Hitachi, Ltd.

Osami Kushizaki

Masahiro Takasago

Kazuo Shigematsu

Takuya Mizokami

Kazuo Isaka

Hiromi Seo

An amplitude difference between a reproduction signal from a preformat portion of an optical disk and a reproduction signal from a recording portion of user's data is obtained. When the amplitude difference exceeds a predetermined value, a first gain value which was set for information from the preformat portion is used as a gain value of an AGC circuit for reproduction and a gain control of the reproduction signal is performed. On the other hand, when the amplitude difference is smaller than the predetermined value, a second gain value which was set for the user's data is used. Thus, a situation such that a noise and a remaining signal of the user's data which was not erased are erroneously recognized as an inherent reproduction signal can be prevented. A discrimination to see if the data has been recorded in the recording portion of the user's data or not can be also accurately performed.

Automatic gain control method and apparatus in optical disk system

The peak value of upper envelope of an optical disk read signal is detected, and a signal indicative of the detected peak value or upper envelope is used to correct the total reflected light amount signal. That is to say, two output signals delivered from a pair of horizontally symmetrical photo detectors, which detect the reflected light of a light spot, added together, and furthermore a signal indicative of the result of this addition is added to the signal indicative of the peak value or upper envelope to produce a total reflected light amount signal which is not influenced by the pits on the optical disk.

Detecting light spot movement direction for an optical disk

An optical recording/reproducing apparatus for recording and reproducing information along tracks on an optical disc by irradiating the optical disc with a laser beam comprises a tracking error detecting circuit for detecting the digression of the laser beam from the center line of each track and a level detector for detecting that the output of the tracking error detecting circuit exceeds a predetermined level. An operation for recording information in the optical disc by the laser beam is stopped when the output of the level detector takes a predetermined state indicating that the output of the tracking error detecting circuit exceeds the predetermined level, for a first predetermined time, and a signal indicating the occurrence of off-track is generated when the duration time of the predetermined state in the output of the level detector exceeds a second predetermined time which is longer than the first predetermined time.

Defect detecting optical apparatus enabling recording in an alternate

An optical information recording and reproducing apparatus for irradiating a disk-shaped recording medium having spiral tracks with a light beam so that the information recorded along the tracks may be reproduced. The apparatus is equipped with a circuit for detecting the displacement of the light beam from said tracks and a clipping circuit for clipping a tracking error signal or the output signal of said detecting circuit with a predetermined threshold value. The light beam has its position corrected along the tracks in accordance with the output signal of said clipping circuit so that it may be prevented from tracking erratically.

Growing community of inventors

Hiratsuka, Japan

Osami Kushizaki