Dual-Gate Transistor CAM Cell for Compact Memory
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Solution Overview
Problem
Conventional content-addressable memories (CAM) require a large surface area and high power consumption due to the need for multiple transistors and a power supply line, limiting miniaturization and efficiency.
Innovation Solution
A content-addressable memory cell design using a semiconductor-on-insulator substrate with two transistors, each with a front and back control gate, where the transistors are configured to store a data bit and its complement, and a comparison circuit operates them in read mode to detect current on a source line, indicating bit identity, reducing the number of transistors and eliminating the need for a power supply line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional NOR-type CAM cells are used with multiple transistors, then comparison function is achieved, but surface area occupied increases significantly
Solution Approach 1:
The patent combines the storage function and comparison function into a single integrated memory cell structure. The dual-gate transistor design allows the same transistor to both store data bits and participate in comparison operations, eliminating the need for separate comparison circuits for each bit cell. This merging of functions dramatically reduces the surface area from 300 F2 to approximately 30 F2 per cell.
Solution Approach 2:
The memory cell transistors are designed to serve multiple purposes: they store data bits, enable comparison through back-gate control, and provide readout signals. The dual-gate transistor structure allows the same physical component to perform what in conventional designs would require multiple specialized components, achieving multi-functionality that reduces overall cell size.
2Ease of operation
If conventional CAM memory with power supply line is implemented, then comparison operation is enabled, but power consumption increases
Solution Approach 1:
The patent extracts and eliminates the dedicated power supply line from the CAM memory structure. By using the back-gate control mechanism on existing transistors, the design removes the need for separate power distribution networks that consume significant power in conventional CAM implementations, thereby reducing overall power consumption while maintaining comparison functionality.
Solution Approach 2:
The memory cell transistors use their own back-gate control capability to perform comparison operations without requiring external power supply lines. The transistors self-regulate their conduction state based on back-gate voltages applied during comparison, eliminating the need for continuous power supply and reducing static power consumption.
3Measurement precision
If more transistors are used in CAM cell, then comparison accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the comparison logic into the basic memory cell structure itself. By using the back-gate control of the storage transistors to enable or disable conduction based on data matching, the design achieves accurate comparison without adding separate comparison transistors or circuits, thereby maintaining comparison accuracy while reducing device complexity.
Solution Approach 2:
The back-gate voltage acts as an intermediary control mechanism that enables accurate comparison without requiring additional transistors. By modulating the back-gate voltage, the system can precisely control whether a transistor conducts based on data match conditions, achieving high comparison accuracy through voltage control rather than through additional physical components.
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 design significantly reduces the surface area occupied by CAM cells, minimizes power consumption, and maintains comparison speed, enabling more efficient and compact content-addressable memory arrays.
Implementation Method 1
each of the transistors having a front control gate and a back control gate that can be controlled to block the associated transistor
Implementation Method 2
with one of the transistors passing and the other blocked
Implementation Method 3
detect a current on a source line linked to the source of each of the transistors. The presence or absence of such a current indicates whether the proposed bit and the stored bit are identical or not
Data Source
AI summary
The invention provides a content-addressable memory cell formed by two transistors that are configured so that one of the transistors is for storing a data bit and the other for is storing the complement of the data bit. Each transistor has a back control gate that can be controlled to block the associated transistor. The device also includes a comparison circuit that is configured to operate the first and second transistors in read mode while controlling the back control gate of each of the transistors so as to block the passing transistor if a proposed bit and the stored bit correspond. Then, the presence or absence of current on a source line linked to the source of each of the transistors indicates whether the proposed bit and the stored bit are identical or not. The invention also provides methods for operating the content-addressable memory cells of this invention, as well as content-addressable memories having a plurality of the content-addressable memory cells of this invention.