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Method and apparatus for code conversion of binary to multilevel signals

  • US 4,408,189 A
  • Filed: 05/18/1981
  • Issued: 10/04/1983
  • Est. Priority Date: 05/18/1981
  • Status: Expired due to Term
First Claim
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1. A code converter comprising:

  • means for converting blocks of binary bits into words of multilevel symbols, the words being grouped into frames;

    a running digital sum counter for determining the running digital sum of all previously converted multilevel symbol words;

    a digital sum variation counter for determining the digital sum variation of each word;

    means responsive to the counters for inverting selected words so as to minimize the accumulated running digital sum of the previously converted multilevel symbol words, and the selected words;

    characterized by;

    means for including a separate multilevel symbol at the end of each frame to indicate the inversion of said selected words; and

    means for initializing the digital sum variation counter at the beginning of each word to a value which compensates for the digital sum variation of the separate multilevel symbol, whereby the polarity of the digital sum variation of the current word may be compared against that of the preceding running digital sum to reestablish frme synchronization.

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