JPH0575192A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To prevent an increase in noise so as to make no continuous light emission even during a change in environment temperature by electrifying a semiconductor laser device always with a constant dc current of less than an emission start current and by adjusting the amplitude of high frequency current superposed on it according to changes in temperature to control emission power at a constant level. CONSTITUTION:A high frequency current superposition circuit 4 superposes high frequency current pulses on electrification current II of a semiconductor laser 1. This process allows the semiconductor laser 1 to emit light, a photodetector 5 to detect emitted light amount, an I-V conversion circuit 6 to produce voltage signals, a deviation detection circuit 7 to output deviation signal S1, and a high frequency current superposition circuit 4 to control the amplitude of high frequency current according to the deviation signal S1 and to keep emitted light average power constant even during a change in environment temperature. In such a way, the semiconductor laser 1 is energized always with a constant dc current i1 which does not exceed an emission start current even during a change in environment temperature; therefore, an increase in noise is prevented.

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 particularly suitable for an optical disk device.

[0002]

2. Description of the Related Art Generally, in an optical disk device, a semiconductor laser element (hereinafter, simply referred to as a semiconductor laser) emits a laser beam, and the optical disk is irradiated with the laser beam through an optical system such as various prisms and lenses. In this case, so-called return light is generated in which a part of the emitted light is reflected by the optical system and returns to the semiconductor laser. This return light becomes noise of the laser light with which the optical disc is irradiated.

In order to reduce such noise, for example, as disclosed in Japanese Patent Laid-Open No. 60-192377, there has been proposed a device in which a high frequency pulse current is superimposed on a direct current for driving a semiconductor laser. ing. In this proposal, as shown in FIG. 10, the semiconductor laser is driven by a current obtained by superimposing a pulse current Ip having a constant amplitude on a direct current Ib that is equal to or less than a threshold current It required for emitting laser light.

At the ambient temperature T, the light quantity-current characteristic, which is the relationship between the light quantity L of the semiconductor laser and the drive current I, is as follows.
It is assumed that the characteristics are as shown by the solid line in the figure. in this case,
The semiconductor laser is synchronized with its pulse current Ip and is shown in FIG.
It emits light as indicated by p.

Conventionally, when the semiconductor laser is driven in this way, the direct current Ib is adjusted so that the average power Po of the light emission amount is always constant.

By the way, the semiconductor laser has a property that the light amount-current characteristic changes according to the change of environmental temperature. For example, if the environmental temperature now rises from T to T ',
The light amount-current characteristic changes as shown by the alternate long and short dash line in FIG. In this case, the direct current is increased to Ib 'to obtain a predetermined average power Po.

However, in this case, since the direct current Ib 'exceeds the threshold current It, the semiconductor laser does not have an off period and continuously emits light. When the semiconductor laser continuously emits light in this way, the noise reduction effect due to the superposition of pulse currents is reduced, and the noise of the laser light with which the optical disc is irradiated is increased.

On the other hand, as a circuit system for controlling the light emission amount to a constant value with respect to the temperature change, for example, Japanese Patent Laid-Open No. 61-4
As disclosed in Japanese Patent No. 2182, there is proposed one in which an ambient temperature is detected by a temperature sensor and the drive current of a semiconductor laser is adjusted according to the detection result. Further, as disclosed in Japanese Patent Application Laid-Open No. 63-124235, there has been proposed one in which a light receiving element detects the amount of light emitted from a semiconductor laser and the drive current of the semiconductor laser is adjusted based on the detection result.

However, these proposals require a temperature sensor and a light receiving element as well as a detection circuit for extracting a detection signal from them, so that the driving circuit of the semiconductor laser is complicated.

[0010]

As described above, conventionally, in order to reduce noise, when a semiconductor laser is driven by a direct current superposed with a high frequency current, the noise of the laser light increases due to a temperature change. There was a problem that it would end up. Further, conventionally, there has been a problem that the circuit configuration of the circuit for controlling the light emission amount constant with respect to the temperature change becomes complicated.

It is an object of the present invention to solve the above problems and to provide a semiconductor laser drive circuit having a simplified circuit configuration while preventing an increase in noise of laser light.

[0012]

To this end, according to one aspect of the present invention, a semiconductor laser device is always supplied with a constant direct current equal to or less than a light emission start current, and a high frequency current is superposed on the constant current. By adjusting the amplitude of the high frequency current according to the temperature change,
The feature is that the emission power is controlled to a constant level. Another invention is to apply a drive current proportional to the base current of one transistor to a semiconductor laser device and adjust the base current,
When a light amount setting circuit for arbitrarily setting the light emission power is provided, the light amount setting circuit is provided with a semiconductor element that lowers the base current according to the temperature rise.

[0013]

According to the above-mentioned invention, the direct current applied to the semiconductor laser is always less than the light emission start current, and continuous light emission does not occur even if the environmental temperature changes, so that the increase of noise is prevented. ..

According to another aspect of the invention, the semiconductor laser drive circuit is simple in circuit configuration because the light emission amount can be controlled to be constant with respect to the temperature change only by disposing a semiconductor element in the light amount setting circuit. become.

[0015]

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

FIG. 1 is a circuit diagram of a semiconductor laser driving circuit according to the first embodiment of the present invention. In the figure, a power supply voltage Va is applied to one end of a semiconductor laser 1, and the other end is connected to a current source circuit 2, a switch circuit 3, and a high frequency current superposition circuit 4. The bias voltage Vb is applied to one end of the light receiving element 5, and the other end is IV.
It is connected to the conversion circuit 6. The output of the IV conversion circuit 6 is input to the deviation detection circuits 7 and 8, respectively. A constant reference voltage Ref1 is input to the deviation detection circuit 7, and a constant reference voltage Ref2 is input to the deviation detection circuit 8. The output of the deviation detection circuit 7 is input to the high frequency current superposition circuit 4. A control signal for turning the circuit operation on and off is input to the high frequency current superimposing circuit 4 from a control circuit (not shown).

The output of the deviation detection circuit 8 is input to the level holding circuit 9, and the output of the level holding circuit 9 is input to the current source circuit 10. One end of the output of the current source circuit 10 is connected to the switch circuit 3, and the other end is grounded. An ON / OFF signal for controlling the switch circuit 3 and a data signal are input to the switching circuit 11 from a control circuit (not shown), and one of them controls the switch circuit 3. ..

With the above structure, the semiconductor laser drive circuit of this embodiment has three operation modes, as shown in FIG. 2, which are a reproduction mode, a recording / erasing mode, and a power control mode. Each mode can be switched as needed.

The reproduction mode is a mode for reading recorded data from an optical disk (not shown). The recording / erasing mode is a mode for recording data on the optical disc and erasing the recorded data. The power control mode is a mode for adjusting the amount of laser light emitted when recording or erasing the data. The operation in the power control mode is executed once immediately after the circuit is started up, and is repeatedly executed after the circuit is started, for example, at regular intervals or every time a certain number of sectors of the optical disk are accessed.

Next, the operation of this semiconductor laser drive circuit will be described.

The current source circuit 2 constantly applies a constant current I1 to the semiconductor laser 1. As shown in FIG. 3, the constant current I1 is set to be equal to or lower than the threshold current It that is the minimum required for the light emission of the semiconductor laser 1.

Now, assume that the reproduction mode is set. In this case, as shown in FIG. 4, the operation of the high frequency current superposition circuit 4 is turned on (process 101) and the switch circuit 3 is turned off (process 102).

When the high frequency current superposition circuit 4 is turned on, FIG.
As shown in, the high frequency current pulse is superimposed on the conduction current I1 of the semiconductor laser 1. As a result, the semiconductor laser 1
Is emitted, and the light receiving element 5 detects the amount of emitted light. I-
The V conversion circuit 6 outputs the detected emitted light amount as a voltage signal. The deviation detection circuit 7 outputs the deviation between the voltage signal and the constant reference voltage Ref1 as a deviation signal S1. The high frequency current superimposing circuit 4 controls the amplitude of the high frequency current output according to the deviation signal S1.

Now, assuming that the semiconductor laser 1 has the light quantity-current characteristics as shown by the solid line in the figure at the ambient temperature T1, the emitted light having a constant average power P1 at a constant amplitude Ih1 of the high frequency current. You will get it.

Here, for example, it is assumed that the ambient temperature rises to T'and the light amount-current characteristic is changed as shown by the alternate long and short dash line. In this case, the amount of light emitted from the semiconductor laser is reduced. When the amount of emitted light decreases, the detection level of the light receiving element 5 decreases, the voltage signal of the IV conversion circuit 6 also decreases, and the deviation signal S1 output by the deviation detection circuit 7 increases. The high frequency current superimposing circuit 4 increases the amplitude of the high frequency current according to the rise of the deviation signal S1. This allows
The amplitude of the high frequency current is increased to Ih2, and the average power P1 of the emitted light is kept constant.

Further, when the environmental temperature is lowered, the average power P1 of the emitted light is similarly maintained by the operation opposite to the above. In this way, the optical disk reproducing operation is executed by the reproducing means (not shown) while the power of the emitted light is kept constant.

Next, assume that the power control mode is set. In this case, as shown in FIG. 5, the operation of the high frequency current superposition circuit 4 is turned off (process 201) and the switch circuit 3 is turned on (process 202).

In this case, the switch circuit 3 supplies the semiconductor laser 1 with the current I2. As a result, the semiconductor laser 1 emits light, the light receiving element 5 detects the amount of emitted light, and the IV conversion circuit 6 outputs a voltage signal indicating the detection level, as described above. The deviation detection circuit 8 outputs the deviation between the voltage signal and the constant reference voltage Ref2 as the deviation signal S2. First, the level holding circuit 9 outputs the inputted deviation signal S2 as it is. Current source circuit 10
Controls the current I2 according to the deviation signal S2.

As a result, as shown in FIG. 6, the semiconductor laser 1 is supplied with a current that is the sum of the currents I1 and I2, and the amount of emitted light is controlled to a constant average power P2 (process 2).
03). The average power P2 is set to be larger than the average power P1 in the reproduction mode. In this state, the level holding circuit 9 holds the value of the input deviation signal S2 (process 204).

Next, it is assumed that the recording / erasing mode is set. In this case, as shown in FIG. 7, the operation of the high frequency current superposition circuit 4 is turned off (process 301). Then, a predetermined data signal is input to the switch circuit 3 (process 302).

This data signal is binary data to be recorded when data is recorded on the optical disk, and is a constant signal such as all "1" when erasing. The current I2 is turned on / off by this data signal. As a result, as shown by the alternate long and short dash line in FIG.
Emits light according to the data signal, and the modulated laser light is emitted. Data recording or erasing is performed on the optical disk by this laser light.

As described above, in this embodiment, the semiconductor laser 1 is always supplied with a constant direct current I1, and in the reproducing mode, a high frequency current is superposed on the constant current.
By adjusting the amplitude of the high frequency current, the amount of light emitted from the semiconductor laser 1 is controlled to a constant level. As a result, even if the environmental temperature changes, the direct current I1
However, since it does not exceed the light emission start current It, an increase in noise is prevented.

In the recording / erasing mode, the superposition of the high frequency current is stopped, another current I2 is superposed, and the current value is adjusted to control the emitted light quantity to a constant level. .. In this way, since the main circuit such as the current source circuit 2 is shared between the reproduction mode and the recording / erasing mode, the number of parts can be reduced.

In the above embodiment, the semiconductor laser 1
The amount of light emitted from the sensor is detected by the light receiving element 5, and the amplitude of the high frequency current is adjusted based on the detection level. However, the amplitude value of the high frequency current adapted to each temperature is stored in advance,
During operation, the ambient temperature may be detected and adjusted to an amplitude corresponding to the detected temperature.

Next, a second embodiment of the present invention will be described.

FIG. 8 is a circuit diagram of a semiconductor laser drive circuit according to the second embodiment of the present invention. In the figure, a diode D2 is connected in parallel to the semiconductor laser D1 in the opposite direction, and a power supply voltage Vc is applied to one end thereof. The other ends are connected to the collectors of the transistors Tr1 and Tr2, respectively. Transistor T
An on / off signal is input to the base of r1 and its emitter is grounded via a resistor R1.

A data signal is input to the base of the transistor Tr2, and its emitter is the transistor Tr3.
Of the transistor Tr4 and the collector of the transistor Tr4. The base of the transistor Tr4 is the base of the transistor Tr5, its collector, and the transistor Tr5.
It is connected to 6 collectors. Transistor Tr4
Of the transistor Tr5 is grounded through the resistor R2, and the emitter of the transistor Tr5 is grounded through the resistor R3.

The power supply voltage Vd is applied to the collector of the transistor Tr3, and the resistor R4 is connected between the collector and the base of the transistor Tr3. The collector of the transistor Tr6 is connected to the line of the power supply voltage Vd via the resistor R5, and its base is connected to the movable terminal of the variable resistor VR via the resistor R6. At one end of the variable resistor VR, via two diodes D3 connected in series,
The power supply voltage Vc is applied, and the other end is grounded via the resistor R7.

In the figure, the circuit without the diode D3, that is, the circuit for directly applying the power supply voltage Vc to one end of the variable resistor VR is a known circuit.

With the above configuration, the semiconductor laser drive circuit of this embodiment has a reproduction mode and a recording / erasing mode as operation modes.

Now, assuming that the playback mode is set,
A constant positive voltage is applied as an on / off signal to the base of the transistor Tr1, and the data signal of the base of the transistor Tr2 is turned off, that is, set to zero voltage.

The transistor Tr1 is turned on by applying the positive voltage to the base. Then, due to the power supply voltage Vc, a constant current flows in the path of the semiconductor laser D1, the transistor Tr1 and the resistor R1,
1 emits light. At this time, the transistor Tr2 is turned off, and no current flows on the transistor Tr2 side.

A predetermined data reading operation from an optical disk (not shown) is executed by the emitted light of the semiconductor laser D1.

Next, assume that the recording / erasing mode is set.
In this case, the on / off signal of the base of the transistor Tr1 is turned off, that is, the voltage is set to zero, and the data signal is input to the base of the transistor Tr2. This data signal is a binary signal in which a constant voltage is turned on / off.

When the constant voltage of the data signal is turned on, the transistor Tr2 is turned on.

On the other hand, at the base of the transistor Tr6,
A current corresponding to the adjustment state of the variable resistor VR flows in, and the collector and the emitter of the variable resistor VR become conductive. Then, the power supply voltage Vd causes a current to flow to the bases of the resistor R5, the transistor Tr6, and the transistor Tr4, and the transistor Tr4 also becomes conductive. Then, the power supply voltage Vc causes a current to flow in the path of the semiconductor laser D1, the transistor Tr2, the transistor Tr4, and the resistor R2, and the semiconductor laser D1 emits light.

In this case, as the movable terminal of the variable resistor VR becomes closer to the terminal on the diode D3 side, the transistor T
The base current of r6 increases and its collector current also increases. This collector current is the base current of the transistor Tr4, and when the base current increases, the energizing current of the semiconductor laser D1 also increases.

The variable resistor VR adjusts the energizing current of the semiconductor laser D1 in this way, and is adjusted in advance so that an appropriate amount of emitted light can be obtained from the semiconductor laser D1.

When the constant voltage of the data signal is turned off, the transistor Tr2 is turned off and the semiconductor laser D1 is turned on.
Turns off. The transistors Tr3, Tr5, and the resistors R4 and R3 serve to stabilize the on / off operation of the transistors Tr2 and Tr4.

In this way, the semiconductor laser D1 emits light according to the data signal. Predetermined information recording or erasing of recorded data is performed on an optical disc (not shown) by the emitted light of the semiconductor laser D1.

By the way, the semiconductor laser D1 has a property that the amount of emitted light changes according to the change of the environmental temperature. For example,
When driven with a constant current, the amount of light emission increases as the environmental temperature rises. Further, in general, a transistor circuit with a grounded emitter has a characteristic that the collector current increases as the temperature rises.

Therefore, in the circuit as in the present embodiment, in which the conduction current of the semiconductor laser D1 is turned on / off by the transistor Tr1, the semiconductor laser D1 is increased when the environmental temperature rises.
The amount of emitted light increases, and the amount of emitted light also decreases as the temperature decreases.

By the way, generally, as shown in FIG. 9, the forward voltage and current of the diode rise when one rises and the other rises. The current amount in the figure is shown on a logarithmic scale. As is clear from this figure, the diode has a characteristic that the voltage decreases when the environmental temperature rises when a constant current flows.

Therefore, in this embodiment, when the environmental temperature rises, the voltage across the diode D3 drops. Since a voltage reduced by the voltage of the diode D3 from the power supply voltage Vc is applied to the diode D3 side terminal of the variable resistor VR, the terminal voltage rises due to the temperature rise and the voltage of the movable terminal also rises. , The base current of the transistor Tr6 decreases. As a result, the collector current of the transistor Tr4 decreases, and the conduction current of the semiconductor laser D1 decreases. Further, when the environmental temperature decreases, the voltage across the diode D3 increases, and conversely to the above, the conduction current of the semiconductor laser D1 increases.

In the present embodiment, such control of the energizing current is set so as to suppress the increase or decrease in the light emission amount of the semiconductor laser D1 and always maintain a constant level.

As described above, in the present embodiment, a drive current proportional to the base current of the transistor Tr6 is applied to the semiconductor laser D1 and the base current is adjusted by the variable resistor VR, so that the emission power can be arbitrarily set. I am trying to set it. Then, the variable resistor VR and the power supply voltage Vc
The diode D2 is inserted between this line and the line to reduce the base current in accordance with the temperature rise, thereby keeping the light emission amount of the semiconductor laser D1 constant.

Therefore, the temperature sensor, the light receiving element and the detection circuit as in the prior art are not required, and the drive circuit can be simply constructed.

In the second embodiment, the amount of emitted light is controlled to be constant with respect to the temperature change only in the recording / erasing mode, but in the reproducing mode as well, the same circuit emits light. The amount of light may be controlled to be constant.

Although the temperature characteristic of the diode is used, it is known that, for example, two terminals out of the three terminals of the transistor have the same characteristics. Therefore, it goes without saying that such other semiconductor elements can be used in the same manner.

[0060]

As described above, according to one invention of the present application, a constant direct current equal to or lower than the light emission start current is passed through the semiconductor laser device, and the amplitude of the high frequency current superimposed on the constant current is changed. By adjusting the average power of the laser light to a constant level, the direct current does not exceed the light emission start current even if the environmental temperature changes, so that the increase of noise is prevented.

According to another aspect of the invention, the semiconductor element is simply arranged in the light quantity setting circuit for adjusting the base current of the transistor to set the quantity of light emitted from the semiconductor laser element. Since the amount can be kept constant, the circuit configuration becomes simple.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of an operation mode of the semiconductor laser drive circuit.

FIG. 3 is a diagram illustrating a driving state of a semiconductor laser in a reproduction mode.

FIG. 4 is an operation flowchart in a reproduction mode.

FIG. 5 is an operation flowchart in a power control mode.

FIG. 6 is a diagram illustrating a driving state of a semiconductor laser in a power control mode and a recording / erasing mode.

FIG. 7 is an operation flowchart in a recording / erasing mode.

FIG. 8 is a circuit diagram of a semiconductor laser drive circuit according to a second embodiment of the present invention.

FIG. 9 is a graph showing a voltage / current characteristic of a diode.

FIG. 10 is a diagram illustrating a driving state of a conventional semiconductor laser.

[Explanation of symbols]

 1, D1 semiconductor laser 2, 10 current source circuit 3 switch circuit 4 high frequency current superimposing circuit 5 light receiving element 6 IV conversion circuit 7, 8 deviation detection circuit 9 level holding circuit 11 switching circuit D2, D3 diode Tr1 to Tr6 transistor R1 ~ R7 resistance VR variable resistor

Claims (3)

[Claims] 1. A semiconductor laser drive circuit, wherein a direct current in which a high-frequency current is superimposed is passed through a semiconductor laser device to cause it to emit light, and the average power of the emitted light is always kept constant regardless of temperature changes. A constant current supply means for supplying a constant direct current equal to or less than the light emission start current, a high-frequency current superimposing means for superimposing a high-frequency current on the constant current, and the amplitude of the high-frequency current being adjusted according to temperature changes A semiconductor laser drive circuit, comprising: a light emission power control means for keeping the average power constant. 2. A direct current superimposing means for stopping the superimposition of the high frequency current and superimposing another direct current on the constant current,
2. A second light emission power control means for maintaining the light emission power of the semiconductor laser at a constant level higher than the average power by adjusting the current value of the other direct current. Semiconductor laser drive circuit. 3. A semiconductor laser device is energized to emit light,
In a semiconductor laser drive circuit that always keeps the average power of the emitted light constant regardless of temperature changes, a semiconductor laser drive circuit that applies a drive current proportional to the base current of one transistor to the semiconductor laser element to emit light.
A light amount setting circuit that arbitrarily sets the light emission power of the semiconductor laser device by arbitrarily adjusting the base current, and a semiconductor device that is inserted into the light amount setting circuit and that lowers the base current according to an increase in environmental temperature. A semiconductor laser drive circuit comprising: