JED - August 2012 - (Page 39)

TECHNOLOGY SURVEY A SAMPLING OF FPGA BOARDS By Ollie Holt The Journal of Electronic Defense | August 2012 his month’s JED product survey looks at Field Programmable Gate Array (FPGA) circuit boards. With the ever-increasing use of FPGA’s in EW systems, multiple companies are providing commercial off the shelf (COTS) multifunction FPGAs. These COTS boards, because of their wide availability, programmability, versatility and low cost are finding their way into EW Systems. Because of that, JED decided to allocate a complete survey to FPGA boards. Before discussing complete FPGA boards, let’s look at what an FPGA is and why it is of interest to an EW system designer. With the development of digital circuits in the early 1970s, the industry quickly transitioned into EW systems designs with the promise of improved performance. The logic behind these systems became very complex and quickly filled circuit cards when one chip – perhaps measuring 0.75 x 0.25 inches with 14 or 16 pins – contained only four or fewer gates. Soon, companies offered to put parts of your design on silicon in Application Specific Integrated Circuits (ASICs). This allowed for a more compact system, lower cost in large quantities and lower power designs. However, the process of designing the ASIC, fabricating it and then testing it was long (one or more years), and if the design had an error it meant the design team had to start the process from the beginning. These disadvantages lead to the development of the FPGA. The FPGA’s advantage was it could be easily programmed on the bench, reprogrammed multiple times as the design matured but with the disadvantage of a higher cost part and lower gate density. Over the years, the density has increased to where FPGAs no longer provide gate counts as a factor of density but Configurable Logic Blocks (CLB) or Logic Array Blocks (LAB) counts as a factor of density. In addition, the FPGA cost as a function of CLBs or LABs has decreased significantly. CLB’s or LAB’s are complete functional blocks like adders, multipliers, and even processor cores. Today’s FPGAs also have memory and can even contain a Power PC core, although more popular processor cores are the MicroBlaze or Nios II. A “core” is a predefined complex function. Most FPGA suppliers have libraries of these predefined functions available for any user of their product. Also, third-party venders have developed “cores” that can be purchased or maybe available “open source.” T The first item in the survey addressed the board function. There are many different varieties of FPGA boards. Some are just designed for controlling things with multiple digital or analog inputs and outputs (I/O). The FPGA maybe be programmed to perform arithmetic operations on the inputs and create new outputs or it may just perform cause and effect logic to turn on or off a device based on an input. Some may just allow digital inputs while others may provide analog-to-digital and digital-to-analog conversion as part of the I/O. In RF applications they are mostly used for control, digital receivers and software-defined radios. In IR applications, they are mostly used for control and image processing. The next column defines the manufacture and type of FPGA. Defining the FPGA type aids in determining how much capability the board may support. It also allows the user to search for available “cores” that may support the desired application. The memory column should be examined in two ways; some boards will have both the memory contained on the FPGA and additional on board memory, while others may just list the additional memory on the board. Also note the type of memory (FLASH, SRAM, SDRAM, etc.). Format basically defines the board size, weather it complies with a standard format. This is nice to know because it aids in defining a complete system. The second part of the complete system equation is the bus format. That question is addressed in the following column defining the bus and I/O types available. In using these available boards in the design of an EW system the designer should select a bus standard that meets the needs of the application and a board format that fits the space available then select the FPGA and other support boards that are compatible with the bus and board format selected. One last item that should be decided upon when selecting an FPGA for your design is the support tools. The major FPGA manufactures provide tools and evaluation kits for simulating and modeling your design. Select an FPGA family that has the tools that support your design needs and also check the availability of “cores” that can make the design effort easier. JED’s next survey, in the September edition, will address IED jammers and communications jammers. 39

Table of Contents for the Digital Edition of JED - August 2012

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
EW and SIGINT Payloads for UAVs
EW Careers: The Changing Market
Technology Survey: FPGA Boards
EW 101
AOC News
Index of Advertisers

JED - August 2012