Hitachi, Ltd.

Hitachi-lg Data Storage, Inc.

Koji Kaniwa

Shigeyuki Itoh

Yoshizumi Watatani

Akira Shibata

Hajime Nishimura

Satoru Moriya

Hiroharu Sakai

Akihiro Ashida

Jinya Ikeda

In an optical disc device, a way of canceling a lens shift due to an electric offset of an output of a tracking actuator driving circuit is desired. A tracking servo control circuit contains a first operation mode for setting an output current of the tracking actuator driving circuit to generally zero and a second operation mode for supplying a predetermined potential to the input. An average potential of a push-pull signal detected in the first operation mode is acquired. An object lens is moved by a predetermined amount in both radial directions by changing a potential supplied in the second mode to acquire correlative relationship between average potential of a push-pull signal relative to a lens movement amount and the supplied potential. An offset amount is acquired from the potential and the correlative relationship to cancel the offset.

Optical disc device and tracking servo control circuit therefor

In an optical disc apparatus, when a signal to be generated corresponding to an amount of reflected light from an optical disc has a signal level below a threshold level for a period exceeding a reference period, a controller controls an actuator to move an objective lens in a direction such that a distance from the optical disc surface to the objective lens increases. The reference period may be set based on a type of the optical disc and a recording or reproducing speed of the optical disc, or based on a surface deflection of the optical disc.

Optical disc apparatus and back off control method for objective lens

A helical scanning type magnetic recording and reproducing apparatus records a signal representing recording conditions on a magnetic tape when a recording is effected thereon, together with a PCM audio signal. At the time of reproduction, reproducing conditions are controlled so as to be the same as the recording conditions on the basis of the signal representing recording conditions reproduced.

Apparatus for recording and reproducing a video signal and for recording

An audio signal transmission system having a noise reduction circuit, which includes a transmission medium such as a magnetic tape to be used to transmit a digital signal converted from an input audio signal and thereafter to output the audio signal reproduced from the digital signal, a digital signal transmitter having a pulse-code modulator and demodulator (MODEM). The noise reduction circuit includes a compressor for compressing the dynamic range of the input audio signal according to the detection level obtained by detecting at least the high-frequency components thereof in order to supply the output from the compression to the digital signal transmitter and an expander for expanding the dynamic range of the demodulated signal from the transmitter according to the detection level of at least the high-frequency components thereof. The transmission system has a low-pass fitler which limits the frequency band of the input signal to be supplied to the dynamic-range compressor to at most half the sampling frequency of the MODEM and thus permits the noise reduction circuit to compress and expand signals supplied thereto in the same frequency band without causing any erroneous operation.

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Yokohama, Japan

Koji Kaniwa