JPH06349097A - Driving circuit for laser diode - Google Patents

Abstract

PURPOSE:To reduce power consumption while to perform switching module laser diodes with high frequency without limiting a frequency characteristic of a constant current circuit by connecting the constant current circuit between a switching transistor and a laser diode. CONSTITUTION:A reverse polarity pulse corresponding to recording data is impressed to bases of NPN transistor(Trs) 20, 22 at the time of a recording mode. When the Tr 20 is turned on, a current is made to flow in a path of a resistor 28, the Trs 20, 24, a resistor 26, and a current is not made to flow in a laser diode(LD). On the other hand, when the Tr 22 is turned on, a current is made to flow in a PNP Tr 30 of a constant current circuit 50, a current larger than this current is made to flow in a LD 37 through a PNP Tr 32. Further, a differential driving circuit 60 for high frequency module of a reproducing mode is inserted between the circuit 50 and the LD 37. Thereby, power consumption is reduced and switching module with high frequency can be performed.

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 suitable for use in an optical recording / reproducing device or an optical recording device such as a magneto-optical disk device.

[0002]

2. Description of the Related Art FIG. 7 shows an example of an optical recording / reproducing apparatus.
1 shows a basic configuration of a magneto-optical disk device. This magneto-optical disk device is a so-called magnetic field modulation overwrite magneto-optical disk drive.

In FIG. 7, the disk 1 is constructed to be rotated at a predetermined speed by a spindle motor 2. An optical head 3, which is also called an optical pickup, is arranged below the disk 1, and a magnetic field head 4 is arranged above the disk 1.

The optical head 3 includes a laser diode and
It has a built-in photodiode as a photodetector. The disc 1 is irradiated with the laser light emitted from the laser diode, and the reflected light of the laser light from the disc 1 is received by the photodiode. An RF signal and an MO signal are output from the photodiode and sent to the servo circuit 10 and the signal decoder 9.

The LD driver 6, which is a laser diode drive circuit, is controlled by a control signal from the controller 5 to drive the laser diode of the optical head 3.

The signal decoder 9 decodes the input signal and supplies it to the controller 5. Servo circuit 1
0 generates a clock from the input signal and outputs it to the controller 5 and the encoder 7.

The servo circuit 10 also generates a focus error signal and a tracking error signal from the input signal, and controls the optical head 3 in response to the error signal.

The encoder 7 encodes the write data supplied from the controller 5 and supplies it to the magnetic field head driver 8. This magnetic field head driver 8 is
The magnetic field head 4 is driven to apply a predetermined magnetic field to the disk 1. The controller 5 is connected to the host computer and controls the recording and reproducing operations for the disc 1.

Next, the operation of the magneto-optical disk device in the recording mode (also referred to as writing) and the reproduction mode (also referred to as reading) will be described with reference to FIG.

First, the recording mode will be described. In the recording mode, write data is supplied to the controller 5 of FIG. 7 from the host computer.

The write data is supplied from the controller 5 to the encoder 7, encoded, and supplied to the magnetic field head 4 via the magnetic field head driver 8. As a result, the magnetic field head 4 performs magnetic field modulation to generate an N-pole magnetic field when recording a logical 1 and an S-pole magnetic field when recording a logical 0 (see FIG. 8A). ).

On the other hand, the controller 5 shown in FIG. 7 sends a control signal to the LD driver 6 to turn on / off the laser diode and write data at the timing of recording the logic 1 and the logic 0 by the magnetic field head 4 (see FIG. 8 (b)).

As a result, logical 1 and logical 0 are recorded magneto-optically on the disk 1.

Next, the reproduction mode will be described. In the reproduction mode, the controller 5 in FIG. 7 basically continuously lights the laser diode built in the optical head 3 via the LD driver 6.

However, in practice, when continuously turned on, noise due to the so-called SCOOP effect is generated.
In order to suppress this, a high frequency signal is superimposed. As a result, the disc 1 is irradiated with laser light that is turned on or off at a high frequency.

The photodiode of the optical head 3 receives the reflected light from the disk 1 and outputs its detection signal.
The signal decoder 9 separates the MO component from the signal output from the photodiode, decodes it, and outputs it to the controller 5 as read data. This read data is transferred from the controller 5 to the host computer.

In the recording mode and the reproducing mode described above, the servo circuit 10 detects the RF signal output from the photodiode of the optical head 3, and based on the astigmatism method or the push-pull method, the focus error signal and the tracking error. Generate a signal. Then, in response to these error signals, the actuator built in the optical head 3 is driven. As a result, the optical head 3 is driven in the focus direction and the tracking direction.

The servo circuit 10 also 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 this clock.

Next, referring to FIG. 9, a conventional laser diode drive circuit for driving a laser diode will be described. The NPN transistors 11 and 12 are differentially connected, and the emitters of these NPN transistors 11 and 12 are grounded via the NPN transistor 13 and the resistor 16. The laser diode 14 is connected to the collector of the NPN transistor 11, and the resistor 15 is connected to the collector of the NPN transistor 12.

Next, the operation of this conventional laser diode drive circuit will be described. In recording mode, NPN
The voltage Vapc is applied to the base of the transistor 13. As a result, a constant current corresponding to this voltage Vapc flows between the collector and the emitter of the NPN transistor 13. On the other hand, the bases of the NPN transistors 11 and 12 have a reverse polarity voltage Dat corresponding to the recording data.
a1 and Data2 are applied.

That is, when the base of the NPN transistor 11 is at high level, the base of the NPN transistor 12 is at low level. Conversely, when the base of the NPN transistor 11 becomes low level, the NPN transistor 12
Will have a high base. The bases of the NPN transistors 11 and 12 are turned on when a high level voltage is applied, and turned off when a low level voltage is applied.

When the NPN transistor 11 is turned on,
The constant current defined by the NPN transistor 13 causes the laser diode 14, the NPN transistor 11, the NPN
It flows through the path of the transistor 13 and the resistor 16. As a result, laser light is generated from the laser diode 14.

On the other hand, when the NPN transistor 12 is turned on, the resistor 15, the NPN transistor 12, N
A current flows through the path of the PN transistor 13 and the resistor 16. At this time, since no current flows through the laser diode 14, laser light is not generated (turned off).

On the other hand, in the reproducing mode, the NPN transistor 11 is continuously turned on and the laser diode 1 is turned on.
4 is turned on (DC light emission), and the NPN transistor 12 is continuously turned off. And then apply a high frequency module,
For example, a high frequency superimposed signal having a frequency of 500 MHz is output and applied to the cathode of the laser diode 14.

As a result, the laser diode 14 is turned on and off in response to this high frequency superimposed signal, and the laser light is blinked at high frequency. The use of the high frequency module 17 in this way is to prevent noise due to the returning light of the laser light in the reproduction mode (during reading). The frequency of this high frequency module is several hundred MHz, for example 500 MHz.
It is necessary to have a high frequency of some degree, and it is desirable that this frequency be as high as possible.

When the laser diode module is switched, the power consumption of the module can be reduced, the stability of the oscillation frequency is increased, the efficiency of the module is improved, and the temperature and the reproduction signal (RF signal) are stabilized. There are advantages.

In this way, the LD driver causes the laser diode to emit a pulse in the recording mode, and as shown in FIG. 8, if the light is emitted while the magnetic field is emitting at the required intensity, it is possible to write neatly, so that the high density recording is performed. Suitable for

[0028]

However, in the conventional laser diode drive circuit, the laser diode 1
4 is connected to one of the differentially connected NPN transistors 11 and 12.

As a result, not only when the laser diode is turned on as described above, but also when the laser diode is turned off, a large current, which is the same as when the laser diode is always turned on, flows through the circuit portion, and power consumption is required. It becomes bigger than that.

Therefore, the present inventor proposes a laser diode drive circuit in which a laser diode is provided via a constant current circuit in order to save power. In this laser diode drive circuit, the current that constantly flows in this drive circuit is made smaller than the current supplied to the laser diode in an attempt to save power.

In contrast to the power saving type laser diode drive circuit using the constant current circuit proposed by the inventor, the return light of the laser beam is generated in the reproduction mode (reading) as described above. It is assumed that a high frequency module for preventing noise is applied. That is,
Consider a case where a constant current circuit is added to the drive circuit in FIG. 9 and the input signals Data1 and Data2 are turned on / off at a high frequency. In this way, the input signals Data1 and D
When turning on / off ata2 at a high frequency, the following problems occur.

That is, the switching frequency of the high-frequency module is determined by the frequency characteristics of the constant current circuit, and the laser light cannot be used as a high-frequency switching module of about 500 MHz. The reason for this is that in this constant current circuit, the amplitude of the switched signal is amplified at a certain current ratio.
This is because the frequency characteristic deteriorates as the current ratio is increased in this constant current circuit. That is, for example, if the current ratio is set to 1:10, the frequency characteristic becomes 1/10 of that of the transistor alone.

The present invention has been made in order to solve the above problems, and it is possible to reduce the power consumption, and further, it is possible to realize a switching module in which the laser light is at a high frequency regardless of the frequency characteristics of the constant current circuit. Another object of the present invention is to provide a laser diode driving circuit.

[0034]

In order to achieve the above object, according to the present invention, a drive pulse is supplied to a control electrode to perform switching, and a differentially connected switching transistor flows through the switching transistor. A constant current circuit connected between the switching transistor and the laser diode, and a laser diode provided on the output side of the constant current circuit so that a current having a magnitude n times that of the current flows through the laser diode. A differential drive circuit for switching module at high frequency, and a laser diode drive circuit including
To be achieved.

In the present invention, preferably, the constant current circuit is a current mirror circuit or a Wilson constant current circuit.

[0036]

With the constant current circuit connected between the switching transistor and the laser diode, a current having a magnitude n times the current flowing through the switching transistor flows through the laser diode. That is, when the laser light is not emitted from the laser diode, the current flowing in the circuit portion other than the laser diode is small. At this time, the differential drive circuit can switch the laser diode at a high frequency without being limited by the frequency characteristic of the constant current circuit.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the examples described below are suitable specific examples of the present invention, and therefore, various technically preferable limitations are given, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

The laser diode drive circuit of the present invention can be used, for example, in a magneto-optical disk device capable of high density recording. The basic configuration and operation of the magneto-optical disk device in this case are the same as those of the magneto-optical disk device shown in FIGS. 7 and 8.

FIG. 1 shows a laser diode drive circuit having a constant current circuit 50 which is a prerequisite for constructing a preferred embodiment of the laser diode drive circuit of the present invention. The laser diode drive circuit including the constant current circuit 50 of FIG. 1 has the following configuration.

NPN as switching transistor
The transistor 20 and the NPN transistor 22 are differentially connected, and the common connection point of the emitters of these NPN transistors 20 and 22 is the NPN transistor 24 and the resistor 26.
Grounded through.

The collector of the NPN transistor 20 is connected to a predetermined reference potential Vcc via the resistor 28. The collector of the NPN transistor 22 is also connected to the reference potential Vcc via the constant current circuit 50.

A predetermined voltage Vapc is applied to the base of the NPN transistor 24, and the NPN transistor 20
The bases of and 22 are control electrodes, and differential input signals Data1 or Data2 corresponding to recording data (input data) of mutually opposite polarities are applied to these bases, respectively. Furthermore, the constant current circuit 50
A laser diode 37 is connected to.

FIG. 2 specifically shows a preferred configuration example of the constant current circuit 50 in the laser diode drive circuit shown in FIG. 1, and is for the purpose of configuring a preferred embodiment of the laser diode drive circuit of the present invention. This is the circuit that is the premise of.

In FIG. 2, a current mirror circuit is used as an actual preferable example of the constant current circuit 50. The constant current circuit 50 includes a PNP transistor 30.
And a PNP transistor 32. PN
The emitter of the P-transistor 30 is connected to the reference potential Vcc via the resistor 34, and the emitter of the PNP transistor 32 is connected to the reference voltage Vcc via the resistor 36. The collector of the PNP transistor 30 is NPN.
It is connected to the collector of the transistor 22.

The base of the PNP transistor 30 is PN
It is connected to the base of the P transistor 32 and to the collector of the PNP transistor 30. The ratio of the resistance value R34 of the resistor 34 to the resistance value R36 of the resistor 36 is set to n: 1 as shown in Formula 1.

[0046]

[Equation 1]

Thus, the two PNP transistors 3
Instead of adjusting the characteristics of the PNP transistors 30 and 32 to a predetermined value by setting the ratio of the resistance values of 0 and 32, the PNP transistors 30 and 32 may have the same characteristics.

In this embodiment, the connected resistor 34
Since the resistance value of 1 and the resistance value of the resistor 36 are set to n: 1, the ratio of the current flowing between the emitter and collector of the PNP transistors 30 and 32 can be set to 1: n. That is, when a current of 1 flows through the PNP transistor 30, a current n times the current of 1 flowing through the PNP transistor 30 flows through the PNP transistor 32.

As described above, the current value adjusted by the resistance value is easier to manufacture than the case where the characteristics of the transistors themselves are appropriately set to be different from each other.

Next, the operation of the laser diode drive circuit of FIG. 2 will be described. In this laser diode drive circuit, the constant current circuit 50 is differentially driven. The NPN transistors 20 and 22 are current switching transistors, and the PNP transistors 30 and 32 are transistors forming a current mirror circuit. The NPN transistor 24 is a current setting transistor.

A predetermined voltage Vapc is applied to the base of the NPN transistor 24. For this reason,
Set the base-emitter voltage of the NPN transistor 24 to V
When be, a voltage obtained by subtracting the base-emitter voltage Vbe from the voltage Vapc applied to the NPN transistor 24 is applied to the resistor 26. Therefore, the current flowing between the collector and the emitter of the NPN transistor 24 (resistor 2
The current i flowing through 6) can be expressed by Equation 2.

[0052]

[Equation 2]

Here, R26 represents the resistance value of the resistor 26.

Therefore, by controlling the voltage Vapc to a predetermined voltage, the current i flowing through the resistor 26 can be controlled to a constant current.

The recording mode in the drive circuit of FIG. 2 will be described. Recording Mode In the recording mode (during writing), a pulse of opposite polarity corresponding to the recording data is applied to the bases of the NPN transistor 20 and the NPN transistor 22. That is, NP
When a high-level pulse is applied to the base of the N transistor 20 (when Data1 is 1), a low-level pulse (Data2 is 0) is applied to the base of the NPN transistor 22.

On the contrary, when a low level pulse is applied to the base of the NPN transistor 20 (Data1
Is 0), a high level pulse (Data2 is 1) is applied to the base of the NPN transistor 22.

The NPN transistors 20 and 22 turn on when a high level pulse is applied to their bases, and turn off when a low level pulse is applied to their bases.

When the NPN transistor 20 is turned on,
A current flows through the path of the resistor 28, the NPN transistors 20, 24, and the resistor 26. In this case, laser diode 37
No current flows through.

On the other hand, when the NPN transistor 22 is turned on, the constant current circuit 50 and the NPN transistors 22, 2 are turned on.
4. A current flows through the path of the resistor 26.

In this way, when the current i flows through the PNP transistor 30 of the constant current circuit 50, the PNP transistor 32 produces a laser current of n times the current i flowing through the PNP transistor 30 (n is a value larger than 1). It operates so as to flow to the diode 37.

That is, the current flowing through the circuit is (n + 1) times the current i when the laser diode 37 is on, and the current flowing through the circuit is reduced to the current i when the laser diode 37 is off.

Therefore, when the NPN transistor 22 is turned on / off in response to the recording data (Data2), the laser diode 37 generates laser light in response to the on / off.

Next, the reproduction mode in the drive circuit of FIG. 2 will be described. Reproduction mode In reproduction mode (during reading), NPN transistor 20
A low level signal (Data1 is 0) is always input to the NPN transistor 22 and a high level signal (Data2 is 1) is always input to the NPN transistor 22. As a result, the constant current circuit 50 operates so as to always drive the laser diode 37.

By the way, in the configuration of the laser diode drive circuit as shown in FIG. 2, the differential input signals Data1 and Data2 are turned on / off at a high frequency as the high frequency module in the reproduction mode (during reading) described above. think of.

In the case of this laser diode drive circuit, since the differentially switched signal passes through the constant current circuit 50 having a current ratio of 1: n, the amplitude of the switched signal is amplified here. Therefore, the frequency that can be switched follows the frequency characteristic of the constant current circuit 50. In other words, if it is left as it is, several hundreds M
Therefore, a high frequency module of Hz, for example, 500 MHz cannot be used. If the current ratio of the constant current circuit is 1: n,
The frequency characteristic of this circuit is 1 / n of that of a single transistor.

For example, the frequency characteristic of the transistor is 3
Even if it is up to GHz, if n = 10, the constant current circuit has only frequency characteristics up to 300 MHz. If a 500 MHz module is needed, it will not meet the requirements. Here, if n is made small, the amount of current flowing wastefully when the laser diode is turned off increases, which is not preferable.

If it is a differential switching circuit, 3
If a GHz transistor is used, GHz class switching is possible (500 MHz switching is not a problem). Since a constant current literally only flows from the constant current circuit, there is no restriction on the frequency characteristics of the constant current circuit.

Therefore, in order to enable such a high frequency module to be performed regardless of the frequency characteristics of the constant current circuit 50, a laser diode drive circuit as shown in FIG. 3 is used. That is, FIG. 3 shows a preferred embodiment of the laser diode drive circuit of the present invention.

In FIG. 3, on the output side of the constant current circuit 50, a differential drive circuit 60 for the high frequency module is set in relation to the laser diode 37. This differential drive circuit 60 is also referred to as a differential switching circuit, as shown in FIG.
This is specifically shown in.

The differential drive circuit 60 includes PNP transistors 40 and 42. PNP transistor 40
Is connected to the emitter of the PNP transistor 42, and the PNP transistor 32 of the constant current circuit 50 is connected.
Connected to the collector.

The collector of the PNP transistor 40 and the laser diode 37 are connected. The collector of the PNP transistor 42 is grounded via the resistor 44.

Further, the input signal XDmod can be input to the base of the PNP transistor 40, and the input signal Dmod can be input to the base of the PNP transistor 42.
These input signals XDmod and Dmod are signals of opposite phases, and by applying a high frequency as this input signal, a high frequency switching module can be applied.

The NPN transistors 20 and 22 are data driving transistors during writing, and the PNP transistors 40 and 42 are high frequency module transistors during reading.

The module can be applied by applying the opposite phase input signals XDmod and Dmod to the PNP transistors 40 and 42 as a high frequency. In this way, by inserting the differential switching circuit 60 between the constant current circuit 50 and the laser diode 37, a high frequency module with a frequency equal to or higher than the frequency characteristic of the constant current circuit 50 becomes possible.

Next, another preferred embodiment of the present invention will be described. Other Embodiments FIGS. 5 and 6 show another preferred embodiment of the laser diode drive circuit of the present invention. First, in the embodiment of FIG. 5, a constant current circuit 150 is used instead of the constant current circuit 50 used in FIG. In the constant current circuit 150, the characteristics of the PNP transistors 130 and 132 are set as follows without using a resistor.

That is, it is set so that when a predetermined current i flows through the emitter-collector of the PNP transistor 130, a current n times the current i flows through the emitter-collector of the other PNP transistor 132. Is. The PNP transistors 130 and 132 form a current mirror circuit, and the constant current circuit 15
The characteristics are set so that the ratio of input / output current at 0 is 1: n.

In the embodiment of FIG. 6, the constant current circuit 25
0 is composed of a Wilson constant current circuit.

That is, the emitter of the PNP transistor 51 is connected to the reference potential Vcc, and the PNP transistor 51 is connected.
Is connected to the collector of the NPN transistor 22. The base of the PNP transistor 51 is PN
It is connected to the base and collector of the P-transistor 52. The emitter of the PNP transistor 52 has a reference potential V
The collector of the PNP transistor 52 is connected to cc, and the collector of the PNP transistor 52 is connected to the emitter of the PNP transistor 53.

The base of the PNP transistor 53 is PN
It is connected to the collector of P-transistor 51, and PN
The collector of the P transistor 53 is connected to the emitter of the PNP transistor 40 of the differential drive circuit 60.
Also in the embodiment shown in FIG. 6, the PNP transistor 51 is used.
The characteristics of the PNP transistors 51, 52, 53 are adjusted so that when a predetermined current flows through the PNP transistor 52, an n times larger current flows through the PNP transistor 52 and the PNP transistor 53.

By the way, for example, in the embodiment of FIG. 4, P which supplies a large current flowing through the laser diode 37
If the NP transistor 32 and the PNP transistor 30 paired with the NP transistor 32 are integrated into an IC, there is a disadvantage. That is, if the transistors 30 and 32 that flow a large current are integrated into an IC, a metal package is required for heat dissipation, which is expensive. Therefore, the PNP transistors 30 and 32 and the resistor 3
4, 36 are preferably located outside the IC.

On the other hand, the NPN transistor 20,
22, 24 and the resistor 26 can be arranged in the IC. This is because the current flowing therethrough can be small. As described above, when integrated into an IC, the transistor can be driven at a higher speed. This point is the same in the other embodiments shown in FIGS. 5 and 6.

In the optical recording device such as the magneto-optical disk device shown in the embodiment of the present invention, the laser diode is pulse-emitted to realize high density recording. The laser diode drive circuit emits pulsed light when writing (recording mode), and emits DC light when reading (reproducing mode).

When the laser diode emits pulsed light, if the laser diode emits light while the magnetic field is emitted at a required intensity, writing can be performed neatly, which is suitable for high density recording. Further, if the current flowing in the parts other than the laser diode can be reduced during non-light emission, power consumption can be reduced.

When the laser diode module is switched, the power consumption of the module can be reduced, the stability of the oscillation frequency is increased, the efficiency of the module is improved, and the temperature and the reproduction signal (RF signal) are stabilized. There is an advantage.

[0085]

As described above, according to the laser diode drive circuit of the present invention, the constant current circuit is connected between the switching transistor and the laser diode, and the current flowing through the switching transistor is n times as large. Since the current is made to flow through the laser diode, the power consumption can be reduced, and the laser diode can be a high frequency switching module without being limited by the frequency characteristics of the constant current circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a laser diode drive circuit including a constant current circuit which is a prerequisite for constituting a preferred embodiment of a laser diode drive circuit of the present invention.

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

FIG. 3 is a diagram showing a preferred embodiment of a laser diode driving circuit of the present invention.

FIG. 4 is a circuit diagram showing the embodiment of the present invention in FIG. 3 in more detail.

FIG. 5 is a diagram showing another preferred embodiment of the laser diode driving circuit of the present invention.

FIG. 6 is a diagram showing yet another preferred embodiment of the laser diode driving circuit of the present invention.

FIG. 7 is a block diagram showing a configuration example of a conventional magneto-optical disk device.

8 is a timing chart for explaining the operation in the recording mode in the conventional magneto-optical disk device of FIG.

FIG. 9 is a circuit diagram showing a configuration example of a conventional laser diode drive circuit.

[Explanation of symbols]

 20, 22, 24 NPN transistor 30, 32, 40, 42 PNP transistor 37 Laser diode 50, 150, 250 Constant current circuit 60 Differential drive circuit for module

Claims (3)

[Claims] 1. A switching transistor which is differentially connected and which is switched by supplying a drive pulse to a control electrode, and the switching so that a current n times as large as the current flowing through the switching transistor flows through a laser diode. A constant current circuit connected between the transistor and the laser diode; and a differential drive circuit provided on the output side of the constant current circuit for switching the laser diode at a high frequency. And a laser diode drive circuit. 2. The laser diode drive circuit according to claim 1, wherein the constant current circuit is a current mirror circuit. 3. The laser diode drive circuit according to claim 1, wherein the constant current circuit is a Wilson constant current circuit.