JPS59167883A - Disc reproducing device - Google Patents

Abstract

PURPOSE:To compensate track jump by operating a timer device with an output of a flaw detector of a disc to operate a sample-and-hold circuit and switch a driving signal of a pickup driving device to an output of the sample-and-hold circuit. CONSTITUTION:The timer device 21 is controlled by discriminating the presence of a flaw on a disc track by the flaw detecting circuit 12. When no flaw exists, a switch 16 is opened by a control signal of the device 21, a switch 15 is short- circuited to apply a driving voltage of an actuator 11 from a differential amplifier 9 thereby performing normal servo control. If a flaw exists, the sample-hold- circuit 13 is operated for a prescribed time by a control signal of the device 21, the switch 15 is opened and the switch 16 is short-circuited to hold a driving voltage of the actuator 11 to a track error voltage when the actuator enters the flaw, being an output of the circuit 13 for a prescribed time. Thus, when a flaw of the disc is detected, the track jump compensation is attained without any time delay for the detection of the flaw of disc independently of kinds of the flaw.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a digital audio disc (DAD) player and a video disc player, and particularly to a disc optical type that detects defects and scratches on a disc and compensates for track jumps due to defects, etc. One type of pink-up servo for DA and D players is the 3-spot system.

Figure 1 shows the spot method, where 1 is a spot for focus and PCM signal detection.

2 and 3 are spots for dragging +41+42+
43 indicates a signal pitch on a track of the disk.

Spot 2. Each filter is installed so that part of it hangs on the track and the rest hangs on the mirror surface. FIG. 2 is a diagram showing the servo loop of the track, where 5 and 6 are photodetection elements, 7 and 8 are current-voltage converters, 9 is a differential amplifier 10 is a phase compensation circuit, and 11 is a pickup that moves the pickup along the track. This shows the actuator that is used to move it.

Photodetecting elements 5 and 6 receive the reflected light from spots 2 and 6 in FIG. 1, respectively, and output a current according 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, the optical spots 1 to 6 are structured so that they move as one, so if these spots move from the top of the track to the right in Fig. 1, more of the part of spot 2 will hit the mirror surface, Conversely, more of the spot 6 hits the track surface.As a result, the current in the photodetector element 5 increases, the current in the photodetector element B decreases, and a positive voltage is generated at the output of the differential amplifier 9. On the other hand, if spots 1 to 6 move to the left from the track, differential amplifier 9
A negative voltage is generated at the output of the differential amplifier 9. Since the output of the differential amplifier 9 is applied to the big amplifier actuator 11 via the phase compensation circuit 10, the spot 1
If the spot 2 or 2 deviates from the track to the right or left, the positive or negative output voltage of the differential amplifier 9 causes the actuator to completely correct this deviation. Tracking differential amplifier 9
The servo is applied so that the output of . As a result, there is a problem in that a tracking error signal cannot be detected, servo is disabled, and a track jump occurs, so compensation for this is essential.

The inventors of the present application previously proposed this track jump compensation device in Japanese Patent Application No. 146911/1983; Fig. 6 I shows an example of the device, and 12 in the figure shows a flaw detection circuit for the track jump compensation device. , 13-digit sample-and-hold circuit for detecting trunk loop error voltage, 14i switches 15 and 16
This is a switching device consisting of:

When there is a scratch on the disc, this device operates the sample bold circuit 15 based on the output of the scratch detection circuit 12, and at the same time switches 15 and 16f of the switching device 14@
(a) and (b) in the scratch area A shown in Figure 4, respectively.
The pickup actuator is separated from the track loop and connected to the sample/hold circuit, and the pressure applied to the actuator is held at a constant value eH at the moment the pickup enters the wound.

By the way, there are various scratches and defects on discs.

FIG. 5 shows PCM detection signals for direct scratches and defects. (a) is a typical example of black spots and scratches on the disk surface; the maximum value (mirror surface) level of the PCM signal is greatly reduced because the incident light on the disk and the reflected light from the spot are significantly reduced. (b) shows the detection signal in the case of a fingerprint, but there is not such a large reduction in the reflected light of the person 9, and the decrease in the maximum level is smaller than in the case of a scratch in (a).

What's more important here is that it is necessary to compensate for dropouts when the PCM signal is missing, that is, when it exhibits a waveform like (a). ), the S/N may be slightly lower due to fingerprints, dirt on the disc, etc.
Since the tracking error signal can be detected sufficiently by only causing deterioration of the dropout, compensation for dropout should not be performed. On the other hand, in case (b), if dropout compensation, that is, pre-holding of the track error voltage, is performed, the hold time will be long (in terms of distance, the scratch on the tee and the defect will be approximately 1
(20+17A or more for the jam), there is a problem of warping and causing track jumps.

For the above reasons, the flaw detection circuit 12 which operates the compensation device of FIG. 6 is required to have a function of determining the type of flaw (d).

An example of realizing this is shown in FIG. This figure shows a constant DC shift between the output eo1 of the detector 17 that detects the maximum value of the PCM signal qt and the output of the detector 18 that detects a change in the maximum value. 2
For example, the shift voltage ER
If it is set larger than the low knee voltage Eo of the PCM signal maximum level of a fingerprint etc. in FIG. is obtained, making it possible to distinguish it from fingerprints, etc.

However, as can be seen from (a), this circuit has the advantage of being able to identify the type of damaged car, but on the other hand, since the output of one of the detectors is shifted to DC, there is a time delay τo' in detecting the damage. In other words, if the sample-and-hold circuit 1'5 shown in FIG. 6 is operated with this circuit, the track error voltage at a time delayed by τ0 from the time when the pickup enters the scratch will be held, so that the track error voltage shown in FIG. As shown by the broken line, there is a drawback that an error e'e occurs in the hold voltage and the dropout compensation effect due to the hold is reduced.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a disc playback device that eliminates the above-mentioned drawbacks and compensates for track jumps without causing a time delay in detecting scratches on the disc and without being affected by the type of scratches. It is in.

[Summary of the invention]

In order to achieve the above object, the present invention provides a method for detecting a decrease in the maximum value of the P C [vl signal by 1 novel directly without any time delay without providing the flaw detector with the above-described flaw type discrimination function. Therefore, the timer is controlled by this detection signal, and the timer is used to adjust the flaw type and time width.
Regardless of V or i, the start-up actuator is always separated from the track loop for a certain period of time and connected to a sample/hold circuit to hold the voltage applied to the actuator at a certain value.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 7 is a diagram showing an embodiment of the present invention. In the figure, numeral 21 indicates a timer, and other parts with the same reference numerals as in Figs. 2 and 6 refer to the same or equivalent parts.

In this embodiment, the scratch detection circuit 12 determines whether there is a scratch on the disk trunk and limits the timer 21. If there is no scratch, the switch 16 is opened by the control signal of the timer 21 and the switch is switched off. 15 as a smoke path, the drive voltage of the actuator 11 is supplied from the differential amplifier 9 to perform normal servo operation, and if there is a flaw, the timer 21
0 control signal for a certain period of time sample/hold circuit 16
t - At the same time as operation, switch 15 is opened, switch 16 is shorted, and the drive voltage of the actuator is sampled.
The output of the hold circuit is to hold the track difference voltage at the time of entering the flaw for a certain period of time. 2. FIG. 8 shows a specific embodiment of FIG. 7. In the figure, 22 is a disk, 20 is a motor for driving the disk, 24 is an optical big amplifier which is a signal reading device, 25 is a current-voltage converter, 26 is a voltage comparator, 67
Reference numerals 69 to 69 indicate junction field effect transistors (hereinafter referred to as FETs) as electronic switches, and other parts with the same reference numerals as in FIGS. 6 and 7 refer to the same or equivalent parts.

The operation of the circuit shown in FIG. 8 will be explained below with reference to the waveforms of each part shown in FIG.

The level detector 17 is a transistor 27. It consists of a well-known emitter-follower detector consisting of a 29° resistor and a capacitor filter 1, and a transistor 28 for level shifting to correct the voltage drop between the base and emitter of a transistor 270.
It functions to detect and hold a maximum of one wave of the M input signal ei. If the discharge time constant of the switching resistor 29 and the capacitor 61 is set sufficiently large for the time corresponding to the scratch width B on the disk shown in FIG. 9(a), the detection output G
o+ is equal to the peak value of signal ei, as shown in (b).

Further, the level detector 18 is a circuit that detects the maximum value of the input signal, similar to the level detector 17. This is resistance 5
The discharge time constant of 4 and capacitor 66 is set small to follow the change in the PCM signal depression due to scratches, and its output eo2 has an input signal e as shown in (b).
The envelope of the maximum value of i is obtained.

In addition, the voltage comparator 20 compares the levels of the outputs of the level detector 17 and 189, and when eo+ > eo2, (c)
A pulse indicated by K is generated, that is, flaw detection is performed.

The timer 21 is composed of, for example, a well-known monostable multivibrator, and the pulse e03 of the voltage comparator 20
It operates to output a negative pulse eo4'c with a constant time width such as d) <To in synchronization with the rising edge of .

Each of the FETs 57 to 69 is turned on when a negative bias is applied between the input electrode and the gate electrode and the 0FFL bias voltage becomes zero.

That is, the timer 2 is activated by the control signal of the flaw detection circuit 12.
When the output of 1 becomes negative, for example, in the FET 37, a DC current of io flows from the input electrode through the resistor 43 and the diode 40, and the gate electrode is connected to the resistor 43 with respect to the input electrode.
OF
F, and when the output of the timer W21 becomes positive, the diode 40
Due to the rectification action of , io is cut off, the bias voltage between the input electrode and the gate electrode becomes zero, and it operates to turn on.

Further, the resistor 48 and the capacitor 49 constitute a low-pass filter, whose time constant is set to a value that follows the output eB of the differential amplifier 9.

Further, the voltage comparator 26 is an inverter for inverting the output eQd of the timer 21.

With the above configuration, FET 3s is ON'L, F in the area A of Fig. 9 1a) where there is no scratch on the disk track.
Since the ET filter 9 is ``Ol+lF'', the output of the differential amplifier 9 is connected to the pickup actuator 11, and normal servo operation is performed.

Furthermore, since the F E 'T 37 is also in the ON state at this time, a tracking error voltage eR' equal to the output eR of the differential amplifier is obtained at the output of the low-pass filter.

Next, at time t1, when a scratch on the disc is detected by the scratch detection circuit 12, the output of the timer 21 is reversed from positive to 9, and the output of the voltage comparator 26 is reversed from negative to positive. This allows the FE
T37 and 38 are ON-raOF, FFI:T
39 is inverted from OFF to ON, the low-pass filter output eR' is held at the value eH at the moment t1 when the pickup enters the scratch on the disc, and at the same time, this voltage eH is applied to the buffer amplifier 46.39. It is output via FET59. That is, the voltage eA applied to the actuator 11
is the track error voltage eR to FE as shown in (e).
It is held at a constant value eH via the thread path of T39.

Then, at time t2 when a certain period of time 'l''0 determined by the timer w21 has elapsed, the timer 210 (ill) is activated again.
The inversion of the signal causes FETs 37 and 58 to become OF li
Since the FET 39 is turned from ON to OFF, the drive signal eA of the actuator 11 is switched from the hold voltage eH to the track error voltage eR, and normal servo operation is resumed.

The above is a description of the embodiment shown in Fig. 8 (Also, the operation waveforms shown in Fig. 9 are for the case of a scratch shown in Fig. 5 (a), but in the case of a fingerprint etc. shown in Fig. 5 (b)) A similar operation is performed.As mentioned above, there is no need to compensate for disc dirt such as fingerprints because track jumps do not occur in the first place; However, in the present invention, the compensation time range is restricted by the timer, so that no truck jump occurs.

The embodiments of the present invention have been described above. The specific value of the pulse width To of the timer may be designed to a value that can compensate for track jumps by holding the track error'anal pressure.

〔Effect of the invention〕

As described above, according to the present invention, the timer is operated by the control signal of the flaw detection circuit, and the timer operates the sample.
By controlling the hold circuit, even if there are fingerprints or dirt on the disk, the drive signal of the pickup actuator is held at a constant value for a certain period of time, just like in the case of scratches or defects, so it is possible to prevent scratches from occurring like in the conventional example. It is not affected by the type and is caused by the scratch discrimination function. ・It is possible to eliminate the detection delay of the L hold voltage, and it is possible to accurately detect the tracking error signal at the moment when the pickup enters the scratch or dirt on the disc, making it possible to detect track jumps. It is possible to realize a servo circuit with less noise.

[Brief explanation of the drawing]

Fig. 1 shows the positional relationship between signal bits and 6 spots on a disk track, Fig. 2 shows a conventional l-racking servo circuit, and Fig. 4, 5, 1d and 6 showing an example of the operation explanation waveform diagram, 6k to 6 showing an example of the flaw detection circuit, and 7 is an embodiment of the present invention. A block diagram showing
Figure 8 is a diagram showing the specific circuit of Figure 7, and Figure 91 is a diagram showing the specific circuit of Figure 7.
It is a waveform diagram for explaining the operation of the figure. 12...Flaw detection circuit 16...Sample/hold circuit 14...Switching device 21...Time-limited agent patent attorney Akira Takao ffi 1st (21 2nd article 31 yen) 3 Figure 4 457 - Figure 5 No. 6 (0-) (b)

Claims (1)

[Claims] A disc playback device using an optical pickup or the like includes a disc scratch detection device, a timer, a sample hold circuit for sample-bold tracking error signals detected by the pickup, and an input signal for the pickup drive device. Switching device f
d, if there is a scratch on the disc, the timer is controlled by the output of the scratch detector, and the sample bold circuit is operated for a certain period of time by the output of the timer, and the switching device is controlled to drive the pickup. A disc playback device characterized in that a drive signal of the device is switched to the output of the sample and hold circuit.