JPH0827959B2 - Laser diode drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser diode drive circuit used in an optical disc inspection apparatus for measuring the recording characteristics of an optical disc and controlling the power of laser light applied to the optical disc. is there.

<Prior Art> Generally, the emission modes of laser light in an optical disc inspection apparatus are roughly classified into a read mode and a recording mode (write mode). In read mode,
The optical disk is irradiated with laser light of constant power (small power), and in the recording mode, laser light of large power is irradiated onto the optical disk as pulsed light according to a recording signal.

FIG. 3 is a block diagram showing an example of a conventional laser diode drive circuit. In the figure, LD is a laser diode,
Tr1 is a drive transistor that supplies the laser diode LD with the drive current I1 for reading, Tr2 is a drive transistor that supplies the laser diode LD with the drive current I2 for recording, and PD is a part of the laser light emitted from the laser diode LD. Is a photodiode that receives light. Further, 1 is a current-voltage conversion circuit, 2 is a smoothing circuit, 3 is a control circuit which generates a control output Vc1 by comparing a feedback voltage Vf1 with a read power setting voltage Vr1, SW1 is a switch which is turned on in a read mode, 4
Is a drive circuit for operating the drive transistor Tr1 according to the control output Vc1.

That is, in the read mode, the magnitude of the drive current I1 is controlled so that the emission power of the laser diode LD becomes a constant power according to the read power setting voltage Vr1 (hereinafter, abbreviated as APC operation). A control circuit is configured. On the other hand, in the recording mode, although a specific circuit configuration is not shown, constant current driving is often adopted, and a pulse signal (recording pulse) Sw having a constant amplitude is applied to the driving transistor Tr2. , Drive the laser diode LD with a constant current.

<Problems to be Solved by the Invention> However, in constant current driving, even if the magnitude of the driving current I2 is constant, there is a drawback that the emission power changes due to the influence of temperature drift or the like.

Some APC circuits are designed to perform APC operation even in the recording mode, but in general, the response is delayed in the APC circuit, so the power of the emitted light immediately after switching the modes becomes insufficient, and a portion (head) of the recording signal is lost. It may fall out.

The present invention eliminates the drawbacks of the conventional device as described above, can perform the APC operation even in the recording mode, and has a simple structure of the laser diode drive circuit that can prevent the power shortage at the time of mode switching. It is intended to be realized.

<Means for Solving the Problems> The laser diode drive circuit of the present invention is a read control circuit that supplies a drive current to the laser diode LD so that the emission power of the laser diode LD is controlled to a constant value in the read mode. 10 and the laser diode
A constant current drive circuit 30 that drives the LD with a constant current, a recording power control circuit 20 that controls the magnitude of the drive current so that the emission power of the laser diode LD becomes a constant power according to the set voltage, and the constant current. Drive circuit 30 recording power setting voltage
Supply Vr2 and set voltage Vr2 and recording signal waveform
Sw is equipped with a multiplier 5 that performs multiplication and multiplication.
The output of the recording power control circuit 20 as a set voltage Vr3.
A recording power setting circuit 40 to be supplied to the recording power setting circuit 40, a comparison circuit 50 which outputs a signal when the feedback signal Vf2 in the recording power control circuit 20 becomes equal to a set voltage Vr3 obtained from the multiplier 5 of the recording power setting circuit 40, In the mode, when the feedback signal Vf2 in the recording power control circuit 20 becomes equal to the set voltage Vr3, the constant current drive circuit 30 drives the laser diode by the output signal of the comparison circuit.
And a changeover switch SW2 for changing over to the control output side of the recording power control circuit 20 from the output of.

<Operation> As described above, when switching to the recording mode, constant current driving is performed, and after the feedback signal in the recording power control circuit becomes equal to the set voltage, the driving of the laser diode is switched to the recording power control circuit. It is possible to start APC operation after the feedback signal of the recording power control circuit rises and the response of the system stabilizes, to perform APC operation even in the recording mode, and to prevent power shortage during mode switching. it can.

<Embodiment> FIG. 1 is a block diagram showing an embodiment of a laser diode drive circuit of the present invention. In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals. Enclosed by a chain line in the figure
10 is a read power control circuit similar to that in FIG. 3, 20 is a recording power control circuit, 30 is a constant current drive circuit, 40 is a recording power setting circuit, and 50 is a feedback signal Vf2 in the recording power control circuit 20, which is set. It is a comparison circuit for comparing with the voltage Vr3.
SW2 is a constant current drive circuit 30 according to the output Sc of the comparison circuit 50.
The control switch Vc3 and the control output Vc2 of the recording power control circuit 20 are supplied to the drive circuit 4 for driving the transistor Tr3. In the recording power setting circuit 40, 5 is a multiplier for multiplying the recording power setting voltage Vr2 and the recording signal waveform (Sw), the output of which is supplied to the recording power control circuit 20 as the setting voltage Vr3. There is.

In the laser diode drive circuit configured as described above, in the read mode, the read power control circuit 10 supplies the drive current I1 and the emission power of the laser diode LD is controlled to be constant by the APC operation. At this time,
The generation of the recording signal Sw is prohibited, or the recording power setting voltage Vr2 of the recording power setting circuit 40 becomes 0, and the drive current I2 is not supplied.

Next, when the recording mode is switched, the switch SW1 is turned off in the read power control circuit 10, and the feedback signal Vf2 is smaller than the set voltage Vr3 in the recording power control circuit 20 due to the delay of the smoothing circuit 2 or the like. Therefore, the changeover switch SW2 is connected to the constant current drive circuit 30 side. Therefore, the laser diode LD is driven with a constant current by a constant current according to the recording power setting voltage Vr2.

After that, when the feedback signal Vf2 increases with the rise of the recording power control circuit 20 and becomes equal to the set voltage Vr3, the output Sc of the comparison circuit 50 is inverted and the changeover switch SW2 is switched to the recording power control circuit 20 side. At this time, the set voltage
Since Vr3 is obtained by multiplying the recording power setting voltage Vr2 by the recording signal waveform, the recording signal Sw in the feedback signal Vf2 is changed.
The effect of the duty ratio of is compensated, and the APC operation can be started after the response of the recording power control circuit 20 becomes stable. That is, since the magnitude of the recording signal Vf2 changes according to the duty ratio of the recording signal Sw, the magnitude of the set voltage Vr3 also needs to change according to the duty ratio of the recording signal Sw.

FIG. 2 is a waveform diagram showing the operation at the time of such mode switching. As shown in the figure, at time t0, assuming that the reading mode is switched to the recording mode, the feedback signal Vf2 increases according to the duty ratio of the recording signal Sw and becomes equal to the set voltage Vr3 (t1). The changeover switch SW2 is changed over to the recording power control circuit 20 side. Therefore, after switching to the recording mode, the APC operation can be started with the response of the recording power control circuit 20 being stable.

<Effects of the Invention> As described above, in the laser diode drive circuit of the present invention, the constant current drive circuit for driving the laser diode with a constant current and the emission power of the laser diode become constant power according to the set voltage. A recording power control circuit for controlling the magnitude of the drive current, and a recording power setting voltage is supplied to the constant current drive circuit, and the recording power setting voltage is multiplied by the recording signal waveform, and the output is used as the setting voltage. A recording power setting circuit to be supplied to the recording power control circuit, the laser diode is driven by the constant current drive circuit when switching to the recording mode, and the feedback signal in the recording power control circuit becomes equal to the set voltage. After that, the drive of the laser diode is switched to the recording power control circuit side. , The feedback signal of the recording power control circuit rises, the APC operation can be started after the system response is stabilized, the APC operation can be performed even in the recording mode, and the power shortage at the time of mode switching can be prevented. It is possible to realize a laser diode drive circuit that can be realized with a simple configuration.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser diode drive circuit of the present invention, FIG. 2 is a waveform diagram showing its operating state, and FIG. 3 is a block diagram showing an example of a conventional laser diode drive circuit. . 10 ... Read power control circuit, 20 ... Recording power control circuit, 30 ... Constant current drive circuit, 40 ... Recording power setting circuit, 50 ... Comparison circuit, LD ... Laser diode, PD ...
Photodiode, 5 ... Multiplier.

Claims (1)

[Claims] 1. A laser diode LD in a reading mode.
A read control circuit 10 which supplies a drive current to the laser diode LD so that the emission power of the laser diode is controlled to a constant value.
A constant current drive circuit 30 that drives the laser diode LD with a constant current, and a recording power control circuit 20 that controls the magnitude of the drive current so that the emission power of the laser diode LD becomes a constant power according to a set voltage. The recording power setting voltage Vr2 is supplied to the constant current drive circuit 30 and a multiplier 5 for multiplying the setting voltage Vr2 and the recording signal waveform Sw is provided, and the output of the multiplier 5 is set as the setting voltage Vr3. Recording power setting circuit 40 to be supplied to the power control circuit 20, and a feedback signal in the recording power control circuit 20.
The comparison circuit 50 that outputs a signal when Vf2 becomes equal to the set voltage Vr3 obtained from the multiplier 5 of the recording power setting circuit 40, and the feedback signal Vf2 in the recording power control circuit 20 in the recording mode is equal to the set voltage Vr3. Then, a changeover switch SW for switching the drive of the laser diode from the output of the constant current drive circuit 30 to the control output side of the recording power control circuit 20 by the output signal of the comparison circuit.
2. A laser diode drive circuit comprising: