JP3143887B2 - Laser diode drive circuit and optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode drive.
Circuit and optical disc device, especially switching
Constant current circuit between transistor and laser diode
Connection to reduce power consumption.
Laser diode drive circuit and optical disc drive
Related.

[0002]

2. Description of the Related Art FIG. 10 shows a basic configuration of a magneto-optical disk drive. Disk 1 is a spindle motor 2
To rotate at a predetermined speed. An optical head 3 is arranged on the lower surface of the disk 1, and a magnetic field head 4 is arranged on the upper surface. The optical head 3 incorporates a laser diode and a photodiode, and irradiates the disk 1 with laser light emitted from the laser diode, and receives the reflected light by the photodiode.

The LD driver 6 is controlled by the controller 5 and drives a laser diode. The signal output from the photodiode is supplied to the signal decoder 9 and the servo circuit 10. The signal decoder 9 decodes the input signal and supplies the decoded signal to the controller 5. The servo circuit 10 generates a clock from the input signal and outputs the clock to the controller 5 and the encoder 7. The servo circuit 10 generates a focus error signal and a tracking error signal from the input signal, and controls the optical head 3 according to the error signal.

The encoder 7 encodes write data supplied from the controller 5 and supplies the encoded data to the magnetic field head driver 8. The magnetic field head driver 8 drives the magnetic field head 4 to apply a predetermined magnetic field to the disk 1. Controller 5
It is connected to a host computer (not shown) and controls recording and reproducing operations on the disk 1.

Next, the operation will be described with reference to FIG. In the recording or reproducing mode, the disk 1 is rotated at a predetermined speed by the spindle motor 2. In the recording mode, the controller 5 is supplied with write data from the host computer. The write data is supplied to the encoder 7, encoded, and supplied to the magnetic field head 4 via the magnetic field head driver 8. Thereby, the magnetic field head 4 generates a magnetic field of N pole when recording, for example, a logic 1, and generates a magnetic field of S pole when recording a logic 0 (FIG. 11A).

On the other hand, the controller 5 has logics 1 and 0
At the timing of recording, the optical head 3 is controlled via the LD driver 6 to cause the laser diode to generate laser light (FIG. 11B). As a result, logic 1 and 0 are magneto-optically recorded on the disk 1.

On the other hand, in the reproduction mode, the controller 5
The laser diode built in the optical head 3 is basically continuously turned on via the LD driver 6. However, in practice, when the light is turned on continuously, the so-called SCOOP
Since noise due to the effect is generated, a high frequency signal is superimposed to suppress the noise. As a result, a laser beam that is turned on or off at a high frequency is applied to the disk 1.

A photodiode built in the optical head 3 receives the reflected light from the disk 1 and outputs a detection signal. The signal decoder 9 separates the MO component from the signal output by the photodiode, decodes the MO component, and outputs the decoded data to the controller 5 as read data.
This data is transmitted from the controller 5 to a host computer (not shown).

In the above recording and reproducing modes,
The servo circuit 10 detects an RF signal output from the photodiode and generates a focus error signal and a tracking error signal based on an astigmatism method or a push-pull method. Then, the actuator incorporated in the optical head 3 is driven according to the error signal. Thereby, the optical head 3 is driven in the focus direction and the tracking direction.

[0010] The servo circuit 10 extracts a clock component from the RF signal and supplies it to the controller 5 and the encoder 7. The controller 5 and the encoder 7 execute processing of write data and read data based on the clock.

Next, a configuration example of a laser diode driving circuit for driving a laser diode will be described with reference to FIG. NPN transistors 21 and 22 are differentially connected, and the emitter is grounded via NPN transistor 23 and resistor 26. NPN transistor 2
1 is connected to a laser diode 24,
The resistor 25 is connected to the collector of the NPN transistor 22. The module 27 is connected to the collector of the NPN transistor 21.

Next, the operation will be described. In the recording mode, the voltage Va is applied to the base of the NPN transistor 23.
pc is applied. As a result, the NPN transistor 23
A constant current corresponding to this voltage Vapc flows between the collector and the emitter. On the other hand, voltages data1 and data2 corresponding to recording data of opposite polarities are applied to the bases of the NPN transistors 21 and 22, respectively.

That is, when the base of the NPN transistor 21 is at a high level, the base of the NPN transistor 22 is at a low level. Conversely, when the base of the NPN transistor 21 goes low, the NPN transistor 22
Will be at a high level. The NPN transistors 21 and 22 turn on when a high-level voltage is applied to their bases, and turn off when a low-level voltage is applied to their bases.
When the NPN transistor 21 is turned on, a constant current defined by the NPN transistor 23 flows through the path of the laser diode 24, the NPN transistor 21, the NPN transistor 23, and the resistor 26. At this time, the laser diode 24 is turned on.

On the other hand, when the NPN transistor 22 is turned on, the resistor 25, the NPN transistor 22,
A current flows through the path of the PN transistor 23 and the resistor 26. At this time, since no current flows through the laser diode 24, no laser light is generated (turned off).

On the other hand, in the reproduction mode, the NPN transistor 21 is continuously turned on and the NPN transistor 22 is continuously turned off. And module 27
Outputs a high frequency superimposed signal having a frequency of, for example, 500 MHz and applies the signal to the cathode of the laser diode 24. As a result, the laser diode 24 turns on and off in response to the high-frequency superimposed signal, and the laser light is turned on and off at high frequency.

[0016]

In the conventional laser diode driving circuit, as described above, the laser diode 24 is connected to the differentially connected NPN transistors 21 and 22.
To be connected to one of them. As a result, there is a problem that the current having the same value as that when the laser is always turned on flows even when the laser is turned on as well as when the laser is turned off, and the power consumption becomes unnecessarily large.

The present invention has been made in view of such circumstances, and aims to reduce power consumption.

[0018]

According to a first aspect of the present invention, there is provided a laser diode drive circuit, wherein NPN transistors 31, 32 as differentially connected switching transistors are switched by supplying a drive pulse to a base as a control electrode. And a constant current circuit 36 connected between the NPN transistors 31 and 32 and the laser diode 37 so that a current having a magnitude n times larger than that flowing through the NPN transistors 31 and 32 flows through the laser diode 37. It is characterized by the following.

The constant current circuit 36 can be a current mirror circuit. Further, the constant current circuit 36 can be a Wilson constant current circuit. Further, the NPN transistors 31 and 32 can be built in the IC, and the constant current circuit 36 can be arranged outside the IC.

When driving a laser diode 37 used for recording or reproducing data on a recording medium, N
A drive pulse can be supplied to the bases of the PN transistors 31 and 32 when recording data, and a high-frequency superimposed pulse can be supplied when reproducing data.

A module 38 is connected to the bases of the NPN transistors 31 and 32.
A delay circuit 86 that delays an input by a predetermined time and outputs the delayed signal;
When recording data, of the output or the drive pulse of the delay circuit 86, a drive pulse is selected and output. When data is reproduced, an output of the delay circuit 86 is selected and supplied to the delay circuit 86, and a high frequency And a selector 81 that generates a superimposed pulse.

Alternatively, when recording or reproducing data on a recording medium, when driving the laser diode 37, the NPN transistors 31, 32 and the constant current circuit 36 are used.
A module 38 that generates a high-frequency superimposed pulse to be applied to the laser diode 37 when data is reproduced from the recording medium can be connected to the connection point with Claim 8
The optical disk device described in the above is a laser diode drive circuit
However, a drive pulse is supplied to the base as a control electrode.
Switching, differentially connected switching transformers
NPN transistors 31 and 32 as transistors and NP
N times the current flowing through N transistors 31 and 32
NPN so that the current of
Between the transistors 31 and 32 and the laser diode 37
And a constant current circuit 36 connected to the
You.

[0023]

The laser diode driving circuit according to claim 1,
And the optical disk device according to claim 8, wherein NP
When a current flows through one of the N transistors 31 or 32 (for example, 32), a current n times as large flows through the laser diode 37 connected through the constant current circuit 36. Therefore, the current that always flows is supplied to the laser diode 37
1 / n of the current supplied to the

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The laser diode drive circuit of the present invention can be used, for example, in a magneto-optical disk drive. The basic configuration and operation of the magneto-optical disk device in this case are the same as those shown in FIGS.

FIG. 1 shows an example of the configuration of a laser diode drive circuit according to the present invention. In this embodiment, NP
N-transistors 31 and 32 are differentially connected, and a common connection point of the emitters is an NPN transistor 33 and a resistor 35.
Grounded. The collector of NPN transistor 31 is connected to a predetermined reference potential Vcc via resistor 34. The collector of the NPN transistor 32 is also connected to the reference potential Vcc via the constant current circuit 36. A predetermined voltage Vapc is applied to the base of the NPN transistor 33, and signals data1 and data2 corresponding to recording data of opposite polarities are applied to the bases of the NPN transistors 31 and 32, respectively. .

A laser diode 37 is connected to the constant current circuit 36. A module 38 is connected to a connection point between the constant current circuit 36 and the laser diode 37.

Next, the operation will be described. NPN
Since a predetermined voltage Vapc is applied to the base of the transistor 33, when the base-emitter voltage of the NPN transistor 33 is set to Vbe, a current flowing between the collector and the emitter of the NPN transistor 33 (the resistor 3)
5) can be expressed by the following equation. i = (Vapc−Vbe) / R ₃₅ Here, R ₃₅ indicates the resistance value of the resistor 35.

Therefore, by controlling the voltage Vapc to a predetermined voltage, the current i flowing through the resistor 35 can be controlled to a constant current.

In the recording mode, a pulse of the opposite polarity corresponding to the recording data is applied to the bases of the NPN transistors 31 and 32. That is, when a high-level pulse is applied to the base of the NPN transistor 31, a low-level pulse is applied to the base of the NPN transistor 32. Conversely, when a low-level pulse is applied to the base of the NPN transistor 31, a high-level pulse is applied to the base of the NPN transistor 32.

The NPN transistors 31 and 32 turn on when a high-level pulse is applied to their bases, and turn off when a low-level pulse is applied. When the NPN transistor 31 is turned on, a current flows through the path of the resistor 34, the NPN transistors 31, 33 and the resistor 35,
When the transistor 32 is turned on, the constant current circuit 36, N
A current flows through the path of the PN transistors 32 and 33 and the resistor 35.

The constant current circuit 36 includes an NPN transistor 3
When a current flows through the laser diode 2, the laser diode 37 operates so that an n-fold current (n is a value greater than 1) flows through the laser diode 37. Therefore, when the NPN transistor 32 is turned on and off in response to the recording data (data2), the laser diode 37 generates a laser beam corresponding to the on / off.

In the reproducing mode, a low-level signal is always input to the NPN transistor 31, and a high-level signal is always input to the NPN transistor 32. As a result, the constant current circuit 36 operates to always drive the laser diode 37. However, in practice, a high-frequency superimposed signal having a frequency of, for example, 500 MHz is applied to the anode of the laser diode 37 from the module 38. As a result, the laser diode 37 turns on and off in response to the high frequency superimposed signal.

FIG. 2 shows a configuration example of the constant current circuit 36. In this embodiment, the constant current circuit 36 is a PNP
It comprises transistors 41 and 42. PNP
The emitter of transistor 41 is connected to reference potential Vcc, and its collector is connected to the collector of NPN transistor 32. The base of the PNP transistor 41 is connected to the base of the PNP transistor 42 and to the collector of the PNP transistor 41.

The characteristics of the PNP transistors 41 and 42 are set such that when a predetermined current flows through the emitter-collector of the PNP transistor 41, n times the current flows through the emitter-collector of the PNP transistor 42. ing. That is, in this embodiment, the constant current circuit 36 is constituted by a current mirror circuit composed of PNP transistors 41 and 42, and the ratio of the input / output current is 1
The characteristic is set so as to be n.

FIG. 3 shows another configuration example of the constant current circuit 36. In this embodiment, the constant current circuit 36 is constituted by a Wilson constant current circuit. That is, PN
The emitter of P transistor 51 is connected to reference potential Vcc, and its collector is connected to the collector of NPN transistor 32. The base of the PNP transistor 51 is connected to the base and the collector of the PNP transistor 52. The emitter of PNP transistor 52 is connected to reference potential Vcc, and the collector is connected to the emitter of PNP transistor 53.

The base of the PNP transistor 53 is PN
The collector is connected to the collector of the P transistor 51, and the collector is connected to the laser diode 37.
Also in this embodiment, the characteristics are adjusted so that when a predetermined current flows through the PNP transistor 51, n times the current flows through the PNP transistors 52 and 53.

FIG. 4 shows a third embodiment of the constant current circuit 36. In this embodiment, the PN in FIG.
Similarly to the P-transistors 41 and 42, the emitters of the PNP transistors 61 and 62 having a current mirror circuit configuration are connected to resistors 63 and 64, respectively. The ratio of the resistance value R ₆₃ of the resistor ₆₃ to the resistance value R ₆₄ of the resistor 64 is set to n: 1 as shown by the following equation. R ₆₃ : R ₆₄ = n: 1

That is, in the embodiment of FIG. 2, the characteristics of the PNP transistors 41 and 42 are adjusted to predetermined values so that the current flowing between the emitter and the collector becomes 1: n. However, in this embodiment, the PNP transistors 61 and 62 are set to have the same characteristics. However, as described above, since the values of the connected resistors 63 and 64 are set to n: 1,
The ratio of the current flowing between the emitter and collector of the PNP transistors 61 and 62 can be set to 1: n.

When the current value is adjusted by the resistance as shown in FIG. 4, the manufacturing becomes easier as compared with the case where the characteristics of the transistors themselves are made different from each other as shown in FIG.

The value of the resistance R ₃₄ of the resistor ₃₄ and the value of the resistance R ₆₃ of the resistor ₆₃ are, for example, 4.7Ω, respectively.
The resistance value R ₃₅ as 1.18Omu, the resistance value R of the resistor 64
₆₄ can be 0.78Ω. By setting such a value, for example, a drive current as shown in FIG. 5 can be supplied to the laser diode 37 by the laser diode drive circuit having the configuration shown in FIG. As is clear from FIG. 5, the rise time of the pulse is about 3 ns, and the fall time is about 2 ns. That is, as shown in FIG. 12, it can be seen that the rising and falling slopes can be made steep as in the case of driving by differentially connected transistors.

When the constant current circuit 36 is configured as shown in FIG. 4, the module 38 can be connected as shown in FIG. That is, in this embodiment, the switching circuit 71 is connected to the bases of the NPN transistors 31 and 32, and the data (high-frequency superimposed pulse) output from the module 38 and the write data are supplied to the switching circuit 71. Has been made. And the switching circuit 71
In the recording mode, switching is performed so that write data is selected, and in the reproduction mode, output of the module 38 is selected. Thus, in the recording mode, the laser diode 37 is driven as in the above-described embodiment.

In the reproducing mode, the switching circuit 71 selects the high-frequency superimposed pulse output from the module 38 instead of the write data. Therefore, in the reproducing mode, the laser diode 37 outputs the recording pulse in the recording mode. Instead of (driving pulse), driving is performed in response to a high-frequency superimposed pulse.

A PNP transistor 62 for supplying a large current flowing through the laser diode 37 and a PN pair
The P-transistor 61 is disadvantageous if it is formed into an IC. In other words, if a transistor that flows a large current is made into an IC,
For heat dissipation, a metal package is required, which is expensive.
Therefore, PNP transistors 61 and 62, resistors 63 and 6
4 is preferably located outside the IC.

On the other hand, the NPN transistors 31 to 33 and the resistor 35 can be arranged in an IC together with the switching circuit 71 and the module 38. This is because the current flowing there can be small. in this way,
With the use of an IC, the transistor can be driven at higher speed.

As shown in FIG. 6, the module 38 is
When the connection is made to the base of the N-transistor 31, the power consumption is reduced and the stability of the circuit is increased as compared with the case where the connection is made to the anode of the laser diode 37. Further, since the coupling with the laser diode 37 is not performed directly, the influence of the variation of the laser diode 37 is reduced. Further, since the high-frequency superimposed pulse is generated by switching, the current flowing through the laser diode 37 becomes almost zero when the laser diode 37 is turned off, so that the efficiency can be improved.

In the embodiment shown in FIG. 6, since a one-chip IC can be formed except for the current mirror circuit portion, the power consumption of the IC can be reduced and an inexpensive package having a small heat capacity can be used. . As a result, the laser diode drive circuit can be reduced in size, and the package and the process become cheaper, so that the cost can be further reduced.

As shown in FIG. 6, when one of the high-frequency superimposed pulse and the write pulse output from the module 38 is selected and supplied to the bases of the differentially connected NPN transistors 31 and 32. In, the module 38 and the switching circuit 71 can be configured, for example, as shown in FIG. In this embodiment, the switching circuit 71 is constituted by the selector 81 and the module 3
8 comprises the selector 81 and the delay circuit 86.

The input terminal DA of the selector 81 is connected to a resistor 83
And is connected to the output of the delay circuit 86. The input terminal DB is configured to be supplied with write data and to be grounded via a resistor 84. The input terminal SEL grounded via the resistor 85 has a
Control signal (switch signal) of logic H and logic L in playback mode
Is input. Also, the selector 81
A predetermined voltage (for example, 5 V) is applied to the terminal VCC, and a capacitor 82 is connected to the terminal VCC. The terminal VEE is grounded.

When logic H is input to the terminal SEL (in the recording mode), the selector 81 selects the signal input to the input terminal DB, and outputs the signals from the output terminals Q and QI as signals of opposite phases. It has been made to be. When logic L is input to the terminal SEL (in the reproduction mode), the selector 81 selects the signal input to the input terminal DA, and outputs an in-phase signal and a reverse-phase signal to the output terminals Q and Q.
I output each. The output of the output terminal QI is fed back to the input terminal DA via the delay circuit 86.

Next, the operation will be described. In the recording mode, a logic H control signal is input to the terminal SEL from a circuit (not shown). At this time, the selector 81 outputs data having the same phase as the data input to the input terminal DB from the output terminal Q, and outputs data having the opposite phase from the output terminal QI. This data corresponds to the NPN transistor 31 in FIG.
And 32 bases respectively.

On the other hand, in the reproduction mode, a logic L control signal is input to the terminal SEL. At this time, the selector 81
Selects a signal input from the input terminal DA, outputs an in-phase signal to the output terminal Q, and outputs an in-phase signal to the output terminal QI.
Output to The signal of the opposite phase output from the output terminal QI is delayed by a predetermined time by the delay circuit 86,
The signal is returned to the input terminal DA again. As a result, a ring oscillator is formed by the selector 81 and the delay circuit 86, and a pulse having a period twice as long as the delay time in the delay circuit 86 is generated from the output terminal QI. This pulse is used as a high-frequency superimposed pulse,
Supplied to bases 1 and 32.

This ring oscillator is constituted by
Only in playback mode. Therefore, there is less possibility that unnecessary radiation is generated.

In the embodiment of FIG.
Power consumption can be reduced, and the stability of the oscillation frequency can be increased. Also, unnecessary radiation is reduced.
Further, since the module 38 is not directly connected to the laser diode 37, the oscillation frequency is prevented from changing even if the impedance of the laser diode 37 varies due to the rod or the like. Further, since the switching operation is basically performed, the efficiency of the module 38 is improved.

FIG. 8 shows output waveforms when the laser diode 37 is driven at 1 mW and 6 mW with the configuration of FIG. It can be seen from the figure that the switching is performed at a sufficiently high speed.

FIG. 9 shows still another embodiment.
In this embodiment, the module 38 is connected to a connection point between the collector of the NPN transistor 32 and the collector of the PNP transistor 61.

In this configuration, the amount of current output from the module 38 is larger than that in the configuration shown in FIG. 6, but it is larger than when the module 38 is connected to the anode of the laser diode 37. , The output current of the module 38 can be reduced.

[0057]

As described above, the laser die according to claim 1 is provided.
9. An optical drive circuit and the optical disk device according to claim 8.
According to the method, a constant current circuit is connected between the switching transistor and the laser diode, and a current n times larger than the current flowing through the switching transistor flows through the laser diode, so that power consumption can be reduced. it can. Further, the number of transistors through which a large current flows decreases, so that the circuit scale can be reduced. Furthermore, faster switching becomes possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a laser diode drive circuit according to the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a constant current circuit 36 of the embodiment of FIG.

FIG. 3 is a circuit diagram showing another configuration example of the constant current circuit 36 of FIG.

FIG. 4 is a circuit diagram showing still another configuration example of the constant current circuit 36 of FIG.

FIG. 5 is a waveform diagram illustrating drive characteristics of the embodiment of FIG.

FIG. 6 is a circuit diagram showing a configuration example of another embodiment of the laser diode drive circuit of the present invention.

FIG. 7 is a circuit diagram showing a configuration example of a module 38 and a switching circuit 71 in FIG. 6;

FIG. 8 is a diagram showing an output signal waveform of FIG. 7;

FIG. 9 is a circuit diagram showing the configuration of still another embodiment of the laser diode drive circuit of the present invention.

FIG. 10 is a block diagram illustrating a configuration example of a magneto-optical disk device.

FIG. 11 is a timing chart illustrating an operation in a recording mode of FIG. 10;

FIG. 12 is a circuit diagram showing a configuration example of a conventional laser diode drive circuit.

[Explanation of symbols]

 31, 32, 33 NPN transistor 36 Constant current circuit 37 Laser diode 38 Module 61, 62 PNP transistor 63, 64 Resistance 71 Switching circuit 81 Selector 86 Delay circuit

Claims (8)

(57) [Claims] 1. A differentially connected switching transistor for switching by supplying a drive pulse to a control electrode, and said switching transistor so that a current of n times the current flowing through said switching transistor flows through a laser diode. A laser diode drive circuit, comprising: a constant current circuit connected between a transistor and the laser diode. 2. The laser diode drive circuit according to claim 1, wherein said constant current circuit is a current mirror circuit. 3. The laser diode drive circuit according to claim 1, wherein said constant current circuit is a Wilson constant current circuit. 4. The laser diode drive circuit according to claim 1, wherein said switching transistor is built in an IC, and said constant current circuit is arranged outside said IC. 5. The laser diode is driven when recording or reproducing data on a recording medium. The drive pulse is supplied to the control electrode of the switching transistor when recording the data, and the data is transmitted to the control electrode of the switching transistor. 5. The laser diode driving circuit according to claim 1, wherein a high-frequency superimposed pulse is supplied during reproduction. 6. A module is connected to the control electrode of the switching transistor, the module comprising: a delay circuit for delaying an input by a predetermined time and outputting the output; and an output of the delay circuit or the drive pulse. When recording the data, select and output the drive pulse, when reproducing the data, select the output of the delay circuit, supply to the delay circuit, and a selector for generating the high-frequency superimposed pulse, The laser diode drive circuit according to claim 5, comprising: 7. The laser diode is driven when recording or reproducing data on or from a recording medium, and a connection point between the switching transistor and the constant current circuit is connected to the laser when reproducing the data from the recording medium. 5. The laser diode drive circuit according to claim 1, wherein a module for generating a high-frequency superimposed pulse applied to the diode is connected. 8. An optical device comprising a laser diode drive circuit.
A disk device, The laser diode drive circuit, A drive pulse is supplied to the control electrode to perform switching,
A differentially connected switching transistor; N times larger than the current flowing through the switching transistor
So that a large current flows through the laser diode.
Between the switching transistor and the laser diode
A constant current circuit connected to the
Disk device.