JPH02206187A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To realize a semiconductor laser drive circuit capable of detecting maximum rating of optical output reliably and causing a semiconductor laser to stop emission of light by providing means which make a reference voltage of a comparator detecting a voltage of the driving state variable such that it always corresponds to driving current with which an optical output is close to the maximum rating, according to a relation between the driving current and the optical output of the laser. CONSTITUTION:An AD converter 20 attached additionally to a conventional laser drive circuit converts a monitor voltage VM 5 as an analog signal into a digital signal VAD 21. A latch 23 holds digital data from a CPU 22 for setting an optical output and DA 1 converts an output from the latch 23 into an analog voltage VD 9. A latch 25 holds digital data from the CPU 22 for setting a predetermined reference voltage that a comparator 16 uses as a reference. A DA 2 converts an output from the latch 25 into an analog voltage. An output of the comparator 16 is inputted into the CPU 22. If the CPU 22 detects any abnormal optical output, the CPU 22 causes a semiconductor laser 1 to stop emission of light.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention records information on an optical disk using a fine spot focused on the light of a semiconductor laser, or erases and reproduces recorded information on an optical disk. Among optical disk devices, the present invention particularly relates to semiconductor laser drive ports and paths.

BACKGROUND OF THE INVENTION FIG. 3 shows a block diagram of a conventional semiconductor laser drive circuit and abnormality detection circuit. Reference numeral 1 denotes a semiconductor laser, and a pin diode 2 receives its optical output, and generates a pin current Ip corresponding to the optical output. The pin current Ip of 3 is converted into the monitor voltage VM of 5 by the current/voltage converter 4. A differential amplifier 7 calculates the difference between the monitor voltage VN and the reference voltage VPL 6 for setting the optical output, and outputs the drive voltage V 9. 8 is an analog switch that opens when the output of the AND gate 10 is "HIGH", and activates the differential amplifier 7. When the output of the AND gate 10 is "LOW", the analog switch is closed, the negative input of the differential amplifier 7 is grounded, the output vll becomes a positive power supply voltage, and no current flows through the semiconductor laser 1. One input to the AND gate 10 is the light emission command LDON 11, and the other is the output of a flip-flop (hereinafter referred to as FF) 18 for detecting an abnormality. The light emission command LDON becomes "HIGH" when causing the semiconductor laser 1 to emit light. The FF 18 becomes "HIGH" when the optical output of the semiconductor laser 1 is normal, and becomes "LOW" when it is abnormal. Reference numeral 12 denotes a current source transistor for supplying a current to the semiconductor laser 1, and the current is controlled by a drive voltage V. 13 is a load resistor RLl 14 is a semiconductor laser 1
This is the drive current IL flowing through. 15 is a power supply voltage Vcc. In the following explanation, Vcc specifically refers to +12 volts,
RL is 30 ohm. A comparator 16 compares the drive voltage VD and the slice voltage V s L of 17. The slice voltage V8 is set in accordance with the driving current IL in the vicinity where the optical output of the semiconductor laser 1 exceeds the rated value. Comparator 1
The output of 6 enters FF18 and is latched.

The operation of the conventional example will be explained using FIG. First, when the light emission command LDON of the semiconductor laser in (a) becomes ``HIGH'', the output of the AND gate 10 in (C) becomes ``HIGH'', and the differential amplifier 7 operates.

Then, the drive voltage V of (e) which is the output of the differential amplifier 7
The power supply voltage o decreases from 12 volts to 9 volts, a driving current IL flows through the semiconductor laser 1, and the optical output is set from O (mW) to PpL (mW) as shown in (f). The drive current IL at this time is (12-9-0,8)/assuming that the pace-emitter voltage of the transistor 12 is 0.8 volts.
30=80mA.

The FF output in (b) remains "HIGH" unless the output of the comparator 1B changes from "HIGH" to "LOW".

Here, if the slice voltage VSL of the comparator 16 is detected with the driving current of the semiconductor laser 1 being 220mA, then V8L=12-30*220mA-0.
Set 6=6 volts. Now, if an abnormality occurs in the circuit and the driving current IL of the semiconductor laser increases, the driving voltage vIl in (e) decreases accordingly.

vll, which was 9 volts during normal operation, becomes the slice voltage V$
When L equals 6 volts, comparator 16 operates and (
The comparator output of d) falls from "HIG)I" to "LOW". FF18 latches the output of comparator 16 (b)
FF output goes from HIGH to LOW.FF1
One of the outputs of 8 is directed to the anime game), 10, and the other is directed to the system.

When the FF output of (b) becomes “LOWl”, the AN of (c)
The D output becomes "LOW", the drive voltage Vn which is the output of the differential amplifier 7 becomes the power supply voltage, the drive current IL stops flowing to the semiconductor laser, and the semiconductor laser 1 stops emitting light. The output of FF18 to the system is to notify the system of an abnormality and to activate the light emission command LDON.
As described above, when it is detected that the drive voltage Vn of the semiconductor laser 1 has become below the fixed slice voltage V 8 L set in the comparator 1B, the semiconductor laser 1 has stopped emitting light.

Problem to be Solved by the Invention However, in the above configuration, since the slice voltage V S L of the comparator 16 is fixed, the semiconductor laser 1
If you replace the drive current I'L and drive voltage VD
The problem was that the maximum optical output could not be reliably detected because it differed greatly from laser to laser. This problem will be explained using FIG. 5. FIG. 5 shows the relationship between drive current I and optical output P of two semiconductor lasers, LDI and LD2.

PMIIk is the maximum rated optical output. The optical output PPL is the optical output during normal operation. semiconductor laser LD
In I, the drive current when the optical output PP1 is I IN
Let I SLI be the drive current at P nox. The slice voltage vsL of the comparator 16 that detects an abnormality in the optical output is
It is assumed that the drive voltage VD is set when the drive current is 15LI.

Next, consider a case where semiconductor lasers LD and 2 having different characteristics from the semiconductor laser LD1 are driven. Normal light output PP1
The drive current at the time is IQN Pr+'j) The drive current at the time is 15L2. As you can see from the figure, the semiconductor laser L
The drive current 2 when D2 is normal is larger than the drive current ISL+ when the semiconductor laser D1 is at its maximum rated output. Since the slice voltage V$L of the comparator 16 that detects an abnormality corresponds to the drive current l5LI of the semiconductor laser LDI,
If the semiconductor laser LD2 is driven in this state, the comparator 16 will work even during normal operation, and the semiconductor laser 1 will stop emitting light.

Conversely, if the slice voltage VSL of the comparator 16 is set corresponding to the driving current GL2 at the maximum rated optical output of the semiconductor laser LD2, the optical output of the semiconductor laser LDI becomes the driving current I*LI at the maximum rated optical output. No abnormalities were detected even after this. The comparator 16 detects an abnormality when the optical output of the semiconductor laser LDI becomes several times the maximum rating Pn+x, and at this time the semiconductor laser LDI has already been destroyed and there is no point in detecting an abnormality. .

As described above, if the slice voltage V S L of the comparator 16 that detects an abnormality in the optical output is fixed, the semiconductor laser 1
However, when the characteristics of the drive current and optical output change, abnormalities in the optical output cannot be reliably detected. Furthermore, in the worst case, the semiconductor laser is destroyed and important recorded data on the optical disk is also destroyed.

In addition, even if the semiconductor laser is the same, the drive current will change by twice as much due to temperature and changes over time.
It is difficult to reliably detect the drive current at the maximum rated optical output using a fixed slice voltage.

In view of this, the present invention provides a semiconductor laser that reliably detects an abnormality in which the optical output of a semiconductor laser exceeds its maximum rating, stops the semiconductor laser from emitting light, and prevents the destruction of the semiconductor laser and the data recorded on the optical disk. The purpose is to provide a laser drive circuit.

Means for Solving the Problems The present invention includes a photodetector that receives light from a semiconductor laser and generates a current according to the optical output, and a photodetector that monitors the current of the photodetector to ensure that the optical output of the semiconductor laser reaches a predetermined level. a control circuit that controls a drive stage that causes a current to flow through the semiconductor laser so that the current is supplied to the semiconductor laser; a comparator that compares the voltage or current of the drive stage with a predetermined comparison voltage or current; The semiconductor laser driving circuit includes a variable means for making a change, and a stopping means for stopping driving of the semiconductor laser according to the output of the comparator.

Effect of the Invention The present invention has the above-described configuration, so that the comparison voltage or current of the comparator that detects the voltage or current of the drive stage is adjusted so that the optical output is always near the maximum rating, depending on the relationship between the driving current of the semiconductor laser and the optical output. By varying the current to correspond to the current, it is possible to reliably detect when the optical output of the semiconductor laser has reached its maximum rating, and to stop the semiconductor laser from emitting light to prevent damage to the semiconductor laser and data recorded on the optical disk. Prevent destruction.

Embodiment FIG. 1 shows a block diagram of a semiconductor laser drive circuit in an embodiment of the present invention. For the sake of simplicity, only the parts added to FIG. 3 of the prior art example described above will be explained. 20 is an AD converter which performs AD conversion on the monitor voltage VN, which is an analog signal, and converts it into a digital signal V^1 21. 22 is the CPU
performs general control of the semiconductor laser drive circuit. V^
D is a CPU 22 for setting the optical output of the semiconductor laser 1.
be taken in. 23 is a latch that holds digital data for setting the optical output from the CPU 22.

24 DAI connects the output of latch 23 to analog voltage v11
This is a DA converter that converts The analog voltage VD is a drive voltage that drives the transistor 12 and sets the drive current IL flowing through the semiconductor laser 1. Reference numeral 25 denotes a latch that holds digital data from the CPU 22 that sets a predetermined comparison voltage (hereinafter referred to as slice voltage) Vsc serving as a reference for the comparator 16. DA2 of 26 is a DA converter that converts the output of the latch 25 into an analog voltage VSL. The output of the comparator 16 is input to the CPU 22, and when an abnormality in the optical output is detected, the CPU operates to stop the semiconductor laser 1 from emitting light.

The operation of the semiconductor laser drive circuit of this embodiment configured as described above will be explained using FIG. 2. Second
The figure shows the relationship between the drive current and optical output of the semiconductor laser driven in this example.

In the circuit of this example, two test currents In+ and In2 are set based on the slope of the drive current with respect to the optical output of the semiconductor laser.
Optical output PMI and Pl+ measured by pin current
It is calculated by importing 2 and 2 into the CPU. in particular,
The test current In+ is output to the drive stage as a drive current.

The optical output Pn+ at this time is measured by pin current, AD converted, and taken into the CPU. Next, the test current Ii2 is outputted to the drive stage as a drive current. The optical output Pnp at this time is measured by the pin current, AD converted, and taken into the CPU 22.

From the above data, the slope SLP of the optical output with respect to the drive current of the semiconductor laser 1 is SLP=(pH2-PMI)/(Il+2-IN
I) is calculated by the CPU 22.

After obtaining the slope SLP, the drive current IPL of the optical output PPL during normal operation is =11-IPL=IMl! + (Ppt pH2) /SLP
It is calculated by the CPU 22 as follows. Data on the drive voltage Vn corresponding to the drive current IPL is output from the CPU 22 to the latch 23.

Next, drive current I at maximum rated optical output PIIIX
is calculated similarly.

I $L= I N2+ (PnOx pH2) /
The data of the slice voltage V@L of the comparator 16 corresponding to the SLP drive current ISL is outputted from the CPU 22 to the output terminal 25.

As described above, according to this embodiment, the slope SLP between the optical output and the drive current of the semiconductor laser 1 is measured, and the slope SLP of the semiconductor laser 1 is measured.
Drive current 111L at which the optical output reaches the maximum rating Pr+ox
By calculating the slice voltage V S L of the comparator 16, it is possible to reliably detect that the optical output of the semiconductor laser 1 exceeds the maximum rating, stop the emission of the semiconductor laser 1, and Destruction of the laser 1 and the recorded data on the optical disk can be prevented.

In addition, in the embodiment, the slice voltage V S of the comparator 16
Although the timing for setting L is not specified, it may be set at the time of turning on the power of the optical desk device or at every predetermined cycle. Furthermore, since the optical output is set when the optical disk device starts a recording or erasing operation, the slice voltage VSL of the comparator 16 may be set at that time.

Furthermore, it goes without saying that a configuration may be adopted in which a drive current is detected instead of the drive voltage, and this detected current is compared with a predetermined reference current using a comparator.

As described in detail, according to the present invention, the comparison voltage or current of the comparator for detecting the voltage or current of the drive stage is adjusted so that the optical output is the maximum, depending on the relationship between the driving current of the semiconductor laser and the optical output. By installing a variable means that varies the drive current to correspond to the drive current that is close to the rated value, it is possible to reliably detect that the optical output of the semiconductor laser has reached its maximum rating, stop the semiconductor laser from emitting light, and turn the semiconductor laser off. This has a great practical effect as it can prevent the destruction of the optical disk and the recorded data on the optical disk.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to an embodiment of the present invention, FIG. 2 is a curve diagram showing the relationship between drive current and optical output of the semiconductor laser of the same embodiment, and FIG. 3 is a diagram of a conventional semiconductor laser. FIG. 4 is a block diagram of the drive circuit, FIG. 4 is an operating waveform diagram of the conventional example, and FIG. 5 is a curve diagram showing the relationship between the drive current of the semiconductor laser and the optical output to explain the problems of the conventional example. 1... Semiconductor laser, 2... Pin diode,
4... Current voltage converter, 12... Transistor, 16... Comparator, 20... AD converter,
22...CPU, 23...Latch, 24
...DA converter, 25...latch, 26...
DA converter.

Claims (3)

[Claims] (1) A photodetector that receives light from a semiconductor laser and generates a current according to the optical output; and a photodetector that monitors the current of the photodetector so that the optical output of the semiconductor laser becomes a predetermined value. a control circuit for controlling a drive stage that causes current to flow through the drive stage; a comparator that compares the voltage or current of the drive stage with a predetermined comparison voltage or current; a variable means that varies the predetermined comparison voltage or current; A semiconductor laser drive circuit comprising: a stop means for stopping driving of the semiconductor laser according to an output of a comparator. (2) The semiconductor laser drive circuit according to claim 1, wherein the predetermined comparison voltage or current corresponds to a drive current when the optical output of the semiconductor laser is close to a maximum rating. (3) The variable means measures the slope of the optical output with respect to the driving current of the semiconductor laser, and calculates and sets the driving current of the desired optical output from the measured slope. 2. The semiconductor laser drive circuit according to claim 1, wherein a predetermined comparative voltage or current is calculated and outputted from the calculated voltage and outputted as an input to a comparator.