JP2008033347A - Electronic circuit, its driving method, electrooptical device, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time for writing a voltage to a gate of a drive transistor. <P>SOLUTION: In an initialization period, a node B is fixed at an initial voltage V<SB>INI</SB>and transistors 211 and 214 are turned on to flow a current to an OLED element 230 and to hold the voltage in accordance with the current at a node A. Transistors 214 and 211 are thereafter sequentially turned off to hold the threshold voltage of the drive transistor 210 at the node A. In a write period, a transistor 213 is turned on and a data signal X-j is supplied and the voltage of a node B is changed by the value equivalent to the current flowing to the OLED element 230. The node A changes from the threshold voltage as the voltage change is distributed at a capacity ratio. In a light emission period, a transistor 214 is turned on and the current in accordance with the voltage of the node A flows to the OLED element 230. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electronic circuit for driving a current-driven element such as an organic light-emitting diode element, a driving method for the electronic circuit, an electro-optical device, and an electronic apparatus.

In recent years, organic light emitting diodes (hereinafter referred to as “OLED elements”) elements called organic electroluminescence elements and light emitting polymer elements have attracted attention as next-generation light-emitting devices that replace liquid crystal elements. Since this OLED element is a self-luminous type, it has less viewing angle dependence, and since it does not require a backlight or reflected light, it is suitable for low power consumption and thinning. It has characteristics.
Here, the OLED element is a current-type driven element that does not have voltage holdability like a liquid crystal element and cannot maintain a light emitting state when current is interrupted. Therefore, when an OLED element is driven by an active matrix method, a voltage corresponding to the gradation of the pixel is written to the gate of the driving transistor in the writing period (selection period), and the voltage is held by a gate capacitance or the like. In general, the driving transistor keeps a current corresponding to the gate voltage flowing through the OLED element.

By the way, in this configuration, there is a problem that the display voltage is deteriorated because the brightness of the OLED element is different for each pixel due to the variation of the threshold voltage characteristics of the driving transistor. Therefore, in recent years, during the writing period, the drive transistor is diode-connected, and a constant current is passed from the drive transistor to the data line, so that the current corresponding to the current to be passed to the OLED element is passed to the gate of the drive transistor. There has been proposed a technique that compensates for variations in threshold voltage characteristics of drive transistors by programming to write a voltage (see, for example, Patent Documents 1 and 2).
US Pat. No. 6,229,506 (see FIG. 2) Japanese Patent Laying-Open No. 2003-177709 (see FIG. 3)

However, in this technique, for example, when the driving transistor is an n-channel type, when the current to be passed through the OLED element is set to be small, the gate voltage of the driving transistor is low during the writing period, and the driving transistor As a result, it has been pointed out that the current voltage cannot be written to the gate of the driving transistor within the writing period.
The present invention has been made in view of the above-described circumstances, and an object thereof is an electronic circuit capable of quickly writing a voltage corresponding to a current to be supplied to a driven element to a gate of a driving transistor, An object is to provide a driving method thereof, an electro-optical device using the electronic circuit, and an electronic apparatus.

  In order to achieve the above object, a driving method of an electronic circuit according to the present invention includes a driving transistor that controls a current flowing through a driven element, and a first switching that turns on or off between a gate and a drain of the driving transistor. An electronic circuit driving method comprising: an element; and a capacitive element having one end connected to the gate of the driving transistor, wherein an initial voltage is applied to the other end of the capacitive element and the first switching element is turned on. In this state, a current is passed through the driven element, and then the current is interrupted, and the application of the initial voltage to the other end of the capacitive element is released, and the first switching element is turned off. A second step of applying a voltage corresponding to a current to be passed through the driven element to the other end of the capacitive element; The current according to the voltage, the driving transistor is characterized in that it comprises a third step of flowing the driven element. According to this method, the voltage corresponding to the threshold value of the driving transistor is held at one end of the capacitive element and the gate (node A) of the driving transistor by turning on and off the first switching element in the first step. The Next, in the second step, the other end of the capacitive element is changed from the initial voltage by application of a voltage corresponding to the current to be supplied to the driven element, and the voltage of the node A is also increased by the amount corresponding to this voltage change. Change and hold. In the third step, a current corresponding to the voltage of the node A after the change flows to the driven element, and the threshold current characteristic of the driving transistor is canceled for the current flowing at this time. In addition, since the holding of the capacitor element in the first step is performed by forcing a current to flow through the driven element, no time is required. Furthermore, in the second step, a voltage corresponding to the current to be passed through the driven element is applied to the other end of the capacitive element, and is not applied directly to the gate of the driving transistor. It can be shortened.

In this driving method, in the first step, the first switching element is turned on and a current is passed through the driven element, and a voltage corresponding to the current is applied to one end of the capacitive element and the driving transistor. The first switching element is turned off after the current is cut off while the gate is held, and the voltage held at one end of the capacitive element and the gate of the driving transistor is set to the threshold value of the driving transistor. You may make it transfer to the voltage according to a voltage. According to this method, the driving transistor is diode-connected when the first switching element is turned on, while the node A has a voltage corresponding to the current flowing through the driven element in the connected state. Thereafter, the node A shifts to a voltage corresponding to the threshold voltage of the driving transistor by releasing the diode connection.
In the first step, the first switching element is turned on and a current is passed through the driven element, and a voltage corresponding to the current and the threshold voltage of the driving transistor is set to the capacitance element. One end and the gate of the driving transistor may be held. According to this method, the driving transistor is diode-connected when the first switching element is turned on, while the node A has a voltage corresponding to the current flowing through the driven element in the connected state. For this reason, the holding voltage of the node A is a voltage according to the current and the threshold voltage of the driving transistor.
On the other hand, in the first step, after the first switching element is turned on and a current is passed through the driven element, the current is interrupted and the first switching element is turned off. A voltage corresponding to the threshold voltage may be held at one end of the capacitive element and the gate of the driving transistor. In this method, when the first switching element is turned on, a voltage corresponding to the threshold voltage of the driving transistor can be held at the node A by flowing a relatively small current through the driven element. .
In either method, the first step is independent of the second step before the second step of applying a voltage corresponding to the current to be passed to the driven element to the other end of the capacitive element. It can be executed in a time longer than the second step.

  In order to achieve the above object, an electronic circuit according to the present invention is turned on in a first period between a drive transistor for controlling a current flowing in a driven element and a gate and a drain of the drive transistor, A first switching element that is turned off by the start timing of the second period after the first period, a capacitive element having one end connected to the gate of the driving transistor, and turned on in the first period to generate an initial voltage Is applied to the other end of the capacitor element, while the second switching element is turned off in the second period and a third period after the second period, and the current to be supplied to the driven element. A third switching element that is turned on in the second period is provided between a signal line to which a corresponding voltage is applied and the other end of the capacitor element. According to this electronic circuit, a current can be passed through the driven element without depending on the threshold characteristics of the driving transistor, and the time required for writing a voltage corresponding to the current can be shortened.

In this electronic circuit, a fourth switching element that cuts off a current flowing through the driven element regardless of a gate voltage of the driving transistor when inserted into a path of a current flowing through the driven element and turned off. A fourth switching element which is turned on during part or all of the first period and turned on during the third period may be used. According to this configuration, the time during which the current controlled by the driving transistor flows through the driven element can be adjusted by turning on and off the fourth switching element.
In the case of having a fourth switching element, the first and fourth switching elements are transistors having different conductivity types, the first configuration in which their gates are connected to a common control line, or The first and second switching elements are transistors of the same conductivity type, and preferably have a second configuration in which their gates are connected to a common control line. In any configuration, the number of wirings to the electronic circuit can be reduced.

Further, the second configuration can be applied even when the fourth switching element is not provided. When the second configuration is applied when the fourth switching element is not provided, the driven element and the driving transistor are inserted into a current path between the first and second power supply lines, and The voltage between the second power supply lines may be the initial voltage in the first period and a predetermined power supply voltage in the third period. In this configuration, the second switching element is turned on or off between the other end of the capacitive element and the drain of the driving transistor, and an initial voltage is applied to the other end of the capacitive element via the power line. In other configurations, the second switching element is turned on or off between the other end of the capacitive element and the power supply line to which the initial voltage is applied. The initial voltage may be applied to the other end of the capacitive element via
In the electronic circuit, the driven element is preferably an electro-optical element, and particularly preferably an organic light emitting diode element.

In order to achieve the above object, the electro-optical device according to the present invention includes a pixel corresponding to an intersection of a scanning line and a data line to which a voltage corresponding to a current to be passed through the electro-optical element is applied when sequentially selected. An electro-optical device having a circuit, wherein the pixel circuit is turned on in a first period between a driving transistor that controls a current flowing in the electro-optical element and a gate and a drain of the driving transistor, A first switching element that is turned off by the start timing of the second period after the first period, a capacitor element having one end connected to the gate of the driving transistor, and turned on in the first period to A second switching element that applies a voltage to the other end of the capacitor element and is turned off in the second period and a third period after the second period; and the data line; At between the other end of the serial capacitance element, characterized in that it comprises a third switching element to turn on in the second period. According to this electro-optical device, a current that does not depend on the threshold characteristics of the driving transistor can flow through the electro-optical element, and the time required to write a voltage corresponding to the current can be shortened.
In addition, it is desirable that the electronic apparatus according to the present invention includes this electro-optical device.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram showing the configuration of the electro-optical device according to the first embodiment of the invention. FIG. 2 is a diagram illustrating a configuration of a pixel circuit of the electro-optical device.
First, as shown in FIG. 1, in the electro-optical device 10, a plurality of scanning lines 102 are extended in the horizontal direction (X direction), while a plurality of data lines (signal lines) 112 are vertically arranged in the drawing. It extends in the direction (Y direction). A pixel circuit (electronic circuit) 200 is provided so as to correspond to each intersection of the scanning line 102 and the data line 112.
Here, for convenience of explanation, in the present embodiment, the number of scanning lines 102 (number of rows) is “360”, the number of data lines (number of columns) is “480”, and the pixel circuit 200 is 360 rows × horizontal. Assume a configuration in which the matrix is arranged in a matrix of 480 columns. However, the present invention is not intended to be limited to this arrangement.
Note that the pixel circuit 200 includes an OLED element to be described later, and a predetermined image is displayed in gradation by controlling the current to the OLED element for each pixel circuit 200.

  In FIG. 1, only the scanning line 102 is extended in the X direction. However, in the present embodiment, in addition to the scanning line 102, as shown in FIG. And 108 extend in the X direction for each row. For this reason, the scanning line 102 and the control lines 104, 106, and 108 are combined into one set and used as the pixel circuit 200 for one row.

The Y driver 14 selects the scanning line 102 row by row for each horizontal scanning period, supplies an H level scanning signal to the selected scanning line 102, and outputs various control signals synchronized with the selection. , Are supplied to the control lines 104, 106 and 108, respectively. That is, the Y driver 14 supplies a scanning signal and a control signal to the scanning line 102 and the control lines 104, 106, and 108 for each row.
Here, for convenience of explanation, a scanning signal supplied to the scanning line 102 of the i-th row (i is an integer satisfying 1 ≦ i ≦ 360 and is used for generalizing the row) is represented by _GWRT−. Indicated as _i . Similarly, control signals supplied to the _i-th control lines 104, 106, and 108 are denoted as G _SET-i , G _INI-i, and G _EL-i , respectively.

On the other hand, the X driver 16 applies the pixel circuit for one row corresponding to the scanning line 102 selected by the Y driver 14, that is, to each of the pixel circuits 200 of 1 to 480 columns located in the selected row. A data signal having a voltage corresponding to a current (that is, pixel gradation) to be passed through the OLED element of the circuit 200 is supplied via the data lines 112 in the 1st to 480th columns. Here, the data signal specifies that the pixel is brighter as the voltage is higher, and conversely, the pixel is specified as darker as the voltage is lower.
For convenience of explanation, a data signal supplied to the data line 112 in the j-th column (j is an integer satisfying 1 ≦ j ≦ 480 and generalizing the column) is represented by X−j. write.

All the pixel circuits 200 are respectively supplied with the high voltage V _{EL serving} as the power source of the OLED element via the power line 114. In addition, all the pixel circuits 200 are commonly grounded to the voltage reference potential Gnd in the present embodiment.
The voltage of the data signal X-j that specifies the black is the lowest gradation of the pixel higher than Gnd, the voltage of the data signal X-j that specifies the white is the highest gray level of the pixel is lower than V _EL Is set. In other words, the voltage range of the data signal Xj is set to be within the power supply voltage.
On the other hand, in this embodiment, the pixel circuit 200 is supplied with the initial voltage V _INI via the feeder line 116. Here, in this embodiment, the initial voltage V _INI substantially coincides with the lowest value of the voltage range that the data signal X-j can take, that is, the data signal voltage that specifies the lowest gradation of the pixel.
The control circuit 12 supplies the Y driver 14 and the X driver 16 with clock signals (not shown), respectively, to control both drivers, and supplies the X driver 16 with image data that defines the gradation for each pixel. To do.

In the present embodiment, the pixel circuits 200 arranged in a matrix form all have a common configuration. Therefore, the configuration of the pixel circuit 200 will be described as a representative example of the pixel circuit located in i rows and j columns. As illustrated in FIG. 2, the pixel circuit 200 includes an n-channel driving transistor 210, n-channel transistors 211, 212, 213, and 214 that function as first to fourth switching elements, and capacitive elements. It has a functioning capacitor 220 and an OLED element 230 which is an electro-optic element.
Among these, one end (drain) of the transistor 214 is connected to the power supply line 114, and the other end (source) of the transistor 214 is connected to the drain of the driving transistor 210 and one end (drain) of the transistor 211, respectively. Has been. Here, the gate of the transistor 214 is connected to the control line 108 in the i-th row. Therefore, the transistor 214 is turned on when the control signal G _EL-i is at the H level, and is turned off when the control signal G _EL-i is at the L level.

The source of the driving transistor 210 is connected to the anode of the OLED element 230, while the cathode of the OLED element 230 is grounded to the lower voltage Gnd of the power source. Therefore, OLED device 230, the path between the high side voltage _{V EL} and low voltage Gnd of the power supply, has an electric intervention inserted configuration together with the driving transistor 210 and the transistor 214.
The gate of the driving transistor 210 is connected to one end of the capacitor 220 and the source of the transistor 211. For convenience of explanation, one end of the capacitor 220 (the gate of the driving transistor 210) is a node A. As shown by a broken line in FIG. 2, a capacitance is parasitic on this node A. This capacitance is a parasitic capacitance between the node A and the cathode of the OLED element 230, and the capacitance caused by the gate capacitance of the driving transistor, the capacitance of the OLED element 230, the parasitic capacitance of the wiring between the node A and the cathode, and the like. Contains.

The transistor 211 is electrically inserted between the drain and gate of the driving transistor 210, and the gate of the transistor 211 is connected to the control line 104 in the i-th row. Therefore, the transistor 211 is turned on when the control signal G _SET-i becomes the H level, and causes the driving transistor 210 to function as a diode.
On the other hand, one end (drain) of the transistor 212 is connected to the power supply line 116, while the other end (source) is connected to one end (drain) of the transistor 213 and the other end of the capacitor 220. The gate of the transistor 212 is connected to the i-th control line 106. Therefore, the transistor 212 is turned on when the control signal G _INI-i becomes H level.
Further, the other end (source) of the transistor 213 is connected to the data line 112 in the j-th column, and the gate thereof is connected to the scanning line 102 in the i-th row. Therefore, the transistor 213 is turned on when the scanning signal _GWRT-i becomes the H level, and the data signal Xj (voltage) supplied to the data line 112 in the j-th column is supplied to the capacitor 220. It will be applied to the edge.
Here, for convenience of explanation, the other end of the capacitor (the source of the transistor 212 and the drain of the transistor 213) is referred to as a node B.

  Note that the pixel circuits 200 arranged in a matrix type are formed together with the scanning lines 102 and the data lines 112 on a transparent substrate such as glass. For this reason, the driving transistor 210 and the transistors 211, 212, 213, and 214 are configured by TFTs (thin film transistors) using a polysilicon process. The OLED element 230 has a transparent electrode film such as ITO (indium tin oxide) as an anode (individual electrode) and a single metal film such as aluminum or lithium or a laminated film thereof as a cathode (common electrode) on the substrate. The light emitting layer is sandwiched.

Next, the operation of the electro-optical device 10 will be described. FIG. 3 is a timing chart for explaining the operation of the electro-optical device 10.
First, as shown in FIG. 3, the Y driver 14 scans the scanning lines 102 in the first row, the second row, the third row,..., The 360th row from the start of one vertical scanning period (1F). One line at a time is selected for each horizontal scanning period (1H), and only the scanning signal of the selected scanning line 102 is set to H level, and the scanning signal to other scanning lines is set to L level.
Here, focusing on one horizontal scanning period (1H) in which the _i-th scanning line 102 is selected and the scanning signal _GWRT-i is at the H level, the horizontal scanning period and operations before and after the horizontal scanning period are shown in FIG. 3 and FIG. 4 will be described with reference to FIGS.

As shown in FIG. 3, the preparation for the writing operation of the pixel circuit 200 in the i-th row and the j-th column starts from the timing t1 preceding the timing at which the scanning signal G _WRT-i changes to the H level by the period Ti. . On the other hand, when the scanning signal G _WRT-i changes from the H level to the L level again, light emission based on the written voltage starts.
For this reason, the operation of the pixel circuit 200 in the i row and j column is roughly divided into the first period (1) from the timing t1 until the scanning signal G _WRT-i changes to the H level, and the scanning signal G _WRT−. It can be divided into a second period in which _i is at the H level and a third period after the scanning signal G _WRT-i is changed to the L level.
These first to third periods are referred to as an initialization period (1), a writing period (2), and a light emission period (3), respectively, paying attention to the operation contents. Of these, the initialization period (1) can be further divided into three periods (1a), (1b), and (1c) in the present embodiment.
Hereinafter, the operation during these periods will be described in order.

First, before the timing t1, the scanning signal G _WRT-i , the control signals G _SET-i , G _INI-i, and G _{EL-i are} all at the L level. When the timing t1 is reached, the first period (1a) of the initialization period (1) is reached, and the Y driver 14 sets the control signals G _SET-i , G _INI-i and G _EL-i to H. Level. Therefore, in the pixel circuit 200, as shown in FIG. 4, the transistor 211 is turned on by the control signal G _SET-i at the H level, so that the driving transistor 210 functions as a diode. Further, the transistor 214 is also turned on by the control signal G _EL-i at the H level.
Therefore, in the period (1a), in the pixel circuit 200, the current flows through the path of the power supply line 114 → the transistor 214 → the driving transistor 210 → the OLED element 230 → the ground Gnd, so that the node A has a voltage corresponding to the current, Specifically, this is the gate voltage of the driving transistor 210 through which the current flows.
On the other hand, the control signal G _INI-i becomes H level over the entire initialization period (1) and turns on the transistor 212. For this reason, since the node B is fixed to the initial voltage V _INI over the initialization period (1), the voltage state is maintained in the node A located on the opposite side of the node B as viewed from the capacitor 220. . Therefore, the node A is held at a voltage corresponding to the current flowing through the OLED element 230 in the period (1a).

  In this period (1a), since a current flows through the OLED element 230, the OLED element 230 emits light. However, since this period (1a) is set to be negligibly short as compared with one vertical scanning period (1F) which is a unit period of display, light emission in the period (1a) is a light emission period described later. The light emission in (3), that is, the light emission due to the flow of the target current to the OLED element 230 is not affected.

Next, when the period (1b) start timing of the initialization period (1) is reached, the Y driver 14 returns the control signal G _EL-i to L level, while the control signals G _SET-i and G _INI-i Are both kept at the H level. For this reason, in the pixel circuit 200, as shown in FIG. 5, since the transistor 214 is turned off, the current path of the OLED element 230 is cut off. However, since the transistor 211 is kept on, the driving transistor 210 continues to function as a diode. Therefore, the node A gradually shifts in a self-compensating manner toward the threshold voltage V _thn of the driving transistor 210.
Then, at the end timing of the period (1b), the node A substantially coincides with the threshold voltage V _thn .

Subsequently, at the start timing of the period (1c) of the initialization period (1), the Y driver 14 returns the control signal G _SET-i to the L level. For this reason, in the pixel circuit 200, as shown in FIG. 6, the diode connection of the driving transistor 210 is released, so that the voltage of the node A is determined to be V _thn .

Next, in the writing period (2), the Y driver 14 returns the control signal G _INI-i to the L level, and sets the scanning signal G _WRT-i to the H level. Therefore, as shown in FIG. 7, the transistor 212 is turned off and the transistor 213 is turned on.
In the writing period (2), the X driver 16 supplies the data signal Xj having a voltage corresponding to the gradation of the pixel in the i row and the j column to the data line 112 in the j column. As described above, the voltage of the data signal X-j that specifies the lowest gradation of the pixel is V _INI , and the voltage of the data signal X-j increases as the pixel specifies brighter. Can be expressed as (V _INI + ΔV).
Note that ΔV is a voltage change (rise) from the initial voltage V _INI , and is zero when the pixel is designated as the lowest gradation black, and gradually increases as the bright gradation is designated. Therefore, the node B varies by ΔV from the initialization period (1) to the writing period (2).

On the other hand, in the writing period (2), since the transistor 211 is off in the pixel circuit 200, the node A is held only by the gate capacitance of the driving transistor 210. For this reason, the node A rises from the voltage V _{thn in} the initialization period (1) by the amount of the voltage change ΔV at the node B distributed by the capacitance ratio between the capacitor 220 and the gate capacitance of the driving transistor 210. .
Specifically, when the size of the capacitor 220 is Ca and the gate capacitance of the driving transistor 210 is Cb, the node A _rises from the voltage V _thn by {ΔV · Ca / (Ca + Cb)}. In addition, the voltage Vg at the node A can be expressed as follows.
Vg = V _thn + ΔV · Ca / (Ca + Cb) (a)

In the light emission period (3), the Y driver 14 sets the scanning signal G _WRT-i to the L level and sets the control signal G _EL-i to the H level.
For this reason, in the pixel circuit 200, as shown in FIG. 8, the transistor 213 is turned off, but the voltage holding state in the capacitor 220 does not change, so the node A is maintained at the voltage Vg. On the other hand, since the transistor 214 is turned on, the current I _EL corresponding to the voltage Vg flows through the OLED element 230 through the current path. As a result, the OLED element 230 continues to emit light with brightness according to the current I _EL .

In the light emission period (3), the current I _EL flowing through the OLED element 230 is determined by the conduction state between the source and drain of the driving transistor 210, and the conduction state is set by the voltage of the node A. Here, since the voltage of the gate viewed from the source of the driving transistor 210 is the voltage Vg of the node A itself, the current I _EL is expressed as follows.
I _EL = (β / 2) (Vg−V _thn ) ² (b)
In this equation, β is a gain coefficient of the driving transistor 210.

Here, by substituting equation (a) into equation (b),
I _EL = (β / 2) {ΔV · Ca / (Ca + Cb)} ² (c)
It becomes. As shown in the equation (c), the current I _EL flowing through the OLED element 230 is determined only by the change ΔV from the initial voltage V _INI without depending on the threshold value V _thn of the driving transistor 210. (Capacitances Ca and Cb and gain coefficient β are fixed values).

When the light emission period (3) continues for a predetermined period, the Y driver 14 sets the control signal G _EL-i to the L level. As a result, the transistor 214 is turned off. As a result, the current path is interrupted, so that the OLED element 230 is turned off.
Here, the Y driver 14 performs control such that the H level periods of the control signals G _{EL-1 to} G _EL-360 corresponding to the first to 360th rows are the same. In other words, control is performed so that the proportion of the light emission period (3) is constant in one vertical scanning period for all the OLED elements 230. For this reason, when the light emission period (3) is lengthened, the entire screen is brightened, while when it is shortened, the whole screen can be darkened.
The longest light emission period (3) is the entire period excluding the initialization period (1) and the writing period (2) in one vertical scanning period (1F). Therefore, in the i-th row, the control signal G _EL-i is returned to the i-th row after one vertical scanning period (1F) has elapsed from the timing when the scanning signal G _WRT-i changes from the H level to the L level. The H level can be taken in a period up to timing t1 preceding the timing at which the eye scanning line 102 is selected by a period Ti.

Here, the operation of the pixel circuit 200 in the i row and j column has been described. However, the operations of the initialization period (1), the writing period (2), and the light emission period (3) are simultaneously performed for all the other pixels in the i row. Run in parallel.
Further, the i-th row has been described, but for the first to 360-th rows, the scanning line 102 is selected in order for each horizontal scanning period (1H), and the writing period in the selected period. The operation (2) is executed. The initialization period (1) is executed before the writing period (2), and the light emission period (3) is executed after the writing period (2). For example, for the (i + 1) -th row following the i-th row, as shown in FIG. 3, the initialization period starts from the timing t2 preceding the timing when the scanning signal G _{WRT- (i + 1)} becomes H level by the period Ti. After that, the writing period (2) is reached in a period in which the scanning signal G _{WRT- (i + 1)} is at the H level. In the writing period of the (i + 1) th row, the data signal X-j having a voltage corresponding to the gradation of the pixel in the (i + 1) th row j column is supplied to the data line 112 in the jth column, and the voltage change thereof Minutes are written in the node A, and thereafter, the light emission period (3) is entered.
Therefore, the initialization period (1) may be executed in parallel over two or more adjacent rows. Similarly, the light emission period (3) is also executed in parallel over two or more adjacent rows.

According to the first embodiment, in the period (1a) of the initialization period (1), the drive transistor 210 is diode-connected, and a current is forced to flow through the OLED element 230, whereby the node A is connected to the current A. On the other hand, the node B is fixed to the initial voltage V _INI . Therefore, the node A immediately reaches some voltage and is held. After that, the transistor 214 is turned off while the diode connection is maintained, so that the voltage of the node A is shifted to V _thn by the end timing of the period (1b). Then, in the period (1c), the voltage of the node A is fixed to V _thn . This initialization period (1) is a period unrelated to the writing period (2) in which a row is selected, and is executed in a period before this time. Therefore, in one vertical scanning period (1F), A sufficiently long period can be secured.
Next, in the writing period (2), the data signal X-j is applied to the node B to change the voltage of the other end of the capacitor 220, and the charge is redistributed due to this voltage change. A voltage corresponding to the current to be passed through the OLED element 230 is written. For this reason, coupled with the securing of the initialization period (1), the time required for voltage writing is shortened compared to the method of directly writing the voltage corresponding to the current to be passed through the OLED element 230 to the gate of the driving transistor 210. Can be realized.
Further, in the light emission period (3), the current flowing through the OLED element 230 does not depend on the threshold voltage V _thn of the drive transistor 210. For this reason, even if the threshold voltage V _thn of the drive transistor 210 varies for each pixel circuit 200, the current flowing through the OLED element 230 can be made uniform.
Therefore, according to the electro-optical device according to the first embodiment, even when the number of pixels increases as the resolution increases, the writing time of the data signal can be shortened, and the uniformity of the current flowing through the OLED element 230 can be reduced. It can be secured.

In the pixel circuit 200 according to the first embodiment, the transistor 211 has a function of diode-connecting the driving transistor 210 when turned on, whereas the transistor 214 is turned off and the driving transistor 210 and the OLED element 230 are turned off. These functions are completely different from each other. Therefore, in the first embodiment, as shown in FIG. 2, the transistor 211 is controlled to be turned on and off independently by the control line 104 and the transistor 214 by the control line 108.
However, as shown in FIG. 9, for example, by changing the conductivity type of the transistor 214 to the p-channel type, the channel types of the transistors 211 and 214 are made different from each other, and the on / off control is performed by the common control line 108. It is also good. When such a configuration is adopted, the control line 104 is not necessary as compared with the configuration of FIG. 2, and as a result, one control line is reduced per row, resulting in an improvement in yield and an opening in the case of the bottom emission type. Bright display with an increased rate is possible.
Further, if the transistors 211 and 212 are both of the same channel type, the threshold voltages of the transistors 211 and 212 are equal, so that the same control signal G _INI-i is used as compared with the case of different channel types. The operation can be reliably controlled. For example, malfunctions such as one transistor turning on and the other transistor turning off with respect to the same control signal G _INI-i can be prevented. In addition, by using the same channel type, it is not necessary to provide a margin for injecting impurities into the transistor, and the transistor 211 and the transistor 212 can be arranged closer to each other. Therefore, the transistor occupation region in the pixel region can be minimized, and the transistor characteristics of the transistor 211 and the transistor 212 can be manufactured without variation. Further, if the driving transistor 210 is the same channel type as the transistors 211 and 212, the same effect can be obtained. Further, by using only the same channel type, the voltage range of the power supply with respect to the signal supplied to the pixel circuit can be minimized, so that a highly reliable electronic circuit can be realized.

<Second Embodiment>
Next, an electro-optical device according to a second embodiment of the invention will be described. The electro-optical device according to the second embodiment is obtained by replacing the pixel circuit in the first embodiment with a pixel circuit 200 shown in FIG.
The pixel circuit 200 shown in FIG. 2 has a configuration in which the transistors 211 and 212 are controlled to be turned on and off independently by separate control signals G _SET-i and G _INI-i , but the pixel circuit shown in FIG. Is configured to be commonly controlled by a control signal G _INI-i supplied to the control line 106.

FIG. 11 is a timing chart for explaining the operation of the electro-optical device according to the second embodiment.
As shown in this figure, in the second embodiment, the transistors 211 and 212 are commonly controlled to be turned on and off in accordance with the control signal G _INI-i, so that the period (1c) is included in the initialization period (1). Not included. However, in the pixel circuit 200 shown in FIG. 10, the transistors 211 and 212 are simultaneously turned off at the end of the period (1b), so that the voltage at the node A is determined simultaneously with the end of the initialization period (1b). Become.
Since other operations are the same as those in the first embodiment, description thereof is omitted. According to the electro-optical device according to the second embodiment, similarly to the pixel circuit shown in FIG. 9, the control line 104 is not necessary, and one control line is reduced per row, so that the yield and the aperture ratio are reduced. Can be improved.

<Third Embodiment>
Next, an electro-optical device according to a third embodiment of the invention will be described. The electro-optical device according to the third embodiment is obtained by replacing the pixel circuit in the first embodiment with a pixel circuit 200 shown in FIG.
The pixel circuit 200 shown in FIG. 12 has a configuration in which the transistor 214 is removed from the pixel circuit shown in FIG. Therefore, the control line 108 is not necessary in the pixel circuit 200 shown in FIG.

FIG. 13 is a timing chart for explaining the operation of the electro-optical device according to the second embodiment.
As shown in this figure, in the third embodiment, in the i-th row, the control signal G _{INI is supplied} only during the period Ti before the writing period (2) in which the scanning signal G _WRT-i is at the H level. _An initialization period (1) in which _−i is at the H level is provided.
In this initialization period (1), the transistors 211 and 212 are simultaneously turned on, so that a current flows through the drive transistor 210 and the OLED element 230 (diode-connected). Then, at the end timing of the initialization period (1), the control signal G _INI-i becomes L level and the transistors 211 and 212 are turned off at the same time. Thus, as in the first and second embodiments, the diode of the drive transistor 210 Self-compensating node A voltage shift due to continued connection does not occur.

Therefore, at the end of the initialization period (1), the voltage at the node A is a voltage corresponding to the current flowing through the OLED element 230, which reflects the threshold voltage V _thn of the driving transistor 210, and Compared to the first and second embodiments. Therefore, in the third embodiment, the initial voltage V _INI supplied via the feeder line 116 is also set high in response to the increase in the voltage at the node A.
Specifically, the initial voltage V _INI is a reference voltage when the voltage of the node B changes from the initialization period (1) to the writing period (2), and the voltage corresponding to this voltage change is the writing period (2 ) Is the same as in the first and second embodiments. However, in the third embodiment, since the voltage point of the node A in the initialization period (1) is high, if the initialization voltage V _INI is set low as in the first and second embodiments, the writing period (2 ), The node A only rises from a high voltage point, and a low voltage is written to the node B, so that a current corresponding to a low gradation (dark gradation) cannot flow through the OLED element 230. Therefore, in the third embodiment, the initial voltage V _INI is set higher than those in the first and second embodiments, and not only the node B increases in voltage from the initialization period (1) to the writing period (2), The structure may be lowered.
In this configuration, when a current corresponding to a low gradation (dark gradation) is supplied to the OLED element 230, the node B is lowered (discharged) from the initialization period (1) to the writing period (2). Since the voltage corresponding to the decrease is written into the node A, the voltage at the node B can be lowered and a current corresponding to a low gradation (dark gradation) can be supplied to the OLED element 230. is there.
Note that the initial voltage V _INI in the third embodiment corresponds to the voltage of a data signal that specifies an intermediate gradation (gray) between the lowest gradation (black) and the highest gradation (white) of the pixel. Become.

According to the electro-optical device according to the third embodiment, the control line 104 is not necessary as compared with the pixel circuit shown in FIG. 9 or FIG. Compared to the pixel circuit, the number of transistors is reduced by two), and the number of transistors per pixel circuit is also reduced by one, so that the yield and the aperture ratio can be further increased.
However, in the third embodiment, since the transistor 214 does not exist, the brightness of the entire screen cannot be adjusted by adjusting the light emission period (3). Also in the writing period (2), a current corresponding to the voltage at the node A flows through the OLED element 230.

<Fourth embodiment>
Next, an electro-optical device according to a fourth embodiment of the invention will be described. The electro-optical device according to the fourth embodiment is obtained by replacing the pixel circuit in the first embodiment with a pixel circuit 200 shown in FIG.
The pixel circuit 200 shown in FIG. 14 has a configuration in which, in the pixel circuit shown in FIG. 12, the power supply line 114 is extended in the X direction for each row, and the voltage is changed with time. is there. In other words, the power supply line 114 in the fourth embodiment is combined with the scanning line 102 and the control line 106 to be used as a set for the pixel circuit 200 for one row.
Such a power supply line 114 is driven by, for example, a Y driver 14. In the fourth embodiment, the initial voltage V _INI applied to the power supply line 116 is a voltage that matches the data signal designating the lowest gradation of the pixel, as in the first and second embodiments.

FIG. 15 is a timing chart for explaining the operation of the electro-optical device according to the fourth embodiment.
As shown in this figure, in the fourth embodiment, as in the third embodiment, in the i-th row, the scanning signal G _WRT-i is before the writing period (2) in which the scanning signal G _WRT-i is at the H level. In the initialization period (1), the control signal _GINI-i is at the H level for the period Ti.
However, in the fourth embodiment, during the initialization period, the Y driver 14 sets the voltage V _EL-i of the _i-th power line 114 to the initial voltage Vini. This initial voltage Vini is a voltage that is slightly higher than the sum of the threshold voltage V _thn of the driving transistor 210 and the threshold voltage of the OLED element 230. Specifically, when the initial voltage Vini is applied to the drain of the drive transistor 210 that is diode-connected when the transistor 211 is turned on, the voltage is such that a very small current flows through the drive transistor 210 and the OLED element 230. is there.

On the other hand, also in the fourth embodiment, in the initialization period (1), the node B is fixed to the initial voltage V _INI by turning on the transistor 212, so that the voltage corresponding to the current is held in the node A. Will be.
Here, unlike the third embodiment, the current flowing through the OLED element 230 in the initialization period (1) is very small, so that the voltage held at the node A is approximately equal to the threshold V _{thn of the} driving transistor. It can be made.

Next, when the writing period (2) is reached, the Y driver 14 drops the voltage V _EL-i to Gnd and sets the control signal G _WRT-i to the H level. As a result, the transistor 213 is turned on, so that the voltage at the node B changes by ΔV, and the voltage at the node A rises by the amount corresponding to the change by the capacitance ratio. The gate voltage can be written to the node A in order to pass a current through the OLED element 230.
Subsequently, when the light emission period (3) is reached, the Y driver 14 sets the voltage V _EL-i to the power supply voltage V _EL while setting the control signal G _WRT-i to the L level. As a result, as in the first embodiment and the like, a current corresponding to the voltage of the node A flows through the OLED element 230, and light emission continues at a brightness corresponding to the current.
When the light emission period (3) ends, the Y driver 14 drops the voltage V _EL-i to Gnd. Thereby, the OLED element 230 is turned off, and the light emission period (3) is adjusted.

According to the electro-optical device according to the fourth embodiment, as in the third embodiment, the control line 108 becomes unnecessary as compared with the pixel circuit shown in FIGS. The number of transistors per row (2 compared with the pixel circuit in FIG. 2) is reduced, and the number of transistors per pixel circuit is also reduced by 1. Therefore, the yield and the aperture ratio can be further increased. . Furthermore, according to the fourth embodiment, unlike the third embodiment, the brightness of the entire display screen can be changed by adjusting the light emission period (3).
In the fourth embodiment, the power supply line 114 is extended in the X direction for each row of the scanning line 102. However, one power supply line 114 is extended for each adjacent row and used across the pixel circuits 200 in the plurality of rows. It is good also as composition to do. Such a configuration is advantageous in terms of the aperture ratio because the number of wirings can be reduced.

<Fifth Embodiment>
Next, an electro-optical device according to a fifth embodiment of the invention will be described. The electro-optical device according to the fifth embodiment is obtained by replacing the pixel circuit in the first embodiment with a pixel circuit 200 shown in FIG.
As illustrated in FIG. 16, the pixel circuit 200 according to the fifth embodiment is different from the pixel circuit illustrated in FIG. 14 in that the connection destination of one end (drain) of the transistor 212 is connected from the power supply line 116 to the power supply line 114 for each row. It has been changed to.
The operation of the electro-optical device according to the fifth embodiment is the same as that of the fourth embodiment except that the node B is fixed at the initial voltage Vini of the power supply line 114 in the initialization period (1). The description is omitted.
According to the fifth embodiment, the feeder line 116 is unnecessary, which is advantageous in terms of yield and aperture ratio compared to the fourth embodiment.

The present invention is not limited to the first to fifth embodiments described above, and various modifications are possible.
For example, in each embodiment, the gradation display is performed for a single pixel, but for example, as shown in FIG. 17, corresponding to R (red), G (green), and B (blue). The pixel circuits 200R, 200G, and 200B may be arranged, and one dot may be configured by these three pixels to perform color display. When color display is performed, the light emitting layer is selected so that the OLED elements 230R, 230G, and 230B emit light in red, green, and blue, respectively.
In such a color display configuration, when the light emitting efficiencies of the OLED elements 230R, 230G, and 230B are different from each other, the power supply voltage V _EL and the initial voltage V _INI need to be different for each color.
However, as shown in FIG. 17, the scanning line 102 and the control lines 104, 106 and 108 can be shared.
FIG. 17 is a diagram showing a configuration example when color display is performed using the first embodiment (see FIG. 2). Color display using FIG. 9, the second embodiment (see FIG. 10), the third embodiment (see FIG. 12), the fourth embodiment (see FIG. 14), and the fifth embodiment (see FIG. 16). Of course it is good.

In each of the embodiments described above, the initialization period (1) and the writing period (2) are temporally continuous as shown in FIG. 3, FIG. 11, FIG. 13, and FIG. Both periods may be separated in time. Similarly, the writing period (2) and the light emission period (2) may be separated in time.
Further, in the configurations of FIGS. 2, 9, 10, 14, and 16, the control signal G _{EL-i is set} to the H level not only in the light emission period (3) but also in the writing period (2). The voltage V _EL-i may be set to the voltage V _EL so that a current corresponding to the voltage at the node A flows through the OLED element 230.

In each embodiment, the driving transistor 210 is an n-channel type, but may be a p-channel type. The same applies to the channel types of the transistors 211, 212, 213, and 214. However, in the case of the configuration shown in FIG. 9, as described above, one of the transistors 211 and 214 needs to be a p-channel type and the other an n-channel type. In the case of the configuration shown in FIG. 10, FIG. 12, FIG. 14 or FIG. 16, the transistors 211 and 212 are simultaneously controlled to be turned on or off by the common control line 106. It is necessary to unify the channel type.
Further, each of these transistors may be constituted by a transmission gate in which a p-channel type and an n-channel type are combined in a complementary manner, and the voltage drop may be suppressed to a level that can be almost ignored.
In addition, the OLED element 230 may be connected to the drain side of the transistor 214 instead of connecting the OLED element 230 to the source side of the transistor 214.

  The OLED element 230 is an example of a current-driven element. Instead, an inorganic EL element, a field emission (FE) element, another light emitting element such as an LED, an electrophoretic element, an electrophoretic element, or the like. -You may use a chromic element etc.

Next, an example in which the electro-optical device according to the above-described embodiment is used in an electronic device will be described.
First, a mobile phone in which the above-described electro-optical device 10 is applied to a display unit will be described. FIG. 18 is a perspective view showing the configuration of this mobile phone.
In this figure, a cellular phone 1100 includes the above-described electro-optical device 10 as a display unit, in addition to a plurality of operation buttons 1102, as well as an earpiece 1104 and a mouthpiece 1106.

Next, a digital still camera using the above-described electro-optical device 10 as a finder will be described.
FIG. 19 is a perspective view showing the back surface of the digital still camera. The silver salt camera sensitizes the film with the optical image of the subject, whereas the digital still camera 1200 generates and stores an imaging signal by photoelectrically converting the optical image of the subject with an imaging device such as a CCD (Charge Coupled Device). To do. Here, the display surface of the electro-optical device 10 described above is provided on the back surface of the case 1202 in the digital still camera 1200. Since the electro-optical device 10 performs display based on the imaging signal, it functions as a finder that displays the subject. A light receiving unit 1204 including an optical lens and a CCD is provided on the front side of the case 1202 (the back side in FIG. 19).

  When the photographer confirms the subject image displayed by the electro-optical device 10 and presses the shutter button 1206, the CCD image pickup signal at that time is transferred and stored in the memory of the circuit board 1208. In the digital still camera 1200, a video signal output terminal 1212 for external display and an input / output terminal 1214 for data communication are provided on the side surface of the case 1202.

  In addition to the mobile phone shown in FIG. 18 and the digital still camera shown in FIG. 19, the electronic devices include a TV, a viewfinder type and a monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, and a calculator. , Word processors, workstations, videophones, POS terminals, devices with touch panels, and the like. And it cannot be overemphasized that the electro-optical apparatus mentioned above is applicable as a display part 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 operation | movement explanatory drawing of the pixel circuit. It is a figure which shows another structure of the pixel circuit. FIG. 6 is a diagram illustrating a pixel circuit of an electro-optical device according to a second embodiment of the invention. 6 is a timing chart showing the operation of the electro-optical device. FIG. 10 is a diagram illustrating a pixel circuit of an electro-optical device according to a third embodiment of the invention. 6 is a timing chart showing the operation of the electro-optical device. FIG. 10 is a diagram illustrating a pixel circuit of an electro-optical device according to a fourth embodiment of the invention. 6 is a timing chart showing the operation of the electro-optical device. FIG. 10 is a diagram illustrating a pixel circuit of an electro-optical device according to a fifth embodiment of the invention. 1 is a diagram illustrating a configuration in which an electro-optical device according to an embodiment is colored. FIG. It is a figure which shows the mobile telephone using the same electro-optical apparatus. It is a figure which shows the digital still camera using the same electro-optical apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electro-optical apparatus, 12 ... Control circuit, 14 ... Y driver, 16 ... X driver, 102
... scanning lines 104, 106, 108 ... control lines, 112 ... data lines, 114 ... power supply lines, 116 ... feed lines, 200 ... pixel circuits, 210 ... driving transistors, 211, 212, 213, 214 ... transistors (respectively 1, 2nd, 3rd, 4th switching element), 220 ... capacitance (capacitance element), 230 ... OLED element (driven element), 1100 ... mobile phone, 1200 ... digital still camera

Claims (16)

A drive transistor for controlling the current flowing through the driven element;
A first switching element that turns on or off between the gate and drain of the driving transistor;
A driving method of an electronic circuit comprising: a capacitor element having one end connected to a gate of the driving transistor,
While applying an initial voltage to the other end of the capacitive element and turning on the first switching element, a current is passed through the driven element, and then
A first step of cutting off the current, releasing application of an initial voltage to the other end of the capacitive element, and turning off the first switching element;
A second step of applying a voltage corresponding to a current to be passed through the driven element to the other end of the capacitive element;
A third step of driving an electronic circuit, comprising: a third step of causing the driving transistor to flow a current according to the held gate voltage to the driven element. In the first step,
While turning on the first switching element and passing a current through the driven element, the voltage corresponding to the current is held at one end of the capacitive element and the gate of the driving transistor,
After the current is cut off, the first switching element is turned off, and the voltage held at one end of the capacitive element and the gate of the driving transistor is changed to a voltage corresponding to the threshold voltage of the driving transistor. The electronic circuit driving method according to claim 1, wherein the electronic circuit is driven. In the first step,
The first switching element is turned on and a current is passed through the driven element, and the voltage corresponding to the current and the threshold voltage of the driving transistor is held at one end of the capacitive element and the gate of the driving transistor The electronic circuit driving method according to claim 1. In the first step,
After turning on the first switching element and passing a current through the driven element, the first switching element is turned off along with the interruption of the current, and a voltage corresponding to the threshold voltage of the driving transistor is set. The electronic circuit driving method according to claim 1, wherein the electronic circuit is held at one end of the capacitive element and a gate of the driving transistor. A drive transistor for controlling the current flowing through the driven element;
A first switching element that is turned on in a first period between the gate and drain of the driving transistor and turned off by a start timing of a second period after the first period;
A capacitive element having one end connected to the gate of the driving transistor;
Second switching that turns on in the first period and applies an initial voltage to the other end of the capacitive element, and turns off in the second period and a third period after the second period. Elements,
And a third switching element that is turned on in the second period between a signal line to which a voltage according to a current to be supplied to the driven element is applied and the other end of the capacitor element. An electronic circuit. A fourth switching element that, when inserted into a path of a current flowing through the driven element and turned off, interrupts a current flowing through the driven element regardless of a gate voltage of the driving transistor;
The electronic circuit according to claim 5, further comprising a fourth switching element that is turned on during a part or all of the first period and turned on during the third period. The electronic circuit according to claim 6, wherein the first and fourth switching elements are transistors of different conductivity types, and their gates are connected to a common control line. The electronic circuit according to claim 6, wherein the first and second switching elements are transistors of the same conductivity type, and their gates are connected to a common control line. The electronic circuit according to claim 5, wherein the first and second switching elements are transistors of the same conductivity type, and their gates are connected to a common control line. The driven element and the driving transistor are inserted into a current path between the first and second power supply lines,
The voltage between the first and second power lines is:
In the first period, the initial voltage is,
The electronic circuit according to claim 9, wherein a predetermined power supply voltage is obtained in the third period. The electronic circuit according to claim 10, wherein the second switching element is turned on or off between the other end of the capacitive element and a drain of the driving transistor. The electronic circuit according to claim 6, 7, 8, 9 or 10, wherein the second switching element is turned on or off between the other end of the capacitive element and a power supply line to which the initial voltage is applied. The electronic circuit according to claim 5, wherein the driven element is an electro-optical element. The electronic circuit according to claim 13, wherein the electro-optical element is an organic light-emitting diode element. An electro-optical device having a pixel circuit corresponding to the intersection of a scanning line and a data line to which a voltage corresponding to a current to be passed through the electro-optical element is applied when sequentially selected,
The pixel circuit includes:
A drive transistor for controlling a current flowing through the electro-optic element;
A first switching element that is turned on in a first period between the gate and drain of the driving transistor and turned off by a start timing of a second period after the first period;
A capacitive element having one end connected to the gate of the driving transistor;
Second switching that turns on in the first period and applies an initial voltage to the other end of the capacitive element, and turns off in the second period and a third period after the second period. Elements,
An electro-optical device comprising: a third switching element that is turned on in the second period between the data line and the other end of the capacitor.   An electronic apparatus comprising the electro-optical device according to claim 15.

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