JP5431704B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device.

  Conventionally, an image display device using an organic EL (Electroluminescent) element utilizing electroluminescence has been known (for example, Patent Document 1).

  In the image display device disclosed in Patent Document 1, the gate potential (gate voltage) based on the source is appropriately set in the drive transistor connected in series with the organic EL element before the organic EL element emits light. As a result, the drain current is controlled, and a desired luminance is obtained. A thin film field-effect transistor (TFT) using amorphous silicon (hereinafter referred to as “s-Si”) is frequently applied to the drive transistor.

Japanese Patent Laid-Open No. 2001-60076

However, a TFT using a-Si (a-Si TFT) has a property that a small amount of drain current flows even when the gate voltage is set to 0V. For this reason, in order to set the drain current to not flow at all, it is necessary to set the gate voltage to a negative voltage. In the a-Si TFT, as indicated by a curve C _v0 in FIG. 29, when the gate voltage V _g is positive, the change in the drain current I _d is relatively large with respect to the change in the gate voltage V _g. (Sensitive state). On the other hand, when the gate voltage V _g is negative, the change in the drain current I _d is remarkably small (the sensitivity is poor) with respect to the change in the gate voltage V _g . Therefore, in order to prevent a small amount of drain current I _d from flowing in the a-Si TFT, it is necessary to make the gate voltage V _g a relatively large negative voltage.

  For example, a pixel in which an organic electroluminescence (Organic Electro-Luminescence) element constituted by an organic light-emitting diode (OLED) and a driving transistor constituted by an a-Si TFT are connected in series. In the circuit, even if the gate voltage of the driving transistor is 0V, the organic EL element is lit by a small amount of drain current. For this reason, in order to realize low-luminance light emission and no light emission in the organic EL element, the gate voltage of the driving transistor needs to be a somewhat large negative voltage. Therefore, it is necessary to widen the amplitude of the potential of the image signal line for applying the image signal to each pixel circuit, and the circuit such as a driver for adjusting the potential of the image signal is complicated, increased in size, and increased in cost. Invited various problems.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of suppressing the fluctuation width of the potential of an image signal.

  In order to solve the above-described problems, the invention of claim 1 is an image display device, wherein a light emitting element that emits light when current flows from one end to the other end, a first electrode, and a second electrode And a third electrode, wherein the first electrode is electrically connected to the other end, and a current flowing between the first electrode and the second electrode is applied to the third electrode. A driving transistor that is adjusted according to the potential that is applied, and a resistance member that is electrically connected in parallel to the light-emitting element. In the image display device, the potential applied to the third electrode in a state where a voltage is applied between the one end and the second electrode so that the potential at the one end is higher. When the voltage between the one end and the other end exceeds a threshold voltage of the light emitting element according to the change, a current flows between the one end and the other end, and the light emitting element Emits light. In the image display device, when the voltage between the one end and the other end is equal to or lower than the threshold voltage of the light emitting element, a current flows through the resistance member, and the one end and the other end No current flows between them, and the light emitting element does not emit light.

  According to a second aspect of the present invention, there is provided an image display device having a light emitting element that emits light when a current flows from one end to the other end, and a first electrode, a second electrode, and a third electrode. And a driving transistor in which the second electrode is electrically connected to the one end, and a current flowing between the first electrode and the second electrode is adjusted by a potential applied to the third electrode. And a resistance member electrically connected in parallel to the light emitting element. In the image display device, a voltage is applied to the third electrode between the first electrode and the other end in a state where a voltage is applied so that the potential of the first electrode is higher. When a voltage between the one end and the other end exceeds a threshold voltage of the light emitting element according to a change in potential, a current flows between the one end and the other end to cause the light emission. The element emits light. In the image display device, when the voltage between the one end and the other end is equal to or lower than the threshold voltage of the light emitting element, a current flows through the resistance member, and the one end and the other end No current flows between them, and the light emitting element does not emit light.

  The invention according to claim 3 is the image display device according to claim 1 or 2, wherein the resistance member includes fourth, fifth, and sixth electrodes, and the fourth electrode and the An adjustment transistor is included that adjusts a current flowing between the fifth electrode and the sixth electrode by a potential applied to the sixth electrode. In this image display device, the fourth electrode is electrically connected to the one end, and the fifth electrode is electrically connected to the other end and the sixth electrode. .

  The invention according to claim 4 is the image display device according to claim 1 or 2, wherein the resistance member includes fourth, fifth, and sixth electrodes, and the fourth electrode and the A first adjustment transistor that adjusts a current flowing between the fifth electrode and the seventh electrode according to a potential applied to the sixth electrode; and seventh, eighth, and ninth electrodes; A second adjustment transistor that adjusts a current flowing between the electrodes by a potential applied to the ninth electrode. In this image display device, the fourth electrode is electrically connected to the eighth electrode, and the fifth electrode is electrically connected to the other end and the sixth electrode. The seventh electrode is electrically connected to the one end and the ninth electrode.

  Further, the invention of claim 5 is the image display device according to claim 4, comprising tenth, eleventh and twelfth electrodes, and a current flowing between the tenth electrode and the eleventh electrode. Is further provided with a compensating transistor that adjusts the voltage according to the potential applied to the twelfth electrode. In this image display device, the tenth electrode is electrically connected to the first electrode, and the eleventh electrode is electrically connected to the third electrode.

  The invention according to claim 6 is the image display device according to claim 1 or 2, wherein the resistance member has a voltage applied between one end and the other end, the one end and the other. The current flowing between the ends includes a resistance element having a substantially proportional relationship.

<Terminology>
In this specification, the term “electrically connected” means that one member and the other member are always connected to each other through a wiring or the like, and one member and the other member are connected. Is used in a sense that includes not only conductive wiring and the like, but also a mode of being indirectly connected by other members. In other words, the term “electrically connected” means that one member and the other member are connected to each other depending on the state of another member (for example, a conductive state in which a current can flow between the source and the drain of the transistor). Is used in a meaning including a mode in which the wiring is connected to be conductive by wiring and other members.

In addition, the “gate voltage” in this specification refers to a gate potential based on the source potential, that is, a potential difference between the source and the gate, and is appropriately expressed as “V _g ”.

  According to the present invention, when the voltage applied across the light emitting element exceeds the threshold voltage, a current flows through the light emitting element and the light emitting element emits light, but the voltage applied across the light emitting element is the threshold voltage. In the following cases, current flows through the resistance member, current does not flow through the light-emitting element, and the light-emitting element does not emit light, so that the fluctuation width of the potential of the image signal for setting the gate voltage of the driving transistor is suppressed. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
<Outline of image display device>
FIG. 1 is a diagram illustrating a schematic configuration of an image display apparatus 1A according to an embodiment of the present invention.

  The image display device 1A is an electronic device that displays various images such as a moving image and a still image according to an image signal. The image display device 1A includes, for example, an organic EL display (organic electroluminescence display) having a substantially rectangular outline, and a display unit 200A having driver means for inputting various signals. Note that the organic EL display includes a self-luminous light-emitting element that emits light by flowing current through the organic material.

<Schematic configuration of display unit>
FIG. 2 is a block diagram illustrating a schematic configuration of the display unit 200A. In FIG. 2, two orthogonal XY axes are shown in order to clarify the orientation relationship.

The display unit 200A includes an organic EL display AA, a timing generation circuit TC, a power feeding control unit EC, an image signal line driving circuit (X driver) X _d , and a scanning signal line driving circuit (Y driver) Y _d .

In the organic EL display AA, a large number of pixel circuits 7A are arranged in a matrix (that is, a lattice) along the vertical direction (Y direction) and the horizontal direction (X direction). An image signal line Lis _is provided for each column of pixel circuits 7A parallel to the Y direction, and each image signal line Lis _is electrically connected to the plurality of pixel circuits 7A in common. Further, a scanning signal line L _ss is provided for each row of the pixel circuits 7A parallel to the X direction, and each scanning signal line L _ss is electrically connected to the plurality of pixel circuits 7A in common.

Timing generating circuit TC is image data (e.g., pixel signals of RGB) sent from the outside in synchronization with the D, and the signal for controlling the supply timing of the pixel signals for each image signal line L _IS from the X driver X _d Send to X driver _Xd . Then, it sends a signal for controlling the supply timing of the scanning signal to each scanning signal line L _ss from Y driver Y _d with respect to the Y driver Y _d.

X driver X _d, in response to a signal from the timing generation circuit TC, and supplies a pixel signal to the image signal line L _IS. On the other hand, the Y driver Y _d supplies a scanning signal to the scanning signal line L _ss in response to a signal from the timing generation circuit TC. By such control of the timing generating circuit TC, the pixel signals are appropriately supplied to each pixel circuit 7A via the image signal line L _IS.

  The power supply controller EC is a part that controls the supply of electric power (specifically, electric power required for light emission, etc.) to each pixel circuit 7A, and may be realized by hardware, that is, a circuit configuration, or software executed by the CPU. May be realized.

<Configuration of pixel circuit>
FIG. 3 is a diagram illustrating a configuration example of a pixel circuit (drive circuit) 7A for one pixel constituting the image display device 1A.

  The pixel circuit 7A includes an organic EL element (OLED) 1, a driving transistor 2, a scanning transistor 3, a capacitor 4, and an adjustment transistor 5.

The organic EL element 1 is a light emitting element that is made of an organic substance and the like, and whose emission luminance varies depending on the amount of current (current amount) that flows through the light emitting layer from the anode electrode 1a to the cathode electrode 1b. The anode electrode 1a is electrically connected to a power feeding part P _vd to which a positive high potential (for example, + 10V or the like) is applied when the organic EL element 1 emits light. The anode electrode 1a is electrically connected to the fourth electrode 5ds of the adjustment transistor 5 via the connection point Cp3. In the present embodiment, the anode electrode 1a corresponds to the “one end” of the present invention. Further, the cathode electrode 1 b is grounded via the drive transistor 2. The cathode electrode 1b is electrically connected to the fifth and sixth electrodes 5sd and 5g of the adjustment transistor 5 through the connection points Cp4 and Cp5 in order. In the present embodiment, the cathode electrode 1b corresponds to the “other end” of the present invention.

  The drive transistor 2 is a transistor that is electrically connected in series to the organic EL element 1 and controls the light emission luminance of the organic EL element 1 by adjusting the amount of current in the organic EL element 1. Here, the driving transistor 2 is a thin film transistor (TFT: Thin Film Transistor) which is a type of field effect transistor (FET) that employs a type (n-type) MIS (Metal Insulator Semiconductor) structure in which carriers are electrons. ), I.e., an n-MISFET TFT.

The drive transistor 2 has first to third electrodes 2ds, 2sd, and 2g. The first electrode 2ds is electrically connected to the cathode electrode 1b of the organic EL element 1 via the connection point Cp4, and when the organic EL element 1 emits light, that is, a forward current with respect to the organic EL element 1. Functions as a drain electrode (hereinafter abbreviated as “drain”). On the other hand, when a voltage is applied in the reverse direction to the organic EL element 1, the first electrode 2ds functions as a source electrode (hereinafter abbreviated as “source”). The first electrode 2ds is electrically connected to the fifth and sixth electrodes 5sd and 5g of the adjustment transistor 5 through the connection points Cp4 and Cp5 sequentially. The second electrode 2sd is electrically connected to the other electrode 4b of the wiring (grounding wire) G _d and a capacitor 4 for grounding via the connecting point Cp2, the forward direction with respect to the organic EL element 1 It functions as a source electrode (source) when current flows. On the other hand, when a voltage is applied in the reverse direction to the organic EL element 1, the second electrode 2sd functions as a drain electrode (drain). Further, the third electrode 2g is a so-called gate electrode (hereinafter abbreviated as “gate”), and is electrically connected to the eighth electrode 3sd of the scanning transistor 3 and the one electrode 4a of the capacitor 4 via the connection point Cp1. Connected.

  In the driving transistor 2, the potential applied to the third electrode 2g, more specifically, applied between the first electrode 2ds or the second electrode 2sd and the third electrode 2g (that is, between the gate and the source). By adjusting the voltage value, the amount of current (current amount) flowing between the first electrode 2ds and the second electrode 2sd (hereinafter also referred to as “between the first and second electrodes”) is adjusted. Then, the potential applied to the third electrode (gate) 2g causes the drive transistor 2 to have a state in which a current can flow between the first and second electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

The adjustment transistor 5 has substantially the same performance as that of the drive transistor 2 and is electrically connected to the organic EL element 1 in parallel between the power feeding unit P _vd and the ground wiring G _d , and the drive transistor 2 is electrically connected in series. The adjustment transistor 5 includes fourth to sixth electrodes 5ds, 5sd, and 5g. The fourth electrode 5ds is electrically connected to the anode electrode 1a and the power supply portion P _vd of the organic EL element 1 through the connection point Cp3. The fifth and sixth electrodes 5sd and 5g are electrically connected to the cathode electrode 1b of the organic EL element 1 and the first electrode 2ds of the driving transistor 2 through the connection points Cp5 and Cp4 in sequence. Yes. Furthermore, the fifth electrode 5sd is electrically connected to the sixth electrode 5g which is a gate through a connection point Cp5.

  Further, in the adjustment transistor 5, a potential applied to the sixth electrode 5g, more specifically, the fourth electrode 5ds or the fifth electrode 5sd and the sixth electrode 5g (that is, between the gate and the source) is applied. By adjusting the voltage value, the amount of current (current amount) flowing between the fourth electrode 5ds and the fifth electrode 5sd (hereinafter also referred to as “between the fourth and fifth electrodes”) is adjusted. Then, due to the potential applied to the sixth electrode (gate) 5g, the adjustment transistor 5 has a state in which a current can flow between the fourth and fifth electrodes (that is, between the drain and the source) (conduction state), and a current Is selectively set to a state in which the current cannot flow (non-conducting state). In the present embodiment, the adjustment transistor 5 corresponds to the “resistance member” of the present invention.

The scanning transistor 3 is a transistor that controls the timing at which the potential of the image signal line Lis _is applied to the third electrode (gate) 2 g of the driving transistor 2. Here, the scanning transistor 3 is also composed of an n-MISFET TFT in the same manner as the driving transistor 2.

The scanning transistor 3 has seventh to ninth electrodes 3ds, 3sd, and 3g. Then, the seventh electrode 3ds is electrically connected to the image signal line L _IS. The eighth electrode 3sd is electrically connected to the third electrode (gate) 2g of the drive transistor 2 and the one electrode 4a of the capacitor 4 via the connection point Cp1. Further, the ninth electrode 3g functions as a so-called gate and is electrically connected to the scanning signal line L _ss .

  In the scanning transistor 3, the potential applied to the ninth electrode 3g, more specifically, between the seventh electrode 3ds or the eighth electrode 3sd and the ninth electrode 3g (that is, between the gate and the source). By adjusting the applied voltage value, the amount of current between the seventh electrode 3ds and the eighth electrode 3sd (hereinafter also referred to as “between the seventh and eighth electrodes”) is adjusted. Then, due to the potential applied to the ninth electrode (gate) 3g, the scanning transistor 3 has a state in which a current can flow between the seventh and eighth electrodes (between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

The capacitor 4 has one and other electrodes 4a and 4b. The one electrode 4a is electrically connected to the third electrode 2g of the driving transistor 2 and the eighth electrode 3sd of the scanning transistor 3 via the connection point Cp1. The other electrode 4b through the connection point Cp2, is electrically connected to the second electrode 2sd and grounding wire G _d of the drive transistor 2.

  Here, the description has been given focusing on one pixel circuit 7A, but there are a large number of pixel circuits 7A in the entire organic EL display AA.

<Driving method for light emission of organic EL element>
FIG. 4 is a timing chart showing signal waveforms (drive waveforms) when the organic EL element 1 emits light. Specifically, FIG. 4 shows a timing chart showing drive waveforms when the organic EL element 1 emits light three times in time sequence. In FIG. 4, the horizontal axis indicates time, and in order from the top, (a) the potential (potential V _sl ) applied to the scanning signal line L _ss and (b) the potential applied to the image signal line L _is ( The waveform of the potential V _is ) is shown. Since the potential V _is is an arbitrary value (hereinafter referred to as “V _data ”) determined by the light emission luminance of each organic EL element 1, in FIG. 4, hatching in the range where the potential can exist is convenient. It is attached to. Here, it is assumed that a constant positive high potential (+10 V) is applied to the power feeding unit P _vd . Hereinafter, the light emitting operation of the organic EL element 1 will be described with reference to FIG.

At time t1, the potential V _is is set from the reference potential of 0 V to any positive potential V _data . Subsequently, at time t2, the potential V _sl is set from the low potential V _gL to the high potential V _gH . At this time, the scanning transistor 3 becomes conductive, the potential V _data is applied to the third electrode (gate) 2g, and the gate voltage V _g of the driving transistor 2 becomes V _data . As a result, a current corresponding to the potential V _data together with the flow between the first-second electrode, a current corresponding to the potential V _data to flow toward the cathode 1b of the anode 1a of the organic EL element 1, the organic EL device 1 emits light at a luminance corresponding to the potential _Vdata . Next, at time t3, the potential V _is is set from the potential V _data to the reference potential of 0V. At this time, the gate voltage V _g of the driving transistor 2 becomes 0 V, and the light emission of the organic EL element 1 is completed. At time t4, the potential V _sl is changed from the high potential V _gH to the low potential V _gL .

  Then, at times t5 to t8 and t9 to t12, operations similar to those at times t1 to t4 are performed, respectively, and light emission of the organic EL element 1 is started at a predetermined time interval (for example, 1/60 seconds). Here, the driving when the organic EL element 1 emits light three times in time order has been described, but actually, the organic EL element 1 emits light many times in time order according to the image display period.

<Characteristics of adjustment transistor and merit of adjustment transistor>
FIG. 5 is a diagram schematically illustrating the characteristics of the adjustment transistor 5. In FIG. 5, the horizontal axis indicates the potential, and the vertical axis indicates the current. Then, the potential of the fourth electrode 5ds with reference to the potential of the fifth electrode 5sd of the adjustment transistor 5, that is, the potential difference (voltage) V ₅₀ between the fourth electrode 5ds and the fifth electrode 5sd, and the fourth electrode 5ds relation between the current I ₅₀ toward the fifth electrode 5sd is shown by the curve C _r5.

As shown in FIG. 5, when the voltage V ₅₀ is 0 V or more, the fifth electrode (source) 5 sd and the sixth electrode (gate) 5 g are electrically connected. The potential difference (gate voltage) between them becomes 0V. Therefore, when the voltage V ₅₀ is 0 V or more, the current I ₅₀ increases as the voltage V ₅₀ increases, and is constant at the current I _d0 when the gate voltage is 0 V as shown in FIG. Become. That is, if the potential at the connection point Cp3 is higher than the potential at the connection point Cp4, a current equal to or less than the current I _d0 flows between the fourth and fifth electrodes.

FIG. 6 is a diagram showing the relationship between the gate voltage V _g of the driving transistor 2 and the current flowing through the organic EL element 1. In FIG. 6, the horizontal axis represents voltage and the vertical axis represents current. The relationship between the gate voltage V _g of the driving transistor 2 and the current I _od flowing from the anode electrode 1a to the cathode electrode 1b of the organic EL element 1 is indicated by a thick curve C _od . In FIG. 6, the gate voltage V _g of the driving transistor 2 and the organic EL element 1 when the adjustment transistor 5 is not electrically connected to the organic EL element 1 in parallel as shown in FIG. The relationship with the flowing current I _od is shown by a thin curve C ₁ .

As indicated by the curve C ₁ , if the adjustment transistor 5 does not exist, the current I _od becomes a positive current I _d0 even if the gate voltage V _{g is set} to 0V. Therefore, in order to achieve the emission and non-emission of low luminance in the organic EL element 1 is required to be a relatively large negative voltage to the gate voltage V _g of the drive transistor 2.

In contrast, in the pixel circuit 7A according to the present embodiment, the adjustment transistor 5 to the organic EL element 1 are electrically connected in parallel, as shown in Figure 5, with the voltage V ₅₀ or 0V In some cases, the current I ₅₀ increases as the voltage V ₅₀ increases, and becomes constant at the current I _d0 . Therefore, when the gate voltage V _g of the drive transistor 2 is 0 V, the current I _d0 flowing between the first and second electrodes of the drive transistor 2 does not flow to the organic EL element 1, and the fourth of the adjustment transistor 5 Flows between -5 electrodes.

Therefore, as shown by curve C _od, when the gate voltage V _g of the drive transistor 2 is 0V, the current does not flow toward the cathode 1b of the anode 1a of the organic EL element 1. When gradually increasing the gate voltage V _g of the drive transistor 2 from 0V, the voltage applied between the connection point Cp3 and the connection point Cp4 gradually rises, current I _od increases. That is, when the voltage applied between the connection point Cp3 and the connection point Cp4 is equal to or lower than a predetermined threshold voltage, a current flows between the fourth and fifth electrodes of the adjustment transistor 5, but the current flows in the organic EL element 1. Not flowing. When the voltage applied between the connection point Cp3 and the connection point Cp4 exceeds a predetermined threshold voltage, a current I _d0 flows between the fourth and fifth electrodes of the adjustment transistor 5, and also in the organic EL element 1. Current flows.

FIG. 7 is a diagram schematically showing the relationship between the voltage V _od applied across the organic EL element 1 and the current I _od flowing through the organic EL element 1. In FIG. 7, the horizontal axis represents voltage, and the vertical axis represents current. The relationship between the voltage applied between the connection point Cp3 and the connection point Cp4, that is, the voltage V _od applied between both ends of the organic EL element 1, and the current I _od flowing between both ends of the organic EL element 1 Is shown by curve C _v1 . As shown in FIG. 7, until the voltage V _od reaches the threshold voltage V _t1 , the current I _od is 0 A. When the voltage V _od exceeds the threshold voltage V _t1 , the current I _od increases as the voltage V _od increases. Will increase.

More specifically, a voltage is applied between the anode electrode 1a and the second electrode 2sd so that the potential of the anode electrode 1a is higher than that of the second electrode 2sd. When the voltage between the anode electrode 1a and the cathode electrode 1b exceeds the threshold voltage _Vt1 in accordance with the change in potential, current flows between the first and second electrodes and between the anode electrode 1a and the cathode electrode 1b. Then, the organic EL element 1 emits light. Further, a voltage is applied between the anode electrode 1a and the second electrode 2sd so that the potential of the anode electrode 1a is higher than that of the second electrode 2sd. Is less than or equal to the threshold voltage V _t1 , current flows between the first and second electrodes, but no current flows between the anode electrode 1a and the cathode electrode 1b, and the organic EL element 1 does not emit light. .

The current I _od indicated by the curve C _od becomes that the current indicated by the curve C ₁ minus the constant current I _d0.

As described above, in the image display device 1A according to the first embodiment, when the voltage applied between both electrodes of the organic EL element 1 exceeds a predetermined threshold voltage, a current flows through the organic EL element 1 and The organic EL element 1 emits light. On the other hand, when the voltage applied between both electrodes of the organic EL element 1 is equal to or lower than a predetermined threshold voltage, a current flows through the adjustment transistor 5, and no current flows through the organic EL element 1. Element 1 does not emit light. For this reason, the fluctuation width of the potential (here, V _data ) of the image signal for setting the gate voltage V _g of the driving transistor 2 can be suppressed.

Specifically, by adjusting the gate voltage V _g of the driving transistor 2 as appropriate within a positive voltage range of 0 V or more, all luminance gradations due to light emission of the organic EL element 1 can be realized. In other words, the light emission of the organic EL element 1 can be efficiently controlled with a small change in the potential _Vdata . Therefore, the amplitude of the voltage handled by the X driver X _d that adjusts the potential V _{data of the} pixel signal is reduced, and the power consumption in the X driver X _d can be reduced. For this reason, the X driver _Xd can be manufactured using the latest fine process, and the circuit size and cost of the X driver _Xd can be reduced. Further, since the output switching interval (that is, output accuracy) may be substantially the same even when the amplitude of the output of the X driver X _d (here, the potential V _data ) is reduced, the number of bits handled by the X driver X _d is reduced. Therefore, the circuit of the X driver _Xd can be simplified and downsized.

  Since the adjustment transistor 5 is electrically connected in series with the drive transistor 2, there is a resistance of the adjustment transistor 5 even when the organic EL element 1 is not provided during the manufacturing of the pixel circuit 7A. ing. For this reason, before the organic EL element 1 is formed by vapor deposition, a voltage is appropriately applied to a circuit in which the adjustment transistor 5 and the drive transistor 2 are connected in series, and the current flowing through the circuit is measured. Can be tested for performance.

Second Embodiment
In the image display device 1 </ b> A according to the first embodiment, the adjustment transistor 5 is connected in parallel with the organic EL element 1. In contrast, in the image display device 1B according to the second embodiment, the first and second adjustment transistors 15 and 16 that are electrically connected in series are electrically connected in parallel to the organic EL element 11. Yes. In the second embodiment, the first and second adjustment transistors 15 and 16 correspond to at least one “resistive member” of the present invention.

  The image display device 1B according to the second embodiment is similar in configuration to the image display device 1A according to the first embodiment, but the pixel circuit 7A is changed to a pixel circuit 7B having a different configuration. As a result, the display unit 200A is changed to the display unit 200B. Hereinafter, parts similar to those of the image display apparatus 1A according to the first embodiment are denoted by the same reference numerals and description thereof is omitted, and parts different from the image display apparatus 1A according to the first embodiment are described in the second embodiment. The image display apparatus 1B will be described.

<Configuration of pixel circuit>
FIG. 8 is a diagram showing a configuration example of a pixel circuit (driving circuit) 7B for one pixel constituting the image display device 1B according to the second embodiment of the present invention.

The pixel circuit 7B includes an organic EL element (OLED) 11, a drive transistor 12, a first adjustment transistor 15, a second adjustment transistor 16, a threshold (V _th ) compensation transistor 13, and a capacitor.

  The organic EL element 11 is a light emitting element that has the same configuration as the organic EL element 1 according to the first embodiment, and whose emission luminance varies depending on the amount of current flowing through the light emitting layer. The organic EL element 11 includes an anode electrode 11a and a cathode electrode 11b. In the present embodiment, the anode electrode 11a corresponds to “one end portion” of the present invention, and the cathode electrode 11b corresponds to “other end portion” of the present invention.

The anode electrode 11a is electrically connected to the V _DD line L _vd as a power supply line that is on the high potential side when the organic EL element 11 emits light among the power supply lines. The anode 11a is electrically connected to the seventh and ninth electrodes 16ds and 16g of the second adjustment transistor 16 through the connection points Cn1 and Cn6 in sequence.

The cathode electrode 11b is electrically connected to the V _SS line L _vs as a power supply line that is on the low potential side during light emission of the organic EL element 11 through the connection points Cn2 and Cn4 and the drive transistor 12 sequentially. Connected. The cathode electrode 11b is electrically connected to the fifth and sixth electrodes 15sd, 15g of the adjustment transistor 5 through the connection points Cn2, Cn4, Cn5 in order. Further, the cathode electrode 11b is electrically connected to the tenth electrode 13ds of the _Vth compensation transistor 13 through the connection point Cn2.

  The drive transistor 12 is a transistor that is electrically connected in series to the organic EL element 11 and controls the light emission luminance of the organic EL element 11 by adjusting the amount of current in the organic EL element 11. Here, the drive transistor 12 is configured by an n-MISFET TFT. The drive transistor 12 includes first to third electrodes 12ds, 12sd, and 12g.

The first electrode 12ds is electrically connected to the cathode electrode 11b of the organic EL element 11 through the connection points Cn4 and Cn2 sequentially. The first electrode 12ds functions as a drain when the organic EL element 11 emits light, that is, when a forward current flows through the organic EL element 11. On the other hand, when a voltage is applied to the organic EL element 11 in the reverse direction, the first electrode 12ds functions as a source. The first electrode 12ds is electrically connected to the fifth and sixth electrodes 15sd and 15g of the adjustment transistor 15 via the connection points Cn4 and Cn5 sequentially. Further, the first electrode 12ds is electrically connected to the tenth electrode 13ds of the _Vth compensation transistor 13 through the connection points Cn4 and Cn2 in order.

The second electrode 12sd is electrically connected to the V _SS line L _vs. The second electrode 12 sd functions as a source when a forward current flows through the organic EL element 11. On the other hand, when a voltage is applied in the reverse direction with respect to the organic EL element 11, the second electrode 12sd functions as a drain. Further, the third electrode 12g is a so-called gate, and is electrically connected to the eleventh electrode 13sd of the _Vth compensation transistor 13 and the one electrode 14a of the capacitor 14 via the connection point Cn3.

  In the driving transistor 12, a potential applied to the third electrode 12g, more specifically, applied between the first electrode 12ds or the second electrode 12sd and the third electrode 12g (that is, between the gate and the source). By adjusting the voltage value, the amount of current (current amount) flowing between the first electrode 12ds and the second electrode 12sd (hereinafter also referred to as “between the first and second electrodes”) is adjusted. Then, the potential applied to the third electrode (gate) 12g causes the drive transistor 12 to have a state in which a current can flow between the first and second electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

Each of the first and second adjustment transistors 15 and 16 is configured by an n-MISFET TFT similarly to the drive transistor 12, has substantially the same performance, and is electrically connected in series. Further, a portion configured by connecting the first and second adjustment transistors 15 and 16 in series is electrically connected to the organic EL element 11 between the V _DD line L _vd and the V _SS line L _vs. They are connected in parallel and electrically connected in series to the drive transistor 12.

Specifically, the first adjustment transistor 15 includes fourth to sixth electrodes 15ds, 15sd, and 15g. The fourth electrode 15 ds is electrically connected to the eighth electrode 16 sd of the second adjustment transistor 16. The fifth and sixth electrodes 15 sd and 15 g are electrically connected to the cathode electrode 11 b of the organic EL element 11 and the tenth electrode 13 ds of the V _th compensation transistor 13 through the connection points Cn 5, Cn 4 and Cn 2 in sequence. It is connected. The fifth and sixth electrodes 15 sd and 15 g are electrically connected to the first electrode 12 ds of the drive transistor 12 through the connection points Cn 5 and Cn 4 in order. Further, the fifth electrode 15sd is electrically connected to the sixth electrode 15g which is a gate through the connection point Cn5.

  In the first adjustment transistor 15, the potential applied to the sixth electrode 15g, more specifically, between the fourth electrode 15ds or the fifth electrode 15sd and the sixth electrode 15g (that is, between the gate and the source). By adjusting the applied voltage value, the amount of current (current amount) flowing between the fourth electrode 15ds and the fifth electrode 15sd (between the fourth and fifth electrodes) is adjusted. Then, the potential applied to the sixth electrode (gate) 15g causes the first adjustment transistor 15 to be in a state where the current can flow between the fourth and fifth electrodes (that is, between the drain and the source) (conductive state). , A state in which current cannot flow (non-conduction state) is selectively set.

The second adjustment transistor 16 includes seventh to ninth electrodes 16ds, 16sd, and 16g. The seventh and ninth electrodes 16ds and 16g are electrically connected to the V _DD line L _vd and the anode electrode 11a through the connection points Cn6 and Cn1, respectively. The seventh electrode 16ds is electrically connected to the ninth electrode 16g via the connection point Cn6. The eighth electrode 16 sd is electrically connected to the fourth electrode 15 ds of the first adjustment transistor 15.

  In the second adjustment transistor 16, the potential applied to the ninth electrode 16g, more specifically, between the seventh electrode 16ds or the eighth electrode 16sd and the ninth electrode 16g (that is, between the gate and the source). By adjusting the voltage value to be applied, the amount of current (current amount) flowing between the seventh electrode 16ds and the eighth electrode 16sd (between the seventh and eighth electrodes) is adjusted. Then, due to the potential applied to the ninth electrode (gate) 16g, the second adjustment transistor 16 has a state in which a current can flow between the seventh and eighth electrodes (that is, between the drain and the source) (conductive state). , A state in which current cannot flow (non-conduction state) is selectively set.

The V _th compensation transistor 13 detects the lower limit value (predetermined threshold voltage V _th ) of the potential of the third electrode 12g with respect to the second electrode 12sd when the drive transistor 12 is energized, and the drive transistor 12 This is a transistor for adjusting the gate voltage to a threshold voltage V _th (hereinafter abbreviated as “threshold V _th ”). That is, the “threshold value V _th ” refers to a gate voltage serving as a boundary when the driving transistor 12 changes from an off state (a state where a drain current does not flow) to an on state (a state where the drain current flows). Here, the V _th compensation transistor 13 is also composed of an n-MISFET TFT, like the drive transistor 12.

The V _th compensation transistor 13 has tenth to twelfth electrodes 13ds, 13sd, and 13g. The tenth electrode 13ds is electrically connected to the cathode electrode 11b of the organic EL element 11 through the connection point Cn2. The tenth electrode 13ds is electrically connected to the first electrode 12ds of the drive transistor 12 through the connection points Cn2 and Cn4 in order. Further, the tenth electrode 13ds is electrically connected to the fifth electrode 15sd and the sixth electrode 15g of the first adjustment transistor 15 via the connection points Cn2, Cn4, Cn5 in sequence. The eleventh electrode 13sd is electrically connected to the third electrode 12g of the drive transistor 12 and the one electrode 14a of the capacitor 14 via the connection point Cn3. The twelfth electrode 13g is electrically connected to the scanning signal line L _ss .

In the V _th compensation transistor 13, the potential applied to the twelfth electrode 13g, more specifically, between the tenth electrode 13ds or the eleventh electrode 13sd and the twelfth electrode 13g (that is, between the gate and the source). By adjusting the voltage value applied to, the amount of current (current amount) flowing between the tenth electrode 13ds and the eleventh electrode 13sd (between the tenth and eleventh electrodes) is adjusted. Then, the potential applied to the twelfth electrode (gate) 13g causes the V _th compensation transistor 13 to flow a current between the tenth and eleventh electrodes (that is, between the drain and the source) (conduction state). And a state where current cannot flow (non-conducting state) is selectively set.

Here, since the light emission luminance of the organic EL element 11 is controlled by the current value, the light emission luminance fluctuates sensitively to fluctuations in the gate voltage of the drive transistor 12 during light emission. In particular, when the driving transistor 12 is configured using amorphous silicon, the threshold V _th tends to be different for each driving transistor 12. Therefore, if a function for compensating a different threshold V _th for each pixel (V _th compensation function) is not provided, there is a slight difference between the desired light emission luminance and the actual light emission luminance, resulting in light emission between the pixels. Uneven brightness will occur.

Therefore, the V _th compensation transistor 13 realizes a V _th compensation function that compensates for variations in the threshold V _th in the drive transistor 12 by matching the gate voltage of the drive transistor 12 to the threshold V _th for each pixel before light emission. .

The capacitor 14 includes a first electrode 14a and a second electrode 14b. The one electrode 14a is electrically connected to the third electrode 12g of the drive transistor 12 and the eleventh electrode 13sd of the _Vth compensation transistor 13 via the connection point Cn3. The other electrode 14b is electrically connected to the image signal line L _IS. Here, the retention capacity of the capacitor 14 with a predetermined value C _s.

Incidentally, the organic EL element 11, the voltage of the light emitting time of the reverse is applied to function as a capacitor, to the capacitance (EL element capacitor) with a predetermined value C _o. Further, the drive transistor 12 includes a parasitic capacitance C _gsTd between the second electrode 12 sd and the third electrode 12 g (between the second and third electrodes), and between the first electrode 12 ds and the third electrode 12 g (the first 1-first electrode). A parasitic capacitance C _gdTd between three electrodes). Further, the V _th compensation transistor 13 includes a parasitic capacitance C _gsTth between the eleventh electrode 13sd and the twelfth electrode 13g (between the eleventh and twelfth electrodes), and between the tenth electrode 13ds and the twelfth electrode 13g ( And a parasitic capacitance C _gdTth between the 10th and 12th electrodes). The parasitic capacitances C _gsTd , C _gdTd , C _gsTth , and C _gdTth are predetermined values determined by the configurations of the drive transistor 12 and the V _th compensation transistor 13, respectively.

9, the circuit configuration of the pixel circuit 7B shown in FIG. 8, the parasitic capacitance _{C gsTth, C gdTth, C gsTd} , circuitry (described in dashed line in the drawing) according to the C _GdTd and EL element capacitance C _o It is the schematic diagram which added.

As shown in Figure 9, the pixel circuit 7B, between both electrodes of the organic EL element 11 capacitor (element capacitor) C _ol is present having an EL element capacitance C _o, between 2-3 electrode of the driving transistor 12 _Has a capacitor 12gs having a parasitic capacitance _CgsTd . A capacitor 12 _gd having a parasitic capacitance C _gdTd exists between the first and third electrodes of the drive transistor 12. Further, a capacitor 3gs having a parasitic capacitance C _gsTth exists between the 11th and 12th electrodes of the V _th compensation transistor 13. Further, between the first 10-12 electrodes of V _th compensation transistor 13 capacitor 13gd having parasitic capacitance C _GdTth exists.

Here, the description has been given focusing on one pixel circuit 7B, but there are a large number of pixel circuits 7B in the entire organic EL display AA. For this reason, there are a large number of scanning signal lines L _ss . Therefore, in the following, a large number of scanning signal lines L _ss will be referred to as “Nth scanning signal lines (N is a natural number) L _ss ” as appropriate.

<Characteristics of adjustment transistor and merit of adjustment transistor>
FIG. 10 is a diagram schematically showing the characteristics of the first and second adjustment transistors 15 and 16. In FIG. 10, the horizontal axis represents voltage, and the vertical axis represents current. Specifically, the horizontal axis is based on the voltage applied to both ends of the portion where the first and second adjustment transistors 15 and 16 are electrically connected in series, specifically, the potential at the connection point Cn5. the potential of the connection point Cn6 that, that is, the voltage V ₅₆ between the connection point Cn6 and the connection point CN5. The vertical axis represents the current I ₅₆ that flows from the connection point Cn6 toward the connection point Cn5 through the portion where the first and second adjustment transistors 15 and 16 are electrically connected in series. In FIG. 10, it is assumed that the second adjustment transistor 16 is not provided between the connection point Cn5 and the connection point Cn6, and only the first adjustment transistor 15 is provided, and the voltage V ₅₆ and the current I ₅₆ are provided. A curve C _v15 indicating the relationship with is shown by a broken line. Further, in FIG. 10, it is assumed that the first adjustment transistor 15 is not provided between the connection point Cn5 and the connection point Cn6, and only the second adjustment transistor 16 is provided, and the voltage V ₅₆ and the current I ₅₆ are provided. A curve C _v16 indicating the relationship with is shown by a one-dot chain line.

As shown by the curve C _v15 in FIG. 10, if, if no second adjusting transistor 16 is provided, when the voltage V ₅₆ is equal to or higher than 0V, as shown also in FIG. 5, increase in the voltage V ₅₆ At the same time, the current I ₅₆ increases, and the current I ₅₆ becomes constant at the current I _d0 when the gate voltage shown in FIG. 29 is 0V. However, the voltage V ₅₆ As you are reduced below 0V, current I ₅₆ indicates a negative value, the current from the fifth electrode 15sd toward the fourth electrode 15ds rapidly increases. Therefore, if the second adjustment transistor 16 is not provided, when a voltage is applied to the organic EL element 11 in the direction opposite to the forward direction in which current flows, the connection point is connected via the first adjustment transistor 15. A relatively large current flows from Cn5 toward the connection point Cn6. For this reason, it is not possible to accumulate charges between both electrodes of the organic EL element 11 by using the organic EL element 11 as a capacitor.

On the other hand, as shown by the curve C _v16 in FIG. 10, if, unless the first adjusting transistor 15 is provided, when the voltage V ₅₆ is less than 0V, together with the voltage drop V _56, current I ₅₆ is As shown in FIG. 29, the current I ₅₆ becomes constant at the current −I _d0 when the gate voltage is 0V. However, when the voltage V ₅₆ will be increased by more than 0V, the current I ₅₆ indicates a positive value, the current directed from the seventh electrode 16ds to the eighth electrode 16sd rapidly increases. In other words, when the voltage _V56 is a negative value, no current larger than the current _Id0 flows through the second adjustment transistor 16, and when the voltage _V56 is a positive value, the voltage V56 _. A current I ₅₆ corresponding to the application of flows from the seventh electrode 16ds toward the eighth electrode 16sd.

Figure 11 shows the relationship between the voltage V ₅₆ and the current I _56, i.e., the relationship between the voltage and current of the first and second adjusting transistor 15 and 16 shown schematically between the connection point Cn5 the connection point Cn6 FIG. In Figure 11, the relationship between the voltage V ₅₆ and the current I ₅₆ in between the connection point Cn5 and the connection point Cn6 are drawn by a thick solid curve C _{V56. Further} , the curves C _v15 and C _v16 shown in FIG. 10 are drawn by thin lines, respectively.

In the present embodiment, the first and second adjustment transistors 15 and 16 are electrically connected in series between the connection point Cn5 and the connection point Cn6. Therefore, as shown by the curve C _V56 in FIG. 11, when the voltage V ₅₆ of 0V or more, along with increase in the voltage V _56, current I ₅₆ is increased, becomes constant at current I _d0. On the other hand, when the voltage V ₅₆ is less than 0V, as well as reduction of the voltage V50, the current I ₅₆ is constant at a current -I _d0 decreases.

Therefore, between the connection point Cn1 and the connection point Cn4, voltage as towards the connection point Cn1 becomes higher potential is applied, when the gate voltage V _g of the drive transistor 12 is 0V, the drive transistor 12 Current I _d0 flowing between the first and second electrodes of the first adjusting transistor 15 does not flow between the fourth and fifth electrodes of the first adjusting transistor 15 and between the seventh and eighth electrodes of the second adjusting transistor 16. Flowing.

More specifically, as in the first embodiment, a voltage is applied between the anode electrode 11a and the second electrode 12sd so that the potential of the anode electrode 11a is higher than that of the second electrode 12sd. When the voltage between the anode electrode 11a and the cathode electrode 11b exceeds the threshold voltage _Vt1 in accordance with the change in potential applied to the third electrode 12g, between the first and second electrodes and between the anode electrode 11a and the cathode A current flows between the electrode 11b and the organic EL element 11 emits light. Further, a voltage is applied between the anode electrode 11a and the second electrode 12sd so that the potential of the anode electrode 11a is higher than that of the second electrode 12sd. Is less than or equal to the threshold voltage V _t1 , current flows between the first and second electrodes, but no current flows between the anode electrode 11a and the cathode electrode 11b, and the organic EL element 11 does not emit light. .

Moreover, between the connection point Cn1 and the connection point Cn4, towards the connection point Cn4 is a voltage that the potential is higher is applied, be raised gate voltage V _g of the drive transistor 12, first and second Only a low constant current I _d0 flows through the adjusting transistors 15 and 16.

  Accordingly, charges can be accumulated between both electrodes of the organic EL element 11 by using the organic EL element 11 as a capacitor. Hereinafter, a driving method for controlling the light emission luminance of the organic EL element 11 while using the organic EL element 11 as a capacitor will be described.

<Driving method for light emission of organic EL element>
FIG. 12 is a timing chart showing a signal waveform (drive waveform) when the organic EL element 11 emits light. In FIG. 12, the horizontal axis indicates time, and in order from the top, (a) the potential applied to the V _DD line L _vd (potential V _dd ) and (b) the potential applied to the V _SS line L _vs (potential V _SS ), (c) the potential of the signal applied to the first scanning signal line L _ss (potential V _ls1 ), (d) the potential of the signal applied to the second scanning signal line L _ss (potential V _ls2 ), ( e) The waveform of the potential of the signal (potential V _lis ) applied to the image signal line Lis _is shown.

Further, in FIG. 12, there is shown a driving waveform for lighting the organic EL element 11 once a period of the one emission, sequentially time, C _s initialization period P1 (time t11 to t12) , Preparation period P2 (time t12 to t13), _Vth compensation period P3 (time t13 to t14), writing period P4 (time t14 to t15), element initialization period P5 (time t15 to t16), and light emission period P6 (Time t16-). Since the potential V _lis in the writing period P4 is an arbitrary value determined by the light emission luminance of each organic EL element 11, in FIG. 12, hatched hatching is added for convenience in a range where the potential can exist. Yes.

  FIGS. 13 to 17 are diagrams illustrating the flow of current of the pixel circuit 7B generated in each period when the image display device 1B according to the second embodiment is driven, with black arrows. In FIG. 13 to FIG. 17, among the pixel circuits 7B, circuits that contribute to the current flow are indicated by thick lines, and circuits that hardly contribute to the current flow are indicated by thin lines.

  Hereinafter, a method for driving the image display apparatus 1B according to the second embodiment will be described with reference to FIGS. 12 and 13 to 17 as appropriate.

○ C _s initialization period P1:
FIG. 13 illustrates the flow of current in the pixel circuit 7B in the C _s initialization period P1 (hereinafter abbreviated as “period P1” where appropriate).

In the period P1, a predetermined positive high potential V _DD (for example, 15 V) is applied to the V _DD line L _vd and the V _SS line L _vs. Further, a predetermined positive high potential V _gH (for example, 15 V) is applied to all the scanning signal lines L _ss . Further, a predetermined reference potential to the image signal line L _IS (here, 0V) is applied.

At this time, by the application of high voltage V _gH in the scanning signal line L _ss, positive potential corresponding to the high potential V _gH to the 12 electrodes (gate) 13 g is applied, V _th compensation transistor 13 becomes conductive. On the other hand, since the V _DD line L _vd and the V _SS line L _vs have substantially the same potential, the drive transistor 12 is turned off. Therefore, in the period P1, as shown in FIG. 13, a current flows from the V _DD line L _vd to the capacitor 14 via the tenth and eleventh electrodes 13ds and 13sd of the V _th compensation transistor 13, and the capacitor 14 A predetermined amount of charge (for example, a charge amount corresponding to 15V) is accumulated.

Note that the amount of charge accumulated in the capacitor 14 increases as time elapses in the period P1, and a positive potential exceeding a predetermined value is applied to the third electrode (gate) 12g, so that the driving transistor 12 may be in a conductive state. However, since the V _DD line L _vd and the V _SS line L _vs are both set to the same potential V _DD , no current flows between the first and second electrodes of the drive transistor 12.

○ Preparation period P2:
FIG. 14 illustrates the flow of current in the pixel circuit 7B in the preparation period P2 (hereinafter abbreviated as “period P2” as appropriate).

In the period P2, a negative predetermined potential −V _p (for example, −7 V) is applied to the V _DD line L _vd . Further, a predetermined reference potential (0 V in this case) is applied to the V _SS line L _vs. In addition, a predetermined low potential V _gL (for example, −10 V) is applied to all the scanning signal lines L _ss . Moreover, given the high potential V _dH to the image signal line L _IS (e.g. 10V) is applied.

At this time, since the low potential V _gL is applied to the scanning signal line L _ss , almost no positive potential is applied to the twelfth electrode (gate) 13 g, so that the V _th compensation transistor 13 is turned off. On the other hand, when the high potential V _{dH is applied to} the image signal line Lis, a positive potential (for example, 15 + 10 = 25 V) corresponding to the high potential V _dH is applied to the third electrode (gate) 12g, and the drive transistor 12 is turned on. Become.

Since the high potential V _p towards the V _SS line L _vs than V _DD line L _vd, as shown in Figure 14, the second and first electrode 12sd of the driving transistor 12 from the V _SS line L _vs, 12ds A current flows toward the organic EL element 11 sequentially. At this time, a slight current I _d0 flows from the connection point Cn5 to the connection point Cn6 as indicated by the outlined arrows in the first and second adjustment transistors 15 and 16. However, since the current I _d0 is a very small current, a predetermined amount of electric charge (for example, according to the potential difference between the V _DD line L _vd and the V _SS line L _vs is applied to the organic EL element 11, that is, the element capacitor C _ol. 7) is stored.

○ _Vth compensation period P3:
FIG. 15 illustrates the flow of current in the pixel circuit 7B in the V _th compensation period P3 (hereinafter abbreviated as “period P3” where appropriate).

In the period P3, a predetermined reference potential (here, 0 V) is applied to the V _DD line L _vd and the V _SS line L _vs. Further, the high potential V _gH is applied to all the scanning signal lines L _ss . Further, a high potential V _dH (for example, 10 V) _{is applied} to the image signal line Lis.

At this time, by applying the high potential V _{gH to} the scanning signal line L _ss , a positive potential corresponding to the high potential V _gH is applied to the twelfth electrode (gate) 13 g, and the V _th compensation transistor 13 becomes conductive. Further, in the initial period P3, the potential V _dH granted to charge the image signal line L _IS accumulated in the capacitor 14, the driving transistor 12 becomes conductive.

Therefore, at the beginning of the period P3, as shown in FIG. 15, the current accompanying the electric charge accumulated in the capacitor 14 is supplied from the capacitor 14 to the eleventh and tenth electrodes 13sd and 13ds of the _Vth compensation transistor 13, and further to the drive. It flows toward the V _SS line L _vs through the first and second electrodes 12ds and 12sd of the transistor 12 in sequence. The current caused by the charges accumulated in the element capacitor C _ol is the first and second electrode 12ds of the driving transistor 12, it flows toward the V _SS line L _vs by sequentially through 12SD.

However, as the current accompanying the charge accumulated in the capacitor 14 flows from the capacitor 14 toward the V _SS line L _vs , the charge accumulated in the capacitor 14 decreases. The second potential of the third electrode 12g to the electrode 12SD (gate voltage) V _g of the drive transistor 12 when reduced to substantially the threshold V _th, the driving transistor 12 becomes nonconductive. At this time, the capacitor 14 is in a state where charges according to the threshold value V _th are accumulated. As described above, in the period P3, electric charges corresponding to the threshold value _Vth are accumulated in the capacitor 14, and variations in the threshold value _{Vth that} are different for each pixel are compensated.

○ Writing period P4:
FIG. 16 illustrates the flow of current in the pixel circuit 7B in the writing period P4 (hereinafter abbreviated as “period P4” as appropriate).

In the period P4, the reference potential 0V is applied to the V _DD line L _vd and the V _SS line L _vs , respectively, and scanning is performed in the execution target pixel of the process (data writing process) for accumulating charges according to the pixel signal. A high potential V _gH is applied to the signal line L _ss , and a potential (V _dH −V _data ) _{is applied} to the image signal line Lis. Note that the potential V _data is a potential of the pixel signal, and is a potential corresponding to a value corresponding to the luminance gradation of the pixels constituting the image.

At this time, by applying the high potential V _{gH to} the scanning signal line L _ss , a positive potential corresponding to the high potential V _gH is applied to the twelfth electrode (gate) 13 g, and the V _th compensation transistor 13 becomes conductive. On the other hand, since the potential (V _dH −V _data ) equal to or lower than the potential V _dH in the period P3 _{is applied} to the image signal line L _{is and} the gate voltage V _g of the drive transistor 12 is equal to or lower than the threshold V _th , the drive transistor 12 becomes a non-conduction state.

Therefore, in the period P4, as shown in FIG. 16, the organic EL element 11 (that is, the element capacitor C _ol ) is directed to the capacitor 14 via the tenth and eleventh electrodes 13ds and 13sd of the V _th compensation transistor 13 sequentially. Current flows. As a result, the charge corresponding to the potential V _data is added to the charge corresponding to the threshold value V _th already accumulated in the capacitor 14 and accumulated. That is, in the period P4, electric charges corresponding to the light emission luminance of the organic EL element 11 are accumulated in the capacitor 14. In other words, in the period P4, the charge corresponding to the pixel signal is accumulated in the capacitor 14 in the pixel circuit 7B.

Note that the amount of change in the potential of the one electrode 14a of the capacitor 14 (that is, the gate potential of the driving transistor 12) _is the amount of change in the potential of the image signal line Lis, the holding capacitance C _s of the capacitor 14, and the EL of the element capacitor C _ol . It relies on the product of the ratio of the device capacitance C _o (volume ratio). That is, in the present embodiment, when the potential of the image signal line L _IS changes from V _dH to V _data, the gate potential of the driving transistor 12 _{is, (V data -V dH) ×} C s / (C s + C o )Change. For _{example, V dH = 10V, V data} = 5V, C s: C o = 1: When a 2, the potential of the image signal line L _IS is -5V changes, the gate potential V _g of the drive transistor 12, Due to the movement of charge from the organic EL element 11 to the capacitor 14, (5-10) × 1 / (1 + 2) = − 5 / 3V changes. Thus, the change in the potential of the image signal line Lis _is reflected in the gate potential of the drive transistor 12 due to the movement of the charge accumulated in the capacitor 14.

○ Element initialization period P5:
In the element initialization period P5 (hereinafter abbreviated as “period P5” as appropriate), a predetermined negative potential −V _p is applied to the V _DD line L _vd and the V _SS line L _vs. Further, the low potential V _gL is applied to all the scanning signal lines L _ss . Further, the high potential V _{dH is applied} to the image signal line Lis. At this time, the V _th compensation transistor 13 is turned off, and the drive transistor 12 is turned on. Since there is no potential difference between the V _DD line L _vd and the V _SS line L _vs and the V _SS line L _vs is set to the negative potential −V _p , the organic EL element 11 (that is, the element capacitor C _ol ) The charge accumulated in the organic EL element 11 passes through the V _SS line L _vs and the charge accumulated in the organic EL element 11 is wiped out.

○ Light emission period P6:
FIG. 17 illustrates the flow of current in the pixel circuit 7B in the light emission period P6 (hereinafter abbreviated as “period P6” where appropriate).

In the period P6, the positive high potential V _DD is applied to the V _DD line L _vd . Further, a reference potential of 0 V is applied to the V _SS line L _vs. Further, the low potential V _gL is applied to the scanning signal line L _ss . Further, the high potential V _{dH is applied} to the image signal line Lis.

At this time, the application of the low potential V _{gL to} the scanning signal line L _ss causes the V _th compensation transistor 13 to become non-conductive. Meanwhile, since the high potential V _dH is applied to the image signal line L _IS, the amount of charge stored in the capacitor 14 in the period P4 potential fraction corresponding to (the amount of charge corresponding to the potential V _data), the gate voltage V _g becomes higher than the threshold value V _th , and the driving transistor 2 becomes conductive.

For example, when V _data = 5 V and C _s : C _o = 1: 2, the charge accumulated in the capacitor 14 in the period P4 is 5/3 V lower than the threshold V _th ([V _th -5 / 3] V). Then, in the period P6, V _data (= 5V) content higher potential than the period P4 is applied to the image signal line L _IS, the third electrode (gate) 12 g, 10 / 3V than the threshold value V _th A high potential ([V _th +10/3] V = [V _th − (5/3) +5] V) is applied.

Then, the V _DD line L _vd is higher than the V _SS line L _vs by the potential V _DD , and the driving transistor 12 is in a conductive state in which a current flows between the first and second electrodes according to the potential V _data . For this reason, as shown in FIG. 17, a current corresponding to the potential V _data flows through the organic EL element 11. As a result, the organic EL element 11 emits light with a luminance corresponding to the potential V _data . That is, in the period P6, light having a luminance corresponding to the pixel signal is emitted from each pixel.

As described above, in the image display device 1 </ b> B according to the second embodiment, the first and second adjustment transistors 15 and 16 are provided in parallel with the organic EL element 11. Therefore, when the gate voltage V _g of the drive transistor 12 is 0V, the current flows through the first and second adjusting transistor 15 and 16, no current flows through the organic EL element 11. Therefore, the same effect as the image display device 1A according to the first embodiment can be obtained. Further, the organic EL element 11 can be used as a capacitor by applying a voltage in the opposite direction to the case where a current flows through the organic EL element 11.

Further, the V _th compensation transistor 13 is provided, and the V _th compensation function is realized while the organic EL element 11 is used as a capacitor. Therefore, it is possible to cause the organic EL element 11 to emit light with a desired luminance while compensating for variations in characteristics of the drive transistor 12.

<Others>
The present invention is not limited to the above-described embodiments, and various changes and improvements can be made without departing from the scope of the present invention.

<Modification 1>
In the image display device 1A according to the first embodiment, the adjustment transistor 5 is electrically connected in parallel with the organic EL element 1, but the present invention is not limited to this. For example, instead of the adjustment transistor 5, a resistance member such as a resistor (hereinafter referred to as “current adjustment resistor”) 6 for adjusting a current electrically in parallel with the organic EL element 1 may be connected.

  FIG. 18 is a diagram illustrating a configuration example of a pixel circuit 7C for one pixel constituting the image display device 1C according to the first modification of the present invention. The image display device 1C according to the modified example 1 is similar in configuration to the image display device 1A according to the first embodiment, but the pixel circuit 7A is changed to a pixel circuit 7C having a different configuration. As a result, the display unit 200A is changed to the display unit 200C. Specifically, as shown in FIG. 18, a current adjustment resistor 6 is provided instead of the adjustment transistor 5 of the pixel circuit 7A according to the first embodiment shown in FIG. More specifically, the current adjustment resistor 6 is connected in parallel with the organic EL element 1 between the connection point Cp3 and the connection point Cp4. In FIG. 18, parts similar to those of the image display device 1 </ b> A according to the first embodiment are denoted by the same reference numerals, and redundant description of these parts is omitted.

FIG. 19 is a diagram illustrating characteristics of the current adjustment resistor 6. In FIG. 19, the horizontal axis represents voltage, and the vertical axis represents current. The relationship between the voltage V _r applied across the current adjusting resistor 6 and the current I _r flowing through the current adjusting resistor 6 is indicated by a straight line C _R5 . As shown in FIG. 19, in the current adjustment resistor 6, the voltage applied between one end and the other end and the current flowing between the one end and the other end show a substantially proportional relationship.

FIG. 20 is a diagram illustrating the relationship between the voltage V _od applied between both electrodes of the organic EL element 1 and the current I _od flowing through the organic EL element 1. In FIG. 20, as in FIG. 6, the horizontal axis represents voltage and the vertical axis represents current. The relationship between the voltage V _od and the current I _od is indicated by a thick curve C _od . In FIG. 20, the relationship between the voltage V _od and the current I _od when the adjustment transistor 5 is not electrically connected in parallel to the organic EL element 1 is indicated by a thin curve C _ol . . In FIG. 20, the relationship between the voltage V _od (that is, the voltage V _r ) and the current I _r flowing through the current adjustment resistor 6 is indicated by a broken line C _R5 .

As shown in Figure 20, the current I _r is increased in proportion to the increase in the voltage V _r applied across the current regulation resistor 6. Therefore, when the gate voltage V _g of the driving transistor 2 is 0 V, the current I _d0 flowing between the first and second electrodes of the driving transistor 2 flows through the current adjustment resistor 6 without flowing into the organic EL element 1. . When the gate voltage V _g of the driving transistor 2 is increased, the voltage V _od (that is, the voltage V _r ) gradually increases. When the gate voltage V _g exceeds a predetermined voltage, the voltage V _od exceeds the threshold voltage V _t1, and all of the current flowing between the first and second electrodes of the driving transistor 2 does not flow through the current adjustment resistor 6. The remaining current flows through the organic EL element 1. Specifically, when the gate voltage V _g of the driving transistor 2 is gradually increased from a predetermined voltage, the current I _od increases.

That is, when the voltage V _od applied between the connection point Cp3 and the connection point Cp4 is less than the predetermined threshold voltage V _t1 , current flows through the current adjustment resistor 6, but current does not flow through the organic EL element 1. When the voltage V _od is applied between the connection point Cp3 and the connection point Cp4 exceeds a predetermined threshold voltage V _t1, with current flows I _r the current regulation resistor 6, a current to the organic EL element 1 Flowing. Here again, as in the first embodiment, until the voltage V _od between both electrodes of the organic EL element 1 reaches the threshold voltage V _t1 , the current I _od flowing through the organic EL element 1 is 0 A, and the voltage V _{od Exceeds the} threshold voltage V _t1 , the current I _od increases as the voltage V _od increases.

More specifically, as in the first embodiment, a voltage is applied between the anode electrode 1a and the second electrode 2sd so that the potential of the anode electrode 1a is higher than that of the second electrode 2sd. When the voltage between the anode electrode 1a and the cathode electrode 1b exceeds the threshold voltage _Vt1 in accordance with the change in potential applied to the third electrode 2g, between the first and second electrodes and between the anode electrode 1a and the cathode A current flows between the electrode 1b and the organic EL element 1 emits light. Further, a voltage is applied between the anode electrode 1a and the second electrode 2sd so that the potential of the anode electrode 1a is higher than that of the second electrode 2sd. Is less than or equal to the threshold voltage V _t1 , current flows between the first and second electrodes, but no current flows between the anode electrode 1a and the cathode electrode 1b, and the organic EL element 1 does not emit light. .

As described above, in the image display device 1 _{</ b} > C according to the first modification, when the voltage V _od applied between both electrodes of the organic EL element 1 exceeds the predetermined threshold voltage V _t1 , a current is supplied to the organic EL element 1. Then, the organic EL element 1 emits light. On the other hand, when the voltage V _od applied between both electrodes of the organic EL element 1 is equal to or lower than a predetermined threshold voltage V _t1 , a current flows through the current adjustment resistor 6 and a current flows through the organic EL element 1. Therefore, the organic EL element 1 does not emit light. Therefore, the amplitude of the image signal potential (here, V _data ) for setting the gate voltage V _g of the drive transistor 2 can be suppressed with a simple configuration such as the current adjustment resistor 6.

  Therefore, in the “resistive member” of the present invention, when the voltage applied between both electrodes of the organic EL element exceeds a predetermined threshold voltage, a current flows through both the resistive member and the organic EL element. Then, the organic EL element is caused to emit light due to the current flowing through the organic EL element. Furthermore, when the voltage applied between both electrodes of the organic EL element is equal to or lower than a predetermined threshold voltage, the resistance member flows only through the resistance member and does not flow through the organic EL element. The EL element does not emit light.

  In the first modification, one current adjustment resistor 6 is provided, but two or more current adjustment resistors 6 may be provided. That is, a resistance member such as at least one current adjustment resistor 6 that is electrically connected in parallel to the organic EL element 1 and electrically connected in series to the driving transistor 2 may be provided.

<Modification 2>
In the second embodiment, the pixel circuit 7B in which the two adjustment transistors 15 and 16 are applied to the pixel circuit including the two transistors 12 and 13 has been described as an example. However, the present invention is not limited thereto, and pixel circuits having different configurations are used. Two adjustment transistors may be applied. Hereinafter, a specific example will be described.

FIG. 21 is a diagram illustrating a configuration example of a pixel circuit 7D for one pixel constituting the image display device 1D according to the second modification of the present invention. The image display device 1D according to the modified example 2 is similar in configuration to the image display device 1B according to the second embodiment, but the pixel circuit 7B is changed to a pixel circuit 7D having a different configuration. Thus, the display unit 200B is changed to the display unit 200D. Specifically, the pixel circuit 7D shown in FIG. 21 includes an organic EL element 21, a drive transistor 22, a V _th compensation transistor 23, a first capacitor 24, a second capacitor 28, a first adjustment transistor 25, and a second adjustment transistor. 26 and a scanning transistor 27.

The organic EL element 21 emits light when a potential difference exceeding the threshold voltage of the organic EL element 21 is generated between the anode electrode 21a and the cathode electrode 21b, and a current flows between the anode electrode 21a and the cathode electrode 21b. Have The anode electrode 21 a is electrically connected to the V _DD line L _vd to which a positive high potential (for example, +10 V or the like) is applied when the organic EL element 21 emits light.

  The anode electrode 21a is electrically connected to the seventh and ninth electrodes 26ds, 26g of the second adjustment transistor 26 via the connection points Ct1, Ct6 in order. In the second modification, the anode electrode 21a corresponds to the “one end” of the present invention.

The cathode electrode 21 b is grounded via the drive transistor 22. The cathode electrode 21b is electrically connected to the tenth electrode 23ds of the V _th compensation transistor 23 via the connection point Ct2. Further, the cathode electrode 21b is electrically connected to the fifth and sixth electrodes 25sd and 25g of the first adjustment transistor 25 through the connection points Ct2 and Ct5 sequentially. In the second modification, the cathode electrode 21b corresponds to the “other end” of the present invention. Further, the organic EL element 21, the voltage of the light emitting time of the reverse is applied to function as a capacitor, to the capacitance (EL element capacitor) C _ol2 a predetermined value C _2.

  The drive transistor 22 is a transistor that is electrically connected in series to the organic EL element 21 and controls the light emission luminance of the organic EL element 21 by adjusting the amount of current in the organic EL element 21. Here, the drive transistor 22 is configured by an n-MISFET TFT. The drive transistor 22 includes first to third electrodes 22ds, 22sd, and 22g.

The first electrode 22ds is electrically connected to the cathode electrode 21b of the organic EL element 21 and the tenth electrode 23ds of the _Vth compensation transistor 23 via the connection point Ct2. The first electrode 22ds is electrically connected to the fifth and sixth electrodes 25sd and 25g of the first adjustment transistor 25 via the connection points Ct2 and Ct5 sequentially. Further, the first electrode 2ds functions as a drain when the organic EL element 21 emits light, that is, when a forward current flows through the organic EL element 21. On the other hand, when a voltage is applied in the reverse direction to the organic EL element 21, the first electrode 22ds functions as a source.

The second electrode 22sd is electrically connected wires for grounding via the node Ct7 to the other electrode 28b of the (grounding wire) G _d and the second capacitor 28, forward with respect to the organic EL element 21 It functions as a source when a directional current flows. On the other hand, when a voltage is applied in the reverse direction to the organic EL element 21, the second electrode 22sd functions as a drain. Furthermore, the third electrode 22g is a gate, and is electrically connected to the eleventh electrode 23sd of the _Vth compensation transistor 23 and the one electrode 24a of the first capacitor 24 via the connection point Ct3.

  In the driving transistor 22, the potential applied to the third electrode 22g, more specifically, applied between the first electrode 22ds or the second electrode 22sd and the third electrode 22g (that is, between the gate and the source). By adjusting the voltage value, the amount of current (current amount) flowing between the first electrode 22ds and the second electrode 22sd (between the first and second electrodes) is adjusted. Then, the potential applied to the third electrode (gate) 22g causes the drive transistor 22 to have a state in which a current can flow between the first and second electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

Each of the first and second adjustment transistors 25 and 26 is composed of an n-MISFET TFT similarly to the drive transistor 22, has substantially the same performance, and is electrically connected in series. In addition, a portion formed by connecting the first and second adjustment transistors 25 and 26 in series is electrically connected to the organic EL element 21 between the V _DD line L _vd and the ground wiring G _d. They are connected in parallel and electrically connected to the drive transistor 22 in series.

Specifically, the first adjustment transistor 25 includes fourth to sixth electrodes 25ds, 25sd, and 25g. The fourth electrode 25ds is electrically connected to the eighth electrode 26sd of the second adjustment transistor 26. The fifth and sixth electrodes 25 sd and 25 g are connected to the cathode electrodes 21 b of the organic EL element 21, the first electrode 22 ds of the driving transistor 22, and the tenth electrode of the V _th compensating transistor 23 through the connection points Ct 5 and Ct 2 in sequence. 23 ds is electrically connected to each other. Further, the fifth electrode 25sd is electrically connected to the sixth electrode 25g which is a gate through the connection point Ct5.

  In the first adjustment transistor 25, the potential applied to the sixth electrode 25g, more specifically, between the fourth electrode 25ds or the fifth electrode 25sd and the sixth electrode 25g (that is, between the gate and the source). By adjusting the voltage value to be applied, the amount of current (current amount) flowing between the fourth electrode 25ds and the fifth electrode 25sd (between the fourth and fifth electrodes) is adjusted. The first adjustment transistor 25 is in a state in which current can flow between the fourth and fifth electrodes (that is, between the drain and the source) due to the potential applied to the sixth electrode (gate) 25g (conductive state). , A state in which current cannot flow (non-conduction state) is selectively set.

The second adjustment transistor 26 includes seventh to ninth electrodes 26ds, 26sd, and 26g. The seventh and ninth electrodes 26ds, 26g are electrically connected to the V _DD line L _vd and the anode electrode 21a through the connection points Ct6, Ct1, respectively. The seventh electrode 26ds is electrically connected to the ninth electrode 26g via the connection point Ct6. The eighth electrode 26 sd is electrically connected to the fourth electrode 25 ds of the first adjustment transistor 25.

  In the second adjustment transistor 26, the potential applied to the ninth electrode 26g, more specifically, between the seventh electrode 26ds or the eighth electrode 26sd and the ninth electrode 26g (that is, between the gate and the source). By adjusting the applied voltage value, the amount of current (current amount) flowing between the seventh electrode 26ds and the eighth electrode 26sd (between the seventh and eighth electrodes) is adjusted. Then, due to the potential applied to the ninth electrode (gate) 26g, the second adjustment transistor 26 has a state (conduction state) in which a current can flow between the seventh and eighth electrodes (that is, between the drain and the source). , A state in which current cannot flow (non-conduction state) is selectively set.

The V _th compensation transistor 23 detects the lower limit (predetermined threshold voltage V _th ) of the potential of the third electrode 22g with respect to the second electrode 22sd of the drive transistor 22 when the drive transistor 22 is energized. This is a transistor for adjusting the gate voltage of the drive transistor 22 to the threshold voltage V _th (threshold V _th ). Specifically, the V _th compensation transistor 23 has a V _th compensation function that compensates for variations in the threshold V _th in the drive transistor 22 by matching the gate voltage of the drive transistor 22 to the threshold V _th for each pixel before light emission. Realize. Here, the V _th compensation transistor 23 is also composed of an n-MISFET TFT, like the drive transistor 22.

The V _th compensation transistor 23 has tenth to twelfth electrodes 23ds, 23sd, and 23g. The tenth electrode 23ds is electrically connected to the cathode electrode 21b of the organic EL element 21 and the first electrode 22ds of the drive transistor 22 via the connection point Ct2. Further, the tenth electrode 23ds is electrically connected to the fifth and sixth electrodes 25sd and 25g of the first adjustment transistor 25 via the connection points Ct2 and Ct5 in sequence. The eleventh electrode 23sd is electrically connected to the third electrode 22g of the drive transistor 22 and the one electrode 24a of the first capacitor 24 via the connection point Ct3. Further, a twelfth electrode 23g is electrically connected to the compensation control line L _th.

In the V _th compensation transistor 23, the potential applied to the twelfth electrode 23g, more specifically, between the tenth electrode 23ds or the eleventh electrode 23sd and the twelfth electrode 23g (that is, between the gate and the source). By adjusting the voltage value applied to, the amount of current (current amount) flowing between the tenth electrode 23ds and the eleventh electrode 23sd (between the tenth and eleventh electrodes) is adjusted. Then, due to the potential applied to the twelfth electrode (gate) 23g, the V _th compensation transistor 23 can flow a current between the tenth and eleventh electrodes (that is, between the drain and the source) (conductive state). And a state where current cannot flow (non-conducting state) is selectively set.

The first capacitor 24 includes one electrode 24a and the other electrode 24b. The one electrode 24a is electrically connected to the third electrode 22g of the drive transistor 22 and the eleventh electrode 23sd of the _Vth compensation transistor 23 via the connection point Ct3. The other electrode 24b is electrically connected to one electrode 28a of the second capacitor 28 and the thirteenth electrode 27ds of the scanning transistor 27 via the connection point Ct4. Here, the holding capacity of the first capacitor 24 is set to a predetermined value C _s1 .

The second capacitor 28 includes one electrode 28a and the other electrode 28b. The one electrode 28a is electrically connected to the other electrode 24b of the first capacitor 24 and the thirteenth electrode 27ds of the scanning transistor 27 via the connection point Ct4. The other electrode 28b is electrically connected to the second electrode 22sd and grounding wire G _d of the driving transistor 22 through the connection point Ct7. Here, the holding capacity of the second capacitor 28 is set to a predetermined value _Cs2 .

The scanning transistor 27 has thirteenth to fifteenth electrodes 27ds, 27sd, and 27g. The thirteenth electrode 27ds is electrically connected to the other electrode 24b of the first capacitor 24 and the one electrode 28a of the second capacitor 28 via the connection point Ct4. In addition, the 14 electrodes 27sd are electrically connected to the image signal line L _IS. Further, the fifteenth electrode 27g is electrically connected to the scanning signal line L _ss .

  In the scanning transistor 27, the potential applied to the fifteenth electrode 27g, more specifically, applied between the thirteenth electrode 27ds or the fourteenth electrode 27sd and the fifteenth electrode 27g (that is, between the gate and the source). By adjusting the voltage value to be adjusted, the amount of current (current amount) flowing between the thirteenth electrode 27ds and the fourteenth electrode 27sd (between the thirteenth and fourteenth electrodes) is adjusted. Then, due to the potential applied to the fifteenth electrode (gate) 27g, the scanning transistor 27 has a state (conduction state) in which a current can flow between the thirteenth and fourteenth electrodes (that is, between the drain and the source), It is selectively set to a state where current cannot flow (non-conducting state).

The V _DD line L _vd supplies a predetermined voltage to the drive transistor 22. The compensation control line L _th supplies a signal for switching the V _th compensation transistor 23 between a conductive state and a non-conductive state. The scanning signal line L _ss supplies a signal for switching the scanning transistor 27 between a conductive state and a non-conductive state. Image signal line L _IS supplies a voltage of the pixel signal to the first capacitor 24. In FIG. 21, as a configuration for supplying a predetermined voltage to the organic EL element 21, the organic EL element 21 is arranged between the high potential V _DD line L _vd and the low potential ground wiring G _d. While being so, the low potential side to the V _DD line L _vd, or at a fixed potential as grounding wire G _d the high potential side, or may be or driving them.

  Next, driving of the pixel circuit 7D of the image display device 1D according to the modification 2 will be described.

FIG. 22 is a timing chart showing signal waveforms (drive waveforms) when the organic EL element 21 emits light. In FIG. 22, the horizontal axis indicates time, and in order from the top, (a) the potential applied to the V _DD line L _vd (potential V _dd ), (b) the potential applied to the compensation control line L _th (potential V _tt), (c) the potential of the signal applied to the scanning signal line L _ss (potential V _sl), (d) the potential of the image signal line signal applied to L _iS (potential V _lis), the waveform shown ing.

Further, FIG. 22 shows a drive waveform for causing the organic EL element 21 to emit light once, and the period related to one light emission is a preparation period Pt1 (time t21 to t22), V _{th in} time sequence. A compensation period Pt2 (time t22 to t23), an initialization period Pt3 (time t23 to t24), a writing period Pt4 (time t24 to t25), and a light emission period Pt5 (time t25) are configured. Since the potential V _lis in the writing period Pt4 is an arbitrary value determined by the light emission luminance of each organic EL element 21, in FIG. 22, hatched hatching is added for convenience in the range where the potential can exist. Yes.

  FIG. 23 to FIG. 27 are diagrams illustrating the flow of current of the pixel circuit 7D generated in each period when the image display device 1D according to the modification 2 is driven, with black arrows. In FIG. 23 to FIG. 27, among the pixel circuits 7D, circuits that contribute to the current flow are indicated by thick lines, and circuits that hardly contribute to the current flow are indicated by thin lines.

  Hereinafter, a driving method of the image display device 1D according to the modification 2 will be described with reference to FIGS. 22 and 23 to 27 as appropriate.

○ Preparation period Pt1:
In the preparation period Pt1, the potential V _dd of the V _DD line L _vd is low (−V _p ), the potential V _tt of the compensation control line L _th is low (V _gL ), and the potential V _sl of the scanning signal line L _ss is a high potential (V _gH), the potential V _lis image signal line L _iS is set to a high potential (e.g., the maximum potential V _dH of the pixel signals such as 10V or 15V). At this time, the scanning transistor 27 is turned on, the _Vth compensation transistor 23 is turned off, and the drive transistor 22 is turned on. Here, as indicated by the white arrows in the first and second adjustment transistors 25 and 26, a slight current I _d0 flows from the connection point Ct5 to the connection point Ct6. However, this current I _d0 is a very small current. Therefore, as shown in FIG. 23, a current flows from the ground wiring G _d to the organic EL element capacitance C _ol2 via the drive transistor 22, and charges are accumulated in the EL element capacitance C _ol2 of the organic EL element 21. The

○ _Vth compensation period Pt2:
In the V _th compensation period Pt2, the potential V _tt of the compensation control line L _th is set to the high potential (V _gH ), and the V _DD line L _vd is set to the reference potential (here, slightly delayed from the timing when the potential V _tt becomes high potential). 0V). On the other hand, the potential V _sl of the scanning signal line L _ss is maintained at a high potential (V _gH ). Note that the potential V _lis of the image signal line Lis _{is set} to the reference potential (here, 0 V) immediately before the transition to the _Vth compensation period Pt2, and the potential V _lis is maintained at the reference potential. At this time, the V _th compensation transistor 23 becomes conductive, and the gate and drain of the drive transistor 22 are connected. As a result, as shown in FIG. 24, the charges accumulated in the EL element capacitance _Col2 and the first capacitor 24 are discharged until the gate potential with respect to the source of the drive transistor 22 reaches the threshold voltage V _th , via a current flows through a path of the grounding wire G _d. When the potential difference between the gate and source of the drive transistor 22 reaches the threshold voltage _Vth of the drive transistor 22, the drive transistor 22 is turned off. At this time, the threshold voltage V _th is generated at both extremes of the first capacitor 24.

○ Initialization period Pt3:
In the initialization period Pt3, the potential V _dd of the V _DD line L _vd is maintained at the reference potential (here, 0 V), and the potential V _sl of the scanning signal line L _ss is maintained at the high potential (V _gH ). On the other hand, the potential V _tt of the compensation control line L _th is set to a low potential (V _gL ). Further, the potential V _lis of the image signal line Lis _is set to, for example, the maximum potential (V _dH ) of the pixel signal. At this time, the drive transistor 22 becomes conductive again. As a result, as shown in Figure 25, current flows through a path of the grounding wire G _d through the driving transistor 22 from the organic EL element 21, the charge remaining in the EL element capacitance C _ol2 is discharged. By this operation, the influence on the light emission due to the residual charge in the organic EL element 21 itself is avoided.

In the initialization period Pt3, as shown in FIG. 22, the potential V _lis of the image signal line Lis _is set from the maximum potential (V _dH ) to the reference potential (here, 0 V) during the initialization period Pt3. Is done. The scanning signal line L _ss is set from the high potential (V _gH ) to the low potential (V _gL ) after a lapse of a predetermined time after the image signal line Lis _{is set} to the reference potential (here, 0 V).

○ Writing period Pt4:
In the writing period Pt4, the potential V _dd of the V _DD line L _vd is maintained at the reference potential (here, 0 V), and the potential V _tt of the compensation control line L _th is maintained at the low potential (V _gL ). On the other hand, it is supplied pixel signal to the image signal line L _IS, potential V _lis is set to (a predetermined level of potential corresponding to the pixel signal) V _data potential of the pixel signal. Then, the scanning signal is supplied to the scanning signal line L _ss while the potential V _lis is maintained at the potential V _data , and the potential V _sl is set to the high potential V _gH . At this time, the scanning transistor 27 becomes conductive, as shown in Figure 26, current flows through the second capacitor 28 through the scanning transistor 27 from the image signal line L _IS, the pixel signal to the second capacitor 28 The corresponding voltage is held. In the second modification, pixel signals are not written to all the pixel circuits at once, and the pixel signals are sequentially written for each of a plurality of pixel circuits (pixel circuit group) connected in common to each scanning signal line L _ss . Writing is performed.

○ Light emission period Pt5:
In the light emission period Pt5, the potential V _dd of the V _DD line L _vd is set to the high potential V _DD and the potential V _lis of the image signal line Lis _is set to the reference potential (here, 0 V). On the other hand, the potential V _tt compensation control line L _th is a low potential (V _gL), the potential V _sl of the scanning signal line L _ss is maintained at a low potential (V _gL). At this time, the first capacitor 24 that holds the threshold voltage V _th of the drive transistor 22 and the second capacitor 28 that holds the voltage corresponding to the pixel signal are connected in series, and the sum of the voltages of both is the gate of the drive transistor 22. And between the source and the source. As a result, as shown in FIG. 27, the drive transistor 22 becomes conductive, and a current flows from the V _DD line L _vd to the ground wiring G _d through the organic EL element 21 and the drive transistor 22 sequentially. The organic EL element 21 emits light.

In the image display device 1D according to the modified example 2, the first and second adjustment transistors 25 and 26 are provided in electrical parallel with the organic EL element 21 as in the image display device 1B according to the second embodiment. It has been. Therefore, when the gate voltage V _g of the driving transistor 22 of 0V is current flows through the first and second adjusting transistor 25 and 26, no current flows through the organic EL element 21. Therefore, the image display device 1D according to the second modification can obtain the same effects as those of the image display device 1B according to the second embodiment. Further, the organic EL element 21 can be used as a capacitor by applying a voltage in the opposite direction to the case where a current flows through the organic EL element 21. Further, the V _th compensation transistor 23 is provided, and the V _th compensation function is realized while the organic EL element 21 is used as a capacitor. Therefore, it is possible to cause the organic EL element 21 to emit light with a desired luminance while compensating for variations in the characteristics of the drive transistor 22.

<Modification 3>
In the first embodiment, the organic EL element 1 and the drive transistor 2 are electrically connected in series in this order from the power supply portion P _vd side, which becomes the high potential side during light emission, to the ground wiring G _d . However, it is not limited to this. For example, the drive transistor and the organic EL element may be electrically connected in series in this order from the power supply portion P _vd side, which becomes the high potential side during light emission, toward the ground wiring G _d . Hereinafter, a specific example of such a configuration will be described.

  FIG. 28 is a diagram illustrating a configuration example of a pixel circuit 7E for one pixel constituting the image display device 1E according to the third modification of the present invention. The image display device 1E according to the modified example 3 has the same general configuration as the image display device 1A according to the first embodiment, but the pixel circuit 7A is changed to a pixel circuit 7E having a different configuration. Thus, the display unit 200A is changed to the display unit 200E. Specifically, the pixel circuit 7E illustrated in FIG. 28 includes an organic EL element 31, a driving transistor 32, a scanning transistor 33, a capacitor 34, and an adjustment transistor 35.

The organic EL element 31 has a configuration similar to that of the organic EL element 1 and is a light emitting element in which the light emission luminance varies depending on the amount of current (current amount) flowing through the light emitting layer from the anode electrode 31a toward the cathode electrode 31b. The anode electrode 31a is electrically connected to the third electrode 32sd of the drive transistor 32 and the other electrode 34b of the capacitor 34 through the connection points Cp33 and Cp32 sequentially. The anode 31a is electrically connected to the fourth electrode 35ds of the adjustment transistor 35 via the connection point Cp33. The cathode electrode 31b is electrically connected to the grounding wire G _d via the node CP34. The cathode electrode 31b is electrically connected to the fifth and sixth electrodes 35sd and 35g of the adjustment transistor 35 via the connection points Cp34 and Cp35 in sequence. In the third modification, the anode electrode 31a corresponds to “one end portion” of the present invention, and the cathode electrode 31b corresponds to “other end portion” of the present invention.

  The drive transistor 32 is a transistor that is electrically connected in series to the organic EL element 31 and controls the light emission luminance of the organic EL element 31 by adjusting the amount of current in the organic EL element 31. Here, the drive transistor 32 is configured by an n-MISFET TFT. The drive transistor 32 includes first to third electrodes 32ds, 32sd, and 32g.

The first electrode 32ds is electrically connected to a power feeding unit P _vd to which a positive high potential (for example, + 10V or the like) is applied when the organic EL element 31 emits light. The first electrode 32 ds functions as a drain when the organic EL element 31 emits light, that is, when a forward current flows through the organic EL element 31. On the other hand, when a voltage is applied in the reverse direction to the organic EL element 31, the first electrode 32ds functions as a source.

  The second electrode 32sd is electrically connected to the anode electrode 31a and the fourth electrode 35ds of the adjustment transistor 35 via the connection points Cp32 and Cp33 in sequence. The second electrode 32sd is electrically connected to the other electrode 34b of the capacitor 34 via the connection point Cp32. The second electrode 32 sd functions as a source when the organic EL element 31 emits light, that is, when a forward current flows through the organic EL element 31. On the other hand, when a voltage is applied in the reverse direction to the organic EL element 31, the second electrode 32sd functions as a drain.

  The third electrode 32g is a so-called gate, and is electrically connected to the seventh electrode 33sd of the scanning transistor 33 and the one electrode 34a of the capacitor 34 via the connection point Cp31.

  In the driving transistor 32, the potential applied to the third electrode 32g, more specifically, applied between the first electrode 32ds or the second electrode 32sd and the third electrode 32g (that is, between the gate and the source). By adjusting the voltage value to be adjusted, the amount of current (current amount) flowing between the first electrode 32ds and the second electrode 32sd (between the first and second electrodes) is adjusted. In addition, the potential applied to the third electrode (gate) 32g causes the driving transistor 32 to have a state in which a current can flow between the first and second electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

The adjustment transistor 35 has substantially the same performance as that of the drive transistor 32, and is electrically connected in parallel to the organic EL element 31 between the power feeding unit P _vd and the ground wiring G _d , and the drive transistor 32 is electrically connected in series. The adjustment transistor 35 includes fourth to sixth electrodes 35ds, 35sd, and 35g. The fourth electrode 35ds is electrically connected to the anode electrode 31a of the organic EL element 31 through the connection point Cp33. The fourth electrode 35ds is electrically connected to the third electrode 32sd and the other electrode 34b through the connection points Cp33 and Cp32 sequentially. The fifth electrode 35sd is electrically connected to the cathode electrode 31b and the grounding wire G _d are sequentially via the node Cp35, Cp34. Furthermore, the fifth electrode 35 sd is electrically connected to the sixth electrode 35 g which is a so-called gate through the connection point Cp 35.

  In the adjustment transistor 35, the potential applied to the sixth electrode 35g, more specifically, applied between the fourth electrode 35ds or the fifth electrode 35sd and the sixth electrode 35g (that is, between the gate and the source). By adjusting the voltage value, the amount of current flowing (current amount) between the fourth electrode 35ds and the fifth electrode 35sd (between the fourth and fifth electrodes) is adjusted. Then, due to the potential applied to the sixth electrode (gate) 35g, the adjustment transistor 35 has a state in which a current can flow between the fourth and fifth electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state). In the third modification, the adjustment transistor 35 corresponds to the “resistive member” of the present invention.

The scanning transistor 33 is a transistor that controls the timing at which the potential of the image signal line Lis _is applied to the third electrode (gate) 32 g of the driving transistor 32. Here, the scanning transistor 33 is also composed of an n-MISFET TFT, like the driving transistor 32.

The scanning transistor 33 has seventh to ninth electrodes 33ds, 33sd, and 33g. Then, the seventh electrode 33ds is electrically connected to the image signal line L _IS. The eighth electrode 33 sd is electrically connected to the third electrode (gate) 32 g of the drive transistor 32 and the one electrode 34 a of the capacitor 34 via the connection point Cp 31. Further, the ninth electrode 33g functions as a so-called gate and is electrically connected to the scanning signal line L _ss .

  In the scanning transistor 33, the potential applied to the ninth electrode 33g, more specifically, between the seventh electrode 33ds or the eighth electrode 33sd and the ninth electrode 33g (that is, between the gate and the source). By adjusting the voltage value to be applied, the amount of current between the seventh electrode 33ds and the eighth electrode 33sd (between the seventh and eighth electrodes) is adjusted. Then, due to the potential applied to the ninth electrode (gate) 33g, the scanning transistor 33 has a state in which a current can flow between the seventh and eighth electrodes (between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

  The capacitor 34 has one and other electrodes 34a and 34b. The one electrode 34 a is electrically connected to the third electrode 32 g of the driving transistor 32 and the eighth electrode 33 sd of the scanning transistor 33 via the connection point Cp 31. The other electrode 34b is electrically connected to the second electrode 32sd of the drive transistor 32 via the connection point Cp32. The other electrode 34b is electrically connected to the anode electrode 31a and the fourth electrode 35ds via the connection points Cp32 and Cp33 sequentially.

  Here, the description has been given focusing on one pixel circuit 7E, but there are many pixel circuits 7E in the entire organic EL display AA. Further, the signal waveform (driving waveform) when the organic EL element 31 emits light is the same as that of the image display device 1A according to the first embodiment.

In the pixel circuit 7E according to the third modification, a voltage is applied between the first electrode 32ds and the cathode electrode 31b so that the potential of the first electrode 32ds is higher than that of the cathode electrode 31b. When the voltage between the anode electrode 31a and the cathode electrode 31b exceeds the threshold voltage V _t1 according to the change in potential applied to the third electrode 32g, the voltage between the first and second electrodes and between the anode electrode 31a and the cathode A current flows between the electrode 31b and the organic EL element 31 emits light. In addition, when the voltage between the anode electrode 31a and the cathode electrode 31b is equal to or lower than the threshold voltage _Vt1 , a current flows between the first and second electrodes, while between the anode electrode 31a and the cathode electrode 31b. No current flows and the organic EL element 31 does not emit light.

As described above, in the image display device 1E according to the modification 3, the voltage applied between both electrodes of the organic EL element 31 is the predetermined threshold voltage V _t1 , as in the image display device 1A according to the first embodiment. When the current exceeds the value, a current flows through the organic EL element 31, and the organic EL element 31 emits light. On the other hand, when the voltage applied between both electrodes of the organic EL element 31 is equal to or lower than the predetermined threshold voltage V _t1 , a current flows through the adjustment transistor 35, and no current flows through the organic EL element 31. The organic EL element 31 does not emit light. For this reason, the fluctuation width of the potential (here, V _data ) of the image signal for setting the gate voltage V _g of the drive transistor 32 can be suppressed.

<Other variations>
For example, in the above embodiment, the configuration in which the organic EL elements 1, 11, 21, and 31 are used as the light emitting elements has been described, but the present invention is not limited thereto. The light emitting element may be another light emitting element such as a light emitting diode (LED) made of an inorganic material.

  In the first embodiment and the third modification, the adjustment transistors 5 and 35 are provided in parallel with the organic EL elements 1 and 31, but the present invention is not limited to this. For example, for the organic EL elements 1 and 31, two or more adjustment transistors in which a source electrode and a gate are electrically connected at the time of light emission may be provided in parallel.

  In the second embodiment and the second modification, the portion where the first and second adjustment transistors 15, 16, 25 and 26 are electrically connected in series is electrically connected to the organic EL elements 11 and 21. However, the present invention is not limited to this. One or more first adjustment transistors in which a source electrode and a gate are electrically connected during light emission, and one or more second adjustment transistors in which a drain electrode and a gate are electrically connected during light emission The part electrically connected in series should just be provided in parallel with respect to the organic EL elements 11 and 21. FIG.

  In addition, about the structure described in the said 1st and 2nd embodiment and the modifications 1-3, you may combine suitably in the range which does not contradict.

It is a figure which illustrates schematic structure of the image display apparatus which concerns on embodiment of this invention. It is a block diagram which shows schematic structure of the display part which concerns on embodiment of this invention. It is a figure which shows the structural example of the pixel circuit for 1 pixel which concerns on 1st Embodiment of this invention. It is a timing chart which shows the drive waveform of the display part concerning a 1st embodiment. It is a figure which shows the characteristic of an adjustment transistor typically. It is a figure which shows the relationship between the gate voltage of a drive transistor, and the electric current of an organic EL element. It is a figure which shows typically the relationship between the voltage applied between the both ends of an organic EL element, and the electric current which flows through an organic EL element. It is a figure which shows the structural example of the pixel circuit for 1 pixel which concerns on 2nd Embodiment of this invention. It is a figure which shows typically the parasitic capacitance which generate | occur | produces in a pixel circuit. It is a figure which shows typically the characteristic of a 1st and 2nd adjustment transistor. It is a figure which shows typically the relationship between the voltage and electric current which concern on a 1st and 2nd adjustment transistor. It is a timing chart which shows the drive waveform of the display part concerning a 2nd embodiment. It is a diagram illustrating the flow of current in the pixel circuit in the C _s initialization period. It is a figure which illustrates the flow of the electric current in the pixel circuit in a preparation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in a _Vth compensation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the writing period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the light emission period. It is a figure which shows the structural example of the pixel circuit for 1 pixel which concerns on the modification 1 of this invention. It is a figure which shows the characteristic of an electric current adjustment resistance. It is a figure which shows typically the relationship between the voltage applied between the both ends of an organic EL element, and the electric current which flows through an organic EL element. It is a figure which shows the structural example of the pixel circuit for 1 pixel which concerns on the modification 2 of this invention. 10 is a timing chart showing drive waveforms of a display unit according to Modification 2. It is a figure which illustrates the flow of the electric current in the pixel circuit in a preparation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in a _Vth compensation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in an initialization period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the writing period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the light emission period. It is a figure which shows the structural example of the pixel circuit for 1 pixel which concerns on the modification 3 of this invention. It is a figure which shows the characteristic of a-SiTFT typically.

Explanation of symbols

1,11,21,31 Organic EL element 1a, 11a, 21a, 31a Anode electrode 1b, 11b, 21b, 31b Cathode electrode 1A-1E Image display device 2, 12, 22, 32 Drive transistor 5,35 Adjustment transistor 6 Current Adjustment resistor 15, 25 First adjustment transistor 16, 26 Second adjustment transistor

Claims (4)

A light emitting element that emits light when current flows from one end to the other end;
A first electrode, a second electrode, and a third electrode, the first electrode being electrically connected to the other end, and a current flowing between the first electrode and the second electrode A driving transistor that adjusts according to a potential applied to the third electrode;
A resistance member electrically connected in parallel to the light emitting element;
With
In response to a change in the potential applied to the third electrode in a state where a voltage is applied between the one end and the second electrode so that the potential at the one end is higher, the one end When the voltage between the one end and the other end exceeds a threshold voltage of the light emitting element, a current flows between the one end and the other end, the light emitting element emits light, and the one end and the one end When the voltage between the other end is equal to or lower than the threshold voltage of the light emitting element, current flows through the resistance member, no current flows between the one end and the other end, and the light emitting element Does not fire,
The resistance member includes fourth, fifth, and sixth electrodes, and a first adjustment that adjusts a current flowing between the fourth electrode and the fifth electrode by a potential applied to the sixth electrode. A second adjustment transistor having a transistor and seventh, eighth, and ninth electrodes, and adjusting a current flowing between the seventh electrode and the eighth electrode by a potential applied to the ninth electrode; Including
The fourth electrode is electrically connected to the eighth electrode;
The fifth electrode is electrically connected to the other end and the sixth electrode;
The seventh electrode is electrically connected to the one end and the ninth electrode;
A compensation transistor having tenth, eleventh, and twelfth electrodes, and adjusting a current flowing between the tenth electrode and the eleventh electrode by a potential applied to the twelfth electrode;
Further comprising
The tenth electrode is electrically connected to the first electrode;
The image display device , wherein the eleventh electrode is electrically connected to the third electrode . The image display device according to claim 1 ,
An image display, wherein the resistance member includes a resistance element in which a voltage applied between one end and the other end and a current flowing between the one end and the other end have a substantially proportional relationship. apparatus. A light emitting element that emits light when current flows from one end to the other end;
A first electrode, a second electrode, and a third electrode, the second electrode being electrically connected to the one end, and a current flowing between the first electrode and the second electrode, A drive transistor that adjusts according to a potential applied to the third electrode;
A resistance member electrically connected in parallel to the light emitting element;
With
In a state where a voltage is applied between the first electrode and the other end so that the potential of the first electrode is higher, according to a change in potential applied to the third electrode, When the voltage between the one end and the other end exceeds the threshold voltage of the light emitting element, a current flows between the one end and the other end so that the light emitting element emits light, and the one end When the voltage between the one end and the other end is equal to or lower than the threshold voltage of the light emitting element, a current flows through the resistance member, and no current flows between the one end and the other end. The element does not emit light ,
The resistance member includes fourth, fifth, and sixth electrodes, and a first adjustment that adjusts a current flowing between the fourth electrode and the fifth electrode by a potential applied to the sixth electrode. A second adjustment transistor having a transistor and seventh, eighth, and ninth electrodes, and adjusting a current flowing between the seventh electrode and the eighth electrode by a potential applied to the ninth electrode; Including
The fourth electrode is electrically connected to the eighth electrode;
The fifth electrode is electrically connected to the other end and the sixth electrode;
The seventh electrode is electrically connected to the one end and the ninth electrode;
A compensation transistor having tenth, eleventh, and twelfth electrodes, and adjusting a current flowing between the tenth electrode and the eleventh electrode by a potential applied to the twelfth electrode;
Further comprising
The tenth electrode is electrically connected to the first electrode;
The image display device , wherein the eleventh electrode is electrically connected to the third electrode . The image display device according to claim 3 ,
An image display, wherein the resistance member includes a resistance element in which a voltage applied between one end and the other end and a current flowing between the one end and the other end have a substantially proportional relationship. apparatus.

Images