FIR Equalizer Gain Phase Stabilization in HDD Read Channels
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Solution Overview
Problem
Conventional read channels in hard disk drives face issues due to interactions between the FIR equalizer, automatic gain controller, and analog digital converter, causing tap values of the FIR response to change unpredictably, leading to increased gain and phase instability, which existing constraints fail to effectively manage.
Innovation Solution
An apparatus that adapts the FIR equalizer by determining gain and phase directions and calculating constraints to prevent adaptation in these directions, using memory to store previous values and applying conditions to update constraints only when necessary, thereby stabilizing the FIR response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional constraints (Fix2 or Rank2) are applied to restrict FIR equalizer adaptation, then interactions between AGC and ADC are reduced, but the constraints are not based on tap values and become useless when constraints are 0 or very small
Solution Approach 1:
The patent applies different constraint strategies to different tap values based on their individual characteristics. The constraint magnitude is locally adjusted for each tap according to its signal-to-noise ratio and correlation with other taps, rather than applying a uniform constraint to all taps. This allows the constraint to be effective where needed and adaptable where not needed.
Solution Approach 2:
The constraint value is made dynamic and adaptive rather than fixed. The patent continuously updates constraint magnitudes based on real-time estimation of tap signal-to-noise ratios and tap correlations. This dynamic adjustment allows the constraint to remain effective across varying operating conditions and prevents it from becoming useless when initial constraint values are 0 or very small.
2Measurement precision
If FIR equalizer adaptation is allowed to proceed without constraints, then equalization performance is optimized, but interactions with AGC and ADC cause tap values to diverge and gain/phase instability increases
Solution Approach 1:
The patent implements a feedback mechanism where the constraint values are continuously updated based on the estimated signal-to-noise ratios and correlations of the FIR taps. This feedback loop allows the system to maintain optimal equalization performance while automatically adjusting constraints to prevent divergence caused by AGC-ADC interactions.
Solution Approach 2:
The patent changes the parameters of the constraint based on the operating conditions. By adjusting constraint magnitudes according to tap signal-to-noise ratios and correlations, the system maintains equalization accuracy while preventing instability. The constraint parameters are dynamically modified rather than kept fixed.
Data Source
AI summary
A method and apparatus for adapting an FIR equalizer in a hard disk drive read channel which determines again direction and/or a phase direction of an FIR response c of the FIR equalizer, and calculates a constraint so that the update does not change the FIR response in its gain and/or phase direction.