Architecture for a hard disk drive write amplifier circuit...

Details Architecture for a hard disk drive write amplifier circuit... Architecture for a hard disk drive write amplifier circuit...

2000-02-15

2004-01-27

Hudspeth, David (Department: 2697)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C360S046000, C360S068000

Reexamination Certificate

active

06683740

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of write amplifier circuits within magnetic storage systems. More particularly, the present invention relates to write amplifier circuits supplying a write current and having circuitry to improve response time and quality when recording data on a magnetic storage system.
BACKGROUND OF THE INVENTION
A magnetic storage system, such as a conventional hard disk drive, is generally used for mass storage of data. Typically, the conventional hard disk drive includes a magnetic medium, an inductive element positioned near the surface of the magnetic medium, and a write amplifier circuit which provides a write current to the inductive element. The magnetic medium usually includes one or more disks composed of a metallic material such as an aluminum alloy. A magnetizable coating is deposited on the disk surface and serves as a data medium.
Generally, the inductive element comprises a head which writes data onto the disk as small magnetizations in the data medium by converting the write current into a magnetic field which magnetizes the surface area of the disk below the head. The small magnetizations align according to the generated magnetic field and a “1” is written. By inverting the polarity of the magnetic field, the small magnetizations are also aligned, but in another direction, thus a “0” is written. The polarity of the magnetic field is inverted by changing the direction of the write current supplied to the head. The head is generally a ferrite head or a thinfilm head. The thinfilm head typically is smaller and lighter in weight than the ferrite head. The thinfilm head can be positioned closer to the disk surface than the ferrite head, thus requiring a less intense magnetic field to write data to the disk.
FIG. 1
illustrates a schematic diagram of the conventional write amplifier circuit
100
. The conventional write amplifier circuit includes differential input signals WDX and WDY, a top switch driver
30
, a bottom switch driver
40
, output terminals HX and HY, and H-switch transistors Q
1
, Q
2
, Q
3
, and Q
4
. The head
50
is coupled to the output terminals HX and HY.
In practice, the differential input signals WDX and WDY determine whether the npn transistor Q
3
and the npn transistor Q
4
are turned on or whether the npn transistor Q
1
and the npn transistor Q
2
are turned on. If the transistors Q
3
and Q
4
are turned on, the write current Iw(t) travels from the emitter of the transistor Q
3
to the output terminal HX. From the output terminal HX, the write current Iw(t) enters the head
50
and then returns to the output terminal HY. From the output terminal HY, the write current Iw(t) enters the collector of the transistor Q
4
. In essence, the transistor Q
3
sources the write current Iw(t) while the transistor Q
4
sinks the write current Iw(t).
If the transistors Q
1
and Q
2
are turned on, the transistor Q
1
sources the write current Iw(t) while the transistor Q
2
sinks the write current Iw(t). However, the write current Iw(t) enters the head
50
through the output terminal HY and then returns to the output terminal HX. Hence, the direction of the write current Iw(t) through the head
50
is opposite of the direction described above with respect to the situation when the transistors Q
3
and Q
4
are turned on. This change in the direction of the write current Iw(t) facilitates writing data as a “1” and a “0” on the disk surface.
The top switch driver
30
defines the DC voltages of the output terminals HX and HY and controls the H-switch transistors Q
1
and Q
3
. The bottom switch driver
40
controls the H-switch transistors Q
2
and Q
4
and determines the DC current of the write current Iw(t). Additionally, the bottom switch driver
40
is coupled to a variable current source Iw/K.
The conventional write amplifier circuit
100
has a number of deficiencies. The write current Iw(t) supplied by the conventional write amplifier circuit
100
has a large undershoot and a long ringing. The undershoot and the ringing slow down the writing speed of the magnetic storage system, such as a hard disk drive, and distort the written data when the head converts the write current into a magnetic field. Therefore, the undershoot and the ringing affect the speed and the performance of a magnetic storage system including a conventional write amplifier circuit such as illustrated in FIG.
1
.
SUMMARY OF THE INVENTION
A write amplifier circuit in a magnetic storage system has a cross coupling circuit and an active damp circuit to supply an improved write current to the head writing the data onto the media within the magnetic storage system. The inclusion of the cross coupling circuit decreases a rise time and a fall time associated with the write current. The active damp circuit reduces the undershoot and ringing of the write current. Thus, the write amplifier circuit is suitable for high speed data storage writing applications requiring minimal distortion of the data written to a magnetic medium. The write amplifier circuit achieves these improvements in the waveform of the write current by incorporating circuit elements and using both a negative feedback path and a feedforward path.
In particular, the cross coupling circuit provides a feedforward path within the write amplifier circuit to a first current which creates a second current that is proportional and greater than the first current such that the second current increases the write current available for the head.
Similarly, the active damp circuit provides a negative feedback path from the output terminals of the write amplifier circuit to a third current which creates a fourth current that is proportional and greater than the third current such that the fourth current damps an undershoot and ringing associated with the write current.
In one aspect of the present invention, a cross coupling circuit for decreasing a switching response time of a write current supplied to an inductive element by a write amplifier circuit including a first driving circuit having an output terminal, a second driving circuit having a current amplifier, and a switching circuit coupled to the first and second driving circuits and to the inductive element, wherein the inductive element writes data to a magnetic medium, includes a first terminal coupled to the output terminal for providing a feedforward path to a first current, a second terminal coupled to the current amplifier for supplying the first current to the current amplifier such that a second current which is proportional to and greater than the first current is simultaneously formed in the switching circuit, wherein the switching circuit supplies the write current to the inductive element such that the second current increases the write current available for the inductive element and a feedforward element coupled to the first terminal and to the second terminal for controlling the first current.
In another aspect of the present invention, a damping circuit for reducing an undershoot and a settling time of a write current supplied to an inductive element by a write amplifier circuit including a driving circuit having a current amplifier and a switching circuit coupled to the driving circuit and having a first output terminal coupled to the inductive element and a second output terminal coupled to the inductive element, wherein the inductive element writes data to a magnetic medium, includes a first terminal coupled to the first and second output terminals for providing a negative feedback path to a first current, a second terminal coupled to the current amplifier for supplying the first current to the current amplifier such that a second current which is proportional to and greater than the first current is simultaneously formed in the switching circuit, wherein the switching circuit supplies the write current to the inductive element such that the second current damps a ringing associated with the write current and an impedance element coupled to the first terminal and to the second terminal for adjusting a wav

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