Timing acquisition for low-SNR data storage channels

As magnetic data storage densities are pushed toward Tb/in² and beyond, advanced signal-detection algorithms are being suggested to cope with the expected lower signal-to-noise ratios (SNRs). However, at low SNR, loss of lock will frequently occur in the current timing-recovery system. This paper illustrates that inadequate timing acquisition is the major cause for loss of lock in hard disk drives. Motivated by the digital zero phase start (DZPS) technique, a digital zero frequency/phase start (DZF/PS) technique is proposed to quickly reduce the initial frequency and phase errors. Kalman filter-based acquisition can be used subsequently to fine-tune acquisition based on the buffered symbol-rate samples of a preamble readout signal. Numerical simulations show that DZF/PS can reduce preamble length significantly (when used in acquisition) compared with DZPS.