Voltage Generator Slope Control for NAND Flash Word Line Charging
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Solution Overview
Problem
In vertical-NAND flash memory devices, increasing parasitic capacitance and peak current between word lines can lead to erroneous operations and performance deterioration, as maintaining word line charge current is challenging due to peak current generation.
Innovation Solution
A voltage generator with a driving circuit, current sensing unit, peak detect unit, and slope control unit that adjusts the slope of the word line charge voltage based on sensed charge current, allowing for variable control to prevent peak current generation and optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the magnitude of word line charge current is maintained to maintain memory performance, then memory performance is improved, but peak current is generated causing erroneous operations
Solution Approach 1:
The patent applies dynamics by making the voltage slope adjustable rather than fixed. The voltage generator dynamically changes the slope of the word line charge voltage based on real-time current sensing feedback. When peak current is detected, the slope is reduced; when current is within safe limits, the slope can be increased to maintain performance. This dynamic adjustment resolves the contradiction between maintaining high performance and avoiding peak current.
Solution Approach 2:
The patent implements feedback control through a current sensing unit that continuously monitors the charge current and feeds this information back to the voltage generator. The feedback mechanism allows the system to detect when current approaches peak levels and automatically adjust the voltage slope accordingly. This closed-loop feedback system enables the reconciliation of high performance requirements with peak current prevention.
2Object-affected harmful factors
If the magnitude of word line charge current is reduced to prevent peak current, then peak current is prevented, but word line setup time increases and memory performance deteriorates
Solution Approach 1:
The voltage slope is made dynamic rather than static. Instead of using a consistently low current magnitude that would prevent peak current but increase setup time, the system uses a low slope only when necessary (when current approaches peak levels) and allows higher slopes when safe. This dynamic approach prevents peak current while minimizing the impact on word line setup time and overall performance.
Solution Approach 2:
The patent changes the parameter of voltage slope dynamically based on operating conditions. By adjusting this parameter in real-time according to current sensing feedback, the system can operate at high performance levels when safe and reduce to safe levels when necessary, rather than being constrained to a fixed low-performance operating point throughout.
3Reliability
If a fixed standby time is used to charge word lines, then charging is completed, but standby time cannot be reduced even when charge current is sufficient
Solution Approach 1:
The patent uses feedback from the current sensing unit to determine when word line charging is complete, rather than relying on a predetermined fixed time. The feedback mechanism allows the system to monitor the actual charging progress and terminate the standby period as soon as the word line is sufficiently charged, eliminating unnecessary waiting time while ensuring charging completeness.
Solution Approach 2:
The system performs preliminary monitoring of charge current during the charging process itself, allowing early detection of charging completion. By continuously sensing the current and comparing it against threshold values, the system can determine in advance when the word line has reached sufficient charge level, enabling earlier termination of the standby period than a fixed time approach would allow.
Data Source
AI summary
There are provided a method of operating a voltage generator. The method includes providing a reference voltage, sensing a magnitude of a charge current for increasing voltages of a plurality of word lines based on the reference voltage, determining whether the sensed magnitude of the charge current is greater than a peak current value, increasing the reference voltage in accordance with a first slope when the sensed magnitude of the charge current is less than or equal to the peak current value, and increasing the reference voltage in accordance with a second slope less than the first slope when the detected magnitude of the charge current is greater than the peak current value.