Note: Descriptions are shown in the official language in which they were submitted.
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OPTICAL DISK, OPTICAL DISK DEVICE, AND OPTICAL DISK
RECORDING METHOD FOR REDUCING JITTER
AT THE TIME OF REPRODUCTION
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to an optical disk, an
optical disk device, and an optical disk recording method. The
present invention is applied to, for example, a compact disk.
By correcting the timing of a modulation signal according to a
change pattern of a modulation signal, a jitter at the time of
reproduction is reduced and recorded data can be surely
reproduced.
Description of the Related Art:
In a conventional compact disk, data to be recorded
are subjected to data processing and thereafter subjected to an
EFM (Eight-to-Fourteen Modulation) modulation. For a
predetermined fundamental period T, a pit sequence having a
period in the range of 3T to 11T is thereby formed. Thereby,
audio data or the like, for example, are recorded.
Corresponding to this, a compact disk player
irradiates a laser beam on the compact disk and receives a
returned light therefrom. The compact disk player thus obtains
a reproduced signal having a signal level changed according to
the light quantity of the returned light, converts this
reproduced signal to a binary value by using a predetermined
slice level, and thus generates a binary signal. Furthermore,
the compact disk player drives a PLL circuit in response to this
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binary signal to generate a reproduction clock and latches
binary signals successively by using the reproduction clock.
Thereby, the compact disk player generates reproduced data
having a period in the range of 3T to 11T and corresponding to
the pit sequence formed on the compact disk.
The compact disk player conducts data processing
corresponding to the data processing conducted at the time of
recording, on the reproduced data thus generated. In this way,
the compact disk player reproduces audio data or the like
recorded on the compact disk.
By the way, in the conventional compact disk player,
a jitter is contained in the reproduced signal. It may be
considered that this jitter occurs by various causes such as a
noise of a laser beam used for readout, a thermal noise of an
electric system, a disk noise or the like. The jitter reduces
the phase margin of the reproduced signal. In an extreme case,
the jitter makes it difficult to reproduce data correctly.
However, this jitter is essentially due to an inter-
symbol interference caused by preceding and succeeding pits
(Shigeo Kubota, "Aplanatic condition required to reproduce
jitter-free signals in an optical digital disk system", App.
Optics 1987, Vol. 26, No. 18, pp. 3961-3970). The jitter
changes according to the land and pit located before and behind
the laser beam radiation position.
SUMMARY OF THE INVENTION
In view of the points heretofore described, the
present invention has been made. The present invention attempts
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to propose an optical disk, an optical disk device, and an
optical disk recording method capable of reducing a jitter
caused at the time of reproduction and reproducing surely the
recorded data.
In order to solve the above described problems, in an
optical device and an optical disk recording method according to
the present invention, the timing of a modulation signal is
corrected according to a change pattern of the modulation
signal.
Furthermore, in an optical disk, the position of an
.edge is changed from its fundamental position according to the
pit length and the land length located before and behind the
edge.
Furthermore, in an optical disk device and an optical
disk recording method, the timing at which a laser beam is
raised up to a light quantity for writing is corrected in an
interlinked relation to light quantity switching of the writing
operation.
Furthermore, in an optical disk, a high reflectance
area and a low reflectance area are formed dependent on a
difference in pit width. In order to correct a change of a
returned light caused by this difference in pit width, pits to
which the same data is assigned are formed so as to be different
in pit length.
By correcting a timing of the modulation signal, a
change caused in signal level at the time of reproduction can be
corrected. If this timing correction is executed on the basis
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of the change pattern of the modulation signal, a.reproduced
signal can be corrected so as to correct. an inter-symbol
interference changing according to this change pattern. As a
result, the jitter of the reproduced signal can be reduced.
So as to correspond to this in an optical disk, the
position of an edge is changed from a fundamental position
according to the pit length and the land length located before
and behind the edge to thereby form the pit. Whereby, the pit
shape is changed so as to correspond to the change pattern of
the modulation signal. As a result, a jitter caused by inter-
symbol interference can be avoided.
Furthermore, if the timing at which the laser beam is
raised up to the light quantity for writing is corrected in an
interlinked relation to light quantity switching of the writing
operation, asymmetry changed by light quantity switching can be
corrected.
So as to correspond to this, in an optical disk, a
high reflectance area and a low reflectance areas are formed
dependent on a difference in pit width. Thereby, characters or
the like can be recorded on the information recording surface so
as to be observable with eyes. If at this time pits to which
the same data is assigned are formed so as to be different in
pit length so as to correct a change of a returned light caused
by this difference in pit width, asymmetry differing in the high
reflectance area and the low reflectance area can be corrected.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an optical disk
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device according to a first embodiment of the present
invention.;
FIGS. 2A to 2E are each a signal waveform diagram
used for description of the operation of an edge position
correction circuit included in the optical disk device of FIG.
1;
FIG. 3 is a block diagram showing a rising edge
correction circuit included in the optical disk device of FIG.
1.;
FIG. 4 is a process diagram showing the production
process of a correction value table included in the optical disk
device of FIG. 1;
FIG. 5 is a flow chart showing the processing
procedure of a computer in the process of FIG. 4;
FIG. 6 is a block diagram showing an optical disk
device according to a second embodiment of the present
invention.;
FIG. 7 is a block diagram showing a character signal
generation circuit included in the optical disk device of FIG.
6;
FIG. 8 is a top view showing a compact disk produced
by the optical disk device of FIG. 6;
FIG. 9 is a signal waveform diagram showing a
reproduced signal of a portion of the compact disk using a light
quantity of 100%.;
FIG. 10 is a signal waveform diagram showing a
reproduced signal of a portion of the compact disk using a light
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quantity of 85%;
FIG. 11 is a signal waveform diagram showing a change
in slice level caused by a difference in light quantities; and
FIG. 12 is a signal waveform diagram showing a
reproduced signal obtained from the compact disk of FIG. 8, in
comparison with FIG. 11.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereafter, an optical disk, an optical disk device,
and an optical disk recording method according to embodiments of
the present invention will be described by suitably referring to
the accompanying drawings.
(1) First Embodiment
FIG. 1 is a block diagram showing an optical disk
device according to an embodiment of the present invention.
This optical disk device 1 records audio data D1 output from a
digital audio tape recorder 3 by exposing an original disk 2 to
a light. In a manufacturing process of an optical disk, this
original disk 2 is subjected to development, and then subjected
to electroforming processing. Thereby, a mother disk is
produced. From this mother disk, a stamper is produced.
Furthermore, in the optical disk manufacturing process, a disk-
like substrate is produced from the stamper thus produced. By
forming a reflective film and a protective film on this disk-
like substrate, a compact disk is produced.
That is, in this optical disk device 1, a spindle
motor 4 drives and rotates the original disk 2. From an FG
signal generator held at the bottom thereof, there is output an
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FG signal FG having a signal level which rises up at every
predetermined rotation angle. According to the exposure
position of the original disk 2, a spindle servo circuit 5
drives the spindle motor 4 so as to make the frequency of this
FG signal equivalent to a predetermined frequency. As a result,
the original disk 2 is driven so as to be rotated under the
condition of a constant linear velocity.
A recording laser 7 is formed by a gas laser or the
like, and emits a laser beam L for exposure of the original
disk. A light modulator 8 is formed of an electro-acousto-
,optical element and effects on-off control on the laser beam L
by using a modulation signal S1 to emits a resultant beam. A
mirror 10 bends the optical path of this laser beam L and emits
a resultant beam toward the original disk 2. An objective lens
11 focuses the light reflected by the mirror 10 on the original
disk 2. The mirror 10 and the objective lens 11 are
successively moved in the radial direction of the original disk
2 in synchronism with the rotation of the original disk 2 by a
sled mechanism which is not illustrated. As a result, the
position of exposure to the laser beam L is successively
displaced in the outer peripheral direction of the original disk
2.
In such a state that the original disk 2 is driven
and rotated in this optical disk device 1, a track is formed so
as to take a helical shape by the movement of the mirror 10 and
the objective lens 11, and pits are successively formed on this
track so as to correspond to the modulation signal S1.
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The audio data Dl is inputted from the digital audio
tape recorder 3 to a modulation circuit 13. In addition,
subcode data corresponding to the audio data Dl is inputted to
the modulation circuit 13. The modulation circuit 13 conducts
data processing on the audio data Dl and the subcode data by
using a data processing scheme stipulated for a compact disk.
In other words, the modulation circuit 13 adds error correction
codes to the audio data Dl and the subcode data, thereafter
conducts interleave processing thereto, subsequently conducts an
EFM modulation, and outputs an EFM signal S2.
An edge position correction circuit 14 detects a
change pattern of the EFM signal S2 and corrects the timing of
the EFM signal S2 so as to effectively avoid the inter-symbol
interference at the time of reproduction according to this
change pattern.
Specifically, in the edge position correction circuit
14, a level conversion circuit 15 corrects the signal level of
the EFM signal S2 having an output amplitude value of 1 [V] to a
TTL level having an output amplitude value of 5 [V] . A
resulting signal is outputted therefrom. A PLL circuit 16
generates a clock CK (FIG. 2B) from the EFM signal S2 (FIG. 2A),
and outputs the clock CK. In the FFM signal S2, the signal
level changes with a period in the range of 3T to 11T for the
fundamental period T. Therefore, the PLL circuit 16 thus
generates the clock CK which changes in signal level according
to the fundamental period T synchronized to this EFM signal S2.
As shown in FIG. 3, a rising edge correction circuit
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17A includes thirteen latch circuits 19A through 19M connected
in series and operated by the clock CK. An output signal S3 of
the level conversion circuit 15 is inputted to the series
circuit of the latch circuits 19A to 19M. The rising edge
correction circuit 17A samples the output signal S3 of the level
conversion circuit 15 with the timing of the clock CK, and
detects the change pattern of the EFM signal S2 on the basis of
sampling results of thirteen consecutive points. Namely, in the
case where a latch output of, for example, "0001111000001" is
obtained, it can be recognized as a change pattern containing
pits of a length 4T continued after a space of a length 5T. In
the same way, in the case where a latch output of, for example,
"0011111000001" is obtained, it can be recognized as a change
pattern containing pits of a length 5T continued after a space
of a length 5T.
A correction value table 20 is formed of a read only
memory storing a plurality correction data. By using latch
outputs of the latch circuits 19A through 19M as an address, the
correction value table 20 outputs correction value data DF
corresponding to the change pattern of the EFM signal S2. As an
input, a monostable multivibrator (MM) 21 receives the latch
output of the latch circuit 19G located at the center of
thirteen latch circuits 19A to 19M connected in series. By
using the rising timing of this latch output as a reference, the
monostable multivibrator 21 outputs a rising pulse signal which
.is raised in signal level for a predetermined interval of time
(an interval sufficiently shorter than the period 3T).
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A delay circuit 22 has tap outputs of twelve stages.
The delay time difference between the respective taps is set
equal to the resolution of timing correction of the modulation
signal in the edge position correction circuit 14. The delay
circuit 22 successively delays the rising pulse signal outputted
from the monostable multivibrator 21 and outputs the delayed
signal from each tap. A selector 23 selects and outputs a tap
output of the delay circuit 22 according to the correction value
data DF. As a result, a rising pulse signal SS (FIG. 2(D))
changed in delay time according to the correction value data DF
is selected and outputted from the selector 23.
Thereby, the rising edge correction circuit 17A
generates the rising edge signal SS which rises in signal level
in response to each rising of the signal level of the EFM signal
S2. The delay time of each rising edge with respect to the EFM
signal S2, such as Ar(3, 3), Ar(4, 3), A(3, 4), Ar(5, 3), ... is
changed according to the change pattern of the EFM signal S2
detected by the corresponding rising edges of the EFM signal S2,
i.e., by thirteen sampling operations before and after in total.
In FIG. 3, the change pattern of the modulation
signal S2 is represented by a pit length p and a pit interval b
while taking one period of the clock (i.e., channel clock) CK as
the unit. The delay time from the rising edge is represented by
Ar(p, b). In FIG. 2D, therefore, the second delay time Ar(4, 3)
is the delay time in the case where a blank of three clocks
precedes a pit having a length of four clocks. In the
correction value table 20, correction value data DF
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corresponding to all combinations of p and b are stored
beforehand.
In general, the compact disk is exposed to the laser
beam L according to the EFM signal S2 and pits are thus formed
thereon. For the range of 12T where the fundamental period T is
taken as the unit, the rising edge correction circuit 17A
detects the pattern of pits formed on the compact disk, and
generates the rising edge signal SS according to this pattern.
A falling edge correction circuit 17B has the same
configuration as the rising edge correction circuit 17A except
that the monostable multivibrator 21 is operated on the basis of
the falling edge of the latch output and contents of the
correction value table 20 are different.
Thereby, the falling edge correction circuit 17B
generates a falling edge signal SR (FIG. 2C) which rises in
signal level in response to each falling of the signal level of
the EFM signal S2. The delay time of each falling edge with
respect to the EFM signal S2, such as Af(3,3) ,Af(4,4), Af(3,3),
Af(5,4), ===- is changed according to the change pattern of the
EFM signal S2 detected by the corresponding falling edges of the
EFM signal S2, i.e., by thirteen sampling operations in total.
In FIG. 3, the delay time from each falling edge is represented
by Af(p, b) by using the pit length p and the pit space b in the
same way as the delay time for a rising edge.
For the range of 12T where the fundamental period T
is taken as the unit, the falling edge correction circuit 17B
detects the pattern of pits formed on the compact disk, corrects
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the timing of a falling edge of the EFM signal S2 :functioning as
the timing of termination of exposure to the laser beam
according to the pattern, and generates the falling edge signal
SR.
A flip-flop (F/F) 25 (FIG. 1) combines the rising
edge signal SS and the falling edge signal SR, and outputs a
resultant signal. In other words, the rising edge signal SS and
the falling edge signal SR are input to a set terminal S and a
reset terminal R of the flip-flop 25, respectively. As a
result, the flip-flop 25 generates a modulation signal S5 which
rises in signal level in response to each rising edge of the
signal level of the rising edge signal SS and which then falls
in signal level in response to each rising edge of the signal
level of the falling edge signal SR. A level inverse conversion
circuit 26 corrects the signal level of this modulation signal
S5 having an output amplitude of a TTL level, and outputs it
with the original output amplitude of 1 V.
As a result, the modulation signal Si is outputted
with the timing of the rising edge and the falling edge
corrected according to the pit length and land length located
before and behind. Corresponding to this, the timing of
exposure of the original disk 2 to the laser beam L is also
corrected according to the pit length and land length located
before and behind. In the compact disk produced by this
original disk 2, therefore, each edge position is changed from
its fundamental position according to the pit length and land
length located before and behind. As a result, between pits
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having the same data allocated thereto, the pit length is
changed. Thereby, the optical disk device 1 corrects the
positions of the front edge and the rear edge of each pit at the
time of reproduction so as to reduce the jitter caused by the
inter-symbol interference.
FIG. 4 is a process diagram for the explanation of
the generation of the correction value table 20 thus used to
correct the edge timing. By suitably setting this correction
value table 20 in the optical disk device 1, positions of the
front edge and the rear edge of each pit can be set to optimum
positions, and reproduced signals can be changed according to
correct timing synchronized to the clock CK. specifically, even
if the pit size and lengths of the preceding and succeeding
blanks change, reproduced signals thus pass through a
predetermined slice level at correct timing synchronized to the
clock CK. As a result, reproduced signals reduced in jitter can
be obtained. The correction value table 20 is present in both
the rising edge correction circuit 17A and the falling edge
correction circuit 17B. Its setting method is the same for both
of them. Therefore, explanation will now be limited to the
rising edge correction circuit 17A.
In this process, a correction value table is set on
an original disk for evaluation by the optical disk device 1 on
the basis of the result of reproduction of a compact disk
produced from this original disk.
When this original disk for evaluation is produced,
the correction value table 20 for evaluation reference is set in
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the optical disk device 1. In this correction value table 20
for evaluation reference, the correction value data DF is set so
as to always select and output the center tap output of the
delay circuit 22 by the selector 23. In this process,
therefore, the original disk 2 is exposed to light under the
same condition as in the case where the light modulator 8 is
driven directly by the EFM signal S3, i.e., under the same
condition as the conventional compact disk producing process.
In this process, the original disk 2 thus exposed to
light is subjected to development, and then subjected to
_electroforming processing. Thereby, a mother disk is produced.
From this mother disk, a stamper 40 is produced. Furthermore,
in the same way as the conventional compact disk producing
process, a compact disk 41 is produced from the stamper 40.
A compact disk player (CD player) 42 conducts
reproduction operation for the compact disk 41 for evaluation
thus produced. At this time, the compact disk player 42
switches its operation under the control of a computer 44, and
outputs a reproduced signal RF from its internal signal
processing circuit to a digital oscilloscope 43. This
reproduced signal RF has a signal level changed according to the
light quantity of the returned light which is obtained from the
compact disk and is output from an output of an optical pickup
via a predetermined buffer circuit. Thus, this compact disk 41
is produced under the same condition as the usual compact disk.
If this reproduced signal RF is observed on the digital
oscilloscope 43 by using the reproduced clock as a trigger,
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therefore, a jitter can be observed.
The digital oscilloscope 43 switches its operation
under the control of the computer 44, conducts analog-digital
conversion on the reproduced signal RF with a sampling frequency
which is 20 times as high as the frequency of the channel clock,
and outputs a resultant digital signal to the computer 44.
In addition to controlling the operation of the
digital oscilloscope 43, the computer 44 conducts signal
processing on the digital signal output from the digital
oscilloscope 43, and thereby successively calculates the
-correction value data DF. Furthermore, the computer 44 drives a
ROM writer 45 to store the calculated correction value data DF
successively in a read only memory, and thereby forms the
correction value table 20. In this process, a compact disk is
finally manufactured by using this correction value table 20.
FIG. 5 is a flow chart showing the processing
procedure in the computer 44. In this processing procedure, the
computer 44 proceeds from step SP1 to step SP2, and sets a
jitter detection result Ar(p,b) and the number of times of
jitter measurement n(p,b) equal to values 0. Around each edge
which is the subject of jitter detection, the computer 44
calculates the jitter detection result Ar(p,b) for each
combination of the pit length p and the pit interval b, and
counts the number of times of jitter measurement n(p,b). At
step SP2, therefore, the computer 44 sets all of the jitter
detection result Ar(p,b) and the number of times of jitter
measurement n(p,b) equal to initial values.
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Subsequently, the computer 44 proceeds to step SP3.
By comparing the digital signal output from the digital
oscilloscope 43 with a predetermined slice level, the computer
converts the reproduced signal RF to a binary value and thus
generates a digital binary signal. In this processing, the
computer 44 converts the digital signal to a binary value so as
to provide a digital signal of the slice level or higher with a
value 1 and provide a digital signal of less than the slice
level with a value 0.
Subsequently, the computer 44 proceeds to step SP4,
.and generates a reproduced clock from a binary signal formed
digital signal. Here, the computer 44 simulates the operation
of the PLL circuit by conducting computation processing on the
basis of the binary signal, and thereby generates the reproduced
clock.
In subsequent step SP5, the computer 44 samples the
binary signal at timing of each falling edge of the reproduced
clock thus generated, and thereby decodes the EFM signal.
(Hereafter, this EFM signal thus decoded is referred to as a
decoded EFM signal.)
Subsequently, the computer 44 proceeds to step SP6,
and detects a time difference e measured from the time point of
a rising edge of the binary signal to the time point of a
falling edge of the reproduced clock closest to the former cited
falling edge. Thereby, the computer 44 measures the time of
jitter at this edge. Subsequently at step SP7, the computer 44
detects the preceding and succeeding pit length p and pit
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interval b from the decoded EFM signal for the edge the time of
which has been measured at the step SP6.
Subsequently at step SP8, the computer 44 adds the
time difference e detected at the step SP6 to the jitter
detection result Ar(p,b) corresponding to the preceding and
succeeding pit length p and pit interval b, and increases the
corresponding number of times of jitter measurement n(p,b) by a
value of 1. Subsequently, the computer 44 proceeds to step SP9,
and determines whether or not the time measurements for all
rising edges have been completed. If a negative result is
obtained here, the computer returns to the step SP5.
As a result, the computer 44 repeats the processing
procedure of steps SP5-SP6-SP7-SP8-SP9-SP5, accumulates the
jitter detection results measured for time every change pattern
appearing in the reproduced signal RF, and counts the number of
additions.
If jitter time measurements for all edges have thus
been completed, an affirmative result is obtained at the step
SP9. As a result, the computer 44 proceeds to step SP10. For
each change pattern appearing in the reproduced signal RF, the
computer averages the jitter detection results measured for
time. Namely, the jitter detected at the step SP6 is influenced
by a noise. By thus averaging the jitter detection results, the
computer 44 improves the precision of jitter measurement.
Upon thus averaging the jitter detection results, the
computer 44 subsequently proceeds to step SP11. On the basis of
the detection result, the computer generates the correction
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value data DF for each change pattern and outputs each
correction value data DF to the ROM writer 45. Denoting the
delay time difference between taps in the delay circuit 22
by -r, this correction value data DF is calculated by executing
the computation processing of the following equation (1).
- a Or (p, b)
Hr1 (p,b) = + HrO (p,b) ....(1)
Here, Hrl(p,b) denotes a tap of the delay circuit 22
selected by the correction value data DF. In case of the value
0, the center tap is represented. Furthermore, HrO(p,b) denotes
a tap of the delay circuit 22 selected by the correction value
data DF which is the initial value. In this embodiment, HrO(p,
b) is preset to 0. Furthermore, "a" is a constant. In this
embodiment, "a" is set to a value of 1 or less (for example,
such as 0.7 or the like). Multiplication is conducted so as to
be capable of making the correction value surely converge even
if there is an influence of a noise or the like.
Upon thus storing the correction value data DF in the
ROM writer 45, the computer 44 proceeds to step SP12 and
terminates this processing procedure. Subsequently, the
computer 44 executes a similar processing procedure for falling
edges of the digital binary signal, and thereby completes the
correction value table 20.
In the configuration heretofore described, the
correction value tables 20 in the rising edge correction circuit
17A and the falling edge correction circuit 17B included in the
optical disk device 1 (FIG. 1) are set equal to initial values.
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Under the same condition as the production condition of the
conventional disk, the original disk 2 for evaluation is
produced (FIG. 4). From this original disk 2, the compact disk
41 for evaluation is produced.
In the compact disk 41 for evaluation, by the EFM
signal changing in signal level with a period equivalent to an
integer multiple of the fundamental period T, the laser beam L
is subjected to on-off control. The original disk 2 is
successively exposed to light, and pits are formed. In the
compact disk 41 for evaluation, therefore, the reproduced signal
-undergoes inter-symbol interference from the adjacent pit and
land. Therefore, the timing at which the reproduced signal
obtained from this compact disk 41 crosses the slice level
changes according to the shape of the pit and land located
before and behind, i.e., according to the change pattern of the
EFM signal. Thus, a jitter occurs.
This compact disk 41 undergoes the reproduction
operation conducted by the compact disk player 42. The
reproduced signal RF is converted to a digital signal by the
digital oscilloscope 43. Thereafter, the binary signal, the
decoded EFM signal, and the reproduced clock are generated by
the computer 44. Furthermore, for each edge of the binary
signal from the compact disk 41, the pit and land located before
and after are detected from the decoded EFM signal, and the
change pattern of the EFM signal is detected. For each change
pattern, the jitter quantity of each edge for the reproduced
clock is measured in the form of time.
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Furthermore, these time measurement results are
averaged for each change pattern. The jitter quantity caused by
the inter-symbol interference is detected for each change
pattern. By using the jitter quantity thus detected, the
compact disk 41 executes the computation processing of the
equation (1), which is based on the delay time difference r
between taps of the delay circuit 22 (FIG. 3) and which includes
the jitter correction unit. By taking the center tap of the
delay circuit 22 as the reference, the tap position of the delay
circuit 22 capable of canceling the detected jitter quantity is
-detected. The data specifying this tap position is stored in
the read only memory as the correction value data DF. As a
result, the correction value table 20 is formed.
By thus forming the correction value table 20, the
audio data Dl and subcode data input from the digital audio tape
recorder 3 (FIG. 1) are subjected to stipulated data processing
in the modulation circuit 13 and converted to the EFM signal S2,
which changes in signal level while taking the fundamental
period T as the unit. This EFM signal S2 is converted in signal
level to the TTL level by the level conversion circuit 15.
Thereafter, the clock CK is reproduced by the PLL circuit 16.
In the rising edge correction circuit 17A and the falling edge
correction circuit 17B (FIG. 3), the signal is successively
latched in the 13-stage latch circuits 19A through 19M, and the
change pattern is detected.
Furthermore, the EFM signal S2 is input from the
latch circuit located at the middle of the latch circuits 19A
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through 19M to the monostable multivibrator 21. The monostable
multivibrator 21 is triggered at the timing of the rising edge
in the rising edge correction circuit 17A and at the timing of
the falling edge in the falling edge correction circuit 17B. In
the rising edge correction circuit 17A and the falling edge
correction circuit 17B, the rising pulse signal and the falling
pulse signal which rise in signal level respectively at the
timing of the rising edge and the falling edge are generated,
respectively.
Respectively in the delay circuits 22 of the rising
,edge correction circuit 17A and the falling edge correction
circuit 17B, the rising pulse signal and the falling pulse
signal are successively delayed while taking the delay time r
used to calculate the correction value data DF as the unit. Tap
outputs of this delay circuit 22 are output to the selector 23.
As for the change pattern of the EFM signal S2 detected by the
latch circuits 19A through 19M, accessing the correction value
table 20 by using the latch outputs of the latch circuits 19A
through 19M yields detection of the corresponding correction
value data DF. By this correction value data DF, contacts of
the selector 23 are switched.
Respectively from the selectors 23 of the rising edge
correction circuit 17A and the falling edge correction circuit
17B, the rising edge signal SS and the falling edge signal SR
respectively corrected in timing of the rising edge and the
falling edge of the EFM signal S2 so as to correct the jitter
detected in the compact disk 41 for evaluation are output. The
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rising edge signal SS and the falling edge signal SR (FIG. 1)
are combined by the flip-flop 25. The output signal S5 of the
flip-flop 25 is corrected in signal level by the inverse level
conversion circuit 26. As a result, the modulation signal S1
corrected in timing of each edge of the EFM signal S2 so as to
correct the jitter detected on the compact disk 41 for
evaluation, i.e., so as to reduce the inter-symbol interference
is generated. By this modulation signal S1, exposure of the
original disk 2 is conducted.
As a result, pits are formed successively on the
-original disk 2 with edge positions corrected so as to cancel
the inter-symbol interference. From this original disk 2, a
compact disk significantly reduced in jitter as compared with
the conventional compact disk is produced.
In the configuration heretofore described, the
modulation signal S1 is generated by correcting the timing of
the EFM signal S2 according to the change pattern of the EFM
signal S2, and the original disk 2 is exposed to light by using
this modulation signal S1. As a result, the jitter caused by
the inter-symbol interference changing according to the change
pattern can be reduced significantly as compared with the
conventional compact disk.
Furthermore, at this time, the compact disk for
evaluation is produced and the correction value data DF is
generated. Therefore, even if the production condition of the
compact disk has changed, the compact disk can be produced by
means of always proper correction value data DF by newly
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deriving the correction value data DF.
(2) Second Embodiment
FIG. 6 is a block diagram showing an optical disk
device according to a second embodiment of the present
invention. In this optical disk device 50, the light quantity
of the laser beam L is made to rise at a predetermined timing,
and the original disk 2 is exposed to the light. Thereby, a pit
widened in width is locally formed, and the reflectance of the
compact disk is locally changed. So as to make a character, an
image, and the like observable and confirmable with eyes by this
local change of reflectance, the character, the image and the
like are recorded on the information recording surface of the
compact disk in this optical disk device 50. In the components
shown in FIG. 6, the same components as those of the optical
disk device 1 described before with reference to the first
embodiment are denoted by corresponding reference numerals and
duplicated description thereof will be omitted.
That is, in this optical disk device 50, a character
signal generation circuit 51 outputs a light quantity switching
signal SC1, drives a light modulator 52 inserted in the optical
path of the laser beam L, and thereby switches and controls the
light quantity of the laser beam L.
In the character signal generation circuit 51, as
shown in FIG. 7, a counter modulo N 53 is formed by a ring
counter, counts the FG signal FG, and outputs a count value M.
At a rotation period of the spindle motor 4, the count value is
switched to 0. At this time, a track signal C1 is output.
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A counter modulo M 54 is formed by a counter modulo M
counting the track signal C1, and outputs a count value CT2. By
using the counter modulo N 53 and the counter modulo M 54, the
character signal generation circuit 51 outputs the count values
CT1 and CT2, which respectively represent positions of the
original disk 2 in the circumferential direction and in the
radial direction.
A character signal generation table 55 is formed by a
read only memory circuit which holds pixel values of various
kinds of character information. By using the count values CT1
.and CT2 as an address, the character signal generation table 55
outputs data of each pixel value. The data of each pixel value
is formed by data of each bit which represents, in a bit map
form, the characters and image to be recorded on the original
disk 2.
A level conversion circuit 56 successively latches
the data of pixel values successively input, and outputs them
with a signal level suitable for driving the light modulator 52
(FIG. 6). In this embodiment, the light modulator 52 is thus
driven to switch the light quantity of the laser beam L from the
light quantity of 100% to the light quantity of 85%. As a
result, the characters, image and the like are recorded on the
surface of the disk as shown in FIG. 8.
If the light quantity of the laser beam L is thus
controlled to be switched from the light quantity of 100% to the
light quantity of 85%, the reproduced signal also changes. To
be concrete, amplitude Wi and W2 of the reproduced signal change
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CA 02524155 2010-09-13
as shown in FIGS. 9 and 10 respectively illustrating eye
patterns of the reproduced signals using the light quantity of
100% and the light quantity of 85% as shown in FIG. 11. If it
is observed as a continuous waveform, a slice level SL1 for
correctly converting the reproduced signal to a binary value in
the case of the light quantity of 100% is different from a slice
level SL2 for correctly converting the reproduced signal to a
binary value in the case of the light quantity of 85%. In other
words, asymmetry in the portion obtained with the light quantity
of 100% changes largely from that in the portion obtained with
the light quantity of 85%.
Conventional compact disk players have an automatic
slice level adjusting circuit for correcting the slice level
according to such a change in asymmetry. If the light quantity
of the laser beam L is abruptly changed to emphasize the contour
so as to make the recorded characters, image and the like
clearly observable and confirmable with eyes, however, it
eventually becomes difficult for the automatic slice level
adjusting circuit to follow such an abrupt change. In the
boundary portions of the characters, image and the like,
therefore, very long burst errors occur.
In this embodiment, therefore, modulation signals S1A
and SiB respectively corresponding to the light quantities of
100% and 85% are output from two edge correction circuits 57A
and 57B. The modulation signal S1A or SiB is selected by a data
selector 58 in an interlinked relation to the switching of the
light quantity of the laser beam L.
CA 02524155 1997-07-11
Thus, in the optical disk device 50, the light
quantity of the laser beam L is switched over, and the
modulation signal S1A or SIB is selected to vary the timing of
exposure to the laser beam according to the pit width thus
changed. As a result, the edge position in each pit is varied
so as to correspond to the change of the pit width. In the
compact disk produced by this original disk 2, pits to which the
same data is allocated are formed to be different in pit length
so as to correct a change in the returned light caused by a
difference in pit width.
At this time, the degree of the inter-symbol
interference for respective light quantities also changes due to
a change in pit width. According to the change pattern of the
EFM signal S2, therefore, timings of the modulation signals SIA
and SIB are varied by the edge position correction circuits 57A
and 57B, respectively. As a result, the jitter is reduced.
Thus, the edge position correction circuits 57A and 57B hold the
correction value data DF respectively produced by the light
quantities of 100% and 85% in the correction value table.
As shown in FIG. 12 illustrating a result observed in
an experiment, the change of asymmetry could be effectively
avoided by switching over the timing of the modulation signal.
With a slice level SL, therefore, the reproduced signal obtained
from the light quantity of 100% and the reproduced signal
obtained from the light quantity of 85% could be accurately
converted to a binary value.
In the configuration shown in FIG. 6, the modulation
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CA 02524155 1997-07-11
signal S1A and S1B are switched over by the data selector 58 to
switch over the timing of the modulation signal in an
interlinked relation to the switching of the light quantity of
the laser beam. As a result, the reproduced signal can be
accurately converted to a binary value by using a single slice
level. Accordingly, errors can be effectively avoided and data
can be reproduced precisely.
(3) other embodiments
In the above described embodiments, the case where
the correction value table produced by using the compact disk
_for evaluation is directly used to produce a compact disk has
been described. However, the present invention is not limited
to this, but by using the correction value table produced by
means of the compact disk for evaluation, a compact disk for
evaluation may be newly produced so as to modify the correction
value table by using the newly produced compact disk for
evaluation. If the correction value table is thus modified
repeatedly, the jitter can be reduced positively by that amount.
In the above described embodiments, the case where
the EFM signal is sampled 13 times to detect the change pattern
has been described. However, the present invention is not
limited to this, but the number of sampling points may be
increased, if necessary, to thereby cope with a longer recording
information pattern.
In the above described embodiments, the case where
the jitter quantity is measured by measuring the time of the
binary signal based upon the fundamental clock and the
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CA 02524155 1997-07-11
correction value data are generated from the measurement results
has been described. However, the present invention is not
limited to this. In the case where a practically sufficient
precision can be assured, the correction value data may be
generated by signal level detection of the reproduced signal
based upon the fundamental clock instead of the measurement of
the jitter quantity using this time measurement. In this case,
error voltage from the detected signal level of the reproduced
signal the slice level is calculated, and correction value data
is calculated from the error voltage and the transient response
-characteristic of the reproduced signal.
In the above described embodiments, the case where
the timing of the modulation signal is corrected according to
the correction value data stored in a table form has been
described. However, the present invention is not limited to
this. In the case where a practically sufficient precision can
be assured, the correction value data may be calculated by
computation processing instead of the correction value data
detected beforehand and the timing of the modulation signal may
be corrected by using the correction value data thus calculated.
In the above described embodiments, the case where
the correction value data is calculated by using the compact
disk for evaluation has been described. However, the present
invention is not limited to this. In the case where the present
invention is applied to, for example, an optical disk device of
a write-once type, the correction value data may be calculated
on the basis of trial writing result in a so-called trial
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CA 02524155 1997-07-11
writing area.
In the above described embodiments, the case where
the present invention is applied to the compact disk has been
described. However, the present invention is not limited to
this, but the present invention can be widely applied to optical
disk devices for recording various data by using pits. The
present invention can be widely applied to optical disk devices
adapted to conduct multi-value recording of various data by
difference in transient response characteristics of the
reproduced signal.
In accordance with the present invention, the timing
of the modulation signal is corrected according to the change
pattern of the modulation signal as described above. As a
result, the jitter caused by the inter-symbol interference can
be reduced. The reading margin can be improved by that amount,
and recorded data can be reproduced surely.
Furthermore, in an interlinked relation to the
switching over of the light quantity of the laser beam, the
timing of the modulation signal is corrected. Thereby,
asymmetry is corrected, and data can be reproduced accurately
with a single slice level. Furthermore, degradation of jitter
caused by the light quantity switching over of the laser beam
can be effectively avoided. From these facts, it becomes
possible to record an image, a character and the like, and
surely reproduce recorded data.
Having described preferred embodiments of the present
invention with reference to the accompanying drawings, it is to
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CA 02524155 1997-07-11
be understood that the present invention is not limited to the
above-mentioned embodiments and that various changes and
modifications can be effected therein by one skilled in the art
without departing from the spirit or scope of the present
invention as defined in the appended claims.
