Method for differentially writing to a memory disk

Details Method for differentially writing to a memory disk Method for differentially writing to a memory disk

2000-08-30

2003-01-28

Holder, Regina N. (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C327S110000

Reexamination Certificate

active

06512649

ABSTRACT:

BACKGROUND OF THE INVENTION
Description of the Related Art
The present invention relates to a method for writing to a memory disk, and particularly to a method for controlling the write head of a disk drive device.
Most computer systems include one or more associated disk drives, which may be built into or external to the computer system. Typically, disk drives have at least one rotating magnetic medium and associated head mechanisms that are carried adjacent the magnetic material. The heads are radially positionable to selectively write information to, or read information from, precise positions on the disk medium. Such disk drives may be, for example, hard disk drives, floppy drives, or the like.
Data is written to the associated data disk by applying a series of signals to a write head according to the digital information to be stored on the magnetic disk media. The write head has a coil and one or more associated pole pieces that are located in close proximity to the disk media. As signals cause the magnetic flux to change in the head, the magnetic domains of the magnetic media of the disk are aligned in predetermined directions for subsequent read operations. Typically, a small space of unaligned magnetic media separates each magnetic domain transition to enable successive transitions on the magnetic media to be distinguished from each other.
Since the disk is moving relative to the head, it can be seen that if the small space separating the magnetic domain transitions is not sufficiently wide, difficulty may be encountered in distinguishing successive magnetic transitions. This may result in errors in reading the data contained on the disk, which is, of course, undesirable.
Meanwhile, as computers are becoming faster, it is becoming increasingly important to increase the speed at which data can be written to and read from the disk media. However, since the data signals are in the form of square wave transitions, if the rise time of the leading edges of the square waves is large, the small space between magnetic media transitions also becomes large, which reduces the effective rate at which data can be accurately written and read. Since the write head assembly includes at least one coil, forcing the current to rise rapidly, or to reverse flux directions within the write head is difficult.
In the past, data writing circuits and/or write drive circuits used to supply such write signals to the heads included preamplifier circuits to drive the current through selected legs of an “H-bridge” circuit, which is capable of allowing relatively fast current reversals for accurate data reproduction.
An example of a typical H-bridge write head drive circuit
10
, according to the prior art, is shown in FIG.
1
. The circuit
10
includes four MOS transistors,
12
-
15
connected between a high reference voltage V
dd
and a low reference voltage Vss at line
17
. A coil
19
, used, for example, to supply data pulses for writing to a disk drive media is integrated into the write head mechanism. The coil
19
is connected between the center legs of the H-bridge, as shown.
It can been seen that, depending on the gate biases applied to the respective transistors
12
-
15
, the current flows through the coil
19
in one direction or another. That is, one current flow path includes the transistor
14
, coil
19
from right to left, and transistor
13
. The other current flow path includes transistor
12
, the coil
19
from left to right, and the transistor
15
.
In the H-bridge circuit
10
, the transistors
12
and
14
serve as switching transistors, which are controlled by the out-of-phase signals on a pair of respective input lines
28
and
29
. The transistors
13
and
15
serve as current controlling transistors, which are controlled by the out-of-phase signals on the respective input lines
29
and
28
in a manner opposite from the connections to the switching transistors
12
and
14
, via respective control transistors
31
and
32
. The magnitude of the current through the transistors
13
and
15
is controlled by a transistor
21
, with which the transistors
13
and
15
form respective current mirrors, when connected via respective transmission gates
24
and
25
. The transmission gates
24
and
25
are controlled by the signals on the respective input lines
29
and
28
, in the same manner as the associated transistors
31
and
32
. A reference current source
26
supplies the reference current to the transistor
21
, which is mirrored by currents in respective transistors
13
and
15
, as described above. In conventional driver circuits for controlling the write head of a disk drive, the steady state voltage levels to which the two terminals of write head
19
settle are both typically near either the high reference voltage level Vdd or the low reference voltage level Vss.
One problem encountered in disk drives employing existing drive circuitry for the write head coil
19
is that the wires or lines connecting the write head coil
19
to the write drive circuitry are located proximally to the wires or lines connecting the read head to the read channel circuitry (not shown in FIG.
1
). The close proximity between the wires capacitively couples the wires together. As a result, voltage spikes or other voltage transitions appearing on the lines connected to write head coil
19
may have a greater tendency to appear as noise on the lines connected to the read head of the disk drive and potentially damage the read head as a result. In addition to the capacitive coupling between the lines associated with the write head, a significant degree of coupling within the structure of the write head itself may disadvantageously occur.
Because of the inductive nature of the write head coil
19
and because conventional steady state voltage levels for the write head terminals are approximately near the high reference voltage level Vdd, a relatively sizeable voltage spike or undershoot typically may be generated on a terminal of write head
19
(the terminal of write head
19
having a voltage signal experiencing a falling transition) during the time that the current passing through write head
19
transitions from one direction to another. In other words, a relatively sizeable voltage spike appears on a terminal of the write head when the write head transitions between steady states.
FIG. 2
shows a plot of the voltage appearing on each terminal of a write head during the reversal of current flow through a write head using existing write head drive techniques. As can be seen, a relatively sizeable voltage spike or undershoot may be capacitively coupled to the lines associated with the read head of the disk drive and thereby damage the read head.
During the time the direction of current flow in the write head transitions (i.e., during the time between steady state conditions), the common mode voltage at the write head is different from the common mode voltage at the write head during steady state conditions. This can be seen in
FIG. 2
, where the common mode voltage of the write head during the time the direction of current flow therein transitions (around time 0.5 ns) is noticeably less than the common mode voltage of the write head during steady state conditions (after time 2 ns).
As data rates increase, the rates at which the heads can accurately write the data to the magnetic media is limited by the speed at which the flux in the coil
19
(and its associated components) can be reversed. Relatedly, the amplitude of voltage spikes appearing on a write head terminal (and coupled current appearing on the corresponding read head terminals) is based in part upon the rate of flux reversal. The maximum data rate is thus limited to the maximum physical flux reversal rate of the write head drive circuitry and the maximum allowable coupled current that may be tolerated at the read head during the period of flux reversal.
What is needed, therefore, is a method for driving an inductive load of the type used in conjunction with a write head of a disk drive with a signal that enables a maxi

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