Threshold Voltage Distribution Tracking in Memory Read Calibration
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Solution Overview
Problem
Existing memory read calibration techniques are inaccurate and latency-prone due to their inability to effectively track and compensate for shifts in threshold voltage distributions caused by factors like charge loss, temperature, and physical defects, leading to uncorrectable read data.
Innovation Solution
Utilizing memory device-originated metrics, such as failed byte count and failed bit count, to iteratively adjust read voltage levels through calibration operations, minimizing latency and ensuring accuracy by mapping these metrics to read voltage adjustments using lookup tables or mathematical transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional memory read calibration techniques are used, then the read operation can be performed, but the calibration accuracy is insufficient and latency increases due to inability to track voltage distribution shifts
Solution Approach 1:
The patent implements feedback by using metrics from failed read operations to iteratively adjust read voltage levels. The controller receives metrics characterizing voltage distributions from failed reads, determines adjusted read voltage levels based on these metrics, and applies the adjusted voltages in subsequent read operations. This closed-loop feedback mechanism continuously improves calibration accuracy while minimizing latency by only performing calibration when needed.
Solution Approach 2:
The memory device performs self-calibration by generating and providing its own voltage distribution metrics to the controller. The device autonomously characterizes its own voltage distributions and uses this self-generated information to enable the controller to determine appropriate voltage adjustments, reducing the need for external intervention and minimizing calibration overhead.
2Reliability
If read voltage levels are not adjusted, then calibration operations are fast, but voltage distribution shifts cause uncorrectable read data and high bit error rates
Solution Approach 1:
The patent changes the read voltage level parameter based on observed voltage distribution shifts. Instead of complex recalibration procedures, the system adjusts the voltage parameter directly using metrics from failed reads. This parameter adjustment approach improves read data accuracy by compensating for voltage shifts while keeping the calibration operation relatively simple and efficient.
Solution Approach 2:
The system performs partial calibration by only adjusting voltage levels when failures occur and metrics indicate specific distribution shifts. Rather than performing full calibration on every operation, the system applies targeted voltage adjustments based on actual observed failures, reducing overall calibration complexity while maintaining reliability.
3Measurement precision
If comprehensive calibration is performed to track all voltage distribution shifts, then read accuracy improves, but the time and computational resources required increase significantly
Solution Approach 1:
The system performs preliminary analysis by examining metrics from failed read operations before determining voltage adjustments. By using information from actual failures to guide calibration, the system avoids unnecessary comprehensive calibration operations, thus maintaining voltage distribution tracking accuracy while preserving read operation throughput through selective calibration.
Data Source
AI summary
Described are systems and methods for memory read calibration based on memory device-originated metrics characterizing voltage distributions. An example memory device includes: a memory array having a plurality of memory cells and a controller coupled to the memory array. The controller is to perform operations including: receiving a first metric characterizing threshold voltage distributions of a subset of the plurality of memory cells; determining a first read voltage adjustment; receiving a second metric characterizing the threshold voltage distributions; determining a second read voltage adjustment; and applying the second read voltage adjustment for reading the subset of the plurality of memory cells.