Parity- sensitive Viterbi detector and method for recovering information from a read signal

A Viterbi detector, comprising:

• an input terminal operable to receive a signal that represents a sequence of values;
• a register;
• and
• a recovery circuit coupled to the input terminal and to the register, the circuit operable to,
• recover only groups of values having a predetermined parity, and
• load the recovered groups into the register.

A Viterbi detector, comprising:

• an input terminal operable to receive a signal that represents a sequence of values;
• a register;
• and
• a circuit coupled to the input terminal and to the register, the circuit operable to,
• recover the sequence from the signal by calculating a branch length between a first potential state of the sequence representing a first sequence parity and a second potential state of the sequence representing a second sequence parity, and
• load the recovered sequence into the register.

A Viterbi detector, comprising:

• an input terminal operable to receive a signal that represents a sequence of values;
• a register;
• and
• a circuit coupled to the input terminal and to the register, the circuit operable to,
• calculate a first set of branch lengths between first and second sets of possible sequence states according to a first set of branches, each branch originating from a respective state that represents a first sequence parity,
• calculate a second set of branch lengths between third and fourth sets of possible sequence states according to a second set of branches, each branch ending on a respective state that represents a second sequence parity,
• recover the sequence of values from the first and second sets of branch lengths, and
• load the recovered sequence into the register.

A Viterbi detector, comprising:

• an input terminal operable to receive a signal that represents a code word;
• a register;
• and
• a circuit coupled to the input terminal and to the register, the circuit operable to,
• calculate path lengths according to a first set of state-transition branches,
• update the path lengths more than once according to a second set of state-transition branches that is different than the first set,
• update the path lengths according to a third set of state-transition branches that is different than the first and second sets,
• recover the code word from the updated path lengths, and
• load the recovered code word into the register.

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
• a Viterbi detector coupled to the read head and operable to recover a sequence of the stored information values from the read signal by calculating a branch length between first and second potential states of the sequence, the first potential state representing a first parity of the sequence and the second potential state representing a second parity of the sequence.

A method, comprising:

• receiving a signal that represents a sequence of values;
• calculating first branch lengths between first potential sequence states and second potential sequence states along respective first state-transition branches, each first state-transition branch originating from a respective first state that represents a first parity of the sequence;
• calculating second branch lengths between third potential sequence states and fourth potential sequence states along respective second state-transition branches, each second state-transition branch ending on a respective fourth state that represents a second parity of the sequence;
• and
• recovering the sequence from the signal using the first and second branch lengths.

A method, comprising:

• receiving a signal that represents a code word;
• calculating path lengths during a first period according to a first set of state-transition branches;
• updating the path lengths during a plurality of periods following the first period according to a second set of state-transition branches that is different than the first set;
• updating the path lengths during a third period following the plurality of periods according to a third set of state-transition branches that is different than the first and seconds sets;
• and
• recovering the code word from the signal using the updated path lengths.