JPH07334859A - Semiconductor laser driving device - Google Patents

Abstract

PURPOSE:To stably drive a semiconductor laser even when the power supply voltage is made low. CONSTITUTION:When a driving pulse VGATE of a transistor Q1 side constituting a deferential switching circuit of a first step is at a high level, an inversion driving pulse V/GATE of a transistor Q2 side is made to be at a low level. At this time, the transistor Q1 is turned on and the transistor Q2 is turned off, and current i flows to the transistor Q1 from a constant current circuit 38. A transistor Q5 constituting a differential switching circuit of a second step constitutes a current mirror circuit with a resistor R3 connected to an emitter of the transistor Q5 and a resistor R1 connected to a base of the transistor Q5 through a diode D1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device used in an optical information recording / reproducing device for recording / reproducing information using a semiconductor laser as a light source.

[0002]

2. Description of the Related Art Conventionally, in an optical information recording / reproducing apparatus for recording / erasing / reproducing information on / from an optical recording medium, a semiconductor laser is used as a light source, and laser light supplied from the semiconductor laser causes an optical recording medium on the optical recording medium. Information is recorded / erased or reproduced by forming a light spot on the recording surface.

As a semiconductor laser driving device for driving the above-mentioned semiconductor laser, there is a semiconductor laser driving device as disclosed in, for example, Japanese Patent Laid-Open No. 64-66837.
In the semiconductor laser drive device of Japanese Unexamined Patent Publication No. 7, as shown in FIG. 4, a modulation signal for driving the semiconductor laser is input to the terminal 55. The transistors Q _11, Q ₁₂ functions as a switching element, each of the transistors Q _11,
The drive pulse V _GATE and V _{/ GATE} obtained by inverting this logic by an inverter 57 are supplied via a buffer 56 to the base pulled up by the resistors R ₁₄ and R ₁₃ via the resistors R ₁₅ and R ₁₆ of Q _12. .

The emitters of the transistors Q ₁₁ and Q ₁₂ are connected to the collector of a transistor Q ₁₃ which constitutes a constant current circuit 58 which supplies a current for modulating and driving the semiconductor laser LD.

The base voltage of the transistor Q ₁₃ is
The power supply voltage V _CC is controlled by a voltage obtained by dividing the power supply voltage V _CC by the resistors R ₁₁ and R ₁₂ , and the emitter is connected to the power supply voltage V _CC through the emitter resistor R _E. The anode side of the semiconductor laser (LD) 60 is connected to the collector of the transistor Q ₁₂ , and the cathode side is grounded.

In the semiconductor laser drive circuit of FIG. 4, when the drive pulse V _GATE on the transistor Q ₁₁ side is high, the drive pulse V _{/ GATE} on the transistor Q ₁₂ side is low. At this time, the transistor Q ₁₁ is turned off, the transistor Q ₁₂ is turned on, the current from the constant current circuit is supplied to the semiconductor laser 60, and the semiconductor laser 60 emits light. Conversely, when the drive pulse V _GATE on the transistor Q ₁₁ side is low, the transistor Q
The drive pulse V _{/ GAT E} on the _12th side becomes high. At this time, the transistor Q ₁₁ is turned on and the transistor Q ₁₂ is turned off,
The current is dropped to the ground via the transistor Q ₁₁ and the resistor R ₁₇ , and the current is not supplied to the semiconductor laser 60.

[0007]

However, in the recent optical information recording / reproducing apparatus, it is desired to reduce the size and power consumption of the apparatus. When V _CC is lowered, there is a problem that the operating voltage of the transistor Q ₁₂ necessary for switching current at high speed cannot be secured.

That is, the voltage drop in the constant current circuit 58 of FIG. 4 is due to the emitter-collector voltage V _{CE of the} transistor Q ₁₃ forming the constant current circuit 58, the emitter resistance R _E and the constant current source. Product of current i from the section R _E × i
When the emitter-collector voltage V _{CE2 of} the transistor Q ₁₂ and the forward voltage of the semiconductor laser 60 are V _F , V _CC = V _CE + R _E × i + V _CE2 + V _F (1) Considering the operating voltage of the transistor,
Generally, in order to switch a transistor at high speed, it is desirable that the voltage V _CE between the emitter and collector of the transistor is large. For example, V _CE = V _CE2 = 1
When it is attempted to secure (V), the forward voltage of the semiconductor laser 60 is about 2.5 V, so from the equation (1), V _CC = _RE × i + 4.5 (V) (2) Become. When R _E × i = 0.5 (V), V _CC =
It becomes 5.0 (V).

The conventional driving power supply voltage is, for example, about 12 V, so that there is no problem, but the driving voltage of the logic element is usually 5
Since it is about V, it is difficult to always switch the current at a high speed in a stable state when the semiconductor laser drive circuit is driven by the drive voltage of 5 V of the logic element, in consideration of element variations and power supply voltage variations. Is.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor laser driving device capable of stably driving a semiconductor laser even when the power supply voltage is lowered. I am trying.

[0011]

A semiconductor laser driving device of the present invention is a semiconductor laser that emits laser light, a first differential switching means that is composed of a pair of transistors that are switched by a driving pulse, and the differential switching. Constant current means connected so that the sum of the emitter currents of a pair of transistors constituting the means is constant, and the current supplied to the semiconductor laser is the same as the emitter current of the transistor of the first differential switching means or A second differential switching means composed of at least one set of transistors, which is switched as a current value multiplied by a coefficient, and has the same current value as the emitter current of the transistor of the first differential switching means by the second differential switching means. Current is switched and supplied to the semiconductor laser, Even when the low voltage the voltage, making it possible to drive the semiconductor laser stable.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 relate to a first embodiment of the present invention, and FIG. 1 is a structural diagram showing the structure of a semiconductor laser driving device,
FIG. 2 is a configuration diagram showing a configuration of an optical disc device including the semiconductor laser drive device of FIG.

As shown in FIG. 2, an optical disk device 1 as an example of a device to which the semiconductor laser driving device of this embodiment is applied, includes a signal processing section 2 for modulating and demodulating information,
An optical pickup unit 4 that generates a laser by a modulation signal modulated by the signal processing unit 2 and records or reproduces information on an optical disc 3, which is an optical recording medium, and an optical pickup unit 4.
The optical pickup section 4 based on the information detected by
And a servo unit 5 for controlling the.

The optical pickup unit 4 includes a semiconductor laser driving device 15 for supplying a laser beam composed of a laser driving circuit 11 and a semiconductor laser 12 on the basis of a modulation signal from the signal processing unit 2, and a semiconductor laser driving device 15. A collimator lens 16 for converting, for example, P-polarized laser light oscillated from the semiconductor laser 12 into parallel light, and P that has become parallel light
A beam splitter 17 that transmits polarized laser light, a quarter-wave plate 18 that converts P-polarized light that has passed through the beam splitter 17 into circularly polarized light, and a laser light that has been circularly polarized by the quarter-wave plate 18 is an optical disc. And a condenser lens 19 for condensing the S-polarized return light reflected by the optical disc 3 and separated by the beam splitter 17 through the condenser lens 19 and the quarter-wave plate 18. ,
It is composed of a photodetector 21 for detecting the return light condensed by the condenser lens 20.

The signal processing unit 2 includes a modulation circuit 22 for modulating an input signal, an RF detection circuit 23 for detecting a reproduction signal from the return light detected by the photodetector 21, and an FES detection circuit 24 for detecting a focus error signal. And a TES detection circuit 25 for detecting the tracking error signal and a demodulation circuit 26 for demodulating the reproduction signal detected by the RF detection circuit 23.

The servo unit 5 includes an FES detection circuit 24 and a TES.
Optical pickup unit 4 detected by ES detection circuit 25
With the focus error signal and the tracking error signal, the focusing actuator 27 and the tracking actuator 28 of the optical pickup unit 4 are driven to move the condenser lens in the optical axis direction and the track direction of the optical disc, thereby performing focus and tracking control. It is composed of a control circuit 29 and a tracking control circuit 30.

Since this optical disk device 1 is publicly known except for the semiconductor laser driving device 15 of this embodiment, the description of the operation of the publicly known parts will be omitted.

Next, a detailed structure of the semiconductor laser driving device 15, which is a main part of this embodiment, will be described.

The semiconductor laser driving device 15 shown in FIG.
As shown in, the modulation signal from the modulation circuit 22 is supplied to the terminal 36 to switch the laser.

The transistor Q which constitutes the differential switching circuit 40 as the first differential switching means.
₁ and Q ₂ function as switching elements, and the resistors R ₁₅ and R ₁₆ of the respective transistors Q ₁ and Q ₂ are used to connect the resistor R
_The buffer drive pulse V _GATE via the buffer 37 and the inverted drive pulse V _{/ GATE} obtained by inverting this logic by the inverter 39 are supplied to the base pulled up by ₁₄ and R ₁₃ .

[0022] The transistors Q _1, resistors R ₁ to the collector of Q _2, R _2, power supply voltage is supplied V _CC via the diodes D _1, D _2, transistors Q _1, Q
The emitter of ₂ is connected to the collector of a transistor Q ₃ which constitutes a constant current circuit 38 as a constant current means. The base of the transistor Q ₃ is connected to the control voltage V ₁ of the constant current circuit 38, and the emitter is dropped to the ground via the emitter resistor R _E.

Further, the transistor Q ₄ , which constitutes the differential switching circuit 41 as the second differential switching means,
Q ₅ functions as a switching element, and the bases of the transistors Q ₄ and Q ₅ are connected to the collectors of the transistors Q ₁ and Q ₂ , respectively, and the transistors Q ₁ and
Drive pulse V that is differentially switched by Q _{2
The GATE} and the inversion drive pulse V _{/ GATE} are supplied. The power supply voltage V _CC is supplied to the emitters of the transistors Q ₄ and Q ₅ via the resistor R ₃ . The collector of the transistor Q ₄ is dropped to the ground, and the collector of the transistor Q ₅ is connected to the anode of the semiconductor laser 12. Semiconductor laser 1
The cathode of 2 is connected to ground.

It should be noted that instead of the diodes D ₁ and D ₂ , the bases of the same type of transistors as the transistors Q ₄ and Q ₅ ,
You may use the thing which short-circuited the collector.

The operation of the semiconductor laser driving device 15 thus constructed will be described.

When the drive pulse V _GATE on the side of the transistor Q ₁ forming the first stage differential switching circuit is high,
The inversion drive pulse V _{/ GATE} on the transistor Q ₂ side becomes low. At this time, the transistor Q ₁ is turned on, the transistor Q ₂ is turned off, and the current i flows from the constant current circuit 38 to the transistor Q ₁ .

The transistor Q ₅ constituting the differential switching circuit of the second stage is connected via a diode D ₁ to the base of the resistor R ₃ and a transistor Q ₅ which is connected to the emitter of the transistor Q ₅ Since a current mirror circuit is constituted by the resistor R ₁ , if the semiconductor laser 12 having a voltage drop in the diode D ₁ equal to the base-emitter voltage of the transistor Q ₅ is used, i × R ₁ / R ₃ Current flows.

On the contrary, when the drive pulse V _GATE on the side of the transistor Q ₁ forming the first stage differential switching circuit is low, the drive pulse V _{/ GATE} on the side of the transistor Q ₂ becomes high. At this time, the transistor Q ₁ is turned off and the transistor Q ₂ is turned on, and the current i from the constant current circuit 38 flows through the transistor Q ₂ . Transistors Q ₄ constituting the differential switching circuit of the second stage, the transistor Q ₄
Resistor R ₃ and transistor Q ₄ connected to the emitter of
Since a current mirror circuit is constituted by the resistor R ₂ connected to the base of the transistor through the diode D ₂ , a current of i × R ₁ / R ₂ flows through the transistor Q ₄ and the semiconductor laser 12 Is not supplied with current.

Therefore, the power supply voltage V _CC is equal to the transistor Q.
₅ Emitter-collector voltage V _CE and emitter resistance R
Since the sum of the forward voltage V _F of the product i × R ₃ and the semiconductor laser 12 and the current i flowing through the ₃ Toko the resistor portion R _3, expressed as _{V CC = V CE + i ×} R 3 + V F. If R ₃ is determined by the value of i such that i × R ₃ = 0.5 (V), the forward voltage of the semiconductor laser 12 is about 2.5 (V), so V _CC = V _CE +3 It becomes 0.0 (V). Considering driving this circuit at a power supply voltage of 5.0 (V), the emitter-collector voltage V _CE of the transistor Q ₅ can be secured up to 2.0 (V), which is a comparison with the conventional example. As a result, a large voltage of 1.0 (V) can be secured. Therefore, the current can be switched at a high speed at a stable speed.

Also, instead of the diodes D ₁ and D ₂ , the bases of the transistors of the same type as the transistors Q ₄ and Q ₅ ,
If the collector is short-circuited, the error in the voltage drop at the pn junction of the semiconductor will be smaller than in the case of a diode, and even if the ambient temperature changes, the pn junction of the semiconductor will change.
Since the temperature characteristics of the junction are equal, a more stable current can be supplied to the semiconductor laser 12.

The optical disk device is an optical disk device for recording on a write-once type, phase change type or magneto-optical type optical disk, and the driving method thereof is, for example, the CLV method or CA.
This embodiment can be applied to either the C method or the ZCAV method.

Further, although the semiconductor laser driving device is applied to the optical disk device in the present embodiment, the present invention is not limited to this, and it can also be applied to a semiconductor laser used in, for example, a laser printer, an optical communication device or the like. Needless to say.

Next, a second embodiment will be described. FIG. 3 is a configuration diagram showing a configuration of a semiconductor laser driving device according to the second embodiment of the present invention. Since the second embodiment is almost the same as the first embodiment, only different configurations will be described, the same configurations will be denoted by the same reference numerals, and description thereof will be omitted.

In the second embodiment, as the second differential switching means, in addition to the differential switching circuit 41 including the transistors Q ₄ and Q ₅ for switching the current supplied to the semiconductor laser of the first embodiment, this difference is provided. A differential switching circuit configured in the same manner as the dynamic switching circuit is connected in parallel to supply a current to the semiconductor laser.

That is, the transistor Q is connected in parallel to the differential switching circuit 41 including the transistors Q ₄ and Q _5.
A differential switching circuit 42 composed of ₆ and Q ₇ and a differential switching circuit 43 composed of transistors Q ₈ and Q ₉ are provided, and the emitters of the transistors Q ₆ and Q _{7 and} the emitters of the transistors Q ₈ and Q ₉ are resistor R ₄ and R ₅ are connected to the power supply voltage V _CC , the driving pulse V _{G ATE is} supplied to the bases of the transistors Q ₆ and Q ₈ , the collector is grounded, and the inversion driving pulse is supplied to the bases of the transistors Q ₇ and Q _9. V _{/ GATE is} supplied and the collector is grounded. The other structure is the same as that of the first embodiment.

In the semiconductor laser driving device of the second embodiment in which three second stage differential switching circuits are connected in parallel, when the driving pulse voltage V _GATE supplied to the base of the transistor Q ₁ is high, current i from the constant current circuit 38 flows through the transistor Q _1, the transistors Q _5, Q _7,
Q ₉ is connected to the emitters of the transistors Q ₅ , Q ₇ , Q ₉ by resistors R ₃ , R ₄ , R ₅ and the bases of the transistors Q ₅ , Q ₇ , Q ₉ via a diode D _1. Since a current mirror circuit is constituted by the connected resistor R ₁ , when the resistors R ₃ , R ₄ and R _{5 have} the same value, the transistors Q ₅ , Q ₇ and Q ₉ have constant current circuits. A current equal to the current i from 38 flows. Therefore, the semiconductor laser 12 is supplied with a current 3 × i which is three times as large as the total of them.

Conversely, when the drive pulse voltage V _GATE supplied to the base of the transistor Q ₁ is low, the drive pulse voltage V _{/ GATE} supplied to the base of the transistor Q ₂ becomes high. At this time, the current i from the constant current circuit flows through the transistor Q _2, the transistors Q _4, Q _6, Q _8, the transistors Q _4, Q _6, and is connected to a respective emitter resistor of Q ₈ R _3, R ₄ , R ₅ and transistors Q ₄ , Q ₆
, Q _{8 and} the resistor R ₁ connected via the diode D ₁ to the base of the current mirror circuit, the transistors Q ₄ , Q ₆ , and Q ₈ receive the current from the constant current circuit 38, respectively. A current equal to i flows. Therefore, no current is supplied to the semiconductor laser 12.

Therefore, in this embodiment, in addition to the effects of the first embodiment, even if a plurality of differential switching circuits for switching the current supplied to the semiconductor laser 12 are connected in parallel, the same effects as in the first embodiment are obtained. An operating voltage for operating the element at high speed can be secured, and by connecting in parallel a differential switching circuit that switches the current supplied to the semiconductor laser, the current flowing through the transistors that make up this differential switching circuit can be adjusted. Therefore, a stable current can be supplied to the semiconductor laser.

In this embodiment, three differential switching circuits are connected in parallel, but the number of circuits is not particularly limited to three, and a plurality of circuits may be formed if necessary.

That is, when n differential switching circuits of the second stage are connected in parallel, n times the current (current n × i) from the constant current source is supplied to the semiconductor laser 12.

Further, by selectively mounting a plurality of differential switching circuits on the substrate or selectively operating the mounted differential switching circuits by the switching means, a plurality of different characteristics can be obtained with the same configuration. It becomes possible to drive the semiconductor laser.

[0042]

As described above, according to the semiconductor laser driving device of the present invention, the second differential switching means supplies a current having a current value which is the same as or a factor times the emitter current of the transistor of the first differential switching means. Since the semiconductor laser is switched and supplied to the semiconductor laser, there is an effect that the semiconductor laser can be stably driven even when the power supply voltage is lowered.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a semiconductor laser driving device according to a first embodiment.

2 is a configuration diagram showing a configuration of an optical disc device including the semiconductor laser driving device of FIG.

FIG. 3 is a configuration diagram showing a configuration of a semiconductor laser driving device according to a second embodiment.

FIG. 4 is a configuration diagram showing a configuration of a semiconductor laser driving device according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical disk device 2 ... Signal processing part 3 ... Optical disk 4 ... Optical pickup part 5 ... Servo part 12 ... Semiconductor laser 15 ... Semiconductor laser drive device 38 ... Constant current circuit 40, 41, 42, 43 ... Differential switching circuit

Claims (2)

[Claims] 1. A semiconductor laser that emits a laser beam, a first differential switching unit that includes a pair of transistors that are switched by a drive pulse, and a sum of emitter currents of the pair of transistors that form the differential switching unit. Constant current means connected so as to keep constant, and at least one set of switching current supplied to the semiconductor laser as a current value which is the same as or a multiple of the emitter current of the transistor of the first differential switching means. A semiconductor laser driving device comprising: a second differential switching means including a transistor. 2. The second differential switching means comprises a plurality of sets of transistors, and the first differential switching means is connected to the plurality of sets of transistors in parallel. Item 2. The semiconductor laser drive device according to item 1.