Circuit and method for writing to a memory disk

Details Circuit and method for writing to a memory disk Circuit and method for writing to a memory disk

2001-04-20

2002-09-24

Zweizig, Jeffrey (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Gating

Utilizing three or more electrode solid-state device

Reexamination Certificate

active

06456148

ABSTRACT:

BACKGROUND OF THE INVENTION
Technical Field of the Invention
The present invention relates to circuit and method for writing to a memory disk, and particularly to a circuit and method for driving the write head of a disk drive device.
Background of the Invention
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 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 data driving circuit
10
, according to the prior art, is shown in FIG.
1
. The circuit
10
includes four MOS transistors,
12
-
15
connected between a V
cc
voltage
11
and ground reference
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 transistor
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.
Thus, the data drive signals supplied to the head mechanism associated with the circuit
10
may be controlled by applying appropriate signals to the input lines
28
and
29
. However, as mentioned, 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. The maximum data rate is thus limited to the maximum physical flux reversal rate of the driver circuitry.
What is needed, therefore, is a method and circuit 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 maximum flux reversal rate in the driver coil.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings in prior systems and thereby satisfies a significant need for a driver circuit for the write head of a disk storage device. The driver circuit provides a current to the write head so that current flows through the write head in one direction or the other. The driver circuit includes a pair of identical sub-circuits, each sub-circuit being connected to a distinct terminal of the write head. Each driver sub-circuit forms a leg of an H-bridge driver circuit.
Each driver sub-circuit includes a pull-up and/or switching device having a first terminal connected to a voltage supply and a second terminal coupled to the corresponding write head terminal. The driver sub-circuit further includes first and second current sink circuits coupled to the terminal of the write head in parallel relation to each other. The first and second current sink circuits are each capable of sinking current from the corresponding terminal of the write head. The driver circuit further includes a control circuit connected to the pull-up device and the first and second current sink circuits of each driver sub-circuit, for controlling current flow through the write head so as to write data on a corresponding magnetic storage disk.
In general terms, the control circuit activates the pull-up device of one driver sub-circuit so as to provide a current to one terminal of the write head, while activating the first current sink circuit of the other driver sub-circuit in order to sink the provided current from the other terminal of the write head. In this way, the control circuit is capable of passing a predetermined current level through the write head in either direction as desired to write data on the storage disk.
As stated above, it is desirous for H-bridge driver circuits to cause the current flowing through the write head to relatively quickly switch directions. In order to lessen the transition time between the current flowing through the write head in one direction and current flowing therethrough in the opposite direction, the control circuit activates the appropriate first current sink circuit as well as the corresponding second current sink circuit during the current transition. The activation of both first and second current sink circuits causes the current passing through the write head to quickly ramp towards the destination intended current level. The second current sink circuit is activated by the control circuit until the current level in the write head approximately reaches the intended current level. The control circuit thereupon deactivates the second current sink circuit so as to limit the overshoot of current flowing through the write head. Substantially immediately after the second curr

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