Dynamic magnetic information storage or retrieval – General processing of a digital signal – In specific code or form
Reexamination Certificate
2001-02-14
2003-12-02
Dorvil, Richemond (Department: 2697)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
In specific code or form
C360S046000, C360S048000, C360S077080, C714S794000, C714S795000
Reexamination Certificate
active
06657800
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention is related generally to electronic circuits, and more particularly to a Viterbi detector and technique for recovering a binary sequence from a read signal. In one embodiment, a servo channel includes a pruned PR4 Viterbi detector that recovers Gray coded servo data read from a data-storage disk. As compared to other servo channels, this PR4 targeted channel allows synchronous detection of the track ID information without oversampling, which allows a significant increase in the density of the servo data stored on the disk, and thus which allows a significant reduction in the disk area allocated to servo data. More specifically, constructing the servo channel to fit a target PR4 power spectrum (defined by a PR4 polynomial) allows the servo channel to perform a lower level of equalization on the servo signal. Lowering the level of equalization often lowers the level of equalization noise introduced into the servo signal, and thus causes less degradation of the servo signal's signal-to-noise ratio (SNR). Furthermore, the PR4 Viterbi detector is pruned to match a Gray code coding scheme. This pruning increases the minimum Euclidian distance of error events. Therefore, such a pruned PR4 Viterbi detector can often recover servo information from a servo signal having an SNR that is lower than other Viterbi detectors can tolerate. Consequently, because it can process a servo signal having a lower SNR and because it causes less degradation of the servo signal's SNR, such a servo channel allows a disk to have a higher servo-data storage density.
BACKGROUND OF THE INVENTION
FIG. 1
is a plan view of a conventional magnetic data-storage disk
10
. The disk
10
is partitioned into a number—here eight—of disk sectors
12
a
-
12
h
, and includes a number—typically in the tens or hundreds of thousands—of concentric data tracks
14
a
-
14
n
. File data is stored in respective data sectors (not shown) within each track
14
. Although the disk
10
is described as having eight disk sectors
12
a
-
2
h
, it may have more or fewer disk sectors
12
.
Referring to
FIG. 2
, respective servo wedges
16
are located within each track
14
at the beginning of each disk sector
12
. For clarity, only servo wedges
16
a
-
16
c
are shown, it being understood that the other servo wedges are similar. The servo wedges
16
contain respective servo data that allows a head position system (
FIG. 11
) to position a read-write head (
FIGS. 4 and 5
) over the track
14
to be read from or written to. The manufacturer of a disk drive (
FIG. 11
) containing the disk
10
typically writes the servo wedges
16
onto the disk
10
before shipping the disk drive to a customer; neither the disk drive nor the customer alters the servo wedges
16
thereafter.
FIG. 3
is a diagram of the servo wedge
16
a
of
FIG. 2
, it being understood that the other servo wedges
16
are similar. Write splices
18
a
and
18
b
respectively separate the servo wedge
16
a
from adjacent data sectors (not shown). A servo address mark (SAM)
20
indicates to the head position system that the read-write head is at the beginning of a servo wedge
16
, and thus at the beginning of a disk sector
12
. A servo preamble
22
synchronizes the sample clock of a servo channel (FIGS.
4
and
5
), and a servo synchronization mark (SSM)
24
identifies the beginning of a head-location identifier
26
. A data preamble and a data synchronization mark, which are sometimes similar to the servo preamble
22
and the SSM
24
, respectively, are discussed in U.S. patent application Ser. No. 09/410,274, filed Sep. 30, 1999, which is incorporated by reference. The location identifier
26
allows the head position system to coarsely determine and adjust the position of the read-write head with respect to the surface of the disk
10
. More specifically, the location identifier
26
includes a sector identifier
28
and a track identifier
30
, which respectively identify the disk sector
12
—here the sector
12
a
—and the data track
14
—here the track
14
a
—that contain the servo wedge
16
a
. Because the read-write head may read the location identifier
26
even if the head is not directly over the track
14
a
, the servo wedge
16
a
also includes bursts
32
a
-
32
n
, which allow the head position system to finely determine and adjust the position of the read-write head.
FIG. 4
is a block diagram of a conventional read-write head
34
and a read channel
36
, which recovers the location identifier
26
from the servo wedges
16
of
FIGS. 2 and 3
and provides the recovered identifier to the head position system. The channel
36
is typically used to recover both servo and read data, and thus functions as a servo channel while it is recovering servo data. Therefore, the channel
36
is hereinafter called servo channel
36
.
The servo channel
36
includes a preamplifier
38
, a continous lowpass filter (LPF)
37
, a gain stage
39
, an analog-to-digital converter (ADC)
40
, a finite-impulse-response (FIR) filter
42
, a Viterbi detector
44
, and a decoder
46
. The head
34
converts the bit sequence that composes the servo wedge
16
into a servo signal, and the preamplifier
38
amplifies the servo signal. The LPF
37
equalizes the servo signal, the gain stage
39
amplifies the signal so as to control the overall gain of the channel
36
, the ADC
40
samples and digitizes the amplified signal, and the FIR filter
42
boosts the power of the signal to better equalize consecutive digitized samples—here two samples at a time—to the target polynomial (e.g., PR4) of the channel
36
. The Viterbi detector
44
, which is designed for the target polynomial, recovers the servo bit sequence from the servo signal by processing the equalized samples—here two samples at a time. The decoder
46
decodes the recovered bit sequence and provides the decoded bit sequence to the head position system. Alternatively, if the servo bit sequence is not coded, then the decoder
46
may be omitted such that the Viterbi detector provides the recovered bit sequence directly to the head position system. Other circuit blocks, which are omitted from
FIG. 3
for clarity, detect the SAM
20
and the SSM
24
(
FIG. 3
) and control the timing and other characteristics of the channel
36
.
Referring to
FIGS. 1 and 4
, the storage capacity of the disk
10
is typically limited by its surface area and the minimum servo-signal SNR specified for the Viterbi detector
44
. Specifically, the diameter of the disk
10
, and thus its surface area, are typically constrained to industry-standard sizes. Therefore, the option of increasing the surface area of the disk
10
to increase its storage capacity is usually unavailable to disk-drive manufacturers. Furthermore, the SNR of the servo signal is a function of the servo-data-storage density on the surface of the disk
10
; the higher the storage density, the lower the SNR of the servo signal, and vice-versa. Typically, as the SNR of the servo signal decreases, the number of errors that the Viterbi detector
44
introduces into the recovered servo data increases. Unfortunately, an increase in the number of errors may degrade the effective servo-data-recovery speed of a disk drive to unacceptable levels.
One way to increase the data-storage capacity of the disk
10
is to decrease radial distance, i.e., the pitch, between adjacent data tracks
14
. This allows the manufacturer to fit more tracks
14
, and thus more data, onto the disk
10
.
Unfortunately, decreasing the pitch of the data tracks
14
often decreases the SNR of the servo signal by increasing the inter-symbol interference (ISI) and media noise during reading of the servo data. ISI, media noise, and the affect ISI and media noise have on the SNR of a data read signal such as the servo signal are discussed in U.S. patent application Ser. No. 09/409,923, entitled “PARITY-SENSITIVE VITERBI DETECTOR AND METHOD FOR RECOVERING INFORMATION FROM A READ SIGNAL”, filed Sep. 30,1999, which is incorporated by reference.
Furthermore,
Byrne Jason D.
Heydari Fereidoon
Ozdemir Hakan
Dorvil Richemond
Figueroa Natalia
Jorgenson Lisa K.
Santarelli Bryan A.
STMicroelectronics Inc.
LandOfFree
Viterbi detector and method for recovering a binary sequence... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Viterbi detector and method for recovering a binary sequence..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Viterbi detector and method for recovering a binary sequence... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3094684