On timing recovery from full-wave-rectified magnetic signals

Fullwave rectified magnetic readback signals have a frequency component at the bit frequency, which can be utilized for timing. Feedforward timing can provide quick bit resync when recovering from thermal asperities, since it doesn't depend on a sync field. To be usable, the timing phase must vary little with the binary data, and the timing signal amplitude range must be reasonable. We compute the phase and amplitude distributions for all periodic patterns of length 9, as well as for PRBS patterns. We conclude that the lower the signal ISI, the smaller the timing phase shift. A rate 8/9 code reduces the timing shift to 2% for PR4, 5% for EPR4. Uncoded PRBS signals produce less than 2% timing shift.