FPGA (FIELD-PROGRAMMABLE GATE ARRAY)

FPGA (FIELD-PROGRAMMABLE GATE ARRAY)

An FPGA is a gate array that can be reprogrammed at run time after it is manufactured. It reduces development costs since instructions can be programmed at any point in time. However, FPGAs are slower than ICs and consume more power. They are used in register-heavy and pipelined applications.

How an FPGA works:

The FPGA is made up of look-up tables (LUT), routing blocks, dedicated RAM and some common logical blocks such as multipliers or adders. The LUT is a one-bit storage block and acts as a programmable gate. The input refers to the address lines of the storage element and the output is the stored value at that address. A flip-flop is placed between the gate and the output for clocked logic.

One or more routing blocks with wires connect inputs and outputs to various LUTs to each other. Routing blocks are designed so that only certain paths through the block are allowed. The LUTs and routing blocks are placed in an array in the FPGA. Hardware description language like VHDL and Verilog are used to program the instructions.

FPGA selection:

§ Configurable logic blocks (CLB): contain RAM LUTs and flip-flops. CLBs can be programmed to store data (e.g. 62,208 nos).

§ IOBs: control data flow between I/O pins and the logic elements of the device.

§ Block RAM: for data storage (e.g. 432 / 576 / 1728 K).

§ Multiplier Blocks: use 18-bit binary numbers as input (e.g. 24, 32, 96).

§ DCM: digital clock manager for internal calibration between elements (e.g. 4).

Types of devices used in FPGAs are:

PROMs (programmable read only memory): Data can be written only once.
EPROM (erasable programmable read-only memory): Exposing the chip to ultraviolet rays can erase data and a new program can be written.
PLAs (programmable logic array): This has a programmable AND plane and a fixed OR plane.
PAL/GALs (programmable array logic/generic array logic): These use a combination of different types of arrays.

Applications:

Some of the manufacturers of FPGAs are Xilinx, Altera, Lattice Semiconductor, Actel, Cypress, Atmel, QuickLogic and ST Microelectronics. FPGAs are used in digital signal processing, software-defined radio, aerospace and defense systems, ASIC prototyping, medical imaging and many other emerging markets like computer vision, speech recognition, cryptography, bioinformatics, etc.