U.S. patent application number 09/954024 was filed with the patent office on 2002-04-25 for information recording and reproducing apparatus.
Invention is credited to Inokuchi, Chikashi, Kamioka, Yuuichi, Konno, Kohjyu, Osada, Yutaka, Ueki, Yasuhiro, Yanagisawa, Osamu.
Application Number | 20020048239 09/954024 |
Document ID | / |
Family ID | 18798759 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020048239 |
Kind Code |
A1 |
Ueki, Yasuhiro ; et
al. |
April 25, 2002 |
Information recording and reproducing apparatus
Abstract
An apparatus operates for recording and reproducing information
on and from a recording medium formed with a track and pre-pits.
The track has a wobble. The pre-pits are in a predetermined phase
relation with the wobble of the track. The apparatus includes a
pickup for reproducing a signal from the recording medium. A
limiter operates for limiting an amplitude of the signal reproduced
by the pickup in response to a limiting level, and thereby
processing the signal reproduced by the pickup into a
limiting-resultant signal. A filter operates for suppressing
components of the limiting-resultant signal, and thereby processing
the limiting-resultant signal into a filtering-resultant signal.
The components have specified frequencies, and are caused by the
pre-pits. The limiting level for the limiter is generated in
response to the filtering-resultant signal. A signal caused by the
wobble of the groove is extracted from the filtering-resultant
signal.
Inventors: |
Ueki, Yasuhiro;
(Sagamihara-shi, JP) ; Osada, Yutaka;
(Fujisawa-shi, JP) ; Yanagisawa, Osamu;
(Chiba-shi, JP) ; Inokuchi, Chikashi; (Osaka,
JP) ; Kamioka, Yuuichi; (Osaka, JP) ; Konno,
Kohjyu; (Osaka, JP) |
Correspondence
Address: |
LAW OFFICES OF LOUIS WOO
Suite 501
1901 North Fort Myer Drive
Arlington
VA
22209
US
|
Family ID: |
18798759 |
Appl. No.: |
09/954024 |
Filed: |
September 18, 2001 |
Current U.S.
Class: |
369/47.17 ;
369/124.11; 369/124.13; 369/47.25; 369/53.37; G9B/20.035;
G9B/27.027; G9B/7.025; G9B/7.035 |
Current CPC
Class: |
G11B 20/1403 20130101;
G11B 27/24 20130101; G11B 2220/216 20130101; G11B 7/00718 20130101;
G11B 7/24082 20130101; G11B 2220/218 20130101; G11B 27/3027
20130101; G11B 7/0053 20130101; G11B 2220/2562 20130101 |
Class at
Publication: |
369/47.17 ;
369/47.25; 369/53.37; 369/124.11; 369/124.13 |
International
Class: |
G11B 007/005 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2000 |
JP |
2000-320480 |
Claims
What is claimed is:
1. An apparatus for recording and reproducing information on and
from a recording medium formed with a track and pre-pits, the track
having a wobble, the pre-pits being in a predetermined phase
relation with the wobble of the track, the apparatus comprising: a
pickup for reproducing a signal from the recording medium; a
limiter for limiting an amplitude of the signal reproduced by the
pickup in response to a limiting level, and thereby processing the
signal reproduced by the pickup into a limiting-resultant signal; a
filter for suppressing components of the limiting-resultant signal
generated by the limiter, and thereby processing the
limiting-resultant signal into a filtering-resultant signal, the
components having specified frequencies and being caused by the
pre-pits; first means for generating the limiting level for the
limiter in response to the filtering-resultant signal generated by
the filter; and second means for extracting, from the
filtering-resultant signal generated by the filter, a signal caused
by the wobble of the groove.
2. An apparatus as recited in claim 1, further comprising third
means for controlling the limiting level for the limiter in
response to whether the apparatus is operating in a recording mode
or a reproducing mode.
3. An apparatus for recording and reproducing information on and
from a recording medium formed with a track and pre-pits, the track
having a wobble, the pre-pits being in a predetermined phase
relation with the wobble of the track, the apparatus comprising: a
pickup for reproducing a signal from the recording medium; a
limiter for limiting an amplitude of the signal reproduced by the
pickup in response to a limiting level, and thereby processing the
signal reproduced by the pickup into a limiting-resultant signal; a
filter for suppressing components of the limiting-resultant signal
generated by the limiter, and thereby processing the
limiting-resultant signal into a filtering-resultant signal, the
components having specified frequencies and being caused by the
pre-pits; a phase adjuster for adjusting a phase of the
filtering-resultant signal generated by the filter, and thereby
changing the filtering-resultant signal generated by the filter
into an adjustment-resultant signal; first means for generating the
limiting level for the limiter in response to the
adjustment-resultant signal generated by the phase adjuster; and
second means for extracting, from the filtering-resultant signal
generated by the filter, a signal caused by the wobble of the
groove.
4. An apparatus as recited in claim 3, wherein the phase adjuster
comprises means for adjusting the phase of the filtering-resultant
signal by a variable quantity.
5. An apparatus for recording and reproducing information on and
from a recording medium formed with a track and pre-pits, the track
having a wobble, the pre-pits being in a predetermined phase
relation with the wobble of the track, the apparatus comprising: a
pickup for reproducing a signal from the recording medium; a first
amplifier for amplifying the signal reproduced by the pickup into a
first amplification-resultant signal at a gain corresponding to a
factor of X, where X denotes a predetermined positive number; a
limiter for limiting an amplitude of the first
amplification-resultant signal generated by the first amplifier in
response to a limiting level, and thereby processing the first
amplification-resultant signal into a limiting-resultant signal; a
low pass filter for suppressing components of the
limiting-resultant signal generated by the limiter, and thereby
processing the limiting-resultant signal into a first
filtering-resultant signal, the components having specified
frequencies and being caused by the pre-pits; first means for
generating the limiting level for the limiter in response to the
first filtering-resultant signal generated by the low pass filter;
a high pass filter for processing the first filtering-resultant
signal generated by the low pass filter into a second
filtering-resultant signal; second means for converting the second
filtering-resultant signal generated by the high pass filter into a
signal corresponding to the wobble of the groove; a second
amplifier for amplifying the first filtering-resultant signal
generated by the low pass filter into a second
amplification-resultant signal at a gain corresponding to a factor
of 1/X; and a comparator for comparing the signal reproduced by the
pickup and the second amplification-resultant signal generated by
the second amplifier to generate a signal corresponding to the
pre-pits.
6. An apparatus as recited in claim 5, wherein the limiting level
for the limiter is variable.
7. An apparatus as recited in claim 5, further comprising third
means for controlling the limiting level for the limiter in
response to whether the apparatus is operating in a recording mode
or a reproducing mode.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an apparatus for recording and
reproducing information on and from a recording medium formed with
a wobbling track and pre-pits.
[0003] 2. Description of the Related Art
[0004] Optical discs include a DVD-R (DVD Recordable) and a DVD-RW
(DVD Rewritable). Each of the DVD-R and the DVD-RW has a disc
member formed with a spiral of a wobbling groove on and from which
main information can be recorded and reproduced. The wobble of the
groove indicates first auxiliary information recorded on the disc
member. The first auxiliary information contains a reference clock
signal. The disc member has land portions between neighboring
groove portions. A groove portion and a pair of land portions
adjoining the groove portion compose a track portion. Second
auxiliary information (land pre-pit signals) is previously recorded
on the land portions. Specifically, the second auxiliary
information is represented by land pre-pits formed in the land
portions. The second auxiliary information contains address
information from which the position of an arbitrary point on the
disc member can be detected.
[0005] During the recording of main information on the DVD-R or the
DVD-RW or the reproduction of main information therefrom, the track
is scanned by a laser beam while the disc is rotated. In this case,
the wobble of the groove in the track and the pre-pits in the lands
in the track are detected. A wobble signal is generated in response
to the detection of the wobble of the groove. The reference clock
signal is reproduced from the wobble signal. Rotation of the disc
is controlled in response to the reproduced reference clock signal.
Land pre-pit signals are generated in response to the detection of
the pre-pits. The position of a currently-accessed point on the
disc is detected from the land pre-pit signals.
[0006] The generation of the land pre-pit signals is implemented as
follows. The wobble of the groove and the positions of the pre-pits
in the lands are in a predetermined phase relation. A reflected
laser beam coming from the disc is converted into an electric
signal. A wobble signal is extracted from the electric signal. The
wobble signal has a level which alternates in accordance with the
wobble of the groove. Spike-like peak signals caused by the
pre-pits are superimposed on the wobble signal. The wobble signal
is compared with a reference signal of a fixed threshold level so
that high-level portions of the wobble signal which exceed the
threshold level are selected. A gate signal synchronous with the
wobble signal is generated. AND operation is executed between the
gate signal and the high-level portions of the wobble signal,
thereby extracting the spike-like peak signals from the high-level
portions of the wobble signal. The extracted spike-like peak
signals constitute the land pre-pit signals.
[0007] Japanese patent application publication number 10-320781
discloses an apparatus for detecting pre-pit signals. In the
apparatus of Japanese application 10-320781, a first wobble signal
is extracted from the output signal of an optical pickup. Pre-pit
signals each having a spike-like waveform are superimposed on the
first wobble signal. A PLL-based servo circuit generates a sync
signal in response to the first wobble signal. The sync signal is
equal in phase and frequency to the first wobble signal. The sync
signal periodically peaks. A timing of every peak of the sync
signal coincides with a moment at which a pre-pit signal is
expected to be superimposed on the first wobble signal. The sync
signal is basically equal in waveform to the first wobble signal
except spike-like components corresponding to pre-pit signals. The
first wobble signal is biased by a reference voltage, being changed
into a second wobble signal. The second wobble signal and the sync
signal are compared with each other so that the pre-pit signals are
extracted or detected. In the case where the second wobble signal
has a noise component at a time position near a pre-pit signal, it
tends to be difficult to discriminate the pre-pit signal from the
noise component.
[0008] Japanese patent application publication number 10-241260
discloses an apparatus for recording information on a DVD-R. In the
apparatus of Japanese application 10-241260, a first wobble signal
is extracted from the output signal of an optical pickup. Pre-pit
signals each having a spike-like waveform are superimposed on the
first wobble signal. The first wobble signal is subjected to an
amplitude limiting process responsive to an upper limiting signal
and a lower limiting signal so that pre-pit signals in the first
wobble signal are suppressed. The upper limiting signal and the
lower limiting signal are generated from the first wobble signal.
Accordingly, the upper limiting signal and the lower limiting
signal depend on the first wobble signal. The limiting-resultant
wobble signal, which is called a second wobble signal, propagates
through a band pass filter tuned to a true wobble frequency. The
band pass filter attenuates the pre-pit signals in the second
wobble signal. The output signal from the band pass filter is
referred to as a final wobble signal. The final wobble signal is
binarized into a reference clock signal used for the control of
rotation of the DVD-R. In the case where the pre-pit signals remain
in the final wobble signal to a considerable degree, the reference
clock signal tends to have an unacceptable frequency error.
SUMMARY OF THE INVENTION
[0009] It is a first object of this invention to provide an
information recording and reproducing apparatus which can reliably
discriminate pre-pit signals from noise signal components.
[0010] It is a second object of this invention to provide an
information recording and reproducing apparatus which can reliably
separate a true wobble signal from pre-pit signals and noise signal
components.
[0011] A first aspect of this invention provides an apparatus for
recording and reproducing information on and from a recording
medium formed with a track and pre-pits, the track having a wobble,
the pre-pits being in a predetermined phase relation with the
wobble of the track. The apparatus comprises a pickup for
reproducing a signal from the recording medium; a limiter for
limiting an amplitude of the signal reproduced by the pickup in
response to a limiting level, and thereby processing the signal
reproduced by the pickup into a limiting-resultant signal; a filter
for suppressing components of the limiting-resultant signal
generated by the limiter, and thereby processing the
limiting-resultant signal into a filtering-resultant signal, the
components having specified frequencies and being caused by the
pre-pits; first means for generating the limiting level for the
limiter in response to the filtering-resultant signal generated by
the filter; and second means for extracting, from the
filtering-resultant signal generated by the filter, a signal caused
by the wobble of the groove.
[0012] A second aspect of this invention is based on the first
aspect thereof, and provides an apparatus further comprising third
means for controlling the limiting level for the limiter in
response to whether the apparatus is operating in a recording mode
or a reproducing mode.
[0013] A third aspect of this invention provides an apparatus for
recording and reproducing information on and from a recording
medium formed with a track and pre-pits, the track having a wobble,
the pre-pits being in a predetermined phase relation with the
wobble of the track. The apparatus comprises a pickup for
reproducing a signal from the recording medium; a limiter for
limiting an amplitude of the signal reproduced by the pickup in
response to a limiting level, and thereby processing the signal
reproduced by the pickup into a limiting-resultant signal; a filter
for suppressing components of the limiting-resultant signal
generated by the limiter, and thereby processing the
limiting-resultant signal into a filtering-resultant signal, the
components having specified frequencies and being caused by the
pre-pits; a phase adjuster for adjusting a phase of the
filtering-resultant signal generated by the filter, and thereby
changing the filtering-resultant signal generated by the filter
into an adjustment-resultant signal; first means for generating the
limiting level for the limiter in response to the
adjustment-resultant signal generated by the phase adjuster; and
second means for extracting, from the filtering-resultant signal
generated by the filter, a signal caused by the wobble of the
groove.
[0014] A fourth aspect of this invention is based on the third
aspect thereof, and provides an apparatus wherein the phase
adjuster comprises means for adjusting the phase of the
filtering-resultant signal by a variable quantity.
[0015] A fifth aspect of this invention provides an apparatus for
recording and reproducing information on and from a recording
medium formed with a track and pre-pits, the track having a wobble,
the pre-pits being in a predetermined phase relation with the
wobble of the track. The apparatus comprises a pickup for
reproducing a signal from the recording medium; a first amplifier
for amplifying the signal reproduced by the pickup into a first
amplification-resultant signal at a gain corresponding to a factor
of X, where X denotes a predetermined positive number; a limiter
for limiting an amplitude of the first amplification-resultant
signal generated by the first amplifier in response to a limiting
level, and thereby processing the first amplification-resultant
signal into a limiting-resultant signal; a low pass filter for
suppressing components of the limiting-resultant signal generated
by the limiter, and thereby processing the limiting-resultant
signal into a first filtering-resultant signal, the components
having specified frequencies and being caused by the pre-pits;
first means for generating the limiting level for the limiter in
response to the first filtering-resultant signal generated by the
low pass filter; a high pass filter for processing the first
filtering-resultant signal generated by the low pass filter into a
second filtering-resultant signal; second means for converting the
second filtering-resultant signal generated by the high pass filter
into a signal corresponding to the wobble of the groove; a second
amplifier for amplifying the first filtering-resultant signal
generated by the low pass filter into a second
amplification-resultant signal at a gain corresponding to a factor
of 1/X; and a comparator for comparing the signal reproduced by the
pickup and the second amplification-resultant signal generated by
the second amplifier to generate a signal corresponding to the
pre-pits.
[0016] A sixth aspect of this invention is based on the fifth
aspect thereof, and provides an apparatus wherein the limiting
level for the limiter is variable.
[0017] A seventh aspect of this invention is based on the fifth
aspect thereof, and provides an apparatus further comprising third
means for controlling the limiting level for the limiter in
response to whether the apparatus is operating in a recording mode
or a reproducing mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a perspective view, partially in section, of a
portion of an optical disc.
[0019] FIG. 2 is a diagram of main information recorded on the
optical disc, and pre-pits and a wobbling groove formed
therein.
[0020] FIG. 3 is a block diagram of an information recording and
reproducing apparatus according to a first embodiment of this
invention.
[0021] FIG. 4 is a block diagram of a wobble signal extractor in
FIG. 3.
[0022] FIG. 5 is a block diagram of a pre-pit signal decoder in
FIG. 3.
[0023] FIG. 6 is a block diagram of a servo circuit in FIG. 3.
[0024] FIG. 7 is a time-domain diagram of various signals in the
apparatus of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0025] First Embodiment
[0026] With reference to FIG. 1, an optical disc 1 is a DVD-R (DVD
Recordable) or a DVD-RW (DVD Rewritable). The optical disc 1
includes an information recording layer 5 having a pigment film or
a phase change film. The optical disc 1 includes a metal-deposited
layer (for example, a gold-deposited layer) 6 which extends below
the information recording layer 5 as viewed in FIG. 1. The
metal-deposited layer 6 acts to reflect a light beam (a laser beam)
B.
[0027] The optical disc 1 has an information recording area formed
with a spiral of a wobbling groove 2 and a spiral of a land 3. It
should be noted that FIG. 1 illustrates the groove 2 and the land 3
in an opposite manner. Specifically, FIG. 1 illustrates the groove
2 and the land 3 as those in a stamper for an optical disc. A
portion of the land 3 is located between neighboring portions of
the groove 2. A groove portion and a pair of land portions
adjoining the groove portion compose a track portion. The groove 2
and the land 3 are coated with a protective film 7. For an easier
understanding, groove portions, land portions, and track portions
which neighbor in a radial direction of the optical disc 1 are also
referred to as grooves, lands, and tracks, respectively.
[0028] Alternatively, the optical disc 1 may have a set of
concentric circular wobbling grooves 2 and lands 3 formed between
neighboring grooves 2.
[0029] Main information can be recorded on and reproduced from the
groove (or the grooves) 2. First auxiliary information is
previously recorded on the optical disc 1 as the wobble of the
groove (or the grooves) 2. Second auxiliary information (pre-pit
signals or land pre-pit signals) is previously recorded on the land
(or the lands) 3. Specifically, the second auxiliary information is
represented by pre-pits 4 formed in the land (or the lands) 3. The
first auxiliary information and the second auxiliary information
are used for the recording of main information on the optical disc
1 or the reproduction of main information therefrom.
[0030] The first auxiliary information contains a reference clock
signal which is used for the control of rotation of the optical
disc 1. The second auxiliary information contains address
information from which the position of an arbitrary point on the
optical disc 1 can be detected.
[0031] During the recording of main information on the optical disc
1 or the reproduction of main information therefrom, the track is
scanned by the light beam B while the optical disc 1 is rotated. In
this case, the wobble of the groove (or the grooves) 2 and the
pre-pits 4 in the land (or the lands) 3 are detected. A wobble
signal is generated in response to the detection of the wobble of
the groove (or the grooves) 2. The reference clock signal is
reproduced from the wobble signal. Rotation of the optical disc 1
is controlled in response to the reproduced reference clock signal.
Land pre-pit signals are generated in response to the detection of
the pre-pits 4. The position of a currently-accessed point on the
optical disc 1 is detected from the land pre-pit signals.
[0032] The light beam B is focused into a light spot SP on the
optical disc 1. A tracking process forces the center of the light
spot SP to move along a substantial central line of the groove 2
during the rotation of the optical disc 1. The light spot SP
extends over the groove 2 of interest and also the lands 3
adjoining the groove 2 of the interest. The light beam B is
reflected by the optical disc 1, traveling back as a reflected
light beam. The reflected light beam is sensed by a photodetector.
The photodetector has segments separated by a line parallel to the
direction of rotation of the optical disc 1. According to a radial
push-pull method using the photodetector, the second auxiliary
information represented by the pre-pits 4 is reproduced from
portions of the reflected light beam which correspond to the
light-spot portions extending over the lands 3. At the same time,
the first auxiliary information represented by the wobble of the
groove 2 is reproduced from a portion of the reflected light beam
which corresponds to the light-spot portion extending over the
groove 2. The reference clock signal is detected from the first
auxiliary information. The reference clock signal is used for the
control of rotation of the optical disc 1.
[0033] With reference to FIG. 2, the main information recorded on
the optical disc 1 is divided into a sequence of sync frames
composed of even-numbered frames and odd-numbered frames. One
recording sector is composed of 26 successive sync frames. One ECC
(error correction code) block is composed of 16 successive
recording sectors. Every sync frame has a length of 1488T where T
denotes a unit length corresponding to a bit interval prescribed by
the format of the recording of the main information on the optical
disc 1. A head of every sync frame which has a length of 14T is
occupied by sync information SY for providing synchronization per
sync frame. The sequence of sync frames is recorded along the
wobbling groove 2. Thus, the groove 2 has spaced portions each
storing the sync information SY.
[0034] The land 3 has first spaced portions and second spaced
portions. The first spaced portions of the land 3 adjoin portions
of the groove 2 which store even-numbered sync frames respectively.
The second spaced portions of the land 3 adjoin portions of the
groove 2 which store odd-numbered sync frames. The first spaced
portions of the land 3 are formed with pre-pits 4 while the second
spaced portions thereof are devoid of pre-pits 4. Alternatively,
the second spaced portions of the land 3 may be formed with
pre-pits 4. In this case, the first spaced portions of the land 3
are devoid of pre-pits 4.
[0035] The land 3 has first spaced regions which neighbor the
sync-information storing portions of the even-numbered-sync-frame
regions of the groove 2 respectively. Each of the first spaced
regions of the land 3 is formed with a pre-pit 4 indicating a sync
signal. The land 3 has second spaced regions which neighbor the
former halves of the even-numbered-sync-frame regions of the groove
2 respectively. Each of the second spaced regions of the land 3 is
formed with at most one or two pre-pits 4 indicating address
information.
[0036] In the case where the second spaced portions of the land 3
are formed with pre-pits 4 while the first spaced portions thereof
are devoid of pre-pits 4, the pre-pit arrangement is designed as
follows. The land 3 has first spaced regions which neighbor the
sync-information storing portions of the odd-numbered-sync-frame
regions of the groove 2 respectively. Each of the first spaced
regions of the land 3 is formed with a pre-pit 4 indicating a sync
signal. The land 3 has second spaced regions which neighbor the
former halves of the odd-numbered-sync-frame regions of the groove
2 respectively. Each of the second spaced regions of the land 3 is
formed with at most one or two pre-pits 4 indicating address
information.
[0037] The groove 2 wobbles at a constant frequency f0 in common
for all the sync frames. The wobble frequency f0 is equal to, for
example, 140 kHz at which one sync frame corresponds to 8 cycles or
8 periods of the wobble. The wobble frequency f0 is detected by
sensing the wobble of the groove 2. The detected wobble frequency
f0 is used for the control of rotation of the optical disc 1.
[0038] The positions of the pre-pits 4 are in a predetermined phase
relation with the wobble of the groove 2. As shown in FIG. 2, the
positions of the pre-pits 4 coincide with points at which the
sinusoidal waveform of the wobble of the groove 2 is maximized.
[0039] FIG. 3 shows an apparatus S for recording and reproducing
information on and from the optical disc 1 according to a first
embodiment of this invention. Operation of the apparatus S can be
changed among various modes including a recording mode, a playback
mode, and a preliminary mode. During the recording mode of
operation, the apparatus S records main information on the optical
disc 1. During the playback mode of operation, the apparatus S
reproduces main information from the optical disc 1. The apparatus
S is operated in the preliminary mode before being operated in the
recording mode. During the preliminary mode of operation, the
apparatus S senses the pre-pits 4 in the optical disc 1 and thereby
reproduces the address information. The reproduced address
information is used during the recording mode of operation.
Specifically, the position of a currently-accessed point on the
optical disc 1 is detected by referring to the address information
during the recording mode of operation.
[0040] As shown in FIG. 3, the apparatus S includes a pickup (an
optical head) 10, a reproducing amplifier 11, a decoder 12, a
pre-pit signal decoder 13, a spindle motor 14, a servo circuit 15,
a processor or a CPU 16, an encoder 17, a power control circuit 18,
a laser drive circuit 19, an interface 20, a wobble signal
extractor 22, an X-fold amplifier 33, and a 1/X-fold amplifier
35.
[0041] The pickup 10 can access the optical disc 1. The pickup 10
is connected with the reproducing amplifier 11, the servo circuit
15, and the laser drive circuit 19. The reproducing amplifier 11 is
connected with the decoder 12, the pre-pit signal decoder 13, the
CPU 16, and the X-fold amplifier 33. The decoder 12 is connected
with the servo circuit 15 and the CPU 16. The pre-pit signal
decoder 13 is connected with the servo circuit 15, the CPU 16, and
the 1/X-fold amplifier 35. The spindle motor 14 acts to rotate the
optical disc 1. The spindle motor 14 is connected with the servo
circuit 15. The servo circuit 15 is connected with the encoder 17
and the wobble signal extractor 22. The servo circuit 15 controls
the spindle motor 14. The servo circuit 15 can move the pickup 10
in a radial direction of the optical disc 1. The CPU 16 is
connected with the interface 20 and the wobble signal extractor 22.
The CPU 16 is also connected with the servo circuit 15 although the
connection therebetween is omitted from FIG. 3. The encoder 17 is
connected with the power control circuit 18 and the interface 20.
The power control circuit 18 is connected with the laser drive
circuit 19. The interface 20 can be connected with an external host
computer 21. Digital information SRR to be recorded can be fed to
the interface 20 from the host computer 21. The digital information
SRR is main information. The wobble signal extractor 22 is
connected with the X-fold amplifier 33 and the 1/X-fold amplifier
35.
[0042] The pickup 10 includes a laser diode, a deflection beam
splitter, an objective lens, and a photodetector. The pickup 10
receives a laser drive signal SDL from the laser drive circuit 19.
The laser diode in the pickup 10 is activated by the laser drive
signal SDL. Thus, the pickup 10 generates a light beam (a laser
beam) B in response to the laser drive signal SDL. The pickup 10
applies the light beam B to an information recording surface of the
optical disc 1. The light beam B is reflected by the information
recording surface of the optical disc 1, traveling back as a return
light beam. A portion of the return light beam is incident to the
photodetector in the pickup 10. Thus, the pickup 10 converts the
portion of the return light beam into a corresponding electric
signal SDT. The pickup 10 senses the pre-pits 4 and the wobble of
the groove 2 through the portion of the reflected light beam in the
radial push-pull method. During the recording mode of operation,
the digital information (the main information) SRR is transmitted
to the pickup 10 from the host computer 21 via the interface 20,
the encoder 17, the power control circuit 18, and the laser drive
circuit 19. The pickup 10 records the digital information SRR on
the optical disc 1. During the playback mode of operation, the
pickup 10 reproduces digital information (main information) from
the optical disc 1 through the portion of the reflected light beam.
The pickup 10 outputs the electric signal SDT representative of the
reproduced digital information to the reproducing amplifier 11.
[0043] The reproducing amplifier 11 separates the output signal SDT
of the pickup 10 into a signal SP containing the reproduced main
information and a signal SPP containing first auxiliary information
and second auxiliary information. The first auxiliary information
is represented by the wobble of the groove 2. The second auxiliary
information is represented by the pre-pits 4. The reproducing
amplifier 11 outputs the main-information signal SP to the decoder
12. The reproducing amplifier 11 outputs the auxiliary-information
signal SPP to the pre-pit signal decoder 13 and the X-fold
amplifier 33.
[0044] The auxiliary-information signal SPP is composed of a true
wobble signal caused by the wobble of the groove 2, and spike-like
peak signals (pre-pit signals) and spike-like valley signals caused
by the pre-pits 4. The level of the true wobble signal alternates.
The spike-like peak signals are in phase with the true wobble
signal. Specifically, the moments of occurrence of the spike-like
peak signals substantially coincide with time points at which the
level of the true wobble signal is maximized. This phase relation
between the spike-like peak signals and the true wobble signal is
provided by the positional relation between the pre-pits 4 and the
wobble of the groove 2.
[0045] The reproducing amplifier 11 includes a detector for
extracting RF components of the output signal SDT of the pickup 10,
and for detecting a level (an amplitude) of the extracted RF
components. The detector in the reproducing amplifier 11 feeds a
signal RF-ENV representative of the detected RF signal level to the
CPU 16.
[0046] The decoder 12 subjects the main-information signal SP to
8-16 demodulation and de-interleaving to get a main
demodulation-resultant signal SDM and a servo
demodulation-resultant signal SSD. The decoder 12 outputs the main
demodulation-resultant signal SDM to the CPU 16. The decoder 12
outputs the servo demodulation-resultant signal SSD to the servo
circuit 15.
[0047] The X-fold amplifier 33 amplifies the auxiliary-information
signal SPP at a gain corresponding to a factor of X, where X
denotes a predetermined positive number. The X-fold amplifier 33
outputs the amplification-resultant signal SPPX to the wobble
signal extractor 22.
[0048] The pre-pit signal decoder 13 extracts, from the
auxiliary-information signal SPP, signals caused by the pre-pits 4.
The extracted signals compose a pre-pit detection signal SPDT. The
pre-pit signal decoder 13 outputs the pre-pit detection signal SPDT
to the servo circuit 15. The pre-pit signal decoder 13 decodes the
pre-pit detection signal SPDT into a demodulation-resultant pre-pit
signal SPD. The pre-pit signal decoder 13 outputs the
demodulation-resultant pre-pit signal SPD to the CPU 16.
[0049] As shown in FIG. 4, the wobble signal extractor 22 includes
a limiter 101, a limiting level generator 102, a phase adjuster
102a, a switch 103, a band pass filter (BPF) 106, and a binarizing
device 107. The limiting level generator 102 has a lower level
shift circuit 109 and an upper level shift circuit 110. The band
pass filter 106 has a low pass filter (LPF) 104 and a high pass
filter (HPF) 105.
[0050] The limiter 101 receives the output signal SPPX of the
X-fold amplifier 33. The limiter 101 is connected with the LPF 104,
the lower level shift circuit 109, and the upper level shift
circuit 110. The LPF 104 is connected with the switch 103 and the
HPF 105. The LPF 104 is also connected with the 1/X-fold amplifier
35 (see FIG. 3). The switch 103 is connected with the phase
adjuster 102a, the HPF 105, and the CPU 16 (see FIG. 3). The phase
adjuster 102a is connected with the lower level shift circuit 109,
the upper level shift circuit 110, and the CPU 16. The lower level
shift circuit 109 is connected with the limiter 101 and the CPU 16.
The upper level shift circuit 110 is connected with the limiter 101
and the CPU 16. The HPF 105 is connected with the binarizing device
107. The binarizing device 107 is connected with the servo circuit
15 (see FIG. 3).
[0051] The limiter 101 receives a lower limiting signal SWL from
the lower level shift circuit 109. The limiter 101 receives an
upper limiting signal SUL from the upper level shift circuit 110.
The device 101 limits the amplitude of the output signal SPPX of
the X-fold amplifier 33 to within a range whose lower and upper
limits are determined by the lower and upper limiting signals SWL
and SUL respectively. The amplitude limitation suppresses or
attenuates spike-like peak signals (pre-pit signals) in the output
signal SPPX of the X-fold amplifier 33. The limiter 101 outputs the
limiting-resultant signal LL to the low pass filter 104. The
limiting-resultant signal LL passes through the LPF 104, becoming a
low-pass-filtering resultant signal (an LPF-resultant signal) SL.
The spike-like peak signals (the pre-pit signals) have relatively
high frequencies, and the LPF 104 suppresses or attenuates the
spike-like peak signals (the pre-pit signals). In other words, the
LPF 104 suppresses or attenuates components of the
limiting-resultant signal LL which have specified high frequencies,
and which are caused by the pre-pits. The LPF 104 outputs the
LPF-resultant signal SL to the HPF 105. The LPF-resultant signal SL
passes through the HPF 105, becoming a high-pass-filtering
resultant signal (an HPF-resultant signal) SB. The HPF 105 has a
predetermined cutoff frequency lower than the frequency f0 of the
true wobble signal. Thus, the true wobble signal passes through the
HPF 105 without being considerably attenuated. The HPF 105 outputs
the HPF-resultant signal SB to the binarizing device 107. The
binarizing device 107 converts the output signal SB of the HPF 105
into a corresponding binary signal SDTT referred to as a reproduced
wobble signal. The reproduced wobble signal SDTT has a frequency
equal to the wobble frequency f0. The binarizing device 107 outputs
the reproduced wobble signal SDTT to the servo circuit 15 (see FIG.
3).
[0052] The switch 103 receives the LPF-resultant signal SL from the
LPF 104. The switch 103 receives the HPF-resultant signal SB from
the HPF 105. The switch 103 selects one from the LPF-resultant
signal SL and the HPF-resultant signal SB in response to a control
signal fed from the CPU 16 (see FIG. 3). The switch 103 outputs the
selected signal to the phase adjuster 102a. The device 102a adjusts
the phase of the output signal of the switch 103 in response to
phase adjustment data PAD fed from the CPU 16. The phase adjustment
by the phase adjuster 102a compensates for signal delays caused by
the LPF 104, the HPF 105, the switch 103, the lower level shift
circuit 109, and the upper level shift circuit 110. The phase
adjuster 102a outputs the adjustment-resultant signal SSW to the
lower level shift circuit 109 and the upper level shift circuit
110.
[0053] The lower level shift circuit 109 generates the lower
limiting signal SWL in response to the output signal SSW of the
phase adjuster 102a. The lower level shift circuit 109 outputs the
lower limiting signal SWL to the limiter 101. The upper level shift
circuit 110 generates the upper limiting signal SUL in response to
the output signal SSW of the phase adjuster 102a. The upper level
shift circuit 110 outputs the upper limiting signal SUL to the
limiter 101. The lower level shift circuit 109 and the upper level
shift circuit 110 receive a setting signal SSL from the CPU 16. The
lower level shift circuit 109 can set the lower limiting signal SWL
to a suitable level in response to the setting signal SSL. The
upper level shift circuit 110 can set the upper limiting signal SUL
to a suitable level in response to the setting signal SSL. By use
of the setting signal SSL, the lower limiting signal SWL and the
upper limiting signal SUL can be set to suitable levels which
depend on whether the apparatus S is operating in the recording
mode or the playback mode.
[0054] The LPF 104 is used in two ways. The first way is to
generate the lower limiting signal SWL and the upper limiting
signal SUL. The second way is to suppress or attenuate the
spike-like peak signals (the pre-pit signals) and the spike-like
valley signals. The use of the LPF 104 in the two ways is
advantageous in simplifying the structure of the apparatus S.
[0055] With reference back to FIG. 3, the 1/X-fold amplifier 35
receives the LPF-resultant signal SL from the wobble signal
extractor 22. The 1/X-fold amplifier 35 amplifies the LPF-resultant
signal SL at a gain corresponding to a factor of 1/X. The gain of
the 1/X-fold amplifier 35 is inverse or reciprocal with respect to
that of the X-fold amplifier 33. Therefore, the 1/X-fold amplifier
35 retrieves the original signal amplitude which occurs at the
circuit stage immediately preceding the X-fold amplifier 33. The
1/X-fold amplifier 35 outputs the amplification-resultant signal
SLL to the pre-pit signal decoder 13.
[0056] The servo circuit 15 generates a pickup servo signal SSP in
response to the pre-pit detection signal SPDT and the servo
demodulation-resultant signal SSD. The servo circuit 15 outputs the
pickup servo signal SSP to the pickup 10. The pickup servo signal
SSP is designed to enable the pickup 10 to implement focus servo
control and tracking servo control. The servo circuit 15 generates
a spindle servo signal SSS in response to the wobble frequency f0
of the reproduced wobble signal SDTT. The servo circuit 15 outputs
the spindle servo signal SSS to the spindle motor 14. The spindle
servo signal SSS is designed to implement servo control of the
rotation of the spindle motor 14, that is, servo control of the
rotation of the optical disc 1. The servo circuit 15 generates a
recording clock signal WRCLK in response to the wobble frequency f0
of the reproduced wobble signal SDTT. The servo circuit 15 outputs
the recording clock signal WRCLK to the encoder 17. The servo
circuit 15 generates a PLL signal SPL synchronized with and locked
to the reproduced wobble signal SDTT. The servo circuit 15 outputs
the PLL signal SPL to the pre-pit signal decoder 13.
[0057] The interface 20 is controlled by the CPU 16. Under the
control by the CPU 16, the interface 20 transmits the digital
information (the main information) SRR from the host computer 21 to
the encoder 17. The encoder 17 includes an ECC generator, an
interleaving circuit, an 8-16 modulator, and a scrambler. The
encoder 17 divides the digital information SRR into blocks in
response to the recording clock signal WRCLK. The encoder 17
generates ECC signals in response to the blocks, respectively. The
encoder 17 adds the ECC signals to the blocks to form ECC blocks.
The encoder 17 subjects the ECC blocks to interleaving, 8-16
modulation, and scrambling in a prescribed order and in response to
the recording clock signal WRCLK, thereby converting the ECC blocks
into a modulation-resultant signal SRE. The encoder 17 feeds the
modulation-resultant signal SRE to the power control circuit
18.
[0058] The power control circuit 18 generates a record signal SD in
response to the modulation-resultant signal SRE. The power control
circuit 18 outputs the record signal SD to the laser drive circuit
19. The laser drive circuit 19 generates the laser drive signal SDL
in response to the record signal SD. The laser drive circuit 19
feeds the laser drive signal SDL to the laser diode in the pickup
10. The laser diode generates the light beam (the laser beam) B in
response to the laser drive signal SDL. The digital information
(the main information) SRR is contained in the laser drive signal
SDL. The light beam B is applied to the optical disc 1 so that the
digital information (the main information) SRR is recorded
thereon.
[0059] The CPU 16 includes a combination of an input/output port, a
processing section, a ROM, and a RAM. The CPU 16 operates in
accordance with a control program stored in the ROM. The control
program is designed to enable the CPU 16 to implement the
previously-mentioned steps and also later-mentioned steps of
operation.
[0060] The CPU 16 can access the pickup 10 and the spindle motor 14
via the servo circuit 15. The CPU 16 derives the address
information from the demodulation-resultant pre-pit signal SPD. In
response to the address information, the CPU 16 adjusts the pickup
10 and the spindle motor 14 via the servo circuit 15, and thereby
controls the place on the optical disc 1 in which the digital
information (the main information) SRR is recorded.
[0061] As previously mentioned, the CPU 16 receives the main
demodulation-resultant signal SDM from the decoder 12 which
contains the reproduced main information. The CPU 16 converts the
main demodulation-resultant signal SDM into a reproduced signal SOT
corresponding to the reproduced main information. The CPU 16
outputs the reproduced signal SOT to an external device (not
shown).
[0062] The CPU 16 generates the control signal for the switch 103
(see FIG. 4). In addition, the CPU 16 generates the setting signal
SSL for the lower level shift circuit 109 and the upper level shift
circuit 110 (see FIG. 4). Furthermore, the CPU 16 generates the
phase adjustment data PAD for the phase adjuster 102a (see FIG. 4).
Also, the CPU 16 generates a digital signal WW representative of a
given value. The CPU 16 outputs the digital signal WW to the
pre-pit signal decoder 13.
[0063] As shown in FIG. 5, the pre-pit signal decoder 13 includes a
D/A (digital-to-analog) converter 23, a threshold-value setting
device 24, a comparator 25, a decoder 26, a peak hold circuit 34,
and a composite detector 36.
[0064] The D/A converter 23 receives the digital signal WW from the
CPU 16. The D/A converter 23 is connected with the threshold-value
setting device 24. The threshold-value setting device 24 is
connected with the comparator 25. The comparator 25 receives the
auxiliary-information signal SPP from the reproducing amplifier 11
(see FIG. 3). The comparator 25 is connected with the composite
detector 36 and the servo circuit 15. The composite detector 36
receives the PLL signal SPL from the servo circuit 15. The
composite detector 36 is connected with the decoder 26 and the CPU
16. The decoder 26 is connected with the CPU 16. The peak hold
circuit 34 receives the output signal SLL of the 1/X-fold amplifier
35. The peak hold circuit 34 is connected with the threshold-value
setting circuit 24 and the CPU 16.
[0065] The D/A converter 23 changes the digital signal WW
representative of the given value into a corresponding analog
signal. The analog signal has a DC level depending on the given
value provided by the CPU 16. The D/A converter 23 outputs the
analog signal to the threshold-value setting device 24. The peak
hold circuit 34 samples and holds every peak of the output signal
SLL of the 1/X-fold amplifier 35. The peak hold circuit 34 outputs
a signal Sph representative of the sampled and held peak to the
threshold-value setting device 24 and the CPU 16. The
threshold-value setting device 24 includes an adder for adding the
output signal of the D/A converter 23 and the output signal Sph of
the peak hold circuit 34. The threshold-value setting device 24
outputs the addition-resultant signal Sref to the comparator 25.
The addition-resultant signal Sref indicates a threshold value. The
addition-resultant signal Sref is also referred to as the
threshold-value signal. The device 25 compares the
auxiliary-information signal SPP and the threshold-value signal
Sref, thereby converting the auxiliary-information signal SPP into
the pre-pit detection signal SPDT. Accordingly, the comparator 25
acts to generate the pre-pit detection signal SPDT. The comparator
25 outputs the pre-pit detection signal SPDT to the servo circuit
15 and the composite detector 36.
[0066] The composite detector 36 includes a sync detecting section
which generates a sync signal (a frame sync signal) in response to
the PLL signal SPL and the pre-pit detection signal SPDT. The
composite detector 36 outputs the sync signal to the CPU 16 and the
decoder 26. The composite detector 36 includes a signal comparing
section which compares the PLL signal SPL and the pre-pit detection
signal SPDT to get a comparison-resultant signal. The composite
detector 36 outputs the comparison-resultant signal to the decoder
26.
[0067] The decoder 26 decodes the comparison-resultant signal from
the composite detector 36 into a demodulation-resultant pre-pit
signal SPD. The decoder 26 outputs the demodulation-resultant
pre-pit signal SPD to the CPU 16.
[0068] As shown in FIG. 6, the servo circuit 15 includes a
voltage-controlled oscillator (VCO) 270, an 1/N frequency divider
28, a multiplier 29, an amplifier 30, a low pass filter (LPF) 31,
and a band pass filter (BPF) 32. The VCO 270, the frequency divider
28, the multiplier 29, the amplifier 30, and the LPF 31 are
sequentially connected in a loop in that order to compose a
phase-locked loop (PLL) circuit.
[0069] The multiplier 29 receives the reproduced wobble signal SDTT
from the wobble signal extractor 22. The multiplier 29 receives an
output signal from the frequency divider 28. The device 29
multiplies the reproduced wobble signal SDTT and the output signal
of the frequency divider 28, thereby generating a signal
representative of the phase error (the phase difference)
therebetween. The phase-error signal is transmitted from the
multiplier 29 to the LPF 31 via the amplifier 30. The LPF 31
subjects the phase-error signal to a low pass filtering process to
get a control voltage. The LPF 31 outputs the control voltage to
the VCO 270. The VCO 270 oscillates at a frequency depending on the
control voltage. The VCO 270 outputs the resultant oscillation
signal to the frequency divider 28. The device 28 divides the
frequency of the output signal of the VCO 270 by a predetermined
natural number N. The frequency divider 28 outputs the
division-resultant signal to the multiplier 29 and the BPF 32. The
BPF 32 is tuned to the frequency f0 of the true wobble signal. The
BPF 32 subjects the output signal of the frequency divider 28 to a
band pass filtering process to get the PLL signal SPL synchronized
with and locked to the reproduced wobble signal SDTT. The BPF 32
outputs the PLL signal SPL to the pre-pit signal decoder 13 (see
FIG. 3). The oscillation signal outputted from the VCO 270
constitutes the recording clock signal WRCLK. The recording clock
signal WRCLK is transmitted from the VCO 270 to the encoder 17 (see
FIG. 3).
[0070] As shown in FIG. 7, the auxiliary-information signal SPP
outputted from the reproducing amplifier 11 to the pre-pit signal
decoder 13 and the X-fold amplifier 33 has a sinusoidal waveform on
which spike-like peaks and spike-like valleys are superimposed. The
sinusoidal waveform corresponds to a true wobble signal while the
spike-like peaks correspond to desired pre-pit signals. On the
other hand, the spike-like valleys correspond to undesired pre-pit
signals or noise. The time positions of the spike-like peaks
coincide with points at which the sinusoidal waveform is
maximized.
[0071] The X-fold amplifier 33 amplifies the auxiliary-information
signal SPP at a gain corresponding to a factor of X. The
amplification-resultant signal SPPX outputted from the X-fold
amplifier 33 to the wobble signal extractor 22 has a waveform such
as shown in FIG. 7.
[0072] The limiter 101 in the wobble signal extractor 22 slices off
spike-like peaks from the amplification-resultant signal SPPX.
Spike-like peaks and spike-like valleys in the
amplification-resultant signal SPPX are formed by high-frequency
components. The LPF 104 in the wobble signal extractor 22
suppresses or attenuates the spike-like peaks and the spike-like
valleys in the amplification-resultant signal SPPX. In this way,
the limiter 101 and the LPF 104 process the amplification-resultant
signal SPPX into the LPF-resultant signal SL which has a waveform
such as shown in FIG. 7.
[0073] The 1/X-fold amplifier 35 receives the LPF-resultant signal
SL from the wobble signal extractor 22. The 1/X-fold amplifier 35
amplifies the LPF-resultant signal SL at a gain corresponding to a
factor of 1/X. The gain of the 1/X-fold amplifier 35 is inverse or
reciprocal with respect to that of the X-fold amplifier 33.
Therefore, the 1/X-fold amplifier 35 retrieves the original signal
amplitude which occurs at the circuit stage immediately preceding
the X-fold amplifier 33. The 1/X-fold amplifier 35 outputs the
amplification-resultant signal SLL to the pre-pit signal decoder
13. The amplification-resultant signal SLL has a waveform such as
shown in FIG. 7. The amplification-resultant signal SLL is equal to
the auxiliary-information signal SPP in wobble-signal amplitude.
The amplification-resultant signal SLL is in phase with the
auxiliary-information signal SPP.
[0074] The peak hold circuit 34 in the pre-pit signal decoder 13
samples and holds every peak of the output signal SLL of the
1/X-fold amplifier 35. The peak hold circuit 34 outputs the signal
Sph representative of the sampled and held peak to the
threshold-value setting device 24 in the pre-pit signal decoder 13.
The output signal Sph of the peak hold circuit 34 has a waveform
such as shown in FIG. 7.
[0075] It should be noted that the peak hold circuit 34 may be
omitted. In this case, the amplification-resultant signal SLL is
directly applied from the 1/X-fold amplifier 35 to the
threshold-value setting device 24.
[0076] In the pre-pit signal decoder 13, the threshold-value
setting device 24 receives the output signal of the D/A converter
23 which represents the DC level set by the CPU 16. The
threshold-value setting device 24 adds the DC-level signal and the
output signal Sph of the peak hold circuit 34 to generate the
threshold-value signal (the addition-resultant signal) Sref having
a waveform such as shown in FIG. 7. The threshold-value setting
device 24 outputs the threshold-value signal Sref to the comparator
25.
[0077] In the pre-pit signal decoder 13, the device 25 compares the
auxiliary-information signal SPP and the threshold-value signal
Sref, thereby converting the auxiliary-information signal SPP into
the pre-pit detection signal SPDT which has a waveform such as
shown in FIG. 7. Generally, the pre-pit detection signal SPDT is
effective when the threshold-value signal Sref is in a preferable
voltage range between specified levels Sref1 and Sref2 (see FIG.
7).
[0078] The wobble signal extractor 22 will be further explained
below. The switch 103 in the wobble signal extractor 22 selects one
from the LPF-resultant signal SL and the HPF-resultant signal SB in
response to the control signal fed from the CPU 16. The switch 103
outputs the selected signal to the phase adjuster 102a. Setting as
to which of the LPF-resultant signal SL and the HPF-resultant
signal SB should be selected by the switch 103 is performed during
the manufacture of the optical disc 1. The setting may be performed
in accordance with the type of the optical disc 1 and the recording
conditions when the optical disc 1 is inserted into the apparatus
S. Alternatively, the setting may be performed as follows. The
quality of a reproduced wobble signal is evaluated in each of the
first case where the LPF-resultant signal SL is selected and the
second case where the HPF-resultant signal SB is selected. The
setting is performed in accordance with the better quality of the
reproduced wobble signal.
[0079] The device 102a adjusts the phase of the output signal of
the switch 103 in response to the phase adjustment data PAD fed
from the CPU 16. The phase adjuster 102a outputs the
adjustment-resultant signal SSW to the lower level shift circuit
109 and the upper level shift circuit 110. The phase adjustment by
the phase adjuster 102a is set in accordance with which of the
LPF-resultant signal SL and the HPF-resultant signal SB is selected
by the switch 103, and also in accordance with the signal delays
caused by the LPF 104, the HPF 105, the switch 103, the lower level
shift circuit 109, and the upper level shift circuit 110. The
setting of the phase adjustment by the phase adjuster 102a is
performed during the manufacture of the optical disc 1. The setting
may be performed in accordance with the type of the optical disc 1
and the recording conditions when the optical disc 1 is inserted
into the apparatus S. Alternatively, the setting may be performed
as follows. The quality of a reproduced wobble signal is evaluated
while the phase adjustment data PAD are varied, that is, while the
phase adjustment by the phase adjuster 102a is varied. The setting
is performed in accordance with the best quality of the reproduced
wobble signal.
[0080] The lower level shift circuit 109 generates the lower
limiting signal SWL in response to the output signal SSW of the
phase adjuster 102a. The lower level shift circuit 109 outputs the
lower limiting signal SWL to the limiter 101. The upper level shift
circuit 110 generates the upper limiting signal SUL in response to
the output signal SSW of the phase adjuster 102a. The upper level
shift circuit 110 outputs the upper limiting signal SUL to the
limiter 101. The lower limiting signal SWL and the upper limiting
signal SUL can be set by the setting signal SSL fed from the CPU
16. The setting of the lower limiting signal SWL and the upper
limiting signal SUL may be performed during the manufacture of the
optical disc 1. The setting may be performed in accordance with the
type of the optical disc 1 and the recording conditions when the
optical disc 1 is inserted into the apparatus S. Alternatively, the
setting may be performed as follows. The quality of a reproduced
wobble signal is evaluated while the lower limiting signal SWL and
the upper limiting signal SUL are varied. The setting is performed
in accordance with the best quality of the reproduced wobble
signal.
[0081] The device 101 limits the amplitude of the output signal
SPPX of the X-fold amplifier 33 to within a range whose lower and
upper limits are determined by the lower and upper limiting signals
SWL and SUL respectively. Specifically, the limiter 101 slices off
spike-like peaks (pre-pit signals) from the output signal SPPX of
the X-fold amplifier 33. The limiter 101 outputs the
limiting-resultant signal LL to the low pass filter 104.
[0082] As understood from the previous explanation, the lower and
upper limiting signals SWL and SUL are generated on the basis of
the LPF-resultant signal SL or the HPF-resultant signal SB. The
LPF-resultant signal SL and the HPF-resultant signal SB occur at
the circuit stages following the LPF 104 which attenuates
spike-like peaks and spike-like valleys being noise with respect to
a true wobble signal. Therefore, the lower and upper limiting
signals SWL and SUL accurately correspond to the true wobble
signal. In other words, the lower and upper limiting signals SWL
and SUL accurately follow the true wobble signal. Accordingly, the
limiter 101 effectively slices off spike-like peaks (pre-pit
signals) from the output signal SPPX of the X-fold amplifier
33.
[0083] Second Embodiment
[0084] A second embodiment of this invention is a modification of
the first embodiment thereof. The second embodiment of this
invention is designed to handle a recording medium different from a
DVD-R and a DVD-RW. The recording medium is formed with a track
having a wobble representative of auxiliary information for the
control of the recording of main information thereon. The recording
medium is of, for example, a tape-like shape.
* * * * *