JP3855414B2 - LASER CONTROL DEVICE AND OPTICAL DISK DEVICE HAVING THE SAME - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a laser control device and an optical disk device having the laser control device, and more particularly to a laser control device for accurately controlling the output of a laser diode and an optical disk device having the laser control device.
[0002]
[Prior art]
With the spread of multimedia, reproduction-only information recording media such as music CDs and CD-ROMs and information reproduction apparatuses are used. In recent years, in addition to a rewritable information information recording medium represented by a write-once optical disk and a magneto-optical disk, a phase change type information recording medium has attracted attention.
[0003]
The phase change type information recording medium is a medium on which information is recorded by reversibly changing a recording material into a crystalline phase and an amorphous phase. Unlike the magneto-optical disk, the phase-change information recording medium does not require an external magnetic field, and can record and reproduce information using only the laser beam of the semiconductor laser. The phase change type information recording medium can be overwritten in which information is recorded and erased at once by laser light.
[0004]
Here, in general, a method for recording on a phase change information recording medium will be described in detail.
Recording on the phase change information recording medium is performed by forming marks on the phase change information recording medium with laser light having a pulse waveform as shown in FIG. The pulse waveform in FIG. 3 includes an erasing pulse EP (continuous emission of power E) and a recording pulse WP (pulses of power W and power E). For example, in the case of a phase change rewritable disc, the recording pulse WP and the erasing pulse EP. Information is recorded by intermittently irradiating the information recording surface of the recording disk with a recording light beam so that the duty ratio of the recording medium becomes 50%. By using a laser beam having a multi-pulse waveform, a recording mark can be reliably formed.
[0005]
When forming a mark with the multi-pulse waveform described above, it is necessary to form the mark while controlling the output of the laser beam. Therefore, a method for correcting the laser beam output of a diode or the like will be described.
First, the cooling pulse CP (light emission of power C) is independently emitted to perform sampling. Then, the average value of the sum of the recording pulse WP and the cooling pulse CP is sampled, and the erase pulse EP is sampled. Then, a difference ΔCE between the average value of the cooling pulse CP and the erase pulse EP is calculated, and a difference ΔEW between the average value of the erase pulse EP and the average value of the sum of the recording pulse WP and the cooling pulse CP is calculated. Then, correction is performed based on ΔCE and ΔEW.
[0006]
FIG. 4 shows a circuit diagram of a laser control device for realizing the above-described correction. In FIG. 4, the laser control device 1 includes a laser diode 2, a photodiode 3, a switch element 4, a sample hold circuit (hereinafter referred to as “S / H circuit”) 6, an integrator 7, a reference voltage supply unit 8, and the like. ing.
The photodiode 3 receives the laser emitted from the laser diode 2 and detects the light detection signal. The light detection signal is input to the integrator 7 via the switch element 4.
[0007]
Here, in order to sample the detected light detection signal, the switching element 4 is opened / closed at the sampling timing. That is, as shown in FIG. 3, since the recording pulse WP emits a pulse light, the light detection signal is input to the S / H circuit 6 at the light emission timing, and the average value of the sum of the recording pulse WP and the cooling pulse CP is obtained. The recording pulse WP is sampled and held. Therefore, the opening / closing timing of the switch element 4 is synchronized with the timing of light emission. The capacitor 6a also plays a role as an LPF (Low Pass Filter).
[0008]
The integrator 7 includes resistors 7 a and 7 a, a comparison integrator 7 b, and a capacitor 7 c, and the comparison integrator 7 b is connected to the S / H circuit 6 and the reference voltage supply unit 7. A difference between the reference voltage Vref and the photodetection signal is input to the comparison integrator 7b, and the integration value is supplied as an output signal of the laser diode 2. The laser diode 2 outputs a laser based on the supplied output signal of the integrator 7.
[0009]
[Problems to be solved by the invention]
However, since this circuit amplifies the output of the S / H circuit 6 by the integrator 7, there is a problem that the influence of the droop of the hold capacitor 6a is increased. Furthermore, since a gain of 40 dB to 50 dB is obtained, even if the output voltage of the hold capacitor 6a changes slightly, the output signal supplied to the laser diode 2 is greatly affected.
[0010]
In addition, when the initial current value is to be given in the operation of the laser control device 1, it is necessary to control the charge amount of the capacitors 6 a and 7 c, so that the hold capacitor 6 a of the S / H circuit 6 and the integrator 7 It is necessary to control the amount of charge of both capacitors 7c, and there is a problem that the aliasing of the output of the S / H circuit 6 affects the input.
[0011]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laser control device capable of solving the above-described problems and controlling laser light with high accuracy, and an optical disk device having the same.
[0012]
[Means for Solving the Problems]
According to the present invention, in the laser control device for controlling the laser output of the laser diode, the photodiode for detecting the light output from the laser diode, the light detection signal detected by the photodiode, and the supply of the reference voltage are provided. This is integrated between the integrator that temporarily samples and holds the difference from the reference voltage supplied from the unit, and between the integrator and the photodiode, and performs switching operation at ON / OFF timing of the optical output. This is achieved by a laser control device including a first switch element to be performed, and a second switch element that is provided between the reference voltage supply unit and the integrator and performs a switching operation in synchronization with the first switch element.
[0013]
In the present invention, the photodetection signal of the photodiode is directly input to the integrator, and the capacitor of the integrator holds the output signal for the immediately preceding laser diode. Thereby, the influence of droop in the capacitor can be eliminated, and the laser output can be controlled with high accuracy.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these forms.
[0015]
FIG. 1 is a circuit diagram of a preferred embodiment of the laser control apparatus of the present invention. The laser control apparatus (APC circuit) 10 will be described in detail with reference to FIG.
The laser control apparatus 10 in FIG. 1 includes a photodiode 11, a first switch element 13, a second switch element 14, an integrator 15, a reference voltage supply unit 16, and the like. The laser diode 17 is used for recording data on the optical disc or reading data recorded on the optical disc.
[0016]
The photodiode 11 detects the front light detection signal of the laser diode 17 and sends the detected light detection signal of the laser diode 17 to the integrator 15 via the switch element 17. The first switch element 13 is opened and closed at a timing synchronized with a recording signal emitted from the laser diode 17. For example, the integrator 15 for determining the power C is closed only while the power C is emitted. The integrator 15 that determines the power E is closed only while the recording pulse WP (power W and power C pulses) is emitted.
[0017]
The integrator 15 includes resistors 15a and 15a, a comparison integrator 15b, and a capacitor 15c. The resistors 15a and 15a are provided between the reference voltage supply unit 16 and the comparison integrator 15d, respectively. The comparison integrator 15 b and the capacitor 15 c integrate the difference between the photodetection signal sent from the photodiode 11 and the reference voltage signal sent from the reference voltage supply unit 16, and output the output to the laser diode 17. To do.
[0018]
Next, the operation of the laser control apparatus 10 will be described in detail.
First, the laser emitted from the laser diode 17 is detected by the photodiode 11, and the light detection signal is sent to the integrator 15. When the first switch element 13 and the second switch element 14 are turned ON, the difference between the photodetection signal and the reference voltage signal sent from the reference voltage supply unit 16 is input to the integrator 15 in the comparison and integration circuit 15. Applied to the capacitor 15c.
[0019]
At this time, the time constant is determined by the resistance value of the resistor 15a connected to the reference voltage supply unit 16 and the capacitance of the capacitor 15c. Here, the time constant is a constant that determines the response of the servo loop, and is also a time constant for detecting a DC signal from the photodetection signal. Further, when the first switch element 13 and the second switch element 14 are OFF, no voltage is applied to the capacitor 15c, so that the output of the integrator 15 is held at the previous value. At this time, the capacitor 15c serves as an S / H circuit and also serves as an LPF.
[0020]
According to the above embodiment, since the averaging filter and the integrator are integrated, there is no influence even if the capacitor of the integrator is drooped. For example, in the conventional example, the droop amount ΔC of the power C of the averaging filter is multiplied by the gain of the integrator 15 and appears in the output. I can't. On the other hand, since the droop amount ΔC is not multiplied by the gain in the above embodiment, the influence of the droop can be reduced to, for example, 1/100 or less as compared with the conventional case.
[0021]
Further, when the initial current value is given in the operation of the APC circuit 10, it is only necessary to control the charge amount of the capacitor 15 c of the integrator 15, so that not only the current instruction output but also the state of the integrator is memorized and controlled. be able to. In addition, the aliasing of the output of the sample and hold is not affected.
In addition, since the entire APC loop is a quadratic system using the averaging filter 6 and the integrator 7, the time constant of the integrator has to be kept low in order to stabilize the servo loop. In the above embodiment, since the entire APC loop is a first-order system, the servo loop can be stabilized even if the time constant of the integrator 15 is reduced (the band of the servo loop is increased). Accordingly, the response time can be shortened.
[0022]
FIG. 3 shows an example of an optical disk device 20 using the automatic laser control device 10 described above.
In FIG. 3, the optical disk apparatus 20 includes a spindle motor 22 as a driving means for rotating the optical disk 21 and an optical pickup 23.
Here, the spindle motor 22 is driven and controlled by the optical disk drive controller 24 and is rotated at a predetermined rotational speed. Here, the automatic laser control apparatus 10 is accommodated in the optical pickup 23 and the optical disk drive controller 24. The optical disk 21 can select and reproduce a plurality of types of optical disks.
[0023]
The optical pickup 23 irradiates the signal recording surface of the rotating optical disk 21 with light to record the signal, or detects the return light from the signal recording surface. A reproduction signal based on the return light is output to 25.
[0024]
Thus, the recording signal demodulated by the signal demodulator 25 is error-corrected via the error correction circuit 26 and sent to an external computer or the like via the interface 27. Thereby, an external computer or the like can receive a signal recorded on the optical disc 21 as a reproduction signal.
[0025]
The optical pickup 23 is connected to a head access control unit 28 for moving to a predetermined recording track on the optical disc 21 by a track jump or the like. Further, a servo circuit 29 for moving the objective lens in the focusing direction and the tracking direction is connected to a biaxial actuator (described later) that holds the objective lens of the optical pickup 23 at the moved predetermined position. Yes.
[0026]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a laser control apparatus capable of controlling laser light with high accuracy and an optical disk apparatus having the laser control apparatus.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a preferred embodiment of an automatic laser control apparatus of the present invention.
FIG. 2 is a block diagram showing a preferred embodiment of an optical disc apparatus having an automatic laser control apparatus of the present invention.
FIG. 3 is a waveform diagram showing a pulse waveform supplied to a laser diode when information is recorded on a conventional optical information recording medium.
FIG. 4 is a circuit diagram showing a conventional laser automatic control device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Automatic laser control apparatus, 11 ... Photodiode, 13 ... 1st switch element, 14 ... 2nd switch element, 15 ... Integrator, 16 ... Reference voltage supply part, 17: Laser diode.

Claims (3)

In a laser control device that controls the laser output of a laser diode,
A photodiode for detecting light output from the laser diode;
An integrator that temporarily samples and holds the difference between the light detection signal detected by the photodiode and the reference voltage supplied from the reference voltage supply unit;
A first switch element that is provided between the integrator and the photodiode and performs a switching operation at an ON / OFF timing of the optical output;
A laser control apparatus comprising: a second switch element that is provided between the reference voltage supply unit and the integrator and that performs a switching operation in synchronization with the first switch element. The laser control device according to claim 1, wherein when the first switch element and the second switch element are OFF, the capacitor holds the immediately preceding laser output. In an optical disc apparatus having a laser control device for controlling the laser output of a laser diode,
A photodiode for detecting light output from the laser diode;
An integrator that temporarily samples and holds the difference between the light detection signal detected by the photodiode and the reference voltage supplied from the reference voltage supply unit;
A first switch element that is provided between the integrator and the photodiode and performs a switching operation at an ON / OFF timing of the optical output;
An optical disc apparatus having a laser control apparatus, comprising: a second switch element provided between a reference voltage supply unit and an integrator and performing a switching operation in synchronization with the first switch element.

Images