Coded data generation or conversion – Digital code to digital code converters – To or from run length limited codes
Reexamination Certificate
2001-02-21
2002-02-19
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from run length limited codes
C360S040000, C369S059130
Reexamination Certificate
active
06348883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique for converting a number of bits of digitally modulated channel bits and demodulating the same. More particularly, it relates to a technique for converting a number of bits of channel bits and demodulating the same in such a manner that signals from an optical disk may be commonly processed whether it is the DVD (Digital Video Disk) or the CD (Compact Disk).
2. Description of Related Art
As information distribution media employing the optical digital recording, there are CD and DVD. Different types of CDS include CD-ROM for read-only, CD-DA for audio, CD-WO for write-once and CD-R for recordable, all of which constitute the CD family by virtue of the uniformly defined recording/regenerating formats. Similarly, different types of DVDs constitute the DVD family.
Data bits of information to be recorded on CD or DVD are modulated into channel bits by its unique modulation scheme that complies with its unique RLL constraints, whereas a respective demodulating reference table is referred to for demodulating the original data bits during its playback. With regard to modulation of data bits, a notation “RLL (d, k)” represents that the number of successive ‘ZEROS’ occurring between ‘ONES’ in channel bits may be within the range of at least “d” (minimum run-length) and at most “k” (maximum run-length). Further, NRZ (NonReturn-to-Zero) or NRZI (NonReturn-to-Zero Inverted) recording method is employed to record data in such a way that a polarity of a bit ‘ONE’ is inverted at its leading edge or center portion only to represent presence/absence of a pit on an optical disk, while such an inversion is not done for a bit ‘ZERO’. As a result, a modulation scheme that complies with its associated RLL constraints limits the minimum and maximum numbers of successive absences of pits on an optical disk. In so doing, during regeneration of information, it is possible to extract bit clock components for controlling a servo subsystem in a stable manner, and yet it is possible to obtain better regeneration characteristics that are free from wave interference due to a diffraction limit.
The EFM (Eight-to-Fourteen Modulation) modulation scheme has been employed for CD, whereas the 8/16 (alternatively called “EFMPlus”) modulation scheme has been employed for DVD. One symbol of data bits is 8 bits for both of EFM and 8/16 modulation schemes, whereas one symbol of channel bits is 14 bits long for EFM modulation scheme and 16 bits long for 8/16 modulation scheme respectively. Note here that the term “symbol” means a word unit for error correction. Since both of CD and DVD employ different modulation schemes respectively, when one wishes to play back both of CD and DVD by means of a single playback apparatus, it has been required to provide signal processing circuitry (which is responsible for a sequence of operations, from detection of a sync bit pattern in a channel bit stream that enters into the demodulation subsystem up to output of regenerated data bits) for each of the modulation schemes respectively, in addition to provision of individual demodulating reference tables.
FIG. 1
is a schematic block diagram showing a conventional optical disk playback apparatus that is capable of playing back both of CD and DVD.
As seen in
FIG. 1
, information on a medium
10
(CD or DVD) read by an optical head
11
is sent to a DVD data processor
16
and a CD-DA processor
17
via an RF preamplifier
12
as RF analog signals of a channel bit stream. However, data processor
16
or
17
operates to play back its associated medium alone. That is, data processor
16
including an 8/16 demodulator is only used during a DVD playback, whereas data processor
17
including an EFM demodulator is only used during a CD playback. After performing predetermined processing, its resultant data is sent to an interface
18
or a CD audio amplifier
19
. Both of the 8/16 and EFM demodulators are provided with memories for storing demodulating reference tables, which are uniquely associated therewith respectively.
When channel bits of 16 bits long are treated as directly indicating an address of a ROM in the 8/16 demodulator for storing its demodulating reference table, the memory requires a space of 65,536 addresses. On the other hand, the demodulating reference table in the EFM demodulator requires a space of 16,384 addresses in its ROM since its associated channel bits are 14 bits long.
SUMMARY OF THE INVENTION
In said playback apparatus, both of CD and DVD are not concurrently played back. This means that while one of the media is being played back, a data processor associated with the other media is not being operated, which leads to a reduction in availability of its signal processing circuitry. Also, each of the demodulating reference tables separately requires a certain amount of memory capacity respectively, which leads to heavy consumption of memory resources.
It is, therefore, an object of this invention to provide a technique for converting numbers of bits of channel bits modulated by first and second modulation schemes into lesser numbers of bits in such a manner that regenerated signals may be commonly processed by a single processing path.
It is another object of this invention to provide a demodulating reference table, which is formed by consolidating respective reference tables used for demodulating channel bits modulated by first and second modulation schemes, and which is storable in a small capacity memory.
It is another object of this invention to provide a technique for demodulating channel bits that makes use of said converting technique and said demodulating reference table. It is another object of this invention to provide an optical disk playback apparatus characterized by demodulating circuitry for regenerated signals.
Numbers of bits of channel bits to/from CD and DVD are determined by RLL constraints so as to improve recording/playback characteristics of a medium. Note that among those patterns representable by a predetermined number of channel bits, some patterns may not actually exist under the RLL constraints. When channel bits are picked up from an optical disk and introduced into a regeneration subsystem, a number of bits for representing respective patterns of channel bits may be reduced by associating the patterns with other patterns represented by other bits having a lesser number of bits than the channel bits. A fundamental principle of this invention resides in generating signals for use in a playback by converting a number of bits of channel bits modulated by a first or second modulation scheme. Also, another principle of this invention resides in creating a consolidated reference table for use in demodulating patterns of first or second channel bits, thereby enabling to store it into a memory of a smaller address space.
In one aspect of this invention, there is provided a method and an apparatus for converting first or second channel bits, modulated by a first or second modulation scheme, to first or second output bits respectively. While the output bits may be used as address bits for referring to an address of a memory that stores a demodulating reference table, they may be used in a signal processing subsystem as well for processing signals detected from an optical disk. In the bit conversion of this invention, respective patterns actually represented by the channel bits before-conversion are associated with those patterns that are representable by the output bits after-conversion, which have a lesser number of bits than the channel bits. Respective output bits are generated in such a way that they represent patterns, which correspond to patterns represented by the channel bits other than those patterns being unable to exist under RLL constraints. Further, patterns of the second output bits are generated in such a way that they are assigned to discontinuous areas of patterns represented by the first output bits. In so doing, it becomes possible to reduce a number of bits of respective output bits t
Okada Takenori
Tanaka Keisuke
Ushio Teruhiko
Feece Ron
Williams Howard L.
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