JP2003101129A - Circuit and method for driving laser diode, and optical head using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser diode driving circuit which is capable of drive with high frequency without being accompanied with needless power consumption or sharp increase of manufacture cost, even if it is a laser diode of high drive voltage. SOLUTION: This circuit has a ground line L1 which is connected to the cathode terminal of a laser diode 1 for outputting a laser beam, a first power line L2 which is kept at the first potential higher than the ground potential, a second power line L3 which is kept at the second potential higher than the first potential, a constant current source 5 which is connected to the first power line L2 and the second power line L3 and supplies the anode terminal of the laser diode 1 with a drive current, and a light emission control circuit 6 which is connected to the junction between the constant current source 5 and the anode terminal and controls the light emission of the laser diode 1 through bypassing the drive current with specified timing.

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 a drive method mounted on an optical head for writing / reading information to / from a rotating recording medium.
And an optical head using the same.

[0002]

2. Description of the Related Art The fields of application of communication / recording systems using laser light to various information industries are rapidly expanding.
With the recent increase in information transfer speed, a technique for driving a laser diode at high speed has become indispensable for an optical head of an optical disk device that rotates a recording medium to transfer information. Conventionally, various proposals have been made for a drive circuit for realizing high-speed drive of a laser diode.

For example, FIG. 13 shows a drive circuit in which a differential amplifier circuit having transistors Tr20 and Tr21 and a transistor Tr22 as a constant current source are combined in order to switch on / off of a drive current flowing through a laser diode LD at high speed. An example is shown. The collector terminal of the transistor Tr20 is grounded via the resistor R20. The collector terminal of the transistor Tr21 is a laser diode L
It is connected to the cathode terminal of D and the anode terminal of the laser diode LD is grounded. Transistor Tr2
0, the emitter terminals of Tr21 are commonly connected and connected to the collector terminal of the transistor Tr22 of the constant current source, and the emitter terminal of the transistor Tr22 is connected to the negative power source and a negative voltage (-Vcc) is applied. . Figure 1
The driving circuit shown in FIG. 3 can pulse-drive the laser diode LD at high speed, but it requires a negative power supply, and therefore, it normally has an information processing apparatus such as a personal computer using only a positive power supply of + 5V or + 12V. Not suitable for mounting on.

FIG. 14 shows another drive circuit example. Hereinafter, components having the same functions as those in FIG. 13 will be assigned the same reference numerals and explanations thereof will be omitted. In the circuit shown in FIG. 14, the collector terminal of the transistor Tr20 is a resistor R20.
To the positive power supply, and the anode terminal of the laser diode LD is also connected to the positive power supply. On the other hand, the emitter terminal of the transistor Tr22, which is a constant current source, is grounded. The circuit configuration shown in FIG. 14 is advantageous in that it does not require a negative power supply, as compared with the circuit configuration shown in FIG. However, in this configuration, the cathode terminal of the laser diode LD needs to be insulated from the ground potential. Since the housing of the optical head is usually designed to have the same ground potential as the mechanical chassis, the cathode terminal needs to be arranged so as to be insulated from the housing. However,
To suppress heat generation of the laser diode LD due to light emission,
It is superior in terms of heat dissipation efficiency to bring the cathode terminal side into close contact with the metal casing. Therefore, the drive circuit configuration shown in FIG. 14 is not suitable for use in an optical head.

FIG. 15 shows an example of a drive circuit in which the drawbacks of the drive circuit shown in FIG. 14 are improved. In the circuit shown in FIG. 15, the collector terminal of the transistor Tr20 is grounded via the resistor R20, and the cathode terminal of the laser diode LD is grounded. On the other hand, the emitter terminal of the transistor Tr22, which is a constant current source, is connected to the positive power source. According to this circuit configuration, since the cathode terminal of the laser diode LD is grounded, the cathode terminal side can be brought into close contact with the metal casing to improve the heat dissipation efficiency. By the way, in the drive circuit shown in FIG.
A PNP-type bipolar transistor is used as each of the transistors Tr20, Tr21, and Tr22. In general, the mobility of holes is lower than the mobility of electrons, and thus PNP transistors using holes as carriers are not suitable for high-speed switching operation. Therefore, the driving circuit shown in FIG. 15 becomes difficult to use as the switching operation of the driving current flowing through the laser diode LD becomes faster.

FIG. 16 shows a laser diode drive circuit which compensates for the drawbacks of the drive circuit shown in FIGS. 13 to 15, and is disclosed in Japanese Patent Laid-Open No. 5-315686. Less than,
The configuration of the drive circuit shown in FIG. 16 will be described with reference to the description of the publication. First, the laser diode 100 that generates laser light, the constant current circuit 130 connected to the anode terminal of the laser diode 100, and the laser diode 100.
N connected in parallel between the anode and cathode terminals of
PN type transistor 127 and NPN type transistor 1
Differentially connected PNP transistor 1 driving 27
21 and 122 are provided.

The cathode terminal of the laser diode 100 is grounded, and the anode terminal is connected to a constant current circuit 130 including a resistor 129 and a PNP transistor 128. One end of the constant current circuit 130 has a positive voltage source Vcc.
It is connected to the. The base terminal of the PNP transistor 128 is connected to the base terminal of the PNP transistor 131. The emitter terminal of the PNP transistor 131 is connected to the voltage source Vcc via the resistor 132, and the collector terminal is connected to the base terminal. In addition to being connected, it is also connected to the APC terminal. That is, the PNP transistor 128 and the PNP transistor 131 form a current mirror.

An NPN transistor 127 is connected in parallel to the anode terminal and the cathode terminal of the laser diode 100. A differential amplifier 120 is connected to drive the NPN transistor 127. The differential amplifier 120 includes differentially connected PNP transistors 121 and 122, resistors 123 and 124 that ground the collector terminals of the PNP transistors 121 and 122, and PNP transistors 121 and 12, respectively.
The resistor 125 serves as a constant current circuit 126 that connects the common connection point of the two emitter terminals to the voltage source Vcc.

In the laser diode drive circuit having the configuration shown in FIG. 16, an NPN type transistor 127 connected in parallel with the laser diode 100 is driven by PNP type transistors 121 and 122. According to the above-mentioned publication, it is described that the PNP transistors 121, 122 can be of a small power type, and not only high speed driving can be achieved but also power consumption can be reduced. In addition, since the laser diode 100 can be used as a cathode common (the cathode terminal is electrically connected to the housing), the need for floating is eliminated, the mounting structure is simplified, and the cost can be reduced. Has been done.

[0010]

By the way, as the recording density of the recording medium is improved, the emission wavelength of the laser diode is becoming shorter. The driving voltage of the laser diode tends to increase as the emission wavelength becomes shorter. For example, CD-R (writable compact disc) and M
A laser diode element used in a recordable system represented by a D (mini disc) has an emission wavelength of 780n.
m, and the drive voltage required to obtain a predetermined laser light intensity is about 1.5 to 2.0V. However, D
A laser diode element used in a recordable system represented by VD-RAM and DVD-RW has an emission wavelength of 650 nm and a driving voltage of 2.5 to 3.5 V, which is high. Further, in a new high density recording / reproducing system represented by DVR-Blue, the emission wavelength of the laser diode element is 405 nm and the driving voltage is 4.0 to 4.0.
It reaches 7.0V.

In the drive circuit shown in FIG. 16, in order to operate the laser diode 100 having such a high drive voltage, the power supply voltage + Vcc must be set high, and inevitably the other elements are also protected against dielectric breakdown. Therefore, parts with high pressure resistance will be used. Therefore, the drive circuit shown in FIG. 16 has a problem that the manufacturing cost becomes high.

The drive circuit shown in FIG. 16 is characterized in that a switching element (NPN type transistor 127) for bypassing the drive current is connected in parallel with the laser diode 100. However, in the NPN transistor 127, a voltage drop equivalent to that of the laser diode 100 occurs when the laser diode 100 is turned off,
In addition, a current equivalent to that when the laser diode 100 emits light flows, and the NPN transistor 127 acts as a load.
For this reason, with the recent increase in the drive voltage of the laser diode, in the drive circuit shown in FIG. 16, the power consumption of the circuit that does not contribute to light emission increases, and the efficiency of the power consumption decreases significantly. Furthermore, since the amount of heat generated by the driving circuit during operation increases, the margin of the operating temperature range of the circuit with respect to the operating environment temperature of the system decreases. In order to avoid this, the system side needs a measure for strengthening the cooling function of the circuit as compared with the normal design, which causes a problem of increasing the manufacturing cost.

It is an object of the present invention to drive a laser diode which can be driven at high speed (high frequency) without causing unnecessary power consumption and a large increase in manufacturing cost even if the laser diode has a high driving voltage. A circuit and a driving method, and an optical head using the same.

[0014]

The above object is to provide a ground line connected to the cathode terminal of a laser diode that emits laser light, a first power supply line that is maintained at a first potential higher than the ground potential, and A drive current is supplied to the anode terminal of the laser diode at a predetermined timing, which is connected to a second power supply line that is maintained at a second potential that is higher than the first potential, and the first power supply line and the second power supply line. And a constant current source section.

In the laser diode drive circuit according to the present invention, the constant current source section has a constant current source for supplying the drive current to the anode terminal, and a connection point between the constant current source and the anode terminal. And a light emission control circuit which is connected and bypasses the drive current at a predetermined timing to control the light emission of the laser diode.

In the above laser diode drive circuit of the present invention, the reference potentials of various signals input to the circuit are set to the first potential.
It is characterized by further including a voltage level conversion circuit for converting into a potential between the potential and the second potential.

The laser diode drive circuit of the present invention is characterized by further comprising a circuit composed of a resistor and a capacitor inserted in parallel with the laser diode.

In the laser diode drive circuit of the present invention, a switching element that controls the drive current based on a predetermined control signal to determine the emission timing of the laser diode, and the control signal input to the switching element are input. And a capacitor provided in series with the terminal.

Further, the above object is to provide a switching element for controlling a drive current to be supplied to the laser diode based on a predetermined control signal to determine a light emission timing of the laser diode, and an input of the control signal of the switching element. It is achieved by a laser diode drive circuit having a capacitor provided in series with a terminal.

In the laser diode drive circuit according to the present invention, at least two laser diode drive circuits are connected in parallel between the input terminal and a capacitor provided in series with the input terminal and change the voltage level of the control signal. It is characterized by having a resistance of.

The laser diode drive circuit according to the present invention is characterized in that the minimum pulse width of the control signal is 10 nanoseconds (nsec) or less.

Further, the above object is an optical head having a laser diode for emitting a laser beam and a drive circuit for driving the laser diode, wherein the drive circuit comprises:
The present invention is achieved by an optical head including the laser diode driving circuit of the present invention.

Further, the above object is a method of driving a laser diode having a cathode terminal connected to the ground, wherein a circuit for supplying a driving current to the anode terminal of the laser diode is provided with a plurality of levels of power supply voltage higher than the ground potential. It is achieved by a method for driving a laser diode, which is characterized in that

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser diode drive circuit and drive method according to an embodiment of the present invention, and an optical head using the same will be described with reference to FIGS. First, a schematic configuration of an optical disc system equipped with an optical head using the laser diode drive circuit according to the present embodiment will be described with reference to FIG. FIG. 1 shows a state in which a disk-shaped recording medium 92 is rotatably attached together with rotation of a rotary shaft 90 of a spindle motor (not shown). Optical head 5 used for recording / reproducing information
Reference numeral 0 denotes a structure in which the surface of the recording medium 92 can be moved in the radial direction (indicated by an arrow in the figure) by a moving unit (not shown), and the entire information recording area on the surface of the recording medium 92 can be scanned in combination with the rotation of the recording medium 92. Has become.

The optical head 50 has a housing 51 in which a laser diode, an optical system and a light receiving element are arranged. Further, the optical head 50 has a laser diode drive circuit 54 which is arranged on the lower surface of the housing 51 and supplies a predetermined drive current to the laser diode.

In order to electrically connect the optical head 50 serving as a movable portion and a circuit board (not shown) fixed to the chassis to securely transmit and receive signals to and from the laser diode drive circuit 54 and the light receiving element. , FPC (Flexible P
A flexible circuit board 52 having flexibility such as a printed circuit) on which circuit patterns and components are mounted is used. The laser diode drive circuit 54 is conventionally provided on the circuit board side fixed to the chassis. However, in order to prevent signal deterioration due to a high-frequency signal from the drive circuit 54 that occurs with the increase in the writing speed to the recording medium 92 in recent years, as shown in FIG. It is designed to be installed in the vicinity of the housing 51 containing the.

Next, a laser diode drive circuit and a drive method according to this embodiment will be described with reference to FIG. FIG. 2 is a functional block diagram illustrating the laser diode drive circuit 54 according to this embodiment. The laser diode drive circuit 54 includes a ground line L1 connected to the cathode terminal of the laser diode 1 that emits laser light.
Is wired. Also, the laser diode drive circuit 5
Reference numeral 4 denotes a first power supply line L2 maintained at a power supply voltage + V1 (first potential) higher than the ground potential and a second power supply line L3 maintained at a power supply voltage + V2 (second potential) higher than the power supply voltage + V1. And are wired. Further, the laser diode drive circuit 54 is connected to the first power supply line L2 and the second power supply line L3, and supplies a drive current to the anode terminal of the laser diode 1 at a predetermined timing.
Have six.

Based on the above configuration, a plurality of (two in this example) power source voltages + V1 to +2 higher than the ground potential on the positive sign side.
The constant current source unit 56 that constitutes the main part of the laser diode drive circuit 54 is operated between + V2. As a result, a low breakdown voltage circuit element can be used for the constant current source unit 56, and the laser diode 1 whose cathode terminal is connected to the ground line L1 can emit light at a high driving voltage.

According to the above configuration, since the drive circuit except the laser diode 1 is completely insulated from the ground potential, even if the drive voltage of the laser diode 1 needs to be set high, for example, about +7 V, the constant current is maintained. The drive voltage of the source unit 56 can always be set to a value determined by V2-V1. That is, even if the drive voltage of the laser diode 1 with respect to the ground level becomes high, it is not necessary to increase the breakdown voltage of the circuit element accordingly, so that it is possible to suppress an increase in manufacturing cost. Furthermore, by keeping the drive voltage of the constant current source unit 56 low, it is possible to reduce the power loss of the entire circuit and the unnecessary heat generation of the element during the rated operation. Although this example shows an example in which two kinds of power supply voltages are set, three or more kinds of voltages may be set and appropriately used on the circuit if there is no restriction on the system side. The shape and form of the laser diode drive circuit 54 are not particularly limited, and may be individually designed and arranged on the FPC, or a dedicated driver IC may be used.

According to the above configuration, the power supply voltage difference V2-V1
Is maintained at a constant value, the applied voltage to each circuit element of the constant current source unit 56 does not exceed V2-V1 even if the laser diode 1 having different specifications or characteristics is changed. Therefore, according to the laser diode drive circuit and the drive method of the present embodiment, it is possible to obtain the advantage that the conventional low voltage specification circuit can be used as it is. When it is desired to make the laser diode 1 having a higher driving voltage than the conventional one emit light, the absolute value of the power supply voltage is set higher than the ground level while maintaining the difference V2-V1 between the above two kinds of power supply voltages. A desired current can be passed through the laser diode 1 to emit light.

Next, a modified example of the laser diode drive circuit according to this embodiment will be described with reference to the functional block diagram shown in FIG. As shown in FIG. 3, the laser diode drive circuit 54 according to the present modification is provided with a voltage level conversion circuit 58 for converting the voltage levels of various input signals in the preceding stage of the constant current source unit 56 shown in FIG. There is. Usually, in order to control the light emission power and the light emission time of laser light in driving the laser diode 1, various control signals (for example, a DC signal for current control (auto power control (APC control) voltage)) in addition to the power supply voltage, It is necessary to input a rectangular signal for a logic circuit (laser diode (LD) output control signal). In this example, the APC control voltage is the signal line L5.
And the LD output control signal is output to the signal line L4.

The voltage level conversion circuit 58 has a function of converting the reference voltage of the various control signals for driving the laser diode 1 into a level suitable for the power supply voltages + V1 and + V2. The voltage level conversion circuit 58 is arranged in front of the constant current source unit 56. The voltage level conversion circuit 58 may be provided on the fixed substrate side of the system, but if the conversion according to the + V1 and + V2 voltages can be performed on the optical head 50 side as in this example, the circuit on the system side can be changed. The burden is small and convenience is improved.

Next, a specific circuit example of the laser diode drive circuit according to this embodiment will be described with reference to FIG. FIG. 4 shows a circuit example in which the voltage level conversion circuit 58 of FIG. 3 is added to the laser diode drive circuit 54 of FIG. In FIG. 4, the cathode terminal of the laser diode 1 is connected to the ground line L1 maintained at the ground potential. At the anode terminal of the laser diode 1,
The collector terminal of the PNP transistor 2 is connected.

A constant current source (DC power supply) 5 is formed by a resistor 4 connected to the emitter terminal of the transistor 2 and the transistor 2.
Is configured. The emitter terminal of the transistor 2 is maintained at a second potential (+ V2) higher than the first potential (+ V1) higher than the ground potential via the resistor 4
It is connected to the power line L3. The base terminal of the transistor 2 is connected to the connection point between the collector terminal of the NPN transistor 20 and the resistor 22.

The collector terminal of the transistor 20 is connected to the second power supply line L3 via the resistor 22. The emitter terminal of the transistor 20 has a first potential (+ V1) higher than the ground potential but lower than the second potential (+ V2).
Connected to the first power supply line L2 maintained at. A voltage level conversion circuit 58 is provided at the base terminal of the transistor 20.
The APC control voltage, which is a DC signal for current control, whose voltage level has been converted by the differential amplifier 42 which constitutes a part of the above, is input.

Voltage level conversion circuit 5 according to the present embodiment
Reference numeral 8 has a differential amplifier 42 that amplifies the APC control voltage output to the signal line L5, and resistors 28 and 30 that convert the voltage level of the LD output control signal. Resistance 28, 3
Since 0 will be described later, here, the differential amplifier 42
The configuration of will be described. Operational amplifier (operational amplifier) 3
The non-inverting input terminal of the resistor 4 is connected to the signal line L5 to which the APC control voltage is output via the resistor 40, and the resistor 4
It is connected to the first power supply line L2 via 6. On the other hand, the inverting input terminal of the operational amplifier 34 is grounded via the resistor 36. The output terminal of the operational amplifier 34 is connected to the base terminal of the transistor 20 and is also connected to the inverting input terminal via the resistor 38 for negative feedback.

The drive circuit 54 according to the present embodiment is provided with an NPN transistor 6 as an emission control element for controlling the emission of the laser diode 1 by bypassing the drive current from the constant current source 5 at a predetermined timing. ing. The collector terminal of the transistor 6 is connected to the connection point between the constant current source 5 and the anode terminal of the laser diode 1.
The emitter terminal of the transistor 6 has a first potential (+ V1)
Connected to the first power supply line L2 maintained at. The base terminal of the transistor 6 is connected to the differential amplifier circuit 18.

The differential amplifier circuit 18 is composed of two PNP type transistors 8 and 10 and resistors 12, 14 and 16. The emitter terminals of the transistors 8 and 10 are commonly connected and connected to the second power supply line L3 via the resistor 16. The collector terminal of the transistor 8 is connected to the first power supply line L2 via the resistor 12. Transistor 10
The collector terminal of is connected to the first power supply line L2 via the resistor 14. The base terminal of the transistor 8 is connected to the signal line L4 via the capacitor 32 for preventing the fluctuation of the base bias voltage. The base terminal of the transistor 8 has a resistor 28 of the voltage level conversion circuit 58,
The LD output control signal voltage whose voltage level is converted to a value between + V1 and + V2 at 30 is input. On the other hand, the base terminal of the transistor 10 is connected between the two resistors 24 and 26. The resistors 24 and 26 are connected in series in this order and are connected to the first power supply line L2 and the second power supply line L3,
As a result, the resistor 2 is connected to the base terminal of the transistor 10.
+ V1 to + V in the resistance division ratio based on each resistance value of 4 and 26
A voltage of 2 is applied.

Next, the operation of the laser diode drive circuit according to this embodiment will be described. First, the APC control voltage level-converted via the differential amplifier 42 is input to the base terminal of the transistor 20. This allows
When the transistor 20 is turned on, a current flows through the path of the resistor 22 and the transistor 20, the base voltage of the PNP transistor 2 is lowered, and the transistor 2 is turned on. As a result, a constant current is supplied from the constant current source 5 to the anode terminal of the laser diode 1.

Since the APC control voltage is applied as a DC voltage, the reference voltage level is converted using the differential amplifier 42 by the operational amplifier 34 in this example. The input signal is
Normally, it is given according to the ground level standard, but is input to the constant current source section 56 of the laser diode drive circuit 54 as the first potential (+ V1 level) standard by the differential amplifier 42 of this example. Therefore, it is possible to prevent the occurrence of dielectric breakdown or the like in the circuit in the constant current source unit 56.

The LD output control signal output to the signal line L4 is used to control the light emission timing of the laser diode 1. The LD output control signal is a binarized logic signal, and normally a rectangular wave having a voltage level of TTL level (0 to + 4V) is used. In this example, the LD output control signal is converted to a voltage level of approximately V1 to V2 using the capacitor 32 and the resistors 28 and 30.
The conversion level can be appropriately adjusted by changing the ratio of the resistance values of the two resistors 28 and 30 connected for applying the bias voltage.

The LD output control signal level-converted to a voltage value between + V1 and + V2 by the resistors 28 and 30 is applied to the base terminal of the transistor 8 of the differential amplifier circuit 18, and the base terminal of the transistor 10 is applied. , Resistance 24, 2
6, a voltage between + V1 and + V2 is applied. For example, it is assumed that the laser diode 1 is turned off at the H (high) level of the LD output control signal and emitted at the L (low) level. Since the transistor 8 is a PNP type bipolar transistor, the LD output control signal applied to the base terminal is turned off at the H level and turned on at the L level.

When the transistor 8 is turned on, a current flows through the route of the resistor 16, the transistor 8 and the resistor 12,
A voltage is generated across the resistor 12. This voltage is applied to the base terminal of the NPN type transistor 6, and the transistor 6 is turned on. As a result, at least a part of the constant current supplied from the constant current source 5 to the anode terminal of the laser diode 1 flows through the transistor 6, and the laser diode 1 stops emitting light.

On the other hand, when the transistor 8 is turned off, the transistor 6 is also turned off. Therefore, the constant current source 5
From then on, most of the constant current supplied to the anode terminal of the laser diode 1 comes to flow through the laser diode 1, and the laser diode 1 emits light.

As described above, the drive circuit according to the present embodiment shown in FIG. 4 is provided with the input signal level conversion circuit 58 in the front stage and the constant current source unit 56 which is the main part of the laser diode drive circuit in the rear stage. All the circuits constituting the constant current source unit 56 are operated while being insulated from the ground.

In the present embodiment, the LD output control signal is level-converted by the capacitor 32 and the resistors 28 and 30, and then the differential amplifier circuit 1 including the transistors 8 and 10.
I'm trying to make it input to 8. Although it is possible to directly input the LD output control signal after level conversion to the base terminal of the transistor 6 to switch the laser diode 1, the use of the differential amplifier circuit 18 is more effective in removing common mode noise. There is an advantage that the width is not easily affected by noise.

Further, in the present embodiment, the collector terminal of the switching transistor 6 is connected to the collector terminal of the transistor 2 of the constant current source 5 together with the anode terminal of the laser diode 1, so that the high speed switching characteristic of the NPN transistor 6 is improved. Although the circuit configuration is used effectively,
The present invention is not limited to this, and a configuration in which a switching element is inserted in series with the laser diode 1 can be adopted, and it is desirable to use the switching element properly according to various laser emission conditions.

According to the present embodiment described above, the driving voltage of the laser diode becomes higher as the emission wavelength of the laser diode becomes shorter, and for example, DVR-Blue.
Even if the driving voltage of the laser diode used in the high-density recording / reproducing system such as e reaches 4.0-7.0V, it is still possible to use the same low withstand voltage element as the element in the driving circuit. it can. Since it is not necessary to use a component having a high breakdown voltage to prevent dielectric breakdown, the manufacturing cost can be suppressed as compared with the conventional drive circuit.

Since the NPN transistor 127 for bypassing the driving current as shown in FIG. 16 is not connected in parallel with the laser diode 100, the power consumption of the circuit which does not contribute to the light emission is not adopted. Can be suppressed. Further, since the amount of heat generated by the driving circuit during operation can be suppressed, a large margin can be secured in the operating temperature range of the circuit with respect to the operating environment temperature of the system. Therefore, the circuit cooling function can be simplified and the manufacturing cost can be suppressed.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, depending on the impedance characteristics of the laser diode 1, overshoot or undershoot may occur in the light emission waveform. In order to reduce this, it is of course possible to dispose a circuit (snubber circuit) that connects a resistor and a capacitor in parallel to the laser diode 1. Although the snubber circuit is omitted in the above-mentioned embodiment, it is also effective to appropriately connect such a load in order to optimize the light emission waveform.

Further, in the above embodiment, the circuit including the capacitor 32 and the resistors 28 and 30 is used for level conversion of the LD output control signal for controlling the light emission of the laser diode 1. However, for example, when the drive circuit configuration is configured to manage the light emission of the LD by detecting the logical value of the light emission enable signal that permits light emission, the control signal (enable signal) is almost always in the on state or the off state during operation. Therefore, instead of the circuit using only the passive element,
Differential amplifier 42 used for level conversion of APC control voltage
It is preferable to use a level conversion circuit having a circuit configuration similar to the above.

In the above embodiment, the power supply voltage + V
Although 1 (first potential) and power supply voltage + V2 (second potential) are supplied from the system side, the present invention is not limited to this. For example, a resistor and two or more constant voltage diodes are connected between the second power supply line L3 that supplies the power supply voltage + V2 and the ground line L1, and for example, the first constant voltage diode and the second constant voltage diode are connected. Of course, the power supply voltage + V1 may be generated from the terminal between. Further, a transistor for amplifying the current may be provided in the subsequent stage of the first constant voltage diode. With such a configuration, only one power supply is required on the system side, so that a drive circuit and an optical head that are more convenient and have a reduced manufacturing cost can be realized.

Next, the drive circuit 54 according to the above embodiment.
Still another characteristic point of will be described with reference to FIGS. 5 to 12. First, L in the conventional laser diode drive circuit
Handling of the D output control signal will be described with reference to FIG. Note that, after this, for simplification of the description, the illustration and description of the differential amplifier circuit 18 are omitted. As shown in FIG.
The control signal input section of the conventional laser diode drive circuit is
The LD output control signal, which is a TTL level rectangular signal generated with reference to the ground potential, which is output to the signal line L4, is directly input to the base terminal of the NPN transistor 6 to control the blinking timing of the laser diode 1. ing.

Transistor 6 in the circuit shown in FIG.
An example of the signal waveform of the LD output control signal at the base terminal will be described with reference to FIG. The horizontal axis of the graph in FIG. 6 represents time (20 ns / div.), And the vertical axis represents voltage (1.5 V).
/ Div. ) Is represented. In FIG. 6, the pulse period 10
Measurement data in which an LD output control signal of 0 ns and a duty ratio of 50% is measured at the base terminal of the transistor 6 is shown. As shown in FIG. 6, the pulse frequency is 10 MH
With a signal of about z, even if the threshold voltage (threshold voltage: shown by a broken line in the figure) V _TH of the transistor 6 is as low as about 0.6 V, the duty of the on-voltage of the transistor 6 on the basis of the threshold voltage V _TH. The ratio can be about 53%, so the laser diode 1
The emission / non-emission of can be controlled.

However, as described in the above prior art,
In today's society in which the amount of information to be handled is increasing year by year, there are increasing demands for improving the data transfer rate as well as the recording capacity of the medium. Particularly in a large-capacity recording system using an optical disk, it is an important technical subject to increase the recording speed to the same level as a magnetic disk, and a recording medium adapted to this is being actively developed.

In order to improve the recording speed of the optical recording system, it becomes necessary for the laser diode to emit light with a pulse width shorter than before. In the conventional system, for example, the minimum pulse width when a rewritable CD-RW medium is recorded at 4 × speed is about 29 ns, and the rectangular signal for controlling the timing of this light emission is the laser diode drive shown in FIG. The configuration of the control signal input section of the circuit also works sufficiently.

However, in order to further improve the recording speed, the laser diode must emit light with a shorter pulse width. On the other hand, the commonly used TT
The rising speed (time) of the rectangular wave represented by the L signal is about 1 ns, but in an actual electronic circuit, impedance mismatch of the input / output terminals and stray impedance of the transmission line exist, so that the rectangular wave of the signal Dullness will occur. When the pulse width is sufficiently long, this rounding of the waveform does not cause a serious problem in operation, but when the pulse width becomes short, the duty ratio of the switching time shifts depending on the threshold voltage of the switching element.

In the case of a circuit using NPN type transistors as switching elements, the threshold voltage is about 0.6 V, the pulse amplitude is 5 V, and the pulse width is 50 ns. As described using 6, the switching time duty ratio is set to about 50%.
Can be kept at However, if the pulse width is 10n
When it is narrowed to s, the duty ratio of the off voltage of the transistor 6 on the basis of the threshold voltage V _TH is lowered to about 35% as shown in FIG.

Transistor 6 in the circuit shown in FIG.
Another signal waveform example of the LD output control signal at the base terminal will be described with reference to FIG. The horizontal axis of the graph in FIG. 7 represents time (5 ns / div.), And the vertical axis represents voltage (1.5 V).
/ Div. ) Is represented. In FIG. 7, the pulse period 20
Measurement data is shown in which an LD output control signal of ns and a duty ratio of 50% is measured at the base terminal of the transistor 6. As shown in FIG. 7, the pulse frequency is 50 MHz
When it reaches a certain level, the signal waveform becomes rounded. Therefore, if the threshold voltage V _TH of the transistor 6 is as low as about 0.6 V, the transistor 6 based on the threshold voltage V _TH is used.
The duty ratio of the ON voltage of is about 65%,
The duty ratio is largely deviated from the desired duty ratio (50%). As a result, the emission timing of the laser diode 1 deviates from the optimum condition, and predetermined recording cannot be performed.

FIG. 8 is a circuit diagram of the LD shown in FIG.
An example of a signal waveform at the base terminal of the transistor 6 when the pulse width of the output control signal is further shortened is shown.
The horizontal axis of the graph in FIG. 8 represents time (5 ns / div.), And the vertical axis represents voltage (1.5 V / div.).
The graph shows measurement data obtained by measuring the LD output control signal with a pulse cycle of 10 ns and a duty ratio of 50% at the base terminal of the transistor 6. Thus, when the pulse frequency is increased to about 100 MHz, the amplitude of the binarized voltage is reduced in addition to the rounding of the waveform.
A low threshold voltage V _TH of no longer makes it possible to control the predetermined on / off of the transistor 6.

If this phenomenon occurs during the recording operation on the optical disk, a sufficiently high energy is not supplied to the disk, so that the recording signal cannot be written correctly, which causes a reading error during signal reproduction. That is, the conventional control signal input section as shown in FIG. 5 has a drawback that its recording performance cannot be sufficiently maintained during high-speed recording.

In view of the above background, in the present embodiment, even when the period (pulse width) of the rectangular input signal is short, the laser diode drive capable of achieving a good duty ratio of the recording signal adapted to the threshold voltage of the switching element. A circuit and an optical head including the circuit are realized.

FIG. 9 shows an example in which a capacitor 32 is connected to the control signal input section shown in FIG. As shown in FIG.
Capacitor (capacitor capacity is 0.01μF) 3
2 is connected in series to the base terminal of the transistor 6 on the signal line L4.

FIG. 10 shows an example of the signal waveform of the LD output control signal at the base terminal of the transistor 6 in the circuit shown in FIG. The horizontal axis of the graph in FIG. 10 indicates time (5
ns / div. ), And the vertical axis represents the voltage (1.5 V / di
v. ) Is represented. The graph shows measurement data obtained by measuring the LD output control signal with a pulse cycle of 20 ns and a duty ratio of 50% at the base terminal of the transistor 6. Thus, since the capacitor 32 is inserted in series with the input stage, it is possible to cut the DC (direct current) component of the input signal even when the pulse frequency is about 50 MHz. Thus, even if the threshold voltage V _TH of the transistor 6 is as low as about 0.6V, it is possible to the duty ratio of the ON voltage of the transistor 6 in the threshold voltage V _TH reference to approximately 53%, at a predetermined timing Light emission / non-light emission of the laser diode 1 can be controlled.

FIG. 11 shows a control signal input in which two resistors 28 and 30 for changing the voltage level of the LD output control signal are connected in parallel between the capacitor 32 shown in FIG. 9 and the base terminal of the transistor 6. The structure of the part is shown. This example is equivalent to the control signal input section in the laser diode drive circuit according to the present embodiment shown in FIG. In this example, the capacitance of the capacitor is 0.01 μF, and the value of the additional resistors 28 and 30 is 4 k for the resistor 28 (Vcc side).
Ω, and the resistance 30 (Vee side) is 1 kΩ.

FIG. 12 is a circuit diagram of the circuit shown in FIG.
The signal waveform example of the LD output control signal at the base terminal of the transistor 6 is shown. The horizontal axis of the graph is time (5 ns /
div. ), And the vertical axis represents voltage (1.5 V / div.).
Is represented. The graph shows measurement data obtained by measuring the LD output control signal with a pulse cycle of 10 ns and a duty ratio of 50% at the base terminal of the transistor 6.

As shown in FIG. 11, the capacitor 32 is inserted in series with the base terminal of the transistor 6, and the LD is provided between the capacitor 32 and the base terminal of the transistor 6.
Two resistors 2 that change the voltage level of the output control signal
Since 8 and 30 are connected in parallel,
The DC component of the input signal can be removed, and the threshold voltage V _TH of the transistor 6 can be raised to about 1.2V. As a result, as shown in FIG. 12, even if the pulse frequency is about 100 MHz, the duty ratio of the on-voltage of the transistor 6 based on the threshold voltage V _{TH can be} set to about 50% and the transistor 6 can be turned on. Therefore, the laser diode 1 can emit light at a predetermined light emission timing.

As described above, according to the control signal input section of the present embodiment, the minimum pulse width of the LD output control signal is 10
It is possible to control the light emission / non-light emission of the laser diode 1 at an extremely accurate light emission timing even for nanoseconds (nsec) or less.

[0069]

As described above, according to the present invention, even a laser diode having a high driving voltage can be driven at a high speed (high frequency) without unnecessary power consumption and a large increase in manufacturing cost. be able to.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical head using a laser diode drive circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a laser diode drive circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing a schematic configuration in which a voltage level conversion circuit is provided in a laser diode drive circuit according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration example of a laser diode drive circuit according to an embodiment of the present invention.

FIG. 5 is a diagram showing a control signal input unit of a conventional laser diode drive circuit.

6 is a diagram showing a signal waveform example of an LD output control signal at the base terminal of a transistor 6 in the circuit shown in FIG.

7 is a diagram showing another example of the signal waveform of the LD output control signal at the base terminal of the transistor 6 in the circuit shown in FIG.

8 is a diagram showing still another example of the signal waveform of the LD output control signal at the base terminal of the transistor 6 in the circuit shown in FIG.

FIG. 9 is a diagram showing an example of a control signal input unit of the laser diode drive circuit according to the embodiment of the present invention.

10 is a circuit diagram of the transistor 6 in the circuit shown in FIG.
FIG. 6 is a diagram showing an example of a signal waveform of an LD output control signal at the base terminal of FIG.

FIG. 11 is a diagram showing another example of the control signal input unit of the laser diode drive circuit according to the embodiment of the present invention.

12 is a diagram showing a signal waveform example of an LD output control signal at the base terminal of a transistor 6 in the circuit shown in FIG.

FIG. 13 is a circuit diagram showing a configuration example of a conventional anode common (anode terminal side is electrically connected to the casing) laser diode drive circuit.

FIG. 14 is a circuit diagram showing another configuration example of a conventional anode common laser diode drive circuit.

FIG. 15 is a circuit diagram showing a configuration example of a conventional cathode common (cathode terminal side is electrically connected to the housing) laser diode drive circuit.

FIG. 16 is a circuit diagram showing a conventional laser diode drive circuit described in a prior art document.

[Explanation of symbols]

1,100 Laser diode 2,8,10,121,122,128,131 PN
P-type transistors 4, 12, 14, 16, 22, 24, 26, 28, 3
0, 36, 38, 40, 46, 123, 124, 12
5, 129, 132 Resistor 5 Constant current source 6, 20, 127 NPN type transistor 18 Differential amplifier circuit 32 Capacitor 34 Operational amplifier 42 Differential amplifier 50 Optical head 51 Housing 52 FPC 54 Laser diode drive circuit 56 Constant current source section 58 Voltage level conversion circuit 90 Rotation shaft 92 Recording medium 120 Differential amplifier 126, 130 Constant current circuit L1 Ground line L2 First power supply line L3 Second power supply line L4, L5 Signal line LD Laser diode R20 Resistor Tr20, Tr21, Tr22 Transistor

Claims (10)

[Claims] 1. A ground line connected to a cathode terminal of a laser diode that emits laser light, a first power supply line maintained at a first potential higher than the ground potential, and a second potential higher than the first potential. Second maintained at
A laser diode, comprising: a power supply line; and a constant current source unit that is connected to the first power supply line and the second power supply line and supplies a drive current to an anode terminal of the laser diode at a predetermined timing. Drive circuit. 2. The laser diode drive circuit according to claim 1, wherein the constant current source section includes a constant current source that supplies the drive current to the anode terminal, and the constant current source and the anode terminal. A laser diode drive circuit, which is connected to a connection point and which controls the emission of the laser diode by bypassing the drive current at a predetermined timing. 3. The laser diode drive circuit according to claim 1, wherein the reference potential of various signals input to the circuit is converted to a potential between the first potential and the second potential. A laser diode drive circuit, further comprising a conversion circuit. 4. The laser diode drive circuit according to claim 1, further comprising a circuit including a resistor and a capacitor inserted in parallel with the laser diode. Diode drive circuit. 5. The laser diode drive circuit according to claim 1, wherein the switching element controls the drive current based on a predetermined control signal to determine the emission timing of the laser diode. And a capacitor provided in series with the control signal input terminal of the switching element. 6. A switching element that controls a drive current to be supplied to the laser diode based on a predetermined control signal to determine a light emission timing of the laser diode, and a switching element connected in series to an input terminal of the control signal of the switching element. A laser diode drive circuit comprising: a provided capacitor. 7. The laser diode drive circuit according to claim 5, wherein the voltage level of the control signal is connected in parallel between a capacitor provided in series with the input terminal and the input terminal. A laser diode drive circuit having at least two resistors for changing the voltage. 8. The laser diode drive circuit according to claim 7, wherein the minimum pulse width of the control signal is 10 nanoseconds (nse).
c) A laser diode drive circuit characterized by the following. 9. A laser diode for emitting a laser beam,
An optical head having a drive circuit for driving the laser diode, wherein the drive circuit has the laser diode drive circuit according to any one of claims 1 to 8. head. 10. A method of driving a laser diode having a cathode terminal connected to a ground, wherein a circuit for supplying a driving current to the anode terminal of the laser diode is operated at a plurality of levels of power supply voltage higher than ground potential. And a method for driving a laser diode.