Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
1998-02-13
2001-05-01
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S047150, C369S059160
Reexamination Certificate
active
06226236
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an information data transfer system which can be applied to a reproducing device for an optical disk such as a CD (compact disk), and more particularly to a system for controlling the error correction ability based on occurrence of a track jump.
A CD which was originally used as an audio recording medium becomes more widely used by utilizing the feature of high-speed access and the large recording capacity of the optical disk and it is now applied not only in the field of music but also in the computer field and video field.
In a disk reproducing device, an EFM signal recorded on the disk is optically read by a pickup, the signal is amplified by an RF circuit, demodulated, de-interleaved and subjected to the correction process by a signal processing circuit, and then output as audio data or computer data. The above operations are controlled by a system controller. The signal processing circuit includes a PLL circuit, EFM demodulating circuit, subcode demodulation circuit, memory control circuit, memory, correction circuit and data output circuit.
A bit clock is extracted from the EFM signal in the PLL circuit, and the EFM demodulation and subcode demodulation are effected by use of the bit clock. In EFM data, one block which is called one frame is constructed by 588 bit clocks, and one symbol of subcode and 32 symbols of data are included in one frame. Among data which has been subjected to the EFM demodulation, one symbol of subcode is supplied to the subcode demodulating circuit and the 32 symbols of data are written into the memory by the memory control circuit and then corrected in the correction circuit.
In the CD system, an error correction code called CIRC (Cross Interleaved Reed-Solomon Code) is used. The feature of CIRC is that Reed-Solomon codes (C1, C2) of two stages which are combined in an interleaved form are used to enhance the correction ability.
In the series of C1 and C2, parities necessary for correction, that is, P-parity and Q-parity of four symbols are attached in the respective frames. That is, symbols of one-fourth of the 32 data symbols in total are used for correction.
First, based on the four symbols of the P-parity in the C1 series, correction of random errors occurring by jitter or interference between codes is made in the remaining 28 data symbols. In the next C2 series, a long-range interleaving process is effected for a maximum of 108 frames to cope with a long and large burst error which occurs when the synchronized operation is not attained because of malfunctioning of the disk reproducing device, the servo operation is disturbed, or a relatively large defect occurs on the disk.
The interleaving process can be easily realized by use of the memory.
The correction process is explained more in detail with reference to FIG.
1
.
The number of symbols which can be corrected by use of the four symbols of the P-parity in the C1 series is up to two symbols. When correction of two symbols in the C1 series is made or when an error of three of more symbols occurs and cannot be corrected, a pointer is set in the frame. Then, correction is made again in the C2 series on the assumption that all of the symbols of the frame in the C1 series in which the pointer is set contain error factors. The number of symbols contained in the Q-parity used in the C2 series is four, but since the position of the error is almost determined by the pointer information set at the time of correction for the C1 series ,a maximum of four symbols can be corrected.
As described above, the signal is restored with high fidelity by effecting the correction process twice for the C1 series and C2 series in the error correction circuit of the signal processing circuit. However, as shown in
FIG. 2
, since the C2 correction process is effected based only on the pointer information attached in the C1 series in the conventional system if a track jump occurs in the burst error of 16 frames occurring in the C1 series, data which is not originally required to be corrected is also subjected to the correction process. The track jump means that the pickup is moved to a different track by the influence of a scratch made on the disk while a certain track is being reproduced.
Therefore, there occurs a problem that the quadruplex correction ability used for effectively coping with occurrence of the long and huge burst error may adversely cause erroneous correction when the track jump has occurred.
BRIEF SUMMARY OF THE INVENTION
This invention has been made to solve the above problem and an object of this invention is to provide a data transfer system capable of preventing occurrence of erroneous correction when a track jump has occurred.
In order to attain the above object, an information data transfer system of this invention comprises a circuit for reading information data as reproduction data and subcode data and demodulating the read data; a circuit for subjecting the information data to the error correction process; a circuit for generating a track jump signal; a system controller for controlling the correction ability of the error correction circuit based on the track jump signal; and an output circuit for outputting information data which has been subjected to the error correction process.
With the above construction, the high correction ability can be normally used, but at the time of occurrence of a track jump which may cause erroneous correction with strong possibility, the erroneous correction caused by occurrence of the track jump can be prevented by lowering the correction ability preferably from the quadruplex correction level to the triplex correction level based on a track jump detection signal.
In a case where the above system is applied to a CD reproducing device, the circuit for reading and demodulating the information data preferably includes a PLL circuit for generating a PLL clock which is synchronized with an EFM signal and used for reading the EFM signal, and an EFM demodulating circuit for effecting the EFM demodulation and receiving the PLL clock to generate a reproduction frame frequency in which one frame corresponds to one clock, and the track jump signal generating circuit preferably includes a subcode demodulating circuit for receiving the reproduction frame frequency and subcode symbol from the EFM demodulating circuit, demodulating the subcode data, and outputting a track jump detection signal based on the result of demodulation.
Further, the subcode demodulation circuit preferably includes a 1/98 frequency-dividing counter for counting the number of frames to construct a subcode block by using the reproduction frame frequency output from the EFM demodulating circuit as a clock, a decoder for detecting count values of “96” and “97” of the 1/98 frequency-dividing counter and outputting an output signal, a sync detecting circuit for detecting subcode sync based on a subcode symbol output from the EFM demodulating circuit, and a track jump signal generating circuit for outputting a track jump signal based on the output timing of the subcode symbol and the detection timing of the subcode sync.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 4996679 (1991-02-01), Yoshio
patent: 5526328 (1996-06-01), Oshima et al.
patent: 5793724 (1998-08-01), Ichikawa et al.
Yamamoto Koji
Yamashita Mitsuaki
Kabushiki Kaisha Toshiba
Neyzari Ali
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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