Write head fault detection circuit and method

Details Write head fault detection circuit and method Write head fault detection circuit and method

2000-07-21

2004-02-03

Faber, Alan T. (Department: 2651)

Dynamic magnetic information storage or retrieval

Monitoring or testing the progress of recording

C360S068000, C360S046000, C369S053420, C340S652000

Reexamination Certificate

active

06687064

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to the field of information storage, and more particularly to a circuit and method for detecting faults on a write head of a hard-disk drive.
BACKGROUND OF THE INVENTION
Hard-disk drives are mass storage devices that may include a magnetic storage media, e.g., rotating disk or platters, a spindle motor, read/write heads, an actuator, a preamplifier, a read channel, a write channel, a servo circuit and control circuitry to control the operation of the hard-disk drive and to properly interface the hard-disk drive to a host system or bus.
FIG. 1
shows an example of a prior art disk drive mass storage system
10
. Disk drive system
10
includes a number of rotating platters
12
mounted on a base. Platters
12
are used to store data that is represented as magnetic transitions on the magnetic platters
12
, with each platter
12
coupleable to an arm
14
having a read head
16
and a write head
18
at the tip thereof. The read head
16
and write head
18
are adapted to transfer data to and from the platters
12
via a preamplifier
20
. The preamplifier
20
is coupled to circuitry
22
that processes the data being read from and written to platters
12
and controls the various operations of disk drive system
10
.
Data is stored to and retrieved from each side of magnetic platters by write heads
18
and read heads
16
, respectively, at the tip of arms
14
. The read heads
16
comprise magneto-resistive heads adapted to read data from platters
12
when current is passed through them. The write heads
18
comprise inductive wires (coils) that transmit data to magnetic media platters
12
. Heads
16
,
18
are coupled to preamplifier
20
that serves as an interface between read/write heads
16
/
18
of disk drive system
10
and circuitry
22
. The preamp
20
may comprise a single chip containing a reader amplifier, a writer circuit, fault detection circuitry, and a serial port interface, for example.
The write head
18
comprises a coil through which current is passed to create a magnetic field and write data onto platters
12
. A problem in hard-disk drive systems
10
is that the write head
18
coil may be open or short at various times during manufacturing or in the field for a variety of reasons. The open or short faults may occur due to a faulty coil that has severed, creating an open circuit, or a faulty coil that has fused together, creating a short circuit. If the hard-disk drive is moved, the vibration may cause the write head coil to temporarily short to ground, for example. In any of these situations, the write head fault needs to be reported immediately, for example, from preamplifier
20
to circuitry
22
. If the write head
18
coil is permanently damaged, it needs to be repaired or replaced. Furthermore, the electrical resistance of the write head
18
coil may be too high to function properly.
Because these faults in the write head
18
coil can occur, a hard-disk drive system
10
requires a function to detect write head
18
faults. Prior art write fault detection methods typically are performed during the write mode, a very noisy mode. Typically, a hard-disk drive system
10
has two active operating modes: a read mode during which data is read from platters
12
via read heads
16
, and a write mode, during which write heads
18
write data to platters
12
. The reamplifier
20
includes control circuitry for both the read head
16
and the write head
18
. Therefore, it has two exclusive active operation modes: read and write. The read mode is a more passive, quiet and steady mode, and the write mode is more of an active mode, because a large amount of current (usually around 30 to 70 mA), with the current polarity being switched frequently, for example, every 1 or 2 nanoseconds, is passed through the coil in order to write data to platters
12
.
During the write mode, the preamplifier
20
provides a substantial current to write head
18
coil to create a magnetic field that writes data to the platters
12
. More recent designs of hard-disk drive systems
10
have higher data rates such as 1 gigabits per second, and the write current has to switch direction or polarity faster, accordingly. This results in a complicated write signal waveform, making it difficult to detect write head faults correctly. For example, when the write head is operating normally at high data rate, prior art methods of detecting write head faults may give a false detection and indicate that the write head has an open fault or short to ground. Alternatively, write head faults may not be detected with prior art detection circuits and methods due to their limited frequency range for correct operation.
SUMMARY OF THE INVENTION
The present invention provides an accurate circuit and method for detecting write head faults in a disk drive circuit. The fault detection is performed during a read mode using a small DC current, avoiding problems that arise when performing a write head fault detection during the write mode of a hard-disk drive. Several devices that may be pre-existing in a writer circuit are used to build the present DC detection circuit, which provides reliable and accurate write fault detection while minimizing the circuit overhead needed to perform the write head fault detection function. A first and second serially connected resistor having equal values are coupled across the coil of the write head, with a transistor coupled to a common node between the two resistors and ground to maintain a DC current path to ground. The voltages across the two resistors and with respect to the common node are analyzed to determine the fault status of the write head coil.
Disclosed is a circuit for detecting faults on a write head of a hard-disk drive. The circuit includes a first resistor coupled to a first end of the write head coil at a node a, and a second resistor coupled to a second end of the coil at a node b. A transistor is coupled to the first and second resistors at a common node c. Faults on the write head coil are detectable by analyzing the voltages across the nodes a, b and c.
Also disclosed is a method of detecting faults on a write head of a hard-disk drive. The method comprises the steps of coupling a first end of the write head coil to a first resistor at a node a, coupling a second end of the coil to a second resistor at a node b, and coupling a transistor to the first and second resistors at a common node c. Faults are detected on the coil by analyzing the voltages across nodes a, b and c.
The present invention provides a reliable, accurate means of detecting faults on a write head of a disk drive system by performing a write head fault detection during a quiet operating mode of the hard-disk drive. Errors in write head fault detection are avoided by use of the present invention. Standard components are utilized that are inexpensive and easily implementable into electronic circuitry. The invention is advantageous in discriminating between an open or short fault, which is not possible with prior art fault detection circuits. The write head fault detection is frequency-independent because the detection is performed during a non-writing mode. Transient faults with short duration (<150 nanoseconds) are ignored by means of a timing delay.


REFERENCES:
patent: 4203137 (1980-05-01), Beck et al.
patent: 5087884 (1992-02-01), Brannon
patent: 5457391 (1995-10-01), Shimizu et al.
patent: 6104199 (2000-08-01), Sako

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