JP2009237425A - Display device, method for driving display device, and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely correct the threshold voltage Vth and mobility μ of a driving transistor and threshold dispersion following the aging degradation of an organic EL element by preventing turn-on of the organic EL element within a mobility correction period. <P>SOLUTION: An organic EL display device carries out mobility correction processing of applying negative feedback to the gate input side of the driving transistor with the correction quantity ΔV corresponding to a current (a current Ids between a drain and a source) flowing to the driving transistor, side by side with write processing of signal voltage Vsig of an image signal by a writing transistor. In the signal writing period and mobility correction period, the potential Ds of a power supply line is not maintained to high potential Vccp but lowered to third source potential Vccp2 lower than the high potential Vccp and allowing the conductive state of the driving transistor to be maintained. Turn-on of the organic EL element within the signal writing period and mobility correction period is thereby prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device, a driving method of the display device, and an electronic apparatus, and more particularly, a flat-type (flat panel type) display device in which pixels including electro-optical elements are two-dimensionally arranged in a matrix (matrix shape), and the display The present invention relates to a device driving method and an electronic apparatus having the display device.

  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, as a light emitting element of a pixel, a so-called current-driven electro-optical element whose light emission luminance changes according to a current value flowing through the device, for example, a phenomenon of emitting light when an electric field is applied to an organic thin film is used. An organic EL display device using an organic EL (Electro Luminescence) element has been developed and commercialized.

  The organic EL display device has the following features. That is, since the organic EL element can be driven with an applied voltage of 10 V or less, the power consumption is low. Since the organic EL element is a self-luminous element, image visibility is higher than that of a liquid crystal display device that displays an image by controlling the light intensity from a light source (backlight) with a liquid crystal for each pixel. In addition, since an illumination member such as a backlight is not required, it is easy to reduce the weight and thickness. 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.

  As in the liquid crystal display device, the organic EL display device can adopt a simple (passive) matrix method and an active matrix method as its driving method. However, although the simple matrix display device has a simple structure, the light-emission period of the electro-optic element decreases with an increase in the number of scanning lines (that is, the number of pixels), thereby realizing a large-sized and high-definition display device. There are problems such as difficult.

  Therefore, in recent years, an active element in which an electric current flowing through an electro-optic element is controlled by an active element provided in the same pixel as the electro-optic element, for example, an insulated gate field effect transistor (generally, a TFT (Thin Film Transistor)). Matrix display devices have been actively developed. An active matrix display device can easily realize a large-sized and high-definition display device because the electro-optic element continues to emit light over a period of one frame.

  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 a pixel circuit using an N-channel TFT as a transistor for driving an organic EL element with current (hereinafter referred to as “driving transistor”), the organic EL element is connected to the source electrode side of the driving transistor. In addition, when the IV characteristic of the organic EL element deteriorates with time, the gate-source voltage Vgs of the driving transistor changes, and as a result, the emission luminance of the organic EL element also changes.

  This will be described more specifically. The source potential of the drive transistor is determined by the operating points of the drive transistor and the organic EL element. When the IV characteristic of the organic EL element deteriorates, the operating point of the driving transistor and the organic EL element fluctuates. Therefore, even if the same voltage is applied to the gate electrode of the driving transistor, the source potential of the driving transistor is Change. As a result, since the source-gate voltage Vgs of the drive transistor changes, the value of the current flowing through the drive transistor changes. As a result, since the value of the current flowing through the organic EL element also changes, the light emission luminance of the organic EL element changes.

  In addition, in a pixel circuit using a polysilicon TFT, in addition to the deterioration over time of the IV characteristics of the organic EL element, the threshold voltage Vth of the driving transistor and the mobility of the semiconductor thin film that constitutes the channel of the driving transistor (hereinafter referred to as the following) The μ changes over time, and the transistor characteristics of the threshold voltage Vth and the mobility μ vary from pixel to pixel due to variations in manufacturing processes (transistor characteristics of each pixel vary). There is).

  If the threshold voltage Vth and mobility μ of the driving transistor differ from pixel to pixel, the current value flowing through the driving transistor varies from pixel to pixel, so even if the same voltage is applied between the pixels to the gate electrode of the driving transistor, The light emission luminance of the organic EL element varies among pixels, and as a result, the uniformity of the screen is impaired.

  Therefore, even if the IV characteristic of the organic EL element deteriorates with time, or the threshold voltage Vth or mobility μ of the driving transistor changes with time, the light emission luminance of the organic EL element is not affected by those effects. In order to keep constant, the compensation function for the characteristic variation of the organic EL element, the correction for the variation of the threshold voltage Vth of the driving transistor (hereinafter referred to as “threshold correction”), the mobility μ of the driving transistor Each pixel circuit is provided with a correction function for correction of fluctuations (hereinafter referred to as “mobility correction”) (see, for example, Patent Document 1).

  As described above, each of the pixel circuits has the compensation function for the characteristic variation of the organic EL element and the correction function for the threshold voltage Vth and the mobility μ of the driving transistor, so that the IV characteristic of the organic EL element is improved. Even if the threshold voltage Vth or mobility μ of the driving transistor changes with time, the light emission luminance of the organic EL element can be kept constant without being affected by the deterioration. The display quality of the display device can be improved.

JP 2006-133542 A

  However, when the organic EL element is turned on in a correction period for performing mobility correction (hereinafter also referred to as “mobility correction period”), the threshold voltage Vth of the driving transistor, the mobility μ, and the time of the organic EL element are changed. Since it becomes impossible to correct the threshold variation due to the deterioration (details will be described later), the uniformity of the screen is impaired.

  Therefore, the present invention can reliably execute correction of threshold voltage Vth of the drive transistor, mobility μ, and threshold variation due to deterioration of the organic EL element over time by preventing turn-on of the organic EL element within the mobility correction period. It is an object of the present invention to provide a display device, a driving method of the display device, and an electronic apparatus having the display device.

In order to achieve the above object, the present invention provides:
An electro-optic element;
A write transistor having a gate electrode connected to the scan line and one electrode connected to the signal line;
A driving transistor having a gate electrode connected to the other electrode of the writing transistor, one electrode connected to a power supply line, and the other electrode connected to an anode electrode of the electro-optic element;
A pixel array section in which pixels having one storage electrode connected to the gate electrode of the driving transistor and the other electrode connected to the other electrode of the driving transistor are arranged in a matrix;
A first power supply potential, a second power supply potential lower than the first power supply potential, and a third power supply potential lower than the first power supply potential and capable of maintaining the conductive state of the driving transistor are selectively applied to the power supply line. A power supply scanning circuit for supplying to
Performing threshold correction processing for changing the potential of the other electrode of the drive transistor toward the potential obtained by subtracting the threshold voltage of the drive transistor from the initialization potential with reference to the initialization potential of the gate electrode of the drive transistor, A mobility correction process for applying negative feedback to the gate input side of the drive transistor with a correction amount corresponding to the current flowing through the drive transistor after the threshold correction process is performed in parallel with the video signal write process by the write transistor. In the display device to perform,
Supplying the second power supply potential to the power supply line before performing the threshold correction processing;
Supplying the first power supply potential to the power supply line instead of the second power supply potential when performing the threshold correction processing;
When the mobility correction process is performed, the third power supply potential is supplied to the power supply line instead of the first power supply potential.

  In the display device having the above structure and an electronic apparatus using the display device, the potential of the power supply line is not maintained at the first power supply potential during the period in which the mobility correction processing is performed in parallel with the video signal writing processing. By reducing the third power supply potential lower than the first power supply potential and maintaining the conduction state of the drive transistor, the amount of drain-source current flowing in the drive transistor during mobility correction is reduced, and the source of the drive transistor The increase in potential can be made slower than in the case where the potential of the power supply line is maintained at the first power supply potential. Thereby, it is possible to prevent the electro-optic element from being turned on within the period in which the mobility correction process is performed. As a result, the threshold voltage Vth, the mobility μ of the driving transistor 22 and the threshold variation due to deterioration with time of the organic EL element 21 can be reliably corrected, so that a display image with good image quality can be obtained.

  According to the present invention, it is possible to prevent the electro-optical element from being turned on within the period for performing the mobility correction process, thereby allowing the threshold voltage Vth of the driving transistor, the mobility μ, and the threshold variation due to the deterioration of the electro-optical element over time. Can be reliably corrected, and a display image with good image quality can be obtained.

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

[System configuration]
FIG. 1 is a system configuration diagram showing an outline of the configuration of an active matrix display device to which the present invention is applied.

  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, an organic EL display device 10 according to this application example includes a plurality of pixels (PXLC) 20 including light emitting elements, and a pixel array in which the pixels 20 are two-dimensionally arranged in a matrix (matrix shape). The unit 30 and the drive unit that drives each pixel 20 are arranged around the pixel array unit 30. For example, a writing scanning circuit 40, a power supply scanning circuit 50, and a signal output circuit 60 are provided as driving units for driving the pixels 20.

  Here, when the organic EL display device 10 is a display device for color display, one pixel is composed of a plurality of sub-pixels (sub-pixels), and this sub-pixel corresponds to the pixel 20. More specifically, in a display device for color display, one pixel includes a sub-pixel that emits red light (R), a sub-pixel that emits green light (G), and a sub-pixel that emits blue light (B). It consists of three sub-pixels of a pixel.

  However, one pixel is not limited to the combination of RGB three primary color subpixels, and one pixel may be configured by adding one or more color subpixels to the three primary color subpixels. Is possible. More specifically, for example, at least one sub-pixel that emits white light (W) is added to improve luminance to form one pixel, or at least one that emits complementary color light to expand the color reproduction range. It is also possible to configure one pixel by adding subpixels.

  The pixel array unit 30 supplies power to the scanning lines 31-1 to 31-m along the first direction (left-right direction / horizontal direction in FIG. 1) with respect to the arrangement of the pixels 20 in m rows and n columns. Lines 32-1 to 32-m are wired for each pixel row, and signal lines 33-1 to 33-33 are arranged along a second direction (vertical direction / vertical direction in FIG. 1) orthogonal to the first direction. n is wired for each pixel column.

  The pixel array unit 30 is usually formed on a transparent insulating substrate such as a glass substrate. Thereby, the organic EL display device 10 has a flat panel structure. The drive circuit for each pixel 20 in the pixel array section 30 can be formed using an amorphous silicon TFT or a low-temperature polysilicon TFT. When the low-temperature polysilicon TFT is used, the write scanning circuit 40, the power supply scanning circuit 50, and the signal output circuit 60 can also be mounted on the display panel (substrate) 70 that forms the pixel array unit 30.

  The write scanning circuit 40 is configured by a shift register or the like that sequentially shifts (transfers) the start pulse sp in synchronization with the clock pulse ck, and the scanning line 31-is used for writing the video signal to each pixel 20 of the pixel array unit 30. By sequentially supplying write pulses (scanning signals) WS1 to WSm to 1-31 to m, each pixel 20 of the pixel array unit 30 is sequentially scanned (line sequential scanning) in units of rows.

  The power supply scanning circuit 50 includes a shift register that sequentially shifts the start pulse sp in synchronization with the clock pulse ck, and the first power supply potential Vccp and the first power supply potential Vccp in synchronization with the line sequential scanning by the writing scanning circuit 40. The power supply line potentials DS1 to DSm that are switched at the second power supply potential Vini lower than the power supply potential Vccp are supplied to the power supply lines 32-1 to 32-m, thereby controlling the light emission / non-light emission of the pixel 20. A drive current is supplied to the organic EL element which is a light emitting element.

  The signal output circuit 60 has either a signal voltage (hereinafter also simply referred to as “signal voltage”) Vsig or a reference potential Vofs of a video signal corresponding to luminance information supplied from a signal supply source (not shown). Either one is selected as appropriate, and writing is performed, for example, in units of rows to each pixel 20 of the pixel array unit 30 via the signal lines 33-1 to 33-n. That is, the signal output circuit 60 adopts a line-sequential writing drive mode in which the signal voltage Vsig of the video signal is written in units of rows.

  Here, the reference potential Vofs is a reference potential (for example, a potential corresponding to the black level) of the signal voltage Vsig of the video signal corresponding to the luminance information. The second power supply potential Vini is lower than the reference potential Vofs, for example, a potential lower than Vofs−Vth, preferably a potential sufficiently lower than Vofs−Vth when the threshold voltage of the driving transistor 22 is Vth. Is set.

(Pixel circuit)
FIG. 2 is a circuit diagram illustrating a specific configuration example of the pixel (pixel circuit) 20.

  As shown in FIG. 2, the pixel 20 includes a current-driven electro-optical element whose emission luminance changes according to a current value flowing through the device, for example, an organic EL element 21, and a drive circuit that drives the organic EL element 21. It is constituted by. The organic EL element 21 has a cathode electrode connected to a common power supply line 34 that is wired in common to all the pixels 20 (so-called solid wiring).

  The drive circuit that drives the organic EL element 21 includes a drive transistor 22, a write transistor 23, a storage capacitor 24, and an auxiliary capacitor 25. Here, N-channel TFTs are used as the drive transistor 22 and the write transistor 23. However, the combination of conductivity types of the drive transistor 22 and the write transistor 23 is merely an example, and is not limited to these combinations.

  Note that when an N-channel TFT is used as the driving transistor 22 and the writing transistor 23, an amorphous silicon (a-Si) process can be used. By using the a-Si process, it is possible to reduce the cost of the substrate on which the TFT is formed, and thus to reduce the cost of the organic EL display device 10. Further, when the drive transistor 22 and the write transistor 23 have the same conductivity type, both the transistors 22 and 23 can be formed by the same process, which can contribute to cost reduction.

  The write transistor 23 has a gate electrode connected to the scanning line 31 (31-1 to 31-m), one electrode (source / drain electrode) connected to the signal line 33 (33-1 to 33-n), The other electrode (drain / source electrode) is connected to the gate electrode of the drive transistor 22.

  In the drive transistor 22 and the write transistor 23, one electrode refers to a metal wiring electrically connected to the source / drain region, and the other electrode refers to a metal wiring electrically connected to the drain / source region. Say. Further, depending on the potential relationship between one electrode and the other electrode, if one electrode becomes a source electrode, it becomes a drain electrode, and if the other electrode also becomes a drain electrode, it becomes a source electrode.

  The storage capacitor 24 has one electrode connected to the gate electrode of the drive transistor 22 and the other electrode connected to the other electrode of the drive transistor 22 and the anode electrode of the organic EL element 21.

  The drive circuit of the organic EL element 21 is not limited to a circuit configuration including two transistors, the drive transistor 22 and the write transistor 23, and one capacitor of the storage capacitor 24. The other electrode is connected to the anode electrode of the organic EL element 21 at a fixed potential, so that the capacity shortage of the organic EL element 21 is compensated for, and the auxiliary capacity for increasing the video signal write gain to the holding capacity 24 It is also possible to adopt a circuit configuration provided as necessary.

  In the pixel 20 having the above-described configuration, the writing transistor 23 is turned on in response to the high-level scanning signal WS applied to the gate electrode from the writing scanning circuit 40 through the scanning line 31, thereby outputting a signal through the signal line 33. The signal voltage Vsig or the reference potential Vofs of the video signal corresponding to the luminance information supplied from the circuit 60 is sampled and written into the pixel 20. The written signal voltage Vsig or reference potential Vofs is applied to the gate electrode of the driving transistor 22 and held in the holding capacitor 24.

  When the potential DS of the power supply line 32 (32-1 to 32-m) is at the first power supply potential Vccp, the drive transistor 22 has one electrode as a drain electrode and the other electrode as a source electrode in a saturation region. It operates and receives current from the power supply line 32 to drive the organic EL element 21 to emit light by current driving. More specifically, the drive transistor 22 operates in the saturation region to supply a drive current having a current value corresponding to the voltage value of the signal voltage Vsig held in the holding capacitor 24 to the organic EL element 21. The organic EL element 21 is caused to emit light by current driving.

  Further, when the potential DS of the power supply line 32 (32-1 to 32-m) is switched from the first power supply potential Vccp to the second power supply potential Vini, the drive transistor 22 has one electrode as a source electrode and the other electrode as By operating as a switching transistor as a drain electrode, supply of drive current to the organic EL element 21 is stopped, and the organic EL element 21 is brought into a non-light emitting state. That is, the drive transistor 22 also has a function as a transistor that controls light emission / non-light emission of the organic EL element 21.

  By the switching operation of the drive transistor 22, a period during which the organic EL element 21 is in a non-light emitting state (non-light emitting period) is provided, and duty control is performed to control the ratio (duty) between the light emitting period and the non-light emitting period of the organic EL element 21. By doing so, it is possible to reduce the afterimage blur caused by the pixels emitting light over one frame period. As a result, the picture quality of the moving image can be particularly improved.

(Pixel structure)
FIG. 3 is a cross-sectional view illustrating an example of the cross-sectional structure of the pixel 20. As shown in FIG. 3, in the pixel 20, an insulating film 202, an insulating planarizing film 203, and a window insulating film 204 are formed in that order on a glass substrate 201 on which a driving circuit including a driving transistor 22 and the like is formed. The organic EL element 21 is provided in the recess 204A of the insulating film 204. Here, only the drive transistor 22 is shown in the components of the drive circuit, and the other components are omitted.

  The organic EL element 21 includes an anode electrode 205 made of metal or the like formed on the bottom of the recess 204A of the window insulating film 204, and an organic layer (electron transport layer, light emitting layer, hole transport) formed on the anode electrode 205. Layer / hole injection layer) 206 and a cathode electrode 207 made of a transparent conductive film or the like formed on the organic layer 206 in common for all pixels.

  In the organic EL element 21, the organic layer 206 is formed by sequentially depositing a hole transport layer / hole injection layer 2061, a light emitting layer 2062, an electron transport layer 2063 and an electron injection layer (not shown) on the anode electrode 205. It is formed. Then, current flows from the driving transistor 22 to the organic layer 206 through the anode electrode 205 under current driving by the driving transistor 22 in FIG. 2, so that electrons and holes are recombined in the light emitting layer 2062 in the organic layer 206. It is designed to emit light.

  The driving transistor 22 includes a gate electrode 221, a source / drain region 223 provided on one side of the semiconductor layer 222, a drain / source region 224 provided on the other side of the semiconductor layer 222, and a gate electrode of the semiconductor layer 222. 221 and a portion of the channel formation region 225 facing the portion 221. The source / drain region 223 is electrically connected to the anode electrode 205 of the organic EL element 21 through a contact hole.

  Then, as shown in FIG. 3, the organic EL element 21 is formed on the glass substrate 201 on which the drive circuit including the drive transistor 22 is formed, with the insulating film 202, the insulating planarizing film 203, and the window insulating film 204 interposed therebetween. After the formation, the sealing substrate 209 is bonded by the adhesive 210 through the passivation film 208, and the organic EL element 21 is sealed by the sealing substrate 209, whereby the display panel 70 is formed. .

(Circuit operation as a premise of the present invention)
Next, in the organic EL display device 10 having the above-described configuration, the circuit operation that is the premise of the present invention will be described based on the timing waveform diagram of FIG. 4 and the operation explanatory diagrams of FIGS.

  In the operation explanatory diagrams of FIGS. 5 and 6, the write transistor 23 is illustrated by a switch symbol for simplification of the drawing. Further, since the organic EL element 21 has a capacitance component (equivalent capacitance) Cel, the capacitance component Cel is also illustrated.

  The timing waveform diagram of FIG. 4 shows a change in the potential (scanning signal) WS of the scanning line 31 (31-1 to 31-m) and the power supply line 32 (with a common time axis for a pixel row to be corrected. 32-1 to 32 -m), and changes in the gate potential Vg and the source potential Vs of the driving transistor 22 are shown.

<Light emission period of previous frame>
In the timing waveform diagram of FIG. 4, the period before time t1 is the light emission period of the organic EL element 21 in the previous frame (field). In the light emission period of the previous frame, the potential DS of the power supply line 32 is at the first power supply potential (hereinafter referred to as “high potential”) Vccp, and the write transistor 23 is in a non-conductive state.

  At this time, since the driving transistor 22 is set to operate in the saturation region, a driving current (drain-source) corresponding to the gate-source voltage Vgs of the driving transistor 22 as shown in FIG. Current Ids is supplied from the power supply line 32 to the organic EL element 21 through the drive transistor 22. Therefore, the organic EL element 21 emits light with a luminance corresponding to the current value of the drive current Ids.

<Threshold correction preparation period>
At time t1, a new frame (current frame) for line sequential scanning is entered. As shown in FIG. 5B, the second power supply potential (hereinafter, referred to as the potential DS of the power supply line 32 is sufficiently lower than Vofs−Vth with respect to the reference potential Vofs of the signal line 33 from the high potential Vccp. Switch to Vini) (described as “low potential”).

  Here, when the threshold voltage of the organic EL element 21 is Vth (el) and the potential of the common power supply line 34 is Vcath, and the low potential Vini is Vini <Vth (el) + Vcath, the source potential Vs of the driving transistor 22 is set. Is substantially equal to the low potential Vini, so that the organic EL element 21 is in a reverse bias state and extinguishes.

  Next, at time t2, the potential WS of the scanning line 31 transitions from the low potential WS_L side to the high potential WS_H side, so that the writing transistor 23 is turned on as illustrated in FIG. At this time, since the reference potential Vofs is supplied from the signal output circuit 60 to the signal line 33, the gate potential Vg of the drive transistor 22 becomes the reference potential Vofs. Further, the source potential Vs of the driving transistor 22 is at a potential Vini that is sufficiently lower than the reference potential Vofs.

  At this time, the gate-source voltage Vgs of the drive transistor 22 is Vofs-Vini. Here, if Vofs−Vini is not larger than the threshold voltage Vth of the drive transistor 22, threshold correction processing described later cannot be performed, and therefore it is necessary to set a potential relationship of Vofs−Vini> Vth.

  As described above, the process of fixing (initializing) the gate potential Vg of the drive transistor 22 to the reference potential Vofs and the source potential Vs to the low potential Vini is a preparation before performing a threshold correction process described later. (Threshold correction preparation) processing. Therefore, the reference potential Vofs and the low potential Vini become the initialization potentials of the gate potential Vg and the source potential Vs of the drive transistor 22, respectively.

<Threshold correction period>
Next, at time t3, as shown in FIG. 5D, when the potential DS of the power supply line 32 is switched from the low potential Vini to the high potential Vccp, the gate potential Vg of the drive transistor 22 is maintained. The source potential Vs of the drive transistor 22 starts to increase toward the potential obtained by subtracting the threshold voltage Vth of the drive transistor 22 from the gate potential Vg. Eventually, the gate-source voltage Vgs of the drive transistor 22 converges to the threshold voltage Vth of the drive transistor 22, and a voltage corresponding to the threshold voltage Vth is held in the storage capacitor 24.

  Here, for convenience, with the gate potential Vg of the drive transistor 22 maintained, the initialization potential (reference potential) Vofs of the gate electrode of the drive transistor 22 is used as a reference and the threshold voltage Vth of the drive transistor 22 from the initialization potential Vofs. The source potential Vs of the drive transistor 22 is changed, specifically increased, toward the potential obtained by subtracting the voltage, and the gate-source voltage Vgs of the drive transistor 22 finally converged is detected as the threshold voltage Vth of the drive transistor 22. A period during which a process corresponding to holding the voltage corresponding to the threshold voltage Vth is held in the holding capacitor 24 is called a threshold correction period.

  In the threshold correction period, the common power supply line 34 is set so that the organic EL element 21 is cut off in order to prevent the current from flowing exclusively to the storage capacitor 24 side and to the organic EL element 21 side. The potential Vcath is set in advance.

  Next, when the potential WS of the scanning line 31 transitions from the high potential WS_H side to the low potential WS_L side at time t4, the writing transistor 23 is turned off as illustrated in FIG. At this time, the gate electrode of the drive transistor 22 is electrically disconnected from the signal line 33 to be in a floating state. However, since the gate-source voltage Vgs is equal to the threshold voltage Vth of the drive transistor 22, the drive transistor 22 Is in a cut-off state. Therefore, the drain-source current Ids does not flow through the driving transistor 22.

<Signal writing period & mobility correction period>
Next, at time t5, as shown in FIG. 6B, the potential of the signal line 33 is switched from the reference potential Vofs to the signal voltage Vsig of the video signal. Subsequently, at time t6, the potential WS of the scanning line 31 transitions to the high potential side, so that the writing transistor 23 becomes conductive as shown in FIG. 6C, and the signal voltage Vsig of the video signal is sampled. To write in the pixel 20.

  By writing the signal voltage Vsig by the writing transistor 23, the gate potential Vg of the driving transistor 22 becomes the signal voltage Vsig. When the driving transistor 22 is driven by the signal voltage Vsig of the video signal, the threshold voltage correction is performed by canceling the threshold voltage Vth of the driving transistor 22 with a voltage corresponding to the threshold voltage Vth held in the holding capacitor 24. Done. The principle of threshold correction will be described later.

  At this time, since the organic EL element 21 is initially in a cut-off state (high impedance state), a current (drain-source current Ids) that flows from the power supply line 32 to the drive transistor 22 according to the signal voltage Vsig of the video signal. Flows into the capacitance component Cel of the organic EL element 21, and charging of the capacitance component Cel is started.

  Due to the charging of the capacitive component Cel, the source potential Vs of the driving transistor 22 rises with time. At this time, the variation in the threshold voltage Vth of the drive transistor 22 has already been corrected, and the drain-source current Ids of the drive transistor 22 depends on the mobility μ of the drive transistor 22.

  Here, assuming that the write gain (ratio of the holding voltage Vgs of the holding capacitor 24 to the signal voltage Vsig of the video signal) is 1 (ideal value), the source potential Vs of the driving transistor 22 rises to a potential of Vofs−Vth + ΔV. Thus, the gate-source voltage Vgs of the drive transistor 22 becomes Vsig−Vofs + Vth−ΔV.

  That is, the increase ΔV of the source potential Vs of the drive transistor 22 is subtracted from the voltage (Vsig−Vofs + Vth) held in the holding capacitor 24, in other words, the charge of the holding capacitor 24 is discharged. And negative feedback was applied. Therefore, the increase ΔV of the source potential Vs becomes a feedback amount of negative feedback.

  In this way, by applying negative feedback to the gate input side of the drive transistor 22, that is, the gate-source voltage Vgs, with a feedback amount ΔV corresponding to the drain-source current Ids flowing through the drive transistor 22, the drive transistor 22 The mobility correction is performed to cancel the dependence of the drain-source current Ids 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 amplitude Vin (= Vsig−Vofs) of the video signal written to the gate electrode of the drive transistor 22 increases, the absolute value of the feedback amount ΔV of the negative feedback increases. The value also increases. Therefore, the mobility correction according to the light emission luminance level is performed.

  Further, when the signal amplitude 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 drive transistor 22 increases. Can do. Therefore, it can be said that the feedback amount ΔV of the negative feedback is a correction amount for mobility correction. Details of the principle of mobility correction will be described later.

<Light emission period>
Next, when the potential WS of the scanning line 31 transitions from the high potential WS_H side to the low potential WS_L side at time t7, the writing transistor 23 is turned off as illustrated in FIG. 6D. As a result, the gate electrode of the driving transistor 22 is electrically disconnected from the signal line 33 and is in a floating state.

  Here, when the gate electrode of the driving transistor 22 is in a floating state, if the storage capacitor 24 is connected between the gate and the source of the driving transistor 22 and the source potential Vs of the driving transistor 22 fluctuates, The gate potential Vg of the drive transistor 22 also varies in conjunction with (follows) the variation in the potential Vs. Thus, the operation in which the gate potential Vg of the drive transistor 22 varies in conjunction with the variation in the source potential Vs is a bootstrap operation by the storage capacitor 24.

  At the same time, the drain-source current Ids of the drive transistor 22 starts to flow into the organic EL element 21, so that the anode potential of the organic EL element 21 becomes the drain potential of the drive transistor 22. -Increases according to the source-to-source current Ids.

  When the anode potential of the organic EL element 21 exceeds Vth (el) + Vcath, a drive current (light emission current) starts to flow through the organic EL element 21, and thus the organic EL element 21 starts to emit light. The increase in the anode potential of the organic EL element 21 is nothing but the increase in the source potential Vs of the drive transistor 22. When the source potential Vs of the drive transistor 22 rises, the gate potential Vg of the drive transistor 22 also rises in conjunction with the bootstrap operation of the storage capacitor 24.

  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 22 is kept constant at Vsig−Vofs + Vth−ΔV during the light emission period. At time t8, the potential of the signal line 33 is switched from the signal voltage Vsig of the video signal to the reference potential Vofs.

  In the series of circuit operations described above, each processing operation of threshold correction preparation, threshold correction, signal voltage Vsig writing (signal writing), and mobility correction is executed in one horizontal scanning period (1H). Further, the signal writing and mobility correction processing operations are executed in parallel during the period from time t6 to time t7.

  Here, the case of the driving method in which the threshold correction processing is executed only once has been described as an example, but this driving method is only an example, and for example, the threshold correction processing is combined with mobility correction and signal writing processing. In addition to the one horizontal scanning period to be performed, it is also possible to adopt a driving method for performing so-called divided Vth correction, which is performed plural times by being divided into a plurality of horizontal scanning periods preceding the one horizontal scanning period.

  In this way, by adopting a driving method in which the threshold correction processing is executed a plurality of times by dividing into one horizontal scanning period for performing mobility correction and signal writing and a plurality of horizontal scanning periods preceding the one horizontal scanning period, Even when the time allotted to one horizontal scanning period is shortened due to the increase in the number of pixels associated with high definition, a sufficient time can be secured as the threshold correction period, so that the threshold correction process can be performed reliably. .

(Principle of threshold correction)
Here, the principle of threshold correction of the drive transistor 22 will be described. The drive transistor 22 operates as a constant current source because it is designed to operate in the saturation region. As a result, a constant drain-source current (drive current) Ids given by the following equation (1) is supplied from the drive transistor 22 to the organic EL element 21.
Ids = (1/2) · μ (W / L) Cox (Vgs−Vth) ² (1)
Here, W is the channel width of the drive transistor 22, L is the channel length, and Cox is the gate capacitance per unit area.

  FIG. 7 shows characteristics of the drain-source current Ids of the drive transistor 22 versus the gate-source voltage Vgs.

  As shown in this characteristic diagram, when correction for variation in the threshold voltage Vth of the driving transistor 22 for each pixel is not performed, when the threshold voltage Vth is Vth1, the drain-source current Ids corresponding to the gate-source voltage Vgs. Becomes Ids1.

  On the other hand, when the threshold voltage Vth is Vth2 (Vth2> Vth1), the drain-source current Ids corresponding to the same gate-source voltage Vgs is Ids2 (Ids2 <Ids). That is, when the threshold voltage Vth of the drive transistor 22 varies, the drain-source current Ids varies even if the gate-source voltage Vgs is constant.

On the other hand, in the pixel (pixel circuit) 20 having the above configuration, as described above, the gate-source voltage Vgs of the driving transistor 22 during light emission is Vsig−Vofs + Vth−ΔV. Then, the drain-source current Ids is expressed by the following equation (2).
Ids = (1/2) · μ (W / L) Cox (Vsig−Vofs−ΔV) ²
(2)

  That is, the term of the threshold voltage Vth of the drive transistor 22 is canceled, and the drain-source current Ids supplied from the drive transistor 22 to the organic EL element 21 does not depend on the threshold voltage Vth of the drive transistor 22. As a result, even if the threshold voltage Vth of the drive transistor 22 varies from pixel to pixel due to variations in the manufacturing process of the drive transistor 22 and changes over time, the drain-source current Ids does not vary. The brightness does not change.

(Principle of mobility correction)
Next, the principle of mobility correction of the drive transistor 22 will be described. FIG. 8 shows a characteristic curve in a state where a pixel A having a relatively high mobility μ of the driving transistor 22 and a pixel B having a relatively low mobility μ of the driving transistor 22 are compared. When the driving transistor 22 is composed of a polysilicon thin film transistor or the like, it is inevitable that the mobility μ varies between pixels like the pixel A and the pixel B.

  When there is a variation in the mobility μ between the pixel A and the pixel B, for example, when the signal amplitude Vin (= Vsig−Vofs) of the same level is written to both the pixels A and B on the gate electrode of the driving transistor 22, there is no movement. If the degree μ is not corrected, there is a large difference between the drain-source current Ids1 ′ flowing through the pixel A having a high mobility μ and the drain-source current Ids2 ′ flowing through the pixel B having a low mobility μ. It will occur. Thus, when a large difference occurs between the pixels in the drain-source current Ids due to the variation in mobility μ from pixel to pixel, the uniformity of the screen is impaired.

  Here, as is clear from the transistor characteristic equation of Equation (1), the drain-source current Ids increases when the mobility μ is large. Therefore, the feedback amount ΔV in the negative feedback increases as the mobility μ increases. As shown in FIG. 8, the feedback amount ΔV1 of the pixel A having a high mobility μ is larger than the feedback amount ΔV2 of the pixel B having a low mobility.

  Therefore, by applying a negative feedback to the gate input side of the drive transistor 22, that is, the gate-source voltage Vgs with a feedback amount ΔV corresponding to the drain-source current Ids of the drive transistor 22 by mobility correction processing, the movement is performed. As the degree μ is larger, the negative feedback is larger, so that variation in mobility μ for each pixel can be suppressed.

  Specifically, when the feedback amount ΔV1 is corrected in the pixel A having a high mobility μ, the drain-source current Ids greatly decreases from Ids1 ′ to Ids1. On the other hand, since the feedback amount ΔV2 of the pixel B having a low mobility μ is small, the drain-source current Ids decreases from Ids2 ′ to Ids2, and does not decrease that much. As a result, since the drain-source current Ids1 of the pixel A and the drain-source current Ids2 of the pixel B are substantially equal, the variation in the mobility μ is corrected.

  In summary, when there are a pixel A and a pixel B having different mobility μ, the feedback amount ΔV1 of the pixel A having a high mobility μ is larger than the feedback amount ΔV2 of the pixel B having a low mobility μ. That is, the larger the mobility μ, the larger the feedback amount ΔV, and the larger the amount of decrease in the drain-source current Ids.

  Accordingly, by applying negative feedback to the gate input side of the drive transistor 22, that is, the gate-source voltage Vgs, with a feedback amount ΔV corresponding to the drain-source current Ids of the drive transistor 22, pixels of different mobility μ are obtained. The current value of the drain-source current Ids is made uniform. As a result, variation in mobility μ for each pixel can be corrected. That is, the process of applying negative feedback to the gate input side of the drive transistor 22 with the feedback amount ΔV corresponding to the current flowing through the drive transistor 22 (drain-source current Ids) is the mobility correction process.

  Here, in the pixel (pixel circuit) 20 shown in FIG. 2, the relationship between the signal potential (sampling potential) Vsig of the video signal and the drain-source current Ids of the drive transistor 22 depending on the presence or absence of threshold correction and mobility correction. This will be described with reference to FIG.

  In FIG. 9, (A) does not perform both threshold correction and mobility correction, (B) does not perform mobility correction, and performs only threshold correction, (C) performs threshold correction and mobility correction. Each case is shown. As shown in FIG. 9A, when neither threshold correction nor mobility correction is performed, the drain-source current Ids is caused by variations in the threshold voltage Vth and the mobility μ for each of the pixels A and B. A large difference occurs between the pixels A and B.

  On the other hand, when only the threshold correction is performed, as shown in FIG. 9B, although the variation in the drain-source current Ids can be reduced to some extent by the threshold correction, the pixels A and B having the mobility μ A difference in the drain-source current Ids between the pixels A and B due to the variation of each pixel remains.

  Then, by performing both the threshold correction and the mobility correction, as shown in FIG. 9C, the drain between the pixels A and B due to the variation of the threshold voltage Vth and the mobility μ for each of the pixels A and B. -Since the difference between the source currents Ids can be almost eliminated, the luminance variation of the organic EL element 21 does not occur at any gradation, and a display image with good image quality can be obtained.

  Further, the pixel 20 shown in FIG. 2 has the function of bootstrap operation by the holding capacitor 24 described above in addition to the correction functions of threshold correction and mobility correction. Obtainable.

  That is, even if the IV characteristic of the organic EL element 21 changes with time, and the source potential Vs of the drive transistor 22 changes accordingly, the bootstrap operation by the storage capacitor 24 causes the gate-source connection of the drive transistor 22. Since the potential Vgs can be maintained constant, the current flowing through the organic EL element 21 does not change and is constant. Therefore, since the light emission luminance of the organic EL element 21 is also kept constant, even if the IV characteristic of the organic EL element 21 changes with time, it is possible to realize an image display that does not cause luminance deterioration associated therewith.

  As described above, in the organic EL display device 10 having the pixel configuration shown in FIG. 2, if the circuit operation for the bootstrap operation, the threshold value correction operation, and the mobility correction operation is accurately performed, It is possible to prevent deterioration over time and variations in characteristics of the threshold voltage Vth and mobility μ of the driving transistor 22 and to maintain the light emission luminance of the organic EL element 21 without being affected by them. ) Can be improved.

(Organic EL element turn-on)
By the way, as shown in the timing waveform diagram of FIG. 10, when the source potential Vs of the drive transistor 22 reaches the threshold voltage Vth (el) of the organic EL element 21 in the writing period and mobility correction period of the signal potential Vsig. Since the organic EL element 21 changes from the cut-off state to the on state, the source potential Vs of the drive transistor 22 does not increase from the threshold voltage Vth (el) of the organic EL element 21 thereafter (this is the turn-on of the organic EL element). And).

As a result, the gate-source voltage Vgs ′ of the drive transistor 22 during the light emission period of the pixel in which the organic EL element 21 is turned on is
Vgs ′ = Vsig−Vth (el)
It becomes.

The drain-source current Ids at this time is different from the current equation shown in the equation (2) when the threshold correction and the mobility correction are accurately performed, as shown in the following equation (3):
Ids = (1/2) · μ (W / L) Cox (Vsig−Vth (el) −Vth) ²
...... (3)
The threshold voltage Vth (el) of the organic EL element 21 and the threshold voltage Vth of the drive transistor 22 are included in the terms, and the correction term (ΔV) of the mobility μ is not included. .

  That is, when the organic EL element 21 is turned on in the writing period and the mobility correction period of the signal potential Vsig, the threshold voltage Vth of the drive transistor 22, the mobility μ, and the aging of the organic EL element 21 are evident from the equation (3). It becomes impossible to correct the threshold variation due to the deterioration, and as a result, the uniformity of the screen is lost, and a display image with good image quality cannot be obtained.

  Further, when the mobility correction process is performed in a state where the potential of the power supply line 32 is the high potential Vccp, the source potential Vs of the drive transistor 22 rises rapidly and the mobility correction is suddenly applied. Since the current amount of the drain-source current Ids flowing through 22 decreases, sufficient light emission luminance cannot be obtained.

  On the other hand, the write period determined by the pulse width of the write pulse WS so that the source potential Vs of the drive transistor 22 does not reach the threshold voltage Vth (el) of the organic EL element 21 within the write period of the signal potential Vsig and the mobility correction period. By setting the mobility correction period to be short, the organic EL element 21 can be prevented from being turned on during the period.

  However, if the pulse width of the write pulse WS is set narrow in order to shorten the write period and the mobility correction period of the signal potential Vsig, it is caused by the resistance component, parasitic capacitance, etc. of the scanning line 31 (31-1 to 31-m). Due to the influence of the rounded waveform, a luminance difference (shading) occurs between the writing scanning circuit 40 of the display panel 70 and the opposite side (in the example of FIG. 1, the power supply scanning circuit 50 side).

(Characteristics of this embodiment)
Therefore, in the present embodiment, the potential DS of the power supply line 32 (32-1 to 32-m) is maintained at the high potential (first power supply potential) Vccp in the writing period and the mobility correction period of the signal potential Vsig. Instead, a driving method is adopted in which the driving transistor 22 is lowered to the third power supply potential Vccp2 that is lower than the high potential Vccp and can maintain the conduction state of the driving transistor 22 and between the low potential (second power supply potential) Vini.

  The third power supply potential Vccp2 is selectively output from the power supply scanning circuit 50 instead of the high potential Vccp. The third power supply potential Vccp2 may be any potential range that is lower than the high potential Vccp and within the potential range in which the conduction state of the drive transistor 22 can be maintained, but is as low as possible within the potential range, that is, a potential that is close to the lower limit of the potential range. Is preferable.

  The timing at which the potential DS of the power supply line 32 is lowered from the high potential Vccp to the third power supply potential Vccp2 is time t11 immediately before time t5 when the potential of the signal line 33 is switched from the reference potential Vofs to the signal potential Vsig. The timing at which the potential DS of the power supply line 32 is returned from the third power supply potential Vccp2 to the high potential Vccp is time t12 immediately after time t8 when the potential of the signal line 33 is switched from the signal potential Vsig to the reference potential Vofs.

  Next, in the organic EL display device 10 having the pixel configuration shown in FIG. 2, the operation explanatory diagram of FIG. 12 is shown based on the timing waveform diagram of FIG. 11 for the circuit operation when the driving method according to the present embodiment is used. It explains using.

  In the operation explanatory diagram of FIG. 12, the same parts as those in the operation explanatory diagrams of FIGS. 5 and 6 are denoted by the same reference numerals. Times t2 to t8 in the timing waveform diagram of FIG. 11 correspond to times t2 to t8 in the timing waveform diagram of FIG. Since the circuit operation up to time t4 is the same as the circuit operation based on the timing waveform diagram of FIG. 4, the description of the circuit operation is omitted here because it is redundant.

  In the timing waveform diagram of FIG. 11, at time t11 after the threshold correction period ends at time t4, as shown in FIG. 12A, the third power source whose potential of the power supply line 32 is lower than the high potential Vccp. The potential Vccp2 is switched.

  Next, after the potential of the signal line 33 is switched from the reference potential Vofs to the signal voltage Vsig of the video signal at time t5, the potential WS of the scanning line 31 transits from the low potential WS_L side to the high potential WS_H side at time t6. Thus, as shown in FIG. 12B, the writing transistor 23 becomes conductive, the signal voltage Vsig of the video signal is sampled and written into the pixel 20, and the writing period of the signal potential Vsig and the mobility correction period are entered. .

  In the writing period and mobility correction period of the signal potential Vsig, since the organic EL element 21 is initially in a cutoff state (high impedance state), the power supply line 32 changes to the driving transistor 22 in accordance with the signal voltage Vsig of the video signal. The flowing current (drain-source current Ids) flows into the capacitance component Cel of the organic EL element 21, and charging of the capacitance component Cel is started.

  At this time, since the potential of the power supply line 32 is the third power supply potential Vccp2 that is lower than the high potential Vccp, the amount of the drain-source current Ids flowing through the drive transistor 22 during the mobility correction process is The potential of 32 is reduced as compared with the high potential Vccp, and the increase of the source potential Vs of the driving transistor 22 becomes moderate.

  Thus, the source potential Vs of the drive transistor 22 does not reach the threshold voltage Vth (el) of the organic EL element 21 within the writing period and mobility correction period of the signal potential Vsig. The organic EL element 21 is not turned on during the mobility correction period.

  In particular, by setting the third power supply potential Vccp2 as low as possible within a potential range in which the conduction state of the drive transistor 22 can be maintained, the amount of drain-source current Ids flowing through the drive transistor 22 during the mobility correction process can be further increased. Since the increase in the source potential Vs of the drive transistor 22 can be made more moderate, it is possible to more reliably prevent the organic EL element 21 from being turned on during the writing period and the mobility correction period of the signal potential Vsig. it can.

  The mobility correction processing operation in the signal potential Vsig writing period and the mobility correction period is the same as the circuit operation described above. Assuming that the write gain is 1 (ideal value), the source potential Vs of the drive transistor 22 rises to the potential of Vofs−Vth + ΔV, so that the gate-source voltage Vgs of the drive transistor 22 is Vsig−Vofs + Vth. −ΔV.

  Then, at time t7, the potential WS of the scanning line 31 is changed from the high potential WS_H side to the low potential WS_L side, so that the writing transistor 23 is turned off as illustrated in FIG. At this time, the source potential Vs of the drive transistor 22 is at a potential Vel ′ lower than the threshold voltage Vth (el) of the organic EL element 21. When the writing transistor 23 is turned off, the gate electrode of the driving transistor 22 is electrically disconnected from the signal line 33 and is in a floating state.

  Here, when the gate electrode of the driving transistor 22 is in a floating state, the gate potential Vg of the driving transistor 22 varies in conjunction with the variation of the source potential Vs by the bootstrap operation by the storage capacitor 24. At the same time, the drain-source current Ids of the drive transistor 22 starts to flow into the organic EL element 21, so that the anode potential of the organic EL element 21 becomes the drain potential of the drive transistor 22. -Increases according to the source-to-source current Ids.

  When the anode potential of the organic EL element 21 exceeds Vel + Vcath, a driving current (light emission current) starts to flow through the organic EL element 21, and thus the organic EL element 21 starts to emit light. The increase in the anode potential of the organic EL element 21 is nothing but the increase in the source potential Vs of the drive transistor 22. When the source potential Vs of the drive transistor 22 rises, the gate potential Vg of the drive transistor 22 also rises in conjunction with the bootstrap operation of the storage capacitor 24. 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.

  Next, after the potential of the signal line 33 is switched from the signal voltage Vsig of the video signal to the reference potential Vofs at time t8, the potential of the power supply line 32 is changed to the third power source as shown in FIG. The potential Vccp2 is switched to the high potential Vccp. As a result, the amount of the drain-source current Ids flowing through the drive transistor 22 is greater than when the potential of the power supply line 32 is the third power supply potential Vccp2, so that the source potential Vs of the drive transistor 22 is It rises from the potential Vel ″ immediately before the switching of the potential of 32.

  At this time, since the gate electrode of the drive transistor 22 is in a floating state, even if the source potential Vs of the drive transistor 22 rises, the gate potential Vg of the drive transistor 22 is changed to the source potential Vs by the bootstrap operation by the storage capacitor 24. Vsig−Vofs + Vth−ΔV + Vel ″. Therefore, the gate-source voltage Vgs of the driving transistor 22 is kept constant at Vsig−Vofs + Vth−ΔV during the light emission period.

(Operational effect of this embodiment)
As described above, the mobility correction process for applying negative feedback to the gate input side of the drive transistor 22 with the correction amount (feedback amount) ΔV corresponding to the drain-source current Ids flowing through the drive transistor 22 is performed by the write transistor 22. In the organic EL display device 10 executed in parallel with the writing process of the signal voltage Vsig of the video signal, the potential DS of the power supply line 32 is maintained at the high potential Vccp during the writing period of the signal potential Vsig and the mobility correction period. Instead, by lowering to the third power supply potential Vccp2 that is lower than the high potential Vccp and can maintain the conductive state of the drive transistor 22, the following operational effects can be obtained.

  That is, the current amount of the drain-source current Ids at the time of correcting the mobility of the drive transistor 22 is decreased, and the increase of the source potential Vs of the drive transistor 22 is caused when the potential of the power supply line 32 is at the high potential Vccp. Since it can be made gentler than in the case of correction, it is possible to prevent the organic EL element 21 from being turned on within the writing period and the mobility correction period of the signal potential Vsig. As a result, the threshold voltage Vth, the mobility μ of the driving transistor 22 and the threshold variation due to deterioration with time of the organic EL element 21 can be reliably corrected, so that a display image with good image quality can be obtained.

  In addition, since the source potential Vs of the drive transistor 22 is gently increased, mobility correction can be performed more slowly than in the case of mobility correction when the potential of the power supply line 32 is at the high potential Vccp. Therefore, the decrease (ΔV) in the gate-source voltage Vgs of the drive transistor 22 during the mobility correction process can be reduced. As a result, since a large amount of drain-source current Ids can flow through the drive transistor 22, sufficient light emission luminance can be obtained.

  Further, the organic EL element 21 can be prevented from being turned on during the period without setting the writing period and mobility correction period of the signal voltage Vsig determined by the pulse width of the writing pulse WS to be short. As a result, the time until the organic EL element 21 is turned on becomes longer than that in the case of mobility correction when the potential of the power supply line 32 is at the high potential Vccp. Therefore, the writing period and mobility of the signal voltage Vsig It becomes possible to set a long correction period. As a result, it becomes possible to prevent shading of the display panel 70, so that a display image with better image quality can be obtained.

(Modification)
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 circuit 20 has been described as an example. However, the present invention is not limited to this application example. Specifically, for all display devices using current-driven electro-optic elements (light-emitting elements) such as inorganic EL elements, LED elements, semiconductor laser elements, etc., whose emission luminance changes according to the value of current flowing through the device. Applicable.

[Application example]
The display device according to the present invention described above includes, as an example, various electronic devices illustrated in FIGS. 13 to 15, for example, electronic devices such as digital cameras, notebook personal computers, mobile terminal devices such as mobile phones, and video cameras. The present invention can be applied to display devices for electronic devices in various fields that display video signals input to the video signal or video signals generated in the electronic device as images or videos. An example of an electronic device to which the present invention is applied will be described below.

  As described above, by using the display device according to the present invention as a display device for electronic devices in all fields, the display device according to the present invention has the threshold voltage Vth of the drive transistor 22, as is apparent from the above description of the embodiment. Since it is possible to surely correct the mobility μ and the threshold variation accompanying the deterioration with time of the organic EL element 21, high-quality image display can be performed in various electronic devices.

  Note that the display device according to the present invention includes a module-shaped one having a sealed configuration. For example, a display module formed by being affixed to an opposing portion such as transparent glass on the pixel array portion 30 is applicable. 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 signals from the outside to the pixel array unit, an FPC (flexible printed circuit), and the like.

  FIG. 13 is a perspective view showing a television to which the present invention is applied. The television according to this application example includes a video display screen unit 101 including a front panel 102, a filter glass 103, and the like, and is created by using the display device according to the present invention as the video display screen unit 101.

  14A and 14B are perspective views showing a digital camera to which the present invention 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 invention as the display unit 112.

  FIG. 15 is a perspective view showing a notebook personal computer to which the present invention is applied. A 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. It is produced by using.

  FIG. 16 is a perspective view showing a video camera to which the present invention is applied. The video camera according to this application example includes a main body 131, a lens 132 for shooting an object 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 such a display device.

  FIG. 17 is a perspective view showing a mobile terminal device to which the present invention is applied, for example, a mobile phone, in which (A) is a front view in an open state, (B) is a side view thereof, and (C) is closed. (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. And the sub display 145 is manufactured by using the display device according to the present invention.

1 is a system configuration diagram showing an outline of the configuration of an active matrix display device to which the present invention is applied. It is a circuit diagram which shows the specific structural example of a pixel (pixel circuit). It is sectional drawing which shows an example of the cross-sectional structure of a pixel. It is a timing waveform diagram with which it uses for description of the circuit operation | movement used as the premise of this invention. It is explanatory drawing (the 1) of the circuit operation | movement used as the premise of this invention. It is explanatory drawing (the 2) of the circuit operation | movement used as the premise of this invention. It is a characteristic view with which it uses for description of the subject resulting from the dispersion | variation in the threshold voltage Vth of a drive transistor. It is a characteristic view with which it uses for description of the subject resulting from the dispersion | variation in the mobility (mu) of a drive transistor. FIG. 6 is a characteristic diagram for explaining the relationship between the signal voltage Vsig of the video signal and the drain-source current Ids of the drive transistor depending on whether or not threshold correction and mobility correction are performed. It is a timing waveform diagram with which it uses for operation | movement description when an organic EL element turns on in a signal writing period and a mobility correction period. It is a timing waveform diagram with which it uses for description of the circuit operation | movement at the time of using the drive method which concerns on this embodiment. It is explanatory drawing of the circuit operation at the time of using the drive method which concerns on this embodiment. It is a perspective view which shows the external appearance of the television set to which this invention is applied. It is a perspective view which shows the external appearance of the digital camera to which this invention is applied, (A) is the perspective view seen from the front side, (B) is the perspective view seen from the back side. 1 is a perspective view illustrating an appearance of a notebook personal computer to which the present invention is applied. It is a perspective view which shows the external appearance of the video camera to which this invention is applied. BRIEF DESCRIPTION OF THE DRAWINGS It is an external view which shows the mobile telephone to which this invention 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 10 ... Organic EL display device, 20 ... Pixel (pixel circuit), 21 ... Organic EL element, 22 ... Drive transistor, 23 ... Write transistor, 24 ... Retention capacity, 30 ... Pixel array part, 31 (31-1 to 31-31) m) ... scanning line, 32 (32-1 to 32-m) ... power supply line, 33 (33-1 to 33-n) ... signal line, 34 ... common power supply line, 40 ... write scanning circuit, 50 ... Power supply scanning circuit, 60 ... horizontal drive circuit, 70 ... display panel

Claims (4)

An electro-optic element;
A write transistor having a gate electrode connected to the scan line and one electrode connected to the signal line;
A driving transistor having a gate electrode connected to the other electrode of the writing transistor, one electrode connected to a power supply line, and the other electrode connected to an anode electrode of the electro-optic element;
A pixel array section in which pixels having one storage electrode connected to the gate electrode of the driving transistor and the other electrode connected to the other electrode of the driving transistor are arranged in a matrix;
A first power supply potential, a second power supply potential lower than the first power supply potential, and a third power supply potential lower than the first power supply potential and capable of maintaining the conductive state of the driving transistor are selectively applied to the power supply line. A power supply scanning circuit for supplying to
Performing threshold correction processing for changing the potential of the other electrode of the drive transistor toward the potential obtained by subtracting the threshold voltage of the drive transistor from the initialization potential with reference to the initialization potential of the gate electrode of the drive transistor, A mobility correction process for applying negative feedback to the gate input side of the drive transistor with a correction amount corresponding to the current flowing through the drive transistor after the threshold correction process is performed in parallel with the video signal write process by the write transistor. A display device to perform,
The power supply scanning circuit includes:
Supplying the second power supply potential to the power supply line before performing the threshold correction processing;
Supplying the first power supply potential to the power supply line instead of the second power supply potential when performing the threshold correction processing;
The display device, wherein the third power supply potential is supplied to the power supply line instead of the first power supply potential when the mobility correction process is performed. The display device according to claim 1, wherein the third power supply potential is a potential close to a lower limit of a potential range in which the conduction state of the driving transistor can be maintained. An electro-optic element;
A write transistor having a gate electrode connected to the scan line and one electrode connected to the signal line;
A driving transistor having a gate electrode connected to the other electrode of the writing transistor, one electrode connected to a power supply line, and the other electrode connected to an anode electrode of the electro-optic element;
A pixel array section in which pixels having one storage electrode connected to the gate electrode of the driving transistor and the other electrode connected to the other electrode of the driving transistor are arranged in a matrix;
A first power supply potential, a second power supply potential lower than the first power supply potential, and a third power supply potential lower than the first power supply potential and capable of maintaining the conductive state of the driving transistor are selectively applied to the power supply line. A power supply scanning circuit for supplying to
Performing threshold correction processing for changing the potential of the other electrode of the drive transistor toward the potential obtained by subtracting the threshold voltage of the drive transistor from the initialization potential with reference to the initialization potential of the gate electrode of the drive transistor, A mobility correction process for applying negative feedback to the gate input side of the drive transistor with a correction amount corresponding to the current flowing through the drive transistor after the threshold correction process is performed in parallel with the video signal write process by the write transistor. A method for driving a display device, comprising:
Supplying the second power supply potential to the power supply line before performing the threshold correction processing;
Supplying the first power supply potential to the power supply line instead of the second power supply potential when performing the threshold correction processing;
A method for driving a display device, comprising: supplying the third power supply potential to the power supply line instead of the first power supply potential when performing the mobility correction process. An electro-optic element;
A write transistor having a gate electrode connected to the scan line and one electrode connected to the signal line;
A driving transistor having a gate electrode connected to the other electrode of the writing transistor, one electrode connected to a power supply line, and the other electrode connected to an anode electrode of the electro-optic element;
A pixel array section in which pixels having one storage electrode connected to the gate electrode of the driving transistor and the other electrode connected to the other electrode of the driving transistor are arranged in a matrix;
A first power supply potential, a second power supply potential lower than the first power supply potential, and a third power supply potential lower than the first power supply potential and capable of maintaining the conductive state of the driving transistor are selectively applied to the power supply line. A power supply scanning circuit for supplying to
Performing threshold correction processing for changing the potential of the other electrode of the drive transistor toward the potential obtained by subtracting the threshold voltage of the drive transistor from the initialization potential with reference to the initialization potential of the gate electrode of the drive transistor, A mobility correction process for applying negative feedback to the gate input side of the drive transistor with a correction amount corresponding to the current flowing through the drive transistor after the threshold correction process is performed in parallel with the video signal write process by the write transistor. An electronic device having a display device to perform,
The power supply scanning circuit includes:
Supplying the second power supply potential to the power supply line before performing the threshold correction processing;
Supplying the first power supply potential to the power supply line instead of the second power supply potential when performing the threshold correction processing;
An electronic apparatus comprising: supplying the third power supply potential to the power supply line instead of the first power supply potential when performing the mobility correction process.

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