Systems and methods for variable compensated fly height measurement
Various embodiments of the present invention provide systems and methods for determining fly height.
1. A system for determining fly height, the system comprising:
a frequency determination circuit operable to:
receive a first signal corresponding to a first data set, and to provide a first fundamental frequency and a first higher order frequency based on the first signal; and
receive a second signal corresponding to a second data set, and to provide a second fundamental frequency and a second higher order frequency based on the second signal;
a compensation variable calculation circuit, wherein the compensation variable calculation circuit is operable to divide the first fundamental frequency by the first higher order harmonic to yield a compensation variable; and
a fly height calculation circuit, wherein the fly height calculation circuit is operable to divide the second fundamental frequency by the second higher order harmonic and the compensation variable to yield an indication of a fly height.
2. The system of claim 1 , wherein the first data set is derived from a write channel, and the second data set is derived from a read circuit.
3. The system of claim 1 , wherein the system further comprises:
a head assembly disposed in relation to a storage medium;
a write channel;
a read circuit, wherein the read circuit is operable to receive information from both the head assembly and the write channel; and
wherein the fly height is a distance between the head assembly and the storage medium.
4. The system of claim 3 , wherein the first data set is derived from the write channel, and the second data set is derived from the head assembly.
5. The system of claim 1 , wherein the first higher order harmonic and the second higher order harmonic are selected from a group consisting of: a third order harmonic, a fourth order harmonic, and a sixth order harmonic.
6. The system of claim 1 , wherein the frequency determination circuit implements a discrete Fourier transform.
7. The system of claim 3 , wherein the system further comprises a memory, and wherein the memory is operable to receive the compensation variable from the compensation variable calculation module, and wherein the memory is operable to provide the compensation variable to the fly height calculation module.
8. The system of claim 5 , wherein the fly height calculation module receives an indication that the second information is derived from the second zone of the storage medium, and wherein the fly height calculation module is operable to divide the second fundamental frequency by the second higher order harmonic and the second compensation variable to yield an indication of a distance between the head assembly and the storage medium.
9. The system of claim 1 , wherein the system is implemented as storage device.
10. A method for calculating relative fly height, the method comprising:
disposing a head assembly a fly height distance from a storage medium;
receiving a first pattern;
based at least on the first pattern, calculating a compensation variable;
storing the compensation variable;
receiving a second pattern from the storage medium; and
based at least on the second pattern and the compensation variable, calculating an indication of the fly height distance.
11. The method of claim 10 , wherein the first pattern is derived from a source other than the storage medium.
12. The method of claim 1 , wherein the source other than the storage medium is a write circuit.
13. The method of claim 10 , wherein the first pattern and the second pattern are 6T patterns.
14. The method of claim 10 , wherein calculating the compensation variable includes:
determining a fundamental frequency of a signal corresponding to the received first pattern;
determining a higher order harmonic of the signal corresponding to the received first pattern; and
dividing the fundamental frequency by the higher order harmonic to create the compensation variable.
15. The method of claim 14 , wherein the higher order harmonic is selected from a group consisting of: a third order harmonic, a fourth order harmonic, and a sixth order harmonic.
16. The method of claim 10 , wherein calculating the indication of the fly height distance includes:
determining a fundamental frequency of a signal corresponding to the received second pattern;
determining a higher order harmonic of the signal corresponding to the received second pattern; and
dividing the fundamental frequency by the higher order harmonic and the compensation variable to create the indication of the fly height distance.
17. The method of claim 16 , wherein determining the fundamental frequency and determining the higher order harmonic is done by performing a discrete Fourier transform.
18. The method of claim 10 ,
wherein the read circuit includes an analog front end, and wherein the compensation variable compensates for one or more variables of the analog front end selected from a group consisting of: temperature and supply voltage; and
wherein calculating the compensation variable includes calculating a first compensation variable for a first combination including one or more of temperature and supply voltage, and calculating a second compensation variable for a second combination including one or more of temperature and supply voltage;
selecting one of the first compensation variable and the second compensation variable; and
wherein calculating the indication of the fly height distance includes:
determining a fundamental frequency of a signal corresponding to the received second pattern;
determining a higher order harmonic of the signal corresponding to the received second pattern; and
dividing the fundamental frequency by the higher order harmonic and the selected compensation variable to create the indication of the fly height distance.
19. The method of claim 18 , wherein selecting the one of the first compensation variable and the second compensation variable includes:
measuring at least one of temperature and supply voltage; and
selecting one of the first compensation variable and the second compensation variable based on a combination of one or more of a measured temperature and a measured supply voltage.
20. The method of claim 10 , wherein the storage medium includes at least a first disk zone and a second disk zone; wherein the first pattern exhibits a fundamental frequency specific to the first disk zone; wherein the compensation variable is specific to the first disk zone; and wherein the method further comprises:
determining that the second pattern is derived from the first disk zone;
based at least in part on the determination that the second pattern is derived from the first disk zone, selecting the compensation variable;
wherein calculating the indication of the fly height distance includes:
determining a fundamental frequency of a signal corresponding to the received second pattern;
determining a higher order harmonic of the signal corresponding to the received second pattern; and
dividing the fundamental frequency by the higher order harmonic and the selected compensation variable to create the indication of the fly height distance.