Adaptive Read Threshold Voltage Tracking with Gap Estimation
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Solution Overview
Problem
Existing adaptive tracking algorithms for solid state storage devices assume known gaps between default read threshold voltages, which is not always available, leading to limitations in decoding performance and reliability.
Innovation Solution
The proposed method estimates the gap between adjacent default read threshold voltages using statistical characteristics of memory levels, allowing for adjusted read threshold voltage computation and improved robustness by separately characterizing each side of the distribution about the mean.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing adaptive tracking algorithms are used that assume known gaps between default read threshold voltages, then the decoding performance is limited, but the algorithm complexity is reduced
Solution Approach 1:
The patent performs preliminary gap estimation between adjacent default read threshold voltages using statistical characteristics of memory levels before computing adjusted read threshold voltages. This preliminary action of estimating the gap (Equation 1: gap = μ_i - μ_{i-1}) enables subsequent accurate read threshold voltage computation without requiring pre-known gap values, thereby improving decoding performance while maintaining manageable algorithm complexity through a structured two-stage process.
2Measurement precision
If the gap between default read threshold voltages is estimated using statistical characteristics, then the accuracy of read threshold voltage computation is improved, but the measurement and characterization process becomes more complex
Solution Approach 1:
The patent employs feedback by using the estimated gap between default read threshold voltages to compute adjusted read threshold voltages that account for actual memory level distributions. The process reads memory pages at multiple read threshold offset locations, collects disparity statistics, estimates means and standard deviations, computes gaps, and uses these to determine optimal read threshold voltages. This feedback loop continuously refines read threshold accuracy based on actual memory characteristics.
Solution Approach 2:
The patent changes parameters by estimating the gap between default read threshold voltages (μ_i - μ_{i-1}) using statistical characteristics (mean and standard deviation) of memory levels rather than assuming fixed known values. This parameter estimation approach allows the system to adapt to actual memory variations, improving read threshold voltage accuracy while managing measurement complexity through statistical methods.
3Reliability
If separate characterization of each side of voltage distribution about distribution mean is performed, then the robustness of read threshold voltage computation is improved, but the characterization process requires more measurements
Solution Approach 1:
The patent segments the voltage distribution characterization by separately analyzing each side of the distribution about the mean. It reads memory pages at multiple read threshold offset locations (both below and above default read threshold voltages) to collect disparity statistics for different regions. This segmentation allows independent estimation of statistical characteristics (mean, standard deviation) for each memory level, improving robustness by capturing asymmetric distribution characteristics that single-sided measurements would miss.
Data Source
AI summary
Techniques are provided for adaptive read threshold voltage tracking with gap estimation between default read threshold voltages. A read threshold voltage for a memory is adjusted by estimating a gap between two adjacent default read threshold voltages using binary data from the memory, wherein the gap is estimated using statistical characteristics of at least one of two adjacent memory levels of the memory; computing an adjusted read threshold voltage associated with the two adjacent memory levels by using the statistical characteristics of the two adjacent memory levels and the gap; and updating the read threshold voltage with the adjusted read threshold voltage. Pages of the memory are optionally read at multiple read threshold offset locations to obtain disparity statistics, which can be used to estimate mean and/or standard deviation values for a given memory level. The gap is optionally estimated using the mean and/or standard deviation values.