JP2004111984A - Laser driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser driver that inhibits an increase in power consumption even if laser current increases. <P>SOLUTION: The laser driver is provided with a current amplification circuit 20, so that respective values of outflow current Ia and inflow current Ib are smaller than a value of laser current I17. Accordingly, the increase in power consumption is inhibited even if the laser current I17 supplied to a laser 14 increases. Moreover, since a constant current source 30 is provided, even if the value of the laser current I17 is small, constant current Ic flows into NPN transistors 13A, 13B. This suppresses a reduction in switching speed of the NPN transistors 13A, 13B. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a laser driving device.

伴 い With the recent increase in capacity and speed of optical disk devices, there is a demand for high-speed, low-power laser drives for recording and reproduction.

Japanese Patent Publication No. 7-95610 discloses a laser driving device as shown in FIG. 9 as a laser driving device for increasing the switching speed.

In this laser driving device, first, the set current I4 from the current setting circuit 4 sets the inflow current I5A of the inflow type current source 5 and the set current I5B of the outflow type current source 6. The outflow current I6 of the outflow type current source 6 is set by the set current I5B. Inverted recording signals are applied to the bases of the transistors 3A and 3B of the differential current switch 3. When the transistor 3A is turned on and the transistor 3B is turned off, the current I3A flowing through the transistor 3A becomes equal to the inflow current I5A and the outflow current I6. As a result, the laser current I1 becomes 0 and the laser 1 turns off. When the transistor 3A is turned off and the transistor 3B is turned on, the current I3B flowing through the transistor 3B becomes equal to the inflow current I5A, and the current I3A flowing through the transistor 3A becomes zero. As a result, the laser current I1 becomes equal to the outflow current I6, and the laser 1 is turned on.

According to this laser driving device, the switching element is satisfied while satisfying a desirable condition for driving the laser, in which one of the lasers 1 is grounded and the other is connected to the transistor 3A as a switching element by a collector follower. The transistor 3A can be constituted by an NPN transistor having a high switching speed. Thereby, a high-speed switching speed of several nanoseconds or less can be easily achieved.

Generally, in a recording / reproducing laser drive device of an optical disk device, the value of the laser current differs in each of reproduction, erasure, and writing. The current value during writing is large, and the current value during reproduction is small.

However, in the laser driving device shown in FIG. 9, the laser current I1 itself is turned on / off by the differential current switch 3. Therefore, when the laser current I1 increases, the power consumption of the laser driving device also increases accordingly.

(4) When the laser current I1 decreases, the current flowing into the transistors 3A and 3B of the differential current switch 3 also decreases. As a result, the switching speed of the transistors 3A and 3B decreases.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a laser driving device capable of suppressing an increase in power consumption even when a laser current increases. .

Another object of the present invention is to provide a laser driving device capable of suppressing a decrease in switching speed even when a laser current is small.

The laser drive device according to the present invention includes a laser, a first current source, a second current source, a current amplifier circuit, a first transistor, and a second transistor. The first current source supplies a first current having a current value according to the set current value. A second current having a current value corresponding to the set current value flows into the second current source. The current amplification circuit amplifies the current from the first current source to generate a laser current, and supplies the laser current to the laser. The first transistor is connected between the first current source and the second current source. The second transistor is connected between a power supply node supplied with a power supply voltage and the second current source, and turns on / off complementarily to the first transistor.

In the laser driving device, when the first transistor is off, the first current from the first current source is supplied to the current amplification circuit. The current amplification circuit amplifies the current from the first current source to generate a laser current, and supplies the laser current to the laser. This turns on the laser. At this time, the second transistor is turned on, and a second current flows from the power supply node to the second current source through the second transistor. When the first transistor is on, all or part of the first current from the first current source flows into the second current source through the first transistor as a second current. As a result, the current supplied to the current amplification circuit decreases, and the laser current also decreases. As a result, the laser is turned off. At this time, the second transistor is turned off. The values of the first and second currents are determined according to the set current value. Further, the value of the laser current supplied to the laser when the laser is on is determined according to the value of the first current. Therefore, by adjusting the set current value, a required value of laser current can be supplied to the laser.

た め In this laser driving device, the current amplifier circuit is provided, so that the first and second current values are smaller than the laser current value. Therefore, even when the laser current increases, an increase in power consumption by the first current source, the second current source, and the first and second transistors can be suppressed.

Preferably, the laser has an anode connected to a power supply node. The current amplification circuit includes a first NPN transistor, a second NPN transistor, and a third NPN transistor. The first NPN transistor is connected between the first current source and a ground node to which a ground potential is applied, with a common emitter. The second NPN transistor has a collector connected to the power supply node, an emitter connected to the base of the first NPN transistor, and a base connected to the collector of the first NPN transistor. The third NPN transistor is connected between the cathode of the laser and a ground node with a common emitter, and the base is connected to the base of the first NPN transistor.

{Preferably, the current amplification circuit further includes a plurality of fourth NPN transistors. The plurality of fourth NPN transistors are connected between the cathode of the laser and a ground node in parallel with the third NPN transistor with a common emitter, and the base is connected to the base of the first NPN transistor.

カ レ ン ト In the laser driving device, a current mirror circuit is configured by the first to third NPN transistors. A current having a mirror ratio times the current from the first current source flowing through the first NPN transistor flows through the third NPN transistor. This is supplied to the laser as a laser current.

Furthermore, a current mirror circuit is configured by each of the first and second NPN transistors and the plurality of fourth NPN transistors. The sum of the current flowing through each of the plurality of fourth NPN transistors and the current flowing through the third NPN transistor is supplied to the laser as a laser current.

Preferably, the laser is connected to a power supply node whose anode receives a power supply voltage. The current amplification circuit includes a first N-channel MOS transistor, a second N-channel MOS transistor, and a third N-channel MOS transistor. The first N-channel MOS transistor is connected between the first current source and a ground node supplied with a ground potential. The second N-channel MOS transistor is connected between the power supply node and the gate of the first N-channel MOS transistor, and has a gate connected to the first current source. The third N-channel MOS transistor is connected between the cathode of the laser and a ground node, and has a gate connected to the gate of the first N-channel MOS transistor.

{Preferably, the current amplification circuit further includes a plurality of fourth N-channel MOS transistors. The plurality of fourth N-channel MOS transistors are connected between the cathode of the laser and the ground node in parallel with the third N-channel MOS transistor, and have their gates connected to the gate of the first N-channel MOS transistor. .

カ レ ン ト In the laser driving device, a current mirror circuit is formed by the first to third N-channel MOS transistors. A current that is a mirror ratio multiple of the current from the first current source flowing through the first N-channel MOS transistor flows through the third N-channel MOS transistor. This is supplied to the laser as a laser current.

(4) Further, a current mirror circuit is formed by each of the first and second N-channel MOS transistors and the plurality of fourth N-channel MOS transistors. The total of the current flowing through each of the plurality of fourth N-channel MOS transistors and the current flowing through the third N-channel MOS transistor is supplied to the laser as a laser current.

Preferably, the first transistor is an NPN transistor having a collector connected to a first current source and an emitter connected to a second current source, and the second transistor has a collector connected to a power supply node. And an NPN transistor having an emitter connected to the second current source.

{Preferably, the first and second transistors are N-channel MOS transistors.

Preferably, the laser driving device further includes a third current source. The third current source is connected to an interconnection node between the first transistor and the second current source, and receives a third current.

(4) In the laser driving device, when the first transistor is off, the second transistor is on, and a current equal to the sum of the second current and the third current flows. The second current flows into the second current source, and the third current flows into the third current source. When the first transistor is on, the second transistor is off and all or part of the first current from the first current source flows through the first transistor. This current is the sum of the second current and the third current, and the second current flows into the second current source, and the third current flows into the third current source.

Generally, as the value of the current flowing through a transistor decreases, its switching speed decreases. In the above laser driving device, when the value of the laser current supplied to the laser decreases, the value of the second current also decreases. However, since the third current source is provided, even when the value of the laser current is small, the third current, which is a constant current, flows through the first and second transistors. As a result, even when the laser current is small, a decrease in the switching speed can be suppressed.

Preferably, the laser driving device further includes a first diode and voltage applying means. The first diode has an anode connected to the first current source and a cathode connected to the current amplifier circuit. The voltage applying means applies a predetermined voltage in a forward direction of the first diode.

(4) In the above laser driving device, since the first diode is provided, the backflow of the current from the current amplification circuit can be prevented.

However, it is not desirable that the first diode be strongly reverse-biased. Therefore, in the laser driving device, a voltage applying unit is provided to apply a voltage in the forward direction of the first diode to such an extent that the first diode is not turned on.

The following effects are further obtained by this.

場合 When the laser is off, ie, when the first transistor is on, the voltage at the interconnection node between the first transistor and the first current source is about to drop. However, the voltage drops only to the level of the voltage applied by the voltage applying means. Therefore, when the first transistor is turned off next time, the voltage of the interconnection node between the first transistor and the first current source becomes a predetermined level as compared with the case where the voltage applying means is not provided. Since the time to reach is short, the switching speed can be increased.

{Preferably, the voltage applying means includes a fourth current source, m second diodes, and a third transistor. The fourth current source supplies a fourth current. The m second diodes are connected in series between the fourth current source and the cathode of the first diode. The third transistor has a collector connected to the power supply node, an emitter connected to the anode of the first diode, and a base connected to the fourth current source.

In the above-mentioned laser driving device, the voltage of the difference between the voltage drop of the m second diodes due to the fourth current and the base-emitter voltage of the third transistor is applied in the forward direction of the first diode. .

Preferably, the value of m is 2.

Preferably, the voltage applying means further includes n third diodes. The n third diodes are connected in series between the emitter of the third transistor and the anode of the first diode.

In the above laser driving device, the voltage of the difference between the voltage drop of the m second diodes due to the fourth current and the voltage between the base and the emitter of the third transistor is further increased. A voltage lower by the voltage drop is applied in the forward direction of the diode. Accordingly, when the voltage applied by the m second diodes and the third transistor does not sufficiently turn off the first diode, the first diode can be reliably turned off.

Preferably, the laser driving device further includes a fifth current source. The fifth current source is connected to the cathode of the first diode, and the fifth current flows therein.

When the fifth current source is not provided, when the laser is off, that is, when the first transistor is on, the fourth current is supplied to the current amplifier circuit, thereby turning on the laser. Can occur.

(4) In the laser driving device, since all or part of the fourth current flows into the fifth current source as the fifth current, such a disadvantage can be avoided.

Preferably, the voltage applying means further includes a resistor. The resistor is connected between the emitter of the third transistor and the anode of the first diode.

In the above-described laser driving device, a voltage lower than the voltage difference between the voltage drop of the m second diodes due to the fourth current and the base-emitter voltage of the third transistor by the voltage drop due to the resistance. Is applied in the forward direction of the diode. Accordingly, when the voltage applied by the m second diodes and the third transistor does not sufficiently turn off the first diode, the first diode can be reliably turned off.

{Preferably, the second diode is a transistor having a collector and a base connected to each other.

(4) Since the laser drive device according to the present invention includes the current amplifying circuit, it is possible to suppress an increase in power consumption even when the laser current increases.

(4) Further, since the third current source is provided, even when the laser current is small, a decrease in the switching speed can be suppressed.

(4) Since the first diode and the voltage applying means are provided, it is possible to prevent a strong reverse bias from being applied to the first diode, and to further increase the switching speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

(1st Embodiment)
FIG. 1 is a diagram showing an overall configuration of a laser driving device according to a first embodiment of the present invention. The laser driving device shown in FIG. 1 includes a current setting circuit 10, an inflow type current source 11, an outflow type current source 12, a differential type current switch 13, a laser 14, a current amplification circuit 20, a constant current source 30.

The current setting circuit 10 generates a desired setting current I11.

The inflow type current source 11 includes NPN transistors 11A-11C and resistors 11D-11F. The NPN transistor 11A has a collector connected to the output of the current setting circuit 10, an emitter connected to the resistor 11D, and a base connected to its own collector. The NPN transistor 11B has a collector connected to the node N1, an emitter connected to the resistor 11E, and a base connected to the base of the NPN transistor 11A. The NPN transistor 11C has a collector connected to the outflow type current source 12, an emitter connected to the resistor 11F, and a base connected to the base of the NPN transistor 11A. The resistors 11D-11F are respectively connected between the emitters of the NPN transistors 11A-11C and the ground node GND.

The outflow type current source 12 includes PNP transistors 12A and 12B and resistors 12C and 12D. The PNP transistor 12A has an emitter connected to the resistor 12C, a collector connected to the node N2, and a base connected to the base and collector of the PNP transistor 12B. The PNP transistor 12B has an emitter connected to the resistor 12D, a collector connected to the collector of the NPN transistor 11C of the outflow type current source 11, and a base connected to its own collector. The resistors 12C and 12D are connected between a power supply node Vcc receiving a power supply voltage and the emitters of the PNP transistors 12A and 12B, respectively.

The differential current switch 13 includes NPN transistors 13A and 13B. NPN transistor 13A has a collector connected to node N2, an emitter connected to node N1, and receives signal SD1 at its base. NPN transistor 13B has a collector connected to power supply node Vcc, an emitter connected to node N1, and receives signal SD2 at its base.

The current amplification circuit 20 includes NPN transistors 21A-21D and resistors 22A-22C. The NPN transistor 21B has a collector connected to the node N2, an emitter connected to the resistor 22A, and a base connected to the emitter of the NPN transistor 21A. The NPN transistor 21A has a collector connected to the power supply node Vcc, an emitter connected to the base of the NPN transistor 21B, and a base connected to the collector of the NPN transistor 21B. The NPN transistors 21C and 21D have a collector connected to the node N3, an emitter connected to the resistors 22B and 22C, respectively, and a base connected to the base of the NPN transistor 21B. Resistors 22A-22C are connected between the emitters of NPN transistors 21B-21D and ground node GND, respectively.

The laser 14 has an anode connected to the power supply node Vcc and a cathode connected to the node N3.

The constant current source 30 is provided between the node N1 and the ground node GND, and allows the current Ic to flow from the node N1 toward the ground node GND.

Next, the operation of the laser driving device configured as described above will be described.

FIG. 2 is a timing chart for explaining the operation of the laser driving device shown in FIG. Hereinafter, description will be made with reference to FIG.

(4) The set current I11 from the current setting circuit 10 is supplied to the collector and the base of the NPN transistor 11A of the inflow type current source 11. NPN transistors 11A and 11B form a current mirror circuit. Therefore, the inflow current Ib is determined by the set current I11 and the mirror ratio of the current mirror circuit. The NPN transistors 11A and 11C also form a current mirror circuit. Therefore, the inflow current I13 is determined by the set current I11 and the mirror ratio of the current mirror circuit.

(4) The PNP transistors 12A and 12B of the outflow type current source 12 constitute a current mirror circuit. Therefore, the outflow current Ia is determined by the inflow current I13 and the mirror ratio of the current mirror circuit. That is, the outflow current Ia is determined by the set current I11. Here, it is assumed that the mirror ratio of the current mirror circuit is set so that the value of the outflow current Ia is equal to the sum of the inflow current Ib and the current Ic.

信号 Complementary signals SD1 and SD2 are applied to the bases of the transistors 13A and 13B of the differential current switch 13.

(4) When turning on the laser 14, the signal SD1 is set at the L level and the signal SD2 is set at the H level. As a result, the NPN transistor 13A turns off and the NPN transistor 13B turns on. Current I15B flowing through NPN transistor 13B is equal to the sum of inflow current Ib and current Ic. On the other hand, the current I15A flowing through the NPN transistor 13A becomes 0. Thus, the current I10 supplied to the current amplification circuit 20 becomes the outflow current Ia. The NPN transistors 21A-21C of the current amplifying circuit 20 form a current mirror circuit. Therefore, a current I20A obtained by multiplying the inflow current I10 flowing through the NPN transistor 21B by the mirror ratio of the current mirror circuit is induced in the NPN transistor 21C. The NPN transistors 21A, 21B, 21D also constitute a current mirror circuit. Therefore, a current I20B obtained by multiplying the current I10 by the mirror ratio of the current mirror circuit is induced in the NPN transistor 21D. The sum of the currents I20A and I20B becomes the laser current I17 and is supplied to the laser. Thereby, the laser 14 is turned on. At this time, assuming that the gain of the current amplification circuit 20 is Ai, the relationship between the current I10 and the laser current I17 is expressed as I17 = I10 × Ai.

(4) When turning off the laser 14, the signal SD1 is set at the H level and the signal SD2 is set at the L level. This turns on the NPN transistor 13A and turns off the NPN transistor 13B. All of the outflow current Ia becomes the current I15A flowing through the transistor 13A, and further becomes the inflow current Ib and the current Ic. As a result, the current I10 supplied to the current amplification circuit 20 becomes 0, and the laser 14 is turned off.

(4) When such a laser drive device is applied to an optical disk device, the value of the laser current I17 differs in each of writing, reproducing, and erasing on the optical disk. Normally, the value of the laser current I17 is large during writing, and small during reproduction. In this laser driving device, the values of the inflow current Ib and the outflow current Ia are adjusted by adjusting the value of the set current I11. Further, the value of the laser current I17 is adjusted by adjusting the value of the outflow current Ia. That is, by adjusting the value of the set current I11 from the current setting circuit 10, a required value of the laser current I17 can be supplied to the laser 14.

(4) In this laser drive device, the current amplifier circuit 20 is provided, so that the outflow current Ia and the inflow current Ib are smaller than the value of the laser current I17. Therefore, even when the laser current I17 supplied to the laser 14 increases, such as when writing to an optical disk, the current setting circuit 10, the inflow type current source 11, the outflow type current source 12, and the differential type current switch 13 This can suppress an increase in power consumption.

Generally, as the value of the current flowing through a transistor decreases, its switching speed decreases. In this laser driving device, when the value of the laser current I17 supplied to the laser 14 decreases, the value of the inflow current Ib also decreases. However, since the constant current source 30 is provided, even when the value of the laser current I17 is small, the constant current Ic flows through the NPN transistors 13A and 13B. Thus, even when the laser current I17 supplied to the laser 14 is small, a decrease in the switching speed of the NPN transistors 13A and 13B can be suppressed.

Here, it is assumed that the value of outflow current Ia is equal to the sum of inflow current Ib and current Ic, but a part of outflow current Ia may be equal to the sum of inflow current Ib and current Ic. . However, when the laser 14 is off, that is, when the NPN transistor 13A is on, the value of the laser current I17 due to the current I10 supplied to the current amplifying circuit 20 in the outflow current Ia is smaller than the threshold value of the laser 14. Is required.

Further, between the node N3 and the ground node GND, a plurality of NPN transistors and resistors may be further provided in parallel with the NPN transistors 21C and 21D and the resistors 22B and 22C. Thereby, the gain of the current amplification circuit 20 can be adjusted to a desired value.

Further, NPN transistors 11A-11C of the inflow type current source 11, PNP transistors 12A and 12B of the outflow type current source 12, NPN transistors 13A and 13B of the differential type current switch 13, and NPN transistors 21A-21D of the current amplification circuit 20. Instead, as shown in FIG. 3, N-channel MOS transistors 11A to 11C, P-channel MOS transistors 12A and 12B, N-channel MOS transistors 13A and 13B, and N-channel MOS transistors 21A to 21D may be used.

(Second embodiment)
FIG. 4 is a diagram showing an overall configuration of a laser driving device according to a second embodiment of the present invention. The laser driving device shown in FIG. 4 includes, in addition to the laser driving device shown in FIG. 1, a backflow prevention diode 40, an outflow type current source 50, a constant current source 60, clamping diodes 71 and 72, And a clamping transistor 73. The outflow type current source 50, the constant current source 60, the diodes 71 and 72 for clamping, and the transistor 73 for clamping constitute voltage applying means.

The backflow prevention diode 40 is an NPN transistor having a collector and a base connected to each other. The collector and the base constitute an anode, and the emitter constitutes a cathode. The anode is connected to the node N2, and the cathode is connected to the collector of the NPN transistor 21B of the current amplification circuit 20.

The outflow type current source 50 includes PNP transistors 50A and 50B and resistors 50C and 50D. The PNP transistor 50A has an emitter connected to the resistor 50C, a collector connected to the node N4, and a base connected to the base and collector of the PNP transistor 50B. The PNP transistor 50B has an emitter connected to the resistor 50D, a collector connected to the constant current source 60, and a base connected to its own collector. Resistors 50C and 50D are connected between a power supply node Vcc receiving a power supply voltage and the emitters of PNP transistors 50A and 50B, respectively.

The constant current source 60 is provided between the collector of the PNP transistor 50B and the ground node GND, and allows the current I20 to flow from the collector of the PNP transistor 50B toward the ground node GND.
The clamping diodes 71 and 72 are NPN transistors having a collector and a base connected to each other. The collector and the base constitute an anode, and the emitter constitutes a cathode. The anode of the clamping diode 71 is connected to the node N4, and the cathode is connected to the anode of the clamping diode 72. The cathode of the clamping diode 72 is connected to the cathode of the backflow prevention diode 40.

(4) The collector of the clamping transistor 73 is connected to the power supply node Vcc, the emitter is connected to the anode of the backflow prevention diode 40, and the base is connected to the node N4.

Next, the operation of the laser driving device configured as described above will be described.

FIG. 5 is a timing chart for explaining the operation of the laser driving device shown in FIG. Hereinafter, description will be made with reference to FIG.

(4) When turning on the laser 14, the signal SD1 is set at the L level and the signal SD2 is set at the H level. As a result, the NPN transistor 13A turns off and the NPN transistor 13B turns on. Current I15B flowing through NPN transistor 13B is equal to the sum of inflow current Ib and current Ic. On the other hand, the current I15A flowing through the NPN transistor 13A becomes 0. Thus, the current I10 supplied to the current amplification circuit 20 is the sum of the outflow current Ia, the current I21, and the outflow current Id. Thereby, the laser 14 is turned on.

(4) When turning off the laser 14, the signal SD1 is set at the H level and the signal SD2 is set at the L level. This turns on the NPN transistor 13A and turns off the NPN transistor 13B. The outflow current Ia and the current I21 become the current I15A flowing through the transistor 13A, and further become the inflow current Ib and the current Ic. As a result, the current I10 supplied to the current amplification circuit 20 becomes the outflow current Id. Since the outflow current Id is at a level that does not affect the on / off of the laser 14, the laser 14 is turned off.

(4) In this laser driving device, since the backflow prevention diode 40 is provided, the backflow of the current from the current amplification circuit 20 to the node N2 can be prevented. However, it is not desirable that a strong reverse bias is applied to the backflow prevention diode 40. Therefore, this laser driving device is provided with voltage applying means.

(4) The PNP transistors 50A and 50B of the outflow type current source 50 constitute a current mirror circuit. Therefore, the outflow current Id determined by the constant current I20 and the mirror ratio of the current mirror circuit flows through the PNP transistor 50A. The voltage level of the node N4 becomes higher than the voltage level of the cathode of the backflow prevention diode 40 by the voltage drop of the clamping diodes 71 and 72 due to the outflow current Id. The voltage of the node N4 is applied to the base of the clamping transistor 73, and the current I21 flows. Therefore, the voltage level of the anode of the backflow prevention diode 40 is lower than the voltage level of the node N4 by the voltage between the base and the emitter of the clamping transistor 73. In this way, a voltage is applied in the forward direction of the backflow prevention diode 40 to such an extent that the backflow prevention diode 40 is not turned on.

The following effects are further obtained by this.

When the laser 14 is turned off, the NPN transistor 13A turns on. The outflow current Ia and the current I21 become the current I15A flowing through the transistor 13A, and further become the inflow current Ib and the current Ic. As a result, the voltage level of node N2 is about to drop. However, the voltage is reduced only to the level of the voltage applied to the anode of the backflow prevention diode 40 by the voltage applying means. Therefore, the next time the NPN transistor 13A is turned off, the time required for the voltage level of the node N2 to reach the predetermined level is shorter than in the case where the voltage applying means is not provided. That is, the switching speed of the NPN transistors 13A and 13B can be increased.

Here, the number of the clamping diodes 71 and 72 is set to two, but the number is not limited to this, and it is necessary to provide as many as necessary to apply a voltage that does not turn on the backflow prevention diode 40. Can be.

(Third embodiment)
FIG. 6 is a diagram showing the overall configuration of the laser driving device according to the third embodiment of the present invention. The laser driving device shown in FIG. 6 further includes a constant current source 80 in addition to the components of the laser driving device shown in FIG. The constant current source 80 is provided between the cathode of the backflow prevention diode 40 and the ground node GND, and allows the constant current Ie to flow from the cathode of the backflow prevention diode 40 toward the ground node GND.

In the laser driving device shown in FIG. 4, when the laser 14 is turned off, the outflow current Id is supplied to the current amplification circuit 20. If the value of the laser current I17 corresponding to the outflow current Id exceeds the threshold value of the laser 14, the laser 14 will be turned on.

However, according to the laser driving device shown in FIG. 6, since the outflow current Id is pulled by the constant current Ie, it is possible to prevent a situation in which the laser 14 is turned on even when the laser 14 is off.

(Fourth embodiment)
FIG. 7 is a diagram showing an overall configuration of a laser driving device according to a fourth embodiment of the present invention. The laser driving device shown in FIG. 7 further includes a resistor 90 in addition to the components of the laser driving device shown in FIG. The resistor 90 is connected between the emitter of the clamping transistor 73 and the anode of the backflow prevention diode 40.

In the laser driving device shown in FIG. 4, when the voltage level of the anode of the backflow prevention diode 40 does not drop sufficiently and the backflow prevention diode does not turn off sufficiently, a part of the current I21 is supplied to the current amplification circuit 20. As a result, the laser 14 may be turned on.

According to the laser driving device shown in FIG. 7, since the voltage level of the anode of the backflow prevention diode 40 can be reduced by the voltage drop due to the resistor 90, the backflow prevention diode 40 can be reliably turned off.

Although the resistor 90 is provided here, a diode may be provided between the emitter of the clamping transistor 73 and the anode of the backflow prevention diode 40 instead.

(4) Instead of the resistor 90, a plurality of diodes connected in series between the emitter of the clamping transistor 73 and the anode of the backflow prevention diode 40 may be provided.

(Fifth embodiment)
FIG. 8 is a diagram showing an overall configuration of a laser driving device according to a fifth embodiment of the present invention. The laser driving device shown in FIG. 8 further includes, in addition to the laser driving device shown in FIG. 1, a backflow prevention diode 40, an outflow type current source 50, a constant current source 60, clamping diodes 71 and 72 shown in FIG. It includes a clamping transistor 73, a constant current source 80 shown in FIG. 6, and a resistor 90 shown in FIG.

(4) In this laser driving device, when turning on the laser 14, the signal SD1 is set at the L level and the signal SD2 is set at the H level. As a result, the NPN transistor 13A turns off and the NPN transistor 13B turns on. Current I15B flowing through NPN transistor 13B is equal to the sum of inflow current Ib and current Ic. On the other hand, the current I15A flowing through the NPN transistor 13A becomes 0. Thus, the current I10 supplied to the current amplification circuit 20 is the sum of the outflow current Ia, the current I21, the outflow current Id, and the inflow current Ie. The voltage amplification circuit 20 generates a laser current I17 corresponding to the current I10, and supplies the laser current I17 to the laser 14, so that the laser 14 is turned on.

(4) When turning off the laser 14, the signal SD1 is set at the H level and the signal SD2 is set at the L level. This turns on the NPN transistor 13A and turns off the NPN transistor 13B. The outflow current Ia and the current I21 become the current I15A flowing through the transistor 13A, and further become the inflow current Ib and the current Ic. The outflow current Id is pulled by the constant current Ie, and the laser 14 is turned off.

た め In this laser drive device, since the current amplifier circuit 20 is provided, the outflow current Ia and the inflow current Ib are smaller than the value of the laser current I17. Therefore, even when the laser current I17 supplied to the laser 14 increases, such as when writing to an optical disk, the current setting circuit 10, the inflow type current source 11, the outflow type current source 12, and the differential type current switch 13 Can suppress an increase in power consumption.

Also, since the constant current source 30 is provided, the constant current Ic flows through the NPN transistors 13A and 13B even when the value of the laser current I17 is small. As a result, even when the laser current I17 supplied to the laser 14 is small, a decrease in the switching speed of the NPN transistors 13A and 13B can be suppressed.

(4) Since the voltage applying means is provided, it is possible to prevent a strong reverse bias from being applied to the backflow prevention diode 40. Further, the switching speed of the NPN transistors 13A and 13B can be increased as compared with the case where no voltage applying means is provided.

Also, since the constant current source 80 is provided, it is possible to prevent a situation where the laser 14 is turned on even when the laser 14 is off.

(4) Since the resistor 90 is provided, the backflow prevention diode 40 can be reliably turned off.

Note that it is obvious that the above-described first to fifth embodiments operate even when the connection polarity of the laser 14 is changed and the PNP transistor and the NPN transistor are interchanged.

FIG. 1 is a diagram illustrating an entire configuration of a laser driving device according to a first embodiment of the present invention. 2 is a timing chart for explaining the operation of the laser driving device shown in FIG. FIG. 4 is a diagram illustrating a modification of the laser driving device illustrated in FIG. 1. FIG. 6 is a diagram illustrating an overall configuration of a laser driving device according to a second embodiment of the present invention. 5 is a timing chart for explaining the operation of the laser driving device shown in FIG. FIG. 9 is a diagram illustrating an overall configuration of a laser driving device according to a third embodiment of the present invention. It is a figure showing the whole laser drive device composition by a 4th embodiment of the present invention. It is a figure showing the whole laser drive device composition by a 5th embodiment of the present invention. FIG. 9 is a diagram illustrating an overall configuration of a conventional laser driving device.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Current setting circuit 11 Inflow type current source 12, 50 Outflow type current source 13A, 13B NPN transistor 14 Laser 20 Current amplification circuit 30, 60, 80 Constant current source 40 Backflow prevention diode 71, 72 Clamping diode 73 Clamping transistor 90 resistance

Claims (1)

A laser,
A first current source that supplies a first current having a current value according to the set current value;
A second current source into which a second current having a current value according to the set current value flows;
A current amplifier circuit that amplifies a current from the first current source to generate a laser current, and supplies the laser current to the laser;
A first transistor connected between the first current source and the second current source;
A second transistor connected between a power supply node supplied with a power supply voltage and the second current source, the second transistor being turned on / off complementarily to the first transistor; .

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