Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
2000-02-29
2003-07-15
Faber, Alan T (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S061000, C360S066000
Reexamination Certificate
active
06594097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a reproduction amplifier circuit of a hard disk drive, and more particularly relates to a reproduction amplifier circuit of a hard disk drive having a MR (Magneto Resistive) head.
2. Description of Related Art
In the field of the head of the reproduction amplifier circuit of the hard disk drive (referred to as HDD hereinafter), the MR head having an MR element which utilizes resistance change depending on the magnitude of the magnetic field has mainly been used.
A conventional reproduction amplifier circuit of an HDD having a MR head is described herein under.
FIG. 3
is a conventional circuit diagram of a reproduction amplifier circuit of an HDD having a MR head. This HDD reproduction amplifier circuit is a Voltage Bias Current Sensing type reproduction amplifier circuit in which a signal is taken out as a current while both end voltage of the MR is being fixed.
Because both face side and back side of a disc of an HDD are served for recording, two MR heads MR
0
and MR
1
are used for one disc. Because all the discs are recorded/reproduced by use of one circuit in the reading/writing amplifier, change-over switches S
1
and S
2
are provided for selecting an MR head.
When the MR head MR
0
is selected, the switch S
1
is connected to the terminal a side and switch S
2
is connected to the terminal c side, an inverted input (−) of an operational amplifier Gm
1
is connected to the MR
0
and the output is connected to the base of a transistor Q
2
. In such a circuit as described herein above, the operational amplifier functions so that a voltage V
1
generated in the internal is generated at the H
0
terminal. A capacitor C
1
is provided to remove the noise of the operational amplifier Gm
1
. When the resistance value of the MR
0
changes in response to the change of magnetic field on the hard disk in this state, the change is transmitted to the resistor R
1
as a current. The operational amplifier A
1
amplifies the current corresponding to the change and sends it out to an output terminal V
0
. As described herein above, the MR head MR
0
performs reproduction process.
In the case that the MR head MR
1
is selected, the MR head MR
1
performs reproduction processing in the same manner as described herein above. The switch S
1
is connected to the terminal b and the switch
2
is connected to the terminal d, the inverted input (−) of the operational amplifier Gm
1
is connected to the MR
1
and the output is connected to the base of a transistor Q
1
. In such a circuit as described herein above, the operational amplifier Gm
1
functions so that a voltage V
1
generated in the internal is generated at the H
1
terminal. When the resistance value of the MR
1
changes in response to the change of magnetic field on the had disc in this state, the change is transmitted to the resistor R
1
as a current. The operation amplifier A
1
amplifies the current corresponding to the change and sends it out to the output terminal V
0
. As described herein above, the MR head MR
1
performs reproduction process.
The switches S
1
and S
2
are switched simultaneously usually. By switching the switches S
1
and S
2
simultaneously, when, for example, a switching signal of the head is changed from the MR
0
to MR
1
, the switches S
1
and S
2
are switched and V
1
is generated at the H
1
terminal of the MR
1
.
The conventional reproduction amplifier circuit of an HDD having an MR head described herein above is disadvantageous in that an overvoltage is applied to the MR head when the MR head is switched.
In switching of the MR head, for example, when the MR head MR
0
is switched to the MR head MR
1
, an MR head switching signal is transmitted simultaneously to the switch S
1
and switch S
2
, but parasitic capacitance and wiring resistance cause a switching lag between these switches S
1
and S
2
.
FIG. 4
is a timing chart of a conventional reproduction amplifier circuit of an HDD having an MR head. The operation performed when the switch S
1
is switched with a delay of the time t
3
from the switch S
2
is described. When the switching signal of the head changes from the H
0
terminal to the H
1
terminal, first the switch S
2
is switched from the terminal c to the terminal d. During the time t
3
until the switch S
1
is switched, the voltage of the H
1
terminal namely the GND voltage value is connected to the inverted input (−) of the operational amplifier Gm
1
, and the operational amplifier Gm
1
functions to increase the voltage at the A point. During the time, the voltage generated at the H
1
terminal is remained in GND. The switch S
1
is switched from the terminal a to the terminal b with the delay of the time t
3
. At the time when the switch S
1
is switched, the voltage increased by the operational amplifier Gm
1
as described herein above is applied to the H
1
terminal. After that time, the operational amplifier Gm
1
functions to adjust the voltage of the H
1
terminal to V
1
, and the voltage of the H
1
terminal decreases gradually to V
1
and this state is maintained. As described herein above, when the switch S
1
delays from the switch S
2
, an overvoltage is applied to the MR head MR
1
, this is a problem.
The case in which the switch S
2
delays from the switch S
1
by the time t
3
will be described herein under. When the switch S
1
is switched, a voltage V
1
is generated at the H
1
terminal of the MR
1
. During the time t
3
until the time t
3
elapses, the switch S
2
is not switched, and the H
0
terminal which is now going to decrease to GND is connected to the inverted input (−) of the operational amplifier Gm
1
. Because a voltage which is lower than the non-inverted input terminal (+) is applied to the inverted input (−) of the operational amplifier Gm
1
as described herein above, the operational amplifier Gm
1
functions to increase the voltage at the A point similarly to the case that the switch S
1
is switched with a delay as described herein above. As the result, an overvoltage is applied to the MR head MR
1
also when the switch S
2
delays from the switch S
1
.
As described herein above, regardless of the switch that is first switched, when switching causes a lag between the switches S
1
and S
2
, an overvoltage is applied to the MR head to cause the reduction of the reliability of the MR head.
The present invention was accomplished to solve such problem. It is the object of the present invention to provide a reproduction amplifier circuit of a hard disk drive in which an overvoltage is not applied to a head when the head is switched.
SUMMARY OF THE INVENTION
To solve the above-mentioned problem, the present invention provides a reproduction amplifier circuit of a hard disk drive for reproducing the information recorded in the predetermined disc area by use of two MR (Magneto Resistive) heads comprising an MR head switching means for performing switching of the MR head connected to a negative feedback circuit for applying a predetermined voltage on the MR head in response to a head switching signal, first switching means for turning off the operation of an amplifier which forms the negative feedback circuit for a predetermined time, a current source for discharging a capacitor provided on the middle of the negative feedback circuit, and second switching means for turning on the connection between the current source and the capacitor in response to the off operation of the first switching means.
The reproduction amplifier circuit of the hard disk drive having the structure as described herein above fixes both end voltage of the MR head by means of the negative feedback circuit, and reads out (reproduces) the disc by means of the change in resistance value of the MR head depending on the change in magnetic field on the disc. The MR head switching means switches the MR head comprising two heads per one disc, and reproduces a desired disc area. Before the MR head is switched by means of the MR head switching means, the operation of the
Faber Alan T
Kananen, Esq. Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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