Maximum likelihood sequence metric calculator

A maximum likelihood sequence metric calculator for use in a sequence decoder for processing sequences of sampled values from a communication channel or recording device. The metric calculator can be used in a maximum likelihood decoder, where the sequence can be based upon a 2-state trellis. This would include duobinary, dicode, or partial response class IV signalling. The survivor metrics for the two states is proportional to the peak amplitude detected for that state. Thus, the peak amplitude for a state is stored by a peak detector, until an opposite polarity amplitude is detected to switch the trellis path to the opposite polarity state. The path switching threshold to a state is determined by the opposite polarity state's peak amplitude and the maximum likelihood threshold value. Since only the peak amplitude of the state is stored, unbounded metric absolute value growth is not a problem.