Coded data generation or conversion – Digital code to digital code converters – To or from multi-level codes
Patent
1993-12-14
1995-10-24
Hoff, Marc S.
Coded data generation or conversion
Digital code to digital code converters
To or from multi-level codes
375286, H03M 516
Patent
active
054613795
ABSTRACT:
Loss of synchronization, due to a digital data signal having the same signal value for an extended number of bit or symbol periods, is overcome through the use of a coding scheme which assures transitions after each such period despite the absence of transitions in the signal to be encoded. Broadly, within the encoder, a digital input signal having m signal levels is transformed into a coded digital output signal having n possible signal values, where m<n. The transformation alters the current digital input signal value as a function of the previous coded digital output signal value and the current digital input signal value performed in a number system whose modulus is n. In a disclosed embodiment, a binary input signal is coded into an output signal having three signal levels. The transformation provided in the encoder of this disclosed embodiment provides a coded output signal whose value is equal to the previous coded output signal value +1, modulo 3, when the current value of the digital input signal is logical 1 and whose value is the previous coded output signal value -1, modulo 3, or, equivalently, the previous coded output signal value 2, modulo 3, when the current value of the digital input signal is logical "0". Advantageously, this approach can be implemented for the coding of a digital signal having two or more signal levels.
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AT&T IPM Corp.
Bartholomew Steven R.
Hoff Marc S.
Padnes David R.
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