Patent ID: 8442174

Claim:
An apparatus, comprising: a sampler having an input configured to receive a serial data stream and a logic clock signal as inputs, the logic clock signal having sampling periods, wherein the sampler is configured to extract samples from the serial data stream, the extracted samples comprising at least four samples extracted previously during a stored sampling period, wherein the stored sampling period corresponds to a previous sampling period in which there was a transition of the serial data stream, at least four samples extracted during a second sampling period, and at least four samples extracted during a third sampling period, wherein the at least four samples taken during each sampling period comprise a first sample, a second sample, a third sample and a fourth sample, and wherein an interval between the first sample and the second sample of a sampling period corresponds to a first quadrant for the sampling period, an interval between the second sample and the third sample of a sampling period corresponds to a second quadrant of the sampling period, an interval between the third sample and the fourth sample of a sampling period corresponds to a third quadrant of the sampling period, and wherein an interval between the fourth sample and an end of a sampling period corresponds to a fourth quadrant of the sampling period; and a rotational frequency detector configured to receive the samples from the sampler, and to generate one or more states for a first frequency up error signal, a second frequency up error signal, a first frequency down error signal, or a second frequency down error signal based at least partly on timing of the transition in the stored sampling period and on timing of transitions, if any, of the samples of the second sampling period or the third sampling period, and to replace transition data for the stored sampling period with transition data from one of the second sampling period or the third sampling period when a transition is encountered, wherein the first sample taken during the stored, second, and third sampling periods is taken substantially from the beginning of each respective sampling period, and wherein the third sample extracted during the stored, second, and third sampling periods is taken substantially halfway into each respective sampling period.