JP2007230004A - Electro-optics apparatus and electronic instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable it to keep the brightness of an electro-optics element constant by adjusting the electric potential of another side according to the state concerning the resistance of the electro-optics element. <P>SOLUTION: The second high power-source electric potential VH2 and the second low power-source electric potential VL2 are applied to an output buffer processing unit U10i of an electro-optics apparatus. The high level of a drive signal Qi becomes the second high power-source electric potential VH2, meanwhile the low level becomes the second low power-source electric potential VL2. Wherein, the second high power-source electric potential VH2 is set to the potential for making a drive transistor 12 to be off-state, and the second low power-source electric potential VL2 is set to the potential for making the drive transistor 12 to be on-state. The second low power-source electric potential VL2 is adjusted based on a temperature signal detected by a sensor. Thereby, the temperature characteristics of the drive transistor 12 and an OLED element 13 can be corrected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electro-optical device and an electronic apparatus using an electro-optical element.

  A printer as an image forming apparatus uses a light emitting device in which a large number of light emitting elements are arranged in an array as a head unit for forming an electrostatic latent image on an image carrier such as a photosensitive drum. The head portion is often composed of a single line in which a plurality of light emitting elements are arranged along the main scanning direction. In addition, as a light emitting element, a light emitting diode such as an organic light emitting diode (hereinafter simply referred to as “OLED”) element is known.

The head unit includes a plurality of pixel circuits and a drive circuit on a substrate. The pixel circuit includes a pixel circuit including an OLED element and a driving transistor that is provided in the vicinity of the OLED element and supplies a driving current to the OLED element. On the other hand, the drive circuit generates a drive signal for controlling the supply of the drive current. Patent Document 1 discloses a liquid crystal active matrix driving circuit. This drive circuit includes a level shift circuit and an inverter functioning as a buffer at its final stage.
JP 2000-259111 A (FIG. 2)

However, when a level shift circuit is provided, there is a problem that the operation becomes slow. In particular, when an electro-optical element such as an OLED element is PWM-driven and its display gradation is controlled by the pulse width of the drive signal, the drive signal waveform becomes dull due to the level shift circuit, and the gradation cannot be displayed accurately. is there.
When PWM driving is performed by turning on and off the driving transistor, the driving transistor operates in a saturation region in the on state. At this time, the drive current Iel is Iel = β / 2 (Vgs−Vth) ^1/2 . Therefore, there is a problem that accurate gradation cannot be displayed when the threshold voltage Vth of the driving transistor varies.
The present invention has been made in view of such circumstances, and an object of the present invention is to display gradation accurately in PWM driving.

In order to solve this problem, an electro-optical device according to the present invention operates with a logic circuit that operates with a first high power supply potential and a first low power supply potential, with a second high power supply potential and a second low power supply potential, Drive means having an output circuit for outputting a drive signal whose binary level is the second high power supply potential and the second low power supply potential based on the output signal of the logic circuit, and luminance according to the drive current A pixel circuit provided with an electro-optical element that emits light at a time, and a drive transistor that is turned on and off by the drive signal supplied to the gate and supplies the drive current to the electro-optical element in the on state Generating the first high power supply potential and the first low power supply potential, and the second high power supply potential and the second low power supply potential, and one of the second high power supply potential and the second low power supply potential. of Is the potential that turns off the drive transistor when supplied to the gate, and the other potential of the second high power supply potential and the second low power supply potential turns on the drive transistor when supplied to the gate. Power supply potential generating means for adjusting and outputting the other potential.
According to the present invention, the driving means has a logic circuit and an output circuit, and the former power supply potential and the latter power supply potential are independent. Therefore, it is possible to suppress the noise of the logic circuit from being mixed into the output circuit. Further, the logic level of the drive signal is set so that the on / off of the drive transistor can be controlled, and this can be set by the second high power supply potential and the second low power supply potential supplied to the output circuit. . Therefore, it is not necessary to provide a level shift circuit. As a result, the driving means can be operated at high speed, and the configuration can be simplified. In addition, since the other potential that defines the ON state of the drive transistor can be adjusted, variations in the threshold voltage of the drive transistor and variations in the light emission characteristics of the electro-optical element can be corrected.
Note that the electro-optical element is an element whose optical characteristics change depending on electric energy, and includes a current-driven light-emitting element. Such light emitting elements include light emitting diodes such as OLED elements and inorganic light emitting diodes. The electro-optic element may include a field emission element (FED), a surface electric emission element (SED), and a ballistic electron emission element (BSD).

In the electro-optical device described above, the power supply potential generation unit generates the first high power supply potential, the first low power supply potential, the second high power supply potential, and the second low power supply potential so that they are different from each other. May be.
Further, the power supply potential generating means is configured so that a potential difference between the second high power supply potential and the second low power supply potential is smaller than a potential difference between the first high power supply potential and the first low power supply potential. The first high power supply potential and the first low power supply potential, and the second high power supply potential and the second low power supply potential may be generated. In this case, the logic circuit can be operated at high speed while the output circuit can be operated with a small amplitude.
Further, the power supply potential generating means generates the second high power supply potential and the third high power supply potential as the same potential, and adjusts and outputs the second low power supply potential as the other potential. preferable. In this case, since the types of power supply potentials can be reduced, the configuration of the power supply potential generating means can be simplified.

The electro-optical device described above preferably includes detection means for detecting a state relating to light emission of the electro-optical element, and the power supply potential generation means adjusts the other potential based on a detection result of the detection means. The state relating to light emission of the electro-optical element is a concept including not only the state of the electro-optical element itself but also the state of the drive current supplied thereto. For example, when the electro-optical element deteriorates with time, the usage time corresponds to a state related to light emission of the electro-optical element. Alternatively, since the threshold voltage of the drive transistor affects the magnitude of the drive current, it corresponds to a state relating to light emission of the electro-optical element. In the present invention, since the other potential can be adjusted according to the state of the electro-optic element, the luminance of the electro-optic element can be kept constant.
As a specific aspect of the detection means, a temperature sensor that detects the temperature of the environment may be used. In this case, it is possible to correct the characteristics of the driving transistor and the electro-optical element that change according to the temperature, and to make the electro-optical element emit light with a certain luminance.

The electro-optical device described above further includes storage means for preliminarily storing designation data generated based on at least one of the electrical characteristics of the driving transistor and the light-emitting characteristics of the electro-optical element, and the power supply potential generating means Preferably, the other potential is adjusted based on the designated data read from the storage means. In this case, the variation in the manufacturing process can be corrected by causing the electro-optical element to emit light at the time of shipment, measuring the light amount, and generating the designated data based on the measurement result.
In addition, the power source potential generation unit of the electro-optical device described above has one or a plurality of cutting regions in which the other potential can be set by cutting, and the electrical characteristics of the driving transistor and the electro-optical element It is preferable that a part or all of the one or more cutting regions are cut based on at least one of the light emission characteristics. In this case, the storage means for storing the designated data can be omitted.

  In addition, the electro-optical device described above includes a pixel region in which a plurality of the pixel circuits are arranged, and a luminance adjustment unit that generates a luminance adjustment signal that specifies the entire luminance of the pixel region, and the power supply potential generation unit Preferably, the other potential is adjusted based on the luminance adjustment signal. In this case, the brightness of the entire pixel area can be generated based on the brightness adjustment signal.

  In the electro-optical device described above, it is preferable that the logic circuit outputs a signal having a pulse width corresponding to a gradation. In this case, the gradation of the electro-optical element is controlled by the pulse width of the signal. However, various variations can be corrected by adjusting the other potential.

  Next, an electronic apparatus according to the present invention preferably includes the above-described electro-optical device. Examples of such an electric device include an image forming apparatus that prints an image, a display that displays an image, a mobile phone, a personal computer, and the like.

A preferred embodiment of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure.
<1. First Embodiment>
FIG. 1 is a perspective view showing a partial configuration of an image forming apparatus using an optical head according to the first embodiment. As shown in the figure, the image forming apparatus includes an optical head 1, a condensing lens array 150, and a photosensitive drum 110. The optical head 1 has a large number of electro-optical elements arranged in an array. An electro-optical element is an element whose optical characteristics change with electric energy. The electro-optic element corresponds to a current-driven light emitting element. These light emitting elements selectively emit light according to an image to be printed on a recording material such as paper. For example, an organic light emitting diode element (hereinafter referred to as an OLED element) is used as the light emitting element. The condensing lens array 150 is disposed between the optical head 1 and the photosensitive drum 110. The condensing lens array 150 includes a large number of gradient index lenses arranged in an array with each optical axis facing the optical head 1. An example of such a condensing lens array 150 is SLA (Selfoc Lens Array) available from Nippon Sheet Glass Co., Ltd. (Selfoc / SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.). The light emitted from each light emitting element of the optical head 1 passes through each gradient index lens of the condensing lens array 150 and reaches the surface of the photosensitive drum 110. By this exposure, a latent image corresponding to a desired image is formed on the surface of the photosensitive drum 110.

FIG. 2 is a block diagram of the electro-optical device A used in the image forming apparatus. The electro-optical device A includes an optical head 1, a control circuit 40 that is a peripheral circuit thereof, and a power supply potential generation circuit 50. The control circuit 40 converts image data supplied from an external device into a PWM timing signal S and outputs it, and supplies various control signals CTL to the optical head 1.
The PWM timing signal S has a pulse width corresponding to the gradation to be displayed. The image data in this example is 4 bits and designates gradation 0 to gradation 15. FIG. 3 shows the waveform of the PWM timing signal S at each gradation. As shown in this figure, the PWM timing signal S has a wider pulse width in proportion to the gradation. The period Tvb is a vertical blanking period, and the PWM timing signal S is inactive (low level) during this period.
The power supply potential generation circuit 50 illustrated in FIG. 2 generates various power supplies used in the electro-optical device A. In this example, the power supply potential generation circuit 50 includes a first high power supply potential VH1, a first low power supply potential VL1, a second high power supply potential VH2, a second low power supply potential VL2, a third high power supply potential VH3, and a third low power supply. A potential VL3 is generated.

  The optical head 1 includes an output buffer 10, a line memory 20, a sensor 30, and a pixel region 2 in which n pixel circuits P1 to Pn are arranged. The pixel circuits P1 to Pn include OLED elements. The light emission characteristics of the OLED element change according to the state of the OLED element such as the temperature of the environment. The output buffer 10 and the line memory 20 respectively include n processing units corresponding to the pixel circuits P1 to Pn. The sensor 30 outputs a temperature signal T obtained by measuring the temperature. The sensor 30 functions as a detection unit that detects the state of the OLED element, and is not limited to temperature detection. For example, the current flowing through the OLED element may be detected, or the light amount of the OLED element may be detected. In short, any device can be used as long as the state of the OLED element can be detected in order to directly or indirectly know the light emission characteristics of the OLED element.

  FIG. 4 shows the configuration of the i (1 ≦ i ≦ n) -th pixel circuit Pi and the corresponding output buffer 10 and line memory 20. The processing unit U20i of the line memory 20 is supplied with the first high power supply potential VH1 and the first low power supply potential VL1, and the processing unit U10i of the output buffer 10 is supplied with the second high power supply potential VH2 and the second low power supply potential VL2. Then, the third high power supply potential VH3 and the third low power supply potential VL3 are supplied to the pixel circuit Pi.

  The processing unit U20i includes a transfer gate 21, an inverter 22, and a clocked inverter 23. The transfer gate 21 is supplied with a selection signal SEL and an inverted selection signal SELX. The inversion selection signal SELX is obtained by inverting the logic level of the selection signal SEL. When the selection signal SEL becomes active (high level), the PWM timing signal S is captured. The clocked inverter 23 functions as an inverter when the selection signal SEL is active, and puts the output terminal in a high impedance state during the inactive period. Therefore, the inverter 22 and the clocked inverter 23 function as a latch circuit during a period in which the selection signal SEL is active, and function as an inverter in a period in which the selection signal SEL is inactive. The processing unit 20i latches the PWM timing signal S and outputs a data signal Di. The high level of the data signal Di becomes the first high power supply potential VH1, and the low level thereof becomes the first low power supply potential VL1.

  The processing unit U 10 i of the output buffer 10 includes an inverter 11, and the driving capacity of the inverter 11 is greater than that of the inverter 22. Although the wiring connecting the processing unit 10i and the pixel circuit Pi has a parasitic capacitance, since the inverter 11 has a large driving capability, it is possible to sufficiently drive a capacitive load. In other words, the drive capability of the inverter 11 may be determined according to the size of the parasitic capacitance. Inverter 11 converts the logic level of data signal Di and outputs drive signal Qi. The high level of the drive signal Qi becomes the second high power supply potential VH2, and the low level becomes the second low power supply potential VL2.

  In the pixel circuit Pi, the drive transistor 12 and the OLED element 13 are provided between the third high power supply potential VH3 and the third low power supply potential VL3. The drive transistor 12 supplies a drive current Iel corresponding to the gate potential to the OLED element 13 in the on state (saturation region). A drive signal Qi is supplied to the gate of the drive transistor 12.

FIG. 5 shows the relationship between the power supply potentials. First, the second high power supply potential VH2 is set to a potential at which the drive transistor 12 is turned off. Since the third high power supply potential VH3 is supplied to the source of the drive transistor 12, the drive transistor 12 is turned off when the gate potential exceeds VH3-Vth. Therefore, the second high power supply potential VH2 may be VH3−Vth <VH2. For example, when the drive transistor 12 is configured as a depression type, the second high power supply potential VH2 may be higher than the third high power supply potential VH3.
Further, the second low power supply potential VL2 is set to a potential that turns on the driving transistor 12. Since the high level of the drive signal Qi is the second high power supply potential VH2, and the low level thereof is the second low power supply potential VL2, the drive transistor 12 is turned off when the drive signal Qi is high, and on when the drive signal Qi is low. It becomes a state. Since the brightness of the OLED element 13 is determined according to the drive current Iel, the OLED element 13 emits light with a brightness according to the second low power supply potential VL2.

  By the way, the drive transistor 12 and the OLED element 13 have temperature characteristics. Therefore, in order to emit light with a constant luminance regardless of temperature, it is necessary to adjust the magnitude of the second low power supply potential VL2. The power supply potential generation circuit 50 of this embodiment adjusts the level of the second low power supply potential VL2 according to the temperature signal T so that the luminance of the OLED element 13 is constant. Thereby, the density of the latent image formed by the optical head 1 can be kept constant, and the printing quality can be improved.

  Further, the set of the first high power supply potential VH1 and the first low power supply potential VL1 supplied to the logic circuit such as the control circuit 40 or the line memory 20 is set to 5V and 0V as shown in FIG. A set of the high power supply potential VH2 and the second low power supply potential VL2 is set to 4V and 1V. Thus, by independently setting the power supply of the logic circuit and the power supply of the output buffer 10, the logic level of the drive signal Qi can be converted without using a special circuit such as a level shifter. Furthermore, since the power supply of the logic circuit operating at high speed and the analog power supply (the set of the second high power supply potential VH2 and the second low power supply potential VL2) for generating the drive signal Qi can be separated, the logic circuit generates the power supply. It becomes less susceptible to noise and improves reliability. In addition, since the potential difference between the second high power supply potential VH2 and the second low power supply potential VL2 is smaller than the potential difference between the first high power supply potential VH1 and the first low power supply potential VL1, power consumption can be reduced.

<2. Modification>
(1) In the above-described embodiment, the second high power supply potential VH2 and the third high power supply potential VH3 match in this embodiment, but they may be different. Further, the first high power supply potential VH1, the second high power supply potential VH2, and the third high power supply potential VH3 may be the same. In this case, since the types of power supply potentials are reduced, the configuration of the power supply potential generation circuit 50 can be simplified.
Further, the second low power supply potential VL2 may be fixed. Also in this case, the set of the first high power supply potential VH1 and the first low power supply potential VL1 and the set of the second high power supply potential VH2 and the second low power supply potential VL2 supplied to the logic circuit can be set independently. Therefore, it is possible to appropriately set the logic level of the drive signal Qi without using a special circuit such as a level shifter. Further, the first high power supply potential VH1, the second high power supply potential VH2, and the third high power supply potential VH3 may be set to 3V, and the first low power supply potential VL1 and the second low power supply potential VL2 may be set to 0V. . Even when the power supply potential is set in this way, it is possible to enjoy an effect that the influence of noise is less likely by separating the wiring of the power supply wiring.

(2) In the above-described embodiment, the sensor 30 is used to detect the temperature, and the second low power supply potential VL2 is adjusted according to the detected temperature, but a luminance adjustment signal that specifies the overall luminance of the pixel region 2 is provided. A luminance adjustment circuit may be provided, and the power supply potential generation circuit may adjust the level of the second low power supply potential VL2 based on the luminance adjustment signal. Thereby, it is possible to easily adjust the darkness of printing. Note that the luminance adjustment signal may be supplied from a host system.

(3) As shown in FIG. 6, a non-volatile memory 60 may be added to adjust the second low power supply potential VL2. The electro-optical device B shown in FIG. 6 is configured in the same manner as the electro-optical device A shown in FIG. 2 except that a nonvolatile memory 60 is provided instead of the sensor 30. The threshold voltage Vth of the driving transistor 12 and the light emission characteristics of the OLED element 13 vary depending on the manufacturing process. Therefore, correction data for correcting the characteristics and designating the level of the second low power supply potential VL2 so that the OLED element 13 emits light with a predetermined luminance is generated at the time of shipment of the product and stored in the nonvolatile memory 60. Keep it. Then, the power supply potential generation circuit 50 reads the correction data during operation, and generates the second low power supply potential VL2 based on this. As a result, the gate potential at which the drive transistor 12 is turned on can be adjusted in accordance with the variation in the threshold voltage Vth for each optical head 1 or the variation in the light emission characteristics of the OLED element 13, thereby greatly increasing the yield. It can be improved. A measurement circuit that measures the threshold voltage Vth of the drive transistor 12 and the light emission luminance of the OLED element 13 may be provided, and the second low power supply potential VL2 may be adjusted based on the measurement result. In this case, a pixel circuit for measurement may be provided separately.

  In the modification shown in FIG. 6, the correction data is stored in the nonvolatile memory 60, but the present invention is not limited to this. For example, the power supply potential generation circuit 50 has a reference voltage generation unit that generates the second low power supply potential VL2, and by cutting a part of the circuit of the reference voltage generation unit by laser cutting according to the correction value, The second low power supply potential VL2 may be controlled. Alternatively, the power supply potential generation circuit 50 may be configured by a DA conversion circuit, and the second low power supply potential VL2 may be controlled by cutting a part of the DA conversion circuit by laser cutting according to the correction value. More specifically, the power supply potential generation circuit 50 has one or a plurality of cut regions in which the second low power supply potential VL2 can be set by cutting, and the electrical characteristics of the drive transistor and the light emission characteristics of the light emitting element are determined. It is preferable that a part or all of one or a plurality of cutting regions is cut based on at least one of them. Here, it is preferable that the wiring of the power supply potential generation circuit 50 is composed of wirings having a plurality of types of line widths, and the cutting region is composed of the wiring with the narrowest line width, from the viewpoint of reliably cutting the cutting region with laser light. . In this case, since the second low power supply potential VL2 is adjusted by changing the power supply potential generation circuit 50 itself according to variations in the light emission characteristics of the OLED elements 13, the nonvolatile memory 60 can be omitted.

(4) Although the magnitude of the second low power supply potential VL2 is adjusted in the above-described embodiment, since the p-channel type is adopted as the drive transistor 13, the on state is defined by the low level (VL2) of the drive signal Qi. This is because that. Conversely, when the drive transistor 13 is configured as an n-channel type, the second high power supply potential VH2 may be adjusted to fix the second low power supply potential VL2. That is, when one of the second high power supply potential VH2 and the second low power supply potential VL2 is supplied to the gate, the drive transistor 13 is turned off. When the other potential is supplied to the gate, the drive transistor is turned on. The power supply potential generation circuit 50 may adjust and output the other potential.
(5) In the above-described embodiment, the transistor included in the optical head 1 may be configured by a TFT (Thin Film Transistor) or a MOSFET.

<3. Image forming apparatus>
As shown in FIG. 1, the optical head 1 can be used as a line-type optical head for writing a latent image on an image carrier in an image forming apparatus using an electrophotographic system. Examples of the image forming apparatus include a printer, a printing part of a copying machine, and a printing part of a facsimile.
FIG. 7 is a longitudinal sectional view showing an example of an image forming apparatus using the optical head 1. This image forming apparatus is a tandem type full-color image forming apparatus using a belt intermediate transfer body system.

  In this image forming apparatus, four organic EL array exposure heads 1K, 1C, 1M, and 1Y having the same configuration have four photosensitive drums (image carriers) 110K, 110C, 110M, and 110Y having the same configuration. The exposure positions are respectively arranged. The organic EL array exposure heads 1K, 1C, 1M, and 1Y are the optical heads 1 according to any one of the embodiments exemplified above.

  As shown in FIG. 7, this image forming apparatus is provided with a driving roller 121 and a driven roller 122. An endless intermediate transfer belt 120 is wound around these rollers 121 and 122, and an arrow indicates. As shown, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

  Around the intermediate transfer belt 120, four photosensitive drums 110K, 110C, 110M, and 110Y each having a photosensitive layer on the outer peripheral surface are arranged at a predetermined interval. The subscripts K, C, M, and Y mean that they are used to form black, cyan, magenta, and yellow visible images, respectively. The same applies to other members. The photosensitive drums 110K, 110C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

  Around each photosensitive drum 110 (K, C, M, Y), a corona charger 111 (K, C, M, Y), an organic EL array exposure head 1 (K, C, M, Y), and Developers 114 (K, C, M, Y) are disposed. The corona charger 111 (K, C, M, Y) uniformly charges the outer peripheral surface of the corresponding photosensitive drum 110 (K, C, M, Y). The organic EL array exposure head 1 (K, C, M, Y) writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. In each organic EL array exposure head 1 (K, C, M, Y), the arrangement direction of the plurality of OLED elements P is along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). Installed. The electrostatic latent image is written by irradiating the photosensitive drum with light by the plurality of light emitting elements 30 described above. The developing device 114 (K, C, M, Y) forms a visible image, that is, a visible image on the photosensitive drum by attaching toner as a developer to the electrostatic latent image.

  The black, cyan, magenta, and yellow developed images formed by the four-color single-color image forming station are sequentially transferred onto the intermediate transfer belt 120 to be superimposed on the intermediate transfer belt 120. As a result, a full-color image is obtained. Four primary transfer corotrons (transfer devices) 112 (K, C, M, Y) are arranged inside the intermediate transfer belt 120. The primary transfer corotron 112 (K, C, M, Y) is disposed in the vicinity of the photosensitive drum 110 (K, C, M, Y), and the photosensitive drum 110 (K, C, M, Y). The electrostatic image is electrostatically attracted from the toner image to transfer the visible image to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

  A sheet 102 as an object on which an image is to be finally formed is fed one by one from the sheet feeding cassette 101 by the pickup roller 103, and between the intermediate transfer belt 120 and the secondary transfer roller 126 in contact with the driving roller 121. Sent to the nip. The full-color visible image on the intermediate transfer belt 120 is secondarily transferred to one side of the sheet 102 by the secondary transfer roller 126 and fixed on the sheet 102 through the fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed in the upper part of the apparatus by a paper discharge roller pair 128.

Next, another embodiment of the image forming apparatus according to the present invention will be described.
FIG. 8 is a longitudinal sectional view of another image forming apparatus using the optical head 1 or 2. This image forming apparatus is a rotary developing type full-color image forming apparatus using a belt intermediate transfer body system. In the image forming apparatus shown in FIG. 22, a corona charger 168, a rotary developing unit 161, an organic EL array exposure head 167, and an intermediate transfer belt 169 are provided around the photosensitive drum 165.

  The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 165. The organic EL array exposure head 167 writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum 165. The organic EL array exposure head 167 is the optical head 1 of each aspect exemplified above, and is installed such that the arrangement direction of the plurality of light emitting elements 30 is along the bus line (main scanning direction) of the photosensitive drum 165. The electrostatic latent image is written by irradiating the photosensitive drum 165 with light from these light emitting elements 30.

  The developing unit 161 is a drum in which four developing units 163Y, 163C, 163M, and 163K are arranged at an angular interval of 90 °, and can rotate counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toners to the photosensitive drum 165, respectively, and attach the toner as a developer to the electrostatic latent image, thereby the photosensitive drum 165. A visible image, that is, a visible image is formed.

  The endless intermediate transfer belt 169 is wound around a driving roller 170a, a driven roller 170b, a primary transfer roller 166, and a tension roller, and is rotated around these rollers in a direction indicated by an arrow. The primary transfer roller 166 transfers the visible image to the intermediate transfer belt 169 that passes between the photosensitive drum and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 165.

  Specifically, in the first rotation of the photosensitive drum 165, an electrostatic latent image for a yellow (Y) image is written by the exposure head 167, and a developed image of the same color is formed by the developing unit 163Y. The image is transferred to the transfer belt 169. Further, in the next rotation, an electrostatic latent image for a cyan (C) image is written by the exposure head 167, and a developed image of the same color is formed by the developing device 163C. The intermediate transfer is performed so as to overlap the yellow developed image. Transferred to the belt 169. Then, during the four rotations of the photosensitive drum 165, yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169. As a result, a full-color visible image is formed on the transfer belt 169. It is formed. When images are finally formed on both sides of a sheet as an object on which an image is to be formed, the same color images of the front and back surfaces are transferred to the intermediate transfer belt 169, and then the front and back surfaces are transferred to the intermediate transfer belt 169. A full-color visible image is obtained on the intermediate transfer belt 169 by transferring the visible image of the next color.

  The image forming apparatus is provided with a sheet conveyance path 174 through which a sheet passes. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image onto one side of the sheet by electrostatically attracting a full-color developed image from the intermediate transfer belt 169 collectively. The secondary transfer roller 171 can be moved toward and away from the intermediate transfer belt 169 by a clutch (not shown). The secondary transfer roller 171 is brought into contact with the intermediate transfer belt 169 when a full-color visible image is transferred onto the sheet, and is separated from the secondary transfer roller 171 while the visible image is superimposed on the intermediate transfer belt 169.

  The sheet on which the image has been transferred as described above is conveyed to the fixing device 172 and is passed between the heating roller 172a and the pressure roller 172b of the fixing device 172, whereby the visible image on the sheet is fixed. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. In the case of double-sided printing, after most of the sheet passes through the paper discharge roller pair 176, the paper discharge roller pair 176 is rotated in the reverse direction and introduced into the double-sided printing conveyance path 175 as indicated by an arrow G. The Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

Since the image forming apparatus illustrated in FIGS. 7 and 8 uses the OLED element 13 as an exposure unit, the apparatus can be made smaller than when a laser scanning optical system is used. It should be noted that the optical head of the present invention can also be used in electrophotographic image forming apparatuses other than those exemplified above. For example, the optical head according to the present invention can be applied to an image forming apparatus that directly transfers a visible image from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image forming apparatus that forms a monochrome image. Is possible.
In addition, the electro-optical device according to the invention is employed in various electronic apparatuses, for example. Examples of such electronic devices include facsimile machines, copiers, multifunction machines, and printers.
Further, the electro-optical device may be a display device that displays not only the line-shaped optical head 1 but also the pixel circuits P arranged in a matrix and displays an image. In this case, the pixel circuit may be provided with a memory function and an output buffer function, and the respective power supplies may be separated.

1 is a perspective view illustrating a partial configuration of an image forming apparatus using an optical head according to the present invention. 1 is a block diagram illustrating a configuration of an electro-optical device using an optical head. It is a wave form diagram which shows the waveform of a gradation and a PWM timing signal. FIG. 3 is a circuit diagram showing a configuration of an i-th pixel circuit Pi and output buffer 10 and line memory 20 corresponding thereto. It is explanatory drawing which shows the relationship between a 1st high power supply potential and a 1st low power supply potential, a 2nd high power supply potential and a 2nd low power supply potential, and a 3rd high power supply potential and a 3rd low power supply potential. FIG. 10 is a block diagram illustrating a configuration of an electro-optical device B according to a modification. 1 is a longitudinal sectional view showing a configuration of an image forming apparatus using an optical head according to the present invention. It is a longitudinal cross-sectional view which shows the structure of the other image forming apparatus using the optical head which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical head, 2 ... Pixel area | region, 12 ... Drive transistor, 13 ... OLED element, 10 ... Output buffer, 20 ... Line memory, 50 ... Power supply potential generation circuit, 60 ... Nonvolatile memory , S... PWM timing signal, Di... Data signal, Qi... Drive signal, P1 to Pn... Pixel circuit, VH1. 2 high power supply potential, VL2... Second low power supply potential, VH3... Third high power supply potential, VL3.

Claims (10)

A logic circuit that operates at a first high power supply potential and a first low power supply potential, and a logic circuit that operates at a second high power supply potential and a second low power supply potential, and the binary level is based on an output signal of the logic circuit. Drive means having an output circuit for outputting a drive signal to be 2 high power supply potential and the second low power supply potential;
An electro-optical element that emits light with a luminance corresponding to the driving current; and a driving transistor that is controlled to be turned on and off by the driving signal supplied to the gate and supplies the driving current to the electro-optical element in the on-state. A pixel circuit provided with
The first high power supply potential and the first low power supply potential, and the second high power supply potential and the second low power supply potential are generated, and one of the second high power supply potential and the second low power supply potential is generated. Is a potential that turns off the drive transistor when supplied to the gate, and the other of the second high power supply potential and the second low power supply potential is a potential that turns on the drive transistor when supplied to the gate. A power supply potential generating means for adjusting and outputting the other potential;
An electro-optical device.   The power supply potential generating means generates the first high power supply potential, the first low power supply potential, the second high power supply potential, and the second low power supply potential so as to be different from each other. 2. The electro-optical device according to 1.   The power supply potential generating means is configured so that a potential difference between the second high power supply potential and the second low power supply potential is smaller than a potential difference between the first high power supply potential and the first low power supply potential. The electro-optical device according to claim 1, wherein a high power supply potential and the first low power supply potential, and the second high power supply potential and the second low power supply potential are generated.   The power supply potential generating means generates the second high power supply potential and the third high power supply potential as the same potential, and adjusts and outputs the second low power supply potential as the other potential. The electro-optical device according to any one of claims 1 to 3. Detecting means for detecting a state relating to light emission of the electro-optic element;
5. The electro-optical device according to claim 1, wherein the power supply potential generation unit adjusts the other potential based on a detection result of the detection unit.   The electro-optical device according to claim 5, wherein the detection unit includes a temperature sensor that detects an environmental temperature. Storage means for preliminarily storing designated data generated based on at least one of the electrical characteristics of the drive transistor and the light emission characteristics of the electro-optic element;
The power supply potential generating means adjusts the other potential based on the designated data read from the storage means;
The electro-optical device according to claim 1, wherein the electro-optical device is any one of claims 1 to 4. A pixel region in which a plurality of the pixel circuits are disposed;
A luminance adjustment means for generating a luminance adjustment signal for designating the overall luminance of the pixel region,
The power supply potential generating means adjusts the other potential based on the luminance adjustment signal;
The electro-optical device according to claim 1, wherein the electro-optical device is any one of claims 1 to 4.   The electro-optical device according to claim 1, wherein the logic circuit outputs a signal having a pulse width corresponding to a gradation.   An electronic apparatus comprising the electro-optical device according to claim 1.

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