Memory Read Voltage Adjustment After Power-Off Retention Drift
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Solution Overview
Problem
Current memory systems face challenges in accurately determining the equivalent retention duration and power off duration of data stored in memory blocks, leading to difficulties in meeting quality of service requirements for read operations, particularly in enhanced solid state drives.
Innovation Solution
The proposed solution involves determining the equivalent retention duration based on threshold voltage distribution state information of memory cells, updating the equivalent power off duration after the system is re-powered, and re-determining the read voltage accordingly to ensure accurate read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the memory system uses fixed read voltage for read operations, then the operation is simple and fast, but the read accuracy deteriorates when retention duration varies
Solution Approach 1:
The read voltage is changed from a fixed value to a dynamically adjustable parameter. The controller determines the equivalent retention duration of stored data and selects different read voltages from a group of read voltages based on this duration, allowing the read operation to adapt to varying retention conditions and maintain accuracy without excessive complexity
Solution Approach 2:
The patent changes the read voltage parameter based on the equivalent retention duration. By establishing a mapping between retention duration ranges and optimal read voltages, the system adjusts the electrical parameter (voltage) to match the data retention state, thereby improving read accuracy while managing complexity through predefined voltage selections
2Measurement precision
If the memory system determines equivalent retention duration frequently, then the read accuracy is maintained, but the processing time increases
Solution Approach 1:
Instead of continuously monitoring retention duration, the system performs determination only when necessary - specifically when the equivalent retention duration is expected to exceed a threshold value. This partial action approach maintains accuracy when needed while avoiding unnecessary processing time loss during normal operations
Solution Approach 2:
The patent uses a disposable timestamp mechanism to track retention duration. A timestamp is written when data is programmed and read when needed to calculate retention duration, avoiding the need for continuous monitoring. This ephemeral tracking method provides necessary information without persistent overhead
Data Source
AI summary
The implementations of the present disclosure provide memory systems and methods of operating thereof, and computer readable storage media. An example memory system includes a memory and a controller. The memory includes blocks each includes memory cells, each of the memory cells is configured to store one of memory states, the memory states correspond to a group of read voltages, and a read voltage of the group of read voltages is configured to distinguish different memory states. The method includes performing a read operation on a selected memory cell in a selected block based on the read voltage of the group of read voltages when the memory system is re-powered on after power off, and determining an equivalent power off duration of the memory system.