Focusing search circuit and focusing servo circuit which are use

Details Focusing search circuit and focusing servo circuit which are use Focusing search circuit and focusing servo circuit which are use

1992-12-04

1995-05-09

Young, W. R.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4429, 369 4432, G11B 7095

Patent

active

054146810

ABSTRACT:
Disclosed is a focusing search circuit to activate a focusing servo loop of an optical disc player for driving an objective lens and for focusing a laser beam onto a signal recording surface of an optical disc. The circuit has a DC bias applying circuit for applying a DC signal of a predetermined level to an output signal of a photodetector which is a fluctuation of an AC signal centering about a predetermined DC signal level in the focusing search operation. The output signal of the photodetector which has been shifted by the predetermined level is compared with a reference voltage having a predetermined DC level of the photodetector before it is shifted by a comparing circuit. When the laser beam is in almost the in-focus state, the comparing circuit detects the coincidence between both of the above signals and activates the servo loop.

REFERENCES:
patent: 4683560 (1987-07-01), Takeuchi et al.
patent: 4786794 (1988-11-01), Doi
patent: 4998233 (1991-03-01), DiMatteo et al.
patent: 5003521 (1991-03-01), Yoshida et al.
patent: 5103439 (1992-04-01), Bierhoff et al.
patent: 5113384 (1992-05-01), McDonald et al.
patent: 5148423 (1992-09-01), Gleim

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