JP2003273448A - Driving circuit and method for semiconductor laser, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the unfavorable influence of noise in a driving circuit for a semiconductor laser where a current addition system is employed as a superposing system for a high frequency current. <P>SOLUTION: When a semiconductor laser is driven by a driving current including a high frequency current superposed on a DC current, the driving current is generated by adding and superposing the high frequency current on the DC current while controlling a current level of the DC current such that the output power of the semiconductor laser is constant. Simultaneously, a noise component with a predetermined frequency band involved in the driving current is attenuated by a predetermined filter means provided in parallel to the semiconductor laser. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser drive circuit and method, and an optical disk device, for example, a semiconductor laser is driven by a drive current obtained by adding and superposing a high frequency current to a direct current, and a light beam emitted from the semiconductor laser. It is suitable to be applied to an optical disk device that reproduces data recorded on the optical disk by irradiating the optical disk.

[0002]

2. Description of the Related Art Conventionally, as a method for reducing so-called return optical noise in an optical disk device, there is a method of superposing a high frequency current on a direct current for driving a semiconductor laser provided in an optical pickup during a reproducing operation. Widely used.

In this case, in a semiconductor laser drive circuit (hereinafter simply referred to as a semiconductor laser drive circuit) in such an optical disk device, in order to prevent the influence of unnecessary radiation due to superposition of the high frequency current, such high frequency current is generated. And a high frequency generator to control the output power of the laser light emitted from the semiconductor laser to a constant level.
A power control circuit is separately provided, and these are connected in a final stage through a coupling circuit having frequency selectivity such as a series resonance circuit.

In the semiconductor laser driving circuit having such a conventional structure, as shown in FIG. 8, the transmission band (0 to 30 [MHz]) of the reproduction signal in the optical disk device and the high frequency current superposed on the direct current. Band (for example, 200 to 600 [MH
z)) is far away, and due to the existence of such a coupling circuit, the noise component in the high frequency current band out of the wide band noise generated in the high frequency generation part is the drive current (the DC current superposed with the high frequency current). However, the noise component in the transmission band of the reproduction signal was not mixed in the drive current.

[0005]

However, in recent years,
Semiconductor laser drive circuits are being integrated into ICs (Integrated Circuits). As a method of superposing high-frequency currents in such semiconductor laser drive circuits, high-frequency currents can be used without interposing a coupling circuit having frequency selectivity for chip miniaturization. A so-called current addition method, in which the generator and the APC circuit are directly connected, is often adopted.

However, according to this superposition method, as shown in FIG. 9, the broadband noise generated in the high frequency generator is directly added to the DC current. A noise component in the transmission band mixes with the drive current and adversely affects the lighting of the semiconductor laser, causing noise in the laser beam emitted from the semiconductor laser, which causes noise in the reproduction signal.

Specifically, _assuming that the semiconductor laser is an ideal element and its own noise is sufficiently small, the output power of the semiconductor laser is P ₀ , the slope efficiency is η, and the noise current mixed in the drive current is I _n . The noise current I _n
The amount of laser light modulation by

[0008]

[Equation 1]

[0009] Therefore, as the slope efficiency η of the semiconductor laser increases, the output power P of the semiconductor laser increases.
It can be seen that the smaller ₀ is, the larger the noise included in the laser light emitted from the semiconductor laser is.

In this case, the slope efficiency η of the conventional red semiconductor laser was about 0.5 to 0.75, but the slope efficiency of the blue semiconductor laser which is being developed along with high density recording of optical disks in recent years has a slope efficiency η. It becomes as large as 1.25.

Therefore, when the blue semiconductor laser is used as the light source of the optical disk device, in order to reduce the noise contained in the laser light, the noise current I _n mixed in the drive current is reduced.
The reduced or is not the only way to increase the output power P ₀ of the semiconductor laser, generates the semiconductor laser driving circuit IC of the noise is a stationary so determined by the manufacturing process of the IC, and the output power P ₀ Is determined by the specifications of the optical disk device and the coupling efficiency of the optical system (the ratio of the brightness of the reflected return light to the brightness of the emitted light), which cannot be easily reduced.

The present invention has been made in consideration of the above points, and a semiconductor laser drive circuit capable of reducing adverse effects of noise in a semiconductor laser drive circuit using a current addition method as a superposition method of high frequency currents, and A method and an optical disc device are proposed.

[0013]

In order to solve the above problems, according to the present invention, in a semiconductor laser drive circuit for driving a semiconductor laser by a drive current in which a high frequency current is superimposed on a direct current, the output power of the semiconductor laser is constant. So that the control means for controlling the current level of the direct current, the high frequency generating means for generating the high frequency current, the superposition means for generating the drive current by adding the direct current and the high frequency current, and the semiconductor laser in parallel The filter means is provided for attenuating a noise component in a predetermined band included in the drive current. As a result, in this semiconductor laser drive circuit, the noise component in the desired band can be attenuated by the filter unit out of the broadband noise generated in the high frequency generation unit included in the drive current.

Further, in the present invention, in a semiconductor laser driving method for driving a semiconductor laser by a driving current in which a high frequency current is superimposed on a direct current, the current level of the direct current is controlled so that the output power of the semiconductor laser becomes constant. However, a drive current is generated by adding a high-frequency current to the direct current so as to superimpose it, and a noise component in a predetermined band included in the drive current is generated in a predetermined manner in parallel with the semiconductor laser. The first step of attenuating by the filter means and the second step of driving the semiconductor laser by the drive current in which the noise component of the predetermined band is attenuated by the filter means are provided. As a result, according to this semiconductor laser driving method, the noise component in the desired band can be attenuated by the filter unit out of the broadband noise generated in the high frequency generating unit included in the driving current.

Further, according to the present invention, the semiconductor laser is driven by a drive current obtained by superposing a high frequency current on a direct current, and the optical beam emitted from the semiconductor laser is irradiated onto the optical disk so that the information recorded on the optical disk. In an optical disk device for reproducing data, a control means for controlling the current level of the direct current so that the output power of the semiconductor laser is constant, a high frequency generating means for generating a high frequency current, and a direct current and a high frequency current are added. The superimposing means for generating the drive current by the means and the filter means provided in parallel with the semiconductor laser for attenuating the noise component of the predetermined band included in the drive current are provided.
As a result, in this optical disc device, the noise component in the desired band can be attenuated by the filter unit among the broadband noise generated in the high frequency generation unit included in the drive current.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of Semiconductor Laser Driving Circuit According to this Embodiment In FIG. 1, reference numeral 1 denotes the semiconductor laser driving circuit according to this embodiment which is mounted on a read-only optical disk device as a whole. The semiconductor laser 2 is driven by a drive current I ₃ in which a high frequency current I ₂ is superimposed on a direct current I ₁ of a predetermined level.

That is, in the semiconductor laser drive circuit 1, the APC circuit 3 for controlling the current level of the direct current I ₁ so that the output power of the laser light emitted from the semiconductor laser 2 is always constant, and the direct current I _{1. 1} and a high frequency generator 4 for generating a high frequency current I ₂ .

In this case, in the APC circuit 3, a current level corresponding to the output power of the laser light output from the monitoring photodiode 5 for monitoring the output power of the laser light emitted from the semiconductor laser 2 is output. The power detection signal S1 is current-voltage converted by the current-voltage converter 7 including the operational amplifier 6 and the feedback resistor R1, and the power detection voltage signal S2 thus obtained is input to the error detector 8.

The error detecting section 8 has an operational amplifier 9 having an inverting input terminal connected to the output terminal of the operational amplifier 6 of the current-voltage converting section 7 via a resistor R2, and a feedback resistor R3 connected in parallel to the operational amplifier 9. The operational amplifier 9 has a comparison circuit configuration including a feedback resistor R4 and a capacitor C1 connected in parallel, and a non-inverting input terminal of the operational amplifier 9 is applied with a reference voltage of a preset voltage level that can be set from a reference voltage source 10. It

Thus, in the error detection section 8, the voltage level of the power detection voltage signal S2 from the current / voltage conversion section 7 is compared with the voltage level of the reference voltage from the reference voltage source 10, and the difference between these levels (that is, An error signal S3 having a voltage level corresponding to the potential difference is sent to the base of a transistor (hereinafter referred to as an APC circuit output stage transistor) TR1 provided in the output stage of the APC circuit 3.

At this time, the output stage transistor T of the APC circuit
The emitter of R1 is connected to the cathode terminal of the monitoring photodiode 5 via the resistor R5, and the connection midpoint between the resistor R5 and the monitoring photodiode 5 is connected to the constant voltage source Vcc.

As a result, in the APC circuit 3, the AP
Based on the error signal S3 from the error detection unit 8 applied to the base of the C circuit output stage transistor TR1, the DC current I ₁ having a current level corresponding to the voltage level of the error signal S3 is supplied to the APC circuit output stage transistor TR1. It is designed to be able to output from the collector of.

On the other hand, the high-frequency generator 4 has a high-frequency generator 12 whose oscillation frequency can be freely adjusted by operating the frequency controller 11 composed of a variable resistor. The output high frequency current (HF: High Frequency) is input to the base of the first transistor TR2 of the high frequency current level control unit 13.

In this case, the first transistor TR2
A constant reference voltage is applied from the battery 14 to the base of the second transistor TR3 that integrally forms a differential pair with TR2 of the first and second transistors.
The common emitter of TR3 is a constant voltage source 16 including a transistor TR4 and a battery 15 that applies a constant voltage to the base of the transistor TR4, and a level adjusting unit 17 including a variable resistor for adjusting the current level of the high frequency current I _2.
It is grounded through and.

The first and second transistors TR2,
Each collector of TR3 is connected to the constant voltage source Vcc either directly or via a resistor R6, and the middle point of connection between the collector of the second transistor TR3 and the resistor R6 is provided at the output stage of the high frequency generator 4. Further, it is connected to the base of a transistor (hereinafter, referred to as a high frequency generator output stage transistor) TR5 that forms a differential pair integrally with the APC circuit output stage transistor TR1. Further, the emitter of the high frequency generator output stage transistor TR5 has a resistor R
It is connected to the constant voltage source Vcc via 7.

As a result, in the high frequency generator 4, the high frequency current I ₂ generated by the high frequency oscillator 12 is controlled by the high frequency current level controller 13 to a current level preset in the level adjuster 17, and the high frequency generator 12 is generated. The output can be output from the collector of the partial output stage transistor TR5.

In this semiconductor laser drive circuit 1,
The common collector of the APC circuit output stage transistor TR1 and the high frequency generator output stage transistor TR5 is grounded via the semiconductor laser 2.

As a result, in the semiconductor laser driving circuit 1, the DC current I ₁ whose current level is adjusted by the APC circuit 3 and the high frequency current I ₂ generated by the high frequency generating section 4 and having a predetermined frequency and a predetermined current level. Is superposed and supplied to the semiconductor laser 2 as a drive current I ₃ , and the semiconductor laser 2 can be driven to be lit based on the drive current I ₃ .

In addition to the above configuration, in the case of the semiconductor laser drive circuit 1, the APC circuit 3 and the high frequency generator 4 are provided.
In addition, the semiconductor laser 2 is connected between the terminals of the semiconductor laser 2.
A band eliminate filter 20 is connected in parallel with the.

The band eliminate filter 20 is
It has a series resonance circuit configuration formed of a capacitor C2 and a coil L1 connected in series, and its resonance frequency f ₀ is selected to be about 10 to 30 [MHz] which is within the transmission frequency band of the reproduction signal reproduced from the optical disk. ing.

As a result, in the semiconductor laser drive circuit 1, as shown in FIG. 2, of the wide band noise generated in the high frequency generator 4, the noise component near the resonance frequency f ₀ of the band eliminate filter 20 is reduced to the band. Since the band elimination filter 20 can be attenuated by the elimination filter 20 and the band elimination filter 20 is provided in parallel with the semiconductor laser 2, it is possible to reduce the reduction amount of the insertion loss due to the insertion of the band elimination filter 20. Has been done.

(2) Operation and effects of the present embodiment With the above configuration, in the semiconductor laser drive circuit 1, the direct current I ₁ whose current level is controlled by the APC circuit 3 and the high frequency generator in the reproducing operation. The high frequency current I ₂ having the predetermined frequency and the predetermined current level generated by the circuit 4 is added from the common collector of the APC circuit output stage transistor TR1 and the high frequency generating unit output stage transistor TR5, and is given to the semiconductor laser 2 as the drive current I _3. on the other hand,
The drive current I ₃ is filtered by the band eliminate filter 20 connected in parallel with the semiconductor laser 2.

As a result, of the broadband noise generated in the high frequency generator 4 included in the drive current I ₃ , the resonance frequency f ₀ (10 to 10) of the band eliminate filter 20 is generated.
A noise component in the vicinity of 30 [MHz]) is attenuated by the band elimination filter 20, and the semiconductor laser 2 is driven to light based on the filtered drive current I ₃ .

Therefore, in the semiconductor laser driving circuit 1, it is possible to reduce the occurrence of noise in the transmission band of the reproduction signal in the laser beam emitted from the semiconductor laser 2.
Thus, it is possible to effectively and effectively reduce the occurrence of noise in the transmission band of the reproduction signal due to the fluctuation or the like.

In practice, as shown in FIGS. 3 to 6, the band addition filter 20 is connected in parallel with the semiconductor laser 2 as described above from the experiment, and the current addition method is adopted as the superposition method of the high frequency current. It was confirmed that the adverse effects of doing so can be reduced.

Here, FIG. 3 shows a 2T signal (T is the shortest recording wavelength;
T is a measurement result using twice the wavelength), the waveform f1 is an amplifier noise (noise generated in the high frequency generator 4), and the waveform f2 is a physical configuration such as uneven thickness of the optical disk. Noise caused by this (hereinafter referred to as disk noise), f3 indicates noise caused by lighting fluctuation of the semiconductor laser 2 (hereinafter referred to as LD noise), and in this experiment, MTF ( Mo
The dulation transfer function) was 24 [MHz].

The waveforms f5 and f6 are 2T, respectively.
It is the reproduction spectrum of the signal and the noise level is different, but the disk noise is mainly from 0 to 10 [MHz], and the semiconductor laser 2, the RF reproduction (monitor) photodiode (4) and the reproduction at the MTF or higher. It is a combined noise of the respective noises generated in the amp (high-frequency generator 4). From this, it is understood that the noise (hereinafter, referred to as LD noise) due to the fluctuation of the lighting of the semiconductor laser 2 and the like contributes to 10 [MHz] or more.

Therefore, in the present embodiment, as described above, the resonance frequency f of the band eliminate filter 20 is set.
₀ is set to 10 to 30 [MHz] to avoid the reproduction signal transmission band in which the contribution rate of the LD noise is small, and the APC
The band characteristic in the circuit 3 can be sufficiently ensured.

FIG. 4 shows the resonance frequency f ₀ of the band eliminate filter 20 in the semiconductor laser drive circuit 1 according to the present embodiment described with reference to FIG.
z] (the inductance of the coil C2 is 22 [nH],
The capacitance of the capacitor is selected to 470 [pF], a switch for turning on / off is provided in the band eliminate filter 20, and a single sweep is performed from the emitter of the APC circuit output stage transistor TR1 with the switch turned on or off. 3 shows the measurement result of the filter characteristics of the band eliminate filter 20 measured between both terminals of the semiconductor laser 2 by inputting a signal.

As is clear from this measurement result, the van
When the de-eliminate filter 20 is not operated (waveform
Compared to f10), the band elimination filter 20 is activated.
If it is made (waveform f11), band elimination
Resonance frequency f of the filter 20 ₀50 [MHz] odor
Noise of 15 [db] can be obtained, and 15 to 130 [MH]
Attenuation of 6 [db] noise in the z] band
Was confirmed. Also, the high frequency current band is 300 to 400
At [MHz], it is also confirmed that the single sweep signal will not be attenuated.
It was confirmed (waveform f12).

Further, in FIG. 5, a switch for turning on and off is provided in the band eliminate filter 20 as in the above, and the switch and the APC circuit output stage transistor TR are provided.
1 and high frequency generator output stage transistor TR5,
When only the APC circuit output stage transistor TR1 is turned on (waveform f20), the APC circuit output stage transistor TR21 and the high frequency generator output stage transistor TR
When both 5 are turned on (waveform f21), APC
It shows the measurement result of the noise level between the terminals of the semiconductor laser 2 when the circuit output stage transistor TR1, the high frequency generating unit output stage transistor TR5, and the band elimination filter 20 are all turned on (waveform f22).

From FIG. 5, the AP concerned is compared with the case where only the APC circuit output stage transistor TR1 is turned on.
Noise occurs when the C circuit output stage transistor TR1 and the high frequency generator output stage transistor TR5 are turned on.
It can be seen that it increases by 0 [dB]. At 20 MHz or higher, the noise levels output from the APC circuit output stage transistor TR1 and the high frequency generator output stage transistor TR5 are equal. When the band eliminate filter 20 is further operated in this state, these A
It can be confirmed that the noise level of the noise output from the PC circuit output stage transistor TR1 and the high frequency generator output stage transistor TR5 is lowered. Actually, the characteristic is as shown by the waveform f11 in FIG.

Further, FIG. 6 shows that the output power of the semiconductor laser 2 when the band elimination filter 20 is provided with a switch to operate the band elimination filter 20 or to stop the operation as described above ( It shows the characteristics of RIN for Pobj).

As is apparent from FIG. 6, when the band eliminate filter 20 operates, RIN decreases without depending on the output power of the semiconductor laser 2. Normally, the influence of the synthetic noise is obtained by root mean square, but since the noise in the semiconductor laser drive circuit 1 is a signal whose linearity of the slope efficiency η is well modulated, the output power of the semiconductor laser 2 is small and It can be seen that even if the noise of the laser 2 becomes large, the influence does not change because RIN is a relative ratio.

In this way, the band eliminate filter 2
It was confirmed that by connecting 0 to the semiconductor laser 2 in parallel, it is possible to reduce the adverse effect of adopting the current addition method as the superposition method of the high frequency current.

According to the above configuration, the current addition method is used.
DC current I₁High frequency current I_TwoLaser that superimposes
In the drive circuit 1, the resonance frequency is within the reproduction signal transmission band.
Number f ₀Band elimination filter 20 having
Driven by being installed in parallel with the body laser 2.
Current I₁Generated in the high frequency generator 4 included in
Of wideband noise, band elimination filter 2
Resonance frequency f of 0₀(Attenuating nearby noise components
You can To do this, fire from the semiconductor laser 2.
Noise in the transmission band of the reproduced signal occurs in the laser light generated,
Due to this, noise occurs in the transmission band of the reproduced signal.
Can be effectively and effectively reduced.
The current addition method was adopted as the superposition method of high-frequency current.
Semiconductor laser that can reduce the adverse effects of noise in cases
The drive circuit can be realized.

In this case, the band elimination filter 20 is provided in parallel with the semiconductor laser 2 so that the reduction amount of the insertion loss due to the insertion of the band elimination filter 20 in the semiconductor laser drive circuit 1 can be reduced. You can

(3) Other Embodiments In the above-described embodiments, the case where the resonance frequency f ₀ of the band eliminate filter 20 is set to 10 to 30 [MHz] has been described. However, the present invention is not limited to this. Not limited to this, for example, it may be set to be lower than 10 [MHz] or higher than 30 [MHz]. When the semiconductor laser drive circuit according to the present invention is applied to a device other than an optical disc device, the resonance frequency f ₀ of the band eliminate filter 20 is a frequency required or desired in the device other than 10 to 30 [MHz]. The band should be set.

In the above embodiment, the case where the semiconductor laser drive circuit according to the present invention is applied to the read-only optical disk device has been described, but the present invention is not limited to this, and the optical disk for recording and reproducing is described. You may make it apply to an apparatus.

In this case, if the band eliminate filter 20 is kept operating during the recording operation,
The presence of the band eliminate filter 20 may adversely affect the frequency characteristics of the drive current of the semiconductor laser 2 that is modulated and generated based on the recording data.

Therefore, when the semiconductor laser drive circuit according to the present invention is applied to an optical disk device for recording and reproducing,
For example, as shown in FIG. 7, a capacitor C2 and a coil L
A switching transistor TR10 is provided in series with 1,
By applying a constant voltage to the resistor R10 during the reproducing operation, the voltage at the connection midpoint of the resistors R10 and R11 is applied to the base of the switching transistor TR10 to operate the band eliminate filter 30, while during the recording operation, the resistor R10 is applied. The band elimination filter 30 may be constructed so that the switching transistor TR10 is turned off and the operation of the band elimination filter 30 is stopped by stopping the voltage application. In this case, instead of the switching transistor TR10, other switching means capable of switching the operation of the band eliminate filter 20 and its stop may be used.

Incidentally, when the semiconductor laser drive circuit according to the present invention is applied to an optical disk device for recording and reproducing,
By providing the filter means in parallel with the semiconductor laser as in the present invention, there is an advantage that the operation of the filter means and the switching thereof can be easily performed, as compared with the case where the filter means is provided in series with the semiconductor laser.

Further, in the above embodiment, the APC circuit 3 and the high frequency current I ₂ as the control means for controlling the current level of the direct current I ₁ are generated so that the output power of the semiconductor laser 2 becomes constant. The case where the high-frequency generating section 4 as the high-frequency generating means is configured as shown in FIG. 1 has been described, but the present invention is not limited to this, and various other configurations can be widely applied.

Further, in the above-described embodiment, the superimposing means for generating the drive current I ₃ by adding the direct current I ₁ and the high frequency current I ₂ is composed of the APC circuit output stage transistor TR1 and the differential pair with this. The case where the high-frequency generator output stage transistor TR5 is configured has been described, but the present invention is not limited to this. In short, the drive current I ₃ is obtained by adding the direct current I ₁ and the high-frequency current I _2. As long as it can be generated, various other structures can be widely applied as the structure of the superimposing means.

Further, in the above-described embodiment, the band elimination filter 20 configured as shown in FIG. 1 is applied as the filter means for attenuating the noise component of the predetermined band contained in the drive current I ₃ . However, the present invention is not limited to this, and various other configurations can be widely applied.

[0057]

As described above, according to the present invention, in a semiconductor laser drive circuit for driving a semiconductor laser by a drive current in which a high frequency current is superimposed on a direct current, the direct current is controlled so that the output power of the semiconductor laser becomes constant. A control means for controlling the current level of the current, a high frequency generation means for generating a high frequency current, a superposition means for generating a drive current by adding a direct current and a high frequency current, and a drive current provided in parallel with the semiconductor laser. By providing the filter means for attenuating the noise component in the predetermined band included in, the noise component in the desired band among the broadband noise generated in the high frequency generating means included in the drive current is attenuated by the filter means. Therefore, the semiconductor laser drive circuit using the current addition method as the superposition method of the high frequency current The semiconductor laser driving circuit which adversely capable of reducing the noise can be realized that.

Further, according to the present invention, in the semiconductor laser driving method of driving the semiconductor laser by the driving current in which the high frequency current is superposed on the direct current, the current level of the direct current is controlled so that the output power of the semiconductor laser becomes constant. However, a drive current is generated by adding a high-frequency current to the direct current so as to superimpose it, and a noise component in a predetermined band included in the drive current is generated in a predetermined manner in parallel with the semiconductor laser. By including the first step of attenuating by the filter means and the second step of driving the semiconductor laser by the drive current in which the noise component of the predetermined band is attenuated by the filter means, it is included in the drive current. Of the wideband noise generated by the high frequency generator, the noise component in the desired band is filtered. It is attenuated by, thus possible to realize a semiconductor laser drive method capable of reducing the adverse effects of noise in the semiconductor laser drive circuit current addition method is used as a method of superimposing a high-frequency current.

Further, in the present invention, the semiconductor laser is driven by a drive current in which a high frequency current is superimposed on a direct current, and the optical beam emitted from the semiconductor laser is irradiated onto the optical disk, so that the information recorded on the optical disk is recorded. In an optical disk device for reproducing data, a control means for controlling the current level of the direct current so that the output power of the semiconductor laser is constant, a high frequency generating means for generating a high frequency current, and a direct current and a high frequency current are added. By providing a superimposing means for generating a drive current by means of and a filter means provided in parallel with the semiconductor laser for attenuating a noise component of a predetermined band included in the drive current, a high frequency generating means included in the drive current is provided. The noise component in the desired band of the broadband noise generated in Can attenuate I, thus it can realize an optical disc apparatus capable of reducing the adverse effects of noise in the semiconductor laser drive circuit current addition method is used as a method of superimposing a high-frequency current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a semiconductor laser drive circuit according to an embodiment.

FIG. 2 is a schematic waveform diagram for explaining noise mixing in a drive current in the semiconductor laser drive circuit according to the present embodiment.

FIG. 3 is a waveform chart for explaining various measurement results.

FIG. 4 is a waveform chart for explaining various measurement results.

FIG. 5 is a waveform chart for explaining various measurement results.

FIG. 6 is a waveform chart for explaining various measurement results.

FIG. 7 is a circuit diagram showing a configuration example of a band eliminate filter according to another embodiment.

FIG. 8 is a schematic waveform diagram for explaining noise mixing in a drive current in a conventional semiconductor laser drive circuit.

FIG. 9 is a schematic waveform diagram for explaining noise mixing in a drive current in a current addition type semiconductor laser drive circuit.

[Explanation of symbols]

1 ... Semiconductor laser drive circuit, 2 ... Semiconductor laser, 3
... APC circuit, 4 ... high-frequency generation circuit, 20, 30 ...
… Band eliminate filter, C2… Capacitor,
L1 ... coil, TR1 ... APC circuit output stage transistor, TR5 ..., high frequency generator output stage transistor,
TR10 ...... switching transistor, _{I 1} ...... DC current, _{I 2} ...... frequency current, _{I 3} ...... drive current.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D119 AA20 BA01 DA05 EC09 FA05                       HA41 HA55                 5D789 AA20 BA01 DA05 EC09 FA05                       HA41 HA55                 5F073 BA04 EA27 GA12 GA24 GA38

Claims (8)

[Claims] 1. A semiconductor laser drive circuit for driving a semiconductor laser with a drive current in which a high frequency current is superimposed on a direct current, for controlling the current level of the direct current so that the output power of the semiconductor laser becomes constant. Means, high-frequency generation means for generating the high-frequency current, superimposing means for generating the drive current by adding the direct current and the high-frequency current, and provided in parallel with the semiconductor laser, included in the drive current And a filter means for attenuating a noise component in a predetermined band. 2. The semiconductor laser drive circuit according to claim 1, wherein the filter means is a band eliminate filter. 3. The semiconductor laser drive circuit according to claim 1, further comprising switching means for switching the filter means so as to operate or not to operate. 4. A semiconductor laser driving method for driving a semiconductor laser by a driving current in which a high frequency current is superimposed on a direct current, while controlling the current level of the direct current so that the output power of the semiconductor laser becomes constant. A driving current is generated by adding a high frequency current to the direct current so as to superimpose it, and a noise component in a predetermined band included in the driving current is filtered by a predetermined filter provided in parallel with the semiconductor laser. And a second step of driving the semiconductor laser with the drive current in which the noise component of the predetermined band is attenuated by the filter means. Driving method. 5. The method for driving a semiconductor laser according to claim 4, wherein the filter means is a band eliminate filter. 6. An optical disc for reproducing information recorded on the optical disc by driving a semiconductor laser with a drive current obtained by superposing a high frequency current on a direct current and irradiating the optical beam with a light beam emitted from the semiconductor laser. In the device, the control means for controlling the current level of the direct current so that the output power of the semiconductor laser is constant, the high frequency generating means for generating the high frequency current, and the direct current and the high frequency current are added. An optical disk device comprising: a superimposing means for generating the drive current, and a filter means provided in parallel with the semiconductor laser for attenuating a noise component of a predetermined band included in the drive current. 7. The optical disk device according to claim 6, wherein the filter means is a band eliminate filter. 8. The optical disk device according to claim 6, further comprising switching means for switching the filter means to operate or not to operate.