Patent ID: 7508889

Claim:
A soft decision circuit for determining a most likely data content of a differential phase-shift keying (DPSK) modulated optical signal from three differentially detected intermediate signals that are based on comparisons between pairs of a series of three contiguous data bits of the DPSK modulated optical signal, the soft decision circuit comprising: a plurality of comparators, each comparator comparing two of the three intermediate signals and generating a digital signal in accordance with the comparison; and digital logic, the digital logic determining a most likely data content based on the comparator signals, wherein: G= NOR[AND( B>−C, A>−B ), AND( B>A, B>C )], where A represents a first of the intermediate signals based on a comparison between the first and second of the series of three contiguous data bits, B represents a second of the intermediate signals based on a comparison between the second and third of the series of three contiguous data bits, C represents a third of the intermediate signals based on a comparison between the first and third of the series of three contiguous data bits, and G represents the most likely data content.