JP2005221688A - Display device and driving method of display device - Google Patents

Abstract

Image quality deteriorates due to the occurrence of roughness in a display image due to variations in characteristics of TFTs constituting a pixel circuit. Regarding the problem caused by the Vth variation of the TFT, the same can be said not only on the light emitting circuit side but also on the light receiving circuit side.
A driving TFT 222 has a configuration in which a light emitting circuit 22 having a function of correcting a threshold voltage Vth of a driving TFT 22 and a light receiving circuit 23 using a current mirror circuit 232 are combined, and prior to detection of a light receiving signal current. Is supplied to the current mirror circuit 235 as a reference current, and the difference between the current based on the reference current and the current based on the light receiving signal current is taken, thereby causing variations in TFT characteristics, in particular, roughness due to Vth variation. A high-quality display image with no error and imaging data with few errors are obtained.
[Selection] Figure 2

Description

  The present invention relates to a display device and a display device driving method, and in particular, an active matrix display device in which pixels including self-luminous elements (hereinafter referred to as “self-luminous elements”) as display elements are arranged in a matrix. The present invention also relates to a method for driving the display device.

  As a self-luminous element, for example, there is an organic EL (electroluminescence) element that utilizes a phenomenon in which an organic thin film emits light when an electric field is applied. An organic EL display device using this organic EL element as a display element of a pixel has low power consumption because the organic EL element can obtain a luminance of several hundred nits with a driving voltage as low as 10 V or less, and is self-luminous. The liquid crystal display device does not require an illuminating device that is essential for the liquid crystal display device, can be easily reduced in weight and thickness, and the response speed of the organic EL element is as high as about several μs. Compared to a hold-type display device typified by a display device, there is a problem that an afterimage problem does not occur when displaying a moving image, and the display performance is excellent.

  As described above, organic EL display devices having features such as low power consumption, easy weight reduction and thinning, and excellent display performance during moving image display have recently been particularly reduced in power consumption and weight. In addition, it is promising as a flat panel display suitable for use as a display device of a mobile terminal device represented by a mobile phone or a personal digital assistant (PDA) that is required to be thin. Among these organic EL display devices, in particular, active matrix organic EL display devices using a thin film transistor (TFT) having polycrystalline silicon as an active layer are actively developed as pixel drive elements.

  By the way, in recent years, an organic EL display device is used as a display device by providing an organic EL element, which is a self-luminous element, with not only a light emitting function but also a light receiving function, and using the organic EL element as a display element of a pixel. Attempts have been made to use it as a light receiving device or an imaging device (see, for example, Patent Document 1).

JP 2001-203078 A

  However, in an active matrix organic EL display device using a thin film transistor (hereinafter also referred to as “TFT”) as a pixel driving element, characteristics variation of TFTs constituting the pixel circuit, in particular, a threshold voltage Vth of the TFT. As a result, the display image becomes rough due to the variation, and there is a problem that the image quality deteriorates. Regarding the problem caused by the Vth variation of the TFT, the same can be said not only on the light emitting circuit side but also on the light receiving circuit side. Therefore, when an organic EL display device is used as an imaging device, good imaging data cannot be obtained.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce the characteristics of the transistors constituting the light-emitting circuit and the light-receiving circuit when the pixel has both light-emitting and light-receiving functions. It is an object of the present invention to provide a display device and a driving method thereof capable of preventing a deterioration in performance due to this and obtaining a good display image and captured image data.

  In order to achieve the above object, in the present invention, a light receiving circuit having a light emitting circuit having a driving transistor for driving a light emitting element in accordance with a video signal and a current amplifying means for amplifying and outputting a light receiving signal current flowing through the light receiving element. In a display device in which pixels including a circuit are arranged in a matrix, during the light emitting operation of the light emitting circuit, an operation for correcting a variation in threshold voltage of the driving transistor is performed, while during the light receiving operation of the light receiving circuit, Prior to detection of the light receiving signal current, a reference current is supplied to the current amplifying means so as to take a difference between the current based on the reference current and the current based on the light receiving signal current.

  In the display device having the above structure, by correcting the variation in the threshold voltage of the driving transistor during the light emitting operation, it is possible to suppress deterioration in the image quality of the display image due to the variation in the threshold voltage. In the light receiving operation, the reference current is supplied to the current amplifying means prior to the detection of the received light signal current, and the difference between the current based on the reference current and the current based on the received light signal current is taken so that both currents are the same. Since the characteristic variation of the transistors constituting the current amplifying means riding on is canceled, the current corresponding to the actual light reception signal can be detected.

  According to the present invention, in a display device in which a pixel includes a light-emitting circuit and a light-receiving circuit, a light-emitting operation and a light-receiving operation that are not affected by variations in characteristics of transistors that form the light-emitting circuit and the light-receiving circuit can be performed. It is possible to output a display image with high image quality and imaging data with few errors.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a display device according to an embodiment of the present invention, for example, an active matrix organic EL display device in which pixels including organic EL elements that are self-luminous elements as display elements are two-dimensionally arranged in a matrix. It is a block diagram which shows the outline.

  As is clear from FIG. 1, the active matrix organic EL display device 10 according to the present embodiment has a large number of pixels 11 including a light emitting circuit and a light receiving circuit (both not shown) arranged two-dimensionally in a matrix. The pixel array unit (display area unit) 12 has a light emission control unit 13, a light reception control unit 14, and an A / D (analog-digital) conversion unit 15 as peripheral drive circuits. The peripheral drive circuit including 15 is integrally formed on the same substrate (not shown) as the pixel array unit 12.

  In the pixel array unit 12, light emission control line groups 16-1 to 16-m and light reception control lines 17-1 to 17-m are wired for each row with respect to the matrix-like arrangement of the pixels 11 in m rows and n columns. In addition, video signal lines 18-1 to 18-n and light receiving signal lines 19-1 to 19-n are wired for each column. As will be described later, each of the light emission control line groups 16-1 to 16-m includes, for example, four light emission control lines 16A to 16D, and one end is connected to each output end for each row of the light emission control unit 13. ing. One end of each of the light reception control lines 17-1 to 17 -m is connected to an output terminal for each row of the light reception control unit 14.

  The light emission control unit 13 is constituted by a shift register or the like, and sequentially writes the first light emission control lines 16A-1 to 16A-m in a predetermined scanning cycle during the light emission period, and outputs a write control signal WS described later in order. The pixels 11 to be driven to emit light are sequentially selected in units of rows. A video signal is supplied to each pixel 11 in the row selected by the light emission control unit 13 from a video signal source (not shown) through video signal lines 18-1 to 18-n.

  The light reception control unit 14 is configured by a shift register or the like, and is driven by a read control signal RS (described later) that sequentially outputs the light reception control lines 17-1 to 17-m in a predetermined scanning cycle during the imaging period. Thus, the pixels 11 to be driven for light reception are sequentially selected in units of rows. A light reception signal is output from each pixel 11 in the row selected by the light reception control unit 14. This light reception signal is output to the outside of the pixel array section 12 through the light reception signal lines 19-1 to 19-n.

  The A / D conversion unit 15 includes n A / D conversion circuits 15-1 to 15-n connected to one ends of the light receiving signal lines 19-1 to 19-n, and each pixel 11 of the selected row. The analog light reception signals supplied through the light reception signal lines 19-1 to 19-n are converted into digital light reception signals # 1 to #n and output.

(Pixel circuit)
FIG. 2 is a circuit diagram illustrating an example of a circuit configuration of the pixel 11. The pixel circuit 20 according to this example is configured to include an organic EL element 21, a light emitting circuit 22, and a light receiving circuit 23 that are self-luminous elements. The pixel circuit 20 according to this example pays attention to the fact that the organic EL element 21 that is a light emitting element functions as a light receiving element in a reverse bias state, and adopts a configuration in which the organic EL element 21 is also used as a light receiving element.

  The organic EL element 21 has a capacitor Cel, and is provided, for example, with a cathode connected to the ground. The light emitting circuit 22 includes thin film transistors 221 to 225 as drive elements and a storage capacitor 226. Incidentally, a thin film transistor (hereinafter referred to as “TFT”) has polycrystalline silicon as an active layer, and can be formed with a small element size for each pixel due to its high driving capability, which is advantageous for high definition of an organic EL display device. It is.

  The TFT 221 is a video signal sampling transistor for sampling the video signal Sig. The TFT 221 is composed of, for example, an N-channel transistor, and has a gate serving as the first light emission control line 16A (light emission control line groups 16-1 to 16 in FIG. 1). The source is connected to the video signal line 18 (corresponding to the data lines 18-1 to 18-n in FIG. 1). The video signal sampling TFT 221 is turned on (conductive) and samples the video signal Sig when the write control signal WS is applied from the light emission control unit 13 to the gate via the first light emission control line 16A.

  The TFT 222 is a driving transistor for driving the organic EL element 21, and is composed of, for example, a P-channel transistor. The gate is connected to the drain of the video signal sampling TFT 221 via the storage capacitor 226, and the source is connected to the power supply voltage VDD, for example. Are connected to each power line. The voltage of the positive power supply VDD is set to about 10 [V], for example.

  The TFT 223 is a Vth canceling transistor for canceling the threshold voltage (Vth) of the driving TFT 222, and is composed of, for example, an N-channel transistor, and is connected between the gate and the source of the driving TFT 222 (the drain is connected to the gate of the TFT 222, The source is connected to the drain of the TFT 222, and the gate is connected to the second light emission control line 16B (corresponding to the other one of the light emission control line groups 16-1 to 16-m in FIG. 1). Yes. The Vth cancel TFT 223 is turned on when the cancel control signal CAN is given to the gate from the light emission control unit 13 via the second light emission control line 16B, and the gate and the source of the driving TFT 222 are short-circuited. .

  The TFT 224 is a first mode control transistor for controlling the light emission / light reception mode, and is composed of, for example, an N-channel transistor, and has a gate serving as a third light emission control line 16C (the light emission control line group 16- in FIG. 1). 1 to 16-m corresponding to the other one), the drain is connected to the drain of the driving TFT 222, respectively. The first mode control TFT 224 is turned on when the first mode control signal LON1 is given to the gate from the light emission control unit 13 via the third light emission control line 16C, and is turned on from the driving TFT 222. The drive current can be supplied to the organic EL element 21.

  The TFT 225 is a second mode control transistor for controlling the light emission / light reception mode, and is composed of, for example, an N-channel transistor, and has a gate serving as a fourth light emission control line 16D (light emission control line group 16-- in FIG. 1). 1 to 16-m), the drain is connected to the source of the first control TFT 224, and the source is connected to the anode of the organic EL element 21. The second mode control TFT 225 is turned on when the second mode control signal LON2 is applied to the gate from the light emission control unit 13 via the fourth light emission control line 16D. The driving current can be supplied from the TFT 224 to the organic EL element 21.

  The light receiving circuit 23 includes, for example, four N-channel TFTs 231 to 234, and is configured to use the organic EL element 21 as a light receiving element by putting the organic EL element 21 in a reverse bias state during the light receiving period.

  The TFT 231 is a light reception current control transistor for controlling the light reception current of the organic EL element 21, and has a gate connected to the light reception control line 17 (corresponding to the light reception control lines 17-1 to 17-m in FIG. Are connected to the anode of the organic EL element 21, respectively. The light reception current control TFT 231 is turned on when the read control signal RS is applied to the gate from the light reception control unit 14 via the light reception control line 17, and the light reception current of the organic EL element 21 can be read out. .

  The TFT 232 has a diode connection configuration in which the gate and the drain are connected in common, and the gate and the drain are connected to the drain of the TFT 231 and the source is connected to the first bias power supply Vb1. The TFT 233 has a gate commonly connected to the gate and drain of the TFT 232, and forms a current mirror circuit 235 together with the TFT 232. The source of the TFT 233 is connected to the second bias power supply Vb2.

  Here, the voltage of the first bias power supply Vb1 is set so that the organic EL element 21 is in a reverse bias state when receiving light, that is, the anode voltage is lower than the cathode voltage Vk. Specifically, in this example, since the cathode voltage Vk is at the ground level (0 [V]), it is set to a negative power supply voltage, for example, about −5 [V]. On the other hand, the voltage of the first bias voltage Vb2 is set so that a larger bias voltage than the first bias power supply Vb1 can be applied to the organic EL element 21. Specifically, if Vb1 = −5 [V], Vb2 = −10 [V] is set.

  The current mirror circuit 235 is a kind of current amplification circuit for amplifying the light reception signal current of the organic EL element 21 and outputting it to the light reception signal line 19, and has an advantage that a current amplification circuit can be configured with a small number of elements. However, the current amplifier circuit is not limited to a current mirror configuration. The TFT 234 is a light reception signal control transistor, and has a gate connected to the light reception control line 17, a drain connected to the light reception signal line 19, and a source connected to the drain of the TFT 233. The light receiving signal control TFT 234 receives the light receiving signal current output from the current mirror circuit 235 when the read control signal RS is applied to the gate from the light receiving control unit 14 via the light receiving control line 17. Output to the signal line 19.

  In the pixel circuit 20 configured as described above, transistors having enhancement characteristics are used as the TFTs 221 to 225 constituting the light emitting circuit 22 and the TFTs 231 to 234 constituting the light receiving circuit 23. The light receiving signal line 19 is a current output line. The potential of the light receiving signal line 19 is maintained at 0 [V] by an external circuit.

  Next, the active matrix organic EL display device according to the present embodiment having the above-described configuration, that is, the organic EL element 21 is used as a light emitting element and a light receiving element, so that the pixel array unit 12 has both functions of the display device and the imaging device. The operation in one frame in the active matrix organic EL display device will be described with reference to the timing chart of FIG.

  In the timing chart of FIG. 3, the write control signal WS, the read control signal RS, the cancel control signal CAN, the mode control signals LON1 and LON2, the video signal Sig, the drain potential A of the video signal sampling TFT 221 and the gate potential of the driving TFT 222 are shown. B, drain potential C of the driving TFT 222, source potential of the mode control TFT 224 (drain potential of the mode control TFT 224) D, drain potential E of the light receiving current control TFT 231 and detection current (light receiving) output to the light receiving signal line 19 The timing relationship between the EL current and the EL current flowing through the organic EL element 21 is shown.

  As an operation flow of the organic EL display device, a light emitting operation is first performed, and then a light receiving operation is performed. However, the flow of the operation is not limited to the above, and the reverse is also possible, that is, the flow of the operation in which the light receiving operation is first performed and the light emitting operation is performed thereafter.

  First, the light emission operation will be described. In the light emission operation, the write control signal WS is set to a high potential. As a result, the video signal sampling TFT 221 is turned on to capture the video signal Sig, and supply the video signal Sig to the storage capacitor 226. The potential of the video signal line 18 is assumed to be at the signal reference potential Vsmax until the video signal capturing period. Further, the cancel control signal CAN is set to a high potential simultaneously with the write control signal WS. As a result, the Vth canceling TFT 223 is turned on to short-circuit between the drain and gate of the driving TFT 222.

  After setting the cancel control signal CAN to a high potential, both the mode control signals LON1 and LON2 are set to a high potential. As a result, since the mode control TFTs 224 and 225 are both turned on, a drive current from the drive TFT 222 flows to the organic EL element 21. At this time, the gate potential B and drain potential C of the driving TFT 222 and the source potential D of the mode control TFT 224 (the drain potential of the mode control TFT 224) D are determined by the organic EL element 21 and the driving TFT 222 and settle to a certain potential. .

  After that, if the mode control signals LON1 and LON2 are both set to a low potential while the cancel control signal CAN is kept at a high potential, the path between the driving TFT 222 and the organic EL element 21 is cut off. No current flows. Then, the gate potential B and the drain potential C of the driving TFT 222 begin to rise and settle to a certain potential so as to satisfy the cutoff condition of the driving TFT 222.

  When the threshold voltage Vth of the driving TFT 222 is Vth <0, the potential at this time is a potential that is higher than the power supply voltage VDD by the threshold voltage Vth, that is, VDD + Vth. When the cancel control signal CAN is set to a low potential after the gate potential B and the drain potential C of the driving TFT 222 are in a steady state, the drain and gate of the driving TFT 222 are opened. At this time, the gate of the driving TFT 222 holds a voltage of VDD + Vth, and the drain potential C rises to the power supply voltage VDD.

When the potential of the video signal line 18 is set to the potential Vs corresponding to the image data Sig to be displayed after the cancel control signal CAN is set to a low potential, the potential difference between both ends of the storage capacitor 221 is held. The potential (B) Vg is
Vg = VDD + Vth− (Vsmax−Vs)
= VDD−Vth−ΔVs (1)
It becomes.

  After the gate potential (B) Vg of the driving TFT 222 is determined, the write control signal WS is set to a low potential, and the mode control signals LON1 and LON2 are both set to a high potential. As a result, a current corresponding to the image data Sig flows through the organic EL element 21. At this time, the current Iel flowing through the organic EL element 21 is expressed by the following equation, assuming that the driving TFT 222 is guaranteed to operate in the saturation region.

Iel = k · (Vg−VDD−Vth) ²
= K · (ΔVs) ² (2)
Here, k is a value determined by the size of the driving TFT 222 and the electric field mobility.

  As can be seen from the above equation (2), the current Iel flowing through the organic EL element 21 during image display is not affected by the threshold voltage Vth of the driving TFT 222 and is determined by the video signal potential Vs corresponding to the image data Sig. Is done. That is, the light emitting circuit 22 has a correction function for canceling the threshold voltage Vth of the driving TFT 22. With this Vth correction (cancellation) function, a high-quality display image without roughness can be obtained.

  Subsequently, the light receiving operation will be described. First, the light emission operation is terminated by setting both the mode control signals LON1 and LON2 to a low potential. That is, when the mode control signals LON1 and LON2 are both set to a low potential, the mode control TFTs 224 and 225 are both turned off, and the path between the driving TFT 222 and the organic EL element 21 is cut off. No current flows, and the light emitting operation of the organic EL element 21 ends.

  When the light emission operation is completed, the potential of the video signal line 18 is set to a potential lower than the signal reference potential Vsmax by a constant potential ΔVsr. Thereafter, the write control signal WS, the read control signal RS, and the mode control signal LON1 are set to a high potential, and the mode control signal LON2 is set to a low potential. Then, the driving transistor TFT 222, the mode control transistor TFT 224, the light receiving current control TFT 231 and the TFT 232 are turned on, and the path between the power supply VDD and the first bias power supply Vb1 becomes conductive. On the other hand, since the mode control TFT 225 is turned off, no current flows through the organic EL element 21.

At this time, the current (reference current) Ia flowing through the TFT 232 is determined by the driving TFT 222, and the Vth correction of the driving TFT 222 has already been completed during the light emission operation.
Ia = k · (ΔVsr) ² (3)
And a constant current determined by a constant potential ΔVsr. The detection current (light reception signal current) Idet flowing through the light reception signal line 19 during this period is determined by the current Ia flowing through the TFT 232 and the gate potential (E) VE of the TFT 232, and is expressed by the following two expressions.

Ia = Ka. (VE-Vb1-Vtha) (4)
Idet = Kb · (VE−Vb2−Vthb) (5)
Here, Ka is a constant determined by the size and electric field mobility of the TFT 232, Kb is a constant determined by the size and electric field mobility of the TFT 233, Vtha is a threshold voltage of the TFT 232, and Vthb is a threshold voltage of the TFT 233.

  The gate potential VE of the TFT 232 is uniquely determined from the above formula (4), and the detection current Idet is obtained from the above formula (5). Here, the detection current Idet has a value including variations in characteristics of the TFTs 232 and 233 constituting the current mirror circuit 235, in particular, variations in the threshold voltage Vth. Therefore, the detected current Idet is stored as a current value Idet1 in a memory (not shown) of an external system.

  In the imaging period, when the write control signal WS, the read control signal RS, and the mode control signals LON1 and LON2 are set to a low potential, the organic EL element 21 is caused to leak to the organic EL element 21 by a light leak current corresponding to a light carrier generated by external light. The charge of the capacitor Cel is discharged. After the imaging period ends, the imaging signal is output.

  At this time, the write control signal WS and the mode control signal LON1 are set to a low potential, and the read control signal RS and the mode control signal LON2 are set to a high potential. As a result, the driving TFT 222 and the mode control TFT 224 are turned off, so that the path between the driving TFT 222 and the organic EL element 21 is cut. On the other hand, the mode control TFT 225 is turned on, so that the organic EL element 21 is turned on. And the light receiving current control TFT 231 are conducted.

  The gate potential (E) VE of the TFT 232 during the imaging signal output period is a value determined by the amount of charge of the capacitor Cel of the organic EL element 21 discharged during the imaging period. The current value output to the light receiving signal line 19 at this time is Idet2. Similarly to the current value Idet1, the current value Idet2 also includes a characteristic variation of the TFTs 232 and 233 constituting the current mirror circuit 235. The current value Idet1 is a value obtained by inputting a known current (reference current) Ia. Therefore, by detecting the difference between the current value Idet1 and the current value and Idet2 in the external system, the detection current Idet corresponding to the actual imaging data not including the characteristic variation of the TFTs 232 and 233 constituting the current mirror circuit 235 is obtained. (real) can be requested.

  As described above, a configuration in which the light emitting circuit 22 having the function of correcting the threshold voltage Vth of the driving TFT 22 and the light receiving circuit 23 using the current mirror circuit 232 is employed, and prior to detection of the received light signal current, the driving circuit is used. The current flowing through the TFT 222 is supplied as a reference current to a current amplifying circuit (in this example, supplied to the current mirror circuit 235, and the difference between the current based on the reference current and the current based on the received light signal current is taken to obtain TFT characteristics. An active matrix organic EL display device having an input / output function (both functions of the display device and the imaging device) for outputting a high-quality display image free from roughness caused by variations, particularly Vth variation, and imaging data with few errors is realized. be able to.

  In the above embodiment, the case where the organic EL element 21 is configured to be used as both a light emitting element and a light receiving element has been described as an example. However, the present invention is not limited to this, and the light receiving element is a light emitting element. It is also possible to adopt a configuration using dedicated elements.

  Further, in the above embodiment, as a correction means for correcting the variation in the threshold voltage Vth of the driving TFT 222, a circuit configuration in which the TFT 223 is connected between the gate and drain of the driving TFT 222 is used. The circuit configuration is not limited, and any circuit configuration capable of correcting variations in the threshold voltage Vth of the driving TFT 222 may be used.

  Furthermore, in the above embodiment, prior to detection of the light reception signal current, the current flowing through the driving TFT 222 is supplied to the current mirror circuit 235 of the light reception circuit 23 as a reference current that does not include the Vth variation of the TFT. It is also possible to employ a configuration in which a dedicated constant current source is provided in the light receiving circuit 23 and a reference current is supplied from the constant current source to the current mirror circuit 235 prior to detection of the received light signal current.

  Since the display device according to the present invention can be used not only as a screen display unit but also as an imaging device, the display device is mounted as a screen display unit and an imaging device on a mobile terminal device such as a mobile phone having a camera function. Can be used.

1 is a block diagram illustrating an outline of a configuration of an active matrix organic EL display device according to an embodiment of the present invention. It is a circuit diagram which shows an example of the circuit structure of a pixel. 6 is a timing chart for explaining an operation in one frame in the active matrix organic EL display device according to the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Pixel, 12 ... Pixel array part, 13 ... Light emission control part, 14 ... Light reception control part, 15 ... A / D conversion part, 20 ... Pixel circuit, 21 ... Organic EL element, 22 ... Light emission circuit, 23 ... Light reception circuit

Claims (11)

A display device in which pixels including a light emitting circuit and a light receiving circuit are arranged in a matrix,
The light emitting circuit is
A driving transistor for driving a light emitting element in accordance with a video signal to be written;
Correcting means for correcting variations in threshold voltage of the driving transistor,
The light receiving circuit is
Current amplifying means for amplifying and outputting a received light signal current flowing through the light receiving element;
Reference current supply means for supplying a reference current to the current amplification means prior to detection of the light receiving signal current;
A display device comprising means for taking a difference between the current based on the reference current and the current based on the light reception signal current. The correction unit is connected between the gate and drain of the driving transistor, and is a transistor that is turned on from the time when the video signal is written to the time when the current supply is stopped after the current is once supplied to the light emitting element. The display device according to claim 1, wherein: The display device according to claim 1, wherein the current amplification unit is a current mirror circuit. The display device according to claim 1, wherein the reference current supply unit supplies the current flowing through the driving transistor to the current amplification unit as the reference current. The display device according to claim 1, wherein the light emitting element and the light receiving element are a single organic EL element. The display device according to claim 5, wherein the light receiving circuit uses the organic EL element as the light receiving element by applying a reverse bias voltage to the organic EL element. A light emitting circuit having a driving transistor for driving a light emitting element in accordance with a video signal;
And a light receiving circuit having current amplifying means for amplifying and outputting a light receiving signal current flowing through the light receiving element, and a method of driving a display device in which pixels are arranged in a matrix.
During the light emitting operation of the light emitting circuit, while performing the operation of correcting the variation of the threshold voltage of the driving transistor,
During the light receiving operation of the light receiving circuit, a reference current is supplied to the current amplifying means prior to detection of the light receiving signal current, and a difference between the current based on the reference current and the current based on the light receiving signal current is obtained. A display device driving method. In the correction of the variation in the threshold voltage, the transistor connected between the gate and the drain of the driving transistor is supplied with current once from the time of writing the video signal, and then the supply of the current is stopped. The display device driving method according to claim 7, wherein the display device is turned on until a point in time. The display device driving method according to claim 7, wherein a current flowing through the driving transistor is supplied to the current amplifying unit as the reference current. The display device driving method according to claim 7, wherein a single organic EL element is used as the light emitting element and the light receiving element. The method for driving a display device according to claim 10, wherein the organic EL element is used as the light receiving element by applying a reverse bias voltage to the organic EL element.

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