JP2009282192A - Display device, method of driving the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress excessive density of layout inside a pixel, and to enable turning it into a high-definition pixel and hence into a high-definition display device. <P>SOLUTION: Auxiliary wirings 35i-1, 35i, 35i+1 are wired for each pixel column of a pixel array part 30, and capacitive elements 36i-1, 36i, 36i+1 are, respectively connected to the auxiliary wirings 35i-1, 35i, 35i+1 at the outside of the pixel array part 30. The capacitive elements 36i-1, 36i, 36i+1 are used as auxiliary capacitance of organic EL elements 21i-1, 21i, 21i+1, by connecting the auxiliary wirings 35i-1, 35i, 35i+1 to respective anode electrodes of the organic EL elements 21i-1, 21i, 21i+1 via switching elements 26i-1, 26i, 26i+1 on the writing of a signal voltage Vsig of a video signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device, a display device driving method, and an electronic apparatus, and more particularly to a flat panel display device in which pixels are two-dimensionally arranged in a matrix (matrix shape), and a driving method of the display device. The present invention also relates to an electronic device 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) are arranged in a matrix are rapidly spreading. As one of flat-type display devices, there is a display device using a so-called current-driven electro-optical element whose light emission luminance changes according to a current value flowing through the device as a light-emitting element of a pixel. As a current-driven electro-optical element, an organic EL (Electro Luminescence) element that utilizes a phenomenon of light emission when an electric field is applied to an organic thin film is known.

  An organic EL display device using an organic EL element as an electro-optical element of a pixel 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, the visibility of the image is higher than that of a liquid crystal display device that displays an image by controlling the light intensity from the light source with a liquid crystal for each pixel, and a backlight. Therefore, 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.

  For this reason, in recent years, active matrix display devices in which the current flowing through the electro-optical element is controlled by an active element provided in the same pixel as the electro-optical element, for example, an insulated gate field effect transistor, have been actively developed. Yes. As the insulated gate field effect transistor, a TFT (Thin Film Transistor) is generally used. 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). Particularly 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”), if the IV characteristic of the organic EL element deteriorates with time, the gate of the driving transistor -The source voltage Vgs changes. As a result, the light emission luminance of the organic EL element changes. This is because the organic EL element is connected to the source electrode side of the driving transistor.

  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 particular, in a pixel circuit using a polysilicon TFT, in addition to deterioration of the IV characteristics of the organic EL element over time, the transistor characteristics of the drive transistor change over time, or the transistor characteristics vary depending on manufacturing processes. It is different for each. That is, the transistor characteristics of the drive transistor vary from pixel to pixel. The transistor characteristics include the threshold voltage Vth of the driving transistor, the mobility μ of the semiconductor thin film constituting the channel of the driving transistor (hereinafter simply referred to as “mobility μ of the driving transistor”), and the like.

  When the transistor characteristics of the driving transistor differ from pixel to pixel, the current value flowing through the driving transistor varies from pixel to pixel. Therefore, even if the same voltage is applied between the pixels to the gate electrode of the driving transistor, the light emission of the organic EL element The luminance varies among pixels. As a result, the uniformity (uniformity) of the screen is impaired.

  Therefore, various corrections (compensations) are made to maintain the light emission luminance of the organic EL element constant without being affected by the deterioration of the IV characteristic of the organic EL element over time or the change in the transistor characteristic of the driving transistor over time. ) A function is given to the pixel circuit (for example, see Patent Document 1).

  Examples of the correction function include a compensation function for characteristic variation of the organic EL element, a correction function for variation in the threshold voltage Vth of the drive transistor, and a correction function for variation in mobility μ of the drive transistor. Hereinafter, the correction for the variation of the threshold voltage Vth of the driving transistor is referred to as “threshold correction”, and the correction for the variation of the mobility μ of the driving transistor is referred to as “mobility correction”.

  In this way, by providing each pixel circuit with various correction functions, the organic EL element is not affected by the deterioration of the IV characteristics of the organic EL element over time or the change of the transistor characteristics of the driving transistor over time. The light emission luminance of the element can be kept constant. As a result, the display quality of the organic EL display device can be improved.

JP 2006-133542 A

  By the way, when the signal voltage Vsig of the video signal is written, a voltage corresponding to the write gain G, that is, a voltage of Vsig · G is applied between the gate and the source of the driving transistor. The write gain G is mainly defined by the capacitance value Ccs of the holding capacitor that holds the written signal voltage Vsig, the capacitance value Cgs of the parasitic capacitance between the gate and the source of the driving transistor, and the capacitance value Coled of the equivalent capacitance of the organic EL element. (The details will be described later).

  Here, in general, the storage capacity, the parasitic capacitance between the gate and the source of the driving transistor, and the equivalent capacity of the organic EL element are insufficient, and a sufficient gain as the write gain G cannot be secured. For example, if the size of the organic EL element is reduced due to pixel miniaturization accompanying the recent increase in definition of display devices, the equivalent capacitance Coled of the organic EL element is reduced, and the write gain G is accordingly reduced.

  In order to compensate for this shortage of capacity, generally, a measure of connecting an auxiliary capacity between the anode electrode of the organic EL element and the fixed potential node is taken. At this time, an auxiliary capacitor is provided for each pixel. In order to bring the write gain close to the ideal value, a large capacity value is required as an auxiliary capacity. However, if an auxiliary capacitor that requires a large area in layout is provided for each pixel, over-density of the layout in the pixel is caused. In addition, pixel miniaturization and thus high definition of the display device are hindered.

  In view of the above, the present invention provides a display device capable of miniaturizing a pixel and thus high-definition of a display device while suppressing over-density of the layout in the pixel, a driving method of the display device, and an electronic apparatus using the display device The purpose is to provide.

In order to achieve the above object, the present invention provides:
An electro-optic element;
A writing transistor for writing a video signal;
A holding capacitor for holding the video signal written by the writing transistor;
In a display device in which pixels having a drive transistor that drives the electro-optic element according to the video signal held in the holding capacitor are arranged in a matrix,
When the video signal is written by the writing transistor, the auxiliary wiring connected to the anode electrode of the electro-optical element for each pixel column of the pixel array section and connected to the capacitor element outside the pixel array section is electrically connected. Connect.

  Capacitance elements are connected to the auxiliary wirings arranged for each pixel column in the pixel array unit outside the pixel array unit. Therefore, the auxiliary wiring is electrically connected to the anode electrode of the electro-optic element when the video signal is written by the writing transistor, so that the capacitive element is connected in parallel to the equivalent capacitance of the electro-optic element through the auxiliary wiring. Is done. Accordingly, the capacitive element functions as an auxiliary capacity that compensates for the shortage of capacity of the electro-optic element. That is, even if an auxiliary capacitor is not provided in the pixel, the capacity shortage of the electro-optical element can be compensated for by the capacitive element provided outside the pixel array portion.

  According to the present invention, since the capacity shortage of the electro-optic element can be compensated for by the capacitive element provided outside the pixel array portion without providing the auxiliary capacity in the pixel, the density of the layout in the pixel is increased. Thus, it is possible to reduce the size of the pixel and thus the display device.

  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, an active matrix organic EL display device using, as an example, 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 as a light-emitting element of a pixel (pixel circuit) This case 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 20 including light emitting elements, a pixel array unit 30 in which the pixels 20 are two-dimensionally arranged in a matrix, and the pixel array. The drive unit is disposed around the unit 30. The drive unit drives each pixel 20 of the pixel array unit 30. As the drive unit, for example, a write scanning circuit 40, a power supply scanning circuit 50, and a signal output circuit 60 are provided.

  Here, when the organic EL display device 10 supports 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 includes scanning lines 31-1 to 31-m and a power supply line 32-1 along the row direction (pixel arrangement direction of pixels in the pixel row) with respect to the arrangement of the pixels 20 in m rows and n columns. ˜32-m are wired for each pixel row. Furthermore, signal lines 33-1 to 33-n are wired for each pixel column along the column direction (pixel arrangement direction of the pixel column).

  The scanning lines 31-1 to 31 -m are connected to the output ends of the corresponding rows of the writing scanning circuit 40, respectively. The power supply lines 32-1 to 32-m are connected to the output terminals of the corresponding rows of the power supply scanning circuit 50, respectively. The signal lines 33-1 to 33-n are connected to the output ends of the corresponding columns of the signal output circuit 60, respectively.

  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. The writing scanning circuit 40 sequentially supplies writing scanning signals WS (WS1 to WSm) to the scanning lines 31-1 to 31-m when writing video signals to the respective pixels 20 of the pixel array section 30. Each pixel 20 of the unit 30 is scanned in order in a row unit (line-sequential scanning).

  The power supply scanning circuit 50 includes a shift register that sequentially shifts the start pulse sp in synchronization with the clock pulse ck. The power supply scanning circuit 50 synchronizes with the line sequential scanning by the write scanning circuit 40 and switches between a first power supply potential Vccp and a second power supply potential Vini lower than the first power supply potential Vccp. ) To the power supply lines 32-1 to 32-m. The light emission / non-light emission of the pixel 20 is controlled by switching the power supply potential DS to Vccp / Vini.

  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 output. The signal voltage Vsig / reference potential Vofs output from the signal output circuit 60 is written in units of rows to each pixel 20 of the pixel array unit 30 via the signal lines 33-1 to 33-n. In other words, the signal output circuit 60 employs a line-sequential writing drive configuration in which the signal voltage Vsig is written in units of rows (lines).

(Pixel circuit)
FIG. 2 is a circuit diagram showing a specific circuit configuration 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 has a drive transistor 22, a write transistor 23, and a storage capacitor 24. 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 drive transistor 22 has one electrode (source / drain electrode) connected to the anode electrode of the organic EL element 21 and the other electrode (drain / source electrode) connected to the power supply line 32 (32-1 to 32-m). It is connected.

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

  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.

  In the pixel 20 configured as described above, the writing transistor 23 becomes conductive in response to a high active writing scanning signal WS applied to the gate electrode from the writing scanning circuit 40 through the scanning line 31. Thereby, the write transistor 23 samples the signal voltage Vsig or the reference potential Vofs of the video signal corresponding to the luminance information supplied from the signal output circuit 60 through the signal line 33 and writes the sampled voltage in 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. Operate. As a result, the drive transistor 22 is supplied with current from the power supply line 32 and drives the organic EL element 21 to emit light by current drive. 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 power supply potential DS is switched from the first power supply potential Vccp to the second power supply potential Vini, the drive transistor 22 operates as a switching transistor with one electrode serving as a source electrode and the other electrode serving as a drain electrode. As a result, the drive transistor 22 stops supplying the drive current to the organic EL element 21 and puts the organic EL element 21 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 the ratio (duty) between the light emitting period and the non-light emitting period of the organic EL element 21 is controlled. By this duty control, the afterimage blur caused by the light emission of the pixels over one frame period can be reduced, so that the quality of the moving image can be particularly improved.

  Here, the reference potential Vofs that is selectively supplied from the signal output circuit 60 through the signal line 33 corresponds to a potential that serves as a reference for the signal voltage Vsig of the video signal corresponding to the luminance information (for example, the black level of the video signal). Potential).

  Of the first and second power supply potentials Vccp and Vini selectively supplied from the power supply scanning circuit 50 through the power supply line 32, the first power supply potential Vccp generates a drive current for driving the organic EL element 21 to emit light. The power supply potential for supplying to The second power supply potential Vini is a power supply potential for applying a reverse bias to the organic EL element 21. The second power supply potential Vini is set to a potential lower than the reference potential Vofs, for example, a potential lower than Vofs−Vth, preferably sufficiently lower than Vofs−Vth when the threshold voltage of the driving transistor 22 is Vth. Is done.

(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, a driving circuit including the driving transistor 22 and the like is formed on the glass substrate 201. The pixel 20 has a configuration in which an insulating film 202, an insulating planarizing film 203, and a window insulating film 204 are formed in this order on a glass substrate 201, and the organic EL element 21 is provided in the recess 204A of the window insulating film 204. It has become. 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, an organic layer (electron transport layer, light emitting layer, hole transport layer / hole injection layer) 206, and a cathode electrode 207. The anode electrode 205 is made of a metal or the like formed on the bottom of the recess 204A of the window insulating film 204. The organic layer 206 is formed on the anode electrode 205. The cathode electrode 207 is made of a transparent conductive film 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 drive transistor 22 includes a gate electrode 221, source / drain regions 223 and 224 provided on both sides of the semiconductor layer 222, and a channel formation region 225 at a portion facing the gate electrode 221 of the semiconductor layer 222. . 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, after the organic EL element 21 is formed on the glass substrate 201 through the insulating film 202, the insulating planarizing film 203, and the window insulating film 204, the passivation film 208 is formed. Then, the sealing substrate 209 is bonded by the adhesive 210. The display panel 70 is formed by sealing the organic EL element 21 with the sealing substrate 209.

(Circuit operation of organic EL display device)
Next, the circuit operation of the organic EL display device 10 in which the pixels 20 having the above-described configuration are two-dimensionally arranged in a matrix will be described with reference to the operation waveform diagrams of FIGS. 5 and 6 based on the timing waveform diagram of FIG. To do. 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, the equivalent capacitance 25 of the organic EL element 21 is also illustrated.

  The timing waveform diagram of FIG. 4 shows changes in the potential (writing scanning signal) WS of the scanning lines 31 (31-1 to 31-m) and the potentials (power supply potentials) of the power supply lines 32 (32-1 to 32-m). ) Changes in DS and changes in the gate potential Vg and source potential Vs of the drive transistor 22 are shown. Further, the waveform of the gate potential Vg is indicated by a one-dot chain line, and the waveform of the source potential Vs is indicated by a dotted line so that the two can be identified.

<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, the drive transistor 22 is designed to operate in a saturation region. As a result, as shown in FIG. 5A, the drive current (drain-source current) Ids according to the gate-source voltage Vgs of the drive transistor 22 passes from the power supply line 32 through the drive transistor 22 to the organic EL element. 21 is supplied. 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, the threshold voltage of the organic EL element 21 is Vthel, and the potential of the common power supply line 34 (cathode potential) is Vcath. At this time, if the low potential Vini is Vini <Vthel + Vcath, the source potential Vs of the drive transistor 22 is substantially equal to the low potential Vini, so that the organic EL element 21 is in a reverse bias state and extinguished.

  Next, when the potential WS of the scanning line 31 transits from the low potential side to the high potential side at time t2, as shown in FIG. 5C, the writing transistor 23 becomes conductive. 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 threshold value is maintained while the gate potential Vg of the driving transistor 22 is maintained. The correction process is started. That is, 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.

  Here, for convenience, processing for changing the source potential Vs toward the potential obtained by subtracting the threshold voltage Vth of the drive transistor 22 from the initialization potential Vofs with reference to the initialization potential Vofs of the gate electrode of the drive transistor 22 is corrected by the threshold value. This is called processing. As the threshold correction process proceeds, the gate-source voltage Vgs of the drive transistor 22 eventually converges to the threshold voltage Vth of the drive transistor 22. A voltage corresponding to the threshold voltage Vth is held in the holding capacitor 24.

  In the period for performing the threshold correction process (threshold correction period), the organic EL element 21 is cut off in order to prevent the current from flowing exclusively to the storage capacitor 24 and not to the organic EL element 21. As described above, the potential Vcath of the common power supply line 34 is set.

  Next, at time t4, the potential WS of the scanning line 31 transitions to the low potential side, so that the writing transistor 23 is turned off as illustrated in FIG. At this time, the gate electrode of the driving 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 cutoff state. Therefore, the drain-source current Ids does not flow through the driving transistor 22.

<Signal writing & 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 the writing of 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 Vth of the driving transistor 22 is canceled with a voltage corresponding to the threshold voltage Vth held in the holding capacitor 24. Details of the principle of threshold cancellation will be described later.

  At this time, the organic EL element 21 is in a cutoff state (high impedance state). Accordingly, the current (drain-source current Ids) flowing from the power supply line 32 to the drive transistor 22 in accordance with the signal voltage Vsig of the video signal flows into the equivalent capacitor 25 of the organic EL element 21 and charging of the equivalent capacitor 25 starts. Is done.

  As the equivalent capacitance 25 of the organic EL element 21 is charged, the source potential Vs of the drive transistor 22 rises with time. At this time, the pixel-to-pixel variation in the threshold voltage Vth of the drive transistor 22 has already been cancelled, and the drain-source current Ids of the drive transistor 22 depends on the mobility μ of the drive transistor 22.

  Here, it is assumed that the ratio of the holding voltage Vgs of the holding capacitor 24 to the signal voltage Vsig of the video signal, that is, the write gain G is 1 (ideal value). Then, 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 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-source voltage Vgs with a feedback amount ΔV corresponding to the drain-source current Ids flowing through the drive transistor 22, the mobility μ of the drain-source current Ids of the drive transistor 22. The dependence on can be negated. This canceling process is a mobility correction process for correcting the variation of the mobility μ of the driving transistor 22 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, mobility correction processing 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, at time t7, the potential WS of the scanning line 31 shifts to the low potential side, so that 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, the storage capacitor 24 is connected between the gate and the source of the driving transistor 22, so that the driving transistor 22 is interlocked with the change in the source potential Vs. The gate potential Vg also varies. 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.

  The gate electrode of the drive transistor 22 enters a floating state, and at the same time, the drain-source current Ids of the drive transistor 22 starts to flow into the organic EL element 21, whereby the anode potential of the organic EL element 21 is set according to the current Ids. To rise.

  When the anode potential of the organic EL element 21 exceeds Vthel + Vcath, the drive current starts to flow through the organic EL element 21, and 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.

(Threshold cancellation principle)
Here, the principle of threshold cancellation (that is, 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, if no cancellation process is performed for the variation of the threshold voltage Vth of the drive transistor 22 for each pixel, the drain-source current corresponding to the gate-source voltage Vgs when the threshold voltage Vth is Vth1. Ids 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 drive transistor 22 at the time of light emission is Vsig−Vofs + Vth−ΔV. Therefore, when this is substituted into the equation (1), 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 can be kept constant.

(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.

  Consider a case where the signal amplitude Vin (= Vsig−Vofs) of the same level is written to both the pixels A and B, for example, in the gate electrode of the drive transistor 22 in a state where the mobility μ varies between the pixel A and the pixel B. In this case, if the mobility μ is not corrected at all, it is 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. There will be a big difference. 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 negative feedback to the gate-source voltage Vgs with the feedback amount ΔV corresponding to the drain-source current Ids of the drive transistor 22 by the mobility correction processing, the negative feedback is increased as the mobility μ is increased. become. As a result, 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 mobility μ from pixel to pixel 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.

  Therefore, by applying negative feedback to the gate-source voltage Vgs with a feedback amount ΔV corresponding to the drain-source current Ids of the driving transistor 22, the current value of the drain-source current Ids of the pixels having different mobility μ. Is made uniform. As a result, variation in mobility μ for each pixel can be corrected. That is, the process for applying negative feedback to the gate-source voltage Vgs 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 voltage 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 is shown in FIG. I will explain.

  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, it is caused by the variation in the mobility μ between the pixels A and B. The difference between the drain-source current Ids between the pixels A and B to be left 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. -The difference in the current Ids between the sources can be almost eliminated. Therefore, 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 source potential Vs of the drive transistor 22 changes with time-dependent changes in the IV characteristics of the organic EL element 21, the gate-source potential Vgs of the drive transistor 22 is set by the bootstrap operation by the storage capacitor 24. Can be kept constant. Therefore, the current flowing through the organic EL element 21 does not change and is constant. As a result, since the light emission luminance of the organic EL element 21 is kept constant, even if the IV characteristic of the organic EL element 21 changes with time, it is possible to realize image display without luminance deterioration associated therewith.

(Problems due to insufficient capacity of organic EL elements)
In the pixel circuit of FIG. 2, the capacitance value of the storage capacitor 22 is Ccs, the capacitance value of the parasitic capacitance between the gate and the source of the driving transistor 22 is Cgs, and the capacitance value of the equivalent capacitance of the organic EL element 21 is Coled. At this time, the write gain G when the signal voltage Vsig of the video signal is written is given by the following equation (3).
G = 1-{(Ccs + Cgs) / (Ccs + Cgs + Coled)} (3)
As is clear from this equation (3), it can be seen that the larger the capacitance value Coled of the equivalent capacitance of the organic EL element 21 is, the closer the write gain G approaches 1 (ideal value).

  On the other hand, in recent years, the pixels 20 tend to be miniaturized more and more as the display devices become higher definition. When the pixel 20 is miniaturized, the size of the organic EL element 21 is inevitably reduced. Then, the capacitance value Coled of the equivalent capacitance of the organic EL element 21 becomes small. As a result, as is clear from the above equation (3), the write gain G decreases.

  As described above, in order to compensate for the shortage of the capacity of the organic EL element 21, generally, a measure of connecting an auxiliary capacity between the anode electrode of the organic EL element 21 and the fixed potential node is taken. However, if an auxiliary capacitor that requires a large area in the layout is added to each pixel 20, the layout in the pixel 20 becomes excessively dense. In addition, the miniaturization of the pixel 20 and, consequently, the high definition of the organic EL display device 10 are hindered.

[Characteristics of this embodiment]
Therefore, in the present embodiment, an auxiliary capacitor is not additionally provided in the pixel 20, but a capacitor element is provided for each pixel column outside the pixel array unit 30, and the capacitor element is used as an auxiliary capacitor of the organic EL element 21. By using it, the lack of capacity of the organic EL element 21 is compensated.

  FIG. 10 is a system configuration diagram showing an outline of the configuration of an organic EL display device 10A according to an embodiment of the present invention. In FIG. 10, the same parts as those in FIG. Here, for simplification of the drawing, the circuit configuration of three adjacent pixels (subpixels) 20i-1, 20i, and 20i + 1 in one row is shown.

  In the pixel array unit 30, the emission color of each pixel 20 is different for each pixel column. Specifically, when one pixel is composed of, for example, three RGB subpixels, the R pixel column, the G pixel column, and the B pixel column are alternately arranged. Here, the pixel 20i-1 in the (i-1) th column is an R subpixel, the pixel 20i in the ith column is a G subpixel, and the pixel 20i + 1 in the (i + 1) th column is a B subpixel. In the pixel array section 30, auxiliary wirings 35i-1, 35i, 35i + 1 are wired for each pixel column.

  Outside the pixel array unit 30, one end of each of the capacitive elements 36i-1, 36i, 36i + 1 is connected to one end of each of the auxiliary wirings 35i-1, 35i, 35i + 1. The other ends of the capacitive elements 36i-1, 36i, 36i + 1 are connected to a fixed potential line 37. One end of each of the reset switches 38i-1, 38i, 38i + 1 is connected to the other end of each of the auxiliary wirings 35i-1, 35i, 35i + 1. The other ends of the reset switches 38i-1, 38i, 38i + 1 are connected to a common power supply line 34 having a cathode potential.

  The pixels 20i-1, 20i, and 20i + 1 have the same pixel configuration as that of the pixel circuit shown in FIG. That is, the pixel 20i-1 has a pixel configuration including the organic EL element 21i-1, the driving transistor 22i-1, the writing transistor 23i-1, and the storage capacitor 24i-1. Similarly, the pixels 20i and 20i + 1 have pixel configurations having organic EL elements 21i and 21i + 1, drive transistors 22i and 22i + 1, write transistors 23i and 23i + 1, and holding capacitors 24i and 24i + 1, respectively.

  These pixels 20i-1, 20i, and 20i + 1 further electrically connect auxiliary wirings 35i, 35i + 1, and 35i + 2 to the respective anode electrodes of the organic EL elements 21i-1, 21i, and 21i + 1 when the signal voltage Vsig of the video signal is written. Switch elements 26i-1, 26i, and 26i + 1. One end of each of the switch elements 26i-1, 26i, 26i + 1 is connected to the anode electrodes of the organic EL elements 21i-1, 21i, 21i + 1 / source electrodes of the drive transistors 22i-1, 22i, 22i + 1, respectively. The other ends of the switch elements 26i-1, 26i, 26i + 1 are connected to auxiliary wirings 35i-1, 35i, 35i + 1, respectively.

  In order to drive the pixels 20 (..., 20i-1, 20i, 20i + 1,...) Configured as described above, the auxiliary scanning circuit 80 includes a peripheral portion of the pixel array unit 30 in addition to the write scanning circuit 40 and the power supply scanning circuit 50. Is provided. The auxiliary scanning circuit 80 outputs the auxiliary scanning signal SS in units of rows in synchronization with the scanning of the writing scanning circuit 40. The auxiliary scanning signal SS performs on (closed) / off (open) driving of the switch elements 26i-1, 26i, and 26i + 1.

  The reset switches 38i-1, 38i, 38i + 1 are turned on (closed) every 1H (H is a horizontal period) by a reset signal RST. This reset signal RST is generated in a 1H cycle by a timing generation circuit (not shown). For the reason described later, a timing signal used in the write scanning circuit 40 can be used as the reset signal RST.

  FIG. 12 is a circuit diagram showing an example of the configuration of the signal output circuit 60. The signal output circuit 60 according to the present example is a time-division drive that supplies signal voltages of RGB video signals supplied in time series through one data line in units of three signal lines corresponding to RGB. The system (selector system) is adopted.

  In FIG. 12, the output terminals of the two selection switches 61-r and 62-r are commonly connected to one end of the R signal line 33i-1. The output terminals of the two selection switches 61-g and 62-g are commonly connected to one end of the G signal line 33i. The output terminals of the two selection switches 61-b and 62-b are commonly connected to one end of the B signal line 33B. The selection switches 61-r, 61-g, 61-b, 62-r, 62-g, and 62-b are configured by, for example, CMOS transistors, but are not limited thereto.

  A video signal is supplied to each input terminal of the selection switches 61-r, 61-g, 61-b through the data line 64. This video signal is a time-series signal in which RGB video signals are supplied in the order of RGB, for example. The selection switch 61-r selects the R video signal by being driven by the switch control signals SEL R and xSEL R that are in reverse phase with each other and are activated in synchronization with the R video signal among the time-series signals. To the signal line 33i-1.

  The selection switch 61-g selects the G video signal by being driven by the switch control signals SEL G and xSEL G having opposite phases that are activated in synchronization with the G video signal among the time-series signals. To the signal line 33i. The selection switch 61-b selects the B video signal by being driven by switch control signals SEL B and xSEL B having opposite phases that are active in synchronization with the B video signal among the time series signals. To the signal line 33i + 1.

  A reference potential Vofs is applied to each input terminal of the selection switches 62-r and 62-g62-b. These selection switches 62-r and 62-g62-b are driven by switch control signals GOFS and xGOFS having opposite phases to selectively output the reference potential Vofs to the signal lines 33i-1, 33i and 33i + 1. .

  Here, the video signal is supplied to the signal output circuit 60 from a driver IC (signal generation unit) (not shown). The reference potential Vofs is supplied to the signal output circuit 60 from a reference potential generation unit (not shown). The switch control signals SEL R, xSEL R, SEL G, xSEL G, SEL B, xSEL B and the switch control signals GOFS, xGOFS are supplied to the signal output circuit 60 from a timing generator (not shown).

(Circuit operation)
Next, the circuit operation of the organic EL display device 10A according to this embodiment having the above-described configuration will be described with reference to the timing waveform diagram of FIG.

  The timing waveform diagram of FIG. 12 shows the timing relationship between the auxiliary scanning signal SS that drives the switch elements 26i-1, 26i, and 26i + 1 and the reset signal RST that drives the reset switches 38i-1, 38i, and 38i + 1. . The timing waveform diagram of FIG. 12 further includes the positive phase switch control signals SEL R, xSEL R, and SEL G used in the signal output circuit 60, the positive phase switch control signal GOFS, and data (signal voltage of the video signal) Data. The timing relationship is shown.

  Although not directly related to the circuit operation of the signal output circuit 60, the timing signals WSEN1 and WSEN2 for controlling the operation of the write scanning circuit 40 are also shown in the same timing waveform diagram with the time axis aligned. Here, the timing signal WSEN1 is a timing signal for generating the write scanning signal WS that determines the write period of the reference potential Vofs in FIG. The timing signal WSEN2 is a timing signal for generating the write scan signal WS that determines the write + mobility correction period of the signal voltage Vsig in FIG.

  First, before the writing period of the signal voltage Vsig of the video signal starts, when the auxiliary scanning signal SS becomes active (in this example, High potential), the switch elements 26i-1, 26i, and 26i + 1 are turned on. In the ON period of the switch elements 26i-1, 26i, and 26i + 1, the write transistors 23i-1, 23i, and 23i + 1 are turned on under the driving by the write scanning signal WS. As a result, the signal voltage Vsig of the video signal is written to the pixels 20i-1, 20i, 20i + 1 according to the write gain G.

  When the signal voltage Vsig is written, the switch elements 26i-1, 26i, 26i + 1 are in the on state, so that the auxiliary wirings 35i-1, 35i, 35i + 1 are connected to the anode electrodes of the organic EL elements 21i-1, 21i + 1. Electrically connected. Capacitance elements 36i-1, 36i, 36i + 1 are connected between the auxiliary wirings 35i-1, 35i, 35i + 1 and a potential line 37 having a fixed potential. Accordingly, the capacitive elements 36i-1, 36i, 36i + 1 are connected in parallel to the equivalent capacitances of the organic EL elements 21i-1, 21i, 21i + 1, and serve as auxiliary capacitors for the organic EL elements 21i-1, 21i, 21i + 1. It will have the function of.

Here, if the capacitance values of the capacitive elements 36i-1, 36i, 36i + 1 are Csub, the write gain G of the signal voltage Vsig is given by the following equation (4).
G = 1-{(Ccs + Cgs)
/ (Ccs + Cgs + Coled + Csub)} (4)

  After the signal voltage Vsig writing + mobility correction period ends, in the next 1H period, for example, the reset signal RST becomes active (high potential in this example) during the reference potential Vofs writing period. Then, the reset switches 38i-1, 38i, 38i + 1 are turned on to apply the cathode potential Vcath to the capacitive elements 36i-1, 36i, 36i + 1. By applying the cathode potential Vcath, the accumulated information of the capacitive elements 36i-1, 36i, 36i + 1 is reset to a charge corresponding to the potential difference between the fixed potential and the cathode potential Vcath.

  That is, the reset switches 38i-1, 38i, 38i + 1 reset the accumulated information of the capacitive elements 36i-1, 36i, 36i + 1 every 1H prior to the writing of the signal voltage Vsig, under the driving by the reset signal RST. Thereby, even if the capacitive elements 36i-1, 36i, 36i + 1 are shared among the pixels in each column for each pixel column as in this example, the influence of the writing information of each pixel in the previous row can be eliminated.

  Specifically, even if the writing information of each pixel in the previous row remains in the capacitive elements 36i-1, 36i, 36i + 1, the remaining information (accumulated information) is transferred to the reset switch 38i− before the writing of the own pixel. It can be reset by the action of 1,38i, 38i + 1. Therefore, it is possible to reliably eliminate the influence of the writing information of each pixel in the previous row on each pixel in the row in which writing is performed this time.

  As described above, by using the capacitive element 36 (36i-1, 36i, 36i + 1) provided outside the pixel array unit 30 as the auxiliary capacity of the organic EL element 21, an auxiliary capacity is added in the pixel 20. Even if it is not, the capacity shortage of the organic EL element 21 can be compensated. Thereby, it is possible to secure a sufficient gain as the write gain G of the signal voltage Vsig of the video signal while suppressing the overdensity of the layout in the pixel 20. Further, by suppressing the over-density of the layout in the pixel 20, it is possible to suppress the occurrence of pixel defects due to a short circuit due to a contaminant in the manufacturing stage. In addition, since the signal voltage Vsig can be written with a sufficient write gain G, a good display image can be obtained.

  Further, since the pixel 20 can be miniaturized as compared with the case where an auxiliary capacitor is added in the pixel 20, it is easy to increase the definition of the organic EL display device 10A. In particular, even when the size of the organic EL element 21 is reduced with the miniaturization of the pixel 20, and the capacity of the organic EL element 21 is insufficient, the capacity element 36 provided outside the pixel array unit 30 is used for the shortage. Therefore, it can greatly contribute to the high definition of the organic EL display device 10A.

  Furthermore, since the capacitive element 36 (36i-1, 36i, 36i + 1) is provided outside the pixel array unit 30, it is possible to easily increase the capacity of the capacitive element 36. Then, by setting the capacitance value of the capacitive element 36 to be large, the write gain G can be made closer to the ideal value.

  In this example, the description has been given on the assumption that the capacitance values Csub of the capacitive element 36i-1 in the R pixel column, the capacitive element 36i in the G pixel column, and the capacitive element 36i + 1 in the B pixel column have the same value. However, it is preferable to set the capacitance value Csub for each emission color. The reason will be described below.

  The organic EL element 21 has different emission efficiency for each emission color due to an organic material or the like. Therefore, the size of the drive transistor 22 that drives the organic EL element 21 by current is generally set to a different size depending on the emission color of the organic EL element 21. If the size of the drive transistor 22 differs depending on the light emission color of the organic EL element 21, a difference occurs in the mobility correction time when performing the mobility correction process depending on the light emission color of the organic EL element 21.

The optimal mobility correction time t is
t = C / (kμVsig) (5)
It is given by Here, the constant k is k = (1/2) (W / L) Cox. Further, C is a capacity of a node that is discharged when performing the mobility correction process, and is a combined capacity of an equivalent capacity of the organic EL element 21, a holding capacity 24, and a capacity element 36 serving as an auxiliary capacity.

  Therefore, in order to make the optimum mobility correction time t constant regardless of the emission color of the organic EL element 21, the size of the organic EL element 21 is changed for each emission color, so that the organic EL element 21 varies between emission colors. What is necessary is to make a difference in equivalent capacity. However, there is a limit to increasing the size of the organic EL element 21 due to the relationship between the aperture ratio of the pixel 20 and the like.

  From such a viewpoint, it is preferable to set the capacitance value Csub of the capacitive element 36 (36i-1, 36i, 36i + 1) for each emission color. Thereby, since the optimal mobility correction time t can be made constant irrespective of the emission color of the organic EL element 21, the optimal mobility correction process can be executed for each emission color. As a result, the display accompanying the mobility correction process Since a quality improvement effect can be sufficiently obtained, a high-quality display image can be obtained.

[Modification]
In the above embodiment, the driving circuit of the organic EL element 21 is basically described as an example of the pixel configuration including the two transistors of the driving transistor 22 and the writing transistor 23. However, the present invention is not limited to this pixel configuration. The application is not limited to. That is, the present invention can be applied to a pixel configuration in which light emission / non-light emission control of the organic EL element 21 is controlled by switching the potential (power supply potential) DS of the power supply line 32 that supplies a drive current to the drive transistor 22. It is.

  As an example, as shown in FIG. 13, in addition to the drive transistor 22 and the write transistor 23, a pixel having a 5Tr circuit configuration composed of five transistors including a light emission control transistor 28 and two switching transistors 29 and 30 as a basic configuration. 20 'is known (see, for example, JP-A-2005-345722). Here, a Pch transistor is used as the light emission control transistor 28 and an Nch is used as the switching transistors 29 and 30, but the combination of these conductivity types is arbitrary.

  The light emission control transistor 28 is connected in series to the drive transistor 22 and selectively controls the light emission / non-light emission of the organic EL element 21 by selectively supplying the high potential Vccp to the drive transistor 22. The switching transistor 29 initializes the gate potential Vg to the reference potential Vofs by selectively applying the reference potential Vofs to the gate electrode of the drive transistor 22. The switching transistor 30 initializes the source potential Vs to the low potential ini by selectively applying the low potential ini to the source electrode of the drive transistor 22.

  Here, the 5Tr circuit configuration has been described as an example of another pixel configuration. For example, the reference potential Vofs is supplied through the signal line 33, and the reference potential Vofs is written by the write transistor 23, thereby switching transistors. Various pixel configurations are possible, such as omitting 27.

  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 20 has been described as an example. However, the present invention is not limited to this application example. . Specifically, the present invention relates to a display device using a current-driven electro-optical element (light-emitting element) such as an inorganic EL element, an LED element, or a semiconductor laser element whose emission luminance changes according to the current value flowing through the device. Applicable to all.

[Application example]
The display device according to the present invention described above can be applied to display devices of electronic devices in various fields that display video signals input to electronic devices or video signals generated in electronic devices as images or videos. Is possible. As an example, the present invention can be applied to various electronic devices shown in FIGS. 14 to 18 such as a digital camera, a notebook personal computer, a mobile terminal device such as a mobile phone, and a display device such as a video camera.

  In this manner, by using the display device according to the present invention as a display device for electronic devices in all fields, high-quality image display can be performed in various electronic devices. That is, as is apparent from the description of the above-described embodiment, the display device according to the present invention can compensate for the shortage of the capacity of the organic EL element without adding an auxiliary capacity in the pixel. It is possible to achieve high definition of the display device while ensuring the above.

  The display device according to the present invention includes a module-shaped one having a sealed configuration. For example, a display module formed by attaching a facing portion such as transparent glass to the pixel array portion 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 a signal to the pixel array unit from the outside, an FPC (flexible printed circuit), and the like.

  Specific examples of electronic devices to which the present invention is applied will be described below.

  FIG. 14 is a perspective view showing an appearance of a television set to which the present invention is applied. The television set 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.

  15A and 15B are perspective views showing the external appearance of a digital camera to which the present invention is applied. FIG. 15A is a perspective view seen from the front side, and FIG. 15B 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. 16 is a perspective view showing an external appearance of 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, and the display device according to the present invention is used as the display unit 123. It is produced by this.

  FIG. 17 is a perspective view showing the appearance of 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 a display device.

  18A and 18B are external views showing a mobile terminal device to which the present invention is applied, for example, a mobile phone. FIG. 18A is a front view in an open state, FIG. 18B 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. A cellular phone according to this application example includes an upper casing 141, a lower casing 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. Then, by using the display device according to the present invention as the display 144 or the sub display 145, the mobile phone according to this application example is manufactured.

1 is a system configuration diagram showing an outline of a configuration of an organic EL display device to which the present invention is applied. It is a circuit diagram which shows the circuit structure of the pixel of the organic electroluminescence display which concerns on this application example. 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 of the organic electroluminescence display which concerns on this application example. It is explanatory drawing (the 1) of the circuit operation | movement of the organic electroluminescence display which concerns on this application example. It is explanatory drawing (the 2) of the circuit operation | movement of the organic electroluminescence display which concerns on this application example. 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. 1 is a system configuration diagram illustrating an outline of a configuration of an organic EL display device according to an embodiment of the present invention. It is a circuit diagram which shows an example of a structure of a signal output circuit. It is a timing waveform diagram which shows the drive timing of the organic electroluminescence display which concerns on this embodiment. It is a circuit diagram which shows an example of the circuit structure of the pixel of another structure. 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 10,10A ... Organic EL display device, 20 (20i-1, 20i, 20i + 1), 20 '... Pixel, 21 ... Organic EL element, 22 ... Drive transistor, 23 ... Write transistor, 24 ... Retention capacity, 25 ... Organic EL Equivalent capacitance of element, 26 (26i-1, 26i, 26i + 1) ... control transistor, 30 ... pixel array section, 31 (31-1 to 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, 35 (35i-1, 35i, 35i + 1) ... auxiliary wiring, 36 (36i-1, 36i, 36i + 1) ... Capacitance element, 38 (38i-1, 38i, 38i + 1) ... reset switch, 40 (40o, 40e) ... write scanning circuit, 50 ... power supply scanning circuit, 60 ... signal output circuit, 70 ... display Nel

Claims (8)

An electro-optic element;
A writing transistor for writing a video signal;
A holding capacitor for holding the video signal written by the writing transistor;
A pixel array unit in which pixels having a driving transistor for driving the electro-optic element in accordance with the video signal held in the holding capacitor are arranged in a matrix;
An auxiliary wiring routed for each pixel column of the pixel array section;
A capacitive element connected to the auxiliary wiring outside the pixel array unit;
And a switch element that electrically connects the auxiliary wiring to the anode electrode of the electro-optic element when the video signal is written by the writing transistor. The display device according to claim 1, further comprising a reset switch that resets accumulated information of the capacitive element. The display device according to claim 2, wherein the reset switch resets accumulated information of the capacitive element every horizontal period. The display device according to claim 2, wherein the reset switch resets accumulated information of the capacitive element to a cathode potential of the electro-optic element. The emission color of each pixel of the pixel array section is different for each pixel column,
The display device according to claim 1, wherein a capacitance value of the capacitive element is set for each emission color. The display device according to claim 5, wherein the pixel has a function of mobility correction processing that applies negative feedback to a potential difference between a gate and a source of the driving transistor with a correction amount according to a current flowing through the driving transistor. An electro-optic element;
A writing transistor for writing a video signal;
A holding capacitor for holding the video signal written by the writing transistor;
In driving a display device in which pixels having a drive transistor for driving the electro-optic element according to the video signal held in the holding capacitor are arranged in a matrix,
When the video signal is written by the writing transistor, the auxiliary wiring connected to the anode electrode of the electro-optical element for each pixel column of the pixel array section and connected to the capacitor element outside the pixel array section is electrically connected. Connected display device drive method. An electro-optic element;
A writing transistor for writing a video signal;
A holding capacitor for holding the video signal written by the writing transistor;
A pixel array unit in which pixels having a driving transistor for driving the electro-optic element in accordance with the video signal held in the holding capacitor are arranged in a matrix;
An auxiliary wiring routed for each pixel column of the pixel array section;
A capacitive element connected to the auxiliary wiring outside the pixel array unit;
An electronic apparatus having a display device, comprising: a switching element that electrically connects the auxiliary wiring to the anode electrode of the electro-optical element when the video signal is written by the writing transistor.

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