Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1998-09-18
2001-07-31
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S067000
Reexamination Certificate
active
06268972
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to signals read from a data storage medium and, more particularly, to a system and method for measuring relative and absolute amplitudes of a signal read from a data storage medium provided in a disk drive system.
BACKGROUND OF THE INVENTION
A typical disk drive system includes a magnetic medium for storing data in magnetic form and a number of transducers used to write and read magnetic data respectively to and from the medium. A typical disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute (RPM).
Digital information is typically stored in the form of magnetic transitions on a series of concentric, spaced tracks formatted on the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a number of sectors, with each sector comprising a number of information fields, including fields for storing data, and sector identification and synchronization information, for example.
An actuator assembly typically includes a plurality of outwardly extending arms with one or more read/write head assemblies being mounted thereon by use of flexible suspensions. A typical read/write head assembly is understood to include a slider body, a read element, and a write element. The slider body lifts the read/write elements off the surface of the disk as the rate of spindle motor rotation increases, and causes the read/write elements to hover above the disk on an air bearing produced by high speed disk rotation. The distance between a read/write head and the disk surface, which is typically on the order of 40-100 nanometers (nm), is commonly referred to as head-to-disk clearance or spacing.
Writing data to a magnetic data storage disk generally involves passing a current through a write element of the read/write head assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the read/write head assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals, commonly referred to as readback signals, in the read element.
Conventional disk drive systems generally employ a closed-loop servo control system for positioning the read/write elements, or transducers, to specified storage locations on the data storage disk. During normal disk drive system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as the read element of the read/write head assembly, is typically employed to read information for the purpose of following a specified track (i.e., track following) and locating (i.e., seeking) specified track and data sector locations on the disk.
In accordance with one known servo technique, embedded servo pattern information is written to the disk along segments extending in a direction generally outward from the center of the disk. The embedded servo patterns are thus formed between the data storing sectors of each track. It is noted that a servo sector typically contains a pattern of data, often termed a servo burst pattern, used to maintain optimum alignment of the read/write transducers over the centerline of a track when transferring data to and from specified data sectors on the track. The servo information may also include sector and track identification codes which are used to identify the location of the transducer.
Within the disk drive system manufacturing industry, much attention is presently being focused on the performance and reliability of the transducers utilized as part of the read/write head. Changes in the operating characteristics of a read transducer, for example, may be indicative of read/write head degradation or impending failure of the head. Changes in the amplitude of a readback signal, for example, may indicate a possible problem with the read element.
Magnetoresistive (MR) elements, also referred to as MR stripes, are being used as read transducers in many disk drive systems. Although an MR read/write head assembly, typically incorporating an MR read element and a thin-film write element, would appear to provide a number of advantages over conventional thin-film heads and the like, it is known by those skilled in the art that MR transducers often exhibit undesirable behavior that is difficult to detect, suppress or quantify.
It has been found, for example, that the amplitude characteristics of a readback signal may provide insight as to the integrity and operating condition of a read transducer. A giant MR (GMR) transducer that is operating in an anomalous manner, by way of example, may produce readback signals of decreasing amplitude over time. The nature and complexity of most read channel designs, however, generally preclude in-situ determination of readback signal characteristics, such as determining readback signal amplitude over time.
There exists a keenly felt need in the disk drive system manufacturing community for an apparatus and method for determining the amplitude of a readback signal obtained from a data storage medium. There exists a particular need for such an apparatus and method that may be implemented in-situ a read channel, and without provision of components and test equipment external to the disk drive system. The present invention fulfills these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method of measuring an amplitude of a readback signal obtained from a data storage medium. Measuring the relative amplitude of a readback signal involves transmitting the readback signal to a gain modifying amplifier, such as a variable gain amplifier (VGA), preferably provided in the read channel. A voltage signal associated with a loop gain of the amplification circuitry is sensed.
The sensed voltage signal is compared with a number of control voltage signals, each of which is associated with a digital word value, until the sensed voltage signal is substantially equal to a selected control voltage signal. The digital word value associated with the last used control voltage signal represents the relative amplitude of the readback signal. The readback signal amplitude measurement may be performed when the read channel is in a read mode, idle mode, or servo mode of operation.
The absolute amplitude of a readback signal may be determined by taking a readback signal amplitude measurement after performing a gain characterization procedure. Determining the gain characteristics of the amplification circuit involves applying each of a number of reference voltage signals to the signal input of the gain modifying amplifier. Each of the reference voltage signals is associated with a corresponding pre-established gain value. For each of the reference voltage signals applied to the amplifier, a control voltage signal is selectively applied to the amplifier until the amplifier output voltage signal is substantially equal to a pre-established reference voltage signal. Following completion of the gain characterization procedure, any number of amplitude measurements may be taken to obtain the absolute amplitude of the readback signals.
An embodiment of a circuit for measuring an amplitude of a readback signal includes a gain modifying amplifier that receives the readback signal. A multiplexer includes a control voltage signal output coupled to the amplifier and a sense output. A sense voltage signal associated with a gain of the amplifier is developed at the sense output of the multiplexer. The circuit further includes a digital-to-analog converter (DAC) having an output and an input. A control circuit, coupled to the input of the DAC,
Philpott Rick Allen
Winn Gregory Scott
Faber Alan T.
Hollingsworth Mark A.
International Business Machines - Corporation
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