Low amplitude skip write detector

Details Low amplitude skip write detector Low amplitude skip write detector

2002-03-06

2003-09-09

Faber, Alan T. (Department: 2651)

Dynamic magnetic information storage or retrieval

Monitoring or testing the progress of recording

C360S075000, C360S053000, C360S077080

Reexamination Certificate

active

06618215

ABSTRACT:

FIELD OF THE INVENTION
This application relates to hard disc drives and more particularly to an apparatus and method for detecting low-amplitude-write/skip-write events.
BACKGROUND OF THE INVENTION
The storage medium for a disc drive is a flat, circular disc capable of retaining localized magnetic fields. The data that are stored upon the disc find physical representation through these localized magnetic fields. The data are arranged on the disc in concentric, circular paths known as “tracks.” The localized magnetic fields can be detected by a magnetically sensitive head when they are brought in close proximity to the head.
During operation, the disc continually rotates, creating an air current that interacts with an air-bearing surface on the head, thereby causing the head to literally float at a small elevation (referred to as a “fly height”) over the surface of the disc. For example, a head may float on the order of 0.35 microinches above the surface of a disc, while the disc rotates.
The elevation at which a head floats above a disc is an important variable that influences the operation of the recording and detection circuitry of a disc drive. The recording circuitry must produce a recording signal (flux field) of sufficient magnetic intensity to saturate the media and write a recoverable signal when read, given the elevation of the head (the greater the span of space between the write head and the disc, the greater the magnetic field required for saturation during writing). Similarly, the detection circuitry must amplify the signals recovered from the disc by a gain factor sufficient to permit detection, given the elevation of the head (the greater the span of space between the read head and the disc, the greater the gain factor that is required for reading).
Occasionally, a particle of matter interrupts the normal air current that causes a head to float above the disc, thus causing the head to momentarily “fly” from its normal elevation to a greater one. For example, a head that normally floats at a height of 0.35 microinches above the surface of a disc may momentarily soar to 0.70 microinches before returning to its ordinary elevation of 0.35 microinches. If such an event occurs during a period of time when the disc drive is executing a write command, the flux field from the write head cannot saturate the media, which in turn results in the signal being recorded on the disk with a reduced intensity. This phenomenon is referred to as a “low-amplitude-write,” a “skip-write” event, or a “write irregularity” because while the head is soaring, it fails to record a satisfactorily strong signal upon the disc. The terms “low-amplitude write,”“skip write,” and “write irregularity” are used interchangeably herein. Other causes may instigate a write irregularity or a low-amplitude-write/skip-write event. For example, the disc drive, itself, may be jarred during the execution of a write command, causing the head to momentarily soar to an abnormal elevation. Broadly speaking, any event that causes a head to depart from its normal path during the course of a write operation is termed a “write irregularity.”
The occurrences of low-amplitude-write/skip-write events are inimical to the goal of efficient data recording and recovery for at least two reasons. First, if the intensity of the signal recorded upon the disc is less than expected by the detection circuitry, the detection circuitry may be initially unable to read the signal. As a consequence, the disc drive will invoke several re-read algorithms in an attempt to recover the data—a costly proposition with respect to time. Secondly, if the intensity of the recorded signal is sufficiently weak, the signal may be utterly irrecoverable, regardless of the re-reading measures taken by the disc drive.
Because of the detrimental effects of low-amplitude-write/skip-write events, there exists a need to detect their occurrence. A desirable characteristic of a low-amplitude-write/skip-write event detection scheme is the requirement of no additional hardware (thus resulting in no additional manufacturing expense). Additionally, a desirable solution would consume minimal printed circuit board space, and would require minimal additional hardware debugging.
SUMMARY OF THE INVENTION
Against this backdrop the present invention has been developed. A method for detecting and responding to low-amplitude-write/skip-write events involves characterizing the gain of a variable gain amplifier embedded in the read path of a disc drive during at least two instances in which the read head passes over a servo sector, prior to a write event. Next, the write event is executed. After the write event, the gain factor employed by the variable gain amplifier is acquired as the read head passes over the following servo sector. Finally, the acquired gain factor is compared to the characterization in order to detect a low-amplitude-write/skip-write event.
According to another embodiment of the invention, a disc drive is configured and arranged to detect a low-amplitude-write/skip-write event A disc drive so configured may include a disc for magnetically storing data. A read head is used to read data from the disc. A variable gain amplifier is operably coupled to the read head; the variable gain amplifier receives a signal from the read head and outputs a signal of approximately constant amplitude. The gain of the variable gain amplifier is controlled by a control signal generated by a gain controller. Finally, a microprocessor is operably coupled to the gain controller, such that the microprocessor has access to a digital representation of the control signal. The microprocessor is programmed to carry out the steps described above.
According to yet another aspect of the invention, a disc drive may be configured and arranged to detect a low-amplitude-write/skip-write event. A disc drive so configured may include a disc for magnetically storing data and a means for detecting a low-amplitude-write/skip-write event.


REFERENCES:
patent: 5721457 (1998-02-01), Sri-Jayantha et al.
patent: 5831781 (1998-11-01), Okamura
patent: 6178058 (2001-01-01), Pan et al.

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