Dual Charge Pump Circuit for NAND Flash Voltage Control
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Solution Overview
Problem
Conventional NAND flash memories face challenges in controlling voltages for unselected word lines, leading to increased circuit complexity and potential voltage ripple due to unbalanced charge pump circuit capabilities, which affects data write and read operations.
Innovation Solution
The semiconductor memory device employs a dual charge pump circuit system, where a first charge pump circuit generates specific voltages for unselected word lines adjacent to the selected word line, and a second charge pump circuit handles other unselected word lines, optimizing voltage generation and distribution to minimize circuit scale and improve controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single charge pump circuit is used to generate voltages for all unselected word lines, then the circuit scale is reduced, but the voltage control precision deteriorates due to unbalanced load and voltage ripple
Solution Approach 1:
The patent divides the charge pump circuit into two independent segments: a first charge pump circuit dedicated to generating voltages for first unselected word lines, and a second charge pump circuit for second unselected word lines. This segmentation allows each charge pump to handle a balanced load, preventing voltage ripple while maintaining reasonable circuit scale. The segmentation resolves the contradiction by enabling precise voltage control without requiring a single oversized charge pump circuit.
2Adaptability or versatility
If the number of voltage types is increased to support multi-level data, then the data storage capability is improved, but the device complexity increases due to more charge pump circuits
Solution Approach 1:
The patent makes the first and second charge pump circuits multi-functional by enabling them to operate in different modes: during write operations, they generate different voltages for different word line groups; during read operations, they generate read voltages. This universality allows the system to support multi-level data storage with only two charge pump circuits, avoiding the need for separate charge pumps for each voltage type and operation mode.
3Reliability
If more charge pump circuits are used to improve voltage control, then the voltage stability is improved, but the ease of operation deteriorates due to increased control difficulty
Solution Approach 1:
By segmenting the charge pump circuits into two independent units with dedicated word line groups, the patent simplifies the control logic. Each charge pump circuit can be controlled independently based on simple criteria (first or second unselected word line), avoiding the complexity of dynamically allocating a single charge pump to multiple word lines. This segmentation maintains voltage stability while improving ease of operation.
Solution Approach 2:
The patent establishes predetermined assignments where the first charge pump circuit is dedicated to first unselected word lines and the second charge pump circuit to second unselected word lines. This preliminary assignment eliminates the need for complex real-time control decisions, as the control circuit simply needs to identify which word line group requires voltage generation, significantly reducing control difficulty while maintaining voltage stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for accurate voltage control, reduces circuit complexity, and enhances operational reliability by balancing the load on charge pump circuits, preventing voltage ripple and improving data integrity during write and read operations.
Implementation Method 1
a voltage generator which includes a first charge pump circuit and a second charge pump circuit and which outputs a voltage generated by the first and second charge pump circuits
Data Source
AI summary
A semiconductor memory device includes a memory cell unit, word lines, a driver circuit, and a voltage generator. The memory cell unit includes a plurality of memory cells connected in series. Each of the memory cells includes a charge accumulation layer and a control gate. The word lines are connected to the control gate. The driver circuit selects one of the word lines and applies voltages to a selected word line and unselected word lines. The voltage generator includes first and second charge pump circuits and outputs a voltage generated by the first and second charge pump circuits to the driver circuit. The first charge pump circuit is exclusively used to generate a voltage for a first word line. The first word line is one of the unselected word lines located adjacent to the selected word line.