Bitline Bias Circuit for NOR Flash Memory Voltage Stability
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Solution Overview
Problem
Conventional bitline bias circuits in NOR flash memory devices face challenges in stably supplying a bias voltage near the power voltage to bitline bias transistors, leading to increased power consumption due to leakage current and instability in voltage supply, especially when the power voltage decreases.
Innovation Solution
A bitline bias circuit is designed with a high voltage generating circuit, a voltage divider circuit, a comparator, and a driver using high voltage transistors to stabilize the bias voltage supply, including a pulse generating circuit that operates the bitline bias circuit in response to a pump enable signal to minimize current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bitline bias circuit is always operated to provide a constant bias voltage, then the bias voltage stability is improved, but the power consumption increases due to leakage current
Solution Approach 1:
The bitline bias circuit is operated periodically based on the pump enable signal rather than continuously. The control logic activates the bitline bias circuit only during specific operation phases (read, verify, program) when bias voltage is needed, and deactivates it during idle periods, thereby reducing leakage current while maintaining voltage stability when required
2Loss of energy
If the power voltage applied to the bitline bias circuit is decreased, then the power consumption is reduced, but the bias voltage applied to the bitline bias transistor is also decreased leading to instability
Solution Approach 1:
The circuit uses high voltage transistors that can operate with higher voltage tolerance to generate a stable bias voltage even when the power voltage is reduced. The high voltage transistors maintain proper transistor operation and bias voltage output across a wider voltage range, ensuring stability despite lower power supply conditions
3Reliability
If a voltage close to the power voltage is supplied to the bitline bias transistor, then the voltage stability is improved, but it is difficult to stably supply due to transistor characteristics
Solution Approach 1:
A dedicated bitline bias circuit acts as an intermediary between the power voltage source and the bitline bias transistor. This intermediate circuit uses high voltage transistors and control logic to properly regulate and stabilize the bias voltage, making it easier to supply a stable voltage close to the power voltage without directly connecting the transistor to the power source
Data Source
AI summary
The NOR flash memory device according to the present invention is operated by a high voltage supplied from bitline selection transistors and includes a bitline bias circuit for supplying a bias voltage of a constant level to the bitline bias transistor. In accordance with the present invention, it is possible to stably supply a desired voltage closing to a power voltage to the bitline bias transistor.