CAM Match Line Control Circuit Reducing Signal Delay
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Solution Overview
Problem
Existing content addressable memory (CAM) devices face signal delay issues due to the use of logic gates in wrapper circuits, which increases circuit area and power consumption.
Innovation Solution
The semiconductor device incorporates a CAM unit with a common match output line and transistors that reduce signal delay by controlling the match line voltage based on discrimination results, using a match signal output circuit that eliminates the need for multistage OR gates, thereby minimizing signal delay and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If logic gates are used in wrapper circuits to perform OR operations on match lines, then mismatch discrimination can be achieved, but signal delay increases
Solution Approach 1:
The patent extracts the OR operation functionality from the wrapper circuit and implements it directly within the CAM entry using transistor logic. Instead of using separate logic gates in the wrapper to perform OR operations on match lines, the invention integrates the OR function into the match line control circuitry of each CAM entry, eliminating the need for external logic gates and reducing signal delay.
Solution Approach 2:
The patent introduces a match line control circuit as an intermediary between the CAM cells and the match output line. This control circuit directly manipulates the match line voltage based on discrimination results, serving as a mediator that eliminates the need for subsequent OR gate operations in the wrapper circuit, thereby reducing signal delay while maintaining mismatch discrimination capability.
2Reliability
If logic gates are used in wrapper circuits, then mismatch discrimination can be achieved, but circuit area increases
Solution Approach 1:
The patent merges the OR operation functionality with the match line control circuitry within the CAM entry structure. By combining these functions into a single integrated circuit block, the invention eliminates the need for separate logic gates in the wrapper circuit, thereby reducing the overall circuit area while maintaining mismatch discrimination capability.
Solution Approach 2:
The match line control circuit is designed to perform multiple functions: it controls the match line voltage based on discrimination results and simultaneously performs the OR operation that would traditionally require separate logic gates. This multi-functionality reduces the need for additional circuit components and decreases overall circuit area.
3Reliability
If logic gates are used in wrapper circuits, then mismatch discrimination can be achieved, but power consumption increases
Solution Approach 1:
The patent extracts the OR operation functionality from the wrapper circuit and implements it within the CAM entry using transistor-based logic. This eliminates the need for power-consuming logic gates in the wrapper circuit, thereby reducing overall power consumption while maintaining mismatch discrimination capability.
Solution Approach 2:
The match line control circuit performs the OR operation as part of its own operational sequence, using the same control signals and circuit resources already allocated for match line management. This self-service approach eliminates the need for additional power-consuming logic gates in the wrapper circuit.
Data Source
AI summary
The plurality of CAM cells MC are configured to discriminate a match or mismatch between stored data stored in advance and search data. A match line is coupled to a plurality of CAM cells, and has a voltage level controlled based on discrimination results of the plurality of CAM cells. A first transistor and a second transistor are coupled in series between a common match output line and a predetermined power source. The first transistor is controlled to be turned ON or OFF based on a voltage level of the match line, and the second transistor is controlled to be turned ON or OFF by a search enabling signal asserted at the time of a search operation.