JP2883040B2 - Low frequency oscillation prevention circuit for optical disc player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo circuit for an optical disk player, and more particularly to an optical disk suitable for preventing low-frequency oscillation caused by delta symmetry of an optical pickup. The present invention relates to a low-frequency oscillation prevention circuit for a player.

[0002]

2. Description of the Related Art As a conventional tracking servo circuit of a CD player, for example, a circuit having a circuit configuration as shown in a block diagram of FIG. 3 has been provided. In the figure, 1
Denotes an optical pickup, 2 denotes an RF amplifier, 6 denotes an actuator driver, 7 denotes a tracking actuator, 8 denotes a disk, 10 denotes a low-frequency delay compensation circuit, and 11 denotes a servo processor.

The operation of the tracking servo circuit system shown in FIG. 3 is as follows. The optical pickup 1 reads data from a disk 8 and the RF amplifier 2 outputs a tracking error signal TE.
Is extracted and added to the servo processor 11. The servo processor 11 accurately determines whether the optical pickup 1 is following the track of the disk 8 based on the tracking error signal TE, and outputs an amount corresponding to the deviation as a tracking correction signal.
The tracking correction signal output from the servo processor 11 is sent to the actuator driver 6 through the low-frequency delay compensation circuit 10 composed of the resistors R ₁ and R ₂ and the capacitor C ₁ , and the correction amount for shifting the tracking actuator 7. Drive to complete the tracking correction.

When the optical pickup 1 is accurately following the track on the disk 8, the output of the optical pickup 1 is output from the RF amplifier 2 in a series of tracking servo loops between the optical pickup 1 and the tracking actuator 7. The obtained tracking error signal is given a specific frequency characteristic by the servo processor 11 and is output as a tracking correction signal.

[0005] The frequency characteristic of the tracking correction signal resonates at an inherent frequency f ₀ due to the inductive reactance of the tracking actuator 7 and a peak is generated. Said
tracking correction signal is phase compared to lower frequency region than the f ₀ is 90 f ^_0. In the frequency region which is late and is higher than the above f ₀ , the phase is further delayed but 180 ^. Since this is not the case, there is a phase margin and oscillation does not occur.

When the optical pickup 1 deviates from the track of the disk 8, there is no tracking error information from the optical pickup 1, and therefore no normal tracking correction signal is output. Therefore, the gain due to the deviation of the tracking error balance due to the movement of the actuator. And a unique gain and phase only in the tracking loop.
Wherein in the frequency region higher than f _0, phase compared to a lower frequency range than the f ₀ is ^180. A positive feedback loop is formed with a delay as described above. Therefore, the phase margin is zero ^. Frequency
It would cause oscillation in f _1. This oscillation is low-band oscillation.

[0007] The to prevent oscillation at the frequency f ₁ f ₀
To select the constants of resistor R ₂ and capacitor C1 of the low-frequency compensation circuit 10, and Shifts the f ₀ of the low-frequency compensation circuit 10 from the f ₀ and to have a phase margin of at the f _0. However, the gain due to delta symmetry has large variations, and oscillation cannot be completely stopped.

[0008]

However, in the above-described tracking servo circuit of the conventional CD player,
As shown in FIG. 2, the optical pickup 1 deviates from the track of the disk 8 and low frequency oscillation of the tracking servo loop occurs. In order to prevent the low-frequency oscillation, there is no means for detecting the low-frequency oscillation and controlling the stop of the oscillation, and only the constant of the low-frequency delay compensating circuit 10 is changed. Has no flexibility in tracking servo design,
There is a drawback that oscillation from the outside of the set of the optical pickup 1 and oscillation with respect to the eccentric disk are easily caused.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to solve the disadvantages of the prior art, to detect when a tracking servo loop causes low-band oscillation, and to perform digital signal processing. An object of the present invention is to provide a low-frequency oscillation prevention circuit for an optical disc player, in which a circuit controls a low-frequency delay compensation circuit to improve the phase characteristics of a tracking servo loop.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided an optical
Low frequency oscillation prevention circuit of disc player, the tracking servo circuit for driving and controlling the optical pickup of the optical disc <br/> player, and the low frequency delay compensation circuit for a low-frequency delay compensation of the tracking servo circuit, the A switch for turning on / off the low-frequency delay compensation circuit; and a digital signal processing circuit configured to control the switch to turn off the low-frequency delay compensation circuit by detecting an abnormality of the EFM signal. It is characterized by consisting of.

[0011]

According to the present invention, an optical disc is provided.
In the tracking servo circuit of the click player, EFM
Since the low frequency oscillation of the tracking servo circuit is detected by detecting the abnormality of the EFM signal due to the loss of frame synchronization of the signal, and the digital signal processing circuit controls the switch so that the low frequency delay compensation circuit is turned off. Even if the optical pickup deviates from the track on the disk due to external shock or eccentric disk, etc., and the low frequency oscillation occurs in the tracking servo loop, the low frequency lag compensation circuit is automatically cut off, and the tracking servo loop is cut off. Is improved, and low-frequency oscillation can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a low-frequency oscillation preventing circuit for a CD player according to the present invention will be described with reference to FIGS. The same parts as those in the conventional example are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1 is a block diagram of a tracking servo loop of a CD player, and FIG. 2A is a characteristic diagram showing a frequency characteristic and a phase characteristic of a tracking correction signal when an optical pickup normally follows a track of a disk. (B) shows the frequency characteristic and phase characteristic of the tracking correction signal when the optical pickup is out of the track of the disk and low frequency oscillation is occurring, and the low frequency delay compensating circuit is separated by the control of the digital signal processing circuit. FIG. 4 is a characteristic diagram illustrating a frequency characteristic and a phase characteristic at the time. In the figure, 3 is a servo processor, 4 is a low-frequency delay compensation circuit, 5 is a digital signal processing circuit, and 9 is a microcomputer.

A tracking error signal TE is extracted from a signal read by the optical pickup 1 by an RF amplifier 2 and applied to a servo processor 3 to output a tracking correction signal having a necessary frequency characteristic. An EFM signal from the RF amplifier 2 is applied to the EFM terminal of the digital signal processing circuit 5.

The tracking correction signal output from the servo processor 3 is applied to a low-frequency delay compensation circuit 4 composed of resistors R ₁ and R ₂ and a capacitor C 1. Low frequency lag compensation circuit 4 of the resistor R ₂ and the capacitor C1 are connected in series, the other end of the capacitor C1 is grounded through an analog switch SW1. The analog switch SW1 has a gate terminal for turning the switch ON / OFF connected to the LOC terminal of the digital signal processing circuit 5, and the switch operation is controlled by a signal at the LOC terminal.

The tracking correction signal applied to the low-pass lag compensation circuit 4 is composed of the following frequency components low frequency as components of more midrange but pass the resistors R ₁ and R ₂ and capacitor C1 It is attenuated by the attenuator circuit, and the apparent low-frequency component is boosted.

The tracking correction signal that has passed through the low-frequency delay compensation circuit 4 is applied to an actuator driver 6, which drives a tracking actuator 7 to move the optical pickup 1 by the amount of the tracking error correction to perform tracking correction.

When the optical pickup 1 is following the track on the disk 8 accurately, the EFM signal output from the RF amplifier 2 does not generate an abnormal signal and the output signal of the LOC terminal of the digital signal processing circuit 5 Is an analog switch
The "H" level for turning on SW1 is maintained.

FIG. 2A shows the frequency characteristic and the phase characteristic when the tracking correction signal of the tracking servo loop when the LOC terminal is maintained at the "H" level is an open loop . , The phase difference is within 180 ° in the entire frequency band, and a phase margin is provided.

When the optical pickup 1 removes a track on the disk 8 due to an external shock or an eccentric disk, the frame synchronization of the EFM signal, which is the output signal of the RF amplifier 2, is lost. Therefore, the digital signal processing circuit 5
Upon detecting an abnormality of the FM signal, the output signal of the LOC terminal is changed from “H” level to “L” level.

Therefore, the analog switch SW1 is turned off by the "L" level signal from the LOC terminal,
Analog switch of capacitor C1 of low-frequency delay compensation circuit 4
The terminal connected to SW1 is also disconnected from the ground level, and the operation of the low-frequency delay compensation circuit 4 is stopped.

When the low-frequency delay compensation circuit 4 stops operating,
The tracking correction signal, which is the output signal of the servo processor 3, has an increased gain over the entire frequency band of the frequency characteristic as shown by a dotted line in FIG.
180 ^. Since the phase difference is within the range, a phase margin is obtained, and low-frequency oscillation does not occur, and the tracking servo loop operates stably.

A series of tracking control operations of the servo processor 3 and the digital signal processing circuit 5 are controlled by a microcomputer 9.

[0023]

According to the low-frequency oscillation preventing circuit of the optical disc player according to the present invention, when low-frequency oscillation occurs due to external vibration or tracking error of the optical pickup due to an eccentric disc, digital signal processing is performed. The circuit can separate the low-frequency delay compensation circuit from the tracking servo loop and change the gain and phase of the tracking servo group, thereby automatically preventing the low-frequency oscillation and forming a stable tracking servo loop.

In addition, it has excellent features such as simple structure and easy implementation because it can be constructed at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a low-frequency oscillation preventing circuit of a CD player according to the present invention.

FIG. 2 is a characteristic diagram of a tracking correction signal.

FIG. 3 is a block diagram of a conventional example.

[Explanation of symbols]

 1: optical pickup 2: RF amplifier 3: servo processor 4: low-frequency delay compensation circuit 5: digital signal processing circuit 6: actuator driver 7: tracking actuator 8: disk 9: microcomputer 10: low-frequency delay compensation circuit 11: servo Processor

Claims (1)

(57) [Claims] 1. A tracking servo circuit for driving and controlling an optical pickup of an optical disk player, comprising: a low-frequency delay compensating circuit for compensating for a low-frequency delay of the tracking servo circuit; Switch, and by detecting the abnormality of the EFM signal,
Low frequency oscillation prevention circuit for optical disc player, characterized by comprising a digital signal processing circuit configured to OFF the low-pass lag compensation circuit by controlling the switch.