# Patent

## Title
Display apparatus and electronic apparatus

## Abstract

Disclosed herein is a display apparatus, including: a foldable substrate; a pixel array section including a plurality of pixels disposed on the substrate and each including an electro-optical device; the foldable substrate being folded at a substrate end portion at least on one side thereof around the pixel array section; a peripheral circuit section disposed on the substrate end portion and adapted to drive the pixels of the pixel array section; and a pad section provided on the substrate end portion on which the peripheral circuit section is provided and adapted to electrically connect the peripheral circuit section to the outside of the substrate.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of U.S. application Ser. No. 13/302,624, filed Nov. 22, 2011, which claims priority to Japanese Patent Application No. JP 2010-276940, filed in the Japan Patent Office on Dec. 13, 2010, the entire contents of which are hereby incorporated by reference in their entirety.


BACKGROUND
This technology relates to a display apparatus and an electronic apparatus, and particularly to a display apparatus wherein a plurality of pixels each including an electro-optical element are disposed in rows and columns or in a matrix and an electronic apparatus which includes a display apparatus.
In recent years, in the field of display apparatus for displaying an image, a display apparatus of a planar type, that is, of a flat panel type in which a plurality of pixels or pixel circuits are disposed in a matrix has been popularized rapidly. As one of flat panel type display apparatus, a display apparatus is available which uses, as a light emitting element of a pixel, an electro-optical element of the current driven type which emits light of the luminance which varies in response to the value of current flowing therethrough. As the current driven type electro-optical element, an organic EL element is known which makes use of a phenomenon that, if an electric field is applied to an organic thin film of an organic material, then it emits light utilizing electroluminescence (EL) of the organic material.
An organic EL displaying element which uses an organic EL element as a light emitting element of pixels has such a characteristic as described below. In particular, since the organic EL element can be driven with an application voltage of 10 V or less, the power consumption can be suppressed low. Further, since the organic EL element is a self-luminous element, visibility of a displayed image is high in comparison with a liquid crystal display apparatus. Besides, since an illuminating member such as a backlight is not required, reduction in weight and thickness can be achieved readily. Furthermore, since the speed of response of the organic EL element is approximately several μ seconds and is very high, an afterimage upon moving picture display does not appear.
The organic EL display apparatus can adopt any of a simple or passive matrix method and an active matrix method as a driving method similarly to the liquid crystal display apparatus. However, although the passive matrix type display apparatus is simple in structure, since the light emission period of the electro-optical element is reduced by increase of the number of scanning lines, or in other words, by increase of the number of pixels, there is a problem in that it is difficult to implement a large-sized and high-definition display apparatus.
Therefore, in recent years, development of an active matrix type display apparatus in which current to flow to an electro-optical element is controlled by an active element such as, for example, by an insulated gate type electric field effect transistor provided in a pixel in which the electro-optical element is provided has been and is proceeding energetically. As the insulated gate type electric field effect transistor, a TFT (Thin Film Transistor) is used popularly. Since, in the active matrix type display apparatus, the electro-optical element continues light emission over a period of one display frame, it can be implemented readily in a large size and high definition.
A pixel circuit including a current-driven type electro-optical element which is driven by the active matrix method includes, in addition to the electro-optical element, a driving circuit for driving the electro-optical element. One of such driving circuits is disclosed, for example, in Japanese Patent Laid-Open No. 2009-103868 (hereinafter referred to as Patent Document 1). The driving circuit of Patent Document 1 is incorporated in a pixel circuit and is configured from a driving transistor 22 for driving a current-driven type electro-optical element such as, for example, an organic EL element 21, a writing transistor 23 and a retaining capacitor 24.
In Patent Document 1, an organic EL display apparatus 10B in which peripheral circuit sections (40, 50 and 60) are mounted on a display panel 70 in which a pixel array section 30 configured from a great number of unit pixels 20b is incorporated is disclosed (refer to paragraph 0027, FIGS. 1, 10 and so forth of Patent Document 1).
Further, in Patent Document 1, it is described to commonly use one power supplying line 32 (32−1 to 32−m) for four subpixels 20W, 20R, 20G and 20B which belong to two vertically neighboring rows which configure the same unit pixel 20b. Furthermore, in Patent Document 1, it is described that, since the circuit scale of the writing scanning circuit 40 can be reduced by commonly using one power supplying line 32, reduction of the width of the molding of the framework of the display panel 70 can be achieved (refer to paragraph 0136 of Patent Document 1). Here, the “molding of the framework” is that region of the display panel 70 around a pixel array section 30 which does not contribute to image display.
SUMMARY
As described above, by reducing the number of circuit elements and wiring lines which configure the peripheral circuit sections for driving pixels of the pixel array section to reduce the circuit scale of the peripheral circuit sections, reduction of the width of the framework molding of the display panel can be achieved. However, since there is a limitation to reduction of the circuit scale by decrease of the number of circuit elements and wiring lines which configure the peripheral circuit sections, there is a limitation also to reduction of width of the framework molding of the display panel. Thus, if it is tried to satisfy a demand for further reduction of the width of the work molding of the display panel, then it is sometimes forced to restrict a function of a peripheral circuit to achieve reduction of the circuit scale of the peripheral circuit section.
Therefore, it is desirable to provide a display apparatus and an electronic apparatus by which further reduction of the width of the framework molding of a display panel can be achieved without restricting a function of a peripheral circuit section which drives pixels of a pixel array section.
According to the disclosed technology, there is provided a display apparatus including a foldable substrate, a pixel array section including a plurality of pixels disposed on the substrate and each including an electro-optical device, the foldable substrate being folded at a substrate end portion at least on one side thereof around the pixel array section, a peripheral circuit section disposed on the substrate end portion and adapted to drive the pixels of the pixel array section, and a pad section provided on the substrate end portion on which the peripheral circuit section is provided and adapted to electrically connect the peripheral circuit section to the outside of the substrate.
In the display apparatus having the configuration described above, since the substrate is folded at a substrate end portion at least on one side thereof around the pixel array section, the region portion around the pixel array section which does not contribute to image display, that is, the framework molding, can be reduced in size by an amount corresponding to the region of the folded substrate end portion. Thereupon, the peripheral circuit section is positioned on the substrate on which the pixel array section is provided through the folding portion. Accordingly, even if contact portions such as terminals are not interposed between the peripheral circuit section and the pixel array section, the peripheral circuit section and the pixel array section can be electrically connected to each other.
Further, the size of the substrate end portion is not limited if it remains within the range of the size of the substrate main body on which the pixel array section is mounted. Accordingly, the scale of the peripheral circuit section disposed on the substrate end portion and hence a function of the peripheral circuit section are not limited. Besides, since the pad section for electrically connecting the peripheral circuit section and the outside of the board to each other is provided on the substrate end portion on which the peripheral circuit section is provided, the distance between the folding portion of the substrate end portion and the peripheral circuit section is small. Thus, even if wiring lines cannot be laid between them, electric connection between the peripheral circuit section and the outside of the substrate can be carried out with certainty.
In summary, with the display apparatus, since a foldable substrate is used and a peripheral circuit section is disposed on a substrate end portion of the board folded at least on one side around the periphery of a pixel array section, further reduction in width of the framework molding of the display panel can be achieved without limiting any function of the peripheral circuit section. Besides, even though the distance between the folding portion of the substrate end portion and the peripheral circuit section is so small that wiring lines cannot be laid between them, electric connection between the peripheral circuit section and the outside of the substrate can be established with certainty.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view schematically showing a structure of a display panel of a display apparatus according to an embodiment of the present technology;
FIGS. 2A and 2B are sectional views showing the display panel of FIG. 1 before and after folding thereof, respectively;
FIG. 3 is a front elevational view schematically showing a different structure of the display panel of FIG. 1;
FIGS. 4A and 4B are schematic views of the display panel of FIG. 1 before and after folding of a substrate end portion;
FIGS. 5A to 5D are schematic views illustrating an example of a procedure of folding of substrate end portions;
FIG. 6 is a partial sectional view showing an example of a structure of the display panel of FIG. 1;
FIG. 7 is a top plan view showing a panel structure which has a water invasion preventing groove at a basic main body section of the display panel of FIG. 1;
FIG. 8 is a top plan view showing another panel structure which has a water invasion preventing groove at a basic main body portion and a substrate end portion of the display panel of FIG. 1;
FIG. 9 is a block diagram showing a general configuration of an organic EL display apparatus to which the display apparatus according to the embodiment of the disclosed technology is applied;
FIG. 10 is a circuit diagram showing an example of a circuit configuration of each pixel of the organic EL display apparatus of FIG. 9;
FIG. 11 is a timing waveform diagram illustrating basic circuit operation of the organic EL display apparatus of FIG. 9;
FIGS. 12A to 12D and 13A to 13D are circuit diagrams illustrating basic circuit operation of the organic EL display apparatus of FIG. 9;
FIGS. 14A and 14B are characteristic diagrams illustrating a subject arising from a dispersion in threshold voltage of a driving transistor and another subject arising from a dispersion in mobility of the driving transistor, respectively;
FIG. 15A is a block diagram showing an example of a configuration of a writing scanning circuit and FIG. 15B is a circuit diagram showing an example of a circuit of a shift register which configures the writing scanning circuit;
FIG. 16A is a circuit diagram showing an example of a circuit configuration of an inverter circuit configured from a combination of one-sided channel transistors and capacitance elements and FIG. 16B is a waveform diagram showing waveforms of an input pulse signal and an output pulse signal of the inverter circuit;
FIG. 17 is a circuit diagram showing an example of a configuration of a signal outputting circuit;
FIG. 18 is a schematic top plan view showing an example of a configuration of electrical connection to the outside of the substrate in the case where a scanning circuit section is provided in the panel;
FIG. 19 is a similar view but showing an example of a configuration of electrical connection to the outside of the substrate in the case where the scanning circuit section is provided outside the panel;
FIG. 20 is a perspective view showing an appearance of a television set to which the display apparatus of the disclosed is applied;
FIGS. 21A and 21B are perspective views showing an appearance of a digital camera, to which the display apparatus of the disclosed is applied, as viewed from the front side and the rear side, respectively;
FIG. 22 is a perspective view showing an appearance of a notebook type personal computer to which the display apparatus of the disclosed is applied;
FIG. 23 is a perspective view showing an appearance of a video camera to which the display apparatus of the disclosed is applied; and
FIGS. 24A and 24B are a front elevational view and a side elevational view, respectively, showing a portable telephone set in an unfolded state, and FIGS. 24C, 24D, 24E, 24F and 24G are a front elevational view, a left side elevational view, a right side elevational view, a top plan view and a bottom plan view, respectively, of the portable telephone set.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the following, a preferred embodiment of the disclosed technology is described in detail with reference to the accompanying drawings. It is to be noted that the description is given in the following order.
1. Embodiment
2. Organic EL Display Apparatus to which the Disclosed Technology Is Applied
2-1. System Configuration
2-2. Basic Circuit Action
2-3. Example of the Configuration of the Driving Circuit Section
3. Modifications
4. Electronic Apparatus
1. Embodiment
FIG. 1 shows a general structure of a display panel of a display apparatus according to an embodiment of the disclosed technology. Meanwhile, FIGS. 2A and 2B show cross sections of the display panel before and after folding thereof, respectively.
Referring to FIGS. 1, 2A and 2B, the display apparatus 10 according to the embodiment is defined most in that a foldable or bendable substrate is used as a substrate which configures a display panel 70, more particularly as a substrate on which pixel circuits are to be formed. For the foldable substrate, a known substrate such as a metal substrate which is a thin plate of a metal, a plastic substrate or the like can be used.
Preferably, the metal substrate is formed, for example, from a stainless steel substrate from a point of view of the corrosion resistance. However, from a point of view of the insulating property, preferably a plastic substrate is used rather than a metal substrate. A thin plate of a stainless steel substrate, a plastic substrate or the like can be folded or bent readily using a known bending jig.
The display panel 70 includes a substrate main body section 70A, and four substrate end portions 70B to 70E folded to the rear face side, for example, along the four sides of a periphery of the substrate main body section 70A. In FIG. 1, of the four substrate end portions 70B to 70E, the substrate end portions 70B and 70C on the opposite left and right sides of the substrate main body section 70A and the substrate end portion 70B on the lower side of the substrate main body section 70A are schematically shown by alternate long and short dash lines.
A plurality of pixels or pixel circuits 20 each including an electro-optical element such as, for example, an electro-optical element of the self luminous type are arrayed two-dimensionally in rows and columns over a substantial overall area of the substrate main body section 70A of the display panel 70 to configure a pixel array section 30. Here, as the electro-optical element of the self luminous type, an organic EL element, an inorganic EL element, an LED element, a semiconductor laser element and so forth are widely known. The electro-optical elements of the self luminous type are light emitting elements of the current driven type whose emitted light luminance varies in response to the value of current flowing therethrough.
Meanwhile, on the substrate end portions 70B and 70C on the opposite left and right sides and the substrate end portion 70B on the lower side of the substrate main body section 70A, peripheral circuit sections 80A to 80C for driving the pixels 20 of the pixel array section 30 are provided. The peripheral circuit sections 80A to 80C are electrically connected to the pixel array section 30 through wiring lines of a wiring line section 81 as seen in FIGS. 2A and 2B. A particular example of the peripheral circuit sections 80A to 80C is hereinafter described.
Upon fabrication of the display panel 70, the pixels 20 of the pixel array section 30 are formed and circuit elements of the peripheral circuit sections 80A to 80C are formed on the bendable or foldable substrate (70A to 70B) in the form of a flat plate as shown in FIG. 2A. Further, wiring lines of the wiring line section 81 for electrically connecting the pixel array section 30 and the peripheral circuit sections 80A to 80C to each other are formed or wired.
For the display panel 70 in the form of a flat plate on which the pixel array section 30, peripheral circuit sections 80A to 80C and wiring line section 81 are formed in this manner, a bending or folding work is carried out, for example, from a start point at which a folding jig 82 is disposed on the rear face of the wiring line section 81 as seen in FIG. 2A. By this folding work, the substrate end portions 70B and 70C (70B) on which the peripheral circuit sections 80A and 80B (80C) are mounted are folded and positioned on the rear side of the substrate main body section 70A, that is, on the opposite side to the display face.
Accordingly, as a molding of a framework on a periphery of the pixel array section 30 of the display panel 70, only part of the wiring line section 81 exists, and therefore, the framework molding of the display panel 70 can be formed narrow or with a small width. In other words, the area of a surplus region which does not contribute to image display around the pixel array section 30 can be suppressed to a minimum necessary degree.
Besides, the pixel array section 30 and the peripheral circuit sections 80A to 80C are electrically connected to the wiring lines of the wiring line section 81 formed on one substrate although the substrate is folded between them. Consequently, there is no necessity to provide pad portions such as terminals which are provided in a case wherein a flexible cable or the like is used to connect an external substrate, for example, to the substrate main body section 70A. Accordingly, since there is no necessity to assure a region for providing pad portions, further reduction in width of the framework molding of the display panel 70 can be anticipated.
Further, the substrate end portions 70B and 70C (70D) are not restricted in size if the size remains within a range of the size of the substrate main body section 70A on which the pixel array section 30 is provided. Accordingly, the circuit scale of the peripheral circuit sections 80A and 80B (80C) disposed on the substrate end portions 70B and 70C (70D) and hence the function of the peripheral circuit sections 80A and 80B (80C) are not restricted.
In the present embodiment, the display panel 70 is folded on the four sides thereof on the periphery of the pixel array section 30, and the peripheral circuit sections 80A, 80B and 80C are mounted on the three substrate end portions 70B, 70C and 70D from the four sides. However, the panel structure of the display panel 70 is not limited to this. For example, on three sides of the periphery of the pixel array section 30 on which the peripheral circuit sections 80A, 80B and 80C are mounted may be bent or folded as seen in FIG. 3. In this instance, since the substrate end portion 70E which remains not bent or folded forms a margin which occupies most part of the framework, it is considered preferable to bend or fold the display panel 70 on the four sides. Further, even if four or three sides are not folded but at least one side of the periphery of the pixel array section 30 is folded, then the effect of reduction of the width of the framework molding in comparison with that in an alternative case wherein none of the four sides is folded.
As described above, as a substrate which configures the display panel 70, a foldable substrate is used. Then, by disposing the peripheral circuit sections 80A, 80B and 80C on the substrate end portions 70B, 70C and 70E folded on at least one side of the periphery of the pixel array section 30, various circuits having various functions can be mounted as the peripheral circuit sections 80A, 80B and 80C without being restricted by the framework molding size. Accordingly, further reduction of the width of the framework molding of the display panel 70 can be achieved without limiting the functions of the peripheral circuit sections 80A, 80B and 80C. Particularly if the pixel array section 30 is folded on the four sides of the periphery thereof, a display apparatus which substantially eliminates the framework mounting portion and uses the overall area of the display face of the display panel 70 as a display area can be implemented.
FIGS. 4A and 4B show the display panel 70 before and after the substrate end portions 70B, 70C and 70D are folded, respectively. In the example of FIGS. 4A and 4B, from among the four sides of the periphery of the pixel array section 30, only three sides of the periphery of the pixel array section 30 on which the peripheral circuit sections 80A, 80B and 80C are mounted are folded while the remaining one side, which is shown on the upper side in FIGS. 4A and 4B, is cut away.
In FIGS. 4A and 4B, the pixel array section 30 is a valid pixel section which contributes to display of an image, that is, a display area section. The substrate end portions 70B and 70C on the opposite left and right sides of the pixel array section 30, that is, on the left and right sides of the substrate main body section 70A, and the substrate end portion 70D on the lower side are folded while the substrate end portion 70D on the upper side is cut off. Details are described below.
First, in order to cut away the substrate end portion 70E on the upper side, a cutting portion 83A is formed between the upper end of the substrate main body section 70A and the substrate end portion 70E such that it extends in a horizontal direction between the opposite ends of the substrate main body section 70A. Then, grooves 83B and 83C are formed between the opposite ends of the cutting portion 83A and the upper end of the substrate end portion 70E. Consequently, the substrate end portion 70E on the upper side can be cut away from the substrate main body section 70A.
Then, in order to fold the substrate end portions 70B and 70C on the opposite left and right sides, grooves 83D and 83E are formed on the substrate end portions 70B and 70C such that they extend along the lower end of the substrate main body section 70A from the opposite left and right sides. Then, before the substrate end portions 70B and 70C are bent, upper end portions 70B0 and 70C0 of them are bent along thick broken lines. Thereafter, the substrate end portions 70B and 70C are bent along the thick broken lines, and the substrate end portions 70B and 70C are bent along the thick broken lines on the boundaries between the substrate end portions 70B and 70C and the substrate main body section 70A.
Then, for example, at an upper end of the upper end portions 70B0 and 70C0 of the substrate end portions 70B and 70C, the peripheral circuit sections 80A and 80B and the outside of the substrate are electrically connected to each other. In particular, pad portions 84A and 84B for fetching a power supply voltage for peripheral circuit sections 80A and 80B and various signals from the outside of the substrate therethrough are provided. The pad portions 84A and 84B are provided on the substrate end portions 70B and 70C on which the peripheral circuit sections 80A and 80B are provided, respectively, more particularly at locations, that is, at the upper end portions 70B0 and 70C0, in the substrate end portions 70B and 70C farther than the bent portions. The pad portions 84A and 84B and the peripheral circuit sections 80A and 80B are electrically connected to each other through wiring lines on the bent portions in the substrate end portions 70B and 70C.
Thereafter, in order to bend the substrate end portion 70D, the opposite end portions 70D1 and 70D2 of the substrate end portion 70D are first bent along thick broken lines on extension lines of bending lines of the substrate end portions 70B and 70C on the boundaries of the grooves 83D and 83E. Then, the substrate end portion 70D is bent along a thick broken line on the boundary between the substrate end portion 70D and the substrate main body section 70A, that is, along a thick broken line interconnecting the grooves 83D and 83E.
Here, it is assumed that, as an example, the peripheral circuit section 80C mounted on the substrate end portion 70D is a signal outputting circuit which outputs a video signal supplied from a signal supply source not shown provided externally of the substrate as hereinafter described to the pixels of the pixel array section 30. In this instance, the pad portion group 84C for fetching a video signal from the outside of the substrate is provided for each pixel column of the pixel array section 30 at a lower end of the substrate end portion 70D. The pad portion group 84C is provided substantially corresponding to the pixel columns of the pixel array section 30 over the width of the pixel array section 30 in the horizontal direction.
A pair of pad portions 84D and 84E for electrically connecting the peripheral circuit section 80C and the outside of the substrate to each other, that is, for fetching gate controlling signals for controlling, for example, transistors which configure the signal outputting circuit described above from the outside of the substrate, are provided, for example, at a lower end of the opposite end portions 70D1 and 70D2 of the substrate end portion 70D, respectively. In particular, the pad portions 84D and 84E are provided on the substrate end portion 70D on which the signal outputting circuit formed from the peripheral circuit section 80C is provided, more particularly at locations, that is, at the opposite end portions 70D1 and 70D2, in the substrate end portion 70D farther than the bent portions. Then, the pad portions 84D and 84E and the peripheral circuit section 80C are electrically connected to each other by wiring lines on the bent portions in the substrate end portion 70D.
As described hereinabove, by cutting away the substrate end portion 70E on the upper side from the substrate main body section 70A and then bending the substrate end portions 70B and 70C on the opposite left and right sides and the substrate end portion 70D on the lower side, the display panel 70 substantially of a size of the substrate main body section 70A can be implemented. However, since it is necessary to assure a bending margin at the bent portions of the substrate end portions 70B, 70C and 70D, the final display panel 70 has some framework molding 70F on the periphery of the substrate main body section 70A as seen in FIG. 4B.
Further, by disposing the peripheral circuit sections 80A, 80B and 80C on the folded substrate end portions 70B, 70C and 70D, circuits having various functions can be incorporated as the peripheral circuit sections 80A, 80B and 80C without being restricted by the framework molding size. Accordingly, further reduction in width of the framework molding of the display panel 70 can be achieved without limiting the functions of the peripheral circuit sections 80A, 80B and 80C.
Besides, pad portions 84A, 84B, 84D and 84E for electrically connecting the peripheral circuit sections 80A, 80B and 80C and the outside of the substrate to each other are provided on the substrate end portions 70B, 70C and 70D on which the peripheral circuit sections 80A, 80B and 80C are provided, respectively. More particularly, the pad portions 84A, 84B, 84D and 84E are provided at locations on the substrate end portions 70B, 70C and 70B farther than the bend portions in the substrate end portions 70B, 70C and 70D, that is, at the upper end portions 70B0 and 70C0 and the opposite end portions 70B1 and 70D2 of the substrate end portions 70B, 70C and 70D. Consequently, the distance between the bent portions in the substrate end portions 70B, 70C and 70D and the peripheral circuit sections 80A, 80B and 80C is small, and even if wiring lines cannot be laid, electric connection between the peripheral circuit sections 80A, 80B and 80C and the outside of the substrate can be established with certainty.
Here, an example of a procedure of bending or folding of the substrate end portions 70B, 70C and 70D of the substrate having the structure described above is described with reference to FIGS. 5A to 5D. FIG. 5A corresponds to FIG. 4A.
In the state illustrated in FIG. 5A, the substrate end portion 70E on the upper side is cut away from the substrate main body section 70A. Then, the upper end portions 70B0 and 70C0 of the substrate end portions 70B and 70C on the opposite left and right sides are folded to the rear face side of the substrate end portions 70B and 70C as indicated by arrow marks in FIG. 5B. Further, the opposite end portions 70D1 and 70D2 of the substrate end portion 70D on the lower side is folded to the rear face side of the substrate end portion 70D as indicated by arrow marks.
Then, the substrate end portions 70B and 70C on the opposite left and right sides are folded to the rear face side of the substrate main body section 70A as indicated by arrow marks, and then the substrate end portion 70D on the lower side is bent or folded to the rear face side of the substrate main body section 70A as indicated by arrow marks. Consequently, the display panel 70 having some framework molding 70F on the periphery of the substrate main body section 70A as seen in FIG. 5D is formed. FIG. 5D corresponds to FIG. 4B.
Now, a structure of the display panel 70 is described with reference to FIG. 6. FIG. 6 shows a partial section of an example of the structure of the display panel 70.
As described hereinabove, the display panel 70 includes the substrate main body section 70A on which the pixel array section 30 is formed, the substrate end portion 70B (70C) on which the peripheral circuit section 80A (80B) is formed, and a folding or bending region 85 positioned between the substrate main body section 70A and the substrate end portion 70B (70C) as seen in FIG. 2. The wiring line section 81 for electrically connecting the peripheral circuit section 80A (80B) and the pixel array section 30 to each other is formed in the folding region 85. In other words, on the wiring line section 81 of the folding region 85, only simple metal wiring lines are laid out while any circuit section including a transistor or the like is not laid out.
In FIG. 6, a circuit section including thin film transistors (TFTs) 22 including a gate electrode 221 and so forth is formed on a foldable substrate 201. Further, an insulating film, that is, a gate insulating film 202, a flattening film 203 and a window insulating film 204 are laminated in this order on the substrate 201. Further, as an electro-optical element, for example, an organic EL element 21 is formed in a recessed portion of the window insulating film 204. The TFTs 22 are, for example, driving transistors for driving such organic EL elements 21.
Each organic EL element 21 includes an anode electrode 205, an organic layer 206, and a cathode electrode 207. The anode electrode 205 is made of a metal formed on the bottom of the recessed portion of the window insulating film 204. The organic layer 206 is formed on the anode electrode 205. The cathode electrode 207 is formed from a transparent conductor film or the like formed commonly to all pixels on the organic layer 206.
In the organic EL element 21, the organic layer 206 is formed from a hole transport layer/hole implantation layer, a light emitting layer, an electron transport layer and an electron implantation layer successively deposited on the anode electrode 205. Then, under current driving by the TFT 22, current flows from the TFT 22 to the organic layer 206 through the anode electrode 205, whereupon electrons and holes are recombined in the light emitting layer in the organic layer 206 to emit light.
The pixel section including the organic EL elements 21 and the TFTs 22 is protected by a protective layer 208 from above. The substrate 201 is covered over an overall area thereof with a sheet resin 209. Further, above the sheet resin 209 on the substrate main body section 70A on which the pixel array section 30 is formed, an opposing substrate 209 which is a second substrate formed from a sealing film, a glass substrate or the like is disposed. In other words, the opposing substrate 210 is disposed only in a region of the substrate main body section 70A so as not to extend to the folding region 85.
As apparently seen from FIG. 6, only metal wiring lines 811 are laid out in the wiring line section 81 of the folding region 85 while a circuit section including a transistor or like is not laid out. In particular, the folding region 85 is configured such that the metal wiring lines 811 are formed on the substrate 201 with the insulating film 202 interposed therebetween and the flattening film 203 and the window insulating film 204 are laminated in order on the metal wiring lines 811 and are covered with the sheet resin 209 from above.
Incidentally, the display panel 70 of the panel structure described above sometimes suffers from crazing or cracking when the display panel 70 is folded at the folding region 85. If cracking occurs, then water or the like may invade into the display panel 70 through the crack and may possibly deteriorate a circuit element of the pixel array section 30.
Therefore, in order to prevent such invasion of water or the like through the crack thereby to prevent deterioration of the circuit elements, the display panel 70 in the present embodiment has a panel structure wherein a water invasion preventing groove 86 is provided on the substrate 201 on the pixel array section 30 side with respect to the folding region 85. The water invasion preventing groove 86 is formed such that it surrounds the pixel array section 30 as seen in a plan view of FIG. 7. The water invasion preventing groove 86 is formed by removing the flattening film 203 and the window insulating film 204 as apparently seen from the sectional view of FIG. 6.
By adopting the panel structure in which the water invasion preventing groove 86 is provided in this manner, even if a crack appears when the display panel 70 is folded, water or the like invading from the crack is accumulated in the water invasion preventing groove 86 and is prevented from further invading to the pixel array section 30 side by the water invasion preventing groove 86. Accordingly, deterioration of the circuit elements which may arise from water or the like invading through the crack can be prevented, and consequently, electric reliability of the display panel 70 is not damaged. In other words, while electric reliability of the display panel 70 is maintained, reduction in width of the framework molding of the display panel 70 by folding of the substrate can be anticipated.
It is to be noted that, while it is described above that the water invasion preventing groove 86 is formed on the substrate 201 on the pixel array section 30 side with respect to the folding region 85 in such a manner as to surround the pixel array section 30, the water invasion preventing groove 86 need not necessarily be formed on the display panel 70 side. In particular, in addition to a water invasion preventing groove 86A on the pixel array section 30, a water invasion preventing groove 86 may be formed at least one of the substrate end portions 70B, 70C and 70D as seen in FIG. 8.
In particular, referring to FIG. 8, water invasion preventing groove 86B, 86C and 86D may be formed on the substrate end portions 70B, 70C and 70D on the peripheral circuit sections 80A, 80B and 80C side with respect to the folding region 85 in such a manner as to surround the peripheral circuit sections 80A, 80B and 80C, respectively. Although it is shown in FIG. 8 that the water invasion preventing groove 86 (86B, 86C and 86D) is formed on all of the substrate end portions 70B, 70C and 70D, it may otherwise be formed on only one of the substrate end portions 70B, 70C and 70D.
By forming the water invasion preventing groove 86 also on the substrate end portions 70B, 70C and 70D side in this manner, even if a crack appears on the substrate end portions 70B, 70C and 70D when the display panel 70 is folded, a working effect similar to that of the substrate main body section 70A can be achieved. In particular, water or the like invading from the crack is accumulated in the water invasion preventing grooves 86B, 86C and 86D and is prevented from further invading toward the peripheral circuit sections 80A, 80B and 80C side by the water invasion preventing grooves 86B, 86C and 86C. Accordingly, otherwise possible deterioration of the circuit elements of the peripheral circuit sections 80A, 80B and 80C arising from water or the like invading through the crack can be prevented, and therefore, electric reliability of the display panel 70 is not damaged. In other words, while electric reliability of the display panel 70 is further maintained, reduction in width of the framework molding of framework of the display panel 70 by folding of the substrate can be achieved.
2. Organic EL Display Apparatus to which the Disclosed Technology is Applied
The display apparatus in which a display panel can be configured by using a foldable or bendable substrate includes a display apparatus of a flat panel type using an electro-optical element of the self luminous type as the electro-optical element of the pixels 20. An organic EL display apparatus making use of an organic EL element as an electro-optical element is described below.
2-1. System Configuration
FIG. 9 shows a general configuration of an active matrix type organic EL display apparatus to which the disclosed technology is applied.
Referring to FIG. 9, the organic EL display apparatus 10A according to the present application includes a pixel array section 30 in which a plurality of pixels 20 each including an organic EL element are arrayed two-dimensionally in rows and columns, and peripheral circuit sections disposed around the pixel array section 30. The peripheral circuit sections include a writing scanning circuit 40, a power supply scanning circuit 50, a signal outputting circuit 60 and so forth and drive the pixels 20 of the pixel array section 30.
If the organic EL display apparatus 10A is ready for color display, then one pixel is configured from a plurality of subpixels, and each of the subpixels corresponds to a pixel 20. More particularly, in a display apparatus for color display, one pixel is configured from three sub pixels including a subpixel for emitting red light (R), another subpixel for emitting green light (G) and a further subpixel for emitting blue light (B).
However, one pixel is not limited to a combination of subpixels of the three primary colors of red, green and blue but may be configured from one subpixel of a color or a plurality of subpixels of different colors in addition to subpixels of the three primary colors. More particularly, in order to improve the luminance, a subpixel for emitting white light (W) may be additionally used to configure one pixel or at least one subpixel for emitting complementary color light for enlarging the color reproduction range may be additionally used to configure one pixel.
The pixel array section 30 corresponds to the pixel array section 30 described hereinabove in connection with the embodiment of the disclosed technology and is formed on a foldable substrate (201), that is, on the substrate main body section 70A of the embodiment described hereinabove. The pixel array section 30 includes scanning lines 311 to 31m, power supply lines 321 to 32m, and signal lines 331 to 33n. The scanning lines 311 to 31m and the power supply lines 321 to 32m are wired for the individual pixel rows along a row direction, that is, along a direction in which the pixels are arrayed in a pixel row, for the array of the pixels 20 arrayed in m rows and n columns. The signal lines 331 to 33n are wired for the individual pixel columns along a column direction, that is, in a direction in which the pixels are arrayed in a pixel column.
The scanning lines 311 to 31m, power supply lines 321 to 32m and signal lines 331 to 33n correspond to wiring lines of the wiring line section 81 in the embodiment described hereinabove. Further, the writing scanning circuit 40, power supply scanning circuit 50 and signal outputting circuit 60 correspond to the peripheral circuit sections 80A, 80B and 80C in the embodiment described hereinabove, respectively.
The scanning lines 311 to 31m are connected to output terminals of corresponding rows of the writing scanning circuit 40. The power supply lines 321 to 32m are connected to output terminals of corresponding rows of the power supply scanning circuit 50. The signal lines 331 to 33n are connected to output terminals of corresponding columns of the signal outputting circuit 60.
The writing scanning circuit 40 is configured from a shift register which shifts or transfers a start pulse sp in response to a clock pulse ck or from a like circuit. A detailed configuration of the writing scanning circuit 40 is hereinafter described. Upon writing of a video signal into the pixels 20 of the pixel array section 30, the writing scanning circuit 40 successively supplies writing scanning signals WS (WS1 to WSn) to the scanning lines 31 (311 to 31m) to successively scan the pixels 20 of the pixel array section 30 in a unit of a row (line-sequential scanning).
The power supply scanning circuit 50 is configured from a shift register which shifts a start pulse sp in response to the clock pulse ck or a like circuit. The power supply scanning circuit 50 supplies power supply potentials DS (DS1 to DSm), which can change over between a first power supply potential Vccp and a second power supply potential Vini which is lower than the first power supply potential Vccp, to the power supply lines 32 (321 to 32m) in synchronism with line-sequential scanning by the writing scanning circuit 40. As hereinafter described, light emission/no-light emission control of the pixels 20 is carried out by changeover of the power supply potential DS between the first power supply potential Vccp and the second power supply potential Vini as hereinafter described.
The signal outputting circuit 60 selectively outputs a signal voltage Vsig of a video signal corresponding to luminance information supplied thereto from a signal supplying source not shown and a reference potential Vofs. Here, the reference potential Vofs is a potential which makes a reference to the signal voltage Vsig of the video signal such as, for example, a potential corresponding to the black level of the video signal, and is used upon a threshold value correction process hereinafter described.
The signal voltage Vsig/reference potential Vofs outputted from the signal outputting circuit 60 is written into the pixels 20 of the pixel array section 30 through the signal lines 33 (331 to 33n) in a unit of a pixel row selected by scanning by the writing scanning circuit 40. In particular, the signal outputting circuit 60 adopts a driving form for line-sequential scanning of writing the signal voltage Vsig in a unit of a row or line.
As described hereinabove, the display panel 70 on which the pixel array section 30, writing scanning circuit 40, power supply scanning circuit 50 and signal outputting circuit 60 are mounted is formed from a foldable substrate and is folded at portions thereof indicated by alternate long and short dash lines on the periphery of the pixel array section 30. Consequently, reduction of the width of the frame molding of the display panel 70 can be achieved without restricting the functions of the writing scanning circuit 40, power supply scanning circuit 50 and signal outputting circuit 60. The functions of the writing scanning circuit 40, power supply scanning circuit 50 and signal outputting circuit 60 are hereinafter described.
Pixel Circuit
FIG. 10 shows an example of a particular circuit configuration of each pixel or pixel circuit 20. A light emitting section of the pixel 20 is formed from an organic EL element 21 which is an electro-optical element of the current driven type which emits light whose luminance varies in response to the value of current flowing therethrough.
Referring to FIG. 10, the pixel 20 is configured from an organic EL element 21, and a driving circuit for supplying current to the organic EL element 21 to drive the organic EL element 21. The organic EL element 21 is connected at the cathode electrode thereof to a common power supply line 34 wired commonly to all pixels 20.
The driving circuit for driving the organic EL element 21 includes a driving transistor 22, a writing transistor 23, a retaining capacitor 24, and an auxiliary capacitor 25. A TFT of the N channel type can be used for the driving transistor 22 and the writing transistor 23. However, the combination of the conduction types of the driving transistor 22 and the writing transistor 23 described here is a mere example, and the combination of conduction types of the driving transistor 22 and the writing transistor 23 is not limited to this specific one.
The driving transistor 22 is connected at one electrode thereof, that is, at one of the source and drain electrodes thereof, to the anode electrode of the organic EL element 21, and at the other electrode thereof, that is, at the drain or source electrode thereof, to a power supply line 32 (321 to 32m).
The writing transistor 23 is connected at one electrode thereof, that is, at one of the source and drain electrodes thereof, to a signal line 33 (331 to 33n) and at the other electrode thereof, that is, at the drain or source electrode thereof, to the gate electrode of the driving transistor 22. Further, the writing transistor 23 is connected at the gate electrode thereof to a scanning line 31 (311 to 31m).
The one of the electrodes of the driving transistor 22 and the writing transistor 23 is a metal wiring line electrically connected to the source/drain region, and the other electrode is a metal wiring line electrically connected to the drain/source region. Further, the one electrode may serve as the source electrode or the drain electrode and the other electrode may serve as the drain electrode and the source electrode depending upon the potential relationship between the one electrode and the other electrode.
The retaining capacitor 24 is connected at one electrode thereof to the gate electrode of the driving transistor 22 and at the other electrode thereof to the other electrode of the driving transistor 22 and the anode electrode of the organic EL element 21.
The auxiliary capacitor 25 is connected at one electrode thereof to the anode electrode of the organic EL element 21 and at the other electrode thereof to the common power supply line 34. The auxiliary capacitor 25 is provided as occasion demands in order to compensate for shortage of the capacitance of the organic EL element 21 and raise the write gain of a video signal into the retaining capacitor 24. In other words, the auxiliary capacitor 25 is not an essentially required component and can be omitted in the case where the equivalent capacitance of the organic EL element 21 is sufficiently high.
While the other electrode of the auxiliary capacitor 25 here is connected to the common power supply line 34, the connection destination of the other electrode of the auxiliary capacitor 25 is not limited to the common power supply line 34 but may be a node of a fixed potential. By connecting the other electrode of the auxiliary capacitor 25 to the node of a fixed potential, it is possible to compensate for shortage of the capacitance of the organic EL element 21 and achieve the intended aim of raising the write gain of a video signal into the retaining capacitor 24.
In the pixel 20 of the configuration described above, the writing transistor 23 is placed into a conducting state in response to a High-active writing scanning signal WS applied to the gate electrode thereof from the writing scanning circuit 40 through the scanning line 31. Consequently, the writing transistor 23 samples the signal voltage Vsig or the reference potential Vofs of the video signal corresponding to luminance information supplied thereto from the signal outputting circuit 60 through the signal line 33 and writes the sampled voltage into a pixel 20. The signal voltage Vsig or reference potential Vofs thus written in is applied to the gate electrode of the driving transistor 22 and retained into the retaining capacitor 24.
When the power supply potential DS of the power supply line 32 (321 to 32m) is the first power supply potential Vccp, the driving transistor 22 operates in a saturation region while the one electrode of the driving transistor 22 serves as the drain electrode and the other electrode of the driving transistor 22 serves as the source electrode. Consequently, the driving transistor 22 receives supply of current from the power supply line 32 and drives the organic EL element 21 by current driving to emit light. More particularly, the driving transistor 22 operates in a saturation region such that it supplies driving current of a current value corresponding to the voltage value of the signal voltage Vsig retained in the retaining capacitor 24 to the organic EL element 21 such that the organic EL element 21 is driven by current driving to emit light.
On the other hand, if the power supply potential DS changes over from the first power supply potential Vccp to the second power supply potential Vini, then the driving transistor 22 operates as a switching transistor while the one electrode serves as the source electrode and the other electrode serves as the drain electrode. Then, the driving transistor 22 is placed into a non-conducting state to stop the supply of driving current to the organic EL element 21 thereto to place the organic EL element 21 into a no-light emitting state. In other words, the driving transistor 22 has also a function as a transistor for controlling light emission/no-light emission of the organic EL element 21.
By this switching operation of the driving transistor 22, it is possible to provide a period within which the organic EL element 21 is in a no-light emitting state, that is, in a no-light emitting period and control the rate between the light emitting period and the no-light emitting period of the organic EL element 21, that is, the duty of the organic EL element 21. By this duty control, remaining image blurring caused by emission of light by a pixel over one display frame period can be reduced, and consequently, the picture quality of a moving picture can be further improved.
Of the first and second power supply potentials Vccp and Vini supplied selectively from the power supply scanning circuit 50 through the power supply line 32, the first power supply potential Vccp is a power supply potential for supplying driving current for driving the organic EL element 21 to emit light to the driving transistor 22. Meanwhile, the second power supply potential Vini is another power supply potential for applying a reverse bias to the organic EL element 21. This second power supply potential Vini is set to a potential lower than the reference potential Vofs, for example, where a threshold voltage of the driving transistor 22 is represented by Vth, to a potential lower than Vofs−Vth, preferably to a potential sufficiently lower than Vofs−Vth.
2-2. Basic Circuit Action
Now, basic circuit action of the display apparatus 10 having the configuration described above is described with reference to FIGS. 11 to 13D. It is to be noted that, in FIGS. 12A to 13D, the writing transistor 23 is indicated by a symbol of a switch for simplified illustration.
In FIG. 11, variations of the potential DS, that is, the write scanning signal WS, of a scanning line 31, the potential DS, that is, the power supply potential, of a power supply line 32, the potential (Vsig/Vofs) of a signal line 33, and the gate potential Vg and the source potential Vs of the driving transistor 22 are illustrated. Further, the waveform of the gate potential Vg of the driving transistor 22 is indicated by an alternate long and short dash line while the waveform of the source potential Vs is indicated by a broken line so that they can be distinguished from each other.
Light Emitting Period of a Pre-Display Frame
In FIG. 11, a period before time t11 is a light emitting period of the organic EL element 21 in a preceding display frame. Within the light emitting period of the pre-display frame, the power supply potential DS of the power supply line 32 exhibits a first power supply potential (hereinafter referred to as “high potential”) Vccp while the writing transistor 23 is in a non-conducting state.
The driving transistor 22 is designed such that, at this time, it operates in a saturation region. Consequently, driving current or drain-source current Ids corresponding to the gate-source voltage Vgs of the driving transistor 22 is supplied from the power supply line 32 to the organic EL element 21 through the driving transistor 22 as seen in FIG. 12A. Consequently, the organic EL element 21 emits light with a luminance corresponding to the current value of the driving current Ids.
Threshold Value Correction Preparation Period
When time t11 comes, a new display frame (current display frame) of line-sequential scanning is entered. Then, the power supply potential DS of the power supply line 32 changes over from the high potential Vccp to the second power supply potential Vini (hereinafter referred to as “low potential”), which is sufficiently lower than Vofs−Vth from the reference potential Vofs of the signal line 33 as seen in FIG. 12B.
Here, the threshold voltage of the organic EL element 21 is represented by Vthel and the potential, that is, the cathode potential, of the common power supply line 34 is represented by Vcath. At this time, if the low potential Vini satisfies Vini<Vthel+Vcath then since the source potential Vs of the driving transistor 22 becomes substantially equal to the low potential Vini, the organic EL element 21 is placed into a reversely biased state and turned off.
Then, since the writing scanning signal WS of the scanning line 31 transits from the low potential side to the high potential side at time t12, the writing transistor 23 is placed into a conducting state as seen in FIG. 12C. At this time, since the reference potential Vofs is supplied from the signal outputting circuit 60 to the signal line 33, the gate potential Vg of the driving transistor 22 becomes the reference potential Vofs. Further, the source potential Vs of the driving transistor 22 is the Vini sufficiently lower than the reference potential Vofs.
At this time, the gate-source voltage Vgs of the driving transistor 22 becomes Vofs−Vini. Here, if Vofs−Vini is not higher than the threshold voltage Vth of the driving transistor 22, then since a threshold value correction process hereinafter described cannot be carried out, it is necessary to set Vofs−Vini to a potential relationship of Vofs−Vini>Vth.
A process of fixing the gate potential Vg of the driving transistor 22 to the reference potential Vofs and fixing the source potential Vs of the driving transistor 22 to the low potential Vini to initialize them is a preparation process, that is, a threshold value correction preparation process, before a threshold value correction process or threshold value correction operation hereinafter described. Accordingly, the reference potential Vofs and the low potential Vini are initialization potentials for the gate potential Vg and the source potential Vs of the driving transistor 22, respectively.
Threshold Value Correction Period
Then, after the power supply potential DS of the power supply line 32 changes over from the low potential Vini to the high potential Vccp at time t13 as seen in FIG. 12D, a threshold value correction process is started in a state in which the gate potential Vg of the driving transistor 22 is kept at the reference potential Vofs. In particular, the source potential Vs of the driving transistor 22 begins its rise toward the potential which is the difference of the threshold voltage Vth from the gate potential Vg.
Here, for the convenience of description, a process of determining the reference potential Vofs for the gate potential Vg of the driving transistor 22 as a reference and varying the source potential Vs toward the potential which is the difference of the threshold voltage Vth from the reference potential Vofs is called threshold value correction process. If this threshold value correction process proceeds, then the gate-source voltage Vgs of the driving transistor 22 soon converges to the threshold voltage Vth of the driving transistor 22. This voltage corresponding to the threshold voltage Vth is retained into the retaining capacitor 24.
It is to be noted that, within a period within which the threshold value correction process is carried out, that is, within a threshold value correction period, in order to allow current to wholly flow toward the retaining capacitor 24 side but prevent current from flowing to the organic EL element 21 side, the potential Vcath of the common power supply line 34 is set such that the organic EL element 21 is placed into a cutoff state.
Then, the writing scanning signal WS of the scanning line 31 transits to the low potential side at time t14, and thereupon, the writing transistor 23 is placed into non-conducting state as seen in FIG. 13A. At this time, the gate electrode of the driving transistor 22 enters a floating state by being electrically disconnected from the signal line 33. However, since the gate-source voltage Vgs is equal to the threshold voltage Vth of the driving transistor 22, the driving transistor 22 is in a cutoff state. Accordingly, drain-source current Ids does not flow to the driving transistor 22.
Signal Writing and Mobility Correction Period
Then at time t15, the potential of the signal line 33 changes over from the reference potential Vofs to the signal voltage Vsig of the video signal. Then at time t16, the writing scanning signal WS of the scanning line 31 transits to the high potential side, whereupon the writing transistor 23 enters a conducting state and samples and writes the signal voltage Vsig of the video signal into 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. Then, 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 by the voltage corresponding to the threshold voltage Vth retained in the retaining capacitor 24. Details of the principle of the threshold value cancellation are hereinafter described.
At this time, the organic EL element 21 is in a cutoff state, that is, in a high impedance state. Accordingly, the current which flows from the power supply line 32 to the driving transistor 22 in response to the signal voltage Vsig of the video signal, that is, the drain-source current Ids, flows into the equivalent capacitor of the organic EL element 21 and the auxiliary capacitor 25 thereby to start charging of the capacitors.
As the equivalent capacitor of the organic EL element 21 and the auxiliary capacitor 25 are charged, the source potential Vs of the driving transistor 22 gradually rises as time passes. At this time, the dispersion of the threshold voltage Vth of the driving transistor 22 among the pixels is canceled already, and consequently, the drain-source current Ids of the driving transistor 22 relies upon the mobility μ of the driving transistor 22. It is to be noted that the mobility μ of the driving transistor 22 is a mobility of a semiconductor thin film which configures the channel of the driving transistor 22.
Here, it is assumed that the rate of the retained voltage Vgs of the retaining capacitor 24 to the signal voltage Vsig of the video signal, that is, the write gain G, is 1 (ideal value). Thus, if the source potential Vs of the driving transistor 22 rises to the potential of Vofs−Vth+ΔV, then the gate-source voltage Vgs of the driving transistor 22 becomes Vsig−Vofs+Vth−ΔV.
In particular, the rise amount ΔV of the source potential Vs of the driving transistor 22 acts so as to be subtracted from the voltage Vsig−Vofs+Vth retained in the retaining capacitor 24, or in other words, so as to discharge the photocharge of the retaining capacitor 24, and this signifies that a negative feedback is applied to the retaining capacitor 24. Accordingly, the rise amount ΔV of the source potential Vs is a feedback amount in negative feedback.
By applying negative feedback to the gate-source voltage Vgs by the feedback amount ΔV corresponding to the drain-source current Ids flowing to the driving transistor 22 in this manner, the dependency of the drain-source current Ids of the driving transistor 22 upon the mobility μ can be canceled. This cancellation process is a mobility correction process for correcting the dispersion of the mobility μ of the driving transistor 22 among the pixels.
More particularly, since the drain-source current Ids increases as the signal amplitude Vin(=Vsig−Vofs) of the video signal to be written into the gate electrode of the driving transistor 22, also the absolute value of the feedback amount ΔV in negative feedback increases. Accordingly, the mobility correction process in accordance with the emitted light luminance level is carried out.
Further, if it is assumed that the signal amplitude Vin of the video signal is fixed, then since the absolute value of the feedback amount ΔV increases as the mobility μ of the driving transistor 22 increases, the dispersion of the mobility μ among the pixels can be removed. Accordingly, the feedback amount ΔV in negative feedback can be regarded also as a correction amount of the mobility correction process. Details of the principle of the mobility correction are hereinafter described.
Light Emitting Period
Then, the writing scanning signal WS of the scanning line 31 transits to the low potential side at time t17, whereupon the writing transistor 23 is placed into a non-conducting state as seen in FIG. 13D. Consequently, the gate electrode of the driving transistor 22 is electrically disconnected from the signal line 33 and consequently placed into a floating state.
Here, when the gate electrode of the driving transistor 22 is in a floating state, since the retaining capacitor 24 is connected between the gate and the source of the driving transistor 22, also the gate potential Vg varies in an interlocking relationship with the variation of the source potential Vs of the driving transistor 22. The operation wherein the gate potential Vg of the driving transistor 22 varies in an interlocking relationship with the variation of the gate potential Vg is a bootstrap operation by the retaining capacitor 24.
Then, since the gate electrode of the driving transistor 22 is placed into a floating state and simultaneously drain-source current Ids of the driving transistor 22 begins to flow to the organic EL element 21, the anode potential of the organic EL element 21 rises in response to the current Ids.
Then, if the anode potential of the organic EL element 21 exceeds Vthel+Vcath then since driving current begins to flow to the organic EL element 21, the organic EL element 21 begins to emit light. The rise of the anode potential of the organic EL element 21 is no more than a rise of the source potential Vs of the driving transistor 22. Then, as the source potential Vs of the driving transistor 22 rises, also the gate potential Vg of the driving transistor 22 rises in an interlocking relationship by a bootstrap operation of the retaining capacitor 24.
At this time, if it is assumed that the bootstrap gain is 1 (ideal value), then the rise amount of the gate potential Vg is equal to a rise amount of the source potential Vs. Therefore, during a light emitting period, the gate-source voltage Vgs of the driving transistor 22 is kept fixed at Vsig−Vofs+Vth−ΔV. Then, at time t18, the potential of the signal line 33 changes over from the signal voltage Vsig of the video signal to the reference potential Vofs.
In the series of circuit operations described above, the processing operations of threshold value correction preparation, threshold value correction, writing of the signal voltage Vsig, that is, signal writing, and mobility correction are executed in one horizontal scanning period (1H). Further, the processing operations of signal writing and mobility correction are executed in parallel within the period from t6 to time t7.
Divisional Threshold Value Correction
It is to be noted here that, while the foregoing description is given taking a case wherein a driving method wherein a threshold value correction process is executed only once is adopted as an example, this driving method is a mere example and the driving method is not limited to the specific method. For example, in addition to a 1H period within which the threshold value correction process is carried out together with the mobility correction and signal writing processes, the threshold value correction process is executed divisionally by a plural number of times over a plurality of horizontal scanning periods executed within the 1H period. Thus, also it is possible to adopt a driving method which involves divisional threshold value correction.
With the driving method which involves divisional threshold value correction, even if the period of time allocated as one horizontal scanning period is shortened by increase of the number of pixels involved in enhancement of the definition, sufficient time can be assured over a plurality of horizontal scanning periods for a threshold value correction period. Accordingly, even if the time allocated as one horizontal scanning period becomes short, the threshold value correction process can be executed with certainty.
Principle of Threshold Value Cancellation
Here, the principle of threshold value cancellation or threshold value correction of the driving transistor 22 is described. Since the driving transistor 22 is designed so as to operate in its saturation region, it operates as a constant current source. Consequently, fixed drain-source current or driving current Ids given by the following expression is supplied from the driving transistor 22 to the organic EL element 21:

Ids=(1/2)·μ(W/L)COX(Vgs−Vth)2  (1)

where W is the channel width of the driving transistor 22, L the channel length and COX the gate capacitance per unit area.

FIG. 14A illustrates a characteristic of the drain-source current Ids with respect to the gate-source voltage Vgs of the driving transistor 22. If the cancellation process or correction process for the dispersion of the threshold voltage Vth of the driving transistor 22 among the pixels is not carried out as seen from the characteristic diagram of FIG. 14A, then when the threshold voltage Vth is Vth1, the drain-source current Ids corresponding to the gate-source voltage Vgs becomes Ids1.
However, when the threshold voltage Vth is Vth2 (Vth2>Vth1), the drain-source current Ids corresponding to the same gate-source voltage Vgs becomes Ids1 (Ids2<Ids1). In particular, if the threshold voltage Vth of the driving transistor 22 varies, then the drain-source current Ids varies even if the gate-source voltage Vgs is fixed.
On the other hand, in the pixel or pixel circuit 20 having the configuration described above, the gate-source voltage Vgs of the driving transistor 22 upon light emission is Vsig−Vofs+Vth−ΔV. Accordingly, if this is substituted into the expression (1), then the drain-source current Ids is represented by the following expression (2):

Ids=(1/2)·μ(W/L)COX(Vsig−Vofs−ΔV)2  (2)

In particular, the term of the threshold voltage Vth of the driving transistor 22 is canceled, and the drain-source current Ids supplied from the driving transistor 22 to the organic EL element 21 does not rely upon the threshold voltage Vth of the driving transistor 22. As a result, even if the threshold voltage Vth of the driving transistor 22 varies among the pixels due to a dispersion in fabrication process, a time-dependent variation and so forth of the driving transistor 22, since the drain-source current Ids does not vary, the emitted light luminance of the organic EL element 21 can be kept fixed.
Principle of Mobility Correction
Now, the principle of mobility correction of the driving transistor 22 is described. FIG. 14B illustrates characteristic curves for comparison of a pixel A wherein the mobility μ of the driving transistor 22 is comparatively high and a pixel B wherein the mobility μ of the driving transistor 22 is comparatively low. In the case where the driving transistor 22 is configured from a polysilicon thin film transistor or the like, it cannot be avoided that the mobility μ disperses among pixels like between the pixel A and the pixel B.
For example, a case is considered wherein signal voltages Vin(=Vsig−Vofs) of an equal level are written into the gate electrodes of the driving transistors 22 of the pixels A and B while the pixel A and the pixel B have a dispersion in mobility μ therebetween. In this instance, if correction of the mobility μ is not carried out, then a great difference appears between the drain-source current Ids1′ flowing through the pixel A having the high mobility μ and the drain-source current Ids2′ flowing through the pixel B having the low mobility μ. If a great difference appears in drain-source current Ids among the pixels arising from a dispersion in mobility μ among the pixels in this manner, then the uniformity of the screen image is damaged.
As apparent from the characteristic expression of the expression (1) given hereinabove, as the mobility μ increases, the drain-source current Ids increases. Accordingly, the feedback amount ΔV in negative feedback increases as the mobility μ increases. As seen from FIG. 14B, the feedback amount ΔV1 of the pixel A whose mobility μ is high is higher than the feedback amount ΔV2 of the pixel B whose mobility μ is low.
Therefore, by applying negative feedback to the gate-source voltage Vgs by the feedback amount ΔV corresponding to the drain-source current Ids of the driving transistor 22 by the mobility correction process, the amount of application of negative feedback increases as the mobility μ increases. As a result, the dispersion of the mobility μ among the pixels can be corrected.
In particular, if correction by the feedback amount ΔV1 is applied to the pixel A whose mobility μ is high, then the drain-source current Ids decreases by a greater amount from Ids1′ to Ids1. On the other hand, since the feedback amount ΔV2 to the pixel B whose mobility μ is low is small, the drain-source current Ids drops from Ids2′ to Ids2 and does not drop by a great amount. As a result, the drain-source current Ids1 of the pixel A and the drain-source current Ids2 of the pixel B become substantially equal to each other, and consequently, the dispersion in mobility μ between the pixels is corrected.
In summary, where a pixel A and a pixel B which are different in mobility μ from each other are available, the feedback amount ΔV1 of the pixel A whose mobility μ is high is greater than the feedback amount ΔV2 of the pixel B whose mobility μ is low. In other words, as the mobility μ increases, the feedback amount ΔV increases and the decreasing amount of the drain-source current Ids increases.
Accordingly, by applying negative feedback to the gate-source voltage Vgs by the feedback amount ΔV corresponding to the drain-source current Ids of the driving transistor 22, the current value of the drain-source current Ids is uniformized among the pixels having different values of the mobility μ. As a result, the dispersion in mobility μ among the pixels can be corrected. Thus, a process of applying negative feedback to the gate-source voltage Vgs of the driving transistor 22, that is, to the retaining capacitor 24, by the feedback amount or correction amount ΔV corresponding to the current flowing through the driving transistor 22, that is, corresponding to the gate-source voltage Vgs, is the mobility correction process.
2-3. Example of the Configuration of the Driving Circuit Sections
Here, an example of the configuration of the circuit sections disposed around the pixel array section 30, that is, the driving circuits sections for driving the pixels 20 of the pixel array section 30, is described.
A. Writing Scanning Circuit
First, as one of the driving circuit sections, the writing scanning circuit 40 for carrying out sequential selection scanning of the pixels 20 of the pixel array section 30 in a unit of a row upon writing of the signal voltage Vsig/reference potential Vofs into the pixels 20 is described by way of an example.
FIGS. 15A and 15B show an example of a configuration of the writing scanning circuit 40, and particularly FIG. 15A shows an example of the configuration of the writing scanning circuit 40 and FIG. 15B shows an example of a circuit of a shift register which configures the writing scanning circuit 40.
Referring first to FIG. 15A, the writing scanning circuit 40 basically includes, as a principal component thereof, a shift register circuit 41 for successively shifting or transferring a start pulse sp in synchronism with a clock pulse ck not shown. Further, the writing scanning circuit 40 includes buffer circuits . . . , 42i, 42i+1, . . . for individual transfer stages or unit circuits . . . , 41i, 41i+1, . . . of the shift register circuit 41 corresponding to the rows of the pixel array section 30.
Here, while the shift register circuit 41 shown is configured such that the two transfer stages 41i and 41i+1 of the ith and i+1th rows, actually the shift register circuit 41 includes a number of transfer stages 411 to 41m equal to the number of rows of the pixel array section 30 connected in cascade connection. Each transfer stage of the shift register circuit 41, for example, the transfer stage 41i of the ith row, includes a shift register (SR) 411, an inverter (INV) 412, another shift register 413 and another inverter 414 connected in cascade connection to form a unit circuit.
A particular circuit example of the inverters 412 and 414 is hereinafter described. Referring to FIG. 15B, the shift register 413 is configured from a transistor Q1 which operates with the clock pulse ck, another transistor Q2 which operates with another clock pulse xck and a capacitor C1. A parasitic capacitor C2 exists between an output terminal of the shift register 413 and an input terminal of the inverter 414.
Referring back to FIG. 15A, the buffer circuit 42i is configured from an inverter 421, a logic circuit 422 and another inverter 423 connected in cascade connection. In this manner, each of the transfer stages 41i and 41i+1 of the shift register circuit 41 and the buffer circuits 42 (42i and 42i+1) is configured using an inverter circuit.
B. Inverter Circuit of a One-Sided Channel Transistor
Incidentally, upon fabrication of the driving circuit sections such as the writing scanning circuit 40, if the driving circuit sections are configured using transistors of a one-sided channel (only of an N channel or of a P channel), then the fabrication cost can be reduced in comparison with that in an alternative case wherein they are configured using both-sided channels. Accordingly, in order to reduce the cost of the display apparatus 10, for example, in the writing scanning circuit 40, inverter circuits which configure the shift register circuit 41 or the buffer circuits 42 is preferably configured using transistors of a one-sided channel.
In the case where an inverter circuit is configured using transistors of a one-sided channel, in order to make circuit operation of the inverter circuit sure, a circuit configuration based on a combination of transistors of a one-sided channel and a capacitance element is adopted. In the following, for example, an inverter circuit formed from a combination of transistors of a one-sided channel and capacitance elements to be used as the inverters 412 and 414 which configure the shift register circuit 41 is described.
Circuit Configuration
FIGS. 16A and 16B show an inverter circuit formed from a combination of transistors of a one-sided channel and capacitance elements, and particularly FIG. 16A shows an example of the circuit configuration and FIG. 16B illustrates waveforms of an input pulse signal INVin and the output pulse signal INVout.
The inverter circuit 90 in the present circuit example substantially inverts the input pulse signal INVin inputted thereto through an input terminal 91 and outputs a pulse signal INVout of a phase opposite to that of the input pulse signal INVin from an output terminal 92. This inverter circuit 90 uses, as power supply voltages, for example, four power supply voltages Vcc1, Vcc2, Vcc3 and Vcc4 for the positive side and, for example, four power supply voltages Vss1, Vss2, Vss3 and Vss4 for the negative side. However, the power supply voltages mentioned here are a mere example, and the power supply voltages are not limited to them. A smaller number of power supply voltages may be used, or it is possible to use one power supply voltage for each of the positive and negative sides.
The inverter circuit 90 is configured such that it includes, for example, seven transistors Tr1 to Tr7, five capacitance element C1 to C5 and a delay circuit 93. The seven transistors Tr1 to Tr7 are MOS (Metal Oxide Semiconductor) thin film transistors, that is, TFTs, of the same channel or one-sided channel such as, for example, the N channel. While it is described here that transistors only of the N channel are used as the transistors Tr1 to Tr7, also it is possible to use transistors only of the P channel.
The transistor Tr1 is connected at the drain electrode thereof to a power supply line L12 of the positive side power supply voltage Vcc2 and at the source electrode thereof to a node N1 and receives a voltage corresponding to an input voltage, that is, the input pulse signal INVin, inputted through the input terminal 91 as a gate input. The transistor Tr2 is connected at the drain electrode thereof to a power supply line L13 of the positive side power supply voltage Vcc3, at the source electrode thereof to a node N2 and at the gate electrode thereof to the node N1. The transistor Tr3 is connected at the drain electrode thereof to a power supply line L14 of the positive side power supply voltage Vcc4, at the source electrode thereof to an output terminal 92 and at the gate electrode thereof to the node N2.
The delay circuit 93 is configured, for example, from two transistors Tr91 and Tr92 connected in parallel to each other. Naturally, the two transistors Tr91 and Tr92 are N-channel MOS transistors similarly to the transistors Tr1 to Tr7. The transistors Tr91 and Tr92 are connected commonly at one of the electrodes, that is, at the source electrode or the drain electrode thereof, and the one electrode serves as a circuit input terminal of the delay circuit 93 while the other electrode, that is, the drain electrode or the source electrode, serves as a circuit output terminal of the delay circuit 93.
In the delay circuit 93, the circuit input terminal is connected to the input terminal 91. Also the transistor Tr91 is connected at the gate electrode thereof to the input terminal 91. The transistor Tr92 is connected at the gate electrode thereof to a power supply line L11 of the positive side power supply voltage Vcc1.
The transistor Tr4 is connected at the drain electrode thereof to the gate electrode of the transistor Tr1, at the gate electrode thereof to a power supply line L21 of the negative side power supply voltage Vss1 and at the gate electrode thereof to the circuit output terminal of the delay circuit 93. The transistor Tr5 is connected at the drain electrode thereof to the node N1 and at the source electrode thereof to a power supply line L22 of the negative side power supply voltage Vss2. In other words, the transistor Tr5 is connected in series to the transistor Tr1 and connected at the gate electrode thereof to the input terminal 91.
The transistor Tr6 is connected at the drain electrode thereof to the node N2 and at the source electrode thereof to a power supply line L23 of the negative side power supply voltage Vss3. In other words, the transistor Tr6 is connected in series to the transistor Tr2 and connected at the gate electrode thereof to the input terminal 91. The transistor Tr7 is connected at the drain electrode thereof to the output terminal 92, at the source electrode thereof to a power supply line L24 of the negative side power supply voltage Vss4 and at the gate electrode thereof to the input terminal 91.
The capacitor C1 is connected at one terminal thereof to the gate electrode of the transistor Tr1 and at the other terminal thereof to the node N1. In other words, the capacitor C1 is connected between the gate and the source of the transistor Tr1. The parasitic capacitor C2 is connected at one electrode thereof to the node N1 and at the other electrode thereof to the input terminal 91. The node N1 is a common connection node of the transistor Tr1 and the transistor Tr5.
The capacitance element C3 is connected at one electrode thereof to the gate electrode of the transistor Tr2 and at the other electrode thereof to the node N2. The capacitance element C4 is connected at one terminal thereof to the gate electrode of the transistor Tr3 and at the other electrode thereof to the output terminal 92. The capacitance element C5 is connected at one electrode thereof to the gate electrode of the transistor Tr4 and at the other electrode thereof to the power supply line L21 of the negative side power supply voltage Vss1.
Here, the delay circuit 93 configured from the transistors Tr91 and Tr92 has a role of a high resistance element which interconnects the input terminal 91 and the gate electrode of the transistor Tr4. Consequently, the input pulse signal INVin inputted through the input terminal 91 passes through the delay circuit 93, whereupon a variation of the potential of the input pulse signal INVin is transmitted after a delay in time to the gate electrode of the transistor Tr4. The delay amount of the delay circuit 93 can be controlled by changing the voltage value of the positive side power supply voltage Vcc1 and the capacitance value of the capacitance element C5.
The transistor Tr1 electrically connects or disconnects the power supply line L12 of the positive side power supply voltage Vcc2 to or from the node N1 in response to a voltage across the capacitor C1. The transistor Tr2 electrically connects or disconnects the power supply line L13 of the positive side power supply voltage Vcc3 and the node N2 in response to the potential difference between the potential of the node N1 and the potential of the node N2, that is, in response to a voltage across the capacitance element C3. The transistor Tr3 electrically connects or disconnects the power supply line L14 of the positive side power supply voltage Vcc4 to or from output terminal 92 in response to the potential difference between the potential of the node N2 and the potential of the output terminal 92, that is, in response to a voltage across the capacitance element C4.
The transistor Tr4 electrically connects or disconnects the gate electrode of the transistor Tr1 to or from the power supply line L21 of the negative side power supply voltage Vss1 in response to the potential difference between the potential at the output terminal of the delay circuit 93 and the negative side power supply voltage Vss1, that is, in response to a voltage across the capacitance element C5. The transistor Tr5 electrically connects or disconnects the node N1 to or from the power supply line L22 of the negative side power supply voltage Vss2 in response to the potential difference between the potential of the input terminal 91 and the negative side power supply voltage Vss2. The transistor Tr6 electrically connects or disconnects the node N2 to or from the power supply line L22 of the negative side power supply voltage Vss3 in response to the potential difference between the potential of the input terminal 91 and the negative side power supply voltage Vss3. The transistor Tr7 electrically connects or disconnects the output terminal 92 to or from the power supply line L24 of the negative side power supply voltage Vss4 in response to the potential difference between the potential of the input terminal 91 and the negative side power supply voltage Vss4.
Circuit Operation
Now, circuit operation when the input pulse signal INVin inputted through the input terminal 91 to the inverter circuit 90 having the configuration described above is placed into an active state or high potential state and into an inactive state or low potential state is described.
When the Input Pulse Signal INVin is Placed into an Active State:
If the input pulse signal INVin is placed into an active state, then the gate potential of the transistor Tr7 is placed into a high potential state and the transistor Tr7 is placed into a conducting state. Therefore, the negative side power supply voltage Vss4 is led out as the low potential of the output pulse signal INVout from the output terminal 92. Simultaneously, also the transistors Tr5 and Tr6 are placed into conducting state, and consequently, the potentials at the nodes N1 and N2 are fixed to the negative side potentials Vss2 and Vss3, respectively.
Consequently, both of the transistors Tr2 and Tr3 are placed into a non-conducting state. Further, the transistor Tr4 is placed into a conducting state in response to a delay output of the delay circuit 93, and consequently, the gate potential of the transistor Tr1 is fixed to the negative side power supply voltage Vss1. Consequently, also the transistor Tr1 is placed into a non-conducting state. In other words, when the input pulse signal INVin is placed into an active state, then all of the positive side transistors Tr1, Tr2 and Tr3 are placed into a non-conducting state.
When the Input Pulse Signal INVin is Placed into an Inactive State:
If the input pulse signal INVin is placed into an inactive state, then all of the transistors Tr5, Tr6 and Tr7 on the negative potential side are simultaneously placed into a non-conducting state. In addition, the potential at the node N1, that is, the gate potential of the transistor Tr2, drops by capacitive coupling of the parasitic capacitor C2 in accordance with the variation amount when the input pulse signal INVin transits from the high potential to the low potential.
At the instant of the potential drop by the capacitive coupling, the gate potential of the transistor Tr4 keeps a high potential state due to a delay by the delay circuit 93, and therefore, the gate potential of the transistor Tr1 is in the state of the negative side power supply voltage Vss1. Accordingly, the gate-source voltage Vgs of the transistor Tr1 increases in response to the potential drop at the node N1 until it exceeds the threshold voltage, whereupon the transistor Tr1 is placed into a conducting state. Consequently, the potential at the node N1 rises to the positive side power supply voltage Vcc1.
Consequently, since also the gate-source voltage Vgs of the transistor Tr2 increases, also the transistor Tr2 is placed into a conducting state. As a result, the potential at the node N2 rises to the positive side power supply voltage Vcc2 and also the gate-source voltage Vgs of the transistor Tr2 increases, and consequently, the transistor Tr3 is placed into a conducting state following the transistor Tr2. Then, when the transistor Tr3 is placed into a conducting state, the positive side power supply voltage Vcc4 is led out as a positive potential of the pulse signal INVout from the output terminal 92.
Here, in order to allow the transistor Tr1 to be placed into a conducting state more rapidly in response to a drop of the gate potential of the transistor Tr2 by the capacitive coupling of the parasitic capacitor C2, the capacitance value of the parasitic capacitor C2 is set to a rather high level. Then, if the transistor Tr1 enters a conducting state rapidly, then the transition timing, that is, the rising/falling timing, of the pulse signal INVout can be defined more accurately.
The transition timing of the output pulse signal INVout defines the pulse width of output pulse signal INVout. Then, in the case where the driving circuit section is the writing scanning circuit 40, the output pulse signal INVout is used as a reference signal for generation of the writing scanning signal WS. Accordingly, the pulse width of the output pulse signal INVout makes a reference for the determination of the pulse width of the writing scanning signal WS and makes a reference for the determination of the operation time of the mobility correction process described hereinabove, that is, the mobility correction time.
Here, even if the pulse width of the writing scanning signal WS when the optimum mobility correction time is long and the pulse width of the writing scanning signal WS when the optimum mobility correction time is short exhibit an equal amount or time period of dispersion, the dispersion of the pulse width of the writing scanning signal WS when the optimum mobility correction time is short is relatively great. Then, the dispersion of the pulse width of the writing scanning signal WS makes a luminance dispersion and makes a cause of deterioration of the picture quality. Also from such a point of view, it is significant to set the capacitance value of the parasitic capacitor C2 to a high level to allow the transistor Tr1 to enter a conducting state rapidly thereby to accurately define the transition timing of the output pulse signal INVout which makes a reference for the determination of the mobility correction time.
As apparent from the foregoing description of the circuit operation, in the inverter circuit 90 configured from transistors of a one-sided channel, in order to make circuit operation sure, the parasitic capacitor C2 for dropping the potential of the node N1 by capacitive coupling is used. In addition to the parasitic capacitor C2, also the capacitance elements C1, C2 and C4 for retaining the gate-source voltage Vgs of the transistors Tr1, Tr2 and Tr3 are used. The capacitance elements C1 to C4 are used in an inverter circuit configured from transistors of a one-sided channel.
The inverter circuit 90 described above which is configured from a combination of transistors of a one-sided channel and capacitance elements can be used not only as the inverters 412 and 414 which configure the shift register circuit 41 of the writing scanning circuit 40 show in FIG. 15A but also as the inverters 421, 423 and so forth which configure the buffer circuits 42. Since also the power supply scanning circuit 50 is configured basically similarly to the writing scanning circuit 40, the inverter circuit 90 can be used also as an inverter which configures the power supply scanning circuit 50.
C. Signal Outputting Circuit
Now, as one of the driving circuit sections, the signal outputting circuit 60 which selectively outputs a signal voltage Vsig/reference potential Vofs in accordance with luminance information to the pixels 20 of a pixel row selectively scanned by the writing scanning circuit 40 is described.
FIG. 17 shows an example of a configuration of the signal outputting circuit 60. The signal outputting circuit 60 of the present example adopts a time-divisional driving method or selector method wherein a video signal DATA supplied in a time sequence through a data line is supplied time-divisionally in a unit of a plurality of pixel columns. Here, a time-divisional driving method wherein a video signal DATA of RGB is supplied time-divisionally in a unit of three pixel columns or signal lines corresponding to R, G and B is described as an example.
Referring to FIG. 17, two selection switches 61R and 62R are connected commonly at an output terminal thereof to one end of a signal line 33i−1 of R. Two selection switches 61G and 62G are connected commonly at an output terminal thereof to en end of a signal line 33i of G. Two selection switches 61B and 62B are connected commonly at an output terminal thereof to an end of the signal line 33i+1 of B.
The selection switches 61R, 61G and 61B and the selection switches 62R, 62G and 62B are configured, for example, from an Nch MOS transistor. However, the selection switches 61R, 61G and 61B and the selection switches 62R, 62G and 62B may otherwise be configured from a Pch MOS transistor or else may be configured from Nch MOS transistors and Pch MOS transistors connected in parallel.
The video signal DATA is a time-sequential signal by which signal voltages of RGB are supplied, for example, in the order of R, G and B, and is applied commonly to input terminals of the selection switches 61R, 61G and 61B from a driver IC or signal generation section not shown through a data line 63. The reference potential Vofs is applied commonly to input terminals of the selection switches 62R, 62G and 62B from a reference potential generation section not shown through a signal line 645.
The selection switches 61R, 61G and 61B are connected at the gate thereof to control lines 641, 642 and 643, respectively. The selection switches 62R, 62G and 62B are connected at the gate thereof commonly to a control line 644. To the control lines 641, 642, 643 and 644, switch control signals SELR, SELG, SELB and GATEofs are applied, respectively, from a timing generation section not shown.
The switch control signal SELR is rendered active, that is, placed into a high level, in synchronism with the signal voltage of R from within the time-sequential signal. The switch control signal SELG is rendered active in synchronism with the signal voltage of G from within the time-sequential signal. The switch control signal SELB is rendered active in synchronism with the signal voltage of B from within the time-sequential signal. The switch control signal GATEofs is rendered active at a writing timing of the reference potential Vofs described hereinabove.
In the configuration described above, the selection switch 61R is placed into a conducting state in response to the switch control signal SELR to select the signal voltage of R and outputs the signal voltage of R to the signal line 33i−1. The selection switch 61G is placed into a conducting state in response to the switch control signal SELG to select the signal voltage of G and outputs the signal voltage of G to the signal line 33i. The selection switch 61B is placed into a conducting state in response to the switch control signal SELB to select the signal voltage of B and outputs the signal voltage of B to the signal line 33i+1. The selection switches 62R, 62G and 62B are placed into a conducting state in response to the switch control signal GATEofs to select and output the reference potential Vofs to the signal lines 33i and 33i+1, respectively.
In the organic EL display apparatus 10A according to the present application described above, the writing scanning circuit 40, power supply scanning circuit 50 and signal outputting circuit 60 correspond to the peripheral driving sections 80A to 80C of the display apparatus 10 in the embodiment described hereinabove, respectively (refer to FIGS. 1, 4A, 4B and 7). Then, for example, in FIG. 7, in order to electrically connect the peripheral driving sections 80A to 80C and the outside of the substrate to each other, the pad portions 84A and 84B, pad portion group 84C and pads 84D and 84E are used.
In particular, referring to FIG. 18, the peripheral driving section 80A mounted on the substrate end portion 70B corresponds to the writing scanning circuit 40; the peripheral driving section 80B mounted on the board end portion 70C corresponds to the power supply scanning circuit 50; and the peripheral driving section 80C mounted on the substrate end portion 70D corresponds to the signal outputting circuit 60. FIG. 18 corresponds to FIG. 7.
The writing scanning circuit 40 which is the peripheral driving section 80A is electrically connected, for example, at a pad portion 84A provided at an upper end portion 70B0 of the substrate end portion 70B, to the outside of the substrate, for example, through a flexible board 87A. Then, to the writing scanning circuit 40, a power supply voltage and the clock pulse ck, start pulse sp and so forth described hereinabove are inputted from the outside of the substrate through the flexible board 87A and the pad portion 84A.
The power supply scanning circuit 50 which is the peripheral driving section 80B is electrically connected, for example, at a pad portion 84B provided at an upper end portion 70C0 of the substrate end portion 70C, to the outside of the substrate, for example, through a flexible board 87B. Then, to the power supply scanning circuit 50, a power supply voltage and the clock pulse ck, start pulse sp and so forth described hereinabove are inputted from the outside of the substrate through the flexible board 87B and the pad portion 84B similarly to the writing scanning circuit 40.
The signal outputting circuit 60 which is the peripheral driving section 80C is electrically connected, at the pad portion group 84C provided on the substrate end portion 70D, to a driver IC 88, which is a signal supplying source provided on the outside of the substrate, for example, through a flexible board group 87g. Then, to the signal outputting circuit 60, the signal voltage Vsig of a video signal is inputted from the driver IC 88 through the flexible board group 87C and the pad portion group 84C.
Further, the signal outputting circuit 60 is electrically connected, at the pad portions 84D and 84E provided at the opposite end portions 70D1 and 70D2 of the substrate end portion 70D, to the outside of the substrate, for example, through the flexible boards 87D and 87E, respectively. Then, to the signal outputting circuit 60, signals for controlling the signal outputting circuit 60 are inputted from the outside of the substrate through the flexible boards 87D and 87E and the pad portions 84D and 84E.
In particular, if it is assumed that the signal outputting circuit 60 adopts the time-divisional driving method as seen from FIG. 17, then gate controlling signals for controlling the transistors which configure the selection switches 61R, 61G and 61B and the selection switches 62R, 62G and 62B are inputted. Here, the gate controlling signals are the switch control signals SELR, SELG, SELB and GATEofs described hereinabove. To the signal outputting circuit 60, the reference potential Vofs is inputted from the outside of the substrate through the flexible boards 87D and 87E and the pad portions 84D and 84E in addition to the gate controlling signals.
Here, in the case where the peripheral driving section 80C particularly is the signal outputting circuit 60, the pad portion group 84C for fetching a video signal from the outside of the substrate for each pixel column of the pixel array section 30 is provided at a lower end of the substrate end portion 70D substantially corresponding to the pixel column over the width of the pixel array section 30 in the horizontal direction. Besides, since the distance between the folding region and the signal outputting circuit 60 is small, wiring lines of a peripheral circuit section cannot be laid.
From such a reason as just described, a space in which pad portions for fetching gate controlling signals, that is, the switch control signals SELR, SELG, SELB and GATEofs and the reference potential Vofs from the outside of the substrate are to be provided cannot be assured on the substrate end portion 70D. Accordingly, the pad portions 84D and 84E for fetching the gate controlling signals and the reference potential Vofs from the outside of the substrate to the signal outputting circuit 60 are provided at a location in the substrate end portion 70D on the substrate end portion 70D farther than the bent portion, that is, at the opposite end portions 70D1 and 70D2. In other words, by providing the pad portions 84D and 84E at the opposite end portions 70D1 and 70D2 of the substrate end portion 70D, even if the distance between the folding region and the signal outputting circuit 60 is small, the gate controlling signals and the reference potential Vofs can be provided with certainty from the outside of the substrate to the signal outputting circuit 60.
3. Modification
In the application described above, the disclosed technology is applied to the organic EL display apparatus 10A which is configured such that the scanning circuit sections, that is, the writing scanning circuit 40 and the power supply scanning circuit 50, are provided in the display panel 70, particularly mounted on the substrate end portions 70B and 70G. However, the disclosed technology is not limited to the application example described above.
In particular, the disclosed technology can be applied similarly also to an organic EL display apparatus 10B which is configured such that, as seen in FIG. 19, the writing scanning circuit 40 and the power supply scanning circuit 50 are not built therein but external drivers are used. In this instance, pad portion groups 84F and 84G may be disposed on the substrate end portions 70B and 70G such that the pixel array section 30 and the outside of the substrate are electrically connected through the pad portion groups 84F and 84G.
Further, while, in the application example described above, the disclosed technology is applied to an organic EL display apparatus which uses an organic EL element as an electro-optical element of the pixel 20, the disclosed technology is not limited to the application example. In particular, the disclosed technology can be applied to various display apparatus wherein elect-optical elements or light emitting elements such as inorganic EL elements, LED elements or semiconductor laser elements are used.
4. Electronic Apparatus
The display apparatus of the embodiment of the disclosed technology described above can be applied as a display apparatus for electronic apparatus in various fields wherein a video signal inputted to the electronic apparatus or a video signal generated in the electronic apparatus is displayed as an image or a picture. For example, the disclosed technology can be applied to such various electronic apparatus as shown in FIGS. 20 to 24A to 24G, for example, to a digital camera, a notebook type personal computer, a portable terminal apparatus such as a portable telephone set and a video camera.
In this manner, the display apparatus according to the embodiment of the disclosed technology can be used as a display apparatus in electronic apparatus in various fields. As apparent from the foregoing description of the embodiments, the display apparatus according to the embodiment of the disclosed technology can achieve further reduction of the width of the framework molding of the display panel without limiting the functions of the peripheral circuit sections for driving pixels of the pixel array section. Accordingly, if the display apparatus of the embodiment of the disclosed technology is used as the display apparatus in various electronic apparatus, then a compact form of the display apparatus can be achieved while the picture quality is maintained.
The display apparatus of the embodiment of the disclosed technology may be formed as of a module type wherein it is encapsulated. For example, the display apparatus may have a form of a display module wherein, for example, a transparent opposing member of glass or the like is pasted to the pixel array section 30. A color filter, a protective film or the like may be provided on the transparent opposing member. It is to be noted that, on the display module, a circuit section, an FPC (flexible printed circuit) or the like for inputting and outputting signals and so forth from the outside to the pixel array section and vice versa.
In the following, particular examples of an electronic apparatus to which the disclosed technology is applied are described.
FIG. 20 shows an appearance of a television receiver to which the disclosed technology is applied. Referring to FIG. 20, the television receiver includes a video signal display face section 101 configured from a front panel 102, a filter glass plate 103 and so forth and is produced using the display apparatus of the embodiment of the disclosed technology as the video signal display face section 101.
FIGS. 21A and 21B show an appearance of a digital camera to which the disclosed technology is applied as viewed from the front side and the rear side, respectively. Referring to FIGS. 21A and 21B, the digital camera shown includes a flash light emitting section 111, a display section 112, a menu switch 113, a shutter 114 and so forth. The digital camera is produced using the display apparatus of the embodiment of the disclosed technology as the display section 112.
FIG. 22 shows an appearance of a notebook type personal computer to which the disclosed technology is applied. Referring to FIG. 22, the notebook type personal computer shown includes a body 121, a keyboard 122 for being operated in order to input characters and so forth, a display section 123 for displaying an image and so forth. The notebook type personal computer is produced using the display apparatus of the embodiment of the disclosed technology as the display section 123.
FIG. 23 shows an appearance of a video camera to which the disclosed technology is applied. Referring to FIG. 23, the video camera shown includes a may body section 131, and a lens 132 provided on a side face directed forwardly for picking up an image of an image pickup object. The video camera further includes a start/stop switch 133 for image pickup, a display section 134 and so forth. The video camera is produced using the display apparatus of the embodiment of the disclosed technology as the display section 134.
FIGS. 24A to 24G show a portable terminal apparatus, as a portable telephone set, for example, to which the disclosed technology is applied. Referring to FIGS. 24A to 24G, the portable terminal apparatus includes an upper side housing 141, a lower side housing 142, a connection section 143 in the form of a hinge section, a display section 144, a sub display section 145, a picture light 146, a camera 147 and so forth. The portable telephone set is produced using the display apparatus of the embodiment of the disclosed technology as the display section 144 and/or the sub display section 145.
The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-276940 filed in the Japan Patent Office on Dec. 13, 2010, the entire content of which is hereby incorporated by reference.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors in so far as they are within the scope of the appended claims or the equivalents thereof.

## Claims

1. A display apparatus, comprising:
a foldable first substrate;
a pixel array including a plurality of pixels on a central portion of the first substrate, respective ones of the plurality of pixels comprising an electro-optical device;
a resin film on the pixel array;
a peripheral circuit on a peripheral portion of the first substrate and configured to drive the pixel array;
pads on the peripheral portion of the first substrate and connected to the peripheral circuit;
a circuit section configured to drive the electro-optical device and including a circuit element formed on the first substrate;
a flattening film and a window insulation film laminated on the circuit element; and
a second substrate disposed above the flattening film and the window insulation film in a region of the first substrate other than the peripheral portion of the first substrate and a folding portion of the peripheral portion of the first substrate,
wherein the first substrate is folded such that the peripheral portion of the first substrate partially overlaps the central portion of the foldable substrate, and the peripheral circuit and the pads are disposed under the pixel array.

2. The display apparatus according to claim 1, wherein the pads are provided at a location on the peripheral portion of the foldable substrate, on which the peripheral circuit is provided, farther than the folding portion.

3. The display apparatus according to claim 2, wherein a groove configured to prevent water invasion is formed in a side of the pixel array with respect to the folding portion in such a manner as to surround the pixel array.

4. The display apparatus according to claim 3, wherein the groove is formed along a side of the peripheral circuit with respect to the folding portion in such a manner as to surround the peripheral circuit.