Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Patent
1985-09-03
1988-12-20
Sloyan, T. J.
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
375 19, 375 27, A03M 304, H04N 713
Patent
active
047927941
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a system in accordance with the type of the main claim. During the magnetic recording of digitally coded electrical signals, low frequency portions or direct voltage components of the digital signals can very often not be recorded or reproduced at all or only at a very limited scope. Therefore, codes are desired which result in digital signals not containing any direct current components. Such codes may also be required for transmitting of digital signals through a transmitting channel which has a high pass filter characteristic, that is a low cutoff frequency limit.
A simple means to obtain freedom from the d.c. components consists in adding a number of bits to each given signal segment, for example, each data word, at such a logic level that the bits of the L and H levels cancel out with each other for the total signal segment. However, this trivial possibility is impractical, since in most of the cases the channel capacity is limited and consequently, redundancy in transmission should be minimized.
A process for transmitting of digitally coded signals is known from U.S. Pat. No. 4,310,860, wherein a given data sequence is separated into sequences with or without a direct current component and that the sequences with the direct current component are replaced by sequences without direct current components. However, thereby it is also required to make available an additional channel capacity for the replacement signal.
In a further known process (Goldberg u.a.: Optical Television Link Employing a Digital Modulated Laser", Journal of the SMPTE, Vol. 88, June 1979, page 414 etc) the digital signal is inverted from scanning value to scanning value. However, this process provided satisfactory results only for certain contents of the signal to be transmitted.
From U.S. Pat. No. 4,491,869, which is based on a previous patent application of applicant, a pulse code modulation system for digital signals is known wherein the signals are fed through a recording or transmission channel with a high pass characteristic. Therein, the band width of the analog signal on which the digital signal is based are limited to such an extent that the highest contained frequencies in the band limited analog signal are smaller than half of the scanning frequency and that the digital signal inverts from scanning to scanning. Thereby, the digital signal is based on a code, wherein within a digital word the number of bits of respective logical levels has a somewhat linear dependency on the given value of the analog signal. By this coding the mean value per digital data word is a substantially linear function of the analog level, so that after the inversion the serial data signal itself does not contain any direct voltage component.
It is an object of the invention to suggest a differential pulse code modulation system, wherein a substantially direct current free digitial signal is generated depending on the signal content, without adding an additional redundancy.
ADVANTAGES OF THE INVENTION
The system in accordance with the invention with the characterizing features of the main claim has the advantage that the digital signals coded in dependency on the signal contents are substantially free from direct current components and that no additional redundancy has to be added.
The system in accordance with the invention may be used in the particularly advantageous manner for recording or transmission of video signals, but also other analog signals, for example, audio signals.
DRAWING
Exemplified embodiments of the invention are illustrated in the drawing and explained in more detailed in the following description. The drawing shows:
FIG. 1 a block diagram of a first embodiment of a device for coding and decoding in accordance with the inventive system,
FIG. 2 in a tabulated form an example for a code being useable in the system in accordance with the invention,
FIG. 3 a block diagram of another embodiment of a device for coding and decoding.
DESCRIPTION OF THE INVENTION
FIG. 1 illustrates o
REFERENCES:
patent: 3831167 (1974-08-01), Tewksbury
patent: 4387366 (1983-06-01), Chow
patent: 4491869 (1985-01-01), Heitmann
patent: 4501000 (1985-02-01), Immink et al.
The Engineering Staff of Analog Devices, Inc., Analog-Digital Conversion Handbook, 6/1972, pp. I-8, II-81.
National Semiconductor Data Sheet for MF6 6th Order Switched Capacitor Butterworth Lowpass Filter, 1983, 1 Sheet.
(Anonymous), Speech Signal Coding Handled by APCM, Electronics Weekly, 25 Jul. 1973, pp. 18 and 19.
Goldberg u.a.:"Optical Television Link Employing a Digitally Modulated Laser", Journal of the SMPTE, vol. 88, Jun. 1979, pp. 414-420.
Robert & Bosch GmbH
Sloyan T. J.
Striker Michael J.
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