JP2002074713A - Information reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always optimize a frequency characteristic of a filter for an information signal, a wobble signal and a servo signal or the like in accordance with a reproducing linear speed without depending on omission of the information signal. SOLUTION: This device is provided with a wobble detecting means 12 which detects a periodic information signal pre-recorded along a track and having a period different from that of the information signal, an average period detecting means 20 which detects the average period of the periodic information signal, and a tracking filter 22 of a digital filter which has a sampling frequency synchronizing with the average period and over sampled at an arbitrary scale factor. Thus, the frequency characteristic of the filter for the information signal, the wobble signal and the servo signal or the like is always optimized in accordance with the reproducing linear speed and also is stabilized even in an unrecorded part and a link recording part, and reliability for a reproducing operation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for reproducing information signals from an optical disk or a magneto-optical disk at a variable speed.

[0002]

2. Description of the Related Art In recent years, mini discs (hereinafter referred to as MD), compact discs (hereinafter referred to as CD), CDs
-R (Recordable) / RW (Rewitable), DVD (Dig
CLV (constant linear velocity) like ital Versatile Disc
An optical disk device that reproduces data at a variable speed from an optical disk recorded by the optical disk has been developed. When data is reproduced from these disks, it is normally necessary to change the rotational speed of the spindle motor depending on the radial position of the disk to be reproduced in order to reproduce at CLV (constant linear velocity). On the other hand, in the variable-speed reproduction method, even if the linear velocity is different from a predetermined value at the time of reproduction, the data is read correspondingly on the signal processing side, thereby reducing the burden of changing the rotation speed on the motor rotation control system. This has many advantages such as reduction of power consumption, heat generation of the motor, and shortening of access time.

As an example using the following prior art,
An information reproducing apparatus for reproducing data from an MD at a variable speed will be described with reference to the drawings.

[0004] In MD, compressed music information data is stored in E
It is FM-modulated (8-14 modulated) and recorded on tracks on the recording surface of the disk by magneto-optical recording. The MD format includes a read-only ROM disk and a recordable RAM disk. In the RAM disk, address information indicating an absolute position on the disk is biphase-modulated, and further FM-modulated, so that a minute recording track is recorded. It is recorded on the disk in advance as a meander (hereinafter referred to as a wobble). This is called ADIP (Address in
Pre-groove) signal. The reproducing apparatus detects the wobble component of the recording track, performs FM demodulation of the wobble component, and further performs biphase demodulation, thereby detecting address information on the disc.

FIG. 9 is a block diagram showing the main components of an information reproducing apparatus using the conventional technique. In FIG. 9, 1
Is a disk (MD), 2 is a motor for rotating the disk 1, 3 is a semiconductor laser for generating a light beam, an objective lens for condensing the light beam on the recording surface of the disk 1, and a reflected light from the disk 1. An optical pickup having a light receiving element to be detected and an associated circuit element, 4 is a focus actuator for moving the objective lens of the optical pickup 3 in a direction perpendicular to the recording surface of the disk 1, and 5 is a disk drive for the objective lens of the optical pickup 3. A tracking actuator that moves vertically with respect to one recording track, 6
Is a focus signal detecting means for detecting a relative position error signal (focus signal) between the light beam and the recording surface of the disk 1, 7 is a focus servo means for performing processing such as phase compensation and low-frequency compensation based on the focus signal, and 8 is a focus servo means. Focus driving means 9 for driving the focus actuator 4 based on the output of the focus servo means 7; tracking signal detecting means 9 for detecting a relative position error signal (tracking signal) between the light beam and the recording track of the disk 1;
Reference numeral denotes a tracking servo unit that performs processes such as phase compensation and low-frequency compensation based on the tracking signal. Reference numeral 11 denotes a tracking driving unit that drives the tracking actuator 5 based on the output of the tracking servo unit. 1
2 is a wobble detecting means for detecting a wobble component of a recording track of the disk 1 based on the output of the optical pickup 3, and 13 performs FM demodulation and biphase demodulation processing on the wobble signal output from the wobble detecting means 12. Address decoding means for decoding an address signal (ADIP signal) recorded on the disk 1. 14 is an information signal detecting means for detecting an information signal (EFM signal) recorded on the disk 1 based on the output of the optical pickup 3, and 15 is detecting and outputting the average frequency of the detected information signal (EFM signal). The average frequency detecting means 16 is an EFM filter for correcting the frequency characteristics of the detected information signal (EFM signal), and has a frequency characteristic according to the average frequency of the information signal detected by the average frequency detecting means 15. 17 is an input terminal for the average frequency information of the EFM filter 16, 18
Is information decoding means for performing processing such as self-clock extraction, EFM demodulation, synchronization detection, and error correction on the output of the EFM filter 16 and decoding the information signal recorded on the disk 1.

The operation of the conventional information reproducing apparatus configured as described above will be described below.

First, the disk 1 is rotated at a predetermined target rotation speed by the motor 2. Generally, an FG that generates a pulse corresponding to the number of rotations of the motor, a period of the FG pulse is measured and compared with a target value, and a rotation control system including a driver or the like that drives the motor 2 according to the result is used. (Not shown). Further, the semiconductor laser light is condensed on the recording surface of the disk 1 by the optical pickup 3 by the objective lens, the reflected light is detected, and the focus signal is detected by the focus signal detecting means 6 based on the reflected light. The focus actuator 4 is driven by the servo means 7 and the focus drive means 8 so that the focus of the light beam follows the recording surface of the disk 1 (focus servo). The tracking signal is detected by the tracking signal detecting means 9 based on the reflected light, and the tracking actuator 5 is driven by the tracking servo means 10 and the tracking driving means 11 based on the tracking signal. Follow (tracking servo).

Next, the wobble detecting means 12 detects a meandering component (wobble component) of the track on the disk 1. This will be described below with reference to FIGS.

FIG. 10 is a schematic diagram showing a wobble of a recording track on an MD RAM disk.
In FIG. 10, a indicates a light beam spot focused on the recording surface of the disk 1, and an arrow indicates a direction in which the light beam spot a relatively moves on the recording surface of the disk 1 as the disk 1 rotates. . When the tracking servo is normally applied, the light beam spot a is correctly positioned on the target track as shown in FIG. 10, and advances in the direction of the arrow with the rotation of the disk. The frequency band that the tracking servo follows is usually about 1 to 2 kHz, but the wobble signal is set to a much higher frequency (22.05 kHz in MD when reproduced at normal linear velocity). Therefore, the tracking servo hardly follows the wobble, which is a minute meander of the recording track, and the light beam spot a advances straight in the direction of the arrow in FIG. Therefore, the wobble component becomes a residual error component of the tracking servo almost as it is. That is, in the wobble detecting means 12,
It is possible to detect the wobble signal by detecting the residual error component of the tracking signal when the tracking servo is operating normally and applying band-pass filter processing to pass only the frequency near the wobble signal component to this. it can.

A method for detecting a tracking signal will be described below with reference to FIG. FIG. 11 is a schematic diagram showing a general method for detecting a trunk signal. In FIG. 11, a is a light receiving element for detecting the reflected light from the disk 1, and is indicated by a dividing line substantially perpendicular to the direction (horizontal axis direction in FIG. 11) corresponding to the radial direction of the disk 1.
Area a1 and a2. b is a subtraction circuit for detecting the difference between the outputs of the divided areas a1 and a2 of the light receiving element a, and c is the disk 1 on the light receiving element a.
The reflected light beam spot d from the optical disk 1 corresponds to the direction of the reflected light beam spot c corresponding to the radial direction of the disk 1 (FIG.
1 (horizontal axis direction). Since the light amount distribution (d in FIG. 11) of the reflected light spot changes according to the relative position of the recording track of the disk 1 and the light beam spot in the disk radial direction, the output of the divided light receiving element areas a1 and a2 The tracking signal can be detected from the difference between the two. This detection method is called a push-pull method or a far-field method, and is widely used in optical disk devices.

The wobble signal detected as described above is subjected to an FM demodulation process in the address decoding means 13 and a bi-phase demodulation process is further performed on the FM demodulation result. Address signal (ADIP signal) can be detected.

Next, the information signal recorded on the recording surface of the disk 1 is reproduced by the information signal detecting means 14 based on the reflected light output from the optical pickup 3. Disc 1
Since the information signal read from the EFM is EFM-modulated, this information signal is referred to as an EFM signal here. The frequency characteristics of the reproduced EFM signal are corrected by the EFM filter 16, and the information decoding unit 18 performs processing such as self-clock extraction, EFM demodulation, synchronization detection, and error correction. Detect signal.

Here, the characteristics of the EFM filter 16 will be described with reference to FIG. FIG. 12 is a frequency characteristic diagram showing general frequency characteristics of the EFM filter 16 in a conventional information reproducing apparatus. In FIG. 12, the horizontal axis represents frequency, the vertical axis represents amplitude pass characteristics, and f1, f2, and f3 each represent a cutoff frequency. Normally, when irradiating a recording mark on an optical disk with a light beam spot and reproducing an information signal from the reflected light, the diameter of the recording mark is so small that it cannot be ignored compared to the spot diameter because the light beam spot diameter is finite. Then, the amplitude of the reproduced signal decreases.
Therefore, when an information signal is reproduced, the smaller the recording mark, that is, the higher the frequency, the lower the signal amplitude tends to be. Generally, in order to correct this, the high-frequency gain is increased as seen in the characteristic between the cutoff frequencies f1 and f2 in FIG. The region higher than the cut-off frequency f3 in FIG. 12 is a region where there is no component of the reproduction information signal, and attenuates the high-frequency gain in order to remove noise due to a semiconductor laser, a disk, a circuit, and the like. This improves the quality of the reproduced signal and reduces data reading errors.

In the MD, since the EFM signal is recorded at CLV (constant linear velocity), if the spindle motor is controlled based on the reproduced EFM signal so as to keep the linear velocity constant, the frequency of the reproduced EFM signal is increased. The band becomes substantially constant, and the frequency characteristic (FIG. 12) of the EFM filter 16 may be fixed. However, as described above, in recent years, the need for “variable speed reproduction” to cope with fluctuations in the reproduction linear velocity on the signal processing side of the reproduction apparatus has been increasing. Variable speed playback reduces the load on the motor rotation control system, which reduces power consumption during portable use. In addition, signals can be read out even if the linear velocity is shifted immediately after access, reducing access time and reducing music playback time. There are advantages such as faster cueing of the head. When the reproduction linear velocity fluctuates, the frequency characteristic of the EFM filter 16 (FIG. 12) is not always optimal,
The quality of the reproduced signal deteriorates, and as a result, data reading errors increase, and the reliability of the system decreases. For this reason, in the conventional information reproducing apparatus, the average frequency of the information signal (EFM signal) reproduced by the average frequency detecting means 15 is detected, and the frequency characteristic of the EFM filter 16 (the cutoff frequency in FIG. f1, f12, f
By changing 3), a device has been devised so as to always perform the optimum correction irrespective of the fluctuation of the reproducing linear velocity.

[0015]

However, the above-described conventional configuration has the following problems.

In the conventional configuration, the frequency characteristic of the correction filter for the EFM signal is varied according to the average frequency of the EFM signal itself. However, the EFM signal in the MD RAM disk is not always recorded continuously. In the case of the MD format, music data is permitted to be divided and recorded in cluster units (1 cluster = 36 sectors, 1 sector = 98 frames). A link area for three sectors is provided, and an unrecorded portion of a maximum of 20 frames is allowed in the link area. When the frequency characteristics of the EFM filter 16 are varied based on the average frequency of the EFM signal as in the above-described conventional configuration, the frequency characteristics of the filter become unstable in such unrecorded portions. Further, even when the reproduction is performed from the recording start point, the frequency characteristic of the filter is not settled before the reproduction starts, and the reproduction of the EFM signal is not performed. Immediately after the operation is started, data may not be correctly read until the frequency characteristics of the filter settle.

In the above-mentioned conventional configuration, the frequency characteristics of the filter can be optimized for the recorded information signal (EFM signal) in accordance with the reproduction linear velocity.
The frequency characteristic of the filter for the IP signal is fixed,
Practical problems may occur. This will be described below with an example.

Since the wobble component on which the ADIP signal is recorded is a meandering track, it is mixed in a tracking signal for performing a tracking servo process. Regardless of the tracking signal detection method, basically the same phenomenon occurs regardless of the push-pull method described with reference to FIG. 11 or the so-called three-beam method. Usually this contaminated component
Since it is outside the response band of the tracking servo loop, it hardly responds as a tracking servo, but a wobble component is mixed in the drive signal for the tracking actuator 5. As a result, the drive stage becomes saturated with the power supply voltage, and the tracking servo becomes unstable, or a problem of consuming extra power occurs. Usually, it is determined whether the tracking servo has deviated by comparing the amplitude of the tracking signal with a predetermined value.However, since the wobble signal is mixed with the tracking signal, even if the tracking servo is settled normally, the tracking servo is not deviated. There is a risk of misjudging that it has come off. To prevent this, it is common to insert a low-pass filter into the tracking signal to reduce the mixed wobble component. However, since the frequency of the wobble component fluctuates due to variable speed reproduction, a low-pass filter having a fixed frequency characteristic is used. Then, it is difficult to optimally remove noise.

In the ADIP signal, an address signal is bi-phase modulated, and bi-phase data is recorded as FM information (ie, period information) of a wobble signal. In order to read out a bi-phase signal with stable quality, it is necessary to detect the period of the wobble signal, remove the necessary periodic noise from this periodic signal using a low-pass filter, and extract only the bi-phase signal component. is there.
However, at the time of variable speed reproduction, the average period of the wobble signal fluctuates, and the average period of the biphase signal also fluctuates accordingly. Therefore, it is difficult to optimally remove noise with a low-pass filter having a fixed frequency characteristic. Average frequency detecting means 15 and EFM filter 16 in conventional information reproducing apparatus
It is also conceivable to apply the concept of the above to a wobble signal and insert a filter having a frequency characteristic according to the average period of the wobble signal into the output of the wobble detection means 12,
In this case, the amplitude noise of the wobble signal can be appropriately removed according to the linear velocity, but it cannot be said that the periodic noise can be properly removed, and it is difficult to obtain sufficient performance.

The present invention solves the above-mentioned conventional problems. Even when the reproduction linear velocity fluctuates greatly, an information signal (an EFM signal in MD) or an address signal (MD in advance) recorded on a disk is used. In this case, the frequency characteristics of the filter for the ADIP signal), the servo signal (the focus signal and the tracking signal) and the like are always optimized according to the reproduction linear velocity, and the unrecorded portion and the link recording portion are also made stable. The purpose is to improve reliability.

[0021]

In order to achieve this object, the present invention provides a period information detecting means for detecting a wobble signal having a predetermined period recorded in advance along a track, and an average period of the wobble signal. And a predetermined signal (servo signal,
And a filter for correcting the frequency characteristic of the information signal or the address signal).

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first invention of the present invention is an information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam, A focus servo loop that causes the focus of the light beam to follow the recording surface; and a servo unit that includes a tracking servo loop that follows the track.
A filter for correcting frequency characteristics in the servo means,
The filter comprising: a period information detection unit that detects a period information signal recorded in advance along the track and has a period different from the information signal; and an average period detection unit that detects an average period of the period information signal. Is for correcting the frequency characteristic according to the average period.

Further, in the first invention, the filter comprises:
For correcting the frequency characteristics of the focus servo loop,
Alternatively, it corrects the frequency characteristics of the tracking servo loop.

According to a second aspect of the present invention, there is provided an information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam. A focus servo unit that forms a focus servo loop that causes the focal point of a beam to follow the recording surface; a tracking signal generation unit that generates a tracking signal that indicates a relative position between the light beam and the track; Tracking servo means forming a tracking servo loop for causing the light beam to follow the track; a filter for correcting the frequency characteristic of the tracking signal; and tracking off detecting that the tracking servo has been released based on the output of the filter. Detection means, pre-recorded along said track And a period information detecting means for detecting a period information signal having a period different from the information signal, and an average period detecting means for detecting an average period of the periodic information signal, wherein the filter has a frequency corresponding to the average period. This is for correcting the characteristics.

According to a third aspect of the present invention, there is provided an information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam. Servo means including a focus servo loop for causing the focal point of a beam to follow the recording surface and a tracking servo loop for following the track; information signal detecting means for detecting the information signal recorded on the track; A filter for correcting frequency characteristics, a period information detecting means for detecting a period information signal recorded in advance along the track and having a period different from the information signal, and an average period for detecting an average period of the period information signal Detecting means, wherein the filter corrects frequency characteristics in accordance with the average period.

In each of the above inventions, the periodic information signal is a signal recorded by meandering of a track,
Alternatively, it is a signal recorded by pre-pits.

According to a fourth aspect of the present invention, an information signal is formed by irradiating a light beam to the track of a disk-shaped recording medium having a meandering track on a recording surface in accordance with an FM-modulated signal. An information reproducing apparatus for reproducing,
Servo means including a focus servo loop for causing the focus of the light beam to follow the recording surface and a tracking servo loop for following the track; wobble detection means for detecting a meandering component of the track and outputting a wobble signal; An average period detection unit that detects an average period of the wobble signal; an FM demodulation unit that FM-demodulates the wobble signal; and a filter that corrects a frequency characteristic of the FM-demodulated signal. The frequency characteristic is corrected accordingly.

Further, in each of the above-mentioned inventions, the frequency characteristics of the filter are fixed when the tracking servo loop is opened or when it is detected that the tracking servo has deviated.

In each of the above inventions, the filter is:
This is a digital filter that operates based on a sampling period according to the average period. Further, the sampling period is shorter than the average period, and the sampling period is 1 / N of the average period (N is an integer of 2 or more. ) As well as those where N = 2.

In the above invention, the average period detecting means counts the period of the period information signal or the wobble signal with a predetermined clock to obtain an average value thereof, and obtains the predetermined clock or its n / m times (n, m). m is an integer of 1 or more), a second counter is provided in synchronization with a clock having a cycle of, and the output value of the second counter is compared with the average value after performing a predetermined weighting. The timing based on the comparison result is used as a sampling period, and the digital filter includes a digital filter of a cyclic type or a non-cyclic type.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) An information reproducing apparatus according to Embodiment 1 of the present invention which reproduces data from an MD at a variable speed and in which noise removal of a tracking signal is optimized will be described below. It will be described using FIG.

FIG. 1 is a block diagram showing main components of the information reproducing apparatus according to the first embodiment of the present invention. In FIG. 1, components 1 to 14 and 18 are the same as those in FIG. 9 used in the description of the conventional information reproducing apparatus, and the description is omitted. 20 is an average period detecting means for detecting an average period of the wobble signal output from the wobble detecting means 12, 21 is
A focus filter 22 for correcting the frequency characteristic of the focus signal output from the focus signal detecting means 6; a tracking filter 22 for correcting the frequency characteristic of the tracking signal output from the tracking signal detecting means 9;
Is an input terminal of the tracking filter 22, to which the average period of the wobble signal output by the average period detecting means 20 is input.

FIG. 2 shows the average period detecting means 2 in FIG.
FIG. 2 is a block diagram illustrating a specific configuration example of a tracking filter and a tracking filter; In FIG. 2, reference numeral 30 denotes a binarizing means for binarizing an input wobble signal by comparing it with a predetermined comparison level, and 31 detects a rising edge of the binarized wobble signal to generate an edge detection signal. The output edge detecting means 32 outputs a clock (CL) having a predetermined frequency.
K) is a first counter that counts the period between the edge detection signals and holds and outputs the count value in synchronization with the edge detection signal. 33 is a clock signal input terminal of the first counter 32 , 34 are the first counter 3
2 is an edge detection signal input terminal, and 35 is a first counter 3
The output terminal 35 outputs a cycle count value of the wobble signal. 36 is a second counter for counting the number of edges of a clock (CLK) having a predetermined frequency, and 37 is a second counter 36
Is a clock input terminal, and is a count value output terminal of the second counter 36. Reference numeral 40 denotes an average value detecting means for obtaining an average value of the period count value of the wobble signal output from the first counter 32, and is constituted by a normal low-pass filter or the like. Reference numeral 41 denotes an average period count value of the wobble signal output from the average value detection means 40,
A coefficient unit for comparing the output value of the coefficient unit 41 and the output value of the second counter 36, and outputting a timing signal based on the comparison result;
39 is an input terminal of the second counter 36,
2 is input. Reference numeral 22 denotes a tracking filter for correcting the frequency characteristic of the tracking signal. Reference numeral 23 denotes an input terminal of the tracking filter 22. The tracking filter 22 includes a comparator 4 input from the input terminal 23.
2 is a digital filter that uses the output signal timing as an operation cycle (sampling cycle).

FIG. 3 is a block diagram showing a specific example of the configuration of the tracking filter 22 shown in FIGS. FIG. 3 shows the configuration of a general transversal digital filter.
2, the tracking filter 22 uses a timing signal input from the input terminal 23 as an operation cycle (sampling cycle). 50, 51 are delay devices for delaying the input signal by one sampling period, 52, 53,
Numeral 54 denotes coefficient multipliers for multiplying the input signal by coefficients, each of which is +
It has coefficient values of 0.25, +0.5, and +0.25. 55
Is an adder that adds the output signals of the coefficient units 52, 53, and 54 to obtain an output value of the tracking filter 22.

The operation of the first embodiment of the present invention configured as described above will be described below with reference to FIGS.

The operations of the rotation control of the disk 1, the focus servo, and the detection of the address signal (ADIP signal) are the same as those of the information reproducing apparatus using the conventional technique, and the reproduction of the information signal (EFM signal) is also an average. Only the filter corresponding to the cycle is omitted, and the basic operation is the same. The basic operation of the tracking servo is the same, except that a tracking filter 22 having a sampling period corresponding to the average period of the wobble signal is provided. Hereinafter, this point will be mainly described.

FIG. 4 is a frequency characteristic diagram showing characteristics of the tracking filter 22 in the information reproducing apparatus according to the first embodiment of the present invention. The horizontal axis represents the frequency, the vertical axis represents the amplitude passing characteristic, and fs represents the sampling frequency (= 1 / sampling period). As shown in FIG. 4, the passing amplitude characteristic of the digital filter having the configuration shown in FIG. 3 is known to exhibit a low-pass filter characteristic in a frequency region where the DC gain is 1 and fs / 2 or less. In particular, frequency = fs / 2
, The amplitude pass characteristic becomes 0 and no signal passes, so that unnecessary noise at this frequency can be completely removed.

The tracking filter 22 removes unnecessary noise from the input tracking signal with the frequency characteristic shown in FIG. At this time, since the sampling period follows the average period of the wobble signal, unnecessary noise of the tracking signal can always be optimally removed in accordance with the reproduction linear velocity. This operation will be described below with reference to FIG.

FIG. 5 is a waveform diagram showing operations of the average period detecting means 20 and the tracking filter 22 in the information reproducing apparatus according to the first embodiment of the present invention. 5A shows an input wobble signal, FIG. 5B shows an edge detection signal output from the edge detecting means 31, and FIG.
(D) is the internal count value of the first counter 32, and (E) is the output count value of the first counter 32 (the internal count value ( (D) is a value sampled and held by the edge detection signal (B)), and (F) shows the output count value of the second counter 36. (D),
(A) shown in (E) and (F) is the output level of the average value detection means 40, and indicates the average value of the output count value (E) of the first counter 32, that is, the average period of the wobble signal.
(G) is a timing signal output from the comparator 42. The timing signal is output every time the output count value (F) of the second counter 36 reaches one half of the average period a. (Sampling cycle)
Becomes

First, the binarizing means 30 binarizes the wobble signal input (FIG. 5A) by comparing it with a predetermined reference level, and the edge detecting means 31 detects the rising edge of the binarized signal. , And an edge detection signal (FIG. 5B). The first counter 32 outputs a clock signal (FIG. 5).
Count up the number of edges in (C)) (Fig. 5 (D))
Then, the count value is held at the timing of the edge detection signal (FIG. 5 (B)) and set as an output value (FIG. 5 (E)). At the same time, the internal count value is cleared and the count-up is started again (FIG. 5D). Wobble signal (Fig. 5
(A)) is FM-modulated and is affected by noise caused by a disc, an optical pickup, a circuit, and the like.
The signal period includes a fluctuation component. Therefore, the wobble cycle count value output from the first counting means 32 includes a fluctuation component as shown in FIG. The average value detection means 40 performs an averaging process on the cycle count value, outputs the average value (a in FIG. 5E), and is halved by the coefficient unit 41 (FIG. 5F A)
2). The second counter 36 outputs a clock signal (FIG. 5).
(C)), the number of edges is counted up, and this is compared with the output value a / 2 of the coefficient unit 41 by the comparator 42, and the second
When the output value of the counter reaches a / 2, a timing signal is output, and the second counter 36 clears the count value in synchronization with the timing signal (FIG. 5F,
(G)).

With the above operation, the timing signal (FIG. 5) having a period which is always 1/2 of the average period of the input wobble signal.
(G)) can be generated. Since the tracking filter 22 performs arithmetic processing in synchronization with the timing signal (FIG. 5 (G)), the sampling cycle of the tracking filter 22 always follows 1/2 of the average cycle of the wobble signal. In other words, the sampling frequency of the tracking filter 22 always follows twice the average frequency of the wobble signal. When the reproduction linear velocity from the disk 1 fluctuates, the average period of the wobble signal follows, and the sampling period of the tracking filter 22 also follows. Since the frequency characteristics of the digital filter are determined with reference to the sampling frequency, by following the sampling cycle in accordance with the reproduction linear velocity, it is possible to always realize the optimum frequency characteristics in accordance with the reproduction linear velocity.

Particularly, in the first embodiment, the sampling frequency (fs) of the digital filter is reduced by using the filter having the frequency characteristic shown in FIG. 4 and halving the period of the wobble signal by the coefficient unit 41 in FIG. Since the average frequency of the wobble signal is always twice (double oversampling), the average frequency of the wobble signal always corresponds to fs / 2, and is almost completely removed by the frequency characteristic of FIG. As described above, the wobble component is generally mixed into the tracking signal, which causes a saturation of the driving stage and a malfunction of detection of tracking loss.
According to the first embodiment, the wobble component mixed in the tracking signal can be almost completely removed irrespective of the reproduction linear velocity, which is extremely effective for improving the reliability of the apparatus.

As described above, according to the information reproducing apparatus of the first embodiment of the present invention, a non-recursive digital filter for correcting the frequency characteristic of the tracking signal, wobble detecting means for detecting the wobble signal, and the wobble signal Average period detecting means for detecting the average period of the wobble signal, the period of the wobble signal is counted with a clock, and the average value is obtained.
Providing a second counter synchronized with the clock, comparing an output value of the second counter with a value obtained by halving the average value, and using the digital filter as a sampling period based on the comparison result. Accordingly, it is possible to always remove the noise of the tracking signal by using a filter having an optimum frequency characteristic according to the reproduction linear velocity, and it is possible to almost completely remove the wobble component mixed in the tracking signal.

In the present embodiment, the description has been given with respect to the tracking signal, but the same applies to the focus signal. That is, the focus filter 21 may have the same configuration as the tracking filter 22.

(Embodiment 2) Next, as an information reproducing apparatus according to Embodiment 2 of the present invention, an information reproducing apparatus for reproducing data from an MD at a variable speed, in which the removal of the periodic noise of the wobble signal is optimized. This will be described with reference to the drawings.

FIG. 6 is a block diagram showing main components of the information reproducing apparatus according to the second embodiment of the present invention. 6, components 1 to 12, 14, and 18 are the same as those in FIG. 9 used in the description of the conventional information reproducing apparatus, and reference numeral 20 denotes FIG. 1 used in the description of the information reproducing apparatus according to the first embodiment. Therefore, the description is omitted. Reference numeral 60 denotes FM demodulation means for performing FM demodulation on the wobble signal output from the wobble detection means 12, and measures the cycle of the wobble signal and outputs cycle data. Reference numeral 61 denotes a periodic filter for removing unnecessary periodic noise included in the periodic data output from the FM demodulator 60, and has a frequency characteristic corresponding to the average period of the wobble signal output from the average period detector 20. 6
Reference numeral 2 denotes a bi-phase demodulation means for detecting an address by bi-phase demodulating the output of the periodic filter 61 based on the output.

The operation of the second embodiment of the present invention configured as described above will be described below.

Disk rotation control, focus servo,
Operations such as tracking servo and detection of an information signal (EFM signal) are substantially the same as those of the conventional information reproducing apparatus and the first embodiment, and therefore, description thereof is omitted. The second embodiment differs from the second embodiment in the processing of the wobble signal output by the wobble detecting means 12. This will be described below.

The conventional information reproducing apparatus and the first embodiment do not include a filter having an optimum frequency characteristic for a wobble signal according to a reproducing linear velocity. Therefore, optimal noise removal cannot be performed during variable speed reproduction. In the second embodiment, the FM demodulation unit 60
, The period of the wobble signal is detected, and unnecessary period noise is removed from the period data output by the period filter 61. Since the periodic filter 61 has a frequency characteristic corresponding to the average period of the wobble signal detected by the average period detecting means 20, it is possible to always perform the optimal noise removal processing according to the reproduction speed. In a conventional information reproducing apparatus,
As shown in FIG. 9, a filter having a frequency characteristic according to the average period of the information signal is inserted into the information signal (EFM signal). In the second embodiment, this is simply applied to a wobble signal. Have different ideas. If the conventional technique is applied to a wobble signal, a filter corresponding to the average period of the wobble signal is inserted into the output of the wobble detection means 12. In this case, the amplitude noise of the wobble signal is appropriately removed according to the linear velocity, but this does not necessarily mean that the periodic noise is properly removed. For example, let us consider a case where distortion occurs instantaneously in the wobble signal as shown in FIG. 5A, and the phase near the zero cross suddenly shifts. Although such a distortion cannot always be effectively removed by a low-pass filter for the wobble signal itself, the periodic data after FM demodulation (FIG. 5)
(E)) suddenly becomes a large noise, which can be easily removed by a low-pass filter. Based on the above idea, the second embodiment does not simply insert a filter into the output of the wobble signal,
The periodic filter 61 is inserted into the demodulated signal, and the frequency characteristic of the periodic filter 61 is set to a characteristic corresponding to the average period of the wobble signal before the FM demodulation. Is to be removed.

The specific configuration of the periodic filter 61 may be a non-recursive digital filter as shown in FIG. 3 used in the description of the first embodiment, or a cyclic (IIR) filter.
Digital filter may be used. In the first embodiment, the sampling period is set to １ ／ of the average period of the wobble signal.
However, in the information reproducing apparatus according to the second embodiment, the same may be applied, but the sampling period may be further shortened (that is, the sampling frequency may be increased). This method will be described below.

In FIG. 2 used in the description of the first embodiment, the coefficient value of the coefficient unit 41 is １ ／ and the value of 平均 of the average period of the wobble signal is used as the output value of the second counter 36. And a configuration for comparison. This realizes a digital filter of oversampling twice the average frequency of the wobble signal. However, by making the coefficient of the coefficient unit 41 smaller (for example, 1/4, 1/8, 1/16, etc.),
The timing cycle output from the comparator 41 becomes shorter, and the sampling frequency of the periodic filter 61 can be set higher. That is, by setting the coefficient value of the coefficient unit 41 arbitrarily, it is possible to configure an oversampling filter synchronized with the average frequency of the wobble signal and having an arbitrary magnification. The same oversampling process can be performed by multiplying the output value of the second counter 36 by a coefficient of 1 or more. Further, in FIG. 2, the clocks of the first counter 32 and the second counter 36 have the same frequency, but clocks of different frequencies may be used.
For example, the coefficient value of the coefficient unit 41 is 1, and the ratio of the clock frequency of the first counter 32 to the clock frequency of the second counter 36 is n:
If m (m and n are each an integer of 1 or more), the sampling frequency of the tracking filter 22 can be set to m / n times the average frequency of the wobble signal. Generally, the frequency characteristic of a digital filter is fs
Therefore, the low-pass filter that can reduce high-frequency noise is limited to the frequency region of fs / 2 or less. That is, by increasing the sampling frequency as described above, even higher-frequency noise can be removed, and the reliability of the device can be improved.

As described above, according to the information reproducing apparatus in the second embodiment of the present invention, the wobble detecting means for detecting the wobble signal, the average cycle detecting means for detecting the average cycle of the wobble signal, and the FM signal An FM demodulator for demodulating the signal and a filter for correcting the frequency characteristic of the signal subjected to the FM demodulation are provided. The filter has a frequency characteristic according to the average period, so that the filter always has an optimal frequency characteristic according to the reproduction linear velocity. It is possible to remove the periodic noise of the wobble signal using a filter, and it is possible to reduce the higher-frequency noise by oversampling at an arbitrary ratio, improving the reliability of the device. Can be done.

(Embodiment 3) Next, as an information reproducing apparatus according to Embodiment 3 of the present invention, an information reproducing apparatus for reproducing data from an MD at a variable speed has an information signal (EFM signal).
The optimization and stabilization of the frequency characteristic correction will be described with reference to the drawings.

FIG. 7 is a block diagram showing main components of an information reproducing apparatus according to Embodiment 3 of the present invention. 7, components 1 to 14 and 18 are the same as those in FIG. 9 used in the description of the conventional information reproducing apparatus, and 20 is the same as FIG. 1 used in the description of the information reproducing apparatus according to the first embodiment. Therefore, the description is omitted. 70 is an information signal detecting means 14
Is an EFM filter for removing unnecessary noise included in the information signal (EFM signal) output from the EFM signal, and has a frequency characteristic corresponding to the average period of the wobble signal output from the average period detecting means 20.

The operation of the third embodiment of the present invention configured as described above will be described below.

Disk rotation control, focus servo,
Operations such as tracking servo and detection of an address signal (ADIP signal) are the same as those of an information reproducing apparatus using a conventional technique, and thus description thereof is omitted. Embodiment 3 is different from the information reproducing apparatus using the conventional technique in that an information signal (EFM) is used.
Signal). This will be described below.

In the conventional information reproducing apparatus, the information signal (EF)
The EFM filter 16 for removing the noise of the (M signal) has a frequency characteristic corresponding to the average frequency of the information signal itself detected by the average period detecting means 15. However, as mentioned above, the MD RAM
Since an unrecorded area of the information signal (EFM signal) exists on the disk, the frequency characteristics of the filter become unstable in the unrecorded area in the above-described conventional configuration. Therefore, in the third embodiment, as shown in FIG. 7, the frequency characteristic of the EFM filter 70 has a frequency characteristic corresponding to the average period of the wobble signal output from the average period detecting means 20. Since the recording track on the MD RAM disk is always a meandering continuous groove (pre-group), the wobble signal is not interrupted unlike the EFM signal. Therefore, with the above-described configuration, the frequency characteristics are always set to an optimum value according to the reproduction linear velocity, and the frequency characteristics of the EFM filter 70 are not disturbed even in a region where the information signal (EFM signal) is lost, and a stable noise removing operation is performed. Becomes possible.

The specific configuration of the EFM filter 70 may be a non-recursive digital filter as shown in FIG. 3 used in the description of the first embodiment, or a recursive (IIR) filter.
Type) digital filter. Generally, in order to suppress distortion of an information signal, a non-recursive filter that can easily flatten the frequency characteristics of group delay is desirable. In MD, the average frequency of the wobble signal when reproduced at a normal linear velocity is 22.05 kHz, and the frequency band of the EFM signal is approximately 200 kHz to 1 MHz. The frequency band of the EFM signal is much higher. Therefore, in order to configure a digital filter that passes the band of the EFM signal, the sampling frequency needs to be higher than that, and it is necessary to set the sampling frequency to be much higher than the average frequency of the wobble signal. For example, if the average frequency of the wobble signal is 256 times, the sampling frequency is 5.6448 MHz (= 22.05 kHz × 256).
Thus, a desired filter characteristic can be realized in a frequency band of 2.8224 MHz (= 5.6448 MHz / 2) or less. Such processing is performed by, for example, setting the coefficient of the coefficient unit 41 to 1/16 and using the clock frequency of the first counter 32 and the second counter 36 in the configuration shown in FIG. 2 used in the description of the first embodiment. It can be easily realized by setting the ratio to 1:16.

As described above, according to the information reproducing apparatus in the third embodiment of the present invention, the wobble detecting means for detecting the wobble signal, the average cycle detecting means for detecting the average cycle of the wobble signal, and the information signal (EFM) Signal), and a filter for correcting the frequency characteristic of the information signal. By setting the filter to have a frequency characteristic corresponding to the average period, an optimal frequency characteristic always corresponding to the reproduction linear velocity is obtained. The frequency characteristic of the information signal (EFM signal) is corrected using the filter provided, and a stable operation can be performed even in a region where the information signal is missing.

(Embodiment 4) Next, as an information reproducing apparatus according to Embodiment 4 of the present invention, an information reproducing apparatus for reproducing data from an MD at a variable speed, in which noise removal of a tracking signal is optimized and stabilized. Will be described with reference to the drawings.

FIG. 8 is a block diagram showing main components of an information reproducing apparatus according to Embodiment 4 of the present invention. 8, components 1 to 14 and 18 are the same as those in FIG. 9 used in the description of the conventional information reproducing apparatus.
Is the same as FIG. 1 used in the description of the information reproducing apparatus according to the first embodiment, and thus the description is omitted. 80 is a selection unit that receives a tracking signal output from the tracking detection unit 9 and an output signal of the tracking filter 22 as input, and selects and outputs one of them according to an output of a tracking-off detection unit 81 described below. This is an off-tracking detecting means which receives the output of the selecting means 80, compares it with a predetermined value, detects whether the tracking servo is off, and outputs the result.

The operation of the fourth embodiment of the present invention configured as described above will be described below.

Disk rotation control, focus servo,
Address signal (ADIP signal) detection, information signal (EFM)
The operation is the same as that of the first embodiment in the operation such as signal) detection and the point that the tracking filter 22 having a frequency characteristic corresponding to the average period of the wobble signal is inserted into the tracking signal. The fourth embodiment is different from the first embodiment in that the fourth embodiment includes a selecting unit 80 and a tracking-off detecting unit 81, and fixes the frequency characteristic of the filter for the tracking signal when detecting that the tracking servo is off. is there. This will be described below.

In order for the wobble signal to be correctly detected by the wobble detection means 12, the light beam spot a must be correctly focused on the target track as shown in FIG. It must be working properly. The wobble signal cannot be detected correctly when the tracking servo loop is opened at the start of the disk reproducing operation or during a transient state such as during access, or when the tracking servo is deviated due to disturbance vibration or a defect on the disk. Therefore, the average period of the wobble signal output by the average period detecting means 20 is disturbed, and accordingly, the sampling frequency of the tracking filter 22 is disturbed, and the frequency characteristics become unstable.

As described above, even when the tracking servo is not settled normally, the tracking signal is
This signal is important for the pull-in of the tracking servo and the access operation, and it is not preferable that the frequency characteristic of the filter for the signal is disturbed. To prevent this, the information reproducing apparatus according to the fourth embodiment performs the following operation.

First, when the tracking servo is normally applied, the selecting means 80 selects the tracking filter 22.
And effectively remove noise such as mixed wobble components. In this state, tracking-off detecting means 8
1 monitors a tracking signal from which noise has been removed, and when the tracking signal exceeds a predetermined amplitude (or continuously exceeds a predetermined amplitude for a predetermined time, for example), it is determined that the tracking servo has deviated. The output of the detecting means 9 is selected. This fixes the frequency characteristics of the filter for the tracking signal. This prevents disturbance of the frequency characteristics of the filter with respect to the tracking signal, and prevents the tracking servo pull-in and the access operation from becoming unstable. Here, in FIG. 8, the tracking filter 22 is configured to pass when the tracking deviation is detected, but it is not always necessary to pass. What is necessary is just to fix the filter characteristic so that it does not follow the average period of the wobble signal when the tracking loss is detected. For example, a configuration may be adopted in which the frequency characteristic of the tracking filter 22 is held at the previous value. Also, in the transient state such as at the start of the playback operation or during the access operation, the tracking servo loop is opened by itself,
In such a case, it is also necessary to fix the frequency characteristics of the filter. The detection method of the tracking deviation is not limited to the above-described method, and various methods are possible using a tracking signal or the amount of reflected light from the recording surface of the disc.
Any method may be used.

As described above, according to the information reproducing apparatus of the fourth embodiment of the present invention, the wobble detecting means for detecting the wobble signal, the average cycle detecting means for detecting the average cycle of the wobble signal, the average of the wobble signal, A tracking filter having a frequency characteristic according to the period and a tracking deviation detecting means are provided, and when the tracking deviation is detected, the frequency characteristic of the tracking filter is fixed to have an optimal frequency characteristic according to the reproduction linear velocity. It is possible to remove the noise of the tracking signal by using a filter, and when the tracking servo loop is opened in a transient state such as at the start of playback or during access, or the tracking servo is caused by disturbance vibration or a defect on the disk. Prevents the frequency characteristics of the filter from becoming unstable when , Always stable operation becomes possible.

In the first to fourth embodiments, the wobble signal (the meandering component of the track) is used as a specific example of the periodic information signal recorded in advance along the track of the disk. However, the present invention is not limited to this. Not a thing. D
In a VD-RAM or the like, an address signal indicating a position on the disk is recorded by pre-pits formed periodically in advance on the recording surface of the disk, but such a periodic signal may be used.

Although the first counter 32 in the first embodiment has counted the period between one edge of the wobble signal, it may count the period between both edges. In this case, the value of the period data is 2 Since the weight is doubled, the weight for comparison with the output of the second counter 36 may be changed.

In the first to fourth embodiments, the tracking signal is detected using a so-called one-beam push-pull method. However, if the tracking signal is detected, a one-beam phase difference method, a three-beam method, etc. The gist of the present invention does not change in any method.

In the first and fourth embodiments, a filter having a frequency characteristic corresponding to the average period of the wobble signal is inserted into the tracking signal, but may be inserted into the focus signal. It is needless to say that, similarly to the tracking signal, it is desirable to remove noise by a filter having an optimum frequency characteristic according to the reproduction linear velocity.

Further, in the fourth embodiment, when the tracking deviation is detected, the frequency characteristic of the filter for the tracking signal is fixed. However, the filter for the information signal (EFM signal), the address signal (ADIP), the focus signal and the like are fixed. The frequency characteristics may be fixed.

The filter in the information reproducing apparatus according to the present invention may be either an analog filter or a digital filter. In the case of a digital filter, any of a recursive type (IIR type) and a non-recursive type (FIR type) can be used. It may be.

Further, the information treated as a period in the present invention has the same concept as a concept even when treated as a frequency, and there is no change in the spirit of the present invention.

[0076]

As described above, the information reproducing apparatus according to the first invention of the present invention has a filter for correcting the frequency characteristic in the servo means, and has a period previously recorded along the track and having a period different from that of the information signal. It has period information detection means for detecting the period information signal, and average period detection means for detecting the average period of the period information signal. The filter has a frequency characteristic corresponding to the average period, so that the filter always has an optimum characteristic corresponding to the reproduction linear velocity. It is possible to remove the noise of the servo signal by using a filter having an appropriate frequency characteristic.

Further, the information reproducing apparatus according to the second invention has
Information signal detection means for detecting an information signal recorded on the track, a filter for correcting the frequency characteristics of the information signal,
Period information detection means for detecting a period information signal recorded in advance along a track and having a period different from the information signal,
An average period detecting means for detecting an average period of the period information signal is provided. Since the filter has a frequency characteristic characteristic corresponding to the average period, the information signal is always used by using a filter having an optimal frequency characteristic corresponding to the reproduction linear velocity. , And stable operation can be performed even in a region where the information signal is missing.

Further, the information reproducing apparatus according to the third aspect of the present invention
Wobble detecting means for detecting a meandering component of the track and outputting a wobble signal; average cycle detecting means for detecting an average cycle of the wobble signal; and F for FM demodulating the wobble signal.
M demodulation means and a filter for correcting the frequency characteristic of the signal subjected to FM demodulation. Since the filter has a frequency characteristic corresponding to the average period, a filter having an optimum frequency characteristic always corresponding to the reproduction linear velocity is used. Thus, the periodic noise of the wobble signal can be effectively removed.

Further, the information reproducing apparatus according to the fourth aspect of the present invention
By fixing the frequency characteristics of the filter when the tracking servo loop is opened or when it is detected that the tracking servo has deviated, the filter with the optimal frequency characteristics according to the reproduction linear velocity can be used for various signals. It is possible to correct frequency characteristics and remove noise by using the tracking servo loop during a transient state such as when starting playback or during access, or when tracking servo is disabled due to disturbance vibration or a defect on the disk. In the case of deviation, the frequency characteristics of the filter are prevented from becoming unstable, and the operation stability is improved.

Further, in addition to the above-mentioned invention, the information reproducing apparatus according to the present invention uses a digital filter based on a sampling cycle corresponding to the average cycle, and makes the sampling cycle shorter than the average cycle, or reduces the sampling cycle to 1 / the average cycle. N (N is an integer of 2 or more), or the sampling period is set to の of the average period, or the period of the period information signal is counted by a predetermined clock to obtain the average value, and the predetermined clock or n A second counter synchronized with a clock having a cycle of / m times (n and m are each an integer of 1 or more) is provided, and the output value of the second counter and the average value are compared after performing predetermined weighting, By providing a recursive or non-recursive digital filter whose sampling period is the timing based on the comparison result, A digital filter that is synchronized with the average frequency of the previously recorded periodic information signal and that is oversampled at an arbitrary magnification can be easily configured to correct frequency characteristics and remove noise even in a high frequency range exceeding the frequency band of the periodic signal. It can be done effectively.

[Brief description of the drawings]

FIG. 1 is a block diagram showing main components of an information reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a specific configuration example of an average period detecting unit and a filter in the information reproducing apparatus.

FIG. 3 is a block diagram showing a specific configuration example of a filter in the information reproducing apparatus.

FIG. 4 is a frequency characteristic diagram showing an example of a frequency characteristic of a filter in the information reproducing apparatus.

FIG. 5 is a waveform chart showing operation waveforms of respective parts of the information reproducing apparatus.

FIG. 6 is a block diagram showing main components of an information reproducing apparatus according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing main components of the information reproducing apparatus according to the third embodiment;

FIG. 8 is a block diagram showing main components of an information reproducing apparatus according to the fourth embodiment.

FIG. 9 is a block diagram showing main components of a conventional information reproducing apparatus.

FIG. 10 is a schematic diagram showing a state of a micro meandering (wobble) of a track of an MD (mini disc).

FIG. 11 is a schematic diagram showing a general method of detecting a tracking signal.

FIG. 12 is a frequency characteristic diagram showing characteristics of a filter in a conventional information reproducing apparatus.

[Explanation of symbols]

 Reference Signs List 1 disc 2 motor 3 optical pickup 6 focus detecting means 9 tracking detecting means 12 wobble detecting means 13 address decoding means 14 information signal detecting means 18 information decoding means 20 average period detecting means 22 tracking filter 32 first counter 36 second counter Reference Signs List 40 average value detection means 41 coefficient unit 42 comparator 61 periodic filter 70 EFM filter 81 tracking out detection means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D090 AA01 BB03 CC04 DD03 DD05 FF02 FF05 GG09 GG22 5D118 AA13 BA01 BB03 BC08 BC13 BD02 BF03 BF16 BF17 CA04 CD02 CD03

Claims (16)

[Claims] 1. An information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam, wherein a focal point of the light beam is focused on the recording surface. A servo unit including a focus servo loop to follow and a tracking servo loop to follow the track; a filter for correcting frequency characteristics in the servo unit; and a pre-recorded along the track and different from the information signal A period information signal detecting unit that detects a period information signal having a period; and an average period detecting unit that detects an average period of the period information signal, wherein the filter corrects a frequency characteristic according to the average period. Information reproducing device. 2. The information reproducing apparatus according to claim 1, wherein the filter corrects a frequency characteristic of the focus servo loop. 3. The information reproducing apparatus according to claim 1, wherein the filter corrects a frequency characteristic of the tracking servo loop. 4. An information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam, wherein a focus of the light beam follows the recording surface. A focus servo unit that forms a focus servo loop to be generated; a tracking signal generation unit that generates a tracking signal indicating a relative position between the light beam and the track; and a tracking that causes the light beam to follow the track based on the tracking signal. Tracking servo means forming a servo loop; a filter for correcting a frequency characteristic of the tracking signal; a tracking error detecting means for detecting that the tracking servo has deviated based on an output of the filter; Recorded in advance and different from the information signal A period information detection unit that detects a period information signal having a predetermined period, and an average period detection unit that detects an average period of the period information signal, wherein the filter corrects a frequency characteristic according to the average period. An information reproducing apparatus characterized by the above-mentioned. 5. An information reproducing apparatus for reproducing an information signal by irradiating a predetermined track formed on a recording surface of a disk-shaped recording medium with a light beam, wherein a focus of the light beam follows the recording surface. A servo unit including a focus servo loop to be followed and a tracking servo loop to follow the track; an information signal detecting unit to detect the information signal recorded on the track; a filter to correct a frequency characteristic of the information signal; A period information signal that is recorded in advance along a track, and detects a period information signal having a period different from the information signal; and an average period detection unit that detects an average period of the period information signal. An information reproducing apparatus for correcting a frequency characteristic according to the average period. 6. The information reproducing apparatus according to claim 1, wherein the periodic information signal is a signal recorded by meandering of a track. 7. The method according to claim 1, wherein the periodic information signal is a signal recorded by pre-pits.
An information reproducing device according to any one of the above. 8. An information reproducing apparatus for reproducing an information signal by irradiating a light beam to a track of a disc-shaped recording medium having a track meandering on a recording surface in accordance with an FM-modulated signal, Servo means including a focus servo loop for causing the focus of the light beam to follow the recording surface and a tracking servo loop for following the track; wobble detection means for detecting a meandering component of the track and outputting a wobble signal; An average period detection unit that detects an average period of the wobble signal; an FM demodulation unit that performs FM demodulation of the wobble signal; and a filter that corrects a frequency characteristic of the FM-demodulated signal. An information reproducing apparatus, wherein the frequency characteristic is corrected according to the information. 9. The information according to claim 1, wherein a frequency characteristic of the filter is fixed when the tracking servo loop is opened or when it is detected that the tracking servo has been deviated. Playback device. 10. The information reproducing apparatus according to claim 1, wherein the filter is a digital filter that operates based on a sampling cycle according to an average cycle. 11. The information reproducing apparatus according to claim 10, wherein the sampling period is shorter than the average period. 12. The sampling period is 1 / the average period.
The information reproducing apparatus according to claim 11, wherein N is an integer of 2 or more. 13. The information reproducing apparatus according to claim 12, wherein N = 2. 14. The average period detecting means counts the period of the period information signal or the wobble signal with a predetermined clock to obtain an average value thereof, and calculates the average value of the predetermined clock or its n.
A second counter synchronized with a clock having a cycle of / m times (n and m are each an integer of 1 or more) is provided, and the output value of the second counter is compared with the average value after performing predetermined weighting. 14. The information reproducing apparatus according to claim 10, wherein the digital filter sets a timing based on the comparison result as a sampling period. 15. The information reproducing apparatus according to claim 10, wherein the digital filter is a recursive type. 16. The information reproducing apparatus according to claim 10, wherein the digital filter is of a non-recursive type.