JP3042093B2 - Laser drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser driving circuit capable of accurately controlling the intensity of a laser beam.

[0002]

2. Description of the Related Art Conventionally, in a magneto-optical disk drive,
By irradiating a recording medium made of a magnetic film having perpendicular magnetic anisotropy with a laser beam to locally raise the temperature and simultaneously apply a magnetic field from the outside, and direct the magnetization of the local region to the direction of the magnetic field, Recording information has been done.

As described above, since light and a magnetic field are used in magneto-optical recording, a magnetic field modulation method in which a signal is converted in the direction of a magnetic field for recording and an optical modulation method in which a signal is converted into blinking laser light for recording are used. It is considered.

In the light modulation method, a laser drive circuit for modulating the output of a laser beam between a maximum output and a minimum output in accordance with the value of a recording signal (a binary signal) in order to blink the laser beam is provided. Required.

FIG. 4 is a diagram showing the configuration of a conventional laser drive circuit disclosed in Japanese Patent Application Laid-Open No. 2-166636. In the figure, a part of a laser beam L1 emitted from a semiconductor laser LD is received by a photodetector PD.
The received light output is amplified by the amplifier circuit 10, and the received light signal SPD
IO is output. This light receiving signal SPDIO is input to the two sample and hold circuits 12 and 13 and is sampled and held by each of the sample and hold circuits. The control of the timing of the sample hold is performed by the pulse generation circuit 11. The pulse generation circuit 11 receives the recording signal SREC, outputs a sampling pulse SPH at the rising edge of the recording signal SREC, and outputs a sampling pulse SPL at the falling edge of the recording signal SREC. At this time, the timing for sampling and holding is determined according to the state of the recording signal. When the recording signal SREC is at the H level, the semiconductor laser L
It is assumed that the intensity of the laser beam from D is maximized, and the intensity of the laser beam from the semiconductor laser LD is minimized when the level is L level. The control for modulating the laser light intensity in this manner is performed by the laser drive amplifier circuit 16.

When the recording signal SREC becomes H level,
The sample and hold circuit 12 samples and holds the light receiving signal SPDIO, and when the recording signal SREC becomes L level, the sample and hold circuit 13 samples and holds the light receiving signal SPDIO. The control of the timing of the sample hold is performed by the pulse generation circuit 11. The pulse generation circuit 11 receives the recording signal SREC, outputs a sampling pulse SPH at the rising edge of the recording signal SREC, and outputs a sampling pulse SPL at the falling edge of the recording signal SREC.

The hold voltages VHH, V obtained by sampling and holding in the two sample and hold circuits 12, 13
HL is input to the differential amplifier circuits 14 and 15, respectively. Then, the differential amplifier circuit 14 outputs a maximum error voltage VERH, which is the difference between the hold voltage VHH and the maximum reference voltage VRH, and the differential amplifier circuit 15 outputs the hold voltage VHL
And the minimum error voltage VER, which is the difference between
L is output. And this maximum value error voltage VERH
And the minimum error voltage VERL are equal to the laser drive amplifier circuit 16.
, The maximum output and the minimum output of the laser beam L1 of the semiconductor laser LD are feedback-controlled.

As described above, the laser light emitted from the semiconductor laser can be modulated between the maximum output and the minimum output, and the maximum output and the minimum output can be separately feedback-controlled.

[0009]

The operating characteristics of a sample-and-hold circuit in a conventional laser drive circuit generally include a linearity error and a gain error.

[0010] The linearity error and the gain error will be further described. The relationship between the input voltage and the hold voltage of the sample and hold circuit has characteristics as shown in FIG.

It is ideally preferable that the input voltage and the hold voltage have a directly proportional relationship. However, in actuality, as shown in FIG.
As the input voltage increases, the increase in the hold voltage decreases. An error caused by this characteristic is a linearity error.

The gain of the hold voltage with respect to the input voltage is ideally 1 (ie, the input voltage minus the input voltage).
(It is preferable that the hold voltage graph is a straight line having a slope of 1), but in practice, the value is smaller than 1. An error caused by this characteristic is a gain error.

As described above, due to the linearity error and the gain error, the hold voltage output from the sample-and-hold circuit contains an error. When the error is fed back to the semiconductor laser to control the laser beam intensity, There is a problem that the laser beam intensity cannot be accurately controlled to a predetermined value.

[0014] Such a problem occurs not only during recording but also during reproduction and erasure. In the above-mentioned conventional laser driving circuit, the received light output from the photodetector is also input to the sample and hold circuit at the time of reproduction and erasing. Cannot be controlled to a value.

An object of the present invention is to provide a laser driving circuit in which the controllability of laser light intensity does not deteriorate.

[0016]

A laser drive circuit according to the present invention includes a monitor for monitoring a laser beam, a sample and hold circuit for sampling and holding an output from the monitor, and a sample and hold circuit for sample and hold. A differential amplifier circuit for outputting a first error signal based on a difference between the hold signal level and a preset first reference value, and an output level from the monitor means and a preset second reference value. An error detection circuit that outputs a second error signal due to the difference between the first error signal and the second error signal.
A laser drive unit for controlling the intensity of the laser light based on the error signal of the first and the second error signals when the laser light is modulated, and the second error signal when the laser light is not modulated. And a switching unit for inputting the error signal to the laser drive unit.

A monitoring means for monitoring the laser light; a differential amplifier circuit for outputting a first error signal based on a difference between an output from the monitoring means and a preset first reference value; A sample and hold circuit that samples and holds the first error signal; an error detection circuit that outputs a second error signal based on a difference between an output level from the monitor unit and a second reference value set in advance; A laser driving unit that controls the intensity of the laser light based on a hold signal sampled and held by a circuit or the second error signal, and a modulation unit that modulates the hold signal and the laser light when the laser light is modulated. And switching means for inputting the second error signal to the laser drive section when not performed.

[0018]

With the above arrangement, when the laser light is not modulated, the output from the monitor means for monitoring the laser light is input to the laser drive unit via the error detection circuit, and the influence of the sample and hold circuit is obtained. Not receive.

When the laser light is modulated,
The differential amplifier circuit inputs a first error signal due to the difference between the output from the monitor means and the first reference value to the sample-and-hold circuit, thereby reducing the effects of the linearity error and the gain error of the sample-and-hold circuit. It is hard to receive.

[0020]

FIG. 1 is a block diagram of a laser drive circuit showing a first embodiment of the present invention. In FIG.
Are the same as those shown in FIG.

The switch 1 is supplied in advance with a reproduction reference voltage VRR, which is a reference voltage for reproduction, and an erase reference voltage VRE, which is a reference voltage for erasure. The switch 1 is supplied with an erase instruction signal. The erase instruction signal is a signal generated when the magneto-optical disk device is erasing a recording medium. The switch 1 is
When the erase instruction signal is generated, the erase reference voltage V
RE is output, and when the erase instruction signal is not generated, the reproduction reference voltage VRR is output.

The error detection circuit 2 compares the level of the received light output SPDIO from the amplifier circuit 10 with a reference voltage (reproduction reference voltage VRR or erase reference voltage VRE) from the switch 1 and detects an error indicating the difference. And outputs a use signal VEC.

The switch 3 has an error detection signal VEC from the error detection circuit 2 and maximum and minimum error voltages VERH and VE from the differential amplifier circuits 14 and 15.
RL has been input. The switch 3 receives the write instruction signal and the aforementioned erase instruction signal.
The write instruction signal is a signal generated when the magneto-optical disk device is recording on a recording medium. Note that the write instruction signal and the erase instruction signal are output from a control CPU or the like outside the circuit. The switch 3 outputs the maximum value error voltage VERH and the minimum value error voltage VERL when the write instruction signal is generated, and when the erase instruction signal is generated, or when both the write instruction signal and the erase instruction signal are output. When no signal is generated, an error detection signal VEC is output. And
The output from the switch 3 is input to the laser drive amplifier circuit 16.

The operation of the laser driving circuit configured as described above will be described below. First, the operation at the time of recording will be described. At the time of recording, a write instruction signal is generated. The switch 3 outputs the maximum value error voltage VERH and the minimum value error voltage VERL to the laser drive amplifier circuit 16. As a result, similarly to the related art, the laser light modulated between the maximum output and the minimum output can be feedback-controlled.

Next, the operation at the time of erasing will be described. At the time of erasing, an erase instruction signal is generated. The switch 1 outputs the erase reference voltage VRE to the error detection circuit 2. Then, the switching unit 3 outputs the error detection signal VEC from the error detection circuit 2.
Is output to the laser drive amplifier circuit 16. At the time of erasing, the laser light is not modulated. Therefore, control may be performed to maintain a constant laser beam intensity. Laser drive amplifier circuit 1
The control unit 6 controls the laser beam intensity to be constant based on the error detection signal VEC.

Next, the operation during reproduction will be described. In this embodiment, when neither the write instruction signal nor the erase instruction signal is generated, the operation at the time of reproduction is performed. Switch 1
Outputs the reproduction reference voltage VRR to the error detection circuit 2.
Then, the switch 3 outputs the error detection signal VEC from the error detection circuit 2 to the laser drive amplification circuit 16. The laser beam at the time of reproduction is not modulated as at the time of erasing. Therefore, control may be performed so as to maintain a constant laser beam intensity.
The laser drive amplifier circuit 16 controls the laser beam intensity to be constant based on the error detection signal VEC. The laser beam intensity at the time of reproduction is smaller than that at the time of recording and erasing.

As described above, the error detection signal VEC input to the laser drive amplifier circuit 16 does not pass through the sample and hold circuit when erasing and reproducing, that is, when the laser beam is not modulated. Unaffected by gain and linearity errors.

Next, a second embodiment of the present invention will be described. In the first embodiment, the effects of the linearity error and the gain error of the sample-and-hold circuit at the time of reproduction and erasure can be removed, but at the time of recording, that is, when the laser beam is modulated, the linearity error and The effect of gain error cannot be eliminated. In the second embodiment, it is possible to reduce the influence of the linearity error and the gain error of the sample and hold circuit during recording.

FIG. 2 is a configuration diagram of a laser drive circuit showing a second embodiment of the present invention. The difference from the configuration of FIG. 1 (first embodiment) is that the positions of the sample hold circuit and the differential amplifier circuit are exchanged. In FIG. 2, the operations at the time of reproduction and at the time of erasure are the same as those in the first embodiment, and therefore description thereof is omitted.

Next, the operation at the time of recording will be described. The light receiving signal SPDIO is input to the differential amplifier circuits 14 and 15.
Then, in the differential amplifier circuit 14, the level of the light receiving signal SPDIO is compared with the maximum value reference voltage VHH, and a difference voltage indicating the difference is output. Further, in the differential amplifier circuit 15, the level of the light receiving signal SPDIO is compared with the minimum value reference voltage VHL, and a difference voltage indicating the difference is output. These difference voltages are input to the sample and hold circuits 12 and 13, respectively.

The sample and hold circuits 12 and 13
As in the prior art, the difference voltage input at the input timing of the sampling pulse from the pulse generation circuit 11 is sampled and held. Then, the hold voltage is output as the maximum value error voltage VERH and the minimum value error voltage VERL. Then, VERH and VERL are input to the laser drive amplifier circuit 16 via the switch 3. The operations of the switching unit 3 and the laser drive amplifier circuit 16 are the same as in the first embodiment.

In the first embodiment, the light receiving signal SPDIO is input to the sample and hold circuit. However, in the present embodiment, the differential voltage output from the differential amplifier circuit is applied to the sample and hold circuit. Is entered. Since the feedback loop formed by the laser drive circuit controls the maximum output value and the minimum output value of the modulated laser light at the time of recording to predetermined values, the difference voltage output from the differential amplifier circuit is controlled. It operates to make it 0. Therefore, the sample and hold circuit operates near the point where the hold voltage becomes 0 when the feedback loop is relatively stable. Therefore, the sample and hold circuit can be operated in a range where the absolute values of the linearity error and the gain error in FIG. 3 are small.

As described above, according to the laser driving circuit of the second embodiment, the linearity error of the sample-and-hold circuit and the feedback control of the laser beam intensity during recording, that is, when the laser beam is modulated, are also improved. The effect of the gain error can be reduced.

In the first and second embodiments, when the magneto-optical disk device does not perform any of the recording, erasing, and reproducing operations, the above-mentioned "operation at the time of reproduction" is performed. No problem. In addition, the first and second
In the embodiment, the write instruction signal and the erase instruction signal are input from outside, but other signals may be used. For example, a write instruction signal, an erase instruction signal, and a read instruction signal (generated during reproduction) may be input.
Further, a signal for identifying whether recording or erasing may be performed and a write instruction signal may be input.

In the first and second embodiments,
During recording (that is, when the laser beam is modulated), the maximum output and the minimum output are feedback-controlled respectively.
Only one may be controlled. For example, when it is desired to accurately control only at the maximum output, feedback control may be performed only at the maximum output. In this case, only one sample hold circuit and one differential amplifier circuit are required.

Further, in the first and second embodiments,
The switch 3 is connected to the output side of the error detection circuit 2 and the differential amplifier circuits 14 and 15, but may be connected to the input side of the error detection circuit 2 and the sample and hold circuits 12 and 13.

[0037]

As described above, according to the present invention, the laser beam intensity can be controlled with high accuracy without being affected by the linearity error and the gain error of the sample and hold circuit.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a laser drive circuit showing a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a linearity error and a gain error of a sample and hold circuit.

FIG. 4 is a configuration diagram showing a conventional laser drive circuit.

[Explanation of symbols]

 1,3 switch 2 error amplifier circuit 10 amplifier circuit 11 pulse generation circuit 12,13 sample hold circuit 14,15 differential amplifier circuit 16 laser drive amplifier circuit PD photodetector LD semiconductor laser

Continuation of front page (56) References JP-A-1-204224 (JP, A) JP-A-64-48239 (JP, A) JP-A-2-98830 (JP, A) JP-A-64-76545 (JP, A) JP-A-64-76542 (JP, A) JP-A-2-130885 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST File (JOIS)

Claims (2)

(57) [Claims] 1. A monitor for monitoring a laser beam, a sample and hold circuit for sampling and holding an output from the monitor, a hold signal level sampled and held by the sample and hold circuit, and a first reference set in advance. A differential amplifier circuit for outputting a first error signal based on a difference between the output value and a second predetermined level.
An error detection circuit that outputs a second error signal due to a difference from the reference value, a laser driving unit that controls the intensity of the laser light based on the first error signal or the second error signal, The first error signal is output when the laser light is modulated, and the second error signal is output when the laser light is not modulated.
And a switching unit for inputting the error signal to the laser drive unit. 2. A monitoring means for monitoring laser light; a differential amplifier circuit for outputting a first error signal based on a difference between an output from the monitoring means and a preset first reference value; A sample-and-hold circuit for sampling and holding the error signal of No. 1;
An error detection circuit that outputs a second error signal due to a difference from the reference value, and a laser that controls the intensity of the laser light based on the hold signal sampled and held by the sample and hold circuit or the second error signal. A drive unit; and switching means for inputting the hold signal when the laser light is modulated, and the second error signal when the laser light is not modulated, to the laser drive unit. A laser driving circuit characterized by the above-mentioned.