JP2751492B2 - Servo circuit and playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo device of an information reproducing apparatus suitable for use in focus servo and tracking servo of an optical disk reproducing apparatus such as a compact disk player.

[Summary of the Invention]

The present invention detects an error signal from a reproduced signal, like a focus servo or a tracking servo of an optical disc reproducing apparatus, supplies this error signal to a controlled section via a servo loop filter, and when a defect occurs, In the servo device of the information reproducing apparatus, in which the low-frequency component of the error signal is supplied to the controlled part to prevent the servo from being disturbed by a defect, the servo loop filter is constituted by a digital filter,
A filter unit having a low-pass filter characteristic of the digital filter is arranged at a preceding stage, and an output of the filter unit having the low-pass filter characteristic and a digitized error signal are switched according to the presence or absence of a defect and supplied to a loop filter. Thus, the servo loop filter is constituted by a digital filter so that the characteristics can be stabilized and the circuit scale can be simplified.

[Conventional technology]

In an optical disk reproducing apparatus such as a compact disk player, a reproduction signal from an optical disk is used to obtain a focus error signal and a tracking error signal.

That is, in the optical disk reproducing apparatus, the reflected light from the optical disk is focused on the four-divided photodetector via the cylindrical lens. The reflected light, which is condensed on the four-segment photodetector via the cylindrical lens, becomes circular at the in-focus position and shifts back and forth from the in-focus position.
Be elliptical. A focus error signal is obtained using the output of each photodiode of the four-segment photodetector.

In the optical disk reproducing apparatus, a laser beam is irradiated to a position corresponding to the track center, and two sub beams are irradiated to positions offset from each other in the opposite direction from the track center. If the tracking shifts, the reflected light levels of the two sub beams reflected by the optical disc differ. A tracking error signal is obtained from the level of the reflected light of the two sub beams from the disk.

As described above, in an optical disc reproducing apparatus that obtains a focus error signal or a tracking error signal by using a reproduced signal from an optical disc, if the recording surface of the optical disc is damaged or dust adheres, and the optical disc is defective, the focus error signal And a tracking error signal cannot be obtained, and the focus servo and the tracking servo are disturbed.

Therefore, in a conventional optical disc reproducing apparatus, a low-pass filter that removes a sudden change in an error signal and holds the error signal is provided in a stage preceding a loop loop filter that forms a focus servo circuit or a tracking servo circuit. .

That is, as shown in FIG. 10, a low-pass filter including a resistor 52 and a capacitor 53 is provided in a stage preceding the loop filter 51 constituting the focus servo and tracking servo circuits.
54 are arranged.

An error signal is supplied to the input terminal 56. This error signal is supplied to the a-side input terminal of the switch circuit 55, and a low-pass filter 54 including a resistor 52 and a capacitor 53 is provided.
Is supplied to the b-side input terminal of the switch circuit 55 via the.

The input terminal 57 is connected to the optical disc according to the presence or absence of a defect.
A defect detection signal is supplied. The switch circuit 55 is switched by the defect detection signal.

The output terminal of the switch circuit 55 is extracted from the output terminal 58 via the loop filter 51.

In the normal state, the switch circuit 55 is switched to the a side. Therefore, in the normal state, the error signal from the input terminal 56 is output from the output terminal 58 via the loop filter 51.

If a defect occurs in the optical disk, a defect detection signal is supplied to the input terminal 57, and the switch circuit 55 is switched to the side b. Therefore, when a defect occurs in the optical disk, the error signal from the input terminal 56 is passed through the low-pass filter 54 and the output signal is passed through the loop filter 51.
Output from 58.

Thus, when the optical disc has a defect,
The error signal from the input terminal 56 is supplied to the loop filter 51 via the low-pass filter 54. Low-pass filter
At 54, the sudden change of the error signal is removed and the error signal is held. Therefore, even if a defect occurs in the optical disc, servo disturbance does not occur.

[Problems to be solved by the invention]

The servo circuit of the conventional optical disk reproducing device is constituted by an analog circuit. However, in analog circuits,
It is susceptible to temperature characteristics, has poor operation stability, is difficult to adjust, and is difficult to integrate into an integrated circuit.

Therefore, digitization of servo circuits has been promoted.

In the analog servo circuit, as described above, a low-pass filter 54 can be easily provided before the loop filter 51 in order to cope with a case where an error signal cannot be obtained due to a defect in the optical disk. That is,
In the analog servo circuit, the low-pass filter 54 can be configured only by disposing the resistor 52 and the capacitor 53.

However, in the digital servo circuit, a low-pass filter for coping with a case where an error signal cannot be obtained due to a defect occurring on the optical disk cannot be easily provided.

That is, in the case of a digital servo circuit, conventionally, as shown in FIG.
A digital low-pass filter 64 is provided in a stage preceding the above. Then, the switch circuit 65 is switched based on the defect detection signal from the input terminal 67.

When there is no defect in the disk, the switch circuit 65 is switched to the a side, and the digital error signal from the input terminal 66 is output from the output terminal 68 via the digital loop filter 61.

If a defect has occurred in the optical disk, a defect detection signal is supplied to the input terminal 67, and the switch circuit 65 is switched to the side b. Then, the digital error signal from the input terminal 66 passes through the digital low-pass filter 64, and is output from the output terminal 68 via the digital loop filter 61.

In FIG. 11, a plurality of delay circuits and a product-sum circuit are required to configure the digital low-pass filter 64.
When this servo circuit is realized by a digital signal processor, the number of processing steps increases if such a digital low-pass filter 64 is provided.

Accordingly, an object of the present invention is to provide a servo apparatus of an information reproducing apparatus which does not increase the circuit scale even when servo is performed by digital signal processing, and does not cause servo disturbance even if a defect occurs on an optical disk. It is in.

[Means for solving the problem]

According to the present invention, an error signal is detected from a signal related to reproduction information, and this error signal is supplied to a controlled portion of an information reproducing apparatus via a servo loop filter to control the same, and a defect has occurred in the reproduction information. Occasionally, a servo device of an information reproducing apparatus configured to supply a low-frequency component of an error signal to a controlled unit has means 19 and 23 for digitizing an error signal, and a servo loop filter 31 is a digital filter. And a filter unit 32, 3 having a low-pass filter characteristic among the digital filters.
3 is arranged at the preceding stage, and the outputs of the filter units 32 and 33 having the low-pass filter characteristic and the digitized error signal are switched according to the presence or absence of a defect and supplied to the loop filter 31. Servo device.

[Action]

The low-pass 32 and the low-pass compensation equalizer 33 are arranged in front of the digital loop filter 31, and when a defect occurs in the optical disc 1, an error signal is passed through a low-pass filter characteristic composed of the low-pass 32 and the low-pass compensation equalizer 33. Are supplied to the loop filter 31. Therefore,
This means that a low-pass filter is provided in the preceding stage of the loop filter 31, so that a sudden change in the error signal is removed,
The error signal is held. Therefore, the optical disk 1
The servo is not disturbed even when a defect occurs.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of an optical disk reproducing apparatus to which the present invention is applied.

In FIG. 2, an optical disk 1 is rotated by a spindle motor 2. The recording signal of the optical disk 1 is reproduced by the optical pickup 3.

The optical pickup 3 is provided with an optical device.

That is, a laser diode 4 is provided in the optical pickup 3, and a laser beam is emitted from the laser diode 4. This laser beam is shaped into a parallel beam by the collimator lens 5, and the beam splitter 6,
The signal is irradiated onto the signal recording surface of the optical disk 1 via the half-wave plate 7 and the objective lens 8.

Light reflected from the optical disc 1 is passed through the objective lens 8, the half-wave plate 7, and the beam splitter 6, and is received by the photodetector 11 through the condenser lens 9 and the cylindrical lens 10.

The objective lens 8 is supported by a biaxial device,
It is possible to move in the tracking direction and the focus direction. The objective lens 8 is driven in the tracking direction according to the current supplied to the tracking coil 12. The objective lens 8 is driven in the focus direction according to the current supplied to the focus coil 13.

The entire optical pickup 3 can be moved in the tracking direction by a slide feed motor 14.

As shown in FIG. 3, the photodetector 11 includes photodiodes 11A to 11C, and photodiodes 11E and 11F. The main beams are received by the photodiodes 11A to 11D constituting the photodetector 11, and the tracking sub-beams are received by the photodiodes 11E and 11F.

The addition signal of the outputs of the photodiodes 11A to 11D of the photodetector 11 is supplied to the reproduction signal processing circuit 15 and also to the defect detection circuit 16.

The reproduction signal of the optical disk 1 is decoded by the reproduction signal processing circuit 15.

The defect detection circuit 16 detects whether a defect has occurred on the signal recording surface of the optical disk 1.
When a defect occurs on the signal recording surface of the optical disc 1 and the reproduction signal level becomes lower than a predetermined value, the defect detection circuit 16
Outputs a defect detection signal Sdef.

Outputs of the photodiodes 11A to 11D of the photodetector 11 are supplied to a focus error detection circuit 17. The focus error detection circuit 17 detects a difference signal between the added output of the photodiodes 11A and 11C and the added output of the photodiodes 11B and 11D. This photodiode 11A and 11C
And a difference signal between the sum output of the photodiodes 11B and 11D is set as a focus error signal.

That is, as shown in FIG. 4, the reflected light passing through the cylindrical lens 10 becomes circular at the in-focus position, and becomes elliptical when shifted from the in-focus position back and forth. Therefore, a focus error signal is obtained from a difference signal between the added output of the photodiodes 11A and 11C and the added output of the photodiodes 11B and 11D.

Outputs of the photodiodes 11B and 11F of the photodetector 11 are supplied to a tracking error detection circuit 18. The tracking error detection circuit 18 uses the photodiode 11E
And the output signal of the photodiode 11F is detected. The difference signal between the output of the photodiode 11E and the output of the photodiode 11F is used as a tracking error signal.

The focus error signal output from the focus error detection circuit 17 is digitized by the A / D converter 19,
It is supplied to the focus servo circuit 20. The output of the focus servo circuit 20 is provided to the focus coil 13 via the D / A co-inverter 21 and the drive amplifier 22. Thereby, the objective lens 13 is moved in the focus direction so as to be at the focal point.

The tracking error signal output from the tracking error detection circuit 18 is digitized by the A / D converter 23 and supplied to the tracking servo circuit 24. The output of the tracking servo circuit 24 is provided to the tracking coil 12 via the D / A converter 25 and the drive amplifier 26. Thereby, the objective lens 13 is moved in the tracking direction so that the beam spot traces the track center.

When a defect occurs in the optical disc 1, the defect detection circuit 16 outputs the defect detection signal Sdef as described above. The defect detection signal Sdef is supplied to the focus servo circuit 20 and the tracking servo circuit 21. Thereby, the characteristics of the digital loop filters provided in the focus servo circuit 20 and the tracking servo circuit 24 are switched.

That is, in a normal state, the focus servo circuit 20
In addition, the characteristics of the digital loop filter of the tracking servo circuit 24 are optimal characteristics according to the gain characteristics and phase characteristics of the loop. Defect detection signal Sdef
Is the focus servo circuit 20 and the tracking servo circuit
When the signal is supplied to the focus servo circuit 20 and the tracking servo circuit 24, a characteristic is obtained in which a low-pass filter is provided in a stage preceding the digital loop filter.

FIG. 1 shows the configuration of a digital loop filter provided in the focus servo circuit 20 and the tracking servo circuit 24.

In FIG. 1, the digital loop filter 31 includes a low-pass filter 32, a low-pass compensation equalizer 33, and a high-pass filter. Low-pass filter 32,
By cascade-connecting the low-frequency compensation equalizer 33 and the high-pass filter 34, optimal characteristics according to the gain characteristics and phase characteristics of the loop can be obtained.

In the conventional digital loop filter, the arrangement order of the low-pass filter, the low-pass compensation equalizer, and the high-pass filter is not particularly considered. However, in the digital loop filter 31 to which the present invention is applied, the low-pass filter 32 comes before the stage. Are arranged as follows.

The output of the digital loop filter 31 is taken out from the output terminal 40.

A switch circuit 35 is provided in a stage preceding the digital loop filter 31. On the a-side input terminal of the switch circuit 35,
A digital error signal is supplied from the input terminal 36.

The output of the connection point between the low-frequency compensation equalizer 33 and the high-pass filter 34 is supplied to the hold register 37. The output of the hold register 37 is supplied to the switch circuit 35 via the buffer 38.
Is supplied to the b-side input terminal.

A defect detection signal Sdef is supplied from the input terminal 39, and the switch circuit 35 is switched by the defect detection signal Sdef. When the defect detection signal Sdef is supplied, the hold register 37 is set to an enabled state. .

In the normal state, the switch circuit 35 is connected to the a side.
At this time, the digital error signal from the input terminal 36 is extracted from the output terminal 40 via the digital loop filter 31 including the low-pass filter 32, the low-pass compensation equalizer 33, and the high-pass filter 34. As a result, optimal characteristics according to the gain characteristics and phase characteristics of the loop can be obtained.

When a defect occurs in the optical disc 1, the defect detection signal Sdef is supplied to the input terminal 39, the switch circuit 35 is switched to the b side, and the hold register 37 is set to the enable state. As a result, the output of the low-frequency compensation equalizer 33 is taken into the hold register 37. Then, the output of the hold register 37 is supplied to the loop filter 31 via the buffer 38 and the switch circuit 35.
Therefore, a low-pass filter including the low-pass filter 32 and the low-frequency compensation equalizer 33 is arranged in a stage preceding the loop filter 31.

That is, FIG. 5 shows an example of the characteristics of the low-pass filter 32. In FIG. 5, A1 indicates the amplitude characteristic of the low-pass filter 32, and A2 indicates the phase characteristic of the low-pass filter 32.

FIG. 6 shows an example of the characteristics of the low-frequency compensation equalizer 33.
In FIG. 6, A2 indicates the amplitude characteristic of the low-frequency compensation equalizer 33, and B2 indicates the phase characteristic of the low-frequency compensation equalizer 33.

FIG. 7 shows an example of the characteristics of the high-pass filter. In FIG. 7, A3 indicates the amplitude characteristic of the high-pass filter 34, and B3 indicates the phase characteristic of the high-pass filter 34.

The digital loop filter 31 is a low-pass filter 32
, A low-pass compensation equalizer 33 and a high-pass filter 34 are cascaded. The characteristics at this time are as shown in FIG.

In FIG. 8, A4 shows its amplitude characteristic, and B4 shows its phase characteristic. As shown in FIG. 8, by cascade-connecting the low-pass filter 32, the low-pass compensation equalizer 33, and the high-pass filter 34, optimal characteristics according to the gain characteristics and phase characteristics of the loop can be obtained.

In a normal state, since the switch circuit 35 is connected to the a side, a digital error signal from the input terminal 36 is output from the output terminal 40 via the digital loop filter 31 having the characteristics shown in FIG. .

When a defect occurs in the optical disc 1, a low-pass filter having a characteristic as shown in FIG. 9 formed by cascade-connecting a low-pass filter 32 and a low-frequency compensation equalizer 33 is provided in front of the digital loop filter 31. Will be done.

FIG. 9 shows a low-pass filter 32 and a low-pass compensation equalizer.
This is the characteristic when 33 is cascaded. In FIG.
A5 shows its amplitude characteristic, and B5 shows its phase characteristic.

When a defect occurs on the signal recording surface of the optical disc 1, the digital error signal passes through a low-pass filter characteristic as shown in FIG. Then, the signal is output from an output terminal 40 via a digital loop filter 31 having characteristics as shown in FIG.

Thus, when the optical disc 1 has a defect,
A low-pass filter having characteristics as shown in FIG. 9 is provided at a stage preceding the digital loop filter 31. For this reason,
The sudden change of the error signal is removed, and the error signal is held. Therefore, even if the optical disc 1 has a defect, the servo will not be disturbed.

〔The invention's effect〕

According to the present invention, the low-pass 32 and the low-frequency compensation equalizer 33 constituting the digital loop filter 31 are arranged at the front stage, and when a defect occurs in the optical disc 1,
The error signal is supplied to a digital loop filter 31 via a low-pass filter characteristic including a low-pass 32 and a low-frequency compensation equalizer 33. Therefore, a low-pass filter is provided in a stage preceding the digital loop filter 31, so that a sudden change in the error signal is removed and the error signal is held.

Therefore, even if the signal recording surface of the optical disc 1 has a defect, the servo is not disturbed. Further, the low-pass filter and the low-pass compensation equalizer 33 constituting the digital loop filter 31 are used to constitute a low-pass filter for coping with defects of the optical disc 1, so that the circuit scale is not increased and the cost is reduced. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a loop filter according to an embodiment of the present invention, FIG. 2 is a block diagram of an example of an optical disk reproducing apparatus to which the present invention is applied, and FIG. 3 is an optical disk to which the present invention is applied. FIG. 4 is a plan view used to describe the configuration of the detector in the reproducing apparatus, FIG. 4 is a perspective view used to describe the focus servo in one embodiment of the present invention, and FIGS. 5 to 9 are used to describe one embodiment of the present invention. FIG. 10 and FIG. 11 are block diagrams showing the configuration of a loop filter in a conventional servo circuit. Explanation of main symbols in the drawings 1: optical disk, 3: optical pickup, 16: defect detection circuit, 31: digital loop filter, 32: low-pass filter, 33: low-pass compensation equalizer, 34: high-pass filter.

Claims (2)

(57) [Claims] A digital loop filter comprising a low-pass filter, a low-pass compensation equalizer, and a high-pass filter for optimizing a gain characteristic and a phase characteristic of a servo loop, and driving an actuator based on an output signal of the high-pass filter; Storage means for holding the output of the low-pass compensation equalizer of the digital loop filter; switching means for selectively switching the output of the storage means and an error signal based on a reproduction signal; and defect detection means for detecting a defect in the reproduction signal. If the defect detection means determines that there is a defect, the output of the storage means is selected and input to the digital loop filter, and if the defect detection means determines that there is no defect, Select the error signal and input to the digital loop filter Servo circuit characterized and. 2. An error signal generating means for generating an error signal based on a reproduction signal reproduced from an optical disk; a low-pass filter, a low-pass compensation equalizer, and a high-pass filter for optimizing a gain characteristic and a phase characteristic of a servo loop. Digital filter; storage means for holding an output of a low-frequency compensation equalizer in the digital filter; switching means for selectively switching the output of the storage means and the error signal generated by the error signal generation means; A defect detection means for detecting a defect in the reproduced signal; and, when the defect detection means determines that there is a defect, an output of the storage means is selected and input to the digital loop filter. If it is determined that there is no error, select the error signal and And switching means control means for inputting to the loop filter, and a drive means driven based on the output of the high pass filter of the digital filter regeneration device.