JP5072254B2 - Display device - Google Patents

Description

The present invention relates to a display device using a light emitting element. Specifically, the present invention relates to an active matrix display device which includes a plurality of pixels arranged in a matrix and each of the plurality of pixels includes a light emitting element. Further, the present invention relates to an electronic device using the display device.

In recent years, research and development of display devices using self-luminous elements have been actively conducted. In particular, a display device using a light-emitting element typified by an electroluminescence (EL) element has been actively researched and developed for practical use in display applications.

When a multi-tone image is displayed in a display device using a light emitting element, an analog driving method (analog gradation method) or a digital driving method (digital gradation method) is employed. The analog driving method is a method in which gradation is obtained by continuously controlling the magnitude of a current flowing through a light emitting element. The digital drive method is a method in which the light emitting element is driven only in two states, an on state (a state in which light is emitted with a luminance of almost 100%) and an off state (a luminance is almost 0%, in a non-light emitting state). is there.

In the digital driving method, since driving is performed only in two states, an on state and an off state, only two gradations can be displayed as it is. Therefore, there is a method combined with a driving method for displaying multiple gradations such as an area gradation method or a time gradation method. The area gradation method is a method in which a subpixel is provided in a pixel, and gradation display is performed depending on the size of the lighted area of the subpixel (see, for example, Patent Document 1). The time gray scale method is a method of expressing a gray scale by controlling the length of a period during which a pixel is lit and the number of times the pixel is lit (see, for example, Patent Document 2 and Patent Document 3).
Japanese Patent Laid-Open No. 11-73158 JP 2001-5426 A JP 2001-343933 A

Hereinafter, an example of a pixel configuration of a display device adopting a digital driving method and an operation thereof will be described. Note that it is difficult to define a source electrode and a drain electrode in a thin film transistor over a substrate having an insulating surface because of its structure. Therefore, hereinafter, one of the source electrode and the drain electrode is referred to as a first electrode and the other is referred to as a second electrode, unless the definition of the source electrode and the drain electrode is particularly required. In general, an N-channel transistor has a source electrode on the low potential side and a drain electrode on the high side, and a P-channel transistor has a source electrode on the high potential side and a drain electrode on the low side.

The pixel 210 includes a writing transistor 203, a driving transistor 205, and a light-emitting element 206 (see FIG. 12). The gate electrode of the writing transistor 203 is connected to the scanning line 202, the first electrode is connected to the signal line 200, and the second electrode is connected to the gate electrode of the driving transistor 205. The driving transistor 205 has a first electrode connected to the power supply line 201 and a second electrode connected to the first electrode of the light-emitting element 206. A second electrode of the light emitting element 206 is connected to a power source 207. In the light-emitting element 206, the first electrode may be an anode and the second electrode may be a cathode, or vice versa. At that time, since the direction of current changes, the potentials of the power supply line 201 and the power supply 207 are set as appropriate.

The capacitor 204 is provided to hold a voltage between the gate electrode and the source electrode of the driving transistor 205 (hereinafter referred to as Vgs). The capacitor 204 may be provided between the gate electrode of the driving transistor 205 and the power supply line 201 or may be provided between the gate electrode of the driving transistor 205 and a wiring kept at a constant potential. Good. Further, the capacitor 204 for holding the voltage between the gate electrode and the source electrode of the driving transistor 205 is not provided, and the gate electrode and the source electrode of the driving transistor 205 are used to hold Vgs of the driving transistor 205. Parasitic capacitance that is parasitic between the two may be used.

The power supply line 201 and the power supply 207 are each kept at a predetermined potential and have a potential difference from each other. The power supply line 201 is kept at a constant potential. The second electrode of the light-emitting element 206 connected to the power source 207 is kept at a constant potential.

When the writing transistor 203 is turned on by a signal input through the scanning line 202, a video signal is input to the gate electrode of the driving transistor 205 through the signal line 200. A potential difference between the potential of the video signal and the potential of the power supply line 201 becomes Vgs of the driving transistor 205. When the driving transistor 205 is turned on by the value of Vgs, a current is supplied to the light emitting element 206, and the light emitting element 206 emits light. On the other hand, when the driving transistor 205 is turned off by the value of Vgs, no current is supplied to the light emitting element 206 and the light emitting element 206 does not emit light. Vgs of the driving transistor 205 is held for a certain period by the capacitor 204 until the next video signal is input to the pixel 210.

Light emission and non-light emission of the light emitting element 206 are determined by turning on and off the driving transistor 205. Therefore, Vgs of the driving transistor 205 needs to be a potential at which the driving transistor 205 is reliably turned on and off, and Vgs of the driving transistor 205 needs to be held so as not to fluctuate for a certain period. is there.

The capacitor 204 is provided in order to hold Vgs of the driving transistor 205. However, when the pixel 210 is miniaturized with high definition, the area of the capacitor element that holds a sufficient charge amount is increased. It was difficult to secure. Further, depending on the degree of miniaturization of the pixel 210, the area where the capacitor element 204 is provided cannot be secured, and Vgs of the driving transistor 205 may be held using the parasitic capacitance of the driving transistor 205.

When the capacitance value of the capacitor 204 is insufficient or a leakage current is generated in the writing transistor 203, the potential of the gate electrode of the driving transistor 205 may gradually vary. In particular, when the pixel 210 displays black, the driving transistor 205 is not completely turned off due to a slight change in the potential of the gate electrode of the driving transistor 205, and a slight current flows through the light emitting element 206. In some cases, light emission (hereinafter referred to as black float) may occur. Black floating is a display defect that is easily recognized and was a major problem.

In view of the above circumstances, an object of the present invention is to provide a display device and an electronic apparatus that can more accurately control light emission and non-light emission of a light emitting element. It is another object of the present invention to provide a display device and an electronic apparatus that can reliably turn on and off a driving transistor in order to more accurately control light emission and non-light emission of a light emitting element.

The present invention provides a display device in which a compensation circuit that constantly applies a constant potential to a gate electrode of a driving transistor for a desired period is provided. By providing the compensation circuit, fluctuations in the potential of the gate electrode of the driving transistor can be prevented. Therefore, the occurrence of black floating that is easily recognized as a display defect particularly in the case of black display is suppressed, and light emission and non-light emission of the light emitting element are controlled more accurately.

Specifically, the voltage value between the anode and the cathode of the light emitting element differs depending on whether the light emitting element emits light or not. The present invention makes use of the voltage value at this time so that when the light emitting element emits light, the potential of the gate electrode of the driving transistor is maintained, and when the light emitting element does not emit light, the driving is performed. Provided is a display device capable of continuing to apply a potential for reliably turning off the potential of the gate electrode of the transistor for use.

The display device of the present invention includes a first transistor, a second transistor (corresponding to a driving transistor), a light emitting element, and a circuit that controls conduction between a gate electrode of the second transistor and a power supply line (in a compensation circuit). A plurality of pixels.

In the display device having the above structure, the gate electrode of the first transistor is electrically connected to the scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the other of the source electrode and the drain electrode is the first electrode. It is electrically connected to the gate electrode of the second transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light-emitting element. The second electrode of the light emitting element is kept at a constant potential. The circuit is turned on or off depending on the potential of the first electrode of the light-emitting element and the potential of the scan line. The potential of the power supply line is kept at a potential different from the potential of the second electrode of the light emitting element.

The display device of the present invention includes a first transistor, a second transistor (corresponding to a driving transistor), a light emitting element, and a circuit that controls conduction between a gate electrode of the second transistor and a power supply line (in a compensation circuit). And a plurality of pixels including a gate electrode of the second transistor and a control element for controlling conduction of the second scan line.

In the display device having the above structure, the gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the source electrode and the drain electrode are connected to each other. The other is electrically connected to the gate electrode of the second transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light-emitting element. The second electrode of the light emitting element is kept at a constant potential. The circuit is turned on or off depending on the potential of the first electrode of the light-emitting element and the potential of the first scan line. The control element is turned on or off based on the potential of the second scan line. The potentials of the power supply line and the second scanning line are kept at a potential for turning off the second transistor.

In the display device having the above structure, the gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the source electrode and the drain are connected. The other electrode is electrically connected to the gate electrode of the second transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light-emitting element. The second electrode of the light emitting element is kept at a constant potential. The circuit is turned on or off depending on the potential of the first electrode of the light-emitting element, the potential of the first scan line, and the potential of the second scan line. The control element is turned on or off based on the potential of the second scan line. The potentials of the power supply line and the second scanning line are kept at a potential for turning off the second transistor.

The display device of the present invention includes a first transistor, a second transistor (corresponding to a driving transistor), a light emitting element, and a circuit that controls conduction between a gate electrode of the second transistor and a power supply line (in a compensation circuit). And a plurality of pixels including a control element that controls conduction between one of the source electrode and the drain electrode of the second transistor and the power supply line.

In the display device having the above structure, the gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the source electrode and the drain electrode are connected to each other. The other is electrically connected to the gate electrode of the second transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line through the control element, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light emitting element. Yes. The second electrode of the light emitting element is kept at a constant potential. The circuit is turned on or off depending on the potential of the first electrode of the light-emitting element and the potential of the first scan line. The control element is turned on or off depending on the potential of the second scan line. The potential of the power supply line is kept at a potential different from the potential of the second electrode of the light emitting element.

The display device of the present invention includes a plurality of pixels each including a first transistor, a second transistor, a light emitting element, a third transistor, and a fourth transistor. The gate electrode of the first transistor is electrically connected to the scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the other of the source electrode and the drain electrode is connected to the gate electrode of the second transistor. One of the source electrode and the drain electrode of the third transistor is electrically connected. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light-emitting element and the gate electrode of the third transistor. Has been. The second electrode of the light emitting element is kept at a constant potential. The other of the source electrode and the drain electrode of the third transistor is electrically connected to one of the source electrode and the drain electrode of the fourth transistor. The gate electrode of the fourth transistor is electrically connected to the scan line, and the other of the source electrode and the drain electrode is electrically connected to the power supply line. The potential of the power supply line is kept at a potential for turning off the second transistor.

The display device of the present invention includes a plurality of pixels each including a first transistor, a second transistor, a light emitting element, a third transistor, a fourth transistor, and a control element. The gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the other of the source electrode and the drain electrode is connected to the second transistor. The gate electrode, one of the source electrode and the drain electrode of the third transistor, and one terminal of the control element are electrically connected. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is electrically connected to the first electrode of the light-emitting element and the gate electrode of the third transistor. Has been. The second electrode of the light emitting element is kept at a constant potential. The other of the source electrode and the drain electrode of the third transistor is electrically connected to one of the source electrode and the drain electrode of the fourth transistor. The gate electrode of the fourth transistor is electrically connected to the first scan line, and the other of the source electrode and the drain electrode is electrically connected to the power supply line. The other terminal of the control element is connected to the second scanning line. The potentials of the power supply line and the second scanning line are kept at a potential for turning off the second transistor.

The display device of the present invention includes a plurality of pixels including a first transistor, a second transistor, a light emitting element, a third transistor, a fourth transistor, a fifth transistor, and a control element. . The gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the other of the source electrode and the drain electrode is connected to the second transistor. The gate electrode is electrically connected to one of the source electrode and the drain electrode of the third transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to the power supply line, and the other of the source electrode and the drain electrode is one of the first electrode of the light emitting element, the gate electrode of the third transistor, and the control element. Is electrically connected to the terminal. The second electrode of the light emitting element is kept at a constant potential. The other of the source electrode and the drain electrode of the third transistor is electrically connected to one of the source electrode and the drain electrode of the fourth transistor. The gate electrode of the fourth transistor is electrically connected to the first scan line, and the other of the source electrode and the drain electrode is electrically connected to one of the source electrode and the drain electrode of the fifth transistor. The other of the source electrode and the drain electrode of the fifth transistor is electrically connected to the power supply line. The other terminal of the control element is connected to the second scanning line. The potentials of the power supply line and the second scanning line are kept at a potential for turning off the second transistor.

In the display device having the above configuration, the control element is a diode. In the display device having the above structure, the control element is a sixth transistor. One terminal of the control element is a gate electrode and a drain electrode of the sixth transistor, and the other terminal of the control element is a source electrode of the sixth transistor. In the display device having the above structure, the first transistor, the second transistor, the light-emitting element, the third transistor, the fourth transistor, the fifth transistor, and the sixth transistor are over the same substrate. Is provided. When the sixth transistor is used as the control element, the first to fifth transistors and the sixth transistor included in the pixel can be manufactured in the same manufacturing process. Therefore, when the sixth transistor is used as the control element, it is not necessary to add a manufacturing process and the transistor can be easily manufactured.

The display device of the present invention includes a plurality of pixels each including a first transistor, a second transistor, a light emitting element, a third transistor, a fourth transistor, and a fifth transistor. The gate electrode of the first transistor is electrically connected to the first scan line, one of the source electrode and the drain electrode is electrically connected to the signal line, and the other of the source electrode and the drain electrode is connected to the second transistor. The gate electrode is electrically connected to one of the source electrode and the drain electrode of the third transistor. One of the source electrode and the drain electrode of the second transistor is electrically connected to one of the source electrode and the drain electrode of the fifth transistor, and the other of the source electrode and the drain electrode is connected to the first electrode and the third electrode of the light-emitting element. The transistor is electrically connected to the gate electrode of the transistor. The second electrode of the light emitting element is kept at a constant potential. The other of the source electrode and the drain electrode of the third transistor is electrically connected to one of the source electrode and the drain electrode of the fourth transistor. The gate electrode of the fourth transistor is electrically connected to the first scan line, and the other of the source electrode and the drain electrode is electrically connected to the power supply line. The gate electrode of the fifth transistor is connected to the second scan line, and the other of the source electrode and the drain electrode is electrically connected to the power supply line.

In the display device having the above structure, the control element is a fifth transistor. The gate electrode of the fifth transistor is connected to the second scanning line, one of the source electrode and the drain electrode is connected to the power supply line, and the other is connected to one of the source electrode and the drain electrode of the second transistor. .

In the display device having the above structure, the third transistor may be a transistor having a plurality of gate electrodes connected to each other. That is, the third transistor may be replaced with a transistor having a plurality of gate electrodes connected to each other (also referred to as a multi-gate transistor). By using a transistor having a plurality of gate electrodes connected to each other, leakage current can be reduced.

In the display device having the above structure, polarities (also referred to as conductivity types) of the first transistor and the fourth transistor are different from each other.

In the display device of the present invention, a driving method capable of realizing high-precision multi-gradation display by a digital driving method or a digital time gradation method can be applied.

In addition, the electronic apparatus (camera such as a portable information terminal, digital camera, video camera, and digital video camera, a mobile phone, a portable television device, a computer such as a notebook computer) according to the present invention has any one of the above-described configurations. The display device is used.

In the present invention, light emission and non-light emission of the light-emitting element can be more accurately controlled by suppressing fluctuations in the potential of the gate electrode of the driving transistor. Therefore, the occurrence of display defects can be suppressed.

Embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below. In the following description, the same reference numerals are used in common between different drawings.

(Embodiment 1)
A structure of a pixel of the display device of the present invention will be described with reference to FIG.

The pixel 110 includes a writing transistor 103, a driving transistor 106, a light emitting element 107, and a circuit for controlling conduction between the gate electrode of the driving transistor 106 and the power supply line 101 (hereinafter referred to as a compensation circuit 109). The compensation circuit 109 includes a transistor 104 and a transistor 105 connected in series.

The pixel 110 may include a capacitor that holds the potential of the gate electrode of the driving transistor 106. A first electrode of the capacitor is connected to a gate electrode of the driving transistor 106, and a second electrode of the capacitor is connected to a source electrode of the driving transistor 106 or a power supply line kept at a constant potential. Hereinafter, a case where the potential of the gate electrode of the driving transistor 106 is held by the capacitance (parasitic capacitance) of the driving transistor 106 will be described.

In the writing transistor 103, the gate electrode is connected to the scanning line 102, the first electrode (one of the source electrode and the drain electrode) is connected to the signal line 100, and the second electrode (the other of the source electrode and the drain electrode) Are connected to the gate electrode of the driving transistor 106 and the first electrode of the transistor 104. In the driving transistor 106, the first electrode (one of the source electrode and the drain electrode) is connected to the first electrode of the light-emitting element 107 and the gate electrode of the transistor 104, and the second electrode (the other of the source electrode and the drain electrode) ) Is connected to the power supply line 101. The second electrode of the light emitting element 107 is connected to a terminal 108 connected to a power source and is kept at a constant potential.

In the transistor 104, the gate electrode is connected to the first electrode of the light-emitting element 107 and the first electrode of the driving transistor 106, and the first electrode (one of the source electrode and the drain electrode) is the gate electrode of the driving transistor 106. And the second electrode (the other of the source electrode and the drain electrode) is connected to the first electrode of the transistor 105. In the transistor 105, the gate electrode is connected to the scan line 102, the first electrode (one of the source electrode and the drain electrode) is connected to the second electrode of the transistor 104, and the second electrode (the source electrode and the drain electrode) The other is connected to the power line 101.

In the light-emitting element 107, the first electrode may be an anode and the second electrode may be a cathode, or vice versa. At that time, since the direction of the current changes, the potential of the power source connected to the power source line 101 or the terminal 108 is set as appropriate.

Both the writing transistor 103 and the transistor 105 are connected to the scanning line 102. The polarities of the writing transistor 103 and the transistor 105 are different from each other. When the writing transistor 103 is on, the transistor 105 is off. Further, when the writing transistor 103 is off, the transistor 105 is on.

Note that in the case where the writing transistor 103 and the transistor 105 have the same polarity, a scanning line corresponding to each of the writing transistor 103 and the transistor 105 is provided.

The transistor 104 is a transistor having a polarity that is turned off when the potential of the power supply connected to the terminal 108 is transmitted.

Next, the operation of the pixel 110 will be described with reference to a timing chart (see FIG. 2). Hereinafter, as an example, the writing transistor 103 is an N-channel transistor, and the driving transistor 106, the transistor 104, and the transistor 105 are P-channel transistors. Further, the potentials of the signal line 100 and the scanning line 102 are determined based on the potential of the power supply line 101. In the signal line 100, the potential on the H level (high potential) side of the video signal is higher than that of the power supply line 101, and the potential on the L level (low potential) side is such that the driving transistor 106 is surely turned on. It is set to a potential (for example, 0 V). In the scanning line 102, the potential on the H level (high potential) side is higher than the potential of the signal line 100 and the potential for surely turning on the writing transistor 103, and the potential on the L level (low potential) side is The potential is lower than the potential of the signal line 100 and the writing transistor 103 is surely turned off. The potentials of the power supply line 101 and the second electrode of the light emitting element 107 are kept constant.

Note that the polarity of the transistor and each power supply potential do not limit the present invention. It is easy for those skilled in the art to configure an equivalent circuit in accordance with the technical idea described in the present invention by changing the polarity of the transistor and each power supply potential, and the present invention includes these configurations. it is obvious.

In the period T1, when the scan line 102 is selected by the gate driver and the potential of the scan line 102 becomes high, the writing transistor 103 is turned on. In addition, a video signal is input from the source driver to the pixel 110 through the signal line 100. Then, the potential of the video signal is applied to the gate electrode of the driving transistor 106 through the writing transistor 103. The on / off state of the driving transistor 106 is determined by the potential difference between the video signal and the power supply line 101. When the driving transistor 106 is on, a current is supplied from the power supply line 101 to the light emitting element 107 and the light emitting element 107 emits light. When the driving transistor 106 is off, the light emitting element 107 does not emit light. In the period T1, it is assumed that the driving transistor 106 is turned off by a video signal input to the pixel 110.

When selection of the scanning line 102 by the gate driver is completed and the potential of the scanning line 102 becomes low, the writing transistor 103 is turned off. Then, the potential of the gate electrode of the driving transistor 106 is held by the driving transistor 106 until the scanning line 102 is selected again and the next video signal is input to the pixel 110.

In the case where the driving transistor 106 is turned off and the light-emitting element 107 does not emit light based on the video signal input to the pixel 110, the potential of the first electrode of the light-emitting element 107 is the same as that of the power source connected to the terminal 108. It is approximately equal to or higher than the same potential and higher than the potential of the terminal 108 by the threshold voltage of the light emitting element 107 (light emission start potential of the light emitting element 107 (potential at which the light emitting element starts light emission)). Accordingly, the transistor 104 is turned on. At this time, the transistor 105 is on. Then, the gate electrode of the driving transistor 106 is connected to the power supply line 101 through the transistor 104 and the transistor 105. As a result, the potential of the power supply line 101 is transmitted to the gate electrode of the driving transistor 106, and the driving transistor 106 is reliably turned off.

In this manner, when the driving transistor 106 is turned off based on the video signal input to the pixel 110, the compensation circuit 109 is turned on, and the gate electrode of the driving transistor 106 and the power supply line 101 are turned on. . Then, by transmitting the potential of the power supply line 101 to the gate electrode of the driving transistor 106, the driving transistor 106 is reliably turned off. As a result, variation in the potential of the gate electrode of the driving transistor 106 can be prevented. Note that the transistor 104 included in the compensation circuit 109 is controlled based on the potential of the first electrode of the light-emitting element 107. In addition, the transistor 105 included in the compensation circuit 109 is controlled by the potential of the scan line 102. As described above, in the present invention, a dedicated circuit for controlling the compensation circuit 109 is not provided, and the compensation circuit 109 is controlled by utilizing the potential of the first electrode of the light-emitting element 107 and the potential of the scanning line 102. It is characterized by doing.

In the period T2, when the scan line 102 is selected by the gate driver and the potential of the scan line 102 becomes high, the writing transistor 103 is turned on. In addition, a video signal is input from the source driver to the pixel 110 through the signal line 100. In the period T2, the driving transistor 106 is turned on by a video signal input to the pixel 110.

When selection of the scanning line 102 by the gate driver is completed and the potential of the scanning line 102 becomes low, the writing transistor 103 is turned off. Then, the potential of the gate electrode of the driving transistor 106 is held by the driving transistor 106 until the next video signal is input to the pixel 110.

When the driving transistor 106 is turned on based on the video signal input to the pixel 110 and the light-emitting element 107 emits light, the potential of the first electrode of the light-emitting element 107 is the same as or substantially the same as that of the power supply line 101. It becomes. Accordingly, the transistor 104 is turned off. Since the potential of the gate electrode of the driving transistor 106 is low, the driving transistor 106 is on.

Note that when the driving transistor 106 is turned on and the light-emitting element 107 emits light, the charge held in the gate electrode of the driving transistor 106 may leak, and the potential may increase slightly. However, when the driving transistor 106 operates in a linear region, the current value supplied to the light-emitting element 107 is determined by the potential difference between the power supply line 101 and the power supply connected to the terminal 108, so that there is almost no problem. Further, when the driving transistor 106 operates in a saturation region, the current value supplied to the light emitting element 107 is determined by the driving transistor 106, and thus the luminance is slightly reduced. However, in the case of the digital driving method, the operation of the light emitting element 107 is controlled only in two states of light emission and non-light emission, and thus it is difficult to recognize the luminance variation.

Note that the transistor 104 included in the compensation circuit 109 may be replaced with transistors 600 to 603 connected in series (see FIG. 6). That is, the transistor 104 may be replaced with a transistor having a plurality of gate electrodes connected to each other (also referred to as a multi-gate transistor). By using a transistor having a plurality of gate electrodes connected to each other, leakage current can be reduced.

(Embodiment 2)
When multi-gradation display is performed by a combination of a digital driving method and a time gradation method, a desired pixel is forcibly turned off using a control signal in order to perform finer control of light emission time. May require action. In this embodiment, an example in which the present invention is applied to a pixel to which a function of forcibly turning off light is added will be described with reference to FIGS.

The pixel 110 includes a writing transistor 103, a driving transistor 106, a light emitting element 107, a compensation circuit 109 that controls conduction between the gate electrode of the driving transistor 106 and the power supply line 101, a gate electrode of the driving transistor 106, and the scanning line 300. A control element 111 that controls conduction is provided. The compensation circuit 109 includes a transistor 104 and a transistor 105. The control element 111 is a diode 301.

Note that the control element 111 may be a transistor 400 in which a gate electrode and a drain electrode are connected to each other to have a rectifying effect (sometimes referred to as a diode-connected transistor 400) (see FIG. 4A). The transistor 400 can be easily formed in the same process as other transistors included in the pixel 110. Note that the configuration of the control element 111 is not limited as long as it is an element having a rectifying effect. Further, as described above, when the transistor 400 is used, the position of the drain electrode differs depending on whether the polarity is an N-channel type or a P-channel type, and thus the connection is changed as appropriate.

Since the connection of the scan line 102, the signal line 100, the writing transistor 103, the driving transistor 106, the power supply line 101, the light-emitting element 107, the transistor 104, and the transistor 105 is similar to that described in Embodiment Mode 1, Then, the explanation is omitted. The first electrode (one terminal) of the diode 301 is connected to the scanning line 300, and the second electrode (the other terminal) is connected to the gate electrode of the driving transistor 106 (see FIG. 3). In the diode-connected transistor 400, the source electrode of the transistor 400 is connected to the scanning line 300, and the gate electrode and the drain electrode are connected to the gate electrode of the driving transistor 106 (see FIG. 4). The potential of the scanning line 300 is kept at a potential at which the driving transistor 106 is turned off.

Next, the operation of the pixel 110 will be described. As an example, the writing transistor 103 is an N-channel transistor, and the driving transistor 106, the transistor 104, the transistor 105, and the transistor 400 are P-channel transistors. Further, the potentials of the signal line 100, the scanning line 102, and the scanning line 300 are determined based on the potential of the power supply line 101. In the signal line 100, the potential on the H level (high potential) side of the video signal is higher than that of the power supply line 101, and the potential on the L level (low potential) side is such that the driving transistor 106 is surely turned on. It is set to a potential (for example, 0 V in this case). In the scanning line 102, the potential on the H level (high potential) side is higher than the potential of the signal line 100 and the potential for surely turning on the writing transistor 103, and the potential on the L level (low potential) side is The potential is lower than the potential of the signal line 100 and the writing transistor 103 is surely turned off. In the scanning line 300, the potential on the H level (high potential) side of the signal is higher than the potential of the signal line 100, and the potential on the L level (low potential) side is lower than the potential of the signal line 100. To do. Note that the polarity of the transistor and each power supply potential do not limit the present invention. It is easy for those skilled in the art to configure an equivalent circuit according to the technical idea described in the present invention by changing the polarity of the transistor and each power supply potential, and it is clear that the present invention includes these structures. It is.

Since the operation of inputting a video signal to the pixel 110 and the operation of lighting and non-lighting the pixel 110 based on the video signal are the same as those described in Embodiment 1, they are omitted here.

Next, an operation for forcibly turning off the pixel 110 will be described.

When the video signal writing operation to the pixel 110 is completed, the gate electrode of the driving transistor 106 is held at a low potential when the light emitting element 107 emits light, and is high when the light emitting element 107 does not emit light. The potential is held.

Here, the scanning line 300 is selected by the gate driver at a timing at which the pixel 110 should be forcibly turned off, and the scanning line 300 becomes a high potential. Then, the control element 111 (the diode 301 or the transistor 400) is turned on, and the potential of the gate electrode of the driving transistor 106 becomes high. More precisely, the potential of the gate electrode of the driving transistor 106 is lower than the high potential side potential of the scanning line 300 by the threshold voltage of the diode 301. By this operation, the driving transistor 106 is turned off, and the current supply to the light emitting element 107 is interrupted. Then, the potential of the first electrode of the light-emitting element 107 is immediately dropped to substantially the same potential as that of the power source connected to the terminal 108, so that the transistor 104 is turned on. The transistor 105 is on. Even after the potential of the scanning line 300 becomes low, the potential of the power supply line 101 is applied to the gate electrode of the driving transistor 106 through the transistor 104 and the transistor 105, so that the driving transistor 106 is turned off. Keep the state of. Through the above operation, the pixel 110 that is once forcibly turned off continues to be in the non-lighted state unless the next video signal is written.

As described above, in the present invention, the control element 111 (the diode 301 or the transistor 400) is turned on at the timing when the pixel 110 should be forcibly turned off. Then, the potential of the scanning line 300 is transmitted to the gate electrode of the driving transistor 106, and the driving transistor 106 is turned off. As described above, by transmitting the potential of the scanning line 300, the driving transistor 106 is turned off. However, in this state, the potential of the gate electrode of the driving transistor 106 may vary. Therefore, in the present invention, the compensation circuit 109 is turned on, and the gate electrode of the driving transistor 106 and the power supply line 101 are turned on. Then, the potential of the power supply line 101 is transmitted to the gate electrode of the driving transistor 106. As a result, fluctuations in the potential of the gate electrode of the driving transistor 106 can be prevented, and the driving transistor 106 can be reliably turned off.

Note that the scanning line 300 is selected, the scanning line 300 becomes a high potential, the control element 111 (the diode 301 or the transistor 400) is turned on, and scanning is performed via the control element 111 (the diode 301 or the transistor 400). When the potential of the line 300 is transmitted to the gate electrode of the driving transistor 106, the driving transistor 106 is turned off and the light emitting element 107 does not emit light. Then, the potential of the first electrode of the light-emitting element 107 immediately drops to substantially the same potential as the power source connected to the terminal 108, and the transistor 104 is turned on.

On the other hand, since the transistor 105 is on, a through path is generated between the scanning line 300 and the power supply line 101 via the transistors 105 and 104 and the control element 111. At this time, there is no problem if the potential when the scanning line 300 is at a high potential and the potential of the power supply line 101 are the same potential, but if there is a potential difference between the two wirings, a current flows.

Therefore, as shown in FIGS. 3B and 4B, the transistor 112 is provided, and when the scanning line 300 becomes a high potential, the transistor 112 is turned off to cut off the path of the through path. Any configuration may be used. There is no particular limitation on the position where the transistor 112 is provided as long as the through path can be blocked. For example, the transistor 112 may be provided between the transistor 104 and the transistor 105. Further, the transistor 112 may be provided between one terminal of the control element 111 and the transistor 104. The transistor 112 is a transistor whose polarity is turned off by a signal transmitted from the scanning line 300 when the control element 111 is turned on by a signal transmitted from the scanning line 300.

Note that in order to hold the potential of the gate electrode of the driving transistor 106 while the pixel 110 is lit, the leakage current of the transistor 104 may be smaller than the leakage current of the diode 301 or the transistor 400. preferable. Therefore, the transistor 104 may be replaced with transistors 600 to 603 connected in series (see FIG. 6). That is, the transistor 104 may be replaced with a transistor having a plurality of gate electrodes connected to each other. By using a transistor having a plurality of gate electrodes connected to each other, leakage current can be further reduced.

(Embodiment 3)
An example in which the present invention is applied to the pixel 110 to which the function of forcibly turning off is added will be described with reference to FIG.

The pixel 110 includes a writing transistor 103, a driving transistor 106, a power supply line 101, a light emitting element 107, a compensation circuit 109 that controls conduction between the gate electrode of the driving transistor 106 and the power supply line 101, and a first of the driving transistor 106. A control element 111 that controls conduction between the electrode and the power supply line 101 is provided. The compensation circuit 109 includes a transistor 104 and a transistor 105. The control element 111 is a transistor 501.

The connection of the scan line 102, the signal line 100 to which a video signal is input, the writing transistor 103, the driving transistor 106, the power supply line 101, the light-emitting element 107, the transistor 104, and the transistor 105 is the same as that described in Embodiment Mode 1. Since it is the same, the description is abbreviate | omitted here. The transistor 501 is connected in series between the second electrode (source electrode or drain electrode) of the driving transistor 106 and the power supply line 101, and the gate electrode thereof is connected to the scanning line 500.

Next, the operation of the pixel 110 will be described. Note that in order to clarify the operation, as an example, the writing transistor 103 is an N-channel transistor, and the driving transistor 106, the transistor 104, the transistor 105, and the transistor 501 are P-channel transistors. Further, the potentials of the signal line 100 and the scanning lines 102 and 500 are determined based on the potential of the power supply line 101. In the signal line 100, the potential on the H level (high potential) side of the video signal is higher than that of the power supply line 101, and the potential on the L level (low potential) side is such that the driving transistor 106 is surely turned on. It is set to a potential (for example, 0 V in this case). In the scanning line 102, the potential on the H level (high potential) side is higher than the potential of the signal line 100 and the potential for surely turning on the writing transistor 103, and the potential on the L level (low potential) side is The potential is lower than the potential of the signal line 100 and the writing transistor 103 is surely turned off. In the scanning line 500, the potential on the H level (high potential) side of the signal is higher than the potential of the power supply line 101, and the potential on the L level (low potential) side is the same as the potential of the signal line 100, or Lower potential. Note that the polarity of the transistor and each power supply potential do not limit the present invention. It is easy for those skilled in the art to configure an equivalent circuit according to the technical idea described in the present invention by changing the polarity of the transistor and each power supply potential, and it is clear that the present invention includes these structures. It is.

Since the operation of inputting a video signal to the pixel 110 and the operation of lighting and non-lighting the pixel 110 based on the video signal are the same as those described in Embodiment 1, they are omitted here.

Next, an operation for forcibly turning off the pixel 110 will be described.

When the writing operation of the video signal to the pixel 110 is completed, the gate electrode of the driving transistor 106 is held at a low potential when the light emitting element 107 emits light, and is high when the light emitting element 107 does not emit light. Is held.

Here, the scanning line 500 is selected by the gate driver at a timing when the pixel 110 should be forcibly turned off, and the scanning line 500 becomes a high potential. Then, the transistor 501 is turned off. By this operation, the current supply path from the power supply line 101 to the light emitting element 107 is interrupted. Then, the potential of the first electrode of the light-emitting element 107 immediately drops to substantially the same potential as that of the power source connected to the terminal 108, and the transistor 104 is turned on. The transistor 105 is on. Therefore, the potential of the power supply line 101 is transmitted to the gate electrode of the driving transistor 106, and the driving transistor 106 is turned off. After that, even when the scanning line 500 is at a low potential, the driving transistor 106 is already off, so that no current is supplied to the light emitting element 107. Through the above operation, the pixel 110 that is once forcibly turned off continues to be in the non-lighted state unless the next video signal is written.

Note that the transistor 104 may be replaced with transistors 600 to 603 connected in series (see FIG. 6). That is, the transistor 104 may be replaced with a transistor having a plurality of gate electrodes connected to each other (also referred to as a multi-gate transistor). By using a transistor having a plurality of gate electrodes connected to each other, leakage current can be further reduced.

The structure of the display device of the present invention will be described with reference to FIG. The display device of the present invention includes a source driver 151, a gate driver 156, and a pixel portion 159. The source driver 151 includes a pulse output circuit 152, latch circuits 153 and 154, and a buffer circuit 155. The gate driver 156 includes a pulse output circuit 157 and a buffer circuit 158. The pulse output circuits 152 and 157 are circuits that output sampling signals, and are, for example, shift registers and decoders. The latch circuits 153 and 154 hold a video signal or output the held video signal to a lower circuit. The buffer circuits 155 and 158 amplify the input signal and output the amplified signal to the lower circuit. The source driver 151 outputs a video signal to the pixel 110 via the signal line. The gate driver 156 outputs a selection signal to the pixel 110 through the scanning line.

The pixel portion 159 includes a plurality of signal lines (S1 to Sx, x is a natural number), a plurality of scanning lines (G1 to Gy, y is a natural number), a plurality of power supply lines (V1 to Vx), and arranged in a matrix. The plurality of pixels 110 are provided. Each of the plurality of pixels 110 includes a writing transistor 103, a driving transistor 106, a transistor 104, a transistor 105, and a light emitting element 107. Note that the configuration of the pixel 110 is not limited to the above configuration, and any of the configurations illustrated in FIGS. 3 to 6 may be used. In addition, the polarity of the transistor included in the pixel 110 is not particularly limited.

A panel which is one embodiment of the display device of the present invention will be described with reference to FIG. The panel includes a source driver 151 including a plurality of elements 125, a gate driver 156, a pixel transistor 159 including a driving transistor 106 and a light emitting element 107 between a substrate 120 and a substrate 121 (FIGS. 8A and 8B). reference). In addition, a connection film 122 provided on the substrate 120 is included. The connection film 122 is connected to a plurality of IC chips. 8A corresponds to AB in FIG. 8A. Further, CD-E in FIG. 8B corresponds to CD-E in FIG.

A sealing material 123 is provided around the source driver 151, the gate driver 156, and the pixel portion 159, and the light-emitting element 107 is sealed with the sealing material 123, the substrate 120, and the substrate 121. The sealing process is a process for protecting the light emitting element 107 from moisture. Here, a method of sealing with a cover material (glass, ceramics, plastic, metal, or the like) is used, but a thermosetting resin or ultraviolet light curing is used. A method of sealing with a functional resin or a method of sealing with a thin film having a high barrier ability such as a metal oxide or a nitride may be used.

When the pixel electrode (first electrode) 160 of the light-emitting element 107 has a light-transmitting property and the counter electrode (second electrode) 161 of the light-emitting element 107 has a light-blocking property, the light-emitting element 107 performs bottom emission ( (See FIG. 8B). In addition, when the pixel electrode 160 of the light-emitting element 107 has a light-shielding property and the counter electrode 161 of the light-emitting element 107 has a light-transmitting property, the light-emitting element 107 performs top emission. In addition, when both the pixel electrode 160 of the light-emitting element 107 and the counter electrode 161 of the light-emitting element 107 have a light-transmitting property, the light-emitting element 107 performs dual emission. Note that the bottom emission means that the light emitting element 107 emits light in the direction of the substrate 120, the top emission means that the light emitting element 107 emits light in the direction of the substrate 121, and the double emission means light emission. It means that the element 107 emits light in the direction of the substrate 120 and the substrate 121.

The light-emitting element 107 includes a layer (hereinafter, abbreviated as an electroluminescent layer 162) containing an electroluminescent material that can obtain luminescence generated by applying an electric field between the pixel electrode 160 and the counter electrode 161. The electroluminescent layer 162 is composed of a single layer or a plurality of layers. In some cases, these layers contain an inorganic compound. The luminescence in the electroluminescent layer 162 includes one or both of light emission (fluorescence) when returning from the singlet excited state to the ground state and light emission (phosphorescence) when returning from the triplet excited state to the ground state.

Note that an element provided over the substrate 120 is preferably formed using a thin film transistor in which a crystalline semiconductor with favorable characteristics such as mobility is used as a channel portion. Then, since the number of external ICs to be connected can be reduced, it is possible to realize a reduction in size, weight, and thickness.

In addition, an element provided over the substrate 120 may be formed using a transistor using an amorphous semiconductor as a channel portion, and the source driver 151 and the gate driver 156 may be formed using an IC chip. The IC chip is bonded onto the substrate 120 or bonded to the connection film 122 by the COG method. An amorphous semiconductor can be easily formed on a substrate with a large area by using a CVD method, and a crystallization step is unnecessary, so that an inexpensive panel can be provided. At this time, if a conductive layer is formed by a droplet discharge method typified by an ink jet method, a cheaper panel can be provided.

One mode of an electronic device using the display device of the present invention will be described with reference to FIGS. The electronic device exemplified here is a mobile phone device, and includes housings 2700 and 2706, a panel 2701, a housing 2702, a printed wiring board 2703, operation buttons 2704, and a battery 2705 (see FIG. 9). The panel 2701 includes a source driver 151, a gate driver 156, and a pixel portion 159, and these circuits are sealed by a pair of substrates. The panel 2701 is detachably incorporated in the housing 2702, and the housing 2702 is fitted on the printed wiring board 2703. The shape and dimensions of the housing 2702 are changed as appropriate in accordance with the electronic device in which the panel 2701 is incorporated. A plurality of IC chips corresponding to one or more selected from a central processing circuit (CPU), a controller circuit, a power supply circuit, and the like are mounted on the printed wiring board 2703.

The panel 2701 is connected to the printed wiring board 2703 through the connection film 2708. A state where the printed wiring board 2703 is mounted on the panel 2701 is called a module. The panel 2701, the housing 2702, and the printed wiring board 2703 are housed in the housings 2700 and 2706 together with the operation buttons 2704 and the battery 2705. A pixel portion included in the panel 2701 is arranged so as to be visible from an opening window provided in the housing 2700.

Note that the casings 2700 and 2706 are examples of the external shape of the mobile phone device, and the electronic device according to the present embodiment can be transformed into various modes depending on the function and application. Therefore, an example of an aspect of the electronic device will be described below with reference to FIG. For example, a camera such as a digital camera or a video camera, a portable game machine, a monitor, a computer, an audio reproduction device such as a car audio, an image reproduction device equipped with a recording medium such as a home game machine, or a portable information terminal such as a PDA ( 10A), a digital video camera (see FIG. 10B), a portable television device (see FIG. 10C), a notebook computer (see FIG. 10D), a television Apparatus (television, television receiver, see FIG. 10E) and the like. The display device of the present invention is used for the display portions 700 to 705 of these electronic devices. In the display device of the present invention, light emission and non-light emission of the light-emitting element can be more accurately controlled by suppressing fluctuations in the potential of the gate electrode of the driving transistor. Therefore, by using the display device of the present invention, it is possible to provide an electronic device in which the occurrence of display defects is suppressed.

A layout diagram of a pixel of the display device of the present invention will be described with reference to FIG. The layout diagram of the pixel 110 illustrated in FIG. 11 corresponds to the equivalent circuit diagram of FIG. The pixel 110 is controlled by signals and potentials transmitted from the scan line 102, the scan line 300, the signal line 100, and the power supply line 101. The pixel 110 includes a writing transistor 103, a transistor 104, a transistor 105, a driving transistor 106, a transistor 400, and a transistor 112. Although not illustrated in the equivalent circuit diagram of FIG. 4B, the pixel 110 includes a capacitor 177. One electrode of the capacitor 177 is connected to the gate electrode of the driving transistor 106, and the other electrode is connected to the power supply line 101. In the layout diagram of FIG. 11, the pixel electrode 178 of the light emitting element 107 included in the pixel 110 is illustrated. In the layout diagram of FIG. 11, the writing transistor 103 is a transistor including two gate electrodes connected to each other, and the transistor 104 is a transistor including a plurality of gate electrodes connected to each other.

FIG. 9 illustrates a structure example of a pixel in a display device of the present invention. The figure which shows a timing chart. FIG. 9 illustrates a structure example of a pixel in a display device of the present invention. FIG. 9 illustrates a structure example of a pixel in a display device of the present invention. FIG. 9 illustrates a structure example of a pixel in a display device of the present invention. FIG. 9 illustrates a structure example of a pixel in a display device of the present invention. 6A and 6B illustrate a display device of the present invention. 6A and 6B illustrate a display device of the present invention. FIG. 11 illustrates an electronic device using a display device of the present invention. FIG. 11 illustrates an electronic device using a display device of the present invention. The figure which shows the layout of a pixel. FIG. 14 illustrates a structure example of a pixel in a display device.

Explanation of symbols

100 signal line 101 power supply line 102 scanning line 103 writing transistor 104 transistor 105 transistor 106 driving transistor 107 light emitting element 108 terminal 109 compensation circuit 110 pixel 111 control element 112 transistor 120 substrate 121 substrate 122 connecting film 123 sealing material 125 plural elements 151 Source driver 152 Pulse output circuit 153 Latch circuit 154 Latch circuit 155 Buffer circuit 156 Gate driver 157 Pulse output circuit 158 Buffer circuit 159 Pixel unit 160 Pixel electrode 161 Counter electrode 162 Electroluminescent layer 177 Capacitance element 178 Pixel electrode 200 Signal line 201 Power supply Line 202 Scan line 203 Writing transistor 204 Capacitance element 205 Driving transistor 206 Light emitting element 207 Power supply 210 300 scan line 301 diode 400 transistor 500 scan line 501 transistor 600 transistor 601 transistor 602 transistor 603 transistor 700 display unit 701 display unit 702 display unit 703 display unit 704 display unit 705 display unit 2700 housing 2701 panel 2702 housing 2703 printed wiring board 2704 Operation button 2705 Battery 2708 Connection film

Claims (1)

A light-emitting element having first to third wirings, first to fourth transistors, a first electrode, and a second electrode;
The first wiring is electrically connected to one of a source and a drain of the first transistor;
The second wiring is electrically connected to a gate of the first transistor and a gate of the second transistor;
The third wiring is electrically connected to one of a source or a drain of the second transistor and one of a source or a drain of the third transistor;
One of a source and a drain of the fourth transistor is electrically connected to the other of the source and the drain of the first transistor and a gate of the third transistor;
The other of the source and the drain of the fourth transistor is electrically connected to the other of the source and the drain of the second transistor;
A gate of the fourth transistor is electrically connected to the other of the source and the drain of the third transistor and the first electrode;
Unlike polarity of said second transistor of said first transistor,
The polarity of the second transistor, the polarity of the third transistor, and the polarity of the fourth transistor are the same,
Before Stories second electrode is electrically connected to the terminal,
The third wiring has a function of supplying a first potential;
The terminal has a function of supplying a second potential;
The potential difference between the second potential and the first potential, Ri potential der that is capable of emitting the light emitting element,
Before SL first wiring has a function of supplying a third potential and the fourth potential,
The second wiring has a function of supplying a fifth potential or a sixth potential;
The third potential is a potential that can turn on the third transistor;
The fourth potential is a potential that can turn off the third transistor;
The fifth potential is a potential that can turn on the first transistor, and a potential that can turn off the second transistor;
The sixth potential is a potential that can turn off the first transistor, and a potential that can turn on the second transistor;
The display device includes a period in which the fifth potential is supplied to the second wiring and the third potential or the fourth potential is supplied to the first wiring .

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