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DC Balancing Resynchronization Symbols

IP.com Disclosure Number: IPCOM000084391D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Cage, KL: AUTHOR [+2]

Abstract

In magnetic recording apparatus employing block codes of the run-length limited type, it is desirable to periodically interleave resynchronization symbols (bytes) in the recorded signal sequence. Such resynchronization symbols must not only properly denote proper phase and framing of the signal sequence for enabling automatic error recovery, but also should maintain DC balance within the desired constraints.

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DC Balancing Resynchronization Symbols

In magnetic recording apparatus employing block codes of the run-length limited type, it is desirable to periodically interleave resynchronization symbols (bytes) in the recorded signal sequence. Such resynchronization symbols must not only properly denote proper phase and framing of the signal sequence for enabling automatic error recovery, but also should maintain DC balance within the desired constraints.

In a most preferred form of resynchronization symbols, the DC balance is always returned to a predetermined value within the range of constraints, preferably at perfect DC balance (zero deviation). This should be accomplished in a minimal number of symbols, preferably not more than two.

When the signal is up (+) for one bit period, it is said that the DC variation has been changed by +1 bit period charge. If it is down for the entire bit period, it is a -1 bit period charge. If there is a transition in the center of a bit period, the DC deviation is 0 (AC balance).

By altering the signal sequence at the one end of the symbol (beginning or trailing end), the digital sum variation (DSV) of the symbol can be controlled. For example, in the solid line version, there is a +2 units of digital variation from DC balance. By changing this signal waveform to that indicated by the dotted line, the digital sum variation is changed to zero. Using this technique, the number of resynchronization symbols is minimized.

In one example app...