A constrained asymmetry LMS algorithm for PRML disk drive read channels

We present an implementation of a constrained least mean square (C-LMS) algorithm with application to high-speed magnetic disk drive read channels. The main advantage offered by the presented C-LMS algorithm is improved stability of the outer timing recovery loop while the spectral shaping of read-back data is performed in the inner adaptation loop. This eliminates any unstable behavior of the timing recovery loop during C-LMS algorithm adaptation. Another benefit derived from this approach is reduction in coefficient switching gradient noise. The proposed algorithm has been implemented and fabricated in a commercial read channel using a 0.18 μm L-effective CMOS technology. It operates at 550 MHz worst case