JPH0466052B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a digital audio disk (DAD) player and a video disk player, and particularly to a disk playback device that detects defects and scratches on a disk and compensates for track jumps due to defects, etc. Regarding.

[Background of the invention]

One type of pickup tracking servo for optical DAD players is the 3-spot system.

Figure 1 shows a three-spot system, where 1 is a focus and PCM signal detection spot, 2 and 3 are tracking spots, 4 ₁ , 4 ₂ ,
4 ₃ indicates a signal pit on the track of the disk.

The spots 2 and 3 are arranged so that a part of each spot is on the track and the remaining part is on the mirror surface. Figure 2 is a diagram showing the servo loop of the track, where 5 and 6 are photodetection elements, 7 and 8
1 is a current-voltage converter, 9 is a differential amplifier, 10 is a phase compensation circuit, and 11 is an actuator for moving the pickup along the track. Photodetecting elements 5 and 6 receive the reflected light from spots 2 and 3 in FIG. 1, respectively, and output a current corresponding to the intensity of the light. These current outputs are converted into voltage values by current-voltage converters 7 and 8, respectively, and a difference between the two is detected by a differential amplifier 9.

Now, light spots 1 to 3 are configured to move as one unit, so if these spots move from the top of the track to the right in Figure 1, more of the part of spot 2 will hit the mirror surface, and vice versa. Spot 3 has a larger portion in contact with the track surface. As a result, the current in the photodetecting element 5 increases and the current in the photodetecting element 6 decreases, so that a positive voltage is generated at the output of the differential amplifier 9. Conversely, when spots 1 to 3 move to the left from the track, a negative voltage is generated at the output of the differential amplifier 9 by the operation opposite to the above. The output of the differential amplifier 9 is applied to the pickup actuator 11 via the phase compensation circuit 10, so if the spots 1 to 3 shift to the right or left from the track, the positive or negative output of the differential amplifier 9 will change. A servo is applied so that the actuator corrects this deviation using the output voltage, that is, the spots 2 and 3 are balanced and tracked, and the output of the differential amplifier 9 becomes zero.

By the way, in the optical servo circuit as described above, if there is a defect in the disk or a scratch on the disk surface, the reflected light from the spot will be lost. For this reason, there is a problem in that the tracking error signal cannot be detected, servo is disabled, and a tracking jump occurs, so compensation for this is essential.

As a way to compensate for this truck jump,
The inventors of the present application previously proposed a circuit in Japanese Patent Application No. 149311/1982. FIG. 3 is a diagram showing one embodiment of the present invention, in which 12 is a disk scratch detection circuit, 13 is a sample and hold circuit for sampling and holding a tracking error signal, and 14 is a switching circuit consisting of switches 15 and 16. The parts shown in FIG. 2 and the same reference numerals as in FIG. 2 refer to the same or equivalent parts.

This circuit focuses on the fact that when a disc is scratched as shown in Figure 4a, the reflected light from the PCM signal detection spot decreases at timing B of the scratch, and the maximum level of the PCM signal decreases. , a flaw detection circuit 12 consisting of a maximum value level detector of the PCM signal, a detector for detecting a change in the maximum value, and a comparator for comparing the levels of these detectors.
Obtain a flaw detection circuit Es such as
4, the switch 15 is turned off and the switch 16 is turned on to hold the drive voltage of the track actuator 11 at the previous value during the scratch period, thereby preventing a track jump.

According to the circuit shown in Figure 3, it is highly effective in compensating for defects such as disk dirt, manufacturing black dots, pinholes, etc., where the PCM signal is missing in a concave shape, and track jumps are prevented to a level that does not pose any practical problems. can do.

However, there are many types of disk defects, and the circuit shown in FIG. 3 is not perfect. For example, for defects such as missing pits on the disk signal surface or bubbles generated in the disk transparent film, the pit surface level rises as shown in Figure 5, and the PCM
The signal appears to be missing in a convex manner.

The circuit shown in FIG. 3 does not compensate for these defects at all, and a normal tracking error signal cannot be obtained in the flawed area, making servo impossible and causing a tracking jump.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a disc playback device that detects scratches on the disc and compensates for track jumps.

[Summary of the invention]

In order to achieve the above object, the present invention focuses on the fact that the PCM detection signal is missing in a convex shape due to defects such as air bubbles in the disk, and has developed a detector that detects the minimum value of the PCM read signal and detects changes in the minimum value. The present invention is to detect flaws by providing a detector for detecting flaws and determining the magnitude relationship between the two levels by a comparator.

Further, the present invention is provided with the above scratch detection circuit, a sample/hold circuit for detecting the track loop error voltage, and a switching device for controlling the drive signal of the pick-up actuator. Therefore, the switching device is controlled at the same time as the sample-and-hold circuit is operated, the pickup actuator is separated from the track loop and connected to the sample-and-hold circuit, and the voltage applied to the actuator is held at a constant value.

[Embodiments of the invention]

FIG. 6 is a diagram showing an embodiment according to the present invention. In the figure, 17 is an information recording disk, 18
19 is a motor for driving a disk, 19 is an optical pickup which is a signal reading device, 20 is a current-to-voltage converter, and 21 is a pickup detection signal, that is, the reflected light from spot 1 shown in FIG. 1 is converted into a current-to-voltage. A detector detects a change in the minimum level of the PCM signal, 22 is a detector that detects the minimum level of the PCM signal, 23 is a voltage comparator, and 34 is an output terminal of the voltage comparator 23.

Referring to the waveform diagram of each part shown in Fig. 7, the following 6.
The operation of the circuit shown in the figure will be explained.

When the disk motor is rotating and the tracking servo is engaged, the reflected light from spot 1 shown in FIG. 1 is received by the pick-up 19 and the current -
It is detected as a signal ei shown in FIG. 7a through the voltage converter 20, and is detected by the level detectors 21 and 22.
is input. Since spot 1 is on the track of the disk and tracks the signal pit, the level of signal ei is constant as shown in area A if there is no scratch. That is, when the spot hits a signal pit, the lowest level signal is output, and when the spot leaves the signal pit and hits the mirror surface, the highest level signal is output.

However, for defects such as missing signal pits on the disk, the highest level signal of the mirror surface is output, and at this time, as shown in area B, the signal level is missing in a large convex shape.

The level detector 21 includes a transistor 24 and a resistor 2.
6. It is composed of a well-known emitter follower detector consisting of a capacitor 28 and a level shift transistor 25 that corrects the base-emitter threshold voltage of the transistor 24, and functions to detect changes in the minimum level of the input signal ei. do. In other words, if the discharge time constant of the resistor 26 and capacitor 28 is set small so as to follow the change in the signal ei due to the disk defect shown in Figure 7, the detected output e ₀₂ will be as shown in Figure 7 b.
The envelope of the minimum value level of ei is obtained as shown in .

Further, the level detector 22 is a circuit that detects the minimum value of the input signal like the level detector 22. Here, the discharge time constant of the resistor 31 and capacitor 33 is set sufficiently large for the time corresponding to the disk defect width B in Figure 7a, and the detected output is
e ₀₁ is equal to the minimum value of the signal ei as shown in FIG. 7b.

In such a configuration, the level detectors 21 and 2
If the voltage comparator 23 compares the levels of the outputs e ₀₂ and e ₀₁ of 2, when e ₀₂ > e ₀₁ , a pulse wave e ₀₃ shown in FIG. can be detected.

By the way, in the circuit of FIG. 6, the level detector 21
If the time constant of the resistor 26 and capacitor 28 is made too small to make the envelope detection too sensitive, or if there is fluctuation in the minimum level of the signal ei, the ripple voltage of _e02 will cause the difference between the output _{of e01} and The magnitude relationship may be reversed and pulses may be generated in areas other than the defective area of the disk as shown by the broken line in FIG. 7c.

FIG. 8 shows another embodiment of the present invention which eliminates the above-mentioned drawbacks. In the same figure, 35
indicates a diode, and other parts with the same reference numerals as in FIG. 6 refer to the same or equivalent parts.

In this example, the envelope detection output of signal ei is
e ₀₂ to its threshold voltage by diode 35.
The level is shifted by V _F , and the output e ₀₂ ' after the level shift and the minimum value detection output of the level detector 22
The comparator 23 attempts to compare the level with e _{01 ,} and as shown _{in FIG .} The generated ripple voltage allows accurate flaw detection without generating unnecessary pulses. Although the embodiment shown in FIG. 8 shows the case where the level of the output _e02 of the level detector 21 is lowered by inserting the diode 35, this is not particularly limited. For example, the transistor of the detector 22 The level of e ₀₁ may be increased by removing the capacitor 30 and directly inputting it to the comparator, or by directly providing an offset to the positive and negative input terminals of the voltage comparator 23. effect can be obtained.

FIG. 10 shows still another embodiment according to the present invention. In the figure, 36 is an inverter, 37 to 39 are junction field effect transistors (hereinafter referred to as FETs) as electronic switches, and 40
42 to 42 are diodes, 43 to 47 are resistors, 4
8 is a capacitor, 49 is a buffer amplifier, 50 is an output terminal of the inverter 36, and other third
Parts with the same reference numerals as in the figures and FIG. 6 refer to the same or equivalent parts.

In this embodiment, a flaw detection device 12 detects the presence or absence of a convex drop in a PCM signal due to a missing pit or the like on a disk track, and if there is no flaw, a switch 39 is activated by a control signal from the flaw detection device. When the switch 38 is opened and the switch 38 is shorted, the actuator 11
A drive voltage of 1 is supplied from the differential amplifier 9 to perform normal servo operation, and if there is a flaw, the sample-and-hold circuit 13 is operated by the control signal from the flaw detection device 12, and at the same time the switch 39 is shorted.
38 is opened and the drive voltage of the actuator 11 is held at the track error voltage at the moment of entry into the flaw, which is the output of the sample and hold circuit.

FETs 37 to 39 are turned off when a negative bias is applied between the input electrode and the gate electrode, respectively.
It turns on when the bias voltage becomes zero.
That is, when the control signal of the flaw detection device 12 becomes negative, for example, in the FET 37, the input electrode is connected to the resistor 34.
A DC current of I ₀ flows through the diode 40 and the gate electrode is negatively DC biased by the voltage drop caused by the resistor 43 with respect to the input electrode.
When it is turned OFF and the control signal of the flaw detection device 12 becomes positive, _I0 is cut off by the rectifying action of the diode 40, the bias voltage between the input electrode and the gate electrode becomes zero, and the device operates so as to turn ON.

Further, the resistor 46 and the capacitor 48 constitute a low-pass filter, whose time constant is set to a value that follows the output e _R of the differential amplifier 9.

Furthermore, as shown in FIG. 11a, the scratch detection device 12 receives a control voltage es which is positive in areas A and C where there are no scratches on the disk and negative in area B where there are scratches, and is complementary to es by passing the control voltage es through an inverter 36. It is configured to output a control voltage es' shown in b.

With the above configuration, the FET 38 is ON in the area A in Fig. 11 where there are no scratches on the disk track.
However, since the FET 39 is turned off, the output of the differential amplifier 9 is connected to the pickup actuator 11, and normal servo operation is performed. Also, at this time
Since the FET 37 is also in the ON state, the low-pass filter output is the output e _R of the differential amplifier 9 shown in Figure 11C.
A track error voltage e _R ' equal to is obtained. Next, at time _T1 , when a scratch on the disk is detected by the scratch detection device 12, the control signal es is reversed from positive to negative, and es' is reversed from negative to positive. This causes FET37 and 38 to go from ON to OFF, and FET39 to go from OFF to
Since it is inverted to ON, the output e _R ' of the low-pass filter is held at the value e _H of T ₁ at the moment when the pick-up enters the scratch on the disk as shown in C. At the same time, this voltage e _H is applied to the buffer amplifier 49 and the FET as shown in d.
39. That is, the voltage e _A applied to the actuator 11 is held at a constant value e _H via the path of the FET 39 from the track error voltage e _R as shown in e.

Then, at time _T2 when the pick-up escapes from the scratch on the disk, FETs 37 and 38 are turned on again from OFF due to the inversion of the control signal of the scratch detection device 12.
Also, since the FET 39 changes from ON to OFF, the drive signal e _A of the actuator 11 becomes the hold voltage e _H
It switches from to the track error voltage _eR and returns to normal servo operation.

By the way, cases where the minimum level of the PCM signal rises and the signal is missing in a convex shape occur not only in the scratched area of the disk described above, but also in the process of pulling in the track servo. Fig. 12 shows this situation, but since the disk necessarily has eccentricity in the process of closing the tracking servo, as the signal reading spot 1 shown in Fig. 1 crosses the track, a The pit surface level changes as shown, and the track error signal also changes accordingly as shown in b. Therefore, if the above-described embodiment is applied as is, the operation of the flaw detection circuit causes an unnecessary sample hold operation to occur when the track loop is drawn in, resulting in a situation in which the servo loop is not closed.

Still another embodiment of the present invention that solves this problem is shown in FIG. In the figure, 51 is an AND circuit, 52 is a state discriminator, and the parts with the same reference numerals as in FIG. 10 refer to the same or equivalent parts. In this circuit, the state discriminator 52
is composed of, for example, a microcomputer that controls the system of the playback device, and is set to "Low" when the tracking servo is pulled in, and "High" when playing the disc (signal readout) after the tracking servo has been pulled. Output a signal. In this configuration, when the track servo is pulled in, the output of the state discriminator 52 is "Low" and the output of the AND circuit 51 is also negative ("Low").
Therefore, the FET 39 is turned off, and the drive voltage of the actuator 11 is not connected to the output of the sample-and-hold circuit during track pull-in. Also, during disk playback after track pull-in is completed, the control signal of the status discriminator 52 is inverted from "Low" to "High", so the sample
The hold path is activated and compensation control similar to the circuit of FIG. 10 is performed in response to detection of a scratch on the disk.

In the circuit shown in FIG. 13, the AND circuit 51 is installed to stop the sample and hold operation when the track servo is pulled in, but the present invention is not limited to this. For example, when the track servo is pulled in, the sample and hold operation is stopped. The positive phase input terminal of the voltage comparator 23 is forcibly biased positively or the negative phase input terminal is forcibly biased negatively by the signal to generate a positive voltage at es and discharge es' to a negative voltage. It is also possible to use means such as setting a time constant and cutting off the FET switch 39.

〔Effect of the invention〕

As described above, according to the present invention, a detection device for detecting defects such as missing pits on a disk signal track can be realized with an extremely simple circuit configuration.

Further, according to the present invention, even if the tracking error signal cannot be detected due to a disk defect, the drive signal of the pickup actuator is held at a constant value of the tracking error signal at the moment the pickup enters the scratch. Therefore, a servo loop that simulates scratches can be constructed, and a servo circuit with less track jump can be realized.

[Brief explanation of the drawing]

Figure 1 shows the signal pits and 3
Figure 2 is a diagram showing the positional relationship of spots, Figure 2 is a diagram showing a conventional tracking servo circuit, Figure 3 is a previously applied circuit diagram for compensating for tracking jumps due to scratches, and Figure 4 is the operation of Figure 3. FIG. 5 is a waveform diagram for explaining a pickup detection signal for a defective disk. FIG. 6 is a diagram showing an embodiment of the present invention. FIG. 7 is a waveform diagram for explaining the operation of FIG. 6. FIG. is a diagram showing another embodiment of the present invention, FIG. 9 is a waveform diagram for explaining the operation of FIG. 8, FIG. 10 is a diagram showing still another embodiment of the present invention, and FIG. 11 is a diagram showing the operation of FIG. An explanatory waveform diagram, FIG. 12 is a diagram showing a pickup detection signal when crossing a track, and FIG. 13 is a diagram showing another embodiment of the present invention. 19...Pickup, 21, 22...Level detector, 23...Voltage comparator, 12...Flaw detection circuit, 13...Sample hold circuit, 14...Switching device.

Claims (1)

[Scope of Claims] 1. In a disc playback device using an optical pickup or the like, the discharge time constant is set to be large relative to the time corresponding to scratches on the disc, so that the pickup output is not affected by scratches on the disc. The first step detects the minimum level of the recorded information signal of
a level detector, and a discharge time constant is set small so as to follow a change in the recorded information signal of the pickup output due to a scratch on the disk, and thus detects a change in the minimum level of the recorded information signal in response to the scratch on the disk. a second level detector for detecting the first level;
and a comparator for comparing the outputs of the second level detector to detect scratches on the disc. 2. The disc playback device according to claim 1, wherein the output of the first or second level detector is passed through a level shift circuit and then compared by the comparator. 3. In a disc playback device using an optical pick-up, the discharge time constant is set to be large relative to the time corresponding to scratches on the disc, so that the minimum recorded information signal of the pick-up output is not affected by scratches on the disc. The first step is to detect the value level.
a level detector, and a discharge time constant is set small so as to follow a change in the recorded information signal of the pickup output due to a scratch on the disk, and thus detects a change in the minimum level of the recorded information signal in response to the scratch on the disk. a second level detector for detecting the first level;
and a flaw detection circuit that includes a comparator that compares the output of the second level detector, a sample and hold circuit that samples and holds a tracking error signal detected by the pickup, and an input signal of the pickup drive device. If there is a scratch on the disk, the scratch detection circuit outputs the sample.
A disc playback device characterized in that the drive signal of the pickup drive device is switched to the output of the sample-and-hold circuit by operating a hold circuit and controlling the switching device. 4. A state discriminator is provided for identifying a tracking servo state of the pickup, and control of the sample/hold circuit and the switching device by the flaw detection circuit is controlled according to the state of the state discriminator. 3. The disc playback device according to item 3.