Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-12-15
2002-11-05
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C360S046000
Reexamination Certificate
active
06477119
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head drive circuit for applying a current for recording an information signal to a magnetic field generating coil provided for a magnetic head. Furthermore, the present invention relates to a magneto-optical recording device for generating a magnetic field whose direction and intensity can be switched according to the information signal on the magnetic head by applying a current to the magnetic field generating coil provided for the magnetic head from the magnetic head drive circuit, applying the magnetic field to a magneto-optical recording medium, and simultaneously emitting an optical beam for recording by an optical head such that the beam can converge at a portion to which the magnetic field is applied, thereby recording the information signal.
2. Related Background Art
Conventionally, a magneto-optical recording device forms a magnetized area having a variable magnetization state on a magneto-optical recording medium. The magneto-optical recording device records an information signal by a magnetic head applying a magnetic field with its direction and intensity switched according to the information signal to a magneto-optical recording medium, and by an optical head emitting an optical beam for recording such that the beam can focus on a potion to which the magnetic field is applied. Patent Application Laid-Open Gazette 63-94406 shows an example of a magnetic head drive circuit, used in the magneto-optical recording device, for applying a current for recording an information signal to a magnetic field generating coil provided for a magnetic head.
FIG. 4
shows the configuration of the magnetic head drive circuit described in the above mentioned gazette. Reference numeral
30
denotes a magnetic field generating coil provided for the magnetic head. Reference numerals
31
a
and
31
b
denote switch elements. Reference numerals
32
a
and
32
b
denote auxiliary coils. Reference numerals
33
a
and
33
b
denote direct current sources. When an information signal is recorded, the switch elements
31
a
and
31
b
are alternately turned on and off according to the information signal. When the switch element
31
a
is ON and the switch element
31
b
is OFF, an electric current is applied to the magnetic field generating coil
30
and the switch element
31
a
from the direct current source
33
a
through the auxiliary coil
32
a
. Simultaneously, the current is applied from the direct current source
33
b
to the switch element
31
a
through the auxiliary coil
32
b.
Alternatively, when the switch element
31
a
is OFF and the switch element
31
b
is ON, an electric current is applied to the magnetic field generating coil
30
and the switch element
31
b
from the direct current source
33
b
through the auxiliary coil
32
b
. Simultaneously, the current is applied from the direct current source
33
a
to the switch element
31
b
through the auxiliary coil
32
a
. The inductance of the auxiliary coils
32
a
and
32
b
is larger than that of the magnetic field generating coil
30
, and a current Ia of the auxiliary coil
32
a
and a current Ib of the auxiliary coil
32
b
can be maintained at a substantially constant value Is during the process of recording an information signal regardless of the status of the switch elements
31
a
and
31
b
. For example, the current Is is about 0.15A. However, the current Ib of the auxiliary coil
32
b
decreases by approximately &Dgr;I when the switch element
31
a
is switched from ON to OFF, and the current Ia of the auxiliary coil
32
a
decreases by approximately &Dgr;I when the switch element
31
b
is switched from ON to OFF. The reduction &Dgr;I of the electric current is small as compared with Is.
Thus, by alternately switching ON and OFF the switch elements
31
a
and
31
b
, an electric current through the auxiliary coil
32
a
and an electric current through the auxiliary coil
32
b
are alternately applied to the magnetic field generating coil
30
. The direction of the current applied to the magnetic field generating coil
30
is alternately switched according to an information signal, and a current with the amplitude of approximately ±Is is applied. In addition, a voltage VQa at a connection point Qa between the auxiliary coil
32
b
and the switch element
31
a
, and a voltage VQb at a connection point Qb between the auxiliary coil
32
a
and the switch element
31
b
change like a pulse with the reduction of the current of the auxiliary coils
32
a
and
32
b
by approximately &Dgr;I due to the electromagnetic induction. When the maximum change speed is 0.015A
s and the current Ih of the magnetic field generating coil
30
is switched, the peak value Vp
1
of the pulse-like voltage is about 15 V.
In the magnetic head drive circuit described in the above mentioned gazette, because it is not necessary for a magnetic head to generate a magnetic field when an information signal is not recorded, it is desired that the consumption of power be reduced by suppressing a current supply from the direct current sources
33
a
and
33
b
. To do this, it is necessary to set both switch elements
31
a
and
31
b
in the OFF state when an information signal is not recorded.
However, if an information signal is not recorded and both switch elements
31
a
and
31
b
are set OFF, then the current Ia of the auxiliary coil
32
a
and the current Ib of the auxiliary coil
32
b
are reduced from Is to 0. Conventionally, the operations have not been carefully considered when both elements
31
a
and
31
b
are set OFF, and the speed of the reduction of the current Ia and the current Ib is nearly equal to the speed of the change when the current Ih of the magnetic field generating coil
30
is switched during the process of recording an information signal. The voltage VQa at the connection point Qa and the voltage VQb at the connection point Qb temporarily increase with the reduction of the current Ia of the auxiliary coil
32
a
and the current Ib of the auxiliary coil
32
b
due to the electromagnetic induction.
Assuming that the inductance of the auxiliary coils
32
a
and
32
b
are L, and the change speed of a current is dIx/dt (where Ix is the current Ia of the auxiliary coil
32
a
or the current Ib of the auxiliary coil
32
b
), the voltages VQa and VQb substantially match −L·dIx/dt. For example, assuming that L is 50 &mgr;H, and |dIx/dt| is 0.015 A
s at maximum, the peak value Vp
2
of the voltage VQa and the voltage VQb is about 750 V. Since the voltages VQa and VQb are applied to the switch elements
31
a
and
31
b
in the OFF state, it is necessary to set the resistible voltage Vt higher than the peak value Vp
2
of the voltages VQa and VQb (for example, at 800 V) to prevent the destruction of the switch elements
31
a
and
31
b.
At this time, for example, assuming that a MOS FET (MOS type electric field effect transistor) is used as a switch element, the ON resistance (between a drain and a source in the ON state) normally increases with a higher resistible voltage between the drain and the source. Therefore, in the above mentioned magnetic head drive circuit, the ON resistance cannot be reduced because of the restriction of the lower limit of the resistible voltage Vt of the switch element. That problem causes power consumption to increase. In addition, to raise the frequency of an information signal to be recorded, it is necessary to switch the current Ih of the magnetic field generating coil
30
at a higher speed. However, at this time, the speed of reducing the current Ia of the auxiliary coil
32
a
or the current Ib of the auxiliary coil
32
b
is also reduced when the recording process is stopped, and the peak value Vp
2
of the voltages VQa and VQb rises. Therefore, a higher switch element has to be used for the resistible voltage Vt. However, since the resistible voltage Vt of a practical MOS FET is about 1,00 V at most, there has been the problem that the frequency of an information signal
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Neyzari Ali
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