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Basic knowledge of FPGA architecture and applications

Date: Jun 14, 2020

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FPGA stands for Field Programmable Gate Array. It is a semiconductor logic chip that can be programmed into almost any type of system or digital circuit, similar to PLD. PLD is limited to hundreds of gates, but FPGA supports thousands of gates. The configuration of the FPGA architecture is usually specified using a language, namely HDL (Hardware Description Language), which is similar to the language used for ASIC (Application Specific Integrated Circuit).

Compared with fixed function ASIC technology (such as standard unit), FPGA can provide many advantages. Normally, ASICs take months to manufacture, and their cost will reach thousands of dollars to obtain the device. However, FPGA manufacturing time is less than a second, and the cost ranges from a few dollars to a thousand dollars. The flexibility of FPGA greatly reduces the cost, power consumption and delay. Compared with the standard unit ASIC, FPGA requires 20 to 35 times the area, and the speed performance is 3 to 4 times slower than ASIC. This article introduces the basic knowledge of FPGA and FPGA architecture modules, including I/O pads, logic blocks and switch matrix. FPGAs are some emerging trends in VLSI.


FPGA architecture

The general FPGA architecture consists of three types of modules. They are I/O blocks or pads, switch matrix/interconnect lines and configurable logic blocks (CLB). The basic FPGA architecture has a two-dimensional array of logic blocks with devices for users to arrange interconnections between logic blocks. The functions of the FPGA architecture module are discussed below:

CLB (configurable logic block) includes digital logic, input and output. It implements user logic.

Interconnections provide directions between logic blocks to implement user logic.

According to logic, the switch matrix provides switching between interconnects.

I/O pads for the outside world communicate with different applications.

The logic block contains MUX (multiplexer), D flip-flop and LUT. The LUT implements the combinational logic function; MUX is used for selection logic, and the D flip-flop stores the output of the LUT.

The basic building block of FPGA is a function generator based on a lookup table. The number of LUT inputs changed from 3, 4, 6 and even 8 after the experiment. Now, we have adaptive LUTs, each of which provides two outputs and implements two function generators.

Xilinx Virtex-5 is the most popular FPGA. It contains a lookup table (LUT) connected to the MUX and a trigger as described above. Current FPGAs consist of about hundreds or thousands of configurable logic blocks. For configuring FPGAs, Modelsim and Xilinx ISE software are used to generate bitstream files and for development.

Application-based FPGA types

Field programmable gate arrays are based on low-end FPGAs, and applications such as mid-range FPGAs and high-end FPGAs fall into three categories.

Low-end FPGA

These types of FPGAs are designed for low power consumption, low logic density, and low complexity per chip. Examples of low-end FPGAs are Altera's Cyclone series, Xilinx's Spartan series, Microsemi's fusion series and Lattice Semiconductor's Mach XO/ICE40.

Mid-range FPGA

These types of FPGAs are the best solution between low-end and high-end FPGAs. They were developed with a balance between performance and cost. Examples of midrange FPGAs are Arria from Altera, Artix-7/Kintex-7 series from Xlinix, IGL002 from Microsemi and ECP3 from Lattice Semiconductor and ECP5 series from Lattice Semiconductor.

High-end FPGA

These types of FPGAs were developed for logic density and high performance. Examples of high-end FPGAs include Altera's Stratix series, Xilinx's Virtex series, Achronix's Speedster 22i series, and Microsemi's ProASIC3 series.

Applications of FPGA:

FPGAs have experienced rapid growth in the past decade because they are suitable for a wide range of applications. Specific applications of FPGAs include digital signal processing, bioinformatics, device controllers, software-defined radio, random logic, ASIC prototyping, medical imaging, computer hardware simulation, integration of multiple SPLDs, speech recognition, encryption, filtering, and communication encoding Wait.

Generally, FPGAs are reserved for specific vertical applications with small production volumes. For these low-volume applications, top companies pay the cost of hardware per unit. Today, new performance dynamics and costs expand the range of feasible applications.

Some of the more common FPGA applications include: aerospace and defense, medical electronics, ASIC prototypes, audio, automotive, broadcasting, consumer electronics, distributed currency systems, data centers, high-performance computing, industrial, medical, scientific instruments, security systems, Video and image processing, wired communication, wireless communication.

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