JP2006284940A - Active matrix type display device and driving method of active matrix type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix type display device capable of performing excellent display operation and suppressing the power consumption, and a driving method thereof. <P>SOLUTION: A plurality of pixel portions each include a display element 16, a driving transistor 22, and a 1st switch 24 and are arranged in matrix in a display area on a substrate. A plurality of video signal wirings X (1 to n) and a signal line driving circuit 15 which supplies a signal wiring current to the respective video signal wirings are provided. A constant current circuit 40 is connected to each video signal wiring. Each constant current circuit has a transistor 42 connected between a video signal wiring and a constant voltage power source and a 2nd switch 45 connected between the drain and gate of the transistor. A scanning line driving circuit after supplying a constant current from the constant current circuit by turning ON the 2nd switch ON to keep the video signal wiring at a designated potential turns ON the 1st switch to write the signal wiring current supplied from the video signal driving circuit to the video signal wiring to the pixel portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an active matrix display device, and more particularly to an active matrix display device that performs signal writing using a current signal and a method for driving the active matrix display device.

  In recent years, the demand for flat display devices typified by liquid crystal display devices has been rapidly increased by taking advantage of the features of thinness, light weight, and low power consumption. In particular, an active matrix display device in which a pixel switch having a function of electrically separating an on pixel and an off pixel and holding a video signal to the on pixel is provided in each pixel has crosstalk between adjacent pixels. Since a good display quality without any problem can be obtained, it has come to be used for various displays including portable information devices.

  As such a flat-type active matrix display device, an organic electroluminescence (EL) display device using a self-luminous element has attracted attention, and research and development has been actively conducted. The organic EL display device does not require a backlight that obstructs the reduction in thickness and weight, is suitable for moving image reproduction because of its high-speed response, and further has a feature that it can be used even in cold regions because the luminance does not decrease at low temperatures.

  The organic EL display device includes an organic EL element as a display element for each pixel and a pixel circuit that supplies a driving current to the display element, and performs a display operation by controlling light emission luminance. For supplying image information to the pixel circuit, a method using a current signal (for example, Patent Document 1) is known.

In a display device that supplies a signal using a current signal, there is a problem in that insufficient writing occurs due to the wiring capacity of a wiring that supplies a signal when a current value to be written is small. In addition, when performing multi-gradation display, writing becomes difficult on the low gradation side where the set current amount is small, resulting in display problems. Therefore, the display device disclosed in Patent Document 1 is driven by dividing the data line current supplied from the data driving means into a data current for writing luminance information for each pixel circuit and a remaining bypass current. Current control means. The bypass current is set equal to or larger than the data current.
JP 2003-50564 A

  According to the display device configured as described above, by adding the bypass current to the data current and supplying it to the data line, the data line current can be increased and writing shortage due to the wiring capacity can be reduced. Is possible.

  However, since the display device has a configuration in which the data current and the bypass current are supplied to the data line at a time, there is a problem that the power consumption increases as compared with the case where only the data current is supplied. Further, since the burden on the data line driving circuit increases, it is necessary to increase the capacity of the data line driving circuit, which causes an increase in manufacturing cost.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an active matrix display device capable of performing a good display operation without being affected by the wiring capacity and suppressing power consumption. And a driving method of an active matrix display device.

  In order to achieve the above object, an active matrix display device according to an aspect of the present invention is connected between a display element, a drive transistor that supplies a drive current to the display element, and a gate and a drain of the drive transistor. A plurality of pixel portions arranged in a matrix in a display area on the substrate, a plurality of video signal wirings connected to each column of the pixel portions, and a signal to the video signal wirings A signal line driving circuit for supplying wiring current, a transistor connected between each video signal wiring and a constant voltage power source, and a second switch connected between the drain and gate of the transistor, respectively ON / OFF control of the first and second switches through the scanning signal line, a plurality of constant current circuits having a plurality of scanning signal lines connected to each row of the pixel portion, and the scanning signal line The second switch is turned on, a constant current is supplied from the constant current circuit to set the video signal wiring to a predetermined potential, and then the first switch is turned on and supplied from the video signal driving circuit to the video signal wiring. And a scanning line driving circuit for writing the signal wiring current thus written into the pixel portion.

An active matrix display device driving method according to another aspect of the present invention includes a display element, a driving transistor that supplies a driving current to the display element, and a first transistor connected between a gate and a drain of the driving transistor. A plurality of pixel portions arranged in a matrix in a display area on the substrate, a plurality of video signal wirings connected to each column of the pixel portions, and a signal wiring current to the video signal wirings A signal line driving circuit for supplying a signal, a transistor connected between each video signal line and a constant voltage power source, and a second switch connected between a drain and a gate of the transistor. A plurality of constant current circuits, a plurality of scanning signal lines connected to each row of the pixel portion, and a scanning line for controlling on / off of the first and second switches through the scanning signal lines And the dynamic circuit, the driving method of the active matrix type display device having,
The second switch is turned on, a constant current is supplied from the constant current circuit, the video signal wiring is set to a predetermined potential, and the first switch is turned on with the video signal wiring maintained at a predetermined potential. The signal wiring current supplied from the video signal driving circuit to the video signal wiring is written into the pixel portion, and the written signal wiring current is supplied to the display element.

  According to the present invention, an active matrix display device capable of performing a good display operation without being affected by the wiring capacity and suppressing power consumption, and a driving method of the active matrix display device are provided. Can be provided.

Hereinafter, an organic EL display device will be described in detail as a first embodiment of the present invention with reference to the drawings.
As shown in FIG. 1, the organic EL display device is configured as, for example, a large active matrix display device of 10 type or more, and includes an organic EL panel 10 and a controller 12 that controls the organic EL panel 10.

  The organic EL panel 10 is arranged in the form of a matrix on an insulating substrate 8 such as a glass plate, and is connected to each row of the display pixels, each of which is connected to each row of the display pixels 11 and independently. The first scanning line Sga (1 to m) and the second scanning line Sgb (1 to m) provided m by number, the scanning line Sga0 connected to the constant current circuit described later, and the display pixel PX are connected to each column. The n video signal lines X (1 to n), the first and second scan lines Sga and Sgb, which are sequentially driven for each row of display pixels, and a plurality of video signal lines X1. ˜Xn are provided. The scanning line driving circuits 14 a and 14 b and the signal line driving circuit 15 are integrally formed on the insulating substrate 8 outside the display area 11. A constant current circuit 40 is connected to one end of each video signal wiring X (1 to n), and is provided on the insulating substrate 8 outside the display region 11.

  Each display pixel PX that functions as a pixel portion includes a display element having a photoactive layer between opposing electrodes, and a pixel circuit 18 that supplies a drive current to the display element. The display element is, for example, a self-luminous element. In this embodiment, the organic EL element 16 including at least an organic light-emitting layer is used as a photoactive layer.

  FIG. 2 shows an equivalent circuit of the display pixel PX and the constant current circuit 40. The pixel circuit 18 is a current signal type pixel circuit that controls light emission of the organic EL element 16 in accordance with a video signal composed of a current signal, and includes a pixel switch 20, a drive transistor 22, a first switch 24, an output switch 26, and a holding circuit. The capacitor Cs is provided. Here, the pixel switch 20, the drive transistor 22, the first switch 24, and the output switch 26 are configured by the same conductivity type, for example, a P-channel type thin film transistor. In this embodiment, all the thin film transistors constituting the pixel circuit 18 are formed in the same process and the same layer structure, and are top gate thin film transistors using polysilicon as a semiconductor layer.

  The drive transistor 22, the output switch 26, and the organic EL element 16 are connected in series in this order between the first voltage power supply line Vdd1 and the reference voltage power supply line Vss. The reference voltage power supply line Vss and the first voltage power supply line Vdd1 are set to potentials of −9 V and +6 V, for example. The drive transistor 22 has a first terminal, here a source, connected to the first voltage power supply line Vdd1. The organic EL element 16 has one electrode, here the cathode, connected to the reference voltage power supply line Vss. The source of the output switch 26 is connected to the second terminal of the drive transistor 22, here the drain. The output switch 26 has a drain connected to the anode of the organic EL element 16 and a gate connected to the second scanning line Sgb.

  The drive transistor 22 outputs a current amount corresponding to the video signal to the organic EL element 16. The output switch 26 is controlled to be on (conductive state) and off (non-conductive state) by a control signal Sb from the second scanning line Sgb, and controls connection / disconnection between the drive transistor 22 and the organic EL element 16.

  The holding capacitor Cs is connected between the first terminal and the control terminal of the driving transistor 22, here, between the source and the gate, and holds the gate control potential of the driving transistor 22 determined by the video signal. The pixel switch 20 is connected between the corresponding video signal wiring X (1 to n) and the drain of the driving transistor 22, and its gate is connected to the first scanning line Sga. The pixel switch 20 takes in a signal wiring current as a gradation current from the corresponding video signal wiring X (1 to n) in response to the control signal Sa supplied from the first scanning line Sga.

  The first switch 24 is connected between the drain and gate of the drive transistor 22, and the gate thereof is connected to the first scanning line Sga. The first switch 24 is turned on / off in response to a control signal Sa from the first scanning line Sga, controls connection / disconnection between the gate and drain of the driving transistor 22, and prevents current leakage from the storage capacitor Cs. regulate.

  As shown in FIGS. 1 and 2, the constant current circuit 40 connected to one end of each video signal wiring X (1 to n) has, for example, a P-channel type thin film transistor as the transistor 42. The source of the transistor 42 is connected to the second power supply voltage line Vdd2. The second voltage power supply line Vdd2 is set to a potential of 8V, for example.

  The constant current circuit 40 includes, for example, a second switch 45 made of a P-channel thin film transistor and a storage capacitor Cs2. The second switch 45 is connected between the drain and gate of the transistor 42, and the gate thereof is connected to the scanning line Sga0. The second switch 45 is controlled to be on (conducting state) and off (non-conducting state) by a control signal Sao from the first scanning line Sga0, and the connection between the transistor 42 and the video signal wiring X (1 to n) is not connected. Control the connection. The holding capacitor Cs2 is connected between the source and gate of the transistor 42 and holds the gate control potential of the transistor 42 determined by the second constant voltage power supply Vdd2.

  In the present embodiment, the transistor 42 and the second switch 45 are formed in the same process and in the same layer structure as the thin film transistor constituting the pixel circuit 18, and are configured as a top gate thin film transistor using polysilicon as a semiconductor layer. .

  The controller 12 shown in FIG. 1 is formed on a printed circuit board disposed outside the organic EL panel 10 and controls the scanning line driving circuits 14 a and 14 b and the signal line driving circuit 15. The controller 12 receives a digital video signal and a synchronization signal supplied from the outside, and generates a vertical scanning control signal for controlling the vertical scanning timing and a horizontal scanning control signal for controlling the horizontal scanning timing based on the synchronizing signal. The controller 12 supplies the vertical scanning control signal and the horizontal scanning control signal to the scanning line driving circuits 14a and 14b and the signal line driving circuit 15, respectively, and outputs a digital video signal in synchronization with the horizontal and vertical scanning timings. This is supplied to the line drive circuit 15.

The signal line driving circuit 15 converts the video signals sequentially obtained in each horizontal scanning period under the control of the horizontal scanning control signal into an analog format to form a signal wiring current IA _{(1 to n)} , and a plurality of video signal wirings X (1 To n) in parallel. The scanning line driving circuits 14a and 14b include a shift register, an output buffer, and the like, sequentially transfer a horizontal scanning start pulse supplied from the outside to the next stage, and control two types of display pixels PX in each row via the output buffer. Signals, that is, control signals Sa (1 to m) and Sb (1 to m) are supplied, and a control signal Sa0 is supplied to the constant current circuit 40. Thus, the first and second scanning lines Sga and Sgb are driven by the control signal Sa and the control signal Sb, respectively, in one horizontal scanning period different from each other.

  FIG. 3 shows a timing chart of the scanning line driving circuits 14a and 14b. For example, the scanning line driving circuits 14a and 14b generate a pulse having a width of one horizontal scanning period (Tw-Starta) corresponding to each horizontal scanning period from a start signal (STV1, STV2) and a clock (CKV1, CKV2). The pulses are output as a control signal Sa and a control signal Sb. Further, the scanning line driving circuit 14a generates a controlled pulse synchronized with the clock (CKV1) and outputs it as a control signal Sa0.

  In the organic EL display device configured as described above, the operation of the pixel circuit 18 is divided into a two-stage video signal writing operation and a light emitting operation. As shown in FIG. 2, for example, a control signal Sa0 at a level (on potential) at which the second switch 45 is turned on, that is, a low level is output to the constant current circuit 40 in the first row. As a result, the second switch 45 is turned on (conductive state), and the precharge operation is started as the first-stage write operation.

In the precharge period, the transistor 42 of the constant current circuit 40 becomes the write state, flows precharge current I _B to the video signal lines X1 through the transistor 42 from the second voltage supply line Vdd 2. Thus, by supplying a pre-charge current I _B in the video signal lines X1, the potential of the video signal lines X1 is varied in a short time to the desired potential necessary to pass the signal line current I _A1 described below be able to.

Precharge current I _B is a constant current signal set to a predetermined value in accordance with the transistor 42, for one horizontal scanning period (t), from highest to lowest gradation display in the wiring capacitance of the video signal lines X (Cp) potential variation of up gradation display is set to a value larger than the charge amount corresponding to a value obtained by multiplying the (maximum voltage change _{ΔV) (I B> Cp ×} ΔV / t). Precharge current I _B is set to, for example, of the same order of magnitude as the drive current for performing the highest gradation display of the organic EL display device. As an example, in the case of performing full color display, in the display pixel PX that emits red light, the driving current at the time of the highest gradation display is about 2 μA.

  After setting the video signal wiring X1 to a desired potential, the first scanning line driving circuit 14a has a level (on potential) at which the pixel switch 20 and the first switch 24 of the display pixel PX in the first row are turned on. Then, a low level control signal Sa1 is output, and the first scanning line driving circuit 14b outputs a level (off potential) for turning off the output switch 26, in this case, a high level control signal Sb1. As a result, the pixel switch 20 and the first switch 24 are turned on (conductive state) and the output switch 26 is turned off (non-conductive state), and the second-stage video signal writing operation is started.

In the video signal writing period, the signal wiring current I _A1 supplied from the signal line driving circuit 15 to the corresponding video signal wiring X1 is supplied to the selected display pixel PX. In the display pixel PX, the pixel switch 20 and the first switch 24 are in the ON state, and the taken signal wiring current I _A1 is supplied to the driving transistor 22 to put the driving transistor 22 in the writing state. As a result, as shown in FIG. 4, a write current flows from the first voltage power supply line Vdd1 to the video signal line X1 through the drive transistor 22, and between the gate and source of the drive transistor 22 corresponding to the amount of current of the signal line current _IA1. The potential is written to the storage capacitor Cs. At the time of writing the video signal, the potential of the video signal line X1 is maintained at a desired potential necessary for flowing the signal line current I _A1 , so that the signal line current I _A1 can be easily written to the display pixel PX. it can.

Next, the control signal Sa1 becomes a high level (off potential), and the pixel switch 20 and the first switch 24 are turned off. This completes the video signal writing operation. Subsequently, the control signal Sb1 becomes low level, and the output switch 26 is turned on. Thereby, the light emission operation starts. As shown in FIG. 5, in the light emission period, the drive transistor 22 is maintained in the on state by the gate control voltage written in the storage capacitor Cs, and the amount of current corresponding to the signal wiring current I _A1 from the first voltage power supply line Vdd1. Is supplied to the organic EL element 16. Thereby, the organic EL element 16 emits light, and the light emission operation is started. The organic EL element 16 maintains the light emission state until the control signal Sb1 becomes the off potential again after one frame period.

  According to the organic EL display device configured as described above, in video signal current writing, a precharge current is supplied from the constant current circuit 40 connected to the video signal wiring, and the video signal wiring potential is changed to a necessary potential. Then, the signal wiring current supplied from the signal line driving circuit through the video signal wiring is written to each display pixel PX. Therefore, even when a low-gradation video signal is written to the display pixel PX, it can be written sufficiently and in a short time without being affected by the wiring capacity. Accordingly, it becomes possible to eliminate the display defect, the unevenness, and the rough feeling at low luminance, and to display a high-quality image.

  Even when a low current write is performed after a high current write to the video signal wiring, a shortage of a low current video signal write can be solved. For example, conventionally, when writing a video signal with the highest gradation display (white display) and then writing with the lowest gradation display (black display), the latter lack of video signal writing causes the higher gradation display (white display) to be written. There is a possibility that the image is in a writing state and the white display has a tail on display. According to the present embodiment, it is possible to eliminate such display defects caused by insufficient writing.

  In addition, the amount of current supplied from the signal line driver circuit to the video signal wiring at a time can be reduced as compared with the case where the signal wiring current is supplied by adding the bypass current to the video signal current. The increase can be suppressed. At the same time, the burden on the signal line driver circuit can be reduced, the capacity of the signal line driver circuit can be reduced, and an increase in manufacturing cost can be prevented.

  The constant current circuit 40 is provided on the same substrate as the insulating substrate 8 on which the organic EL element 16 is formed, and can be formed at the same time as the wiring and the thin film transistor constituting the pixel circuit 18. By incorporating the constant current circuit 40 in the display device, the length of the wiring for supplying the current signal can be reduced, the capacitive load can be reduced, and a stable current signal can be supplied. In addition, the number of connection points with an external circuit can be reduced, and mechanical reliability can be improved. By forming the pixel circuit 18 and the constant current circuit 40 on the same substrate in the same process, the pixel circuit 18 and the constant current circuit 40 can be configured by using elements with similar characteristics, and the variation in drive current to the display element is reduced. can do.

  As described above, according to the present embodiment, an active matrix display device and an active matrix display device that can perform a good display operation without being affected by the wiring capacity and can suppress power consumption. A display device driving method is obtained.

Next, an organic EL display device according to a second embodiment of the present invention will be described with reference to FIG.
According to the second embodiment, the constant current circuit 40 is connected to one end of the video signal wiring X (1 to n). Each constant current circuit 40 includes, for example, a transistor 42 formed of a P-channel thin film transistor, a storage capacitor Cs2, and a second switch 45. The source of the transistor 42 is connected to the second power supply voltage line Vdd2. The second switch 45 is connected to the gate and drain of the transistor 42, and the gate thereof is connected to the scanning line Sag0. The second switch 45 is controlled to be on (conducting state) and off (non-conducting state) by a control signal Sao from the first scanning line Sga0, and the connection between the transistor 42 and the video signal wiring X (1 to n) is not connected. Control the connection. The holding capacitor Cs2 is connected between the source and gate of the transistor 42 and holds the gate control potential of the transistor 42 determined by the second constant voltage power supply Vdd2.

  The constant current circuit 40 further includes a third switch 47 formed of, for example, a P-channel type thin film transistor. The third switch 47 is connected between the drain of the transistor 42 and the video signal wiring X (1 to n). The gate of the third switch 47 is connected to the second voltage power supply line Vdd2, and is always kept on.

In this embodiment, the transistor 42, the second and third switches 45 and 47 are formed in the same process and in the same layer structure as the thin film transistor constituting the pixel circuit 18, and a top gate thin film transistor using polysilicon as a semiconductor layer. It is configured as.
In the second embodiment, other configurations of the organic EL display device are the same as those of the first embodiment described above, and the same reference numerals are given to the same portions, and the detailed description thereof is omitted.
According to the second embodiment having the above-described configuration, the same operational effects as those of the first embodiment described above can be obtained. Each constant current control circuit 40 includes a third switch 47 in addition to the transistor 42 and the second switch 45, and a precharge current flows through the transistor 42 and the third switch 47 when writing a video signal. This substantially corresponds to the configuration and current path of the pixel circuit 18 including the driving transistor 22 and the pixel switch 20. Therefore, variation in the light emission current due to the provision of the constant current circuit 40 can be suppressed, and stable image display can be realized.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  In the above-described embodiment, the precharge current is supplied for each writing operation. However, for example, the second switch 45 is turned off and the constant current circuit 40 is disconnected from the video signal line during high gradation. Good. By controlling the connection state of the constant current circuit according to the video signal, it is possible to suppress undesired power consumption.

  In the above-described embodiment, the case where the thin film transistors constituting the pixel circuit and the thin film transistors of the constant current circuit are all configured with the same conductivity type, here the P channel type, is not limited to this. It is also possible to constitute the thin film transistor. It is also possible to form a pixel circuit with a mixture of different conductive type thin film transistors, such as a pixel switch, an N channel type thin film transistor for the first switch, and a P channel type thin film transistor for the drive transistor and the second switch. It is.

  Further, the semiconductor layer of the thin film transistor is not limited to polysilicon, but can be composed of amorphous silicon. The self-luminous elements constituting the display pixels are not limited to organic EL elements, and various display elements capable of self-luminance are applicable.

FIG. 1 is a plan view schematically showing an organic EL display device according to the first embodiment of the present invention. FIG. 2 is a plan view showing an equivalent circuit of a pixel and a constant current circuit of the organic EL display device. FIG. 3 is a timing chart of supply signals in the scanning line driving circuit of the organic EL display device. FIG. 4 is a plan view showing an equivalent circuit of a pixel and a constant current circuit of the organic EL display device. FIG. 5 is a plan view showing an equivalent circuit of a pixel and a constant current circuit of the organic EL display device. FIG. 6 is a plan view showing an equivalent circuit of a pixel and a constant current circuit of an organic EL display device according to the second embodiment of the present invention.

Explanation of symbols

8 ... Insulating substrate, 10 ... Organic EL panel, 12 ... Controller,
14a, 14b ... scanning line drive circuit, 15 ... signal line drive circuit, 16 ... organic EL element,
18 ... Pixel circuit, 20 ... Pixel switch, 22 ... Drive transistor,
24 ... 1st switch, 26 ... Output switch, 40 ... Constant current circuit,
42 ... transistor 45 ... second switch 47 ... third switch

Claims (8)

A display element; a driving transistor for supplying a driving current to the display element; and a first switch connected between a gate and a drain of the driving transistor, and arranged in a matrix in a display region on the substrate. A plurality of pixel portions,
A plurality of video signal wirings connected to each column of the pixel unit;
A signal line driving circuit for supplying a signal wiring current to the video signal wiring;
A plurality of constant current circuits each having a transistor connected between each video signal line and a constant voltage power supply, and a second switch connected between a drain and a gate of the transistor;
A plurality of scanning signal lines connected to each row of the pixel portion;
The first and second switches are controlled to be turned on and off through the scanning signal lines, the second switch is turned on, a constant current is supplied from the constant current circuit, and the video signal wiring is set to a predetermined potential. A scanning line driving circuit for turning on the switch and writing the signal wiring current supplied from the video signal driving circuit to the video signal wiring to the pixel unit;
An active matrix display device comprising:   The active matrix display device according to claim 1, wherein the constant current circuit is provided on the substrate outside the display region.   2. The active matrix display device according to claim 1, wherein each of the constant current circuits has a storage capacitor that holds a potential difference between a gate and a source of the transistor constant.   Each of the pixel units includes an output switch connected in series with the display element and the drive transistor between constant voltage power supplies, a storage capacitor that holds a potential difference between the gate and the source of the drive transistor, and pixel selection and 2. The active matrix display device according to claim 1, further comprising: a pixel switch that controls non-selection, wherein a drain of the driving transistor is connected to the video signal line through the pixel switch.   Each of the constant current circuits is connected between the drain of the second switch and the transistor and the video signal wiring, and has a gate connected to a constant voltage power source and is maintained in an on state. The active matrix display device according to claim 4, further comprising three switches.   6. The active matrix display device according to claim 1, wherein the transistor of the constant current circuit and the driving transistor are formed of thin film transistors using polysilicon as a semiconductor layer.   The active matrix display device according to claim 1, wherein the display element is a self-light-emitting element having an organic light-emitting layer between opposed electrodes. A display element; a driving transistor for supplying a driving current to the display element; and a first switch connected between a gate and a drain of the driving transistor, and arranged in a matrix in a display region on the substrate. A plurality of pixel portions,
A plurality of video signal wirings connected to each column of the pixel unit;
A signal line driving circuit for supplying a signal wiring current to the video signal wiring;
A plurality of constant current circuits each having a transistor connected between each video signal line and a constant voltage power supply, and a second switch connected between a drain and a gate of the transistor;
A plurality of scanning signal lines connected to each row of the pixel portion;
In a driving method of an active matrix display device comprising: a scanning line driving circuit that controls on and off of the first and second switches through the scanning signal line;
The second switch is turned on, a constant current is supplied from the constant current circuit, the video signal wiring is set to a predetermined potential,
After the video signal wiring is set to a predetermined potential, the first switch is turned on, and the signal wiring current supplied from the video signal driving circuit to the video signal wiring is written to the pixel portion.
A driving method of an active matrix display device, wherein a driving current having a current amount corresponding to the written signal wiring current is supplied to the display element.

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