JPH05102569A - Semiconductor laser driving device - Google Patents

Abstract

PURPOSE:To feed-back control the recording output of a semiconductor laser for stabilizing the same. CONSTITUTION:In order to control the recording output of a semiconductor laser 1, the bottom output of a photodetector 2 detecting the output of the semiconductor laser in the regenerating time is detected by a bottom holding circuit 4 further to be amplifie by an amplifier 9 so that the bottom output may be inputted on the non-inverted input side of a differential amplifier 12 assuming the processed value by the amplifier 9 as a recording output reference voltage. On the other hand, a transfer switch 11 in the regenerating time and recording time is fixed on the inverted input side of the differential amplifier 12 so that, in the regenerating time, the same signal as that on the non-inverted side may be in putted for controlling the rated current source 7 while in the recording time, the peak output from the photodetector 2 may be detected by a peak holding circuit 10 to be transferred by the switch 11 for controlling the rated current source 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device, and more particularly to a semiconductor laser driving device for stabilizing the peak output when the semiconductor laser is pulse-modulated.

[0002]

2. Description of the Related Art As a conventional semiconductor laser driving device, it is used in a write-once type optical disc device which performs recording by irradiating a laser beam formed by directly modulating a semiconductor laser with a recording signal and making a hole in a rotating disc. There is a semiconductor laser driving device that operates.

FIG. 6 is a diagram showing a semiconductor laser drive current-semiconductor laser output characteristic and a photodetector output-semiconductor laser output characteristic. In the figure, a curve A indicates a normal semiconductor laser drive current-semiconductor laser output characteristic, and an arrow G indicates a curve A due to a change in the oscillation threshold of the semiconductor laser.
Changes to curve B and curve C shows the photodetector output. A photodetector is a system in which the optical output of a semiconductor laser is received and the optical output of the semiconductor laser is controlled to be constant by using the output, and there are the following semiconductor laser driving devices.

FIG. 5 is a block circuit diagram of a conventional semiconductor laser driving device. In the figure, 1 is a semiconductor laser,
Reference numeral 2 is a photodetector housed in the same package as the semiconductor laser 1, and 3 is a preamplifier for converting the output of the photodetector 2 into a predetermined voltage level. It constitutes a light detecting means for detecting the. Reference numeral 4 is a bottom hold circuit for holding the bottom output side of the output of the preamplifier 3, 5 is a comparison circuit for comparing the bottom-holded output with a prescribed reproduction output reference voltage (V _r ), and 6 is a semiconductor laser by the output of the comparison circuit 5. 1
, A constant current source 7 for driving the semiconductor laser 1, a constant current source 7 for receiving the recording signal (W _w ) corresponding to the recording level from the microcomputer and superposing the recording current on the semiconductor laser 1, and a constant current source 8 for receiving the recording signal (W _S ). It is a switch that turns on / off the current from the source 7.

Next, the operation will be described. 5 and 6, the optical output of the semiconductor laser 1 at the time of reproduction is constantly monitored by the photodetector 2 and converted into a voltage of a predetermined level by the preamplifier 3. The output of the preamplifier 3 passes through the bottom hold circuit 4 and is compared with the reproduction output reference voltage (V _r ) corresponding to the reproduction output by the comparison circuit 5, and the reproduction current (I _ra ) is supplied by the constant current source 6 and the semiconductor laser 1 is supplied. Is driving. This circuit as a whole constitutes a feedback control system. As a result, the semiconductor laser 1 is maintained at the reference reproduction output (P _r ) shown in FIG.

Next, the operation during recording will be described. The recording signal turns on / off the switch 8, and the switch 8 outputs a voltage (V) corresponding to a predetermined recording level from a microcomputer or the like.
_w ) and a constant recording current (I _wa −
I _ra ) is modulated and superposed on the semiconductor laser 1 as a recording signal current. The output of the semiconductor laser 1 is monitored by the photodetector 2, and the output of the preamplifier 3 converted to a predetermined voltage level by the preamplifier 3 is modulated by the recording signal. The output side is constantly bottom-held and monitored by the bottom hold circuit 4, and compared with the reproduction reference voltage (V _r ) corresponding to the reference reproduction output by the comparison circuit 5, and by the constant current source 6, the same as during reproduction. The semiconductor laser 1 is driven by the output of.

[0007]

Since the conventional semiconductor laser driving device is constructed as described above, it has the following problems. This problem will be described with reference to FIG. In the figure, curves A, B, and C are the same as in the case of FIG. 6 shown in the conventional example. The arrow F indicates the case where the curve B changes to the curve D shown by the broken line due to the fluctuation of the quantization efficiency of the semiconductor laser. In the above conventional semiconductor laser drive device, when the semiconductor laser output characteristic changes from the curve A to the curve B, the drive current of the semiconductor laser is changed to I.
_{Since the} reproduction output was stabilized by moving from _ra to I _rb and the recording current was I _wa −I _ra = I _wb −I _rb , the recording output (P _w ) was also constant. At this time, since the change in the recording output unless the quantization efficiency is not changed (P _w) is suppressed, it has also been stabilized indirectly recording output (P _w).

However, when the quantization efficiency changes as shown by the curve D, the recording output (P _w ) changes corresponding to the change in the quantum efficiency when the recording current (I _wb -I _rb ) is constant. .. Therefore, when the semiconductor laser is modulated by using the conventional LD semiconductor laser driving device, the recording output is controlled only on the bottom output side, so that the recording output is influenced by the temperature characteristic or the secular change of the quantization efficiency of the semiconductor laser. However, there was a problem that it would change.

The present invention has been made to solve the above problems, and an object thereof is to obtain a semiconductor laser driving device in which the recording output of a semiconductor laser is not affected by temperature characteristics or aging. Is.

[0010]

A semiconductor laser drive circuit according to the present invention includes a semiconductor laser, a first current supply means for supplying a reproducing current to the semiconductor laser, and the semiconductor laser drive circuit together with the first current supply means. Second current supply means for supplying a recording current to the laser, photodetection means for detecting the photocurrent by receiving the optical output of the semiconductor laser, and voltage conversion means for converting the photocurrent from the photodetection means into a voltage. A first holding means for holding the reproduction output of the voltage converting means, a second holding means for holding the recording output of the voltage converting means, and a comparison between the output of the first holding means and the reproduction reference voltage. First voltage comparison means, reproduction current control means for controlling the first current supply means with the output of the first voltage comparison means, and amplification means for amplifying the output of the first holding means. A second voltage comparing means for comparing the output of the second holding means with the output of the amplifying means as a recording amplitude reference voltage, and the second current supplying means with the output of the second voltage comparing means. A recording current control means for controlling the recording current control means, and a means for switching the output of the recording amplitude reference voltage and the second holding means is provided before the second voltage comparison means, and the recording amplitude reference voltage is provided. It is intended to be compared with.

[0011]

According to the present invention, during reproduction of the semiconductor laser driving device, a signal corresponding to the recording output is artificially generated from the reproduction output and the recording current supply means is controlled to correspond to the recording current. Feedback control is performed by switching and controlling the recording current supply means.

[0012]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a semiconductor laser, 2
Is, for example, a photodetector housed in the same package as the semiconductor laser 1, and 3 is a preamplifier for converting the output of the photodetector 2 into a predetermined voltage level. The photodetector 2 and the preamplifier 3 output the optical output of the semiconductor laser 1. It constitutes a light detecting means for detecting. Reference numeral 4 denotes a bottom hold circuit that holds the bottom output side of the output of the preamplifier 3, 5 is a comparison circuit that compares the bottom detected output with a specified reproduction output reference voltage (V _r ), and 6 is a semiconductor laser output by the comparison circuit 5. 1, a constant current source for driving 1; a constant current source for superimposing a recording current on the semiconductor laser 1; and a constant current source 7 for receiving a recording signal (W _S ).
A switch for modulating the current from the device, 9 is a bottom detection circuit 5
Of the output of the preamplifier 3 by k times and outputting the output of the preamplifier 3, a peak hold circuit for holding the peak output side of the output of the preamplifier 3, a switch for switching between recording and reproduction in response to the recording gate signal (W _G ), 12 Is a differential amplifier, 1
3, 14, 16, and 17 are resistors, and 15 is a transistor.

Next, the operation will be described with reference to FIGS. 2A to 2F are output waveform diagrams of the respective parts. First, during reproduction, the output of the semiconductor laser 1 is always
It is monitored by the photodetector 2 and converted into a voltage of a predetermined level by the preamplifier 3. The output of the preamplifier 3 passes through the bottom hold circuit 4 and is compared with the reproduction output reference voltage (V _r ) corresponding to the reproduction output by the comparison circuit 5. The constant current source 6 drives the semiconductor laser 1 and the feedback control system as a whole. Is composed of. As a result, the semiconductor laser 1 is maintained at the reference reproduction output (P _r ). Up to this point, it is the same as the conventional example.

Next, the operation during recording will be described. During playback, playback output is P _r (Fig. 3) and recording output is P
_{If w} , the output ratio is k = P _w / P _r . Here, the operational amplifier 9 whose amplification factor is k
Then, the bottom hold circuit output (V _B ) is multiplied by k, and the k-multiplied output of the bottom hold circuit 4 (k · V _B ) is input to the non-inverting input side S _r of the differential amplifier 12, and the reference voltage of the recording power is supplied. And At this time, on the inverting input side of the differential amplifier 12,
The output (k · V _B ) of the bottom hold circuit 4, which is also multiplied by k, is input via the switch 11, and the differential amplifier 12
Let V _o be the output of V _o = V _o = k · V _B −k · V _B = 0.

Here, the bottom hold output (k
V _B ) and the output (V _o ) of the differential amplifier 12 are connected to both ends of resistors 13 and 14 connected in series, and the voltage divided by the resistors 13 and 14 is applied to the transistor 15 and Input to the base of the grounded-emitter circuit composed of resistors 16 and 17, and control the constant current source 7 that supplies the recording current by the collector output of the transistor 15 to set a certain recording current at the time of reproduction. You can

Next, when the recording signal (W _s ) shown in FIG. 2B for explaining the operation at the time of recording is inputted to the switch 8, the recording current determined at the time of reproduction is supplied to the semiconductor laser by the constant current circuit 7. 1 is modulated according to the recording signal (W _s ) and superposed. The signal of the semiconductor laser 1 is monitored by the photodetector 2 and the preamplifier 3, and the monitored signal obtains the bottom value (V _r = V _B ) of the signal modulated by the bottom hold circuit 4, and the signal shown in FIG. Thus, the peak value (V _w = V _p ) of the signal modulated by the peak hold circuit 10 is obtained. At this time, the switch 11 on the reproducing side (S _r ) is turned on by the recording gate signal (W _s ).
Switch to the recording side (S _w ) (Fig. 1). This switch 1
By switching 1 the signal input to the inverting input side of the differential amplifier 12 becomes the peak value (V _w = V _p ) obtained by the peak hold circuit 10, and the output of the differential amplifier 12 (V _o ). A calculation result of V _o = k · V _r −V _w = k · V _B −V _P is output to. At this time, the resistors 13 and 14
Or by adjusting the resistor 13 or the resistor 14 as a variable resistor so that V _o = 0, k · V which is the reference voltage input to the non-inverting input side of the differential amplifier 12 is selected. _r matches V _w input to the inverting input side, and feedback control of the recording output becomes possible. The waveform diagram of the optical output in FIG. 2 shows the output waveform corresponding to V _p and V _B in FIG.

Embodiment 2. In the above embodiment, the amplifier 9 having the amplification factor k is used to multiply the bottom hold output by k times in order to obtain the recording output reference voltage, but the configuration shown in FIG. 4 may be used. In FIG. 4, reference numeral 18 denotes A for converting an analog signal from the bottom hold circuit 4 into a digital signal.
A DC circuit, 19 is a signal processing unit for receiving the digital signal of the ADC circuit 18 to calculate a recording output reference voltage and outputting it as a digital signal, and 20 is for converting the digital output of the signal processing unit 19 as an analog signal into a recording output reference voltage. The DAC circuit is the same as the first embodiment in the other respects. The operation will be briefly described below.

By converting the output obtained from the bottom hold circuit 4 from an analog signal to a digital signal by the ADC circuit 18, calculation in the signal processing unit 19 such as a microcomputer becomes possible, and the signal processing unit 19 executes the above-mentioned operation. Similar to Example 1, the output of the bottom hold circuit 4 is calculated and output k times, and the output from the signal processing unit 19 is output to the DAC circuit 2.
By converting to an analog signal by 0, a recording output reference signal is obtained, and the same effect as that of the above-described first embodiment can be obtained.

[0019]

As described above, according to the present invention, the recording reference voltage obtained by calculating the output of the bottom hold circuit is always input to the non-inverting input side of the differential amplifier, and the bottom hold is applied to the inverting input side. Since the recording reference voltage obtained by calculating the circuit output is input by switching the peak hold circuit output at the time of recording, feedback control of the recording output at the start of recording is possible and recording output setting is easy. become. Further, since the output of the peak hold circuit compared with the recording output reference voltage is almost the same as the recording output reference voltage, there is an effect that the settling time for the target value is shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a semiconductor laser driving device according to an embodiment of the present invention.

FIG. 2 is a voltage waveform diagram for explaining the operation of the semiconductor laser driving device of the present invention.

FIG. 3 is a light output vs. drive current characteristic diagram of a semiconductor laser showing a problem of a conventional semiconductor laser drive device.

FIG. 4 is a diagram showing a semiconductor laser driving device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a conventional semiconductor laser driving device.

FIG. 6 is a diagram showing optical output vs. drive current characteristics of a semiconductor laser.

[Explanation of symbols]

 1 semiconductor laser 2 photodetector 3 preamplifier 4 bottom hold circuit 5 comparison circuit 6 constant current source 7 constant current source 8 switch 9 amplifier 10 peak hold circuit 11 switch 12 differential amplifier

Claims (1)

[Claims] 1. A semiconductor laser, a first current supply means for supplying a reproduction current to the semiconductor laser, and a second current supply means for supplying a recording current to the semiconductor laser together with the first current supply means. A first detecting means for receiving a light output of the semiconductor laser and detecting a photocurrent; a voltage converting means for converting the photocurrent from the light detecting means into a voltage; and a reproduction output of the voltage converting means. Holding means, second holding means for holding the recording output of the voltage converting means, first voltage comparing means for comparing the output of the first holding means with the reproduction reference voltage, and the first voltage The reproduction current control means for controlling the first current supply means by the output of the comparison means, the amplification means for amplifying the output of the first holding means, and the output of the second holding means for the output of the amplification means. To Therefore, the semiconductor laser driving device is provided with a second voltage comparison means for comparing as a recording amplitude reference voltage, and a recording current control means for controlling the second current supply means by the output of the second voltage comparison means. A semiconductor laser drive device, characterized in that a means for switching the recording amplitude reference voltage and the output of the second holding means is provided before the second voltage comparison means, and compares with the recording amplitude reference voltage.