Fracturable 4-LUT FPGA Using Adder Circuitry to Cut Delay
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Solution Overview
Problem
4-LUT FPGA architectures lack fracturability, leading to inefficiencies in implementing functions like adders, which can slow down circuits and increase area usage, while 6-LUT architectures have fracturability but incur extra loading and delay.
Innovation Solution
Implement a 4-LUT with multiplexer stages to enable fracturability, allowing it to be split into multiple LUTs with fewer stages, including adder functions, by exposing outputs for programmable connections in FPGA programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If 4-LUT architectures are used without fracturability, then device complexity is reduced, but area efficiency deteriorates when implementing functions that would benefit from smaller LUTs
Solution Approach 1:
The 4-LUT is segmented into multiple smaller LUTs (2-LUTs and 3-LUTs) by exposing intermediate outputs from different stages of the multiplexer chain. This allows the single 4-LUT to function as multiple independent LUTs with fewer inputs, improving area efficiency without requiring additional physical LUT resources.
Solution Approach 2:
The 4-LUT is designed to be multi-functional by enabling it to operate as a single 4-LUT, multiple 2-LUTs, or multiple 3-LUTs depending on the configuration. This universality allows the same hardware structure to adapt to different functional requirements, optimizing area usage across various design scenarios.
2Area of stationary object
If 6-LUT fracturability is implemented, then area efficiency is improved, but speed deteriorates due to extra loading on the 5th stage output
Solution Approach 1:
The 4-LUT is segmented into multiple smaller LUTs by tapping intermediate outputs from stages 2 and 3 of the multiplexer chain, rather than only from the final stage. This segmentation allows smaller LUTs to be formed without adding loading to a final stage, avoiding the speed penalty experienced in 6-LUT architectures.
Solution Approach 2:
The patent applies asymmetric routing by exposing outputs from different stages (2nd and 3rd stages) of the 4-LUT, rather than treating all outputs symmetrically. This asymmetric approach allows optimization for specific function types (such as adders) by selecting appropriate stage outputs, thereby avoiding unnecessary loading delays.
3Adaptability or versatility
If 4-LUT fracturability is added to support adder functions, then adaptability is improved, but device complexity increases
Solution Approach 1:
The 4-LUT is enhanced with universality by configuring it to support adder functions and other specialized operations through programmable connections to intermediate outputs. This multi-functionality allows the same LUT structure to adapt to various arithmetic and logic functions without requiring separate dedicated circuits for each function type.
Solution Approach 2:
The 4-LUT structure serves itself by using its own internal multiplexer stages to generate the necessary outputs for multiple LUT functions. The intermediate outputs from stages 2 and 3 are directly utilized to form smaller LUTs, eliminating the need for external additional circuitry and allowing the LUT to be self-sufficient in providing fracturability.
Data Source
AI summary
A field programmable gate array (FPGA) has a 4-LUT (lookup table) that has four stages of multiplexers. The 4-LUT is fracturable. The 4-LUT being fracturable includes the capability to implement multiple LUTs in an instance of FPGA programming for functions from a group that includes adder functions and further functions. The 4-LUT has outputs exposed to programmable connection in accordance with FPGA programming. Outputs of the 4-LUT include an output of a first multiplexer in the third stage, an output of a multiplexer in the second stage, and an output of a multiplexer in the second or third stage of the 4-LUT