JPS6231035A - Tracking servocontrol circuit of disk reproducing device - Google Patents

Abstract

PURPOSE:To facilitate handling and to eliminate malfunction, and to perform stable disk reproduction by detecting the extent of a flaw in a disk and varying the open loop gain of a tracking servo loop circuit automatically. CONSTITUTION:The output terminal of an AND circuit 27 is connected to the input terminal of a buffer circuit 26. The output terminal of a vibration detecting circuit 24 is connected to one input terminal of the AND circuit 27 and the output terminal of a counter circuit 28 is connected to the other input terminal. Then a flaw detecting circuit 29 and a timing generating circuit 30 are connected to the counter circuit 28 respectively. If the extent of the flaw in the disk increases and an L-level flaw detection signal S3 is generated by the counter circuit 28, the output of the AND circuit 27 is set to a level L without reference to the output of a vibration detecting circuit 24 and a switch 23 is turned off to set the open loop gain low corresponding to the flaw.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a disc playback device such as a compact disc player, and particularly relates to a tracking servo loop circuit that adjusts the tracking servo loop according to the amount of external vibration generated and the amount of scratches on the disc. This invention relates to an improvement in which the open-loop gain is switched.

[Technical Background of the Invention] As is well known, in an optical disc playback device such as a compact disc player or a video disc player, an optical pickup is provided for reading data recorded on the disc. The objective lens
Tracking servo is applied to always follow the data track of the disk.

This tracking servo generates a tracking error signal corresponding to the deviation of the objective lens from the track based on the data read from the disk, and based on this tracking error signal ``controls the objective lens so that the track deviation is eliminated. This is done by configuring a so-called tracking servo loop circuit.

FIG. 7 shows a conventional tracking servo loop circuit using a three-beam type optical pickup. That is, 11 in the figure is the main beam detector,
A main laser beam that is irradiated onto the disk and reflected through an objective lens (not shown) is received.

Here, the main beam detector 11 is configured in a four-division type having four light-receiving areas a to d, and the signals output from each light-receiving area a to d are added by an adder circuit 12 and multiplied by RF. A signal is generated. This RF multiplied signal is supplied to a demodulation/reproduction circuit system (not shown) via the output terminal 13 for reproduction operation.

Furthermore, the light receiving area tii of the main beam detector 11 is
Signals output from Ja, c, and Ja and d are current-added to each other. And this two current addition signal is
The subtraction circuit 14 performs subtraction, and the low-pass filter circuit 15 removes high-frequency bit signal components, thereby generating a focus error signal FE corresponding to the deviation of the objective lens from the focused position. This focus error message @
The FE is supplied via the output terminal 16 to a focus actuator (not shown) that moves the objective lens in the focus direction, and is used for focus servo.

On the other hand, reference numerals 11a and 11b in the figure are sub-beam detectors, which respectively receive the sub-laser beams irradiated onto the disk through the objective lens and reflected. This sub-beam detector 11a.

The signal output from 11b is subtracted by a subtraction circuit 17, and a high-frequency bit signal component is removed by a low-pass filter circuit 18, thereby generating a tracking error signal TE corresponding to the deviation of the objective lens from the track. Ru.

The tracking error signal TE is transmitted to a gain control circuit 19 consisting of an operational amplifier opi and resistors R1 and R2.
The signal is supplied via a phase compensation circuit 20 and a drive circuit 21 to a tracking actuator coil 22 that moves the objective lens in the tracking direction, where tracking servo is applied.

In this case, the sub-beam detectors IIA, IL
A series of circuits from b to the tracking actuator coil 22 constitute a tracking servo loop circuit, and its open loop gain is controlled by turning on and off a switch 23 connected to the gain control circuit 19. It is designed to be switchable. That is, the open loop gain of the tracking servo loop circuit becomes low when the switch 23 is in the off state, and becomes high when the switch 23 is in the on state.

The switch 23 is normally in an off state, and is controlled to be in an on state by being supplied with a detection signal output from the vibration detection circuit 24 via a manual switch 25 and a buffer circuit 26. . This vibration detection circuit detects, for example, level fluctuations of the above-mentioned 1-racking error signal TE, and detects whether the objective lens has caused or is about to skip a track during disk playback due to externally applied vibrations. It detects this and generates a detection signal.

Here, the main reasons why the objective lens causes or is likely to cause undesired track skipping during disk playback are when external vibrations are applied as mentioned above;
It is thought that there may be scratches (defects) on the disc itself. In this case, external vibration can be dealt with by increasing the open loop gain of the tracking servo loop circuit. However, in order to deal with scratches on the disk, it is necessary to lower the open loop gain of the tracking servo loop circuit, which is a mutually contradictory problem.

Therefore, conventionally, as shown in Fig. 7, the switch 23 is turned off during normal playback to lower the open lube gain in order to prevent scratches on the disc. When the user turns on the manual switch 25 and a detection signal is generated from the vibration detection circuit 24, the switch 23 is turned on and the open loop gain is increased to cope with external vibrations.

The reason why we prioritized dealing with disc scratches over dealing with external vibrations is that external vibrations can be absorbed to some extent by the mounting mechanism of an optical pickup, and in general, In many cases, the tracking error signal TE is used as the detection input of a vibration detection circuit, and in this case, the vibration detection circuit erroneously detects the level fluctuation of the tracking error signal TE due to scratches on the disk as being caused by external vibration, and the detection signal is This is to prevent this from occurring.

[Problems in the Background Art] However, in the conventional open loop gain control means of the tracking servo loop circuit as described above, the user can manually switch 2 in response to external vibrations, scratches on the disk, etc.
5 has to be turned on and off, which makes handling complicated. In addition, especially when there are parts with few scratches and parts with many scratches on a single disc, try to deal with the external vibration in the part with few scratches, and when it reaches the part with many scratches, Switching to deal with wounds is a basolateral impossible task.

Furthermore, in the past, some models have appeared that do not include the manual switch 25, but in this case, fluctuations in the tracking error signal TE due to scratches are mistakenly detected as being caused by vibrations, and the switch 23 is turned on. If this happens, the open loop gain will be high even though there are scratches on the disk, causing a malfunction in which the tracking servo loop circuit will be controlled in a state where it is weak against scratches.

[Purpose of the Invention] This invention was made in consideration of the above circumstances, and is easy to handle because it can accurately detect the amount of scratches on the disk and automatically change the open loop gain of the tracking servo loop circuit. An object of the present invention is to provide an extremely good tracking servo control circuit for a disc playback device that can perform stable disc playback without malfunctions.

[Summary of the Invention] That is, a tracking servo control circuit for a disc playback device according to the present invention includes a vibration detection means for detecting external vibration based on data read from the disc, and a vibration detecting means for detecting external vibration based on data read from the disc, and a vibration detecting means for detecting external vibration based on data read from the disc. a scratch detecting means for detecting a scratch on the disk; a switching means for selectively switching the open loop gain of the tracking servo loop circuit between a first state for dealing with external vibration and a second state for dealing with scratches on the disk; Normally, the second state is switched to the first state according to the detection output of the vibration detection means, and when the frequency of flaw detection by the flaw detection means exceeds a set value, the switching means is switched to the second state regardless of the output of the vibration detection means. By being equipped with a control means that specifies the state of the disk, it is possible to accurately detect the date of scratch on the disk and automatically change the open loop gain of the tracking servo loop circuit, and it is easy to handle and does not malfunction. This allows stable disc playback.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 7 are indicated by the same symbols, and only the different parts will be explained here.

That is, the input terminal of the buffer circuit 26 is connected to the output terminal of the AND circuit 27. This AND circuit 2
The output terminal of the vibration detection circuit 24 is connected to one input terminal of 7, and the output terminal of the counter circuit 28 is connected to the other input terminal. And this counter circuit 28
are connected to a flaw detection circuit 29 and a timing generation circuit 30, respectively.

The vibration detection circuit 24 normally outputs an L level signal, and when external vibration is detected, generates an H level vibration detection signal.

Further, when the output of the AND circuit 21 is at L level, the switch 23 is turned off (the open loop gain of the tracking servo loop circuit is low), and the AND circuit 21
When the output of 7 is at H level, it is controlled to be in an on state (a state in which the open loop gain of the tracking servo loop circuit is high).

Here, the scratch detection circuit 29 detects scratches on the disc by detecting, for example, fluctuations in the level of the tracking error signal TE or the level of the RF envelope signal obtained by extracting the envelope component of the RF signal. Every time a flaw is detected, a flaw detection pulse S1 as shown in FIG. 2 is generated.

Further, the timing generation circuit 30 generates a timing pulse S2 having a constant period TO.

Then, the counter circuit 28 receives a timing pulse S
The flaw detection pulse S1 generated during one cycle period TO of No. 2 is counted, and when the count value exceeds a set value N, an L level flaw detection signal S3 is generated. In other words, this L-level scratch detection signal S3 is generated when the amount of scratches on the disc, that is, the number of occurrences of the scratch detection pulse S1 exceeds the set value N.

Note that the output of the counter circuit 28 is the flaw detection pulse S generated during one cycle period TO of the timing pulse S2.
When the count value of 1 becomes less than the setting 1i1N, it is inverted to the original H level in synchronization with the timing pulse S2.

Therefore, when the amount of external vibration and scratches on the disk is small, the output of the vibration detection circuit 24 is at L level and the output of counter circuit 28 is at H level, so the output of AND circuit 27 is at L level. , switch 23 is turned off and the open loop gain is set low to accommodate the flaw. In this state, when external vibration is detected and an H level pulse signal is generated from the vibration detection circuit 24, the output of the AND circuit 27 becomes H level, the switch 23 is turned on, and the open loop gain is changed to the external vibration. Correspondingly switched to high.

On the other hand, when the amount of scratches on the disc increases and the counter circuit 28 generates an L level scratch detection signal $3, the output of the AND circuit 27 is regulated to the L level regardless of the output of the vibration detection circuit 24. Switch 23 will be turned off and the open loop gain will be set low to accommodate the flaw.

Therefore, according to the configuration of the above embodiment, the open loop gain of the tracking servo loop circuit is normally set low to cope with scratches, and is automatically switched to a high gain every time external vibration is detected. Scratch detection pulse S1
The open-loop gain is forcibly lowered depending on the frequency of scratches, making it easier to handle, and even if there are parts with more scratches and parts with less scratches on a single disc, you can deal with them accordingly. It is something that can be done.

Roughly speaking, since the amount of scratches is determined based on the frequency of occurrence of the scratch detection pulse S1 and the counter circuit 28 outputs an L-level scratch detection signal, the vibration detection circuit 24 may erroneously detect scratches as external vibrations. However, since the open loop gain is kept low, malfunctions can be prevented.

Here, FIG. 3 shows a specific configuration of the vibration detection circuit 24. As shown in FIG. That is, the tracking error signal TE supplied to the input terminal 31 is passed through a low-pass filter circuit 32 consisting of a resistor R3 and a capacitor C1, in which only frequency components of level fluctuations that are considered to be caused by external vibrations are passed. The signal that has passed through this low-pass filter circuit 32 is sent to the non-inverting input terminal + of the comparison circuit 33 and to the non-inverting input terminal + of the comparison circuit 33.
4 inverting input terminals, respectively.

Also, the inverting input terminal of the comparison circuit 33 and the comparison circuit 3
The reference voltages vt and -vt generated by the resistors R4 to R6 are applied to the non-inverting input terminals of the resistors R4 to R6, respectively. Here, when the signal level supplied to the non-inverting input terminal of the comparator circuit 33 is higher than the reference voltage Vt, the comparator circuit 33
The comparison circuit 34 generates an H level signal when the signal level supplied to its inverting input terminal is lower than the reference voltage -Vt.

The output of each comparator circuit 33 and 34 is then connected to the diode D
I, D2, and resistors R7, R8.

The level control circuit 36 consisting of the diode D3 and the buffer circuit 35 converts the signal into, for example, a TTL level, and outputs it from the output terminal 37.

That is, the signal output from the low-pass filter circuit 32 and each reference voltage vt, -vt are as shown in FIG.
), an H-level vibration detection signal as shown in FIG. 4(b) will be generated from the output terminal 37 with the signal level exceeding the reference voltage Vt. It is what it is.

FIG. 5 shows a second embodiment of the present invention, and shows means for generating an L-level flaw detection signal S3 in accordance with the frequency of occurrence of flaw detection pulses S1 output from the flaw detection circuit 29. ing. The following description will be made with reference to the timing chart shown in FIG. 6. The flaw detection pulse S1 turns on and off the transistor Q1 via the resistor R9. Then,
The collector voltage VC of the transistor Q1 is the voltage of the resistor R10 and the capacitor C when the transistor Q1 is off.
The signal is integrated by an integrating circuit 38 consisting of two components, and is supplied to one input terminal of a comparing circuit 39.

Further, the other input terminal of the comparator circuit 39 has a resistor R11,
A reference voltage V generated by R12 is applied. Therefore, when the collector voltage VC becomes lower than the reference voltage V, the comparison circuit 39 outputs an H level pulse signal H.
is generated. This pulse signal H is applied to the diode D4.
A rising delay circuit 40 including a resistor R13 and a capacitor C3 generates a delayed signal Hd at the rising edge. Then, the above signal) 1d rises, and the NOT circuit 4
When the inversion threshold level of 1 is exceeded, an L level flaw detection signal S3 is generated.

That is, the collector voltage VC of the transistor Q1 is reset every time the flaw detection pulse S1 is generated, and then rises with the time constant of the integrating circuit 38. When this collector voltage VC exceeds the reference voltage V, the output signal H of the comparator circuit 39 becomes L level, and when this signal H rises, it rises with the time constant of the rise time constant circuit 40, and as a result, the not circuit 41 A flaw detection signal S3 of L level is generated from the above.

Therefore, when the flaw detection pulse S1 occurs frequently, the collector voltage VC of the transistor Q1 does not exceed the reference voltage V, and the flaw detection signal S3 at the L level is generated.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, it is possible to accurately detect the amount of scratches on a disk and change the open loop gain of the tracking servo loop circuit on its own. ,
It is possible to provide an extremely good tracking servo control circuit for a disc playback device that is easy to handle, does not malfunction, and can perform stable disc playback.

[Brief explanation of drawings]

1 and 2 are block circuit configuration diagrams showing one embodiment of the tracking servo control circuit of a disc playback device according to the present invention, and timing diagrams for explaining its operation, and FIGS. 3 and 4 are respectively A circuit configuration diagram showing the details of the vibration detection circuit used in the same embodiment and a timing diagram for explaining its operation, and FIGS. 5 and 6 are block circuits showing the second embodiment of the present invention, respectively. Configuration diagram and timing diagram for explaining its operation, No. 7
The figure is a block circuit configuration diagram showing a conventional tracking servo loop circuit. DESCRIPTION OF SYMBOLS 11... Main beam detector, 12... Addition circuit, 13... Output terminal, 14... Subtraction circuit, 15.
...Low pass filter circuit, 16...Output terminal, 17
...Subtraction circuit, 18...Low pass filter circuit,
19... Gain control circuit, 20... Phase compensation circuit, 2
DESCRIPTION OF SYMBOLS 1... Drive circuit, 22... Tracking actuator coil, 23... Switch, 24... Vibration detection circuit, 25... Manual switch, 26... Buffer circuit, 21... AND circuit, 28... Counter circuit, 29... Flaw detection circuit, 30... Timing generation circuit, 31... Input terminal, 32... Low pass filter circuit, 33. 34... Comparison circuit, 35...・Buffer circuit, 36...Level control circuit, 37...Output terminal, 38...Integrator circuit, 39...Comparison circuit, 40.
...rise delay circuit, 41...knot circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A disc playback device that reads data recorded on a disc via a pickup element includes a tracking servo loop circuit that performs tracking servo on the pickup element based on data read from the disc; vibration detection means for detecting external vibration; flaw detection means for detecting flaws on the disk based on data read from the disk; a switching means for selectively switching to a second state for dealing with a scratch on the disk; A disc playback device characterized by comprising: control means for setting the switching means to a second state irrespective of the output of the vibration detection means when the frequency of flaw detection by the flaw detection means exceeds a set value. Tracking servo control circuit of the device.