Display device

Abstract

To provide a display device which can be suppressed in reduction of luminance due to transistor leakage without requiring increase of the number of elements, while minimizing the increase if any.SOLUTION: A display device is provided, comprising: a light-emitting element; a write capacitance having one electrode connected to a first power source line; a first and a second transistors writing signal voltage supplied from a data line to the write capacitance and connected in series between the other electrode of the write capacitance and the data line; a drive transistor supplying current corresponding to the voltage stored in the write capacitance to the light-emitting element; a third transistor controlling connection between one of the source node and the drain node of the drive transistor and the anode of the light-emitting element; and a fourth transistor controlling connection between the anode of the light-emitting element and a second power source line.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present disclosure relates to a display device. [Background technology]

[0002] In recent years, in the field of display devices, flat panel display devices in which pixels including light-emitting sections are arranged in a matrix have become mainstream. One type of flat panel display device is an organic electroluminescence (EL) display device that uses a so-called current-driven electro-optical element, such as an organic electroluminescence (EL) element, whose light emission luminance changes according to the value of a current flowing through the light-emitting section.

[0003] In flat display devices such as organic EL display devices, the transistor characteristics (e.g., threshold voltage) of the drive transistor that drives the electro-optical element may vary from pixel to pixel due to process variations, etc. Patent Document 1, for example, discloses a display device technology that enables a reduction in the time required to write an initialization voltage to the gate node of the drive transistor in performing a correction operation for the characteristics of the drive transistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-34861 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such organic EL display devices, a driving method that cuts off the output of the video signal when displaying a still image to reduce power consumption is becoming common. When the output of the video signal is cut off when displaying a still image, the pixel circuit needs to continue to supply a constant current to the organic EL element, and the brightness changes when the operating point of the driving transistor changes. MOS and LTPS (Low Temperature Polycrystalline Silicon) have a relatively large leakage current, and increasing the number of transistors to maintain the operating point of the driving transistor makes it difficult to achieve a pixel layout with a narrow pitch, which hinders the development of high-definition displays.

[0006] Therefore, the present disclosure proposes a new and improved display device that can suppress brightness reduction due to transistor leakage without increasing the number of elements, or if the number of elements is increased, the increase is kept to a minimum. [Means for solving the problem]

[0007] According to the present disclosure, there is provided a pixel circuit comprising: a light-emitting element; a drive transistor that supplies a current to the light-emitting element; a first reset transistor that sets the potential of an anode of the light-emitting element to a predetermined potential; a first write transistor that controls writing of a signal voltage at a gate node of the drive transistor; a storage capacitor having one end connected to the gate node of the drive transistor and holding a threshold voltage of the drive transistor; and a second write transistor connected in series between the gate node of the drive transistor and the first write transistor.

[0008] According to the present disclosure, there is also provided a method for driving a pixel circuit comprising: a light-emitting element; a drive transistor for supplying a current to the light-emitting element; a first reset transistor for setting the potential of the anode of the light-emitting element to a predetermined potential; a first write transistor for controlling writing of a signal voltage at a gate node of the drive transistor; a storage capacitor having one end connected to the gate node of the drive transistor and for holding a threshold voltage of the drive transistor; and a second write transistor connected in series between the gate node of the drive transistor and the first write transistor, the method comprising: turning on the first write transistor and the second write transistor in a first period after light emission is completed; correcting the threshold voltage of the drive transistor in a second period after the first period; writing a signal voltage to the drive transistor in a third period after the second period; and turning off the first write transistor and the second write transistor in a fourth period after the third period, to pass a current through the light-emitting element through the drive transistor to cause the light-emitting element to emit light. Furthermore, according to the present disclosure, a light-emitting element, a writing capacitance having one electrode connected to a first power supply line, first and second transistors connected in series between the other electrode of the writing capacitance and a data line, the first and second transistors writing a signal voltage supplied from the data line to the writing capacitance, a driving transistor supplying a current to the light-emitting element according to the voltage accumulated in the writing capacitance, a third transistor controlling a connection between one of a source node and a drain node of the driving transistor and an anode of the light-emitting element, and a fourth transistor controlling a connection between the anode of the light-emitting element and a second power supply line, A display device is provided, comprising: Effect of the Invention

[0009] As described above, according to the present disclosure, it is possible to provide a new and improved pixel circuit, display device, pixel circuit driving method, and electronic device that are capable of suppressing luminance reduction due to transistor leakage without increasing the number of elements, or, if the number of elements is increased, keeping the increase to a minimum.

[0010] It should be noted that the above effects are not necessarily limiting, and any of the effects shown in this specification, or other effects that can be understood from this specification, may be achieved in addition to or instead of the above effects. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram illustrating a configuration example of a display device 100 according to an embodiment of the present disclosure. [Diagram 2] 2 is an explanatory diagram showing a more detailed configuration example of the display device 100 according to the embodiment. FIG. [Diagram 3] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Figure 4] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Diagram 5] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Figure 6] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Figure 7] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Figure 8] FIG. 2 is an explanatory diagram illustrating an example of a pixel circuit. [Figure 9] FIG. 2 is an explanatory diagram showing an example of a pixel circuit according to the embodiment. [Figure 10] 10 is an explanatory diagram showing a state in which the pixel circuit shown in FIG. 9 is driven. [Figure 11] FIG. 2 is an explanatory diagram showing an example of a pixel circuit according to the embodiment. [Figure 12] 12 is an explanatory diagram showing a state in which the pixel circuit shown in FIG. 11 is driven. FIG. [Figure 13] FIG. 2 is an explanatory diagram showing an example of a pixel circuit according to the embodiment. [Figure 14] 14 is an explanatory diagram showing a state in which the pixel circuit shown in FIG. 13 is driven. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant description will be omitted.

[0013] The explanation will be given in the following order. 1. Embodiments of the present disclosure 1.1. General Description of the Display Device, the Driving Method for the Display Device, and the Electronic Device of the Present Disclosure 1.2. Configuration and operation examples 2. Summary

[0014] 1. Embodiments of the Present Disclosure [1.1. General Description of the Display Device, the Driving Method for the Display Device, and the Electronic Device of the Present Disclosure] The display device of the present disclosure is a planar (flat panel) display device in which a pixel circuit having a sampling transistor and a storage capacitor is arranged in addition to a driving transistor that drives a light-emitting section. Examples of planar display devices include organic EL display devices, liquid crystal display devices, and plasma display devices. Among these display devices, organic EL display devices use the electroluminescence of organic materials, and use organic EL elements that utilize the phenomenon of emitting light when an electric field is applied to an organic thin film as the light-emitting element (electro-optical element) of the pixel.

[0015] An organic EL display device that uses organic EL elements as the light-emitting portion of a pixel has the following features. That is, since the organic EL elements can be driven with an applied voltage of 10 V or less, the organic EL display device consumes low power. Since the organic EL elements are self-emitting elements, the organic EL display device has high image visibility compared to a liquid crystal display device, which is also a flat display device, and since it does not require lighting components such as a backlight, it is easy to make the organic EL display device lighter and thinner. Furthermore, since the response speed of the organic EL elements is extremely fast, on the order of several microseconds, the organic EL display device does not produce afterimages when displaying moving images.

[0016] An organic EL element is a self-luminous element and a current-driven electro-optical element. In addition to organic EL elements, examples of current-driven electro-optical elements include inorganic EL elements, LED elements, and semiconductor laser elements.

[0017] A flat display device such as an organic EL display device can be used as a display unit (display device) in various electronic devices equipped with a display unit. Examples of the various electronic devices include television systems, head-mounted displays, digital cameras, video cameras, game consoles, notebook personal computers, portable information devices such as e-books, and portable communication devices such as PDAs (Personal Digital Assistants) and mobile phones.

[0018] In the display device, the display device driving method, and the electronic device of the present disclosure, the driving unit may be configured to float the gate node of the driving transistor and then float the source node. Also, the driving unit may be configured to write a signal voltage by a sampling transistor while keeping the source node of the driving transistor in a floating state. The initialization voltage may be supplied to a signal line at a timing different from that of the signal voltage, and may be written to the gate node of the driving transistor by sampling from the signal line by the sampling transistor.

[0019] In the display device, the driving method of the display device, and the electronic device of the present disclosure including the above-mentioned preferred configuration, the pixel circuit can be configured to be formed on a semiconductor such as silicon. Also, the driving transistor can be configured to be composed of a P-channel type transistor. The reason for using a P-channel type transistor as the driving transistor, rather than an N-channel type transistor, is as follows.

[0020] When a transistor is formed on a semiconductor such as silicon, rather than on an insulator such as a glass substrate, the transistor has four terminals (source / gate / drain / backgate (base)) rather than three (source / gate / drain).If an N-channel transistor is used as the drive transistor, the backgate (substrate) voltage will be 0V, which will adversely affect operations such as correcting the variation in threshold voltage of the drive transistor for each pixel.

[0021] In addition, the variation in transistor characteristics is smaller in P-channel transistors that do not have an LDD (Lightly Doped Drain) region than in N-channel transistors that have an LDD region, which is advantageous in miniaturizing pixels and thus increasing the resolution of display devices. For these reasons and other reasons, when assuming formation on a semiconductor such as silicon, it is preferable to use P-channel transistors as drive transistors rather than N-channel transistors.

[0022] In the display device, the driving method for the display device, and the electronic device according to the present disclosure including the above-described preferred configuration, the sampling transistor may also be configured to be a P-channel transistor.

[0023] Alternatively, in the display device, the driving method for the display device, and the electronic device of the present disclosure including the above-mentioned preferred configuration, the pixel circuit may be configured to have a light emission control transistor that controls the light emission / non-emission of the light emitting portion. In this case, the light emission control transistor may also be configured to be a P-channel type transistor.

[0024] Alternatively, in the display device, the driving method of the display device, and the electronic device of the present disclosure including the above-mentioned preferred configuration, the storage capacitor may be configured to be connected between the gate node and the source node of the driving transistor, and the pixel circuit may be configured to have an auxiliary capacitor connected between the source node of the driving transistor and a node of a fixed potential.

[0025] Alternatively, in the display device, the driving method of the display device, and the electronic device of the present disclosure including the above-mentioned preferred configuration, the pixel circuit may be configured to have a switching transistor connected between the drain node of the driving transistor and the cathode node of the light-emitting section. In this case, the switching transistor may also be configured to be a P-channel type transistor. Also, the driving section may be configured to make the switching transistor conductive during a non-light-emitting period of the light-emitting section.

[0026] Alternatively, in the display device, the display device driving method, and the electronic device of the present disclosure including the above-mentioned preferred configuration, the driving unit can be configured to activate the signal that drives the switching transistor before the sampling timing of the initialization voltage by the sampling transistor.Then, the signal that drives the light-emission control transistor can be configured to be set to an inactive state after the signal is set to an active state.In this case, the driving unit can be configured to complete sampling of the initialization voltage by the sampling transistor before the signal that drives the light-emission control transistor is set to an inactive state.

[0027] [1.2. Configuration and operation examples] Next, a configuration example of a display device according to an embodiment of the present disclosure will be described. Fig. 1 is an explanatory diagram showing a configuration example of a display device 100 according to an embodiment of the present disclosure. Hereinafter, the configuration example of the display device 100 according to the embodiment of the present disclosure will be described with reference to Fig. 1.

[0028] The pixel section 110 has a configuration in which pixels, each of which is provided with an organic EL element or other self-luminous element, are arranged in a matrix. In the pixel section 110, scanning lines are provided in the horizontal direction for each line of the pixels arranged in a matrix, and signal lines are provided for each column so as to be perpendicular to the scanning lines.

[0029] The horizontal selector 120 sequentially transfers predetermined sampling pulses and sequentially latches image data with these sampling pulses, thereby distributing the image data to each signal line. The horizontal selector 120 also performs analog-to-digital conversion processing on the image data distributed to each signal line, thereby generating a drive signal that indicates the emission luminance of each pixel connected to each signal line in a time-division manner. The horizontal selector 120 outputs this drive signal to the corresponding signal line.

[0030] The vertical scanner 130 generates drive signals for each pixel and outputs them to the scanning lines SCN in response to the driving of the signal lines by the horizontal selector 120. As a result, the display device 100 sequentially drives each pixel arranged in the pixel section 110 by the vertical scanner 130, causes each pixel to emit light at the signal level of each signal line set by the horizontal selector 120, and displays a desired image on the pixel section 110.

[0031] 2 is an explanatory diagram showing a more detailed configuration example of the display device 100 according to the embodiment of the present disclosure. Hereinafter, the configuration example of the display device 100 according to the embodiment of the present disclosure will be described with reference to FIG.

[0032] In the pixel section 110, pixels 111R that display red, pixels 111G that display green, and pixels 111B that display blue are arranged in a matrix.

[0033] The vertical scanner 130 includes an auto-zero scanner 131, a drive scanner 132, and a write scanner 133. Signals are supplied from each scanner to pixels arranged in a matrix in the pixel unit 110, thereby turning on and off the TFTs provided in each pixel.

[0034] Each pixel provided in the pixel section 110 may take various forms. For example, FIG. 3 shows a pixel circuit consisting of three N-channel transistors and one capacitor. The pixel circuit shown in FIG. 3 is a pixel circuit consisting of N-channel transistors T1, T2, and T3, a capacitor C1, and an organic EL element EL. Details of the driving of the pixel circuit are described in, for example, Japanese Patent Application Laid-Open No. 2008-225345 and the like, and detailed description will be omitted. However, the transistor T1 is a driving transistor for supplying a current to the organic EL element EL, the transistor T2 is a writing transistor for writing a video signal, and the transistor T3 is a reset transistor for extinguishing the organic EL element EL and resetting the anode potential. The pixel circuit shown in FIG. 3 is a circuit having a function of correcting the threshold voltage (Vth correction) of the transistor T1, which is a driving transistor, and correcting the variation in mobility.

[0035] Recently, mainly for mobile panels, a driving method that reduces power consumption by stopping the video signal output when displaying a still image is becoming common. In other words, a driving method that performs low-frequency driving when displaying a still image is being adopted. In this case, the pixel circuit needs to continue supplying a constant current to the organic EL element. In other words, the operating point of the driving transistor (transistor T1 in the pixel circuit shown in Figure 3) must not change when displaying a still image. Oxide TFTs have excellent leakage characteristics and are well suited to this driving method. On the other hand, MOS and LTPS have relatively large leakage currents, making it difficult to maintain the operating point of the driving transistor, and the brightness decreases when displaying a still image.

[0036] Therefore, in order to suppress the leakage current of the transistors, a method of adding N-channel type transistors in series to the transistors T2 and T3 in the pixel circuit shown in Fig. 3 can be considered. Fig. 4 is an explanatory diagram showing an example of the configuration of a pixel circuit, in which N-channel type transistors T4 and T5 are added to the pixel circuit shown in Fig. 3. By adding the transistors T4 and T5 in this way, the number of transistors between the gate of the transistor T1, which is the drive transistor, and the signal line to which the signal Vsig is supplied, and between the anode of the organic EL element EL and the signal line to which the reset voltage Vss is supplied, respectively, becomes two.

[0037] In this way, by using two write transistors and two reset transistors connected in series, it is possible to suppress leakage current of the drive transistor and suppress a decrease in luminance during display of a still image.

[0038] So far, we have shown an example of configuring a pixel circuit using N-channel transistors. However, even when configuring a pixel circuit using P-channel transistors, a method of suppressing the leakage current of transistors by connecting the transistors in series can be used.

[0039] Fig. 5 is an explanatory diagram showing an example of a pixel circuit consisting of five P-channel transistors and one capacitor. The pixel circuit shown in Fig. 5 is a pixel circuit consisting of P-channel transistors T11, T12, T13, T14, and T15, a capacitor Cs, and an organic EL element EL. Fig. 5 also shows transistors T16 and T17 and a transfer gate TF that operate when each pixel is driven.

[0040] Details of the operation of the pixel circuit are described in, for example, JP 2015-152775 A and the like, and a detailed description will be omitted here. However, the gate of transistor T1 is connected to signal line DS, the drain is connected to the anode of organic EL element EL, and the source is connected to the drain of transistor T2. A video signal Vsig is supplied to the gate of transistor T2 via transistor T3, and the source is connected to power supply voltage VCCP. The gate of transistor T3 is connected to signal line WS. The gate of transistor T4 is connected to signal line AZ1. The gate of transistor T5 is connected to signal line AZ2.

[0041] Also, in order to speed up the driving of the pixel circuit, a pixel circuit has been proposed in which a correction capacitance line is provided separately and the capacitance line is divided among a plurality of pixels to reduce the capacitance and increase the correction speed. FIG. 6 is an explanatory diagram showing an example of a pixel circuit consisting of six P-channel transistors and one capacitor. The pixel circuit shown in FIG. 6 includes P-channel transistors T11 to T15, T18, an organic EL element EL, and a capacitance element Cs. Details of the driving of the pixel circuit are described in, for example, JP 2016-38425 A, and a detailed description thereof will be omitted.

[0042] The driving transistor in the pixel circuit shown in FIGS. 5 and 6 is transistor T12, and also in the pixel circuit shown in FIGS. 5 and 6, the operating point of transistor T12, which is the driving transistor, must not change when a still image is displayed.

[0043] Therefore, a method can be adopted in which a transistor is added to the pixel circuits shown in FIGS. 5 and 6 to suppress the leakage current of the transistor and thereby suppress the decrease in luminance during display of a still image.

[0044] Fig. 7 is an explanatory diagram showing an example of the configuration of a pixel circuit in which transistors are added to the pixel circuit shown in Fig. 5 to suppress the leakage current of the transistors. The pixel circuit shown in Fig. 7 has a configuration in which P-channel transistors T21, T22, and T23 are added to the pixel circuit shown in Fig. 5. By adding the transistors T21, T22, and T23 in this way, the number of transistors between the gate of the transistor T21, which is a driving transistor, and the signal line through which the signal Vsig is supplied, between the anode of the organic EL element EL and the signal line through which the reset voltage Vss is supplied, and between the gate and the anode of the organic EL element EL is two, respectively. By increasing the number of each transistor, the leakage current from the transistor can be suppressed.

[0045] Fig. 8 is an explanatory diagram showing an example of the configuration of a pixel circuit in which transistors are added to the pixel circuit shown in Fig. 5 to suppress the leakage current of transistors. The pixel circuit shown in Fig. 8 has a configuration in which P-channel transistors T21, T22, and T23 are added to the pixel circuit shown in Fig. 6. By adding the transistors T21, T22, and T23 in this way, the number of transistors between the gate of the transistor T21, which is a drive transistor, and the capacitance line, between the anode of the organic EL element EL and the signal line that supplies the reset voltage Vss, and between the anode of the organic EL element EL and the capacitance line becomes two, respectively, and the leakage current can be suppressed.

[0046] However, the pixel circuit shown in Fig. 4 has two more transistors than the pixel circuit shown in Fig. 3, and the pixel circuits shown in Fig. 7 and Fig. 8 have three more transistors than the pixel circuits shown in Fig. 5 and Fig. 6. Increasing the number of transistors in a pixel circuit in this way to maintain the operating point of the drive transistor makes it difficult to achieve a pixel layout with a narrow pitch, which is an obstacle to achieving higher resolution displays.

[0047] In view of the above, the present disclosure has conducted intensive research into a technology that can suppress leakage current and maintain the operating point of a drive transistor when displaying a still image in a pixel circuit of a display device using an organic EL element, without increasing the number of transistors, or if the number is increased, the increase is minimized, while suppressing leakage current. As a result, as described below, the present disclosure has come up with a technology that can suppress leakage current and maintain the operating point of a drive transistor when displaying a still image in a pixel circuit of a display device using an organic EL element, without increasing the number of transistors, or if the number is increased, the increase is minimized, while suppressing leakage current.

[0048] (Pixel circuit with four transistors) As an embodiment of the present disclosure, first, an example of a pixel circuit configured with three N-channel transistors will be described. FIG. 9 is an explanatory diagram showing an example of a pixel circuit according to an embodiment of the present disclosure. The pixel circuit shown in FIG. 9 includes N-channel transistors T31, T32, T33, and T34, a capacitor C31, and an organic EL element EL. The pixel circuit shown in FIG. 9 is based on the pixel circuit shown in FIG. 3.

[0049] The transistor T31 is a drive transistor for supplying a current to the organic EL element EL, the transistor T32 is a write transistor for writing a video signal, and the transistor T33 is a reset transistor for turning off the organic EL element EL and resetting the anode potential. The pixel circuit shown in Fig. 9 is a circuit having a function of correcting the threshold voltage (Vth correction) of the transistor T1, which is a drive transistor, and correcting the variation in mobility.

[0050] The pixel circuit shown in Fig. 9 is based on the pixel circuit shown in Fig. 3, but differs from the pixel circuit shown in Fig. 4 in that only one N-channel transistor is added to the pixel circuit shown in Fig. 3. In the pixel circuit shown in Fig. 9, by providing transistor T34, the number of transistors between the gate of transistor T31, which is a drive transistor, and signal line 151 to which signals Vsig, Vss, and Vofs are supplied, and between the anode of organic EL element EL and the signal line that supplies reset voltage Vss, is reduced to two.

[0051] By configuring the pixel circuit in this manner, it is possible to suppress leakage current from the drive transistor and suppress a decrease in luminance during display of a still image.

[0052] Fig. 10 is an explanatory diagram showing how the pixel circuit shown in Fig. 9 is driven. An example of driving the pixel circuit shown in Fig. 9 will be described with reference to Fig. 10.

[0053] The light emission period continues until time t1, at which time the light emission period ends and the light-off period begins. At time t1, the signal lines WS1, WS2, and AZ all change from low to high. As the signal lines WS1, WS2, and AZ all change from low to high, the transistors T32, T33, and T34 turn on, respectively. As the transistors T32, T33, and T34 turn on, the gate potential Vg of the transistor T31 and the source potential Vs of the transistor T31 (the anode potential of the organic EL element EL) start to decrease, and all of them decrease to the potential VSS of the signal line 151.

[0054] At time t2, the extinction period ends, and the signal line AZ goes from high to low. When the signal line AZ goes low, the transistor T33 turns off, and the anode of the organic EL element EL is disconnected from the signal line 151.

[0055] Next, at time t3, the Vth correction period starts, and the potential of the signal line 151 rises from Vss to Vofs. As the potential of the signal line 151 rises from Vss to Vofs, the gate potential Vg of the transistor T31 starts to rise to Vofs. In addition, the source potential of the transistor T31, which is connected to the gate of the transistor T31 via the capacitance C31, gradually rises with the rise in the potential of the signal line 151 until it reaches a value obtained by subtracting the threshold voltage Vth of the transistor T31 from Vofs.

[0056] At time t4, the Vth correction period ends, and the signal line WS1 goes from high to low. The signal line AZ going low turns off the transistor T32, and the gate of the transistor T31 is disconnected from the signal line 151.

[0057] After time t4, the potential of the signal line 151 changes from Vofs to the potential Vsig of the video signal, and then at time t5, the signal writing and movement correction period begins. At time t5, the signal line WS1 goes from low to high. When the signal line AZ goes high, the transistor T32 turns on, and the gate of the transistor T31 is connected to the signal line 151. During this period, the output current of the transistor T31 is negatively fed back to the capacitor C31, so that the gate-source voltage Vgs of the transistor T31 has a value that reflects the mobility μ, and after a certain time has passed, the gate-source voltage Vgs has a value that is completely corrected for the mobility μ.

[0058] As a result, the gate potential Vg of the transistor T31 starts to rise to Vsig. Also, the source potential of the transistor T31, which is connected to the gate of the transistor T31 via the capacitor C31, rises as the potential of the signal line 151 rises.

[0059] Next, at time t6, the signal writing and movement correction period ends and the light emission period begins. At time t6, the signal lines WS1 and WS2 go low. When the signal lines WS1 and WS2 go low, the transistors T32 and T34 are turned off, and the gate of the transistor T31 and the anode of the organic EL element EL are disconnected from the signal line 151. This allows the gate potential of the transistor T31 to rise, and while keeping the value of the gate-source voltage Vgs held in the capacitor C31 constant, the potential of the source potential Vs of the transistor T31 also rises in conjunction with the rise in the gate potential Vg of the transistor T31. This eliminates the reverse bias state of the organic EL element EL, and the transistor T31 passes a drain current according to the gate-source voltage Vgs to the organic EL element EL. The current flowing from the transistor T31 causes the organic EL element EL to emit light. The potential of the signal line 151 drops to Vss at any timing during the light emission period.

[0060] In this way, even if the pixel circuit shown in Fig. 9 includes the transistor T34, it can correct the threshold voltage and the mobility variation of the driving transistor T31 without any problems. The pixel circuit shown in Fig. 9 can suppress the leakage current of the driving transistor and suppress the decrease in luminance during the display of a still image.

[0061] (Pixel circuit with 5 transistors) As an embodiment of the present disclosure, an example of a pixel circuit composed of five P-channel transistors will be described below. FIG. 11 is an explanatory diagram showing an example of a pixel circuit according to an embodiment of the present disclosure. The pixel circuit shown in FIG. 11 includes P-channel transistors T41, T42, T43, T44, and T45, a capacitor C41, and an organic EL element EL. The pixel circuit shown in FIG. 11 is based on the pixel circuit shown in FIG. 4. FIG. 11 also shows a capacitance element Csig and P-channel transistors T46, T47, and T48. These transistors T46, T47, and T48 function as a level shift circuit that shifts the output voltage of the transfer gate TF.

[0062] The gate of the transistor T41 is connected to the signal line DS, the drain is connected to the anode of the organic EL element EL, and the source is connected to the drain of the transistor T42. The transistor T42 is a drive transistor. The gate of the transistor T42 is supplied with the video signal Vsig via the transistors T43 and T44, and the source is connected to the power supply voltage VCCP. The transistors T43 and T44 are write transistors. The gate of the transistor T43 is connected to the signal line WS1. The source of the transistor T43 is connected to the signal line 161. The gate of the transistor T44 is connected to the signal line WS2. The source of the transistor T44 is connected to the drain of the transistor T43. The gate of the transistor T45 is connected to the signal line cmp.

[0063] Moreover, the transistor T46 controls the supply of a potential Vss to the signal line 161, and has a gate connected to the signal line Vg_Vss. The transistor T47 controls the supply of a potential Vofs to the signal line 161, and has a gate connected to the signal line Vg_Vofs. The transistor T48 controls the supply of a potential Vrst to the signal line 161, and has a gate connected to the signal line Vg_Vrst. It is assumed that Vofs>Vss.

[0064] The pixel circuit shown in Fig. 11 is based on the pixel circuit shown in Fig. 4, but unlike the pixel circuit shown in Fig. 7, the number of transistors has not increased from that of the pixel circuit shown in Fig. 4. In the pixel circuit shown in Fig. 11, the number of transistors between the gate of transistor T42, which is a drive transistor, and signal line 161, between the drain of transistor T42 and the signal line that supplies signal line 161, and between the gate and drain of transistor T42, which is a drive transistor, is reduced to two by transistor T43.

[0065] By configuring the pixel circuit in this manner, it is possible to suppress leakage current from the drive transistor and suppress a decrease in luminance during display of a still image.

[0066] Fig. 12 is an explanatory diagram showing how the pixel circuit shown in Fig. 11 is driven. An example of driving the pixel circuit shown in Fig. 11 will be described with reference to Fig. 12.

[0067] At time t1 during the light emission period, the signal lines Vg_Vss and Vg_Vrst go from high to low. When the signal lines Vg_Vss and Vg_Vrst go from high to low, the transistors T46 and T48 turn on. At this point, the signal line DS is low, so the transistor T41 is also on.

[0068] After that, at time t2, the light emission period ends and the light-off period begins. At time t2, the signal lines WS1 and cmp go from high to low. As the signal lines WS1 and cmp go from high to low, the transistors T43 and T45 turn on. As the transistors T43 and T45 turn on, the transistors T41 and T46 turn on, and the drain potential Vd of the transistor T42 and the anode potential Vanode of the organic EL element EL drop to Vss.

[0069] After that, at time t3, the extinction period ends and the Vth correction preparation period begins. At time t3, the signal line DS goes from low to high, the signal line WS2 goes from high to low, the signal line Vg_Vss goes from low to high, and the signal line Vg_Vofs goes from high to low. When the signal line DS goes from low to high, the transistor T41 turns off and the drain of the transistor T42 is disconnected from the anode of the organic EL element EL. When the signal line WS2 goes from high to low, the transistor T44 turns on. When the signal line Vg_Vss goes from low to high, the transistor T46 turns off. When the signal line Vg_Vofs goes from high to low, the transistor T47 turns on.

[0070] As a result, the gate potential Vg of the transistor T42 drops to Vofs, and the drain potential Vd of the transistor T42 rises to Vofs. Note that since the transistor T41 is turned off and the drain of the transistor T42 is separated from the anode of the organic EL element EL, there is no change in the anode potential of the organic EL element EL.

[0071] After that, at time t4, the Vth correction preparation period ends and the Vth correction period begins. At time t4, the signal line Vg_Vofs goes from low to high. When the signal line Vg_Vofs goes from low to high, the transistor T47 turns off. As a result, the gate potential Vg and drain potential Vd of the transistor T42 rise to a potential obtained by subtracting the threshold voltage Vth of the transistor T42 from the power supply voltage VCCP.

[0072] After that, at time t5, the Vth correction period ends. At time t5, the signal line cmp goes from low to high. As the signal line cmp goes from low to high, the transistor T45 turns off. As the transistor T45 turns off, the drain of the transistor T42 is disconnected from the signal line 161.

[0073] After that, at time t6, the signal write period begins. At time t6, the signal line Vg_Vrst goes from low to high. Also, at time t6, the signal line Vg_Vsig goes from high to low. As the signal line Vg_Vrst goes from low to high, the transistor T48 is turned off. As the signal line Vg_Vsig goes from high to low, the signal voltage Vsig of the video signal is supplied to the signal line 161.

[0074] At this point, the transistor T45 continues to be off, and the drain of the transistor T42 is disconnected from the signal line 161. Therefore, when the signal voltage Vsig is supplied to the signal line 161, the gate potential Vg of the transistor T42 drops until the potential difference between the gate potential Vg of the transistor T42 and the drain potential Vd of the transistor T42 becomes the signal voltage Vsig of the video signal. This causes the video signal to be written to the transistor T42.

[0075] After that, at time t7, the signal writing period ends and the light emission period begins. At time t7, the signal line DS goes from high to low. Also at time t7, the signal lines WS1 and WS2 go from low to high. Also at time t7, the signal line Vg_Vsig goes from low to high. As a result, the transistor T41 turns on, the transistors T43 and T44 turn off, and the supply of the video signal to the signal line 161 is stopped. As the transistor T41 turns on, the drain potential Vd of the transistor T42 becomes equal to the anode potential Vanode of the organic EL element EL. As the drain potential Vd of the transistor T42 decreases, the transistor T42 passes a current through the organic EL element EL. As the current flows from the transistor T42, the organic EL element EL emits light.

[0076] In this way, the pixel circuit shown in Fig. 11 can easily correct the threshold voltage of transistor T42, which is a drive transistor, without increasing the number of transistors per pixel from the pixel circuit shown in Fig. 5. And the pixel circuit shown in Fig. 11 can suppress the leakage current of the drive transistor and suppress the decrease in luminance during display of a still image, without increasing the number of transistors per pixel from the pixel circuit shown in Fig. 5.

[0077] (Pixel circuit with 6 transistors) As an embodiment of the present disclosure, an example of a pixel circuit composed of six P-channel transistors will be described below. FIG. 13 is an explanatory diagram showing an example of a pixel circuit according to an embodiment of the present disclosure. The pixel circuit shown in FIG. 13 includes P-channel transistors T51, T52, T53, T54, T55, and T56, capacitors Cs1 and Cs2, and an organic EL element EL. The pixel circuit shown in FIG. 13 is based on the pixel circuit shown in FIG. 5. Also shown in FIG. 13 are P-channel transistors T57 and T58. These transistors T57 and T58 function as a level shift circuit that shifts the output voltage of the transfer gate TF.

[0078] The gate of the transistor T51 is connected to the signal line DS, the drain is connected to the anode of the organic EL element EL, and the source is connected to the drain of the transistor T52. The transistor T52 is a drive transistor. The gate of the transistor T52 is supplied with the video signal Vsig via the transistors T53, T54, and T56, and the source is connected to the power supply voltage VCCP. The transistors T53 and T54 are write transistors. The gate of the transistor T53 is connected to the signal line WS1. The source of the transistor T53 is connected to the signal line 171. The gate of the transistor T54 is connected to the signal line WS2. The source of the transistor T54 is connected to the drain of the transistor T53. The gate of the transistor T55 is connected to the signal line cmp. The transistor T56 is provided between the signal line 171 and the capacitance line 172, and the gate is connected to the signal line Vg_RST.

[0079] The transistor T57 controls the supply of a potential Vss to the signal line 171, and has a gate connected to the signal line Vg_Vss. The transistor T58 controls the supply of a potential Vofs to the signal line 171, and has a gate connected to the signal line Vg_Vofs. It is assumed that Vofs>Vss.

[0080] The pixel circuit shown in Fig. 13 is based on the pixel circuit shown in Fig. 6, but unlike the pixel circuit shown in Fig. 8, the number of transistors is not increased from that of the pixel circuit shown in Fig. 6. In the pixel circuit shown in Fig. 13, the number of transistors between the gate of the transistor T52, which is a drive transistor, and the capacitance line 172, between the drain of the transistor T52 and the capacitance line 172, and between the gate and drain of the transistor T52 are two, respectively, due to the transistor T53.

[0081] By configuring the pixel circuit in this manner, it is possible to suppress leakage current from the drive transistor and suppress a decrease in luminance during display of a still image.

[0082] Fig. 14 is an explanatory diagram showing how the pixel circuit shown in Fig. 13 is driven. An example of driving the pixel circuit shown in Fig. 13 will be described with reference to Fig. 14.

[0083] At time t1 during the light emission period, the signal lines Vg_Vss and Vg_RST go from high to low. When the signal lines Vg_Vss and Vg_RST go from high to low, the transistors T57 and T56 turn on. At this point, the signal line DS is low, so the transistor T51 is also on.

[0084] After that, at time t2, the light emission period ends and the light-off period begins. At time t2, the signal lines WS1 and cmp go from high to low. As the signal lines WS1 and cmp go from high to low, the transistors T53 and T55 turn on. As the transistors T53 and T55 turn on, the transistors T51 and T56 turn on, and the drain potential Vd of the transistor T52 and the anode potential Vanode of the organic EL element EL drop to Vss.

[0085] After that, at time t3, the extinction period ends and the Vth correction preparation period begins. At time t3, the signal line DS goes from low to high, the signal line WS2 goes from high to low, the signal line Vg_Vss goes from low to high, and the signal line Vg_Vofs goes from high to low. When the signal line DS goes from low to high, the transistor T51 turns off and the drain of the transistor T52 is disconnected from the anode of the organic EL element EL. When the signal line WS2 goes from high to low, the transistor T54 turns on. When the signal line Vg_Vss goes from low to high, the transistor T57 turns off. When the signal line Vg_Vofs goes from high to low, the transistor T58 turns on.

[0086] As a result, the gate potential Vg of the transistor T52 drops to Vofs, and the drain potential Vd of the transistor T52 rises to Vofs. Note that since the transistor T51 is turned off and the drain of the transistor T52 is separated from the anode of the organic EL element EL, there is no change in the anode potential of the organic EL element EL.

[0087] After that, at time t4, the Vth correction preparation period ends and the Vth correction period begins. At time t4, the signal lines Vg_Vofs and Vg_RST go from low to high. When the signal line Vg_Vofs goes from low to high, the transistor T58 turns off. When the signal line Vg_RST goes from low to high, the transistor T56 turns off. As a result, the gate potential Vg and drain potential Vd of the transistor T52 rise to a potential obtained by subtracting the threshold voltage Vth of the transistor T52 from the power supply voltage VCCP.

[0088] After that, at time t5, the Vth correction period ends. At time t5, the signal line cmp goes from low to high. As the signal line cmp goes from low to high, the transistor T55 turns off. As the transistor T55 turns off, the drain of the transistor T52 is disconnected from the capacitance line 172.

[0089] After that, at time t6, the signal writing period begins. At time t6, the signal line Vg_Vsig goes from high to low. As the signal line Vg_Vsig goes from high to low, the signal voltage Vsig of the video signal is supplied to the signal line 171.

[0090] At this point, the transistor T55 continues to be off, and the drain of the transistor T52 is disconnected from the capacitance line 172. Therefore, when the signal voltage Vsig is supplied to the signal line 171, the gate potential Vg of the transistor T52 decreases until the potential difference between the gate potential Vg of the transistor T52 and the drain potential Vd of the transistor T52 becomes the signal voltage Vsig of the video signal. This causes the video signal to be written to the transistor T52.

[0091] After that, at time t7, the signal writing period ends and the light emission period begins. At time t7, the signal line DS goes from high to low. Also at time t7, the signal lines WS1 and WS2 go from low to high. Also at time t7, the signal line Vg_Vsig goes from low to high. As a result, the transistor T51 turns on, the transistors T53 and T54 turn off, and the supply of the video signal to the signal line 171 is stopped. As the transistor T51 turns on, the drain potential Vd of the transistor T52 becomes equal to the anode potential Vanode of the organic EL element EL. As the drain potential Vd of the transistor T52 decreases, the transistor T52 passes a current through the organic EL element EL. As the current flows from the transistor T52, the organic EL element EL emits light.

[0092] In this way, the pixel circuit shown in Fig. 13 can easily correct the threshold voltage of transistor T52, which is a drive transistor, without increasing the number of transistors per pixel from the pixel circuit shown in Fig. 6. And the pixel circuit shown in Fig. 13 can suppress the leakage current of the drive transistor and suppress the decrease in luminance during display of a still image, without increasing the number of transistors per pixel from the pixel circuit shown in Fig. 6.

[0093] <2. Summary> As described above, according to the embodiments of the present disclosure, in a pixel circuit of a display device using an organic EL element, a pixel circuit is provided in which a gate node of a drive transistor and an anode node of the organic EL element are connected via a transistor, and a transistor is further provided between the gate node and a wiring such as a signal line shared by a plurality of pixels.

[0094] By providing transistors in this manner, the pixel circuit according to the embodiment of the present disclosure connects the gate node of the drive transistor and the anode node of the organic EL element to various signal lines with two transistors. By connecting nodes with two transistors in this manner, the pixel circuit according to the embodiment of the present disclosure can suppress the operating point fluctuation of each node due to leakage current and suppress brightness degradation during low frequency driving without increasing the number of transistors, and even if it is increased, the increase is minimal.

[0095] Also provided are display devices including pixel circuits according to the embodiments of the present disclosure, and electronic devices including such display devices. Such electronic devices include televisions, mobile phones such as smartphones, tablet-type mobile terminals, personal computers, portable game consoles, portable music playback devices, digital still cameras, digital video cameras, wristwatch-type mobile terminals, wearable devices, and the like.

[0096] Although the preferred embodiment of the present disclosure has been described in detail above with reference to the attached drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person having ordinary knowledge in the technical field of the present disclosure can conceive of various modified or amended examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure.

[0097] In addition, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that are apparent to a person skilled in the art from the description of this specification, in addition to or in place of the above effects.

[0098] Note that the following configurations also fall within the technical scope of the present disclosure. (1) A light-emitting element; A driving transistor for supplying a current to the light emitting element; a first reset transistor that sets the potential of the anode of the light-emitting element to a predetermined potential; a first write transistor for controlling writing of a signal voltage at a gate node of the drive transistor; a storage capacitor having one end connected to a gate node of the driving transistor and configured to store a threshold voltage of the driving transistor; a second write transistor connected in series between a gate node of the drive transistor and the first write transistor; A pixel circuit comprising: (2) The pixel circuit according to claim 1, further comprising a light-emitting control transistor that controls a connection between the driving transistor and an anode of the light-emitting element. (3) The pixel circuit according to (2), further comprising a second reset transistor provided between a signal line to which the signal voltage is supplied and a capacitance line to which a capacitance that corrects a threshold voltage of the driving transistor is connected. (4) The pixel circuit according to any one of (1) to (3), wherein the driving transistor, the first reset transistor, the first writing transistor, and the second writing transistor are all N-channel type transistors. (5) The pixel circuit according to any one of (1) to (3), wherein the driving transistor, the first reset transistor, the first writing transistor, and the second writing transistor are all P-channel type transistors. (6) A display device comprising the pixel circuit according to any one of (1) to (5). (7) An electronic device comprising the display device according to (6). (8) A light-emitting element; A driving transistor for supplying a current to the light emitting element; a first reset transistor that sets the potential of the anode of the light-emitting element to a predetermined potential; a first write transistor for controlling writing of a signal voltage at a gate node of the drive transistor; a storage capacitor having one end connected to a gate node of the driving transistor and configured to store a threshold voltage of the driving transistor; a second write transistor connected in series between a gate node of the drive transistor and the first write transistor; In a pixel circuit comprising: In a first period after the emission is completed, the first write transistor and the second write transistor are turned on, In a second period after the first period, a threshold voltage of the driving transistor is corrected; In a third period after the second period, a signal voltage is written to the driving transistor; a fourth period after the third period, turning off the first writing transistor and the second writing transistor, and causing a current to flow through the light-emitting element via the driving transistor to cause the light-emitting element to emit light. (9) The method for driving a pixel circuit according to (8), wherein, in the first period, the first writing transistor is turned on and then the second writing transistor is turned on. (10) The method for driving a pixel circuit according to (8) or (9), wherein the pixel circuit further includes a light-emitting control transistor that controls a connection between the driving transistor and the anode of the light-emitting element. (11) The method for driving a pixel circuit described in (10), wherein the pixel circuit further includes a second reset transistor provided between a signal line to which the signal voltage is supplied and a capacitance line to which a capacitance that corrects a threshold voltage of the driving transistor is connected. [Explanation of symbols]

[0099] 100:Display device 110: Pixel section 111B: Pixel 111G:Pixels 111R: Pixel 120: Horizontal selector 130: Vertical scanner 131: Autozero scanner 132: Driving scanner 133: Write scanner

Claims

1. A light-emitting element; a write capacitor having one electrode connected to a first power line; a first transistor and a second transistor connected in series between the other electrode of the write capacitor and a data line, the first transistor and the second transistor writing a signal voltage supplied from the data line into the write capacitor; a drive transistor that supplies a current to the light emitting element according to a voltage stored in the writing capacitor; a third transistor for controlling a connection between one of a source node and a drain node of the driving transistor and an anode of the light emitting element; a fourth transistor that controls a connection between the anode of the light-emitting element and a second power supply line; A display device comprising:

2. one of a source node and a drain node of the first transistor is connected to the data line; the other of the source node and the drain node of the first transistor is connected to one of the source node and the drain node of the second transistor; the other of the source node and the drain node of the second transistor is connected to the other electrode of the write capacitor and the gate node of the drive transistor; The display device according to claim 1 .

3. 3. The display device according to claim 1, wherein the other of the source node and the drain node of the driving transistor is connected to the first power supply line.

4. one of a source node and a drain node of the third transistor is connected to one of a source node and a drain node of the driving transistor; 4. The display device according to claim 1, wherein the other of the source node and the drain node of the third transistor is connected to the anode of the light-emitting element.

5. one of a source node and a drain node of the fourth transistor is connected to the anode of the light emitting element; the other of the source node and the drain node of the fourth transistor is connected to the second power supply line; The display device according to any one of claims 1 to 4.

6. 6. The display device according to claim 1, wherein the cathode of the light-emitting element is connected to a third power supply line.

7. a first control line is connected to a gate node of the first transistor; a second control line is connected to a gate node of the second transistor; a third control line is connected to a gate node of the third transistor; a fourth control line is connected to a gate node of the fourth transistor; The display device according to any one of claims 1 to 6.

8. 8. The display device according to claim 1, wherein the first transistor, the second transistor and the driving transistor are all P-channel transistors.

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