JPH0784069B2 - Driving device for semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used as a light source for a laser printer,
The present invention relates to a semiconductor laser driving device that controls laser light of a semiconductor laser that can perform optical modulation based on data information, and particularly relates to stabilization of optical output.

(Prior Art) Conventionally, for example, a semiconductor laser drive device used in a laser printer or the like performs optical modulation of a semiconductor laser based on an image signal such as character information from an electronic computer, and the modulated optical beam Is irradiated onto the photosensitive drum via the scanning optical system to form an image on the drum according to the image signal.

However, the optical output of the semiconductor laser fluctuates depending on the ambient temperature, which may adversely affect the image quality in a laser printer or the like.

Therefore, in order to solve this problem, the output of the semiconductor laser is detected by a photodetector, the output of the photodetector is compared with a reference voltage, and the difference signal is used to stabilize the output of the semiconductor laser. Is being carried out. Specific examples thereof include those disclosed in JP-A-57-136382. That is, the output of the semiconductor laser is detected by a photodetector, the output of the photodetector is amplified by an amplifier and input to a peak hold circuit, which outputs an image signal between the previous scan and the next scan. Holds the maximum output of the amplifier for each blanking period. Then, the output signal of the peak hold circuit is compared with the reference voltage by the comparator, and the output signal of the comparator is input to the drive circuit of the semiconductor laser, thereby stabilizing the output of the semiconductor laser.

However, in the case of stabilizing by using the peak hold circuit as described above, if a high output that is larger than usual is generated for some reason even during the blanking period temporarily, the high output is held, so that an error easily occurs. In addition, there is a problem that the held voltage is likely to drop and the voltage greatly changes due to the temperature change of the circuit. Further, in the image signal of a printer or the like, the blanking period is between the scanning of the preceding one row and the following one row,
Since the laser output level is determined until the end of the next row based on the peak hold at that time, there is a problem that if the wrong signal is peak-held, the optical output of the entire row is adversely affected. It was

(Object of the Invention) The present invention has been made in view of the above-mentioned problems of the related art. The laser output is sampled in a predetermined relation with data information such as an image signal to make an error less likely to occur, and an error is initially caused. It is an object of the present invention to provide a semiconductor laser driving device which can always obtain a stable laser output against environmental temperature fluctuations by making a correction function work during the same scanning even if a signal is input.

(Structure of the Invention) The present invention relates to a semiconductor laser drive device that outputs laser light according to the current level of a data signal, and a light receiving element that monitors the laser light from the semiconductor laser, and an output beam from the semiconductor laser. And a photodetector which outputs a horizontal sync signal and which outputs a horizontal sync detection signal for operating the semiconductor laser during the blanking period to obtain the horizontal sync signal, and the horizontal sync signal from the photodetector. To a semiconductor laser for horizontal synchronization of the data signal to the semiconductor laser, sampling signal A generating means for outputting the sampling signal A during the output of the horizontal synchronization detection signal, and a predetermined number of high signals in the data signal. Sampling signal B generating means for outputting the sampling signal B when the above continues and the sampling signals A and B are input Then, a sample hold circuit for sampling the monitor current by the light receiving element and a voltage for stabilizing the output of the semiconductor laser by comparing the output from the sample hold circuit with a reference voltage and feeding back the comparison result. And a current conversion circuit.

With this configuration, the laser output is sampled and held during the period in which the detection signal for synchronizing the data information is output and the period in which the signal of the predetermined level is continuously output in the data information. The laser output can always be stabilized by comparing with the voltage.

(Example) Hereinafter, an example in which the apparatus of the present invention is applied to a laser printer will be described with reference to the drawings. FIG. 1 shows the overall configuration of the device of the present invention. Reference numeral 1 denotes a laser drive system in a laser printer main body, which includes a semiconductor laser 2 including a laser diode (LD),
It has a light receiving element 3 for monitoring the laser beam from the semiconductor laser 2 and an output control means 4 for feedback controlling the output of the semiconductor laser 2 based on the monitor current by the light receiving element 3, and further the output from the semiconductor laser 2. A photodetector 5 which receives a beam and outputs a horizontal synchronizing signal HS, a processing circuit 7 to which the horizontal synchronizing signal HS and a signal from a reference clock 6 are input, and a division clock which receives an output from the processing circuit 7. 8 and an OR gate 9, an AND gate 10, an OR gate 1 which receives the output from the processing circuit 7 and outputs it to the output control means 4.
Has 1 etc. The processing circuit 7 outputs to the OR gate 9 a horizontal sync detection signal HDS which turns on the semiconductor laser 2 for a certain period of time to obtain the horizontal cycle signal HS, and also during the period when this horizontal sync detection signal HDS is high. The sampling signal A for sampling is output to the OR gate 11, and the output area of the semiconductor laser 2 is set appropriately so that a video signal is not mixed in a non-image area with a certain relation to the horizontal synchronizing signal HS as described later. The LD control signal for controlling the range is output to the AND gate 10. The horizontal synchronization signal HS is used for horizontal synchronization (beam scanning direction) of the laser printer 1 and the interface 13 described later.

12 is a host computer that outputs image data signals, 13
Is an interface to which the image data signal from the host computer 12, the horizontal synchronizing signal HS and the output from the divided clock 8 are input. The interface 13 is a bit map memory 14 to which the image data from the host computer 12 is input. Has this bitmap memory
14 data are sent to the laser printer 1 side as a video signal VS by a carrier clock. Further, the data newly formed in the processing system 15 based on the bit map memory 14 is sent to the laser printer 1 side as a sampling signal B by a carrier clock. That is, the video signal VS is AND gate 1
The sampling signal B is output to the OR gate 11. Then, an AND gate 10 ANDs the LD regulation signal and the video signal VS, and an OR gate 9 ORs the AND output and the horizontal synchronization detection signal HDS to obtain an LD output signal and output control means. 4 is input. Further, in the OR gate 11, the sampling signal A
Then, the sampling signal B is ORed to obtain the sampling signal and input it to the output control means 4. The sampling signal B is image data in which the binary value is 1, that is, a high number of high signals are continuously arranged in the bit map memory 14, that is, the photoconductor laser 2 is continuously turned on. At this time, new sampling data is formed, and the video signal VS
And is sent to the laser printer 1 side in synchronism with.

FIG. 2 shows a scanning mechanism by the semiconductor laser 2 in the laser printer 1, 16 and 17 are condensers that pass the laser light from the semiconductor laser 2, 18 is a reflecting mirror, and 19 is laser light irradiation, and an image is displayed. It is a photoreceptor to be formed. This photoconductor
A photodetector 5 for obtaining the horizontal synchronizing signal HS is provided near one side end of 19. Since the structure and operation of this scanning mechanism are well known, detailed description thereof is omitted here.

3 to 5 are time charts of various signals for explaining the operation of the driving device for the semiconductor laser 2 in the laser printer 1. In FIG. 3, (a) shows the horizontal synchronization detection signal HDS output from the processing circuit 7,
As can be seen from the figure, the horizontal synchronization detection signal for an appropriate predetermined time
By turning the semiconductor laser 2 ON by setting HDS to High, the horizontal synchronizing signal HS is obtained from the photodetector 5 (Fig. 2) as shown in Fig. 3 (b). T ₁ indicates one scanning time. 6C shows a sampling signal A generated by the processing circuit 7 during the high period of the horizontal sync detection signal HDS, and FIG. 7D shows an LD regulation signal generated in a predetermined relationship with the horizontal sync signal HS. , T ₂ indicates the time corresponding to the length of one scan from the left end to the right end of the paper (not shown) on which the image formed on the photoconductor 19 is transferred. Further, FIG. 7E shows the video signal VS obtained by the interface 13, and T ₃ shows the image area time in one scanning. FIG. 6F shows the sampling signal B formed by the interface 13, which is output when the high signal of the video signal VS continues for a predetermined time or longer as described above.

FIG. 4 explains that the video signal VS is obtained at the interface 13. FIG. 4A shows image data represented by binary values, FIG. 4B shows the video signal VS, and FIG. Indicates.

Further, FIG. 5 shows the sampling signal B in the processing system 15.
(A) is a carrier clock, (b) is image data, (c) is a video signal VS,
(D) shows the sampling data and (e) shows the sampling signal B. As can be seen from the figure, when the binary value is 1, that is, when the high signals are continuously arranged in the bitmap memory (4 in the figure). Or more), and in processing system 15, "1, 1, 1,
"1" is converted into "0,1,1,0" and all the other memories are converted into "0" to form sampling data. A sampling signal B is formed based on this data.

Next, FIG. 6 to FIG. 9 show an example of a concrete circuit configuration of the drive unit for the semiconductor laser 2, particularly the output control means 4. In these figures, the same reference numerals as those used above indicate the same members, and 41 is a sample-hold circuit 41, which receives a sampling signal 42 which is the output of the OR gate 11 of the sampling signal A and the sampling signal B, and switches 41 ( (FIG. 7) is closed for a certain period of sampling so that the sampling voltage based on the monitor current from the light receiving element 3 is held in the capacitor C _a . Reference numeral 43 is an error amplifier to which the sample hold value of the sample hold circuit 41 is input, where it is compared with the reference voltage by the reference voltage circuit 44, and the voltage-current conversion circuit 45 is driven based on the error voltage obtained as a result. The voltage-current conversion circuit 45 controls the current to the semiconductor laser 2. Reference numeral 46 denotes an LD output signal from the OR gate 9, and the semiconductor laser 2 is ON / OFF controlled based on the LD output signal 46. That is, the semiconductor laser 2 has been driven and controlled by transistor TR _1, the is the collector of the transistor TR ₂ which is operated by LD output signal 46 is connected to the base of the transistor TR _1, the transistor TR ₂ Transistor TR ₁ is activated according to ON and OFF. The reference voltage in the reference voltage circuit 44 is the variable resistor VR _a (8th
Figure) is set. In addition, the voltage-current conversion circuit
Transistor TR ₃ (Fig. 9) in 45 is transistor T
The base current (voltage) of R ₁ is controlled, whereby the emitter current of the transistor TR ₁ is adjusted, and the semiconductor laser 2
The drive of is controlled. VR ₁ is a variable resistor for adjusting the output of the semiconductor laser 2 together with the variable resistor VR _a , OP _a (FIG. 9) is an operational amplifier for converting an error voltage into a current, and OP _b (FIG. 8) is a monitor voltage. Is an operational amplifier for amplifying the difference between the reference voltage and the reference voltage. Further, R is a resistor, C is a capacitor, D is a diode, D _z is a Zener diode, and the symbols A to F on the line in FIG. 6 are the symbols shown in FIGS. 7, 8 and 9, respectively. Shows the part corresponding to.

Because of the circuit configuration as described above, for example, when the ambient temperature rises, the semiconductor laser 2 generally tries to reduce the optical output, but if the optical output decreases, the monitor current by the light receiving element 3 decreases. , The hold voltage by the sample and hold circuit 41 is lower than the reference voltage, and therefore the transistor TR in the voltage-current conversion circuit 45 is
The emitter current of transistor TR ₁ increases because the emitter current of ₃ decreases. Thus, the output of the semiconductor laser 2 tends to be kept constant. That is, the optical output of the semiconductor laser 2 can be stabilized against temperature fluctuations.

Particularly in the present invention, as the sampling signal 42, the sampling signal A output when the horizontal period detection signal HDS between one scanning and the next scanning is in the high state, and the high signal in the video signal VS even during one scanning. When the sampling signal A is output, since the monitor current is sampled by both of the sampling signals B output when a predetermined number or more are continuously output, the optical output of the semiconductor laser 2 is stabilized. Even if an erroneous signal is taken in, the sampling signal B
The correction will be applied at the time of outputting, which contributes to the improvement of image quality. Moreover, since the sample and hold is performed, an average signal can be taken in and an error is unlikely to occur.

In the above description of the embodiment, the laser printer 1 is shown as an example. However, the invention can be widely applied to a device for driving a semiconductor laser capable of high-speed optical modulation based on various data information other than the one based on image data. It is possible.

(Effect of the Invention) As described above, according to the present invention, the horizontal synchronization detection signal for turning on the semiconductor laser for a predetermined time is output so that the horizontal sync signal is obtained from the photodetector by receiving the output beam from the semiconductor laser. Sampling of the sampling signal A when the semiconductor laser is driven and the high output of the data signal for driving the semiconductor laser continues for a predetermined time or more, that is, when the semiconductor laser is turned on for a predetermined time or more. The monitor current from the light receiving element that receives the optical output of the semiconductor laser with a signal is sampled and held, and this is compared with the reference voltage, and the semiconductor laser is driven and controlled so that the output of the semiconductor laser becomes constant with the error voltage. is doing.

Therefore, it is possible to reduce fluctuations in the optical output of the semiconductor laser due to changes in the ambient temperature, stabilize the output with respect to temperature, and there is little room for an erroneous signal to enter the output control system. Even if an erroneous signal is input in the previous sampling signal A, it is corrected by the sampling signal B without causing any trouble to the data signal during the scanning, so that the stability of the output is enhanced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an example in which a semiconductor laser driving device of the present invention is applied to a laser printer, FIG. 2 is a schematic configuration diagram of a scanning mechanism portion of the laser printer, and FIGS.
(F) is a time chart of signals of various parts in the semiconductor laser driving device, FIGS. 4 (a), (b), and (c) are explanatory views for similarly obtaining a video signal, and FIGS.
(E) is an explanatory diagram for similarly obtaining the sampling signal B, FIG. 6 is a configuration diagram showing a specific example of the portion of the output control means in the semiconductor laser driving device, and FIG. 7 is a sample hold in FIG. Specific circuit diagram of circuit part, 8th
6 is a concrete circuit diagram of the error amplifier and the reference voltage circuit portion of FIG. 6, and FIG. 9 is a concrete circuit diagram of the voltage-current conversion circuit portion of FIG. 2 ... Semiconductor laser, 3 ... Light receiving element, 4 ... Output control means, 5 ... Photodetector, 7 ... Processing circuit, 12 ... Host computer, 13 ... Interface, 14 ... Bit map memory, 15 …… Processing system, 41 …… Sample hold circuit, 42 …… Sampling signal, 43 …… Error amplifier,
44 …… Reference voltage circuit, 45 …… Voltage-current conversion circuit, HS…
… Horizontal sync signal, HDS… Horizontal sync detection signal.

Claims (1)

[Claims] 1. A semiconductor laser driving device for outputting a laser beam according to a current level of a data signal, wherein a light receiving element for monitoring the laser beam from said semiconductor laser and a horizontal beam receiving an output beam from said semiconductor laser. A photodetector that outputs a sync signal and a horizontal sync detection signal that operates the semiconductor laser during the blanking period to obtain the horizontal sync signal are output, and the horizontal sync signal from the photodetector is input. When a processing circuit for horizontally synchronizing a data signal to the semiconductor laser, a sampling signal A generating means for outputting a sampling signal A during outputting the horizontal synchronization detection signal, and a predetermined number or more of high signals in the data signal. Sampling signal B generating means for outputting the sampling signal B to the sampling signal A and B
Is input, a sample and hold circuit for sampling a monitor current by the light receiving element and an output from the sample and hold circuit are compared with a reference voltage, and the comparison result is fed back to stabilize the output of the semiconductor laser. A semiconductor laser driving device comprising a voltage-current conversion circuit.