A coherent maximum likelihood head position estimator for PERM disk drives

A coherent digital maximum-likelihood (ML) head position estimator was proposed and examined for sampled-servo magnetic disk drives. Estimating the ML head position is obtained through four ML amplitude estimators of each servo mark readback pulse. When compared to a conventional analog integration detector about 1.7 dB improvement in position estimation accuracy was obtained. To generate a servo clock for coherent estimation, an ML phase estimating digital phase-locked loop (DPLL) was also developed. Since five inner product operations for amplitude and phase estimation are performed by a time-shared multiplier-accumulator, this ML head position estimator is applicable for use in small scale hardware and adaptable to ICs