Global-local read calibration for memory devices
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Solution Overview
Problem
Conventional memory systems face inefficiencies in calibrating read voltages for memory cells due to shifts caused by charge loss, read disturb, and temperature changes, leading to high bit error rates and prolonged data retrieval latency.
Innovation Solution
A global-local read voltage calibration technique is employed, where coarse voltage intervals sample signal and noise characteristics over a wide range to estimate read levels, followed by fine voltage intervals for precise calibration within local ranges, minimizing bit error rates and optimizing read voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage calibration methods are used, then the calibration process is simple, but bit error rate increases due to voltage shifts from charge loss, read disturb, and temperature changes
Solution Approach 1:
The calibration process is divided into two distinct stages: global calibration that scans a wide voltage range to identify approximate read levels, and local calibration that performs fine-tuned measurement around each identified read level. This segmentation allows the system to achieve high precision without requiring an exhaustive search of the entire voltage range, thereby reducing bit error rates while managing calibration complexity.
Solution Approach 2:
The global calibration is performed as a preliminary step to identify approximate read levels before conducting the local calibration. By pre-identifying the regions where read levels are likely to exist, the system prepares the groundwork for more efficient and precise local calibration, avoiding the need to search the entire voltage range during the precision measurement phase.
2Measurement precision
If exhaustive voltage scanning is performed to ensure precise read level calibration, then measurement precision improves, but time consumption increases
Solution Approach 1:
The voltage scanning process is segmented into two phases: a coarse global scan that quickly identifies approximate read level locations, and a fine local scan that performs detailed measurement only in the identified regions. This segmentation eliminates the need to perform exhaustive scanning across the entire voltage range, achieving high measurement precision while significantly reducing the total calibration time.
Solution Approach 2:
The calibration system applies different measurement qualities to different voltage regions: a粗-grained approach for the global voltage range and a fine-grained approach for local regions around identified read levels. This local quality differentiation ensures high precision where it matters most (around actual read levels) while using fewer resources in regions where precision is less critical.
3Reliability
If frequent calibration is performed to maintain accuracy under varying conditions, then reliability improves, but productivity decreases due to increased latency
Solution Approach 1:
The calibration process is structured as a two-stage procedure where the time-consuming global calibration is performed once to establish approximate read levels, followed by quicker local calibration steps that can be performed more frequently when needed. This segmentation allows the system to maintain accuracy through frequent calibration while minimizing the latency impact, as the bulk of the calibration work is done in advance during the global phase.
Data Source
AI summary
A memory device to calibrate voltages used to read a group of memory cells. For example, the memory device measures first signal and noise characteristics of a group of memory cells by reading the group of memory cells at first test voltages that are separated from each other by a first voltage interval. An estimate of a read level of the group of memory cells is determined based on the first signal and noise characteristics. The memory device then measures second signal and noise characteristics of the group of memory cells by reading the group of memory cells at second test voltages that are separated from each other by a second voltage interval that is smaller than the first voltage interval. An optimized read voltage for the read level is computed from the second signal and noise characteristics.