Data storage device with asynchronous position error signal demodulation with split burst servo patterns

1 . A data storage device, comprising:

one or more disks;

an actuator mechanism configured to position a selected head among one or more heads proximate to a corresponding disk surface among the one or more disks; and

one or more processing devices comprising control circuitry, individually or in combination, wherein the control circuitry comprises an asynchronous demodulation module configured to:

receive demodulated split null burst signals based on the selected head reading a first set of bursts and a second set of bursts in a split burst servo pattern of the corresponding disk surface; and

output, based on the demodulated split null burst signals, a radial position signal, indicative of a radial position of the selected head, a first null burst squared signal, and a second null burst squared signal;

wherein:

the first set of bursts comprises a first burst and a third burst each at a same first radial location on the corresponding disk surface;

the second set of bursts comprises a second burst and a fourth burst each at a same second radial location on the corresponding disk surface different than the first radial location; and

respective bursts of the first set of bursts and respective bursts of the second set of bursts are disposed in an alternating manner along a longitudinal direction of a track containing the split burst servo pattern.

2 . The data storage device of claim 1 , wherein the control circuitry further comprises a burst demodulation module configured to output, to the asynchronous demodulation module, the demodulated split null burst signals based on the selected head reading the split burst servo pattern of the corresponding disk surface.

3 . The data storage device of claim 1 , wherein the demodulated split null burst signals comprise:

a first demodulated split null burst signal based on summing a first trigonometric function of respective values of a digital read-back signal sampled at the respective bursts of the first set of bursts;

a second demodulated split null burst signal based on summing a second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the first set of bursts;

a third demodulated split null burst signal based on summing the first trigonometric function of respective values of the digital read-back signal sampled at the respective bursts of the second set of bursts; and

a fourth demodulated split null burst signal based on summing the second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the second set of bursts.

4 . The data storage device of claim 1 , wherein:

the first set of bursts consists of the first burst and the third burst each having a first length in the longitudinal direction; and

the second set of bursts consists of the second burst and the fourth burst each having a second length in the longitudinal direction, the second length being equal to the first length.

5 . The data storage device of claim 1 , wherein:

the first set of bursts consists of the first burst, the third burst, and a fifth burst, the first burst and the fifth burst each having a first length in the longitudinal direction, and the third burst having a second length in the longitudinal direction; and

the second set of bursts consists of the second burst and the fourth burst each having the second length in the longitudinal direction.

6 . The data storage device of claim 1 , wherein:

the first set of bursts consists of the first burst, the third burst, and a fifth burst each having a first length in the longitudinal direction; and

the second set of bursts consists of the second burst, the fourth burst, and a sixth burst each having a second length in the longitudinal direction, the second length being equal to the first length.

7 . The data storage device of claim 1 , wherein the one or more processing devices further comprise a servo control processor, individually or in combination, wherein the servo control processor is configured to receive the radial position signal from the asynchronous demodulation module.

8 . The data storage device of claim 7 , wherein the servo control processor is further configured to receive the first null burst squared signal and the second null burst squared signal from the asynchronous demodulation module.

9 . The data storage device of claim 8 , wherein the servo control processor is further configured to output a position error signal (PES) based on the radial position signal, the first null burst squared signal, and the second null burst squared signal.

10 . The data storage device of claim 1 , wherein the asynchronous demodulation module is further configured to output the radial position signal such that the radial position signal covers substantially a full servo track.

11 . The data storage device of claim 10 , wherein the asynchronous demodulation module is further configured to output the radial position signal such that the radial position signal covers substantially the full servo track from a minus substantially half-track position signal to a plus substantially half-track position signal for the full servo track, corresponding to a minus substantially half-track position of the full servo track to a plus substantially half-track position of the full servo track.

12 . The data storage device of claim 11 , wherein the asynchronous demodulation module is further configured to output the radial position signal such that the radial position signal covers the full servo track with a single continuous position signal with a substantially continuous slope and free of stitching points within the radial position signal covering substantially the full servo track.

13 . A method comprising:

receiving, by an asynchronous demodulation module of control circuitry of a data storage device, demodulated split null burst signals based on a selected head reading a first set of bursts and a second set of bursts in a split null burst servo pattern of a corresponding disk surface; and

outputting, by the asynchronous demodulation module and based on the demodulated split null burst signals, a radial position signal indicative of a radial position of the selected head,

wherein:

the first set of bursts comprises a first burst and a third burst each at a same first radial location on the corresponding disk surface;

the second set of bursts comprises a second burst at a second radial location on the corresponding disk surface different than the first radial location;

the first burst, the second burst, and the third burst are disposed in an alternating manner along a longitudinal direction of a track containing the split null burst servo pattern;

the first burst and the third burst each have a first length in the longitudinal direction;

the second burst has a second length in the longitudinal direction different than the first length; and

wherein the receiving and the outputting are performed by one or more processing devices individually or in combination.

14 . The method of claim 13 , wherein the demodulated split null burst signals comprise:

a first demodulated split null burst signal based on summing a first trigonometric function of respective values of a digital read-back signal sampled at respective bursts of the first set of bursts;

a second demodulated split null burst signal based on summing a second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the first set of bursts;

a third demodulated split null burst signal based on summing the first trigonometric function of respective values of the digital read-back signal sampled at respective bursts of the second set of bursts; and

a fourth demodulated split null burst signal based on summing the second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the second set of bursts.

15 . One or more processing devices, individually or in combination, comprising an asynchronous demodulation module of control circuitry of a data storage device, the asynchronous demodulation module comprising:

means for receiving demodulated split null burst signals based on a selected head reading a first set of bursts and a second set of bursts in a split burst servo pattern of a corresponding disk surface; and

means for outputting, based on the demodulated split null burst signals, a radial position signal, indicative of a radial position of the selected head,

wherein the demodulated split null burst signals comprise:

a first demodulated split null burst signal based on summing a first trigonometric function of respective values of a digital read-back signal sampled at respective bursts of the first set of bursts;

a second demodulated split null burst signal based on summing a second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the first set of bursts;

a third demodulated split null burst signal based on summing the first trigonometric function of respective values of the digital read-back signal sampled at respective bursts of the second set of bursts; and

a fourth demodulated split null burst signal based on summing the second trigonometric function of the respective values of the digital read-back signal sampled at the respective bursts of the second set of bursts.

16 . The data storage device of claim 1 , wherein the radial position signal is generated in read/write channel circuitry.

17 . The data storage device of claim 1 , wherein the asynchronous demodulation module is in read/write channel circuitry separate from a servo control processor.

18 . The data storage device of claim 1 , wherein the first burst precedes the second burst, the second burst precedes the third burst, and the third burst precedes the fourth burst along the longitudinal direction of the track containing the split burst servo pattern.

19 . The data storage device of claim 1 , wherein the respective bursts of the first set of bursts each have a same first pattern polarity and the respective bursts of the second set of bursts each have a same second pattern polarity different than the first pattern polarity.

20 . The data storage device of claim 19 , wherein the first pattern polarity and the second pattern polarity are configured such that a polarity of a read-back signal obtained by reading the first set of bursts is inverted relative to the polarity of the read-back signal obtained by reading the second set of bursts.