Patent ID: 7253582

Claim:
A disk drive comprising: (a) a disk; (b) a head actuated over the disk; (c) a spindle motor for rotating the disk, the spindle motor comprising a plurality of windings including at least a first winding, a second winding, and a third winding; (d) disk control circuitry for executing a spin-up operation of the spindle motor by performing the steps of: applying a voltage to the first winding and measuring a first rise time for current flowing through the first winding to reach a predetermined threshold; applying a voltage to the second winding and measuring a second rise time for current flowing through the second winding to reach a predetermined threshold; applying a voltage to the third winding and measuring a third rise time for current flowing through the third winding to reach a predetermined threshold; computing a difference in response to the first rise time, the second rise time, and the third rise time; and estimating an angular position of the spindle motor by computing an arctangent in response to the difference.