JP2010173163A - Light emitting device, method for driving the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a size of a circuit in a light emitting device having a plurality of light emitting elements. <P>SOLUTION: This light emitting device 10 includes the light emitting elements P1 to P4, unit circuits U1 to U4 that operate in a unit time period including a common light emitting time period as a cycle, a drive IC 91 for supplying a setting signal to each of the unit circuits, and a control IC 32 for supplying a writing time period signal and a light emitting control signal to each of the unit circuits. In accordance with the setting signal and the writing time period signal, the setting value is written into each of the unit circuits in a predetermined unit time period, but not written thereinto in a unit time period other than the above. In accordance with the light emitting control signal, supplying of electric energy corresponding to the setting value to the light emitting elements is prohibited in a time period other than the light emitting time period. However, the supplying is allowed in the light emitting time period with respect to each of the unit circuits corresponding to light emitting elements to be energized in the light emitting time period, but is prohibited with respect to each of the unit circuits corresponding to light emitting elements to be not energized in that light emitting time period. Accordingly, with the use of the light emitting device 10, it is possible to reduce the number of unit circuits into which the setting is written in an identical unit time period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting device, a driving method thereof, and an electronic apparatus.

  As a light-emitting device including a plurality of light-emitting elements, a display device for displaying an image or an area-gradation image forming device for forming an image (for example, a printer, a facsimile machine or a copier) for a line head There is. As one type of light-emitting device for display devices, there is an active matrix drive light-emitting device including a unit circuit for driving each light-emitting element with electric energy (current or voltage) corresponding to a set value (see Patent Document 1). .

  The unit circuit includes a light emitting element that emits light at a luminance corresponding to the supplied electric energy, a setting holding unit that holds a written setting value, and light emission of electric energy that corresponds to the setting value held in the setting holding unit. A light emission control unit (switch) for permitting / prohibiting supply to the element. In each unit circuit, a unit period of a certain length is repeatedly and continuously visited. The unit period includes a previous writing period and a subsequent light emission period. In the writing period, the set value is written in the setting holding unit, and in the light emitting period, the electric energy corresponding to the setting value held in the setting holding unit is written. Supply to the light emitting element is permitted. Note that the light emission period is common to a plurality of unit circuits.

  Even in a light-emitting device for line head use, a unit circuit similar to the above is provided for each light-emitting element, and in each unit circuit, a unit period of a certain length is repeatedly and continuously visited (see Patent Document 2). Therefore, it is possible to change the set value to be written and correct the variation in the light emission power (light emission amount) due to the deterioration of the unit circuit over time. In the light emitting device for line head use, the light emission period is common to all unit circuits.

JP 2008-089726 A JP 2007-276332 A

  By the way, in order to write a set value to the unit circuit, it is necessary to supply analog data obtained by converting digital data representing the set value to the unit circuit. A DAC (digital / analog converter) is used for this conversion. Since the circuit scale decreases as the number of DACs decreases, the light emitting device is generally configured such that one DAC is responsible for a plurality of unit circuits by time division multiplexing. However, in the conventional light-emitting device, when the number of unit circuits that one DAC is responsible for increases, the number of unit circuits to which the one DAC should write setting values by time-division multiplexing before the start of the light-emitting period in the unit period increases. This is because the manufacturing cost increases due to the increase in processing speed required for the DAC, the printing speed or the display speed decreases, the light emission power decreases due to the reduction of the ratio of the light emission period to the unit period (light emission duty), or the lifetime of the light emitting element. Lead to shortening. In addition, there is a limit to speeding up the DAC.

  The present invention has been made in view of such circumstances, and provides a light-emitting device, a driving method thereof, and an electronic apparatus that can reduce the circuit scale without causing the above-described various disadvantages. It is a problem to be solved.

In order to solve this problem, the present invention is provided with a plurality of light emitting elements that emit light at a luminance corresponding to supplied electric energy, and corresponding to the plurality of light emitting elements, and each writes a set value. A setting holding unit that holds the set value written by the write signal for the light source, and permits the supply of electric energy according to the set value to the corresponding light emitting element based on the light emission control signal that controls the light emission. A plurality of unit circuits that operate with a unit period including a common light emission period as a cycle, and a signal supply that supplies the write signal and the light emission control signal to the plurality of unit circuits The write signal for each of the plurality of unit circuits is written to the setting holding unit in a certain unit period, and is written in the other unit period. The light emission control signal is a signal that does not write a set value, and the light emission control signal supplies the light energy to the light emitting element according to the set value, and the light emission control unit of the plurality of unit circuits during the period other than the light emission period. In the light emission period, the light emission control unit of the unit circuit corresponding to the light emitting element that should emit light during the light emission period is allowed during the light emission period, while light emission that should not be emitted during the light emission period There is provided a light emitting device characterized by being a signal prohibited by the light emission control unit of a unit circuit corresponding to an element.
The light emission period is a period during which light emission of the light emitting element can be permitted, and comes at a constant cycle. The light emitting element does not emit light during a period other than the light emitting period, and the light emitting element does not always emit light even during the light emitting period. Further, “a certain unit period” and “another unit period” are relative names, and may be different for each unit circuit. For example, a “certain unit period” in a certain unit circuit does not necessarily match a “certain unit period” in another unit circuit.
In the above light emitting device, each unit circuit does not perform the writing process in “another unit period”, so that the number of unit circuits to which the set value is written in one unit period is reduced. Therefore, according to the above light emitting device, when one DAC handles a plurality of unit circuits, the number of unit circuits handled by one DAC is increased, that is, the circuit scale is reduced without causing the above-described various problems. be able to.
Note that the above light-emitting device is premised on that it can cover a plurality of light-emitting periods with one set value. As such a light emitting device, there is a light emitting device for a line head of an area gradation image forming apparatus. In this light emitting device, since the gradation is expressed by an area, basically, the electric energy supplied to each light emitting element can be fixed. Of course, there may be a form in which the set value is changed to correct the variation in the light emission power due to the deterioration of the unit circuit over time, but the print quality does not deteriorate so much even if the electric energy supplied to each light emitting element is fixed over a plurality of lines. Even in such a form, a plurality of light emission periods can be covered with a single set value. Some active matrix drive display devices can cover a plurality of light emission periods with a single set value, such as a display device that only needs to display a still image.

  In the above light emitting device, a unit period for writing the setting value in the setting holding unit may be different among the plurality of unit circuits. In this light emitting device, the number of unit circuits that must be written before the start of the light emitting period in each unit period is 1 or less. In other words, when one DAC is responsible for a plurality of unit circuits, the number of unit circuits to which the DAC should write the set value in one unit period is 1 or less. Therefore, according to this light emitting device, a further effect can be obtained.

  Furthermore, in this light emitting device, the write signal may be a signal that does not write the set value in any of the setting holding units of the plurality of unit circuits in a certain unit period. According to this light emitting device, there are unit periods in which no writing process is performed in any of the unit circuits. Therefore, these unit periods and the unit periods in which the writing process is performed in any of the unit circuits are appropriately arranged. Thus, a further effect can be obtained. For example, when one DAC is responsible for a plurality of unit circuits, a unit period in which a set value is written in any unit circuit and a unit period in which a set value is not written in any unit circuit are alternately visited. By doing so, the number of unit circuits handled by one DAC can be doubled, or the processing speed required for the DAC can be halved.

  Further, in each of the light emitting devices, the light emission control signal is transmitted to the light emission control units of all of the plurality of unit circuits until the writing of the setting values is completed for all of the plurality of unit circuits. It may be a signal for prohibiting the supply of electrical energy to the light emitting element according to the set value. According to this light emitting device, it is possible to avoid a situation where the light emitting element emits light with an inappropriate luminance.

  In each of the above light emitting devices, each of the setting holding units of the plurality of unit circuits holds one setting value for a plurality of unit periods, and generates a current corresponding to the holding setting value. The light emission control signal is a binary signal, and each of the light emission control units of the plurality of unit circuits has a current flow path to a corresponding light emitting element based on the value of the light emission control signal. You may make it control opening and closing. In this light emitting device, light emission / non-light emission control is performed by opening and closing a current path based on a binary light emission control signal.

  Moreover, this invention provides an electronic device provided with each said light-emitting device. The electronic apparatus includes a display device including each of the light emitting devices described above, an image carrier, a charger for charging the image carrier, and a latent image obtained by irradiating light on a charged surface of the image carrier. Each of the above-described light emitting devices and a developing unit that forms a visible image by attaching toner to the latent image, and forms the image by transferring the visible image to another object. An image forming apparatus can be exemplified.

  Further, the present invention is provided with a plurality of light emitting elements that emit light at a luminance corresponding to the supplied electric energy, and corresponding to each of the plurality of light emitting elements, and each is provided by a write signal for writing a set value. A setting holding unit for holding the written set value; and a light emission control unit for permitting / prohibiting supply of electrical energy corresponding to the set value to a corresponding light emitting element based on a light emission control signal for controlling light emission; And a plurality of unit circuits that operate with a unit period including a common light emission period as a cycle, wherein each of the plurality of unit circuits is provided in the setting holding unit. The set value is written in a unit period, and the write signal that does not write the set value in another unit period is supplied to the plurality of unit circuits, and an electric power corresponding to the set value is supplied. The supply of energy to the light emitting element is prohibited by the light emission control unit of the plurality of unit circuits during a period other than the light emission period, and light emission is performed during the light emission period of the plurality of unit circuits during the light emission period. The light emission control unit of the unit circuit corresponding to the light emitting element to be allowed is allowed, while the light emission control unit of the unit circuit corresponding to the light emitting element that should not emit light during the light emission period has an electric energy corresponding to the set value. There is provided a driving method of a light emitting device, characterized in that the light emission control signal for prohibiting supply to a light emitting element is supplied to the plurality of unit circuits.

It is a perspective view which shows the external appearance of the light-emitting device 10 which concerns on embodiment of this invention. 2 is a cross-sectional view of the light emitting device 10. FIG. 1 is a diagram illustrating a mounting configuration of a light emitting device 10. FIG. FIG. 5 is a diagram showing another mounting configuration of the light emitting device 10. 2 is a circuit diagram showing an electrical configuration of a unit circuit Ui of the light emitting device 10. FIG. 2 is a diagram showing an electrical configuration of the light emitting device 10. FIG. 3 is a timing chart for explaining the operation of the light emitting device 10. It is a figure which shows the electrical constitution of the light-emitting device which concerns on the comparative example contrasted with embodiment of this invention. It is a timing chart for demonstrating operation | movement of the light-emitting device which concerns on a comparative example. It is a timing chart for demonstrating the modification of embodiment of this invention. It is a timing chart for demonstrating another modification of embodiment of this invention. 6 is a circuit diagram illustrating another configuration of a unit circuit Ui of the light emitting device 10. FIG. 6 is a circuit diagram showing still another configuration of a unit circuit Ui of the light emitting device 10. FIG. 1 is a longitudinal sectional view of an image forming apparatus to which an embodiment of the present invention is applied. It is a longitudinal cross-sectional view of another image forming apparatus to which the embodiment of the present invention is applied.

  Embodiments of the present invention will be described with reference to the drawings. However, in each drawing, the ratio of the dimension of each part is appropriately different from the actual one. Further, the present invention is not limited to the embodiments described below, and can be obtained by applying various modifications obtained by modifying the present embodiment, or the present embodiment or modifications thereof. Forms can also be included in the technical scope.

<Light emitting device>
FIG. 1 is a perspective view showing an appearance of a light emitting device 10 according to an embodiment of the present invention. As shown in the cross-sectional view of FIG. 2, the light-emitting device 10 is used as a line head of an electrophotographic image forming apparatus. The light-emitting device 10 emits light by being fixed to the frame 1 having a concave cross section and the outside of the frame 1. A light emitting panel 2, a control device 3 that is disposed inside the frame 1 and controls the light emitting panel 2, a flexible substrate 4 that connects the light emitting panel 2 and the control device 3, a control device 3 and a host device (not shown) A cable 5 to be connected, a lens array 6 such as a SELFOC lens array (SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.), a spacer glass 7 interposed between the light emitting panel 2 and the lens array 6, And a cover 8 for blocking outside light.

  The light-emitting panel 2 prevents the glass substrate 21 including unit circuits and wirings formed of a light-emitting element array, TFTs, and the like, and the light-emitting element P included in the light-emitting element array from being deteriorated by moisture, oxygen, or the like. And a sealing substrate 22 made of glass or the like. Light emitted from the light emitting element array is transmitted through the substrate 21, the spacer glass 7, and the lens array 6, is emitted from the light emitting surface of the lens array 6 (the surface exposed from the cover 8), and is irradiated onto the image carrier. The light emitting panel 2 is a bottom emission type in which light emission of the light emitting element array proceeds through the substrate 21, but a top emission type light emitting panel may be adopted as the light emitting panel 2, and the substrate 21 may be other than glass. You may employ | adopt the board | substrate formed with the material. The control device 3 includes a rigid substrate 31 and a control IC (integrated circuit) 32 that is provided on the rigid substrate 31 and controls light emission of the light emitting element array.

  FIG. 3 is a diagram illustrating a mounting configuration of the light emitting device 10. As shown in this figure, the light emitting element array includes a plurality of light emitting elements P (P1 to P16) and a plurality of unit circuits U (U1 to U16) provided corresponding to these light emitting elements, respectively. The light emitting element P is an element that emits light with a luminance corresponding to the supplied electric energy, and is specifically an organic EL (Electro Luminescent) element. The unit circuit U is a circuit for driving the light emitting element P, holds the written set value, and supplies electric energy corresponding to the held set value to the corresponding light emitting element P. In the present embodiment, the number of light emitting elements P and unit circuits U is set to 16 for ease of explanation, but an actual line head includes far more light emitting elements P and unit circuits U. Prepare. For example, a line head of an image forming apparatus capable of printing at A4 size and 600 dpi includes 600 dpi / 2.54 cm × 21 cm = about 5000 light emitting elements P and unit circuits U.

  Although not shown in FIG. 2, a plurality of driving ICs 9 (91 to 94) that drive the light emitting elements P <b> 1 to P <b> 16 are mounted on the flexible substrate 4. The drive IC 91 has unit circuits U1 to U4, the drive IC 92 has unit circuits U5 to U8, the drive IC 93 has unit circuits U9 to U12, the drive IC 94 has unit circuits U13 to U16, and the kth drive IC 9k has a set value. Is generated as a potential and supplied to all unit circuits U. The drive IC 9 may be formed on the substrate 21 by COG (Chip On Glass) as shown in FIG. 4 instead of being mounted on the flexible substrate 4.

  The clock signal CLK and the print signal d are supplied to the control IC 32 of FIG. The print signal is a digital signal in which binary print data indicating light emission / non-light emission is linked. The control IC 32 supplies the clock signal CLK to the drive ICs 91 to 94. In addition, the control IC 32 permits (permits / inhibits) the supply of the write period signal G indicating the period (write period) in which the set value is written to the unit circuits U1 to U16 and the supply of electric energy to the corresponding light emitting element P. 2 (active level / first inactive level) light emission control signal L is supplied. In the present embodiment, this supply is performed directly, but it may be performed via the drive IC 9.

<Unit circuit>
FIG. 5 is a circuit diagram showing an electrical configuration of the i-th unit circuit Ui. As shown in this figure, the light emitting element Pi driven by the unit circuit Ui is interposed between a power supply line supplied with a fixed power supply potential Vel and a ground line supplied with a ground potential. A p-channel type driving transistor Ta is interposed in a path from the power supply line to the light emitting element Pi, and a transistor Tb is interposed between the driving transistor Ta and the light emitting element Pi.

  The drive transistor Ta generates a current (electric energy) corresponding to the voltage Vgs between the source and the gate, the source is the power supply line and the first electrode R1 of the capacitor C1, and the gate is the capacitor C1. The drain of the second electrode R2 is connected to the transistor Tb. The capacitive element C1 is for holding the written voltage (set value), and this voltage becomes the voltage Vgs.

  The setting signal Vk is supplied to the second electrode R2 of the capacitive element C1 via the transistor Tc functioning as a switching element, and the write period signal Gm is supplied to the gate of the transistor Tc. Therefore, only when the potential of the write period signal Gm is in the active level, the transistor Tc is turned on, and the setting signal Vk is supplied to the second electrode R2 of the capacitive element C1, that is, the voltage Vgs is written. The write period signal Gm is a write period signal G supplied to the m-th unit circuit U in each of the four groups of unit circuits U that the drive ICs 91 to 94 handle, and the upper limit of m is the upper limit of each drive IC 9. Corresponds to the number (4) of unit circuits U.

  As is clear from the above description, the setting signal Vk and the writing period signal Gm are writing signals for writing setting values. Therefore, the control IC 32 and the drive ICs 91 to 94 function as a signal supply circuit that supplies the write signal and the light emission control signal L to the unit circuits U1 to U16. In each unit circuit U, the drive transistor Ta, the capacitive element C1, and the transistor Tc functions as a setting holding unit S that holds the setting value written by the write signal.

  The transistor Tb functions as a switching element, and a light emission control signal Li is supplied to its gate. Therefore, only when the potential of the light emission control signal Li is in an active level, the transistor Tb is turned on, and supply of a current (current corresponding to the voltage Vgs) from the drive transistor Ta to the light emitting element Pi is permitted. That is, the transistor Tb functions as a light emission control unit E that permits / prohibits the supply of electric energy corresponding to the set value held in the setting holding unit S to the light emitting element Pi based on the light emission control signal Li. .

  The unit circuit Ui operates with a unit period including one light emission period as a cycle. The light emission period is a period during which light emission of the light emitting element P can be permitted, and is indicated by a light emission period signal PLS described later. In the following description, the length of the light emission period is 1H. None of the light emitting elements P emits light during the period other than the light emitting period (electrical energy supply to any of the light emitting elements P is permitted), and all the light emitting elements P even during the light emitting period. May not emit light (supply of electric energy to all the light emitting elements P may be prohibited).

<Signal supply circuit>
FIG. 6 is a diagram showing an electrical configuration of the light emitting device 10, and FIG. 7 is a timing chart for explaining the operation of the light emitting device 10. As shown in FIG. 6, the drive IC 91 has a memory 9A and a DAC 9B. The memory 9A stores setting data (q1 to q4) for the drive circuits U1 to U4. The driving IC 91 cyclically reads setting data for the driving circuits U1 to U4 one by one for each unit period from the memory 9A, generates a digital setting signal Q1, and converts the analog setting signal Q1 by the DAC 9B. Is supplied to the setting holding unit S of all the unit circuits U1 to U4. As shown in FIG. 7, the period of the setting signal Q1 and the setting signal V1 is 4H.

  Further, the drive IC 91 starts the unit period of the first first line after the end of the unit period of the last n-th line in order to correct the variation in the light emission power (light emission amount) due to the deterioration of the unit circuit over time. In the meantime, the degree of deterioration with time of the light emitting elements P1 to P4 is measured, and the setting data (q1 to q4) in the memory 9A is updated based on the result of this measurement. Accordingly, the settings for the unit circuits U1 to U4 are fixed over a period of at least n lines (1H × 4 × n).

  In FIG. 7, only writing related to the drive IC 91 is shown regarding the writing of the set value, but the same operation as described above is also performed in the drive ICs 92 to 94. The present embodiment may be modified so that the above correction is not performed. In this case, the set value for each unit circuit U can always be fixed. Further, the present embodiment may be modified so that a period in which the set value for each unit circuit U is fixed is a period for a plurality of lines smaller than n lines.

  On the other hand, the control IC 32 sets the write period signal G1 as unit circuits U1, U5, U9 and U13, the write period signal G2 as unit circuits U2, U6, U10 and U14, and the write period signal G3 as unit circuits U3, U7, U11 and U15 and the writing period signal G4 are supplied to the setting holding unit S of the unit circuits U4, U8, U12 and U16. The writing period signal G1 is a 4H cycle pulse indicating a writing period common to the unit circuits U1, U5, U9, and U13, and the period in which the potential is at the active level is the writing period. The writing period precedes the light emitting period included in the same unit period as that period (for example, the first unit period in FIG. 7). The write period signal G2 is a signal obtained by delaying the write period signal G1 by 1H, the write period signal G3 is a signal obtained by delaying the write period signal G2 by 1H, and the write period signal G4 is provided by a write period signal. This is a signal obtained by delaying G3 by 1H.

  Therefore, the setting values of the first lines for the unit circuits U1, U5, U9, and U13 are written to the setting holding units S in the first unit period, and for the unit circuits U2, U6, U10, and U14 in the next unit period. The first line setting values are written in the respective setting holding units S, and in the next unit period, the first line setting values for the unit circuits U3, U7, U11 and U15 are written in the respective setting holding units S. In the next unit period, the setting values of the first lines for the unit circuits U4, U8, U12 and U16 are written in the respective setting holding units S, and for the unit circuits U1, U5, U9 and U13 in the next unit period. The setting value of the second line is written in each setting holding unit S, and so on, and so on. The setting values are written in parallel between the driving ICs 9 and in each driving IC 9 by time division multiplexing at intervals of 1H.

  Further, as shown in FIG. 6, the control IC 32 includes a 16-stage shift register 3A that operates based on a clock signal CLK that is a pulse having a constant period, and a latch circuit 3B that can hold 16 pieces of print data. And, based on the clock signal CLK, the shift register 3A performs a shift operation and repeatedly writes the next print data in the first stage. The cycle of the clock signal CLK is 1/4 of 1H. The latch circuit 3B repeatedly performs a latch operation based on the latch signal LAT.

  In each latch operation, 16 pieces of print data held in the shift register 3A are held in the latch circuit 3B. The latch signal LAT is generated based on the clock signal CLK so that the latch operation is performed every time print data (d1 to d16) for one line is stored in the shift register 3A. That is, the latch circuit 3B always holds one line of print data, and these print data are updated all at once in the 4H cycle.

  Further, the control IC 32 generates a light emission period signal PLS that is a 1H cycle pulse based on the clock signal CLK, and based on the light emission period signal PLS and the print data (d1 to d16) held in the latch circuit 3B. The light emission control signals L1 to L16 are generated, and each light emission control signal L is supplied to the light emission control unit E of the corresponding unit circuit U. The light emission period signal PLS is a 1H cycle pulse, and the period from when the potential transitions from the inactive level to the active level until the transition to the inactive level is the light emission period.

  The potential of the light emission control signal Li becomes an active level during the light emission period when the print data (di) held in the latch circuit 3B indicates “light emission”, and becomes an inactive level during other periods. Accordingly, the light emitting element Pi does not emit light in the first 4H, and in the subsequent period, the unit circuit Ui is in the light emitting period when the print data for the unit circuit Ui held in the latch circuit 3B indicates “light emission”. While light is emitted with electrical energy corresponding to the set value held in the setting holding unit S, light is not emitted in other periods.

  However, the latch circuit 3B holds 16 pieces of data indicating “non-light emission” until the print data (d1 to d16) of the first line is stored in the shift register 3A. Accordingly, the light emission control signals L1 to L16 are signals for prohibiting the light emission control unit E from supplying electric energy until the setting values have been written to all the unit circuits U1 to U16. Therefore, none of the light emitting elements P1 to P16 emits light until the writing of the set value is completed in all the unit circuits U1 to U16.

<Comparative example>
FIG. 8 is a diagram illustrating an electrical configuration of a light emitting device according to a comparative example compared with the present embodiment, and FIG. 9 is a timing chart for explaining an operation of the light emitting device. As shown in FIG. 8, in the light emitting device according to the comparative example, the light emission period signal PLS is supplied to the light emission control unit E of each unit circuit U. Therefore, the supply of electrical energy to each light emitting element P is always permitted during the light emission period. That is, in this light emitting device, the light emission control unit E does not perform light emission control based on the print data.

  In this light emitting device, the setting holding unit S performs light emission control based on print data. For this reason, the setting data (w1 to w4) based on the print data (d1 to d4) is stored in the memory of the driving IC that is responsible for the unit circuits U1 to U4, and the setting signal W1 that is a combination of these setting data is output by the DAC. The set value is written in the setting holding unit S of the unit circuits U1 to U4 by the setting signal Y1 obtained by the conversion. At this time, the potential of the setting signal Y1 becomes a level corresponding to the print data as shown in FIG. 9, and is switched at a time interval far shorter than 1H. That is, in each unit period, the setting values related to the unit circuits U1 to U4 are written in time division multiplexing prior to the light emission period. The above operation is the same for other drive ICs.

<Contrast>
In the light emitting device according to the comparative example, when attention is paid to each DAC, it is necessary to write setting values to four unit circuits U every 1H, whereas when attention is paid to each unit circuit U, it is necessary to write setting values every 1H. In the light emitting device 10, it is only necessary to write a set value in one unit circuit U every 1H when paying attention to each DAC 9 </ b> B, and it is sufficient to write a set value every 4 H when paying attention to each unit circuit U. In addition, in the light emitting device 10, the unit period in which the set value is written is different between the unit circuits U that the same DAC 9B handles. Therefore, the processing capability of the DAC 9B of the light emitting device 10 has a margin four times that of the DAC 9B of the light emitting device according to the comparative example. That is, according to the light emitting device 10, the number of units is four times that of the light emitting device according to the comparative example without increasing the processing speed required for the DAC, reducing the printing speed, or reducing the light emission duty. The circuit U can be handled by one DAC 9B, that is, the circuit scale can be reduced.

  In the light emitting device 10, the light emission control signal Li receives the light emitting element P corresponding to the light emission control unit E of the unit circuit U until the writing of the set value is completed for all the unit circuits U that the drive IC 9 i is responsible for. It becomes a signal that prohibits the supply of electrical energy to. Therefore, according to the light emitting device 10, it is possible to avoid a situation in which the light emitting element P emits light with inappropriate luminance and timing.

<Modification>
In addition, the light emitting device 10 is modified, and as shown in FIG. 10, the light emission control signals L1 to L16 are supplied with electric energy to the light emitting element P immediately after the setting values are written to the unit circuits U1 to U16. The signal may be permitted. The first unit period during which the supply of electrical energy to the light emitting element P can be permitted is the fifth unit period in FIG. 7, but is the fourth unit period in FIG.

  Alternatively, the light emitting device 10 or the above-described modification may be modified so that the write control signal G is a signal that does not write a set value in any of the setting holding units S of the unit circuits U1 to U20 in a certain unit period. According to this modification, since there is a unit period in which no set value is written in any unit circuit U, a unit period in which the set value is written in any one of the unit circuits U which one DAC 9B is responsible for is appropriately arranged. By doing so, the above-described effect can be further increased. A timing chart of an example of a light-emitting device obtained by applying this modification to the light-emitting device 10 is shown in FIG. In the example of this figure, the unit period in which the set value is written in any one of the unit circuits U handled by one DAC 9B and the unit period in which the set value is not written in any of the unit circuits U handled by this DAC 9B are alternated. Therefore, it is possible to double the number of unit circuits that one DAC 9B is responsible for and to halve the processing speed required for the DAC 9B.

  In addition, the light emitting device 10 and each of the modifications described above may be modified so that the unit circuit having the configuration shown in FIG. Each of these unit circuits has an n-channel type drive transistor Td instead of the p-channel type drive transistor Ta, and the light emission control unit E including the transistor Tb is provided between the feeder line and the setting control unit S. Has been placed. In the unit circuit of FIG. 12, the light emitting element Pi is disposed between the power supply line and the light emission control unit E, whereas in the unit circuit of FIG. 13, the light emitting element Pi is disposed between the ground line and the setting holding unit S. Has been placed.

  Further, the light emitting device 10 and each of the above-described modifications may be modified so that the set value is written only once in a period of less than 4H or more than 5H in each unit circuit U. However, this period is limited to a period within the set value holding capability of the setting holding unit S. For example, when the frame rate is 60 Hz in a display device of an active matrix drive system, the setting holding unit of each unit circuit is required to have the ability to hold the written setting value for a period of about 1/60 = 16.7 ms. However, when the light emitting device is used as a line head of the image forming apparatus, 1H is generally several tens μs to several hundreds μs, and therefore the setting holding unit S of the light emitting device 10 displays the above display. If each unit circuit U has a setting value holding capability equivalent to that of the setting holding unit of the apparatus, the setting value can be written only once within a period of 100H or more.

  Further, if there is a margin in the processing speed of each DAC 9B, the set value may be written in a plurality of unit circuits U that are handled by the same DAC 9B in a certain unit period. As a specific example, in the first unit period, first, the set value is written to the unit circuit U1, then the set value is written to the unit circuit U2, and in the next unit period, the set value is first written to the unit circuit U3. There is a form in which the set value is written in the unit circuit U4. Further, the light emitting device 10 and each of the above-described modifications may be modified, and an LED (Light Emitting Diode) or an LD (Laser Diode) may be employed as the light emitting element P instead of the organic EL element.

<Application example>
The light emitting device 10 and each of the above-described modifications can be applied to an area gradation image forming apparatus.
FIG. 14 is a longitudinal sectional view of an image forming apparatus that employs the light emitting device 10 or the light emitting device according to each of the above modifications as a line head. This image forming apparatus is a tandem type full-color image forming apparatus using a belt intermediate transfer body method, and four line heads 10K, 10C, 10M, and 10Y having the same configuration are provided with four pieces having the same configuration. The photosensitive drums (image carriers) 110K, 110C, 110M, and 110Y are disposed at exposure positions, respectively. Each line head is the light emitting device 10 or the light emitting device according to each of the above modifications.

  As shown in the figure, 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, as indicated by arrows. Are rotated around the rollers 121 and 122. 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, photosensitive drums 110K, 110C, 110M, and 110Y having photosensitive layers on four outer peripheral surfaces are arranged at predetermined intervals. 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), there is a corona charger 111 (K, C, M, Y), a line head 10 (K, C, M, Y), and a developing unit. 114 (K, C, M, Y) are arranged. 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 line head 10 (K, C, M, Y) writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. Each line head 10 (K, C, M, Y) is installed such that the arrangement direction of the plurality of light emitting elements P is along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). The The electrostatic latent image is written by irradiating the photosensitive drum with light from the plurality of light emitting elements P 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 visible 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.

  FIG. 15 is a longitudinal sectional view of another image forming apparatus that employs the light emitting device 10 or the light emitting device according to each of the above-described modifications as a line head. This image forming apparatus is a rotary developing type full color image forming apparatus using a belt intermediate transfer body system. Around a photosensitive drum (image carrier) 165, a corona charger 168 and a rotary type developing unit 161 are provided. A line head 167 and an intermediate transfer belt 169 are provided.

  The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 165. The line head 167 writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum 165. The line head 167 is a light-emitting device according to each of the above-described exposure apparatuses or modifications thereof, so that the arrangement direction of the plurality of light-emitting elements P is along the bus (main scanning direction) of the photosensitive drum 165. Installed. The electrostatic latent image is written by irradiating the photosensitive drum with light from the plurality of light emitting elements P described above.

  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 9, the 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.

  This image forming apparatus is provided with a sheet conveyance path 174 through which a sheet is passed. 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 to 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 closer to 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.

  Moreover, the light-emitting device 10 or the light-emitting device according to each of the above-described modifications can be used as a display device that displays an image. However, all of these light emitting devices are premised on that a plurality of light emission periods can be covered with one set value. Therefore, a display device to which these light emitting devices can be applied is preferably a display device that can display a still image.

  The present invention can be used in electronic devices such as image forming apparatuses and display devices.

9 (91 to 94): drive IC, 10: light emitting device, 32: control IC, E: light emission control unit, G (G1 to G4): write period signal, L (L1 to L16) ... ... light emission control signal, P (P1 to P16) ... light emitting element, S ... setting holding unit, U (U1 to U16) ... unit circuit, V (V1 to V4) ... setting signal.

Claims (7)

A plurality of light emitting elements that emit light at a luminance corresponding to the supplied electrical energy;
Each of the plurality of light emitting elements is provided in correspondence with each other, each of which is based on a setting holding unit that holds the setting value written by a write signal for writing a setting value, and a light emission control signal that controls light emission. A plurality of unit circuits having a light emission control unit that permits / prohibits the supply of electric energy according to the set value to the corresponding light emitting element, and operates with a unit period including a common light emission period as a cycle,
A signal supply circuit for supplying the write signal and the light emission control signal to the plurality of unit circuits,
For each of the plurality of unit circuits, the write signal is a signal that writes the setting value in a certain unit period and does not write the setting value in another unit period to the setting holding unit.
The light emission control signal prohibits the light emission control unit of the plurality of unit circuits from supplying electric energy to the light emitting element according to the set value in a period other than the light emission period, and in the light emission period, Among the plurality of unit circuits, the light emission control unit of the unit circuit corresponding to the light emitting element that should emit light during the light emitting period is allowed, while the light emission of the unit circuit corresponding to the light emitting element that should not emit light during the light emitting period. It is a signal to prohibit the control unit,
A light emitting device characterized by that. A unit period for writing the setting value to the setting holding unit is different between the plurality of unit circuits.
The light-emitting device according to claim 1. The write signal is a signal that does not write the set value to any of the setting holding units of the plurality of unit circuits in a certain unit period.
The light-emitting device according to claim 2. The light emission control signal emits electric energy corresponding to the set value to all of the light emission control units of the plurality of unit circuits until writing of the set value is completed for all of the plurality of unit circuits. It is a signal that prohibits the supply to the element,
The light-emitting device according to any one of claims 1 to 3. Each of the setting holding units of the plurality of unit circuits holds one set value over a plurality of unit periods, and generates a current corresponding to the held set value,
The light emission control signal is a binary signal,
Each of the light emission control units of the plurality of unit circuits controls opening and closing of the flow path of the current to the corresponding light emitting element based on the value of the light emission control signal.
The light emitting device according to claim 1, wherein the light emitting device is a light emitting device.   An electronic device comprising the light emitting device according to claim 1. A plurality of light emitting elements that emit light with a luminance corresponding to the supplied electric energy, and the setting values that are provided corresponding to the plurality of light emitting elements, respectively, written by a write signal for writing a setting value And a light emission control unit for permitting / prohibiting the supply of electrical energy according to the set value to the corresponding light emitting element based on a light emission control signal for controlling light emission. A driving method of a light emitting device comprising a plurality of unit circuits that operate with a unit period including a light emitting period as a cycle,
For each of the plurality of unit circuits, the setting value is written to the setting holding unit in a certain unit period, and the write signal that does not write the setting value in another unit period is sent to the plurality of unit circuits. Supply
The supply of electrical energy according to the set value to the light emitting element is prohibited by the light emission control unit of the plurality of unit circuits during a period other than the light emission period, and during the light emission period, the plurality of unit circuits Among these, the light emission control unit of the unit circuit corresponding to the light emitting element that should emit light during the light emission period is allowed, while the setting is made in the light emission control unit of the unit circuit corresponding to the light emitting element that should not emit light during the light emission period. Supplying the light emission control signal for prohibiting the supply of the electrical energy corresponding to the value to the light emitting element to the plurality of unit circuits;
A driving method of a light-emitting device.

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