Tracking Circuit Reference Current for Memory Sensing
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Solution Overview
Problem
In non-volatile memory devices, accurately determining the state of memory cells is challenging due to significant leakage current paths within the memory array, especially when distinguishing between high and low resistance states, which affects the accuracy of current or voltage sensing operations.
Innovation Solution
A tracking circuit is used to generate a reference current that is the geometric mean of the current values for high and low resistance states, accounting for leakage currents, and is applied to sense amplifiers to improve sensing accuracy by providing a middle reference point for comparison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current or voltage sensing operations are used to determine memory cell state, then the logic state of memory cells can be sensed, but significant leakage current paths within the memory array make it difficult to accurately determine the state of a memory cell
Solution Approach 1:
A tracking circuit is introduced as an intermediary component that generates a reference current by simulating the leakage current paths present in the memory array. This reference current serves as a mediator between the sensed current and the ideal current without leakage, allowing accurate state determination by comparing the difference between sensed current and reference current.
Solution Approach 2:
The tracking circuit creates a copy of the leakage current characteristics by using identical circuit topology and component values (transistors, capacitors, resistors) as the memory array cells. This copied leakage current is then subtracted from the sensed current to eliminate the harmful effect of leakage.
2Device complexity
If the array does not comprise an access transistor for each memory cell, then device complexity is reduced and memory density is increased, but significant leakage current path exists within the memory array when sensing a particular memory cell
Solution Approach 1:
The tracking circuit acts as an intermediary that compensates for the leakage current inherent in the simplified array structure without access transistors. By generating a reference current that matches the leakage characteristics, the system can accurately sense memory cell states despite the simplified structure that enables higher density.
3Device complexity
If a reference current is generated without accounting for leakage currents, then device complexity is reduced, but the ability to accurately distinguish between high and low resistance states deteriorates
Solution Approach 1:
The tracking circuit generates a reference current that includes leakage current components as an intermediary step. This allows the sensing circuit to compare the sensed current against a reference that already accounts for leakage, thereby maintaining high accuracy in distinguishing resistance states without overly complicating the overall system.
Solution Approach 2:
The tracking circuit dynamically adjusts the reference current parameters to match the leakage characteristics under different operating conditions (temperature, process variations). By changing the reference current parameters to account for leakage, the system maintains accurate sensing without requiring complex additional circuitry.
Data Source
AI summary
Broadly speaking, embodiments of the present techniques provide apparatus and methods for generating a reference current for a memory array sensing scheme, and for using the generated reference current to sense the state of memory cells within the memory array. The generated reference current is particularly suitable for distinguishing between a high resistance state and a low resistance state.