TABLE OF CONTENTS Bob Zeidman
Field-programmable gate arrays are given this name because they are structured very much like a gate array ASIC. Like an ASIC, the FPGA consists of a regular array of logic, an architecture that lends itself to very complex designs.
Each FPGA vendor has its own FPGA architecture, but in general terms they are all a variation of that shown in Figure 29.1. The architecture consists of configurable logic blocks, configurable I/O blocks, and programmable interconnect to route signals between the logic blocks and I/O blocks. Also, there is clock circuitry for driving the clock signals to each flip-flop in each logic block. Additional logic resources such as ALUs, memory, and decoders may also be available. The two most common types of programmable elements for an FPGA are static RAM and antifuses. Antifuse technology is a cousin to the programmable fuses in EPROMs. You will learn about antifuses, along with these other aspects of FPGAs, in the following sections.
The important thing to note about the FPGA architecture is its regular, ASIC like structure. This regular structure makes FPGAs useful for all kinds of logic designs.
Configurable logic blocks (CLBs) contain the programmable logic for the FPGA. The diagram in Figure 29.2 shows a typical CLB, containing RAM for creating arbitrary combinatorial logic functions. It also contains flip-flops for clocked storage elements and multiplexers in order to route the logic within the block and to route the logic...
