Simplified branch metric for reducing the cost of a trellis sequence detector in a sampled amplitude read channel

A sampled amplitude read channel for reading data recorded on a disk storage medium by detecting an estimated binary sequence from a sequence of discrete-time sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, the sampled amplitude read channel comprising:

• (a) a sampling device for sampling the analog read signal to generate the discrete-time sample values;
• (b) a timing recovery circuit, responsive to the discrete-time sample values, for generating synchronous sample values xk;
• and
• (c) a trellis sequence detector for detecting the estimated binary sequence from the synchronous sample values xk, the trellis sequence detector comprising a branch metric calculator for calculating a simplified branch metric calculated proportional to
• ((xk2+2A−rem(xk2,2A))/2A)−nxk+An2/2
• where A is an even positive integer, n is an integer, An represents an ideal sample value of a target partial response, and the function rem(a,b) returns the remainder of a/b.

A method reading data recorded on a disk storage medium by detecting an estimated binary sequence from a sequence of discrete-time sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, comprising the steps of:

• (a) sampling the analog read signal to generate the discrete-time sample values;
• (b) extracting synchronous sample values xk from the discrete-time sample values;
• and
• (c) detecting the estimated binary sequence from the synchronous sample values xk by calculating a simplified branch metric of a trellis by effectively adding a positive offset to a Euclidean branch metric to make it a multiple of a scaler and dividing by the scaler, thereby reducing a number of bits used to represent the simplified branch metric.