JP2007017479A - Light emitting apparatus, driving method and driving circuit thereof, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control brightness of each light emitting element with high precision, regarding technology for controlling light emitting element such as an organic light emitting diode (OLED). <P>SOLUTION: Each of the plurality of light emitting elements 12 emits light by applying a light emitting voltage Vb. A current supply section 33 supplies a constant current IO to each light emitting element 12. A specific circuit 35 specifies a measurement voltage according to a voltage Va of an anode of each light emitting element 12 when the constant current IO is supplied. A selection circuit 313 and a buffer 314 output the light emitting voltage Vb according to the measurement voltage specified by the specific circuit 35. A timing control circuit 311 and a switch 315 apply the light emitting voltage Vb output from the buffer 314 to the light emitting element 12 with time density according to grayscale designated by the light emitting element 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for controlling a light emitting element such as an organic light emitting diode (hereinafter referred to as “OLED (Organic Light Emitting Diode)”) element.

2. Description of the Related Art Conventionally, light emitting devices in which light emitting elements such as OLED elements are arranged in a planar shape or a linear shape have been proposed as display devices and exposure devices for various electronic devices. In this type of light emitting device, the characteristics of each light emitting element may vary due to manufacturing errors and changes in characteristics over time. Patent Document 1 discloses a passive matrix light-emitting device that compensates for such variations and suppresses uneven gradation. In this light emitting device, the anode voltage of each light emitting element when a predetermined current is supplied is measured in advance, and the constant current supplied to each light emitting element in actual use is corrected based on the result of this measurement. It has become so.
JP 2002-229513 (paragraphs 0075 to 0078, FIG. 6)

  By the way, a light emitting element such as an OLED element and a wiring connected to the light emitting element accompany a capacitance component. Therefore, in a light emitting device of a method in which the luminance of each light emitting element is designated by current as in Patent Document 1 (hereinafter referred to as “current driving method”), even if an attempt is made to supply a corrected constant current to each light emitting element, Actually, the current supplied to each light emitting element only gradually increases in accordance with the time constant caused by the capacitance component. For example, even if an attempt is made to supply a current having the waveform indicated by the broken line A in FIG. 8 to the light emitting element, the waveform of the current actually supplied to each light emitting element is caused by the capacitance component as indicated by the solid line B in FIG. And so on. Therefore, it is still difficult to control the brightness of each light emitting element to a desired value with high accuracy, even though the current is corrected so as to compensate for variations in the characteristics of each light emitting element. There is. This invention is made | formed in view of such a situation, and it aims at the solution of the subject of controlling the brightness | luminance of each light emitting element with high precision.

In order to solve this problem, a driving method of a light emitting device according to the present invention includes a plurality of light emitting elements each including a first electrode, a second electrode, and a light emitting layer that emits light by applying a light emission voltage between both electrodes. The first electrode is formed for each light emitting element, and the current is supplied to each light emitting element (for example, the constant current I0 in each embodiment). The voltage of the first electrode of each light emitting element (for example, the adjustment anode voltage Va in each embodiment) is specified, and the light emission voltage corresponding to the voltage specified for each light emitting element is determined according to the gradation specified for the light emitting element. Applied to the light emitting element at a predetermined time density. Note that the light emitting voltage in the present invention is a voltage for causing the light emitting element to emit light (that is, a voltage exceeding the threshold voltage of the light emitting element), but the luminance of the light emitting element when this light emitting voltage is applied is arbitrary.
According to this method, since the light emission voltage is applied to the light emitting element at a time density corresponding to the gradation, the time required for the current flowing through the light emitting element to reach the expected value is shorter than that of the current driving method. . Therefore, the luminance of each light emitting element can be controlled with high accuracy. Moreover, the light emission voltage is a voltage corresponding to the voltage of the first electrode of each light emitting element during the supply of current. That is, since the light emission voltage can be variably selected so that the characteristics of each light emitting element (particularly, the relationship between voltage and current) can be compensated for, the luminance error due to the characteristics of each light emitting element (each light emitting element) Variation in luminance between them and an error in luminance of one light emitting element) can be reduced.

  Note that, in a light-emitting device that employs a light-emitting element that defines a forward direction and a reverse direction, such as an OLED element, whether the first electrode and the second electrode correspond to an anode or a cathode is arbitrary. That is, the first electrode may be an anode and the second electrode may be a cathode as in each of the embodiments described later. Conversely, the first electrode may be a cathode and the second electrode may be an anode. Good. Moreover, the aspect of the second electrode is arbitrary. For example, the second electrode may be individually formed for each light emitting element, or the second electrode (common electrode) may be formed so as to be continuously distributed over a plurality of light emitting elements.

The drive circuit according to the present invention is a drive circuit for a light-emitting device that includes a plurality of light-emitting elements that each emit light upon application of a light-emission voltage, and is provided corresponding to the light-emitting elements, and each of which varies the light-emission voltage. A plurality of voltage adjusting means (for example, the selection circuit 313 and the buffer 314 in FIG. 1) to be output to and the light emission voltage output from each voltage adjusting means in accordance with the gradation specified for the light emitting element corresponding to the voltage adjusting means Further, gradation control means (for example, the timing control circuit 311 and the switch 315 in FIG. 1) for applying to the light emitting element at the time density is provided. For example, the gradation control unit applies a light emission voltage to each light emitting element in a period of time corresponding to the gradation designated for the light emitting element in a predetermined period, while in the remaining period. A non-light emitting voltage (that is, a voltage lower than the threshold voltage of the light emitting element) is applied.
According to this configuration, since the light emitting element is applied to the light emitting element at a time density corresponding to the gradation, the current flowing through each light emitting element is quickly reached to the expected value, and each brightness is controlled with high accuracy. be able to. In addition, since the light emission voltage output by each voltage adjusting means is independently variable, each luminance can be adjusted by selecting the light emission voltage so that the characteristics (particularly the relationship between voltage and current) of each light emitting element are compensated. The error can be reduced.

  In a desirable mode of the drive circuit according to the present invention, each voltage adjusting unit includes a selecting unit (for example, the selecting circuit 313 in FIG. 1) for selecting any one of a plurality of reference voltages having different voltage values. Outputs a light emission voltage corresponding to the selected reference voltage. According to this aspect, the light emission voltage can be generated with a simple configuration in which one of a plurality of reference voltages is selected.

A more desirable mode is that current supply means for supplying current to each light emitting element (for example, the current supply section 33 in FIG. 1, the current source 332 and each switch SW1 in FIG. 3), and the current supply means supply current. Specifying means (for example, the specifying circuit 35 in FIGS. 1 and 3) for specifying a measurement voltage corresponding to the voltage of the first electrode of each light emitting element when each of the light emitting elements is in operation. The light emitting voltage corresponding to the measured voltage specified by the specifying means for the light emitting element corresponding to is output. According to this aspect, each light emitting voltage can be adjusted in accordance with the actual characteristics of each light emitting element (that is, the voltage of the first electrode when the current supply means supplies a current). It is possible to reliably compensate for an error in (voltage-current characteristics).
For example, the specifying unit compares the voltage of the first electrode of each light emitting element when the current supply unit supplies the current with a plurality of reference voltages having different voltage values, and based on the result of this comparison. Select one of multiple reference voltages as the measurement voltage. According to this aspect, the measurement voltage can be specified with a simple configuration in which any one of the plurality of reference voltages is selected.

  Another aspect of the present invention includes a reference voltage generation unit that generates a plurality of reference voltages each having a different voltage value, and the voltage adjustment unit selects any one of the plurality of reference voltages generated by the reference voltage generation unit. Including a selecting unit that selects based on the measured voltage specified by the specifying unit, and outputs a light emission voltage corresponding to the reference voltage selected by the selecting unit, and the specifying unit is configured so that each current supply unit supplies current. The voltage of the first electrode of the light emitting element is compared with a plurality of reference voltages generated by the reference voltage generating means, and one of the plurality of reference voltages is selected as a measurement voltage based on the result of this comparison. According to this aspect, since the plurality of reference voltages generated by the reference voltage generating unit are shared by the voltage adjusting unit and the specifying unit, the reference voltage used by the voltage adjusting unit and the reference voltage used by the specifying unit are separately provided. As compared with the generated configuration, the configuration can be simplified and the circuit scale can be reduced.

  In a preferred aspect of the present invention, the current supply means supplies a current to each of the plurality of light emitting elements in a time-sharing manner, and the specifying means includes the first light emitting element when the current is supplied to each light emitting element. The voltage of one electrode is specified sequentially. According to this aspect, since the current supply means and the specifying means are shared for adjusting the light emission voltage by each voltage adjusting means, the current supply means and the specifying means are compared with the configuration provided for each voltage adjusting means. Therefore, the circuit scale can be reduced. In addition, in the configuration in which the current supply unit is provided for each voltage adjustment unit (for example, the first embodiment illustrated in FIG. 1), there is a possibility that the current output from each current supply unit may vary. According to the configuration in which the current supply unit is shared as in this aspect, variation in the current supplied from the current supply unit to each light emitting element cannot occur in principle. Therefore, according to this aspect, the light emission voltage can be adjusted to a desired voltage value with high accuracy. A specific example of this aspect will be described later as a second embodiment (FIG. 3).

Still another aspect includes storage means (for example, the memory 312 in FIGS. 1 and 3) for storing voltage designation data for designating voltage for each light emitting element, and each voltage adjustment means is a light emission corresponding to the voltage adjustment means. The light emission voltage designated by the voltage designation data stored in the storage means for the element is output. According to this aspect, the light emission voltage can be easily adjusted according to the voltage designation data stored in the storage unit.
In a more desirable mode, storage means for storing voltage designation data for designating voltage for each light emitting element, current supply means for supplying current to each light emitting element, and the current supply means supply current. And specifying means for causing the storage means to store voltage designation data corresponding to the voltage of the first electrode of each light emitting element when each voltage adjusting means is stored in the storage means for the light emitting element corresponding to the voltage adjusting means. The light emission voltage specified by the specified voltage specification data is output.

  The present invention is also implemented as a light emitting device including the drive circuit according to each aspect exemplified above. The light-emitting device includes a plurality of light-emitting elements that each emit light by applying a light-emission voltage, a plurality of voltage adjusting units that are provided corresponding to the light-emitting elements and that each output a light-emission voltage variably, and each voltage adjustment unit includes Gradation control means for applying the output light emission voltage to the light emitting element at a time density corresponding to the gradation designated for the light emitting element corresponding to the voltage adjusting means. Also with this configuration, the same operation and effect as the drive circuit of the present invention can be obtained.

  A desirable mode of the light emitting device according to the present invention is based on a current supply unit that supplies a current to each light emitting element and a voltage of the first electrode of each light emitting element when the current supply unit supplies a current. Specifying means for specifying the measurement voltage, and each voltage adjustment means outputs a light emission voltage corresponding to the measurement voltage specified by the specification means for the light emitting element corresponding to the voltage adjustment means. According to this aspect, since the current supply unit and the specifying unit are installed in the light emitting device, the light emission voltage is adjusted according to the actual characteristics of each light emitting element, for example, at any time after the light emitting device is shipped. It becomes possible.

Note that the characteristics of the light-emitting element (the relationship between the voltage between both ends of the light-emitting element, the current flowing between the both ends, and the luminance of the light-emitting element) may vary depending on the temperature of the light-emitting element. Therefore, a desirable aspect of the present invention is a temperature sensor that detects the temperature of each light emitting element or its surroundings, and a correction unit that corrects the measurement voltage specified by the specifying unit according to the temperature detected by the temperature sensor (for example, FIG. 3). The voltage adjusting means outputs a light emission voltage corresponding to the measured voltage corrected by the correcting means. According to this aspect, it is possible to compensate for an error in the characteristics of the light emitting element due to a change in temperature.
In addition, the characteristics of the light emitting element may change over time. In view of this, another aspect of the present invention includes a time measuring unit that specifies a time length during which the light emitting device has been used, and a correction unit that corrects the measurement voltage specified by the specifying unit according to the time length specified by the time measuring unit. In addition, the voltage adjusting unit outputs a light emission voltage corresponding to the measurement voltage corrected by the correcting unit. According to this aspect, it is possible to compensate for the change over time in the characteristics of the light emitting element. In addition, the specific example of the aspect which correct | amends a measurement voltage as mentioned above is later mentioned as 3rd Embodiment.

  The light emitting device according to the present invention is used in various electronic devices. A typical example of this electronic device is a device using a light emitting device as a display device. Examples of this type of electronic device include a personal computer and a mobile phone. However, the use of the light emitting device according to the present invention is not limited to image display. For example, the light emitting device of the present invention can also be applied as an exposure device (exposure head) for forming a latent image on an image carrier such as a photosensitive drum by irradiation of light.

<A: First Embodiment>
FIG. 1 is a block diagram showing a configuration of a light emitting device according to the first embodiment of the present invention. The light emitting device D of the present embodiment is used as an exposure head for exposing a photoconductor in an image forming apparatus (printing apparatus) that forms a latent image by exposing a photoconductor such as a photoconductor drum. As shown in FIG. 1, the light-emitting device D includes a light-emitting unit 10 in which n (n is a natural number) light-emitting elements 12 are linearly arranged along the main scanning direction, and driving for driving each light-emitting element 12. A circuit 20 and a control circuit 40 for controlling the operation of the drive circuit 20 are included.

  Each light-emitting element 12 is a current-driven element that emits light with a luminance corresponding to the current flowing therethrough. For example, an OLED element in which a light-emitting layer made of an organic EL (Electro Luminescent) material is interposed in a gap between an anode and a cathode. It is. The anode is an electrode formed individually for each light emitting element 12. On the other hand, the cathode is an electrode distributed continuously over all the light emitting elements 12 and is grounded. By controlling the voltage of each anode individually for each light emitting element 12 and selectively causing each of the plurality of light emitting elements 12 to emit light, a latent image corresponding to an image (a visible image) to be formed on a recording material such as paper is obtained. An image is formed on the surface of the photoreceptor. Here, an example in which an electrode (individual electrode) formed individually for each light emitting element 12 is used as an anode and an electrode facing this electrode (that is, a common electrode common to all the light emitting elements 12) is used as a cathode is illustrated. However, conversely, a configuration in which the individual electrode is a cathode and the common electrode is an anode is also employed.

  The control circuit 40 controls the operation of the drive circuit 20 by supplying various signals such as a clock signal (for example, a control signal CTL, which will be described later), and also supplies gradation data G that specifies the gradation of each light emitting element 12 to the drive circuit. 20 is output. The gradation data G in this embodiment is 4-bit digital data that designates, for each light emitting element 12, any one of a total of 16 gradations from gradation “0” to gradation “15”.

  On the other hand, the drive circuit 20 includes a line memory 21 for storing the gradation data G, and a plurality (n corresponding to the total number of the light emitting elements 12) of processing units U (U1, U2) each corresponding to a separate light emitting element 12. ,..., Un) and one reference voltage generation circuit 23. The line memory 21 receives gradation data G (G1, G2,..., Gn) corresponding to each of the n light emitting elements 12 from the control circuit 40 and sequentially stores them. The n pieces of gradation data G stored in the line memory 21 are simultaneously read out at the timing designated by the control circuit 40 and supplied to the processing units U1 to Un. Gradation data Gi designating the gradation of the light emitting element 12 in the i-th stage (i is an integer satisfying 1 ≦ i ≦ n) is supplied to the i-th processing unit Ui counting from the left in FIG. Is done.

  The reference voltage generation circuit 23 is means for generating a plurality of (five types in this embodiment) voltages VR (VR1, VR2,..., VR5) having different voltage values. These voltages (hereinafter referred to as “reference voltages”) VR1 to VR5 are such that when each is applied to the anode of the light emitting element 12, a current flows through the light emitting element 12 to emit light (that is, the threshold voltage of the light emitting element 12). The voltage value is selected so that The reference voltages VR1 to VR5 are supplied in common to the n processing units U1 to Un.

  As shown in FIG. 1, each processing unit U includes a data output unit 31. The data output unit 31 of each processing unit U outputs a data signal Vd (Vd [1], Vd [2],..., Vd [n]) to the anode of the light emitting element 12 corresponding to the processing unit U. It is. The data signal Vd [i] causes the i-th light emitting element 12 to emit light in a period of time corresponding to the gradation data Gi in a predetermined period (hereinafter referred to as “unit period”), and the remainder thereof. This is a voltage signal for turning off the light during the period.

  One data output unit 31 includes a timing control circuit 311, a memory 312, a selection circuit 313, a buffer 314, and a switch 315 as described below. Since each of the n data output units 31 has the same configuration, the configuration of the data output unit 31 of the processing unit Ui will be representatively described below, which also serves as an explanation of the other data output units 31. .

  The timing control circuit 311 generates a pulse signal SP having a pulse width corresponding to the gradation data Gi. FIG. 2 is a timing chart showing the relationship between the gradation specified by the gradation data Gi and the waveform of the pulse signal SP generated by the timing control circuit 311. As shown in the figure, the pulse signal SP has a longer time length (that is, a pulse width) for maintaining the high level in the unit period P as the numerical value (gradation) specified by the gradation data Gi is larger. Is generated as follows. However, the pulse signal SP corresponding to the lowest gradation “0” is a signal that maintains the low level over the entire period of the unit period P. Further, in the present embodiment, the pulse signal SP corresponding to the highest gradation “15” is maintained at a high level throughout the entire period of the unit period P except for the blanking period Pb.

  A memory 312 shown in FIG. 1 is a circuit (for example, EEPROM) that stores data (hereinafter referred to as “voltage specifying data”) Dv for specifying any of the reference voltages VR1 to VR5 in a nonvolatile manner. On the other hand, the selection circuit 313 selects and outputs the reference voltage designated by the voltage designation data Dv of the memory 312 among the reference voltages VR1 to VR5 outputted from the reference voltage generation circuit 23. The buffer 314 is a voltage follower operational amplifier that outputs a voltage (hereinafter referred to as “light emission voltage”) Vb corresponding to the voltage output from the selection circuit 313. The light emission voltage Vb is set to a voltage value at which the light emitting element 12 emits light when it is applied to the anode of the light emitting element 12 (that is, a voltage value exceeding the threshold voltage of the light emitting element 12).

  The switch 315 is interposed between the anode of the light emitting element 12 and the output end of the buffer 314, and switches between conduction and non-conduction of both in accordance with the pulse signal SP. More specifically, when the pulse signal SP is at a high level, the switch 315 is turned on and the anode of the light emitting element 12 is connected to the output terminal of the buffer 314. Therefore, the data signal Vd [i] at this time becomes the light emission voltage Vb. On the other hand, if the pulse signal SP is at a low level, the switch 315 is turned off and the connection between the anode of the light emitting element 12 and the output terminal of the buffer 314 is released.

  With the above configuration, the data signal Vd [i] supplied from the data output unit 31 to the anode of the light emitting element 12 becomes the light emission voltage Vb at a time density corresponding to the gradation data Gi. Since the light emission voltage Vb exceeds the threshold voltage of the light emitting element 12, the light emitting element 12 to which the data signal Vd [i] is supplied is turned on in the unit period P for a period of time corresponding to the gradation data Gi. The light is extinguished during the remaining period (that is, light is emitted at a time density corresponding to the gradation data Gi). By controlling the light emission time length in this way, each light emitting element 12 is controlled to a gradation corresponding to the gradation data Gi (gradation control by pulse width modulation).

  As described above, in this embodiment, a method of driving each light emitting element 12 by applying the light emission voltage Vb (hereinafter referred to as “voltage driving method”) is adopted. According to this voltage driving method, the voltage of the anode of the light emitting element 12 can be quickly set to an expected value, so that the time required for the current flowing through the light emitting element 12 to reach the expected value is the current driving method. Is shorter than. Therefore, the luminance of each light emitting element 12 can be controlled with high accuracy.

  By the way, the relationship (voltage-current characteristics) between the voltage between the anode and the cathode of the light emitting element 12 and the current flowing through the light emitting element 12 may be different for each light emitting element 12 due to various factors such as manufacturing errors. Further, even if the characteristics of each light emitting element 12 are uniform at the time of manufacture, the voltage-current characteristics of each light emitting element 12 may change over time. As described above, if the light-emitting voltage Vb applied to each light-emitting element 12 is set to the same voltage in spite of an error in the voltage-current characteristics of each light-emitting element 12, the current flowing through each light-emitting element 12 varies. As a result, there is a problem that the luminance of each light emitting element 12 is different. Each of the processing units U1 to Un in the present embodiment compensates for the voltage-current characteristics of each light emitting element 12 and equalizes the luminance of each light emitting element 12, in addition to the data output unit 31, the current supply unit 33. And a specific circuit 35. The current supply unit 33 and the specific circuit 35 of the i-th processing unit Ui are means for adjusting the light emission voltage Vb of the data signal Vd [i] according to the characteristics of the i-th light-emitting element 12. .

  As shown in FIG. 1, the current supply unit 33 includes a switch 331 and a current source 332. The current source 332 is interposed between the power supply line (power supply voltage Vdd) and the anode of the light emitting element 12 to generate a constant current I0. On the other hand, the switch 331 is means for switching between conduction and non-conduction between the current source 332 and the anode of the light emitting element 12. The switches 331 of the processing units U1 to Un are collectively controlled by a control signal CTL supplied from the control circuit 40. The control circuit 40 shifts the control signal CTL to a high level (a level at which each switch 331 is turned on) during the period in which the light emission voltage Vb is adjusted, and after the period elapses, the control signal CTL is set to a low level. (The level at which each switch 331 is turned off). In the present embodiment, it is assumed that the light emission voltage Vb is adjusted prior to the control of the light emitting element 12 according to the gradation data G every time the light emitting device D is turned on. Therefore, the control signal CTL maintains a high level in a period from when the light emitting element 12 is turned on until a predetermined time length elapses, and then maintains a low level.

  When the control signal CTL transits to a high level and the switch 331 is turned on, the constant current I0 generated by the current source 332 passes through the switch 331 and the light emitting element 12 as shown by the dashed arrow in FIG. To be supplied. The light emitting element 12 emits light by supplying the constant current I0. When the constant current I0 is supplied, the anode of the light emitting element 12 has a voltage Va (hereinafter referred to as “adjusting anode voltage”) Va corresponding to the constant current I0 and the voltage-current characteristics of the light emitting element 12. Become.

  The specifying circuit 35 is a means for specifying the adjustment anode voltage Va when the control signal CTL is at a high level and the constant current I 0 is supplied to the light emitting element 12. More specifically, the specifying circuit 35 compares the adjustment anode voltage Va with each of the reference voltages VR1 to VR5 generated by the reference voltage generation circuit 23, thereby adjusting the adjustment anode voltage Va of the reference voltages VR1 to VR5. The voltage closest to (hereinafter referred to as “measurement voltage”) is specified. Then, the specifying circuit 35 generates data (hereinafter referred to as “voltage specifying data”) Dv for identifying the specified measurement voltage, and writes the voltage specifying data Dv into the memory 312. That is, voltage designation data Dv corresponding to the adjustment anode voltage Va reflecting the voltage-current characteristics of the light emitting element 12 is written in the memory 312.

  Since the selection circuit 313 selects one of the reference voltages VR1 to VR5 based on the voltage designation data Dv generated by the above procedure, the light emission voltage Vb output from the buffer 314 of the processing unit Ui is the i-th stage. The voltage value corresponds to the voltage-current characteristics of the light emitting element 12 of the eye. For example, if the adjustment anode voltage Va of the i-th light emitting element 12 is equal to any of the reference voltages VR1 to VR5, the light emission voltage Vb of the data signal Vd [i] is equal to the adjustment anode voltage Va. Value. By applying this light emission voltage Vb to the anode of the light emitting element 12, regardless of the voltage-current characteristics of each light emitting element 12, it is close to the constant current I0 generated by the current source 332 (ideally matches). Current is supplied to each light emitting element 12. That is, according to the present embodiment, it is possible to compensate for the voltage-current characteristics of each light emitting element 12 and to reduce unevenness in luminance.

<B: Second Embodiment>
Next, a second embodiment of the present invention will be described. In the first embodiment, the configuration in which the current supply unit 33 and the specific circuit 35 are included in each of the n processing units U1 to Un is illustrated. On the other hand, in the present embodiment, one current source 332 and one specific circuit 35 are shared by the n processing units U1 to Un. In addition, the same code | symbol is attached | subjected about the element similar to 1st Embodiment among this embodiment, and the description is abbreviate | omitted suitably.

  FIG. 3 is a block diagram showing a configuration of the light emitting device D according to the present embodiment. As shown in the figure, the light emitting device D of the present embodiment includes one current source 332 and one specific circuit 35. Each of the n processing units U1 to Un includes a switching unit 37 including a switch SW1 and a switch SW2 in addition to the data output unit 31 having the same configuration as that of the first embodiment. The output end of the current source 332 is connected in common to one end of the switch SW1 in each processing unit U. The specifying circuit 35 is connected in common to one end of the switch SW2 in each processing unit U. The other end of the switch SW1 and the other end of the switch SW2 in the processing unit Ui are commonly connected to the anode of the i-th light emitting element 12.

  The control circuit 40 generates a control signal CTL (CTL1, CTL2,..., CTLn) for each processing unit U and outputs it to the switch SW1 and the switch SW2 in each switching unit 37. Each of the control signals CTL1 to CTLn sequentially changes to a high level (a level at which the switches SW1 and SW2 are turned on). The switches SW1 and SW2 of each processing unit U are sequentially turned on in response to the control signals CTL1 to CTLn, thereby supplying the constant current I0 to each light emitting element 12 and adjusting anode voltage Va at the time of supply. Identification and generation of voltage designation data are executed in a time-sharing manner for each processing unit U.

  For example, when the control signal CTLi transitions to a high level, both the switch SW1 and the switch SW2 of the switching unit 37 in the processing unit Ui are turned on. Therefore, the constant current I0 generated by the current source 332 is supplied to the i-th light emitting element 12 via the switch SW1 of the processing unit Ui. Further, the adjustment anode voltage Va of the i-th light emitting element 12 at this time is supplied to the specific circuit 35 via the switch SW2 of the processing unit Ui. As in the first embodiment, the specifying circuit 35 selects a reference voltage closest to the adjustment anode voltage Va of the i-th light emitting element 12 among the reference voltages VR1 to VR5 as a measurement voltage, and this measurement voltage The voltage designation data Dv for designating is generated. Then, the specifying circuit 35 writes the voltage designation data Dv into the memory 312 of the processing unit Ui that is the selection target at that time.

  By performing the above operation in a time-sharing manner for each of the processing units U1 to Un, a voltage corresponding to the voltage-current characteristics of the light emitting element 12 corresponding to the processing unit U is stored in the memory 312 of each processing unit U. The designated data Dv is written. Accordingly, the same effects as those of the first embodiment can be obtained in this embodiment. In addition, according to this embodiment, since the current source 332 and the specific circuit 35 are shared by the plurality of processing units U1 to Un, the current supply unit 33 and the specific circuit 35 are arranged for each processing unit U. Compared with the first embodiment, the configuration can be simplified and the circuit scale can be reduced. Further, in the configuration in which the current supply unit 33 is installed for each processing unit U as in the first embodiment, the constant current I 0 supplied to the light emitting element 12 may vary for each current supply unit 33. On the other hand, according to this embodiment in which the constant current I0 generated by one current supply unit 33 is distributed to each light emitting element 12, the constant current supplied to each light emitting element 12 when measuring the adjustment anode voltage Va. Since the currents I0 are consistent with each other, there is an advantage that variations in the voltage-current characteristics of the light emitting elements 12 can be compensated with high accuracy.

<C: Third Embodiment>
Next, a third embodiment of the present invention will be described.
In the above embodiments, the configuration in which the light emission voltage Vb of the data signal Vd [i] is controlled in accordance with the adjustment anode voltage Va of each light emitting element 12 has been exemplified. However, the characteristics of each light emitting element 12 also vary depending on the temperature of each light emitting element 12 and its surroundings (hereinafter referred to as “element temperature”). For example, even when the same light emission voltage Vb is applied to the light emitting element 12, if the temperature of the light emitting element 12 changes, the luminance of the light emitting element 12 in each case is different. Therefore, in the present embodiment, the measurement voltage corresponding to the adjustment anode voltage Va is corrected according to the element temperature. In addition, the same code | symbol is attached | subjected about the element similar to 1st Embodiment among this embodiment, and the description is abbreviate | omitted suitably.

  FIG. 4 is a block diagram showing the configuration of the light emitting device D according to this embodiment. As shown in the figure, the light emitting device D of this embodiment includes a temperature sensor 50. The temperature sensor 50 is a means (for example, a thermistor) for detecting the element temperature.

  In addition, a correction circuit 317 is interposed between the memory 312 and the selection circuit 313 of each processing unit U. The element temperature detected by the temperature sensor 50 is output to the correction circuit 317 of each processing unit U. The correction circuit 317 corrects the voltage designation data Dv read from the preceding memory 312 based on the element temperature supplied from the temperature sensor 50 (that is, corrects the measured voltage based on the element temperature). This is means for outputting the subsequent voltage designation data Dv (hereinafter referred to as “correction voltage designation data Dv1” in particular) to the selection circuit 313.

  More specifically, the correction circuit 317 includes a table for each temperature detected by the temperature sensor 50. In each table, the voltage designation data Dv stored in the memory 312 is associated with the correction voltage designation data Dv1 output from the correction circuit 317. The voltage specified by the correction voltage specifying data Dv1 in each table is emitted by the light emitting element 12 to which the light emission voltage Vb corresponding to the correction voltage specifying data Dv1 is applied, with a luminance corresponding to the voltage specifying data Dv regardless of the element temperature. It is selected experimentally or statistically in advance.

  In the above configuration, the correction circuit 317 first selects a table corresponding to the element temperature notified from the temperature sensor 50 among these tables, and secondly, the memory 312 from the selected table. The correction voltage designation data Dv1 corresponding to the voltage designation data Dv output by is searched and output. On the other hand, the selection circuit 313 selects one of the reference voltages VR1 to VR5 according to the correction voltage designation data Dv1. Therefore, the light emission voltage Vb output from the buffer 314 has a voltage value corresponding to the element temperature.

  As described above, according to the present embodiment, since the light emission voltage Vb corresponding to the adjustment anode voltage Va and the element temperature is applied to each light emitting element 12, in addition to the effects of the first embodiment, There is an effect that each light emitting element 12 can be controlled to a desired luminance regardless of the element temperature.

  Here, the configuration in which the light emission voltage Vb is controlled according to the element temperature is illustrated, but the relationship between the voltage and the luminance in each light emitting element 12 is the length of time that the light emitting device D is actually used (hereinafter referred to as “use”). It may be changed by various factors other than the element temperature, such as “time”. Therefore, instead of the configuration of the present embodiment or together with this configuration, the light emission voltage Vb may be corrected based on factors other than the element temperature. For example, after providing a timer (time measuring means) for measuring the usage time, a table for associating the voltage designation data Dv with the correction voltage designation data Dv1 is created for each usage time (or for each range in which the usage time is divided). The correction circuit 317 is installed. Then, the correction circuit 317 selects a table corresponding to the usage time measured by the timer, and searches the correction voltage designation data Dv1 from this table by the same procedure as in the present embodiment. According to this configuration, each light emitting element 12 can be controlled to an intended luminance regardless of the usage time.

  In the above description, the configuration in which the correction voltage specifying data Dv1 is specified by referring to the table is exemplified, but the method for specifying the correction voltage is arbitrary. For example, the correction circuit 317 executes a predetermined calculation using the element temperature detected by the temperature sensor 50 (or the usage time measured by the timer) and the voltage designation data Dv read from the memory 312 as arguments, and the calculated value May be output to the selection circuit 313 as the correction voltage designation data Dv1.

<D: Modification>
Various modifications can be made to each of the above embodiments. An example of a specific modification is as follows. In addition, you may combine each following aspect suitably.

(1) Modification 1
The specific configuration of each unit illustrated in FIG. 1 is appropriately changed. For example, in each embodiment, the configuration in which the voltage designation data Dv is generated by selecting any of the reference voltages VR1 to VR5 according to the adjustment anode voltage Va is illustrated. The method for generating the voltage designation data Dv is not limited to this. For example, an A / D converter that generates digital data representing the voltage value of the adjustment anode voltage Va may be used as the specifying circuit 35, and the digital data may be stored in the memory 312 as the voltage designation data Dv. That is, the element of selecting any one of a plurality of reference voltages according to the adjustment anode voltage Va is not necessarily required in the present invention, and means for specifying a measurement voltage according to the adjustment anode voltage Va (in each embodiment) A specific circuit 35) is sufficient.

  In each embodiment, the configuration selected from the reference voltages VR1 to VR5 according to the voltage designation data Dv is exemplified. However, the method for generating the light emission voltage Vb according to the voltage designation data Dv is limited to this. Not. For example, a voltage output type D / A converter that generates a voltage specified by the voltage specifying data Dv is installed in the data output unit 31, and the light emission voltage Vb is generated based on the voltage generated by the D / A converter. It is good also as a structure. That is, in the present invention, the element of selecting any one of a plurality of reference voltages for generating the light emission voltage Vb is not necessarily required, and the light emission voltage Vb corresponding to the adjustment anode voltage Va (or voltage designation data Dv) is not required. It suffices to have means for variably outputting (selection circuit 313 and buffer 314 in each embodiment).

  Further, in each of the embodiments, the reference voltages VR1 to VR5 generated by the reference voltage generation circuit 23 are illustrated as being shared by the specifying circuit 35 and the selection circuit 313 of each processing unit U. The reference voltage used by the circuit 35 and the reference voltage used by the selection circuit 313 of each processing unit U may be generated by separate circuits. In addition, the total number of reference voltages (“5” in each embodiment) to be selected by the specifying circuit 35 and the selection circuit 313 is arbitrarily changed.

(2) Modification 2
In each embodiment, the light emitting device D in which the plurality of light emitting elements 12 are arranged in a line is illustrated, but the present invention is similarly applied to the light emitting device D in which the plurality of light emitting elements 12 are arranged in a matrix (planar shape). Applies to In this configuration, the light emitting element 12 is formed in each region where each of the plurality of scanning lines and each of the plurality of data lines face each other. Each light emitting element 12 is sequentially selected by the scanning line driving circuit in units of rows, while the driving circuit 20 (in this case, the data line driving circuit) is used for each light emitting element 12 in the selected row as in each embodiment. Is performed.

  Further, in each embodiment, the configuration in which the light emission voltage Vb is variable for each light emitting element 12 is exemplified, but the range as a unit for adjusting the light emission voltage Vb is arbitrary. For example, in a configuration in which n light emitting elements 12 of the light emitting unit 10 are divided into groups with a predetermined number as a unit, the light emission voltage Vb is variably generated independently for each group, and each light emitting element belonging to one group The light emission voltage Vb of the group may be shared for 12 light emission. Further, for example, in a configuration in which a plurality of light emitting elements 12 are arranged in a matrix, a configuration in which the light emission voltage Vb is adjusted in units of the arrangement of the plurality of light emitting elements 12 along the scanning lines or data lines (that is, the same or A configuration in which a common light emission voltage Vb is applied to a plurality of light emitting elements 12 belonging to the same column may be employed.

(3) Modification 3
In each embodiment, the configuration in which the supply of the constant current I0 to each light emitting element 12 and the identification and holding of the adjustment anode voltage Va are executed when the power of the light emitting device D is turned on is illustrated. However, these operations are executed. The timing and opportunity to be determined are arbitrary. For example, it may be executed every time an instruction is input by the user, or may be executed when the mode is changed to a mode in which the operation of the light emitting device D is paused.

  Moreover, in each embodiment, the structure which the electric current supply part 33 and the specific circuit 35 were installed in the light-emitting device D was illustrated. According to this configuration, even after the light emitting device D is shipped, the light emission voltage Vb is adjusted at any time. For example, even when the voltage-current characteristic of the light emitting element 12 changes over time, the change A light emission voltage Vb according to the later characteristics can be generated. However, it is not always necessary that the light emitting device D includes the current supply unit 33 and the specific circuit 35.

  For example, an adjustment device including the current supply unit 33 and the specific circuit 35 similar to those in each embodiment may be created and used separately from the light emitting device D. In this configuration, the current supply unit 33 of the adjusting device mounted on the light emitting device D supplies a constant current I 0 to each light emitting element 12, and the specific circuit 35 of this adjusting device uses the adjusting anode voltage of each light emitting element 12. Va is specified. When the voltage designation data Dv corresponding to the specific result of the adjustment anode voltage Va is written into each memory 312 by the specifying circuit 35, the adjustment device is removed from the light emitting device D. The operation when using the light emitting device D is the same as that of each embodiment. Also with this configuration, since the light emission voltage Vb corresponding to the adjustment anode voltage Va of each light emitting element 12 is generated, the difference in characteristics (voltage-current characteristics) of each light emitting element 12 is compensated for. The effect of controlling the brightness with high accuracy is exhibited. As described above, the means for supplying a constant current to each light emitting element and the means for specifying the measurement voltage corresponding to the voltage of the anode of each light emitting element during the supply are arbitrary for the light emitting device of the present invention and its drive circuit. Is an element.

(4) Modification 4
In the above description, the light emitting device D using the OLED element is illustrated, but the present invention is also applied to a light emitting device using other light emitting elements. For example, a display device using an inorganic EL element, a field emission display (FED), a surface-conduction electron emission display (SED), a ballistic electron emission display (BSD) The present invention is applied to various light emitting devices such as emitting display) and display devices using light emitting diodes.

<E: Application example>
In each embodiment, the light emitting device used as the exposure device of the image forming apparatus is exemplified, but the application of the light emitting device according to the present invention is not limited to exposure. For example, a light emitting device in which a plurality of light emitting elements 12 are arranged in a matrix is used as a device for displaying various images. Examples of electronic devices using the light emitting device according to the present invention are as follows.

  Next, an electronic apparatus using the light emitting device according to the present invention will be described. FIG. 5 is a perspective view showing a configuration of a mobile personal computer that employs the light emitting device D according to any one of the embodiments described above as a display device. The personal computer 2000 includes a light emitting device D as a display device and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the light-emitting device D uses an OLED element as the light-emitting element 12, it is possible to display an easy-to-see screen with a wide viewing angle.

  FIG. 6 shows a configuration of a mobile phone to which the light emitting device D according to the embodiment is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and a light emitting device D as a display device. By operating the scroll button 3002, the screen displayed on the light emitting device D is scrolled.

  FIG. 7 shows a configuration of a personal digital assistant (PDA) to which the light emitting device D according to the embodiment is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and a light emitting device D as a display device. When the power switch 4002 is operated, various kinds of information such as an address book and a schedule book are displayed on the light emitting device D.

  Electronic devices to which the light emitting device according to the present invention is applied include those shown in FIGS. 5 to 7, digital still cameras, televisions, video cameras, car navigation devices, pagers, electronic notebooks, electronic papers, calculators. , Word processors, workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices equipped with touch panels, and the like.

It is a block diagram which shows the structure of the light-emitting device which concerns on 1st Embodiment of this invention. It is a timing chart which shows the relationship between gradation data and the waveform of a pulse signal. It is a block diagram which shows the structure of the light-emitting device which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the light-emitting device which concerns on 3rd Embodiment of this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a timing chart for demonstrating the problem of the prior art.

Explanation of symbols

D: Light emitting device, 12: Light emitting element, 20: Drive circuit, U: Processing unit, 23: Reference voltage generation circuit, 31: Data output unit, 311: Timing control circuit, 312: Memory 313... Selection circuit, 314... Buffer, 317... Correction circuit, 33... Current supply unit, 35... Specific circuit, 37. …… Adjustment anode voltage, Vb …… Light emission voltage, Vd [i] …… Data signal, Dv …… Voltage designation data, G (G1, G2,…, Gn) …… Gradation data, CTL …… Control signal.

Claims (14)

Driving a light-emitting device including a plurality of light-emitting elements each including a first electrode, a second electrode, and a light-emitting layer that emits light by applying a light-emitting voltage between the two electrodes, wherein the first electrode is formed for each light-emitting element A method,
Supplying a current to each of the light emitting elements, and specifying a voltage of the first electrode of each of the light emitting elements during the supply;
A driving method of a light emitting device, wherein a light emitting voltage corresponding to a voltage specified for each light emitting element is applied to the light emitting element at a time density corresponding to a gradation specified for the light emitting element. A driving circuit for a light emitting device including a plurality of light emitting elements each emitting light by applying a light emitting voltage,
A plurality of voltage adjusting means provided corresponding to the light emitting elements, each of which variably outputs a light emission voltage;
A gradation control means for applying a light emission voltage output from each voltage adjusting means to the light emitting element at a time density corresponding to a gradation designated for the light emitting element corresponding to the voltage adjusting means. Driving circuit. 3. The voltage adjustment unit includes a selection unit that selects one of a plurality of reference voltages having different voltage values, and outputs a light emission voltage corresponding to the reference voltage selected by the selection unit. Driving circuit for the light emitting device. Each of the light emitting elements includes a first electrode and a second electrode, and a light emitting layer that emits light by applying a light emission voltage between both electrodes, and the first electrode is formed for each light emitting element.
Current supply means for supplying a current to each of the light emitting elements;
Specifying means for specifying a measurement voltage according to the voltage of the first electrode of each light emitting element when the current supply means supplies current, and each voltage adjustment means includes the voltage adjustment means The drive circuit of the light-emitting device according to claim 2, wherein a light-emitting voltage corresponding to the measurement voltage specified by the specifying unit is output for the light-emitting element corresponding to the above. The specifying unit compares the voltage of the first electrode of each light emitting element when the current supply unit supplies a current with a plurality of reference voltages having different voltage values, and determines the result of this comparison. The drive circuit of the light-emitting device according to claim 4, wherein any one of the plurality of reference voltages is selected as a measurement voltage based on the measurement voltage. A reference voltage generating means for generating a plurality of reference voltages having different voltage values,
The voltage adjusting unit includes a selecting unit that selects any one of a plurality of reference voltages generated by the reference voltage generating unit based on the measurement voltage specified by the specifying unit, and sets the reference voltage selected by the selecting unit. Output the corresponding light emission voltage,
The specifying unit compares the voltage of the first electrode of each light emitting element when the current supply unit supplies a current with a plurality of reference voltages generated by the reference voltage generation unit, and the result of this comparison The drive circuit for the light-emitting device according to claim 4, wherein any one of the plurality of reference voltages is selected as a measurement voltage based on the reference. The current supply means supplies current in a time division manner to each of the plurality of light emitting elements,
The drive circuit of the light emitting device according to claim 4, wherein the specifying unit sequentially specifies a measurement voltage corresponding to a voltage of the first electrode of the light emitting element when a current is supplied to the light emitting elements. Comprising storage means for storing voltage designation data for designating voltage for each light emitting element;
The drive circuit of the light emitting device according to claim 2, wherein each of the voltage adjustment units outputs a light emission voltage designated by voltage designation data stored in the storage unit for a light emitting element corresponding to the voltage adjustment unit. Storage means for storing voltage designation data for designating voltage for each light emitting element;
Current supply means for supplying a current to each of the light emitting elements;
A specifying unit that causes the storage unit to store voltage designation data corresponding to the voltage of the first electrode of each of the light emitting elements when the current supply unit supplies a current; and The drive circuit of the light emitting device according to claim 2, wherein a light emission voltage designated by voltage designation data stored in the storage means is output for the light emitting element corresponding to the voltage adjusting means. A plurality of light emitting elements each emitting light by application of a light emission voltage;
A plurality of voltage adjusting means provided corresponding to the light emitting elements, each of which variably outputs a light emission voltage;
And a gradation control unit that applies the light emission voltage output from each voltage adjusting unit to the light emitting element at a time density corresponding to the gradation specified for the light emitting element corresponding to the voltage adjusting unit. Current supply means for supplying a current to each of the light emitting elements;
Specifying means for specifying a measurement voltage according to the voltage of the first electrode of each light emitting element when the current supply means supplies current, and each voltage adjustment means includes the voltage adjustment means The light-emitting device according to claim 10, wherein a light-emitting voltage corresponding to the measurement voltage specified by the specifying unit is output for a light-emitting element corresponding to the above. A temperature sensor for detecting the temperature of each light emitting element or its surroundings;
Correction means for correcting the measurement voltage specified by the specifying means in accordance with the temperature detected by the temperature sensor, and the voltage adjustment means, the light emission voltage according to the measurement voltage corrected by the correction means. The light emitting device according to claim 11 that outputs the light emitting device. A timing means for identifying the length of time the light emitting device has been used;
Correction means for correcting the measured voltage specified by the specifying means according to the time length specified by the time measuring means, and the voltage adjusting means is a light emission voltage according to the measured voltage corrected by the correcting means. The light emitting device according to claim 11. An electronic apparatus comprising the light emitting device according to any one of claims 10 to 13.

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