Rotation Filter for Digital Timing Recovery in Hard Disk Drives
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Solution Overview
Problem
Existing digital timing recovery techniques in hard disk drives face challenges due to latency introduced by feedback loops and buffering needed for two-dimensional magnetic recording, which affects the accuracy and efficiency of clock recovery from oversampled analog signals.
Innovation Solution
A method and circuitry for digital timing recovery that involves computing filter coefficients for oversampled analog signals, using a rotation filter to compensate for oversampling, and deriving a starting phase and magnitude to recover a clock in a timing recovery loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback loops are used in analog timing recovery, then clock recovery is achieved, but substantial latency is introduced
Solution Approach 1:
The patent replaces the analog feedback-based timing recovery system with a digital timing recovery system. The digital system processes oversampled ADC outputs directly through digital signal processing algorithms, eliminating the need for analog feedback loops and PLL circuits. This substitution of digital processing for analog feedback mechanisms achieves clock recovery while significantly reducing the latency inherent in analog feedback systems.
Solution Approach 2:
The patent applies preliminary digital filtering and phase rotation to the oversampled ADC outputs before timing recovery processing. By pre-processing the signals with digital filters and applying phase rotation based on estimated timing offsets, the system prepares the signals in advance, reducing the need for iterative feedback adjustments and thereby reducing overall latency.
2Measurement precision
If oversampling is applied to analog signals, then timing recovery accuracy is improved, but filter complexity increases
Solution Approach 1:
The patent segments the timing recovery process into distinct digital signal processing stages: oversampling, digital filtering, phase rotation, and timing offset calculation. By dividing the complex filtering operation into manageable digital processing steps, each stage can be optimized independently, reducing overall system complexity while maintaining timing recovery accuracy.
Solution Approach 2:
The patent changes the sampling parameter by applying oversampling to the ADC outputs. This parameter change allows the use of simpler digital filters with lower cutoff frequencies, which are easier to implement in digital domain while achieving the same timing recovery accuracy that would require complex analog filters at lower sampling rates.
3Reliability
If buffering is implemented for two-dimensional magnetic recording, then data from multiple heads is captured, but additional latency is introduced
Solution Approach 1:
The patent implements continuous digital processing of oversampled signals from multiple read heads without interrupting the data flow for buffering. By processing signals in real-time through digital filtering and phase rotation, the system maintains continuous useful action, eliminating the start-stop nature of buffered processing and reducing latency while still capturing data from multiple heads for TDMR.
Data Source
AI summary
A method for digital timing recovery from oversampled analog signals includes computing filter coefficients for digitized samples of the oversampled analog signals based on an oversampling factor of the oversampled analog signals, using the filter coefficients in a rotation filter to compensate for the oversampling factor in the digitized samples of the oversampled analog signals, deriving a starting phase and magnitude from the compensated digitized samples of the oversampled analog signals, and using the starting phase and magnitude in a timing recovery loop to recover a clock from the compensated digitized samples of the oversampled analog signals. The rotation filter may include a plurality of taps, and the circuitry may be configured to compute respective sets of coefficients for respective taps. Each set of coefficients may be dependent on another set of coefficients, or the coefficients may be approximate with each set of approximate coefficients being independent.