Focus error detection system for an optical recording/reproducin

Details Focus error detection system for an optical recording/reproducin Focus error detection system for an optical recording/reproducin

1989-05-24

1991-07-09

Envall, Jr., Roy N.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4411, 369 4441, 369 51, G11B 700, G11B 509

Patent

active

050311670

ABSTRACT:
An apparatus is described for recording/reproducing to/from an optical record carrier by means of a laser light beam. The record carrier has pre-recorded sarvo marks aligned in a track. In order to get a focus error signal, the apparatus measures phase difference between signals from two photo sensor elements which receive the laser light beam through the record carrier. A circuit for measuring the phase difference has a first and a second phase shift circuits, RS flip-flops and a focus error converter which has a shift register and a low-pass filter. The signals from the photo sensor elements are fed to the first and second phase shift circuits, respectively. The second phase shift circuit is composed of a plurality of delay elements, output of which are fed to the S inputs of the RS flip-flops. Data at the S inputs are latched in response to an output signal of the first phase shift circuit which is fed to R inputs of the RS flip-flops. Latched data are fed to the shift register for converting to a serial signal. The serial signal, then, is low-pass-filtered to become a focus error signal.

REFERENCES:
patent: 4025784 (1977-05-01), Lehureau et al.
patent: 4051527 (1977-09-01), Braat
patent: 4562564 (1985-12-01), Bricot et al.

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