Dynamic information storage or retrieval – Binary pulse train information signal – Including sampling or a/d converting
Reexamination Certificate
2003-03-11
2004-12-28
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Including sampling or a/d converting
C360S065000
Reexamination Certificate
active
06836457
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an information reproducing method and an information reproducing device, in particular to an information reproducing method and an information reproducing device that can perform adaptive equalization of digital signals reproduced from an information recording medium with favorable equalization properties without sacrificing information storage capacities.
BACKGROUND OF THE INVENTION
When digital signals are reproduced from information recording media, such as optical disks, waveform equalization is used for the suppression of interference between symbols, which can negatively affect the symbol error rate, and for the realization of partial response technology, which improves the symbol error rate by generating a specified interference between symbols.
Because property variations of the transmission path are caused by the slightly varying properties of each information recording medium, adaptive equalization technology is used, which updates the equalization properties of the waveform equalizer to adapt to the changes of the transmission path properties.
An example of adaptive equalization technology, which is explained in the prior art section of Publication of Unexamined Japanese Patent Application No. H9-7031, is a technique in which a special learning region is provided on the information recording medium, the learning region is reproduced before the reproduction of the data region, and the generation of the reproduction clock and adaptive learning processing are performed using the resulting signal.
FIG. 12
shows an optical disk reproducing device employing this conventional adaptive equalization technology. Moreover,
FIG. 13
shows the sector configuration of the optical disk in FIG.
12
.
The sector
1010
shown in
FIG. 13
is a recording unit when digital information is to be recorded on an information recording medium, and consists of an address portion
1001
and a data portion
1002
.
The address portion
1001
indicates the physical location of the sector
1010
, and is prerecorded at the time the optical disk is manufactured.
The data portion
1002
is the region where the user records information, and includes a VFO region
1003
, an adaptive learning region
1004
, and a data region
1005
.
The VFO region
1003
is a continuous data pattern that is provided to precisely generate the reproduction clock necessary at the time of signal reproduction, and the reproduction clock generator
130
in
FIG. 12
generates the reproduction clock using the reproduction signal from this pattern.
FIG. 14
shows the configuration of the reproduction clock generator. As shown in
FIG. 14
, a comparator
131
compares the reproduction signal with a predetermined slice level, and detects its zero crossing point. A VCO
134
oscillates at a frequency proportional to the input voltage, and is the oscillator for outputting the reproduction clock signal. A phase comparator
132
compares the timing of the zero crossing of the reproduction signal with the timing of the edge of the reproduction clock signal outputted by VCO
134
, and outputs a pulse whose width is proportional to the phase error determined by the phase comparator. A low-pass filter (LPF)
133
lets only low frequency components outputted by the phase comparator
132
pass, and feeds this output to the VCO
134
.
With this configuration, a reproduction clock can be generated that depends on the variations of the disk's rotation speed, because when the output voltage of the phase comparator
132
changes in accordance with the phase difference, the VCO
134
changes its oscillator frequency accordingly.
In the adaptive learning region
1004
, a known bit pattern is recorded for performing an adaptation learning process, which updates the equalization properties of the waveform equalizer
107
. The equalization error is determined by determining the difference between the digital reproduction signal attained by reproducing this bit pattern and an equalization target value uniquely set for each bit pattern. Adaptive learning processing is performed by determining, in an adaptation algorithm, the equalization property values of the waveform equalizer
107
minimizing this equalization error.
With an optical disk having such a sector configuration, the optical disk reproducing device in
FIG. 12
first of all accesses the sector
1010
, in accordance with the information recorded in the address portion
1001
.
If the access to the target sector
1010
is successful, the VFO region
1003
is reproduced by the optical head
103
, the reproduction clock generator
130
generates the reproduction clock based on this reproduced signal, and the reproduction clock is then fed to various parts of the optical disk reproducing device.
Then, the optical head
103
reproduces the adaptive learning region
1004
, and this reproduced signal is A/D converted in synchronization with the regeneration clock, thereby obtaining the digital reproduction signal. The obtained digital reproduction signal is fed to the waveform equalizer
107
and the adaptive learning device
108
.
The waveform equalizer
107
performs waveform equalization, and the adaptive learning device
108
adjusts the waveform equalizer
107
to appropriate equalization properties by performing adaptive learning processing.
After the adaptive learning is finished, the data region
1005
is reproduced, and after the waveform has been equalized with the waveform equalizer
107
, it is demodulated with a demodulator
111
.
With this processing, it is possible to synchronize the reproduction time of the data region constantly with the reproduction clock, and to perform waveform equalization with equalization properties commensurate with the properties of the transmission path.
However, in the adaptive equalization processing with this conventional information reproducing device, VFO regions and adaptive learning regions, which cannot store user data, have to be provided to obtain good reproduction properties. As a result, some of the limited data capacity of the information recording medium has to be sacrificed.
To avoid sacrificing data capacity, methods without adaptive learning regions have been proposed, which determine a prediction equalization error by presupposing the reproduction signal with a certain threshold as a reference, and perform an adaptive learning operation to reduce this prediction equalization error. But with this structure, the performance of the adaptive learning is worse than if known data on the adaptive learning region are reproduced to determine a precise equalization error.
In particular, in the initial stage of the adaptive learning, there is no guarantee that the equalization properties of the waveform equalizer are suited to the transmission path of the circuit. In such a case, the prediction equalization error is wrong, and as a result, the convergence speed of the adaptive learning decreases, and in the worst case may even diverge.
Moreover, in the case of an information reproduction medium such as an optical disk reproducing device, when defocussing or variations of the disk reflectivity, or level variations in the reproduction signal waveform due to power variations of the laser occur, then the position of the zero crossing point output by the comparator
131
strays from its initial position, and the VCO
134
cannot generate a precise reproduction clock.
When no precise reproduction clock can be supplied, the timing of the sampling of the reproduction signal performed by the A/D converter
106
in
FIG. 12
becomes off, and the signal level of the digital reproduction signal obtained as the output of the A/D converter
106
varies. As a result, the properties of the adaptive learning process performed with the digital reproduction signal deteriorate, and it becomes difficult to perform suitable waveform equalization.
Moreover, in the adaptive learning processing with a conventional information reproducing device, the reproduction signals from the adaptive learning region all ar
Hino Yasumori
Miyatake Norio
Nakamura Tadashi
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Thang V.
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