U.S. patent application number 13/941472 was filed with the patent office on 2014-12-11 for systems and methods for media defect detection with pattern qualification.
The applicant listed for this patent is LSI Corporation. Invention is credited to Scott Dziak, Jefferson E. Singleton.
Application Number | 20140362462 13/941472 |
Document ID | / |
Family ID | 52005275 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140362462 |
Kind Code |
A1 |
Singleton; Jefferson E. ; et
al. |
December 11, 2014 |
Systems and Methods for Media Defect Detection With Pattern
Qualification
Abstract
An apparatus for detecting media flaws includes an envelope
based media defect detector operable to identify a media defect
based on an envelope of an input signal, a periodic pattern
detector operable to determine whether the input signal comprises a
data pattern, and a media flaw signal generation circuit operable
to indicate a media defect when the envelope based media defect
detector identifies the media defect and the periodic pattern
detector determines that the input signal does not comprise the
data pattern.
Inventors: |
Singleton; Jefferson E.;
(Westminster, CO) ; Dziak; Scott; (Ft. Collins,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LSI Corporation |
San Jose |
CA |
US |
|
|
Family ID: |
52005275 |
Appl. No.: |
13/941472 |
Filed: |
July 13, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61832136 |
Jun 6, 2013 |
|
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|
Current U.S.
Class: |
360/48 |
Current CPC
Class: |
G11B 20/182
20130101 |
Class at
Publication: |
360/48 |
International
Class: |
G11B 20/18 20060101
G11B020/18 |
Claims
1. An apparatus for detecting media flaws, comprising: an envelope
based media defect detector operable to identify a media defect
based on an envelope of an input signal; a periodic pattern
detector operable to determine whether the input signal comprises a
data pattern; and a media flaw signal generation circuit operable
to indicate a media defect when the envelope based media defect
detector identifies the media defect and the periodic pattern
detector determines that the input signal does not comprise the
data pattern, wherein the periodic pattern detector is operable to
indicate that the input signal comprises the data pattern when a
level of energy at a frequency of the data pattern in the input
signal is greater than a percentage of a total energy of the input
signal.
2. The apparatus of claim 1, further comprising at least one
control loop operable to control at least one processor that is
operable to process the input signal.
3. The apparatus of claim 2, wherein the media flaw signal
generation circuit comprises a coast signal generator operable to
assert a coast signal when the envelope based media defect detector
identifies the media defect and the periodic pattern detector
determines that the input signal does not comprise the data
pattern.
4. The apparatus of claim 3, wherein the at least one control loop
does not actively control the at least one processor when the coast
signal is asserted.
5. The apparatus of claim 2, wherein the at least one processor
comprises an analog to digital converter.
6. The apparatus of claim 1, wherein the data pattern comprises a
"1100" pattern.
7. The apparatus of claim 1, wherein the periodic pattern detector
is operable to determine whether the input signal comprises the
data pattern based on a total energy of the input signal compared
to a level of the energy of the data pattern in the input
signal.
8. (canceled)
9. The apparatus of claim 1, wherein the periodic pattern detector
is further operable to indicate that the input signal comprises the
data pattern only when the total energy of the input signal is
greater than a threshold value.
10. The apparatus of claim 1, the periodic pattern detector
comprising: a window circuit operable to select a plurality of
samples from the input signal within a sample window; a sum of the
squares calculator operable to calculate the sum of the squares of
the plurality of samples to yield a total energy value for the
plurality of samples; a filter operable to pass the plurality of
samples at a frequency of the data pattern to yield filtered
samples; a second sum of the squares calculator operable to
calculate the sum of the squares of the filtered samples to yield
an energy value at the frequency of the data pattern for the
plurality of samples; and a comparator operable to compare the
energy value at the frequency of the data pattern with the total
energy value.
11. The apparatus of claim 10, further comprising a scaling circuit
operable to scale the total energy value before compare the energy
value at the frequency of the data pattern with a scaled version of
the total energy value.
12. The apparatus of claim 10, further comprising a second
comparator operable to compare the total energy value with a
threshold value.
13. The apparatus of claim 1, wherein the apparatus is implemented
as an integrated circuit.
14. The apparatus of claim 1, wherein the apparatus is incorporated
in a magnetic storage device and is operable to detect flaws on the
storage medium in the magnetic storage device.
15. The apparatus of claim 14, wherein the apparatus is operable to
place a control loop in a coasting mode when the envelope based
media defect detector identifies the media defect and the periodic
pattern detector determines that the input signal does not comprise
the data pattern.
16. A method of detecting media flaws, comprising: processing input
data based on an error signal from a control loop to yield data
samples; performing envelope-based media defect detection to detect
whether the data samples were obtained from media with a defect;
determining whether the data samples comprise a periodic data
pattern that would cause an error in the envelope-based media
defect detection, wherein the envelope-based media defect detection
detects when an envelope of the data samples is attenuated, and
wherein sampling the periodic data pattern in the input data in an
analog to digital converter also causes an attenuation of the
envelope of the data samples; and causing the control loop to coast
when the envelope-based media defect detection detects that the
data samples were obtained from media with a defect and the data
samples do not comprise the periodic data pattern.
17. The method of claim 16, wherein determining the data samples
comprise a periodic data pattern comprises determining whether an
energy level of the data samples at a frequency of the periodic
data pattern exceeds a percentage of a total energy of the data
samples.
18. The method of claim 17, wherein determining the data samples
comprise a periodic data pattern further comprises determining that
the total energy of the data samples is greater than a
threshold.
19. (canceled)
20. A storage system comprising: a storage medium; a read/write
head assembly operable to read data on the storage medium and to
yield an analog signal; an analog to digital converter operable to
generate data samples representing the analog signal; a control
loop operable to generate an error signal to adjust the analog to
digital converter; an envelope based media defect detector operable
to identify a media defect based on an envelope of the data
samples; a periodic pattern detector operable to determine whether
the data samples comprise a periodic data pattern that would cause
an incorrect result in the envelope based media defect detector,
wherein the periodic pattern detector is operable to indicate that
the data samples comprise the data pattern when a level of energy
at a frequency of the data pattern in the data samples is greater
than a percentage of a total energy of the data samples; and a
coast signal generation circuit operable to cause the control loop
to coast when the envelope based media defect detector identifies
the media defect and the periodic pattern detector determines that
the data samples do not comprise the periodic data pattern.
21. The storage system of claim 20, wherein the envelope-based
media defect detector is operable to detect when an envelope of the
data samples is attenuated, and wherein sampling the periodic data
pattern in the data samples in the analog to digital converter also
causes an attenuation of the envelope of the data samples.
22. The storage system of claim 20, wherein the periodic pattern
detector is further operable to indicate that the data samples
comprise the data pattern only when the total energy of the data
samples is greater than a threshold value.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to (is a
non-provisional of) U.S. Pat. App. No. 61/832,136, entitled
"Systems and Methods for Media Defect Detection With Pattern
Qualification", and filed Jun. 6, 2013 by Singleton et al, the
entirety of which is incorporated herein by reference for all
purposes.
FIELD OF THE INVENTION
[0002] Various embodiments of the present invention provide systems
and methods for detecting media flaws, and more particularly to
systems and methods for envelope-based defect detection with
pattern qualification.
BACKGROUND
[0003] In a typical magnetic storage system, digital data is stored
in a series of concentric circular tracks along a storage medium.
Data is written to the medium by positioning a read/write head
assembly over the medium at a selected location as the storage
medium is rotated, and subsequently passing a modulated electric
current through the head assembly such that a corresponding
magnetic flux pattern is induced in the storage medium. To retrieve
the stored data, the head assembly is positioned anew over the
track as the storage medium is rotated. In this position, the
previously stored magnetic flux pattern induces a current in the
head assembly that can be converted to the previously recorded
digital data. Defective regions may exist in the storage medium.
Writing data to a defective region can result in the loss of such
data. To avoid this, various approaches have been developed for
identifying defective regions. However, some of these approaches
can yield false positives in some environments, incorrectly
identifying a region of the storage medium as defective.
BRIEF SUMMARY
[0004] Embodiments of the present invention provide systems and
methods for detecting defects on storage media with pattern
qualification using a digital data detector in a data processing
system.
[0005] In some embodiments, an apparatus for detecting media flaws
includes an envelope based media defect detector operable to
identify a media defect based on an envelope of an input signal, a
periodic pattern detector operable to determine whether the input
signal comprises a data pattern, and a media flaw signal generation
circuit operable to indicate a media defect when the envelope based
media defect detector identifies the media defect and the periodic
pattern detector determines that the input signal does not comprise
the data pattern.
[0006] This summary provides only a general outline of some
embodiments according to the present invention. Many other
embodiments of the present invention will become more fully
apparent from the following detailed description, the appended
claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] A further understanding of the various embodiments of the
present invention may be realized by reference to the figures which
are described in remaining portions of the specification. In the
figures, like reference numerals are used throughout several
figures to refer to similar components. In some instances, a
sub-label consisting of a lower case letter is associated with a
reference numeral to denote one of multiple similar components.
When reference is made to a reference numeral without specification
to an existing sub-label, it is intended to refer to all such
multiple similar components.
[0008] FIG. 1 depicts a storage system including a read channel
with envelope-based defect detection with pattern qualification in
accordance with some embodiments of the present invention;
[0009] FIG. 2 is a block diagram of a magnetic storage medium that
may be scanned for defects using envelope-based defect detection
with pattern qualification in accordance with some embodiments of
the present invention;
[0010] FIG. 3 depicts an exemplary data input signal derived from
both defective media regions and non-defective media regions;
[0011] FIG. 4 depicts digital data samples including some from a
periodic pattern that exhibits envelope loss;
[0012] FIG. 5 is a block diagram of a data processing system with
coasting control loops and envelope-based defect detection with
pattern qualification in accordance with some embodiments of the
present invention;
[0013] FIG. 6 depicts an envelope detector that may be used in an
envelope-based defect detector with pattern qualification in
accordance with some embodiments of the present invention;
[0014] FIGS. 7a-7b graphically depict an exemplary operation of the
envelope detector of FIG. 6 during data retrieval from both
non-defective media regions and defective media regions;
[0015] FIG. 8 is a block diagram of a periodic pattern detector
that may be used for pattern qualification in an envelope-based
defect detector with pattern qualification in accordance with some
embodiments of the present invention; and
[0016] FIG. 9 depicts a flow diagram of an operation for media
defect detection with pattern qualification in accordance with some
embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] As data is retrieved from a storage medium such as a
magnetic hard disk platter, it is processed by a variety of
processing circuits such as analog filters and amplifiers, analog
to digital converters, etc. Such processing circuits are controlled
by control loops based on feedback in the processing circuits, such
as, but not limited to, controlling the sampling phase of an analog
to digital converter. In some embodiments, a coasting control loop
applies media defect detection to detect media flaws and to place
the control loops in a coasting mode when processing data retrieved
from a defective media region, to prevent misadaptation of
processing circuits based on flawed data. Envelope-based defect
detection can be a low-latency alternative to more robust
error-based & reliability-based defect detection methods, used
in some embodiments to place control loops in coasting mode.
However, envelope-based detectors can be tricked by envelope loss
associated with narrow-spectrum signals, referred to herein as
2T-periodic patterns, such as but not limited to a repeating "1100"
data pattern.
[0018] A media defect detector with pattern qualification uses a
pattern detector to qualify the results from the envelope-based
defect detector to avoid undesired control loop coasting. Thus, the
media defect detector with pattern qualification places the control
loops in coasting mode when processing data from defective media
regions detected by envelope-based detection, but not when
processing 2T-periodic patterns which produce the same or similar
signal envelopes as data from a defective media region.
[0019] The media defect detector with pattern qualification
disclosed herein is applicable to processing data stored in or
transmitted over virtually any channel or storage of information on
virtually any media. Transmission applications include, but are not
limited to, optical fiber, radio frequency channels, wired or
wireless local area networks, digital subscriber line technologies,
wireless cellular, Ethernet over any medium such as copper or
optical fiber, cable channels such as cable television, and
Earth-satellite communications. Storage applications include, but
are not limited to, hard disk drives, compact disks, digital video
disks, magnetic tapes and memory devices such as DRAM, NAND flash,
NOR flash, other non-volatile memories and solid state drives. For
example, the data processing system may be, but is not limited to,
a read channel in a magnetic hard disk drive, detecting and
decoding data sectors from the drive.
[0020] Turning to FIG. 1, a storage system 100 is illustrated as an
example application of a media defect detector with pattern
qualification in accordance with some embodiments of the present
invention. The storage system 100 includes a read channel circuit
102 with a media defect detector with pattern qualification, which
includes control loops that are placed in coasting mode when
processing data from defective media regions detected by
envelope-based detection, but not when processing 2T-periodic
patterns. Storage system 100 may be, for example, a hard disk
drive. Storage system 100 also includes a preamplifier 104, an
interface controller 106, a hard disk controller 110, a motor
controller 112, a spindle motor 114, a disk platter 116, and a
read/write head assembly 120. Interface controller 106 controls
addressing and timing of data to/from disk platter 116. The data on
disk platter 116 consists of groups of magnetic signals that may be
detected by read/write head assembly 120 when the assembly is
properly positioned over disk platter 116. In one embodiment, disk
platter 116 includes magnetic signals recorded in accordance with
either a longitudinal or a perpendicular recording scheme.
[0021] In a typical read operation, read/write head assembly 120 is
accurately positioned by motor controller 112 over a desired data
track on disk platter 116. Motor controller 112 both positions
read/write head assembly 120 in relation to disk platter 116 and
drives spindle motor 114 by moving read/write head assembly 120 to
the proper data track on disk platter 116 under the direction of
hard disk controller 110. Spindle motor 114 spins disk platter 116
at a determined spin rate (RPMs). Once read/write head assembly 120
is positioned adjacent the proper data track, magnetic signals
representing data on disk platter 116 are sensed by read/write head
assembly 120 as disk platter 116 is rotated by spindle motor 114.
The sensed magnetic signals are provided as a continuous, minute
analog signal representative of the magnetic data on disk platter
116. This minute analog signal is transferred from read/write head
assembly 120 to read channel circuit 102 via preamplifier 104.
Preamplifier 104 is operable to amplify the minute analog signals
accessed from disk platter 116. In turn, read channel circuit 102
decodes and digitizes the received analog signal to recreate the
information originally written to disk platter 116. This data is
provided as read data 122 to a receiving circuit. As part of
processing the received information, read channel circuit 102
performs media defect detection with pattern qualification. In some
embodiments, this is performed to correctly place control loops in
coasting mode. Such a media defect detector with pattern
qualification can be implemented consistent with that disclosed
below in relation to FIGS. 5-8. In some cases, the media defect
detection with pattern qualification may be performed consistent
with the flow diagram disclosed below in relation to FIG. 9. A
write operation is substantially the opposite of the preceding read
operation with write data 124 being provided to read channel
circuit 102. This data is then encoded and written to disk platter
116.
[0022] Turning to FIG. 2, a magnetic storage medium 200 with servo
wedges (e.g., 212, 214) containing servo data is depicted in
accordance with one or more embodiments of the present invention.
Two exemplary data tracks 216, 220 are shown, indicated as dashed
lines. The tracks 216, 220 are segregated by servo data written
within wedges 212, 214.
[0023] The servo wedges 212, 214 may extend from an inner diameter
222 to an outer diameter 224, may have any suitable shape and
arrangement, and any number of servo wedges may be provided on
storage medium 200. It should be noted that while two tracks 216,
220 and two servo wedges 212, 214 are shown, hundreds of wedges and
tens of thousands of tracks may be included on a given storage
medium.
[0024] In operation, storage medium 200 is rotated in relation to a
sensor that senses information from the storage medium. In a read
operation, the sensor would sense servo data from wedge 112
followed by user data from a user data region between wedge 212 and
wedge 214 and then servo data from wedge 214. In a write operation,
the sensor would sense servo data from wedge 212 then write data to
the user data region between wedge 212 and wedge 214, with location
information in the user data region provided by a user sync mark
244 and a user preamble 246. The signal from the sensor is
processed by a data processing circuit including a media defect
detector with pattern qualification, which can be used to correctly
place control loops in coasting mode when reading user data and/or
when reading data from some servo data regions.
[0025] Turning to FIG. 3, a timing diagram 300 depicts an exemplary
data input signal 302 derived from both defective media regions 306
and non-defective media regions 304, 310. It should be noted that
the various data inputs and outputs are merely exemplary and that
circuit operation will vary depending upon the particular data
inputs and system implementation. Of note, data from the defective
portion may include a DC offset that may be eliminated through use
of a filter (not shown) as will be appreciated by one of ordinary
skill in the art based on the disclosure provided herein. Data from
the non-defective medium (portions 304, 310) exhibits a relatively
high amplitude when compared with that from the defective medium
(portion 306), that is, the envelope is attenuated in the defective
media region 306.
[0026] Turning to FIG. 4, a plot 400 of digital data samples from
an analog to digital converter (ADC) illustrates the change in
envelope that can result from a 2T-periodic pattern even under
ideal conditions. When processing typical random data at regions
402, 406, the data samples produced by the analog to digital
converter in some embodiments range in value from about 30 to -32.
However, when sampling a 2T-periodic pattern such as, but not
limited to, "1100" as at region 404, the envelope is attenuated and
the data samples range in value from about 22 to -22. The envelope
is attenuated the most when sampling the analog input signal at the
shoulders rather than at peaks and zero crossings. Sampling the
analog input signal at the shoulders is a valid sampling phase, and
the total signal energy remains the same, but the peak amplitude is
reduced by about 30% when sampling at the shoulders. Notably, the
envelope attenuation shown in FIG. 4 in the 2T-periodic pattern
region 404 is similar to or the same as the envelope attenuation
shown in the defective media region 306 of FIG. 3, and pattern
qualification is used to prevent the media defect detector from
placing the control loops in coasting mode when processing the
2T-periodic pattern.
[0027] Turning to FIG. 5, a block diagram illustrates a data
processing system 500 with coasting control loops 532 and
envelope-based media defect detection with pattern qualification in
accordance with some embodiments of the present invention. Data
processing system 500 includes an analog to digital converter 504
that receives an analog input 502. Analog input 502 may be, but is
not limited to, a minute analog electrical signal derived from a
read/write head assembly (not shown) that is disposed in relation
to a storage medium. Analog input 502 may have also been filtered
and amplified by an analog front end circuit (not shown). Based
upon the disclosure provided herein, one of ordinary skill in the
art will recognize a variety of sources from which analog input 502
may be derived. Analog to digital converter 504 converts analog
input 502 into a corresponding series of digital samples 506.
Analog to digital converter 504 may be any circuit known in the art
that is capable of producing digital samples corresponding to an
analog input signal. Based upon the disclosure provided herein, one
of ordinary skill in the art will recognize a variety of analog to
digital converter circuits that may be used in relation to
different embodiments of the present invention.
[0028] Digital samples 506 are provided to an envelope detector 514
which measures the amplitude of the envelope of the digital samples
506 and which yields an envelope amplitude signal 516. The envelope
amplitude signal 516 is an averaged signal in some embodiments,
giving the envelope amplitude within a time window. The envelope
amplitude signal 516 is compared with a threshold 520 in a
comparator 522, yielding a media defect error signal 524 when the
envelope of the digital samples 506 indicates the presence of a
media defect. Based upon the disclosure provided herein, one of
ordinary skill in the art will recognize a variety of
envelope-based media defect detection circuits that may be used in
relation to different embodiments of the present invention. In some
embodiments, the envelope detector 514 and comparator 522 are
combined in a media defect detection circuit.
[0029] The digital samples 506 are also provided to a 2T-periodic
pattern detector 510 which determines whether the digital samples
506 correspond with a 2T-periodic pattern such as, but not limited
to, "1100". The 2T-periodic pattern detector 510 yields a periodic
pattern signal 512 that is asserted when the digital samples 506
correspond with a 2T-periodic pattern. A 2T-periodic pattern may be
detected in any suitable manner, such as, but not limited to, based
on the signal energy of the digital samples 506. Based upon the
disclosure provided herein, one of ordinary skill in the art will
recognize a variety of 2T-periodic pattern detector circuits that
may be used in relation to different embodiments of the present
invention.
[0030] The media defect error signal 524 and the periodic pattern
signal 512 are combined in a combining circuit 526 such as an AND
gate with an inverting input, yielding a coast signal 530 that is
asserted when the envelope detector 514 detects a media defect and
the 2T-periodic pattern detector 510 confirms that the diminished
envelope of the digital samples 506 is not due to a 2T-periodic
pattern.
[0031] The coast signal 530 is provided to adaptive control loops
532, which generate an error signal 534 provided to the analog to
digital converter 504 and/or analog front end (not shown),
facilitating correction of phase and frequency sampling errors,
gain, etc. In some embodiments, control loops 532 include three
adaptive feedback loops. The first loop includes a digital phase
lock loop circuit and is operable to adaptively adjust the sampling
period used by analog to digital converter 504 to sample analog
input 502 (i.e., adjusting the phase and/or frequency of a clock
signal). The second loop includes an offset circuit (not shown)
that is used to adaptively adjust any DC offset from the received
analog input. The third loop includes a gain calculation circuit
(not shown) that is used to adaptively adjust the gain used in
pre-processing the received analog input signal. When analog input
502 includes a media defect region such as that depicted in FIG. 3,
the operation of the feedback loops is harmful to the system
operation. In particular, when analog input 502 is derived from the
defect region, a large number of errors in an ideal output compared
to digital samples 506 will be expected resulting in a dramatic
increase in the magnitude of an error signal 534 generated by
control loops 532. While this error result is not adaptively
correctable due to the defective media, each of the three feedback
loops will generate an output seeking to adaptively correct the
error. This potentially results in an unnecessary circuit
oscillation. Such circuit oscillation is prevented by the coast
signal 530 which places the control loops 532 in coasting mode,
either zeroing out the error signal 534 or causing the analog to
digital converter 504 and any other elements such as, but not
limited to, an analog front end (not shown) to ignore incoming
error signals (e.g., 534) from the control loops 532 while in
coasting mode.
[0032] Turning to FIG. 6, an envelope-based media defect detector
circuit 600 is shown in accordance with one or more embodiments of
the present invention. This and other embodiments of an
envelope-based media defect detector which may be used in place of
envelope detector 514 are disclosed in U.S. Pat. No. 8,139,457,
issued Mar. 20, 2012 for "Systems And Methods For Low Latency Media
Defect Detection", which is incorporated herein for all purposes.
Media defect detector circuit 600 includes a moving average filter
circuit 610. A signal received from a defective region of a medium
often exhibits a significant DC shift. Maintaining a moving average
of the received digital samples 605, and subtracting the resulting
average from the current digital samples operates to combat any DC
shift occurring in relation to a defective medium region. Moving
average filter circuit 610 includes the ability to average digital
samples 605 across a large enough period to assure that the output
of moving average filter circuit 610 adequately represents any DC
offset in the received signal. In some embodiments of the present
invention, samples for five or more bit periods are averaged at a
time, with the oldest value of digital samples 605 being replaced
by the most recent value of digital samples 605.
[0033] The resulting moving average from moving average filter
circuit 610 is subtracted from the current value of digital samples
605 using a summation element. This subtraction yields a
substantially DC free sample value at the output of summation
element 620. An output 622 from summation element 620 is provided
in parallel to four separate envelope detector circuits: a fast
positive envelope detector circuit 630, a fast negative envelope
detector circuit 635, a slow positive envelope detector circuit
640, and a slow negative envelope detector circuit 645. Fast
positive envelope detector circuit 630 applies the following
algorithm to output 622:
e.sup.+.sub.fast(k+1)=max{x.sub.k,e.sup.+.sub.fast(k)-.DELTA..sup.+.sub.-
fast},
[0034] where x.sub.k indicates a prior value of output 622,
e.sup.+.sub.fast(k) indicates a prior value of an output 632 of
fast positive envelope detector 630, e.sup.+.sub.fast(k+1)
indicates the next value of output 632, and .DELTA..sup.+.sub.fast
indicates a fast decay rate. Fast negative envelope detector
circuit 635 applies the following algorithm to output 622:
e.sup.-.sub.fast(k+1)=min{x.sub.k,e.sup.-.sub.fast(k)+.DELTA..sub.fast},
[0035] where e.sup.-.sub.fast(k) indicates a prior value of an
output 634 of fast negative envelope detector 635,
e.sup.-.sub.fast(k+1) indicates the next value of output 634, and
.DELTA..sup.-.sub.fast indicates the same fast decay rate of
.DELTA..sup.+.sub.fast. Slow positive envelope detector circuit 640
applies the following algorithm to output 622:
e.sup.+.sub.slow(k+1)=max{x.sub.k,e.sup.-.sub.slow(k)-.DELTA..sup.+.sub.-
slow},
[0036] where e.sup.+.sub.slow(k) indicates a prior value of an
output 636 of slow positive envelope detector 640, e.sup.+.sub.slow
(k+1) indicates the next value of output 636, and
.DELTA..sup.+.sub.slow indicates a slow decay rate that is less
than fast decay rate, .DELTA..sup.+.sub.fast. Slow negative
envelope detector circuit 645 applies the following algorithm to
output 622:
e.sup.-.sub.slow(k+1)=min{x.sub.k,e.sup.-.sub.slow(k)+.DELTA..sup.-.sub.-
slow},
[0037] where e.sup.-.sub.slow (k) indicates a prior value of an
output 638 of slow negative envelope detector 645,
e.sup.-.sub.slow(k+1) indicates the next value of output 638, and
.DELTA..sup.-.sub.slow indicates the same slow decay rate
.DELTA..sup.+.sub.slow. It should be noted, however, that the decay
rates for the negative and positive envelope calculations do not
need to be the same.
[0038] Outputs 632, 634 are each provided to a fast envelope
calculation circuit 650, and outputs 636, 638 are each provided to
a slow envelope calculation circuit 655. Fast envelope calculation
circuit 650 provides an output 652 described by the following
equation:
e.sub.fast(k+1)=e.sup.+.sub.fast(k+1)-e.sup.-.sub.fast(k+1).
[0039] Similarly, slow envelope calculation circuit 655 provides an
output 654 described by the following equation:
e.sub.slow(k+1)=e.sup.+.sub.slow(k+.sup.1)-e.sup.-.sub.slow(k+1).
[0040] Outputs 652, 654 are each provided to a media defect
determination circuit 660 that combines the values of the outputs
for comparison against a threshold to determine whether a media
defect is detected. Media defect determination circuit 660 provides
an output 662 defined by the following equation:
Defect Ratio = e fast e slow . ##EQU00001##
[0041] Where the defect ratio is greater than a defined threshold,
output 662 is asserted. Output 662 is provided to a media defect
signal generation circuit 670 that is operable to control the
immediacy of an assertion of a defect output 675 and the duration
of the assertion. In some embodiments of the present invention,
media defect signal generation circuit 670 includes a
re-settable/re-loadable counter that counts the number of periods
after the media defect region is cleared. In such cases, defect
output 675 may remain asserted until the counter reaches a defined
count value.
[0042] FIG. 7a graphically depicts an exemplary operation of media
defect detector 600 during data retrieval from a non-defective
media region. A timing diagram 701 shows output 622 as a cyclical
signal with a reasonably consistent amplitude as would be expected
when data is being retrieved from a non-defective region of a
medium. As shown, the value of e+.sub.fast (output 632) changes by
an amount (.DELTA..sup.+.sub.fast) that is slower than the rate at
which output 622 decreases. Output 632 assumes the value of output
622 or of the value degraded by .DELTA..sup.+.sub.fast depending
upon whichever is greater in accordance with the following
equation:
e.sup.+.sub.fast(k+1)=max{x.sub.k,e.sup.+.sub.fast(k)-.DELTA..sup.+.sub.-
fast}.
[0043] The value of e.sup.-.sub.fast (output 634) changes by an
amount (.DELTA..sup.-.sub.fast) that is slower than the rate at
which output 622 increases. Output 634 assumes the value of output
622 or of the value degraded by .DELTA..sup.-.sub.fast depending
upon whichever is less in accordance with the following
equation:
e.sup.-.sub.fast(k+1)=min{x.sub.k,e.sup.-.sub.fast(k)+.DELTA..sup.-.sub.-
fast}.
[0044] The value of e.sup.+.sub.slow (output 636) changes by an
amount (.DELTA..sup.+.sub.slow) that is slower than the rate at
which output 622 decreases. Output 636 assumes the value of output
622 or of the value degraded by .DELTA..sup.+.sub.slow depending
upon whichever is greater in accordance with the following
equation:
e.sup.+.sub.slow(k+1)=max{x.sub.k,e.sup.+.sub.slow(k)-.DELTA..sup.+.sub.-
slow}.
[0045] The value of e.sup.-.sub.slow (output 638) changes by an
amount (.DELTA..sup.-.sub.slow) that is slower than the rate at
which output 622 increases. Output 638 assumes the value of output
622 or of the value degraded by .DELTA..sup.-.sub.slow depending
upon whichever is less in accordance with the following
equation:
e.sup.-.sub.slow(k+1)=min{x.sub.k,e.sup.-.sub.slow(k)+.DELTA..sup.-.sub.-
slow}.
[0046] A timing diagram 702 depicts the values of e.sub.fast
(output 652 shown as solid lines) and e.sub.slow (output 654 shown
as dashed lines) at different calculation periods (t, t+1, t+2, . .
. ). As discussed above, outputs 652, 654 respectively correspond
to the following equations:
e.sub.fast(k+1)=e.sup.+.sub.fast(k+1)-e.sup.-.sub.fast(k+1),
and
e.sub.slow(k+1)=e.sup.+.sub.slow(k+1)-e.sup.-.sub.slow(k+1).
[0047] Of note, the values of outputs 652, 654 are reasonably
constant over the calculation periods, and at all times exceed a
defect threshold value 703. Further, the ratio of output 652 to
output 654 remains reasonably constant over the depicted period. As
the ratio at all times exceeds a defect threshold value 703, a
defect is not indicated, and thus defect output 675 remains
deasserted. This situation is expected where the received data is
not derived from a defective region of the media.
[0048] FIG. 7b graphically depicts an exemplary operation of media
defect detector 600 during data retrieval during a transition from
a non-defective media region to a defective media region. A timing
diagram 751 shows output 622 as a cyclical signal with a degrading
amplitude representing the transition to a defective region of the
media from which the data is derived. As shown, the value of
e.sup.+.sub.fast (output 632) changes by an amount
.DELTA..sup.+.sub.fast) that is slower than the rate at which
output 622 decreases. Output 632 assumes the value of output 622 or
of the value degraded by .DELTA..sup.+.sub.fast depending upon
whichever is greater. The value of e.sup.-.sub.fast (output 634)
changes by an amount (.DELTA..sup.-.sub.fast) that is slower than
the rate at which output 622 increases. Output 634 assumes the
value of output 622 or of the value degraded by
.DELTA..sup.-.sub.fast depending upon whichever is greater. The
value of e.sup.+.sub.slow (output 636) changes by an amount
(.DELTA..sup.+.sub.slow) that is slower than the rate at which
output 622 decreases. Output 636 assumes the value of output 622 or
of the value degraded by .DELTA..sup.+.sub.slow depending upon
whichever is greater. The value of e.sup.-.sub.slow (output 638)
changes by an amount (.DELTA..sup.-.sub.slow) that is slower than
the rate at which output 622 increases. Output 638 assumes the
value of output 622 or of the value degraded by
.DELTA..sup.-.sub.slow depending upon whichever is greater.
[0049] A timing diagram 752 depicts the values of e.sub.fast
(output 652 shown as solid lines) and e.sub.slow (output 654 shown
as dashed lines) at different calculation periods (t, t+1, t+2, . .
. ). Of note, the values of outputs 652, 654 continue to decrease
as the transition from the non-defective media region to the
defective media region occurs. Further, the ratio of output 652 to
output 654 declines dramatically between calculation period t+2 and
calculation period t+3. Once this ratio falls below a defect
threshold value 753, a defect is indicated. At this point, defect
output 675 is asserted. It should be noted that in some embodiments
of the present invention the threshold must be exceeded for a
certain number of consecutive calculation periods before defect
output 675 is asserted. Such an approach operates to filter out any
spurious noise that is not necessarily indicative of a defective
medium. Based on the disclosure provided herein, one of ordinary
skill in the art will recognize a variety of filters and/or
filtering techniques that may be used in relation to different
embodiments of the present invention to assure a more accurate
designation of the media defect output.
[0050] It should be noted that transition from a defective media
region to a non-defective media region is substantially the reverse
of that shown in FIG. 7b. In such a case, once the ratio of output
654 to output 652 exceeds defect threshold 753, defect output 675
is again deasserted. In some cases, deassertion of defect output
may be delayed for a defined period or for a certain number of
consecutive calculation periods where the ratio exceeds defect
threshold 753. Such an approach operates to filter out any spurious
noise that is not necessarily indicative of the end of a defect
region. Based on the disclosure provided herein, one of ordinary
skill in the art will recognize a variety of filters and/or
filtering techniques that may be used in relation to different
embodiments of the present invention to assure a more accurate
designation of the media defect output.
[0051] Turning to FIG. 8, a periodic pattern detector 800 is
disclosed that may be used in place of 2T-periodic pattern detector
510 for pattern qualification in an envelope-based media defect
detector in accordance with some embodiments of the present
invention. In some embodiments, the 2T-periodic pattern detection
is based on spectral energy, calculating the total energy of the
signal at the 2T frequency and comparing that against the total
energy of the signal. For a 2T-periodic pattern, the energy at the
2T frequency will be a substantial percentage of the total energy
of the signal. Because there will typically be some noise in the
signal, even data samples containing only a repeating "1100"
pattern will contain some energy outside of the 2T frequency, and a
threshold is used to establish the percentage of energy at the 2T
frequency which the signal should contain to indicate that the data
contains or consists of a 2T-periodic pattern. The level of the
threshold may be established based on expected channel conditions
and the desired balance between active adaptation of the control
loops in the possible presence of errors and coasting in the
possible presence of 2T-periodic patterns simulating a nonexistent
media defect.
[0052] Data samples 802 are provided to a window selection circuit
804 which yield data samples 806 within a window of time. The
length of within which the window selection circuit 804 selects
samples may be adapted to any desired duration, such as, but not
limited to, 12 or 16 bits. The selected data samples 806 are
provided to an energy calculation circuit 810, which calculates the
sum of the square of the values of the selected data samples 806
(.SIGMA.x.sup.2, where x are the values of the data samples 806),
yielding the total energy in the signal 812. The total energy in
the signal 812 is compared with a threshold 814 in a comparator
816, yielding a minimum signal energy signal 820 that is asserted
when the total energy in the signal 812 is greater than the
threshold 814. This prevents the periodic pattern detector 800 from
finding a 2T-periodic pattern when the overall signal energy is too
low or nonexistent.
[0053] The selected data samples 806 are also provided to a
bandpass filter 822 that operates at the 2T frequency, yielding
filtered samples 824 at the 2T frequency. The bandpass filter 822
effectively correlates the selected data samples 806 against a 2T
pattern to determine the amount of 2T energy in the selected data
samples 806. In some embodiments, the bandpass filter 822 performs
a Discrete Fourier Transform. The filtered samples 824 are provided
to an energy calculation circuit 826 which performs the same
function as the energy calculation circuit 810, yielding the total
amount of 2T energy in the signal 830. The energy calculation
circuit 826 calculates the sum of the square of the values of the
filtered samples 824 (.SIGMA.x.sub.2T.sup.2, where x.sub.2T are the
values of the filtered samples 824).
[0054] The total amount of 2T energy in the signal 830 is compared
with a scaled version 836 of the total energy in the signal 812 in
comparator 840, yielding an intermediate 2T pattern indicator 842
that is asserted when a 2T-periodic pattern is detected. The total
energy in the signal 812 is scaled by a scaling factor .alpha. 832
in multiplier 834, yielding scaled total energy in the signal 836.
The scaling factor .alpha. 832 establishes the threshold that
determines how much of the total energy in the signal must be at
the 2T frequency to identify a 2T-periodic pattern. The bandpass
filter 822, energy calculation circuits 810, scaling factor .alpha.
832 and comparator 840 implement the following equation, where a
2T-periodic pattern is identified when the comparison holds
true:
.SIGMA.x.sub.2T.sup.2>.alpha..SIGMA.x.sup.2
[0055] where .SIGMA.x.sub.2T.sup.2 is the total amount of 2T energy
in the signal 830, and a .SIGMA.x.sup.2 is the scaled total energy
in the signal 836.
[0056] The intermediate 2T pattern indicator 842 is combined with
the minimum signal energy signal 820 in AND gate 844, yielding a 2T
pattern indicator 842 that is asserted when a 2T-periodic pattern
is identified in the selected data samples 806 and when the total
energy in the signal 812 is greater than threshold 814.
[0057] Turning to FIG. 9, a flow diagram 900 depicts a method for
control loop coasting using envelope-based media defect detection
with pattern qualification in accordance with some embodiments of
the present invention. The method of FIG. 9, or variations thereof,
may be performed in data processing systems such as those disclosed
in FIGS. 5-8. Following flow diagram 900, input data is processed
based on error signals from control loops, yielding digital data.
(Block 902) In various embodiments, the error signals correct
parameters such as, but not limited to, sampling phase and
frequency, gain, DC offset, etc. The error signals are disabled
when operating in a coasting mode, so that data processing does not
attempt to adapt to error signals generated from data retrieved
from media defect regions. Envelope-based media defect detection is
performed to detect whether the digital data was obtained from a
defective media region. (Block 904) In parallel with the media
defect detection, it is determined whether the digital data
contains a 2T-periodic pattern. (Block 906) A determination is made
as to whether the digital data was obtained from a defective media
region, and does not contain a 2T pattern. (Block 910) If so, the
system is placed in coasting mode. (Block 912) If the
envelope-based media defect detection did not detect a defect or if
the 2T-periodic pattern detection determined that the digital data
was a 2T-periodic pattern, coasting mode is turned off. (Block
914)
[0058] It should be noted that the various blocks discussed in the
above application may be implemented in integrated circuits along
with other functionality. Such integrated circuits may include all
of the functions of a given block, system or circuit, or a portion
of the functions of the block, system or circuit. Further, elements
of the blocks, systems or circuits may be implemented across
multiple integrated circuits. Such integrated circuits may be any
type of integrated circuit known in the art including, but are not
limited to, a monolithic integrated circuit, a flip chip integrated
circuit, a multichip module integrated circuit, and/or a mixed
signal integrated circuit. It should also be noted that various
functions of the blocks, systems or circuits discussed herein may
be implemented in either software or firmware. In some such cases,
the entire system, block or circuit may be implemented using its
software or firmware equivalent. In other cases, the one part of a
given system, block or circuit may be implemented in software or
firmware, while other parts are implemented in hardware.
[0059] In conclusion, embodiments of the present invention provide
novel systems, devices, methods and arrangements for media defect
detection with pattern qualification. While detailed descriptions
of one or more embodiments of the invention have been given above,
various alternatives, modifications, and equivalents will be
apparent to those skilled in the art without varying from the
spirit of the invention. Therefore, the above description should
not be taken as limiting the scope of embodiments of the invention
which are encompassed by the appended claims.
* * * * *