Word Line Discharge Skip for Faster NAND Flash Read Time
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Solution Overview
Problem
In NAND flash memory systems, the process of fully discharging unselected word lines between consecutive read operations is time-consuming, leading to increased read time and energy consumption due to the need for word line voltage stabilization before subsequent page reads can commence.
Innovation Solution
Implementing a dynamic approach where unselected word line discharge cycles are skipped or accelerated, merging Vread spikes and unselected string discharging into a single phase, allowing for partial discharge periods to expedite the transition from unselected to selected word line voltage, thereby reducing the time between read operations within the same memory block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If unselected word lines are fully discharged between consecutive read operations, then word line voltage stabilization is achieved, but read time increases and energy consumption increases
Solution Approach 1:
The patent applies partial discharge to unselected word lines instead of full discharge. The controller discharges unselected word lines to a partial discharge voltage level that is sufficient to reduce coupling effects but does not require complete discharge to ground. This partial action maintains voltage stabilization reliability while significantly reducing the time and energy required for discharge operations between consecutive read operations.
Solution Approach 2:
The controller performs preliminary discharge of unselected word lines to a partial discharge voltage before initiating the next read operation. This preliminary partial discharge action prepares the word lines for the upcoming operation by reducing coupling effects, eliminating the need for complete discharge and subsequent full recharging, thereby reducing overall read time while maintaining voltage stability.
2Reliability
If unselected word lines are fully discharged between consecutive read operations, then word line voltage stabilization is achieved, but energy consumption increases
Solution Approach 1:
The patent applies partial discharge to unselected word lines instead of full discharge. The controller discharges unselected word lines to a partial discharge voltage level that is sufficient to reduce coupling effects but does not require complete discharge to ground. This partial action maintains voltage stabilization reliability while significantly reducing the time and energy required for discharge operations between consecutive read operations.
3Reliability
If conventional word line discharge cycles are used, then voltage stabilization is ensured, but read performance is limited
Solution Approach 1:
The patent introduces dynamic control of word line discharge based on operational context. The controller determines whether to perform full discharge or partial discharge based on factors such as the sequence of operations, word line status, and coupling effects. This dynamic approach allows the system to optimize between voltage stabilization and read performance by selecting the appropriate discharge strategy in real-time.
Solution Approach 2:
The patent applies partial discharge to unselected word lines instead of full discharge. The controller discharges unselected word lines to a partial discharge voltage level that is sufficient to reduce coupling effects but does not require complete discharge to ground. This partial action maintains voltage stabilization reliability while significantly reducing the time and energy required for discharge operations between consecutive read operations.
Data Source
AI summary
Methods for improving read time performance and energy consumption when reading multiple pages within a memory block by dynamically skipping or accelerating unselected word line discharge cycles are described. In some cases, a controller or one or more control circuits in communication with word lines and bit lines associated with a memory block may detect that a read command or instruction for reading a second page within the memory block has arrived prior to the word line discharge phase associated with reading a first page within the memory block, and in response, the controller may skip the discharge cycle for unselected word lines within the memory block prior to reading the second page and initiate the next page read for the second page after a partial discharge period of time.