Patent ID: 8201066

Claim:
A disk drive comprising: a disk; a head actuated over the disk to generate a read signal; a sampling device operable to sample the read signal to generate a sequence of signal sample values; and a trellis detector for detecting an estimated data sequence from the signal sample values, the trellis detector comprising a plurality of add/compare/select (ACS) circuits each corresponding to a state in a trellis, wherein each ACS circuit comprises: a first error generator for generating a first error relative to a signal sample value and a first expected value corresponding to a first branch in the trellis; a first adder for adjusting the first error in response to a first delta to generate a first adjusted error; a first branch metric calculator for computing a first branch metric in response to the first adjusted error; a first update circuit for updating the first delta in response to the first adjusted error; a second error generator for generating a second error relative to the signal sample value and a second expected value corresponding to a second branch in the trellis; a second adder for adjusting the second error in response to a second delta to generate a second adjusted error; a second branch metric calculator for computing a second branch metric in response to the second adjusted error; and a second update circuit for updating the second delta in response to the second adjusted error.