Method and apparatus for controlling fly-height of a perpendicular-magnetic-recording head in a hard disk drive

1. A method for controlling proximity of a read element of a perpendicular-magnetic-recording head to a perpendicular-magnetic-recording disk, said method comprising:

a) writing recorded data with a write element of said perpendicular-magnetic-recording head to said perpendicular-magnetic-recording disk;

b) providing a proximity-control setting to a proximity-control element;

c) positioning said read element of said perpendicular-magnetic-recording head with said proximity-control element as determined by said proximity-control setting in communication with said perpendicular-magnetic-recording disk for reading said recorded data back from said perpendicular-magnetic-recording disk;

d) measuring a resolution of a read-back signal of said recorded data on said perpendicular-magnetic-recording disk associated with said proximity-control setting;

e) determining if said resolution measured for said read-back signal of said recorded data on said perpendicular-magnetic-recording disk satisfies a criterion for said resolution of said read-back signal of said recorded data, wherein said resolution is measured by T 50 obtained from said read-back signal of said recorded data written with a low-frequency, square-wave waveform; and

f) changing said proximity-control setting, and repeating b), c), d) and e), unless said resolution satisfies said criterion, wherein proximity of said read element is controlled by said resolution of said read-back signal of said recorded data.

2. The method recited in claim 1 , wherein said method further comprises:

providing said proximity-control setting corresponding to said resolution that satisfies said criterion to said proximity-control element if said resolution satisfies said criterion;

positioning said read element of said perpendicular-magnetic-recording head with said proximity-control element as determined by said proximity-control setting in communication with said perpendicular-magnetic-recording disk for reading other recorded data back from said perpendicular-magnetic-recording disk.

3. The method recited in claim 2 , wherein said proximity-control element is a thermal-fly-height-control element.

4. The method recited in claim 3 , wherein proximity-control setting is a thermal-fly-height-control signal provided to said thermal-fly-height-control element.

5. The method recited in claim 1 , wherein said criterion is that T 50 is less than or equal to 28 nanometers.

6. The method recited in claim 1 , wherein said writing recorded data with a write element of said perpendicular-magnetic-recording head to said perpendicular-magnetic-recording disk further comprises:

driving said write element of said perpendicular-magnetic-recording head with a square-wave waveform to write said recorded data to said perpendicular-magnetic-recording disk.

7. The method recited in claim 6 , wherein said measuring a resolution of a read-back signal of said recorded data on said perpendicular-magnetic-recording disk associated with said proximity-control setting further comprises:

reading said recorded data from said perpendicular-magnetic-recording disk with a read element of said perpendicular-magnetic-recording head;

providing a read-back signal of said recorded data written using said square-wave waveform from said read element;

measuring said resolution of said read-back signal of said recorded data written using said square-wave waveform, wherein said resolution is defined by a time interval selected from the group consisting of a rise-time at an up-step portion of a read-back-signal, square-wave waveform and a fall-time at a down-step portion of a read-back-signal, square-wave waveform, said read-back-signal, square-wave waveform corresponding to said square-wave waveform used to write said recorded data.

8. The method recited in claim 7 , wherein said square-wave waveform is a low-frequency, square-wave waveform.

9. The method recited in claim 1 , wherein said proximity-control element is a thermal-fly-height-control element.

10. The method recited in claim 9 , wherein proximity-control setting is a thermal-fly-height-control signal provided to said thermal-fly-height-control element.

11. The method recited in claim 1 , wherein said resolution is measured by T 50 .

12. The method recited in claim 11 , wherein said criterion is that T 50 is less than or equal to 28 nanometers.

13. The method recited in claim 1 , further comprising a method for controlling proximity of said read element of said perpendicular-magnetic-recording head to said perpendicular-magnetic-recording disk without contacting said perpendicular-magnetic-recording disk.

14. A thermal-fly-height-control circuit configured to control proximity of a read element of a perpendicular-magnetic-recording head to a perpendicular-magnetic-recording disk, said thermal-fly-height-control circuit comprising:

a thermal-fly-height-control-signal synthesizer configured to generate a thermal-fly-height-control signal associated with a resolution of a read-back signal having satisfied a criterion for said resolution of said read-back signal, wherein said resolution is measured by T 50 obtained from said read-back signal of said recorded data written with a low-frequency, square-wave waveform; and

a thermal-fly-height-control element electrically coupled to said thermal-fly-height-control-signal synthesizer and configured to be driven with said thermal-fly-height-control signal to position said read element of said perpendicular-magnetic-recording head in communication with said perpendicular-magnetic-recording disk for reading recorded data from said perpendicular-magnetic-recording disk, wherein said proximity of said read element is controlled by said resolution of said read-back signal having satisfied a criterion for said resolution of said read-back signal.

15. The thermal-fly-height-control circuit of claim 14 , wherein said thermal-fly-height-control-signal synthesizer further comprises:

a digital-signal processor programmed to generate a digital signal for synthesizing said thermal-fly-height-control signal;

a digital-to-analog convertor electrically coupled to said digital-signal processor wherein said digital-to-analog convertor converts said digital signal into an analog signal; and

a thermal-fly-height-control-element driver to amplify said analog signal to generate said thermal-fly-height-control signal.

16. The thermal-fly-height-control circuit of claim 14 , wherein said criterion is that T 50 is less than or equal to 28 nanometers.

17. The thermal-fly-height-control circuit of claim 14 , wherein said proximity of said read element of said perpendicular-magnetic-recording head to said perpendicular-magnetic-recording disk is controlled without contacting said perpendicular-magnetic-recording disk.

18. A hard-disk drive configured to control proximity of a read element of a perpendicular-magnetic-recording head to a perpendicular-magnetic-recording disk, said hard-disk drive comprising:

said perpendicular-magnetic-recording disk rotatably mounted on a spindle;

a head-gimbal assembly comprising:

said perpendicular-magnetic-recording head comprising:

a write element for writing data to said perpendicular-magnetic-recording disk;

said read element for reading data from said perpendicular-magnetic-recording disk; and

a thermal-fly-height-control element configured to position said read element of said perpendicular-magnetic-recording head in communication with said perpendicular-magnetic-recording disk for reading recorded data from said perpendicular-magnetic-recording disk; and

a lead suspension attached to said perpendicular-magnetic-recording head; and

a load beam attached at a gimbal portion of said load beam to a slider including said perpendicular-magnetic-recording head; and

a drive motor having a motor shaft attached to said spindle for rotating said perpendicular-magnetic-recording disk;

a voice-coil motor comprising:

an armature including a voice-coil attached to said arm; and

a stator including a voice-coil magnet;

wherein said armature of said voice-coil motor is attached to said arm and is configured to move said head-arm assembly to access portions of said perpendicular-magnetic-recording disk; and

a thermal-fly-height-control circuit comprising:

a thermal-fly-height-control-signal synthesizer configured to generate a thermal-fly-height-control signal controlled by a resolution of a read-back signal having satisfied a criterion for said resolution of said read-back signal, wherein said resolution is measured by T 50 obtained from said read-back signal of said recorded data written with a low-frequency, square-wave waveform; and

said thermal-fly-height-control element electrically coupled to said thermal-fly-height-control-signal synthesizer.

19. The hard-disk drive of claim 18 , wherein said thermal-fly-height-control-signal synthesizer further comprises:

a digital-signal processor programmed to generate a digital signal for synthesizing said thermal-fly-height-control signal;

a digital-to-analog convertor electrically coupled to said digital-signal processor wherein said digital-to-analog convertor converts said digital signal into an analog signal; and

a thermal-fly-height-element driver to amplify said analog signal to generate said thermal-fly-height-control signal.

20. The hard-disk drive of claim 19 , wherein said criterion is that T 50 is less than or equal to 28 nanometers.

21. The hard-disk drive of claim 18 , wherein said proximity of said read element of said perpendicular-magnetic-recording head to said perpendicular-magnetic-recording disk is controlled without contacting said perpendicular-magnetic-recording disk.