Dynamic information storage or retrieval – Binary pulse train information signal – Including sampling or a/d converting
Reexamination Certificate
2000-11-01
2001-11-20
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
Including sampling or a/d converting
C369S047280
Reexamination Certificate
active
06320834
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a demodulating method suitable for reproducing digital data signals, as recorded on an optical disk, and an optical disk device using the method.
BACKGROUND OF THE INVENTION
One method far recording/reproducing information data as a pit train on/from an optical disk, is one in which data having a value of [1], for example, are recorded corresponding to the leading edge or trailing edge of a pit and in which the original data are reproduced by detecting these edge positions within a reproduced signal waveform. This mark edge recording method can be used to make a higher density recording than a “pit position” method in which the pits are recorded to correspond to the data [1] irrespective of pit edges.
The data recording/reproducing method by the mark edge recording method will be described with reference to FIG.
15
. Here, the description will be made corresponding to the case in which the user data are modulated by the encoding method having the minimum run length such as a (2, 7) RLL modulation at 2. If the decode window is indicated by T, the smallest pit length and space length are at 3T. Moreover, it is assumed that the reproduced channel characteristics to be determined by the optical disk and the reading optical spot are PR (1, 2, 3, 3, 2, 1). This implies that when a data string “---0001000---” are recorded in the optical disk, the reproduced response waveform takes a format of “---01233210---”. When the encoding method having the minimum run length at 2 is adopted, the level of the reproduced signal to be taken at a data recognition point is understood to take eleven levels of 0, 1, 2, 3, 4, 6, 8, 9, 10, 11 and 12 by superposing the PR (1, 2, 3, 3, 2, 1) characteristic. The levels 5 and 7 do not appear due to the run-length limitation.
If similar operations are performed for a random pattern, there is obtained an eye pattern, as shown in FIG.
14
(
a
). The PR (1, 2, 3, 3, 2, 1) characteristic has a wide range of response waveform so that the eye takes a small opening height. This eye pattern is prominently different from eye patterns of the PR (1, 3, 3, 1) characteristic, the PR (1, 2, 2, 1) characteristic and the PR (1, 2, 1) characteristic, as shown at (b), (c) and (d) in FIG.
14
. In any of these cases, however, the edge positions, as obtained by slicing at the center level, are concentrated at one point so that the data can be reproduced by detecting the edge position.
By inverting the polarity of recording data
2001
with the data [1], a recording data pulse train
2002
is obtained. By subjecting this pulse train
2002
to a (not-shown) suitable recording waveform control, a recording mark train
2003
is recorded on the disk. By scanning the recording mark with a reading optical spot, a reproduced signal
2004
is obtained. This reproduced signal
2004
is made binary as pulses
2006
along a suitable slice level
2005
. At the timings of the rising and falling edges of the binary pulses
2006
, a pulse signal
2007
is obtained. This pulse signal
2007
is fed to a PLL circuit (i.e., a phase locked loop circuit, not shown) so that a synchronized clock signal
2008
is outputted from the PLL circuit. As shown, the rising edge of the pulse signal
2007
and the rising edge of the lock signal
2008
are synchronized. By latching the pulse signal
2007
with the falling edge of the clock signal
2008
, read data pulses
2009
are obtained. If the read data are made to correspond to the data [1] when the read data pulses
2009
are at “H”, there are obtained reproduced data which are identical to the recording data.
There has also been proposed another method. The pulse signal
2007
is divided into rising/falling pulse trains, and these pulse trains are operated independently of each other. After this, the leading edge data and the trailing edge data are recomposed by absorbing their timing discrepancy with a synchronous pattern. Japanese Patent Laid-Open No. 212718/1996 is enumerated as prior art of this kind.
A conventional method other than the data recording/reproducing method shown in
FIG. 15
will be described with reference to
FIGS. 16 and 17
. The operations corresponding to obtaining a recording data pulse train
2102
from recording data
2101
to that of obtaining a reproduced signal
2104
from a recording mark train
2103
are identical to those of FIG.
15
. According to this method, the reproduced signal is sampled with a clock signal, and the edge data are extracted, while synchronizing the clock signal with the reproduced signal
2104
, from the data of a sampled data train
2105
. These operations will be described with reference to
FIG. 17. A
reproduced signal
2201
is sampled with a clock signal
2208
in an A/D converter
2202
. The sampled data are cleared of the inter-symbol interference by a digital equalizer
2203
and are equalized according to the PR (1, 2, 3, 3, 2, 1) characteristic. After this, the sampled data are cleared of the amplitude fluctuation and the level fluctuation by an amplitude/level compensator
2204
and are fed to a data decider
2205
. These operations are wholly carried out in synchronism with the clock signal
2208
. The sampled data
2209
, having passed through the amplitude/level compensator
2204
, are fed to a phase comparator
2206
, in which the sample timing discrepancy of the A/D conversion is detected in terms or a voltage, so that the clock signal
2208
is obtained by controlling the oscillation frequency of a VCO (Voltage Control Oscillator)
2207
. In the data decider
2205
, whether or not the sampled data are the edge data is decided with two threshold levels
2106
and
2107
, and reproduced data
2210
are outputted. IN other words, reproduced data
2108
identical to the recording data
2101
are obtained by deciding the sampled data between those levels at [1] and the remaining data at [0].
The method of FIG.
15
and the method of
FIG. 16
will be discriminated by calling the former the analog operations and the latter the digital operations.
The prior art, as described with reference to
FIGS. 15 and 16
, are sensitive to the level fluctuation and the amplitude fluctuation of the reproduced signal. As means for improving the reliability, therefore, there has been devised a technique of compensating the slice level. The analog operations are disclosed in Japanese Patent Laid-Open No. 81324/1990 or No. 254514/1987, and the digital operations are disclosed in Japanese Patent Laid-Open No. 263943/1996.
SUMMARY OF THE INVENTION
In the prior art involving the analog operations, the data are detected from phase data using only the edge data. It is, therefore, anticipated that the necessary error factor is difficult to retain when the height of the eye opening is reduced with higher density, thereby lowering the SN ratio.
In the prior art involving the digital operations, on the other hand, the digital sampling that is employed for extracting edge data causes similar problems. In accordance with a rise in the transfer rate, the clock frequency rises limited by the processing speed to be realized by the actual circuit. This makes it necessary to enlarge the circuit scale by using parallel operations.
An object of the invention is to provide a method capable of reducing the increase in the circuit scale to a relatively small value and lowering the processing speed necessary for decisions in a data demodulation by digital processing, by using sampled data before and after edge data as the data to be used for decoding the recorded data.
In order to achieve the above specified object, means are provided for determining edge data from a sampled data string. Two thresholds are established to define a signal level indicative of a leading or trailing edge. A sample can be lower than, equal to (i.e. within the thresholds), or higher than the edge level. The sampled data are given a [1] value if they fall within the established thresholds, indicating an edge, or a value of &lsq
Edun Muhammad
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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