Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1985-02-15
1987-06-09
Sloyan, T. J.
Communications: electrical
Audible indication
Percussion-type sound producer
360 40, 360 41, 360 42, H03M 700
Patent
active
046723633
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of modulating digital data which is applied to the case where an information signal such as an audio signal or video signal is converted to a digital signal and is recorded on an optical disc or magnetic tape.
BACKGROUND ART
In case of recording a digital information signal, a digital modulation called a channel coding is performed to raise a recording density on a recording medium and to reduce the DC component of a transmission signal.
A Miller modulation is known as a conventional channel coding. However, the Miller modulation cannot reduce the DC component of the modulated output to zero. For example, in case of recording an audio PCM signal by a rotary head, a recording signal is transmitted through a rotary transformer. If the DC component is included in this recording signal, since the rotary transformer cannot transmit the DC component, there will be caused a problem such that the waveform of the recording signal is distorted. In the case where many low frequency components are included in the recording signal, it is necessary to extend the frequency characteristic of the rotary transformer to a low frequency band. Further, in case of using a recording method whereby the crosstalk between the adjacent tracks is suppressed by making the extending directions of the gap of the recording head differ with regard to the adjacent tracks, the effect of suppressing the crosstalk with respect to the low frequency component of the recording signal becomes insufficient.
In case of reproducting an optical disc whose surface is coated by a reflecting layer, DC noises are caused due to the dust adhered on the reflecting layer, scratches on the reflecting layer or the like. If the digital signal recorded on the disc includes no DC component, such DC noises can be eliminated by a filter.
From the above viewpoint, it is required to reduce the DC component of the recording signal to zero. For this purpose, a modified Miller (referred to as M.sup.2) modulation has been proposed. Further, a modulating method (referred to as M3 modulation) having the effect of suppressing the DC component even more than the M.sup.2 modulation has also been proposed.
In these M.sup.2 and M3 modulating methods, the minimum transition interval of the modulated output is T (where, T is a length of one bit cell) and the maximum transition interval is 3T. It is desirable that the maximum transition interval, namely, the maximum value of the interval between data value transitions, be short in order to reduce the low frequency component and to improve the clock recovery capability in a reproducing circuit.
DISCLOSURE OF INVENTION
The present invention relates to a method of modulating binary digital data to reduce the DC component to zero and intends to propose a digital modulating method which can shorten the maximum transition interval as compared with the cases of the M.sup.2 modulation and M3 modulation.
That is, since the invention can reduce the DC component to zero, by applying the invention to a channel coding in a recording apparatus using a rotary head, an optical disc reproducing apparatus or the like, the distortion (peak shift) of the recording waveform can be decreased and the low frequency noise can be eliminated. In addition, the invention can shorten the maximum transition interval as compared with the cases of the M.sup.2 modulation and M3 modulation and can further reduce the low frequency component of the modulated output, and at the same time the clock recovery capability can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a waveform diagram which is used in explanation of a first embodiment of the invention;
FIG. 2 is a waveform diagram which is used in explanation of a second embodiment of the invention;
FIG. 3 is a block diagram of an example of a modulating circuit to which the invention is applied;
FIG. 4 are time charts which are used in explanation of this modulating circuit;
FIG. 5 is a block diagram of an example of a demodulating circuit
REFERENCES:
Taub, Elimination of DC Component in MFM-Type Codes, IBM Technical Disclosure Bulletin, vol. 21, No. 1, 6/1978, pp. 361 & 362.
Frazier, Improved Modified Frequency Modulation Code, IBM Technical Disclosure Bulletin, vol. 24, No. 4, 9/1981, pp. 2055 & 2056.
Himeno Takuji
Tanaka Masato
Eslinger Lewis H.
Sinderbrand Alvin
Sloyan T. J.
Sony Corporation
LandOfFree
Frequency modulation coding methods with reduced transition inte does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Frequency modulation coding methods with reduced transition inte, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Frequency modulation coding methods with reduced transition inte will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1831744