JPH02260134A - Tracking servo circuit for disk reproducing device - Google Patents

Abstract

PURPOSE:To obtain a superior defect servo characteristic by providing a device to delay a signal corresponding to the reflected light of an auxiliary light beam by time corresponding to distance along the rotating direction of a disk and a switching device to permit or prevent selectively this delaying operation. CONSTITUTION:A connection point between a auxiliary photodetector 13 and a resistor R1 is connected to reference potential VD through a capacitor C3 and a switch 21 in series. In this case, a current signal IE outputted from the detector 13 is delayed by the time T for the distance (d) between the auxiliary light beams by a filter consisting of the resistor R1 and the capacitor C3 by turning on the switch 21. Besides, the values of the capacitor C1 and the resistor R2 of an RF amplifier 15 are made cut-off frequencies at which stable servo can be realized when the switch 21 is turned off. Here, in a usual disk reproducing state, the switch 21 is turned on and the current IE is delayed so that defect resisting property is provided. Then, at the time of search or when external vibration is detected and servo gain the required to be matched, the switch 21 is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to a 3-beam type optical disc reproducing device, and particularly relates to an improvement of its tracking servo circuit.

(Prior Art) As is well known, an optical disc playback device such as a compact disc player or a laser video disc player irradiates a disc with a light beam from an optical pickup and converts the reflected light into an electrical It converts it into a signal and plays the disc.

This main optical disc playback device irradiates the disc with only one light beam and uses the reflected light to obtain data recorded on the disc and data for controlling the tracking and focusing of the light beam. One type of beam type, the main light beam is irradiated onto the disc, data recorded on the disc is obtained from the reflected light, and a pair of sub-light beams are irradiated onto the disc, and the main light beam is tracked from the reflected light. There is also a 3-beam type that obtains data for controlling focus and the like.

FIG. 3 shows a tracking servo circuit in such a three-beam type optical disc reproducing apparatus. That is, in the figure, reference numeral 11 denotes an optical pickup, which includes a main photodetector 12 that receives reflected light of the main light beam;
A pair of sub-photodetectors 13 and 14 are provided, each of which receives each reflected light of the pair of sub-light beams.

Here, the pair of secondary light beams are irradiated onto the disc with their positions shifted along the rotational direction of the disc,
It is assumed that the pair of photodetectors 13 and 14 respectively receive the reflected light of the sub-light beams that are leading and trailing in the rotational direction of the disk (not shown) among the pair of sub-light beams.

The sub-light beam received by the sub-photodetector 13 is converted into a current signal IE corresponding to the amount of light, and after passing through a resistor R1, is sent to an operational amplifier opi.

It is converted into a voltage signal VE by an RF (high frequency) amplifier 15 consisting of a capacitor C1 and a resistor R2. Further, the sub-light beam received by the sub-photodetector 14 is converted into a current signal IF corresponding to the amount of light, and after passing through the resistor R3,
Operational amplifier OP2. It is converted into a voltage signal VP by an RF amplifier 16 consisting of a capacitor C2 and a resistor R4.

After that, the RF amplifier 15. Each of the voltage signals VE and VI' outputted from Ift passes through a resistor R5°R6, and then is added by an adder 17 consisting of an operational amplifier OP3 and a resistor R7°R8, thereby reducing the tracking error of the main light beam. A tracking error signal TE corresponding to the amount is generated.

This tracking error signal TE is phase-compensated by an equalizer circuit 18 and then supplied to a tracking actuator coil 20 for moving an objective lens (not shown) that controls the main light beam in the tracking direction via a drive circuit 19. , here, the tracking sabot for the main light beam is performed.

Here, in a normal disc playback state, the capacitors C1 and C2 constituting the RF amplifiers 15 and 16 only need to function to block extra high-frequency components included in the current signals IE and IF, so R2 =R4, there is no problem with setting C1=C2.

By the way, when there is a defect (scratch) on the disk, the current signals IE, IP output from each sub-photodetector 3.14 are as shown in FIGS. 4(a) and 4(b), respectively.
As shown in the figure, there is a large change. In this case, the pair of sub-light beams are irradiated onto the disk with their positions shifted along the disk rotation direction, so if they are set to C1-C2, the delay amounts of the current signals IE and IF are the same. Therefore, the current signal I P is generated with a delay of time T corresponding to the distance between the sub-light beams with respect to the current signal I E. This delay time T increases the distance between the sub-light beams by d1.
If the rotational linear velocity of the disk is V, then T = d /
v.

Therefore, a problem arises in that the adder 17 generates a tracking error signal TE regardless of the tracking error of the main light beam, as shown in FIG. 4(c).

Therefore, conventionally, the capacitances of the capacitors C1 and C2 are changed so that the current signal IE is delayed by the delay time T, that is, R2C1-R4C2=T. Then, even if there is a defect on the disk, the voltage signals VE and VP output from the RF amplifier 1516 will be as shown in FIG. 5(a).
, as shown in FIG. 5(b), and the disturbance of the tracking error signal TH can be reduced as shown in FIG. 5(c).

However, the following problems occur in the conventional tracking servo circuit as described above. That is, in order to obtain a sufficient effect against all kinds of defects in a normal disc playback state, it is necessary to lower the cutoff frequency of CI R2 on the preceding sub-light beam side to a certain degree.

On the other hand, in an actual tracking servo, when the search converges or when external vibration is detected, it is necessary to increase the open loop gain of the servo and increase the servo band to improve convergence and vibration resistance. In this case, if the cutoff frequency on the preceding sub-light beam side is low, CL R2
Due to the phase delay caused by this, stable servo characteristics cannot be obtained.

For this reason, in the past, servo characteristics such as convergence and vibration resistance were more important than defect countermeasures, and CI
R2 is set higher than the desired value.

(Problems to be Solved by the Invention) As described above, in the conventional tracking servo circuit, emphasis is placed on servo characteristics such as convergence and vibration resistance, and there is a problem in that sufficient countermeasures against defects are not taken.

Therefore, this invention was made in consideration of the above circumstances, and provides an extremely good tracking servo circuit for a disc playback device that not only has servo characteristics for convergence and vibration resistance, but also has sufficient effects against defects. The purpose is to provide.

[Structure of the Invention (Means for Solving the Problems) A tracking servo circuit of a disc playback device according to the present invention reflects a main light beam and a pair of sub-light beams on a disc surface, and The object of this invention is to control the main light beam in the tracking direction according to the tracking error signal generated based on the signals corresponding to the respective reflected lights.

Then, among the pair of secondary light beams, a signal corresponding to the reflected light of the secondary optical beam that precedes the rotational direction of the disk is delayed by a time corresponding to the distance of the pair of secondary optical beams along the rotational direction of the disk. and switching means for selectively allowing or blocking the delay operation of the delay means.

(Function) According to the above-mentioned configuration, the switching means allows the operation of the delay means under normal disk playback conditions, so that a sufficient effect can be obtained against defects, and when the search converges or external vibration When you want to increase the servo gain, such as when the servo gain is detected, the switching means can block the operation of the delay means and improve the servo characteristics for convergence and vibration resistance. In addition, sufficient effects can be obtained even against defects.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 3 are denoted by the same reference numerals, and only the different parts will be described here. That is, the sub photodetector 13 and the resistor R1
The difference from the conventional method is that the connection point between the capacitor C3 and the switch 21 is connected to the reference potential point VD through the capacitor C3 and the switch 21 in series.

In this case, the current signal IE output from the sub-photodetector 13 is changed to a delay time T corresponding to the distance d between the sub-light beams.
By turning on the switch 21, the function of delaying by the amount of time is realized by a filter consisting of a resistor R1 and a capacitor C3.

Further, the values of the capacitor C1 and the resistor R2 of the RF amplifier 15 are set to a cutoff frequency that provides stable servo characteristics when the switch 21 is turned off.

Here, in the normal disc playback state, the switch 21
is turned on and the current signal IP is delayed so that a sufficient effect against defects can be obtained. Then, during a search or in a state where an increase in servo gain is required when external vibration is detected, the switch 21 is turned off, the current signal IE is not delayed, and the high cutoff frequency specified by the capacitor C1 and the resistor R2 is set. According to
Servo characteristics with respect to convergence and vibration resistance can be improved.

The switch 21 can be turned on and off by using a normally closed switch as the switch 21, and by setting up a control system that automatically turns the switch 21 off when a search operation request or external vibration is detected. It's good.

FIG. 2 shows another embodiment of the present invention, and the difference from FIG. 1 is that the connection point between the sub-photodetector 14 and the resistor R3 is connected to the reference potential through a capacitor c4 and a switch 22 in series. The reason is that it is connected to point VD. The switch 22 is controlled to be turned on or off in conjunction with the switch 21.

According to this configuration, in a normal disk playback state, the switch 22 as well as the switch 21 are in the on state, so that the trailing side current signal I F obtained from the sub-photodetector 14 is connected to the resistor R3 and the capacitor C4. Since high-frequency components are sufficiently removed by a filter with a sufficiently low cutoff frequency, it is possible to improve the tracing ability of the main light beam against all kinds of defects.

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] As detailed above, according to the present invention, an extremely good tracking servo circuit for a disc playback device can be obtained which not only has good servo characteristics in terms of convergence and vibration resistance, but also has sufficient effects against defects. can be provided.

[Brief explanation of drawings]

FIG. 1 is a blower circuit configuration diagram showing one embodiment of the tracking servo circuit of a disc playback device according to the present invention, FIG. 2 is a block circuit diagram showing another embodiment of the invention, and FIG. 3 is a conventional blower circuit diagram. 4 and 5 are waveform diagrams for explaining the operation of the conventional tracking servo circuit, respectively. 11... Optical pickup, 12... Main photodetector, 13. 14... Sub photodetector, 1
51B RF amplifier, 17... Adder, 1B... Equalizer circuit, 19... Drive circuit, 20... Tracking actuator coil, 21.22... Switch.

Claims (2)

[Claims] (1) A main light beam and a pair of sub-light beams are reflected on a disk surface, and the main light beam is In a tracking servo circuit of a disk playback device that controls a beam in a tracking direction, a signal corresponding to the reflected light of the preceding sub-light beam with respect to the rotational direction of the disk is transmitted to the pair of sub-light beams. and a first switching means for selectively allowing and blocking the delay operation of the delay means. Features a tracking servo circuit for disc playback devices. (2) High-frequency component removing means for lowering the cutoff frequency of a signal corresponding to the reflected light of the secondary light beam trailing with respect to the rotational direction of the disk, among the reflected lights of the pair of secondary light beams; , and second switching means for selectively allowing and blocking the operation of the high-frequency component removing means in conjunction with the switching operation of the first switching means. tracking servo circuit for disc playback devices.