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Claims  |
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What is claimed as new and desired to be secured by Letters Patent of the
United States is:
1. An information record and playback apparatus configured to perform at
least one of a recording operation and a playback operation of an optical
disk,
said optical disk being provided with data recording tracks having a
surface wobbled at a predetermined frequency and a plurality of prepits
formed on said surface with a predetermined phase relation to a position
for data recording,
said apparatus comprising:
a prepit signal generation unit configured to detect said prepits when the
apparatus is performing said at least one of a recording operation and a
playback operation, and generate and output prepit signals in response to
detecting said prepits;
a data decoding circuit configured to receive and decode said prepit
signals and extract decoded information data therefrom;
a data error detection unit configured to receive said information data and
compare a pattern of said information data to a pattern of predetermined
data and output said decoded information data with a predetermined error
flag if said patterns are not in coincidence with each other; and
a data error correction unit configured to receive said error flag and
compute a position of an error on a basis of said error flag and provide
error correction to said decoded information data.
2. The information record and playback apparatus according to claim 1,
wherein,
said data error correction unit is configured to carry out erasure
correction with a Reed-Solomon code prior to error correction of said
decoded information data.
3. The information record and playback apparatus according to claim 1,
wherein,
said data error correction unit is configured to carry out a detection of a
position, and a correction, of error data bits using only data bits
decoded by said data decoding unit if a number of error flags added by
said data error detection unit exceeds a predetermined number.
4. An information record and playback apparatus configured to perform at
least one of a recording operation and a playback operation of an optical
disk,
said optical disk being provided with data recording tracks having a
surface wobbled to indicate information data by phase inversion according
to a dual phase modulation method,
comprising:
a wobbling signal generation unit configured to detect wobbling components
previously recorded on said data recording tracks and generate wobbling
signals;
a data decoding unit configured to receive said wobbling signals and to
phase-demodulate the wobbling signals and extract decoded information data
therefrom;
a data error detection unit configured to receive said decoded information
and to integrate said decoded information data for patterns thereof,
compare a data pattern of said decoded information data with a
predetermined value to obtain a comparison result, detect an error for
said data pattern on a basis of said comparison result, and output said
data pattern as well as a predetermined error flag; and
a data error correction unit configured to compute a position of said error
on a basis of said error flag and provide error correction to said decoded
information data.
5. The information record and playback apparatus according to claim 4,
wherein,
said data error correction unit is configured to carry out inversion
processing of said decoded information data when said decoded information
data form a predetermined data pattern such that an integration value of
said data pattern reaches one of a maximum value and a minimum value,
and said error correction unit outputs said data pattern added with a
predetermined error flag if a resultant integration value of said data
pattern is obtained between said maximum and minimum values.
6. The information record and playback apparatus according to claim 4,
wherein,
said data error correction unit is configured to carry out erasure
correction with a Reed-Solomon code prior to error correction of said
decoded information data.
7. The information record and playback apparatus according to claim 4,
wherein,
said data error correction unit is configured to carry out a detection of a
position, and a correction, of error data bits using only data bits
decoded by said data decoding unit if a number of error flags added by
said data error detection unit exceeds a predetermined number.
8. An information record and playback apparatus configured to perform at
least one of a recording operation and a playback operation of an optical
disk, said optical disk being provided with data recording tracks and
having a surface wobbled at a predetermined frequency and a plurality of
prepits formed on said surface with a predetermined phase relation to a
position for data recording,
comprising:
prepit signal generation means for detecting said prepits and generating
and outputting prepit signals;
data decoding means for decoding said prepit signals and extracting decoded
information data;
data error detecting means for comparing a pattern of said information data
to that of a predetermined data, and outputting said decoded information
data added with a predetermined error flag, if both of said patterns are
not in coincidence each other; and
data error correcting means for computing a position of an error on a basis
of said error flag and providing error correction to said decoded
information data.
9. The information record and playback apparatus according to claim 8,
wherein,
said data error correcting means is configured to carry out erasure
correction with a Reed-Solomon code prior to error correction of said
decoded information data.
10. The information record and playback apparatus according to claim 8,
wherein,
said data error correcting means is configured to carry out a detection of
a position, and
a correction, of error data bits using only data bits decoded by said data
decoding means if a number of error flags added by said data error
detection means, exceeds a predetermined number.
11. An information record and playback apparatus configured to perform at
least one of a recording operation and a playback operation of an optical
disk,
said optical disk being provided with data recording tracks having a
surface wobbled to indicate information data by phase inversion according
to a dual phase modulation method,
comprising:
wobbling signal generating means for detecting wobbling components
previously recorded on said data recording tracks and generating wobbling
signals;
data decoding means for phase-demodulating said wobbling signals and
extracting decoded information data;
data error detecting means for integrating said decoded in formation data
for each of a number of patters thereof, comparing a data pattern of said
decoded information data with a predetermined value to obtain a comparison
result, detecting an error for said data pattern on a basis of said
comparison result, and outputting said data pattern added with a
predetermined error flag; and
data error correcting unit for computing a position of said error on a
basis of said error flag and providing error correction to said decoded
information data.
12. The information record and playback apparatus according to claim 11,
wherein,
said data error correcting means is configured to carry out inversion
processing of said decoded information data when said decoded information
data form a predetermined data pattern such that an integration value of
said data pattern reaches one of a maximum value and a minimum value,
and said data error correcting means outputs said data pattern added with a
predetermined error flag if a resultant integration value of said data
pattern is obtained between said maximum and minimum values.
13. The information record and playback apparatus according to claim 11,
wherein,
said data error correcting means is configured to carry out erasure
correction with a Reed-Solomon code prior to error correction of said
decoded information data.
14. The information record and playback apparatus according to claim 11,
wherein,
said data error correcting means is configured to carry out a detection of
a position, and a correction, of error data bits using only data bits
demodulated by said data decoding means if a number of error flags added
by said data error detection unit exceeds a predetermined number.
15. A method of carrying out at least one of a recording operation and a
playback operation of an optical disk provided with data recording tracks
having a surface wobbled at a predetermined frequency and a plurality of
prepits formed on said surface with a predetermined phase relation to a
position for data recording,
said method comprising:
detecting said prepits when performing said at least one of a recording
operation and a playback operation, and generating and outputting prepit
signals in response to detecting said prepits;
decoding said prepit signals and extracting decoded information data
therefrom;
receiving said decoded information data and comparing a pattern of said
information data to a pattern of predetermined data and outputting said
decoded information data with a predetermined error flag if said patterns
are not in coincidence with each other; and
receiving said error flag and computing a position of an error on a basis
of said error flag and providing error correction to said decoded
information data. |
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Claims |
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Description |
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BACKGROUND
1. Field
This patent specification relates to an information record and playback
apparatus in use for information recording media such as optical disks,
magneto-optical disks and other similar media, and more particularly, to a
demodulation circuit in such apparatus configured to carry out address
demodulation.
2. Discussion of the Background
In data recording media such as optical disks, for example, it has been
known to provide data prefabricated on the disk and include address
information utilized for specifying the position for recording data, and
information such as synchronization signals and wobbling signals for
controlling the disk rotation, and other similar data.
As optical recording media capable of additionally writing (or recording)
information data on the basis of these pre-data, also known previously are
CD-recordable (CD-R) disks which have the approximately same storage
capacity as compact disks (CDs).
The pre-data are in general prepared by forming in advance recording tracks
such as grooves and lands for recording information data, in which the
pre-data to be recorded are first frequency modulated (FM) to obtains FM
signals. Subsequently, the pre-data to be recorded are incorporated into
the disk by forming recording tracks to have a wobbling surface with the
wobbling frequency corresponding to the FM signal frequency.
In order to additionally record information data into the CD-R disks, a
playback apparatus detects wobbling signals from the wobbling pattern on
the disk to obtain a wobbling frequency, then extracts standard clock
signals for controlling the disk rotation on the basis of the wobbling
frequency. In addition, the apparatus generates necessary drive signals
for controlling the rotation of a spindle motor in use for the CD-R disk
rotation, then generates recording clock signals including timing signals
in synchronous with the CD-R disk rotation.
Also in the CD-R disks, address information on the disks needed for
information data recording is obtained by first playing back the pre-data
during the data recording and subsequently detecting the position to
record on the basis of the pre-data, to thereby be able to achieve the
recording.
High density recording media have also been put into practical use
recently, such as digital video disks or digital versatile disks (DVDs),
which has an increased storage capacity over the previous CDs.
Among the higher density storage media exemplified by the DVDs, information
data tracks (e.g., grooved tracks) are formed, having the aforementioned
wobbling surface on the basis of the frequency corresponding to standard
clock signals. This method is used in optical recording media such as
write once type DVD recordable (DVD-R) and DVD Rewritable (DVD+RW) media.
Regarding error correction for the pre-data recorded into the DVD-R and
DVD+RW disks, it is necessary to add a plurality of data to be utilized in
the error correction, since the position and pattern of an error have to
be computed. The error correction data are typically exemplified by the
Reed-Solomon code which has been in use for not only DVD disks but also
CDs and digital audio tapes (DATs).
As the data to be added for the error correction using the Reed-Solomon
code, parity words consisting of at least 2t words are necessary for
correcting an error of t words.
For example, for land prepit data (which is hereinafter referred to as
`LPP`), a parity word consisting of three words is added to an address
information data of three words, and one oneword error in the address
information can be corrected. In contrast, for the case of address data in
pre-groove (which is hereinafter referred to as `ADIP`), a five-words
parity word is added to an eight-words address multiplex (MUX) information
data, and one two-words error in the address MUX information can be
corrected.
As described above, in error correction steps for the address data played
back from the DVD type disks, there have previously persisted drawbacks
such as low efficiency in the error correction, for example, in which the
number of words which is successfully corrected is relatively small
compared with the number of added parity words.
SUMMARY
Accordingly, it is an object of the present disclosure to provide an
information record and playback apparatus, having most, if not all, of the
advantages and features of similar employed apparatuses, while eliminating
many of the aforementioned disadvantages.
It is another object of the present disclosure to provide an information
record and playback apparatus which is capable of achieving improved
efficiency in error correction for DVD type optical disks.
The following brief description is a synopsis of only selected features and
attributes of the present disclosure. A more complete description thereof
is found below in the section entitled "Description of the Preferred
Embodiments"
An information record and playback apparatus disclosed herein is configured
to perform record and playback operations of an optical disk which is
provided with data recording tracks having the surface wobbled at a
predetermined frequency and a plurality of prepits formed on the surface
with a predetermined phase relation to the position for data recording.
The apparatus includes a preset signal generation unit configured to detect
the prepits, and generate and output prepit signals; a data decoding
circuit configured to decode the prepit signals, and extract decoded
information data; a data error detection unit configured to compare the
pattern of information data to that of a predetermined data, and output
the decoded information data added with a predetermined error flag, if
both of the patterns are not in coincidence each other; and a data error
correction unit configured to compute the position of an error on the
basis of the error flag and provide error correction to the decoded
information data.
The data error correction unit is configured to carry out erasure
correction with the Reed-Solomon code prior to error correction of the
decoded information data. In addition, the data error correction unit
carries out the detection of the position of, and the correction of, error
data bits using only data bits demodulated by the data demodulation unit
if a number of error flags that is added by the data error detection unit
exceeds a predetermined number.
In another aspect disclosed herein, an information record and playback
apparatus is configured to perform record and playback operations of an
optical disk which is provided with data recording tracks having the
surface wobbled so as to be capable of indicating information data by
phase inversion according to the dual phase modulation method.
The apparatus includes a wobbling signal generation unit configured to
detect wobbling components previously recorded on the data recording track
and generate wobbling signals; a data decoding unit configured to
phase-demodulate the wobbling signals and extract decoded information
data; a data error detection unit configured to integrate the decoded
information data for each pattern of the data, compare a data pattern of
the decoded information data with a predetermined value to obtain a
comparison result, detect an error for the data pattern on the basis of
the comparison result, and output the data pattern added with a
predetermined error flag; and a data error correction unit configured to
compute the position of the error on the basis of an error flag to
subsequently provide error correction to the decoded information data.
The data error correction unit is configured to carry out inversion
processing of the decoded information data when the decoded information
data form a predetermined data pattern, such that the integration value of
data pattern reaches either a maximum value or a minimum value, and output
the data pattern added with a predetermined error flag if a resultant
integration value of the data pattern is obtained between the maximum and
minimum values.
In addition, the data error correction unit is configured to carry out
erasure correction with the Reed-Solomon code prior to error correction of
the decoded information data. Further, the data error correction unit is
configured to carry out the detection of the position of, and the
correction of error data bits using only data bits demodulated by the data
demodulation unit if a number of error flags that is added by the data
error detection unit exceeds a predetermined number.
The present disclosure and features and advantages thereof will be more
readily apparent from the following detailed description and appended
claims when taken with drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an information record and play back
apparatus according to one embodiment disclosed herein;
FIG. 2 is a perspective view illustrating the structure of the DVD-R disk
of FIG. 1;
FIG. 3A is a diagram illustrating the portions related to prepit signals in
the format for recording pre-data and disk rotation control signals;
FIG. 3B is a diagrams illustrating the entire portion of the format for
recording pre-data and disk rotation control signals;
FIG. 4 includes charts illustrating the position of prepit signals with
respect to wobbling signals disclosed herein;
FIG. 5 contains the table illustrating the results obtained by decoding
prepit signals;
FIG. 6 is a block diagram of the major parts of the demodulation circuit 19
of FIG. 1;
FIG. 7 is a block diagram of the major parts of the LPP detector of FIG. 6;
FIG. 8 includes charts illustrating the waveform generated by respective
parts of the LPP detector of FIG. 7;
FIG. 9 is a block diagram of the major parts of the LPP decoder of FIG. 6;
FIG. 10 contains the table illustrating truth values in the pattern
detector of FIG. 9;
FIGS. 11 and 12 constitutes a flow chart illustrating process steps with an
LPP error detection and correction circuit of FIG. 6;
FIG. 13 is a block diagram illustrating an information record and play back
apparatus according to another embodiment disclosed herein;
FIG. 14 is a block diagram of the major parts of the demodulation circuit
of FIG. 13;
FIG. 15 is a block diagram of the major parts of the PM demodulation
circuit of FIG. 14;
FIGS. 16A and 16B include timing charts illustrating the waveform generated
in respective parts of the PM demodulation circuit of FIG. 15;
FIG. 17 is a block diagram of the major parts of the ADIP decoder of FIG.
14; and
FIGS. 18 and 19 a flow chart illustrating process steps with an ADIP error
detection and correction circuit of FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the detailed description which follows, specific embodiments of the
apparatus and method are described, which are particularly useful for
record and playback in use for information data using optical disks. It is
understood, however, that the present disclosure is not limited to these
embodiments. For example, the modulation and demodulation apparatus
disclosed herein may also be adaptable to any form of information
recording and playing back. Other embodiments will be apparent to those
skilled in the art upon reading the following description.
FIG. 1 is a block diagram illustrating an information record and playback
apparatus according to one embodiment disclosed herein.
Referring to FIG. 1, the record and playback apparatus 10 includes at least
one microcomputer provided with CPU, ROM, RAM and other similar devices,
which is configured to be capable of detecting prepit signals that are
utilized in recording digital information data transmitted from a host
computer into a DVD-R disk 1 which serves as a data recording medium. The
term `prepits` refers herein to the pits prefabricated on the disk in
order to achieve several purposes detailed herein below such as, for
example, controlling the disk rotation.
In addition to the prepits pertaining address information, prefabricated in
the DVD-R disk 1 are grooved tracks having a wobbling surface. In the
record and playback apparatus 10, recording digital information data into
a DVD-R disk 1 is carried out into the recording position which is
specified by an address signal on the basis of prepits obtained during
recording steps.
Referring to FIG. 2, the structure of the DVD-R disk 1 will be described.
The DVD-R disk 1 disclosed herein is a dye-coated write-once type optical
recording disk provided with a dye layer 5. This disk is further provided
with grooved tracks 2 which serve as data tracks, and land tracks 3 which
are adjacent to the grooved tracks 2 and utilized for guiding a light beam
B. The light beam B such as, for example, a laser beam is utilized in
recording and playing back information data.
A plurality of the prepits 4 are provided on the land tracks 3
corresponding to preset information data (which is hereinafter referred to
as `pre-data`) and they are prefabricated during optical disk formation.
In addition, the DVD-R disk 1 is further provided with an evaporated layer
of metal 6 to reflect the light beam B during the playback steps of
recorded information data, and a protective layer 7 to serve for
protecting the grooved track 2, land track 3, prepits 4, and dye layer 5.
Along with the thus described construction, the record and playback
apparatus 10 is configured to record into DVD-R disk 1 several information
data to be recorded presently such as image data in addition to the above
described pre-data and control data for the disk rotation.
Namely, the apparatus 10 operates to control the velocity of rotation of
DVD-R disk 1 so as to be at predetermined values with respect to the
frequencies obtained from the wobbling of the grooved track 2, and to
acquire preset disk drive data detected from the detected prepits 4.
Based on the data obtained from the detected prepits 4, the apparatus 10
also operates to adjust the light beam B to have optimum output
intensities and acquire addressing information regarding the address of
the position on the disk to subsequently carry out data recording into the
proper position determined for the present recording.
During data recording with the record and playback apparatus 10, the data
recording is achieved by forming each information data bits by irradiating
the light beam B such that the center of the beam is coincident with that
of the grooved track 2. In addition, the size SP of the beam spot is
adjusted during the irradiation so as to cover portions of the neighboring
land tracks 3 as well as the grooved track 2.
The acquisition of the pre-data by the record and playback apparatus 10 is
carried out through detecting the prepits 4 using a portion of the
reflected light from the beam spot SP irradiated on the land tracks 3 by
either the push-pull method or a modified push-pull method. The latter
utilizes a split light detector divided along the line running parallel to
the direction of the DVD-R disk rotation, which is hereinafter referred to
as `radial push-pull method`.
At the same instance, the record and playback apparatus 10 also detects
wobbling signals from the grooved track 2 to subsequently acquire clock
signals for controlling the disk rotation.
Referring now to FIGS. 3A and 3B, formats for recording the pre-data and
disk rotation control signals will be detailed, Among the signals played
back from recorded information data, the portion related to the prepit
signals are shown in FIG. 3A, while the entire portion of these signals
are shown in FIG. 3B.
As illustrated in FIGS. 3A and 3B, the wave pattern of the wobbling signals
is formed as the reflection of wobbling pattern prefabricated on the
grooved track 2. Also, information data recorded on the DVD-R disk 1 are
formed being subdivided beforehand into synch frame units, each of which
serves as a data recording unit. One recording sector has twenty-six synch
frames and sixteen recording sectors form one error correcting code (ECC).
Incidentally, each synch frame has a length of 1488T, with the parameter T
being the unit which is defined on the basis of the bit interval dictated
in the recording format utilized in data recording.
The groove track 2 is provided with the wobbling pattern which is formed
over respective synch frames with a constant wobbling frequency f0 of 141
kHz (where one synch frame corresponds to eight wobbling periods). By
detecting the thus provided constant wobbling frequency f0, the apparatus
10 acquires necessary signals for controlling the rotation of a spindle
motor.
In contrast, the aforementioned pre-data on the DVD-R disk 1 are recorded
for every synch frame. In recording the pre-data by means of prepits 4,
one of them is always formed as a synchronization signal in the portion of
the land track 3 adjacent to the region into which the synchronization
signal for each synch frame is to be recorded.
At the same time, additional one or two prepits 4 are formed as the signals
indicative of pre-data (such as address data) into the portion of the land
track 3 adjacent to the region which precedes the above portion for the
synchronization signal for each synch frame to be recorded.
It is noted that, in some instances, none of the pre-bits 4 may be formed
in the preceding portion of the synch frame depending on the content of
the present pre-data. Also, in a certain recording sector, the pre-data
may be recorded with prepits 4 formed only in either even-numbered or
odd-numbered synch frame, which are hereinafter referred to as EVEN- or
ODD-frame, respectively.
Played back signals from the thus formed prepits 4 are superimposed on
wobbling signals, as illustrated in FIGS. 3A and 3B, and prepit signals
generally appear in EVEN synch frames. When a plurality of the prepits 4
are formed adjacent to each other, a cross talk may result among the
prepit signals. In such a case, prepits 4 may be formed in an ODD-frame
for proper prepit signals to be obtained, as shown with a dotted circle in
FIG. 3B. To the contrary, prepits 4 may be transferred from an ODD-frame
to EVEN-frame in some other cases.
In addition, as shown in FIG. 3A, prepit signals appear at three positions
b0, b1 and b2 among the first eight cycles of the wobbling signal.
The features of the prepit signals b0, b1 and b2 will be detailed herein
below, referring to FIG. 4, in which triangles and squares indicate the
positions where prepit signals appear for the ODD and EVEN synch frames,
respectively.
There shown respectively from the top in FIG. 4 are the position and form
of wobbling and prepit signals (signal position and form 1, or SPF 1),
prepit signals with respect to the wobbling signals (SPF 2), marks
dividing each of eight cycles of the wobbling (SPF 3), prepit signals
appearing in case without signal transfer between EVEN and ODD synch
frames (SPF 4), and with the signal transfer (SPF 5).
As illustrated by SPFs 2 and 3 in FIG. 4, prepit signals in each synch
frame appear in the first three, but not the following five, positions
among the first eight cycles of the wobbling signal. Also, as illustrated
by SPFs 4 and 5 in FIG. 4, the prepit signal at b0 appears in each synch
frame. Therefore, this prepit signal is formed to represent always the
value `1` and serve as a synch bit to be used in synchronization of
detected prepit signals.
In addition, the prepit signal at the position b1 appears only in the first
synch frame and the value of this signal is always `1`. When no prepit
signal appears at b1, the prepit signal at the next b2 is regarded as to
represent address data. In contrast, when a prepit signal appears at b1,
the prepit signal at b2 serves to distinguish between EVEN and ODD synch
frames.
Namely, as illustrated by SPFs 4 and 5 in FIG. 4, when prepits appear at
both b1 and b2, they are regarded as being in the first frame of the EVEN
synch frame. In contrast, when a prepit appears at b1 with no prepit at
b2, it is regarded as being in the first frame of the ODD synch frame.
In addition, when no prepit signal appears at b1, the value for data are
indicated by the next prepit signal, in which the values are set to be `1`
and `0` for the cases with and without prepit signal at b2, respectively.
For example, there are shown by SPFs 4 and 5 in FIG. 4, that the data of
BIT 1 and BIT 2 are `1` and `0`, respectively.
Therefore, each sector consists of one leading synch frame (which is
indicated as `LPP synch` in SPF 5 of FIG. 4 and a plurality of BIT 1
through BIT 12, which serve as data synch frames. Several information data
such as SYNCH information and data information may be obtained through
decoding prepit signals, and the results from decoding prepit signals are
illustrated in the table included in FIG. 5.
Referring again to FIG. 1, there detailed is the construction of the
information record and playback apparatus 10 disclosed herein.
Digital information S.sub.rr to be recorded is input from an external host
computer into the record and playback apparatus 10 by way of an interface
18.
A pickup unit 11 includes a laser diode, deflecting light beam splitter,
objective lens and photo-detector. The pickup unit 11 operates the laser
beam B be irradiated onto a recording layer of the DVD-R disk 1. A portion
of the laser beam B is reflected from the recording layer and subsequently
utilized in detecting signals from prepits 4 and wobbling pattern on the
grooved tracks 2 by means of the aforementioned radial push-pull method.
With thus obtained signals, the recording of the digital information
S.sub.rr can be achieved. In addition, when any digital information
recorded previously is found, the pickup unit 11 detects the information
using the laser beam B.
A playback amplifier 12, which is also included in the apparatus 10, serves
to amplify several signals such as prepits 4 output from the pickup unit
11, and detected signals Sdt, which contain information data corresponding
to wobbling signals from the grooved tracks 2.
The playback amplifier 12 then outputs pre-information signals Spp
corresponding to the prepits signals and wobbling signals, together with
amplification signals Sp corresponding to the previously recorded digital
information.
A decoder 13 serves to decode the amplification signals Sp through the
application of the eight-sixteen demodulation and interleave processing
steps, and subsequently output demodulated signals Sdm to a CPM 14.
Under the control of the CPM 14, an interface 18 carries out, interfacing
process steps for the digital information S.sub.rr, which is transferred
from the host computer to be input into the record and playback apparatus
10. The interface 18 subsequently outputs the above interfaced digital
information S.sub.rr to an encoder 15 by way of the CPM 14.
The encoder 15 carries out several processing steps such as
error-correcting code (ECC) generation, eight-sixteen demodulation and
scrambling, to subsequently generate modulated signals Sre to be output to
a power control circuit 16.
The power control circuit 16 carries out waveform transformation of the
modulated signals S.sub.re to improve the shape of recorded bits to be
formed on the DVD-R disk 1, that is so called right strategy processing.
Resultant signals are output as recording signals Sd to be used for
driving a laser diode in the pickup 11.
Based on the thus prepared recording signals Sd, a laser driving circuit 17
operates to output laser driving signals Sd1 for actually carrying out the
driving the laser diode and emitting the laser beam B.
On the other hand, a demodulation circuit 19 serves to demodulate the
pre-data signals S.sub.pp fed from the playback amplifier 12 to
subsequently obtain pre-data decoded signals Spj. The pre-data decoded
signals Spj are then output to the CPU 14.
Based on the pre-data decoded signals Spj output by the demodulation
circuit 19, the CPU 14 acquires pre-data and serves to control digital
information S.sub.rr to be recorded at proper positions on the DVD-R disk
1 corresponding to address data contained in the pre-data decoded signals
Spj.
At the same time, on the basis of the demodulated signals Sdm, the CPU 14
outputs played back signals corresponding to the previously recorded
digital information by way of the interface 18 toward the exterior of the
apparatus 10, and also assumes overall control of the record and playback
apparatus 10.
Incidentally, the aforementioned rotation control signals for the DVD-R
disk 1 are supplied to the spindle motor via a spindle driver.
FIG. 6 is a block diagram of the major parts of the demodulation circuit 19
of FIG. 1.
Referring to FIG. 6, the demodulation circuit 19 includes an LPP detector
31, LPP decoder 32, LPP error detection and correction circuit 33,
phase-locked loop (PLL) circuit 34, and timing signal generation circuit
35.
Into the LPP detector 31 and PLL circuit 34, pre-data signals S.sub.pp are
input from the playback amplifier 12. In addition, the PLL detection
circuit 34 is supplied with clock signals CLK from the exterior of the
apparatus 10, then extracts another set of clock signals WBCLK which are
in synchronous with one cycle of the wobbling signal, and subsequently
output the clock signals WBCLK to the timing signal generation circuit 35.
On the basis of the input clock signals WBCLK, the timing signal generation
circuit 35 generates and then outputs predetermined control signals to be
fed to the LPP decoder 32 and LPP error detection and correction circuit
33.
The LPP detector 31 detects LPP pulses from the input pre-data signals
S.sub.pp to output to the LPP decoder 32.
The LPP decoder 32 detects the pattern of the LPP pulse series output by
the LPP detector 31, generates LPP data bits and error flags F, both of
which are to be latched serially with time by a shift register, and
outputs the LPP data words and error flags Fw corresponding thereto.
The LPP error detection and correction circuit 33 carries out erasure
correction of the Reed-Solomon codes using the LPP data words and error
flags Fw output from LPP decoder 32, and output resultant pre-data decoded
signals S.sub.pj.
FIG. 7 is a block diagram of the major parts of the LPP detector 31 of FIG.
6, and FIG. 8 includes timing charts illustrating the waveform generated
by respective parts of the LPP detector 31 of FIG. 7.
Referring to FIGS. 7 and 8, operation steps in the LPP detector 31 will be
detailed.
As shown in FIG. 7, the LPP detector 31 includes an LPP detection
comparator 41, zero cross comparator 42, leading edge detection circuit
43, and RS flip-flop 44.
The LPP detector 41 is configured to extract only prepit signals from the
input pre-data signals S.sub.pp and input to the set terminal S of the RS
flip-flop 44.
The zero cross comparator 42 detects zero cross points of the wobbling
signals included in the input pre-data signals S.sub.pp and transforms the
wobbling signals into corresponding square wave forms to subsequently
output.
The leading edge detection circuit 43 detects leading edges of input square
waves, generates pulses corresponding thereto, to subsequently input to
the reset input terminal R of the RS flip-flop 44.
Based on these signals input into the S and R input terminals, the RS
flip-flop 44 generates LPP pulses illustrated in FIG. 8, which are
subsequently output to the LPP decoder 32 of FIG. 6.
FIG. 9 is a block diagram of the major parts of the LPP decoder 32 of FIG.
6.
Referring to FIG. 9, the LPP decoder 32 includes a first shift register 51,
second shift register 52, third shift register 53, pattern detector 54,
AND circuit 55, and OR circuit 56.
The first shift register 51 stores the data which indicate either presence
or absence of the LPP pulses output from the RS flip-flop 44 with respect
to the clock signals WBCLK input from the timing signal generation circuit
35 of FIG. 6.
A series of the thus stored data R0.about.R4 are subsequently output to the
pattern detector 54 which, in turn, outputs several data such as a word
synch, bit synch, LPP data bit, and bit error such as shown in the table
included in FIG. 10.
Incidentally, in the truth-table included in FIG. 10, it is shown that the
datum R2 represents the aforementioned prepit signal appeared at b0
position shown in FIG. 3. Similarly, the data R1 and R0 represent the
prepit signals at b1 and b2 positions in FIG. 3, respectively.
The pattern detector 54 respectively outputs the word synch data to the
timing signal generation circuit 35 of FIG. 6, bit synch data to one of
input terminals of the AND circuit 55, LPP data bit to the second shift
register 52, and bit error data to the third shift register 53.
To the other input terminal of the AND circuit 55, an LPP detected position
signal is input, which is obtained from the word synch after counting for
a predetermined period of time and used to specify the position of the bit
synch. In addition, it is shown that a `high` LPP detected position signal
corresponds to the bit synch position.
The second and third shift registers 52 and 53 are each provided with
enabling capability, and become enabled when `high` signals are input to
respective enabling terminals EN thereof.
To the enabling terminals EN of respective shift registers 52 and 53,
signals are output from the AND circuit 55. Therefore, when the bit synch
data output from the pattern detector 54 and the LPP detected position
signals output from the timing signal generation circuit 35 are both
`high`, the second and third shift registers 52 and 53 are both rendered
enabled.
The second shift register 52 stores LPP data bits output from the pattern
detector 54 on the basis of the timing signals for sampling from the
timing signal generation circuit 35.
Since eight bits of the LPP data bit constitute one LPP word, the second
shift register 52 operates to output previously stored eight-bits LPP data
bits in the form of the LPP word to the LPP error detection and correction
circuit 33 of FIG. 6.
The third shift register 53, on the other hand, operates to store bit error
data output by the pattern detector 54 according to the sampling timing
signals output from the timing signal generation circuit 35 of FIG. 6.
In the third shift register 53, therefore, error bit data are stored so as
to correspond to respective LPP data bits stored in the second shift
register 52. The stored error bit data are subsequently input to
corresponding input terminals of the OR circuit 56.
The OR circuit 56 outputs a `high` error flag Fw to the LPP error detection
and correction circuit 33 of FIG. 6, when a `high` data is input to at
least one of input terminals.
The error flag Fw is thus designed to be indicated when even one bit in
error is detected out of eight bits of the LPP data.
The LPP error detection and correction circuit 33 carries out erasure
correction with the Reed-Solomon code using the input LPP data words and
error flags Fw.
There will be described hereinbelow error correction processing steps with
LPP error detection and correction circuit 33. Since the method of the
erasure correction with the Reed-Solomon code is well known, the following
description will be presented in a rather simple manner.
In the LPP data format for DVD-R system, parity words consisting of three
LPP data words are added to address information having three LPP data
words.
For the single-error case, in which one error datum is detected in the
input six data described above, an assumption is made, in that the error
is located at i (i=0, . . . , 5) having a pattern ei.
A plurality of syndromes S0.about.S2 are given by the equations (1) through
(3).
S0=ei (1)
S1=.alpha..sup.i.multidot.ei (2)
S2=.alpha..sup.2i.multidot.ei (3)
From (1) and (2) there obtained is the relation .alpha..sup.i =S1/S0, then
error position information is obtained as
I=log.sub..alpha. (S1/S0) (4).
The error correction is then carried out using the i and ei values, only
when i and ei (=S0) both satisfy the equation (3).
For the two-error data case, or double-error case, the position of the
errors at i and j (0.ltoreq.i<j.ltoreq.5) and their error patterns ei
and ej are assumed, respectively. Syndromes S0.about.S2 are then given by
the equations (5) through (7).
S0=ei+ej (5)
S1=.alpha..sup.i.multidot.ei+.alpha..sup.j.multidot.ej (6)
S2=.alpha..sup.2i.multidot.ei+.alpha..sup.2j.multidot.ej (7)
From (5) and (6), the equation (8) is obtained, which leads to (9)
.alpha..sup.j.multidot.S0+S1=(.alpha..sup.I | | |
