Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-01-10
2002-12-31
Faber, Alan T (Department: 2818)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S053000, C360S045000, C360S046000, C360S051000, C360S025000
Reexamination Certificate
active
06501607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to the field of mass storage devices, and more particularly to a system and method of providing error margin information for threshold errors and peak shift errors, respectively, in read channel circuits.
BACKGROUND OF THE INVENTION
Hard disk drives such as the exemplary drive
10
illustrated in
FIG. 1
include a stack of magnetically coated platters
12
that are used for storing information. The magnetically coated platters
12
are mounted together in a stacked position through a spindle
14
which may be referred to as a platter stack. The platter stack is typically rotated by a motor that is referred to as a spindle motor or a servo motor (not shown). A space is provided between each platter to allow an arm
18
having a read/write head or slider
20
associated therewith to be positioned on each side of each platter
12
so that information may be stored and retrieved. Information is stored on each side of each platter
12
and is generally organized into sectors, tracks, zones, and cylinders.
Each of the read/write heads or sliders
20
are mounted to one end of the dedicated suspension arm
18
so that each of the read/write heads may be positioned as desired. The opposite end of each of the suspension arms
18
are coupled together at a voice coil motor
16
(VCM) to form one unit or assembly (often referred to as a head stack assembly) that is positionable by the voice coil motor. Each of the suspension arms
18
are provided in a fixed position relative to each other. The voice coil motor
16
positions all the suspension arms
18
so that the active read/write head
20
is properly positioned for reading or writing information. The read/write heads
20
may move from at least an inner diameter to an outer diameter of each platter
12
where data is stored. This distance may be referred to as a data stroke.
Hard disk drives also include a variety of electronic circuitry for processing data and for controlling its overall operation. This electronic circuitry may include a preamplifier, a read channel, a write channel, a servo controller, a motor control circuit, a read-only memory (ROM), a random-access memory (RAM), and a variety of disk control circuitry (not shown) to control the operation of the hard disk drive and to properly interface the hard disk drive to a system bus. The preamplifier may contain a read preamplifier and a write preamplifier that is also referred to as a write driver. The preamplifier may be implemented in a single integrated circuit or in separate integrated circuits such as a read preamplifier and a write preamplifier or write driver. The disk control circuitry generally includes a separate microprocessor for executing instructions stored in memory to control the operation and interface of the hard disk drive.
Hard disk drives perform write, read, and servo operations when storing and retrieving data. Generally, a write operation includes receiving data from a system bus and storing the data in the RAM. The microprocessor schedules a series of events to allow the information to be transferred from the RAM to the platters
12
through the write channel. Before the information is transferred, the read/write heads
20
are positioned on the appropriate track and the appropriate sector of the track is located. The data from the RAM is then communicated to the write channel as a digital write signal. The write channel processes the digital write signal and generates an analog write signal. In doing this, the write channel may encode the data so that the data can be more reliably retrieved later. The digital write signal may then be provided to an appropriate read/write head
20
after first being conditioned by the preamplifier. Writing data to the recording medium or platter
12
is typically performed by applying a current to a coil of the head
20
so that a magnetic field is induced in an adjacent magnetically permeable core, with the core transmitting a magnetic signal across a spacing of the disk to magnetize a small pattern or digital bit of the media associated with the disk.
Circuitry associated with a read operation is illustrated in
FIG. 2
, and designated at reference numeral
30
. In a read operation, the appropriate sector to be read is located and data that has been previously written to the platters
12
is detected. The appropriate read/write head
20
(illustrated as a magneto-resistive load
20
a
in
FIG. 2
) senses the changes in the magnetic flux and generates a corresponding analog read signal. The analog read signal is provided back to the electronic circuitry where a preamplifier circuit
32
amplifies the analog read signal. The amplified analog read signal is then provided to a read channel circuit
34
where the read channel conditions the signal and detects “zeros” and “ones” from the signal to generate a digital read signal. The read channel may condition the signal by amplifying the signal to an appropriate level using, for example, automatic gain control (AGC) techniques. The read channel may then filter the signal to eliminate unwanted high frequency noise, equalize the channel, perform the data recovery from the signal, and format the digital read signal. The digital read signal is then transferred from the read channel and is stored in the RAM (not shown). The microprocessor may then communicate to the host that data is ready to be transferred.
Each bit of information stored on a disk or platter
12
corresponds to a magnetic transition, and a read head generates electrical signals corresponding to the magnetic transition. A “1” may be used to designated the presence of a magnetic transition, and a “0” to designate the lack of a magnetic transition. The read head generates either a positive or a negative pulse for each magnetic transition depending on the polarity of the transition. Data are read from the disk by processing the pulse transition responses.
The read channel circuit
34
may be implemented using any of a variety of known or available read channels. For example, the read channel
34
may be implemented as an analog peak detection type read channel or as a digital peak detection type of read channel. One conventional analog peak detection method is to differentiate the signal and detect zero crossings of the signal derivative. The signal derivative is zero for local minimums and local maximums. The amplitude of the signal where the derivative is zero is then compared to a threshold level to identify peak samples. Such peak detection methods typically have a sample comparison window two to three samples wide.
A conventional digital peak detection method includes converting the analog samples to digital samples, and then comparing a sample to the previous sample and the subsequent sample. If the sample is greater than the previous and subsequent samples, then the sample is compared with a threshold level. If the sample exceeds the threshold then the sample is identified as a pulse or peak. Similar to the conventional analog peak detection system, such digital methods typically have a peak comparison window that is three samples wide.
Two primary sources of reading error in digital peak detection read channels are threshold errors and peak shift errors. In one type of threshold error, an error occurs when the peak of the pulse falls below the threshold and is not detected. This source of threshold error is often called a “missing bit” error. Another type of threshold error occurs when a peak is falsely identified. This type of threshold error is often referred to an “extra bit” error. A peak shift error is often called a “bit shift error” because the peak (associated with a data bit) is shifted undesirably into the next timing window.
There is a need in the art to provide read channel circuits having improved reliability and therefore there is a need for systems and methods for characterizing such circuit reliability with respect to threshold errors and peak shift errors, respectively.
SUMMARY OF THE INVENTION
The present invention rel
Keirn Zachary A.
Woods Daniel D.
Brady W. James
Faber Alan T
Swayze, Jr. W. Daniel
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