JP2010139699A - Display, method for driving display, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a luminance variation area from being visually recognized as a linear defect even if a gate of a driving transistor and a cathode of an organic EL element are electrically short-circuited in a pixel. <P>SOLUTION: In a display, pixels each of which includes an organic EL element 1D, a writing transistor 1A, a driving transistor 1B and a holding capacitor 1C are arranged in a matrix state. In this case, while a scanning signal is being given to a scanning line in a period during which a pixel line of preceding stage is driven, a video signal reference potential is given to a signal line DTL to correct the threshold value of the driving transistor 1B in its own pixel. At that time, the video signal reference potential and the cathode potential 1H of the organic EL element 1D both become the same potential Va. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device, a display device driving method, and an electronic apparatus. Specifically, the present invention relates to a planar (flat panel type) display device in which pixels including electro-optic elements are arranged in a matrix (matrix shape), a driving method of the display device, and an electronic apparatus.

  In recent years, in the field of display devices that perform image display, flat display devices in which pixels (pixel circuits) including light emitting elements are arranged in a matrix are rapidly spreading. As a flat display device, for example, an organic EL display device using an organic EL (Electro Luminescence) element that utilizes a phenomenon of emitting light when an electric field is applied to an organic thin film has been developed and commercialized.

  Since the organic EL element can be driven with an applied voltage of 10 V or less, it has low power consumption. Since the organic EL element is a self-luminous element, it has a feature that a light source (backlight) essential for a liquid crystal display device is not required. Furthermore, since the response speed of the organic EL element is as high as about several μsec, an afterimage at the time of displaying a moving image does not occur.

  In the organic EL display device, as in the liquid crystal display device, a simple (passive) matrix method and an active matrix method can be adopted as the driving method. In recent years, active matrix display devices in which active elements such as insulated gate field effect transistors (generally TFT (Thin Film Transistor)) are provided in a pixel circuit have been actively developed.

  By the way, it is generally known that the IV characteristic (current-voltage characteristic) of the organic EL element is deteriorated with time (so-called deterioration with time). In addition, the threshold voltage Vth of the driving transistor and the mobility of the semiconductor thin film constituting the channel of the driving transistor (hereinafter referred to as “mobility of the driving transistor”) μ change over time or due to variations in the manufacturing process. It varies from pixel to pixel.

  Therefore, in order to keep the light emission luminance of the organic EL element constant without being affected by these effects, a compensation function for the characteristic variation of the organic EL element, and further correction for the variation of the threshold voltage Vth of the driving transistor (hereinafter, referred to as the threshold voltage Vth). , And “correction of threshold value”), and correction for variations in the mobility μ of the driving transistor (hereinafter referred to as “mobility correction”). (For example, refer to Patent Document 1).

JP 2006-133542 A

  However, in the potential setting in the conventional pixel circuit, when the gate and the cathode of the driving transistor are short-circuited in the pixel, not only the defective pixel does not emit light, but also the luminance fluctuation area becomes linear in the pixel before the transfer. The problem of being visually recognized arises. From the viewpoint of visibility, it is not allowed to set a standard for the number of non-light-emitting pixels depending on the number in the display area. In particular, when it occurs in the display area, there is a problem of being visually recognized in a linear shape.

  In the present invention, even when the gate and the cathode of the driving transistor are electrically short-circuited in the pixel, the defective pixel is stopped only so as not to emit light, and the luminance variation area is not visually recognized as a linear defect. The purpose is to do.

  In the present invention, an anode electrode of an organic EL (Electro Luminescence) element and a source electrode of a driving transistor are connected, a gate electrode of the driving transistor and a source electrode or a drain electrode of a writing transistor are connected, and a gate-source of the driving transistor. A pixel array unit in which pixels including a circuit configuration in which a storage capacitor is connected between electrodes is arranged in a matrix, and a scan that provides a scanning signal to the gate electrode of the writing transistor, and is wired for each pixel row of the pixel array unit A power supply line that is wired for each pixel row of the pixel array portion and selectively applies a first potential and a second potential lower than the first potential to the drain electrode of the driving transistor, and the pixel array portion Video signal and video signal with respect to the drain electrode or source electrode of the writing transistor. A signal line that selectively applies a quasi-potential, and a video signal reference potential is applied to the signal line while the scanning signal is applied to the scanning line within the driving period of the preceding pixel row, and the threshold value of the driving transistor in the own pixel In performing the correction, the display device is such that the video signal reference potential is the same as the potential of the cathode electrode of the organic EL element. Further, the display device driving method is such that the video signal reference potential and the potential of the cathode electrode of the organic EL element are the same. Furthermore, the display device is an electronic device provided in a main body housing.

  In the present invention, even when the gate electrode and the cathode electrode of the driving transistor are electrically short-circuited within the pixel by setting the video signal reference potential and the cathode electrode potential to the same potential. The reference potential of the pixels in the previous pixel row can be made constant.

  According to the present invention, even when the gate electrode and the cathode electrode of the driving transistor are electrically short-circuited, the defective pixel is stopped only to emit no light, and the luminance variation area is prevented from being viewed in a linear shape. Is possible.

The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described below. The description will be given in the following order.
1. Display device (system configuration, pixel circuit, circuit operation) as a premise of the present embodiment
2. Problems when the gate and cathode of the drive transistor are short-circuited (equivalent circuit, timing waveform diagram)
3. Configuration example of this embodiment (pixel circuit, system configuration, driving method)
4). Application examples (various application examples to electronic devices)

<1. Display Device as Premise of Present Embodiment>
[System configuration]
FIG. 1 is a system configuration diagram showing an outline of the configuration of an active matrix display device which is a premise of the present embodiment.

  Here, as an example, a current-driven electro-optic element whose emission luminance changes in accordance with the value of current flowing through the device, for example, an organic EL element (organic electroluminescence element) is used as a light emitting element of a pixel (pixel circuit). The case of a matrix type organic EL display device will be described as an example.

  As shown in FIG. 1, the organic EL display device 100 includes a pixel array unit 102 in which pixels (PXLC) 101 are two-dimensionally arranged in a matrix (matrix shape), and a periphery of the pixel array unit 102. And a driving unit that drives each pixel 101. For example, a horizontal driving circuit 103, a writing scanning circuit 104, and a power supply scanning circuit 105 are provided as driving units that drive the pixels 101.

  In the pixel array unit 102, scanning lines WSL-1 to WSL-m and power supply lines DSL-1 to DSL-m are wired for each pixel row with respect to a pixel array of m rows and n columns, and each pixel column is provided. Are wired with signal lines DTL-1 to DTL-n.

  The pixel array unit 102 is usually formed on a transparent insulating substrate such as a glass substrate, and has a planar (flat) panel structure. Each pixel 101 of the pixel array unit 102 can be formed using an amorphous silicon TFT (Thin Film Transistor) or a low-temperature polysilicon TFT. When the low-temperature polysilicon TFT is used, the horizontal drive circuit 103, the write scanning circuit 104, and the power supply scanning circuit 105 can also be mounted on the display panel (substrate) that forms the pixel array unit 102.

  The write scanning circuit 104 is configured by a shift register or the like that sequentially shifts (transfers) the start pulse sp in synchronization with the clock pulse ck. When writing a video signal to each pixel 101 of the pixel array unit 102, the scanning line WSL- By sequentially supplying writing pulses (scanning signals) WS1 to WSm to 1 to WSL-m, each pixel 101 of the pixel array unit 102 is sequentially scanned (line sequential scanning) in units of rows.

  The power supply scanning circuit 105 includes a shift register that sequentially shifts the start pulse sp in synchronization with the clock pulse ck. The power supply scanning circuit 105 synchronizes with the line sequential scanning by the writing scanning circuit 104 and supplies power supply line potentials DS1 to DSm that are switched between the first potential Vcc_H and a second potential Vcc_L lower than the first potential Vcc_H. DSL-1 to DSL-m are selectively supplied. Thereby, the light emission / non-light emission of the pixel 101 is controlled.

  The horizontal driving circuit 103 includes a signal voltage Vsig of a video signal (hereinafter sometimes simply referred to as “signal voltage”) Vsig and a signal line reference potential Vo corresponding to luminance information supplied from a signal supply source (not shown). Any one of these is appropriately selected, and writing is performed, for example, in units of rows to each pixel 101 of the pixel array unit 102 via the signal lines DTL-1 to DTL-n. In other words, the horizontal driving circuit 103 adopts a line-sequential writing driving mode in which the signal voltage Vin of the video signal is written in units of rows.

  Here, the signal line reference potential Vo is a reference voltage (for example, a voltage corresponding to the black level) of the signal voltage Vin of the video signal. The second potential Vcc_L is lower than the signal line reference potential Vo, for example, a potential lower than Vo−Vth when the threshold voltage of the driving transistor is Vth, preferably sufficiently lower than Vo−Vth. Is set.

[Pixel circuit]
FIG. 2 is a circuit diagram illustrating a specific configuration example of a pixel (pixel circuit).

  As shown in FIG. 2, the pixel 101 has a current-driven electro-optical element, for example, an organic EL element 1D, whose emission luminance changes according to a current value flowing through the device, as the light-emitting element. In addition, the pixel configuration includes a driving transistor 1B, a writing transistor 1A, and a storage capacitor 1C, that is, a 2Tr / 1C pixel configuration including two transistors (Tr) and one capacitance element (C).

  In the pixel 101 having such a configuration, an N-channel TFT is used as the driving transistor 1B and the writing transistor 1A. However, the combination of the conductivity types of the driving transistor 1B and the writing transistor 1A here is only an example, and is not limited to these combinations.

  In the organic EL element 1D, a cathode electrode is connected to a common power supply line 1H wired in common to all the pixels 101. The drive transistor 1B has a source electrode connected to the anode electrode of the organic EL element 1D and a drain electrode connected to the power supply line DSL (DSL-1 to DSL-m).

  The write transistor 1A has a gate electrode connected to the scanning line WSL (WSL-1 to WSL-m) and one electrode (source electrode / drain electrode) connected to the signal line DTL (DTL-1 to DTL-n). The other electrode (drain electrode / source electrode) is connected to the gate electrode of the driving transistor 1B.

  The storage capacitor 1C has one electrode connected to the gate electrode of the drive transistor 1B and the other electrode connected to the source electrode of the drive transistor 1B (the anode electrode of the organic EL element 1D).

  In the pixel 101 having the pixel configuration of 2Tr / 1C, the writing transistor 1A is turned on in response to the scanning signal WS applied to the gate electrode from the writing scanning circuit 104 through the scanning line WSL, and thus is horizontally connected through the signal line DTL. The signal voltage Vin or the signal line reference potential Vo of the video signal corresponding to the luminance information supplied from the drive circuit 103 is sampled and written into the pixel 101.

  The written signal voltage Vin or signal line reference potential Vo is applied to the gate electrode of the driving transistor 1B and held in the holding capacitor 1C. When the potential DS of the power supply line DSL (DSL-1 to DSL-m) is at the first potential Vcc_H, the driving transistor 1B is supplied with current from the power supply line DSL and is held in the storage capacitor 1C. A drive current having a current value corresponding to the voltage value of the signal voltage Vin is supplied to the organic EL element 1D, and the organic EL element 1D is caused to emit light by current driving.

[Circuit operation of organic EL display device]
Next, the circuit operation of the organic EL display device 100 configured as described above will be described using the operation explanatory diagrams of FIGS. 4 to 6 based on the timing waveform diagram of FIG. In the operation explanatory diagrams of FIGS. 4 to 6, the write transistor 1 </ b> A is illustrated by a switch symbol for simplification of the drawings. Further, since the organic EL element 1D has a capacitive component, the EL capacitor 1I is also illustrated.

  In the timing waveform diagram of FIG. 3, the change in the potential (write pulse) WS of the scanning line WSL (WSL-1 to WSL-m), the potential DS (Vcc_H //) of the power supply line DSL (DSL-1 to DSL-m). Vcc_L), and changes in the gate potential Vg and the source potential Vs of the driving transistor 1B.

(Light emission period)
In the timing waveform diagram of FIG. 3, the organic EL element 1D is in the light emitting state before the time t1 (light emitting period). In this light emission period, the potential DS of the power supply line DSL is at the first potential Vcc_H, and the writing transistor 1A is in a non-conduction state.

  At this time, since the driving transistor 1B is set to operate in the saturation region, as shown in FIG. 4A, the gate-source voltage of the driving transistor 1B is supplied from the power supply line DSL through the driving transistor 1B. A drive current (drain-source current) Ids corresponding to Vgs is supplied to the organic EL element 1D. Therefore, the organic EL element 1D emits light with a luminance corresponding to the current value of the drive current Ids.

(Threshold correction preparation period)
At time t1, a new field of line sequential scanning is entered, and the potential DS of the power supply line DSL is changed from the first potential (hereinafter referred to as “high potential”) Vcc_H as shown in FIG. 4B. The second potential (hereinafter referred to as “low potential”) Vcc_L that is sufficiently lower than the signal line reference potential Vo−Vth of the signal line DTL is switched.

  Here, when the threshold voltage of the organic EL element 1D is Vel and the potential of the common power supply line 1H is Vcath, if the low potential Vcc_L is Vcc_L <Vel + Vcath, the source potential Vs of the driving transistor 1B is substantially equal to the low potential Vcc_L. For this reason, the organic EL element 1D becomes in a reverse bias state and extinguishes.

  Next, when the potential WS of the scanning line WSL transits from the low potential side to the high potential side at time t2, as shown in FIG. 4C, the writing transistor 1A is turned on. At this time, since the signal line reference potential Vo is supplied from the horizontal drive circuit 103 to the signal line DTL, the gate potential Vg of the drive transistor 1B becomes the signal line reference potential Vo. The source potential Vs of the drive transistor 1B is at a potential Vcc_L that is sufficiently lower than the signal line reference potential Vo.

  At this time, the gate-source voltage Vgs of the drive transistor 1B is Vo-Vcc_L. Here, if Vo−Vcc_L is not larger than the threshold voltage Vth of the driving transistor 1B, a threshold correction operation described later cannot be performed. Therefore, it is necessary to set a potential relationship of Vo−Vcc_L> Vth. In this way, the operation for fixing and fixing the gate potential Vg of the driving transistor 1B to the signal line reference potential Vo and the source potential Vs to the low potential Vcc_L is the threshold correction preparation operation.

(First threshold correction period)
Next, at time t3, as shown in FIG. 4D, when the potential DS of the power supply line DSL is switched from the low potential Vcc_L to the high potential Vcc_H, the source potential Vs of the driving transistor 1B starts to increase. The second threshold correction period starts. In the first threshold correction period, the source potential Vs of the drive transistor 1B rises, whereby the gate-source voltage Vgs of the drive transistor 1B becomes a predetermined potential Vx1, and this potential Vx1 is held in the holding capacitor 1C. .

  Subsequently, at time t4 in the second half of the horizontal period (1H), as shown in FIG. 5A, the signal voltage Vin of the video signal is supplied from the horizontal drive circuit 103 to the signal line DTL. As a result, the potential of the signal line DTL transits from the signal line reference potential Vo to the signal voltage Vin. In this period, the signal voltage Vin is written to the pixels in other rows.

  At this time, in order to prevent writing of the signal voltage Vin to the pixels in the own row, the potential WS of the scanning line WSL is changed from the high potential side to the low potential side, and the writing transistor 1A is turned off. To do. As a result, the gate electrode of the driving transistor 1B is disconnected from the signal line DTL and is in a floating state.

  Here, when the gate electrode of the drive transistor 1B is in a floating state, if the source potential Vs of the drive transistor 1B varies due to the storage capacitor 1C being connected between the gate and source of the drive transistor 1B, the source The gate potential Vg of the drive transistor 1B varies in conjunction with (follows) the variation in the potential Vs. This is a bootstrap operation by the storage capacitor 1C.

  Even after time t4, the source potential Vs of the drive transistor 1B continues to rise and rises by Va1 (Vs = Vo−Vx1 + Va1). At this time, due to the bootstrap operation, the gate potential Vg also rises by Va1 (Vg = Vo + Va1) in conjunction with the rise of the source potential Vs of the drive transistor 1B.

(Second threshold correction period)
At the time t5, the next horizontal period starts, and as shown in FIG. 5B, the potential WS of the scanning line WSL transitions from the low potential side to the high potential side, and the writing transistor 1A becomes conductive, and at the same time, the horizontal drive is performed. The signal line reference potential Vo is supplied from the circuit 103 to the signal line DTL instead of the signal voltage Vin, and the second threshold correction period starts.

  In the second threshold correction period, the signal line reference potential Vo is written by turning on the write transistor 1A, so that the gate potential Vg of the drive transistor 1B is initialized to the signal line reference potential Vo again. At this time, the source potential Vs also decreases in conjunction with the decrease in the gate potential Vg. Again, the source potential Vs of the drive transistor 1B starts to rise.

  In the second threshold correction period, the source potential Vs of the drive transistor 1B rises, whereby the gate-source voltage Vgs of the drive transistor 1B becomes a predetermined potential Vx2, and this potential Vx2 is held in the holding capacitor 1C. Is done.

  Subsequently, at time t6 when the second half of the horizontal period starts, as shown in FIG. 5C, the signal voltage Vin of the video signal is supplied from the horizontal drive circuit 103 to the signal line DTL, so that the signal The potential of the line DTL transits from the offset voltage Vo to the signal voltage Vin. In this period, the signal voltage Vin is written to the pixels in another row (the row next to the previous writing row).

  At this time, in order to prevent writing of the signal voltage Vin to the pixels in the own row, the potential WS of the scanning line WSL is changed from the high potential side to the low potential side, and the writing transistor 1A is turned off. To do. As a result, the gate electrode of the driving transistor 1B is disconnected from the signal line DTL and is in a floating state.

  Even after time t6, the source potential Vs of the drive transistor 1B continues to rise and rises by Va2 (Vs = Vo−Vx1 + Va2). At this time, due to the bootstrap operation, the gate potential Vg also increases by Va2 in conjunction with the increase in the source potential Vs of the drive transistor 1B (Vg = Vo + Va2).

(Third threshold correction period)
At the time t7, the next horizontal period starts, and as shown in FIG. 5D, the potential WS of the scanning line WSL transitions from the low potential side to the high potential side, and the writing transistor 1A becomes conductive, and at the same time, the horizontal drive is performed. The signal line reference potential Vo is supplied from the circuit 103 to the signal line DTL instead of the signal voltage Vin, and the third threshold correction period starts.

  In the third threshold correction period, the signal line reference potential Vo is written by turning on the write transistor 1A, so that the gate potential Vg of the drive transistor 1B is initialized to the signal line reference potential Vo again. At this time, the source potential Vs also decreases in conjunction with the decrease in the gate potential Vg. Again, the source potential Vs of the drive transistor 1B starts to rise.

  When the source potential Vs of the driving transistor 1B rises and the gate-source voltage Vgs of the driving transistor 1B eventually converges to the threshold voltage Vth of the driving transistor 1B, a voltage corresponding to the threshold voltage Vth becomes a holding capacitor 1C. Retained.

  Through the above-described three threshold correction operations, the threshold voltage Vth of the drive transistor 1B for each pixel is detected, and a voltage corresponding to the threshold voltage Vth is held in the storage capacitor 1C. In order to prevent the current from flowing exclusively to the storage capacitor 1C and not to the organic EL element 1D in the three threshold correction periods, a common power supply is provided so that the organic EL element 1D is cut off. Assume that the potential Vcath of the line 1H is set.

(Signal writing period & mobility correction period)
Next, at time t8, the potential WS of the scanning line WSL shifts to the low potential side, so that the writing transistor 1A is turned off as shown in FIG. 6A, and at the same time, the potential of the signal line DTL is offset. The voltage Vo is switched to the signal voltage Vin of the video signal.

  When the writing transistor 1A is turned off, the gate electrode of the driving transistor 1B enters a floating state. However, since the gate-source voltage Vgs is equal to the threshold voltage Vth of the driving transistor 1B, the driving transistor 1B is cut off. Is in a state. Therefore, the drain-source current Ids does not flow through the driving transistor 1B.

  Subsequently, at time t9, the potential WS of the scanning line WSL transitions to the high potential side, so that the writing transistor 1A becomes conductive as shown in FIG. 6B, and the signal voltage Vin of the video signal is sampled. To write in the pixel 101. By writing the signal voltage Vin by the writing transistor 1A, the gate potential Vg of the driving transistor 1B becomes the signal voltage Vin.

  When the driving transistor 1B is driven by the signal voltage Vin of the video signal, the threshold voltage correction is performed by canceling the threshold voltage Vth of the driving transistor 1B with the voltage corresponding to the threshold voltage Vth held in the holding capacitor 1C. Done. The principle of threshold correction will be described later.

  At this time, since the organic EL element 1D is initially in a cut-off state (high impedance state), a current (drain-source current Ids) that flows from the power supply line DSL to the drive transistor 1B according to the signal voltage Vin of the video signal. Flows into the EL capacitor 1I of the organic EL element 1D, and thus charging of the EL capacitor 1I is started.

  Due to the charging of the EL capacitor 1I, the source potential Vs of the driving transistor 1B rises with time. At this time, the variation of the threshold voltage Vth of the driving transistor 1B has already been corrected (threshold correction), and the drain-source current Ids of the driving transistor 1B depends on the mobility μ of the driving transistor 1B.

  Eventually, when the source potential Vs of the drive transistor 1B rises to the potential of Vo−Vth + ΔV, the gate-source voltage Vgs of the drive transistor 1B becomes Vin + Vth−ΔV. That is, the increase ΔV of the source potential Vs is subtracted from the voltage (Vin + Vth−ΔV) held in the holding capacitor 1C, in other words, it acts to discharge the charge stored in the holding capacitor 1C, thereby negative feedback. Has been applied. Therefore, the increase ΔV of the source potential Vs becomes a feedback amount of negative feedback.

  In this way, the drain-source current Ids flowing through the drive transistor 1B is negatively fed back to the gate input of the drive transistor 1B, that is, the gate-source voltage Vgs, so that the drain-source current Ids of the drive transistor 1B is reduced. Mobility correction is performed to cancel the dependence on the mobility μ, that is, to correct the variation of the mobility μ for each pixel.

  More specifically, since the drain-source current Ids increases as the signal voltage Vin of the video signal increases, the absolute value of the feedback amount (correction amount) ΔV of negative feedback also increases. Therefore, the mobility correction according to the light emission luminance level is performed. In addition, when the signal voltage Vin of the video signal is constant, the absolute value of the feedback amount ΔV of the negative feedback increases as the mobility μ of the driving transistor 1B increases, so that the variation in mobility μ for each pixel is removed. Can do. The principle of mobility correction will be described later.

(Light emission period)
Next, at time t10, the potential WS of the scanning line WSL shifts to the low potential side, so that the writing transistor 1A is turned off as illustrated in FIG. 6C. As a result, the gate electrode of the driving transistor 1B is disconnected from the signal line DTL and is in a floating state.

  The gate electrode of the driving transistor 1B enters a floating state, and at the same time, the drain-source current Ids of the driving transistor 1B starts to flow into the organic EL element 1D, whereby the anode potential of the organic EL element 1D becomes the drain of the driving transistor 1B. -Increases according to the source-to-source current Ids.

  The increase in the anode potential of the organic EL element 1D is none other than the increase in the source potential Vs of the drive transistor 1B. When the source potential Vs of the driving transistor 1B increases, the gate potential Vg of the driving transistor 1B also increases in conjunction with the bootstrap operation of the storage capacitor 1C.

  At this time, assuming that the bootstrap gain is 1 (ideal value), the amount of increase in the gate potential Vg is equal to the amount of increase in the source potential Vs. Therefore, the gate-source voltage Vgs of the drive transistor 1B is kept constant at Vin + Vth−ΔV during the light emission period. At time t11, the potential of the signal line DTL is switched from the signal voltage Vin of the video signal to the signal line reference potential Vo.

  As is apparent from the above description of the operation, in this example, a threshold correction period is provided over a total of 3H periods, that is, a 1H period in which signal writing and mobility correction are performed and a 2H period preceding the 1H period. . As a result, a sufficient time can be secured as the threshold correction period, so that the threshold voltage Vth of the drive transistor 1B can be reliably detected and held in the storage capacitor 1C, and the threshold correction operation can be performed reliably.

  Although the threshold correction period is provided over the 3H period, this is only an example. If a sufficient time can be secured as the threshold correction period in the 1H period in which signal writing and mobility correction are performed, the preceding period is set. It is not necessary to set the threshold correction period over the horizontal period, and the 1H period becomes shorter as the definition becomes higher, and even if the threshold correction period is provided over the 3H period, sufficient time cannot be secured. For example, the threshold correction period can be set over the 4H period.

<2. Problems when the gate-cathode of the drive transistor is short-circuited>
[Equivalent circuit]
FIG. 7A shows an equivalent circuit when the gate g and the cathode 1H of the driving transistor 1B are electrically short-circuited in the pixel circuit shown in FIG. As an example of the operation timing, the video signal reference potential Vo is written as shown in FIGS. 4D, 5B, and 5D.

  Thus, when the gate g of the driving transistor 1B is electrically short-circuited with the cathode 1H wired with a low impedance, the video signal line DTL and the gate g of the driving transistor 1B can be obtained when the writing transistor 1A is on. The cathode 1H enters the same state. Therefore, the video signal reference potential Vo supplied to the video signal line DTL is drawn to the cathode potential Vcath.

  FIG. 7B is a schematic diagram showing a display state when the defect of FIG. 7A occurs. A defective pixel, that is, a pixel in which the gate g and the cathode 1H of the driving transistor 1B are electrically shorted as shown in FIG. 7A does not emit light. Further, several pixels in the pre-transfer stage are brightness variation areas. The luminance variation area depends on the transfer direction, and always occurs on the pre-transfer side.

[Timing waveform diagram]
FIG. 8 is a timing waveform diagram when the defect of FIG. Further, in FIG. 7, the relationship of Vo> Vcath is taken as an example. In this timing waveform diagram, Vn−6 to Vn + 2 indicate the scanning line timing at the scanning line number, and the defective pixel corresponds to Vn. In addition, switching of the video signal potential is shown in DTL. Each period of FIGS. 8A to 8L corresponds to one horizontal period (1H).

  As shown in FIG. 7A, when the gate g and the cathode 1H of the driving transistor 1B are electrically short-circuited, a problem occurs in the period of FIGS. 8F to 8J. That is, when the scanning line WSL of the defective pixel Vn transitions to the high potential side during this period, the potential supplied to the video signal line DTL at that timing is drawn to the cathode potential Vcath.

  As a result, in the pixels Vn−4 to Vn−1, the video signal reference potential Vo immediately before the video signal potential sampling is drawn to Vcath. As a result, the input amplitude to the gate g of the driving transistor 1B is not Vin = Vsig−Vo but Vin ′ = Vsig−Vcath.

  In FIG. 8, since Vo> Vcath, the pixels Vn−4 to Vn−1 are equivalently written with higher amplitude than when the video signal reference potential Vo is used as a reference. Therefore, the luminance rises during the period from Vn-4 to Vn-1. As a result, a luminance increase occurs for several pixels preceding the defective pixel and is visually recognized as a linear luminance increase area. The defective pixel Vn does not emit light because the video signal potential Vsig is also drawn to the cathode potential Vcath.

<3. Configuration example of this embodiment>
[Pixel circuit]
FIG. 9 is a circuit diagram for explaining pixel potential setting according to an example of the present embodiment. The pixel circuit includes an organic EL element 1D, a driving transistor 1B, a writing transistor 1A, and a storage capacitor 1C.

  Specifically, the anode electrode of the organic EL element 1D and the source electrode of the drive transistor 1B are connected, and the gate electrode of the drive transistor 1B and the source electrode or drain electrode of the write transistor 1A are connected. A holding capacitor 1C is connected between the gate and source electrodes of the driving transistor 1B.

  The signal line DTL is connected to the drain electrode or the source electrode of the writing transistor 1A. A scanning line (not shown) is connected to the gate electrode of the writing transistor 1A, and given timing is given. The power supply line DSL is connected to the drain electrode of the drive transistor 1B.

  In such a pixel circuit configuration, in this embodiment, the video signal reference potential Vo applied to the signal line DTL and the cathode electrode potential (cathode potential) Vcath of the organic EL element 1D are set to the same potential Va. ing. As a result, the video signal reference potential Vo is not drawn to a potential higher or lower than Va even during the period of FIGS. 8F to 8J, and the occurrence of a luminance variation area can be prevented for the previous pixel. It becomes possible.

  Here, the video signal reference potential and the cathode potential are not values that can be arbitrarily set with respect to other driving potentials, and must satisfy the driving conditions such as the threshold correction operation shown in FIG. In order to make the video signal reference potential and the cathode potential equal, in addition to adjusting the video signal reference potential to the cathode potential, the cathode potential may be adjusted to the video signal reference potential. Further, it may be adjusted to a constant potential other than these. Preferably, Va satisfies the driving condition shown in FIG. 3 by setting it to the conventional setting potential Vo or Vcath.

[System configuration]
FIG. 10 is a system configuration diagram illustrating an example of the present embodiment. As shown in FIG. 10, the organic EL display device 100 includes a pixel array unit 102 in which pixels (PXLC) 101 are two-dimensionally arranged in a matrix (matrix shape), and a periphery of the pixel array unit 102. And a driving unit that drives each pixel 101. For example, a horizontal driving circuit 103, a writing scanning circuit 104, and a power supply scanning circuit 105 are provided as driving units that drive the pixels 101.

  In the pixel array unit 102, scanning lines WSL-1 to WSL-m and power supply lines DSL-1 to DSL-m are wired for each pixel row with respect to a pixel array of m rows and n columns, and each pixel column is provided. Are wired with signal lines DTL-1 to DTL-n. These configurations are the same as the system configuration shown in FIG.

  In the present embodiment, the video signal reference potential Vo given to each pixel 101 from the signal lines DTL-1 to ETL-n and the potential (cathode potential) at the cathode electrode of the organic EL element of each pixel 101 are the same potential. It is set to Va.

  Here, the cathode potential is applied as a common potential to the organic EL element of each pixel 101. Therefore, the potential Va is applied to the common wiring COM that is electrically connected to the cathode electrode of the organic EL element of each pixel 101.

  On the other hand, the video signal reference potential Vo given from the signal lines DTL-1 to ETL-n is also set to the potential Va. The horizontal drive circuit 103 selectively gives a signal potential Vin and a video signal reference potential Vo to the signal lines DTL-1 to ETL-n. Therefore, when the video signal reference potential Vo is selected, control is performed so as to apply the potential Va.

  As a result, while the scanning signal is supplied to the scanning line within the driving period of the previous pixel row, the video signal reference potential is Va during the period in which the video signal reference potential is applied to the signal line and the threshold value of the driving transistor in the own pixel is corrected. It is not drawn to a higher or lower potential. That is, even when the gate of the drive transistor and the cathode of the organic EL element are electrically short-circuited, it is possible to prevent the occurrence of a luminance variation area for the previous stage pixel.

[Driving method]
FIG. 11 is a timing waveform diagram illustrating a method for driving the display device according to the present embodiment. The timing waveform diagram shown in FIG. 11 repeats the light emission period, threshold correction period, sampling period & mobility correction period as in the timing waveform diagram shown in FIG. 3, but the video signal reference potential applied to the signal line is the cathode. The difference is that Va is the same potential as the potential.

  The video signal line potential (DTL) is selectively switched between the video signal Vin and the video signal reference potential Va. At this time, when the video signal reference potential becomes Va, the gate potential (Vg) of the driving transistor is set to the potential Va in the threshold correction period. Since the same potential Va is used for all the pixels, the luminance uniformity is not lost.

  FIG. 12 is a timing waveform diagram when a defect in which the gate g and the cathode 1H of the driving transistor 1B are electrically short-circuited occurs in the pixel configuration of the present embodiment shown in FIG. In this timing waveform diagram, Vn−6 to Vn + 2 indicate the scanning line timing at the scanning line number, and the defective pixel corresponds to Vn. In addition, switching of the video signal potential is shown in DTL. Each period of FIGS. 12A to 12L corresponds to one horizontal period (1H).

  As shown in FIG. 9, when the gate g and the cathode 1H of the driving transistor 1B are electrically short-circuited, a problem occurs in the period of FIGS. 8F to 8J in the conventional configuration. That is, when the scanning line WSL of the defective pixel Vn transitions to the high potential side during this period, the potential supplied to the video signal line DTL at that timing is drawn to the cathode potential Vcath (see the broken line in FIG. 12).

  On the other hand, in the configuration of the present embodiment, the video signal reference potential Vo applied to the DTL is Vo = Va, and the cathode potential Vcath is Vcath = Va. That is, control is performed so that the video signal reference potential Vo = cathode potential Vcath = Va.

  As a result, in the pixels Vn−4 to Vn−1, the video signal reference potential immediately before the video signal potential sampling is Va, which is the same reference as other pixels. As a result, the input amplitude to the gate g of the driving transistor 1B becomes Vin = Vsig−Va, and the luminance does not increase for several pixels preceding the defective pixel Vn.

  In the above embodiment, the case where the present invention is applied to an organic EL display device using an organic EL element as the electro-optical element of the pixel 101 has been described as an example. However, the present invention is not limited to this application example. The present invention can be applied to all display devices using current-driven electro-optic elements (light-emitting elements) whose light emission luminance varies depending on the value of current flowing through the device.

  In addition, as a configuration of the pixel 101, a 2Tr / 1C pixel configuration including two transistors (Tr) and one capacitor element (C) is taken as an example, but the present invention is not limited to this. For example, four transistors Other pixel configurations such as a 4Tr / 1C pixel configuration including (Tr) and one capacitor (C) are also applicable.

<4. Application example>
The display device according to the present embodiment described above is applied to various electronic devices shown in FIGS. 13 to 17 as an example. For example, any video signal input to an electronic device such as a digital camera, a notebook personal computer, a portable terminal device such as a mobile phone, a video camera, or a video signal generated in the electronic device is displayed as an image or video. It can be applied to display devices of electronic devices in the field.

  As described above, since the display device according to this embodiment can be used as a display device for electronic devices in various fields, the image quality of a display image can be improved. Therefore, various electronic devices can display high-quality images. There are advantages that can be made.

  Note that the display device according to the present embodiment includes a module-shaped one with a sealed configuration. For example, a display module formed by being attached to an opposing portion such as transparent glass on the pixel array portion 102 corresponds. The transparent facing portion may be provided with a color filter, a protective film, and the like, and further the above-described light shielding film. Note that the display module may be provided with a circuit unit for inputting / outputting a signal and the like from the outside to the pixel array unit, an FPC (flexible printed circuit), and the like.

  Hereinafter, specific examples of electronic devices to which the display device of this embodiment is applied will be described.

  FIG. 13 is a perspective view showing an appearance of a television set to which the present embodiment is applied. The television television set according to this application example includes a video display screen unit 107 including a front panel 108, a filter glass 109, and the like, and is created by using the display device according to the present embodiment as the video display screen unit 107. The

  14A and 14B are perspective views showing the external appearance of a digital camera to which the present embodiment is applied. FIG. 14A is a perspective view seen from the front side, and FIG. 14B is a perspective view seen from the back side. The digital camera according to this application example includes a light emitting unit 111 for flash, a display unit 112, a menu switch 113, a shutter button 114, and the like, and is manufactured by using the display device according to the present embodiment as the display unit 112.

  FIG. 15 is a perspective view showing an appearance of a notebook personal computer to which the present embodiment is applied. The notebook personal computer according to this application example includes a main body 121 including a keyboard 122 that is operated when characters and the like are input, a display unit 123 that displays an image, and the like. The display unit 123 includes the display device according to the present embodiment. It is produced by using.

  FIG. 16 is a perspective view showing an appearance of a video camera to which the present embodiment is applied. The video camera according to this application example includes a main body 131, a subject shooting lens 132 on a side facing forward, a start / stop switch 133 at the time of shooting, a display unit 134, and the like. It is manufactured by using the display device.

  17A and 17B are external views showing a mobile terminal device, for example, a mobile phone, to which the present embodiment is applied. FIG. 17A is a front view in an opened state, FIG. 17B is a side view thereof, and FIG. (D) is a left side view, (E) is a right side view, (F) is a top view, and (G) is a bottom view. The mobile phone according to this application example includes an upper housing 141, a lower housing 142, a connecting portion (here, a hinge portion) 143, a display 144, a sub display 145, a picture light 146, a camera 147, and the like. The sub-display 145 is manufactured by using the display device according to the present embodiment.

1 is a system configuration diagram showing an outline of the configuration of an active matrix organic EL display device as a premise of the present invention. It is a circuit diagram which shows the specific structural example of a pixel (pixel circuit). FIG. 6 is a timing waveform diagram for explaining the operation of the active matrix organic EL display device as a premise of the present invention. It is explanatory drawing (the 1) of the circuit operation | movement of the active matrix type organic electroluminescent display apparatus used as the premise of this invention. It is explanatory drawing (the 2) of the circuit operation | movement of the active matrix type organic electroluminescent display apparatus used as the premise of this invention. It is explanatory drawing (the 3) of the circuit operation | movement of the active matrix type organic electroluminescent display apparatus used as the premise of this invention. It is a figure explaining the influence by the short of a drive transistor. It is a timing waveform diagram when a defect occurs. It is a circuit diagram for demonstrating pixel electric potential setting which shows an example of this embodiment. It is a system configuration figure showing an example of this embodiment. It is a timing waveform diagram explaining the drive method of the display device according to the present embodiment. It is a timing waveform diagram when a defect occurs in the pixel configuration of the present embodiment. It is a perspective view which shows the external appearance of the television set to which this embodiment is applied. It is the perspective view which shows the external appearance of the digital camera to which this embodiment is applied, (A) is the perspective view seen from the front side, (B) is the perspective view seen from the back side. It is a perspective view which shows the external appearance of the notebook type personal computer to which this embodiment is applied. It is a perspective view which shows the external appearance of the video camera to which this embodiment is applied. BRIEF DESCRIPTION OF THE DRAWINGS It is an external view which shows the mobile telephone to which this embodiment is applied, (A) is the front view in the open state, (B) is the side view, (C) is the front view in 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.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Organic EL display device, 101 ... Pixel (pixel circuit), 102 ... Pixel array part, 103 ... Horizontal drive circuit, 104 ... Write scanning circuit, 105 ... Power supply scanning circuit, 1A ... Write transistor, 1B ... Drive transistor, 1C: holding capacitor, 1D: organic EL element, DSL-1 to DSL-m: power supply line, DTL-1 to DTL-n: signal line, WSL-1 to WSL-m: scanning line

Claims (6)

An anode electrode of an organic EL (Electro Luminescence) element and a source electrode of a driving transistor are connected, a gate electrode of the driving transistor and a source electrode or a drain electrode of a writing transistor are connected, and between the gate and source electrodes of the driving transistor A pixel array unit in which pixels including a circuit configuration to which a storage capacitor is connected are arranged in a matrix;
A scanning line that is wired for each pixel row of the pixel array unit and that supplies a scanning signal to the gate electrode of the writing transistor;
A power supply line that is wired for each pixel row of the pixel array portion and selectively applies a first potential and a second potential lower than the first potential to the drain electrode of the drive transistor;
A signal line that is arranged for each pixel column of the pixel array section and selectively applies a video signal and a video signal reference potential to a drain electrode or a source electrode of the write transistor;
While the scanning signal is applied to the scanning line within the driving period of the previous pixel row, the video signal reference potential is applied to the signal line and the threshold value of the driving transistor in the pixel is corrected. The display device in which the potential of the cathode electrode of the organic EL element is the same. The display device according to claim 1, wherein the video signal reference potential is matched with the potential of the cathode electrode. The display device according to claim 1, wherein a potential of the cathode electrode is adjusted to the video signal reference potential. An electro-optical element; a writing transistor for writing a video signal; a holding capacitor for holding the video signal written by the writing transistor; and driving the electro-optical element based on the video signal held in the holding capacitor. A pixel array unit in which pixels including drive transistors are arranged in a matrix;
A scanning line that is wired for each pixel row of the pixel array unit and that supplies a scanning signal to the writing transistor;
A power supply line that is wired for each pixel row of the pixel array portion and selectively applies a first potential and a second potential lower than the first potential to the drain electrode of the drive transistor;
A signal line that is arranged for each pixel column of the pixel array unit and selectively gives a video signal and a video signal reference potential to the writing transistor;
While the scanning signal is applied to the scanning line within the driving period of the previous pixel row, the video signal reference potential is applied to the signal line and the threshold value of the driving transistor in the pixel is corrected. A display device in which the common potential of the electro-optic element is the same. An anode electrode of an organic EL (Electro Luminescence) element and a source electrode of a driving transistor are connected, a gate electrode of the driving transistor and a source electrode or a drain electrode of a writing transistor are connected, and between the gate and source electrodes of the driving transistor A pixel array unit in which pixels including a circuit configuration to which a storage capacitor is connected are arranged in a matrix;
A scanning line that is wired for each pixel row of the pixel array unit and that supplies a scanning signal to the gate electrode of the writing transistor;
A power supply line that is wired for each pixel row of the pixel array portion and selectively applies a first potential and a second potential lower than the first potential to the drain electrode or the source electrode of the drive transistor;
A display device that is provided for each pixel column of the pixel array unit and includes a signal line that selectively applies a video signal and a video signal reference potential to the drain electrode of the write transistor.
While the scanning signal is applied to the scanning line within the driving period of the previous pixel row, the video signal reference potential is applied to the signal line and the threshold value of the driving transistor in the pixel is corrected. And the potential of the cathode electrode of the organic EL element are set to the same potential. The main unit housing is equipped with a display device,
The display device
An anode electrode of an organic EL (Electro Luminescence) element and a source electrode of a driving transistor are connected, a gate electrode of the driving transistor and a source electrode or a drain electrode of a writing transistor are connected, and between the gate and source electrodes of the driving transistor A pixel array unit in which pixels including a circuit configuration to which a storage capacitor is connected are arranged in a matrix;
A scanning line that is wired for each pixel row of the pixel array unit and that supplies a scanning signal to the gate electrode of the writing transistor;
A power supply line that is wired for each pixel row of the pixel array portion and selectively applies a first potential and a second potential lower than the first potential to the drain electrode of the drive transistor;
A signal line that is arranged for each pixel column of the pixel array section and selectively applies a video signal and a video signal reference potential to a drain electrode or a source electrode of the write transistor;
While the scanning signal is applied to the scanning line within the driving period of the previous pixel row, the video signal reference potential is applied to the signal line, and the threshold value of the driving transistor in the own pixel is corrected. An electronic device in which the potential of the cathode electrode of the organic EL element is the same.

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