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FPGA Structures

FPGA mainly consists of reconfigurable logic elements, flip-flops, and a reprogrammable interconnects structure. A course-grained configurable logic block (CLB) can be implemented using a PLA-based AND/OR elements, multiplexers, or SRAM-based table look-up (LUT) elements.

Look-up Table (LUT)-Based CLB :

The basic unit of look-up table based FPGAs is the configurable logic block. The configurable logic block implements the logic functions. The look-up table based FPGA is the Xilinx 4000-series FPGA. Further, configurable logic block implements functions.

PLA-Based CLB :

PLA-based FPGA devices are based on conventional PLDs. The important advantage of this structure is the logic circuits are implemented using only a few level logic. To improve integration density logic expander is used.

Multiplexer-Based CLB :

In Multiplexer-based FPGAs to implement the logic circuits the multiplexers are used. The main advantage of multiplexer-based FPGA is to provide more functionality by using minimum transistors. Due to large number of inputs, multiplexer-based FPGAs place high demands on routing