Abstract: A light beam detector receiver a light beam reflected from an optical disk and generates two electrical signals, each corresponding to the amount of the light beam. The detector includes an adder for adding the two electrical signals to generate a first operation signal, a subtracter for subtracting one electrical signal from the other to generate a second operation signal, and a converter for converting the second operation signal into digital data in accordance with a conversion gain determined by the amplitude of the first operation signal. The digital data obtained is used for adjusting a position of an objective lens with respect to the optical disk.

Abstract: Two detect signals for correcting a detracking, which is derived from a first photo sensor are supplied to a differential amplifier and an adder, through amplifiers. The amplifiers amplify the supplied detect signals at a first amplification degree in the reproduction mode to reproduce the information from an optical disc. In the record mode, a second amplification degree is used, which is 1/A in the reproduction mode, when the average level of each detect signal is A times that in the reproduction mode. The difference signal between the detect signal from the differential amplifier and the sum signal of them from the adder are supplied to a normalizer. The normalizer divides the difference signal by the sum signal. An objective is moved by the output signal from the normalizer, to correct the detracking. A defocus is corrected, in the same manner as the detracking correction, by using two detect signals for correcting the defocus from a second photo sensor.

Abstract: A current-voltage converter circuit includes a current source outputting a current having a low-pass signal component and a high-pass signal component, a band splitter, a first converter, and a second converter. The band splitter splits the current output from the current source into the low-pass signal component and the high-pass signal component. the first converter converts the low-pass signal component split off by the band splitter into a first output signal having a first prescribed voltages. The second converter converts the output signal from the first converter and the high-pass signal component split off by the band splitter into a second output signal having a second prescribed voltage.