JP5082324B2 - Active matrix light emitting device and electronic device - Google Patents

Description

  The present invention relates to an active matrix light emitting device and a pixel driving method of the active matrix light emitting device. In particular, the present invention relates to a technique that can efficiently compensate for threshold fluctuations of a driving transistor that drives a self-luminous element such as an electroluminescence (EL) element.

  In recent years, an electroluminescence (EL) element having features such as high efficiency, thinness, light weight, and low viewing angle dependency has attracted attention, and a display using the EL element has been actively developed. An EL element is a self-luminous element that emits light when an electric field is applied to a fluorescent compound. An inorganic EL element using an inorganic compound such as zinc sulfide as a luminescent substance layer and an organic compound such as diamines as a luminescent substance layer It is divided roughly into the organic EL element used as.

  In recent years, organic EL elements can be easily colored and can be operated with a direct current with a voltage much lower than that of inorganic EL elements.

  The organic EL element injects holes from the hole injection electrode toward the luminescent material layer and injects electrons from the electron injection electrode toward the luminescent material layer, so that the injected holes and electrons are recombined. Thus, the organic molecule constituting the emission center is excited, and when the excited organic molecule returns to the ground state, fluorescence is emitted. Therefore, the organic EL element can change the luminescent color by selecting the fluorescent material constituting the luminescent material layer.

  In an organic EL element, a positive voltage is applied to the transparent electrode on the anode side, while charges are accumulated when a negative voltage is applied to the metal electrode on the cathode, and the voltage value is the barrier voltage or emission threshold voltage specific to the element. If it exceeds, current starts to flow. Then, light emission having an intensity substantially proportional to the direct current value is generated. That is, the organic EL element can be said to be a current-driven self-luminous element, like a laser diode or a light emitting diode.

  The driving method of the organic EL display device is roughly divided into a passive matrix method and an active matrix method. However, in the passive matrix driving method, the number of display pixels is limited, and there are limitations in terms of life and power consumption. Therefore, as an organic EL display device driving method, an active matrix driving method that is advantageous for realizing a large-area, high-definition display panel is often used, and active matrix driving type displays have been developed. It is actively done.

  In the display device of the active matrix driving system, one electrode is patterned in a dot matrix shape, and an organic EL element formed on each electrode is driven independently. A polysilicon thin film transistor (polysilicon TFT) is formed. A polysilicon TFT is also used as a drive transistor for driving the organic EL element.

  Polysilicon TFTs have a high driving capability and can be designed to have a small pixel size, but on the other hand, it is known that variations in characteristics are large. Therefore, in the pixel drive circuit of the active matrix light-emitting device, it is important to compensate for variations in characteristics of polysilicon TFTs (particularly, variations in threshold voltage (Vth) of drive transistors that drive organic EL elements).

  That is, as described above, the luminance of each pixel is determined by the drive current value. Variations in the characteristics of the drive transistors are directly related to fluctuations in the drive current value (that is, luminance). Therefore, even if the characteristics of the drive transistor fluctuate, it is necessary to devise a circuit for keeping the drive current value constant.

  As a drive current variation compensation method, there are a current programming method (see Patent Literature 1) and a voltage programming method (see Patent Literature 2 and Patent Literature 3). Here, in the current programming method, since the amount of drive current of the data line is limited, it can be said that the voltage programming method is more advantageous in terms of faster programming.

  Patent Document 2 discloses a basic circuit configuration of a voltage programming type threshold voltage compensation pixel circuit (this technique is also described in detail in “Prior Art” section of Patent Document 3). )

  Hereinafter, the principle of threshold voltage compensation disclosed in Patent Document 2 will be briefly described.

In general, the luminance Loled of an organic EL element is proportional to the current Ioled flowing through the organic EL element. Therefore, the following formula is established between the luminance Loled of the organic EL element and the current Ioled.
Loled Ｉ Ioled = k (Vdata−Vth) ² (1)
Here, “Vdata” is a voltage (gate voltage) actually applied to the gate of the driving transistor via the data line. Vth is a threshold voltage of the driving transistor. As can be seen from this equation, the drive current is proportional to the square of the voltage obtained by subtracting the threshold voltage (Vth) of the drive transistor from the gate voltage (Vdata) of the drive transistor. The variation in (Vth) is directly related to the variation in the light emission luminance of the organic EL element. Note that k = 1/2 · μ · Cox · W / L. “Μ” is the carrier mobility of the driving transistor, “Cox” is the gate capacitor per unit area of the driving transistor, “W” is the gate width of the driving transistor, and “L” is the gate length of the driving transistor.

  Therefore, in the technique disclosed in Patent Document 2, the voltage (Vdata) applied to the gate of the drive transistor is adaptively corrected. That is, the threshold voltage (Vth) of the drive transistor itself is taken out as a correction value and stored in a capacitor, and the actual gate voltage (Vdata) given through the data line is added to the threshold value as the correction value. A voltage (vth) is applied to correct the gate voltage.

That is, (Vdata + Vth) is applied to the gate of the driving transistor. Then, the above equation (1) is transformed into the following equation (2).
Ioled = k (Vdata + Vth−Vth) ² = k · Vdata ² (2)
That is, the drive current value does not depend on the threshold voltage (Vth) of the drive transistor.

  However, this explanation is only a fundamental explanation, and the actual Vdata in the equation (2) is divided by two capacitors and the voltage value changes. That is, if the capacitor values of the two capacitors are C1 and C2, the Vdata in the equation (2) is actually Vdata · {C1 / (C1 + C2)}.

  In the technique disclosed in Patent Document 2, the writing transistor and the driving transistor are connected in an AC manner via a coupling capacitor. First, the initialization voltage (V0) is written to one end of the coupling capacitor via the data line, and then the DC potential at the connection point between the coupling capacitor and the driving transistor is set to the threshold voltage (Vth) of the driving transistor. ) Is converged to the potential reflecting.

  Then, the write transistor is turned on, and a write voltage (corresponding to Vdata in the above description) is applied from the data line. The AC component of the write voltage passes through the coupling capacitor, and the AC component (Vdata) is superimposed on the DC potential adjusted in advance (that is, the potential reflecting Vth of the driving transistor). Thus, the write voltage (Vdata) is corrected.

  The technique disclosed in Patent Document 2 is a basic technique for compensating the threshold voltage of the drive transistor, and the present invention also uses this basic technique.

  However, in the technique of Patent Document 2, first, after writing an initialization voltage to one end of the coupling capacitor via the data line, the potential at the other end of the coupling capacitor is not released without releasing the connection state with the data line. Is eventually converged to a potential reflecting the Vth of the driving transistor, after all, the above-described compensation operation is performed during one horizontal synchronization period (1H) in which the pixel is selected, and then the writing operation is also performed. It needs to be terminated. Therefore, as 1H becomes shorter, it becomes difficult to secure a sufficient compensation period.

  That is, it takes time to converge the direct current potential at the connection point between the coupling capacitor and the drive transistor to a potential reflecting Vth of the drive transistor, and this period is difficult to shorten. Therefore, if 1H becomes shorter, a necessary compensation period may not be ensured.

  Therefore, in the technique disclosed in Patent Document 3, a power supply line (compensation power supply line) for writing an initialization voltage to the coupling capacitor is provided for each pixel separately from the data line. By providing the compensation power supply line separately from the data line, the threshold voltage compensation operation can be freely performed in a state where the pixel is disconnected from the data line. That is, the threshold voltage compensation operation can be performed in parallel with the data write operation to other pixels via the data line.

According to the technique of Patent Document 3, the compensation operation is completely separated from the data write operation using the data line, and the compensation operation can be performed in an arbitrary period. Therefore, the entire 1H period is used for the compensation operation. And a sufficiently long compensation period can be secured.
Japanese Patent Laid-Open No. 2003-22049 US Pat. No. 6,229,506 JP 2004-133240 A

  As a result of the study by the inventors of the present invention, the following matters became clear.

  (1) In the technique described in Patent Document 3, a power supply line (compensation power supply line) for writing an initialization voltage to the coupling capacitor is provided for each pixel separately from the data line. The wiring layout becomes complicated.

  (2) The voltage program drive circuit described in Patent Document 2 and Patent Document 3 can write voltage data at a higher speed than the current program drive circuit described in Patent Document 1, On the other hand, as the panel becomes larger, fluctuations in the gate voltage of the driving transistor are likely to occur due to crosstalk.

  That is, when the writing transistor is turned off, the pixel is separated from the data line, but the writing transistor has a parasitic capacitor (Cds) between the source and the drain. Therefore, when the potential of the data line changes for writing to another pixel, the fluctuation component leaks through the parasitic capacitor (Cds) of the writing transistor, thereby changing the gate potential of the driving transistor. There is. In addition, when the potential of another adjacent data line varies, the gate potential of the driving transistor may change due to electromagnetic coupling.

  The present invention has been made on the basis of such considerations. The object of the present invention is to perform threshold voltage compensation of the driving TFT without complicating the circuit configuration and wiring layout, and to achieve crosstalk. Therefore, it is possible to effectively prevent fluctuations in the gate potential of the driving transistor.

  (1) An active matrix light emitting device according to the present invention includes a plurality of scanning lines, a plurality of data lines selected by a data line driver including a precharge circuit, the plurality of scanning lines, and the plurality of data lines. A plurality of pixels provided corresponding to the intersection, and each of the plurality of pixels includes a light emitting element, a write transistor having one end connected to the data line and selected by the scan line, and the write A driving transistor connected to the transistor via a coupling capacitor for supplying a driving current to the light emitting element; one end connected to a connection point between the coupling capacitor and the driving transistor; A first holding capacitor connected to a direct current potential; and provided between the drive transistor and the light emitting element; When it is necessary to precharge the light-emission control transistor that is turned on and the coupling capacitor, the precharge voltage of the data line is turned on in synchronization with the precharge timing of the data line by the precharge circuit. At least one pixel precharge transistor that precharges the coupling capacitor using a power source and a period for compensating for a variation in threshold voltage of the drive transistor. A compensation transistor that is in a diode-connected state and converges the DC potential of the coupling capacitor after precharging to a voltage value reflecting the threshold voltage of the driving transistor.

  In the present invention, in addition to the basic configuration similar to the conventional technology, each pixel is provided with a pixel precharge transistor, and when the precharge (initialization) of the coupling capacitor in the pixel is performed, the pixel precharge transistor is provided. The charge transistor is turned on in accordance with the data line precharge period. That is, in the present invention, the precharge (initialization) of the coupling capacitor of each pixel is performed by utilizing the precharge function of the data line. The precharging of the data line is performed by restoring the biased data line potential caused by data writing to a predetermined potential (for example, the midpoint potential of the power supply voltage), so that the data line at the time of the next data writing This is implemented in order to prevent the potential change delay, and it is also desirable to implement it in an organic EL panel or the like in which data is written via the data line. By using this data line precharge for the initialization (precharge) of the coupling capacitor in each pixel, a special power supply is provided only for initializing the coupling capacitor as described in Patent Document 3. There is no need to provide a line. The data line precharge is automatically performed for a very short time immediately after the start of one horizontal period (1H), and the pixel is separated from the data line at the end of the precharge period. For example, thereafter, the threshold voltage compensation operation in the pixel can be freely performed regardless of the data write operation to other pixels via the data line. That is, according to the present invention, the threshold voltage compensation operation can be performed in parallel with the data write operation to other pixels via the data line without laying a special power supply line. The data line precharge circuit is designed so that a long data line can be precharged in a short time, and has a high current driving capability. Therefore, by using the precharge current to initialize the coupling capacitor in each pixel, it is possible to easily achieve high-speed initialization. As the light-emitting element, a current-driven spontaneous light-emitting element such as an organic EL element or an inorganic EL element can be widely used, and can be applied to drive a laser diode or a light-emitting diode.

(2) Moreover, in one aspect of the active matrix light-emitting device of the present invention, the drive transistor is a first conductivity type insulated gate thin film transistor,
Each of the write transistor, the light emission control transistor, the pixel precharge transistor, and the compensation transistor is a second conductivity type insulated gate thin film transistor, and when the potential of the data line changes during data writing, The AC component accompanying the potential change is transmitted to the gate of the drive transistor through the coupling capacitor, and the charge generated by the AC component is generated as a result of being distributed by the coupling capacitor and the first holding capacitor. The potential is superimposed on the voltage value reflecting the threshold voltage of the driving transistor, and the resulting compensation voltage is supplied to the gate of the driving transistor, and the driving transistor is driven according to the gate voltage. Generating current and driving power But it is supplied to the light emitting element via the light emission control transistor.

  The type of transistor used in the pixel circuit in the present invention is clarified, and a mechanism for generating a voltage (compensation voltage) that is applied to the gate of the driving transistor and compensates for variations in threshold voltage, and a light emitting element The procedure to drive is clarified. That is, a first conductivity type (for example, P type) MOS TFT is used as the drive transistor, and a second conductivity type (for example, N type) MOS TFT is used as the write transistor, the pixel precharge transistor, and the like. In addition, a charge is generated in the first holding capacitor due to the AC component of the write voltage, and the voltage generated by the charge is distributed to the coupling capacitor and the first holding capacitor connected in series, so that the divided voltage is As a result, the divided voltage is superimposed on a DC potential that reflects the threshold voltage of the driving transistor, which has been adjusted in advance, and a compensation voltage is generated. Then, the compensation voltage is converted into voltage / current by the drive transistor to generate a drive current, and the drive current is supplied to the light emitting element via the light emission control transistor (switching TFT), and according to the drive current. Luminous emission occurs.

  (3) In another aspect of the active matrix light emitting device of the present invention, the value of the precharge voltage of the data line is larger than the white pixel potential and reflects the threshold voltage of the driving transistor. Below the voltage value.

  In the present invention, since the precharge of the data line is also used to initialize the coupling capacitor in the pixel, the precharge voltage of the data line is set to a value suitable for the initialization of the coupling capacitor. There is a need. When a P-type MOSTFT is used as the drive transistor, and the white potential is 8 to 9 V, for example, and the black potential is 13 V to 13.5 V, the precharge voltage never becomes lower than the white potential. In addition, the purpose of precharging (initializing) the coupling capacitor is to bring the gate potential of the driving transistor close to a voltage value reflecting the threshold voltage of the driving transistor, which is the target value, and then set the target value thereafter. In consideration of the point of speeding up the convergence of the potential to the target value, the target value (that is, the voltage value reflecting the threshold voltage of the driving transistor) is not exceeded.

  (4) Further, in another aspect of the active matrix light emitting device of the present invention, a second one in which one end is connected to the end on the write transistor side of the coupling capacitor and the other end is connected to a predetermined DC potential. The holding capacitor is further included.

  A holding capacitor (capacitor for stabilizing potential) is connected not only to the drive transistor end of the coupling capacitor but also to the end of the write transistor, so that the potential fluctuation at both ends of the coupling capacitor due to crosstalk is effective. It is to suppress. In other words, in the case of voltage-programming organic EL panels and the like, with the progress of larger scale and higher definition, crosstalk with the data line through the parasitic capacitor of the write transistor and electromagnetic coupling with other data lines The gate potential of the driving transistor is likely to fluctuate due to crosstalk due to the ring. Therefore, a capacitor is connected to each of both ends of the coupling capacitor to suppress potential fluctuations and stabilize light emission luminance.

  (5) In another aspect of the active matrix light-emitting device of the present invention, the capacitance ratio of the coupling capacitor and the first and second holding capacitors connected to both ends of the coupling capacitor is 1: 1: 1 is set.

  With this configuration, the combined capacitance as viewed from both ends of the coupling capacitor is maximized, and the effect of suppressing potential fluctuation can be enhanced.

  (6) In another aspect of the active matrix light emitting device of the present invention, an operation of precharging the coupling capacitor by turning on the pixel precharge transistor, and an operation of the coupling capacitor by turning on the compensation transistor are provided. The operation of converging the DC potential at the end connected to the drive transistor to a voltage value reflecting the threshold voltage of the drive transistor is performed over a plurality of horizontal synchronization periods.

  In the present invention, when the precharge period ends, the pixel precharge transistor is turned off to separate the pixel from the data line. Therefore, the threshold voltage compensation operation in the pixel can be freely performed in parallel with the data writing operation to other pixels via data. Accordingly, for example, the compensation operation of the threshold voltage in the pixel is performed using two horizontal synchronization periods (2H) immediately before the period in which one pixel is selected (that is, sufficient time is required). The gate potential of the driving transistor can be converged to the target value), or only one initialization (precharge) of the coupling capacitor is performed in one horizontal synchronization period (1H), and the next horizontal synchronization is performed. An irregular compensation operation in which the gate potential of the driving transistor is converged to the target value in the period (1H) is also possible.

  (7) In another aspect of the active matrix light-emitting device of the present invention, the light-emitting element is an organic EL element.

  In recent years, the use of organic EL elements as large display panels and the like has been expected due to advantages such as easy colorization and operation with a DC current of a much lower voltage than inorganic EL elements. According to the present invention, it is possible to reduce the luminance variation of the pixel due to the characteristic variation of the driving transistor, and further, by adopting a configuration in which a capacitance is connected to each of both ends of the coupling capacitor, crosstalk and An organic EL panel resistant to noise can be realized.

  (8) According to another aspect of the active matrix light-emitting device of the present invention, the active matrix light-emitting device has the light-emitting element formed on a substrate and the side opposite to the substrate from the light-emitting element. It has a top emission type structure in which light is emitted toward.

  In the present invention, it is necessary to provide each pixel with a pixel precharge transistor (a transistor for initializing a coupling capacitor using precharge of a data line), which increases the number of elements compared to a conventional pixel circuit. To do. In addition, when capacitors are added to suppress potential fluctuation due to crosstalk, the number of elements further increases. In a bottom emission type light emitting device in which light is emitted toward the substrate side, an increase in the number of elements arranged on the substrate may reduce the aperture ratio, and the amount of emitted light may be reduced. On the other hand, when a top emission type structure in which light is emitted toward the opposite side of the substrate is employed, a situation in which the aperture ratio decreases due to an increase in the number of elements arranged on the substrate does not occur. As a structure of the light emitting device of the present invention, it can be said that it is desirable to adopt a top emission type structure (however, it is not limited to this, and a bottom emission type can also be used).

  (9) The electronic device of the present invention is equipped with the active matrix light emitting device of the present invention.

  An active matrix light-emitting device is advantageous in realizing a display panel with a large area and high definition. Further, during the compensation period of the threshold voltage of each pixel, by turning off the light emission control transistor (switching element provided in each pixel), the coupling capacitor is initialized or the gate of the driving transistor is set. When the potential is converged to the target value, the current accompanying the compensation operation does not flow into the light emitting element, and no problem occurs.

  (10) In one aspect of the electronic apparatus of the present invention, the active matrix light-emitting device is used as a display device or a light source.

  The active matrix light-emitting device of the present invention can be used, for example, as a display panel mounted on a portable terminal or as an indicator of a vehicle-mounted device such as a car navigation device, and as a high-definition and large-screen display panel. Can also be used. For example, it can also be used as a light source in a printer.

  (11) In the pixel driving method of the active matrix light-emitting device of the present invention, the process for converging the gate potential of the driving transistor to a voltage value reflecting the threshold voltage of the driving transistor prior to data writing. After that, data writing is performed, and when writing the data, the AC component accompanying the change in potential of the data line at the time of writing is transmitted to the gate of the driving transistor via the writing transistor and the coupling capacitor. The voltage generated corresponding to the AC component is superimposed on the voltage value reflecting the threshold voltage of the driving transistor, thereby generating a corrected gate voltage for driving the driving transistor. The drive transistor is driven by the voltage to generate a drive current, and the drive current A pixel driving method for an active matrix light emitting device, which is supplied to a light emitting element via a light emission control transistor, wherein the gate potential of the driving transistor is converged to a voltage value reflecting the threshold voltage of the driving transistor. The processing for precharging the coupling capacitor using the precharge of the data line, thereby reflecting the gate potential of the drive transistor to the threshold voltage of the drive transistor, which is a target value. A first step of electrically disconnecting a pixel from the data line when the precharge period of the data line is finished, and after the precharge period of the data line is finished, the coupling capacitor Is charged via the diode-connected drive transistor, The gate voltage of the driving transistor, includes a second step to reach in a short period of time to a voltage value that reflects the threshold voltage of the driving transistor is a target value.

  In the pixel driving method of the present invention, the process for converging the gate potential of the driving transistor to a voltage value reflecting the threshold voltage of the driving transistor is performed in two stages (first step and second step). I know. In the first step, the coupling capacitor is initialized using the precharge of the data line, whereby the gate potential of the driving transistor is brought close to a voltage value reflecting the threshold voltage of the driving transistor, which is the target value. In addition, when the precharge period of the data line ends, the pixel is electrically disconnected from the data line. In the second step, the coupling capacitor is charged via a diode-connected driving transistor, whereby the gate voltage of the driving transistor is set to a target value (a voltage value reflecting the threshold voltage of the driving transistor). Make it reach in a short time. The data line precharge circuit is designed to precharge a long data line and has a high current driving capability. Therefore, if the precharge current of the data line is used, when the coupling capacitor is initialized in the first step, for example, the potential at both ends of the coupling capacitor can be rapidly increased (or decreased) to a predetermined level. In this respect, speeding up of the threshold voltage compensation operation in each pixel is realized.

  (12) Further, in one aspect of the pixel driving method of the active matrix light emitting device of the present invention, the other end of the capacitor, one end of which is connected to a fixed potential, is connected to each end of the coupling capacitor. Thus, potential fluctuations at both ends of the coupling capacitor are suppressed.

  By connecting capacitors to both ends of the coupling capacitor, potential fluctuation due to crosstalk can be effectively suppressed, and light emission luminance can be stabilized.

In the present invention, by utilizing the precharge function of the data line, it is not necessary to provide a special power supply line for each pixel in order to initialize the coupling capacitor of each pixel.
That is, variation in light emission luminance due to variation in characteristics of the drive transistor can be reduced without complicating the configuration of the pixel circuit.

  In addition, if the pixel is separated from the data line at the end of the precharge period, the threshold voltage compensation operation in the pixel is performed thereafter, and the data writing operation to other pixels via the data line is performed. It can be done freely regardless of That is, the threshold voltage compensation operation can be performed in parallel with the data write operation to other pixels via the data line. Therefore, the threshold voltage compensation operation in each pixel can be performed over a plurality of horizontal synchronization periods.

  The data line precharge circuit is designed so that a long data line can be precharged in a short time, and has a high current driving capability. Therefore, by using the precharge current to initialize the coupling capacitor in each pixel, high-speed initialization can be achieved without difficulty.

  In addition, when a configuration in which a capacitor is connected to each of both ends of the coupling capacitor is adopted, the crosstalk with the data line through the parasitic capacitor of the write transistor or electromagnetic coupling with another data line is caused. Potential fluctuation due to crosstalk is effectively suppressed, and the light emission luminance is further stabilized.

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

(First embodiment)
FIG. 1 is a block diagram showing the overall configuration of an example of an active matrix light-emitting device of the present invention (here, an organic EL display panel).

  In the organic EL display panel of FIG. 1, an organic EL element is used as a light emitting element, and a polysilicon thin film transistor (TFT) is used as an active element. In the following description, “polysilicon thin film transistor” may be referred to as “thin film transistor”, “TFT”, or simply “transistor”.

  The organic EL element is formed on a substrate on which a thin film transistor (TFT) is formed. In addition, the organic EL element has a structure in which an organic layer including a light emitting layer is sandwiched between two electrodes. In the present invention, a top emission type structure is preferably employed (for this point, refer to FIG. 10). Will be described later).

  The active matrix light-emitting device of FIG. 1 includes pixels (pixel circuits) 100a to 100f including organic EL elements, data lines (DL1, DL2), and scanning lines each having a plurality of sets arranged in a matrix. (WL1 to WL4), a scanning line driver 200, a data line driver 300 including a data line precharge circuit (M1), and pixel power supply lines (SL1, SL2).

  The pixel precharge circuit (M1) is composed of an N-type insulated gate TFT (MOSTFT) having sufficient current drive capability. This TFT (M1) is controlled to be turned on / off by a data line precharge control signal (NRG), its drain is connected to a data line precharge voltage (sometimes simply referred to as precharge voltage) VST, and its source is Are connected to the data lines (DL1, DL2). Further, the data line precharge voltage (VST) is set to 10 V or more, for example.

  The scanning line (WL1) controls on / off of a writing transistor (not shown in FIG. 1) in each pixel (100a to 100f) by a writing control signal GWRT.

  The scanning line (WL2) controls pixel precharge transistors (not shown in FIG. 1) in each pixel (100a to 100f) by a pixel precharge control signal (GPRE).

  The scanning line (WL3) controls compensation transistors (not shown in FIG. 1) in each pixel (100a to 100f) by a compensation control signal (GINIT).

  Further, the scanning line (WL4) controls light emission control transistors (not shown in FIG. 1) in each pixel (100a to 100f) by a light emission control signal (GEL).

  The scanning line driver 200 periodically drives these four scanning lines (WL1 to WL4) at a predetermined timing.

  Further, the pixel power supply line (SL1) supplies a high level power supply voltage (Vel: for example, 13 V) for causing the organic EL element to emit light to each pixel. The pixel power supply line (SL2) supplies a low level power supply voltage (VST: for example, ground potential) to each pixel.

  FIG. 2 is a circuit diagram showing a specific circuit configuration example of a main part (X portion surrounded by a dotted line in FIG. 1) of the organic EL display panel of FIG.

  As illustrated, the pixel (pixel circuit) 100a includes a write transistor (M2), a coupling capacitor (Cc), first and second holding capacitors (Ch1, ch2), and a drive transistor (M6). The pixel precharge transistor (M3, M4), the compensation transistor (M4, M5), the light emission control transistor (M7), and an organic EL element (OELD) as a light emitting element.

  The write transistor (M2) is composed of an N-type TFT, and one end is connected to the data line (DL1), the other end is connected to one end of the coupling capacitor (Cc), and the gate is connected to the scanning line WL1. The write transistor (M2) is turned on when data is written by a write control signal (GWRT).

  The drive transistor (M6) is composed of a P-type TFT, and one end is connected to the pixel power supply voltage (VEL) and the gate is connected to the other end of the coupling capacitor (Cc). The drive transistor (M6) is turned on during the light emission period of the organic EL element (OELD), and supplies a drive current to the organic EL element (OELD).

  The coupling capacitor (Cc) is interposed between the other end of the write transistor (M2) and the gate of the drive transistor (M6). In the data write period, the change component (AC component) of the write voltage is transmitted to the gate of the drive transistor (M6) through the coupling capacitor (Cc).

  One end of the first holding capacitor (ch1) is connected to the common connection point of the drive transistor (M6) and the coupling capacitor (Cc), and the other end is connected to the pixel power supply voltage (VEL). Here, the other end of the first holding capacitor (ch1) can be connected to the ground (GND) instead of the VEL. That is, the other end of the first holding capacitor (ch1) is connected to a stable DC potential.

  The first holding capacitor (ch1) holds write data (write voltage) and can maintain the light emission of the organic EL element (OELD) even in the non-selection period. The first holding capacitor (ch1) also has a function of stabilizing the gate voltage of the drive transistor (M6).

  One end of the second holding capacitor (ch2) is connected to the common connection point of the write transistor (M2) and the coupling capacitor (Cc), and the other end is connected to the pixel power supply voltage (VEL). Here, the other end of the second holding capacitor (ch2) can be connected to the ground (GND) instead of the VEL. That is, the other end of the second holding capacitor (ch1) is connected to a stable DC potential.

  This second holding capacitor (ch1) is used for crosstalk with the data line (DL1) due to the source / drain capacitance (parasitic capacitance) of the write transistor (M2) and electromagnetic coupling with other data lines. It is provided in order to suppress fluctuations in the potential at one end of the coupling capacitor due to crosstalk. As a result, the potential of the gate of the driving transistor (M6) is stabilized. This point will be described later with reference to FIG.

  One end of the pixel precharge transistor (M3) is connected to the data line DL1, and the gate is connected to the scanning line (WL2). The pixel precharge transistor (M3) is turned on in the data line precharge period (period in which the data line precharge circuit M1 is turned on) by the pixel precharge control signal (GPRE), and the coupling capacitor (Cc) is precharged. (initialize. As a result, the potential at both ends of the coupling capacitor (Cc) is raised to a level close to the convergence target voltage (this point will be described with reference to FIG. 3). Further, the pixel precharge transistor (M3) is turned off when the data line precharge period ends, whereby the pixel (specifically, the coupling capacitor Cc) is disconnected from the data line (DL1).

  Since the compensation transistor (M4) also contributes to precharging (initializing) the coupling capacitor (Cc), it can be said that the compensation transistor (M4) also functions as a pixel precharge transistor. .

  The gates of the compensation transistors (M4, M5) are connected to the scanning line (WL3), and are turned on during the threshold voltage compensation period by the compensation control signal (GINIT). The compensation transistors (M4, M5) have a direct current potential at the end of the coupling capacitor (Cc) on the write transistor (M2) side as a target value (a voltage value reflecting the threshold voltage of the drive transistor M6 (that is, write data). It is a compensation value (correction value) that is added to (1))) and forms a current path for convergence. That is, it works to generate a compensation value (correction value) of the gate voltage for absorbing variations in the threshold voltage of the drive transistor (M6). Focusing on this point, the transistors (M4, M5) Is referred to as a “compensation transistor”.

  In addition, as described above, the compensation transistor (M4) also has a function of forming a current path for precharging (initializing) the coupling capacitor (Cc).

  The light emission control transistor (M7) is interposed between the drive transistor (M6) and the organic EL element (OLED), and its gate is connected to the scanning line (WL4). The light emission control transistor (M7) is turned on in the light emission period of the organic EL element (OLED) by the light emission control signal (GEL), and supplies a drive current to the organic EL element light emission control transistor (M7) (OLED). An organic EL element (OLED) is caused to emit light. Since the light emission control transistor (M7) exists, the pixel (pixel circuit) 100a is an active matrix pixel (pixel circuit).

  Next, the operation of the pixel (pixel circuit) in FIG. 2 will be described. FIG. 3 is a diagram for explaining the operation timing of the pixel (pixel circuit) of FIG. 2 and the change in the gate voltage waveform of the drive transistor.

  In FIG. 3, each of time t1 to time t2, time t2 to time t6, time t6 to time t9, and time t9 to time t10 corresponds to one horizontal synchronization period (denoted as 1H in the figure).

  In the case of FIG. 3, before the time t2 and after the time t9 are “light emission periods” in which the organic EL elements (OLEDs) emit light. Further, the period from time t3 to time t5 is a “compensation period” for compensating for the threshold voltage variation of the drive transistor (M6). The period from time t7 to time t8 is a “writing period” in which data is written from the data line (DL1) through the writing transistor and the coupling capacitor.

  In a very short period immediately after the start of each horizontal synchronization period (1H), the data line precharge signal (NRG) becomes a high level, thereby turning on the data line precharge circuit (M1) and precharging the data line. Charging is performed.

  For the pixel 100a in FIG. 2, the pixel precharge control signal (GPRE) becomes high level from time t3 to time t4 (that is, becomes high level in synchronization with the data line precharge period). During a period in which the pixel precharge control signal (GPRE) is at a high level, the pixel precharge transistor (M3) is turned on, and the pixel 100a is connected to the data line (DL1) via the pixel precharge transistor (M3). The As a result, the coupling capacitor (Cc) is precharged (initialized). However, the pixel precharge transistor (M3) is turned on only during the precharge period of the data line (DL1), and is turned off as soon as that period ends.

  Further, the compensation control signal (GINIT) is at a high level during the period (compensation period) from time t3 to time t5. As a result, the compensation transistors (M4, M5) are turned on, the drive transistor (M6) is in a diode connection state, and a current path is formed that connects the anode of the diode and both ends of the coupling capacitor (Cc). Is done. The potential across the coupling capacitor (Cc) converges to a voltage value (VEL−Vth) reflecting the threshold voltage (Vth) of the drive transistor (M6).

  The write control signal (GWRT) is at a high level during the period from time t7 to time t8, whereby the write transistor (M2) is turned on. The nth data (DATAn) is written into the pixel 100a from the data line (DL1). As a result, the drive transistor (M6) is turned on. Further, the written data (write voltage) is held even during the non-selection period of the pixel 100a because the first holding capacitor (ch1) exists.

  The light emission control signal (GEL) becomes a high level at time t9 after the data writing is completed, whereby the light emission control transistor (M7) is turned on. A drive current from the drive transistor (M6) is supplied to the organic EL element (OLED), and the organic EL element (OLED) emits light.

  The lower side of FIG. 3 shows how the gate voltage of the driving transistor (M6) changes. At time t3, the pixel precharge signal (GPRE) becomes high level and the pixel precharge transistor (M3) is turned on. At time t3, the compensation control signal (GINIT) also changes to high level. The transistor (M4) is also turned on at the same time. As a result, the data line (DL1) and each of both ends of the coupling capacitor (Cc) are electrically connected. Therefore, in the period from time t3 to time t4, the coupling capacitor (Cc) is rapidly precharged by the precharge current of the data line (DL1). Therefore, the gate potential of the driving transistor (M6) rapidly rises to the precharge voltage of the data line (VST: voltage connected to one end of the data line precharge circuit (M1)). Since the data line precharge circuit (M1) has a high current drive capability, the coupling capacitor (Cc) can be precharged at high speed.

  At time t4, since the pixel precharge transistor (M3) is turned off, the pixel 100a is disconnected from the data line (DL1). At this time, when the compensation transistor M5 is turned on, the gate and drain of the driving transistor are short-circuited, and the diode is connected.

  Therefore, from time t4 to time t7, the forward current from the diode-connected driving transistor (M6) is directly supplied to the driving transistor (M6) side end of the coupling capacitor (Cc). The forward current is also supplied to the end of the coupling capacitor (Cc) on the side of the writing transistor (M2) via the compensation transistor (M4) which is turned on, and thereby the coupling capacitor (Cc) Both ends are charged and rise with time, and eventually converge to a potential (VEL−Vh) reflecting the threshold voltage (Vth) of the drive transistor (M6). Since the gate potential of the driving transistor (M6) is the potential (VST) close to the convergence target value due to the precharge, the convergence to (VEL−Vth) is accelerated. This converged voltage value (VEL−Vth) becomes a compensation (correction) voltage value for compensating (correcting) the normal write voltage.

  In addition, although it takes a certain amount of time for the gate voltage of the drive transistor (M6) to converge to (VEL−Vth), in the present invention, after the pixel precharge period, the pixel is electrically connected from the data line (DL1). Therefore, data writing to another pixel via the data line (DL1) and compensation operation inside the pixel 100a can be performed in parallel, and the compensation operation is performed over a plurality of horizontal synchronization periods. Therefore, a sufficient compensation period can be ensured.

  Data is written at time t7, and the written data is retained after time t8.

  Next, a series of operations shown in FIG. 3 will be specifically described with reference to FIGS.

  4 to 7 are circuit diagrams for explaining specific operations (in particular, on / off states and current paths of the respective transistors) of the pixel (pixel circuit) in FIG. In FIG. 4 to FIG. 7, the other transistors except the drive transistor (M6) are expressed as switches in order to clarify their open / closed state.

(1) Pixel precharge (initialization) operation (operation at times t2 to t3 in FIG. 3)
As shown in FIG. 4, both ends of the coupling capacitor (Cc) are precharged (initialized) via the current path (1). As a result, the potential across the coupling capacitor (Cc) rises rapidly to the data line precharge voltage (VST).

(2) Compensation voltage generation operation (operation at times t4 to t7 in FIG. 3)
As shown in FIG. 5, the forward current is supplied from the diode-connected driving transistor (M6) via the current path (2), whereby the potential across the coupling capacitor (Cc) is It converges to a voltage value (VEL−Vth) reflecting the threshold voltage (Vth) of the driving transistor (M6).

(3) Write operation (operation at times t7 to t8 in FIG. 3)
As shown in FIG. 6, the potential of the data line (DL1) changes, and the alternating current component (VDATA) accompanying the potential change passes through the coupling capacitor (Cc) (that is, through the current path (3)). ), And is transmitted to the gate of the driving transistor (M6).

  Then, a charge corresponding to the write voltage (VDATA) is generated in the first holding capacitor (Ch1). Assuming that one end of the first holding capacitor (Ch1) is connected to the pixel power supply voltage (VEL), (VEL-VDATA) is applied to both ends of the first holding capacitor (Ch1), and accordingly Accumulated charge.

  The charge generated by the write voltage (VDATA) is distributed by the coupling capacitor (Cc) and the first holding capacitor (Ch1) (current path (4) in FIG. 6), thereby dividing the voltage. .

  The resulting voltage is ({Cc / (Cc + Ch1)} · (VEL−VDATA)). This is the voltage generated by the AC component accompanying the write operation. This voltage is superimposed on the voltage value (VEL−Vth) reflecting the threshold voltage of the drive transistor (M6), and the resulting compensation voltage ((VEL−Vth) − {Cc / (Cc + Ch1)}. (VEL-VDATA)) is supplied to the gate of the driving transistor (M6).

(4) Light emission operation (operation after time t9 in FIG. 3)
As shown in FIG. 7, the drive transistor (M6) generates a drive current corresponding to the gate voltage, and the drive current is supplied to the organic EL element (OLED) via the light emission control transistor (M7) (see FIG. 7). Current path (7)). Thereby, light (EM) is emitted from the organic EL element (OLED).

  Next, the effect of suppressing potential fluctuation by adding the second storage capacitor (Ch2) will be described.

  FIG. 8 is a circuit diagram for explaining the effect of connecting the holding capacitor not only to the end on the drive transistor side of the coupling capacitor but also to the end on the write transistor side. The configuration of the pixel (pixel circuit) 100a in FIG. 8 is the same as that of the pixel (pixel circuit) shown in FIG. 2, but FIG. 8 is similar to FIGS. 4 to 7 except for the drive transistor (M6). This transistor is expressed as a switch.

  A point to be noted in FIG. 8 is that a parasitic capacitance (Cds) is interposed between the source and drain of the writing transistor (M2), and the pixel 100a and the data line (DL1) are interposed via this parasitic capacitance. Due to the occurrence of crosstalk (AZ1 and AZ2 in the figure are noise components due to crosstalk) and electromagnetic coupling with other data lines (DL2), the coupling capacitor (Cc ) Each potential (A, B) at both ends may fluctuate. In the figure, a dotted arrow (AZ3) indicates noise due to electromagnetic coupling between the data line (DL2) and the coupling capacitor (Cc).

  That is, in the case of a voltage programming type organic EL panel or the like, along with the progress of large scale and high definition, when writing data to another pixel (100b), the parasitic capacitor (Cds) of the writing transistor (M2) in the pixel 100a. ) Through the data line (DL1). Further, the potential of the end point of the coupling capacitor (Cc) is likely to vary due to crosstalk caused by electromagnetic coupling with another data line (DL2). The potential fluctuation at the end point of the coupling capacitor (Cc) is directly linked to the fluctuation of the gate potential of the driving transistor (M6), which causes variations in the light emission luminance of the organic EL element (OLED).

  Therefore, in the pixel (pixel circuit) 100a in FIG. 8 (FIG. 2), not only the end (B) on the drive transistor (M6) side of the coupling capacitor (Cc) but also the end (A) on the write transistor (M2) side. In addition, a second holding capacitor (capacitor for stabilizing the potential: Ch2) is connected to effectively suppress the fluctuation of the potential at both ends of the coupling capacitor due to crosstalk.

  That is, the second holding capacitor (Ch2) releases high-frequency noise to a stable DC potential (VEL or GND), and, for low-frequency noise, absorbs charges due to noise and suppresses potential fluctuations. This enhances the effect of suppressing fluctuations in the gate potential of the drive transistor (M6).

  Here, the capacitance ratio between the coupling capacitor (Cc) and the first and second holding capacitors (Ch1, Ch2) connected to both ends of the coupling capacitor (Cc) is 1: 1: 1. Is preferably set. That is, with this configuration, the combined capacitance seen from both ends of the coupling capacitor is maximized, and the effect of suppressing potential fluctuation can be further enhanced.

  Next, an example in which the compensation operation in each pixel is performed over a plurality of horizontal synchronization periods will be described.

  FIGS. 9A and 9B are diagrams for describing an embodiment when the compensation operation in each pixel is performed over a plurality of horizontal synchronization periods.

  As described above, in the organic EL panel of the present embodiment, when the pixel precharge period ends, the pixel precharge transistor is turned off to separate the pixel from the data line. Therefore, the threshold voltage compensation operation in the pixel can be freely performed in parallel with the data writing operation to other pixels via data. Accordingly, the compensation operation in each pixel can be performed over a plurality of horizontal synchronization periods, and a sufficient compensation period can be ensured with certainty.

  In FIG. 9A, the threshold voltage compensation operation in the pixel is performed using two horizontal synchronization periods (t1 to t4) immediately before the pixel selection period (t4 to t6). ing. In the example of FIG. 9A, the coupling capacitor (Cc) is precharged from time t1 to time t2, and the gate potential of the driving transistor is converged to (VEL−Vth) at time t2 to time t4. We are carrying out.

  In FIG. 9B, only the coupling capacitor (Cc) is precharged in the first horizontal synchronization period (time t1 to t3). Then, in the next horizontal synchronization period (time t3 to t4), an operation of converging the gate potential of the driving transistor to (VEL−Vth) is performed. Such an irregular compensation operation can be performed freely.

  Next, a cross-sectional structure of a pixel and a daylighting method in an active matrix organic EL panel will be described.

  10A and 10B are cross-sectional views of a device for explaining a cross-sectional structure of a pixel and a daylighting method in an active matrix type organic EL panel, and FIG. 10A is a bottom emission type. FIG. 10B is a diagram showing a structure, and FIG. 10B is a diagram showing a top emission type structure.

  10 (a) and 10 (b), reference numeral 21 is a transparent glass substrate, reference numeral 22 is a transparent electrode (ITO), and reference numeral 23 is an organic light emitting layer (an organic electron transport layer or The reference numeral 24 is a metal electrode such as aluminum, and the reference numeral 25 is a TFT (polysilicon thin film transistor) circuit.

  As the polysilicon thin film transistor constituting the TFT circuit 25, it is preferable to use a so-called “low temperature polysilicon thin film transistor” in which the maximum temperature during manufacture is suppressed to 600 ° C. or less.

  The organic light emitting layer 23 can be formed by, for example, an ink jet printing method. Moreover, the transparent electrode 22 and the metal electrode 24 can be formed by sputtering method, for example.

  In the bottom emission type structure of FIG. 10A, light (EM) is emitted through the substrate 21. On the other hand, in the top emission type structure of FIG. 10B, light (EM) is emitted in the direction opposite to the substrate 21.

In the case of the bottom emission structure of FIG. 10A, if the number of elements constituting the pixel circuit is increased and the occupied area of the TFT circuit 25 is increased, the aperture ratio of the light emitting portion is reduced accordingly, and the emission luminance is reduced. It may be reduced. In this regard, in the top emission type structure of FIG. 10B, there is no concern that the aperture ratio will decrease even if the area occupied by the TFT circuit 25 increases. In the present invention, considering that the number of elements of the pixel circuit is slightly increased, it can be said that the organic EL panel of the present invention preferably employs the top emission type structure of FIG. However, the present invention is not limited to this, and a bottom emission type structure can also be adopted when a slight decrease in the aperture ratio is not a problem.
(Second Embodiment)
In this embodiment, an electronic device using the active matrix light-emitting device of the present invention will be described.

  Note that the light-emitting device of the present invention is particularly effective when used in small portable electronic devices such as a mobile phone, a computer, a CD player, and a DVD player. Of course, it is not limited to these.

(1) Display Panel FIG. 11 is a diagram showing an overall layout configuration of a display panel using the active matrix light-emitting device of the present invention.

  This display panel includes an active matrix organic EL element 200 having voltage-programmed pixels, a scanning line driver 210 incorporating a level shifter, a flexible TAB tape 220, and an external analog driver LSI 230 with a RAM / controller.

(2) Mobile Computer FIG. 12 is a perspective view showing an appearance of a mobile personal computer equipped with the display panel of FIG.

  In FIG. 12, a personal computer 1100 includes a main body 1104 including a keyboard 1102 and a display unit 1106.

(3) Mobile Phone Terminal FIG. 13 is a perspective view showing an overview of a mobile phone terminal equipped with the display panel of the present invention.

  The cellular phone 1200 includes a plurality of operation keys 1202, a speaker 1204, a microphone 1206, and the display panel 100 of the present invention.

(4) Digital Still Camera FIG. 14 is a diagram showing the appearance and usage of a digital still camera using the organic EL panel of the present invention as a viewfinder.

  The digital still camera 1300 includes an organic EL panel 100 that performs display based on an image signal from a CCD on the rear surface of the case 1302. Therefore, the organic EL panel 100 functions as a finder that displays a subject. A light receiving unit 1304 having an optical lens and a CCD is provided on the front surface (rear of the drawing) of the case 1302.

  When the photographer determines the subject image displayed on the organic electroluminescence element panel 100 and releases the shutter, the image signal from the CCD is transmitted and stored in the memory in the circuit board 1308. In the digital still camera 1300, a video signal output terminal 1312 and a data communication input / output terminal 1314 are provided on the side surface of the case 1302. As shown, a TV monitor 1430 and a personal computer 1440 are connected to a video signal terminal 1312 and an input / output terminal 1314, respectively, as necessary. By a predetermined operation, an image signal stored in the memory of the circuit board 1308 is output to the TV monitor 1430 and the personal computer 1440.

  The present invention includes a TV set, a viewfinder type and a monitoring type video tape recorder, a PDA terminal, a car navigation system, an electronic notebook, a calculator, a word processor, a workstation, a TV phone, a POS system terminal, It can be used as a display panel in a device with a touch panel.

  The light emitting device of the present invention can also be used as a light source for a printer or the like. The pixel driving circuit according to the present invention can be applied to, for example, a magnetoresistive RAM, a capacitor sensor, a charge sensor, a DNA sensor, a night vision camera, and many other devices.

  The pixel driving circuit according to the present invention can be used not only for driving organic / inorganic EL elements but also for driving laser diodes (LD) and light emitting diodes.

  As described above, according to the present invention, the threshold voltage compensation is performed in parallel with the data write operation to other pixels via the data line without complicating the circuit configuration and the wiring layout. It may be possible to perform the operation.

Further, when a configuration in which a capacitor is connected to each of both ends of the coupling capacitor is employed, crosstalk with the data line via the parasitic capacitor (Cds) of the write transistor or electromagnetic connection with other data lines is possible. The potential fluctuation due to crosstalk due to coupling is effectively suppressed, and the light emission luminance is further stabilized. The active matrix light-emitting device of the present invention is capable of data without complicating the circuit configuration and wiring layout. It is possible to perform the threshold voltage compensation operation in parallel with the data write operation to other pixels via the line, and therefore the active matrix light emitting device and the active matrix light emission It is useful as a pixel driving method for an apparatus, and particularly for an electroluminescence (EL) element. This is useful as a technique for efficiently compensating for threshold fluctuations of a driving transistor for driving such a self-light emitting element.

1 is a block diagram illustrating an overall configuration of an example of an active matrix light-emitting device of the present invention (here, an organic EL display panel). FIG. 2 is a circuit diagram illustrating a specific circuit configuration example of a main part (X portion surrounded by a dotted line in FIG. 1) of the organic EL display panel of FIG. FIG. 3 is a diagram for explaining an operation timing of the pixel (pixel circuit) of FIG. 2 and a change in a gate voltage waveform of a drive transistor. 2 is a circuit diagram for explaining a specific operation (on / off state and current path of each transistor) at the time of precharging in the pixel (pixel circuit) of FIG. 2 is a circuit diagram for explaining a specific operation (on / off state and current path of each transistor) when a compensation voltage is generated in the pixel (pixel circuit) of FIG. FIG. 2 is a circuit diagram for explaining a specific operation (on / off state and current path of each transistor) at the time of data writing in the pixel (pixel circuit) of FIG. FIG. 2 is a circuit diagram for explaining a specific operation (on / off state and current path of each transistor) during light emission in the pixel (pixel circuit) of FIG. FIG. 6 is a circuit diagram for explaining the effect of connecting a holding capacitor not only to the end on the drive transistor side of the coupling capacitor but also to the end on the write transistor side. (A), (b) is a figure for demonstrating the embodiment in the case of implementing the compensation operation in each pixel over several horizontal synchronizing periods, respectively. 10A and 10B are cross-sectional views of a device for explaining a cross-sectional structure of a pixel and a daylighting method in an active matrix organic EL panel, and FIG. 10A is a view showing a bottom emission type structure. (B) is a diagram showing a top emission type structure. 1 is a diagram showing an overall layout configuration of a display panel using an active matrix light emitting device of the present invention. It is a perspective view which shows the external appearance of the mobile personal computer carrying the display panel of FIG. It is a perspective view which shows the external appearance of the mobile telephone terminal carrying the display panel of this invention. It is a figure which shows the external appearance and usage aspect of a digital still camera using the organic EL panel of this invention as a finder.

Explanation of symbols

21 glass substrate, 22 transparent electrode (ITO), 23 organic light emitting layer,
24 metal electrode layer, 25 TFT circuit,
100 (100a to 100f) pixel (pixel circuit), 200 scanning line driver,
300 data line drivers, WL1-WL4 scan lines, DL1, DL2 data lines,
M1 data line precharge circuit (data line precharge transistor),
M2 write transistor, M3 pixel precharge transistor,
M4 and M5 compensation transistors (where M4 also serves as a pixel precharge transistor), M6 drive transistor (drive TFT), M7 light emission control transistor,
Light emitting elements such as OLED organic EL elements, Ch1 first holding capacitor,
Ch2 second holding capacitor (stabilizing capacity), Cc coupling capacitor,
VEL pixel power supply voltage (high level), VCT pixel power supply voltage (low level),
SL1 SL2 pixel power line, NRG data line precharge control signal,
GWRT write control signal, GPRE pixel precharge control signal,
GINIT compensation control signal, GEL emission control signal,
VDATA write data (write voltage)

Claims (10)

A plurality of scan lines;
A plurality of data lines selected by a data line driver comprising a precharge circuit;
A plurality of pixels provided corresponding to intersections of the plurality of scanning lines and the plurality of data lines,
Each of the plurality of pixels is
A light emitting element;
A driving transistor for supplying a driving current to the light emitting element;
A write transistor having one end connected to one of the plurality of data lines and turned on in a write period selected by one of the plurality of scan lines;
A coupling capacitor connected between the other end of the write transistor and the gate of the drive transistor;
A first holding capacitor having one end connected to a connection point between the coupling capacitor and the driving transistor and the other end connected to a predetermined DC potential;
A light emission control transistor provided between the drive transistor and the light emitting element and turned on during a light emission period of the light emitting element;
A first transistor connected between a connection point of the coupling capacitor and the write transistor and the data line and turned on in a precharge period synchronized with a precharge timing of the data line by the precharge circuit;
A second transistor connected to both ends of the coupling capacitor;
A third transistor for setting the driving transistor in a diode connection state;
Have
The second transistor and the third transistor are turned on in a compensation period including the precharge period and the subsequent period before the write period .
The active matrix light emitting device, wherein the address period is set within one horizontal scanning period, and the compensation period is provided over a plurality of horizontal scanning periods . The active matrix light-emitting device according to claim 1 ,
The first transistor and the second transistor are turned on during the precharge period and function as a pixel precharge transistor that precharges the coupling capacitor using a precharge voltage of the data line,
The second transistor and the third transistor are turned on during the compensation period to place the driving transistor in a diode connection state, and the DC potential of the coupling capacitor after precharging is set to the threshold voltage of the driving transistor. Functions as a compensation transistor that converges to the reflected voltage value,
An active matrix light-emitting device characterized by the above. The active matrix light-emitting device according to claim 1 or 2 ,
The driving transistor is a first conductivity type insulated gate thin film transistor,
Each of the write transistor, the light emission control transistor, the first transistor, the second transistor, and the third transistor is a second conductivity type insulated gate thin film transistor,
In addition, when the potential of the data line changes during the data write period, an AC component accompanying the potential change is transmitted to the gate of the drive transistor via the write transistor and the coupling capacitor, and is generated by the AC component. The potential generated as a result of the charge being distributed by the coupling capacitor and the first holding capacitor is superimposed on the voltage value reflecting the threshold voltage of the driving transistor, and the resulting compensation voltage is The drive transistor is supplied to a gate of the drive transistor, the drive transistor generates a drive current according to the gate voltage, and the drive current is supplied to the light emitting element through the light emission control transistor. Active matrix light emitting device. An active matrix type light emitting device according to any one of claims 1 to 3,
The active matrix light emitting device according to claim 1, wherein a value of a precharge voltage of the data line is larger than a white pixel potential and not more than a voltage value reflecting a threshold voltage of the driving transistor. An active matrix type light emitting device according to any one of claims 1-4,
An active matrix light-emitting device, further comprising: a second holding capacitor having one end connected to the end of the coupling capacitor on the side of the writing transistor and the other end connected to a predetermined DC potential. The active matrix light-emitting device according to claim 5 ,
An active matrix type wherein a capacitance ratio of the coupling capacitor and the first and second holding capacitors connected to both ends of the coupling capacitor is set to 1: 1: 1 Light emitting device. An active matrix type light emitting device according to any one of claims 1 to 6,
The active matrix light-emitting device, wherein the light-emitting element is an organic EL element. An active matrix type light emitting device according to any one of claims 1-7,
The active matrix light-emitting device has a top emission type structure in which the light-emitting element is formed on a substrate and light is emitted from the light-emitting element toward the opposite side of the substrate. An active matrix light emitting device. Electronic device equipped with the active matrix light-emitting device according to any one of claims 1-8. The electronic device according to claim 9 ,
The active matrix light-emitting device is used as a display device or as a light source.

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