HDD Degauss Circuitry With AC DC Decay Segments
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Solution Overview
Problem
Hard disk drives (HDDs) face issues with degraded recording performance due to phenomena like erase after write (EAW), where residual magnetization causes degradation of previously written tracks, leading to off-track recording problems as storage capacity increases.
Innovation Solution
Generating a degauss signal waveform with alternating current (AC) and direct current (DC) decay segments, allowing for improved write head demagnetization by alternating between these types of decay segments to prevent EAW and enhance recording performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If storage capacity is increased by shrinking track dimensions, then more data can be stored on each disk, but recording performance degrades due to erase after write effects
Solution Approach 1:
The patent applies preliminary action by implementing a degaussing operation immediately after writing data to the storage medium. This preliminary demagnetization step removes residual magnetic fields from the write head before it can cause erase after write effects on adjacent or previously written tracks, thereby preventing recording performance degradation while maintaining high storage capacity
Solution Approach 2:
The patent converts the harmful residual magnetization effect into a beneficial process by intentionally applying a controlled degaussing signal. The same residual magnetization that causes EAW problems is harnessed through controlled application to systematically demagnetize the write head, transforming a harmful phenomenon into a useful cleaning mechanism that protects recording integrity
2Device complexity
If a simple decaying sinusoidal degauss signal is used, then the circuit is simple, but it cannot effectively address both near and far track erasure problems
Solution Approach 1:
The patent segments the degauss signal into multiple distinct portions: an initial high-amplitude portion for addressing near track erasure, followed by one or more decaying portions for addressing far track erasure. This segmentation allows each portion to be optimized for specific EAW scenarios, improving overall effectiveness without significantly increasing circuit complexity
Solution Approach 2:
The patent implements dynamics by making the degauss signal adaptable and variable rather than fixed. The signal transitions between different amplitude levels and decay rates depending on the writing operation being performed, allowing the system to dynamically adjust the degaussing strength to match the specific recording conditions and track geometry
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of AC and DC decay segments in the degauss signal waveform effectively prevents write head remanent magnetization, leading to improved recording performance and reduced EAW, thereby enhancing the overall operating efficiency of HDDs.
Implementation Method 1
The preamplifier may alternatively comprise degauss circuitry configured to generate an alternating current waveform having both a steady state portion and an overshoot portion
Implementation Method 2
data is read from and written to tracks of the storage disk via a read/write head
Implementation Method 3
In the MAMR technique, an additional write head is configured to emit an AC magnetic field that excites ferromagnetic resonance in the media, building up energy that eases the process of writing data
Data Source
AI summary
A hard disk drive or other disk-based storage device comprises a storage disk, a write head configured to write data to the disk, and control circuitry coupled to the write head. The control circuitry comprises a write driver and degauss circuitry associated with the write driver. The degauss circuitry is configured to generate a degauss signal to be applied to the write head by the write driver. The degauss signal has a waveform comprising a plurality of decay segments including at least one alternating current decay segment and at least one direct current decay segment. An initial decay segment of the plurality of decay segments may comprise an alternating current decay segment or a direct current decay segment, and may be immediately followed by a decay segment of the opposite type.