Flash Memory Read Voltage Adjustment via Bit Change Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The threshold voltage distribution of data bits in the erased state differs from that in other programmed states, making it difficult to detect errors and increasing the likelihood of decoding failure in flash memory systems.
Innovation Solution
A data accessing method that adjusts the read voltage level or log likelihood ratio based on the bit change ratio of dummy data included in the codeword, improving decoding efficiency by compensating for threshold voltage distribution variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed read voltage level is used for reading data from flash memory, then the reading process is simple and fast, but the decoding accuracy deteriorates due to threshold voltage distribution variations in erased state
Solution Approach 1:
The patent implements dynamic read voltage adjustment by calculating a compensation value based on the bit change ratio of dummy data and applying it to modify the read voltage level or log-likelihood ratio. This transforms the static reading process into a dynamic one that adapts to threshold voltage distribution variations, thereby improving decoding accuracy without excessive complexity
Solution Approach 2:
The patent changes the reading parameter (voltage level or log-likelihood ratio) based on the calculated bit change ratio from dummy data. By adjusting this parameter dynamically, the system compensates for threshold voltage distribution shifts in erased state, improving measurement precision while maintaining reasonable process complexity
2Reliability
If the threshold voltage distribution difference between erased and programmed states is not compensated, then the reading process is straightforward, but the error detection capability and decoding success rate deteriorate
Solution Approach 1:
The patent employs feedback by using dummy data to calculate the bit change ratio, which then feeds back into adjusting the read voltage level or log-likelihood ratio. This closed-loop feedback mechanism compensates for threshold voltage distribution differences, improving decoding success rate while managing system complexity through iterative refinement
Solution Approach 2:
The patent introduces dummy data as an intermediary element to measure and characterize threshold voltage distribution variations. This intermediary enables indirect measurement of the distribution shift, which then informs the compensation strategy, improving reliability without directly complicating the main data reading path
Data Source
AI summary
A data accessing method, a memory controlling circuit unit, and a memory storage device are provided. The method includes: reading a codeword stored in a physical programming unit, and calculating a bit change ratio of a bit value change in dummy data included in the codeword; adjusting a read voltage level or a log likelihood ratio according to the bit change ratio; and performing a decoding operation on the codeword by using the adjusted read voltage level or the adjusted log likelihood ratio.