JPH06139602A - Tracking error detection circuit for optical disk device - Google Patents

Abstract

PURPOSE:To improve tracking accuracy by generating a continuously effective tacking error signal for a recording track having a preformat form using a three beam method jointly with a heterodyne method. CONSTITUTION:The photoelectric conversion signals of light beams corresponding to subspots for tracking are supplied from photo-detectors 52, 53 to average light quantity detection parts 54, 55, averaged and the fluctuation of the photoelectric conversion signal caused by a pit for preformatting is compensated. The outputs S54, S55 of detection parts 54, 55 are sent to an error detection part 56 having three beam system and the mutual difference is detected. On the other hand, a quadripartite photodetector 51 outputs four photoelectric conversion signals corresponding to a main spot to an error detection part 57 with a heterodyne system and the detection part 57 detects the phase of a dyagonal signal which is two sets of sum signals located at the dyagonal positions with each other based on the total sum of the four signals. A signal synthesizing part 58 synthesizes respective outputs of the detection parts 56, 57 and generates a tracking error signal ST.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to recording (writing) of information.
The present invention relates to a track error detection circuit of a rewritable and write-once type optical disc device capable of performing the above.

The magneto-optical disk device which has already been put into practical use as a rewritable optical disk device has a larger storage capacity per disk as a recording medium than a magnetic disk device, and moreover, like the flexible disk, the disk is exchanged. Since it can be freely used, it is rapidly spreading as an external storage device for computers.

Therefore, in order to improve the compatibility of the disc and to facilitate the use, a disc structure standard has been established. Along with this, it has become necessary to realize highly accurate tracking in a magneto-optical disk device that uses a disk conforming to the standard.

[0004]

2. Description of the Related Art In an optical disk device, optical system servo control for causing a light beam to follow a recording track to be accessed, that is, tracking for positioning a light spot in the radial direction of a disk (optical disk or magneto-optical disk) is essential. is there.

In the read-only type optical disk device, the position of the recording track in the disk radial direction is specified by the pit row corresponding to the recorded information. In addition, in the write-once and rewritable optical disk devices, the position of a recording track is specified by a spiral pre-groove provided in advance on the disk.

Various methods such as a three-beam method, a push-pull method, and a heterodyne method are known as methods for detecting a track error (positional deviation of a light spot with respect to a recording track).

In the three-beam method, three light beams are incident on a disc so that a main spot for recording or reproducing information is formed and sub-spots are formed at points symmetrical with respect to the main spot. Then, the relative value of the reflected light amount of the two light beams corresponding to the sub-spot (the light amount of the light beam reflected by the disk and traveling toward the detector) is detected.

Further, the push-pull method is a method of detecting a reflected light amount distribution in a light spot according to diffraction generated at an edge of an optical step (a pit or the like) on a disc by using a two-divided photodetector. Compared with the three-beam method, this method has an advantage that the optical system can be simplified because a diffraction grating that divides the light beam is not necessary, but it is greatly affected by beam shift and disc tilt due to minute movement of the lens. Therefore, there is a drawback in that it is disadvantageous in terms of tracking accuracy.

The heterodyne method is disclosed in JP-A-2-12242.
As disclosed in Japanese Patent Publication No. 8, a method of detecting a phase of a diagonal difference signal which is a difference between two pairs of sum signals at diagonal positions with reference to the total sum of four output signals of a four-division photodetector. is there.

The magneto-optical disk device records information by forming a specific magnetic domain region and reproduces the information by utilizing the magnetic Kerr effect. Although it is possible in principle to form the magnetic domain region in the pre-groove, on-land recording in which the magnetic domain region is formed between the pre-grooves (lands) is advantageous in terms of the S / N ratio of the reproduced signal. Therefore, the on-land recording method (that is, the method using the land portion as a recording track) is also adopted in the international standard.

Further, in the magneto-optical disk device, in order to facilitate access to the recording track, each sector obtained by dividing the recording track is further provided with a header part (also referred to as a ROM part) and a data part (a part forming a magnetic domain area). The so-called pre-format, in which data management information such as track number and sector number or index information is written in advance in the header part, is becoming popular. The pre-formatting is performed by forming pits, and the depth of the pits is defined as λ / 4n (λ is the wavelength of the light beam, n is the refractive index of the disk substrate) which is twice the depth of the pre-groove. The pit is read by detecting the amount of reflected light according to the presence or absence of the pit.

When a pre-formatted disc, that is, a disc in which pits are formed on a part of the land portion (header portion) is used, a continuous effective track error signal is generated by the three-beam method and the heterodyne method. Can't get

That is, according to the three-beam method, FIG.
As shown in FIG. 5, in the data portion ED having no pits, a pair of sub-spots SS1 and SS2 that sandwich the main spot MS.
If the distance is properly selected, the track error can be properly detected by utilizing the difference in reflectance between the land portion LA and the pre-groove PG. However, as shown in FIG. 3A, in the header portion EH having the pits P, when one of the sub-spots SS1 overlaps the pits P, the reflected light amount of the sub-spot SS1 changes to the sub-spot SS2 on the pre-groove PG. Since the amount of reflected light is less than that of, the correct track error signal cannot be obtained.

On the contrary, according to the heterodyne method, although the track error can be detected in the header portion EH, since the diffraction by the leading edge and the trailing edge of the pit P is used,
The data portion ED without the pit P cannot detect it.

Therefore, in the conventional magneto-optical disk device, the track error is detected by the push-pull method. According to the push-pull method, the optical step is λ
In the case of / 4n, the distribution of the amount of reflected light becomes uniform regardless of the presence or absence of a step. Therefore, the pit P having a depth of λ / 4n has almost no effect on the detection, and the diffraction generated at the edges on both sides of the land LA is suppressed. It is possible to continuously obtain a valid track error signal.

[0016]

However, as described above, in the track error detection by the push-pull method, a DC offset is generated in the error signal due to the beam shift and the tilt of the disk, and the offset is shifted by the offset amount. In this state, the light spot follows the recording track, and the tracking accuracy is impaired.

In view of the above problems, the present invention has an object to improve the tracking accuracy of an optical disk device using a preformatted disk.

[0018]

In order to solve the above-mentioned problems, a detection circuit according to the invention of claim 1 is an optical beam for forming a main spot for recording / reproducing on a disc as shown in FIG. A four-division photodetector 51 for detecting the amount of reflected light, and two photodetectors 52, 53 for detecting the amount of reflected light of each of the light beams forming the sub-spots for tracking on both sides of the main spot. An average light amount detection unit 54 for averaging the photoelectric conversion signals of the photo detectors 52 and 53,
55, and the output signal S of each of the average light intensity detection units 54 and 55.
54 and S55, a three-beam type error detection unit 56, a heterodyne type error detection unit 57 that detects the phase of a diagonal difference signal corresponding to the four photoelectric conversion signals of the four-division photodetector 51, and the three Beam system error detector 56 and the heterodyne system error detector 5
And a signal synthesizing section 58 for outputting a synthesized signal of the detection signals of No. 7 as a track error signal ST.

In the detection circuit according to the second aspect of the present invention, the signal synthesizing section 58 comprises a high-pass filter 90 for cutting off the DC component of the output signal of the three-beam type error detecting section 56.

[0020]

[Operation] By using the three-beam method and the heterodyne method together,
A continuously effective track error signal ST is generated for the preformatted recording track.

That is, the photo detectors 52, 53
Outputs photoelectric conversion signals of the light beam corresponding to the tracking sub-spots, respectively. These photoelectric conversion signals are averaged by the average light intensity detectors 54 and 55, whereby the fluctuations of the photoelectric conversion signals due to the pits for preformatting are compensated. Each average light amount detection unit 54, 55
The output signals S54 and S55 are sent to the three-beam method error detection unit 56, and their differences are detected. The output signal of the 3-beam type error detection unit 56 becomes a valid track error signal in the data portion having no pit.

On the other hand, the four-division photo detector 51 outputs four photoelectric conversion signals corresponding to the main spots for recording and reproduction. The heterodyne method error detector 57
The phase of the diagonal difference signal, which is the difference between the two sets of sum signals at the diagonal positions, is detected based on the total sum of the four photoelectric conversion signals.
The output signal of the heterodyne type error detection section 57 becomes a valid track error signal in the header section having pits.

The signal combiner 58 combines the output signals of the three-beam type error detector 56 and the heterodyne type error detector 57 to generate a track error signal ST. At that time, the high-pass filter 90 blocks the DC component of the output signal of the three-beam method error detection unit 56.

In the three-beam type error detector 56, the light amount of the side spot is smaller than that of the main spot by about one digit, and a high amplification factor is required in the circuit, so that the circuit offset easily occurs. On the other hand, in the heterodyne method, since the offset is canceled in a time division manner by switching the polarity, the circuit offset of the heterodyne type error detection unit 57 is small. Therefore, by blocking the DC component of the output signal of the 3-beam type error detection unit 56, the track error detection circuit 50 becomes an error detection system with a small circuit offset as a whole.

[0025]

FIG. 2 is a circuit diagram showing an example of the configuration of a track error detection circuit 50 according to the present invention. In the figure,
The components corresponding to those in FIG. 1 are designated by the same reference numerals.

The average light amount detecting section 54 comprises a voltage follower using an operational amplifier 61. The upper limit of the effective gain band of the operational amplifier 61 is selected to be a value sufficiently lower than the recording frequency of information by the pits, whereby a signal obtained by averaging the photoelectric conversion signals of the photodetector 52 can be obtained. The average light amount detection unit 54 also includes a voltage follower using an operational amplifier 62.

The three-beam type error detector 56 is composed of a subtractor using an operational amplifier 63, and the average light amount detector 5
A signal corresponding to the difference between the output signals S54 and S55 of 4, 55 is output to the signal synthesizing unit 58 as a data portion error signal S56.

On the other hand, the heterodyne type error detector 57
Is composed of adders 71, 72, 74, a differential amplifier 73, a differentiating circuit 81, a comparator 75, a polarity inverter 82, and the like.

The photoelectric conversion signals corresponding to the two light receiving surfaces arranged in one diagonal direction of the four-division photo detector 51 are:
It is synthesized by the adder 71. Further, the photoelectric conversion signals corresponding to the two light receiving surfaces arranged in the other diagonal direction are combined by the adder 72.

The outputs of the adders 71 and 72 are input to the differential amplifier 73 and the adder 74 via the high-pass capacitors, respectively. Output signal S73 of the differential amplifier 73
Is a so-called diagonal difference signal, and the output signal S73 of the adder 74 is the sum signal of the photoelectric conversion signals corresponding to the four light receiving surfaces.

The output signal S73 (summation signal) is differentiated by a differentiation circuit 81 composed of a capacitor and a resistor, and then input to the comparator 75. Comparator 75
Determines the polarity of the differential signal S81, and the determination signal S7
5 is output to the polarity inverter 82.

The polarity inverter 82 is composed of an output switching unit (balanced modulation circuit) 77 composed of a multiplier and a differential amplifier 76 substantially composed of an integrator, and based on the discrimination signal S75, a diagonal difference signal S73. A signal of one of the two polarities is inverted and then integrated (smoothed), and the resultant signal is output to the signal synthesis chart 58 as a header error signal S82.

Signal synthesis FIG. 58 is composed of a high-pass filter 90 made of a capacitor and an inverting amplification section made of an operational amplifier 78 and the like, and the DC cut component of the data error signal S56 and the header error signal S82 are added. And the signal as a track error signal ST.

According to the above-described embodiment, it is possible to surely detect the track error by the heterodyne method for each sector of the recording track, and to increase the frequency so as to cut off a component of a frequency sufficiently lower than the detection interval. By selecting the characteristics of the bandpass filter 90, the three-beam method error detection unit 5
Stable tracking can be realized by reducing the influence of the circuit drift of 6.

[0035]

According to the present invention, even when a preformatted disc is used, it is possible to perform highly accurate tracking with little influence of beam shift and disc tilt.

According to the invention of claim 2, the tracking accuracy can be further improved.

[Brief description of drawings]

FIG. 1 is a principle block diagram showing a configuration of the present invention.

FIG. 2 is a circuit diagram showing an example of a configuration of a track error detection circuit according to the present invention.

FIG. 3 is a plan view showing how track errors are detected by a three-beam method in a preformatted disc.

[Explanation of symbols]

 51 4-division photo detector 52, 53 Photo detector 54, 55 Average light intensity detector S54, S55 Output signal 56 3-beam error detector 57 Heterodyne error detector 58 Signal combiner ST Track error signal 90 High-pass filter

Claims (2)

[Claims] 1. A four-division photodetector (51) for detecting the amount of reflected light of a light beam forming a recording / reproducing main spot on a disk, and tracking sub-spots on both sides of the main spot. Two photo detectors (52) (53) for detecting the respective reflected light amounts of the light beams, and an average light amount detection unit (54) (5) for averaging the photoelectric conversion signals of the photo detectors (52) (53), respectively.
5) and the output signals (S) of the average light intensity detection units (54) and (55).
54) (S55) 3-beam system error detection unit (56), and heterodyne system error detection that detects the phase of the diagonal difference signal corresponding to the four photoelectric conversion signals of the 4-split photodetector (51). A section (57) and a signal combining section (58) for outputting a combined signal of the detection signals of the three-beam method error detecting section (56) and the heterodyne method error detecting section (57) as a track error signal (ST). A track error detection circuit for an optical disk device, comprising: 2. The signal synthesizer (58) comprises a high-pass filter (90) for blocking a DC component of an output signal of the three-beam method error detector (56). 2. A track error detection circuit of the optical disk device described in 1.