De-Embedding Test Fixtures For High-Speed Digital Applications

High-speed digital interfaces like USB, PCIe, and HDMI are widely used in commercial and industrial equipment for data transfer both internally and externally. As these interfaces continually evolve to increase speed and reduce size, it becomes challenging to ensure reliable contact and accurate signal acquisition for verification, debugging, and compliance testing.

One solution involves employing a test fixture to access the device under test (DUT) signals on one connector and lead them to another, typically a coaxial connector. However, at higher data rates, these fixtures have a significant impact, particularly in debug measurements and sometimes compliance testing. This application note addresses this issue by explaining methods to characterize a test fixture, deembed the characterized model for oscilloscope time domain measurements, and analyze its effects on signal integrity, using the USB Type-C® interface as an illustrative example, which offers varying data rates (Gen1: 5 Gbps, Gen2: 10 Gbps) for more comprehensive analysis.