Architecture of field-programmable gate arrays: the effect of logic block functionality on area efficiency

The relationship between the functionality of a field-programmable gate array (FPGA) logic block and the area required to implement digital circuits using that logic block is examined. The investigation is done experimentally by implementing a set of industrial circuits as FPGAs using CAD (computer-aided design) tools for technology mapping, placement, and routing. A range of programming technologies (the method of FPGA customization) is explored using a simple model of the interconnection and logic block area. The experiments are based on logic blocks that use lookup tables for implementing combinational logic. Results indicate that the best number of inputs to use (a measure of the block´s functionality) is between three and four, and that a D flip-flop should be included in the logic block. The results are largely independent of the programming technology. More generally, it was observed that the area efficiency of a logic block depends not only on its functionality but also on the average number of pins connected per logic block