JP2004361935A - Semiconductor device and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device in which a signal current can be written quickly in a current source circuit of a current input type. <P>SOLUTION: The semiconductor device has a signal line and a current source circuit which is connectable to the signal line through a switch, is provided with a plurality of unit circuits including the switch and the current source circuit as one unit circuit and is provided with a current supply means supplying a first current to current source circuits of M unit circuits selected from the plurality of unit circuits in a pre-charge period, and supplying a second current to current source circuits of N unit circuits selected from the plurality of unit circuits in a setting period. As a result, a signal current is written after performing a pre-charge operation, therefore, the writing is performed quickly. In the pre-charge operation, a current is supplied to a plurality of circuits. At this time, the current size is made greater according to the number of the circuits to be supplied with the current, by which the steady state can be obtained quickly. In addition, a current may be supplied to a circuit other than the one to be inputted with a signal in the pre-charge operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor device provided with a function of controlling a current supplied to a load with a transistor, and more particularly to a pixel formed of a current-driven light-emitting element whose luminance changes according to a current, and a signal line driving circuit for driving the pixel And a method for driving the same.

  2. Description of the Related Art In recent years, a so-called self-luminous display device in which a pixel is formed of a light-emitting element such as a light-emitting diode (LED) has attracted attention. As a light emitting element used in such a self-luminous display device, an organic light emitting diode (also referred to as an OLED (Organic Light Emitting Diode), an organic EL element, an electro luminescence (Electro Luminescence: EL) element, etc.) attracts attention. And are being used for organic EL displays and the like.

  Since such a light-emitting element is a self-luminous type, it has advantages such as higher pixel visibility than a liquid crystal display, no need for a backlight, high response speed, and the like. Can be controlled.

  In a display device using such a self-luminous light emitting element, a simple matrix system and an active matrix system are known as driving systems. The former has a simple structure, but has problems such as difficulty in realizing a large-sized and high-brightness display. In recent years, an active matrix system in which a current flowing through a light-emitting element is controlled by a thin film transistor (TFT) provided inside a pixel circuit. Development is active.

  In the case of the active matrix type display device, there is a problem that the current flowing through the light emitting element changes due to the variation of the current characteristic of the driving TFT, and the luminance of each light emitting element forming the display screen varies. In other words, in the case of such an active matrix type display device, a driving TFT for driving a current flowing through the light emitting element is used in the pixel circuit, and the characteristics of the driving TFT vary, so that the current flowing through the light emitting element is reduced. This causes a problem that the luminance changes.

  Therefore, even if the characteristics of the driving TFT in the pixel circuit vary, the current flowing through the light emitting element does not change, and various circuits have been proposed for suppressing variations in luminance (for example, see Patent Documents 1 to 4).

Patent application publication number 2002-517806 WO 01/06484 pamphlet Patent Application Publication No. 2002-514320 WO 02/39420 pamphlet

  Patent Documents 1 to 4 all disclose the configuration of an active matrix type display device. Patent Documents 1 to 3 disclose current flowing through a light emitting element due to variation in characteristics of a driving TFT arranged in a pixel circuit. A circuit configuration that does not change is disclosed. This configuration is called a current writing type pixel or a current input type pixel. Patent Document 4 discloses a circuit configuration for suppressing a change in signal current due to a variation in TFT in a source driver circuit.

  FIG. 6 shows a first configuration example of a conventional active matrix display device disclosed in Patent Document 1. 6 includes a source signal line 601, first to third gate signal lines 602 to 604, a current supply line 605, TFTs 606 to 609, a storage capacitor 610, an EL element 611, and a video signal input current source 612. .

  A gate electrode of the TFT 606 is connected to a first gate signal line 602, a first electrode is connected to a source signal line 601, and a second electrode is a first electrode of the TFT 607, a first electrode of the TFT 608, And the first electrode of the TFT 609. The gate electrode of the TFT 607 is connected to the second gate signal line 603, and the second electrode is connected to the gate electrode of the TFT 608. The second electrode of the TFT 608 is connected to the current supply line 605. The gate electrode of the TFT 609 is connected to the third gate signal line 604, and the second electrode is connected to the anode of the EL element 611. The storage capacitor 610 is connected between the gate electrode of the TFT 608 and the current supply line 605, and holds the gate-source voltage of the TFT 608. Predetermined potentials are input to the current supply line 605 and the cathode of the EL element 611, and have a potential difference from each other.

  The operation from signal current writing to light emission will be described with reference to FIG. In the figure, the figure numbers indicating the respective parts conform to FIG. FIGS. 7A to 7C schematically show the current flow. FIG. 7D shows the relationship between the currents flowing through the respective paths when the signal current is written, and FIG. 7E shows the voltage accumulated in the storage capacitor 610, that is, the TFT 608 when the signal current is written. Is shown for the gate-source voltage.

  First, a pulse is input to the first gate signal line 602 and the second gate signal line 603, and the TFTs 606 and 607 are turned on. At this time, a current flowing through the source signal line, that is, a signal current is defined as Idata.

  Since the current Idata flows through the source signal line, as shown in FIG. 7A, the current path in the pixel flows into I1 and I2 separately. FIG. 7D shows these relationships. It goes without saying that Idata = I1 + I2.

  At the moment when the TFT 606 is turned on, the charge is not yet held in the storage capacitor 610, so the TFT 608 is turned off. Therefore, I2 = 0 and Idata = I1. That is, during this period, only the current caused by the accumulation of the electric charge in the storage capacitor 610 flows.

  Thereafter, charges are gradually accumulated in the storage capacitor 610, and a potential difference starts to be generated between the two electrodes (FIG. 7E). When the potential difference between the two electrodes becomes Vth (point A in FIG. 7E), the TFT 608 turns on, and I2 occurs. As described above, since Idata = I1 + I2, I1 gradually decreases, but the current still flows, and the charge is accumulated in the storage capacitor.

  In the storage capacitor 610, charge accumulation continues until the potential difference between the two electrodes, that is, the gate-source voltage of the TFT 608 becomes a desired voltage, that is, the voltage (VGS) enough to allow the TFT 608 to flow the current of Idata. . When the accumulation of the electric charge is completed (point B in FIG. 7E), the current I1 stops flowing, and further, a current commensurate with the VGS at that time flows in the TFT 608, and Idata = I2 (FIG. 7B). . Thus, a steady state is reached. Thus, the signal writing operation is completed. Finally, selection of the first gate signal line 602 and the second gate signal line 603 is completed, and the TFTs 606 and 607 are turned off.

  Subsequently, the operation proceeds to a light emitting operation. A pulse is input to the third gate signal line 604, and the TFT 609 is turned on. Since the storage capacitor 610 holds the previously written VGS, the TFT 608 is ON and the current Idata flows from the current supply line 605. Thus, the EL element 611 emits light. At this time, if the TFT 608 is operated in the saturation region, Idata can flow without change even if the source-drain voltage of the TFT 608 changes.

  The operation of outputting the set current in this way is called an output operation. As an advantage of the current writing type pixel described above as an example, even when the characteristics and the like of the TFT 608 fluctuate, the gate-source voltage required to flow the current Idata is stored in the storage capacitor 610. Since the current is held, a desired current can be accurately supplied to the EL element, and therefore, there is a point that a variation in luminance due to a variation in characteristics of the TFT can be suppressed.

  The above example relates to a technique for correcting a change in current due to a variation in a driving TFT in a pixel circuit, but the same problem occurs in a source driver circuit. Patent Literature 4 discloses a circuit configuration for preventing a change in signal current due to a variation in manufacturing TFTs in a source driver circuit.

  As described above, in the conventional current driving circuit and the display device using the same, the signal current and the current for driving the TFT or the signal current and the current flowing to the light emitting element at the time of light emission are equal or proportional. It is configured as follows.

  Therefore, when the driving current of the driving TFT for driving the light emitting element is small, or when the light emitting element is to display a dark gradation, the signal current is also reduced in proportion thereto. Therefore, the parasitic capacitance of the wiring used to supply the signal current to the driving TFT or the light emitting element is extremely large. Therefore, when the signal current is small, the time constant for charging the parasitic capacitance of the wiring becomes large, and the signal writing speed becomes slow. There is a problem that. That is, there is a problem in that the speed at which a current is supplied to the transistor and the voltage required for the transistor to flow the current at the gate terminal is reduced is reduced.

  Therefore, techniques for increasing the signal writing speed have been studied (for example, see Patent Documents 5 and 6).

Patent Application Publication No. 2003-50564 Patent application publication number 2003-76327

  Patent Document 5 discloses a display including a current control unit that drives a data line current supplied from a data line driving unit by dividing the data line current into a data current for writing luminance information for each of the pixel circuits and a remaining bypass current. An apparatus is disclosed. For example, as shown in FIG. 33, a pixel circuit on which writing is not performed is used as a data current control circuit (bypass current).

  34 and 35 show the drive timing. X consecutive (x = 2 in FIG. 33) pixel circuits are simultaneously selected. As described above, when two pixel circuits are simultaneously selected, a part of the data line current for driving the data line is written as the luminance data current for one pixel circuit. At this time, the luminance data current is not written to a part of the other one pixel circuit, but is used as a data current control circuit (bypass current) for flowing the rest of the data line current.

  In particular, in the example of FIG. 35, when x (in FIG. 33, x = 2) pixel circuits that are continuous in the column direction are regarded as one block, when writing a data current to one pixel circuit in this block, the same block is used. The other pixel circuits are not written with data current and are used as bypass current. At this time, in the pixel circuit to which the data current is being written, both the first scanning line WS and the second scanning line ES are selected. For example, in FIG. 33, when the pixel circuit 11-k-1 is a pixel circuit for writing a data current, both WS k-1 and ES k-1 are selected.

  On the other hand, in the pixel circuit which does not write the data current but is used as the bypass current, only the first scanning line WS is selected. In the example of FIG. 33, WSk is selected, and the second scanning line ESk is not selected. Thus, the TFTs 24 and 25 function as a data current control circuit used as a bypass current. That is, in the pixel circuit shown in FIG. 33, since the second scanning line ESk is not selected and the TFT 26 is in the off state, the charge corresponding to the luminance data held in the capacitor 23 is not discharged through the TFT 26. It remains retained. At this time, only a part of the circuits, that is, only the TFTs 24 and 25 function as a data current control circuit (bypass current).

  As described above, in an active matrix type organic EL display device using a current writing type pixel circuit, two pixel circuits adjacent in the column direction are simultaneously selected, and a part of the data line current Iw0 is used to write luminance data. By supplying the remaining current to the circuit and using a part of the other pixel circuit as a bypass current to flow the remaining current, the size of the TFTs 24 and 25 in the pixel circuit can be suppressed from being increased. The data line current Iw0 can be set to be larger than the data current Iw1 flowing to the data line 25. As a result, the data writing time can be greatly reduced, and the size and definition of the organic EL display device can be increased.

  On the other hand, Patent Document 6 discloses a circuit shown in FIG. That is, the auxiliary transistor 12 having n times the current driving capability of the drive transistor 7 is connected in parallel with the drive transistor 7 so that the drain current flows through the auxiliary transistor 12 during a part of the selection period (acceleration period). At the same time, the signal current itself flowing through the signal line 3 is also made (n + 1) times. As a result, the charge and discharge of the storage capacitor and the parasitic capacitor are performed quickly, and the gate potential of the drive transistor surely reaches the predetermined potential during the selection period, and the signal current (input signal) is reduced. There is an effect that the current drive element can be driven with an appropriate drive current even when it is minute. Therefore, when the current drive element is an organic EL element, the organic EL element is driven with the intended drive current, thereby preventing the display quality from deteriorating.

  As described above, techniques for increasing the signal writing speed have been studied, but there are some problems.

  For example, in the case of Patent Document 5, when writing a data current, two (x = 2) pixel circuits adjacent in the column direction are simultaneously selected. However, the number of pixel circuits is not limited to two and may be more. It is possible to select pixel circuits simultaneously. By increasing the number of selected pixel circuits and increasing the number of pixel circuits used as data current pulses, the transistor size in the pixel circuit can be further reduced, in other words, the current value of the data line current Iw0 can be further increased. It is possible to do.

  However, because of the trade-off relationship, the distance between the transistors forming the current mirror circuit is long, and the effect of compensating for variations in transistor characteristics is reduced by that much.

  Therefore, the number of pixel circuits selected at the same time is limited. Therefore, the magnitude of the current value of the data line current is also limited. Therefore, the signal writing speed is reduced. In addition, if many pixel circuits are selected at the same time, the currents flowing through each pixel circuit are averaged, so that an accurate current is not input to the pixel circuit to which the data current is input, and the transistor characteristics vary accordingly. , The effect of compensation is reduced.

  On the other hand, in the case of Patent Document 6, an auxiliary transistor 12 having n times the current driving capability of the drive transistor 7 is connected in parallel with the drive transistor 7, and the drain is also supplied to the auxiliary transistor 12 during a part of the selection period (acceleration period). The current is made to flow, and the signal current itself flowing through the signal line 3 is also made (n + 1) times.

  However, if n is too large, the area occupied by the auxiliary transistor 12 becomes too large. Therefore, the aperture ratio decreases. Also, the size of n is limited by the layout area. Therefore, in a part of the selection period (acceleration period), the magnification of the signal current flowing through the signal line 3 becomes small. As a result, the signal writing speed is reduced.

  The present invention has been made to solve such a problem, and an object of the present invention is to enable a signal writing speed to be sufficiently improved even when a signal current is small. In this case, it is an object to provide a technique that is not limited by the layout area of the pixel, does not reduce the aperture ratio, and does not reduce the effect of compensating for variations in transistor characteristics.

  Therefore, in the present invention, in order to quickly complete the setting operation, a precharge period is provided before the setting period to perform the precharge operation. Then, as a precharge operation, current is caused to flow through transistors other than the transistor to which a signal is input. Then, as much as the number of transistors through which current flows is increased, more current is made to flow. Therefore, a large amount of current flows, and a steady state can be quickly established. At this time, the state is almost equal to the time when the setting operation is completed (when the state becomes a steady state). Thereafter, a setting operation is performed. Before the setting operation is performed, the state is almost the same as when the setting operation is completed, so that the setting operation can be completed quickly.

  Note that the setting operation refers to an operation in which a current is supplied to a transistor to which a signal is input and a voltage required for the transistor to flow the current is generated in a gate terminal.

  Further, in order to quickly complete the setting operation, an operation of passing a current not only to a transistor to which a signal is input but also to other transistors is called a precharge operation, and a circuit having such a function is referred to as a precharge means. I will call it.

  The present invention has a signal line and a current source circuit connectable via a switch, the switch and the current source circuit as one unit circuit, a plurality of unit circuits, and in a precharge period, The first current is supplied to the current source circuits of the M unit circuits selected from the plurality of unit circuits, and the second current is supplied to the current source circuits of the N unit circuits selected from the plurality of unit circuits during the setting period. And a current supply means for supplying the current.

  Note that the current source circuit includes at least one transistor and often includes a capacitor.

  In other words, when the setting operation is performed on the unit circuit (the transistor constituting the current source circuit), if the current value is small, it does not easily reach a steady state, and the current writing operation is not completed. Therefore, before performing the setting operation, the precharge operation is performed. By performing the precharge operation, the state is substantially equal to the steady state when the setting operation is performed. That is, the potential of the gate terminal of the transistor included in the current source circuit is quickly charged by performing the precharge operation. By the precharge operation, the potential of the gate terminal of the transistor forming the current source circuit is substantially equal to the potential at the time of the setting operation. Therefore, when the setting operation is performed after the precharge operation, the operation can be completed earlier.

  Further, the present invention has a current source circuit connectable through a signal line and a switch, and includes a plurality of unit circuits each including the switch and the current source circuit as one unit circuit. The first current is supplied to the current source circuits of the M unit circuits selected from the plurality of unit circuits, and during the setting period, the first current is selected from the unit circuits other than the M unit circuits selected from the plurality of unit circuits. A current supply means for supplying a second current to the current source circuits of the N unit circuits.

  That is, it is usually desirable to perform the precharge operation in a form including a unit circuit that performs the setting operation from the viewpoint of characteristic variation. However, it is not limited to this. When performing the precharge operation, a unit circuit other than the unit circuit that performs the setting operation may be used.

  Further, the present invention is the semiconductor device according to the above structure, wherein N = 1.

  Normally, the setting operation is performed for one unit circuit. However, it is not limited to this. In the setting operation, a current may be supplied to a plurality of unit circuits.

  Further, the present invention is the semiconductor device according to the above structure, wherein a ratio of the magnitude of the first current to the magnitude of the second current is M: N.

  Note that there is no limitation on the type of transistor that can be used in the present invention. For example, a thin film transistor (TFT) may be used. Among the TFTs, the semiconductor layer may be amorphous, polycrystalline (polycrystal), or single crystal. Other transistors may be transistors formed on a single crystal substrate, transistors formed on an SOI substrate, transistors formed on a glass substrate, or formed on any substrate. It may be a transistor. In addition, a transistor formed of an organic substance or a carbon nanotube may be used. Further, a MOS transistor or a bipolar transistor may be used.

  Note that being connected is synonymous with being electrically connected. Therefore, another element, switch, or the like may be arranged therebetween.

  In the present invention, a precharge operation is performed before the setting operation. Therefore, the setting operation can be performed quickly even if the current value is small. Therefore, an accurate current can be output in the output operation.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, it is easily understood by those skilled in the art that the present invention can be implemented in many different aspects, and that the form and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of the embodiments.

  According to the invention, a pixel is formed using an element whose emission luminance can be controlled by a current value flowing through a light-emitting element. Typically, an EL element can be used. There are various known structures of EL elements, but any element structure can be applied to the present invention as long as the luminance can be controlled by the current value. That is, an EL element is formed by freely combining a light emitting layer, a charge transport layer, or a charge injection layer. As a material therefor, a low molecular organic material, a medium molecular organic material (having no sublimability, Further, an organic light-emitting material having a number of molecules of 20 or less or a chain of molecules having a length of 10 μm or less) or a high molecular weight organic material can be used. Further, those obtained by mixing or dispersing an inorganic material into these may be used.

  Further, the present invention can be applied to not only a pixel having a light emitting element such as an EL element but also various analog circuits having a current source. Therefore, in the present embodiment, first, the principle of the present invention will be described.

  First, FIG. 1 shows a configuration based on the basic principle of the present invention. A basic current source 101 is connected to the signal line 108 via a switch 102, and an additional current source 103 is connected to the signal line 108 via a switch 104 in parallel with the basic current sources 101 to constitute a current supply unit. Needless to say, the current supply means is not limited to the configuration shown in FIG. 1 and may be any configuration capable of supplying a predetermined current to the unit circuit described below according to the operation timing. For example, a switch may be omitted and a current source whose output can be freely changed may be used. Alternatively, the number of current sources may be increased instead of two, or may be integrated into one.

  A plurality of unit circuits 105a to 105e are connected to the signal line 108. In FIG. 1, five unit circuits are connected. Each unit circuit is composed of at least a switch circuit and a current source circuit. For example, the unit circuit 105a is composed of at least a switch circuit 106a and a current source circuit 107a. The same applies to the other unit circuits 105b to 105e. Further, the current source circuit includes at least one transistor, and often includes a capacitor. The switch circuit includes at least one switch.

  Various configurations can be used as the unit circuit. Therefore, in this embodiment, as an example, FIG. 2 illustrates a unit circuit in which a circuit similar to that in FIG. 6 is used. The switch circuit 106 of the unit circuit 105 corresponds to the TFT 606 in FIG. The current source circuit 107 of the unit circuit 105 includes a current source transistor 208, a capacitor 210, and switches 207 and 209. A load 201 is connected to the end of the switch 209. The transistor 208 of the current source circuit 107 corresponds to the TFT 608 in FIG. 6, the capacitor 210 corresponds to the storage capacitor 610, the switch 207 corresponds to the TFT 607, and the switch 209 corresponds to the TFT 609. The load 201 corresponds to the EL element 611 in FIG.

  Next, the operation of the circuit of FIG. 1 will be described. First, as shown in FIG. 3, a precharge operation is performed. In the precharge operation, current is caused to flow not only in a unit circuit to which a signal is input but also in other unit circuits. Then, the total current is increased by an amount corresponding to the increase in the number of unit circuits through which the current flows.

  That is, the switch 104 is turned on and the switch 102 is turned off so that the current of the additional current source 103 flows. Then, in a plurality of unit circuits, the switch circuits are turned on, and current flows. In FIG. 3, the switch circuits 106a to 106e are turned on, and current flows through five unit circuits. Therefore, the current of the additional current source 103 is five times as large as that of the basic current source 101. Since a large current flows as described above, a steady state can be quickly established. In the precharge operation, the potential of the signal line 108 at the time of the steady state is set to Vp.

  During the precharge operation, it is preferable that each current source circuit be in a state where the gate terminal and the drain terminal of the current source transistor are connected. For example, in the case of FIG. 2, the switch 207 is preferably turned on. At that time, in the case of FIG. 2, it is preferable that the switch 209 is turned off in order to prevent a current from flowing toward the load 201. However, it is not limited to this.

  Next, a setting operation is performed as shown in FIG. Here, it is assumed that the unit circuit to which a signal is input is the unit circuit 105a. Therefore, current is made to flow only in the unit circuit 105a, and current is made not to flow in the unit circuits 105b to 105e. Therefore, the switch circuit 106a is on, and the switch circuits 106b to 106e are off. Further, the switch 104 is turned off, the switch 102 is turned on, and the current of the basic current source 101 flows. However, the magnitude of the current of the basic current source 101 is small. Therefore, in the related art, a steady state has not been easily achieved. However, in the case of FIG. 4, the precharge operation is performed before the setting operation. Therefore, the potential of the signal line 108 is Vp. Vp is substantially equal to the potential of the signal line 108 when the setting operation is completed. Therefore, it is possible to quickly complete the setting operation and bring the system into a steady state.

  Thus, a large current flows during the precharge operation (precharge period). For example, an A-fold current is passed. At this time, current is caused to flow through the A unit circuits. Then, since the current value is large, a steady state can be quickly established. In other words, the influence of the load (such as wiring resistance and cross capacitance) parasitic on the wiring through which the current flows can be reduced, and the steady state can be quickly achieved. Then, in a setting period, a setting operation is performed by flowing a current of one time to one unit circuit. However, due to the precharge operation, the potential of the wiring through which the current flows is substantially equal to the state when the setting operation is completed. This is because the current magnification (A times) at the time of the precharge operation corresponds to the number of unit circuits (A) through which the current flows. As described above, since the precharge operation is performed, the setting operation can be performed quickly.

  Therefore, for example, when the load 201 is an EL element, a signal can be written quickly even when writing a signal when the EL element is to emit light at a low gradation, that is, even when the current value at the time of the setting operation is small. I can do it.

  Note that the potential of the signal line when the precharge operation is completed is substantially equal to the potential of the signal line when the setting operation is completed. If they are completely equal, it means that the setting operation has been completed when the precharge operation is completed. If the potentials are not completely equal, the potential is adjusted by the setting operation by the potential difference. Therefore, the fluctuation of the potential of the signal line from the start to the end of the setting operation is small, and the steady state can be quickly achieved.

  Whether the potential of the signal line when the precharge operation is completed is equal to the potential of the signal line when the setting operation is completed depends on the current characteristics of the current source transistors in each of the current source circuits 107a to 107e. It depends on the degree of variation. If the current characteristics do not vary, the gate-source voltage of the current source transistor is the same during the precharge operation and during the setting operation. However, if the current characteristics vary, the gate-source voltage of the current source transistor differs between the precharge operation and the setting operation. Accordingly, the potential of the signal line 108 also differs between when the precharge operation is completed and when the setting operation is completed. Therefore, it is desirable that the current source transistors in each of the current source circuits 107a to 107e have uniform current characteristics. If the current characteristics are uniform, it is possible to quickly set a steady state in the setting operation. In order to make the current characteristics of the current source transistor uniform, it can be improved by, for example, performing laser irradiation in the same shot when crystallizing the semiconductor layer of the transistor.

  In FIG. 1, five unit circuits are connected, but this is not a limitation.

  Further, at the time of the precharge operation, in FIG. 3, current is input to the five unit circuits, but the present invention is not limited to this. For example, as shown in FIG. 5, a current may flow through four unit circuits. In this case, the current of the additional current source 103 is desirably four times as large as that of the basic current source 101. Further, in FIG. 5, the switch circuits 106b to 106e are on and the switch circuit 106a is off, but this is not a limitation. Here, since the unit circuit to which a signal is to be input is the unit circuit 105a, it is desirable to input a current to the unit circuit 105a at the time of the precharge operation from the viewpoint of variations in the current characteristics of the transistors. However, as shown in FIG. 5, the precharge may be performed by turning off the switch circuit 106a so that no current is input to the unit circuit 105a.

  Further, at the time of the setting operation, the current is input to one unit circuit in FIG. 4, but the present invention is not limited to this. For example, a current may flow through a plurality of unit circuits. In this case, it is necessary to increase the current of the basic current source 101 in accordance with the number thereof.

  In FIG. 1, the signal line 108 and each of the current source circuits 107a to 107e are connected via each of the switch circuits 106a to 106e, but the present invention is not limited to this. What is necessary is just to be able to control whether or not a current is input from the signal line 108 to each of the unit circuits 105a to 105e. Although a current is input to each unit circuit via a signal line in FIG. 1, other signals may be input. For example, a voltage may be input to the unit circuit via another wiring.

  Note that, in the precharge operation, in FIG. 3, the switch 102 is off and the switch 104 is on, but the invention is not limited to this. If the magnitude of the current is adjusted, the switch 102 may be turned on so that the current flows from both the basic current source 101 and the additional current source 103.

  In FIG. 1, the signal line 108 is connected to the basic current source 101 via the switch 102 and connected to the additional current source 103 via the switch 104 for simplicity of explanation. Not done. It is sufficient that the magnitude of the current flowing to the signal line 108 can be controlled between the time of the precharge operation and the time of the setting operation. Therefore, the switches 102 and 104 may be arranged anywhere as long as the magnitude of the current flowing from the basic current source 101 and the additional current source 103 can be controlled. If the basic current source 101 and the additional current source 103 have a function of switching whether or not to output a current, the switches 102 and 104 need not be provided. In addition, if the device has a function of switching the magnitude of the current between the precharge operation and the setting operation, the basic current source 101 and the additional current source 103 can be combined into one current source. Good.

  In FIGS. 1 to 4, the current is arranged to flow from the unit circuit to the basic current source 101 and the additional current source 103, but the present invention is not limited to this. A current may flow from the basic current source 101 or the additional current source 103 toward the unit circuit. However, in that case, it is necessary to pay attention to the current source circuit in each unit circuit. That is, when the current source circuit has a configuration as shown in FIG. 2, the polarity of the current source transistor 208 needs to be changed from a P-channel type to an N-channel type. This is because the source terminal and the drain terminal of the transistor are switched depending on the direction in which the current flows. If a current flows from the basic current source 101 or the additional current source 103 to the unit circuit and the polarity of the current source transistor is a P-channel type, the configuration shown in FIG. is there. In FIG. 8, a capacitor 810 is connected between the gate and source of the current source transistor 808. Since the magnitude of the current flowing through the transistor is controlled by the gate-source voltage, it is necessary to maintain the gate-source voltage. Therefore, it is preferable that the capacitor 810 be connected between the gate and the source of the current source transistor 808. The switch 807 is connected between the gate and the drain of the current source transistor 808. As described above, the source terminal and the drain terminal are determined by the direction in which the current flows, that is, by the level of the potential. Therefore, it is necessary to determine the connection structure accordingly.

  The load 201 in FIGS. 2 and 8 may be anything. An element such as a resistor, a transistor, an EL element, another light emitting element, a current source circuit including a transistor, a capacitor, a switch, and the like, or a wiring to which any circuit is connected may be used. It may be a signal line or a signal line and a pixel connected thereto. The pixel may include any display element such as an EL element or an element used in an FED. Further, a current source circuit in a signal line driving circuit that supplies a current to a pixel may be used.

  Note that the capacitor 210 in FIG. 2 and the capacitor 810 in FIG. 8 can be substituted by a gate capacitor of the current source transistor 208 and the like. In that case, the capacitor 210 and the capacitor 810 can be omitted.

  Note that the capacitor 210 is connected to the gate terminal and the source terminal of the current source transistor 208, but is not limited to this. Most preferably, it is connected to the gate terminal and the source terminal of the current source transistor 208. Because the operation of a transistor is determined by the voltage between the gate and the source, holding the voltage between the gate terminal and the source terminal causes other effects (such as the effect of voltage drop due to wiring resistance, etc.). Because it is hard to receive. If the capacitor 210 is disposed between the gate terminal of the current source transistor 208 and another wiring, the potential of the gate terminal of the current source transistor 208 may change due to the voltage drop in the other wiring. There is.

  Although FIG. 1 shows five current source circuits 107a to 107e, the current capability of the current source circuits, that is, the gate width W and the gate length L of each current source transistor are different in all the unit circuits. , May be the same or different. If they are different, it is necessary to make an adjustment so that the potential of the signal line 108 at the time of the precharge operation and the setting operation at the time of the steady state becomes substantially equal.

  Note that the switches illustrated in FIG. 1 and the like may be electrical switches or mechanical switches, and may be anything. Anything can be used as long as it can control the current flow. It may be a transistor, a diode, or a logic circuit combining them. Therefore, when a transistor is used as a switch, the transistor operates as a simple switch, and there is no particular limitation on the polarity (conductivity type) of the transistor. However, in the case where it is desirable that the off-state current be small, it is preferable to use a transistor having the polarity with the small off-state current. As a transistor with small off-state current, there is a transistor provided with an LDD region. In the case where the transistor operated as a switch operates in a state in which the source terminal potential is close to the low potential side power supply (Vss, Vgnd, 0 V, or the like), the n-channel type is used. When operating near a side power supply (such as Vdd), it is desirable to use a p-channel type. This is because the absolute value of the gate-source voltage can be increased, and the switch can easily operate. Note that a CMOS switch may be used by using both the n-channel type and the p-channel type.

  Note that the circuit of the present invention is shown in FIGS. 1, 2, 8, and the like, but the configuration is not limited to this. By changing the number of unit circuits, the number of each current source, the arrangement and number of switches, the polarity of each transistor, the number and arrangement of current source transistors, the potential of each wiring, the direction of current flow, etc., various circuits can be implemented. It can be configured by using. In addition, by combining the respective changes, the circuit can be configured using various circuits.

  In the case of FIG. 1, the precharge operation is performed as shown in FIGS. 3 and 5, and then the setting operation is performed as shown in FIG. 4, but the present invention is not limited to this.

  For example, the precharge operation shown in FIGS. 3 and 5 may be performed a plurality of times. For example, in the first precharge operation, as in the case of FIG. 3, the magnitude of the current is increased by a factor of 5, and the current flows through the five unit circuits. Next, in the second precharge operation, as shown in FIG. 9, the magnitude of the current is tripled, and the current flows through the three unit circuits. Finally, as a setting operation, the magnitude of the current may be increased by one to allow the current to flow through one unit circuit.

  As described above, by performing the precharge operation a plurality of times, it is possible to smoothly shift to the setting operation.

  Alternatively, another precharge operation may be combined.

  For example, as shown in FIG. 10, another precharge may be performed before the precharge operation as shown in FIG. In FIG. 10, a voltage is supplied from a terminal 1001 via a switch 1002. In the precharge operation and the setting operation, the potential is set to a value substantially equal to the potential at the time of the steady state. That is, as shown in FIG. 10, the switch 1002 is turned on to supply the potential of the terminal 1001. Since a voltage is applied, a large amount of current can flow instantaneously. This allows quick precharge. After that, the switch 1002 is turned off, and the precharge operation is performed as in FIG. A technique for performing precharge by supplying a voltage is described in Japanese Patent Application No. 2003-019240 filed by the same applicant. There, various precharge techniques are disclosed, and the contents can be combined with the present invention.

  Further, for example, in each unit circuit (current source circuit), the operation of performing the precharge by changing the magnitude of the current flowing therethrough in a plurality of stages may be combined with the precharge operation as shown in FIG. 11 and 12 show configuration examples in which the current flowing through the current source circuit 107 can be changed in a plurality of stages.

  In the case of FIG. 11, the second current source transistor 1111 is connected in series with the current source transistor 1108. A switch 1112 for short-circuiting the source and drain of the second current source transistor 1111 is connected. When the switch 1112 is off, the gate terminal of the current source transistor 1108 and the gate terminal of the second current source transistor 1111 are connected to each other, so that the current source transistor 1108 and the second current source transistor 1111 The transistor operates as a multi-gate transistor. At this time, the gate length L of the multi-gate transistor is larger than the gate length L of the current source transistor 1108. Therefore, the current flowing there is also small. On the other hand, when the switch 1112 is on, the source and the drain of the second current source transistor 1111 are short-circuited, so that no current flows between the source and the drain of the second current source transistor 1111. Therefore, substantially, only the current source transistor 1108 is operating. From the above, the current flowing to the current source transistor 1108 can be changed by turning on and off the switch 1112. By performing this operation before, after, or during FIG. 3 or FIG. 4, precharge can be performed more quickly.

  FIG. 11 shows an example in which the second current source transistor 1211 is connected in parallel with the current source transistor 1208, while FIG. Also in this case, when a large amount of current is desired to flow, by turning on the switch 1212, the current can be caused to flow also to the second current source transistor 1211.

  As shown in FIGS. 11 and 12, a configuration in which the current flowing through the current source circuit 107 can be changed in a plurality of stages is described in Japanese Patent Application No. 2003-055018 filed by the same applicant. ing. Various configurations are disclosed therein, and the contents can be combined with the present invention.

  Note that it is desirable that the transistors used in the precharge operation and the transistors used in the setting operation have the same characteristics as much as possible. For example, in the case of FIG. 1, it is desirable that the current source transistors 208, 808, 1108, 1208 and the second current source transistors 1111, 1211 in the current source circuit have the same current characteristics in the current source circuits 107a to 107e. Therefore, in the process of forming the current source transistor and the second current source transistor, it is desirable to make efforts so that current characteristics are as uniform as possible. For example, in the case where the semiconductor layer of the current source transistor or the second current source transistor is manufactured by irradiating the semiconductor layer with a laser, it is desirable to irradiate the laser so that the current characteristics of the current source transistor or the second current source transistor are uniform. Therefore, for example, when irradiating a linear laser, it is desirable to irradiate the laser in parallel with the signal line 108 and scan the laser in a direction perpendicular to the signal line 108.

  When the basic current source 101 and the additional current source 103 are realized by transistors operating in a saturation region, it is desirable that the respective gate electrodes be connected. It is desirable to control the magnitude of the current of each current source by adjusting the ratio of the gate width W to the gate length L of each transistor.

  Thus, the arrangement and number of switches, the polarity of each transistor, the number and arrangement of current source transistors, the type and number and arrangement of basic current sources, the configuration and number of unit circuits, the configuration of current source circuits in unit circuits, By changing the number of times of precharge, the presence or absence of a combination with another precharge method, the direction of current flow, and the like, the present invention can be configured using various circuits. Accordingly, the present invention can be configured using various circuits.

(Embodiment 2)
In the first embodiment, the case where the unit circuit to which a signal is input, that is, the unit circuit to which the setting operation is performed, is the unit circuit 105a in FIGS. In the present embodiment, an operation in a case where a unit circuit for which a setting operation is performed sequentially changes with time will be described.

  Although the operation is described using the configuration shown in FIG. 1, the configuration and the operation are not limited to this. Note that the contents of this embodiment can be combined with the contents described in Embodiment 1.

  It is assumed that the number of unit circuits to which a current is input during the precharge operation is three for simplicity. Note that the number of unit circuits to which a current is input during the precharge operation is not limited to this.

  First, it is assumed that a unit circuit to which a signal is input, that is, a unit circuit to which a setting operation is performed is the unit circuit 105a. Therefore, before performing the setting operation on the unit circuit 105a, a precharge operation is performed. Here, for simplicity, it is assumed that a precharge operation is performed by passing a current through the three unit circuits. Therefore, as shown in FIG. 13, a current is supplied to the unit circuits 105b, 105c, and 105d to perform a precharge operation.

  Here, as the precharge operation performed before the setting operation to the unit circuit 105a, the reason why the circuit for flowing the current is the unit circuits 105b, 105c, and 105d will be described. This is because the unit circuit to be set is next to the unit circuit 105a, the unit circuit 105b, the unit circuit 105c, and the unit circuit 105d. That is, depending on the configuration of the unit circuit, when a current is supplied to the unit circuit as a precharge operation, the state when the setting operation is performed on the unit circuit may change. Therefore, if the setting operation is performed immediately thereafter, there is little problem even if a current flows for the precharge operation.

  Therefore, if a current is applied to a unit circuit as a precharge operation and the state when the setting operation is performed on the unit circuit does not change, if a unit circuit other than the unit circuits 105b, 105c, and 105d does not change. , A precharge operation may be performed.

  It is desirable that the state of the signal line 108 be substantially equal between the setting operation and the precharge operation. For this purpose, it is desirable that the unit circuit (current source circuit) performing the setting operation and the unit circuit (current source circuit) performing the precharge operation have the same current characteristics. Therefore, it is desirable to perform the precharge operation using a unit circuit arranged near the unit circuit 105a (that is, a unit circuit that performs a setting operation). Of course, the precharge operation may be performed using the unit circuit 105a (that is, the unit circuit that performs the setting operation).

  As described above, as a precharge operation to be performed before a setting operation to a certain unit circuit, the unit circuit that flows a current performs a setting operation to the unit circuit when a current flows to the unit circuit as a precharge operation. If the state at the time of the change is changed, it is desirable to select a unit circuit that performs the setting operation after the precharge operation. If the state when the setting operation is performed on the unit circuit does not change, it is desirable to select a unit circuit arranged near the unit circuit that performs the setting operation. However, it is not limited to this.

  Next, after the precharge operation as shown in FIG. 13, a setting operation is performed on the unit circuit 105a as shown in FIG.

  Then, it is assumed that the unit circuit to which a signal is to be input, that is, the unit circuit to which the setting operation is to be performed, has changed to the unit circuit 105b. Then, a precharge operation is performed before the setting operation is performed on the unit circuit 105b. Therefore, as shown in FIG. 15, a current is supplied to the unit circuits 105c, 105d, and 105e to perform a precharge operation. It is not desirable to supply a current to the unit circuit 105a as a precharge operation immediately after the setting operation is completed.

  Next, as shown in FIG. 16, a setting operation is performed on the unit circuit 105b.

  In this manner, the target of the setting operation changes sequentially with time, and the precharge operation and the setting operation are performed as shown in FIGS.

  Note that when a precharge operation is performed before a setting operation to the unit circuit 105c, there is no unit circuit next to the unit circuit 105e. Therefore, in the precharge operation, it is only necessary to return to the first unit circuit as a unit circuit for flowing a current and flow a current to the unit circuits 105d, 105e, and 105a. The operation at this time is shown in FIGS.

  Similarly, when the setting operation is performed on the unit circuit 105d depending on the time, the current is supplied to the unit circuits 105e, 105a, and 105b to perform the precharging operation. As shown in FIG. 20, the setting operation is performed on the unit circuit 105d. Next, similarly, as shown in FIGS. 21 and 22, the precharge operation and the setting operation are performed.

  With this operation, the setting operation can be sequentially performed on each unit circuit. By performing the precharge operation before the setting operation, the setting operation can be completed quickly even if the current is small.

  Note that when performing the precharge operation, after performing the precharge operation, current is supplied to the other unit circuits without including the unit circuit that performs the setting operation, but the present invention is not limited to this. For example, as shown in FIG. 14, when the setting operation is performed on the unit circuit 105a, the precharge operation before that includes the unit circuit 105a to be set, as shown in FIG. 21 instead of FIG. Then, a current may flow.

  The contents described in the present embodiment correspond to those in which a certain operation in the configuration described in the first embodiment is described in detail, but are not limited thereto, and may be various as long as the gist is not changed. Various deformations are possible. Therefore, the contents described in the first embodiment can be applied to the present embodiment.

(Embodiment 3)
In Embodiment 1, as illustrated in FIGS. 2, 8, 11, 12, and the like, various configurations can be used as the unit circuit. Therefore, in this embodiment, another example of the unit circuit and the operation of the unit circuit will be described.

  First, FIG. 23 shows a circuit example. In the case of the circuit in FIG. 23, when the switch 207 is turned on, the gate-source voltage of the transistor 2309 becomes 0. Therefore, the transistor 2309 is turned off, and no current flows to the load 201. Therefore, when performing a precharge operation, the switches 106 and 207 may be turned on. In the case of the circuit of FIG. 23, when a current is supplied to a unit circuit as a precharge operation, the state when the setting operation is performed on the unit circuit changes. Therefore, after the precharge operation is performed, it is not desirable to supply a current to the load until a new setting operation is performed. Therefore, in such a case, when the switch 106 is turned off, the switch 207 may be turned on. When the switch 106 is turned off, no current enters the unit circuit. On the other hand, since the switch 207 is on, no current flows through the load 201. To supply a current to the load 201, the switches 106 and 207 may be turned off. When performing a setting operation, the switches 106 and 207 may be turned on.

  Another example is shown in FIG. In the case of the circuit in FIG. 24, when the switch 2407 is turned on, the gate-source voltage of the transistor 2409 becomes 0. Therefore, the transistor 2409 is turned off, and no current flows from the power supply line 2413 to the load 201. Therefore, when performing a precharge operation, the switches 106 and 2407 may be turned on. However, the current flows through the load 201 as it is, so that the switch 2411 is turned on so that the current flows to the wiring 2412. If the potential of the wiring 2412 is adjusted, a current does not often flow through the load 201; however, if the current flows, the switch 209 may be turned off. In the case of the circuit of FIG. 24, when a current is supplied to a unit circuit as a precharge operation, a state when the setting operation is performed on the unit circuit changes. Therefore, after the precharge operation is performed, it is not desirable to supply a current to the load until a new setting operation is performed. Therefore, in such a case, the switch 106 may be turned off and the switch 2407 may be turned on. Alternatively, the switch 209 may be turned off. When the switch 106 is turned off, no current enters the unit circuit. On the other hand, since the switch 2407 is on, no current flows from the power supply line 2413 to the load 201. When a current flows through the load 201, the switches 106, 2407, and 2411 may be turned off and the switch 209 may be turned on. When performing a setting operation, the switches 106, 2407, and 2411 may be turned on.

  The configuration shown in FIGS. 23 and 24 is described in Japanese Patent Application No. 2002-274680 filed by the same applicant. The contents can be combined with the present invention.

  Next, examples using a current mirror circuit are shown in FIGS. In the case of FIG. 25, when a current flows through a unit circuit as a precharge operation, the state when the setting operation is performed on the unit circuit changes. Therefore, it is necessary to control whether a current flows through the load 201 by the switch 2509. However, in the case of FIG. 26, even if a current flows to a unit circuit as a precharge operation, if the switch 2601 is turned off, the state when the setting operation is performed on the unit circuit does not change. That is, the signal stored in the capacitor 2510 does not change. Therefore, even when the precharge operation is performed, the current can flow to the load 201.

  Next, another example is shown in FIG. FIG. 28 shows a specific example of the circuit in FIG. 27. The configurations and operations shown in FIGS. 27 and 28 are disclosed in International Publication No. 03/027997 pamphlet by the same applicant. The contents can be combined with the present invention.

  As described above, in the present embodiment, the unit circuits having various configurations have been described. However, the present invention is not limited thereto, and various modifications are possible as long as the gist of the unit circuits is not changed. Further, the contents described in this embodiment mode can be freely combined with Embodiment Modes 1 and 2.

(Embodiment 4)
In this embodiment, a structure and operation of a display device, a signal line driver circuit, and the like are described. The circuit of the present invention can be applied to a part of a signal line driver circuit or a pixel.

  The display device includes a pixel array 2901, a gate line driver circuit 2902, and a signal line driver circuit 2910 as shown in FIG. The gate line driver circuit 2902 sequentially outputs a selection signal to the pixel array 2901. The signal line driver circuit 2910 sequentially outputs video signals to the pixel array 2901. The pixel array 2901 displays an image by controlling the state of light according to a video signal. Video signals output from the signal line driver circuit 2910 to the pixel array 2901 are often currents. That is, the state of the display element and the element that controls the display element arranged in each pixel is changed by the video signal (current) input from the signal line driver circuit 2910. Examples of a display element arranged in a pixel include an EL element and an element used in an FED (field emission display).

  Note that a plurality of gate line driver circuits 2902 and signal line driver circuits 2910 may be provided.

  The structure of the signal line driver circuit 2910 is divided into a plurality of parts. For example, the circuit is roughly divided into a shift register 2903, a first latch circuit (LAT1) 2904, a second latch circuit (LAT2) 2905, and a digital / analog conversion circuit 2906, for example. The digital / analog conversion circuit 2906 also has a function of converting a voltage to a current, and may have a function of performing gamma correction. That is, the digital-to-analog conversion circuit 2906 includes a circuit that outputs a current (video signal) to the pixel, that is, a current source circuit, and the present invention can be applied thereto.

  Each pixel has a display element such as an EL element. A circuit for outputting a current (video signal) to the display element, that is, a current source circuit is provided, and the present invention can be applied thereto.

  Thus, the operation of the signal line driver circuit 2910 will be briefly described. The shift register 2903 includes a plurality of columns of flip-flop circuits (FF) and the like, and receives a clock signal (S-CLK), a start pulse (SP), and a clock inversion signal (S-CLKb). The sampling pulses are sequentially output in accordance with the timing of.

  The sampling pulse output from the shift register 2903 is input to a first latch circuit (LAT1) 2904. A video signal is input to a first latch circuit (LAT1) 2904 from a video signal line 2908, and the video signal is held in each column according to the timing at which a sampling pulse is input. When the digital / analog conversion circuit 2906 is provided, the video signal is a digital value. The video signal at this stage is often a voltage.

  However, when the first latch circuit 2904 and the second latch circuit 2905 are circuits that can store analog values, the digital-analog conversion circuit 2906 can be omitted in many cases. In that case, the video signal is often a current. When data output to the pixel array 2901 is binary, that is, a digital value, the digital-analog conversion circuit 2906 can be omitted in many cases.

  When the first latch circuit (LAT1) 2904 completes holding the video signal up to the last column, a latch pulse (Latch Pulse) is input from the latch control line 2909 during the horizontal retrace period, and the first latch circuit (LAT1) The video signal held in 2904 is simultaneously transferred to the second latch circuit (LAT2) 2905. After that, the video signal held in the second latch circuit (LAT2) 2905 is input to the digital-to-analog conversion circuit 2906 simultaneously for one row. Then, a signal output from the digital / analog conversion circuit 2906 is input to the pixel array 2901.

  While the video signal held in the second latch circuit (LAT2) 2905 is input to the digital-to-analog conversion circuit 2906, and while being input to the pixel 2901, the shift register 2903 outputs a sampling pulse again. That is, two operations are performed simultaneously. This enables line-sequential driving. Thereafter, this operation is repeated.

  Note that in the case where the current source circuit included in the digital-to-analog conversion circuit 2906 is a circuit that performs a setting operation and an output operation, the current source circuit requires a circuit for flowing a current. In such a case, a reference current source circuit 2914 is provided.

  As described above, the transistor in the present invention may be any type of transistor or may be formed on any substrate. Therefore, the circuits as illustrated in FIGS. 29 and 30 may be entirely formed over a glass substrate, may be formed over a plastic substrate, or may be formed over a single crystal substrate. However, it may be formed on an SOI substrate, or may be formed on any substrate. Alternatively, part of the circuit in FIGS. 29 and 30 may be formed over one substrate, and another part of the circuit in FIGS. 29 and 30 may be formed over another substrate. That is, all of the circuits in FIGS. 29 and 30 need not be formed over the same substrate. For example, in FIGS. 29 and 30, the pixel 2901 and the gate line driver circuit 2902 are formed using a TFT over a glass substrate, and the signal line driver circuit 2910 (or a part thereof) is formed over a single crystal substrate. The IC chip may be formed, and the IC chip may be connected on a glass substrate by connecting with a COG (Chip On Glass). Alternatively, the IC chip may be connected to a glass substrate using TAB (Tape Auto Bonding) or a printed circuit board.

  That is, the signal line driver circuit and a part thereof are not provided on the same substrate as the pixel array 2901, and may be configured using, for example, an external IC chip.

  Note that the structure of the signal line driver circuit and the like is not limited to FIG.

  For example, when the first latch circuit 2904 or the second latch circuit 2905 is a circuit that can store an analog value, as shown in FIG. 30, a video signal is supplied from the reference current source circuit 2914 to the first latch circuit (LAT1) 2904. A signal (analog current) may be input. Also, in FIG. 30, the second latch circuit 2905 may not exist. In such a case, more current source circuits are often arranged in the first latch circuit 2904.

  For example, there may be two current source circuits, one of which performs a setting operation and the other of which performs a normal operation to output a current and switch between them. Thus, the setting operation and the normal operation can be performed simultaneously.

  The specific configuration and the like are described in WO 03/038793 pamphlet, WO 03/038794 pamphlet, WO 03/038795 pamphlet, WO 03/038796 pamphlet, and WO 03/038796 pamphlet. Since it is described in the pamphlet of No. 038797, the content can be applied to the present invention or can be combined with the present invention.

  In such a case, the present invention can be applied to the current source circuit in the digital-to-analog conversion circuit 2906 in FIG. There are many unit circuits in the digital / analog conversion circuit 2906, and the basic current source 101 and the additional current source 103 are arranged in the reference current source circuit 2914.

  Alternatively, the present invention can be applied to the current source circuit in the first latch circuit (LAT1) 2904 in FIG. There are many unit circuits in the first latch circuit (LAT1) 2904, and the basic current source 101 and the additional current source 103 are arranged in the reference current source circuit 2914.

  Alternatively, the present invention can be applied to the pixels in the pixel array 2901 in FIGS. 29 and 30 (the current source circuit therein). There are many unit circuits in the pixel array 2901, and the basic current source 101 and the additional current source 103 are arranged in the signal line driver circuit 2910.

  Next, an example of the gate line driver circuit 2902 is shown in FIG. A plurality of switch units (for example, the switch units 106a to 106e in FIG. 1) of the unit circuit are turned on in the precharge period. Then, in the set period, one switch unit is turned on. Thus, as shown in FIG. 31, the shift register 3101 outputs a signal that turns on a plurality of rows during the precharge period. On the other hand, the shift register 3102 outputs a signal such that one row is turned on during the setting period. By controlling the control signal line 3103, the output of the shift register 3101 and the output of the shift register 3102 are switched and output to the gate line.

  Note that on / off of other switches included in the pixel (unit circuit) can be controlled by a gate line driver circuit using a similar technique.

  Note that when the present invention is applied to a pixel, current may not be supplied to a load (a light-emitting element or the like) during a precharge period depending on the configuration of the pixel (unit circuit). In such a case, the light emitting element does not emit light. Therefore, it is not a hold-type light emission that continuously emits light during one frame period, but an impulse light emission that emits light for a certain period during one frame period. In the case of the hold type light emission, when a moving image is displayed, an afterimage may be seen due to an afterimage effect of the eyes. On the other hand, in the case of impulse-type light emission, afterimages are difficult to see even when a moving image is displayed. Therefore, when the present invention is applied to a pixel, an afterimage when a moving image is displayed can be suppressed.

  The contents described in the present embodiment correspond to those using the contents described in Embodiments 1 to 3. Therefore, the contents described in the first to third embodiments can be applied to the present embodiment.

(Embodiment 5)
In the above embodiments, the case where a current is supplied through a signal line is described; however, the present invention is not limited to this. A voltage may be supplied in addition to the current. For example, the technology described in Japanese Patent Application No. 2003-123000 filed by the same applicant can be combined with the present invention.

  In the Japanese Patent Application No. 2003-123000, not only a current but also a voltage is supplied as shown in FIG. The voltage is also supplied by forming a feedback circuit using the amplifier circuit 3707. A detailed description of the operation is omitted here.

  FIG. 38 illustrates a case where a plurality of transistors 3808 of the current source circuit in FIG. 37 are provided. Note that an example is shown in which an operational amplifier 3707 is used as an amplifier circuit. Here, for simplicity, a case where two transistors (or pixels) of the current source circuit are arranged is shown. However, it is not limited to these.

  As shown in FIG. 38, unit circuits 105A and 105B are connected. There is a signal line 108 for supplying current and a signal line 3803 for supplying voltage. These signal lines and the current source circuits in each unit circuit are connected via switch circuits (switches 106A and 3807A). By controlling switch circuits (switches 106A and 3807A and switches 106B and 3807B) of each unit circuit, a precharge operation and a setting operation are performed. Thus, a signal can be written quickly.

  Although FIG. 38 shows only the current source 3701 as a current source for simplicity, it is assumed that the magnitude of the current can be controlled in the precharge operation and the setting operation. Alternatively, as shown in FIG. 1, it is assumed that the current source 3701 includes switches 102 and 104, the basic current source 101, the additional current source 103, and the like.

  Note that the configuration of the unit circuit is not limited to FIG. 38, and various configurations are possible. Further, the feedback circuit is configured as shown in FIGS. 37 and 38, and an amplifier circuit is used. However, the present invention is not limited to this, and various configurations are possible.

  Note that the contents described in the present embodiment can be freely combined with the contents described in Embodiments 1 to 4, and the contents described in Embodiments 1 to 4 are also applied to this embodiment. Applicable.

(Embodiment 6)
In FIGS. 13 to 21, five unit circuits 105a to 105e are connected to the signal line 108, and a precharge operation is performed by flowing a current through three unit circuits. In this embodiment mode, a case where a larger number of pixels, that is, unit circuits are connected to one signal line will be described.

  For example, in the case of a display device for a mobile phone, a QVGA device is used and the display is vertically long. In that case, 320 pixels (unit circuits) are connected to one signal line. . In addition, in the case of a display device for car navigation, a VGA device is used, and since it is a horizontally long display, 480 pixels (unit circuits) are connected to one signal line. In the case of a computer display device, an XGA display device or the like is used, and since the display is horizontally long, 768 pixels (unit circuits) are connected to one signal line.

  As described above, in the case where many pixels (unit circuits) are connected to one signal line, the number of pixels (unit circuits) through which current flows at the time of a precharge operation will be described.

  It is desirable that the number of pixels (unit circuits) through which current flows during the precharge operation be large. This is because the current flowing during the precharge operation is large, so that a steady state can be quickly established. However, if the current value is too large, power consumption will increase. Further, when the number of pixels (unit circuits) through which a current flows during the precharge operation is large, the number of pixels through which a current can flow through the light emitting element may decrease. That is, the duty ratio may be reduced. This is because the precharge operation may destroy the information stored by the setting operation, and if a current is applied to the light emitting element in that state, an erroneous display will result, and the current cannot be supplied to the light emitting element. This is because a period occurs. The reduced duty ratio may shorten the life of the light emitting element. Therefore, the number of pixels (unit circuits) through which a current flows during the precharge operation may be determined based on these trade-offs.

  For example, if the number of pixels (unit circuits) through which current flows during the precharge operation is set to 50, the value of the current flowing during the precharge operation can be increased by 50 times. In the case of a QVGA display mobile phone, 320 pixels (unit circuits) are connected to one signal line, so the ratio of the number of pixels (unit circuits) that flow current during precharge operation is 50/320. = 16%. The duty ratio is (320-50) / 320 = 84%, which is an allowable range. Also, if the value of the current flowing during the precharge operation can be increased by a factor of 50, the time required to achieve a steady state can be shortened. In particular, in the case of a display device for a mobile phone, the length of the signal line is short because the size of the display region (pixel array portion) is small. Therefore, since the load capacitance associated with the signal line is small, if the current flowing during the precharge operation can be increased by a factor of 50 or more, the time until the steady state is achieved can be sufficiently reduced. Therefore, the number of pixels (unit circuits) that flow current during precharge operation is 50 or more, the ratio of pixels (unit circuits) that flow current during precharge operation is 16% or more, and the duty ratio is 84% or less. It is preferable that

  However, if the duty ratio is less than 5%, the life of the light emitting element may be shortened. Therefore, the current during the precharge operation is set so that the duty ratio becomes 5% or more, more preferably 10% or more. It is desirable to determine the number of pixels (unit circuits) to flow.

  For example, if the number of pixels (unit circuits) through which a current flows during the precharge operation is set to 100, the value of the current flowing during the precharge operation can be increased by 100 times. In the case of a VGA display device for car navigation, since 480 pixels (unit circuits) are connected to one signal line, the ratio of the number of pixels (unit circuits) through which current flows during the precharge operation is as follows: 100/480 = 20%. The duty ratio is (480-100) / 480 = 79%, which is an allowable range. Further, if the value of the current flowing during the precharge operation can be increased by a factor of 100, the time required to achieve a steady state can be shortened. In particular, in the case of a display device for car navigation, since the size of the display area (pixel array portion) is not so large, the length of the signal line is not so long. Therefore, since the load capacity of the signal line is not large, if the value of the current flowing during the precharge operation can be increased to 100 times or more, the time required for the steady state can be sufficiently reduced. Therefore, the number of pixels (unit circuits) that flow current during precharge operation is 100 or more, the ratio of the number of pixels (unit circuits) that flow current during precharge operation is 20% or more, and the duty ratio is 79% or less. It is preferable that

  However, if the duty ratio is less than 5%, the life of the light emitting element may be shortened. Therefore, the current during the precharge operation is set so that the duty ratio becomes 5% or more, more preferably 10% or more. It is desirable to determine the number of pixels (unit circuits) to flow.

  For example, if the number of pixels (unit circuits) through which a current flows during the precharge operation is set to 200, the value of the current flowing during the precharge operation can be increased by 200 times. In the case of an XGA display device for a personal computer, since 768 pixels (unit circuits) are connected to one signal line, the ratio of the number of pixels (unit circuits) through which current flows during the precharge operation is 200. / 768 = 26%. The duty ratio is (768-200) / 768 = 73%, which is an allowable range. Further, if the value of the current flowing during the precharge operation can be increased by a factor of 200, the time required to achieve a steady state can be shortened. Therefore, the number of pixels (unit circuits) that flow current during precharge operation is 200 or more, the ratio of pixels (unit circuits) that flow current during precharge operation is 26% or more, and the duty ratio is 73% or less. It is preferable that

  However, if the duty ratio is less than 5%, the life of the light emitting element may be shortened. Therefore, the current during the precharge operation is set so that the duty ratio becomes 5% or more, more preferably 10% or more. It is desirable to determine the number of pixels (unit circuits) to flow.

  Note that the number of pixels (unit circuits) through which current flows during the precharge operation is not limited to this. For example, the number of pixels (unit circuits) through which current flows during the precharge operation is determined such that the number of pixels (unit circuits) through which current flows during the precharge operation is increased so that the duty ratio becomes about 50%. May be.

(Embodiment 7)
Examples of the electronic device using the present invention include a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproducing device (car audio, audio component, etc.), a notebook personal computer, a game device, and a portable information terminal. (A mobile computer, a mobile phone, a portable game machine, an electronic book, or the like), an image reproducing apparatus provided with a recording medium (specifically, a recording medium such as a Digital Versatile Disc (DVD) can be reproduced and its image can be displayed Display device). FIG. 32 shows specific examples of these electronic devices.

  FIG. 32A illustrates a light-emitting device, which includes a housing 13001, a support 13002, a display portion 13003, a speaker portion 13004, a video input terminal 13005, and the like. The present invention can be used for an electric circuit included in the display portion 13003. According to the present invention, the light emitting device shown in FIG. 32A is completed. Since the light-emitting device is a self-luminous type, it does not require a backlight and can be a display portion thinner than a liquid crystal display. Note that the light-emitting device includes all display devices for displaying information, such as for personal computers, for receiving TV broadcasts, and for displaying advertisements.

  FIG. 32B illustrates a digital still camera, which includes a main body 13101, a display portion 13102, an image receiving portion 13103, operation keys 13104, an external connection port 13105, a shutter 13106, and the like. The present invention can be used for an electric circuit included in the display portion 13102. According to the present invention, a digital still camera shown in FIG. 32B is completed.

  FIG. 32C illustrates a laptop personal computer, which includes a main body 13201, a housing 13202, a display portion 13203, a keyboard 13204, an external connection port 13205, a pointing mouse 13206, and the like. The present invention can be used for an electric circuit included in the display portion 13203. According to the present invention, the light-emitting device shown in FIG. 32C is completed.

  FIG. 32D illustrates a mobile computer, which includes a main body 13301, a display portion 13302, a switch 13303, operation keys 13304, an infrared port 13305, and the like. The invention can be used for an electric circuit included in the display portion 13302. According to the present invention, the mobile computer shown in FIG. 32D is completed.

  FIG. 32E illustrates a portable image reproducing device (specifically, a DVD reproducing device) including a recording medium, which includes a main body 13401, a housing 13402, a display portion A 13403, a display portion B 13404, and a recording medium (such as a DVD). A reading unit 13405, operation keys 13406, a speaker unit 13407, and the like are included. The display portion A13403 mainly displays image information and the display portion B13404 mainly displays character information. The present invention can be used for an electric circuit included in the display portions A, B13403, and 13404. Note that the image reproducing device provided with the recording medium includes a home game machine and the like. According to the present invention, the DVD reproducing device shown in FIG.

  FIG. 32F shows a goggle type display (head-mounted display), which includes a main body 13501, a display portion 13502, and an arm portion 13503. The present invention can be used for an electric circuit included in the display portion 13502. Further, according to the present invention, the goggle type display shown in FIG. 32 (F) is completed.

  FIG. 32G illustrates a video camera, which includes a main body 13601, a display portion 13602, a housing 13603, an external connection port 13604, a remote control receiving portion 13605, an image receiving portion 13606, a battery 13607, a voice input portion 13608, operation keys 13609, and the like. . The present invention can be used for an electric circuit included in the display portion 13602. According to the present invention, a video camera shown in FIG. 32G is completed.

  FIG. 32H illustrates a mobile phone, which includes a main body 13701, a housing 13702, a display portion 13703, a sound input portion 13704, a sound output portion 13705, operation keys 13706, an external connection port 13707, an antenna 13708, and the like. The present invention can be used for an electric circuit included in the display portion 13703. Note that the display portion 13703 can reduce current consumption of the mobile phone by displaying white characters on a black background. According to the present invention, a mobile phone shown in FIG. 32H is completed.

  If the light emission luminance of the light emitting material increases in the future, the light including the output image information can be enlarged and projected by a lens or the like and used for a front-type or rear-type projector.

  In addition, the electronic devices often display information distributed through electronic communication lines such as the Internet and CATV (cable television), and in particular, opportunities to display moving image information are increasing. Since the response speed of the light-emitting material is extremely high, the light-emitting device is preferable for displaying moving images.

  Further, in the light emitting device, the light emitting portion consumes power. Therefore, it is desirable to display information so that the light emitting portion is reduced as much as possible. Therefore, when a light emitting device is used for a portable information terminal, particularly a display portion mainly for character information such as a mobile phone or a sound reproducing device, the character information is driven by a light emitting portion with a non-light emitting portion as a background. It is desirable to do.

  As described above, the applicable range of the present invention is extremely wide, and the present invention can be used for electronic devices in all fields. In addition, the electronic device of this embodiment may use any of the semiconductor devices described in Embodiments 1 to 6.

FIG. 4 illustrates a structure of a semiconductor device of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 6 illustrates a structure of a conventional pixel. FIG. 4 illustrates an operation of a conventional pixel. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates a structure of a semiconductor device of the present invention. FIG. 4 illustrates a structure of a semiconductor device of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates operation of a semiconductor device of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 4 illustrates an example of a configuration of a unit circuit of the present invention. FIG. 2 is a diagram illustrating a configuration of a display device of the present invention. FIG. 2 is a diagram illustrating a configuration of a display device of the present invention. FIG. 2 is a diagram illustrating a configuration of a gate line driving circuit of the present invention. 1 is a diagram of an electronic device to which the present invention is applied. FIG. 6 illustrates a structure of a conventional pixel. FIG. 4 is a diagram illustrating a timing chart of a conventional pixel. FIG. 4 is a diagram illustrating a timing chart of a conventional pixel. FIG. 6 illustrates a structure of a conventional pixel. FIG. 4 illustrates a structure of a semiconductor device of the present invention. FIG. 4 illustrates a structure of a semiconductor device of the present invention.

Claims (7)

A current source circuit connectable via a signal line and a switch,
The switch and the current source circuit as one unit circuit, comprising a plurality of unit circuits,
A first current is supplied to current source circuits of M unit circuits selected from the plurality of unit circuits during a precharge period, and currents of N unit circuits selected from the plurality of unit circuits are set during a set period. A semiconductor device, comprising: current supply means for supplying a second current to a source circuit. A current source circuit connectable via a signal line and a switch,
The switch and the current source circuit as one unit circuit, comprising a plurality of unit circuits,
A first current is supplied to the current source circuits of the M unit circuits selected from the plurality of unit circuits during a precharge period, and a current other than the M unit circuits selected from the plurality of unit circuits is set during the set period. A semiconductor device, comprising: current supply means for supplying a second current to current source circuits of N unit circuits selected from the unit circuits.   3. The semiconductor device according to claim 1, wherein N = 1.   The semiconductor device according to claim 1, wherein the unit circuit includes a light emitting element connected to the current source circuit.   5. The semiconductor device according to claim 1, wherein a ratio between the magnitude of the first current and the magnitude of the second current is M: N. 6. A current source circuit connectable via a signal line and a switch, the switch and the current source circuit as one unit circuit, and a plurality of the unit circuits;
Supplying a first current to current source circuits of M unit circuits selected from the plurality of unit circuits;
A method for driving a semiconductor device, comprising: supplying a second current to current source circuits of N unit circuits selected from unit circuits other than the M unit circuits selected from the plurality of unit circuits. 7. The device according to claim 6, wherein the first current supplies M times the current according to the number of the selected M unit circuits, and the second current includes the number of the selected N unit circuits. A method for driving a semiconductor device, comprising supplying an N-fold current according to the following.

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