JPH01206366A - Semiconductor laser output controller - Google Patents

Abstract

PURPOSE:To set an optical output by a semiconductor laser so as to be faithful to image information and also, to obtain a state that an output fluctuation is corrected by selecting one of driving current setting parts provided by plural stages in accordance with the input of a signal. CONSTITUTION:The title controller is constituted of a driving current setting part provided with plural switches 2, 3 for operating plural constant-current sources, and correcting parts C, C for correcting an output fluctuation caused by thermal coupling of a semiconductor laser for emitting a light beam by a driving current in this setting part. In this state, in accordance with the input of a signal, one of those plural driving current setting parts is selected. In such a way, an image can be reproduced faithfully in accordance with the state of an image to be reproduced, and also, an output fluctuation by the semiconductor at the time of its reproduction can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser output control device used in laser printers, laser fax machines, and the like.

(Prior Art) As is well known, a semiconductor laser, which is one of the elements used as a light source, has a light output whose optical output increases with the oscillation threshold current at a driving current T, as shown in Figure 3. It shows a rise that is faithful to the laser current vs. power characteristics.

For this reason, it is necessary to control the drive current as described above, and as an example of a control device, the optical output of the semiconductor laser is detected by a photodetector circuit, and the result is compared with a standard value by a comparator. There is a device in which an up-down counter is made to count up or down, and a drive current corresponding to the counted value is caused to flow through the semiconductor laser.

In this control device, the drive current is set by the up-down counter mentioned above, and the output of the count value from the counter is determined by the time when the output from the comparator is reversed from a low level or a high level. The optical output of the semiconductor laser is set to a predetermined value based on this standard (for example, Japanese Patent Laid-Open No. 60-1999).
17], Publication No. 863).

However, with such a semiconductor laser output control device, while it is possible to control the optical output to a predetermined value, the setting of the optical output is simply a predetermined drive current when the semiconductor laser is in operation. In other words, in the case of a laser printer, it is only done to obtain a predetermined output of the semiconductor laser at the time of image formation, so it is only necessary to distinguish between the presence or absence of an image. However, there is a problem in that it is not possible to faithfully reproduce the density, halftone, etc. of an image, and as a result, it is not possible to faithfully reproduce the image condition.

Moreover, in such a control device, since the optical output of the semiconductor laser fluctuates due to its thermal coupling, the drive current of the semiconductor laser is adjusted using the method described above.
Even if the driving current is kept constant, the optical output when the semiconductor laser emits light (at the time of rising) becomes larger than the optical output determined by the driving current value of the semiconductor laser and settles to the set value with a certain time constant. In this state, for example, when a semiconductor laser is turned on/off using a modulation signal as shown in FIG. 4, the output of the semiconductor laser changes as shown in the diagram.

Such a phenomenon, that is, output fluctuation, occurs in devices that use semiconductor lasers, such as laser printers.
It may appear as density unevenness in the image, or it may appear as uneven density in the image.
- There is a risk that the image cannot be faithfully reproduced.

(Purpose) Therefore, in view of the problems of the conventional semiconductor laser output control device, it is an object of the present invention to reproduce an image in a device using a semiconductor laser as a light source, for example, by adjusting the state of the image to be reproduced. It is an object of the present invention to provide a semiconductor laser output control device that can faithfully perform the process and correct output fluctuations in the semiconductor laser when reproducing the process.

(Structure) In order to achieve this object, the present invention provides, for example, a multi-stage drive current setting section so that a light output on the semiconductor laser side corresponding to image information including image density etc. can be obtained.
The present invention proposes that any one of the plurality of drive current setting sections can be selected in accordance with the input of a signal.

According to the present invention, it is possible to obtain a light output on the semiconductor laser side according to image information including image density, and to correct the light output to correspond to output fluctuations when the semiconductor laser is actually turned on. You can get it.

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing a semiconductor laser output control device according to an embodiment of the present invention, and in the same figure, the semiconductor laser output control device 1 of the embodiment includes a plurality of constant current sources,
It consists of a drive current control section having a plurality of switches that operate this constant current source, and a correction section that corrects output fluctuations due to thermal coupling of a semiconductor laser emitted by the drive current in this control section.

That is, the semiconductor laser 1 has its cathode connected to one of two transistors 2B, 3A, 3B, 4A, and 4B that constitute a differential amplifier circuit 2.3.4 provided in multiple stages. The above-mentioned differential amplifier circuit 2゜3.4 has a switch circuit that is turned on/off by a code signal, which will be described later, and a 1-transistor 5 on both emitter sides.
．． A constant current circuit consisting of 6.7 is connected. Among these constant current circuits 5, 6, and 7, the constant current circuit 7 is for supplying a bias current to the semiconductor laser 1.

In this embodiment, a 2-bit code signal is input to the above-mentioned differential amplifier circuits 2, 3.4, and this code signal corresponds to image information including image density. It is connected to the base of one transistor 2A in the differential amplifier circuit 2, and is connected to the OR gate 8.
The voltage is applied to the transistors 3A and 4A in the other differential amplifier circuit 3.4 through the circuit. Therefore, the constant ′ according to this code signal? 8. Kaku from flow circuit 5.6.7! III current is semiconductor laser 1
In this embodiment, since it is 2 bits, for example, the following drive current is set, and the optical output of the semiconductor laser 1 due to this drive current is obtained. It is made possible to do so.

(1) When the code signal is rOJ, no current flows to the semiconductor laser.

(2) When the code signal is “1”, (I, + I
th') flows, and the optical output becomes Lo.

(3) When the code signal is “2”, (2I, +
Ith') flows, and the optical output becomes 2×Lo.

(4) If No. 143 is “3”, (3I. +
') and the light output is 3XL.

In this way, the drive current setting section determines the drive current for the semiconductor laser 1 and supplies that current to the semiconductor laser 1. However, the relationship between the current sources for setting the drive current is determined by the bias The current value is determined between each current circuit, except for the constant current circuit 4 that sets the current, so that it is 2'' times the basic current value.

On the other hand, one of the constant current circuits 5, 6.7 that apply a driving current to the semiconductor laser 1 has one of them, that is, the differential amplifier circuit 4 that can apply a bias current to the semiconductor laser 1 has one A correction circuit C1C is provided to correct output fluctuations due to thermal coupling.

That is, this correction circuit C2C has a photodetector 9 consisting of a photodiode that receives the laser beam emitted backward from the semiconductor laser 1, and this photodetector 9 outputs a current proportional to the intensity of the laser beam. do. This current is then converted into a voltage by the amplifier 10 and compared with the base voltage V ref by the comparator 11 . The output voltage of the comparator 11 becomes a high level or a low level depending on the magnitude relationship of the surface input voltage of the comparator 11, and controls the counting mode of the up/down counter 12. for example,
When the intensity of the laser beam from the semiconductor laser 1 is weaker than the basic value, the output of the comparator 11 becomes a low level, and the up/down counter 12 enters a state in which it operates as an up counter.

By the way, an edge detection circuit 13 that controls the enable state of the up/down counter 12 is connected to this up/down counter I2.
3 is 1 For example, as shown in Figure 2.

The comparator 11 is actuated by a signal called a power set signal (indicated by power set in the figure), which disappears when an image is recorded by scanning the photoreceptor with the optical output of the semiconductor laser 1. Detects the rising edge of the up/down counter 12 and outputs a signal instructing the up/down counter 12 to enable and cancel the enable.

Therefore, when scanning a non-photoreceptor, if the intensity of the laser beam from the photodetector 9 is weak when the power set signal is issued, the rising edge of the output from the comparator 11 is detected by the detection circuit 13. In response to the enable signal from the edge detection circuit 13, the up/down counter 12 increases its count value using the tarlock signal from the oscillator 14. This up/down counter 12
The counting output is converted into an analog quantity by the digital/analog converter 14 and applied to the base of the transistor 4A of the operational amplifier that applies a bias current to the semiconductor laser 1. Therefore, the semiconductor laser 1 is turned on/off by the modulation signal, and the count value of the up/down counter 12 gradually increases, thereby increasing the optical output. When the semiconductor laser 1 scans the photoreceptor, the power set signal disappears, the up/down counter 12 becomes disabled, and the output is adjusted! :If f is unfinished, it is interrupted.

When scanning a non-photoreceptor, a signal is output from the power cellar 1, the up/down counter 12 is enabled, and the output adjustment of the semiconductor laser 1 is restarted. After this, when the output of the comparator 11 is inverted from low level to high level, the edge detection circuit 13 detects the rising edge of the output of the comparator 11, and the up/down counter 12 is disabled by the edge detection circuit 3. The up/down counter 12 holds the counted value, and the magnitude of the drive current of the semiconductor laser 1 is held unchanged.

On the other hand, if the output of the comparator If is at a high level when the disabled state of the up/down counter 12 is released, the up/down counter 12 enters the down count mode and counts down the clock. Therefore, the driving current of the semiconductor laser 1 decreases, and the output of the amplifier IO decreases. Then, the output of the amplifier lO is the reference voltage V re
When the output of the comparator 11 is reversed from a high level to a low level because the output of the comparator 11 becomes smaller than f, the edge detection circuit 13 switches the output of the comparator 11
The rising edge of the output of is detected and the up/down counter 12 is returned to the disabled state. Therefore, the up/down counter 12 holds the count value, and the magnitude of the driving current of the semiconductor laser 1 is maintained as it is.

In the above-described embodiment, the power set signal is output in response to scanning of the non-photoreceptor, but the present invention is not limited to this, and the trigger signal may be generated using other methods.

(Effects) As described above, according to the present invention, when performing optical scanning using a semiconductor laser, it is possible to select one of the drive current setting units provided in multiple stages according to the input of a signal,
With this, when the input signal is image information including image density, it becomes possible to set the light output of the semiconductor laser faithfully to the image information. Moreover, when supplying a driving current to such a semiconductor laser, a state is obtained in which the output fluctuations of the semiconductor laser are corrected, so it is possible to reproduce images while eliminating output fluctuations due to thermal coupling of the semiconductor laser. It can be done faithfully.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a semiconductor laser output control device according to an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the main parts in the block diagram shown in FIG. 1, and FIG. A diagram for explaining the relationship between drive current and optical output, and FIG. 4 is a diagram showing the characteristics of a semiconductor laser. 1...Semiconductor laser, 2.3...Differential amplifier circuit forming a switch in the drive current setting section, 4...Differential amplifier circuit forming a switch for setting the bias drive current of the semiconductor laser, 5.6, constant current circuit, 7
... Bias current circuit, 8... OR gate.

Claims (1)

[Scope of Claims] A semiconductor laser output control device receiving signals corresponding to a plurality of light intensity levels, comprising a plurality of constant current sources, switching elements for each of the constant current sources are provided in series, and the above-mentioned A semiconductor laser output control device characterized in that one of the plurality of constant current sources is selected according to a signal.