Nakamichi Corporation

Akio Terada

Makoto Yamamoto

Gohji Uchikoshi

A circuit for shifting the level of a signal inputted in the focussing or tracking servocircuit provided with an automatic gain control device in an optical disc apparatus. The circuit comprises a plurality of variable gain amplifiers arranged at a stage prior to detecting a focussing or tracking error and forming the corresponding error signal, inclusive of gain set apparatus for selecting one of a plurality of gains of said gain amplifiers depending on the detected level range of the light quantity reflected from the optical disc.

Level shift circuit of optical disc apparatus

This invention relates to a servo system for positioning and driving a movable member such as a pickup head of an optical reading system, for example. A sinewave signal is generated by a position detector in response to movement of the movable member. A first reference signal is used with the sinewave signal to position the movable member. A second reference signal is used with a modified signal which is generated by differentiating and rectifying the sinewave signal, to drive the movable member.

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Kodaira, Japan

Akio Terada