Magnetic recording writing circuit

Details Magnetic recording writing circuit Magnetic recording writing circuit

2001-06-12

2004-05-04

Faber, Alan T. (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C360S046000, C327S110000

Reexamination Certificate

active

06731449

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a writing circuit in a magnetic recording apparatus such as a hard disk drive (HDD) or a floppy disk drive (FDD) drive. More particularly, this invention relates to a magnetic recording writing circuit which can arbitrarily control the waveform of a write current in writing.
BACKGROUND OF THE INVENTION
FIG. 4
is a circuit diagram of a conventional writing circuit in a magnetic recording apparatus. An arrangement of the circuit will be explained below.
As shown in
FIG. 4
, head
1
of this magnetic recording apparatus incorporates an equivalent circuit including inductance L
1
, resistor R
1
, capacitor C
1
, and resistor R
3
for reducing the impedance at a resonance frequency of the head
1
.
I
1
denotes a reference current source for supplying a reference current for a write current Iw. The reference current source I
1
is connected at one terminal to the collector of an NPN transistor Q
1
and the base of another NPN transistor Q
2
. The base of the NPN transistor Q
1
is connected to the emitter of the NPN transistor Q
2
and the base of a further transistor Q
16
. The collector of the NPN transistor Q
2
as well as the other terminal of the current source I
1
are connected to a third power source V
3
. The emitter of the NPN transistor Q
1
and the emitter of the NPN transistor Q
16
are connected to a second power source V
2
via two resistors R
4
and R
5
respectively.
The collector of the NPN transistor Q
16
is connected to the emitters of two NPN transistors Q
17
and Q
18
which are in turn connected at their collectors to the emitters of two transistors Q
19
and Q
20
respectively. The collectors of the two transistors Q
19
and Q
20
are connected to a first power source V
1
. Connected between the collectors of the two transistors Q
17
and Q
18
is the head
1
.
The bases of the transistors Q
17
, Q
18
, Q
19
, and Q
20
are connected to four terminals J, K, L, and M respectively.
Because of a current mirror function in
FIG. 4
, the collector of the NPN transistor Q
16
receives a current I
5
which is proportional to the transistor size of both the NPN transistors Q
1
and Q
16
at the reference current I
1
.
FIG. 5
illustrates the waveforms of input voltages at the terminals J, K, L, and M and the waveforms of corresponding currents I
2
, I
3
, I
4
, I
5
, and Iw.
During the period T
9
, the terminals K and L are fed with signals having low logical level and the terminals J and M are fed with signals having high logical level. This switches the NPN transistors Q
19
and Q
18
off and the NPN transistors Q
17
and Q
20
on. Accordingly, during the period T
9
, the current running from the source V
1
is passed through the NPN transistor Q
20
and turned to Iw in the head
1
and the current I
3
is passed through the NPN transistor Q
17
and turned to I
5
.
During the next period T
10
, the current from the source V
1
is passed through the NPN transistor Q
19
so the current Iw in the head
1
runs in a reverse of the direction in T
9
. The current I
2
is passed through the NPN transistor Q
18
and turned to I
5
.
The current Iw in the head
1
has a waveform shown in
FIG. 5
because of the action of inductance L
1
, parasitic capacitance C
1
, resistance R
1
, and damping resistance R
3
. More specifically, the waveform includes an overshoot at the rise a
7
and its recovery a
8
before the normal write signal period at one polarity and another overshoot at the fall a
9
and its recovery a
10
before the normal write signal period at the other polarity.
In the conventional magnetic record writing circuit, such various time factors of the current Iw or the write current for magnetic recording, which include the rise speed and overshoot at each rise a
7
, overshoot recovery a
8
, fall speed and overshoot at each fall a
9
, and overshoot recovery a
10
, can hardly be controlled.
While an arrangement for increasing the write current with a fixed level at the rise is disclosed in U.S. Pat. No. 5,869,988, no attempt has been successfully made to provide a magnetic recording writing circuit controlling the overshoot and the overshoot recovery and modifying the current in response to a change in the reference current I
1
.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a magnetic record writing circuit which can control the rise and fall of a write current to minimize the write time and the overshoot period.
In the magnetic record writing circuit according to one aspect of this invention, an arrangement is provided such that, a current having a higher level than a level of a write current is supplied for a desired period of time during rise and fall of the write current, and a current having a lower level than the level of the write current is supplied for a desired period of time during overshoot at the rise and fall of the write current.
In the magnetic record writing circuit according to another aspect of this invention, the current for driving a head is supplied by the action of a transistor group where the current source transistor is joined in parallel with at least one damping transistor and released from the head by the action of load transistors via a mirror transistor which comprises a reference current source and a mirror circuit.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.


REFERENCES:
patent: 5869988 (1999-02-01), Jusuf et al.
patent: 6201653 (2001-03-01), Contreras
patent: 8-45008 (1996-01-01), None
patent: 9-219004 (1997-08-01), None
patent: 2000-57509 (2000-02-01), None

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