Inverting FPGA Flip-Flop to Cut Multiplexer Chain Delay
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Solution Overview
Problem
Current FPGA architectures face performance degradation due to long series connections of multiplexers, which can cause significant signal delay, especially when using CMOS buffers that introduce additional delay.
Innovation Solution
Incorporating an inverting multiplexer in series with the data input signal of the flip-flop, acting as a tri-state inverter, breaks the long chain of pass transistors and reduces RC delay, while compensating for logical inversions through design software transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMOS buffers are used in the signal path, then signal buffering is provided, but signal delay increases significantly
Solution Approach 1:
The patent extracts and removes CMOS buffers from the signal path between LUT and flip-flop. By eliminating these buffering stages, the design achieves faster signal propagation without the delay penalty associated with CMOS buffer operation, while maintaining signal integrity through alternative routing strategies.
Solution Approach 2:
The patent inverts the conventional approach by using pass-transistor logic instead of CMOS buffers. Rather than actively buffering signals with high-gain stages, the design uses transmission gates and pass transistors to directly transfer signals, inverting the traditional buffering paradigm to achieve lower delay.
2Adaptability or versatility
If long series connections of multiplexers are used, then routing flexibility is maintained, but performance degrades due to signal delay
Solution Approach 1:
The patent segments the long series connection of multiplexers into shorter stages by introducing intermediate logic blocks and alternative routing paths. This breaks up the critical path delay while maintaining the overall routing flexibility needed for complex logic designs.
Solution Approach 2:
The patent introduces intermediate logic blocks and routing elements that act as mediators between distant multiplexer stages. These intermediaries provide signal regeneration and alternative pathways, reducing the cumulative delay of long multiplexer chains while preserving routing adaptability.
3Reliability
If multiple gain stages are used, then signal strength is maintained, but device complexity increases
Solution Approach 1:
The patent uses pass transistors and transmission gates instead of expensive, complex CMOS buffer stages. These simpler, lower-cost elements provide sufficient signal transfer capability for the application, reducing overall device complexity while maintaining acceptable signal strength through direct pass-transistor logic paths.
Data Source
AI summary
A flip-flop for use in a field programmable gate array integrated circuit device is disclosed. The flip-flop comprises a data output terminal coupled to a first programmable routing element, a data input terminal coupled to a second programmable routing element, and a clock input terminal, wherein a signal appearing at the data output terminal in response to a signal applied to the clock input terminal has the opposite logical polarity with respect to the corresponding logical signal applied to the data input terminal.