JP4536403B2 - Display device - Google Patents

Description

  The present invention relates to a display device using an electro-optical element such as an organic EL (Electro Luminescence) display or FED (Field Emission Display).

  In recent years, the amount of light emission is controlled in accordance with the amount of electric charge (current amount) supplied to the element, such as an organic EL (Electro Luminescence) display, an inorganic EL display, an LED (Light Emitting Diode) display, and an FED (Field Emission Display). Research on display devices using electro-optical elements has been actively conducted. In particular, an organic EL display is attracting attention as an application product for portable devices as a display capable of emitting light with low voltage and low power consumption.

  As a driving method of an electro-optical element (organic EL element) used in an organic EL display, there are a simple matrix method and an active matrix method. Although the organic EL display adopting the simple matrix system has a simple structure, it is difficult to realize a large and high-definition display. For this reason, development of an organic EL display employing an active matrix method has been actively conducted.

  When driven by the active matrix method, the active matrix circuit has an active element (switching element) for controlling the current supplied to the organic EL element. Examples of the active element include a diode and MIM (Metal Insulator Metal), and a thin film transistor (hereinafter referred to as “TFT”) having excellent switching characteristics is more preferably used. The silicon film of this TFT may be amorphous, but it is smaller in size and can be driven by supplying more current than amorphous, as well as continuous grain boundary crystalline silicon (Continuous Grain Silicon as shown in Non-Patent Document 2). Silicon: hereinafter abbreviated as “CG silicon”), a crystallized silicon film such as single crystal silicon is preferably used.

  FIG. 14 shows a pixel configuration example in the case where a TFT using polycrystalline silicon, CG silicon, or the like is used as a switching element and an organic EL element is used as an electro-optical element. Since the basic configuration of the organic EL element is described in Non-Patent Document 3 and the like, detailed description thereof is omitted here. A pixel circuit Aij in FIG. 14 is a diagram of a pixel circuit configuration using a constant current control method. Note that the pixel circuit Aij indicates one pixel of a display device in which pixels are arranged in an M × N matrix, and if there are RGB pixels, indicates one pixel.

  The pixel circuit Aij includes a current-driven organic EL element EL10, n-channel (n-type) TFT elements Q10 and Q20, p-channel (p-type) TFT element Q30, capacitor C10, gate wiring Ei110, and power supply wiring. A PW 210 and a control wiring Gi 910 are arranged.

  A TFT element Q30 is connected to the power supply wiring PW210. The gate terminal of the TFT element Q30 is connected to the gate wiring Ei110. Further, the TFT element Q10 and the organic EL element EL10 are connected in series with the TFT element Q10 on the TFT element Q30 side on the side opposite to the connection point of the TFT element Q30 with the power supply wiring PW210. The anode of the organic EL element EL10 is on the TFT element Q10 side, and a common voltage 510 is disposed on the cathode side of the organic EL element.

  The capacitor C10 is connected between the gate terminal and the source terminal of the TFT element Q10. The TFT element Q20 is connected between the gate terminal of the TFT element Q10 and the TFT element Q30. The gate terminal of the TFT element Q20 is connected to the control wiring Gi910. A current source circuit 310 and a voltage source circuit 410 are switchably connected to the power supply wiring PW210.

  By the way, the above-described constant current control method is a method in which a gate-source current of a driving TFT (TFT element Q10 in FIG. 14) connected in series to an organic EL element is converted to a current source circuit such as a driver IC outside the pixel. This means a method of giving the current gradation data and controlling the light emission amount of the organic EL element by this current value.

  The pixel circuit shown in FIG. 14 is devised so that the aperture ratio in the pixel (the ratio of the light emitting area in one pixel) is as large as possible to improve the yield. For example, as shown in FIG. 15, in Non-Patent Document 1, a source wiring PW218 for writing current and a power supply wiring PW219 for supplying a voltage to the organic EL are used separately. The pixel circuit shown in FIG. 14 has a simple pixel configuration in which each wiring is used as a common line and the number of TFTs is reduced, so that the yield can be improved and the aperture ratio can be increased. ing.

  Therefore, when setting the current value of the organic EL element for each pixel, the current source circuit 310 is connected to the power supply wiring PW210, and the current value of the organic EL element is determined using the current value supplied from the current source circuit 310. It is set. That is, the current value supplied to the TFT element Q10 is fixed by holding the voltage applied to the gate terminal, and after setting the current value, the connection of the power supply wiring PW210 is switched to the voltage source circuit 410. As a result, during the period in which the TFT element Q30 is in a conductive state, the organic EL element is driven with a current having a set value by the applied voltage from the voltage source circuit 410 regardless of the driving state of the organic EL elements of other pixels. can do.

  Further, in the configuration in which the pixel circuits Aij are arranged in a matrix of M × N, in order to ensure a gradation display that is finer than the number of current values of the current source circuit 410 (that is, more than analog operation), a predetermined period of time is ensured. In addition, the current setting operation + the light emission operation is performed a plurality of times within a predetermined period in accordance with the total period during which the current is supplied to the organic EL element (that is, by a time-division digital gradation method).

Here, a basic operation of one pixel in the display device when the current setting operation + the light emission operation is repeated a plurality of times within a predetermined period in the pixel circuit Aij in FIG. 14 will be described. Unlike the pixel circuit of FIG. 15, the pixel circuit Aij has a unified current writing wiring and power supply wiring. Therefore, if there are a plurality of pixels, the pixel circuit Aij enters the light emission period immediately after current writing. I can't. Therefore, after the current setting operation for all pixel display device, although the light emitting operation is necessary that intends all pixels simultaneously row, in this way, it is expected that dynamic false contour is conspicuous.

As a method for reducing the moving image false contour, for example, one frame period is divided into N unit periods, each unit period is further divided into A selection periods, and the A pieces of the unit periods are formed. The selection period is set to the first occupation period from the first occupation period to the Ath occupation period, and a plurality (A pieces) of data corresponding to the set current values to be output to the respective active elements are respectively designated as the first data to the Ath data. It is preferable to use a driving method in which the set current value output to each active element in each occupation period is a current value fixed to any one of the first data to the A data (N And A are both positive integers).
Koji Hattori and three others, “Circuit Simulation of Current-Specified Polysilicon TFT Active Matrix Drive Organic LED Display”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, April 2001, ED2001-8 SDM2001-8 Vol. 101, no. 15, p. 7-14 Takayama, T. et al., "Continuous Grain Silicon Technology and Its Applications for Active Matrix Display", AM-LCD 2000, Semiconductor Energy Laboratory, p.25-28 Friend, RH, `` Polymer Light-Emitting Diodes for use in Flat panel Display '', AM-LCD'01, University of Cambridge, Cavendish Laboratory, p.211-214

  In order to realize the driving method for reducing the above moving image false contour, for example, the timing chart of FIG. 16 (in FIG. 16, the frame period is divided by focusing on one pixel in the display device for easy understanding). When a current set in advance is supplied from the current source circuit 310 while the conduction state of the TFT element Q30 continues in the first field period, as shown in FIG. The TFT element Q20 is turned on, and a gate voltage is written so that a set current is supplied to the TFT element Q10. Thereafter, the switch of the TFT element Q20 is cut off and switched to the voltage source circuit 410, and the current set in the pixel by the voltage applied from the voltage source circuit 410 is supplied to the organic EL element EL10.

  Then, until the next current writing period within a predetermined period comes, the pixel blocks the TFT element Q30 while other pixels on the same power supply wiring PW210 are writing current from the current source circuit 310. When the power supply wiring PW210 is switched to the voltage source circuit 410, the TFT element Q30 is turned on, and the organic EL element EL10 repeats the operation of light emission and non-light emission, so that the light emission time can be secured as much as possible. Become.

  However, while the organic EL element EL10 repeats the light emission and non-light emission operations, the voltage in the pixel is applied to the organic EL element EL10 while the switch of the TFT element Q30 is cut off. It approaches to be equal to the common voltage 510 on the cathode side. For this reason, when the TFT element Q30 is turned on after switching from the current source circuit 310 to the voltage source circuit 410, a potential difference between the common voltage 510 and the power supply wiring PW210 is generated. Overshoot current) flows for a moment.

  When the current setting operation and the light emission operation are repeated a plurality of times within a predetermined period, if the period of repeating this light emission and non-light emission becomes long, the overshoot current is switched to the switch state (conduction, cutoff or these of each TFT element in the pixel). In the middle state). For this reason, the potential difference between the gate and the source of the TFT element Q10 changes over time with respect to the initially set potential difference, and the light emission luminance of the organic EL element EL10 becomes larger (or smaller) than the setting, which is desired. The brightness of the gray level that has been actually increased (or decreased). As a result, each gradation does not change linearly (or the contrast deteriorates), causing display unevenness in an image such as a moving image.

  In order to solve the above problem, for example, if the on-switching time of the gate signal Ei110 is moderately (extended) so that the voltage from the voltage source circuit 410 gradually enters the pixel, the overshoot current is reduced. Can be prevented. However, although the on-switching time depends on the potential difference between the pixel and the power supply wiring PW210, an error due to waveform rounding occurs due to the wiring load of the capacitance / resistance existing in the gate signal Ei110, so that overshoot does not occur. It is expected that it is difficult to control the set sweep waveform by applying it to the gate voltage. In addition, there is a method of newly inserting a resistor in order to give a signal propagation delay, but this is not preferable because power consumption is increased accordingly.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a display device having a pixel circuit configuration that supplies a current having a set value to an electro-optical element, and has a desired luminance. An object of the present invention is to provide a display device capable of obtaining a linear gradation and smoothly displaying a moving image or the like.

In order to solve the above problems, a display device according to the present invention sets a value of a current supplied to each electro-optical element to each pixel including the electro-optical element, and drives the electro-optical element with the current value. In the apparatus, each pixel has a first wiring for supplying the current to the electro-optical element and a path for supplying a current from the first wiring to the electro-optical element in series with the electro-optical element. A first active element that is inserted and has a control terminal for conduction resistance; and a first active element that is inserted in series with the electro-optic element and the first active element in the path and has a control terminal for conduction / cutoff. 2 active elements and a first charge holding unit that applies charges to the control terminal of the first active element as a control voltage for the conduction resistance of the first active element. And a third stage inserted on the charge supply path for the first charge holding means and having a control terminal for conduction / cutoff, and holds the charge accumulated in the first charge hold means by the cutoff. An active element, a second wiring that applies a control voltage for conduction / cutoff to the control terminal of the second active element, and a control voltage for conduction / cutoff are applied to the control terminal of the third active element. A second charge holding means in which one is connected between the third wiring and the first active element and the second active element, and the other is connected to the fourth wiring for applying a constant voltage; The constant current source circuit and the constant voltage source circuit are switchably connected to the first wiring, and the constant current source circuit and the constant voltage source circuit are switched during the light emission period of the electro-optical element. as characterized by repeating the That.

  According to the above configuration, in each pixel, when the second and third active elements are turned on by applying a control voltage from the second and third wirings to the control terminal, the first active line is connected to the first active line. The electric current of a predetermined value can be supplied to the electro-optical element through the element. At this time, if the charge corresponding to the current value is accumulated in the first charge holding means, and then the third active element is cut off by applying the control voltage from the third wiring, The first charge holding means holds the charge so that a control voltage is applied to the control terminal of the first active element such that a current of value is supplied to the first active element. Accordingly, the value of the current supplied to the electro-optical element can be set thereby.

  If the second active element is cut off by applying a control voltage from the second wiring, the current supplied to the electro-optic element can be cut off while the first charge holding unit holds the charge. . In this cutoff period, for example, the value of the current supplied to the electro-optical element in another pixel connected to the same first wiring can be set. If the current value of the electro-optical element is set in each pixel in this way and the second active element is turned on again, the electro-optical element can be driven with the set current.

  In addition, a second charge holding means is arranged in which one is connected between the first active element and the second active element, and the other is connected to a fourth wiring for applying a constant voltage. As a result, the voltage change between the first active element and the third active element when the second active element is turned on again becomes gentle, and the overshoot current can be reduced.

  Thereby, it is possible to avoid malfunctioning of the switch state of each active element in the pixel. Further, the initially set potential difference between the gate and source of the first active element is held so as to be substantially constant regardless of the passage of time. Therefore, the electro-optic element can emit light with a desired gradation of luminance, and can obtain a linear gradation. As a result, there is an effect that a moving image or the like can be displayed smoothly.

  The electro-optical element means an element whose light emission amount is controlled in accordance with the amount of electric charge (current amount) supplied to the element. Examples of the electro-optical element include an organic EL element, LED (Light Emitting Diode), and FED (Field Emission Display).

  The active element means an element that is used for controlling a current (switching between current conduction and interruption) and can change a conduction resistance supplied to the element. Examples of the active element include a diode element, a MIM (metal insulator metal) element, and a thin film transistor (TFT). Of these, TFT elements having excellent switching characteristics are preferably used.

In the display device according to the present invention, the first wiring as compared with the case where connecting a current source circuit and a voltage source circuit because the are that is connected switching to the individual wiring as in the prior art Thus, the number of TFT elements and the number of wirings in the pixel can be reduced. As a result, the yield of TFT elements and the like can be improved, and luminance gradation can be accurately displayed. The current source circuit means a circuit that can always supply a current set to a certain value. The voltage source circuit means a circuit that can continuously apply a voltage set to a certain value.

  In the display device according to the aspect of the invention, the voltage source circuit is connected after the first operation of connecting the current source circuit to the first wiring and setting the value of the current supplied to the electro-optic element to each pixel. A second operation is performed to connect the first wiring and supply the current of the value set in the first operation to the electro-optic element of each pixel, and the current source circuit can output the second operation. There are a plurality of current values, and it is preferable to perform the first operation and perform the second operation after the first operation a plurality of times in a predetermined period.

  According to the above configuration, the current value of the electro-optic element can be set in each pixel by the current from the current source circuit by the first operation, and then set by the first operation by the second operation. The electro-optical element can be driven by supplying a current having a value obtained from the voltage source circuit to the electro-optical element.

  Further, according to the above configuration, the type of current value of the electro-optic element that can be set for each pixel by the first operation, that is, the type of current value that can be output from the current source circuit is more than the set number of gradations. Even if there are cases where the number is limited, it is possible to perform multi-gradation display as follows. That is, performing the first operation and performing the second operation after the first operation are performed a plurality of times in a predetermined period. This is equivalent to performing the current setting operation + the light emission operation a plurality of times within a predetermined period. Accordingly, it is possible to ensure gradation display that is finer than the number of current values of the current source circuit according to the total length of the periods in which current is supplied to the electro-optical element in a predetermined period.

  In particular, when the current source circuit connected to the first wiring is made of a TFT or the like, the number of current values that can be output from the current source circuit is limited, that is, the number of output current values is The gradation display of the present invention is effective because it is often limited to an integer value of 2 or more including zero.

  In the display device according to the present invention, it is preferable that the third wiring and the fourth wiring are the same wiring. According to said structure, while being able to make a pixel high-definition, an aperture ratio can be improved.

The display device according to the reference of the present invention, in order to solve the above problem, by setting the value of the current supplied to each pixel comprising an electro-optical element in the electro-optical element, said current value an electro-optical element In the display device driven by the above, each of the pixels is provided with a first wiring for supplying the current to the electro-optical element and a path for supplying a current from the first wiring to the electro-optical element. A first active element inserted in series with the element and having a control terminal for conduction resistance, and an electro-optic element and the first active element inserted in series in the path, and control for conduction / cutoff A second active element having a terminal, a charge that is accumulated, and a voltage corresponding to the accumulated charge is applied to the control terminal of the first active element as a control voltage for the conduction resistance of the first active element. A charge holding means and a charge supply path for the first charge holding means, and has a control terminal for conduction / cutoff, and holds the charge accumulated in the first charge hold means by being cut off. A third active element; a second wiring for applying a control voltage for conduction / cutoff to the control terminal of the second active element; and a control voltage for conduction / cutoff to the control terminal of the third active element. And a fourth active element in which one is connected between the first active element and the second active element and the other is connected to a fifth wiring for applying a signal voltage And are arranged.

  According to the above configuration, in each pixel, when the second and third active elements are turned on by applying a control voltage from the second and third wirings to the control terminal, the first active line is connected to the first active line. The electric current of a predetermined value can be supplied to the electro-optical element through the element. At this time, if the charge corresponding to the current of the above value is accumulated in the first charge holding means, and then the third active element is cut off by applying the control voltage from the third wiring, the above value can be obtained. The first charge holding means holds the electric charge so that a control voltage is applied to the control terminal of the first active element so that the current is supplied to the first active element. Accordingly, the value of the current supplied to the electro-optical element can be set thereby.

  If the second active element is cut off by applying a control voltage from the second wiring, the current supplied to the electro-optic element can be cut off while the first charge holding unit holds the charge. . In this cutoff period, for example, the value of the current supplied to the electro-optical element in another pixel connected to the same first wiring can be set.

  After that, a fourth active element is arranged in which one is connected between the first active element and the second active element, and the other is connected to the fifth wiring for applying the signal voltage. Then, a voltage is applied from the fifth wiring to cause the electro-optical element to emit light. This operation eliminates the need to repeatedly conduct or cut off the second active element during driving of the electro-optic element, thereby eliminating the problem that the overshoot current repeatedly occurs over a long period of time.

  Thereby, it is possible to avoid malfunctioning of the switch state of each active element in the pixel. Further, the initially set potential difference between the gate and source of the first active element is held so as to be substantially constant regardless of the passage of time. Therefore, the electro-optic element can emit light with a desired gradation of luminance, and can obtain a linear gradation. As a result, there is an effect that a moving image or the like can be displayed smoothly.

  The electro-optical element means an element whose light emission amount is controlled in accordance with the amount of electric charge (current amount) supplied to the element. Examples of the electro-optical element include an organic EL element, LED (Light Emitting Diode), and FED (Field Emission Display).

  The active element means an element that is used for controlling a current (switching between current conduction and interruption) and can change a conduction resistance supplied to the element. Examples of the active element include a diode element, a MIM (metal insulator metal) element, and a thin film transistor (TFT). Of these, TFT elements having excellent switching characteristics are preferably used.

In the display device according to the reference of the present invention , the fourth active element is preferably a diode element or a thin film transistor having a conduction / cutoff control terminal connected to the fifth wiring.

  According to the above configuration, the fourth active element and the fifth wiring can be used as a power supply for the electro-optical element. In this case, current leakage to the outside of the pixel can be prevented when setting the value of the current supplied to the electro-optical element. Further, when driving the electro-optical element, a predetermined current can be spontaneously supplied to the electro-optical element. As a result, generation of overshoot current can be eliminated.

  Further, the thin film transistor having the conduction / interruption control terminal connected to the fifth wiring has the gate terminal wired so as to have the same function as the diode element. For this reason, generation of overshoot current can be eliminated as in the case of the diode element.

In the display device according to the reference of the present invention , it is preferable that a current source circuit is connected to the first wiring, and a signal voltage applied from the fifth wiring is used as a voltage source of the electro-optical element. Further, in the display device according to the reference of the present invention , after performing the third operation for setting the value of the current supplied to the electro-optic element to each pixel, the signal voltage applied from the fifth wiring is used. In addition, it is preferable that the fourth operation for supplying the current of the value set in the third operation to the electro-optical element of each pixel is performed.

  According to the above configuration, since the current source circuit is connected to the first wiring, the current value of the electro-optic element can be set in each pixel by the current from the current source circuit by the third operation. . In addition, since the signal voltage applied from the fifth wiring is used as the voltage source of the electro-optic element, the fourth operation is performed after the third operation, so that the current of the value set in the third operation is obtained. Can be supplied to the electro-optical element from the fifth wiring to drive the electro-optical element. The current source circuit means a circuit that can always supply a current set to a certain value.

In the display device according to the reference of the present invention , it is preferable that the fourth active element is a p-channel or n-channel thin film transistor, and the fifth wiring and the second wiring are the same wiring.

  According to the above configuration, when the fourth active element is a p-channel or n-channel thin film transistor and the fifth wiring and the second wiring are the same wiring, one wiring becomes unnecessary, and the pixel The aperture ratio can be improved.

  In the display device according to the present invention, it is preferable that a precharge circuit is connected to the first wiring. According to the above configuration, the time for writing current to the pixel can be shortened and desired current writing can be performed more reliably, so that a moving image or the like can be expressed more smoothly.

  In the display device according to the present invention, the pixel preferably has a top emission structure. According to the above configuration, luminance gradation can be accurately displayed while improving the display life of the electro-optic element.

In the display device according to the present invention, as described above, each pixel is supplied with the first wiring for supplying the current to the electro-optical element and the current from the first wiring to the electro-optical element. A first active element inserted into the path in series with the electro-optic element and having a control terminal for conduction resistance, and inserted into the path in series with the electro-optic element and the first active element and conducted. A second active element having a control terminal for blocking / blocking, and a control terminal of the first active element using a voltage corresponding to the stored charge as a control voltage for the conduction resistance of the first active element. A first charge holding means to be applied to the first charge holding means and a charge supply path for the first charge holding means, and has a control terminal for conduction / cutoff. A third active element that holds the generated charge, a second wiring that applies a control voltage for conduction / cutoff to the control terminal of the second active element, and a conduction / conduction to the control terminal of the third active element. One is connected between the third wiring for applying the control voltage for blocking and the first active element and the second active element, and the other is connected to the fourth wiring for applying a constant voltage. A second charge holding means , a constant current source circuit and a constant voltage source circuit are switchably connected to the first wiring, and the constant current source circuit is connected during the light emission period of the electro-optical element. And switching between the constant voltage source circuit is repeated .

In the display device according to the reference of the present invention, as described above, each pixel has a first wiring for supplying the current to the electro-optical element, and the first wiring to the electro-optical element. A first active element that is inserted in series with the electro-optical element in a path for supplying current and that has a control terminal for conduction resistance is inserted in series with the electro-optical element and the first active element in the path. And a second active element having a control terminal for conduction / cut-off, and a first active element using the voltage corresponding to the accumulated charge as a control voltage for the conduction resistance of the first active element. First charge holding means to be applied to the control terminal of the element, and inserted on the charge supply path to the first charge holding means, and has a control terminal for conduction / cutoff. A third active element for holding the charge accumulated in the holding means; a second wiring for applying a control voltage for conduction / cutoff to the control terminal of the second active element; and control of the third active element One is connected between the third wiring for applying the control voltage for conduction / cutoff to the terminal and the first active element and the second active element, and the other is connected to the fifth wiring for applying the signal voltage. Is connected to the fourth active element.

  Thereby, the overshoot current can be relaxed or eliminated. Therefore, the electro-optic element can emit light with a desired gradation of luminance, and can obtain a linear gradation. As a result, there is an effect that a moving image or the like can be displayed smoothly.

  Hereinafter, the present invention will be described in detail with reference to various embodiments.

As each switching element used in the present invention, a diode, MIM (Metal Insulator Metal), amorphous silicon TFT, polycrystalline silicon TFT, CG silicon TFT, or the like can be used. Among them, it is preferable to use a polycrystalline silicon TFT or a CG silicon TFT in terms of excellent switching characteristics. In the embodiment described below, a CG silicon TFT will be described as an example. Regarding the CG silicon TFT process, so that it has been published in the Non-Patent Document 2 or the like, the detailed description is omitted here.

  In the following embodiments, an organic EL element will be described as an example of an electro-optical element used in the present invention. Since the configuration of this organic EL element has been announced in Non-Patent Document 3 and the like, detailed description thereof is omitted here.

  In the following embodiment, a display device having a pixel size of 100 PPI (Pixel Per Inch) will be described, but the display device applicable to the present invention is not limited to this.

Further, the form of the display device in the form status Contact and reference of the present invention is described below, is described as an example what pixel size is composed 100PPI (Pixel Per Inch), it is limited to It is not a thing. The display device of this embodiment forms condition Contact and reference embodiment, as shown in FIG. 2, the pixel display part, the selection signal output section (gate portion), the image signal output unit (source unit), a current supply unit, the driving signal It has a generating part. The drive signal generator generates a drive signal for driving the display device, and outputs the drive signal to the selection signal output unit and the image signal output unit. The current supply unit supplies a predetermined current value to the image signal output unit. The selection signal output unit outputs a selection signal to the image display unit based on the drive signal input from the drive signal generation unit. The image signal output unit outputs an image signal corresponding to the current value supplied from the current supply unit to the image display unit based on the drive signal input from the drive signal generation unit. The image display unit includes pixels arranged in an M × N matrix, and displays an image based on signals output from the selection signal output unit and the image signal output unit.

[Form state of implementation]
For implementation of the embodiment of the present invention are described below with reference to FIGS. 1 to 9. FIG. 1 is a circuit diagram showing a pixel circuit Aij (1) of the display device according to the present embodiment. The pixel circuit Aij (1) indicates one pixel, and if there are RGB pixels, indicates one.

  The pixel circuit Aij (1) includes a current-driven organic EL element (electro-optical element) EL11, n-channel (n-type) TFT elements (first active element / third active element) Q11 / Q21, and p-type. TFT element (second active element) Q31, capacitor (first charge holding means) C11, gate wiring (second wiring) Ei111, power supply wiring (first wiring) PW211 and control wiring (third wiring) ) Gi911 is arranged. The n-type TFT element Q21 has an LDD (Lightly Doped Drain) structure with excellent charge retention capability.

  The source terminal of the TFT element Q31 is connected to the power supply wiring PW211. The gate terminal of the TFT element Q31 is connected to the gate wiring Ei111. The TFT element Q11 and the organic EL element EL11 are connected in series on the opposite side of the connection point of the TFT element Q31 with the power supply wiring PW211. The organic EL element EL11 has an anode (using a transparent electrode such as ITO (Indium Tin Oxide)) connected to the TFT element Q11 side, and a cathode (for example, using a metal such as Al-Li) on the side. A common voltage 511 is arranged.

  The capacitor C11 is connected between the gate terminal and the source terminal of the TFT element Q11. The TFT element Q21 is connected between the gate terminal of the TFT element Q11 and the drain terminal of the TFT element Q31. The gate terminal of the TFT element Q21 is connected to the control wiring Gi911. A capacitor C22 is connected between the TFT element Q21, the TFT element Q11, and the TFT element Q31. One of the capacitors (second charge holding means) C22 is connected to a constant voltage wiring (fourth wiring) 611 having a certain voltage. Further, a current source circuit 311 and a voltage source circuit 411 are switchably connected to the power supply wiring PW211.

  Further, a precharge circuit 811 is connected to the power supply wiring PW211. The precharge circuit 811 has a voltage value determined on the gate side of the TFT element Q11 so that a desired current value is supplied to the organic EL element EL11 before the current is written from the current source circuit 311 into the pixel. This is a circuit prepared so that a voltage value is given to the gate of the TFT element Q11 and the current writing time in the pixel can be shortened.

  Further, a non-light emitting voltage source for applying a non-light emitting voltage is arranged on the gate terminal side of the TFT element Q11 in order to cause the organic EL element EL11 to emit no light for a predetermined period (not shown). The non-light emitting voltage source is connected to the power supply wiring PW211.

  In the present embodiment, the current setting value of the current source circuit 311 is 1.6 μA, the voltage value of the voltage source circuit is 9 V, the voltage of the control wiring Gi911 and the gate wiring Ei111 is 16 V or 0 V, the common voltage is 0 V, and the constant voltage wiring Is set to 0V, and the voltage applied from the precharge circuit is set to 9.4V. However, the setting of the current value, the setting of the voltage value, or the element configuration such as the inner layer, the anode layer, and the cathode layer of the organic EL element is not limited to the above.

  The TFT elements are not limited to the above, and may be either n-type or p-type, but it is preferable that all TFT elements in the pixel are the same type. That is, an ON signal or an OFF signal input from the gate wiring Ei111 or the control wiring Gi911 is changed to a signal voltage that matches the n-type or p-type, or between the gate and the source according to the n-type or p-type of the TFT element Q11. It is necessary to dispose the capacitor C11 on the side and the TFT element Q21 on the side between the gate and the drain. When all the TFT elements in the pixel are of the same type, for example, when all the TFT elements in the pixel are configured as an n-type, a mask for creating a p-type TFT element becomes unnecessary, and thus the cost is reduced. It leads to reduction.

  Next, a driving method of the display device having the above configuration will be described. The brightness of the organic EL element varies depending on the magnitude of the supplied current. For this reason, for example, when the level of current from one output is divided into 256 levels, 256 gradation display can be performed. Therefore, in order to express the set number of gradations, it is conceivable to use the same number of current values as the number of gradations.

  However, since the actual current value is very small, the number of current values that can be achieved due to technical problems may be less than the number of gradations, particularly when the current source circuit is composed of TFT elements. . In order to divide the light emitting element into the light emitting state and the non-light emitting state, two or more current values including zero are required.

  In order to obtain a predetermined number of gradations under such restrictions, for example, the light emission operation is repeated a plurality of times within a predetermined period so as to compensate for the number of insufficient current values, and the number of times is multiplied by the light emission time. It is conceivable to use a time-division gradation method that expresses gradations with weights corresponding to the number of bits.

  For this reason, in order to express a plurality of gradations, the current source circuit has a current value having a plurality of values of at least 2 or more, and in this embodiment, at least to divide into light emission and non-light emission. , So that it has a plurality of values of 2 or more including the case of zero. By setting the current value to a plurality of values along with the number of times of light emission, there is an advantage that circuit design and element drive condition setting are facilitated.

  In other words, the display device of this embodiment is implemented by gradation driving by time division having a binary current value. In order to make the present invention easier to understand, the basic operation of Aij (for one pixel) arranged in an M × N matrix will be described.

In the display device of this embodiment, the current setting operation and the light emission operation (current setting operation + light emission) are performed a plurality of times (in this embodiment, 7 times) within one frame period (1/60 seconds≈16.66 milliseconds). Operation). For example, when a temporal weight (division specific gravity) of 1: 2: 4: 7: 14: 14: 21: 0 is given to the seven operations, the corresponding light emission period is assigned. 0.3: 0.5: 1.1: 1.9: 3.7: 3.7: 5.6: 0. Therefore light emission period including a current write time, although different from the exact time allocation slightly, the current writing time is shorter than the emission period, may not considered because it does not affect the contents of the present invention. The current writing time per allocation is a value obtained by dividing one frame period by the number of pixels and the number of divisions. In the simulation of the present embodiment, the number of pixels is 103 pixels × 103 pixels (7 pixels are dummy pixels), and the current writing time (+ light emission time) is about 20 microseconds.

  In the present embodiment, 64 gradations of 63 gradations + 1 gradation (non-light emission) are expressed by assigning the division specific gravity as shown in FIG. However, in FIG. 3, a desired gradation is obtained on the assumption that no current decrease or increase (luminance decrease or increase) of the organic EL element EL11 occurs during the light emission period (or the current change is close to 0%). In the case where a current change occurs, a change occurs in the values of S1 to S7 representing the amount of apparent light emission luminance described later. Further, the division specific gravity of the gradation expression by the time division is merely an example, and is not limited to this.

  FIG. 4 is a timing chart showing the voltage of each wiring in one time period obtained by dividing one frame period (field period × plurality). In FIG. 4, in order to make the explanation easy to understand, attention is paid to one pixel in the display device. As shown in FIG. 4, when the current set from the current source circuit 311 is supplied while the conduction state of the TFT element Q31 continues in the first field period (current writing period + light emission period), the TFT element Q21. And a gate voltage is written such that a set current is supplied to the TFT element Q11 (first operation). As a result, charges are supplied to the capacitor C11 so that the gate-source voltage of the TFT element Q11 becomes a desired potential.

  After that, until the next current writing period within a predetermined period, the other pixel on the same power supply wiring PW211 is writing current from the current source circuit 311 while the pixel is turned off. Keep it. When the connection of the power supply wiring PW211 is switched to the voltage source circuit 411, the TFT element Q31 is turned on (second operation). Thereby, the organic EL element EL11 repeats the light emission and non-light emission operations.

  As described above, in this embodiment, the current source circuit 311 for writing current to the TFT element Q11 and the voltage source circuit 411 for supplying current to the organic EL element EL11 are unified to the power supply wiring PW211. Yes. That is, since the current source circuit 311 is used during the current writing period, current (voltage from the voltage source circuit 411) is not supplied to the organic EL element EL11 until the pixel that has already been written is switched to the voltage source circuit 411. Therefore, when the voltage source circuit 411 is switched without emitting light, current is supplied to the organic EL element EL11 to emit light.

  The ratio of the current writing time (including other pixels) and the light emission time (all pixel common time) may be any ratio, but in this embodiment, 1: 1 = 10 μm. Second: 10 microseconds is set. If the current writing time is increased, the light emission time is shortened, so that the apparent average luminance is lower than the assignment of 1: 1. Further, when the light emission time is increased, the current writing time is reduced, light is emitted without setting the current value necessary for the in-pixel TFT element Q11, and the light emission varies. For this reason, the ratio between the current writing time (including other pixels) and the light emission time (common time for all pixels) depends on the design conditions such as the number of pixels used in the display device, the load capacity of the TFT elements, the wiring load, and the set current value. It may be appropriately selected depending on the situation.

  Note that it is generally known that an organic EL element has a substantially proportional relationship between a current supplied to the element and light emission luminance. When the ratio of the current writing time (including other pixels) and the light emission time (all pixel common time) is 1: 1, the desired light emission luminance during the light emission period is compared with the pixel configuration shown in FIG. It means to become 1/2. For this reason, for example, when the current setting value of the current source circuit for obtaining a desired light emission luminance is 0.8 μA, in this embodiment, a setting current value of 1.6 μA, which is twice 0.8 μA, is set. I need.

  Here, during the longest light emission period (about 5.6 milliseconds in the above setting), the luminance of the time during which the organic EL element EL11 repeats light emission and non-light emission is averaged (1/2 in the above setting) to emit light. Is ongoing. In this case, if the inside of the pixel is cut off from the outside within 5.6 milliseconds and is not affected by external influences (for example, a sudden change in potential of the power supply wiring PW211), the leakage current of the TFT elements in the pixel, etc. It is considered that the current value supplied to the organic EL element EL11 changes with time almost exponentially due to the influence of the above.

  Therefore, the maximum light emission time in the time division is T (here, about 5.6 milliseconds), the current decrease rate after t time when the current value of the initial light emission is 1, X is the time of the initial light emission. Assuming that the normalized current value is I, I = exp (−kt) and k = ln (1−X) / T. The apparent light emission luminance amount is an integral value S = 1 / k * (1-exp (−kt)) of the current value I, and each gradation is a total value of the integral values S1 to S7 that can be divided into the above seven times. It is represented by Q.

  In the conventional pixel configuration shown in FIG. 14, X is −2.180, and the output current for each gradation is calculated based on the X value using the above-described equation S and gradation assignment shown in FIG. 3. In the present embodiment, the organic EL element EL11 is used, and this output current means output luminance proportional to the current. Based on the calculation result of the output current, the gradation inputted from the display device and the luminance actually outputted from the pixel (normalized with the maximum value of the desired output luminance being 1) are shown in FIG. Thus, a distorted line different from the desired gradation is drawn. For this reason, a moving image cannot be displayed smoothly.

  In the present invention, by providing the capacitor C22, a desired luminance can be obtained. FIG. 6 shows the gate-source potential difference ΔGATE (V) of the TFT element Q11 and the change amount ΔIOLED (%) of the current supplied to the organic EL element EL11 with respect to each capacitance value of the capacitor C22 after the light emission period of 5.6 milliseconds. It is a graph which shows. As shown in FIG. 6, by setting the capacitor C22 to a certain capacitance value or more, ΔGATE generated exponentially after 5.6 milliseconds can be suppressed, and ΔIOLED can be significantly suppressed. . As a result, the X value can be significantly suppressed. For example, when the capacitor C22 is 300 (fF), the X value is −0.040, and the decrease rate is close to 0. Therefore, as shown in FIG. In addition, gradation display can be expressed almost linearly for each gradation. For this reason, it becomes possible to display a moving image etc. smoothly.

Here, the rise of the voltage is expressed by Vo (output voltage) = Vi (input voltage) (1−e ^{−t / RC} ), and greatly depends on the time constant τ = RC. In the present invention, since the capacitor C22 is provided, it is possible to delay the rapid voltage rise (suppress overshoot current). As a result, it is possible to suppress ΔGATE that occurs due to an instantaneous malfunction of the switch state of the TFT element Q11. In addition, when the above malfunction is repeated hundreds of times, it is possible to avoid the problem that ΔGATE becomes a large change and the current supplied to the organic EL element EL11 is greatly deviated from the initial value.

  The capacitor C22 can obtain the effect of suppressing the overshoot current as the capacitance value increases, but cannot sufficiently obtain the suppression effect when the capacitance value is too small. Further, when the capacitance value is too large, the ratio shown in the pixel of the capacitor C22 increases, and there is a problem that the aperture ratio is greatly reduced or high-definition pixel design becomes difficult. For this reason, it is preferable that the capacitance value of the capacitor C22 is 300 fF to 700 fF.

The potential of the control wiring Gi911 is a fixed potential of 0 V during the light emission period. When there is a wiring or the like that applies a constant voltage during such a light emission period, the same effect can be obtained by unifying the constant voltage wiring 611 of FIG. 1 into the control wiring Gi 911 as shown in FIG. Can do. In FIG. 7, the power supply circuit of the constant voltage wiring outside the pixel can be omitted, and the wiring in the pixel can be reduced as compared with the pixel configuration of FIG. 1, and the aperture ratio can be further improved. . For this reason, in the case of the bottom emission structure which takes out the light emission of an organic EL element toward the board | substrate (TFT board | substrate) side in which the TFT element was provided, it can use especially suitably.

  Further, for example, the effect of the present invention can be obtained even in the case of a pixel configuration of a top emission structure in which light emission of the organic EL element is extracted from the opposite side of the TFT substrate as shown in FIG.

  Here, the bottom emission structure is, for example, the structure shown in FIG. The top emission structure is a structure in which the anode and the cathode are reversed in the structure of FIG. However, the structure is not limited to the above two structures. For example, if a transparent electrode is used for the cathode, the bottom emission structure can emit light similar to the top emission structure in which the light emission of the organic EL element is extracted from the opposite side of the TFT substrate. It can be. In this case, compared with the bottom emission structure shown in FIG. 9, the light emission area can be increased (that is, the light emission amount can be increased) by the light emission area of the TFT element, the capacitor, and the like. Thereby, the effect that the lifetime of the light emitting element such as the organic EL element whose lifetime is shortened when the luminance is increased can be increased.

[Reference of form state]
A reference embodiment of the present invention will be described below with reference to FIGS. Figure 10 is a circuit diagram showing a pixel circuit Aij of a display device according to this reference embodiment (2). The pixel circuit Aij (2) indicates one pixel, and if there are RGB pixels, indicates one.

  The pixel circuit Aij (2) includes a current-driven organic EL element (electro-optic element) EL12, n-channel (n-type) TFT elements (first active element / third active element) Q12, Q22, p-channel type (p-type) TFT element (second active element) Q32, capacitor (first charge holding means) C12, gate wiring (second wiring) Ei112, power supply wiring (first wiring) PW212, In addition, a control wiring (third wiring) Gi912 is arranged. The n-type TFT element Q22 has an LDD (Lightly Doped Drain) structure with excellent charge holding capability.

  The source terminal of the TFT element Q32 is connected to the power supply wiring PW212. The gate terminal of the TFT element Q32 is connected to the gate wiring Ei112. The TFT element Q12 and the organic EL element EL12 are connected in series on the side opposite to the connection point between the TFT element Q32 and the power supply wiring PW212. The organic EL element EL12 has an anode (using a transparent electrode such as ITO (Indium Tin Oxide)) side connected to the TFT element Q12 side, and a cathode (for example, using a metal such as Al-Li) side. A common voltage 512 is arranged.

  The capacitor C12 is connected between the gate terminal and the source terminal of the TFT element Q12. The TFT element Q22 is connected between the gate terminal of the TFT element Q12 and the drain terminal of the TFT element Q32. The gate terminal of the TFT element Q22 is connected to the control wiring Gi912. An n-type TFT element (fourth active element) Q42 is connected between the TFT element Q22, the TFT element Q12, and the TFT element Q32. One of the TFT elements Q <b> 42 is connected to a signal wiring (fifth wiring) 712 that transmits a signal that can be turned off during a current writing period into the pixel and can be turned on during a light emission period. The power supply wiring PW212 is connected to the current source circuit 312.

In the arrangement according to this reference embodiment, the signal line 712 also serves as the voltage supply circuit for applying a voltage during light emission of the organic EL element EL 12 is a scanning line. Note that it is necessary to change the voltage so that no current is distributed to the signal wiring 712 (no current leakage) during a current writing period into the pixel. Therefore, the signal wiring 712 is not a voltage source circuit that supplies a constant voltage but a voltage source circuit that operates with a binary voltage.

Further, the power supply wiring PW212, on purpose likewise form of the above-described precharge circuit 812 is connected. Further, the shape on purpose likewise the above embodiment, the organic EL element EL 12 to be a predetermined period emission, are arranged non-emission voltage source for applying a non-light emission voltage to the gate terminal of the TFT element Q12 ( Not shown). The non-light emitting voltage source is connected to the power supply wiring PW212.

The TFT element Q42 is not particularly limited as long as an element capable of supplying a desired current to only one in the same direction as the direction of the current supplied to the organic EL element EL 12. As an element satisfying this condition, a diode element or an element having the same function as the diode element can be preferably used. In the present embodiment, the gate terminal of the TFT element Q42 is connected to the signal wiring 712, thereby providing the same function as the diode element.

The driving method of the display device in the present reference embodiment employs a shape on purpose similar time division gray scale driving method described above. Also in the present reference, is carried out in gradation driving by time division with a current value of the binary, where since the similarly performed on the gray scale expression method (division method) form also performed on purpose its Description is omitted.

In this reference embodiment, 0.8Myuei the current setting value of the current source circuit 312, the control wire Gi912, the voltage of the gate wiring Ei112 and the signal wiring 712 16V or 0V, the voltage applied to the common voltage 0V, the precharge circuit Is set to 8.4V. However, the setting of the current value, the setting of the voltage value, or the element configuration such as the inner layer, the anode layer, and the cathode layer of the organic EL element is not limited to the above.

  The TFT elements are not limited to the above, and may be either n-type or p-type, but it is preferable that all TFT elements in the pixel are the same type. That is, an ON signal or an OFF signal input from the gate wiring Ei112 or the control wiring Gi912 is changed to a signal voltage that matches n-type or p-type, or between the gate and source according to the n-type or p-type of the TFT element Q12. It is necessary to dispose the capacitor C12 on the side and the TFT element Q22 on the side between the gate and the drain. When all the TFT elements in the pixel are of the same type, for example, when all the TFT elements in the pixel are configured as an n-type, a mask for creating a p-type TFT element becomes unnecessary, and thus the cost is reduced. It leads to reduction.

  Next, a driving method of the display device having the above configuration will be described. In the present embodiment, in order to make it easier to understand, a description will be given focusing on the basic operation of the pixels Aij (for one pixel) arranged in an M × N matrix.

  FIG. 11 is a timing chart showing the voltage of each wiring in one time period obtained by dividing one frame period (field period × plurality). In FIG. 11, for ease of explanation, attention is paid to one pixel in the display device. As shown in FIG. 11, when the current set from the current source circuit 312 is supplied while the conduction state of the TFT element Q32 continues in the first field period (current writing period + light emission period), the TFT element Q22. And a gate voltage is written such that a set current is supplied to the TFT element Q12 (third operation). Thereby, charges are supplied to the capacitor C12 so that the gate-source voltage of the TFT element Q12 becomes a desired potential.

  Thereafter, the switch of the TFT element Q22 and the switch of the TFT element Q32 are cut off, and the voltage set in the pixel is supplied to the TFT element Q42 by setting the voltage of the signal wiring 712 to a HIGH voltage (16V). The determined potential is applied to the drain side of the TFT element Q12 (fourth operation). Thus, by using the voltage applied to the drain side of the TFT element Q12 as the power source of the voltage source circuit of the organic EL element EL12, the current set in the pixel is supplied to the organic EL element EL12, and the organic EL The element EL12 emits light.

  Here, as shown in the timing chart of FIG. 11, the TFT element Q32 during the light emission period is continuously in the OFF state. For this reason, a constant voltage corresponding to the set current is applied from the signal wiring 712 during the light emission period, and the organic EL element EL12 continues to emit light regardless of the current writing period to other pixels. As a result, it is possible to avoid the occurrence of the overshoot current itself, which has been regarded as a conventional problem.

It is also in the present reference, if you deliberately same form of embodiment calculates the X value, X value to obtain substantially the same luminance as desired luminance since become -0.065, the reduction ratio is close to 0 In addition, gradation display can be expressed almost linearly for each gradation. For this reason, it becomes possible to display a moving image etc. smoothly.

Further, it is generally known that the display life of an organic EL element is shortened as light is emitted by increasing the current supplied to the element (or the luminance of the element). In this reference embodiment, as compared to the pixel configuration of a conventional pixel configuration and implementation form status of, since it is the emission intensity of the appearance to decrease the value of current supplied even if the same, the lifetime of the organic EL device This is a preferred mode for a display device. Note that the display life referred to here means the time until the luminance is halved from the initial luminance.

Note that in the present reference embodiment uses an n-type TFT device as TFT elements Q42, it is also possible to use a p-type. When the TFT element Q42 is p-type, the gate line of the TFT element Q42 may be connected to the TFT element Q12 side.

  Further, the potential of the gate wiring Ei112 is 0V during the period of writing current in the pixel and 16V during the light emission period in accordance with the switching characteristics of the p-type TFT element Q32. Same signal voltage operation. Therefore, the direction of the current supplied to the TFT element Q42 having the same function as that of the diode is made the same as the direction of the current supplied to the organic EL element EL12, and the organic EL element EL12 can emit light during the light emission period. When there is another signal line (here, the gate line Ei112) that can be set to such a high potential (here, 16V), for example, as shown in FIG. 12, the signal line 712 used in the n-type TFT element Q42 is used. May be unified to the gate wiring Ei112, and an equivalent effect can be obtained.

  Further, in FIG. 12, a circuit for sending a signal of the signal wiring outside the pixel can be omitted, and the wiring in the pixel can be reduced as compared with FIG. 10, and the aperture ratio can be further improved. For this reason, in the case of the bottom emission structure which takes out the light emission of an organic EL element toward the board | substrate (TFT board | substrate) side in which the TFT element was provided, it can use especially suitably.

Further, for example, it can be obtained effects from the opposite side of the TFT substrate in the case of a pixel structure of a top emission structure in which light is extracted in the organic EL device to the outside as shown in FIG. 13.

  Even in the case of the pixel configuration of the top emission structure, the direction of the current supplied to the p-type TFT element Q42 having the same function as the diode and the direction of the current supplied to the organic EL element Q42 are made the same. When the potential can be lowered so that the organic EL element Q42 can emit light during the light emission period, the gate wiring Ei112 and the signal wiring can be shared.

Further, the shape on purpose likewise the above embodiment, using a transparent electrode as a cathode, capable of emitting the same top emission is taken out from the opposite side of the TFT substrate light emission of the organic EL element to the outside at a bottom emission structure structure It can be.

  In this case, compared with the bottom emission structure shown in FIG. 9, the light emission area can be increased (that is, the light emission amount can be increased) by the light emission area of the TFT element. Thereby, the effect that the lifetime of the light emitting element such as the organic EL element whose lifetime is shortened when the luminance is increased can be increased.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  As described above, in the display device according to the present invention, the capacitor, the diode element, the TFT element, or the like for suppressing the overshoot current is arranged in each pixel. Therefore, the display device according to the present invention can obtain a linear gradation having a desired luminance and can smoothly display a moving image or the like.

  Therefore, the present invention can be suitably used in an industrial field for manufacturing an organic EL display, an FED display, or the like provided with an electro-optical light emitting element and an industrial field for manufacturing the component.

It is an equivalent circuit diagram showing one pixel portion of a display device according to the shape condition of the present invention. A schematic configuration of a display device according to the shape condition Contact and reference to the embodiment of the present invention is a block diagram showing. Is a diagram illustrating a dividing density method gradations for representing 64 gradations display time division gray scale according to the shape condition of the present invention. 2 is a timing chart in the pixel configuration shown in FIG. 1. It is a graph which shows the output luminance in the pixel configuration shown in FIG. 1 and the output luminance in the conventional pixel configuration. 10 is a graph showing a gate-source potential difference ΔGATE (V) of a TFT element Q11 and a change amount ΔIOLED (%) of a current supplied to the organic EL element. FIG. 3 is an equivalent circuit diagram when the control wiring Gi911 and the constant voltage wiring 611 shown in FIG. 1 are unified. Pixel structure of a display device according to the shape condition of the present invention, an equivalent circuit diagram showing a pixel portion in the case of a top emission structure. Pixel structure of the display device in the form status Contact and reference to the embodiment of the present invention, a cross-sectional view of a case of a bottom emission structure. FIG. 10 is an equivalent circuit diagram showing one pixel portion of a display device according to a reference embodiment of the present invention. 11 is a timing chart in the pixel configuration shown in FIG. 10. FIG. 11 is an equivalent circuit diagram when the gate wiring Ei112 and the signal wiring 712 shown in FIG. 10 are unified. FIG. 11 is an equivalent circuit diagram showing one pixel portion when the pixel configuration of the display device according to the reference embodiment of the present invention is a top emission structure. It is an equivalent circuit diagram which shows the 1 pixel part of the conventional display apparatus. It is another equivalent circuit diagram which shows the 1 pixel part of the conventional display apparatus. FIG. 15 is a timing chart of one pixel portion in the display device of FIG.

Aij (1), Aij (2) Pixel circuit (pixel)
EL11, EL12 Organic EL element (electro-optic element)
Q11, Q12 TFT element (first active element)
Q21, Q22 TFT element (third active element)
Q31, Q32 TFT element (second active element)
Q42 TFT element (fourth active element)
C11, C12 capacitors (first charge holding means)
C22 capacitor (second charge holding means)
Ei111, Ei112 Gate wiring (second wiring)
PW211, PW212 Power supply wiring (first wiring)
Gi911, Gi912 control wiring (third wiring)
311, 312 Current source circuit 411, 412 Voltage source circuit 611 Constant voltage wiring (fourth wiring)
712 Signal wiring (5th wiring)
811 and 812 precharge circuit

Claims (5)

In a display device that sets a value of a current supplied to the electro-optic element to each pixel including the electro-optic element, and drives the electro-optic element with the current value.
In each of the above pixels,
A first wiring for supplying the current to the electro-optic element;
A first active element inserted in series with the electro-optic element in a path for supplying a current from the first wiring to the electro-optic element, and having a conduction resistance control terminal;
A second active element inserted into the path in series with the electro-optic element and the first active element and having a control terminal for conduction / cutoff;
First charge holding means for accumulating electric charge and applying a voltage corresponding to the accumulated electric charge as a control voltage for the conduction resistance of the first active element to a control terminal of the first active element;
A third active element that is inserted on the charge supply path for the first charge holding means and has a control terminal for conduction / cutoff, and holds the charge accumulated in the first charge holding means by being cut off; ,
A second wiring for applying a control voltage for conduction / cutoff to the control terminal of the second active element;
A third wiring for applying a control voltage for conduction / cutoff to the control terminal of the third active element;
A second charge holding means having one connected between the first active element and the second active element and the other connected to a fourth wiring for applying a constant voltage ;
A constant current source circuit and a constant voltage source circuit are switchably connected to the first wiring, and switching between the constant current source circuit and the constant voltage source circuit is repeated during the light emission period of the electro-optic element. Characteristic display device. In a display device that sets a value of a current supplied to the electro-optic element to each pixel including the electro-optic element, and drives the electro-optic element with the current value.
In each of the above pixels,
A first wiring for supplying the current to the electro-optic element;
A first active element inserted in series with the electro-optic element in a path for supplying a current from the first wiring to the electro-optic element, and having a conduction resistance control terminal;
A second active element inserted into the path in series with the electro-optic element and the first active element and having a control terminal for conduction / cutoff;
First charge holding means for accumulating electric charge and applying a voltage corresponding to the accumulated electric charge as a control voltage for the conduction resistance of the first active element to a control terminal of the first active element;
A third active element that is inserted on the charge supply path to the first charge holding means and has a control terminal for conduction / cutoff, and holds the charge accumulated in the first charge holding means by being cut off; ,
A second wiring for applying a control voltage for conduction / cutoff to the control terminal of the second active element;
A third wiring for applying a control voltage for conduction / cutoff to the control terminal of the third active element;
A second charge holding means having one connected between the first active element and the second active element and the other connected to a fourth wiring for applying a constant voltage;
A current source circuit and a voltage source circuit are switchably connected to the first wiring,
After the first operation of connecting the current source circuit to the first wiring and setting the value of the current supplied to the electro-optic element to each pixel, the voltage source circuit is connected to the first wiring, A second operation for supplying a current having a value set in the first operation to the electro-optical element of each pixel is performed;
There are multiple current values that the current source circuit can output,
A display device characterized by performing the first operation and performing the second operation after the first operation a plurality of times in a predetermined period. In a display device that sets a value of a current supplied to the electro-optic element to each pixel including the electro-optic element, and drives the electro-optic element with the current value.
In each of the above pixels,
A first wiring for supplying the current to the electro-optic element;
A first active element inserted in series with the electro-optic element in a path for supplying a current from the first wiring to the electro-optic element, and having a conduction resistance control terminal;
A second active element inserted into the path in series with the electro-optic element and the first active element and having a control terminal for conduction / cutoff;
First charge holding means for accumulating electric charge and applying a voltage corresponding to the accumulated electric charge as a control voltage for the conduction resistance of the first active element to a control terminal of the first active element;
A third active element that is inserted on the charge supply path to the first charge holding means and has a control terminal for conduction / cutoff, and holds the charge accumulated in the first charge holding means by being cut off; ,
A second wiring for applying a control voltage for conduction / cutoff to the control terminal of the second active element;
A third wiring for applying a control voltage for conduction / cutoff to the control terminal of the third active element;
One is connected between the first active element and the second active element;
A second charge holding unit having the other connected to the third wiring for applying a constant voltage as the blocking control voltage during the light emission period of the electro-optic element;
A constant current source circuit and a constant voltage source circuit are switchably connected to the first wiring, and switching between the constant current source circuit and the constant voltage source circuit is repeated during the light emission period of the electro-optic element. Characteristic display device. Display device according to any one of claims 1 to 3, characterized in that the precharge circuit is connected to the first wiring. The pixel is a display device according to claims 1, wherein in any one of 3 to be a top emission structure.

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