TCAM Sub-Array Control Logic for Power Reduction

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Solution Overview

Problem

TCAM devices face high power consumption due to unnecessary search current when all TCAM cells in a sub-array are set as 'don't care', leading to inefficient energy use.

Innovation Solution

Implementing a control logic circuit that activates a register to indicate when all TCAM cells are 'don't care', allowing the system to skip search operations in such sub-arrays, thereby reducing power consumption by preventing precharge and operation of match amplifiers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If search operations are performed on all sub-arrays, then complete search coverage is achieved, but power consumption increases due to unnecessary search current in sub-arrays with all 'don't care' cells

Engineering Contradiction:

Improvepower consumptionVSAvoidsearch completeness

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies preliminary action by setting control bits during the data writing phase to indicate whether all TCAM cells in a sub-array are 'don't care'. This preliminary marking allows the search operation to skip unnecessary sub-arrays, reducing power consumption while maintaining search completeness. The control bits are prepared in advance during write operations, enabling efficient search without re-evaluating the content of each sub-array during search.

Inventive Principle:

Principle #10Preliminary action

2Speed

If multiple sub-arrays are searched concurrently, then search speed is improved, but peak current increases due to simultaneous search current generation

Engineering Contradiction:

Improvesearch speedVSAvoidpeak current

Core Design Contradiction:

SpeedVSPower

Solution Approach 1:

The patent applies partial action by selectively activating only the necessary subset of sub-arrays during search operations based on the control bits. Instead of searching all sub-arrays concurrently, the system performs search on only those sub-arrays that contain actual data, reducing peak current while maintaining search speed for the relevant data. This partial activation approach avoids the excessive current draw of searching all sub-arrays simultaneously.

Inventive Principle:

Principle #16Partial or excessive action

3Adaptability or versatility

If all TCAM cells are configured for full search capability, then search functionality is maximized, but device complexity increases due to additional control logic and registers

Engineering Contradiction:

Improvesearch functionalityVSAvoidcontrol logic complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies merging by combining the control bit storage function with the existing TCAM write operation infrastructure. The control bits are integrated into the write path and automatically set based on the content being written, eliminating the need for separate control mechanisms. This merging approach maintains full search functionality while avoiding additional complexity by reusing existing circuitry for control bit management.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS10366755B2Semiconductor device including TCAM cell arrays capable of skipping TCAM-cell search in response to control signal

Publication Date: 2019.07.30 RENESAS ELECTRONICS CORP

AI summary

The consumption current of a TCAM device is reduced. A semiconductor device includes multiple sub-arrays each including a TCAM cell array. Each sub-array searches the corresponding part of the input search data. Each sub-array outputs the search result indicative of a match for every entry without searching, when the corresponding first control signal is activated.