JPS61145737A - Signal omission detecting circuit of optical disk reproducer - Google Patents

Abstract

PURPOSE:To detect a flaw on a vapor deposition surface as well as one on a transparent substrate by supplying a tracking error signal and the output of a through rate limiting circuit to a subtractor for extraction of the differential component between them, and controlling variably the open loop gain of a tracking servo. CONSTITUTION:The output S20 of the 2nd level comparator 20 is kept at an L level. However, a tracking error signal TE has a big change of amplitude wen a flaw part on the vapor deposition surface is reproduced. Then the output S25 of a through rate limiting circuit 25 is shown by a figure (e) owing to an internal time constant. Here the output S25 is subtracted from the tracking error signal TE of a subtractor 24 and the subtraction signal S24 is shown by a figure (f) and exceeds continuously the reference voltage + or -Vref2 of the 1st level comparator 26 when the flaw part is reproduced. Thus the comparator 26 outputs the pulse signals S26 continuously. Then the 1st detection signal S27 outputted from a monostable multivibrator 27 which uses the signal S26 as a trigger signal is set at an H level (h) when the flaw part is reproduced. Thus the flaws are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical disc playback device suitable for, for example, a CD (compact disc) type DAD (digital audio disc). This invention relates to improvements in a signal dropout detection circuit that detects signal dropout portions caused by scratches on the internal vapor deposition surface, distortion, etc.

[Technical Background of the Invention] Conventionally, optical disc playback devices have been provided with a track jump prevention circuit to prevent the track from being traced (track jump) when playing a scratched part of the disc. There is. Figure 6 shows the conventional CD
1 shows the configuration of a track jump prevention circuit applied to a disc playback device (hereinafter referred to as a CD playback device).

That is, in this CD playback device, as is well known, the RF signal generated from the output signal of an optical pickup (not shown) is used.
After AC coupling with the signal doubler capacitor 11, the waveform shaping circuit 12 makes the amplitude constant, and the EFM signal generating circuit 13
After converting into an FM signal, the information signal recorded on the disk is read out by leading it to a data demodulation system (not shown), and a tracking error signal TE is generated based on the output signal of the pickup, and the tracking error signal TE is generated based on the output signal of the pickup. The signal TE is transmitted through an amplifier 14, an attenuation circuit 15 (described later), a phase compensation circuit 16, and an actuator drive circuit 17.
By supplying the light to the tracking actuator coil 18 through the optical pickup, tracking servo is performed by controlling the movement of the objective lens in the pickup so that the light beam emitted from the pickup always correctly traces the pit row.

In such a CD playback device, the track jump prevention circuit includes a signal dropout detection circuit that detects a signal dropout due to a scratch on the disc from the RF multiplied signal level change, and a detection output of this detection circuit that detects the open loop gain of the tracking servo. It is composed of an attenuation circuit 15 that controls the
The signal loss detection circuit is composed of an envelope detection circuit 19 and a level comparison circuit 20, and the attenuation circuit 15 is composed of resistors R1°R2 and an analog switch SW.

That is, the signal loss detection circuit extracts the output signal of the waveform shaping circuit 12, supplies it to the envelope detection circuit 19, and detects the RF multiplied signal peak envelope. Then, the envelope signal S19 is sent to the level comparison circuit 2.
0 and compares it with the reference voltage Vref1, and detects that the envelope signal 819 has become lower than the reference voltage Vref1, and generates the switching control signal 820. It is supplied to the control input of the analog switch SW of the circuit 15. This attenuation circuit 15 is designed to increase or decrease the open loop gain of the tracking servo by switching the analog switch SW in accordance with the switching control signal S20.

In this manner, the track jump prevention circuit reduces the tracking servo open loop gain when reproducing scratched portions of the disc, making it difficult for track jumps to occur.

That is, when tracing a scratched portion on the transparent base material of the disk, a signal missing portion as shown in FIG. 7(a) occurs in the RF multiplied signal. Then, the above envelope signal S
19 is a signal missing portion where the reference voltage V ref1 is lower than the reference voltage V ref1 as shown in FIG. At this time, the tracking error signal TE changes greatly at the signal missing portion even though the light beam is correctly tracing the pit row as shown in FIG.
0 to switch 111 @ signal 320 as shown in the same figure (d).
is output, so it is attenuated by the attenuation circuit 15 and supplied to the tracking actuator coil 17. Therefore, track jumping of the light beam can be prevented even when reproducing a scratched part of the disc.

[Problems with the Background Art] By the way, for example, in the above-mentioned CD system disc, as shown in FIG. , protection@C, and label d are formed by overlapping them.

However, the signal dropout detection circuit used in the track jump prevention circuit of the conventional optical disc playback device as described above is
Since it does not operate unless the double signal envelope signal S19 becomes equal to or lower than the reference voltage V ref , for example, scratches, distortions, and dust on the vapor deposition surfaces of the transparent base material a and the reflective material ab that occur during disk manufacturing. etc. (hereinafter collectively referred to as scratches on the vapor deposition surface), it is often impossible to detect them.

In other words, even if the scratched portion of the evaporation surface is reproduced, it is unlikely that the entire signal component will be lost as shown in FIG. 9(a) of the RF multiplied signal. In such a case, the envelope signal 819 is equal to the reference voltage V r as shown in m(b).
Do not go below efl. However, if there is a scratch on the reflective film b1 of the disk on which the light beam is focused, that is, on the vapor deposition surface, it will have a large effect on the reflected light and will disturb the signal components, so the tracking error signal TE will be traced even though it is correctly traced. This results in a large change as shown in FIG. 3(C). At this time, the level comparison circuit 20 is
), since the switching control signal S20 is not output,
The tracking error signal TE is directly output to the tracking actuator coil 18, making it easy to cause track jumps.

For this reason, it has been strongly desired that the signal loss detection circuit be capable of detecting not only scratches on the transparent substrate of the disk but also scratches on the vapor deposition surface.

[Purpose of the Invention] This invention was made in consideration of the above circumstances, and it is possible to detect not only scratches on the transparent base material of the disk but also scratches on the vapor deposition surface, thereby reliably preventing track jumps. It is an object of the present invention to provide a signal dropout detection circuit for an optical disc playback device that can also perform the following steps.

[Summary of the Invention] That is, the signal loss detection circuit of the optical disc playback device according to the present invention is applicable to a disc formed by forming pit row grooves corresponding to information signals in a transparent base material and depositing a reflective film on the transparent base material. , an optical pickup is used to emit a light beam, and the reflected light is received and photoelectrically converted to read out the information signal recorded on the disk, and the tracking error is detected based on the output signal of this optical pickup. The tracking servo has an open loop in which the light beam is always irradiated to the center of the pit row by generating a signal and controlling the movement of the objective lens based on the tracking error signal, wherein the tracking error signal is input to a slew rate limiting circuit to limit the slew rate, the tracking error signal and the output of the slew rate 11 limiter are input to a subtracter to extract the difference component, and this difference component is input to the comparison circuit. The present invention is characterized in that the open loop gain of the tracking servo can be variably controlled based on the comparison result of the comparison circuit.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to FIGS. 1 to 3. However, in FIG. 1, the same parts as in FIG. 5 are designated by the same reference numerals, and only the different parts will be described here.

FIG. 1 shows a configuration in which the present invention is applied to a CD playback device, and numeral 21 in the figure is an optical pickup.

A frequency signal (RF low signal) corresponding to the presence or absence of pits detected by the optical pickup 21 is amplified by the amplifier 22, then the capacitor 11, waveform shaping circuit 12, E
The signal is converted into an EFM digital signal via the FM signal generation circuit 13.

Further, the frequency signal output from the pickup 21 is supplied to a tracking error signal generation circuit 23, and the tracking error signal TE is generated. This tracking error signal TE is transmitted to the amplifier 14 and the attenuation circuit 1.
5. The signal is supplied to the tracking actuator coil 18 via the phase compensation circuit 16 and the actuator drive circuit 17, and is used for the tracking servo described above.

In the CD playback device as described above, a track jump prevention circuit using the signal loss detection circuit according to the present invention has the following features:
The tracking error signal TE is taken out and subtracted by a subtracter 24.
The output signal 825 of the slew rate limiting circuit 25 is supplied to the (+) input terminal of the subtracter 24 as well as to the slew rate limiting circuit 25 having a predetermined time constant.
) is supplied to the input terminal. The output signal @S24 of this subtracter 24 is then sent to the first level comparator circuit 2.
6, it is compared with the reference voltage ±vref2. This level comparison circuit 26 has an input signal 324 of a reference voltage ±V ref2.
H level when it is above, L level when it is below ±V ref2
It outputs a pulse signal 826 that becomes a level, and this pulse signal 826 is supplied to the mono multivibrator 27 as a trigger signal. The output signal (first detection signal) S27 of this mono multivibrator 27 is supplied to one input end of an OR gate circuit 28. Further, the RF low signal outputted from the waveform shaping circuit 12 is envelope-detected by the envelope detection circuit 19 as described above, and this envelope signal S19 is sent to the level comparison circuit (hereinafter referred to as tube 2).
(referred to as a level comparison circuit) 20, and is compared with a reference voltage V refl. The output (second detection signal) S20 of the second level comparison circuit 20 is supplied to the other input terminal of the OR gate circuit 28. The output signal 828 of this OR gate circuit 28 is supplied to the control input terminal of the analog switch SW of the attenuation circuit 15.

The operation of the above configuration will be described below with reference to FIGS. 2 and 3.

First, suppose there is a scratch on the transparent base material of the playback disc.
When reproducing the RF low signal flawed part, the signal component is lost as shown in FIG. 2(a), which causes the envelope signal 8
19 becomes equal to or lower than the reference voltage Vref1, as shown in FIG. Therefore, the second level comparison circuit 20 detects that there is a scratch on the disc and outputs a second detection signal 320 as shown in FIG. At this time, the tracking error signal TE generates a large amplitude as shown in FIG. Since the open-loop gain of the tracking servo in that portion is reduced, the signal is attenuated by the attenuation circuit 15 and then led to the actuator coil 19.

In other words, when reproducing the scratched part, the open loop gain of the tracking servo decreases, making it difficult for track jumps to occur.

The tracking error signal TE is also supplied to the slew rate limiting circuit 25, which outputs a signal S25 as shown in FIG. 2(e) using an internal time constant. A subtracter 24 extracts the tracking error signal TE from the slew rate limiting circuit 2.
When the output 825 of 5 is subtracted, the subtracted signal 824 becomes as shown in FIG.
Do not exceed the reference voltage ±V ref2. Therefore, as shown in (Gl) and (h) in the figure, since the output 826 of the level comparison circuit 26 remains at the L (low) level, the first detection signal 8 output from the mono multivibrator 21
27 also remains at L level.

Next, if there is a scratch on the evaporated surface of the reproduction disk, the amplitude level of the RF low signal changes as shown in FIG. 3(a). Therefore, the envelope signal 819 is as shown in FIG.
However, the voltage does not become lower than the reference voltage V ref1. Therefore, the output S of the second level comparison circuit 20
20 maintains the L level as shown in FIG. 2(C). However, when reproducing such a scratched part on the vapor deposition surface, the tracking error signal TE shows a large amplitude change when reproducing the scratched part, as shown in FIG. Since the output 825 becomes as shown in FIG. 2(e) due to an internal time constant, when the output 825 of the slew rate limiting circuit 25 is subtracted from the tracking error signal TE by the subtracter 24, the subtracted signal S24 becomes as shown in FIG.
), the reference voltage ±V ref2 of the first level comparator circuit 26 is continuously exceeded when the damaged portion is regenerated. For this reason, the level comparison circuit 26 is
), the first detection signal 82 output from the mono multivibrator 21 uses this pulse signal 826 as a trigger signal.
7 becomes H level when the scratched portion is reproduced, as shown in FIG. 7(h), and it is detected that there is a scratch on the evaporated surface of the reproduced disk. Therefore, since the OR gate circuit 28 outputs the output 827 of the mono multivibrator 27, the open loop gain of the tracking servo decreases when reproducing the scratched portion, making it difficult to cause track jumps.

Therefore, if a track jump prevention circuit is configured in a CD playback device using the signal dropout detection circuit as described above,
The open loop gain of the tracking servo is variably controlled by detecting not only scratches on the transparent substrate of the disc but also scratches on the vapor deposition surface, making it possible to reliably prevent track jumps and ensure stable disc playback. be able to.

Incidentally, in the above embodiment, all the signals are subjected to analog processing, but they may be configured as shown in FIG. 4 and processed digitally. That is, in FIG. 4, the output 819 of the envelope detection circuit 19 is a tracking comparison type analog signal composed of an analog comparator 29, an up/down (U/D) counter 30, and a digital/analog (D/A) converter 31. The converted digital data D1 (corresponding to TE) is input to the digital (A/D) converter and is sent to the data comparator circuit 32 at the reference voltage ■refl shown in FIG.
It is compared with slice level data D2 corresponding to . This data comparison circuit 43 outputs a pulse signal (corresponding to S20) that becomes H level when the data D1 becomes less than or equal to D2, and this pulse signal is supplied to the OR gate circuit 28. Further, the tracking error signal TE is transmitted to an A/D converter 33 having the same configuration as the A/D converter.
The data is converted into digital data D3 and inputted to a slew rate limiting circuit section composed of a digital comparator 34 and an LJ/D counter 35. Here, U/D counter 3
5 is operated, the Otsukku pulse CP2 (frequency f2
) is made smaller than the reference clock CP1 (frequency f1°N > f2) of the A/D conversion section, the output data D4 (corresponding to 825) of the slew rate limiting circuit section
does not follow the data D3, and as a result, the slew rate is limited. The data D3 and D4 are subtracted by the digital subtracter 36, and the subtracted data D5 is compared with the slice level data D6 corresponding to the reference voltage ±V ref2 in FIG. 1 by the data comparison circuit 31. When this occurs, a pulse signal (corresponding to 826) is generated. This pulse signal drives the mono-multivibrator 27. Therefore, according to the above configuration, it is possible to digitally process the detection of scratches on the reproduction disc and the variable control of the open loop gain of the tracking servo.

Furthermore, the mono multivibrator 27 used in each embodiment is of a re-trigger type, and a pulse signal 827 is used to connect the short pulse train 326 output from the level comparison circuit 26 to determine the regeneration period of the damaged part. Therefore, as shown in FIG. 5, the first and second inverters 27a and 27b and the resistor R3
, a time constant circuit 2 consisting of a diode D and a capacitor C
7c.

[Effects of the Invention] As detailed above, according to the present invention, an optical system that can detect not only scratches on the transparent base material of a disk but also scratches on the vapor deposition surface, thereby reliably preventing track jumps, is provided. According to the present invention, a signal loss detection circuit for a type disc playback device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block circuit configuration diagram showing an embodiment of a track jump circuit of an optical disc playback device according to the present invention, and FIGS. 2 and 3 show output waveforms of each part to explain the operation of the same embodiment, respectively. 4 is a block circuit configuration diagram showing another embodiment of the present invention, FIG. 5 is a block circuit diagram showing the configuration of a mono multivibrator used in each of the above embodiments, and FIG. 6 is a block circuit diagram showing the configuration of a mono multivibrator used in each of the above embodiments. A block circuit diagram showing the structure of a jump circuit, FIG. 7 is an output waveform diagram of each part to explain the operation of a conventional track jump prevention circuit, FIG. 8 is a cross-sectional view showing the structure of a CD system disc, and FIG. 9 These are output waveform diagrams of various parts for explaining the problems of the conventional track jump prevention circuit. DESCRIPTION OF SYMBOLS 11... AC coupling capacitor, 12... Waveform shaping circuit, 13... EFM signal generation circuit, 14... Amplifier, 15... Attenuation circuit, 16... Phase compensation circuit, 1
7... Actuator drive circuit, 18... Tracking actuator coil, 19... Envelope detection circuit, 20... Level comparison circuit, 21... Optical pickup, 22... Amplifier, 23... Tracking error signal generation circuit, 24... Subtractor, 25...
- Slew rate limiting circuit, 26... first level comparison circuit, 27... mono multivibrator, 28...
OR gate circuit, 29...analog comparator, 3
0...U,/D counter, 31...D/A converter, 32...data comparison circuit, 33...A/D conversion section, 34...digital comparator, 35...LJ
/D counter, 36... digital subtracter, 31...
Data comparison circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 1 + vrene-"hh Figure 2 Figure 3 Figure 5 Z/ Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] An optical pickup is used to irradiate a light beam onto a disk made of a transparent substrate with pit row grooves formed in response to information signals and a reflective film deposited on it, and the reflected light is received for photoelectric conversion. The information signal recorded on the disk is read out by generating a tracking error signal based on the output signal of the optical pickup and controlling the movement of the objective lens based on the tracking error signal. In an optical disc playback device having an open loop of a tracking servo, the tracking servo always illuminates the center of the pit row; It includes a subtracter that inputs the signal and the output of the slew rate limiting circuit and detects the difference component thereof, and a comparison circuit that inputs the output of the subtracter and compares it with a reference value. 1. A signal dropout detection circuit for an optical disc playback device, characterized in that the open loop gain of the tracking servo can be variably controlled based on the above.