Relating to driving brushless DC (BLDC) motors

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.