Tracking control apparatus for a multi-layer optical disc and me

Details Tracking control apparatus for a multi-layer optical disc and me Tracking control apparatus for a multi-layer optical disc and me

1996-12-09

1998-06-09

Tran, Thang V.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4437, 369 94, G11B 7095

Patent

active

057646066

ABSTRACT:
In a three-spot tracking control system for a multi-layer optical disc, stray light of the signal-reproducing main beam from a layer other than the layer being reproduced leaks into first and second photodetectors receiving the reflected beam of two auxiliary tracking controlling beams to render the tracking operation unstable. In order to overcome this drawback, a first photodetector detects one auxiliary reflected beam from one or the other of the information signal layers of a double-layer optical disc. The second photodetector detects the other reflected auxiliary beam from the information signal layer. A first upper envelope detector detects the upper envelope signal of the reflected auxiliary beam. A second upper envelope detector detects the upper envelope signal of the detection signal of the other reflected auxiliary beam. A first subtractor subtracts the detected output by the first upper envelope detector 6 from the detection signal of the first photodetector. A second subtractor subtracts the detected output by the second upper envelope detector from the detection signal of the second photodetector. A third subtractor performs subtraction between outputs of the first subtractor and the second subtractor.

REFERENCES:
patent: 4712206 (1987-12-01), Kanda
patent: 4750162 (1988-06-01), Tajima
patent: 5202875 (1993-04-01), Rosen et al.
patent: 5408452 (1995-04-01), Sakemoto et al.

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