A Study of Timing Recovery for High-Recording-Density Tape Systems

A timing recovery method for a high-density tape storage system is studied in this paper. Since tape systems suffer from large speed variations compared with disk systems, the design of a stable timing recovery scheme that can operate under low signal-to-noise ratio (SNR) conditions is important. In such low SNR scenarios, decision errors made by the detector occasionally cause the phase-locked loop circuit to lose track of the correct signal, which is often called the loss-of-lock (LOL) phenomenon. In order to mitigate the LOL issue, soft information from the Viterbi detector is utilized. It is clarified that the negative effect of unreliable decisions from the detector can be compensated for by dynamically controlling the feedback gain of the timing recovery loop as a function of decision reliability. It is shown that the LOL rate performance can be improved by this approach, with only a minor increase in the implementation complexity.