Preamplifier read recovery parade

Details Preamplifier read recovery parade Preamplifier read recovery parade

2000-07-19

2004-06-15

Hudspeth, David (Department: 2697)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

C360S051000, C360S053000

Reexamination Certificate

active

06751034

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 for enhancing a preamplifier read recovery when the mass storage device transitions from a non-read state to a read state.
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 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 pre-amplifier, 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 pre-amplifier may contain a read pre-amplifier and a write pre-amplifier that is also referred to as a write driver. The pre-amplifier may be implemented in a single integrated circuit or in separate integrated circuits such as a read pre-amplifier and a write pre-amplifier 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 pre-amplifier. 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 read. 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.
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 a peak detection type read channel or as a more advanced type of read channel utilizing discrete time signal processing. The peak detection type read channel involves level detecting the amplified analog read signal and determining if the waveform level is above a threshold level during a sampling window. The discrete time signal processing type read channel synchronously samples the amplified analog read signal using a data recovery clock. The sample is then processed through a series of mathematical manipulations using signal processing theory to generate the digital read signal. There are several types of discrete time signal processing read channels such as a partial response, maximum likelihood (PRML) channel; an extended PRML channel; an enhanced, extended PRML channel; a fixed delay tree search channel; and a decision feedback equalization channel.
As the disk platters
12
are rotating, the read/write heads
20
must align or remain on a particular track. This is accomplished by a servo operation through the use of a servo controller provided in a servo control loop. Referring to
FIG. 3
which represents a plan view of an exemplary platter
12
, in a servo operation a servo wedge
40
is read from a track
42
that generally includes track identification information and track misregistration information
44
. The track misregistration information may also be referred to as position error information. The position error information
44
may be provided as servo bursts and may be used during both read and write operations to ensure that the read/write heads are properly aligned on a track. As a result of receiving the position error information, the servo controller generates a corresponding control signal to position the read/write heads
20
via the voice coil motor. The track identification information
44
from the servo wedge
40
is also used during read and write operations so that a track
42
may be properly identified.
Hard disk drive designers strive to provide higher capacity drives that operate at a high signal-to-noise ratio and a low bit error rate. To achieve higher capacities, the density of the data stored on each side of each platter must be increased. This places significant burdens on the hard disk drive electronic circuitry. For example, as the density increases, the magnetic transitions that are used to store data on the platters must be physically located more closely together. This often results in intersymbol

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