JP2711575B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding the improvement of an optical disk device, an object of the present invention is to provide an optical disk device capable of stably controlling a light spot and a light amount. A laser light source for irradiating laser light, a light amount control means for controlling the light amount from the laser light source, and a light spot control means for focusing the laser light on the optical disc and following the track of the optical disc. The control band of the light amount control means is wider than the control band of the light spot control means.

[Industrial applications]

The present invention relates to an improvement in an optical disk device.

[Conventional technology]

FIG. 3 is a block diagram showing a basic circuit for laser diode control. In the figure, PD indicates a photo diode, and LD indicates a laser diode.

Part of the light output from the laser diode LD is received by the photodiode PD. Photo diode
The current flowing through the PD is converted to a voltage. This voltage is compared with the target value, and an error is detected. The detected error is integrated, and a current proportional to the integrated value flows through the laser diode LD.

FIG. 4 is a diagram showing a configuration example of a laser diode control circuit. In the figure, 1 is an LD unit, 3 'is a read power level detector, 4 is a read power level setting unit, 5 is a read power level current adjuster, 6
Is a write power level current adjustment section, 7 is a D / A converter, 8 is a write power level setting section, 10 is a write power level current subtraction section, 11 is a level shift section,
12 'is PD current / voltage converter, 14 is D / A converter, 16 is A
A / D converter, 17 is a write power level current subtraction setting unit, 21 is an MPU, 50 is a balance unit, 53 and 55 are switches, and 57 is a resistor network.

The laser diode control circuit shown in FIG.
Since it is the same as that disclosed in Japanese Patent No. 3327, it will be briefly described.

When reading data, the transistors TR2 and TR7
Is turned off. Light output from the laser diode LD is received by the photodiode PD, and a current proportional to the amount of received light flows through the photodiode PD. This current is converted into a voltage by the PD current / voltage converter 12 ', and this voltage is compared with a target value, and an error is detected. The detected error is input to the integrator. The output of the integrator is a transistor
Applied to the base of TR1.

When writing data, the transistors TR2 and TR7 are turned on. As a result, part of the current flowing through the laser diode LD flows through the transistors TR2 and TR4, and part of the current input to the negative input terminal of the operational amplifier 31 flows through the transistors TR7 and TR5. The other points are the same as the case of reading data.

FIG. 5 is a diagram showing a configuration example of an optical disk device. In the figure, 100 is an optical disk, 100a is a spindle motor, 100b is a spindle, 200 is an optical head, 220 is a laser light source, 221a is a collimator lens, 221b is a condenser lens, 222 is a beam splitter, 223 is a prism, 224a is a mirror, 224b is a half mirror, 225 is an objective lens, 226
Is a track actuator, 227 is a focus actuator, 228 is an RF detector, 229 is a servo detector, 229a is a prism, 300 is a carriage, 400 is a focus servo controller, 500 is a track servo controller, and RFS
Indicates reproduction signals.

The laser light emitted from the laser light source 220 includes a collimator lens 221a, a beam splitter 222, a prism 223,
The light is focused on the disk 100 through the mirror 224a and the objective lens 225. The light reflected on the surface of the disk 100 is divided into an objective lens 225, a mirror 224a, a beam splitter 222, and a prism 2.
23, focuses on the RF detector 228 through the half mirror 224b and the condenser lens 221b. A part of the reflected light is focused on the servo detector 229 through the half mirror 224b and the prism 229a.

The output of the servo detector 229 is input to the focus servo controller 400 and the track servo controller 500. The focus / servo control unit 400 controls the distance between the disc 100 and the objective lens 225 so that the laser light is focused on the recording film.
The output of 0 is sent to the focus actuator 227.
The focus actuator 227 moves the objective lens 225 up and down according to an output signal from the focus servo control unit 400. The track servo control unit 500 performs control for positioning the spot of the laser beam on a track on the disk 100. The output of the track servo control unit 500 is sent to the track actuator 226. The track actuator 226 is
Objective lens 225 according to the output signal from servo controller 500
Move left and right.

FIG. 6 is a block diagram showing a configuration example of a light spot control system. In the figure, 440 is an operational amplifier, 441 is a focus actuator drive circuit, 442 is an operational amplifier, 550 is an operational amplifier, 551 is a track actuator drive circuit, 5
52 is a switch, 600 is a microprocessor, 620 is an A / D converter, 630 is a D / A converter, 650 is a sample holder, R101 to R115 are resistors, FES is a focus error signal, TES is a tracking error signal, and OS Indicates an offset signal.

The servo detector 229 has four detector parts a,
It is divided into four, b, c, and d. These detector parts a,
The outputs of b, c, and d are sent to the operational amplifier 440 and also sent to the operational amplifier 550. The output of the operational amplifier 440 becomes the focus error signal FES. The operational amplifier 442 outputs the sum of the focus error signal FES and the offset signal OS. The output of the operational amplifier 442 is supplied to the focus actuator 2 via the focus actuator drive circuit 441.
Sent to 27.

The output of the operational amplifier 550 is the tracking error signal TES
Becomes The output of the operational amplifier 550 is sent to the track actuator 226 via the track actuator drive circuit 551 and the switch 552.

[Problems to be solved by the invention]

As described above, in the optical disk apparatus, laser light is used for recording / reproduction, and as shown in JP-A-63-133327, control is performed so as to keep the laser light quantity constant. And, by the control, even if there is temperature fluctuation,
The purpose was to keep the light quantity constant. However, as shown in FIG. 7, as a characteristic of the laser diode, there is a characteristic that the characteristic fluctuates when there is a return light, which is a factor that the light amount fluctuates. FIG. 7 is quoted from "Semiconductor Laser and Applied Technology" Engineering Co., Ltd. Furthermore, the servo signal for controlling the light spot is obtained by detecting the reflected (or transmitted) light of the laser, and when the light amount fluctuates, the servo signal is also affected, and conversely, the light spot changes. Changes the state of the return light. That is, the laser light amount and the servo signal interfere with each other, and there is a problem that the light spot control becomes unstable.

The present invention has been made in view of this point,
It is an object of the present invention to provide an optical disc device capable of stably performing light spot control and light quantity control.

[Means for solving the problem]

FIG. 1 is a diagram illustrating the principle of the present invention. The optical disk device of the present invention includes: an optical disk device mechanism 700; a laser light source 710 for irradiating the optical disk with laser light; and a light amount control means 720 for controlling the amount of light from the laser light source 710.
And a light spot control means 73 for focusing the laser light on the optical disk and following the track of the optical disk.
In the optical disc device having 0 and 2, the control band of the light amount control means 720 is wider than the control band of the light point control means 730.

[Action]

By making the control band of the light amount control wider than the control band of the light point control (control to a high frequency range), the light amount becomes constant in the range of the control band of the light point control, the influence of mutual interference is eliminated, and a stable light point Control can be performed.

〔Example〕

FIG. 2 is a diagram showing an example of control characteristics in the present invention.

In the light spot control, since the focus actuator 227 and the track actuator 226 are driven, the control band is limited by the actuator, and is usually set to several KHz. As an example, here, 2 KHz (the open loop is 0 dB (Frequency at the crossing point).

In light quantity control, the band of the operational amplifier is the upper limit because there are no moving parts. However, in consideration of stability, it is set to 10 KHz (frequency at which the open loop crosses 0 dB).

In the illustrated example, the light point control band (= 2 KHz) <the light amount control band (10 KHz). As a result of the experiment, the frequency indicating the upper limit of the light amount control band is two times the frequency indicating the upper limit of the light spot control band.
If it is twice or more, it has been found that the device operates stably without being affected by the return light.

The reason why the mutual interference between the light quantity control and the light spot control can be reduced by making the control band of the light quantity control wider than the control band of the light spot control will be described. As described above, the amount of light changes with the return light, and when the amount of light fluctuates, the position of the light spot on the optical disk changes, and when the position of the light spot on the optical disk changes, the return light changes.

In the control characteristics shown in FIG.
The frequency of 0 dB is not only a point at which the disturbance suppression ability by the servo becomes 0, but also a critical frequency in the servo theory, and if a disturbance of this critical frequency is inputted, the disturbance may be expanded. is there. The return light can be treated as a disturbance. When the critical frequency in the light quantity control and the critical frequency in the light spot control are close to each other, and the light quantity control and the light spot control interfere with each other, disturbances may be mutually increased.

For example, it is assumed that the critical frequency of the light quantity control and the critical frequency of the light spot control are the same, and the frequency is set to ωc. When a disturbance having a frequency of ωc enters the light amount control system, the disturbance is not compressed, and the light amount greatly changes from a target value. Light point control is also affected by this change in light quantity.

When the light amount changes at the frequency ωc in the light spot control, the light spot position changes from the target value. The change in the light spot position affects the light quantity control. As described above, when the critical frequency of the light amount control and the critical frequency of the light spot control are close to each other, they affect each other, and stable control cannot be performed.

In the present invention, the control band of the light amount control system is made wider than the control band of the light spot control system. In the example of FIG. 2, the control band of the light amount control system is 0 to 10 KHz, and the control band of the light spot control system is 0 to 2 KHz. In the light quantity control system, the gain of the open loop in the band of 0 to 2 KHz is
10dB or more. That is, the gain of the open loop of the light quantity control in the control band of the light spot control is 6 dB (2
Times), whereby the light amount fluctuation component in the light spot control band can be compressed until it can be regarded as zero. The ability to compress the fluctuation component is proportional to the gain of the open loop, and there is no compression ability at 0 dB or less. Within the control band of the light spot control system, especially open loop
If the amount of light is constant near the frequency where the gain is 0 dB,
Light spot control is the same as conventional control, and stability can be ensured.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the light amount becomes constant within the band of the light spot control, and stable control can be obtained.

[Brief description of the drawings]

1 is a diagram illustrating the principle of the present invention, FIG. 2 is a diagram showing an example of control characteristics in the present invention, FIG. 3 is a diagram showing a basic circuit of laser diode control, and FIG. 4 is a laser diode control circuit FIG. 5 is a diagram showing a configuration example of an optical disc device, FIG. 6 is a block diagram showing a configuration example of a light spot control system, and FIG. 7 is an IL characteristic curve due to near-end reflection. FIG. 7 is a diagram showing the undulation and changes in the vertical mode. 1 ... LD unit, 3 '... Read power level detection unit, 4 ... Read power level setting unit, 5 ... Read power level current adjustment unit, 6 ... Write power level current Adjustment unit, 7 D / A converter, 8
Write power level setting section, 10 ... Write power level current subtraction section, 11 ... Level shift section, 12 '...
... PD current / voltage converter, 14 ... D / A converter, 16 ... A
/ D converter, 17: Write power level current subtraction setting unit, 21: MPU, 50: Balance unit, 53 and 55 ... Switch, 57: Resistor net, 100: Optical disk, 100a: Spindle Motor, 100b spindle, 200 optical head, 220 laser light source, 221a collimator lens, 221b condenser lens, 222 beam splitter, 223 prism, 224a mirror 224b Half mirror 225 Objective 226 Track actuator 227 Focus actuator 2
28 …… RF detector, 229 …… Servo detector, 229
a: prism, 300: carriage, 400: focus servo controller, 500: track servo controller.

Claims (1)

(57) [Claims] An optical disk drive mechanism (700), a laser light source (710) for irradiating a laser beam onto an optical disk, and a light amount control means (720) for controlling the amount of light from the laser light source (710). A light point control means (73) for focusing the laser light on the optical disc and following the track of the optical disc.
0) and the optical band control of the light point control means (73).
An optical disc device characterized by having a control band wider than that of (0).