Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal gain processing
Patent
1984-11-07
1987-08-04
Canney, Vincent P.
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal gain processing
369 48, H04N 576, G11B 509
Patent
active
046850988
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to apparatus for reproducing a data signal from a recording medium, such as an optical digital audio disc, having a track on which is recorded a digital data signal modulated in accordance with a modulation system in which the interval between each two successive level transitions from one to the other of two different levels corresponding to binary data "1" and "0", respectively, is provided in a predetermined manner so that the data signal is recorded with constant recording density together with a synchronous signal.
TECHNICAL BACKGROUND
In the optical digital audio disc which is a rotatable disc provided with a spiral recording track on which an audio signal digitalized in accordance with the pulse code modulation (PCM) is recorded with constant recording density so as to be optically read out, the digital data signal recorded thereon is formed into a predetermined format which, for example, contains a series of frame units, each of which is formed with, for example, 588 channel bits to include a frame synchronous signal at the beginning and a data portion following the frame synchronous signal. When the digital data signal thus formed is recorded on the optical digital audio disc, the so-called run length limited code modulation is adopted. The run length limited code modulation in a modulation system in which two different levels of the recording signal are provided in accordance with each binary data "0" and each "1", respectively, and the minimum run length (the minimum interval between two successive level transitions) is made relatively long, so that recording efficiency is increased. Moreover, the maximum run length (the maximum interval between two successive level transitions) is made relatively short so that self-clocking in the reproducing process is facilitated. The maximum run length is arranged to correspond to, for example, 11 channel bits and the minimum run length is arranged to correspond to, for example, 3 channel bits. In addition, since the maximum run length does not appear successively in the normal modulated output, a specific pattern of waveform formed with two successive intervals at the levels of "1" and "0" each corresponding to the maximum run length is added to the modulated output to be used as the frame synchronous signal.
In data, signal reproducing apparatus that uses a reading light beam to reproduce a data signal from an optical recording medium, such as an optical digital audio disc, on which a digital data signal having a waveform obtained by the run length limited code modulation, wherein the maximum run length and the minimum run length are fixed appropriately is recorded with constant recording density together with a synchronous signal having the pattern of waveform formed with two successive intervals each corresponding to the maximum run length, the optical recording medium is driven to move so that the recording track of the optical recording medium is scanned at a constant velocity by a reading device, that is, an optical head of the apparatus for emitting the reading light beam, and thereby the digital data signal recorded on the optical recording medium is read by the reading light beam to produce a head output signal.
The head output signal thus obtained is supplied to a level comparing circuit forming a waveform shaping portion wherein the level of the head output signal is compared with a predetermined level (a cut-off level) and shaped into a rectangular waveform taking, for example, a level of "1" when the level of the head output signal is equal to or higher than the cut-off level and a level of "0" when the level of the head output signal is lower than the cut-off level.
In the case of the optical digital audio disc, for example, since the digital data signal recorded thereon is modulated as described above, a reproduced signal with a rectangular waveform obtained by shaping the head output signal from the disc is formed to contain a series of frame periods, each of which commences with a frame sync
REFERENCES:
patent: 4572965 (1986-02-01), Yamamura
Canney Vincent P.
Eslinger Lewis H.
Sinderbrand Alvin
Sony Corporation
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