Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1986-09-08
1988-09-27
Cardillo, Raymond F.
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
369 44, 369 45, 369 46, 369 54, 369 59, G11B 7095, G11B 1100
Patent
active
047746980
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical disc recording and reproducing apparatus suitable for recording a digital signal and reproducing the same.
BACKGROUND ART
Recently, there has been developed and commercialized so far such an apparatus which employs an optical disc (Writable disc or DRAW) on which a digital data can be recorded one time and an optical disc (optical magnetic recording disc or the like) from which a digital data can be erased as an external storage or to record other digital data.
By the way, when such apparatus is developed and commercialized, a digital conversion system (Channel Modulation) to substantially convert a digital data to a recorded pattern on the disc becomes a serious problem. The digital modulation is a system to convert a raw data series to a certain data which can be matched with characteristics of media (discs). One of the necessary conditions in this system is that an energy of a servo frequency band in a low frequency range has to be small within a spectrum of a modulation signal. If the energy of the servo frequency band in the low frequency range is high, it affects a servo loop as an external disturbance, obstructing a servo from being effected accurately as it is expected. This condition is also taken into consideration for a disc such as a compact disc that is used only for the playback. Particularly, in the case of a recordable disc apparatus, upon recording, a laser light source must be driven by a modulation signal so that in the modulation system with much low frequency components, an energy applied as an external disturbance becomes rather large to disturb very much the servo from being carried out precisely.
In view of such aspect, this invention is made and provides an optical disc recording and reproducing apparatus by which even in a modulation system in which an energy of a low frequency component is relatively large, a focusing servo and a tracking servo can be stably carried out in the recording mode.
DISCLOSURE OF INVENTION
An optical disc recording and reproducing apparatus according to this invention is constructed such that upon recording, an output of a digital modulation circuit 18 is supplied to a low pass filter 19 which extracts a low frequency component of the modulated signal, a gain thereof is adjusted to subtract the above low frequency component from a servo error signal and a servo is effected by the servo error signal from which the modulated low frequency component is removed.
Upon recording, a digital signal is supplied to the digital modulation circuit 18 as a raw data in which it is modulated according to a predetermined modulation system. The signal modulated is supplied to the low pass filter 19 and thereby the low frequency component contained in the modulated signal is extracted. The gain of the low frequency component extracted is adjusted by a gain adjusting circuit 20, added to the error signal containing the above mentioned low frequency component which is derived from the servo loop and the low frequency component is subtracted from the error signal. As a result, there is obtained only a true servo error signal the modulated low frequency component of which is removed and thus the servo is effected by this true servo error signal.
BRIEF DESCRIPTION OF DRAWING
The attached drawing is a block diagram showing one embodiment of this invention.
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of this invention, applied to an optical magnetic recording and reproducing apparatus, by way of example, will hereinafter be described in detail with reference to the attached drawing.
Reference numeral 1 designates a disc, 2 a winding for generating recording and erasing auxiliary magnetic fields, 3 a lens support member, 4 an objective lens attached to one side of the lens support member in opposing relation to the disc 1, 5 a focusing/tracking actuator, 6 a half mirror, 7 a grating, 8 a beam correcting prism, 9 a collimator lens, and 10 a laser diode. The beam from the laser diode 10 is collimated as
REFERENCES:
patent: 4607157 (1986-08-01), Millar et al.
patent: 4627040 (1986-12-01), Arai et al.
patent: 4661942 (1987-04-01), Yoshimoto et al.
Henmi Fumiaki
Yamagami Tamotsu
Cardillo Raymond F.
Nguyen Hoa T.
Sony Corporation
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