Oscilloscopes track intermittent signals
Rick Nelson, Chief Editor -- Test & Measurement World, 2/1/2007
The oscilloscope is one of the most familiar test-engineering tools—one whose operation you mastered in college, if not sooner. But scopes continue to evolve, and that one on your bench may offer valuable capabilities of which you are unaware. In the Webcast “Finding and Troubleshooting Intermittent Signal Faults,” Dr. Michael Lauterbach, director of product management for LeCroy, describes a variety of functions that you can use to isolate runts, glitches, and other signal abnormalities.
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A waterfall diagram generated in sequence mode can help you determine how often an after-pulse anomaly (shown in blue) occurs. |
Scopes are primarily time-domain tools, but most can provide statistical-domain views as well, which Lauterbach says can provide the best way to characterize the amount of instability in a key signal parameter. He notes that you can use a histogram display to see the maximum range of parameter values, their RMS variation, and the shape of the distribution.
The Webcast also covers exclusion triggering, which provides a way to trigger on a rare signal fault when you do not know what the fault looks like. With an exclusion trigger, you might, for instance, ask your scope to trigger upon encountering clock pulses that are less than 980 ns or greater than 1.02 µs. Lauterbach discusses the use of an exclusion trigger in combination with persistence mode—a technique that can help you find signals with rise times that are too fast (and therefore could cause crosstalk) or too slow (and therefore could cause timing problems).
Lauterbach also describes eye diagrams and mask testing, and he explains how you can determine whether a failure is coincident with crosstalk, with power-supply noise, or with some other trouble source. He concludes by describing a waveform-search function that can help you locate and analyze rare events that can't be captured using hardware triggering schemes.
You can view the archived Webcast, sponsored by LeCroy and Test & Measurement World, at www.tmworld.com/webcasts.
