JP2003205640A - Driver of light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce thermal interference while suppressing lowering of lifetime or variation of driving current characteristics for a plurality of light emitting elements. <P>SOLUTION: When driving currents are fed to light emitting elements 11 and 12 constituting a multibeam diode according to driving signals D1 and D2, bias currents are fed to the light emitting elements 11 and 12 by applying bias signals B1 and B2 during a specified interval T1 before rising of the driving signals D1 and D2 and a specified interval T2 after falling thereof in order to arrange the rising and falling characteristics of the driving currents of the light emitting elements 11 and 12 thus preventing deterioration of image quality. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element driving device, and more particularly to a light emitting element such as a multi-beam laser, which is suitable for driving a plurality of light emitting elements that can be driven independently. A drive device.

[0002]

2. Description of the Related Art A laser printer is generally used for outputting a document in an office in consideration of its printing speed and image quality. In recent years, the output of a color laser printer has been changed with the colorization of the document. It has increased. In particular, in on-demand printing and the like, it is necessary to perform a large amount of printing in a short time, so it is required to improve the printing speed.

In order to improve the printing speed, it is necessary to drastically improve various performances including the improvement of the sensitivity of the photoconductor. Particularly for the exposure system, it is necessary to increase the rotation speed of the polygon motor for scanning the laser beam and the clock frequency of the laser modulation signal. However, it is difficult to further increase the printing speed because there is a limit in increasing the rotation speed of the polygon motor and the clock frequency of the laser modulation signal.

On the other hand, generally, by increasing the number of laser beams and exposing a plurality of lines at the same time, the printing speed is increased without increasing the rotation speed of the polygon motor or the clock frequency of the laser modulation signal. We are trying to improve

As a method of increasing the number of laser beams,
There is a method of combining multiple laser diodes and a method of using a multi-beam laser diode having multiple light emitting elements in one chip. For a small and low-priced laser printer, the optical system configuration is simple and the cost is low. The latter one, which can be converted, is suitable.

However, in the multi-beam laser diode, since the respective light emitting elements are arranged close to each other, the heat generation of the respective light emitting elements interfere with each other and the amount of emitted light fluctuates, which causes thermal interference and the image quality deteriorates. I have something to do.

In order to deal with such a problem, for example, as described in Japanese Patent Application Laid-Open No. 2-150088, a method of constantly applying a bias current to all the light emitting elements constituting a multi-beam laser is proposed. There has been proposed a method of applying a bias current to all the light emitting elements when at least one of the image signals for driving each light emitting element is on.

[0008]

However, as in the former method of the prior art, in the method of constantly applying the bias current to all the light emitting elements, the level of the heat generation state of each light emitting element is kept within a certain range. Although it is possible to reduce the thermal interference, the life of the light emitting element may be significantly reduced.

Further, in the latter method, since a bias current is applied to the light emitting element at any time, the life of the light emitting element is extended, but the light emitting element starts driving (rises) and is driven depending on the driving state of other light emitting elements. At the end (falling), the presence / absence of bias current application changes.

As shown in FIG. 2, the presence or absence of the bias current affects the response of the drive current of the light emitting element, and causes a large difference in the light emission timing and the light emission time width. This difference is remarkable at the time of rising, and in particular, as shown in FIG. 3, in one-dot diagonal lines, image distortion may occur.

An object of the present invention is to provide a light emitting element driving apparatus capable of reducing thermal interference with respect to a plurality of light emitting elements while suppressing a decrease in life and fluctuation of characteristics of driving current.

[0012]

In order to solve the above problems, the present invention generates a drive signal for causing the plurality of light emitting elements to independently emit light based on light emission information regarding the plurality of light emitting elements. Drive signal generation means for applying to each of the plurality of light emitting elements, and bias for generating a bias signal for supplying a bias current to such an extent that the plurality of light emitting elements do not emit light and applying the bias signal to each of the light emitting elements. A bias signal generating means, wherein the bias signal generating means is based on a driving period from a rising edge to a falling edge of a driving signal for any one of the plurality of light emitting elements, as a reference, all or a predetermined period before or after the driving period. In part,
At least one of the light emitting elements constitutes a light emitting element driving device which generates a bias signal for making the state of the bias current the same. The following elements can be added when constructing the light emitting element driving device.

(1) The bias signal generating means applies a bias signal to other light emitting elements during a period in which a drive signal is applied to any one of the light emitting elements.

(2) The bias signal generating means applies to at least one of the light emitting elements at least in all or part of a predetermined period before and after a driving period in which a drive signal is applied to the one of the light emitting elements. A bias signal is applied.

According to the above-mentioned means, since the applied state of the bias current before and after the driving period of each light emitting element is always the same, at least one of the rising and falling characteristics of the driving current can be kept the same. It will be possible. Further, since the bias current is applied to the light emitting element at any time, it is possible to prevent the decrease in the life of the light emitting element while reducing the thermal interference.

Further, according to the present invention, drive signal generating means for generating a drive signal for causing the plurality of light emitting elements to independently emit light based on light emission information regarding the plurality of light emitting elements and applying the drive signal to each of the plurality of light emitting elements. And bias signal generation means for generating a bias signal for flowing a bias current to such an extent that the plurality of light emitting elements do not emit light and applying the bias signal to each of the light emitting elements, and the bias signal generating means. Is based on the drive period from the rise to the fall of the drive signal for each of the light emitting elements, for supplying a bias current to each of the light emitting elements during all or part of the drive period and a predetermined period before and after the drive period. This is a structure of a light emitting element driving device that generates a bias signal.

In constructing the light emitting element driving device, the bias signal generating means is set to each driving period and a predetermined period before the driving period based on the driving period from the rising to the falling of the driving signal for each of the light emitting elements. It can be configured by generating a bias signal for supplying a bias current to each of the light emitting elements during the period.

According to the above means, since the bias current is always applied before and after the driving period of each light emitting element, at least one of the rising and falling characteristics of the driving current can be improved. Further, when the bias current is constantly applied in the period before the driving period of each light emitting element, the rising characteristic of the driving current can be improved. Furthermore, since a bias current is supplied to each light emitting element at any time, it is possible to prevent thermal life reduction of the light emitting element while reducing thermal interference.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. FIG. 1 is a configuration diagram of an exposure system of a laser printer showing an embodiment when the present invention is applied to the laser printer. In FIG. 1, an exposure system of a laser printer includes a multi-beam diode 1, a collimator lens 2, a cylinder lens 3, a polygon mirror 4, an Fθ lens 5, a photoconductor drum 6, a photodetector 7, and an exposure which constitute one element of the multibeam laser. The control circuit 8, the light emitting element drive circuit 9, and the beam detect circuit 10 are provided.

The multi-beam diode 1 is composed of two light-emitting elements (not shown) that can be driven independently, and each light-emitting element has a drive signal for causing each light-emitting element to emit light independently. A bias signal for applying a bias current to the extent that each light emitting element does not emit light is applied. When a drive signal is applied to each light emitting element, a drive current flows through each light emitting element, and two laser beams are emitted from the multi-beam diode 1 toward the collimator lens 2. The two laser beams are once converted into parallel light by the collimator lens 2 and then rotated at a constant rotation speed via the cylinder lens 3 having power only in the sub-scanning direction (radial direction of the photoconductor drum 6). It is incident on the polygon mirror 4. The cylinder lens 3 is for correcting the surface tilt of the polygon mirror 4, and is configured to focus the laser beam on the polygon mirror 4.

The laser beam incident on the polygon mirror 4 is scanned in the rotational direction by changing the reflection direction due to the rotation of the reflection surface, and is incident on the photosensitive drum 6 via the Fθ lens 5. The Fθ lens 5 is configured such that the focal length F changes depending on the scanning angle θ so that the laser beam is focused at all positions on the main scanning line on the photosensitive drum 6.

When the laser beam is sequentially scanned along the axial direction (main scanning direction) of the photoconductor drum 6, the photodetector 7 arranged at a position outside the photoconductor drum 6 within the scanning range of the laser beam. When the laser beam is applied to the photodetector 7, a detection signal is output from the photodetector 7 to the beam detect circuit 10. The beam detect circuit 10 outputs a beam detect signal to the exposure control circuit 8 every time the writing position is detected by the photo detector 7.

The exposure control circuit 8 outputs n as the light emission information.
Data for two lines, line and n + 1 lines, are input, and the exposure control circuit 8 outputs a light emission signal as light emission data or exposure data to the light emitting element drive circuit 9 based on the input data. It is like this.
Further, the exposure control circuit 8 is adapted to sequentially output a horizontal synchronizing signal to a printer controller (not shown) in response to the beam detect signal from the beam detect circuit 10.

The light-emitting element drive circuit 9 is a light-emitting element drive device, and a bias signal and a drive signal for controlling the bias current and drive current of the two light-emitting elements based on the light-emission signal input from the exposure control circuit 8. It is configured to generate a signal and apply a bias signal and a drive signal to each light emitting element.

Specifically, the light emitting element drive circuit 9 is shown in FIG.
As shown in FIG. 3, in order to drive the light emitting elements 11 and 12 independently, the drive current sources 13 and 14, the drive current switching transistors 15 and 16, and the bias current source 1
7, 18, bias current switching transistor 1
9 and 20, and as shown in FIG.
1 delay circuit 21, 22, T2 delay circuit 23, 24, OR
It is configured to include circuits 25, 26, and 27, and is configured to input a light emission signal to the T1 delay circuits 21 and 22, respectively.

When the light emission signal is input, the T1 delay circuits 21 and 22 delay the input light emission signal by a predetermined period (predetermined time), for example, a predetermined period T1, and the delayed light emission signal is the drive signal D1. , D2, and
The delayed light emission signal is output to each of the T2 delay circuits 23 and 24 and the OR circuit 25. In response to the output signals of the T1 delay circuits 21 and 22, the T2 delay circuits 23 and 24 delay the output signals by a predetermined period (predetermined time), for example, a predetermined period T2, and the delayed signals are OR circuits 26, It outputs to 27 respectively. OR
The circuit 26 is a light emission signal input to the T1 delay circuit 21,
The bias signal B1 is output to the base of the transistor 19 in response to the output signal of the T2 delay circuit 23 or the output signal of the OR circuit 25. On the other hand, OR circuit 2
7 outputs a bias signal B2 to the base of the transistor 20 in response to the light emission signal input to the T1 delay circuit 22, the output signal of the T2 delay circuit 24, or the output signal of the OR circuit 25.

The predetermined time T1 is equal to each light emitting element 1 in the period before the driving period in which each light emitting element 11 and 12 is driven.
It is set as a period in which a bias current is supplied to the light emitting elements 11 and 12, and the predetermined period T2 is a period after a drive period in which a drive current is flowing to the light emitting elements 11 and 12 and a bias current to the light emitting elements 11 and 12, respectively. It is set as a period of time for which

The transistor 15 is turned on in response to the drive signal D1, and is configured to supply the drive current from the drive current source 13 to the light emitting element 11. The transistor 16 is turned on in response to the drive signal D2 and supplies the drive current from the drive current source 14 to the light emitting element 12.

On the other hand, the transistor 19 has a bias signal B
In response to 1, the bias current from the bias current source 17 is supplied to the light emitting element 11. Also, the transistor 20 turns on in response to the bias signal B2,
The bias current from the bias current source 18 is applied to the light emitting element 12
It is designed to be applied to.

That is, the T1 delay circuits 21 and 22, the transistors 15 and 16 and the drive current sources 13 and 14 are configured as one element of the drive signal generating means, and the T2 delay circuits 23 and 24 and the OR circuits 25 and 26 are provided. , 27, transistors 19, 20 and bias current sources 17, 18 are configured as one element of the bias signal generating means.

Next, the operation of the light emitting element drive circuit 9 will be described with reference to FIG. A light emission signal is input from the exposure control circuit 8 to the light emitting element drive circuit 9, and, for example, at timing t1.
When the driving of the light emitting element 11 is commanded in the driving period of t4 to t4 and the driving of the light emitting element 12 is commanded in the driving period of timing t2 to t3,
The light emitting element drive circuit 9 generates drive signals D1 and D2 and bias signals B1 and B2 based on the input light emission signal,
The bias signal B1 is applied to the light emitting element 11 to flow the bias current through the light emitting element 11 before the predetermined time T1 from the timing t1, and then the drive signal D1 is supplied at the timing t1.
Is applied to the light emitting element 11 to supply a drive current to the light emitting element 11. Further, the bias signal B2 is applied to the light emitting element 12 from timing t1 to apply a bias current to the light emitting element 12, and the drive signal D is applied to the light emitting element 12 at timing t2.
2 is applied and a drive current is passed through the light emitting element 12.

The bias signal B1 is continuously applied to the light emitting element 11 from the timing t4 to the predetermined period T2, and the bias signal B2 is applied to the transistor 20 from the timing t3 to the timing t4 after elapse of the predetermined period T2. That is, at least a bias current flows through each of the light emitting elements 11 and 12 in the predetermined period T1 before the drive signals D1 and D2 rise, and also in the predetermined period T2 after the drive signals D1 and D2 fall. An electric current flows.

As described above, in the present embodiment, at least the bias current flows during the predetermined period T1 before the rising of the drive signals D1 and D2 of the light emitting elements 11 and 12 and the predetermined period T2 after the falling of the drive signals D1 and D2. 1
The rising and falling characteristics of the drive current of No. 2 can be made uniform, and the disturbance of the image quality can be prevented. Furthermore, since a bias current is applied to each of the light emitting elements 11 and 12 intermittently as needed, it is possible to prevent thermal life reduction of the light emitting elements 11 and 12 while reducing thermal interference.

In the present embodiment, considering that the rising of the drive current is more influential, the respective periods are set so that the predetermined period T1 before rising> the predetermined period T2 after falling. There is.

Further, in the present embodiment, a delay (delay time) T1 is generated in the drive signal for each light emitting element 11, 12 with respect to the light emission signal, but the influence of the delay T1 on the scanning width is slight. , There is no particular problem. If a problem occurs, it can be dealt with by adjusting the generation timing of the horizontal synchronizing signal.

When the driving period of the driving signal D1 is set to timings t6 to t7 and the driving period of the driving signal D2 is set to timings t5 to t8, the bias signals B1 and B2 are generated with reference to the generation timing of the driving signal D2. As a result, the rising and falling characteristics of the drive current for the light emitting elements 11 and 12 can be made uniform.

Further, in the above-described embodiment, the respective periods are set so that the predetermined period T1 before rising> the predetermined period T2 after falling, but the predetermined period T1 before rising ≦ after falling. Each period can be set to be the predetermined period T2. In addition, each predetermined period T1, T2
Can also be set to different values according to the characteristics of the light emitting elements 11 and 12.

Next, another embodiment of the present invention will be described with reference to FIGS. In this embodiment, the delay circuit and the logic circuit are T1 delay circuits 21 and 22, OR circuits 25 and 2,
Drive signals D1 and D of the light emitting elements 11 and 12
2 each light emitting element 1 only in the predetermined period T1 before the rise
A bias signal is applied to 1 and 12, and other configurations are the same as in the above-described embodiment.

In this embodiment, when the driving period of the driving signal D1 is set to t1 to t4 and the driving period of the driving signal D2 is set to timings t2 to t3,
Since the bias current flows through at least the light emitting elements 11 and 12 only during the predetermined period T1 before the rise of the drive signals D1 and D2, the rising characteristics of the drive current of each of the light emitting elements 11 and 12 are simpler than those of the above embodiment. The circuits can be arranged in the same configuration, which can contribute to the improvement of image quality.

In the present embodiment, the driving element 1
Since a bias current is applied to 1 and 12 intermittently at any time, it is possible to prevent reduction in the life of the light emitting elements 11 and 12 while reducing thermal interference.

In the above embodiment, the bias current is supplied to the light emitting elements 11 and 12 during the predetermined period T1 before rising and the predetermined period T2 after falling, but before and after the driving period. It is also possible to make the drive current characteristics of the respective light emitting elements 11 and 12 uniform by not supplying a bias current to them.

Further, the characteristics of the driving current are made uniform by making the bias current flow in either one of the rising and falling periods of the driving signal, and the characteristics of the driving current are made not to flow in the other period. Can also be arranged.

Although the number of light emitting elements is two in each of the above-described embodiments, the present invention can be provided to a device having three or more light emitting elements.

Further, in each of the above-mentioned embodiments, the laser printer has been described, but the present invention is not limited to the laser printer, and the present invention can be applied to a system using other multi-beam lasers such as an optical disk. Is possible.

[0045]

As described above, according to the present invention,
At least one of the rising and falling characteristics of the drive current can be improved, and the thermal interference can be reduced while preventing the life of the light emitting element from being shortened.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an exposure system of a laser printer to which the present invention is applied.

FIG. 2 is a diagram for explaining the response of a drive current depending on the presence or absence of a bias current.

FIG. 3 is a diagram for explaining a dot shape at the time of oblique line recording that occurs depending on the presence or absence of a bias current.

FIG. 4 is a circuit configuration diagram of a drive unit of a light emitting element drive circuit.

FIG. 5 is a configuration diagram of a delay circuit and a logic circuit of the light emitting element drive circuit.

FIG. 6 is a waveform diagram for explaining the operation of the light emitting element drive circuit.

FIG. 7 is a main-portion circuit configuration diagram showing another embodiment of a light-emitting element drive circuit.

FIG. 8 is a waveform diagram for explaining the operation of another embodiment of the light emitting element drive circuit.

[Explanation of symbols]

1 Multi-beam laser diode 11, 12 Light emitting element 13, 14 Drive current source 15, 16 Drive current switching transistor 17, 18 Bias current source 19, 20 Bias current switching transistors 21, 22 T1 delay circuit 23, 24 T2 delay circuit 25, 26, 27, 28 OR circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/113 H04N 1/04 104A (72) Inventor Junichi Shoji 1-1-1 Higashitaga-cho, Hitachi-shi, Ibaraki No. 1 in Hitachi Taga Electronics Co., Ltd. (72) Inventor Kazuyoshi Matsuo 1-1-1 Higashi Taga-cho, Hitachi City, Ibaraki 2C362 AA12 AA16 AA55 AA56 AA59 AA60 AA61 AA75 BA51 BA52 BA66 BA67 2H045 AA01 BA22 BA32 CB61 5C051 AA02 CA07 DB30 DE03 5C072 AA03 DA02 HA02 HA06 HA09 HA13 HB02 XA05 5F073 AB05 AB27 AB29 BA07 EA14 EA17 GA24 GA26 GA27 GA37

Claims (5)

[Claims] 1. A drive signal generating means for generating a drive signal for causing the plurality of light emitting elements to emit light independently based on light emission information about the plurality of light emitting elements and applying the drive signal to the plurality of light emitting elements, respectively. Each of the light emitting elements generates a bias signal for flowing a bias current to such an extent that the light emitting element does not emit light, and applies the bias signal to each of the light emitting elements. Based on the drive period from the rise to the fall of the drive signal for any of the light emitting elements of, the whole or part of a predetermined period before and after that,
A light-emitting element drive device that generates a bias signal for making at least one of the light-emitting elements have the same bias current state. 2. The light emitting element driving device according to claim 1, wherein the bias signal generating means biases other light emitting elements during a period when a drive signal is applied to one of the light emitting elements. A light emitting element drive device characterized by applying a signal. 3. The light-emitting element driving device according to claim 1, wherein the bias signal generating means includes all or part of a predetermined period before and after a driving period in which a driving signal is applied to any one of the light-emitting elements. 2. A light emitting element driving device according to claim 1, wherein a bias signal is applied to at least one of the light emitting elements. 4. A drive signal generating means for generating a drive signal for causing the plurality of light emitting elements to emit light independently based on light emission information about the plurality of light emitting elements and applying the drive signal to the plurality of light emitting elements, respectively. A bias signal generating means for generating a bias signal for flowing a bias current to such an extent that the light emitting element does not emit light, and applying the bias signal to each of the light emitting elements. Generating a bias signal for flowing a bias current to each light emitting element in all or part of each drive period and a predetermined period before and after each drive period based on the drive period from the rise to the fall of the drive signal for the light emitting element. A device for driving a light emitting element. 5. A drive signal generating means for generating a drive signal for independently causing the plurality of light emitting elements to emit light based on light emission information regarding the plurality of light emitting elements and applying the drive signal to the plurality of light emitting elements, respectively. A bias signal generating means for generating a bias signal for flowing a bias current to such an extent that the light emitting element does not emit light, and applying the bias signal to each of the light emitting elements. A light emitting element that generates a bias signal for supplying a bias current to each of the light emitting elements in each of the driving periods and a predetermined period before the driving period based on the driving period from the rising to the falling of the driving signal for the light emitting element. Drive.