Memory Controller Adaptive Read Voltage Selection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In nonvolatile memory devices, especially flash memory devices, the reliability decreases and read failure rates increase as more bits are programmed per cell, making it challenging to precisely determine optimal read voltages for data stored in memory cells.
Innovation Solution
A memory controller method that performs hard and soft decision read operations, assigns log likelihood ratio (LLR) values, and determines an optimal read reference voltage based on raw and error-free data to improve data read accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit cells are used to store more data per cell, then storage density is improved, but reliability and read accuracy deteriorate
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting read reference voltages based on threshold voltage distributions of memory cells. Different read reference voltages are selected according to the specific voltage region and distribution characteristics of the memory cell array, allowing optimal read accuracy for multi-bit cells while maintaining high storage density
Solution Approach 2:
The patent implements dynamics by making the read reference voltage selection adaptive rather than fixed. The system dynamically determines which read reference voltage to use based on real-time analysis of threshold voltage distributions and hard decision read results, enabling the system to adapt to varying memory cell characteristics and maintain reliability across different storage density scenarios
2Speed
If traditional hard decision read operations are used, then read speed is maintained, but read failure rate increases in flat voltage regions
Solution Approach 1:
The patent applies feedback by using hard decision read results and error correction decoding outcomes to determine optimal read reference voltages for subsequent soft decision read operations. The system feeds back information about read successes and failures to adjust future read operations, thereby reducing read failure rates in flat voltage regions while maintaining efficient read speeds through intelligent voltage selection
Solution Approach 2:
The patent introduces an intermediary approach by inserting soft decision read operations between the hard decision read and the final data retrieval. This intermediary soft decision read with LLR values provides additional information about cell states, enabling more accurate error correction and reducing read failures without significantly impacting overall read speed
3Measurement precision
If multiple read reference voltages are tested to find optimal voltage, then read accuracy is improved, but processing time increases
Solution Approach 1:
The patent applies preliminary action by performing hard decision read operations and error correction decoding before initiating soft decision read operations with multiple voltage regions. This preliminary processing categorizes memory cells into voltage regions and prepares reference voltage candidates in advance, reducing the time needed for subsequent optimal voltage determination while maintaining high read accuracy
Solution Approach 2:
The patent implements partial action by testing and using only the necessary number of read reference voltages based on the specific voltage region and distribution characteristics. Rather than exhaustively testing all possible voltages, the system performs partial voltage testing targeted at the most likely optimal voltages, reducing processing time while maintaining sufficient accuracy for reliable data retrieval
Data Source
AI summary
A method for operating a memory controller includes: performing a hard decision read operation to read hard decision data from a memory device; if a hard decoding for the hard decision data fails, assigning log likelihood ratio (LLR) values to cells falling in a plurality of voltage regions corresponding to a plurality of read reference voltages; performing a soft decision read operation based on the LLR values and a soft decoding for the soft decision data to generate an error free data; performing a read operation to read data from the memory device using each of the plurality of read reference voltages to generate raw data for each of the plurality of read reference voltages; and determining an optimal read reference voltage among the plurality of the read reference voltages based on the raw data and the error free data.