Optimized reconfigurable cell array architecture for high-performance field programmable gate arrays

Revisiting the Cascade Circuit in Logic Cells of Lookup Table Based FPGAs

“…The only difference would be the polarity of the signals generated from the CLBs, i.e., the equal signal from 1 Of course, one can combine intermediate results by using an extra logic cell; however, this solution uses more logic cells and requires more routing resource than the above solution. A logic cell, called logic element (LE), of the Flex 8000 FPGA contains a cascade circuit which is either a 2-input AND gate or a 2-input OR gate.…”

“…The coarsegrain FPGA contains logic cells each of which has rich functionality, while the ne-grain FPGA contains logic cells with limited functionality. Coarse-grain FPGAs include AT&T's ORCA [1,2,3], Xilinx's XC4000 [4,5], Altera's Flex 8000 [6], and XC/ATT 3000 [7,8]. As an example, Figure 1 shows the combinational portion of a logic cell, called PLC (programmable logic cell), of the ORCA FPGA.…”

“…Note that the pfunand gates in cell-2 through cell-8 collect (or cascade) partial results to produce the nal result. 1 The cascading pattern in Figure 2 is \linear" because one needs N-1 cascading stages to collect partial results from N logic cells. Now, let us consider the XC4000 FPGA.…”