A servo writing system for writing servo sectors onto a disk includes a
direct digital synthesizer (DDS) that forms a phase and frequency
adjustable continuous wave signal based upon a reference digital clock
signal. A PLL coupled to the DDS measures repeatable timing errors (RTEs)
associated with the continuous wave signal and generates an output clock
signal that is used to clock the writing of servo sectors onto the disk.
A digital control system is coupled to the DDS and the PLL, which
calculates repeatable error compensation adjustment values based on the
RTEs measured using the PLL. The compensation adjustment values may be
applied to the DDS such that the DDS compensates for the RTEs and such
that the output clock signal used to clock the writing of the servo
sectors onto the disk includes minimal RTEs.