Method and apparatus for detecting focussing position deviation

Details Method and apparatus for detecting focussing position deviation Method and apparatus for detecting focussing position deviation

1987-02-09

1988-12-27

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 44, G01J 120

Patent

active

047942444

ABSTRACT:
A method and apparatus for detecting a focussing position wherein a difference between photoelectric outputs from two photodetectors is amplified by a differential amplifier to detect a deviation of a focal point of a reader/writer head in the reading/writing operation for an optical recording medium.
Prior to the amplification of the difference between the photoelectric outputs from the photodetectors, the output voltage from one of the photodetectors is changed to be input to the differential amplifier and the changing ratio is set so that the output from the differential amplifier will be zero when focalized.
For this purpose, a voltage changing device for changing the photoelectric output from the photodetector is provided between an output of the photodetector and an input of the differential amplifier.

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