Analog Memory Cell Soft Readout With Threshold Offset Compensation
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Solution Overview
Problem
In memory devices, sub-optimal positioning of read thresholds in analog memory cells leads to distorted reliability measures and increased probability of read errors, which existing methods fail to address effectively without re-reading the cells.
Innovation Solution
A method that estimates the offset of read thresholds from their optimal position and modifies reliability measures, such as Log Likelihood Ratios, to compensate for this offset without re-reading the memory cells, using techniques like calculating the mean deviation or empirical distribution matching, to improve decoding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If read thresholds are positioned sub-optimally in analog memory cells, then the reading operation can proceed with fixed thresholds, but the reliability measures become distorted and read error probability increases
Solution Approach 1:
The system performs initial reads with fixed thresholds, computes reliability measures from these reads, uses the reliability measures to estimate threshold offset, and then corrects the reliability measures using the estimated offset. This feedback loop allows the system to adapt to actual threshold positioning errors without requiring precise pre-calibration of the thresholds.
Solution Approach 2:
The system changes the reliability measure parameters by computing corrections based on estimated threshold offsets. The corrected reliability measures are then used for decoding, effectively adjusting the parameter values to compensate for sub-optimal threshold positioning without physically changing the threshold values themselves.
2Measurement precision
If the memory cells are re-read to achieve optimal threshold positioning, then decoding accuracy improves, but latency and power consumption increase
Solution Approach 1:
The system performs preliminary reads with fixed thresholds to gather data for computing reliability measures and estimating threshold offset. These preliminary actions enable subsequent correction of reliability measures without requiring actual re-reading of the cells, thus achieving optimal decoding accuracy while avoiding the latency and power costs of re-reading.
Solution Approach 2:
The reliability measures serve as an intermediary that captures the effect of threshold positioning errors. By computing corrections to these intermediary reliability measures based on estimated offsets, the system indirectly compensates for threshold errors without directly re-reading the memory cells, thus avoiding the associated time and power penalties.
3Reliability
If multiple read operations are performed to compensate for threshold errors, then error probability decreases, but power consumption increases
Solution Approach 1:
The system uses feedback from initial read operations to compute reliability measures and estimate threshold offsets. This feedback mechanism enables the system to correct reliability measures mathematically rather than performing additional physical read operations, thereby reducing power consumption while maintaining improved error probability performance.
Solution Approach 2:
The system replaces the mechanical approach of performing multiple physical read operations with a computational approach. By substituting additional read operations with mathematical corrections to reliability measures based on estimated offsets, the system achieves the same error reduction effect with lower power consumption.
Data Source
AI summary
A method includes storing data in a group of analog memory cells by writing respective analog values into the memory cells in the group. After storing the data, the analog values are read from the memory cells in the group one or more times using one or more respective read thresholds so as to produce readout results. Reliability measures are computed for the read analog values based on the readout results. An offset of the one or more read thresholds from an optimal read threshold position is estimated based on the reliability measures. The reliability measures are modified to compensate for the estimated offset, and the data stored in the analog memory cells in the group is decoded using the corrected reliability measures.