In telecommunications, a paired disparity code is a line code in which at least one of the data characters is represented by two codewords of opposite disparity that are used in sequence so as to minimize the total disparity of a longer sequence of digits.
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.
The simplest paired disparity code is alternate mark inversion signal.
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.