JP2007253501A - Drive circuit for light-emitting element, drive control method for the drive circuit, display unit equipped with the drive circuit for light-emitting element, and electric appliance equipped with the display unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive circuit for a light-emitting element, which can correct variations in the light-emission characteristics of the individual light-emitting elements, without changing the pulse width of a driving signal supplied to the light-emitting element, a control method for the drive circuit, a display unit equipped with the drive circuit, and an electric appliance equipped with the display unit. <P>SOLUTION: This drive circuit comprises: the plurality of light-emitting elements which are arranged in line, and which each have the amount of light emission controlled depending on a current value and the pulse width, constituting the driving signal; a pulse control means for controlling the current value of the driving signal; and a driving means for supplying the driving signal to each of the light-emitting elements. The pulse control means controls the driving signal so that the current values of intermediate parts except front and back ends of the driving signal can be smaller than those of the front and back ends of the driving signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an organic light emitting diode (hereinafter referred to as “OLED (Organic Light Emitting Diode)”).
" The present invention relates to a drive control method for controlling the amount of light emitted from a light emitting element such as an element, a display device including the light emitting element drive circuit, and an electronic apparatus including the display device.

A light-emitting element array in which a plurality of light-emitting elements are arranged in the main scanning direction, sub-scanning means for relatively moving the light-emitting element array and the photosensitive member in a sub-scanning direction substantially orthogonal to the main scanning direction, and a gradation image And a drive circuit that controls the light emission time (light emission pulse width) of each of the plurality of light emitting elements based on the image data to be processed, and an image forming apparatus that exposes the photosensitive member to the gradation image indicated by the image data Conventionally known.

As a light emitting element used in this image forming apparatus, a semiconductor laser element, LED (ligh
t emitting diode) element, OLED element, and the like. When the light emitting characteristics of the light emitting elements arranged in the same light emitting element array are different, the light emitting elements are driven based on the same image data. A difference occurs in the exposure amount received by the photosensitive member. Therefore, when such a difference in light emission characteristics exists between adjacent light emitting elements, a density difference occurs in the main scanning direction in the formed image, and streaky density unevenness (so-called streak) extending in the sub scanning direction occurs. village)
Had occurred.

Therefore, a method has been proposed in which the light emission characteristics of the light emitting element are corrected by controlling the light emission pulse width while keeping the pulse height (current flowing through the light emitting element) constant (Patent Document 1).
And 2).

JP-A-2005-81696 JP 2005-103816 A

However, in the above-described image forming apparatus, the photosensitive member is exposed while being relatively moved in the sub-scanning direction by the sub-scanning unit. Therefore, there is a method for controlling the light emission pulse width to correct the light emission characteristics of each light-emitting element. If used, the light emission time of each light emitting element will be different. That is,
By changing the light emission pulse width, the length of the latent image formed on the photoreceptor varies in the sub-scanning direction. FIG. 15 shows the relationship between the light emission pulse width, the pulsed current value, and the latent image formed on the photosensitive member when the light emission pulse width is changed. As shown in FIG. 15, the length of the latent image formed on the photoconductor in the sub-scanning direction becomes longer as the emission pulse width becomes larger. Therefore, when a method of correcting the light emission characteristics of each light emitting element by controlling the light emission pulse width, there is a problem that an image formed in accordance with the amount of correction deteriorates.

In view of the circumstances described above, the present invention provides a drive circuit for a light emitting element capable of correcting variations in light emission characteristics of each light emitting element without changing the pulse width of a current supplied to the light emitting element, a control method thereof, and It is an object of the present invention to provide a display device including the light emitting element driving circuit and an electronic device including the display device.

A first aspect of the present invention that solves the above-described problem is a light-emitting element that is arranged in a plurality of lines and whose light emission amount is controlled according to a current value and a pulse width constituting a drive signal, and the drive signal Pulse control means for controlling the current value of the light source, and drive means for supplying the drive signal to each of the light emitting elements, wherein the pulse control means is more than the front edge portion and the rear edge portion of the drive signal. In the light emitting element driving circuit, the driving signal is controlled so that the current value of the other intermediate portion is low.
In the first aspect, it is possible to correct variations in the light emitting elements without changing the pulse width of the drive signal supplied to the light emitting elements. In addition, since the current values of the front edge portion and the rear edge portion can be made higher than the intermediate portion of the pulse-like drive signal, a sharp latent image can be formed.

According to a second aspect of the present invention, in the drive circuit for a light emitting device according to the first aspect, the pulse control means includes a bypass path having switching means connected in parallel to the light emitting element, and the switching In the drive circuit for a light emitting element, the drive signal is controlled so that the current value of the intermediate portion other than the front edge portion and the rear edge portion of the drive signal becomes lower by turning on the means. is there.
In the second aspect, the drive circuit for the light emitting device can be easily manufactured.

According to a third aspect of the present invention, a plurality of light emitting elements are arranged in a line, and each light emission amount is controlled according to a current value and a pulse width constituting the drive signal, and the current value of the drive signal is controlled. Pulse control means, and drive means for supplying the drive signal to each of the light emitting elements,
The pulse control means controls the drive signal so that the current value of the drive signal gradually decreases from the front end toward the central portion and gradually increases from the central portion toward the rear end. In the drive circuit.
In the third aspect, the same effect as in the first aspect can be obtained.

According to a fourth aspect of the present invention, in the light emitting element driving circuit according to the third aspect, the pulse control means includes a correction transistor connected in series with the light emitting element with respect to a power source, The driving signal supplied to the light emitting element is applied to the gate electrode of the correcting transistor by applying a pulsed voltage that gradually decreases from the front end toward the center and gradually increases from the center toward the rear end. A light-emitting element driving circuit is formed.
In the fourth aspect, the light emitting device drive circuit can be easily manufactured.

According to a fifth aspect of the present invention, there are provided a plurality of light emitting elements arranged in a line shape, each light emission amount of which is controlled according to a current value and a pulse width of a drive signal including a pulse group, and a current value of the drive signal. Pulse control means for controlling the light emission, and drive means for supplying the drive signal to each of the light emitting elements, wherein the pulse control means gradually reduces the light emission amount of the light emitting elements from the front end toward the center. In the light emitting element driving circuit, the duty value of the pulse is controlled so as to gradually increase from the central portion toward the rear end.
In the fifth aspect, the same effect as in the first aspect can be obtained.

According to a sixth aspect of the present invention, in the light emitting element drive circuit according to the fifth aspect, the duty value is controlled by supplying a gate electrode of a pulse width control transistor connected in series with the light emitting element. The light-emitting element drive circuit is configured to perform correction data via a pulse width modulation circuit that controls ON / OFF of the pulse width control transistor.
In the sixth aspect, the light emitting device drive circuit can be easily manufactured.

A seventh aspect of the present invention is a display device including the light emitting element driving circuit according to any one of the first to seventh aspects.
In the seventh aspect, it is possible to provide a display device in which variations in light emitting elements are suppressed.

According to an eighth aspect of the present invention, there is provided an electronic apparatus including the display device according to the seventh aspect.
According to the eighth aspect, it is possible to provide an electronic device in which variations in light emitting elements are suppressed.

According to a ninth aspect of the present invention, there is provided a light emitting element that is arranged in a plurality of lines and whose light emission amount is controlled according to a current value and a pulse width constituting the drive signal, In the method of controlling the light emitting element driving circuit, the driving signal having a current value lower than that of the rear edge portion in the intermediate portion is supplied.
In the ninth aspect, variations in the light emitting elements can be corrected without changing the pulse width of the drive signal supplied to the light emitting elements. In addition, since the current values of the front edge portion and the rear edge portion can be made higher than the intermediate portion of the pulse-like drive signal, a sharp latent image can be formed.

According to a tenth aspect of the present invention, there is provided a light emitting element that is arranged in a plurality of lines and whose light emission amount is controlled in accordance with a current value and a pulse width constituting the drive signal. In the method of controlling a light emitting element driving circuit, the driving signal that gradually decreases from the center toward the center and gradually increases from the center toward the rear end is supplied.
In the tenth aspect, the same effect as in the ninth aspect can be obtained.

According to an eleventh aspect of the present invention, a light emitting element that is arranged in a plurality of lines and whose light emission amount is controlled in accordance with a current value and a pulse width of a drive signal composed of a pulse group is used. In the method of controlling the light emitting element drive circuit, the duty value of the pulse is controlled so that the pulse width gradually decreases from the front end toward the center and gradually increases from the center toward the rear end.
In the eleventh aspect, the same effect as in the ninth aspect is obtained.

Hereinafter, the best mode for carrying out the present invention will be described. The description of the present embodiment is an exemplification, and the present invention is not limited to the following description.

(Embodiment 1)
FIG. 1 is a block diagram showing a display device according to Embodiment 1 of the present invention. The display device 10 is used as an exposure head for exposing a photoconductor in an image forming apparatus (printing apparatus) that forms a latent image by exposing the photoconductor. As shown in FIG.
0 includes a head module 20 that emits a light beam according to a desired image toward the surface of the photosensitive member, and a controller 30 that controls the operation of the head module 20.

The head module 20 includes a light emitting unit 22, a drive control unit 24, and a storage device 26. The light emitting unit 22 is a part in which n (n is a natural number) light emitting elements E are arranged in a line along the main scanning direction. The storage device 26 stores light emission characteristic data of each light emitting element E, and includes, for example, an EEP-ROM. The light emission characteristic data is measured in advance.

On the other hand, the controller 30 includes a control unit 31 and a buffer memory 32. Control unit 31
Are connected to the storage device 26 and to the drive control unit 24. And the control part 3
1 acquires the light emission characteristic data of each light emitting element E stored in the storage device 26, calculates correction data Da1 corresponding to the light emission characteristic data of each light emitting element E, and then uses the correction data Da1 as the drive control unit 24. Can be output to. Here, although details will be described later, the correction data Da1 is data for designating a current value of a correction current to be bypassed by the light emitting element E in accordance with the gradation data.

The buffer memory 32 is connected to the drive control unit 24 and can sequentially output the stored display data (gradation data) to the drive control unit 24.

The present invention corrects the variation of the light emission characteristics of each light emitting element E by correcting the shape of the drive signal without changing the pulse width according to the gradation data of the pulsed drive signal supplied to the light emitting element. The correction is characterized by the configuration of the drive control unit 24 and its driving method.

Therefore, the drive control unit 24 will be described in detail. The drive control unit 24 includes a unit drive circuit U
The driving timing and the current value of the driving signal are controlled by n unit driving circuits U each corresponding to a separate light emitting element E, and a driving circuit. The drive control unit 24 may be composed of a plurality of IC chips arranged for each group in which n light emitting elements E are divided into a predetermined number, or one IC for controlling all the light emitting elements E. It may be constituted by a chip.

FIG. 2 is a block diagram showing a specific configuration of a part of the drive control unit 24 and the light emitting element E corresponding to the part. In the drawing, the J-th unit drive circuit U and the light emitting element E (J is an integer satisfying 1 ≦ j ≦ n) are shown, but the configurations of other unit drive circuits U and light emitting elements E are also shown. It is the same. Note that the light emitting element E in the present embodiment is 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.

The drive circuit generates pulse width data Dt, correction pulse width data Dta, and correction current value data Dia based on the gradation data and correction data Da2 output from the controller 30. The unit drive circuit U includes pulse width data Dt, which will be described later, and correction pulse width data D.
A drive signal Xj is generated based on ta and the correction current value data Dia, and is output to the light emitting element E.

FIG. 3 is a timing chart showing the waveform of the drive signal Xj output from the unit drive circuit U. As shown in FIG. 3, the pulse width data Dt is based on the gradation data, and each light emitting element is actually turned on during a period T (hereinafter referred to as “unit period”) T that is a unit of control of each light emitting element E. This is data specifying the time length of the light emission period (that is, the pulse width of the drive signal Xj) T [j], and the correction pulse width data Dta is the current value in the pulse width T [j] which is the time length of the light emission period. Is a data designating a time length (that is, a correction width) Ta [j] for correcting. The correction current value data Dia is based on the gradation data and the correction data Da2, and the correction current value I
This is data for designating a [j]. Here, although details will be described later, correction current value data Dia
Preferably specifies a current value of 10 to 30% of the current value before correction.

As shown in FIG. 2, the unit drive circuit U to which such data is input includes a first current generation circuit 241, a second current generation circuit 242, and a pulse drive circuit 243. The first current generation circuit 241 is means for generating a current having a preset current value Imax.
As the first current generation circuit 241, for example, a DAC (Digit that generates a current having a current value Imax) is used.
al to Analog Converter). Note that the same first current generation circuit 241 is disposed in each unit drive circuit U.

The second current generation circuit 242 is means for generating a current having a corrected current value Ia [j] based on the corrected current value data Dia. Examples of the second current generation circuit 242 include a DAC that generates a current having a correction current value Ia [j] specified by the correction current value data Dia.

On the other hand, the pulse drive circuit 243 adjusts the pulse width (time length of the light emission period) of the drive signal Xj to the pulse width T [j] specified by the pulse width data Dt, and the drive signal Xj
This is a means for correcting the shape of j. As the pulse driving circuit 243, for example, a circuit shown in FIG.

FIG. 4 is a schematic diagram of the pulse driving circuit 243. As shown in FIG. 4, the pulse driving circuit 2
43 has two transistors TR 1 and TR 2, and a current value Imax is supplied from the first current generation circuit 241. As a manufacturing process of TR1 and TR2, a polysilicon layer is formed on a glass substrate using a laser annealing shot.
In addition to the case where the light emitting element E is formed on the same glass substrate using FT (Thin Film Transistor), the case where a semiconductor IC is used may be considered.

The switching transistors TR1 and TR2 are n-channel type. The drain electrode of TR1 is connected to the first current generation circuit 241 while its source electrode is connected to the light emitting element E. The gate electrode of TR1 is connected to the drive circuit, and pulse width data Dt corresponding to the gradation data is supplied. Therefore, when the pulse width data Dt is input to the gate electrode of TR1, a pulse current having a current value Imax flows between the source and drain electrodes of TR1 in accordance with the pulse width data Dt. That is, the gradation is controlled by the pulse width data Dt input to TR1.

The drain electrode of TR2 is connected to the source electrode of TR1, while the source electrode is the second
Are connected to the current generation circuit 242. Similarly to the gate electrode of TR1, the gate electrode of TR2 is connected to the drive circuit, and the correction pulse width data Dta is supplied. Therefore, when the correction pulse width data Dta is input to the gate electrode of TR2, a current of the correction current value Ia [j] flows between the source and drain electrodes of TR2 in accordance with the correction pulse width data Dta. . That is, the current value I flowing between the source and drain electrodes of TR1
Part of the max pulse current will be bypassed. And this pulse drive circuit 24
3, currents I 1, I 2, and Ioled as shown in FIG. 5 flow in the unit drive circuit U by simultaneously driving TR 1 and TR 2.

As described above, according to the display device 10 of the present embodiment, the intermediate portion other than the front edge portion and the rear edge portion of the pulse-shaped drive signal corrected based on the light emission characteristic data of the light emitting element E is used. Since the current Ioled having a low current value can be supplied to the light emitting element E, the pulse width of the pulse current (
It is possible to correct variations in the light emission characteristics of the respective light emitting elements without changing the light emission pulse width), and as a result, it is possible to perform printing with high quality. In addition, since the current values of the leading edge and the trailing edge can be made higher than the intermediate portion of the pulse-like drive signal, there is an effect that a sharp latent image can be formed.

In the present embodiment, the pulse width data Dt, the correction pulse width data Dta, and the correction current value data Dia are generated by the control drive unit, but may be generated by the controller 30.

(Embodiment 2)
In the first embodiment, the drive control unit as described above is used to control the pulsed drive signal Xj supplied to the light emitting element E. However, the light emitting element E is used using the drive control unit described below.
The pulse-shaped drive signal Xj supplied to may be controlled.

FIG. 6 is a block diagram illustrating a configuration of a part of the drive control unit according to the present embodiment and the light emitting element E corresponding to the part. In the drawing, the J-th unit drive circuit U and the light emitting element E (J is an integer satisfying 1 ≦ j ≦ n) are shown, but the configurations of other unit drive circuits U and light emitting elements E are also shown. It is the same. In addition, since constituent elements other than the constituent elements of the drive control unit described below are the same as those of the drive control unit according to the first embodiment, the same reference numerals are given and description thereof is omitted.

The drive control unit according to the present embodiment is supplied with correction data Da2 from a controller (not shown). Here, the correction data Da2 is generated by the controller based on the light emission characteristic data of each light emitting element E stored in the storage device of the head module. Here, although details will be described later, the correction data Da2 is data for specifying a correction amount of the current value supplied to the light emitting element E.

As illustrated in FIG. 6, the drive control unit according to the present embodiment includes a unit drive circuit U and a drive circuit that controls the drive timing of the unit drive circuit U and the current value of the drive signal. The drive circuit is provided with a level voltage generation circuit 246 connected to each unit drive circuit U via a reference voltage line Lr so that the level voltage Vr can be supplied to each unit drive circuit U. It has become. The level voltage generation circuit 246 is a circuit that generates a preset level voltage Vr. The level voltage generation circuit 246 may be common to all the unit drive circuits U, or may be provided for each unit drive circuit U. Here, the level voltage Vr is for setting the current value of the drive signal Xj. The drive circuit generates pulse width data Dt, correction voltage value data Dva, and a reset signal Dp based on gradation data and correction data Da2 output from a controller (not shown). Here, as described above, the pulse width data Dt is the time length of the light emission period in which each light emitting element is actually turned on (
That is, it is data that specifies the pulse width T [j] of the drive signal Xj, and the correction voltage value data Dva is data that specifies the lowest voltage in the intermediate portion of the triangular wave signal, which will be described later, according to the gradation data. It is. The reset signal Dp is input immediately before the pulse width data Dt is input to the unit drive circuit U. The function of the reset signal Dp will be described later.

The unit drive circuit U includes a pulse drive circuit 243A and a triangular wave generation circuit 245 connected to the pulse drive circuit 243A via a triangular wave signal line Lt, and the pulse width data Dt,
Based on the correction voltage value data Dva and the gradation data, a drive signal Xj is generated to generate the light emitting element E.
Output to.

The triangular wave generation circuit 245 is a means for generating a triangular wave signal based on the pulse width data Dt and the correction voltage value data Dva. Examples of the triangular wave generation circuit 245 include a circuit that has a width specified by the pulse width data Dt and generates a triangular wave signal in which the central voltage drops by the voltage specified by the correction voltage value data Dva.

On the other hand, the pulse drive circuit 243A adjusts the pulse width (time length of the light emission period) of the drive signal Xj to the pulse width T [j] specified by the pulse width data Dt, and corrects the shape of the drive signal Xj. Means. As the pulse driving circuit 243A, for example, a circuit shown in FIG.

FIG. 7 is a schematic diagram of the pulse drive circuit 243A. As shown in FIG. 7, the pulse drive circuit 243A has five transistors TR1A to TR5A, and a common power supply voltage Vcc and level voltage Vr are supplied to each unit drive circuit U from a drive circuit (not shown). It has become. In the manufacturing process of TR1A to TR5A, a TFT (Thin Film Transistor) that forms a polysilicon layer on a glass substrate using a laser annealing shot is used to form the light emitting element E on the same glass substrate. The case where a semiconductor IC is used can be considered.

The driving transistor TR1A is a p-channel type, and the switching transistors TR2A to TR5A are n-channel type. The source electrode of TR1A is the power supply voltage Vcc
The drain electrode is connected to the drain electrode of TR2, and current is applied between the source and gate electrodes of TR1A according to the potential applied to the gate electrode of TR1A. It comes to flow. The gate electrode of TR1A is connected to the drain electrode of TR5A via the capacitive element C.

The source electrode of TR2A is connected to the light emitting element E, and its gate electrode is connected to the signal line L2 to which the pulse width data Dt based on the gradation data is input, and is supplied to the light emitting element E by the pulse width data Dt. The pulse width of the current can be controlled. That is, the gradation is controlled by the pulse width data Dt input to TR2A.

The drain electrode of TR3A is connected to the reference voltage line Lr to which the level voltage Vr is applied, while its source electrode is connected to the drain electrode of TR4 together with the gate electrode of TR1A. The source electrode of TR4A is connected to the drain electrode of TR5A. And
The gate electrode of TR3A is connected to the signal line L1 together with the gate electrode of TR4A. Here, the signal line L1 is supplied with a reset signal Dp that is input immediately before the pulse width data Dt is input to the signal line L2. When the reset signal Dp is input to the signal line L1, the capacitive element C is short-circuited to reset the capacitive element C, and the level voltage Vr is applied to the gate electrode of TR1A.

The source electrode of TR5A is connected to the triangular wave signal line Lt, and its gate electrode is connected to the signal line L2 together with the gate electrode of TR2A.

In such a configuration, when the reset signal Dp becomes H level, the n-channel TR3
Since A and TR4A are turned on, the level voltage Vr is applied to the gate electrode of TR1A.

When the reset signal Dp becomes L level, TR3A and TR4A are turned off. At this time, since the input impedance at the gate electrode of TR1A is extremely high, T1
The charge accumulation state at the gate electrode of TR1A at the moment when R3A and TR4A are turned off does not change. That is, the potential of the gate electrode of TR1A at the moment when the reset signal Dp becomes H level is held as it is.

Next, when the pulse width data Dt and the triangular wave signal Dtt are simultaneously at the H level, TR5A
Is turned on, a voltage obtained by superimposing the level voltage Vr applied to the gate electrode of TR1A and the triangular wave signal Dtt is applied to the gate electrode of TR1A. Also,
At the same time, TR5A is turned on, and current flows between the source and drain electrodes of TR1A and between the source and drain electrodes of TR2A. As a result, current Ioled shown in FIG.
Is supplied to the light emitting element E.

Therefore, as with the first embodiment, according to the display device 10 of the present embodiment, the current Ioled that gradually decreases from the front end toward the center and gradually increases from the center toward the rear end is supplied to the light emitting element E. Therefore, as in the first embodiment, the variation in the light emitting element can be corrected without changing the pulse width of the pulse current supplied to the light emitting element E. As a result, high quality printing can be performed. There is an effect. Further, since the current values at the front end and the rear end can be made higher than the central portion of the pulse-like drive signal, there is an effect that a sharp latent image can be formed.

In the present embodiment, the triangular wave generation circuit 245 is used to control the current Ioled so as to gradually decrease from the front end toward the center and gradually increase from the center toward the rear end. Is not particularly limited as long as the current Ioled can be controlled so as to gradually decrease toward the rear end and gradually increase toward the rear end, for example, using a circuit that generates an exponential waveform Also good.

(Embodiment 3)
In Embodiments 1 and 2, the drive control unit as described above is used to control the pulsed drive signal supplied to the light emitting element E. However, the drive control unit shown below is used to control the light emitting element E. You may make it control the drive signal supplied.

FIG. 9 is a block diagram illustrating a configuration of a part of the drive control unit according to the present embodiment and the light emitting element E corresponding to the part. In the figure, only the Jth unit drive circuit U and the light emitting element E (J is an integer satisfying 1 ≦ j ≦ n) are shown, but the configuration of the other unit drive circuit U and the light emitting element E is shown. Is the same. In addition, since constituent elements other than the constituent elements of the drive control unit described below are the same as those of the drive control unit according to the first embodiment, the same reference numerals are given and description thereof is omitted.

The drive control unit according to the present embodiment is supplied with gradation data, correction data Da3, and clock data CK from a controller (not shown) via a drive circuit. The correction data Da3 is data that specifies the duty value of the pulse current supplied to the light emitting element E based on the light emission characteristic data of each light emitting element stored in the storage device of the head module. The clock data CK is data that defines an operation time of a pulse width modulation circuit described later.

As shown in FIG. 9, the drive control unit according to the present embodiment includes a unit drive circuit U and a drive circuit. The drive circuit controls the drive timing of the unit drive circuit U and the current value of the drive signal, and generates light emission data De based on the gradation data supplied from the controller 30. Here, the light emission data De is data specifying the time length (pulse width T [j]) of the light emission period in which each light emitting element is actually turned on according to the gradation data.

On the other hand, the unit drive circuit U includes a current generation circuit 241B, a pulse width modulation control circuit (PWM control circuit) 248, and a pulse drive circuit 243B. The current generation circuit 241B is a means for generating a current having a preset current value Imax. As the current generation circuit 241B,
For example, a DAC that generates a current value Imax may be used. The PWM control circuit 248 is means for generating a pulse group including a plurality of pulses based on the light emission data De, the correction data Da3, and the clock data CK. As a PWM control circuit, for example, light emission data De
And a circuit that defines the width of each pulse group (pulse width T [j]) and the width W of each pulse with a duty value specified by the correction data Da3 and the clock data CK. An example of the pulse driving circuit 243B is the circuit shown in FIG.

FIG. 10 is a schematic diagram of the pulse driving circuit 243B. As shown in FIG. 10, the pulse drive circuit 243B includes a transistor TR1B, and a current having a current value Imax is supplied from the current generation circuit 241B. In the manufacturing process of TR1B, a TFT (Thin Fil) that forms a polysilicon layer on a glass substrate using laser annealing shots.
In addition to the case where it is formed on the same glass substrate as the light-emitting element E using a m Transistor), a semiconductor IC
The case where it uses is considered.

The switching transistor TR1B is an n-channel type. The drain electrode of TR1B is connected to a current generation circuit 241B to which a current having a current value Imax is supplied, while its source electrode is connected to the light emitting element E. The gate electrode of TR1B is connected to the PWM control circuit 248. By controlling the width of the pulse group and the duty value of the pulse by the PWM control circuit 248, as shown in FIG. The light emitting element E can be made to emit light so that the light emission amount of the other intermediate part becomes smaller than the front edge part and the rear edge part of the light emission period of the light emitting element E.

FIG. 11 is a diagram illustrating a relationship between the current I1, the current Ioled, and the light emission amount F [j] of the light emitting element E illustrated in FIG. As shown in FIG. 11, according to the display device of the present embodiment, the width W of the pulse located in the middle part of the pulse group without changing the width of the pulse group (pulse width T [j]).
Since the light emitting element can emit light so that the light emission amount of the light emitting element gradually decreases from the front end toward the center and gradually increases from the center toward the rear end. Similarly, the variation of the light emitting element can be corrected without substantially changing the pulse width T [j] of the pulse current supplied to the light emitting element E, and as a result, high quality printing can be performed. There is an effect. In addition, since the current values of the front edge portion and the rear edge portion can be made higher than the central portion of the pulse-like drive signal, there is an effect that a sharp latent image can be formed.

(Embodiment 4)
In the first embodiment, the current value at the front edge portion and the current value at the rear edge portion of the current supplied to the light emitting element E are symmetric with respect to the central portion of the current. Good. Further, although the width of the front edge portion and the width of the rear edge portion of the current supplied to the light emitting element E are symmetric with respect to the central portion of the current, they may not be symmetric. For example, the current shown in FIG. 12 may be supplied to the light emitting element E by instantaneously changing the timing of the correction pulse width data Dta input to the unit drive circuit U and the current value data Di. Even if it does in this way, the effect similar to Embodiment 1 will be acquired.

(Other embodiments)
In Embodiments 1 to 4, the display device in which a plurality of light emitting elements E are arranged in a line of lines has been described, but the light emitting elements E may be arranged in a plurality of lines. Even if it does in this way, the effect similar to Embodiments 1-4 will be acquired.

<Application example>
<Image forming apparatus>
Next, with reference to FIG. 13, an image forming apparatus which is one aspect of the electronic apparatus according to the invention will be described. This image forming apparatus is a tandem type full-color image forming apparatus using a belt intermediate transfer body system.

In this image forming apparatus, four display devices 10K, 10C, and 10 each having the same configuration.
M and 10Y are four photosensitive drums (image carriers) 110K and 11 having the same configuration.
They are arranged at positions facing the image forming surfaces 110A of 0C, 110M, and 110Y, respectively. The display devices 10K, 10C, 10M, and 10Y are the display devices 10 according to the above embodiments.

As shown in FIG. 13, this image forming apparatus is provided with a driving roller 121 and a driven roller 122, and an endless intermediate transfer belt 120 is wound around these rollers 121 and 122, as indicated by arrows. As shown, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

Around the intermediate transfer belt 120, there are four photosensitive drums 1 each having a photosensitive layer on the outer peripheral surface.
10K, 110C, 110M, and 110Y are arranged at predetermined intervals. Subscript "
"K", "C", "M", and "Y" mean that they are used to form black, cyan, magenta, and yellow visible images, respectively. The same applies to other members. The photosensitive drums 110K, 110C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

Around each photosensitive drum 110 (K, C, M, Y), a corona charger 111 (K, C,
M, Y), a display device 10 (K, C, M, Y), and a developing device 114 (K, C, M, Y) are arranged. The corona charger 111 (K, C, M, Y) uniformly charges the image forming surface 110A (outer peripheral surface) of the corresponding photosensitive drum 110 (K, C, M, Y). The display device 10 (K, C, M, Y) writes an electrostatic latent image on the charged image forming surface 110A of each photosensitive drum. In each display device 10 (K, C, M, Y), the photosensitive drum 110 (K, C) is used.
, M, Y), a plurality of light emitting elements E are arranged along the bus (main scanning direction). The electrostatic latent image is written by irradiating the photosensitive drum 110 (K, C, M, Y) with light by a plurality of light emitting elements E. The developing device 114 (K, C, M, Y) attaches toner as a developer to the electrostatic latent image to thereby develop a visible image (that is, a visible image) on the photosensitive drum 110 (K, C, M, Y). ).

Black, cyan, magenta, and black formed by such a four-color monochromatic image forming station
The yellow visible images are sequentially transferred onto the intermediate transfer belt 120 to be superposed on the intermediate transfer belt 120. As a result, a full-color visible image is formed. Inside the intermediate transfer belt 120, four primary transfer corotrons (transfer devices) 112 (K, C,
M, Y) are arranged. The primary transfer corotrons 112 (K, C, M, Y) are respectively arranged in the vicinity of the photosensitive drums 110 (K, C, M, Y), and the photosensitive drums 110 (
By electrostatically attracting the visible image from K, C, M, Y), the visible image is transferred to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

A sheet 102 as an object (recording material) 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 is subjected to secondary transfer with the intermediate transfer belt 120 in contact with the driving roller 121. Sent to the nip between the rollers 126. 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 by passing through a fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed on the upper part of the apparatus by a paper discharge roller pair 128.

Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. This image forming apparatus is a rotary developing type full-color image forming apparatus using a belt intermediate transfer body system. As shown in FIG. 14, around the photosensitive drum 110, a corona charger 16 is provided.
8, a rotary developing unit 161, the display device 10 according to the above embodiment, and an intermediate transfer belt 169.

The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 110. Display device 1
0 writes an electrostatic latent image on the charged image forming surface 110 </ b> A (outer peripheral surface) of the photosensitive drum 110. In the display device 10, a plurality of light emitting elements E are arranged along the bus (main scanning direction) of the photosensitive drum 110. The electrostatic latent image is written by irradiating the photosensitive drum 110 with light from the light emitting elements E.

The developing unit 161 includes four developing units 163Y, 163C, 163M, and 163K.
The drums are arranged at an angular interval of ° and can be rotated counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toner to the photosensitive drum 110, respectively, and attach the toner as a developer to the electrostatic latent image, thereby causing the photosensitive drum 110 to adhere. A visible image (ie, 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 110 and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 110.

Specifically, the first rotation of the photosensitive drum 110 causes yellow (Y
) An electrostatic latent image for the image is written, a developed image of the same color is formed by the developing device 163Y, and further transferred to the intermediate transfer belt 169. Further, in the next rotation, an electrostatic latent image for a cyan (C) image is written by the display device 10, and a developed image of the same color is formed by the developing device 163C.
The image is transferred to the intermediate transfer belt 169 so as to overlap the yellow visible image. Then, during the four rotations of the photosensitive drum 110 in this manner, the yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169, and as a result, a full-color visible image is formed on the transfer belt 169. Formed on top. 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 formed on the intermediate transfer belt 169 in such a manner that the visible image of the next color is transferred.

The image forming apparatus is provided with a sheet conveyance path 174 through which a sheet passes. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image 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). And
The secondary transfer roller 171 moves the intermediate transfer belt 169 when transferring a full-color visible image 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.
75. Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

Since the image forming apparatus illustrated in FIGS. 13 and 14 uses a light source (exposure means) that employs an OLED element as a light emitting element E, the apparatus is made smaller than when a laser scanning optical system is used. . Note that the display device of the present invention can also be employed in electrophotographic image forming apparatuses other than those exemplified above. For example, the display device according to the present invention can be applied to an image forming apparatus that directly transfers a visible image from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image forming apparatus that forms a monochrome image. Can be applied.

<Others>
In the above, a display device used as an exposure head has been exemplified, but the use of the display device of the present invention is not limited to exposure of a photoreceptor. For example, the display device of the present invention is employed in an image reading device such as a scanner as a line-type optical head (illumination device) that irradiates a reading target such as a document with light. As this type of image reading apparatus, there is a scanner, a copying machine or a reading part of a facsimile, a barcode reader, or a two-dimensional image code reader for reading a two-dimensional image code such as a QR code (registered trademark). In addition, a display device in which a plurality of light emitting elements are arranged in a planar shape,
It is also used as a backlight unit arranged on the back side of the liquid crystal panel.

The display device of the present invention is also used as a display device that displays an image. In this display device, a plurality of light emitting elements are arranged in a matrix in the row direction and the column direction. Then, the scanning line driving circuit selects each row for each unit period (horizontal scanning period), and a drive signal Xj is supplied from the drive control unit 24 to each light emitting element E in the selected row.

Examples of the electronic apparatus in which the display device of the present invention is used for displaying an image include a portable personal computer, a mobile phone, and a personal digital assistant (PDA).
istants), digital still cameras, TVs, video cameras, car navigation devices,
Examples include pagers, electronic notebooks, electronic paper, calculators, word processors, workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices equipped with touch panels, and the like.

1 is a schematic diagram of a display device according to Embodiment 1. FIG. The block diagram which shows a part of drive control part in FIG. The timing chart of each signal in FIG. FIG. 2 is a circuit diagram showing a unit drive circuit in the display device shown in FIG. 1. 4 is a timing chart showing currents flowing through the unit drive circuit shown in FIG. 1. FIG. 6 is a block diagram illustrating a part of a drive control unit according to a second embodiment. FIG. 7 is a circuit diagram showing the unit drive circuit shown in FIG. 6. The timing chart of each signal and electric current Ioled input into a unit drive circuit. FIG. 9 is a block diagram illustrating a part of a drive control unit according to a third embodiment. The circuit diagram which shows the unit drive circuit shown in FIG. The figure which shows the relationship between the electric current which flows through the unit drive circuit, and the light-emission quantity of a light emitting element. 10 is a timing chart of each signal in the fourth embodiment. FIG. 11 is a perspective view showing a specific example (image forming apparatus) of an electronic apparatus according to the invention. FIG. 11 is a perspective view showing a specific example (image forming apparatus) of an electronic apparatus according to the invention. The figure which shows the relationship at the time of changing the light emission pulse width by the conventional correction method.

Explanation of symbols

10 display device, 20 head module, E light emitting element, 24 drive control unit,
U unit drive circuit, 241, 242 current generation circuit, 243 pulse drive circuit,
26 storage devices, 30 controllers, 31 control units, 32 buffer memories,
Xj drive signal, CK clock data, Da correction data, De light emission data, Dia correction current value data, Dp reset signal, Dt pulse width data,
Dta correction pulse width data, Dtt triangular wave signal, Dva correction voltage value data

Claims (11)

A plurality of light emitting elements that are arranged in a line and whose light emission amount is controlled according to a current value and a pulse width constituting a drive signal;
Pulse control means for controlling the current value of the drive signal;
Driving means for supplying the driving signal to each of the light emitting elements,
The light emitting element driving circuit according to claim 1, wherein the pulse control unit controls the driving signal so that a current value in an intermediate portion other than the leading edge portion and the trailing edge portion of the driving signal is lower. The light-emitting element drive circuit according to claim 1,
The pulse control means comprises a bypass having a switching means connected in parallel with the light emitting element,
Driving the light emitting element, wherein the driving signal is controlled by turning on the switching means so that the current value of the intermediate portion other than the leading edge portion and the trailing edge portion of the driving signal is lower. circuit. A plurality of light emitting elements that are arranged in a line and whose light emission amount is controlled according to a current value and a pulse width constituting a drive signal;
Pulse control means for controlling the current value of the drive signal;
Driving means for supplying the driving signal to each of the light emitting elements,
The pulse control means controls the drive signal so that the current value of the drive signal gradually decreases from the front end toward the central portion and gradually increases from the central portion toward the rear end. Drive circuit. In the light emitting element drive circuit according to claim 3,
The pulse control means comprises a correction transistor connected in series with the light emitting element with respect to a power source,
The driving signal supplied to the light-emitting element by applying a pulse-like voltage gradually decreasing from the front end toward the central portion and gradually increasing from the central portion toward the rear end to the gate electrode of the correction transistor. A drive circuit for a light-emitting element, characterized by comprising: A plurality of light emitting elements that are arranged in a line and whose light emission amount is controlled according to the current value and pulse width of a drive signal composed of a pulse group;
Pulse control means for controlling the current value of the drive signal;
Driving means for supplying the driving signal to each of the light emitting elements,
The pulse control means controls the duty value of the pulse so that the light emission amount of the light emitting element gradually decreases from the front end toward the central portion and gradually increases from the central portion toward the rear end. Drive circuit for light emitting element. In the drive circuit for light emitting elements according to claim 5,
The duty value is controlled by correction data supplied to the gate electrode of the pulse width control transistor connected in series with the light emitting element. The ON / OF of the pulse width control transistor
A drive circuit for a light-emitting element, which is configured to be performed via a pulse width modulation circuit for controlling F. A display device comprising the light emitting element driving circuit according to claim 1. An electronic apparatus comprising the display device according to claim 7. A plurality of light emitting elements arranged in a line and whose light emission amount is controlled according to the current value and the pulse width constituting the drive signal are arranged in the middle other than the front edge and the rear edge of the drive signal. A driving method for a light emitting element driving circuit, wherein the driving signal having a low current value is supplied. A plurality of lines are arranged in a line, and the current value of the drive signal gradually decreases from the front end toward the center part to the light emitting element in which each light emission amount is controlled according to the current value and the pulse width constituting the drive signal, A method for controlling a driving circuit for a light emitting element, wherein the driving signal gradually increasing from the central portion toward the rear end is supplied. A plurality of light emitting elements arranged in a line and whose light emission amount is controlled according to the current value and pulse width of the drive signal consisting of a pulse group, the light emission amount of the light emitting element gradually decreases from the front end toward the center. And controlling the duty value of the pulse so as to gradually increase from the central portion toward the rear end.

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