Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1991-01-31
1992-10-20
Nguyen, Hoa
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
360114, 360 59, 360 66, G11B 1304, G11B 1110, G11B 1112
Patent
active
051576414
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for generating a magnetic biasing field for recording in a magneto-optical memory. By magneto-optical memory is meant any medium for magneto-optical recording presenting magnetic anisotropy perpendicular to its surface.
A medium of magneto-optical recording, or a magneto-optical memory, comprises essentially a magnetic layer stable at ambient temperature. To record in this type of memory, the magnetic layer is first magnetized perpendicular to its surface, e g. upwards. Information is recorded by locally inverting the direction of magnetization by heating the zone to be recorded to a temperature above Curie point and simultaneously applying an external magnetic field. When it cools to the ambient temperature, the new direction of magnetization is "frozen". The zone to be recorded is generally heated using a laser beam, while the magnetic field is obtained using a magnetic field generator such as a coil. Therefore, to record information, either the laser beam or the magnetic field generator can be modulated.
The solution consisting in modulating the magnetic field generator has a number of advantages. In fact, there is perfect symmetry between the two directions of magnetization, upwards and downwards, thus there are no second-order harmonics in the re-read signal. It is therefore not necessary to use an erasure cycle before writing. However, modulation of the magnetic field generator requires manipulation of great energy at high frequency, which causes large-scale losses by dissipation.
As a result, the present invention aims to provide a new apparatus for generating a magnetic biasing field for recording in a magneto-optical memory which substantially reduces dissipation losses.
The present invention also aims to provide a new apparatus for generating a magnetic biasing field for recording in a magneto-optical memory of particularly simple construction and usable whatever the modulation code used for the information signals to be recorded.
SUMMARY OF THE INVENTION
Thus, the object of the present invention is an apparatus for generating a magnetic biasing field for recording in a magneto-optical memory, characterized by the fact that it comprises, mounted in parallel, a first coil generating a magnetic field of polarity defined by the information signal, a capacitor and a switching circuit, the opening and closing of the switching circuit being controlled by a first pulse of fixed duration, generated at each transition of the information signal to be recorded.
According to a preferred embodiment, to avoid energy losses, the first pulse has a duration t=.pi. .sqroot.LC, where L represents the inductance of the coil and C the capacitance value. Thus, the closing pulses of the switching circuit occur when the voltage across the capacitor equals zero, i.e. when the capacitor is completely discharged.
The first pulse is generated by a monostable connected in such a way as to trigger at each transition of the information signal to be recorded.
According to a preferred embodiment, the switching circuit is constituted of at least one MOS power transistor receiving the first fixed-duration pulse on its gate.
However, to prevent the passing diode effect on the drain of the MOS transistor, the switching circuit is preferentially constituted of two MOS transistors mounted head to tail, each receiving on their base the first pulse of fixed duration.
According to another feature of present invention, the apparatus for generating a magnetic biasing field also includes a triggering and sustaining circuit.
According to a preferred embodiment, the triggering and sustaining circuit is formed of a second coil mounted on the same core as the first coil and connected between the earth and the common point between two switches connected to a positive voltage and a negative voltage respectively, the opening and closing of the switches being controlled respectively by a second and a third pulse of fixed duration, the second pulse being generated by the t
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patent: 4872078 (1989-10-01), Gerber et al.
patent: 4907211 (1990-03-01), Horimai et al.
Froess, "Current Reversal in Inductive Loads", IBM Tech. Disclosure Bulletin, vol. 11, No. 10, Mar. 1969, p. 1365.
I.E.E.E. Transactions on Magnetics, vol. 24, No. 1, Jan. 1988, New York, U.S.A., pp. 666-669; D. Rugar: "Magnetooptic Direct Overwrite Using a Resonant Bias Coil".
"Thomson-CSF"
Nguyen Hoa
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