Sense Amplifier for Concurrent Multi-State Program Verify
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Solution Overview
Problem
Current sensing techniques for non-volatile memory devices face limitations in distinguishing between different negative threshold voltage states, particularly due to the unavailability of negative read voltages and the shallow range of negative threshold voltage sensing, which restricts the ability to store more data states per cell.
Innovation Solution
A sense amplifier structure and technique where the source line is discharged through a selected memory cell into the bit line and sense amplifier, reversing the usual current flow, allowing for deeper negative threshold voltage sensing without the need for negative read voltages, and incorporating decoupling capacitors and auxiliary keeper currents to reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensing techniques are used with unavailable negative read voltages, then the sensing circuit cannot operate, but this restricts the ability to sense deeply negative threshold voltage states
Solution Approach 1:
The patent inverts the conventional sensing approach by reversing the current flow direction. Instead of flowing current from bit line to source line, the source line is discharged through the memory cell into the bit line and sense amplifier. This inversion enables sensing of deeply negative threshold voltage states without requiring negative read voltages, as the reversed current path allows the sense amplifier to detect voltage drops in the opposite direction
2Quantity of substance
If the threshold voltage window is reduced to store more data states per cell, then data storage density increases, but the ability to distinguish between different data states becomes more difficult
Solution Approach 1:
The patent changes the sensing parameter from voltage level detection to current flow direction and magnitude detection. By measuring the amount of charge discharged from the source line through the memory cell, the system can distinguish between multiple data states even when their threshold voltages are closely spaced. The sense amplifier quantizes the discharged charge to determine the specific data state, enabling accurate differentiation within a compressed threshold voltage window
3Productivity
If multiple data states are sensed concurrently, then productivity increases, but noise from multiple simultaneous operations may increase
Solution Approach 1:
The patent merges multiple sensing operations by discharging the source line simultaneously through multiple memory cells connected to different bit lines. The sense amplifiers on each bit line independently measure the discharged charge, allowing concurrent sensing of multiple data states. This parallel operation increases productivity while the distributed architecture prevents noise from one sensing operation from interfering with others
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
Enables accurate sensing of multiple data states per cell, including deeply negative threshold voltage states, improving data storage density and reliability by enhancing the ability to differentiate between various data states within a smaller threshold voltage window.
Implementation Method 1
the source line is discharged through a selected memory cell into the bit line and sense amplifier
Implementation Method 2
incorporating decoupling capacitors and auxiliary keeper currents to reduce noise
Implementation Method 3
incorporating decoupling capacitors and auxiliary keeper currents to reduce noise
Data Source
AI summary
A sense amplifier for a memory circuit that can sense into the deep negative voltage threshold region is described. A selected memory cell is sensed by discharging a source line through the memory cell into the bit line and sense amplifier. While discharging the source line through the memory cell into the sense amplifier, a voltage level on the discharge path is used to set the conductivity of a discharge transistor to a level corresponding to the conductivity of the selected memory cell. A sense node is then discharged through the discharge transistor. By allowing the sense amplifier to bias a memory cell being sensed to a selected one of multiple bias levels during a sensing operation, multiple target data states can be concurrently program verified, leading to higher performance when writing data.