Definition
An FPGA (Field-Programmable Gate Array) is an integrated circuit built from a grid of configurable logic blocks and programmable interconnects, so its digital circuitry can be defined — and redefined — after the chip leaves the factory. Unlike a fixed-function ASIC, an FPGA is "wired" by loading a bitstream at power-up. In Bitcoin mining hardware, FPGA fabric appears as the programmable-logic section of the Xilinx Zynq SoC on Antminer control boards.
FPGA versus ASIC in mining
FPGAs were briefly used as standalone Bitcoin miners around 2011-2012, bridging the gap between GPUs and purpose-built ASICs. They lost that race quickly: a fixed ASIC can pack far more SHA-256 engines per watt than a reconfigurable FPGA. Today the FPGA's job in an Antminer is not hashing at all — it is the high-speed glue logic that streams work and results between the ARM cores and the hashing chips.
The control-board role
On the Zynq, the FPGA fabric implements the serial buses that talk to each hashboard, handling timing-critical I/O the CPU cannot do deterministically. This division of labor — CPU for Linux and networking, FPGA for fast hardware links — is why the Zynq is so well suited to mining controllers.
For the larger picture of how the FPGA combines with a CPU on one die, see System-on-Chip (SoC); for the specific part used in Antminers, see Zynq SoC.
In Simple Terms
An FPGA (Field-Programmable Gate Array) is an integrated circuit built from a grid of configurable logic blocks and programmable interconnects, so its digital circuitry can…