WO1986005914A1

WO1986005914A1 - Tracking error detecting apparatus for optical disks

Info

Publication number: WO1986005914A1
Application number: PCT/JP1986/000160
Authority: WO
Inventors: Hiroshi Oinoue
Original assignee: Sony Corporation
Priority date: 1985-04-05
Filing date: 1986-04-03
Publication date: 1986-10-09
Also published as: JPS61230637A

Abstract

Tracking error detecting apparatus used for an optical disk in which a signal is recorded so that the period of a regenerative output signal varies, such as a compact disk in which the lengths of a pit and a land vary within predetermined ranges. In this apparatus, the return light from a disk is received by four-divided optical detecting unit (1)-(4), and a regenerative output signal, which is obtained from an output of the sum of these reception signals, is delayed by about 1/4 of a minimum period thereof by a delay circuit (21). This delayed signal and a signal representative of a difference between the sum of outputs from a pair of diagonally opposite portions of the four-divided optical detecting unit (1)-(4) and that of outputs from the other pair of diagonally opposite portions thereof are multiplied in a multiplier (12), and a signal which is then passed through a low-pass filter (13) is determined as a tracking error signal. Thus, an accurate tracking error signal can be obtained by an inexpensive apparatus.

Description

Description Optical disk tracking error detector Technical field

The present invention relates to an optical disc in which a signal is recorded in a form in which the period of a reproduction output signal changes like a compact disk in which the length of each of a pit and a land changes within a predetermined range. The present invention relates to a tracking error detection device used to track a disc recording track.

Background art

FIG. 1 shows a tracking system disclosed in Japanese Patent Application Laid-Open No. Sho 52-92332 (Japanese Patent Publication No. Sho 56-30610), which is a first conventional example of the present invention. 4 shows an error detection device.

In this first conventional example, four light detecting sections are respectively divided into a recording track direction (y-axis direction) and an orthogonal direction (X-axis direction) of an optical disk (not shown). It has a photodetector consisting of sections 1 to 4, and a reproduced output signal having a waveform as shown in FIG. 2A is obtained at point によって by adders 5 to 7. Then, since the reproduced output signal is input to the phase shifter 8 which shifts the phase by 90 *, a signal having a waveform as shown in FIG. 2B is obtained at the point B.

On the other hand, the subtracter 11 subtracts the output signals from the adders 5 and 6, but the signal at point C which is the output signal (diagonal difference signal) from the subtracter 11 is As shown in Fig. 2C, if the beam is shifted to the right with respect to the recording track, the phase is delayed by 90 'from the reproduced output signal, and if the beam is shifted to the left, 90 · Only the phase is advanced. Since the signals at the points B and C are multiplied by the multiplier 12, a signal having a waveform as shown in FIG. 2D is obtained at the point D. At point E after passing through the low-pass filter 13, as shown in FIG. 2E, a positive DC signal is obtained if the beam is shifted to the right with respect to the recording track, If it is shifted to the left, a negative DC signal is obtained. If the beam is on the recording track, the DC signal shown in Fig. 2E will not appear.

Therefore, the signal at point E indicates a tracking error, and tracking servo can be performed based on the tracking error signal.

In addition, as a second conventional example of the present invention, as described in Japanese Patent Application Laid-Open No. 57-T48737, both the rising and falling of the signal at point A in FIG. There is a method in which the signal at point C is sampled separately at the loss point, the signals that have been sampled are subtracted, and the signal resulting from this subtraction is used as a tracking error signal.

Further, as a third conventional example of the present invention, as described in Japanese Patent Application Laid-Open No. 57-118143, the output signals of the respective Kaminos 5 and 6 in FIG. There is also a method in which only the phase information is used as a tracking error signal.

However, the method of the first conventional example described above shifts the phase of the reproduced output signal by 90 ', and is effective only in the case of a single carrier. In other words, in the case of the EFM format, which is the NRZ format used in compact disks, etc., it is difficult to perform the 90 'phase shift over a wide band when the frequency of the carrier fluctuates significantly. However, there is a problem that an accurate tracking error signal cannot be obtained.

In addition, the method of the second conventional example requires a high-speed switch element and the like, has a complicated configuration, and cannot be easily integrated into an IC. Therefore, there is a problem that the cost is high. Furthermore, the method of the third conventional example described above uses only phase information and does not use amplitude information, so that it is weak to noise (poor playability), that is, an accurate tracking error signal is obtained. There is a problem that you cannot do that.

Disclosure of the invention

An optical disc tracking error detecting device according to the present invention is formed by dividing a recording track of an optical disc into a tangential direction of a recording track and a direction perpendicular to the tangential direction. A photodetector comprising first, second, third and fourth photodetectors for detecting reflected light from the optical disc; and first, second, third and fourth light detectors. A second signal based on a first signal, which is a sum signal of the respective detection outputs of the detection unit, and a sum signal of the respective detection outputs of the first and third light detection units on a diagonal line and the second signal. And a third signal, which is the difference between the sum signals of the respective detection outputs of the fourth photodetector, and a low-pass filter to which the output of the multiplier is supplied. An optical disk track that obtains a tracking error signal from the output of the low-pass filter. In the error detecting device, a signal is recorded on the optical disk in a form in which the period of the first signal changes, and the second signal is obtained by converting the first signal by a delay circuit. It is characterized by being a signal delayed by about 1/4 period of the minimum period.

Therefore, according to the tracking error detecting device of the present invention, an accurate tracking error signal can be obtained even for an optical disc on which a signal is recorded in a form in which the carrier frequency changes. Can be

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of a first conventional example of the present invention, and FIG. 2 is a signal waveform diagram in the first conventional example. 3 to 12 show an embodiment of the present invention. FIG. 3 is a block diagram of the i-th embodiment, FIG. 4 is a signal waveform diagram in the first embodiment, and FIG. Is a perspective view of the optical system of the first embodiment, FIG. 6 is a block diagram of the second embodiment, FIG. 7 is a circuit diagram of a main part of the second embodiment, and FIG. 8 is a diagram of the third embodiment. Block diagram, FIG. 9 is a signal waveform diagram in the third embodiment, FIG. 10 is a block diagram of the fourth embodiment, FIG. 11 is a circuit diagram of a main part of the fourth embodiment, FIG. 12 is a waveform diagram of signals in the fourth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, first to fourth embodiments of the present invention will be described with reference to FIGS. 3 to 12. FIG.

FIG. 3 to FIG. 5 show the first embodiment. The first embodiment has substantially the same configuration as the first conventional example described above, except that a delay circuit 21 is used in place of the phase shifter 8 as shown in FIG. You can. -If the carrier frequency of the reproduction output signal is single, setting the delay time of the delay circuit 21 to 1 / '4 of the carrier cycle will result in a phase delay of 90, Become equivalent. Therefore, in this case, a tracking error signal can be obtained according to the same principle as the first conventional example described above. If the playback output signal is in the NRZ format, for example, the EFM format, the delay time is set to approximately 12 of the shortest bit length, ie, approximately 1 to 4 periods of the minimum period. Thus in the case of co Npaku Toddy disk, since the minimum peak Tsu preparative length is about 7 0 O ns, the delay ^time: setting the r = 3 5 0 ns.

As a result, the reproduced output signal at the point A in FIG. 3 as shown in FIG. 4A is delayed by the time r by the delay circuit 21 and at the point B in FIG. 3 as shown in FIG. 4B. Signal. On the other hand, the signal at point C is generated by inverting each other around the zero-cross point of the rising and falling of the reproduction output signal. In this case, as shown in Fig. 4C, if the beam is shifted to the right with respect to the recording track, it becomes negative at the rise, positive at the fall, and rises if it is shifted to the left. Positive, negative on falling.

As a result, a signal having a waveform as shown in FIG. 4D is obtained at point D. At point E, as shown in Fig. 4E, a positive DC signal is obtained if the beam is shifted to the right with respect to the recording track, and a negative DC signal is obtained if the beam is shifted to the left. Can be If the beam is on the recording track, the DC signal shown in Fig. 4E will not appear.

That is, similarly to the first conventional example described above, the signal at the point E indicates a tracking error.

FIG. 5 shows the optical system of the first embodiment. A beam 23 emitted from a light source 22 such as a semiconductor laser is passed through a beam splitter 24, a collimator lens 25, and an objective lens 26 to an optical disk (not shown). ). The beam 23 reflected from the optical disc passes through the objective lens 26, the collimator lens 25, and the beam splitter 24, and the light detection units 1 to It is incident on 4.

FIG. 6 and FIG. 7 show a second embodiment. The second embodiment is a system for binarizing a reproduction output signal as digital data, for example, like a compact disk.

Therefore, in the second embodiment, as shown in FIG. 6, a binarizing circuit 27 is provided before the point A for obtaining a reproduced output signal, and a two-pole circuit is provided before the multiplier 12. Circuit 28, that is, a circuit that outputs a + signal when the input signal is 1 and outputs a-signal when the input signal is 0 is provided. Examples of the polarization circuit 28 include a method of adding a bias to a digital signal, a method of AC coupling, and a method of level conversion as shown in FIG. ·

The level conversion type bipolar circuit 28 shown in FIG. 5 comprises an NOT circuit 31, a resistor 32, a transistor 33, and a resistor 34. When a + V cc signal is input, a + V cc signal is output, and when a 0 signal is input, a -V signal is output.

The signal obtained from the bipolarization circuit 28 has substantially the same rising and falling edges, but is substantially the same as the signal shown in FIG. 4B. Therefore, also in the second embodiment, a tracking error signal can be obtained based on the same principle as in the first embodiment.

In this case, the multiplier 12 is used in each of the first and second embodiments.In the actual multiplier 12, the input signals are a and b, and the output signal c is ,

c = k [a b k z a + k 3 b

k i>> k 2, k 3

And -kz and k3 are coefficients for determining the amount of feedthrough, and are 0 when the multiplier 12 is an ideal one. However, if the multiplier 1 2 are omitted or when or null adjustment is inexpensive is, k ₂ or k ₃ are relatively rather large, it is impossible to ignore the influence. '

When k ₂ or k ₃ is relatively large, leaks calibration Li A, S bets la luck ring error signal is deteriorated. In particular, when the pit length is long, the spectrum of the leakage signal spreads to low frequency components, so that the low-pass filter 13 may not be able to sufficiently filter. FIG. 8 and FIG. 9 show a third embodiment capable of coping with such a situation. 9A to 9H show the waveforms of the signals at points A to H in FIG. 8, respectively.The NOT circuit 35, the AND circuit 36, the NOR circuit 37, and the subtractor 38 The output signal has a waveform as shown in FIGS. 9B, 9D, 9E, and 9F, respectively. Therefore, also in the third embodiment, a tracking error signal can be obtained on the same principle as in the first embodiment described above.

However, the symbol at the point F which is the carrier input to the multiplier 12 has a frequency component with a low spectrum removed as shown in FIG. 9F. For this reason, it is possible to prevent the S / N of the tracking error signal from deteriorating.

FIGS. I0 to 12 show a fourth embodiment. In the fourth embodiment, a phase switching amplifier 41 is used in place of the bipolar circuit 28 and the multiplier 12 of the second embodiment shown in FIG.

The second phase switching amplifier 41 is a non-inverting amplifier when the signal at the point A in FIG. 10 which is an input signal is 1: 1 is a non-inverting amplifier, and when it is 0, it is an inverting amplifier. In. It has been established.

That is, the signal at point B in FIG. 12B as shown in FIG. 12B is detected by turning on and off the signal at point A in FIG. 10 as shown in FIG. At point C in FIG. 10, a signal as shown in FIG. 12C is obtained. Accordingly, a smoothed tracking error signal is obtained from the low-pass filter 13.

The first 1 Figure shows a specific circuit example of the phase switching amplifier 4 1, this phase switching amplifier 4 1, consists operational amplifier 4 2, sweep rate pitch 4 3, and a resistor R, ~ R ₃ ing.

Switch 4 3 is off when the signal at point A is 1 and 0 It is configured to turn on when. Therefore, when the signal at point A is 1, the amplification A of the phase switching amplifier 41 is

R 2 R 2

A = 1 + = 1

• R i R 1

When the signal at point A is 0, R z

A = = 1 1 (R, = R ₂ )

R ₁

Becomes That is, the phase switching amplifier 41 can switch the phase by 180.

Industrial applications

As described above, according to the present invention, an accurate track can be obtained even for a compact disc in which the period of the reproduction output signal i changes or an optical disc in which a signal is recorded in a form in which the carrier frequency fluctuates. A kicking error signal is obtained.

Therefore, the configuration is ¾, and it is easy to change to C. It is possible to obtain an accurate tracking error signal with the fg cost device.

Claims

The scope of the claims

1. The first, second, third and fourth light beams formed by being divided into a tangential direction of a recording track of an optical disc and a direction perpendicular to the tangential direction, respectively. A photodetector comprising a detection unit for detecting reflected light from the optical disk;

A second signal based on a first signal, which is a sum signal of the respective detection outputs of the first, second, third, and fourth light detection units, and the third and third lights on a diagonal line; A multiplier for multiplying a sum signal of the respective detection outputs of the detection unit and a third signal which is a difference between the sum signals of the respective detection outputs of the second and fourth light detection units;

A tracking error detecting device for an optical disc, comprising a low-pass filter to which the output of the multiplier is supplied, and a tracking error signal obtained from the output of the low-pass filter. At

A signal is written on the optical disk such that the period of the first signal changes.

The second signal is a signal obtained by delaying the first signal by a delay circuit by approximately 1/4 period of its minimum period, and the tracking error detection of an optical disc is performed. apparatus.

2. The second signal is obtained by binarizing the first signal by a binarizing circuit, and the binarized signal is delayed by a delay circuit to approximately one-fourth of the minimum period of the first signal. 2. The tracking error detecting device for an optical disk according to claim 1, wherein the signal is a signal obtained by delaying the delayed signal only by a bipolar circuit.