The high-definition multimedia interface (HDMI) is an emerging consumer electronics standard that offers the first industry-supported, all-digital audio/video, one-cable interface. It supports data rates as fast as 5 Gb/s through a single connector instead of several cables as used in the past. Consequently, HDMI cables require careful design and analysis techniques to ensure that they pass required compliance tests.
The time-domain reflection and transmission (TDR/T) measurement of the HDMI cable helps locate and model discontinuities caused by the geometrical features of a connector and frequency-dependent losses of a cable itself. In cases where it is not possible to measure TDT data directly, an accurate prediction of the transmission behavior can be made.
Moreover, topological models can be built for each part of the HDMI cable assembly, verified with the measurement data, and then used to predict time- and frequency-domain response for a longer HDMI cable. The topological modeling methodology can accurately approximate the electrical behavior of the DUT even before the longer prototype is manufactured.
A 3-meter-long cable is used to build a topological model from TDR data. The model is scaled up and electrical performance predicted for a 10-meter-long prototype. The SPICE simulation linked with IConnect modeling software (1) shows correlation between the prediction and the actual TDR/T measurement for a 10-meter-long HDMI cable assembly in the time and frequency domains. The circuit model generated from TDR measurements allows an eye diagram to be obtained, which then is compared with an eye diagram generated from TDT measurements for the fabricated HDMI cable prototype.
Such an eye diagram can be generated directly from TDT measurements, but the TDR-only approach works best when only one side of the DUT is accessible. The result of an eye mask test from model prediction agrees with the test performed for the fabricated prototype. This technique allows a designer to quickly accomplish interconnect modeling and analysis tasks, resulting in faster design time and lower design costs.
The TDR measurements normally are done with a time-domain sampling oscilloscope such as Tektronix TDS8200 or similar. This instrument is a very wide bandwidth equivalent-time sampling oscilloscope with an internal step generator.
The TDR sends a step stimulus to the DUT. Based on reflections from the DUT, a designer can deduce a great deal of information about the DUT's properties such as location of failures, DUT impedance, and time delay, and he can generate an eye diagram for the system. (2)
An engineer also can use TDT measurements to measure crosstalk or characterize lossy transmission line parameters such as rise-time degradation and insertion loss as well as skin effect and dielectric losses. The frequency-dependent behavior of the system can be calculated from the time-domain (TD) measurements using the time-domain network analysis technique (TDNA). (3)
The TDR measurements are visual and intuitive to the digital designers due to the transient nature of this technique. As the incident step propagates through the discontinuities in the DUT, it causes the reflections that indicate the exact locations of discontinuities and their...