Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
2000-06-06
2003-01-14
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S067000, C360S324100, C360S075000
Reexamination Certificate
active
06507447
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to storage of information and more particularly to a magnetic storage device having a high-sensitivity magnetic sensor and a signal processing circuit for processing an output of the high-sensitivity magnetic sensor.
With increase of recording density in magnetic storage devices called hard disk drive, recent, leading-edge hard disk drives generally use a GMR (giant magneto-resistive) sensor in a magnetic head for picking up information from a magnetic disk. A GMR magnetic sensor is a device that changes a magneto-resistance thereof in response to an external magnetic field and is able to detect a feeble magnetic field produced by a tiny magnetization spot formed on a magnetic disk.
On the other hand, a GMR magnetic sensor has a drawback in that the magnetic polarization of the magnetic materials used therein easily undergoes reversal. Such a reversal may be caused by an electrostatic discharge and causes an inversion of polarity in the output signal representing the result of the reading operation. Further, such a reversal of the magnetic polarity may induce a distortion in the electric signal produced by the GMR magnetic sensor. When such an inversion of polarity or distortion is caused in the output signal, the desired reproduction of the information signal is not possible or severely impaired.
In view of the foregoing drawback of the GMR magnetic sensors, there is a proposal to use a spin-valve magnetic sensor in a magnetic head for reading the information from the magnetic disk.
FIG. 1
shows an example of a magnetic disk device
1
according to a related art.
Referring to
FIG. 1
, the magnetic disk drive
1
includes a magnetic disk
2
accommodated in an enclosure
10
having a cover
11
and stores information on the magnetic disk
2
in the form of concentric tracks. The magnetic disk
2
is mounted on a spindle motor
6
for rotation, and a floating magnetic head
5
scans over the surface of the magnetic disk
2
. The magnetic head
5
is mounted at an end of a swing arm
7
, wherein the arm
7
is connected to a voice coil motor
8
and the voice coil motor
8
actuates the arm
7
for swinging motion. With the swinging motion of the arm
7
thus caused by the voice coil motor
8
, the magnetic head
5
scans over the surface of the magnetic disk
2
generally in a radial direction thereof. Thereby, the magnetic head
5
is controlled so as to trace a desired track on the disk
2
.
The voice coil motor
8
is supplied with an electric signal from a read/write amplifier
9
for actuating the arm
7
, while the read/write amplifier
9
further supplies an electric signal to the magnetic head
5
via the arm
7
for writing or reading of information on or from the magnetic disk
2
. Thus, in response to the electric signal, the magnetic head
5
senses, or alternatively induces, a magnetization on the magnetic disk
2
and writing or reading of information is achieved on or from the magnetic disk
2
.
It should be noted that the electric signal thus supplied to the magnetic head
5
from the read/write amplifier
9
corresponds to the data created and supplied from a host device (not shown), wherein the host device supplies the data to a circuit substrate
4
of the magnetic disk device
1
via a connector
3
, and the electric circuit provided on the circuit substrate
4
converts the data to the electric signal.
In the construction of
FIG. 1
, it should be noted that the magnetic disk
2
, the magnetic head
5
, the spindle motor
6
, the arm
7
, the voice coil motor
8
and the read/write amplifier
9
are accommodated in the enclosure
10
having the cover
11
.
FIG. 2
shows the construction of the signal processing system used in the magnetic disk device
1
of
FIG. 1
in the form of a block diagram.
Referring to
FIG. 2
, the processing system is formed on the circuit substrate
4
and includes an HDIC (head IC) unit
13
that amplifies an output signal produced by a GMR magnetic sensor or spin-valve magnetic sensor of the magnetic head
5
. The HDIC unit
13
is also called a head amplifier and is provided on the magnetic head
5
together with the GMR or spin-valve magnetic sensor. The output signal of the magnetic sensor
5
is then supplied to an RDC (read channel) unit
14
on the circuit substrate
4
wherein, the RDC unit
14
demodulates the original information recovered from the magnetic disk
2
by the magnetic sensor
5
in an encoded form, by conducting a sampling process.
The information thus demodulated is then supplied to an HDC (hard disk controller) unit
15
on the circuit substrate
4
, wherein the HDC unit
15
transmits the information thus demodulated by the RDC unit
14
to a host device via the connector
3
not shown in FIG.
2
. Further, the HDC unit
15
recovers the information related to servo control of the magnetic disk
2
or tracking control of the magnetic head
5
from the output of the RDC unit
14
and supplies the same to an MCU (micro-control unit)
16
provided also on the circuit substrate
4
. Thereby, the MCU
16
controls the spindle motor
6
and the voice coil motor
8
via a servo control circuit
17
such that the magnetic disk
2
rotates at a predetermined, controlled speed as represented in
FIG. 2
by an arrow A.
The MCU
16
further controls the operation of the RDC unit
14
. Under control of the MCU
16
, the arm
7
is caused to swing as represented in
FIG. 2
by an arrow B, and the magnetic head
5
traces a track formed on the magnetic disk
2
.
FIG. 3
shows the construction of a spin-valve magnetic sensor
22
provided in the magnetic head
5
for reading the magnetic information from the magnetic disk
2
.
Referring to
FIG. 3
, the spin-valve magnetic sensor
22
is constructed on a substrate
23
of a magnetic material constituting a yoke and includes a free layer
18
typically formed of a ferromagnetic material such as a Ni-Fe alloy, a non-magnetic layer
19
formed on the free layer
18
of a non-magnetic material such as Cu, a pinned layer
20
of a ferromagnetic material such as a Ni-Fe alloy, and a pinning layer
21
of an anti-ferromagnetic material such as an Fe-Mn ordered alloy.
The pinning layer
21
is magnetized in the direction as indicated in
FIG. 3
by an arrow P and creates a stable magnetic field associated with the magnetization P, wherein, due to the anti-ferromagnetic nature of the pinning layer
21
, the magnetization P does not change easily even when the external magnetic field is changed. Due to the stable magnetic field thus created by the pinning layer
21
, the magnetization of the pinned layer
20
is fixed on pinned in the counter direction as represented in
FIG. 3
by an arrow Q. On the other hand, the magnetization in the free layer
18
, which is separated from the pinned layer
20
by the non-magnetic layer
19
, changes the magnetization thereof in response to the external magnetic field created by the magnetization spot formed on the magnetic disk
2
, as represented by arrows S and T.
FIG. 4
shows the operation of the spin-valve magnetic sensor
22
.
Referring to
FIG. 4
, it can be seen that the pinned layer
20
is magnetized in the fixed direction represented by the arrow Q, while the magnetization of the free layer changes or rotates in response to the magnetic signal on the magnetic disk
2
as represented by the arrows S and T. Thereby, the angle between the magnetization of the pinned layer
20
and the magnetization in the free layer
18
is changed in response to the magnetic signal on the magnetic disk
2
.
FIGS. 5A and 5B
show the two operational states of the spin-valve magnetic sensor
22
, wherein
FIG. 5A
shows the case in which the magnetization Q in the pinned layer
20
is anti-parallel with respect to the magnetization S in the free layer
18
, while
FIG. 5B
shows the case in which the magnetization Q is parallel to the magnetization T in the free layer
18
.
In the state of
FIG. 5A
, the electrons in the pinned layer
20
are polarized either to an up-spin state
Greer Burns & Crain Ltd.
Holder Regina N.
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