Nonvolatile Memory ECC Switching Using On-Chip Syndrome Checking
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Solution Overview
Problem
Nonvolatile memory devices face issues with read errors due to distorted threshold voltage or resistance distributions caused by events like charge leakage and program disturbances, leading to incorrect data retrieval.
Innovation Solution
Incorporating an on-chip syndrome checker circuit in nonvolatile memory devices to generate a syndrome result value, allowing for efficient hard-decision or soft-decision ECC decoding based on the syndrome result, thereby reducing latency and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard-decision ECC decoding is always performed, then error correction capability is maintained, but decoding latency increases and performance deteriorates
Solution Approach 1:
The patent performs syndrome calculation in advance before ECC decoding to predict error patterns. By calculating the syndrome value beforehand and comparing it with predetermined thresholds, the system can determine whether hard-decision or soft-decision decoding is needed before actually performing the decoding operation, thus avoiding unnecessary latency
Solution Approach 2:
The patent dynamically selects between hard-decision and soft-decision ECC decoding based on the calculated syndrome result. When the syndrome value indicates low error probability (below threshold), hard-decision decoding is used for speed. When error probability is high (above threshold), soft-decision decoding is used for reliability. This dynamic adaptation resolves the contradiction between speed and reliability
2Reliability
If soft-decision ECC decoding is always performed, then error correction performance is improved, but computational complexity and processing time increase
Solution Approach 1:
The patent applies soft-decision decoding only partially - specifically when the syndrome calculation indicates high error probability. For cases with low error probability, simpler hard-decision decoding suffices. This partial application of the more complex algorithm reduces overall computational complexity while maintaining error correction performance where needed
3Loss of time
If syndrome checker circuit is integrated in nonvolatile memory device, then decoding latency is reduced, but device area increases
Solution Approach 1:
The patent extracts only the essential syndrome calculation and threshold comparison functions from the full ECC decoding process and places them in the nonvolatile memory device. The more resource-intensive soft-decision decoding algorithm remains in the external memory controller. This selective extraction reduces the area overhead in the memory device while still achieving latency reduction by avoiding data transfer for error-free cases
Data Source
AI summary
A memory system includes a nonvolatile memory device including a memory cell array and an on-chip syndrome checker, and a memory controller including an error check code (ECC) decoder and configured to control operation of the nonvolatile memory device. The nonvolatile memory device is configured to sequentially read out and store hard-decision data and soft-decision data from the memory cell array based on one read command transferred from the memory controller. The on-chip syndrome checker of the nonvolatile memory device is configured to generate a syndrome result value by calculating a syndrome of the hard-decision data. The ECC decoder of the memory controller is configured to, depending on the syndrome result value, either perform hard-decision ECC decoding based on the hard-decision data or perform soft-decision ECC decoding based on the hard-decision data and the soft-decision data by omitting the hard-decision ECC decoding.