JPH06104518A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To eliminate droop or DC light emitting region from a control voltage being held when a semiconductor laser is driven with the control voltage being held at the time of recording. CONSTITUTION:The semiconductor laser drive circuit comprises a differential amplifier 4 for comparing a monitor signal fed from an optical detector with a recording voltage and producing a control voltage, and a sample & hold means for receiving the control voltage from the differential amplifier and producing a control voltage during a sample interval whereas holding a control voltage at the time of setting after switching of optical output from replay to recording through storage of charges during a hold interval. Furthermore, a control voltage being held is subjected to A/D conversion through an A/D converter 30, output therefrom is then latched and subjected to D/A conversion through a D/A converter 31. When modulation is carried out with recording signals, the control voltage is switched to an output subjected to D/A conversion upon completion of D/A conversion.

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, or for erasing, reproducing or overwriting 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 controls the optical output of a semiconductor laser.

[0002]

2. Description of the Related Art In recent years, as one control method of a semiconductor laser drive circuit in an optical disk device, in order to control the optical output with high accuracy and at high speed, when the optical output is set to a predetermined value at the start of recording, A hold method is used in which the control voltage is held and the semiconductor laser is driven by an open loop control system.

A conventional semiconductor laser driving circuit using the hold method will be described. FIG. 13 is a block diagram of a semiconductor laser drive circuit using this conventional hold method.
13, 1 denotes a semiconductor laser, 2 is a light detector for generating a monitor current I _M corresponding to the light output of the semiconductor laser 1, the monitor voltage V by the monitoring current I _M of the resistor RI 3
It is a current-voltage converter (I / V converter) for converting into M.
Reference numeral 4 denotes a differential amplifier, which compares the monitor voltage VM with a reference voltage VR that sets the optical output, and generates a control voltage VS. The reference voltage VR is the power source 5 of the reference voltage VP for reproduction.
And either the power source 6 of the reference voltage VW for recording,
Either of the analog switch 7 and the analog switch 8 is selected. The selection is the recording gate WG that indicates the recording section
And the output of the inverter 10. Note that, hereinafter, all the operations of the analog switch are turned on when the signal of the control terminal is "high" and turned off when the signal is "low".

The analog switch 9 has a hold gate H.
It is controlled by the LD and the inverter 18, and supplies the control voltage VS to the buffer amplifier 12. Analog switch 9,
The capacitor 11 and the buffer amplifier 12 form a sample hold circuit. The sample hold circuit samples the control voltage VS when the analog switch 9 is turned on, and forms a closed loop control system. When the analog switch 9 is off, the control voltage VS is held by the charge stored in the capacitor 11, and the control system changes from the closed loop to the open loop. The output VH of the buffer amplifier 12 becomes the control voltage of the current source, and the resistor 14 (RL)
And a driving current I _LD is supplied to the semiconductor laser 1 by being connected to a transistor 13 which constitutes a constant current source. The drive current I _LD is
It is modulated by two transistors 15 and 16 that perform modulation. The modulation is controlled by the recording signal WDT and the inverter 17.

The operation of the conventional hold system configured as described above will be described with reference to the operation waveform diagram of FIG. In the waveform diagram of FIG. 14, (a) is a recording gate WG showing a recording section, (b) is a hold gate HLD showing a holding section, (c) is a recording signal WDT recorded on an optical disc, and (d) is a differential signal. Amplifier control voltage VS, (e)
Is the control voltage VH of the current source, and (f) is the optical output of the semiconductor laser 1. Up to time t1, there is a reproduction sample section, and up to time t2, a recording sample section. From time t2 to t
Up to 3 is a hold section, and from time t3 is a reproduction sample section.

The reproducing section up to time t1 is the recording gate W
G is "L", and the reference voltage VP for reproducing the analog switch 7 is connected to the reference voltage VR for setting the light output.
The hold gate HLD is "low", the analog switch 9 is turned on, and the sample hold circuit is in the sample state. The output VH of the buffer amplifier 12 is shown in FIG.
As shown in, the control voltage VSP during reproduction is output as it is. The recording signal WDT is “high”, and the drive current I _LD of the constant current source all flows through the semiconductor laser 1. By the closed loop control system, the optical output of the semiconductor laser 1 is set to the reproduction optical output PP set by the reference voltage VP.

At time t1, the recording gate WG becomes "high", and the setting of the optical output PW for recording starts. The reference voltage VW for recording of the analog switch 8 is connected to the reference voltage VR for setting the light output. Hold gate HLD
Remains "low" and the sample and hold circuit is in the sampled state. As the output VH of the buffer amplifier 12, the recording control voltage VSW is sampled. Recording signal WDT
Is "high", and the drive current I _LD of the constant current source all flows through the semiconductor laser 1. Due to the closed loop control system,
The optical output of the semiconductor laser 1 is set to the recording optical output PW set by the reference voltage VW.

At time t2, the recording optical output PW becomes stable, the hold gate HLD becomes "high", and the sample section changes to the hold section. Analog switch 9
Is turned off, and the sample hold circuit is in the hold state. As the output VH of the buffer amplifier 12, the recording control voltage VSW held by the charge accumulation is output. The drive current I _LD is modulated by the recording signal WDT.
As a result, the optical output of the semiconductor laser 1 is set to the optical output PW of the recording in the open loop by the recording control voltage VSW held by the charge accumulation, and is modulated by the recording signal WDT. At time t3, the recording gate WG becomes “low”, and the recording returns to the reproduction. The control of the optical output is switched from the open loop to the closed loop control system.

[0009]

However, in the above-mentioned conventional hold system configuration, the hold section for recording modulation and the control voltage VSW for recording are held by the charge accumulation in the capacitor 11. Therefore, when the recording section becomes long, the control voltage VSW being held changes due to the droop due to the leakage current or the like. Figure 1
As shown in the control voltage VH of 4 (e), the times t2 and t3
Control voltage VS of recording due to drooping over time
W is changing. Since the control system is an open loop between the times t2 and t3, there is a problem that the optical output of the semiconductor laser 1 directly changes due to the change of the control voltage VH of the current source. In order to eliminate the droop of the control voltage VH, the capacity of the hold capacitor 11 may be increased, but in reality the capacity is limited by the response frequency of the servo system and cannot be increased easily.

Therefore, as a method for reducing the influence of the hold type droop due to charge accumulation, the control voltage VS is used.
It is possible to latch the digital data obtained by analog-to-digital conversion of W (hereinafter referred to as A / D conversion) and then perform digital-analog conversion (hereinafter referred to as D / A conversion). D
The / A-converted control voltage VSW does not have the possibility of drooping even if the recording section is long, and the light output can be stably controlled. The method of holding the control voltage VSW by using the A / D conversion, the latch, and the D / A conversion is hereinafter referred to as a digital hold method. A semiconductor laser drive circuit using this digital hold method will be described.

FIG. 15 is a block diagram of a semiconductor laser drive circuit using a digital hold method. FIG. 13 is a configuration diagram of the hold method by charge accumulation described above.
The added and changed parts will be explained. The analog switches 19 and 20 are alternately opened and closed by the hold gate HLD. The A / D converter 21 A / D converts the control voltage VS into digital data VD. The D / A converter 22 converts the digital data VD into analog and outputs the digital hold voltage VHD. Although not shown, the latch circuit that digitally latches the digital data VD is A /
It is assumed to be included in the D converter 21 or the D / A converter 22.

The operation of the digital hold system configured as described above will be described with reference to the operation waveform diagram of FIG. In the waveform diagram of FIG. 16, (a) is a recording gate WG showing a recording section, (b) is a hold gate HLD showing a holding section, (c) is a recording signal WDT recorded on an optical disk, and (d) is a differential signal. Control voltage VS of amplifier 4,
(E) is the digital hold voltage VH of the D / A converter 22
D, (f) are the control voltage VH of the current source selected by the analog switches 19 and 20, and (g) is the optical output of the semiconductor laser 1. Reproduction sample section until time t4, time t
Up to 7 is a sample section of recording. Time t7 to t8
Up to the hold section, from time t8 to the reproduction sample section.

In the reproducing section up to time t4, the recording gate WG is "low" and the optical output of the semiconductor laser 1 is the reproducing optical output PP set by the reference voltage VP, as in the conventional example. The closed loop control system is configured so that

At time t4, the recording gate WG becomes "high" and the setting of the recording optical output PW is started. The reference voltage VW for recording of the analog switch 8 is connected to the reference voltage VR. The optical output of the semiconductor laser 1 is controlled by the closed loop control system so as to become the recording optical output PW set by the reference voltage VW.

As shown in FIGS. 16 (d) and 16 (e), time t
5, when the recording control voltage VSW becomes stable, A /
A / D conversion by the D converter 21 and the D / A converter 22,
Latch and D / A conversion start. At time t6, A /
D conversion, latch, and D / A conversion are completed. The recording control voltage VSW is output to the D / A converter 22 as a digital hold voltage VHD. At time t7, when the hold gate HLD becomes "high", the hold section starts. As a result, the analog switch 19 connected to the current source is turned off and the analog switch 20 is turned on,
The control system becomes an open loop. Control voltage VH of current source
From the control voltage VS of the differential amplifier 4 to the D / A converter 2
It is switched to the digital hold voltage VHD of 2.

The recording signal WDT becomes a modulated signal for recording on the optical disk, and the drive current I _LD is modulated. As a result, the optical output of the semiconductor laser 1 is set to the optical output PW for recording in the open loop by the digital hold voltage VHD that is digitally held, and is modulated by the recording signal WDT. The digital hold voltage VHD has no influence of droop and can keep the optical output PW stable even if the recording section becomes long.

However, in the above digital hold method, the recording control voltage VSW is A / D-converted and D / A-converted when the digital hold voltage VHD is created, and therefore, it is shown in the section of t5 and t6 in FIG. It takes such a time. This settling is a normal A / D converter, D /
If the A converter is used, it takes about several tens of μs. this is,
A wasteful area is required before the recording of the recording signal, which reduces the utilization efficiency of the recording area of the optical disc.
Further, in the settling section, the optical output of recording is DC and emits light for a long time, and considerable energy is injected into the recording film. This causes a large damage to the recording film and causes deterioration of the number of repetitions. In addition, the life of the semiconductor laser may be shortened.

The present invention solves such a problem, and when the semiconductor laser at the time of recording is driven by the open loop by the control voltage held, the droop of the held control voltage is eliminated and the A / D conversion is performed. To provide a semiconductor laser drive circuit capable of improving the utilization efficiency of a recording area of an optical disc, reducing damage to a recording film, and performing stable recording by eliminating a DC light emitting area for recording required for D / A conversion. With the goal.

[0019]

According to a first aspect of the present invention, 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 reproducing or recording light are provided. A reference voltage generator that generates a reference voltage corresponding to the output, a differential amplifier that compares the monitor signal with the reference voltage to generate a control voltage, and the control voltage of the differential amplifier as input, and outputs the control voltage in the sample section. However, in the hold section, the sample-hold means for holding the control voltage at the time of settling after the reference voltage is switched from the reproduction to the optical output for recording by the charge accumulation, and the current flowing through the semiconductor laser according to the output of the sample-hold means Between the power source and the hold section, the modulation means for modulating the current of the current source according to the recording signal, and the control voltage held by the sample hold means are analog. An analog-digital converter for digital conversion, a latch circuit for digitally holding the output of the analog-digital converter, a digital-analog converter for converting the output of the latch circuit to digital-analog, a section of modulation by a recording signal, digital-analog conversion Switching means for switching the drive of the current source from the output of the sample hold means to the output of the digital-analog converter when the digital-analog conversion of the converter is completed.

According to a second aspect of the present invention, a semiconductor laser for generating a light beam, a photodetector for generating a monitor signal according to the light output of the semiconductor laser, and a reference voltage corresponding to the light output for reproduction or recording are provided. , A differential amplifier that compares the monitor signal with the reference voltage to generate a control voltage, and the control voltage of the differential amplifier as input, outputs the control voltage in the sample section, and reproduces it in the hold section. Sample hold means for holding the control voltage at the time of settling after the reference voltage is switched to the optical output for recording by charge accumulation, a current source for supplying a current to the semiconductor laser according to the output of the sample hold means, and a hold section. Between,
Modulating means for modulating the current of the current source according to the recording signal,
An analog-digital converter that performs analog-digital conversion of the control voltage held by the sample-hold means, a latch circuit that digitally holds the output of the analog-digital converter, and a digital-analog converter that performs digital-analog conversion of the output of the latch circuit, An addition unit that adds the output of the digital-analog converter to the charge accumulation point of the sample-hold unit that holds the control voltage when the digital-analog conversion of the digital-analog converter is completed during the period of modulation by the recording signal. Be prepared.

According to the invention of claim 7 of the present application, 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 reference corresponding to the reproduction or the first optical output. A first reference voltage generating means for generating a voltage, a first differential amplifier for comparing a monitor signal with the first reference voltage to generate a first control voltage, and a control voltage for the first differential amplifier. As input, the first in the first sample interval
And a first sample-hold means for holding the first control voltage during settling after the reference voltage is switched from the reproduction to the first optical output in the first hold section by charge accumulation. A first current source for supplying a current to the semiconductor laser according to the output of the first sample and hold means;
A first analog-digital converter for analog-digital converting the first control voltage held by the first sample-hold means, and a first latch circuit digitally holding the output of the first analog-digital converter, A first digital-analog converter for digital-analog converting the output of the first latch circuit, a second reference voltage generating means for generating a reference voltage corresponding to the second optical output, a monitor signal and a second signal.
A second differential amplifier that generates a second control voltage by comparing the reference voltages of the second differential amplifier and the control voltage of the second differential amplifier,
In the second sample section, the second control voltage is output and the second control voltage is output.
In the hold section, the second sample hold means for holding the second control voltage at the time of settling after the reference voltage is switched to the second optical output by charge accumulation and the output of the second sample hold means A second current source for adding the current to the current of the first current source and flowing the current; a second hold section; a modulation means for modulating the current of the second current source according to the recording signal; A second analog-digital converter that performs analog-digital conversion on the second control voltage held by the sample-hold means, a second latch circuit that digitally holds the output of the second analog-digital converter, and a second The second that converts the output of the latch circuit to digital-analog
When the digital-analog converter of the first digital-analog converter is completed, and the digital-analog conversion of the first digital-analog converter is completed during the period of modulation by the recording signal, the first current source is driven from the output of the first sample-hold means to The first switching means for switching to the output of the first digital-analog converter, the section of the modulation by the recording signal, and the second current source is driven when the digital-analog conversion of the second digital-analog converter is completed. Second switching means for switching the output of the second sample-hold means to the output of the second digital-analog converter.

According to an eighth aspect of the present invention, in the semiconductor laser drive circuit according to the seventh aspect, the first switching means and the second switching means are provided.
In place of the switching means, the section of the modulation by the recording signal, the first section
When the digital-analog conversion by the digital-analog converter is completed, the output of the first digital-analog converter is added to the charge accumulation point of the first sample-hold means that holds the first control voltage. When the second analog-to-digital converter completes the digital-analog conversion by the second digital-analog converter, the charge accumulation point of the second sample-hold means that holds the second control voltage Second adding means for adding the outputs of the second digital-analog converter.

[0023]

The invention according to claim 1 of the present application has the above-mentioned structure.
The control voltage obtained by comparing the monitor signal of the photodetector and the reference voltage controls the optical output of the semiconductor laser in a closed loop to emit the optical output of recording. When the light output becomes stable, the sample-hold means holds the control voltage by accumulating charges. The control system configuration is from closed loop,
Become an open loop. The current source causes a current to flow through the semiconductor laser according to the control voltage held by the charge accumulation, and the light output is controlled to the light output for recording. The current of the current source is modulated according to the recording signal, and the optical output is modulated. While the light output is modulated, the control voltage held by the charge accumulation is A / D converted, latched, and D / A converted to generate a digital hold voltage. When the D / A conversion is completed, the control voltage held by the charge accumulation is switched to the digital hold voltage, and thereafter the optical output of recording is controlled by the open loop by the digital hold voltage.

In this way, after the control voltage is held by the charge accumulation, the modulation of the recording is started, and the control voltage held by the charge accumulation and the digital hold voltage are switched during the modulation of the recording to thereby modulate the recording. The recording area for A / D conversion, latching, and D / A conversion is made unnecessary before.

Further, in the invention of claim 2, the hold voltage is stabilized by adding the A / D conversion output to the charge accumulation point of the sample hold means after the D / A conversion is completed. Further, in the invention of claim 7 of the present application, first and second sample and hold means are provided, and after sample and hold, A
When the D / A conversion and the D / A conversion are completed, the semiconductor laser is driven at different levels by switching to the D / A conversion output, and the respective levels can be stabilized. According to the invention of claim 8, in the invention of claim 7, the output of the sample hold circuit can be stabilized by adding the D / A conversion output to the charge accumulation points of the sample hold circuit.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of a semiconductor laser drive circuit according to a first embodiment of the present invention. The part added to FIG. 13 which is the configuration diagram of the conventional example described above will be described. In FIG. 1, the A / D converter 30 has a control voltage V held by the buffer amplifier 12 by accumulating charges.
It is for A / D converting HA into digital data VD. The D / A converter 31 converts the digital data VD into an analog digital hold voltage VHD. Although not shown, a latch circuit that digitally latches the digital data VD is included in the A / D converter 30 or the D / A converter 31. The analog switches 32 and 33 are controlled by the switching gate EXC, and constitute a switching means for selecting the control voltage VHA held by charge accumulation or the digital hold voltage VHD. The inverter 34 inverts the polarity of the switching gate EXC.

The operation of the semiconductor laser driving circuit of the first embodiment of the present invention constructed as above will be described with reference to FIG. In the waveform diagram of FIG. 2, (a) is a recording gate WG indicating a recording section, (b) is a hold gate HLD indicating a holding section, and (c) is a holding section in which the control voltage VHA or digital hold held by charge accumulation is held. A switching gate EXC for switching the voltage VHD, (d) a recording signal WDT recorded on the optical disc, (e) a control voltage VS of the differential amplifier 4, and (f) a buffer amplifier 12.
The output of the control voltage VHA, (g) is the D / A converter 3
1 is the digital hold voltage VHD, (h) is the control voltage VH of the current source, and (i) is the optical output of the semiconductor laser 1.

Up to time t9 is a reproduction sample section, and up to time t10 is a recording sample section. The hold section is from time t10 to t13, and the reproduction sample section is from time t13.

The reproduction section up to time t9 is the recording gate W
G, the hold gate HLD, and the switching gate EXC are "low", and the analog switches 9 and 32 are on. In the sample-hold circuit, in the sampled state, a closed-loop control system is constructed as in the conventional example. The optical output of the semiconductor laser 1 is controlled to be the reproduction optical output PP set by the reference voltage VP.

At time t9, when the recording gate WG becomes "high", the sample-hold circuit remains in the sampling state, the reference voltage is switched to VW, and the optical output P of recording is changed.
The setting of W starts. The recording signal WDT is “high”, and the drive current I _LD of the constant current source all flows through the semiconductor laser 1. Therefore, the optical output of the semiconductor laser 1 is the reference voltage VW.
The control voltage changes to VSW so that the optical output PW for recording set by is obtained.

At time t10, the recording control voltage VS
When W becomes stable, the hold gate HLD is "high",
The sample hold circuit is in the hold state. The control system switches from closed loop to open loop. The output VHA of the buffer amplifier 12 becomes the recording control voltage VSW held by the charge accumulation in the capacitor 11.
The control voltage VH of the current source is the output V of the buffer amplifier 12.
HA is connected and the optical output PW for recording is set by an open loop control system. At time t10, the modulation of the drive current I _LD by the recording signal WDT starts, and the optical output PW
Is modulated. Also, from time t10, A / D conversion, latching, and D / A conversion of the control voltage VSW for recording held by charge accumulation starts.

At time t11, A / D conversion, latch, D /
A conversion is completed. As the digital hold voltage VHD which is the output of the D / A converter, the recording control voltage VSW is output.

At time t12, the switching gate EXC becomes "high". The control voltage VH of the current source is switched from the control voltage VHA held by charge accumulation to the digital hold voltage VHD. Since the control voltage VHA and the digital hold voltage VHD held by the charge accumulation are the same control voltage VSW for recording, even if the control voltage is switched, the optical output PW for recording is stable under open loop control. As shown in FIGS. 2 (f) and 2 (g), after time t13
Although the control voltage VHA gradually rises due to the influence of the troop, the stable digital hold voltage VHD drives the current source in the open loop.

At time t13, the recording gate WGT,
The hold gate HLD and the switching gate EXC become "low", and the recording returns to the reproduction. The control of the optical output is switched from the open loop to the closed loop control system. Since the recording light output PW is controlled by the digital hold voltage VHD from time t12 to time t13, even if the current source is driven by the open loop, the influence of droop is small and stable.

As described above, in the present embodiment, when the D / A conversion is completed during the modulation by the recording signal, the driving of the current source is switched from the output of the sample hold means to the output of the D / A converter. There is. Therefore, it is possible to eliminate the DC emission of the optical output of recording for a long time required for A / D conversion and D / A conversion, improve the utilization efficiency of the recording area of the optical disc, and reduce the damage to the recording film. it can. Further, since the A / D conversion and the D / A conversion are performed while the recording is modulated by the control voltage held by the charge accumulation,
The conversion speed of the A / D converter and the D / A converter does not need to be so high, and the effect that the circuit cost can be reduced can be obtained.

Next, a second embodiment of the present invention will be described. In the second embodiment, in the semiconductor laser drive circuit of the first embodiment, instead of switching between the control voltage held by charge accumulation and the digital hold voltage at the time when D / A conversion is completed, the buffer amplifier input is used. The digital hold voltage is added to the charge storage point of a certain capacitor.

FIG. 3 is a block diagram of a semiconductor laser drive circuit according to the second embodiment of the present invention. Description will be given of a portion additionally modified from FIG. 1, which is the configuration diagram of the first embodiment described above. In FIG. 3, the analog switch 40 is controlled by the addition gate ADD, and is open in the sample section and the section in which the current source is driven by the control voltage held by the charge accumulation. In this embodiment, the buffer amplifier 1
The two outputs are given to the A / D converter 30. The A / D converter 30 converts this into a digital signal, and its output is given to the D / A converter 31. A / D converter 3
A latch circuit (not shown) is included between 0 and the D / A converter 31. The output of the D / A converter 31 is given to one end of the analog switch 40. The analog switch 40 closes the analog switch 40 after the control voltage VH held by charge accumulation is A / D converted, latched, and D / A converted to generate the digital hold voltage VHD. By adding the digital hold voltage VHD to the control voltage held by the charge accumulation, the control voltage VH of the current source that is stable for a long time is obtained.

The operation of the semiconductor laser drive circuit of the second embodiment of the present invention constructed as above will be described with reference to FIG. In the waveform diagram of FIG. 4, (a) is a recording gate WG showing a recording section, (b) is a hold gate HLD showing a hold section, and (c) is a charge accumulation point of the capacitor 11 when D / A conversion is completed. Is added to the digital hold voltage VHD with an addition gate ADD, (d) is a recording signal WDT recorded on the optical disc, (e) is a control voltage VS of the differential amplifier 4, and (f) is a digital signal of the D / A converter 31. Hold voltage VHD, (g) is the control voltage V of the current source
H and (h) are optical outputs of the semiconductor laser 1. Time t9
Up to the time t10 is a sample section for reproduction, and up to time t10 is a sample section for recording. The hold section is from time t10 to t13, and the reproduction sample section is from time t13.

In the reproduction section up to time t9, the optical output of the semiconductor laser 1 is controlled by the closed loop so that the optical output of the semiconductor laser 1 becomes the reproduction optical output PP set by the reference voltage VP, as described in the first embodiment. It

At time t9, when the recording gate WG becomes "high", the reference voltage remains VW with the closed loop.
Then, the setting of the optical output PW for recording is started. The control voltage changes to VSW so that the optical output of the semiconductor laser 1 becomes the recording optical output PW set by the reference voltage VW.

At time t10, the recording control voltage VS
When W becomes stable, the hold gate HLD becomes "high" and the sample hold circuit enters the hold state. The control system switches from closed loop to open loop.
The control voltage VH of the current source is connected to the control voltage VSW of the recording held by the capacitor 11 by the charge accumulation, and the optical output PW of the recording is set by the open loop control system. At time t10, the modulation of the drive current I _LD by the recording signal WDT starts, and the optical output PW is modulated. Further, from time t10, A / D conversion, latching, and D / A conversion of the recording control voltage VSW held by the charge accumulation are started.

At time t11, A / D conversion, latch, D /
A conversion is completed. As the digital hold voltage VHD which is the output of the D / A converter, the recording control voltage VSW is output.

At time t12, the addition gate ADD becomes "high", and the digital hold voltage V is applied to the charge accumulation point of the capacitor 11 which holds the recording control voltage VSW.
HD is added. Here, the digital hold voltage VH
Since D is equal to the control voltage VSW for recording, the control voltage VH of the current source, which is the output of the buffer amplifier 12, remains the control voltage VSW for recording, and the optical output PW for recording is stable under open loop control. is there.

Since the digital hold voltage VHD is added to the charge accumulation point of the capacitor 11, the capacitor 11
Has the effect of a noise filter, and the fluctuation of the control voltage of the current source at the moment of addition is suppressed. As a result, the fluctuation of the recording light output can be suppressed, and the deterioration of the semiconductor laser 1 can be prevented.

At time t13, the recording gate WGT,
The hold gate HLD and the addition gate ADD become "low", and the recording returns to the reproduction. The control of the light output is switched from the open loop to the closed loop control system.

As described above, in this embodiment, when the D / A conversion is completed, the addition means for adding the digital hold voltage to the charge accumulation point of the capacitor, which is the input of the buffer amplifier, is provided to perform the recording. In the hold section where the modulation is performed, it is possible to suppress the fluctuation of the control voltage of the current source and stabilize the control of the optical output.

Next, a third embodiment of the present invention will be described. In the third embodiment, in the first and second embodiments described above, the hold of the control voltage due to the charge accumulation of the sample hold circuit is the time until the D / A conversion is completed.

FIG. 2 which is an explanatory view of the operation of the first embodiment.
In (f), the control voltage VHA held by charge accumulation changes due to droop toward the end of recording. However, since the driving of the current source is performed by the digital hold voltage VHD shown in FIG. 2 (g), there is no influence of the change of the control voltage VHA held by the charge accumulation. Therefore, the time for stably holding the control voltage VHA due to charge accumulation is sufficient until the D / A conversion is completed, and is not necessary until the recording is completed. Also in the second embodiment, the capacitor 1 is used at the stage when D / A conversion is completed.
By adding the D / A conversion value VHD to the charge accumulation point of 1, the output of the sample hold circuit, that is, the control voltage VH of the current source can be stabilized. The hold time for charge accumulation depends on the capacitance of the capacitor 11, and shortening the hold time can reduce the capacitance of the capacitor. The capacitance of the capacitor is related to the frequency characteristic of the control system at the same time as the hold time. Therefore, when the capacitance of the capacitor is reduced, the frequency characteristic is improved, and the rise of recording from reproduction can be accelerated.

As described above, according to the present embodiment, the sample-hold circuit holds the control voltage by charge accumulation from the start of holding to the completion of D / A conversion, thereby reducing the capacitance of the capacitor. Thus, the frequency characteristics of the control system can be extended to speed up the rise of recording from reproduction.

Next, a fourth embodiment of the present invention will be described. When the control voltage VH of the current source fluctuates at the timing of switching between the control voltage VHA held by charge accumulation and the digital hold voltage VHD, and the optical output of recording peaks, the optical output of the semiconductor laser exceeds the specified value. There is a risk that In this case, the semiconductor laser will be damaged, and in the worst case, it will be destroyed. Therefore, in the fourth embodiment, the switching of the control voltage VHA held by charge accumulation and the digital hold voltage VHD in the first embodiment described above is performed so that the modulation of the optical output of recording becomes the bottom (low level). This is done in different sections.
This can be easily realized by adding a gate for giving the output of the switching gate EXC to the analog switch 33 and the inverter 34 only when the recording signal WDT is at the L level in FIG. 1, for example. When the control voltage VH of the current source fluctuates at the bottom timing of the recording optical output, the influence on the optical output of the semiconductor laser 1 is remarkably small, and as a result, the deterioration of the semiconductor laser 1 can be prevented. it can.

As described above, according to the present embodiment, the control voltage VHA held by the charge accumulation and the digital hold voltage VHD are switched in the section where the modulation of the optical output of recording is at the bottom, so that the control voltage is controlled. It is possible to prevent the deterioration of the semiconductor laser due to the fluctuation of

Next, a fifth embodiment of the present invention will be described. When the control voltage VH of the current source fluctuates at the timing of adding the digital hold voltage VHD to the charge accumulation point of the capacitor holding the control voltage, and when the optical output of recording is at the peak, the optical output of the semiconductor laser May exceed the specified value. In this case, the semiconductor laser will be damaged, and in the worst case, it will be destroyed. Therefore, in the fifth embodiment, in the second embodiment described above, the addition of the digital hold voltage VHD to the charge accumulation point of the capacitor holding the control voltage is performed by adjusting the optical output of recording to the bottom. I decided to do it in the section that became. Also in this case, by adding a gate circuit that can add the addition gate ADD to the analog switch 40 only when the recording signal WDT is at the low level,
Easy to implement. If the digital hold voltage VHD is added to the charge storage point of the capacitor that holds the control voltage when the optical output of recording is at the bottom, the optical output of the semiconductor laser 1 is significantly less affected, and as a result. The deterioration of the semiconductor laser 1 can be prevented.

As described above, according to this embodiment, the addition of the digital hold voltage VHD to the charge accumulation point of the capacitor holding the control voltage is performed in the section where the modulation of the recording optical output is at the bottom. As a result, it is possible to prevent the semiconductor laser from deteriorating due to fluctuations in the control voltage.

Next, a sixth embodiment of the present invention will be described. The sixth embodiment is one in which the present invention is applied to a semiconductor laser drive circuit that controls and modulates two optical outputs of a peak and a bottom of an optical pulse. A semiconductor laser drive circuit that controls and modulates a light output between a peak and a bottom is used for a rewritable recording medium. In particular, it is used for a recording medium that can be overwritten by one beam using phase change, a magneto-optical medium having a two-layer recording medium that can be overwritten, and the like. In order to control two optical outputs, peak and bottom, the conventional method of A / D conversion, latching, and D / A conversion before modulation of the recording signal requires the length required for A / D conversion and D / A conversion. The DC light emitting area of the period is also doubled, and the utilization efficiency of the recording area of the optical disk is further deteriorated. Furthermore, because it is rewritable,
The damage to the recording film repeatedly deteriorates the characteristics. The sixth embodiment solves this problem.

FIGS. 5 and 6 are block diagrams showing a semiconductor laser drive circuit according to the sixth embodiment of the present invention.
Description will be given of a portion additionally modified from FIG. 1, which is the configuration diagram of the first embodiment described above. First, the configuration of the block of the portion that controls the first light output corresponding to the bottom of the recording light output will be described with reference to FIG.

In FIG. 5, the first differential amplifier 50 has a monitor voltage VM and a first reference voltage VR for setting an optical output.
1 and a first control voltage VS1 is generated. There are two first reference voltages VR1; a reproduction reference voltage VP 51 and a first optical output reference voltage VW1 52, which are analog switch 53 and analog switch 54.
Either is selected by. The selection is controlled by the first recording gate WG1 indicating the recording section and the output of the inverter 55, and one of the reference voltages is the analog switch 56.
Added to. The analog switch 56 is controlled by the first hold gate HLD1 and the inverter 57, and supplies the first control voltage VS1 to the buffer amplifier 59.
The analog switch 56, the capacitor 58, and the buffer amplifier 59 form a first sample hold circuit. The first sample and hold circuit samples the first control voltage VS1 when the analog switch 56 is on,
The control system consists of a closed loop. Further, when the analog switch 56 is off, the first control voltage V
Hold HA1 and configure the control system as an open loop. The first A / D converter 63 converts the first control voltage VHA1 held by the charge accumulation into the first digital data V
A / D conversion into D1 is performed. The first D / A converter 64 outputs the first digital hold voltage VHD1. Although not shown, a first latch circuit for digitally latching the first digital data VD1 is included in the first A / D converter 63 or the first D / A converter 64. I shall. Analog switch 6
0 and 61 are an inverter 62 and a first switching gate EXC1.
The first control voltage V controlled by
It constitutes a first switching means for selecting either HA1 or the first digital hold voltage VHD1. Analog switch 6
The outputs VH1 of 0 and 61 are connected to the resistor 66 (RL) and the transistor 65 that constitutes the first current source, and the current I _L1
Shed. The current I _L1 controls the bottom which is the first light output.

Next, the second, which corresponds to the peak of the recording light output,
The configuration of the lower half block that controls the optical output of the above will be described with reference to FIG. A part similar in operation to the upper half block will be briefly described.

In FIG. 6, the monitor voltage VMH is also applied to the second differential amplifier 67. The differential amplifier 67 compares the monitor voltage VM with the second reference voltage VR2 that sets the optical output, and generates the second control voltage VS2. The second reference voltage VR2 is the ground level for zero light output and the reference voltage VW2 for the second light output 68.
Are selected by the analog switch 69 and the analog switch 70. The analog switches 69 and 70 are controlled by a second recording gate WG2 indicating a recording section and an inverter 71. The analog switch 72 is controlled by the second hold gate HLD2 and the inverter 73, and supplies the second control voltage VS2 to the buffer amplifier 75.

The analog switch 72, the capacitor 74,
The buffer amplifier 75 constitutes a second sample hold circuit. The second sample and hold circuit samples the second control voltage VS2 when the analog switch 72 is on, and configures the control system in a closed loop. Further, when the analog switch 72 is off, the second control voltage VHA2 is held by the charge accumulation, and the control system is configured as an open loop. The second A / D converter 79 A / D converts the second control voltage VHA2 held by the charge accumulation into the second digital data VD2. The second D / A converter 80 outputs the second digital hold voltage VHD2. Although not shown, the second digital data VD2
The second latch circuit for digitally latching is assumed to be included in the second A / D converter 79 or the second D / A converter 80. The analog switches 76 and 77 are controlled by the inverter 78 and the second switching gate EXC2, and select the second control voltage VHA2 held by charge accumulation or the second digital hold voltage VHD2.
Of the switching means. Analog switch 76,7
The output VH2 of No. 7 is connected to the resistor 82 (RL) and the transistor 81 forming the second current source, and flows the current I _L2 . The current I _L2 is modulated by the inverter 85 and the transistors 83 and 84 according to the recording signal WDT,
It is superimposed on the current I _L1 . The current I _L2 controls the peak which is the second light output.

Operation of the semiconductor laser drive circuit of the sixth embodiment of the present invention constructed as described above will be described with reference to FIGS.
Will be explained. In the waveform diagram of FIG. 7, (a) is the first recording gate WG1 and (b) is the second recording gate WG.
2 or the first hold gate HLD1, (c) is the second hold gate HLD2, (d) is the first switching gate EXC1, (e) is the second switching gate EXC2,
(F) is the recording signal WDT. (G) is the first control voltage VS1, (h) is the first control voltage VHA1 held by charge accumulation, and (i) is the first digital hold voltage VHD1. Further, in the waveform diagram of FIG. 8, (j) is the first control voltage VH1 of the current source, (k) is the second control voltage VS2, (l) is the second control voltage VHA2 held by charge accumulation, ( m) is the second digital hold voltage VHD2, (n) is the second control voltage VH2 of the current source,
(O) is an optical output.

The first sample section is up to time t15, the first hold section is from time t15 to time t19, and the first sample section is after time t19. Also time t1
5 to time t16, the second sample section, time t1
From 6 to time t19 is the second hold section.

In FIG. 7, a reproduction section is shown up to time t14. The first sample and hold circuit is in the sample state,
The control system constitutes a closed loop, and the optical output of the semiconductor laser 1 is controlled to be the reproduction optical output PP set by the reference voltage VP.

At time t14, the first recording gate W
G1 goes "high" and remains in closed loop.
The reference voltage of VW1 is switched to VW1 and the first optical output PW1
, The first control voltage changes to VSW1.

At time t15, the first hold section and the second sample section start. First control voltage VS
1 becomes stable at VSW1, the first hold gate HL
D1 becomes "high", and the first sample hold circuit enters the hold state. The control system switches from closed loop to open loop. Output VH of buffer amplifier 59
A1 becomes the first control voltage VSW1 held in the capacitor 58 by the charge accumulation. The output VHA1 of the buffer amplifier 59 is connected to the first control voltage VH1 of the current source, and the first optical output PW1 is set by the open loop control system. At the same time, as shown in FIG. 7I, A / of the first control voltage VSW1 held by the charge accumulation is held.
D conversion, latch, and D / A conversion are started.

At time t15, the second recording gate WG2 becomes "high", and the second loop output control system sets the second optical output PW2. The second control voltage VS2 changes to VSW2 corresponding to the second light output PW2.

At time t16, the second hold section starts. As shown in FIG. 8 (k), the second control voltage VS
2 becomes stable at VSW2, the second hold gate HL
D2 becomes "high" and the second sample hold circuit enters the hold state. The control system switches from closed loop to open loop. The output VHA2 of the buffer amplifier 75 shown in FIG. 8 (l) becomes the second control voltage VSW2 held in the capacitor 74 by charge accumulation. The second control voltage VH2 of the current source becomes the output VHA2 of the buffer amplifier 75, and the second optical output PW2 is set by the open loop control system as shown in FIG. At the same time, the second control voltage VSW2 held by charge accumulation
A / D conversion, latch, and D / A conversion are started.

At time t16, the modulation of the current I _L2 by the recording signal WDT starts. The optical output is the first optical output PW1
And the second light output PW2.

As shown in FIG. 7D, at time t17, the first switching gate EXC1 becomes "high". At this time, the A / D conversion and D / A conversion of the first control voltage VSW1 are completed, and the first digital hold voltage VHD1 is VS.
W1 is output. The first control voltage VH1 of the current source is switched from the first control voltage VHA1 held by the charge accumulation to the first digital hold voltage VHD1 by the first switching gate EXC1.

As shown in FIG. 7 (l), at the next time t18, the second switching gate EXC2 becomes "high".
At this time, A / D conversion and D / A conversion of the second control voltage VSW2 are completed, and VSW2 is output as the second digital hold voltage VHD2. Second switching gate EXC2
As a result, the second control voltage VH2 of the current source is switched from the second control voltage VHA2 held by the charge accumulation to the second digital hold voltage VHD2. Later,
First and second digital hold voltages VHD1 and VHD2
The optical output is stably modulated by. At time t19, the control of the optical output shifts from the open loop to the closed loop, and the optical output changes from recording to reproduction.

As described above, according to this embodiment, during the recording modulation, the first control voltage and the first digital hold voltage held by charge accumulation are switched, and the second control voltage held by charge accumulation is changed. By switching between the control voltage of 2 and the second digital hold voltage, the first and second A /
It is possible to eliminate the DC emission of a long-time optical output required for D conversion and D / A conversion. Further, the utilization efficiency of the recording area of the optical disc can be improved.

In the write-once type recording medium, the optical output of recording in the same area is emitted only once. However, in a rewritable recording medium, the optical output of recording in the same area is rewritable, so that light is repeatedly emitted. Therefore, the damage to the recording medium due to the DC light emission at the start of recording is increased by the number of repetitions. In this embodiment, the recording D necessary for A / D conversion and D / A conversion
Since the C emission is eliminated, the repeating characteristics of the recording medium can be improved. Further, by setting the first light output to near zero, the present laser drive circuit can be applied not only to a rewritable recording medium but also to a write-once recording medium.

Next, a seventh embodiment of the present invention will be described. In the seventh embodiment, in the semiconductor laser drive circuit of the sixth embodiment, at the time when the first D / A conversion is completed, the first digital signal is stored at the charge accumulation point holding the first control voltage. The hold voltage is added, and when the second D / A conversion is completed, the second digital hold voltage is added to the charge storage point holding the second control voltage.

9 and 10 are block diagrams showing a semiconductor laser drive circuit according to the seventh embodiment of the present invention. The part added and modified to the previously described sixth embodiment will be described. In FIG. 9, the analog switch 90 is controlled by the first addition gate ADD1, and is controlled by the first control voltage held by the first sampling period and the charge accumulation.
The section that is driving the current source is open. A / D conversion of the first control voltage VH1 held by charge accumulation,
Latch, D / A conversion, first digital hold voltage V
After making HD1, the analog switch 90 is closed. The first digital hold voltage VHD1 is added to the first control voltage held by charge accumulation, and a stable control voltage VH1 of the first current source is obtained.

The analog switch 91 is controlled by the second addition gate ADD2. Similar to the analog switch 90 described above, the second control voltage VH2 held by charge accumulation is A / D converted, latched, and D / A converted to generate the second digital hold voltage VHD2, and then the analog The switch 91 is closed. The second digital hold voltage V is added to the second control voltage held by the charge accumulation.
HD2 is added to stabilize the control voltage VH of the second current source.
2 is obtained.

The operation of the semiconductor laser drive circuit of the seventh embodiment of the present invention constructed as described above will be described with reference to FIGS.
2 is used for the explanation. In the waveform diagram of FIG. 11, (a)
Is the first recording gate WG1, (b) is the second recording gate WG2 or the first hold gate HLD1, (c)
Is the second hold gate HLD2, (d) is the first addition gate ADD1, (e) is the second addition gate ADD2,
(F) is the recording signal WDT. (G) is the first control voltage VS1, (h) is the first digital hold voltage VHD
It is 1. 12 (i) is the first control voltage VH1 of the current source, (j) is the second control voltage VS2, and (k) is the second control voltage VS2.
The digital hold voltage VHD2, (1) is the second control voltage VH2, m of the current source is the optical output.

The first sampling period is from time t15 to the first holding time from time t15 to time t19, and the first sampling period is from time t19 onward. Also time t1
5 to time t16, the second sample section, time t1
From 6 to time t19 is the second hold section.

11 and 12, the reproduction section is shown up to time t14. The first sample-hold circuit is in a sampled state, the control system constitutes a closed loop, and the optical output of the semiconductor laser 1 is controlled to be the reproduction optical output PP set by the reference voltage VP.

As shown in FIG. 11A, at time t14, the first recording gate WG1 becomes "high", the first reference voltage is switched to VW1 in the closed loop, and the first optical output is obtained. The first control voltage changes to VSW1 so as to reach PW1. As shown in FIG. 11B, at time t15, the first hold gate HLD1 becomes "high" and the first sample hold circuit enters the hold state. The control system switches from closed loop to open loop. The first control voltage VH1 of the current source is the first control voltage VH held in the capacitor 58 by the charge accumulation.
SW1 is connected, and the first optical output PW1 is set by the open loop control system as shown in FIG. 12 (m). At the same time, as shown in FIGS. 11G and 11H, A / D conversion, latching, and D / A conversion of the first control voltage VSW1 held by charge accumulation are started.

At time t15, the second recording gate WG2 becomes "high", and the second loop output control system sets the second optical output PW2. The second control voltage VS2 changes to VSW2 corresponding to the second light output PW2.

At time t16, the second hold gate HL
D2 becomes "high" and the second sample hold circuit enters the hold state. The control system switches from closed loop to open loop. Second control voltage VH2 of current source
Is connected to the second control voltage VSW2 held by the charge accumulation in the capacitor 74, and the second optical output PW2 is set by the open loop control system. Figure 12 at the same time
As shown in (k) and (l), A / D conversion, latch, D / A of the second control voltage VSW2 held by charge accumulation
The conversion starts.

At time t16, the modulation of the current I _L2 by the recording signal WDT starts. The optical output is the first optical output P
It is modulated between W1 and the second light output PW2.

At time t17, the first addition gate A
DD1 goes "high" and the analog switch 58 is turned on. At this time, A / D conversion of the first control voltage VSW1
Latching and D / A conversion have been completed, and the first digital hold voltage VHD1 has been output. The first addition gate ADD1 adds the first digital hold voltage VHD1 to the charge accumulation point of the capacitor 58 that holds the first control voltage VSW1. Since the value of the first digital hold voltage VHD1 is equal to the first control voltage VSW1, the first control voltage VH1 of the current source is VSW1.
The first optical output PW1 is stable under the control of the open loop. Further, there is an effect of the noise filter by the condenser 58, and the fluctuation of the optical output at the moment of addition is suppressed.

At time t18, the second addition gate A
DD2 becomes "high" and the analog switch 91 is turned on. At this time, A / D conversion of the second control voltage VSW2,
Latching and D / A conversion are completed, and the second digital hold voltage VHD2 is output. The second addition gate ADD2 adds the second digital hold voltage VHD2 to the charge accumulation point of the capacitor 74 which holds the second control voltage VSW2. Since the value of the second digital hold voltage VHD2 is equal to the second control voltage VSW2, the second control voltage VH2 of the current source is VSW2.
The second optical output PW2 is stable under open loop control. Further, there is an effect of the noise filter by the condenser 74, and the fluctuation of the optical output at the moment of addition is suppressed.

After that, until the time t19, the two current sources are
Are driven in open loop by the control voltages VH1 and VH2 obtained by adding the digital hold voltage VHD1 and the second digital hold voltage VHD2. Time t19
In, the control of the optical output shifts from the open loop to the closed loop, and the optical output is changed from recording to reproduction.

As described above, according to this embodiment, the first D
A first addition means for adding the first digital hold voltage to the charge accumulation point holding the first control voltage when the A / A conversion is completed, and a time when the second D / A conversion is completed Thus, by providing a second addition means for adding the second digital hold voltage to the charge storage point holding the second control voltage, the first and second digital signals are added during the recording modulation. By adding the hold voltage without switching, it is possible to suppress the fluctuation of the control voltage in the open loop and stabilize the control of the light output.

Next, an eighth embodiment of the present invention will be described. In the eighth embodiment, in the sixth and seventh embodiments described above, one shared A / D converter is used instead of the first A / D converter and the second A / D converter. A D converter and an input selection means for selecting one of the output of the first buffer amplifier and the output of the second buffer amplifier and inputting it to the shared A / D converter are provided.

Since the times when the first and second A / D converters perform A / D conversion do not overlap, one shared A / D converter can be used. Shared A
The input to the / D converter switches one of the output of the first buffer and the output of the second buffer by the input selection means.
As a result, one A / D converter can serve as two A / D converters, and the cost of the circuit can be reduced.

In the sixth, seventh and eighth embodiments of the present invention, the two light outputs of the bottom and the peak are controlled, but it goes without saying that this can be applied to three or more light outputs. Further, in the sixth embodiment of the present invention, if the control voltage held by the charge accumulation is switched to the digital hold voltage in the section where the optical output is at the bottom, the fluctuation of the optical output due to the switching can be suppressed. Needless to say. In addition, in the seventh embodiment of the present invention, if the digital hold voltage is added to the charge accumulation point of the capacitor holding the control voltage in the interval where the optical output is at the bottom, the fluctuation of the optical output due to the addition is suppressed. It goes without saying that you can do it.

[0089]

As described above, according to the first to sixth aspects of the present invention, the control voltage held by the charge accumulation during the recording modulation and the digital hold voltage of the D / A converter are switched or the digital hold is performed. Since the voltage is added to the charge storage point of the sample hold means, A / D conversion, D /
It is possible to eliminate the DC emission of the optical output for long-time recording required for A conversion, improve the utilization efficiency of the recording area of the optical disc, and reduce the damage to the recording film.

Furthermore, since the section in which the recording control voltage is held by the charge accumulation is the settling section in A / D conversion and D / A conversion, the holding time is shortened and the capacity of the capacitor is reduced. You can This improves the frequency characteristics of the servo system and makes it possible to speed up the rising of recording from reproduction.

Moreover, while the recording voltage is modulated by the control voltage held by the charge accumulation, A / D conversion and D / D conversion are performed.
Since the A conversion is performed, the conversion speed of the A / D converter and the D / A converter does not need to be very high, and the circuit cost can be reduced.

Further, in the rewritable recording medium, since the two optical outputs of the peak and the bottom are controlled, the area for A / D conversion, latching, and D / A conversion is doubled before the modulation of the recording signal. In the inventions of claims 7 to 9 of the present application, areas for A / D conversion, latching, and D / A conversion are not required. Therefore, it is possible to improve the utilization efficiency of the recording area, eliminate high-power DC emission to the same area due to rewriting, and prevent deterioration of repetitive characteristics such as the number of rewriting.

[Brief description of drawings]

FIG. 1 is a configuration diagram 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 of the present invention.

FIG. 3 is a configuration diagram 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 a second embodiment of the present invention.

FIG. 5 is a configuration diagram (part 1) of a semiconductor laser drive circuit according to a sixth embodiment of the present invention.

FIG. 6 is a configuration diagram (part 2) of a semiconductor laser drive circuit according to a sixth embodiment of the present invention.

FIG. 7 is an operation explanatory view (No. 1) of the semiconductor laser drive circuit according to the sixth embodiment of the present invention.

FIG. 8 is an operation explanatory diagram (2) of the semiconductor laser drive circuit according to the sixth embodiment of the present invention.

FIG. 9 is a configuration diagram (part 1) of a semiconductor laser drive circuit according to a seventh embodiment of the present invention.

FIG. 10 is a configuration diagram (part 2) of a semiconductor laser drive circuit according to a seventh embodiment of the present invention.

FIG. 11 is an operation explanatory diagram (1) of the semiconductor laser drive circuit according to the seventh embodiment of the present invention.

FIG. 12 is an operation explanatory diagram (2) of the semiconductor laser drive circuit according to the seventh embodiment of the present invention.

FIG. 13 is a configuration diagram of a semiconductor laser drive circuit according to a conventional hold method.

FIG. 14 is an operation explanatory diagram of a semiconductor laser drive circuit according to a conventional hold method.

FIG. 15 is a configuration diagram of a semiconductor laser drive circuit according to a conventional digital hold system.

FIG. 16 is an operation explanatory diagram of a semiconductor laser drive circuit according to a conventional digital hold system.

[Explanation of symbols]

1 semiconductor laser 2 photodetector 3 current / voltage converter 4 differential amplifier 5 reference voltage for reproduction 6 reference voltage for recording 12 buffer amplifier 13 transistor 21, 30 A / D converter 22, 31 D / A converter 7 ~ 9, 32, 33, 40, 56, 69, 70, 72,
90, 91 Analog switch 50 First differential amplifier 51 Buffer amplifier 63 First A / D converter 64 Second D / A converter 75 Buffer amplifier 79 Second A / D converter 80 Second D / A converter

Claims (9)

[Claims] 1. 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 reference voltage generation that generates a reference voltage corresponding to the optical output of reproduction or recording. Means, a differential amplifier for comparing the monitor signal with the reference voltage to generate a control voltage, and a control voltage of the differential amplifier as an input, outputting the control voltage in the sample section, and reproducing from the recording in the hold section Sample hold means for holding the control voltage at the time of settling after the reference voltage is switched to the optical output by charge accumulation, a current source for flowing a current to the semiconductor laser according to the output of the sample hold means, and the hold Modulating means for modulating the current of the current source according to the recording signal during the interval, and the control voltage held by the sample hold means An analog-digital converter that performs analog-digital conversion, a latch circuit that digitally holds the output of the analog-digital converter, a digital-analog converter that performs digital-analog conversion of the output of the latch circuit, and a section of modulation by the recording signal , When the digital-analog conversion of the digital-analog converter is completed, driving the current source from the output of the sample hold means,
A semiconductor laser drive circuit comprising: switching means for switching to an output of the digital-analog converter. 2. 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 reference voltage generation that generates a reference voltage corresponding to the optical output of reproduction or recording. Means, a differential amplifier for comparing the monitor signal with the reference voltage to generate a control voltage, and a control voltage of the differential amplifier as an input, outputting the control voltage in the sample section, and reproducing from the recording in the hold section Sample hold means for holding the control voltage at the time of settling after the reference voltage is switched to the optical output by charge accumulation, a current source for flowing a current to the semiconductor laser according to the output of the sample hold means, and the hold Modulating means for modulating the current of the current source according to the recording signal during the interval, and the control voltage held by the sample hold means An analog-digital converter that performs analog-digital conversion, a latch circuit that digitally holds the output of the analog-digital converter, a digital-analog converter that performs digital-analog conversion of the output of the latch circuit, a section of modulation by a recording signal, When the digital-analog conversion of the digital-analog converter is completed, an adder means for adding the output of the digital-analog converter to the charge accumulation point of the sample-hold means holding the control voltage is provided. Drive circuit. 3. The sample hold means, during the hold period, at least from the start of hold until the digital-analog conversion of the digital-analog converter is completed.
The semiconductor laser drive circuit according to claim 1, wherein the control voltage is held by accumulating charges. 4. The sample hold means, during the hold period, at least from the start of hold until the digital-analog conversion of the digital-analog converter is completed.
The semiconductor laser drive circuit according to claim 2, wherein the control voltage is held by accumulating charges. 5. The semiconductor laser drive circuit according to claim 1, wherein the switching means switches from the output of the sample hold means to the output of the digital-analog converter in a section where the optical output of the modulated recording is at the bottom. 6. The adding means adds the output of the digital-analog converter to the charge accumulation point of the sample-hold means holding the control voltage in the section where the optical output of the modulated recording is at the bottom. The semiconductor laser drive circuit according to item 2 or 4. 7. 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. A reference voltage generating means, a first differential amplifier that compares the monitor signal with the first reference voltage to generate a first control voltage, and a control voltage of the first differential amplifier as an input, The first control voltage is output in the first sample section, and the first control voltage at the time of settling after the reference voltage is switched from the reproduction to the first optical output in the first hold section is accumulated by charge accumulation. First sample-hold means for holding, a first current source for supplying a current to the semiconductor laser according to the output of the first sample-hold means, and first control held by the first sample-hold means A first analog-to-digital converter that converts a voltage into an analog-to-digital value, a first latch circuit that digitally holds the output of the first analog-to-digital converter, and a digital-to-analog conversion output of the first latch circuit A first digital-to-analog converter, a second reference voltage generating means for generating a reference voltage corresponding to a second optical output, a second control voltage for comparing the monitor signal with the second reference voltage. And a control voltage of the second differential amplifier as an input, the second control voltage is output in the second sample section, and the second control voltage is output in the second hold section. Second sample and hold means for holding the second control voltage at the time of settling after the reference voltage is switched to the optical output by charge accumulation, and an electric power corresponding to the output of the second sample and hold means. A second current source which is added to the current of the first current source and flows, a second holding section, a modulator for modulating the current of the second current source according to a recording signal, A second analog-digital converter for analog-digital converting the second control voltage held by the second sample-hold means; and a second latch circuit for digitally holding the output of the second analog-digital converter. A second digital-analog converter for converting the output of the second latch circuit into a digital-analog signal, a section of modulation by the recording signal, and at the time point when the digital-analog conversion of the first digital-analog converter is completed, First switching means for switching the drive of the first current source from the output of the first sample-hold means to the output of the first digital-analog converter; During the period of signal modulation, when the digital-analog conversion of the second digital-analog converter is completed, the second current source is driven from the output of the second sample-hold means to the second digital-analog. And a second switching means for switching to the output of the converter. 8. The semiconductor laser drive circuit according to claim 7, wherein instead of the first switching means and the second switching means, a section of modulation by a recording signal, digital-analog conversion by the first digital-analog converter. Recording means for adding the output of the first digital-analog converter to the charge accumulation point of the first sample-hold means that holds the first control voltage when During the period of modulation by the second digital-analog converter, the second digital-analog converter completes the digital-analog conversion. A semiconductor laser drive circuit comprising: a second adding means for adding the outputs of the analog converters. 9. The semiconductor laser drive circuit according to claim 7, wherein, instead of the first analog-digital converter and the second analog-digital converter, one shared analog-digital converter is used. , The first
2. A semiconductor laser drive circuit comprising: an input selection means for selecting one of the output of the sample hold means and the output of the second sample hold means and inputting it to the shared analog-digital converter.