Timing recovery frequency error detector for sampled amplitude magnetic recording

Claim 1

A timing recovery circuit in a synchronous read channel utilized in reading data from a magnetic medium, said synchronous read channel detects digital data from a sequence of discrete time sample values Y(n) generated by sampling pulses in an analog read signal from a magnetic read head positioned over the magnetic medium, said timing recovery circuit for adjusting a phase and frequency of a sampling clock signal relative to a phase and frequency of the pulses, said timing recovery circuit comprises a frequency error detector comprising: (a) an input connected to receive the sample values Y(n); and (b) an output for outputting a frequency error ƒe computed in response to three of the sample values Y(n), wherein; the analog read signal is substantially periodic and the sample values Y(n) for computing the frequency error ƒe span more than half of a period of the analog read signal; and The frequency error ƒe is commuted proportional to: sgn(Y(1))·(Y(4)-Y(0)) if |Y(1)|>|Y(2)|; and sgn(Y(2))·(Y(5)-Y(1)) if |Y(1)|<|Y(2)|, where the function sgn(x) returns the sign of the parameter x.