DSOs find and display anomalous waveforms before you can explain why they are unusual
By Dan Strassberg, Contributing Technical Editor -- EDN, October 2, 2006
One of the most frustrating aspects of using a digital scope to diagnose intermittent malfunctions in a UUT (unit under test) is that, to get the scope to display the anomalous waveforms, you generally must describe to it what is unusual about those waveforms. However, until you can see the anomalies, you can't describe them. Is the problem a runt pulse, a slow or misplaced edge, a unit interval of slightly incorrect length? You don't know … and, because a quick glance at a large group of waveforms may reveal nothing unusual, even scopes that let you use normal waveforms to create a trigger mask often fail to provide the needed insights.
Many EEs are likely to characterize the WaveScan feature of LeCroy's WaveSurfer and WaveRunner series of large screen, small-footprint (6-in.-deep) digital oscilloscopes as the ultimate scope-based troubleshooting aid, based on the degree of automation the feature brings to the identification of elusive malfunctions. WaveScan-equipped scopes can determine which anomalies are significant and then find the few that exist among thousands of nearly identical signals. The company has made the feature standard on all members of the two scope families, whose bandwidth, with the addition of new models, now extends to 2 GHz (WaveRunner) and 1 GHz (WaveSurfer).
WaveScan finds aberrant waveforms without your having to tell it—or even know—what unusual signal characteristics to look for. It then displays only the atypical signals. Moreover, it can do so either in real time—as waveforms arrive—or retrospectively on previously captured signals. Hence, in a UUT that fails intermittently, WaveScan can unearth the associated anomalous waveforms and provide statistical analyses of their salient parameters without your having to figure out what conditions to use as criteria.
The tool accomplishes this feat by measuring multiple parameters of each waveform, finding the norm for each characteristic, and determining—based on your estimate of how far out on the tails of the probability distribution the interesting waveforms lie—whether each waveform's measured values constitute an abnormal set. However, if you want to tell WaveScan what anomalous characteristics to look for, the tool lets you specify them in exquisite detail. As Director of Product Management Mike Lauterbach, PhD, points out, scope users have been clamoring for such a capability for years.
In the WaveRunner line, the new models are the $22,250, 2-GHz-bandwidth 204Xi and the $16,250, 1-GHz 104Xi. Both acquire 5G samples/sec on four channels simultaneously and 10G samples/sec on two channels. In the WaveSurfer line, the new model is the $12,890, 1-GHz 104Xs. This unit acquires 2.5G samples/sec on four channels simultaneously and 5G samples/sec on two channels.
LeCroy has also announced a new series of small, low-cost, high-impedance scope probes with bandwidths of 1.5 GHz and 900 MHz for $1190 and $490, respectively. Input impedance is 1 MV in parallel with 0.9 pF. The 1.5-GHz probes allow the use of 1-GHz-bandwidth scopes at full bandwidth; the 900-MHz units allow use of 600-MHz scopes at full bandwidth. The ZS probe family includes a large group of tips and ground-lead accessories for accessing hard-to-reach signals with minimum degradation at high frequencies.
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again - keep up the good work!
jim henson - 2006-2-10 09:55:00 PDT -
great article!
Jon Tellon - 2006-2-10 09:33:00 PDT
