JPH0770069B2 - Tracking servo circuit in optical recording / reproducing apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking servo circuit in an optical recording / reproducing apparatus, and more particularly to a tracking servo circuit suitable for performing tracking servo by a wobbling pit. .

[Outline of Invention]

The tracking servo circuit of the present invention detects, for example, a wobbling pit formed at a predetermined position of a track by embossing or the like and forms a tracking error signal, thereby When the added value is calculated and the AC component of this added value exceeds the reference value, the sample and hold function of the tracking error signal detected from the wobbling pit is stopped, so the surface of the optical disk is not scratched. , Or when dust or the like adheres to the wobbling pit due to improper embossing, etc.
It is possible to construct a tracking servo system that does not cause disorder.

[Conventional technology]

Most of the optical discs on which music or video signals are recorded are read-only, but in recent years, information can be recorded by adopting a magnetic film having a photomagnetization effect on the irradiation surface of laser light. Has been put to practical use.

FIG. 3 is a plan view showing an example of such an optical disk, and the recording surface of the optical disk 1 is provided with a perpendicular magnetic film exhibiting a magneto-optical effect. And the recording track on the circumference is, for example,
The servo data S is divided into 36 sectors.
B and address data area A are added by embossing or the like.

The recording area W is a flat magnetic film that is magnetized when the laser light modulated by the recording data is irradiated. In this portion, wobbling pits are formed at predetermined intervals as shown in FIG. An uneven surface is formed by 2A, 2B and the clock pit 3, and this servo data serves as an index of the recording track T.

Therefore, if such pits are formed in a spiral shape or a concentric shape at predetermined intervals, a tracking error signal for knowing the position of the track T can be generated by detecting the pits, and a focus error on the track is generated. It is also possible to form a signal.

That is, as shown in the enlarged view of the pits in FIG. 5, when the spot S of the laser light relatively moves in the direction of the arrow along the track T ₀ , the reflection when passing through the wobbling pits 2A, 2B light e ₂ becomes in e _1, t ₂ time at time point t _1, the reflected light when further passing through the clock pit 3
It becomes e ₃ .

However, when the spot S is deviated in the + v direction, each reflected light e ₁ , e ₂ , e ₃ changes as shown by the alternate long and short dash line, and when the spot S is deviated in the −v direction, it is indicated by the dotted line. It changes as shown.

Therefore, when the levels of the reflected lights e ₁ and e ₂ are sampled and held at time points t ₁ and t ₂ and the value of e ₁ −e ₂ is calculated, the amount of deviation of the spot S from the track T, that is, the tracking error signal is To be detected.

Further, the focus error signal is detected by detecting the light reflected from the intermediate area 4 between the wobbling pits 2A and 2B and the clock pit 3, and the reflected light at the portion of the clock pit 3 corresponds to the linear velocity of the optical disc. It is possible to extract the clock component to be used.

[Problems to be solved by the invention]

By the way, in the above-described detection operation, in particular, the tracking error signal detected from the wobbling pits 2A and 2B shows an accurate detrack amount when obtained from the normal reflected light at time points t ₁ and t _2. But the wobbling pit 2A, 2
If scratches or dust F adheres to one or both areas of B, the reflection level from the pit 2B is abnormally lowered, as shown in FIG. 6, and the spot S passes over the track T. Tracking error signal
The value of e _t becomes high, and for example, as shown in FIG. 7, a large tracking error signal e _{t is obtained} even at the just track point t _0.
Is output, the tracking servo will operate erroneously.

Especially, since such pits are formed by embossing or the like at 43 places in one sector,
There is a possibility that a considerable number of defective pits may be formed in the manufacturing process of the optical disc, and there is a problem that the performance of the tracking servo is significantly deteriorated.

[Means for solving problems]

The present invention has been made for the purpose of solving such a problem, and is a means for detecting a tracking error signal from a wobbling pit, and the detected tracking error signal is formed from a normal pit. Identification means is provided for forming a signal for detecting whether or not the tracking error signal detected from the defective wobbling pit is not sampled and held by the signal output from the identification means.

[Action]

The method of forming the tracking error signal from the wobbling pit requires a sampling means. Therefore, if the sample pulse supplied to the sampling and holding circuit which constitutes the sampling means is controlled by the signal which detects the defective wobbling pits, it is possible to detect an abnormal state by adding a few circuit means to the conventional tracking error detection circuit. It is possible to prevent the tracking error signal from being output, prevent the tracking servo from operating erroneously even in the case of a defective optical disk, and it is possible to exert a stable servo function.

〔Example〕

FIG. 1 is a block diagram of a tracking servo circuit showing an embodiment of the present invention, in which a laser emission source L, a polarization beam splitter B, a .lambda. / 4 plate P, an objective lens L, a light receiving element PD and the like are incorporated. The optical system of the optical pickup is shown, and the return light reflected from the optical disc 1 as described above is the light receiving element PD.
Is converted into an electric signal. 11, 12 is a sampling and holding circuit for detecting the reflected light of the wobbling pit, 13 is a subtracting circuit for forming a tracking error signal, 14 is an adding circuit for detecting a pit defect, and 15 is a binary value. Window comparator to which the reference signals + V and -V are input, 16 is an AND circuit, 17 is a sampling and holding circuit that holds the tracking error signal, and its output is driven through a transfer compensation circuit as is well known. A tracking servo circuit is formed by driving the objective lens L supplied to the circuit.
Reference numeral 18 is a clock signal generator for forming a clock signal corresponding to a pit of recorded data from the reflected light of the optical disc D, 19
Shows a timing circuit for supplying a sampling pulse to the sampling circuits 11, 12, 17 and the like.

The electric signal output from the light receiving element PD is RF during playback.
The recording data is demodulated in the signal processing block 20,
Further, the focus error signal component can be detected by detecting the reflected light of the inter-pit area 4 in the sampling and holding circuit 21.

FIG. 2 is a main waveform diagram of the tracking servo circuit of the present invention. The operation will be described below with reference to this figure.

When the spot irradiated on the optical disc D passes through the wobbling pits 2A and 2B as described above, the reflected light has an intensity of the reflected light corresponding to the deviation from the track T as shown in FIG. Changes and is input to the light receiving element PD. Then, the electric signals (E ₁ , E ₂ ) output from the light receiving element PD also change.

The sampling and holding circuits 11 and 12 are timing circuits 1.
Time points t ₁ and t _{2 due to the} sample pulse supplied from 9
Detects and holds the levels of the electric signals E ₁ and E ₂ , and supplies the difference signal to the subtraction circuit 13 to output the tracking error signal E _t . This tracking error signal E _t changes in a sine wave shape as shown in FIG. 7 when the spot is traversing between tracks.

On the other hand, the outputs of the sampling and holding circuits 11 and 12 are input to the adding circuit 14 to form the pit defect signal S _F.

By the way, the pit defect signal S _F is Uo Bring pit 2
It is the sum of the reflected lights e ₁ and e ₂ at the times t ₁ and t ₂ that have passed A and 2B,
As shown in FIG. 5, assuming that the pitch between tracks is Q and the distance between the wobbling pits 2A and 2B and the track center is d = Q / 4, the spot position v is now ± mQ.
When moving relative to (m = ± 1, ± 2, ... ± n), the reflected light from each pit is It depends on (C is a constant bias value) Therefore, the pit defect signal formed by these sum signals e ₁ + e ₂ is Since d = 4 / Q, Therefore, the sum signal e ₁ + e ₂ of the reflected light indicating the defect signal S _F is always a constant value 2C when reflected from the normal wobbling pit, but at the defect pit portion, the reflection of the formula (1) is performed. A large change occurs in the level signal, and at this point, the defect signal S _F does not have a constant value and an AC component is included.

Therefore, this AC component is input to the window comparator via the capacitor C ₀ and has a different polarity reference signal + V,-
To be compared with V.

When the defect signal S _F is S _F > V or −S _F <−V, a “1” level signal P ₁ (flag) is set on the output side and input to the AND circuit 16 via the inverter.

As shown in FIG. 6, the signal of the adder circuit 14 suddenly changes when the level of the reflected light is lowered due to scratches or dust F adhering to either or both of the wobbling pits 2A and 2B. Since an AC component is generated, this value is + V
Or when -V or more, signal from window comparator 15
P _F is output and the timing pulse supplied to the sampling and holding circuit 17 (this timing pulse is
The t ₂ may be any value after that, and the output of (for example, the detection sample pulse of the clock pit 3 is used) is blocked by the AND circuit 16.

As a result, when the sampling and holding circuit 17 encounters a defective wobbling pulse, it outputs the tracking error signal E _{tn held} in the preceding stage as it is as shown by E _t ′ in FIG. Error tracking error signal generated by defective pits
E _n can be removed.

Reference voltage + V input to window comparator 15,
The absolute value | V | of −V may be set to a value slightly larger than the level of the AC component contained in the sum signal of the reflected light obtained from the normal wobbling pit.

The window comparator 15 can be formed by two independent comparators.

〔The invention's effect〕

As described above, the tracking servo circuit in the optical recording / reproducing apparatus of the present invention removes the abnormal tracking error signal generated by the defect of the wobbling pit by the level of the AC component of the sum signal forming the pit defect signal. Therefore, even if some scratches, bubbles, etc. are created in the pit part of the optical disc during processing,
There is an effect that information can be recorded or reproduced in a good tracking state. Therefore, there is an advantage that the specification standard of the optical disk is relaxed and the yield can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, FIG. 3 is a plan view showing an example of a recordable optical disk, and FIG. FIG. 5 is an enlarged view, FIG. 5 is an explanatory view of pits and reflected light thereof, FIG. 6 is an explanatory view of reflected light of a defective portion, and FIG. 7 is a waveform diagram of a tracking error signal. In the figure, 2A and 2B are wobbling pits, PD is light blocking, 1
1, 12 and 17 are sampling and holding circuits, 13 is a subtraction circuit, 1
Reference numeral 4 is an adder circuit, 15 is a window comparator, and 19 is a timing circuit.

Claims (1)

[Claims] 1. An optical disc in which first and second wobbling pits are formed which are separated from each other by a predetermined distance with respect to the circumferential direction of the track and are radially displaced from the center of the track. A light receiving element for detecting the first and second wobbling pits, a subtraction circuit for subtracting the first and second electric signals detected from the light receiving element to form a tracking error signal, First
An adder circuit for adding the first and second electric signals and a window comparator for comparing the alternating current component output from the adder circuit with a binary reference signal are provided, and the output of the window comparator is equal to or more than the absolute value of the reference signal. The tracking servo circuit in the optical recording / reproducing apparatus is characterized in that the sampling and holding operation of the tracking error signal output from the subtraction circuit is stopped when the above signal is output.