PXI powers event-based testing

A: If you look at the EDA tools that designers use to evaluate the chips they are developing, their test files produce a sequence of time differences, or events, along with the value changes for signals in the chip at those events. These event files mimic real-world signals. A traditional validation tester does not do that. Because it is cycle-based, it is unable to accurately recreate signal events as they occur but must lock its output levels to a set of clocks. This requires making compromises in the signal timing because of clocking limitations in the tester.

Q: What do these differences mean for test engineers?

A: Cycle-based testing requires different test vector streams than the ones used in EDA. This leaves us with two domains: design and test. Each domain has its knowledge base, tools, and languages, and they have little in common. That puts a wall between the two that makes it hard to transfer the test requirements and results between the two.

Q: Why has event-based testing not been done before?

A: Everyone in the industry has toyed with the idea of event-based testing, but memory technology has been a limitation. Event-based testing consumes as much as two times more memory than cycle-based. Making the shift also required us to rethink the way validation test is to be done. We had to continually ask ourselves, “What is the test supposed to accomplish?” rather than, “How do we do that?” to make sure that we could make a successful transition.

Q: What is the role of PXI in this new approach?

A: We developed a prototype on a proprietary backplane, but we wanted our design to be based on an open architecture. PXI is a well-established architecture that is laboratory oriented. In addition, it has seen a lot of innovation in the last few years. Many of the top-of-class instruments now available are in the PXI, not benchtop, format. The open architecture allowed us to concentrate our design on the digital portion of the tester and purchase other boards as needed to create the test capability the customer wanted. In addition, the open architecture allows customers to expand their test system with new boards or to design their own. (Editor’s note: Advantest’s Certimax system is the resulting PXI-based validation tester; see story.)

Q: Any other advantages to PXI?

A: The compact form factor and low power requirements of PXI allowed us to create a system with a small footprint that only required 110-V power. Also, PXI is at the lower end of the cost spectrum. It let us produce a test instrument that companies could afford to own without requiring a test volume high enough to support dedicated equipment and staff. And because it is event-based, it can use the test vectors that the EDA tools generate, bringing test back closer to the design domain.