JPS63146233A - Tracking servo circuit for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To avoid the occurrence of hunting even when the wobbling pits have a defect due to the scratches produced on the surface of an optical disk or the dust, etc., stuck the disk surface or a defective emboss process, etc., by calculating the addition value of the beams reflected from the wobbling pits and stopping the sample/hold actions of the tracking error signal detected from the wobbling pit if the AC component of said addition value exceeds a reference value. CONSTITUTION:The signal of an addition circuit 14 produces an AC component that changes suddenly when the scratches are produced at one or both of wobbling pits 2A and 2B or the sticking of the dust F and the levels of reflected beams of those pits are lowered. Thus a signal PF is outputted from a wobbling pit 15 when the value of the AC component exceeds the binary reference signal +V or -V. Then the output of the timing pulse supplied to a sample/hold circuit 17 is prevented by a NAND circuit 16 to eliminate the error tracking signal that is produced by a defective pit.

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 suitable for performing tracking servo using wobbling pits. .

[Summary of the invention]

The tracking servo circuit of the present invention has the following features: 1. For example, when detecting a wobbling pit formed at a predetermined position on a track by embossing or the like and forming a tracking error signal, the tracking servo circuit detects the light reflected from the wobbling pit. An additional value is calculated, and when the AC component of this additional value exceeds a reference value, the sample and hold function of the tracking error signal detected from the wobbling pit is stopped, so there is no possibility of scratches on the surface of the optical disc. It is possible to construct a tracking servo system that does not cause disturbances even when a defect occurs in the wobbling pit due to adhesion of dust or the like or defective embossing.

[Conventional technology]

Most optical discs on which music or video signals are recorded are intended for playback only, but in recent years, it has become possible to record information by using a magnetic film that has a photomagnetization effect on the surface irradiated with laser light. Optical discs have been put into 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. The recording track on the circumference is divided into, for example, 36 sectors, and servo data SB and address data area A are added to each sector by embossing or the like.

The recording area W is a flat magnetic film that is magnetized when it is irradiated with a laser beam modulated by the recording data, and wobbling pits are formed at predetermined intervals in this area, as shown in Figure 4. )2A.

2B and the clock pits 3 form an uneven surface, and this servo data is used as an index of the recording track T.

Therefore, if pits are formed spirally or concentrically at predetermined intervals, a tracking error signal can be generated to know the position of the track T by detecting these pits, and a focus error on the track can be generated. It is also possible to form a signal.

That is, as shown in the enlarged view of the pit in FIG. 5, when the laser light spora) S moves relatively along the track To in the direction of the arrow, wobbling pits) 2A,
The reflected light when passing through 2B is el, t at time 11.
At point 2, it becomes e2.

Furthermore, the reflected light when passing through clock pit 3 is e3
becomes.

However, when the spot S is deviated in the +V force direction, each of the reflected lights 81, e2, and e3 changes as shown by the dashed line, and when the spot S is deviated in the -V force direction, the reflected lights 81, e2, and e3 change as shown by the dotted line. Changes to

Therefore, the level of reflected light elle2 is set at times tl and t.
Sampling and holding at 2 and calculating the value of el - e2, the amount by which S (spora) S is shifted from track T,
That is, a tracking error signal is detected.

In addition, a focus error signal is detected by detecting the light reflected from the intermediate region 4 between the wobbling bits 2A, 2B and the clock pit 3, and further, the linear velocity of the optical disc is determined from the reflected light from the clock pit 3. It is possible to extract the clock component.

[Problem that the invention seeks to solve]

By the way, in the above-mentioned detection operation, the tracking error signal detected from the wobbling bits 2A and 2B indicates an accurate amount of detracking if it is obtained from normal reflected light at time points tl and t2. Warbling Pit) 2A, 2B (7) If scratches or dust F etc. are attached to one or both areas, the reflection level from the pit 2B will be abnormally reduced as shown in FIG. 6, for example.
Even though the spot S is passing over the track T, the value of the tracking error signal el is high, and for example, as shown in FIG. 7, a large tracking error signal e is output even at the just track point to. If this happens, the tracking servo will operate incorrectly.

In particular, since such pits are formed by embossing, etc. at 43 locations within the l sector, there is a risk that a considerable number of defective pits will be formed during the manufacturing process of the optical disk, which will significantly affect the performance of the tracking servo. There are openings where the road deteriorates rapidly.

[Means for solving problems]

The present invention has been made with the aim of solving such problems, and includes a means for detecting a tracking error signal from wobbling bits, and a means for detecting a tracking error signal from a normal pit. A discrimination means is provided for forming a signal for detecting whether or not the defective wobbling bit is detected, and the tracking error signal detected from the defective wobbling bit is controlled so as not to be sampled and held by the signal output from the discrimination means.

[Effect]

The method of forming a tracking error signal from wobbling pits requires sampling means. Therefore, if the sample pulse supplied to the sampling hold circuit constituting the sampling means is controlled by the signal 9 that detects the defective wobbling pit, it is possible to detect abnormalities by adding a small number of circuit means to the configuration of the conventional tracking error detection circuit. This prevents the tracking error signal from being output, and even in the case of a defective optical disc, the tracking servo will not operate erroneously, and stable servo function can be achieved.

〔Example〕

FIG. 1 is a block diagram of a tracking servo circuit showing an embodiment of the present invention, where lO is a laser light source L, a polarizing beam slitter B, a λ/4 plate P, an objective lens L, and a light receiving element FD.
The return light reflected from the optical disc 1 as described above is converted into an electric signal at the light receiving element FD. 11.12 is a sampling and holding circuit for detecting reflected light from wobbling pits, 13 is a subtraction circuit for forming a tracking error signal, 14 is an addition circuit for detecting pit defects, and 15 is a binary circuit. Reference signal +V, -V
16 is a NAND circuit, and 17 is a sampling and hold circuit that holds the tracking error signal.As is well known, the output is supplied to the drive circuit via a phase compensation circuit, and is then connected to the objective lens. By driving L, a tracking servo circuit is formed. Reference numeral 18 indicates a clock signal generator that generates clock signals corresponding to pits of recording data from reflected light from the optical disc D, and reference numeral 19 indicates a timing circuit that supplies sample pulses to the sampling circuits 11, 12, 17, etc.

The electric signal output from the light-receiving element FD is demodulated as recorded data in the RF signal processing block 20 during reproduction, and is converted into a focus error signal by detecting the reflected light of the inter-bit area 4 in the sampling hold circuit 21. The components can be detected.

FIG. 2 shows a main waveform diagram of the tracking servo circuit of the present invention, and the operation will be explained below with reference to this diagram.

When the spot irradiated onto the optical disk D passes through the wobbling pits 2A and 2B as described above, the intensity of the reflected light increases in response to the deviation from the track T, as shown in FIG. The light intensity changes and is input to the light receiving element FD. Then, an electric signal (E!) is output from this light receiving element FD.

E2) also changes.

Sampling hold circuit 11. and 12 detect and hold the level of the electrical signal EI+E2 at time points tl and t2 using sample pulses supplied from the timing circuit 19, and output the tracking error signal El by supplying the difference signal to the subtraction circuit 13. . This tracking error signal Et changes sinusoidally 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 adder circuit 14 to form a pit defect signal SF.

. By the way, the bit defect signal Sr is a wobbling pit)
Reflected light el at time tl+t2 after passing through 2A and 2B, 6
As shown in Figure 5, if the pitch between the tracks is Q and the distance between the wobbling pits 2A, 2B and the track center is d = Q/4, the spot position V is now the sum of the tracks. Position output mQ (m=±1.±2.....
...±n), the reflected light of each pit changes. (C is a constant bias value) Therefore, the pit defect signal formed by these sum signals el +82 is: (2) Because d=4/Q.

=2C...(3) Therefore, the sum signal el + of the reflected light indicating the defect signal SF
67 is always a constant value of 2C when reflected from a normal wobbling pit, but a large change occurs in the reflection level signal of equation (1) at the defective pit portion.
In this respect, the defect signal SF does not become -.set, but contains an alternating current component.

Therefore, this alternating current component is a reference signal +v of different polarity that is input to the window comparator via the capacitor CG.
, '-v.

When the defect signal S[ is Sr>V and -3F<-V, a signal P1 (flag) of "L" level is set on the output side and input to the NAND circuit 16.

As shown in FIG. 6, the signal of the adder circuit 14 suddenly changes when scratches or dust F adheres to one or both of wobbling pins 2A and 2B, and the level of the reflected light decreases. Since an AC component is generated, if this value becomes +■ or -V or more, the window comparator 1
5 outputs a signal PF, which is supplied to the sampling and hold circuit 17.The timing pulse (this timing pulse only needs to be after time t2, for example,
The detection sample pulse of clock pit 3 is used)
The output is blocked by the NAND circuit 16.

As a result, when the sampling and holding circuit 17 encounters a defective wobbling pulse, the EL of FIG.
As shown in ', the tracking error signal Etn held in the previous stage is output as is, and the erroneous tracking error signal En generated by the defective pit can be removed.

Reference voltage input to window comparator 15 +
The absolute value IVI of V and -V may be set to a value slightly larger than the level of the AC component included in the sum signal of reflected light obtained from normal wobbling pits.

Note that the window comparator 15 can be formed by two independent comparators.

〔Effect of the invention〕

As explained above, the tracking servo circuit in the optical recording/reproducing apparatus of the present invention removes the abnormal tracking error signal generated due to the wobbling pit defect by adjusting the level of ACJ & of the sum signal forming the pit defect signal. This has the effect that even if some scratches or bubbles are formed in the pit portion of the optical disc during processing, information can be recorded or reproduced in a good tracking state. Furthermore, the specification standards for optical discs are relaxed, and there is an advantage that the yield can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram explaining the operation of FIG. 1, FIG. 3 is a plan view showing an example of a recordable optical disc, and FIG. An enlarged view, FIG. 5 is an explanatory diagram of a pit and its reflected light, FIG. 6 is an explanatory diagram of reflected light from a defective portion, and FIG. 7 is a waveform diagram of a tracking error signal. In the figure, 2A and 2B are wobbling bits, FD is a light receiving element, 11, 12.17 are sampling and holding circuits, 13 is a subtraction circuit, 14 is an addition circuit, 15 is a window comparator, and 19 is a timing circuit. Figure 1 Waveform diagram of the main part of the blank Figure 2 Plan view of the optical disc Figure 3 Procedure person 11 and 7 given (voluntarily) February 2, 1988

Claims (1)

[Claims] For 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, the first, a light receiving element for detecting a second wobbling pit; a subtraction circuit for subtracting first and second electrical signals detected from the light receiving element to form a tracking error signal;
an adding circuit that adds up the electrical signals of the adding circuit, and a window comparator that compares the alternating current component outputted from the adding circuit with a binary reference signal, and the output of the window comparator outputs a signal that is greater than or equal to the absolute value of the reference signal. When it is done,
A tracking servo circuit in an optical recording/reproducing device, characterized in that the sampling and holding operation of the tracking error signal output from the subtraction circuit is stopped.