JP2013186447A - Display device and driving method of the same, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device capable of reducing a decrease in light emission luminance due to depression shift, a driving method of the display device, and an electronic apparatus including the display device.SOLUTION: The display device has: a display section including a light-emitting element and a pixel circuit on a display area for each pixel; and a driving section driving the pixel circuit in accordance with a video signal. The pixel circuit has a drive transistor driving the light-emitting element, and a writing transistor controlling the application of a signal voltage corresponding to the video signal to a gate of the drive transistor. The driving section controls an off voltage so that a difference between a threshold voltage of the writing transistor and an off voltage applied to the gate of the writing transistor when turning off the writing transistor always falls within a predetermined range.

Description

  The present technology relates to a display device including a light emitting element such as an organic EL (Electro Luminescence) element for each pixel and a driving method thereof. The present technology also relates to an electronic device including the display device.

  In recent years, in the field of display devices that perform image display, display devices that use current-driven light-emitting elements, such as organic EL elements, whose light emission luminance changes according to the value of a flowing current have been developed as light-emitting elements for pixels. Is being promoted. Unlike a liquid crystal element or the like, the organic EL element is a self-luminous element. Therefore, a display device (organic EL display device) using an organic EL element does not require a light source (backlight), so that it can be made thinner and brighter than a liquid crystal display device that requires a light source. .

  By the way, in general, the current-voltage (IV) characteristics of the organic EL element deteriorate (deteriorate with time) as time elapses. In a pixel circuit that current-drives an organic EL element, when the IV characteristic of the organic EL element changes with time, the voltage division ratio between the organic EL element and the drive transistor connected in series to the organic EL element changes. The gate-source voltage of the transistor also changes. As a result, since the current value flowing through the drive transistor changes, the current value flowing through the organic EL element also changes, and the light emission luminance also changes according to the current value.

  In addition, the threshold voltage (Vth) and mobility (μ) of the driving transistor may change over time, and the threshold voltage and mobility may vary from pixel circuit to pixel circuit due to variations in the manufacturing process. When the threshold voltage and mobility of the driving transistor differ from pixel circuit to pixel circuit, the current value flowing through the driving transistor varies from pixel circuit to pixel circuit. Therefore, even if the same voltage is applied to the gate of the driving transistor, the organic EL element emits light. The brightness varies, and the uniformity of the screen is lost.

  Therefore, even if the IV characteristic of the organic EL element changes with time or the threshold voltage or mobility of the driving transistor changes with time, the light emission luminance of the organic EL element is kept constant without being affected by them. In order to maintain the display device, a display device has been developed that incorporates a compensation function for variation in the IV characteristics of the organic EL element and a correction function for variation in the threshold voltage and mobility of the driving transistor (for example, Patent Document 1). reference).

JP 2008-083272 A

  The Vth correction for bringing the gate-source voltage of the transistor closer to the threshold voltage of the driving transistor is performed by turning on the writing transistor connected to the gate of the driving transistor. Similarly, the μ correction for adjusting the application period of the signal voltage corresponding to the video signal according to the mobility of the driving transistor is performed by turning on the writing transistor. That is, the period of Vth correction and μ correction is equal to the ON period of the write transistor. Here, the on period of the writing transistor is determined by the width of the pulse applied to the gate of the writing transistor, for example, as shown in FIG.

  However, the above-mentioned pulse is not a perfect rectangular wave but has a dullness as shown in FIG. Therefore, in practice, the period of Vth correction and μ correction can vary depending on the Vth of the writing transistor, as shown in FIG. When the μ correction period fluctuates, as shown in FIG. 6, the magnitude of the current Ids that flows through the organic EL element when the organic EL element emits light changes, and the emission luminance also changes accordingly. Therefore, it is preferable that the μ correction period does not vary as much as possible.

  The threshold voltage of the write transistor changes (decreases), for example, when a negative bias is continuously applied to the gate-source voltage of the write transistor. That is, as shown in FIG. 7, the threshold voltage characteristic of the write transistor shifts from enhancement to depletion. Here, the negative bias refers to a bias state in which the gate potential is negative with respect to the source potential. Enhancement refers to a state where a channel is formed when a write pulse is applied to the gate and a current flows between the source and drain. Depletion refers to a state in which a current flows between the source and drain without applying a write pulse to the gate.

  Usually, a negative bias is applied to the write transistor during the light emission period and extinction period of the organic EL element. When a negative bias is continuously applied to the gate-source voltage of the writing transistor, a depletion shift occurs in the threshold voltage characteristic of the writing transistor. For example, as shown in FIG. 5B, Vth changes from Vth1 to Vth2. Fluctuate (decrease). As a result, the μ correction period becomes longer by Δt1 + Δt2 than the initial period. As a result, as shown in FIG. 6, the current Ids flowing through the organic EL element when the organic EL element emits light is reduced by ΔIds, and the emission luminance is also reduced accordingly. That is, the light emission luminance decreases with the passage of the use period of the organic EL display device.

  Even when Vth correction and μ correction are not performed, a negative bias is applied to the writing transistor during the light emission period and extinction period of the organic EL element. Therefore, the threshold voltage characteristic of the write transistor shifts from enhancement to depletion regardless of the presence or absence of Vth correction and μ correction. As a result, for example, as shown in FIG. 7, even when a voltage for turning off the write transistor (off voltage Voff) is applied to the gate of the write transistor, a leak current flows without being sufficiently cut off, In some cases, the light emission luminance is lowered.

  The above problem can occur in various pixel circuits that drive current-driven light-emitting elements such as organic EL elements.

  The present technology has been made in view of such problems, and an object of the present technology is to provide a display device capable of reducing a decrease in light emission luminance due to a depletion shift, a driving method thereof, and such a display device. To provide electronic equipment.

  The display device of the present technology includes a display unit having a light emitting element and a pixel circuit for each pixel in a display region, and a drive unit that drives the pixel circuit based on a video signal. The pixel circuit includes a driving transistor that drives the light emitting element, and a writing transistor that controls application of a signal voltage corresponding to the video signal to the gate of the driving transistor. The driving unit controls the off voltage so that a difference between a threshold voltage of the writing transistor and an off voltage applied to the gate of the writing transistor when the writing transistor is turned off is always within a predetermined range. It has become.

  An electronic apparatus of the present technology includes the display device described above.

  The display device driving method of the present technology is a driving method of a display device in which a light emitting element and a pixel circuit are provided for each pixel in a display region. The pixel circuit includes a driving transistor that drives the light emitting element, and a writing transistor that controls application of a signal voltage corresponding to the video signal to the gate of the driving transistor. In the display device driving method according to the present technology, the difference between the threshold voltage of the writing transistor and the off-voltage applied to the gate of the writing transistor when the writing transistor is turned off is always in the display device having such a configuration. The step of controlling the off voltage so as to be within the predetermined range is included.

  In the display device of the present technology, the driving method thereof, and the electronic device, the difference between the threshold voltage of the writing transistor and the off voltage applied to the gate of the writing transistor when the writing transistor is turned off is always within a predetermined range. Thus, the off-voltage is controlled. Thereby, the amount of current leakage due to the shortage of the difference can be reduced. Further, since acceleration of the depletion shift of the threshold voltage characteristic of the writing transistor can be minimized, Vth correction for bringing the gate-source voltage of the transistor close to the threshold voltage of the driving transistor, and a signal voltage corresponding to the video signal When the μ correction is performed to adjust the application period according to the mobility of the drive transistor, the amount of change in the ON period of the write transistor due to the depletion shift can be reduced.

  According to the display device, the driving method thereof, and the electronic apparatus of the present technology, the current leakage amount of the writing transistor due to the depletion shift can be reduced, so that the decrease in light emission luminance due to the depletion shift is reduced. can do. Further, when performing Vth correction and μ correction, it is possible to reduce the amount of change in the ON period of the write transistor due to the depletion shift. Therefore, also in this case, it is possible to reduce a decrease in light emission luminance due to the depletion shift.

1 is a schematic configuration diagram of a display device according to an embodiment of the present technology. It is a figure showing an example of the circuit structure of the pixel of FIG. It is a figure showing an example of a structure of the display control circuit of FIG. It is a figure showing an example of the table stored in the memory of FIG. It is a figure explaining an example of the pulse waveform applied to the gate of a writing transistor. It is a figure explaining an example of the relationship between the length of micro correction | amendment period, and the electric current value which flows into an organic EL element. It is a figure explaining a depletion shift. FIG. 3 is a diagram illustrating an example of a time lapse of a threshold voltage of the write transistor in FIG. 2. FIG. 3 is a diagram illustrating an example of a relationship between a threshold voltage of the write transistor in FIG. 2 and an off voltage applied to the gate of the write transistor. FIG. 6 is a diagram for explaining another example of the relationship between the threshold voltage of the write transistor of FIG. 2 and the off voltage applied to the gate of the write transistor. It is a figure showing an example of a pixel structure in the display apparatus used for creating the table of FIG. It is a wave form diagram for demonstrating an example of operation | movement of the display apparatus of FIG. It is a figure showing the modification of the display apparatus of FIG. It is a figure showing an example of a structure of the dummy pixel of FIG. It is a perspective view showing the external appearance of the application example 1 of the said display apparatus. (A) is a perspective view showing the external appearance seen from the front side of the application example 2 of the said display apparatus, (B) is a perspective view showing the external appearance seen from the back side. It is a perspective view showing the external appearance of the example 3 of application of the said display apparatus. It is a perspective view showing the external appearance of the application example 4 of the said display apparatus. (A) is the front view of the application example 5 of the said display apparatus in the open state, (B) is the side view, (C) is the front view of the closed state, (D) is a left side view, (E) is A right side view, (F) is a top view, and (G) is a bottom view.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings. The description will be given in the following order.

1. Embodiment (display device)
2. Modified example (display device)
3. Application example (electronic equipment)

<1. Embodiment>
[Constitution]
FIG. 1 illustrates a schematic configuration of a display device 1 according to an embodiment of the present technology. The display device 1 includes a display panel 10 and a drive circuit 20 that drives the display panel 10 based on a video signal 20A and a synchronization signal 20B input from the outside. The drive circuit 20 includes, for example, a display control circuit 21, a signal line drive circuit 22, a write line drive circuit 23, a power supply line drive circuit 24, and a measurement circuit 25.

(Display panel 10)
The display panel 10 has a plurality of pixels 11 two-dimensionally arranged over the entire display area 10 </ b> A of the display panel 10. The display panel 10 displays an image based on the video signal 20 </ b> A input from the outside when each pixel 11 is driven in an active matrix by the drive circuit 20. Here, the video signal 20 </ b> A is, for example, a digital signal of a video displayed on the display panel 10 for each field, and includes a digital signal for each pixel 11. The pixel 11 corresponds to a minimum unit point constituting a screen on the display panel 10. When the display panel 10 is a color display panel, the pixel 11 corresponds to a sub-pixel that emits light of a single color such as red, green, or blue, and when the display panel 10 is a monochrome display panel, the pixel 11 Reference numeral 11 corresponds to a pixel that emits monochromatic light (white light). FIG. 2 illustrates an example of a circuit configuration of the pixel 11. The pixel 11 includes, for example, a pixel circuit 12 and an organic EL element 13. The organic EL element 13 has, for example, a configuration in which an anode electrode, an organic layer, and a cathode electrode are sequentially stacked.

  For example, the pixel circuit 12 includes a drive transistor Tr1, a write transistor Tr2, and a storage capacitor Cs, and has a circuit configuration of 2Tr1C. The write transistor Tr2 controls application of a signal voltage corresponding to the video signal 20A to the gate of the drive transistor Tr1. Specifically, the write transistor Tr2 samples a voltage of a signal line DTL described later and writes it to the gate of the drive transistor Tr1. The drive transistor Tr1 drives the organic EL element 13. Specifically, the drive transistor Tr1 controls the current flowing through the organic EL element 13 in accordance with the magnitude of the voltage written by the write transistor Tr2. The holding capacitor Cs holds a predetermined voltage between the gate and source of the driving transistor Tr1. Note that the pixel circuit 12 may have a circuit configuration different from the above-described 2Tr1C circuit configuration.

  The drive transistor Tr1 and the write transistor Tr2 are, for example, n-channel MOS type thin film transistors (TFTs). Note that the type of TFT is not particularly limited, and may be, for example, an inverted staggered structure (so-called bottom gate type) or a staggered structure (top gate type). The drive transistor Tr1 or the write transistor Tr2 may be a p-channel MOS type TFT.

  The display panel 10 further includes a plurality of write lines WSL extending in the row direction, a plurality of signal lines DTL extending in the column direction, and a plurality of power supply lines DSL extending in the row direction. Yes. A pixel 11 is provided in the vicinity of the intersection of the signal line DTL and the write line WSL. Each signal line DTL is connected to the output end (not shown) of the signal line drive circuit 22 and the source or drain of the write transistor Tr2. Each write line WSL is connected to the output terminal (not shown) of the write line drive circuit 23 and the gate of the write transistor Tr2. Each power supply line DSL is connected to the output end (not shown) of the power supply line drive circuit 24 and the source or drain of the drive transistor Tr1.

  The gate of the write transistor Tr2 is connected to the write line WSL. The source or drain of the write transistor Tr2 is connected to the signal line DTL, and the terminal not connected to the signal line DTL among the source and drain of the write transistor Tr2 is connected to the gate of the drive transistor Tr1. The source or drain of the drive transistor Tr1 is connected to the power supply line DSL, and the terminal not connected to the power supply line DSL among the source and drain of the drive transistor Tr1 is connected to the anode of the organic EL element 13. One end of the storage capacitor Cs is connected to the gate of the drive transistor Tr1, and the other end of the storage capacitor Cs is connected to the source of the drive transistor Tr1 (terminal on the organic EL element 13 side in FIG. 2). That is, the storage capacitor Cs is inserted between the gate and source of the drive transistor Tr1. The organic EL element 13 has an element capacitance Coled.

  The display panel 10 further includes a cathode line CTL connected to the cathode of the organic EL element 13 as shown in FIG. The cathode line CTL is connected to the input end of the measurement circuit 25 and the cathode of the organic EL element 13. The cathode line CTL is constituted by, for example, a strip-like electrode formed in a strip shape corresponding to the pixel column. The display panel 10 further includes a frame region 10B that does not contribute to video display, for example, at the periphery of the display region 10A. The frame region 10B is covered with, for example, a light shielding member.

(Drive circuit 20)
Next, the drive circuit 20 will be described. As described above, the drive circuit 20 includes the display control circuit 21, the signal line drive circuit 22, the write line drive circuit 23, the power supply line drive circuit 24, and the measurement circuit 25, for example. The display control circuit 21 includes, for example, a conversion circuit 31, a controller 32, and a memory 33 as shown in FIG.

  For example, as shown in FIG. 3, the memory 33 stores a table 33A and a threshold 33B. For example, as shown in FIG. 4, the table 33 </ b> A corresponds to a plurality of off voltages Voff or a list corresponding to a plurality of off voltages Voff. Here, the “off voltage Voff” refers to a voltage applied to the gate of the write transistor Tr2 when the write transistor Tr2 is turned off. Examples of “one corresponding to the off voltage Voff” include a control signal (for example, a bit corresponding to the magnitude of the off voltage Voff) used for setting (changing) the off voltage Voff. The threshold 33B is, for example, the maximum value Imax that can be tolerated as the amount of current leakage when the write transistor Tr2 is off. The maximum value Imax is obtained through experiments, simulations, and the like.

  For example, the controller 32 controls the control signals 32A, 21B, which control the operation timing of the conversion circuit 31, the signal line drive circuit 22, the write line drive circuit 23, and the power supply line drive circuit 24 from the synchronization signal 20B supplied from the outside. 21C and 21D are generated. Examples of the synchronization signal 20B include a vertical synchronization signal, a horizontal synchronization signal, and a dot clock signal.

  The controller 32 sets (changes) the off voltage Voff so that the difference (margin) between the threshold voltage Vth of the write transistor Tr2 and the off voltage Voff is always within a predetermined range. The lower limit of the margin corresponds to the maximum value allowable as the amount of current leakage when the write transistor Tr2 is off. The upper limit of the margin corresponds to the maximum value allowable as the depletion shift amount. Specifically, the controller 32 controls the off voltage Voff applied to the gate of the write transistor Tr2 by using the detection signal 25A input from the measurement circuit 25, the table 33A and the threshold value 33B in the memory 33. To (change). The controller 32 includes a control signal related to the magnitude of the off voltage Voff in the control signal 21C and outputs the control signal to the write line driving circuit 23.

  Incidentally, the Vth correction for bringing the gate-source voltage of the drive transistor Tr1 close to the threshold voltage Vth of the drive transistor Tr1 is performed by turning on the write transistor Tr2 connected to the gate of the drive transistor Tr1. Similarly, μ correction for adjusting the application period of the signal voltage corresponding to the video signal 20A according to the mobility μ of the drive transistor Tr1 is performed by turning on the write transistor Tr2. That is, the period of Vth correction and μ correction is equal to the ON period of the write transistor Tr2. Here, the ON period of the write transistor Tr2 is determined by the width of the pulse applied to the gate of the write transistor Tr2, for example, as shown in FIG.

  However, the above-mentioned pulse is not a perfect rectangular wave but has a dullness as shown in FIG. Therefore, in practice, the period of Vth correction and μ correction can vary depending on the Vth of the writing transistor, as shown in FIG. When the μ correction period varies, as shown in FIG. 6, the magnitude of the current Ids that flows through the organic EL element 13 when the organic EL element 13 emits light changes, and the emission luminance also changes accordingly. Therefore, it is preferable that the μ correction period does not vary as much as possible.

  The threshold voltage Vth of the write transistor Tr2 changes (decreases) when a negative bias is continuously applied to the gate-source voltage of the write transistor Tr2. That is, the threshold voltage characteristic of the write transistor Tr2 shifts from enhancement to depletion. Here, the negative bias refers to a bias state in which the gate potential is negative with respect to the source potential. Enhancement refers to a state where a channel is formed when a write pulse is applied to the gate and a current flows between the source and drain. Depletion refers to a state in which a current flows between the source and drain without applying a write pulse to the gate.

  Usually, a negative bias is applied to the write transistor Tr2 during the light emission period and the extinction period of the organic EL element 13. When a negative bias is continuously applied to the gate-source voltage of the write transistor Tr2 (that is, as the drive period of the write transistor Tr2 elapses), a depletion shift occurs in the threshold voltage characteristic of the write transistor Tr2. As shown in FIG. 5 (B), Vth varies (decreases) from Vth1 to Vth2. As a result, the μ correction period becomes longer by Δt1 + Δt2 than the initial period. As a result, as shown in FIG. 6, the current Ids flowing through the organic EL element 13 when the organic EL element 13 emits light is reduced by ΔIds, and the emission luminance is also reduced accordingly. That is, as the usage period of the display device 1 elapses, the light emission luminance decreases.

  Further, as described above, since a negative bias is applied to the write transistor Tr2 during the light emission period and extinction period of the organic EL element 13, the threshold voltage characteristic of the write transistor Tr2 shifts from enhancement to depletion. As a result, for example, as shown in FIG. 7, even when an off voltage Voff is applied to the gate of the write transistor Tr2, a leakage current flows without sufficient cutoff, resulting in a decrease in light emission luminance. There is. Therefore, in order to sufficiently cut off the write transistor Tr2, for example, as shown in FIG. 8, the off voltage Voff is changed to a value (Voff_b) that is lower than the current value (Voff_a). It is possible to do. However, in such a case, the depletion shift is accelerated by the amount by which the off voltage Voff is lowered. For this reason, the time until the above-mentioned margin disappears is not significantly different between before and after the off voltage Voff is changed.

  On the other hand, in the present embodiment, the controller 32 sets (changes) the off voltage Voff so that the margin is always within a predetermined range. For example, as shown in FIG. 9, the controller 32 continuously changes the off voltage Voff with time so that the margin is always within a predetermined range. Note that, for example, as illustrated in FIG. 10, the controller 32 may be configured to intermittently change the off voltage Voff over time so that the margin is always within a predetermined range. . In this way, by changing the off voltage Voff over time so that the margin is always within a predetermined range, the acceleration of the depletion shift and the increase in leakage current due to the lack of the margin are minimized. Can be suppressed. Therefore, the controller 32 reduces the amount of change in the ON period and the amount of current leakage of the write transistor Tr2 due to the depletion shift of the threshold voltage characteristic of the write transistor Tr2 by changing the OFF voltage Voff.

  The above-described table 33A and threshold value 33B make it possible to adjust the off voltage Voff. The controller 32 resets the off voltage Voff when the detection signal 25A exceeds the threshold value Ith. That is, the controller 32 resets the off voltage Voff every time the detection signal 25A exceeds the threshold value 33B. When the controller 32 resets the off-voltage Voff, for example, in the table 33A, the voltage listed next to the voltage value (Voff (i)) (i is an integer of 1 or more) that is currently used. The value (Voff (i + 1)) is used. That is, every time the detection signal 25A exceeds the threshold value 33B, the controller 32 has a voltage value (Voff (i + 1)) listed next to the voltage value (Voff (i)) currently used in the table 33A. ), The OFF voltage Voff is reset.

  Next, the conversion circuit 31 in the display control circuit 21 will be described. The conversion circuit 31 includes, for example, a frame memory, a write circuit, a read circuit, and a decoder. The frame memory is a video display memory having a storage capacity larger than at least the resolution of the display area 10A. For example, the row data, the column address, and the gradation data of each pixel 11 associated with the row address and the column address Can be memorized. The writing circuit uses the synchronization signal 20B to generate a write address for the video signal 20A and outputs it to the frame memory in synchronization with the synchronization signal 20B. The write address includes, for example, a row address and a column address. The read circuit generates a read address based on the control signal 32A and outputs it to the frame memory. The decoder outputs the gradation data output from the frame memory as signal data 21A.

  For example, the signal line driving circuit 22 applies an analog signal voltage corresponding to the signal data 21A input from the conversion circuit 31 to each signal line DTL in response to the input of the control signal 21B. The signal line drive circuit 22 can output, for example, two types of voltages (Vofs, Vsig). Specifically, the signal line driving circuit 22 supplies two types of voltages (Vofs, Vsig) to the pixel 11 selected by the writing line driving circuit 23 via the signal line DTL. Here, Vsig is a signal voltage corresponding to the video signal 20A. Vofs is a constant voltage unrelated to the video signal 20A. The minimum voltage of Vsig is a voltage value lower than Vofs, and the maximum voltage of Vsig is a voltage value higher than Vofs.

  The write line drive circuit 23 outputs a scan pulse for selecting each pixel 11 in a predetermined unit (for example, row unit) to the write line WSL based on the address data specified from the control signal 21C. It has become. For example, the write line drive circuit 23 sequentially selects a plurality of write lines WSL for each predetermined unit (for example, row unit) in accordance with the input of the control signal 21C. The write line drive circuit 23 can output, for example, two types of voltages (Von, Voff). Specifically, the write line drive circuit 23 supplies two kinds of voltages (Von, Voff) to the drive target pixel 11 via the write line WSL, and performs on / off control of the write transistor Tr2. It has become.

  Here, Von has a value equal to or higher than the ON voltage of the write transistor Tr2. Von is a peak value of a write pulse output from the write line drive circuit 23 in a “Vth correction period” or “write / μ correction period” described later. The off voltage Voff is lower than the on voltage of the write transistor Tr2. Further, the off voltage Voff is a value such that the above-described margin is always within a predetermined range.

  Further, the writing line driving circuit 23 can change the off-voltage Voff applied to the pixel 11 to be driven in accordance with the input of the control signal 21C. Specifically, the write line drive circuit 23 sets (changes) the off voltage Voff applied to the gate of the write transistor based on the set value of the off voltage Voff included in the control signal 21C. It has become. Here, the set value of the off voltage Voff may be the value of the off voltage Voff itself or a control signal indicating the value of the off voltage Voff. The write line drive circuit 23 changes the off voltage Voff so as to reduce the amount of change in the on period and the amount of current leakage of the write transistor Tr2 due to the depletion shift of the threshold voltage characteristics of the write transistor Tr2. It has become.

  For example, the power supply line driving circuit 24 sequentially selects a plurality of power supply lines DSL for each predetermined unit (for example, for each row) in accordance with the input of the control signal 21D. The power line drive circuit 24 can output, for example, two types of voltages (Vcc, Vss). Specifically, the power supply line drive circuit 24 supplies two types of voltages (Vcc, Vss) to the pixels 11 selected by the write line drive circuit 23 via the power supply line DSL. Here, Vss is a voltage value lower than a voltage (Vel + Vcath) obtained by adding the threshold voltage Vel of the organic EL element 13 and the cathode voltage Vcath of the organic EL element 13. Vcc is a voltage value equal to or higher than the voltage (Vel + Vcath).

  The measurement circuit 25 measures the current flowing through the organic EL element 13 (or the drive transistor Tr1). For example, as shown in FIG. 2, the measurement circuit 25 includes an ammeter, and outputs a current value measured by the ammeter as a detection signal 25A.

  Note that the measurement circuit 25 may measure a physical quantity corresponding to a current flowing through the organic EL element 13 (or the drive transistor Tr1). For example, the measurement circuit 25 may be configured to include a voltmeter, and output a voltage value measured by the voltmeter as the detection signal 25A. The voltage value is, for example, the voltage value of the anode or cathode of the organic EL element 13. At this time, the threshold value 33B is, for example, the value of the anode or cathode of the organic EL element 13 when the maximum value Imax allowable as the amount of current leakage when the write transistor Tr2 is off flows to the write transistor Tr2. It is a voltage value. The measurement circuit 25 may output a measurement value measured by an ammeter or a voltmeter as a detection signal 25A. However, the measurement circuit 25 can obtain the measurement value by performing a predetermined calculation on the measurement value. The obtained value may be output as the detection signal 25A.

[Create table]
Next, an example of a method for creating the table 33A according to the present embodiment will be described. FIG. 11 illustrates an example of a circuit configuration of pixels included in the display device (master) for creating the table 33A. A pixel 111 illustrated in FIG. 11 has the same configuration as the pixel 11 in the display device 1.

  First, Voff (1) is selected as the off voltage Voff, and the same type of waveform as the waveform applied to the pixel 11 (for example, the waveforms shown in FIGS. 12A to 12C described later) is repeated for the pixel 111 described above. Apply. In FIG. 12A, a period during which the off voltage Voff is applied to the writing line WSL is surrounded by a broken line. At this time, the detection signal 25A is monitored during the light emission period in the initial cycle, and the monitored value is a reasonable value (Ids1) as the amount of current leakage when the write transistor Tr2 is off. Keeps Voff (1) in the record as the off-voltage Voff.

  Subsequently, Voff (1) is selected as the off voltage Voff, and for example, when the waveforms of FIGS. 12A to 12C are repeatedly applied to the pixel 111, for each predetermined period, The detection signal 25A during the light emission period is monitored. When the monitor value exceeds a predetermined threshold value Ith, the value of the off-voltage Voff is gradually lowered from Voff (1), and the monitor value obtained at that time coincides with (or substantially coincides with) Ids1. Search for the value of voltage Voff. Then, the value found by the search is recorded as Voff (2). Here, the threshold value Ith is a maximum value allowable as a current leakage amount when the write transistor Tr2 is turned off.

  Next, when Voff (2) is selected as the off voltage Voff and the waveforms of FIGS. 12A to 12C are repeatedly applied to the pixel 111, for example, at predetermined intervals, The detection signal 25A during the light emission period is monitored. When the monitored value exceeds a predetermined threshold value Ith, the value of the off-voltage Voff is gradually lowered from Voff (2), and the monitored value obtained at that time coincides with (or substantially coincides with) Ids1. Search for the value of voltage Voff. Then, the value found by the search is recorded as Voff (3).

  Thereafter, the above procedure is repeated. That is, Voff (i) (voltage value found during the i-th process) is selected as the off voltage Voff, and the waveforms shown in FIGS. 12A to 12C are repeatedly applied to the pixel 111, for example. The detection signal 25A during the light emission period is monitored at predetermined intervals. When the monitored value exceeds a predetermined threshold value Ith, the value of the off-voltage Voff is gradually lowered from Voff (i), and the monitored value obtained at that time coincides with (or substantially coincides with) Ids1. Search for the value of voltage Voff. Then, the value found by the search is recorded as Voff (i + 1).

  In this way, the table 33A is completed. The completed table 33A is stored in the memory 33 by the operator.

[Operation]
Next, the operation (operation from quenching to light emission) of the display device 1 of the present embodiment will be described. In the present embodiment, even if the IV characteristic of the organic EL element 13 changes with time or the threshold voltage or mobility of the driving transistor Tr1 changes with time, the organic EL element is not affected by the change. In order to keep the light emission luminance of 13 constant, a compensation operation for variation of the IV characteristic of the organic EL element 13 and a correction operation for variation of the threshold voltage and mobility of the drive transistor Tr1 are incorporated.

  FIG. 12 shows an example of various waveforms in the display device 1. FIG. 12 shows a state in which a binary voltage change occurs every moment in the write line WSL, the power supply line DSL, and the signal line DTL. Further, FIG. 12 also shows that the gate voltage Vg and the source voltage Vs of the drive transistor Tr1 change from moment to moment according to the voltage change of the write line WSL, the power supply line DSL, and the signal line DTL. Yes.

(Vth correction preparation period)
First, preparation for Vth correction is performed. Note that Vth correction refers to correction for bringing the gate-source voltage Vgs of the drive transistor Tr1 closer to the threshold voltage of the drive transistor Tr1. Specifically, when the voltage of the write line WSL is Voff, the voltage of the signal line DTL is Vofs, and the voltage of the power supply line DSL is Vcc (that is, the organic EL element 13 emits light). The power line drive circuit 24 lowers the voltage of the power line DSL from Vcc to Vss in response to the control signal 21D (T1). Then, the source voltage Vs decreases to Vss, and the organic EL element 13 is quenched. At this time, the gate voltage Vg also decreases due to coupling via the storage capacitor Cs.

  Next, while the voltage of the power supply line DSL is Vss and the voltage of the signal line DTL is Vofs, the write line drive circuit 23 determines the voltage of the write line WSL according to the control signal 21C. Is raised from Voff to Von (T2). Then, the gate voltage Vg decreases to Vofs. At this time, the potential difference Vgs between the gate voltage Vg and the source voltage Vs may be smaller than, equal to, or larger than the threshold voltage of the driving transistor Tr2.

(Vth correction period)
Next, Vth is corrected. Specifically, while the voltage of the signal line DTL is Vofs and the voltage of the write line WSL is Von, the power supply line driving circuit 24 determines the power supply line DSL according to the control signal 21D. Is raised from Vss to Vcc (T3). Then, a current Ids flows between the drain and source of the drive transistor Tr1, and the source voltage Vs increases. At this time, when the source voltage Vs is lower than Vofs−Vth (when the Vth correction is not yet completed), until the drive transistor Tr1 is cut off (until the potential difference Vgs becomes Vth), A current Ids flows between the drain and the source. As a result, the gate voltage Vg becomes Vofs, the source voltage Vs rises, and as a result, the storage capacitor Cs is charged to Vth, and the potential difference Vgs becomes Vth.

  Thereafter, before the signal line drive circuit 22 switches the voltage of the signal line DTL from Vofs to Vsig according to the control signal 21B, the write line drive circuit 23 changes the voltage of the write line WSL according to the control signal 21C to Von. To Voff (T4). Then, since the gate of the drive transistor Tr1 is in a floating state, the potential difference Vgs can be maintained as Vth regardless of the magnitude of the voltage of the signal line DTL. As described above, by setting the potential difference Vgs to Vth, even when the threshold voltage Vth of the drive transistor Tr1 varies for each pixel circuit 12, it is possible to eliminate the variation in the light emission luminance of the organic EL element 13. it can.

(Vth correction suspension period)
Thereafter, during the suspension period of Vth correction, the signal line drive circuit 22 switches the voltage of the signal line DTL from Vofs to Vsig.

(Signal writing / μ correction period)
After the Vth correction pause period ends, signal writing and μ correction are performed. Specifically, while the voltage of the signal line DTL is Vsig and the voltage of the power supply line DSL is Vcc, the write line drive circuit 23 responds to the control signal 21C in accordance with the control signal 21C. Is increased from Voff to Von (T5), and the gate of the drive transistor Tr1 is connected to the signal line DTL. At this time, the write line drive circuit 23 applies a write pulse whose pulse width is changed according to the control signal 21C to the write line WSL.

  Then, the gate voltage Vg of the drive transistor Tr1 becomes the voltage Vsig of the signal line DTL. At this time, the anode voltage of the organic EL element 13 is still lower than the threshold voltage Vel of the organic EL element 13 at this stage, and the organic EL element 13 is cut off. Therefore, the current Ids flows to the element capacitance Coled of the organic EL element 13 and the element capacitance Coled is charged. Therefore, the source voltage Vs increases by ΔVs, and the potential difference Vgs eventually becomes Vsig + Vth−ΔVs. In this way, μ correction is performed simultaneously with writing. Here, since ΔVs increases as the mobility μ of the drive transistor Tr1 increases, the variation in mobility μ for each pixel 11 can be eliminated by reducing the potential difference Vgs by ΔV before light emission.

(Light emission)
Finally, the write line drive circuit 23 lowers the voltage of the write line WSL from Von to Voff according to the control signal 21C (T6). Then, the gate of the drive transistor Tr1 becomes floating, the current Ids flows between the drain and source of the drive transistor Tr1, and the source voltage Vs rises. As a result, a voltage equal to or higher than the threshold voltage Vel is applied to the organic EL element 13, and the organic EL element 13 emits light with a desired luminance.

  In the display device 1 according to the present embodiment, as described above, the pixel circuit 12 is controlled to be turned on / off in each pixel 11, and a driving current is injected into the organic EL element 13 of each pixel 11. And recombine to emit light. At this time, the drive circuit 20 sets (changes) the off voltage Voff by the above-described method so that the margin is always within a predetermined range. Thereby, an image with excellent image quality emitted at a desired luminance can be obtained.

[effect]
Next, the effect in the display apparatus 1 of this Embodiment is demonstrated.

  Incidentally, the Vth correction and the μ correction are performed by turning on the write transistor Tr2 connected to the gate of the drive transistor Tr1. That is, the period of Vth correction and μ correction is equal to the ON period of the write transistor Tr2. Here, the ON period of the write transistor Tr2 is determined by the width of the pulse applied to the gate of the write transistor Tr2, for example, as shown in FIG.

  However, the above-mentioned pulse is not a perfect rectangular wave but has a dullness as shown in FIG. Therefore, in practice, the period of Vth correction and μ correction can vary depending on the Vth of the writing transistor, as shown in FIG. When the μ correction period varies, as shown in FIG. 6, the magnitude of the current Ids that flows through the organic EL element 13 when the organic EL element 13 emits light changes, and the emission luminance also changes accordingly. Therefore, it is preferable that the μ correction period does not vary as much as possible.

  The threshold voltage Vth of the write transistor Tr2 changes (decreases) when a negative bias is continuously applied to the gate-source voltage of the write transistor Tr2. That is, the threshold voltage characteristic of the write transistor Tr2 shifts from enhancement to depletion. Usually, a negative bias is applied to the write transistor Tr2 during the light emission period and the extinction period of the organic EL element 13. When a negative bias is continuously applied to the gate-source voltage of the write transistor Tr2 (that is, as the drive period of the write transistor Tr2 elapses), a depletion shift occurs in the threshold voltage characteristic of the write transistor Tr2. As shown in FIG. 5 (B), Vth varies (decreases) from Vth1 to Vth2. As a result, the μ correction period becomes longer by Δt1 + Δt2 than the initial period. As a result, as shown in FIG. 6, the current Ids flowing through the organic EL element 13 when the organic EL element 13 emits light is reduced by ΔIds, and the emission luminance is also reduced accordingly. That is, as the usage period of the display device 1 elapses, the light emission luminance decreases.

  Further, as described above, since a negative bias is applied to the write transistor Tr2 during the light emission period and extinction period of the organic EL element 13, the threshold voltage characteristic of the write transistor Tr2 shifts from enhancement to depletion. As a result, for example, as shown in FIG. 7, even when an off voltage Voff is applied to the gate of the write transistor Tr2, a leakage current flows without sufficient cutoff, resulting in a decrease in light emission luminance. There is. Therefore, in order to sufficiently cut off the write transistor Tr2, for example, as shown in FIG. 8, the off voltage Voff is changed to a value (Voff_b) that is lower than the current value (Voff_a). It is possible to do. However, in such a case, the depletion shift is accelerated by the amount by which the off voltage Voff is lowered. For this reason, the time until the above-mentioned margin disappears is not significantly different between before and after the off voltage Voff is changed.

  On the other hand, in the present embodiment, the off voltage Voff is controlled (changed) so that the margin is always within a predetermined range. Thereby, the amount of current leakage due to the lack of the margin can be reduced. As a result, it is possible to reduce a decrease in light emission luminance due to a depletion shift. Furthermore, in this embodiment, since the acceleration of the depletion shift of the threshold voltage characteristic of the write transistor Tr2 can be minimized, the amount of change in the ON period of the write transistor Tr2 due to the depletion shift can be reduced. Can do. Thereby, even when Vth correction and μ correction are performed, it is possible to reduce a decrease in light emission luminance due to a depletion shift.

<2. Modification>
[Modification 1]
FIG. 13 illustrates a schematic configuration of a modification of the display device 1. In this modification, the display panel 10 has two types of dummy pixels 14 and 15 (a first dummy pixel and a second dummy pixel) in the frame region 10B. The configuration is different. Therefore, hereinafter, differences from the display device 1 of the above-described embodiment will be mainly described, and description of common points with the display device 1 of the above-described embodiment will be appropriately omitted.

  In this modification, the display panel 10 has two types of dummy pixels 14 and 15 as described above. As shown in FIG. 14A, the dummy pixel 14 has the same components as the pixel 11 of the above embodiment. On the other hand, as shown in FIG. 14B, the dummy pixel 15 corresponds to a circuit in which the organic EL element 13 is removed from the pixel 11 of the above-described embodiment and the portion where the organic EL element 13 is located is short-circuited.

  Next, a method for creating the table 33A in this modification will be described. In this modification, the drive circuit 20 uses the dummy pixels 14 and 15 at any time while the user is using the display device 1 after the display device 1 according to the modification is shipped, The table 33A is updated.

  In the display device 1 according to the present modification, for example, the drive circuit 20 first sets Voff (1) as the off voltage Voff, and the same type of waveform as the waveform applied to the pixel 11 with respect to the dummy pixels 14 and 15. Is repeatedly applied. At this time, the drive circuit 20 monitors each detection signal 25A during the light emission period (or the period corresponding thereto) in the initial period. Then, the drive circuit 20 can measure how the value of the detection signal 25A on the dummy pixel 14 side gradually decreases. At this time, for example, the drive circuit 20 matches (or substantially matches) the value of the detection signal 25A during the light emission period (or during the period corresponding thereto) with respect to the dummy pixels 14 at predetermined intervals. The value of the off voltage Voff to be searched is searched. For example, the drive circuit 20 gradually lowers the value of the off voltage Voff applied to the dummy pixel 14 from Voff (1) and keeps the value of the off voltage Voff for the dummy pixel 15 at Voff (1). The value (difference current value) obtained by subtracting the value of the detection signal 25A on the dummy pixel 14 side from the value of the detection signal 25A on the dummy pixel 15 side matches (or substantially matches) the initial difference current value. Search for the value of. Then, the drive circuit 20 records the value of the off voltage Voff found by the search in the memory 33, and executes this every time the value of the off voltage Voff is searched. The drive circuit 20 adds the created table 33A to the memory 33 each time the value of the off voltage Voff is searched.

  Next, effects of the display device 1 according to this modification will be described. In this modification, the off-voltage Voff is controlled (changed) using the table 33A updated as described above so that the margin is always within a predetermined range. Thereby, the fall of the light-emission brightness resulting from a depletion shift can be reduced. Furthermore, in this modification, since the acceleration of the depletion shift of the threshold voltage characteristic of the write transistor Tr2 can be minimized, the amount of change in the ON period of the write transistor Tr2 due to the depletion shift can be reduced. it can. Furthermore, the amount of current leakage due to the lack of the margin can be reduced. Thereby, even when Vth correction and μ correction are performed, it is possible to reduce a decrease in light emission luminance due to a depletion shift.

[Modification 2]
In the above embodiment and Modification 1, the drive circuit 20 performs Vth correction and μ correction, but these may be omitted. Even in this case, since the negative bias is applied to the write transistor Tr2 during the light emission period or the extinction period of the organic EL element 13, the threshold voltage characteristic of the write transistor Tr2 can be shifted from enhancement to depletion. However, in the present modification, as in the above-described embodiment and Modification 1, the off-voltage Voff is controlled (changed) so that the margin is always within a predetermined range. Thereby, since the amount of current leakage due to the lack of the margin can be reduced, it is possible to reduce the decrease in light emission luminance due to the depletion shift.

<3. Application example>
Hereinafter, application examples of the display device 1 described in the above embodiment and the modifications thereof will be described. The display device 1 according to the above-described embodiment or the like receives a video signal input from the outside or a video signal generated inside, such as a television device, a digital camera, a notebook personal computer, a mobile terminal device such as a mobile phone, or a video camera. The present invention can be applied to display devices of electronic devices in various fields that display as images or videos.

(Application example 1)
FIG. 15 illustrates an appearance of a television device to which the display device 1 according to the above-described embodiment or the like is applied. This television apparatus has, for example, a video display screen unit 300 including a front panel 310 and a filter glass 320, and the video display screen unit 300 is configured by the display device 1 according to the above-described embodiment or the like. .

(Application example 2)
FIG. 16 illustrates an appearance of a digital camera to which the display device 1 according to the above-described embodiment or the like is applied. The digital camera includes, for example, a flash light emitting unit 410, a display unit 420, a menu switch 430, and a shutter button 440. The display unit 420 is configured by the display device 1 according to the above-described embodiment or the like. Yes.

(Application example 3)
FIG. 17 illustrates an appearance of a notebook personal computer to which the display device 1 according to the above-described embodiment or the like is applied. The notebook personal computer includes, for example, a main body 510, a keyboard 520 for inputting characters and the like, and a display unit 530 for displaying an image. The display unit 530 is a display device such as the above-described embodiment. 1.

(Application example 4)
FIG. 18 illustrates an appearance of a video camera to which the display device 1 according to the above-described embodiment or the like is applied. This video camera has, for example, a main body 610, a subject photographing lens 620 provided on the front side surface of the main body 610, a start / stop switch 630 at the time of photographing, and a display 640. Reference numeral 640 denotes the display device 1 according to the above-described embodiment or the like.

(Application example 5)
FIG. 19 illustrates an appearance of a mobile phone to which the display device 1 according to the above-described embodiment and the like is applied. For example, the mobile phone is obtained by connecting an upper housing 710 and a lower housing 720 with a connecting portion (hinge portion) 730, and includes a display 740, a sub-display 750, a picture light 760, and a camera 770. Yes. The display 740 or the sub-display 750 is configured by the display device 1 according to the above-described embodiment or the like.

  As described above, the present technology has been described with reference to the embodiment and its modified examples and application examples, but the present technology is not limited to the above-described embodiment and the like, and various modifications are possible.

  For example, in the above embodiment and the like, the configuration of the pixel circuit 12 for active matrix driving is not limited to that described in the above embodiment and the like, and a capacitor and a transistor may be added as necessary. In that case, in addition to the display control circuit 21, the signal line drive circuit 22, the write line drive circuit 23, the power supply line drive circuit 24, the measurement circuit 25, and the like according to the change of the pixel circuit 12, necessary drive is performed. A circuit may be added.

For example, this technique can take the following composition.
(1)
A display unit having a light emitting element and a pixel circuit for each pixel in a display region;
A drive unit for driving the pixel circuit based on a video signal,
The pixel circuit includes:
A driving transistor for driving the light emitting element;
A write transistor that controls application of a signal voltage corresponding to a video signal to the gate of the drive transistor;
The drive unit is configured so that a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. A display device that controls the voltage.
(2)
The display device according to (1), wherein the driving unit is configured to reduce a current leak amount of the write transistor due to a depletion shift of a threshold voltage characteristic of the write transistor by controlling the off voltage. .
(3)
The drive unit includes a measurement unit that measures a value of a current flowing through the light emitting element or a physical quantity corresponding thereto,
The drive unit controls the off-voltage using a measurement value obtained by the measurement unit or a value obtained by performing a predetermined calculation on the measurement value. (1) Or the display apparatus as described in (2).
(4)
The drive unit has a table corresponding to a plurality of off voltages or a list of ones corresponding to a plurality of off voltages,
The driving unit uses the measurement value in the measurement unit or a value obtained by performing a predetermined calculation on the measurement value, a predetermined threshold value, and the table, to calculate the off voltage. The display device according to (3), wherein the display device is controlled.
(5)
The display section includes a first dummy pixel having the same structure as the light emitting element and the pixel circuit in a frame region around the display area, and the light emitting element is removed from the first dummy pixel and the light emitting element is removed. A second dummy pixel corresponding to a circuit short-circuited
The display device according to (4), wherein the driving unit is configured to update the table using the first dummy pixel and the second dummy pixel.
(6)
A display device,
The display device
A display unit having a light emitting element and a pixel circuit for each pixel in a display region;
A drive unit for driving the pixel circuit based on a video signal,
The pixel circuit includes:
A driving transistor for driving the light emitting element;
A write transistor that controls application of a signal voltage corresponding to a video signal to the gate of the drive transistor;
The drive unit is configured so that a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. An electronic device that is designed to control voltage.
(7)
A light emitting element and a pixel circuit are provided for each pixel in a display area, and the pixel circuit controls driving of a light emitting element and application of a signal voltage corresponding to a video signal to a gate of the driving transistor. In a display device including a transistor, a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. A method for driving a display device, comprising: controlling the off voltage.

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 10 ... Display panel, 10A ... Display area, 10B ... Frame area, 11, 111 ... Pixel, 12 ... Pixel circuit, 13 ... Organic EL element, 14, 15 ... Dummy pixel, 20 ... Drive circuit, 20A ... Video signal, 20B ... Synchronization signal, 21 ... Display control circuit, 21A ... Signal data, 21B, 21C, 21D, 32A ... Control signal, 22 ... Signal line drive circuit, 23 ... Write line drive circuit, 24 ... Power supply line Drive circuit, 24 ... measurement circuit, 25A ... detection signal, 31 ... conversion circuit, 32 ... controller, 33 ... memory, 33A ... table, 33B ... threshold, 300 ... video display screen section, 310 ... front panel, 320 ... filter glass , 410: Light emitting unit, 420, 530, 640 ... Display unit, 430 ... Menu switch, 440 ... Shutter button, 510 ... Main unit, 520 ... Key Board, 610 ... main body, 620 ... lens, 630 ... start / stop switch, 710 ... upper housing, 720 ... lower housing, 730 ... connecting portion, 740 ... display, 750 ... sub-display, 760 ... picture light, 770 ... Camera, Coled ... Element capacitance, Cs ... Retention capacitance, CTL ... Cathode line, DTL ... Signal line, DSL ... Power supply line, Ids ... Current, Vcc, Vofs, Von, Vsig, Vss ... Voltage, Vg ... Gate voltage, Vgs: gate-source voltage, Voff, Voff1, Voff2, Voff_a, Voff_b ... off voltage, Vs ... source voltage, Vth, Vth0, Vth1 ... threshold voltage, Tr1 ... drive transistor, Tr2 ... write transistor, WSL ... write line.

Claims (7)

A display unit having a light emitting element and a pixel circuit for each pixel in a display region;
A drive unit for driving the pixel circuit based on a video signal,
The pixel circuit includes:
A driving transistor for driving the light emitting element;
A write transistor that controls application of a signal voltage corresponding to a video signal to the gate of the drive transistor;
The drive unit is configured so that a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. A display device that controls the voltage. 2. The display device according to claim 1, wherein the drive unit is configured to reduce a current leakage amount of the write transistor due to a depletion shift of a threshold voltage characteristic of the write transistor by controlling the off voltage. . The drive unit includes a measurement unit that measures a value of a current flowing through the light emitting element or a physical quantity corresponding thereto,
2. The drive unit controls the off-voltage using a measurement value obtained by the measurement unit or a value obtained by performing a predetermined calculation on the measurement value. The display device described in 1. The drive unit has a table corresponding to a plurality of off voltages or a list of ones corresponding to a plurality of off voltages,
The driving unit uses the measurement value in the measurement unit or a value obtained by performing a predetermined calculation on the measurement value, a predetermined threshold value, and the table, to calculate the off voltage. The display device according to claim 3, wherein the display device is controlled. The display section includes a first dummy pixel having the same structure as the light emitting element and the pixel circuit in a frame region around the display area, and the light emitting element is removed from the first dummy pixel and the light emitting element is removed. A second dummy pixel corresponding to a circuit short-circuited
The display device according to claim 4, wherein the driving unit is configured to update the table using the first dummy pixel and the second dummy pixel. A display device,
The display device
A display unit having a light emitting element and a pixel circuit for each pixel in a display region;
A drive unit for driving the pixel circuit based on a video signal,
The pixel circuit includes:
A driving transistor for driving the light emitting element;
A write transistor that controls application of a signal voltage corresponding to a video signal to the gate of the drive transistor;
The drive unit is configured so that a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. An electronic device that is designed to control voltage. A light emitting element and a pixel circuit are provided for each pixel in a display area, and the pixel circuit controls driving of a light emitting element and application of a signal voltage corresponding to a video signal to a gate of the driving transistor. In a display device including a transistor, a difference between a threshold voltage of the write transistor and an off voltage applied to the gate of the write transistor when the write transistor is turned off is always within a predetermined range. A method for driving a display device, comprising: controlling the off voltage.

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