Memory Read Voltage Offset Selection for Low-Latency Vt Drift Detection
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Solution Overview
Problem
Existing techniques for determining threshold voltage (Vt) drift in memory cells have high latency, impairing the performance of memory systems and limiting when Vt drift detection procedures can be performed.
Innovation Solution
A memory system performs a Vt drift detection procedure with reduced latency by iteratively reading memory cells using different reference voltages based on offset values associated with different ranges of Vt drift, comparing the quantity of memory cells with Vt levels above the reference voltage to a target quantity, and selecting an offset value based on the determined Vt drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing Vt drift detection procedures are used, then threshold voltage drift can be detected, but latency is high which impairs memory system performance
Solution Approach 1:
The patent segments the Vt drift detection process into multiple read operations with different reference voltages. Instead of a single comprehensive detection procedure, the system performs multiple targeted reads at different voltage thresholds to determine the distribution of threshold voltages in memory cells, thereby reducing the latency of the overall detection process while maintaining accuracy.
Solution Approach 2:
The patent performs preliminary read operations to determine the distribution of threshold voltages before actual data retrieval. By conducting these preliminary reads at different reference voltages and determining the cumulative distribution function, the system prepares voltage offset adjustments in advance, reducing the latency impact on subsequent operations.
2Reliability
If Vt drift detection procedures are performed frequently, then read accuracy is maintained, but processing time increases
Solution Approach 1:
The patent applies partial action by performing read operations only at specific reference voltages that are necessary for determining the threshold voltage distribution. Instead of exhaustive reading of all memory cells at all possible voltages, the system selects critical voltage points to accurately determine the distribution characteristics, thereby maintaining reliability while improving productivity.
Solution Approach 2:
The patent implements feedback by using the results of preliminary read operations to determine voltage offsets that are then applied to subsequent read operations. The cumulative distribution function obtained from preliminary reads provides feedback information that adjusts the reference voltages for future operations, ensuring accuracy while reducing the frequency of comprehensive detection procedures.
Data Source
AI summary
Methods, systems, and devices for determining reference voltage offsets for read operations in a memory system are described. A memory system may read a memory page using a first reference voltage that is based on a first offset value and using a second reference voltage that is based on a second offset value. The memory system may determine, based on reading the page using the first reference voltage, a first quantity of memory cells with threshold voltages above the first reference voltage. The memory system may determine, based on reading the page using the second reference voltage, a second quantity of memory cells with threshold voltages above the second reference voltage. The memory system may select, based on the first quantity, the second quantity, and a target quantity, an offset value for a set of pages that that is between the first offset value and the second offset value.