Clock recovery in a sampled received signal including removal of ISI effects from data samples used to detect zero-crossing

摘要

A zero-crossing of a sampled received signal can be determined by looking at the values and polarities of successive samples using, e.g., the Gardner algorithm. However where the signal is subject to inter-symbol interference (ISI) these values are affected by "contributions" from previous and following symbols in the signal (fig.15, not shown). The present invention seeks to compensate for ISI by subtracting these contributions from a sample between first and second samples having opposite polarities, and therefore potentially a zero-crossing point. The values of the first and second samples are not included in the caalculation. The contribution may be expressed as, e.g., a weighted summation, hash function or other function of samples immediately preceding and following the first and second samples. The calculation is done in an equaliser (171) and the output may be applied to a PLL for clock recovery.