JPH06267099A - Driving circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce the thermal load to a medium thereby to improve the repetition characteristic by avoiding constant high-power for every sector in an optical output setting area. CONSTITUTION:To a semiconductor laser driving circuit in the conventional constitution are added hold continuing means 40, 41 for keeping the holding state of a first and a second holding means 17, 26 continuously over a predetermined number of sectors, and current source controlling means 42, 43 for supplying currents from a first and a second current sources 21, 30 to a limited signal recording area in the sector where the hold continuing means 40, 41 keep holding. Since a first controlling voltage VH1 and a second controlling voltage VH2 are continuously held over a predetermined number of sectors at the recording time, constant high-power emission is prevented from every time in the optical output setting area, so that the thermal load to a medium load to a medium is reduced and the repetition characteristic is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for recording a signal on an optical disk having a sector structure or reproducing a signal on a recorded optical disk by using a light spot obtained by narrowing the light of a semiconductor laser. In particular, the present invention relates to a semiconductor laser drive circuit that holds a control voltage corresponding to a desired light output set at the start position of a sector and controls the light output by the held control voltage.

[0002]

2. Description of the Related Art A track of a recordable optical disk used as an external storage device of a computer is divided into recording units called sectors. The sector is roughly divided into an address area indicating an address and a signal recording area for recording a signal. An optical output setting area for setting the optical output of the semiconductor laser at the time of recording is provided between the address area and the signal recording area. The optical output of the recording set in the optical output setting area is modulated by the recording signal and recording is performed in the signal recording area. When the signal recording area ends, the optical output of the semiconductor laser returns from recording to reproduction and reproduces the address area of the next sector. After reading the address information, the optical output for recording is set again in the next optical output setting area, and recording is performed in the signal recording area. Thus, in recording on the optical disk, reproduction of an address, setting of optical output for recording, and recording of a signal are repeated for each sector. The type of optical output set in the optical output setting area differs depending on the medium of the optical disc and the recording method. For a normal write-once type disc or a magnetic field modulated magneto-optical disc, it is only necessary to set one optical output for recording. On the other hand, in a phase change type disc that can be overwritten by one beam and a magneto-optical disc that can be overwritten by optical modulation, it is necessary to set two levels of optical output called bias and peak. In the following description, the first optical output of recording will be referred to as bias, and the second optical output of recording will be referred to as peak.

As one conventional method for controlling such a plurality of light outputs with high accuracy and high speed, Japanese Patent Laid-Open No. 1073/1998 has been proposed.
There is a semiconductor laser drive circuit disclosed in Japanese Patent No. 35. This is because the control voltage when the optical output of the bias is settled to a predetermined value is held in the optical output setting area of the sector, and then the control voltage when the optical output of the peak is settled to a predetermined value is held, and the signal is recorded. In the area, a hold method is used in which the semiconductor laser is modulated by the peak and bias optical outputs by an open loop control system.

One configuration example of the semiconductor laser drive circuit using the conventional hold method will be described with reference to FIG.

In FIG. 7, 1 is a semiconductor laser, and 2 is a photodetector, which generates a monitor current IM according to the optical output of the semiconductor laser 1. 3 is a current-voltage converter, which is a monitor current I
M is converted into a monitor voltage VM by a resistor RI. A reproduction control voltage generation circuit 4 compares the monitor voltage VM with the reproduction reference voltage VP of 7 to generate a reproduction control voltage VSP. The reproduction reference voltage VP is selected by the analog switch 6. The selection is a signal SW that becomes "high" during playback and recording.
It is controlled by P. When the signal SWP is "low", the current of the reproducing current source becomes zero. Hereinafter, all analog switches are turned on when the control terminal is “high” and turned off when the control terminal is “low”. A reproduction hold circuit 8 is composed of an analog switch 9, a capacitor 10, a buffer amplifier 11, and an inverter 32. The analog switch 9 is controlled by the signal HLDP which becomes “high” in the optical output setting area and the signal recording area during recording. During normal reproduction, the signal HLDP is "low", the analog switch 9 is turned on, and the input reproduction control voltage VS
Output P as it is. When recording starts and enters the optical output setting area, the signal HLDP becomes "high", the analog switch 9 is turned off to form an open loop, and the reproduction control voltage VSP is held and the signal VHP is output. The output VHP of the buffer amplifier 11 becomes the control voltage of the reproducing current source 12, and the drive current ILP is passed through the semiconductor laser 1.

Reference numeral 13 denotes a first control voltage generation circuit, which compares the monitor voltage VM with a first reference voltage VW1 of 16 to generate a first control voltage VS1. The first reference voltage VW1 is selected by the analog switch 15. If not selected, the current of the first current source will be zero. The selection is controlled by the signal SW1 having the same operation as the signal HLDP described above. Reference numeral 17 denotes a first hold circuit, which includes an analog switch 18, a capacitor 19, a buffer amplifier 20,
It is composed of an inverter 33. The analog switch 18
It is controlled by the signal HLD1 which becomes “high” after the optical output of the bias is settled in the optical output setting area during recording. At the start of the optical output setting region, the signal HLD1 signal is "low", the analog switch 18 remains on, the input first control voltage VS1 is output as it is, and the bias optical output rises in a closed loop. When the light output with a predetermined bias is reached, the signal HLD1 becomes "high", the analog switch 18 is turned off to form an open loop, and the first control voltage VS1 is held and the signal VH1 is output. The output VH1 of the buffer amplifier 20 becomes the control voltage of the first current source 21, is added to the current ILP of the reproducing current source 12, and the drive current IL1 is passed through the semiconductor laser 1.

A second control voltage generating circuit 22 compares the monitor voltage VM with a second reference voltage VW2 of 25 to generate a second control voltage VS2. The second reference voltage VW2 is selected by the analog switch 24. If not selected, the current of the second current source will be zero. The selection is controlled by the signal SW2 having the same operation as the signal HLD1 described above. 26 is a second hold circuit, which includes an analog switch 27, a capacitor 28, a buffer amplifier 29,
It is composed of an inverter 34. The analog switch 27
It is controlled by a signal HLD2 which becomes “high” after the peak light output is settled in the light output setting area during recording. At the start of the light output setting region, the signal HLD2 signal is "low", the analog switch 27 remains on, the input second control voltage VS2 is output as it is, and the peak light output rises in a closed loop. When the light output of a predetermined peak is reached, the signal HLD2 becomes "high", and the analog switch 27
Turns off to form an open loop, and the second control voltage V
Hold S2 and output signal VH2. The output VH2 of the buffer amplifier 29 becomes the control voltage of the second current source 30, and is added to the current ILP of the reproducing current source 12 and the current IL1 of the first current source 21 to flow the drive current IL2 to the semiconductor laser 1. A modulation circuit 31 modulates the current IL2 in the signal recording area with the recording signal WTDT.

The operation of the semiconductor laser drive circuit configured as above will be described with reference to FIG.

In FIG. 8, from the top, the waveform of the disk area and the optical output, the signal HLDP (SW1), and the signal HLD1.
(SW2), signal HLD2, reproduction control voltage VHP, output VH1 of the first hold circuit 17, and output VH2 of the second hold circuit 26. In the optical output waveform, the optical output for reproduction is omitted for simplicity.

After reproducing the address of sector 1, time t
The optical output setting area is entered from 22, and the signal HLDP becomes “high”. The reproduction control voltage VHP is held in the reproduction hold circuit 8. At the same time, the signal SW1 becomes "high", the first reference voltage VW1 is supplied, and the optical output of the bias rises. When the optical output of the bias is settled at time t23, the signal HLD1 becomes “high”, and the first control voltage V
H1 is held by the first hold circuit 17. At the same time, the signal SW2 becomes "high", the second reference voltage VW2 is supplied, and the peak optical output rises. When the peak optical output is settled at time t24, the signal HLD2 becomes “high”, and the second control voltage VH2 becomes the second hold circuit 26.
Hold on. In the signal recording area from time t24 to time t25, the current IL2 of the second current source 31 is modulated by the recording signal WTDT. Signal HL at time t25
DP, HLD1, and HLD2 are all "low", and the optical output is reproduced by the control of the closed loop. Time t26
After reproducing the address of the sector 2 at time t27, the light output setting area is entered at time t27, the light output is set to the bias and peak again, and then recording is performed in the signal recording area from time t29 to t30.

Thereafter, address reproduction, bias in the optical output setting area, setting of peak optical output, and recording in the signal recording area are repeated.

[0012]

However, in the conventional semiconductor laser drive circuit using the above-mentioned hold method,
Since DC-like light that is not modulated with high peak power is emitted every time in the light output setting region, a large heat load is applied to the medium of the optical disc. Therefore, in a repeatable medium such as a phase change type disk, a large thermal load is repeated in the light output setting area, and as a result, the repeating characteristics deteriorate from the start of the sector. In addition, there is a possibility that the life of the semiconductor laser device may be shortened by causing the light to be emitted in a DC manner at the peak high power.

The present invention solves the above-mentioned problems of the prior art. In the recording, the control voltage is continuously held over a predetermined number of sectors, and the optical output is set to DC in each sector in the optical output setting area.
It is an object of the present invention to provide a semiconductor laser drive circuit that eliminates light emission, reduces a heat load on a medium, and improves repetitive characteristics.

[0014]

In order to achieve this object, a semiconductor laser drive circuit of the present invention corresponds to a photodetector for generating a monitor signal according to the optical output of a semiconductor laser and a first optical output. And a first control voltage generating means for generating a first control voltage by comparing the monitor signal with the first reference voltage in the recording light output setting area. A first holding means for holding the first control voltage, a first current source for adding a current according to an output of the first holding means to a current of a reproducing current source, and flowing the second current source. Second reference voltage generating means for generating a reference voltage corresponding to the optical output of the second and a second reference voltage generating means for comparing the monitor signal with the second reference voltage in the recording light output setting area to generate a second control voltage. Control voltage generating means, and the second Second hold means for holding a control voltage, and a second current source for adding and flowing a current according to the output of the second hold means to the current of the reproducing current source and the current of the first current source. A modulation means for modulating the current of the second current source according to the recording signal in the signal recording area, and the hold states of the first holding means and the second holding means are continued over a predetermined number of sectors. Hold holding means and current source control means for supplying the currents of the first current source and the second current source only in the signal recording area in a section in which the hold operation is continued by the hold continuing means. ing.

[0015]

According to the present invention, with the above-mentioned structure, the hold continuation means continues the hold states of the first hold means and the second hold means over a predetermined number of sectors. The current source control means causes the currents of the first current source and the second current source to flow only in the signal recording area in the section where the hold operation is continued.

Therefore, when the hold state is continued over the sectors, the first hold means and the second hold means hold without setting the first control voltage and the second control voltage each time in the light output setting area. The first to continue
The recording can be performed with the control voltage and the second control voltage. The number of times the first control voltage and the second control voltage are set in the light output setting area decreases according to the number of sectors that continue the hold state.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to the first embodiment of the present invention. What is newly added and changed to FIG. 7, which is a configuration diagram of the conventional example described above, will be described. Reference numerals 40 and 41 denote OR gates serving as a hold continuation means, which take the OR of the signal HLD1 or signal HLD2 and the hold continuation signal CONT, respectively, and output the hold control signal HLD11 or HLD22. Reference numerals 42 and 43 denote switches serving as current control means, which are controlled by a current control signal CRNT. Current control signal CR
When NT is “high”, it is turned on and the current of the current source is supplied to the semiconductor laser 1.

The operation of the semiconductor laser drive circuit of the first embodiment constructed as above will be described with reference to FIG.

In FIG. 2, from the top, the waveform of the disk area and the optical output, the signal HLDP (SW1), and the signal HLD1.
(SW2), signal HLD2, hold continuation signal CON
T, hold control signals HLD11 and HLD22, current control signal CRNT, output VH of the first hold circuit 17
The output VH2 of the first and second hold circuits 26 is shown.

First, the operation of setting the optical output in the normal recording setting section (up to time t5) in sector 1 is exactly the same as the above-mentioned conventional example. From time t2, the optical output setting area is entered, the signal SW1 becomes “high”, and the first reference voltage VW is reached.
1 is supplied and the optical output of the bias rises. Time t
At 3, the first control voltage VH1 is held by the first hold circuit 17, and at the same time, the signal SW2 becomes “high”, the second reference voltage VW2 is supplied, and the peak optical output rises. At time t4, the second control voltage VH2 is held by the second hold circuit 26. Time t4 to time t
In the signal recording area up to 5, the current IL2 of the second current source 31 is modulated by the recording signal WTDT. At time t5, the signals HLDP, HLD1 and HLD2 all become "low", and the optical output is reproduced by the control of the closed loop. From time t1 to t5, the current control signal CRNT is “high”, the first current source 21 and the second current source 30 are controlled by the outputs VH1 and VH2 of the hold circuits 17 and 26, and the currents IL1 and IL2 are changed. Flowing.

At time t5, the hold continuation signal CONT becomes "high". Hold continuation signal CONT and signal HL
Hold control signal HL which is OR with D1 and HLD2
D11 and 22 also become "high". First hold circuit 1
7, the analog switch 18 remains off, and the hold operation of the first control voltage VH1 is continued. Further, the second hold circuit 26 also continues the hold operation of the second control voltage VH2 while the analog switch 27 remains off. The first current source 21 tries to flow the current IL1 corresponding to the control voltage VH1, but the current control signal CRNT becomes “low” at time t5, the switch 42 is turned off, and the current supply is cut off. Further, the current IL2 of the second current source 30 is also cut off when the switch 43 is off. As a result, the normal reproduction light output is emitted at time t5.

In sector 2, the light output setting area in the hold continuation section is entered from time t7. Current source control signal C
Since RNT is “low”, the currents IL1 and IL2 of the first current source 21 and the second current source 30 do not flow into the semiconductor laser 1. Therefore, in the light output setting region, the light output does not rise to the bias or peak light output. When the signal recording area starts at time t9, the current control signal CRN
T becomes “high”, the switches 42 and 43 are turned on, and the current IL of the first current source 21 and the second current source 30 is increased.
1, IL2 are supplied to the semiconductor laser 1, and the optical output is set to the bias and the peak. In the signal recording area from time t9 to time t10, the current I of the second current source 30
L2 is modulated by the recording signal WTDT. At time t10, the signals HLDP, HLD1, and HLD2 all become "low", and the optical output for reproduction emits light under the control of the closed loop.
At the same time, the current control signal CRNT also becomes “low”, the switches 42 and 43 are turned off, and the currents IL1 and IL2 of the first current source 21 and the second current source 30 become the semiconductor laser 1 respectively.
Not supplied to. Further, since the hold continuation signal CONT remains “high”, the first hold circuit 17 keeps the analog switch 18 off and outputs the first control voltage VH1.
The hold operation of is continued. Further, the second hold circuit 26 also continues the hold operation of the second control voltage VH2 while the analog switch 27 remains off.

In sector 3, as in sector 2, no bias or peak optical output is emitted in the optical output setting area. The currents IL1 and IL2 driven by the first control voltage VH1 and the second control voltage VH2 that are continuously held are caused to flow only in the signal recording area by the current control signal CRNT.

When the signal recording area of the sector 3 is completed, the hold continuation signal CONT becomes "low", and the analog switch 18 of the first hold circuit 17 turns on and the first hold circuit 17 turns on.
Control voltage VH1 changes to a direction in which current IL1 becomes zero. Also, in the second hold circuit 26, the analog switch 27 is turned on and the second control voltage VH2 changes to the current IL2.
Changes to zero. When entering the sector 4, it becomes a normal recording setting section, and the bias optical output and the peak optical output rise in the optical output setting area.

As described above, according to the first embodiment, the photodetector (2) for generating the monitor signal according to the optical output of the semiconductor laser, the reproduction reference voltage generating means (7),
A reproduction control voltage generating means (4), a reproduction hold means (8) for holding the reproduction control voltage, a reproduction current source (12) for supplying a current to the semiconductor laser according to the output of the reproduction hold means, A first reference voltage generating means (16) for generating a reference voltage corresponding to the first light output is compared with the monitor signal and the first reference voltage in a recording light output setting area to obtain a first control voltage. A first control voltage generating means (13) for generating, a first holding means (17) for holding the first control voltage, and a current source for reproducing a current according to the output of the first holding means. First current source (21) which is added to the current of the second current and flows, and second reference voltage generating means (2) which generates a reference voltage corresponding to the second light output.
5), second control voltage generating means (22) for comparing the monitor signal with the second reference voltage in the recording light output setting area to generate a second control voltage, and the second control voltage. A second holding means (26) for holding, and a second current flowing according to the output of the second holding means, which is added to the current of the reproducing current source and the current of the first current source and then flows.
Current source (30) and modulation means (3) for modulating the current of the second current source in the signal recording area according to the recording signal.
1), a hold continuation means (40, 41) for continuing the hold states of the first hold means and the second hold means over a predetermined number of sectors, and a section where the hold operation is continued by the hold continuation means. By providing current source control means (42, 43) for supplying the currents of the first current source and the second current source only in the signal recording area, the first source is provided over a predetermined number of sectors during recording. It is possible to keep the control voltage and the second control voltage held, to eliminate the DC light emission of the peak light output every time in the light output setting region, reduce the heat load on the medium, and improve the repeating characteristics.

Next, the configuration of the second embodiment of the present invention will be described with reference to FIG. The configuration of the second embodiment is the first
In this embodiment, the hold continuation means 40 of the first hold circuit 17 and the current control switch 42 are omitted. Therefore, in the light output setting region, the bias light output is emitted every time and a new first control voltage VH1 is held in the first hold circuit 17. The peak light output does not emit in the light output setting area over a predetermined number of sectors.

The operation of the semiconductor laser drive circuit of the second embodiment having the above-mentioned structure will be described with reference to FIG. In the signal of FIG. 4, the hold control signal HLD1
The signals are all the same as those in FIG. 2 for explaining the operation of the first embodiment except that there is no 1.

The operation of setting the optical output in the normal recording setting section in sector 1 and sector 4 is completely the same as in the first embodiment described above and will not be described.

At time t15 when the recording of the sector 1 is completed, the signal HLD1 of the first hold circuit 17 becomes "low", the analog switch 18 is turned on, and the first control voltage VH1 is supplied to the first current source. The current IL1 changes so as to become zero. On the other hand, at time t15, the hold continuation signal CON
T becomes “high”, and the hold control signal HLD22 of the second hold circuit 26 remains “high”. The analog switch 27 of the second hold circuit 26 remains off, and the hold operation of the second control voltage VH2 is continued. Further, at time t15, the current control signal CRNT becomes “low”, and the current IL2 of the second current source 30 is cut off when the switch 43 is off.

The sector 2 is entered, and from time t17, the light output setting area in the hold continuation section is entered. At time t17, the bias optical output rises as in the normal recording setting section. At time t18, the first control voltage VH1 is held by the first hold circuit 17. At time t18, the current control signal CRNT remains “low” and the second current source 30
Current IL2 does not flow into the semiconductor laser 1. Therefore, the peak optical output does not rise, and only the bias optical output emits light.

At time t19, the signal recording area starts, the current control signal CRNT becomes "high", the switch 43 turns on, the current of the second current source 30 is supplied to the semiconductor laser 1, and the optical output peaks. Is set. Unlike the first embodiment, the bias optical output is set every time, so the accuracy of the bias optical output is improved. Since the peak light output current IL2 is added on top of the bias light output current IL1, if the accuracy of the current IL1 is high, as a result, the peak light output accuracy is also high. Therefore, the hold continuation section can be made longer than in the first embodiment. Also,
In the light output setting area, the bias light output is emitted every time,
The value is small compared to the peak light output, and the thermal load on the medium is not a problem.

In the signal recording area from bias time t19 to time 20, the current IL2 of the second current source 30 is modulated by the recording signal WTDT. At time t20, the optical output returns from recording to reproduction. The recording operation of the sector 3 is in the hold continuation section and is exactly the same as that of the sector 2, and the description thereof will be omitted.

As described above, according to the second embodiment, in the semiconductor laser drive circuit of the first embodiment, the hold state of only the second hold means (26) is continued over a predetermined number of sectors. Hold continuation means (4
By providing 1) and the current source control means (43) for supplying the current of the second current source (30) only in the signal recording area in the section where the hold operation is continued by the hold continuing means, 2nd over a certain number of sectors during recording
The control voltage is continuously held, the DC light emission of the peak light output is eliminated every time in the light output setting region to improve the repeating characteristics of the medium, and at the same time, the first control voltage is updated every time in the light output setting region. The accuracy of the bias light output and the peak light output can be improved.

Next, the configuration of the third embodiment of the present invention will be described with reference to FIG. The configuration of the third embodiment is the second
In the second embodiment, the circuit for reproduction and the first light output is shared to simplify the circuit configuration. The reproduction control voltage generation circuit 4 is eliminated and shared by the first control voltage generation circuit 13. Reproduction reference voltage VP and first reference voltage VW1
Are switched by the signal SW1 and the inverter 50. The reproduction hold circuit 8 is eliminated and shared by the first hold circuit 17. The reproduction current source 12 is eliminated and shared by the first current source 21.

The operation of the semiconductor laser drive circuit of the third embodiment having the above-mentioned structure will be described with reference to FIG. The signals of FIG. 6 are all the same as those of FIG. 4 for explaining the operation of the second embodiment except that there is no signal HLDP for holding the reproduction.

First, the operation of setting the optical output in the normal recording setting section in sector 1 will be described. Until time t12, the signal SW1 is "low", the reproduction reference voltage VP is selected,
The optical output of reproduction emits light. From time t12, the optical output setting area is entered, the signal SW1 becomes “high”, and the reproduction reference voltage V
The bias optical output rises by switching from P to the first reference voltage VW1. At time t13, the first control voltage VH
At the same time that 1 is held by the first hold circuit 17, the signal SW2 becomes "high" and the second reference voltage VW2
Is supplied and the peak light output rises. Time t14
Then, the second control voltage VH2 is held by the second hold circuit 26. In the signal recording area from time t14 to time t15, the current IL2 of the second current source 30 is modulated by the recording signal WTDT. Signal HLD at time t15
1 and HLD2 are all "low", and the optical output is reproduced by the closed loop control. From time t11 to time t15, the current control signal CRNT is “high”, the second current source 30 is controlled by the output VH2 of the hold circuit 26, and the current IL2 flows.

At time t15 when the recording of the sector 1 is completed, the hold continuation signal CONT becomes "high", the analog switch 27 of the second hold circuit 26 remains off, and the hold operation of the second control voltage VH2 is continued. To do. Also,
At time t15, the current control signal CRNT becomes “low”, and the current IL2 of the second current source 30 is cut off when the switch 43 is off.

The sector 2 is entered, and from time t17, the light output setting area in the hold continuation section is entered. At time t17, the bias optical output rises as in the normal recording setting section. At time t18, the first control voltage VH1 is held by the first hold circuit 17. At time t18, the current control signal CRNT remains “low” and the second current source 30
Current IL2 does not flow into the semiconductor laser 1. Therefore, the peak optical output does not rise, and only the bias optical output emits light.

At time t19, the signal recording area starts, the current control signal CRNT becomes “high”, the switch 43 is turned on, the current of the second current source 30 is supplied to the semiconductor laser 1, and the optical output peaks. Is set. In the signal recording area from time t19 to time 20, the current IL2 of the second current source 30 is modulated by the recording signal WTDT. At time t20, the optical output returns from recording to reproduction. The recording operation of the sector 3 is in the hold continuation section and is exactly the same as that of the sector 2, and the description thereof will be omitted.

As described above, according to the third embodiment, in the semiconductor laser drive circuit of the second embodiment, the reproduction and the first optical output circuits are shared and the same operation as the second embodiment is performed. The effect can be obtained, the circuit system can be simplified, and the cost can be reduced.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, a hold continuation means for maintaining a hold state over a predetermined number of sectors is added with a limitation of being within a predetermined time range.

The operation of the optical disk device at the time of recording may be such that the sectors are continuously recorded or the sectors are recorded while jumping. When recording sectors continuously, if a predetermined number of sectors are counted, the accurate time can be measured, and the hold continuation means continues the hold operation for a predetermined time and operates correctly. However, when recording is performed while jumping sectors, the time between sectors does not reach a predetermined time, and the time measured by counting the number of sectors is not constant but fluctuates. Therefore, if the hold continuation means is operated by counting the number of sectors, in the worst case where the hold time fluctuates and becomes long, the optical output of the semiconductor laser fluctuates and the recording characteristics deteriorate.

Therefore, in the fourth embodiment, the elapsed time from the start of the hold state is measured. The hold continuation unit keeps the hold state over a predetermined number of sectors within a predetermined range of elapsed time. If the elapsed time is likely to exceed the specified range even if the specified number of sectors is not reached, the hold state is released, the control voltage of the semiconductor laser is reset, and recording is performed while jumping the sectors. However, fluctuations in light output can be suppressed.

In the first to third embodiments, the case where the number of sectors in which the hold operation is continued is three has been described.
The number of sectors is determined by the time during which the hold circuit can hold the control voltage in a stable manner, the time for one sector, the amount of change in the optical output during constant current driving of the semiconductor laser, and the like.
Therefore, if the hold circuit is composed of a digital latch means and a digital-analog converter instead of a capacitor, an analog switch, and a buffer amplifier, the number of sectors for which the hold operation is continued can be increased.

The control voltage generating means compares the analog monitor voltage with the reference voltage to generate the analog voltage. The analog-digital converted monitor voltage and the digital reference voltage are compared with each other by a digital comparator to generate a digital signal. It is also possible to generate the control voltage of. If the generated digital control voltage is latched, digital-analog converted, and used as the control voltage of the current source, the duration of the hold operation can be increased.

Further, in the embodiment, the case where the recording optical output is the first and second kinds has been described, but it is needless to say that the present invention can be applied to the case where the recording optical output is three kinds or more.

[0048]

As described above, in this embodiment, the first control voltage generating means for comparing the monitor signal with the first reference voltage to generate the first control voltage, and the first control voltage are held. The first holding means for controlling the current, the first current source for adding and flowing the current according to the output of the first holding means to the reproduction current, and the second reference voltage by comparing the monitor signal with the second reference voltage. Second control voltage generating means for generating a control voltage, second holding means for holding the second control voltage, current corresponding to the output of the second holding means for reproduction and the first Second current source that is added to the current of the current source to flow, a modulation unit that modulates the current of the second current source in the signal recording region according to a recording signal, the first holding unit, and the second holding unit. The hold status of the holding means is divided into a predetermined number of sectors. And hold continuation means to continue Ri,
In the section where the hold operation is continued by the hold continuation means, the current source control means for supplying the currents of the first current source and the second current source in a limited manner to the signal recording area is provided, so that a predetermined time is provided at the time of recording. The first control voltage and the second control voltage are continuously held for several sectors to eliminate the DC light emission of the peak optical output every time in the optical output setting region, thereby reducing the heat load on the medium and improving the repeatability characteristics. Can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a semiconductor laser drive circuit according to a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the semiconductor laser drive circuit according to the first embodiment.

FIG. 3 is a block diagram showing a configuration of a semiconductor laser drive circuit according to a second embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of a semiconductor laser drive circuit according to the second embodiment.

FIG. 5 is an operation explanatory diagram of a semiconductor laser drive circuit according to a third embodiment of the present invention.

FIG. 6 is an operation explanatory diagram of a semiconductor laser drive circuit according to a third embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a conventional semiconductor laser drive circuit.

FIG. 8 is an operation explanatory diagram of the conventional semiconductor laser drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser 2 photodetector 3 current-voltage converter 4 reproduction control voltage generation circuit 8 reproduction hold circuit 12 reproduction current source 13 first control voltage generation circuit 17 first hold circuit 21 first current source 22 second Control voltage generation circuit 26 second hold circuit 30 second current source 40, 41 hold continuation means 42, 43 current source control means

Claims (4)

[Claims] 1. A semiconductor laser for generating a light beam, a photodetector for generating a monitor signal according to the optical output of the semiconductor laser, and a reproduction reference voltage generating means for generating a reference voltage corresponding to the reproduction optical output. A reproduction control voltage generating means for comparing the monitor signal with the reproduction reference voltage to generate a reproduction control voltage; and inputting the reproduction control voltage, outputting the reproduction control voltage at the time of reproduction, at a sector start position. In the recording light output setting area and in the signal recording area following the recording light output setting area, reproduction holding means for outputting the held reproduction control voltage, and reproduction for supplying a current to the semiconductor laser according to the output of the reproduction holding means A current source, a first reference voltage generating means for generating a reference voltage corresponding to a first light output, and the monitor signal in the recording light output setting area. First generating the first comparison reference voltage first control voltage and
Control voltage generating means and the first control voltage as an input, the first control voltage is output until the first control voltage is settled in the recording light output setting region, and after the settling, the first control voltage is held. A first holding means for outputting a control voltage of 1; a first current source for adding and flowing a current corresponding to the output of the first holding means to the current of the current source for reproduction; Second reference voltage generating means for generating a reference voltage corresponding to the output, and second for generating the second control voltage by comparing the monitor signal with the second reference voltage in the recording light output setting area.
Control voltage generating means and the second control voltage as an input, the second control voltage is output until the second control voltage is settled in the recording light output setting region, and the second control voltage is held after the setting. Second holding means for outputting a control voltage of 2; and a second holding means for adding a current corresponding to the output of the second holding means to the current of the reproducing current source and the current of the first current source and flowing the second current. Current source, a modulation unit that modulates the current of the second current source according to a recording signal in the signal recording region, and a predetermined number of hold states of the first holding unit and the second holding unit. Hold continuation means for continuing over the sector, and a current source control for supplying the currents of the first current source and the second current source only in the signal recording area in a section where the hold operation is continued by the hold continuation means. hand The semiconductor laser drive circuit with and. 2. A hold continuation means for continuing the hold state of only the second hold means instead of continuing the hold states of the first hold means and the second hold means, and the hold continuation means. 2. The semiconductor laser drive circuit according to claim 1, further comprising a current source control unit that supplies the current of the second current source only in the signal recording area in a section where the hold state is continued. 3. A semiconductor laser that generates a light beam, a photodetector that generates a monitor signal according to the optical output of the semiconductor laser, and a first voltage that generates a reference voltage corresponding to reproduction or a first optical output. Inputting the control voltage of the first control voltage generation means, the first control voltage generation means for generating the first control voltage by comparing the monitor signal with the first reference voltage During reproduction and in the recording light output setting area, the first control voltage is output until the reference voltage is switched from the reproduction to the first light output and the first control voltage is settled, and is held after the settling. First holding means for outputting the first control voltage, a first current source for supplying a current to the semiconductor laser according to the output of the first holding means, and a reference corresponding to a second optical output. Second to generate voltage Second reference voltage generating means for comparing the monitor signal with the second reference voltage in the recording light output setting region to generate a second control voltage.
The control voltage generating means and the second control voltage are input, the second control voltage is output until the second control voltage is settled in the recording light output setting area, and the set voltage is held after the setting. Second holding means for outputting a second control voltage, and a current corresponding to the output of the second holding means for the first holding means.
A second current source that flows in addition to the current of the current source; a modulation unit that modulates the current of the second current source according to a recording signal in the signal recording area; and a second holding unit. In the hold continuation unit that continuously continues the hold state over a predetermined number of sectors, and in the section in which the hold state is continued by the hold continuation unit, the current of the second current source is supplied only to the signal recording area. A semiconductor laser drive circuit comprising: a current source control means. 4. The semiconductor laser drive circuit according to claim 1, wherein the hold continuation means continues the hold state over a predetermined number of sectors within a predetermined time range.