Webcast sheds light on switching systems
Rick Nelson, Chief Editor -- Test & Measurement World, 9/1/2007
Switching systems are probably among the most overlooked and misunderstood pieces of hardware in an ATE system, says Jeffrey Lum, Giga-tronics' CTO and president of the company's Ascor division. He sheds light on the subject of switching in the Webcast, “Designing good switching modules for ATE,” in which he covers the need for switching, types of switching, design challenges, and available switching-module platforms.
Most test switches can benefit from switching, Lum explains, noting that switching systems help efficiently allocate tester resources to support one or more UUTs. Switches, he continues, come in a variety of formats, ranging from simple Form A single-pole single-throw (SPST) types to more complex configurations, such as the one shown in the figure. He describes multiplexer, or tree, configurations as well as star switches and cross-point matrices, explaining which ones best serve specific applications.
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Switches range from simple SPST types to more complex configurations, such as this four-wire 1xN implementation. |
Lum provides details on how to avoid problems associated with long transmission lines, lack of shielding, and improper impedance matching. “Test your UUT, not your switching system,” he advises, while providing hints on how to minimize reflections, eliminate ground loops, and avoid transmission-line stubs. He recommends that to keep your switch system invisible to your measurement resources, you should establish a chassis earth ground and maintain separate grounds for analog and digital signals.
Lum also provides advice on harnesses, noting that cables can be the “Achilles' heel” of a switching system, and he describes a harness-free switch design. He concludes with a detailed example of a star-switch design for 500-MHz signals.
For more details, including insertion-loss data from signal-transmission examples, view the archived Webcast, sponsored by Giga-tronics and Test & Measurement World, at www.tmworld.com/webcasts.
