plurality of combinations of subframe periods selected for displaying a certain gray scale, and different tables can be set according to the combinations.

Such a table is a kind of lookup table, and is stored in a memory such as a ROM or a RAM as hardware.

In FIG. 17, when displaying gradations 12 to 63, the length of each subframe period is determined so that the sharing rate R _sh (%) is maintained at 70% or more. Incidentally, the definition of the sharing ratio R _sh, the gradation 0,1, sharing ratio R _sh (%) is not satisfied. In FIG. 17, the sharing rate R _sh (%) is not satisfied at the relatively low gradations 2 to 11. This is because it is not always necessary to satisfy the sharing rate R _sh (%) because pseudo contours hardly occur at low gradations.

Thus, a plurality of different tables can be set by determining the subframe period in consideration of the sharing rate. By applying the plurality of tables to each pixel, it is possible to prevent false contours.

(Embodiment 3)
In the present embodiment, a case will be described in which the table corresponding to each pixel is changed for each frame period without being fixed.

For example, tables a and b are provided for the adjacent pixels (A) and (B) as shown in FIG.

In the (T + 1) th frame, as shown in FIG. 2 (B), the tables a and b provided corresponding to the positions of the pixels (A) and (B) are provided so as to be reversed. Thus, the table provided corresponding to each pixel position can be changed for each frame. The contents of this table and information on changes can be stored in ROM or RAM.

As described above, the pseudo contour can be further prevented by changing the table corresponding to each pixel for each frame, that is, by replacing the table storing the data defining the subframe period in which the light emission is performed.

Note that although cases have been described with the present embodiment where a table is provided for each of the pixels (A) and (B), the present invention is not limited to this. For example, when four tables are provided, the pixels provided with the respective tables may be arranged in a rectangular shape.
That is, according to the present invention, by providing a table for each of at least two or more pixels, pseudo contours can be prevented as compared with the conventional method.

(Embodiment 4)
In this embodiment, a specific structure of a light-emitting device that is one of display devices is described. FIG. 7A illustrates a structure of the light-emitting device of the present invention as an example in a block diagram. The light emitting device illustrated in FIG. 7 includes a panel 104, a controller 102, and a table 103. Further, the panel 104 includes a pixel portion 100 having a light emitting element in each pixel, a signal line driver circuit 105, and a scanning line driver circuit 106.

The table 103 is stored in a memory such as a ROM or a RAM as hardware, and a plurality of tables are provided according to pixels. The memory also stores pixel arrangement information corresponding to each table. According to the subframe rate R _SF , the memory stores the number and length of a plurality of subframe periods included in one frame period, and a subframe period in which light is emitted among the plurality of subframe periods in each gradation. The data for determining is stored. The subframe rate R _SF is calculated according to the sharing rate R _sh determined by the frame frequency.

In accordance with the data stored in the table 103, the controller 102 can determine a sub-frame period in which light is emitted according to the gradation of the input video signal, and output it. In addition, the controller 102 includes a frame memory, and a clock signal in accordance with the length of each of a plurality of subframe periods stored in the table 103, the driving frequency of the signal line driver circuit 105 or the scanning line driver circuit 106, and the like. Various control signals such as a start pulse signal can be generated.

Note that FIG. 7A illustrates an example in which the video signal conversion and the control signal generation are both performed by the controller 102; however, the present invention is not limited to this structure. A controller that converts video signals and a controller that generates control signals may be provided separately in the light emitting device.

FIG. 7B illustrates an example of a more specific structure of the panel 104 illustrated in FIG.

In FIG. 7B, the signal line driver circuit 105 includes a shift register 110, a latch A111, and a latch B112. Various control signals such as a clock signal (CLK) and a start pulse signal (SP) are input to the shift register 110. When the clock signal (CLK) and the start pulse signal (SP) are input, a timing signal is generated in the shift register 110. The generated timing signals are sequentially input to the first-stage latch A111. When the timing signal is input to the latch A111, the video signal input from the controller 102 is sequentially written and held in the latch A111 in synchronization with the pulse of the timing signal. Note that in this embodiment mode, video signals are sequentially written in the latch A111; however, the present invention is not limited to this structure. A plurality of stages of latches A111 may be divided into several groups, and so-called divided driving may be performed in which video signals are input in parallel for each group. Note that the number of groups at this time is called the number of divisions. For example, when the latches are divided into groups for every four stages, it can be said that the driving is divided into four.

A period until video signal writing to the latches of all stages of the latch A111 is completed is called a row selection period. Actually, the row selection period may include a period in which a horizontal blanking period is added to the row selection period.

When the one row selection period ends, a latch signal corresponding to one of the control signals is supplied to the second-stage latch B112, and the video signal held in the latch A111 in synchronization with the latch signal is latched into the latch B112. Are written all at once. In the latch A111 that has finished sending the video signal to the latch B112, the video signal of the next bit is sequentially written in synchronization with the timing signal from the shift register 110 again. During this second row selection period, the video signal written and held in the latch B 112 is input to the pixel portion 100.

Instead of the shift register 110, a circuit capable of selecting a signal line such as a decoder may be used.

Next, the configuration of the scanning line driving circuit 106 will be described. The scan line driver circuit 106 includes a shift register 113 and a buffer 114. Moreover, you may have a level shifter. In the scan line driver circuit 106, when the clock signal (CLK) and the start pulse signal (SP) are input to the shift register 113, a selection signal is generated. The generated selection signal is amplified in the buffer 114 and supplied to the corresponding scanning line. Since the operation of the transistors included in the pixels for one row is controlled by the selection signal supplied to the scan line, a buffer 114 that can supply a relatively large current to the scan line is used. It is desirable.

Note that instead of the shift register 113, a circuit capable of selecting a signal line such as a decoder may be used.

In the present invention, the scanning line driver circuit 106 and the signal line driver circuit 105 may be formed on the same substrate as the panel 104 or may be formed on a different substrate. Alternatively, the scan line driver circuit 106 or the signal line driver circuit 105 may be formed using an IC chip and mounted. Further, the panel included in the light-emitting device of the present invention is not limited to the structure illustrated in FIGS. 7A and 7B. The panel 104 may have a configuration in which the gradation of the pixel is controlled in accordance with the video signal input from the controller 102.

By using a plurality of tables in such a light emitting device, pseudo contour can be prevented.

In other display devices, a pseudo contour can be prevented by using a memory in which a plurality of tables are stored.

(Embodiment 5)
Next, an equivalent circuit diagram of a pixel included in the light-emitting device of the present invention will be described with reference to FIG.

FIG. 8A illustrates an example of an equivalent circuit diagram of a pixel, which includes a signal line 6114, a power supply line 6115, a scanning line 6116, a light-emitting element 6113, transistors 6110 and 6111, and a capacitor 6112. A video signal is input to the signal line 6114 by a signal line driver circuit. The transistor 6110 can control supply of the potential of the video signal to the gate of the transistor 6111 in accordance with a selection signal input to the scan line 6116. The transistor 6111 can control supply of current to the light-emitting element 6113 in accordance with the potential of the video signal. The capacitor 6112 can hold the voltage between the gate and the source of the transistor 6111. Note that although the capacitor 6112 is illustrated in FIG. 8A, the capacitor 6112 is not necessarily provided when it can be covered by the gate capacitance of the transistor 6111 or other parasitic capacitance.

FIG. 8B is an equivalent circuit diagram of a pixel in which a transistor 6118 and a scan line 6119 are newly provided in the pixel shown in FIG. The transistor 6118 can set the gate and the source of the transistor 6111 to the same potential and can forcibly prevent a current from flowing to the light-emitting element 6113, so that a subframe can be obtained as compared with a period in which video signals are input to all pixels. The length of the period can be shortened. Accordingly, display with a high total number of gradations can be performed while suppressing the driving frequency.

FIG. 8C is an equivalent circuit diagram of a pixel in which a transistor 6125 and a wiring 6126 are newly provided in the pixel illustrated in FIG. The potential of the gate of the transistor 6125 is fixed by the wiring 6126. The transistor 6111 and the transistor 6125 are connected in series between the power supply line 6115 and the light-emitting element 6113. Therefore, in FIG. 8C, the value of the current supplied to the light-emitting element 6113 is controlled by the transistor 6125, and the presence or absence of the current supplied to the light-emitting element 6113 can be controlled by the transistor 6111.

Note that the pixel circuit included in the light-emitting device of the present invention is not limited to the structure described in this embodiment mode, and the present invention can be applied to any display device that performs time grayscale display. This embodiment can be freely combined with the above embodiment.

(Embodiment 6)
In this embodiment, the driving method of the present invention shown in FIG. 6 is taken as an example, and the timing at which each subframe period appears will be described.

FIG. 9 shows a timing chart in the case of displaying 4-bit gradation using the driving method of the present invention shown in FIG. In FIG. 9, the length of the subframe periods SF _{1 to} SF ₉ appearing in one frame period is shown on the horizontal axis, and the vertical axis shows the selection order of the scanning lines. The ratio of the lengths of the subframe periods SF _{1 to} SF ₉ is 1: 1: 1: 1: 1: 2: 2: 3: 3 in order from SF ₁ . Therefore, when displaying, for example, three gradations, the sum of SF ₁ - SF _3, and either SF ₁ - SF _4, the sum of one of SF _6, SF _7, sub selected from SF _8, or SF ₉ The frame period can be a light emission state. Therefore, the table can have redundancy, and a different table can be provided for each pixel.

When each subframe period starts, video signals are input for each row of pixels sharing a scan line. When a video signal is input to a pixel, the light-emitting element enters a light-emitting state or a non-light-emitting state in accordance with information included in the video signal. Then, until the next subframe period starts, the light emitting element of each pixel maintains a light emitting state or a non-light emitting state according to the video signal.

Note that FIG. 9 illustrates a timing chart in the case where a light-emitting element is in a light-emitting state or a non-light-emitting state in accordance with information included in the video signal at the same time as the video signal is input to the pixel. It is not limited to this configuration. Until the video signal is input to all the pixels, the light emitting element is in a non-light emitting state. After the video signal is input to all the pixels, the light emitting element is turned on or off according to the information included in the video signal. It may be in a non-light emitting state.

Further, FIG. 9 shows a timing chart when all subframe periods appear continuously, but the present invention is not limited to this configuration. A period (non-display period) in which the light-emitting element is forcibly brought into a non-light-emitting state may be provided between the sub-frame period and the sub-frame period. The non-display period can be provided by discharging the charge of the capacitor 6112 using the transistor 6118 illustrated in FIG. 8B or 8C. The non-display period may appear after the video signal is input to all the pixels in the subframe period that appears immediately before the non-display period, or may appear before the video signal is input to all the pixels. May be.

(Embodiment 7)
In this embodiment, a cross-sectional structure of a pixel in the case where a transistor that controls supply of current to a light-emitting element is a p-type thin film transistor (TFT) will be described with reference to FIGS. Note that in the present invention, of the two electrodes of the anode and the cathode included in the light-emitting element, one electrode whose potential can be controlled by a transistor is a first electrode and the other electrode is a second electrode. 10 illustrates the case where the first electrode is an anode and the second electrode is a cathode, the first electrode may be a cathode and the second electrode may be an anode.

FIG. 10A is a cross-sectional view of a pixel in the case where the TFT 6001 is p-type and light emitted from the light-emitting element 6003 is extracted from the first electrode 6004 side. In FIG. 10A, the first electrode 6004 of the light-emitting element 6003 and the TFT 6001 are electrically connected.

The TFT 6001 is covered with an interlayer insulating film 6007, and a partition wall 6008 having an opening is formed over the interlayer insulating film 6007. A part of the first electrode 6004 is exposed in the opening of the partition wall 6008, and the first electrode 6004, the electroluminescent layer 6005, and the second electrode 6006 are sequentially stacked in the opening.

The interlayer insulating film 6007 is formed using an organic resin film, an inorganic insulating film, or an insulating film including a Si—O—Si bond (hereinafter referred to as a siloxane-based insulating film) formed using a siloxane-based material as a starting material. Can do. The siloxane-based insulating film has hydrogen as a substituent and can have at least one of fluorine, an alkyl group, and aromatic hydrocarbon. A material called a low dielectric constant material (low-k material) may be used for the interlayer insulating film 6007.

The partition wall 6008 can be formed using an organic resin film, an inorganic insulating film, or a siloxane-based insulating film. For example, acrylic resin, polyimide, polyamide, or the like can be used for the organic resin film, and silicon oxide, silicon nitride oxide, or the like can be used for the inorganic insulating film. In particular, a photosensitive organic resin film is used for the partition wall 6008, an opening is formed on the first electrode 6004, and the side wall of the opening is formed to have an inclined surface formed with a continuous curvature. Thus, the connection between the first electrode 6004 and the second electrode 6006 can be prevented.

The first electrode 6004 is formed using a light-transmitting material or film thickness, and is formed using a material suitable for use as an anode. For example, another light-transmitting oxide conductive material such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), or zinc oxide added with gallium (GZO) is used for the first electrode 6004. Is possible. For the first electrode 6004, ITO, zinc oxide containing silicon oxide, indium tin oxide containing silicon oxide (hereinafter also referred to as ITSO), and ITSO mixed with 2 to 20% zinc oxide (ZnO) are used. May be. In addition to the light-transmitting oxide conductive material, for example, a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., titanium nitride and aluminum are used. The first electrode 6004 can be formed using a stack including a main component film, a three-layer structure including a titanium nitride film, an aluminum main component film, and a titanium nitride film. Note that in the case where a material other than the light-transmitting oxide conductive material is used, the first electrode 6004 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm).

The second electrode 6006 can be formed using a material and a film thickness that reflect or shield light, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and Ca ₃ N ₂ , rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used.

The electroluminescent layer 6005 is composed of one or more layers. When composed of a plurality of layers, these layers can be classified into a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like from the viewpoint of carrier transport characteristics. In the case where the electroluminescent layer 6005 includes any of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer in addition to the light emitting layer, the first electrode 6004 to the positive hole injection layer, A hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are laminated in this order. Note that the boundaries between the layers are not necessarily clear, and there are cases where the materials constituting the layers are partially mixed and the interface is unclear. For each layer, an organic material or an inorganic material can be used. As the organic material, any of a high molecular weight material, a medium molecular weight material, and a low molecular weight material can be used. The medium molecular weight material corresponds to a low polymer having a number of repeating structural units (degree of polymerization) of about 2 to 20. The distinction between a hole injection layer and a hole transport layer is not necessarily strict, and these are the same in the sense that hole transportability (hole mobility) is a particularly important characteristic. For convenience, the hole injection layer is a layer in contact with the anode, and the layer in contact with the hole injection layer is referred to as a hole transport layer to be distinguished. The same applies to the electron transport layer and the electron injection layer. The layer in contact with the cathode is called an electron injection layer, and the layer in contact with the electron injection layer is called an electron transport layer. The light emitting layer may also serve as an electron transport layer, and is also referred to as a light emitting electron transport layer.

In the case of the pixel shown in FIG. 10A, light emitted from the light-emitting element 6003 can be extracted from the first electrode 6004 side as shown by a hollow arrow.

Next, FIG. 10B is a cross-sectional view of a pixel in the case where the TFT 6011 is a p-type and light emitted from the light-emitting element 6013 is extracted from the second electrode 6016 side. In FIG. 10B, the first electrode 6014 of the light-emitting element 6013 and the TFT 6011 are electrically connected. In addition, an electroluminescent layer 6015 and a second electrode 6016 are sequentially stacked over the first electrode 6014.

The first electrode 6014 is formed using a material and a film thickness that reflect or shield light, and is formed using a material that is suitable for use as an anode. For example, in addition to a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., a laminate of titanium nitride and a film containing aluminum as a main component, a titanium nitride film A three-layer structure of a film mainly containing aluminum and aluminum and a titanium nitride film can be used for the first electrode 6014.

The second electrode 6016 can be formed using a light-transmitting material or film thickness, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and Ca ₃ N ₂ , rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used. Then, the second electrode 6016 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm). Note that other light-transmitting oxide conductive materials such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide to which gallium is added (GZO) can also be used. Alternatively, ITO, zinc oxide containing silicon oxide, indium tin oxide containing silicon oxide (ITSO), or ITSO mixed with 2 to 20% zinc oxide (ZnO) may be used. In the case of using a light-transmitting oxide conductive material, it is preferable to provide an electron injection layer in the electroluminescent layer 6015.

The electroluminescent layer 6015 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG.

In the case of the pixel shown in FIG. 10B, light emitted from the light-emitting element 6013 can be extracted from the second electrode 6016 side as shown by a hollow arrow.

Next, FIG. 10C is a cross-sectional view of a pixel in the case where the TFT 6021 is p-type and light emitted from the light-emitting element 6023 is extracted from the first electrode 6024 side and the second electrode 6026 side. In FIG. 10C, the first electrode 6024 of the light-emitting element 6023 and the TFT 6021 are electrically connected. Further, an electroluminescent layer 6025 and a second electrode 6026 are sequentially stacked over the first electrode 6024.

The first electrode 6024 can be formed in a manner similar to that of the first electrode 6004 in FIG. The second electrode 6026 can be formed in a manner similar to that of the second electrode 6016 in FIG. The electroluminescent layer 6025 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG.

In the case of the pixel shown in FIG. 10C, light emitted from the light-emitting element 6023 can be extracted from the first electrode 6024 side and the second electrode 6026 side as indicated by white arrows.

This embodiment mode can be freely combined with the above embodiment modes.

(Embodiment 8)
In this embodiment, a cross-sectional structure of a pixel in the case where an n-type TFT is used as a transistor that controls supply of current to a light-emitting element will be described with reference to FIGS. Note that although FIG. 11 illustrates the case where the first electrode is a cathode and the second electrode is an anode, the first electrode may be an anode and the second electrode may be a cathode.

FIG. 11A is a cross-sectional view of a pixel in the case where the TFT 6031 is n-type and light emitted from the light-emitting element 6033 is extracted from the first electrode 6034 side. In FIG. 11A, the first electrode 6034 of the light-emitting element 6033 and the TFT 6031 are electrically connected. Further, an electroluminescent layer 6035 and a second electrode 6036 are sequentially stacked over the first electrode 6034.

The first electrode 6034 can be formed using a light-transmitting material or film thickness, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and Ca ₃ N ₂ , rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used. Then, the first electrode 6034 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm). Further, a light-transmitting conductive layer is formed using a light-transmitting oxide conductive material so as to be in contact with or under the conductive layer having a thickness enough to transmit light, and the first electrode 6034 is formed. The sheet resistance may be suppressed. Note that only conductive layers using other light-transmitting oxide conductive materials such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide to which gallium is added (GZO) should be used. Is also possible. Alternatively, ITO, zinc oxide containing silicon oxide, indium tin oxide containing silicon oxide (ITSO), or ITSO mixed with 2 to 20% zinc oxide (ZnO) may be used. In the case of using a light-transmitting oxide conductive material, it is preferable to provide an electron injection layer in the electroluminescent layer 6035.

The second electrode 6036 is formed of a material and a film thickness that reflect or shield light, and is formed using a material that is suitable for use as an anode. For example, in addition to a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., a laminate of titanium nitride and a film containing aluminum as a main component, a titanium nitride film A three-layer structure of a film containing aluminum and aluminum as main components and a titanium nitride film can be used for the second electrode 6036.

The electroluminescent layer 6035 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG. However, in the case where the electroluminescent layer 6035 includes any one of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer in addition to the light emitting layer, the first electrode 6034 to the electron injection layer The electron transport layer, the light emitting layer, the hole transport layer, and the hole injection layer are laminated in this order.

In the case of the pixel shown in FIG. 11A, light emitted from the light-emitting element 6033 can be extracted from the first electrode 6034 side as shown by a hollow arrow.

Next, FIG. 11B is a cross-sectional view of a pixel in the case where the TFT 6041 is an n-type and light emitted from the light-emitting element 6043 is extracted from the second electrode 6046 side. In FIG. 11B, the first electrode 6044 of the light-emitting element 6043 and the TFT 6041 are electrically connected. Further, an electroluminescent layer 6045 and a second electrode 6046 are sequentially stacked over the first electrode 6044.

The first electrode 6044 can be formed using a material and a film thickness that reflect or shield light, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and Ca ₃ N ₂ , rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used.

The second electrode 6046 is formed using a light-transmitting material or film thickness, and is formed using a material suitable for use as an anode. For example, another light-transmitting oxide conductive material such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), or zinc oxide added with gallium (GZO) is used for the second electrode 6046. Is possible. Alternatively, ITO, zinc oxide containing silicon oxide, indium tin oxide containing silicon oxide (ITSO), or ITSO mixed with 2 to 20% zinc oxide (ZnO) may be used for the second electrode 6046. In addition to the light-transmitting oxide conductive material, for example, a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., titanium nitride and aluminum are used. The second electrode 6046 can be formed using a stack of a main component film, a three-layer structure including a titanium nitride film, an aluminum main component film, and a titanium nitride film. Note that in the case where a material other than the light-transmitting oxide conductive material is used, the second electrode 6046 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm).

The electroluminescent layer 6045 can be formed in a manner similar to that of the electroluminescent layer 6035 in FIG.

In the case of the pixel shown in FIG. 11B, light emitted from the light-emitting element 6043 can be extracted from the second electrode 6046 side as shown by a hollow arrow.

Next, FIG. 11C is a cross-sectional view of a pixel in the case where the TFT 6051 is an n-type and light emitted from the light-emitting element 6053 is extracted from the first electrode 6054 side and the second electrode 6056 side. In FIG. 11C, the first electrode 6054 of the light-emitting element 6053 and the TFT 6051 are electrically connected. Further, an electroluminescent layer 6055 and a second electrode 6056 are stacked over the first electrode 6054 in this order.

The first electrode 6054 can be formed in a manner similar to that of the first electrode 6034 in FIG. The second electrode 6056 can be formed in a manner similar to that of the second electrode 6046 in FIG. The electroluminescent layer 6055 can be formed in a manner similar to that of the electroluminescent layer 6035 in FIG.

In the case of the pixel shown in FIG. 11C, light emitted from the light-emitting element 6053 can be extracted from the first electrode 6054 side and the second electrode 6056 side as indicated by white arrows.

This embodiment mode can be freely combined with the above embodiment modes.

(Embodiment 9)
In this embodiment, the case where a light-emitting device is formed using a printing method typified by a screen printing method, an offset printing method, or a droplet discharge method will be described. The droplet discharge method means a method of forming a predetermined pattern by discharging droplets containing a predetermined composition from the pores, and includes an ink jet method and the like in its category. By using the above printing method and droplet discharge method, various wirings typified by signal lines, scanning lines, selection lines, TFT gates, and light emitting element electrodes can be formed without using an exposure mask. Is possible. However, it is not necessary to use a printing method or a droplet discharge method for all the steps of forming a pattern. Therefore, for example, a printing method or a droplet discharge method is used in at least a part of the process, for example, a printing method or a droplet discharge method is used to form a wiring and a gate, and a lithography method is used to pattern a semiconductor film. As long as it is, a lithography method may be used in combination. A mask used for patterning may be formed by a printing method or a droplet discharge method.

FIG. 12 shows an example of a cross-sectional view of a light-emitting device of the present invention formed using a droplet discharge method. In FIG. 12, 1301 and 1302 correspond to TFTs, and 1304 corresponds to a light emitting element. The TFT 1302 is electrically connected to the first electrode 1350 of the light-emitting element 1304. The TFT 1302 is preferably n-type. In this case, the first electrode 1350 is preferably a cathode, and the second electrode 1331 is preferably an anode.

The TFT 1301 functioning as a switching element includes a gate 1310, a first semiconductor film 1311 including a channel formation region, a gate insulating film 1317 formed between the gate 1310 and the first semiconductor film 1311, and a source or drain. The semiconductor device includes functional second semiconductor films 1312 and 1313, a wiring 1314 connected to the second semiconductor film 1312, and a wiring 1315 connected to the second semiconductor film 1313.

The TFT 1302 includes a gate 1320, a first semiconductor film 1321 including a channel formation region, a gate insulating film 1317 formed between the gate 1320 and the first semiconductor film 1321, and a second functioning as a source or a drain. The semiconductor films 1322 and 1323, the wiring 1324 connected to the second semiconductor film 1322, and the wiring 1325 connected to the second semiconductor film 1323 are included.

The wiring 1314 corresponds to a signal line, and the wiring 1315 is electrically connected to the gate 1320 of the TFT 1302. The wiring 1325 corresponds to a power supply line.

By forming a pattern using a droplet discharge method or a printing method, a series of steps such as photoresist film formation, exposure, development, etching, and peeling performed by a lithography method can be simplified. Further, unlike the lithography method, the droplet discharge method and the printing method do not waste material that is removed by etching. Further, it is not necessary to use an expensive exposure mask, so that the cost for manufacturing the light-emitting device can be suppressed.

Further, unlike the lithography method, it is not necessary to perform etching to form the wiring. Therefore, the time spent for the process of forming the wiring can be significantly shortened compared to the case of the lithography method. In particular, when the wiring thickness is 0.5 μm or more, more desirably 2 μm or more by using a printing method, the wiring resistance can be suppressed, so that the time required for the wiring manufacturing process can be suppressed, and the light emitting device The increase in wiring resistance due to the increase in size can be suppressed.

Note that the first semiconductor films 1311 and 1321 may be either an amorphous semiconductor or a semi-amorphous semiconductor (SAS).

An amorphous semiconductor can be obtained by glow discharge decomposition of a silicide gas. Typical silicide gases include SiH ₄ and Si ₂ H ₆ . This silicide gas may be diluted with hydrogen, hydrogen and helium.

SAS can also be obtained by glow discharge decomposition of silicide gas. A typical silicide gas is SiH ₄ , and in addition, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _{4 and the} like can be used. In addition, it is easy to form a SAS by diluting and using this silicide gas with hydrogen or a gas obtained by adding one or more kinds of rare gas elements selected from helium, argon, krypton, and neon to hydrogen. It can be. It is preferable to dilute the silicide gas at a dilution rate in the range of 2 to 1000 times. Furthermore, a carbide gas such as CH ₄ or C ₂ H ₆ , a germanium gas such as GeH ₄ or GeF ₄ , F ₂ or the like is mixed in the silicide gas, so that the energy bandwidth is 1.5-2. You may adjust to 4 eV or 0.9-1.1 eV. A TFT using SAS as the first semiconductor film can obtain a mobility of 1 to 10 cm ² / Vsec or more.

Alternatively, the first semiconductor films 1311 and 1321 may be formed using a semiconductor obtained by crystallizing an amorphous semiconductor or a semi-amorphous semiconductor (SAS). For example, an amorphous semiconductor or SAS can be crystallized using a laser or a heating furnace.

This embodiment mode can be freely combined with the above embodiment modes.

(Embodiment 10)
In this embodiment, the appearance of a panel corresponding to one embodiment of the light-emitting device of the present invention will be described with reference to FIGS. FIG. 13A is a top view of a panel in which a TFT and a light-emitting element formed over a first substrate are sealed with a sealing material between the second substrate and FIG. 13B. FIG. 13A corresponds to a cross-sectional view taken along line AA ′ of FIG.

A pixel portion 4002, a signal line driver circuit 4003, and a scan line driver circuit 4004 are provided over the first substrate 4001, and a sealant 4005 is provided so as to surround at least the pixel portion. A second substrate 4006 is provided over at least the pixel portion 4002 with a sealant 4005 interposed therebetween. In the light-emitting device illustrated in FIG. 13, the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 are combined with a filler 4007 by a first substrate 4001, a sealant 4005, and a second substrate 4006. Sealed.

In addition, the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 provided over the first substrate 4001 each include a plurality of TFTs. In FIG. A TFT 4008 included in 4003 and a TFT 4009 included in the pixel portion 4002 are illustrated.

Reference numeral 4011 corresponds to a light-emitting element, and a part of the wiring 4017 connected to the drain of the TFT 4009 functions as a first electrode of the light-emitting element 4011.
The transparent conductive film 4012 functions as the second electrode of the light-emitting element 4011.
Note that the structure of the light-emitting element 4011 is not limited to the structure described in this embodiment. As in the above embodiment mode, the structure of the light-emitting element 4011 can be changed as appropriate depending on the direction of light extracted from the light-emitting element 4011, the polarity of the TFT 4009, or the like.

Further, various signals and voltages supplied to the signal line driver circuit 4003, the scan line driver circuit 4004, or the pixel portion 4002 are not shown in the cross-sectional view of FIG. 13B, but are routed through lead wirings 4014 and 4015. It is supplied from the connection terminal 4016.

In this embodiment, the connection terminal 4016 is formed using the same conductive film as the first electrode included in the light-emitting element 4011. Further, the lead wiring 4014 is formed of the same conductive film as the wiring 4017. The lead wiring 4015 is formed of the same conductive film as the gates of the TFTs 4009 and 4008.

The connection terminal 4016 is electrically connected to a terminal included in the FPC 4018 through an anisotropic conductive film 4019.

Note that as the first substrate 4001 and the second substrate 4006, glass, metal (typically stainless steel), ceramics, or plastic can be used. As the plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a mylar film, a polyester film, or an acrylic resin film can be used. A sheet having a structure in which an aluminum foil is sandwiched between PVF films or mylar films can also be used.

However, board located in the direction in which light is extracted from the light-emitting element 4011 should have a light-transmitting property. In that case, a light-transmitting material such as a glass plate, a plastic plate, a polyester film, or an acrylic film is used.

Further, as the filler 4007, an ultraviolet curable resin or a thermosetting resin can be used in addition to an inert gas such as nitrogen or argon. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicon resin, PVB (Polyvinyl butyral) or EVA (ethylene vinyl acetate) can be used. In this embodiment, nitrogen is used as the filler.

This embodiment mode can be freely combined with the above embodiment modes.

(Embodiment 11)
Since the display device of the present invention can suppress the occurrence of pseudo contours, it can be used as a display portion included in a portable electronic device such as a mobile phone, a portable game machine, an electronic book, a video camera, or a digital still camera. Ideal for. In addition, since the display device of the present invention can prevent false contours, the display device is optimal for an electronic apparatus having a display unit for viewing a video, which can reproduce a moving image.

Other electronic devices that can use the display device of the present invention include a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproduction device (car audio, audio component, etc.), and a notebook type personal computer. And an image reproducing apparatus (typically, an apparatus having a display that can reproduce a recording medium such as a DVD: Digital Versatile Disc and display the image). In this embodiment, specific examples of these electronic devices are illustrated in FIGS.

FIG. 14A illustrates a mobile phone, which includes a main body 2101, a display portion 2102, a voice input portion 2103, a voice output portion 2104, and operation keys 2105. By manufacturing the display portion 2102 using the display device of the present invention, a mobile phone which is one of the electronic devices of the present invention can be completed.

FIG. 14B illustrates a video camera, which includes a main body 2601, a display portion 2602, a housing 2603, an external connection port 2604, a remote control receiving portion 2605, an image receiving portion 2606, a battery 2607, an audio input portion 2608, operation keys 2609, and an eyepiece. Part 2610 and the like. By manufacturing the display portion 2602 using the display device of the present invention, a video camera which is one of the electronic devices of the present invention can be completed.

FIG. 14C illustrates a display device, which includes a housing 2401, a display portion 2402, a speaker portion 2403, and the like. By manufacturing the display portion 2402 using the display device of the present invention, a display device which is one of the electronic devices of the present invention can be completed. The display device includes all information display devices for personal computers, TV broadcast reception, advertisement display, and the like.

As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields. Further, this embodiment mode can be freely combined with the above embodiment modes.

Example 1
In the present embodiment, an experiment on the relationship of pseudo contour generation to the sharing rate will be described.

The present inventor conducted the following experiment in order to investigate the relationship between the sharing rate and the occurrence of the pseudo contour.

First, one frame period is divided into _two subframe periods SF ₁ and SF ₂ , and a pattern as shown in FIG. 3 is displayed in the first frame period and the second frame period. Specifically, to display a checkerboard pattern in the sub-frame periods SF _1, displaying white in the entire region in the sub-frame period SF _2. Note that in the adjacent first frame period and second frame period, a pattern in which the white area and the black area are inverted with each other in the subframe period SF ₁ is displayed.

Then, two frames were made to appear alternately, and the presence or absence of a pseudo contour was examined. In this case one frame period, the length ratio of the subframe periods SF ₁ when the R ₁ (%), for R ₁ (%), the lowest frame frequency F which generation of a pseudo contour is observed in (Hz) The values are as shown in FIG. Subframe periods SF ₁ this time, as shown in FIG. 3, have different display for each frame period. As can be seen from FIG. 4, the lower the frame frequency F (Hz) at which the occurrence of the pseudo contour is recognized, the lower the ratio R ₁ (%) of the length of the subframe period for performing different display in the two frames. became. Conversely, the higher the R ₁ (%), the higher the lowest frame frequency F (Hz) at which the occurrence of a pseudo contour is recognized.

Thus, for each frame period the adjacent, more subframe periods SF ₁ is short, it can be said that the false contour hardly occurs. On the other hand, it can be said that the pseudo contour is less likely to occur as the sub-frame period SF ₂ having the same display is longer every two frame periods. In this state, it can be said that the ratio of the length of the subframe period SF ₂ in the common light emission state is high in _two frame periods, that is, the sharing rate is high.

From the results of the above experiment, it was found that the generation of pseudo contours can be suppressed as the sharing rate increases in two adjacent frame periods. The sharing rate (%) corresponds to 100-R ₁ (%).

(Example 2)
In the present embodiment, an example in which a constant subframe rate R _SF is applied from SF _n to SF ₁ is shown, but the present invention is not limited to this configuration. For example, even when a display with a total number of gradations of 2 ⁿ is performed, the number of subframe periods is not necessarily n. When the length calculated according to Equation 9 is reflected in each subframe period, the number of subframe periods is often n or more. However, a short subframe period for displaying a low gradation does not necessarily contribute to the generation of a pseudo contour even if the value of the sharing rate R _sh described above is not necessarily satisfied. This is because, in the case of a low gradation, the reciprocal of the gradation × 100 (gradation ratio) is larger than that in the case of a high gradation, so that the contour due to the difference in gradation is visually recognized, and conversely the pseudo contour is This is because it doesn't stand out.

In order to explain this, FIG. 15 shows the result of examining the relationship between the gradation ratio (%) and the lowest frame frequency F (Hz) at which the occurrence of the pseudo contour is recognized. In FIG. 15, the horizontal axis indicates the gradation ratio (%), and the vertical axis indicates the lowest frame frequency F (Hz) at which the occurrence of a pseudo contour is recognized. From FIG. 15, it can be seen that the higher the gradation ratio (%), that is, the lower the gradation, the more the generation of pseudo contour can be suppressed even at a lower frame frequency. Therefore, a short subframe period for displaying a low gradation does not necessarily satisfy the above-described sharing rate.

In light of the above, it is better to focus on reducing the drive frequency of the drive circuit rather than creating many short subframe periods that are not involved in the generation of pseudo contours. For this reason, it is preferable to set the other subframe periods to satisfy the sharing rate by thinning out the short subframe periods. In calculation, when there are a plurality of subframe periods having a short period corresponding to gradation 1, one or several of them can be set without satisfying the sharing ratio value.

Specifically, the total number of gradations is divided into three, and the value of the sharing rate R _sh does not necessarily have to be satisfied in the lowest gradation among the three divided total gradation numbers. On the other hand, the value of the sharing rate R _sh is satisfied in the intermediate gray level and the highest gray level among the total number of gray levels divided into three. For example, when the total number of gradations is 2 ⁶ = 64, 21 is obtained by dividing the gradations 0 to 63 into three equal parts. In this case, the lower gradation is 0 to 21, the intermediate gradation is 22 to 42, and the highest gradation is 43 to 63. If the total number of tones is not evenly divided by three, the fraction may be rounded up or down.

(Example 3)
In this embodiment, a specific timing chart in the case where four tables are provided and the tables will be described.

As shown in FIG. 18, there is a pixel portion 100 having a plurality of pixels 101. From this pixel 101, certain pixels (A), (B), (C), and (D) are taken out. The arrangement of the pixels (A), (B), (C), and (D) is (m, n) (m, n + 1) (m + 1, n) (m + 1, n + 1). Note that m corresponds to an arbitrary number of pixels in the row direction in the pixel portion, and n corresponds to an arbitrary number of pixels in the column direction in the pixel portion.

A timing chart and table in the case of using pixels (A), (B), (C), and (D) adjacent to the rectangle among the pixels 101 will be described.

FIG. 19 shows a timing chart. The frame frequency is 60 Hz, and there are 60 frames per second as shown in FIG. At this time, the length of one frame period is approximately 16.67 ms. In one frame period, 16 subframe periods are provided, and these subframes appear randomly in one frame period. In this _{embodiment, SF 2, SF 4, SF} 6, SF 8, SF 1 0, SF 12, SF 14, SF 16, SF 15, SF 13, SF 11, SF 9, SF 7, SF 5, SF 3 , SF ₁ appear in the order of SF ₁ . The ratio of the length of each subframe period is as follows: SF ₁ : SF ₂ : SF ₃ : SF ₄ : SF ₅ : SF ₆ : SF ₇ : SF ₈ : SF ₉ : SF ₁₀ : SF ₁₁ : SF ₁₂ : SF _{13: SF 14: SF 15:} SF 16 = 1: 2: 4: 8: 10: 10: 10: 12: 12: 14: 17: 21: 25: 30: 36: and has a 43. Then, as shown in FIG. 19B, display is performed in order from the first row to the last row of pixels. Below the display of the last row pixel in FIG. 19B, the ratio of the length of the subframe period is shown.

FIG. 19C shows scanning timing by the erasing scanning line driver circuit. In this embodiment, in the sub-frame periods SF ₁ - SF _15, is provided an erasing period Se1～Se15.

FIG. 19D shows scanning timing by the scanning line driver circuit for writing, and writing periods Ta1 to Ta16 are provided in each subframe period.

As shown in FIG. 19E, one writing period is provided with one column scanning period, and all rows (324 rows in this embodiment) are selected during this period.

Further, in one frame period, a reverse voltage application period (DS period) is provided. As a result of applying the reverse voltage to the light emitting element, the deterioration state of the light emitting element can be improved and the reliability can be improved. In addition, the light emitting element may have an initial failure in which the anode and the cathode are short-circuited due to adhesion of foreign matters, pinholes due to fine protrusions on the anode or the cathode, and non-uniformity of the electroluminescent layer. By applying a reverse voltage, this initial failure can be eliminated and an image can be displayed satisfactorily. Such insulation of the short-circuit portion is preferably performed before shipment.

In such a sub-frame period, there is selectivity in the sub-frame period for light emission in order to display a certain gradation like SF ₅ , SF ₆ , SF ₇ , S _F8 , and SF ₉ . Therefore, a plurality of tables can be provided.

Tables 1 to 4 show examples of specific tables in the case of the timing chart. In Tables a to d shown in Tables 1 to 4, “0” is a non-light emitting state and “1” is a light emitting state.

The tables a to d are a kind of look-up table, and are stored in a memory such as a ROM or a RAM in terms of hardware. Of course, the data of the table is not limited to the tables a to d, and can be arbitrarily provided according to the power consumption and the required image quality.

In these tables a to d, for example, looking at the 191st gradation, it can be seen that the subframe periods in which the light emission state is different in each table.

In this way, a plurality of tables are provided and a combination of adjacent pixels corresponding to these tables is designated. For example, since there are four tables, combinations of pixels (A) to (D) as shown in FIG. 18 can be designated. That is, the number of tables and the number of pixels constituting the combination are preferably the same. In other words, tables a to d selected from a plurality of tables storing data defining subframe periods in which light emission is performed are prepared, and at least two pixels are adjacent to adjacent pixels (A) to (D). On the other hand, a table a is provided for the pixel (A), a table b is provided for the pixel (B), a table c is provided for the pixel (C), and a table d is provided for the pixel (D). .

Note that the pixel arrangement is not limited to that shown in FIG. For example, when four tables are provided for four pixels divided as a set as shown in FIG. 18, the pixels (A) to (D) may be arranged in one vertical row or one horizontal row. . However, at least two pixels provided with different tables need to be adjacent to each other.

Therefore, it is possible to change the subframe period selected when displaying a certain gradation between adjacent pixels. As a result, it is possible to spatially disperse gradations where pseudo contours are likely to occur. Note that a gradation in which a pseudo contour is likely to occur is a low sharing ratio and an intermediate gradation or a high gradation.

In this embodiment, the timing chart divided into 16 subframes when the frame frequency is 60 Hz has been described. However, the number of subframes can be changed by considering the frame frequency.

Further, as shown in the above embodiment, the table corresponding to each pixel may be changed for each frame without fixing. That is, for each frame, a table in which data defining subframe periods in which light emission is performed is stored may be replaced.

It is the figure which showed the pixel part and table of this invention It is the figure which showed the pixel part and table of this invention It is a figure which shows the pattern used for the display in the experiment conducted in order to investigate the relationship between a share rate and generation | occurrence | production of a pseudo contour. It is a graph showing the relationship between R1 (%) and the lowest frame frequency at which the occurrence of a pseudo contour is recognized, where the ratio of the subframe period SF1 in _one frame period is R1 (%). It is a graph which shows the relationship between a frame frequency and the lowest share rate which can suppress generation | occurrence | production of a pseudo contour. It is a graph which shows the sharing rate when comparing the relationship between the sub-frame period in the light emission state and the gradation, and the case where the gradation is one step lower. It is the block diagram which showed the structure of the light-emitting device of this invention It is the figure which showed an example of the pixel which the light-emitting device of this invention has 4 is a timing chart when displaying 4-bit gradation in the driving method of the present invention. It is sectional drawing which showed the pixel which the light-emitting device of this invention has It is sectional drawing which showed the pixel which the light-emitting device of this invention has It is sectional drawing which showed the pixel which the light-emitting device of this invention has It is the top view and sectional view showing the light emitting device of the present invention. It is a figure which shows the electronic device of this invention It is a graph which shows the relationship between a gradation ratio and the minimum frame frequency where generation | occurrence | production of a pseudo contour is recognized. It is the figure which showed the conventional sub-frame period and the sub-frame period of this invention It is a graph which shows a share rate when the relationship between the sub-frame period in the light emission state and the gradation is compared with the case where the gradation is one step lower. It is the figure which showed the pixel part and table of this invention It is the figure which showed the timing chart of this invention

Claims (2)

One frame period has a plurality of subframe periods,
A first table to a fourth table in which data defining a subframe period in which light is emitted among the plurality of subframe periods are stored;
A controller that outputs a video signal according to the data;
In accordance with the output video signal, the pixel portion is controlled in gradation,
The first table stores the plurality of subframe periods corresponding to (m, n) pixels in the pixel portion,
The second table stores the plurality of subframe periods corresponding to (m, n + 1) pixels in the pixel portion,
The third table stores the plurality of subframe periods corresponding to (m + 1, n) pixels in the pixel portion,
The fourth table stores the plurality of subframe periods corresponding to (m + 1, n + 1) pixels in the pixel portion,
In the first table to the fourth table, the number and length of subframe periods in which the combined light emission states are set to display at least intermediate gradation and high gradation are different,
The number and length of the plurality of sub-frame periods are the same as the sub-frames that are in the light emission state in two sub-frame periods in which the gradations in the intermediate gradation and the high gradation differ by one step in each table. A display device characterized in that the ratio of the period is determined so as to be a ratio that does not generate a pseudo contour . In claim 1,
A display device comprising a memory in which the first to fourth tables are stored.

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