NAND Source Line Voltage Control via Dynamic Current Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As NAND flash memory technology advances, controlling the voltage of source lines in NAND memory systems becomes challenging due to instability issues during sense steps and recovery periods, affecting the accuracy of data state sensing in multi-level cell configurations.
Innovation Solution
A pre-charge and recovery circuit is implemented to rapidly pre-charge and stabilize the source line voltage using a high current, followed by a low recovery current to maintain stability during recovery periods, with the recovery current level selected based on testing to minimize instability and ensure accurate sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high current is used to rapidly pre-charge the source line voltage, then the speed of voltage stabilization is improved, but the stability during recovery periods deteriorates
Solution Approach 1:
The patent implements periodic action by using different current levels at different time periods: a high pre-charge current is applied during the initial charging phase to rapidly establish voltage, then switched to a lower recovery current during subsequent recovery periods to maintain stability. This temporal segmentation of current application resolves the contradiction between fast stabilization and long-term stability.
Solution Approach 2:
The patent applies dynamics by making the current level adjustable and time-dependent rather than fixed. The pre-charge and recovery circuit dynamically transitions between different current states (high current for pre-charge, low current for recovery) based on the operational phase, allowing the system to optimize both speed and stability at appropriate moments.
2Stability of the object's composition
If a low recovery current is used to maintain stability during recovery periods, then the voltage stability is improved, but the speed of returning to target voltage deteriorates
Solution Approach 1:
The patent applies preliminary action by using a high pre-charge current to rapidly bring the source line voltage close to the target voltage before switching to the lower recovery current. This preliminary high-current phase performs the bulk of the voltage restoration work, allowing the subsequent low-current phase to focus on fine-tuning and stabilization without sacrificing overall recovery speed.
3Device complexity
If the source line voltage is not properly stabilized, then the circuit complexity is reduced, but the measurement precision of data states deteriorates
Solution Approach 1:
The patent implements feedback by monitoring the source line voltage and using this information to control the pre-charge and recovery current. The circuit responds to voltage conditions by adjusting current application, ensuring the source line reaches and maintains the appropriate voltage level for accurate sensing. This feedback mechanism achieves high measurement precision without requiring overly complex external stabilization circuits.
Data Source
AI summary
An example of an apparatus includes a plurality of memory cells arranged in a plurality of NAND strings that are connected to a source line and a control circuit connected to the source line. The control circuit is configured to provide a first current to the source line to pre-charge the source line to a target voltage for sensing data states of the plurality of memory cells and provide a second current to the source line to return the source line to the target voltage in a recovery period between sensing data states. The control circuit is configured to provide the second current at any one of a plurality of current levels.