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    • 专利摘要:
    PURPOSE: A display device and a method for driving the same are provided to reduce a power consumption when a high brightness representation is not necessary. CONSTITUTION: A device includes a display(100), a display controller(102), a first member, and a second member. The first member divides one frame period into a plurality of subframe periods and sets one of lighting and non-lighting to each of the plurality of subframe periods. The first member displays n-bits gradation(n is a natural number of two or more) based on a total lighting time during the one frame period. The second member does not divides one frame period into a plurality of subframe periods and sets one of lighting and non-lighting to the one frame period. The second member displays 1-bit gradation according to a total lighting time during the one frame period and operates the display with a lower clock frequency and a lower driving voltage than the first member. The first and second members are controlled by the display controller.
    公开号:KR20040042867A
    申请号:KR1020030080158
    申请日:2003-11-13
    公开日:2004-05-20
    发明作者:코야마준；키무라하지메；야마자키유
    申请人:가부시키가이샤 한도오따이 에네루기 켄큐쇼；
    IPC主号:
    专利说明:

    DISPLAY DEVICE AND DRIVING METHOD OF THE SAME}
    [25] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for inputting a digital video signal to display an image, and more particularly to a display device having a light emitting element. The present invention also relates to an electronic apparatus using a display device.
    [26] A display device that displays an image by disposing light emitting elements for each pixel and controlling the light emission of those light emitting elements will be described below.
    [27] In the present specification, the light emitting element is described as showing an element (OLED element) having a structure in which an organic compound layer that emits light when an electric field is generated between an anode and a cathode is represented, but the light emitting element of the present invention is limited thereto. It doesn't work. Any element that emits light by applying an electric field between the anode and the cathode can be used freely.
    [28] The display device is composed of a display and a peripheral circuit which inputs a signal to the display.
    [29] A block diagram is shown in FIG. 17 regarding the configuration of the display. In FIG. 17, the display 1700 includes a source signal line driver circuit 1701, a gate signal line driver circuit 1702, and a pixel portion 1703. The pixel portion has a configuration in which pixels are arranged in a matrix.
    [30] A thin film transistor (hereinafter referred to as TFT) is disposed in each pixel of the pixel portion. Here, a method of disposing two TFTs for each pixel and controlling the light emission of the light emitting element of each pixel will be described.
    [31] 7 shows the configuration of a pixel portion of a display. In the pixel portion 700, source signal lines S1 to Sx, gate signal lines G1 to Gy, and power supply lines V1 to Vx are arranged, and pixels of x columns y (x and y are natural numbers) are arranged. have. Each pixel 800 has a switching TFT 801, a driving TFT 802, a holding capacitor 803, and a light emitting element 804, respectively.
    [32] FIG. 8 is an enlarged view of one pixel of the pixel portion illustrated in FIG. 7. The pixel includes one S of the source signal lines S1 to Sx, one G of the gate signal lines G1 to Gy, one V of the power supply lines V1 to Vx, a switching TFT 801, and a driving TFT 802. And a storage capacitor 803 and a light emitting element 804.
    [33] The gate electrode of the switching TFT 801 is connected to the gate signal line G, the source region or the drain region of the switching TFT 801 is connected to the source signal line S, and the other side is the driving TFT 802. Is connected to one of the electrodes of the storage capacitor 803. One of the source region and the drain region of the driving TFT 802 is connected to the power supply line V, and the other is connected to the anode or cathode of the light emitting element 804. Of the two electrodes of the storage capacitor 803, the side not connected to the driving TFT 802 and the switching TFT 801 is connected to the power supply line V. As shown in FIG.
    [34] Here, in the present specification, when the source region or the drain region of the driving TFT 802 is connected with the anode of the light emitting element 804, the anode of the light emitting element 804 is called a pixel electrode, and the cathode is the opposite electrode. It is called. On the other hand, when the source region or the drain region of the driving TFT 802 is connected to the cathode of the light emitting element 804, the cathode of the light emitting element 804 is called a pixel electrode, and the anode is called an opposing electrode.
    [35] In addition, the potential given to the power supply line V is called a power supply potential, and the potential given to the counter electrode is called a counter potential.
    [36] The switching TFT 801 and the driving TFT 802 may be p-channel TFTs or n-channel TFTs.
    [37] At this time, the storage capacity 803 does not necessarily need to be installed.
    [38] For example, when an n-channel TFT used as the driving TFT 802 has an LDD region provided so as to overlap with the gate electrode via a gate insulating film, this overlapped region is a parasitic generally called a gate capacitance. Although the capacitance is formed, it is also possible to actively use this parasitic capacitance as a storage capacitance for storing the voltage supplied to the gate electrode of the driver TFT 802.
    [39] The operation when displaying an image having the above-described pixel configuration will be described below.
    [40] A signal is input to the gate signal line G, the potential of the gate electrode of the switching TFT 801 is changed, and the gate voltage is changed. In this way, a signal is input from the source signal line S to the gate electrode of the driving TFT 802 through the source and the drain of the switching TFT 801 which are brought into a conductive state. In addition, a signal is stored in the storage capacity 803. By the signal input to the gate electrode of the driver TFT 802, the gate voltage of the driver TFT 802 is changed, and the source and the drain are brought into a conductive state. The potential of the power supply line V is given to the pixel electrode of the light emitting element 804 via the driving TFT 802. In this way, the light emitting element 804 emits light.
    [41] A method of expressing gray scales in the pixels having such a configuration will be described.
    [42] There are two types of gradation representations, analog and digital. Compared with the analog system, the digital system has the advantage of being resistant to variations in the TFT and increasing the gradation.
    [43] As an example of the digital gradation expression method, a time gradation method is known. The driving method of this system is a method of expressing gray scales by controlling the period during which each pixel of the display device emits light (see Patent Document 1).
    [44] When the period for displaying one image is one frame period, one frame period is divided into a plurality of subframe periods.
    [45] Each sub frame period is turned on or off, that is, the light emitting element of each pixel is made to emit or not emit light, and the period during which the light emitting element emits light is controlled to express the gradation of each pixel.
    [46] The driving method of the time gradation method will be described in detail with reference to the timing chart of FIG. 5 shows an example in which gray scales are expressed using a 4-bit digital video signal. At this time, for the configuration of the pixel and the pixel portion, reference is made to those shown in FIGS. 7 and 8. Here, the counter potential is an electric potential similar to the potential (power supply potential) of the power supply lines V1 to Vx by an external power supply (not shown), or between the potentials of the power supply lines V1 to Vx. The light emitting element 804 can be switched so as to have a potential difference that is enough to emit light.
    [47] In FIG. 5A, one frame period F1 is divided into a plurality of subframe periods SF1 to SF4.
    [48] In the first subframe period SF1, first, the gate signal line G1 is selected, and digital video signals are input from the source signal lines S1 to Sx, respectively, in pixels having the switching TFT 801 connected to the gate signal line G1 with the gate electrode. do. By this input digital video signal, the driving TFT 802 of each pixel is in an ON state or an OFF state.
    [49] Here, in the present specification, the "on state" of the TFT indicates that the source and drain are in a conductive state by the gate voltage thereof. The "off state" of the TFT means that the gate voltage is in a non-conductive state between the source and the drain.
    [50] At this time, since the opposite potential of the light emitting element 804 is set to be almost equal to the potential (power potential) of the power supply lines V1 to Vx, the light emitting element 804 is also used in the pixel in which the driving TFT 802 is turned on. Does not emit light.
    [51] 5B is a timing diagram showing an operation of inputting a digital video signal to the driving TFT 802 of each pixel.
    [52] In Fig. 5B, the periods for sampling signals corresponding to each source signal line in the source signal line driver circuit (not shown) are represented by S1 to Sx. The sampled signal is simultaneously output to all source signal lines in the retrace period in the figure. The signal output in this manner is input to the gate electrode of the driver TFT 802 in the pixel where the gate selection line is selected.
    [53] The above operation is repeated for all the gate signal lines G1 to Gy, and the writing period ends. At this time, the recording period of the first subframe period SF1 is referred to as Ta1. In general, the recording period of the jth (j is a natural number) subframe period is called Taj.
    [54] When the recording period Ta1 ends, the opposing potential changes so as to have a potential difference such that the light emitting element 804 emits light between the power supply potential. In this way, the display period Ts1 starts. At this time, the display period of the first subframe period SF1 is referred to as Ts1. In general, the display period of the jth subframe period of j (j is a natural number) is called Tsj. In the display period Ts1, the light emitting element 804 of each pixel is in a state of emitting or not emitting light in accordance with the input signal.
    [55] The above operation is repeated for all subframe periods SF1 to SF4, and one frame period F1 ends. Here, the lengths of the display periods Ts1 to Ts4 of the subframe periods SF1 to SF4 are appropriately set, and the gradation is based on the cumulative display period of the subframe periods in which the light emitting element 804 emits light per one frame period F1. Express In short, gradation is expressed according to the total lighting time in one frame period.
    [56] In general, a method of expressing 2 n gradations by inputting an n-bit digital video signal will be described. At this time, for example, one frame period is divided into n subframe periods SF1 to SFn, and the ratio of the lengths of the display periods Ts1 to Tsn of each subframe period SF1 to SFn is Ts1: Ts2: ...: Tsn- 1: Tsn = 2 o : 2 -1 : ··: 2 -n + 2 : 2 -n + 1 At this time, the lengths of the recording periods Ta1 to Tan are the same.
    [57] In the light emitting element 804 in one frame period, by obtaining the sum of the display periods Ts in which the light emission state is selected, the gray level of the pixel in the frame period is determined. For example, when n = 8, the luminance when the pixel emits light in all display periods is 1%. When the pixel emits light in Ts8 and Ts7, the luminance of 1% can be expressed, and Ts6 and Ts4. And when Ts1 is selected, 60% luminance can be expressed.
    [58] At this time, one subframe period may be further divided into a plurality of subframe periods.
    [59] It is preferable that the display device use as little power consumption as possible here. In the case where the display device is inserted and used in a portable information device or the like, it is particularly desirable to reduce the power consumption.
    [60] In this case, in the display device which inputs the above 4-bit signal and expresses the gray level of 2 4 , a method of expressing the gray level using only the signal of the upper 1 bit and reducing the power consumption of the display device has been used ( See Patent Document 2).
    [61] [Patent Document 1]
    [62] Japanese Patent Laid-Open No. 2001-343933
    [63] [Patent Document 2]
    [64] Japanese Patent Laid-Open No. 11-133921
    [65] A drive method of a display device in a second display mode in which the driving of the display in the first display mode method of representing a gray level of 24 in the timing diagram of Figure 13a showing, expressing gray scales by using only the signal of the higher 1 bit Fig. 13B is a timing diagram showing Figs.
    [66] In the second display mode, since one subframe period is sufficient for the driving method, the frequencies of the start pulse and the clock pulse input to the driving circuit (source signal line driving circuit and gate signal line driving circuit) can be reduced. The power consumption can be made smaller than the driving method for expressing the gradation of the upper 1 bit in one display mode.
    [67] In addition, when the total length of the recording periods of the first display mode is longer than the total length of the recording periods of the second display mode, the effective display per one frame period is changed by changing the voltage between the cathode and the anode of the light emitting element according to the display period. The percentage of periods increases.
    [68] However, in such a display device, the voltage input to each driving circuit does not lead to lower power consumption, like the first display mode and the second display mode.
    [69] Therefore, it is an object of the present invention to provide a display device with less power consumption when driving with reduced number of gray scales to be expressed.
    [1] 1 is a timing diagram showing a method of driving a display device of the present invention;
    [2] 2 is a configuration diagram of a memory controller of the display device of the present invention;
    [3] 3 is a configuration diagram of a display controller of a display device of the present invention;
    [4] 4 is a block diagram showing a configuration of a display device of the present invention;
    [5] 5 is a timing diagram showing a driving method of a time gradation method;
    [6] 6 is a block diagram showing a configuration of a display device of the present invention;
    [7] 7 is a configuration diagram of a pixel portion of a display device;
    [8] 8 is a configuration diagram of pixels of a display device;
    [9] 9 is a timing diagram showing a driving method of a conventional display device;
    [10] 10 is a timing diagram showing a method of driving a display device of the present invention;
    [11] 11 is a timing diagram showing a method of driving a display device of the present invention;
    [12] 12 is a view showing the operating conditions of the driving TFT of the present invention;
    [13] 13 is a timing diagram showing a driving method of a conventional display device;
    [14] 14 is a view showing the electronic device of the present invention,
    [15] 15 is a configuration diagram of a source signal line driver circuit of the display device of the present invention;
    [16] 16 is a configuration diagram of a gate signal line driver circuit of the display device of the present invention;
    [17] 17 is a block diagram showing the structure of a conventional display;
    [18] 18 is a timing diagram showing a method of driving a display device of the present invention;
    [19] 19 is a timing diagram showing a method of driving a display device of the present invention.
    [20] * Description of the symbols for the main parts of the drawings *
    [21] 100: display 101: signal control circuit
    [22] 102: display controller 103: memory controller
    [23] 104: CPU 105: Memory A
    [24] 106: memory B
    [70] The display device of the present invention has a first display mode capable of expressing high gradations and a second display mode capable of expressing two gradations and low power consumption, and the two modes can be used interchangeably. In the second display mode as compared with the first display mode, the memory controller of the signal control circuit of the display device removes the recording of the lower bit digital video signal into the memory. It also removes reading of the low bit digital video signal from the memory. In this way, each driving circuit inputs a digital video signal (second digital video signal) having a reduced information amount to the source signal line driving circuit with respect to the digital video signal (first digital video signal) in the first display mode. In response to this operation, the display controller changes the drive voltage to a lower value and a lower frequency of the start pulse and the clock pulse input to each drive circuit (source signal line driver circuit and gate signal line driver circuit). The recording period and the display period involved in the display can be set long, so that the power consumption can be reduced.
    [71] In this case, the two-gradation display indicates that the display device is a two-color display of white and black when the display device is a black and white photo display device, and an eight-color display when the display device is a color display device.
    [72] In addition, compared with the first display mode, the second display mode can set a longer period of one frame. Needless to say, the start pulse and the clock pulse can be stopped in the period in which the display content is confirmed and the recording is not necessary.
    [73] When driving the display device in the second display mode, the voltage for operating the display controller may be set low, and the power consumption of the display controller may be reduced.
    [74] According to the above configuration, in the second display mode, it is possible to provide a display device with low power consumption and a large percentage of the effective display period.
    [75] The display device of the present invention,
    [76] With display,
    [77] With display controller,
    [78] One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    [79] Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, expressing one-bit grayscale according to the total lighting time in the one frame period, and displaying the display. A second means for operating at a lower clock frequency and a lower driving voltage than said first means,
    [80] The first and second means are controlled by the display controller.
    [81] The display device of the present invention,
    [82] With display,
    [83] With display controller,
    [84] One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    [85] Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, and a gray level of one bit is expressed according to the total lighting time in the one frame period. And second means for operating the display at a lower clock frequency and a lower driving voltage than the first means, having a frame period longer than one display mode,
    [86] The first and second means are controlled by the display controller.
    [87] The display device of the present invention has a frame memory,
    [88] In the first means, n (n is a natural number of two or more) bits are written and read to display the data, and
    [89] The second means records and reads one bit of data for display.
    [90] The display device of the present invention has a light emitting element for each pixel,
    [91] A specific voltage is applied to the light emitting device,
    [92] The voltage applied to the light emitting element in the first means is higher than the voltage applied to the light emitting element in the second means.
    [93] The display device of the present invention has a light emitting element for each pixel,
    [94] A specific current is applied to the light emitting device,
    [95] The current supplied to the light emitting element in the first means is greater than the current supplied to the light emitting element in the second means.
    [96] In the display device of the present invention, the first means configures the one frame period into three periods of a recording period, a display period, and an erasing period.
    [97] In the display device of the present invention, the display controller is operated at a lower voltage than the first means in the second means.
    [98] A driving method of a display device of the present invention is a driving method of a display device having a display and a display controller.
    [99] One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. A first display mode expressing
    [100] Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, expresses one gray level according to the total lighting time in the one frame period, and displays the display. Has a second display mode for operating at a lower clock frequency and a lower driving voltage than the first display mode,
    [101] The first and second display modes are controlled by the display controller.
    [102] A driving method of a display device of the present invention is a driving method of a display device having a display and a display controller.
    [103] One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and a gray level of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. A first display mode to express,
    [104] Instead of dividing one frame period into subframe periods, the one frame period is set to one of on and off, and one-bit grayscale is expressed according to the total lighting time in the one frame period, and the first display is performed. Has a frame period longer than that of the mode, and has a second display mode for operating the display at a lower clock frequency and a lower driving voltage than the first display mode,
    [105] The first and second display modes are controlled by the display controller.
    [106] In the driving method of the display device of the present invention, the display device has a frame memory, and in the first display mode, n (n is a natural number of two or more) bits is written and read and displayed, and the second display is performed. In mode, one bit of data is recorded, read and displayed.
    [107] In the method of driving the display device of the present invention, the display device has a light emitting element for each pixel, a specific voltage is applied to the light emitting element, and the voltage applied to the light emitting element in the first display mode is the second. It is higher than the voltage applied to the light emitting element in the display mode.
    [108] In the method of driving the display device of the present invention, the display device has a light emitting element for each pixel, a specific current is supplied to the light emitting element, and the current supplied to the light emitting element in the first display mode is the second. It is larger than the current supplied to the light emitting element in the display mode.
    [109] In the driving method of the display device of the present invention, the first display mode is composed of three periods: a recording period, a display period, and an erasing period.
    [110] In the method of driving the display device of the present invention, the display controller operates at a voltage lower than that of the first display mode in the second display mode.
    [111] In the display device and the driving method thereof of the present invention, the display device or the driving method of the display device is applied to an electronic device.
    [112] The display device of the present invention has a first display mode capable of expressing high gradations and a second display mode capable of expressing low gradations and low power consumption, and the two modes can be used interchangeably. Regarding the first display mode In the second display mode, the memory controller of the signal control circuit of the display device removes the recording of the low-bit signal of the digital video signal into the memory. It also removes reading of the low bit digital signal from the memory. In this way, each driving circuit inputs a digital video signal having a reduced information amount to the source signal line driving circuit with respect to the digital video signal in the first display mode. In response to this operation, the display controller changes the drive voltage to a low value by reducing the frequency of the start pulse and the clock pulse input to each drive circuit (source signal line drive circuit and gate signal line drive circuit). As a result, the recording period and the display period related to the display can be set long, and power consumption can be reduced.
    [113] In addition, when driving the display device in the second display mode, the voltage for driving the display controller may be set low to reduce the power consumption of the display controller.
    [114] With the above configuration, it is possible to provide a display device and a driving method thereof in which the power consumption is small and the ratio of the effective display period to one frame period is high in the second display mode.
    [115] The display device of the present invention,
    [116] With display,
    [117] With display controller,
    [118] One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    [119] One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and m (m is a natural number smaller than n) bits according to the total lighting time in the one frame period. Second means for expressing gradation and for operating said display at a lower clock frequency and a lower driving voltage than said first means,
    [120] The first and second means are controlled by the display controller.
    [121] The display device of the present invention has a frame memory,
    [122] The first means records and reads and displays n (n is a natural number of two or more) bits, and the second means writes and reads and displays m (m is a natural number less than n) bits. .
    [123] The display device of the present invention has a light emitting element for each pixel,
    [124] A specific voltage is applied to the light emitting device,
    [125] The voltage applied to the light emitting element in the first means is higher than the voltage applied to the light emitting element in the second means.
    [126] The display device of the present invention has a light emitting element for each pixel,
    [127] The light emitting element is supplied with a specific current,
    [128] The current supplied to the light emitting element in the first means is greater than the current supplied to the light emitting element in the second means.
    [129] In the display device of the present invention, the first means configures the one frame period into three periods of a recording period, a display period, and an erasing period.
    [130] In the display device of the present invention, the second means configures the one frame period into three periods of a recording period, a display period, and an erasing period.
    [131] In the display device of the present invention, the display controller operates at a voltage lower than that of the first means in the second means.
    [132] The present invention is directed to a method of driving a display device having a display and a display controller,
    [133] One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. And a first display mode representing
    [134] One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and m (m is a natural number smaller than n) bits according to the total lighting time in the one frame period. A second display mode expressing a gray scale and operating the display at a lower clock frequency and a lower driving voltage than the first display mode,
    [135] The first and second display modes are controlled by the display controller.
    [136] In the driving method of the display device of the present invention, the display device has a frame memory, and in the first display mode, n (n is a natural number of two or more) bits is written and read and displayed, and the second display is performed. In mode, one bit of data is recorded, read and displayed.
    [137] In the method of driving the display device of the present invention, the display device has a light emitting element for each pixel, and a specific voltage is applied to the light emitting element, and the voltage applied to the light emitting element in the first display mode is the first voltage. 2 is higher than the voltage applied to the light emitting element in the display mode.
    [138] In the method of driving the display device of the present invention, the display device has a light emitting element for each pixel, and a specific current is supplied to the light emitting element, and the current supplied to the light emitting element in the first display mode is the first. 2 is larger than the current supplied to the light emitting element in the display mode.
    [139] In the driving method of the display device of the present invention, the first display mode is composed of three periods: a recording period, a display period, and an erasing period.
    [140] In the method of driving the display device of the present invention, the second display mode is composed of three periods: a recording period, a display period, and an erasing period.
    [141] In the method of driving the display device of the present invention, the display controller operates at a voltage lower than that of the first display mode in the second display mode.
    [142] In the display device and the driving method thereof of the present invention, the display device or the driving method of the display device is applied to an electronic device.
    [143] [Examples of the Invention]
    [144] Embodiment 1
    [145] Embodiment 1 of this invention is described. Here, the first display mode will be described as an example of 4 bits as in the conventional example.
    [146] 1A and 1B are timing diagrams showing a method of driving the display device of the present invention. In general, n (n is a natural number) in the display by inputting the digital video signal of a bit device, in the first display mode, by using the digital image signal of n bits by the n subframe periods SF1~SFn 2 n The gray scale can be expressed, and it is also applicable to the case where two bits are represented by using a digital video signal of 1 bit in the second display mode by the switching operation.
    [147] Further, in general, in a display device for inputting a digital video signal of n (n is a natural number) bits, in the first display mode, n bits of a digital video signal are input and n is obtained using at least n subframe periods. Gray scales can be expressed, and the switching operation can be applied to the case where two bits are represented by using a digital video signal of 1 bit in the second display mode. The reason why the number of gray levels is not set to the power of two of the subframes is to take countermeasures such as pseudo contours on the display. This content is described in Japanese Patent Application No. 2001-257163.
    [148] FIG. 1A is a timing diagram in the case of the first display mode in which 4 bits of signals are input and expresses 2 4 grayscales.
    [149] In each display period of the subframe periods SF1 to SF4 constituting one frame period, the light emission or non-light emission state of each pixel is selected. Here, the counter potential is set to be substantially the same as the power source potential during the recording period, and is changed so as to have a potential difference that the light emitting element emits light between the power source potential and the display period. Since this operation is the same as the conventional example, detailed description thereof will be omitted.
    [150] Fig. 1B shows a timing diagram in the second display mode in which gray scales are expressed using only the signals of the upper 1 bit. Compared with the subframe period corresponding to the upper bits of the first display mode shown in FIG. 1A, the entire period of the recording period and the display period is set longer.
    [151] Therefore, in the second display mode, the luminance of the light emitting element in which the light emitting state is selected can be made smaller in comparison with the luminance of the light emitting element in which the light emitting state is selected in the display period of the subframe period corresponding to the upper bit in the first display mode. Can be. Therefore, in the second display mode, in the display period, the voltage applied between the anode and the cathode of the light emitting element can be set small.
    [152] 19A and 19B show an example in which the frame period of the second display mode is set longer than that of the first display mode. When using time gradation, the frame period cannot be set too long. This is because the longer the frame period is, the longer the subframe period is, in proportion to it, the flicker becomes visible. Therefore, the first display mode cannot lengthen the frame period. However, since the second display mode is two gradations, the problem of flicker caused by the gradations does not occur. Therefore, determining the frame period is determined in the sustain time in the pixel. For this reason, the frame period can be set long by increasing the capacity of the pixel and reducing the leakage. If the frame period becomes longer, the number of recording periods of the screen can be reduced, so that the power consumption can be reduced.
    [153] 3 shows a configuration of a display controller. In Fig. 3, the power source control circuit 305 for the light emitting element maintains the potential (counter potential) of the counter electrode of the light emitting element at the same potential as the power source potential during the writing period, and between the power source potential in the display period. Is controlled so as to have a potential difference that the light emitting element emits light. Here, when the second display mode is selected, the gray scale control signal 34 is input to the power supply control circuit 305 for the light emitting element. As a result, in the pixel in which the light emitting state is selected, the potential of the counter electrode of the light emitting element is changed so that the voltage applied between both electrodes of the light emitting element becomes smaller as the light emitting element emits light.
    [154] In the second display mode, since the magnitude of the voltage applied between the positive electrodes of the light emitting device can be reduced, the stress caused by the applied voltage of the light emitting device can be reduced.
    [155] In addition, the power supply control circuit 306 for driving circuits controls the power supply voltage input to each driving circuit. Here, when the second display mode is selected, the gray scale control signal 34 is inputted to the power supply control circuit 306 for the driving circuit, thereby changing the output power supply voltage for the driving circuit. Since the frequency of the clock pulse of each driving circuit is smaller in the second display mode than in the first display mode, each driving voltage can be operated with a low power supply voltage.
    [156] At this time, although the display device for switching the two modes of the first display mode and the second display mode is shown, in addition to the first display mode and the second display mode, at least one or more modes in which the number of gray levels to be expressed is changed in more detail. Is further set, and it is applicable to the case where the display is performed by switching the plurality of display modes.
    [157] Here, as the configuration of the pixel portion of the display of the display device of the present invention, the pixel having the configuration shown in Fig. 7 can be used in the conventional example. Moreover, the pixel of other well-known structure can also be used freely.
    [158] In addition, a circuit having a known structure can be freely used for the source signal line driver circuit and the gate signal line driver circuit of the display of the display device of the present invention.
    [159] In addition, when driving the display device in the second display mode, the voltage for driving the display controller may be set low to reduce the power consumption of the display controller.
    [160] In addition, the present invention can be applied not only to display devices using OLED devices as light emitting devices but also to self-luminous display devices such as field emission displays and plasma displays.
    [161] Embodiment 2
    [162] Embodiment 2 of the present invention will be described. Here, the first display mode will be described as an example of 4 bits as in the conventional example.
    [163] 18A and 19B show timing diagrams showing a method of driving the display device of the present invention. In general, n (n is a natural number) in the display by inputting the digital video signal of a bit device, in the first display mode, by using the digital image signal of n bits by the n subframe periods SF1~SFn 2 n Can be expressed, and in the second display mode, a gray level of 2 m can be expressed by using a digital video signal of m (m is a natural number less than n) bits.
    [164] Furthermore, in a display device for inputting a digital video signal of n (n is a natural number) bits, in the first display mode, an n-bit digital video signal is input and n gray levels are expressed using at least n subframe periods. By the switching operation, it is also applicable to the case where m (m is a natural number less than n) digital video signal is used in the second display mode and m gradation is expressed. The reason why the number of gray levels is not set to the power of two of the subframes is to take countermeasures such as pseudo contours on the display. This content is described in Japanese Patent Application No. 2001-257163.
    [165] Fig. 18A shows a timing diagram in the case of the first display mode in which 4 bits of signals are input and expresses 2 4 gray levels.
    [166] In each display period of the subframe periods SF1 to SF4 constituting one frame period, the light emission or non-light emission state of each pixel is selected. Here, the counter potential is set to be substantially the same as the power source potential during the recording period, and is changed so as to have a potential difference that the light emitting element emits light between the power source potential and the display period. Since this operation is the same as in the conventional example, detailed description thereof will be omitted.
    [167] Fig. 18B shows a timing chart in the case of the second display mode in which gray scales are expressed using only the signals of the upper two bits. Compared with the accumulated subframe periods corresponding to the upper two bits of the first display mode shown in Fig. 18A, the entire period of the recording period and the display period is set longer. Therefore, in the second display mode, the luminance of the light emitting element in which the light emitting state is selected is small compared with the luminance of the light emitting element in which the light emitting state is selected in the display period of the subframe period corresponding to the upper two bits in the first display mode. can do. Therefore, in the second display mode, in the display period, the voltage applied between the anode and the cathode of the light emitting element can be set small.
    [168] The display controller can be configured with the same configuration as that described in the first embodiment.
    [169] EXAMPLE
    [170] Hereinafter, embodiments of the present invention will be described.
    [171] (Example 1)
    [172] A circuit for inputting a signal for performing the time gradation driving method to the source signal line driving circuit and the gate signal line driving circuit of the display will be described with reference to FIG.
    [173] In this specification, a video signal input to the display device is called a digital video signal. In this case, a display device for inputting a 4-bit digital video signal and displaying an image will be described as an example. However, the present invention is not limited to 4 bits.
    [174] The digital video signal is read by the signal control circuit 101 and outputs the digital video signal VD to the display 100.
    [175] In addition, in this specification, the digital video signal which the signal control circuit 101 edited and converted into the signal input to a display is called a digital video signal.
    [176] The signal and drive voltage for driving the source signal line driver circuit 1107 and the gate signal line driver circuit 1108 of the display 100 are input by the display controller 102.
    [177] At this time, the source signal line driver circuit 1107 of the display 100 includes a shift register 1110, a LAT (A) 1111, and a LAT (B) 1112. In addition, although not shown, a level shifter, a buffer, or the like may be provided. In addition, this invention is not limited to such a structure.
    [178] The signal control circuit 101 is composed of a CPU 104, a memory A 105, a memory B 106, and a memory controller 103.
    [179] The digital video signal input to the signal control circuit 101 is input to the memory A 105 via a switch controlled by the memory controller 103. Here, the memory A 105 has a capacity capable of storing four-bit digital video signals corresponding to all the pixels of the pixel portion 1109 of the display 100. When a signal for one frame period is stored in the memory A 105, the signal of each bit is sequentially read by the memory controller 103, and is input to the source signal line driver circuit as the digital video signal VD.
    [180] When the reading of the signal stored in the memory A 105 starts, this time, the digital video signal corresponding to the next frame period is input to the memory B 106 via the memory controller 103 and starts to be stored. Similarly to memory A 105, memory B 106 also has a capacity capable of storing four-bit digital video signals corresponding to all pixels of the display device.
    [181] In this manner, the signal control circuit 101 has a memory A 105 and a memory B 106 capable of storing four-bit digital video signals for one frame period, respectively. The B 106 are alternately used to sample the digital video signal.
    [182] Here, although the two memory A 105 and the memory B 106 are shown with respect to the signal control circuit 101 which alternately uses and stores a signal, in general, the memory which can store the information of several frames is shown. And these memories can be used alternately.
    [183] 4 is a block diagram of a display device that performs the above operation. The display device is composed of a signal line control circuit 101, a display controller 102, and a display 100.
    [184] The display controller 102 supplies the start pulse SP, the clock pulse CLK, and the drive voltage to the display 100.
    [185] In Fig. 4, a display device for inputting a 4-bit digital video signal and expressing gray scales using a 4-bit digital video signal in the first display mode is shown as an example. The memory A 105 is configured by memories 105_1 to 105_4 that store information of the first to fourth bits of the digital video signal, respectively. Similarly, memory B 106 is also constituted by memories 106_1 to 106_4 that store information of the first to fourth bits of the digital video signal, respectively. The memory corresponding to each of these bits has a storage element capable of storing a signal of one bit as many as the number of pixels constituting one screen.
    [186] In general, in a display device capable of expressing gray scale using an n-bit digital video signal, the memory A 105 is a memory 105_1 to 105_n that stores information of the first to nth bits, respectively. It is composed. Similarly, the memory B 106 also includes memories 106_1 to 106_n that store information of the first to nth bits, respectively. The memory corresponding to each of these bits has a capacity capable of storing signals of one bit each as many as the number of pixels constituting one screen.
    [187] The configuration of the memory controller 103 is shown in FIG. In Fig. 2, the memory controller 103 includes a gray scale limit circuit 201, a memory R / W circuit 202, a reference oscillator circuit 203, a variable frequency divider circuit 204, an x counter 205a, and a y counter ( 205b), x decoder 206a, and y decoder 206b.
    [188] The memory A 105 and the memory B 106 described in Figs. 4 and 6 and the like are processed together and represented as a memory. The memory is composed of a plurality of memory elements. The storage element is made to be selected by the address of (x, y).
    [189] The signal from the CPU 104 is input to the memory R / W circuit 202 through the gray scale limit circuit 201. In the gradation limiting circuit 201, a signal is input to the memory R / W circuit 202 in accordance with either the first display mode or the second display mode. The memory R / W circuit 202 selects whether or not each of the digital video signals corresponding to each bit is written to the memory in accordance with the signal of the gradation limiting circuit 201. Similarly, an operation of reading the digital video signal recorded in the memory is selected.
    [190] The signal from the CPU 104 is input to the reference oscillator circuit 203. The signal from the reference oscillator circuit 203 is input to the variable frequency divider circuit 204 and converted into a signal of an appropriate frequency. Here, a signal from the gradation limiting circuit 201 according to either the first display mode or the second display mode is input to the variable frequency divider circuit 204. Based on this signal, the signal from the variable division circuit 204 selects the x address of the memory through the x counter 205a and the x decoder 206a. Similarly, the signals in the variable division circuit are input to the y counter 205b and the y decoder 206b to select the y address of the memory.
    [191] By using the memory controller 103 of such a structure, when the high gradation display is not necessary, the amount of information of the signal recorded in the memory and read from the memory can be suppressed among the digital video signals input to the signal control circuit. have. It is also possible to change the frequency at which signals are read from the memory.
    [192] Hereinafter, the configuration of the display controller 102 will be described.
    [193] 3 is a diagram illustrating a configuration of the display controller of the present invention. The display controller 102 includes a reference clock generation circuit 301, a variable division circuit 302, a horizontal clock generation circuit 303, a vertical clock generation circuit 304, a power supply control circuit 305 for a light emitting element, and a driving circuit. A power supply control circuit 306.
    [194] The clock signal 31 input from the CPU 104 is input to the reference clock generation circuit 301 to generate a reference clock. This reference clock is input to the horizontal clock generation circuit 303 and the vertical clock generation circuit 304 through the variable frequency divider circuit 302. The gray scale control signal 34 is input to the variable frequency divider circuit 302. This signal changes the frequency of the reference clock.
    [195] The degree of changing the frequency of the reference clock in the variable frequency divider circuit 302 can be appropriately determined by the practitioner.
    [196] In addition, the horizontal clock circuit 303 is input from the CPU 104 to the horizontal cycle signal 32 that determines the horizontal cycle, and outputs the clock pulses S_CLK and the start pulse S_SP for the source signal line driver circuit. Similarly, the vertical clock generation circuit 304 receives the vertical period signal 33 for determining the vertical period from the CPU 104, and outputs the clock pulses G_CLK and the start pulse G_SP for the gate signal line driver circuit.
    [197] In this way, in the memory controller of the signal control circuit, the lower bit signal is not read from the memory, and the frequency of reading the signal from the memory is reduced. In response to this operation, the display controller writes the subframe period in which the frequency of the sampling pulse SP and the clock pulse CLK input to each of the driving circuits (source signal line driving circuit and gate signal line driving circuit) is reduced to represent an image. And the display period can be set long.
    [198] For example, in the first display mode, one frame period for each of the display period Ts1 of the sub-frame period is divided into four sub-frame periods, and: Ts2: Ts3: the ratio of Ts4 2 0: 2 -1: 2 - 2: a 2-3, using a digital video signal of 4 bits, think a display device for expressing gray scales of 24. For simplicity, the lengths of the display periods Ts1 to Ts4 of each subframe period are 8, 4, 2, and 1, respectively. Further, the length of the recording periods Ta1 to Ta4 of each subframe period is set to one. In the second display mode, a case of expressing gray scale using a signal of higher order 1 bit is considered.
    [199] At this time, in the second display mode, the ratio of the subframe period in the first display mode corresponding to the bit involved in the gradation expression per one frame period is 9/19.
    [200] When the configuration of the present invention is not used, for example, when using the conventional driving method as shown in Fig. 9, in the second display mode, 10/19 within one frame period is not involved in the display. It becomes period.
    [201] In the second display mode, on the other hand, in the second display mode, the present invention changes the frequency of the clock signal and the like input to the respective driving circuits of the display and records 19/9 times the length of the recording period in the first display mode. The period is set, and the display period is similarly set to the length 19/9 times the display period Ts1 of the subframe period SF1 corresponding to the first bit of the first display mode. As a result, one frame period can be occupied by the subframe period SF1. Therefore, in the second display mode, it is possible to decrease the period not involved in the display in one frame period.
    [202] In this way, even in the second display mode, the display period of the light emitting element per one frame period can be increased.
    [203] In this embodiment, in the first display mode, one frame period is divided into four subframe periods, and the gray level of 2 4 is expressed using a 4-bit digital video signal. The period may be further divided into a plurality of subframe periods. For example, one frame period may be divided into six subframe periods.
    [204] The light emitting element power supply control circuit 305 maintains the potential (counter potential) of the counter electrode of the light emitting element at a potential substantially equal to the power source potential during the writing period, and the light emitting element is placed between the power source potential in the display period. It is controlled to have a potential difference of the degree of light emission. Here, the gray scale control signal 34 is also input to the power supply control circuit 305 for the light emitting element. As a result, in the pixel in which the light emitting state is selected, the potential of the counter electrode of the light emitting element is changed so that the voltage applied between both electrodes of the light emitting element becomes smaller as the light emitting element emits light.
    [205] In the second display mode, since the voltage applied between the positive electrodes of the light emitting device can be reduced, the stress caused by the voltage applied to the light emitting device can be reduced.
    [206] In addition, the power supply control circuit 306 for driving circuits controls the power supply voltage input to each driving circuit. Here, the gray scale control signal 34 is also input to the power supply control circuit 306 for the driving circuit, thereby changing the output power supply voltage for the driving circuit. Since the frequency of the clock pulse of each driving circuit is smaller in the second display mode than in the first display mode, each driving voltage can be operated with a low power supply voltage.
    [207] Under the present circumstances, you may use the thing of well-known structure, such as the technique disclosed by Japanese Patent Application No. 3110257, for the power supply control circuit 306 for drive circuits.
    [208] Moreover, when driving a display apparatus in a 2nd display mode, you may have a means which can set the voltage which drives a display controller low so that the power consumption of a display controller can be made small.
    [209] The signal control circuit 101, the memory controller 103, the CPU 104, the memory 105, 106, and the display controller 102 described above may be formed integrally with the display 100 on the same substrate as the pixels. May be formed using an LSI chip and bonded with COG on the substrate of the display 100, or may be bonded on the substrate using TAB, and formed on a substrate separate from the display and connected by electric wiring. You may also
    [210] (Example 2)
    [211] In this embodiment, a configuration example of a source signal line driver circuit of the display device of the present invention will be described. 15 shows an example of the configuration of the source signal line driver circuit.
    [212] The source signal line driver circuit is composed of a shift register 1501, a scanning direction switching circuit, a LAT (A) 1502, and a LAT (B) 1503. 15 shows only a part of the LAT (A) 1502 and a part of the LAT (B) 1503 corresponding to one of the outputs from the shift register 1501, but all from the shift register 1501. Regarding the output, LAT (A) 1502 and LAT (B) 1503 of the same configuration correspond.
    [213] The shift register 1501 is composed of a clock inverter, an inverter, and a NAND. The start pulse S_SP for the source signal line driver circuit is input to the shift register 1501, and the clock inverter is driven by the clock pulse S_CLK for the source signal line driver circuit and the inverted clock pulse S_CLKB for the source signal line driver circuit which is a signal whose polarity is inverted. By changing from the conduction state to the non-conduction state, sampling pulses are output from the NAND to the LAT (A) 1502 in order.
    [214] In addition, the scanning direction switching circuit is composed of a switch, and performs an operation of switching the operation direction of the shift register 1501 from left to right in the front of the drawing. In FIG. 15, when the left / right switching signal L / R corresponds to the Lo signal, the shift register 1501 sequentially outputs sampling pulses from left to right in front of the drawing. On the other hand, when the left / right switching signal L / R corresponds to the Hi signal, sampling pulses are sequentially output from the right side to the left side in the front of the drawing.
    [215] The LAT (A) 1502 of each stage consists of a clock inverter and an inverter.
    [216] Here, "LAT (A) 1502 of each stage" indicates LAT (A) 1502 which introduces a video signal input to one source signal line.
    [217] Here, the digital video signal output from the signal control circuit described in the embodiment is inputted by p-dividing (p is a natural number) the VD. In short, signals corresponding to outputs to the p source signal lines are input in parallel. When the sampling pulses are simultaneously input through the buffer to the clock inverters of the L stages (A) 1502 of the p stages, the p-divided input signals are simultaneously sampled at the LAT (A) 1502 of the p stages, respectively. .
    [218] Since a source signal line driver circuit for outputting signal voltages to x source signal lines is described here as an example, x / p sampling pulses are sequentially output from the shift register per horizontal period. In accordance with each sampling pulse, the LAT (A) 1502 of the p stages simultaneously samples the digital video signal corresponding to the output to the p source signal lines.
    [219] In this specification, a method of dividing a digital video signal input to a source signal line driver circuit into p-phase parallel signals and simultaneously receiving p digital video signals by one sampling pulse is called p-division driving. . In FIG. 15, 4 divisions are performed.
    [220] By performing the division driving, the sampling of the shift register of the source signal line driver circuit can be made margin. In this way, the reliability of the display device can be improved.
    [221] When all signals of one horizontal period are input to the LAT (A) 1502 of each stage, the latch pulse LS and the inverted latch pulse LSB whose polarities are inverted are input, and the LAT (A) 1502 of each stage is input. The input signals are simultaneously output to the LAT (B) 1503 of each stage.
    [222] In this case, the " LAT (B) 1503 of each stage "here means a LAT (B) 1503 that inputs signals from the LAT (A) 1502 of each stage, respectively.
    [223] Each stage of the LAT (B) 1503 is composed of a clock inverter and an inverter. The signal output from each stage of the LAT (A) 1502 is held in the LAT (B) 1503 and simultaneously output to the respective source signal lines S1 to Sx.
    [224] At this time, although not shown here, a level shifter, a buffer, or the like may be provided as appropriate.
    [225] The start pulses S_SP, clock pulses S_CLK, and the like input to the shift register 1501, the LAT (A) 1502, and the LAT (B) 1503 are input from the display controller shown in the first embodiment of the present invention.
    [226] In the present invention, the operation of inputting a digital video signal having a small number of bits to the LAT (A) of the source signal line driver circuit is performed by the signal control circuit, and at the same time, the clock pulse S_CLK inputted to the shift register of the source signal line driver circuit, The display controller performs an operation of decreasing the frequency of the start pulse S_SP or the like to lower the driving voltage for operating the source signal line driving circuit.
    [227] In this way, in the second display mode, the source signal line driver circuit can reduce the operation of sampling the digital video signal, thereby reducing the power consumption of the display device.
    [228] At this time, the display device of the present invention is not limited to the configuration of the source signal line driver circuit of the second embodiment, and the source signal line driver circuit of the known configuration can be freely used.
    [229] In addition, according to the configuration of the source signal line driver circuit, the number of signal lines input from the display controller to the source signal line driver circuit and the number of power supply lines of the driving voltage also differ.
    [230] This embodiment can be implemented in combination with Example 1 freely.
    [231] (Example 3)
    [232] In the third embodiment, a configuration example of the gate signal line driver circuit of the display device of the present invention will be described.
    [233] The gate signal line driver circuit is composed of a shift register, a scanning direction switching circuit, and the like. At this time, although not shown here, a level shifter, a buffer, or the like may be provided as appropriate.
    [234] The start pulse G_SP, the clock pulse G_CLK, the drive voltage, and the like are input to the shift register to output a gate signal line selection signal.
    [235] The configuration of the gate signal line driver circuit will be described with reference to FIG. The shift register 3601 is composed of clock inverters 3602 and 3603, inverters 3604, and a NAND 3607. The start register G_SP is input to the shift register 2601, and the clock inverters 3602 and 3603 change to the conduction state and the non-conduction state by the clock pulse G_CLK and the inverted clock pulse G_CLKB, which is a signal in which its polarity is inverted. The sampling pulses are sequentially output from the NAND 3607.
    [236] The scanning direction switching circuit is composed of switches 3605 and 3606, and performs an operation of switching the operation direction of the shift register from left to right in front of the drawing. In Fig. 16, when the scan direction switching signal U / D corresponds to the Lo signal, the shift register outputs sampling pulses sequentially from left to right in the front of the figure. On the other hand, when the scanning direction switching signal U / D corresponds to the Hi signal, sampling pulses are sequentially output from the right side to the left side in the front of the drawing.
    [237] The sampling pulse output from the shift register is input to the NOR 3608 and calculated by the enable signal ENB. This operation is performed to prevent the situation where adjacent gate signal lines are simultaneously selected by weakening the sampling pulse. The signal output from the NOR 3608 is output to the gate signal lines G1 to Gy through the buffers 3609 and 3610.
    [238] At this time, although not shown here, a level shifter, a buffer, or the like may be provided as appropriate.
    [239] The start pulse G_SP, clock pulse G_CLK, drive voltage, and the like input to the shift register are input from the display controller shown in the first embodiment.
    [240] In the present invention, in the second display mode, an operation of reducing the frequency of the clock pulse G_CLK, the start pulse G_SP, or the like input to the shift register of the gate signal line driving circuit, and lowering the driving voltage for operating the gate signal line driving circuit, By a display controller.
    [241] In this way, in the second display mode, the sampling operation of the gate signal line driver circuit can be reduced, and the power consumption of the display device can be controlled.
    [242] At this time, the gate signal line driver circuit of the display device of the present invention is not limited to the structure of the gate signal line driver circuit of the third embodiment, and the gate signal line driver circuit of the known structure can be freely used.
    [243] In addition, according to the structure of the gate signal line driver circuit, the number of signal lines input from the display controller to the gate signal line driver circuit and the number of power supply lines of the driving voltage also differ.
    [244] This embodiment can be implemented in combination with any of the first to second embodiments.
    [245] (Example 4)
    [246] In the display device using time gradation, in addition to the above-described method of separating the address period and the display period, a driving method for simultaneously performing recording and display is also proposed. Specifically, the use of the pixel structure as shown in FIG. 8 is disclosed in Japanese Patent Laid-Open No. 2001-343933. In this method, the number of gradations can be increased by adding an erasing TFT in addition to the conventional switching TFT and driving TFT.
    [247] Specifically, a plurality of gate signal line driver circuits are provided to write in the first gate signal line driver circuit, and the second gate signal line driver circuit is erased before all the lines are written. In the case of 4 bits, there is not much effect, but it is a very effective measure when the gradation becomes 6 bits or more, or when the subframe must be increased a lot by the pseudo contour measure. The present invention is also applicable to a display device employing such a driving method.
    [248] Fig. 10A shows a timing chart when the display is performed in the first display mode. In Fig. 10A, the second gate signal line driver circuit is erased at the fourth bit to shorten the display period.
    [249] 10B shows a timing chart when the display is performed in the second display mode. In Fig. 10B, since it is not necessary to erase in the second gate signal line driver circuit, it is not necessary to input the start pulse G_SP and the clock pulse G_CLK to the second gate signal line driver circuit.
    [250] This embodiment can be combined freely with Examples 1-3.
    [251] (Example 5)
    [252] In addition, although the number of gray scales that can be displayed is small, a method of simultaneously performing the address period and the display period as in the fourth embodiment is also proposed. 11A and 11B show timing charts in the first display mode and the second display mode, respectively. The pixel structure in this case is the same as the conventional structure as shown in FIG. Since there is no erasing period and a display period shorter than the address period can be formed, there is a drawback that the number of gradations in the first display mode is small. However, since the circuit configuration can be simplified, it is possible to adapt to a cheap display device. Do. This embodiment can be combined freely with Examples 1-3. In this case, although the frame period of the present embodiment is divided in the second display mode, the present invention can be applied to a configuration in which the frame period is not divided.
    [253] (Example 6)
    [254] In the above, the time gradation is driven by the constant voltage driving, that is, the driving TFT in the pixel is operated in the linear region, so that the external power supply voltage is driven as it relates to the light emitting element. However, in this system, when the light emitting element is deteriorated and the characteristic between the applied voltage and the luminance is changed, the image persists and the display quality is deteriorated. Therefore, there is a driving method that uses the driving TFT as a current source by operating constant current driving, that is, driving the driving TFT in the pixel in a saturated region. Even in this case, time gradation is possible by controlling the operation period of the driving TFT. The technique for this is described in Japanese Patent Application No. 2001-224422, but the present invention can also be applied to such constant current time gradation. 12 is an operating point of the driving TFT. In the case of constant current driving, in the saturation region with the operating point 2705, the constant voltage driving is performed in the linear region with the operating point 2706.
    [255] This embodiment can be implemented freely in combination with Examples 1 to 5.
    [256] (Example 7)
    [257] In the present specification, the light emitting element is an element (OLED element) having a structure in which an organic compound layer that emits light when an electric field is generated is inserted between an anode and a cathode, but the light emitting element of the present invention is not limited to this structure. .
    [258] In addition, the description herein uses elements that use light emission (fluorescence) when transitioning from the singlet exciter to the ground state, and elements that use light emission (phosphorescence) when transitioning from the triplet exciter to the ground state. use.
    [259] The organic compound layer includes a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and the like. The light emitting element is basically a structure laminated in the order of an anode, a light emitting layer, and a cathode, but in addition, a structure laminated in the order of an anode, a hole injection layer, a light emitting layer, an electron injection layer, and a cathode; Layers, hole transport layers, light emitting layers, electron transport layers, electron injection layers, and cathodes.
    [260] In this case, the organic compound layer is not limited to a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and the like having a clearly distinguished laminated structure. Specifically, the organic compound layer may have a structure in which the materials constituting the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the like are mixed.
    [261] In addition, an inorganic material may be mixed with the organic compound layer.
    [262] The organic compound layer of the OLED device may be any one of a low molecular material, a polymer material, and a medium molecule material.
    [263] At this time, in this specification, the middle molecular material refers to a material which does not sublimate with a molecular number of 20 or less or a length of molecules to be chained up to 10 μm or less.
    [264] This embodiment can be implemented in free combination with Examples 1 to 6.
    [265] (Example 8)
    [266] In this embodiment, an electronic device using the display device of the present invention will be described with reference to Figs. 14A to 14F.
    [267] 14A shows a schematic diagram of a portable information terminal using the display device of the present invention. The portable information terminal is composed of a main body 2701a, an operation switch 2701b, a power switch 2701c, an antenna 2701d, a display portion 2701e, and an external input port 2701f. The display device of the present invention can be used in the display portion 2701e.
    [268] 14B shows a schematic diagram of a personal computer using the display device of the present invention. The personal computer is composed of a main body 2702a, a housing 2702b, a display portion 2702c, an operation switch 2702d, a power switch 2702e and an external input port 2702f. The display device of the present invention can be used in the display portion 2702c.
    [269] 14C shows a schematic diagram of an image reproducing apparatus using the display apparatus of the present invention. The image reproducing apparatus is composed of a main body 2703a, a housing 2703b, a recording medium 2703c, a display portion 2703d, an audio output portion 2703e and an operation switch 2703f. The display device of the present invention can be used in the display portion 2703d.
    [270] 14D shows a schematic diagram of a television using the display device of the present invention. The television is composed of a main body 2704a, a housing 2704b, a display portion 2704c, and an operation switch 2704d. The display device of the present invention can be used in the display portion 2704c.
    [271] 14E shows a schematic diagram of a head mounted display using the display device of the present invention. The head mounted display is composed of a main body 2705a, a monitor portion 2705b, a headband 2705c, a display portion 2705d, and an optical system 2705e. The display device of the present invention can be used in the display portion 2705d.
    [272] 14F shows a schematic diagram of a video camera using the display device of the present invention. The video camera is composed of a main body 2706a, a housing 2706b, a connecting portion 2706c, an image receiving portion 2706d, an eyepiece portion 2706e, a battery 2706f, an audio input portion 2706g, and a display portion 2706h. The display device of the present invention can be used in the display portion 2706h.
    [273] The present invention is not limited to the application electronic device described above, and can be applied to various electronic devices.
    [274] This embodiment can be implemented in combination with any of the first to seventh embodiments.
    [275] According to the present invention, the power consumption of the display device can be reduced. In addition, in the second display mode, it is possible to take a long display period per one frame period, and it becomes possible to provide a display device and a method of driving the device that enable clear image display.
    [276] In addition, since the display period of the light emitting element per one frame period can be increased, when the same brightness is expressed per frame, the voltage applied between the anode and the cathode of the light emitting element can be set small. In this way, it is possible to provide a highly reliable display device.
    [277] INDUSTRIAL APPLICABILITY The present invention is applicable to not only a display device using an OLED element but also a self-luminous display device such as an electric field display and a plasma display as a light emitting element.
    权利要求:
    Claims (44)
    [1" claim-type="Currently amended] With display,
    With display controller,
    One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, expresses one gray level according to the total lighting time in the one frame period, and displays the display. A second means for operating at a lower clock frequency and a lower driving voltage than the first means,
    And controlling the first and second means to the display controller.
    [2" claim-type="Currently amended] With display,
    With display controller,
    One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of lit and unlit, expressing one bit gray scale according to the total lighting time in the one frame period, and n-bit gray scale Second means for operating the display at a lower clock frequency and a lower driving voltage than the first means, having a longer frame period compared to the one frame period to be expressed;
    And controlling the first and second means to the display controller.
    [3" claim-type="Currently amended] The method of claim 1,
    The display device further includes a frame memory,
    In the first means, the display operation is performed by recording and reading n (n is a natural number of two or more) bits,
    And the second means writes and reads one bit of data to perform a display operation.
    [4" claim-type="Currently amended] The method of claim 2,
    The display device further includes a frame memory,
    In the first means, the display operation is performed by recording and reading n (n is a natural number of two or more) bits,
    And the second means writes and reads one bit of data to perform a display operation.
    [5" claim-type="Currently amended] The method of claim 1,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element by the first means is higher than a voltage applied to the light emitting element by the second means.
    [6" claim-type="Currently amended] The method of claim 2,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element by the first means is higher than a voltage applied to the light emitting element by the second means.
    [7" claim-type="Currently amended] The method of claim 1,
    The display device further includes a light emitting element for each pixel,
    A specific current is applied to the light emitting device,
    And a current supplied to the light emitting element by the first means is greater than a current supplied to the light emitting element by the second means.
    [8" claim-type="Currently amended] The method of claim 2,
    The display device further includes a light emitting element for each pixel,
    A specific current is applied to the light emitting device,
    And a current supplied to the light emitting element by the first means is greater than a current supplied to the light emitting element by the second means.
    [9" claim-type="Currently amended] The method of claim 1,
    And said first means comprises said one frame period in three periods: a recording period, a display period, and an erasing period.
    [10" claim-type="Currently amended] The method of claim 2,
    And said first means comprises said one frame period in three periods: a recording period, a display period, and an erasing period.
    [11" claim-type="Currently amended] The method of claim 1,
    And said display controller operates at said second means at a lower voltage than said first means.
    [12" claim-type="Currently amended] The method of claim 2,
    And said display controller operates at said second means at a lower voltage than said first means.
    [13" claim-type="Currently amended] With display,
    With display controller,
    One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. First means for expressing,
    One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and m (m is a natural number smaller than n) bits according to the total lighting time in the one frame period. Second means for expressing gradation and for operating said display at a lower clock frequency and a lower driving voltage than said first means,
    And controlling the first and second means to the display controller.
    [14" claim-type="Currently amended] The method of claim 13,
    The display device further includes a frame memory,
    In the first means, the display operation is performed by recording and reading n (n is a natural number of two or more) bits,
    And the second means writes and reads data of m (m is a natural number smaller than n) and performs a display operation.
    [15" claim-type="Currently amended] The method of claim 13,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element by the first means is higher than a voltage applied to the light emitting element by the second means.
    [16" claim-type="Currently amended] The method of claim 13,
    The display device further includes a light emitting element for each pixel,
    The light emitting element is supplied with a specific current,
    And a current supplied to the light emitting element by the first means is greater than a current supplied to the light emitting element by the second means.
    [17" claim-type="Currently amended] The method of claim 13,
    And said first means comprises said one frame period in three periods: a recording period, a display period, and an erasing period.
    [18" claim-type="Currently amended] The method of claim 13,
    And the second means comprises the one frame period in three periods: a recording period, a display period, and an erasing period.
    [19" claim-type="Currently amended] The method of claim 13,
    The display controller is characterized in that the second means operates at a voltage lower than that of the first means.
    [20" claim-type="Currently amended] In a driving method of a display device having a display and a display controller,
    One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. A first display mode expressing
    Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, expresses one gray level according to the total lighting time in the one frame period, and displays the display. Has a second display mode for operating at a lower clock frequency and a lower driving voltage than the first display mode,
    And controlling the first and second display modes with the display controller.
    [21" claim-type="Currently amended] In a driving method of a display device having a display and a display controller,
    One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and a gray level of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. A first display mode to express,
    Instead of dividing one frame period into a plurality of subframe periods, the one frame period is set to one of on and off, and a gray level of one bit is represented according to the total lighting time in the one frame period, and the first display is performed. Has a frame period longer than that of the mode, and has a second display mode for operating the display at a lower clock frequency and a lower driving voltage than the first display mode,
    And controlling the first and second display modes with the display controller.
    [22" claim-type="Currently amended] The method of claim 20,
    The display device further includes a frame memory,
    In the first display mode, a display operation is performed by writing and reading n (n is a natural number of two or more) bits, and
    And a display operation by recording and reading one bit of data in the second display mode.
    [23" claim-type="Currently amended] The method of claim 21,
    The display device further includes a frame memory,
    In the first display mode, a display operation is performed by writing and reading n (n is a natural number of two or more) bits, and
    And a display operation by recording and reading one bit of data in the second display mode.
    [24" claim-type="Currently amended] The method of claim 20,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element in the first display mode is higher than a voltage applied to the light emitting element in the second display mode.
    [25" claim-type="Currently amended] The method of claim 21,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element in the first display mode is higher than a voltage applied to the light emitting element in the second display mode.
    [26" claim-type="Currently amended] The method of claim 20,
    The display device further includes a light emitting element for each pixel,
    The light emitting element is supplied with a specific current,
    And the current supplied to the light emitting element in the first display mode is greater than the current supplied to the light emitting element in the second display mode.
    [27" claim-type="Currently amended] The method of claim 21,
    The display device further includes a light emitting element for each pixel,
    The light emitting element is supplied with a specific current,
    And the current supplied to the light emitting element in the first display mode is greater than the current supplied to the light emitting element in the second display mode.
    [28" claim-type="Currently amended] The method of claim 20,
    And the first display mode comprises three periods: a recording period, a display period, and an erasing period.
    [29" claim-type="Currently amended] The method of claim 21,
    And the first display mode comprises three periods: a recording period, a display period, and an erasing period.
    [30" claim-type="Currently amended] The method of claim 20,
    And the display controller is operated at a voltage lower than that of the first display mode in the second display mode.
    [31" claim-type="Currently amended] The method of claim 21,
    And the display controller is operated at a voltage lower than that of the first display mode in the second display mode.
    [32" claim-type="Currently amended] In a driving method of a display device having a display and a display controller,
    One frame period is divided into a plurality of subframe periods, and the plurality of subframe periods are set to one of lit and unlit, and gradation of n (n is a natural number of two or more) bits according to the total lighting time of the one frame period. A first display mode expressing
    One frame period is divided into a plurality of subframe periods, the plurality of subframe periods are set to one of on and off, and m (m is a natural number smaller than n) bits according to the total lighting time in the one frame period. A second display mode expressing gray scale and operating the display at a lower clock frequency and a lower driving voltage than the first display mode,
    And controlling the first and second display modes with the display controller.
    [33" claim-type="Currently amended] The method of claim 32,
    The display device further includes a frame memory,
    In the first display mode, a display operation is performed by writing and reading n (n is a natural number of two or more) bits, and
    And a display operation by recording and reading one bit of data in the second display mode.
    [34" claim-type="Currently amended] The method of claim 32,
    The display device further includes a light emitting element for each pixel,
    A specific voltage is applied to the light emitting device,
    And a voltage applied to the light emitting element in the first display mode is higher than a voltage applied to the light emitting element in the second display mode.
    [35" claim-type="Currently amended] The method of claim 32,
    The display device further includes a light emitting element for each pixel,
    The light emitting element is supplied with a specific current,
    And the current supplied to the light emitting element in the first display mode is greater than the current supplied to the light emitting element in the second display mode.
    [36" claim-type="Currently amended] The method of claim 32,
    And the first display mode comprises three periods: a recording period, a display period, and an erasing period.
    [37" claim-type="Currently amended] The method of claim 32,
    And said second display mode comprises three periods: a recording period, a display period, and an erasing period.
    [38" claim-type="Currently amended] The method of claim 32,
    And the display controller is operated at a voltage lower than that of the first display mode in the second display mode.
    [39" claim-type="Currently amended] The method of claim 1,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing device, a television, a head mounted display, and a video camera.
    [40" claim-type="Currently amended] The method of claim 2,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing device, a television, a head mounted display, and a video camera.
    [41" claim-type="Currently amended] The method of claim 13,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing device, a television, a head mounted display, and a video camera.
    [42" claim-type="Currently amended] The method of claim 20,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing apparatus, a television, a head mounted display, and a video camera.
    [43" claim-type="Currently amended] The method of claim 21,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing apparatus, a television, a head mounted display, and a video camera.
    [44" claim-type="Currently amended] The method of claim 32,
    And the display device is used for one electronic device selected from the group consisting of a portable information terminal, a personal computer, an image reproducing apparatus, a television, a head mounted display, and a video camera.
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    同族专利:
    公开号 | 公开日
    CN100397875C|2008-06-25|
    CN1501698A|2004-06-02|
    US7502039B2|2009-03-10|
    TW200421225A|2004-10-16|
    KR100991444B1|2010-11-03|
    US20040095364A1|2004-05-20|
    TWI359394B|2012-03-01|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    2002-11-14|Priority to JPJP-P-2002-00331344
    2002-11-14|Priority to JPJP-P-2002-00331331
    2002-11-14|Priority to JP2002331344A
    2002-11-14|Priority to JP2002331331A
    2003-11-13|Application filed by 가부시키가이샤 한도오따이 에네루기 켄큐쇼
    2004-05-20|Publication of KR20040042867A
    2010-11-03|Application granted
    2010-11-03|Publication of KR100991444B1
    优先权:
    申请号 | 申请日 | 专利标题
    JPJP-P-2002-00331344|2002-11-14|
    JPJP-P-2002-00331331|2002-11-14|
    JP2002331344A|JP4397576B2|2002-11-14|2002-11-14|Driving method of display device|
    JP2002331331A|JP5116202B2|2002-11-14|2002-11-14|Driving method of display device|
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