JP2008122836A - Electroluminescence element, pixel circuit, display device, and exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pixel circuits which achieve a longer life and a display device with the pixel circuits. <P>SOLUTION: The pixel circuits 10 respectively disposed in correspondence to the intersections of a plurality of gate lines and a plurality of source lines arrayed to intersect each other include first light emitting elements 103 and second light emitting elements 103, first transistors 104 and second transistors 106 which are respectively connected to the anodes of the first light emitting elements 103 and the second light emitting elements 105 and drive the respective first light emitting elements 103 and the second light emitting elements 105, first power source lines 101 which are connected to the cathodes of the second light emitting elements 105 and the side of the first transistors 104 not connected to the first light emitting elements 103, and second power source lines 102 which are connected to the cathodes of the first light emitting elements 103 and the side of the second transistors 106 of the side not connected to the second light emitting elements 105 and are different in their polarity from the first power source lines 101. The polarities of the first power source lines 101 and the second power source lines 102 are switched at prescribed time intervals. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pixel circuit including a self-luminous element such as an electroluminescence (EL) element or an electroluminescence element, a display device including the pixel circuit, and an exposure apparatus.

  In recent years, interest in FPD (Flat Panel Display) has been increased in place of CRT (Cathode Ray Tube). As typical FPD, LCD (Liquid Crystal Display) and PDP (Plasma Display Panel) have already been put into practical use. However, it has been pointed out that these FPDs have the following problems.

  That is, since the LCD itself does not emit light, a high-brightness backlight is required, and as a result, power consumption tends to increase. The LCD is also inferior to the CRT in view angle and response speed. On the other hand, the PDP uses a self-luminous element, and has a viewing angle and response speed equivalent to or better than those of a CRT. However, in the case of a PDP, a high voltage is required for driving, and thus there is a problem that it is difficult to realize low power consumption.

  While LCDs and PDPs have the problems as described above, organic EL devices may be able to solve these problems. Therefore, a display device including an organic EL device has attracted attention as a candidate for the next generation FPD.

  An organic EL device is usually produced by the following method. First, an anode (anode) is formed on a washed support substrate such as glass, quartz, or plastic, and patterning is performed. Generally, ITO (Indium Tin Oxide) having a high work function is selected as the anode, but other metals may be used. A sputtering method is usually used to form the anode.

  After forming the anode in this way, an organic EL layer is formed. Generally, in the case of a low molecular organic EL, the organic EL layer is formed by a vacuum vapor deposition method, while in the case of a high molecular organic EL, it is formed by a spin coating method or an ink jet method. Here, the ink jet method is selected when it is necessary to separately coat the organic EL.

  In some cases, an intermediate layer (interlayer) is formed before and after the organic EL layer is formed in order to increase the light emission efficiency.

  After the formation of the organic EL layer, a cathode (cathode) is formed by vacuum deposition or the like and sealed. Thereby, an organic EL device is completed.

  When the organic EL device thus created is applied to a display device, the organic EL devices are generally arranged in a matrix. A thin film transistor (TFT) is formed together with an organic EL device, and an organic EL device driven by the TFT is called an active matrix drive type display device, and a device driven only by an electrode without forming a TFT is passive. It is called a matrix drive type display device.

  In the case of an organic EL device, when a voltage higher than that of the cathode is applied to the anode, a current flows through the organic EL to emit light. When a voltage higher than that of the anode is applied to the cathode, a so-called diode characteristic is shown in which almost no current flows and no light is emitted. Therefore, the organic EL device is generally driven by a DC voltage.

  One of the reasons why organic EL elements are difficult to put into practical use despite their excellent characteristics is that their lifetime is short. It is generally considered that the cause of the short lifetime of the organic EL element is that electric charges are accumulated in the organic EL element with direct current drive. Therefore, in order to extend the lifetime of the organic EL element, two organic EL elements are provided in one pixel, and when one emits light, the other does not emit light, and the other organic EL element that does not emit light There have been proposed a driving method and a display device for performing AC driving in which a reverse bias is applied to the.

For example, a drive device has been proposed in which two organic EL elements are connected in antiparallel and a forward voltage and a reverse bias voltage are alternately applied between the two organic EL elements (for example, see Patent Document 1). reference.). In addition, a display device is proposed that is configured to apply an AC voltage of opposite polarity from a common AC power supply circuit to the opposing power supply terminal of one organic EL element and the opposing power supply terminal of the other organic EL element. (For example, refer to Patent Document 2).
JP 2001-203077 A JP 2005-50797 A

  However, the conventional driving method and display device as described above have the following problems. In other words, the driving method disclosed in Patent Document 1 can be applied to a passive matrix driving type display device, but the point applied to an active matrix driving type display device is clearly disclosed in Patent Document 1. Therefore, there is a problem that it is unclear what configuration should be made.

  Further, in the case of the display device disclosed in Patent Document 2, there is a problem that the number of wirings of the organic EL panel increases as compared with the case of driving with direct current. Such an increase in the number of wirings may cause a decrease in the aperture ratio and a decrease in yield.

  Furthermore, there is a problem that driving the organic EL panel with alternating current increases power consumption, and depending on the driving frequency, there is a possibility that it may be recognized as flicker during image display.

  The present invention has been made in view of such circumstances, and its purpose is to increase the lifetime of light-emitting elements including organic EL elements without increasing the number of wires, increasing power consumption, and generating flicker. It is an object of the present invention to provide a pixel circuit that can be extended as compared with the case of direct current driving, and an active matrix driving display device including the pixel circuit.

  In order to solve the above-described problem, a pixel circuit of the present invention includes a first pixel circuit arranged corresponding to the intersection of a plurality of gate lines and a plurality of source lines arranged to cross each other. And the first light-emitting element and the second light-emitting element, and the first light-emitting element and the second light-emitting element connected to the anode of the first light-emitting element and the second light-emitting element, respectively, and driving the first light-emitting element and the second light-emitting element, respectively. A first power line connected to a side of the first transistor that is not connected to the first light emitting element; and a first power line connected to a side of the first transistor that is not connected to the first light emitting element; The second light-emitting element is connected to the cathode of the first light-emitting element and the side of the second transistor that is not connected to the second light-emitting element, and has a polarity different from that of the first power supply line. And a source line, the polarity of the first power supply line and said second power supply line is configured to be switched.

  With this configuration, since either one of the first light-emitting element and the second light-emitting element is forward-biased and the other is reverse-biased, one of them emits light and the other is accumulated. It is possible to recover the deteriorated characteristics by releasing the charged charges. As a result, the life can be extended.

  The pixel circuit according to the present invention may be configured such that polarities of the first power supply line and the second power supply line are switched at predetermined time intervals.

  In the pixel circuit according to the invention, when the power is turned on, the polarities of the first power supply line and the second power supply line are different from those when the power is turned off last time. It may be configured.

  In the pixel circuit according to the invention, the polarities of the first power supply line and the second power supply line are switched according to the deterioration state of the first light emitting element and the second light emitting element. It may be configured.

  In the pixel circuit according to the invention, polarities of the first power supply line and the second power supply line are switched in accordance with a decrease in luminance of the first light emitting element and the second light emitting element. It may be configured.

  In the pixel circuit according to the invention, the polarities of the first power supply line and the second power supply line are switched in accordance with a decrease in current flowing through the first light emitting element and the second light emitting element. It may be configured as follows.

  In addition, the display device of the present invention is provided in correspondence with a plurality of gate lines and a plurality of source lines arranged so as to cross each other, and an intersection of the plurality of gate lines and the plurality of source lines. Each of the pixel circuits is connected to a first light emitting element and a second light emitting element, and an anode of the first light emitting element and the second light emitting element, respectively. A first transistor and a second transistor for driving each of the first light-emitting element and the second light-emitting element, a cathode of the second light-emitting element, and the first light-emitting element of the first transistor The first power line connected to the unconnected side, the cathode of the first light emitting element, and the second light emitting element of the second transistor are not connected. And a second power supply line having a polarity different from that of the first power supply line, and the polarities of the first power supply line and the second power supply line included in each of the pixel circuits. The switching circuit which switches is provided.

  The display device according to the invention further includes a timer that outputs a switching signal instructing switching of the polarity of the power supply line to the switching circuit at a predetermined time interval, and the switching circuit responds to an input of the switching signal. The polarities of the first power supply line and the second power supply line included in each of the pixel circuits may be switched.

  In the display device according to the invention described above, the switching circuit includes the first circuit that each of the pixel circuits includes so that the polarity when the power is turned on is different from that when the power is turned off last time. The polarity of the second power supply line and the second power supply line may be switched.

  The display device according to the invention further includes light emitting element deterioration detecting means for detecting a deterioration state of the first light emitting element and the second light emitting element included in each of the pixel circuits, and the switching circuit includes The polarities of the first power supply line and the second power supply line included in each of the pixel circuits may be switched in accordance with a detection result by the light emitting element deterioration detection unit.

  Further, in the display device according to the invention, the light emitting element deterioration detecting unit detects a deterioration state according to the luminance of the first light emitting element and the second light emitting element included in each of the pixel circuits. It may be configured.

  In the display device according to the invention, the light emitting element deterioration detecting unit detects a deterioration state in accordance with a current flowing through the first light emitting element and the second light emitting element included in each of the pixel circuits. It may be configured as follows.

  In each of the pixel circuits in the display device according to the invention, the first light emitting element and the second light emitting element are arranged in a column direction (or a row direction), and the pixel circuit is Each of the first light-emitting elements and the second light-emitting elements may be arranged in a matrix so as not to be aligned in the row direction (or column direction).

  The electroluminescence element of the present invention includes a first light emitting element, a first light emitting unit composed of a first transistor for driving the first light emitting element, a second light emitting element, and the first light emitting element. A second light emitting unit composed of a second transistor for driving two light emitting elements, a first power supply line connected to the anode side of the first light emitting unit and the cathode side of the second light emitting unit; A second power source line connected to the cathode side of the first light emitting unit and the anode side of the second light emitting unit, the first light emitting element and the second light emitting element constitute one pixel, Further, the polarities of the first power supply line and the second power supply line are switched.

  With this configuration, since either one of the first light-emitting element and the second light-emitting element is forward-biased and the other is reverse-biased, one of them emits light and the other is accumulated. It is possible to recover the deteriorated characteristics by releasing the charged charges. As a result, a long-life electroluminescence element can be provided.

  The present invention also includes a light emitting device constituted by the above-described electroluminescence element, and an exposure device.

  Since the organic electroluminescence element according to the present invention can have a very long life, the product life of the light emitting device and the exposure device can be extended.

  The present invention also includes an exposure apparatus configured such that the polarity of the power supply line is switched to the unit of one line of exposure.

  Usually, since one line period of the exposure apparatus is about several hundreds μs, a reverse bias is periodically applied to the light emitting element, and the life of the light emitting element can be extended.

  The present invention also includes an exposure apparatus configured such that the polarity of the power supply line can be switched to one page unit for image formation.

  In image formation, since a predetermined interval is provided between normal pages, switching timing of light emitting elements can be performed with a simple configuration during this period.

  According to the present invention, the lifetime of a light emitting element such as an organic EL element can be extended as compared with the case of direct current drive without increasing the number of wirings, increasing power consumption, and generating flicker.

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

(Embodiment 1)
[Configuration of display device]
FIG. 1 is a block diagram showing a configuration of a display device according to Embodiment 1 of the present invention. As shown in FIG. 1, the display device 1 includes an EL display panel 20, a control circuit 12 for driving the EL display panel 20, a gate driver 13, a source driver 14, a switching circuit 21, and a timer 22. ing.

  The EL display panel 20 is an active matrix drive type organic EL display element. In the EL display panel 20, the gate lines 110 and the source lines 111 are arranged so as to cross each other alternately, and the pixel circuits 10 are arranged corresponding to the intersections of the gate lines 110 and the source lines 111. ing. Thereby, the plurality of pixel circuits 10 are arranged in a matrix.

  The gate line 110 and the source line 111 are driven by the gate driver 13 and the source driver 14, respectively. The operations of the gate driver 13 and the source driver 14 are controlled by the control circuit 12.

  The switching circuit 21 is a circuit for switching the polarities of two power supply lines included in the pixel circuit 10 configured as described later. The timer 22 is configured to output a switching signal for instructing switching of the polarity of the power supply line to the switching circuit 21 at a predetermined time interval.

[Pixel circuit configuration]
Next, the configuration of the pixel circuits 10 arranged in a matrix as described above will be described.

  FIG. 2 is a circuit diagram showing an example of the configuration of the pixel circuit 10 provided in the display device 1 according to Embodiment 1 of the present invention. As shown in FIG. 2, the pixel circuit 10 includes a first organic EL element 103 and a second organic EL element 105 which are light emitting elements having diode characteristics, and the first organic EL element 103 and the second organic EL element. The first transistor 104 and the second transistor 106 that are respectively connected to the anodes of the EL elements 105 and drive the organic EL elements, and control the operations of the first transistors 104 and the second transistors 106. And a control transistor 107. The control transistor 107 is connected to the gate line 110 and the source line 111.

  The pixel circuit 10 includes a first power supply line 101 and a second power supply line 102. The first power supply line 101 is connected to the cathode of the second organic EL element 105 and the side of the first transistor 104 that is not connected to the first organic EL element 103, and the second power supply line 102 is connected to the cathode of the first organic EL element 103 and the side of the second transistor 106 not connected to the second organic EL element 105.

  The first power supply line 101 and the second power supply line 102 are configured to always have different polarities during the operation of the display device 1. That is, when the first power supply line 101 is High, the second power supply line 102 is Low, and when the first power supply line 101 is Low, the second power supply line 102 is High.

  That is, when this configuration is viewed from the viewpoint of the light-emitting element, the first light-emitting unit (organic EL element 103) and the first light-emitting unit including the first transistor 104 that drives the first light-emitting element , A second light-emitting unit (organic EL element 105), a second light-emitting unit composed of the second transistor 106 that drives the second light-emitting element, the anode side of the first light-emitting unit, and the second A first power supply line 101 connected to the cathode side of the light emitting unit, and a second power supply line 102 connected to the cathode side of the first light emitting unit and the anode side of the second light emitting unit. The first light emitting element (organic EL element 103) and the second light emitting element (organic EL element 105) constitute one pixel (see FIG. 12), and further, the first power supply line and the second light emitting element It is configured so that the polarity of the power line can be switched. .

  Note that a capacitor may be added to the configuration described above. FIG. 3 is a circuit diagram illustrating another example of the configuration of the pixel circuit 10 included in the display device 1 according to Embodiment 1 of the present invention. As shown in FIG. 3, a capacitor 108 is provided between the first transistor 104 and the first power supply line 101, and a capacitor 109 is provided between the second transistor 106 and the second power supply line 102. It has been.

  In the pixel circuit 10 configured as described above, the capacitor 108 only needs to be able to hold a voltage between the drain of the control transistor 107 and the gate of the first transistor 104, and thus the first transistor 104 And the second power supply line 102 may be provided. This is the same for the capacitor 109, and the capacitor 109 may be provided between the second transistor 106 and the first power supply line 101.

  Note that whether or not to provide these capacitive elements 108 and 109 is determined according to the design needs.

  The semiconductor layers of the transistors 104, 106, and 107 are made of, for example, amorphous silicon, polysilicon, single crystal silicon, an inorganic compound, an organic compound, or the like.

  By the way, in this embodiment, the transistors 104, 106, and 107 are P-channel transistors whose holes are carriers. However, the present invention is not limited to this, and as shown in FIG. 4, these transistors may be constituted by N-channel transistors in which electrons are carriers.

  FIG. 4 is a circuit diagram showing another example of the configuration of the pixel circuit 10 included in the display device 1 according to Embodiment 1 of the present invention. As illustrated in FIG. 4, the pixel circuit 10 in this case includes an N-channel first transistor 204, a second transistor 206, and a control transistor 207. The first transistor 204 drives the first organic EL element 203, the second transistor 206 drives the second organic EL element 205, and the control transistor 207 includes the first transistor 204 and the first transistor 204. The operation of the second transistor 206 is controlled. The control transistor 207 is connected to the gate line 210 and the source line 211.

  The pixel circuit 10 includes a first power supply line 201 and a second power supply line 202.

  Note that a structure in which the capacitor elements 208 and 209 are added may be used as in the case where the transistors are P-channel transistors. A circuit diagram showing such a configuration is shown in FIG.

  In this manner, both P-channel and N-channel transistors can be used. However, when considering the manufacturing process, it is preferable to configure only one of them from the viewpoint of manufacturing cost, tact time, yield, etc., rather than configuring both of the P channel type and the N channel type.

[Operation of display device]
In the display device 1 configured as described above, the control circuit 12 generates a video signal to be output to the source driver 14 based on a video signal input from an external device. The control circuit 12 outputs the video signal thus generated to the source driver 14 and outputs control signals to the gate driver 13 and the source driver 14. As a result, the gate driver 13 outputs a scanning signal corresponding to a voltage for turning on the control transistor 107 included in each pixel circuit 10 to the gate line 110, whereby the control transistor 107 of each pixel circuit 10 is output. Turn on sequentially. On the other hand, the source driver 14 writes a video signal to each pixel circuit 10 via the source line 111 in accordance with the timing. As a result, a current corresponding to the video signal flows to the first organic EL element 103 or the second organic EL element 105 of each pixel circuit 10. As a result, the first organic EL element 103 or the second organic EL element 105 of each pixel circuit 10 emits light, and as a result, an image corresponding to the video signal is displayed on the EL display panel 20.

  Which of the first organic EL element 103 and the second organic EL element 105 a current corresponding to the video signal flows and which of the organic EL elements emits light is determined by the first power supply line. It differs depending on the polarities of 101 and the second power line 102. Hereinafter, the timing at which the first organic EL element 103 or the second organic EL element 105 emits light will be described.

  FIG. 6 is a timing chart showing an operation example of the display device 1 according to Embodiment 1 of the present invention. As shown in FIG. 6, in the period P1, the polarity of the first power supply line 101 is set to High, and the polarity of the second power supply line 102 is set to Low. In this period P1, the gate driver 13 outputs a scanning signal to the gate line 110, thereby turning on the control transistor 107 of each pixel circuit 10. Note that in this embodiment mode, since the control transistor 107 is a P-channel type, a scanning signal is output so that the gate line 110 becomes a low voltage. In accordance with this timing, the source driver 14 outputs the video signal to the source line 111, whereby the video signal is written to the pixel circuit 10.

  Here, since the cathode of the first organic EL element 103 and the second power supply line 102 are at the same potential, and the potential of the cathode is lower than the potential of the anode in the period P1, the first organic EL element A forward bias is applied to the element 103 and a current flows. As a result, the first organic EL element 103 emits light. On the other hand, since the cathode of the second organic EL element 105 and the first power supply line 101 are at the same potential, and the potential of the cathode is higher than the potential of the anode in the period P1, the second organic EL element A reverse bias is applied to 105. As a result, the charge accumulated in the second organic EL element 105 is released, so that the characteristics deteriorated due to the charge accumulation can be recovered.

  After such a period P <b> 1 continues for a predetermined time, the timer 22 outputs a switching signal to the switching circuit 21. When the switching circuit 21 receives this switching signal, the switching circuit 21 switches the polarities of the first power supply line 101 and the second power supply line 102. As a result, the polarity of the first power supply line becomes Low, and the polarity of the second power supply line 102 becomes High. These operations are performed in the period P2.

  After the period P2, the period P3 in which the polarity of the first power supply line is set to Low and the polarity of the second power supply line 102 is set to High is started. In this period P3, a reverse bias is applied to the first organic EL element 103, and as a result, the degraded characteristics of the first organic EL element 103 are recovered. On the other hand, a forward bias is applied to the second organic EL element 105, and as a result, a current flows through the second organic EL element 105. As a result, the second organic EL element 105 emits light.

  As in the case of the period P1, the timer 22 outputs a switching signal to the switching circuit 21 after the period P3 continues for a predetermined time. Thereafter, the display device 1 operates in the same manner. As a result, the polarities of the first power supply line 101 and the second power supply line 102 are switched at predetermined time intervals, and the first organic EL element 103 and the second organic EL element 105 emit light alternately. Will do.

  Note that the timer 22 preferably outputs a switching signal to the switching circuit 21 so that the period P1 and the period P3 illustrated in FIG. 6 are longer than one frame time. Thereby, the occurrence of flicker can be prevented.

[Comparative example]
FIG. 7 is a circuit diagram showing a configuration of a pixel circuit included in a conventional display device as a comparative example. As shown in FIG. 7, the pixel circuit 300 included in the display device of the comparative example includes an organic EL element 313, a transistor 314 that drives the organic EL element 313, and a control transistor 315 that controls the operation of the transistor 314. And a capacitor element 316 for holding. The side of the transistor 314 that is not connected to the organic EL element 313 is connected to the first power supply line 311, and the cathode of the organic EL element 313 is connected to the second power supply line 312. Further, the control transistor 315 is connected to the gate line 317 and the source line 318.

  The display device of the comparative example includes an EL display panel in which the pixel circuits 300 configured as described above are arranged in a matrix, and a known gate driver and source driver for driving the EL display panel. .

  FIG. 8 is a timing chart illustrating an operation example of the display device of the comparative example. As shown in FIG. 8, the first power supply line 311 is set to High, and the second power supply line 312 is set to Low. In this case, since the forward bias is applied to the organic EL element 313, a current flows, and as a result, the organic EL element 313 emits light.

  Since the control transistor 315 is a P-channel type, the transistor 315 becomes conductive when the gate line 317 is at a low voltage, and the voltage of the source line 318 is applied to the transistor 314. As a result, a current corresponding to the voltage is supplied to the organic EL element 313 via the transistor 314, and the organic EL element 313 emits light.

  As described above, in the display device of the comparative example, only the organic EL element 313 emits light. Therefore, charges are accumulated in the organic EL element 313 according to the usage time, and the deterioration of the organic EL element 313 proceeds. .

  On the other hand, in the case of the display device 1 of the present embodiment, as described above, in one period, one organic EL element emits light, and the other recovers the degraded characteristics by releasing the accumulated charge. It will be. Thereby, the lifetime of the display device is remarkably extended as compared with the conventional display device.

  Further, even in the case of the display device 1 of the present embodiment having two organic EL elements, the same number of wirings as in the case of the display device of the comparative example is sufficient. Therefore, the aperture ratio and the yield are not reduced.

  Furthermore, there is no problem of increased power consumption and occurrence of flicker as in the case of a conventional display device using AC driving.

(Embodiment 2)
As described above, the display device according to the first embodiment is configured to switch the polarities of the first power supply line and the second power supply line at predetermined time intervals. In contrast, in the display device according to the second embodiment, when the power is turned on, the polarities of the first power supply line and the second power supply line are previously turned off as described later. It is comprised so that it may become a different polarity.

  FIG. 9 is a block diagram showing a configuration of a display device according to Embodiment 2 of the present invention. As shown in FIG. 9, the display device 2 according to the second embodiment is connected to a first power supply line 101 and a second power supply line 102, and these first power supply line 101 and second power supply line are connected. A switching circuit 31 for switching the polarity of 102 is provided. The switching circuit 31 includes a nonvolatile memory 31 a that stores polarity information indicating the polarity of the first power supply line 101 and the second power supply line 102 when the display device 2 is powered off.

  In addition, since the other structure of the display apparatus 2 which concerns on Embodiment 2 is the same as that of the case of Embodiment 1, it attaches | subjects the same code | symbol and abbreviate | omits description.

  In the display device 2 configured as described above, the switching circuit 31 reads the polarity information stored in the nonvolatile memory 31a when the power is turned on. Then, the switching circuit 31 detects the polarities of the first power supply line 101 and the second power supply line 102 indicated by the read polarity information, that is, the first power supply line 101 and the second power supply at the previous power-off time. The polarities of the first power supply line 101 and the second power supply line 102 are set so as to have a polarity different from the polarity of the line 102.

  As a result, the polarity of the first power supply line 101 and the second power supply line 102 is switched every time the power is turned on, and accordingly, the first organic EL element and the second organic EL element included in each pixel circuit 10 are switched. The EL elements emit light alternately. As a result, as in the case of the first embodiment, the display device 2 can significantly extend its life compared to the conventional display device.

  In the present embodiment, the switching circuit 31 includes the nonvolatile memory 31a. However, the switching circuit 31 is not limited to this, and is a memory that can retain stored contents even when the power is turned off. I just need it. Therefore, instead of the nonvolatile memory 31a, for example, a ROM (Read Only Memory) may be used.

(Embodiment 3)
As described later, the display device according to Embodiment 3 switches the polarities of the first power supply line and the second power supply line in accordance with a decrease in luminance of the first light emitting element and the second light emitting element. It is configured.

  FIG. 10 is a block diagram showing a configuration of a display device according to Embodiment 3 of the present invention. As shown in FIG. 10, the display device 3 according to the third embodiment is connected to a first power supply line 101 and a second power supply line 102, and the first power supply line 101 and the second power supply line are connected. A switching circuit 41 for switching the polarity of the two; four photo detectors 43 disposed near the four corners of the EL display panel 20; and a comparison circuit 42 for comparing the output current of these photo detectors 43 with a preset reference current. ing.

  As described above, in the present embodiment, the photodetectors 43 are disposed at the four corners of the EL display panel 20, but the present invention is not limited to this. The number and position of the photodetectors are determined according to the usage environment. Although the detection sensitivity can be improved by increasing the number of photodetectors, a large area is required for arranging these photodetectors, and there is a problem that the cost increases.

  Moreover, as long as it is a structure which can detect the brightness | luminance of a 1st organic EL element and a 2nd organic EL element, things other than the structure which uses the above photodetectors may be sufficient.

  In addition, since the other structure of the display apparatus 3 which concerns on Embodiment 3 is the same as that of the case of Embodiment 1, it attaches | subjects the same code | symbol and abbreviate | omits description.

  In the display device 2 configured as described above, the comparison circuit 42 repeatedly compares the output current of the photodetector 43 with the reference current. When the output current of the photodetector 43 is lower than the reference current, that is, when the brightness of the EL display panel 20 of the display device 3 is lower than the reference brightness, the comparison circuit 42 is a switching circuit. 41 outputs a switching signal.

  When receiving the switching signal output from the comparison circuit 42, the switching circuit 41 switches the polarities of the first power supply line 101 and the second power supply line 102.

  By operating as described above, the polarities of the first power supply line 101 and the second power supply line 102 are switched according to the decrease in the luminance of the organic EL element included in each pixel circuit 10, and accordingly, The first organic EL element and the second organic EL element emit light alternately. As a result, similar to the case of the first embodiment, the display device 3 can significantly extend its life compared to the conventional display device.

(Embodiment 4)
As described above, the display device according to Embodiment 3 is configured to switch the polarities of the first power supply line and the second power supply line in accordance with the decrease in the luminance of the organic EL element. On the other hand, the display device according to Embodiment 4 is configured to switch the polarity of these power supply lines in accordance with a decrease in current flowing through the organic EL element.

  FIG. 11 is a block diagram showing a configuration of a display device according to Embodiment 4 of the present invention. As shown in FIG. 11, the display device 4 according to the fourth embodiment is connected to a first power supply line 101 and a second power supply line 102, and the first power supply line 101 and the second power supply line are connected. Switching circuit 51 for switching the polarity of 102, two current monitors 52 for detecting currents flowing through the first power supply line 101 and the second power supply line 102, and the currents detected by these current monitors 52 and preset A comparison circuit 53 is provided for comparing the reference current.

  As described above, in the present embodiment, the two current monitors 52 are provided. However, the present invention is not limited to such a configuration, and the current characteristics of the first organic EL element and the second organic EL element are determined. Any other configuration may be used as long as it can be detected.

  In addition, since the other structure of the display apparatus 4 which concerns on Embodiment 4 is the same as that of the case of Embodiment 1, it attaches | subjects the same code | symbol and abbreviate | omits description.

  In the display device 4 configured as described above, the comparison circuit 53 repeatedly compares the current detected by the current monitor 52 with the reference current. When the current detected by the current monitor 52 falls below the reference current, that is, when the brightness of the EL display panel 20 of the display device 4 falls below the reference brightness, the comparison circuit 53 A switching signal is output to the switching circuit 51.

  When the switching circuit 51 receives the switching signal output from the comparison circuit 53, the switching circuit 51 switches the polarities of the first power supply line 101 and the second power supply line 102.

  By operating as described above, the polarities of the first power supply line 101 and the second power supply line 102 are switched according to the decrease in the current characteristics of the organic EL elements included in each pixel circuit 10, and accordingly The first organic EL element and the second organic EL element emit light alternately. As a result, the display device 4 can significantly extend its life as compared with the conventional display device, as in the case of the first embodiment.

  As described above, in the third embodiment, according to the decrease in the luminance of the organic EL element, and in the fourth embodiment, the first according to the decrease in the current flowing through the organic EL element. Although the polarities of the power supply line and the second power supply line are switched, the present invention is not limited to these. In addition to these, for example, the polarity of the two power supply lines may be switched according to a change in voltage applied to the organic EL element or a change in resistance in the organic EL element.

(Embodiment 5)
As described above, in the present invention, each pixel circuit includes the first organic EL element and the second organic EL element, and these two organic EL elements are configured to emit light alternately. Here, various modes can be considered for the arrangement of the first organic EL element and the second organic EL element. For example, the first organic EL element and the second organic EL element may be provided side by side in the vertical direction with respect to the EL display panel, or may be provided side by side in a direction parallel to the EL display panel. Conceivable.

  Hereinafter, in the present invention, a preferable arrangement of the first organic EL element and the second organic EL element will be described.

  FIG. 12 is a conceptual diagram illustrating an example of a configuration of an EL display panel included in the display device of the present invention. As shown in FIG. 12, the EL display panel 60 includes a plurality of pixels 70 arranged in a matrix. The pixel 70 includes a first subpixel 71 provided with a first organic EL element and a second subpixel 72 provided with a second organic EL element. For convenience of explanation, the first subpixel 71 is hatched.

  In each pixel 70, the first sub-pixel 71 and the second sub-pixel 72 are arranged in the column direction. In this case, the first organic EL element and the second organic EL element are arranged in the column direction.

  Each pixel 70 is arranged in a matrix so that the first light emitting element and the second light emitting element are not aligned in the row direction. Therefore, as shown in FIG. 12, when viewed in the row direction, the first sub-pixels 71 and the second sub-pixels 72 are alternately arranged.

  Note that in the display device of the present embodiment, the configuration other than the first sub-pixel 71 and the second sub-pixel 72 arranged in this way is the same as that of the first embodiment, and thus the description will be given. Omitted.

  When the display device according to the present embodiment configured as described above operates as described in the first embodiment to perform image display, the first subpixel 71 and the second subpixel 71 in each pixel 70 are displayed. Any one of the sub-pixels 72 is turned on, and these sub-pixels 71 and 72 do not emit light at the same time. For this reason, the lit subpixels do not line up in a straight line, and so-called vertical stripe unevenness, which is particularly problematic when a polysilicon TFT is used, can be made inconspicuous.

  Unlike the above-described case, the first organic EL element and the second organic EL element are arranged in the row direction, and each pixel 70 includes the first light emitting element and the second light emitting element. They may be arranged in a matrix so that they do not line up in the column direction. Such a configuration is shown in FIG. When configured in this way, it is possible to make so-called uneven horizontal stripes inconspicuous.

  As described above, a favorable image display can be realized by arranging the first light emitting element and the second light emitting element provided in each pixel so as not to be in a line.

  In each of the above-described embodiments, the organic EL element is exemplified as the light emitting element included in the pixel circuit. However, the present invention is not limited to this, and other elements may be used as long as they are self-luminous elements. Is possible. Examples of such light emitting elements include inorganic EL elements and light emitting diodes (LEDs).

(Embodiment 6)
Although Embodiments 1 to 5 have been described with a focus on a display device, an example in which the electroluminescence element and the pixel circuit according to the present invention are applied to an image forming apparatus will be described in detail below.

  FIG. 14 is a configuration diagram of an image forming apparatus according to the sixth embodiment of the present invention.

  The image forming apparatus 501 in FIG. 14 includes a yellow developing station 502Y, a magenta developing station 502M, a cyan developing station 502C, a black developing station 502K, a toner bottle 517, and developing stations 502Y and 502M arranged in a stepwise manner in the vertical direction. , 502C and 502K, exposure devices 513Y, 513M, 513C, and 513K, a paper feed tray 504, and a recording paper transport path 505 that serves as a transport path for the recording paper 503 supplied from the paper feed tray 504, A sheet feeding roller 518, a registration roller 519 and a pinch roller 520 constituting an inlet side nip conveying means, a fixing device 523 constituting an outlet side nip conveying means, a recording paper conveying drum 533, and a face-down paper discharging Portion 534, kick roller 535, and paper discharge And a lay-539.

  The image forming apparatus 501 also includes a drive source 538, a controller 541, and an engine control unit 542. Further, the image forming apparatus 501 includes a recording paper passage detection sensor 521 disposed between the paper feed roller 518 and the nip conveyance unit on the entrance side, and a recording paper rear end disposed below the recording paper conveyance drum 533. A detection sensor 528 and a toner image detection sensor 532 disposed on the side of the recording paper transport drum 533 are provided.

  The developing stations 502Y to 502K form toner images using toners supplied from yellow, magenta, cyan, and black toner bottles 517, respectively. The toner bottle 517 stores yellow, magenta, cyan, and black toner, and supplies the toner to the developing stations 502Y to 502K. The supply of the toner is performed via a toner transport pipe (not shown) disposed between the toner bottle 517 and each of the development stations 502Y to 502K.

  The yellow developing station 502Y includes a photosensitive member 508Y, the magenta developing station 502M includes a photosensitive member 508M, the cyan developing station 502C includes a photosensitive member 508C, and the black developing station 502K includes a photosensitive member 508K. The photoreceptors 508Y to 508K are exposed by the exposure devices 513Y to 513K, and electrostatic latent images are formed on the surfaces thereof. Each of the developing stations 502Y to 502K includes a member that realizes a developing process in a series of electrophotographic processes, such as a developing sleeve and a charger described later.

  Since the developing stations 502Y to 502K have the same configuration except for the colors to be developed, the developing stations 502Y to 502K are described as the developing station 502 unless otherwise specified for the sake of simplicity. Explain without specifying. The corresponding photoconductors 508Y to 508K and exposure devices 513Y to 513K are also described as the photoconductor 508 and the exposure device 513 in the same manner.

  Note that the first organic EL element 103, the second organic EL element 105, and the pixel circuit 10 (all of which are shown in FIG. 2) described in Embodiment 1 and the like are included in the exposure apparatus 513.

  In the following description, when these two organic EL elements are described together, they are referred to as organic EL elements 103 and 105.

  FIG. 15 is a peripheral configuration diagram of the developing station 502 in the image forming apparatus 501 according to the sixth embodiment of the present invention.

  The developing station 502 in FIG. 15 includes stirring paddles 507a and 507b, a photoreceptor 508, a charger 509, a developing sleeve 510, and a thinning blade 511, and inside the container in which the stirring paddles 507a and 507b are accommodated. A developer 506 which is a mixture of carrier and toner is filled. An exposure device 513 is disposed below the developing station 502, and a transfer roller 516 is disposed at a position facing the photoconductor 508 across the recording paper conveyance path 505.

  The agitation paddles 507a and 507b are members for agitating the developer 506, and the toner in the developer 506 is charged to a predetermined potential by friction with the carrier by the rotation of the agitation paddles 507a and 507b. Further, the toner and the carrier are sufficiently stirred and mixed by circulating inside the container of the developing station 502.

  The photoconductor 508 is an image carrier that carries an image formed by exposure by the exposure device 513, and a charge generation layer and a charge transport layer (both not shown) are laminated on a base material such as aluminum, and at least This is a so-called organic photosensitive drum in which the charge transport layer is made of an organic material. The photoconductor 508 is rotated in the direction D3 by a driving source (not shown). The charger 509 charges the surface of the photoconductor 508 to a predetermined potential.

  The developing sleeve 510 has a magnet roll 512 having a plurality of magnetic poles formed therein, and is rotated in the direction D4 by a driving source (not shown). The developer 506 is supplied to the surface of the developing sleeve 510 by this rotation and the action of the magnetic poles of the magnet roll 512. The thinning blade 511 regulates the layer thickness of the developer 506 supplied to the surface of the developing sleeve 510. The developer 506 on the surface of the developing sleeve 510 develops an electrostatic latent image formed on the photosensitive member 508 by an exposure device 513 described later, and the developer 506 that has not been transferred to the photosensitive member 508 is contained inside the container of the developing station 502. To be recovered.

  The exposure device 513 exposes the photoconductor 508 in units of one line, and the organic EL elements 103 and 105 (see FIG. 2) described in detail in the first embodiment and the like with a resolution of 1200 dpi (dot per inch). It has light emitting element rows (see FIG. 17) arranged in rows.

  The organic EL elements 103 and 105 that constitute a light emitting unit that emits light for exposing the photoconductor 508 are selectively turned on / off according to image data, and charged to a predetermined potential by a charger 509. An electrostatic latent image having a maximum A4 size can be formed on the photoconductor 508. That is, the exposure apparatus 513 forms a two-dimensional electrostatic latent image on the surface of the photoconductor 508 by performing exposure for each line a plurality of times on the photoconductor 508 that moves relative to the exposure apparatus 513. Then, only the toner of the developer 506 supplied to the surface of the developing sleeve 510 adheres to the electrostatic latent image portion, and the electrostatic latent image is visualized.

  The transfer roller 516 is provided at a position facing the photoconductor 508 across the recording paper conveyance path 505, and is rotated in the direction D5 by a driving source (not shown). A predetermined transfer bias is applied to the transfer roller 516, and the toner image formed on the photoconductor 508 is transferred to the recording paper 503 conveyed through the recording paper conveyance path 505.

  Returning to FIG. 14, the description will be continued.

  The paper feed tray 504 is disposed above the developing stations 502Y to 502K arranged in a stepwise manner in the vertical direction, and stores recording paper 503. The recording paper 503 supplied from the paper feed tray 504 is conveyed in the vertical direction from the upper side to the lower side on the recording paper conveyance path 505.

  The paper feed roller 518 is rotated in the direction D1 by controlling an electromagnetic clutch (not shown), and feeds the recording paper 503 loaded in the paper feed tray 504 to the recording paper transport path 505.

  The registration roller 519 and the pinch roller 520 pair constitute a nip conveyance unit on the entrance side. The registration roller 519 and the pinch roller 520 constitute a recording paper conveyance path 505 positioned between the paper feed roller 518 and the transfer portion of the most upstream yellow developing station 502Y. Is provided. The registration roller 519 and the pinch roller 520 pair temporarily stop the recording paper 503 conveyed by the paper supply roller 518 and convey it in the direction of the yellow developing station 502Y at a predetermined timing. This temporary stop restricts the leading edge of the recording paper 503 in parallel with the axial direction of the registration roller 519 and pinch roller 520 pair, and prevents the recording paper 503 from skewing.

  The recording paper passage detection sensor 521 detects the passage of the recording paper 503. The recording paper passage detection sensor 521 is composed of a reflection type sensor (photo reflector), and detects the leading edge and the trailing edge of the recording paper 503 based on the presence or absence of reflected light.

  Since the feeding mechanism of the recording paper 503 is configured as described above, when the rotation of the registration roller 519 is started by controlling the power transmission by an electromagnetic clutch or the like (not shown), the recording paper 503 that has been temporarily stopped. Is conveyed in the direction of the yellow developing station 502Y along the recording paper conveyance path 505. Then, starting from the rotation start timing of the registration roller 519, the electrostatic latent image writing timing by the exposure devices 513Y to 513K arranged in the vicinity of the developing stations 502Y to 502K, ON / OFF of the developing bias, and transfer bias ON / OFF and the like are controlled independently.

  The fixing device 523 constituting the nip conveying means on the outlet side is provided in the recording paper conveying path 505 located further downstream of the most downstream black developing station 502K. The fixing device 523 includes a heating roller 524, a pressure roller 525, and a temperature sensor 527.

  The temperature sensor 527 is for detecting the temperature of the heating roller 524. The temperature sensor 527 is a ceramic semiconductor obtained by sintering at a high temperature using a metal oxide as a main raw material, and measures the temperature of a contacted object by applying a change in load resistance according to the temperature. It is. The output of the temperature sensor 527 is input to an engine control unit 542, which will be described later. The engine control unit 542 controls the power supplied to the heat source built in the heating roller 524 based on the output of the temperature sensor 527, and the surface of the heating roller 524 The temperature is controlled to be about 170 ° C.

  When the recording paper 503 on which the toner image is formed is passed through the fixing device 523, the toner image on the recording paper 503 is heated and pressed by the temperature-controlled heating roller 524 and the pressure roller 525, and the toner The image is fixed on the recording paper 503.

  The recording paper trailing edge detection sensor 528 monitors the discharge state of the recording paper 503. The toner image detection sensor 532 detects the position and density of the toner image. The toner image detection sensor 532 is a reflective sensor unit that uses a plurality of light emitting elements (both visible light) having different emission spectra and a single light receiving element. The image density is detected by utilizing the fact that the absorption spectrum differs depending on the image. Further, since the toner image detection sensor 532 can detect not only the image density but also the image forming position, the image forming apparatus 501 is provided with two toner image detection sensors 532 in the width direction of the image forming apparatus 501 and formed on the recording paper 503. The image formation timing is controlled based on the detected position of the detected image position deviation amount detection pattern.

  The recording paper conveyance drum 533 conveys the recording paper 503 after fixing. The recording paper transport drum 533 is a metal roller whose surface is covered with rubber having a thickness of about 200 μm, and the fixed recording paper 503 is transported along the recording paper transport drum 533 in the direction D2. Thereafter, the recording paper 503 is conveyed in the direction D6 by the kick roller 535 and is discharged to the paper discharge tray 539.

  The face-down paper discharge unit 534 is configured to be rotatable around the support member 536. When the face-down paper discharge unit 534 is opened, the recording paper 503 is discharged in the direction D7. In the closed state, the face-down paper discharge unit 534 is formed with ribs 537 along the conveyance path on the back so as to guide conveyance of the recording paper 503 together with the recording paper conveyance drum 533.

  The drive source 538 drives each drive unit included in the image forming apparatus 501 and employs a stepping motor. Peripheral portions of the developing stations 502Y to 502K including a paper feed roller 518, a registration roller 519, a pinch roller 520, photoconductors 508Y to 508K, and a transfer roller 516 (see FIG. 15) are included in the drive unit driven by the drive source 538. , A fixing device 523, a recording paper transport drum 533, and a kick roller 535.

  The controller 541 receives image data from an external computer (not shown) via an external network or the like, and develops the received image data to generate printable image data. The controller 541 includes a power source for driving the organic EL elements 103 and 105 with different polarities.

  The engine control unit 542 controls the image forming apparatus 501 in general. The control performed by the engine control unit 542 includes control of hardware and mechanism of the image forming apparatus 501 for forming a color image on the recording paper 503 based on image data transferred from the controller 541, and a heating roller of the fixing device 523. 524 temperature control and the like are included.

  The operation of the image forming apparatus 501 configured as described above will be described with reference to FIGS. 14 and 15. In the following description, for the description related to the overall configuration and operation of the image forming apparatus 501, mainly using FIG. 14, the development stations 502Y to 502K, the photoreceptors 508Y to 508K, and the exposure apparatuses 513Y to 513K are divided into colors. It explains separately. Further, the description relating to the single color, such as the exposure and development process, will be described mainly using FIG. 15 without distinguishing the colors such as the developing station 502, the photoconductor 508, and the exposure device 513 for the sake of simplicity.

  When image data is transferred to the controller 541 from, for example, a computer connected via a network, the controller 541 develops the image data in an image memory (not shown) as binary image data that can be printed. When the development of the image data is completed, a controller CPU (not shown) mounted on the controller 541 issues a startup request to the engine control unit 542. The activation request is received by an engine control CPU (not shown) mounted on the engine control unit 542, and the engine control CPU that has received the activation request immediately rotates the drive source 538 and starts preparation for image formation. .

  When preparation for image formation is completed, the engine control CPU mounted on the engine control unit 542 controls an electromagnetic clutch (not shown) to rotate the paper feed roller 518 and start conveying the recording paper 503. The paper feed roller 518 is, for example, a half-moon roller that lacks a part of the entire circumference. When the leading edge of the conveyed recording paper 503 is detected by the recording paper passage detection sensor 521, the engine control CPU controls the electromagnetic clutch and rotates the registration roller 519 after providing a predetermined delay period. As the registration roller rotates, the recording paper 503 is supplied to the recording paper conveyance path 505.

  The engine control CPU controls the electrostatic latent image writing timing by each of the exposure devices 513Y to 513K independently from the rotation start timing of the registration roller 519. The timing for writing the electrostatic latent image directly affects color misregistration and the like in the image forming apparatus 501. Therefore, the engine control CPU that controls the task by the real-time OS that presupposes the occurrence of delay is not directly generated. Specifically, the engine control CPU presets the electrostatic latent image writing timing by each exposure device 513 in a timer or the like which is hardware not shown, and each exposure device starts from the rotation of the registration roller 519 described above. Timer operations corresponding to 513Y to 513K are started simultaneously. Each timer outputs an image data transfer request to the controller 541 when a preset time has elapsed.

  Receiving the image data transfer request, the controller CPU (not shown) of the controller 541 sends the image data to each of the exposure devices 513Y to 513K in synchronization with the timing signal generated by the timing generation unit (not shown) of the controller 541. Transfer independently. In this way, the image data is sent to the exposure apparatuses 513Y to 513K, and on / off of the organic EL elements constituting the exposure apparatuses 513Y to 513K is controlled based on the image data, and the photoconductors 508Y to 508K corresponding to the respective colors are controlled. Exposed.

  The latent image formed by exposure is visualized by toner contained in the developer 506 supplied onto the developing sleeve 510 as shown in FIG. The visualized toner images of the respective colors are sequentially transferred onto the recording paper 503 conveyed through the recording paper conveyance path 505. The recording paper 503 that has completed the transfer of the four color toner images is conveyed to the fixing device 523, and is nipped and conveyed by the heating roller 524 and the pressure roller 525 constituting the fixing device 523. The transferred toner image is fixed on the recording paper 503 by the heat of the heating roller 524 and the pressure of the pressure roller.

  When the image to be formed is a plurality of pages, the engine control CPU (not shown) rotates the registration roller 519 after the trailing edge of the recording paper 503 of the first page is detected by the recording paper passage detection sensor 521. Once stopped, the feeding roller 518 is rotated after a lapse of a predetermined time to start the conveyance of the next recording paper 503, and the rotation of the registration roller 519 is started again after the lapse of the predetermined time, so that the recording paper for the next page 503 is supplied to the recording paper conveyance path 505. As described above, when the image is formed over a plurality of pages by the timing control of the rotation ON / OFF of the registration roller 519, the time interval between the recording sheets 503 can be set. The time required for the conveyance interval of the recording paper 503 (hereinafter referred to as an inter-paper period) differs depending on the specifications of the image forming apparatus 501, but is generally set to about 500 ms. Of course, a normal image forming operation (that is, an exposure operation for the photoconductor 508 by the exposure device 513 based on image data supplied from the outside of the image forming apparatus 501) is not performed during this paper interval.

  The controller 541 supplies power to the organic EL elements 103 and 105 in addition to signals relating to lighting control of the organic EL elements 103 and 105 such as a clock signal and a line synchronization signal. That is, the switching circuit 21 (see FIG. 1) of the organic EL elements 103 and 105 described in the first embodiment and the like is included in the controller 541 in the sixth embodiment.

  In the image forming apparatus 501 of the sixth embodiment, the first organic EL element 103 and the second organic EL element 105 are switched for each line at the time of image formation. The one-line formation time of the image forming apparatus in the present embodiment is set to about 350 μs, and the first organic EL element 103 and the second organic EL element 105 constituting the exposure apparatus 13 are alternately cycled at 350 μs. Lights up (however, when the image data is 0, that is, when image data indicating non-lighting is input, it does not light up). As a result, a reverse bias is periodically applied to the organic EL elements 103 and 105, and the lifetime of the organic EL elements 103 and 105 can be extended.

  Further, the organic EL elements 103 and 105 may be switched during the above-described inter-paper period. In this case, the organic EL elements 103 and 105 are switched in units of pages.

  In the image forming apparatus 501, since the number of lines and the number of pages are counted by the controller 541, the configuration in which the power source line is switched by the controller 541 becomes the simplest.

  FIG. 16 is a block diagram of exposure apparatus 513 in image forming apparatus 501 according to the sixth embodiment of the present invention.

  16 includes a glass substrate 550, a lens array 551, a relay substrate 552, a connector A553a, a connector B553b, a housing A554a, and a housing B554b.

The glass substrate 550 is a colorless and transparent substrate on which organic EL elements 103 and 105 (see FIG. 2) as exposure light sources and thin film transistors constituting a control circuit and a drive circuit are formed, and is, for example, borosilicate glass. Borosilicate glass is advantageous in terms of cost, but when it is necessary to efficiently dissipate the organic EL elements 103 and 105 and the thin film transistor, the thermal conductivity of MgO, Al ₂ O _3, CaO, ZnO, etc. Glass containing an additive factor or quartz may be used.

  On the surface A of the glass substrate 550, the first organic EL element 103 and the second organic EL element 105 are alternately formed at a resolution of 1200 dpi in a direction (main scanning direction) perpendicular to the drawing. As described above, since the two organic EL elements 103 and 105 constitute one pixel, the effective resolution is 600 dpi in the image forming apparatus 501 of the sixth embodiment.

  The lens array 551 includes rod lenses (not shown) made of plastic or glass arranged in a line, and the light emitted from the organic EL elements 103 and 105 formed on the surface A of the glass substrate 550 is corrected. This is to guide the image to the surface of the photoconductor 508 as an image of the same magnification. The positional relationship of the glass substrate 550, the lens array 551, and the photoconductor 508 is adjusted so that one focus of the lens array 551 is the surface A of the glass substrate 550 and the other focus is the surface of the photoconductor 508. Yes. That is, when the distance L1 from the surface A to the surface closer to the lens array 551 and the distance L2 from the other surface of the lens array 551 to the surface of the photoconductor 508, L1 = L2. .

  The relay board 552 relays image data supplied from the outside, the power supply lines of the organic EL elements 103 and 105, and other control signals. For example, the relay board 552 is an electronic circuit formed on a glass epoxy board. is there. At least a connector A 553a and a connector B 553b are mounted on the relay substrate 552. The various signals described above are supplied from the controller 541 (see FIG. 14) via a cable 556 such as a flexible flat cable, and are relayed to the glass substrate 550 once via the connector B553b.

  Since it is difficult to directly mount the connector on the surface of the glass substrate 550 in consideration of bonding strength and reliability in various environments, the exposure apparatus 513 in FIG. 16 uses the connector A553a of the relay substrate 552 and the glass substrate 550. FPC (flexible printed circuit) is employed as a connection means (not shown), and the glass substrate 550 and FPC are joined using, for example, an ACF (anisotropic conductive film), for example, ITO previously formed on the glass substrate 550. A (tin-doped indium oxide) electrode is connected directly.

  In general, connection by ACF or the like often has a problem of bonding strength, but by providing the connector B 553b for connecting the exposure apparatus 513 on the relay substrate 552 in this way, an interface directly accessed by the user can be obtained. Sufficient strength can be ensured.

  The casing A554a is formed by bending a metal plate, for example, by bending. An L-shaped part 555 is formed on the side of the housing A 554 a facing the photoconductor 508, and the glass substrate 550 and the lens array 551 are disposed along the L-shaped part 555. Forming accuracy of the L-shaped portion 555 is achieved by aligning the end surface of the housing A554a on the photoconductor 508 side with the end surface of the lens array 551 and further supporting one end of the glass substrate 550 by the housing A554a. If the surface property is ensured, the positional relationship between the glass substrate 550 and the lens array 551 can be accurately adjusted. As described above, since the housing A554a is required to have dimensional accuracy, it is preferable that the housing A554a be made of metal. Further, by making the housing A554a made of metal, it is possible to suppress the influence of noise on a control circuit formed on the glass substrate 550 and an electronic component such as an IC chip surface-mounted on the glass substrate 550. It is.

  The housing B554b is obtained by molding a resin. A notch (not shown) is provided in the vicinity of the connector B553b of the housing B554b, and the user can access the connector B553b from this notch. From the controller 541 (see FIG. 14) already described via the cable 556 connected to the connector B 553b to the exposure device 513, image data, power supply lines for the organic EL elements 103 and 105, control signals such as clock signals and line synchronization signals, Drive power for the control circuit is supplied. As shown in FIG. 16, the relay substrate 552 is disposed in a space formed by the casing A 554a and the casing B 554b.

  17A is a top view of glass substrate 550 included in exposure apparatus 513 in image forming apparatus 501 according to Embodiment 6 of the present invention, and FIG. 17B is an enlarged view of the main part thereof. Hereinafter, the configuration of the glass substrate 550 will be described in detail with reference to FIGS. 17 and 16.

  The glass substrate 550 is a rectangular substrate having a thickness of about 0.7 mm and at least a long side and a short side. In the long side direction (main scanning direction), a plurality of exposure light sources for the photoconductor 508 are provided. The organic EL elements 103 and 105 are formed in rows at 1200 dpi (21.2 μm pitch). As already described, two organic EL elements 103 and 105 constitute one pixel.

  With respect to these organic EL elements 103 and 105, a light receiving element 620 is formed in the normal direction of the surface of the glass substrate 550. That is, the organic EL elements 103 and 105 and the light receiving element 620 have a laminated structure as a whole, and the light receiving element 620 and the organic EL elements 103 and 105 are formed from the side closer to the glass substrate 550. An insulating layer is provided between the light receiving element 620 and the organic EL elements 103 and 105.

  In the long side direction of the glass substrate 550 in FIG. 17, organic EL elements 103 and 105 and a light receiving element 620 necessary for at least A4 size (210 mm) exposure are arranged. One light receiving element 620 is provided for each pixel composed of the organic EL elements 103 and 105 (that is, two light emitting units). In the case of the sixth embodiment, 10240 organic EL elements 103 and 105 are received. 5120 elements 620 are arranged. The long side direction of the glass substrate 550 is 250 mm including the arrangement space of the control circuit 12 described later.

  In FIG. 17, the glass substrate 550 is described as a rectangle for the sake of simplicity. However, a notch is provided in a part of the glass substrate 550 for positioning or the like when the glass substrate 550 is attached to the housing A 554a. May be accompanied by various deformations. In addition, the organic EL elements 103 and 105 formed on the glass substrate 550 are arranged in a row, but the organic EL elements 103 and 105 may be configured in a plurality of rows or in a plurality of rows and staggered shapes. Good.

  Along with the organic EL elements 103 and 105 and the light receiving element 620, the glass substrate 550 is provided with a TFT (Thin Film Transistor) circuit 562, and the individual organic EL elements 103 and 105 are turned on and off, and the amount of emitted light is detected independently. To control. At this time, as described in detail in Embodiment 1 or the like, the first organic EL element 103 is switched by switching the polarity of the power supply line supplied from the outside of the glass substrate 550 (see the controller 541 and FIG. 14 described above). Then, the second organic EL element 105 is selectively turned on.

  Note that the TFT circuit 562 includes the gate driver 13 described with reference to FIG.

  The organic EL elements 103 and 105 and a part of the TFT circuit 562 are sealed with a sealing glass 564. When the organic EL elements 103 and 105 are affected by moisture, the light emission characteristics are extremely deteriorated due to shrinkage of the light emitting region over time (shrinking), non-light emitting portions (dark spots) in the light emitting region, and the like. Therefore, moisture is blocked by the sealing glass 564.

  The sealing glass 564 in FIG. 17 is attached to the glass substrate 550 by a solid sealing method that is attached via an adhesive. Note that the organic EL elements 103 and 105 in FIG. 17 employ a polymer material as the material of the light-emitting layer forming the light-emitting region. The so-called glass transition temperature of the polymer material is not clear, and even at high temperatures. Since there is little characteristic deterioration due to crystallization, a thermosetting resin having a better gas barrier property than that of a photocurable resin can be employed for sealing.

  A control circuit 12 is provided at one end of the glass substrate 550, and an FPC (flexible printed circuit) 560 as an interface unit is further connected.

  The control circuit 12 receives image data supplied from the outside of the glass substrate 550, a control signal such as a clock signal and a line synchronization signal, and a power supply line of the organic EL elements 103 and 105, and based on these signals, the organic EL element 103 and 105 are controlled.

  The FPC 560 connects the connector A 553a of the relay substrate 552 and the glass substrate 550, and is directly connected to a circuit pattern (not shown) provided on the glass substrate 550 without using a connector or the like. The image data, the control signal such as the clock signal and the line synchronization signal, the drive power supply of the control circuit, and the power supply lines of the organic EL elements 103 and 105 that have already been described are temporarily passed through the relay board 552 shown in FIG. It is supplied to the glass substrate 550 and connected to the circuit pattern described above.

  The source driver 14 is an IC chip that controls driving of the organic EL elements 103 and 105, and is flip-chip mounted on the glass substrate 550. In consideration of surface mounting on the glass surface, the source driver 14 adopts a bare chip product. The source driver 14 is supplied with control-related signals such as a power source, a clock signal, a line synchronization signal, and 8-bit image data from the outside of the exposure apparatus 513 via the FPC 560. The source driver 14 sets a driving current for driving the individual organic EL elements 103 and 105 based on the image data output from the controller 541 (see FIG. 14).

  The TFT circuit 562 formed on the glass substrate 550 includes a gate driver which is a logic circuit that controls the timing of turning on / off the organic EL elements 103 and 105 (as one pixel) such as a shift register and a data latch unit. It is out.

  In the case of the exposure apparatus 513, the organic EL elements 103 and 105 are arranged in a row, and each organic EL element is driven by the above-described source driver 14 and a gate driver included in the TFT circuit 562. The active matrix circuit is configured in the same manner as the display device described in (1).

  Note that the configuration of the pixel circuit has been described in detail in Embodiment 1 and the like, and thus the description thereof is omitted.

  Since the electroluminescence element, the pixel circuit, and the display device of the present invention can have a long lifetime by appropriately switching between the first light-emitting element and the second light-emitting element to emit light, they can be used for computers and household appliances. It can be applied to various displays such as the beginning.

  Similarly, the present invention can be applied to an image forming apparatus, that is, an exposure apparatus mounted on an MFP (multifunction printer), a multifunction peripheral, a printer, or the like.

The block diagram which shows the structure of the display apparatus which concerns on Embodiment 1 of this invention. 1 is a circuit diagram illustrating an example of a configuration of a pixel circuit included in a display device according to Embodiment 1 of the present invention. FIG. 6 is a circuit diagram illustrating another example of the configuration of the pixel circuit included in the display device according to Embodiment 1 of the present invention. FIG. 6 is a circuit diagram illustrating another example of the configuration of the pixel circuit included in the display device according to Embodiment 1 of the present invention. FIG. 6 is a circuit diagram illustrating another example of the configuration of the pixel circuit included in the display device according to Embodiment 1 of the present invention. Timing chart showing an operation example of the display device according to the first embodiment of the present invention. The circuit diagram which shows the structure of the pixel circuit with which the conventional display apparatus which is a comparative example is provided Timing chart showing operation example of display device of comparative example The block diagram which shows the structure of the display apparatus which concerns on Embodiment 2 of this invention. The block diagram which shows the structure of the display apparatus which concerns on Embodiment 3 of this invention. The block diagram which shows the structure of the display apparatus which concerns on Embodiment 4 of this invention. 1 is a conceptual diagram illustrating an example of a configuration of an EL display panel included in a display device of the present invention. The conceptual diagram which shows the other example of a structure of EL display panel with which the display apparatus of this invention is provided. Configuration of an image forming apparatus according to a sixth embodiment of the present invention FIG. 7 is a peripheral configuration diagram of a developing station in an image forming apparatus according to a sixth embodiment of the present invention. Configuration diagram of an exposure apparatus in an image forming apparatus according to Embodiment 6 of the present invention (A) is a top view of a glass substrate included in the exposure apparatus in the image forming apparatus according to Embodiment 6 of the present invention, and (b) is an enlarged view of the main part thereof.

Explanation of symbols

1, 2, 3, 4 Display device 10 Pixel circuit 12 Control circuit 13 Gate driver 14 Source driver 20 EL display panel 21 Switching circuit 22 Timer 31 Switching circuit 31a Non-volatile memory 41 Switching circuit 42 Comparison circuit 43 Photo detector 51 Switching circuit 52 Current Monitor 53 Comparison circuit 60 EL display panel 70 Pixel 71 First subpixel 72 Second subpixel 101 First power supply line 102 Second power supply line 103 First organic EL element 104 First transistor 105 Second Organic EL element 106 Second transistor 107 Control transistor 110 Gate line 111 Source line 501 Image forming apparatus 502Y, 502M, 502C, 502K Development station 503 Recording paper 508Y, 508M, 508C, 5 08K photoconductor 513Y, 513M, 513C, 513K Exposure device 541 Controller 542 Engine control unit 550 Glass substrate 551 Lens array 552 Relay substrate 553a Connector A
553b Connector B
556 Cable 562 TFT circuit 564 Sealing glass 620 Light receiving element

Claims (18)

In the pixel circuits respectively disposed corresponding to the intersections of the plurality of gate lines and the plurality of source lines arranged to cross each other,
A first light emitting element and a second light emitting element;
A first transistor and a second transistor connected to anodes of the first light-emitting element and the second light-emitting element, respectively, for driving the first light-emitting element and the second light-emitting element;
A first power line connected to a cathode of the second light emitting element and a side of the first transistor not connected to the first light emitting element;
A second power supply line connected to a cathode of the first light emitting element and a side of the second transistor not connected to the second light emitting element, and having a polarity different from that of the first power supply line; With
The pixel circuit, wherein the first power line and the second power line are switched in polarity.   The pixel circuit according to claim 1, wherein polarities of the first power supply line and the second power supply line are switched at a predetermined time interval.   2. The configuration according to claim 1, wherein when power is turned on, the first power supply line and the second power supply line are configured to have different polarities from those when power was previously turned off. Pixel circuit.   2. The device according to claim 1, wherein polarities of the first power supply line and the second power supply line are switched according to a deterioration state of the first light emitting element and the second light emitting element. Pixel circuit.   5. The configuration according to claim 4, wherein polarities of the first power supply line and the second power supply line are switched in accordance with a decrease in luminance of the first light emitting element and the second light emitting element. The pixel circuit described.   5. The polarities of the first power supply line and the second power supply line are configured to be switched in accordance with a decrease in current flowing through the first light emitting element and the second light emitting element. The pixel circuit according to 1. In a display device comprising a plurality of gate lines and a plurality of source lines arranged so as to intersect with each other, and pixel circuits respectively disposed corresponding to the intersections of the plurality of gate lines and the plurality of source lines,
Each of the pixel circuits is
A first light emitting element and a second light emitting element;
A first transistor and a second transistor connected to anodes of the first light-emitting element and the second light-emitting element, respectively, for driving the first light-emitting element and the second light-emitting element;
A first power line connected to a cathode of the second light emitting element and a side of the first transistor not connected to the first light emitting element;
A second power supply line connected to a cathode of the first light emitting element and a side of the second transistor not connected to the second light emitting element, and having a polarity different from that of the first power supply line; Comprising
A display device comprising: a switching circuit that switches polarities of the first power supply line and the second power supply line included in each of the pixel circuits. A timer for outputting a switching signal for instructing switching of the polarity of the power line to the switching circuit at a predetermined time interval;
The switching circuit is configured to switch polarities of the first power supply line and the second power supply line included in each of the pixel circuits in response to an input of the switching signal. The display device described.   The switching circuit has the first power supply line and the second power supply line included in each of the pixel circuits so that when the power is turned on, the polarity is different from that when the power is turned off last time. The display device according to claim 7, wherein the display device is configured to switch a polarity of the display. A light emitting element deterioration detecting means for detecting a deterioration state of the first light emitting element and the second light emitting element included in each of the pixel circuits;
The switching circuit is configured to switch polarities of the first power supply line and the second power supply line included in each of the pixel circuits according to a detection result by the light emitting element deterioration detection unit. The display device according to claim 7.   11. The light emitting element deterioration detection unit is configured to detect a deterioration state according to the luminance of the first light emitting element and the second light emitting element included in each of the pixel circuits. The display device described.   The light emitting element deterioration detecting unit is configured to detect a deterioration state in accordance with a current flowing through the first light emitting element and the second light emitting element included in each of the pixel circuits. The display device described in 1. In each of the pixel circuits, the first light emitting element and the second light emitting element are arranged side by side in a column direction (or a row direction),
8. The display device according to claim 7, wherein the pixel circuit is arranged in a matrix so that each of the first light emitting elements and the second light emitting elements is not arranged in a row in a row direction (or a column direction). . A first light emitting unit including a first light emitting element and a first transistor for driving the first light emitting element;
A second light emitting unit composed of a second light emitting element and a second transistor for driving the second light emitting element;
A first power line connected to the anode side of the first light emitting unit and the cathode side of the second light emitting unit;
A second power supply line connected to the cathode side of the first light emitting unit and the anode side of the second light emitting unit;
The first light emitting element and the second light emitting element constitute one pixel,
Furthermore, the electroluminescent element comprised so that the polarity of the said 1st power supply line and the said 2nd power supply line could be switched.   A display device comprising the electroluminescence element according to claim 14.   An exposure apparatus constituted by the electroluminescence element according to claim 14. The exposure apparatus according to claim 16, wherein
An exposure apparatus configured such that the polarity of the power supply line is switched to a unit of one line of exposure. The exposure apparatus according to claim 16, wherein
An exposure apparatus configured such that the polarity of the power supply line is switched in units of one page for image formation.

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