Definition: FPGA

(Field Programmable Gate Array) A chip that has its internal logic circuits programmed by the customer. The Boolean logic circuits are left "unwired" in an FPGA, and they are either permanently programmed one time or reprogrammed every time power is delievered to the chip. See Boolean logic and glue logic.

With a variety of architectures on the market, FPGA chips contain millions of programmable logic gates. FPGAs also have a lower gate density compared to regular, finished "ASIC" chips (see ASIC).

To Clarify
Whereas a regular CPU follows instructions in the software, an FPGA sets up connections that actually reconfigure the hardware. Hardware is always much faster than software because it immediately processes the data without having to first fetch and analyze instructions. See software.

Why Use FPGAs?
When hundreds of thousands of the same chip are required, a "non-changeable" ASIC is often designed; however, ASIC development costs millions, and FPGAs can be used to test the market and refine the design before going into full-blown ASIC production. They can also enable finished goods to reach the market sooner.

FPGAs are ideal for installations where changing requirements demand updated processing. For example, migrating a cell tower from 3G to 4G can be accommodated on premises by inputting different data into an FPGA. The data "rewires" the hardware, and the racks of equipment do not have to be replaced.

SRAM, Flash and Antifuse Varieties
The vast majority of FPGAs use volatile static RAM (SRAM) cells to define the logic. Each time the FPGA is powered up, the SRAM is loaded with its configuration, typically from a flash memory chip. SRAM FPGAs can also be dynamically reconfigured in operation (see adaptive computing). See static RAM.

Flash memory-based FPGAs hold their content without power, and they can be reprogrammed in place. Permanently programmed antifuse-based FPGAs are popular for aerospace design because they are more radiation hardened (rad hard). See PLD, adaptive computing and gate array.

Versal System-on-Chip (FPGA and More)

With more than 35 billion transistors, Xilinx's very comprehensive Versal chip includes FPGA circuits (adaptable hardware) along with CPUs, RAM, I/O and DSP engines (see Versal). (Image courtesy of Xilinx.)

An Excellent Resource

Everything you wanted to know about FPGAs and more is in Clive "Max" Maxfield's book. Written in Maxfield's inimitable style, which makes it thoroughly enjoyable, this book is the definitive guide to the subject. (Newnes, 2004)