JPS6196529A - Tracking servo-circuit - Google Patents

Abstract

PURPOSE:To prevent the turbulence caused by a flaw of a disk of tracking control by holding a low band component of tracking error signal of an opening contact, when a tracking servo-circuit is opened, and leading it exactly into a usual servo-state, when the servo-circuit is closed thereafter. CONSTITUTION:The ordinary servo-system of a tracking servo-circuit of an optical pickup is constituted of the first and the second phase compensating circuits 1, 2 for inputting an error signal TR, driver amplifying circuit 3, and a switching means 5 provided between the circuits 1, 2, and the output of the circuit 3 is supplied to a tracking coil 4. Also, the level of an envelope signal of an HF signal from an information sensor is detected by a level detecting circuit 8, and the signal of a low level period from the circuit 8 is detected by a level detecting means 11. By such a signal, the means 5 is opened, and the error signal of an opening contact is held in the capacitor C1 of a holding means 6. When the servo-system is closed thereafter, a usual servo-state is obtained exactly.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Technical field of application The present invention relates to a tracking servo circuit for an optical pickup device.

BACKGROUND OF THE INVENTION Various tracking servo circuits for optical pickup devices have been proposed. Japanese Patent Publication No. 59-31129 discloses a technique of adding a track jump pulse to the low frequency component of a tracking error signal in order to achieve a good track jump. However, no countermeasures against scratches on the disc are disclosed.

C1 Problems to be Solved by the Invention If there is a scratch on the disc, the tracking error signal will be greatly disturbed, making normal tracking control impossible. The present invention suppresses disturbances in tracking control caused by scratches.

20 Means for Solving Problems Level detection means for detecting the level of a reproduced signal (for example, an information signal) is provided, and a switching means for opening the tracking servo circuit in response to the output of the level detection means, and a switching means for opening the tracking servo circuit. A holding means is provided for holding the low-frequency components of the tracking error signal.

E1 Effect: If there are scratches, dents, etc. on the disc, the level of the reproduced signal changes, so the presence or absence of scratches, dents, etc. can be detected by the level detection means.

In response to the output of the level detection means, the tracking servo circuit is opened, and the low frequency component of the tracking error signal at the time of opening is held by the holding means. When the tracking servo circuit is closed again, tracking control is resumed from the magnitude of the tracking error signals fl and fC held by the holding means. For example, the length of the wound is 3
If it is about 00 μm, it is possible to sufficiently return to the normal tracking servo state after restarting.

In the embodiment, the tracking error signal (TR) is generated by the first phase compensation circuit (
1;, via the second phase compensation circuit (2), the driver circuit (
3), is amplified and then applied to the tracking coil (4), thereby forming a normal tracking servo circuit. The switching means (5) are normally closed. A capacitor (C
1) is that when the tracking servo is released when the switching means (5) is released, the low-frequency component (for example, about 8 H) of the tracking error signal (TR) at the time of release is
It has an elongation value suitable for maintaining the The phase characteristics of the tracking servo yarn include the circuit constants of the holding means (6) and the first and second phase compensation circuits +11 f21
In addition, the 1st and @2 phases should be optimized as a whole? Tt] is determined by selecting the circuit constants of the compensation circuits (1) and (2).

Now, the switching means (5) is controlled to open and close depending on the scratches on the disk, but when it is used for reconnaissance, attention is paid to changes in the level of the reproduced signal. Although a tracking error signal or a focus error signal can be used as the reproduction signal, in this embodiment, an information (HF) signal is used.

The 7'CHF signal (HF) output from the information sensor is amplified by the amplifier circuit (7) and has a waveform as shown in Figure 2 (a).The amplifier circuit (7) detects the envelope of the HF signal. The output HF envelope signal (HFE
N) (see 弗2图山)] is also output. When the detection circuit (81) detects that the level of the amplified HF signal (HF) is higher than a predetermined level, the output signal (HF) is detected by the detection circuit (81).
OK) is at a low level, for example, the focus search operation is stopped and the information reproduction state is entered. Furthermore, a switching transistor (9) is connected to the output of the level detection circuit (8).
1 conducts, and the capacitor (C2) becomes a conductor f.
cc5) are connected in parallel. Such Condan FCC5)
The purpose of this switching is to switch the frequency characteristics of the amplifier circuit (7) when the disk starts and stops rotating, and when the disk rotates steadily.

The HF envelope signal (HFEN) is passed through the filter circuit (1
0I (see Figure 2 (0)), level detection means (11
1. The level detection means 0υ is a comparison circuit (12
1. Comparison circuit Comprising a clamp circuit (t13) that clamps the output of the mackerel to a predetermined level, and an inverter (141) for matching the logic with the following circuit.Input signal level to the comparison circuit (12) [Figure 2 ( 0] becomes smaller than the predetermined level Ce) of the comparator circuit 1z, the level detection means α
The output of υ is as shown in FIG. 2(d). This output (
During the low level period d), the switching means (51) is opened and the tracking servo circuit is opened. Therefore, the tracking error signal (TR), which had been changing as shown in FIG. During the opening period of the servo circuit, the magnitude is held constant at the time of opening.

The size of a detectable flaw can be determined by the constant of the integrating circuit used to obtain the HF envelope signal from the HF signal, the predetermined level f) set with a variable resistor, etc., but if it is too small, Switching noise will frequently occur in the reproduced information signal, which is undesirable. In reality 5
The determination is made so that scratches of approximately 0.0 m can be detected. The predetermined level also relates to the speed of response to scratches and the open period of the tracking servo circuit.

According to the present invention, when the tracking servo circuit is opened, the low-frequency component of the tracking error signal at the time of opening is held, so that when the tracking servo circuit is subsequently closed, the low frequency component of the tracking error signal is retained. However, the tracking servo can be reliably brought into the normal tracking servo state, and tracking control can be prevented from being disturbed due to scratches on the disk.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a tracking servo circuit according to the present invention, and FIG. 2 is an operation waveform diagram. (Switching means, (6)... Holding means, υ
...Level detection means.

Claims (1)

[Claims] (1) A tracking servo circuit in an optical pickup device configured to perform tracking control based on a tracking error signal, which includes a level detection means for detecting the level of a reproduced signal and a response to the output of the level detection means. A tracking servo circuit comprising: a switching means for opening the tracking servo circuit; and a holding means for holding a low-frequency component of a tracking error signal when the circuit is opened.