Editor's Note: I am delighted to have the opportunity to present the following piece from the third quarter issue of the Xcell Journal, with the kind permission of Xilinx Inc.
Electronic systems designs headed to space naturally require high reliability, but the design task is further complicated by exposure to radiation that can cause sporadic circuit failures. From a functional perspective, FPGAs with inherent reconfigurable attributes are a perfect match for space. FPGAs enable a single system to perform multiple tasks and let mission teams remotely reconfigure a system, either fixing a bug or adding new functionality. Now Xilinx has an FPGA—the Virtex-5QV—that is rad-hard and can deliver the full benefits of programmability to space programs. The design teams get an off-the-shelf solution with all the advantages of a 65-nanometer commercial SRAM-based FPGA, including ready access to development and prototyping tools.
Figure 1 – Xilinx built its latest space-grade FPGA, the Virtex-5QV, to be rad-hard.
Virtex-5QV device offers a flexible, cost-effective alternative for
design teams working on advanced, reconfigurable space applications.
It’s hard to underestimate the value an FPGA can offer in an application such as space-bound systems. Once a system, satellite, rocket or spacecraft is deployed, there is little or no ability to make hands-on changes to it, so the reprogrammability of an FPGA is a huge benefit. To be sure, microprocessors and microcontrollers can also be reprogrammed. But FPGAs excel in data-flow applications where functions such as packet inspection or signal-processing algorithms implemented in hardware logic offer far more processing throughput than do traditional microprocessors. And the FPGA hardware can be easily reconfigured to support new algorithms.
Given the advances in circuit density and the mix of hardwired IP blocks and configurable logic, the latest FPGA technologies can capture the bulk of a system’s functionality. For example, the Virtex-5QV includes Ethernet MAC functions and high-speed transceivers to go along with DSP slices and configurable logic (for details on the FPGA capabilities, see sidebar).
A rad-hard IC that's derived from a commercial FPGA family also offers significant benefits in the development process. Design teams can do development work with readily available commercial devices and development tools and then seamlessly move the design to the rad-hard target system platform at any point in the development process.
Space presents reliability challenges
To deploy FPGAs in space applications, however, designers have to understand the environment and learn how to mitigate issues that affect reliability. For example, a number of radiation-induced effects have been identified as a problem area for space-based designs. The list includes single-event upsets, single-event functional interrupts, single-event latchups, single-event transients and total ionizing dose effects. (See the second sidebar for more information on these effects.)
Designers working on space applications haven’t traditionally had the freedom to use ICs such as FPGAs without carefully considering ways to mitigate radiation effects. Specialty ASIC houses have radiation-hardened IC manufacturing processes. But ASIC design cycles are lengthy and expensive, and the quantity of devices the application will actually need simply doesn’t justify the time and effort, given viable alternatives.
The radiation-hardened ASIC processes are also many generations behind state-of-the-art commercial IC processes. For example, the rad-hard ASICs are still in the 150-nm or less-dense process nodes. Indeed, modern FPGAs offer performance and circuit density that match those of radiation-hardened ASICs, along with much faster development cycles.