E2PR4 viterbi detector and method for adding a branch metric to the path metric of the surviving path after selecting the surviving path

Abstract

An E 2 PR4 Viterbi detector includes a recovery circuit and receives a signal that represents a sequence of values, the sequence having a potential state. The recovery circuit recovers the sequence from the signal by identifying a surviving path to the potential state and, after identifying the surviving path, adding a modified branch metric to the path metric of the surviving path to generate an updated path metric for the potential state. Updating the path metric of the surviving path after the surviving path is selected allows the E 2 PR4 Viterbi detector to be smaller and/or faster than an E 2 PR4 Viterbi detector that updates the path metric before selecting the surviving path.

1 . An E 2 PR4 Viterbi detector, comprising:
 an input terminal operable to receive a signal that represents a sequence of values, the sequence having a potential state; and   a recovery circuit coupled to the input terminal and operable to recover the sequence from the signal by,
 identifying as a surviving path of the sequence to the potential state the path having the smallest path metric, and 
 adding a modified branch metric to the smallest path metric after identifying the surviving path to generate a modified path metric for the potential state. 
   
   
   
       2 .- 4 . (canceled) 
   
   
       5 . The E 2 PR4 Viterbi detector of  claim 1  wherein the recovery circuit is operable to:
 identify the surviving path by,   adding a respective remainder branch metric to each of the path metrics to generate updated path metrics,   calculating the respective differences between each pair of the updated path metrics,   determining from the differences which of the updated path metrics is the smallest updated path metric; and   add the modified branch metric to the smallest updated path metric to generate the modified path metric.   
   
   
       6 . An E 2 PR4 Viterbi detector, comprising:
 an input terminal operable to receive samples of a signal that represents a sequence of values, the sequence having a potential state;   a surviving-path register; and   a recovery circuit coupled to the first input terminal and to the register and operable to recover the sequence from the samples by,   comparing the path metrics of sequence paths that terminate at the potential state,   selecting the path having the smallest path metric,   adding a modified branch metric to the path metric of the selected path after selecting the path to generate a modified path metric for the potential state, and   loading the selected path into the surviving-path register.   
   
   
       7 .- 10 . (canceled) 
   
   
       11 . The E 2 PR4 Viterbi detector of  claim 6  wherein the recovery circuit is operable to compare the path metrics of the paths that terminate at the potential state of the sequence by,
 adding a respective remainder branch metric to each of the path metrics to generate updated path metrics, and   calculating the respective differences between each pair of the updated path metrics.   
   
   
       12 . An E 2 PR4 Viterbi detector, comprising:
 a branch-metric unit operable to receive samples of a signal that represents a sequence of values, the sequence having potential states, and to calculate from the samples a modified branch metric for each of the potential states; and   a compare-select-add unit operable to compare path metrics of sequences paths that terminate at each of the potential states to one another, select a surviving sequence path to each of the potential states, and respectively add the modified branch metrics to the path metrics of the surviving sequence paths to generate respective updated path metrics for the potential states.   
   
   
       13 . The E 2 PR4 Viterbi detector of  claim 12  wherein the branch-metric unit calculates the modified branch metrics from two samples. 
   
   
       14 . The E 2 PR4 Viterbi detector of  claim 12 , further comprising a surviving-metric unit operable to store the surviving sequence paths and the updated path metrics for the potential states of the sequence. 
   
   
       15 . A disk-drive system, comprising:
 a data-storage disk having a surface and operable to store information values;   a motor coupled to and operable to rotate the disk;   a read head operable to generate a read signal;   a read-head positioning assembly operable to move the read head over the surface of the disk; and   an E 2 PR4 Viterbi detector coupled to the read head and operable to recover a sequence of the stored information values from the read signal by,   comparing the path metrics of paths that terminate at a potential state of the sequence,   selecting the path having the smallest path metric, and   adding a modified branch metric to the path metric of the selected path after selecting the path to generate a modified path metric for the potential state.   
   
   
       16 .- 21 . (canceled) 
   
   
       22 . A method of recovering a sequence of values from a signal, for each potential state of the sequence the method comprising:
 identifying as the surviving E 2 PR4 path to the potential state the E 2 PR4 path having the smallest path metric; and   after identifying the surviving path, adding a modified E 2 PR4 branch metric to the smallest path metric to generate a modified path metric for the potential state.   
   
   
       23 .- 25 . (canceled) 
   
   
       26 . The method of  claim 22  wherein:
 identifying the surviving path comprises,   adding a respective remainder branch metric to each of the path metrics for the E 2 PR4 paths to the potential state of the sequence to generate updated path metrics,   calculating the respective differences between each pair of the updated path metrics, and   determining from the differences which of the updated path metric is the smallest updated path metric; and   adding the modified E 2 PR4 branch metric comprises adding the modified E 2 PR4 branch metric to the smallest updated path metric.