JPH0540947A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To sufficiently reduce noise generated from a servo circuit without spoiling the stability of the servo circuit. CONSTITUTION:The noise reduction circuit 8 is provided with a control signal generating circuit 13, in which a control signal is generated in accordance with the timing as a noise is generated in focus error signals, and a gain adjusting circuit 12 by which a gain in the servo circuit is adjusted based on the control signal. The gain in the servo circuit is reduced at the area where the noise is generated in the focus error signals, and the gain in the servo circuit is not reduced elsewhere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction circuit for use in a magneto-optical disk device for recording / reproducing information on / from a magneto-optical disk and for reducing noise emitted from a servo circuit of the magneto-optical disk device. ..

[0002]

2. Description of the Related Art In a magneto-optical disk device, a focus servo circuit and a tracking servo circuit perform control in order to accurately focus a laser beam on a recording position of information on the magneto-optical disk.

In the focus servo circuit and the tracking servo circuit, a focus error signal and a tracking error signal are generated based on the reflected light from the magneto-optical disk detected by the photodetector, and in accordance with these error signals, The actuator drives the objective lens in the focus direction and the track direction.

As shown in FIG. 5, the magneto-optical disk 3 is formed with a data area 3a for recording information and a pre-format area 3b in which address information, synchronization signals and the like are recorded in advance. There is. In the pre-formatted area 3b, information is read out by the pits formed in an uneven shape. On the other hand, in the data area 3a, the magnetic domain is read by utilizing the magneto-optical effect in which the rotation of the polarization plane is different depending on the magnetization.
There is no pit formed in the preformat area 3b.

For this reason, when the laser beam passes through the pre-formatted area 3b, harmonic noise is generated in the error signal, and a high-pitched noise audible from the servo circuit is emitted.

The magneto-optical disk 3 is often used as a memory of a computer or the like, and the quietness of the device is one of the important factors in performance. Further, the noise emitted from the device gives an unpleasant feeling to the user, and it is desired to reduce the noise emitted from the servo circuit.

Therefore, conventionally, in order to reduce such noise, a method of providing a gain adjusting circuit in the servo circuit and lowering the gain of the servo circuit has been adopted.

[0008]

However, in the above-mentioned conventional configuration, the preformatted area 3 in which noise is generated is generated.
The gain of the servo circuit is always reduced, not only when passing through b, so that the error signal when driving the actuator becomes small and the stability of the servo circuit is impaired. Therefore, a situation may occur in which focus pull-in performed at the time of starting the magneto-optical disk device fails, or the servo goes out even during operation.

Further, since it is necessary to avoid the situation as described above, the rate of decrease in gain by the gain adjusting circuit is not so large, and noise cannot be sufficiently reduced.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a noise reduction circuit capable of sufficiently reducing noise emitted from the servo circuit without impairing the stability of the servo circuit. is there.

[0011]

In order to solve the above problems, the noise reduction circuit of the present invention is a gain adjustment for adjusting the gain of a servo circuit that generates a servo signal based on the reflected light from a magneto-optical disk. The following measures are taken in the noise reduction circuit including the circuit.

That is, it has a control signal generating circuit for generating a control signal in accordance with the timing when noise occurs in the servo signal, and the gain adjusting circuit adjusts the gain of the servo circuit based on the control signal.

[0013]

According to the above construction, the servo signal is generated by the servo circuit based on the reflected light from the magneto-optical disk. The gain of the servo circuit is adjusted by the gain adjusting circuit.

The magneto-optical disk has a data area and a preformatted area, and the servo signal generated based on the reflected light from the preformatted area contains a harmonic noise component. .. Further, noise also occurs in the servo signal generated when access or track jump is performed, for example.

The control signal is generated by the control signal generation circuit at the timing when the reflected light is obtained from the pre-formatted area or at the timing when the access or track jump is performed (that is, the timing when noise occurs in the servo signal). , Is output to the gain adjustment circuit. Then, the gain of the servo circuit is sufficiently reduced by the gain adjusting circuit based on the control signal output in synchronization with the noise generation timing as described above.

As described above, the gain of the servo circuit is reduced where the noise occurs in the servo signal, and the gain of the servo circuit is not reduced elsewhere, so that the stability of the servo circuit is not deteriorated and the servo circuit is not degraded. The noise emitted from the can be reduced sufficiently.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

The case where the noise reduction circuit according to the present invention is applied to the focus servo circuit of the magneto-optical disk device will be described below.

The magneto-optical disk device of this embodiment is provided with an optical pickup 1 as shown in FIG. The optical pickup 1 includes a laser diode 2, an objective lens 4 for condensing light from the laser diode 2 on a magneto-optical disk 3, and reflected light from the magneto-optical disk 3 at a substantially right angle to a photodetector 5. A half mirror 6 for guiding, a photodetector 5 having four light receiving portions, a focusing actuator (not shown) for driving the objective lens 4 to move toward or away from the magneto-optical disk 3, and an illustration for driving the objective lens 4 in the track direction. Not equipped with a tracking actuator.

The optical pickup 1 is driven by an optical pickup feed mechanism (not shown) to move in the radial direction of the magneto-optical disk 3.

The focus servo circuit of the magneto-optical disk device is mainly composed of the photodetector 5, the focus error signal generation circuit 7, the noise reduction circuit 8, the division circuit 9, the phase compensation circuit 10 and the drive amplification circuit 11. There is.

Each light receiving portion of the photodetector 5 generates a current according to the intensity of the light reflected by the magneto-optical disk 3.
Then, the currents of the two pairs of light receiving portions on the diagonal lines are added and sent to the focus error signal generation circuit 7.

The focus error signal generating circuit 7 includes a current-voltage converting circuit and a subtracting circuit, which are not shown, respectively. After converting each input current into a voltage by the current-voltage converting circuit, the difference is taken by the subtracting circuit, A focus error signal (servo signal) is generated.

The noise reduction circuit 8 is a circuit for reducing the noise generated from the servo circuit by adjusting the gain of the servo circuit, and its details will be described later.

The division circuit 9 receives the focus error signal output from the noise reduction circuit 8, and divides this focus error signal by the total amount signal received by the photodetector 5 to change the level of the focus error signal. Reduce.

The focus error signal output from the division circuit 9 is input to the drive amplification circuit 11 after phase compensation is performed in the phase compensation circuit 10. Then, the drive amplification circuit 11 drives the focusing actuator based on the input focus error signal.

Details of the noise reduction circuit 8 will be described below.

As shown in FIG. 1, the noise reduction circuit 8 comprises a gain adjustment circuit 12 for adjusting the gain of the servo circuit, and a control signal generation circuit 13 for generating a control signal at a noise generation timing, which will be described later. ing. Then, the gain adjusting circuit 12 adjusts the gain of the servo circuit based on the control signal generated by the control signal generating circuit 13.

FIG. 2 shows an example of a specific configuration of the gain adjusting circuit 12. The gain adjusting circuit 12 has an electric resistance R
₁ and the analog switch SW ₁ are connected in parallel, the electric resistance R ₂ and the analog switch SW ₂ are connected in parallel, and these two parallel connections are connected in series.

When both the analog switches SW ₁ and SW ₂ are ON, the gain is not reduced. When the analog switch SW ₁ is OFF, the gain is reduced by the electric resistance R ₁ . Also, the analog switch SW ₂ is OF
When F, the gain is reduced by the electric resistance R ₂ .
The electric resistance R ₁ is set higher than the electric resistance R ₂ (R ₁ > R ₂ ).

Also, an example of a concrete configuration of the control signal generating circuit 13 is shown in the same figure.

The control signal generation circuit 13 is configured so that the outputs of the two OR gates 14 and 15 are input to the NAND gate 16 and generates a control signal S _1, and an inverter that generates a control signal S _2. It is composed of 17 and.

A track jump signal is input to the input terminal a of the OR gate 14, and a read area switching signal is input to the input terminal b.

The track jump signal is a signal for driving the tracking actuator when the track jump is performed. That is, the track jump signal indicates during track jump (noise generation timing).

In the magneto-optical disk device, when the information in the data area 3a for recording information on the magneto-optical disk 3 is read out, and when the information in the pre-format area 3b in which the address information, the synchronizing signal and the like are recorded in advance is read out. The method of reading information is different from that of time (see FIG. 5). Therefore, when the read area is changed from the data area 3a to the preformat area 3b, the read area switching signal is output. This read area switching signal is output while the preformat area 3b is being read. That is, the read area switching signal indicates that the laser light is passing through the preformat area 3b of the magneto-optical disk 3 (noise generation timing).

The track jump signal is input to the input terminal c of the OR gate 15, and the radial signal is input to the input terminal d.

The radial signal is a signal output at a high level when the tracking servo circuit is closed and the tracking servo circuit is operating.

An access signal is input to the inverter 17. This access signal is a signal for driving the optical pickup feed mechanism when an access operation (moving the optical pickup 1 to a target track of the magneto-optical disk 3) is performed. That is, the access signal is
It is during access (noise generation timing).

The access is to drive the optical pickup feeding mechanism to roughly move the optical pickup 1 to the target track of the magneto-optical disk 3. After that, the access is performed.
The track jump is to drive the tracking actuator to accurately align the objective lens 4 with the target track.

The analog switches SW ₁ and SW ₂ are
Opening and closing are controlled by control signals S ₁ and S ₂ generated by the control signal generation circuit 13, respectively. The analog switch SW ₁ is turned on when the control signal S ₁ is at high level.
The state becomes OFF, and the state becomes OFF at the Low level. Further, the analog switch SW ₂ is in the ON state when the control signal S ₂ is at the High level and is in the OFF state when at the Low level.

The operation of the noise reduction circuit 8 having the above configuration will be described below.

At the time of starting the magneto-optical disk device, the objective lens 4 is pulled into a range where servo can be applied.
The tracking servo circuit is opened until the pull-in operation is completed, and the circuit is closed after the pull-in operation is completed. That is, the radial signal is at the low level during the pull-in operation. Further, during the pull-in operation, the laser light may pass through the pre-formatted area 3b of the magneto-optical disk 3, but no access or track jump is performed.

Therefore, the signal input to the control signal generation circuit 13 during the pull-in operation is the read area switching signal H level.
Even if it goes high, the track jump signal, radial signal, and access signal are always low.
It is a level. That is, during the pull-in operation, the OR gate 15
Since the signals input to the input terminals c and d are always at the low level, the NAND gate 16 always outputs the high-level control signal S ₁ . In addition, the inverter 1
The access signal input to 7 is also always at the Low level, and the control signal S ₂ is always at the High level.

From the above, during the pull-in operation, the analog switches SW ₁ and SW ₂ are always in the ON state, and the gain adjustment circuit 12 does not reduce the gain. Therefore, when the magneto-optical disk device is activated, a stable pull-in operation can be performed by the normal focus error signal.

Since the tracking servo circuit is closed after the pull-in operation is completed, the radial signal is always at the high level after the pull-in operation is completed. For this reason,
After the pull-in operation is completed, the OR gate 15 to which the radial signal is input always outputs a high level signal to the NAND gate 16.

Therefore, the control signal S ₁ becomes low level only when the high level signal is output from the OR gate 14. The high level signal is output from the OR gate 14 when either the track jump signal or the read area switching signal input to the input terminals a and b is H level.
It was when it reached the high level. That is, the control signal S ₁ becomes High level only when the track jump is in progress or the laser light is passing through the pre-format area 3 b of the magneto-optical disk 3, and the analog switch SW ₁
Is turned off.

Note that the read area switching signal is not output during access and during track jump (Low level). Further, since the track jump is performed after the access is completed, the track jump signal and the access signal do not become High level at the same time.

From the above, when the track jump or the laser beam is passing through the preformat area 3b of the magneto-optical disk 3 after the completion of the pull-in operation, the control signal generating circuit 13 outputs the low-level control signal. S ₁ and the high-level control signal S ₂ are output, the analog switch SW ₁ of the gain adjusting circuit 12 is turned off, the analog switch SW ₂ is turned on, and the gain is the electric resistance R ₁
Is lowered by.

Further, at the time of access, the control signal generation circuit 13 outputs the high-level control signals S ₁ and Low.
The level control signal S ₂ and the gain control circuit 1 are output.
The second analog switch SW ₁ is turned on, the analog switch SW ₂ is turned off, and the gain is reduced by the electric resistance R ₂ .

After completion of the pull-in operation, when access and track jump are not performed and the laser light does not pass through the preformat area 3b of the magneto-optical disk 3 (that is, when it passes through the data area 3a). High level control signal S ₁ from the control signal generation circuit 13
S ₂ is output, the analog switches SW ₁ and SW ₂ of the gain adjusting circuit 12 are both turned on, and the gain adjusting circuit 1
The gain is not reduced by 2.

That is, the focus error signal after passing through the noise reduction circuit 8 is used when the laser light passes through the preformatted area 3b of the magneto-optical disk 3, as shown in FIG. Only at this time (noise generation timing), the noise becomes smaller and the noise is removed. Although noise occurs in the focus error signal during access and track jump, such noise can be reduced in the present embodiment.

When the gain is reduced by the electric resistance R ₁ , the focus error signal becomes so small that the servo does not work. However, the track jump period and the laser light is preformatted in the pre-formatted area 3b.
Since the period of passing through is extremely short, the stability of the servo circuit is not affected and the servo does not fall off.

Since the access period is longer than the track jump period and the pre-formatted region 3b passing period, the rate of decrease in gain due to the electric resistance R ₂ is set so as not to affect the stability of the servo circuit. ing.

As described above, the noise reduction circuit 8 matches the timing when the laser light passes through the pre-formatted area 3b of the magneto-optical disk 3 and the timing of access and track jump (that is, noise generation timing). The gain of the focus servo circuit is reduced by the above, and the gain is not reduced at other timings. In particular, since the gain can be sufficiently lowered when passing through the pre-formatted area 3b which does not affect the stability of the servo circuit or when the track jumps, the noise generated from the servo circuit is sufficiently reduced without deteriorating the stability of the servo circuit. it can.

In this embodiment, the noise reduction circuit 8
Is connected between the focus error signal generation circuit 7 and the division circuit 9, but the noise reduction circuit 8 is connected between the division circuit 9 and the phase compensation circuit 10 or between the phase compensation circuit 10 and the drive amplification circuit 11. It is also possible to put it in between.

Further, although the noise reduction circuit 8 according to the present invention is applied to the focus servo circuit in the present embodiment, it may be applied to the tracking servo circuit.

[0057]

As described above, the noise reduction circuit of the present invention has the control signal generation circuit for generating the control signal in accordance with the timing when the noise occurs in the servo signal, and the gain adjustment circuit outputs the control signal to the control signal. Based on this, the gain of the servo circuit is adjusted.

Therefore, the gain of the servo circuit is reduced where noise is generated in the servo signal, and the gain of the servo circuit is not reduced in other places, so that the stability of the servo circuit is not impaired and the gain of the servo circuit is reduced. The effect that the noise emitted can be reduced sufficiently is produced.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a schematic block diagram showing a configuration of a noise reduction circuit.

FIG. 2 is a circuit diagram showing an example of a configuration of the noise reduction circuit.

FIG. 3 is a schematic block diagram showing a configuration of a focus servo circuit when the noise reduction circuit is applied to a focus servo circuit of a magneto-optical disk device.

FIG. 4 is an explanatory diagram illustrating a waveform of a focus error signal after passing through the noise reduction circuit.

FIG. 5 is an explanatory diagram showing a data area and a preformatted area formed on the magneto-optical disk.

[Explanation of symbols]

3 magneto-optical disk 8 noise reduction circuit 12 gain adjustment circuit 13 control signal generation circuit S ₁ · S ₂ control signal

Claims (1)

[Claims] 1. A noise reduction circuit comprising a gain adjustment circuit for adjusting the gain of a servo circuit for generating a servo signal based on the reflected light from a magneto-optical disk, in accordance with the timing at which noise occurs in the servo signal. A noise reduction circuit having a control signal generation circuit for generating a control signal, wherein the gain adjustment circuit adjusts the gain of the servo circuit based on the control signal.