Memory Controller Read Voltage Indexing by Time Difference
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Solution Overview
Problem
Existing memory systems face inefficiencies in read operations due to variations in threshold voltage distributions over time, leading to errors and increased retry rates, particularly in NAND flash memory systems where data retention and interference between memory cells affect read accuracy.
Innovation Solution
A memory system that includes a memory controller capable of managing write and read operations by storing time-related information and using historical data to adjust read conditions, such as shifting read voltages based on stored time differences and index values, thereby optimizing read operations and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read operations are performed without adjusting for time-related threshold voltage shifts, then read operations are simpler and faster initially, but read accuracy deteriorates over time leading to increased retry rates and errors
Solution Approach 1:
The system performs preliminary actions by storing time-related information and index values during write operations, and pre-calculating adjusted read voltages based on time differences before read operations are needed. This allows the read operation to directly apply pre-computed voltage adjustments rather than performing complex real-time calculations, thereby maintaining high read accuracy without increasing operational complexity.
Solution Approach 2:
The system implements feedback by using historical read data and time difference information to dynamically adjust read voltages. The memory controller monitors time elapsed since write operations and uses stored index values to determine appropriate voltage adjustments, creating a closed-loop system that continuously optimizes read accuracy based on temporal characteristics of threshold voltage drift.
2Reliability
If the memory system performs frequent read voltage adjustments based on time differences, then read accuracy is maintained, but processing time and operational overhead increase
Solution Approach 1:
The system performs preliminary calculations of voltage adjustments during write operations or idle periods, storing the computed index values and time-related parameters in advance. When a read operation is needed, the system simply retrieves pre-computed adjustment values based on the time difference, avoiding time-consuming real-time calculations and maintaining fast read speeds while ensuring data retention accuracy.
Solution Approach 2:
The system changes parameters by storing multiple index values corresponding to different time intervals and threshold voltage distribution characteristics. Instead of performing continuous complex calculations, the memory controller selects appropriate pre-stored index values based on the time difference between write and read operations, efficiently adapting to threshold voltage drift without increasing processing time.
3Measurement precision
If the memory system stores and processes time-related information for each memory page, then read operation accuracy is improved, but memory controller complexity and storage overhead increase
Solution Approach 1:
The system applies universality by using a single set of time-related parameters and index values that can be applied across multiple memory pages with similar characteristics. Instead of maintaining separate complex adjustment mechanisms for each page, the memory controller uses generalized time-difference-based indexing that works universally for pages within the same time window, reducing overall controller complexity while maintaining precision.
Solution Approach 2:
The system manages complexity by changing parameters from page-specific detailed threshold voltage measurements to time-difference-based index values. This parameter transformation reduces the dimensionality of the problem, allowing the memory controller to achieve precise voltage adjustments using simpler time-based parameters rather than complex page-specific characteristics.
Data Source
AI summary
A memory system includes a non-volatile memory in which data is stored in a plurality of pages including a first page and a second page and a memory controller. The controller is configured to perform a first write operation on the first page at a first time, perform a second write operation on the second page at a second time after the first time, perform a first read operation on the first page at a time after the first time using a first parameter and store a first index value in association with the first page and the first parameter, and determine a second parameter for a second read operation to be performed on the second page using a time difference between the first time and the second time and the first index value stored in association with the first page.