U.S. patent application number 14/044009 was filed with the patent office on 2015-03-26 for system and method for monitoring preamble signal quality.
This patent application is currently assigned to LSI Corporation. The applicant listed for this patent is LSI Corporation. Invention is credited to Jason D. Byrne, Scott M. Dziak.
Application Number | 20150085392 14/044009 |
Document ID | / |
Family ID | 52575088 |
Filed Date | 2015-03-26 |
United States Patent
Application |
20150085392 |
Kind Code |
A1 |
Dziak; Scott M. ; et
al. |
March 26, 2015 |
System and Method for Monitoring Preamble Signal Quality
Abstract
The disclosure is directed to a system and method of determining
signal quality based upon at least one of: a comparison of energy
content of the signal to a threshold energy content, a comparison
of energy content of the fundamental harmonic of the signal to a
specified percentage of the energy content of the signal, and a
comparison of a difference between phase of the signal and a target
phase to a threshold phase difference.
Inventors: |
Dziak; Scott M.; (Fort
Collins, CO) ; Byrne; Jason D.; (Lyons, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LSI Corporation |
San Jose |
CA |
US |
|
|
Assignee: |
LSI Corporation
San Jose
CA
|
Family ID: |
52575088 |
Appl. No.: |
14/044009 |
Filed: |
October 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61880259 |
Sep 20, 2013 |
|
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Current U.S.
Class: |
360/31 |
Current CPC
Class: |
G11B 20/10462 20130101;
G11B 20/10305 20130101; G11B 27/36 20130101 |
Class at
Publication: |
360/31 |
International
Class: |
G11B 20/10 20060101
G11B020/10; G11B 5/09 20060101 G11B005/09; G11B 27/36 20060101
G11B027/36 |
Claims
1. A system for analyzing signal quality, the system comprising at
least one processor communicatively coupled to a storage medium,
the at least one processor being configured to: receive a signal
from the storage medium; determine an energy content of the signal;
determine an energy content of a fundamental harmonic of the
signal; determine a phase of the signal; and determine a quality of
the signal based upon at least one of: the energy content of the
signal, the energy content of the fundamental harmonic of the
signal, and the phase of the signal.
2. The system of claim 1, wherein the at least one processor is
further configured to: square digital samples derived from the
signal; and determine the energy content of the signal by summing
the squares of the digital samples.
3. The system of claim 2, wherein the digital samples comprise
normalized digital samples.
4. The system of claim 1, wherein the at least one processor is
further configured to: determine sine and cosine components of a
discrete Fourier transform of the signal; and determine the energy
content of the fundamental harmonic of the signal by summing a
square of the sine component and a square of the cosine
component.
5. The system of claim 1, wherein the at least one processor is
further configured to: determine the phase of the signal utilizing
an output of a bandpass filter.
6. The system of claim 5, wherein the bandpass filter comprises an
nT bandpass filter, where n is an integer defined by the
fundamental harmonic of the signal.
7. The system of claim 1, wherein the at least one processor is
further configured to: compare the energy content of the signal to
a threshold energy content; and determine the quality of the signal
based at least partially upon the comparison of the energy content
of the signal to the threshold energy content.
8. The system of claim 1, wherein the at least one processor is
further configured to: compare the energy content of the
fundamental harmonic of the signal to a specified percentage of the
energy content of the signal; and determine the quality of the
signal based at least partially upon the comparison of the energy
content of the fundamental harmonic of the signal to the specified
percentage of the energy content of the signal.
9. The system of claim 1, wherein the at least one processor is
further configured to: compare a difference between the phase of
the signal and a target phase to a threshold phase difference; and
determine the quality of the signal based at least partially upon
the comparison of the difference between the phase of the signal
and the target phase to the threshold phase difference.
10. The system of claim 9, wherein the at least one processor is
further configured to: determine the target phase during a zero
phase start operation.
11. The system of claim 9, wherein the threshold phase difference
is approximately a 1/2 bit difference.
12. A method of analyzing signal quality, comprising: receiving a
signal from the storage medium; determining an energy content of
the signal; determining an energy content of a fundamental harmonic
of the signal; determining a phase of the signal; and determining a
quality of the signal based upon at least one of: the energy
content of the signal, the energy content of the fundamental
harmonic of the signal, and the phase of the signal.
13. The method of claim 12, further comprising: squaring digital
samples derived from the signal; and determining the energy content
of the signal by summing the squares of the digital samples.
14. The method of claim 12, further comprising: determining sine
and cosine components of a discrete Fourier transform of the
signal; and determining the energy content of the fundamental
harmonic of the signal by summing a square of the sine component
and a square of the cosine component.
15. The method of claim 12, further comprising: comparing the
energy content of the signal to a threshold energy content; and
determining the quality of the signal based at least partially upon
the comparison of the energy content of the signal to the threshold
energy content.
16. The method of claim 12, further comprising: comparing the
energy content of the fundamental harmonic of the signal to a
specified percentage of the energy content of the signal; and
determining the quality of the signal based at least partially upon
the comparison of the energy content of the fundamental harmonic of
the signal to the specified percentage of the energy content of the
signal.
17. The method of claim 12, further comprising: comparing a
difference between the phase of the signal and a target phase to a
threshold phase difference; and determining the quality of the
signal based at least partially upon the comparison of the
difference between the phase of the signal and the target phase to
the threshold phase difference.
18. A method of analyzing signal quality, comprising: receiving a
signal from the storage medium; comparing an energy content of the
signal to a threshold energy content; comparing an energy content
of a fundamental harmonic of the signal to a specified percentage
of the energy content of the signal; comparing a difference between
a phase of the signal and a target phase to a threshold phase
difference; and determining a quality of the signal based upon at
least one of: the comparison of the energy content of the signal to
the threshold energy content, the comparison of the energy content
of the fundamental harmonic of the signal to the specified
percentage of the energy content of the signal, and the comparison
of the difference between the phase of the signal and the target
phase to the threshold phase difference.
19. The method of claim 18, further comprising: squaring digital
samples derived from the signal; and determining the energy content
of the signal by summing the squares of the digital samples.
20. The method of claim 18, further comprising: determining sine
and cosine components of a discrete Fourier transform of the
signal; and determining the energy content of the fundamental
harmonic of the signal by summing a square of the sine component
and a square of the cosine component.
Description
PRIORITY
[0001] The present application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Application Ser. No. 61/880,259,
entitled SYSTEM AND METHOD FOR MONITORING PREAMBLE SIGNAL QUALITY,
By Scott M. Dziak et al., filed Sep. 20, 2013, which is currently
co-pending, or is an application of which currently co-pending
application(s) are entitled to the benefit of the filing date. The
above-referenced provisional application is hereby incorporated by
reference in its entirety.
FIELD OF INVENTION
[0002] The disclosure relates to the field of signal monitoring and
flaw detection during read events.
BACKGROUND
[0003] In data storage system read channel operations, read and
servo events are typically prepended with periodic signals, often
referred to as "preamble" signals, with substantially uniform
transition spacing to align phase and gain prior to data recovery.
Gain or phase errors are sometimes encountered as result of defects
in storage media or environmental forces. During the signal
acquisition process, gain and phase errors can significantly
complicate the recovery process. It is thus advantageous to
determine signal quality prior to data recovery.
SUMMARY
[0004] The disclosure is directed to a system and method for
analyzing signal quality according to a plurality of factors
including, but not limited to, the energy content of the signal,
the energy content of the fundamental harmonic of the signal, and
the phase of the signal. According to various embodiments, a series
of comparisons are made utilizing the foregoing factors. The energy
content of the signal is compared to a threshold energy content.
The energy content of the fundamental harmonic of the signal is
compared to a specified percentage of the energy content of the
signal. The difference between a phase of the signal and a target
phase is compared to a threshold phase difference. Then the signal
quality is determined based upon at least one of: the comparison of
the energy content of the signal to the threshold energy content,
the comparison of the energy content of the fundamental harmonic of
the signal to the specified percentage of the energy content of the
signal, and the comparison of the difference between the phase of
the signal and the target phase to the threshold phase
difference.
[0005] It is to be understood that both the foregoing general
description and the following detailed description are not
necessarily restrictive of the disclosure. The accompanying
drawings, which are incorporated in and constitute a part of the
specification, illustrate embodiments of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The embodiments of the disclosure may be better understood
by those skilled in the art by reference to the accompanying
figures in which:
[0007] FIG. 1A is a block diagram illustrating a system for
analyzing signal quality and detecting media defects, in accordance
with an embodiment of the disclosure;
[0008] FIG. 1B is a block diagram illustrating the system for
analyzing signal quality and detecting media defects, wherein a
signal monitoring module and a media defect
detection/classification module of the system are software or
firmware modules stored by at least one carrier medium, in
accordance with an embodiment of the disclosure;
[0009] FIG. 2 illustrates various portions of a data record, in
accordance with an embodiment of the disclosure;
[0010] FIG. 3A is a flow diagram illustrating a method of analyzing
signal quality, in accordance with an embodiment of the disclosure;
and
[0011] FIG. 3B is a flow diagram illustrating the method of
analyzing signal quality, in accordance with an embodiment of the
disclosure.
DETAILED DESCRIPTION
[0012] Reference will now be made in detail to the embodiments
disclosed, which are illustrated in the accompanying drawings.
[0013] FIGS. 1A through 3B illustrate embodiments of a system and
method for analyzing quality of a periodic signal, such as a
preamble signal, which precedes a user data signal to align phase
and gain prior to data recovery. Detecting a low or poor quality
preamble signal is often indicative of fault condition, such as a
media defect or a negative environmental influence. Because the
user data signal is likely to be affected by the same fault
condition as the preamble, it is advantageous to report marginal
preamble signals or detected fault conditions. Accordingly,
correctable fault conditions can be repaired before retrying data
recovery, and system resources are not expended trying to read
unrecoverable data.
[0014] Some existing methods of preamble qualification are lacking
because they are not gain error insensitive (i.e. small signals
flagged as faults), not phase error insensitive (i.e. off-phase
signals flagged as faults), and fail to consider the entire
preamble signal region. In addition, current early MDD
architectures can result in undesirable loop coasting over certain
patterns, such as read-through gap or low density parity check
(LDPC) flawscan patterns. Early media defect detection (MDD) coasts
loops based on change in analog-to-digital conversion (ADC) signal
envelope. A pattern with 4-bit periodic intervals (e.g. 1100),
sometimes referred to as a "2T pattern", may exhibit significant
envelope loss even under ideal conditions, thus resulting in
undesirable loop coasting. While the embodiments discussed and
illustrated herein are often described according to the detection
or analysis of a 2T pattern having 4-bit periodic intervals,
reference to a 2T pattern (e.g. 2T signal, 2T energy, 2T bandpass
filter, 2T samples) is intended to cover any nT pattern, where n is
an integer value. In any of the embodiments described herein, the
2T pattern, hence the "2T" modifier, may be replaced by a 3T
pattern (e.g. 111000), a 4T pattern (e.g. 11110000), or any other
nT pattern.
[0015] FIGS. 1A and 1B illustrate embodiments of a system 100 for
analyzing signal quality and detecting media defects. The system
100 includes a signal monitoring module 104 and a MDD module 106
configured to process ADC samples read from a storage medium 102,
such as a hard-disk drive (HDD). To avoid undesirable loop coasting
the MDD module 106 is conditioned on detection of a signal having a
2T pattern, such as a preamble signal, by the signal monitoring
module 104. The signal monitoring module 104 is configured to
detect 2T patterns according to at least one metric, such as signal
energy or ratio of total signal energy to 2T signal energy.
[0016] In some embodiments, the signal monitoring module 104 is
configured to determine the signal energy by summing squares of the
ADC samples (i.e. E.sub.signal=.SIGMA.x.sup.2, where x are the ADC
samples for an analyzed window of the signal). The signal
monitoring module 104 compares the signal energy against a
specified threshold energy (i.e. E.sub.signal>E.sub.thresh),
where signals with energy content exceeding the threshold energy
content are 2T signal candidates. In some embodiments, the
monitoring module 104 is further configured to determine whether
the energy content of the fundamental harmonic exceeds a specified
percentage of the signal energy. Stated another way, the ratio of
2T energy content of the signal to total energy content exceeds a
specified threshold ratio (i.e. E.sub.2T/E.sub.signal>R). In
some embodiments, the 2T energy content of the signal is determined
by summing squares of 2T ADC samples isolated using a 2T bandpass
filter (i.e. E.sub.2T=.SIGMA.(X.sub.2T).sup.2, where
x.sub.2T=BPF.sub.2T(x)).
[0017] When the incoming samples are determined to belong to a 2T
pattern signal, the signal monitoring module 104 is configured to
enable the MDD module 106 to analyze the ADC samples for fault
conditions, such as media defects. Accordingly, media defect
detection is controlled to the preamble or other 2T signals. As
noted above, the system and method described herein are modifiable
to allow detection and monitoring of other periodic signals (e.g.
1T, 2T, 3T . . . , nT). In some embodiments, the MDD module 106 is
further configured to report defect information, such as detected
defects, defect type or classification, defect correctability, and
the like.
[0018] In addition to selectively enabling the MDD module 106, the
signal monitoring module 104 is further configured to determine
signal quality based upon energy content of the signal, energy
content at the fundamental harmonic of the signal, and signal
phase. The signal monitoring module 104 is configured to determine
energy content of an analyzed portion of the signal by summing the
squares of the ADC samples corresponding to the analyzed portion or
sample window, as explained above. In some embodiments, the signal
monitoring module 104 is configured to determine the mean squared
energy (MSE) by summing squares of normalized ADC samples.
[0019] The signal monitoring module 104 is further configured to
determine energy content at the fundamental harmonic (e.g. 2T
energy content) by summing squares of the 2T ADC samples. In some
embodiments, the 2T ADC samples are isolated by digitally filtering
the window of ADC samples. For example, sine and cosine components
derived from a discrete Fourier transform (DFT) of the signal over
the analyzed window can be isolated to extract 2T samples. The
signal monitoring module 104 is then enabled to determine the 2T
energy by summing squares of the sine and cosine DFT
components.
[0020] The signal monitoring module 104 is further configured to
determine the signal phase at the output of the 2T bandpass filter.
In some embodiments, the signal phase is compared against a
projected target phase to determine a signal phase difference or
slip, where the target phase is projected during zero phase start
(ZPS) operation. The quadrant of the 2T preamble signal should not
change from the value computed during ZPS. Substantial phase
difference can, therefore, indicate poor signal quality or fault
conditions.
[0021] With the foregoing metrics, the signal monitoring module 104
is configured to determine signal quality based upon comparisons
with user, program, or system specified thresholds. The signal
monitoring module 104 determines the signal is marginal (i.e. low
or poor quality) when one or more conditions arise from the
following: (1) energy content of the signal is less than a
specified threshold; (2) ratio of 2T energy to total energy content
of the signal is less than a specified ratio (i.e. 2T energy is
less than a specified percentage of signal energy); or (3)
difference between signal phase and target phase exceeds a
specified allowable phase difference (e.g. .about.1/2 bit). In some
embodiments, the signal monitoring module 104 is further configured
to report low signal quality or fault conditions by sending a
notification signal or triggering an indicator, such as by setting
designated flags or bits (e.g. preamble quality flag "pq_flg" and
preamble quality flag triggered "PQ_FLT" bit field).
[0022] In some embodiments, as shown in FIG. 1B, at least one of
the signal monitoring module 104 and the MDD module 106 is a
software module executable by at least one processor 108 from at
least one carrier medium 110 in the form of a programmed set of
instructions. According to said embodiments, the processor 108 is
communicatively coupled to the storage medium 102 and configured to
execute program instructions from the carrier medium 110 to perform
functions or operations described with regard to at least one of
the signal monitoring module 104 and the MDD module 106. In some
embodiments, one or more of the functions or operations is
alternatively performed by a dedicated set of electronic circuitry
or a dedicated controller. The components of system 100 are further
enabled to perform any operations or functions required to carry
out various steps described herein, such as the steps of method 300
described below. In some embodiments, for example, the processor
108 is configured to perform steps of method 300 in accordance with
program instructions executed from the carrier medium 110.
[0023] As shown in FIG. 2, a data record 200 typically includes a
preamble 202 preceding user data 204. Data records 200 are
accompanied by a preamble 202 to enable read synchronization during
data read-back, of timing recovery circuits in the recording
channel, in preparation for reception of the stored user data 204.
The boundary between the preamble 202 and user data 204 is
identified by a synchronization mark 206. In some embodiments, the
data record 200 further includes an error correction code (ECC)
field 208 to protect data integrity of the user data 204. As
discussed above, the preamble signal quality is important because
it is often indicative of whether user data 204 will be
successfully recovered or not.
[0024] FIGS. 3A and 3B illustrate a method 300 of assessing
preamble signal quality. In some embodiments, method 300 is
manifested by system 100. Further, method 300 is inclusive of any
steps required to carry out operations or functions described with
regard to embodiments of system 100. It is noted, however, that
method 300 is not restricted to any embodiment of system 100.
Rather, method 300 may be embodied in any system configured to
perform the following steps.
[0025] At step 302, shown in FIG. 3A, a preamble signal is read
from a storage medium, such as an HDD. ADC samples of the preamble
or an analyzed portion or window of the preamble are directed to a
processor for pattern detection and signal quality analysis. The
entire preamble signal may be analyzed by sequentially analyzing
adjacent sample windows (e.g. every 4T). At step 304, the energy
content (i.e. MSE) of the preamble signal for each sample window is
determined by summing squares of normalized ADC samples of the
respective window. At step 306, the energy content of the
fundamental harmonic (i.e. 2T frequency) of the preamble signal is
determined by summing squares of the DFT output cosine and sine
components over the same sample window used to determine MSE.
Accordingly, any delays and latencies occurring in the sample
window are accounted for in both measurements of signal energy and
2T energy. At step 308, the phase difference between signal phase
output by the 2T bandpass filter used to isolate 2T samples and the
target phase determined during ZPS operation is determined.
[0026] At step 310, the metrics determined in steps 302 through 308
are used to determine signal quality. FIG. 1B illustrates step 310
in further detail, where the signal quality determination is based
upon at least one of: (1) energy content of the preamble signal,
(2) energy content of the fundamental harmonic of the preamble
signal, or (3) drift or slip in signal phase of the preamble
signal.
[0027] At sub-step 312, signal energy determined over at least one
sample window is compared against a specified threshold energy. At
sub-step 314, the fundamental harmonic energy determined over at
least one sample window is compared against a specified percentage
of the signal energy determined for the same sample window. In
other words, the ratio of the fundamental harmonic energy to the
signal energy for at least one sample window is compared against a
specified threshold ratio. In some embodiments, the comparisons at
sub-steps 312 and 314 are repeated until substantially all portions
or sample windows of the preamble have been considered. At step
316, the phase difference between the signal phase of the 2T
bandpass filter output and the projected target phase determined
during ZPS are compared against a specified threshold phased
difference (e.g. 1/2 bit difference or 1T slip).
[0028] At sub-step 318, the preamble signal is determined to have
low or poor quality when any of thresholds from sub-steps 312
through 316 are violated. The preamble signal is determined to be
low or poor when: (1) the signal energy is less than the specified
threshold energy; (2) the ratio of fundamental harmonic energy to
signal energy is less than the specified threshold energy; or (3)
the difference between signal phase and target phase is less than
the specified threshold difference. In some embodiments, low
quality signals or fault conditions are reported by setting
designated flags or bits. Further, an error message or notification
can be communicated via user interface.
[0029] In some embodiments of the system 100 and method 300
described above, the value determination and comparisons may occur
in parallel or in a different sequence from that described above.
Some steps or operations may be omitted or superseded by specified
events. For example, analyzing fundamental harmonic energy and
phase difference may be unnecessary if the preamble signal is
already determined to be low or poor quality based upon failure to
meet the specified threshold signal energy.
[0030] In some embodiments, the three comparisons are performed
over a window of ADC samples succeeding the ADC samples used for
ZPS, where each check runs until the synchronization mark is
detected. An advantage of the system and method described herein is
that a single flag (e.g. pq_flg) can be used to indicate a failure
to satisfy any of the specified thresholds. In some embodiments,
this flag is sufficiently delayed with respect to a sync mark
detector to ensure that when the sync mark is found, the flag is
still based on the ADC samples of the 2T preamble. In some
embodiments, the flag status is captured in the PQ_FLT bit field
which indicates when the preamble quality flag is triggered.
[0031] It should be recognized that the various functions,
operations, or steps described throughout the present disclosure
may be carried out by any combination of hardware, software, or
firmware. In some embodiments, various steps or functions are
carried out by one or more of the following: electronic circuits,
logic gates, field programmable gate arrays, multiplexers, or
computing systems. A computing system may include, but is not
limited to, a personal computing system, mainframe computing
system, workstation, image computer, parallel processor, or any
other device known in the art. In general, the term "computing
system" is broadly defined to encompass any device having one or
more processors, which execute instructions from a carrier
medium.
[0032] Program instructions implementing methods, such as those
manifested by embodiments described herein, may be transmitted over
or stored on carrier medium. The carrier medium may be a
transmission medium, such as, but not limited to, a wire, cable, or
wireless transmission link. The carrier medium may also include a
storage medium such as, but not limited to, a read-only memory, a
random access memory, a magnetic or optical disk, or a magnetic
tape.
[0033] It is further contemplated that any embodiment of the
disclosure manifested above as a system or method may include at
least a portion of any other embodiment described herein. Those
having skill in the art will appreciate that there are various
embodiments by which systems and methods described herein can be
effected, and that the implementation will vary with the context in
which an embodiment of the disclosure is deployed.
[0034] Furthermore, it is to be understood that the invention is
defined by the appended claims. Although embodiments of this
invention have been illustrated, it is apparent that various
modifications may be made by those skilled in the art without
departing from the scope and spirit of the disclosure.
* * * * *