Read Threshold Calibration for Cross-Temperature Sequential Reads
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Solution Overview
Problem
Existing memory devices face challenges in maintaining Quality of Service (QoS) standards due to lack of process uniformity caused by NAND process shrinking and 3D stacking, leading to increased variability in memory dies, blocks, and pages across different conditions, which affects read throughput and IOPS requirements, especially under temperature shifts during long sequential reads.
Innovation Solution
Implementing a Read Level Tracking (RLT) method that performs a plurality of read operations to determine the bit error rate (BER) of an indicative word line, adjust read threshold levels based on the BER, and calibrate read threshold voltages to maintain optimal read performance without high latency operations like BES or VS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BER Estimation Scan (BES) or Valley Search (VS) operations are performed to optimize read thresholds, then read recovery flow is improved, but latency increases and performance deteriorates
Solution Approach 1:
The patent performs read threshold calibration in advance during idle periods or low-utilization times using BES or VS operations. The calibrated thresholds are stored and reused during high-utilization periods, avoiding the need to perform calibration operations when latency must be minimized. This separates the calibration function from the read path, allowing optimization without performance penalty during active reads.
Solution Approach 2:
The patent implements a dynamic threshold calibration system that adapts its behavior based on system conditions. During high-utilization periods, it uses stored calibration data to maintain low latency. During low-utilization periods, it performs full calibration operations to update thresholds. This dynamic approach allows the system to optimize between accuracy and latency based on real-time conditions.
2Reliability
If read threshold calibration is performed frequently to track temperature shifts, then read performance is maintained, but system performance is significantly impaired
Solution Approach 1:
The patent implements periodic threshold calibration at predetermined intervals rather than continuously or on every read operation. The calibration is triggered by time-based or operation-count-based counters that increment with each read operation. When the counter reaches a threshold value, calibration is performed and the counter is reset. This periodic approach maintains adequate threshold accuracy while minimizing the performance impact of calibration operations.
Solution Approach 2:
The patent uses feedback from read operations to trigger calibration only when necessary. The system monitors read performance metrics and system utilization, and only initiates calibration operations when performance degrades or during low-utilization periods. This feedback-driven approach ensures calibration is performed frequently enough to maintain performance but not so frequently as to impair system productivity.
3Productivity
If adaptive read threshold tracking is implemented to meet QoS requirements, then read throughput and IOPS are maintained, but device complexity increases
Solution Approach 1:
The patent divides the calibration function into separate modules: a calibration engine that performs threshold calibration, a counter module that tracks read operations, and a control logic that determines when to trigger calibration. This segmentation allows each component to be optimized independently and simplifies the overall control logic by separating calibration management from the read path, reducing the complexity burden while maintaining adaptive performance.
Data Source
AI summary
A system and method for calibrating read threshold voltages includes performing a plurality of read operations, determining to perform a read level tracking method, and performing the read level tracking method. The determining may be based on a temperature change or a bit error rate (BER). The read level tracking method includes determining the BER of an indicative word line, determining an adjusted read threshold level based on the BER, and adjusting read threshold levels according to the adjusted read threshold level.