JPH073701B2 - Tracking servo circuit for optical recording / reproducing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a tracking servo circuit in an optical recording / reproducing apparatus, and is particularly fast when detecting wobbling pits in a servo area formed on a recordable disc. The present invention relates to a tracking servo circuit suitable for pulling in.

[Outline of Invention]

The tracking servo circuit of the present invention detects a wobbling pit formed at predetermined intervals of a track by embossing or the like to form a tracking error signal, and detects a diffractive differential signal from this wobbling pit. By doing so, the polarity of the tracking error signal is detected, and especially the time for pulling from the detrack state to the tracking servo state during eccentricity or traverse is shortened.

[Conventional technology]

An optical disc on which music or video signals are recorded can reproduce high-density information, but since such an optical disc is exclusively for reproduction, an optical disc capable of recording / erasing information has been developed in recent years. It is in the stage of practical application.

FIG. 4 shows a plan view of such a recordable optical disk (recording disk). The recording surface of the optical disk 1 is provided with a perpendicular magnetization film exhibiting a magneto-optical effect. Then, as shown in the enlarged view of FIG. 5, three concave pit groups 2A, 2B and 3 are embossed at a predetermined interval on the track T on the circumference where information is recorded. And the like, are continuously formed at a depth of λ / 4 to λ / 8 (λ is the wavelength of the laser beam). The first pick of this pit group
2A and the second pit 2B are the intervals (pitch) of the track T
When Q is Q, as shown in the enlarged view of FIG.
The third pit 3 is formed at a position shifted from the track center in directions different from each other by 1 / 4Q to detect a tracking error, and the third pit 3 is formed at the center of the track by a predetermined distance L. Used as a clock reference signal.

The next pit groups 2A ', 2B', and 3'are used as a recording area 4 for recording information by laser light.

In such a recording disk, a tracking error signal and a clock reference signal are extracted from the reflected light of the laser beam applied to the pit groups 2A, 2B and 3 at the time of recording or reproducing, and further, the tracking error signal and the clock reference signal are extracted between A focus error signal is formed by the reflected light from the mirror portion L.

The tracking error signal is obtained when the reflected light when the light spot 5 passes through the first and second pits 2A and 2B in the arrow direction is sampled.

That is, as shown in FIG. 6A, when the light spot 5 is passing on the track T in the direction of the arrow (on-track), the level of the reflected light of each pit 2A, 2B and 3 is shown in FIG. When the level becomes as shown in a and the locus of the light spot 5 passes above the track T as shown in FIG. 6B, reflected light as shown in FIG.

In addition, as shown in C of FIG.
When it is shifted to the lower side, reflected light of a level as shown by c in the figure is detected.

Therefore, if these reflected light intensities are sampled at time points T ₁ and T ₂ and the reflected light intensity Sb at T ₂ is subtracted from the reflected light intensity Sa at T ₁ , the light spot is An amount deviated from T, that is, a tracking error signal is obtained, and when the tracking servo mechanism is controlled by this sampled tracking error signal, the light spot can be controlled to always pass on the track of the optical disc. .

[Problems to be solved by the invention]

By the way, when the tracking error signal is formed by the method as described above and the position of the objective lens of the optical pickup is controlled, seek (access) to a predetermined portion of the optical disk is performed.
When a relative velocity or relative acceleration is applied between the optical pickup irradiating the light spot and the optical disk, as seen after the track jump that is performed every time, it becomes difficult to return to the tracking state again.

Hereinafter, this point will be described in detail.

As shown in FIG. 4, when the radial position of the light spot 5 is v and the track pitch is Q, the spot position v
Is equal to the track position ± mQ (m = 0, ± 1, ± 2, ± 3, ...), the tracking error signal et = Sa-
Sb = 0 and at other positions The tracking error signal et sampled by the sine wave function changes to a sine wave when the spot position v changes as shown in FIG.

As shown in the change diagram of the tracking error signal et, the tracking error signal et is 0 at the track position mQ.
However, the tracking error et is 0 even at the point where the track position is ± 1 / 2Q.

However, the point that becomes 0 at ± 1 / 2Q is that the difference signal between the 1st pit 2A and the 2nd pit 2B of the adjacent tracks is calculated. The range F of 1 / 4Q cannot be used as a tracking signal,
It is shown that a range N of ± 1 / 4Q centered on the position of mQ is a tracking error signal proportional to the deviation with respect to the track T.

Therefore, when the tracking error signal et as shown in FIG. 7 is directly supplied to the tracking servo circuit in the state where there is relative motion between the optical pickup and the optical disk (during traverse), the optical spot coincides with the track in the range of N. However, if the optical spot approaches the track in the range of F, the tracking error signal becomes large and it becomes difficult to converge (pull in) the tracking state.

Therefore, in the case of the conventional optical disc reproducing apparatus, for example,
As shown in Japanese Patent Publication No. 59-8893, the reproduction RF signal of the optical disk is detected as a pull-in during the traverse, and the level of the reproduction RF signal generated when the track is deviated and the phase of change and tracking error. It is practiced to compare the phases of the signals and extract the braking signal for pull-in.

However, such a pull-in means is effective for a reproduction-only optical disc in which a reproduction RF signal is continuously output, but in the case of an optical disc without recorded information,
It cannot be used as a retraction means.

The present invention has been made in view of such problems,
The present invention provides a tracking servo circuit which is quickly pulled in only by the information output from the first and second pits (wobbling pits) for tracking detection.

[Means for solving problems]

In the tracking servo circuit of the optical recording / reproducing apparatus of the present invention, a light receiving element in which at least two or more light receiving surfaces are formed in order to detect a wobbling pit, and a change in a fair field image obtained from the light receiving element. A sampling circuit for sampling at the detection position of the wobbling pit, a calculation circuit for calculating a signal obtained from the sampling circuit and outputting a tracking polarity signal, and a circuit for detecting the polarity of the tracking polarity signal. The opening and closing of the servo loop is controlled according to the tracking polarity.

[Action]

As a light receiving element for receiving the reflected light of the wobbling pit, by using a light receiving surface having at least two divided light receiving surfaces in the radial direction of the light receiving spot,
A far field image of the wobbling pit can be detected. Then, by converting the position of the fair field image into an electric signal by the divided light receiving elements, the polarity of the tracking error signal, that is, the relative movement direction of the irradiated light spot and the optical disk can be detected.

Therefore, if the tracking servo is controlled to be opened / closed by this detection signal, the settling time from the access to the lock in the tracking state is shortened, and the pull-in is easily performed.

Further, even when the amount of eccentricity of the optical disc is large, a stable tracking state can be maintained by the narrow band servo loop circuit.

〔Example〕

FIG. 1 is a block diagram of a tracking servo circuit showing an embodiment of the present invention, and 10 shows an optical system for irradiating an optical disc D with a laser beam.

The laser light P is incident on the deflection beam splitter B from a light emitting element (not shown), and passes through the objective lens L ₁ to the optical disc D.
Is irradiated on the recording surface of. Then, the reflected light is again deflected in the orthogonal direction by the deflecting beam splitter, and is incident on the light receiving element 11 via the converging lens L ₂ .

As shown in the figure, the light receiving element is divided into two light receiving surfaces A and B, and the spot S of the reflected light is arranged substantially at the center of the divided surface. The electric signals E _A and E _B output from the light receiving surfaces A and B are input to the subtraction circuit 12A and the addition circuit 12B that form the first and second signal processing circuits 20 and 30, respectively.

The E _A and −E _B signals output from the subtraction circuit 12A are the timings T ₁ and T 2 of the wobbling pits (2A, 2B) described above.
The signal (E _{A A} supplied to the first and second sampling and holding circuits 13A and 13B for sampling at T ₂ and sampled
The difference output of −E _B ) _T1 and (E _A −E _B ) _T2 is calculated in the subtraction circuit 15A, and is input to, for example, the third sampling hold circuit 16A that samples and holds at the timing T ₃ of the clock pit (3). As described later, it is output as the polarity signal ep of the tracking error signal.

Similarly, the signal E _A + E _B output from the adder circuit 12B
The first and second sampling and holding circuits 14A and 14B sample and hold at time points T ₁ and T ₂ , and the subtraction circuit 15B calculates (E _A + E _B ) _T1 − (E _A + E _B ) _T2 to perform tracking error. The signal et is output. The tracking error signal et in the third sample and hold circuit 16B follows, is held for example at T _3.

17 is a comparator of the tracking polarity signal ep described above,
Reference numeral 18 denotes a zero-cross detector for detecting the zero-cross point of the tracking error signal, and 19 denotes a D-flip-flop circuit, which form a third signal processing circuit 40 for detecting the polarity.

Reference numeral 50 denotes a tracking servo circuit, a low pass filter 51 for inputting the tracking error signal et output from the third sampling and holding circuit 16B, a switch circuit 52,
The actuator for focus adjustment by the objective lens L ₁ is composed of a phase compensation circuit 53 and a drive circuit 54, and is driven by the current value flowing into the tracking coil 55. Reference numeral 60 represents a timing circuit for forming a sampling pulse.

In the tracking servo circuit of the optical disk of the present invention, the reflected light from the wobbling pits (2A, 2B) is detected by the light receiving element 11 which is divided into two as described above. It is the sum signal of the two output electrical signals E _A and E _B. This sum signal E _A + E _B changes depending on the position v of the irradiated laser light, and as shown in FIG. 6, the reflected light (E _A + E _B ) _T1 of the first pit 2A and the second pit The difference between the reflected light (E _A + E _B ) _T2 becomes the tracking error signal et. That is, et = (A + B) _T1− (A + B) _T2 (1) When the optical disc has eccentricity or when there is relative movement between the laser beam spot and the optical disc, such as during traverse, this As the signal et changes, as described above, the spot position is v, the track interval is Q, and the track position is m.
Assuming that the distance d between Q and the wobbling pits (2A, 2B) and the track center is 1 / 4Q, v
When = 0, the reflected light from the first pit 2A becomes the lowest at the position of v = d, and v = − at the second pit 2B.
It becomes the lowest at the position of d. Therefore, Therefore, the tracking error signal is output from the third sampling and holding circuit 16B as shown in FIG. On the other hand, as is well known, the intensity of the reflected light incident on the light receiving element 11 causes strong interference due to the depth of the wobbling pits (2A, 2B) which are concave surfaces. Then, a far field image is formed on the surface of the light receiving element due to the interference of the reflected light at the pit portion and the peripheral portion thereof.

Therefore, as shown in FIGS. 2 (a) and 2 (c), when the edge of the pit portion is irradiated with the spot, the electric signals E _A , E _B output from the two light-receiving surfaces A, B are divided. Even if the spot is at the center, the signal E _A ≠ E _B has a different value depending on this far-field image, and when the spot is irradiated at the center of the pit, as shown in (b) of FIG. _A
−E _B = 0.

Such a signal is known as a diffractive differential signal and when the spot is on the track the first and second pits
The far-field images formed by 2A and 2B are reversed.

Therefore, also in this case, when the difference signal ep when the light spot is moving in the radial direction on the disk surface is calculated, ep = (A−B) _T1− (A−B) _T2 = 0, the spot is on the first pit (2A) and v = d (E _A −
E _B ) _T1 = 0 (however, the offset is C) When v = -d on the second pit (2B), (E _A -E _B ) _T2 = 0, therefore Therefore, the tracking polarity signal ep is out of phase with the tracking error signal et by 2 / π as shown in FIG.

This tracking polarity signal ep is compared with, for example, 0 voltage in the next comparator 17, and the comparator output Pd is D-
While being input to the D terminal of the flip-flop 19, the tracking error signal et is
The 0 level point is detected, and the trigger pulse Pt is output at this point.

Therefore, the output SW of the D-flip-flop 19 is obtained as shown in FIG.

The polarity of this output SW is inverted in accordance with the relative movement direction of the spot and the optical disk. If the switch of the tracking servo circuit 30 is closed at the H level of this output SW, the tracking servo loop will move in the + v direction. At the time of traverse, a signal in the range of B _R shown by the diagonal line of the tracking error signal is supplied to the tracking coil 55, and a brake signal m for returning the spot to the ± Q points of the track is formed.

In other words, when the light spot is relatively moving in the + V direction on the outer circumference, by applying the B _R part of the tracking error signal, the light spot moving away from the track Q, 2Q, 3Q ,. The tracking servo signal, and pulling back the tracking servo faster.

Similarly, when the light spot is relatively moving in the inner peripheral direction (-v direction), the output SW shown by the dotted line is generated, and the signal in the B _F range of the tracking error signal is within the tracking servo loop. Similarly, it acts as a brake signal only when the light spot moves away from the track (± Q).

As described above, in the tracking servo circuit of the present invention, when the wobbling pit is detected, the light receiving element capable of detecting the far field image is adopted, and the tracking polarity signal is extracted from the diffraction differential signal. Even when the laser spot is relatively moving on the recording surface, it can be easily pulled into the tracking state.

The third sampling circuits 16A and 16B may be circuits having an appropriate time constant.

〔The invention's effect〕

As described above, the tracking servo circuit of the optical recording / reproducing apparatus of the present invention samples and detects the tracking polarity signal from the optical disc on which the wobbling pits are formed, and pulls the tracking polarity signal into the tracking state. Since such a breaking signal is formed, the pull-in performance is improved even in the case of a recording type optical disc, and even in the case of various operation traces of the apparatus, there is an effect that the just track state can be set in a short time.

There is also an advantage that the number of crossing tracks at the time of traverse can be counted by counting the tracking polarity signal, and the track access can be surely controlled.

[Brief description of drawings]

FIG. 1 is a block diagram of a tracking servo according to the present invention, FIGS. 2 (a), (b), and (c) are explanatory views of a far field image, and FIG. 3 is a timing waveform diagram of a main part of FIG. , FIG. 4 is a plan view of an optical disk in which servo pits are formed, FIG. 5 is an enlarged view of tracks, FIG. 6 is an enlarged view of servo pits, a level waveform diagram of reflected light, and FIG. 7 is sampled. It is a waveform diagram of the tracking error signal. In the figure, 10 is an irradiation beam optical system, 20 is a second signal processing circuit that forms a tracking polarity signal, 30 is a first signal processing circuit that forms a tracking error signal, and 40 is a third signal processing circuit that forms a polarity signal. Is a signal processing circuit, 50 is a tracking servo circuit, and 6 is a timing circuit.

Claims (1)

[Claims] 1. An optical disc having first and second wobbling pits which are separated from each other by a predetermined distance with respect to the circumferential direction of the track and are displaced from each other in the radial direction from a sensor of the track. In order to detect the first and second wobbling pits, at least 2 in the radial direction is used.
A light receiving element having a divided light receiving surface, and a first and a second electric signal output from the light receiving element are added to correspond to a detection time of the first and second wobbling pits. First, a tracking error signal is formed by sampling and holding at the second timing.
Signal processing circuit, a second signal processing circuit that forms a tracking polarity signal by sampling and holding the difference between the first and second electric signals at the first and second timings, and the first signal processing A third signal processing circuit for detecting the polarity of the tracking polarity signal at the 0 cross point of the signal obtained from the circuit is provided, and the tracking servo circuit is controlled to be opened and closed by the output of the third signal processing circuit. Tracking servo circuit for optical recording / reproducing device.