Pilot Signal Read Level Estimation in Nonvolatile Memory
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Solution Overview
Problem
Existing methods for optimizing read levels in nonvolatile memory, such as one-shot estimation and read-voltage tracking loop, fail to utilize unused space in memory pages effectively, leading to suboptimal read performance and inefficient use of memory resources.
Innovation Solution
The method involves programming pilot signals into unused bytes of a memory page, allowing a memory controller to estimate optimal read voltages based on the number of cells storing these signals, thereby improving read level estimation and utilizing otherwise unused space for data storage and retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If one-shot estimation or RVTL methods are used for read level optimization, then read level estimation can be performed, but unused memory space is not utilized and estimation accuracy is limited due to symbol mapping changes and errors between symbols
Solution Approach 1:
The patent introduces pilot signals as intermediary reference data inserted into unused memory locations. These pilot signals serve as a mediator between the storage system and read level estimation process, providing known reference values that enable accurate threshold voltage estimation without relying on assumptions about data distribution or symbol mapping. The pilot signals are specifically placed in unused bytes of compressed pages, converting wasted space into a useful resource for read optimization.
Solution Approach 2:
The system uses its own unused memory capacity to generate the reference signals needed for read level estimation. Instead of requiring external calibration data or additional hardware, the storage system self-generates pilot signals within its own structure, making the estimation process self-sufficient and eliminating dependencies on external calibration equipment or assumptions about data uniformity.
2Productivity
If compression is applied to reduce write amplification, then storage efficiency improves, but unused space after compression is not utilized
Solution Approach 1:
The patent makes the unused memory space serve multiple functions: it continues to provide capacity for compressed data storage while simultaneously serving as the location for pilot signal insertion. This multi-functional use of the same physical space enables both compression benefits and read level optimization without requiring additional memory resources. The unused bytes become a dual-purpose resource for both data storage and calibration.
3Reliability
If traditional read level estimation methods are used, then the process can be completed, but estimation errors occur due to symbol mapping changes and errors between symbols
Solution Approach 1:
The patent extracts the read level estimation function from the actual data pages and performs it separately using dedicated pilot signal pages. By separating the calibration function from the data storage function, the system eliminates errors that arise from symbol mapping changes in compressed data. The pilot signals provide a clean, controlled reference that is independent of the variable data patterns in compressed pages, thereby improving reliability without adding complexity to the data path.
Data Source
AI summary
A method, executed by a memory controller, for estimating read levels of a nonvolatile memory includes reading voltages stored by memory cells of a page space within the nonvolatile memory to which pilot signals of a predetermined symbol are programmed. The number of memory cells are identified whose voltages, read from the page space, are less-than/greater-than a read-voltage applied in reading the voltages stored by the memory cells. A voltage to be applied for reading data stored in the page space is estimated based upon the identified number of memory cells.