Field-programmable gate arrays (FPGAs) are used in a wide range of markets that have differing cost, performance and power consumption requirements. It would be advantageous if a single device family could serve these varied needs but the economics of catering to this wide distribution of market demands suggest more than one family is appropriate. Consequently, FPGA vendors have moved to provide a more diverse set of families that sit at different points in the areaspeed-power design space. In this work, our goal is to understand the circuit and architectural design attributes of an FPGA that enable tradeoffs between area and speed, and to determine the magnitude of the possible trade-offs. This will be useful for architects seeking to determine the number of device families in a suite of offerings, as well as the changes to make between families. We have found that varying both architecture and transistor sizing of an FPGA allows the effective area to change by a factor of 3.6 from largest to smallest and the speed to change by a factor of 2.6 from fastest to slowest. It is interesting to observe that the range of area and delay tradeoffs possible by varying only the transistor sizing of a single architecture is larger than the ranges observed in past architectural experiments. In addition to transistor size, we note that LUT size is one of the most useful parameters for trading off area and delay.

Abstract—A complete circuit-level description of a representative FPGA is presented in this paper, from which a simple RC delay model as a function of architectural and technology parameters is derived. Using this model, the expression for the optimal delay of any path through the FPGA can be formulated. We distill our model into being purely architecture dependent, and use it to capture new insight into how FPGA parameters can directly affect its delay. Several applications of this model are: (1) to gain better intuition of how architecture and process parameters affect the delay path in an FPGA, (2) for initial studies into new circuit designs and integrated circuit technologies, (3) in CAD tools for optimisation and sensitivity analysis. The technique described can be applied to arbitrary circuits, and simulations show that our closed form equations give delay values that are accurate to approximately 10 % when compared to HSPICE simulation. I.

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