JP2012220723A - Display panel, display device, and electronic appliance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display panel capable of changing the display luminance depending on the luminance of external light at low-cost and on a simple system, and provide a display device and an electronic appliance including the display panel.SOLUTION: An organic EL element 11 and a pixel circuit 12 for driving the organic EL element 11 are provided for each subpixel 13. The pixel circuit 12 includes a holding capacitor Cs, a writing transistor Tws writing voltage corresponding to an image signal in the holding capacitor Cs, and a driving transistor Tdr driving the organic EL element 11 based on the voltage of the holding capacitor Cs. The pixel circuit 12 further includes a transistor Tr1 feeding back the voltage corresponding to the level of the luminance of external light to gate voltage of the driving transistor Tdr.

Description

  The present invention relates to a display panel including an organic EL (electro luminescence) element, a display device including the display panel, and an electronic apparatus.

  In recent years, in the field of display devices that perform image display, display devices using current-driven optical elements, such as organic EL elements, whose light emission luminance changes according to the value of a flowing current have been developed as light-emitting elements of pixels. (See, for example, Patent Document 1). Unlike a liquid crystal element or the like, the organic EL element is a self-luminous element. Therefore, a display device (organic EL display device) using an organic EL element does not require a light source (backlight), and thus has higher image visibility and lower power consumption than a liquid crystal display device that requires a light source. And the response speed of the element is fast.

  In the organic EL display device, similarly to the liquid crystal display device, there are a simple (passive) matrix method and an active matrix method as its driving method. Although the former has a simple structure, there is a problem that it is difficult to realize a large-sized and high-definition display device. For this reason, active matrix systems are currently being actively developed. In this method, a current flowing through a light emitting element arranged for each pixel is controlled by an active element (typically a thin film transistor (TFT)) provided in a drive circuit provided for each light emitting element.

  By the way, in general, in an organic EL display device, visibility under strong external light is not so good. In order to improve the visibility under strong external light, it is necessary to increase the light emission luminance of the organic EL element. However, the conventional organic EL display device does not have a function of detecting and feeding back external light. Therefore, for example, it is conceivable that an external light luminance sensor is provided outside the panel, and the video signal is changed according to the luminance to change the luminance.

JP 2008-083272 A

  However, in such a case, there is a problem that not only the system becomes complicated, but also the manufacturing cost increases.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a display panel capable of changing the display luminance in accordance with the external light luminance with a low-cost and simple system, and a display including the display panel. It is to provide an apparatus and an electronic device.

  The display panel according to the present invention includes a self-light emitting element and a pixel circuit for driving the self-light emitting element for each pixel. The pixel circuit includes a storage capacitor, a first transistor that writes a voltage corresponding to the video signal to the storage capacitor, and a second transistor that drives the self-luminous element based on the voltage of the storage capacitor. The pixel circuit further feeds back a voltage corresponding to the intensity of the external light to the gate voltage of the second transistor.

  A display device according to the present invention includes a display panel having a self-light-emitting element, a pixel circuit for driving the self-light-emitting element for each pixel, and a drive circuit for driving the pixel circuit. The display panel included in this display device has the same components as the above display panel. An electronic apparatus according to the present invention includes the above display device.

  In the display panel, the display device, and the electronic apparatus according to the present invention, a voltage corresponding to the magnitude of the brightness of external light is fed back to the gate voltage of the second transistor. As a result, when the pixels are driven based on the same video signal, the luminance difference between the pixels having a relatively high light emission efficiency and the pixels having a relatively low light emission efficiency is reduced.

  In the present invention, the pixel circuit may include a third transistor arranged at a position where external light is incident. In this case, the pixel circuit charges the storage capacitor with a leak current according to the brightness of the external light incident on the third transistor. In addition, when the pixel circuit includes the third transistor, the third transistor is inserted between, for example, a wiring to which a voltage higher than the gate voltage of the second transistor is applied and the storage capacitor. . At this time, the gate of the third transistor is electrically connected to the first storage capacitor, for example.

  In the present invention, the display panel may further include a wiring connected to the self-light emitting element of each pixel for each one or a plurality of pixel rows. In this case, for example, the driving circuit applies a voltage that is always lower than the voltage written in the storage capacitor by the first transistor to the wiring while the light emitting element emits light. .

  According to the display panel, the display device, and the electronic apparatus according to the present invention, when the pixels are driven based on the same video signal, the pixels with relatively high luminous efficiency and the pixels with relatively low luminous efficiency Since the difference in luminance is made small, the burn-in can be reduced.

1 is a schematic diagram of a display device according to a first embodiment. FIG. 2 is a circuit diagram of a subpixel in FIG. 1. FIG. 2 is a layout diagram of subpixels in FIG. 1. It is sectional drawing of the sub pixel of FIG. FIG. 3 is a waveform diagram illustrating an example of an operation of a subpixel in FIG. 2. It is a wave form diagram for demonstrating the amount of leak currents by the difference in the intensity of EL light. It is a wave form diagram showing a mode that the voltage according to the intensity of EL light is fed back to the gate. FIG. 6 is a layout diagram of subpixels in a display device according to a second embodiment. It is sectional drawing of the sub pixel of FIG. FIG. 3 is a circuit diagram of a modification of the subpixel of FIG. 2. FIG. 4 is a layout diagram illustrating a modified example of the subpixel of FIG. 3. It is sectional drawing of the sub pixel of FIG. FIG. 9 is a layout diagram illustrating a modification of the sub-pixel in FIG. 8. It is sectional drawing of the sub pixel of FIG. FIG. 11 is a waveform diagram illustrating an example of the operation of the sub-pixel in FIG. 10. It is a top view showing schematic structure of the module containing the display apparatus of each said embodiment. It is a perspective view showing the external appearance of the application example 1 of the display apparatus of the said embodiment. (A) is a perspective view showing the external appearance seen from the front side of the application example 2, (B) is a perspective view showing the external appearance seen from the back side. 12 is a perspective view illustrating an appearance of application example 3. FIG. 14 is a perspective view illustrating an appearance of application example 4. FIG. (A) is a front view of the application example 5 in an open state, (B) is a side view thereof, (C) is a front view in a closed state, (D) is a left side view, and (E) is a right side view, (F) is a top view and (G) is a bottom view.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings. The description will be given in the following order.

1. First embodiment
Transistors that are exposed to external light
Example provided separately from the write transistor
An example in which the display panel has a bottom emission structure. Second embodiment
Transistors that are exposed to external light
Example provided separately from the write transistor
2. An example in which the display panel has a top emission structure. Modified example
3. Example in which the transistor irradiated with external light is a writing transistor Modules and application examples

<1. First Embodiment>
[Constitution]
FIG. 1 illustrates an example of the overall configuration of the display device 1 according to the first embodiment. The display device 1 includes a display panel 10 and a drive circuit 20 that drives the display panel 10.

  The display panel 10 has a display area 10A in which a plurality of display pixels 14 are two-dimensionally arranged. The display panel 10 displays an image based on the video signal 20A input from the outside by driving each display pixel 14 in an active matrix. Each display pixel 14 includes a red sub-pixel 13R, a green sub-pixel 13G, and a blue sub-pixel 13B. In the following, the subpixel 13 is used as a general term for the subpixels 13R, 13G, and 13B.

  FIG. 2 illustrates an example of a circuit configuration of the subpixel 13. As shown in FIG. 2, the subpixel 13 includes an organic EL element 11 and a pixel circuit 12 that drives the organic EL element 11. The organic EL element 11 corresponds to a specific example of “self-luminous element” in the claims. The subpixel 13R is provided with an organic EL element 11R that emits red light as the organic EL element 11. Similarly, the organic EL element 11G that emits green light is provided as the organic EL element 11 in the subpixel 13G. The subpixel 13B is provided with an organic EL element 11B that emits blue light as the organic EL element 11.

  The pixel circuit 12 includes, for example, a write transistor Tws, a drive transistor Tdr, a luminance correction transistor Tr1, and a storage capacitor Cs, and has a circuit configuration of 3Tr1C. Note that the pixel circuit 12 is not limited to the circuit configuration of 3Tr1C, and may include two write transistors Tws connected in series with each other, or may include transistors other than those described above or capacitors. Also good.

  The write transistor Tws is a transistor that writes a voltage corresponding to the video signal to the storage capacitor Cs. The drive transistor Tdr is a transistor that drives the organic EL element 11 based on the voltage of the storage capacitor Cs written by the write transistor Tws. The transistor Tr1 feeds back a voltage corresponding to the magnitude of the external light luminance to the gate voltage of the driving transistor Tdr. The transistors Tws, Tdr, Tr1 are configured by, for example, n-channel MOS thin film transistors (TFTs). The transistors Tws, Tdr, and Tr1 may be configured by p-channel MOS type TFTs.

  The write transistor Tws in the present embodiment corresponds to a specific example of “first transistor” in the claims, and the drive transistor Tdr in the present embodiment corresponds to the “second transistor” in the claims. This corresponds to a specific example. Further, the transistor Tr1 of the present embodiment corresponds to a specific example of “third transistor” in the claims. Further, the storage capacitor Cs of the present embodiment corresponds to a specific example of “storage capacitor” in the claims.

  The drive circuit 20 includes a timing generation circuit 21, a video signal processing circuit 22, a data line drive circuit 23, a gate line drive circuit 24 and a drain line drive circuit 25. The display panel 10 includes a data line DTL connected to the output of the data line driving circuit 23, a gate line WSL connected to the output of the gate line driving circuit 24, and a drain line connected to the output of the drain line driving circuit 25. DSL. The display panel 10 further includes a power supply line VDDL connected to a power supply (not shown) that outputs a voltage Vdd higher than the gate voltage of the write transistor Tws, and a cathode line CTL connected to the cathode of the organic EL element 11. And have. The cathode line CTL is a wiring to which a reference potential is applied. For example, the cathode line CTL is a common wiring connected to the cathode of the organic EL element 11 of each subpixel 13. The cathode line CTL is connected to the ground, for example, and becomes a ground voltage when connected to the ground.

  The timing generation circuit 21 controls, for example, the data line driving circuit 23, the gate line driving circuit 24, and the drain line driving circuit 25 to operate in conjunction with each other. For example, the timing generation circuit 21 outputs a control signal 21A to these circuits in response to (in synchronization with) a synchronization signal 20B input from the outside.

  For example, the video signal processing circuit 22 corrects a digital video signal 20A input from the outside, converts the corrected video signal into analog, and outputs a signal voltage 22B to the data line driving circuit 23. is there.

  In response to (in synchronization with) the input of the control signal 21A, the data line driving circuit 23 applies the analog signal voltage 22B input from the video signal processing circuit 22 via each data line DTL to the display pixel to be selected. 14 (or sub-pixel 13). For example, the data line driving circuit 23 can output a signal voltage 22B and a constant voltage unrelated to the video signal.

  In response to (in synchronization with) the input of the control signal 21A, the gate line driving circuit 24 sequentially applies a selection pulse to the plurality of gate lines WSL, thereby applying the plurality of display pixels 14 (or sub-pixels 13) to the gate line WSL. The unit is selected sequentially. The gate line driving circuit 24 can output, for example, a voltage applied when the write transistor Tws is turned on and a voltage applied when the write transistor Tws is turned off.

  The drain line driving circuit 25 outputs a predetermined voltage to the drain of the driving transistor Tdr of each pixel circuit 12 via each drain line DSL in response to (in synchronization with) the input of the control signal 21A. ing. The drain line drive circuit 25 can output, for example, a voltage applied when the organic EL element 11 emits light and a voltage applied when the organic EL element 11 is quenched.

  Next, with reference to FIG. 2 and FIG. 3, the connection relationship and arrangement of each component will be described. FIG. 3 shows an example of the layout of the sub-pixel 13.

  The gate line WSL extends in the row direction, and is connected to the gate 31A of the write transistor Tws via the contact 37A. The drain line DSL is also formed to extend in the row direction, and is connected to the drain 32C of the drive transistor Tdr via the contact 37B. The data line DTL extends in the column direction and is connected to the drain 31C of the write transistor Tws via the contact 37C. The power line VDDL is connected to the drain 36C of the transistor Tr1 through the contact 37E.

  The source 31B of the write transistor Tws is connected to the gate 32A of the drive transistor Tdr and one end (terminal 33A) of the storage capacitor Cs. The source 32B of the drive transistor Tdr and the other end (terminal 33B) of the storage capacitor Cs are connected to the anode 35A of the organic EL element 11 via the contact 37D. The organic layer 35C of the organic EL element 11 is disposed on the anode 35A. The cathode 35B of the organic EL element 11 is disposed on the organic layer 35C and is connected to the cathode line CTL. The gate 36A of the transistor Tr1 is connected to the source 36B of the transistor Tr1 via a contact 37F. Further, the gate 36A of the transistor Tr1 is connected to the gate 32A of the drive transistor Tdr and one end (33A) of the storage capacitor Cs.

  Next, the transistor Tr1 in the display panel 10 and a cross-sectional configuration in the vicinity thereof will be described. FIG. 4 illustrates an example of a cross-sectional configuration of the subpixel 13 in FIG. For example, as shown in FIG. 4, the display panel 10 includes a transistor Tr1, a drive transistor Tdr, and a storage capacitor Cs on a substrate 41 in the vicinity of the transistor Tr1. FIG. 4 shows only the gate 36A and the channel layer 36D of the transistor Tr1. FIG. 4 shows only the gate 32A and the channel layer 32D of the drive transistor Tdr. For example, as shown in FIG. 4, the display panel 10 includes an insulating film 43, an insulating film 44, an insulating film 45, an insulating film 46, and a substrate 47 placed on the transistor Tr <b> 1 in the vicinity of the transistor Tr <b> 1. It has in this order from the side. The insulating layer 43 has an opening 43A, and a contact 37C is provided in the opening 43A. The insulating layer 44 also has an opening 44A, and a contact 37D and an anode electrode 35A in contact with the contact 37D are provided in the opening 44A.

  The substrates 41 and 47 are made of, for example, a glass substrate, a silicon (Si) substrate, a resin substrate, or the like. The anode electrode 35 </ b> A is a flat film that follows the flat surface of the insulating layer 44. The anode electrode 35A is made of a conductive material transparent to visible light, for example, ITO (Indium Tin Oxide). The cathode electrode 35B is formed in contact with at least the upper surface of the organic layer 35C, and functions as a common electrode formed on the entire surface including the insulating layer 43, for example. Although not shown in FIG. 4, the organic layer 35C includes, for example, in order from the anode electrode 35A side, a hole injection layer that increases the hole injection efficiency, and a hole transport layer that increases the hole transport efficiency to the light emitting layer. And a light emitting layer that generates light emission due to recombination of electrons and holes, and an electron transport layer that increases electron transport efficiency to the light emitting layer. The cathode electrode 35B is made of a metal material and functions as a reflection mirror. Accordingly, light emitted from the organic layer 35C of the organic EL element 11 is output to the outside through the anode electrode 35A, the insulating layers 44 and 43, and the substrate 41. Therefore, the back surface (surface opposite to the transistor Tr1) of the substrate 41 is the video display surface S, and the display panel 10 has a bottom emission structure.

  By the way, in the present embodiment, for example, as shown in FIG. 4, the transistor Tr1 is disposed in the vicinity of the image display surface S, and a structure that blocks external light from directly entering the transistor Tr1. Not provided. That is, the transistor Tr1 is arranged at a position where external light is directly incident. On the other hand, although not shown, a structure for blocking external light from entering the write transistor Tws is provided. That is, the write transistor Tws is disposed at a position where external light does not directly enter.

[Operation]
Next, an example of operation | movement of the display apparatus 1 of this Embodiment is demonstrated.

  In this display device 1, a signal voltage 22B corresponding to the video signal 20A is applied to each data line DTL by the data line driving circuit 23, and a selection pulse corresponding to the control signal 21A is driven to the gate line driving circuit 24 and the drain line driving. The circuit 25 sequentially applies to the plurality of gate lines WSL and drain lines DSL. Actually, an image is displayed through an operation described below.

  Note that a voltage Vdd higher than the voltage of the gate 36A of the transistor Tr1 is applied to the drain 36C of the transistor Tr1, and the transistor Tr1 is always in a reverse bias state. Therefore, the transistor Tr1 is always off when no external light is incident, and no current flows through the transistor Tr1. Therefore, when no external light is incident, the operation is the same as that of a general 2Tr1C pixel circuit in which the transistor Tr1 is not provided. The following is a description of the operation when no external light is incident on the transistor Tr1.

  FIG. 5 shows an example of a voltage waveform applied to a certain pixel circuit 12 and an example of changes in the gate voltage Vg and source voltage Vs of the drive transistor Tdr. FIG. 5A shows a state in which the signal voltage Vsig and the offset voltage Vofs are applied to the data line DTL. FIG. 5B shows a state where a voltage Von for turning on the write transistor Tws and a voltage Voff for turning off the write transistor Tws are applied to the gate line WSL. FIG. 5C shows a state where the voltage Vcc and the voltage Vini are applied to the drain line DSL. Further, in FIGS. 5D and 5E, the gate voltage Vg and the source voltage Vs of the driving transistor Tdr change from time to time in response to voltage application to the drain line DSL, the data line DTL, and the gate line WSL. The situation is shown.

(Threshold correction preparation period)
First, preparation for threshold correction is performed. Specifically, when the voltage of the gate line WSL is Voff and the voltage of the drain line DSL is Vcc (that is, when the organic EL element 11 emits light), the drain line driving circuit 25 is The voltage of the drain line DSL is lowered from Vcc to Vini (T1). Then, the source voltage Vs becomes Vini, and the organic EL element 11 is quenched. Thereafter, when the voltage of the data line DTL is Vofs, the gate line driving circuit 24 raises the voltage of the gate line WSL from Voff to Von, and sets the gate of the driving transistor Tdr to Vofs.

(First threshold correction period)
Next, threshold correction is performed. Specifically, while the write transistor Tws is on and the voltage of the data line DTL is Vofs, the drain line drive circuit 25 increases the voltage of the drain line DSL from Vini to Vcc (T2). Then, a current Ids flows between the drain and source of the drive transistor Tdr, and the source voltage Vs increases. Thereafter, before the data line driving circuit 23 switches the voltage of the data line DTL from Vofs to Vsig, the gate line driving circuit 24 lowers the voltage of the gate line WSL from Von to Voff (T3). Then, the gate of the drive transistor Tdr becomes floating, and the threshold value correction is paused.

(First threshold correction suspension period)
During the period in which the threshold correction is paused, for example, the voltage of the data line DTL is sampled in another row (pixel) different from the row (pixel) on which the previous threshold correction has been performed. At this time, since the source voltage Vs is lower than Vofs−Vth (Vth is the threshold voltage of the driving transistor Tdr) in the row (pixel) on which the previous threshold correction is performed, the previous threshold correction is performed even during the threshold correction pause period. In the row (pixel) subjected to threshold correction, the current Ids flows between the drain and source of the drive transistor Tdr, the source voltage Vs rises, and the gate voltage Vg also rises due to coupling via the storage capacitor Cs.

(Second threshold correction period)
Next, threshold correction is performed again. Specifically, when the voltage of the data line DTL is Vofs and threshold correction is possible, the gate line drive circuit 24 raises the voltage of the gate line WSL from Voff to Von, and the gate of the drive transistor Tdr. The voltage is set to Vofs (T4). At this time, when the source voltage Vs is lower than Vofs−Vth (when threshold correction is not yet completed), until the drive transistor Tdr is cut off (until the gate-source voltage Vgs becomes Vth), A current Ids flows between the drain and source of the driving transistor Tdr. Thereafter, before the data line driving circuit 23 switches the voltage of the data line DTL from Vofs to Vsig, the gate line driving circuit 24 lowers the voltage of the gate line WSL from Von to Voff (T5). Then, since the gate of the driving transistor Tdr is in a floating state, the gate-source voltage Vgs can be maintained constant regardless of the magnitude of the voltage of the data line DTL.

  In the threshold correction period, when the storage capacitor Cs is charged to Vth and the gate-source voltage Vgs becomes Vth, the drive circuit 20 ends the threshold correction. However, if the gate-source voltage Vgs does not reach Vth, the drive circuit 20 repeatedly executes threshold correction and threshold correction pause until the gate-source voltage Vgs reaches Vth.

(Writing / mobility correction period)
After the threshold correction suspension period is over, writing and mobility correction are performed. Specifically, while the voltage of the data line DTL is Vsig, the gate line drive circuit 24 raises the voltage of the gate line WSL from Voff to Von (T6), and the gate of the drive transistor Tdr is changed to the data line DTL. Connecting. Then, the gate voltage Vg of the drive transistor Tdr becomes the voltage Vsig of the data line DTL. At this time, the anode voltage of the organic EL element 11 is still smaller than the threshold voltage Vel of the organic EL element 11 at this stage, and the organic EL element 11 is cut off. Therefore, the current Ids flows through the element capacitance (not shown) of the organic EL element 11, and the element capacitance is charged. Therefore, the source voltage Vs increases by ΔV, and the gate-source voltage Vgs eventually becomes Vsig + Vth−ΔV. . In this way, mobility correction is performed simultaneously with writing. Here, as the mobility of the drive transistor Tdr increases, ΔV also increases. Therefore, by reducing the gate-source voltage Vgs by ΔV before light emission, it is possible to remove variations in mobility for each subpixel 13. .

(Bootstrap period)
Finally, the gate line driving circuit 24 lowers the voltage of the gate line WSL from Von to Voff (T7). Then, the gate of the drive transistor Tdr becomes floating, the current Ids flows between the drain and source of the drive transistor Tdr, and the source voltage Vs rises. As a result, a voltage equal to or higher than the threshold voltage Vel is applied to the organic EL element 11, and the organic EL element 11 starts to emit light with a desired luminance.

  As described above, in the display device 1 according to the present embodiment, the pixel circuit 12 is controlled to be turned on / off in each subpixel 13, and the driving current is injected into the organic EL element 11 of each subpixel 13, thereby generating holes and electrons. Recombine with each other to emit light, and the light is extracted outside. As a result, an image is displayed in the display area 10 </ b> A of the display panel 10.

[effect]
Next, effects of the display device 1 according to the present embodiment will be described. In the present embodiment, the display panel 10 has a bottom emission structure, and the transistor Tr1 is disposed at a position where external light incident from the video display surface S directly enters. Therefore, the characteristics of the transistor Tr1 change due to external light.

In general, when a transistor receives light, the characteristic changes as shown in FIG. 6, and the leakage current in the off region increases according to the light intensity. Consider this by applying it to the pixel circuit 12. First, the transistors Tr1, when the external light enters, as shown in FIG. 2, current leakage occurs in transistors Tr1, the leakage current I _L flows from the power supply line VDDL toward the storage capacitor Cs, the charge in the storage capacitor Cs Is charged. Therefore, for example, as shown in FIGS. 5D and 5E, the gate-source voltage Vgs of the drive transistor Tdr increases and the current increases. As a result, the light emission luminance of the organic EL element 11 is also increased. 5D and 5E, when the normal gate-source voltage is Vgs0, the gate-source voltage is Vgs1 larger than Vgs0 in this embodiment. It has been shown.

  The leakage current from the power supply line VDDL depends on the light intensity. Therefore, as shown in FIG. 7, the speed at which the storage capacitor Cs is charged by the leak current also changes according to the luminance. Therefore, when the external light luminance is high, the speed of charging the storage capacitor Cs is fast, so that the increase in the light emission luminance of the organic EL element 11 also increases. On the other hand, when the external light luminance is low, the speed of charging the storage capacitor Cs is slow, so the increase in luminance is small. Thus, the light emission luminance of the organic EL element 11 can be automatically changed according to the external light luminance without changing the signal voltage or providing a special circuit. Therefore, the display luminance can be changed according to the external light luminance with a low-cost and simple system.

<2. Second Embodiment>
[Constitution]
Next, a display device according to a second embodiment will be described. The display device of the present embodiment is mainly different from the configuration of the display device 1 of the above embodiment in that the display panel 10 has a top emission structure. Therefore, in the following, differences from the above embodiment will be mainly described, and description of common points with the above embodiment will be omitted as appropriate.

  FIG. 8 shows an example of the layout of the sub-pixel 13 in the present embodiment. FIG. 9 illustrates an example of a cross-sectional configuration of the subpixel 13 in FIG.

  In the present embodiment, the anode electrode 35 </ b> A and the organic layer 35 </ b> C of the organic EL element 11 are widely formed on the upper surface of the subpixel 13. The anode electrode 35A has an opening H immediately above the transistor Tr1. The anode electrode 35A is made of a metal material and functions as a reflection mirror. The organic layer 35C is widely formed on the upper surface of the sub-pixel 13 including just above the transistor Tr1, and the opening H and the organic layer 35C are visible directly above the transistor Tr1. The cathode electrode 35B is made of a conductive material that is transparent to visible light, such as ITO. That is, the transistor Tr1 is disposed in a region facing the opening H, and is disposed at a position where external light is incident through the opening H, the organic layer 35C, and the cathode electrode 35B. Therefore, in the display panel 10, external light is incident on the transistor Tr1 through the insulating layer 44, the organic layer 35C, the cathode electrode 35B, the insulating layer 46, and the substrate 47.

[effect]
Next, the effect of the display device of this embodiment will be described. In the present embodiment, the display panel 10 has a top emission structure, and the transistor Tr1 is disposed at a position where external light is directly incident. Therefore, the characteristics of the transistor Tr1 change due to external light.

In the present embodiment, as in the first embodiment, when external light is incident on the transistor Tr1, as shown in FIG. 2, current leakage occurs in the transistor Tr1, and the power line VDDL is connected to the storage capacitor Cs. A leak current I _L flows toward the storage capacitor Cs, and charges are charged. Therefore, for example, as shown in FIGS. 5D and 5E, the gate-source voltage Vgs of the drive transistor Tdr increases and the current increases. As a result, the light emission luminance of the organic EL element 11 is also increased.

  The leakage current from the power supply line VDDL depends on the light intensity. Therefore, as shown in FIG. 7, the speed at which the storage capacitor Cs is charged by the leak current also changes according to the luminance. Therefore, when the external light luminance is high, the speed of charging the storage capacitor Cs is fast, so that the increase in the light emission luminance of the organic EL element 11 also increases. On the other hand, when the external light luminance is low, the speed of charging the storage capacitor Cs is slow, so the increase in luminance is small. Thus, the light emission luminance of the organic EL element 11 can be automatically changed according to the external light luminance without changing the signal voltage or providing a special circuit. Therefore, the display luminance can be changed according to the external light luminance with a low-cost and simple system.

<3. Modification>
[Constitution]
In each of the embodiments described above, each subpixel 13 includes the transistor Tr1, but may be omitted as shown in FIG. 10, for example. In such a case, first, the cathode line CTL extends in the row direction (extension direction of the drain line DSL), and is a strip shape shared by the plurality of organic EL elements 11 arranged in the row direction. It must be an electrode. The plurality of cathode lines CTL are arranged in parallel to each other and are common wirings connected to the cathodes of the organic EL elements 11 of the subpixels 13 for each one or a plurality of pixel rows. In this modification, each cathode line CTL is connected to the drive circuit 20 instead of the ground.

  Next, when the display panel 10 has a bottom emission structure, for example, as shown in FIGS. 11 and 12, the write transistor Tws is disposed close to the video display surface S, and A structure for blocking external light from directly entering the write transistor Tws is not provided. That is, the write transistor Tws is arranged at a position where external light is directly incident.

  When the display panel 10 has a bottom emission structure, for example, as illustrated in FIGS. 13 and 14, the anode electrode 35 </ b> A has an opening H immediately above the write transistor Tws. The organic layer 35C is widely formed on the upper surface of the sub-pixel 13 including immediately above the write transistor Tws, and the opening H and the organic layer 35C are visible immediately above the write transistor Tws. That is, the write transistor Tws is disposed in a region facing the opening H, and is disposed at a position where external light enters the opening H, the organic layer 35C, and the cathode electrode 35B.

  Further, regardless of the structure of the display panel 10, the drive circuit 20 sequentially applies selection pulses to the plurality of cathode lines CTL in response to (in synchronization with) the input of the control signal 21 </ b> A. It is necessary to become.

  The drive circuit 20 sequentially applies a selection pulse to the plurality of cathode lines CTL in response to (in synchronization with) the input of the control signal 21A, thereby causing the plurality of display pixels 14 (or subpixels 13) to be in units of cathode lines CTL. It is designed to select sequentially. For example, as illustrated in FIG. 15, the drive circuit 20 generates a voltage Va applied when the organic EL element 11 emits light and a voltage Vb (> voltage Va) applied when the organic EL element 11 is quenched. It is possible to output. For example, as illustrated in FIG. 15, the drive circuit 20 applies the voltage Va to the cathode line CTL while the organic EL element 11 emits light, and the organic EL element 11 is extinguished. Meanwhile, the voltage Vb is applied to the cathode line CTL. Here, the voltage Va is a voltage that is always lower than the voltage written to the storage capacitor Cs by the write transistor Tws (that is, the voltage of the data line DTL).

  In this modification, a voltage such that the gate voltage Vg of the drive transistor Tdr is always lower than the voltage of the data line DTL is applied to the cathode line CTL while the organic EL element 11 is emitting light. As a result, when external light is incident on the write transistor Tws and the off current of the write transistor Tws increases while the organic EL element 11 emits light, the charge is transferred to the data line DTL via the write transistor Tws. To the storage capacitor Cs. As a result, as in the above embodiments, the light emission luminance of the organic EL element 11 can be automatically changed according to the external light luminance without changing the signal voltage or providing a special circuit. . Therefore, the display luminance can be changed according to the external light luminance with a low-cost and simple system.

<4. Modules and application examples>
Hereinafter, application examples of the display device 1 described in the first and second embodiments and the modifications thereof will be described. The display device 1 displays an externally input video signal or an internally generated video signal as an image or video, such as a television device, a digital camera, a notebook personal computer, a mobile terminal device such as a mobile phone, or a video camera. The present invention can be applied to display devices for electronic devices in all fields.

[module]
The display device 1 is incorporated into various electronic devices such as application examples 1 to 5 described later, for example, as a module shown in FIG. In this module, for example, an area 210 exposed from a member (not shown) that seals the display panel 10 is provided on one side of the substrate 3, and the timing generation circuit 21 and the video signal processing circuit 22 are provided in the exposed area 210. The data line driving circuit 23, the gate line driving circuit 24, and the drain line driving circuit 25 are extended to form external connection terminals (not shown). The external connection terminal may be provided with a flexible printed circuit (FPC) 220 for signal input / output.

[Application Example 1]
FIG. 17 illustrates an appearance of a television device to which the display device 1 is applied. The television apparatus has a video display screen unit 300 including, for example, a front panel 310 and a filter glass 320, and the video display screen unit 300 is configured by the display device 1.

[Application Example 2]
FIG. 18 shows the appearance of a digital camera to which the display device 1 is applied. The digital camera includes, for example, a flash light emitting unit 410, a display unit 420, a menu switch 430, and a shutter button 440, and the display unit 420 includes the display device 1.

[Application Example 3]
FIG. 19 shows an appearance of a notebook personal computer to which the display device 1 is applied. The notebook personal computer has, for example, a main body 510, a keyboard 520 for inputting characters and the like, and a display unit 530 for displaying an image. The display unit 530 is configured by the display device 1. .

[Application Example 4]
FIG. 20 shows the appearance of a video camera to which the display device 1 is applied. This video camera has, for example, a main body 610, a subject photographing lens 620 provided on the front side surface of the main body 610, a start / stop switch 630 at the time of photographing, and a display 640. Reference numeral 640 denotes the display device 1.

[Application Example 5]
FIG. 21 illustrates an appearance of a mobile phone to which the display device 1 is applied. For example, the mobile phone is obtained by connecting an upper housing 710 and a lower housing 720 with a connecting portion (hinge portion) 730, and includes a display 740, a sub-display 750, a picture light 760, and a camera 770. Yes. The display 740 or the sub display 750 is configured by the display device 1.

  While the present invention has been described with reference to each of the above embodiments and application examples, the present invention is not limited to these, and various modifications can be made.

  For example, in the above embodiment and the like, the case where the display device is an active matrix type has been described. However, the configuration of the pixel circuit 12 for driving the active matrix is not limited to that described in the above embodiment and the like. Therefore, a capacitor and a transistor can be added to the pixel circuit 12 as necessary. In that case, in addition to the timing generation circuit 21, the video signal processing circuit 22, the data line driving circuit 23, the gate line driving circuit 24, and the drain line driving circuit 25 described above, a necessary driving circuit according to the change of the pixel circuit 12. May be added.

  In the above embodiment and the like, the timing generation circuit 21 and the video signal processing circuit 22 control the driving of the data line driving circuit 23, the gate line driving circuit 24, and the drain line driving circuit 25. You may make it control these drives. Control of the data line driving circuit 23, the gate line driving circuit 24, and the drain line driving circuit 25 may be performed by hardware (circuit) or software (program).

  In the above-described embodiments and the like, it has been described that the source and drain of the write transistor Tws and the source and drain of the drive transistor Tdr are fixed. Needless to say, depending on the direction in which the current flows, The opposing relationship between the source and the drain may be opposite to the above description.

  In the above embodiments and the like, it has been described that the write transistor Tws and the drive transistor Tdr are formed of n-channel MOS type TFTs. However, at least one of the write transistor Tws and the drive transistor Tdr is p It may be formed by a channel MOS type TFT. When the drive transistor Tdr is formed of a p-channel MOS type TFT, the anode 35A of the organic EL element 11 is a cathode and the cathode 35B of the organic EL element 11 is an anode in the above-described embodiment and the like. . In the above-described embodiment and the like, the write transistor Tws and the drive transistor Tdr do not always need to be amorphous silicon type TFTs or micro silicon type TFTs. For example, even a low temperature polysilicon type TFT may be used. Good.

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 10 ... Display panel, 10A ... Display area, 11, 11R, 11G, 11B ... Organic EL element, 12 ... Pixel circuit, 13, 13R, 13G, 13B ... Sub pixel, 14 ... Display pixel, 20 ... Drive circuit, 20A ... video signal, 20B ... synchronization signal, 21 ... timing generation circuit, 21A ... control signal, 22 ... video signal processing circuit, 23 ... data line drive circuit, 24 ... gate line drive circuit, 25 ... drain line drive Circuit, 31A, 32A, 36A ... Gate, 31B, 32B, 36B ... Source, 31C, 32C, 36C ... Drain, 31D, 32D, 36D ... Channel, 33A, 33B ... Terminal, 35A ... Anode electrode, 35B ... Cathode electrode, 35C ... organic layer, 37A, 37B, 37C, 37D, 37E ... contact, 41, 47 ... substrate, 42 ... gate insulating film 43, 44, 45, 46 ... insulating film, 43A, 44A ... opening, 300 ... video display screen part, 310 ... front panel, 320 ... filter glass, 410 ... light emitting part, 420, 530, 640 ... display part, 430 ... Menu switch, 440 ... shutter button, 510 ... main body, 520 ... keyboard, 610 ... main body, 620 ... lens, 630 ... start / stop switch, 710 ... upper housing, 720 ... lower housing, 730 ... connecting portion, 740 ... Display, 750 ... Sub-display, 760 ... Picture light, 770 ... Camera, Cs ... Retention capacity, CTL ... Cathode line, DSL ... Drain line, DTL ... Data line, H ... Aperture, S ... Video display surface, Tdr ... Drive transistor, Tr1 ... transistor, Tws ... write transistor, WSL ... gate line.

Claims (8)

A display panel including a self-light emitting element and a pixel circuit for driving the self-light emitting element for each pixel,
The pixel circuit includes a storage capacitor, a first transistor that writes a voltage corresponding to a video signal to the storage capacitor, and a second transistor that drives the light-emitting element based on the voltage of the storage capacitor. A display panel configured to feed back a voltage corresponding to the intensity of light to the gate voltage of the second transistor. The pixel circuit includes a third transistor disposed at a position where external light is incident, and charges the storage capacitor with a leakage current according to the luminance level of the external light incident on the third transistor. The display panel according to claim 1. The third transistor is inserted between a wiring to which a voltage higher than the gate voltage of the second transistor is applied and the storage capacitor,
The display panel according to claim 2, wherein a gate of the third transistor is electrically connected to the storage capacitor. The display panel according to claim 1, further comprising a wiring connected to the self-light emitting element of each pixel for each one or a plurality of pixel rows. A display panel having a self-luminous element and a pixel circuit for driving the self-luminous element for each pixel;
A drive circuit for driving the pixel circuit,
The pixel circuit includes a storage capacitor, a first transistor that writes a voltage corresponding to a video signal to the storage capacitor, and a second transistor that drives the light-emitting element based on the voltage of the storage capacitor. A display device configured to feed back a voltage corresponding to the intensity of light to the gate voltage of the second transistor. The pixel circuit includes a third transistor disposed at a position where external light is incident, and the storage capacitor is charged with a leakage current according to the luminance level of the external light incident on the third transistor. The display device according to claim 5. The display panel further includes a wiring connected to a self-light emitting element of each pixel for each one or a plurality of pixel rows,
The drive circuit applies a voltage that is always lower than a voltage written in the storage capacitor by the first transistor to the wiring while the light-emitting element emits light. 5. The display device according to 5. A display device,
The display device
A display panel having a self-luminous element and a pixel circuit for driving the self-luminous element for each pixel;
A drive circuit for driving the pixel circuit,
The pixel circuit includes a storage capacitor, a first transistor that writes a voltage corresponding to a video signal to the storage capacitor, and a second transistor that drives the light-emitting element based on the voltage of the storage capacitor. An electronic device configured to feed back a voltage corresponding to a luminance level of light to a gate voltage of the second transistor.

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