JPH0567343A - Tracking error detecting device - Google Patents

Abstract

PURPOSE:To obtain a stable tracking error signal by level-varying a sum signal obtained by adding each of two sub-beam signals, extracting this varied part and superposing it to a tracking error signal. CONSTITUTION:A reflected light of a sub-beams E is converted into an E signal of a current level corresponding to the light quantity by a photoelectric converter 12, passes through a current-voltage transducer 52 and is supplied to each one input terminal of a subtracter 53 and an adder 54. The reflected light of the sub-beam F is converted into an F signal of a current level corresponding to the light quantity by a photoelectric converter 13, passes through a current- voltage transducer 51 and is supplied to each the other input terminal of the subtracter 53 and the adder 54. When the sub-beam F becomes a preceding beam, the subtracter is selected as a signal superposing means, and when the sub-beam E becomes a preceding beam, the adder is selected as the signal superposing means. Subsequently, a compensated tracking error signal compensated by a differential signal D is supplied to a tracking servo-phase compensator 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detecting device for an optical disk reproducing device, and more particularly to a 3-beam type tracking error detecting device.

[0002]

2. Description of the Related Art In an optical disc player, an information read signal is obtained from a track of a disc carrying information by an optical pickup. For this reason, the pickup requires a focus servo for maintaining the reading spot (light spot) on the pit row forming the track of the disk in a constant shape, a tracking servo for causing the reading spot to follow the track, and the like.

FIG. 6 shows a conventional example of focus servo and tracking servo of a three-beam type pickup. The main beam modulated by a pit row (not shown) is divided into four light receiving surfaces A and B of the photoelectric converter 11. , C
And the center of D. The two sub-beams modulated by the pit train are photoelectric converters 12 and 1, respectively.
It is incident on the light receiving surfaces F and E of No. 3.

The shape of the incident light on the light receiving surface of the photoelectric converter 11 changes depending on the position of an objective lens (not shown) that converges the reading spot on the disk surface. For example, if the objective lens is closer to the disk surface than the reference position, the axis becomes an ellipse in the BC direction, and if it is far, the axis becomes an ellipse in the AD direction. Moreover, when the position of the objective lens is at the reference position, the shape of the incident light becomes circular. The current outputs of the light receiving surfaces A and D are the current-voltage converter 14a.
Is converted into a voltage signal by the subtractor 15 and the adder 1
6 is supplied to each one input terminal. The current outputs of the light-receiving surfaces B and C are converted into voltage signals by the current-voltage converter 14b and supplied to the other input ends of the adder 15 and the subtractor 16. The subtracter 15 obtains a focus error (FE) signal from the difference signals between the light receiving surfaces A, D and B, C. The adder 16 obtains the sum output of each light receiving surface and carries the read information RF
The signal is output and supplied to a demodulation unit (not shown).

The focus error signal is adjusted by the focus servo phase compensator 17 to gain and phase characteristics required for the focus servo system and supplied to the focus actuator driver 18. In response to the focus error signal, the driver 18 drives a focus actuator 19 which swings an objective lens arranged in an optical system of a pickup (not shown) in a direction perpendicular to the disc surface.

2 output from the photoelectric converters 12 and 13
The two sub-beam signals are the current-voltage converters 22 and 21 respectively.
Is converted into a voltage signal via and is supplied to the positive and negative input terminals of the subtracter 21. The subtractor 23 outputs the level difference signal of both input signals as a tracking error (TE) signal. The tracking error signal is adjusted by the tracking servo phase compensator 24 to have a gain characteristic and a phase characteristic required for the tracking servo system, and then supplied to the tracking actuator driver 25. The driver 25 responds to the tracking error signal by a tracking actuator 26 that swings the objective lens in the radial direction of the disk.
To drive. Current-voltage converters 21 and 22, subtractor 23
Constitutes a tracking error detector 20.

A concrete configuration example of the tracking error detector 20 is shown in FIG. Current-voltage converters 21 and 22
Is composed of an operational amplifier and a time constant circuit composed of a resistor and a capacitor, and a reduced signal component of 20 kHz or less necessary for the servo system is extracted. The subtractor 23 is composed of an operational amplifier and a plurality of resistors. Current-voltage converter 2
A capacitor 36 is added to the time constant circuit of 1 if necessary.

The role of the capacitor 36 will be described. FIG. 8 shows the relationship among the defect portion, the pit row, the main beam and the sub beam, which greatly reduces the amount of reflected light of the reading spot on the disk surface. The two sub-beam spots F and E, which follow in the traveling direction, are arranged at the same distance from the main beam spot with the main beam spot centered therebetween. The photoelectric converter 13 generates an F signal having a current level according to the amount of reflected light of the preceding sub beam spot F. The photoelectric converter 12 generates an E signal having a current level according to the amount of reflected light of the sub beam spot E that follows. FIG. 9 shows signal waveforms when the sub-beam spots F and E pass through a defect portion due to scratches or dirt on the disc. The current value of the F signal becomes 0 at the defect portion, and the current value of the E signal also becomes 0 after a delay of Δτ. After passing through the defect portion, the original state is restored in the order of the F signal and the E signal. When the F signal and the E signal change with such a time difference, the amplitude of the tracking error signal based on the two signals fluctuates in the defect portion, although there is no deviation between the track and the read spot as shown in FIG. Then, the tracking servo circuit malfunctions and an incorrect track jump is performed.

Therefore, the capacitor 36 is added to the signal system on the preceding beam side to delay the F signal by an amount corresponding to the beam difference Δτ. By doing so, it is possible to prevent the generation of an erroneous error signal by matching the timings of the level drops occurring in the F signal and the E signal due to the defect portion.

[0010]

However, if the gain characteristics and the like of the current-voltage converters 21 and 22 are different, the output level does not become exactly 0 even when the reading spot is on the track and there is no tracking error. In addition, FIG.
As shown in, the amplitude is biased to the positive or negative side in the high frequency part of the tracking error signal obtained when the tracking servo loop is opened and a search is performed, and the tracking error signal is not output positively and negatively, Correct information cannot be transmitted to a tracking servo circuit or a track counter (not shown) that counts the number of jump tracks.

Therefore, it is an object of the present invention to provide a tracking error detecting device capable of suppressing the fluctuation of the tracking error signal caused by dirt or scratches on the disk surface without affecting the tracking servo circuit. To do.

[0012]

In order to achieve the above object, the tracking error detecting apparatus of the present invention is designed to follow at least a main beam spot and two sub beam spots preceding and following the main beam spot on a track of an optical recording disk. A three-beam type pickup that generates two sub-beam signals whose levels complementarily change according to the deviation from the track center, and a tracking error signal generation that generates a tracking error signal according to the level difference between the two sub-beam signals Means, adding means for adding the two sub-beam signals to each other to obtain a sum signal, differentiating means for differentiating the sum signal to generate a differential signal, and signal superposition for superimposing the differential signal on the tracking error signal. And means.

[0013]

The sum signal obtained by adding the two sub-beam signals has its level changed in a range corresponding to the error portion generated in the tracking error signal by the defect portion of the disk. The changed portion is extracted by the differentiating circuit and superposed on the tracking error signal. Then,
The error caused by the defect in the tracking error signal is canceled.

[0014]

Embodiments of the present invention will be described below with reference to FIG. In FIG. 1, parts corresponding to the parts shown in FIG. 6 are designated by the same reference numerals, and the description of such parts will be omitted.

First, the reflected light of the sub-beam E is converted by the photoelectric converter 12 into an E signal having a current level corresponding to the amount of light, and the one signal input terminal of each of the subtractor 53 and the adder 54 via the current-voltage converter 52. Is supplied to. The reflected light of the sub beam F is converted by the photoelectric converter 13 into an F signal having a current level corresponding to the amount of light, and is supplied to the other input ends of the subtracter 53 and the adder 54 via the current-voltage converter 51. The current-voltage converters 51 and 52 having the same operating characteristics are used. The difference signal output of the subtractor 53 is supplied as a tracking error (TE) signal to one input end of the subtractor 54 which is a signal superimposing means. The sum signal output C of the adder 54 consists of in-phase components of both signals and is supplied to the differentiating circuit 56. The differentiating circuit 56 obtains the differential signal D of the sum signal output. This differential signal D is supplied to the other input terminal of the subtractor 55. The subtractor 55, which is a signal superimposing means, superimposes the differential signal D on the tracking error signal. When the sub beam F becomes the preceding beam, a subtractor is selected as the signal superimposing means,
When the sub beam E is the preceding beam, the adder is selected as the signal superimposing means. This is because whether the error component is positive or negative is determined by the reverse of the pickup scanning direction. The compensated tracking error signal compensated by the differential signal D is supplied to the tracking servo phase compensator 24.
The current-voltage converter 51 to the subtractor 55 form a tracking error detector 50. Other configurations are similar to those of the conventional circuit.

FIG. 2 shows a specific configuration example of the tracking error detector 50, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. The current-voltage converters 51 and 52 are composed of an operational amplifier whose non-inverting input terminal is grounded, and a time constant circuit in which a resistor and a capacitor are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier. It has a low-pass characteristic with a cutoff frequency of 20 kHz. The subtractor 53 is composed of an operational amplifier 53a and resistors 53b to 53e. The adder 54 includes an operational amplifier 54a and a resistor 5
4b to 54d constitute an inverting adder. The subtractor 55 includes an operational amplifier 55a and resistors 55b to 55.
and e constitute an inverting addition coefficient unit. The differentiating circuit 56 is composed of a series circuit of a capacitor 56a and a resistor 55d, and has a time constant differentiating characteristic of the capacitor 56a and the resistor 55d.

Next, the operation of the tracking error detector 50 will be described with reference to the signal waveforms shown in FIG. When the sub-beam spot of the pickup passes through the defect portion of the disc, the F and E signals are shown in FIG.
And, as in the case of (B), a rapid level of attenuation occurs. F
There is a delay time difference between the signal and the E signal corresponding to the sub-beam spot interval. When the F signal and the E signal, which have been voltage-converted by the adder 54, are added and adjusted to an appropriate level, the sum signal C whose level fluctuates in the range in which the defect portion affects the tracking error signal as shown in (C) of FIG. obtain. This sum signal C is differentiated by the differentiating circuit 56 to become the D signal shown in (D). In the D signal, a waveform substantially similar to the erroneous detection waveform generated in the tracking error signal due to the defect portion as shown in (E) occurs at substantially the same time. So D
The signal and the tracking error signal are superposed by a subtractor 55 at an appropriate ratio to obtain a compensated tracking error signal in which the defect error portion is canceled as shown in FIG.

FIG. 4 shows the waveforms of the above-mentioned F signal, E signal, C signal, D signal and tracking error signal when the track search is performed by opening the tracking servo loop of the above embodiment. .. Since the waveforms of the F signal and the E signal when the sub beam crosses the track have opposite phases to each other, the C signal obtained by adding both signals becomes a DC signal, and the level of the D signal which is the differential value thereof is substantially zero. Therefore, the tracking error signal input to the subtractor 55 is directly output as the compensation tracking error signal.

From this, it can be seen that a stable tracking error signal can be obtained in which there is no deviation in the amplitude of the tracking error signal as shown in FIG. 10 in the compensation tracking error signal.

Another configuration example of the tracking error detector 50 is shown in FIG. 5, parts corresponding to those in FIG. 2 are designated by the same reference numerals. In this embodiment, the functions of the subtracters 53 and 55 shown in FIG.
Has been replaced with a simpler circuit configuration. Since the circuit operation is the same, the description is omitted.

[0021]

As described above, the tracking error detection device of the present invention does not delay one of the sub-beam signals as in the conventional device, and causes a large level change of the tracking error signal due to scratches on the reflecting surface of the disk. There is an advantage that the tracking error signal amplitude can be suppressed and bias of the tracking error signal amplitude does not occur at the time of track search.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a tracking error detector.

FIG. 3 is a signal waveform diagram showing waveforms of signals of respective portions of the embodiment.

FIG. 4 is an explanatory diagram illustrating a tracking error signal according to an embodiment.

FIG. 5 is a circuit diagram showing a configuration example of another tracking error detector.

FIG. 6 is a block diagram showing a conventional pickup servo system.

FIG. 7 is a circuit diagram showing a configuration example of a conventional tracking error detector.

FIG. 8 is an explanatory diagram showing a relationship between a defect of a disc and a beam spot.

FIG. 9 is a signal waveform diagram showing waveforms of signals of respective parts of a conventional tracking error detector.

FIG. 10 is a signal waveform diagram showing a conventional tracking error signal in track search.

[Explanation of symbols]

 11 Photoelectric Converter 12 Photoelectric Converter 51 Current Voltage Converter 52 Current Voltage Converter 53 Subtractor 54 Adder 55 Subtractor 56 Differentiation Circuit

Claims (2)

[Claims] 1. A main beam spot and a sub beam spot following the main beam spot are made to follow on a track of an optical recording disk to generate two sub beam signals whose levels change complementarily at least in accordance with a deviation from the track center. A three-beam type pickup, a tracking error signal generating means for generating a tracking error signal according to a level difference between the two sub-beam signals, and an adding means for adding the two sub-beam signals to obtain a sum signal, A tracking error detecting device comprising: a differentiating unit that differentiates the sum signal to generate a differential signal; and a signal superimposing unit that superimposes the differential signal on the tracking error signal. 2. A subtraction circuit for generating a tracking error signal having an amplitude corresponding to a level difference between two signals whose levels complementarily change in accordance with a deviation from a track center of a read spot following a track carrying information. An adder circuit for adding the two signals to obtain a sum signal, a differentiator circuit for differentiating the sum signal to generate a differential signal, and a signal superimposing circuit for superimposing the differential signal on the tracking error signal, A tracking error detection circuit comprising: