Flash Memory Read Voltage Optimization via Lookup Table
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flash memory systems face read errors due to variations in threshold voltage distributions caused by increased integration and density, leading to inefficiencies in determining optimum read voltages, especially in multi-level and triple-level cell systems, which impact bit error rate and memory throughput.
Innovation Solution
A method is introduced to find an optimum read voltage by calculating difference values between state bit counts within a threshold voltage region, determining a direction and offset for adjusting the current read reference voltage, and iteratively refining the voltage until successful reading is achieved, utilizing a lookup table for efficient offset determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read retry methods blindly search for reference voltage, then read error rate is reduced, but memory throughput is severely impacted
Solution Approach 1:
The patent performs preliminary actions by pre-calculating and storing optimal reference voltage offsets in lookup tables during system initialization or idle periods. When a read operation is needed, the system retrieves pre-computed offset values rather than performing blind search, significantly reducing read retry time while maintaining high reliability in detecting stored data values
Solution Approach 2:
The patent implements feedback mechanisms by monitoring read error rates and using this information to adjust future read operations. The system learns from previous read successes or failures to optimize subsequent reference voltage selections, reducing the need for extensive blind search while improving detection accuracy
2Measurement precision
If multiple reference voltages are used for MLC/TLC flash memory, then data detection accuracy is improved, but read retry time increases exponentially
Solution Approach 1:
The patent pre-calculates optimal reference voltage offsets for multiple reference voltages and stores them in lookup tables. When reading MLC or TLC flash memory, the system retrieves pre-computed offset values for multiple reference voltages simultaneously, eliminating the need for sequential blind search and reducing read retry time exponentially while maintaining high data detection accuracy
Solution Approach 2:
The patent transforms the search space from a one-dimensional sequential search through multiple reference voltages to a multi-dimensional parallel approach using lookup tables. By organizing offset values in structured data structures and retrieving them in parallel, the system achieves both high accuracy across multiple reference voltages and reduced time complexity
3Device complexity
If reference voltage windows are assumed to have Gaussian distributions, then detection is simplified, but errors occur when operating environment changes
Solution Approach 1:
The patent adapts reference voltage offsets dynamically based on detected threshold voltage distribution characteristics. Instead of assuming fixed Gaussian distributions, the system monitors actual distribution parameters (mean, standard deviation) and adjusts offset values accordingly, maintaining high detection reliability across varying operating conditions while managing complexity through automated parameter adaptation
Data Source
AI summary
A method for finding an optimum read voltage includes acquiring difference values between state bit counts of different positions. A direction for finding the optimum read voltage is determined based on the difference values. An offset for finding the optimum read voltage is determined based on correspondence between a difference value of bit count and offset. Reading is performed with the offset applied to a current read reference voltage, wherein upon read-success, the current reference voltage superimposed with the offset is the optimum read voltage, and upon read-error, new first and second positions are obtained based on the direction and the offset for finding the optimum read voltage until reading becomes successful.