Data pattern for fly height measurement
View Patent ↗A hard disk drive that includes a disk and a head that is separated from the disk by a flying height. The disk drive also includes a circuit that determines the flying height from an equation that uses a third harmonic of a read signal. The read signal includes a data pattern that is a product of a first data pattern and a second data pattern. The resultant data pattern provides a third harmonic with a relatively high magnitude and improved signal to noise ratio.
1. A hard disk drive, comprising:
a disk;
a spindle motor that rotates said disk;
a head coupled to said disk and separated from said disk by a flying height; and,
a circuit coupled to said head, said circuit determines said flying height from an equation that uses a third harmonic of a read signal, said read signal includes a data pattern that is a product of a first data pattern and a second data pattern, said first and second data patterns having a different sequence of ones and zeros.
2. The disk drive of claim 1 , wherein said first data pattern is a 1T pattern and said second data pattern is a 4T pattern.
3. The disk drive of claim 1 , wherein said read signal is generated at a clock rate of F and said third harmonic has a frequency of ⅜ F.
4. The disk drive of claim 3 , wherein said first data pattern has a frequency of ½ F and said second data pattern has a frequency of ⅛ F.
5. The disk drive of claim 1 , wherein said equation uses a first harmonic of said read signal.
6. The disk drive of claim 1 , wherein said read signal is a square wave.
7. A hard disk drive, comprising:
a disk;
a spindle motor that rotates said disk;
a head coupled to said disk and separated from said disk by a flying height; and,
circuit means for determining said flying height from an equation that uses a third harmonic of a read signal, said read signal includes a data pattern that is a product of a first data pattern and a second data pattern, said first and second data patterns having a different sequence of ones and zeros.
8. The disk drive of claim 7 , wherein said first data pattern is a 1T pattern and said second data pattern is a 4T pattern.
9. The disk drive of claim 7 , wherein said read signal is generated at a clock rate of F and said third harmonic has a frequency of ⅜ F.
10. The disk drive of claim 9 , wherein said first data pattern has a frequency of ½ F and said second data pattern has a frequency of ⅛ F.
11. The disk drive of claim 7 , wherein said equation uses a first harmonic of said read signal.
12. The disk drive of claim 7 , wherein said read signal is a square wave.
13. A method for determining a flying height of a head of a hard disk drive, comprising:
generating a read signal with a data pattern that is a product of a first data pattern and a second data pattern, said first and second data patterns having a different sequence of ones and zeros; and,
determining a flying height of a head with an equation that uses a third harmonic of the read signal.
14. The method of claim 13 , wherein the first data pattern is a 1T pattern and the second data pattern is a 4T pattern.
15. The method of claim 13 , wherein the read signal is generated at a clock rate of F and the third harmonic has a frequency of ⅜ F.
16. The method of claim 15 , wherein the first data pattern has a frequency of ½ F and the second data pattern has a frequency of ⅛ F.
17. The method of claim 13 , wherein the equation uses a first harmonic of the read signal.
18. The method of claim 13 , wherein the read signal is a square wave.