JPS63144429A - Tracking servo circuit for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To shorten the time required for leading from the detracking state for eccentricity or traverse to the tracking servo state by controlling a servo loop to open or close it in accordance with the detected polarity of tracking. CONSTITUTION:The photodetector on which light receiving faces A and B divided at least into two in the radial direction of a received light spot are formed is used as a photodetector 11, which receives the reflected light from a wobbling pit, to detect the fair field image of the wobbling pit. The position of this image is converted to an electric signal by the divided photodetector 11 to detect the polarity of a tracking error signal et, namely, the direction of relative movement of the projected light spot and an optical disk. Opening and closing of a tracking servo 50 are controlled by this detection signal to shorten the settling time required for locking in the tracking state after access, and leading into the tracking servo state is facilitated. Even if the extent of eccentricity of an optical disk D is large, the stable tracking state is held by a narrow-band servo loop circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tracking servo circuit in an optical recording/reproducing device, and particularly relates to a tracking servo circuit in an optical recording/reproducing device, and particularly to a tracking servo circuit in an optical recording/reproducing device. This invention relates to a tracking servo circuit that is suitable for performing fast pull-in by detecting.

[Summary of the invention]

The tracking servo circuit of the present invention detects wobbling pits formed at predetermined intervals on a track by embossing or the like to form a tracking error signal, and also generates a diffraction differential signal from the wobbling bits. By detecting the polarity of the tracking error signal, the time required to enter the tracking servo state from the detrack state particularly during eccentricity or traverse is shortened.

[Conventional technology]

Optical discs that record music or video signals can reproduce high-density information, but since such optical discs are only for playback, in recent years optical discs that can record and erase information have been developed. It has moved to the stage of practical application.

FIG. 4 shows a plan view of such a recordable optical disk (recording disk), and the recording surface of the optical disk 1 is provided with a perpendicular magnetization film exhibiting a magneto-optical effect. As shown in the enlarged view of FIG. 5, three concave bit groups 2A, 2B, and 3 are embossed, for example, at predetermined intervals on the track T on the circumference where information is recorded. They are continuously formed at a depth of 1/4 to 1/8 (in is the wavelength of the laser beam). Of this bit group, the first
The pitch h2A and the second bit 2B are at positions shifted in different directions from the track center by, for example, 1/4Q, as shown in the enlarged view of FIG. 6, when the interval (pitch) of the tracks T is Q. is formed to detect a tracking error, and the third bit 3 is a predetermined pressure gIL.
It is formed only at the center of the track and is mainly used as a data clock reference signal.

The next bit groups 2 A', 2 B', and 3' are used as a recording area 4 in which information is recorded 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 irradiated to the pit groups 2A, 2B, and 3 during recording or reproduction, and a tracking error signal and a clock reference signal are extracted from the reflected light of the laser beam irradiated to the pit groups 2A, 2B, and 3. A focus error signal is formed by reflected light from a portion of the mirror.

The light spot 5 is the first and second
It is obtained by sampling the reflected light when passing through 2A and 2B in the direction of the arrow.

That is, when the light spot 5 is passing over the track T in the direction of the arrow as shown in A of FIG. 6 (on-track), the level of the reflected light of each bit 2A, 2B, and 3 is as shown in The level will be as shown in a, and the level B in Figure 6 will be reached.
When the trajectory of the light spot 5 passes above the track T as shown in the figure, reflected light as shown in the figure is detected.

Also, as shown in FIG. 6C, the light spot 5 is located on the track T.
When it is shifted to the lower side, reflected light at a level as shown in C in the same figure is detected.

Therefore, the intensities of these reflected lights are determined at T1 and 12
By sampling at the time point and subtracting the intensity sb of the reflected light at time 12 from the intensity Sa of the reflected light at time T1, the amount by which the light spot is shifted from the track T, that is, the tracking error signal, is obtained. By controlling the tracking servo mechanism using the sampled tracking error signal, it is possible to control the optical spot so that it always passes over the track of the optical disc.

[Problem that the invention seeks to solve]

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

This point will be explained in detail below.

As shown in FIG. 4, the radial position of the light spot 5 is
, when the track pitch is Q, the spot position V is the track position ±mQ (m=0).

±1. ±2. ±3. ), the tracking error signal et=3a −sb =0
and at other positions, the sampled tracking error signal e(e) changes sinusoidally as the spot position V changes, as shown in FIG.

As seen in this diagram of changes in the tracking error signal et, at the track position mQ, the tracking error signal e
Although t is O, the tracking error et is also O at the point where the track position is Q.

However, the point that becomes O in this ±HQ is the calculated difference signal between the first pit 2A and the second pit 2B of adjacent tracks, and the difference signal between the first pit 2A and the second pit 2B of adjacent tracks is calculated, and
The range F cannot be used as a tracking signal, and the range N of ±5/iQ centered at the position mQ is a tracking error signal proportional to the deviation with respect to the track T.

Therefore, when there is relative movement between the optical pickup and the optical disk (during traverse), a tracking error signal etti as shown in FIG. A controlling effect occurs, but
In the range of F, when the optical spot approaches the track, the tracking error signal becomes large, making it difficult to converge (pull in) to the tracking state.

Therefore, in the case of a conventional optical disc playback device, for example,
As seen in Japanese Patent Publication No. 59-8893, optical disc playback RF is used as a pull-in during traversing.
A braking signal for pull-in is extracted by detecting a signal and comparing the phase of a level change that occurs when the reproduced RF signal is out of track with the phase of a tracking error signal.

However, although such a pull-in means is effective for a read-only optical disc on which a reproduction RF signal is continuously output, it cannot be used as a pull-in means for an optical disc without recorded information.

The present invention has been made in view of these problems.
This provides a tracking servo circuit that can be quickly pulled in using only information output from the first and second pits (wobbling pits) for tracking detection.

[Means for solving problems]

The tracking servo device of the optical recording/reproducing device of the present invention includes a light receiving element having a light receiving surface divided into at least two parts for detecting wobbling pits, and a change in a fair field image obtained from the light receiving element. A sampling circuit that samples the signal at a detection position of the wobbling pit, an arithmetic circuit that calculates a signal obtained from the sampling circuit and outputs a tracking polarity signal, and a circuit that detects the polarity of the tracking polarity signal, The servo loop is controlled to open and close depending on the tracking polarity.

[Function] By using a light-receiving element that receives the reflected light from the wobbling pit, the light-receiving surface is divided into at least two parts in the radial direction of the light-receiving spot.1. Far field images can be detected. By converting the position of this fair field image into an electrical signal using a divided light receiving element, it is possible to detect the polarity of the tracking error signal, that is, the direction of relative movement between the irradiated light spot and the optical disk.

Therefore, when the tracking servo is opened/closed using this detection signal, the settling time from access to locking to the tracking state is shortened, and retraction is easily performed.

Further, even when the amount of eccentricity of the optical disk 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 device showing an embodiment of the present invention, and numeral 10 indicates an optical system for irradiating an optical disc D with a laser beam.

The laser beam P enters the polarizing beam splitter B from a light emitting element (not shown), and is irradiated onto the recording surface of the optical disc D via the objective lens L. Then, the reflected light is again polarized in the right angle direction by the polarizing beam splitter, and is incident on the light receiving element ll via the converging lens L2.

As shown, the light-receiving element is divided into two light-receiving surfaces A and B, and the light-receiving element is arranged so that the reflected light beam S is located approximately at the center of the divided surface. The electrical signals E^ and EB output from the light receiving surfaces A and B are sent to the first and second signal processing circuits 20.
and 30, the subtraction circuit 12A, and the addition circuit 12
It is input to B.

Then, EA is output from the subtraction circuit 12A.

-EB signal is the aforementioned wobbling pit (2A
, 2B) in which sampling is performed at timings TI and T2. Second sampling hold circuit 13A, 13B
The difference output of the sampled signals (EA-Ea)r and (EA-EB)T2 which are supplied to the subtracter circuit 15A is calculated, and the difference output is calculated, for example, by a third sampling hold which performs sampling and holding at the timing T3 of the clock pit (3). The polarity signal e of the tracking error signal is input to the circuit 16A and output as a polarity signal e of the tracking error signal, as will be described later.

Further, the signal EA +Ee output from the adder circuit 12B
Similarly, the first. Second sampling and hold circuit 14
At time TI, T2 is sampled and held at A, 14B, and (to E to E8) TI is sampled and held at the subtraction circuit 15B.
-(EA+EB)T2 is calculated and a tracking error signal ei is output. This tracking error signal et is also held in the next third sampling and holding circuit 16B at, for example, time T3.

17 is a comparator for the tracking polarity signal ep, 18 is a zero-cross detector for detecting the zero-crossing point of the tracking error signal, and 19 is a D-flip-flop circuit, which connects a third signal processing circuit 40 for detecting the polarity. is forming.

Reference numeral 50 denotes a tracking servo circuit, which includes a low-pass filter 51 that inputs the tracking error signal ej output from the third sampling and hold circuit 16B, a switch circuit 52, a phase compensation circuit 53, and a drive circuit 54, and which controls the focus by the objective lens L1. The actuator for adjustment is driven by the current value flowing into the tracking coil 55. Note that 60 indicates a timing circuit for forming sampling pulses.

In the optical disk tracking servo circuit of the present invention, as described above, the light receiving element 11 divided into two detects the reflected light from the wobbling pins (2A, 2B). This is the sum signal of two electrical signals EA and EB output from the . This sum signal E^+EB changes depending on the position V of the irradiated laser beam, and as shown in FIG. E
A + EB) T2 becomes the tracking error signal eL. That is, et = (A+B)y+ -(A+B)T2...
...(1) When the optical disk is eccentric, or when there is relative movement between the laser beam spot and the optical disk, such as during traversal, this signal et changes, and the spot position changes as described above. If V is the track interval, Q is the track position, mQ is the track position, and %Q is the distance d between the wobbling bits (2A, 2B) and the track center, then the current track Q
When V=O, the reflected light from the first pit 2A is the lowest at the position v=d, and the second pit)
In 2B, it is lowest at the position of v=-d. Therefore, = -2sin(2π-) (where d=Q/4)π (2) This tracking error signal is output from the third sampling and hold circuit 16B as shown in FIG. is output to. (Shows as an analog waveform) On the other hand, as is well known, the intensity of the reflected light incident on the light receiving element 11 is affected by strong interference depending on the depth of the wobbling pits (2A, 2B), which are concave surfaces. A far-field image is formed on the surface of the light-receiving element due to the interference of reflected light from the pit portion and its surrounding area.

Therefore, when the edge of the pit area is illuminated as shown in Fig. 2 (a) and (C), the electric signals E^ and E output from the two divided light receiving surfaces A and B are
Even if the spot B is at the center, the signal EA ≠ EB will be different due to this far-field image, and when the center of the bit is irradiated with the light beam, the signal will be as shown in Figure 2 (b). Then E^-E8=0.

Such a signal is known as a diffraction differential signal, and when the spot is on the track, the far field images formed by the first and second bits 2A, 2B are inverted.

Therefore, in this case as well, if we calculate the difference signal ep when the optical boat is moving in the radial direction on the disk surface, we get ep = (A-B) TI (^-B) T2 Now, in a certain track Q When V=O, the spot is the first
) (2A) When V=d above (EA −E
B) Tl=O (however, the offset is C) 2nd
) (2B) When V=-d above (E^-E
a) T2=0, therefore, this tracking polarity signal e is out of phase with the tracking error signal ej by 2/π as shown in FIG.

This tracking polarity signal ep is sent to the next comparator 17.
is compared with, for example, the O voltage, and its comparator output Pd
is input to the D terminal of the D-flip-flop 19, and the tracking error signal et is input to the zero cross detector 1.
8, the O 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 reversed depending on the direction of relative movement between the spot and the optical disk, and when the switch of the tracking servo circuit 30 is closed at the H level of this output SW, the tracking servo loop is inverted in the +V force direction. During traversal, a tracking error signal in the range of BR shown by diagonal lines is supplied to the tracking coil 55 to form a brake signal m that returns the spot to the ±Q point of the track.

In other words, when the light spot is moving relatively in the outer peripheral direction +V force direction, by applying the BR part of the tracking error signal, tracks Q, 2Q, 3Q, . . .
...The light spot moving away from the nQ point is pulled back by a tracking error signal of negative polarity, and the tracking servo pull-in is accelerated.

Similarly, when the light spot is relatively moving in the inner circumferential direction (-v direction), the output SW shown by the dotted line is generated,
A signal in the BF range of the tracking error signal flows in the tracking servo loop and similarly operates as a brake signal only when the light spot moves away from the track (±Q).

As described above, when detecting wobbling pits, the tracking servo circuit of the present invention employs a light-receiving element that can detect a far-field image of the wobbling pit, and extracts the tracking polarity signal from the diffraction differential signal. , even when the laser spot is moving relative to the recording surface, it can be easily brought into the tracking state.

Note that the third sampling circuits 16A and 16B may be circuits with regular time constants.

〔Effect of the invention〕

As explained 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 wobbling bits are formed, and uses this tracking polarity signal to enter the tracking state. Since a braking signal is generated, the pull-in performance is improved even when using a recordable optical disc, and even after various operations of the apparatus, it is possible to achieve a just-track state in a short time.

Further, by counting the tracking polarity signal No. 1, the number of tracks traversed during traversal can be counted, which has the advantage that track access can be reliably controlled.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tracking servo according to the present invention, FIGS. 2(a), (b), and (c) are explanatory diagrams of far-field images, and FIG. 3 is a timing waveform diagram of the main parts of FIG. 1. , Fig. 4 is a plan view of the optical disk on which servo bits are formed, Fig. 5 is an enlarged view of the track, Fig. 6 is an enlarged view of the servo bit and the level waveform of reflected light, and Fig. 7 is a diagram of the sampled light. FIG. 3 is a waveform diagram of a tracking error signal. In the figure, 10 is an optical system for the irradiation beam, 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
5 shows a third signal processing circuit that forms a polar signal, 50 a tracking servo circuit, and 6 a timing circuit. Enlarged view of the trunk 1 5th vA A Enlarged view of the pit Figure 6 Tracking error signal Figure 7 Procedural amendment stamp date February 2, 1986

Claims (1)

[Claims] The first and second wobbling pits are formed on an optical disc in which first and second wobbling pits are formed, which are spaced apart from each other by a predetermined distance in the circumferential direction of the track and mutually deviated from the center of the track in the radial direction. In order to detect the second wobbling pit, a light receiving element having a light receiving surface that is divided into at least two in the radial direction, and a first and second electric signal outputted from the light receiving element are added, and the first and second electric signals are added.
and a first signal processing circuit that forms a tracking error signal by sampling and holding at first and second timings corresponding to the detection time of a second wobbling pit; a second signal processing circuit that samples and holds the difference at the first and second timings to form a tracking polarity signal; A tracking servo circuit for an optical recording/reproducing device, characterized in that a third signal processing circuit for detecting polarity is provided, and the opening/closing of the tracking servo circuit is controlled by the output of the third signal processing circuit.