Disk drive employing commutation phase modulation and current modulation of a spindle motor

1. A disk drive comprising:

(a) a disk;

(b) a head actuated over the disk;

(c) a spindle motor for generating a torque output to rotate the disk, the spindle motor comprising a plurality of windings;

(d) a power driver comprising a plurality of commutation switches for selectively energizing the windings;

(e) a commutation sequencer for controlling the commutation switches to configure the windings into a plurality of commutation states over a plurality of commutation intervals;

(f) a phase modulator for phase modulating the commutation intervals; and

(g) a current modulator for controlling a current applied to the windings in each of the commutation states to substantially reduce discontinuities in the torque output of the spindle motor caused by the phase modulator.

2. The disk drive as recited in claim 1 , wherein the phase modulator and the current modulator reduce internal vibrations.

3. The disk drive as recited in claim 2 , wherein the phase modulator and the current modulator reduce internal vibrations that cause audible noise.

4. The disk drive as recited in claim 1 , wherein the current modulator modulates the torque output over the commutation intervals to reduce the discontinuities in the torque output of the spindle motor.

5. The disk drive as recited in claim 1 , further comprising a commutation clock generator for generating a nominal commutation clock, wherein:

the phase modulator modulates a phase of the nominal commutation clock to generate a phase modulated commutation clock;

the commutation sequencer uses the phase modulated commutation clock to change the commutation state;

phase modulating the commutation clock spreads commutation energy over a frequency spectrum to reduce audible noise generated by the spindle motor;

phase modulating the commutation clock generates torque discontinuities when the commutation sequencer changes the commutation state; and

the current modulator reduces the torque discontinuities caused by phase modulating the commutation clock.

6. The disk drive as recited in claim 1 , wherein:

the current modulator generates a pulse width modulated (PWM) signal; and

a duty cycle of the PWM signal is adjusted in response to a current command comprising:

a speed correction current command; and

a current modulation value corresponding to the commutation interval.

7. A method of operating a disk drive, the disk drive comprising, a disk, a head actuated over the disk, and a spindle motor for generating a torque output to rotate the disk, the spindle motor comprising a plurality of windings, the method comprising the steps of:

(a) selectively energizing the windings based on a plurality of commutation states over a plurality of commutation intervals;

(b) modulating a phase of the commutation intervals; and

(c) modulating a current applied to the windings in each of the commutation states to substantially reduce discontinuities in the torque output of the spindle motor caused by modulating the phase of the commutation intervals.

8. The method as recited in claim 7 , wherein the steps of modulating the phase of the commutation intervals and modulating the current applied to the windings reduces internal vibrations.

9. The method as recited in claim 8 , wherein the steps of modulating the phase of the commutation intervals and modulating the current applied to the windings reduces internal vibrations that cause audible noise.

10. The method as recited in claim 7 , wherein the step of modulating the current applied to the windings modulates the torque output over the commutation intervals to reduce the discontinuities in the torque output of the spindle motor.

11. The method as recited in claim 7 , wherein the step of modulating the phase of the commutation intervals comprises the steps of:

generating a nominal commutation clock;

modulating a phase of the nominal commutation clock to generate a phase modulated commutation clock; and

changing the commutation state in response to the phase modulated commutation clock,

wherein:

modulating the phase of the commutation clock spreads commutation energy over a frequency spectrum to reduce audible noise generated by the spindle motor;

modulating the phase of the commutation clock generates torque discontinuities when the commutation state changes; and

modulating the current applied to the windings reduces the torque discontinuities caused by phase modulating the commutation clock.

12. The method as recited in claim 7 , wherein the step of modulating the current applied to the windings comprises the steps of:

generating a pulse width modulated (PWM) signal; and

adjusting a duty cycle of the PWM signal in response to a current command comprising:

a speed correction current command; and

a current modulation value corresponding to the commutation interval.