JP2006235601A - Method of driving display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of driving a display device for performing time-division gray scale display, where the method is capable of inputting accurate data into a panel, with a single memory. <P>SOLUTION: In one frame period, a pair of a first period and a second period continuous to the first period is is repeated for m (m is a natural number that is not less than n) times. A controller writes video signals into the memory in the first period of at least one time among the m times and reads out the video signals from the memory in the second period, whenever the pair is repeated. The start timing of reading out video signals from the memory is synchronized with the start timing of each of the n sub-frame periods. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a driving method of a display device having an active matrix driving method in which a switching element is provided for each pixel and having a memory for storing an image signal input to the pixel. In particular, the present invention relates to a driving method of a display device that expresses gradation by controlling a period in which each pixel is bright. The present invention relates to a driving method of a display device that expresses gradation by controlling a period during which each pixel emits light.

  As a method for driving the display device, one frame period is divided into a plurality of subframe periods, an image signal is input to each pixel in each subframe period, and gradation is expressed by selecting the brightness of each pixel (hereinafter, sometimes referred to as time). There has been proposed a driving method of a display device (also referred to as divided gradation display) (see Patent Document 1).

For example, one frame period is divided into a first subframe period to a third subframe period, and (length of light emission period in first subframe period): (length of light emission period in second subframe period): The length of the light emission period in the third subframe period is defined as 2 ⁰ : 2 ¹ : 2 ² . Here, the light emission period in each subframe period is a period in which a pixel whose light emission state (bright) is selected in each subframe period emits light. Eight gradations can be expressed by inputting an image signal to each pixel in each of the first to third subframe periods and selecting light emission (bright) or non-light emission (dark) of each pixel.

  A display device that performs time-division gray scale display includes a panel having a plurality of pixels and a driver circuit that inputs image signals to the plurality of pixels, and a peripheral circuit that inputs signals to the panel. The peripheral circuit generates an image signal and a timing signal and inputs them to the panel. Based on the signal input from the peripheral circuit, the panel performs time division gradation display.

A peripheral circuit of a display device that performs time-division gradation display includes a memory and a controller that controls the memory. The controller writes (stores) an image signal (hereinafter also referred to as a source image signal) input to the display device in the memory, reads the written (stored) image signal from the memory, and inputs the image signal to the panel. In order to perform time-division gradation display, it is necessary to read an image signal from the memory every subframe period. That is, it is necessary to synchronize the reading of the image signal from the memory with each subframe period. On the other hand, the source image signal is input to the display device regardless of the subframe period. That is, the writing of the source image signal to the memory is asynchronous with each subframe period.
JP 2001-5426 A

  In a peripheral circuit of a display device that performs time-division gray scale display, the timing of writing a source image signal to the memory is different from the timing of reading the image signal from the memory. For this reason, two memories (single port memories) are provided in the peripheral circuit, and the method of reading the image signal stored in the other memory while writing the source image signal in one memory is used. In this method, the peripheral circuit requires two memories and a circuit for controlling writing and reading of image signals to and from the two memories, which complicates the configuration of the peripheral circuit and leads to an increase in the size of the display device.

  There is a method of using one dual port memory instead of providing two memories in the peripheral circuit. In the dual port memory, the writing of the source image signal and the reading of the image signal can be performed independently. That is, the image signal written in the dual port memory can be read simultaneously with the writing of the source image signal in the dual port memory. However, when writing the source image signal and reading the image signal at the same time in the dual port memory, the storage area where the source image signal is written and the storage area where the image signal is read are the same storage area. Mixed with the signal read from the memory. For this reason, there has been a problem that the image signal cannot be accurately input to the panel and the image is disturbed.

  In a display device that performs time-division gradation display, it is possible to reduce the size of the display device by simplifying the configuration of the peripheral circuit with a single memory, and to display a good image by inputting accurate data to the panel. It is an object to propose a driving method.

  A memory; a controller that controls writing of an image signal to the memory and reading of the image signal from the memory; and a panel that includes a plurality of pixels and to which the image signal read from the memory is input. A display device driving method in which one frame period is divided into n (n is a natural number of 2 or more) subframe periods, and the brightness of each of a plurality of pixels is selected in each of the n subframe periods. The method is used.

  In one frame period, a set of the first period and the second period continuous to the first period is repeated m (m is a natural number equal to or greater than n) times. The controller writes the image signal to the memory in the first period at least once out of repeating the group m times, and reads the image signal from the memory in the second period each time the group is repeated. The timing to start reading the image signal from the memory is synchronized with the timing to start each of the n subframe periods.

  In the above method, the controller is not limited to the configuration in which the image signal is read from the memory in the second period each time the set is repeated. The controller writes the image signal to the memory in the first period at least k (k is a natural number equal to or less than n) times when the set is repeated m times, and n times from the memory in the second period when the set is repeated m times. The signal may be read out.

  In one frame period, the number of times of reading out the image signal from the memory is made larger than the number of times of writing the image signal into the memory.

  The memory also includes a first storage area and a second storage area. In the i-th (i is a natural number) frame period, an image signal is written in the first storage area and the second storage area is stored. The image signal stored in the area is read out, and the image signal is written in the second storage area in the (i + 1) th frame period continuous to the i-th frame period, and the image stored in the first storage area Read the signal, write the image signal to the first storage area and read the image signal stored in the second storage area in the (i + 2) th frame period continuous to the (i + 1) th frame period. Can do.

  The first storage area has a storage capacity for storing first image signals corresponding to a plurality of pixels, and the second storage area stores second image signals corresponding to the plurality of pixels. The first image signal and the second image signal have a storage capacity and can be image signals corresponding to different frame periods.

  The second period may be longer than the first period. The memory may be an SRAM. Each of the plurality of pixels may have a light emitting element as a display element or a liquid crystal element.

  Since the writing of the image signal to the memory and the reading of the image signal from the memory are performed in the first period and the second period, only one memory is required, and the signal written to the memory and the signal read from the memory And will not mix. In addition, since a plurality of sets of the first period and the second period are provided in one frame period and the image signal is selectively written to the memory, the number of times the image signal is written to the memory is reduced from the memory. The number of image signal readouts can be increased. Thus, even when the timing of writing the source image signal to the memory is asynchronous with the subframe period, the reading of the image signal from the memory can be synchronized with the subframe period, and time-division gradation display is performed. Can do.

  As described above, in a display device that performs time-division gray scale display, it is possible to reduce the size of the display device by simplifying the configuration of the peripheral circuit with a single memory, and by inputting accurate data to the panel, a good image can be obtained. A driving method capable of display can be provided.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a timing chart showing a method for driving the display device. FIG. 2 is a diagram showing a configuration of a display device using the driving method shown in the timing chart of FIG.

  2A, the display device 100 includes a panel 101 having a plurality of pixels and a peripheral circuit 102. The peripheral circuit 102 includes a controller 104 and a memory 103. The source image signal SVD input to the display device is input to the peripheral circuit 102 (indicated as “IN” in FIG. 2A). The source image signal SVD input to the peripheral circuit 102 is written into the memory 103 by the controller 104. The image signal written in the memory 103 is read by the controller 104 and output from the peripheral circuit 102 as the image signal VD (denoted as “OUT” in FIG. 2A). The image signal VD is input to the panel 101. The panel 101 displays an image using the image signal VD. That is, the image signal VD input to the panel 101 is input to each pixel, and the brightness of each pixel is selected. Thus, the panel performs image display.

  FIG. 2B is a diagram showing in detail the configuration of the controller 104 in FIG. 2B, the controller 104 includes a writing memory 105, a reading memory 106, and a selector 107. The source image signal SVD is continuously input to the peripheral circuit 102 (indicated as “IN” in FIG. 2B). Of the source image signal SVD, an image signal input to the peripheral circuit 102 within a predetermined period is stored in the writing memory 105 of the controller 104. The selector 107 selects whether to write a signal to the memory 103 or read a signal from the memory 103 via a bus connecting the selector 107 and the memory 103. When the selector 107 selects signal writing to the memory 103, the image signal stored in the writing memory 105 is written to the memory 103 via the bus. When reading of the signal from the memory 103 is selected by the selector 107, a part of the signal written to the memory 103 is read via the bus, and the read image signal is temporarily stored in the reading memory 106. Is done. The stored image signal is output from the peripheral circuit 102 as the image signal VD (denoted as “OUT” in FIG. 2B).

  The timing chart of FIG. 1 shows the driving method of the display device having the configuration of FIG. 2 with particular attention to the driving method of the memory. The driving method of the memory 103 is shown in relation to the frame period, the subframe period, and the source image signal SVD. A method for driving the display device of the present invention will be described with reference to FIG. In addition, the code | symbol of FIG. 2 is used for description.

  The driving of the memory 103 means writing an image signal from the writing memory 105 and reading an image signal to the reading memory 106. A state where an image signal is written in the memory 103 is indicated by “W”. A state in which an image signal is read from the memory 103 is indicated by “R”.

  The frame period is indicated by Fi (i is a natural number), F (i + 1), and F (i + 2). Fi, F (i + 1), and F (i + 2) are each one frame period, which is a period for displaying one image. F (i + 1) is a frame period continuous to Fi, and F (i + 2) is a frame period continuous to F (i + 1). The subframe period is denoted as SF. In the timing chart of FIG. 1, one frame period has two subframe periods SF1 and SF2.

  A source image signal SVD input to the controller 104 is indicated by IN. A source image signal SVD corresponding to the image signal VD displayed in the frame period F (i + 1) is indicated by SVD (F (i + 1)). A source image signal SVD corresponding to the image signal VD displayed in the frame period F (i + 2) is indicated by a source image signal SVD (F (i + 2)). A source image signal SVD corresponding to the image signal VD displayed in the frame period F (i + 3) is indicated by a source image signal SVD (F (i + 3)). A source image signal SVD corresponding to the image signal VD displayed in the frame period F (i + 4) is indicated by a source image signal SVD (F (i + 4)).

  In each of the frame periods Fi, F (i + 1), and F (i + 2), the set of the first period and the second period that is continuous with the first period is repeated a plurality of times. In FIG. 1, the first period is indicated by “1” and the second period is indicated by “2”.

  A method for driving the memory 103 in the frame period Fi will be described.

  An operation in the subframe period SF1 will be described. In the first period of the first group (hereinafter referred to as the first group) of the subframe period SF1, the image signal stored in the writing memory 105 is written into the memory 103. The image signal written in the first period of the first set is input to the peripheral circuit 102 immediately before the first period, and the source image signal SVD (F (i + 1)) stored in the writing memory 105 is stored. It is a part. Next, in the first period of the second period, a part of the signal written in the memory 103 is read, and the read image signal is stored in the reading memory 106. The image signal read from the memory 103 in the first period of the second period is an image signal corresponding to the subframe period SF1 of the frame period Fi. The image signal stored in the reading memory 106 is output from the peripheral circuit 102 as the image signal VD and input to the panel 101. The image signal VD input to the panel 101 is input to each pixel, and the brightness of each pixel is selected. Thus, the panel 101 starts displaying an image.

  The image signal stored in the writing memory 105 is written into the memory 103 in the first period of the second set that is continuous with the first set. The image signal written in the first period of the second set is input to the peripheral circuit 102 immediately before the first period, that is, during the first set, and is stored in the writing memory 105. Part of SVD (F (i + 1)). In FIG. 1, it is assumed that all the source image signals SVD (F (i + 1)) are written in the memory 103 during the first period of the first set and the first period of the second set. Next, in the second period of the second set, part of the signal written in the memory 103 is read, and the read image signal is stored in the reading memory 106. The image signal read from the memory 103 in the second period of the second set is an image signal corresponding to the subframe period SF1 of the frame period Fi. The image signal stored in the reading memory 106 is output from the peripheral circuit 102 as the image signal VD and input to the panel 101.

  The image signal stored in the writing memory 105 is not written in the memory 103 in the first period of the third set that is continuous with the second set. This is because all the source image signals SVD (F (i + 1)) are already written in the memory 103 during the first period of the first set and the first period of the second set. In the second period of the third set, part of the signal written in the memory 103 is read, and the read image signal is stored in the reading memory 106. The image signal read from the memory 103 in the third set of the second period is an image signal corresponding to the subframe period SF1 of the frame period Fi. The image signal stored in the reading memory 106 is output from the peripheral circuit 102 as the image signal VD and input to the panel 101.

  Through the operations of the first to third groups, all image signals corresponding to the subframe period SF1 are read from the memory 103 and input to the panel 101.

  The operation in the subframe period SF2 will be described. Since all the source image signals SVD (F (i + 1)) have already been written in the memory 103, the image signals stored in the writing memory 105 are stored in the memory 103 in the first period of the first set of the subframe period SF2. Is not written to. In the second period of the set, part of the signal written in the memory 103 is read, and the read image signal is stored in the reading memory 106. The image signal read from the memory 103 in the second period of the set is an image signal corresponding to the subframe period SF2 of the frame period Fi. The image signal stored in the reading memory 106 is output from the peripheral circuit 102 as the image signal VD and input to the panel 101.

  The same operation is repeated in a group that is continuous with the first group in the subframe period SF2. In this way, all image signals corresponding to the subframe period SF2 are read from the memory 103 and input to the panel 101. Through the above operation, image signals corresponding to all subframe periods included in the frame period Fi are read from the memory 103 and input to the panel 101. Thus, the panel 101 displays the image corresponding to the frame period Fi in a time-division gray scale.

  As described above, by writing the image signal to the memory 103 and reading the image signal from the memory 103 in the first period and the second period, the image signal is read from the memory 103 in the frame period Fi. The source image signal SVD (F (i + 1)) can be written into the memory 103 while being input to the panel 101. Even if there is only one memory 103, a signal written to the memory 103 and a signal read from the memory 103 are not mixed. Further, a plurality of sets of the first period and the second period are provided in one frame period, and image signals are selectively written into the memory 103 during the plurality of first periods. The number of times of reading the image signal from the memory 103 can be increased with respect to the number of times of writing. Thus, even when the timing of writing the source image signal to the memory 103 is asynchronous with the subframe period, the reading of the image signal from the memory 103 can be synchronized with the subframe period, and time-division gradation display can be performed. It can be carried out.

  Also in the frame period other than the frame period Fi, the memory 103 is operated in the same manner as the driving method in the frame period Fi described above.

  In the timing chart of FIG. 1, a configuration in which one frame period has two subframe periods SF1 and SF2 is shown. Note that the present invention is not limited to this, and the display device driving method of the present invention can also be applied to a case where one frame period has n (n is a natural number of 2 or more) subframe periods. In addition, when the number of subframes per frame period is n, the number of repetitions of the set of the first period and the second period per frame period may be m (m is a natural number greater than or equal to n) times. it can.

  Although FIG. 1 shows a configuration in which writing to the memory 103 is performed twice in one frame period, the present invention is not limited to this, and a configuration in which writing is performed once in one frame period may be used. A plurality of sets of writing may be performed. Further, FIG. 1 shows a configuration in which image signals are read from the memory 103 in three groups in each of the subframe periods SF1 and SF2, but the present invention is not limited to this. Reading of the image signal from the memory 103 can be performed any number of times in each subframe period. For example, image signals from the memory 103 may be read out in the second period of all sets. Further, in FIG. 1, the lengths of the first period and the second period are shown to be almost the same, but the present invention is not limited to this. The second period may be longer than the first period.

  In the driving method of the display device of the present invention, the number of gradations of an image, the number of subframe periods in one frame period, the storage capacity of the writing memory 105, the storage capacity of the reading memory 106, the writing speed to the memory 103, the memory The number of times the image signal is written to the memory 103 per frame period, the number of times the image signal is read from the memory 103 per subframe period, the length of the first period, and the second period Optimize the length ratio, etc.

(Second Embodiment)
A second embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing a more detailed configuration of the memory 103 of the display device shown in FIG. 2 and a driving state of the memory 103 in each of two consecutive frame periods Fi and F (i + 1). FIG. 4 is a timing chart showing a method for driving the display device when the memory shown in FIG. 3 is used as the memory 103 in FIG. 4 that are the same as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIGS. 3A and 3B, the memory 103 includes a first storage area 301 and a second storage area 302. Each of the first storage area 301 and the second storage area 302 has a storage capacity capable of storing image signals corresponding to a plurality of pixels of the panel 101. The first storage area 301 has a storage capacity for storing a first image signal corresponding to a plurality of pixels of the panel 101. The second storage area 302 has a storage capacity for storing the second image signal corresponding to the plurality of pixels of the panel 101. The first image signal and the second image signal are image signals corresponding to different frame periods.

  In the frame period Fi, an image signal is written into the first storage area 301 (indicated as “W” in FIG. 3A), and the image signal stored in the second storage area 302 is read out (FIG. 3 ( A) Indicated as “R” in the middle). In a frame period F (i + 1) continuous to the frame period Fi, an image signal is written in the second storage area 302 (denoted as “W” in FIG. 3B) and stored in the first storage area 301. The image signal is read (denoted as “R” in FIG. 3B).

  FIG. 4 shows a timing chart when the memory 103 having the configuration shown in FIG. 3 is used. For each frame period, the storage area for writing the image signal and the storage area for reading the image signal are switched.

  In order to perform the driving method shown in FIG. 4, the most significant address bit of each of the memory cells of the memory 103 is used to distinguish between the memory cell that selects image signal writing and the memory cell that selects image signal reading. The most significant address bit may be changed every frame period.

  For example, in the frame period Fi, a signal “0” is input to the most significant address bit of the memory cell corresponding to the first memory area 301 shown in FIG. A signal “1” is input to the most significant address bit of the memory cell to be stored. In the frame period F (i + 1), a signal “1” is input to the most significant address bit of the memory cell corresponding to the first memory area 301 shown in FIG. A configuration in which a “0” signal is input to the most significant address bit of the corresponding memory cell can be adopted.

  This embodiment mode can be implemented freely combining with the first embodiment mode.

(Third embodiment)
In the third embodiment, an example of the panel 101 in FIG. 2 will be described with reference to FIG. In FIG. 5A, the panel 101 includes a pixel portion 501 including a plurality of pixels 500 arranged in a matrix. The pixel portion 501 can have an active matrix structure in which a switching element such as a thin film transistor is provided for each pixel 500. As a display element of the pixel 500, a light-emitting element such as an electroluminescence element or a liquid crystal element may be provided. When a light emitting element is provided as a display element of the pixel 500, the pixel 500 is selected to be in a light emitting state (bright) or a non-light emitting state (dark) by an image signal VD.

  Note that as illustrated in FIG. 5B, a driver circuit for driving the pixel portion 501 may be provided over the same substrate as the substrate over which the pixel portion 501 is formed. 5B, the same portions as those in FIG. 5A are denoted by the same reference numerals, and description thereof is omitted. In FIG. 5B, the first driver circuit 503 and the second driver circuit 504 are illustrated as driver circuits. Note that the present invention is not limited to this, and a driver circuit may be further provided in addition to the first driver circuit 503 and the second driver circuit 504. The driver circuit may be mounted on a substrate over which another pixel portion 501 is formed. The driver circuit may be formed using a thin film transistor formed in the same process as the thin film transistor included in the pixel 500 over the same substrate as the substrate over which the pixel portion 501 is formed. The channel formation region of the thin film transistor may be formed of a polycrystalline semiconductor or an amorphous semiconductor.

  This embodiment mode can be implemented by being freely combined with Embodiment Mode 1 and Embodiment Mode 2.

(Fourth embodiment)
FIG. 6A illustrates a configuration example (hereinafter referred to as a first configuration) of the pixel portion 501 illustrated in FIGS. 5A and 5B. Pixel portion 501 includes a plurality of first signal lines _S 1 _{to S} p (p is a natural number), a plurality of second signals provided so as to intersect the plurality of first signal lines _S 1 to S _p line _G 1 _~G q (q is a natural number) and, a pixel 600 provided at each intersection of the first signal line _S 1 to S _p and the second signal lines _G 1 ~G _q.

A structure of the pixel 600 in FIG. 6A is illustrated in FIG. In FIG. 6 (B), and one _S x of the plurality of first signal lines _S 1 to S _p (x is a natural number not exceeding p), among the plurality of second signal lines _G 1 ~G _q The pixel 600 formed at the intersection with one G _y (y is a natural number equal to or less than q) is shown. The pixel 600 includes a first transistor 601, a second transistor 602, a capacitor 603, and a light-emitting element 604. Note that this embodiment shows an example in which a light-emitting element 604 includes a pair of electrodes and an element that emits light when current flows between the pair of electrodes. Further, as the capacitor 603, the parasitic capacitance or the like of the second transistor 602 may be positively used. The first transistor 601 and the second transistor 602 may be n-channel transistors or p-channel transistors. A thin film transistor can be used as a transistor included in the pixel 600.

The gate of the first transistor 601 is connected to the second signal line G _y , one of the source and the drain of the first transistor 601 is connected to the first signal line S _x , and the other is connected to the second transistor 602. The gate and one electrode of the capacitor 603 are connected. The other electrode of the capacitor 603 is connected to a terminal 605 which is the potential _{V 3} is applied. One of a source and a drain of the second transistor 602 is connected to one electrode of the light emitting element 604, the other is connected to a terminal 606 is supplied with a potential V _2. The other electrode of the light emitting element 604 is connected to a terminal 607 the potential _{V 1} is applied.

  A display method of the pixel portion 501 illustrated in FIGS. 6A and 6B is described.

An image signal is input to all the pixels 600 of the pixel portion 501 in each of a plurality of subframe periods in one frame period. The input image signal is a digital signal. A method for inputting image signals to all the pixels 600 will be described below. Inputting an image signal to ₁ to S _p all of the plurality of first signal lines S while one of the plurality of second signal lines G ₁ ~G _q is selected. Thus, an image signal is input to the pixels in one row of the pixel portion 501. A plurality of second signal lines G _{1 to} G _q are sequentially selected and the same operation is performed, and an image signal is input to all the pixels 600 of the pixel portion 501.

One _{G y} is selected, pixel image signal is input from one _{S x} of the plurality of first signal lines _S 1 to S _p of the plurality of second signal lines _G 1 ~G _q The operation 600 will be described. When the second signal line _Gy is selected, the first transistor 601 is turned on. The on state of the transistor means that the source and the drain are conductive, and the off state of the transistor means that the source and the drain are nonconductive. When the first transistor 601 is turned on, the image signal input to the first signal line _Sx is input to the gate of the second transistor 602 through the first transistor 601. The second transistor 602 is selected to be on or off depending on the input image signal. When the on state of the second transistor 602 is selected, the drain current of the second transistor 602 flows to the light-emitting element 604, and the light-emitting element 604 emits light.

The potential V ₂ and the potential V ₃ are kept so that the potential difference is always constant when the second transistor 602 is turned on. A potential _{V 2} and the potential _{V 3} may be the same potential. If a same potential and potential V ₂ and the potential V ₃ may be connected to the terminal 605 and the terminal 606 in the same wiring. The potential V ₁ and the potential V ₂ are set to have a predetermined potential difference when the light emitting element 604 is selected to emit light. In this manner, a current is supplied to the light emitting element 604 to cause the light emitting element 604 to emit light.

  This embodiment mode can be implemented by being freely combined with the first to third embodiment modes.

(Fifth embodiment)
FIG. 7A illustrates a configuration example of the pixel portion 501 illustrated in FIGS. 5A and 5B. FIG. 7A shows an example (hereinafter referred to as a second configuration) different from the first configuration shown in the fourth embodiment. Pixel portion 501 includes a plurality of first signal lines _S 1 _{to S} p (p is a natural number), a plurality of second signals provided so as to intersect the plurality of first signal lines _S 1 to S _p Lines G _{1 to} G _q (q is a natural number) and a plurality of third signal lines R _{1 to} R _q , first signal lines S _{1 to} S _p , second signal lines G _{1 to} G _q, and third And a pixel 700 provided at each intersection of the signal lines R _{1 to} R _q .

A structure of the pixel 700 in FIG. 7A is illustrated in FIG. In FIG. 7 (B), and one _S x of the plurality of first signal lines _S 1 to S _p (x is a natural number not exceeding p), among the plurality of second signal lines _G 1 ~G _q 1 G _y (y is a natural number equal to or less than q) and a pixel 700 formed at an intersection with one of a plurality of third signal lines R _{1 to} R _q R _y . Note that in the pixel having the structure illustrated in FIG. 7B, the same portions as those in FIG. 6B are denoted by the same reference numerals, and description thereof is omitted. FIG. 7B is different in that the pixel 600 illustrated in FIG. 6B includes a third transistor 701. The third transistor 701 may be an n-channel transistor or a p-channel transistor. A thin film transistor can be used as a transistor included in the pixel 700.

The gate of the third transistor 701 is connected to the third signal line R _y , one of the source and the drain of the third transistor 701 is connected to the gate of the second transistor 602 and one electrode of the capacitor 603, the other is connected to a terminal 702 is supplied with a potential _{V 4.}

  A display method of the pixel portion 501 illustrated in FIGS. 7A and 7B is described.

The method for causing the light emitting element 604 to emit light is the same as the method described in the fourth embodiment. In the pixel having the structure illustrated in FIGS. 7A and 7B, the third signal line R _y and the third transistor 701 are included, whereby an image signal input from the first signal line S _x is converted into an image signal. Regardless, the light-emitting element 604 of the pixel 700 can be made to emit no light. The time during which the light emitting element 604 of the pixel 700 emits light can be set by a signal input to the third signal line R _y . In this way, it is possible to set the light emission period shorter than the period in which the second signal lines G _{1 to} G _q are sequentially selected and all the second signal lines G _{1 to} G _q are selected.

Potential V _4, the second transistor 602 may be set to be turned off when the third transistor 701 is turned on. For example, it is possible the third transistor 701 when the turned on, setting the potential V ₄ to be the same potential as the potential V _3. By making the potential V ₃ and the potential V _{4 the} same potential, the charge held in the capacitor 603 is discharged, the voltage between the source and the gate of the second transistor 602 is set to zero, and the second transistor 602 is turned off. State. In the case where the same potential and the potential V ₃ and the potential V ₄ may be connected to the terminal 605 and the terminal 702 in the same wiring.

Note that the third transistor 701 is not limited to the arrangement shown in FIG. For example, the third transistor 701 may be arranged in series with the second transistor 602. In this structure, the third transistor 701 is turned off by a signal input to the third signal line R _y to cut off the current flowing through the light-emitting element 604 and make the light-emitting element 604 non-light-emitting. Can do.

A diode can be used instead of the third transistor 701 illustrated in FIG. A structure of a pixel in which a diode is used instead of the third transistor 701 is illustrated in FIG. Note that in FIG. 7C, the same portions as those in FIG. 7B are denoted by the same reference numerals, and description thereof is omitted. One electrode of the diode 771 is connected to the third signal line R _y , and the other electrode is connected to the gate of the second transistor 602 and one electrode of the capacitor 603.

  The diode 771 allows a current to flow from one electrode to the other electrode. The second transistor 602 is a p-channel transistor. By increasing the potential of one electrode of the diode 771, the potential of the gate of the second transistor 602 can be increased, so that the second transistor 602 can be turned off.

In FIG. 7C, the diode 771 is configured such that a current flows from one electrode connected to the third signal line R _y to the other electrode connected to the gate of the second transistor 602. Although a structure in which the transistor 602 is a p-channel transistor is shown, the invention is not limited to this. The diode 771 allows current to flow from the other electrode connected to the gate of the second transistor 602 to one electrode connected to the third signal line R _y , so that the second transistor 602 is an n-channel transistor. The configuration may be as follows. When the second transistor 602 is an n-channel transistor, the potential of one electrode of the diode 771 is decreased to decrease the potential of the gate of the second transistor 602, so that the second transistor 602 is turned off. It can be.

  As the diode 771, a diode-connected transistor may be used. A diode-connected transistor refers to a transistor having a drain and a gate connected to each other. As the diode-connected transistor, a p-channel transistor or an n-channel transistor may be used.

  This embodiment mode can be implemented freely combining with any of Embodiment Modes 1 to 4.

  In this embodiment, an example in which a pixel is actually manufactured will be described. FIG. 8A and FIG. 8B are cross-sectional views of the pixels of the panel described in the third to fifth embodiments. An example in which a TFT is used as a switching element arranged in a pixel and a light emitting element is used as a display element arranged in the pixel will be described.

  8A and 8B, 1000 is a substrate, 1001 is a base film, 1002 is a semiconductor layer, 1102 is a semiconductor layer, 1003 is a first insulating film, 1004 is a gate electrode, 1104 is an electrode, 1005 Is a second insulating film, 1006 is an electrode, 1007 is a first electrode, 1008 is a third insulating film, 1009 is a light emitting layer, and 1010 is a second electrode. Reference numeral 1100 denotes a TFT, 1011 denotes a light emitting element, and 1101 denotes a capacitor element. In FIG. 8, a TFT 1100 and a capacitor 1101 are shown as representatives as elements constituting the pixel. The structure in FIG. 8A will be described.

  As the substrate 1000, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, a ceramic substrate, or the like can be used. Alternatively, a metal substrate containing stainless steel or a semiconductor substrate with an insulating film formed on the surface thereof may be used. A substrate made of a synthetic resin having flexibility such as plastic may be used. The surface of the substrate 1000 may be planarized by polishing such as a CMP method.

As the base film 1001, an insulating film such as silicon oxide, silicon nitride, or silicon nitride oxide (SiO _x N _y or SiN _x O _y where x> y) can be used. The base film 1001 can prevent alkali metal such as Na or alkaline earth metal contained in the substrate 1000 from diffusing into the semiconductor layer 1002 and adversely affecting the characteristics of the TFT 1100. Although the base film 1001 has a single-layer structure in FIG. 8, it may be formed of two or more layers. Note that the base film 1001 is not necessarily provided when diffusion of impurities such as a quartz substrate does not cause any problem.

  As the semiconductor layer 1002 and the semiconductor layer 1102, a crystalline semiconductor film or an amorphous semiconductor film processed into an arbitrary shape can be used. The crystalline semiconductor film can be obtained by crystallizing an amorphous semiconductor film. As a crystallization method, a laser crystallization method, a thermal crystallization method using RTA (rapid thermal annealing) or a furnace annealing furnace, a thermal crystallization method using a metal element that promotes crystallization, or the like can be used. The semiconductor layer 1002 includes a channel formation region and a pair of impurity regions to which an impurity element imparting a conductivity type is added. Note that an impurity region to which the impurity element is added at a lower concentration than the pair of impurity regions may be provided between the channel formation region and the pair of impurity regions. The semiconductor layer 1102 can have a structure in which an impurity element imparting conductivity is added to the whole.

  As the first insulating film 1003, silicon oxide, silicon nitride, silicon nitride oxide, or the like can be used, and a single layer or a plurality of films can be stacked.

  As the gate electrode 1004 and the electrode 1104, a single layer or a stacked structure including one kind of element selected from Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, or an alloy or compound containing a plurality of such elements is used. be able to.

  The TFT 1100 includes a semiconductor layer 1002, a gate electrode 1004, and a first insulating film 1003 between the semiconductor layer 1002 and the gate electrode 1004. In FIG. 8, only the TFT 1100 connected to the first electrode 1007 of the light-emitting element 1011 is illustrated as a TFT included in the pixel; however, a structure including a plurality of TFTs may be used. In this embodiment, the TFT 1100 is shown as a top gate type transistor. However, it may be a bottom gate type transistor having a gate electrode below the semiconductor layer, or a dual gate having gate electrodes above and below the semiconductor layer. It may be a gate type transistor.

  The capacitor 1101 includes a first insulating film 1003 as a dielectric, and a semiconductor layer 1102 and an electrode 1104 that face each other with the first insulating film 1003 interposed therebetween as a pair of electrodes. Note that in FIG. 8, as a capacitor element included in a pixel, one of a pair of electrodes is a semiconductor layer 1102 formed simultaneously with the semiconductor layer 1002 of the TFT 1100, and the other electrode is an electrode 1104 formed simultaneously with the gate electrode 1004 of the TFT 1100. However, the present invention is not limited to this configuration.

  As the second insulating film 1005, a single layer or a stacked layer of an inorganic insulating film or an organic insulating film can be used. As the inorganic insulating film, a silicon oxide film formed by a CVD method, a silicon oxide film applied by an SOG (Spin On Glass) method, or the like can be used. As an organic insulating film, polyimide, polyamide, BCB (benzoic acid) is used. A film such as cyclobutene), acrylic or positive photosensitive organic resin, or negative photosensitive organic resin can be used.

  Alternatively, the second insulating film 1005 can be formed using a material having a skeleton structure formed of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (for example, an alkyl group or an aromatic hydrocarbon) can be used. Further, a fluoro group may be used as a substituent. Alternatively, an organic group containing at least hydrogen and a fluoro group may be used as a substituent.

  As the electrode 1006, a single layer or a laminated structure including a film made of one kind of element selected from Al, W, Mo, Ti, Pt, Cu, Ta, and Au, or a film made of an alloy containing a plurality of such elements is used. be able to. Further, as the electrode 1006, a single layer or a laminated structure including a film made of an alloy containing one or more of these elements and one or more elements selected from Ni, C, and Mn or a plurality of the elements is used. Can do.

  One or both of the first electrode 1007 and the second electrode 1010 can be a transparent electrode. As the transparent electrode, 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 be used. Examples of the light-transmitting oxide conductive material include indium tin oxide containing ITO and silicon oxide (hereinafter referred to as ITSO), indium tin oxide including ITO and titanium oxide (hereinafter referred to as ITTO), ITO and molybdenum oxide. Indium tin oxide (hereinafter referred to as ITMO) can also be used. Furthermore, as a light-transmitting oxide conductive material, a target in which titanium, molybdenum, or gallium is added to ITO, or a target in which 2 to 20 wt% zinc oxide (ZnO) is mixed with indium oxide containing silicon oxide is used. You may use what was formed.

The other of the first electrode 1007 and the second electrode 1010 may be formed using a material that does not transmit light. For example, 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 (CaF ₂ , In addition to calcium nitride), rare earth metals such as Yb and Er can be used.

  The third insulating film 1008 can be formed using a material similar to that of the second insulating film 1005. The third insulating film 1008 is formed around the first electrode 1007 so as to cover the end portion of the first electrode 1007, and has a function of separating the light emitting layer 1009 in adjacent pixels.

  The light emitting layer 1009 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 properties. 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 light-emitting element 1011 includes a light-emitting layer 1009 and a first electrode 1007 and a second electrode 1010 that overlap with each other with the light-emitting layer 1009 interposed therebetween. One of the first electrode 1007 and the second electrode 1010 corresponds to an anode, and the other corresponds to a cathode. When a voltage larger than the threshold voltage is applied between the anode and the cathode with a forward bias, the light-emitting element 1011 emits light by current flowing from the anode to the cathode.

  The structure in FIG. 8B will be described. Note that the same portions as those in FIG. 8A are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 8B illustrates a structure in which the insulating film 1108 is provided between the second insulating film 1005 and the third insulating film 1008 in FIG. The electrode 1006 and the first electrode 1007 are connected to each other through the electrode 1106 in a contact hole provided in the insulating film 1108.

  The insulating film 1108 can have a structure similar to that of the second insulating film 1005. The electrode 1106 can have a structure similar to that of the electrode 1006.

  This embodiment can be implemented in combination with the best mode for carrying out the invention.

  In this embodiment, a structure in which a substrate over which pixels are formed is sealed will be described with reference to FIGS. FIG. 9A is a top view of a panel formed by sealing a substrate on which pixels are formed. FIGS. 9B and 9C are respectively A- It is sectional drawing in A '. FIG. 9B and FIG. 9C are examples in which sealing is performed by different methods.

  9A to 9C, a pixel portion 1302 having a plurality of pixels is provided over a substrate 1301, a sealant 1306 is provided so as to surround the pixel portion 1302, and a sealing material 1307 is attached. ing. As for the structure of the pixel, the best mode for carrying out the invention described above or the structure shown in Embodiment 1 can be used.

  In the display panel in FIG. 9B, the sealing material 1307 in FIG. 9A corresponds to the counter substrate 1321. A transparent counter substrate 1321 is attached using the sealant 1306 as an adhesive layer, and a sealed space 1322 is formed by the substrate 1301, the counter substrate 1321, and the sealant 1306. The counter substrate 1321 is provided with a color filter 1320 and a protective film 1323 for protecting the color filter. Light emitted from the light emitting elements arranged in the pixel portion 1302 is emitted to the outside through the color filter 1320. The sealed space 1322 is filled with an inert resin or liquid. Note that a light-transmitting resin in which a hygroscopic material is dispersed may be used as the resin filled in the sealed space 1322. Alternatively, the sealing material 1306 and the material filled in the sealed space 1322 may be the same material, and the counter substrate 1321 may be bonded and the pixel portion 1302 may be sealed at the same time.

  In the display panel illustrated in FIG. 9C, the sealing material 1307 in FIG. 9A corresponds to the sealing material 1324. A sealing material 1324 is attached using the sealing material 1306 as an adhesive layer, and a sealed space 1308 is formed by the substrate 1301, the sealing material 1306, and the sealing material 1324. The sealing material 1324 is provided with a hygroscopic agent 1309 in the concave portion in advance, and plays a role in adsorbing moisture, oxygen, and the like in the sealed space 1308 to keep a clean atmosphere and suppressing deterioration of the light emitting element. This concave portion is covered with a fine mesh-shaped cover material 1310. The cover member 1310 allows air and moisture to pass through, but does not allow the moisture absorbent 1309 to pass. Note that the sealed space 1308 may be filled with a rare gas such as nitrogen or argon, and may be filled with a resin or a liquid if inactive.

  An input terminal portion 1311 for transmitting a signal to the pixel portion 1302 and the like is provided on the substrate 1301, and a signal such as a video signal is transmitted to the input terminal portion 1311 via an FPC (flexible printed circuit) 1312. The In the input terminal portion 1311, the wiring formed over the substrate 1301 and the wiring provided in the FPC 1312 are electrically connected using a resin in which a conductor is dispersed (anisotropic conductive resin: ACF). .

  A driver circuit that inputs a signal to the pixel portion 1302 may be formed over the substrate 1301 over which the pixel portion 1302 is formed. A driver circuit for inputting a signal to the pixel portion 1302 may be formed using an IC chip and connected to the substrate 1301 by COG (Chip On Glass), or the IC chip may be connected using a TAB (Tape Auto Bonding) or a printed circuit board. You may arrange | position on the board | substrate 1301. FIG.

  This embodiment can be carried out in any combination with the best mode for carrying out the invention, Embodiment 1.

  The present invention can be applied to a display module in which a circuit for inputting a signal to the panel is mounted on the panel.

  FIG. 10 shows a display module in which a panel 900 and a circuit board 904 are combined. FIG. 10 illustrates an example in which the controller 905, the signal dividing circuit 906, and the like are formed on the circuit board 904. The circuit formed on the circuit board 904 is not limited to this. Any circuit may be formed as long as it generates a signal for controlling the panel.

  Signals output from these circuits formed on the circuit board 904 are input to the panel 900 through the connection wiring 907.

  The panel 900 includes a pixel portion 901 having a plurality of pixels, a first drive circuit 902, and a second drive circuit 903. The configuration of the panel 900 can be the same as the configuration shown in the first embodiment, the second embodiment, or the like. FIG. 10 illustrates an example in which the first driver circuit 902 and the second driver circuit 903 are formed over the same substrate as the substrate over which the pixel portion 901 is formed. However, the display module of the present invention is not limited to this. Only the second driver circuit 903 may be formed over the same substrate as the substrate over which the pixel portion 901 is formed, and the first driver circuit 902 may be formed over the circuit substrate. Both the first drive circuit 902 and the second drive circuit 903 may be formed on a circuit board.

  By incorporating such a display module, display portions of various electronic devices can be formed.

  This embodiment can be implemented by freely combining with the best mode for carrying out the invention, Embodiment 1 and Embodiment 2.

  The present invention can be applied to various electronic devices. Electronic devices include cameras (video cameras, digital cameras, etc.), projectors, head-mounted displays (goggles type displays), navigation systems, car stereos, personal computers, game devices, portable information terminals (mobile computers, mobile phones or electronic books) Etc.), and an image reproduction apparatus (specifically, an apparatus equipped with a display capable of reproducing a recording medium such as Digital Versatile Disc (DVD) and displaying the image). An example of the electronic device is illustrated in FIG.

  FIG. 11A illustrates a laptop personal computer, which includes a main body 911, a housing 912, a display portion 913, a keyboard 914, an external connection port 915, a pointing mouse 916, and the like. The present invention is applied to the display unit 913. By using the present invention, the display unit can be downsized and a good image can be displayed.

  FIG. 11B shows an image reproducing device (specifically, a DVD reproducing device) provided with a recording medium, which includes a main body 921, a housing 922, a first display portion 923, a second display portion 924, a recording medium ( DVD, etc.) includes a reading unit 925, operation keys 926, a speaker unit 927, and the like. The first display unit 923 mainly displays image information, and the second display unit 924 mainly displays character information. The present invention is applied to the first display portion 923 and the second display portion 924. By using the present invention, the display unit can be downsized and a good image can be displayed.

  FIG. 10C illustrates a mobile phone, which includes a main body 931, an audio output portion 932, an audio input portion 933, a display portion 934, operation switches 935, an antenna 936, and the like. The present invention is applied to the display unit 934. By using the present invention, the display unit can be downsized and a good image can be displayed.

  FIG. 10D shows a camera, which includes a main body 941, a display portion 942, a housing 943, an external connection port 944, a remote control receiving portion 945, an image receiving portion 946, a battery 947, an audio input portion 948, operation keys 949, and the like. The present invention is applied to the display portion 942. By using the present invention, the display unit can be downsized and a good image can be displayed.

  This embodiment can be carried out in any combination with the best mode for carrying out the invention, Embodiment 1 to Embodiment 3.

The figure which shows 1st Embodiment. The figure which shows 1st Embodiment. The figure which shows 2nd Embodiment. The figure which shows 2nd Embodiment. The figure which shows 3rd Embodiment. The figure which shows 4th Embodiment. The figure which shows 5th Embodiment. FIG. 3 is a diagram illustrating Example 1; FIG. FIG. FIG.

Explanation of symbols

100 Display device 101 Panel 102 Peripheral circuit 103 Memory 104 Controller 105 Write memory 106 Read memory 107 Selector 301 First storage area 302 Second storage area 500 Pixel 501 Pixel unit 503 First drive circuit 504 Second drive Circuit 600 Pixel 601 First transistor 602 Second transistor 603 Capacitor element 604 Light emitting element 605 Terminal 606 Terminal 607 Terminal 700 Pixel 701 Third transistor 702 Terminal 771 Diode 900 Panel 901 Pixel portion 902 First driver circuit 903 Second Drive circuit 904 circuit board 905 controller 906 signal dividing circuit 907 connection wiring 911 body 912 case 913 display unit 914 keyboard 915 external connection port 916 pointing mouse 921 body 22 Housing 923 First display unit 924 Second display unit 925 Recording medium (DVD etc.) reading unit 926 Operation key 927 Speaker unit 931 Main unit 932 Audio output unit 933 Audio input unit 934 Display unit 935 Operation switch 936 Antenna 941 Main unit 942 Display unit 943 Case 944 External connection port 945 Mocon receiver 946 Image receiver 947 Battery 948 Audio input unit 949 Operation key 1000 Substrate 1001 Base film 1002 Semiconductor layer 1003 First insulating film 1004 Gate electrode 1005 Second insulating film 1006 Electrode 1007 First electrode 1008 Third insulating film 1009 Light emitting layer 1010 Second electrode 1011 Light emitting element 1100 TFT
1101 Capacitance element 1102 Semiconductor layer 1104 Electrode 1106 Electrode 1108 Insulating film 1301 Substrate 1302 Pixel portion 1306 Sealing material 1307 Sealing material 1308 Sealed space 1309 Hygroscopic agent 1310 Cover material 1311 Input terminal portion 1312 FPC
1320 Color filter 1321 Counter substrate 1322 Sealed space 1323 Protective film 1324 Sealing material

Claims (9)

A driving method of a display device, wherein one frame period is divided into n (n is a natural number of 2 or more) subframe periods, and the brightness of each of a plurality of pixels is selected in each of the n subframe periods.
In one frame period, a set of a first period and a second period continuous to the first period is repeated m (m is a natural number of n or more) times,
The controller writes the image signal to the memory in the first period at least once out of repeating the set m times, and reads the image signal from the memory in the second period each time the set is repeated,
A method for driving a display device, characterized in that a timing for starting reading of an image signal from the memory is synchronized with a timing for starting each of the n subframe periods. A driving method of a display device, wherein one frame period is divided into n (n is a natural number of 2 or more) subframe periods, and the brightness of each of a plurality of pixels is selected in each of the n subframe periods.
In one frame period, a set of a first period and a second period continuous to the first period is repeated m (m is a natural number of n or more) times,
The controller writes an image signal to the memory in the first period at least k (k is a natural number less than or equal to n) times out of repeating the set m times, and n times in the second period out of repeating the set m times. Reading image signals from the memory in
A method for driving a display device, characterized in that a timing for starting reading of an image signal from the memory is synchronized with a timing for starting each of the n subframe periods. In claim 1 or claim 2,
An apparatus driving method characterized in that the number of times of reading an image signal from the memory is larger than the number of times of writing the image signal to the memory in one frame period. , In any one of Claims 1 thru | or 3,
The memory has a first storage area and a second storage area,
In the i-th (i is a natural number) frame period, the image signal is written to the first storage area, the image signal stored in the second storage area is read,
In the (i + 1) th frame period that is continuous with the i-th frame period, the image signal is written to the second storage area, and the image signal stored in the first storage area is read,
In the (i + 2) th frame period that is continuous to the (i + 1) th frame period, the image signal is written to the first storage area and the image signal stored in the second storage area is read out. A display device driving method. In claim 4,
The first storage area has a storage capacity for storing a first image signal corresponding to the plurality of pixels,
The second storage area has a storage capacity for storing a second image signal corresponding to the plurality of pixels,
The method for driving a display device, wherein the first image signal and the second image signal are image signals corresponding to different frame periods. In any one of Claims 1 thru | or 5,
The method for driving a display device, wherein the second period is longer than the first period. In any one of Claims 1 thru | or 6,
The display device driving method, wherein the memory is an SRAM. In any one of Claims 1 thru | or 7,
Each of the plurality of pixels includes a light emitting element. In any one of Claims 1 thru | or 7,
Each of the plurality of pixels includes a liquid crystal element.

Images