Patent ID: 7697650

Claim:
A phase measurement system for measuring a phase difference between an input signal having a first frequency and embedded in a medium separate from user information carried by the medium and a write data timing reference signal having a second frequency in an approximate range of 32 to 196 times the first frequency, the phase measurement system comprising: a phase comparator having a first input receiving a first sample of the input signal and a second sample of the input signal and having a second input receiving a clock derived from the write data timing reference signal, the phase comparator having an output representing a time between a crossing of a first threshold by the clock and a predetermined time along an interval from the first sample to the second sample where the input signal crosses a second threshold on the interval; an interpolator coupled to the first input and having an output indicative, at a resolution that is a fraction less than one period of the write data timing reference signal having the second frequency, of an interpolated time of the second-threshold-crossing on the interval in the input signal; a phase calculator coupled to the phase comparator output and the interpolator output and which computes the phase difference relative to the second frequency by combining the phase comparator output and the interpolator output; and a write data output circuit producing a write data output to the medium having timing based on the write data timing reference signal at the second frequency.