Analog Signal Output Nonvolatile Memory for Multi-Bit Read Accuracy
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Solution Overview
Problem
Multi-bit flash memory devices face errors during read operations due to variations in threshold voltages, which are exacerbated by charge leakage and program disturbance, necessitating a technique to improve data accuracy and storage density.
Innovation Solution
A memory system that outputs analog signals from selected memory cells during read operations, utilizing a converter to convert these signals into binary data with enhanced resolution, and a memory controller that performs error correction through a soft decision algorithm, reducing the number of read operations required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit flash memory stores more data per memory cell by using more distinguishable threshold voltages, then storage density is improved, but read operation errors increase due to threshold voltage variation
Solution Approach 1:
The patent changes the read operation parameter from binary threshold-based reading to analog voltage-level reading. By reading the actual analog voltage level of the memory cell rather than making binary decisions based on fixed thresholds, the system can accurately distinguish between multiple data states even when threshold voltages vary due to charge leakage and program disturbance. This parameter change enables accurate retrieval of multi-bit data while maintaining high storage density.
2Device complexity
If conventional binary read operations are used in multi-bit flash memory, then device complexity is kept low, but data accuracy deteriorates due to threshold voltage variation and charge leakage
Solution Approach 1:
The patent replaces the mechanical/threshold-based binary read system with an analog voltage measurement system. Instead of using fixed voltage thresholds to make binary decisions (0 or 1), the system measures the actual analog voltage level of the memory cell, which provides continuous information about the stored data state. This substitution enables more precise data retrieval while maintaining relatively simple hardware implementation through the use of analog output circuits and voltage-level detection.
3Reliability
If multiple read operations are performed to correct threshold voltage variation, then data accuracy is improved, but read operation time increases
Solution Approach 1:
The patent performs preliminary action by reading the actual analog voltage level of the memory cell in a single operation, rather than performing multiple sequential read operations with different threshold voltages. By obtaining the complete voltage information upfront, the system can then process this data through error correction algorithms without needing to repeat the read operation. This preliminary analog read provides sufficient information for both data retrieval and error correction, significantly reducing the total read operation time while maintaining high data accuracy.
Data Source
AI summary
A memory system and a nonvolatile memory device therein are disclosed. The memory system comprises a memory device outputting a plurality of analog signals during a read operation, a converter to convert the plurality of analog signals into binary data, and a memory controller to operate an error correction operation on the binary data. The error correction operation uses a soft decision algorithm.