Read Channel Signal Correction Using Soft Information Feedback
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Solution Overview
Problem
Current data storage devices face challenges in accurately detecting data bits due to magnetic and electrical anomalies that cause baseline wander and increased error rates, particularly in magnetic storage mediums using perpendicular recording technology.
Innovation Solution
A signal correction circuit is introduced in the read channel that utilizes soft information from a soft output detector to determine a correction value for the input signal, incorporating a switch, expectation signal generator, residue calculator, low confidence zeroing logic, and residue aggregator to correct the signal and reduce baseline wander.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PRML detection is used in read channels, then the system maintains compatibility with existing detection schemes, but baseline wander and signal errors increase due to magnetic AC poles and electrical anomalies
Solution Approach 1:
The patent implements feedback by using detected data bits and soft information to generate expected signal values, comparing these with actual input signals to calculate residue terms, and applying corrections back to the input signal. This closed-loop feedback mechanism continuously reduces baseline wander and improves detection accuracy
Solution Approach 2:
The patent changes signal parameters by calculating residue terms that represent differences between expected and actual signals, then applying corrections to modify the input signal parameters. This transforms the signal to compensate for baseline wander and magnetic AC pole effects
2Reliability
If soft information from SOVA detector is used for signal correction, then baseline wander compensation improves, but device complexity increases due to additional correction circuits
Solution Approach 1:
The patent makes the SOVA detector multi-functional by having it not only detect data bits but also provide soft information for signal correction. The same detector output is used for both data recovery and baseline wander compensation, reducing the need for separate correction circuits
Solution Approach 2:
The patent merges the signal correction function with the existing SOVA detection circuitry. The residue calculator and correction logic are integrated into the read channel processing path, combining multiple functions into a unified processing pipeline rather than adding separate independent correction systems
3Reliability
If iterative detection with LDPC codes is implemented, then error correction capability improves, but processing time and computational resources increase
Solution Approach 1:
The patent performs preliminary signal correction before iterative LDPC decoding by removing baseline wander and magnetic AC pole effects in advance. This preliminary action cleans the input signal, making subsequent iterative decoding faster and more efficient by reducing the computational burden of error correction
Data Source
AI summary
Example systems, read channel circuits, data storage devices, and methods to provide signal correction based on soft information in a read channel are described. The read channel circuit includes a soft output detector, such as a soft output Viterbi algorithm (SOVA) detector, and a signal correction circuit. The soft output detector passes detected data bits and corresponding soft information to the signal correction circuit. The signal correction circuit uses the soft information to determine a signal correction value, which is combined with input signal to return a corrected signal to the soft output detector for a next iteration. In some configurations, the signal correction value may compensate for DC offset, AC coupling poles, and/or signal asymmetries to reduce baseline wander in the read channel.