Variable Load Resistor for Stable Memory Read-Out
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Solution Overview
Problem
Conventional semiconductor memory devices face challenges in maintaining the reference voltage within the operating range during verify operations, especially when the power supply voltage is reduced, leading to potential data read-out resolution reduction or malfunctions.
Innovation Solution
Incorporating a current-voltage conversion circuit with a variable load resistor connected to the bit line, allowing the resistance to be adjusted through load resistor selection signals, thereby modifying the threshold cell current without altering the reference voltage, ensuring the reference voltage remains within the operating range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power supply voltage is reduced to lower power consumption, then energy efficiency is improved, but the input operating voltage range of the sense amplifier narrows, causing the reference voltage to fall outside the operating range and reducing data read-out resolution
Solution Approach 1:
The patent changes the resistance value of the load resistor in the current-voltage conversion circuit to adjust the threshold cell current. By modifying this parameter, the system can maintain proper read-out operation even when the power supply voltage is reduced, preventing the reference voltage from falling outside the sense amplifier's operating range and thus preserving data read-out resolution
Solution Approach 2:
The patent introduces a variable load resistor that can dynamically adjust its resistance value based on operating conditions. This dynamic adjustment allows the threshold cell current to be optimized for different power supply voltages, ensuring the reference voltage remains within the valid operating range of the sense amplifier across varying power consumption levels
2Reliability
If the reference voltage is adjusted to maintain it within the operating range during verify operations, then operational reliability is improved, but the threshold cell current cannot be optimized, leading to reduced read-out performance
Solution Approach 1:
Instead of adjusting the reference voltage, the patent changes the load resistor value to modify the threshold cell current. This parameter change allows the system to maintain both operational reliability (by keeping the reference voltage within the operating range) and optimized read-out performance (by adjusting the threshold current to match the verify operation requirements)
3Device complexity
If a fixed load resistor is used in the current-voltage conversion circuit, then circuit simplicity is maintained, but the threshold cell current cannot be adjusted for different verify operations, reducing adaptability
Solution Approach 1:
The patent replaces the fixed load resistor with a variable load resistor that can adjust its resistance value. This dynamic element provides different resistance values for different verify operations (such as first verify and second verify with different threshold currents), significantly improving adaptability while adding only minimal circuit complexity through simple switching mechanisms
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 approach stabilizes the read-out operation even when the input operating voltage range narrows, preventing data read-out resolution reduction and ensuring reliable data retrieval.
Implementation Method 1
a current-voltage conversion circuit converting the cell current flowing through the bit line into a data voltage and having a variable load resistor connected to the memory cell through the bit line
Data Source
AI summary
This invention offers a semiconductor memory device, with which a resolution to read-out data is not reduced even at the time of verify and a stable read-out operation is possible even when a power supply voltage is reduced. A read-out circuit is provided with a current-voltage conversion circuit, that converts a cell current into a data voltage, and a sense amplifier that compares the data voltage with a reference voltage. The current-voltage conversion circuit is formed to include a variable load resistor that is connected to the memory cell through a bit line. The variable load resistor is formed to include P channel type MOS transistors that make load resistors and P channel type MOS transistors that constitute a switching circuit.