US Patent 7346836 E

An E2PR4 Viterbi detector receives a signal that represents a sequence of values, the sequence having a potential state. The detector includes a recovery circuit that recovers the sequence from the signal by identifying the surviving path to the potential state and simultaneously adding a modified branch metric to the path metric of the surviving path. By simultaneously identifying the surviving path and adding a modified branch metric to its path metric, such an E2PR4 Viterbi detector can operate faster than a conventional add-compare-select E2PR4 Viterbi detector.