Test Challenges of Multi-Gigabit Serial Buses

As the complexity and bandwidth requirements of modern avionics increase, new high speed digital buses are needed to support these requirements, and bring with them unique test challenges. Parallel bus interfaces often begin to exhibit problems with timing alignment and signal integrity when data rates approach several hundred Mbps. By converting single-ended parallel interfaces to differential signaling, their use can be extended to around 1 Gbps. As data rates rise beyond 1 Gbps, parallel buses become unusable due to skew issues and are replaced by multi-gigabit serial buses that alleviate the problems of parallel buses and can provide much higher data rates. As multi-gigabit serial buses become more prevalent in automated test, test engineers are finding that these buses come with their own set of test challenges. Multi-gigabit serial buses over copper media are difficult to interface and require special attention be paid to signal integrity and use of emphasis and equalization to produce a reliable test interface. Higher bandwidth test interfaces require generation, sourcing, processing, and storage of large amounts of test data. Some of the physical challenges of high speed serial buses over copper media can be resolved with optical interfaces. However, optical interfaces present yet again a new set of challenges. While traditional signal integrity is no longer a problem with optical interfaces, signal attenuation and optical link budgets must be understood. This paper discusses the progression from parallel data buses to electrical multi-gigabit serial buses to optical multi-gigabit serial buses, and beyond. Test challenges that must be addressed with each type of interface are discussed in detail. By understanding these test challenges, a test engineer can be prepared to reliably interface to and test modern avionics.