JP4517927B2 - Electro-optical device and electronic apparatus - Google Patents

Description

  The present invention relates to a unit circuit suitable for driving a driven element and an electronic element such as an organic light emitting element and a liquid crystal element, a control method thereof, an electronic device such as an electro-optical device, and an electronic apparatus.

  Transistors are generally used to actively drive electro-optic elements such as liquid crystal elements, organic light emitting diodes (hereinafter simply referred to as “OLED elements”). In order to achieve this, it is necessary to precisely control the transistor.

  Conventionally, a low-temperature polysilicon (LTPS) transistor has been used for this type of drive transistor. However, in recent years, the manufacturing cost can be reduced and uniform characteristics can be easily obtained. Transistors are attracting attention. However, it is known that the threshold voltage of an amorphous silicon transistor fluctuates when a voltage in the same direction such as a positive voltage or a negative voltage is continuously applied to the gate electrode. It has been pointed out that the display quality deteriorates due to changes in the brightness of the OLED element due to the fluctuation.

This is because the characteristics change due to the influence of accumulated carriers or the like when carriers are allowed to flow through the transistor. This tendency is particularly noticeable when an amorphous silicon transistor is used as a drive transistor. In order to stabilize the characteristics, a technique of applying a negative voltage after applying a positive voltage to the gate electrode of the drive transistor has been proposed. (For example, refer nonpatent literature 1).
Bong-Hyun You, 4 others, “Polarity-Balanced Driving to Reduce VTHShift in a to reduce the threshold voltage shift of a-Si used in active matrix OLED devices -Si for Active-Matrix OLEDs), SID Symposium Digest of Technical Papers, (USA), Society for Information Display, May 2004, 35th Volume 1, No. 1, p. 272-275 (see FIG. 3 (a) and (b))

However, in the above technique, there is a problem that the circuit configuration is complicated such that two drive transistors are required and two capacitive elements are required for each drive transistor. In particular, when the number of circuit elements such as transistors and capacitors increases, the circuit area increases correspondingly, resulting in a problem that the aperture ratio decreases.
In the above technique, the negative voltage to be applied to the gate electrode of the driving transistor is supplied separately from the positive voltage, so that not only the circuit configuration is complicated, but also the dynamic range of the voltage value is wide. Therefore, there is an adverse effect that the load on the circuit and the power consumption increase.

  One of the objects of the present invention is a unit circuit that can apply a negative voltage to a drive transistor with a simple circuit configuration when the transistor is used as a drive transistor of a driven element in consideration of the above-described circumstances. An object is to provide a control method, an electronic apparatus, an electro-optical apparatus, and an electronic apparatus.

  In order to solve the above problems, a unit circuit according to the present invention includes a first electrode, a second electrode, and a capacitor including a dielectric layer sandwiched between the first electrode and the second electrode. An element, a transistor having a gate electrode connected to the first electrode, a first switching element for controlling electrical connection between the first electrode and a predetermined potential, and the second electrode A second switching element, and after the first switching element is turned on, the potential of the first electrode is set to the predetermined potential, and then the first switching element is turned off. Thus, the first operation is supplied to the second electrode through the second switching element set to the on state in a state where the first electrode is electrically disconnected from the predetermined potential. The first signal The potential of the pole is set to the first potential, and the first switching element is turned on after the end of the first period in which the potential of the first electrode is set to the first potential. A second period in which a second operation signal is supplied to the second electrode through the second switching element in which the potential of the first electrode is set to the predetermined potential and set to the on state. Provided, and after the end of the second period, the first switching element is turned off, so that the first electrode is electrically disconnected from the predetermined potential and set to the on state. The potential of the first electrode is set to the second potential by the third operation signal supplied to the second electrode via the second switching element, and the first potential and the second potential are set. The predetermined potential is the reference potential. It is the potential of the opposite sign to each other in case, characterized by.

  According to the present invention, since the first switching element and the second switching element are simultaneously turned on in the second period, the gate electrode of the transistor connected to the first electrode of the capacitor element has a predetermined potential. On the other hand, the second operation signal is supplied to the second electrode of the capacitor. As a result, a potential difference occurs between both ends of the capacitive element. Then, after the second period ends, when the first switching element is turned off, the gate electrode of the transistor is in a floating state. Under this state, the second electrode of the capacitor element is connected to the second electrode through the second switching element. A third operating signal is provided. Then, the potential of the first electrode changes while maintaining the potential difference of the capacitor. Here, the potential of the first electrode is set to a second potential having the opposite sign to the first potential when the predetermined potential is set as a reference potential. As described above, according to the present invention, the first potential and the second potential having different polarities can be applied to the gate electrode of the transistor with a simple circuit configuration including two switching elements and one capacitance element. As a result, it is possible to suppress a change in threshold voltage due to the influence of accumulated carriers and the like by continuing carrier flow through the transistor. In particular, an amorphous silicon transistor has a large effect in the case of employing an amorphous silicon transistor because a variation in threshold voltage caused by flowing carriers in one direction is large. Note that the first period and the second period are not necessarily continuous, and it is a matter of course that a margin may be provided between them.

  In this unit circuit, it is preferable that the first potential is higher than the predetermined potential, and the second potential is lower than the predetermined potential. In the unit circuit described above, the first operation signal and the second operation signal may have different potentials, but preferably have the same potential. In this case, the magnitude of the potential difference between the predetermined potential and the first potential and the potential difference between the predetermined potential and the second potential can be made equal.

  Next, a method for controlling a unit circuit according to the present invention includes a first electrode, a second electrode, and a dielectric layer sandwiched between the first electrode and the second electrode. A transistor having a gate electrode connected to the first electrode, a first switching element for controlling electrical connection between the first electrode and a predetermined potential, and a first electrode connected to the second electrode 2 is a method for controlling a unit circuit comprising: a switching element; wherein the first switching element is turned on to set the potential of the first electrode to the predetermined potential; When the first switching element is turned off, the first electrode is electrically disconnected from the predetermined potential, and the second electrode is set via the second switching element set to the on state. The first movement supplied to The potential of the first electrode is set to a first potential by a signal, and the first switching element is turned on after the period in which the potential of the first electrode is set to the first potential. In the state where the potential of the first electrode is set to the predetermined potential, a second operation signal is supplied to the second electrode via the second switching element set to the on state, By turning off the first switching element, the first electrode is electrically disconnected from the predetermined potential, and the second switching element is set to the on state via the second switching element. By supplying a third operation signal to the electrode, the potential of the first electrode is set to the second potential, and the first potential and the second potential are set to the reference potential as the predetermined potential. Set the potentials to opposite signs And, characterized by. According to the present invention, the first potential and the second potential having different polarities can be applied to the gate electrode of the transistor in a simple unit circuit configuration including two switching elements and one capacitance element. Thereby, a change in characteristics of the transistor can be suppressed. In particular, an amorphous silicon transistor has a large effect in the case of employing an amorphous silicon transistor because a variation in threshold voltage caused by flowing carriers in one direction is large.

  Next, an electronic device according to the present invention includes a plurality of first signal lines, a plurality of second signal lines, a plurality of power supply lines, and a plurality of unit circuits, and the plurality of unit circuits. Each of which includes a first electrode, a second electrode, and a capacitor layer including the first electrode and a dielectric layer sandwiched between the second electrode, and a gate electrode on the first electrode. , A first switching element for controlling electrical connection between the first electrode and one of the plurality of power supply lines, and a second connected to the second electrode. The first switching element is turned on, and the first switching element is turned off after the first electrode is electrically connected to the one power line. Therefore, the first electrode is the one power line. A first operation signal supplied to the second electrode through the second switching element set to an on state in the electrically disconnected state causes the potential of the first electrode to be the first. After the end of the first period in which the potential of the first electrode is set to the first potential, the first switching element is turned on, so that the first electrode becomes There is provided a second period in which a second operation signal is supplied to the second electrode through the second switching element that is electrically connected to the one power supply line and set to the on state. After the end of the second period, the first switching element is turned off, so that the first electrode is electrically disconnected from the one power supply line and set to the on state. Through the second switching element By the third operation signal supplied to the second electrode, the potential of the first electrode being set to the second potential, characterized by.

  According to this electronic device, different potentials such as the first potential and the second potential can be applied to the gate electrode of the transistor. Here, it is preferable that the one power supply line is set to a predetermined potential, and the first potential and the second potential are potentials having opposite signs when the predetermined potential is a reference potential. In this case, since a potential with the opposite sign can be applied to the gate electrode of the transistor, it is possible to suppress changes in the characteristics of the transistor.

  Next, an electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, and a plurality of pixel circuits provided corresponding to intersections of the plurality of scanning lines and the plurality of data lines. A scanning line driving circuit for driving the plurality of scanning lines, and a data line driving circuit for supplying a data signal to the plurality of data lines, wherein the plurality of scanning lines include a plurality of scanning lines. Each of the plurality of pixel circuits includes an electro-optical element, a transistor that drives the electro-optical element, and one end connected to the gate electrode of the transistor. On / off is controlled based on a first control signal that is connected to the capacitive element and the one end of the capacitive element and is supplied through one first control line of the plurality of first control lines. The one end of the capacitive element at a predetermined potential A second control signal provided between the first switching element, the other end of the capacitive element, and the data line, and supplied via one second control line of the plurality of second control lines; And a second switching element that supplies the data signal to the other end of the capacitor element during the on-state.

  According to the present invention, in a simple pixel circuit configuration of two switching elements and one capacitive element, the polarity of the gate electrode of the transistor can be controlled by appropriately controlling on / off of the first and second switching elements. Different potentials can be applied. Thereby, a change in characteristics of the transistor can be suppressed. In particular, an amorphous silicon transistor has a large effect in the case of employing an amorphous silicon transistor because a variation in threshold voltage caused by flowing carriers in one direction is large.

  More specifically, in a state where the potential of the gate electrode of the transistor is an operating potential that is higher than a reference potential by a positive voltage corresponding to the luminance of the electro-optic element, the scanning line driving circuit is connected to the first switching element. After generating the first control signal and the second control signal so that the second switching element is turned on, and after the data line driving circuit supplies the data signal at the operating potential to the data line The scanning line driving circuit supplies the first control signal and the second control signal so that the first switching element is off and the second switching element is kept on, and the data It is preferable that a line driving circuit supplies the data signal whose level drops from the operating potential to the data line.

  According to the present invention, since the first switching element and the second switching element are simultaneously turned on in the state where the operating potential is applied to the gate electrode of the transistor, the potential at one end of the capacitive element is a predetermined potential. And the other end potential becomes the operating potential. As a result, a potential difference occurs between both ends of the capacitive element. When the first switching element is turned off, one end of the capacitive element enters a floating state. Under this state, the voltage applied to the other end of the capacitive element via the second switching element drops. Along with the voltage drop at the other end, the voltage at one end of the capacitive element becomes a negative voltage. As a result, a negative voltage is applied to the gate electrode of the transistor. As described above, according to the present invention, it is possible to apply a positive voltage and a negative voltage to the gate electrode of the transistor with a simple circuit configuration of two switching elements and one capacitive element, thereby changing the characteristics of the transistor. Can be suppressed. The electro-optical element means an element whose optical characteristics can be controlled by an electric action, and includes, for example, an organic light-emitting diode and an inorganic light-emitting diode.

  Further, in the above-described electro-optical device, in the initialization period, the scanning line driving circuit outputs the first control signal and the second control signal so that the first switching element and the second switching element are turned on. And the data line driving circuit sets the level of the data signal as a reference potential, and the scanning line driving circuit turns off the first switching element and the second switching in an operation period following the initialization period. The first control signal and the second control signal are generated so as to turn on the element, and the data line driving circuit changes the level of the data signal from the reference potential to a positive voltage corresponding to the luminance of the electro-optical element. After the changed operating potential, the scanning line driving circuit turns off the first switching element and the second switching element. As described above, the first control signal and the second control signal are generated, and the scan line driver circuit turns on the first switching element and the second switching element in a reset period following the operation period. In addition to generating the first control signal and the second control signal, the data line driving circuit sets the level of the data signal to the operating potential, and in the recovery period following the reset period, the scanning line driving circuit performs the first control signal. The data line driving circuit sets the level of the data signal to the reference potential in a state where the first control signal and the second control signal are generated to turn off one switching element and turn on the second switching element. And generating the second control signal so that the scanning line driving circuit turns off the second switching element. Masui.

  According to the present invention, the potentials at both ends of the capacitive element are initialized in the initialization period. Here, if the reference potential matches the predetermined potential, the voltage applied to the capacitor element is “0”, but the present invention is not limited to this. In the operation period, one end of the capacitor is brought into a floating state and the potential at the other end is increased by a positive voltage. At this time, the potential at one end of the capacitive element rises from the predetermined potential by a positive voltage. After that, even when the second switching element is turned off, the operating potential is held in the gate capacitance of the transistor, so that the transistor remains on. In the reset period, since a predetermined potential is applied to the gate electrode of the transistor, the transistor is turned off. In addition, a potential difference is generated between both ends of the capacitive element. In the recovery period, the gate electrode of the transistor is set in a floating state, and the potential of the other end of the capacitor is lowered from the operating potential to the reference potential. As a result, the potential at one end of the capacitor element drops, and a negative voltage can be applied to the gate electrode of the transistor.

According to the present invention, a negative voltage can be applied to the gate electrode of the amorphous silicon transistor that drives the electro-optic element, and fluctuations in the characteristics of the amorphous silicon transistor are suppressed. In particular, since fluctuations in the characteristics (threshold voltage) of the amorphous silicon transistor are suppressed, the luminance of the electro-optic element does not vary and the display quality can be kept high. In addition, since the circuit configuration for applying a negative voltage to the transistor is simple, a decrease in the aperture ratio can be suppressed.
In addition, since a negative voltage can be applied to the gate electrode of the transistor simply by supplying a positive voltage from the second switching element, there is no need to supply a negative voltage from the outside to the pixel circuit, and the dynamic range of the voltage level can be increased. There is no need to spread. Therefore, circuit design and the like are facilitated and power consumption does not increase.

  Next, an electronic apparatus according to the present invention includes the above-described electro-optical device, and corresponds to, for example, a large display, a personal computer, a cellular phone, a portable information terminal, and the like that connect a plurality of panels.

  FIG. 1 is a block diagram illustrating a schematic configuration of an electro-optical device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a pixel circuit. As shown in FIG. 1, the electro-optical device 1 includes a display panel A, a scanning line driving circuit 100, a data line driving circuit 200, a control circuit 300, and a power supply circuit 500. Among these, on the display panel A, m (for example, m = 360) scanning lines 101 and m control lines 102 are formed in parallel with the X direction. In addition, n (for example, n = 480) data lines 103 are formed in parallel with the Y direction orthogonal to the X direction. A pixel circuit 400 is provided corresponding to each intersection of the scanning line 101 and the data line 103. The pixel circuit 400 includes an OLED element 430. Each pixel circuit 400 is supplied with the power supply voltage Vdd via the power supply line L, and all the pixel circuits 400 are connected to the lower (reference) voltage Vss of the power supply circuit 500 via the power supply line 108 (see FIG. 2). Connected in common. In the present embodiment, the low voltage Vss is set to “0 volt”.

  In FIG. 1, only the scanning line 101 extends in the X direction. However, in the present embodiment, as shown in FIG. 2, the first scanning line 101 is shown as shown in FIG. The control line 101a and the second control line 101b are used. For this reason, the control lines 101a and 101b are combined into one set for the pixel circuit 400 for one row.

  The scanning line driving circuit 100 supplies a first control signal SEL1 to the first control line 101a and a second control signal SEL2 to the second control line 101b for each row. Specifically, the scanning line driving circuit 100 selects the scanning lines 101 one row at a time in one horizontal scanning period, and the first and second control lines 101a send the first and second control signals corresponding to the selection. , 101b. The first control signal SEL1 supplied to the i-th first control line 101a is expressed as SEL1i, and the second control signal SEL2 supplied to the i-th second control line 101b is expressed as SEL2i.

The data line driving circuit 200 supplies a current (that is, a pixel current) to be passed through the OLED element 430 of the pixel circuit 400 to each pixel circuit 400 corresponding to the scanning line 101 selected by the scanning line driving circuit 100. A data signal having a voltage corresponding to (gradation) is supplied via the data line 103. Here, the data signal (data voltage) is specified such that the higher the voltage is, the brighter the pixel is. On the contrary, the lower the voltage is, the darker the pixel is specified. For convenience of explanation, a data signal supplied to the data line 103 in the j-th column is denoted as Xj.
The control circuit 300 supplies a clock signal (not shown) or the like to the scanning line driving circuit 100 and the data line driving circuit 200 to control both driving circuits, and also controls the gray level for each pixel in the data line driving circuit 200. The image data specified in is supplied.

  Next, the pixel circuit 400 will be described in detail with reference to FIG. Although shown in the figure, the pixel circuit 400 corresponds to the i-th row. As shown in FIG. 2, the pixel circuit 400 includes a driving transistor 410, n-channel transistors 411 and 412 that function as first and second switching units, a capacitor element 420 that functions as a capacitor element, and an electro-optic. And an OLED element 430 as an element. Here, the driving transistor 410 is an n-channel amorphous silicon transistor. Note that the transistors 411 and 412 are also formed by the same process as that of the driving transistor 410 and thus are formed of amorphous silicon transistors. The OLED element 430 is a light emitting element that emits light at a luminance corresponding to a forward current, and an organic EL (Electronic Luminescence) material corresponding to an emission color is used for the light emitting layer. In the manufacturing process of the light emitting layer, the organic EL material is ejected as droplets from an inkjet head and dried.

  The drain electrode of the driving transistor 410 is connected to the power supply line L and supplied with the power supply voltage Vdd, while the source electrode of the driving transistor 140 is connected to the anode of the OLED element 430. The cathode of the OLED element 430 is connected to the low voltage Vss of the power source. For this reason, the OLED element 430 is configured to be electrically inserted together with the drive transistor 410 in the path between the power supply voltage Vdd and the lower voltage Vss. The cathode of the OLED element 430 is a common electrode throughout the pixel circuit 400.

  A gate electrode of the driving transistor 410 is connected to one end of the capacitor 420 and a source electrode of the transistor 411. For convenience of explanation, one end of the capacitor 420 (the gate electrode of the driving transistor 410) is a node N1. As shown by a broken line in FIG. 2, a capacitance is parasitic on this node N2. This capacitance is parasitic capacitance between the node N and the cathode of the OLED element 430, and is caused by the gate capacitance of the driving transistor 410, the capacitance of the OLED element 430, the parasitic capacitance of the wiring between the node N1 and the cathode, and the like. Is included.

  The drain electrode of the transistor 411 is connected to the power supply line 108 and supplied with a low voltage Vss (predetermined potential), while the gate electrode of the transistor 411 is connected to the first control line 101a. That is, the first control signal SEL1i is supplied to the gate electrode of the transistor 411 via the first control line 101a. When the first control signal SEL1i becomes H level, the transistor 411 is turned on, and the node N1 Is connected to the power supply line 108, and the voltage becomes the low voltage Vss (= 0 volts).

  The transistor 412 is interposed between the other end of the capacitor 420 and the data line 103, and its source electrode is connected to the other end of the capacitor 420, while its drain electrode is connected to the data line 103. Yes. The gate electrode of the transistor 412 is connected to the second control line 101b. That is, the second control signal SEL2i is supplied to the gate electrode of the transistor 412 through the second control line 101b. Therefore, the transistor 412 is turned on when the second control signal SEL2i becomes the H level, and the data signal (voltage) supplied to the data line 103 is applied to the other end of the capacitor 420. For convenience of explanation, the other end of the capacitor 420 (the source of the transistor 412) is a node N2.

Next, the operation of the electro-optical device 1 will be described. FIG. 3 is a timing chart for explaining the operation of the electro-optical device 1.
First, as shown in FIG. 3, the scanning line driving circuit 100 scans the first, second, third,..., Mth scanning lines 101 from the start of one vertical scanning period (1F). Are selected one by one for each horizontal scanning period (1H), and only the scanning signal of the selected scanning line 101 is set to the H level, and the scanning signals to the other scanning lines are set to the L level.

Here, the operation when the scanning line 101 in the i-th row is selected and the scanning signal Yi becomes the H level will be described with reference to FIGS. 4 to 7 together with FIG.
As shown in FIG. 3, the operation of the pixel circuit 400 in the i row and j column is roughly divided into an initialization period (1), an operation period (2), a reset period (3), and a recovery period (4). It can be divided into four.
Hereinafter, the operation during these periods will be described in order.

  The initialization period (1) starts from the timing t0 when the first control signal SEL1i changes to the H level, and in this period, the writing operation of the pixel circuit 400 is prepared in advance. Specifically, before the timing t0, both the first control signal SEL1i and the second control signal SEL2i are at the L level. When the timing t0 is reached, the scanning line driving circuit 100 sets both the first control signal SEL1i and the second control signal SEL2i to the H level. Therefore, in the pixel circuit 400, as shown in FIG. 4, the transistor 411 is turned on by the first control signal SEL1i at the H level. Therefore, in the initialization period (1), in the pixel circuit 400, the node N1, which is one end of the capacitor 420, is connected to the power supply line 108 through the transistor 411, and the voltage of the node N1 becomes the low voltage Vss (0 volt). Become. At this timing t0, the transistor 412 is also turned on by the H-level second control signal SEL2i, and the node N2, which is the other end of the capacitor 420, is connected to the data line 103 via the transistor 412, and the voltage of the node N2 Becomes the reference potential Vsus (described later) of the data line 103.

  In the operation period (2), the data signal Xj having a data voltage corresponding to the gray level of the pixel in the i row and j column is supplied to the pixel circuit 400 via the data line 103, and the OLED element has a brightness corresponding to the data voltage. 430 emits light. More specifically, when reaching the timing t1, the scanning line driving circuit 100 returns the control signal SEL2i to the L level and keeps the control signal SEL1i at the H level. Therefore, as shown in FIG. 5, the transistor 411 is turned off, the path from the node N1 to the power supply line 108 is cut, and the node N1 enters a floating state.

  When the timing t2 is reached, the data line driving circuit 200 supplies the data signal Xj corresponding to the gradation of the pixel in the i row and the j column to the data line 103 in the j column. More specifically, the data signal Xj is based on the reference potential Vsus, and the gradation of the pixel is designated by changing (raising) the voltage by ΔVdata from the reference potential Vsus. Vsus + ΔVdata is the operating potential. Therefore, ΔVdata is zero when the pixel is designated as black with the lowest gradation, and ΔVdata gradually increases as a bright gradation is designated.

  In this case, the voltage at the node N2, which is the other end of the capacitive element 420, increases by ΔVdata as the voltage of the data signal Xj changes. When the timing t3 is reached, the scanning line driving circuit 100 returns the second control signal SEL2i to the L level and turns off the transistor 412. After that, when the timing t4 is reached, the level of the data signal Xj returns to the reference potential Vsus. To do.

Here, at the timing t3, the transistor 411 and the transistor 412 are both turned off, so that the node N1 is held only by the gate capacitance of the driving transistor 410. For this reason, the voltage at the node N1 rises from the voltage during the initialization period (1) by an amount corresponding to the voltage change ΔVdata at the node N2 distributed by the capacitance ratio between the capacitive element 420 and the drive transistor 410.
Specifically, when the capacitance value of the capacitive element 420 is Ca and the gate capacitance value of the driving transistor 410 is Cb, the node N1 is switched from the low voltage Vss (= 0 volts) to {ΔVdata · Ca / (Ca + Cb). } Will rise. In general, the gate capacitance value Cb of the drive transistor 410 is negligibly small with respect to the capacitance value Ca of the capacitor 420, and can be regarded as ΔVdata · Ca 2 / (Ca + Cb) ≈ΔVdata. Therefore, the voltage at the node N1 is low. The voltage Vss rises by ΔVdata and becomes Vdata ′ (≈Vss + ΔVdata = ΔVdata).

Since the driving transistor 410 is turned on by the voltage Vdata ′ held at the node N1, the anode of the OLED element 430 is connected to the power supply line L, and a current Iel corresponding to the voltage at the node N1 flows. Thus, the OLED element 430 continues to emit light with brightness according to the current Iel.
Here, the current Iel flowing through the OLED element 430 is determined by the voltage between the gate and the source of the driving transistor 410, and the voltage is the voltage of the node N1, that is, Vdata ′. As a result, the OLED element 430 emits light with the luminance defined by the voltage of the data signal Xj. When the gate capacitance Cb of the driving transistor 410 cannot be ignored with respect to the size of the capacitive element 420, the voltage at the node N1 is Vdata ′ = Vss + {ΔVdata · Ca / (Ca + Cb)}, and the voltage is equal to the gate capacitance Cb. Decrease by minutes. Therefore, in this case, it is desirable to supply the data signal Xj having a voltage corrected in advance by the gate capacitance Cb.

  Now, in the reset period (3) following the operation period (2), the voltage of the node N1 is reset to the lower voltage Vss, and accordingly, the OLED element 430 is turned off. Specifically, when the timing t5 is reached, the scanning line driving circuit 100 sets the first control signal SEL1i and the second control signal SEL2i to the H level. Accordingly, as shown in FIG. 6, since the transistor 411 is turned on, the node N1 which is one end of the capacitor 420 is connected to the power supply line 108, and the voltage is reset to the low voltage Vss (= 0 volts). As a result, the driving transistor 410 is turned off, the anode of the OLED element 430 is cut off from the power line L, and the OLED element 430 is turned off.

Further, the transistor 412 is turned on by the H-level second control signal SEL <b> 2 i, and the node N <b> 2 which is the other end of the capacitor 420 is connected to the data line 103.
Here, the data line driving circuit 200 supplies the data signal Xj having a voltage increased by ΔVdata from the reference potential Vsus to the data line 103 in the j-th column when the reset timing (3) start timing t5 is reached. . As described above, at the timing t5, the node N2 is connected to the data line 103 and the node N1 is connected to the power supply line 108 and is maintained at the low voltage Vss (= 0 volts). As the voltage fluctuates, the voltage at the node N2 increases by ΔVdata. As a result, a potential difference of Vdata ′ is generated between the node N1 and the node N2.

  In the recovery period (4) following the reset period (3), the voltage at the node N1 becomes a negative voltage, and a reverse bias (negative voltage) is applied to the gate electrode of the drive transistor 410. Specifically, at timing t6, the scanning line driving circuit 100 returns the first control signal SEL1i to the L level and maintains the second control signal SEL2i at the H level. As a result, as shown in FIG. 7, the transistor 411 is turned off and the node N1 is disconnected from the power supply line 108 to be in a floating state, and the transistor 412 is turned on and the node N2 is connected to the data line 103. Become. In this state, since the data signal Xj having the data voltage of (Vsus + ΔVdata) is continuously supplied via the data line 103, the potential difference between the node N1 and the node N2 is maintained at Vdata ′.

  Then, at timing t7, the data line driving circuit 200 drops the data voltage of the data signal Xj by ΔVdata and returns to the reference potential Vsus. As a result, the voltage of the node N2, which is the other end of the capacitive element 420, drops by ΔVdata. At this time, since the potential difference of Vdata ′ is held between the node N1 and the node N2, and the node N1 is in a floating state, the voltage of the node N1 is increased by the voltage drop of the node N2. As a result, the voltage becomes −Vdata ′. As a result, a negative voltage is applied to the gate electrode of the driving transistor 410. The reset period (3) continues until the timing t8 when the i-th scanning line 101 is selected in the next vertical scanning period (1F) and the first control signal SEL1i becomes the H level. The voltage will continue to be applied. Then, at the timing t8, in the pixel circuit 400, the initialization period (1), the light emission period (2), the reset period (3), and the recovery period (4) are repeated.

The lengths of the initialization period (1), the operation period (2), the reset period (3), and the recovery period (4) can be set as appropriate. In particular, the entire screen can be brightened by lengthening the light emission period (3), and the whole screen can be darkened by shortening it.
Although the i-th row has been described, the pixel circuits 400 in other rows operate similarly. That is, during a period from when the scanning line 101 is selected and the scanning signal becomes H level to when the scanning line 101 is selected and the scanning signal becomes H level in the next vertical scanning period (1F). A series of operations of an initialization period (1), an operation period (2), a reset period (3), and a recovery period (4) are executed.

  Conventionally, a low-temperature polysilicon (LTPS) transistor has been used as the driving transistor 410 for driving the OLED element 430. However, in recent years, the manufacturing cost can be suppressed and uniform characteristics can be easily obtained. As an example, amorphous silicon transistors are attracting attention. However, it is known that the threshold voltage of an amorphous silicon transistor fluctuates when a voltage in the same direction such as a positive voltage or a negative voltage is continuously applied to the gate electrode. Due to the fluctuation, the brightness of the OLED element 430 changes, and the display quality deteriorates. On the other hand, according to the above-described embodiment, since a positive voltage is applied to the gate electrode of the drive transistor 410 during the operation period and a negative voltage is applied during the recovery period, an amorphous silicon transistor is employed as the drive transistor 410. Even so, fluctuations in the threshold voltage of the drive transistor 410 can be significantly suppressed, so that variations in the light emission luminance of the OLED element 430 can be prevented, and high-quality display quality can be achieved. Note that the characteristics of other types of transistors such as a low-temperature polysilicon transistor are similar to those of an amorphous silicon transistor in that the characteristics change due to the influence of accumulated carriers and the like if carriers are allowed to flow through the transistor. Therefore, the embodiment described above is also useful when a low-temperature polysilicon transistor or the like is used as the driving transistor 410.

  Furthermore, according to the present embodiment, a negative voltage is applied to the gate electrode (node N1) of the drive transistor 410 with a simple circuit configuration in which the two transistors 411 and 412 and one capacitive element 420 are combined. Variations in the characteristics of 410 can be suppressed. In addition, the number of elements such as transistors and capacitors included in the pixel circuit 400 can be reduced as compared with the conventional one, and the area occupied by these elements in the pixel circuit 400 can be suppressed, so that the aperture ratio can be maintained well. Can do.

In the reset period (3), the data line driving circuit 200 supplies a positive voltage data signal Xj to the data line 103, so that a negative voltage can be applied to the gate electrode of the driving transistor 410. There is no need to supply a negative voltage to the drive transistor 410, and there is no need to expand the dynamic range of the voltage level of the electro-optical device 1. This facilitates circuit design and does not increase power consumption.
In the reset period (3), the data line driving circuit 200 supplies a signal having the same voltage as the data signal Xj supplied to the data line 103 in the operation period (2). The negative voltage having the same magnitude as the voltage (Vdata ′) applied during the operation period (2) is continuously applied to the gate electrode (node N1). As a result, fluctuations in the characteristics of the drive transistor 410 can be more effectively suppressed.

  Note that the OLED element 430 uses a light-emitting organic material such as a low molecule, a polymer, or a dendrimer. The OLED element 430 is an example of a current-driven element. Instead, an inorganic EL element, a field emission (FE) element, a surface conduction emission (SE) element, a ballistic electron emission (BS) element, an LED Other self-luminous elements such as electrophoretic elements and electrochromic elements may also be used. The present invention can also be applied to electro-optical devices such as write heads used in optical writing type printers and electronic copying machines, as in the above embodiments.

  In addition, the present invention can be applied to any device including a unit circuit in which an amorphous transistor is a driving transistor of a driven element, and can be applied to a sensing device such as a biochip, for example. Here, the unit circuit corresponds to the pixel circuit 400, and various driven elements are provided instead of the OLED element 430.

Next, an electronic apparatus to which the electro-optical device 1 according to the above-described embodiment is applied will be described. FIG. 8 shows the configuration of a mobile personal computer to which the electro-optical device 1 is applied. The personal computer 2000 includes the electro-optical device 1 as a display unit and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the electro-optical device 1 uses the OLED element 430, it is possible to display an easy-to-see screen with a wide viewing angle.
FIG. 9 shows a configuration of a mobile phone to which the electro-optical device 1 is applied. A cellular phone 3000, a plurality of operation buttons 3001, scroll buttons 3002, and the electro-optical device 1 as a display unit are provided. By operating the scroll button 3002, the screen displayed on the electro-optical device 1 is scrolled.
FIG. 10 shows a configuration of a portable information terminal (PDA: Personal Digital Assistants) to which the electro-optical device 1 is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and the electro-optical device 1 as a display unit. When the power switch 4002 is operated, various types of information such as an address book and a schedule book are displayed on the electro-optical device 1.
The electronic apparatus to which the electro-optical device 1 is applied includes the digital still camera, the liquid crystal television, the viewfinder type, the monitor direct-view type video tape recorder, the car navigation device, the pager, Examples include electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, and devices equipped with touch panels. The electro-optical device 1 described above can be applied as a display unit of these various electronic devices. In addition, it is not limited to a display unit of an electronic device that directly displays an image or a character, but is applied as a light source of a printing device that is used to indirectly form an image or a character by irradiating light to the photosensitive member. Also good.

1 is a block diagram illustrating a configuration of an electro-optical device according to a first embodiment of the invention. FIG. It is a figure which shows the pixel circuit of the same electro-optical apparatus. 6 is a timing chart showing the operation of the electro-optical device. It is operation | movement explanatory drawing of the pixel circuit. It is operation | movement explanatory drawing of the pixel circuit. It is operation | movement explanatory drawing of the pixel circuit. It is operation | movement explanatory drawing of the pixel circuit. It is a figure which shows the personal computer using the same electro-optical apparatus. It is a figure which shows the mobile telephone using the same electro-optical apparatus. It is a figure which shows the portable information terminal using the same electro-optical apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electro-optical apparatus, 100 ... Scanning line drive circuit, 101 ... Scanning line, 103 ... Data line, 108, L ... Power supply line, 101a, 101b ... Control line, 200 ... Data line drive circuit, 300 ... Control circuit, 400 ... pixel circuit, 410 ... driving transistor, 411, 412 ... transistor (first and second switching means, respectively), 420 ... capacitive element, 430 ... OLED element, 500 ... power supply circuit.

Claims (3)

An electro-optical device, comprising: a plurality of scanning lines; a plurality of data lines; and a plurality of pixel circuits provided corresponding to intersections of the plurality of scanning lines and the plurality of data lines,
A scanning line driving circuit for driving the plurality of scanning lines;
A data line driving circuit for supplying a data signal to the plurality of data lines,
The plurality of scanning lines include a plurality of first control lines and a plurality of second control lines,
Each of the plurality of pixel circuits is
An electro-optic element;
A transistor for driving the electro-optic element;
A capacitive element having one end connected to the gate electrode of the transistor;
On / off is controlled based on a first control signal connected to the one end of the capacitive element and supplied via one first control line of the plurality of first control lines. A first switching element connecting one end of the element to a lower reference potential of the power supply ;
On / off is controlled based on a second control signal provided between the other end of the capacitive element and the data line and supplied via one second control line of the plurality of second control lines, A second switching element that supplies the data signal to the other end of the capacitive element while being on,
An electro-optical device. During the initialization period,
The scanning line driving circuit generates the first control signal and the second control signal so that the first switching element and the second switching element are turned on, and the data line driving circuit generates a level of the data signal. Is the reference potential,
In the operation period following the initialization period,
The scanning line driving circuit generates the first control signal and the second control signal so as to turn off the first switching element and turn on the second switching element, and the data line driving circuit After the level of the data signal is changed from the reference potential to an operating potential that is changed by a positive voltage corresponding to the luminance of the electro-optic element, the scanning line driving circuit changes the first switching element and the second switching element. Generating the first control signal and the second control signal to turn off;
In the reset period following the operation period,
The scanning line driving circuit generates the first control signal and the second control signal so as to turn on the first switching element and the second switching element, and the data line driving circuit generates the data signal. The level is the operating potential,
In the recovery period following the reset period,
The data line driving circuit generates the first control signal and the second control signal so that the scanning line driving circuit turns off the first switching element and turns on the second switching element. After the signal level is set to the reference potential, the scanning line driving circuit generates the second control signal so that the second switching element is turned off.
The electro-optical device according to claim 1 . An electronic apparatus comprising the electro-optical device according to claim 1 .

Images