Paired disparity code: Difference between revisions

Revision as of 05:52, 24 April 2012

Revision as of 18:04, 27 July 2012

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In a paired disparity code, every codeword that averages to a negative level (negative disparity) is paired with some other codeword that averages to a positive level (positive disparity).

In a system that uses a paired disparity code, the transmitter must keep track of the running DC buildup, -- the [[running disparity]] -- and always pick the codeword that pushes the DC level back towards zero. The receiver is designed so that either codeword of the pair decodes to the same data bits.

Most line codes use either a paired disparity code or a [[constant-weight code]].

The simplest paired disparity code is [[Alternate Mark Inversion|alternate mark inversion signal]].

Other paired disparity codes include [[8B10B]], the [[modified AMI code]]s, [[coded mark inversion]], and [[4B3T]].

The digits may be represented by disparate physical quantities, such as two different frequencies, phases, voltage levels, magnetic polarities, or electrical polarities, each one of the pair representing a 0 or a 1.