A Viterbi decoder identifies errors in an early decision output and includes an early decision generator that generates the early decision output. A full decision generator generates a full decision output. An error detector detects errors in the early decision output and generates a disable signal. A secondary early decision generator generates a secondary early decision output. The error detector includes a comparing circuit that disables a prior early decision output if the secondary early decision output is different than the prior early decision output. Alternately, a best path flag generator generates a best path flag when the Viterbi decoder identifies two best paths having the same path metric. A comparing circuit disables the early decision output if a prior secondary early decision output is different than the early decision output, the best path flag is true and a prior best path flag is true.
Method and apparatus for detecting Viterbi decoder errors due to quasi-catastophic sequences