JPS6190334A - Optical disc player - Google Patents

Abstract

PURPOSE:To restrain a track-jump by establishing an error circuit to detect the top level of an RF signal and by muting the tracking error signal and focus error signal by the output of the error detection output. CONSTITUTION:An RF signal reflected from an optical disc is inputted to an error detection circuit 1, and the circuit 1 detects the top level of the RF signal. The detection signal of the circuit 1 is retained by a latch circuit 2 for about a time corresponding to one rotation of the optical disc, and inputted to an AND gate through an inverter IV. The tracking error signal and focus error signal are supplied to a tracking coil Lt and focus coil Lf through amplifiers 6 and 7 respectively. Transistors Q1 and Q2 are connected by the output of the circuit 1. And, a shocking circuit 3 detects the level of abnormal cycle which is included in the tracking signal. The track-jump is restrained in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical disc player that reproduces information recorded on an optical disc, and particularly relates to a servo control circuit added to an optical pickup. .

[Conventional technology]

Optical disc players that record information about video and audio signals in a spiral shape on the recording surface of an optical disc, irradiate the optical disc with laser light, and reproduce video or audio signals from the reflected light usually use a pickup. It is essential to apply tracking servo so that the spot of the laser beam output from the device moves while accurately tracing the recording track.

As is well known, in order to apply tracking servo, it is necessary to calculate the strength of the spot beam reflected from the optical disk and detect a so-called tracking error signal. ) (BlackDot), etc., the level of reflected light varies, so a pseudo tracking error signal may be output even though the reproduction is at a normal tracking position. Then, this erroneous tracking error signal causes a track jump in which the spotlight moves to an adjacent track, resulting in song skipping, video disturbances, and the like.

In addition, when an optical disc player is mounted on a car, etc., tracking and
And the focus goes out, which also causes a tracking jump.

By the way, in order to provide vibration resistance to the tracking servo and focus servo, it is better to increase the loop gain of the tracking servo. It is preferable to lower the servo loop gain to improve defect tolerance.

Figure 3 shows the patent application No. 58-18060 proposed by the present applicant.
6 is a block diagram showing an outline of the tracking servo circuit described in No. 6, in which 10 is a positive phase amplifier, 11 is a negative phase amplifier, 12.13 is a base voltage Vr1. A comparator with Vr2 added to one input terminal, 14.15 a diode, 16.17 a time constant circuit, and 18.19 an output amplifier.

The operation of this circuit will be explained below with reference to the waveform diagram in FIG.

The RF multiplied signal output from the optical pickup device is 1
It is assumed that the user encounters scratches or dust on the optical disc at a point, and receives an external shock at three points. Further, the RF multiplied signal indicates the output of the amplifier 1 which is in reverse phase, and the RF multiplied signal which is the output of the normal phase amplifier 10 is compared with the reference voltage Vrl by the next comparator 12, so the reference voltage Vrl is voltage v
At a level lower than r1, diode 14 conducts and charges capacitor C1. Therefore, the defective part of the RF multiplied signal generated at one point is output from the output amplifier 18 as the detection signal C, but the distortion of the RF multiplied signal due to the shock at three points is caused by the reference voltage Vrl being set high. Since the diode 74 is not made conductive, it is not detected.

In addition, even in the comparator 13 to which the RF multiplied signal with the opposite phase is supplied, the diode 1 is turned off at a level lower than the reference voltage Vr2.
5 is conductive, but in this part 1, which is a scratch on the optical disc, is conductive.
The defect signal at one point is not detected, but the shock-like distortion modulation at three points is detected, and a detection signal is outputted from the output amplifier 19.

Therefore, according to this circuit, the RF signal distortion modulation output from the optical pickup device can be detected for each cause, so the loop gain E of the tracking servo circuit is determined by the detection signal C that detects scratches, dust, etc.
If the loop gain E of the tracking servo circuit is increased using a detection signal detecting a disturbance shock or vibration, the tracking servo function will be improved.

[Problem that the invention seeks to solve]

However, the above circuit has the following problems.

Defects in the optical disc are detected from the return light of the optical disc, so by the time a defect signal is detected, the reflected light has already decreased, and a normal focus error signal cannot be obtained, especially when the defect is large. Not only that, but a pseudo focus error signal is output and the defocus condition 7
Become U1. Therefore, a pseudo tracking error signal is also output.

That is, as shown in FIG. 5, when an RF multiplied signal indicating a defect is output, the period t is
During period t1, the gain E of the tracking servo circuit is controlled to be reduced by the detection signal C. However, during this period t1, there is almost no reflected light, so stray light in the optical system and a false focus error signal due to offset are generated. ef' is output, and further a pseudo track signal et' is output.

These two error signals then shift the objective lens and reflection mirror from their normal positions. the result,
Distortion also occurs in the lower envelope of the RF multiplied signal, and a normal tracking servo state may not be achieved even at the end of the detection signal C, resulting in a track jump.

This invention was made to solve this problem, and when the optical disk moves to a defective part during playback, a pseudo focus error signal and a pseudo tracking error signal generated by the disturbance of reflected light are generated. An object of the present invention is to provide an optical disc player in which the occurrence of track jumps can be suppressed by having a structure that does not affect the objective lens or reflection mirror of a pickup.

[Means for solving problems]

The present invention provides a defect detection circuit for detecting a defective portion of an optical disc, and a muting circuit for suppressing a tracking error signal and a focus error signal using signals obtained from the defect detection circuit, and suppresses tracking error signals and focus error signals generated at the defective portion. Prevent a pseudo tracking error signal or a pseudo focus error signal from being supplied to the tracking control coil and the focus control coil.

[Effect]

When the optical pickup detects a defective part of the optical disc,
Muting is applied to the circuit that supplies the tracking error signal and the focus error signal by the detection signal output from the defect detection circuit. Therefore, the objective lens or reflection mirror is prevented from being moved significantly by the pseudo trunking error signal and pseudo focus error signal generated at the defective part, so that after passing through the defective part, the normal tracking error signal or focus error signal is generated. When an error signal is obtained, the objective lens or reflection mirror immediately follows this signal and enters a normal tracking state, making it possible to suppress track jumps.

〔Example〕

FIG. 1 is a block diagram showing a servo control circuit of an optical disc player which is an embodiment of the present invention, and FIG.
The figure is a main waveform diagram in the block diagram of FIG. 1.

In these figures, 1 is a defect detection circuit into which a reproduced signal reflected from the optical disk (hereinafter referred to as RF signal) is input, and 2 is a defect detection circuit that receives the detection signal of the defect detection circuit 1 approximately in one rotation time (330 ms) of the optical disk. The holding latch circuit may be, for example, a ridrigger type monostable multivibrator. 3 shows a shock detection circuit that detects the level of abnormal period included in the tracking error signal, and a band pass filter 4 that detects a signal component with a high period generated by adjustment etc. It is constituted by a window comparator 5 which outputs a signal when the above value is reached. 6 is a tracking amplifier that supplies the tracking error signal to the tracking coil Lt, and as described later, when the signal is output from the AND gate A, the amplification gain is increased and the phase constant is slightly changed. . A focus amplifier 7 amplifies the focus error signal and supplies it to the focus coil Lf.

Ql and Q2 indicate muting transistors formed in the supply path of the tracking error signal and the focus error signal, and are turned on by the output of the defect detection circuit 1.

Note that r3 + rS is the coupling resistance, r,, l r
(, indicates a base resistance, and R4 and C4 indicate a time constant circuit of approximately 0.5 ms.

Next, the operation of the circuit will be explained with reference to the waveform diagram in FIG.

The waveform (a) showing the RF multiplied signal reproduced from the optical disc includes shock modulation distortion as shown by the 8 points and distortion modulated by scratches and black dots on the disc as shown by the BD point. .

When the shock generated at 8 points modulates the RF multiplied signal waveform as shown in (a) (normally, in the case of a shock, R
The lower envelope of the F-fold signal is modulated), and at this point the tracking error signal e as shown by the waveform (fo) is generated.
t and a focus error signal ef represented by a waveform (jO) are output, but the focus error signal (fo) included in the tracking error signal et is detected by the bandpass filter 4 in the detection circuit 3. Furthermore, the reference level Er1. set in the window comparator 5. Er
A signal when the value is 2 or more is detected as shown in waveform (g).

Then, this waveform (g) increases the gain of the tracking amplifier 6 through the analogue (A), so it is used in the optical disc player. When Ii 9x is added, the loop gain of the tracking servo is improved, effectively preventing track jumps caused by shock.

On the other hand, when the RF signal is modulated by the defect occurring at the BD point, the upper envelope is detected by the diode DI of the defect detection circuit 1 and the time constant circuits R1 and C, so the signal shown in waveform (b) is is supplied to one input terminal of the comparator CMP via the capacitor co. moreover,
Diode D2, and large time constant circuit R2+C2
A waveform (C) indicating the RF multiplied signal peak level is outputted by the RF signal and supplied to the input terminal of the comparator CMP. Since the forward voltage of the diode D3 is added to the waveform (b), the output of the comparator CMP is the waveform (d).
As shown in the figure, a signal indicating the position of point BD, which is the defective part, is output.

Since this waveform (d) is applied to the transistor Q1.92, the waveform (f+) of the pseudo tracking error signal et generated when a defective portion is detected, and the waveform (f+) of the pseudo focus error signal ef ( jo) is the transistor Q1. The conduction of Q2 causes the signal to be bypassed and is prevented from being supplied to the tracking coil Lt and the focus coil Lf. That is, this muting effect prevents the objective lens or reflection mirror of the optical pickup from being moved by a false error signal.

Therefore, when the spot light of the optical pickup deviates from the defective part, a normal tracking error signal etc.
, or the focus error signal ef becomes easy to follow, and disturbances immediately after a defect are effectively prevented.

Note that if the defect continues for more than 1 ms, the objective lens or reflective mirror will completely deviate from the focal position during that time.
Since there is a risk of deviation from the tracking lock range, it is preferable that the muting period of the focus error signal ef is limited to about 0.5 ms by the time constant circuits C4 and R4.

The output of the defect detection circuit 1 is held in the latch circuit 2 for approximately one rotation period (330 ms) of the disk, and is input to the AND gate A via the inverter IV.
According to the waveform (e), when a defective part is encountered, the detection signal of the shock detection circuit 3 is prohibited from being input to the tracking amplifier 5 until the laser beam of the optical pickup travels through the defective part in the radial direction and exits the defective part. .

Therefore, 2 BD points and 3 R0 points after the 2nd round...
・Pseudo tracking signal et' caused by a defect in
is sent to the tracking amplifier 5 via the shock detection circuit 3.
, and prevents the tracking servo circuit from increasing its loop gain.

Furthermore, even if the focus servo is muted for about 0.5ms, it will not immediately become defocused.
Defects in ordinary optical discs have little effect.

Although the embodiment uses the transistor Q++Q2 as the muting circuit, other muting circuits may also be used.

〔Effect of the invention〕

As explained above, the optical disc player of the present invention performs muting so as not to supply pseudo tracking error signals and pseudo focus error signals caused by defects in the optical disc to the objective lens or the control coil of the reflection mirror. This has the advantage that it is possible to effectively prevent track jumps from occurring due to pseudo error signals caused by defects.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the servo control circuit employed in the optical disc player of the present invention, Fig. 2 is a main waveform diagram showing the operation of Fig. 1, and Fig. 3 is a circuit diagram showing the operation of the prior art. FIG. 4 is an operational waveform diagram of FIG. 3, and FIG. 5 is a waveform diagram for explaining a pseudo error signal. In the figure, 1 is a defect detection circuit, 2 is a latch circuit, 3 is a shock detection circuit, 4 is a band pass filter, 5 is a window comparator, 6 is a tracking amplifier, 7 is a focus amplifier, Ql, Q2 are transistors for muting shows. ^ To ^
■ -C・-Φ
Figure 5 Procedural amendment (former h)

Claims (1)

[Claims] RF output from optical disc player pickup
Equipped with a defect detection circuit that detects the top level of the signal and outputs a signal indicating a defective portion of the optical disc, and a muting circuit that operates based on the output of this defect detection circuit and mutes the tracking error signal and focus error signal. An optical disc player characterized by: