Method and system for estimating an input data sequence based on an output data sequence and hard disk drive incorporating same

A hard disk drive system comprising:

• a storage media system;
• and
• a read channel for reading data from the storage media system, the read channel including a detector operable to estimate a plurality of data values written to the storage media based on a plurality of data values written to the storage media based on a plurality of data values read from the storage media, the detector comprising:
• a branch metric generator operable to generate a branch metric for a data value read from the storage media with respect to each of a plurality of targets;
• and
• an add-compare-select system comprising a plurality of add-compary-select unites, each add-compare-select unit being operable in one clock cycle to receive a branch metric, a path metric upper portion, and first and second provisional path metric lower portions, and generate an updated path metric upper portion and first and second updated provisional path metric lower portions.

A method for determining a current input data value based on a plurality of received data values, the received data values each having a plurality of targets, the method comprising the steps of:

• operating a detector in a clock cycle for each target;
• generating a branch metric for a received data value corresponding to the received input data value, the branch metric represented by a plurality of binary digits ranging from a least-significant bit to a most-significant bit;
• and
• for each possible current state of a first number of sequential input data values including the received input data value:
• providing first and second provisional path metric lower portions and first and second provisional path metric lower portions each respectively comprising at least one lesser significant bit of first and second provisional path metrics associated with transitioning from each of first and second possible states of the first number of data values immediately preceding the received input data value to the current state of the first number of input data values including the received input data value, the first and second provisional path metric upper portions each respectively comprising at least one significant bit of the first and second provisional path metrics associated with transitioning from each of first and second possible states of the first number of data values immediately preceding the received input data value to the current state of the first number of input data values including the received input data value;
• adding each of the first and second provisional path metric lower portions with a branch metric lower portion to produce, respectively, an updated first provisional path metric lower portion candidate and an updated second provisional path metric lower portion candidate, the branch metric lower portion comprising lesser significant bits of a branch metric associated with a target associated with transitioning from the first possible state of the first number of data values immediately preceding the received input data value to the current state of the first number of input data values including the received input data value;
• receiving a selection signal designating one of the first and second provisional path metric lower portion candidates to produce an updated path metric lower portion candidate;
• adding any carry component of the selected updated path metric lower portion candidate with a path metric upper portion and a branch metric upper portion to produce a first updated path metric upper portion candidate;
• comparing the updated path metric upper portion candidate to at least one other updated path metric upper portion candidate;
• selecting one of the updated path metric upper portion candidates as the updated path metric upper portion;
• and
• providing a decision signal indicating which updated path metric upper portion candidate was selected.

A method for generating an updated path metric, the method comprising:

• operating a detector in a single clock cycle;
• receiving a path metric divided into an upper portion and a lower portion;
• receiving a branch metric having at least a lower portion;
• adding the lower portion of the path metric to the lower portion of the branch metric to produce a first sum having first and second portions;
• adding, during a first clock cycle, the first portion of the first sum to a second sum;
• delaying comparison of the second portion of the first sum;
• and
• comparing, during a subsequent clock cycle, the second portion of the first sum to a third sum.