Testing and Diagnosing High-Speed Circuits for Military Applications Through Standard Input/Output Ports

Traditionally, tests have been focused on the quality of the circuit elements that produce responses by the unit under test (UUT) to strategically selected test stimuli. In this paper we discuss tests of UUTs comprised of circuitry connected to buses. This is especially challenging when the input/output (I/O) of each subsystem is on a high-speed bus, such as the USB 3.0 (also known as USB 3.2 Gen 1) that runs at 5 Gbps. This speed is above the threshold of most automatic test equipment (ATE), including all military ATE. We discuss the limitations of military automatic testing methods and highlight their weaknesses in dealing with high-speed I/O (HSIO). We then discuss how bus testing is performed for both low-speed and high-speed buses and introduce the concept of utilizing synthetic instruments (SIs) to test HSIO. The significant advantage of this approach is that the SI test is bus oriented and is consistent for all UUTs of that particular bus. As a result, test program development is greatly eased and speeded up by reuse of the HSIO test for that bus. We show a sample system that could present itself as a typical Line Replaceable Unit (LRU) at the depot and show how by testing through the HSIO, one could provide a good end-to-end test as well as diagnostics to isolate to the faulty subsystem or shop replaceable unit (SRU). The same HSIO tester can then also be used test each SRU to isolate to faulty components.