Fracturable FPGA 4-LUT Using Adder Circuitry to Cut Delay
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Solution Overview
Problem
4-LUT FPGA architectures lack fracturability, leading to inefficiencies in implementing smaller functions and increased loading that slows down the circuit, while existing methods to fracture 4-LUTs for adder functions incur additional delays.
Innovation Solution
Implementing a 4-LUT with multiplexer stages to enable fracturability, allowing it to be split into multiple LUTs with fewer stages, including 2-input and 3-input functions, without additional circuitry, by reusing adder circuitry to tap into specific stages for programmable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If 4-LUT is fractured to implement multiple LUTs with fewer inputs, then area efficiency is improved, but additional loading is added that slows down the LUT
Solution Approach 1:
The 4-LUT is segmented into multiple smaller LUTs (e.g., two 2-input LUTs or a 2-input and a 3-input LUT) by tapping outputs from different multiplexer stages. This allows the single 4-LUT to function as multiple independent LUTs, improving area efficiency by reducing the need for additional LUT resources while maintaining functional capability.
Solution Approach 2:
The patent utilizes the temporal/dimensional aspect of the multiplexer stages within the 4-LUT architecture. By tapping outputs from different stages (second stage, third stage, or fourth stage) and using programmable connections, the patent creates multiple functional outputs from a single LUT structure, effectively adding a dimension of functionality without increasing physical area.
2Adaptability or versatility
If 4-LUT fracturability is implemented for adder functions, then functional versatility is improved, but delay penalties increase due to extra routing
Solution Approach 1:
The 4-LUT is designed with universal fracturability that can implement multiple functions including adder functions (generate, propagate, sum), arbitrary logic functions, and multiple LUT configurations. The programmable connections allow the same hardware structure to be reconfigured for different functions, achieving high functional versatility without requiring separate dedicated circuits for each function.
Solution Approach 2:
The patent pre-establishes the multiplexer stage structure and programmable connection framework in advance, allowing the LUT to be quickly configured for different functions including adder operations. The carry-in and carry-out connections are pre-wired through the programmable logic array, enabling rapid function switching without additional routing delays during operation.
3Speed
If 4-LUT is used without fracturability, then circuit speed is maintained, but area efficiency decreases due to under-utilization
Solution Approach 1:
The 4-LUT structure serves itself by providing multiple functional outputs from a single LUT instance. The programmable connections and multiplexer stages enable the LUT to automatically configure itself for different functions (adder, logic operations, multiple LUTs) based on the programmed settings, eliminating the need for external control logic and reducing overall circuit complexity while improving area efficiency.
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.