Static NAND TCAM Cell Architecture for Power Reduction
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Solution Overview
Problem
Conventional dynamic TCAM architectures, such as dynamic NOR and NAND, suffer from high power consumption and complex timing control due to pre-charging match lines, and are prone to errors from charge-sharing issues, limiting their speed and efficiency in IP address forwarding applications.
Innovation Solution
A static NAND TCAM architecture is introduced, eliminating the need for pre-charging match lines by using parallel pull-down and series pull-up transistors, reducing complexity and power consumption, and minimizing charge-sharing problems through a serial operation with PMOS transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If dynamic NOR or NAND architecture is used for TCAM, then the TCAM can perform content addressable memory operations, but power consumption increases due to pre-charging match lines
Solution Approach 1:
The patent inverts the conventional dynamic TCAM approach by using a static circuit design that does not require pre-charging match lines. Instead of dynamically charging and discharging capacitors, the invention uses complementary pull-up and pull-down networks that naturally maintain logic levels through resistive dividers, eliminating the pre-charge operation and associated power consumption while maintaining reliable operation.
Solution Approach 2:
The static TCAM cell design employs self-biasing circuits where the pull-up and pull-down networks automatically establish stable voltage levels without external pre-charging signals. The circuit uses the inherent properties of the transistor networks and resistive dividers to maintain their own logic states, eliminating the need for external timing control and pre-charge operations.
2Device complexity
If dynamic TCAM architecture with pre-charging is used, then match line evaluation can be performed, but timing control complexity increases
Solution Approach 1:
The static TCAM circuit automatically establishes stable logic levels through its complementary pull-up and pull-down networks. The circuit design inherently provides noise margins and stable intermediate voltage levels through resistive dividers, eliminating the need for external pre-charge signals and complex timing control while maintaining fast match evaluation capability.
3Reliability
If dynamic NAND architecture is used, then TCAM operations can be performed, but charge-sharing errors occur
Solution Approach 1:
The patent extracts and eliminates the problematic capacitor charging/discharging mechanism that causes charge-sharing errors in dynamic NAND TCAM. By removing the dynamic capacitor-based storage and using static resistive divider circuits instead, the invention eliminates the charge-sharing phenomenon while maintaining operational speed through the inherent speed of the complementary transistor networks.
4Ease of operation
If pre-charging of match lines is implemented, then match evaluation can be performed, but power consumption increases
Solution Approach 1:
Instead of pre-charging match lines to a high voltage level and evaluating for discharge, the patent inverts the approach by using static resistive divider circuits that maintain stable voltage levels continuously. The match line evaluation is performed through the natural voltage division in the complementary pull-up and pull-down networks without requiring periodic pre-charging, significantly reducing power consumption while maintaining ease of operation.
Data Source
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AI summary
A static, ternary content addressable memory (TCAM) includes a key cell and a mask cell coupled to intermediate match lines. The key cell is coupled to a first pull-down transistor and a first pull-up transistor. The mask cell is coupled to a second pull-down transistor and a second pull-up transistor. The first pull-down transistor and second pull-down transistor are connected in parallel and the first pull-up transistor and second pull-up transistor are connected in series. A match line output is also coupled to the first pull-down transistor and second pull-down transistor and further coupled to the first pull-up transistor and second pull-up transistor.