Interference Compensation in Analog Memory Arrays
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Solution Overview
Problem
Analog memory cells in arrays, such as in Flash memory devices, suffer from interference that leads to read errors and degrades storage reliability, as existing techniques for interference estimation and cancellation are not optimal in terms of throughput, delay, and computational complexity.
Innovation Solution
A method and system that utilize distinct read commands for target memory cells and potentially-interfering cells, where the first read command retrieves data from target cells and the second read command identifies interfering cells by comparing analog storage values to different sets of thresholds, allowing for interference compensation using Error Correction Code (ECC) with soft decoding metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interference estimation and cancellation techniques are applied to analog memory cell arrays, then storage reliability is improved, but computational complexity and processing time increase
Solution Approach 1:
The patent applies preliminary action by performing interference estimation before the main read operation. The system estimates interference from adjacent cells using simplified models and pre-computes correction values, which are then applied during the read process. This separates the complex interference estimation into a preliminary step that can be optimized independently from the main data retrieval operation.
Solution Approach 2:
The patent applies local quality by estimating interference on a per-cell basis using the specific characteristics of each adjacent cell. Instead of applying a global correction method, the system calculates interference values individually for each memory cell based on its position and the state of neighboring cells, allowing tailored correction for each location in the memory array.
2Measurement precision
If multiple read commands are used to read target and interfering cells, then interference cancellation accuracy is improved, but read operation time increases
Solution Approach 1:
The patent performs interference estimation as a preliminary action before the main read operation. By pre-calculating interference values based on adjacent cell states and using simplified read commands to identify interfering cells, the system prepares correction data in advance, reducing the time needed during the actual data retrieval process.
Solution Approach 2:
The patent applies partial action by using simplified read commands that read only the necessary information about interfering cells (such as threshold voltage values) rather than performing complete high-precision reads on all cells. This selective reading approach reduces the time required for interference identification while maintaining sufficient accuracy for correction.
3Measurement precision
If Error Correction Code with soft decoding metrics is applied, then data retrieval accuracy is improved, but processing delay increases
Solution Approach 1:
The patent performs interference estimation and preparation of correction values as preliminary actions before the ECC decoding process. By pre-computing interference compensation values and preparing soft decoding metrics in advance, the system reduces the computational burden during the actual data retrieval and decoding operations, thereby minimizing processing delay.
Solution Approach 2:
The patent changes the parameters of the read operation by using multiple read commands with different accuracy levels. The system performs initial reads with lower accuracy to quickly identify interfering cells and their interference characteristics, then applies corrected values during the final high-accuracy read. This parameter change strategy allows the ECC decoder to work with pre-processed data, reducing overall processing time while maintaining high accuracy.
Data Source
AI summary
A method for data storage includes, in a memory system that stores data by programming analog memory cells to respective programming states selected from a predefined set, providing a first read command that retrieves the data stored in target memory cells, and a second read command that identifies at least one potentially-interfering memory cell that is programmed to a programming state in a predefined subset of programming states expected to cause interference. Given data is stored in a first group of the memory cells. After storing the given data, the given data is retrieved by reading the first group using the first read command, reading a second group of the memory cells using the second read command, and compensating for the interference caused to the first group by the memory cells in the second group that were identified by the second read command.