Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Aspects of the disclosure provide a method for detecting land pre-pits.
The method includes extracting a land pre-pit data stream from a signal
responsive to land pre-pits on an optical medium based on a land pre-pit
threshold, detecting a bit stream pattern from the land pre-pit data
stream, comparing one or more bits in the land pre-pit data stream at
locations relative to the bit stream pattern with pre-known bit
information, and adjusting the land pre-pit threshold based on the
comparison.

Claims:

1. A method for detecting land pre-pits, comprising: extracting a land
pre-pit data stream from a signal responsive to land pre-pits on an
optical medium based on a land pre-pit threshold; detecting a bit stream
pattern from the land pre-pit data stream; comparing one or more bits in
the land pre-pit data stream at locations relative to the bit stream
pattern with pre-known bit information; and adjusting the land pre-pit
threshold based on the comparison.

2. The method according to claim 1, further comprising: determining an
initial land pre-pit threshold during a calibration process.

3. The method according to claim 1, wherein adjusting the land pre-pit
threshold based on the comparison further comprises: generating an error
signal based on the comparison; and adjusting the land pre-pit threshold
based on the error signal.

4. The method according to claim 3, wherein adjusting the land pre-pit
threshold based on the error signal further comprises: adjusting the land
pre-pit threshold based on an average of the error signal.

5. The method according to claim 4, further comprising: averaging the
error signal based on a programmable gain.

6. The method according to claim 5, wherein averaging the error signal
based on the programmable gain, further comprising: multiplying the error
signal with the programmable gain; and accumulating the multiplied error
signal.

7. The method according to claim 1, wherein adjusting the land pre-pit
threshold based on the comparison further comprising: adjusting a digital
representation corresponding to the land pre-pit threshold; and
converting the digital representation to an analog voltage of the land
pre-pit threshold.

8. The method according to claim 1, wherein the optical medium is at
least one of DVD-R, DVD-RAM and DVD-RW.

9. An apparatus, comprising: an extractor configured to extract a land
pre-pit data stream from a signal responsive to land pre-pits on an
optical medium based on a land pre-pit threshold; and a controller
configured to detect a bit stream pattern from the land pre-pit data
stream, compare one or more bits in the land pre-pit data stream at
locations relative to the bit stream pattern with pre-known bit
information, adjust the land pre-pit threshold based on the comparison.

10. The apparatus according to claim 9, wherein the controller is further
configured to determine an initial land pre-pit threshold during a
calibration process.

11. The apparatus according to claim 9, wherein the controller further
comprises: a memory device configured to store the pre-known bit
information.

12. The apparatus according to claim 9, wherein the controller is further
configured to generate an error signal based on the comparison, and
adjust the land pre-pit threshold based on the error signal.

13. The apparatus according to claim 12, wherein the controller is
configured to adjust the land pre-pit threshold based on an average of
the error signal.

14. The apparatus according to claim 12, wherein the controller further
comprises: a multiplier configured to multiply the error signal with a
programmable gain; and an accumulator configured to accumulate the
multiplied error signal.

15. The apparatus according to claim 9, wherein the controller further
comprises: a memory device configured to store a digital representation
corresponding to the land pre-pit threshold; and a digital to analog
converter (DAC) configured to convert the digital representation to an
analog voltage of the land pre-pit threshold.

16. An optical drive, comprising: an optical pickup unit configured to
generate a signal in response to a track on an optical medium; an
extractor configured to extract a land pre-pit data stream from the
signal based on a land pre-pit threshold; and a controller configured to
detect a bit stream pattern from the land pre-pit data stream, comparing
one or more bits in the land pre-pit data stream at locations relative to
the bit stream pattern, with pre-known bit information, adjusting the
land pre-pit threshold based on the comparison.

17. The apparatus according to claim 16, wherein the controller further
comprises: a memory device configured to store the pre-known bit
information.

18. The apparatus according to claim 16, wherein the controller is
further configured to generate an error signal based on the comparison,
and adjust the land pre-pit threshold based on the error signal.

19. The apparatus according to claim 18, wherein the controller further
comprises: a multiplier configured to multiply the error signal with a
programmable gain; and an accumulator configured to accumulate the
multiplied error signal, and the controller is configured to adjust the
land pre-pit threshold based on the accumulated error signal.

20. The apparatus according to claim 16, wherein the controller further
comprises: a memory device configured to store a digital representation
corresponding to the land pre-pit threshold; and a digital to analog
converter (DAC) configured to convert the digital representation to an
analog voltage of the land pre-pit threshold.

Description:

INCORPORATION BY REFERENCE

[0001] This application is a continuation of U.S. patent application Ser.
No. 12/249,248, "Method and Apparatus for Detecting Land Pre-Pits" filed
Oct. 10, 2008, which claims the benefit of U.S. Provisional Application
No. 60/980,000, "Land Pre-Pit Detector with Adaptive Threshold" filed on
Oct. 15, 2007. The entire disclosures of the above-identified
applications are incorporated herein by reference in their entirety.

BACKGROUND

[0002] Land pre-pits can be used to embed information, such as address
information, disk information, for memory media, such as DVD-R, DVD-RAM,
DVD-RW, and the like. For example, a memory medium may include a spiral
groove with a spiral land. The spiral groove and the spiral land can be
wobbled to incorporate timing information. Additionally, a memory medium,
such as DVD-R, DVD-RAM and DVD-RW, may utilize land pre-pits, which can
be in the form of little pieces of mirrors deposited at specific
locations of the spiral land of the memory medium, to embed address
information and disk information. The land pre-pits can be detected by a
medium recording device to obtain the address information and the disk
information of the memory medium. The address information and the disk
information can assist the medium recording device to record user data at
the specific address in the spiral groove of the memory medium.

SUMMARY

[0003] However, land pre-pits can be incorrectly detected by a medium
recording device due to reasons, such as variations in manufacturing,
noises and interferences of adjacent grooves, and the like. Aspects of
the disclosure can provide a method for detecting land pre-pits. The
method can adaptively adjust a threshold for detecting the land pre-pits
in order to improve the correctness of detecting.

[0004] The method for detecting land pre-pits can include extracting a
land pre-pit data stream from a reading signal based on a land pre-pit
threshold, the reading signal corresponding to land pre-pits of an
optical medium, comparing the land pre-pit data stream with format
information of the optical medium to obtain an error signal, and
adjusting the land pre-pit threshold based on the error signal.

[0005] Further, the method can include determining an initial land pre-pit
threshold during a calibration process.

[0006] To compare the land pre-pit data stream with the format
information, the method can further include detecting a SYNC frame from
the land pre-pit data stream, and comparing the land pre-pit data stream
and the format information with reference to the SYNC frame.

[0007] To extract the land pre-pit data stream, the method can further
include comparing the reading signal with the land pre-pit threshold to
determine a state, such as a binary state, of the reading signal.

[0008] Additionally, to adjust the land-pit threshold based on the error
signal, the method can further include adjusting the land pre-pit
threshold based on an average of the error signal. Further, the method
can include averaging the error signal based on a programmable gain.

[0009] To average the error signal based on the programmable gain, the
method can further include multiplying the error signal with the
programmable gain, and accumulating the multiplied error signal.

[0010] To adjust the land pre-pit threshold, the method can further
include adjusting a digital representation corresponding to the land
pre-pit threshold based on the error signal, and converting the digital
representation to an analog voltage of the land pre-pit threshold.

[0011] According to an aspect of the disclosure, the optical medium is at
least one of DVD-R, DVD-RAM and DVD-RW.

[0012] Aspects of the disclosure can also provide an apparatus for
detecting land pre-pits. The apparatus can include an extractor
configured to extract a land pre-pit data stream from a reading signal
based on a land pre-pit threshold, the reading signal corresponding to
land pre-pits of an optical medium, and a controller configured to
compare the land pre-pit data stream with format information of the
optical medium to obtain an error signal, and adjust the land pre-pit
threshold based on the error signal.

[0013] Furthermore, aspects of the disclosure can provide an optical
drive. The optical drive can include an optical pickup unit configured to
generate a reading signal corresponding to land pre-pits of an optical
medium, and record data on the optical disc based on information
extracted from the reading signal, an extractor configured to extract a
land pre-pit data stream from the reading signal based on a land pre-pit
threshold, and a controller configured to compare the land pre-pit data
stream with format information of the optical medium to obtain an error
signal, and adjust the land pre-pit threshold based on the error signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Various exemplary embodiments of this disclosure will be described
in detail with reference to the following figures, wherein like numerals
reference like elements, and wherein:

[0015] FIGS. 1A and 1B show a block diagram of an exemplary medium device
and an exemplary memory medium;

[0016] FIGS. 2A and 2B show a block diagram of an exemplary land pre-pit
read channel coupled to an exemplary optical pick-up unit (OPU) and an
exemplary pick-up signal;

[0017]FIG. 3 shows a block diagram of an exemplary land pre-pit loop
controller;

[0022] FIGS. 1A and 1B show a block diagram of an exemplary medium device
with an exemplary memory medium. The medium device 100 can include a
processor 110, an optical drive 115, a RAM unit 130, and a non-volatile
memory 140. These elements can be coupled together as shown in FIG. 1A.

[0023] The optical drive 115 can further include an optical pickup unit
(OPU) 120. The OPU 120 can receive signals corresponding to various
information, such as timing information, address information, disc
information, user data, and the like, in a memory medium, such as an
optical disc 190. For example, the OPU 120 may direct a laser beam to a
location of the optical disc 190. The laser beam can be reflected from
the location of the optical disc 190. The reflected laser beam may have
light properties that can correspond to information embedded at the
location of the optical disc 190. The light properties can be detected by
a light detector of the OPU 120. Further, the light detector of the OPU
120 may convert the light properties to electrical signals for other
components of the optical drive 115 to extract the various information,
for example.

[0024] In addition, the OPU 120 can be configured to record user data on
the optical disc 190 according to the extracted information, such as
timing information, address information, disc information, and the like.
For example, the OPU 120 may direct a recording laser beam to a recording
location of the optical disc 190. The recording laser beam may have a
laser power determined according to the extracted disc information, and
may have a turn-on time determined according to the extracted timing
information. In addition, the recording location may be determined based
on the extracted address information, for example.

[0025] According to the disclosure, the optical drive 115 may include a
land pre-pit (LPP) read channel 125 that can be configured to detect land
pre-pits from an electrical signal converted by the light detector in
order to extract the embedded information. The land pre-pit read channel
125 can include an adaptive land pre-pit threshold. The adaptive land
pre-pit threshold can be used to determine a status, such as a binary
status, of the electrical signal to detect the land pre-pits.

[0026] As shown in FIG. 1A, the optical disc 190 can generally include a
spiral recording track, for example in the form of a spiral groove
adjacent to a spiral land. On the spiral recording track, user data can
be stored on a recording layer by forming either data pits or data marks.
The data pits or data marks can be preferred to have a substantially
constant linear length to improve the data storage capability of the
optical disc 190. To assist maintaining constant length of data marks or
data pits, timing and address information can be encoded in the spiral
groove and the spiral land during disc manufacturing. In an example, the
timing information can be encoded by wobbling the spiral groove and the
spiral land. Further, address information and disk information can be
encoded via land pre-pits (LPP) for certain kinds of memory media, such
as DVD-R, DVD-RAM and DVD-RW, and the like.

[0027]FIG. 1B shows an enlarged portion of an exemplary optical disc 190.
The optical disc 190 can include alternatively arranged groove fields and
land fields. The land fields can include land pre-pits. The land pre-pits
can be produced by disc manufacturer. For example, during disc
manufacturing, the disc manufacturer can deposit little pieces of
mirrors, such as aluminum, at specific locations of the land fields to
form the land pre-pits.

[0028] The mirrors may have a higher reflectivity than areas without the
land pre-pits. The higher reflectivity can be detected by the OPU 120.
For example, the OPU 120 may direct a laser beam onto a location of the
optical disc 190. The laser beam can be reflected by the location. The
reflected laser beam may have light properties that can correspond to a
reflectivity of the location. When the laser beam is reflected by a
location with a deposited mirror, the reflected laser beam may have a
higher light intensity, for example. Further, the light properties may be
detected by a detector of the OPU 120. The detector may generate
electrical signals corresponding to the light properties. For example,
the detector can generate a push-pull signal from the detected light. The
push-pull signal may have an amplitude spike corresponding to a location
with a mirror.

[0029] Further, the push-pull signal can be compared to a land pre-pit
threshold to determine a status, such as a binary status, at a location.
For example, when an amplitude of the electrical signal corresponding to
a location is larger than the land pre-pit threshold, an amplitude spike
can be detected. Therefore, the location can be determined to have a
mirror. Thus, the location can be determined storing binary one, for
example.

[0030] Generally, a land pre-pit threshold can be determined by a
calibration process, and may be used globally to detect the land
pre-pits. However, the globally used land pre-pit threshold can result in
land pre-pit reading errors due to various reasons, such as manufacturing
variations, gain variations and baseline variations of the electrical
signal, noises and interferences of adjacent groove fields, and the like.
Further, the land pre-pit reading errors may result in poor recording
qualities.

[0031] According to the disclosure, the medium device 100 can include an
adaptive land pre-pit threshold. The adaptive land pre-pit threshold can
be adjusted based on format information of the land pre-pits. The
adaptive land pre-pit can be used to reduce land pre-pit reading errors
to improve recording quality.

[0032] The processor 110 of the medium device 100 can execute system and
application codes. The non-volatile memory 140 can hold information even
when power is off. Therefore, the non-volatile memory 140 can be used to
store system and application codes, such as firmware. The RAM unit 130 is
readable and writable. Generally, the RAM unit 130 can have a fast access
speed. It can be preferred that data and codes are stored in the RAM unit
130 during operation, such that the processor 110 can access the RAM unit
130 for the codes and data instead of the non-volatile memory 140.

[0033] It should be understood that the memory device 100 may include more
than one processor 110. Further, the non-volatile memory 140 may include
various non-volatile memory devices, such as battery backup RAM, read
only memory (ROM), programmable ROM (PROM), flash PROM, electrical
erasable PROM (EEPROM) magnetic storage, optical storage, and the like.
Some non-volatile memory 140 can be updated, such as various types of
PROM. The RAM unit 130 may also include various RAM devices, such as
DRAM, SRAM and the like.

[0034] For the ease and clarity of description, the embodiments are
presented with a bus type architecture, however, it should be understood
that any other architectures can also be used to couple components inside
memory device 100.

[0035] Additionally, the memory device 100 may include a user input module
160. The user input module 160 may enable the user to control operations
of the memory device 100. The user input module 160 may include various
user input devices, such as keyboard, mouse, touch screen, and the like.
In addition, the user input module 160 may include interfaces that can
enable external user input devices.

[0036] In an embodiment, the memory device 100 may include an audio/video
module 150. The audio/video module 150 may include various audio and
video devices, such as microphone, display screen, and the like. In
addition, the audio/video module 150 may include interfaces that can
enable external audio and video devices. The audio/video module 150 can
be utilized to play audio data/video data that can be stored in the
optical disc 190.

[0037] In another embodiment, the memory device 100 may include a network
module 170. Furthermore, the memory device 100 may include a wireless
communication module 180. The network module 170 and the wireless
communication module 180 may enable the memory device 100 to communicate
the data stored in the optical disc 190 to other devices.

[0038] FIGS. 2A and 2B show a block diagram of an exemplary land pre-pit
read channel receiving a push-pull signal and an exemplary waveform of a
push-pull signal. FIG. 2A shows the block diagram of the exemplary land
pre-pit read channel 225 coupled with an exemplary optical pickup unit
220. Further, the land pre-pit read channel 225 can include a land
pre-pit extractor 230 and a land pre-pit loop controller 240. Theses
elements can be coupled as shown in FIG. 2A.

[0039] The optical pickup unit 220 may include a detector, such as a
quadrant photo detector 210 shown in FIG. 2A. The quadrant photo detector
210 may detect a light beam 215, and generate various signals, including
a push-pull signal (PPS), corresponding to the light beam 215. The
push-pull signal can correspond to wobbled groove and land fields on a
memory medium. Further, the push-pull signal can correspond to land
pre-pits in the land fields for certain memory medium, such as DVD-R,
DVD-RAM and DVD-RW.

[0040] The land pre-pit extractor 230 can receive the push-pull signal.
Further, the land pre-pit extractor 230 can compare the push-pull signal
with an adaptive land pre-pit threshold to determine a land pre-pit data
stream. In an embodiment, the land pre-pit extractor 230 may include an
analog comparator (not shown). The analog comparator may compare the
push-pull signal with the adaptive land pre-pit threshold to obtain a
pulse signal. Further, the pulse signal can be converted to the land
pre-pit data stream based on a clock signal, such as a wobble clock
signal that can also be extracted from the push-pull signal.

[0041] The land pre-pit loop controller 240 can receive the extracted land
pre-pit data stream and adjust the adaptive land pre-pit threshold based
on the extracted land pre-pit data stream. Further, the adjusted adaptive
land pre-pit threshold can be used by the land pre-pit extractor 230 to
extract a subsequent land pre-pit data stream from a following portion of
the push-pull signal. In such a way, the land pre-pit loop controller 240
can couple the land pre-pit extractor 230 to form a land pre-pit feedback
loop.

[0042] According to the disclosure, land pre-pits are formed by disc
manufacture according to a pre-known format, such as an industry
standard. Therefore, the land pre-pit loop controller 240 may include the
pre-known format information about the land pre-pits. The land pre-pit
loop controller 240 may extract detected format from the land pre-pit
data stream. Further, the land pre-pit loop controller 240 can compare
the detected format with the pre-known format information, and adjust the
adaptive land pre-pit threshold accordingly.

[0043]FIG. 2B shows an exemplary waveform of a push-pull signal. The
push-pull signal 250 can have a sinusoid shape as a result of wobbled
groove and land fields. Further, the push-pull signal 250 may include
spikes 260 as a result of land pre-pits at specific locations of land
fields. Due to various variations, noises and interferences, amplitudes
of the spikes 260 may vary. Further, the amplitude variations of the
spike 260 may result in detecting errors in the land pre-pit data stream.

[0044]FIG. 3 shows a block diagram of an exemplary land pre-pit loop
controller according to disclosure. The land pre-pit loop controller 340
may include a comparator 310, a threshold adjuster 320 and a land pre-pit
format retainer 330 holding pre-known land pre-pit format information.
These elements can be coupled together as shown in FIG. 3.

[0045] The comparator 310 can receive a land pre-pit data stream and
compare the land pre-pit data stream with the pre-known land pre-pit
format information. Then, the comparator 310 can output an error signal
corresponding to difference between the land pre-pit data stream and the
pre-known land pre-pit format information. In an embodiment, the
comparator 310 can be implemented as a software code module, which can be
executed by a processor (not shown) to compare the land pre-pit data
stream with the pre-known land pre-pit format information. In another
embodiment, the comparator 310 can be implemented as a hardware module,
such as application specific integrated circuit (ASIC), to perform the
above functions.

[0046] The threshold adjuster 320 can receive the error signal and adjust
the adaptive land pre-pit threshold based on the error signal. In an
embodiment, the threshold adjuster 320 may adjust the adaptive land
pre-pit threshold based on an average of the error signal. Additionally,
the threshold adjuster 320 may include a programmable parameter, such as
a programmable gain, which can be used to change properties of the land
pre-pit feedback loop.

[0047] The land pre-pit format retainer 330 can include pre-known land
pre-pit format information. In an embodiment, the land pre-pit format
retainer 330 can be implemented in software codes that can be stored in a
memory medium, such as the random access memory (RAM) 130, the
non-volatile memory 140, and the like, to hold the pre-known land pre-pit
format information. In another embodiment, the land pre-pit format
retainer 330 can include memory devices, such as registers, to hold the
pre-known land pre-pit format information.

[0048] FIGS. 4A and 4B show tables of exemplary land pre-pit format
information. FIG. 4A shows an exemplary pre-pit physical block format
information according to a standard. The pre-pit physical block 400 can
be encoded in the land fields, and can correspond to 16 sectors of data
blocks, which are generally referred as ECC blocks, in the groove fields.

[0049] The pre-pit physical block 400 can include 16 sets pre-pits No.
0-No. 15. Each set of pre-pits can include 26 SYNC frames, which are
assigned even (E) SYNC frames or odd (O) SYNC frames according to their
sequences. Each SYNC frame may include 8 wobble periods, and each wobble
period can be encoded a binary wobble bit depending on whether the wobble
period includes a pre-pit. For example, a wobble period can be encoded
with a binary wobble bit one if the wobble period includes a pre-pit,
otherwise the wobble period can be encoded with a binary wobble bit zero.

[0050] The wobble bits can be used to encode address information and disc
information according to certain format. In the example of FIG. 4A, every
two SYNC frames can use the wobble bits to encode a code. The code can be
encoded at either the even SYNC frame or at the odd SYNC frame. Further,
the code can be a SYNC code or a binary bit code according to certain
coding format.

[0051]FIG. 4B shows an exemplary coding format according to a standard.
The coding format can use three wobble binary bits b2-b0 to
encode the SYNC code and the binary bit code in every two SYNC frames. In
the example of FIG. 4B, when the SYNC code is in even SYNC frame, the
three wobble binary bits b2-b0 are 111; when the SYNC code is
in odd SYNC frame, the three wobble binary bits b2-b0 are 110;
when binary one is encoded, the three wobble binary bits b2-b0
are 101; and when binary zero is encoded, the three wobble binary bits
b2-bo are 100.

[0052] Accordingly, wobble bits information can be pre-known at certain
locations. For example, two SYNC frames that encode a SYNC code can
either be 1110000000000000 or 0000000011000000. In an embodiment, a
comparator can generate an error signal based on the two SYNC frames that
encode a SYNC code. The comparator may store detected wobble bits of two
SYNC frames corresponding to a SYNC code in registers, which can be
referred as rawLPP[0:15]. Further, the comparator can generate the error
signal by comparing the detected wobble bits with the pre-known format
information. For example, the comparator may assign -1 to the error
signal when 0 is detected at a location that should be 1 according to the
pre-known format, and may assign 1 to error signal when 1 is detected at
a location that should be 0 according to the pre-known format.

[0053] In an embodiment, a comparator can be configured to generate an
error signal according to following pseudo codes:

[0054] According to the disclosure, the error signal can be used by the
threshold adjuster 320 to adjust the adaptive pre-pit threshold to
improve the pre-pit detecting correctness. In an embodiment, the
threshold adjuster 320 can adjust the adaptive pre-pit threshold based on
an average of the error signal.

[0055]FIG. 5 shows a block diagram of an exemplary integrator circuit
that can be included in a threshold adjuster to generate a control signal
based on an error signal. The integrator 500 can include a multiplier
510, an accumulator 520, and a register 530. These elements can be
coupled as shown in FIG. 5.

[0056] The multiplier 510 can receive an error signal, and multiply the
error signal with a programmable gain. The programmable gain can be used
to adjust properties of the land pre-pit feedback loop.

[0057] The accumulator 520 and the register 530 can be coupled together to
integrate the multiplied error signal to generate an integrated error
signal. Further, the integrated error signal can be used to adjust the
adaptive land pre-pit threshold.

[0058] In an embodiment, a most significant bit of the integrated error
signal can be used to adjust a digital representation of the adaptive
land pre-pit threshold. Further, the digital representation of the
adaptive land pre-pit can be converted to an analog voltage signal by a
digital to analog converter (DAC).

[0059] FIGS. 6A-6C show waveforms of an exemplary land pre-pit detector.
FIG. 6A shows waveforms of an exemplary push-pull signal read from an
optical medium. The waveforms can include two portions, a wobble baseline
portion 610 and a spike portion 620. The spike portion can correspond to
amplitude spikes that area result from land pre-pits. However, as can be
seen, the wobble based line portion 610 and the spike portion 620 may not
distinguishable by a single global threshold.

[0060]FIG. 6B and FIG. 6c show waveforms of exemplary adaptive land
pre-pit threshold according to two feedback loop settings, respectively.
In an embodiment, the two feedback loop settings can correspond to
different values of a programmable gain of a feedback loop. For example,
FIG. 6B can correspond to a feedback loop setting having a larger
programmable gain, and FIG. 6c can correspond to a feedback loop setting
having a smaller programmable gain. Accordingly, the adaptive land
pre-pit threshold may have different properties. For example, the
adaptive land pre-pit threshold waveform in FIG. 6B can have a smaller
bandwidth, while the adaptive land pre-pit threshold waveform in FIG. 6c
can have a larger bandwidth.

[0061] FIG. 7 shows a flowchart outlining an exemplary process for
detecting land pre-pit. The process starts at step S710 and proceeds to
step S720. In step S720, a land pre-pit read channel, such as the land
pre-pit read channel 225, may receive a push-pull signal. Further, the
land pre-pit read channel may extract a land pre-pit data stream based on
an adaptive pre-pit threshold. In an embodiment, the adaptive pre-pit
threshold can be determined initially by a calibration process that
calibrates parameters for a memory medium. The initial adaptive pre-pit
threshold can be one that is good for a portion of the memory medium. In
another embodiment, the initial adaptive pre-pit threshold can be a good
nominal threshold that can be pre-programmed in the memory medium. Then,
the process proceeds to step S730.

[0062] In step S730, a controller, such as the land pre-pit loop
controller 240, may compare a portion of the land pre-pit data stream
with a pre-known format to obtain an error signal. In an embodiment, the
controller may first detect a SYNC code. Once the SYNC code has been
detected and verified, the controller can compare the land pre-pit stream
with the known format accordingly. For example, SYNC codes can appear
every 26 SYNC frames according to a standard. Further, each SYNC code can
have a format of 1110000000000000 or a format of 000000001100000. In an
embodiment, the controller may generate -1 for missing a pre-pit at a
location, and generate +1 for an unexpected pre-pit at a location. Then
the process proceeds to step S740.

[0063] In step S740, the controller may adjust the adaptive land pre-pit
threshold based on the error signal. In an example, the controller may
adjust the adaptive land pre-pit threshold based on an average of the
error signal. Then, the adjusted adaptive land pre-pit threshold can be
used to extract land pre-pits from coming push-pull signal. The process
then proceeds to step S750 and terminates.

[0064] While the invention has been described in conjunction with the
specific exemplary embodiments thereof, it is evident that many
alternatives, modifications, and variations will be apparent to those
skilled in the art. Accordingly, exemplary embodiments of the invention
as set forth herein are intended to be illustrative, not limiting. There
are changes that may be made without departing from the spirit and scope
of the invention.