Balanced Codewords for Ternary Memory Drift Compensation
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Solution Overview
Problem
Existing memory devices face challenges in maintaining accurate sensing due to threshold voltage drift in memory cells, particularly in ternary cells, which are not compatible with techniques used for binary cells, leading to reliability issues and increased power consumption.
Innovation Solution
Implementing a dynamic sensing technique that uses balanced codewords, generated through a coding scheme, to distribute ternary cells into predetermined states, reducing the quantity of cells in an undesirable state and compensating for threshold voltage drift by setting precise read voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If binary cell sensing techniques are used for ternary cells, then device complexity is reduced, but sensing accuracy deteriorates due to threshold voltage drift incompatibility
Solution Approach 1:
The patent changes the parameter distribution of codewords from uniform to balanced (with constrained weight), where balanced codewords have a specific distribution of 0s and 1s that compensates for threshold voltage drift. This parameter change in codeword structure enables ternary cell sensing to remain accurate despite drift, as the balanced distribution creates a more robust sensing margin.
2Ease of manufacture
If unbalanced codewords are used, then coding simplicity is improved, but power consumption increases due to excessive cells in undesirable states
Solution Approach 1:
The patent imposes a weight constraint parameter on codewords, requiring that the number of 1s (or 0s) falls within a specific range. This parameter constraint transforms the coding process from simple unconstrained encoding to balanced encoding, which reduces the number of ternary cells forced into undesirable intermediate states, thereby lowering power consumption during read operations.
3Measurement precision
If balanced codewords are implemented, then sensing accuracy is improved, but device complexity increases due to additional coding requirements
Solution Approach 1:
The patent applies balanced coding as a preliminary action before data is written to memory. By pre-processing the data into balanced codewords with constrained weight distribution, the system prepares the data in a form that is inherently more resistant to threshold voltage drift. This preliminary transformation simplifies the actual sensing operation, as the balanced structure provides built-in compensation for drift without requiring complex real-time adjustments during sensing.
4Quantity of substance
If ternary cells are used instead of binary cells, then storage capacity is improved, but reliability deteriorates due to threshold voltage drift susceptibility
Solution Approach 1:
The patent changes the statistical parameters of the stored data by using balanced codewords with constrained weight. This parameter transformation ensures that ternary cells are not forced into extreme or intermediate states as frequently, creating a more reliable storage system. The balanced distribution of 0s and 1s in codewords results in a more uniform utilization of ternary states, reducing the impact of threshold voltage drift on data integrity.
Data Source
AI summary
Methods, systems, and devices for balanced codewords for reducing a selected state in memory cells are described. A memory device may divide a sequence of data bits into sets of bits associated with different bit-positions in a coding scheme. The memory device may then balance a first codeword that includes the first set of the data bits in the binary domain to reach a target ratio of logic values for the codeword. Using the first codeword and the other set(s) of data bits, the memory device may balance the remaining two states in the state domain to reach an overall target distribution of the three states. The memory device may then generate one or more codeword(s) for the other set(s) of data bits so that the memory device can write all of the codewords to ternary cells.