Harmonic Fly-Height Detection Circuit Phase Invariance
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Solution Overview
Problem
Current methods for determining fly-height in magnetic storage systems are limited by their dependency on sampling phase and the performance of equalization and timing loops, leading to inconsistent harmonic measurements.
Innovation Solution
The implementation of a harmonic fly-height change detection circuit that samples a periodic data pattern at an aggregate frequency, adjusted by an offset frequency, to calculate magnitudes using discrete Fourier transforms and compare them to a baseline value, thereby detecting changes in fly-height independently of sampling phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If harmonic measurements are performed using a single discrete Fourier transform integration, then the measurement process is simple, but the measurement precision deteriorates due to dependency on sampling phase
Solution Approach 1:
The patent divides the measurement process into multiple discrete Fourier transform integrations at different frequencies (including the Nyquist frequency and adjacent frequencies). This segmentation allows the system to measure harmonic content at multiple points, thereby eliminating dependency on a single sampling phase while maintaining computational feasibility through structured frequency analysis.
Solution Approach 2:
The patent introduces a frequency dimension by performing Fourier transforms at multiple frequencies around the Nyquist frequency, not just at a single frequency. This dimensional expansion from single-frequency to multi-frequency analysis provides phase-invariant measurement capability, as the combined spectral information from adjacent frequencies compensates for phase variations.
2Measurement precision
If the correlation is performed over a large number of samples for accurate measurements, then the measurement precision improves, but the loss of time increases due to extended measurement duration
Solution Approach 1:
The patent performs discrete Fourier transform integrations at specific, strategically chosen frequencies (Nyquist frequency and adjacent frequencies) rather than requiring exhaustive correlation over all possible phases. This partial action approach at critical frequency points provides sufficient measurement precision while significantly reducing the total measurement time compared to complete phase sweeping.
Solution Approach 2:
The patent changes the frequency parameter by analyzing the spectrum at multiple discrete frequencies around the Nyquist frequency. This parameter variation allows the system to capture harmonic information efficiently without requiring prolonged time-domain correlation, as the frequency-domain analysis at multiple points provides equivalent or superior information with reduced computational time.
3Manufacturing precision
If fly-height is determined based on harmonic measurements, then the positioning accuracy improves, but the reliability deteriorates due to dependency on equalization and timing loop performance
Solution Approach 1:
The patent implements a feedback mechanism where the harmonic measurements at multiple frequencies are combined to produce a phase-invariant fly-height determination. The measurement system continuously monitors the harmonic content and uses this feedback to adjust or validate the fly-height calculation, reducing dependency on external timing loops and equalization performance while maintaining positioning accuracy.
Solution Approach 2:
The patent creates an equipotential measurement approach by measuring harmonic content at multiple frequencies symmetrically around the Nyquist frequency. This symmetric multi-frequency measurement ensures that the result is independent of the sampling phase, effectively equalizing the measurement process across all phase conditions and eliminating variability introduced by timing loop performance.
Data Source
AI summary
Various embodiments of the present invention provide systems and methods for determining changes in fly-height. For example, various embodiments of the present invention provide storage devices that include a storage medium, an offset frequency, a read/write head assembly, and a harmonic fly-height change detection circuit. The storage medium includes a periodic data pattern that repeats at a data frequency. The read/write head assembly disposed in relation to the storage medium such that it senses the periodic data pattern and provides a sensed periodic data pattern. The harmonic fly-height change detection circuit samples the sensed periodic data pattern at an aggregate frequency to yield a first set of samples and a second set of samples. The aggregate frequency is the data frequency adjusted by the offset frequency. The harmonic fly-height change detection circuit calculates a first magnitude of the first set of samples and a second magnitude of the second set of samples.