FPGA Logic Cell Carry Chain for Counters and Independent LUT Logic
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Solution Overview
Problem
Existing FPGA logic cells are inefficient in implementing counters and compressors, as they require additional connections to the programmable routing network, increasing complexity and cost, and limit the use of LUTs for other functions.
Innovation Solution
A logic cell design that allows for the implementation of one bit of a counter or adder while preserving the use of K-input LUTs for independent functions, with reduced connections to the programmable routing network, enabling efficient implementation of counters and compressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If prior-art logic cells implement counter functions using multiplexers and carry chains, then counter functionality is achieved, but the LUT inputs are fully utilized for counter operations leaving no capacity for independent functions
Solution Approach 1:
The logic cell is designed to perform multiple functions simultaneously: it can implement counter operations using the carry chain while the LUT remains available to implement independent logic functions. This multi-functionality resolves the contradiction by allowing the same hardware resources to serve dual purposes - the carry chain handles counter arithmetic while the LUT handles general logic operations, eliminating the need to dedicate all LUT inputs to counter operations.
2Reliability
If additional connections are made to the programmable routing network for counter implementation, then counter functionality is improved, but routing network complexity and cost increase
Solution Approach 1:
The carry chain is integrated directly into the logic cell structure, merging the counter implementation with the existing logic cell resources. This integration eliminates the need for separate connections to the programmable routing network, as the carry-in and carry-out signals are handled through dedicated inputs and outputs of the logic cell itself, thereby reducing routing network complexity while maintaining reliable counter operation.
3Productivity
If more logic is packed into the FPGA chip, then device density increases, but routing network complexity and power consumption increase
Solution Approach 1:
By integrating the counter functionality within the logic cell using the carry chain, the design reduces the need for external routing connections. This allows more logic to be packed into the FPGA chip without proportionally increasing routing network complexity, as the counter operations are handled internally within each logic cell rather than requiring extensive inter-cell routing.
Data Source
AI summary
A logic cell for a programmable logic integrated circuit having K function inputs, where K is the largest number such that the logic cell can compute any function of K inputs, and where the logic cell is configurable to implement one bit of a counter in parallel with any independent function of K-1 of the K inputs.