Memory Read Voltage Search Using Signal and Noise Feedback
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Solution Overview
Problem
Existing memory systems face inefficiencies in searching for an optimized read voltage for memory cells due to shifts in threshold voltages caused by factors like charge loss and temperature variations, leading to long latency and inefficient retry processes.
Innovation Solution
A memory sub-system efficiently calculates an optimized read voltage by measuring signal and noise characteristics of memory cells, adjusting test voltage ranges based on these characteristics, and using predictive models to determine the optimal voltage location, allowing concurrent reading of hard and soft bit data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage searching methods are used to account for threshold voltage shifts, then reading accuracy can be maintained, but latency increases and retrieval efficiency deteriorates
Solution Approach 1:
The system performs preliminary calibration to establish the relationship between read voltage and bit count before actual data retrieval. This preliminary action creates a lookup table or model that enables fast voltage selection during operation, avoiding time-consuming searches while maintaining accuracy.
Solution Approach 2:
The patent replaces traditional iterative voltage searching (mechanical trial-and-error process) with a predictive model based on bit count analysis. The model calculates optimal voltage directly from measured bit counts, substituting the mechanical search process with a computational approach that is significantly faster.
2Reliability
If iterative retry processes are implemented to handle voltage shifts, then data retrieval reliability improves, but productivity decreases due to redundant operations
Solution Approach 1:
The system uses bit count feedback from initial read attempts to dynamically adjust the read voltage. By monitoring the actual bit counts returned and comparing them against expected values, the system provides feedback that drives voltage optimization, ensuring reliable retrieval without requiring multiple blind retry attempts.
Solution Approach 2:
The patent dynamically changes the read voltage parameter based on observed bit count characteristics. Instead of using fixed voltage values or exhaustive search sequences, the system adjusts voltage parameters adaptively based on real-time measurements, optimizing both reliability and speed.
3Measurement precision
If comprehensive signal and noise characterization is performed across voltage ranges, then voltage optimization accuracy improves, but measurement complexity and device complexity increase
Solution Approach 1:
The patent divides the voltage measurement process into manageable segments or ranges. Instead of attempting to characterize the entire voltage range in one complex operation, the system segments the measurement into discrete steps or regions, making the measurement process more tractable and less complex while maintaining overall accuracy.
Data Source
AI summary
A memory device to search for a voltage optimized to read a group of memory cells. In response to a read command, the memory device measures first signal and noise characteristics of the memory cells by reading the memory cells at first test voltages. Based on the first signal and noise characteristics, the memory device may determine that the optimized read voltage is outside of a range of the first test voltages. In response, the memory device determines, based on the first signal and noise characteristics, an estimate of the optimized read voltage, and measures second signal and noise characteristics by reading at second test voltages configured around the estimate. The optimized read voltage can be computed based at least in part on the second signal and noise characteristics. The memory device retrieves data from the memory cells using the optimized read voltage.