JP5016953B2 - Display element drive circuit and image display device - Google Patents

Description

  The present invention relates to a display element driving circuit for driving a display element such as an organic electroluminescence (EL) element and an image display apparatus using the same.

  Conventionally, an active-matrix (hereinafter referred to as AM) type organic EL display has been studied as a light-emitting display device having pixels composed of organic EL elements and drive circuits in a matrix.

  FIG. 23 shows the configuration of the pixel, and FIG. 24 shows the configuration of the AM type organic EL display. In the AM type organic EL display, gradation control is performed by controlling the emission intensity.

  It has been pointed out that the voltage-luminescence characteristics of organic EL elements change with time, and that there are variations in the characteristics of thin film transistors (Thin-Film-Transistors, hereinafter referred to as TFTs) used in driving circuits. Therefore, in order to realize a display without variations, it is necessary to use a drive circuit and a drive method that are not easily affected by changes in the characteristics of organic EL elements over time and variations in TFT characteristics.

  As a first technique for solving this problem, a drive circuit shown in FIG. 25 has been proposed (for example, Patent Document 1). The variation in TFT characteristics can be regarded as a variation in threshold value and mobility. In the first technique, a current is supplied from the outside to the TFT (Tr1) in which the gate and the drain in the drive circuit are short-circuited. By doing so, the gate of the TFT can be set to a voltage through which an external current flows according to the threshold value and mobility of the TFT.

  Thereafter, if the current path is directed to the organic EL element LED1 after the gate voltage is held, the voltage between the gate and the source of the TFT becomes the same as the voltage at which an external current flows. Therefore, the TFT functions as a current source that supplies a constant current having the same magnitude as the current from the outside, and can pass a current having the same magnitude as the current from the outside to the organic EL element.

  Therefore, in the first technique, if there is no variation in the current from the outside, a constant current can be supplied to the organic EL element regardless of variations in TFT characteristics, and display without variation is possible.

  As a second technique for solving the above-described problem, a drive circuit shown in FIG. 26 has been proposed (Patent Document 2). The second technique includes a voltage comparator (CMP) and a switch TFT (Tr1) in which the output of the voltage comparator is connected to the gate, and the source and drain are connected to the power source and the organic EL element LED1.

In the second technique, after a reference analog voltage is held at the input of the voltage comparator, a sweep voltage in an appropriate range is sequentially applied. The voltage comparator outputs a high level (low level) voltage when the sweep voltage is higher (lower) than the reference voltage, and the switch TFT is turned on (OFF), so that the voltage application to the organic EL element is controlled on / off. can do. Therefore, the light emission time of the organic EL element can be controlled by the applied waveform of the sweep voltage, and multi-gradation display is possible.
JP-T-2002-517806 JP 2003-223136 A

  Currently, the current-luminance characteristics of the organic EL element are improved, and the supply current to the organic EL element is decreasing. Therefore, particularly in the case of a low current corresponding to a low gradation, in the first prior art, the gate of the TFT in the drive circuit is connected to a voltage at which an external current flows according to the threshold value and mobility of the TFT. It takes time to perform the operation, and it is difficult to apply to a large screen display device.

  On the other hand, in the second conventional technique, a voltage is applied to the organic EL element by the switching TFT in the drive circuit.

  An object of the present invention is to provide a display element drive circuit that can be applied to a large-screen image display apparatus and can also cope with the deterioration of the voltage-luminance characteristics of the display element, and an image display apparatus using the same. There is to do.

  The driving circuit according to the present invention includes a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element. And a period. The display device driving circuit includes a current source circuit for supplying a constant current to the display element and a control circuit for controlling a time for supplying the constant current from the current source circuit to the display element. .

  The current source circuit includes a holding circuit that holds a value corresponding to a constant current supplied to the display element in the first period. Further, the control circuit controls a time for supplying a constant current from the current source circuit to the display element in the third period in accordance with the gradation voltage supplied in the second period.

The gist of the first aspect of the present invention is that a first period for setting a current to be supplied to a display element, a second period for setting a gradation of the display element, and a drive current to the display element. A drive circuit for performing drive control including a third period for supply,
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor; a capacitor element having one end connected to the gate of the third transistor and the other end connected to a wiring; A control circuit in which the light emission time of the display element is controlled by controlling the second transistor in a period of 3,
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor and the threshold voltage of the third transistor are accumulated,
In the third period, an ON voltage is applied to the gate of the second transistor, and an ON time of the second transistor is controlled by applying a sweep voltage to the capacitor. It is characterized by.

According to a second aspect of the present invention, a first period for setting a current to be supplied to a display element, a second period for setting a gradation of the display element, and a driving current for the display element are provided. A drive circuit for performing drive control including a third period for supply,
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor; a capacitor element having one end connected to the gate of the third transistor and the other end connected to a wiring; A control circuit for controlling a light emission time of the display element by controlling the second transistor during a period of 3,
After a certain voltage is applied from the wiring in the second period, a gradation voltage is applied, and the capacitor element has a charge based on a difference between the gradation voltage and the threshold voltage of the third transistor. Accumulated,
In the third period, a voltage that turns on the second transistor through the third transistor is applied to the gate of the second transistor, and then a sweep voltage is applied to the capacitor element, whereby the second transistor is turned on. The on-time of the second transistor is controlled.

According to a third aspect of the present invention, there is provided a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element. In a display element drive circuit having a period of
A current source circuit having a first transistor and a holding circuit for holding the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor connected in series with the first transistor; a capacitor element having one end connected to the gate of the second transistor and the other end connected to a wiring; and in the third period A control circuit for controlling a light emission time of the display element by controlling the second transistor;
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor element and the gate voltage of the second transistor are accumulated,
The on-time of the second transistor is controlled by applying a sweep voltage to the capacitor in the third period.

According to a fourth aspect of the present invention, there is provided a first period for setting a current supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element. In a display element drive circuit having a period of
A current source circuit having a first transistor and a holding circuit for holding the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor connected in series with the current source circuit and connected in parallel with the display element, and a capacitor element having one terminal connected to the gate of the second transistor and the other end connected to a wiring And a control circuit for controlling a light emission time of the display element by controlling the second transistor in the third period,
A constant voltage is applied from the wiring during the first period;
In the second period, a gradation voltage is applied from the wiring, the gate of the second transistor and one terminal are short-circuited, and the capacitor element has a gradation voltage and a gate of the second transistor. Charge based on the difference from the voltage is accumulated,
The on-time of the second transistor is controlled by applying a sweep voltage in the third period.

The fifth aspect of the present invention is that a first period for setting a current to be supplied to a display element, a second period for setting a gradation of the display element, and a drive current to the display element. A drive circuit for performing drive control including a third period for supply,
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor, a capacitor having one end connected to the gate of the third transistor and the other end connected to the wiring through a switch; A control circuit that controls the light emission time of the display element by controlling the second transistor in the third period,
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor and the threshold voltage of the third transistor are accumulated,
In the third period, an ON voltage is applied to the gate of the second transistor, and an ON time of the second transistor is controlled by applying a sweep voltage to the capacitor. It is characterized by.

  Another image display apparatus according to the present invention is characterized in that the drive circuits and display elements according to the first to fifth aspects of the present invention are arranged in a matrix on a substrate.

Another display element drive circuit according to the present invention is the drive circuit according to any one of the first to fifth aspects of the present invention, comprising a current source in the control circuit,
The current source supplies the charge to one end of the capacitive element or removes the charge to form the sweep voltage in the control circuit.

  In another drive circuit for a display element according to the present invention, in the drive circuit according to the first to fourth inventions, in the second transistor, the constant current is a current in a subthreshold region, The off current is 0.1% or less of the constant current.

In another display element driving circuit according to the present invention, a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, A third period for supplying a driving current to the display element,
A current source circuit having a holding circuit for holding a value corresponding to a constant current supplied to the display element in the first period, and the third period in accordance with the gradation voltage supplied in the second period. And a control circuit for controlling a time for supplying a constant current from the current source circuit to the display element,
The current source circuit includes at least a first transistor,
In the control circuit, a source and a drain are connected in series between the current source circuit and the display element, a gate is connected to one end of a capacitive element directly or via a switch, and the constant current is A second transistor having a gate voltage-drain current characteristic in a subthreshold region and having an off-current of 0.1% or less of the constant current;
In the third period, a constant current is supplied to the display element by changing the gate voltage of the second transistor over time and controlling the time during which the source and drain of the second transistor are turned on. It is characterized by controlling the time to perform.

In another display element driving circuit according to the present invention, a first period for setting a current supplied to the display element, a second period for setting a gradation of the display element, and driving the display element A third period for supplying current;
A current source circuit having a holding circuit for holding a value corresponding to a constant current supplied to the display element in the first period, and the third period in accordance with the gradation voltage supplied in the second period. And a control circuit for controlling a time for supplying a constant current from the current source circuit to the display element,
The current source circuit includes at least a first transistor,
In the control circuit, the display element and the source / drain are connected in parallel to the current source circuit, the gate is connected to one end of the capacitor element directly or via a switch, and the constant current is gate voltage-drain. A second transistor having a sub-threshold region of current characteristics and having an off-current of 0.1% or less of the constant current;
In the third period, a constant current is supplied to the display element by changing the gate voltage of the second transistor over time and controlling the time during which the source and drain of the second transistor are turned off. It is characterized by controlling the time to perform.

  According to the present invention, it is possible to provide a novel driving circuit that can be applied to a large-screen image display device and can reduce a change in luminance due to deterioration of voltage-luminance characteristics of a display element.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. In the following embodiments, an example in which an organic EL element is used will be described. However, the present invention is not limited to the organic EL element, and can be applied to driving other display elements.

(First embodiment)
The drive circuit according to this embodiment will be described. The circuit configuration will be described with reference to FIG. The driving circuit here means a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a driving current to the display element. And a third circuit for performing drive control including the third period.

  The driving circuit according to the present invention holds the gate voltage of the first transistor (Tr1) and the first transistor in the first period at a voltage corresponding to a constant current supplied to the display element (for example, LED1). Current holding circuit (for example, C1).

  Further, a second transistor (Tr2) for switching a current from the current source circuit to the display element is provided.

  Then, the third transistor (Tr3) in which one of the source and drain terminals is connected to the gate of the second transistor, one end connected to the gate of the third transistor, and the other end to the wiring (L3) And a capacitive element (C2) connected to the capacitor. And a control circuit in which the light emission time of the display element is controlled by controlling the second transistor in the third period.

  Here, in the second period, charges based on the difference between the grayscale voltage supplied from the wiring and the threshold voltage of the third transistor are accumulated in the capacitor (C2).

  Next, in the third period, an on-voltage is applied to the control terminal of the second transistor (Tr2), and a sweep voltage is applied from the wiring to the capacitive element, whereby the second voltage is applied. The on-time of the transistors is controlled.

  With such a configuration, when the display element is driven by supplying a constant current, the supply period can be controlled.

  Hereinafter, the invention according to this embodiment will be described in detail using specific components constituting the drive circuit and a timing chart. Note that the gate of the above transistor means a gate electrode.

  The configuration of the first embodiment of the present invention is shown in FIG. In the present embodiment, an organic EL element LED1 having one end connected to the first wiring L1 and a drive circuit for driving the organic EL element LED1 are provided. The drive circuit is configured as follows.

  First, a p-type transistor Tr1 which is a first transistor having a source connected to one end of the first capacitor C1 and the fourth wiring L4 and a gate connected to the other end of the first capacitor C1 is provided. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided.

  The first capacitor C1, the first transistor Tr1, the first switch SW1, and the second switch SW2 constitute a current source circuit.

  Further, a fourth switch SW4 having one end connected to the drain of the first transistor Tr1 is provided. The second transistor has a source connected to one end of the organic EL element LED1 that is not connected to the wiring L1 and a drain connected to the drain of the first transistor Tr1 via the fourth switch SW4. An n-type transistor Tr2 is provided.

  In addition, a second capacitor C2 having one end connected to the gate of the second transistor Tr2 via the fifth switch SW5 and the other end connected to the third wiring L3 is provided. In addition, an n-type transistor Tr3 which is a third transistor in which one end of either the drain or the source is connected to the fifth wiring L5 is provided.

  The gate of the third transistor Tr3 is connected to the second capacitor C2 and one end of the fifth switch SW5, and the other end of the source and drain is connected to the gate of the second transistor Tr2 and the other end of the switch SW5. ing. Further, a seventh switch SW7 having one end connected to the gate of the second transistor Tr2 and the other end connected to the wiring L4 is provided.

  The second transistor Tr2, the third transistor Tr3, the second capacitor C2, and the switches SW4, SW5, and SW7 constitute a control circuit that controls the light emission time of the organic EL element LED1.

  A timing chart of the operation of this embodiment is shown in FIG. Note that constant voltages VSS1, VDD1, and VSS2 are applied to the wirings L1, L4, and L5, and a constant current Id is supplied to the wiring L2. The gate voltage of the second transistor Tr2 is Va.

  First, as shown in FIG. 2, in the current setting period, the switches SW1 and SW2 are turned on, and the switches SW4, SW5 and SW7 are turned off. At this time, the current Id is supplied to the first transistor Tr1 from the wiring L2, and the gate voltage of the first transistor Tr1 is a voltage at which the current Id flows in a stable state. Thereafter, the switches SW1 and SW2 are turned off with the end of the current setting period, so that a voltage at which the current Id flows is held in the gate of the first transistor Tr1 and the first capacitor C1.

  Next, as shown in FIG. 2, in the gradation setting period, first, the switches SW5 and SW7 are turned on. Thereby, the voltage of Va becomes a voltage near VDD1 from the wiring L4. However, since the switch SW4 is off, no current is supplied to the organic EL element LED1, and the organic EL element LED1 does not emit light. Subsequently, the switch SW7 is turned off.

  At that time, the gradation voltage Vd is applied from the wiring L3 to one end of the capacitor C2. On the other hand, the voltage Va is the threshold voltage Vth of the third transistor Tr3. Accordingly, the voltage Vd is applied to one end of the second capacitor C2, and the voltage Vth is applied to the other end. At this time, if the capacitance value of C2 is C2, charge Q2 = C2 × (Vd−Vth) is accumulated in the second capacitor C2. Thereafter, when the fifth switch SW5 is turned off, the second capacitor C2 holds the charge Q2.

  Next, as shown in FIG. 2, first, the seventh switch SW7 is turned on in the light emission period. As a result, the voltage of Va becomes VDD1. Next, after the switch SW7 is turned off, the switch SW4 is turned on, and the wiring L3 sweeps a voltage in a range from VL to VH over an appropriate time. At that time, the gate voltage of the third transistor Tr3 becomes Vth or less in the range where the wiring L3 is less than Vd due to the charge pump effect in which the second capacitor C2 holds the charge Q2.

  At this time, the voltage of Va holds VDD1, and the second transistor Tr2 is on, so that the current Id is supplied to the organic EL element LED1 to emit light. Similarly, when the wiring L3 becomes equal to or higher than Vd, the gate voltage of the third transistor Tr3 becomes equal to or higher than Vth, and thus the voltage of Va becomes VSS2 of the wiring L5. At this time, since the second transistor Tr2 is turned off, no current is supplied to the organic EL element LED1, and light is not emitted.

  In this way, the sweep voltage is applied to the capacitor so that the gate voltage value of the third transistor exceeds the threshold voltage.

  As a result, even if Vth, which is the characteristic of the third transistor Tr3, varies, the second transistor Tr2 can be controlled from on to off in accordance with the gradation voltage Vd applied from the wiring L3 when setting the gradation. Therefore, it is possible to control the period during which the organic EL element LED1 emits light based on the gradation voltage Vd value regardless of the variation of the transistors.

  In addition, since the writing current in the current setting period is set to a large current and the current value is constant, the current setting period does not need to be long even for a small current corresponding to a low gradation, and a high definition, large screen It can be used for the image display apparatus.

  Furthermore, since the organic EL element LED1 is driven by a constant current, it is possible to cope with a decrease in luminance due to deterioration of the voltage-luminance characteristics of the organic EL element LED1.

  Further, since the display element (organic EL element) is not driven by using the comparator as described as the second technique in the background art column, it is not affected by the noise or leakage current of the comparator. The current of the organic EL element does not fluctuate.

  These effects are obtained similarly in all the following embodiments.

  If the voltage variation held in the first capacitor C1 due to leakage at the time of switch-off is small, the current setting period can be provided every frame or every several frames. At this time, the gradation setting period and the light emission period can be made longer.

  Further, by turning on the switch SW4 during the gradation setting period, an operating voltage is applied to the second transistor Tr2, so that the effect of parasitic capacitance can be reduced. However, in this case, a current flows through the organic EL element LED1 during the gradation setting period to emit light, but the light emission period at the time of gradation setting is very short compared to the light emission period at the time of gradation display. Is not a problem.

  Further, the same operation and function can be realized by providing the third switch SW3 between the second transistor Tr2 and the organic EL element LED1 instead of the switch SW4.

  Further, an n-type transistor can be used as the first transistor Tr1 instead of the p-type transistor. A circuit example in that case is shown in FIG. 3, and a timing chart is shown in FIG. In FIG. 3, the same parts as those in FIG.

  In this case, the first transistor Tr1 includes a first capacitor C1 between the source and the gate. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided. Furthermore, a ninth switch SW9 having one end connected to the fourth wiring L4 and the other end connected to the drain of the first transistor Tr1 is provided.

  In this circuit, the switch SW9 performs the inversion operation of the switches SW1 and SW2 as shown in FIG. 4, and the same function can be realized by performing other operations in the same manner as in FIG. However, as shown in FIG. 4, in order to secure a current path in the current setting period, the switch SW4 is turned on to pass a current through the organic EL element LED1. There is no problem when the light emission period at the time of this current setting is much shorter than the light emission period at the time of gradation display.

  Further, as shown in FIG. 5, SW10 is provided as a tenth switch having one end connected to the source of the first transistor Tr1 and one end of the switch SW4 and the other end connected to the wiring L1 (or wiring L5). May be. The difference from FIG. 3 is that a tenth switch SW10 is provided. A timing chart in that case is shown in FIG.

  First, as shown in FIG. 6, in the current setting period, by turning off the switch SW4 and turning on the switch SW10, a current path different from that of the organic EL element LED1 is formed, and thus light emission at the time of current setting can be suppressed. The switch SW10 is always off except during the current setting period.

  The same operation and function can be realized even if the switch SW2 between the wiring L2 and the gate of the first transistor Tr1 is arranged between the drain and gate of the first transistor Tr1. This is the same whether the first transistor Tr1 is p-type or n-type.

  When the first transistor Tr1 is an n-type transistor as in the examples shown in FIGS. 3 and 5, VDD1 is applied to the wiring L2 and the switch SW1 is turned on at least in the light emission period other than the current setting period. To do. By doing so, the same function can be realized without using the wiring L4 and the switch SW9.

  Further, for example, by providing the switch SW6 between the wiring L3 and the second capacitor C2 and holding the gradation voltage, the voltage of Va can be held at Vth. If the design is such that the second transistor Tr2 is turned off when Va is Vth and turned on when Vth is greater than Vth, the current path to the organic EL element LED1 is blocked by the second transistor Tr2 instead of the switch SW4. Is done. Therefore, by providing the current setting period after the gradation voltage setting period, the same function can be realized without the switch SW4.

  Further, for example, a fourth transistor Tr4 may be provided instead of the switch SW7 as shown in FIG. That is, the p-type transistor Tr4 is used as a fourth transistor having a source connected to the wiring L4, a drain connected to the drain of the third transistor Tr3, and a gate connected to the gate of the third transistor Tr3. A timing chart in that case is shown in FIG. The only difference from FIG. 1 is that a fourth transistor Tr4 is used instead of the switch SW7.

  At this time, the third and fourth transistors Tr3 and Tr4, the switch SW5, and the second capacitor C2 cancel the logical inversion voltage (Vinv) variation of the inverter due to the characteristic variation of the third and fourth transistors Tr3 and Tr4. An inverter type comparator can be configured. Therefore, the same function can be realized.

  Further, it is desirable that the second transistor Tr2 has such a characteristic that a constant current supplied to the organic EL element LED1 becomes a subthreshold region below a threshold value. In this case, the second transistor Tr2 is turned on or off by a slight change in the gate voltage of Tr2. Therefore, whether or not to supply current to the organic EL element LED1 can be quickly changed. Further, if the off current of Tr2 is 0.1% or less of the constant current, the gradation control is not affected.

  In order for the second transistor Tr2 to become a subthreshold region with a constant current, it is necessary to sufficiently increase the current capability of Tr2. This can be achieved by increasing the size of the transistor or by using a transistor having a high mobility semiconductor as a channel layer.

  Moreover, this invention arrange | positions the light emitting display device containing the above organic EL element LED1 and its drive circuit in a matrix form on a board | substrate. A matrix light-emitting display device (image display device) can be realized by performing a current setting period and a gradation setting period for each line, preparing a wiring L3 for each column and supplying a gradation voltage. It is.

  In the above description, an organic electroluminescence element is shown as an example of the display element. However, the present invention is not limited to this, and can be applied to, for example, an inorganic light emitting element.

  Further, the above-described transistors and switch elements can be constituted by thin film transistors (TFTs). The material of the TFT is not particularly limited. For example, amorphous silicon, polycrystalline silicon, or single crystal silicon can be applied to the channel. In addition, as a material of the channel film, an amorphous oxide semiconductor film including In and Zn can be used. In the invention according to this embodiment and the following embodiments, an n-type thin film transistor or a p-type thin film transistor is applied as the thin film transistor.

  In particular, a TFT using an amorphous oxide semiconductor film as a channel film is a desirable TFT because of its high mobility, low off-state current, easy manufacturing, and the like. Furthermore, the conductivity type of the transistors constituting the drive circuit according to the present embodiment may be configured from only one of n-type and p-type.

  An image display device can also be configured by providing the drive circuit described above for each pixel and arranging them in a matrix. Note that examples of these display elements, transistor materials, conductivity types, and the like can be applied to the inventions according to the following embodiments as long as no contradiction arises.

  In addition, although described as an organic EL element LED element, an organic light emitting diode (OLED) is also applicable. The same applies to the following embodiments.

(Second embodiment)
Hereinafter, the components of the drive circuit according to the present embodiment will be described with reference to FIG.

  Note that the driving circuit here means a first period for setting a current to be supplied to the display element, a second period for setting a gray level of the display element, and a driving current for the display element. A drive circuit for performing drive control including a third period for supplying the power.

  In this embodiment, as shown in FIG. 9, the voltage of the gate of the first transistor (Tr1) and the first transistor in the first period is maintained at a voltage corresponding to a constant current supplied to the display element (LED1). A current source circuit having a holding circuit (for example, C1).

  Further, a second transistor (Tr2) for switching a current from the current source circuit to the display element, and a third transistor in which one of a source and a drain is connected to the gate of the second transistor (Tr3). Further, it includes a capacitor element (C2) having one end connected to the gate of the third transistor and the other end connected to the wiring (L3). And a control circuit for controlling a light emission time of the display element by controlling the second transistor in the third period.

  Then, after a certain voltage is applied from the wiring in the second period, a gradation voltage is applied, and the capacitance element (C2) has a gradation voltage and a threshold voltage of the third transistor. Charge based on the difference is accumulated.

  A voltage that turns on the second transistor (Tr2) through the third transistor (Tr3) is applied to the gate of the second transistor in the third period, and then a sweep voltage is applied from the wiring to the capacitor. Is applied. Thus, the on-time of the second transistor (Tr2) is controlled.

  Hereinafter, a more specific description will be given using the timing charts of FIGS. 9 and 10. The configuration of the second embodiment of the present invention is shown in FIG. In this embodiment, the organic EL element LED1 having one end connected to the first wiring L1 and a drive circuit thereof are provided. The drive circuit is configured as follows.

  First, a p-type transistor Tr1 which is a first transistor having a source connected to one end of the first capacitor C1 and the fourth wiring L4 and a gate connected to the other end of the first capacitor C1 is provided. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided.

  The first capacitor C1, the first transistor Tr1, the first switch SW1, and the second switch SW2 constitute a current source circuit.

  Further, a fourth switch SW4 having one end connected to the drain of the first transistor Tr1 is provided. Further, the n-type transistor is a second transistor whose source is connected to one end of the organic EL element LED1 that is not connected to the wiring L1 and whose drain is connected to the drain of the first transistor Tr1 via the switch SW4. A transistor Tr2 is provided.

  In addition, a second capacitor C2 having one end connected to the gate of the second transistor Tr2 via the fifth switch SW5 and the other end connected to the third wiring L3 is provided. Further, an n-type transistor Tr3 which is a third transistor having one end of the drain and the source connected to the fifth wiring L5 is provided.

  The gate of the third transistor Tr3 is connected to the second capacitor C2 and one end of the switch SW5, and the other end of the source and drain is connected to the gate of the second transistor Tr2 and the other end of the switch SW5. Yes.

  The second and third transistors Tr2 and Tr3, the second capacitor C2, and the switches SW4 and SW5 constitute a control circuit that controls the light emission time of the organic EL element LED1.

  A timing chart of the operation of this embodiment is shown in FIG. However, constant voltages VSS1 and VDD1 are applied to the wirings L1 and L4, and a constant current Id is supplied to the wiring L2. Let Va be the gate voltage of the second transistor Tr2.

  First, as shown in FIG. 10, in the current setting period, the switches SW1 and SW2 are turned on and the switches SW4 and SW5 are turned off. The voltage of the wiring L5 is VDL. At this time, the current Id is supplied from the wiring L2 to the first transistor Tr1, and in a stable state, the gate voltage of the first transistor Tr1 becomes a voltage at which the current Id flows. Thereafter, the switches SW1 and SW2 are turned off with the end of the current setting period, so that a voltage at which the current Id flows is held in the gate of the first transistor Tr1 and the first capacitor C1.

  Next, as shown in FIG. 10, in the gradation setting period, first, the voltage VHH is applied from the wiring L3. Here, VHH is a voltage that allows the gate voltage of the third transistor Tr3 to be higher than the threshold Vth voltage of the transistor Tr3 by the charge pump effect. At this time, no matter what the voltage of Va corresponding to the gate voltage of the second transistor Tr2 is, the switch SW4 is off, so that no current is supplied to the organic EL element LED1, and no light is emitted. Subsequently, the switch SW5 is turned on.

  At that time, the gradation voltage Vd is applied from the wiring L3. At this time, the voltage of Va becomes the threshold voltage Vth of the third transistor Tr3 because the gate and drain of the third transistor Tr3 are short-circuited. Accordingly, the voltage Vd is applied to one end of the second capacitor C2, and the voltage Vth is applied to the other end. At this time, if the capacitance value of C2 is C2, charge Q2 = C2 × (Vd−Vth) is accumulated in the second capacitor C2. Thereafter, when the switch SW5 is turned off, the second capacitor C2 holds Q2.

  Next, as shown in FIG. 10, in the light emission period, first, the wiring L3 is set to VHH and the wiring L5 is set to VDH. Here, VDH is a voltage that allows the voltage of Va to be higher than Vth by several V due to the charge pump effect in which the second capacitor C2 holds the charge Q2.

  Subsequently, after setting the wiring L5 to VDL, the switch SW4 is turned on, and the wiring L3 sweeps a voltage in the range of VL to VH over an appropriate time. However, VDL is a voltage at which the second transistor Tr2 is turned off when applied to the gate of the second transistor Tr2.

  Due to the charge pump effect, the gate voltage of the third transistor Tr3 is equal to or lower than Vth when the wiring L3 is in the range from VL to less than Vd. At this time, the voltage Va is maintained at a voltage several V higher than Vth, and the second transistor Tr2 is on, so that the current Id is supplied to the organic EL element LED1 to emit light.

  Similarly, when the wiring L3 becomes equal to or higher than Vd, the gate voltage of the third transistor Tr3 becomes equal to or higher than Vth, and thus the voltage of Va becomes VDL. At this time, since the second transistor Tr2 is turned off by VDL, no current is supplied to the organic EL element LED1, and light emission does not occur.

  As a result, even if Vth, which is the characteristic of the third transistor Tr3, varies, the second transistor Tr2 can be controlled from on to off in accordance with the gradation voltage Vd applied from the wiring L3 when setting the gradation. Therefore, control of the period during which the organic EL element LED1 emits light based on the Vd value can be performed regardless of the variation of the transistors.

  Further, if the voltage variation held in the first capacitor C1 due to leakage at the time of switch-off is small, the current setting period can be provided for each frame or every several frames. At this time, the gradation setting period and the light emission period can be made longer.

  Further, when the switch SW4 is turned on during the gradation setting period, the voltage at the time of operation is applied to the second transistor Tr2, so that the effect of the parasitic capacitance can be reduced. However, in this case, a current flows through the organic EL element LED1 during the gradation setting period to emit light, but the light emission period at the time of gradation setting is very short compared to the light emission period at the time of gradation display. Is not a problem.

  Further, the same operation and function can be realized by providing the third switch SW3 between the second transistor Tr2 and the organic EL element LED1 instead of the switch SW4.

  As in the first embodiment, an n-type transistor can be used instead of the p-type transistor as the first transistor Tr1. In that case, as described above, the transistor Tr1 and its periphery may have the same configuration as that shown in FIGS.

  The same operation and function can be realized even if the switch SW2 between the wiring L2 and the gate of the first transistor Tr1 is arranged between the drain and gate of the first transistor Tr1. This is the same whether the first transistor Tr1 is p-type or n-type.

  Further, when the first transistor Tr1 is an n-type transistor as described above, VDD1 is applied to the wiring L2 at least in the light emission period other than the current setting period, and the switch SW1 is turned on. By doing so, the same function can be realized without using the wiring L4 and the switch SW9.

  Further, for example, by providing the switch SW6 between the wiring L3 and the second capacitor C2 and holding the gradation voltage, the voltage of Va can be held at Vth. If the design is such that the second transistor Tr2 is turned off when Va is Vth and turned off when the voltage is higher than Vth, the current path to the organic EL element LED1 by the second transistor Tr2 instead of the switch SW4. Is cut off. Therefore, by providing the current setting period after the gradation voltage setting period, the same function can be realized without the switch SW4.

  Further, it is desirable that the second transistor Tr2 has such a characteristic that a constant current supplied to the organic EL element LED1 becomes a subthreshold region below a threshold value. In this case, the second transistor Tr2 is turned on or off by a slight change in the gate voltage of Tr2. Therefore, whether or not to supply current to the organic EL element LED1 can be quickly changed. Further, if the off current of Tr2 is 0.1% or less of the constant current, the gradation control is not affected.

  The control circuit that controls the time for supplying a constant current from the current source circuit to the display element in the third period in accordance with the gradation voltage supplied in the second period satisfies the following requirements. Configuration is good. That is, the control circuit has a source / drain connected in series between the current source circuit and the display element, and a gate connected to one end of the capacitor element directly or via a switch. The constant current is in a subthreshold region of gate voltage-drain current characteristics, and the second transistor has an off-current of 0.1% or less of the constant current.

  In the third period, the gate voltage of the second transistor is changed over time, and the time during which the source and drain of the second transistor is turned on is controlled to supply a constant current to the display element. Control the time to do.

  In order for the second transistor Tr2 to become a subthreshold region with a constant current, it is necessary to sufficiently increase the current capability of Tr2. This can be achieved by increasing the size of the transistor or by using a transistor having a high mobility semiconductor as a channel layer.

  In the invention according to this embodiment and other embodiments, the off-state current of Tr2 is preferably 5% or less, preferably 1% or less, and preferably 0.1% or less of the constant current. The invention is not limited to that.

  Furthermore, in the present invention, a light-emitting display device including the organic EL element LED1 as described above and its driving circuit is arranged in a matrix on a substrate. A matrix light-emitting display device (image display device) can be realized by performing a current setting period and a gradation setting period for each line, preparing a wiring L3 for each column and supplying a gradation voltage. It is.

(Third embodiment)
The configuration of the drive circuit of the invention according to this embodiment will be described with reference to FIG. Here, the driving circuit includes a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element. A display element drive circuit including:

  In the present embodiment, as shown in FIG. 11, the first transistor (Tr1) and the gate of the first transistor in the first period are held at a voltage corresponding to a constant current supplied to the display element (LED1). Current holding circuit (for example, C1).

  A second transistor (Tr2) connected in series with the first transistor (Tr1) and a capacitor having one end connected to the gate of the second transistor and the other end connected to the wiring (L3) Element (C2). And a control circuit for controlling a light emission time of the display element by controlling the second transistor in the third period.

  In the second period, charges based on the difference between the grayscale voltage supplied from the wiring and the gate voltage of the second transistor are accumulated in the capacitor (C2). Then, the on-time of the second transistor is controlled by applying a sweep voltage from the wiring (L3) to the capacitor (C2) in the third period.

  Hereinafter, the invention according to this embodiment will be described in detail with reference to FIG. 11 and a timing chart (FIG. 12). The configuration of the third embodiment of the present invention is shown in FIG. In this embodiment, the organic EL element LED1 having one end connected to the first wiring L1 and a drive circuit thereof are provided. The drive circuit is configured as follows.

  First, a p-type transistor Tr1 which is a first transistor having a source connected to one end of the first capacitor C1 and a gate connected to the other end of the first capacitor C1 is provided. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided.

  The first transistor Tr1, the first capacitor C1, and the first and second switches SW1 and SW2 constitute a current source circuit.

  Further, a fourth switch SW4 having one end connected to the drain of the first transistor Tr1 is provided. Further, an n-type transistor which is a second transistor whose source is connected to one end of the organic EL element LED1 that is not connected to the wiring L1 and whose drain is connected to the drain of the first transistor Tr1 via the switch SW4. Tr2 is provided.

  In addition, a second capacitor C2 is provided that has one end connected to the gate of the second transistor Tr2 and the other end connected to the third wiring L3. Further, a seventh switch SW7 having one end connected to the gate of the second transistor Tr2 and the other end connected to the drain of the second transistor Tr2 is provided. The second transistor Tr2, the second capacitor C2, and the switches SW4 and SW7 constitute a control circuit that controls the light emission time of the organic EL element LED1.

  A timing chart of the operation of this embodiment is shown in FIG. However, constant voltages VSS1 and VDD1 are applied to the wirings L1 and L4, and a constant current Id is supplied to the wiring L2. The drain voltage of the second transistor Tr2 is Va.

  First, as shown in FIG. 12, in the current setting period, the switches SW1 and SW2 are turned on and the switches SW4 and SW7 are turned off. At this time, the current Id is supplied from the wiring L2 to the first transistor Tr1, and in a stable state, the gate voltage of the first transistor Tr1 becomes a voltage at which the current Id flows. After that, as shown in FIG. 12, with the end of the current setting period, the switches SW1 and SW2 are turned off, so that a voltage at which the current Id flows is held in the gate of the first transistor Tr1 and the first capacitor C1. .

  Next, as shown in FIG. 12, in the gradation setting period, the switches SW4 and SW7 are turned on, and the gradation voltage Vd is applied from the wiring L3. At this time, since the switch SW4 is on, the current Id is supplied from the first transistor Tr1 to the second transistor Tr2 and the organic EL element LED1. In addition, since the switch SW7 is on, the gate and drain of the second transistor Tr2 are short-circuited, and the second transistor Tr2 passes a current Id.

  Therefore, Va and the gate voltage of the second transistor Tr2 are voltages Vinv through which the current Id flows. Therefore, the voltage Vd is applied to one end of the second capacitor C2, and the voltage Vinv is applied to the other end. At this time, if the capacitance value of the second capacitor C2 is C2, the charge Q2 = 2 × (Vd−Vinv) is accumulated in the second capacitor C2. Thereafter, the switches SW4 and SW7 are turned off, and the second capacitor C2 holds the charge Q2.

  Next, as shown in FIG. 12, in the light emission period, the switch SW4 is turned on, and the wiring L3 sweeps a voltage in the range of VL to VH over an appropriate time. At that time, due to the charge pump effect in which the second capacitor C2 holds the charge Q2, the gate voltage of the second transistor Tr2 becomes less than Vinv when the wiring L3 is in the range from VL to less than Vd.

  At this time, the voltage of Va becomes higher than Vinv, but since the voltage drop in the second transistor Tr2 is large, the voltage at the source of the second transistor Tr2 and one end of the organic EL element LED1 is low. Therefore, no current flows through the organic EL element LED1, and no light is emitted. When the wiring L3 becomes Vd or higher, the gate voltage of the second transistor Tr2 becomes VinV or higher. At this time, the voltage of Va becomes Vinv, and the current Id is supplied to the organic EL element LED1 to emit light.

  As a result, even if Vinv, which is the characteristic of the second transistor Tr2, varies, the second transistor Tr2 supplies the current Id according to the gradation voltage Vd applied from the wiring L3 during gradation setting, and the organic EL element LED1. The current Id can be controlled to flow from a state in which no current flows. Therefore, control of the period during which the organic EL element LED1 emits light based on the Vd value can be performed regardless of the variation of the transistors.

  Further, if the voltage variation held in the first capacitor C1 due to leakage at the time of switch-off is small, the current setting period can be provided for each frame or every several frames. At this time, the gradation setting period and the light emission period can be made longer.

  Further, the same operation and function can be realized by providing the third switch SW3 between the second transistor Tr2 and the organic EL element LED1 instead of the switch SW4.

  As in the first embodiment, an n-type transistor can be used instead of the p-type transistor as the first transistor Tr1. In that case, as described above, the transistor Tr1 and its periphery may have the same configuration as that shown in FIGS.

  Further, the same operation and function can be realized even when the switch SW2 between the wiring L2 and the gate of the first transistor Tr1 is connected between the drain and gate of the first transistor Tr1. This is the same whether the first transistor Tr1 is p-type or n-type.

  When the first transistor Tr1 is an n-type transistor, the wiring L4 and the switch SW9 are used by applying VDD1 to the wiring L2 and turning on the switch SW1 at least in the light emission period other than the current setting period. The same function can be realized without.

  Further, the switch SW4 can be reduced by changing the voltage of the wiring L4. The configuration in that case is shown in FIG. 13 and the timing chart is shown in FIG. In this case, as shown in FIG. 14, the voltage of the wiring L4 is set to VDD1 in the gradation setting period and the light emission period, and is set to VSS1 in other periods including the current setting period. In the current setting period, when the voltage of the wiring L2 is set to VSS1 or lower in order to pass the current Id through the wiring L2, the voltage of Va becomes VSS1 or lower.

  For this reason, a negative bias of VSS1 is applied to the cathode and a voltage equal to or lower than VSS1 is applied to the anode of the organic EL element LED1, and no current flows through the organic EL element LED1. In order to perform the current setting operation accurately, it is necessary to allow the current Id to flow only through the first transistor Tr1 without flowing through other current paths.

  In this configuration, since no current flows through the organic EL element LED1, the current of the first transistor Tr1 can be set. Thereafter, the same operation as described above is performed during the gradation setting period and the light emission period.

  The same configurations and operations as those of the first and second embodiments and all the following embodiments can be applied. However, the present embodiment has the smallest number of elements, and further switches. It is most effective to apply to the present embodiment in the sense that can be reduced.

  Further, it is desirable that the second transistor Tr2 has such a characteristic that a constant current supplied to the organic EL element LED1 becomes a subthreshold region below a threshold value. In this case, the second transistor Tr2 is turned on or off by a slight change in the gate voltage of Tr2. Therefore, whether or not to supply current to the organic EL element LED1 can be quickly changed. Further, if the off current of Tr2 is 0.1% or less of the constant current, the gradation control is not affected.

  In order for the second transistor Tr2 to become a subthreshold region with a constant current, it is necessary to sufficiently increase the current capability of Tr2. This can be achieved by increasing the size of the transistor or using a transistor having a high mobility semiconductor as a channel layer.

  Moreover, in this Embodiment shown above, an electric current flows into organic EL element LED1 in the gradation setting period, and it light-emits. This period can be made sufficiently smaller than the entire light emission period to prevent display problems.

  Here, a switch SW8 is provided between the wiring L5 to which the same voltage as the wiring L1 or a voltage lower than the operating voltage of the organic EL element LED1 is applied, and the source of the second transistor Tr2 and L5, and a gradation setting period. Only SW8 is turned on and turned off in other periods. Thereby, the light emission of the organic EL element LED1 in the gradation setting period can be suppressed, and the contrast can be further increased.

  Furthermore, in the present invention, a light-emitting display device including the organic EL element LED1 as described above and its driving circuit is arranged in a matrix on a substrate. A matrix light-emitting display device (image display device) can be realized by performing a current setting period and a gradation setting period for each line, preparing a wiring L3 for each column and supplying a gradation voltage. It is.

(Fourth embodiment)
The components of the drive circuit according to the present embodiment will be described with reference to FIG. The driving circuit here means a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element. A driving circuit having a period.

  In the present embodiment, as shown in FIG. 15, the first transistor (Tr1) and the gate of the first transistor in the first period are held at a voltage corresponding to a constant current supplied to the display element. A current source circuit having a holding circuit (for example, C1).

  The second transistor (Tr2) connected in series with the current source circuit and connected in parallel with the display element (LED1), one terminal is connected to the gate of the second transistor, and the other end Includes a capacitor (C2) connected to the wiring (L3). And a control circuit for controlling a light emission time of the display element by controlling the second transistor in the third period.

  Then, a constant voltage is applied from the wiring (L3) in the first period. Further, a gradation voltage is applied from the wiring in the second period, and the gate and one terminal of the second transistor are short-circuited, and the gradation voltage and the second transistor are connected to the capacitor element. Charge based on the difference from the gate voltage is accumulated.

  Further, the on-time of the second transistor is controlled by applying a sweep voltage from the wiring (L3) in the third period.

  Hereinafter, a more detailed description will be given using FIG. 15 and a timing chart (FIG. 16). The configuration of the fourth embodiment of the present invention is shown in FIG. In this embodiment, the organic EL element LED1 having one end connected to the first wiring L1 and a drive circuit thereof are provided. The drive circuit is configured as follows.

  First, a p-type transistor Tr1 which is a first transistor having a source connected to one end of the first capacitor C1 and a gate connected to the other end of the first capacitor C1 is provided. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided.

  The first transistor Tr1, the first capacitor C1, the first switch SW1, and the second switch SW2 constitute a current source circuit.

  Furthermore, a fourth switch SW4 whose one end is connected to the drain of the first transistor Tr1 and a third switch SW3 whose one end is connected to one end not connected to the wiring L1 of the organic EL element LED1. It has.

  In addition, an n-type transistor Tr2 which is a second transistor having a source connected to the sixth wiring L6 and a drain connected to one end of the switch SW4 on the side not connected to the drain of the first transistor Tr1 is provided. ing.

  Furthermore, a second capacitor C2 having one end connected to the gate of the second transistor Tr2 and the other end connected to the third wiring L3 is provided. Further, a seventh switch SW7 having one end connected to the gate of the second transistor Tr2 and the other end connected to the drain of the second transistor Tr2 is provided.

  The second transistor Tr2, the second capacitor C2, the third switch SW3, the fourth switch SW4, and the seventh switch SW7 constitute a control circuit that controls the light emission time of the organic EL element LED1.

  A timing chart of the operation of this embodiment is shown in FIG. However, VSS2 that is a voltage equal to or lower than the constant voltages VSS1, VDD1, and VSS1 is applied to the wirings L1, L4, and L6, respectively, and a constant current Id is supplied to the wiring L2. The voltage at the drain of the second transistor Tr2 is Va.

  First, as shown in FIG. 16, in the current setting period, the switches SW1 and SW2 are turned on, and the switches SW3, SW4 and SW7 are turned off. The voltage of the wiring L3 is VH or higher. At this time, the current Id is supplied from the wiring L2 to the first transistor Tr1, and in a stable state, the gate voltage of the first transistor Tr1 becomes a voltage at which the current Id flows. Thereafter, since the switches SW1 and SW2 are turned off with the end of the current setting period, a voltage at which the current Id flows is held in the gate of the first transistor Tr1 and the first capacitor C1.

  Next, as shown in FIG. 16, in the gradation setting period, the switches SW4 and SW7 are turned on, and the gradation voltage Vd is applied from the wiring L3. At this time, since the switch SW4 is on, the current Id is supplied from the first transistor Tr1 to the second transistor Tr2. In addition, since the switch SW7 is on, the gate and drain of the second transistor Tr2 are short-circuited, and the second transistor Tr2 passes a current Id.

  Therefore, Va and the gate voltage of the second transistor Tr2 are voltages Vinv through which the current Id flows. Therefore, the voltage Vd is applied to one end of the second capacitor C2, and the voltage Vinv is applied to the other end. At this time, if the capacitance value of the second capacitor C2 is C2, the charge Q2 = C2 × (Vd−Vinv) is accumulated in the second capacitor C2. Thereafter, the switches SW4 and SW7 are turned off, and the second capacitor C2 holds the charge Q2.

  Next, as shown in FIG. 16, in the light emission period, the switch SW4 is turned on, and the wiring L3 sweeps a voltage in the range of VH to VL over an appropriate time. At that time, due to the charge pump effect in which the second capacitor C2 holds the charge Q2, the gate voltage of the second transistor Tr2 becomes equal to or higher than Vinv when the wiring L3 is in the range of VH to Vd.

  At this time, by setting the voltage VSS2 of the wiring L6 to VSS1 or less, the voltage of Va lowers the source of the second transistor Tr2 and the one end voltage of the organic EL element LED1 so that no current flows through the organic EL element LED1. The organic EL element LED1 does not emit light.

  On the other hand, when the wiring L3 becomes less than Vd, the gate voltage of the second transistor Tr2 becomes VinV or less. At this time, since the second transistor Tr2 has a high resistance, no current flows through the second transistor Tr2, and the current Id is supplied to the organic EL element LED1 to emit light.

  As a result, even if Vinv, which is the characteristic of the second transistor Tr2, varies, the second transistor Tr2 supplies the current Id according to the gradation voltage Vd applied from the wiring L3 during gradation setting, and the organic EL element LED1. The current Id can be controlled to flow from a state in which no current flows. Therefore, control of the period during which the organic EL element LED1 emits light based on the Vd value can be performed regardless of the variation of the transistors.

  Further, if the voltage variation held in the first capacitor C1 due to leakage at the time of switch-off is small, the current setting period can be provided for each frame or every several frames. At this time, the gradation setting period and the light emission period can be made longer.

  Further, the same operation and function can be realized by providing the third switch SW3 between the second transistor Tr2 and the organic EL element LED1 instead of the switch SW4.

  Further, instead of the switch SW4, the same operation is possible by providing an eighth switch SW8 between the gate and source of the second transistor Tr2 as shown in FIG. A timing chart in that case is shown in FIG. As shown in FIG. 18, the eighth switch SW8 is turned on during the current setting period, and the gradation setting period and the light emission period are turned off.

  As in the first embodiment, an n-type transistor can be used instead of the p-type transistor as the first transistor Tr1. In that case, as described above, the transistor Tr1 and its periphery may have the same configuration as that shown in FIGS.

  Further, the same operation and function can be realized even if the switch SW2 between the wiring L2 and the gate of the first transistor Tr1 is arranged between the drain and gate of the first transistor Tr1. This is the same whether the first star Tr1 is p-type or n-type.

  When the first transistor Tr1 is an n-type transistor, the wiring L4 and the switch SW9 are used by applying VDD1 to the wiring L2 and turning on the switch SW1 at least in the light emission period other than the current setting period. The same function can be realized without any problem.

  Further, it is desirable that the second transistor Tr2 has such a characteristic that a constant current supplied to the organic EL element LED1 becomes a subthreshold region below a threshold value. In this case, the second transistor Tr2 is turned on or off by a slight change in the gate voltage of Tr2. Therefore, whether or not to supply current to the organic EL element LED1 can be quickly changed. Further, if the off current of Tr2 is 0.1% or less of the constant current, the gradation control is not affected.

  In order for the second transistor Tr2 to become a subthreshold region with a constant current, it is necessary to sufficiently increase the current capability of Tr2. This can be achieved by increasing the size of the transistor or using a transistor having a high mobility semiconductor as a channel layer.

  Furthermore, in the present invention, a light-emitting display device including the organic EL element LED1 as described above and its driving circuit is arranged in a matrix on a substrate. A matrix light-emitting display device (image display device) can be realized by performing a current setting period and a gradation setting period for each line, preparing a wiring L3 for each column and supplying a gradation voltage. It is.

(Fifth embodiment)
Components of the drive circuit according to the present embodiment will be described with reference to FIG. Here, the driving circuit means a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a driving current to the display element. And a third period for performing drive control.

  As shown in FIG. 19, the first transistor (Tr1) and the holding for holding the voltage of the gate of the first transistor in the first period at a voltage corresponding to a constant current supplied to the display element. A current source circuit having a circuit (eg, C1).

  A second transistor (Tr2) that switches a current from the current source circuit to the display element (LED1) is included.

  In addition, a third transistor (Tr3) having one terminal connected to the gate of the second transistor, one end connected to the gate of the third transistor, and the other end connected via a switch (SW6) And a capacitor element (C2) connected to the capacitor. And a control circuit in which the light emission time of the display element is controlled by controlling the second transistor in the third period.

  In the second period, charges based on the difference between the grayscale voltage supplied from the wiring and the threshold voltage of the third transistor are accumulated in the capacitor (C2).

  Thereafter, in the third period, an ON voltage is applied to the gate of the second transistor (Tr2), and a sweep voltage is applied to the capacitor. With this configuration, the on-time of the second transistor (Tr2) is controlled.

  Next, the invention according to this embodiment will be described in more detail using the drive circuit shown in FIG. 19 and a timing chart (FIG. 20). The configuration of the fifth embodiment of the present invention is shown in FIG. In this embodiment, the organic EL element LED1 having one end connected to the first wiring L1 and a drive circuit thereof are provided. The drive circuit is configured as follows.

  First, a p-type transistor Tr1 which is a first transistor having a source connected to one end of the first capacitor C1 and the fourth wiring L4 and a gate connected to the other end of the first capacitor C1 is provided. Also, one end is connected to the drain of the first transistor Tr1, the other end is connected to the second wiring L2, and one end is connected to the gate of the first transistor Tr1. A second switch SW2 having one end connected to the wiring L2 is provided.

  The first transistor Tr1, the first capacitor C1, the first switch SW1, and the second switch SW2 constitute a current source circuit.

  Further, a fourth switch SW4 having one end connected to the drain of the first transistor Tr1 is provided. An n-type transistor is a second transistor whose source is connected to one end of the organic EL element LED1 that is not connected to the wiring L1 and whose drain is connected to the drain of the first transistor Tr1 via the switch SW4. Tr2 is provided.

  The second capacitor C2 has one end connected to the gate of the second transistor Tr2 via the fifth switch SW5 and the other end connected to the third wiring L3 via the sixth switch SW6. It has.

  In addition, one end of the drain and the source is connected to the wiring L5, the gate is connected to one end of the capacitor C2, and one end on the side not connected to the drain or source wiring L5 is connected to the gate of the transistor Tr2. Three transistors Tr3 are provided. The third transistor Tr3 is an n-type transistor.

  Furthermore, one end is connected to the gate of the second transistor Tr2, the other end is connected to the wiring L4, the seventh switch SW7, the source is connected to the wiring L4, and the gate is connected to the gate of the first transistor Tr1. A fourth transistor Tr4 is provided. The fourth transistor Tr4 is a p-type transistor. The drain of the fourth transistor Tr4 is connected to one end of the second capacitor C2 via the eleventh switch SW11, and further connected to the wiring L3 via the switch SW6.

  The second, third, and fourth transistors Tr2, Tr3, Tr4, the second capacitor C2, the switches SW4 to SW7, and the switch SW11 constitute a control circuit that controls the light emission time of the organic EL element LED1.

  A timing chart of the operation of this embodiment is shown in FIG. However, constant voltages VSS1, VDD1, and VSS2 are applied to the wirings L1, L4, and L5, and a constant current Id is supplied to the wiring L2. The gate voltage of the second transistor Tr2 is Va, and the voltage at one end of the second capacitor C2 connected to the wiring L3 via the switch SW6 is Vb.

  First, as shown in FIG. 20, in the current setting period, the switches SW1 and SW2 are turned on, and the switches SW4, SW5, SW6, SW7, and SW11 are turned off. At this time, the current Id is supplied from the wiring L2 to the first transistor Tr1, and in a stable state, the gate voltage of the first transistor Tr1 becomes a voltage at which the current Id flows. Thereafter, the switches SW1 and SW2 are turned off with the end of the current setting period, so that a voltage at which the current Id flows is held in the gate of the first transistor Tr1 and the first capacitor C1.

  Next, as shown in FIG. 20, in the gradation setting period, first, the switches SW5, SW6, SW7 are turned on. Thereby, the voltage of Va becomes a voltage near VDD1, and the voltage of Vb becomes Vd. However, since the switch SW4 is off, no current is supplied to the organic EL element LED1, and the organic EL element LED1 does not emit light. Subsequently, the switch SW7 is turned off.

  At that time, the gradation voltage Vd is applied from the wiring L3. At this time, the voltage Va becomes the threshold voltage Vth of the third transistor Tr3. Accordingly, the voltage Vd is applied to one end of the second capacitor C2, and the voltage Vth is applied to the other end.

  At this time, if the capacitance value of the second capacitor C2 is C2, the charge Q2 = C2 × (Vd−Vth) is accumulated in the second capacitor C2. After that, when the switches SW5 and SW6 are turned off, the voltages Va and Vb hold Vth and Vd, and the second capacitor C2 holds Q2.

  Next, as shown in FIG. 20, first, the switches SW6 and SW7 are turned on in the light emission period. However, VL is applied from the wiring L3. As a result, the voltage of Va becomes VDD1 and the voltage of Vb becomes VL. Subsequently, after the switches SW6 and SW7 are turned off, the switches SW4 and SW11 are turned on. Then, charges are injected from the fourth transistor Tr4, and the voltage of Vb changes gradually from VL to VH. However, VH is a voltage determined by the threshold characteristic of the fourth transistor Tr4.

  At this time, due to the charge pump effect in which the second capacitor C2 holds Q2, the gate voltage of the third transistor Tr3 becomes Vth or less in a range where Vb is less than Vd from VL. At this time, the voltage of Va holds VDD1, and the second transistor Tr2 is on, so that the current Id is supplied to the organic EL element LED1 to emit light.

  Similarly, when Vb becomes equal to or higher than Vd, the gate voltage of the third transistor Tr3 becomes equal to or higher than Vth, and thus the voltage of Va becomes VSS2. At this time, since the second transistor Tr2 is turned off, no current is supplied to the organic EL element LED1, and light is not emitted.

  As a result, even if there is a variation in the characteristic Vth of the third transistor Tr3, the second transistor Tr2 can be controlled from on to off according to the gradation voltage Vd applied from the wiring L3 at the time of gradation setting. Therefore, control of the period during which the organic EL element LED1 emits light based on the Vd value can be performed regardless of the variation of the transistors.

  In addition, by configuring the current source transistor Tr4 to sweep the voltage Vb of the second capacitor C2 during the light emission period, even if the wiring load such as the screen size becomes large, all regions A sweep voltage can be applied. For this reason, the luminance differs depending on the position on the screen, and the display accuracy does not deteriorate.

  Further, it is desirable that the second transistor Tr2 has such a characteristic that a constant current supplied to the organic EL element LED1 becomes a subthreshold region below a threshold value. In this case, the second transistor Tr2 is turned on or off by a slight change in the gate voltage of Tr2. Therefore, whether or not to supply current to the organic EL element LED1 can be quickly changed. Further, if the off current of Tr2 is 0.1% or less of the constant current, the gradation control is not affected.

  In order for the second transistor Tr2 to become a subthreshold region with a constant current, it is necessary to sufficiently increase the current capability of Tr2. This can be achieved by increasing the size of the transistor or using a transistor having a channel layer of a semiconductor with high mobility.

  In this embodiment, the light emission period control is performed using the current (charge) from the current source transistor Tr4 based on the first embodiment, but the same light emission period control is performed in the second, third, The present invention can also be applied to the fourth embodiment.

  Furthermore, in the present invention, a light-emitting display device including the organic EL element LED1 as described above and its driving circuit is arranged in a matrix on a substrate. A matrix light-emitting display device (image display device) can be realized by performing a current setting period and a gradation setting period for each line, preparing a wiring L3 for each column and supplying a gradation voltage. It is.

  In the first to fifth embodiments of the present invention, the transistors defined as n-type transistors and p-type transistors have opposite polarities by changing the polarity of applied voltage or the connection of organic EL elements. Transistors can be used.

  Each switch SW can be formed of a transistor. For example, in the third embodiment, an example in which the switch is configured by a transistor is shown in FIG.

  For example, the switch SW1 of the third embodiment corresponds to SWTr1 that moves by CL1. Since all the switches are n-type transistors, H is short-circuited and L is open as shown in the switch timing chart. Therefore, if the operation is performed as shown in FIG. 12 (timing chart of the third embodiment), the operation / function described in the third embodiment is possible.

  Furthermore, in the first to fifth embodiments of the present invention, it is possible to configure the transistors and switches only with n-type transistors and p-type transistors. For example, FIG. 22 shows an example of the case where the n-type transistor alone is used in the third embodiment.

  Here, in the present invention, since it is a constant current that is supplied from the current source circuit to the organic EL element, an effect of suppressing the influence of deterioration of characteristics with respect to the voltage can be obtained. Further, since the constant current is the maximum value of the current supplied to the organic EL element, the load can be driven at high speed.

  Further, the gate of the first transistor Tr1 in the current source circuit is separated from the other parts except for one end of the first capacitor C1 during a period in which current is supplied to the organic EL element. Therefore, if the voltage on the side different from the side connected to the first transistor in the drain of the first transistor and the first capacitor C1 (wiring L4) is constant, the gate voltage of the first transistor is stable. Thus, the current from the current source circuit to the organic EL element becomes stable.

  Further, by using the switch (SW4) between the current source circuit and the organic EL element, an effect of suppressing an excess current to the organic EL element can be obtained.

  Further, as shown in FIG. 19, a current source different from the current source circuit is connected to one end of the second capacitor C2, and the voltage at one end of the second capacitor is varied by injecting or extracting charge from the current source. Can do. Therefore, since the voltage at one end of the second capacitor can be varied in each pixel, a change in luminance due to the screen position can be suppressed even in a large image display device with a large wiring load.

  In all the above embodiments, all transistors including switches use field effect transistors using crystalline Si for the channel, and thin film transistors using amorphous Si, poly-Si, organic semiconductor, oxide semiconductor, or the like for the channel. Can do. In particular, by using a thin film transistor, a large matrix light-emitting display device (image display device) can be manufactured over a glass or plastic substrate.

By using an amorphous oxide semiconductor having a carrier density of less than 10 ¹⁸ (cm ⁻³ ), a matrix type light emitting display device can be formed by a thin film transistor that has higher mobility than an amorphous Si thin film transistor and has a low current during off and can be formed at room temperature. Can be made.

Since an amorphous oxide semiconductor has high mobility and can perform circuit operation at high speed, a large-sized, high-definition, and inexpensive image display device can be manufactured. Note that when an amorphous oxide semiconductor material containing In or Zn is used for a channel, the carrier electron density is preferably set in the following range. That is, it is less than 10 ¹⁸ (cm ⁻³ ), preferably 10 ¹⁷ (cm ⁻³ ) or less, and more preferably 10 ¹⁶ (cm ⁻³ ) or less.

  Note that the concept of a repair circuit can also be introduced when a transparent amorphous oxide as described in the pamphlet of International Publication No. 2005/088726 is used for the active layer of a TFT. For example, a plurality of TFTs are prepared in one pixel as driving TFTs for a display element such as an organic EL. If there is a defective portion, a spare TFT is used using an excimer laser.

  More specifically, two sets of TFTs are prepared as switching transistors for each pixel, and two sets of TFTs are prepared as TFTs for driving an organic EL (diode). If there is no defective part, one of the two sets is a dummy TFT. If the TFT is transparent, even if a plurality of TFTs are prepared for repair, the aperture ratio is not greatly affected. The repair circuit is described in detail in Japanese Patent Application Laid-Open No. 2000-227769.

It is a circuit diagram which shows the structure of 1st embodiment of this invention. It is a timing chart which shows operation | movement of 1st embodiment. It is a circuit diagram showing an example at the time of using an n-type transistor as the first transistor Tr1 of the first embodiment. 4 is a timing chart showing the operation of FIG. 3. It is a circuit diagram which shows the example which added switch SW10 in 1st embodiment. 6 is a timing chart showing the operation of FIG. 5. 5 is a circuit diagram illustrating an example in which a transistor Tr4 is used instead of the switch SW7 in the first embodiment. FIG. It is a timing chart which shows the operation | movement of FIG. It is a circuit diagram which shows the structure of 2nd embodiment of this invention. It is a timing chart which shows operation of a second embodiment. It is a circuit diagram which shows the structure of 3rd embodiment of this invention. It is a timing chart which shows operation of a third embodiment. It is a circuit diagram which shows the example which reduced SW4 in 3rd embodiment. 14 is a timing chart showing the operation of FIG. It is a circuit diagram which shows the structure of 4th embodiment of this invention. It is a timing chart which shows operation of a 4th embodiment. It is a circuit diagram which shows the example which used SW8 instead of SW4 in 4th embodiment. It is a timing chart which shows the operation | movement of FIG. It is a circuit diagram which shows the structure of 5th embodiment of this invention. It is a timing chart which shows operation of a 5th embodiment. It is a circuit diagram which shows the example at the time of comprising a switch with a transistor in 3rd embodiment of this invention. It is a circuit diagram which shows the example at the time of comprising a switch and a transistor only by n-type transistor in 3rd embodiment of this invention. It is a figure which shows the example of the pixel which consists of an organic EL element and a drive circuit. It is a figure which shows the example of AM type organic electroluminescence display. It is a circuit diagram which shows a 1st prior art. It is a circuit diagram which shows a 2nd prior art.

Explanation of symbols

LED1 Organic EL element Tr1 First transistor Tr2 Second transistor Tr3 Third transistor Tr4 Fourth transistor C1 First capacitor C2 Second capacitor SW1 First switch SW2 Second first switch SW3 Third switch SW4 41st switch SW5 5th switch SW6 6th switch SW7 7th switch SW8 8th switch SW9 9th switch SW10 10th switch SW11 11th switch L1 1st wiring L2 2nd Wiring L3 Third wiring L4 Fourth wiring L5 Fifth wiring L6 Sixth wiring SWTr1 transistor SWTr2 transistor SWTr4 transistor SWTr7 transistor SWTr9 transistor

Claims (12)

A first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element; A drive circuit for performing drive control including:
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor; a capacitor element having one end connected to the gate of the third transistor and the other end connected to a wiring; A control circuit in which the light emission time of the display element is controlled by controlling the second transistor in a period of 3,
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor and the threshold voltage of the third transistor are accumulated,
During the third period, an on-voltage is applied to the gate of the second transistor, and a sweep voltage is applied to one end of the capacitor, thereby controlling the on-time of the second transistor. A display element drive circuit.   2. The display element driving circuit according to claim 1, wherein the sweep voltage is applied to the capacitor so that a gate voltage value of the third transistor exceeds the threshold voltage. 3. A first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element; A drive circuit for performing drive control including:
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor; a capacitor element having one end connected to the gate of the third transistor and the other end connected to a wiring; A control circuit for controlling a light emission time of the display element by controlling the second transistor during a period of 3,
After a certain voltage is applied from the wiring in the second period, a gradation voltage is applied, and the capacitor element has a charge based on a difference between the gradation voltage and the threshold voltage of the third transistor. Accumulated,
In the third period, a voltage that turns on the second transistor through the third transistor is applied to the gate of the second transistor, and then a sweep voltage is applied to the capacitor, whereby the second transistor is turned on. A display element driving circuit, wherein an ON time of the second transistor is controlled. Driving a display element having a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a drive current to the display element In the circuit
A current source circuit having a first transistor and a holding circuit for holding the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor connected in series with the first transistor; a capacitor element having one end connected to the gate of the second transistor and the other end connected to a wiring; and in the third period A control circuit for controlling a light emission time of the display element by controlling the second transistor;
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor element and the gate voltage of the second transistor are accumulated,
The display element driver circuit, wherein an on-time of the second transistor is controlled by applying a sweep voltage to one end of the capacitor in the third period. Driving a display element having a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a drive current to the display element In the circuit
A current source circuit having a first transistor and a holding circuit for holding the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor connected in series with the current source circuit and connected in parallel with the display element, and a capacitor element having one terminal connected to the gate of the second transistor and the other end connected to a wiring And a control circuit for controlling a light emission time of the display element by controlling the second transistor in the third period,
A constant voltage is applied from the wiring during the first period;
In the second period, a gradation voltage is applied from the wiring, the gate of the second transistor and one terminal are short-circuited, and the capacitor element has a gradation voltage and a gate of the second transistor. Charge based on the difference from the voltage is accumulated,
The display element driver circuit, wherein an on-time of the second transistor is controlled by applying a sweep voltage to one end of the capacitor in the third period. A first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a driving current to the display element; A drive circuit for performing drive control including:
A current source circuit comprising: a first transistor; and a holding circuit for holding the voltage of the gate of the first transistor at a voltage corresponding to a constant current supplied to the display element in the first period;
A second transistor for switching a current from the current source circuit to the display element;
A third transistor having one terminal connected to the gate of the second transistor, a capacitor having one end connected to the gate of the third transistor and the other end connected to the wiring through a switch; A control circuit that controls the light emission time of the display element by controlling the second transistor in the third period,
In the second period, charges based on the difference between the gradation voltage supplied from the wiring to the capacitor and the threshold voltage of the third transistor are accumulated,
In the third period, an ON voltage is applied to the gate of the second transistor, and an ON time of the second transistor is controlled by applying a sweep voltage to the capacitor. A display element driving circuit.   7. The device according to claim 1, wherein, in the second transistor, the constant current is a current in a subthreshold region, and an off-current is 0.1% or less of the constant current. A driving circuit for the display element. The display element, a drive circuit for a display device according to any one of claims 1 to 7, characterized in that the organic electroluminescent device. On a substrate, a display device, an image display apparatus characterized by a drive circuit of a display device according to any one of claims 1 to 7 are arranged in a matrix. A first period for setting a current to be supplied to the display element; a second period for setting a gradation of the display element; and a third period for supplying a drive current to the display element; In a display element drive circuit having
A current source circuit having a holding circuit for holding a value corresponding to a constant current supplied to the display element in the first period, and the third period in accordance with the gradation voltage supplied in the second period. And a control circuit for controlling a time for supplying a constant current from the current source circuit to the display element,
The current source circuit includes at least a first transistor,
In the control circuit, a source and a drain are connected in series between the current source circuit and the display element, a gate is connected to one end of a capacitive element directly or via a switch, and the constant current is A second transistor having a gate voltage-drain current characteristic in a subthreshold region and having an off-current of 0.1% or less of the constant current;
In the third period, a constant current is supplied to the display element by changing the gate voltage of the second transistor over time and controlling the time during which the source and drain of the second transistor are turned on. A display element driving circuit, characterized by controlling a time for the display element to operate. Driving a display element having a first period for setting a current to be supplied to the display element, a second period for setting a gradation of the display element, and a third period for supplying a drive current to the display element In the circuit
A current source circuit having a holding circuit for holding a value corresponding to a constant current supplied to the display element in the first period, and the third period in accordance with the gradation voltage supplied in the second period. And a control circuit for controlling a time for supplying a constant current from the current source circuit to the display element,
The current source circuit includes at least a first transistor;
In the control circuit, the display element and the source / drain are connected in parallel to the current source circuit, the gate is connected to one end of the capacitor element directly or via a switch, and the constant current is gate voltage-drain. A second transistor having a sub-threshold region of current characteristics and having an off-current of 0.1% or less of the constant current;
In the third period, a constant current is supplied to the display element by changing the gate voltage of the second transistor over time and controlling the time during which the source and drain of the second transistor are turned off. A display element driving circuit, characterized by controlling a time for the display element to operate. 3. A third transistor in which a gate and a source (or drain) of the second transistor are connected to each other, and the gate of the third transistor is connected to one end of the capacitor. a drive circuit for a display device according to 10.