CN100481180C - Image display device and driving method thereof - Google Patents

Abstract

An image display device is provided with a light emitting element; a driving transistor wherein a gate electrode, a source electrode and a drain electrode are provided and one edge of the light emitting element is electrically connected with one of the electrodes of the source electrode and the drain electrode; a first switching transistor, which short-circuits the gate electrode of the driving transistor and the one electrode of the driving transistor in response to a scanning signal; a capacitor element wherein a first electrode and a second electrode are provided and the gate electrode of the driving transistor is connected with the first electrode; a signal line connected with the second electrode of the capacitor element; a signal line driving circuit, which supplies the signal line with a brightness potential and a reference potential indicating a standard of the brightness potential; and a power source supplying circuit, which controls a potential of the other electrode of the source electrode and the drain electrode of the driving transistor.

Description

Image display device and driving method thereof

technical field

[0001]

The present invention relates to an image display device, in particular to an image display device capable of improving contrast.

Background technique

[0002]

In the prior art, the scheme of an image display device using an organic EL (Electonic Luminescent) element having the function of generating light by combining holes injected into the light-emitting layer and electrons to emit light has long been available.

[0003]

This image display device includes, for example: a plurality of pixel circuits arranged in rows and columns; a signal line drive circuit for supplying a luminance signal described later to the plurality of pixel circuits through a plurality of signal lines; A scanning line driver circuit that supplies a scanning signal of a pixel circuit of a luminance signal to a pixel circuit through a plurality of scanning lines.

[0004]

In addition, the above-mentioned pixel circuit (one pixel unit) has: the above-mentioned organic EL element having the function of injecting current to emit light—a light-emitting element; a driver element for controlling the current flowing into the light-emitting element; two or three switch element. These driver elements and switching elements are thin film transistors (TFT). In this way, the image display device of the prior art becomes a 3TFT with 3 (1 driver element + 2 switch elements) or 4 (1 driver element + 3 switch elements) thin film transistors in each pixel circuit. structure or 4TFT structure.

[0005]

FIG. 15-1 is a diagram showing the configuration of main parts (one pixel unit) of the image display device proposed in Non-Patent Document 1. FIG. In the image display device shown in the figure, the signal line supply circuit 102 has a function of supplying a luminance signal through the signal line 101 . The scanning line driving circuit 104 has a function of supplying a scanning signal for selecting a pixel circuit to which a luminance potential is supplied via the scanning line 103 . The potential power supply circuit 105 has a function of supplying a high-level potential to one electrode of the electrostatic capacitor 112 and an electrode of the switching element 108 . The reset control circuit 114 supplies a reset potential to the switching element 109 via the reset line 115 . The drive control circuit 116 supplies a control signal to the switching element 118 through the drive control line 117 as a medium.

[0006]

Also, in the image display device, the light emitting element 107, the switching element 108, the switching element 109, the electrostatic capacitor 112, the switching element 118, the electrostatic capacitor 119, and the switching element 122 constitute a pixel circuit of one pixel. The light emitting element 107 has a function of emitting light by injecting a current, and is formed of the above-mentioned organic EL element. The switching element 108 has a function of controlling the current flowing into the light emitting element 107 .

[0007]

Here, as shown in FIG. 16-1, the light-emitting element 107 has a current-voltage characteristic in which a current flows when a potential difference (potential difference between anode and cathode) equal to or greater than the threshold voltage Vth _,iv is generated. In addition, as shown in FIG. 16-2, the light-emitting element 107 has a luminance-voltage characteristic that emits light (brightness>0) after a potential difference (potential difference between anode and cathode) above the threshold voltage Vth _{, Lv} is generated. .

[0008]

In addition, the value of the threshold voltage V _th,iv is lower than the threshold voltage V _th,Lv . In this way, when the potential difference between the anode and the cathode of the light emitting element 107 is equal to or greater than the threshold voltage Vth _,Lv , the light emitting element 107 is in a state of emitting light while a current flows into the light emitting element 107 . In addition, when the potential difference between the anode and the cathode of the light-emitting element 107 is the threshold voltage Vth _,iv or more and less than the threshold voltage Vth _,Lv , the light-emitting element 107 does not emit light even though a current flows into the light-emitting element 107. .

[0009]

Specifically, the driver element 108 has a function of controlling the current flowing into the light-emitting element 107 in accordance with a potential difference applied between the first terminal and the second terminal equal to or greater than the driving threshold, and during the period when the potential difference is applied, the The function of current continuously flowing into the light emitting element 107 . The driver element 108 is formed of a p-type thin film transistor, and controls the light emission luminance of the light emitting element 107 in accordance with the potential difference applied between the gate electrode corresponding to the first terminal and the source electrode corresponding to the second terminal.

[0010]

In the above structure, the following four steps are repeatedly performed: a reset step, a threshold voltage detection step, a data writing step, and a light emitting step. Next, the initial reset procedure will be described.

[0011]

As the first step, a reset step of resetting the potential applied to the gate electrode of the driver element 108 at the time of past light emission is performed. In this reset step, as shown in FIG. 15-2, the signal line 101 becomes a high-level potential, the reset line 115 becomes a low-level potential, the drive control line 117 becomes a low-level potential, and the scanning line 103 becomes a low-level potential. .

[0012]

Here, the potential difference between the anode and the cathode of the light emitting element 107 is the difference between Va and zero potential (cathode potential of the light emitting element 107) when the switching element 118 is in the on state.

[0013]

Fig. 17 is a graph showing transient response characteristics in a reset step. That is, this figure shows the potential Va, the potential Vb, the current _{id flowing in the light emitting element 107 shown in FIG. 15-1, and the transient response characteristics of the OLED} .

[0014]

It can be seen from this figure that after the reset step is executed at Time=0.00, the potential of the source electrode of the driver element 108 is a high-level potential, so while the potential Vb drops sharply, the potential Va rises, and the anode-cathode gap between the anode and cathode of the light-emitting element 107 The potential difference becomes higher rapidly, becoming more than the threshold voltage V _{th, Lv} shown in Fig. 16-2. In this way, while the current _{id, OLED} flows into the light emitting element 107, it also emits light. In addition, light emission in the reset step is unnecessary as will be described later.

[0015]

Then, after the reset step is completed, the above-mentioned threshold voltage detection step and data writing step are passed, and in the light emitting step, the light emitting element 107 emits light.

[0016]

We know that in an image display device, the greater the number of thin film transistors in each pixel circuit, the lower the fineness. Therefore, the fineness of the 2TFT structure is higher than that of the 3TFT structure or the 4TFT structure.

[0017]

18-1 is a diagram showing the structure of a main part (one pixel) of an image display device having a 2TFT structure proposed in Non-Patent Document 2. FIG. In addition, Fig. 18-2 is a sequence diagram illustrating its operation. In the image display device shown in FIG. 18-1, the switching element T1, the driver element T2, the electrostatic capacitor CCs, and the light emitting element OLED are connected as shown in the figure to form a 2TFT structure (switching element T1 and driver element T2). The switching element T1 and the driver element T2 are thin film transistors.

[0018]

In the above structure, as shown in the period _t1 in Fig. 18-2 and Fig. 19-1, in the preparatory step, the potential of the scanning line Select is V _gL , the potential of the data line Data is 0 potential, and the potential of the common line COM is VGG Afterwards, the switching element T1 is turned off, the driver element T2 is turned on, and the potential a of the source electrode of the driver element T2 becomes V _GG +V _OLED (the voltage drop of the light-emitting element OLED)+V _data '(according voltage)+V _t (threshold voltage of the driver element T2), the potential b of the anode of the light emitting element OLED, becomes V _GG +V _OLED . Thus, the current i flows, the potential a changes from V _GG +V _OLED +V _data '+V _t to V _data '+V _t , and the potential b changes from V _GG +V _OLED to zero potential.

[0019]

Next, as shown in period _t2 of FIG. 18-2 and FIG. 19-2, in the threshold voltage detection step, the potential of the scanning line Select is V _gH , the potential of the data line Data is 0 potential, and the potential of the common line COM is 0. After the potential is turned on, the switching element T1 is turned on, the driver element T2 is turned on, the potential a of the source electrode of the driver element T2 becomes 0 potential, and the potential b changes from 0 potential to -α(V _data '+Vt)-(1 —α) V _GG . Then, the current i flows, and the potential b changes from -α(V _data '+V _t )-(1-α)V _GG to -V _t . Here, α is CC _S /(CC _S +C _OLED ). CC _S is the value of the electrostatic capacitor CC _S. C _OLED is the value of the electrostatic capacitance of the light-emitting element OLED.

[0020]

Next, as shown in the period _t3 of Figure 18-2 and Figure 19-3, in the data writing step, the potential of the scanning line Select is V _gH , the potential of the data line Data is the data potential V _data , and the potential of the common line COM After the potential is 0, the switching element T1 is turned on, the driver element T2 is turned on, the potential a of the source electrode of the driver element T2 changes from 0 to V _data , and the potential b changes from -V _t to αV _data -V _t . Then, current i flows. Here, the potential b changes from -V _t to V _data -V _t when V _data is smaller than V _t . On the other hand, when V _data is larger than V _t , potential b becomes zero potential.

[0021]

Next, as shown in period _t4 of FIG. 18-2 and FIG. 19-4, in the light emitting step, the potential of the scanning line Select is V _gL , the potential of the data line Data is 0 potential, and the potential of the common line COM is -V _EE Thereafter, the switching element T1 is turned off, the driver element T2 is turned on, and the potential a of the source electrode of the driver element T2 becomes V _t +V _OLED +V _EE or V _data +V _OLED +V _EE .

[0022]

Here, when the potential a becomes V _t +V _OLED +V _EE , the potential b shown in FIG. 19-3 corresponds to V _data −V _t (V _data <V _t ). At this time, in the light-emitting element OLED, the current _id (=0) does not flow ( _id =0). On the other hand, when the potential a becomes V _data +V _OLED +V _EE , the potential b shown in FIG. 19-3 corresponds to 0 (V _data >V _t ). At this time, a current _id (=(β/2)(V _data −V _t ) ² ) flows into the light emitting element OLED. that is. The light-emitting element OLED emits or does not emit light because the current _id flows or does not flow due to the magnitude relationship between V _data and V _t . That is to say, the light emitting state of the light emitting element OLED depends on the threshold voltage V _t of the driver element T2.

[0023]

Non-Patent Document 1: Dawson et al., "Design Of an Improved Pixel for Polysilicon Active—Matrix Organic LED Display", "Design Of an Improved Pixel for Polysilicon Active—Matrix Organic LED Display," Society of Information Display 1998 Digest (Society of Information Display 1998 Digest), 1998, p.11-14

Non-Patent Document 2: J.L.Sanford et al., Proc.of IDRC 03 p.38

[0024]

However, in the image display device proposed in Non-Patent Document 1, since the potential of the source electrode of the driver element 108 shown in FIG. The potential difference between the anode and the cathode becomes the threshold voltage V _{th, Lv} shown in Fig. 16-2. Therefore, in the reset step, the light-emitting element 107 is caused to emit light, and although it is originally intended to be a black pixel, it becomes a white pixel. Contrast drop problem.

[0025]

In addition, in the image display device described above, since the driver element is turned on in the reset step, the amount of current flowing into the light emitting element in the reset step increases. Therefore, there is a problem in that the amount of light emitted from the light-emitting element increases in the reset step, and the contrast ratio further decreases.

[0026]

As an image display device in the prior art, in order to improve the fineness, although an image display device with a 2TFT structure described with reference to FIGS. 18-2 and 19-1 to 19-4 has been proposed, as shown in FIG. 19-3 As described in Figure 19-4, due to the relationship between V _data and V _t , the current _id sometimes flows into the light-emitting element OLED, and sometimes does not flow into the light-emitting element OLED, so the light-emitting state of the light-emitting element OLED is unstable. That is to say, the image display device with the 2TFT structure is not yet available for practical use.

[0027]

In this way, the image display device in the prior art still has a 3TFT structure or a 4TFT structure in the practical stage, and there is a problem that it is difficult to improve the fineness.

Contents of the invention

[0028]

The present invention has been developed in view of the above problems, and an object of the present invention is to provide an image display device capable of improving contrast.

[0029]

In order to solve the above problems and achieve the purpose, the image display device according to the present invention includes: a light emitting element; a driving transistor having a gate electrode, a source electrode and a drain electrode, one end of the light emitting element, and the source electrode electrically connected to one of the drain electrodes; a first switching transistor that short-circuits the gate electrode of the driving transistor and the one electrode of the driving transistor according to a scan signal; a capacitor element, The capacitor element has a first electrode and a second electrode, the gate electrode of the driving transistor is connected to the first electrode; a signal line is connected to the second electrode of the capacitor element; the signal line drives a circuit, the signal line drive circuit supplies a luminance potential and a reference potential representing a reference of the luminance potential to the signal line; a power supply circuit, the power supply circuit controls other components of the source electrode and the drain electrode of the drive transistor. The potential of the electrode.

[0030]

In addition, the image display device according to the present invention includes a plurality of pixels including a light-emitting element, a drive transistor electrically connected to one end of the light-emitting element, and a capacitor element connected to the drive transistor. For the area S ₁ of a pixel, the ratio of the area S ₂ of the drive transistor to each pixel (S ₂ /S ₁ ), and/or for the area S ₁ of a pixel, the area of the capacitor element The ratio of S ₃ to each pixel (S ₃ /S ₁ ) is 0.05 or more.

[0031]

In addition, the method for driving an image display device according to the present invention comprises a light-emitting element, a drive transistor (the drive transistor has a gate electrode, a source electrode, and a drain electrode, and the light-emitting element is connected to the source electrode and the drain electrode. In the driving method of the image display device of a switching transistor (the switching transistor short-circuits the gate electrode of the driving transistor and the one electrode of the driving transistor according to the scanning signal), including a first step of setting the switching transistor to conduction by controlling the potential of the gate electrode of the switching transistor, and by controlling the source electrode and the drain electrode of the driving transistor The potential of the other electrode in the drive transistor is set to the cut-off state, and the potential is supplied to the gate electrode of the drive transistor of each pixel; the second step is to control the switch by controlling the The potential of the gate electrode of the transistor sets the switching transistor to conduct, and by controlling the potential of the other electrode of the drive transistor, the drive transistor is set to conduct, thereby making the pair The potential current of the gate electrode of the other electrode of the driving transistor is higher than the driving threshold, and then passes through the switching transistor as an intermediary, from the gate electrode of the driving transistor to the driving transistor. The other electrode supplies a current so that the potential of the gate electrode with respect to the other electrode of the drive transistor serves as a drive threshold.

[0032]

In addition, the driving method of an image display device according to the present invention is characterized in that: a plurality of pixels (these pixels are equipped with a light-emitting element, a driving transistor (the driving transistor has a gate electrode, a source electrode, and a drain electrode, so The light-emitting element is electrically connected to one of the source electrode and the drain electrode), a switching transistor (the switching transistor makes the gate electrode of the driving transistor and the one of the driving transistor electrode short-circuit)) in the driving method of an image display device, in the reset step of supplying a potential to the gate electrode of the driving transistor of each pixel through the intermediary of the light emitting element and the switching transistor, an external The potential difference between both ends of the light-emitting element is equal to or higher than a first threshold voltage of the light-emitting element at which current starts to flow into the light-emitting element, and not greater than a second threshold voltage of the light-emitting element at which the light-emitting element starts emitting light.

[0033]

After adopting the present invention, in the reset step, current flows into the light-emitting element, and a predetermined potential that makes the light-emitting element not emit light is supplied, so even if the potential of the gate electrode of the drive transistor is reset through the light-emitting element, the number of light-emitting elements can be reduced. The extra light emitting time can obtain the effect of further improving the contrast compared with the prior art.

[0034]

In addition, after adopting the present invention, even if the number of transistors in each pixel is reduced to 2 or 3, the driving threshold of the driving transistor can be detected and compensated, and the fineness can be improved.

[0035]

In addition, after adopting the present invention, the area occupied by the driving transistor or the area occupied by the capacitive element in each pixel can be enlarged by more than 5%. In this way, the resistance of the driving transistor can be reduced, and the power consumption of the image display device can be reduced. In addition, even if the area of one pixel is as small as 7000 μm ² to 50000 μm ² , it is easy to ensure that the capacitance of the capacitor element has an appropriate size.

Description of drawings

[0036]

FIG. 1 is a diagram showing the overall configuration of an image display device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing the state of potential variation of each component for describing the operation of the image display device according to the first embodiment.

Fig. 3-1 is a diagram showing a reset procedure of the image display device according to the first embodiment.

Fig. 3-2 is a diagram showing a threshold voltage detection procedure of the image display device according to the first embodiment.

3-3 is a diagram showing the data writing procedure of the image display device according to the first embodiment.

3-4 are diagrams showing light emission steps of the image display device according to the first embodiment.

FIG. 4 is a graph showing transient response characteristics after the first switching element 13 shown in FIG. 3-1 is turned on.

Fig. 5 is an enlarged plan view of the image display device of Fig. 1 .

6 is a diagram showing the overall configuration of an image display device according to a second embodiment of the present invention.

FIG. 7 is a timing chart showing the state of potential variation of each component for describing the operation of the image display device according to the second embodiment.

Fig. 8-1 is a diagram showing a reset procedure of the image display device according to the second embodiment.

Fig. 8-2 is a diagram showing a preparation procedure for the image display device according to the second embodiment.

Fig. 8-3 is a graph showing the threshold voltage detection procedure of the image display device according to the second embodiment.

8-4 are diagrams showing the data writing procedure of the image display device according to the second embodiment.

8-5 are diagrams showing a second reset procedure of the image display device according to the second embodiment.

8-6 are diagrams showing light emission steps of the image display device according to the second embodiment.

Fig. 9 is an enlarged plan view of the image display device of Fig. 6 .

FIG. 10 is a diagram showing the overall configuration of an image display device according to a third embodiment of the present invention.

Fig. 12-1 is a graph showing the threshold voltage detection procedure of the image display device according to the third embodiment.

Fig. 12-2 is a diagram showing the data writing procedure of the image display device according to the third embodiment.

Fig. 12-3 is a diagram showing a reset procedure of the image display device according to the third embodiment.

Fig. 12-4 is a diagram showing the light emitting procedure of the image display device according to the third embodiment.

Fig. 13-1 is a diagram showing the configuration of main components of an image display device according to a fourth embodiment.

FIG. 13-2 is a timing chart drawn to describe the operation of the image display device according to the fourth embodiment.

Fig. 14-1 is a diagram showing the configuration of main components of an image display device according to a fifth embodiment.

FIG. 14-2 is a timing chart drawn to describe the operation of the image display device according to the fifth embodiment.

Fig. 15-1 is a diagram showing the structure of a main part (one pixel) of a conventional image display device.

Fig. 15-2 is a timing chart drawn to describe the operation of the conventional image display device.

Fig. 16-1 is a graph showing current-voltage characteristics in a light emitting element (organic EL element).

Fig. 16-2 is a graph showing luminance-voltage characteristics in a light-emitting element (organic EL element).

FIG. 17 is a graph showing transient response characteristics after the switching element 109 and the driver element 108 shown in FIG. 15-1 are turned on.

Fig. 18-1 is a diagram showing the structure of a main part (one pixel) of a conventional image display device having a 2TFT structure.

FIG. 18-2 is a timing chart drawn to describe the operation of a conventional image display device having a 2TFT structure.

Fig. 19-1 is a diagram showing a preparation procedure for the image display device shown in Fig. 18-1.

Fig. 19-2 is a graph showing the threshold voltage detection procedure of the image display device shown in Fig. 18-1.

Fig. 19-3 is a diagram showing a data writing procedure of the image display device shown in Fig. 18-1.

Fig. 19-4 is a diagram showing the light emission steps of the image display device shown in Fig. 18-1.

Symbol Description

[0037]

1, 20, 50 pixel circuits

6 Constant potential supply circuit

8 power supply circuit

10, 27, 57 Light-emitting elements

11 2nd switching element

12, 28.58 driver element

13 1st switching element

25, 55 The first power supply circuit

26, 56 Second power supply circuit

29, 59 Switching elements

Detailed ways

[0038]

Embodiments of the image display device according to the present invention will be described in detail below with reference to the drawings. In addition, the present invention is not limited to employing this embodiment mode.

[0039]

FIG. 1 is a diagram showing the overall configuration of an image display device according to a first embodiment of the present invention. The image display device shown in FIG. 1 has a function of preventing light emission in a reset step that should improve contrast, and has a plurality of pixel circuits 1 (these pixel circuits 1 are arranged in rows and columns), a signal line driver circuit 3 (the The signal line driver circuit 3 supplies a plurality of pixel circuits 1 with luminance signals described later through the intermediary of the plurality of signal lines 2), and the scanning line driver circuit 5 (the scanning line driver circuit 5 uses the plurality of scanning lines 4 as the intermediary). , to supply the pixel circuit 1 with a scanning signal for selecting the pixel circuit 1 to which the luminance signal is supplied).

[0040]

In addition, the image display device further includes: a constant potential supply circuit 6 for supplying a constant conduction potential to the anode of a light emitting element 10 (described later) included in the pixel circuit 1; a drive control circuit 7 , the drive control circuit 7 controls the driving of the second switching element 11 (described later) in the pixel circuit 1 through the control line 9 as a medium; The source electrode of the element 12 is supplied with ON potential, and is supplied with 0 potential in other steps.

[0041]

The pixel circuit 1 has: a light emitting element 10, the anode of which is electrically connected to the constant potential supply circuit 6; a second switching element 11, one electrode of which is electrically connected to the cathode of the light emitting element 10; a driver Element 12, the driver element 12 is formed by an n-type thin film transistor, its drain electrode is electrically connected to the other electrode of the first switching element 13, and its source electrode is electrically connected to the power supply circuit 8; threshold voltage detection part 14, the threshold voltage The detection unit 14 is formed of the first switching element 13 that controls the conduction state between the gate and the drain of the thin film transistor forming the driver element 12 .

[0042]

The light emitting element 10 has a mechanism for emitting light by injecting a current, and is formed of, for example, an organic EL element. The organic EL element has a structure having at least the following layers: an anode layer and a cathode layer formed of Al, Cu, ITO (Inaium TinOxide), etc. The light-emitting layer is formed of organic materials such as benzoquinoline compounds, benzokinolinolato, and beryllium complexes. The organic EL element has a function of generating light by utilizing the light-emitting recombination of holes and electrons injected into the light-emitting layer.

[0043]

The second switching element 11 has a function of controlling conduction between the light emitting element 10 and the driver element 12, and is formed of an n-type thin film transistor in this embodiment. That is to say, the drain electrode and the source electrode of the thin film transistor are respectively connected to the light-emitting element 10 and the driver element 12, and on the other hand, the gate electrode is electrically connected to the driving control circuit 7, and is controlled according to the potential supplied by the driving control circuit 7. Conduction state between light emitting element 10 and driver element 12 .

[0044]

The driver element 12 has a function to control the current flowing into the light emitting element 10 . Specifically, the driver element 12 has a function of controlling the current flowing into the light emitting element 10 in accordance with a potential difference equal to or greater than a driving threshold applied between the first terminal and the second terminal. In this embodiment, the driver element 12 is formed of an n-type thin film transistor, and controls the light emission luminance of the light emitting element 10 according to the potential difference applied between the gate electrode corresponding to the first terminal and the source electrode corresponding to the second terminal.

[0045]

The electrostatic capacitor 15 is combined with the signal line driving circuit 3 to form a luminance potential/reference potential supply unit 16 . The luminance potential/reference potential supply unit 16 has a function of detecting a potential difference (hereinafter referred to as "threshold voltage") corresponding to the drive threshold of the driver element 12 and a function of supplying a reference potential as luminance potential supply means.

[0046]

The threshold voltage detection unit 14 is an element for detecting the threshold voltage of the driver element 12 . In the present embodiment, the threshold voltage detection unit 14 is formed of the first switching element 13 composed of an n-type thin film transistor. That is to say, one source/drain electrode of the first switching element 13 is connected to the drain electrode of the driver element 12, and the other source/drain electrode is connected to the gate electrode of the driver element 12, and the gate electrode of the thin film transistor is connected to the scan line drive. A structure in which the circuit 5 is electrically connected. In this way, the threshold voltage detection unit 14 has the function of conducting between the gate and the drain of the thin film transistor constituted by the first switching element 13 according to the potential supplied from the scanning line driving circuit 5, and also has the function of making the gate and the drain conduct. This function detects the threshold voltage when it is turned on.

[0047]

2 is a timing chart showing how the potentials of the constituent elements of the image display device according to the first embodiment of the present invention fluctuate during operation. In FIG. 2, the scanning line (n-1) is a diagram showing a timing chart of the scanning line and the control line corresponding to the pixel circuit 1 in the previous stage as a reference. 3-1 to 3-4 are graphs showing states of the pixel circuit 1 corresponding to periods t ₁ to t ₄ shown in FIG. 2 .

[0048]

First, a reset step of resetting the potential applied to the gate electrode of the driver element 12 at the time of past light emission is performed. Specifically, as shown in period t1 of FIG. ₂ and FIG. 3-1, the potentials of the power supply circuit 8, the drive control circuit 7, and the scanning line 4 (scanning line driving circuit 5) change to the ON potential. In addition, the potential of the constant potential supply circuit 6 always becomes a constant on-potential. On the other hand, the potential of the signal line 2 becomes V _DL .

[0049]

That is, as shown in FIG. 3-1 , the second switching element 11 and the first switching element 13 are turned on. On the other hand, since the potential of the power supply circuit 8 is the on potential, the driver element 12 is in an off state. Thus, the potential of the first electrode 17 forming the electrostatic capacitor 15 becomes a value obtained by subtracting the voltage drop in the light emitting element 10 from the potential on the anode side of the light emitting element 10 supplied by the constant potential supply circuit 6 . In general, since the on-potential supplied by the constant potential supply circuit 6 has a very high value, the potential of the first electrode 17 (that is, the potential of the gate electrode of the driver element 12) is kept higher than the threshold voltage _Vth . The value of - V _t .

[0050]

On the other hand, as shown in FIG. 2 , since the potential of the signal line 2 becomes V _DL , the potential of the second electrode 18 , which is the other electrode forming the electrostatic capacitor 15 , becomes V _DL . In this way, the potential of V _r (>V _th ) is supplied to the first electrode 17 and the potential of V _DL is supplied to the second electrode 18 during the period t1 in FIG. ₂ and the steps shown in FIG. 3-1 .

[0051]

FIG. 4 is a graph showing transient response characteristics after the first switching element 13 shown in FIG. 3-1 is turned on (driver element 12: off state). That is, in this figure, the cathode potential Va' of the light emitting element 10, the potential V _r (>V _th ) of the gate electrode (first electrode 17) of the driver element 12, and the current id flowing through the light emitting element 10 are shown _{. , Transient response characteristics of OLEDs} .

[0052]

From this figure, it can be seen that when the first switching element 13 is turned on (driver element 12: off state) at Time=0.00, the potential Va' slightly falls and then rises as the potential Vr rises.

[0053]

Here, in the first embodiment, the parameters C _S and C _OLED in the following formula (1) are set so that the potential difference between the anode and the cathode of the light emitting element 10 (from The difference between the conduction potential of the constant potential supply circuit 6 and the potential Va') is greater than or equal to the threshold voltage V _th,iv (FIG. 14-1) and smaller than the threshold voltage V _th,Lv (FIG. 14-2). The parameter C _S is the value of the electrostatic capacitor 15 . The parameter C _OLED is the capacitance component of the light emitting element 10 .

V _{th, Lv} >(C _s /(C _s +C _OLBD )) V _{th, iv} (1)

Thus, in the first embodiment, since the potential difference between the anode and the cathode of the light-emitting element 10 in the reset step is equal to or greater than the threshold voltage V _th,iv ( FIG. 14-1 ) and smaller than the threshold voltage V _{th, Lv} , so as shown in Figure 4, although the current _{id, OLED} ' flows slightly, but does not emit light.

[0054]

Next, as shown in period t2 of FIG. ₂ and FIG. 3-2 , the potential of the power supply circuit 8 changes from the on potential to the zero potential. In addition, when the potential of the drive control circuit 7 changes from the on potential to the off potential, the second switching element 11 is turned off. In addition, after the potential of the scanning line 4 is maintained at the on potential, the first switching element 13 is maintained in the on state. Furthermore, the potential of the signal line 2 is maintained at 0 potential.

[0055]

First, the potential change of the first electrode 17 will be described. As described above, since the driver element 12 is turned into an on state, the gate electrode and the drain electrode are electrically connected in the driver element 12 . On the other hand, as described above, until the last step, the gate electrode of the driver element 12 maintains a value higher than the threshold voltage V _th , and the source electrode is supplied with the potential V _DL by the power supply circuit 8, so that it becomes a source-drain connection. The potential difference between them is V _r , and the driver element 12 is turned on.

[0056]

In this way, with regard to the driver element 12, each of the drain electrode and the source electrode is turned on from the gate electrode through the first switching element 13, and the current i flows according to the charge held in the gate electrode. Since the current i flows until the driver element 12 is turned off, the potential difference between the gate and the drain in the driver element 12 finally becomes a value equal to the threshold voltage V _th , and since the source electrode maintains 0 potential, the driver The potential of the gate electrode of the element 12 , that is, the potential of the first electrode 17 becomes V _th . On the other hand, the potential of the second electrode 18 is supplied to V _DL via the signal line 2 . In addition, when a low-mobility element such as a thin-film transistor made of amorphous silicon is used as a driver element, it is preferable to provide a period t ₂ . However, even if the period t ₂ is not provided for a high-mobility element such as polysilicon, It can also be activated.

[0057]

Next, as shown in period _t3 of FIG. 2 and FIG. 3-3 , the signal line driving circuit 3 supplies the luminance potential V _data through the signal line 2 as a medium. At this time, the potential of the gate electrode becomes higher than V _th again, a current flows through the first switching element 13 and the driver element 12 , and the potential of the gate electrode of the driver element 12 becomes V _th again. Finally, in the light emitting step, as shown in period _t4 of FIG. 2 and FIGS. 3-4 , the reference potential V _DHd is supplied from the signal line drive circuit 3 through the signal line 2, and the potential of the first electrode 17 becomes V _th −V _data +V _DH , the current _id (=(β/2)(V _DH −V _data ) ² ) flows into the light emitting element 10 . In addition, β is a value proportional to the mobility of carriers in the driver element 12, and is a unique value in the driver element 12 of the pixel.

[0058]

As described above, according to the first embodiment, in the reset step of resetting the potential applied to the first terminal (gate electrode) of the driver element 12 at the time of light emission in the past, the potential supplied to each part is generated. Since the electric current flows into the light-emitting element 10 and the potential difference is within a predetermined range where no light is emitted, no light is emitted in the reset step, and contrast can be improved.

[0059]

Fig. 5 is an enlarged plan view of the image display device according to the first embodiment. FIG. 5 particularly shows the layout of the lower layer from the lower electrode (not displayed) of the light emitting element 10 . In one pixel, three TFTs (driver element 12, first switching element 13, and second switching element 11) and electrostatic capacitor 15 are shown. The layers constituting each element are sequentially composed of the lower electrode layer (the area painted with a dot pattern in the figure), the insulating layer (the area other than the part painted in black in the figure), and the active layer (the area painted with a dot pattern in the figure) in order from the lower layer. Areas painted with oblique lines) and the upper electrode layer (areas surrounded by solid lines in the figure and not blackened). In addition, a terminal LT in the figure is connected to one end of the light emitting element 10 .

[0060]

The lower electrode layer is formed on the substrate, including the gate electrode of the driver element 12, the gate electrode of the first switching element 13 (scanning line 4), the gate electrode of the second switching element 11 (control line 9) and the power supply circuit 8. The power line GL and the first electrode 17 of the electrostatic capacitor 15 . The insulating layer is formed over the entire surface except for the two openings (portions painted in black in the figure) on the lower electrode layer. This insulating layer functions as a gate insulating film for the three TFTs, and functions as a dielectric layer for the electrostatic capacitor 15 . The active layer is formed on the insulating layer and includes active layers of three TFTs. The upper electrode layer is formed on the active layer, and includes source/drain electrodes of the three TFTs, the second electrode 18 of the electrostatic capacitor 15 , and the signal line 2 .

[0061]

In addition, the insulating layer has an opening for connecting the power line GL connected to the power supply circuit 8 to the gate electrode of the driver element 12, and has an opening for connecting the first electrode 17 of the electrostatic capacitor 15 and the gate electrode of the driver element 12 to the first electrode 17 of the driver element 12. The openings to which the drain electrodes of the switching elements are connected are connected to the upper and lower layers.

[0062]

In addition, as constituent materials of each layer, aluminum or its alloys can be used for the lower electrode layer and the upper electrode layer, silicon nitride film, silicon oxide film or their mixture can be used for the insulating film layer, and amorphous material can be used for the active layer. Silicon, polysilicon, etc.

[0063]

As can be seen from this figure, in this embodiment, since the threshold voltage V _th,iv can be compensated by using 3TFT, there is room in the layout of one pixel, and the area of the driver element 12 and the electrostatic capacitor 15 can be enlarged. . Thus, the resistance of the driver element 12 can be reduced, and the power consumption of the image display device can be reduced. In particular, the effect is greater when the driver element 12 is formed of an amorphous silicon transistor having a large resistance. In addition, according to this embodiment, even when the area of one pixel is as small as 7000 μm ² to 50000 μm ² , the capacitance of the electrostatic capacitor 15 can be ensured to be an appropriate size.

[0064]

In addition, for the area S ₁ of one pixel, the ratio (S ₂ /S ₁ ) of the area S ₂ of the driver element 12 in each pixel, and/or for the area S ₁ of one pixel In other words, the ratio (S ₃ /S ₁ ) of the area S ₃ of the electrostatic capacitor 15 to each pixel is preferably set to 0.05 or more (preferably 0.07 or more, more preferably 0.1). In the present embodiment, S ₂ /S ₁ is 0.1 and S ₃ /S ₁ is 0.12 when the size of one pixel is 51 μm×153 μm.

[0065]

In addition, S ₂ /S ₁ and S ₃ /S ₁ are preferably 0.25 or less. This is because if _S2 and _S3 are too large, the area that can be occupied by other circuits becomes smaller, and the circuit configuration becomes troublesome.

[0066]

In addition, since a current larger than the first and second switching elements 13 and 11 flows through the driver element 12, it is preferable to set the area of the driver element 12 to the area _S4 of each of the first and second switching elements 13 and 11 (S ₂ /S ₄ ) of the S ₂ ratio is set to 2 to 10 (5 to 10 is more preferable).

[0067]

In addition, the "area S ₁ " refers to an area surrounded by boundary lines that divide each pixel into an equal area. In addition, the "area S ₂ " refers to the total area of the source electrode and the drain electrode of the driver element 12 and the active layer sandwiched between the source electrode and the drain electrode. In addition, the term "source electrode and drain electrode" refers to a region connected to an active layer among electrode layers constituting these electrodes. Furthermore, the “area S ₃ ” refers to the area where the first electrode 17 and the second electrode 18 of the electrostatic capacitor 15 face each other. In addition, the "area S ₄ " refers to the total area of the source electrode and the drain electrode of each switching element 11 and 13 and the active layer sandwiched between the source electrode and the drain electrode.

[0068]

In the above-mentioned first embodiment, as shown in FIG. 1 , the application of the 3TFT structure in which three thin film transistors (the second switching element 11, the driver element 12, and the first switching element 13) are provided in each pixel circuit 1 was described. An example of the glow function during the reset step. However, the function related to the 2TFT structure having two thin film transistors in each pixel circuit 1 can also be applied. Hereinafter, such an example will be described as a second embodiment.

[0069]

6 is a diagram showing the overall configuration of an image display device according to a second embodiment of the present invention. The image display device shown in FIG. 6, like the image display device shown in FIG. 1, has the function of preventing light emission in the reset step that should improve the contrast, and has a plurality of pixel circuits 20 (these pixel circuits 20 are matrix arrangement), signal line driver circuit 22 (the signal line driver circuit 22 supplies a luminance signal to be described later to a plurality of pixel circuits 20 via a plurality of signal lines 21), a scanning line driver circuit 24 (the scanning The line driver circuit 24 supplies the pixel circuit 20 with a scanning signal for selecting the pixel circuit 20 to which the luminance signal is supplied through the intermediary of the plurality of scanning lines 23 ).

[0070]

In addition, the image display device further includes: a first power supply circuit 25, which supplies constant conduction to the anode of a light-emitting element 27 (described later) in the pixel circuit 20 when the first power supply circuit 25 is reset. Potential; the second power supply circuit 26, the second power supply circuit 26 supplies a conduction potential to the source electrode of the driver element 28 in the reset step, and supplies a negative potential of 0 potential in other steps.

[0071]

The pixel circuit 20 includes: a light emitting element 27, the anode of which is electrically connected to the first power supply circuit 25; a driver element 28, whose source electrode is electrically connected to the second power supply circuit 26; The output unit 30 is formed by the switching element 29 that controls the conduction state between the gate and the drain of the thin film transistor forming the driver element 28 .

[0072]

The light emitting element 27 has a mechanism for emitting light by injecting a current, and is formed of, for example, an organic EL element. The driver element 28 has a function of controlling the current flowing into the light emitting element 27 . Specifically, the driver element 28 has a function of controlling the current flowing into the light-emitting element 27 in accordance with a potential difference greater than or equal to the driving threshold value applied between the first terminal and the second terminal, and also has a function of controlling the current flowing in the light emitting element 27 during the period when the potential difference is applied. The function that current flows continuously into the light emitting element 27 . In the second embodiment, the driver element 28 is formed of an n-type thin film transistor, and controls the light emission of the light emitting element 27 in accordance with the potential difference applied between the gate electrode corresponding to the first terminal and the source electrode corresponding to the second terminal. brightness.

[0073]

The electrostatic capacitor 31 is combined with the signal line driving circuit 22 to form a luminance potential/reference potential supply unit 32 . The luminance potential/reference potential supply unit 32 has a function of supplying a light emission luminance voltage corresponding to the light emission luminance of the light emitting element 27 and a function of supplying a reference potential as a luminance potential supply means.

[0074]

7 is a timing chart showing how the potentials of the constituent elements of the image display device according to the second embodiment fluctuate during operation. In FIG. 7, the scanning line (n-1) is a diagram showing a timing chart of the scanning line and the control line corresponding to the pixel circuit 20 in the previous stage as a reference. FIG. 8-1 is a graph showing the state of the pixel circuit 20 corresponding to a period t ₁ among periods t ₁ to t ₆ shown in FIG. 7 , that is, a reset step.

[0075]

First, a reset step of resetting the potential applied to the gate electrode of the driver element 28 at the time of past light emission is performed. Specifically, as shown in period t1 of FIG. ₇ and FIG. 8-1, the potentials of the first power supply circuit 25 and the second power supply circuit 26 become V _DD , and the potential of the scanning line 23 (scanning line driving circuit 24) becomes V DD . changes to the on-potential.

[0076]

That is, as shown in FIG. 8-1, the switching element 29 is turned on. On the other hand, since the potential of the second power supply circuit 26 is V _DD , the driver element 28 is turned on. Thus, the potential of the first electrode 33 forming the electrostatic capacitor 31 becomes a value obtained by subtracting the voltage drop V _OLED in the light emitting element 27 from the potential V _DD supplied to the anode of the light emitting element 27 by the first power supply circuit 25 . In general, since the potential V _DD supplied by the first power supply circuit 25 has a very high value, the potential of the first electrode 33 (that is, the potential of the gate electrode of the driver element 28 ) is maintained at a value higher than the threshold voltage V _th High value - (V _DD -V _OLED ).

[0077]

On the other hand, as shown in FIG. 7 , since the potential of the signal line 21 becomes V _DL , the potential of the second electrode 34 , which is the other electrode forming the electrostatic capacitor 31 , becomes V _DL . Thus, in the period t1 in FIG. ₇ and the steps shown in FIG. 8-1 , the potential (V _DD −V _OLED ) is supplied to the first electrode 33 and the potential V _DL is supplied to the second electrode 34 .

[0078]

In FIG. 8-1 , after the switching element 29 is turned on (the driver element 28 is turned off), the cathode potential Va of the light emitting element 27 slightly falls and then rises as the potential (V _DD -V _OLED ) rises.

[0079]

Here, as shown in FIG. 16-1, the light-emitting element 27 has a current-voltage characteristic in which a current flows when a potential difference (potential difference between anode and cathode) equal to or greater than the threshold voltage Vth _,iv is generated. In addition, as shown in FIG. 16-2, the light-emitting element 27 has a luminance-voltage characteristic that emits light (brightness>0) when a potential difference (anode-cathode potential difference) above the threshold voltage Vth _{, Lv} is generated.

[0080]

In addition, the threshold voltage V _th,iv is a value lower than the threshold voltage V _th,Lv . In this way, when the potential difference between the anode and the cathode of the light emitting element 27 is equal to or higher than the threshold voltage Vth _,Lv , the light emitting element 27 is in a state of emitting light as a current flows. Also, when the potential difference between the anode and the cathode of the light emitting element 27 is greater than or equal to the threshold voltage V _th,iv and less than the threshold voltage V _th,Lv , the light emitting element 27 is in a state where no light is emitted although current flows.

[0081]

Set the parameters C _S and C _OLED in the above formula (1) so that the potential difference between the anode and the cathode of the light-emitting element 27 (from the first power supply circuit The difference between the conduction potential V _DD and the potential Va of 25) is above the threshold voltage V _th,iv (Fig. 16-1) and less than the threshold voltage V _th,Lv (Fig. 16-2). In the second embodiment, the parameter C _S is the value of the electrostatic capacitor 15 . The parameter C _OLED is the capacitance component of the light emitting element 27 .

[0082]

In this way, in FIG. 8-1, since in the reset step, the potential difference between the anode and the cathode of the light-emitting element 27 is above the threshold voltage V _th,iv ( FIG. 16-1 ) and less than the threshold voltage V _th,Lv , so although the current i _{d flows into the OLED} slightly, it does not emit light, so the contrast can be improved.

[0083]

Next, as shown in period t2 of FIG. ₇ and FIG. 8-2, in the preparation step, the potential of the first power supply circuit 25 is -V _E (<V _th ), the potential of the signal line 21 is V DH , and the potential of the first power supply circuit 25 is V _DH . 2. After the potential of the power supply circuit 26 is V _DD and the potential of the scanning line 23 is the cut-off potential, the potential of the gate electrode of the driver element 28 becomes V _DD -V _OLED (voltage drop of the light-emitting element OLED)+V _DH -V _DL , Above the threshold voltage V _th of the driver element 28 . In addition, the switching element 29 is in an OFF state. Thus, the driver element 28 is turned on, and the current i flows.

[0084]

Next, as shown in period _t3 of FIG. 7 and FIG. 8-3, in the threshold voltage detection step, the potential of the first power supply circuit 25 is 0 potential, the potential of the signal line 21 is V DH , and the potential of the second power supply circuit 25 is V _DH . When the potential of the circuit 26 is 0 potential and the potential of the scanning line 23 is the on potential, the switching element 29 is turned on. In this way, the current i flows through the switching element 29 and the driver element 28 as intermediaries.

[0085]

Next, as shown in period _t4 of FIG. 7 and FIG. 8-4, in the data writing step, the potential of the first power supply circuit 25 is 0 potential, and the signal line 21 supplies the luminance potential V _DATA , and the second power supply When the potential of the supply circuit 26 is 0 potential and the potential of the scanning line 23 is the on potential, the switching element 29 is turned on. Thus, the potential of the gate electrode of the driver element 28 becomes α(V _DATA −V _DH )+V _th . In addition, α is C _S /(C _S +C _OLED ).

[0086]

Here, since the switching element 29 is turned on, the potential of the cathode electrode of the light emitting element 27 is equal to the potential of the cathode electrode of the driver element 28 .

[0087]

Next, as shown in the period t5 of Fig. ₇ and Fig. 8-5, in the second reset step, the potential of the first power supply circuit 25 is -V _E , the potential of the signal line 21 is V _DH , and the potential of the second power supply When the potential of the supply circuit 26 is _-VE and the potential of the scanning line 23 is the off potential, the switching element 29 is in the off state. Thus, the potential of the gate electrode of the driver element 28 becomes (1-α)(V _DH -V _DATA )+V _th . During this period _t5 , the potential of the cathode electrode of the light emitting element 27 becomes -V _E and is reset.

[0088]

Next, as shown in period _t6 of FIG. 7 and FIG. 8-6, in the light emitting step, the potential of the first power supply circuit 25 is V _DD , the potential of the signal line 21 is V _DH , and the potential of the second power supply circuit 26 After the potential of the scanning line 23 is 0 potential and the potential of the scanning line 23 is the cut-off potential, the current _id (=(β/2)((1—α)(V _DH —V _data )) ² ) flows into the light emitting element 27, and the light emitting element 27 glow. Here, the current _id does not depend on the threshold voltage V _th .

[0089]

In summary, according to the second embodiment, since the driver element 28 is provided (the driver element 28 controls the light-emitting element according to the potential difference higher than the predetermined threshold voltage V _th applied between the first terminal and the second terminal 27) and the switching element 29 (the switching element 29 detects a potential difference corresponding to the threshold voltage V _th between the first terminal and the second terminal), before the light-emitting step of causing the light-emitting element 27 to emit light, as The potential of the threshold voltage V _th at the time of detection of the threshold voltage performed in the step before the step is supplied to the driver element 28 and the light emitting element ₂₇ (see FIG. 7 and FIG. 8-5 ), and in the light emitting step (see FIG. 8-6), since a potential for flowing a current _id independent of the threshold voltage V _th is supplied, the 2TFT structure of the driver element 28 and the switching element 29 can be used to improve the fineness.

[0090]

Fig. 9 is an enlarged plan view of an image display device according to a second embodiment. The figure shows the layout of the lower layer from the lower electrode (not shown) of the light emitting element 27 . In one pixel, two TFTs (driver element 28, switching element 29) and electrostatic capacitor 31 are shown. The layers constituting each element are sequentially composed of the lower electrode layer (the area painted with a dot pattern in the figure), the insulating layer (the area other than the part painted in black in the figure), and the active layer (the area painted with a dot pattern in the figure) in order from the lower layer. Areas painted with oblique lines) and the upper electrode layer (areas surrounded by solid lines in the figure and not blackened). In addition, a terminal LT in the figure is connected to one end of the light emitting element 27 .

[0091]

The lower electrode layer is formed on the substrate and includes the gate electrode of the driver element 27, the gate electrode of the switching element 29 (scanning line 24), the power line GL connected to the second power supply circuit 26, and the first electrode 33 of the electrostatic capacitor 31. The insulating layer is formed over the entire surface except for the two openings in the lower electrode layer. This insulating layer functions as a gate insulating film for the two TFTs, and functions as a dielectric layer for the electrostatic capacitor 31 . The active layer is formed on the insulating layer and includes active layers of two TFTs. The upper electrode layer is formed on the active layer, and includes source/drain electrodes of two TFTs, the second electrode 34 of the electrostatic capacitor 31 , and the signal line 21 .

[0092]

In addition, the insulating layer has an opening for connecting the power line connected to the second power supply circuit 26 to the source electrode of the driver element 12, and an opening for connecting the first electrode 33 of the electrostatic capacitor 31 and the gate electrode of the driver element 28 to the switching element 29. The openings connected to the drain electrodes of the electrodes are used to connect the upper and lower layers. In addition, the constituent materials of each layer are the same as those of the first embodiment.

[0093]

As can be seen from the figure, in the second embodiment, since the threshold voltage _Vth can be compensated by two TFTs, the areas of the driver element 28 and the electrostatic capacitor 31 can be enlarged compared to the first embodiment. In addition, in the second embodiment, S ₂ /S ₁ is 0.15 and S ₃ /S ₁ is 0.14 when the size of one pixel is 51 μm×153 μm.

[0094]

FIG. 10 is a diagram showing the overall configuration of an image display device according to a third embodiment of the present invention. The image display device shown in FIG. 10 is provided with a plurality of pixel circuits 50 (these pixel circuits 50 are arranged in rows and columns), a signal line driver circuit 52 (the signal line driver circuit 52 is interposed by a plurality of signal lines 51, A luminance signal to be described later is supplied to a plurality of pixel circuits 50), a scanning line driving circuit 54 (the scanning line driving circuit 54 supplies a luminance signal for selectively supplying a luminance signal to the pixel circuit 50 through a plurality of scanning lines 53 as a medium). The scanning signal of the pixel circuit 50). The image display device adopts a 2TFT structure.

[0095]

In addition, the image display device further includes: a first power supply circuit 55 that supplies a potential to a drain electrode of a driver element 58 (described later) included in the pixel circuit 50; The second power supply circuit 56 supplies a potential to the cathode of the light emitting element 57 .

[0096]

The pixel circuit 50 includes: a light emitting element 57, the cathode of which is electrically connected to the second power supply circuit 26; a driver element 58, whose drain electrode is electrically connected to the first power supply circuit 25; The output unit 60 is formed by the switching element 59 that controls the conduction state between the gate and the drain of the thin film transistor forming the driver element 58 .

[0097]

The light emitting element 57 has a mechanism for emitting light by injecting a current, and is formed of the above-mentioned organic EL element. The driver element 58 has a function of controlling the current flowing into the light emitting element 57 . Specifically, the driver element 58 has a function of controlling the current flowing into the light-emitting element 57 in accordance with a potential difference greater than or equal to the drive threshold value applied between the first terminal and the second terminal, and also has a function of controlling the current flowing into the light emitting element 57 while the potential difference is applied. The function of current continuously flowing into the light emitting element 57 . In the third embodiment, the driver element 58 is formed of an n-type thin film transistor, and controls the light emitting element 57 in accordance with a potential difference applied between the gate electrode corresponding to the first terminal and the source electrode corresponding to the second terminal.

[0098]

The electrostatic capacitor 61 is combined with the signal line driving circuit 52 to form a luminance potential/reference potential supply unit 64 . The luminance potential/reference potential supply unit 64 has a function of supplying a light emission luminance voltage corresponding to the light emission luminance of the light emitting element 57 and a function of supplying a reference potential as a luminance potential supply means.

[0099]

FIG. 11 is a timing chart showing how the potentials of the constituent elements of the image display device according to the third embodiment fluctuate during operation. In FIG. 11, scanning line (n-1) is a diagram showing the timing chart of the scanning line and the control line corresponding to the pixel circuit 50 in the preceding stage as a reference. FIG. 12-1 corresponds to the period t ₁ among the periods t ₁ to t ₄ shown in FIG. 11 , that is, the threshold voltage detection step.

[0100]

That is, as shown in period t1 of FIG. ₁₁ and FIG. 12-1, in the threshold voltage detection step, the potential of the first power supply circuit 55 is 0 potential, the potential of the signal line 51 is V _DH , and the potential of the second power supply When the potential of the supply circuit 56 is V _E2 and the potential of the scanning line 53 is the on potential, the switching element 59 is turned on. In this way, the current i flows through the switching element 59 and the driver element 58 as intermediaries.

[0101]

Next, as shown in period _t2 of FIG. 11 and FIG. 12-2, in the data writing step, the potential of the first power supply circuit 55 is 0 potential, the luminance potential V _DATA is supplied from the signal line 51, and the second power supply circuit 55 is supplied with luminance potential V DATA . When the potential of the circuit 56 is V _E2 and the potential of the scanning line 53 is the on potential, the switching element 59 is turned on. Thus, the potential of the gate electrode of the driver element 58 becomes α(V _DATA −V _DH )+V _th . In addition, α is C _S /(C _S +C _OLED ).

[0102]

Next, as shown in period _t3 of FIG. 11 and FIG. 12-3, in the reset step, the potential of the first power supply circuit 55 is -V _E1 (<-V _th ), and the potential of the signal line 51 is V _DH When the potential of the second power supply circuit 56 is V _E2 and the potential of the scanning line 53 is the off potential, the switching element 59 is in the off state. Thus, the potential of the gate electrode of the driver element 58 becomes (1-α)(V _DH -V _DATA )+V _th . During this period _t3 , the potential of the cathode of the light emitting element 57 becomes -V _E1 and is reset.

[0103]

Next, as shown in period _t4 of FIG. 11 and FIG. 12-4, in the light emitting step, the potential of the first power supply circuit 55 is 0 potential, the potential of the signal line 51 is V _DH , and the potential of the second power supply circuit 56 After the potential of the scanning line 53 is -V _EE and the potential of the scanning line 53 is the cut-off potential, the current _id (=(β/2)((1-α)(V _DH -V _DATA )-(V _EE +V _OLED )) ² ) flows into the light emitting element 57, and the light emitting element 57 emits light. Here, the current _id does not depend on the threshold voltage V _th .

[0104]

In addition, the function of preventing light emission in the reset step can also be applied to the image display device with the structure shown in Fig. 13-1 and Fig. 14-1. In the image display device (fourth embodiment) shown in FIG. 13-1, the switching element T1, the switching element T2, the switching element T3, the driver element T4, the electrostatic capacitor C1, the electrostatic capacitor C2, and the light emitting element OLED are as shown in the figure. Connect to the ground, and act according to the timing diagram shown in Figure 13-2.

[0105]

The switching elements T1 to T3 and the driver element T4 are p-type thin film transistors. In the reset step, Power (off potential) is supplied from the driver element T4. At this time, since the cathode of the light emitting element OLED is grounded and has an off potential, the driver element T4 is in an off state, and the switching element T2 is in an on state. At this time, as in the first embodiment, the optical element OLED does not emit light although current flows.

[0106]

In addition, in the image display device (fifth embodiment) shown in FIG. 14-1, the switching element T1', switching element T2', switching element T3', driver element T4', electrostatic capacitor C1', electrostatic capacitor C2 ' and the light-emitting element OLED' are connected as shown in the figure, and operate according to the timing diagram shown in Figure 14-2.

[0107]

The switching elements T1'˜T3' and the driver element T4' are n-type thin film transistors. In the reset step, Power (off potential) is supplied from the driver element T4'. At this time, since the cathode of the light-emitting element OLED' is supplied with the on-potential V _DD , the driver element T4' is turned off, and the switching element T2' is turned on. At this time, as in the first embodiment, the optical element OLED' does not emit light although current flows.

[0108]

As mentioned above, according to the fourth and fifth embodiments, the same effect as that of the first embodiment can be obtained. In addition, in the above-mentioned first to fifth embodiments, the case where the above-mentioned formula (1) is satisfied has been described. However, in the above-mentioned first to fifth embodiments, when the formula (1) is not satisfied, the driver element is in the OFF state in the reset step, so the amount of current passing through the light-emitting element can be made smaller than in the prior art, and Reducing the amount of light emitted by the light-emitting element can increase the contrast ratio compared with the prior art.

[0109]

Other effects and modifications can be easily derived by people in the industry. Therefore, the wider aspects of the present invention are not limited to the specific details and representative embodiments described above. Accordingly, various changes may be made without departing from the spirit and scope of the general inventive concept defined by the appended claims and their equivalents.

[0110]

For example, in the present first to second embodiments, in the reset step, the potential V _r higher than the driving threshold value V _th is supplied to the gate electrode of the driving transistor. However, this potential V _r does not necessarily have to be higher than the driving threshold V _th , and is preferably higher than the driving threshold V _th . When the potential V _r is lower than the driving threshold V _th , the source potential and the signal line potential of the initial driving transistor in the threshold voltage detection step are adjusted so that the gate-source of the initial driving transistor in the threshold voltage detection step The potential difference is greater than the drive threshold V _th .

[0111]

As described above, the image display device according to the present invention is very useful as a display device using organic EL elements, and is particularly suitable for image display requiring high-definition display.

Claims (9)

1, a kind of image display apparatus is characterized in that, possesses:

A plurality of pixels, this pixel has:

Organic EL;

Driving transistors, this driving transistors has gate electrode, source electrode and drain electrode, and an end of described organic EL is electrically connected with side's electrode in described source electrode and the described drain electrode;

The 1st switching transistor, the 1st switching transistor make the described gate electrode of described driving transistors and described side's electric pole short circuit of described driving transistors according to sweep signal; And

The described gate electrode that capacitor element, this capacitor element possess the 1st electrode and the 2nd electrode, described driving transistors is connected with described the 1st electrode;

Signal wire, this signal wire is connected with described the 2nd electrode of described capacitor element;

Signal-line driving circuit, this signal-line driving circuit are supplied with the reference potential of brightness current potential and this brightness current potential benchmark of expression to described signal wire; And

Power-supply circuit, this power-supply circuit are controlled the current potential of described the opposing party's electrode of the described source electrode of described driving transistors and described drain electrode,

The 1st threshold voltage of this organic EL that electric current begins to flow in described organic EL is V _{Th, i-v}, the 2nd threshold voltage of luminous this organic EL of beginning is V in described organic EL _{Th, L-v}, described organic EL electrostatic capacitance value be C _OLBD, described capacitor element capacitance be C _s, then satisfy the following relationship formula:

V _th，L-v>(C _s/(C _s+C _OLBD))·V _th，i-v。

2, image display apparatus as claimed in claim 1 is characterized in that, possesses: the 1st power-supply circuit, and the 1st power-supply circuit is connected jointly with the other end of the described organic EL of described each pixel, supplies with the 1st current potential to the described other end; With

The 2nd power-supply circuit, the 2nd power-supply circuit is supplied with the 2nd current potential to described the opposing party's electrode of described driving transistors, utilizes the 2nd current potential, controls the conduction and cut-off of described driving transistors, described the 2nd power-supply circuit is described power-supply circuit.

3, image display apparatus as claimed in claim 1, it is characterized in that: also possess the 2nd switching transistor, the 2nd switching transistor is according to driving current potential, controls the conducting between described side's electrode of the described end of described organic EL and described driving transistors.

4, image display apparatus as claimed in claim 2 is characterized in that: described the 1st power-supply circuit, with fixing current potential, supply with described the 1st current potential.

5, image display apparatus as claimed in claim 2 is characterized in that: described the 1st power-supply circuit, according to described the 2nd current potential, control described the 1st current potential.

6, a kind of driving method of image display apparatus is characterized in that: described image display apparatus possesses:

Light-emitting component;

Driving transistors, this driving transistors has gate electrode, source electrode and drain electrode, and described light-emitting component is electrically connected with side's electrode in described source electrode and the described drain electrode;

Capacitor element, this capacitor element have the 1st electrode and the 2nd electrode, and the described gate electrode terminal of described driving transistors is connected with described the 1st electrode; And

Switching transistor, this switching transistor make the described gate electrode of described driving transistors and described side's electric pole short circuit of described driving transistors according to sweep signal,

The driving method of described image display apparatus comprises:

The 1st step, this step is at the current potential of the described gate electrode that passes through the described switching transistor of control, set described switching transistor for conducting, and by the described source electrode of the described driving transistors of control and the current potential of the opposing party's electrode in the described drain electrode, described driving transistors is set under the state that ends, supplied with current potential to the described gate electrode of the driving transistors of described each pixel; With

The 2nd step, this step is by the current potential of the described gate electrode of the described switching transistor of control, set described switching transistor for conducting, and the current potential of described the opposing party's electrode by the described driving transistors of control, set described driving transistors for conducting, thereby make current potential be higher than drive threshold for the described gate electrode of described the opposing party's electrode of described driving transistors, then, from the gate electrode of described driving transistors through the described the opposing party electrode supplying electric current of described switching transistor to described driving transistors, thereby will be for the current potential of the described gate electrode of described the opposing party's electrode of described driving transistors, as drive threshold

In described the 1st step, through described light-emitting component, the current potential that supply is supplied with to the gate electrode of described driving transistors, and in described the 1st step, make the outer potential difference (PD) that adds to the two ends of described light-emitting component, the 1st threshold voltage that is in this light-emitting component that electric current begins to flow in the described light-emitting component is above, in described light-emitting component below the 2nd threshold voltage of luminous this light-emitting component of beginning.

7, the driving method of image display apparatus as claimed in claim 6, it is characterized in that: the driving method of described image display apparatus, also comprise the 3rd step, this step is by the current potential of the described gate electrode of the described switching transistor of control, described switching transistor set for end, and, control the current potential of the described gate electrode of described driving transistors by described capacitor element, set described driving transistors for conducting, thereby make described light-emitting component luminous.

8, as the driving method of claim 6 or 7 described image display apparatus, it is characterized in that: described light-emitting component is an organic EL.

9, a kind of driving method of image display apparatus is characterized in that: described image display apparatus possesses a plurality of pixels, and these pixels possess:

Light-emitting component;

Driving transistors, this driving transistors has gate electrode, source electrode and drain electrode, and described light-emitting component is electrically connected with side's electrode in described source electrode and the described drain electrode;

Switching transistor, this switching transistor make the described gate electrode of described driving transistors and described side's electric pole short circuit of described driving transistors according to sweep signal; And

Capacity cell, this capacity cell have the 1st electrode and the 2nd electrode, and described the 1st electrode is connected with the described gate electrode of described driving transistors,

Through described light-emitting component and described switching transistor, supply with in the reset process of current potential to the described gate electrode of the described driving transistors of each pixel, adding to the potential difference (PD) at the two ends of described light-emitting component outward, is that the 1st threshold voltage of this light-emitting component that electric current begins to flow in the described light-emitting component is above, described light-emitting component begins below the 2nd threshold voltage of this luminous light-emitting component.

Images