FPGA And-Inverter Cone Logic Blocks Beyond LUT Input Limits
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Solution Overview
Problem
Field-Programmable Gate Arrays (FPGAs) face challenges with increasing LUT inputs due to exponential area and delay growth, limiting their practicality beyond 4-6 inputs, and existing FPGA structures either consume excessive area or static power, while lacking flexibility and efficient input/output handling.
Innovation Solution
The implementation of And-Inverter Cones (AICs) as logic blocks in FPGAs, which use 2-input AND gates coupled with optional inverters, providing multiple outputs and a linear increase in complexity and logarithmic delay growth, enabling more efficient mapping and coverage of logic depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the number of LUT inputs is increased to cover larger parts of a circuit, then the coverage area increases, but the LUT complexity and area increase exponentially
Solution Approach 1:
The patent segments the circuit coverage into multiple smaller LUTs working in parallel rather than using a single large LUT. Each LUT handles a subset of inputs, and their outputs are combined through OR logic. This segmentation approach allows covering larger circuit areas while keeping individual LUT complexity manageable (avoiding exponential growth).
Solution Approach 2:
The patent merges multiple LUT outputs through OR logic to achieve comprehensive circuit coverage. By combining the outputs of several smaller LUTs, the system achieves the functional equivalence of a larger LUT without the exponential area and complexity penalty, thus resolving the contradiction between coverage area and device complexity.
2Area of stationary object
If the number of LUT inputs is increased, then the coverage area increases, but the delay introduced by the LUT grows linearly
Solution Approach 1:
The patent segments the logic function into multiple smaller LUTs with fewer inputs each. This segmentation reduces the delay of individual LUTs since delay grows with input count. The overall coverage area is maintained by parallelizing these smaller, faster LUTs rather than using a single slow, large LUT.
3Productivity
If small PAL-like structures with 7-10 inputs are used, then performance gains are achieved, but the area increases
Solution Approach 1:
The patent uses standard 4-input LUTs that can be universally applied and configured to implement various logic functions. By utilizing the programmable nature of LUTs and combining multiple instances, the system achieves performance gains equivalent to specialized PAL structures without dedicating fixed hardware, thus improving area efficiency while maintaining productivity.
4Area of stationary object
If K-input multiple-output PAL-style logic blocks are used, then area efficiency is improved, but static power consumption becomes unacceptable
Solution Approach 1:
The patent employs standard LUT building blocks that are optimized for low power consumption in modern FPGA architectures. These LUTs are designed to be self-service units with efficient power management. By using proven low-power LUT designs rather than custom PAL-style blocks, the system maintains area efficiency while avoiding unacceptable static power consumption.
Data Source
AI summary
New logic blocks capable of replacing the use of Look-Up Tables (LUTs) in integrated circuits, such as Field-Programmable Gate Arrays (FPGAs), are disclosed herein. In one embodiment, the new logic block is an AND-Inverter Cone (AIC), which is a binary tree including one or more AND gates with a programmable conditional inversion and a number of intermediary outputs. Compared to LUTs, AICs are richer in terms of input and output bandwidth, because the area of the AICs grows only linearly with the number of inputs. Also, the delay grows only logarithmically with the input count. The new logic blocks can map circuits more efficiently than LUTs, because the AICs are multi-output blocks and can cover more logic depth due to the higher input bandwidth.