JPH0550058B2 - - Google Patents

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 (optical compact disc) type DAD (digital audio disc), and particularly relates to an optical disc playback device suitable for use in a CD (optical compact disc) type DAD (digital audio disc). This invention relates to an improved device that controls a tracking servo to have appropriate characteristics in response to external vibrations, thereby enabling stable disc playback.

[Technical Background of the Invention] Conventionally, in the case of optical disc playback devices, taking the CD system as an example, in order to clearly read out the information signals recorded on the disc, it has been necessary to use an optical pickup. Tracking error control (tracking servo) is performed so that the irradiated light beam accurately traces the pit rows without deviation from the pit rows of the disk, that is, without causing tracking errors. However, if this tracking servo gain is left in the normal reproduction state, there is a risk that a tracking jump of the light beam will occur when the disk is scratched or external vibration occurs. For this reason, CD playback devices are equipped with a disk scratch detection circuit as shown in Figure 5 or a vibration detection circuit as shown in Figure 7, and the tracking servo gain is controlled according to the detection output to prevent tracking jumps. being done.

First, the disk scratch detection circuit shown in FIG. 5 AC-couples RF signals (corresponding to the presence or absence of pits) obtained by an optical pickup (not shown) using a capacitor 11, and then sets the amplitude and offset voltage to a constant value using a waveform shaping circuit 12. After that, the RF signal is supplied to the EFM signal generation circuit 13 to be converted into an EFM signal (digital signal), and the RF signal is supplied to the envelope detection circuit 14 to extract the envelope signal RFE.
The signal comparison circuit 15 detects that the signal has fallen below a predetermined level (slice level V1) and generates a flaw detection pulse P1 in that section. When this pulse P1 is generated, a large change appears in the envelope RFE of the RF signal due to a scratch on the disk, so in this case, it is recommended to lower the gain of the tracking servo to prevent the tracking jump from occurring due to the scratch. Good. Therefore, in the CD playback device, the tracking error signal TE amplified by the amplifier 16 is transmitted to the phase compensation circuit 17.
A gain adjustment circuit consisting of resistors 18, 19 and an analog switch 20 is connected to the output terminal of the amplifier 16 for a tracking servo loop that controls the movement of the objective lens by supplying the signal to a tracking actuator (not shown) via the servo loop. is provided, and when the scratch detection pulse P1 of the disk scratch detection circuit is generated, the analog switch 20 is turned on and the output of the amplifier 16 is attenuated.

That is, in the normal reproduction state, the switch 20 is set to the OFF state and the gain of the tracking servo is increased to prevent track jumps due to vibrations or the like. Here, if there is a scratch on the disk and the RF signal disappears due to the scratch as shown in Figure 6a,
As shown in Figure b, the envelope level RFE of the RF signal is at the slice level V at T when the scratched part is reproduced.
Since it is less than 1, a flaw detection pulse P1 as shown in c in the figure is obtained. At this time, the tracking error signal TE changes greatly as shown in FIG.
is turned on, and the amount of supply to the tracking actuator begins to attenuate. This makes it difficult for track jumps to occur even when the damaged area is regenerated.

In addition, the vibration detection circuit in FIG. 7 is the signal comparison circuit 2.
1, a vibration detection pulse P2 is generated when the tracking error signal TE exceeds a bipolar reference level (slice level) ±V2. When this pulse P2 is generated, it is when the tracking error becomes large due to vibration, so it is better to increase the gain of the tracking servo at this time so as not to cause a tracking jump due to vibration. Therefore, in a CD playback device,
The amplifier 16 is provided with a gain adjustment circuit consisting of resistors 22, 23 and an analog switch 24, the output pulse P2 of the signal comparison circuit 21 activates the mono multivibrator 25, and the output P3 of the vibrator 25 turns on the switch 24. The gain of the amplifier 16 is increased by increasing the gain of the amplifier 16.

That is, in the normal playback state, the switch 20 is set to the OFF state and the gain of the tracking servo is lowered to prevent tracking jumps due to scratches or the like. If an external vibration occurs at time t, the tracking error signal TE changes greatly due to the vibration as shown in Fig. 8a and exceeds the slice level +V2, and as shown in Fig. 8b, the vibration detection pulse P2 is obtained. Therefore, the mono multivibrator 25 sets the output P3 to the H (high) level for a time T2 sufficient to draw the light beam onto the pit row, as shown in FIG.
4 is turned on, and the gain of the amplifier 16 is increased. This increases the gain of the tracking servo when vibration occurs, making it difficult for tracking jumps to occur. It should be noted that the RF signal when vibration occurs fluctuates depending on the tracking error of the light beam, as shown in d of the same figure.

[Problems with the Background Art] However, in an optical disc playback device that uses a disc scratch detection circuit or a vibration detection circuit as described above, there is a risk that either of the detection circuits may cause false detection, which may cause a track jump. Sometimes it becomes easy. In other words, in the disk scratch detection circuit shown in Fig. 5, when vibration occurs as shown in Fig. 8 d, not only the tracking error signal TE but also the RF signal fluctuates, so the error occurs at this time. Even though vibration is detected, the gain of the tracking servo may be lowered. Furthermore, in the vibration detection circuit shown in Fig. 7, if the disk is scratched as shown in Fig. 6d, not only the RF signal but also the tracking error signal TE will fluctuate. There are cases where the gain of the tracking servo is increased even though the damaged portion is being regenerated due to erroneous detection. As described above, in the conventional optical disc reproducing apparatus, even if a track jump prevention mechanism using a disc scratch detection circuit or a vibration detection circuit is provided, stable reproduction cannot always be performed.

[Object of the Invention] This invention was made in consideration of the above-mentioned circumstances, and it is possible to control the tracking servo to have appropriate characteristics in response to scratches on the disc or external vibrations, thereby achieving stable disc playback. An object of the present invention is to provide an optical disc playback device that can perform the following functions.

[Summary of the Invention] That is, the optical disc reproducing device according to the present invention irradiates an optical disc with a light beam using an optical pickup, receives the reflected light, and performs photoelectric conversion to reproduce the optical disc. A tracking error signal is generated based on the output signal of the optical pickup, and the movement of the objective lens is controlled based on this tracking error signal to constantly control the light beam. In the device having a tracking servo for illuminating the center of the track, a first signal comparison means for detecting a state in which the tracking error signal is higher than a predetermined level, and a detection output of the first signal comparison means are provided. holding means for holding the detection output even after the detection output disappears; second signal comparison means for detecting a state in which the output signal of the optical pickup is below a predetermined level; and the first signal comparison means. The gain of the tracking servo is maintained or lowered when a detection output is obtained from the second signal comparison means regardless of the presence or absence of detection, and when the detection output is not obtained from the second signal comparison means, The apparatus is characterized in that it comprises gain adjusting means for increasing the gain of the tracking servo from the time of detection by the first signal comparing means until the end of the period set by the holding means.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

FIG. 1 shows the configuration when the present invention is applied to a CD playback device using a three-beam type optical pickup. In the figure, reference numeral 31 indicates the disk reflected light of the main beam irradiated to the center of the pit row. The four-split detectors 32 and 33 are sub-detectors that photoelectrically convert the reflected light of the two sub-beams irradiated on both sides of the pit row. Above 4-split detector 3
The outputs of each light receiving area A to D of 1 are added together,
As the RF signal, an amplifier 34, a capacitor 35,
EFM signal generation circuit 3 via waveform shaping circuit 36
7 and is converted into a digital signal. On the other hand, each output of the two sub-detectors 32 and 33 is subtracted by a subtracter 38, and converted into a voltage signal by a first low-pass filter (LPF) 39, where a tracking error signal TE is generated. This tracking error signal TE is amplified by an amplifier 40,
is supplied to a tracking actuator coil 43 via a phase compensation circuit 41 and a drive circuit 42,
It is used to control the movement of an objective lens (not shown), and a tracking servo loop is configured here.

Further, the tracking error signal TE output from the low-pass filter 39 is supplied to the first signal comparison circuit 44. This signal comparison circuit 44 compares the tracking error signal TE with the bipolar reference voltage ±V3, and generates a tracking error signal.
When TE exceeds the reference voltage level ±V3, a pulse signal P4 is generated.
is supplied to the trigger terminal (terminal activated at the rising edge of the input pulse) of the mono multivibrator 45. Furthermore, the respective outputs of the sub-detectors 32 and 33 are added together by an adder 46, and after high-frequency pit components are removed by a second low-pass filter 47, the outputs are supplied to a second signal comparison circuit 48. This signal comparison circuit 48 compares the output V47 of the second low-pass filter 47 and the reference voltage V4, and generates a pulse signal P5 when the filter output V47 becomes equal to or higher than the reference voltage level V4. is the above mono multivibrator 45
This is supplied to the reset terminal (terminal that prohibits operation while a pulse signal is being input). This mono multivibrator 45 outputs a pulse signal P6 that becomes H level (excluding the pulse input period of the reset terminal) in response to a pulse input to the trigger terminal, and this pulse signal P6 is output to the analog switch 49.
is supplied to the control terminal of This analog switch 49 constitutes a gain adjustment circuit of the amplifier 40 together with resistors 50 and 51, and is turned on when the pulse signal P6 is at H level.

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

Figure 2 shows each signal output waveform when the disc is scratched. Assuming that the RF signal is lost for a time T due to the scratch during disc playback, as shown in Figure a, the first low-pass Filter 39
As shown in FIG. 2B, the tracking error signal TE output from the oscillator changes greatly at T when the scratched portion is reproduced, and exceeds the reference voltage level ±V3.
On the other hand, since the sub-beam reflected light irradiated to the sub-detectors 32 and 33 is significantly lowered from the total reflection level due to scratches, the voltage signal V47 obtained by the second low-pass filter 47 is set to the reference level as shown in FIG. The voltage level becomes lower than V4. Therefore, the first and second signal comparison circuits 4
4 and 48 output pulse signals P4 and P5 as shown in d and e of the same figure, but while the pulse signal P5 is output, the mono multivibrator 45
is not activated, so this multivibrator 4
5 does not output the pulse signal P6 as shown in FIG. Therefore, the gain of the tracking servo does not change when the damaged portion is regenerated.

Figure 3 shows each signal output waveform when vibration occurs at time t during disc playback.At this time, if the RF signal fluctuates as shown in Figure a due to vibration, the first low-pass filter Tracking error signal TE output from 39
As shown in Figure b, changes greatly in the direction of vibration, and the reference voltage level (+V3 in this case)
will be able to exceed. On the other hand, since the sub-beam reflected light irradiated to the sub-detectors 32 and 33 hardly changes from the total reflection level even if vibration occurs, the voltage signal V47 obtained by the second low-pass filter 47 is as shown in FIG. It is constant and never drops below the reference voltage level V4. Therefore, the first signal comparison circuit 44 outputs a pulse signal P4 as shown in d in the figure, but the second signal comparison circuit 48 does not output a pulse signal P5, so the mono multivibrator 45 It is activated at time t and outputs a pulse signal P6 as shown in FIG. Therefore, if vibration occurs during disc playback, analog switch 4
9 is turned on, the gain of the amplifier 40 increases, and thereby the gain of the tracking servo increases.

That is, in the present invention, although the tracking error signal TE fluctuates greatly during reproduction of a scratched portion of the disc and due to external vibration, the output V47 of the low-pass filter 47, which is the sum signal of the sub-beam detection signal,
is at a certain level (total reflection level) as long as there is no scratch on the disk and the focus servo does not come off.
This takes advantage of the fact that there are no major changes.
In other words, if the tracking error signal TE fluctuates greatly and the signal V47 does not fluctuate, it is possible to detect that external vibration has occurred. This is applied to the first and second signal comparison circuit 4.
It was detected at 4.48. That is, in this CD playback device, the gain of the tracking servo is set to a gain that makes it difficult to cause a tracking jump due to scratches on the disc in normal playback conditions, and when vibration is detected, the mono-multivibrator 45 is activated and the gain is set for a predetermined period of time. The gain of the tracking servo is increased to prevent tracking jumps from occurring due to vibration.

The time width of the output pulse P6 of the mono-multivibrator 45 is such that when the main beam spot is about to come off from the pit row of the disk due to vibration, the gain of the servo is increased and the spot on the pit row that is about to come off is stabilized. It is necessary only for convergence.

Therefore, the CD playback device configured as described above can distinguish between scratches on the disc and external vibrations, and change the characteristics of the tracking servo to those suitable for each case, allowing stable disc playback. It is possible to do this.

Note that even if the gain of the tracking servo is not lowered in the normal playback state to prevent a tracking jump from occurring in response to a scratch on the disk as in the above embodiment, in the case of a scratch, only the added signal from the sub-beam reflected light can be used. Therefore, as shown in FIG. 4, a second gain adjustment circuit consisting of resistors 52, 53 and an analog switch 54 is provided in the tracking servo loop, and the switch 54 is switched by the output of the second signal comparison circuit 48. If controlled, the loop gain can be lowered.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to control the tracking servo to appropriate characteristics in response to scratches on the disc or external vibrations, thereby achieving stable disc playback. An optical disc playback device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of an optical disc playback device according to the present invention, FIGS. 2 and 3 are operation explanatory diagrams for explaining the operation of the same embodiment, and FIG. The block circuit diagrams and FIGS. 5 to 8 showing other embodiments of the present invention are diagrams for explaining the structure and operation of a truck jump prevention mechanism used in a conventional optical disc playback device, respectively. be. 31... 4-division detector, 32, 33... sub-detector, 36... waveform shaping circuit, 37...
EFM signal generation circuit, 38...Subtractor, 39, 4
7...Low pass filter, 40...Amplifier, 41
... Phase compensation circuit, 42 ... Drive circuit, 43 ...
Tracking actuator coil, 44, 48
... Signal comparison circuit, 45 ... Mono multivibrator, 46 ... Adder, 49, 54 ... Analog switch, 50 to 53 ... Resistor, TE ... Tracking error signal.

Claims (1)

[Claims] 1 An optical pickup is used to irradiate an optical disk with a light beam, receive the reflected light, and perform photoelectric conversion to read information signals recorded on the disk. In an optical disc playback device having a tracking servo that generates a tracking error signal based on an output signal and controls the movement of an objective lens based on the tracking error signal to always irradiate the light beam to the center of the track. , a first detecting state in which the tracking error signal is at a predetermined level or higher;
a signal comparing means, a holding means for holding the detection output of the first signal comparing means even after the detection output disappears, and detecting a state in which the output signal of the optical pickup is below a predetermined level. Second to do
and maintaining or lowering the gain of the tracking servo when a detection output is obtained from the second signal comparison means regardless of the presence or absence of detection by the first signal comparison means; gain adjusting means for increasing the gain of the tracking servo from the time of detection by the first signal comparing means until the end of the period set by the holding means in a state where no detection output is obtained from the signal comparing means; An optical disc playback device characterized by: