JP2695191B2 - Tracking error detection method - Google Patents

Description

The present invention relates to a tracking error detecting method for detecting a tracking error in an information storage device such as an optical disc device which uses an optical information storage medium such as an optical disc, an optical tape, an optical card, or the like. Regarding

[Conventional technology]

Conventionally, a tracking error detecting method in an information storage device such as an optical disc device using an optical information storage medium provided with wobbled pits is known from Japanese Patent Laid-Open No. 62-183037.

4 to 7 are explanatory views of this tracking error detecting method. In FIG. 4, reference numerals 1 and 2 denote the center lines of adjacent information tracks on an optical information storage medium such as an optical disc, and 3, 4, 5, and 6 are left and right with respect to these center lines 1 and 2, respectively. It shows a pair of wobbled pits that are offset by the same distance on both sides) and are offset by a predetermined distance in the front-rear direction on center lines 1 and 2. Reference numerals 7 and 8 denote pits for timing marks, and reference numeral 9 denotes a spot of a converged laser beam applied to the optical information storage medium. The spot 9 of the condensed laser beam relatively moves and scans on the information track at a constant speed.

FIG. 5 shows an example of an optical system (pickup) for detecting a signal from an optical information storage medium. An optical disc 12 having a transparent substrate 10 and an information recording surface 11 including concave and convex pits is driven to rotate at a constant rotational speed or a constant linear speed by a spindle motor 13. On the other hand, the laser beam emitted from the laser diode 14 is collimator lens 15, polarizing prism 16,
The information recording surface 11 of the optical disc 12 is irradiated with a light spot diameter of about 1 μm full width at half maximum by a condensing lens 18 having a quarter-wave plate 17 and a numerical aperture of about 0.5, and the spot is irradiated on the optical disc.
The 12 information tracks are scanned at a constant speed, and the reflected light is re-entered into a recursive optical system consisting of a polarizing prism 16, a quarter-wave plate 17, and a condensing lens 18, reflected by the polarizing prism 16, and detected. The signal 19 is detected by the detector 19 as a change in the amount of reflected light, and a reproduced signal a is obtained.

The wobbled pits 3, 4, 5, 6 and the pits 7, 8 for timing marks have a depth of λ / 4 (λ is the wavelength of the laser beam).
It is an uneven pit of a degree, and on this uneven pit, a light reflecting layer such as a metal film or a metal such as Te, Se, Bi, Ti, an alloy, a cyanine dye, a triphenylmethane dye, a squarylium dye, a pyrylium dye, etc. A light absorbing / reflecting recording film or a magneto-optical recording film is provided. The light intensity of the focused beam spot 9 is weakened to such an extent that the shape of the concave and convex pits is not changed, and the focused beam spot 9 moves along the information track, and a time series signal as shown in FIG. 6 is obtained as the reproduction signal a by the optical system. To be In FIG. 6, 20 and 21 are signals corresponding to the wobbled pits 3, 4 or 5, 6, and 22 is a signal corresponding to the timing mark pits 7 and 8. When the focused beam spot 9 is moving on the center lines 1 and 2 of the information track, the amplitudes of the signals 20 and 21 are equal to each other, but the focused beam spot 9 has The amplitude of the signal 21 becomes larger than the amplitude of the signal 20 when it shifts downward in FIG. 4, and when the focused beam spot 9 shifts upward with respect to the center lines 1 and 2 of the information track in FIG. The amplitude becomes larger than the amplitude of the signal 21. Utilizing this, the deviation of the focused beam spot 9 from the information track centerlines 1 and 2 is detected from the time-series signal a, and the tracking actuator determines the focused beam spot 9 from the information track centerline 1 based on this detection signal. , 2 and the tracking servo control is performed. The wobbled pits 3, 4, 5 and 6 are combined with the timing mark pits 7 and 8 to form a predetermined pattern (a pattern selected so as not to appear in other information signals),
The time passing of the pattern from the time-series signal a is detected by the electric circuit means, and only the signals 20 and 21 corresponding to the wobbled pits 3, 4, 5 and 6 are extracted based on the timing, and the tracking error described above is detected. The signal is obtained. In the pit train pattern composed of wobbled pits 3, 4, 5, 6 and pits 7, 8 for timing marks, 500 to 2000 sets are provided at equal intervals on one track of the optical disc 12, and the frequency band of the tracking error signal is provided. And the necessary and sufficient number of samplings are selected. To make the explanation easier to understand, as shown in FIG. 7, wobbled pits 3, 4
Alternatively, the levels of the signals 20 and 21 corresponding to 5 and 6 are A and B, the signal level of a portion of the time-series signal a without pits on the optical disk is C, and the signal 22 corresponding to the pits 7 and 8 for timing marks. , The tracking error signal TE is conventionally detected as TE = (A−C) − (B−C).

[Problems to be solved by the invention]

In the above conventional tracking error detection method, since the tracking error signal is detected by the difference in the amplitude of the signals 20, 21 corresponding to the wobbled pits 3, 4 or 5, 6, the level of the reflected light of the optical information storage medium The fluctuation causes the gain of the tracking error signal to fluctuate. For this reason, it is not possible to increase the permissible value for the fluctuation of the reflectance of the recording film of the optical information storage medium, the fluctuation of the intensity of the laser beam, the dirt of the optical system, and the fluctuation of the signal level of the information pit, which causes a practical problem. there were.

It is an object of the present invention to eliminate the above-mentioned drawbacks and provide a tracking error detection method capable of obtaining a stable tracking error signal with a small gain variation.

[Means for solving the problem]

According to the present invention, a pair of wobbled pits provided at the same distance left and right with respect to the center line of an information track in an optical information storage medium and at a predetermined distance in front and back are provided at a constant speed on the information track. The reflected light is detected while scanning with a relatively moving focused beam spot, and this detection signal is compared with a threshold value set between the pit signal level and the non-pit signal level to obtain a binary value. Then, the width of the pulse corresponding to the pair of wobbled pits in the binarized signal is detected, the difference between these pulse widths is calculated, and a tracking error signal is obtained based on this difference.

〔Example〕

The embodiment of the present invention detects the difference in the amplitudes of the signals 20, 21 corresponding to the wobbled pits 3, 4 or 5, 6 from the time series signal a as shown in FIG. 3 in the above tracking error detecting method. Rather, the time-series signal a is binarized by comparing it with a threshold Th set between the signal level of the pit and the signal level of the non-pit portion, and the wobbled pit in the binarized signal b is compared. When the pulse width corresponding to 3, 4 or 5, 6 is ΔT _A , ΔT _B and the pulse width corresponding to the timing mark pits 7, 8 is ΔT _D , the tracking error signal TE is TE = ΔT _The feature is that it is detected as _A −ΔT _B. In this case the threshold Th
May be set to the ground level with respect to the time series signal a extracted via the AC coupling circuit, and the level P of the time series signal a when the focused beam spot 9 passes through the pit center and the above level. A value intermediate to C, for example, (C + P) / 2 may be set. Therefore, the tracking error signal obtained by this embodiment is not the amplitude level of the time-series signal a affected by the manufacturing variations of the optical information storage medium and the assembly variations of the pick-up, but the pulse after binarization of the time-series signal a. Since it is based on the width, it is possible to obtain a stable tracking error signal in which the gain fluctuation hardly occurs with respect to the level fluctuation of the time series signal a.

FIG. 1 shows the circuit used in the embodiment of the present invention, and FIG. 2 is its timing chart.

The time series signal a from the photodetector 19 is input to the comparator 31 and the pattern comparator 32, and the time series signal a
Is compared with the comparison voltage (threshold value Th) of the comparison power supply 33 in the comparator 31 and binarized to form a pulse signal as shown in FIG. The output signal 34 of the comparator 31 is delayed by the delay circuits 35 and 36, respectively, and the delay time of the delay circuits 35 and 36 is generally the pulse corresponding to the wobbled pit 3 or 5 and the timing mark pits 7 and 8. The distances are different from each other by a time corresponding to the distance between each pair of wobbled pits 3, 4 or 5, 6 (approximately the time when the focused beam spot 9 passes between the pair of wobbled pits). Therefore, as shown in FIG. 2, signals 37, 38 in which the pulses having the pulse widths ΔT _A , ΔT _B corresponding to the pair of wobbled pits 3, 4 or 5, 6 are temporally overlapped are obtained from the delay circuits 35, 36. To be These signals 37 and 38 are processed by the difference calculator 39 to calculate a pair of wobbled pits.
The difference between the pulses having pulse widths ΔT _A and ΔT _B corresponding to 3, 4 or 5, 6 is taken, and a signal 40 as shown in FIG. 2 is obtained. On the other hand, the pattern comparator 32 detects whether the strong sequence signal a from the photodetector 19 is a pattern of a specific pit including a pair of wobbled pits, and outputs an output signal 41 as shown in FIG. Then, the pulse generator 42 generates a gate pulse 43 having a predetermined pulse width as shown in FIG. 2 based on the output signal 41 of the pattern comparator 32. The gate circuit 44 is the difference calculator 39
From the output signal 40 of, the pulse width ΔT _A corresponding to the pair of wobbled pits 3, 4 or 5, 6 is extracted by the gate pulse 43 from the pulse generator 42 only the portion of the difference in pulse width ΔT _B , The output signal 45 of this gate circuit 44 as shown in FIG.
Is converted into an analog signal by the integrator 46 or the like and output as a tracking error signal TE.

The circuit shown in FIG. 1 is a circuit used in one embodiment of the present invention, and the present invention can be implemented by using other well-known digital and analog electric circuits.

〔The invention's effect〕

As described above, according to the present invention, a pair of wobbled pits provided at the same distance to the left and right with respect to the center line of the information track in the optical information storage medium and at the front and rear by a predetermined distance are provided. The threshold value is set between the pit signal level and the non-pit signal level by detecting the reflected light while scanning the focused beam spot that moves relatively at a constant speed on the track. Is binarized by comparing with, and the width of the pulse corresponding to the pair of wobbled pits in this binarized signal is detected to calculate the difference between these pulse widths, and a tracking error signal is obtained based on this difference. Therefore, the reflectance of the storage film of the optical information storage medium may be different, the pit signal level of the optical information storage medium may be different, or the optical system or the signal detection circuit system may have variations. Stable tracking error signal is small gain variation is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit used in one embodiment of the present invention, FIG. 2 is a timing chart showing the operation of the circuit,
FIG. 3 is a timing chart for explaining the present invention,
FIG. 4 is a diagram showing wobbled pits and timing mark pits on the optical disc, FIG. 5 is a diagram showing an example of an optical system used for detecting a tracking error, and FIG. 6 shows signals obtained by the optical system. The waveform chart shown in FIG. 7 is a waveform chart for explaining a conventional tracking error detection method. 31 …… Comparator, 32 …… Pattern comparator, 33 …… Comparison power supply, 35,36 …… Delay circuit, 39 …… Difference calculator, 42 ……
Pulse generator, 44 …… Gate circuit, 46 …… Integrator circuit.

Claims (1)

(57) [Claims] 1. A pair of wobbled pits provided on the information track in the optical information storage medium such that a pair of wobbled pits are provided on the left and right sides of the center line of the information track and are offset from each other by a predetermined distance. The reflected light is detected while scanning with a focused beam spot that moves relatively at a speed, and this detection signal is compared with a threshold value set between the pit signal level and the non-pit signal level. It is characterized in that it is binarized, a pulse width corresponding to the pair of wobbled pits in this binarized signal is detected, a difference between these pulse widths is calculated, and a tracking error signal is obtained based on this difference. Tracking error detection method.