4-Input LUT Multiplexer Tree Layout for Lower FPGA Area
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Solution Overview
Problem
LUT6 modules in integrated circuits are inefficient due to occupying more than three times the area of LUT4 modules, requiring four times as many configuration memory cells, and resulting in up to 40% slower performance and increased routing area, making them costly and resource-intensive for configuring 4-input multiplexers.
Innovation Solution
Configuring a 4-input multiplexer using a combination of 4-input lookup table modules with specific multiplexer arrangements that form a tree structure, allowing for efficient use of resources and reduced area requirements, while maintaining performance comparable to LUT4 modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LUT6 modules are used to configure 4-input multiplexers, then the multiplexer configuration capability is achieved, but the area occupation increases by more than three times compared to LUT4 modules
Solution Approach 1:
The patent segments the 4-input multiplexer configuration into two separate LUT4 modules, where the first LUT4 configures the lower two data inputs and the second LUT4 configures the upper two data inputs. This segmentation allows achieving the same multiplexer configuration capability as LUT6 but with reduced area occupation, since two LUT4 modules occupy less area than one LUT6 module.
2Adaptability or versatility
If LUT6 modules are used to configure 4-input multiplexers, then the multiplexer configuration capability is achieved, but the configuration memory cell requirements increase by four times compared to LUT4 modules
Solution Approach 1:
The configuration memory cells are segmented between two LUT4 modules, with each module containing its own set of configuration memory cells. This segmentation reduces the total number of configuration memory cells required compared to using a single LUT6 module, as each LUT4 module uses fewer memory cells and the overall structure is more efficient.
3Adaptability or versatility
If LUT6 modules are used to configure 4-input multiplexers, then the multiplexer configuration capability is achieved, but the propagation delay increases by up to 40% compared to LUT4 modules
Solution Approach 1:
The multiplexer configuration is segmented across two LUT4 modules with optimized interconnection, where the first LUT4 handles lower data inputs and the second LUT4 handles upper data inputs. This segmentation with proper routing optimization reduces the propagation delay compared to the LUT6 approach, as the signal paths are shortened and optimized through the two-module architecture.
4Adaptability or versatility
If LUT6 modules are used to configure 4-input multiplexers, then the multiplexer configuration capability is achieved, but the routing area increases by more than 50% compared to LUT4 modules
Solution Approach 1:
The routing architecture is segmented into two separate LUT4 modules with dedicated interconnections, where each module has its own optimized routing paths. This segmentation reduces the overall routing area required compared to LUT6, as the routing resources are distributed and optimized across two smaller modules rather than concentrated in one large module.
Data Source
AI summary
A 4-input lookup table module including eight first-rank 2-input multiplexers, four second-rank multiplexers, two third-rank multiplexers, and one fourth-rank multiplexer, the first-rank through fourth-rank multiplexers forming a tree structure. A select input of the fourth-rank multiplexer is coupled to a first input node. Select inputs of the third-rank multiplexers are coupled to a second input node. Select inputs of a first and a second adjacent ones of the second rank 2-input multiplexers are electrically isolated from select inputs of a third and a fourth adjacent ones of the second rank 2-input multiplexers. Select inputs of a first through a fourth adjacent ones of the first rank 2-input multiplexers are electrically isolated from select inputs of a fifth through an eighth adjacent ones of the first rank 2-input multiplexers.