Digital spindle control architecture

A method for measuring an electrical period of a three-phase spindle motor having three terminals, each terminal being driven with a pulse width modulated drive signal, the method iteratively comprising:

• detecting zero crossings in a back electromotive force signal induced at a first terminal of the motor, determining a time between successive zero crossings;
• determining a rotational position of the motor;
• and
• wherein the zero crossings are detected by selecting a time window during which the back electromotive force signal is sensed for zero crossings, the time window being selected as a function of the last measured electrical period and the rotational position of the motor.

A motor controller for controlling rotation of a three-phase spindle motor having three terminals, each terminal being driven with a pulse width modulated drive signal, the motor controller comprising:

• period measurement circuitry for coupling to a first terminal of the motor to measure an electrical period of the motor by detecting zero crossings in a back electromotive force signal induced at the first terminal and for determining the time between successive zero crossings;
• state dividing circuitry coupled to the period measurement circuitry for determining a rotational position of the motor;
• and
• a pulse width modulation generator coupled to the state dividing circuitry for generating pulse width modulated drive signals that are synchronized with the measured electrical period of the motor, the synchronized pulse width modulated drive signals being provided for coupling to the motor;
• wherein the zero crossings are detected by operating the period measurement circuitry and the state dividing circuitry to select a time window during which the back electromotive force signal is sensed for zero crossings, the time window being selected as a function of the last measured electrical period and the rotational position of the motor.