Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1998-06-12
2001-03-13
Kim, W. Chris (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S068000, C327S110000
Reexamination Certificate
active
06201653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of magnetic data recording. More particularly, the present invention relates to an apparatus and a method for improving data recording performance of a magnetic storage device at high data rates.
2. Description of the Related Art
A write driver (WD) in a magnetic storage device is a circuit that bi-directionally drives a write current through a write head for recording data on magnetic media, such as a magnetic disk.
FIG. 1
shows an exemplary disk drive system
10
having a magnetic read/write head
11
that is positioned over a selected track on a magnetic disk
12
for recording data.
One impediment for improving performance of magnetic data recording at high data rates, that is, the speed at which data is written to a magnetic medium, is that the flux reversal time for a transition is slowed by eddy current damping in the core of the write head.
Another impediment for improving performance of magnetic data recording are parasitic capacitances that are associated with silicon devices of the write driver, the inductance and the parasitic capacitance of the write head and the losses due to the interconnect between the write driver and the write head that cause the rise and fall times of the write-current transitions through the write head to increase, thus degrading the performance of the write driver.
FIG. 2
is a schematic block diagram showing a parasitic capacitance C
D
associated with a write driver WD, an inductance L
H
, a resistance R
H
and a parasitic capacitance C
H
associated with the write head, and an interconnect modelled as a transmission line by the distributed network consisting of the inductances L
I
and the capacitances C
I
between the write driver WD and the write head. The rise and fall times of the write-current transitions are slowed because the write current I
W
from the write driver must pass through the network shown in
FIG. 2
, which essentially forms a low-pass filter, to reach the write head.
The rise- and fall-time increase also degrades data-recording performance by causing nonlinear transition shift (NLTS) effects during write-current transitions and slowing the field transitions in the magnetic field at the pole tips of the write element.
A conventional write driver is typically configured to have current-switching H drivers, such as FET drivers, differential amplifier drivers and current-mirroring H drivers. Such a conventional configuration has a limited current output capability. Consequently, a conventional write driver has limited capability for compensating for the increase in flux reversal time caused by eddy current damping in the write head, the parasitic capacitance associated with the silicon devices of the write driver, the write head impedance and the interconnect losses between the write driver and the write head.
What is needed is a technique that compensates for eddy current dampening effects in the core of a write head, while also compensating for the parasitic capacitance associated with the silicon devices of the write driver, the write head impedance and the interconnect losses between the write driver and the write head to speed up the flux reversal time.
SUMMARY OF THE INVENTION
The present invention provides a technique that compensates for eddy current dampening effects in the core of the write head by providing a write current that temporarily “overshoots” the steady-state write current to decrease the flux reversal time in the write head. Additionally, the present invention provides a technique that compensates for the parasitic capacitance associated with the silicon devices of the write driver, the write head impedance and the interconnect losses between the write driver and the write head.
The advantages of the present invention are provided by a magnetic-head write-driver circuit having a write-driver circuit and a by-pass circuit. The write-driver circuit has a signal path between an input and an output of the magnetic-head write-driver circuit. The write-driver circuit receives an input signal having transitions and outputs a first write signal that is related to the input signal. The by-pass driver circuit is coupled in parallel to the signal path of the write-driver circuit, and outputs an assist signal that is related to transitions of the first write signal and that is coupled to the first write signal to form an output write signal. According to the invention, the assist signal acts to shorten a current reversal time through the write head, by temporarily increasing an amplitude of the output write circuit, and/or to charge and discharge a parasitic capacitance associated with the output of the magnetic-head write-driver circuit by adding a current to, or enforcing a voltage on, the first write signal to form the output write signal. The added signal can correspond to a selected function f(t) that varies either the amplitude of the assist signal or the duration of the assist signal, or both.
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J.A. Bailey et al., Predriver For “H” Configured Write Drive For Magnetic Recording, IBM Technical Disclosure Bulletin, vol. 23 No. 11, Apr. 1981, pp. 5167-5168.
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Contreras John T.
Klaassen Klaas Berend
van Peppen Jacobus
Banner & Witcoff , Ltd.
International Business Machines - Corporation
Kim W. Chris
Tran Khanh Q.
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