State-dependent read voltage adaptation for NAND flash memory
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Solution Overview
Problem
Conventional techniques for adapting read voltage thresholds in NAND flash memory systems do not account for differences in the rate and amount of distortion of programmed threshold voltage distributions based on various operating states, leading to improper threshold selection and increased bit errors over time.
Innovation Solution
A controller adapts read voltage thresholds for a non-volatile memory system by determining the operating state of the memory unit and adjusting the thresholds based on specific strategies tailored to the identified state, using statistics such as P/E cycles, data retention, and read disturb effects to dynamically select optimal offset values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques are used to adapt read voltage thresholds, then the adaptation process is simple, but the bit error rate increases rapidly due to improper threshold selection
Solution Approach 1:
The patent implements dynamic adaptation of read voltage thresholds by continuously monitoring the operating state (P/E cycles, data retention, read disturb) and adjusting thresholds in real-time based on the current state, rather than using static conventional techniques. This dynamic approach maintains low bit error rates while adapting to changing memory conditions.
Solution Approach 2:
The patent changes the parameters used for threshold adaptation from conventional simple methods to state-dependent parameters including P/E cycle count, data retention time, and read disturb effects. By incorporating these additional parameters into the adaptation process, the system achieves better reliability despite increased complexity.
2Speed
If conventional techniques adapt read voltage thresholds, then the process is fast and simple, but the thresholds become outdated quickly due to slow tracking of abrupt distribution changes
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the operating state of memory blocks and uses this information to adjust read voltage thresholds. By feeding back state information (P/E cycles, data retention, read disturb) to the threshold adaptation process, the system can quickly track abrupt changes in voltage distributions while maintaining accurate thresholds.
Solution Approach 2:
The patent performs preliminary adaptation of read voltage thresholds based on predicted operating states before actual degradation occurs. By anticipating changes based on the operating state, the system prepares threshold adjustments in advance, enabling faster response to abrupt distribution changes while maintaining reliability.
3Reliability
If state-dependent adaptation is implemented, then the bit error rate is minimized, but the device complexity increases due to multiple operating states to track
Solution Approach 1:
The patent segments the memory system into distinct operating states (P/E cycling, data retention, read disturb) and applies specific adaptation strategies to each state. By dividing the complex adaptation problem into manageable state-specific segments, the system achieves low bit error rates while keeping the implementation complexity manageable through modular state handling.
Solution Approach 2:
The patent applies different adaptation qualities and strategies to different operating states rather than using a uniform approach. Each state receives tailored threshold adaptation based on its specific characteristics, achieving optimal reliability for each state while managing overall complexity through localized optimization.
4Measurement precision
If read voltage thresholds are adapted frequently, then the thresholds remain accurate, but the productivity decreases due to increased adaptation overhead
Solution Approach 1:
The patent implements periodic adaptation of read voltage thresholds based on the operating state, adapting thresholds at appropriate intervals rather than continuously. This periodic approach maintains sufficient threshold accuracy while minimizing adaptation overhead and preserving memory operation productivity.
Solution Approach 2:
The patent applies partial adaptation only when and where needed based on operating state conditions, rather than performing full adaptation across all memory blocks continuously. This selective partial action maintains threshold accuracy in critical areas while reducing overall adaptation overhead and preserving productivity.
Data Source
AI summary
A controller adapts the read voltage thresholds of a memory unit in a non-volatile memory. In one embodiment, the controller determines, based on statistics for a memory unit of the non-volatile memory, an operating state of the memory unit from among a plurality of possible operating states and adapts at least one read voltage threshold for a memory cell in the memory unit based on the determined operating state.