JP2823017B2 - Optical disc playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and more particularly, to an optical disk reproducing apparatus suitable for applying to an optical disk reproducing apparatus which records a recording signal by utilizing a lateral displacement of a groove. Things.

B. Summary of the Invention In an optical disk reproducing apparatus, the present invention obtains envelope information of a reproduced signal from a reproduced signal generated based on an output signal obtained from a light receiving element, and obtains a signal level of the reproduced signal based on the envelope information. Is corrected, the recorded signal can be reliably reproduced.

C Prior Art Conventionally, in this type of optical disc reproducing apparatus, a groove (hereinafter referred to as a groove) extending in a circumferential direction of the optical disc.
There has been proposed a method of recording desired data by utilizing the lateral displacement of the data.

That is, in FIG. 3, reference numeral 1 denotes an optical disk device as a whole, and the optical disk 2 is driven by a spindle motor 3 to rotate at a predetermined rotational speed.

On the optical disc 2, the groove 4 the depth with respect to the wavelength lambda of the light beam LA1 to be irradiated on the optical disc 2 becomes the value lambda / 8 is formed concentrically at predetermined Toratsukupitsuchi T _P, the groove 4 is ± 0.05 to ± 0 depending on the recording signal.
The optical disc 2 is displaced in the radial direction within a range of about 1 [μm] (that is, the optical disc 2 is laterally displaced).

On the other hand, the semiconductor laser 5 emits a light beam LA having a wavelength λ.
1, the light beam LA1 is focused on the groove 4 via the condenser lens 6, the half mirror 7, and the objective lens 8, and the resulting reflected light beam is received in the extension direction of the groove 4. The light is condensed on an optical detector 9 (hereinafter, referred to as a two-divided optical detector) obtained by dividing the surface into two parts via an objective lens 8 and a half mirror 7.

The optical splitter 9 splits the output signal into an amplifier circuit 10 and
Output to the subtraction circuit 12 via 11.

As a result, as shown in FIG. 4, a difference signal _SPP whose signal level changes in accordance with the lateral displacement amount of the groove 4 is obtained via the subtraction circuit 12, and the displacement amount of the groove 4 is detected. The data recorded on the disk 2 can be reproduced.

In the optical disc reproducing apparatus issues the way this type D invention is to provide, since the groove 4 is formed in Toratsukupitsuchi T _P, the signal level of the difference signal S _PP is relative displacement of the groove 4 It varies sinusoidally with a period of Toratsukupitsuchi T _P.

In this case, in order to detect the displacement with high accuracy, it is necessary to detect the displacement of the groove 4 within a range in which the signal level of the difference signal _SPP changes linearly.

Specifically, if you set the Toratsukupitsuchi T _P to 1.6 [μm], the maximum and minimum values of the signal levels of ± 0.1 [μm] or less of the range (difference signal S _PP to displacement of the groove 4 About 40%), the difference signal S _PP
Changes in proportion to the amount of displacement within a practically sufficient range.

In particular, in the case of recording using the lateral displacement of the groove 4, a high CN (carrer p) can be obtained even with a displacement of about several tens [nm].
since it is possible to obtain a difference signal S _PP in er noize) ratio, even if you set the displacement amount in the minute range of ± 0.1 [μm] or less, it is considered possible to detect the displacement amount with high accuracy.

However, as shown in FIG. 5, when thus displacement is very small, due tracking error, there is a problem that the envelope of the differential signal S _PP varies greatly.

That is, in this type of optical disc reproducing apparatus,
The accuracy of tracking control is still insufficient compared to the amount of displacement, and ± 0.1 [μm] for ordinary optical disc devices
The tracking control of the light beam is performed with the following accuracy.

In this case, when a tracking error of about ± 0.1 [μm] occurs, the relative position of the groove 4 to the light beam is ± 0.1 [μm] as in the case where the groove 4 is displaced in the lateral direction.
Since the m] displacement, the DC level of the difference signal S _PP varies in accordance with the tracking error amount.

Accordance connexion, in case of reproducing the recorded signal from the eye pattern of the difference signal S _PP is due to the variation of the DC level, it becomes difficult to reliably reproduce the recorded signal.

The present invention has been made in consideration of the above points, and has as its object to propose an optical disc reproducing apparatus capable of reliably reproducing a recording signal recorded by lateral displacement of a groove.

E. Means for Solving the Problem In order to solve such a problem, in the present invention, a groove extending in the circumferential direction is provided, and by providing a displacement in a direction orthogonal to the extending direction of the groove, desired data can be obtained. In an optical disc reproducing apparatus for reproducing a recorded optical disc, a light receiving means for receiving reflected light of a light beam applied to a groove of the optical disc, and a signal corresponding to a displacement of the groove based on an output signal from the light receiving means Reproduction signal generation means for generating a reproduction signal whose level changes, filter means for extracting an envelope of the reproduction signal from the reproduction signal generated by the reproduction signal generation means, and reproduction signal generated by the reproduction signal generation means And the difference between the output signal output from the filter means and the reproduced signal generated by the tracking error. And a correction means for correcting the fluctuation of the DC component.

F action The envelope of the reproduction signal is extracted from the reproduction signal by the filter means, and the difference between the reproduction signal and the output signal of the filter means is calculated, whereby the fluctuation of the DC component of the reproduction signal caused by the tracking error is calculated. With the correction, the fluctuation of the DC component due to the tracking error is corrected, and the recorded data recorded by the displacement of the groove can be reliably reproduced from the reproduction signal.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. 3 are assigned the same reference numerals, reference numeral 15 denotes an optical disk device as a whole, and binary recording is performed by switching the amount of displacement of the groove 4 up and down relative to the track center. The recorded signal is reproduced from the optical disk 16 on which the signal is recorded.

That lowpass filter circuit 21, by extracting and outputting tracking error signal S _TE from the difference signal S _PP to tracking control circuit 23, adapted to constitute a tracking servo circuit as a whole, thereby the light beam LA1 Is tracked to a predetermined groove 4.

Therefore, the low-pass filter circuit 21 adjusts the cut-off frequency of the servo band so that the phase characteristic of the tracking servo circuit does not change within a frequency band (hereinafter, referred to as a servo band) required for correcting the tracking error. On the other hand, it is composed of a primary filter circuit whose frequency band is about 10 times.

On the other hand, the low-pass filter circuit 22 is composed of a secondary filter circuit whose cut-off frequency is the cut-off frequency of the servo band, and thereby converts the low-frequency signal S _LP equal to or lower than the cut-off frequency from the difference signal S _PP to the phase. Is extracted so as not to disturb.

Thus, as shown in FIG. 2, the via a low-pass filter circuit 22, the difference signal S _PP low frequency signal signal level according to variation of the envelope of (FIG. 2 (A)) from the difference signal S _PP is changed S _LP (FIG. 2 (B)) can be obtained, whereby the envelope information of the difference signal S _PP can be obtained.

The differential amplifier circuit 24 receives the low-frequency signal S _LP and the difference signal S _PP , thereby _changing the envelope of the difference signal S _PP to the low-frequency signal S _PP.
A difference signal S _OUT (FIG. 2 (C)) clamped at the signal level of _LP is output.

Thus it is possible to envelope via the differential amplifier circuit 24 to obtain a difference signal S _OUT that is corrected to a certain signal level, ensuring recording signal thereby outputting the difference signal S _OUT to a predetermined signal processing circuit Can be played.

In practice, in this type of optical disk device, since the displacement amount is very small, not only tracking errors but also dust, scratches and dirt on the optical disk, and insufficient servo gain of the tracking servo circuit, etc. even Niyotsu, there is a problem that the envelope of the differential signal S _PP is varied.

Accordance connexion In this embodiment, on the basis of the envelope information extracted from the difference signal S _PP, by the variation of the envelope was corrected, not only tracking error,
By correcting the variation of the envelope of the difference signal S _PP produced Te cowpea to dust on the optical disk can be reproduced reliably recorded signal.

Further, in this type of optical disk device, there is a type in which the frequency band of a recording signal is widened and its spectrum penetrates into a servo band. In such an optical disk device, a difference signal _SPP is _generated . There is a problem that it is difficult to obtain a difference signal _SOUT having no fluctuation in the envelope simply by band separation.

However, as in this embodiment, on the basis of the envelope information extracted from the difference signal S _PP, if so as to correct the variation of the envelope, the spectrum of the recording signal is have up for optical disc system such as entering the servo band Also, the fluctuation of the envelope can be corrected, and the recorded signal can be reliably reproduced.

In the above configuration, the two-divided light Deitekuta 9, the signal level in response to the lateral displacement of the groove 4 the difference signal S _PP to change is obtained, tracking error signal S _TE and low respectively pass filter circuit 21 and 22 The frequency signal S _LP is extracted.

Tracking error signal S _TE is output to the tracking control circuit 23, thereby the light beam is tracking controlled to a predetermined groove 4.

Low-frequency signal S _LP contrast is output to the differential amplifier circuit 24, thereby the difference signal S envelope of _PP, low-frequency signal S difference signal is obtained by clamping the signal level of the _LP S _OUT
Is output.

According to the above configuration, it extracts the envelope information from the difference signal S _PP via a low-pass filter circuit 22, by correcting the signal level of the difference signal S _PP based on the envelope information, to correct the variation of the envelope Thus, the recorded signal can be reliably reproduced.

In the above-described embodiment, the case where a recording signal composed of a binary digital signal is reproduced has been described. However, the recording signal is not limited to a binary digital signal, but may be a ternary or more digital signal, or an analog signal. The present invention can be widely applied, for example, when reproducing a recorded signal.

Further, in the above-described embodiment, the case where the secondary low-pass filter circuit is used to extract the envelope information has been described. However, the low-pass filter circuit is not limited to the secondary, and various low-pass filter circuits can be widely applied. it can.

Furthermore, in the above-described embodiment, the case where the cut-off frequency of the low-pass filter circuit is set to the cut-off frequency of the servo band has been described. What is necessary is just to set so that it can correct within a suitable range.

Furthermore, in the above-described embodiment, the case where the envelope of the difference signal is clamped at the low-frequency signal level in the differential amplifier circuit has been described. However, the clamp means is not limited to the differential amplifier circuit, and various clamp means can be widely used. Can be applied.

As described above, according to the present invention, the tracking error is extracted by extracting the envelope of the reproduction signal from the reproduction signal by the filter means and calculating the difference between the reproduction signal and the output signal of the filter means. Thus, the variation of the DC component of the reproduced signal caused by the correction can be corrected, so that the variation of the DC component due to the tracking error can be corrected. Thus, the recorded data recorded by the displacement of the groove from the reproduced signal can be reliably obtained. Thus, an optical disc reproducing apparatus capable of reproducing information in a short time can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical disk device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining its operation, FIG. 3 is a block diagram showing a conventional optical disk device,
FIG. 4 is a characteristic curve diagram for explaining the operation, and FIG. 5 is a signal waveform diagram for explaining the problem. 1, 15 ... optical disk device, 2, 16 ... optical disk, 4
…… Groove, 21, 22 …… Low-pass filter circuit, 24…
... Differential amplifier circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-43839 (JP, A) JP-A-61-120379 (JP, A) JP-A-63-181134 (JP, A) JP-A-63-181134 148427 (JP, A) Fully open 60-6020 (JP, U)

Claims (1)

(57) [Claims] 1. A circumferentially extending groove is provided,
An optical disc reproducing apparatus for reproducing an optical disk on which desired data is recorded by providing a displacement in a direction orthogonal to the extending direction of the groove, comprising: a light receiving device for receiving reflected light of a light beam applied to the groove of the optical disk; Means, a reproduction signal generation means for generating a reproduction signal whose signal level changes in accordance with the displacement of the groove, based on an output signal from the light receiving means, and the reproduction generated by the reproduction signal generation means. Filtering means for extracting an envelope of the reproduction signal from the signal; and calculating a difference between the reproduction signal generated by the reproduction signal generation means and an output signal output from the filter means, thereby causing a tracking error. Correction means for correcting a change in the DC component of the reproduction signal that occurs. Reproducing apparatus.