Patent ID: 8212508

Claim:
An electric motor comprising: a rotor; a stator having a plurality of phase windings; a back EMF sampling unit operable to sample a back EMF signal during an undriven period, wherein the back EMF sampling unit comprises an integrator connected to a sample and hold circuit, the integrator being operable to integrate the back EMF signal in response to a switch close signal and output to the sample and hold circuit and being operable to output a signal indicative of the integrated back EMF signal value in response to a switch open signal which stops the integration process; wherein the motor is driven by a method comprising the steps of: driving at least one of the plurality of phase windings with a suitable driving current waveform; providing an undriven period during the driving waveform; sampling the back EMF signal in the at least one of the plurality of phase windings on two or more occasions during the undriven period; and interpolating the back EMF signal based on back EMF samples to thereby determine a zero crossing point for the at least one of the plurality of phase windings; wherein the position of the rotor is sensed by a method comprising the steps of: determining a zero crossing point for one or more of the plurality of phase windings by driving the one or more of the plurality of phase windings with a suitable driving current waveform; providing the undriven period during the driving waveform; sampling the back EMF signal in the one or more of the plurality of phase windings on two or more occasions during the undriven period; interpolating the back EMF signal based on back EMF samples; and determining the position of the rotor based at least in part on the determined zero crossing point and interpolated back EMF signal.