Calculation of head media separation (HMS) from servo preamble in a hard disk drive
View Patent ↗A method of calculating a Head Media Separation (HMS) from a preamble of embedded servo sectors in a disk drive may include steps of reading the preamble, the read preamble being amplified by a variable gain amplifier (VGA) set at a predetermined gain; transforming samples of the read preamble into a first and a second frequency using a discrete time-to-frequency domain transform such as a Discrete Fourier Transform (DFT); calculating the ratio of the magnitude of the discrete time-to-frequency domain transform of the first frequency to the magnitude of the discrete time-to-frequency domain transform of the second frequency; determining the HMS from the calculated ratio, and enabling the predetermined gain to be updated in synchronism with the transforming step.
1. A method of calculating a Head Media Separation (HMS) from a preamble of at least one embedded servo sector in a disk drive, the disk drive including at least one disk, comprising:
reading the preamble of the at least one embedded servo sector, the read preamble being amplified by a variable gain amplifier (VGA) set at a predetermined gain;
transforming samples of the at least one read preamble into a first and a second frequency using a discrete time-to-frequency domain transform;
calculating a ratio of a magnitude of the discrete time-to-frequency domain transform of the first frequency to a magnitude of the discrete time-to-frequency domain transform of the second frequency;
determining the HMS from the calculated ratio; and
enabling the predetermined gain to be updated only at a beginning of a window of width modulo-N, wherein N is a wavelength of a lower one of the first and second frequencies.
2. The method of claim 1 , wherein the first frequency is a fundamental frequency of a signal encoded within the preamble and wherein the second frequency is a harmonic frequency of the signal encoded within the preamble.
3. The method of claim 1 , wherein the first and second frequencies are a fundamental frequency and an odd harmonic frequency, respectively, of a square wave encoded with the preamble.
4. The method of claim 3 , wherein the odd harmonic frequency is a third harmonic frequency.
5. The method of claim 1 , wherein the discrete time-to-frequency transform includes a Discrete Fourier Transform (DFT).
6. The method of claim 1 , further including a step of updating the predetermined gain at a beginning of the window of width modulo-N and returning to the reading step with the VGA being set to the updated predetermined gain.
7. The method of claim 1 , further including a step of updating the predetermined gain synchronously with the transforming step.
8. The method of claim 7 , wherein the updating step is carried out in a step-wise linear manner.
9. The method of claim 1 , further including a step of updating the predetermined gain in a step-wise linear manner, the updating being timed to coincide with at least some of beginnings of windows of width modulo-N and returning to the reading step with the VGA being set to the updated predetermined gain.
10. The method of claim 1 , wherein the predetermined gain is maintained constant between beginnings of windows of width modulo-N.
11. A disk drive, comprising:
a disk;
a head configured to read and write data to the disk, and
a processor, the processor being controlled by a program that causes the processor to carry out steps of:
while a Variable Gain Amplifier (VGA) is set to a predetermined gain, receiving an output of the head amplified by the predetermined gain, the amplified output including a signal representative of the preamble of the at least one embedded servo sector;
transforming samples of the at least one read preamble into a first and a second frequency using a discrete time-to-frequency domain transform;
calculating a ratio of a magnitude of the discrete time-to-frequency domain transform of the first frequency to a magnitude of the discrete time-to-frequency domain transform of the second frequency;
determining a Head Media Separation (HMS) from the calculated ratio, and
enabling the predetermined gain to be updated only at a beginning of a window of width modulo-N, wherein N is a wavelength of a lower one of the first and second frequencies.
12. The disk drive of claim 11 , wherein the first frequency is a fundamental frequency of a signal encoded within the preamble and wherein the second frequency is a harmonic frequency of the signal encoded within the preamble.
13. The disk drive of claim 11 , wherein the first and second frequencies are a fundamental frequency and an odd harmonic frequency, respectively, of a square wave encoded with the preamble.
14. The disk drive of claim 13 , wherein the odd harmonic frequency is a third harmonic frequency.
15. The disk drive of claim 13 , wherein the discrete time-to-frequency transform includes a Discrete Fourier Transform (DFT).
16. The disk drive of claim 13 , wherein the program is further configured to carry out steps of updating the predetermined gain at a beginning of the window of width modulo-N and returning to the reading step with the VGA being set to the updated predetermined gain.
17. The disk drive of claim 13 , wherein the program is further configured to carry out a step of updating the predetermined gain synchronously with the transforming step.
18. The disk drive of claim 17 , wherein the program is further configured to carry out a step of updating the predetermined gain in a step-wise linear manner.
19. The disk drive of claim 13 , wherein the program is further configured to carry out steps of updating the predetermined gain in a step-wise linear manner, the updating being timed to coincide with at least some of beginnings of windows of width modulo-N and returning to the reading step with the VGA being set to the updated predetermined gain.
20. The disk drive of claim 13 , wherein the program is further configured to carry out a step of maintaining the predetermined gain constant between beginnings of windows of width modulo-N.
21. A method of calculating a Head Media Separation (HMS) from a preamble of at least one embedded servo sector in a disk drive, the disk drive including at least one disk, comprising:
reading the preamble of the at least one embedded servo sector, the read preamble being amplified by a variable gain amplifier (VGA) set at a predetermined gain;
transforming samples of the at least one read preamble into a first and a second frequency using a discrete time-to-frequency domain transform;
calculating a ratio of a magnitude of the discrete time-to-frequency domain transform of the first frequency to a magnitude of the discrete time-to-frequency domain transform of the second frequency;
determining the HMS from the calculated ratio; and
enabling the predetermined gain to be updated in synchronism with the transforming step.
22. The method of claim 21 , further comprising a step of updating the predetermined gain in synchronism with the transforming step and returning to the reading step with the VGA being set to the updated predetermined gain.
23. The method of claim 21 , wherein the enabling step includes enabling the VGA to be updated at an N sample boundary, wherein N is a wavelength of a lower one of the first and second frequencies transformed from the preamble of the at least one embedded servo sector.