Servo writing a disk drive from spiral tracks by shifting a demodulation window an integer number of sync mark intervals

1. A method of writing product servo sectors to a disk of a disk drive, the disk drive comprising control circuitry and a head disk assembly (HDA) comprising the disk, an actuator arm, a head coupled to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk, the disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval, the method comprising the steps of:

(a) using the head internal to the disk drive to read the spiral tracks to generate a read signal;

(b) processing the read signal to detect the sync marks in the spiral tracks to synchronize a servo write clock;

(c) using the servo write clock to open a demodulation window;

(d) demodulating the high frequency signal in the spiral tracks into a plurality of servo burst signals during the demodulation window to generate a position error signal used to maintain the head internal to the disk drive along a first servo track;

(e) using the head internal to the disk drive to write product servo sectors along the first servo track;

(f) shifting the demodulation window by an integer number of sync mark intervals to initiate a seek to a second servo track; and

(g) using the head internal to the disk drive to write product servo sectors along the second servo track.

2. The method as recited in claim 1 , wherein the integer number is one.

3. The method as recited in claim 1 , wherein the integer number is greater than one.

4. The method as recited in claim 1 , wherein the step of generating the position error signal comprises the step of computing a difference between the servo burst signals.

5. The method as recited in claim 4 , wherein the step of shifting the demodulation window an integer number of sync mark intervals causes the plurality of servo burst signals to shift a corresponding amount to generate a non-zero position error signal.

6. A disk drive comprising:

(a) a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval;

(b) a head actuated over the disk; and

(c) control circuitry for writing a plurality of product servo sectors to the disk to define a plurality of radially spaced, concentric data tracks by:

using the head internal to the disk drive to read the spiral tracks to generate a read signal;

processing the read signal to detect the sync marks in the spiral tracks to synchronize a servo write clock;

using the servo write clock to open a demodulation window;

demodulating the high frequency signal in the spiral tracks into a plurality of servo burst signals during the demodulation window to generate a position error signal used to maintain the head internal to the disk drive along a first servo track;

using the head internal to the disk drive to write product servo sectors along the first servo track;

shifting the demodulation window by an integer number of sync mark intervals to initiate a seek to a second servo track; and

using the head internal to the disk drive to write product servo sectors along the second servo track.

7. The disk drive as recited in claim 6 , wherein the integer number is one.

8. The disk drive as recited in claim 6 , wherein the integer number is greater than one.

9. The disk drive as recited in claim 6 , wherein the control circuitry generates the position error signal by computing a difference between the servo burst signals.

10. The disk drive as recited in claim 9 , wherein shifting the demodulation window an integer number of sync mark intervals causes the plurality of servo burst signals to shift a corresponding amount to generate a non-zero position error signal.