Semiconductor Memory Sense Amplifier Noise Cancellation
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Solution Overview
Problem
In semiconductor memory devices with resistance-variable elements, the influence of semi-selected memory cells on data reading is significant due to their nonlinear resistance characteristics, especially in 3D stacked configurations where the number of semi-selected cells increases, leading to noise interference and potential data reading errors, especially when multiple bits are stored.
Innovation Solution
The semiconductor memory device employs a sense amplifier that senses cell currents in two steps, first by setting both selected and semi-selected memory cells to a first semi-selected state and then to a selected and second semi-selected state, allowing the amplifier to read data based on the difference between the cell currents in these states, thereby reducing the influence of semi-selected memory cells by equalizing noise magnitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If 3D stacked configuration is used to increase memory capacity, then storage density is improved, but noise interference from semi-selected cells increases
Solution Approach 1:
The reading process is segmented into two distinct steps: first sensing all cells (selected and semi-selected) together, then sensing only selected cells. This segmentation allows the noise from semi-selected cells to be isolated and subtracted from the total signal, enabling accurate data retrieval from the selected cell while maintaining high memory capacity through 3D stacking.
Solution Approach 2:
The patent changes the voltage parameters applied to bit lines during the two sensing steps. In the first step, a first voltage is applied to sense all cells; in the second step, a second voltage (different from the first) is applied to sense only selected cells. By controlling and varying these voltage parameters, the system can differentiate between signals from selected and semi-selected cells, reducing noise interference while maintaining high storage density.
2Quantity of substance
If multiple bits are stored per memory cell, then storage capacity is improved, but data reading accuracy deteriorates due to increased noise from semi-selected cells
Solution Approach 1:
The sensing operation is divided into two segmented phases: a first sensing phase that captures signals from all cells including semi-selected ones, and a second sensing phase that captures signals only from selected cells. By subtracting the first sensed signal from the second, the patent eliminates noise from semi-selected cells, thereby maintaining high reading accuracy even when multiple bits are stored per cell.
Solution Approach 2:
The patent employs a feedback mechanism where the signal sensed from all cells (including semi-selected) is used as a reference to subtract from the signal sensed from selected cells only. This feedback-based noise cancellation ensures that multi-bit data can be read accurately despite the presence of semi-selected cell interference, preserving both high storage capacity and reading precision.
3Measurement precision
If two-step sensing is implemented to reduce semi-selected cell influence, then data reading accuracy is improved, but operation complexity increases
Solution Approach 1:
The sense amplifier is designed with multi-functionality to perform both sensing operations (first sensing all cells, then sensing selected cells) using the same hardware circuitry. This universal design allows the system to achieve high reading accuracy through two-step sensing without requiring additional dedicated hardware for each sensing phase, thereby limiting the increase in operational complexity despite the improved measurement precision.
4Object-affected harmful factors
If sense amplifier distinguishes between selected and semi-selected cells, then noise cancellation is improved, but circuit complexity increases
Solution Approach 1:
The sense amplifier distinguishes between selected and semi-selected cells by changing voltage parameters applied to bit lines during different sensing phases, rather than by complex circuit differentiation. By controlling voltage levels and timing, the amplifier can selectively sense different cell groups using the same circuit structure, achieving effective noise cancellation without significantly increasing circuit complexity.
Data Source
AI summary
A semiconductor memory device includes a first memory cell having a first end connected to a first wiring and a second end connected to a second wiring and a second memory cell having a first end connected to the first wiring and a second end connected to a third wiring. A sense amplifier is configured to: sense a first current flowing in the first wiring when a first voltage is applied to the second and third wirings and a second voltage, larger than the first voltage, is applied to the first wiring; and sense a second current flowing in the first wiring when a third voltage larger than the second voltage is applied to the first wiring, the first voltage to the second wiring, and the second voltage to the third wiring. The sense amplifier reads data according to a difference between the first current and the second current.