JPS63200322A - Optical disk device - Google Patents

Abstract

PURPOSE:To obtain an optical disk device with a superior S/N, by using an error signal by a three beam method at a low frequency and using it after adding the error signal by a push-pull method at a high frequency, as the error signal for a tracking actuator. CONSTITUTION:Out of three spots projected on the information track 1 of an optical disk, the spot 2 is positioned in the center of the track 1, and the front and rear spots 3 and 4 are positioned so as to be projected on the opposite edges with each other of the track 1. The signals of the spots 3 and 4 are detected by detectors 6 and 7, and the error signal by the three beam method can be obtained by a differential amplifier 11. Also, the detector 5 of the spot 2 is divided quarterly, and the added values of each bi-sected share are found by amplifiers 8 and 9, and those values are taken out by a differential amplifier 10, and its DC component is cut by a high-pass filter 11 of cutoff fc, then, a push-pull signal can be obtained. By adding the signal on the error signal by the three beam method and attaching a desired characteristic with a high frequency via a compensation circuit 13, the S/N can be increased by 2<1/2> times.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in tracking servo in an optical disc device.

2. Description of the Related Art Tracking servo is conventionally performed in optical disk devices such as compact disks (C!D) in order to stably maintain a light spot for reading along minute information tracks.

For this reason, a tracking error signal is required, and in order to obtain the tracking error signal, a three-beam method, a push-pull method, etc. are used, and these tracking error signals are amplified and fed to a tracking actuator to perform tracking servo. When obtaining a tracking error signal using this method, in addition to the tracking error signal for the information track, low-frequency components (carrier leakage) of the information signal are also included. The S/N ratio of the tracking error signal has deteriorated. On the other hand, as shown in Figure 4, the servo looseness is 12 dB1 towards the high range due to the mass of the tracking actuator.
It is falling at 0ct. Therefore, in order to obtain a phase margin at the OdB intersection P, the high frequency is raised and the frequency near this point is 6 d.
I'm trying to make it B/oct.

Problems that the invention seeks to solve: Due to these problems, the tracking actuator has IKH.
Noise components such as carrier leakage before and after Z are added. During playback, these noises become acoustic output from the optical head and directly output C.
I can hear devices such as D players. For this reason, C
When performing high-quality playback as shown in D, direct noise from the device is harmful, and it is desirable to reduce the sound when high-speed access is performed across the zero or track. Also, in order to count the tracking error signal, the objective is to obtain a good tracking error signal.

A solution to the problem: At low frequencies, the tracking error signal is stable and S
The S/N ratio is improved by adding the error signal obtained from the spot at the center of the tonneau track using the push-pull method at a high frequency using detection signals from three beams with a good /N ratio.

Embodiment One embodiment is shown in FIG. 1 and will be described. Three light spots 2, 3.4 are applied to the information track 1 of the optical disc, the center spot 2 is located at the center of the track 1, and the spots that appear on the edges of the track 1 before and after it are opposite to each other. 3 and 4, these reflected lights are extracted by detectors 5, 6, and 7. The detector 5 corresponding to the central spot 2 is divided into four parts (5-1, ~5~
4) These four shift focus error signals,
Obtain a reproduction signal of the information signal. Along this 4-divided track, 2-divided signals 5-1 and 5-2 are added to the left and right, and 5
-3.5-4 addition signal is obtained by an 8°9 amplifier.

By extracting this two-split signal with the differential amplifier 10, a ship-pull signal is obtained, and the depth of track 1 is 1/8
It is used as a tracking error signal (a) in optical discs such as general OD such as human and 1/6 human. However, a direct current offset error occurs in the tracking error signal due to movement of the objective lens, etc., so it cannot be used for eccentric disks. On the other hand, the detection signals of the bases 3 and 4 applied to the edge are detected by the detector 6.7 and sent to the differential amplifier 11 to obtain a track error signal (b) by the three-beam method. Generally this (
Based on the signal b), racking servo 9) is performed.

Next, by passing the previous bushing signal (A) through a bypass filter 11 and attenuating or removing the DC component, a signal containing no DC offset can be obtained even if the objective lens moves in the tracking direction. If the cutoff frequency at this time is fc, the frequency characteristics at this time will be as shown in FIG. 2 (c). -The error signal obtained by the three-beam method at the tip of the sword is flat as shown in (b).

The signals (b) and (c) are added by an adder circuit 12.

As a result, the previous signal (b) as shown in (d)
A signal increased by 6 dB is obtained above c. This signal (
d) Compensation filter 1 that makes the desired loop characteristics
3, the frequency characteristics of the output can be phase-advanced to form an upward curve at point P, as shown at OUT. Here, in the band above fc, both signals (a) and (b) are superimposed. These signals are obtained from different spots as shown in FIG. That is, the error signal is detected in the same phase and becomes noise.The carrier leakage is twice that of the signal whose phase is random, and the noise is r' times the root mean square, and the S/N increases by a factor of σ.

Also, noise caused by dropouts and the like is similarly effective, although it depends on the size. Also, as shown in Fig. 3, by setting the bypass filter + cutoff of the push-pull signal (A) near the OdB intersection P, the protection filter B becomes I''.
As shown in B', it is also possible to obtain the desired curve OUT/ using only the high-frequency rise curve. As described above, the detector 5 corresponding to the central spot 2 is generally divided into four sections for focus servo, and there is no need to add any special components. Therefore, it is possible to easily improve the S/N ratio, reduce carrier leakage, and obtain a stable tracking error signal OUT that is resistant to dropouts.

Effects of the Invention As described above, according to the present invention, it is possible to improve the S/N, reduce carrier leakage, and obtain a stable tracking error signal that is resistant to dropouts. 4゜

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the present invention, FIGS. 2 and 3 are diagrams showing frequency characteristics, and FIG. 4 is a diagram showing conventional characteristics. 1...Track 2,3.4...
・Spot 5, 6, 7...detector s,
9, <-4-knee...Amplifier 10, H...Differential amplifier 12...Addition circuit 13...Sl
, is a filter. 1st! ! I

Claims (2)

[Claims] (1) Pick up the reflected signals of the spots that hit the center of the information track and the opposite track edges of the front and back tracks, and output the differential output of the reflected signals from the front and rear edges and the center detector. An optical disc device characterized in that it is divided into two parts in the track direction and the differential outputs thereof are added to form a tracking error signal. (2) Claim 1 characterized in that means is provided for attenuating the low frequency signal of the two-divided differential output of the central detector.
Optical disc device described in Section 1.