Avionics data bus technology meets the SWaP challenge

In military avionics, SWaP is a major challenge. As major contractors refresh and redesign electronics systems, in light of less funding availability, they are asking their suppliers to create smaller, less expensive, subsystem solutions, such as data communications modules. These subsystem solutions, moreover, are expected to be priced and supported as Commercial Off-the-Shelf (COTS) products even though they were created as one-of-a-kind responses to unique requirements.

The resolution to the SWaP challenge and the custom/COTS paradox in data bus and other avionics technologies depends on the provider’s flexibility, expertise, and the ability to roll new features into its “stable” of standard products, recovering the cost of development and supporting future development with standard product sales. This constant recycling of ideas keeps front-end innovation going, costs contained, customers happy, and the product line on a healthy growth curve.

Shrinking bus board size and cost

Shrinking the size of a subsystem typically involves consolidating the cards by using smaller, higher-density components. A three-card data bus solution providing multiple channels of multiple bus protocols, for example, can be downsized into a single card by incorporating smaller, less power-hungry components and by implementing some bus elements in more efficient packages. This approach is often a win-win for the customer because – thanks to competitive pressures and the evolution of technology in the market – the new card is likely to cost less than the old ones. The new subsystem will use less power, as well. And the slimmed-down replacement allows the overarching system to be lighter and smaller – always virtues in avionics – or of equivalent size and weight but with more functions and features.

Shrinking the footprint of data bus and other avionics cards is possible, thanks to the trajectory of electronics technology. Moore’s Law still holds sway over microelectronics: Components are increasing in density and decreasing in size at a rapid rate. FPGAs, for example, have undergone phenomenal growth in gate counts, while decreasing in size and power consumption. Bus card vendors are finding ways to shrink MIL-STD-1553 and ARINC 429 protocol implementations by incorporating some bus features in FPGAs or ASICs.

An FPGA can incorporate 1553 bus control logic that deciphers bit patterns and generates the proper responses, buffering, and processing for the 1553 bus controller, remote terminal, and monitor functions, as well as PCIe drivers and logic that enable the card to communicate with the host. As FPGA densities increase, more 1553 channels can be implemented on the device. A case in point is the RAR15-XMC, the latest GE Intelligent Platforms avionics data bus card, which squeezes four dual-redundant MIL-STD-1553A channels, 10 ARINC 429 receive channels, and eight ARINC 429 transmit channels plus memory and protocol processing into approximately 8 square inches of board real estate (Figure 1). A spinoff from custom mil/aero projects that replaced two- or three-PMC card subsystems with a single XMC module that cut customer costs in half, the RAR15 is a standard, off-the-shelf, conduction-cooled product that implements key 1553 and 429 technology and protocol processing in a single FPGA.

Figure 1: The GE Intelligent Platforms RAR15-XMC is a multiprotocol embeddable avionics module.
(Click graphic to zoom by 1.9x)

While ASICs can be implemented in smaller sizes than FPGAs and can burn less power, the downside is that when ASICs go obsolete, it’s more difficult to migrate the software in them to a new board. FPGAs, on the other hand, are more easily swappable from one generation to another, allowing as close to a drop-in replacement as possible.

Memory densities also have increased, allowing these chips to take up less space. And power circuitry is becoming smaller and more efficient. New data bus cards exploit hardware consolidation, miniaturization, and power savings trends to extract maximum performance for minimum footprint. Data bus card developers use all these opportunities to create customized solutions and then incorporate these advances into standard cards.

Win-win situation for avionics

Data bus cards, like every other subsystem on an avionics platform, have to earn their way into an aircraft by meeting challenges such as size, weight, and power. By exploiting the trend toward ever smaller, lower-power-yet-denser electronics, designers are able to meet unique system demands while expanding their technology stables.