Memory Controller Feedback for Compressed Soft-Decision Reads
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Solution Overview
Problem
Existing memory systems face challenges in effectively correcting errors in non-volatile memory devices due to deteriorated threshold voltage distributions, leading to high probabilities of uncorrectable errors in hard decision data, especially in triple-level cell (TLC) memory devices.
Innovation Solution
The system employs a memory controller that receives compressed soft decision data, counts the number of specific bit positions, and requests a change in voltage offset to improve data reliability, enabling error correction through log-likelihood ratio calculations and low-density parity check methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If soft decision data is compressed to reduce data transmission volume, then data transmission efficiency is improved, but data bit loss increases and compression quality deteriorates
Solution Approach 1:
The memory controller counts the number of position values in compressed soft decision data and uses this count as feedback to determine whether to request re-compression with a different voltage offset. When the position value count exceeds a threshold, indicating poor compression quality, the system requests re-compression with an adjusted voltage offset to improve data integrity.
Solution Approach 2:
The system changes the voltage offset parameter used during soft decision data reading based on the compression quality assessment. When compression quality is poor (indicated by high position value count), the memory controller requests the memory device to re-read the soft decision data using a different voltage offset, which can improve the compression quality and reduce bit loss.
2Speed
If hard decision reading is used for fast data retrieval, then reading speed is improved, but error correction capability deteriorates under deteriorated threshold voltage distributions
Solution Approach 1:
The system merges hard decision data reading with soft decision data reading. The memory controller reads both hard decision data (for speed) and soft decision data (for error correction capability) simultaneously or in close succession, combining the advantages of both approaches to achieve fast reading with improved error correction.
Solution Approach 2:
Soft decision data acts as an intermediary that bridges the gap between hard decision data and error correction. The soft decision data provides reliability information that enhances the error correction capability of hard decision data, allowing the system to maintain fast reading speeds while improving error correction performance.
3Reliability
If voltage offset is adjusted to improve soft decision data quality, then error correction performance is improved, but additional reading operations increase time consumption
Solution Approach 1:
The system performs voltage offset adjustment and re-reading only partially - specifically when the compression quality assessment indicates poor quality (position value count exceeds threshold). This selective approach avoids unnecessary re-reading operations while still improving error correction performance when needed, reducing overall time consumption.
Solution Approach 2:
The system performs a preliminary assessment of compression quality by counting position values in the compressed soft decision data. Based on this preliminary assessment, it decides whether voltage offset adjustment and re-reading are necessary, avoiding unnecessary operations and reducing time consumption while maintaining error correction performance.
Data Source
AI summary
An example memory system includes a memory device and a memory controller. The memory device is configured to read, from a memory cell array, hard decision data based on a hard read voltage and first soft decision data based on first soft read voltages obtained based on the hard read voltage and a first voltage offset, generate a first compressed sub-segment based on encoding a position of a bit having a first value into a position value for each of first soft decision sub-segments in the first soft decision data, and output first compressed data including first compressed sub-segments. The memory controller is configured to receive the first compressed data, count the number of position values in each of the first compressed sub-segments, and provide, to the memory device based on the counted number, a command to request a change of a voltage offset and a recompression operation.