4T2R Ternary CAM Cell with RC-Delay Search
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Solution Overview
Problem
Conventional non-volatile ternary content-addressable memories face challenges with read disturb and occupy more circuit area due to the number of transistors in each cell, which affects their efficiency and reliability.
Innovation Solution
A non-volatile ternary content-addressable memory 4T2R cell is designed with a write transistor, two variable resistive elements, and a charge control transistor, optimized for RC-delay search, reducing the number of transistors and current usage to minimize read disturb and area occupancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional non-volatile TCAM cells are used, then data storage capability is achieved, but read disturb increases due to large voltage stress and current
Solution Approach 1:
The patent changes the operating parameters by using variable resistive elements with high resistance states to limit current flow during read operations. The resistive elements are configured to provide different resistance values that control the voltage stress and current through the non-volatile memory cells, thereby reducing read disturb while maintaining storage capability
Solution Approach 2:
The patent introduces variable resistive elements as intermediary components between the read circuitry and the non-volatile memory cells. These resistive elements act as mediators that control and limit the voltage stress and current applied to the memory cells during read operations, preventing direct high-stress conditions that cause read disturb
2Adaptability or versatility
If more transistors are used in each cell, then storage functionality is improved, but circuit area increases
Solution Approach 1:
The patent merges multiple functions into fewer transistor components. The reduced transistor cell structure integrates storage, read, and write control functions into a compact configuration that uses fewer transistors per cell while maintaining the ability to perform ternary content-addressable memory operations
Solution Approach 2:
The patent extracts and removes redundant transistor components from the conventional TCAM cell structure. By taking out unnecessary transistors and replacing them with variable resistive elements, the design achieves the same storage functionality with a reduced transistor count and smaller circuit area
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
The 4T2R cell achieves reduced read disturb and smaller chip area compared to conventional TCAMs, ensuring efficient data storage and retrieval while maintaining low current application.
Implementation Method 1
The first variable resistive element is electrically coupled to the source of the write transistor. The first transistor is electrically coupled to the first variable resistive element in series
Implementation Method 2
optimized for RC-delay search, reducing the number of transistors and current usage to minimize read disturb and area occupancy
Data Source
AI summary
The 4T2R cell comprises a write transistor, a first variable resistive element, a first transistor, a second variable resistive element, a second transistor, and a charge control transistor. The first transistor is electrically coupled to the first variable resistive element in series, and the second transistor is electrically coupled to the second variable resistive element in series, for providing search paths. For operating in a search phase, a pulse voltage is applied across the gate electrode and the source electrode of the first transistor (or across the gate electrode and the source electrode of the second transistor) for determining whether the gate voltage of the charge control transistor changes larger than a match threshold during the period of the pulse. Different RC-delay of the variable resistive elements controlling the voltage change speed of the gate voltage of the charge control transistor determines the matching result.