Dynamic information storage or retrieval – Binary pulse train information signal – Including sampling or a/d converting
Reexamination Certificate
2001-07-13
2004-12-28
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Including sampling or a/d converting
C369S047350, C369S124020
Reexamination Certificate
active
06836456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an apparatus for reproducing information from a recording medium such as an optical disc.
2. Description of the Related Art
Japanese patent application publication number 9-320200 discloses an apparatus for reproducing information from an optical disc in a 3-beam method. The apparatus of Japanese application 9-320200 applies three forward laser beams to three neighboring tracks on the optical disc, respectively. The three forward laser beams are reflected by the optical disc before returning to the apparatus. The three return laser beams are converted into three readout signals respectively. The readout signal which corresponds to central one among the three forward laser beams (or central one among the three neighboring tracks) is called the first readout signal. The other readout signals are called the second and third readout signals, respectively.
In the apparatus of Japanese application 9-320200, the first, second, and third readout signals are sampled into first, second, and third sequences of signal samples respectively. The first, second, and third sample sequences are passed through first, second, and third variable-coefficient filters to generate first, second, and third filtering-resultant sample sequences, respectively. The first filter is designed to remove signal components caused by intersymbol interferences. The second filter is designed so that the second filtering-resultant sample sequence will correspond to a crosstalk between the central track and the related track neighboring the central track. The third filter is designed so that the third filtering-resultant sample sequence will correspond to a crosstalk between the central track and the related track neighboring the central track. The second and third filtering-resultant sample sequences are subtracted from the first filtering-resultant sample sequence to generate a readout sample sequence. A final reproduced signal is derived from the readout sample sequence.
The apparatus of Japanese application 9-320200 includes a device for extracting, from the final readout sample sequence, every sample (every zero-cross sample) corresponding to a time point at which the value represented by the final readout sample sequence crosses “0”. The value represented by the extracted zero-cross sample is used as an error signal reflecting crosstalk-caused signal components. Filtering coefficients used by the first, second, and third filters are updated in response to the error signal so that the error signal can converge on “0” or crosstalk-caused components can be completely removed from the readout sample sequence. The updating of the filtering coefficients in response to the error signal is based on an LMS (least-mean-square) adaptive algorithm.
In the apparatus of Japanese application 9-320200, since only zero-cross samples are used in generating the error signal, the rate of the convergence of the error signal on “0” tends to be low. The apparatus of Japanese application 9-320200 does not implement partial-response waveform equalization. Therefore, the apparatus of Japanese application 9-320200 can not use a viterbi decoding process in recovering original information from a reproduced signal.
An analog signal representative of digital information which is read out from an optical disc in a tangential push-pull method has a waveform of a differential type. Also, a signal read out from a hard disk or a magnetic tape has a differential-type waveform. A differential-waveform signal takes a continuous value near “0”. Therefore, it is difficult for a zero-cross detection technique to sense a data change point in the differential-waveform signal. Accordingly, the apparatus of Japanese application 9-320200 can not properly operate on a differential-waveform signal.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an information reproducing apparatus which can remove crosstalk-caused components from a readout signal having a differential-type waveform.
A first aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the first signal read by the first means to generate a subtraction-resultant signal; a peak detector for detecting whether or not a level represented by the first signal read by the first means peaks, and generating peak-point information representing a timing at which the level represented by the first signal peaks; a second subtracter for generating an error signal indicative of a difference between the subtraction-resultant signal and a prescribed reference signal at a timing equal to the timing represented by the peak-point information; and third means for controlling the filtering characteristic of the filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A second aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a transversal filter subjecting the first signal read by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; a controllable filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the equalization-resultant signal to generate a subtraction-resultant signal; third means for detecting whether or not one of (1) the first signal read by the first means and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; a temporary decision device for calculating a temporary decision value of the subtraction-resultant signal on the basis of a PR mode signal, an RLL mode signal, the peak-point information, and an actual value of the subtraction-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; a second subtracter for calculating a difference between the temporary decision value of the subtraction-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; and fourth means for controlling the tap coefficients of the transversal filter and the filtering characteristic of the controllable filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A third aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a first A/D converter for converting the first signal read by the first means into a first digital signal; a second A/D converter for converting the second signal read by the second means into a second digital signal; third means for re-sampling the first digital signal generated by the first A/D converter to generate a first resampling-resultant signal; fourth means for generating a bit clock signal from the first dig
Huber Paul W.
Victor Company of Japan Ltd.
Woo Louis
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